mms notes by polarao sir

MMS NOTES-1 UNIT-I

Ronanki .Pola Rao, Asso.Prof, Dept of ME,GMRIT-Rajam [email protected];[email protected]

Introduction to Atomic Structure :

Atoms are composed of electrons, protons, and neutrons. Electrons and protons are negative

and positive charged particles respectively. The magnitude of each charged particle in an

atom is 1.6 × 10-19

Coulombs.

The mass of the electron is negligible with respect to those of the proton and the neutron,

which form the nucleus of the atom. The unit of mass is an atomic mass unit (amu) = 1.66 ×

10-27

kg, and equals 1/12 the mass of a carbon atom. The Carbon nucleus has Z=6, and A=6,

where Z is the number of protons, and A the number of neutrons. Neutrons and protons have

very similar masses, roughly equal to 1 amu each. A neutral atom has the same number of

electrons and protons, Z.

A mol is the amount of matter that has a mass in grams equal to the atomic mass in amu of

the atoms. Thus, a mole of carbon has a mass of 12 grams. The number of atoms in a mole is

called the Avogadro number, Nav

= 6.023 × 1023

. Note that Nav

= 1 gram/1 amu.

Calculating n, the number of atoms per cm3 of a material of density δ (g/cm

3):

MNnavδ=

where M is the atomic mass in amu (grams per mol). Thus, for graphite (carbon) with a

density δ = 1.8 g/cm3, M =12, we get 6 × 10

23 atoms/mol × 1.8 g/cm

3 / 12 g/mol) = 9 × 10

22 C

atoms/cm3.

Reference:

1.Elements of Material science -V. Rahghavan

2.Engineering materials and metallurgy-R.K.Rajput/ S.Chand.

3. Material Science -Prof. Satish V. Kailas

S.SANYASIRAO [email protected]

MMS NOTES-2 UNIT-I


Atomic bonding in solids

In order to understand the why materials behave like they do and why they differ in

properties, it is necessary that one should look at atomic level. The study primarily

concentrates on two issues: what made the atoms to cluster together, and how atoms are

arranged. As mentioned in earlier chapter, atoms are bound to each other by number of

bonds. These inter-atomic bonds are primarily of two kinds: Primary bonds and Secondary

bonds. Ionic, Covalent and Metallic bonds are relatively very strong, and grouped as primary

bonds, whereas van der Waals and hydrogen bonds are relatively weak, and termed as

secondary bonds. Metals and Ceramics are entirely held together by primary bonds - the ionic

and covalent bonds in ceramics, and the metallic and covalent bonds in metals. Although

much weaker than primary bonds, secondary bonds are still very important. They provide the

links between polymer molecules in polyethylene (and other polymers) which make them

solids. Without them, water would boil at -80°C, and life as we know it on earth would not

exist.

Ionic Bonding: This bond exists between two atoms when one of the atoms is negative (has

an extra electron) and another is positive (has lost an electron). Then there is a strong, direct

Coulomb attraction. Basically ionic bonds are non-directional in nature. An example is NaCl.

In the molecule, there are more electrons around Cl, forming Cl- and fewer electrons around

Na, forming Na+. Ionic bonds are the strongest bonds. In real solids, ionic bonding is usually

exists along with covalent bonding.


MMS NOTES-2 UNIT-I


Covalent Bonding: In covalent bonding, electrons are shared between the atoms, to saturate

the valency. The simplest example is the H2 molecule, where the electrons spend more time in

between the nuclei of two atoms than outside, thus producing bonding. Covalent bonds are

stereo-specific i.e. each bond is between a specific pair of atoms, which share a pair of

electrons (of opposite magnetic spins). Typically, covalent bonds are very strong, and

directional in nature. The hardness of diamond is a result of the fact that each carbon atom is

covalently bonded with four neighboring atoms, and each neighbor is bonded with an equal

number of atoms to form a rigid three-dimensional structure.

Metallic Bonding: Metals are characterized by high thermal and electrical conductivities.

Thus, neither covalent nor ionic bondings are realized because both types of bonding localize

the valence electrons and preclude conduction. However, strong bonding does occur in

metals. The valence electrons of metals also are delocalized. Thus metallic bonding can be

viewed as metal containing a periodic structure of positive ions surrounded by a sea of

delocalized electrons. The attraction between the two provides the bond, which is non-

directional.


MMS NOTES-2 UNIT-I


Reference:





MMS NOTES-3 UNIT-I


Fluctuating Induced Dipole Bonds: Since the electrons may be on one side of the atom or

the other, a dipole is formed: the + nucleus at the center, and the electron outside. Since the

electron moves, the dipole fluctuates. This fluctuation in atom A produces a fluctuating

electric field that is felt by the electrons of an adjacent atom, B. Atom B then polarizes so that

its outer electrons are on the side of the atom closest to the + side (or opposite to the – side)

of the dipole in A.

Polar Molecule-Induced Dipole Bonds: Another type of secondary bond exists with

asymmetric molecules, also called polar molecules because of positively and negatively

charged regions. A permanent dipole moment arises from net positive and negative charges

that are respectively associated with the hydrogen and chlorine ends of the HCl molecule,

leading to bonding. The These two kinds of bonds are also called van der Waals bonds. Third

type of secondary bond is the hydrogen bond. It is categorized separately because it produces

the strongest forces of attraction in this category.

Permanent Dipole Bonds / Hydrogen bonding: It occurs between molecules as covalently

bonded hydrogen atoms – for example C-H, O-H, F-H – share single electron with other atom

essentially resulting in positively charged proton that is not shielded any electrons. This

highly positively charged end of the molecule is capable of strong attractive force with the

negative end of an adjacent molecule. The properties of water are influenced significantly by

the hydrogen bonds/bridges. The bridges are of sufficient strength, and as a consequence


MMS NOTES-3 UNIT-I


water has the highest melting point of any molecule of its size. Likewise, its heat of

vaporization is very high. magnitude of this bond will be greater than for fluctuating induced

dipoles.

Reference:





MMS NOTES-4 UNIT-I


Crystal structures

All metals, a major fraction of ceramics, and certain polymers acquire crystalline form when

solidify, i.e. in solid state atoms self-organize to form crystals. Crystals possess a long-range

order of atomic arrangement through repeated periodicity at regular intervals in three

dimensions of space. When the solid is not crystalline, it is called amorphous. Examples of

crystalline solids are metals, diamond and other precious stones, ice, graphite. Examples of

amorphous solids are glass, amorphous carbon (a-C), amorphous Si, most plastics.

There is very large number of different crystal structures all having long-range atomic order;

these vary from relatively simple structures for metals to exceedingly complex structures for

ceramics and some polymers. To discuss crystalline structures it is useful to consider atoms

as being hard spheres, with well-defined radii. In this scheme, the shortest distance between

two like atoms is one diameter. In this context, use of terms lattice and unit cell will be

handy. Lattice is used to represent a three-dimensional periodic array of points coinciding

with atom positions. Unit cell is smallest repeatable entity that can be used to completely

represent a crystal structure. Thus it can be considered that a unit cell is the building block of

the crystal structure and defines the crystal structure by virtue of its geometry and the atom

positions within.

Important properties of the unit cells are

• The type of atoms and their radii R.

• Cell dimensions (Lattice spacing a, b and c) in terms of R and

• Angle between the axis α, β, γ

• a*, b*, c* - lattice distances in reciprocal lattice , α*, β*, γ* - angle in reciprocal lattice

• n, number of atoms per unit cell. For an atom that is shared with m adjacent unit cells,

we only count a fraction of the atom, 1/m.

• CN, the coordination number, which is the number of closest neighbors to which an

atom is bonded.

• APF, the atomic packing factor, which is the fraction of the volume of the cell actually

occupied by the hard spheres. APF = Sum of atomic volumes/Volume of cell.


MMS NOTES-4 UNIT-I



MMS NOTES-4 UNIT-I


Reference:





MMS NOTES-5 UNIT-I


Crystalline and Non-crystalline materials

Single Crystals: Crystals can be single crystals where the whole solid is one crystal. Then it

has a regular geometric structure with flat faces.

Polycrystalline Materials: A solid can be composed of many crystalline grains, not aligned

with each other. It is called polycrystalline. The grains can be more or less aligned with

respect to each other. Where they meet is called a grain boundary.

Non-Crystalline Solids: In amorphous solids, there is no long-range order. But amorphous

does not mean random, since the distance between atoms cannot be smaller than the size of

the hard spheres. Also, in many cases there is some form of short-range order. For instance,

the tetragonal order of crystalline SiO2

(quartz) is still apparent in amorphous SiO2

(silica

glass).

Miller indices:

It is understood that properties of materials depend on their crystal structure, and many of

these properties are directional in nature. For example: elastic modulus of BCC iron is greater

parallel to the body diagonal than it is to the cube edge. Thus it is necessary to characterize

the crystal to identify specific directions and planes. Specific methods are employed to define

crystal directions and crystal planes.

Methodology to define crystallographic directions in cubic crystal:

a vector of convenient length is placed parallel to the required direction.

- the length of the vector projection on each of three axes are measured in unit cell

dimensions.

- these three numbers are made to smallest integer values, known as indices, by

multiplying or dividing by a common factor.

- the three indices are enclosed in square brackets, [uvw]. A family of directions is

represented by <uvw>.

Methodology to define crystallographic planes in cubic crystal:

- determine the intercepts of the plane along the crystallographic axes, in terms of unit cell

dimensions. If plane is passing through origin, there is a need to construct a plane

parallel to original plane.

- take the reciprocals of these intercept numbers.

- clear fractions.


MMS NOTES-5 UNIT-I


- reduce to set of smallest integers.

- The three indices are enclosed in parenthesis, (hkl). A family of planes is represented by

{hkl}.

For example, if the x-, y-, and z- intercepts of a plane are 2, 1, and 3. The Miller indices are

calculated as:

- take reciprocals: 1/2, 1/1, 1/3.

- clear fractions (multiply by 6): 3, 6, 2.

- reduce to lowest terms (already there). => Miller indices of the plane are (362).

Figure : depicts Miller indices for number of directions and planes in a cubic crystal.

Some useful conventions of Miller notation:

- If a plane is parallel to an axis, its intercept is at infinity and its Miller index will be

zero.

- If a plane has negative intercept, the negative number is denoted by a bar above the

number. Never alter negative numbers. For example, do not divide -1, -1, -1 by -1 to

get 1,1,1. This implies symmetry that the crystal may not have!


MMS NOTES-5 UNIT-I


- The crystal directions of a family are not necessarily parallel to each other. Similarly,

not all planes of a family are parallel to each other.

- By changing signs of all indices of a direction, we obtain opposite direction. Similarly,

by changing all signs of a plane, a plane at same distance in other side of the origin

can be obtained.

- Multiplying or dividing a Miller index by constant has no effect on the orientation of the

plane.

- The smaller the Miller index, more nearly parallel the plane to that axis, and vice versa.

- When the integers used in the Miller indices contain more than one digit, the indices

must be separated by commas. E.g.: (3,10,13)

- By changing the signs of all the indices of (a) a direction, we obtain opposite direction,

and (b) a plane, we obtain a plane located at the same distance on the other side of the

origin.

More conventions applicable to cubic crystals only:

- [uvw] is normal to (hkl) if u = h, v = k, and w = l. E.g.: (111) ┴ [111].

- Inter-planar distance between family of planes {hkl} is given by:

[uvw] is parallel to (hkl) if hu + kv + lw = 0.

- Two planes (h1k

1l1) and (h

2k

2l2) are normal if h

1h

2 + k

1k

2 + l

1l2=0.

- Two directions (u1v

1w

1) and (u

2v

2w

2) are normal if u

1u

2 + v

1v

2 + w

1w

2=0

- Angle between two planes is given by:

Why Miller indices are calculated in that way?

- Using reciprocals spares us the complication of infinite intercepts.


MMS NOTES-5 UNIT-I


- Formulas involving Miller indices are very similar to related formulas from analytical

geometry.

- Specifying dimensions in unit cell terms means that the same label can be applied to any

plane with a similar stacking pattern, regardless of the crystal class of the crystal.

Plane (111) always steps the same way regardless of crystal system.

Reference:





MMS NOTES-6 UNIT-I


Differences between crystal, dendrite, grain and grain boundary.

Crystal

A solid composed of atoms, iortS or molecules arranged in a three dimensional pattern is

called a crystal. Since atoms’ tend to. Assume relatively fixed positions, this gives the

formation of crystals in the solids. The atoms, instead of being fixed they oscillate about

same fixed locations and they are in a dynamic equilibrium. The imaginary lines drawn

connecting the atoms in three-dimensions is called the space lattice, and the smallest unit

having full symmetry of the crystal is called a unit cell. The structure of the orderly packed

crystals is called crystal structure.

Dendrite

When the temperature of the metal has dropped below the freezing point temperature

sufficiently, nuclei appear in the liquid spontaneously. The nuclei will get solidified and

they act as centers far further crystallization of the liquid metal. When codling is still

continued the atoms tend to. freeze and they attach themselves to solidified atoms are form

nuclei if their own. Crystal growth continues in three dimensions. The atoms attach

themselves along the axis of , the crystals in so preferred directions. This gives a tree like

structure called the dendrite. The nuclei is farmed by change, so the crystal axes are pointed

randomly and the dendrites grow indifferent directions in each crystal.

Grain and grain boundaries

When the transition of liquid to solid is fully completed fanning many crystals, these crystals

are called polycrystalline metals. These polycrystalline metals possess irregular shape, these

irregular polycrystalline metals are called grains. The atoms in this grains are regularly

packed

in a geometrical pattern. Grain boundaries are those that separate the individual grains. These

grain boundaries are formed after the complete solidification process has finished or stopped

'because of the inter phase with that of the adjacent structure. From one grain to another there

is a

Crystallographic orientation taking place through the grain boundary and at the grain

boundary between two grains there exists a transient zone.


MMS NOTES-7 UNIT-I


Coordination Number:

Simple Cubic Crystal Structure (SCC)

In simple cubic structure, there is one atom at each corner of the cube arid any corner atom has 4

Nearest neighbor atoms in the same plane and two .nearest neighbours in the material plane.

Hence coordination number4 + 2 = 6.

Body Centered Crysta1 Structure (BCC)

In BCC structure, there is one atom at each corner of the cube and one atom at the, centre of

cube. The corner atom is surrounded by eight unit cells having eight body centered atoms. Hence

coordination number is 8.

This type of crystal structure is found in the following metals,

Li, Na, K, V,Ta,a-Cr, Mo, a-Fe etc.

Face Centered Crystal Structure (FCC)

In FCC structure, there is one atom at each corner of the cube and one atom at the centre of each

face of the cube. For any corner atom, the nearest are the face centered atoms.

Hence coordination number =12

This type of crystal structurejs found in the following metals.

Hexagonal Close Packed Structure (HCP)

In HCP crystal the coordination number is 12

It is shared , by two unit cells. The three atoms at interior remain unshared

Reference:





MMS NOTES-8 UNIT-II


Alloy – It is a material having two or more elements, in which one should be a metal.

(or)The substance having metallic properties and composed of two or more elements of

which one is a metal .

Super Alloys -A group of alloys that retain high strength at elevated temperatures.

Alloying elements- All the elements that make an Alloy .

These are two types

(i) Base metal -The metal present In the larger proportion in an alloy

(ii) Alloying elements- the remaining metallic and non-metallic elements

Alloying of element is done to get certain desirable properties which are not available in

the base metal initially.

Therefore,” An alloy is a material which is expected of a metal, but it is not a pure metallic

element “

Alloy system- consists of all the alloys that can be formed by the combination of several

elements in all possible proportions.

Alloy systems may be classified depending on their equilibrium diagram.

Binary - (composed of two elements),

Ternary - (composed of three elements), and so on.

A homogeneous alloy - consists of single phase

Heterogeneous alloy - consists of several phases.

If a homogeneous alloy is in solid state, then it can be only a solid solution or compound.

If the alloy is heterogeneous, it is composed of any combination of the phases possible in

the solid state.

Based on microstructure or metallurgical structure

Single Phase Alloy : Alloy consisting of single phase (i.e.,liquid or solid).

Example :Transformer iron.

Multiple Phase Alloy :Alloy consisting of multiple phases.

Example: Muntz metal (60% Cu and 40% Zn) is a two phase alloy.


MMS NOTES-8 UNIT-II


Alloy –It is a material having two or more elements, in which one should be a metal.

All the elements that make an Alloy are called alloying elements.

Reference Books:

1. Elements of Material science / V. Rahghavan

2. Science of Engineering Materials / Agarwal



MMS NOTES-9 UNIT-II

Ronanki .Pola Rao, Asso.Prof, Dept of ME,GMRIT-Rajam [email protected],[email protected]

The alloying elements are classified generally as.

1.Based on the relation with carbon

Graphitizing events -such as silicon, nickel,. copper and aluminum

Carbide forming elements- like manganese, chromium, molybdenum,

tungsten, vanadium and so on. Neutral elements like cobalt

2.Based on their effect of critical points - elements of two types

Austenite stabilizers -nickel, manganese, copper and cobalt

Ferrite stabilizers - chromium, tungsten molybdenum and vanadium.

These alloys are added to the metal to overcome their limitations and to provide

properties suited for use in the required areas.

Alloys are produced to fulfill anyone of the the following needs

(a) Improve hardness and wear resistance.

(b) Improve corrosion resistance.

(c) Improve both the magnetic and electric properties.

(d) Improve the machinability, weldability.

(e) Also to improve the" strength and toughness.

Cobalt is added- to improves the strength of the metal at high temperatures.

Copper is added- for improving corrosion resistance of metals. '

The addition of alloys to metals improve their metal properties and hence, are used

widely by industry

Reference Books:





MMS NOTES-10 UNIT-II


Difference between Pure metal and Alloy:

Pure metal

1. Pure metal are single phased materials Composing of elements that readily give up electrons

to form a metallic bond.

2. E.g., Aluminum, copper etc.

3. Pure metal are rarely used in engineering applications because of the poor physical and

mechanical properties.

4. Pure metals are difficult to produce, these are obtained by refining the ore

5. Pure metals possess high electrical and thermal conductivity.

Alloy:

1. Alloys are formed by when two or more relatively pure metals are melted together

to form a new material

2. E.g, Steels, brasses, bronzes etc

3. Alloys are used more predominantly in engineering applications as they bring a

significant change in the properties of the base metal.

4. These are easily formed by the blending of two or more elements.

5. Alloys have better mechanical properties than pure metals.

Reference Books:





MMS

Ronanki .Pola Rao, Asso.Prof, Dept of ME,[email protected],[email protected]

Solid Solutions:

A simple structure of alloys is termed as a solid solution.

This solid solution has two elements soluble in each other and exist in single phase in

solid state.

The two elements are:

The major element -called the

The minor element -called he

Types of solid solutions:

(a) Substitutional solid solution

(b) Interstitial solid solution.

NOTES-11 UNIT

Asso.Prof, Dept of ME,GMRIT-Rajam [email protected],[email protected]

A simple structure of alloys is termed as a solid solution.


called the solvent

called he solute.

(a) Substitutional solid solution

(b) Interstitial solid solution.

UNIT-II





Substitutional solid solution:

In substitutional solid solution, the arrangement of the solute atoms may be disordered

(random) or ordered.

Solute atoms can be substituted for the solvent atoms in a crystal lattice for this

system solutions.

The addition of this will not change the crystal structure of the solvent, but there

may be some distortion due to the presence of the solute atoms.

This happens generally when there is a difference in the diameters' of the solute and

solvent atoms.

Example- The alloy for gold silver systems, the crystal structure for this is Face

Centered Cubic (FCC) lattice.

Silver atoms may be substituted for gold atoms and there will be no change in the

lattice structure, it will be a FCC structure.

In the same way, gold atoms can‘ also be substituted for silver atoms without any

change in the lattice structure.

This entire system contain a series of solid solutions.

When atoms of small atomic radii fit into the space of the lattice structure of the

larger solvent atoms the interstitial solid solutions are formed .

Due to the restriction in space size of the lattice structure only the atom that have an

angstrom number less than one are capable of forming interstitial solid solutions.

Examples :




Hydrogen with 0.46AO, carbon with 0.77AO and oxygen with 0.6 AO

This type of solid solutions have limited solubility with little importance. Carbon

dissolving in iron is a good example.

For this type the solubility of γ-iron (FCC) in carbon is at 11300 with 2% solubility

which is maximum.

Reference Books:







INTERMETALLIC COMPOUNDS

Intermetallic compounds are generally formed when one metal (for example

magnesium) has chemical properties which are strongly metallic and the other

metal (for example antimony, tin or bismuth) has chemical properties which are

only weakly metallic.

Examples of intermetallic compounds are Mg2Sn, Mg2Pb, Mg3Sb2 and Mg3 Bi2.

These intermetallic compounds have higher melting point than either of the parent

metal.

This higher melting point indicates the high strength of the chemical bond in

intermetallic compounds.

Substitutional solid solution

Solute atoms can be substituted for the solvent atoms in a crystal lattice for this

system solutions.

The addition of this will not change the crystal structure of the solvent, but there

may be some distortion due to the presence of the solute atoms.

This happens generally when there is a difference in the diameters' of the solute and

solvent atoms.

Example- the alloy for gold silver systems, the crystal structure for this is Face

Centered Cubic (FCC) lattice.

Silver atoms may be substituted for gold atoms and there will be no change in the

lattice structure, it will be a FCC structure.

In the same way, gold atoms can‘ also be substituted for silver atoms without any

change in the lattice structure.

This entire system contain a series of solid solutions.

Reference Books:







Hume Rothery’s Rules:

Some alloy systems exhibit complete solid solubility (e.g. Cu-Ni,Cd-Mg), and others

show only limited solubility at any temperature.

Several factors determine the limits of solubility.

These are expressed as a series of rules often called William Hume-Rothery Rules.

1.Crystal structure factor

For complete solid solubility, the two elements should have the same type of crystal

structure .

i.e., both elements should have either F.C.C. or B.C.C. or H.C.P. structure.

2.Atomic Size Factor (the 15%)

Extensive substitutional solid solution occurs only if the relative difference between

the atomic diameters (radii) of the two species is less than 15%. If the difference >

15%, the solubility is limited.

Example: Both silver and lead have F.C.C. structure and the relative size factor is

about 20 percent. Therefore the solubility of lead in solid silver is about 1.5 percent

and the solubility of silver in solid lead is about 0.1 percent. Copper and nickel are

completely soluble in each other in all proportions. They have the same type of

crystal structure (F.C.C.) and differ in atomic radii by about 2 percent.

3.Relative valence factor:




It is found that a metal of lower valence tends to dissolve more of a metal of higher

valence than vice versa.

Example : In aluminium-nickel alloy system- nickel (lower valance) dissolves 5

percent aluminium ,but aluminium (higher valence) dissolves only 0.04 percent

nickel.

4.Chemical affinity factor:

Solid solubility is favoured when the two metals have lesser chemical affinity. If the

chemical affinity of the two metals is greater then greater is the tendency towards

compound formation.

Generally, if the two metals are separated in the periodic table widely then they

possess greater chemical affinity and are very likely to form some type of compound

instead of solid solution.

Hume-Rothery rules can be applied for interstitial solid solutions:

Interstitial solid solutions are formed if

1. a solute is smaller than pores in the lattice of a solvent;

2. a solute has approximately the same electronegativity as a solvent.

There are very few elements that create ions, small enough to fit in interstitial

positions, therefore, appreciable solubility is rare for interstitial solid solutions.

Ions that often may be a solute in solid solutions are: H, Li, Na, B.

Reference Books:







Difference between alloy and intermetallic compound?

If we take example of binary alloy and binary intermetallic compound then in case of

binary intermetallic compound the position of two types of atoms in a particular

lattice structure remain fixed but in case of binary alloy the atoms position is not

fixed although they formed the same lattice structure but the position of two types

of atoms may not fixed in the lattice.

Difference between amalgam and alloys

All combinations of different metals form alloys.

An alloy composed by mercury and other metal is an amalgam.

In dentistry, amalgams may be composed by 3, 4, 5 or even more elements, so they

are called binary, ternary, etc. Traditional dental amalgams contain Mercury, Silver,

Copper, Tin and sometimes Zinc. Other metals like Palladium or Indium have been

added by a few manufacturers, to modify the physical properties of the alloy.

Difference between an alloy and a compound

An alloy is a substance composed of two or more elements, at least one is a metal.

Generally alloys have metallic properties. If you want to make an alloy, you can add

any element to a metal.

Then it can form a solid solution or compound based on the valence rules.

Compound is a phase which comes as a sub classification of an alloy. Further more,

an alloy is based on metals. A compound can have any two metals as their

components.

For example, H2O is a compound but not an alloy.

Difference between compound and elements

An element is a pure substance composed of 1 type of atom.

A compound is a pure substance composed of 2 or more types of atom chemically

bonded together.

Reference Books:





MMS


Electron Compounds

Electron to Atom Ratio It is the ratio of number of valance electrons to the number of

atoms

Solid solubility is affected by the relative valence of the elements.

The ratio of the number of valence electrons per atom

Solutes that rise the e/a,

the e/a.

Far example" the solid solution of lithium in magnesium is 24.5 atomic percentage,

whereas the solubility Of magnesium in lithium is 70

Like wise the solubility of aluminum in copper is much greater than the solubility of

copper in aluminum.

There are three such ratios,referred as H

21/14, 21/13,

NOTES-15 UNIT

.Pola Rao, Asso.Prof, Dept of ME,GMRIT-Rajam [email protected],[email protected]

It is the ratio of number of valance electrons to the number of


The ratio of the number of valence electrons per atom e/a, effects the solubility.

e/a, generally have higher solubility than to those that lower


whereas the solubility Of magnesium in lithium is 70 atomic‘ percentage.


There are three such ratios,referred as H-R ratios

21/13, 21/12

UNIT-II

It is the ratio of number of valance electrons to the number of


effects the solubility.

generally have higher solubility than to those that lower


atomic‘ percentage.





e/a=21/13:

Cu9Al4

valence electrons=9x1+4x3=21

Total number of atoms=13

e/a=6/4

Ag3Al

valence electrons=3x1+1x3=6


e/a=7/4

CuZn3

valence electrons=1+2x3=7


Reference Books:





MMS NOTES-16 UNIT-III


SYSTEM

A part of the universe under study is called system.

PHASE

Phase is homogeneous, physically distinct and mechanically separable part of the system under study.

VARIABLE

A particular phase exists under various conditions of temperature, pressure and concentration. These

parameters are called as the variables of the phase

COMPONENT

The elements present in the system are called as components.

Eg : Cu - Al system contains compounds Cu Al and CuAI2 and therefore all compositions can be expressed

by the molecular spaces of Cu and Al and hence it is a two component system, i.e. binary system.

LIQUIDUS TEMPERATURE

The start of solidification temperature is called liquidus temperature because above this, the metal or

alloy is in the liquid state.

SOLIDUS TEMPERATURE

The end of solidification temperature is called solidus temperature because below this, the metal or

alloy is in the solid state.

Reference Books:







GIBS'S PHASE RULE:

Phase equilibrium – It refers to the set of conditions where more than one phase may exist

An equilibrium state of solid system can be reflected in terms of characteristics of the

microstructure, phases present and their compositions, relative phase amounts and their

spatial arrangement or distribution.

Variables of a system – 3Variables

Two external variables namely temperature and pressure along

One Internal variable such as composition (C) and

Number of phases (P).

Number of independent variables among these gives the degrees of freedom (F) or variance.

All these are related for a chosen system as follows:

P+F=C+2

which is known as Gibbs Phase rule.

The degrees of freedom cannot be less than zero .

For practical purpose, in metallurgical and materials field, pressure can be considered as a

constant, and thus the condensed phase rule is given as follows.

P+F=C+1

Reference Books:





MMS


COOLING CURVES - FOR PURE METALS

COOLING CURVES - BINARY SOLID SOLUTION ALLOYS

COOLING CURVES - BINARY EUTECTIC ALLOYS

FOR OFF--EUTECTIC BINARY ALLOYS

NOTES-18 UNIT


FOR PURE METALS

BINARY SOLID SOLUTION ALLOYS

BINARY EUTECTIC ALLOYS

EUTECTIC BINARY ALLOYS

UNIT-III


MMS


Reference Books:


2. Science of Engineering

3. Material Science

NOTES-18 UNIT


Elements of Material science / V. Rahghavan

Science of Engineering Materials / Agarwal

Material Science -Prof. Satish V. Kailas

UNIT-III


MMS


Equilibrium Diagrams :

It is a graphical representation of different

It is also known as equilibrium or

It indicates the phases existing in the system at any temperature and composition

Equilibrium diagrams can be plotted by using several techniques :

� Thermal analysis,

� Dialometry,

� Optical and electron microscopy,

� X-ray and electron diffraction,

� Thermodynamic data analysis,

� Electrical resistivity and

� Magnetic measurements.

Lever Rule :

It is used for finding out the amounts of phases existing in a binary system for a given alloy at any

temperature under consideration.

NOTES-19 UNIT


It is a graphical representation of different -states of alloy system.

or constitutional diagram


can be plotted by using several techniques :

Optical and electron microscopy,

and electron diffraction,

Thermodynamic data analysis,

Electrical resistivity and

Magnetic measurements.


temperature under consideration.

UNIT-III






Let us Consider an isomorphous system (Systems in which two metals are completely

soluble in liquid as well as solid state) of two metals A and B .

Z -be the composition of the alloy under consideration and

T- be the temperature at Which the amounts of phases are to be found out.

CD-Tie line

CF-arm of liquid,

FD-arm of solid

Total amount is assumed to be 1.

Amount of solid be S and

Amount of liquid (L) will be 1-S,

The amount of B in the alloy = Amount of B in the solid + Amount of B in the liquid

The composition of liquid is C, and

composition of solid is D

Z = S x D + (1 - S) x C

Z =SD+ C- SC

Z - C = S (D - C)


MMS


Problem: Find the amount of liquid and amount of solid for alloy composition of 60 percent

percent A at a temperature T.

NOTES-19 UNIT


Problem: Find the amount of liquid and amount of solid for alloy composition of 60 percent

UNIT-III

Problem: Find the amount of liquid and amount of solid for alloy composition of 60 percent B and 40




% Amount of solid=(UC/UV)X100==(30/60)X100=50 %

% Amount of liquid=(CV/UV)X100==(30/60)X100=50 %

Reference Books:





MMS


Basic types of Binary Alloy Systems :

1. Isomorphous systems:

liquid and solid state is called isomorphous system.

2. Eutectic systems: A system in which components are soluble in liquid state but

insoluble or partially soluble in solid state

3. Peritectic systems: Two components having different melting points are involved and in

which a liquid react with solid first formed to form a new solid on cooling is called peritectic

system, and this reaction between solid and liquid called peritectic reaction

4. Eutectoid systems: A solid phase decomposes into two solid phases isothermally

NOTES-20 UNIT


Basic types of Binary Alloy Systems :

A system in which components are completely soluble in both

liquid and solid state is called isomorphous system.

A system in which components are soluble in liquid state but

insoluble or partially soluble in solid state

Two components having different melting points are involved and in


tion between solid and liquid called peritectic reaction

A solid phase decomposes into two solid phases isothermally

UNIT-III

A system in which components are completely soluble in both

A system in which components are soluble in liquid state but

Two components having different melting points are involved and in


tion between solid and liquid called peritectic reaction



MMS


Reference Books:



3. Material Science

NOTES-20 UNIT




terial Science -Prof. Satish V. Kailas

UNIT-III




Isomorphous systems

A system in which components are completely soluble in both liquid and solid state is called

isomorphous system .

Phase diagram consists of three regions.

(i) Liquid phase above liquidus line

(ii) Liquid + solid phase between liquidus and solidus line

(iii) Solid phase below solidus line

Eutectic systems

Soluble in liquid state but insoluble in solid state

C -melting temperatures of A

G-melting temperatures of B

CEG- liquidus line

CDEFG- solidus line

Region above CEG -only liquid phase

Region between CE and DE -contains liquid phase and solid A,

Region between GE and EF -contains liquid phase and solid B,

Region at the left of E- A and eutectic alloy and

Region at the right of E - B and eutectic alloy.

During cooling,

Eutectic transformation occurs at the line DF except at the points D and F.




The composition indicated by point E is eutectic composition and temperature is

eutectic temperature.

Eutectic reaction takes place during cooling. In this reaction liquid transforms into

two solids.

The mixture of these solids is called eutectic mixture. So liquid phase, and two solid

phases exist

at eutectic point.

Soluble in liquid state but partially soluble in solid state

CEG- Liquidus line

CDEFG - Solidus line.

Above CEG - Liquid phase and

Below CDEFG - Solid state.

Left of CDH and Right of GFK - Solid solution.

Point D - Maximum solubility of B in A

Point F- Maximum solubility of A in B.

HD,FK- Solvus lines

DEF- Eutectic Arm

E - Eutectic composition and Eutectic Temperature.

� The lowest temperature at which the liquid can exist when cooled under equilibrium

conditions is known as eutectic temperature (E).

� Terminal solid solutions -The regions of limited solid solubility at each end of a phase

diagram (α + β) .They appear at ends of the diagram.

� When the liquid of eutectic composition is cooled, at or below eutectic temperature

this liquid transforms simultaneously into two solid phases (two terminal solid

solutions, represented by α and β).

� Liquid (L) ↔ solid solution-1 (α) + solid solution-2 (β)

� The lowest temperature at which the liquid can exist when cooled under equilibrium

conditions is known as eutectic temperature (E).

� Terminal solid solutions -The regions of limited solid solubility at each end of a phase

diagram (α + β) .They appear at ends of the diagram.




� When the liquid of eutectic composition is cooled, at or below eutectic temperature

this liquid transforms simultaneously into two solid phases (two terminal solid

solutions, represented by α and β).

� Liquid (L) ↔ solid solution-1 (α) + solid solution-2 (β)

� There exist

Three single phase regions- liquid (L), α and β phases.

There also exist three two phase regions -L+α, L+β and α+β.

� These three two phase regions are separated by horizontal line corresponding to the

eutectic temperature

� Below the eutectic temperature, the material is fully solid for all compositions.

� Hypo-eutectic compositions -Compositions that are on left-hand-side of the eutectic

composition

� Hyper-eutectic compositions- compositions on right-hand-side of the eutectic

composition

� Compositions and relative amount of the phases can be determined using tie-lines and

lever rule

Reference Books:







EUTECTOID REACTION


� A solid phase (usually a solid solution) is converted into two or more intimately

mixed solids on cooling.

� The number of solids formed being the same as the number of components in the

system.

� Examples: Cu - Al , Cu - Zn, Al - Mn , Cu - Be etc.

� As it is slowly cooled, γ solid solution is formed when the liquidus line is crossed at

YI.

� More and more γ is formed until the solidus line is crossed at Y2

� It remains a uniform solid solution until the solvus line is crossed at Y3

� The pure metal A must now start to undergo an allotropic change, forming the α solid

solution.

� The composition of γ is gradually moving down and along the line ME, γ solution

comes richer in metal B.

� When alloy reaches the eutectoid temperature Te, γ the reaches eutectoid

point E.

The microstructure at room temperature consists of primary α for pro eutectoid α

which was formed

between Y3 and Y4 surrounded by the eutectoid mixture of α + β

Practical example of the eutectoid reaction occurs in the Fe-Carbon system

Reference Books:





MMS


Types of Metals and Alloys

Metallic materials are broadly of two kinds

Ferrous- In which iron (Fe) is the principle constituent.

Non-Ferrous Materials- All other materials

Alloys of copper, aluminium, magnesium, nickel, zinc, tin, lead, etc.

Another classification is made based on their formability.

Cast alloys- If materials are hard to form, components with these materials

are fabricated by casting,

Wrought alloys - Material can be deformed.

Materials are usually strengthened by two methods

Strengthening by heat treatment involves either precipitation hardening or martensitic

transformation, both of which constitute specific heat treating procedure. When a material

cannot be strengthened by heat treatment, it is referred as non

Ferrous alloys with less than 2.14% C are termed as Steels.

Ferrous alloys with higher than 2.14% C ar

Cast Iron - Alloy of Iron and Carbon with more than 2.0% carbon.

Most cast irons contains :

NOTES-23 UNIT

Asso.Prof, Dept of ME,GMRIT-Rajam [email protected],[email protected]

Metallic materials are broadly of two kinds

) is the principle constituent.

All other materials


Another classification is made based on their formability.

If materials are hard to form, components with these materials

d by casting,

Material can be deformed.

Materials are usually strengthened by two methods –Cold work and Heat Treatment.


ich constitute specific heat treating procedure. When a material

cannot be strengthened by heat treatment, it is referred as non-heat-treatable alloys.

Ferrous alloys with less than 2.14% C are termed as Steels.

Ferrous alloys with higher than 2.14% C are termed as Cast Irons

lloy of Iron and Carbon with more than 2.0% carbon.

UNIT-IV


If materials are hard to form, components with these materials

Cold work and Heat Treatment.


ich constitute specific heat treating procedure. When a material

treatable alloys.


MMS NOTES-23 UNIT-IV


2.5 to 3.7% Carbon,

0.5 to 3.0% Silicon and

Other elements as impurities.i.e., Mn,S,P

Cast iron is widely used for cast components for which are not required to withstand impact

or shock loads.

It has many advantages over steel as a casting metal

Advantages are:

1.Low melting point approximately 12000C (melting point of steel is about 1380°C) and good

machinability.

2. High fluidity and low shinkage on cooling,

3. Better corrosion and wear resistance than steel.

4. High compression strength and castings can withstand to heavy weights placed upon them.

5. Free graphite in cast iron can acts as a lubricant to reduce the friction between sliding

surfaces. (machine tool slide ways)

6. It is an inexpensive materials.

7. High damping capacity

The main disadvantages of cast iron are :

� It is brittle.

� It cannot be forged or hardened, and

� It is very weak in tension

Reference Books:





MMS


COMPOSITION OF CAST IRON

Carbon : Free Carbon (graphite)Graphite Flakes act as Lubricants

Combined form (cementite)-makes it very hard, brittle and almost unmachinable. very hard and wear resistant

Silicon : Tends to destabilise cement ie., produce graphite Improves casting properties by increasing the fluidity and decreasing shrinkage

Manganese : Reduce the effect of sulphur,Refine the grains, and Increases strength and hardness

Sulphur : Increases the brittleness, Increases shrinkages, Decreases fluidity

Phosphorus : Improves the fluidity and decreases shrinkage

Reference Books:



3. Material Science

NOTES-24 UNIT


COMPOSITION OF CAST IRON

Carbon : Free Carbon (graphite)-Results Low Tensile Strength and Low Impact values. Graphite Flakes act as Lubricants

makes it very hard, brittle and almost unmachinable. very hard

Tends to destabilise cement ie., produce graphite Improves casting properties by increasing the fluidity and decreasing shrinkage

Reduce the effect of sulphur,Refine the grains, and Increases strength and

the brittleness, Increases shrinkages, Decreases fluidity

Improves the fluidity and decreases shrinkage




UNIT-IV

Results Low Tensile Strength and Low Impact values.

makes it very hard, brittle and almost unmachinable. very hard

Tends to destabilise cement ie., produce graphite Improves casting properties by

Reduce the effect of sulphur,Refine the grains, and Increases strength and

the brittleness, Increases shrinkages, Decreases fluidity




GREY CAST IRON

CHARACTERISTICS:

� Grey iron basically is an alloy of carbon and silicon with iron.

� It is readily cast into a desired shape in a sand mould.

� Graphite flakes occupy about 10%of the metal volume

� When fractured, a bar of gray cast iron gives gray appearance.

� Possesses high fluidity and hence it can be cast into complex shapes and thin sections.

� It possesses machinability better than steel.

� It has high resistance to wear (including sliding wear),

� It possess high vibration damping capacity.

� Grey iron has low ductility and low impact strength as compared with steel

� Solidification range of2400 - 20000F.

� Shrinkage of 1/8 inch/foot (1 mm / 100 mm).

� Possesses high compressive strength

USES :

� Machine tool structures -Gas or water pipes for underground purposes.

� Manhole covers - Cylinder blocks and heads for I.c. engines.

� Tunnel segment - Piston rings - Rolling mill and general machinery

� parts - Household appliances,

MALLEABLE CAST IRON

CHARACTERISTICS:

� It is one which can be hammered and rolled to obtain different shapes

� It is obtained from hard and brittle white iron through a controlled heat conversion process.

� It possesses high yield strength.

� It has high young's modulus and low coefficient of thermal expansion.




� It possesses good wear resistance and vibration damping capacity.

� It has a solidification ranges of2500 - 2065°F

� It has shrinkage of 3/16 inch per foot (1.5 mm / 100 mm).

� It has low to moderate cost.

USES :

� Automotive industry. Rail road. Agricultural implements.

� Electrical line hardware. Conveyor chain links. Gear case.

� Universal joint yoke. Rear axle banjo housing.

� Truck tandem axle assembly parts. Automotive crankshaft.

� Crankshaft sprocket etc.

Reference Books:







� White Cast Iron

� CHARACTERISTICS:

� White cast iron derives its name from the fact that its freshly broken surface shows a bright white fracture.

� Possesses excellent abrasive wear resistance

� Under normal circumstances is brittle and not machinable

� Castings can be made in sand moulds

� Solidification range of white iron is 2550 - 2065°F.

� Shrinkage is 1/8 inch per foot (1 mm / 100 mm).

� First step in the production of malleable iron castings.

� USES :

� For producing malleable iron castings.

� For manufacturing those component parts which require a hard and abrasion resistant material

Nodular (Spheroidal) Cast Iron

CHARACTERISTICS:

� Unlike long flakes as in gray cast iron, graphite appears as rounded particles, or nodules or spheroids in Nodular cast iron.

� When added to melt eliminate sulphur and oxygen

� Soft annealed grades of nodular cast iron can be

turned at very high feeds and speeds

� The properties of nodular cast iron depend upon

the metal composition and the cooling rate.

� It possesses damping capacity intermediate between

cast iron and steel.

� It possesses excellent castability and wear resistance.

USES :




� Paper industries machinery. Internal combustion engines.

� Power transmission equipment. Farm implements and tractors.

� Earth moving machinery. Valves and fittings.

� Steel mill rolls and mill equipment. Pumps and compressors.

� Construction machinery

Reference Books:







ALLOY CAST IRONS

� Cast irons - Have low values of

� Impact resistance,

� Corrosion resistance, and

� Temperature resistance.

� These properties are increased by adding certain alloying elements in suitable amount.

� Most common alloying elements - Ni , Cr , Mo , V, Cu and Si.

� Ni-Hard: The hardness and wear resistance of white cast iron is increased by the addition of nickel and chromium with improvement in toughness.

� If only nickel is added for the above purpose, there is a danger of graphitization because nickel is a graphitizer.

� To avoid the risk of graphitization, chromium is added which is a carbide former.

� Ni-Hard: 3 to 5% nickel and 1 to 3% chromium.

� Modified Ni-hard : 4 to 8% nickel and 4 to 15% chromium .

� Ni-Resist :

� Increase the corrosion resistance of a gray or nodular cast iron

� Contains 14 to 36% nickel and 1 to 5% chromium

� Microstructure consists of flakes or nodules C graphite

� Used in applications requiring high corrosion, erosion, and heat resistance

Reference Books:







STEELS:

� Steels are alloys of iron and carbon plus other alloying elements.

� In steels, carbon present in atomic form, and occupies interstitial sites of Fe microstructure.

� Alloying additions are necessary for many reasons including:

� Improving properties,

� Improving corrosion resistance, etc.

Steels are classified based on their Carbon content

Steels are basically three kinds

Low-carbon steels (% wt of C < 0.3),

Medium carbon steels (0.3 <% wt of C < 0.6) and

High-carbon steels (% wt of C > 0.6).

The other parameter available for classification of steels is amount of alloying additions. Based on this steels are two kinds:

(Plain) carbon steels and

Alloy-steels.

CLASSIFICATION OF STEELS (PLAIN CARBON STEELS)

(1) Amount of carbon

(a) Low carbon steels (b) Medium carbon steels (c) High Carbon steels

(2) Amount of alloying elements and carbon

(a) Low Alloy steels (Alloy element < 10%) (b) High Alloy steels (Alloy elements>10%)

(3) Amount of deoxidization

(a) Rimmed steels (b) Killed steels (c) Semi killed steels

(4) Grain coarsening characteristics




(a) Coarse grained steels (b) Fine grained steels

(5) Method of manufacture

(a) Basic open hearth (b) Electric furnace (c) Basic oxygen process

(d) Acid open hearth (e) Acid bessemes

(6) Depth of hardening

(a)Non hardenable steels (b) Shallow hardening steels (c) Deep hardening steels

(7) On the basis of form and use

(a) Cast steels (b) Wrough steels

Reference Books:





MMS


Composition of Plain Carbon Steel

American Iron and Steel Institution (AISI) adopted and expanded the standardization for steel used in the automotive industry which was provided by Society of Automotive Engineers (SAE).

Denoted by four digit number:

First digit - Major alloying elements,

Second digit- Primary alloying element

Last two digits- Carbon content in percentage value.

LOW CARBON STEELS(OR) MILD STEELS

� These are produced in the greatest quantities than other alloys.

� Carbon present in thesmaterials by heat treatment; hence these alloys are strengthened by cold work.

� Their microstructure consists of ferrite and pearlite,

� These alloys are thus relatively soft, ductile combined with

� Hence these materials are easily machinable and weldable.

� Typical applications of these alloys:

� structural shapes,

� tin cans,

NOTES-29 UNIT


Composition of Plain Carbon Steel

American Iron and Steel Institution (AISI) adopted and expanded the standardization for steel used in the automotive industry which was provided by Society of Automotive Engineers

Denoted by four digit number:

Major alloying elements,

Primary alloying element

Carbon content in percentage value.

LOW CARBON STEELS(OR) MILD STEELS

These are produced in the greatest quantities than other alloys.

Carbon present in these alloys is limited, and is not enough to strengthen these materials by heat treatment; hence these alloys are strengthened by cold work.

Their microstructure consists of ferrite and pearlite,

These alloys are thus relatively soft, ductile combined with high toughness.

Hence these materials are easily machinable and weldable.

Typical applications of these alloys:

structural shapes,

tin cans,

UNIT-IV

American Iron and Steel Institution (AISI) adopted and expanded the standardization for steel used in the automotive industry which was provided by Society of Automotive Engineers

e alloys is limited, and is not enough to strengthen these materials by heat treatment; hence these alloys are strengthened by cold work.

high toughness.




� automobile body components,

� buildings, etc.

� A special group of ferrous alloys with noticeable amount of alloying additions are known as HSLA (high-strength low-alloy) steels.

� Common alloying elements are: Cu, V, Ni, W, Cr, Mo, etc.

� These alloys can be strengthened by heat treatment, and yet the same time they are ductile, formable.

� Typical applications of these HSLA steels include:

� support columns,

� bridges,

� pressure vessels.

Reference Books:






[Type text]

Ronanki .Pola Rao, Asso.Prof, Dept of ME, GMRIT-Rajam

[email protected],[email protected]

� Medium carbon steels

� These are stronger than low carbon steels.

� However these are of less ductile than low carbon steels.

� These alloys can be heat treated to improve their strength.

� Usual heat treatment cycle consists of austenitizing, quenching, and tempering at suitable conditions to acquire required hardness. They are often used in tempered condition.

� As hardenability of these alloys is low, only thin sections can be heat treated using very high quench rates.

� Ni, Cr and Mo alloying additions improve their hardenability.

� Typical applications include:

� Railway tracks & wheels, gears, other machine parts which may require good combination of strength and toughness.

� High carbon steels

� These are strongest and hardest of carbon steels, and of course their ductility is very limited.

� These are heat treatable, and mostly used in hardened and tempered conditions. They possess very high wear resistance, and capable of holding sharp edges.

� Thus these are used for tool application such as knives, razors, hacksaw blades, etc. With addition of alloying element like Cr, V, Mo, W which forms hard carbides by reacting with carbon present, wear resistance of high carbon steels can be improved considerably.

� ADVANTAGES AND DISADVANTAGES OF ALLOY STEEL

� ADVANTAGES :

� Greater hardenability

� Less distortion and Cracking

� Greater stress relief at given hardness



[Type text]

Ronanki .Pola Rao, Asso.Prof, Dept of ME, GMRIT-Rajam

[email protected],[email protected]

� Less grain growth

� Higher elastic ratio and endurance stength

� Greater high temperature strength

� Better machinabillty,atbigh hardness

� DISADVANTAGES :

� Cost

� Special handing

� Tendency to ward austenite retention

� Temper brittleness in certain grades

� PURPOSE OF ALLOYING

� 1. Strengthening of the ferrite

� 2. Improved corrosion resistance

� 3. Better hardenability

� 4. Grain size control

� 5. Greater strength

� 6. Improved machinability

� 7. Improved high or low temperature stability

� 8. Improved ductility

� 9. Improved toughness

� 10. Better wear resistance

� 11. Improved cutting ability

� 12. Improved case hardening properties etc.




� TOOL STEELS

� Tool and Die steels may be defined as special steels which have been developed to form, cut or otherwise change the shape of a material in to a finished or semi finished product.

� Properties of tool steels :

� (i) slight change ofform during hardening

� (ii) Little risk of cracking during hardening

� (iii) Good toughness

� (iv) Good wear resistance

� (v) Very good machinability

� (vi) A definite cooling rate during hardening

� (vii) A definite hardening temperature

� (viii) A good degree of through hardening

� (ix) Resistance to decarburization

� (x) Resistance to softening on heating (red hardness).

� Classification tool steels

� The Joint Industry Conference (He), USA has classified tool steels as follows:


MMS


Example: W8 means water hardening steel with 0.8% C.

INDIAN STANDARD CODE FOR DESIGNATIONOF PLAIN AND ALLOYSTEELS

Steels have been classified on the basis of:

(i) Mechanical properties, and

(iij Chemical composition

Designation of steel on the basis of mechanical properties such as tensile strength or yield stress

Method of deoxidation :

R - Rimming steel

K - Killed steel

No symbol - Semi

NOTES-31 UNIT


means water hardening steel with 0.8% C.

INDIAN STANDARD CODE FOR DESIGNATIONOF PLAIN AND

Steels have been classified on the basis of:

(i) Mechanical properties, and

(iij Chemical composition

Designation of steel on the basis of mechanical properties such as tensile strength or

Method of deoxidation :

Rimming steel

Killed steel

Semi-killed steel

UNIT-IV

INDIAN STANDARD CODE FOR DESIGNATIONOF PLAIN AND

Designation of steel on the basis of mechanical properties such as tensile strength or


MMS


Quality of steel :

QI - Non-ageingquality

Q2 - Freedom from flakes

Q3 - Given size controlled

Q4 - Inclusions controlled

Q5 - Internal homogenity guaranteed

Sulphur and Phosphorus content:

No symbol - 0.055% and 0.025 % S

P25 - 0.025 % P

P70 - 0.07 % P

Weldability guarantee :

W = Fusion weldable steel

WI = Steel weldable by resistance welding but not fusion weldable

Formability :

D1 -Drawingquality

D2 - Deepdrawingquality

D3 - Extra deep drawing quality

High alloy steels (total alloying elements> 10%)

Alloy tool steels

NOTES-31 UNIT


ageingquality

Freedom from flakes

Given size controlled

Inclusions controlled

Internal homogenity guaranteed

Sulphur and Phosphorus content:

0.055% and 0.025 % S

P and 0.025 % S

P and 0.07% S

Weldability guarantee :

= Fusion weldable steel

= Steel weldable by resistance welding but not fusion weldable

Drawingquality

Deepdrawingquality

Extra deep drawing quality

High alloy steels (total alloying elements> 10%)

UNIT-IV

= Steel weldable by resistance welding but not fusion weldable


MMS


Reference Books:



3. Material Science

NOTES-31 UNIT





UNIT-IV


MMS

Ronanki .Pola Rao, Asso.Prof, Dept of ME,[email protected],rpolarao@gm

� The properties of steel depends on the composition and its structure. � These properties can be improved by either changing its composition (i.e. alloying) or

its structure. � The structure of steel and thus the properties can be � It is the most important method of strengthening the metals.� It involves heating the metal within the solid state. � The temperature and time of heating must be strictly controlled, because, it has an

effect on grain size.

After attaining desired uniform temperature throughout, the metal is cooled at specified rate. Mechanical properties are significantly affected by the rate of cooling. Heat Treatment can be defined as the process of changing the structure and properties of metals and alloys by controlled heating and cooling. There are three stages of heat treatment .

(I) Heating to required temperature.(2) Holding at this temperature for a period of time to attain uniform temperature throughout the section. This stage is c(3) Cooling the steel at specified rate.

The major considerations are to produce a satisfactory combination of microstructure and mechanical properties so that the metal can fulfill its intended purpose.

� Relieving internal stresses, and � Refining the grain size to improve mechanical properties.� Improving the machinability.� Altering the surface conditions, and� Increasing the corrosion and wear resistance.

NOTES-32 UNIT


Heat Treatment Of Alloys

The properties of steel depends on the composition and its structure. These properties can be improved by either changing its composition (i.e. alloying) or

The structure of steel and thus the properties can be changed by heat treatment.It is the most important method of strengthening the metals. It involves heating the metal within the solid state. The temperature and time of heating must be strictly controlled, because, it has an

attaining desired uniform temperature throughout, the metal is cooled at specified rate. Mechanical properties are significantly affected by the rate of cooling.

can be defined as the process of changing the structure and properties of etals and alloys by controlled heating and cooling.

There are three stages of heat treatment .

(I) Heating to required temperature. (2) Holding at this temperature for a period of time to attain uniform temperature throughout the section. This stage is called soaking. (3) Cooling the steel at specified rate.

The major considerations are to produce a satisfactory combination of microstructure and mechanical properties so that the metal can fulfill its intended purpose.

Relieving internal stresses, and softening for further deformation. Refining the grain size to improve mechanical properties.

Improving the machinability. Altering the surface conditions, and Increasing the corrosion and wear resistance.

UNIT-V

The properties of steel depends on the composition and its structure. These properties can be improved by either changing its composition (i.e. alloying) or

changed by heat treatment.

The temperature and time of heating must be strictly controlled, because, it has an

attaining desired uniform temperature throughout, the metal is cooled at specified rate.

can be defined as the process of changing the structure and properties of

(2) Holding at this temperature for a period of time to attain uniform temperature

The major considerations are to produce a satisfactory combination of microstructure and


MMS

Ronanki .Pola Rao, Asso.Prof, Dept of ME,[email protected],rpolarao@gm

Heat treatment effects mechanical properties byHeat treatment of steel involves a combination of heating, holding and cooling at controlled rates to produce the desired conditions.

Reference Books:



3. Material Science

NOTES-32 UNIT


Heat treatment effects mechanical properties by changing the structure and grain size. Heat treatment of steel involves a combination of heating, holding and cooling at controlled rates to produce the desired conditions.


Engineering Materials / Agarwal


UNIT-V

changing the structure and grain size.

Heat treatment of steel involves a combination of heating, holding and cooling at controlled


MMS NOTES-33 UNIT-V


Annealing

Annealing can be defined as a heat treatment process in which the material is taken to a high

temperature, kept there for some time and then cooled.

Benefits of annealing are:

� Relieve stresses

� Increase softness, ductility and toughness

� Produce a specific microstructure

Depending on the specific purpose, annealing is classified into various types:

(I) Full annealing

(2) Process annealing (Recrystallisation annealing)

(3) Spheroidise annealing

(4) Isothermal annealing

Full annealing :Heating the steel to austenite phase and then cooling slowly within a closed

furnace by putting-off the heat supply.

Process annealing : Heating the steel to a temperature 600° - 700° (i.e. below critical point,

A1) holding at this temperature for a prolonged period and slow cooling.

Spheroidise annealing :Heating the steel just above the lower critical temperature (730° -

770°) and prolonged holding at this temperature followed by slow cooling to 660°C within

the furnace

Isothermal annealing :Steel is heated above the upper critical temperature and held for a

certain time at this temperature to form austenite. Then the steel is suddenly cooled to a

temperature 50° to 100°Cbelow lower critical temperature.

Term isothermal is associated with transformation of austenite at constant temperature.

Defined as the process of heating the steel to austenite phase and then cooling slowly within a

closed furnace by putting-off the heat supply.

(i) Heating the hypo-eutectoid steel to a temperature 30OC to 50°C above A3 (upper critical

point) and the same amount above A1.3 (lower critical point) for hypereutectoid steel.


MMS


(ii) holding at this temperature for sufficient time to allow necessary changes to occur (i.e. to

obtain austenite structure throughout the volume) and

(iii) slow cooling in the furnace.

It is commonly employed for castings and forgings to reduce the coarse grain structure prior

to machining

Purposes of full annealing :

(i) To soften the steel,

(ii) To relieve the internal stress,

(iii) To improve machinability,

(iv) To refine the grains, and

(v) To reduce the hardness.

After annealing steel becomes more ductile

Heating the steel to a temperature 600

temperature for a prolonged period and slow cooling.

NOTES-33 UNIT



obtain austenite structure throughout the volume) and then,

(iii) slow cooling in the furnace.


(ii) To relieve the internal stress,

machinability,

(iv) To refine the grains, and

(v) To reduce the hardness.

After annealing steel becomes more ductile

Heating the steel to a temperature 600 - 700° (i.e. below critical point,A1) holding at this

for a prolonged period and slow cooling.

UNIT-V



(i.e. below critical point,A1) holding at this


MMS


(i) to reduce the distortion of the crystal lattice produced by cold working.

(ii) to remove the strain hardening i.e., improve the ductility.

(iii) to relieve the internal stresses, and

(iv) to obtain a homogeneous

The process annealing is used extensively in the treatment of sheet and wires. It is also

applied to cold worked steel in order to restore ductility and softness.

Spheroidise Annealing

The spheroidised structure has lowest hardness and strength but good machinability,

toughness and ductility.

Heating the steel just above the lower critical temperature

holding at this temperature followed by slow cooling to

The subsequent cooling maybe conducted in still air.

This results in a completely spheroidised structure

This process is applied to high carbon steel and alloy steel to improve machinability and

ductility

NOTES-33 UNIT



(ii) to remove the strain hardening i.e., improve the ductility.

(iii) to relieve the internal stresses, and

(iv) to obtain a homogeneous fine-grained structure.


applied to cold worked steel in order to restore ductility and softness.

spheroidised structure has lowest hardness and strength but good machinability,

Heating the steel just above the lower critical temperature (730° - 770°

holding at this temperature followed by slow cooling to 660°C within the furnace.

The subsequent cooling maybe conducted in still air.

This results in a completely spheroidised structure


UNIT-V



spheroidised structure has lowest hardness and strength but good machinability,

770°) and prolonged

ithin the furnace.



MMS NOTES-33 UNIT-V


The steel is heated above the upper critical temperature and held for a certain time at this

temperature to form austenite. Then the steel is suddenly cooled to a temperature 50° to

100°Cbelow lower critical temperature.

At this temperature the austenite is completely decomposed to form pearlite.

It is widely employed for reducing the hardness of alloy steel.

The major limitation of the process is that, it is suitable only for small components.

Reference Books:





MMS


Process of heating the steel to above the upper critical temperature (810

cooling in still air.

Purpose:

(i) to relieve the internal stresses. (ii) to refine the grain structure.

(iii) to improve the machinability. (iv) to improve strength and toughness.

Normalising consists of :

(i)Heating the steel 30 to 50°C

and Acm for hyper-eutectoid steel).

(ii) Holding at this temperature for shorter time to prevent grain growth. But the time allowed

should be sufficient so that the temperature is uniform throughout the section, and

(iii) Cooling in air: The cooling rate is the major difference between normalising is similar to

that of annealing. But, slightly more rapid cooling results in finer grained structure than for

annealing.

Reference Books:



3. Material Science

NOTES-34 UNIT


Normalising

Process of heating the steel to above the upper critical temperature (810 - 930°C) followed by

(i) to relieve the internal stresses. (ii) to refine the grain structure.

improve the machinability. (iv) to improve strength and toughness.

50°C above upper critical temperature (A3 for hypo

eutectoid steel).

ure for shorter time to prevent grain growth. But the time allowed


The cooling rate is the major difference between normalising is similar to

annealing. But, slightly more rapid cooling results in finer grained structure than for




UNIT-V

930°C) followed by

improve the machinability. (iv) to improve strength and toughness.

for hypo-eutectoid steel

ure for shorter time to prevent grain growth. But the time allowed


The cooling rate is the major difference between normalising is similar to

annealing. But, slightly more rapid cooling results in finer grained structure than for


MMS NOTES-35 UNIT-V


Hardening

Process of heating steel to austenite phase following by rapid cooling in a liquid bath such as

water or oil.

Consists of heating the steel to a temperature 30° to 500° above A3 point for hypoeutectoid

steels and 30° to 50° above A 1,3 point for hypereutectoid steel, holding at this temperature

for considerable time to complete phase transformation and sudden cooling in water or oil

Purpose: The purposes of hardening followed by tempering are:

(i) to develop high hardness, wear resistance and ability to cut other materials.

(ii) to improve strength and toughness

It not suitable for industrial applications because of the following reasons:

� Martensite obtained due to quenching is extremely brittle and is not stable.

� Quenching produces high internal stresses in the hardening steel which results heavy

distortions and cracking of the part in service

Tempering

Process of heating hardened steel to a temperature below lower critical temperature, followed

by cooling.

Tempering renders the steel tough and ductile.

The hardening increases strength and hardness in steel, but decreases ductility and toughness

i.e. imparts brittleness.

Thus the steel under hardened condition is rarely used and is subsequently tempered to

relieve brittleness

The main purposes of tempering are:

(i) to reduce the thermal stresses.

(ii) to stabilise the structure of the metal.

(iii) to reduce the brittleness, and

(iv) to increase the toughness and ductility.

The tempering temperature must not exceed the critical point, as the steel would become

austenite and the benefits of hardening treatment would be lost.


MMS NOTES-35 UNIT-V


CLASSIFICATION OF TEMPERING PROCESSES:

Low-temperature tempering (150-250°C).

� Cutting tools, measuring tools and the parts that .have been carburised and surface

hardened.

Medium-temperature tempering (350 - 450°C).

� Commonly employed for coils and laminated springs.

High-temperature tempering (500 - 650°C).

� Applied to gear wheels, axles shaft and connecting rods.

Reference Books:





MMS NOTES-36 UNIT-V


THE JOMINY (END-QUENCH) TEST

Hardenability is the ease with which a steel piece can be hardened by martensitic

transformation

Or

It is the depth of hardening produced under the given conditions of cooling.

It is evaluated by determining the minimum cooling rate to transform an austenitized steel to

a structure that is predominately or entirely martensitic,

Or

By determining the thickness of the largest steel section that can be converted to such a

structure under the given conditions of cooling.

Hardenability is most commonly measured by the Jominy end quench test.


MMS NOTES-36 UNIT-V


� The specimen is of cylindrical shape with 25 mm (1.0 inch) diameter and

approximately 100mm (4.0 inch) in length and has a machined shoulder (or a fitted

detachable collar ring) at one end.

� The above specimen is austenitized at a constant temperature for a fixed time and

quickly transferred to a fixture (quenching)

� Water is allowed to flow on the bottom end through a pipe for about 20 minutes.

� At this pressure, water forms a complete umbrella over the bottom surface

of the specimen.

� The temperature of water should be between 21 and 27°C.


MMS NOTES-36 UNIT-V


The cooling rate is maximum at the quenched end of the specimen where usually full

hardening occurs and diminishes steadily towards the air cooled end where the structure is

nearly equivalent to that produced by normalising;

� The hardness (VPN or RC) is measured at intervals of 1.6 mm (1/16inch) distance

from the quenchedend.

� The hardness values are plotted as function of distance trom the quenched end and the

resulting-curveis called as Jominy Hardenability curve.

� The hardness changes most rapidly at a location where the structure is 50%

martensite.

Reference Books:





MMS


Surface layers of the steel parts are heated to the hardening temperature and it is then

quenched in water or some other medium.

Many important industrial products such as cams, gears, camshafts, piston pins, etc. should

have a hard, wear resistant surface and a tough core.

Such conditions in the steel are obtained by the following two methods.

1.Surface hardening:

Only the surface layers of the steel parts are heated to the hardening temperature

and it is then quenched in water or some other medium.

It requires appreciably less time.

Since only a small portion of the component is heated there is a minimum tendency

to crack.

(i)Flame hardening,

(ii)Induction hardening.

2. Chemical heat treatment:

In which the composition of surface layers is altered to make it hard and wear

resistanceand it is also called as case hardening.

(i) Carburising. (ii)Nitriding. (iii) Cyanidi

Carburising :

Introducing carbon into surface of the steel

Nitriding : Introducing nitrogen into the surface of the steel.

Cyaniding :Both carbon and nitrogen are a

Decomposition of molten cyanides salts

Carbonitriding :

Addition of carbon and nitrogen

Gaseous mixture of ammonia and hydro

NOTES-37 UNIT


Surface hardening


quenched in water or some other medium.


have a hard, wear resistant surface and a tough core.

Such conditions in the steel are obtained by the following two methods.

ce layers of the steel parts are heated to the hardening temperature

and it is then quenched in water or some other medium.

It requires appreciably less time.


(ii)Induction hardening.


resistanceand it is also called as case hardening.

(i) Carburising. (ii)Nitriding. (iii) Cyaniding and carbonitriding.

Introducing carbon into surface of the steel

Introducing nitrogen into the surface of the steel.

:Both carbon and nitrogen are added to the surface layers of the steel.

Decomposition of molten cyanides salts

Addition of carbon and nitrogen

Gaseous mixture of ammonia and hydro-carbons.

UNIT-V



ce layers of the steel parts are heated to the hardening temperature



dded to the surface layers of the steel.


MMS NOTES-37 UNIT-V


Flame Hardening

� Consists of heating the metal surface by using an oxyacetylene flame.

� Only a thin layer of the heated surface is brought to the hardening temperature.

� The flame is followed by a stream of cold water which quenches the heated layer of

metal and there by hardens .

� Small parts may be heated individually and then quenched.

� Parts of cylindrical shape may be slowly rotated and heated by exposing their surfaces

to the flame of the torch.

� Parts which may be flame-hardened successfully include machine tool beds, gears,

cams and camshafts.

Induction hardening

� The procedure for induction hardening is the same as flame hardening.

� High temperature is produced by high frequency alternating current.

� The surface to be hardened is enclosed (with out contact) in an induction coil.

� The passage of current through the coil causes induced current to heat the steel very

rapidly to the hardening range, and is immediately followed by spray quenching.

� The process of surface hardening by induction is expensive.

� However, when large quantities of identical parts are to be surface hardened, this

process is economical and efficient.

e.g., crank shafts, transmission shafts, cam shaft, connecting rods,

gears, spindles cylinders, etc.

Reference Books:





MMS


� Introducing carbon into surface

� Carburising is most widely used for securing hard; wear resistant surface and a tough

core.

� In this process, low-

Carbonaceous material

Solid Carburising or Pack Carburising :

� The components are placed in a heat resistant alloy box filled with carburiser

(charcoal) mixed with an energiser (barium carbonate or sodiu

� The filled box is closed with a steel cover and it is heated to about 940°C.

� At that temperature oxygen (air in the box) combines with carbon to form carbon

monoxide and is decomposed.

Gas Carburising :

Tight sealed furnace chamber filled wi

C3H8.

The parts are heated in furnace to the temperature of 900

hydrocarbons decompose with the formation of free carbon.

The steel surface absorb the carbon, liberated in

The advantages of gas carburising are:

(i) Operation time is less.(ii) Plant is more compact for given output.(iii) Carbon content of

the surface layers can be controlled easily, and(iv) The process is very suitable for mass

production.

� Introducing of nitrogen into the surface of the steel.

� Nitriding is usually done at 500

� Parts (machined to accurate size and heat treated) are placed in a gas

through which ammonia is allowed to circulate.

� In this temperature interval ammonia dissociates according to the following reaction.

� The atomic nitrogen combines with elements in the steel to form nitrides. This gives

extreme hardness to the surface

NOTES-38 UNIT


Carburising

Introducing carbon into surface of the steel.

Carburising is most widely used for securing hard; wear resistant surface and a tough

-carbon or low-carbon alloy steel is heated in contact with

Carbonaceous material from which the steel absorbs carbon.

Solid Carburising or Pack Carburising :

The components are placed in a heat resistant alloy box filled with carburiser

(charcoal) mixed with an energiser (barium carbonate or sodium carbonate).

The filled box is closed with a steel cover and it is heated to about 940°C.

At that temperature oxygen (air in the box) combines with carbon to form carbon

monoxide and is decomposed.

Tight sealed furnace chamber filled with a carburising gas such as methane CH

The parts are heated in furnace to the temperature of 900 - 950°C. At this temperature,

hydrocarbons decompose with the formation of free carbon.

The steel surface absorb the carbon, liberated in the process.

The advantages of gas carburising are:



Nitriding

Introducing of nitrogen into the surface of the steel.

Nitriding is usually done at 500 - 600°C.

Parts (machined to accurate size and heat treated) are placed in a gas

through which ammonia is allowed to circulate.

nterval ammonia dissociates according to the following reaction.

The atomic nitrogen combines with elements in the steel to form nitrides. This gives

extreme hardness to the surface

UNIT-V

Carburising is most widely used for securing hard; wear resistant surface and a tough

carbon alloy steel is heated in contact with

The components are placed in a heat resistant alloy box filled with carburiser

m carbonate).

The filled box is closed with a steel cover and it is heated to about 940°C.

At that temperature oxygen (air in the box) combines with carbon to form carbon

th a carburising gas such as methane CH4 and propane

At this temperature,



Parts (machined to accurate size and heat treated) are placed in a gas-tight chamber

nterval ammonia dissociates according to the following reaction.

The atomic nitrogen combines with elements in the steel to form nitrides. This gives


MMS NOTES-38 UNIT-V


� Quenching is not required for development of hardness and therefore the parts do not

tend to crack. Since the parts are slow cooled, no further heat treatment is required.

� Nitriding increases the wear resistance, corrosion resistance and fatigue strength of

the steel. Since nitriding is done at low temperature it requires more time than gas

carburising.

Cyaniding:

� Case hardening process in which both carbon and nitrogen are added to the surface

layers of the steel.

� The process is based on the decomposition of molten cyanides salts with the

formation of free atoms of carbon and nitrogen which diffuse into the surface.

� The steel to be casehardened is placed in the molten salt bath (maintained at 800°C to

900°C) consisting of about 40% sodium cyanide, with about 60% of barium carbonate

and sodium chloride.

� At this temperature the steel will absorb carbon and nitrogen from the bath.

� The usual depth of a cyanide case is about 0.1 to 0.3 mm.


MMS


Involves the addition of carbon and nitrogen (in a single operation) by heating the steel in

a gaseous mixture of ammonia and hydro

This processes increase the surface, wear resistance and fatigue limit.

e.g., gears, pistons, pins, small shafts, etc.

NOTES-38 UNIT


Carbonitriding


of ammonia and hydro-carbons.

This processes increase the surface, wear resistance and fatigue limit.

e.g., gears, pistons, pins, small shafts, etc.

UNIT-V



MMS NOTES-39 UNIT-VI


Non-ferrous Metals and Alloys:

Metallic materials are divided into two large groups namely ferrous and nonferrous. The

iron based materials are called as ferrous materials and the materials which have same

element other than iron as the principle constituent are called as nonferrous materials.

The most extensively used non ferrous materials are alloys of

copper, aluminium, magnesium, nickel, zinc, tin, lead, etc.

COPPER AND COPPER ALLOYS

Properties:

I. Good ductility and malleability because of its FCC structure

2. High electrical and thermal conductivity

3. Non magnetic

4. Pleasing reddish color .

5. Ability of getting alloyed with many other metals which helps in improving its properties

6. Good corrosion resistance to atmosphere.

Applications of Pure Copper:

1. Electrical conductor 2. Bus bars 3. Automobile radiators

4. Roofs 5. Pressure vessels 6. Kettles 7. Utensils.

Classification of Copper Alooys: Four Groups

(a) Brasses (b) Bronzes (c) Cupronickels (d) Nickel silvers

Brasses : Copper and Zinc and containing more than 5 percent zinc

Bronzes : Alloys of copper with all other elements except zinc. Alloys of copper and tin,

aluminium, silicon, or berylium

Cupronickels : Alloys of copper and nickel are called cupro nickels and




contain upto 30 percent nickel

Nickel silvers : Alloys of copper, nickel and zinc

Reference Books:







Brasses :

(a) α brasses or Red brasses : contain zinc upto 36%. α -brasses : having 5 to 22 percent zinc

are reddish in colour and are called as red brasses.

α –brasses: having zinc content between 20 and 36 percent are yellow in colour and are

called yellow brasses.

Commercial Brass: contains 90 percent copper and 10percent zinc. used for

rivets,screws,jewellary

Cartridge Brass : 70 percent copper and 30 percent zinc. used for making cartridge cases,

house hold articles, radiator fins, lamp ,fixtures, etc.

Admirality Brass: contains 70 percent copper, 29 percent zinc and 1 percent tin. used for

propellers and marine works.

Aluminium Brass: 76 percent copper, 22 percent zinc and 2 percent aluminium . extensively

used for marine works

(b ) (α+β ) brasses: contain copper between 54 and 62 percent.

Muntz Metal: Contains 60 percent copper and 40 percent zinc.

It has high strength and excellent hot working properties. Extensively used for marine

fittings, consider heads, radiator cores, springs, chains, etc.

Naval Brass: Contains 60 percent copper, 39 percent zinc and 1 percent tin.

It has high corrosion and abrasion resistances .

Widely used for condenser plates, propeller shafts and in marine works.

Season Cracking of Brasses :

� Season cracking occurs when a cold worked component containing Internal tensile

stresses is in service for some time.

� Internal tensile stresses are developed due to deep drawing, pressing etc.




� The presence of the internal stresses makes that area more susceptible to corrosion

w.r.t other area.

� This increased tendency of corrosion leads to disintegration and failure of component

by inter granular corrosion process.

� This feature is known as season cracking. Season cracking is avoided by annealing the

component at a temperature of 280 - 300°C.

� Only high zinc brasses are attacked by season cracking.

Reference Books:







� Bronzes :

� Copper with all other elements except zinc are called bronzes.

� Most important bronzes are alloys of copper and tin, aluminium, silicon, or berylium.

� These may also contain phosphorus, lead, zinc or nickel.

� Tin Bronzes or Phosphor Bronzes :Alloys of copper and tin and contain tin between 1

and 11 percent. Possess high strength, toughness, high corrosion resistance, low

coefficient of friction and do not susceptible to season cracking.

� Used for bushes, cotter pins, clutch disks, springs, taps, marine pumps, etc.

� Tin bronzes have good castability and are widely used in the foundry.

� Gun Metal:

� Contains 88 percent copper, 10 percent tin and 2 percent zinc.

� It has considerable strength and toughness and resistance to sea water corrosion. It is

used for bushes, nuts, hydraulic fittings, heavy load bearings, marine pumps, etc.

� Aluminium Bronzes : Contain aluminium between 4 and II percent

� Have good cold working properties, good strength and good corrosion resistance.

These are used for corrosion resistant vessels, nuts, condenser tubes, bolts, etc.

� Heat treated aluminium bronzes are used for gears, propellers, pumps parts, bearings,

bushings, drawing and forming dies

� Silicon Bronzes : Contain 90 to 97 percent copper. 1 to 4 percent silicon and small

amounts of zinc,

� iron and manganese.

� The thermal and electrical conductivity of these alloys is about 10 percent of that of

pure copper.




� Silicon bronzes have mechanical properties comparable to that of mild steel and

corrosion resistance comparable to that of pure copper.

� These are used for storage vessels for chemical and gases,marine construction, bolts,

nuts, rivets, etc.

� Beryllium Bronzes :

� Beryllium bronzes contain 1.5 to 2.25 percent of Beryllium.

� These alloys can be easily cast, can be easily hot or cold worked and can be easily

welded.

� Like aluminium alloys, beryllium bronzes can be age hardened

� Used for diaphragms ,springs, surgical and dental instruments, gears,watch parts,

screws, bearings, etc

� Cupronickel: Alloys of copper and nickel . Contain upto 30 percent nickel.

� 25% nickel alloys are used for utensils, coinage and in ships.

� 30percentnickelalloy containing 1 percent manganese and 1percent iron can be cast

� into small castings. These are used in pumps, valves, condenser, tubes due to its good

� resistance to corrosion by sea water.

� Constantan : Constantan is a copper alloy containing 40 percent nickel, 1 percent

manganese and the rest copper. Used for rheostats, thermo couples and heating

devices operating at moderately high temperatures

� Nickel Silver or German Silver:

� Alloys of copper, nickel and zinc and contain 20 to 30 percent nickel, 10 to 30

� percent Zinc and the balance copper.

� The appearance of these alloys is similar to silver and possess good corrosion resistant

characteristics.

� These are mainly used for utensils, costume jewellary, name plates, etc.

Reference Books: Elements of Material science / V. Rahghavan






� ALUMINIUM AND ALUMINIUM ALLOYS

� It has several excellent properties as below:

� It is ductile and malleable due to FCC structure

� It is light in weight

� It has very good thermal and electrical conductivity

� It has excellent ability of getting alloyed with other elements like Cu , Si, Mg , Mn ,

Zn, etc

� It has excellent corrosion and oxidation resistance. This is due to the formation of

� Al2O3 film on the metal surface. Al2O3 is non-toxic which makes the metal suitable

for food

� packaging purpose.

� It is powerful deoxidiser

� It is also used in permanent magnets, shape-memory alloys and space alloys due to its

many

� other peculiar properties

� Used for cooking utensils, combs, collar buttons, toasters, mixers, electrical

conductors, food containers, paint, name plates, ashtrays, flowers pots, etc.

� It is also used in transportation industry in the manufacture of bicycles, motorcycles,

trucks and buses, aeroplanes and marine vessels

� The aluminium-silicon alloys :

� Are widely used for the production of castings due to their excellent fluidity and

casting characteristics.

� The properties of aluminium-silicon alloys depend on the amount of silicon.

� Higher the silicon content, better are mechanical properties, better is the corrosion and

oxidation resistance and lower is the coefficient of thermal expansion with improved

fluidity and casting characteristics.

Reference Books:

� Elements of Material science / V. Rahghavan

� Science of Engineering Materials / Agarwal

� Material Science -Prof. Satish V. Kailas �




� Aluminium-Manganese alloys: Magnalium

� It is highly resistant to corrosion, machines well and takes a high polish, and anodises

well.

� It has fairly good strength and is particularly suitable in marine environments.

� Aluminium-Copper alloys:

� LM 11 (4.5% Cu) is a precipitation hardenable alloy and produces good strength after

precipitation hardening.

� It is mainly used for aircraft castings and for other highly stressed parts due to its

good mechanical properties and shock resistance.

� Y-Alloy:

� This is a high strength aluminium alloy and contains about 4% copper, 2% nickel and

1.5% magnesIUm.

� It has an excellent ability to retain the strength at elevated temperatures with fairly

good corrosion

� resistance.

� It can be easily cast and rolled, but it is chiefly used in the cast form. It is mainly used

for pistons and cylinder heads of diesel and high duty petrol engines.

� Hinduminium:

� It contains about 5% Cu and 1.5%Ni with small amounts of Mn , Ti , Sb , Co and Zr.

� It is superior toy-alloy at elevated temperature service particularly in respect of creep

resistance.

� It is used in aero engines and other continuous elevated temperature service

applications upto 300°C.

Reference Books:







� Titanium and its alloys:

� Titanium is the fourth most abundant metallic element in the earth's rust.

Unfortunately, winning the metal from its ore is complicated and costly.

� Titanium is one of the few allotropic metals (steel is a:1other);that is, it can exist in

two different Crystallographic forms.

� At room temperature, it has a close-packed hexagonal structure, designated as the

Alpha phase.

� At around 885°C, the alpha phase transforms to a body-centered cubic structure,

known as the betaphase, which is stable upto titanium's melting point of about 1680°C

� The presence of a thin, tough oxide surface film provides excellent resistance to

atmospheric and sea environments as well as a wide range of chemicals, including

chlorine and organics containing chlorides.

� Being near the cathodic end of the galvanic senes, titanium performs the function of a

noble metal.

� Other notable properties are a higher melting point than iron, low thermal

conductivity, low coefficient of expansion, and high electrical resistivity

� Alpha Alloys :

� These alloys contain such alloying elements as aluminum tin, columbium, zirconium,

vanadium, and molybdenum in amounts varying from about I to 10percent.

� They are non heat-treatable, having good stability upto 540°C and down as low as -

220°C .

� They have a good combination of weldability, strength,and toughness.

� The 5 percent aluminium and 25 percent tin alloy, perhaps, the most widely used

alpha alloy,has been employed in numerous space and aircraft applications.

� It has a strength at room temperature of 8400 kg/cm2, acceptable ductility and is

useful at temperatures upto 430 and 540°C.

� In addition, it has good oxidation resistance, and good weldability and formability.

Reference Books:







� Alpha-Beta Alloy:

� It is the largest and most widely used group of titanium alloys.

� Because these alloys are a two-phase combination of alpha and beta alloys, their

behavior falls in a range between the two single-phase alloys.

� They are heat-treatable, useful upto 430°C, more formable than alpha alloys, but less

tough and more difficult to weld

� Beta Alloys:

� Although the beta alloys have exceptionally high strengths - over 14085 kg/cm2 - their

lack of toughness and low fatigue strength limits their use.

� They retain an unusually high percentage of strength upto320°C, but cannot be used

at much higher temperatures, and they become brittle at temperatures below

� -400°C.

Reference Books:





MMS NOTES-46 UNIT-VII


ABRASIVE:

Abrasive is a small ,non metallic hard particle having sharp edge and irregular shape .

They are capable of removing small amounts of material from a surface in form of small

chips.

In modern industry , the use of abrasives contributed to produce the

components with close tolerance and good surface finishes . Hence abrasives are used for

such operations as scratching , grinding, cutting, rubbing and polishing.

CLASSIFICATION:

Abrasives used in industries are classified under : 1. Hard

2.Siliceous

3.Soft

4. Artificial

HARD ABRASIVES:

Hard abrasives are diamond, corundum , emery and garnet.

DIAMOND: Diamond is a crystalline form of carbon found in nature .It is the hardest

material. Diamond therefore used for those applications where the life of other abrasives is

poor. Typical applications are in brick and concrete saws , wire drawing dyes, diamond

drills for drilling hard rocks and cutter for cutters for machining hard metals like any

abrasives

CORUNDUM: Corundum is aluminium oxide. This is used in grinding glasses and making

grinding wheels.

EMERY: Emery is a mixture of corundum and magnetic. This is used cheaply in making

grinding wheels , polishing glass and other materials.

GARNET: Garnet is either alamandite or grossularite .It is mainly used for rough polishing

plate glass

Reference Books:







SILICEOUS ABRASIVES:

Siliceous abrasives are Quartz , Flint, Quartzite ,Sand stone , plumice which are all composed

chiefly of silica. Most of them are used for sharpening stone and very fine edged instruments.

SOFT ABRASIVES:

These are non siliceous materials. The most common soft abrasives are rottenstone,

viennalime and metallic oxides. These soft abrasives are used for buffing .

ARTIFICIAL ABRASIVES:

The most important artificial abrasives are : 1.silicon carbide

2.Aluminium oxide.

SILICON CARBIDE:

Silicon carbide is manufactured in electric induction furnace. It is then manufactured under

trade names of carborundum, Crystolon , Carbolon ,electrolon etc.,

Silicon carbide is harder ,but not tougher than aluminium oxide. They

are used for grinding material sof low tensile strength such as cast iron ,brass, bronze, etc.,

TYPES:

GREEN GRIT ABRASIVES : It contains 97% SiC . It is mainly used for cementite

carbides and other harder materials

BLACK GRIT ABRASIVES : It contains 95% SiC. This is harder but weaker than green

silicon carbide. Black SiC is used for grinding cast iron ,Al,Cu and their alloys.It is also

suitable for grinding ceramics.

ALUMINIUM OXIDE:

It is manufactured from calcined bauxite in an electric arc furnace. It is then

manufactured under the trade names of aloxite , alundum , borolon.

Aluminium oxide is tough and not easily fractured. It is used for

grinding high tensile strength materials such as steel , malleable cast iron , wrought iron

,alloy steel and tough bronzes.

Reference Books:






Ronanki .Pola Rao, Asso.Prof, Dept of ME,GMRIT-Rajam [email protected],[email protected] Page 94

Advanced ceramics: these are newly developed and manufactured in limited range for

specific applications. Usually their electrical, magnetic and optical properties and

combination of properties are exploited. Typical applications: heat engines, ceramic

armors, electronic packaging, etc.

Some typical ceramics and respective applications are as follows: Aluminium oxide /

Alumina (Al2O

3): it is one of most commonly used ceramic material. It is used in many

applications such as to contain molten metal, where material is operated at very high

temperatures under heavy loads, as insulators in spark plugs, and in some unique

applications such as dental and medical use. Chromium doped alumina is used for making

lasers.

Aluminium nitride (AlN): because of its typical properties such as good electrical

insulation but high thermal conductivity, it is used in many electronic applications such as

in electrical circuits operating at a high frequency. It is also suitable for integrated

circuits. Other electronic ceramics include – barium titanate (BaTiO3) and Cordierite

(2MgO-2Al2O

3-5SiO

2).

Diamond (C): it is the hardest material known to available in nature. It has many

applications such as industrial abrasives, cutting tools, abrasion resistant coatings, etc. it

is, of course, also used in jewelry.

Lead zirconium titanate (PZT): it is the most widely used piezoelectric material, and is

used as gas igniters, ultrasound imaging, in underwater detectors.

Silica (SiO2): is an essential ingredient in many engineering ceramics, thus is the most

widely used ceramic material. Silica-based materials are used in thermal insulation,

abrasives, laboratory glassware, etc. it also found application in communications media as

integral part of optical fibers. Fine particles of silica are used in tires, paints, etc.

Silicon carbide (SiC): it is known as one of best ceramic material for very high

temperature applications. It is used as coatings on other material for protection from

extreme temperatures. It is also used as abrasive material. It is used as reinforcement in

many metallic and ceramic based composites. It is a semiconductor and often used in high

temperature electronics. Silicon nitride (Si3N

4) has properties similar to those of SiC but

is somewhat lower, and found applications in such as automotive and gas turbine engines.




Titanium oxide (TiO2): it is mostly found as pigment in paints. It also forms part of

certain glass ceramics. It is used to making other ceramics like BaTiO3.

Titanium boride (TiB2): it exhibits great toughness properties and hence found

applications in armor production. It is also a good conductor of both electricity and heat.

Uranium oxide (UO2): it is mainly used as nuclear reactor fuel. It has exceptional

dimensional stability because its crystal structure can accommodate the products of

fission process.

Yttrium aluminium garnet (YAG, Y3Al

5O

12): it has main application in lasers (Nd-YAG

lasers).

Zirconia (ZrO2): it is also used in producing many other ceramic materials. It is also used in

making oxygen gas sensors, as additive in many electronic ceramics. Its single crystals are

part of jewelry.

Reference Books:







Fabrication and processing of ceramics

Ceramics melt at high temperatures and they exhibit a brittle behavior under tension. As a

result, the conventional melting, casting and thermo-mechanical processing routes are not

suitable to process the polycrystalline ceramics. Inorganic glasses, though, make use of

lower melting temperatures due to formation of eutectics. Hence, most ceramic products

are made from ceramic powders through powder processing starting with ceramic

powders. The powder processing of ceramics is very close to that of metals, powder

metallurgy. However there is an important consideration in ceramic-forming that is more

prominent than in metal forming: it is dimensional tolerance. Post forming shrinkage is

much higher in ceramics processing because of the large differential between the final

density and the as-formed density.

Glasses, however, are produced by heating the raw materials to an elevated temperature

above which melting occurs. Most commercial glasses are of the silica-soda-lime variety,

where silica is supplied in form of common quartz sand, soda (Na2O) in form of soda ash

(Na2CO

3) while the lime (CaO) is supplied in form of limestone (CaCO

3). Different

forming methods- pressing, blowing, drawing and fiber forming- are widely in practice to

fabricate glass products. Thick glass objects such as plates and dishes are produced by

pressing, while the blowing is used to produce objects like jars, bottles and light bulbs.

Drawing is used to form long objects like tubes, rods, fibers, whiskers etc. The pressing

and blowing process is shown in figure




Figure: Schematic diagram of pressing and blowing processes

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Ceramic powder processing consists of powder production by milling/grinding, followed

by fabrication of green product, which is then consolidated to obtain the final product. A

powder is a collection of fine particles. Synthesis of powder involves getting it ready for

shaping by crushing, grinding, separating impurities, blending different powders, drying

to form soft agglomerates. Different techniques such as compaction, tape casting, slip

casting, injection molding and extrusion are then used to convert processed powders into

a desired shape to form what is known as green ceramic. The green ceramic is then

consolidated further using a high-temperature treatment known as sintering or firing.

As-mined raw materials are put through a milling or grinding operation in which particle

size is reduced to and physically ‘liberate’ the minerals of interest from the rest of the

‘gangue’ material. Wet milling is much more common with ceramic materials than with

metals. The combination of dry powders with a dispersant such as water is called slurry.

Ball- and vibratory- milling is employed to further reduce the size of minerals and to

blend different powders.

Ceramic powders prepared are shaped using number of techniques, such as casting,

compaction, extrusion/hydro-plastic forming, injection molding. Tape casting, also

known as doctor blade process, is used for the production of thin ceramic tapes. The

schematic diagram of tape casting process is shown in figure 10.2. In this technique slurry

containing ceramic particles, solvent, plasticizers, and binders is then made to flow under

a blade and onto a plastic substrate. The shear thinning slurry spreads under the blade.

The tape is then dried using clean hot air. Later-on the tape is subjected to binder burnout

and sintering operations. Tape thickness normally range between 0.1 and 2 mm.

Commercially important electronic packages based on alumina substrates and barium

titanate capacitors are made using this technique. A schematic diagram of doctor blade

process is shown in the figure.




Figure: Schematic diagram of tape casting process

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Slip casting is another casting technique widely used. This technique uses aqueous slurry,

also known as slip, of ceramic powder. The slip is poured into a plaster of Paris

(CaSO4:2H

2O) mold. As the water from slurry begins to move out by capillary action, a

thick mass builds along the mold wall. When sufficient product thickness is built, the rest

of the slurry is poured out (drain casting). It is also possible to continue to pour more

slurry in to form a solid piece (solid casting). The schematic diagram of slip casting

process is shown in figure

Figure: Schematic diagram of slip casting process

Extrusion and injection molding techniques are used to make products like tubes, bricks,

tiles etc. The basis for extrusion process is a viscous mixture of ceramic particles, binder

and other additives, which is fed through an extruder where a continuous shape of green

ceramic is produced. The product is cut to required lengths and then dried and sintered.

Injection molding of ceramics is similar to that of polymers. Ceramic powder is mixed

with a plasticizer, a thermoplastic polymer, and additives. Then the mixture is injected

into a die with use of an extruder. The polymer is then burnt off and the rest of the

ceramic shape is sintered at suitable high temperatures. Ceramic injection molding is

suitable for producing complex shapes. Figure shows schematically the injection molding




process

Figure: Schematic diagram of Injection molding

Most popular technique to produce relatively simple shapes of ceramic products in large

numbers is combination of compaction and sintering. For example: electronic ceramics,

magnetic ceramics, cutting tools, etc. Compaction process is used to make green

ceramics that have respectable strength and can be handled and machined. Time for

compaction process varies from within a minute to hours depending on the complexity

and size of the product. Basically compaction process involves applying equal pressure in

all directions to a mixture ceramic powder to increase its density. In some cases,

compaction involves application of pressure using oil/fluid at room temperatures, called

cold iso-static pressing (CIP). Then the green ceramic is sintered with or without

pressure. CIP is used to achieve higher ceramic density or where the compaction of more

complex shapes is required. In some instances, parts may be produced under conditions in

which compaction and sintering are conducted under pressure at elevated temperatures.

This technique is known as hot iso-static pressing (HIP), and is used for refractory and

covalently bonded ceramics that do not show good bonding characteristics under CIP.

HIP is also used when close to none porosity is the requirement. Another characteristic

feature of HIP is high densities can be achieved without appreciable grain growth.

Sintering is the firing process applied to green ceramics to increase its strength. Sintering

is carried out below the melting temperature thus no liquid phase presents during

sintering. However, for sintering to take place, the temperature must generally be

maintained above one-half the absolute melting point of the material. During sintering,




the green ceramic product shrinks and experiences a reduction in porosity. This leads to

an improvement in its mechanical integrity. These changes involve different mass

transport mechanisms that cause coalescence of powder particles into a more dense mass.

With sintering, the grain boundary and bulk atomic diffusion contribute to densification,

surface diffusion and evaporation condensation can cause grain growth, but do not cause

densification. After pressing, ceramic particles touch one another. During initial stages of

sintering, necks form along the contact regions between adjacent particles thus every

interstice between particles becomes a pore. The pore channels in the compact grow in

size, resulting in a significant increase in strength. With increase in sintering time, pores

become smaller in size. The driving force for sintering process is the reduction in total

particle surface area, and thus the reduction in total surface energy. During sintering,

composition, impurity control and oxidation protection are provided by the use of vacuum

conditions or inert gas atmospheres.

Reference Books:





MMS NOTES-53 UNIT-VIII


COMPOSITE MATERIALS

� With the invention and continued progress of modern technology, need for

materials with special properties are growing.

� Basic conventional engineering materials are not able to serve the purpose.

� New class of materials, known as composites, is thus emerged to serve the

specific needs of modern technology.

� A composite is made artificially and it contains at least two chemically distinct

constituents, which are insoluble in each other.

� Thus it achieves properties of both the constituents, which are otherwise does not

exist together.

� An engineer needs to have a very good knowledge about these materials for

efficient use of composites, and also to develop a new category of composites.

� There is a great need for materials with special properties with emergence of new

technologies.

� However, conventional engineering materials are unable to meet this requirement

of special properties like high strength and low density materials for aircraft

applications.

� Thus, emerged new class of engineering materials – composites.

Composites :

� Any multiphase material that is artificially made and exhibits a significant proportion

of the properties of the constituent phases.

� The constituent phases of a composite are usually of macro sized portions, differ in

form and chemical composition and essentially insoluble in each other.

� Composites are, thus, made by combining two distinct engineering materials in most

cases;

� one is called matrix -that is continuous and surrounds the other phase – dispersed

phase.

� The properties of composites are a function of the properties of the constituent phases,

their relative amounts, and size-and-shape of dispersed phase.

� Composite materials are classified based on different criteria like:




1.type of matrix material –

metal matrix composites,

polymer matrix composites and

ceramic matrix composites

2.size-and-shape of dispersed phase –

particle-reinforced composites,

fiber-reinforced composites and

structural composites

� That properties of composite materials are nothing but improved version of properties

of matrix materials due to presence of dispersed phase.

� However, engineers need to understand the mechanics involved in achieving the

better properties.

Reference Books:





MMS


Particle-reinforced composites

Most widely used composites mainly because they are widely available and cheap.

Two kinds: Dispersion

Particulate

These two classes are distinguishable based upon strengthening mechanism : dispersion

strengthened composites and particulate composites.

Dispersion-strengthened:

� Particles are comparatively smaller, and are of 0.01

� Here the strengthenin

� i.e. mechanism of strengthening is similar to that for precipitation hardening in

metals .

� Where matrix bears the major portion of an applied load

� Examples:

� Thoria (ThO2) dispersed Ni

strength.

� SAP (sintered aluminium powder)

extremely small flakes of alumina (Al2O3).

Particulate-reinforced composites

� Contain large amounts of comparatively coarse particles.

� Large particle composite

polymers, and ceramics)

NOTES-54 UNIT


reinforced composites


Two kinds: Dispersion-strengthened and

Particulate-reinforced composites.

These two classes are distinguishable based upon strengthening mechanism : dispersion

strengthened composites and particulate composites.

Particles are comparatively smaller, and are of 0.01-0.1µm in size.

Here the strengthening occurs at atomic/molecular level

i.e. mechanism of strengthening is similar to that for precipitation hardening in

Where matrix bears the major portion of an applied load

Thoria (ThO2) dispersed Ni-alloys (TD Ni-alloys) with high

SAP (sintered aluminium powder) – where aluminium matrix is dispersed with

extremely small flakes of alumina (Al2O3).

reinforced composites

Contain large amounts of comparatively coarse particles.

Large particle composites are utilized with all three material types (metals,

polymers, and ceramics)

UNIT-VIII

Page 105


These two classes are distinguishable based upon strengthening mechanism : dispersion-

m in size.

i.e. mechanism of strengthening is similar to that for precipitation hardening in

alloys) with high-temperature

where aluminium matrix is dispersed with

s are utilized with all three material types (metals,




� The particles should be of approximately the same dimension in all directions

(equiaxed). For effective reinforcement, the particles should be small and

evenly distributed throughout the matrix.

� The mechanical properties are enhanced with increasing particulate content.

� Concrete- Being composed of cement ( the matrix) and sand and gravel (the

particulates).

� It is also known as Portland cement concrete.

� Its strength can be increased by additional reinforcement such as steel

rods/mesh.

� Cermets are examples of ceramic-metal composites

� Cemented carbide-

� Extremely hard particles of a refractory carbide ceramic such as tungsten

carbide (WC) or titanium carbide (TiC), embedded in a matrix of a metal such

as cobalt or nickel.

� These composites are utilized extensively as cutting tools for hardened steels.

Reference Books:





MMS


Fiber-reinforced composites :

� Most fiber-reinforced composites provide improved strength and other

mechanical Properties and strength

stiff.

� The matrix material acts as a medium to transfer the load to the fibers, which

carry most off the applied load.

� The matrix also provides protection to fibers from external loads and

atmosphere.

� Classified as either continuous or discontinuous.

� The highest strength and stiffness are obtained with continuous reinforcement.

Discontinuous fibers are used only when manufacturing economics dictate the

use of a process.

Mechanical properties of fiber

• The properties of the fib

• The degree of which an applied load is transmitted to the fibers by the matrix

phase.

• Length of fibers, their orientation and volume fraction

• Direction of external load application

Structural composites

• These are special class of composites, usually

composite materials.

NOTES-55 UNIT


reinforced composites :

reinforced composites provide improved strength and other

mechanical Properties and strength-to-weight ratio by incorporating strong,

The matrix material acts as a medium to transfer the load to the fibers, which

carry most off the applied load.

The matrix also provides protection to fibers from external loads and

Classified as either continuous or discontinuous.

st strength and stiffness are obtained with continuous reinforcement.


use of a process.

Mechanical properties of fiber-reinforced composites depend on:

The properties of the fiber

The degree of which an applied load is transmitted to the fibers by the matrix

Length of fibers, their orientation and volume fraction

Direction of external load application

These are special class of composites, usually consists of both homogeneous and

composite materials.

UNIT-VIII

Page 107

reinforced composites provide improved strength and other

weight ratio by incorporating strong,

The matrix material acts as a medium to transfer the load to the fibers, which

The matrix also provides protection to fibers from external loads and

st strength and stiffness are obtained with continuous reinforcement.


The degree of which an applied load is transmitted to the fibers by the matrix

consists of both homogeneous and




• Properties of these composites depend not only on the properties of the

constituents but also on geometrical design of various structural elements.

Classification:

Laminar composites, and

Sandwich structures.

Reference Books:







Laminar composites

� There are composed of two-dimensional sheets/layers that have a preferred strength

direction.

• These layers are stacked and cemented together according to the requirement.

Materials used in their fabrication include:

• Metal sheets, cotton, paper, woven glass fibers embedded in plastic matrix, etc.

Examples: thin coatings, thicker protective coatings, claddings, bimetallics,

laminates.

• Many laminar composites are designed to increase corrosion resistance while

retaining low cost, high strength or light weight.

� Sandwich structures.

� Consist of thin layers of a facing material joined to a light weight filler

material. Neither the filler material nor the facing material is strong or rigid,

but the composite possesses both properties.

� Example: corrugated cardboard.

� The faces bear most of the in-plane loading and also any transverse bending

stresses. Typical face materials include Al-alloys, fiber-reinforced plastics,

titanium, steel and plywood.

� The core serves two functions :

� It separates the faces and resists deformations perpendicular to the face plane;

provides a certain degree of shear rigidity along planes that are perpendicular

to the faces.

� Typical materials for core are: foamed polymers, synthetic rubbers, inorganic

cements, balsa wood. Sandwich structures are found in many applications like

roofs, floors, walls of buildings, and in aircraft for wings, fuselage and

tailplane skins.

Polymer Matrix Materials:

� Polymers make ideal materials as they can be processed easily, possess

lightweight, and desirable mechanical properties.

� High temperature resins are extensively used in aeronautical applications.

� Two main kinds of polymers are thermosets and thermoplastics.




Thermosets :

� Thermosets have qualities such as a well-bonded three-dimensional molecular

structure after curing.

� They decompose instead of melting on hardening.

� They are most suited as matrix bases for advanced conditions fiber reinforced

composites

� Find wide ranging applications in the chopped fiber composites form particularly

when a premixed or moulding compound with fibers of specific quality and aspect

ratio happens to be starting material as in epoxy, polymer and phenolic polyamide

resins.

� Thermosets are the most popular of the fiber composite matrices without which,

research and development in structural engineering field could get truncated.

� Aerospace components, automobile parts, defense systems etc., use a great deal of

this type of fiber composites.

� Epoxy matrix materials are used in printed circuit boards and similar areas

Thermoplastics:

� Have one or two-dimensional molecular structure and they tend to at an elevated

temperature and show exaggerated melting point.

� Another advantage is that the process of softening at elevated temperatures can

reversed to regain its properties during cooling, facilitating applications of

conventional compress techniques to mould the compounds.

� The advantage of thermoplastics systems over thermosets are that there are no

chemical reactions involved, which often result in the release of gases or heat.

Techniques for Producing Fiber Reinforcement Plastics (FRP)

Open Mold Process

• Spray lay-up - Chopped roving and resin sprayed simultaneously, rolled.

• Hand lay-up - Lay-up of fibres or woven cloth, impregnate, no heat or pressure.

• Filament winding. • Sheet molding compound.

• Expansion tool molding. • Contact molding.

Closed Mold Process

• Compression molding – Load with raw material, press into shape.

• Vacuum bag, pressure bag, autoclave - Prepreg laid up, bagged, cured.




• Injection molding – Mold injected under pressure.

• Resin Transfer – Fibres in place, resin injected at low temperature.

Continuous Process :

• Pultrusion. • Braiding

Hand Lay up:

1. gel coat is applied to the open mould.

2. Fiber glass reinforcement in the form of cloth is manually placed in mould.

3. The base resin mixed with catalysts and accelerators is applied by pouring,

brushing or spraying.

4. Rollers or squeezers are used to thoroughly wet the reinforcement with the resin

and to remove entrapped air.

5. To increase the wall thickness of part being produced, layers of fiber glass that

roving and resin and added.

Examples: Tanks, Housings and building panels are made by this process.

Reference Books:






Page 112

Ronanki .Pola Rao, Asso.Prof, Dept of ME, [email protected],[email protected]

Spray up process:

1. If fiber glass is used continuous strand roving is fed through a combination of

chopper and spray gun that simultaneously deposits chopped roving and catalyzed

resin into the mould.

2. The deposits laminate is then identified with a roller or squeeze to remove air to

make sure the resin impregnates the reinforcing fibers.

3. Multiple layers are added to produce desired thickness.

4. Curing is done at room temperature. Sometimes curing is accelerated by

application of moderate amount of heat.

� Filament winding process:


MMS


� 1.The fiber reinforcement is fed through a resin both and then wound on the suitable

mandrel.

� 2. When sufficient layers are applied, the wound mandrel is cured either at room

temperature or at an elevated temperature in an oven.

� 3. The moulded part is thin stripped from the mandrel

Reference Books:



3. Material Science

NOTES-58 UNIT

Ronanki .Pola Rao, Asso.Prof, Dept of ME, [email protected],[email protected]

1.The fiber reinforcement is fed through a resin both and then wound on the suitable

2. When sufficient layers are applied, the wound mandrel is cured either at room

temperature or at an elevated temperature in an oven.

3. The moulded part is thin stripped from the mandrel




UNIT-VIII

Page 113

1.The fiber reinforcement is fed through a resin both and then wound on the suitable

2. When sufficient layers are applied, the wound mandrel is cured either at room


MMS


Pultrusion process:

� Used for the manufacture of components having continuous lengths and a constant

cross-sectional shape (i.e., rods, tubes, beams, etc).

� With this technique, continuous fiber rovings are first impregnated with a

thermosetting resin.

� these are then pulled through a steel die which performs to the desired shape and also

establishes the resin/fiber ratio.

� The stock then passes through a curling die which imparts the final shape; this die is

also heated in order to initiate.

� Curing of the resin matrix.

Laminating Plastics:

A laminated material is made by bonding together two or more thin layers of materials to

form a single unit or sheet.

Plywood, which is a laminated wood, is made up of many thin sheets of wood .

The same principle is used in the laminating plastics also.

Reference Books:



3. Material Science

NOTES-59 UNIT


Used for the manufacture of components having continuous lengths and a constant

sectional shape (i.e., rods, tubes, beams, etc).

With this technique, continuous fiber rovings are first impregnated with a

these are then pulled through a steel die which performs to the desired shape and also

establishes the resin/fiber ratio.

The stock then passes through a curling die which imparts the final shape; this die is

also heated in order to initiate.

the resin matrix.


form a single unit or sheet.


s used in the laminating plastics also.




UNIT-VIII

Page 114

Used for the manufacture of components having continuous lengths and a constant

With this technique, continuous fiber rovings are first impregnated with a

these are then pulled through a steel die which performs to the desired shape and also

The stock then passes through a curling die which imparts the final shape; this die is






PROPERTIES OF COMPOSITE MATERIALS :

Composite materils are used to:

I. To increase heat deflection temeprature 2. To reduce costs

3. To decreasethermal expansion 4. To reduce weight

5. To increase' toughness 6. To increase stiffness, strength

7. To increase mechanical damping 8. To increase dimensional stability

9. To reduce permeability to gases and liquids 10. To modify electrical properties

11. To maintain strength/stiffness at high temperatures

12. To improve design flexibility.

LIMITATIONSOF COMPOSITE MATERIALS:

1. Sophisticated technology requires high cost.

2. Skilled labourarerequired.

3. Theprocessof manufacturingcompositematerialsis suitableonlyformassproduction.

4. Choppedfiber reinforcementstend to extra moldwear from abrasion from the

reinforcement and

melt flow problems.

5. Materials cost is very high.

6. Glass and carbon as a reinforcement after fabrication machining can be abrasive to

tools.

7. Aramid can cause surface finish problems.

8. The process is not economical for small scale production

C – C composites:Carbon/Carbon (C/C) is a lightweight, high-strength composite

material capable of withstanding temperatures over 3000°C in many environments.

Carbon/Carbon Composites use the strength and modulus of carbon fibers to reinforce a

carbon matrix to resist the rigors of extreme environments. Using FMI (Fiber Materials, Inc)

specialty weaving techniques, composite structures can be tailored to meet varied physical

and thermal requirements through weaving architecture design.

FMI woven reinforcements are impregnated with resin or pitch and carbonized to yield

finished, fully dense composites using well controlled temperature and pressure processes

(up to 15000 psi).

At one-tenth the density, C/C offers a high performance, cost effective alternative to

refractory metals. Aerospace components commonly fabricated from C/C include rocket

motor nozzle throats and exit cones, nosetips/leading edges and thermal protection




systems. Reliable performance is the most critical requirement of these components. FMI

C/C Composites have demonstrated reliability and reduced systems costs, especially when

multiple components in an assembly can be replaced with a one-piece C/C design.

Commercial applications of Carbon/Carbon materials are:

• Missile Nosetips • Leading Edges • Solid Rocket Motor Throats • Heatshields Missiles Furnace Insulation • Heating Elements • Furnace Fixturing, Load Plates

• X-Ray Target

Reference Books:





mms notes by polarao sir

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