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DHANALAKSHMI COLLEGE OF ENGINEERING, CHENNAI
DEPARTMENT OF MECHANICAL ENGINEERING
ME6403 – ENGINEERING MATERIALS AND METALLURGY
1. What is an alloy?
UNIT – I : ALLOYS AND PHASE DIAGRAMS
PART – A (2 marks)
A metal alloy, or simply an alloy, is a mixture of two or more metals or a metal (metals) and a non- metal (non-
metals).
2. How many components are found in an alloy?
Two or more components are found in an alloy.
3. What is meant by base metal?
In an alloy, the element which is present in the largest proportion is called the base metal.
4. What are alloying elements?
In an alloy, all elements other than the base metal are called the alloying elements. 5. Define solid solution. [N-11]
A solid solution is formed when two metals are completely soluble in liquid state and also completely soluble in
solid state. In other words, when homogeneous mixtures of two or more kinds of atoms (of metals) occur in the
solid state, they are known as solid solutions.
6. Differentiate between substitutional and interstitial solid solution.
In substitutional solid solution, the solute atoms (impurities) substitute for parent solvent atoms in a crystal
lattice.
In interstitial solid solution, the solute atoms fit into the space between the solvent or parent atoms.
7. State Hume Rothery‟s rules for formation of substitutional solid solutions. [M-14]
1. Size factor: The atoms must be of similar size, with less than a 15% difference in atomic radius (in order
to minimize the lattice strain).
2. Crystal structure: The materials must have the same crystal structure.
3. Valence: The atoms must have the same valence.
4. Electro negativity: The atoms must have approximately the same electro negativity.
8. What are intermediate phases?
If an alloying element is added in excess of the limit of solid solubility, a second phase appears along
with the primary solution. If the second phase differs in both crystal structure and properties from primary
solid solution, then it is known as an „intermediate‟ phase.
9. What are intermetallic compounds?
The compound formed by two or more metals in apparently stoichiometric proportion is called intermetallic
compounds.
10. What are electron compounds?
If two metals consist of atoms more or less similar size but different valency, then the compounds formed
are called electron compounds.
11. Define „phase‟. What different kinds of phases are possible?
A phase is defined as any physically distinct, homogeneous and mechanically separable portion of a
substance. Three different kinds of phases are solid, liquid and vapour.
12. What is an equilibrium phase diagram?
A phase diagram can be defined as a plot of the composition of phases as a function of temperature in any
alloy system under equilibrium condition.
13. What are the advantages of the equilibrium diagrams?
1. To show what phases are present at different compositions and temperature under equilibrium
conditions?
2. To indicate the equilibrium solid solubility of one element in other element.
3. To indicate the temperature range over which solidification of a material occurs.
4. To indicate the temperature at which different phases start to melt.
14. State Gibb‟s phase rule. [M-14]
Gibb‟s phase rule is given by F=C-P+2 where,
F=degrees of freedom of system or number of variables (such as temperature, pressure or composition) that
may be changed independently without altering the equilibrium;
C=number of components (usually elements or compounds) forming the system; and
P=no of phases present in the system.
15. What are cooling curves?
Cooling curves are obtained by plotting the measured temperatures at equal intervals during the cooling
period of a melt to a solid.
16. What is a liquidus line, a solidus line and a solvus line?
In a phase diagram, liquidus line is the line or boundary that separates liquid and liquid+solid phase
regions.
A Solidus line is a line or boundary that separates solid and solid+liquid phase regions. A
Solvus line separates single-phase solid regions from two-phase solid regions.
17. What is the information that can be obtained from each point in a phase diagram?
Using a phase diagram, one can obtain at least the following three informations.1. The phases that are
present, 2. The composition of each phase, and 3. The amount of each phase present.
18. What is tie-line?
A tie line is simply an isothermal line drawn through point of consideration, extending across the two-phase
region and terminating at the phase boundary lines on either side.
19. Explain the lever-law calculation and what information does it provide?
Phase fraction = (Opposite arm of lever / Total Length of Tie line)
Phase percentage = (Opposite arm of lever /Total length of Tie line) X 100
Using the lever law calculations, one can compute the phase fraction and the phase percentage.
20. What is meant by invariant reaction? [N-13]
The eutectic reaction is also called an invariant reaction since it occurs under equilibrium conditions at a
specific temperature and alloy composition that cannot be varied.
21. Define the Eutectoid reaction. Give examples. [M-12]
In the eutectoid reaction a solid phase decompose into two other solid phases upon isothermal cooling.
Austenite a solid solution of carbon and gamma iron, decomposes in to pearlite a mixture of two solids alpha
iron and iron carbide
In the Fe-Fe3C equilibrium diagram the eutectoid reaction takes place at the temperature of 727°C, at the
composition of 0.8% of C, Austenite is converted into Pearlite mixture during cooling.
22. What is eutectic reaction? [N-13]
Upon cooling a liquid phase is transformed into the two solid phases at eutectic temperature. The opposite
reaction occurs upon heating. This is called eutectic reaction. In general the Eutectic mixture with in a simple
binary alloy system is the lowest melting point mixture within that alloy system.
23. Distinguish between peritectic and peritectoid reactions.
The peritectic reaction can be
written as
The peritectoid reaction can be
written as
24. What do you understand by „allotropy of iron‟?
Allotropy refers to the possibility of existence of two or more different crystal structures for a substance
depending upon temperature.
25. Define: ferrite and austenite. [M-13]
Ferrite is a primary solid solution based oniron having BCC structure. Maximum solubility of carbon in iron is
0.025% carbon at 723°C, while its solubility at room temperature is only about 0.008%.
Austenite is a primary solid solution based oniron having FCC structure. The maximum solubility of carbon in
FCC iron is about 2% at 1140°C.
26. Define: Cementite and Pearlite.
Cementite is the name given to the carbide of iron (Fe3C). It is the hard, brittle, intermetallic compound of iron
with 6.69% of carbon.
Pearlite is the eutectoid mixture of ferrite (87.5%) and cementite (12.5%). It is formed when Austenite
decomposes during cooling. It contains 0.8% of carbon.
27. Define: martensite, and bainite.
Martensite is the super saturated solid solution of carbon iniron. It is formed when steel is very rapidly
cooled from the austenitic state.
Bainite is a decomposition product of austenite, consisting of an aggregate of ferrite and carbide.
Bainite has hardness in between the hardness of pearlite and martensite.
28. Why is the iron-carbon equilibrium diagram usually not shown beyond 6.67% carbon?
This is because in practice, all steels and cast irons have carbon contents less than 6.67 wt % C.
29. What is steel?
The ferrous alloy having the carbon composition ranging from 0.008 to 2% is known as steel.
30. What is meant by eutectoid, hypoeutectoid, hypereutectoid steels? [N-13]
Steels that contain 0.8% C (the eutectoid amount of carbon) are called eutectoid steels.
Steels having less than 0.8% C are known as hypoeutectoid steels.
Steels having more than 0.8% C are known as hypereutectoid steels.
31. How do cast irons differ from steels in terms of carbon content?
Composition from 0.008% to 2% carbon represent steel and those above 2% carbon represent cast iron.
32. Distinguish between hypoeutectic and hypereutectic cast irons.
Cast irons that contain less than 4.3% C are termed as hypoeutectic whereas cast irons that contains
more than 4.3% C termed as hypereutectic.
33. What do you mean by substitutional solid solution? Briefly explain the rules governing the formation of
substitutional solid solution. [M-09]
When the solute atoms (impurities) substitute for parent solvent atoms in a crystal lattice they are called
substitutional atoms and the mixture of the two elements is called a substitutional solid solution. Hume Rothery‟s
rules govern the formation of substitutional solid solution.
1. Size factor 2.Crystal structure 3.Valence 4.Electronegativity
34. Why carbon solubility is more in an austenite? [M-09]
Austenite is a primary solid solution based on γ iron having FCC structure.
Carbon solubility is more in austenite, because austenite is an interstitial solid structure of carbon in iron. 35. What is substitutional solid solution? Give two examples. [N-07]
When the solute atoms (impurities) substitute for parent solvent atoms in a crystal lattice, they are called
substitutional atoms, and the mixture of the two elements is called a substitutional solid solution. E.g.,Cu-Ni
system, Cu-Zn system and Au-Cu system.
36. Distinguish between hypo-eutectoid steels and hyper-eutectoid steels. [M-07]
Hypoeutectoid steels: Steels having less than 0.8% C are known as hypoeutectoid steels. Hypereutectoid
steels: Steels having more than 0.8% C are known as hypereutectoid steels.
37. State the conditions under which two metallic elements will exhibit solid solubility.
To exhibit unlimited solid solubility, the solute and solvent elements should obey the general rules of Hume
Rothery‟s: 1.Size factor 2.Crystal structure 3.Valence 4.Electronegativity
38. Define polymorphism and Allotropy.
Polymorphism is a physical phenomenon where a material may have more than one crystal structure. A material
that shows polymorphism exists in more than one type of space lattice in the solid state. If the change in
structure is reversible, then the polymorphic change is known as allotropy. The best known example for
allotropy is iron.
39. Name the various micro structures of Fe-Fe3C phase diagram.
Various micro structures of Iron carbon equilibrium diagram are Ferrite, Austenite, Pearlite, Cementite, Ledeburite,
Martensite, Troostite, Sorbite and Bainite.
PART - (16 Marks)
1. What are cooling curves? Explain the time-temperature cooling curve of a pure metal, binary solid solution and
binary eutectic system?
2. Explain the following invariant reactions with reference to a phase diagram: (i) Eutectic reaction (ii) Eutectoid
reaction (iii) Peritectic reaction (iv) Peritectoid reaction. [N-13] [M-12]
3. What are the micro-constituents of iron-carbon alloys? Explain the general characteristics of each.
4. Draw iron-iron carbide equilibrium diagram and mark all salient temperatures and composition fields on it?
5. Describe the phase changes that occur when a molten 0.35% C steel solidifies and cools slowly from 1700° C
to room temperature. Also draw the probable microstructure of steel at about 800°C and 25 °C. [M-14]
6. Name the phase reactions occurring in Fe –FeC system. What are the temperatures and compositions at
which they occur?
7. Explain the primary crystallization of eutectoid steels, hypoeutectoid steels and hypereutectoid steels.
8. Explain the primary crystallization of eutectoid cast irons, hypoeutectoid cast irons and hypereutectoid cast
irons.
9. Two metals A and B have melting points at 900 °C and 800°C .The alloy pair forms an eutectic at 600°C of
composition 60% B and 40%A. A and B have unlimited mutual solubilities. Their solid solubilities are as
follows: 10%B in A at 600°C and 5%B in A at 0°C. [M-14]
10. Explain with neat sketch the eutectic systems. Give examples for this system. [M-13]
11. With neat sketch explain the two types of solid solution. [M-13]
12. Draw the indicative eutectic phase diagram (partially soluble type).
1. Define the term „heat treatment‟.
UNIT – II : HEAT TREATMENT
PART – A (2 Marks)
Heat treatment may be defined as an operation or combination of operations involving heating and cooling
of a metal/alloy in solid state to obtain desirable properties.
2. What are the purposes of the processing heat treatments?
1. To relieve internal stresses. 2. To improve machinability. 3. To refine grain size.
4. To soften the metal. 5. To improve hardness of the metal surface.
6. To improve mechanical properties (like tensile strength, hardness, ductilityy, etc.)
3. Draw the cooling curve for a pure metal and an alloy.
4. List the various stages of a heat treatment process.
Stage 1: Heating a metal/alloy beyond the critical temperature.
Stage 2: Holding at that temperature for a sufficient period of time to allow necessary changes to occur.
Stage 3: Cooling the metal/alloy (i.e., quenching) at a rate necessary to obtain the desired properties.
That is, cooling at a rate necessary to obtain the desired changes in the nature form, size and
distribution of micro-constituents.
5. List some of the important heat treatment operations widely used.
1. Annealing 2.Normalizing 3.Hardening 4.Tempering 5.Austempering 6.Martempering and 7.Case
hardening.
6. What is meant by annealing?
Annealing is defined as a softening process consisting of heating the steal to a temperature at or
near the critical point, holding there for a proper time and then allowing it to cool slowly in the furnace itself.
7. What are the purposes of annealing?
1. To relieve or remove stresses. 2. To induce softness. 3. To refine grain structure, 4. To alter ductility,
toughness, electrical, magnetic or other properties. 5. To remove gases 6. To produce a definite
microstructure. 8. List the different types of annealing.
a) Full annealing. b) Process annealing. c) Stress relief annealing. d) Recrystallization annealing, and e)
Spheroidizing annealing.
9. What is meant by full annealing? [M-12]
Full annealing consists of heating the steels 15 degrees to 40 degrees centigrade above A3
temperature in case of hypoeutectoid steels and above A1 temperature in case of hypereutectoid steels
and cooling very slowly in the furnace itself. Austenitic steel is the most ductile of the steels and has a very
high relative strength. It is held at this temperature until all the material transforms and then slowly cools
in a furnace to about 50 degrees Celsius when it can be then cooled through convection in the room. In
this process hardness and strength are restored by additional heat treatments after machining
10. What is meant by process annealing? [M-13]
Process annealing is applied to cold worked materials to negate effects of cold work. Commonly
sandwiched between two cold work operations, it improves ductility. This is used to treat worked metals,
such as two pieces of metal that have been welded together. This makes it possible for the metal to undergo
further work without fracturing. The metal is heated to just below the A1 temperature line (see blue arrow);
it is held there long enough for the metal to change the size and distribution of its grain structure and
then cooled naturally in air. This process is cheaper than Full Annealing or Normalizing because the metal
is not heated to high temperatures
11. What is meant by stress relief annealing and spheroidizing? State its importance. [N-13]
Stress relief – purpose of it is to remove stresses. Temperatures are low such that cold work effects are
not affected. Reduces the residual stresses in large castings and welded parts. These stresses are caused by
thermal cycling or work hardening. The metal is heated to 600 degrees Celsius (see green line), held at that
temperature level for over an hour and then cooled in air.
Spheroidizing: Medium and high carbon steels are too hard to machined. Prolonged cycling between
temperatures just below and above A1 line will develop spheroidite structure.This results in maximum
softness and ductility.
12. What is meant by normalizing?
Normalizing is similar to full annealing, but cooling is established in still air i n s t e a d in the furnace.
13. Differentiate between normalizing and full annealing.
Sl. No.
Normalising
Full Annealing
1.
Normalizing is more economical than
full annealing (since no furnace is
required to control the cooling rate).
Full annealing is costly
2. Normalizing is less time consuming. Full annealing is more time consuming.
3.
Normalizing temperature is higher
than full annealing.
Annealing temperature is lower than
normalising.
4. It provides a fine grain structure. It provides coarse grain structure.
14. What is quenching? List some of the quenching medium generally used in industries. [M-14]
Quenching refers to accelerated cooling.Some of the quenching medium that are used generally in
industries are: 5-10% caustic soda, 5-20% brine (NaCl), cold water, warm water, mineral oil (obtained
during the refining of crude petroleum), animal oil, vegetable oil (such as linseed, cottonseed, and
rapeseed).
15. What are the factors should be considered while selecting a quenching medium?
1. Desired rate of heat removal. 2. Required temperature interval.3. Boiling point. 4. Viscosity. 5. Flash point (if
combustible).6. Stability u n d e r r e p e a t e d u s e . 7. Possible r e a c t i o n s w i t h t h e m a t e r i a l b e i n g
quenched. 8. Cost.
2. 16. What are the three stages for quenching?
Stage 1: Vapour-jacket stage. Stage 2: Vapour-transport cooling stage. Stage 3: Liquid Cooling stage.
17. Rate the order the effectiveness of the following quench media: oil, brine, water, and molten salt?
Molten salt, brine, water and oil.
18. What does the term hardening refer to? What are the factors that affect the hardness?
Hardening refers to the heat treatment of steel which increases its hardness by quenching. The
hardness obtained from the hardening process depends upon the following factors: 1. Carbon content,
2. Quenching medium, 3. Specimen size, and 4. Other factors
19. Distinguish the work hardening process with the age hardening process.
Work hardening also known as strain hardening, is the process of hardening a metal, while working on it
(under cold-working conditions). Age h a r d e n i n g a l s o known p r e c i p i t a t i o n h a r d e n i n g , is t h e
p r o c e s s o f hardening a metal when allowed to remain or age after heat treatment.
20. The tempering process usually follows hardening process. Justify. [N-13]
The martensite which is formed during hardening process is too brittle and lacks good ductility and toughness.
Hence, it cannot be used for more applications. Also the internal residual stresses that are introduced
during hardening have a weakening effect. The ductility and toughness of martensite can be enhanced and
these internal stresses are relieved by a heat treatment process known as tempering.
21. What is the effect of: (a) tempering temperature, and (b) tempering time, on the hardness of steels?
a) The hardness gradually decreases as the temperature is increased. b) The hardness decreases with the
increase in tempering.
22. What do you mean by temper embrittlement?
The tempering of some steels/steel alloys may result in a reduction of toughness (i.e., increase in
brittleness). This phenomenon is referred as temper embrittlement.
23. What is TTT diagram?
The TTT diagram is a plot of temperature versus the logarithm of time for a steel alloy of definite
composition. It is a tool used by heat treaters to predict quenching reactions in steels.
24. What is the significance of TTT diagram in the heat treatment of steel? [M-14]
The TTT diagram is most useful in giving an overall picture of the transformation behavior of
austenite. This enables the metallurgist to interpret the response of steel to any specified heat treatment.
Using a TTT diagram, one can plan practical heat treatment operations to get desirable micro constituents,
to control limited hardening or softening, and the time of soaking.
25. Why are TTT diagrams usually not applicable to industrial engineering practices?
The data for the construction of TTT diagrams are obtained from the isothermal transformation of
austenite at differing temperatures. But most industrial heat treatments involve continuous cooling from the
austenitic temperature to room temperature. Thus a TTT diagram may not five a fully accurate
representation of the temperatures and times of the transformations occurring. 26. What is CCT diagram?
The CCT diagram is a plot of temperature versus the logarithm of time for a steel alloy of definite
composition. It is used to indicate when transformations occur as the initially austenitised material is
continuously cooled at a specified rate. In addition, it is also used to predict the final microstructure and
mechanical characteristics.
27. Define the term critical cooling rate. What are the factors affecting it?
The slowest rate of cooling of austenite that will result in 100% martensite transformation is known as the
critical cooling rate.Factors affecting the critical rate are:1. Chemical composition of steel, 2. Hardening
temperature, and 3. Metallurgical nature (i.e, Purity) of steel.
28. What is significance of the critical cooling rate?
The critical cooling rate is most important in hardening. In order to obtain a 100% martensitic structure on
hardening, the cooling must be must be much higher than the critical cooling rate.
29. What is meant by hardenability? What are the factors that affect it? [M-12]
The term hardenability refers to the ease with which hardness may be attained.
In other words, hardenability is a measure of ease of forming martensite. The factors affecting the
hardenability are: 1.Composition of the steel, 2. Austenitic grain size, 3. Structure of the st ee l be fo re
quenching, and 4. Quenching medium and the method of quenching.
30. What is the difference between hardness and hardenability? [M-14]
The term hardness is the property of a material by virtue of which it is able to resist abrasion, indentation and
scratching. It is a mechanical property related to strength and is a strong function of the carbon content of a
metal.
On the other hand, hardenability is the susceptibility of a material to get hardened. It is affected by the
alloying elements in the material and grain size.
31. What is the benefit of the Jominy end-quench test?
For determining the hardenability of a given material.
32. What are hardenability curves? What are the uses of them?
The hardness curves are obtained from the data of Rockwell C hardness readings taken along the
length and the distance from the quenched end.The main practical uses of end-quench hardenability curves
are:
1. If the quench rate (i.e., cooling rate) for a given part is known, the Jominy hardenability curves can predict
the hardness of that part.
2. If the hardness at any point can be measured, the cooling rate at that point may be obtained from thehardenability curve for that material.
33. What are Martempering and Austempering?
Martempering, also known as mar quenching, is a interrupted cooling procedure used for steels to minimize
stresses, distortion and cracking of steels that may develop during rapid quenching.
Austempering is an isothermal heat treatment process, usually used to reduce quenching distortion and to
make tough and strong steels.
34. What do you mean by the term case hardening?
In many applications, it is desirable that the surface of the components should have high hardness, while
the inside or core should be soft. The treatments given to steels to achieve this are called surface heat
treatments or surface hardening.
35. List some of the surface-hardening techniques employed for altering surface chemistry? [M-13]
1. Diffusion methods: a) Carburizing, b) Nitriding, c) Cyaniding, and d) Carbonitriding.
2. Thermal methods: a) Flame hardening, and b) Induction hardening.
36. What are the differences between surface hardening by diffusion methods and thermal methods?
In diffusion surface-hardening method, the hardness of the surface is improved by diffusing interstitial
elements like carbon, nitrogen, or both into the surface of steel components.
In thermal method of surface hardening, only the surface of the steel components are heated to
temperature above the upper critical temperature and is suddenly quenched to get martensite formation on
the surface which gives higher hardness at the surface.
37. Differentiate between pack carburizing and gas carburizing.
In pack carburizing, the components to be treated are packed into steel boxes, along with the
carburizing mixture, so that a space of roughly 50 mm exists between them.
Gas carburizing overcomes the drawbacks of pack carburizing by replacing the solid carburizing mixture with
a carbon-providing gas.
38. In what ways, cyaniding differ from carburizing?
The salt bath composition for cyaniding gives a case high in nitrogen, whereas carburizing gives a
case rich in carbon.
39. What is meant by selective hardening technique?
Selective hardening (or heating) technique is a technique by which different properties are obtained simply
by varying the thermal histories of the various regions.
40. What are the selective heating techniques employed for surface hardening?
1. Flame hardening, and 2. Induction hardening.
41. In what ways, flame hardening differs from induction hardening?
The mechanism and purpose of induction hardening are the same as for flame hardening. The main
difference is that in induction hardening the source of heat input is an induced electric current instead of
using flame.
42. Define Carburizing process.
Carburising is the process of heating steel at 870–950 °C (1600–1750 °F) in an atmosphere of carbonaceous
gases (gas carburizing) or carbon-containing solids (pack carburizing) and then quench. A hard, high-carbon
surface is produced. Hardness 55 to 65 HRC. Case depth < 0.5–1.5 mm ( < 0.020 to 0.060 in.). Some
distortion of part during heat treatment. Applications like surface hardening of Gears,cams, shafts, bearings,
piston pins, sprockets, clutch plates.
43. Explain briefly about carbonitriding.
Heat steel at 700–800 °C (1300–1600 °F) in an atmosphere of carbonaceous gas and ammonia. Then quench
in oil. Surface hardness 55 to 62 HRC. Case depth 0.07 to 0.5 mm (0.003 to 0.020 in.). Less distortion than in
carburizing. This process can be applied to bolts, nuts, and gears.
44. What is flame hardening?
This involves heating the surface of a steel with an oxyacetylene flame (transforming the structure of the
surface layers to austenite), and then immediately quenching the surface with cold water (changing the
austenite to martensite). The depth of hardening depends on the heat supplied per unit surface area per unit
time. Thus, the faster the burner is moved over the surface, the less the depth of hardening. The temperatures
used in this method are typically of the order of 850°C or more, i.e. above the „A‟ temperature.
45. What are the three types of tempering?
Low temperature tempering, medium temperature tempering and high temperature tempering.
46. What is Induction hardening?
This method involves placing the steel component within a coil, through which a high frequency current is
passed. The form of the induction coil depends on the shape of the component being hardened. The alternating
current induces another alternating current to flow within the surface layers of the steel component, the induced
electrical currents heating the surface layers. The temperatures so produced cause the surface layers to
change to austenite. When the surface has reached the austenitizing temperature, the surface is sprayed with
cold water to transform the austenite to martensite. The depth of heating produced by this method, and hence
the depth of hardening, is related to the frequency of the alternating current used. The higher the frequency, the
less the depth hardened.
47. What is temper embrittlement?
The tempering of some steels may result in a reduction of toughness as measured by impact tests.
This is termed as temper embrittlement.
PART –B (16 Marks)
1. Explain the isothermal transformation diagram for a eutectoid iron-carbon alloy with superimposed cooling
curves? [N-13] 2. Write a short note on a) Hardenability b) Nitriding c) Flame hardening d) Cyaniding. [N-13]
3. What is annealing? Discuss in details on different types of annealing and compare with normalizing.
[M-13] [M-14] [M-12]
4. a) What is tempering? Discuss the structural transformation during tempering.
b) What is carburizing? Discuss Nitriding process and its importance for industrial applications? 5. Explain the various steps followed to determine an isothermal – transformation diagram and draw the IT
diagram for eutectoid steel. [N-12] 6. Explain the following forms: a) Tempering b) Austempering c) Martempering [N-12]
7. a) Distinguish between annealing and normalizing?
b) Explain with neat setup fig the working principle of an induction hardening? [M-14][M-13]
8. (a) What is a CCT diagram? (b) Describe various cooling curves on TTT diagrams. How such curves drawn?
(c) Write short notes on critical cooling rate? 9. Describe the Jominy end-quench test in details for determination of hardenability. [M-13][M-12]
10. Explain briefly the theory of tempering of alloy steels in the heat treatment process?
11. a).What do you understand by isothermal transformation? b).What are TTT diagrams?
c).How a TTT diagram is drawn? d). Draw a neat sketch of the TTT diagram for a eutectoid steel and label the
regions. Mark the different products formed on this diagram.
UNIT – III : FERROUS AND NON-FERROUS METALS
PART – A (2 Marks)
1. What are metals? Classify engineering materials?
Metals are elemental substances. Metals are composed of elements which readily give up electrons
to provide a metallic bond and electrical conductivity.
Types of metals: 1. Ferrous metals, and 2. Non-ferrous metals.
2. What are ferrous metals? Classify ferrous materials.
The metals, which contain iron as their main constituent, are called ferrous metals.
Types of ferrous metals: 1. Steels, and 2. Cast irons.
3. State three reasons why ferrous alloys are used extensively.
1. Iron-based components are relatively abundant and are widely distributed throughout the world.
2. Ferrous materials can be produced very economically.
3. Ferrous materials are versatile. Therefore wide range of mechanical and physical properties of ferrous
materials can be achieved.
4. State three characteristics of ferrous alloys that limit their utilization.
Heavy in weight, Lower electrical and thermal conductivity, lower resistance to corrosion.
5. How do you specify steel? What is the difference between 4140 steel and 4340 steel?
The AISI/SAE designation for the steels is a four digit number: First two digits indicate the alloy
content, and Last two digits indicate the carbon concentration.4140 steels is alloy of Cr-Mo with 0.40%
C, whereas 4340 steel is an alloy of Mo-Cr-Ni with 0.40% C.
6. What are three primary groups of plain carbon steels? [M-13]
1. Low-carbon steels: Those contain less than 0.25% carbon.
2. Medium-carbon steels: Those containing between 0.25 and 0.60% carbon.
3. High-carbon steels: Those containing more than 0.60% carbon.
7. What are alloy steels? How are alloy steels classified?
Alloy steels mean may steels other than carbon steels. Alloy steels can be divided
into two main groups as:
1. Low alloy steels: These contain up to 3 to 4% of alloying elements.
2. High alloy steels: These contain more than 5% of alloying elements.
8. List four important alloying elements added in alloy steels.
The most commonly used alloying elements are chromium, nickel, molybdenum, vanadium, tungsten,
cobalt, boron, copper and others.
9. Why is alloying done?
The alloying steel is generally done: To increase its strength, to improve hardness, to improve toughness, to
improve resistance to abrasion and water, to improve machinability and to improve ductility.
10. What are the primary effects of chromium, and copper as alloying elements in steel? [M-13][M-14]
Effects of alloying chromium: Increases corrosion and oxidation resistance, increases hardenability,
increases high-temperature strength, and resists abrasion and wear (with high carbon).
Effects of alloying copper: Increases strength, a n d i n c r e a s e s c o r r o s i o n resistance.
11. What is the effect of alloying Silicon and Cobalt in steels?
Silicon improves oxidation resistance, strengthens low alloy steels and acts as a deoxidizer.
Cobalt contributes to red hardness by hardening ferrite, improves mechanical properties such as tensile
strengths, fatigue strength and hardness, refines the graphite and pearlite, a mild stabilizer of carbides,
improves heat resistance and retards the transformation of austenite and thus increases hardenability and
freedom from cracking and distortion.
12. What are the effects of Lead and Sulphur on the machinability of steels?
Lead improves the machinability whereas Sulphur reduces it.
13. Which alloy elements are basically a) carbide formers, and b) graphite promoters?
a) Carbide formers: Cr, W, Ti, Mo, Nb, V, and Mn.
b) Graphite promoter: Si, Co, Al, and Ni.
14. What makes stainless steel “stainless”? [N13]
The chromium oxide (extremely dense-thin) protective layer acts as a barrier to retard further oxidation, rust
or corrosion. As this steel cannot be stained easily, it is called stainless steel.
15. Why do stainless steels lose their corrosion resistance when the chromium in solution drops below 12%?
When the weight% of chromium drops below 12% the corrosion rate increases sharply. As the
corrosion rate increases, the resultant chromium-oxide protective layer unable to retard oxidation, rust or
corrosion effectively.
16. What determines whether a stainless steel is austenitic ferritic, or martenistic?
The predominant phase constituent of the microstructure present in a stainless steel determines whether a
stainless steel is austenitic, ferritic, or martenistic.
17. What are the required properties of a tool steel? [N-13]
Tool steels should have the following properties:
1. Good toughness, 2. Good wear resistance, 3. Very good machinability,
4. Slight change of form during hardening, 5. Little risk of cracking during hardening.
5. Resistance to softening on heating.
18. .How can you classify tool steels?
1. Cold work tool steels, 2. Shock resisting tool steels, 3. Hot work tool steels,
High speed tool steels, 5. Plastic mold tool steels and 6. Special purpose tool steels.
19. What is meant by 18-4-1 high speed steel?
Widely used high-speed tool steel is 18-4-1 high speed steel. This steel contains 18% tungsten, 4%
chromium, and 1% vanadium. It is considered to be one of the best of all purpose tool steels.
20. What are HSLA steels? Where are they used?
HSLA steels are nothing but high-strength low-alloy steels. HSLA steels, also known as micro alloyed
steels, are low-carbon steels containing small amounts of alloying elements. These HSLA steels are
widely used as structural or constructional alloy steels.
21. What are Maraging steels? Give its composition. [N-13]
Maraging steels are low-carbon, highly alloyed steels. These are very high- strength materials that can be
hardened to obtain tensile strengths of up to1900 Mpa. Composition: Maraging steels contain 18%
nickel, 7% cobalt, and small amounts of other elements such as titanium. The carbon content is low,
generally less than 0.05%.
22. What are the Heat resisting steels and Free-machining steels?
Steels which can resist the creep and oxidation at high temperatures and retain sufficient strength are called
Heat resisting steels.
Free-machining steels, also known as free cutting steels, machine readily and form small chips so as to
reduce the rubbing against the cutting tool and associated friction and wear.
23. What are the features that make cast iron an important material?
1. It is a cheap metallurgical substance, 2. Good castability, 3. Good mechanical rigidity and good strength
under compression.4. Good machinability can achieve when a suitable composition is selected.
24. What are the effects of carbon on the properties of cast iron?
If a cast iron contains more of the brittle cementite, then its mechanical properties will be poor.
25. What is the influence of cooling rate on the properties of a cast iron?
High rate of cooling results in a weak and brittle cast iron. Slow cooling rate results in tough and strong cast
iron.
26. How do you classify Cast irons?
Cast iron types: 1.Grey C.I 2. White C.I 3.Maleable C.I 4. Spheroidal graphite C.I
27. What is the chemical composition of grey cast iron?
Typical composition of grey cast iron is given below:
Carbon – 2.5 to 4%. Silicon– 1 to 3%. Manganese– 0.4 to 1%. Phosphorus– 0.15 to 1%. Sulphur–
0.02 to 0.15%. Remaining is iron.
28. Where are white cast irons used?
1. White cast iron is used as a raw material in the production of malleable cast iron.
2. The typical applications of white cast irons include rolls, wear plates, pump linings, balls, etc.
3. It is also used for inferior casting and in places where hard coating is required as in the outer surface of
car wheels.
29. What is the difference between malleable cast iron and ductile cast iron?
Malleable cast iron is produced by heat treating unalloyed white iron. The ductile (or SG or nodular)
cast iron is produced by adding magnesium and/or cerium to molten cast iron. Both malleable and ductile
cast irons have the nodules, also called spheroids. But the nodules of ductile cast irons are more perfect
spheres.
30. What are alloy cast irons?
The alloy cast irons, like alloy steels, can be produced by adding alloying elements like Ni, Cr, Mo, Cu,
Si, and Mn Alloy cast irons have been produced to give high-strength materials, hard and abrasion-
resistant materials, corrosion resistant irons, and irons for high- temperature service.
31. What are the primary effects of adding Ni, and Mo in cast irons? [M-12]
S.No. Alloying element General
1.
Nickel (Ni)
It has graphitizing effect on cementite. So ittends to
produce a grey iron.
It has a grain-refining effect, which helps to prevent the
formation of coarse grain.
2.
Molybdenum (Mo)
It increases the hardness of thick sections. It
also improves toughness.
32. What properties do non-ferrous alloys have that usually are not associated with ferrous alloys?
1. Lighter in weight 2. Higher electrical and thermal conductivity 3. Better resistance to corrosion 4. Ease of
fabrication (casting, rolling, forging, welding, and machining) 5. Colour.
33. Write some characteristics of non-ferrous alloys that limit their utilization.
Non-ferrous materials are not produced in as great tonnages and are more costly than ferrous materials.
34. List the outstanding properties of copper and some typical applications.
The copper possesses the following properties:1. Very high electrical conductivity.
2. Very high thermal conductivity.3. Exhibits excellent resistance to corrosion.
4. Very soft, ductile and malleable.
Copper is extensively used for manufacturing power cables, telephone cables, cables for computer networks,
printed circuit boards, connectors, etc.
35. What is the main difference between a brass and a bronze? [M-13]
Brass is an alloy of copper and zinc whereas bronze is an alloy of copper and tin.
36. List at least four types of brasses used.
Gliding metal (or commercial bronze), cartridge brass, standard brass (or cold working brass), Muntz
metal (or yellow metal), Naval brass, Admiralty brass.
37. List some bronze alloys. [M-13]
Bell bronze, phosphor bronze, aluminium bronze, silicon bronze, coinage bronze and leaded bronze.
38. What are gun metals? Give its composition.
Gun metals are alloys of copper, tin, and zinc.
Composition of admiralty gun metal: 88 Cu, 10 Sn, 2 Zn, 2 (max) Ni.
39. State the composition, properties and applications of cupronickel and Monel metal.
The composition of the alloys can vary from 90% Cu–10% Ni to 70% Cu–30% Ni.
Uses: As heat exchanger or condenser tubes in evaporators of desalination plants, process industry plants, air
cooling zones of thermal power plants, high-pressure feed water heaters and Cupronickels are alloys of copper
and nickel.
Monel consists of ( in %) Ni - 66 , Cu- 31.5, Fe- 1.35, Mn- 0.9 plus residuals.
Uses of monel metal: For making propellers, pump fittings, condenser tubes, steam turbine blades, sea
w a t e r exposed parts, tanks, and chemical and food handling plants.
40. What properties have made aluminium and its alloys the most important non-ferrous metal?
i) Light-weight (one-third the weight of steel), ii) High thermal and electrical conductivity, iii) Excellent
corrosion resistance, iv) Non-toxicity, v) Soft and ductile, vi) Low specific gravity, vii) High strength-to-weight
ratio, and viii) High reflectivity.
41. Why does aluminium replace copper as an electrical conductor?
i) The price of the aluminium is much lower than that of copper. ii) The specific gravity of aluminium. iii) The
electrical conductivity of EC-grade (electrical conductor) aluminium is 61% of the conductivity of standard
copper, based on equal cross sections. iv) If equal weights of aluminium and copper conductors of a
given length are compared, it is found that aluminium conducts 201% as much current as does copper.
42. What are the two types of aluminium alloys?
1. Heat-treatable aluminium alloys, and 2. Non-heat treatable aluminium alloys.
43. What is duralumin? Give its composition and applications.
Duralumin is an alloy of aluminium and copper.
Composition: 94 Al, 4Cu, 0.5 Mg, 0.5 Mn, 0.5 Si, 0.5 Fe.
Typical appl icat ions : For a ircraf t and automobi le industries ; for making electric cables, in surgical
and orthopedic implements or gadgets, etc.
44. What is meant by precipitation hardening? [M-12][N-13]
Precipitation hardening, also known as age hardening, is the most important method of improving the
physical properties of some of the non-ferrous alloys by solid state reaction.
45.
46. Differentiate between natural ageing and artificial ageing.
The ageing process done at room temperature is often called natural ageing. Natural ageing takes a
prolonged period of time in terms of several days to reach maximum strength. Ageing at high temperature
of 190° C to 260° C accelerates the precipitation process and the time required is reduced considerably.
This process is called artificial ageing.
47. What is the effect of ageing temperature and time on the material strength?
The strengthening process accelerates with the increase in the ageing temperature. The maximum
strength increases as the ageing temperature decreases.
48. What are the required characteristics of a bearing material?
1. Bearing material should possess sufficient hardness and wear resistance.2. It should have a low coefficient
of friction.3. It should be tough, shock-resistant, and sufficiently ductile.
It should have a sufficient melting point, and high thermal conductivity.5. It should have good casting
qualities, and good resistance to corrosion.
49. List the bearing materials that are commonly used.
1. White metals, 2. Copper-base alloys, 3. Aluminium-base alloys,
Plastic materials, and 5.Ceramics.
50. What are super alloys? [M-14]
Super alloy is a general term used to describe the nickel-base and cobalt-base alloys which have been
developed for use at elevated temperatures.
Super alloys produce a combination of high strength as elevated temperature, resistance to creep at
temperatures up to 1000° C, and resistance to corrosion.
51. What is meant by Babbit metal? Give its composition and applications. [N-11]
Also called as white metal, it is an alloy used to provide the best bearing surface in a plain bearing. It has
properties that help reduce friction which make it a good material to use in a plain bearing. The structure of the
alloy is made up of small hard crystals dispersed in a matrix of softer alloy.
Common compositions for Babbitt alloys:
1) 90% tin 10% copper, 2) 89% tin 7% antimony 4% copper, 3) 80% lead 15% antimony 5% tin
Applications: Internal combustion engines use Babbitt metal which is primarily tin-based because it can
withstand cyclic loading. Lead-based Babbitt tends to work-harden and develop cracks but it is suitable for
constant-turning tools such as saw blades
52. State the effect of alloying elements in Aluminium.
Copper addition increases the strength and machinability but reduces the castability, ductility, and corrosion
resistance. Chromium, Manganese, and Zirconia are used to form compounds which control grain structure.
53. Name the carbide and ferrite stabilizer alloying element of cast iron.
Manganese, Magnesium are carbide stabilizers. Al, Cr, Si, Mo, W, P are ferrite stabilizers
PART – B (16 Marks)
1. Write short notes about the following materials in terms of composition, properties and applications.
a) Maraging steels b) Alpha–Beta brasses c) Austenitic stainless steels d) Ferrite stainless steels. [M-14]
2. Write short notes on a) Tool steels b) HSLA steels c) High speed steels.
3. i) Name nonferrous materials for the following articles
a) Bush b) furnace heating element c) type writer parts d) coins e) girder for airship
f) Big end bearing g) filament of electric lamps h) Turbine blades [M-13]
ii) Write notes on a) Bearing metals b) Brasses. [M-13]
4. Describe the different stainless steels with respect to composition, properties and applications. [M-12]
5. a) Discuss different types of copper alloys and their properties and applications.
b) Write a short note on bearing alloys. [M-12]
6. Explain the following tool properties:
a) safety in hardening b) quenching media c) Toughness d) Heat resistance. [N-12]
7. i) Explain the basic anodizing system with sketch.
ii) Differentiate anodizing and hard coatings and how dimensional changes is occur in above process with
simple sketch [N-12] 8. What are the influences of alloying Al, Cr, Ni, Mo, Si, Mn, V and Cu,Ti,W in steel? Explain in brief. [N-13]
9. What are the properties of aluminium? And what is the effect of different types of alloying elements such as Cu,
Iron, Manganese, Magnesium with aluminium and its application? Explain. [N-13] 10. a. Give the classifications of steels.
b. Describe the properties and typical applications of low-, medium- and high-carbon steels.
c. What is an alloy steel? How are alloy steels classified? Explain them
11. Discuss the composition, properties and typical applications of any four copper alloys?
12. Explain the composition, properties and typical applications of some aluminium alloys?
13. a. What is meant by age hardening? Explain the process of precipitation strengthening treatment for the Al-4%
C alloy system. [M-14]
b. Explain the effects of ageing temperature and time on the properties of the alloys. 14. a. What are the necessary metallurgical characteristics required in a good bearing metal?
b. Compare and contrast lead- base, tin-base, copper-base and aluminium-base bearing alloys. [M-14]
15. Describe the structures of different types of Cast irons and account for their continued use as engineering
material?
1. What are polymers?
UNIT – IV : NON-METALLIC MATERIALS
PART – A (2 Marks)
Polymers are composed of a large number of repeating units of small molecules called manometers.
Polymers may be defined as giant organic, chain-like molecules having molecular weight from 10000 to
more than 1,000,000 g.mol-1.
2. List any four attractive characteristics of polymers.
1. Low density. 2. Good thermal and electrical insulation properties.
3. High resistance to chemical attack. 4. Ease of fabrication. 5. Relatively low cost.
3. Classify polymers.
1. Plastics, 2. Elastomers, 3. Adhesives, 4. Coatings, 5. Fibres.
4. Define the following terms: i) Monometer, ii) Homopolymer, and iii) Copolymer.
Monomer is a small molecule consisting of a single mer i.e., a single unit/blocking block.
Homopolymer is a polymer made out of identical monomer.
Copolymer is a polymer which is obtained by adding different types of monomers.
5. What is meant by isomerism?
Isomerism is a phenomenon wherein different atomic configurations are possible for the same
configuration.
6. What is meant by the term „unsaturated molecule‟? State its significance in plastics. [M-14]
A compound in which the valence bonds of the carbon atoms are not satisfied is said to be unsaturated.
Such unsaturated molecules are important in the polymerization i.e., joining together of small molecules
into large one having the same constituents.
7. What is polymerisation?
Mechanism where smaller molecules combine to form larger molecules. Types: Addition polymerization and
Condensation polymerization.
8. Define the term „degree of polymerisation‟? [M-12] Degree
of polymerisation is the number of repetitive units (or mers) present in one molecule of a polymer.
Mathematically,
Degree of polymerisation = (Molecular weight of a polymer/ Molecular weight of a single monomer.)
9. What is the difference between addition polymerisation and condensation polymerization?
Addition polymerization, also known as chain reaction polymerization, is a process by which two or more
chemically similar monomers are polymerized to form long chain molecules.
Condensation polymerization, also known as step-growth polymerization, is the formation of polymers by
stepwise intermolecular chemical reactions that normally involve at least two different monomers.
10. Why are additives added to polymers?
The various polymer additives include:
1. Filler materials
2. Plasticizers
3. Stabilizers
4. Colorants
5. Flame retardants
6. Reinforcements
7. Lubricants
11. What are the characteristics of plastics which account for their wide use as engineering materials?
Plastics are extensively used in engineering applications due to their important properties such as low price,
colour range, toughness, water resistance, low electrical and thermal conductivity, ease of fabrication, etc.
12. Why are the fillers and plasticizers added to polymers?
Sl. No.
Additive
Names
Purpose
1.
Fillers
To improve tensile and compressive strengths.
To improve dimensional and thermal stability, and other
properties.
To reduce the cost of the final product.
2.
Plasticizers
To improve the flexibility, ductility, and toughness. To
reduce the hardness and stiffness.
To increase and control the flow of the polymer during
molding.
13. Differentiate commodity plastics with engineering plastics?
The plastics which are not generally used for engineering applications are known as commodity
plastics.The plastics which are used in engineering applications are known as engineering plastics.
14. Define plastics. [M-13]
A plastic is defined as an organic polymer, which can be molded into any desired shape and size with the
help of heat, Pressure or both. The plastic in to liquid form is known as resin.
15. Name any four commodity plastics and engineering plastics? [M-12]
Commodity plastics: i) Polyethylene (PE), ii) Polypropylene (PP), iii) Polystyrene (PS),
iv) Polyvinyl chloride (PVC).
Enginering Plastics: i) Ethenic, ii) Polyamides, iii) Cellulosics, iv) Acetals.
16. Distinguish between thermoplastics and thermosetting plastics.
Sl.
No.
Thermoplastics Thermosetting plastics
1.
They are formed by addition polymerisation. They are formed by condensation
polymerisation. 2.
They are l in e a r polymers, so t h e y are
composed of chain molecules.
They are composed of three dimensional
networks of cross-linked molecules. 3.
Softening is possible on reheating
(Because of the weak secondary forces).
Softening is not possible on reheating
(because of strong covalent bonds). 4.
They can be easily moulded on
remoulded into any shape.
They cannot be remoulded into any new
shape.
5. They can be recycled again. They cannot be recycled.
17. Name any four thermoplastics and thermosetting plastics.
Thermoplastics: Polythenes, Polypropylene, Polystyrenes, PVC.
Thermosetting plastics: Polyesters, phenolics, epoxides, melamine formaldehyde.
18. What advantages do thermoplastic polymers have over thermosetting polymers and vice versa?
Since thermoplastics have low melting temperature and can be repeatedly moulded and remoulded to the
desired shape, they have a good resale/scrap value. The thermosetting plastics are generally stronger, harder,
more brittle, more resistant to heat and solvents than thermoplastics.
19. What are the sources of raw materials for plastics?
1. Animal and vegetable by-products, 2. Coal by-products, 3. Petroleum by-products.
20. What are the following „acronyms‟ refer to: PE, PP, PS, PVC, PTFE, PMMA.? [M-12]
PE: Polyethylene; PP: Polypropylene; PS: Polystyrene; PVC; Polyvinyl chloride; PTFE:
Polytetrafluro ethylene; PMMA: Polymethyl methacrylate.
21. List the properties and typical applications of PVC.
Properties: Good low-cost, general purpose materials; ordinary rigid, but can be made flexible with
plasticizers; susceptible to heat distortion.
Typical applications: Pipes, valves, fittings, floor tiles, wire insulations, toys, phonograph records, safety glass
interlayers.
22. What are acrylic materials? Name any two. [N-13] Acrylic
materials are thermoplastic polymers based on the polymerization of esters of acrylic acid and/or
methacrylic acid.
The most commonly used acrylic polymers are:
1. PMMA (Polymethyl methacrylate), 2. PAN (Polyacrylonitrile).
23. Write short notes on nylons.
Polyamides (PA), also known as nylons, are the products of condensation reactions between an amine and
an organic acid.
There are number of common polyamides. They are usually designated as nylon 6, nylon 6/6, nylon 6/10,
nylon 6/12, nylon 11, and nylon 12. These suffixes refer to the number of carbon atoms in each of the reacting
substances involved in the condensation polymerization process.
24. What are bakelites? Also state their applications.
Phenolics, also known as Bakelites, are the oldest family of thermosetting plastics. The most important
phenolic materials is the polyformaldehydes. Typical applications include electrical plugs, sockets, switches,
telephones, door knobs and handles, adhesives, coatings, and laminates.
25. List the characteristics of urea-formaldehyde.
1. They are similar to the phenolics. 2. They are hard and rigid thermosets.
3. They have good electrical insulation properties. 4. They are light in colour.
5. They exhibit good resistance to most chemicals.
26. What are engineering ceramics?
Engineering ceramics are also known as technical/industrial ceramics, are those ceramics that are
specially used for engineering applications or in industries.
27. List some of the distinct characteristics of engineering ceramics.
1. High resistance to abrasion and wear. 2. High strength at high temperature.
3. Good chemical stability. 4. Good electrical insulation characteristics.
28. What are the main classifications of ceramic materials?
Engineering ceramics can be classified into oxides, carbides, sulphides, nitrides, metalloids, or
intermetallics.
29. Name any four engineering ceramics.
1. Alumina (Al2O3). 2. Selicon carbide (SiC). 3. Silicon nitride (Si3N4).
4. Partially stabilized zirconia (PSZ), and 5. Sialons.
30. Compare the fracture toughness of alumina, silicon carbide, and silicon nitride.
Property
MPa m-1/2
Al2O3
SiC
(Sintered)
Si3N4
(Reaction
bonded)
Si3N4
(Hot
pressed)
PSZ
Sialon
Fracture
toughness,
5.5
4
3
5.5
11
10
31. What is meant by PSZ?
Partially stabilized zirconia (PSZ) is nothing but a zirconium oxide (ZrO2) that has been blended and
sintered with some other oxide such as magnesium oxide (MgO), calcium oxide (CaO), and yttria (Y2O3), to
control crystal structure transformations.
32. What are sialons? State their applications. [M-14]
The name sialon is an acronym derived from the ingredients involved, namely Si formed when alumin ium
and oxygen partially substitute for silicon and nitrogen in silicon nitride. Sialons are used for cutting tool
materials, dies for drawing wire and tubes, rock-cutting and coal-cutting equipment, nozzles and welding
shields.
33. What are composites?
Composites are produced when two or more materials are joined to give a combination of properties
that cannot be attained in the original materials.
34. What are the constituents of composites?
Composites are composed of two phases. They are:1. Matrix phase and 2. Dispersed phase.
35. What is the role of matrix material in a composite?
The matrix usually provides the major control over electrical properties, chemical behaviour, and
elevated-temperature use of the composite.
36. List the various matrix materials used.
1. Thermosetting resins: Polyester resins, epoxide resins.
2. Thermoplastics: PA, PAI, PBT, PET, PES, PPS, PEEK
3. Metal matrices: Al, Ti, Mg, Cr and Ni, together with their alloys.
4. Composite materials.
37. List the various matrix materials used.
1. Polymers: Kevlar,nylon, polyethylene. 2. Metals: Be, Boron, W.
3. Glass: E-glass, S-glass. 4. Carbon: HS (high strength), HM (high modulus).
5. Ceramics: Al2O3, B4C, SiC, ZrO2. 6. Whiskers: Al2O3, Cr, graphite, SiC, Si3N4.
38. What are cermets? What are two common uses of cermets?
The term „cermet‟ refers to ceramic-metal composite containing between 80 and 90% of ceramic. Cermets
are composed of ceramic particles in metallic matrix.
Typical applications: Cutting tools slip gauge, wire-drawing dies, rocket motor and jet-engine parts.
39. Draw the molecular structure of polyethylene and polypropelyene.
40. What is ABS and state any two of its applications. [N-13]
Acrylonitrile-butadiene-styrene graft copolymer (ABS). TECARAN ABS
is an amorphous thermoplastic, which has high impact strength even at
low temperatures. The moisture absorption of ABS is low.
Special types of this material are suitable for electroplating. It has high
impact strength, even at low temperatures, low moisture absorption,
poor resistance to weathering and suitable for electroplating.
PART – B (16 Marks)
1. a) Write short note about the different types of matrix materials and reinforcement materials used to make polymer matrix composites. [M-14]
2.
b) Discuss the properties and applications of Al2 O3 and SiC.
Write short notes on a) PVC b) PF c) Glass d) PMMA
[M-13]
3. a)What is polymerization? Describe addition polymerization and condensation polymerization. [M-14]
b) How plastic materials are classified? Explain each classification. [M-13]
4. Write the properties and applications of the following polymers and discuss anyone fabrication methods
Polymers. a) PMMA, b) PP c) ABS d) PTFE [M-12]
5. a) List the important engineering ceramic materials and discuss its general applications of ceramic Materials in
various engineering fields. [M-14]
b) What are the advantages and disadvantages of ceramics? [M-12]
6. Describe the following terms a) linear polymer b) Branched polymer c) chain stiffening
d) Cross linked polymer. [N-12]
7. What is cemented carbide and how they are made. Explain the step by step process.
8. What are the properties and application of PVC, PET, PP and PC? Explain.
9. Write a short note on a) PTFE b) Phenol formaldehyde c) Engg. Ceramics
[N-12]
[N-13]
d) Fiber Reinforced plastic. [N-12]
10. (a).Describe the difference between thermoplastics and thermosetting plastics?
(b).Explain the differences between commodity plastics and Engineering Plastics?
UNIT – V : MECHANICAL PROPERTIES AND DEFORMATION
PART – A (2 Marks)
1. What is meant by mechanical properties of materials?
Mechanical properties are those characteristics of material that describe its behaviour under the action of
external forces.
2. Distinguish between elasticity and plasticity.
Elasticity is the property of a material by virtue of which it is able to retain its original shape and size after the
removal of the load.
Plasticity is the property of a material by virtue of which a permanent
deformation (without fracture) takes place, whenever it is subjected to the action of external forces.
3. Differentiate between ductility and malleability.
Ductility is the property of a material by virtue of which it can be drawn into wires before rupture takes place.
Malleability is the property of a material by virtue of which it can withstand deformation under compression
without rupture.
4. Define the terms brittleness and hardness.
Brittleness is the property of a material by virtue of which it can withstand deformation under compression
without rupture.
Hardness is the property of a material by virtue of which it able to resist abrasion, indentation (or
penetration), machining, and scratching.
5. What do you mean by toughness and stiffness?
Toughness is the property of a material by virtue of which it can absorb maximum energy before
fracture takes place.
Stiffness is the property of a material by virtue of which it resists deformation.
6. List any four technological properties of metals.
1. Machinability, 2. Castability, 3. Weldability, and 4. Formability or workability.
2. 7. What are the factors affecting mechanical properties?
1. Grain size, 2. Heat treatment, 3. Atmospheric exposure, and
4. Low and high temperatures.
8. What is the effect of the grain size on the mechanical properties of the materials? [M-14]
The materials having smaller grains (i.e., fine grained structure) have high yield strength, high tensile
strength, and more hardness. Also fine grain results in better resistance to cracking and better surface finish.
The materials having grains (i.e., coarse grained structure), exhibit better workability, hardenability,
forgeability and creep resistance. But coarse grains result in poor surface finish, less tough and have
greater tendency to cause distortion.
9. What is the effect of heat treatment on the mechanical properties of the materials?
The heat treatment improves mechanical properties like tensile strength, toughness, hardness, ductility,
shock resistance and resistance to corrosion. It also improves workability, forgeability and machinability
of metals.
10. Distinguish between elastic and plastic deformation of solid. [M-13] Sl.No
. Elastic deformation Plastic deformation
1.
It is the deformation of a body with
completely disappearsas Soon as the
external load is removed from the body.
It is the deformation of a body which remains
even after
Removing the external load from the body.
2. It obeys Hook‟s law. It does not obey Hook‟s law.
3.
The elastic deformation is the beginning of
the progress of deformation.
The plastic deformation takes place after the
elasticdeformationhas stopped.
11. Define the terms slip and twinning. [N-14]
Slip may be defined as the sliding of blocks of the crystal over one another along definite a mirror
image of the other part.
Twinning is the process in which the atoms in a part of a crystal subjected to stress, rearrange
themselves so that one part of the crystal becomes a mirror image of the other part.
12. Distinguish between slip and twinning.
During/ in slip During / in twinning Crystal Orientation
Same above and below the slip
Plane
Differ across the twin plane
Size(in terms of atomic
distance)
Multiples Fractions
Occurs on
Widely spread planes Every plane of region
involved
Time required Milli seconds Microseconds Occurance
On many slip systems
simultaneously
On a particular plane
for each crystal
13. State the Schmid‟s law and write the equation for critically resolved shear stress.
The stress required at a given temperature to initiate slip in a pure and perfect single crystal, for a
material is constant. This is known as Schmid‟s law.
14. What are the causes of twins?
1. Mechanical twins: Twins that are produced by mechanical deformation are called mechanical twins.
2. Annealing twins: Twins that are produced by annealing are called annealing twins.
3.
15. What is meant by fracture?
Fracture is the mechanical failure of the material which will produce the separation or fragmentation of a
solid into two or more parts under the action of stresses.
16. List the different types of fracture in a material.
1. Brittle fracture, 2. Ductile fracture, 3. Fatigue fracture, and 4. Creep fracture.
17. State the Griffith‟s criteria.
A crack will propagate when the decrease in elastic energy is at least equal to the
energy required to create the new crack surface. 18. What is brittle fracture?
A brittle fracture may be defined as a fracture which takes place by a slow propagation of crack
with appreciable plastic deformation.
19. What is ductile fracture?
Ductile fracture may be defined as the fracture which takes place by a slow propagation of crack
with appreciable plastic deformation. 20. Distinguish between brittle fracture and ductile fracture.
Sl.No. Brittle fracture Ductile fracture
1. It o c c u r s w i t h n e g l i g i b l e p l a s t i c
deformation.
It occurs with large plastic deformation.
2. It occurs at the point where micro crack is
more.
It occurs in some localised region where
the deformation is very large.
3. The rate of crack propagation is rapid. The rate of crack propagation is slow.
4. Failure is due to the direct stress. Failure is due to the shear stress.
21. How can you prevent the ductile fracture?
In order to prevent the ductile fracture, the material should have the following characteristics:
The material should have fine grains. It should ave higher hardness value.
It should have higher Young‟s modulus and cohesive energy. It should not have any defects/dislocations.
22. What is meant by fatigue fracture?
A fatigue fracture is defined as the fracture which takes place under repeatedly applied fatigue stresses.
23. What is S-N diagram? What is the significance of it? [May/Jun 2012][May/Jun 2014]
The S-N diagram is a graph obtained by plotting the number of cycles of stress reversals (N) required to
cause fracture against the applied stress level (S). Using S-N diagram, the fatigue life of a material can be
determined.
24. What do you mean by DBTT? Explain.
DBTT, is the Ductile Brittle Transition Temperature, The results of impact tests are absorbed energy, usually
as a function of temperature. The ABSORBED ENERGY vs. TEMPERATURE curves for many materials will
show a sharp decrease when the temperature is lowered to some point. This point is called the ductile to
brittle transition temperature (relatively narrow temperature range) .
A typical ductile to brittle transition as a function of temperature. The properties of BCC carbon steel and FCC
stainless steel, where the FCC crystal structure typically leads to higher absorbed energies and no transition
temperature
25. Name the various types of brittle fracture and explain it.
1. Transgranular fracture – Fracture cracks pass through grains. Fracture surface have faceted texture
because of different orientation of cleavage planes in grains.
2. Intergranular fracture - Fracture crack propagation is along grain boundaries (grain boundaries are
weakened or embrittled by impurities segregation etc.) 26. What is meant by super plasticity?
The ability of some metals to deform plastically by 1000 – 2000 % at high temperature and low loading rates.
27. What is creep? Draw a typical creep curve and show different creep stages on it. [M-13]
Creep fracture is the fracture that takes place due to excessive creeping of metals under steady loading.
Deformation that occurs under constant load/stress and elevated temperatures which is time-dependent is
known as creep. Creep deformation (constant stress) is possible at all temperatures above absolute zero.
However, it is extremely sensitive to temperature. Hence, creep in usually considered important at elevated
temperatures (temperatures greater than 0.4 Tm, Tm is absolute melting temperature).
28. Define endurance limit in a fatigue test. [N-14]
It is also known as fatigue limit, The fatigue limit is a maximum stress amplitude below which the material
never fails, no matter how large the number of cycles is. Fatigue life: Number of cycles to fail at specified
stress level. Fatigue strength: stress at which fracture occurs after specified number of cycles (e.g. 107 )
29. Draw the stress – strain diagram for ductile material.
30. What is the purpose of impact test? Why are impact specimens notched?
The purpose of impact test is to determine the susceptibility of materials to brittle behaviour.
31. Define hardness. List various methods to measure it.?
Measures the resistance of a material to penetration by a sharp object. Macrohardness Micro hardness,
and Nano-hardness. Brinell Hardness test, Rockwell Hardness test Vickers hardness test and Knoop
hardness test.
32. What is meant by fracture toughness?
Fracture toughness is a property which describes the ability of a material containing a crack to resist
fracture, and is one of the most important properties of any material for many design applications.
33. What is meant by Slip plane, Slip direction and Slip system?
Dislocations move on a certain crystallographic plane and the plane of greatest atomic density : slip
plane. Dislocations move in a certain crystallographic direction and the close packed direction within the slip
plane : slip direction. The Feasible combination of a slip plane together with a slip direction is considered
as a slip system is called a slip system.
34. Define fracture.
Fracture defined as the separation or fragmentation of a solid body into two or more parts under the action
of stress.
35. Define Fatigue. What are the factors affecting fatigue strength?
Fatigue fracture is the fracture that occurs under repeatedly applied fatigue stresses. This fracture occurs at
a stress well below the tensile strength of the materials
1. Fatigue strength is influenced by many factors such as chemical composition, grain size, and amount
of cold working.
2. Fatigue strength is high at low temperatures and gradually decreases with rise in temperature.
3. Environmental effects such as corrosion of the product by moisture decreases the fatigue strength.
4. The design of the product also influences the fatigue strength.
36. How can you prevent fatigue fracture?
The following methods can be adopted to prevent the fatigue failure.
1. Use of good design to avoid stress concentration by eliminating sharp recesses and severe
stress raisers.
2. Control of the surface finish by avoiding damage to surface machining,
punching, stamping, shearing, etc.
3. Reduction of corrosion environmental effects by surface heat treatments like polishings,
coatings, carburizing, nitriding, etc.
4. The material should have fine grain structure and also it should be free from residual stresses and
dislocations.
37. What is meant by creep fracture?
The creep is defined as the property of a material by virtue of which it deforms continuously under a
steady load.
38. What are the factors affecting creep?
1. Grain, 2. Thermal stability of the micro-structure,3. Chemical reactions, 4. Prior strain.
39. How can you prevent the creep fractures?
The following methods can be adopted to prevent the creep failure.
1. Use of coarse grained materials will avoid creep fracture.
2. Strain hardening can be done to avoid creep fracture.
3. The material should be free from any residual stresses and dislocations.
4. Precipitation-hardened alloys can be used to avoid creep fracture.
40. Differentiate between destructive and non-destructive tests.
In destructive type of testing, the component or specimen to be tested is destroyed and cannot be
reused.
In non-destructive type of testing, the component or specimen to be tested is not destroyed and can be
reused after the test.
41. List some important destructive tests carried out on a material.
1. Tensile test, 2. Impact test, 3. Bend test,
4. Fatigue test, 5. Torsion test and 6. Creep test.
42. List the main parameters which may be determined in a tensile test.
1. Limit of proportionality, 2. Yield point or yield strength, 3. Breaking strength,
4. Maximum tensile strength, 5.Percentage elongation, 6. Modulus of elasticity, and
7. Percentage reduction in area.
43. How does the Rockwell test differ from that of the others?
The principle of the Rockwell test differs from that of the others in that the depth of the impression is
related to the hardness rather than the diameter or diagonal of the impression.
44. Why must Rockwell test numbers always include a letter such as A, B, or C?
The Rockwell scales such A, B, or C are used to denote the type and size of the indenter used and the
total indenting load to be applied.
45. What is the difference between Izod and Charpy impact testing methods? [M-12]
Based on the types of specimen used on impact testing machine, the impact tests can be classified into: 1.
Izod test, and 2. Charpy test. Izod test uses a cantilever specimen of size 75 mm×10mm×10mm.
Charpytestuses a simply-supportedtest specimen ofsize 5mm×10mm×10mm.
46. Define the term notch sensitivity.
The notch sensitivity refers to the tendency of some normal ductile materials to behave like brittle
materials in the presence of notches.
PART B - (16 Marks) 1. Explain the different types of mechanical properties and mechanism of plastic deformation by slip and twinning.
[M-14] [N-12] 2. a) Sketch and describe the fatigue test .Draw the S-N curve for mild steel and aluminium and explain its
features. Explain the procedure used to obtain S-N diagram. [M-13] [M-14] 3. (a)Draw the engineering stress- strain curve for mild steel, aluminium and cast iron. Discuss the tensile test and
different mechanical properties obtained in tensile testing.
b) Write a short note on compression test. [M-12] 4. a) List the various types of hardness testing. Write a short note on Rockwell, brinell and Vickers hardness and
their significance. [M-12] 5. What is meant by ductile fracture? Explain the mechanism of it.
6. (a)Explain the types of impact tests. [N-12] [N-13]
(b)Explain the testing procedure of a shear test
7. Explain in brief the testing of materials to measure tension and compression with a graph and an example.
[N-13] 8. What is brittle fracture? Explain the Griffith‟s theory on brittle fracture and deduce an expression for the critical stress required to
propagate a crack simultaneously in a brittle material?
9. Explain the working principle and the results that obtained from the fatigue tests 10. Write an engineering brief about the creep test.