buehler’s guide to materials preparation - rbridges.comrbridges.com/thins/2005vandervoort5.pdf ·...

Buehler’s Guide to

Materials Preparation

The Science Behind Materials Preparation and Analysis TM

Introduction

Sir Henry Clifton Sir Henry Clifton SorbySorby

• “Anything approaching to a burnished (smeared) surface of polished scratches is fatal to good results.”

• Scientist - Sheffield, England• “Father” of Petrography

and Metallography• Understood Effect of

Abrasion on Microstructure

Preparation Requirements: To Preparation Requirements: To See the True MicrostructureSee the True Microstructure

• Remove cutting, grinding and polishing related deformation

• Avoid thermal damage• Avoid edge rounding• Minimize relief and smearing• Produce scratch-free surfaces

Introduction

Preparation SequencePreparation SequenceEach Step Must be Performed Properly

• Sampling• Sectioning• Mounting (if needed)• Grinding• Polishing• Etching (if needed)

Sampling

Designating Sampling Planes1. Transverse section2. Longitudinal “planar” section parallel to the

rolled surface3. Longitudinal section perpendicular to the rolled

surface

Rolling

Sectioning

SectioningSectioning• Sample a large component or part by

removing a suitably-sized specimen from the larger mass at the desired location and orientation

• Sectioning plane should be as near to the desired location as possible

Aggressive cutting methods will produce excessive damage that must be removed

Sectioning

100 µm

Examples of damage (arrows) from sectioning. Left: cut surface in CP Ti (mod. Weck’s reagent) on a plane

perpendicular to the cut; Right: residual sectioning damage in the plane-of-polish of a CP Ti specimen (Kroll’s reagent).

Sectioning

Heat-affected zone (left) and melting at the surface (right, arrows) due to abrasive sectioning A2 tool steel without a

coolant (nital etch). The cut surface was Ni plated after cutting perpendicular to the first cut (using coolant).

Sectioning

Sectioning MachinesSectioning Machines

Sectioning

Sectioning ParametersSectioning Parameters• Equipment (abrasive cut-off, precision saw)• Blade, Wheel (SiC, Al2O3, CBN, diamond)• Operating Variables:

– Load– Speed– Feed Rate– Contact Area

• Coolant

Note: Delicate materials may require encapsulation

Sectioning

Precision SawsPrecision Saws• Precision positioning• Small kerf loss• Diamond blades, thin abrasive wheels• Applications

– Delicate components– Ceramics, Carbides, Nitrides– Biomaterials

Mounting of Specimens

Why Mount Specimens?Why Mount Specimens?• Protect edges during preparation process

• Protect delicate samples

• Increase life of polishing surfaces

• Uniformity of shape and size for automation

• Simplify specimen identification

To Maximize Edge PreservationTo Maximize Edge Preservation• Select the best mounting compound – EpoMet resin

• Use a press that cools under pressure

• Plate edge with a protective metal – EdgeMet Kit

• Add a filler material to cast resins – Flat Edge Filler

• Use nappless polishing surfaces

Introduction

“Hot” Mounting Presses“Hot” Mounting Presses

Selecting a “Hot” Mounting CompoundSelecting a “Hot” Mounting CompoundPhenolicPhenolic (PhenoCure™)• Lowest Price• High Shrinkage• Poor Edge Retention• Poor Resistance to Hot Etchants

AcrylicsAcrylics (TransOptic™)• Transparent• Long Curing Cycle• High Shrinkage• Defect Prone• Low Chemical Resistance• Poor Heat ResistanceEpoxyEpoxy (EpoMet®)

• Superb Edge Retention• Low Shrinkage• Resistant to Heat and Chemicals• Abrasion Rate Matches Metals

Edge Retention

Salt-bath nitrided 1215 carbon steel mounted in a) Epomet resin, b) phenolic

resin; and c) methyl methacrylate resin and all prepared in the same holder revealing

variations in edge retention (nital etch). The arrows point to the iron nitride surface layer.

The needle-like particles are nitrides.

Castable MountingCastable Mounting“Cold Mounting”

• Acrylic Resins– VariDur– SamplKwick®

• Epoxy Resins– EpoKwick®

– EpoxiCure™– EpoThin®

– EpoColor™– EpoHeat™

Selecting a Castable ResinSelecting a Castable ResinAcrylic ResinsAcrylic Resins• Low Cost

• Rapid Cure

• Poor Edge Retention

• Strong Exothermic Reaction

• High Shrinkage

• Strong Odor

Epoxy ResinsEpoxy Resins• Low Shrinkage

• Transparent

• Adheres to Specimen

• Solvent Resistant

• Moderate to slow cure

• Will Flow into Cracks and Voids (under vacuum)

Castable Resin Processing FactorsCastable Resin Processing Factors• Specimens must be cleaned and dried• Do not use products beyond their shelf life• Mix resin and hardener by specified weights• Resin and hardener must be mixed carefully• Large epoxy volumes generate high heat• To reduce exotherm, use conductive mold• Large specimen size increases cure time

Introduction

Grinding / PolishingGrinding / Polishing

Grinding

Initial Grinding StepInitial Grinding Step• Goals

– Remove the damage resulting from sectioning– Establish a planar surface– Reach a specific plane close to a desired

area/feature

Extent of sectioning damage determines the Extent of sectioning damage determines the selection of the initial abrasive sizeselection of the initial abrasive size

Grinding

Subsequent StepsSubsequent Steps

• Remove damage from previous step(s)• Decreasing abrasive size

– Depth of damage decreases– Removal rate decreases

• Depth of damage is greater for soft materials than hard materials

Polishing

Final PolishingFinal Polishing

• Remove any remaining damage or smear

• Produce a lustrous, scratch-free surface

• Maintain edge retention and flatness

• Yield the true structure with sharpness and good

contrast

Polishing Problems

Examples of poor (a) relief control and (b) good relief control around voids in a

braze (glyceregia etch) and “comet tails” at nitrides in H13 tool steel

(Nomarski DIC, as polished), shown above.

Polishing Problems

Embedding of SiC abrasive is

a common problem with low-melting

metals. Polishing with

diamond abrasive does

not remove the embedded

particles, but alumina does.

SiC embedded in Pb (after 1-µm diam)

5 min polish with 0.05-µm Al2O3

After 3 min. polish with 0.05-µm Al2O3 Vibratory polish, SiO2, Pollack’s etch

Polishing Problems

This shrinkage gap caused bleed out of water after drying which obscures detail and creates confusion.

Polishing Problems

Improper drying has left spots of water on the surface. DIC

Grinding / Polishing

Preparation ParametersPreparation Parameters• Abrasive type, size and amount• Working surface (pad, cloth, etc.)• Wheel and head speeds and directions• Head position• Force applied to specimens• Individual force or central force• Lubrication• Time

AbrasivesAbrasives• Alumina (powders, suspensions)

• Diamond (paste, suspensions, aerosols)

(natural or synthetic; monocrystalline or polycrystalline)

• Colloidal silica (pH 9.5)

• Magnesium oxide (limited use)

• Cerium oxide (glass)

MasterPrepMasterPrep Alumina and Alumina and MasterMetMasterMet Colloidal SilicaColloidal Silica• Both are excellent for most metals and non-metals

MasterMetMasterMet Colloidal SilicaColloidal Silica• Preferred for refractory metals, polymers, sintered carbides

and aluminum alloys• Unsuitable for precious metals; will etch Mg alloys and stains pearlitic cast irons; causes etching problems with stainless steels

and Ni-base superalloys when using etchants with Cl- ions

MasterPrep MasterPrep Alumina SuspensionAlumina Suspension• Free from etching, cleaning and staining problems

• Sol-gel processing yields agglomeration-free suspension – far better than calcined aluminas

Wheel and Head: DirectionWheel and Head: Direction• Contra is slightly more aggressive• Complementary tends to throw abrasive off the wheel• Most methods use a combination of directions

Contra Comp

Central or Individual ForceCentral or Individual ForceCentral ForceCentral Force

– Cannot remove any specimens until preparation is complete

– Yields best flatness and edge retention

IndividualIndividual ForceForce– One or more specimens can be prepared– Can examine specimens easily during preparation– Easy to remove etch or repeat last part of cycle

TimeTime• Each step must remove the deformation

from the previous step• Increase time; increase material removal• Smaller jumps in abrasive size, shorter

times required• Increases in specimen surface area may

require longer times

Traditional MethodTraditional Method

2:00120 - 150/Comp.6 (27)0.05-µm alumina slurryMicroCloth®

2:00120 - 150/Comp.6 (27)1-µm diamond pasteBilliard

2:00120 - 150/Comp.6 (27)6-µm diamond pasteCanvas

1:00240 – 300/Comp.6 (27)600 (P1200) SiC*CarbiMet

Until plane240 – 300/Comp.6 (27)120 (P120) SiC*CarbiMet®

Time (min:sec)

Base Speed (rpm)/Direction

Load Lb. (N)/ SpecimenAbrasive/SizeSurface

Based on 1 ¼ mount size *Water cooled

Contemporary MethodContemporary Method

2:00120 – 150Contra*

6 (27)0.05-µm MasterPrep™alumina suspensionChemoMet®

4:00120 – 150

Comp.6 (27)3-µm MetaDi Supreme

diamond suspensionTriDent™

5:00120 – 150

Comp.6 (27)

9-µm MetaDi®Supreme diamond

suspensionUltraPol™

Until plane240 – 300Comp.

6 (27)180, 240 or 320

(P180, P240, or P400) SiC, water cooled

CarbiMetpaper

Time (min:sec)

Based on 1 ¼ mount size *Use contra only with low-speed heads (<100 rpm)

Preparation Procedures

For Preparation, Metals Are Grouped For Preparation, Metals Are Grouped According to Like CharacteristicsAccording to Like Characteristics

Preparation Procedures

Procedure DevelopmentProcedure Development• Materials are grouped by common

characteristics; periodic table used as a guide• Primary equipment used for development

– 8” (200 mm) platen– six 1.25” (30 mm) diameter specimens– central force holder

Copper, Nickel and Cobalt

Copper ProcedureCopper Procedure

2:00120

Comp.6 (27)

1-µm MetaDi Supremediamond suspension

TriDent

2:00120

Contra5 (22)

0.05-µm MasterMetColloidal silica

MicroCloth

3:00150

Comp.6 (27)

TexMet® 1000

5:00150

diamond suspensionUltraPol

Until plane

240Comp.

6 (27)320- (P400) grit SiC

Water cooledCarbiMet

Time (min:sec)

Load Lb. (N)/

SpecimenAbrasive/SizeSurface

Material• UNS C52400• ASTM B103• SAE J461• Cu – 0.16 P - 10 Sn • Phosphor Bronze

Etchant• Klemm’s III reagent

Description• Dendritic structure of

chill-cast phosphor bronze

Material• Cartridge brass• Cu - 30Zn

Etchant• Klemm’s III

Description• Wrought cartridge

brass, cold reduced 50% and annealed at 704 ºC producing equiaxed alpha grains containing annealing twins. Viewed with cross polarized light and sensitive tint. 50X.

Material• Eutectoid aluminum

bronze• Cu - 11.8Al

Description• Wrought, eutectoid

aluminum bronze, heat treated to form martensite (900 °C-1h, WQ). Viewed with cross polarized light.

Ferrous Metals

Steel ProcedureSteel Procedure

1:30120

Contra6 (27)

0.05-µm MasterPrepalumina suspension

MicroCloth pad

3:00150

Comp.6 (27)

TriDent cloth

5:00150

diamond suspensionApexHercules™ Hrigid grinding disk

Until plane

240Comp.

6 (27)240- (P280) grit SiC

Water cooledCarbiMet paper

Time (min:sec)

Load Lb. (N)/

Ferrous Metals

Material• UNS K11430• ASTM A588• C 0.15 Cr 0.52 Cu

0.32 Mn 1.05 Si 0.22 V 0.6 balance Fe

Etchant• 4% picral followed by

2% nital

Description• Hot-rolled plate steel

etched to reveal a moderately “banded” structure of ferrite and pearlite.

Ferrous Metals

Material• UNS J04001• AMS 1040• C 0.4 Mn 0.85

Si 0.6 balance Fe

Etchant• 2% nital

Description• Microstructure of

annealed carbon steel revealing ferrite and pearlite.

Ferrous Metals

Material• UNS G40270• SAE 4027• C 0.27 Mn 0.80 Mo

0.25 Si 0.25 balance Fe

Etchant• 2% nital

Description• Microstructure of hot-

rolled alloy steel revealing a bainitic structure with a few patches of pearlite, acicular ferrite and some patches of proeutectoid ferrite.

Ferrous Metals

Stainless Steel ProcedureStainless Steel Procedure

2:00120

Contra6 (27)

ChemoMet pad

5:00150

Contra6 (27)

TriDent cloth

5:00150

Contra6 (27)9-µm MetaDi Supreme

diamond suspensionUltraPol cloth

Until plane

240Comp.

6 (27)240- (P280) grit SiC

Time (min:sec)

Ferrous Metals

Material• UNS S41600• AISI 416 (CTC P70)• C 0.10 Cr 13.0 S >0.15

balance Fe

Etchant• Beraha’s CdS reagent

Description• Microstructure of “free-

machining” martensitic stainless steel in the quenched and tempered condition. Note: gray elongated sulfide inclusions, white delta ferrite and martensitic matrix. 500X.

Ferrous Metals

Material• Custom Flo 302 HQ• Fe-<0.08C-18Cr-9Ni-

Etchant• Tint etched with

Beraha’s BI reagent

Description• Microstructure of hot-

rolled and solution annealed and aged precipitation hardened stainless steel revealing a fully austenitic matrix. Magnification bar is 100 µm long.

Ferrous Metals

Cast Iron ProcedureCast Iron Procedure

4:00150

Comp.6 (27)

TexMet 1000 pad

2:00120

Contra6 (27)

ChemoMet pad

3:00120

Comp.6 (27)

TriDent cloth

5:00150

diamond suspensionUltraPol cloth

Until plane

240Comp.

6 (27)240- (P280) grit SiC

Time (min:sec)

Ferrous Metals

Material• Pearlitic Ductile Iron

Etchant• Beraha’s CdS

reagent

pearlitic ductile iron containing graphite nodules surrounded by ferrite. Viewed with polarized light plus sensitive tint. 500X.

Ferrous Metals

Material• Pearlitic Gray Iron

Etchant• Beraha’s CdS

reagent

pearlitic gray cast iron containing ferrite near the flakes.

Precious Metals

Precious Metals ProcedurePrecious Metals Procedure

2:00150-240

Comp.3 (13)

1-µm MetaDi IIdiamond paste*

TexMet 1500

2:00100-150

Comp.2 (9)

0.05-µm MasterPrepAlumina

MicroCloth

3:00150-240

Comp.3 (13)

3-µm MetaDi IIdiamond paste*

TexMet 1500

5:00150-240

Comp.3 (13)9-µm MetaDi II diamond

paste*TexMet ® 1500

Until plane

150-240Comp.

3 (13)220- to 320- (P240 to P400) grit SiC, water cooled

CarbiMet

Time (min:sec)

Load Lb. (N)/

* Use water as the lubricant, but keep the pad relatively dry.

Precious Metals

Material• Fine Silver,~100% Ag

Etchant• Equal parts of 10%

NaCN and 10% ammonium persulfate

Description• Equiaxed FCC grain

structure with annealing twins

Precious Metals

Material• 18-k Gold, 75 Au –

22 Ag – 3 Ni

Etchant• Equal parts of 10%

NaCN and H2O2(30% conc.).

Description• Equiaxed FCC grains

with annealing twins. Specimen was attack polished.

Precious Metals

Material• Paliney 7 (35% Pd –

30% Ag – 14% Cu –10% Pt – 10% Au –1% Zn)

Etchant• Aqua regia

Description• As-cast dendritic

structure.

Precious Metals

200 µm

Material• As-cast ruthenium

Etchant• None, polarized light

Description• As-cast grain

structure of high-purity ruthenium.

Low-Melting Point Metals

LowLow--Melting Point Metals ProcedureMelting Point Metals Procedure

4:00 –5:00

120-150Comp.

5 (22)1-µm Micropolish II alumina suspension

MicroCloth

4:0080-150

Contra4 (18)

0.05-µm MasterPrepAlumina

MicroCloth

3:00150-250

Comp.4 (18)800- (P1500) grit SiC, water

cooled, wax coatedCarbiMet

5:00150-250

Comp.4 (18)600- (P1200) grit SiC, water

cooled, wax coatedCarbiMet

Until plane

150-250Comp.

4 (18)400- (P600) grit SiC, water cooled, wax coated

CarbiMet

Time (min:sec)

Load Lb. (N)/

Use candle wax to coat the SiC paper

Precious Metals

Material• Cd – 20Bi

Description• As-cast dendritic

structure – primary Cd dendrites and a Cd-Bi eutectic

200 µm

Precious Metals

Material• Zn – 0.1Cu – 0.1 Ti

Description• As-cast cellular

structure of alpha-Zinc and a ternary eutectic. Note the large mechanical twins from deformation.

50 µm

Precious Metals

Material• Bi – 40 Sn

Etchant• FeCl3 – HCl - Ethanol

Description• As-cast eutectic of

nearly pure Bi and Sn

20 µm

Precious Metals

Material• Bi – 55% Pb

Etchant• Pollack’s reagent

Description• As-cast. Primary β,

BiPb3, and then a eutectic of β and Bi formed.

50 µm

Introduction

Etching

Techniques– Swab– Immersion– Electrolytic

• Black & White• Color 100 µm

Etching

Etching Reveals• Grain boundaries• Phases• Constituents• Homogeneity• Coatings and Platings• Interfaces• Heat affected zones• Reaction zones

• Dendritic patterns• Segregation• Deformation

Etching

Techniques• Swab

• Immersion

• Electrolytic

Attack controlled by chemical selection, time, current, voltage

Etching

Etchant SelectionLow-carbon sheet steel

2% NitalReveals ferrite grain boundaries and cementite

4% PicralReveals cementite

Beraha’s reagentColored grains based on crystallographic orientation

Etching

2% Nital4% Picral

Microstructure of as-rolled Fe – 1.31% C – 0.35% Mn – 0.25% Si high-carbon water hardenable tool steel. Note the Widmanstätten intragranular cementite that precipitated as pro-

eutectoid cementite before the eutectoid reaction. Originals at 1000X.

Etching

Microstructure of the as-rolled Fe – 1.31% C – 0.35% Mn – 0.25% Si specimen with the intergranular carbide network clearly visible after etching with alkaline sodium picrate, 90 °C –60 s. Original at 500X magnification. Note also some intragranular Widmanstätten cementite.

200 µm

Etching

Cartridge Brass, 50% CR, Fully Annealed

NH4OH-H2O2 (3% Conc.)

Klemm’s I Klemm’s IIPolarized Light + Sensitive Tint

Cartridge Brass, 50% CR, Fully Annealed

Etching

Beraha’s PbSKlemm’s III

Polarized Light + Sensitive Tint

Carbon Steel Weld EtchingHAZ

Base Metal

2% Nital

Klemm’s I

Technical Help

Information AvailabilityInformation Availability•• WebsiteWebsite

– Buehler Book– Tech Notes

•• EmailEmail– Techsupport.com, ask a specific question directly to

Buehler’s lab– Join Buehler’s E-club

• Technical updates• New product information

Etching

buehler’s guide to materials preparation - rbridges.comrbridges.com/thins/2005vandervoort5.pdf ·...

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