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
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
direc
tion
1 2 3
Rolling
direc
tion
1 2 3
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
Mounting of Specimens
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
Mounting of Specimens
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.
Mounting of Specimens
Castable MountingCastable Mounting“Cold Mounting”
• Acrylic Resins– VariDur– SamplKwick®
• Epoxy Resins– EpoKwick®
– EpoxiCure™– EpoThin®
– EpoColor™– EpoHeat™
Mounting of Specimens
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)
Mounting of Specimens
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
Grinding / Polishing
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)
Grinding / Polishing
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
Grinding / Polishing
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
Grinding / Polishing
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
Grinding / Polishing
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
Grinding / Polishing
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
1:00240 – 300/Comp.6 (27)400 (P600) SiC*CarbiMet
1:00240 – 300/Comp.6 (27)320 (P400) SiC*CarbiMet
1:00240 – 300/Comp.6 (27)240 (P280) 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
Grinding / Polishing
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)
Base Speed (rpm)/Direction
Load Lb. (N)/ SpecimenAbrasive/SizeSurface
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)
3-µm MetaDi Supremediamond suspension
TexMet® 1000
5:00150
Comp.6 (27)6-µm MetaDi Supreme
diamond suspensionUltraPol
Until plane
240Comp.
6 (27)320- (P400) grit SiC
Water cooledCarbiMet
Time (min:sec)
Base Speed (rpm)/Direction
Load Lb. (N)/
SpecimenAbrasive/SizeSurface
Copper, Nickel and Cobalt
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
Copper, Nickel and Cobalt
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.
Copper, Nickel and Cobalt
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)
3-µm MetaDi Supremediamond suspension
TriDent cloth
5:00150
Comp.6 (27)9-µm MetaDi Supreme
diamond suspensionApexHercules™ Hrigid grinding disk
Until plane
240Comp.
6 (27)240- (P280) grit SiC
Water cooledCarbiMet paper
Time (min:sec)
Base Speed (rpm)/Direction
Load Lb. (N)/
SpecimenAbrasive/SizeSurface
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)
0.05-µm MasterPrepalumina suspension
ChemoMet pad
5:00150
Contra6 (27)
3-µm MetaDi Supremediamond suspension
TriDent cloth
5:00150
Contra6 (27)9-µm MetaDi Supreme
diamond suspensionUltraPol cloth
Until plane
240Comp.
6 (27)240- (P280) grit SiC
Water cooledCarbiMet paper
Time (min:sec)
Base Speed (rpm)/Direction
Load Lb. (N)/ SpecimenAbrasive/SizeSurface
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-
3.5Cu
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)
3-µm MetaDi Supremediamond suspension
TexMet 1000 pad
2:00120
Contra6 (27)
0.05-µm MasterPrepalumina suspension
ChemoMet pad
3:00120
Comp.6 (27)
1-µm MetaDi Supremediamond suspension
TriDent cloth
5:00150
Comp.6 (27)9-µm MetaDi Supreme
diamond suspensionUltraPol cloth
Until plane
240Comp.
6 (27)240- (P280) grit SiC
Water cooledCarbiMet paper
Time (min:sec)
Base Speed (rpm)/Direction
Load Lb. (N)/ SpecimenAbrasive/SizeSurface
Ferrous Metals
Material• Pearlitic Ductile Iron
Etchant• Beraha’s CdS
reagent
Description• Microstructure of
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
Description• Microstructure of
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)
Base Speed (rpm)/Direction
Load Lb. (N)/
SpecimenAbrasive/SizeSurface
* 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)
Base Speed (rpm)/Direction
Load Lb. (N)/
SpecimenAbrasive/SizeSurface
Use candle wax to coat the SiC paper
Precious Metals
Material• Cd – 20Bi
Etchant• None, polarized light
Description• As-cast dendritic
structure – primary Cd dendrites and a Cd-Bi eutectic
200 µm
Precious Metals
Material• Zn – 0.1Cu – 0.1 Ti
Etchant• None, polarized light
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
Weld
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
Etching
Etching