Metallography.pdf

7/24/2019 Metallography.pdf

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J~ META~06RAPH"'i EUROPE

TABLE OF CONTENTS

CHAPTER

3 day programme layout

1

Microstructure & Sectioning 2

Encapsulation

3

Single Point Tools

4

Surface

reparation to Integrity 5

6

hin Film Measurement

Traceability to ISO 9000

7

Microscopy & Photomicrography

8

Group Questionnaire

9

Material Classification & Preparation

Methods

10

Own Preparation Method

11

Company Standard to ISO 9000 12

Much of this mataial basbea1 aken ItBD he boot 'Surface~~-aDOO &; Mia~ of MaItJiaIs'


2/170

B. BOUSFIELD, Buehler Europe Ltd. Coventry, UK

The first of its kind, this book s d~icat~ to the systematic reparation f a

vast rangeof materialsurfaces,ooking n detail at the problemof

microstruCtUralraceability. Designedo be of practicaluse, he book hasbeen

written in two parts. In the first half, tile book systematically efines he

essential roceduresnvolv~ in surfacepreparation. Having establish~ how

to preparea sampleof integrity, the secondhalf of the book llustrates he best

useof microscopyby discussing,n depth. he different featureswhich

contribute o informativeanalysis.

Completewith over 100stunningcolour photo-micrographsnd ully illustrated

throughout, his book providesan essential eference or researchersnd

technicianswho requirea comprehensiveverviewof microstructural nalysis.

CONTENTS:

PART 1: SURFACE PREPARATION: Introduction; Sectioning; Mounting; Single Point Tools; The

New Concept; Grinding; Polishing; Grinding and Polishing LubricantS; Towards a Metallographic

Standard; Characterization: Auditing aOOTraceable Standards; Traditional Methods Only; Preparation

of Spray Coatings; Preparation of Composites; Preparation of Minerals; Preparation of PCB's aOO

Electronic ComponentS;Thin Film Measurement; Preparation of Soft Materials; Preparation of

Ceramics; Hardness; Training in Metallography; Supplementary Materials, TechniquesaOOMethods;

PART 2: APPLIED MICROSCOPY: The Microscope - A Resume; Microscope Types and

Nomenclature; Creating the Microscope Image; Objective Aberrations; Improving the Image;

MeasurementS; llumination System; EyepiecesaOOCondensers; ntroduction to Interference; Surface

Finish Interference; Contrast Interference; Video Imaging and Archiving; Polarizing Light Microsopy;

Fluorescence, Reflectance and Con-focal Microscopy; Photomicrography; Inverted Techniques;

Photomicrography in Practice

100.00/$164.00

471931810

356pp

1992

ORDER FORM

Y I

IMPORTANT

-

EC Countries please c:ootplcIC details below.

( J I am reg~ for VAT. my VAT regislnoon number s

Please

sendme copy(ies)of:

BOUSFIELDIMirosuPJ

0411931110 I~.IOISIU.DO

Please add IXIsta&eof 2.001$5.00 or single oniers. Multiple orders

a~ POST FREE.

[J I enclose a cheque/bank dRft for

- --.

(paJQbl~ to John Wil~ 40 SolIS LId'

[ ) Please charge my c~iI ani ~JI(

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[ ) I dt, nuc WWI It. receive mailil1ls rrom ocher Companies

You I1\aY elepl\(l1~ our Custon~r Service Dcpl with your onter

by diMlling +44 (0) 243829121 or linkline number 0800 243407

(UK only).

\~ will mUlod your "'Yale.- wiI'-t lIusluR Ir yvu rot aDY a_-cd

I.-k '0 ..18 ~c ~- wiI- )8daJS.

YOlir ..rdel will be ~ PRM..y boA picuc allow 21 days ror

dcl;wcry. All pricd correa al lime ar ~ni~ \0 prcu bul subja:t ~

cllangc

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~ Dare

Reaum 0:Nicky DouClas:Pbys. Sci/A4. JohnWiley a. s- 1..81..

BaffmsLaM. ChidleSlcr.~ Su~. POI9IUD. UK

RF.


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J"i.

METALL06RAPH:'/ EUROPE

CHAPTER 1

DA"'lONE TUTOIUALS

roTORIAL

MET ALLOG RAPHY AND THE

W CROSTRUCfURFJSECn 0 NIN G

DISCUSSION SEcrIONlNG OPTIONS

nJTORIAL

ENCAPSULA TI 0 N ISING LE PO)NT TOOLS

DISCUSSION

ENCAPSULAnON OPnONS

TUTORIAL

SURFACEPREPARAnON TO INTEGRITY

DISCUSSION GRINDING POLISHINGOPriONS

TUTORIAL THIN Fn.M MEASUREMENT I HA RDNESS

IMA G N G AND A RCIDVIN G

SLmE

P~ENTATION

PREPARAnON ARTEFAcrs

roTORIAL

MICROSCOPYAND PHOTOMICROGRAPHY

SLIDE

P~ENTATION

EXAMPL~ OF WELL PREPA RED SAMPLES,

EXPLOITING THE OPTICAL MICROSCOPE

1.1


4/170

DAY TWO / DA YTBR -PRACTlCALS

INSTRUCTOR DEMONSTRAT10NS

AM PM

8.30 DELEGATES SPLIT INTO 3 GROUPS A.B.C. 1.00 STAY IN SAME 3 GROUPS

DAY TWO

W""IA~ I I..

11.10

, 11~.

111~

I

1

11.-.

12M

~

~TA~

1"-'

Is..

-

~~~~

~~ -'8 '

1

I ~

DEIIoNS1RAmNC'~PLETE PAEPARAmN

.30 to 1.00 am

DEIIoNS1RAOON ~ ~PLETE PREPAAA 1ON

.00 to 3.30 pm

4.30 to 5.00 pm

REVEW IN NA iVE LANGUAGE

Otherperloda

D8cuSSlON ~ 11NGTO PAEPARA TIOH UUG A FLOW CHART WITH

OPTIONS

DELEGATES OWN PREPARATION

DAY 3

Delegates split into 2 groups X I: Y

lAM IPM I

I 1.31 I 1.18 I

4.50

COURSE DIRECTORS OVERVIEW OF COMPLETED COURSEWORK


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MET ALLOGRAPH\' EUROPE

CHAPTER

MlCROSTRUC11JRE. SEtnONlN6

Metallography is both an understanding of 'material

sU"Uctures' nd the 'scienceof revealing hose suucwres'.

The sttuctures of materials can be 'macro' (low

magnifICation large field of view) or 'micro' (higher

magnifications

-

small field of view). The material

microstrucblre is the 'rmgerprint' of metallurgy Le. the

microstrucblre is directly related to the performanceof

that material. The materialstructure has a relationship o

the physicalandmechanical ropertiesof the material.

MICROSTRUCTURE

H the microstruCnlre is to be correctly interpreted it

follows that the microstrucblre must be a true and faithful

representation. Since most methods for the surface

preparation of materials involve mechanical working

(stress dislocation) which induce damage into the material

care must be exercised in conn-oIling this damage to a

minimum.

MACROSTRUCTURE

MacrostructUres are often visible to the naked eye, but in

general are aided by the use of magnifying lens,

stereoscopic micr~ope (double image) or the single axis

macroscope. Surface preparation for the analysis of

macroStIUCturess generally confmed to fine silicon carbide

papers.

A macrostructure ould be used o defme:

. FracttJremorphologyand grains

. Dendrites n castings

. Welding ntegrity

. Porosity

. Cracks

.

Exterior swface condition

MICROSTRUCTURES

Microstructures would be observed using a compound

optical microscopewith fields of view as low as O.18mm

and resolution of O.25Jjm. When resolution less than

. O.25Jjm s required it is necessary o use the electron

- microscope. The two basic ypes of electron microscope

being he scanning for morphology) and the transmission

(internal structure). Surface preparation can be

mechanical,chemical (electrolytic) or chemomechanical

(chemicals sed n con.unctionwith the rindin action.

Copyright 1994 BUEHLER Ltd

2.1


6/170


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MET 06RAPH"/ EUROPE

FA 1THFm. REPROOucnON

Brief mentionbas beenmade o the n~ for samples hat

are a faithful reproductionof the original material prior to

~bani~-ti woIting. Sampleshat are a true and faithful

reproductionare often referred o as 'sampleof integrity'.

So what can 'go wrong' as we mechanicallyprepare

material specimens for microstructural analysis?

Elements anbe:-

.

Fractwed

. Pulledout

.

Washed out

.

Etched

.

Smeared

. Distorted

.

Enlarged

.

Transformed

Elements can also be affected by:-

- Heat

-Pressure

- Surfaceriction

- Force irection

Artefactsoccurby incorrect:-

. Abrasive ype/size

.

Abrasive akeangle

.

Abrasivebacking

. Abrasive unction

.

Lubricant

.

Surface peed

.

Grindingsurface

.

Polishing urface

Resultsareaffectedby:-

.

Blunt abrasives

.

Prolonged insufficientpreparationimes

.

Chemicalattack

. Cl~JiQess (lack of)

.

Incorrectencapsulation

. Resincontraction

. Incorrectsectioning

From he our ~ abovet canbe seen ow an ncorrect

approacho surfacepreparation an inttoduce esidual

damage eading to an erroneousanalysis.

2.3


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METALL06RAPIrl EUROPE

SEC"nON1N6

Before any sectioning akes place the need to carefully

selecta representative reacannotbe over stressed. The

microstrucmreover the entire component may not be

unifoml, therefore,decide beforehandwhat the object of

any section s for and wherebest his can be ocated.

Figure 2.3 Sampling Identity

Figure 2.3 is used to illustrate a simple fonnat for

designatinghe samplingposition and the swface of

interest ithin hesample.

Figure2.4 Sample SpecimenDefmition

The word sampleand specimens often used to describe

the same hing, with the conventionas shown n figme 2.4

this shouldnow be overcome.

Sectioning s considered o be one of the most imponant

steps in the preparationof surfaces or microstructural

analysisand before one can proceed rom this point it is

wise to havesome dea of the depthof damage esidual n

the sample esulting rom the sectioning tage.

Copyright 1994BUEHLER Ltd

2.4


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MET ALL06RAPH'/ EUROPE

FIgure2.5 Depth of sectioning amage

This Z axis infonnation is derived by resectioningand

preparing o integrity the surfaceadjacent o the original

cut (figure 2.5)

WHEEL

TRA VERSE

RATE

Slow

Fat

DEPfH OF

DAMAGE (fUD)

10

45

Soft Bond

Alumina Grit

Bard Bond

Alumina Grit

Slow

Fast

20

900

Hacksaw

Normal

70 + 200

Figure 2.6 Sectioningdeformation .37% C Steel

Figure 2.6 gives the results from a series of different

sectionson a pieceof 0.37%CarbonSteel,notice how the

resultant deformation or structural damage varies from

10JUDo

9O0Jl1U.Without this nformation t is impossible

to 'tailor' the most appropriatesubsequentpreparation

steps. To put the 9O0JUDamagento perspective

(A) 3 samples f 0.37%C Steel,diameter 5mm,when

usedon 8" diameter180 grit silicon carbidepaper, or the

life of the paper,would remove100JJIn.e. 9 sheets f 180

grit paper would be required to remove the 900J1m

damage.

(B) 3 samples f ~ C Steelunder the sameconditions

would require 18 sheetsof 180 grit silicon carbidepaper,

Le. 50~ per sheet (These igmes are basedon optimum

cuttingconditions;silicon carbidepaperswill remove wice

the amount quoted but this extra material removal will

induce ntolerable evelsof residualdamage).


10/170

METALLOORAPm' EUROPE

WHEEL

SPEED

IpD

100

DEPnf OF

DAMAGE (JDD)

TIME

MINUTES

METAL

BONDED

DIAMOND

10

~

METAL

BONDED

CBN

100

.

IS

11m

so

~

RaIN BONDED

sn.ICON

CARDa

lUX)

9

2

2(XX)

7

Figure2.7 Sectioning amage luminium Alloy.

The resultant tructuraldamage hown n figure 2.7 is used

to illusttate the relationship hat exis~ between abrasive

type, bond, operating speed. cutting time and residual

damage.Take the diamondwheel n comparisonwith the

cubic boron nitride (CBN) wheel operating at the same

speed. The CBN wheel manifestsa reduced depth of

damage ndcuts n less ime. When he CBN wheel speed

is increased o does the damagedepth and cutting time.

Ftnally the abradable esin bonded silicon carbide wheel

reducescutting times dramaticallywithout an increase n

damagewhen he speed s high. This chart indicates hat

there s (I) an optimum cutting speedand (2) an optimum

abrasiveresulting n (I) a minimum esidualdamageand

(2) a minimumcutting ime.

Figure 2.8 - Sectioning Characteristics.

Sectioning haracteristics ave beenbrought together n a

singlechart figure 2.8), llustrating he effectsof lubricant.

speed, abrasive size and type, abrasive concentration,

wheelbond,wheel hickness ndmechanicalactors.


11/170

METALL06RAPH'{ EUROPE

Figure 2.9 Characteristics Metal Bonded diamond/CBN

wheels

This final chart s intended o give guide ines when dealing

specificallywith metal bondeddiamondor CBN sectioning

wheels. Speeds, lubricity, operating speeds, wheel

dressing,abrasive ize and concentration re all addressed.

2.7

opyright 1994BUEHLER Ltd


12/170

SECTIONING OPTIONSGUIDE CHART

Reference the enclosed (reduced) Wall Chart. From this chart we are able to

select the most appropriate cut-off wheel to suit specific user needs. From

the 'legend' at the bottom of this chart, notice how abrasive concentration is

depicted by the number of abrasives (low and high). Abrasive bond strength

is related to the number of cross-lines i.e. single cross-line weak bond - multi-

cross line strong bond. When dealing with expensive abrasives such as

diamond or cubic boron nitride then the bond/abrasive will be attached to the

'rim' of a circular metal disc, this is depicted by an extra semi-circle. This 'rim'

can be a resin or metal matrix. When metal matrix, the bond is shown as a

square grid. The type of abrasive is also designated by shape viz square =

alumina, triangle = silicon carbide etc. When different size abrasives are

used then a numerical system is employed i.e. 5 = small, progressing to 20 =

large. The first five wheel types are all intended for ferrous materials of

different degrees of hardness, the wheel abrasive being alumina. Notice the

8th wheel on the list, this is also alumina but is a much thinner wheel than the

previous alumina wheels. Being a rubber bonded wheel (as opposed to

resin) it is less likely to fracture when slightly flexed. This wheel is intended

for delicate cutting, it also finds many applications which induced cutting

damage must be kept to a minimum, viz sectioning of plasma coated

materials.

Silicon carbide wheels (6th and 7th) are offered for sectioning non-ferrous

materials. they can however prove equally successful when sectioning

ferrous materials though wheel life would be very much reduced.

The rest of the wheels in the range are of the non abradable type

(diamond/CBN). Much development has gone into these wheels to make

them very specific to the hard and brittle fracture materials as shown under

'Materials Applications'.


2.8


13/170

( )

BUEHLERPTIO~ 5

SfCTJO~JU~

GUIDE,

BLADE

iype-

.ABVAS'VE

SIZE

(-s

M.ATEQ'I~1.

App\.ICA,..OIJS

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CAe&l~, &oe;,..;V-"'O(. 5'\.""; L'fT~U. .

.

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"~IM I. ~o.., c.efAIIC', tLfCTEWC PA(~(O~~.G..~..4I.U

GLA55 ~ Rf.I1'F"ORcn (~IT~'

~~~~

Vr ~'"

n-~:"5

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~ ~Ioi CEr.A~"~.FlA;f RfII:FoeC"'" L'~I~.

c..F't .~,",. CARS~ Ccal't)5CTiS . u=../c~"'" .~.

tu 0&.'1.'(

WET~I.

'5' Lc.

LE-qr)JD


14/170

SECTION1N6

Wheels break for a variety ~ ~DS

and can be frightening whell they CUr.

Abrasive wheelswhen manufacturm are

car8:ully tested to emure safe operating

speem, these operating conditions mlm

be adherm to in use. Wheels can break

be(:aD-~ hey become ammed into the

workpiece, thk Is usually one ~ two

factors (a) the workpi~ (Spedmen)~

moved, or (b) the whee) ~ wandered

(movedoff uis.)

FAULT: WgF:F:I.BRAKA6E

~...

,.

;.-~ sontR

: Wt[L

.

1-_"

SAWPL

To overcome (a) It win be ~ry to

attribute the ca~ of any movement, '

it is s~ caused by dampiug then

siugle pcXntdamps will be necessary. f

the s~ Is within the workpi~ and ~

releasedas the cut tak~ place then the

workpi~ shcx1ldbe 5treG relieved or

incremental cutting adopted.

REf.

ONLY

~a.NAP

ALTERNATIVE

STRESS REUEVE

REDUCE COOLANT FLOW

REDUCE CUTTING FORCE

o oven:c:Mneb) a softer wheel is often

all that is required

FAULT: BURNIN6

Although burning can readily be

o~rved on the cut surface, what is I~

obvious is the depth to whim the

burning hM affected the micr~cture.

This depth for example an vary fnMn

2Oprn to 25OJIIDwithout a dramatic

change in the top surface burned

appearance. Some materials are

adversely affected by thama1 shocking

whel'e It is not ~arlly the

temperature mange but the Iocalised

shock hat occurs through im11ftJdent r

poorly directed coolanL Burning can

very ~ be overcome, ~ng the

coolant k appropriate, by reducing the

traverR rate. Softer wheels, although

the obvious molce, mU give a reduced

wheel ire.

~ ;~." ,

. " ..

",

.

W.

,

)---,

,

,

.

.

:_--~

~

~--,

-,-0

\

\

--I

: SOFTE

: WHEEL

..1

~

~

Al TERNATIVE

REDUCE RATE Of' TRAVERSE

CHANGE POSITION OF'

LUBRICATION

2.10

Copyright 1994BUEHLER Lm


15/170

SECTIONING

FAULT: PICK-UP II. WHL 6LAZlN6

./

.

,

-'.., . sanER

.

.

WHEEL

: c . :

. -.I..1 .

Swarf pick-up is evideut wta merving

~ ~phery of cut off ~ after use.

This oolKlition s m


16/170

SECTIONIN6

FAULT: CONTACTAREA

The contact

area is a vitally imJX>nant

factor in the ability to successfully section

any workpiece or comJX>~nl The

number of abrasives in contact relating to

the generated fttCes ~cessary. With this

in miOO it is always wise with abrasive

sectioning to take ~ least contact area

possible. This is oot always JX>SSible ith

a workpiece that changes the area in

contact as the cut ~ (circle), on

these occasions either iocremenW cutting

a: the oscillating headsystem will improve

cutting performance. S~en rotation is

another m~ of ~~- 1g a constant

contact area, d1is facility also helps to

ensure paralleledi~

romJK>nCn1.e.

it reduces any ~ for the ~ to

drift.

.t'

REDUCE

ONTACT

AREA

~J

,

.~

~

At TERNA TIVE

WHEELsc~nON

INCRE~AL CU1TING

SPECIMEN ROTAnON

FAULT: RSWUAL DAMA6/

WHEEL WEAR

s~ or workpiece

esidual damage s

a factor often ovedooked yet in our field

of miaostroCb1ral analysis we must 00

more dIaD u.\1 section ~ COInIX>nent, e

must adlieve a sample widt ~ least

residual damage. Wtae d1is s a JX'ob1em

a thiDOC'blade (X' ~ wiD often suffice.

These d1in blades are often robber ~

and are also re~ficia1 f(X' sectioning the

more delicate comJX)~nt. Reducing d)e

abrasive particulate size wiD also reduce

defonnation (residua] damage).

FAULT-SPECIMEN RESIDUAL DAMAGE

HIGH DEFORMATION LOW DEFORMATION

f{

~1

\\

0

)

USE THIN

.

WHEEL

ALTERNATIVE

REDUCE ABRASIVE ",

SIZE

f"AULT-RAPIf') WHF"F"I WfAR

Having selected~ 'best' abr3sive/0000

combination axupatible with efficient

sectioning of a particular material ~n

operating fcxcesmust be ~red to. To

use the ~ urm higrer than the

optimized pressurewill certainly reduce

the sectioning ime resulting n rapid wheel

wear, naeaseddefcrmation nd ncreased

generatedheal To inaease the matrix

bond strength of the wheel would also

reducewheel wear.

. " . .

"'"

""'~

"'"

po

"v

,

- - -:

HARDER

. HEEL

.

1'--

~

.

-.

,

ALTERNATIVE

RCOUCEPRESSURE

2.12



17/170

SECTlONIN6

FAULT: SAMPLE BURN1N6

This ackIitional section 00 bIrDing is to

draw attention to ~ lubricant or c(Xjant

which infiuelx:es ~ eflideu;y of any

sectioning ~tion. Cutting wheels wiD

~te differeDtly as ~ tem~

affects ~ resin 1xmd Some wheels fcr

example are designOOo ~te dry aIJd

~ ~te efficiently when ~ ~

temperamre rises. ~ wheels we are

ma:e familiar with are dX)5e which are

'jetted' with coolant to keep ~ sample

(XX)}or ~ totaDY ~ in axiant

avoiding thermal shocking. It is important

with these ~ to target, wIae

possible, ~ jet of coolant into ~ an aDd

arowK1 ~ sample and WOIkpi~

Targeting ~ coolant onto ~ ~

thereby keeping it (XX)}wiD iIKhlce sample

OOming by effectively hardening ~

wheel. Heat must be g~ted wbe:n

'working' any mIface. On this occasion t

is wise to cxmfiDebeat, where possible, to

the swarf and blade.

_R~~

I

~-1--r-;;TTR

.~

~~;;,

--~~~~

-~T---

AMPLE

; ;jATR

WHEEL BONO TOO STRONG

SAMPLE BURMNC

I

~EJtE~~

AlTERNATIVE

USE SOntR BONO WHEEL

TRY LESS LU8R CANT

TRY DRY CUT SLOWER TRAVERSE

FA UL T: WHEL P R OFIL - IN CORR CT

USE

When coolant is used. even when taking

into consideration ~ {X)ints rdised atx>ve.

it will be l~~ to wet ~~. ~

Bow onto ~ ~ must re equal 00d1

sides if unifcml ~ wear is to take

place. ~ ~ pofile can also re a

clue to correct matrix tKmd as sIK>wn n

thesketdl.

'" WHEEL

,

,

"

~

~

POINTED

~

"

/""""""""'~~SUR COOlANT

BOTH SIDES or WHEEL

-

/

CHISEl.

ALTERNATIVE

KEEP COOLANT FLOW

AWA"" FROM SlOES or

WHEEL


2.13

USE

SOFTER


18/170

SECTIONIN6

FAULT: POORSCRATCHPA nRN

It bas been kIXJwn for ~ reflectivity c:t:

~ sediooed surface to re used as a guide

to ~famation free cutting aDd fcx the

weD ~tdl~ surface to re rejected. This

in fact is an ~ assumption since it

is ~ OOrnisbing CX fXX'C cutting blunt

abrasive that causes ~ shiny roOOition.

Efficient cutting takes place ~ using

sharp abrasives and sharp efficient

abrasives leave wen defined saatches. It

is impcxtant thc'efore to recognise a gocx1

saatdl pattern sinre this wiD often JXOve

to re t1M::ime emcient mettxx1, but above

all t1M:: etIxx1 hat least alters ~ material

structure i.e. d1emost faithful.

~

~

- ,

~

RUL(CTMTY HIGI

SOF"TER

WHEr-L

~..,:-

1fA~

YLl

~~~~~ RE~ LOW

FAULT: STRUC11JRAL AMA6

SECTIONING

~

This sketd1 is used to reinforce ~

importance of m~1cing he sectioning stage

~ most imP


19/170

-

SECTIONING

When sectioning coated layers such as plasma

coatings or materials with a friable surface it is wise

to direct the cutting force, first through the coating,

followed by the substrate, failure to do this can result

in delamination as shown. When dealing with a

friable material or a porous coating it is wise to

vacuum impregnate prior to sectioning. The vacuum

necessary will be dictated to a large extent by the

size of interconnecting paths between the pores.

When the specimen has been totally immersed it is

possible to use isostatic pressure to increase resin

penetration. A lower viscosity resin will also improve

resin ingress. Irrespective of any protection

provided it is still wise to direct all forces in the

direction of resin -coating -matrix. Notice from the

sketch how not all pores are 'open pores'.

SEcnONlN6

FAULT: SAMPLE ORIENTATION


2.15


20/170

MET AlJ.06RAPH\' EUROPE

ENCAPSULA110N

HAPTERS

NCAPSULATlON

Specimens

remounted r encapsulatedo (a) protect he

sample material. (b) produce a uniform dimensionally

stable size for subsequentautomatic machine operation or

(c) assist handling for subsequent band operated

procedures. The 2-types of mounting techniques available

are compression hot mounting and castable cold mounting.

Additionally there are two basic types of resins. those that

once set will remain rigid even when subjected to heat

(Thermosetting) and others which once set can be

rendered plastic when subjected o heat (Thermoplastic).

Castable cold mounting resins set after reaching the

exotherm temperature and can be thermoplastic or

thermosetting. These resins do not require pressure to set

and are simply poured into appropriately shaped cups.

Compression hot mountings are also available as

thermoplastic or thermosetting. This powder mixture is

encasedwithin a pressure chamber and requires a specific

temperature relative to pressure to set the resin.

Thermosetting resins 'set' at the hot curing temperature and

as such can be ejected from the mould chamber when hot if

necessary. Thermoplastic 'set' below the peak temperamre

and must therefore he ejected when cool.

Furin~

eatIng

Cooling

~

"

~

f

~

t'

~

Solid

THERMOSETTING

Liquid

k

e

i-

f. '

Heating

CoolIng

Eject

THERMOPLASTIC

Fig 3.1 -CompressionMoulding Conditions

Fig 3.1 llustrates he heating curingconditions or both

the Thennoplastic ndThennosetting ot mounting esins.

Copyright 1994BUEHLER Ltd 3.1


21/170

METALL06RAPHi EUROPE

RESIN REQUIREMENTS

Ideally we would like a resin to have nil contraction, to

adhere to the sample, to have an identical abrasion

characteristic to the sample and be easy to Pombo

Unfortunately this is rarely, if ever, possible to achieve

therefore he object s to define he 'prime' requirementsand

relate hese o the resin. From the point of view of a4hesion,

only Epoxy resins fully satisfy this requirement with the

Phenolics eing he eastaccommodating.With castable old

mounting esinscontraction s an important factor. With hot

compressionmounting the different coefficient of tbennal

expansion etween esin and mount also becomes mportant

As an example he coefficient of lbennal Expansion crE)

for some esinsare as ollows:-

Phenolic3/4.5 x 10"

Acrylic 5/9 x 10"

Epoxy 4n X 10"

Metals 1/3 x 10-'

.

.

.

.

From these igures t is easy o seehow the resins would be

shnmk onto a round samplewhen cooled.

Figure 3.2-Reducing Contraction

Grinding relief betweenmounting esin and sample s to be

avoidedwhenedgeanalysis s to be carried out To avoid

this sitUation he abrasion atesbetween ampleand resin

must be considered.


3.2


22/170

METAu.06RAPH"l EUROPE

ABRASION CONSTANT/If'AT

LASS MATERIAL

Hd.M~

Prek8d 1m-

~

M-.iaII

~

~"-baIaIe

~yRaa

Aaytie

Ccid Mmmtiq

f.paIy

AayIic

~yeIt

AayIio+AV

170

1040

1100

m

M~

Cq.-ADoy

SIerJ(O.37)

A l i.iIaII ADoy

35

12.5

142

Figure 3.3 -Abrasion rates grinding

Figure 3.3 gives comparison rates betWeenvarious materials.

Two important points relating to this chart are (1) the

reduced abrasion rates on compression mounting when

compared to castable resins and (2) the reduced abrasion

rates of metals relative to the resins.

,

S

I Carbon/carbon

" tee I /

henolic

Epoxy

(b)

a)

(c)

Fig 3.4 - Relief Grinding

Figure 3.4 gives examples f positive and negativegrinding

relief. Additionally at (c) is the example of differential

interphase relief. This is vital when ~ing differential

interference ontrast, he heightdifferencehowevermust not

exceed he resolutionof the microscope bjective.

The following is a list of attractions or both compression nd

castablemoulds.


3.3

(JDD/miD)

.160

440

130

SXJ


23/170

NCAPSULA TION OPTIONS 6 UIDE CHART

-- -

Reference the enclosed (reduced) Wall Char1. From this char1 we are able to

see at a glance the variety of moulding materials available and the various

characteristics relating to each resin.

In the field of materialography, encapsulation is via hot compression moulding

or alternatively the so called 'cold' castable method. The word 'cold'

mounting is somewhat a misnomer since exotherm temperatures of 1202 C is

hardly cold'.

The least abrasive resins are the compression hot mounted variety which

also tend to be quicker setting and more dimensionally correct. From the

chart it can be seen how the various categories have been defined. The first

three are phenolics and are also available as pre-moulds. The abrasion

factor is important in trying to match, where possible, the abrasion of the

sample with the moulding material. This factor is related to micrometres per

minute under a given test parameter, this shows the difference between hot

and cold mounting.

In addition to the abrasive rate is the 'polishing ate'. From the legend at the

bottom of the chart it will be noticed how this has been designated by cross-

lines, ust one line for 'high' progressing o many or 'Iow'.

The hardness value (Hv) has also been quoted but at these low values they

must be for comparison purposes only. Note how the hardness value has no

relationship with the abrasion factor. The abrasion factor is the important

value. the hardness is of little importance and again is only quoted for

comparison.

With all these different resins it is important to address the question of

suitable specific applications, the columns starting from 'use' are intended to

help. The cleavage (gap between resin and sample on the inside of a

washer) and the relative grinding relief when comparing resin to steel (0.4%

C) are drawn schematically. .Take for example the black Epomet, this shows

no cleavage and nil relief; the black Edgemount on the other hand has very

slight cleavage still with nil relief. The major difference between the two resins

being cost. These two resins would be totally unsuitable when the sample

material is highly abrasive because on this occasion negative relief would be

created.



24/170

ENCAPSULATION OPTIONS GUIDE CHART - COImHUED

Viscosity, the ability of the resin to flow into small areas, is very important in

particular when the sample is porous, when it may be necessary o vacuum

impregnate. Notice with the hot mountshow the Epometand the Transoptic

have been given a 'start' towards being viscous. With the castable resins

rated from high with one drop to low with a continuous low it is very easy to

match a specific resin o suit particularneeds.

Setting times have been generalisedbut as can be seen, vary from 5 minutes

to 12 hours. Thermosetting esins, hose that set with heat and cannot later

be softened, are shown by shading the upper triangle in the box.

Thermoplastic resins, those that can be softened later by introducing heat,

are shown by shading the lower triangle in the box. Thermoplastics are

usually difficult o polish scratch ree.

Finally we have the peak temperature column for compression mounting

resins, these figures are only valid with a given pressure. The thermoplastic

for example could require 20~ C if the pressure was to be halved. The

quoted peak temperature for the castable resins is the minimum temperature

during the exothermic reaction, it will if not controlled rise above this figure.


3.5


25/170

CIIA MET lJ.06RAP~ EUROPE

FAULT: CONTRACTION

COMPRESSION MOUNTING

CASTABLE MOULDS.

SAMPl

COtfTRACTKIN I

INSERT

PARTCULAT[

AlTERNATIVE

COMPRESSION YOI.MINC - REDUCED COFFUHT or

THERMAL EXPANSOf RESW

CASTA&[ YOUlDS - LOWER RESIN COH1RACTOI

The gap that occurs betweensampleand

mould will always be a problem with

resins that exhibit a high degree of

contraction. This contraction will

inevitably,be higher on the inside of a

washer than the outside. With hot

compressionmounting t is the difference

in coefficient of thenna expansion

between moulding material and sample

that creates he greaterproblem.

With hot compressionmoulding it is the

inside of the washer only where a fissure

is likely to occur. If, as often is the case,

a gap is noticed on the outside of a

compression moWlt it signifies an uncured

mould.

To reduce the area of resin in close

proximity to the sample will reduce the

effect of contraction and coefficient

differentials. To do this an insen can be

introduced as shown or alternativelyuse

particulates of ceramic. Another

alternativewould be to section he washer

giving a 'C' shaped ubject

The useof epoxy castable esinswill

overcomemost problemsascan be seen

from the 'encaosulation otionse:uide'.

FAULT: MOULD CRACKlN6

COMPRESSION MOUNrJNG

CAST ABLE MOln..DS

~:.,


26/170

@A MET ALLOORAPHY EUROPE

FAULT: MOUNT UNCURED

Thennosetting moulding material can

often ook quite good from the outsideyet

be partiBlly uncured on the inside. This

siblation can be confumed by cross

sectioning he moulded unit Specimens

exhibiting what looks like contraction

between esin and sampleoutside ace are

more often than not examples f partially

uncured moulds. When d1is internally

uncuredcondition increases,he specimen

when ejected from the mould unit, will

haveeither a burst on the opposite ace o

the sample or alternatively the sample

itself will stand proud of the mount This

condition is more prevalent when

thermosetting esins are ejectedhot ~

can be seen from the sketch it will be

necessaryo vary pressure,emperatt1rer

cure period as appropriate

CO~ION MOUN11NO.THERM~ RE.sIN

.,., ~

,

~ :-CRAHU~TO

I ~1\M(

~

""...:.:::-:...,

~ . f

~

~~

~~

t'_--'

. .

~

~

,

--:0-

~, I

aMEPERIOO

ALTERNAT1VE

USE THERMOPLASTICRESIN

FAULT:

MOURTURCURED


THERMOPLASTIC RESIN

Clear thermoplastic compressionmoul~

often exhibit what is called a cotton ball

effect, this can be in evidenceon ejection

from the mould or can occur as he mould

cools o ambient emperature.

There are two types of cotton ball effects

and they must be addressed ifferently f

the problem is to be overcome. Firstly

there is the misty effect just below the

sample, his can usually be overcomeby

reducing the rate of cooling, prolonging

the period.When the misty or cloud effect

is replacedwith a distinct combination f

smaIl bubbles then reducing the heating

period should suffice. There s a word of

warning however and that is, both of

theseconditions are temperature/pressure

related. i.e.,. lower the temperature-

increase he pressure.Having established

a good working combination t will be

necessary o retain a similar resin to

sample atio to avoid cloud e-emergence.

0

REDUCE

~~l

~"~5~

l- -

Of

...

\

-~lOUO [MISTY]

r SAMPLE

/

--~~--

Go

--~

CLOUD [SMALL BUBBLES)

AlTI~NA11V(

USE LESS RESIN

3.8

opyright 1994BUEHLER Ltd

REDUC(

I

HEATING PERIOD


27/170

MET Au.06RAPH-{ EUROPE

FAULT: SAllPLEDISTOR110N


THERMOSETTING RESIN

elicate samp~ i~y should not be

subjected o compressionmounting, his

however s sometimes navoidable.Some

users surround the delicate component

with a metal ring thus confining pressure

to the longimdinal axis. If isostatic

pressure s to be used hen thermoplastic

resins are best employed; he mounting

press pre-load being used until the resin

has softened. Since thermoplastic esins

can be moulded at much lower pressure

than the thennosetting esins t is possible

to achieve satisfactory moulds at much

lower pressure han recommended y the

equipment supplier. It is important to

remember hat these moulding resins are

pressure temperature elatedand as such

any lowering of pressure must be

accompanied with a rise in moulding

temperature.

DRYOUT

MOULDING

POWDER

SAMPLE

\...

"

~

4

CIRCUMFERENTIAl

SPLIT

FAULT: MOUNT ADHESION

C~SSION MOUNTING

THERMOSffilNG RESIN

One of the most desirable eatures of

specimenmoWlting s to have he moWlt

material stick to the sample. This

condition is prevalent with epoxy type

resins and all other resins to a lesser

degree. Having established his very

desirable eature t is not surprising o find

the mount sticks to the metalwalls of the

moulding cylinder. Lubrican~ are

available o avoid cylinder wall sticking

andshould be usedat intervaJs ompatible

with the type of moulding resin in use.

Another type of sticking occurs m

compressionmoWlting and that is when

the moulding resin is squeezed etween

the ram and cylinder walls. to rectify this

condition it will be necessaryo replace

the worn out ram

FAULT

SAMPLE DISTORTION

- SAMPLE

r DISTORTION

,

:-i

CHANCE TO

,...:~~~'" THERMOPlASTIC

"-=-:'""~---" REDUCE RESSURE

INCREASE TEMPERATlIRf

"'--~~

ALTERNATIVE

$E CAS1A8LE RESIN

3.9

Copyright 1994BUEIn..ERLtd


28/170

J""

METALL06RAPH"i EUROPE

FAULT: MOULD ADHESION

SPECMN AOttCSOC

Lubricantsare available o avoid cylinder

wall sticking and should be used at

intervw compatible with the type of

moulding esin n use.

I.~

-

~

SPEa..:Nl

--~j~a.

~

FAULT: POORDIMNSIONAL

STAS nnY

CASTABLE RESINS

~~-~

':'-~t REs..

l_J~ ,-

PHENOLIC

RING

FORM

SAMPLE

Most castable~ exhibit a degreeof

contraction. d1is contraction leads to an

irregular shaped mould dipping in the

centre and not too parallel on the outer

diameter. In addition to this poor shape

there is the Jack of dimensionalstability

attributed o varying contraction between

different resins. This problem can be

overcome by using an epoxy type ~

(low contraction, low viscosity) or.

alternatively mould the sample within a

'ring form' as shown n the sketch.

m 6H EX OTHRII

All castable ~ have a 'peat

temperature', this is the minimmn

exotherm emperature eeded o 'set' the

resin. (See encapsulating esin guide).

This exotherm temperature is ~lf

generatingand will if not controlled. far

exceed he peak emperamre. To control

the generated eat (1) reduce he volume

of resin (2) increase he samplesize (3)

blow the exotherm peat temperature

across he setting esin surface.

FAULT

HIGH (XOTHERM

/ 1 C

JO'c

74 METALL06RAPm' EUROPE

FAULT: EXPENSIVERESIN

Associated with improved resin

characteristics s usually a price penalty

Le. better resins are usually .more

expensive. To compensateor this price

increase t is possible o support he front

face of expensive resin with an

inexpensive resin such as standard

phenolicas backingmaterial.

COMPRESSION

MOUNTING

COST SAVING

INEXPENSIVE

RESIN

SAMPLE

EXPENSIVE RESIN

FAULT: POORLCTRICAL CONTACT

Good electrical contact between sample

and anode, for example in electrolytic

polishing/etching, s often required. The

approach an be one of two ways (a) drill

a hole through the resin until contact ~

made with the specimenafter which an

electrical contact can be made or (b)

mount the sample n a conducting esin.

Conducting resim can be metal filled as

used n electropolishingor graphite illed

for scanningelectronmicroscopy.

CONDUCTIVE MOUNTS

r

ETAL CONTACT

OR

METAL OR GRAPHITE

INCLUSION

SAMPLE

NON CONDUCTING RESIN

3.11

Copyright 1994BUEm..ER Ltd


30/170

E-1Jc.A~ULATIO).J

OPT'O~

gUIDE-

( )

BUEHLE~

COMPee-SSlO).1

Mo~L. 'D ItJG

-

Hy

EEt'TIVf I

C...T

u.

D.5t:2rPT10,I

AMASlO'.'

I POL ISHiUG

~ACTO2 RATE-

CLEAVAGe-

26"" /STEEL.

\JSe.

""$(OS,"y ~~~ ~MD

-~A;~:

PUt:

T~.,

0

L4C~ P~'Q.IC

\l

72D-3100

5f.O

4'-

,~~:

6f&.'f'r.4L

P\I~

"7

/50

""J

4(.

--'~~~

GE~ml.

PC~~

~

7

150

~

-W-3~

~c-o

--"~~

~~L

~E;

CQ.UU~

'7

150

"ZO-mo

4-40

IAu,yL.

PJfTHA~

~o

~

~

..,

150

"::li

130O-33CO

"71

\. fe FAce

Ao~esIOU

~

,

"0

~

- ~

to-noo -&0 PllEUQ.IC 5(.0

0 ~ Gt~'ffAL

,

..

PI~ ~:

c.-.& ~,

~UQI 'I8IOL~ , (,0

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--~ ~

CQ.'-M~

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.

~

DALL'fL. ',...0 ~o rMfMICAL --:-y~

.PtfTHALATJC ~15T '

~-

10-3380 -aL~~ "0 ~"71 \"'Sf'ACf ~

: POMET ~ ADJta.ou WM

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w. SOlO &LACI( lto I'"

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Mouv'TS

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.or:

-~o

~~~

~A5TfCH 1000

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I

~::;;;;I-;:::-otTL,lt ~~ I

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.

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. .

ZO-CI40

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.

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OtteslOa,

to

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so

NC~


31/170

@4 METALLOORAPH'i EUROPE

CHAPTER 4-

SIN6L POINT TOOlS (STRESS APPUCA TORS)

Removal of material by

multiple singlepoint tools seems

strange subject to be included in a course of

metallography. In fact a knowledge of how the material

removaloccursand the subsequent amage esulting rom

this 'woIting' is vital to our knowledge f progressing he

surface o integrity is to be achieved Materials fall into

one of two groups i.e., (1) Ductile materials where

material is removed by 'slip plane dislocation', such

materialswould be steel, brass,aluminimnetc. (2) Brittle

materials where material is removed by brittle fracmre

m~hani.an; such materials would be ceramics, bricks.

mineralsetc.

RES\A.:S1t[l \ ~~

RES\A. CERAYIC\-rRAl

OEF~M4TION ANa

R[5C)UAI. STRESS

RtsIOUAl C~AC..-S

Figure 4.1 - Material Removal Phenomina

These wo groups of material emoval are shown n figure

4.1. Dislocationby slip plane mechanisms shown to nm

along the shearstressdirection, his results n a defo1'JDed

structureand a potentialresidualstress. When material~

removed by crack propogation the result is a residual

crackedStI'tlcture ith little if any residualstress. The idea

in materialographys to progress his residualdamage o a

theoretical zero by use of smaller sized abrasivesand

different support surfaces o absorb the cutting shock.

From figure 4.1 it should be noticed how the cutting tool

front face has a different angle (rake angle) for the two

materials. Ductile materials equire a positive rake angle

(see igure 4.2), brittle fracture materials equire a zero to

negative akeangle.



32/170

.A MET ALLOORAPH"l EUROPE

~ t:~] a 0

Positive ow

deformation

Negative high

deformation

Figure4.2 OptimumRakeAngles

This rake anglevaries or different mate~ softer ductile

materialsneed a higher positive angle, harder materials a

lower positive angle. The resultant defomation can be

related o the rake cutting angle. Le. a low positive rake

angle will induce greater specimen esidual damage han

would the optimum arger rake angle. This cutting action

is an exampleof single stress applicators, n the field of

materialography e aremore nvolved with 'multiple stress

applicators'. One such example s silicon carbide paper,

this is shown n figure 4.3. The rake angle of the cutting

abrasivebaswhat s calleda 'critical angle'. Less than the

critical anglewill cut the workpiece (sample),greater han

this 'ploughs' and eventually ubs (to be explained ater).

Silicon carbide particles, as they are electrostatically

excited on the adhesive backing paper are randomly

orientated The result being a combination of different

rake anglespresentedo the approachingworkpiece.



33/170

J~ METALL06RAPH'i EUROPE

Steel

[:::j ~

l~ ~=:J

Critical angle 900

< Cuts> ploughs/rubs

Steel

C:1

Figure 4.3 - Silicon Carbide Paper when new

~

~~~/

Positives become negatives

Figure 4.4 - Silicon Carbide Paper n Use

Figure 4.4 shows he effect of theseSiC particles as they

are used. The ideal positive anglessoon becomenegative

by breakingor shearing t an anglenonnal to the front face

sheardirection.

Cut

Ploughed

Fig;ure 4.5 - Scratch Patterns


~


34/170

~4 METALL06RAPH"l EUROPE

Figure 4.5 shows the effect of using the various angled

abrasives.Sharppositive angleabrasives ive a clean cut.

sharpnegative ake anglestan to plough, causinga break-

up from the clean cut: This u often accompaniedby a

material build-up each side of the groove as shown.

Negative rake angleswhen used with ductile mataeriab

will soon~ome blunt, rom which point there s a greater

tendency o rub than there u to cul The visual effect of

this ast condition s to shineor b~ the surfacegiving a

brighter appearance hich to the untrained eye could be

interpreted as a better finish. Looking at the type of

scratch pattern is essential in u-~-~~g the residual

damage.Just aswith the surface inim after sectioning he

conditionshouldbe a unifoI1D eriesof cleanscratches.As

the scratches arkenso the cutting is lessefficient. beyond

d1is stage as the surface shines then residual damage

(deformation)can be gross. When assessinga scratch

pattern ollowing a grinding processwhere the workpiece

hasbeenorientated hen he scratches hould havea depth

Le. not all on the same plane, some going underneath

othersandat a different orientation.

Figure 4.6 - Degrading Abrasive and Deformation Chart

Figure 4.6 bas combined the relationship between the

cutting abrasive ngle n use and he resultingdefonnation.

The major point being, when using degrading abrasives

such as silicon carbide paper they should only be used

within the ime o~ (T1) period.



35/170

@4 METALLOORAPH"{ UROPE

Figure 4.7 - Factors Affecting Material Removal Residual

Damage

There s an important material removal resultant damage

reJationshiphat occurs elative to a given factor. A list of

factorsaffecting inal resultshave beenshown n figure 4.7

COMPRESSEDCRYSTAL.

J

~~

SLIP P .\.t'Jf

DISLOCATIONS


36/170

J,.\ MET ALLOGRAPH'l EUROPE

DEPTH OF DAMAGE

If we are to progress he preparation sequence owards

sample ntegrity it is important to have an appreciationof

the total defonned ayer (or heat affected zone) resulting

from a particularsectioning grinding or lapping process.

) RtSGuA STRESSARD METAL 2~~

son METAL 50.

-- - BRmL ~TU~ lOOK

~ ~To.

IrAl SPECMH

~RY--

.,:---

-

-~~~ -, TOTAl OEF'ORMATION

Sl.-tPI,AWS ..:::/

(PLASTIC

DlSLO~~,:E ...

F"RAGWENTO L.AY[~

~:I;;;;~~~::::.1 SIZ CO4T

~~~i~~~~~~~~~ ~Al~

PAP[R.c.c~ ... COAT

Figure 4.8 - Plastic Grinding Using Abrasive Particles

Figure 4.8 depicts he Stn1cnJralrtifacts esulting rom the

use of SiC or aluminagrinding papers. These papers are

produced with variable 'weights', heavy papers (thick)

offering more shock absorbing Oess defonnation).

Abrasivegrains adhere o the paper by the 'bond coat' as

shown. The working severity of the grinding paper ~

inf1~nced by the 'size coat'. The thin size coat being

intially more aggressive,hicker size coats ow in material

removaloffering a longeractive working life.

The metal specimen hown m figure 4.8 shows two areas

of slip plane dislocation causedby the abrasivegrinding

process, note the strain boundary and the visible

~fonnation depth. The visible ~fonnation is that which

would be optically revealed after cross sectioning the

ground surfaceand etching. This etched magewould not

~.re-.ssa.-rily

eveal these slip planes but will reveal a

distorted structure m comparisonwith the parent or true

structure. Additionally to the visible defonnation s the top

surface ragmented ayer. When using sharp, optimum to

critical angle abrasives his layer will be extremely small

(2JJ1ntoil). As d1ese rains chip and become runcatedso

the fragmented layer will mcrease as will the visible

~fonnation.

Copyright 1994BUEHLER LId 4.6


37/170

PREFERENTIAL ET.CH AT

SLIP PLANE/STRAIN

BOUNDARY~

"

"

PLASTIC DISLOCATIONS

FROM GRINDING

,

-

METAl SPECIMEN

)

PLASTIC LAYER

ASSOCIATED WITH

POLISHING CLOTH

ABRASIVE PARTICLE_S/~-

/

\

I

DIRECTION

-""

--"

--.c--

\.:.

'""'\

'.:z:~~.-

CLOTH BACKING

ABRASIVE RESTRICTING SURFACE

CLOTH NAP


38/170

.'

. -. .

. ,: -. '" ",.. '.. " . ; '

~"";;.": .A"-':'";-".'..~;;;,I;o""~_I~""",'::.'~'

. ...';.:.;~ j..-':.'~':"-:"-~';',,:,:~~"l'~-::';","~'.'.

,I.. c', .. '" ':',...'.~~:.r-,:,:-':

,:.

:

.:

AFTER

SAMPLE INTEGRITY STAGE

~m

POLISHING STAGE

MPRESSED GRITSWARF n

~INGER

I

ATER JET

...~~~~~~

~:::;;;~. W TE JET

SOAP

- ~~T~~~N~C{)-

CLEAN

~

t

~EJC1.H~ (if

requ red)

~~::~~~:::J::~=:::::~:~

HOT AIR

"""'",~ ALCOHOL

',:

, -

~

~

I'

OPTICAL

-~ ANAL YSIS

@)

SAMPLE

ENCAPSULATION RESIN

FIG

CLEANING


39/170

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METAu.06RAPH'l EUROPE

During the material emoval process t is Hkely that slip

plane action has resulted n residualSttessbeing present

beyond he visible deformation ayer. In considering a

potential total ~formation layer the depth of residual

StreSSas o be taken nto account. Figure 4.8 indicates

the additional ncrements ecessaryo take this factor into

account.

Although this discussionbas been confiDed to plastic

grinding where material removal is by slip plane

dislocation. a dmilar adjustmenthas to be made when

material is removed by brittle fracture m~hani~

(ceramics. ricks. ocks. minerals tc). From the chart this

is shown o be 100% of the visible depth. not because f

residualstressbut ~ause fine cracksare areasof further

crack propagation.

Copyright 1994Bum n..ER Ltd


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@A METAlL06RAPm' EUROPE

CHAM"R 5

CONVlmONS

SURFACEPRPARATlOR 1'0 1RT6Rm'

In the surfacepreparationof materials or microS1rUcUal

analysiswords such as grinding. apping and polishing are

used. To avoid any confusion he following conventions

and definitions are used throughout the book. (these

conventions avebeenwell published ndestablished)

Sample

': :~::::~-

t::

Deformation

Fixedabrasive

Figure 5.1 - Grinding

This s the most aggressivematerial emoval echniq~ we

shall use. Although t is efficient at removing material t

does, as shown, manifest a relatively high level of

deformationwith a ductile material. This is due to the

resultant hear orces

RJ acting

on hesample.To reduce

this deformationwith a fixed grinding abrasive t will be

~-~~ to progressively educe he abrasivesize and/or

increasehe shockabsorbing haracteristics f the grinding

surface.Grinding s a quick operation.

~

ample

Impre.ssed("""",.~ ~

abrasve "" I

II / /, Deformation

~ Compressed grains

00 8~~~~o 000

Rollingabrasive

Figure5.2 . Lapping

..Do

,."p

sorT

&.,.

~

,..,~TE~'~ J

A.Wt1,"~J1 M.M,C)


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J~ METAUaOORAPHi EUROPE

'Ibis techniq~ ,-mli5es flee rolling abrasiveand produces

a much reduced deformation ayer in comparison with

grinding. 'Ibis ~ in part due o the changed esultant orce

(R,) and the shock: absorbing action of the non-fixed

abrasive. Ibis technique~ highly favoured or its extreme

planarity and ~ relevant as a possible echniq~ for an

brittJe fracnJremateriah (not d~). If ~ technique

was to be used for soft metah then impressedgrinding

abrasives would occur as shown. Lapping ~ a slow

operation.

F

Polishing

(note the deformationl

plucked grains, smear and cloth nap)

FIgure 5.3 - Polishing

Po~g is the step used when scratches are to be

removed from the sample often resulting in a '~'.

Defonnatlon s relatively ow as shown (shouldbe nil) but

there s always he chanceof smearing he samplesurface

if prolonged imesor increased ressures applied

Figure 5.4 - Composite Surfaces

Grinding is quick, not so flat and leavesa relatively high

Sample

,...~"'4@\'"

"'.::.:"

i


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@A METALLOGRAPH't{EUROPE

It bas been shown. using the charts, bow operating

parameters an be used to optimise a given preparation

procedure. It is aha shown in the 'options' cban for

grinding and polishing he grinding surfacesavailableand

the severity rating in relation to each other. What ~

~g from all this infonnation is a guide to the

appropriategrinding/polishing urfaces elative to specific

materials.

SAMPLE

PRPARATION

SPECIMEN

MATERIAL

SPECIFIC5.86 TO

5.42

The following chIns are intended o guide the user into

using the correct grindin1/polishing surfaces that are

specimen material specific. All too often a grinding

swface s selected becauset is available' and nowhere s

it stated in literature where these surfacesmust not be

used. Take for example he nickel coated diamond discs

(ULTRA-PREP), they are not intended as replacements

for silicon carbidepaper,nor are hey ntended or use with

very hard materials.These discs will 'clog' with swart' f

used with soft tough materials rendering them useless

within minutes. Thesecharts hereforewill indicate where

best o be usedand by definition shouldNOT re used with

other specimenmaterials.

The material groups have been generalised nd will

inevitablybe incomplete,hey will howevercover the

majorityof materiahikely to beencountered

The Material groupsare:-

.

Very bardmateriaJs

.

Brittle fracturematerials

.

Soft d~e materials

. Ductile materials

-

eneral

. Metal matrix composites

. GlassK::eramic atrix composites

.

Polymermatrix com~tes

Figure 5.36: This chart relates o the use of fixed diamond

grinding surfaces.~ is the area where ncorrect use of

grinding surfaces s most prevalent Very hard materia1s

obviously equirea hard abrasive uch as diamond n order

to abrade the specimen. This diamond must re well

protected against mpact damageotherwise the diamond

will becomedislodged rom its housing. It is for this

reason he resin matrix grinding wheel s used. To use the

nickel platedwheel or thesehard materialswould rendera

much reduced life due to impact damage (see figure

5.36A).


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As the brittle fracwre materialsbecome ofter so the useof

nickel bonded diamond grinding becomes~ (A)

The diamond s deposited nto circular Mesashaped orms

adhering via the nickel to a resin fibre support. The

protruding diamonds are also nickel plated to initiate

efficient cutting. There are a series of these surfaces

allowing progression o the second ntegrity stage. When

observing he scratchpattern rom nickel bondeddiamond

grinding a brittle fracture pattern should be observed. It

will be noticed rom figure 5.36 how the Ultra-Prep disc ~

iJx;luOOdor planar grinding of MMC ma1erials; ~ ~

only possible when the ceramic particulate has a high

concentration. The swart' from cutting the soft metal

matrix will want to weld to the diamondcutting face, t ~

the ceramicparticulate hat will act like a dressing tick as

it is being cut and therefore stop the diamond from

becoming logged.

This grinding surface can also be used for the planar

grinding of soft materialsw~ alternativemethods uchas

silicon carbide or allDDiDiumoxide papers manifest

impressed brasives.When t is used or soft materials he

grinding surfaceshouldbe waxed or oiled prior to use and

could additionally require regular dressing to keep the

diamond acesclean.

Metal mesh discs (UL'I'RA-PLAN) (C) are very much

confiDed o the brittle fracture materia]s, n comparison

with the two previous discs, hey induce ~ damagebut

are slower at removing material. ~~~u..~ the diamond s

'charged' onto the steel mesh,and requires the action of

the ~imen passingover to lodge the diamond nto the

mesh surface, ductile materialswould not be a candidate

for this grinding surface. This is confinned by reference

onceagain o figure 5.36.

Metiap Platens D) which are composites f metaJ/resin r

ceramic/resin equire a chargedabrasiveand as such have

restricteduse when materialductility ~ high. They induce

a restricted evel of defonnationor structural damageand

leaves he specimenn an extremely lat condition. There

are a seriesof platensoffering increased hock absorbing

characteristics or systematicprogression owards sample

integrity. Note how the use of thesehave been estricted

to the harder ductile and brittle fracture materials thus

avoiding any impressed diamond abrasives from soft

me~


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METALLOORAPH"lEUROPE

ULTRA-PREPdiscs E) havea very important role to play

in the brittle fractureseriesof materials.note bow they are

used n the final ntegrity stagese. 2 and 3. The diamond

abrasive s em~M~-rl into dome shaped esin spots on a

resin ibre support. When observing he scratchpattern it

will be noticedbow the previousstage racture mec~

has changed o what looks like a polished appearance.

1bis is due o the material emovalmed1aDismhanging o

a type of slip plane dislocation rom the previous brittle

fracture. This condition is in part shock absorbing

dependent swell asparticlesiu - ie.

20pm nickel plated mIra-Prep disc would induce

brittle fracnue - material removal by crack

propagation.

.

30J1Jn esin bond Ultra-Prep disc would induce a

polishedappearance material removal by slip plane

dis1


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>4 METALL06RAPH"i EUROPE

Figure 5.38 - Grinding cloths are those fabric surfaces

charged with a diamond ~ve and suitable ubricant.

used n ~ grinding mode n the sample ntegrity stage. In

the past these cloths have reen called .polishing' cloths

since no distinction was ~ between grinding and

po~g. In order to carry out efficient grinding mese

surfaces ~d to havea reducedsurface ensionand this ~

achieved y the weaveof the cloth or the porosity within a

resin ngressedextile material. The diameterof the weave

and subsequentmesh denierby weight) dictates he ideal

grinding abrasive~. This s reflected n me selectionand

subsequent ositioningwithin the chart Finally at the last

integrity stage the choice is influenced by the specimen

material abrasion esistance, ard materialsusing Texmet

2000 (N), soft materia]susing he acetate ilk (Q).

Figure 5.39 - Polishingcloths areusedas the word implies

'to polish or shine he surface' n order o achievea scratch

free reflective surface. Those ~en materials hat are

most prone to scratches. hat ~ soft metals, should be

polishedwith a non-saarcbingabrasivesuch as Colloidal

Silica. The cloth equally should be soft and free from

abrasion uch as Mastertex. Notice from figure 5.39 how

tbi cloth ~ used for slWTy polishing (SP) and not

diamond

Specimens hat smear or are 'gummy' will require the

addition of either an acid or an alkaline solution to cause

specimen ~lution and in consequence allow the

abrasiveparticles o polish n a defonnation ree manner.

To ~ end the COOmomet loth for soft materials ~

designated'AK' for attack polish. For general ductile

materials he Clemomet, when used, would be for slurry

polishing SP).

Ceramic material, silicon wafer etc require a totally

different cloth hence he Polimet cr sluny polishing.

When dealing with general ductile materiab the use of

diamond polishing can abo be a choice, the Microcloth

(high nap) beingused or many

~~~c1I :-~.

This~ of cloth

could also be used on difficult MMC materiab where the

matrix requires an additiooal polish. Some ceramic

compositessuch as PODFA used in almninium casting

could require an attack or ~lution polish hence the

Cbemomet or AK.


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J~ META LO6RAPH'iEUROPE

r

D AM 0 lm &RIND IN 6

CLOTHS

Through the adventof the B~bler DeWconcept n

specimenpreparationa greater emphasishas been

placed in what is the specific fmK:tion of

grinding/lappingand polishing surfaces,and when

best o ~ them. Additionally o this ~ the need o

~ the type of abrasivemost suitable for such

surfaces. Considering cloths for grinding tOOy

shouldbe without any nap and have some meansof

retaining the grinding abrasive. Le. considerations

suchas

.

.

.

.

p

have a varying size meshstructure to suit large

andsmall sizedabrasives

.

Surface o be porous

abrasiveso lodgebetween ibres

abrasiveso be orced nto polymer binder

Coths that are chemotexti1esuallyhavea graded

resin binder system based on hardness (usually

between 0 - 90 shoreA). When he resin volume

is high it is re~.ssary o 'buff' the cloth surface n

order to retain the diamondabrasiveand lubricating

medium.

Examples f diamond liDdin& cloths are:-

Utra-pad

Texmet

PeIforatedTexmet

Nyloo

mtra-pol

AcetateSilk (qA~)

Polimet

Although an explanation f which cloths to use for

specific ~ is given later in the text, it ~

thought prudent at this stage to introduce the

subject

Consider the grinding cloth selection at the final

integrity stage or the ollowing materia1s:-

. Very hard TungstenCarbide)

. Medium Hard (0.4% CarbonSteel)

. Very Soft (Aluminium)

.

Brittle Fracture Mineral)


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METAIJ.O6RAPH"l EUROPE

All these our materialscould be prepared using a

Texmet cloth at the final integrity stage, he results

howeverwould be compromised..e.

. Soft materials would be severely

saatcbed.

. Deformation would be higher as the

materialbecomes ofter.

. Surface obbing could cause phasepull

out

.

Integrity would be compromised.

Taking he soft materlaJsirst we ~d a cloth that ~

the leut abrasive soft to the touch), n this case he

acetate silk cloth would be suitable. This cloth

additionallyhasa cross-weave atternwhich helps n

removing surface tension during grinding. The

reduced smface tension by definition means less

surface ubbing which is an added advantagewhen

preparing riabJe~ (graphite n iron).

The mediumbard material

the previousexampleonly

~ to be more resilient

requirement

Hard materials n~d a hard wearing Oat surface

cloth. Cloth abrasion s not important at this stage.

High ~nsity laminAte loths that are fused together

under heat and pressurecould be ~d. The most

popular cloth throughout the world is the

cbemotextile Texmet', this cloth is not quite so

dense.Texmetmade rom absorbentibres n a ~

binOOr xhibitsporosity which is useful for trapping

grindingabrasive nd ubricant

Finally, what is required or brittJe racture mateJials

suchas mineraJs?Soft cloths are unsuitablebecause

of interphaseelief grinding and ~ffici~t material

removal rates. The Texmet cloth, although

marginally suitable, does suffer from robbing and

relief. The answer herefore s to have a fine weave

low weight denim cloth such as natural silt i.e.

mira-pol

These four examples serve to illustrate the

shortcomings n the traditional blinkered approach

with its 6JIIDTexmet and 1JIID Microcloth for an

materials.

;'

requiresa mm,larcloth to

this time the cross-weave

Nylon cloths satisfy this


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MET Au..O6RAPH'i EUROPE

~

Sincepolishing s the stepd1at akesplaceafter

achieving ample ntegrity. ts function mustbe to

remove op surf~ scrau:bes.mprove reflectivity

and wherene~-~ry introducedie submicrometre

interphaseelief n~-~ for differential

interference ontrast.The cloth will be soft (non

abrasive) ndwill exhibit a short nap. One example

of diamond~llihin& cloths s Microcloth

D AM 0 NO PO 1JSHIN 6

CLOTHS

SLURR"'l POlJSHIN6 CLOTHS

J:

The requirement f a slurry polishing cloth is

different o d1at f a diamondpolishing cloth in that

it d~ not havea high densityvertical fibre nap.

Slurry polishingclothsarevery soft and ~ fibres

are non veI1ical. A goodexamplewould be the

Selvytcloth ~d for polishing brassand copper.

One mportant unction s the retentionof liquid and

to this end someclothsencompass foam

subsurface.AnotJr;rexampleof liquid absorbency

would be the felt type cloths. Absorbent ibres such

ascotton will be better or example han man made

fibres.

Examples f slurry ~~& cloths are:-

. Mastertex

. OM:momet

.

Polimet

Suitable lurrieswould be allImina magnesia

cerimnoxide colloidal silica.

SLURR~ &RINDIN& CLOTHS

The thoughtof usingan abrasivegrinding particle

as

small as O.OSJJIn

n a grinding modeat first seemsa

strange ombination. owever, f grinding is

~~-~~ry to achieventegrity hen suchsmall size

abrasiveswill be n~-~~ry. If for example he

sma]1p-~tlementor phasen the specimen o be

prepareds sayO.5JIIDhen a grinding abrasivemuch

~a11P:T

thanO.5JJ1nill be n~-~~ry.

The dangerwhenselecting he sluny grinding cloth

with suchsmall abrasiv~ s to ensure he abrasive

follows the convention or grinding and not

polishing. .e. the abrasivemust not ~ and all at

the point of cutting.

Exampl~ of slUII'Y liDdin& loths are:-

. Texmet

. Utra-pol


52/170

VERY HARD MATERIALS

(tungsten carbide)

M

RnTLE

FRACTURE MATER~S

I

(ceramics/ minerals/ refractaries)

0

0

SOFT DUCTILE MATERIALS

(aluminium/tin/lead/ copper)

DUCTILEMATERIAlSGENERAL

(ferrous/non-ferrous)

M

METAL MATRIX COMPOSITE (MMC)

(high particulate concentration)

0

;0

0

GLASS MATRIX COMPOSITE

N

p

ERAMIC MATRIX COMPOSITE

LEGEND

(in order of severity)

HIGH M=ULTRA-PAD

hard woven cloth

: N=TEXMET 2000

chemotextile cloth

I O=NYLON soft woven ~Ioth

.

P=ULTRA-POL low denier silk cloth

lOW 0= RAM ocetate silk cloth

FIG

5.38

GRINDING

MATERIAL

CH,A.RGED

LOTHS-

SPECIFIC

DIAMOND

ALUMINA


53/170

.

~:"J. ~..'

i.",,-;';~~

VERY HARD MATERIAlS

(tungsten carbide)

POLIMET/SP

RITTLE FRACTUREMATERIALS

(ceramics/ minerals/ refractaries)

ULTRA-POl/DP

CHEMOMET/SP

MASTERTEX/SP

OFT DUcnLE MATERIALS

(aluminium/tin/lead/ copper)

CHEMOMET/AK

MICROCLOTH/DP/SP

RAM/DP

CHEMOMET/SP

DuCTILE MATERIALSGENERAl

(ferrous/ non-ferrous)

MATRIX COMPOSITE (MMC)

POLIMET/SP

(high particulate concentration)

CHEUOMET /SP / At4 METAu.06RAPH'/ EUROPE

~

Figure 5.13 Selection

Figure 5.13 having addressed he question of abrasive

selection,bas concluded hat three of the steps could be

removed without re~~rily oompromLgng he total

procedme sample ntegrity n the shonest ime).

As bas beenshown n the sectioningpart of this manual,

the residual damage can vary from IOJllD to 9O0JllD.

Consider he materialused n figure S.II/ S.12/ S.13 now

to be sectioned under optimised controlled conditions

giving a Z axis damage epth.asshown n figure S.14

Figure 5.14 - Preparation Without Logic

To progress he sample hroughany of the previousstages

would be totally illogical. As shown rom the sketch he

240grit abrasive nduces rather than reduces he Z ~

dimension.

From this simplified explanation t can be seenhow vital

the sectioning tage s to any preparationprocedure. The

knowledgeof residual damage s the factor that dictateS

what the proceeding tepswill be.


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4 METAJJ..06RAPH"i EUROPE

Figure S.lS - Preparation with Logic

figure 5.15 completes he procedure by baving a single

step only. The assumptionmack: n this discussion~ the

absence f anyplanargrinding equirements.

Z AXIS CURVES When 'working' a material here will be a given depth of

residual damage relative to a given grinding

surfaceJabrasiveize and shock absorbingcutting action.

'Ibis depth (z axis) will vary with different materials; an

exampJeor 0.37Steels shown n figure 5.16

Figure 5.16 - Database haIt for 0.37

comparison nly)

Steel

(for

Damage n micrometers s given for a whole series of

silicon carbick: papers and diamond polishing cloth

combinations.To selecta procedureusing silicon carbide

paper he choicewould dependnot on surface inish of the

sample o be prepared,but the estimatedor documented

residualdamage. On dJepolishingside t will be noticed

how the abrasive article size s followed by 'PS. then a

number 9JJ1nS2). PS s short or 'polishing surface. he

number ndicativeof the polishingseverity. 2 being ow in

polishing abrasive) 8 beinghigh n polishing (relief).

5.12


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3 SiI~ C8tIide p.,efS

1 PoIistW'D .

",--

Platen ~

surtaces \

~-, --- ~--:-'I

1 . -ow ', .

~ -- ~ r.uh

'~---' Time -.~ .

Time . Reducedime

greaww.egrttr

..

~

g

~

..

Figure 5.19 - Integrity ChaIt for Material MMC

A four step (3 SiC. 1 Polish) traditional method ~

comparedwith an alternative our step mediod utilising

composite platen surfaces and a grinding cloth. The

grinding cloth ~ a 'polishing ype' cloth used n a grinding

mode. These wo methodsare basedon the preparationof

a metal matrix composite. The important aspectof this

graphicdisplay s the nformation hat can be derived rom

it. Viz.

Dotted ine method according o the ~play)

.

Exhibitsgreaterntegrity

.

Takesessime o prepare, nd

. Doesnot degrade ith time

Continuousine method

Doesnot achieve he samedegree f integrity

Takes onger. and

De~ with time

.

.

.

When comparing he surface~ at the 'best position'

with both methods. hey were considered o be identical.

Figure 5.20 sumsup the two approachese. surface inim

V s residualdamage.


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A METALL06R.APB\' EUROPE

: TRAomONAL

NEW

L

Lx-

SECT10NING

r;~;~G--

GRIND

lX_.uJ=~~

I ~ I ~ I ::::fTY --

I.:L.

~

"

SECTtONING

: MOUNTING

I

ROUGH

yRINDING

I FINE

GRINDING

cL

.

IHTEGRrrY IN THE SHORTEST TIME

I

ROUGH

IPOUSH

FINAL

'POUgH IX

. ,

HIGHLY POUSHED

Figure 5.20 - Surface Finish or Integrity

In comparing he two approachest will be noticed that a

change f terminologybas akenplace. The ~ of words

such as 'rough grinding' and 'rough polishing' are

mimomers m the new terminology. Since all samples

would be ground or Japped o integrity (i.e. we would

ne.Br polish a sample prior to achieving a faithful

structure) his group of stepshave been clA~fied as the

'sample ntegrity stage'. The only polishing that takes

place herefore s after achieving ample ntegrity, this is a

~ stepandmust be kept asshott as possible.

FIgure 5.21 The Concept in use.


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@4 METALL06RA.Pn EUROPE

Figure 5.21 brings together all the be~fits of the ~w

Concept n surfacepreparation ncluding the terminology

of each stageand the appropriateabrasive or each stage.

Notice how the sample ntegrity stagebas been split into

three groupsas he sampleprogressedo integrity. Within

these hreegroups he ab~ve sizebasalso been ncluded.

A severity rating, from 5 the greatest o 1 the least, bas

been ntroduced or all grinding/iapping/polisbingurfaces

used. This rating will apply to planar grinding, the 3

groups in the sample ntegrity and the polishing stage.

(The sketch only shows he rating for the 3 groups n the

sample ntegrity stage). The choi~ of surfacesand its

effect on progressing the sample to integrity will be

~ussed later under preparation ptions'.

MA TR1AL REMaV AL

MECHANISM

The two modes of material removal are by slip plane

dislocation for ductile materlab as a result of the shear

force from the abrasive. The other mode of material

removal is by brittle fracture which is the result of

cracking. Thesecracks emanating rom the shearstress

point having a major crack nmning along the shear axis,

odlers of lesser severity at angles rom the major axis.

Figure 5.22 - Deformation StructuralDamage

Relationship or Brittle Fracture ndDuctile Materials

If we observe he reduction n defonnationwith the steel

samples s shown n figure 5.22, material emoval s totally

by plasticdislocation. The upperpart of this sketchshows

what happens as a ceramic material is progressed to

integrity. Firstly, material s removedby brittle fracture.

Towards completion of the preparationhowever, notice


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A METALL06RA.PH'i EUROPE

how ductile slip plane mechAni.clncccur until slip plane

disl


81/170

METALLOORAPH"iEUROPE

.

..

""TrAil. .

I I I I

R[WOI/A:. , .A~ - - I

. I . I

.

-

0

~ I I I ,

I, . , I

-40-

IwOI"

'5

I I

I I

I I

'~I

I

I

10

~

,

-

,oIcOflol

I

- -

Figure 5.24 - Effect of Lubricant IdenticalOath (Steel)

~

-'[~

~~...

:~

t\

X'

"""7':

.

.

.

.

,

I

'k

.

01.

I

.

.

.

...

0

.

~ ,~' :..

. .

. .

. . .

I . .

. . - I

.

I

.

.

I

-.

.

. . -:

: - - - - :

_Co-i";

- - - - .

- - - -

. ,

. , .-.COQ.. I

-

~ 10 IS 20 2S RS

(-) (rntort)

-UJlfCAL ~ ~.. (T[X'" ~)

-~ *1-. C-.a.: ;.eg:)

-~ 6VIP.DIUIONI

Figure S.2S -

Effect of Lubricant I Identical Ooth

(Ceramic)

A cbemotextilegrinding cloth. dosed with a controlled

amount of 6J1Jn iamond at set intervab when grinding

steel and ceramic specimem,was checked for material

removal at intervaJs f 5 minutes. Figure 5.24 shows he

results from working steel- figure 5.25 the results from

working reactionbonded ilicon carbide. The first point of

interest rom these igures s the compatibility of the Water

baseddiamondsuspension ith both the steeland ceramic.

Copyright1994BU~R Ltd

I

-oi

I

--

~ 10 1~ 20 25 RS

(mnutes) (restort)

-IO(UTICI.L.POlISH..c CLOTH T[x~ 2000)

-SAMPlE UATERIAl0.4%C STEtL

-~ASP.' ~ OIAUONO


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A META.u.06RAPm' EUROPE

the low figure and faIl off when using alcohol was

surprising. These results would abo show how the

reramic s more prone to surface ension as the specimen

surface SIDOOthes'. n the right hand side of both these

figmes is the restan (RS) dimension. his is the ma1erial

removal igure after 5 minuteswhen he specimen asbeen

reUJrned o its original ground condition. This restan

figure is what would be expected n real life use. From

these~ water is by far the most efficient with this

combination. t doesnot follow however hat these esults

would be identical f for examplea nylon weave grinding

cloth was o be used.

The 'smoother' and planar he grinding surface he greater

will be surface ension, igure 5.26 and 5.27 are examples

of material removal still using the steel and ceramic

samples,only this time using composite platen surfaces

(metal/resin).

10

t 1

~ PLATmf tJRPAa (~6)

~ WA1DJALo.4~ ITEm.

ABRASIVB 9 pM aAA*D

Figure 5.26 - Effect of Lubricant CompositeSurface

(Steel)

Copyright 1994Bt~R Ltd


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MET ALL06RA.PH"l EUROPE

...I(~

R(~...

.)0

2S

20

i/LH

"~

/i:' : :

'/: : .

II ~~

: :

1O

s

-

0

s ,~ I~ :0

\-"""",

-c~ ~Tt.. Sij$J'A(( (~~ .)

~ WA1t~ Ct~; (R6SC)

-.aAASN( I ~:O

Figure 5.27 - Effect of Lubricant I Composite Surface

(Ceramic)

With both these igures here ~ a tendency o peak, after

which time material emoval decreases.his is thought to

be causedby surface ension. Alcohol ~ better for both

materials;attributed o surface ension break-down, here

are problemshoweverusing alcohol (Surfacepick-up and

vapour). Taking the first 5 min~ which ~ a real-life

figure then water ~ nearly as good for the ceramic. oil

beingslightly better or the steel

A&.O"\

MAT~~

ee...O/AL

~

IIR"~L

~A.L

Figure 5.28 - Use of Extender

Copyright 1994 BUEm..ER Ltd


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eA METAu.06RAPH'l EUROPE

When using automatic abl3Sive dosing devi~ it ~

possible to monitor the dosing period and also the

economicdosingamount. t doesnot follow that the more

abrasive ispensed nto the grinding/po1ishingwface hat

an ~uiva1ent improvement n material removal will take

place. Increasedabrasivedosing can impede mate.ria1

removal. In general here s a point where unher dosing

of abrasivewill give little if any benefit, this is shown n

figure 5.28. From d1iseconomic dose the interval then

must be de~.d. It was found empirically that a loss of

effici~ was not encounteredf the abrasivesuspension

wasalternatedwith a compatible olution of lubricantonly.

thereby reducing consumable costs by half. The

explanationoffered for d1issiUJations the extenderwill

'clean' the abrasive urf~ extending ts useful ife.

DIFFRENT CLOTHS

The experimentsused to define lubricant efficiency was

also used to illustrate how different cloths give totally

different results. Seven different grinding cloths. an

recommendedor steel were tested for material removal

~~. From figure 5.29 t can be shown how 3 at the

bottom of the graph are so ;nPffi~P:Dt to be considered

W1Suitableor this ~~lication. The efficiencyof the other

four varies from 20JJlnSo 28~s (figures taken from

restartposition).

WA18AL

8BI8OVAl.

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Metallography.pdf