Specimen Preparation Techniques of Materials

for Microstructural Analysis

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Reference

MetallographyMaterialography

• Metallography: the study of the microstructure of metals

– Can also be used to examine ceramics(ceramography岩相), polymers(plastography) and semiconductors

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The aim of material preparation:to reveal the true structure of the sample

• Specimen preparation quality is the determining factor.

• The classic computer adage, “garbage in =garbage out.”

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Gray Cast Iron Cu-10.5%SThe dendrites in aluminum alloy

Applications

Applications

IntergratedChip

The addition of fibber improves the strength of tennis racket

Heat-resistant Ceramic

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Sectioning 取样

Preparation 制样

Etching 浸蚀

Observation

Sectioning

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The specimens selected for preparation must be representative

Saw

Hammer

ViseClamp

Sectioning

Electric Spark Cutting

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Damage of Sectioning

10Cutting damage of an annealed titanium specime

Recast layer after spark cuttingAISI P20

• Precautions: Avoid alternation of the microstructure in the area of interest.

Sectioning

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Section

Preparation

Etching

Observation

Preparing metallographic specimens

• Objective: Remove the damaged layer to give a smooth surface

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Mounting (optional)• Hot Mounting• Cold

Mounting• Clamping

Grinding

Polishing• Mechanical

Polishing• electrolytic

polishing

Mounting

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Mounting

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Mounting

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Marking of specimens

• Engraving

• Stamping a code in the specimen

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Mounting (optional)• Hot Mounting• Cold

Mounting• Clamping

Grinding

Polishing• Mechanical

Polishing• electrolytic

polishing

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Grinding

The specimen is successively ground with finer and finer abrasive paper

The common grinding abrasives : SiC

Abrasive Paper

Larger the number, finer the abrasive particle

Cross Section of the Sample

Manual “Hand” Grinding

Grinding in one direction is usually better for maintaining flatness than grinding in both directions

Tips

• To protect your hand, round the sharp corner of the sample at the beginning

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Grinding-checking method

Grinding on the Rotating Disc attached with the SiC paper

Wet grinding minimizes specimen heating, prevents the abrasive from becoming loaded with metal removed from the specimen

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Mounting (optional)• Hot Mounting• Cold

Mounting• Clamping

Grinding

Polishing• Mechanical

Polishing• electrolytic

polishing

Mechanical Polishing

• To produce a deformation-free surface that is flat, scratch free, and mirror-like in appearance

• Carried out on polishing clothes with fine abrasive particles(eg: Al2O3, SiO2, Diamond, etc grain size 10~0.05 µm)

Polishing Particles smoothing the surface of the specimen

Manual “Hand” Polishing

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Specimen under LOM

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Washing and Drying

• After polishing, the specimen iswashed by running water, then rinsed withethanol, and dried in a stream of warm air

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Section

Preparation

Etching

Observation

Etching

• Chemical• Electrolytical• Special method

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selective corrosion

Etching

Commonly Used Etchants for Metals and Alloys

Composition CommentsNital 90-99 ethanol ,

1-10 mLHNO3

Most common etchant for Fe, and steels, cast ironUse by immersion or swabbing of sample for up to about 60 seconds.

Keller’s reagent

95 mL water 2.5 mL HNO3 1.5 mL HCI 1.0 mL HF very popular for Al and Al alloys.

Immerse sample 10-20 seconds, wash in warm water

90-100 mLwater 0.1-10 mL HF

General for Al alloys. Attacks FeAl3, other constituents outlined. The 0.5% concentration of HF is very popular

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Electrolytic Polishing/Etching)

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Simplified Procedure

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The Science Behind Materials Preparation——————

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Reference

AutomaticGrinder/Polisher

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