Specimen Preparation Techniques of Materials for Microstructural Analysis

看真相不要看假相

1 Reference e-Book Buehler® SUM-MET™ The Science behind Materials Preparation —————— free down: www.buehler.com Metallography Materialography

• Metallography: the study of the microstructure of metals – Can also be used to examine ceramics(ceramography岩相), polymers(plastography) and semiconductors

3 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.”

4 Applications

Gray Cast Iron The dendrites in aluminum alloy Cu-10.5%S Applications The addition of fibber improves the strength of Intergrated tennis racket Chip

Heat-resistant Ceramic Sectioning 取样

Preparation 制样

Etching 浸蚀

Observation 7 Sectioning The specimens selected for preparation must be representative

Hammer

Vise Clamp

Saw 8 Sectioning

Electric Spark Cutting

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

Recast layer after spark cutting AISI P20 Cutting damage of an 10 annealed titanium specime Sectioning

11 Section

Preparation

Etching

Observation 12 Preparing metallographic specimens • Objective: Remove the damaged layer to give a smooth surface

Mounting Polishing (optional) • Mechanical Polishing • Hot Mounting Grinding • electrolytic • Cold polishing Mounting • Clamping

13 Mounting

14 Mounting

15 Mounting

16 Marking of specimens

• Engraving

• Stamping a code in the specimen Mounting Polishing (optional) • Mechanical Polishing • Hot Mounting Grinding • electrolytic • Cold polishing Mounting • Clamping

18 19 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

24 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 Mounting Polishing (optional) • Mechanical • Hot Mounting Polishing Grinding • electrolytic • Cold polishing Mounting • Clamping

27 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

30 31 Specimen under LOM

32 33 34 35 36 Washing and Drying

• After polishing, the specimen is washed by running water, then rinsed with ethanol, and dried in a stream of warm air

37 Section

Preparation

Etching

Observation 38 Etching

• Chemical • Electrolytical • Special method

selective corrosion

39 Etching Commonly Used Etchants for Metals and Alloys

Composition Comments Nital 90-99 ethanol , Most common etchant for Fe, and steels, cast iron 1-10 mL Use by immersion or swabbing of sample for up to HNO3 about 60 seconds. 95 mL water 2.5 mL HNO3 Keller’s 1.5 mL HCI 1.0 mL HF very popular for Al and Al alloys. reagent Immerse sample 10-20 seconds, wash in warm water

90-100 mL General for Al alloys. Attacks FeAl3, other constituents water 0.1-10 outlined. The 0.5% concentration of HF is very popular mL HF

41 Electrolytic Polishing/Etching)

42 43 Simplified Procedure

44 Reference e-Book of Buehler®

The Science Behind Materials Preparation ——————

Free down: www.buehler.com Automatic Grinder/Polisher

A high efficiency with a higher degree of quality