看真相不要看假相 Specimen Preparation Techniques of Materials for Microstructural Analysis 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 46.