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Chapter 5

Chapter 5. Metallography. Metallographic Examination • Quantitative Metallography • Macroscopic Examination. Longitudinal and transverse orientations of specimens from a worked metal exhibit different microstructures.

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Chapter 5

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  1. Chapter 5 Metallography Metallographic Examination • Quantitative Metallography • Macroscopic Examination

  2. Longitudinal and transverse orientations of specimens from a worked metal exhibit different microstructures.

  3. Microstructures of specimens obtained from castings depend on the localized solidification in the casting.

  4. Surface plating is used for protection of the edge of coated, corroded, or surface-treated metals during specimen preparation.

  5. Diamond-tipped cutoff wheels are used on small specimens where precision cuts are required.

  6. Mounting presses use compression and heat to encapsulate the specimen in a plastic mounting resin.

  7. Mounting resins must satisfy a variety of conditions.

  8. In taper sectioning, the specimen is mounted at an angle that magnifies the coating thickness.

  9. Belts used in four-stage belt grinding start with 240 grit and finish with 600 grit paper.

  10. The mount is rotated 90º between successive papers and thoroughly washed between papers to prevent carryover of abrasive material.

  11. Automatic polishing in an automatic polishing machine establishes a complex motion for the mount relative to the rotation of the polishing wheel.

  12. Electrolytic polishing removes rough peaks on a specimen with the flow of current between an anode and a cathode.

  13. For optimum viewing of the microstructure, the mount is etched until a bloom appears on the surface.

  14. Properly etched specimens reveal true microstructural features when viewed in a metallurgical microscope.

  15. Metallurgical microscopes vary from small benchtop units to larger units that have their own framework.

  16. The four illumination forms for micrographs are brightfield, darkfield, polarized, and Normarski illumination.

  17. Heat treatment of a medium-carbon steel during cutting leads to artifacts in the microstructure.

  18. To prevent artifacts, certain metals and alloys require different metallographic preparation procedures.

  19. A pressure vessel steel plate has a fine grain size for toughness. A nickel alloy used for high-temperature service has a coarse grain size for creep strength.

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