What is the purpose of preparation of a specimen in Metallography?

Answer 1

Metallographic etching is the process of revealing microstructural details that would otherwise not be evident on the as-polished sample. Etching is not always required as some features are visible in the as-polished condition such as porosity, cracks and inclusions.

A properly prepared specimen will reveal properties such as grain size, segregation, and the shape, size, and distribution of the phases and inclusions that are present, while other aspects such as mechanical deformation and thermal treatments may also be able to be determined.

Metallographic Etching ProcessesThere main etching processes used in metallographic sample preparation are:

• Chemical etching

• Electrolytic etching

• Heat tinting

Chemical EtchingThis typically involves immersing the sample in an etchant such or swabbing the surface with an etchant. The etchant selectively corrodes microstructural features. Immersion time or etching time is highly dependent on the system and in most cases requires experience. The selection of the optimum etchant is also very important in sample production.

Deeper etches are preferred for low magnification examinations, while shallow etches are preferred for higher magnification etches.