Metallography

What is metallography?

Metallography is a key step in determining the quality of metals by analyzing the microstructure (the microscopic structure that determines the properties and performance). Metallography provides:

"Penguins on the March" - that's one viewpoint of this microstructure.

“Penguins on the March” or “Winter forest” – What do you see in this microstructure?

  • Characterization of the structure and substructure of metals, usually with a focus on examining the grains, phases, inclusions, defects, and other details.
  • A process for analyzing and understanding metal alloys and their structures.
  • A great tool for determining quality, defects, inclusions, and other important details.

Traditionally, metallography [1] is performed along with optical microscopy, electron microscopy, and X-ray diffraction to identify and characterize different crystalline phases and other critical materials properties that are invisible to the naked eye.

The Metallographic Analysis Process

  1. The first step is cutting a specimen, and (if needed) mounting in Bakelite, acrylic, or other materials.
  2. The metallography sample specimen is then ground with successively finer grits of sandpaper until the surface is quite smooth, at which point silica, alumina, or diamond polishes are used to achieve a mirror-like finish.
  3. Chemical or electrochemical etching of the surface is performed; depending on the method chosen, a variety of details can be identified and characterized.
  4. Color metallographic etchants (chemicals that attack the surface in different ways) may be used to further distinguish the important constituents of the metal.
  5. Finally, microscopy, x-ray diffraction, and other characterization techniquesare used toevaluate the critical details at magnification levels from 1 to 200,000X.
    1. Optical microscopy is performed from the macro level to 1,000X or higher magnification. This is the bread-and-butter of metallography, used every day to examine for microstructure analysis, defects, cracks, and other microstructure effects. Etchants are often used to highlight the features of interest. Image analysis software may also be used for statistical analysis of microstructural details.
    2. Electron microscopy, combined with EDS analysis, can measure and analyze specific phases, inclusions, and other observed constituents of the microstructure, including semi-quantitative assessment of the chemical content by element.
    3. X-ray diffraction may be used to measure the diffraction pattern of an x-ray beam from the crystal lattice to assess the compounds and phases present, crystallinity, and other characteristics of crystalline materials.

Additional Resources:

www.metallography.com/ – A reference resource with more information about metallography

www.metallographic.com – A provider of metallography supplies and materials

Photomicrographs are taken using high-quality microscopes to provide accurate and extensive characterization of the microstructure and other properties of the specimens. Micrographs of different steel compositions are shown below, with varied phases (the different black, grey, and white colored regions), precipitates, and other features that are highlighted by high-quality metallography.