Sample preparation prior to imaging the materials
microstructure consists of cutting a specimen to an appropriate size and then
mounting it in plastic to hold it prior to polishing its surface in a special
polishing machine. The sample is then examined in the Polished state.
The sample may then be subsequently etched to better show its grain morphology.
Alternatively photographs of a broken or Fracture surface may be taken.
This is frequently done to better understand the cause of failure in a load
bearing application or as part of the development of improved materials.
The database can be searched to show only polished samples
or those that have been polished and etched. Low magnification photos of samples
are listed under the keyword Macro in the search. Samples can be
examined several ways to exhibit microstructural features. Optical
microscopy employs reflected white light and is generally used for large
grain size materials, and for the examination of fracture surfaces. Sometimes
the microstructural features are shown more easily with polarized light.
In Cathode Luminescence Microscopy different phases in the
microstructure are shown in different colors. Scanning Electron Microscopy (SEM)
is used to analyze fine grain materials typically in the range of 0.1 micron to
50 micron grain size, whereas Transmission Electron Microscopy (TEM) is
used to analyze grain boundaries and line defects in grains. Usually samples
have to be reduced to a very thin section prior to being examined under the
electron microscope. Such samples are said to have been ion milled. Alternatively
the surface of the sample is replicated on carbon and the surface of the
carbon replica examined in the electron microscope In a few micrographs the
distribution of atomic elements is shown. Such micrographs can be found using
the keywords Electron Backscatter and Microprobe or in the keyword
search as SEM_BSE.
Many of the ceramics in the database have been examined
after mechanical testing at elevated temperature to determine their tensile
strength, bend strength, stress rupture or fatigue behavior. In these cases the
ceramic test sample has usually been broken during testing and researchers
investigating the causes of failure will generally examine the broken surface,
otherwise called the fracture surface. This maybe with a low power
optical microscope or at higher magnifications using a scanning electron
microscope (SEM).
For additional information on sample preparation consider
the following texts:
Ceramography:Preparation and Analysis of Ceramic
Materials; Richard E. Chinn;
American Society of Materials
International (ASM), Materials Park OH, 2002.
Metallographic Polishing by Mechanical Methods 3rd
Edition, Leonard E. Samuels; ASM INTL, Materials Park, OH,1985.
Metallography: Principles and Practice; George
F. Vander Voort, McGraw-Hill Book Company, New York 1984.
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