Micro Hardness Testing of metals, composites and ceramics are employed where a 'macro' hardness test is not usable. Micro hardness tests can be used to provide necessary data when measuring individual microstructures within a larger matrix, or testing very thin foil like materials, or when determining the hardness gradient of a specimen along a cross section.
The term Micro Hardness Testing usually refers to static indentations made by loads of 1kgf. or less. The Baby Brinell Hardness Test uses a 1mm carbide ball, while the Vickers Hardness Test employs a diamond with an apical angle of 136°, and the Knoop Hardness Test uses a narrow rhombus shaped diamond indenter. The test surface usually must be highly polished. The smaller the force applied the higher the metallographic finish required. Microscopes with a magnification of around 500x are required to accurately measure the indentations produced.
Vickers and Knoop hardness test are defined by standards ASTM E 92 (for indentation forces of 1 kgf. to 120 kgf.) and ASTM E 384 (for indentation forces below 1 kgf.), while ASTM E 10 is the standard for Brinell Hardness Testing.
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