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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. |
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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. |
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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. |
