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 This specification covers both the
Knoop and Vickers Hardness Tests
when conducted
using test forces in the 1 to 1000 gf. range. While this test method is primarily
designed for metals, it may be used on other materials as well. With the Vickers
Hardness Test a diamond with an apical angle of 136° is used. While the Knoops
Hardness Test employs a narrow rhombus shaped diamond indenter.
Hardness Testing is very useful
for quality control of manufacturing processes,
materials evaluation, and for research and development purposes. Although
hardness is empirical in nature, it is an indication of ductility and resistance to
wear. Hardness may also be shown to correlate to tensile strength in many
metals.
The Microindentation Hardness Test (commonly referred to as
a micro hardness
test) extends hardness testing to materials too thin or too small to use
macroindentation test methods. Micro hardness testing can be applied to specific
phases or constituents, gradients or region too small for the larger hardness
tests.
Because of hardness variations
that may exist in a material, a single micro
hardness test may not be representative of over all hardness.
In these tests,
a hardness number (either Vickers or Knoop depending on
which indenter is used) is determined by measuring accurately with the
aide of a microscope, a very small indentation produced by the application of a
relatively low force (compared to the regular hardness test). The measurements
now obtained, are then plugged into the appropriate formula, or cross referenced
with the proper charts and a hardness number is obtained.
Complete specifications for ASTM E
384 may be obtained from
ASTM International.
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