Microhardness Testing Shimadzu Model HMV-M3
Microhardness testing, also called microindentation testing, uses smaller applied loads and is suitable for finer spatial scale hardness testing than either Rockwell or Brinell hardness testing. The test units are grams and micrometers, rather than kilograms and millimeters.
Practical applications of microhardness testing include determining depth of case hardening of machine parts, hardness testing of small or thin artifacts, and evaluation of material phases or constituents too small for Rockwell or Brinell hardness testing.
A Vickers (square-based pyramidal geometry) diamond indenter is employed to conduct Vickers microhardness testing with a Shimadzu Model HMV-M3 Micro Hardness Tester. Applied loads are 25 to 1,000 grams, and indentation diagonals from a few micrometers up to a couple hundred micrometers across can be measured. The least count of the fine scale is 1/2 micrometer. Indentation depths are related to diagonal size. The instrument optics are used to visually measure the indentation size after the load is applied and removed automatically by the machine.
The hardness at a precise location may be evaluated and a change of hardness may be evaluated within a sub-millimeter distance, as the indentations are of that small size and the test specimen stage incorporates micrometers for fine 2D motion.
The Vickers Hardness Number HV is defined as Applied Load divided by Indentation Surface Area and is computed from the equation:
where
- P is the applied load of up to 1,000g.
- d is the mean diagonal length of the indentation in micrometers.
Applied loads of 25, 50, 100, 200, 300, 500, and 1,000g are available for the Shimadzu tester.
The loading dwell period is selectable from 5, 10, 15, 30, or 45 seconds.
Note: A Knoop (rhombic-based pyramidal geometry) diamond indenter could be employed, if available, for Knoop microhardness testing. The Knoop Hardness Number HK is determined differently from HV, due to the different Knoop indenter geometry and the Knoop Hardness Number HK basic definition as:
Knoop Hardness Number HK = Applied Load divided by Projected Indentation Area (not a square).
See ASTM Standard E384 for more information.