Definition - What does Microhardness mean?

Microhardness is the hardness of a material gauged with instruments using small indenters. Therefore, a lower amount of force is applied relative to the standard measuring instruments, allowing measurements on thinner sheets or smaller test materials that may not respond accurately to measurements conducted with standard instruments. Typically, the indentations are so tiny that microscopic measurement is required to obtain precise readings.

When testing materials like metals, the microhardness linearly correlates with the tensile strength. This allows cost-effective and beneficial non-invasive testing as well as portable measuring equipment.

Corrosionpedia explains Microhardness

Microhardness is a broadly used term referring to the testing of hardness involving materials by using small applied loads. A more appropriate term to describe this is microindentation hardness testing. In this testing method, the use of a diamond indenter with a particular shape is used to make an impression called a "test load" or "applied force," which can be at 1-1000 gf, on the material under testing.

Normally, microindentation tests involve 2N forces, which are roughly equivalent to 200 gf. This force can produce an indentation of around 50 µm. Because of its specificity, this type of testing is applicable in cases where there is a need to watch for hardness changes on a microscopic level. Unfortunately, the standardization of microhardness can be difficult since it any material’s microhardness tends to be higher than its macrohardness. The values of microhardness may also change according to work-hardening and the load. Two of the most popular tests used to measure microhardness, but are applicable for heavier loads as well, are the Knoop hardness test and the Vickers hardness test.

This type of test is not only used in metals, but ceramics and composites where macrohardness indentation tests cannot be applied. Microhardness tests are useful in giving required data when taking measurements of single microstructures situated within a bigger matrix and testing foil-like or thin materials.

In any material being tested, the following should be considered:

  • For all types of loads, hardness significantly increases at diagonal and low lengths.
  • The effect can be more pronounced when the load is lessened.
  • In a vertical position, small measurements can result in large hardness differences.

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