Surface Mechanical Properties: Hardness and Micro-hardness

The hardness of a sample is actually a measure of it’s resistance to plastic deformation. When a sample is indented by applying force through a pointed diamond or hardened steel ball, the depth of indentation and the indented area vary between the materials.

The most common measure of hardness is given by Vicker’s Hardness which is:
H_V = 1.854 F/d²

and is denoted as NH_VF (N – Vicker’s Hardness number, F applied force in KgF) multiplying H_V by 9.81 x 10^_-3 one can convert it into GPa. The normal range of Force is from 10-100 KgF.

Micro-hardness test is in principle same as the conventional hardness test, however the force for static indentation should not exceed 1 KgF. This type of test is particularly useful when the mechanical property of a coating over a base material is evaluated. Microscope is used to precisely measure the depth of indentation up to an accuracy of ±0.2 micrometer.