Prevest Research Institute uses a Shimadzu Micro Vickers Hardness tester, Model No. HMV-G31-ST. The system is capable of 16 stages of test forces and the loading unit is automatic with automatic force changing. Indentation reading system is based on automatic readings via digital image analysis, and manual settings for line length measurement in the PC window also available.
Hardness tests have been extensively used for evaluation materials such as metals, ceramics, and composites, quality control of manufacturing processes and research and development efforts. Hardness, although empirical in nature, can be correlated to tensile strength for many metals, and is an indicator of wear resistance and ductility. Microindentation tests extend hardness testing to materials too thin or small for macro-indentation tests. Microindentation tests allow specific phases or constituents and regions or gradients too small for macro-indentation testing to be evaluated.
Microindentation hardness testing is a method for measuring the hardness of a material on a microscopic scale. The hardness test is performed using a calibrated machine to force a diamond indenter of specific geometry into the surface of the material being evaluated, in which the test forces range from 9.807 mN to 19.61 N, and the indentation diagonal, or diagonals are measured with digital camera attached after load removal; for any microindentation hardness test, it is assumed that the indentation does not undergo elastic recovery after force removal.
Vickers indenter is a square based pyramidal-shaped diamond indenter with face angles of 136°. Vickers Hardness Number, HV is an expression of hardness obtained by dividing the force applied to a Vickers indenter by the surface area of the permanent impression made by the indenter. Vickers hardness is calculated from the following equation using the test sample load at the time an indentation is formed in the test sample surface and the average length of diagonal lines across the indentation.
Where, HV= Vickers hardness [no unit symbol is used for HV values]
f = Test load (N)
d= Mean of the indentation diagonal length (mm)