Correct option is D
The Vickers hardness test uses a diamond pyramid-shaped indenter, which is its most distinctive feature. The indenter has a square base with an angle of 136° between opposite faces, allowing it to produce a geometrically similar indentation regardless of the applied load. This makes the Vickers test highly versatile, as it can be used for both soft and very hard materials with high accuracy.
In this test, the diamond indenter is pressed into the material under a specific load, and the diagonals of the indentation are measured using a microscope. From this, the hardness value (Vickers Hardness Number, HV) is calculated. The use of diamond ensures minimal deformation of the indenter itself, even when testing very hard metals.
