The Vickers testing method consists in impressing in the piece to be examined, with a determined force, a pyramid-shaped indenter with a square base, having an angle of 136 ° at the top, and in measuring the diagonal (d) of the impression left on the piece, after removing the load. The Vickers hardness is the quotient of the test load (F in kgf) for the footprint area (in mm), considered as an inverted square pyramid.

SCOPE

Vickers testing method has been found to be very useful for materials evaluation, 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.

PRINCIPLES

An indentation hardness test using a verified machine to force an indenter, under specified conditions, into the surface of the material under test. After the indentation process, the shape of the resulting indentation is measured after removal of the force. The general principle of the Vickers and Knoop indentation hardness test consists of two steps:

Step 1 – Vickers applicable specified indenter is brought into contact with the test specimen in a direction normal to the surface, and the test force F is applied. The test force is held for a specified dwell time and then removed.

Step 2 – For the Vickers hardness test, the lengths of the two diagonals are measured and the mean diagonal length is calculated, which is used to derive the Vickers hardness value.

For the Knoop hardness test, the length of the long diagonal is measured, which is used to derive the Knoop hardness value. For micro indentation testing, the indenter shall contact the specimen at a velocity between 15 and 70 μm/s and should not exceed 0.2 mm/s. The time from the initial application of the force until the full test force is reached shall not be more than 10 s. So, the full test force shall be applied for 10 to 15 s unless otherwise specified.