Vickers hardness test

The Vickers method is a static hardness test method that can be further characterised as follows:

• It is one of the standardised methods (ISO 6507, ASTM E92, ASTM E384)
• The Vickers method works with test loads from 1 gf according to ISO or from 1 gf to 120 kgf according to ASTM, i.e. this method can be used to test hardness in all load ranges (from the micro range to the small load range to the macro range)
• This is an optical method. To determine the hardness value of a test piece, the indentation size left by the indenter is measured.
• Shape and material of the indenter: The indenter is an equilateral pyramid (square base) made of diamond with a dihedral angle of 136°

When using the Vickers hardness testing method, it is usually necessary to prepare the surface of the specimen to be tested, as the specimen surface quality requirements are significantly stricter than those for the Rockwell method, in which it is sufficient for the surface to be free of impurities.

In detail, the specimen to be measured should meet the following requirements for the Vickers method:

• The specimen should be polished (micro hardness testing) or precision-ground (macro hardness testing).
• The specimen should preferably be clamped strongly, so that it cannot move during the testing process (practical tip: measure with nose cone resp. with suitable test anvil, fix embedded specimen in a specimen holder).

In addition, to avoid affecting the test result, care must be taken to ensure that the test is not disturbed by any shock or vibration (an anti-vibration table, etc., may be required).

The representation of a Vickers hardness value follows a standardised notation:

1. The numeric hardness value (between 1 and 3000);
2. The two letters "HV", standing for "Hardness according to Vickers";
3. The applied test load in kgf;
4. According to ISO 6507: The dwell time of the test load, but only if this is not between 10 and 15 seconds (uncommon in practice)

Vickers hardness value

The Vickers hardness indicates how resistant a material is to penetration by an even harder body. It is determined using the Vickers method, in which a diamond indenter is pressed into the test piece under a defined test force. The Vickers hardness value (HV) is calculated from the size of the permanent indentation. The smaller the indentation, the harder the material. Vickers hardness is particularly suitable for very thin components, fine structures and a wide range of materials.

The Vickers hardness (HV) is determined by dividing the applied test force (in Newtons) by the surface area of the permanent indentation in the material. The indentation is made with a pyramid-shaped diamond with an apex angle of 136°. The mean value of the two diagonals of the square indentation is used to calculate the indentation surface, as this is often slightly distorted in practice.
The calculation is carried out in accordance with ISO 6507 or ASTM E384. The typical measuring range extends from around 1 HV to 3000 HV - depending on the material and test load.