What is Vickers hardness? - Axiotek - Vickers and Shore hardness testers made in Italy

The Vickers hardness test is one of the static mechanical tests that can be used to measure the hardness of materials.

In specific, the force used for the indentation of the material is determined, followed by the optical measurement of the size of the indentation.

This means that it is the optical acquisition of the indentation size generated by the indenter, together with the value of the load force, that determines the hardness value.

The range of hardnesses applicable in this case is very wide. For the purpose of convenience, we speak of two “families”, separate from each other:

Vickers micro hardness “family”: range of forces between 0.009807 N (1gf) and 0.9807 N (100gf), according to ISO 6507-1;
Vickers macro hardness “family”: force is greater than 0.9807N (100gf and up), according to ISO 6507-1.

However, there are variables that must be considered when choosing which load forces to use, including:

the thickness and the sizes of the test sample;
the size of the area to be measured.

We recommend identifying the best procedure based on specific personal needs with the help of the ISO 6507-1, ASTM E92 and ASTM E384 standards (the latter in the case of Vickers micro hardness).

How does Vickers hardness work?

Imagine a bench top hardness tester equipped with an indenter in the shape of a straight pyramid (with a vertex angle of 136°), with a square diamond base. The hardness test starts when the indenter comes into contact with the surface of the sample to be measured.

After a localized pressure of a few seconds (usually between 10 and 15 seconds), the force is removed.

At this point, a special algorithm processes the images from the optical system on the basis of the Vickers hardness principle and calculates the average of the diagonals of the indentation generated by the indenter, therefore allowing to calculate the hardness value (for which the unit of measure is indicated with “HV”).

Immagine di prova durezza Vickers - Axiotek

To be more precise, this value is determined by the ratio between the applied force (expressed in Newton or kgf) and the lateral surface of the indentation after the force has been removed. Here’s the formula:

This formula is developed further to arrive at the final calculation expressed below:

In practice, however, to quickly calculate the hardness value it is sufficient to refer to the tables attached to the reference standards, without having to materially apply the formula just described.

When to use Vickers hardness?

SUITABLE FOR LABORATORY USES

Vickers hardness is best suited for the laboratory environment. It allows very thorough investigations, perfect for an ad-hoc hardness study. It is therefore no coincidence that we offer the possibility of this type of hardness test mainly through a bench top hardness tester.

This is the only way to manage your work as best as possible, avoiding vibrations and ensuring thorough investigations.

TO MEASURE ANY OBJECTS

The Vickers test is suitable for measurements of any objects (including the smallest), even using very small forces and without the need to change the indenter.

SINGLE AND MULTIPLE TESTS

Suitable for both single and multiple tests (otherwise known as stitching).

These are perfect for testing the hardness of a test specimen at multiple points, especially in case of materials with different coatings and that can therefore show significant variations in hardness from point to point.

What are the prerequisites for carrying out a Vickers hardness test?

POLISHED, SMOOTHED AND CLEANED SAMPLE

The sample must be suitably polished, smoothed and cleaned, to ensure the absence of oxidation. Only then will the optical acquisition be accurate and suitable for the calculation of the Vickers hardness.

FIRMLY CLAMPED SAMPLE ON THE HARDNESS TESTER

The sample must be firmly clamped on the bench top hardness tester, in order to avoid vibrations.

We know how difficult it is for a photograph to come out sharp when what we want to photograph is moving all the time.

Vickers hardness pros and cons

Benefits

Vickers hardness ensures a high degree of repeatability, regardless of the sample being measured;
The range of hardnesses that can be measured is very wide, and also allows for the use of reduced forces, suitable for extremely fragile materials (such as porcelain, for example), or particularly smaller samples (such as pins);
Versatility, because it can be used to measure any metals, as the scale used is unique. In this sense, the Vickers test perfects and exceeds the Brinell test, thanks to the almost unlimited application, both as far as the hardness and the thickness of the sample to be tested;
There is no need to change the indenter (unlike other hardness tests, such as Brinell).

Disadvantages

Slow (compared with other hardness tests, such as Rockwell), because for the calculation of the hardness the Vickers test is done through optical acquisition;
Precision and care in cleaning the sample to be measured, in order to have the clearest possible picture of the indentation generated by the indenter;
Higher cost than other measuring instruments, because it relies on powerful optical lenses.