The hardness of a material is defined as its resistance to another material penetrating its surface and is related to its wear resistance and strength. Higher hardness is related generally related to higher strength, which in turn is related to its structure.
Vickers hardness is determined similarly to Brinnell hardness. It is classified as a microhardness determination method and is the more common, compared to Knoop microhardness.
It is measured by forcing an indenter into the surface of the sample. It differs in that it uses a 136° square pyramid indenter, which produces a square indentation in the specimen, rather than a spherical or conical indenter, which Rockwell and Brinnell hardness techniques use. The square indenter is advantageous over the round indentations as the square indentations are easier to measure than the round impressions from spherical and conical indenters.
Measuring Vickers Hardness
The Vickers hardness tester is equipped with an adjustable height stage, which is wound up to close to the indenter prior to the test. The test is executed with a lever or button, with all the rest of the test parameters being controlled automatically. Indenter loads vary between 1 and 120 kg. The indentation is then measured with a microscope across the diagonals of the square indentation.
Calculating Vickers Hardness
The hardness is calculated by dividing the load by the surface area of the indentation, such that Vickers hardness is determined using the following formula:
where Hv = Vickers hardness (in MPa), F = load and A = surface area of the impression.
Similarly, tables are often available to convert load and impression measurements to Vickers hardness values.
Advantages of the Vickers Hardness System
This test also leaves only tiny indentations that are usually not a problem for production items, making it suitable for quality control. The other advantage of the Vickers system other than the increased degree of accuracy, is that it does not have a number of different scales and indenters, as does the Rockwell and Brinnell scales.