The Vickers hardness test is a versatile hardness test method, used for both macro and micro hardness testing. It has a broad load range, and is suitable for a wide range of applications and materials.

The Vickers hardness scale is often regarded as easier to use than other hardness methods: The process can be performed on a universal or micro hardness tester; the required calculations are independent of the size of the indenter; and the same indenter (a pyramidal diamond) can be used for all materials, irrespective of hardness.

The Vickers Hardness calculation

The Vickers Hardness (HV) is calculated by optically measuring the diagonal lengths of the impression left by the indenter. These measurements are than converted into a hardness value using a standard formula or reference table. Modern hardness testing instruments are equipped with integrated calculators that automatically compute and display the HV value.​

HV = 1854.4 F/d^2

HV: Vickers hardness
F: Test load (gf)
d: Average diagonal length (µm)

• Load range: From 1 gf up to 100 kgf

Vickers Loads

• Indentation time: 10-15 seconds
• Sample thickness ASTM: At least 10 times the indentation depth
• Sample thickness ISO: At least 1.5 times the diagonal length.

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Regardless of the micro hardness tester you use, when you perform a Vickers hardness test, your indentation will deform the surrounding material and alter its properties. In order to avoid misinterpretations of perceived hardness, the Vickers hardness testing standards prescribe a certain distance between multiple indentations.

Steel and copper

• At least 3 diagonal widths between indentations

Lead, zinc and aluminum

• At least 6 diagonal widths between indentations

Diagonal widths

To ensure accurate reading of the indents, the Vickers hardness testing standards prescribe a minimum diagonal width of 20 µm. 

For instance, this implies that CHD (see below) measurements using less than HV0.2 should generally be avoided, as they will produce indents smaller than 20 µm.

Specimen​
Before placing a sample on the micro hardness testing machine, ensure that the surface is properly prepared. The required surface finish depends on the test load being applied.​

Macrohardness testing (loads > 1 kgf)​

• The test surface should be ground to provide a smooth, uniform finish.​

Microhardness testing (loads ≤ 1 kgf)​

• The test surface should be mechanically polished or electropolished to ensure accurate measurement of the small indentation.​

Proper surface preparation is essential for obtaining reliable and repeatable Vickers hardness results.​

Equipment​
To ensure reliable and traceable results, the Vickers hardness tester should undergo direct verification and calibration at least annually by an accredited calibration laboratory. In-between direct calibrations, operators are encouraged to perform regular indirect verifications using certified reference test blocks with known hardness values.​

Environment​
Among all hardness testing methods, the Vickers test is the most sensitive to shock and vibration, particularly when performing microhardness measurements. To ensure accurate and repeatable results, the instrument should be installed on a stable, rigid surface. Vibrations from nearby machinery, foot traffic, or other external sources should be minimized or eliminated whenever possible.​

ISO and ASTM standards specify an operating temperature between 10 °C and 35 °C.​

Operator​
The operator is responsible for ensuring that the specimen is correctly positioned and remains stable throughout the complete test cycle. To prevent measurement errors caused by material deformation, indentations should be spaced sufficiently apart and away from the specimen edges.​

As a general guideline:​

• The distance between the centers of two adjacent indentations should be at least 3 times the diagonal length (3d) for steel and copper alloys.​
• For light metals, the spacing should be at least 6 times the diagonal length (6d).​
• The distance between an indentation and the edge of the test piece should be 2.5d to 3d, where d is the average identation diagonal length.

For specific applications, always consult the relevant Vickers testing standard to confirm the required spacing and testing conditions.​

Below you can see an overview of the Vickers hardness test methods and the most common applications:

Hardness testing, especially the Vickers method, is widely used to determine the hardness distribution and effective case depth of surface-hardened steels. This is done by making a series of hardness indents from the edge of the cross-sectioned sample towards the center. The hardness progression is plotted in a graph and the distance from the surface to the hardness limit is calculated.

• Case depth = Distance from surface to hardness limit

Hardness mapping provides a detailed visualization of hardness distribution across a material’s surface or cross-section. By recording hundreds or even thousands of individual hardness values over a defined area, intuitive color maps can be generated to clearly visualize hardness distribution and identify variations across the sample.​

This enables users to quickly identify hardness variations, gradients, and critical zones that may not be visible with individual hardness measurements alone. Hardness mapping is particularly valuable for the analysis of heat-treated materials, welds, and components under investigation for failure or damage.​

In most cases, the Vickers hardness test is used to determine hardness in materials in the micro hardness test load range. However, in some cases the Vickers method has some constrains where the Vickers indents sizes is a poor fit. For many of those cases the Knoop hardness test is often a solution, for example for coatings, or to overcome the problem of cracking in brittle materials.

Read more about Knoop Hardness Testing

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