Vickers Hardness Test

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The Vickers hardness test is a static hardness test method, used for both macro and microhardness testing. It is an optical method of testing where the size of the indentation left by the indenter is measured to determine the hardness value of a test specimen.

It is a standard test method recommended by ASTM E384, ISO 6507 and JIS Z 2244. The microhardness methods are used to conduct tests on metals, ceramics, composites and almost any type of material.

Equipment Required

1. Vickers hardness tester
2. Pyramid indentor

Theory and Principle of the Test

1. The penetrator to be used consists of a four-sided diamond pyramid, the angle of which is 136 degree between the sides facing each other.
2. The load stage most frequently used is 10 kg, 30kg, and 60kg.
3. The depth of the specimen should not be less than 1.5 times the diagonal of the impression.
4. The distance between the center of the impression and the edge of the adjacent impression or edge of the specimen should be at least 3 times the diagonal of the impression.

Surface Preparation

Before placing the sample material in the microhardness testing machine, it must be ensured that it is correctly prepared. The required surface condition for the Vickers hardness test depends on the load used.

• For macro hardness testing, the loads applied must be higher than 1 kgf and the surface should be ground.
• For microhardness testing, the loads applied must be below or equal to 1 kgf and the surface should be mechanically polished or electropolished.

Test Procedure

1. Set the machine to the required stage of test load and dwell time.
2. Place the specimen carefully on the testing table.
3. Bring the objective to the "set" position.
4. Turn the hand wheel slowly in the clockwise direction so that the specimen gets focused on the front screen sharply.
5. Now bring the inventor to the "set" position and turn on the loading, dwell- unloading cycle.
6. Bring the objective back to the "set" position.
7. The indentation is now projected on the front focusing screen.
8. Measure the diagonals along both the axis of the impression and record them.

Results

F= Load applied in kgf
d= Arithmetic mean of the two diagonals, d1, and d2 in mm.

Formula and Calculation

Vicker's Hardness (HV) =

The obtained results are reported as 800 HV/10, where 800 is the Vickers hardness and 10 is the load applied. But it is a general practice to report the Vickers hardness in SI units (MPa or GPa).

• To convert HV to MPa, multiply by 9.807
• To convert HV to GPa, multiply by 0.009807

Application of Vickers Method Depending on the respective Load Range

Advantages of the Vicker's Method

1. The Vickers method can be used with any and all materials and test specimens, from soft to hard, as the procedure covers the entire hardness range.
2. There is only one type of indenter, which can be used for all Vickers methods.
3. Non-destructive testing is possible, so the test specimen can be used for other purposes.

Disadvantages of the Vickers Method

1. The surface quality of the specimen must be good, because the indent is measured optically. This means that the test location must be prepared (ground and polished), otherwise precise evaluation is difficult.
2. The process is rather slow (compared with the Rockwell method). The test cycle takes somewhere between 30 and 60 seconds, not including the time taken to prepare the specimen.
3. Due to the need to conduct optical indent evaluation, Vickers hardness testers must be equipped with an optical system, which makes them more expensive to purchase than Rockwell testers.

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