Vickers Hardness Test
Vickers Hardness Test: Due to the broad variety of ball sizes and loads available, the Brinell technique is capable of testing a very wide range of hardness values.
Due to the fact that the Brinell test employs very high loads and therefore a relatively big imprint, it is often employed to evaluate the hardness of material used in large forgings or castings.
It is an approved standard test technique by ASTM E384, ISO 6507, and JIS Z 2244. Microhardness tests are performed on metals, ceramics, composites, and almost any other kind of material.
- Vickers hardness tester
- Pyramid indenter
The Test’s Theory and Principle
- The penetrator to be utilized is a four-sided diamond pyramid with a 136-degree angle between the facing sides.
- The most commonly utilized load stages are 10 kg, 30 kg, and 60 kg.
- The specimen’s depth should not be less than 1.5 times the impression’s diagonal.
- The distance between the impression’s center and the edge of the next impression or the specimen’s edge should be at least three times the impression’s diagonal.
Preparation of the Surface
Prior to inserting the sample material into the microhardness testing equipment, it must be properly prepared. The surface condition needed for the Vickers hardness test varies according on the force applied.
- Macro hardness testing requires weights greater than 1 kgf and a ground surface.
- Microhardness testing requires stresses of less than or equal to 1 kgf and a mechanically or electropolished surface.
Procedure for Testing
- Adjust the machine to the appropriate test load and dwell duration stage.
- Carefully place the specimen on the testing bench.
- Return the goal to its “set” state.
- Slowly turn the hand wheel clockwise until the specimen is sharply focused on the front screen.
- Adjust the inventor to the “set” position and start the loading, dwell, and unloading cycle.
- Restore the goal to its “fixed” location.
- On the front focusing screen, the indentation is now projected.
- Take diagonal measurements along both axes of the imprint and record them.
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 resulting values are given as 800 HV/10, where 800 denotes Vickers hardness and 10 denotes the applied load. However, it is customary to report 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
The Vicker’s Method’s Advantages
- The Vickers technique is applicable to all materials and test specimens, from soft to hard, since it covers the full hardness range.
- There is just one kind of indenter that is universally applicable to all Vickers techniques.
- Non-destructive testing is feasible, allowing the test specimen to be reused.
The Vickers Method’s Drawbacks
- The specimen’s surface quality must be satisfactory, since the indent is optically measured. This requires preparation of the test site (ground and polished), since otherwise accurate assessment is impossible.
- The procedure is very lengthy (compared with the Rockwell method). The test cycle takes between 30 and 60 seconds, not counting time for specimen preparation.
- Vickers hardness testers should be equipped with an optical system in order to perform optical indent assessment, which makes them more costly to buy than Rockwell testers.