The Vickers (HV) test was developed in England is 1925 and was formally known as the Diamond Pyramid Hardness (DPH) test. The Vickers test has two distinct force ranges, micro (10g to 1000g) and macro (1kg to 100kg), to cover all testing requirements. The indenter is the same for both ranges therefore Vickers hardness values are continuous over the total range of hardness for metals (typically HV100 to HV1000). With the exception of test forces below 200g, Vickers values are generally considered test force independent. In other words, if the material tested is uniform, the Vickers values will be the same if tested using a 500g force or a 50kg force. Below 200g, caution must be used when trying to compare results.
Vickers test methods are defined in the following standards:
- ASTM E384 - micro force ranges - 10kg to 1kg
- ASTM E92 - macro force ranges - 1kg to 100kg
- ISO 6507- 1,2,3 - micro and macro ranges
Vickers Test Method
All Vickers ranges use a 136° pyramidal diamond indenter that forms a square indent.
- The indenter is pressed into the sample by an accurately controlled test force.
- The force is maintained for a specific dwell time, normally 10 – 15 seconds.
- After the dwell time is complete, the indenter is removed leaving an indent in the sample that appears square shaped on the surface.
- The size of the indent is determined optically by measuring the two diagonals of the square indent.
- The Vickers hardness number is a function of the test force divided by the surface area of the indent. The average of the two diagonals is used in the following formula to calculate the Vickers hardness.
HV = Constant x test force / indent diagonal squared
The constant is a function of the indenter geometry and the units of force and diagonal. The Vickers number, which normally ranges from HV 100 to HV1000 for metals, will increase as the sample gets harder. Tables are available to make the calculation simple, while all digital test instruments do it automatically. A typical Vickers hardness is specified as follows:
Where 356 is the calculated hardness and 0.5 is the test force in kg.
Because of the wide test force range, the Vickers test can be used on almost any metallic material. The part size is only limited by the testing instrument's capactiy
- One scale covers the entire hardness range
- A wide range of test forces to suit every application
- Nondestructive, sample can normally be reused
- The main drawback of the Vickers test is the need to optically measure the indent size. This requires that the test point be highly finished to be able to see the indent well enough to make an accurate measurement
- Slow. Testing can take 30 seconds not counting the sample preparation time