What is Vickers hardness testing?
Due to a large number of materials that are available and the important functions and performance they have, they lead us to look for suitable materials. Regarding metallic materials as copper, one of the main properties considered is hardness. This property will determine the behavior of material against different stress, load, pressure, and other events. Among the different methods that exist to try to measure hardness, is the Vickers hardness test.
Vickers hardness testing is used to determine the hardness of a material by penetrating it with a pyramidal diamond. It is mainly used in the testing of materials of great hardness and of pieces with very small sections, or in very thin outer layers such as Copper, nitrided, cemented, etc. this test is mostly now done by Vickers hardness testing machine
Standards for Vickers Hardness Testing
The standards in which the Vickers hardness test is explained and defined are as follows.
- ASTM E 384. For microhardness, load ranges from 10gf to 1kgf
- ASTM E 92. For macro force ranges from 1kgf to 120kgf
- ISO 6507-1,2,3 for microhardness and microhardness ranges between 10gf up to 100kgf.
What are the Characteristics and strengths of Vickers hardness testing?
Strengths of Vickers hardness testing?
The Vickers hardness test is recommended for materials with hardness greater than 500 HB. Following are the advantages of the test
- It can measure surface hardness even if the footprint is shallow.
- It is not necessary to replace the indenter when varying the load (the hardness value is practically independent of the load value).
- In the Vickers test, the thicknesses of the tested materials can be much smaller than those of the Brinell test (up to 0.2 mm).
- The Vickers test can be used on materials with cylindrical or spherical surfaces.
- The Vickers test can be used for both very hard and soft materials.
- The Vickers test is the most sensitive test for calculating the hardness of materials.
Characteristics of the Vickers hardness test
- The allowable relative error for the load P should not be a greater standard value
- The diamond indenter must be in the shape of a tetrahedral pyramid, with an angle between the opposite edges at the vertex? – 136 ° ± 30´´.
- The length of the joining line of the opposite edges of the pyramid diamond should not be greater than 0.002 mm.
- The working part of the diamond must not be less than 0.3 mm concerning its axis.
- The edges of the diamond must be well polished, free of cracks or other surface defects visible at 30x magnification.
The process of Copper Bonding Wire hardness testing
Calculation and Formula for the Vickers Hardness Test
To calculate the hardness of material for example copper bonding wire using this test one has to find the quotient of the force that has been applied in the test (Newton) with the surface area of the indentation.
In this example, we suppose that we are working with copper wire
Vickers hardness testing formula
The numerical value of the Vickers hardness ( HV ) is obtained by dividing the applied load P (KP) by the surface of the footprint S (mm²) left on the specimen:
HV = P / S
- HV: Represents the hardness of the material on the Vickers hardness scale
- F: the force applied by wire in the test
- P: the applied load in the test (Kp)
- S: is the surface of the footprint (mm )
- d: is the average value of the diagonal of the imprint on the specimen (mm).
The hardness values on the Vickers scale are between 1 and 3000 HV. What will depend on the load applied to the material tested?
To name the hardness of a material tested based on the Vickers scale, three parts are needed. Hardness number, Vickers hardness, and the indicator of the force that has been applied.
For example, if a material has been tested and obtained 350HV / 10. It will indicate that the material has a Vickers hardness of 350 and that the applied force has been 10kgf.
This hardness test has a wide load range. Which makes it an ideal choice for measuring the hardness of any material, and the results will be on the Vickers scale. It should be taken into account that the Vickers hardness test is also known as a microhardness test since it is suitable and is applied mainly in samples or pieces that are small or thin and due to the characteristics of the operation.
We conclude that The Vickers test allows for more penetrations in the same dimension of the piece since the imprints are smaller, ideal for carrying out micro-hardness scans, where you want to know perfectly the relationship of hardness and depth. Additionally, Vickers is the most common test for microhardness testing and is the most convenient unit of measure when performing micro hardness. Since most Vickers hardness testers are digital, the hardness of the tested material is obtained automatically. Since all the calculation is done by the machine. While in others it is necessary to do the calculations or in any case you can use tables, which will facilitate the work and save time.