Introduction
A hardness test is a metallurgical engineering procedure to determine a material’s hardness. The tests are usually performed on various metals such as steel, cast iron, and aluminum.
Vickers hardness test is a standard method for measuring materials’ hardness. Vickers hardness test is based on the indentation of a material by a spherical indenter with a known radius of curvature and penetration depth. It is commonly used to measure the hardness or softness of substances like metals, minerals, and plastics.
Vickers hardness testing machines are used for both research and production testing.
I. What is the Vickers Hardness Test?
The Vickers Hardness Test method uses an optical system of measurement. The indenter hardness tester uses a microscope to view the contact ball-on-flat. A metal ball indents the material surface placed on the flat holder. The metal ball is forced into the surface of a test piece by an applied load. The indentation depth can be observed when compared to a scale micrometer or microscope eyepiece reticle. Vickers Hardness Test shows both dynamic and static measurement.
II. Why Use the Vickers Hardness Test?
The Vickers Hardness Test makes very small indentations on the test sample. This makes it useful for testing very thin materials such as aluminum foils and other microstructures. The Vickers Hardness Test method is very accurate and is fast. The metallurgical engineers can use the test result for rapid process control. This makes the Vickers Hardness Test a very common method of measurement used to check hardness and softness on materials like steel, aluminum bars, etc.
III. Principle of Vickers Hardness Test
The principle of the Vickers hardness test is based upon micro-indentation. The test method is usually performed with a hardened steel ball pressed into a flat surface of the material being tested. The Vickers hardness can be calculated from the formula once the mean diagonal of the indentation has been established. However, conversion tables are more convenient to use. It is significantly superior to the other hardness testing methods’ arbitrary changing of the 5 scales to provide almost equal hardness numbers on hom*ogenous material when several varied loading settings are used.
The Vickers Hardness Test is a very accurate test method. The results are obtained quickly and are easy to use. It can be used for bulk, sheet, and wire materials and is suitable for soft and hard materials. The accuracy, reproducibility, ability to produce small samples, and test speed have made this method popular in all engineering sectors, such as the automotive, aerospace, and other similar industrial sectors. The flexibility of this test method makes it very useful for manufacturers when testing new materials and quality control testing on existing materials.
IV. Vickers Hardness Test Procedure/ How to Perform a Vickers Hardness Test?
The procedure for performing Vickers Hardness Test is as follows:
- Measurements: Equipment measuring range 10-0 kN/mm2 (7-0 MPa). Indentation depth appears on the microscope eyepiece reticle. The glass microscope objective lets you observe the loading volume at this depth.
- Apparatus: The Vickers hardness test equipment is composed of a holder, an anvil, a stand, an indicator, and a microscope.
- Place the Vickers hardness test sample on the profile sleeve. Place two restraining pins into two holes that sit against the shoulders or stop on both sides.
- Compress the specimen by applying pressure on the compressed thumb wheel until the specimen contacts the indenter.
- Measure in microns (1mm) for depth of indentation of the specimen as it contacts the ball indenter, using a micrometer or a microscope eyepiece reticle.
- Unloading The Sample: Relax the sample from the thumb wheel, remove its support pins, and it will return to its original shape without any indentation marks.
- Calculating The Vickers Hardness Value: The hardness value is calculated by dividing the indentation depth of the sample by 3.2, giving a hardness value expressed in Kg/mm² or on the Brinell scale.
- The penetration of the indenter is measured by microscope eyepiece reticle when the sample is unloaded from the holder. The measurement is recorded on a piece of paper to check for consistency.
- Repeat The Test. Repeat the test on the same sample and record results in the same manner as before.
V. Brinell Hardness Test Procedure/ How to Perform a Brinell Hardness Test?
The formula for calculating the Vickers hardness value is as follows:
Vickers Hardness = (Depth of Indentation / 3.2) x Kg/mm²
Where:
Vickers Hardness Value = indenter depth / 3.2 = Micro-indentation of the specimen / Total micro-indentation of the specimen
The value of the Vickers hardness test is used to check the hardness and softness of materials.
When calculating Vickers Hardness, the indenter radius and the penetration depth are not included into the equation. Only the micro-indentation is taken into consideration with the formula.
Conclusion
The Vickers Hardness Test is an extremely accurate, fast, and easy test method. It can be used to test a wide range of materials such as thin aluminum foils and other micro-structural materials. It has a high surface finish for fine-grain metals and can be performed on bulk, sheet or wire materials. The flexibility of the Vickers Hardness Test method makes it very useful for manufacturers when testing new materials as well as quality control testing on existing materials.
