Vickers hardness test

Vickers Hardness Test

The Vickers hardness test is a widely used method for measuring the hardness of materials. It was developed by George E. Vickers in the early 1920s and has since become one of the most popular hardness testing techniques.

Principle

The Vickers hardness test is based on the principle of indentation hardness testing. In this test, a diamond indenter with a square-based pyramid shape is pressed into the surface of the material being tested. The applied load is gradually increased, and the hardness is determined by measuring the diagonal lengths of the resulting indentation.

Procedure

To perform a Vickers hardness test, a sample of the material is prepared by grinding and polishing its surface. The sample is then placed on a testing machine, and the diamond indenter is brought into contact with the surface. A load is applied for a specific duration, typically ranging from a few seconds to a minute.

After the load is removed, the indentation is measured using a microscope equipped with an eyepiece reticle. The diagonals of the indentation are measured, and the average value is calculated. The Vickers hardness number (HV) is determined by dividing the applied load by the surface area of the indentation.

Advantages

The Vickers hardness test offers several advantages over other hardness testing methods. Firstly, it can be used to measure the hardness of a wide range of materials, including metals, ceramics, and composites. Secondly, it provides a high level of accuracy and repeatability, making it suitable for quality control and research purposes. Lastly, the Vickers hardness number can be converted to other hardness scales, such as Rockwell or Brinell, allowing for easy comparison between different testing methods.

Limitations

Despite its advantages, the Vickers hardness test also has some limitations. One of the main limitations is the requirement for a polished surface, which can be time-consuming and may not be feasible for certain materials. Additionally, the test is sensitive to surface roughness and can be affected by the presence of residual stresses or surface coatings. Furthermore, the Vickers hardness test is a destructive testing method, as it leaves a permanent indentation on the material being tested.

Applications

The Vickers hardness test finds applications in various industries, including manufacturing, aerospace, automotive, and materials research. It is commonly used to assess the hardness and quality of materials, determine their suitability for specific applications, and evaluate the effects of heat treatment or other processing techniques. The test is also utilized in failure analysis investigations to identify the cause of material failures.

References

1. Vickers, G. E. (1925). "The Hardness of Metals". Proceedings of the Institution of Mechanical Engineers. 1 (1): 623–641. 2. ASTM E92-17, Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials.

See Also

• Hardness Testing
• Rockwell Hardness Test
• Brinell Hardness Test