Ever wondered if you have prepared your specimen adequately when carrying out the Vickers hardness test?
While the Vickers hardness test is considered one of the most popular and standard hardness tests around, a devious mistake you can make is not meeting the specimen requirements for an accurate result. Still, some operators of Vickers hardness test machines don’t even know what these standard specimen requirements are. Fortunately, this article aims to end this obliviousness as you’ll find out everything you need to know for adequate preparation of your specimen for an accurate Vickers hardness test.
I. Vickers Test
The Vickers test is one of the most popular hardness testing procedures standardized by specifications, including ISO 6507, ASTM E384, and ASTM E92. Additionally, the Vickers test is often preferred for testing a wide range of materials. This ability results from its load range, which falls between the very low range of 1gf to as high as 120kgf. However, there is often the need to integrate an optical measuring device like a microscope to help inspect the impression imprinted on the material surface by the applied load. The reason is that this impression is often not large, and it will be difficult to measure this indentation accurately without an optical instrument.
II. Why is the Vickers Hardness Test Used?
One of the good things the Vickers test has is the ability to measure a diverse range of materials, including small, thin, and thick materials. This makes the Vickers hardness test one of the most versatile hardness tests around. But that’s not all. Its accuracy is also very high, owing to its use of a highly sensitive optical instrument in reading and measuring the indentation resulting from the load application. Also, the Vickers hardness test is preferred due to its high measuring consistency since its indenter is only one type. However, because it is a static hardness test, it is often suitable for measuring material hardness in the laboratory.
III. How is the Vickers Test Performed?
To perform the Vickers hardness test, a pyramid-shaped diamond indenter with a load ranging from 1gf to 120kgf is often applied to the surface of a test material. Leaving the load after application for 10 to 15 seconds allows the indenter to stabilize before removing the load. The width of the impression made on the material surface is measured with a microscope as the impression isn’t that deep. This measurement helps to calculate the sloping surface area and the hardness value on the Vickers scale.
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IV. Specimen Requirements for the Vickers Method
Surface preparation for materials is often essential to the Vickers hardness testing method. For the Vickers test, the specimen needs to be polished or precision ground depending on if it is a micro-hardness or macro-hardness test that is to be done. Also, the specimen should be rigidly clamped on a support platform to ensure that it is not tossed about during the test. Any movement during the test might significantly affect the accuracy of the result. Hence, surrounding vibrations and shock waves should be avoided despite its firm clamping to the support platform.
V. Why are the Samples for Vickers Hardness Testing Polished before Testing?
Using an optical instrument in the Vickers test requires that there be no obstruction to the operator’s view while reading the width measurements. To ensure that any roughness does not obstruct the optical instruments, the surface of the specimen is often polished. Also, since the impression made on the material surface isn’t always deep, it is important to polish the surface to see the impression made on the specimen.
In conclusion, the Vickers test often has strict specimen requirements due to the high sensitivity of the optical reading instrument and the need to get an accurate result. Meeting this requirement often depends on careful planning and preparation of the specimen before beginning the test. Ultimately, an awareness of these standard requirements will go a long way toward arriving at an accurate result.