Hardness is the ability of a material to resist a change in its shape when a force is applied to it, and indentation hardness testing uses an indenter that probes into the surface to create a dent. The size and shape of the indentation are then used to determine the resistance of the surface to deformation.
Microhardness testing deals with very small sample sizes, with a typical load less than 10N. This load is applied to the surface and the indentation is measured for the given pressure.
The most popular tests for microhardness are the Vickers test and the Knoop test. Their main difference is in the type of indenter used for nanoindentation. The Vickers test uses a pyramid-shaped probe, while the Knoop test probe has more of a rectangular edge shape. They are used differently depending on the type of indentation that has to be made and measured.
Microhardness testing is useful in determining the mechanical properties of metals, ceramics, and composites. The studies on the physical properties of these materials, in turn, find their application in the fields of medicine, goods and packaging, films and coatings, etc. where these materials are used.
For accurate results in these tests, some of the prerequisites are proper sample preparation (like polishing of the sample surface), sample positioning and vibration isolation.
The placing of the specimen surface under the indenter must be such that the surface is perpendicular to the indenter probe. External vibrations can cause the surface under the indenter to move, causing the force to be applied at a wrong angle. The effects of vibration on the apparatus when the indenter is lowered into the sample can be huge since the measurements are taken in the micro range. Vibration isolation of the hardness tester is important so that inaccurate measurements may be avoided at all costs.
Lower loads are more susceptible to external interference than bigger ones. Hence, some instruments even recommend the setting up of devices to take measurements on very small loads during the night, when activity in the lab is minimal. Significant vibration isolation can also be achieved by providing an anti-vibration table to mount your microhardness testers.
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