Microhardness Testers

During the last decade the interest to mechanical properties of surfaces and objects with thickness of around 10-20 m has risen sharply. One of popular methods of researching these properties is microhardness measurement. During microhardness measurements the indenter under load penetrates slowly into the tested sample. After that the characteristic dimensions of the restored indentation are measured. Indenters can be of different shapes: ball, cone, trihedral pyramid, tetrahedral pyramid. In most cases Vickers diamond tetrahedral pyramid is used as an indenter. Consequently the method of microhardness measurement is the same as the method of hardness measurement on Vickers scales with the only difference being that in micrihardness testers the applied load varies from 1 gf to 2 kgf. In most cases microhardness testers use a direct mechanism of load application. For microhardness testers operating with loads less than 100 gf an electromagnetic loading method can be used. The highest error of hardness measurements is introduced by a system of microhardness testers. It can look just like the one in Vickers hardness testers, but the objective lenses in this system have higher magnification. But in case the indentation dimensions are lower than 10-20 m, even an optical system with high magnification will distort the measurement results due to fraction. If the size of indentations on the tested object is small, one can use a microhardness tester equipped with an atomic-force microscope to measure its diagonal lengths. Deviations from the indenter's geometrical shape have a greater impact on hardness measurements with a microhardness tester than with a Vickers hardness tester, that is why the requirements to the pyramid used in the microhardness tester are stricter. The maximum permissible size of the intersection is 0,2 m. The angle between the opposite facets should equal (136 0,2)0. The error of hardness meas-urements by microhardness testers varies from 11% (for loads of 1 gf) to 5% (for loads of 2 kgf). The error also depends on the hardness level of the tested sample. The range of microhardness measurements lies in between 8HV and 1500HV, but at that at high hardness levels it is advisable to use higher load for the error reduction. The state of the tested sample surface is very important for microhardness measurements. Polished surfaces will make it possible to conduct more qualitative measurements. Vibrations can also influence measurements at low loads.

See also:

Miniature ultrasonic hardness testers

Rockwell hardness tester -HRC
hardness tester
Brinell hardness tester -HB
-HB / MET-B50
hardness tester
Vickers hardness tester
-HV / MET-V50
hardness tester
Shore hardness tester MET-HSD
hardness tester

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