David Pye's blog series on hardness testing continues.
Vickers Microhardness Test
The Vickers microhardness test method is made in exactly the same manner as the manual test. The indenter is ground to the same precise angles as the manual unit indenter. The load is now applied through an electronic load cell to give a precise load on each hardness test made.
A wide variety of microhardness test machines are available, ranging from relatively simple, low-priced units to semi-automated systems up to fully automated units. In most cases, either a Knoop or a Vickers indenter can be used with the same machine, and it is a relatively simple matter to exchange indenters.
Most electronic (load-cell) units use an automated load test cycle, applying the pre-set load for a selected dwell time and unloading to give uniformity of the test. The electronic systems are susceptible to floor vibrations. Vibrations must be very carefully controlled, which becomes even more important as the load force decreases.
Manual application and removal of the applied force must not be forced due to the potential damage to the indentation and in preventing vibrations that will enlarge the indent size. The indenter must be exactly at right angles to the test piece. A small error, as little as 2 degrees from perpendicular, will distort the indentation shape and produce a false reading. A larger tilt angle may cause the specimen to move under the applied force.
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