Improving the accuracy of low-load Vickers microhardness testing of hard thin films

摘要

Experiments that involved the testing of different steel samples over a wide range of loads were conducted in order to investigate the influence of micro-loads on accuracy of Vickers microindentation hardness testing. We found that for the same material the Vickers microhardness decreases with the decreasing of test load. The measuring error of Vickers microhardness on a steel block sample with known hardness was -25 % when we used 10 gf load force. This is due to the fact that diagonal length values are in the range of micrometers and the precision of reading using optical microscopy is ± 0.5 urn in length for most operators In order to improve accuracy of the reading of indents diagonals length we used two additional methods: scanning electron microscopy and graphical image processing. By this approach the measuring error of HV_(0.01) was reduced to an error of 3.78 %. On samples coated with nanostructured (TiAlSi)N hard thin films developed by DC unbalanced magnetron sputtering, with thickness of 2...3 μm, we found values around 2500 HV_(0.01) using this improved Vickers microhardness testing methodology.