Analysis of the indentation size effect in the microhardness measurement of some cobalt-based alloys

The load dependence of the Vickers microhardness of some cobalt-based alloys subjected to heat treatment at different temperatures for various duration has been investigated using Hanemann's method and a PMT-3 hardness tester. It is found that even for the same sample Hanemann's method shows a decrease in microhardness with applied load (i.e., normal indentation size effect) while the PMT-3 hardness testing exhibits a reverse effect. The experimental data were analysed using Meyer's law, Hays-Kendall's model, the elastic/plastic deformation model of Bull et al., the proportional specimen resistance model of Li and Bradt and the energy balance approach of Buckle. The analysis of the experimental data revealed that: (1) the Meyer hardness index n decreases linearly with logarithm of the so-called standardised hardness constant A, (2) within the limits of experimental errors, the load-independent microhardness of a given sample predicted by the other models used is constant, (3) the quantities contributing to the load dependence of hardness are inversely related with the constants describing the load-independent hardness, (4) the quantities contributing to the load dependence of hardness are related with the Meyer hardness index n and (5) the constants of the energy balance approach are mutually related but the load-independent microhardness predicted by this approach is erratic with respect to that obtained by the other models. (C) 2002 Elsevier Science B.V. All rights reserved.