Semi-empirical relationship between the hardness, grain size and mean free path of WC–Co

Abstract

The Vickers hardness of several well-characterized grades of WC–Co (23 in total) was measured. The mean grain size of these samples ranged from 0.6 to 5.0 μm and the cobalt content from 6 to 50 wt%. An empirical formula between hardness of WC–Co, grain size of WC and mean free path in Co was obtained. It was found that the empirical formula fitted our measured hardness well. However, when used against results of other researchers, it did not reproduce them satisfactorily at values higher than 1500 HV. A theoretical model, based on the assumption that plastic deformation of WC–Co begins at the WC–WC necks and that the mean length of the cross-section of the WC–Co necks is proportional to the square root of the mean WC grain size, was subsequently derived. The results obtained from this model were in good agreement with those of the empirical formula and like the empirical formula, did not reproduce high hardness values of other researchers. Thus, the model was modified by introducing semi-empirical terms which led to a satisfactory fitting of the data.