Vickers microindentation of WC–12%Co thermal spray coating: Part 1: statistical analysis of microhardness data

A high quality WC–12%Co coating was polished to various surface finishes and then tested for microhardness on both the polished cross-section and the plane surface of the coating. The indentation data obtained was analyzed using both Gaussian and Weibull statistical models. We demonstrated that, though the microindentation technique is a useful laboratory procedure that can be used for coating optimization, research and quality control purposes, poor understanding often leads to worthless data and, thus, to erroneous conclusions. The necessity for rigorous statistical procedures of data analysis is shown. For this coating, it was indicated that microhardness was less sensitive to the surface finish than appears at first, and that the testing direction is of little significance despite the obvious anisotropy of the coating structure. No significant variation of hardness with depth was shown. In part 2 of this two-part paper, we have demonstrated that in microhardness testing in the load-hardness regime that is almost universally used for these materials, poor between-operator reproducibility can lead to a variation of as much as 20% in the average microhardness values obtained. Alternative procedures that might be of value in determining coating hardness data are discussed.