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 an d then tested for microhardness on both the polished cross-section and the plane surface of the coating. The indentation data obtained was analyzed us ing both Gaussian and Weibull statistical models. We demonstrated that, tho ugh the microindentation technique is a useful laboratory procedure that ca n be used for coating optimization, research and quality control purposes, poor understanding often leads to worthless data and, thus, to erroneous co nclusions. The necessity for rigorous statistical procedures of data analys is is shown. For this coating, it was indicated that microhardness was less sensitive to the surface finish than appears at first, and that the testin g direction is of little significance despite the obvious anisotropy of the coating structure. No significant variation of hardness with depth was sho wn. In part 2 of this two-part paper, we have demonstrated that in microhar dness testing in the load-hardness regime that is almost universally used f or these materials, poor between-operator reproducibility can lead to a var iation of as much as 20% in the average microhardness values obtained. Alte rnative procedures that might be of value in determining coating hardness d ata are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.