Vickers microindentation of WC–12%Co thermal spray coating: Part 2: the between-operator reproducibility limits of microhardness measurement and alternative approaches to quantifying hardness of cemented-carbide thermal spray coatings

The between-operator reproducibility of microhardness statistics is considered. Three sets of 10 microhardness indentations were made on the polished cross-section of a WC–12%Co thermal spray coating. The 30 indents were measured by eight different personnel using the eyepiece micrometer of the same microhardness tester. Three personnel including those recording the largest and the smallest grand-average microhardness values repeated their measurements. Analysis of variance (ANOVA) shows that there is a consistent, statistically significant variation in microhardness readings as performed by different operators. Image analysis and confocal microscopy were used to explain the underlying reasons for this variation. When microhardness is used to provide quantitative statistics for hard materials such as cemented carbides and ceramic materials, this variation is technologically significant, and challenges the validity of reported data as published in the literature. Alternative methods of measuring microhardness indentation size and alternative approaches to measuring the hardness of these materials are discussed.