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 spraycoatings

The between-operator reproducibility of microhardness statistics is conside red. 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 meas ured by eight different personnel using the eyepiece micrometer of the same microhardness tester. Three personnel including those recording. the large st and the smallest grand-average microhardness values repeated their measu rements. Analysis of variance (ANOVA) shows that there is a consistent, sta tistically significant variation in microhardness readings as performed by different operators. Image analysis and confocal microscopy were used to ex plain the underlying reasons for this variation. When microhardness is used to provide quantitative statistics for hard materials such as cemented car bides and ceramic materials, this variation is technologically significant, and challenges the validity of reported data as published in the literatur e. Alternative methods of measuring microhardness indentation size and alte rnative approaches to measuring the hardness of these materials are discuss ed. (C) 2000 Published by Elsevier Science S.A. All rights reserved.