Comparison of EBSD and conventional methods of grain size measurement of hardmetals

Accurate measurements of grain size are required to underpin development of models to predict properties, particularly of hybrid and multiphase materials. The conventional method for WC grain size determination in WC/Co is to use linear intercept measurements from light microscope or scanning electron microscopic images, usually requiring lengthy manual measurements, and subjective interpretation of grain boundary positions according to the level of etching and change in contrast. The possibilities offered by electron backscattering diffraction (EBSD) for improving the characterisation of both the WC and Co phase size, and contiguity between them, has been investigated. Samples covering a range of grain sizes have been examined by both EBSD and conventional methods to determine mean values and size distributions, with a special emphasis on the measurement of small grains. Diameters determined by both area (to give a circle equivalent diameter) and linear intercept from EBSD data are compared with the SEM image linear intercept method. It is shown that although the EBSD method is automated, great care must be taken in data analysis to identify and handle consistently small size values. If care is taken in the data handling then a good correlation can be shown between the EBSD and optical techniques. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.