A straightforward method for analysing the grain-size distribution in tungsten carbide - cobalt hardmetals

Measurement of the grain-size distribution of sintered hardmetals is indispensable in research and production. In this study we present a method consisting of etching hardmetals in order to remove the cobalt binder and to analyse the remaining tungsten-cobalt (WC) crystallites on the basis of scanning electron microscopy images subjected to a PC-based image analysis by use of MATLAB®. Sample preparation is easy and quick to perform, i.e. it does not require metallographic polishing. It consists of either deep etching of the cobalt binder of cut and optionally hand-ground surfaces or etching of fracture surfaces. Two different computational routines and one combination thereof are described. Two hardmetal grades with average WC grain sizes slightly larger as well as smaller than 200 nm were investigated. The results of the computer algorithms are compared to data obtained by manual linear intercept analysis. The analysis has good potential to avoid time-consuming metallographic preparation and pre-treatment for grain-size analysis, which is especially true for hardmetals with extremely fine grain size.