Comparison of the friction and wear behaviour of WC-Ni-Co-Cr and WC-Co hardmetals in contact with steel at high temperatures

A tribological test has been designed for analysing the wear behaviour of WC-Co and WC-Ni-Co-Cr alloys in contact with steel at high temperatures (725-775°C) and pressures (between 113 and 134. MPa). The test, based on a particular block-on-ring configuration, allows to measure wear and friction occurring between a cemented carbide sample and a steel wheel rotating at high speed in absence of lubrication. In general, wear resistance increases with hardness, which, keeping constant the WC grain size, depends mainly on the metallic content of the alloy. Thus, cemented carbides with 15. wt.% of metallic content exhibit lower mass losses than those with 25. wt.% of metal. Nevertheless, when compositions with the same metallic content are compared, it is confirmed that the wear resistance is similar for the compositions based on Ni-Co-Cr binders in spite of their lower hardness. This is likely due to the higher oxidation resistance of these alloys compared to those based on cobalt. Friction coefficients are lower for the compositions with higher metallic content, what is likely due to the formation of continuous oxide tribofilms with lubricant properties.