Dependence of microscale abrasion mechanisms of WC-Co hardmetals on abrasive type

Abstract

Sintered WC-Co hardmetals are employed as wear resistant materials in a wide variety of applications, some of which require resistance to abrasive wear. Such materials usually contain WC particles of less than 10 μm in size. Assessment of wear resistance is often made with tests such as those described in the ASTM standards G65 and B611 both of which employ abrasive particles significantly larger than the size of the carbides in the hardmetals. However, when the abrasive particle size is of the same order of magnitude as the carbide size (or less), then the mechanism of wear changes as the abrasive particles are able to interact with the carbides and matrix phase separately. In certain conditions of use, abrasion of WC-Co materials may primarily be due to small abrasive particles and thus, conventional abrasion tests may not be appropriate. In this work, microscale abrasive wear testing of a range of WC-Co sintered hardmetals was examined with three types of abrasive particle slurries (diamond, silicon carbide and alumina suspended in water) all with a similar size distribution in the range 1–10 μm. The hardmetals varied in carbide size and binder volume fraction resulting in a range of hardnesses between 9.4 and 16.4 GPa. The silicon carbide and alumina abrasives primarily caused wear by preferential removal of the binder phase followed by pullout of the WC particles. As expected, with a given WC grain size in the hardmetal, the wear rate increased as the binder volume fraction increased. However, with a fixed binder phase volume fraction, the wear rate increased as the WC grain size in the hardmetal decreased (i.e. as hardness increased). Behaviour with the diamond abrasive was very different, and apparently not dominated by binder phase removal and carbide pullout. Here, the wear rates of all the cermets examined were similar and may be explained following the model of Engqvist and Axén (Tribology Int., 32 (1999) 527–534).