Abrasion Of Ultrafine Wc-co By Fine Abrasive Particles

Abrasion of ultrafine WC-Co by fine abrasive particles P. V. Krakhmalev Department of Mechanical and Materials Engineering, Karlstad University, SE-651 88 Karlstad, Sweden Received 15 July 2007; accepted 10 September 2007 Abstract: Abrasive wear of a series of WC-(5%−14%, mass fraction)Co hardmetals was investigated employing coarse and fine SiC abrasive under two-body dry abrasion conditions with pin-on-disc and edge-on-disc test arrangements. Unexpectedly, it is found that submicron grades demonstrate substantially higher wear rates comparing with the coarse grades if fine abrasive is utilized in pin-on-disc tests. Such a behavior is attributed to changes in a ratio of abrasive size to size of hard phase as finer abrasive is used. The edge-on-disc test demonstrates that edge wear may be described in two stages with the highest wear rates at the beginning stage. This behavior is associated with a transition of wear mechanisms as edge is wider due to wear. Compared with the ultrafine grades of the same Co content, the coarse grades demonstrate higher wear rates at the beginning, but lower wear rates at the final stage. Wear rates and mechanisms observed at final stage correlate well to the results observed for pin-on-disc tests employing fine abrasive. Key words: WC-Co hardmetal; abrasion; edge wear; wear mechanisms; microstructural effect 1 Introduction Abrasive wear of WC-Co hardmetals has been extensively examined last decades with a particular focus on the comparison of novel nanoscale and ultrafine composites to conventional WC-Co grades that usually demonstrate superior performance compared with the conventional WC-Co grades[1]. In common experience, the smaller the WC particles, the better the abrasion resistance of WC-Co hardmetals[1−2,4]. This trend has been observed using standard test methods utilizing high loads and coarse abradant of a few hundred micrometers in size[2−4]. Ploughing, fracture of WC grains and binder extrusion wear mechanisms[5−6] have been found usual wear mechanisms observed in abrasion of WC-Co hardmetals by the coarse SiC particles. Nevertheless, as it has been illustrated in several recent researches[7−9], ultrafine grades may demonstrate higher wear rates in comparison with the conventional micron grades. This effect has been discussed in terms of the operative wear mechanisms, i.e. the rate of material removal by ploughing observed for the ultrafine grades may be higher than that for the preferable binder removal following by WC grains pullout, studied for the micron scale grades[9]. Although abrasive wear of WC-Co hardmetals has been investigated thoroughly us