Effect of Ni aids on the unlubricated tribological behaviour of WC cemented carbides fabricated by pressureless infiltration of Cu alloy binder

Abstract

The unlubricated sliding-wear behaviour of WC cemented carbides fabricated by pressureless infiltration of the Cu–30Mn–1P alloy without and with Ni infiltration aids (in the range of 3–10 wt%) was investigated. Firstly, detailed microstructural characterisation showed that these cemented carbides are all dense and consist of extra coarse WC grains (∼62 μm) embedded into Cu0.96Mn0.04 (with traces of P), plus secondary Mn2P and Mn3P phases segregated at the grain/binder interfaces. When infiltrated with Ni aids, the binder contains Ni solutes and there is also interfacial segregation of NiP2 and Mn3Ni20P6. Secondly, the mechanical characterisation showed that the Ni infiltration aids resulted in stronger and more ductile cemented carbides, with no reduction in hardness below 5 wt% Ni aids. Specifically, it was found that 3 wt% Ni infiltration is optimal, which maximises the strength, ductility, and toughness of these cemented carbides as a consequence of the optimised cohesion of the WC grains in the metal binder. And thirdly, the tribological characterisation against Al2O3 showed that all these cemented carbides are wear-resistant, with specific wear rates increasing with applied load, but in the order of 10−5 mm3/(N·m) or lower. Importantly, it was found that Ni infiltration aids up to 5 wt% are beneficial to the wear resistance of these cemented carbides, but more becomes increasingly detrimental. As for the other mechanical properties, Ni infiltration at 3 wt% also maximised the wear resistance. Detailed microstructural characterisation of the worn surfaces of the cemented carbides revealed that wear took place first by two-body abrasion, in which a tribolayer is formed, and then by three-body abrasion, in which partial removal and formation of the tribolayer occur dynamically over time, with the severity of the abrasions depending on the proportion of Ni infiltration aids and the applied load.