Comprehensive utilization of micro-oxidation and Co coating on the surface of WC particles to greatly reduce the harmful η phase in WC-Co composites - A new strategy

WC-Co composites are extensively used in the mining and cutting-tool industries owing to their superior mechanical properties, including high hardness, exceptional fracture toughness, and outstanding wear resistance. However, the inevitable decarburization of WC powders will cause the formation of η phase, which is detrimental to mechanical performance, especially fracture toughness. To solve this problem, this work proposes a new surface treatment strategy to completely solve the above thorny problem. Here, the core-shell structured WC-Co (Co@WC) powder, consisting of Co-coated WC particles, was prepared via a two-step process involving pre-oxidation followed by hydrazine hydrate reduction, and was systematically characterized using infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results show that varying the concentration of CoSO 4 ·7H 2 O during reduction enables accurate, quantitative control of the Co coating content on WC particles. When utilized as a raw material for sintering WC-Co composites, the Co@WC powder exhibited remarkably distinct advantages over conventional mixed powders: the content of detrimental η phase in the sintered composites was dramatically reduced by up to 50%. The striking suppression of the η phase can be attributed to the formation of WO 3 at the critical WC-Co binder interface during the pre-oxidation, and this oxide layer effectively blocks the direct reaction between Co and WC during sintering.