Investigation of microstructure, mechanical and oxidation properties of WC-Co-Ni-Fe-Al multicomponent hardmetals

In this paper, the influences of Al element originating from AlN additives on the mechanical properties and oxidation behavior of WC-Co-Ni-Fe hardmetals were studied systematically. During the sintering process, Al element diffused into the WC hard grains and led to the formation of (Ni,Co,Fe)₃Al particles in the metal binder phase of hardmetals. A small amount of Al element enhanced the hardness of WC-Co-Ni-Fe hardmetal via the solution strengthening and dispersion strengthening. However, the addition of Al element decreased the fracture toughness of hardmetals. The hardness and fracture toughness of multicomponent hardmetals with the addition of 0.5 wt% AlN were 90.4HRA and 10.6 MPa m^1/2, respectively. Additionally, the introduction of Al also significantly improved the oxidation resistance of hardmetals due to the existence of Al in WO₃ and (Ni,Co,Fe)WO₄. With the addition of 2.0 wt% AlN, the weight gain of WC-Co-Ni-Fe-Al multicomponent hardmetal after 5 h of oxidation at 700 °C was 66.82 % of that of the Al-free hardmetal.