Remarkable improvement in high temperature oxidation resistance of WC-12Co by the addition of CrSi2

Abstract

WC-Co has excellent mechanical properties at a temperature below 700 °C, but above it, the mechanical properties of WC-Co decrease severely because of the oxidation effect. In the present study, the addition of metal silicide of CrSi2 was considered to enhance the oxidation resistance of cementite carbide. The WC-12Co compacts containing 0, 12.5, and 25 wt% CrSi2 were prepared using mechanical alloying and spark plasma sintering techniques at 1150 °C. According to the results of metallographic characterization, the sintered WC-12Co is composed mainly of WC and Co phases. The addition of CrSi2 leads to the formation of new phases as CrSi, CoSi, Co6W6C, and SiC depending on the compact composition. It is found that the WC-12Co compact with 12.5 wt% CrSi2 content exhibits a lower measured density and higher hardness compared to that of CrSi2-free compact. After the first cycle of exposure at 900 °C, the WC-12Co is severely oxidized, forming porous and crack oxide scales. On the contrary, the addition of 12.5 wt% CrSi2 shows the lowest mass gain and displays the most resistance to oxidation attributed to the formation of mainly SiO2 scales. Further increase in CrSi2 concentration, however, the alloy compact experiences breakaway oxidation after the fifth cycle of exposure. Accordingly, it can be proposed that the addition of 12.5 wt% CrSi2 is the most promising composition to allow the cemented carbide used at high temperatures and oxidizing atmospheres.