Thermal stability of modified surface microstructure on WC-Co cemented carbide after high current pulsed electron beam irradiation

Abstract

Investigation on the thermal stability of the modified surface microstructure on WC-Co cemented carbide after high current pulsed electron beam (HCPEB) irradiation was carried out. Microstructural analysis showed that the micro-WC grains were melted and a compact microstructure was formed in the surface layer. Nano-grained cubic phase WC1-x was identified as the predominant phase in the modified layer, resulted from HCPEB-induced superfast heating, melting and re-solidification cycles. The modified specimens were subjected to annealing process at varied temperatures in an Ar ambience for 1 h. Post-annealing microstructural inspection results revealed that the modified microstructure was stable when the annealing temperature did not exceed 500 °C. When the annealing temperature was elevated to 600–700 °C, the cubic phase WC1-x gradually transferred into two hexagonal phases, WC and W2C. Further elevating the annealing temperature up to 900 °C, significant amount of ternary phases, Co6W6C and Co2W4C, formed in the surface layer. The evaluation of surface microhardness indicated a strengthening effect of the annealing on the modified microstructure. The maximum microhardness (2530 HV) was obtained after annealing at 700 °C.