Investigation of Interface Reaction of WC/Co Using Diffusion Couple Technique

Abstract

The microstructure of WC/Co interface at 1623 K was investigated using the WC-Co diffusion couples with small amount of tungsten or carbon addition to the couple halves, and from the microstructure, the diffusion path at the interface was inferred. The microstructure and diffusion path depend on the W and C additives. The η phase formation was observed at the interface in the ((WC)₉₈ + C₂)-Co and WC-(Co₉₈ + C₂) diffusion couples. In the case of ((WC)₉₈ + W₂)-Co and WC-Co diffusion couples, both η and η’ phase were formed. The η, η’, W₂C and W phases were seen in the (WC)-(Co₉₈ + W₂) diffusion couple. Three diffusion paths were inferred from these microstructures. In the case of ((WC)₉₈ + W₂)-Co and WC-Co diffusion couples, the diffusion path of Co⇔η’⇔η⇔WC regions was inferred on the isothermal section of C-Co-W ternary phase diagram at 1623 K (path 1). The path 2 (observed in ((WC)₉₈ + C₂)-Co and WC-(Co₉₈ + C₂) diffusion couples) was through the Co⇔η⇔WC phase regions. The WC-(Co₉₈ + W₂) diffusion couple showed the path through the Co⇔η’⇔η⇔WC regions with crossing the (η + W) and (η + W₂C) two phase regions (path 3).