Mechanism of solid-state dissolution of WC in Co-based solutions

Abstract The dissolution mechanism of WC in solid solutions (Co, W, C) with different C/W ratios and Cr or V additions is studied at 1200°C using the diffusion couple technique. Depending on the composition of the Co-based phase (β), three sequences are generated: with no intermediate phase layer (β/WC), or with one (β/η/WC) or two (β/η/η′/WC) layers of η (Co3W3C) and η′ (Co6W6C). The experimental results — diffusion profiles, interface compositions, layer widths — show that WC dissolution is limited by diffusion and lead to values of the diffusion coefficient of 3×10 −15 , 2×10 −15 and 6.5×10 −15 m 2 s −1 for β, η and η′, respectively. The Cr or V addition does not significantly change the WC solubility in Co but it reduces the limit W content corresponding to the formation of η and η′.