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

• Published in: Acta materialia 2002-04, Vol.50 (7), p.1683-1692
• Main Authors: Lavergne, O., Robaut, F., Hodaj, F., Allibert, C.H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbides; Chemical Sciences; Condensed matter: structure, mechanical and thermal properties; Diffusion; Dissolution; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Material chemistry; Metals. Metallurgy; Physics; Solubility, segregation, and mixing; phase separation
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(02)00011-3

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 (Co 3W 3C) and η′ (Co 6W 6C). 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′.