The development of W-Cr-Al alloys by spark plasma sintering and their oxidation behavior

Abstract

Tungsten-based self-passivating metal alloys with reduced thermo-oxidation (SMART), which using Cr or Si as oxidation-resistant elements, have exhibited great potential for oxidation resistance application at high temperature compared with pure W. In this work, aluminum (Al) was added to WCr SMART systems to further improve the oxidation resistance, and the novel W-17.8Cr-6.4Al alloys were successfully developed using spark plasma sintering (SPS) technique. The influence of sintering pressure and temperature on the densification process was systematically investigated, and the oxidation behaviors were studied at 800 °C and 1000 °C. The sintering curves exhibit that there is the liquidation of Al above around 630 °C, and the rapid densification of W-Cr-Al alloys starts above 923–950 °C. The intermetallic compounds of (WCr)Al₁₂ and (WCr)Al₄ are generated when sintered at 650 °C and 700 °C, respectively. When sintered above 1000 °C, W-Cr-Al alloys mainly consist of two BCC phases of W-Cr-Al solution. Dense bulk W-Cr-Al alloys, with a density of around 11.6 g/cm³, could be manufactured by sintering above 1200 °C at 20 MPa for 15 min. At the end of oxidation, the oxides formed at 800 °C mainly consist of WO₃, Cr₂WO₆ and Al₂W₃O₁₂, while WO₃ disappears at 1000 °C due to the volatilization of WO₃ and the reaction with Cr₂O₃. In addition, no obvious variation trend of mass gain is observed when oxidized at 800 °C compared with pure W, while a double parabolic trend of mass gain is found during oxidization at 1000 °C. The parabolic oxidation parameter, $k_p$, is around (7–8) × 10⁻⁵ mg²/(cm⁴$\bullet$min) and (4–5) × 10⁻⁴ mg²/(cm⁴$\bullet$min), respectively. Compared to the linear oxidation behavior of pure W, W-Cr-Al alloys exhibit its potential for oxidation resistance application at high temperature.