Influence of Al on microstructural evolution and mechanical behaviour of Nb–9Ti–8C alloys

Abstract

Nb–9Ti–8C–xAl (at.-%) alloys with Al content of 0, 5%, 10% and 15% were prepared using the vacuum arc-melting method, and microstructural evolution and mechanical behaviour were investigated. Nb–9Ti–8C–(0, 5)Al alloys are composed of body-centred cubic (bcc) Nb solid solution (Nbss), face-centred cubic (fcc) (Nb, Ti)C and close-packed hexagonal Nb₂C phases. As Al content increases, besides Nbss and (Nb, Ti)C, Nb₃Al phase precipitates. After heat treatment at 1100°C for 24 h, Nb₂C phase disappears gradually and massive Nb₃Al phase precipitates. Nbss and internal Nb₃Al phase exhibit lamellar structure. Al addition favours the enhancement of compressive strength (σ _0.2 and σ _max), Nb₃Al precipitation can significantly improve the strength of Nb–9Ti–8C alloy, but reduce its toughness. With test temperature increases, the strength decreases obviously.