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

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 degrees 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 (sigma(0.2) and sigma(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.