Microstructure and mechanical properties of as-cast and aged Nb–15 at.% Al–10 at.% Ti, –25 at.% Ti and –40 at.% Ti alloys

Compression tests have been conducted at 900 °C at a strain rate of 10−4 s−1 for Nb–15 at.% Al–10 at.% Ti, –25 at.% Ti and –40 at.% Ti alloys in the initial conditions and after aging. The 10Ti and 25Ti alloys were in the as-cast condition, and the 40Ti alloy was in the hot-rolled condition. Specimens were aged for 10 or 100 h at 873 K (600 °C), 1173 K (900 °C) and 1373 K (1100 °C). The microstructures were characterized by optical and scanning electron microscopy. There was a marked increase in strength for all conditions as the Nb content increased. This is attributed not only to solid solution strengthening of the β phase, but also increased volume fraction of the harder Nb3Al δ phase. The 40Ti alloy remained a single phase (B2 structure) for all heat treatments, but δ and an unidentified phase (probably O) was present after testing following aging at 1173 K (900 °C). There was no significant effect of aging on the strength. The 25Ti and 10Ti alloys showed increased strength with increasing aging temperature and time, which correlated to the increased amount of the δ phase.