Microstructural evolution of cast TiAlNb intermetallics for third generation gas turbine components

AbstractThe microstructural evolution of Ti–45·9Al–8Nb and Ti–45·9Al–8Nb–0·2C (at-%) alloys fabricated by centrifugal investment casting is studied. It is found that both Ti–45·9Al–8Nb and Ti–45·9Al–8Nb–0·2C are mainly composed of γ phase and a small amount of α2 phase, and the microstructure is mainly fully lamellar in C containing alloy but again the C free alloy is mainly nearly fully lamellar. Nb distributes homogeneously in the γ and α2 phases but is depleted in the interdendritic regions. The addition of C reduces the lamellar spacing of Ti–45·9Al–8Nb alloy. The mean interlamellar spacings between α2 and α2 of Ti–45·9Al–8Nb and Ti–45·9Al–8Nb–0·2C alloys are about 950 and 700 nm, and those between γ and α2 lamellae are about 320 and 220 nm respectively. Oil cooling from the α phase field after 1h treatment at 1360°C leads to massive transformation to γm for both Ti–45·9Al–8Nb and Ti–45·9Al–8Nb–0·2C alloys. Subsequent aging in the α+γ phase field results in α phase precipitates within the γm phase, wh...