Microstructure development during directional solidification of Ti-45Al-8Nb alloy

Microstructure development and phase transition were investigated by quenching during directional solidification (DS) of Ti-45Al-8Nb (at.%) alloy. The solidification route and process can be controlled by adjustment of the solidification condition. A coexisted region of L + β + α was found at a low growth rate. The high temperature α phase, produced by peritectic transformation or β → α solid-state transformation or direct solidification from interdendritic liquid, was determined by the solidification conditions and can be identified by checking the β-segregation pattern in dendritic region. Lamellar orientation control was achieved when the interdendritic α grew on the top of peritectically formed α. High temperature α can be aligned continuously although α partly grew from the region of primary β interdendrite. Some elongated B2 particles were generated due to β-stablizers were centralized in interdendritic liquid during DS process. The volume fraction of the B2 particle decreased with decreasing growth rate (V).