Solidification and metastable phase formation in conventional and planar flow cast Ti-48.8at%Al-2.2at%V

Abstract
The solidification paths and subsequent solid state transformations of conventional and planar flow cast Ti-48.8at.%Al-2.2at.%V alloy were studied. At low cooling rates, [MATH] is the first phase to form from the melt. The primary hexagonal dendrites subsequently underwent the [MATH] solid state transformation resulting in a lath structure made of {111} [MATH] twins separated by thin [MATH] layers. The Al rich interdendritic areas consisted of [MATH] solidified from the segregated melt. Under higher cooling rates, [MATH] is the first phase to form from the melt. This was confirmed by the lath-free microstructure of the dendrites and by the fact that these dendrites were richer in Al than the interdendritic area leading to reverse segregation. The Al lean areas were [MATH] formed from an [MATH] parent phase by either the massive [MATH] or the [MATH] solid state transformations. For the largest melt undercoolings, the microstructure was free of chemical segregation and disordered [MATH] formed directly from the melt. Extremely fine networks of ordered domains were also observed, showing the subsequent ordering process of the [MATH] phase.