Containerless solidification studies of the alpha-1/1 crystal approximant in Ti-Cr-Si-O alloys

The nucleation behavior of alpha(TiCrSiO), a 1/1 Fibonacci crystal approxim ant phase, was investigated in alloys made near the stoichiometric composit ion. Containerless solidification studies were made with electromagnetic ra dio-frequency levitation and the 105-m NASA Drop Tube. The solidification m icrostructures indicate that the alpha-Ti hexagonal solid solution was the primary crystallizing phase in these alloys, growing dendritically, The alp ha(TiCrSiO) phase nucleated in the remaining liquid. The competition betwee n these two phases resulted from the high oxygen concentration needed to fo rm alpha(TiCrSiO), which also stabilized the hexagonal-close-packed alpha-T i phase.