Casting microstructure and phase-specific deformation behavior of Ti–20Ni alloy containing Ti2Ni phase

Abstract

Understanding the microstructural formation mechanisms and phase-specific deformation behaviors is essential for optimizing the mechanical properties of Ti alloys containing intermetallic phases. Thus, the present study investigated Ti-20 wt% Ni as a model alloy system and elucidated the formation of casting microstructure and the phase-specific deformation behavior. The as-cast microstructure reveals a dendritic region consisting of a mixture of lamellar α-Ti and Ti2Ni and an interdendritic region consisting of Ti2Ni, TiC, and a mixture of α-Ti phase and a small amount of Ti2Ni. The dendritic region displayed lower and relatively more uniform hardness than that of the interdendritic region. The phase-specific hardness decreased in the following order: dendritic region < dendritic region/Ti2Ni interface < Ti2Ni < TiC. After 6% cold-rolling, the fractured sample showed that the density of cracks in the interior of Ti2Ni and TiC was much higher than that at the α-Ti/Ti2Ni interfaces. Thus, the dispersion of the Ti2Ni and TiC phases inside the α-Ti phase is essential for achieving high-strength and high-formability Ti–Ni alloys.