Abstract: Conventional microstructure regulation in titanium alloys relies on complex thermomechanical processing. In this work, we demonstrate a simplified solidification-controlled approach that achieves superior microstructures with high-density subgrain boundaries and uniformly distributed nanoscale precipitates. The commercial Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy and self-designed Ti-23Fe-3Al-3Mo-3V (Ti-233) alloy with high Fe content were investigated using the electrostatic levitation technique characterized by a containerless condition. As the liquid undercooling increased, the growth velocities of the primary β-Ti dendrites increased according to the power function. The increase in Fe content led to a decrease in the dendrite growth velocity, which was 40.0 m/s at the undercooling of 363 K (0.19 T_L) in Ti-55511 alloy and 6.6 m/s at the undercooling of 388 K (0.24 T_L) in Ti-233 alloy. The spherical single crystal with high-density subgrain boundaries formed in both alloys under high undercooling conditions owing to the rapid growth of a single nucleus. It was confirmed that rapid solidification significantly affected the formation of the precipitated phase through microstructural heredity. Numerous ultrafine α-Ti lamellae uniformly precipitated fromβ-Ti after high undercooling coupled with heat treatment in Ti-55511 alloy, and the Ti-233 single crystal alloy containing nanoscale TiFe precipitates was directly processed using a containerless technique. Under the synergistic effect of solution strengthening and second phase strengthening, the nanohardness of Ti-55511 and Ti-233 alloys processed by the containerless technique was enhanced to 5.3 and 7.2 GPa, respectively.

Key words: Titanium alloy, Rapid solidification, High undercooling, Single crystal growth, Microstructural heredity