Phase-Field Simulation of β → α Phase Transformation in TC4-DT Titanium Alloy During Directed Energy Deposition: Effects of Elastic Strain Energy, Cooling Rate, and Oscillating Laser Heat Source

This study systematically investigates the effects of different heat-source modes and process parameters on the microstructure of the β → α phase transformation in titanium alloys. By incorporating chemical free energy, interfacial energy, and elastic strain energy, the explicit nucleation and subsequent growth behavior of multiple α variants are described. The results indicate that elastic strain energy intensifies the asymmetrical competition among different variants. As the cooling rate increases, the total number of nuclei increases, and the final microstructure exhibits a more pronounced trend of refinement and dispersion. Further comparison of the thermal history and phase-transformation microstructure at identical locations under different heat-source modes reveals that an oscillating laser primarily improves the uniformity of lateral heat distribution, reduces differences in microstructural evolution between the center and edge positions, and yields more consistent precipitate morphology and characteristic dimensions. This study provides a theoretical basis for the homogenization of microstructures and the optimization of performance in titanium alloys during directed energy deposition processes.