Effect of High-Pressure Torsion Process on Precipitation Behavior of α Phase in β-Type Ti-15Mo Alloy

Precipitation behavior of a phase in Ti-15Mo alloy during isothermal aging after straining by high-pressure torsion (HPT) was investigated and compared with that without HPT process. Upon isothermal aging, ultrafine equiaxed a phase particles and acicular a phase plates were obtained in HPT-processed samples, while only the coarse acicular a phase plates were obtained in the samples without HPT process. The precipitation of equiaxed a phase occurred faster than the precipitation of acicular a phase in HPT-processed samples. It seemed that a high density of dislocations resulted in highly strained area and enhanced atomic diffusivity, promoting the formation of equiaxed a phase. The HPT-processed samples exhibited higher hardness and ultimate tensile strength but lower ductility than those of the specimens without HPT process.