Enhancing microstructure refinement and strengthening efficiency of TiBw/near α-Ti composites by combining solid-solution treatment with hot processing

Microstructure refinement can improve the strength of materials without trading off ductility. Plastic deformation is the most adopted method for microstructure refinement of metallic materials. However, excessive deformation can fracture reinforcements in metal matrix composites. To extensively refine the microstructure of TiBw/near α-Ti composites with limited deformation degree, solid-solution treatment above β transformation temperature was adopted before hot deformation in α+β region. Through the hot compression test at 870 °C–950 °C, the ideal deformation temperatures and strain rates for solid-solution treated composites were determined to be at 910 °C–940 °C, 0.01 s−1-0.001 s−1. Following this, large billets were prepared by isothermal hot pressing with and without solid-solution treatment, to testify the evolution of microstructure and mechanical properties. The microstructure of the composites deformed after solid solution treatment was more homogeneous and refined, attributed to the increase in the number of α/β interfaces and the decrease in the diffusion distance of β-stabilizer elements. An improvement of 10% in the yield strength was brought about by the solid-solution treatment. This extra strengthening was contributed by microstructure refinement and the dispersion of silicide particles, but weakened by the decrease in dislocation density. This work presents an effective method to refine the microstructure of TiBw/near α-Ti composites, and explains the underlying mechanisms behind the microstructure refinement and mechanical property improvement.