Achieving high strength and ductility of a metastable β-titanium alloy via coupling thermomechanical processing and heat treatments

A metastable beta-titanium Ti-Al-Mo-V-Cr-Nb alloy exhibits a synergistic increasing in strength and ductility via coupling thermomechanical processing and heat treatment in present work. Synergistic effect of the thermomechanical processing and heat treatment on microstructure evolution and mechanical properties of the metastable beta-Ti alloy was systematically investigated. alpha+beta rolled sample sheet consumes less time to finish recrystallization, and leads to more uniformly distribution and smaller size of beta grains than beta rolled sample after same solution treatment. Primary alpha phase in alpha+beta rolled sample hinders the growth of beta grains during solution treatment and the spacing distance of alpha lamella in alpha+beta rolled sample is smaller than beta rolled sample after aging treatment, enhancing the strength significantly. The small spacing distance of alpha lamella is due to an increase in precipitation density. The small size and homogeneous distribution of beta grains provides moderate ductility. After solution treatment at 770 degrees C for 2 h and aging treatment at 525 degrees C for 6 h, alpha+beta rolled samples exhibit higher ultimate tensile strength (1550 MPa) and better ductility (6.5 %) than beta rolled sample. The relationship between the average grain size of beta grains, the average spacing distance of alpha lamella, and the yield strength of the alloy is quantitatively calculated using mathematical methods. The mechanisms of synergistic enhancement of strength and ductility in the alloy is qualitatively analyzed. These findings facilitate manufacturing high-performance metastable beta-Ti alloys at an industry scale using commercially available thermomechanical processing.