Microstructure evolution, grain refinement, and mechanical properties of a metastable β titanium alloy during cold rolling and recrystallization annealing

While grain refinement is a promising approach for enhancing the performance of structural alloys, an improved understanding of the mechanisms underlying grain-refinement processes and their influence on mechanical properties is required. Therefore, in this study, we investigated the microstructure and mechanical properties of the single beta-phase TB18 alloy (Ti-5.3Cr-4.9Mo-4.9 V-4.3Al-0.9Nb-0.3Fe) during cold rolling and annealing, with dislocation slip as well as kink and shear band formation identified as the main deformation mechanisms during the cold-rolling process, which ensured good workability of the cold-rolled plate at room temperature. Shear bands formed preferentially in gamma-fiber (< 111 >//normal direction (ND))-oriented grains such as {111}< 110 > grains. The high density of subgrains and dislocations in the shear bands and surrounding regions promoted nucleation of the recrystallized grains, resulting in an increased nucleation rate and grain refinement. The texture after cold rolling mainly had rotated cube {001}<110> and {111}<110> components. During subsequent annealing, these components rotated to alpha*-fiber ({11h} < 1 2 1/h>) and {111}< 112 > components, respectively, thereby forming the final recrystallized texture. Thus, cold rolling and recrystallization annealing of the TB18 alloy resulted in a fine microstructure with a mean grain size of 25 mu m and excellent mechanical properties. In particular, the ultimate tensile strength and elongation of the pure beta microstructure increased to 850 +/- 2 MPa and 28.8 +/- 2.2%, respectively. Thus, these results indicate that cold rolling and recrystallization annealing could be considered as promising techniques for developing metastable beta titanium alloys with enhanced mechanical properties.