Influence Of Primary Alpha-Phase Volume Fraction On The Mechanical Properties Of Ti-6al-4v Alloy At Different Strain Rates And Temperatures

Bimodal microstructures with primary alpha-phase volume fractions ranging from 14.3% to 57.1% were gained in Ti-6Al-4V (Ti-64) alloy through annealed in two-phase region at various temperatures below the beta-transus point. Then the influence of the primary alpha-phase volume fraction on the mechanical properties of Ti-64 were studied. The results show that, at room temperature and a strain rate of 10(-3) s(-1), the yield stress decreases but the fracture strain augments with added primary alpha-phase volume fraction. The equiaxed primary alpha-phase possesses stronger ability to coordinate plastic deformation, leading to the improvement of the ductile as well as degradation of the strength of Ti-64 with higher primary alpha-phase volume fraction. As the temperature goes up to 473 K, the quasi-static yield stress and ultimate strength decrease first and then increase with the incremental primary alpha-phase volume fraction, due to the interaction between the work hardening and the softening caused by the DRX and the growth of the primary alpha-phase. At room temperature and a strain rate of 3x10(3) s(-1), the varying pattern of strength with the primary alpha-phase volume fraction resembles that at a quasi-static strain rate. However, the flow stress significantly increases but the strain-hardening rate decreases compared to those at quasi-static strain rate due to the competition between the strain rate hardening and the thermal softening during dynamic compression process.