Constitutive analysis of the high-temperature deformation mechanisms of Ti-6Al-4V and Ti-6.85Al-1.6V alloys

The high-temperature deformation mechanisms of a near-α titanium alloy (Ti-6.85Al-1.6V) and an α + β titanium alloy (Ti-6Al-4V) were deduced within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on the two alloys at temperatures ranging from 750 to 900 °C. The stress versus strain rate curves of both alloys were well fit with inelastic-deformation equations which consisted of grain-matrix deformation (GMD) and grain-boundary sliding (GBS). The constitutive analysis revealed that the grain-boundary sliding resistance is higher in the near-α alloy than in the two-phase α + β alloy due to the difficulty in relaxing stress concentrations at the triple-junction regions in the near-α alloy. In addition, the internal-strength parameter (σ*) of the near-α alloy was much higher than that for the α + β alloy, thus implying that dislocation emission/slip transfer at α/α boundaries is more difficult than at α/β boundaries.