Constitutive analysis of compressive deformation behavior of ELI-grade Ti–6Al–4V with different microstructures

In this study, a constitutive analysis of the flow responses of Ti–6Al–4V under various strain rates \( \dot{\varepsilon } \) was conducted by separately quantifying the hardening and softening effects of microstructure, interstitial solute and deformation heating on the total stress. For this purpose, a series of compression tests on an extra-low interstitial grade alloy with equiaxed, lamellar, or bimodal microstructures was performed at \( 10^{ - 3} \le \dot{\varepsilon } \le 10\;{\text{s}}^{ - 1} \) until the metal fractured, and the results were compared to those of the commercial grade alloy. The thermal stress σ^* increased with an increasing interstitial solute concentration; the athermal stress increased in the order of equiaxed, lamellar, and bimodal microstructures. Load–unload–reload tests revealed that the flow softening at a relatively high \( \dot{\varepsilon } \) was likely caused by deformation heating rather than by microstructure change; thus flow softening was attributed to a decrease in σ^*. Finally, a mechanical threshold stress model was extended to capture those observations; the modified model can provide a reasonable prediction of flow stress in Ti–6Al–4V with different microstructures and interstitial solute concentrations.