Unveiling the dynamic softening mechanism via micromechanical behavior for a near- titanium alloy deformed at a high strain rate

For near -beta high-strength titanium alloys, rheological softening is the key step during thermal deformation to determine the microstructure and mechanical properties. Nevertheless, the intrinsic softening mechanism during the rheological stage is still an open question due to the special complexity of the process. In this study, the deformation process of near -beta titanium alloy TC18 (Ti-5Al-5Mo-5V-1Cr-1Fe, wt.%) in a dual-phase region at a high strain rate was investigated. The micromechanical behavior of TC18 alloy during thermal deformation at 785 C-degrees and 0.1/s was revealed by using in-situ highenergy X-ray diffraction (HEXRD). The stress partitioning and microstructure evolution mechanism for this alloy were discussed in detail. It has been confirmed that the main softening mechanisms of TC18 alloy during thermal deformation are dynamic recovery (DR) and continuous dynamic recrystallization (cDRX). The stress partitioning between constituent phases featured by higher stress in the alpha phase than in the beta phase induces an inhomogeneous strain field near a phase lamellae to promote the dislocation pile-up in subgrains. The cDRX process of beta grains is composed of dislocation slipping, DR and sub grains formation, and transformation of recrystallized grains with high-angle grain boundaries (HAGB). Schmid factor and micro stress have a remarkable effect on dynamic recrystallization (DRX) behavior. The soft <200>(beta)//LD oriented grains are more likely to undergo cDRX than the hard <111>(beta)//LD oriented grains. This work may have implications for understanding the deformation mechanism and provide a fundamental basis for selecting appropriate processing technology for near -beta titanium alloys.(c) 2023 The Authors. Published by Elsevier B.V.