In-situ synchrotron X-ray diffraction of Ti-6Al-4V during thermomechanical treatment in the beta field

This work aims to identify the mechanisms of restoration occurring in Ti-6Al-4V during hot plastic deformation and subsequent heat treatment. The allotropic phase transformation that occurs during cooling distorts the interpretation of the restoration mechanisms taking place at high temperatures. Therefore, analysis of deformed samples by conventional microscopy have led to controversies in the interpretation of the main dynamic restoration mechanism. Additionally, static restoration of the microstructure can occur during slow cooling, modifying the microstructure. These facts were mainly the reasons why discontinuous dynamic recrystallization and/or dynamic recovery has been reported as the main dynamic restoration mechanism for Ti-6Al-4V. In this work, we use in-situ synchrotron X-ray diffraction combined with conventional microscopy to determine the dynamic and static mechanisms of restoration during and after deformation at different strain rates. The results show dynamic recovery as main mechanism of restoration during deformation in the β field, denoted by sub-grain formation and a misorientation dependency of the strain rate. After deformation, static recrystallization, grain growth, and coarsening of the β grains can be observed, especially at strain rates higher than 0.1s⁻¹. It is also demonstrated that the nucleation of new grains can occur within the very first seconds of the isothermal heat treatment.