Characterization and unified modelling of creep and viscoplasticity deformation of titanium alloy at elevated temperature

A unified model to characterize the mechanism transitions in a wide range of strain rates at elevated temperatures of titanium alloys has been developed and validated in this study. Models of microstructure-based backstress and strain rate dependent stress sensitivity covering both creep and viscoplasticity domains have been proposed, so as to predict different deformation behaviors concurrently for hot forming. Systematical experiments, including hot tensile, creep, stress-relaxation, and corresponding loading-unloading tests have been designed and performed, to get the different deformation behaviors, as well as the evolution of backstresses of titanium alloys at elevated temperatures. Microstructural observations, such as electron backscatter diffraction (EBSD), have also been performed to assist the mechanisms characterization. Based on the microstructural and macro properties results, the developed unified model has been calibrated and further implemented for typical cases of hot stamping - stress-relaxation forming (HS-SRF). The developed model achieved an excellent accuracy for all the tensile, creep, and stressrelaxation behaviors concurrently, with an error of only about 4.9 %, and a comparative 71.8 % - 90.8 % reduction in springback prediction error has been reported for hot forming of typical thin-walled titanium alloy components when compared with the conventional modelling strategy where a single deformation mechanism is considered. The potential of the proposed model for process design and optimizations has also been discussed.