Microstructure evolution and a unified constitutive model for a Ti-55511 alloy deformed in β region

Abstract The microstructure evolution of a Ti-55511 alloy deformed at high temperatures (from 1163 K to 1253 K) and wide strain rate range (from 10 s-1 to 0.001 s-1) is studied by isothermal compression tests. Based on the sensitivity of dislocation density to deformation conditions, a unified constitutive equation is established to describe the evolution of flow stress, grain size and dynamic recrystallization (DRX) fraction. The results show that the initial grain boundaries are serrated, and the sub-grains and DRX grains are formed with the further deformation. Furthermore, the discontinuous and geometric DRX mechanisms are dominant recrystallization mechanism. Increasing the deformation temperature can increase the DRX fraction and sub-grain size. However, the abnormal growth of β grains occurs at 1253 K. The DRX fraction decreases with the increased strain rate. Meanwhile, the chain-like small DRX grains and the flow localization occur at high strain rates. Also, the established constitutive model is verified by the experimental results, and the correlation coefficient is 0.9929, indicating the excellent prediction ability of the established constitutive model.