Tao Sun

The hot deformation behavior and mechanism of Ti65 alloy with a bimodal microstructure were investigated by isothermal compression experiments conducted on the Thermecmastor-Z simulator equipment at temperatures ranging from 950 to 1110 °C and strain rates ranging from 0.01 to 10.0 s⁻¹. The Arrhenius constitutive model, based on strain compensation, and Grey Wolf optimization-neural network with back propagation model (GWO–BP), were both established. The differences between the experimental and predicted value of flow stress were compared and analyzed using the two models. The results show that the prediction accuracy of GWO–BP in the two-phase region is higher than that of Arrhenius model. In the single-phase region, both methods demonstrated high prediction accuracy. Compared to the single-phase region, the flow stress of Ti65 alloy shows a higher degree of softening in the two-phase region. During deformation in the two-phase region, the initial lamellar α phase transformed from a kinked and elongated morphology to a globularized topography as the strain rate decreased. Boundary-splitting was the primary mechanism leading to the spheroidization process. The degree of recrystallization increased with the increase in strain rate during the deformation in the single-phase region, while dynamic recovery and strain-induced grain boundary migration were the main deformation mechanisms at a lower strain rate. Discontinuous dynamic recrystallization may be the dominant recrystallization mechanism under a high strain rate of 10 s⁻¹.

Interstitial free steels with various grain sizes and textures were prepared by cold-rolling followed by an annealing process. The effect of grain size, crystallographic orientations and stored energy on corrosion behavior of interstitial free steel was investigated. It was found that the deformed microstructure and dislocation boundaries were consumed by recrystallizing grains during annealing. The average grain size increase ranging from 0.61 μm to 11 μm and the volume fraction of recrystallized grains was about 96% after annealing for 64 h; meanwhile, the γ fiber was the dominated recrystallized texture component. The stored energy gradually decreased due to the reduction in dislocation density by annealing. The potentiodynamic polarization and Nyquist plots show that the corrosion potential exhibits a more positive shift and depressed capacitive semicircle radius increase with rising annealing time. The 64 h annealed specimens had the biggest depressed semicircle in the Nyquist plots and the highest positive corrosion potential, which indicates the enhancement of corrosion resistance. Such an improvement of corrosion resistance is attributed to the increase in the volume fraction of the γ fiber and decrease in the stored energy.