A dislocation-based model for the microstructure evolution and the flow stress of a Ti5553 alloy

The plastic deformation at high temperatures of two-phase titanium alloys is modelled using a mesoscale approach to describe the complex interactions between different populations of dislocation densities. The static and dynamic recovery, as well as of continuous dynamic recrystallization, is modelled. The flow stresses of both α and β phases are calculated using constitutive equations combined with a load partitioning model between the α and β phases. The dislocation populations are separated into three categories, named mobile, immobile and walls, and separated rate equations are developed for each reaction between them. Several microstructure features are calculated, such as mean subgrain size, grain size, dislocation densities and boundary misorientation. Additionally, glide velocity is also estimated. Hot compression experiments of a Ti-5553 alloy at temperatures between 1073 K and 1193 K and strain rates between 0.001 s⁻¹ and 10 s⁻¹ are used for validation. The flow softening observed in the α+β domain is attributed to the change in load partitioning. Moreover, the decrease in grain and subgrain size with the increase in strain rate and decrease in temperature is well predicted by the proposed model as well as the evolution of a fully static recrystallized microstructure into a continuous dynamic recrystallized one.