The role of zirconium in the formation of structure and properties of titanium alloys during superplastic deformation

This study investigates the effect of zirconium on the superplastic properties of titanium alloys at various temperatures and strain rates. It has been established that zirconium significantly influences the strain rate sensitivity coefficient (m), mechanical stability, and plasticity. At elevated temperatures, zirconium-containing alloys exhibit a stable m-value within a specific strain rate range, followed by a sharp decline. In contrast, zirconium-free alloys show a gradual decrease in m as the strain rate increases. The optimal temperature-strain rate conditions for superplastic deformation depend on zirconium content. Alloys with lower zirconium concentrations demonstrate high plasticity at moderate temperatures and intermediate strain rates, whereas alloys with higher zirconium content require lower strain rates to achieve uniform deformation. Beyond a certain threshold, an increase in zirconium content results in reduced plasticity and strain localization. Additionally, zirconium increases flow stress, while higher temperatures contribute to its reduction; however, this is accompanied by grain coarsening, which negatively affects mechanical properties. Microstructural analysis using scanning electron microscopy revealed that after superplastic deformation, all investigated alloys develop a fine-grained structure consisting of equiaxed α- and β-grains. The average grain size increases compared to the initial state, indicating dynamic recovery and recrystallization processes. The results confirm the feasibility of using these titanium alloys in superplastic forming technologies. The identified correlations provide a basis for optimizing thermomechanical processing parameters to achieve a balance between high plasticity and mechanical stability, which is crucial for industrial applications.