High-Temperature Deformation Characteristics of a β-Type Ti-29Nb-13Ta-4.6Zr Alloy

The hot deformation behavior of a biomedical beta-type Ti-Nb-Ta-Zr alloy has been studied through applying hot compression tests over a wide range of temperatures and strain rates (600-900 A degrees C and 0.003-0.3 s(-1)). The main microstructural feature of the specimens, which were deformed at 900 A degrees C, is the pancaked primary grains decorated by the serrated boundaries. The latter may well imply to the occurrence of dynamic recovery. The dynamic recrystallization however is considered as the main restoration mechanism in the specimens, which were deformed at 800 A degrees C under all strain rates. The sizes of the new recrystallized grains well follow the serration amplitude of the primary grain boundaries. At lower deformation temperatures (600 and 700 A degrees C), the strain rate sensitivity is suddenly decreased and ended to the strain localization in the form of macro shear band. The higher accumulated energy within the shear band zones appears to stimulate the occurrence of dynamic recrystallization. To further clarify the high-temperature flow behavior of the experimental alloy, a quantitative approach has been also employed. The observed flow hardening and softening has been justified considering the evolved microstructural features.