Hot Deformation and Dynamic Recrystallization of Ti-6Al-7Nb Biomedical Alloy in Single-Phase β Region

The aim of this investigation is to evaluate the hot deformation behavior and critical conditions for onset of dynamic recrystallization in Ti-6Al-7Nb biomedical alloy. The effects of temperature and strain rate on the hot deformation behavior of Ti-6Al-7Nb alloy were studied by employing hot compression tests. The experiments were conducted at temperatures of 1050, 1100, and 1150 degrees C under strain rates of 0.0025, 0.025, and 0.25 s(-1) up to a true strain of 0.65. The evolution of compressive flow stress during deformation of the experimental alloy in the single-phase beta region was investigated. The obtained microstructures showed the occurrence of partial dynamic recrystallization along the prior grain boundaries, which was discussed relying on the continuous recrystallization process. Using the strain-hardening rate curves (d sigma/d epsilon versus sigma), two characteristic parameters including the critical strain for DRX initiation (epsilon(c)) and the strain for peak stress (epsilon(p)) were identified. The normalized critical stress and strain for initiation of DRX were, respectively, found to be 0.9 and 0.67. True stress-true strain curves have been used to construct proper constitutive equations for the experimental alloy. The obtained activation energy for hot deformation was discussed considering the dominant restoration processes. Moreover, the flow stress was modeled for different strain levels, where good agreement with the experimental alloy was found.