Phase transformation and evolution of dislocation structure in the β phase of Ti-17 alloy during hot deformation

^a Institute for Materials Research, Tohoku University, Sendai, Japan
^b Department of Materials and Environmental Engineering, National Institute of Technology, Sendai College, Natori, Japan
^c Department of Advanced Materials Science, Faculty of Engineering, Kagawa University, Takamatsu, Japan

^* k_yamanaka@imr.tohoku.ac.jp

Abstract

The hot deformation behavior and microstructural evolution of Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti-17) alloy in the β-phase field were examined. Hot compression tests were conducted at temperatures ranging from 700 and 1100 °C and strain rates ranging from 10^-3 to 1 s^-1. The obtained true stress–true strain curves exhibited steady-state flow behavior at temperatures above the β-transus temperature (T_β ~ 890 °C). The microstructural observations suggested that the dynamic recovery process represents a dominant mechanism for the β-phase of the alloy. In contrast, the flow softening was identified at 700 °C at a strain rate of 10^–3 s^–1. The formation of fine acicular α microstructures was noticed in such a deformation condition, indicating that dynamic phase transformation can occur in the metastable β-phase during hot deformation. Such a dynamic phase transformation also occurred preferentially at the initial β-grain boundaries as well as sub-boundaries that created within the βmatrix via dynamic recovery. The β-processing conditions were also examined by constructing processing maps based on the dynamic materials model (DMM).