Stepped superplasticity deformation-induced plastic enhancement of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si alloy

A novel superplasticity deformation (SPD) approach called stepped superplasticity deformation (Stepped-SPD) is proposed for the SPD of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si alloy. The effect of Stepped-SPD process on the microstructural evolution and mechanical properties of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si alloy was explored by the Stepped-SPD tensile experiment which was divided into two forming steps to carry out. The former step adopted the constant speed deformation and the latter one chose the maximum m superplasticity deformation (MaxmSPD). The plastic strain in the former step and clearance time between the two steps in Stepped-SPD were controlled in order to facilitate the grain refinement and microstructure property improvement which induced plastic enhancement. Furthermore, the single-step constant velocity SPD (ConstvSPD) and the single-step MaxmSPD tensile tests were also conducted. The experimental results of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si alloy showed that the Stepped-SPD tensile method obtained the best SPD capability, with an elongation of 2053%, whereas the MaxmSPD and constant speed tensile method produced the biggest elongations of 1347% and 753.9%, respectively. Thus, it is indicated that the Stepped-SPD induces the plastic enhancement in comparison with the single-step deformation method.

► The Stepped-SPD method: Constant speed + Clearance stage + MaxmSPD method.
► The Stepped-SPD induces the plastic enhancement in comparison with the single-step deformation.
► The elongation: 2053% by the Stepped-SPD; 1347% by the MaxmSPD; 753.9% by constant speed deformation.
► The material occurres dynamic and the static or meta-dynamic recrystallization at clearance stage.
► The advantage of grain refinement and structure property improvement in Stepped-SPD is prominent.