Study on the maximum m superplasticity deformation of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

A new superplasticity deformation (SPD) approach called the maximum m (strain-rate sensitivity exponent) superplasticity deformation process (MaxmSPD) is proposed for the SPD of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy. The effect of the alloy's original microstructure on the MaxmSPD process was explored by using different billet pre-processing deformation procedures such that different microstructures were obtained for the MaxmSPD experiments. The deformation route and condition at which m has the maximum value were determined in order to identify the optimal MaxmSPD condition and provide the basis for experimentation. To highlight the uniqueness of MaxmSPD, the traditional constant velocity SPD (ConstvSPD) and the constant strain-rate SPD (Const ε˙ SPD) experiments were also conducted. The experimental results showed that the MaxmSPD process had the best SPD capability, with an elongation of 2300%, whereas the other two processes produced best elongations of 1100% and 1260%, respectively. The experiments also revealed the relationships between strain-rate sensitivity exponent m, deformation temperature and the cyclic change of strain rate in the MaxmSPD process. Finite element method (FEM) simulation was conducted to further explore the deformation behaviour in the MaxmSPD process. The deformation behaviour and the variation of physical variables in the MaxmSPD process, derived by experimentation or simulation, were compared and showed good agreement.