Optimization and verification of hot tensile deformation parameters of Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy based on processing map theory

Abstract

The high temperature tensile experiment of Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy was completed at 750–900 °C and strain rate of 10⁻⁵–10⁻³ s⁻¹. The processing map corresponding to the tensile process was established, and both optimal and instability zones were identified. The microstructure of different zones of processing map were observed in detail, and the justness of processing map was proved. The results show that the strain rate sensitivity index and energy dissipation rate increase with change of deformation conditions from low temperature/high stretching rate to high temperature/low stretching rate. The parameters of thermal tensile instability zone are: 750–795 °C/10⁻⁴–4 × 10⁻⁴s⁻¹ and 750–778 °C/10⁻⁴–10⁻⁵s⁻¹. The optimal hot deformation parameters are as follows: the temperature is 880–900 °C and the strain rate is 2.5 × 10⁻⁴–10⁻⁵s⁻¹. The obvious cracks and holes appear in the deformation structure corresponding to the instability zone, which are preferentially generated at the lamellar interface. The ratio of recrystallized structure corresponding to the optimal deformation parameter zone is higher than that in the instability zone, and the plastic deformation ability is greatly improved. The deformation characteristics of the instability zone are the dislocation pile-up, which is caused by the hindrance of the lamellar boundary and lamellar structure to the dislocation movement, and the substructure formed by the entanglement of the high-density dislocation regions in the lamellar structure. At the same time, there are also twins with a certain angle between the lamellar structure. The characteristics of deformation structure corresponding to the optimal deformation parameter region are dislocation, twin and recrystallization. The dislocation density in the recrystallized structure decreases, which can slow down the stress concentration inside the deformed structure, and the probability of instability such as cracks inside the alloy decreases.