Effect of deformation and heat treatment on the microstructure and mechanical properties of β-Zr40Ti5Al4V alloy

A kind of β-Zr40Ti5Al4V alloy was studied in detail on the cold rolling and the subsequent heat treatment process (including furnace cooling (FC) and air cooling (AC)). The analysis of the phase composition and microstructure of the rolled alloy indicated that a strain-induced phase transformation process from body-centred cubic β to orthorhombic α″ occurred during the cold rolling process and there was a parallel orientation relationship [0 0 1]α″//[1 1 0]β between the two phases. The transitional α″ phase transformed back to β or further transformed to α phase via a process of α″ → β → α during heat treatment. After the FC treatment, the α phase dominated the microstructure, and the alloy exhibited high strength but low ductility properties. In comparison, more β phase (∼67.1%) was retained after the AC treatment at 600 °C and a full β phase microstructure was produced when the temperature exceeded 670 °C. The amount of β phase made the AC specimens exhibit low strength and high ductility properties. The statistical results showed an increased β grain size with increasing temperature and the calculated results revealed that the activation energy for grain growth between 700 °C and 850 °C was ∼147.9 kJ/mol. Then a relationship between β grain size D and temperature T was obtained: D = 5.7 × 105exp(−1.78 × 104/T).