Effects of thermomechanical treatment on microstructure and shape memory effect of Ti-13V-3Al lightweight shape memory alloy

The effects of thermomechanical treatment on microstructure, mechanical properties and shape memory effect of Ti-13V-3Al alloy were investigated. A dual-phase structure which consists of α phase and α″ martensite phase forms after thermomechanical treatment. As annealing temperature increases, the amount of α phase decreases and its morphology changes. Stress plateau decreases when annealing temperature increases and elongation shows the opposite trend. Ti-13V-3Al alloy annealed at 700 °C has the best comprehensive mechanical property. Recoverable strain first increases then decreases as annealing temperature increases. Ti-13V-3Al alloy annealed at 700 °C for 0.5 h displays a large fully recoverable strain of 7.5%. It is believed that small, uniformly distributed α phase benefits the shape memory effect. With the help of α phase, martensite variants become small. The variants are supposed to have a good mobility and that reduces the chance of introducing irrecoverable strain during tensile test. The microstructure evolution of Ti-13V-3Al alloy annealed at 700 °C during deformation was investigated. When the pre-strain is less than 7.5%, the recoverable martensite reorientation process contributes to the deformation. When the pre-strain exceeds 7.5%, the crossover of martensite plates leads to the deterioration of shape memory effect.