The evolution of microstructure, martensitic transformation and mechanical properties in Ti–V–Al-based shape memory alloys with changing annealing temperatures

Abstract

In the present study, the effects of annealing temperature on the microstructure, martensitic transformation and mechanical properties of Ti–V–Al-Gd shape memory alloys were investigated. The results revealed that the phase constituents were dependent on annealing temperatures. The coexistence of the α'´ martensite phase, β phase, hard α second phase and ω phase was found in Ti–V–Al-Gd shape memory alloy annealed at 650 °C. With increasing annealing temperature, the amount of β phase and α second phase gradually decreased. Meanwhile, the grain size of the Ti–V–Al-Gd shape memory alloy increased continuously with increasing annealing temperature. Merely α'´→β reverse martensitic transformation was found in all annealed Ti–V–Al-Gd shape memory alloys, regardless of the annealing temperature. The evolution of the martensitic transformation temperatures can be attributed to the compressive effect of the chemical composition, grain size and type and number of second phases. In addition, the yield strength gradually decreased owing to the coarsening of the grain size and reduction in the amount of the α phase, whereas the elongation became superior in Ti–V–Al-Gd shape memory alloy annealed at higher annealing temperatures due to the elimination of dislocations and defects. In proportion, the strain recovery characteristics gradually decreased as the annealing temperature increased from 700 °C to 800 °C.

Keywords

• Ti–V–Al lightweight shape memory alloy
• Annealing treatment
• Microstructural evolution
• Martensitic transformation
• Mechanical properties