Microstructural design for achieving high performances in Ti-V-Al lightweight shape memory alloys by optimizing Zr content
Xiaoyang Yi, Lijie Sheng, Guoqiang Fu, Bin Sun, Bowen Huang, Kuishan Sun, Xianglong Meng, Zhiyong Gao, Shangzhou Zhang, Haizhen Wang
Abstract
In the present study, the quaternary Zr element was introduced to replace Ti in Ti-V-Al based shape memory alloys. The addition of Zr element resulted in the microstructural features of Ti-V-Al based shape memory alloys, such as the phase evolution of αˊˊ → β, the precipitation of C14-type Laves phase, reduction of grain size etc. Moreover, the two-stage martensitic transformation corresponding to ω → β and αˊˊ → β transformation gradually evolved into single ω → β martensitic transformation during heating process in Ti-V-Al based shape memory alloys, as Zr content was increased from 0.5 at.% to 5.0 at.%, which was firstly reported in Ti-V-Al based shape memory alloys. Meanwhile, the martensitic transformation temperatures of Ti-V-Al based shape memory alloys were decreased with Zr increasing. By optimizing Zr content, the highest yield strength and largest microhardness can be gained in Ti-V-Al based shape memory alloy with controlling 5.0 at.% Zr, as a result of solution strengthening, grain refinement and precipitation strengthening. Besides, the moderate Zr content caused the precipitation of C14-type Laves phase and formed the quasi-continuous network structure, which contributed to the superior elongation. And the perfect fracture ductility with an elongation of 40% in the present Ti-V-Al based shape memory alloys with 3.0 at.% Zr was significantly larger than that the other reported Ti-V-Al based shape memory alloys. Moreover, the superior strain recovery characteristics with a fully recoverable strain of 4% can be achieved in Ti-V-Al based shape memory alloys through controlling 3.0 at.% Zr.