A polymer-like ultrahigh-strength metal alloy

Futuristic technologies such as morphing aircrafts and super-strong artificial muscles depend on metal alloys being as strong as ultrahigh-strength steel yet as flexible as a polymer. However, achieving such strong yet flexible alloys has proven challenging because of the inevitable trade-off between strength and flexibility. Here we report a Ti-50.8 at.% Ni strain glass alloy showing a combination of ultrahigh yield strength of σy = 1.8 GPa and polymer-like ultralow elastic modulus of E = 10.5 GPa, together with super-large rubber-like elastic strain of approximately 8%. As a result, it possesses a high flexibility figure of merit of σy/E = 0.17 compared with existing structural materials. In addition, it can maintain such properties over a wide temperature range of −80 °C to +80 °C and demonstrates excellent fatigue resistance at high strain. The alloy was fabricated by a simple three-step thermomechanical treatment that is scalable to industrial lines, which leads not only to ultrahigh strength because of deformation strengthening, but also to ultralow modulus by the formation of a unique dual-seed strain glass microstructure, composed of a strain glass matrix embedded with a small number of aligned R and B19' martensite seeds. In situ X-ray diffractometry shows that the polymer-like deformation behaviour of the alloy originates from a nucleation-free reversible transition between strain glass and R and B19' martensite during loading and unloading. This alloy with the potential for mass producibility may enable technologies such as morphing aerospace vehicles, super-strong artificial muscles and artificial organs.

Zhizhi Xu, Yuanchao Ji, Chang Liu, Liqiang He, Hui Zhao, Ye Yuan, Yu Qian, Jin Cui, Andong Xiao, Wenjia Wang, Yang Yang, Tianyu Ma, Xiaobing Ren