A polymer-like ultrahigh-strength metal alloy
Zhizhi Xu, Yuanchao Ji, Chang Liu, Liqiang He, Huijun Zhao, Ye Yuan, Qian Yu, Jin Cui, Andong Xiao, Wenjia Wang, Yang Yang, Tianyu Ma, Xiaobing Ren
Abstract
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 polymer1–3. However, achieving such ‘strong yet flexible’ alloys has proven challenging4–9 because of the inevitable trade-off between strength and flexibility5,8,10. 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 exotic alloy with the potential for mass producibility may open a new horizon for many futuristic technologies, such as morphing aerospace vehicles, superman-type artificial muscles and artificial organs. A polymer-like ultrahigh-strength TiNi alloy was fabricated by a simple three-step process to give a combination of a polymer-like ultralow elastic modulus and a steel-like ultrahigh yield strength over a wide temperature range, and such exotic properties arise from a unique strain glass state.