A polymer-like ultrahigh-strength metal alloy

Futuristic technologies like morphing aircrafts and superstrong artificial muscles are hinged on metal alloys being as strong as an ultrahigh-strength steel yet as flexible as a polymer1-3. However, achieving such “strong yet flexible” alloys has proven challenging4-9 due to the inevitable trade-off between strength and flexibility 5,8,10. Here we report a Ti-50.8 at.% Ni strain glass alloy showing an unprecedented combination of ultrahigh yield strength σy ~1.8 GPa with polymer-like ultralow elastic modulus E ~10.5 GPa, together with superlarge rubber-like elastic strain of ~8%. As a result, it possesses the highest flexibility figure of merit σy/E ~0.17 among existing structural materials. In addition, it can maintain such property over a wide temperature range of -80 ℃~+80 ℃ and demonstrates excellent fatigue resistance at high strain. The alloy was fabricated by a simple 3-step thermomechanical treatment scalable to industrial lines, which leads to not only ultrahigh strength due to deformation strengthening, but also ultralow modulus by forming a unique “dual-seed strain glass” microstructure, being a strain glass matrix embedded with a small amount of aligned R and B19' martensite “seeds”. In-situ x-ray diffractometry reveals that the polymer-like deformation behavior of the alloy originates from a nucleation-free reversible transition between strain glass and R and B19’ martensite during loading/unloading. This exotic alloy with mass-producibility may open a new horizon for many futuristic technologies such as morphing aero/space vehicles, superman-type artificial muscles, and artificial organs.