Effect of N addition on nano-domain structure and mechanical properties of a meta-stable Ti-Zr based alloy

This study showed that a superior combination of high strength and ultra-low modulus can be achieved by the addition of N in a meta-stable β-type Ti–Zr based alloy undergoing stress-induced martensitic transformation. A Ti–18Zr–3Nb–2Mo–3Sn alloy exhibited a very low Young's modulus; however, the stress-induced martensitic transformation occurred at a low stress level. The addition of N facilitated the formation of nano-sized lattice modulation (nano-domain) structure and impeded the stress-induced martensitic transformation, leading to higher apparent yield stress, narrower stress hysteresis and large non-linear elasticity. A Ti–18Zr–3Nb–2Mo–3Sn–1.2N alloy exhibited an excellent combination of a low Young^'s modulus of 41 GPa and a high strength of 920 MP along with a large recovery strain with negligible hysteresis.