Beta TiNbSn Alloys with Low Young’s Modulus and High Strength

Young’s modulus and tensile strength were investigated in relation to phase transformation and microstructural changes occurring during cold rolling and subsequent heat treatment using β (Ti–35 mass%Nb)–4 mass%Sn and (Ti–35 mass%Nb)–7.9 mass%Sn alloys. Stress-induced α″ martensite is generated on cold rolling of (Ti–35Nb)–4Sn whose martensitic transformation start temperature is around room temperature. Young’s modulus in the rolling direction is lowered by the generation of stress induced α″ phase with preferred texture, while it is recovered by the reverse martensitic transformation to β at 523 K. The reverse transformation yields fine β grains which are elongated approximately along the rolling direction and have an average grain size in width of less than 1 μm. This fine microstructure leads to high strength over 800 MPa with keeping low static Young’s modulus of 43 GPa. In contrast, mechanical properties of (Ti–35Nb)–7.9Sn in which matensite is not stress-induced are not so significantly improved by cold rolling and heat treatment.