Microstructures and mechanical properties of metastable β TiNbSn alloys cold rolled and heat treated

The influence of stress-induced α″ martensitic transformation by cold rolling and its reverse transformation to β by subsequent heat treatment on mechanical properties, such as Young's modulus and tensile properties was examined using metastable β (Ti-35 mass% Nb)-4 mass% Sn. Two types of α″ rolling textures (2 2 0)_α″ [ 0 0 1 ]_α″ and (2 0 0)_α″ [ 0 1 0 ]_α″ are formed for the stress-induced martensite α″ by obeying the orientation relationship between β and α″; the former forms at low rolling reduction corresponding to β recrystallization texture of {2 1 1}_β〈1 1 0〉_β and the latter forms with increasing rolling reduction corresponding to β rolling texture of {1 0 0}_β〈1 1 0〉_β. β microstructure is refined and fine α precipitation occurs by heat treatment at 523 K for the completion of reverse martensitic transformation from stress-induced α″ to β. Young's modulus slightly increases at a rolling reduction of 30%, while it decreases with increasing rolling reduction over 50%, and reaches 43 GPa at a reduction of 89%. After the heat treatment at 523 K, Young's modulus is recovered to the initial value before cold rolling. Tensile strength of quenched (Ti-35 mass% Nb)-4 mass% Sn drastically increases by cold rolling and further increases by subsequent heat treatment at 523 K without sacrificing low Young's modulus. The obtained results on mechanical properties of metastable β (Ti-35 mass% Nb)-4 mass% Sn are explained in relation to microstructures evolved during thermomechanical processing.