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

摘要

The influence of stress-induced alpha" martensitic transformation by cold rolling and its reverse transformation to beta by subsequent heat treatment on mechanical properties, such as Young's modulus and tensile properties was examined using metastable beta (Ti-35 mass percent Nb)-4 mass percent Sn. Two types of alpha" rolling textures (220)_(alpha")[001]_(alpha") and (200)_(alpha")[010]_(alpha") are formed for the stress-induced martensite alpha" by obeying the orientation relationship between beta and alpha"; the former forms at low rolling reduction corresponding to beta recrystallization texture of {211}_(beta)<110>_(beta) and the latter forms with increasing rolling reduction corresponding to beta rolling texture of {100}_(beta)<110>_(beta). beta microstructure is refined and fine alpha precipitation occurs by heat treatment at 523 K for the completion of reverse martensitic transformation from stress-induced alpha" to beta. Young's modulus slightly increases at a rolling reduction of 30 percent, while it decreases with increasing rolling reduction over 50 percent, and reaches 43 GPa at a reduction of 89 percent. 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 percent Nb)-4 mass percent 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 beta (Ti-35 mass percent Nb)-4 mass percent Sn are explained in relation to microstructures evolved during thermomechanical processing.