ABSTRACT
Gradient materials have been reported to have superior strength-ductility combinations. This chapter presents a study, in which gradient α″ martensite were introduced along the radial direction of cylindrical Ti-10V-2Al-3Fe samples by torsional straining, which simultaneously improved strength and ductility. α″ martensite had parallel and V-shaped morphology, which not only divided coarse β grains into finer β blocks but also blocked dislocation slip. In addition, dislocation slip in the α″ martensite and β blocks led to grain refinement. An optimal gradient distribution exists in torsion-processed samples for the optimal mechanical properties. In metastable β titanium alloys with low stacking fault energy, especially for those with molybdenum equivalent higher than 8%, stress-induced martensitic transformation, which is a transformation from β phase to orthorhombic α″ martensite, could occur under applied stresses. The reduction of plasticity with increasing torsional angle is a result of brittle fracture caused by a higher volume fraction of α″ martensite.
