Achieving Gradient Martensite Structure and Enhanced Mechanical Properties in a Metastable β Titanium Alloy

Gradient materials have been reported to have superior strength–ductility combinations. In this study, gradient α″ martensite were introduced along the radial direction of cylindrical Ti-10V-2Al-3Fe (Ti-1023) samples by torsional straining, which simultaneously improved strength and ductility. The torsional strain gradient produced martensite gradient with increasing density and decreasing thickness from center to surface. 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. The formation of geometrically necessary dislocation (GNDs) and the increasing shear stress required for martensitic transformation contributed to high strain hardening. An optimal gradient distribution exists in torsion-processed samples for the optimal mechanical properties.