Effect of cold rolling on structure and tensile properties of cast Ti-7.5Mo alloy

The present study evaluates the cold-workability and mechanical performance of a fast-cooled and cold-rolled Ti-7.5Mo alloy. The effects of cold rolling on the morphology, crystal structure and tensile properties of the alloy are investigated. The results indicate that, with carefully controlled rolling parameters, the fast-cooled cast alloy with orthorhombic α″ phase can be rolled down by an accumulated reduction of >80% in thickness. The as-cast alloy has an acicular morphology comprising fine, α″ platelets/needles uniformly distributed throughout the alloy. During rolling, a stress-assisted α″-to-α′ phase transformation accompanied with a strong preferred orientation toward α′ (002) plane occurs. EBSD-IPFs indicate that the as-cast alloy sample has several different preferred orientations. When the alloy was cold-rolled by 20% reduction in thickness, a texture toward [10-10] orientation was observed. With increased reduction in thickness, the preferred orientation gradually shifted from [10-10] toward [2-1-10]. TEM examination confirms that α″ and α′ phases co-exist in all cold-rolled samples, and the phase transformation appears more extensive in more severely cold-rolled samples. When heavily cold-rolled, distortion and fracture of the martensitic platelets/needles as well as boundary kinks/curls are frequently observed. With YS of 855 MPa, UTS of 1138 MPa, elongation of 11.6% and tensile modulus of only 62 GPa, the CR50 sample demonstrates a high potential for use as an orthopedic implant material.