Study on Grain Refinement Mechanisms and Mechanical Properties of bi-Modal Ti-55511 Titanium Alloy during Hot Rolling

Multi-pass hot rolling was performed on bi-modal Ti-55511 alloy with 50% rolling reduction at 700 degrees C. Mechanical properties were evaluated by tensile test, and microstructure evolution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the Ti-55511 alloy with bi-modal microstructure exhibits good strength and high ductility (1102 MPa, 21.7%). Comparatively, after 50% hot rolling, an enhanced strength and decreased ductility were obtained. The refinement of alpha phases leads to the increased tensile strength, while the fragmentation of the equiaxed alpha phase results in a decreased ductility. The fragmentation process of equiaxed alpha phases followed the sequence of: elongation of alpha phases -> formation of grooves and localized shear bands -> the final fragmentation accomplished via deepening grooves.