Microstructures and mechanical properties of Ti-55511 alloy subjected to rolling in the α plus β dual-phase region

In this study, dual-phase region rolling was conducted on a Ti-55511 alloy with different initial rolling reductions in the single-phase region. The mechanical properties and microstructural characteristics of the alloy with different deformation conditions were investigated. Microstructure observations show the formation of a heterogeneous structure with a gradient size distribution of the alpha phase at the recrystallized grain boundaries, induced by the non-uniform stress distribution. The alpha phase and the (3 matrix exhibit the Burgers orientation relationship in the recrystallized region with the gradient structure. However, in the unrecrystallized region of the partially recrystallized specimens and in the grain interiors of the fully recrystallized specimens, the alpha phase and the (3 phase exhibit Pitsch-Schrader orientation relationship (P-S OR). A large number of the nano-sized alpha" martensite bands were observed after the dual-phase region rolling. These bands originated from the alpha/(3 interfaces and grew towards the interiors of the alpha phase. As the deformation increased, these nano-bands underwent a transformation into the {10 1 1}alpha deformation twins, resulting in the fragmentation of the alpha phase. Mechanical testing results show that the mechanical properties of the alloy can be improved by the dislocation strengthening, the generation of profuse alpha phase and other microstructures including the heterogeneous distribution of the alpha phase, the nano-sized alpha" martensite and the {10 1 1}alpha deformation twins.