Fabrication of bulk ultrafine grained titanium alloy via equal channel angular pressing based thermomechanical treatment

Equal channel angular pressing (ECAP) is one of the most feasible severe plastic deformation (SPD) techniques for fabrication of bulk ultrafine grained or even nanostructured materials. Previous studies show that the microstructure of titanium alloy (Ti-alloy) subjected to ECAP processing can only be refined to micron-scaled (1-5μm), rather than nano-scaled. In this paper, the ECAP based thermomechanical treatment was successfully conducted for fabrication of bulk ultrafine grained and nanostructured Ti-alloy. In detail, a near α titanium alloy was firstly processed by ECAP at the temperature above α-β transformation temperature (Tβ) and then followed by immediate quenching. The alloy was further pressed at the temperature of α+β phase region (below Tβ). Through observation and analysis of the microstructure evolution, it is found that the ultrafine grained Ti-alloy with partly equiaxed nano-scaled microstructure was successfully produced by the thermomechanical treatment process. To have an in-depth understanding of the process, the microstructure evolution in this grain refinement process and the property improvement after the refinement were extensively examined and discussed.