Microstructure And Properties Of CP-Ti Processed By ECAP At Room Temperature

Equal Channel Angular Pressing (ECAP) is a unique processing method in fabricating materials with high properties. ECAP has attracted much attention because of its usefulness in producing bulk materials with ultra-fine grains (UFG).ECAP of commercial pure titanium (CP-Ti) via rout Bc was successfully processed to four passes at room temperature, using a die with the internal angleφof 120°and outer curvature angleψof 20°. The equivalent strain was up to～2.54. Microstructure and mechanical properties of as-pressed CP-Ti were studied by means of optical microscope, transmission electron microscope and electronic tensile equipment. The effect of pressing passes and annealing temperature on microstructure and mechanical properties were investigated, and the deformation mechanism, microstructure refinement mechanism and strengthening mechanism were studied. The results show that UFG with high-angle boundaries were obtained and the average grain size was about 200nm after the fourth ECAP pass. Bands structure and twins produced by ECAP crossed each other, and plenty of dislocation evolved into cellular structure or subgrains, and consequently dynamic Recovery occurred. All of these resulted in the grains refinement. After the fourth ECAP pass, CP-Ti exhibited the ultimate tensile strength (UTS) of 773 MPa, while preserving sufficient ductility, elongation to failure of 16.8%. When the annealing temperature is below 400℃, microhardness slightly decreased, after then, mircohardness went through the sharp decrease owning to recrystallization.In the same experimental environment, ECAP of CP-Ti via routes A, route B, and route C were processed to two passes at room temperature. The effect of processing routes on microstructure and mechanical properties was investigated. The results show that the deformation microstructure and morphology were different which depended on the specific route. For route A and route B, bands structure was the main deformation microstructure. For route C, block structure was the main deformation microstructure. Moreover, the ECAP route does not have significant effect on mechanical properties and thermal stability of CP-Ti.