Tension-Compression Asymmetry in Ultrafine-grained Commercially Pure Ti Processed by ECAP

A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP). Tension- compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests. The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior. The basal and prismatic < a > slip are suppressed either for tension or compression, which is the easiest to activate. The tension twin system {101(over bar)2}< 1(over bar)011 > is easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor, consequently resulting in a lower yield strength under compression than tension. ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement. The interaction among the dislocations, grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation, while the interaction between the dislocations and grain boundaries for tension deformation. Deformation twins lead to the higher work hardening under compression than tension.