Influence of Deformation Stress Triaxiality on Microstructure and Microhardness of Pure Copper Processed by Simultaneous Torsion and Tension

Simultaneous torsion and tension deformation (STTD) modes were applied on commercial pure copper to investigate the influence of stress triaxiality on microstructure evolution and hardness distribution at room temperature. STTD was divided into pure torsion (PT, a special STTD) and general STTD according to tension loading. Microstructure evolution was observed by optical microscopy, electron backscattering diffraction and transmission electron microscopy. The microhardness distribution was measured on the cross section, and the fracture morphology was observed by scanning electron microscopy. Microstructure observations show that ultrafine grains are separated by high-angle grain boundaries. Microhardness measurements exhibit hardness increased more significantly and uniformly in the specimen processed by general STTD mode than PT mode. Additionally, the fracture morphology indicates the fracture mechanism is different between STTD and PT.