The Fatigue Property Of Ultrafine-grained Copper Produced By ECAP

Ultra fine-grained (UFG) material is a new type of structural material to adapt the developments and the requirements of society, which exhibits excellent mechanical properties. In this thesis, the microstructure and fatigue behavior of Equal Channel Angular Pressing-ECAP Cu with different purity were investigated by means of tensile test, SEM, TEM and EBSD techniques. The main results are as follows:The fatigue properties of High and low purity copper were investigated and discussed in detail by stress-controlled and strain-controlled experimentation, The main results are as follows: During the stress-controlled experimentation, the fatigue life of ECAP low purity copper is significantly longer than that of their coarse grain (CG) counterparts, the fatigue limit of UFG low purity copper is 142MPa and CG copper is 74MPa. The fatigue life of high purity UFG copper is longer than low purity UFG copper's and the fatigue properties of route Bc UFG copper is higher than C route's under high stress amplitude, It's just the opposite under low stress amplitude. There is almost no different in fatigue properties of 4 and 6 passes UFG low purity copper. During the strain-controlled experimentation, the fatigue life of ECAP low purity copper is significantly shortened than that of their coarse grain (CG) counterparts, the fatigue life of UFG high purity copper is longer than UFG low purity's in low plastic strain amplitude, it's just opposite in high plastic strain amplitude, UFG and CG low purity changed from softened rapidly to slowly with strain amplitude decreasing at the beginning of loading. UFG softened in high strain amplitude and hardened in low train amplitude. Formation of shear bands (SBs) is the most important damage mechanism caused fatigue failure of UFG Cu. there is no inevitable relationship between formation of SBs and grain coarsening or cyclic softening. The formation of SBs and damage of UFG high purity copper is easier in high strain amplitude than in low strain amplitude. During cyclic deformation, the oriented distribution of defects along the shear plane of the last ECAP processing is one of the dominating mechanisms of SBs formation. The fracture of UFG low purity copper shows the characteristic of brittle and the UFG low purity copper shows plastic fracture. The fatigue life and its relevant coefficients in the energetic approach can be estimated with the conventional mechanical data, which provide a simple and reliable mathematical models and prediction methods for the engineering application of UFG materials, predictive value and measured value matched well...