The criteria for microstructure evolution of Cu and Cu-Al alloys induced by cyclic loading

The microstructure evolution behaviors and corresponding quantitative rules of polycrystalline pure Cu and Cu-Al alloys under cyclic push-pull loading with rather large strain amplitudes (Δε/2=±2%~±9.5%) were systematically investigated. Besides common dislocation structures, deformation twins (DTs), shear bands (SBs) and ultra-fine grains (UFGs) were observed for the first time in fatigued specimens with certain composition and strain amplitude. Based on careful observation and brief classification, a distribution diagram of above microstructures at various Al contents and strain amplitudes was summarized. Then, three corresponding criteria were proposed by developing theoretical models of microstructure evolution, to provide critical distributions of dislocation structures, DTs and UFGs. The calculated results display good agreements with the experimental observations. Both the experimental results and the theoretical analyses indicate the existence of general rules that dominate the microstructure evolution behaviors under cyclic loading. The investigation of these rules is of great significance for the further achievements on both the fatigue mechanism and the life prediction.