Fatigue behavior of Cu-SiO2, alloy at elevated temperatures

Copper polycrystal with dispersed sphere SiO2 particles was cyclically deformed at temperatures between ambient temperature and 687K. For comparison, copper single crystal and bicrystal containing SiO2 particles were also prepared to reveal effect of grain boundary on the fatigue behavior at the elevated temperatures, Though the polycrystal tended to show longer life than the single crystals at lower temperature, the life of the polycrystal became shorter than that of the single crystal especially under applied low stress amplitude at high-temperature region. At the critical stress amplitude where the life of the polycrystal becomes shorter than that of the single crystal, dominant cracking manner was supposed to change from nucleation in grain to on grain boundary. It is because that preferential crack nucleation at grain boundary and the propagation along the grain boundary took place more easily with increasing temperature and decreasing stress amplitude. All the bicrystals, whose grain boundaries could geometrically slide easily, fractured intergranularly when cyclically deformed at 673K. From these results, the observed loss of life or endurance at higher temperatures in the polycrystal should be caused by grain-boundary cracking induced by the occurrence of grain-boundary sliding.