Temperature dependence of fatigue–fracture-mode change in Cu–SiO2 alloy

Copper polycrystals, single crystals and bicrystals with dispersed spherical SiO2 particles were cyclically deformed at temperatures between ambient temperature and 673 K. All the crystals showed typical cyclic creep behavior. Though the polycrystals tended to show longer life than that of the single crystals at lower temperatures under higher stress amplitude, the life became shorter than that of the single crystals, especially at higher temperatures under applied low stress amplitude. The stress amplitude, where the life of the polycrystal becomes shorter than that of the single crystal, became lower as the temperature increased. At such a stress amplitude (transient stress amplitude), dominant cracking and propagation mode changed from transgranular to intergranular. The fracture mode of the bicrystals also changed sharply at the critical stress amplitude from transgranular to intergranular with increasing temperature. The observed fracture-mode change at the critical stress amplitude is discussed in relation to grain-boundary sliding and grain-boundary cracking.