Cyclic creep and fracture of a Cu–SiO2 bicrystal at an intermediate temperature of 673 K

Cyclic creep and fracture behavior at 673 K of orientation-controlled Cu–SiO2 bicrystals with [0 0 1] twist 20° grain boundaries was investigated. The cyclic creep and life depended on both the stress amplitude and the frequency of the cyclic load. Most bicrystals fractured intergranularly. The number of cycles to failure shortened drastically with decreasing the frequency and with increasing the stress amplitude, while the time to failure remained nearly the same irrespective of the frequency. Since the cyclic creep life was controlled by the occurrence of grain-boundary fracture, the above observations can be understood reasonably by considering stress concentration and void formation at grain-boundary SiO2 particles. When grain-boundary sliding takes place, the particles impede the sliding and the stress concentration sites are created. This causes the intergranular fracture and controls the cyclic creep life.