Cyclic creep and fracture behavior of Cu–SiO2 bicrystals with [0 1 1] twist boundaries

Orientation-controlled copper bicrystals with dispersed SiO2 particles were cyclically deformed at 673 K in vacuum. Although the fatigue lives of all the bicrystals increased monotonically with decreasing stress amplitude at a higher stress amplitude region, some of them showed discontinuous and abrupt life shortening at a lower stress amplitude region. This transition of the cyclic creep behavior was brought about by the occurrence of brittle intergranular fracture caused by grain-boundary sliding (GBS) and particle dragging by GBS to form the elongated voids. At the lower stress region, such voids were easily formed by GBS. At the higher stress region, however, grain-boundary steps that densely formed by plastic deformation effectively suppressed GBS, resulting in the absence of brittle intergranular fracture. The mechanism of grain-boundary and stress-amplitude-dependent fracture behavior will be discussed in relation to GBS.