Deformation and fracture of Cu-SiO₂ bicrystals with [011] twist boundaries

Several kinds of Cu-SiO₂ bicrystals having [011] twist boundaries with different misorientation angles were tensile tested at various temperatures from 473-1023 K at strain rates from 4.2 × 10 ^-5-4.2 × 10^-3 s^-1 in vacuum. Most of bicrystals fractured intergranularly. The grain-boundary strength and fracture behavior of the Cu-SiO₂ bicrystals strongly depended on the grain-boundary character, temperature and strain rate. As the misorientation angle or grain-boundary energy increases, grain-boundary fracture takes place more easily at lower temperatures with lower fracture stresses. Furthermore, fracture stress and elongation to fracture decrease almost monotonically with increasing temperature and decreasing strain rate. The observed grain-boundary character and test condition dependence of grain-boundary strength can be understood reasonably by considering the occurrence of stress-concentration sites around the grain-boundary SiO₂ particles to form voids and cracks caused by grain-boundary sliding.