Morphological Evolution of Grain-Boundary SiO2 in Internally Oxidized Cu-Si Bicrystals

Abstract

Cu-0.78 mass%Si bicrystals are internally oxidized at various conditions and morphological evolution of amorphous SiO2 formed on a grain boundary (GB) is observed. After the reaction of Si atoms with oxygen, a film-like SiO2 phase with holes is initially formed on GB of Cu. At temperatures used for the internal oxidation, the holes rapidly grow and the morphology of the film-like SiO2 changes to a particulate equilibrium shape through formation of two-dimensional SiO2 network and its subsequent breakup. During the morphological evolution, the volume of SiO2 on GB is conserved. The morphological evolution of SiO2 on GB is caused by diffusional flow of matter to decrease the sum of Cu/SiO2 interface and Cu grain-boundary energies. The activation energy Q of the morphological evolution is obtained as Q ≈ 290 kJ/mol. Among the values of activation energies reported in the previous studies on diffusion in SiO2, Q ≈ 290 kJ/mol is close to that for the volume-diffusion of SiO in SiO2, QSiO ≈ 268 kJ/mol. This supports that the morphological evolution of SiO2 on GB is controlled by the volume-diffusion of SiO in SiO2.