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 SiO 2 on GB is conserved. The morphological evolution of SiO2 on GB is caused by diffusional flow of matter to decrease the sum of Cu/SiO 2 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.