Analytical transmission electron microscopy studies on copper-alumina interfaces

Abstract

A diffusion bonded copper-alumina interface had been studied using energy dispersive x-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Investigations of polycrystalline alumina showed that silica, a common commercial impurity, was present at the triple junctions in the form of fine mullite crystals in a glassy, silicon rich phase. Silicon was also detected along the alumina grain boundaries near triple junctions. There was no observed diffusion of Cu into alumina or alumina into copper. TEM results indicated no interface phase in the these vacuum formed samples. EDX studies of the interfaces revealed that silicon was present in varying concentrations from 1.O at.% to 10.0 at.%. Using spatial difference, PEELS at the interface showed two distinct residuals: a coordination similar to an aluminosilicate for silicon rich areas and a coordination similar to a metal to metal coordination for low silicon regions. Comparison of the Si rich interface residual PEELS spectra to that of the alumina triple junction PEELS spectra showed that the interface had atomic environments similar to that of as aluminosilicate, such as mullite. The interface results suggest that Si segregation may contribute to the observed higher strength of the metal-ceramic composite by void filling and modified bond character.