Spatially resolved electron energy‐loss studies of metal–ceramic interfaces in transition metal/alumina cermets

Abstract

Summary: Composites consisting of an alumina matrix and 20 vol.% transition metal (Ni or Fe) particles, prepared by hot pressing powder blends, have been studied using spatially resolved transmission electron energy‐loss spectroscopy (EELS), and, to a lesser extent, by high‐resolution electron microscopy (HREM). Particular attention was paid to the elucidation of the chemical bonding mechanisms at the metal‐ceramic interface; EELS spectra from interfacial regions being obtained via a spatial difference technique. From both qualitative and quantitative interpretation of EELS near‐edge structures, as well as observed HREM images, the data appear to be consistent with the presence of an Al‐terminated alumina at the interface and the formation of direct transition metal – aluminium bonds in Al(O₃M) (M = Ni or Fe) tetrahedral units, possibly as a result of the dissolution and interfacial reprecipitation of Al during processing. These results correlate well with similar model studies on diffusion‐bonded Nb/Al₂O₃ interfaces and may, in the light of recent theoretical electronic structure calculations, have implications for the resultant interfacial bond strength in such materials.