SPATIALLY-RESOLVED ELECTRON-ENERGY-LOSS STUDIES OF METAL-CERAMIC INTERFACES IN TRANSITION-METAL ALUMINA CERMETS

Composites consisting of an alumina matrix and 20 vol.% transition met al (Ni or Fe) particles, prepared by hot pressing powder blends, have been studied using spatially resolved transmission electron energy-los s spectroscopy (EELS), and, to a lesser extent, by high-resolution ele ctron microscopy (HREM). Particular attention was paid to the elucidat ion of the chemical bonding mechanisms at the metal-ceramic interface; EELS spectra from interfacial regions being obtained via a spatial di fference technique. From both qualitative and quantitative interpretat ion of EELS near-edge structures, as well as observed HREM images, the data appear to be consistent with the presence of an Al-terminated al umina at the interface and the formation of direct transition metal - aluminium bonds in Al(O(3)M) (M = Ni or Fe) tetrahedral units, possibl y as a result of the dissolution and interfacial reprecipitation of Al during processing. These results correlate well with similar model st udies on diffusion-bonded Nb/Al2O3 interfaces and may, in the light of recent theoretical electronic structure have implications for the res ultant interfacial bond strength in such materials.