CHEMICAL-REACTIONS AT METAL-CERAMIC INTERFACES DURING DIFFUSION BONDING

By diffusion bonding Ni and Zr to a single crystal of yttria-doped zirconia (ZrO2 electrolyte) two interfaces Ni/ZrO2 and Zr/ZrO2 were produced. Different from the Ni/ZrO2 interface studies for a Ni/ZrO2/Ni composite, where no reaction was observed, the intermetallic phases Ni5Zr and Ni7Zr2 were formed at 1273 K at the Ni/ZrO2 phase boundary within the Ni/ZrO2/Zr composite. At the phase boundary Zr/ZrO2 the formation of monoclinic zirconia occurred. The formation of the phases and the corresponding chemical reactions can only be conclusively explained by considering both the ionic and electronic transport properties of the ZrO2 electrolyte in an open circuit electrochemical cell. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for the characterization of the microstructure and chemistry of the reaction phases.