Characterization of yttria-stabilized-zirconia/stainless steel joint interfaces with gold-based interlayers for solid oxide fuel cell applications

YSZ/stainless steel joints using two commercial gold-based interlayers, 96.4Au–3Ni–0.6Ti and 97.5Au–0.75Ni–1.75V (in wt.%), were fabricated and analyzed for the microstructure of interlayer matrix, interlayer/steel interface, and interlayer/YSZ interface by SEM and TEM/EDS. At the 96.4Au–3Ni–0.6Ti/steel interface, a plate-like Au-rich phase precipitated in the steel and a dense Au-rich layer formed between steel and interlayer. No such Au-rich layer formed at the 97.5Au–0.75Ni–1.75V/steel interface. Needle-like Fe-rich phase precipitates within the Au-rich matrix were observed in both gold-based interlayers. At the 96.4Au–3Ni–0.6Ti/YSZ interface, a Ti2O3 layer and a small amount of Ni3Si2 were detected. However, at the 97.5Au–0.75Ni–1.75V/YSZ interface, no interfacial layer was observed, except dispersed micro-cavities and a large amount of Au in the grain boundaries of zirconia. These observations are used to propose a scheme for the development of joint microstructure. The 96.4Au–3Ni–0.6Ti interlayer appears to be a better choice for joining of YSZ to steel in SOFC applications.