Interfacial characterization of nickel-yttria-stabilized zirconia cermet anode/interconnect joints with Ag-Pd-Ga active filler for use in solid-oxide fuel cells

Nickel-yttria-stabilized zirconia cermet anode (Ni-YSZ)/interconnect joints with silver-palladium-gallium (Ag-9Pd-9Ga) active fillers are prepared by vacuum brazing. The joint structure and microstructure are analyzed by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), and by using an electron probe microanalyzer (EPMA). SEM observations of the joint show no cracks near the interface, confirming the compatibility of the Ag-9Pd-9Ga filler with a different anode and interconnect. The XRD pattern of the joint specimens oxidized at 800°C for 250 h shows Cr₂O₃ and (Mn,Cr)₃O₄ surface layers. EPMA analysis of the cell/Ag-9Pd-9Ga/alloys joint at the cross section shows Cr, O, Fe, Zr, Ni, Ag, Pd, Ga, Y, and Mn. Overall, the results indicate that the bonding between metal and cermet is well established and the interface is smooth. By correlating the XRD and EPMA analysis results, we also analyzed the possible stages during joint oxidation. The joint strength was evaluated at 25 and 800°C under shear and tensile loading conditions, respectively, and the brazed Ag-9Pd-9Ga sealant compared favorably with the commercially available glass-ceramic GC-9 counterpart.