Ag–SiO₂ - An optimized braze for robust joining of commercial coated stainless steel to ceramic solid oxide cells

In this study, Ag–SiO₂ was successfully used to join Ce/Co coated AISI 441 stainless steels produced by Sandvik to Solid Oxide Cells. Defect-free and robust joints were obtained at 950 °C when brazing in air. The influence of the chemical composition of the braze and the brazing temperature on the microstructure and mechanical properties of joints was studied. An enhanced interfacial adherence was achieved through the reaction of the SiO₂ in the braze and the Co coating of the steel during the air brazing process. The obtained joints possess excellent mechanical robustness with a fracture energy of 96.5 J/m², and a superior gas tightness (leak rate of 5.4 × 10⁻⁴ sccm cm⁻¹) compared to the existing brazing systems. Long-term aging in air or the exposure to reducing atmosphere only had minor effects on the measured fracture energy.