Evolution of microstructure and properties in reactive air brazing of 3YSZ ceramic and aluminized Crofer22h stainless steel using Pd-modified Ag–CuO filler

Reactive air brazing of 3YSZ ceramic and aluminized Crofer22H stainless steel was conducted using Pd-modified Ag-2CuO fillers in this study. The influence of Pd content on the interfacial microstructure and the mechanical properties of the joints at room (25 °C) and high temperatures (600 °C) was thoroughly investigated. The results revealed that an increase in Pd content resulted in a decrease in the solubility of O element in the filler system, thereby altering the form of CuO at high temperatures and significantly enhancing its reactivity with aluminized Crofer22H stainless steel. Additionally, there was a significant deterioration observed in the wettability of the fillers on ceramics. Well-joined joints were only achieved with the use of Ag2CuO-3 wt.% Pd filler, resulting in a 27.9% increase in room temperature shear strength due to enhanced interface reaction. At 600 °C, plastic deformation caused Ag-based filler to soften through dynamic recrystallization, but the addition of Pd dissolved in the matrix produced a solute drag effect that inhibited this process and increased joint shear strength by 41.1%.