Reactive air brazing of YSZ ceramic with novel Al₂O₃ nanoparticles reinforced Ag-CuO-Al₂O₃ composite filler: Microstructure and joint properties

The YSZ ceramic coated with a copper layer (~ 5 μm) was successfully reactive air brazed using novel Al₂O₃ nanoparticles (NPs) reinforced Ag-CuO-Al₂O₃ composite filler. The effects of Al₂O₃ NPs content on the interfacial microstructure and joint properties were investigated. When the content of Al₂O₃ NPs was 8 wt.%, YSZ joints obtained fine interfacial microstructure and optimal mechanical properties. The coefficient of thermal expansion of composite filler was calculated to be 16.26 × 10^− 6 K^− 1, presenting a decline of 12.1% compared to that of Ag-CuO base filler. The hardness and modulus values of braze joint slightly increased to 2.6 GPa and 164 GPa, respectively, possessing a better ability to resist deformation. Consequently, the YSZ joint possessed a maximum shear strength of 60 MPa, which was 25 MPa (~ 71%) higher than that of the joints brazed using Ag-CuO base filler. The leakage rate of YSZ-tube/AgCuO-8Al₂O₃/YSZ-block samples was measured to be 3.2 ± 0.9 × 10^− 10 Pa m³ s^− 1, which met the leakage rate requirements for vacuum tight components (less than 10^− 9 Pa m³ s^− 1). It implied that this novel method was an effective way to obtain hermetic YSZ joints.