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

Abstract

The YSZ ceramic coated with a copper layer (~5μm) 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 8wt.%, YSZ joints obtained fine interfacial microstructure and optimal mechanical properties. The coefficient of thermal expansion of composite filler was calculated to be 16.26×10−6K−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 2.6GPa and 164GPa, respectively, possessing a better ability to resist deformation. Consequently, the YSZ joint possessed a maximum shear strength of 60MPa, which was 25MPa (~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±0.9×10−10Pam3s−1, which met the leakage rate requirements for vacuum tight components (less than 10−9Pam3s−1). It implied that this novel method was an effective way to obtain hermetic YSZ joints.