Interfacial microstructure and mechanical properties of zirconia ceramic and niobium joints vacuum brazed with two Ag-based active filler metals

Abstract

Reliable brazing of a zirconia ceramic and pure niobium was achieved by using two Ag-based active filler metals, Ag-Cu-Ti and Ag-Cu-Ti+Mo. The effects of brazing temperature, holding time, and Mo content on the interfacial microstructure and mechanical properties of ZrO2/Nb joints were investigated. Double reaction layers of TiO and Ti3Cu3O formed adjacent to the ZrO2 ceramic, whereas TiCu4+Ti2Cu3+TiCu compounds appeared in the brazing interlayer. With increasing brazing temperature and time, the thickness of the Ti3Cu3O layer increased with consumption of the TiO layer, and the total thickness of the reaction layers increased slightly. Meanwhile, the blocky Ti-Cu compounds in the brazing interlayer tended to accumulate and grow. This microstructural evolution and its formation mechanism are discussed. The maximum shear strength was 157MPa when the joints were brazed with Ag-Cu-Ti at 900°C for 10min. The microstructure and bonding properties of the brazed joints were significantly improved when Mo particles were added into the Ag-Cu-Ti. The shear strength reached 310MPa for joints brazed with 8.0wt% Mo additive, which was 97% higher than that of joints brazed with single Ag-Cu-Ti filler metal.