Enhanced Ag–Nb2O5/SiC wetting and brazing by SiC pre-oxidation: Experiments and first-principles study

This study investigates the effect of SiC pre-oxidation on the air reactive wetting and brazing behavior of Ag–Nb 2 O 5 fillers. An obvious SiO 2 layer induced by the pre-oxidation can improve the wettability of the Ag–Nb 2 O 5 /SiC system as the contact angle decreases from ∼75° to ∼25° with increasing Nb 2 O 5 content, accompanied by localized AgNbO 3 formation at the interface and the triple line. Moreover, the Nb 2 O 5 addition promotes a progressive growth of AgNbO 3 , transforming the interfacial structure from Ag/SiO 2 /SiC to Ag/AgNbO 3 /SiO 2 /SiC. An optimal Nb 2 O 5 content effectively reduces the direct Ag/SiO 2 contact while avoiding excessive AgNbO 3 formation and associated thermal stresses, resulting in a maximum shear strength at 4% Nb 2 O 5 . First-principles calculations demonstrate that the AgNbO 3 /SiO 2 interface exhibits a higher bonding strength than the Ag/SiO 2 interface, showing a strong interfacial charge transfer between AgNbO 3 and SiO 2 , which is consistent with enhanced mechanical performance. The insights gained from SiC pre-oxidation offer a potential pathway for advancing the air brazing of other non-oxide ceramic systems.