A Study Of Brazing Process And Mechanism Of Si₃N₄ Ceramic Using High-Temperature Filler Alloy

Silicon nitride is one of the most promising structural ceramics for high temperature applications, it is extremely important in both theory and practice to investigate the bonding of the Si₃N₄ ceramic. In this paper Si₃N₄ ceramic was bonded by active brazing using active filler alloy of Cu-Pd-Ti and Au-Ni-V. The effect of brazing parameters of joining on the microstructure and properities of the joint was investigated. The distribution of element and reactants at the joints was analysed by means of SEM, EDS and XRD. The joining mechanism of joint was discussed.The Cu-Pd-Ti alloy was used as a filler alloy for brazing the pre-metallic Si₃N₄ ceramic. The joints were composed of the reaction layer (TiN) close to Si₃N₄ ceramic, bonding layer composed of (TiN ,Ti₅Si₃) between reaction layer and filler alloy, Cu-riched solid solution in the middle of seam and reactants(TiN, PdTiSi,Pd₂Si) in the solid solution. The microstructure and properties of joint depend on the brazing parameters. When brazing temperature and holding time increased, the thickness of reaction layer almost didn't change, however bonding layer became much thicker, and the amount and size of reactants (TiN, Pd₂Si) in the Cu-riched solid solution increased, and the mount of PdTiSi ternary phase decreased. At temperature below 1423K, the bending strength improved with the increasing temperature and holding time. When the temperature is above 1423K, the strength of joint decreased sharply with both brazing temperature and holding time increasing. The bonding mechanism of the Si₃N₄/Si₃N₄ joint brazed with Cu-Pd-Ti filler alloy is the formation of reaction layer (TiN) between the Si₃N₄ ceramic and filler alloy.The Au-Ni-V alloy was also used as a filler alloy for brazing the Si₃N₄ ceramic, and a realiable joint could be obtained. The joint was composed of reaction layer (VN) near to Si₃N₄ ceramic, Au-riched solid solution in the midst of seam and the reactants of Ni-riched phase at the solid solution, As brazing temperature elevated, reaction layer appeared much thicker, the strength increased with increasing bonding temperature. When the bonding time increased, the reaction layer of interface became much thicker, and the size of Ni-riched...