PROPERTIES OF VACUUM BRAZED Si₃N₄/STEEL JOINT USING ACTIVE BRAZING FILLER METAL

The influence of active element Ti in Ag-Cu-Ti filler metal on wettability and joint strength has been studied. Filler metal with 3%Ti achieved good results in direct brazing of silicon nitride to steel. For the sake of improving joint strength, different interlayers have been synthetically investigated. Experiments showed that interlayer of low yield strength material may reduce the residual stress in the joint and increase Joint strength more effectively than that of interlayer of low coefficient of expansion material. Stress magnitude and distribution was calculated and analysed by thermal elastoplastic FEM and compared with experiment results. By means of SEM, EDX, and EPMA analyses the joining mechanism was investigated. Active element Ti in the brazing alloy diffused into Si₃N₄ and chemical reactions occured in ceramic-metal interface, certain chemical compounds consist of N and Ti produced.