Microstructure and corrosion behavior of Si3N4/316L joints brazed with Ag-Cu/Ag/Mo/Ag/Ag-Cu-Ti multilayer filler

ABSTRACT In this work, a novel Mo/Ag composite interlayer was designed for joining of Si3N4 to 316L stainless steel. The effect of Mo/Ag composite interlayer on the microstructure evolution and corrosion behavior of the joint was studied. It was verified that the addition of Ag layer in the 316L/Ag-Cu/Ag/Mo/Ag/Ag-Cu-Ti/Si3N4 joint could eliminate Cu-rich phase and relieve residual stress of the joint. When inserting the thickness of 0.3 mm Ag into the joint, the bulk Cu-rich phase is almost divided into tiny particles and distributed in Ag-based solid solution. By the observation of scanning electron microscope after performing the potentiodynamic polarization test, the resistance corrosion of the seam in the joint was enhanced due to the formation of Ag-based solid solution, but had a slight unfavorable effect on that of the 316L substrate and Mo. The corrosion current density of the joint was 1.97 μA/cm2. Large Cu-rich phase was eliminated by inserting Ag layer into the seam. The corrosion mechanism was changed from the pitting of Cu to the uniform corrosion of 316L and Mo, which can improve the stability of joint. In addition, it was found that the 316L substrate was subjected to residual tensile stress by FEM analysis. This residual tensile stress may have a negative effect on corrosion resistance of the 316L substrate of the joint.