Comparison of the core–shell and mechanical mixing of the Ni–Cr-P-Cu composite filler metal

The Cu@BNi-7 core–shell structure composite filler metal prepared by the electroless plating method and the mechanical mixing BNi-7 + 5%Cu composite filler metal is applied for the improvement of the uniform distribution of the element Cu in the brazing seam. The microstructure and the mechanical properties of the joint brazed with Inconel 718 using the two types of composite filler metals are investigated. Compare to the joint brazed using the mechanical mixing filler metal, the core–shell structure composite filler metal is beneficial for the formation of the Ni(Cu, Fe, Cr)_ss solid solution, which is evenly distributed in the joint. The brazing temperature influences the element diffusion and results in the formation of the incomplete diffused granular structure with large numbers in the joint when the temperature is lower. The nanoindentation and the shear strength test of the joints are conducted, and the large-area distributed Ni(Cu, Fe, Cr)_ss solid solution could release the residual stress and make the crack expand around the solid solution. Consequently, the core–shell structure Cu@BNi-7 composite filler metal shows better performance. The maximum shear strength of the brazed joint using Cu@BNi-7 composite filler metal is 220 MPa, which is 53% higher than the brazed joint using the BNi-7 + 5%Cu composite filler metal.