Effect of Ni interlayer on the microstructure and mechanical properties of vacuum-brazed C92900/12Cr2Ni4A dissimilar bimetallic joints: Experimental and simulation perspectives

ABSTRACT: For copper–steel bimetallic components, such as plunger pumps and bushings used in the automotive and aerospace industries, issues including mismatched thermal expansion coefficients, interfacial intermetallic compounds, and low welding strength often occur during the joining process. In this study, a Ni layer was electroplated on the alloy steel, and C92900 tin bronze/12Cr2Ni4A alloy steel dissimilar bimetallic joints were successfully prepared by vacuum brazing. The microstructure, interfacial characteristics, mechanical properties, and potential bonding mechanism of the brazed joints were investigated through a combination of experiments and simulations. The results showed that the Ni interlayer effectively inhibited grain-boundary penetration cracks and segregation on the steel side of the copper/steel bimetallic joint. First-principles calculations confirmed that Ni had a smaller weakening effect on Fe grain boundaries, enabling Fe–Fe metallic bonds to maintain high fracture strain and stress. Finite element simulation results indicated that the addition of the Ni interlayer reduced the interfacial residual stress by 27.74%, made the stress distribution more uniform, and inhibited crack initiation. Meanwhile, the average shear strength of the joint was increased by 154.9% after the addition of the Ni interlayer, and the fracture exhibited typical ductile fracture characteristics. In addition, the mechanism by which the Ni interlayer regulated the interfacial reaction during copper/steel dissimilar bimetallic brazing was clarified. This study provides an experimental basis for the preparation of bimetallic materials composed of wear-resistant copper alloys and high-strength steel and expands their application scope.