Investigation of the microstructure and mechanical properties of FV520B stainless steel joints brazed using a CoNiCuMn multi-component alloy

To further enhance the comprehensive performance of brazed FV520B impeller blades, this study, guided by the concept of high-entropy alloying, developed a CoNiCuMn multi-component brazing filler metal. The effects of different brazing temperatures on the microstructural evolution, elemental diffusion and mechanical properties of the brazed joints were compre­hensively studied. The results indicate that the CoNiCuMn multi-component filler metal exhibited good bonding at all tested brazing temperatures, and the brazed joints were free from defects such as cracks and pores. The microstructure in the weld zone of the joints brazed at 1200 °C and 1250 °C achieved a high-entropy composition. When the brazing temperature was increased to 1300 °C, excessive diffusion of Fe element into the weld zone disrupted the high-entropy composition, resulting in a microstructure consisting of an Fe-based solid solution. At the brazing temperature of 1200 °C, the precipitation of a Cu–Ni phase in the weld zone inhibited grain growth, refined the grain structure, and consequently enhanced the strength of the brazed joint. As the brazing temperature increased, the precipitated Cu–Ni phase in the weld zone gradually diminished, weakening its beneficial effect on the properties. The maximum shear strength of the brazed joint was 229 MPa when brazed at 1200 °C.