A synergistic strategy for enhanced performance of CoCrNi/GH99 brazed joints after post weld heat treatment

The brazing of CoCrNi and GH99 medium-entropy alloys is essential for producing reliable, lightweight precision components for aerospace applications. However, as-brazed joints often exhibit degraded performance due to γ′ phase coarsening and brittle boride formation. In this study, post-weld heat treatment (PWHT) was applied to CoCrNi/BNi-5a/GH99 joints to refine precipitates and homogenize the microstructure of joints. Following a comprehensive and in-depth analysis, PWHT reduced boride content and improved both microstructural uniformity and the distribution of γ′ precipitates within the brazing seam. Higher PWHT temperatures and longer aging times further decreased boride content. The fracture mode transitioned from quasi-cleavage in the as-brazed condition to ductile fracture after PWHT, with simultaneous gains in strength and plasticity. Reduced boride content lowered stress concentration in the brazing seam, while deformation twins which were formed during shearing worked synergistically with γ′ precipitates to enhance mechanical performance of joints. This work offers valuable insights into microstructure regulation and precipitation strengthening for medium-entropy alloy brazed joints, suggesting a viable route for fabricating high-performance lightweight aerospace assemblies.