Influence of mixed brazing filler metal on microstructure and mechanical properties of wide gap brazed joints of nickel-based single crystal superalloy

Objective A method combining a new type of nickel-based brazing filler metal with high-melting-point alloy powder that matched composition of base material was used to create mixed brazing filler metal. Effect of particle size and proportion of added high-melting-point alloy powder on microstructure and mechanical properties of brazed joints was explored. Methods Precipitated phase, element distribution and microstructure of brazed joints were analyzed by scanning electron microscope, and hardness and creep life of brazed joints were tested. Results It revealed that brazed joints mainly consisted of filler alloy zone (FAZ), interface bonding zone (IBZ) and diffusion affected zone (DAZ). FAZ predominantly comprised M₃B₂ and M₈B type borides, along with γ/γ′ phases. IBZ was composed of γ and γ′ precipitation-strengthened phases. When alloy powder particle size was 44 μm and 75 μm, defect-free brazed joints were obtained. However, pores defects formed in brazing seam when particle size reached 177 μm. Conclusion As the proportion of alloy powder increased, there was a rise in microhardness of bonding area of brazed joints. When alloy ratio was increased from 30% to 50%, creep life of brazed joints extended from 15 h to 34 h. However, further increasing proportion to 60% led to a reduction in creep life of brazed joints to 0.6 h. The results of this study provided a theoretical basis and reference value for realizing connection and repair of high-temperature hot-end components in engineering applications.