Microstructure and mechanical properties of GH4169 superalloy vaccum brazed joints with AuNi brazing filler metal

Objective The aim is to study microstructure and mechanical properties of GH4169 superalloy brazed joints with AuNi brazing filler metal. Methods GH4169 superalloy was brazed with BAu82Ni950 brazing filler metal at 1 000 ℃ for 20 min, and then brazed joints were subjected to post-brazing heat treatment. Microstructure evolution of brazed joints after solid solution and two-stage aging treatment was compared and studied. Results The results show that no intermetallic compounds are formed in GH4169 brazed joints with AuNi brazing filler metal. Closed to GH4169 base material, diffusion zone of (Au,Ni) solid solution phase forms by mutual diffusion between brazing filler metal and base material. And the central part of brazed joints is mainly the residual AuNi brazing filler metal. After solid solution treatment at 980 ℃ for 15 min, diffusion zone near the interface is completely homogenized, but there is still spherical phase in the central part of brazed joints. After two-stage aging treatment, spherical phase grows up slightly and has convergence to brazed microstructure due to structure inheritance. After post-brazing heat treatment, average tensile strength of brazed joints at room temperature is increased from 829.5 MPa to 996 MPa, but tensile strength of brazed joints at 650 ℃ is decreased to less than half of that at room temperature. Conclusion Post-brazing heat treatment can effectively refine microstructure and significantly improve performance of brazed joints, while the main reason for the significant decrease in high-temperature strength of joints at 650 ℃ is attributed to insufficient high-temperature resistance of AuNi brazing filler metal.