Effects of surface pretreatment and heat treatment on vacuum localized induction heating diffusion welded joints of single crystal/powder superalloys

Objective The aim is to achieve high-quality welding of dissimilar materials between single crystal/powder superalloys. Methods Effects of surface pretreatment of FGH96 and DD6 material on performance of vacuum localized induction heating diffusion welded joints of single crystal/powder superalloys were investigated through mechanical property testing, scanning electron microscopy, and energy-dispersive spectroscopy, as well as on microstructure of base metal. Influence of compatible heat treatment on performance of joints were also examined. Results Diffusion welding of single crystal and powder superalloys was successfully achieved by vacuum localized induction heating diffusion welding combined with a nickel plating process. Due to the relatively short holding time in vacuum localized induction heating diffusion welding, nickel plating layer did not fully diffuse into base metal, adversely affecting performance of joints. Laser-cleaned joints exhibited high tensile strength at 760 ℃ and excellent creep rupture property but showed some instability. The applied vacuum localized induction heating diffusion welding did not induce recrystallization in the near-weld zone of DD6 single-crystal material. The compatible heat treatment process had minimal impact on performance of joints. Conclusion The weld and near-weld zone of diffusion-welded joints produced by vacuum localized induction heating diffusion welding demonstrates that welding thermal cycle has a very limited effect on microstructure of base metal, and no recrystallization occurs in single crystal DD6. After post-weld heat treatment at 760 ℃ for 8 h, diffusion-welded joints exhibits stable room-temperature tensile strength, high-temperature tensile strength at 760 ℃ and creep rupture property at 750 ℃, meeting performance requirements of weld.