Microstructure and mechanical properties of brazed joints of GH4738/GH3536 dissimilar superalloys

Vacuum brazing of GH4738 and GH3536 Ni-based superalloys was conducted with BNi-2 brazing filler metal under the condition of 1040 ℃ × 10 min. Microstructure and phase composition of GH4738/GH3536 brazed joints were performed by scanning electron microscope and energy dispersive spectrometer, respectively. High temperature mechanical properties of brazed joints were also tested. The results indicated that interface between brazing seam and base metal was well bonded, and microstructure of brazing seam was dense. Microstructure of brazed joints consisted of three distinct microstructural zones, including diffusion-affected zone (DAZ), isothermal solidification zone (ISZ) and athermal solidification zone (ASZ). ISZ was composed of Ni-based solid solutions, while ASZ contained Ni₃Si intermetallic compounds and Cr-Mo rich borides in addition to Ni-based solid solutions. Tensile strength of brazed joints was 259 MPa at 730 ℃. Brazed joints fractured along ASZ during tensile process, and micro-cracks formed in brittle phases such as Ni₃Si and borides promoted fracture of brazed joints.