Study on microstructure and mechanical properties of single crystal/powder superalloy pulsed current diffusion bonded joints

Abstract To optimize the overall structure design of the aero-engine turbine disks, the study of pulsed current diffusion bonding on the second generation nickel-based single-crystal superalloy DD5 and the third generation powder superalloy FGH98 was performed, and high-quality joints were obtained after post-welding heat treatment(PWHT). The microstructure and element diffusion were analyzed by using SEM and EDS, and the microhardness and room / high temperature tensile strength were analyzed. It can be seen from the results that with the pulse current, the diffusion bonding produced a high-temperature gradient from the interface to the base metal, which protected the base metal. The precipitation phase of γ′ phase within the connection interface near the FGH98 side within 200 µm exhibits very small granular-large-size unstable petals-larger granular similar to the base metal. The γ′ phase in DD5 grows abnormally at the interface. Large granular γ′ enhancement phases occurred on the FGH98 side after heat treatment with no significant changes on the DD5 side. The microhardness of the joints is not less than 400HV; and from DD5 side to FGH98 side, the hardness decreases first and then increases. The average tensile strength of the joints at room temperature is 1078 MPa, which is 99% of the tensile strength of the base metal with low performance. The average tensile strength of joints at high temperature (650 °C) is 1089 MPa, which is equivalent to the strength of the base metal.