Effects of Brazing Temperature on Microstructure and High-Temperature Strength of Joints Using a Novel Fourth-Generation Nickel-Based Single Crystal Superalloy

A novel fourth-generation nickel-based single crystal superalloy was bonded by vacuum brazing at 1230 degrees C, 1260 degrees C and 1290 degrees C for 60 min using a new type of Co-based filler alloy. The effects of the brazing temperature on the microstructure and mechanical properties of the brazed joint were investigated. The brazed joint was mainly composed of the non-isothermal solidification zone (M3B2 type-boride, CrB boride, Ni3B boride and MC carbide), isothermal solidification zone (gamma and gamma' Phase) and base metal. With the increase of brazing temperature, the volume fraction of borides and gamma' phase in the center of the joint decreased and increased, respectively. The high-temperature tensile test results show that the tensile strength of the joints was improved with increasing brazing temperature, and the maximum tensile strength of the joint was 766 MPa after brazing at 1290 degrees C for 60 min. Fracture observation shows that the fracture modes of the joints were the same, which belongs to the typical quasi cleavage fracture. The element distribution in the joint was homogenized to a certain extent at 1290 degrees C. The segregation of Si and Ru was found, but they were still dissolved in the gamma solid solution. The experimental results help to better understand the microstructure characteristics of the novel fourth-generation nickel-based single crystal superalloy and provide guidance for further optimizing the process parameters of the brazed joint.