Microstructure and mechanical properties of K480 nickel-based superalloy brazed joint

K480 nickel-based superalloy was brazed with Ni-Nb-W-Co-Cr-Al nickel-based filler. Microstructure of the joints and effect of brazing holding time on microstructure were studied with scanning electron microscopy. The high temperature tensile properties were studied with tensile testing machine. A dense and complete brazed joint was formed with metallurgical reaction between nickel-based filler and superalloy powder at 1 220 °C for 15 min. The joint was mainly composed of high melting point alloy powder, γ+γ′ eutectic phase, boride phase with Si, and Nb-rich Ni3Si phase. (Nb,Ti)C and (Mo,W,Cr,Ni)3B2 phases were formed by diffusion of Nb and W elements to the base metal. With the extension of brazing holding time, the alloy powder particles grew up, and the total amount of brittle compounds in the joint decreased. However, the boride phase with Si gradually changed from block or strip to (Mo,W,Cr,Ni)3B2 skeleton structure. When holding time exceeded 1 h, large-size cavity defects appeared in the joints. When holding time was 15 min, the best properties of joint could be obtained, and the tensile strength at 980 ℃ was 585 MPa, which was more than 90% that of the base metal. When holding time exceeded 1 h, high temperature tensile properties of the brazed joints showed a downward trend, which was mainly due to the appearance of (Mo,W,Cr,Ni)3B2 skeleton structure and large-size cavity defects.Highlights: (1) K480 alloy was brazed with Ni-Nb-W-Co-Cr-Al nickel-based filler metal, whose high temperature tensile strength could reach 90% that of the base metal.(2) Prolonging brazing holding time was conducive to the diffusion of elements in the joint, which could reduce brittle compound phase and improve performance of the joint.(3) For the large gap brazing process with Ni-Nb-W-Co-Cr-Al nickel-based filler, with the increase of holding time, the total amount of brittle compound phase in the joint decreased, and the boride phase with Si gradually changed from block and strip to (Mo,W,Cr,Ni)3B2 skeleton structure, which had a worse impact on performance of the joint. When holding time exceeded 1 h, large-sized cavity defects even appeared in the joint, and performance of the joint showed a declining trend.