Effect of brazing gap on microstructures and tensile properties of K465 superalloy joint

To improve the high-temperature performance of brazed repair joints for service cracks in K465 superalloy blades, a novel Co-Cr-Ni-W-Al-Ti-Ta-B brazing filler metal is employed to braze K465 superalloy with gap widths of 0.05 mm and 0.2 mm under the condition of 1220 ℃/15 min. The microstructure, elemental distribution, and high-temperature tensile properties of two joints are analyzed. The results show that the brazing filler metal exhibits excellent metallurgical compatibility with the base metal, with significant interdiffusion of elements occurring during the brazing process. The joint with a 0.05 mm gap consists of a γ/γ′ dual phase matrix with dispersed γ′ phase, as well as compound phases including (W, Cr)B, Ti-rich boride, and NiAl. For the joint with a 0.2 mm gap, the introduction of superalloy powder as a filler material results in dispersed and refined compound phases, while the phase types remain unchanged. The high-temperature tensile properties at 1000 ℃ of two joints are comparable: the tensile strength of the 0.05 mm and 0.2 mm gap joint is 383 MPa and 396 MPa, respectively, reaching approximately 70% of the K465 base metal. Due to the favorable metallurgical compatibility between the brazing filler metal and the base metal, as well as the strengthening effect of the B2-ordered NiAl phase, two kinds of brazed joints exhibit excellent high-temperature tensile properties.