K417G alloy finds extensive application in the fabrication of aero-engine turbine blades. To tackle damage, such as cracks that emerge after prolonged service, brazing is a commonly adopted repair method. In this research, two gap sizes, namely 0.05 mm and 0.2 mm, are deliberately designed to mimic cracks of varying widths in the K417G alloy. Vacuum brazing experiments are carried out using BCo-1 cobalt-based filler metal at 1160 ℃ with different holding times. The microstructure and interfacial evolution of the joints are thoroughly analyzed via scanning electron microscopy, and their high-temperature tensile properties are tested on universal testing machine. The results reveal that the BCo-1 filler metal can establish a high-quality metallurgical bond with the K417G alloy. No defects, including pores or unbonded area, are detected in the joint area. The joint phases primarily comprise γ + γ′ phases, Cr-Mo-rich boride phase, and silicide phases. As the holding time is extended, the morphology of the compound phases in the 0.05 mm narrow-gap joint undergoes significant changes, and their content exhibits a trend of initially increasing and then decreasing. In the 0.2 mm wide-gap joint, the superalloy powder particles and compound phases gradually coarsen. The holding time has a relatively minor impact on the high-temperature performance of the 0.05 mm narrow-gap joint, which demonstrates tensile strength of 298 MPa at 950 ℃. In contrast, an extended holding time leads to deterioration in the performance of the 0.2 mm wide-gap joint. The optimal properties, with tensile strength of 460 MPa at 950 ℃, are achieved under the parameter set of 1160 ℃ for 15 min holding time.

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.