Microstructure and mechanical properties of K417G alloy joints using BCo-1filler with various gap widths

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.