Microstructure and properties of conventional and hybrid joints of IN718 brazed with VZ2177

Abstract

Brazing hybrid joints of additively manufactured and conventionally produced components made of IN718 opens new application possibilities for additive manufacturing processes, such as PBF-LB/M, in industrial production processes. The combination of hybrid structures enables cost-effective production of large-volume parts with complex features. In this work, the differences between hybrid and conventional joints are analysed, due to the different microstructure of additive manufactured IN718 compared to bulk material. The differences in the microstructures lead to different diffusion paths of the elements from the molten braze alloy along the grain boundaries and to different wetting behaviors. This has a significant effect on the microstructure and the mechanical properties of the joints. To investigate the effect of the microstructure of PBF-LB/M base materials on the brazing of IN718 with the braze alloy VZ2177, vacuum brazing with varying dwell time has been employed to manufacture joints of the bulk material and hybrid joints, consisting of additively manufactured and bulk IN718. Due to the phosphorus in the filler metal, brittle phases in the center of the brazing zone have formed in both joint types. With increasing brazing, the width of the brazing area grew. In the hybrid joint, a strong formation of IMC phases could be observed at the PBF-LB/M side of the joint leading to a higher hardness, which was more pronounced at longer brazing times. The increase in hardness was accompanied with a crack formation that was located near the PBF-LB/M-side only in those hybrid joints with long brazing time and occurred most probably due to stress relief during cooling.