Vacuum brazing of the ultrathin-walled structure using particulate-reinforced composite filler metal: Microstructural evolution and mechanical properties

A novel Inconel 718 particulate reinforced composite filler metal was used to fabricate the Ni-based superalloy ultrathin-walled structure by vacuum brazing. The brazing process was carried out at various temperatures (1423 K, 1443 K, 1463 K). Moreover, the effects of brazing temperature and the particulate content on wettability, solidification behaviour, typical microstructural evolution and the mechanical properties of the brazed ultrathin-walled structure were investigated in detail. The results indicate that increasing reinforced particulate would result in a worse wettability and higher liquidus temperature of the composite filler metal, which is attributed to the inevitable diffusion phenomenon. The microstructure in the brazed region is mainly composed of γ-Ni solid solution, Ni₅Si₂, Cr₃Ni₅Si₂, G-phase and Ni–Si–Nb intermetallic compound. The elevated brazing temperature would cause a significant decrease in the mechanical properties of the ultrathin-walled structure. With the addition of the reinforced particulate, the mechanical properties increase obviously and the response effect of the particulate is better at higher brazing temperature. Meanwhile, the area of the Ni-based solid solution and the dispersion degree of the eutectic phase in the brazing fillet increase as the increase of the particulate content. However, the solute loss phenomenon induced by adding excessive reinforced particulate would decrease the mechanical properties. The result reveals that the tensile strength increases by 70 MPa, 103 MPa and 100 MPa, while the elongation increases by 0.8%, 5.4% and 6.8% at various brazing temperatures, comparing with the ultrathin-walled structure using the initial filler metal.