| Abstract Scope |
A new multi-principal element alloy (MPEA) was developed as a filler material for vacuum brazing of Inconel 718 (IN718) at 1000°C, aiming to balance melting temperature, metallurgical compatibility and mechanical properties. High-throughput simulations using thermodynamic and other multi-physics principles were used to down-select a candidate FCC alloy composition with a liquidus of 952°C. The MPEA alloy was cold rolled to 300 μm thick foils to vacuum braze IN718 coupons at 1000°C for 15 and 90 minutes, respectively. Postmortem metallurgical characterizations performed on the as-brazed coupons observed acceptable wetting and viscosity of the MPEA filler as indicated by low amounts of porosity in the braze and fillets on both end of the IN718 substrate material. Consistent with the predicted MPEA solidification behavior, no terminal eutectic phases were observed in the microstructure. However, secondary phases were observed populating grain boundaries along both the filler-substrate interface and the braze centerline. These phases were characterized using energy-dispersive spectroscopy (EDS) results in tandem with thermodynamic and kinetic simulations. The EDS analysis detected elevated concentrations of Nb, Mo, Cr, and Fe within the secondary phase particles, a group of elements known to together form topologically closed packed (TCP) phases within Ni-base alloys. Microhardness testing of the 15-minute braze measured average hardness values of 210 HV at the centerline, 265 HV at the filler-substrate interface, and 293 HV within the IN718 base material. The formation of secondary phases necessitates the future tuning of the MPEA compositions for enhanced metallurgical compatibility and phase stability with IN718 brazing. |