The microstructural evolution of infrared brazed Fe3Al by BNi-2 braze alloy

The present work reports a novel approach in joining Fe3Al by infrared vacuum brazing using BNi-2 (7.0 Cr, 3.1 B, 4.5 Si, 3.0 Fe, 0.06C, and Ni balance) as the brazing filler alloy. Based on the related alloy phase diagrams and solidification theory, the species and morphology of phases in the brazed joint are extensively examined. Many transient phases, including: (Ni,Fe)3Al, (Ni,Fe)3(Si,Al), (Fe,Ni,Cr)3B and BCr, were observed after infrared brazing. With increasing the homogenization time of the brazement at 1000 °C, the stoichiometry of both (Ni,Fe)3Al and (Ni,Fe)3(Si,Al) phase has changed into (Ni,Fe)2Al and (Ni,Fe)2(Si,Al), respectively. Meanwhile, the amounts of the chromium boride and (Fe,Ni,Cr)3B phases are greatly decreased. Finally, a single-phase joint can be obtained if sufficient time is applied in homogenization treatment of the brazement.