Influence of Boron on the Microstructural Evolution, Impact and Creep Properties Stability of IN718 Superalloy During...

The impact of boron (B) on the microstructure evolution and stabilization of mechanical properties in the IN718 superalloy during aging at 680 °C for 3000 h is investigated. The results indicated that B had negligible effects on grain size and the intragranular γ″ phase growth. In contrast, it effectively suppressed the precipitation and growth of the δ phase during long-term aging, which is attributed to grain boundary segregation of B that retards the diffusion of alloying elements. Adding B could improve the impact toughness and stability of the creep properties of the alloy. The primary mechanism is that the addition of B enhances grain boundary cohesion and suppresses the coarsening of the δ phase, while the beneficial effect of B on mechanical stability becomes negligible during the later stages of aging, as the severe coarsening of grain boundary phases offsets the enhanced grain boundary cohesion resulting from B segregation. Furthermore, the presence of slip bands was observed in the creep deformation mechanism of B-added alloys, which is likely attributable to B promoting dislocation slip at grain boundaries. With prolonged aging time, the dominant creep deformation mechanism in the B-modified alloy shifts from being primarily governed by twinning and dislocation slip to a mechanism involving twinning, stacking fault shearing γ″ phase, and dislocation slip.