Enhancing mechanical properties of IN718 through promoted intragranular γ'' phase precipitation during solidification by coupling hypergravity with rapid cooling

Abstract

The simultaneous enhancement of strength and ductility of casting superalloy remains a challenge. In this work, a novel method combining hypergravity and rapid cooling was developed to optimize the solidification microstructure, to further improve the mechanical properties of nickel-based superalloy. Under conditions of 1000 G hypergravity and rapid cooling, dense IN718 with uniform fine grains was prepared. The process also promoted dislocation nucleation, refined Laves phase to 2 μm, and promoted intragranular γ′′ phase precipitation. Through the synergistic effects of grain refinement, precipitation strengthening, and dislocation strengthening, coupled with refined Laves phase and activation of slip systems, the IN718 exhibited a superior combination of ultimate tensile strength and elongation of 1115.5 $\pm$ 12 MPa and 24.2$\pm$ 0.8 %, respectively. The combined effects of hypergravity and rapid cooling generated high pressure and thermal stress in the molten metal, forming dislocation networks that served as preferential nucleation sites for intragranular precipitation. Moreover, hypergravity increased the nucleation driving force of the γ'' phase, thereby promoting intragranular γ'' precipitation. Due to the competitive precipitation effect, the precipitation of Laves phase was restricted, resulting in fine and dispersed Laves particles that no longer serve as stress concentrators. The fine-grained microstructures with high pre-existing dislocations ensured slip system activation and efficient strain accommodation, resulting in the delayed onset of necking and improved elongation. This work provides a new perspective for fabricating high-performance as-cast IN718. Moreover, the results of microstructure-property relationship under hypergravity may improve the understanding of the solidification behavior and plastic deformation of IN718 and guide a further upgrading.