Excellent mechanical properties of micro-grain nickel-based superalloy by coupling super-gravity fields with layered solidification

A novel method combining super-gravity fields with layered solidification was proposed to optimize the solidification microstructure and mechanical properties of nickel-based superalloys. By using a simple interlayer pause strategy, this approach ensures uniform deposition and rapid solidification of each melt layer, achieving approximately 80 % improvement in grain refinement and a higher equiaxed grain fraction compared to continuous solidification. Under 500G (500 times standard gravity, g) and 10 s interlayer pause, fully micro-grain IN718 alloy was prepared. The grain refinement arises from the sequential activation of following mechanisms in each layer: (1) scouring and remelting of coarse dendrites and enhanced heterogeneous nucleation at interlayer regions; (2) “crystal rain” during initial solidification; (3) enhanced dendritic remelting and nucleation and a (4) thermo-mechanical synergistic dendrite fragmentation mechanism. Further microstructural analysis reveals reduced Laves phases, promoted γ’’ phases precipitation, and a high-density of low-angle grain boundaries (LAGBs). Grain refinement and LAGB evolution enhance strain compatibility and dislocation transmission, thereby improving strength and ductility. These synergistic effects result in excellent tensile strength (1127.8 $\pm$ 21 MPa) and elongation (22.3 $\pm$ 1.1 %). This work provides a simple yet effective approach and valuable insights for the preparation of micro-grain as-cast nickel-based superalloys with exceptional mechanical properties.