Effect of liquid characteristics during final stage of solidification on shrinkage porosity in IN718 superalloy

• Mechanism of low shrinkage porosity tendency of IN718 is revealed • Solid-liquid density difference during terminal solidification is low (<0.05 g/cm 3 ). • Residual liquid has low viscosity and certain wettability on the dendrite. • Surface tension of residual liquid at final solidification is high (∼1403.21 mN/m). The formation of shrinkage porosity is influenced by multiple factors during solidification. This study investigates the effect of characteristics of residual liquid during final stage of solidification on the susceptibility to shrinkage porosity in IN718. The microstructural evolution and elemental segregation at final solidification stage are analyzed through pouring experiments, isothermal solidification experiments, differential scanning calorimetry, and microstructural characterization. The results indicate that IN718 exhibits severe elemental segregation during terminal solidification, with Nb, Mo, and Ti enriching in the liquid phase, which leads to a large solidification temperature range of 168°C. Thermodynamic calculations and molecular dynamics simulations were employed to investigate the residual liquid properties based on measured composition at final solidification. The results reveal that, compared to high-carbon nickel-based superalloy, the residual liquid possesses a minimal solid–liquid density difference (<0.05 g/cm 3 ), low viscosity (∼9.11 mPa·s), and high surface tension (∼1403.21 mN/m). These properties reduce volumetric shrinkage, enhance fluidity of liquid metal, and increase the critical pressure for porosity formation, thereby effectively mitigating porosity tendency despite a wide solidification interval. This work elucidates the mechanistic connections between properties of liquid phase and low porosity susceptibility in IN718, providing theoretical support for controlling casting defects in complex multi-component superalloys.