Evaluation Method for Shrinkage Porosity Tendency in Superalloys Based on Residual Liquid Parameters

Shrinkage porosity in superalloy ingots significantly compromise the service reliability. Its formation is governed by coupled effects of residual liquid characteristics during terminal solidification. In this study, five typical nickel-based superalloys (GH4738, GH4151, GH4169, GH4975, and GH4065) were investigated. Pouring experiments, isothermal solidification quenching experiments, directional solidification experiments, and differential scanning calorimetry experiments were conducted to systematically characterize shrinkage porosity tendency, microstructural evolution, and elemental segregation behavior. Based on the measured solid/liquid phase compositions during terminal solidification, the characteristic parameters of residual liquid were calculated using thermodynamic methods. By combining these parameters with dendrite arm spacing and the difficult-feeding temperature range, the coupled effects on shrinkage porosity were quantified. The results show that the solid–liquid density difference and residual liquid viscosity are the dominant factors. Based on Darcy’s Law, a shrinkage porosity tendency evaluation method was developed for different superalloys, based on the solid–liquid density difference and residual liquid viscosity at the terminal solidification stage. The predicted shrinkage porosity tendencies for various superalloys are in good agreement with experimental results. This approach provides a solid theoretical basis and practical guidance for the compositional design and process optimization of multi-component superalloys.