Numerical tools have gained increasing importance in alloy development, as they allow an efficient selection of candidate alloys in the vast possible composition space. Developing a new alloy can be treated as a multi-criteria optimization problem. The design goals are alloy properties typically described by CALPHAD calculations in thermodynamic equilibrium.

We attempted to develop a low-density CoNi-base superalloy computationally using an in-house developed alloy design tool. The resulting alloy has high strength at 800 °C but contains large β-NiAl precipitates in the interdendritic region. These are detrimental to ductility and fatigue properties due to their high brittleness.

CALPHAD predicts the interdendritic formation of β phase only through non-equilibrium calculation of the solidification with Scheil modeling. Therefore, an efficient Scheil calculation scheme was integrated into the design tool to model the fraction of β phase forming during solidification.

A second design iteration was run where the solid solution strengthening and the γ′ solvus temperature were maximized. Additionally, the formation of β-NiAl was minimized. Two alloys were chosen for experimental investigation. The tensile strength and creep strength were lower than in state-of-the-art Co-base superalloys. However, an extremely homogeneous composition for a multinary superalloy was found in the as-cast state, as confirmed by electron microprobe mappings. Additionally, no detrimental β-NiAl was present in the alloys. The resulting alloys could be candidates for casting large components since little homogenization heat treatment is required. Non-equilibrium models thus open new possibilities for the development of superalloys.