Numerical design methods have the potential to accelerate the development of superalloys significantly. Through thermodynamic modeling by CALPHAD calculations, material properties can be predicted with reasonable accuracy, allowing the fast screening of a composition space for alloys with desirable properties.

Often, alloy properties in the thermodynamic equilibrium are calculated to predict an alloy’s performance under operating conditions. However, the manufacturability must also be considered to ensure that the designed alloys are processable. To this end, the chemical segregation that occurs during casting – still the most important manufacturing process for high-performance single-crystalline superalloys – can be calculated by Scheil solidification.

In this contribution, we present a universally applicable alloy design approach that couples CALPHAD calculations to predict thermo-physical properties as well as the creep strength with multicriteria optimization methods. Thereby, the vast space of possible compositions can be scanned efficiently by optimizing compositions toward, e.g., high creep strength and low density since low-performing composition regions are excluded early from the calculations.

CoNi-base superalloys are an upcoming alternative to Ni-base superalloys. While they are not yet employed in commercial applications, they have received increasing research interest in recent years. We apply the above design method to develop novel CoNi-base alloys toward i) maximum creep resistance and ii) minimum segregation in the as-cast state.

CoNi-base superalloys are prone to forming the brittle β-NiAl phase, which may degrade the ductility and fatigue properties. While a high γʹ phase fraction and, correspondingly, a high flow and creep strength were obtained in case i), the detrimental β phase was found in the interdendritic regions. Optimizing the compositions toward a minimum β phase fraction by incorporating Scheil solidification yielded extremely homogeneous alloys that, however, exhibited inferior mechanical properties. Despite the lower creep strength, such nearly segregation-free alloys may be attractive for forging or additive manufacturing.