New insights into the partitioning behavior of Mo in nickel-based superalloys and its effect on microstructure using CALPHAD-assisted phase field modeling

Elemental partitioning behaviors are critical in determining the high-temperature capabilities of superalloys. In multi-component superalloys, these behaviors are influenced by the competition among elements. This study examines the effects of Cr concentration on elemental distribution behaviors and γ′ evolution in Ni–10Al–4Mo–xCr superalloys using CALPHAD-informed phase field modeling. Our simulations show that Mo's preference shifts from γ′ precipitates to γ matrix as Cr concentration increases. This shift results from the competitive interactions between Mo and Cr atoms at the corner sites of Ni₃Al, reducing Mo's solubility in γ′ precipitates. Further analysis reveals that with increasing Cr concentration, more Mo is displaced by Cr at the B sites of γ′-A₃B. Additionally, the Mo content in γ′ precipitate decreases with rising Cr content, resulting in an abnormal rise in the γ′ volume fraction based on Mo mass balance. Moreover, γ′ coarsening rate initially rises and then falls with increasing Cr concentration in an inverted “V” shape, a change attributable to variations in the γ matrix supersaturation. These findings provide new insights into Mo distribution in nickel-based superalloys and offer guidance for designing superalloys with improved microstructural stability.