Element interactions and local structure in molten NiRe and NiAlRe alloys: Implications for the aggregation and partition of Re

The element interactions and local structure in molten NiRe and NiAlRe alloys have been investigated via ab initio molecular dynamics (AIMD) simulations. It has been found that the self-interaction of Re evolves from repulsion to attraction with increased Re content, i.e., Re experiences a transition from ordering to clustering, and the trend is further enhanced by Al alloying to NiRe alloys. The finding implies that the aggregation of Re, which is believed to be the main mechanism of Re in improving the mechanical properties of Ni-based single crystal superalloys, may be a kind of positive-feedback process. Our simulation plus experimental results also reveal that the addition of Al enlarges the partition coefficient of Re, which obviously will promote the formation of freckle defect. Both chemical short-range order (CSRO) and relative compactness of solute-centered coordination shell compared with solvent-centered one, obtained in AIMD simulations, are successful in judging the variation of the partition coefficient of Re with added Al. The two quantities may be also useful in revealing the partitioning behavior of elements in complex multi-component alloys whose experimental interaction parameters are lacking.