Chemical order/disorder phase transitions in NiCoFeAlTiB multi-principal element alloys: A Monte Carlo analysis

Multi-principal element solid solutions are prone to develop local chemical inhomogeneities, e.g., chemical order/clustering and/or compositional undulation. To model the structural transformation of complex multi-principal element alloys (MPEAs), a flexible pairwise-energy model is developed. Lattice Monte Carlo (MC) simulations, coupled with discrete atomic pair energies, are extensively conducted to investigate thermodynamic atomic structures of NiCoFe-based alloys. The results of simulations are consistent with reported experimental data and provide insights into phase decomposition, species segregation/preferences, and chemical order/disorder. The simulations also offer microscopic views of atomic segregation by incorporating small atom (e.g., Boron) at grain boundaries. By employing Cahn’s wetting theory, the observed phase transformation processes, ranging from perfect to partial/pre-wetting, are explained and validated thermodynamically by the model. The current approach has the potential to be extended to a variety of MPEA systems with constant lattices.