Short-Range Order Modeling in Alloys

The short and long-range orders in alloys can be assessed based on a new expression for the combinatorial factor, which is more convenient and intuitive than the traditionally used form. This novel expression can be directly applied to reproduce the results of several well-known statistical-thermodynamic models that are typically considered independent or even inconsistent. The short list of models includes Quasichemical Theory, Associated Solution Model, Surrounded Atom Model, and Cluster Site Approximation. As a result, the formalism and interpretation of these models are significantly clarified, allowing us to identify and fix several long-standing errors that might otherwise have gone unnoticed. Multicomponent generalization of these models is also greatly simplified. For systems undergoing a phase transition, an extended version of the theory provides a mechanism that allows the correct critical temperature of phase transition to be reproduced, as well as a significant increase in the accuracy of thermodynamic functions. In the case of order-disorder transformations, the new theory ensures an integrated description of short and long-range orders, which has long been considered an important and difficult problem.