Finite temperature clustering/ordering tendencies in alloys from first-principles

A solid solution, on quenching, undergoes ordering and/or clustering processes leading to the formation (precipitation) of an ordered phase. These ordering and/or clustering processes may occur either sequentially or simultaneously resulting in a definite course of transformation mechanism. These inherent tendencies, although may be affected by the rate of quenching, are primarily dictated by the magnitude and sign of interatomic potentials or effective pair interactions (EPI). These EPIs can be determined from first-principles and can be incorporated into a mean-field based free energy model (e.g., Static Concentration Wave (SCW) model or Cluster Variation Method (CVM) to arrive the mechanism of a give phase transformation. This will be illustrated by taking a Ni-Mo alloy, where the ground state phase stability and EPIs have been calculated using the density functional theory based calculations and then SCW free energy model has been used to arrive at the thermodynamic ordering and clustering tendencies and mechanism of transformation. Further, these calculational results will be compared with the experimentally (mainly TEM) observed transformation path. (author)