The influence of site preference on the elastic properties of FCC_CoCrFeNi multi-principal element alloy

The influence of the existing site preference of the constituent elements on the sublattice on elastic properties is rarely explored in multi-principal element alloys (MPEAs). In this work, in order to explore the influence of the site preference of constituent atoms on the thermodynamic properties and elastic properties, the ordered configurations based on the previously predicted site occupying fractions (SOFs) and the disordered configuration based on a special quasi-random structure (SQS) were established, and the thermodynamic properties and elastic properties were predicted using the quasi-harmonic approximation (QHA) method first. It was found that the site preferring behaviors of atoms on the sublattices will not only improve the stability of the structure but will also lead to bigger elastic properties than its ideal disordered structure. Although the prediction of the temperature-dependent elastic properties using the QHA method shortens the time costs by only considering the effects of thermal expansion, it ignores the significant effect of lattice vibration on elastic properties at high temperatures. In order to explore the influence of lattice vibration on the temperature-dependent elastic properties further, the elastic properties of the ordered FCC_CoCrFeNi MPEA were predicted using the ab initio molecular dynamics (AIMD) method at several selective temperatures. The results show that except for the elastic constant C12 and bulk modulus, the lattice vibration reduces other elastic properties on the basis of thermal expansion. The predicted temperature-dependent shear and Young's moduli agree well with the limited experimental literature data. Thus, the temperature-dependent elastic properties can be reasonably predicted using the AIMD method based on site preference. The predicted polycrystalline elastic moduli B, G, and E of FCC_CoCrFeNi MPEA at 973 K are 146.68, 53.79, and 143.78 GPa, respectively.