Third-order elastic constants and anharmonic properties of three fcc high-entropy alloys from first-principles

Abstract

Third-order elastic constants (TOECs) are very important for understanding the nonlinear mechanical response of materials and evaluating the anharmonicity of crystal lattices. Here, we are concerned with investigating the six independent TOECs and related anharmonic properties of three face-centered cubic (fcc) high-entropy alloys (HEAs), namely CrFeCoNi, CrMnFeCoNi, and Cr10Mn40Fe40Co10, using density-functional simulations. To benchmark computational accuracy, three ab initio codes are used to obtain the complete set of TOECs for fcc Ni. For the HEAs, we observe that the TOECs C123 and C456 are positive, and C123 is particularly large. The Cauchy relations for the TOECs are partially satisfied for the three studied HEAs. With the help of the derived TOECs, the average TOECs for an isotropic polycrystal are estimated. Using the obtained TOECs, we reveal the pressure derivatives of the effective second-order elastic constants and polycrystalline moduli as well as derive the nonlinearity constant δ. The obtained pressure derivative of bulk modulus agrees very well with the available experimental data for CrMnFeCoNi. For the three considered HEAs, δ along high-symmetry directions orders as δ[011]>δ[111]>δ[100].