First-principles interatomic potentials for transition-metal aluminides. II. Application to Al-Co and Al-Ni phase diagrams

Abstract

Aluminum-rich intermetallic compounds and alloys are important for their technological applications and scientifically interesting for their complex structures such as quasicrystals. Detailed knowledge of interatomic interactions can help explain structural and mechanical properties of these systems. The first paper of this series [Phys. Rev. B 56, 7905 (1997)] derived first-principles interatomic potentials for alloys of aluminum with first row transition metals from generalized pseudopotential theory (GPT). This paper assesses the ability of those potentials to reproduce and elucidate the binary alloy phase diagrams of ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}$ and ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}$. When the full theory is taken into account, we successfully reproduce the phase diagrams up to $x=0.3.$ While many of the general features of the phase diagrams can be obtained with $x=0$ GPT pair potentials alone, the volume and composition dependence of the total energy become important by $x=0.25.$ In addition, for certain complex structures, we introduce partial aluminum occupancy and demonstrate its importance. At high transition-metal concentration $xg0.25,$ we must further include three- and four-body transition-metal interactions to account for the stability of ${\mathrm{Al}}_{5}{\mathrm{Co}}_{2}$ in the ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}$ phase diagram.