Nonequilibrium solid phases studied by thermodynamic calculation, molecular dynamics simulation, ab initio calculation and ion-beam manipulation in an immiscible Au–Co system at equilibrium

For an immiscible Au–Co system at equilibrium, a calculated Gibbs free energy diagram suggests that the composition range favoring metallic glass formation is approximately 22–83 at.% Co and that the nonequilibrium crystalline phases at both Co75Au25 and Co25Au75 prefer to be in a face-centred cubic (fcc) structure. Based on a proven realistic n-body Au–Co potential, molecular dynamics simulations predict that the metallic glass-forming range of the Au–Co system is 18–88 at.% Co. Employing the Vienna ab initio simulation package, the first principles calculations indicate that the L12 (fcc) and D019 (hexagonal close packed (hcp)) structures could relatively be stable for both nonequilibrium crystalline AuCo3 and Au3Co phases, whereas the Bh (hcp) structure could be stable for the AuCo phase. Interestingly, ion beam manipulation confirms that a uniform Au42Co58 amorphous phase is indeed obtained and that some nonequilibrium fcc-type and hcp-type Au–Co phases can also be formed, the lattice constants of which are in agreement with those derived from the ab initio calculations.