Defect structures in ZrCo₂ Laves phase

Point defect structures in the C15 ZrCo₂ alloys were studied by bulk density and X-ray lattice parameter measurements. It was found that, for the ZrCo₂ alloys quenched from 1000°C, the lattice parameter increases linearly as the Zr content increases up to 33.3 at.% Zr. The lattice parameter of the Laves phase remains constant for the alloys with Zr content higher than 33.3 at.%, indicating that the solubility range of Zr in ZrCo₂ on the Zr-rich side is essentially zero. The constitutional defects were found to be of the anti-site type. Thermal vacancies exhibiting a maximum at the stoichiometric composition were observed in the ZrCo₂ Laves phase alloys after quenching from 1250 and 1000°C, with higher thermal vacancies obtained from 1250°C. The defect structures in the ZrCo₂ phase may be correlated to the relative magnitude of formation enthalpies for anti-site and quadruple defects in this compound. Thermal vacancy concentration at a level of 1% in ZrCo₂ does not affect fracture toughness at room temperature.