Defect structures in ZrCo2 Laves phase

Point defect structures in the C15 ZrCo2 alloys were studied by bulk densit y and X-ray lattice parameter measurements. It was found that, for the ZrCo 2 alloys quenched from 1000 degrees C, the lattice parameter increases line arly 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 t han 33.3 at.%, indicating that the solubility range of Zr in ZrCo2 on the Z r-rich side is essentially zero. The constitutional defects were found to b e of the anti-site type. Thermal vacancies exhibiting a maximum at the stoi chiometric composition were observed in the ZrCo2 Laves phase alloys after quenching from 1250 and 1000 degrees C, with higher thermal vacancies obtai ned from 1250 degrees C. The defect structures in the ZrCo2 phase may be co rrelated to the relative magnitude of formation enthalpies for anti-site an d quadruple defects in this compound. Thermal vacancy concentration at a le vel of 1% in ZrCo2 does not affect fracture toughness at room temperature. Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.