Point defects in binary laves phase alloys

Point defects in the binary C15 NbCr2 and NbCo2, and C14 NbFe2 systems on both sides of stoichiometry were studied by bulb; density and X-ray lattice parameter measurements. It was found that the vacancy concentrations in these systems after quenching from 1000 degrees C are essentially zero. The constitutional defects on both sides of stoichiometry for these systems were found to be of the anti-site type in comparison with model predictions. Thermal vacancies exhibiting a maximum at the stoichiometric composition were observed in NbCr2 Laves phase alloys after quenching from 1400 degrees C. However, there are essentially no thermal vacancies in NbFe2 alloys after quenching from 1300 degrees C. Anti-site hardening was found on both sides of stoichiometry for all the three Laves phase systems studied. Neither the anti-site defects nor the thermal vacancies affect the fracture toughness of the Laves phases significantly. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd.! All rights reserved.