Vacancy Induced Ordering in Cu3Au

Abstract

A two-stage quenching process by which a specimen can be quenched from a temperature well above the critical temperature for long-range ordering to liquid air temperature has been designed. Provision is made for subsequent rapid transfer of the specimen to and from the liquid air bath to an annealing bath. By these means the isothermal ordering of quenched Cu₃Au wires has been investigated, using the resistivity of the wire as an indicator of the state of order, at various temperatures of anneal down to 30 °C. Even at quench rates of 60 000 deg sec^-1 appreciable ordering occurs during the quench and the short-range ordering stage is not completely preserved for observation during the subsequent anneal. The activation energy for migration of quenched-in defects appears to increase with degree of long-range order. The principal mobile defects are single vacancies and they have a migration energy of 1.0 eV in Cu₃Au in the early stages of long-range ordering. Isothermal ordering at 100 °C is found to increase with pre-quench temperature up to about 650 °C and then decrease. Trivacancies in high concentration are considered as a factor contributing to the anomalous decrease.