Excess Vacancies Induced by Disorder-Order Phase Transformation in Ni₃Fe

Abstract

The order-disorder transformation and lattice defects in Ni₃Fe have been studied by positron lifetime measurements. Anomalous vacancy-generation during ordering transformation, which was originally found on the ordering process of super-cooled disordered Cu₃Au, has been confirmed on the ordering transformation of Ni₃Fe. Disordered fcc solid solution of Ni₃Fe was brought to room temperature by quenching the specimen from temperatures above the order-disorder transformation point T_C. The ordering process into L1₂ structure was promoted by heating the sample isochronally or isothermally. It has been found that vacancies are generated in both heating processes, i.e., during the ordering process of super-cooled disordered Ni₃Fe. Generated vacancies are not stable up to T_C and annealed out at temperatures below T_C.