Analysis of triple dislocations in ordered phases of the type Ni8X

摘要

Superdislocations comprising a group of three (1/2)a 〈110〉 dislocations lying in a close‐packed plane have been observed in ordered face‐centered‐tetragonal Ni8Ta and Ni8Nb alloys. The antiphase boundary (APB) energies of the areas between the dislocations have been evaluated for Ni8Ta in terms of the first‐ and higher‐order nearest‐neighbor atom pairs associated with the introduction of the dislocations in the ordered material. Values for the pair interaction have been calculated by employing a polar model for the ordering and a long‐range oscillatory atomic pair interaction energy. The results indicate that higher than first nearest‐neighbor interactions account for approximately 40% of the total ordering energy. The critical temperature of Ni8Ta has been estimated on the basis of Cowley''s ordering theory and the calculated values of the pair interaction energies. The theoretical value for the critical temperature is within 12% of the value that was determined by experiment.