Geometrical shapes of planar single‐faulted defects in quenched face‐centered cubic metals and alloys

摘要

Arguments are presented in favor of a rationalized understanding of the variety of geometrical shapes of the various polygonal single-faulted dislocation loops observed in quenched face-centered cubic (fcc) materials. By considering the minimization of the defect energy and the crystal anisotropy, the primary vacancy clusters in all these materials (at the time of collapse to form dislocation loops) are taken to be regular hexagonal in shape, with sides along the close-packed directions and lying on the close-packed {111} planes. Based on this common origin for all single-faulted loops, it is shown how factors such as the exact moment of collapse of the vacancy disk, the stacking fault energy, and the purity of the specimen can affect the subsequent development of the regular hexagons into various possible polygonal shapes during the remainder of the quench period. Direct experimental evidence is presented of the influence of impurity segregation on the shape and annealing behavior of certain faulted loops observed in quenched Al1.5 wt.% Mg. To fit the only observations of faulted loops which have been made in nickel to date into the general proposed scheme, it is suggested that the stacking fault energy of nickel is lower than the figures available in the literature, and that vacancy disks collapse at a relatively early stage of the quench for this material.