Formation of Diamond-Shaped Prismatic Loops in Quenched fcc Metals

Abstract

The concept of dissociated prismatic dislocation loops is proposed to explain the formation of diamond-shaped loops observed in several metals after quench aging. The dissociated prismatic loop is composed of parallel segments on {111} planes having a/6 <112> Burgers vectors. It is shown that diamond-shaped loops form from either a triangular or hexagonal Frank loop, and once formed can rotate on the glide cylinder to any orientation between and including {111} and {110}. Climb kinetics are qualitatively discussed in terms of the equilibrium separation of partials. The separation is approximately equal to the core radius (2|b|) in Al, but is large enough in Cu (∼12|b|) to be experimentally detected. These considerations may explain why large loops are not often observed in metals other than aluminum.