The nucleation and growth of multi-layer defects in quenched aluminium

Abstract

Edington and West have recently observed four-layer defects in quenched aluminium in which the inner vacancy loop has apparently nucleated and grown inside a perfect (unfaulted) loop. This observation precludes the vacancy–stacking-fault interaction as a cause of such inner loop formation and also suggests that the nucleation and growth of such loops in faulted regions (the inner loops in two and three-layer structures) has probably occurred for reasons other than the vacancy–stacking-fault interaction. Bullough and Hardy have recently made a discrete lattice estimate of the effective (continuum) dilatation associated with a vacancy in aluminium. This value is used to calculate the size effect and inhomogeneity interactions between a small dislocation loop and a vacancy. The results suggest that nucleation of a loop inside another small loop is possible without invoking a vacancy–stacking-fault interaction and once such nucleation has been achieved subsequent growth of the inner loop should take place at a later stage.