Dislocation loops in quenched aluminium

Abstract Electron transmission micrographs of polycrystalline aluminium quenched from ∼ 600°c into iced brine show that the specimens contain many dislocation loops with diameters of the order of several hundred Å. Some of the loops are hoxagonal in shape, and occur on (111) planes, and have a Burgers vector ½ 110 not in the plane of the loop. The loops are thought to be producod by the collapse of discs of vacancies, and the corresponding vacancy concentration is 10−4 Some of the loops disappear, while under observation in the microscope, by a mechanism of prismatic slip. In the neighbourhood of grain boundaries there is a zone depleted of loops; similar zones are observed near dislocations, whose complex configurations suggest that climb may have taken place. The observations are discussed in relation to the problems of ‘annealing out’ of vacancies, of quench-hardening, and of the origin of the dislocation network.