Dislocation debris in aluminium fatigued at 78°K

Abstract

THE predominant characteristic of the defect structure revealed by transmission electron microscopy studies of metals fatigued by reversed stresses is the presence of an excessively large number of dislocation loops or debris ranging in size from a few thousand angstroms to the resolution limit of the technique employed (25–50 A). Singular dislocation lines are heavily jogged and usually possess many sharp cusps. Dislocation loops which are elongated generally lie along the projection of (112) in f.c.c. metals and the density of cyclic stress generated loops usually approaches, and often exceeds, the loop density in quenched metals. Dislocation [debris] has been observed in fatigued polycrystalline copper, nickel and gold (Segall et aE. 1961), aluminum (Wilson and Forsyth 1959, Segall and Partridge 1959, Grosskreutz and Waldow 1963), alpha-brass (Segall and Finney 1963), magnesium and niobium (Segall 1963), stainless steel (Hirsch et al. 1959), and copper single crystals (Segall et al. 1961). All of these results have been obtained from initially annealed metals fatigued by reversed stresses at room temperature.