Climb dissociation of superlattice dislocations and the strength anomaly in β-brass

Abstract

Abstract Dislocation structures and mechanical properties of β-brass single crystals have been studied in detail. The core structures of the 〈111〉 superlattice dislocations in β-brass deformed between 77 and 463 K were investigated by means of the weak-beam imaging technique. The 〈111〉 superlattice dislocations are climb dissociated when they are introduced by deformation above 200 K and the extent of climb increases with increasing deformation temperature. In order to distinguish contributions to plastic flow of edge dislocations from those of screw dislocations, thin crystals with two different geometries, in which the deformation is carried mainly by edge dislocations (E-type crystals) or screw dislocations (S-type crystals) respectively, have been deformed between 77 and 523 K. The yield stress of E-type crystals is much higher than that of S-type crystals above room temperature. The effect of orientation and pre-straining temperature on the strength anomaly obtained in the subsequent deformation tests at high temperatures has also been studied. Based on these observations, a mechanism for the strength anomaly in β-brass is proposed.