Dislocation loops in elastically anisotropic materials II. Formation and equilibrium shapes of vacancy loops inβ'-brass

Dislocation loops produced by β'-brass (Cu-50 at.% Zn) by quenching, and by annealing under conditions in which a controlled evaporation of zinc was occurring, have been analysed. The loop populations produced by the two procedures were found to be quite different. In the quenched and aged specimens hexagonal loops with b = ⟨111⟩ were common and loops with b = ⟨100⟩ were also observed. However, only loops with b = ⟨100⟩ were present in the zinc-loss annealed specimens. Most of the loops observed were of pure edge character. The line directions of the loop edges, ⟨112 ⟩ for the hexagonal b = ⟨ 111 ⟩ loops and ⟨010⟩ for the large b = ⟨100⟩ loops, were those for which the dislocation had the minimum line energy in the zone normal to b. The mechanisms of dislocation loop formation involved in the two types of specimen preparation are discussed.