The dislocation structures of 30%Zn single crystals which had been cyclically deformed to plastic strains of 3.8 x 10-5 to 6.4 x 10-3 were studied by means of transmission electron microscopy in order to understand cyclic deformation mechanisms operating in the material. It was shown that the fatigue dislocation structures had 2 basic configurations, depending upon the strain amplitude which was applied. At low strain amplitudes (less than 3 x 10-4), the dislocation structure was characterized by dislocation segments and multipoles. This structure was very similar to that formed during stage-I tensile deformation of the same material. At high strain amplitudes (above 3.0 x 10-4), the dislocation structure was dominated by planar dislocation loops and tangles. In this case, a small number of dislocation multipoles and a zig-zag structure were also detected. Secondary slips were found to be activated, starting from a very low strain amplitude (3.8 x 10-5). This behavior was attributed to the lower stress for dislocation generation as compared with the cyclic flow stresses, and to heterogeneous deformation at low strain amplitudes which resulted in a weak local latent hardening effect. Cyclic deformation mechanisms at low and high strain amplitudes were analyzed in terms of the motion of dislocation multipoles, and the dislocation reactions between primary and secondary slip systems. The critical strain amplitude for transition between the deformation mechanisms was also theoretically determined to be 3 x 10-4, in good agreement with results on the cyclic deformation response and the features of the dislocation structures.

Cyclic Deformation Behavior of Cu-30%Zn Single Crystals Oriented for Single Slip II. Dislocation Structures. B.Gong, Z.Wang, Z.G.Wang: Acta Materialia, 1999, 47[1], 317-24