The effect of the start-up procedure upon the cyclic stress-strain behavior, surface topography and dislocation sub-structures of polycrystalline material was studied by using scanning and transmission electron microscopy. Two different loading ramps were used which resulted in differing magnitudes of unidirectional strain, saturation plastic strain-range, density of surface slip markings, persistent slip band formation, and differing dislocation sub-structures. In the case of one ramp, the persistent slip bands nucleated preferentially at tensile deformation bands. Microscopic models were developed on the basis of transmission electron microscopic observations. Stabilization of the vein structure occurred via secondary dislocations gliding on primary planes. Destabilization of the veins, and the nucleation of persistent slip bands, could be caused by local internal stresses which arose from secondary dislocations gliding on secondary planes. This model yielded a consistent explanation for the formation of coarse slip-lines, a correlation between slip lines and persistent slip bands, a larger density of such bands and lower cyclic hardening in some cases, the occurrence of differing cyclic hardening behaviors for differing ramp lengths, and a maximum near to the persistent slip band nucleation stress.

H.P.Karnthaler, S.Kong, B.Mingler, R.Stickler, B.Weiss: Acta Metallurgica et Materialia, 1995, 43[8], 3017-26