Dislocation structures in fatigued critical and conjugate double-slip-oriented copper single crystals

Abstract

The dislocation structures induced by cyclic deformation of [017] critical and, [ 1 ̄ 12] , [ 1 ̄ 17] conjugate double-slip-oriented Cu single crystals were investigated using transmission electron microscopy (TEM) and electron channeling contrast (ECC) technique in scanning electron microscopy (SEM). It was found that the crystallographic orientation has a notable effect on the dislocation structures in cyclically saturated critical and (or) conjugate double-slip-oriented Cu single crystals. Such an orientation dependence of dislocation structure can account well for the corresponding orientation dependence of the plateau behavior in the cyclic stress–strain (CSS) curve. In cyclic deformation of the [ 1 ̄ 12] crystal, the formation of persistent slip band (PSB) ladder structures is a general phenomenon; PSBs occur even under the low strain amplitude, which is below the plateau region in the CSS curve. The experimental result above indicates that there is not a complete one-to-one correlation between the formation of PSBs and the presence of a plateau region of the CSS curve. In certain double-slip oriented Cu single crystals investigated here, the actual size of microstructures is in fact, found to be changeable with varying strain amplitude, which is one of the main reasons for the disappearance of a clear plateau in the CSS curve of these crystals. For example, the decrease in the width of vein channels with increasing strain amplitude and the absence of PSB ladder structure are the major reason for non-existence of a clear plateau region in the CSS curve of the [ 1 ̄ 17] crystal, while the joint effects of the scale change of the labyrinth structure and the formation of PSB ladder-like structures lead to the occurrence of only a narrow quasi-plateau in the CSS curve of the [017] crystal.