Thickness-Dependent Mechanical Behavior of 〈111〉-Oriented Cu Single Crystals

To explore the dependence of mechanical behavior on the crystal size, the [1¯11]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ [\bar{1}11] $$\end{document}-oriented Cu single crystal was selected as a target material, and the variations of tensile and tension–tension fatigue behavior with the crystal specimen thickness (t) were systematically investigated. The results show that, with the decrease of t, the tensile yield strength continuously increases, especially as t < 0.4 mm, which is related to an enhanced role of surfaces in affecting dislocation activity; ultimate tensile strength first increases and elongation has almost no change as t is decreased from 2.0 to 1.0 mm, but with continuously decreasing t, both of them decrease; as t = 0.1 mm, the slight increases in ultimate tensile strength and elongation occur. With the decrease of t, the corresponding dislocation structures are evolved from the cell walls into the cells and tangles; meanwhile, the density of slip bands (SBs) decreases. Moreover, the obvious concentrated SB regions and notable cross-slip traces are clearly observed in thicker crystals. The fatigue life has no notable change as t = 2.0 and 1.0 mm, but increases subsequently with decreasing t due to the decrease in the plastic strain accumulation together with an enhanced interaction between the dislocations in the surface zone.