Thickness-Dependent Mechanical Behavior of ⟨111⟩-Oriented Cu Single Crystals

To explore the dependence of mechanical behavior on the crystal size, the [1 over bar 11]-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.