Plastic-Strain-Amplitude Dependence of Dislocation Structures in Cyclically Deformed 〈112〉-Oriented Cu-7 at. pct Al Alloy Single Crystals

Dislocation structures in \( [\overline{1} 12] \) Cu-7 at. pct Al alloy single crystals cyclically deformed at different plastic strain amplitudes were investigated by transmission electron microscope (TEM) and compared with the results of \( [\overline{1} 12] \) Cu single crystals. It is found that the plastic strain amplitude γ _pl has an obvious effect on the slip deformation mode, and consequently on the cyclic hardening behavior of \( [\overline{1} 12] \) Cu-7 at. pct Al alloy single crystals with an intermediate stacking fault energy. For instance, a high slip planarity (i.e., only formation of planar-slip bands) contributes to the occurrence of a gentle cyclic hardening with a much lower saturation stress at a low γ _pl of 4.5 × 10⁻⁴. A mixed planar/wavy-slip mode (e.g., persistent Lüder’s bands/wall-like microstructures) at an intermediate γ _pl of 2.2 × 10⁻³ causes an obvious cyclic hardening up to a comparable saturation stress to that for the \( [\overline{1} 12] \) Cu single crystal. In contrast, the deformation mode is dominated by wavy slip (e.g., ill-defined dislocation cells and walls) at the highest γ _pl of 7.2 × 10⁻³, causing that its cyclic hardening curve is quite similar to that for the \( [\overline{1} 12] \) Cu single crystal; in this case, a slightly higher saturation stress level than that for the Cu single crystal is reached due to the additional solid solution strengthening.