Mechanical properties and deformation behaviours of submicron-sized Cu–Al single crystals

Tuning stacking fault energy (SFE) via alloying provides a robust protocol to manipulate deformation mechanism and consequently the mechanical properties of metallic materials. Mechanical behaviours of materials with small dimensions have received significant attention due to the increasing requirement of the miniaturisation and the development of micro-electromechanical smart systems. However, the effects of SFE on the size-dependent plasticity have rarely been studied. Herein, we employed quantitative in-situ compression transmission electron microscopy to systematically uncover the size effects on the mechanical properties and deformation mechanisms of submicron-sized Cu–Al single-crystalline pillars. The SFE was controlled by adjusting the Al content in Cu–Al alloys. Our research found that the sample size effect on strength apparently decreased with reducing SFE or increasing Al content. A theoretical model was proposed to capture the size dependency of the strength by incorporating the effect of SFE on dislocation sources. Size-dependent work-hardening behaviour and deformation mechanism were comprehensively explored, which were controlled by the interplay among sample size, SFE and alloying induced short-range ordering. Lastly, a deformation map was constructed for submicron-sized Cu–Al alloys, which is directly correlated with mechanical properties.