Effects of twinning configurations on the mechanical performance of small-scale FCC metallic materials

The increasing demand for high-performance miniaturised devices has sparked extensive interest in enhancing the mechanical properties of micro- and nano-sized materials. Deformation twinning, a fundamental mechanism known for enabling strength–ductility synergy in bulk materials, has emerged as a potential strengthening strategy for small-scale systems. However, the relationship between twinning behaviour and the mechanical performance of small-sized materials remains poorly understood. This study employs quantitative in-situ tensile straining transmission electron microscopy combined with comprehensive microstructural characterisation to investigate the effects of three critical aspects of twinning behaviour on mechanical performance in small-sized face-centred cubic metallic materials: twin density, twin–twin interactions, and modes of twin boundary motion. The findings reveal that: (1) increasing twin density improves ductility of small-sized samples, but this effect hinges on the absence of stress-concentration sites; (2) twin–twin interactions, caused by their intersecting behaviour, induce stress concentration and promote necking, resulting in a distinct fracture mechanism compared to single-system twinning; and (3) twin-boundary sliding, in contrast to twin-boundary migration, leads to highly localised deformation, pronounced softening, and significantly reduced ductility. These results provide important insights into the structural design of small-sized single-crystalline materials where twinning-induced plasticity is a dominant deformation mechanism.