A new form of pseudo-elasticity in small-scale nanotwinned gold

Molecular dynamics simulations are used to show a new type of pseudo-elasticity and shape memory effects in small-scale nanotwinned metals. Nanotwinned Au thin-films and nanowires are found to achieve full recovery of up to 20% tensile and −6.25% compressive strains upon reverse loading when the twin boundaries make a special angle of 70.53°from the principal axis. This phenomenon results in superelastic recoverable strains up to 5 times larger than the useful range of deformation that can be induced in some advanced bulk shape-memory-alloys and small-scale ceramics, with a tensile strength above 1 GPa. The pseudo-elastic behavior stems from a unique interplay between deformation twinning and slip in grains composed of non-{1 1 1} free surfaces and discontinued twin boundary migration in those exposing only {1 1 1} free surfaces. This finding could open up new opportunities for small-scale nanotwinned metals as advanced materials for vibration damping and mechanical energy storage applications.