Twisting of pre-twinned α-Fe nanowires: from mild to wild avalanche dynamics

International audienceWe studied the torsion behavior of a-Fe nanowires seeded with twin boundaries (TBs) using moleculardynamics simulations. Twisting the wire generates topological defects in the twin walls, namely kinks insidethe twin walls for small twist angles, and junctions between kinks for large twist angles. During twisting thekink motion is jerky and uncorrelated at small twist angles. The probability density function (PDF) of jerksstrength follows approximately a Gaussian distribution, indicating a mild deformation mode. The kinkdynamics transforms from mild to wild at larger twist angles when complex twin patterns with a high densityof junctions are generated. The collective motion of kinks now shows avalanche behavior with theenergy being power-law distributed. The wildness, which measures the proportion of strain energy relaxedthrough such avalanches, is correlated with the junction density, and controlled by the external length scale(wire diameter) as well as an internal length scale (twin boundary spacing). Good strain-stress recoverabilityis achieved when unloading the wire before the formation of complex twin patterns. We correlate the evolutionof twin patterns with a statistical analysis of jerk dynamics, which identifies the unique mechanicalproperties governed by twin boundary motion in nanowires