Precursor Dislocation Avalanches in Small Crystals: The Irreversibility Transition

The transition from elastic to plastic deformation in crystalline metals shares both history dependence and scale-invariant avalanche behaviors with other non-equilibrium systems under external loading. Many of these other systems, however, typically exhibit purely elastic behavior only after training through repeated cyclic loading; recent studies in these other systems show power laws and scaling of the hysteresis magnitude and training time as the peak load approaches a reversible—irreversible transition (RIT). We discover here that deformation of small crystals shares these key features. Yielding and hysteresis in uniaxial compression experiments of single-crystal Cu nano- and micropillars decay under repeated cyclic loading; the amplitude and decay time diverge as the peak stress approaches the failure stress, with power laws and scaling as seen in RITs in other nonequilibrium systems. We observe that these effects become smaller as the pillars become larger, perhaps explaining why scale-invariant training effects have not been observed in macroscopic samples.