Strain rate effects on the mechanical response in multi- and single-crystalline Cu micropillars: Grain boundary effects

Homogeneous interfaces like grain boundaries (GBs) play an important role in crystalline plasticity as they often serve as obstacles for dislocation motion, as well as dislocation sources/sinks. In the present work, microcompression experiments were carefully performed to uncover the effects of GBs on mechanical response of submicron-sized Cu multi-crystalline (MC) micropillars (containing several grains) by comparing with the single-crystalline (SC) samples at different strain rates. It is clearly demonstrated that, while the SC pillars suffer from intermittent and stochastic strain bursts, introducing GBs appropriately into the SC pillars can dramatically improve the smoothness of their plastic flow and enhance their strength and strain rate sensitivity (SRS), especially at greater strain rates. The presence of GBs can significantly suppress the strain bursts observed in the MC/SC Cu micropillars, which is simply quantified by considering the size and strain rate related-capacity of dislocation absorption by the GBs. These findings provide deep insights into the controllability of plastic deformation of small volume materials. The possible transition of strengthening mechanisms with plastic strain is also highlighted.