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In this study, the plasticity behavior of an AZ31B magnesium alloy subjected to short-duration (100 μs), high-frequency (120–800 Hz) pulsed current was investigated using tensile tests. The key finding is that the effect of pulsed current on plastic deformation goes beyond the Joule heating effect. In our experiments, the frequency was adjusted to maintain a constant effective current density and, thus, the same Joule heating effect. A comparison with continuous current having the same Joule heating effect was made as well. It was observed that when the peak current density is higher than a critical value, a higher peak current density will yield a more significant reduction in flow stress even though the thermal heating effect is the same. This critical current density decreases with the increase in the effective current density. Pulsed current with a higher peak current density can more effectively reduce the dislocation density through electric-induced annealing, induce more severe grain rotation, and, thus, lower the resistance for dislocations to pass through barriers like grain boundaries, resulting in a more significant flow stress reduction. X-ray diffraction characterizations were also conducted for the deformed specimen to show that a higher peak current density induces more severe grain rotation and, thus, more effectively decreases dislocation density. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to study the frictional behavior of graphene. It is found that the friction between a diamond tip and graphene decreases with increasing number of graphene layers. This behavior is also affected by the graphene sheet size; specifically, the effect of the number of layers on friction becomes significant only when the modeled graphene sheets exceed a critical length. We further show that the frictional behavior can be directly correlated to the height of near-contact wrinkles that resist sliding. These observations are rationalized in terms of the ability of multiple sheets to act as a single material as they resist wrinkle formation. [ABSTRACT FROM AUTHOR]