A high-speed creep process mediated by rapid dislocation absorption was found in the nanoindentation creep test on nanocrystalline Cu. The creep strain and creep strain rate depend strongly on the loading strain rate and are far higher than those predicted by the models of Coble creep and thermally activated grain boundary sliding. Our analysis revealed that grain boundary dislocation sources can be activated and emitted dislocations from grain boundaries can be stored effectively at a high loading strain rate, but cannot at a low loading strain rate. The observed high-speed creep process is mediated mainly by the rapid absorptions of the stored dislocations and the dislocations newly nucleated during the holding period. An implication of our experimental finding is that dislocation structure in nanocrystalline metals is highly unstable and dislocation activity can proceed after loading and lead to a significant post-loading plasticity.

The cold rolling strain effect on the tensile properties of a high nitrogen alloyed austenitic steel was systemically investigated. Quasi-static tensile experiments were performed on the samples with different cold rolling strain. The material possessed good balance between strength and ductility in the entire rolling strain range. Mechanical property and microstructure of the nitrogen alloyed austenitic steel were greatly affected by cold rolling strain. With the increase in cold rolling strain, the strength increased sharply but the ductility declined. That is related to the gradual changes of microstructure induced by the cold rolling process. The cold rolling process leads to substantial microstructural change, from the appearance of slip bands and twins at low cold rolling strain; the microtwins formation at intermediate cold rolling strain and followed by sequences of their bending, breaking and disappearance; and finally to the formation of drossy twins at the high cold rolling strain.

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Nanocrystalline Cu films were prepared by electric brush-plating. Microstructure characterization by X-diffraction analysis and transmission electron microscope reveals that the average grain size of the nanocrystalline Cu films increases from 24.4 to 150.5 nm with decreases in current density and concentration of Cu ions in bath. A number of growth twins are observed at lower current density and concentration of Cu ions. The results reveal that the nanocrystalline Cu films with wider ranges of grain size and/or high content of growth twins can be prepared by brush-plating technique with suitable controls of current density and concentration of Cu ions in bath.