ABSTRACT
One of the most notable properties of nanostructured materials is their extremely high hardness and strength, which makes them attractive for structural applications where strength and weight are critical. The widespread enthusiasm for research on the mechanical behavior of nanocrystalline materials is driven by both scientific curiosity and this technological promise. A key tenant for nanoscale research involves the search for new physics arising from length-scale effects that result in unusual properties at the nanoscale. In the case of mechanical behavior, it would be interesting to know if dislocation activity, the dominant deformation mode in coarse-grained ductile materials, still plays an important role as grain sizes approach tens of nanometers, and if novel deformation modes that cannot be activated in coarse-grained materials emerge. From the application point of view, with the increasing number of applications of nanocrystalline materials in microelectromechanical systems (MEMS), micro/nano devices, precise cutting tools, surface coating, and high-performance structural applications, it is important to develop a detailed understanding of the intrinsic mechanical behavior and underlying deformation mechanisms that govern the mechanical response of nanocrystalline materials. This fundamental knowledge is needed to be able to model and predict mechanical performance and to design for the use of nanocrystalline materials in devices. In this chapter, we present a brief overview of our current understanding of deformation behavior, focusing on experimental findings that are accepted by the community as representative of the general deformation response of nanocrystalline metals, and on the underlying deformation mechanisms that have been proposed to explain these results. The picture is far from complete, and we have made an effort to highlight outstanding questions and critical issues that appear to warrant further investigation.
