Nanocrystalline materials have been attracting rapidly increasing interest in the last decade and have the potential of revolutionizing traditional materials design in many applications via atomic-level structural control to tailor the engineering properties. In addition to interesting physical properties in the areas of magnetics, catalysis, and optics, this class of materials exhibits a broad range of fascinating mechanical behavior. Superplastic deformation behavior has been observed at significantly lower temperatures in ceramic nanoscale powders. Ultrahigh hardnesses have been measured in nanoscale superlattices made of metallic and ceramic materials. Tensile and compressive strengths in nearly all material systems studied have shown anomalously high values at the nanometer-length scale.

The development of nanostructured materials is now raising the question of how the different properties change as the microstructural scale is reduced to nanometer dimensions. Among potential applications of nanostructured materials, the design to achieve optimum mechanical properties is a common concern. Traditionally the mechanical strength σ of crystalline materials is believed to be largely controlled by the grain size d, often in the manner described by the Hall-Petch relationship σ= kd−1/2 +σ0. As the structural scale reduces to the nanometer range, the limits to the conventional descriptions of yielding need to be established, and new mechanisms that may come into play at these very small dimensions need to be explored and studied. In addition the intrinsically high interface-to-volume ratio of the nanostructured materials may enhance interface-driven processes to extend the strain to failure and plasticity. These potential gains will have profound technological impact in a wide range of engineering applications, and need to be validated and exploited.