The past decade has seen considerable progress in the development of a new generation of metals and alloys characterized by grain sizes with dimensions less than 100nm. Such structures are called “nanocrystalline” metals. Their attraction is their high strength coupled to their high sensitivity to strain rate, a property that may lead to superplasticity in certain circumstances. In addition to nanocrystalline metals, the very attractive properties of simple face centered cubic metals characterized by twins with lamella spacing less than 100nm has led to an intense interest in their properties and the synthesis of bulk forms of these metals. Such metals may be called nano-twinned metals. This talk will 1) review some of the attractive properties of such materials with a focus on the viability of these new materials for structural applications; 2) review attempts to develop quantitative models to describe the mechanical behavior of nanocrystalline and nano-twinned metals;  3) review and analyze issues such as grain instability that may place limits on the usefulness, and thereby the viability, of these materials; and 4) provide perspectives on promising future pathways for further development.

The past decade has seen considerable progress in the development of a new generation of metals and alloys characterized by grain sizes with dimensions less than 100nm. Such structures are called “nanocrystalline” metals. Their attraction is their high strength coupled to their high sensitivity to strain rate, a property that may lead to superplasticity in certain circumstances. In addition to nanocrystalline metals, the very attractive properties of simple face centered cubic metals characterized by twins with lamella spacing less than 100nm has led to an intense interest in their properties and the synthesis of bulk forms of these metals. Such metals may be called nano-twinned metals. This talk will 1) review some of the attractive properties of such materials with a focus on the viability of these new materials for structural applications; 2) review attempts to develop quantitative models to describe the mechanical behavior of nanocrystalline and nano-twinned metals;  3) review and analyze issues such as grain instability that may place limits on the usefulness, and thereby the viability, of these materials; and 4) provide perspectives on promising future pathways for further development.