Cryomilled nanostructured materials: Processing and properties

Nanostructured (i.e., 1–200 nm grain size) and ultrafine-grained (i.e., 200–500 nm grain size) metals are of interest, not only as a result of their unusual combinations of physical and mechanical properties, but also because they can be readily synthesized using well-developed synthesis techniques. Cryomilling, i.e., mechanical alloying in liquid nitrogen, is representative of a class of synthesis techniques that attain the nanostructured state via severe plastic deformation. In this overview, published data related to cryomilled materials are reviewed and discussed with particular emphasis on cryomilling mechanisms; microstructure and thermal stability of cryomilled powders; primary consolidation and secondary processing methods; microstructural evolution during consolidation; and mechanical response of consolidated materials. The deformation behavior and the underlying mechanisms that govern cryomilled materials are discussed and compared with those of nanostructured materials processed via other methods, in an effort to shed light into the fundamental behavior of ultrafine-grained and nanostructured materials.