Nanostructured Metals Reveal Their Secret Strengthening Mechanisms
It is well known that metals are hardened by deformation and soften by annealing. How about nanostructured metals? Can we reply on conventional metal-working lore? In a paper in Science (Huang et al., Science, 312 (2006) 249), Xiaoxu Huang and colleagues at the Riso National Laboratory, Denmark and Osaka University, Japan have found that nanostructured aluminum behaves in contrast to the conventional theories; annealing makes it stronger and tougher whereas deformation (cold working) gains ductility with a trade-off of lowering the strength. The structural scale affects fundamental mechanisms of dislocation-dislocation and dislocation-interface reactions. This finding may stimulate the applied mechanics community to study the fundamental strengthening mechanisms of nanostructured materials from both experimental and theoretical approaches.