| Abstract Scope |
There are now many examples—both in the scientific literature and deployed in engineering products—in which grain boundary segregation has been used to stabilize a nanocrystalline structure. Such stabilization is necessary for the long-term use of nanocrystalline metals, and it opens interesting questions in processing science as well. Most notably, grain boundary segregation competes energetically with bulk second phase formation, so processing pathways that are sufficiently far from equilibrium to avoid bulk phases are often desirable. However, processes that are very far from equilibrium often also suppress grain boundary segregation, which is counter to the goal of stabilizing the nanostructure. In some cases subsequent thermal treatments can evoke the grain boundary segregated state in a nanocrystalline material. In every case the balance between “driven” or “ballistic” driving forces (those that drive away from equilibrium) with diffusional processes (that favor equilibrium) is a pivotal issue. This talk will review the interplay of alloying effects, grain boundary segregation, and non-equilibrium processing in the fabrication of nanocrystalline materials. |