Grain boundary segregation, chemical ordering and stability of nanocrystalline alloys: Atomistic computer simulations in the Ni-W system

Atomistic computer simulations are used to investigate the equilibrium solute distribution and alloying energetics in nanocrystalline Ni-W. Composition and grain size-dependent trends in grain boundary segregation and chemical ordering behavior are evaluated and we find the equilibrium state to be significantly influenced by the nanostructure. The energetics of alloying are assessed through computation of the segregation, formation, and grain boundary energy, and these quantities are linked to previous thermodynamic models of nanostructure stability. With comparison to experiments, we conclude that nanocrystalline Ni-W alloys are synthesized in a metastable state. These findings have important consequences for theories of nanostructure control in general and particularly for the thermal stability of nanocrystalline Ni-W. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.