An alloy selection and processing framework for nanocrystalline materials

Abstract

Nanocrystalline materials have a unique set of properties due to their nanometer-scale grain size. To harness these properties, grain growth in these materials needs to be suppressed, particularly in order to process bulk nanocrystalline components and to use them reliably. Alloying the material with the right elements has the potential to produce remarkably stable nanocrystalline states, particularly if the nanocrystalline state is thermodynamically stable against grain growth. This thesis builds upon previous models for selecting alloy combinations that lead to thermodynamic stability against grain growth, by developing frameworks that extend to negative enthalpy of mixing systems and ordered grain boundary complexions. These models are used to develop a generalized stability criterion based on bulk thermodynamic parameters, which can be used to select alloy systems that are formally stable against grain growth. A robust statistical mechanics framework is developed for reliable thermodynamic observations using Monte Carlo simulations to produce free energy diagrams and phase diagrams for stable nanocrystalline alloys.