Influence of grain misorientation on grain growth in nanocrystalline metals

It is well known that the grain size of a material controls its properties, including mechanical strength, electrical conduction, and corrosion resistance. Typically, a fine grain size is desirable, since it allows for these properties to be increased. Nanocrystalline materials have been engineered in order to maximize the benefits associated with this fine grain size. Unfortunately, the high density of grain boundaries for a given volume of the material leads to an increase in the excess energy that is associated with grain boundaries. This excess energy can act as a driving force for grain growth, which causes these nanocrystalline structures to be unstable, with this grain growth often times being detrimental to the material properties. This research investigated the influence of grain boundary mobility and the applied driving force on grain growth in nanocrystalline metal films by focusing on the role grain boundary misorientation plays in regulating grain growth. The was be accomplished by completing two types of studies: (i) Annealing sputter-deposited thin films to study mobility in a case where the driving force is assumed to be dominated by grain boundary curvature and (ii) Mechanically indenting thin films with different microstructural features while submerged in liquid nitrogen. In terms of the latter study, the mobility was expected to be extremely low due to the cryogenic temperatures. Both sets of films were then characterized using precession-enhanced diffraction-based orientation analysis in the transmission electron microscope to quantify the evolution in grain size, grain morphology, and in the grain-to-grain misorientation. (Published By University of Alabama Libraries