Physics-based modeling of disk superalloys is inherently complex due to the strong influence of microstructure on properties, as well as the multitude of deformation mechanisms operative at elevated temperatures. The present contribution will focus on the effects of monotonic and cyclic loading conditions, and the underlying deformation mechanisms will be discussed. Detailed substructure analysis of deformed specimens was conducted with scanning transmission electron microscopy diffraction-contrast methods. These characterization efforts have led to a series of phase field simulations in which the interaction of various deformation modes with experimentally measured precipitate configurations can be explored and critical parameters quantified. Additionally, these results have been incorporated into a novel, dislocation-densitybased crystal plasticity model that has been calibrated based on a single crystal response, and enables the computationally efficient modeling of polycrystalline behavior.

Elevated temperature in-situ experiments, local crystallographic mapping and digital image correlation techniques have been used to gain insight into strain localization near grain boundaries in polycrystalline René-104. Samples were heat treated to create either smooth (standard) or serrated grain boundaries. Deformation experiments concluded that strain tended to localize at triple points and special boundaries in the standard microstructure, while strain had a less-pronounced correlation in the serrated microstructure. Both materials exhibited grain boundary sliding (GBS), but the standard microstructure proved to be more susceptible. Site-specific extraction of TEM foils indicated that boundaries that exhibited strain localization experienced activation of multiple slip systems, while boundaries showing GBS showed activation of only a single slip system. Based on m′ analysis, slip transmission was expected to be difficult in boundaries that exhibited strain localization while boundaries that showed sliding allowed for easy slip transmission. A volume containing a boundary that exhibited GBS was analyzed to assess boundary surface topography and indicated that the boundary was macroscopically planer with local deviations that were on the order of the secondary γ′ size.