Digital image correlation of laser-ablated platinum nanoparticles on the surface of a polycrystalline metal (nickel-based superalloy Rene´88DT) was used to obtain the local strain behavior from an in-situ scanning electron microscope tensile experiment at room temperature. By fusing this information with crystallographic orientations from electron backscatter diffraction (EBSD), a subsequent analysis shows that the average maximum shear strain tends to increase with increasing Schmid factor. Additionally, the range of the extreme values for the maximum shear strain also increases closer to the grain boundary, signifying that grain boundaries and triple junctions accumulate plasticity at strains just beyond yield in polycrystalline Rene´88DT. In-situ experiments illuminating microstructure-property relationships of this ilk may be important for understanding damage nucleation in polycrystalline metals at high temperatures.

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Variability in the fatigue behavior of two common nickel-base superalloys is discussed, with emphasis given to understanding the behavior of short fatigue cracks. René88DT and IN100 are the materials of interest and serve important roles in many turbine engine systems. Multiple specimens of each material were tested under low cycle fatigue (LCF) conditions at elevated temperature. Two IN100 specimens that exhibited significant difference in cycles to failure and three René88DT specimens having dissimilar short fatigue crack growth rates were interrogated to determine the reasons for these variations. This paper will discuss the microstructure adjacent to the initiation sites in these specimens and its role in affecting the observed disparate crack growth behavior. Additionally, an image correlation technique, used to evaluate the development of strain concentrations in a René88DT tensile specimen at room temperature, is described. The utility of image correlation for identifying microstructural 'hot spots' (i.e. initiation sites) in concert with LCF testing is considered.

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