Figure 8 (a) Final strain distribution as compared with the (b) Schmid factor for {111}<110> slip. Blue and green grains are those that have low Schmid factors for octahedral slip CONCLUSIONS The ambient temperature data shows there are strain heterogeneities observed in this alloy at the grain size level that cannot be directly linked to Schmid factors. There appears to be a relationship between the extreme strain values and proximity to grain boundaries and grain boundary triple points, this is consistent with another ambient temperature study on a similar nickel based superalloy [17]. Future work includes set-up of the resistance heating equipment for conducting high temperature experiments, 600-800°C. For these high temperature conditions slip by {111} <112> partial dislocations should be predominate. This study also indicates that the lithography pattern created was too dense to facilitate imaging at low enough magnifications to have a statistically significant representation of grain orientations and grain boundary triple points. At lower magnifications the discreet pattern was not longer recognizable and interference fringes are produced. The lithography pattern needs to be optimized to allow for SEM images at desired magnifications and testing temperatures. In addition, we would like to develop procedures for depositing hafnia speckle patterns, in order to have a pattern that is compatible with high-temperature testing between 600 and 800°C, as other studies have shown that gold and platinum speckles exhibit transient behavior on the surface of Ni-based superalloys at temperatures above 500°C [18]. Another needed modification is the placement of special markers (numbers, different shapes, etc) to help the researcher manually overlay the strain images with EBSD grain images taken after testing. Also, a series of lines parallel and/or perpendicular to the tensile axis needs to be added if grain boundary sliding contributions are to be examined [19]. Following calibration of the equipment for high temperature testing using conventional nickel based superalloys, the system will be utilized to probe heterogeneities in hybrid nickel based superalloys. Testing will be conducted on two different hybrid alloys, a dual heat treatment turbine disc and a bonded turbine disc [3, 4]. The dual heat treatment disc has a very shallow microstructural gradient, while the bonded disc has a very sharp microstructural gradient. This full field in-situ technique should help facilitate better understanding and in turn modeling of deformation behavior in these gradients in microstructures. ACKNOWLEDGEMENTS This work is funded by the Air Force Research Laboratory (AFRL) STW-21 program. The author would like to thank Aimee Bross of the Ohio State University Nanotechnology Center for her invaluable assistance with development on the lithography techniques for the speckle patterning. The support received from the Materials & Manufacturing Directorate of the Air Force Research Laboratory has been instrumental for the development of the in-situ tensile frame. 47
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