A specialty class of alloys known as tungsten heavy alloys (WHAs) possess extremely desirable qualities for adoption in nuclear fusion reactors. Their high temperature stability, improvement in fracture toughness over other brittle candidates, and promising performance in initial experimental trials have demonstrated their utility, and recent advancements have been made in understanding and applying these multiphase materials systems. To that end, Pacific Northwest National Laboratory in collaboration with Virginia Tech have sought to understand and tailor the structure and properties of these materials to optimize them for service in fusion reactor interiors; thereby improving the robustness, efficiency, and longevity of structural materials selected for service in an extremely hostile environment. In this analysis of material viability, a multiscale investigation of the connections between structure-property relationships in these multiphase composite microstructures has been undertaken, employing advanced characterization techniques to bridge the macro, micro, and nanoscales for the purpose of generating a framework for the understanding of the ductile phase toughening effect in these systems. This analysis has yielded evidence suggesting the effectiveness of WHA microstructures in the simultaneous expression of high strength and toughness owes to the intimately bonded nature of the boundary which exists between the dissimilar phases in these bi-phase microstructures. Analytical techniques have been employed to provide added dimensionality to traditional materials characterization techniques, providing the first three-dimensional microstructure reconstructions exhibiting the effects of thermomechanical processing on these dual-phase microstructures, and the first time-resolved approach to the observation of WHA deformation through in-situ uniaxial tension testing. The contributions of purposefully introduced microstructural anisotropy and its contribution to texturing and boundary conformations is discussed, and an emphasis has been placed on the study of the interface between the dissimilar phases and its role in the overall expression of ductile phase toughening. In short, this collective work utilizes multiscale and multidimensional characterization techniques in the in-depth analysis and discussion of WHA systems to connect their structure to the properties which make them excellent candidates for fusion reactor systems. / Doctor of Philosophy / In the ongoing effort to realize nuclear fusion for commercial energy generation, there are numerous hurdles which must be overcome. A primary issue in the creation of these reactors is the implementation of materials which interface with the superheated plasma in the reactor interior, called plasma facing materials and components (PFMCs). These PFMCs must be able to withstand environmental conditions which will melt, irradiate, embrittle, and fracture a majority of common structural materials. Therefore these materials must exhibit unparalleled robustness in the form of high thermal and irradiation resistance. One class of alloys which is currently being considered for this purpose is tungsten heavy alloys (WHAs). These materials have exhibited excellent viability in early-stage experimental trials, and have necessarily become the subject of extended examination as PFMC candidates. In a joint collaboration between Pacific Northwest National Laboratory and Virginia Tech, these materials have been subjected to rigorous experimental testing and analysis to determine what underlying physics are responsible for their excellent properties. Advanced analytical techniques have been applied to observe the connections which exist between the atomic structure of boundaries and have been connected to the expression of observable properties on the macroscale. This work has provided the first available data on the full three-dimensional approach to the study of WHAs as well as the first dynamic observation of how the materials deform, leading to the conclusion that the two-phase composite-like structure of these alloys owe their combination of strength and ductility to the strong bond which exists between the two phases. This information on how material structure influences properties can be used to improve alloy design and produce even more effective WHA materials going forward.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110440 |
| Date | 03 June 2022 |
| Creators | Haag IV, James Vincent |
| Contributors | Materials Science and Engineering, Murayama, Mitsuhiro, Robertson, Jennifer E., Bai, Xianming, Edward, Danny J., Reynolds, William T. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/vnd.openxmlformats-officedocument.wordprocessingml.document |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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