High Temperature Furnace Testing of Structural Materials for Advanced Terrestrial and Space Reactors
- Author
- Searight, William T.
- Published
- [University Park, Pennsylvania] : Pennsylvania State University, 2023.
- Physical Description
- 1 electronic document
- Additional Creators
- Motta, A. T. (Arthur T.)
Access Online
- etda.libraries.psu.edu , Connect to this object online.
- Graduate Program
- Restrictions on Access
- Open Access.
- Summary
- Advanced reactors, both fission and fusion, have much more demanding environments than light-water reactors in terms of high temperature/heat flux, radiation flux and corrosion. To enable these reactor systems, advanced alloys and composite materials must be developed to survive in these conditions for lengthy exposure times, particularly reactors in remote locations (including outer space). While there has been significant study done on candidate materials, additional experimental data on environmental degradation is needed to qualify materials for long-term service with infrequent maintenance. This work focuses on high-temperature testing of advanced reactor structural material candidate samples, informed by those identified from a literature survey. Structural material selection for advanced reactor systems is limited to iron and nickel-based alloys, ceramics & composites, and refractory metal alloys. Thin film coated steels, plain & coated Highly Oriented Pyrolytic Graphite, and the refractory alloy TZM were held in a backfilled tube furnace facility at holding temperatures of ~1500 K for 40 hours (along with heating and cooling periods) as an assessment of environmental survivability. Gas mixtures of hydrogen, helium and argon were backfilled into the furnace to provide relevant environmental conditions. Electron microscopy, X-ray Diffraction and Optical Profilometry were used to characterize the sample surfaces, and mechanical indentation to assess thermomechanical properties. Thermogravimetric Analysis (TGA) was used to verify the decomposition temperature of pyrolytic graphite used, and hydrogen retention post-exposure was assessed for coated samples using Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The TZM survived all three environments, while increasing in mechanical hardness due to increased oxide and carbide phases embrittling the base alloy. The HOPG samples decomposed in the He and 5% H2 furnace runs, which upon TGA investigation was found to have onset temperatures around 800 °C, which is slightly higher than seen in pyrolytic graphite TGA results seen in other studies. The HOPG decomposition in the furnace environment was likely accelerated by the presence of oxygen; the tube furnace was reported to have cracked sometime during the course of experiments, likely causing significant additional oxidation. The coated steels were largely unable to prevent embrittlement of their stainless steel substrates. The TiN and ZrN coatings were the best surviving coatings, but the nitrogen disappeared as the metals oxidized completely. The formation of oxide phases from the base steels was a consistent feature in all coated steel sample furnace runs, with structures like those expected from a surface deposition process. ToF-SIMS results showed the TiN coated steel retaining an order of magnitude less hydrogen post-5% H2 furnace exposure, with TiO2 coated steel retention about the same as the unexposed sample. To improve the high temperature protection of base substrates, coating thicknesses should be increased/layered with other ceramic materials with synergistic effects, and coatings should completely surround the substrate material to provide no easily permeable pathways for corrosion/embrittlement to take place. The resulting experimental data from these test campaigns will aid in the development of larger, prototypical assemblies for testing long-term service in extreme environments with combined effects (corrosion, high heat flux, high dose rate). Due to the large costs and lead times associated with fabrication of larger material samples and adaption of test facilities to accommodate these samples, subscale testing of components can reduce risk and expedite the down selection of the best suited materials for advanced reactor systems.
- Other Subject(s)
- Genre(s)
- Dissertation Note
- Ph.D. Pennsylvania State University 2023.
- Reproduction Note
- Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 30551173)
- Technical Details
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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