Compositional Testing of Refractory High Entropy Allys to Provide Oxidation Resistance in Air at 1000˚C

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The refractory high entropy alloy that consists of refractory and oxidation-resistant elements is a rather new material that has shown excellent resistance to oxidation at both high temperatures and long periods of time. However, an abundance of research has not been conducted to examine all the potential chemical combinations that could provide such oxidation resistance due to the large compositional space. For this research, six high entropy alloys of the theorized chemical compositions: WTaNbTiAlCr, WTaNbTiAlCrMo, WNbAlTiCr, WTaNbAlCr, WMoNbAlTi, and WMoNbAlCr were created to examine the oxidation resistance that different sequences of elements provided. A powder metallurgy process was utilized to form all the samples. High energy planetary ball milling was used to uniformly mixed or even pre-alloyed powders, which would allow for high densification and full alloying of the powders during the spark plasma sintering process (SPS). Post sintering and polishing, as fabricated microstructure, hardness, elastic modulus, and phase identification were investigated to rule out any samples with undesirable properties. Upon review of X-ray diffraction (XRD)and scanning electron microscopy(SEM)results, the samples comprised of WTaNbTiAlCr, WNbAlTiCr, and WMoNbAlTi were the only samples to form a single densified phase. Subsequently, oxidation tests of 2, 12, and 24 hours at 1000°C were conducted on separate sample specimens. A single composition, WTaNbTiAlCr, provided the best oxidation resistance along every timeline, while the two other samples showed severe/full oxidation at 12 and 24 hours.
Thesis completed in partial fulfillment of the requirements for the Alfred University Honors Program.
Honors thesis, Refractory High Entropy Alloy, Oxidation, Glass Engineering