Development of reduced activation high entropy alloy composites for fusion plasma facing applications = 핵융합 플라즈마 대면재용 저방사화 고엔트로피 합금 복합재 개발

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dc.contributor.advisorRyu, Ho Jin-
dc.contributor.authorWaseem, Owais Ahmed-
dc.description학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2019.2,[v, 91 p. :]-
dc.description.abstractA reduced activation high-entropy alloy with $W_{0.3}TaTiVCr$ and its derivative alloys with increased W content up to 90at.% were prepared via the mixing of elemental powders followed by spark plasma sintering for fusion plasma-facing materials. Characterization of the sintered samples revealed a BCC lattice and a multi-phase structure. Mechanical tests of the samples revealed improvement in the hardness (~800HV) and strength (~2000MPa) due to solid-solution strengthening and dispersion strengthening. This study explored the potential of SPSed $W_{0.5}TaTiVCr$ alloy, which shows enhanced strength and hardness along with higher W content as well. WxTaTiVCr was subjected to thermogravimetric analysis at 1000oC for 3 hours in air environment. The oxide layers have been characterized. The results disclosed significantly reduced mass gain (16 mg/$cm^2$) in $W_{0.5}TaTiVCr$ as compared to pure W due to significant concentration of Cr and Ti. The micrographs of oxidized samples also confirmed higher oxidation resistance of $W_{0.5}TaTiVCr$ as it showed considerably low thickness of oxide scale (~767µm) as compared to that on pure W (~949 µm). Considering improved mechanical strength and oxidation resistance of $W_{0.5}TaTiVCr$, $W_{short fibers}$ and $W_{particles}$ both were embedded in $W_{0.5}TaTiVCr$ to improve its fracture strain. Isotropic composites with >99% relative densities were developed via 3D mixing and spark plasma sintering. Random dispersion of well-bonded reinforcement in $W_{0.5}TaTiVCr$ matrix were observed. A four-times increase in fracture toughness (from ~7.7 to ~29.6 MPa·$m^{1/2}$) was observed due to debonding, fractional pull put, and limited plastic deformation of $W_{short fibers}$. 200 keV He ion irradiation of $W_{0.5}TaTiVCr$/10wt.%$W_{short fibers}$ didn’t impart any effect on surface morphology as no irradiation induced nanostructures were observed. TEM examination revealed irradiation damage in the form of randomly dispersed black spots, which caused a slight increase in nanoindentation hardness near irradiated surface. At 200nm depth, the relative hardness ratio ($H^{irr}/H^{unirr}$) for $W_{short fibers}$ (pure W) was 1.6, which remained limited to 1.3 for the $W_{0.5}TaTiVCr$ matrix. Lower $H^{irr}/H^{unirr}$ for $W_{0.5}TaTiVCr$ suggests its enhanced irradiation resistance as compared to pure W. 1.24 MeV electron irradiation of $W_{0.5}TaTiVCr$ at 25oC, 400oC and 800oC up to 1.12x$10^{26}$ /$m^2$ showed no indication of irradiation damage in contrast to pure W. The promising behavior of $W_{0.5}TaTiVCr$/$W_{short fibers}$ forecasts its potential applications in future fusion plasma-facing applications.-
dc.subjectHigh entropy alloy▼atungsten alloy▼acomposites▼afracture toughness▼aplasma-facing material-
dc.subject고 엔트로피 합금▼a텅스텐 합금▼a복합재료▼a파괴 인성▼a플라즈마 대면 재료-
dc.titleDevelopment of reduced activation high entropy alloy composites for fusion plasma facing applications = 핵융합 플라즈마 대면재용 저방사화 고엔트로피 합금 복합재 개발-
dc.description.department한국과학기술원 :원자력및양자공학과,-
dc.contributor.alternativeauthor왓심 오와이스 아흐메드-
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