Papers by Keyword: Reactive Elements

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Authors: Ammar Naji, Michael Schütze
Abstract: Reformer materials are exposed to severe operating conditions at high temperature in aggressive catalyzer and combustion atmospheres. Therefore, materials used for the construction of the reformer reactor have to possess appropriate high temperature resistance. Diffusion coatings improve the high temperature resistance of materials by enrichment of the alloy surface with thermodynamically stable oxide formers. Beside conventional mono-element diffusion coatings (e.g. Al coating), multi-element diffusion coatings can be developed in a single process step. In this work we developed Al diffusion and Al-Si and Al-Si-RE (RE: reactive element Y, Ce) co-diffusion coatings on a low cost austenitic 18Cr10Ni-steel. The high temperature resistance of coated and uncoated 18Cr10Ni-steel, 20Cr31Ni-steel and 23Cr18Fe-Ni base alloy was tested in catalyzer and combustion atmosphere under cyclic operation conditions.
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Authors: Zhi Yang Zhang, Hong Bo Guo, Hui Peng, Sheng Kai Gong, Hui Bin Xu
Abstract: Intermetallic compound NiAl is considered as a potential candidate material for bond coat in thermal barrier coating (TBC) system due to its capability of forming a continuous and uniform alumina scale at temperatures even high than 1200 °C, but its cyclic oxidation is rather poor. Previous study has found that cyclic oxidation resistance of NiAl alloys and coatings can be drastically improved by minor Dy doping as reactive element. In this paper, NiAlDy alloys were produced by vacuum arc-melting and the effects of various Dy contents on the microstructure and hardness of NiAl alloys were investigated. The results suggest that Dy tends to segregate at grain boundaries and precipitate within grains as brittle DyNi2Al3 phase with little DyNiAl needles in it. The addition of minor Dy resulted in grain refinement. The grain size of NiAl alloy were reduced from ~1 mm to ~300 µm, with increasing the content of Dy to 0.5 at.%. The addition of ~0.1 at.% Dy caused a 10 % improvement in both the microhardness and macrohardness due to Dy solid-solution and grain-boundary segregation, but the alloy revealed decreased microhardness and macrohardness with further increasing the content of Dy to 0.5 at.% as the formation of Dy-rich phase.
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