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The oxidation kinetics of TiAl alloys with and without 3, 5 and 10 wt.% additions of Si₃N₄ particles were studied between 900 and 1100℃ in atmospheric air. The Si₃N₄ dispersoids effectively increased the oxidation resistance of TiAl alloys, the more pronouncing the more Si₃N₄ dispersoids were added. The oxide scales formed on pure TiAl alloys were primarily composed of TiO₂and some Al₂O₃, whereas those formed on TiAl-Si₃N₄ alloys consisted of TiO₂, Al₂O₃, and SiO₂. The increased oxidation resistance of TiAl-Si₃N₄alloys compared with Si₃N₄-free TiAl alloys was mainly attributed to; (i) increased scale adherence via stabilized, refined oxide grains, (ii) thin scale formation owing to the presence of silica phase and the promotion of Al₂O₃-rich scale formation.

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To develop the advanced zirconium alloy for nuclear fuel cladding, the corrosion behaviors of Zr-X (X=Nb, Cu) binary alloys were investigated. Microstructures were observed by using optical microscopy and transmission electron microscopy(TEM). The corrosion tests were performed in three different conditions, water at 360℃, 70 ppm LiOH at 360℃ and steam at 400℃ for 100 days. In addition, the oxide crystal structure was characterized by low angle diffraction method of X-ray. The grain sizes of Zr-based binary alloys were gradually decreased with alloying additions, while the size and number of precipitates were increased. The corrosion resistance of both Zr-xNb and Zr-xCu alloys was decreased with alloying additions. Zr-xCu alloy showed higher corrosion rate than Zr-xNb alloy in LiOH solution. Both alloys had less amounts of tetra-ZrO₂ phases in oxide with alloying additions. It was considered that the increase of corrosion rate with Nb and Cu addition would be resulted from the early transition of oxide structure from protective tetra-ZrO₂ to non-protective mono-ZrO₂.

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To investigate the effects of Nb content and annealing parameter on corrosion resistance in Zr 0.8Sn-xNb(x = 0.2, 0.4, 0.8%) alloys, corrosion tests have been carried out under 400℃ steam and 360℃ LiOH water conditions. As the annealing parameter increased, the corrosion resistance was rapidly increased in Zr-0.8Sn-0.2Nb alloys but decreased in Zr-0.8Sn-0.4Nb and Zr-0.8Sn-0.8Nb alloys in both corrosion conditions. The degradation of corrosion resistance in Zr-0.8Sn-0.4Nb was resulted from the decrease of Nb concentration in matrix and the increase of Nb concentration in precipitates due to the formation of Nb-containing precipitates when the annealing parameter increased. The increase of tetragonal ZrO₂ in the oxide of Zr-0.8Sn-0.4Nb gave rise to increase the corrosion resistance with decreasing the annealing parameter. And it was thought that the corrosion resistance of Zr-0.8Sn-0.8Nb increased with the decrease of super-saturated Nb content in matrix caused by the formation of β-Nb.

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In present study, the effect of Sr-inoculation on microstructure and corrosion behavior of as-cast magnesium alloy was investigated by the various corrosion test and microstructure analyses such as X-ray diffraction and measurement of grain size and microporosity. The optimum content of Sr-inoculation for the reduction of grain refinement and microporosity was a range of 0.014-0.02 wt.%Sr. The microstructure of as cast alloys was not remarkably varied with Sr-addition, except the formation of acicular Al₄Sr phase. At optimum Sr content, the corrosion rate of as-cast alloy is slightly increased in both alloy systems. This is due to the increase of the average Al concentration in Mg-rich matrix by grain refinement. However, the precipitates such as Mg₄Sr, Mg₂Sr, Al₄Sr which is formed by Sr-inoculation have no prominent effect on the corrosion behavior of Sr-inoculated alloy.

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Aluminum oxide thin films were deposited by plasma-assisted atomic layer controlled deposition method in the temperature range of 100-125℃ using DMEAA (Dimethylethylamine alane [(CH₃)₂(C₂H_5)N:AlH₃]) as a source gas. Al was deposited by plasma-assisted ALD(Atomic Layer Deposition) method. And then, the Al films were oxidized into Al₂O₃ by the plasma oxidation in the same chamber without breaking the vacuum. For physical and electrical measurements, Al₂O₃ thin films of 15 ㎚ thickness were prepared by repetition of the above mentioned process. Thus prepared Al₂O₃ thin films showed a refractive index of 1.68. The thickness and the refractive index fluctuation of the film over a 4 in. wafer were ±2.3% and ±1.9%, respectively, for atomic layer controlled film, while those were ±7.8%, ±6.4% for all the sputter-deposited film. The leakage current density and breakdown field were measured to be about 10^(-8) Ａ/㎠ at 1 ㎹/㎝ and 7 ㎹/㎝, respectively. Considerable improvement of the electrical properties could be realized by the post oxygen-plasma annealing at 200℃.

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The effect of partial replacement of Mo with W on the corrosion resistance of simulated heat-affected zone (HAZ) in 22Cr-5Ni base duplex stainless steels has been investigated. The steels were simulated with various times at the cooling stage in the temperature range of 1200∼800℃(Δt_(1200/800)). In order to evaluate the intergranular and pitting corrosion resistance, Heuy test and electrochemical pitting corrosion test were carried out. Cooling rate and the substitution of W for Mo affected on the microstructure of duplex stainless steels. The amount of austenite phase in the heat affected zone increased linearly with decrease of cooling rate. The grain size in the HAZ also increased approximately linearly with decrease of cooling rate. Corrosion weight loss was varied with the cooling rate at the range of Δt_(1200/800) = 5∼270 sec, which could be influenced by the increase of the amount of autente phase, element partitioning in δ and γ-phases and the increase of γ-grain size at the cooling stage. At Δt _(1200/800) = 33∼270 sec, W-substituted alloy showed better corrosion resistance than the alloy containing only Mo. The W-substituted duplex stainless steel showed the enhanced corrosion resistance only when Δt_(1200/800) $gt; 33 sec. If Δt_(1200/800) is less than 14 sec, the steel only with Mo showed better corrosion resistance of HAZ.

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