WANG Fuhui LOU Hanyi WU Weitao Corrosion Science Laboratory
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Institute of Corrosion and Protection of Metals
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Academia Sinica
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Shenyang
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China associate professor
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Institute of Corrosion and Protection of Metals
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Academia Sinica
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Shenyang 110015
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China
金属学报(英文版)
Effect of a sputtered Co-30Cr-5Al microcrystalline coating on oxidation resistance of intermetallic compound TiAl and oxidation behavior of the bare TiAl were investigated at 900—1000℃ in static air.The oxidation kinetics for the TiAl alloy seems to approximately follow a linear rate law.Poor oxidation resistance of TiAl is due to the formation of the mixed Al_2O_3+TiO_2 scale which is loosely packed and easily spalled off.but not of dense and adherent pure Al_2O_3.A sputtered Co-30Cr-5Al coating,30 μm thickness,can remarkably improve the oxidation resistance of TiAl owing to the formation of adherent Al_2O_3 protective scale.However,many Kirkendall voids were formed between coating and substrate.
关键词:
CoCrAl microcrystalline coating
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null
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WANG Fuhui LOU Hanyi WU Weitao Corrosion Science Laboratory
,
Institute of Corrosion and Protection of Metals
,
Academia Sinica
,
Shenyang
,
China Research Assistant
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Institute of Corrosion and Protection of Metals
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Academia Sinica
,
Shenyang 110015
,
China
金属学报(英文版)
An investigation was carried out of the resistance to cyclic oxidation of the as-cast normal-grained Co-30Cr-5Al alloy substrate at 1000℃ in air together with its sputtered coating of microcrystallized CoCrAl alloy grains sized less than 0.5μm.Acoustie emissi on counts showed that the initially formed Al_2O_3 scale on the bare alloy substrate cracked and spalled severely off after only one or two cycles on cooling and then the worse protective layer of Cr_2O_3 and CoCr_2O_4 spinel occurred on surface.While such substrate coated with sputtered microcrystallized CoCrAl alloy film was not damaged under oxidation even through 100 cycles at 1000℃.In comparison with the normal-grained alloy,the microcrystallized al- loy,coating of similar constitution exhibite excellent resistance to oxide spalling on surface.
关键词:
microcrystallized CoCrAl coating
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null
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Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
The influence of sputtering on the high temperature oxidation resistance of the cast superalloy M17F has been studied. The as-sputtered microcrystalline layer has a homogeneous gamma phase structure with very fine gl ain size (20-100 nm), while the as-cast alloy is composed of gamma, gamma' and carbides. The oxidation resistance of the microcrystalline coating of K17F alloy is much better than that of the as-cast alloy, and is even superior to that of the pack aluminized alloy. At the initial oxidation stage, the oxide scale which formed on the as-cast alloy is composed of complex oxides of Cr, Ti, Ni and Al. As the: oxidation time is prolonged, the amount of alpha-Al2O3 increases and becomes the main product. However, the scale which formed on the microcrystalline coating consists only of alpha-Al2O3. Cyclic oxidation and acoustic emission examination showed that the oxide scale on the cast M17F alloy easily spalled during cooling, but the alpha-Al2O3 scale on the sputtered layer had excellent adhesion. The beneficial effects of microcrystalline structure on oxidation resistance are discussed briefly.
关键词:
K17F;sputtering;oxidation behavior
Oxidation of Metals
The effect of an NiAl microcrystalline coating prepared by magnetron sputtering on the high-temperature oxidation behavior of NiAl-28Cr-5Mo-1Hf was investigated in static air at 1000-1150degreesC. The additions of Cr, Mo, and Hf changed the single beta-phase structure into a multiphase structure [beta-NiAl, alpha-Cr(Mo), and Heusler phase]. The NiAl-28Cr-5Mo-1Hf alloy formed a nonprotective mixed scale of Al2O3 + Cr2O3 + HfO2 and exhibited relatively large weight gains. The large weight gains were attributed to extensive internal oxidation. The sputtered NiAl microcrystalline coating remarkably improved the oxidation resistance of NiAl-28Cr-5Mo-1Hf due to the formation of a compact and adherent Al2O3 scale at all test temperatures. It was found that the theta- alpha-Al2O3 transformation caused the anomalous behavior of the oxidation-kinetics cures of the NiAl microcrystalline coating in the temperature range 1000-1150degreesC. A change in the morphology of scales occurred with the transformation.
关键词:
beta-NiAl;multiphase alloy;NiAl microcrystallne coating;oxidation;rod-plate transition;in-situ composites;mechanical-properties;matrix;composites;cr alloys;resistance;additions;superalloy;compound;systems
Oxidation of Metals
The thermally- grown alumina formed at 1000, 1100, and 1200degreesC on magnetron- sputtered, nanocrystalline CoCrAl coatings, with and without yttrium, has been characterized using photostimulated- luminescence spectroscopy. The measurements enable the evolution of initially- formed transient alumina to its stable, alpha phase to be followed, and in particular, the effect of yttrium on the transformation. Yttrium retards the transformation from gamma to theta alumina and also its subsequent transformation to alpha alumina. The retardation of the transformation decreases with increasing oxidation temperature until at similar to 1200degreesC the transformation is complete within minutes. The presence of yttrium in the coatings also affects the residual stress in the thermally- grown oxide. For samples oxidized at 1100 and 1200degreesC the residual stress is similar to 0.3 GPa higher in the oxide on the Y- containing coating, whereas the residual stresses are the same after oxidation at 1000degreesC.
关键词:
oxidation;alumina scale;phase transformation;magnetron-sputtering;nanocoating;CoCrAl;yttrium;piezospectroscopy;oxide;alloys;scale;behavior;morphology;yttrium;stress;growth;nickel
Corrosion Science
The electrochemical behaviour of microcrystalline pure aluminium coating (mc-Al), fabricated by a magnetron sputtering technique, has been investigated in NaF as well as NaF + NaCl aqueous solutions. Results indicate that the anodic polarization characteristic changes with NaF concentration. F(-) anions promote the formation of a passive film, whose semiconducting properties were investigated. When the F(-) concentration is high ([F(-)] >= 0.03 mol/L) the passive film is mainly composed of aluminium fluoride, which is an n-type semiconductor on mc-Al and a p-type semiconductor on polycrystalline Al (pc-Al). In NaF + NaCl aqueous solutions, Cl(-) and F(-) ions compete in affecting the type of semiconducting passive films formed on mc-Al. (C) 2008 Elsevier Ltd. All rights reserved.
关键词:
Aluminium;Sputtered films;Passive films;pitting corrosion;crevice corrosion;pit initiation;noise-analysis;pure aluminum;chloride;sulfate;alloy;ions;susceptibility
Oxidation of Metals
Microcrystalline Ni-20Cr-3Al coatings were deposited on Ni-20Cr-3Al substrates by unbalanced magnetron-sputter deposition. The grain size of the coatings was varied by using different Ar pressures. Cyclic-oxidation testing was performed at 1100 degrees C, It was found that (1) an external alpha-Al2O3 scale formed on coating A (4.7 mu m thick, 50 nm grain size), (2) an external Cr2O3 scale and internal Al2O3 oxide formed on coating B (14 mu m thick, 500 nm grain size); and (3) an outer layer scale of Cr2O3+NiCr2O4 and interior laver of Al2O3 formed on the as-cast alloy. Extensive spallation of the Cr2O3+NiCr2O4 scale took place on the as-cast alloy, but no obvious spallation occurred on the two coatings. Improvement of the spallation resistance of the scale is explained by effective diffusional creep of the coatings and the micropegging effect of the inward-grown oxides.
关键词:
Ni-Cr-Al alloy;magnetron-sputter deposition;microcrystalline coatings;cyclic oxidation;scale spallation;oxidation resistance;temperature;transport;systems;alloys
