Papers by Keyword: High Temperature Oxidation

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Authors: Ho Sung Lee, Jong Hoon Yoon, Yeong Moo Yi
Abstract: The surface oxidation behavior was investigated over a range of solid state bonding condition of the Ti-6Al-4V ELI alloy. Since the oxides at the bonding interface may prevent the materials from complete bonding, it is important to understand the oxidation behavior at solid state bonding condition. The activation energy of oxidation of Ti-6Al-4V ELI is estimated to be 318 KJ/mol in an environment of solid state bonding process. For Ti-6Al-4V ELI alloy, strucutral integrity of bonding interface without oxides have been obtained at 850°C applying pressure of 3MPa for 1 hour. Solid state diffusion bonding of Ti-15V-3Cr-3Sn-3Al alloy was also obtained under a pressure of 6MPa for 3 hours at 925°C.
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Authors: Jordan Graham, Savko Malinov, Roy Douglas, Rose Mary Stalker
Abstract: A systematic testing procedure has been employed to investigate the high temperature oxidation kinetics of AISI 316L. Thermo-gravimetric (TG) analysis was carried out at 950°C, 1050°C, 1150°C and 1250°C for 8h. Alongside this, isothermal furnace treatments were carried out on samples of the same material at the same temperatures for time periods of 0.5h, 1h, 2h, 4h and 8h. Changes in oxidation kinetics were observed on mass gain curves plotted from data derived from the TG analysis. When a change in oxidation kinetics was identified, the structure, thickness and composition of the oxides formed on the isothermal treatment samples at time periods before and after the change occurred could be studied. It was found that this systematic testing procedure provided a great deal of useful information allowing more meaningful conclusions to be made on the influence of oxide layer thickness, structure and composition on high temperature oxidation kinetics.
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Authors: Toshio Narita, Takeshi Izumi, Takumi Nishimoto, Yoshimitsu Shibata, Kemas Zaini Thosin, Shigenari Hayashi
Abstract: To suppress interdiffusion between the coating and alloy substrate in addition to ensuring slow oxide growth at very high temperatures advanced coatings were developed, and they were classified into four groups, (1) the diffusion barrier coating with a duplex layer structure, an inner σ−(Re-Cr-Ni) phase as a diffusion barrier and outer Ni aluminides as an aluminum reservoir formed on a Ni based superalloy, Hastelloy X, and Nb-based alloy. (2) the up-hill diffusion coating with a duplex layer structure, an inner TiAl2 + L12 and an outer β-NiAl formed on TiAl intermetallic and Ti-based heat resistant alloys by the Ni-plating followed by high Al-activity pack cementation. (3) the chemical barrier coating with a duplex layer structure, an inner* γ + β + Laves three phases mixture as a chemical diffusion barrier and an outer Al-rich γ-TiAl as an Al reservoir formed by the two step Cr / Al pack process. (4) the self-formed coating with the duplex structure, an inner α-Cr layer as a diffusion barrier and an outer β-NiAl as an Al-reservoir on Ni-(2050)at% Cr alloy changed from the δ-Ni2Al3 coating during oxidation at high temperature. The oxidation properties of the coated alloys were investigated at temperatures between 1173 and 1573K in air for up to 1,000 hrs (10,000 hrs for the up-hill diffusion coating). In the diffusion barrier coating the Re-Cr-Ni alloy layer was stable, existing between the Ni-based superalloy (or Hastelloy X) and Ni aluminides containing 1250at%Al when oxidized at 1423K for up to 1800ks. It was found that the Re-Cr-Ni alloy layer acts as a diffusion barrier for both the inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate. In the chemical barrier coating both the TiAl2 outermost and Al-rich γ-TiAl outer layers maintained high Al contents, forming a protective Al2O3 scale, and it seems that the inner, γ, β, Laves three phase mixture layer suppresses mutual diffusion between the alloy substrate and the outer/outermost layers.
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Authors: Vadim Kovrov, Yuriy Zaikov, Vladimir Tsvetov, Yuriy Shtefanyuk, Vitaliy Pingin, Matvey Golubev
Abstract: Anodic current-supplying pins (ACP) made of low-carbon steel corrode intensively due to the sulfur contamination of the carbon-based Soderberg anode and iron sulfides formation in the present aluminium production technology. The aluminide coatings produced by the liquid-phase method followed by the fluoride flux treatment of the steel samples were applied for the ACP protection. The protective layer based on α-Al2O3 and FeAl2O4 was formed on the steel surface in the course of the test run in the industrial Soderberg anode during the aluminium electrolysis. The aluminized ACP wear rates calculated by the linear extrapolation of data obtained during 150 days workout were 4.0 and 5.4 cm/year for the ACP with the aluminide coating and without it, respectively. The current load on the ACP remained almost the same for the aluminized and original uncoated samples with the exception of the initial “heating” period (400-600°C).
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Authors: Susumu Takamori, Yoshiaki Osawa, Hideki Kakisawa, Kazumi Minagawa, Kohmei Halada
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Authors: Krzysztof Adamaszek, Zbigniew Jurasz
Abstract: In this paper we give a presentation of the recently developed approaches concerned of the rate of oxidation the Arema steel at high-temperature in first stage of this process. The comparison analysis was performed on the basis of the experimental results of oxidation of cylindrical specimens made of above steel. The experiment was carried out in chamber furnace on series of specimen with dimension Φ = 20 , l=30 mm. The specimens were oxidized at 1000 °C for 10 - 2280 minutes in air and then quenched in silica sand, afterwards were measured and weighed both with and without of scale. The analysis reveals that for longer oxidation time than one hour influence of linear dependence on parabolic growth of scale can be neglected.
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Authors: Xiao Zhou Cao, Zhu Xian Qiu, Zhong Ning Shi, Xian Wei Hu, Yun Gang Ban, Zhao Wen Wang
Abstract: Al-Si metal anode was fabricated by cold-press sintering with Al and Si as embedded powder in argon atmosphere. The anti-oxidation in the air and anti-corrosion in molten cryolite properties of Al-Si metal anode at high temperature were examined. The experimental results showed that the oxidation kinetics curve obeyed the parabolic law. The corrosion behavior Al-Si metal anode was studied in electrolysis test. The electrolyte consisted of Na3AlF6(90 wt%),CaF2(5 wt%) and Al2O3(5 wt%) which corresponded to molecular ratio of 2.4. The results indicated that the cell voltage was stable and the electric polarized corrosion rate was higher than the static corrosion rate of metal anode. SEM photographs showed an oxidation film formed in the surface of Al-Si metal anode which can obstruct the further corrosion in molten cryolite. It may be concluded that Al-Si metal anode has good combination property and can replace the carbon anode in the aluminum cell.
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Authors: Jerzy Jedlinski
Abstract: The 18O2 exposure-based approach was used to investigate the failure mechanisms of the oxide scales growing on alumina-forming materials. The scale spallation mechanisms and cracking processes were studied at various oxidation stages of FeCrAl alloys and β-NiAl intermetallic compound. High spatial resolution SIMS was applied to determine the distribution of the oxygen isotopes and other elements in the scales. It was found that the scales spall away according to an adhesive mode. However, t is process usually occurs at temperatures high enough to cause the reoxidation of the exposed bare substrat which results in thin oxide film on the metal. The thickness of this film and its composition depend on the alloy and the region at the interface. Spallation on reactive-element free FeCrAl alloys occurs at relatively high temperatures and the film is fairly thick, while on Zr-containing material very thin oxide layer is formed because the scale is better resistant to spalling and this process occurs at quite low temperature. The thin oxide layer formed on smooth regions comprises essentially the alumina, while the sequence of iron, chromium and aluminium oxide appears on regions exhibiting 'oxide imprints'. The applied approach enabled to find that the through-scale cracking observed at early oxidation stages of β-NiAl occurs at high temperatures and not during cooling. Formation of such cracks affects the further growth of the scale in terms of its microstructure, morphology and generation of stresses. Oxygen inward penetration through cracked scales formed during thermal cycling of FeCrAl alloys occurred mainly via oxide grain boundaries.
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