Papers by Keyword: Aluminizing

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Authors: Hong Bing Liu, Jie Tao, Jiang Xu, Zhao Feng Chen, Xian Jun Sun
Abstract: Based on the favorable effect of the elements Al and Si on the improvement in reducing hydrogen permeability, a new combined process of simultaneous aluminizing and siliconizing, followed by oxidizing treatments using double glow plasma technology on 316L substrate was developed in this work. Microstructure and phase structure of as- prepared coating was examined by scanning electronic microscopy (SEM), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that the simultaneous aluminizing and siliconizing coating consisted of an outer aluminide layer (dissolved Si) and a diffusion zone. After a combined process, a continuous and compact Al2O3-rich coating was formed at the outermost surface. SiO2 was also detectable in the oxide coating.
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).
Authors: Tomohiro Sasaki, Takahiro Yagi, Takehiko Watanabe
Abstract: Aluminizing the surface of a TiAl-based alloy (49.1 at% Al) was carried out by thermally spraying a pure aluminum coating and subsequent diffusion treatment at 1100°C. The influence of the diffusion time for the formation of Ti-Al intermetallic phases in the coating layers and the oxidation resistance of the aluminized TiAl-based alloys were investigated. The layer formed on the outermost surface was comprised of the Al-rich intermetallic T2iAl5 and contained pores. On the other hand, an intermediate layer consisting of TiAl2 and TiAl was formed between the outermost layer and the substrate. The thickness of the outermost layer decreased as the diffusion time increased, while the thickness of the intermediate layer increased. In addition, the coating/substrate interface changed from a wavy to a linear form with the growth of the intermediate layer. The aluminized coating showed good oxidation resistance at 900°C for all diffusion times.
Authors: Tomohiro Sasaki, Takahiro Yagi, Takehiko Watanabe, Atsushi Yanagisawa
Abstract: Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl3 was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti2Al5 (at 1100°C), TiAl2 and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl3 during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl3 layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl2 and Al-rich TiAl developed by solid-state diffusion from TiAl3 layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl2 and 292 kJ/mol for Al-rich TiAl.
Authors: Hideyuki Murakami, K. Kamiya, Akihiro Yamaguchi, Ying Na Wu, Seiji Kuroda
Abstract: In the present study, high temperature properties of Ir-modified and Ir-Hf-modified aluminide coatings on Ni-based single crystal superalloy TMS-82+ were discussed. They were prepared by depositing pure Ir and Ir-Hf alloys on TMS-82+ using magnetron sputtering and EB-PVD, followed by a conventional Al-pack cementation process. The effects of Hf addition on the oxidation resistance and top-coat spallation resistance were investigated. Cyclic oxidation test at 1423K for 1h as one heating cycle revealed that while there is a small difference in oxidation kinetics and spallation lives between Ir and Ir-Hf coatings, drastic difference in surface morphology was observed. After 50 oxidation cycles the Ir-modified aluminide coating showed surface rumpling whereas the Ir-Hf modified aluminide coatings kept the flat surface. It was also revealed that excessive addition of Hf promoted the internal oxidation, resulting in the deterioration of substrates. These results agree with the conventional Pt-modified aluminide coatings and Ni-Al-Hf alloys.
Authors: Liang Ruan, Xu Dong Ren, Yong Zhuo Huangfu, Yong Kang Zhang
Abstract: The heat-resistant steel after aluminized was treated by laser shock processing (LSP) with high power Nd:YAG laser, and then was tensile tested at 400°C. The effects of the high-temperature behavior after LSP were analyzed from residual stress and fracture organization. The results showed that the yield strength and tensile strength of heat-resistant steel after aluminized were improved obviously during the tensile testing at high temperature, and the High-temperature fatigue life of 00Cr12 with composite processing was enhanced vastly. Compared with the LSP, the High-temperature fatigue life of 00Cr12 heat-resistant steel by aluminizing and LSP had a larger increase.
Authors: Yuriy Pavlovich Zaikov, Vadim Anatolyevich Kovrov, Irina Brodova, Yuriy Shtefanyuk, Vitaliy Pingin, Dmitriy Vinogradov
Abstract: A multilayer intermetallic coating on low-carbon steel was obtained during aluminum electrodeposition in NaF-KF-AlF3 melt at 920 °C. The current density effect on morphology and intermetallic layer composition was investigated. Electrolytically aluminized steel samples represented a good oxidation resistance at 900 °C.
Authors: Elisabetta Gariboldi, Xing Hua Han, Giulioantonio Longo, Giovanni Paolo Zanon
Abstract: Aluminising processes are well-known techniques industrially adopted to enrich of aluminium the surface layers of Ni-based alloys thus improving their resistance to environmental interaction at high-temperature. The results of aluminising processes are typically described in terms of the presence, compositions and thickness of the sequence of layers at the surface of the treated parts. Following this approach, the microstructural features of the diffusion layers obtained under different holding times via vapour-phase type high-temperature low-activity process were experimentally investigated on single crystal CMSX4 alloy. The attention was particularly focused on the effect of the crystallographic orientation of the crystal on the coating features. The evolution of the diffusion layers under different process conditions was then taken into account.
Authors: Takeshi Ishizaki, Dung Thi Mai Do, Makoto Nanko
Abstract: A metallurgical method for preparing oxide nano-rod array structure was developed with internal oxidation of Ni(Al) solid solution obtained by aluminizing Ni with a pack cementation technique. The present method was applied in order to fabricate nano-rod array on the micro-channel surface of microreactor. A micro-channel with 1 mm in depth, 1mm in width and 10 mm in length was fabricated on the Ni disk by an electric discharge machining and electropolishing. The Ni disk with a micro-channel was annealed at 1300°C for 12 h in vacuum. The sample was aluminized by a pack cementation using pack powder mixture consisting of 10 mass% of Ni3Al, 88 mass% of Al2O3 and 2 mass% of NaCl at 1100°C for 12 h in a flow of argon gas. The sample was oxidized from 1000 to 1200°C for 6 h with the Co/CoO buffer. Ni matrix in internally oxidized zone was removed by electropolishing to expose nano-rods. Al2O3 nano-rod array located on the micro-channel surface was successfully fabricated with the proposed technique. Diameter and height of nano-rods were ranged from 100 to 300 nm and from 1.5 to 3 µm, respectively.
Authors: Min Jung Kim, Dong Bok Lee
Abstract: The pack-cementation is one of economical, efficient coating processes for Fe-base alloys. It can provide good protection against high-temperature oxidation and corrosion. In this study, the high-temperature corrosion behavior of the aluminized diffusion-coating on low-carbon T20 steel (Fe-2.0Cr-0.5Mo-0.8Mn-0.3S in at.%) was studied at 800 °C in N2/H2O/H2S-mixed gas. The aluminized coating consisted of Fe3Al. The aluminized T20 steel after corrosion at 800 °C for 10~100h in N2/H2O/H2S-mixed gases, the scale formed on the Fe3Al coating consisted primarily of α-Al2O3, Al2S3, FeAl2O4 and FeO, with relatively slow scaling rates. The Fe3Al intermetallics has reasonable corrosion-and oxidation-resistance, because it can form a protective alumina scale. Without the aluminized diffusion-coating, T20 steel corroded fast with serious scale failure. At the surface, coarse FeS grains with cracks formed. Since FeS has a very high concentration of cation vacancies, it grew fast through the outward diffusion of Fe2+ ions.
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