Papers by Keyword: Pack Cementation

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Authors: N. Pistofidis, G. Vourlias, D. Chaliampalias, F. Stergioudis, Efstathios K. Polychroniadis
Abstract: In the present work the phases of the zinc coatings deposited with hot-dip galvanizing, pack cementation and wire flame spraying are examined with Scanning Electron Microscopy and Transmission Electron Microscopy. The different phases which are observed are identified with the combined results of electron and X-Ray diffraction. From the results it is concluded that pack cementation coatings are consisted by two different layers while hot dip galvanized coatings are composed by the same phases and additionally two extra phases of the Fe-Zn phase diagram. Flame sprayed coatings are composed by pure zinc, in the form of thin lamellae, together with nanocrystaline zinc oxide which is formed from the oxidation of liquid metallic droplets during the spray procedure.
Authors: G. Vourlias, N. Pistofidis, D. Chaliampalias, F. Stergioudis
Abstract: One of the most effective methods for the protection of ferrous substrates from corrosion is zinc hot-dip galvanizing. Although this method has many advantages, it is characterized by a very negative effect on the environment. In the present work Zn coatings were formed with thermal spraying, pack cementation and fluidized bed reactor, which are friendlier to the environment. Their microstructure was characterized with X-ray diffraction and scanning electron microscopy, while their corrosion performance was estimated with exposure in a salt spray chamber. From this investigation it was deduced that CVD coatings are composed by two layers referring to Γ-Fe11Zn40 and δ-FeZn10 phase of the Fe-Zn phase diagram. By contrast the thermal coatings are very porous and composed by pure Zn. However, the corrosion performance of all coatings is similar. This conclusion is very important because it verifies that hot-dip galvanizing could be replaced by the other coating methods.
Authors: D. Zeng, S. Yang, Zhi Dong Xiang
Abstract: This study is an attempt to codeposit N and Cr into the surface of austenitic stainless steels by pack cementation process to simultaneously increase their surface hardness and corrosion resistance. The pack powders were prepared using Cr2N powder as a source of both N and Cr, NH4Cl as activator and Al2O3 as inert filler. Specimens of the AISI204 austenitic stainless steel were treated in the 2 wt% NH4Cl activated 15Cr2N-85Al2O3 (wt%) pack at 1100 °C for different times. It was demonstrated that a top Cr2N layer with a Cr enriched zone underneath can be formed on the steel surface via the vapour phase generated in the activated powder pack. The effect of adding Cr powder into the pack powders on the surface layer formation and on the hardness profile at the cross-section of the specimen surface was also investigated. Hardness values of more than 1800 HV were obtained at the outermost surface of the treated specimen.
Authors: Feng Zhou, Ming Gao, Gan Feng Tu, Kui Liu, Ke Wu Peng
Abstract: Alumincoating was prepared on a Ni-Cr-W-Al nickel-base superalloy by pack cementation, the effects of Al content and aluminizing temperature on coating formation were investigated. Coating microstructures were investigated using optical and scanning electron microscopes, EDS and X-ray diffraction (XRD) techniques. The results showed that the coatings prepared at 800°C in the powders with 15%, 30% and 99% Al were different. NiAl3 coating was obtained in the conditions of aluminizing temperature of 700°C, 750°C, 850°C and of Al content of 99%.
Authors: E.K. Ampaw, E.K. Arthur, O.O. Adewoye, A.R. Adetunji, S.O.O. Olusunle, Winston O. Soboyejo
Abstract: In this paper, ductile iron was produced using a rotary furnace. The microstructures of the ductile iron (with and without cyanided coatings) were then characterized using optical microscopy, scanning electron microscopy (SEM) and energy diffraction X-ray spectroscopy (EDS). The surfaces of the ductile iron were then subjected to high temperature carbonitriding using a pack cementation process in which carbon and nitrogen were diffused into the ductile iron from powder mixtures consisting of ground cassava leaves and barium carbonate (BaCO3) energizers. The wear behavior of the coated and uncoated ductile iron was studied using the pin-on-disk method. The wear mechanisms were also elucidated using a combination of SEM and EDS. The mechanisms of wear were also studied using nanoscratch experiments. The resulting wear rates are then compared with those from micron-scale wear tracks obtained from pin-on-disk experiments. The implications of the results are then discussed for the design of wear resistant ductile irons.
Authors: Ahmed Moosa, Jalil Karim Ahmed, Ali Hoobi
Abstract: In this work Inconel 600 alloy was coated with two different types of coatings, Crmodified aluminide coating and Y- doped chromium modified aluminide coating . Diffusion coating was carried at 1050 oC for 8 hrs under Ar atmosphere by single step aluminizing- chromizing process and by single step aluminizing- chromizing- yttriumizing process. The cyclic hot corrosion tests of IN 600 and its coated systems deposited with 2 mg / cm2 NaCl / Na2SO4 (100/0, 50/50, and 0/100 wt. %) deposits were conducted at 900 oC in air for 105 hrs at 15 hrs cycle. The hot corrosion kinetic of uncoated Inconel 600 alloy follows parabolic rate law when oxidized with 100% Na2SO4 deposits, whereas it follows a linear rate law when oxidized with 100% NaCl deposits and with (50% NaCl + 50% Na2SO4) deposits. In cyclic hot corrosion tests, the parabolic rate constant (kP) values for Cr- modified aluminide coating when oxidized with NaCl / Na2SO4 concentrations (100/0, 50/50, and 0/100 wt. %) deposits are: 2.67x10-6, 2.73x10-6, and 8.34x10-7 (mg2/cm4)/s. respectively. But for Y- doped chromium modified aluminide coating are: 2.10x10-6, 1.51x10-6, and 6.66x10-7 (mg2/cm4)/s. respectively, under the same test conditions. The kP values for both coated systems oxidized with 100% Na2SO4 deposits are one order of magnitude lower than that for 100% NaCl, and for (50% NaCl + 50% Na2SO4) deposits under the same test conditions.
Authors: Nai Ming Lin, Fa Qin Xie, Tao Zhong, Xiang Qing Wu, Wei Tian
Abstract: The rare earth (RE) modified chromizing coating was obtained on P110 oil casing tube steel (P110 steel) substrate by means of pack cementation technique to enhance the resistance against corrosion of P110 steel. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) were employed to research microstructure, composition distribution and phase constitution of the chromizing coating. The effect of minor addition of RE on the microstructure of chromizing was discussed. Corrosion resistance of chromizing coating was investigated and compared with that of bare P110 steel via electrochemical corrosion and immersion corrosion in simulated oilfield brine solution, respectively. The results showed that a uniform, continuous and compact coating was formed on P110 steel. The coating with RE addition was more compact than that of the coating added no RE, and a small amount of RE addition could promote the chromizing procedure notably. From SEM and EDX investigation, it had been confirmed that the coating was composed of two different layers, an out layer and an inner layer; the coating mainly contains Fe and Cr; the concentration of Cr decreased as the distance from the surface increased, yet Fe presented the inverse trend. XRD analysis indicated the coating was built up by (Cr, Fe)23C6 referring to the out layer, (Cr, Fe)7C3, Cr7C3 and α-(Cr, Fe) corresponding to the inner layer. Electrochemical corrosion consequence was obtained as follows: the self-corroding electric potential of chromizing coating was higher, and the corrosion current density was lower than that of bare P110 steel, which revealed that chromizing coating had better anti-corrosion performance; immersion corrosion results demonstrated the mass loss of chromized P110 steel was lower, and this meant that chromizing coating had a better corrosion resistance than that of bare P110 steel on the experimental condition. A compact (Cr, Fe)xCy coating can be fabricated by pack cementation technique. As a result of minor RE addition, microstructure and corrosion resistance of the chromizing coating are improved obviously.
Authors: Jing Hu, Shu Kai Wang, Zheng Hua Zhou, Fei Xie, Xian Bo Pan
Abstract: A low-temperature silicon pack cementation has been developed by applying direct current field (DCF) between the treated sample and the powder agents. The cross-sectional microstructures, coating thickness and high temperature oxidation resistance after siliconizing under different processes were investigated. The results show that DCF can significantly reduce the treating temperature and heating duration comparing with the conventional silicon pack cementation, the heating temperature could be lowered to 750°С from higher than 1050°С normally used. When the treating temperature was 800°С with appropriate intensity of DCF, the siliconizing coatings with thickness around 40μm was produced, while at this temperature, almost no coating could be formed by conventional silicon pack cementation,and the coating rapidly formed at lower temperature had good oxidation resistance below 700°С .
Authors: César A.C. Sequeira, Fernand D.S. Marquis
Abstract: The effects of aluminising on the hot corrosion resistance of two nickel-chromium alloys containing 10 and 30 weight percent chromium, respectively, were examined. The Ni/Cr specimens were aluminised by pack cementation in Ar and underwent cyclic hot corrosion testing in Na2SO4- NaCl molten salt. XRD analysis indicated that a NiAl phase formed between the coating layer and substrate. Cyclic hot corrosion test results indicated that the effects of aluminising are more pronounced in the case of the 10 % Cr than in the case of 30 % Cr. The ductile NiAl phase suppressed the potential for crack initiation during thermal cycling of the 10 % Cr specimens, and reinforced the hot cyclic corrosion resistance in molten salt for the 30 % Cr specimens.
Authors: Jae Won Kim, Seoung Soo Lee, Dong Ho Park, Yeon Gil Jung, Je Hyun Lee, Chang Yong Jo
Abstract: Silicon carbide (SiC) microtubes with villus-like morphology have been successfully fabricated through a reaction between carbon fiber and SiO gas via the pack cementation process. The effect of gas flow nature (argon and/or hydrogen) on silicon carbide microtube synthesis has been studied. The morphology of the microtubes and the production yield are greatly influenced by the nature of gas flow. Mixed ratio of argon to hydrogen gas has a strong influence on the thickness of the microtubes.
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