Chromium coatings with and without Al_2O_3 or Y_2O_3 particles were prepared by chromizing the as-deposited Ni-film with and without Al_2O_3 or Y_2O_3 particles using a conventional pack-cementation method at 800 ℃. ...Chromium coatings with and without Al_2O_3 or Y_2O_3 particles were prepared by chromizing the as-deposited Ni-film with and without Al_2O_3 or Y_2O_3 particles using a conventional pack-cementation method at 800 ℃. The cyclic oxidation at 800 ℃ and hot corrosion in molten 75% Na2SO4＋25% NaC1 at 800 ℃ of the three different chromizing coatings were investigated. The effects of Al_2O_3 or Y_2O_3 on the cyclic oxidation and hot corrosion behavior of the chromizing coatings were discussed. Microstructure results show that the codeposited Al_2O_3 or Y_2O_3 particles significantly retard the grain growth of the chromizing coating, which increases the cyclic oxidation and hot corrosion resistance of the chromizing coatings, due to the more rapid formation of purer and denser chromia scnle展开更多
Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）...Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）.Effects of different fillers on the isothermal and cyclic oxidation resistance of chromizing coating in air at 850 ℃ were comparably investigated.Microstructure results show that the addition of CeO2 into the filler significantly retards the grain growth of the chromizing coating.Oxidation results indicate that the chromizing coating using CeO2 as filler exhibits somewhat increased oxidation resistance than the normal chromizmg coating,while the chromizing coating using Al2O3＋CeO2 as filler exhibits much better oxidation resistance.The effects of different fillers on the oxidation behaviors were discussed in detail.展开更多
By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline...By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.展开更多
An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a follow...An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive deposition and diffusion （TRD） chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that the chromizing speed at 500℃ was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1/~m in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500℃ for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.展开更多
A series of rare earth （RE） dispersed chromizing coatings were produced on P 110 steel by pack cementation. The orthogonal array design （OAD）was applied to set the experiments. An artificial neural network （ANN）...A series of rare earth （RE） dispersed chromizing coatings were produced on P 110 steel by pack cementation. The orthogonal array design （OAD）was applied to set the experiments. An artificial neural network （ANN） approach is employed to predict the thickness values of the obtained chromizing coatings based on the OAD tests results. The results revealed that the built model was reliable, the thickness values of chromizing coatings were well predicted at selected process parameters, and the predicted error lied in rational range.展开更多
Al-containing coatings were prepared on AZ31 magnesium alloy by pack-cementation technology.X-ray diffraction(XRD),backscattered electron imaging(BSEI)and energy dispersive spectroscopy(EDS)were jointly employed to ch...Al-containing coatings were prepared on AZ31 magnesium alloy by pack-cementation technology.X-ray diffraction(XRD),backscattered electron imaging(BSEI)and energy dispersive spectroscopy(EDS)were jointly employed to characterize the phases,microstructure and composition of the coated samples.The results show that the feedstock composition has a significant impact on the phases,microstructure and thickness of the coatings.For the sample with AlCl3 powder as the activator,the coating is very thick and composed of gradient phases and structures from surface to inside,including small amount ofb-Mg2Al3,coarse eutectic-like structure ofγ-Mg17Al12+δ-Mg,and fineγ-Mg17Al12 precipitations.In contrast,for the sample with AlCl3 and pure Al composite powders as the activator,the coating is relatively thin and contains a thin Al2O3 layer and a small amount of fineγ-Mg17Al12 precipitates.For the pack-cementation aluminizing that is not protected by high-vacuum or inert gas,the addition of pure Al powders can easily introduce the Al2O3 layer into the coating to prevent active Al ions further penetrating into the magnesium matrix,resulting in the thin Al-containing coating.The microhardness and corrosion behavior of the two kinds of aluminized coatings were also studied and discussed.展开更多
The segregation of thermal diffusion salt bath chromizing process was analyzed. The experimental chromizing ingredients were prepared by the four groups A, B, C, and D. In order to study the segregation status of this...The segregation of thermal diffusion salt bath chromizing process was analyzed. The experimental chromizing ingredients were prepared by the four groups A, B, C, and D. In order to study the segregation status of this case, the cooling molten salt in the crucible was removed by drilling from the heart core of molten salt. The core of molten salt was analyzed by X-ray fluorescence spectroscopy and XRD. Through the analysis, we can conclude that the Cr element deposited in the bottom was 4.51 times than the top. Chloride added to the molten salt will reduce segregation. Meantime we proposed some measures to overcome the segregation problem.展开更多
A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of ...A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of the chromized layer were characterized by using the scanning and transmission electron microscopy,a nano-indenter and a tribo-meter.It was shown that a continuous chromized layer of approximately 30 μm in thickness was formed on the SNC specimen after a dual chromizing treatment at both 600℃ and 1050℃ consecutively,as thick as about 3 times of that on the coarse-grained specimen after the same chromizing treatment.In addition,the wear resistance of the SNC-chromized specimen was enhanced significantly,due to a smaller grain size and a higher hardness,as well as smoother gradient variations of the microstructure,composition and hardness across a greater depth in the formed chromized surface layer.展开更多
A Y2O3-modified chromizing coating was produced by chromizing an as-electrodeposited Ni-Y2O3 composite film using pack cementation method at 1 100 ℃ for 3 h.For comparison,chromizing was also performed under the same...A Y2O3-modified chromizing coating was produced by chromizing an as-electrodeposited Ni-Y2O3 composite film using pack cementation method at 1 100 ℃ for 3 h.For comparison,chromizing was also performed under the same condition on an as-deposited Ni film without Y2O3 particles.Oxidation at 900 ℃ for 120 h indicates that although on both two chromizing coatings chromia scales grow during oxidation,the Y2O3-modified chromizing coating exhibits an increased oxidation resistance due to the formation of thinner,denser and finer-grain scale.The effect of Y2O3 on the coating formation and the coating oxidation behavior was discussed in detail.展开更多
IN 600 alloy was coated with two different types of coatings, Cr-modified aluminide coating this is called aluminizing-chromizing and Y-doped chromium modified aluminide coating this is called aluminizing-chromizing-y...IN 600 alloy was coated with two different types of coatings, Cr-modified aluminide coating this is called aluminizing-chromizing and Y-doped chromium modified aluminide coating this is called aluminizing-chromizing-yttriumizing. Diffusion coating was carried at 1 050℃ for 8 h under Ar atmosphere by simultaneous aluminizing-chromizing process and by simultaneous aluminizing-chromizing- yttriumizing. Cyclic oxidation tests were conducted on the uncoated and on the coated Inconel 600 alloy in the temperature range 800- 1 000℃ in CO2 for 100 h at 10 h cycle.The results showed that the oxidation kinetics for uncoated Inconel 600 alloy in CO2 is parabolic and the phases present are NiO, （Fe, Cr）2O3 , NiFe2O4 and NiCrO4. The oxidation kinetics for both coated systems in CO2 was found to be parabolic and the value ofkp for both coated systems were found to be lower than that for uncoated Inconel 600 alloy. Oxide phases that formed on coated systems are Al2O3 and NiCrO4. The role of yttrium can be attributed to its ability to improve the adherence of the oxide scale.展开更多
W 1-1.0C steel was chromized at 1173 K with double glow plasma surface alloying process, and the distribution of Fe, Cr, and C contents in the chromized layer was measured using glow discharge spectrum analysis （GDA...W 1-1.0C steel was chromized at 1173 K with double glow plasma surface alloying process, and the distribution of Fe, Cr, and C contents in the chromized layer was measured using glow discharge spectrum analysis （GDA）. The behavior and mechanism of carbon migration during the formation of chromized layer were studied through thermodynamic analysis and calculation. The gradient of carbon chemical potential was regarded as the driving force of carbon migration. An equation was derived to describe the carbon content varying with the chromium content within the carbon-rich region. The calculated results from the equation approximated closely to the experimental ones.展开更多
Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properti...Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.展开更多
Chemical vapour deposition of chromium on the surface of carbon steel has been investigated using a novel CVD method that combines the low cost of pack cementation method with advantages of vacuum technique. The proce...Chemical vapour deposition of chromium on the surface of carbon steel has been investigated using a novel CVD method that combines the low cost of pack cementation method with advantages of vacuum technique. The processes have been performed in chromium chlorides atmosphere at a low pressure range from 1 to 800 hPa, the treatment temperature 800 to 950°C. Studies of the layers thickness, the phase composition, Cr, C and Fe depth profiles in diffusion zone have been conducted. The effect of the vacuum level during the process and the process parameters such as time and temperature on layer diffusion growth on the carbon steel surface has been investigated.展开更多
基金Project(11531319)supported by Scientific Research Fund of Heilongjiang Provincial Education Department,China
文摘Chromium coatings with and without Al_2O_3 or Y_2O_3 particles were prepared by chromizing the as-deposited Ni-film with and without Al_2O_3 or Y_2O_3 particles using a conventional pack-cementation method at 800 ℃. The cyclic oxidation at 800 ℃ and hot corrosion in molten 75% Na2SO4＋25% NaC1 at 800 ℃ of the three different chromizing coatings were investigated. The effects of Al_2O_3 or Y_2O_3 on the cyclic oxidation and hot corrosion behavior of the chromizing coatings were discussed. Microstructure results show that the codeposited Al_2O_3 or Y_2O_3 particles significantly retard the grain growth of the chromizing coating, which increases the cyclic oxidation and hot corrosion resistance of the chromizing coatings, due to the more rapid formation of purer and denser chromia scnle
基金Project (11551419) supported by Scientific Research Fund of Heilongjiang Provincial Education DepartmentProject (12511469) supported by Heilongjiang Provincial Science and Technology Department
文摘Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）.Effects of different fillers on the isothermal and cyclic oxidation resistance of chromizing coating in air at 850 ℃ were comparably investigated.Microstructure results show that the addition of CeO2 into the filler significantly retards the grain growth of the chromizing coating.Oxidation results indicate that the chromizing coating using CeO2 as filler exhibits somewhat increased oxidation resistance than the normal chromizmg coating,while the chromizing coating using Al2O3＋CeO2 as filler exhibits much better oxidation resistance.The effects of different fillers on the oxidation behaviors were discussed in detail.
基金Project(11531319)supported by Scientific Research Fund of Heilongjiang Provincial Education Department,China
文摘By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.
基金This work was financially supported by the National Natural Science Foundation of China(Granted No.50671038).
文摘An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive deposition and diffusion （TRD） chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that the chromizing speed at 500℃ was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1/~m in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500℃ for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.
基金Funded by the National Natural Science Foundation of China(No.51171125)the China Postdoctoral Science Foundation (No.2012M520604)+1 种基金the Youth Foundation of Taiyuan University of Technology (No.2012L050)the Foundation for Talents Introduction of Taiyuan University of Technology
文摘A series of rare earth （RE） dispersed chromizing coatings were produced on P 110 steel by pack cementation. The orthogonal array design （OAD）was applied to set the experiments. An artificial neural network （ANN） approach is employed to predict the thickness values of the obtained chromizing coatings based on the OAD tests results. The results revealed that the built model was reliable, the thickness values of chromizing coatings were well predicted at selected process parameters, and the predicted error lied in rational range.
基金the National Natural Science Foundation of China(No.51575073)International Cooperation Special Project in Science and Technology of China(No.2015DFR70480)Scientific and Technological Research Program of Chongqing,China(Nos.cstc2017jcyjBX0031,cstc2018jszx-cyzdX0126).
文摘Al-containing coatings were prepared on AZ31 magnesium alloy by pack-cementation technology.X-ray diffraction(XRD),backscattered electron imaging(BSEI)and energy dispersive spectroscopy(EDS)were jointly employed to characterize the phases,microstructure and composition of the coated samples.The results show that the feedstock composition has a significant impact on the phases,microstructure and thickness of the coatings.For the sample with AlCl3 powder as the activator,the coating is very thick and composed of gradient phases and structures from surface to inside,including small amount ofb-Mg2Al3,coarse eutectic-like structure ofγ-Mg17Al12+δ-Mg,and fineγ-Mg17Al12 precipitations.In contrast,for the sample with AlCl3 and pure Al composite powders as the activator,the coating is relatively thin and contains a thin Al2O3 layer and a small amount of fineγ-Mg17Al12 precipitates.For the pack-cementation aluminizing that is not protected by high-vacuum or inert gas,the addition of pure Al powders can easily introduce the Al2O3 layer into the coating to prevent active Al ions further penetrating into the magnesium matrix,resulting in the thin Al-containing coating.The microhardness and corrosion behavior of the two kinds of aluminized coatings were also studied and discussed.
基金Funded by the National Natural Science Foundation of China (No.50675165)the National Key Technology R&D Program (No.2006BAF02A29)
文摘The segregation of thermal diffusion salt bath chromizing process was analyzed. The experimental chromizing ingredients were prepared by the four groups A, B, C, and D. In order to study the segregation status of this case, the cooling molten salt in the crucible was removed by drilling from the heart core of molten salt. The core of molten salt was analyzed by X-ray fluorescence spectroscopy and XRD. Through the analysis, we can conclude that the Cr element deposited in the bottom was 4.51 times than the top. Chloride added to the molten salt will reduce segregation. Meantime we proposed some measures to overcome the segregation problem.
基金supported by the National High-Tech.R&D Program(the National 863 plans projects,Grant No.2007AA03Z352)the National Science Foundation of China(Grant No.50701044 and 50890171)
文摘A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of the chromized layer were characterized by using the scanning and transmission electron microscopy,a nano-indenter and a tribo-meter.It was shown that a continuous chromized layer of approximately 30 μm in thickness was formed on the SNC specimen after a dual chromizing treatment at both 600℃ and 1050℃ consecutively,as thick as about 3 times of that on the coarse-grained specimen after the same chromizing treatment.In addition,the wear resistance of the SNC-chromized specimen was enhanced significantly,due to a smaller grain size and a higher hardness,as well as smoother gradient variations of the microstructure,composition and hardness across a greater depth in the formed chromized surface layer.
基金Project(06-13) supported by the Scientific Research Startup Foundation of Heilongjiang Institute of Science and Technology,China
文摘A Y2O3-modified chromizing coating was produced by chromizing an as-electrodeposited Ni-Y2O3 composite film using pack cementation method at 1 100 ℃ for 3 h.For comparison,chromizing was also performed under the same condition on an as-deposited Ni film without Y2O3 particles.Oxidation at 900 ℃ for 120 h indicates that although on both two chromizing coatings chromia scales grow during oxidation,the Y2O3-modified chromizing coating exhibits an increased oxidation resistance due to the formation of thinner,denser and finer-grain scale.The effect of Y2O3 on the coating formation and the coating oxidation behavior was discussed in detail.
基金Iraqi International Center for Science and Industry (IICSI, 2005-1)
文摘IN 600 alloy was coated with two different types of coatings, Cr-modified aluminide coating this is called aluminizing-chromizing and Y-doped chromium modified aluminide coating this is called aluminizing-chromizing-yttriumizing. Diffusion coating was carried at 1 050℃ for 8 h under Ar atmosphere by simultaneous aluminizing-chromizing process and by simultaneous aluminizing-chromizing- yttriumizing. Cyclic oxidation tests were conducted on the uncoated and on the coated Inconel 600 alloy in the temperature range 800- 1 000℃ in CO2 for 100 h at 10 h cycle.The results showed that the oxidation kinetics for uncoated Inconel 600 alloy in CO2 is parabolic and the phases present are NiO, （Fe, Cr）2O3 , NiFe2O4 and NiCrO4. The oxidation kinetics for both coated systems in CO2 was found to be parabolic and the value ofkp for both coated systems were found to be lower than that for uncoated Inconel 600 alloy. Oxide phases that formed on coated systems are Al2O3 and NiCrO4. The role of yttrium can be attributed to its ability to improve the adherence of the oxide scale.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50374050).
文摘W 1-1.0C steel was chromized at 1173 K with double glow plasma surface alloying process, and the distribution of Fe, Cr, and C contents in the chromized layer was measured using glow discharge spectrum analysis （GDA）. The behavior and mechanism of carbon migration during the formation of chromized layer were studied through thermodynamic analysis and calculation. The gradient of carbon chemical potential was regarded as the driving force of carbon migration. An equation was derived to describe the carbon content varying with the chromium content within the carbon-rich region. The calculated results from the equation approximated closely to the experimental ones.
基金This work was financially supported by the Research Fund for the Doctoral Program of High Education of China(No.20030561001)by the National Natural Science Foundation of China(Grant No.50371028).
文摘Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.
文摘Chemical vapour deposition of chromium on the surface of carbon steel has been investigated using a novel CVD method that combines the low cost of pack cementation method with advantages of vacuum technique. The processes have been performed in chromium chlorides atmosphere at a low pressure range from 1 to 800 hPa, the treatment temperature 800 to 950°C. Studies of the layers thickness, the phase composition, Cr, C and Fe depth profiles in diffusion zone have been conducted. The effect of the vacuum level during the process and the process parameters such as time and temperature on layer diffusion growth on the carbon steel surface has been investigated.
