Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor depositi...Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD) alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 ℃ was compared. The results show that the C/C-SiC substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of many bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense SiC layer and porous Si-Mo layer. Dense SiC layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating.展开更多
Carbon-carbon composite （C/C） materials are prone to severe oxidation and volatilization problems. To address these issues, mullite （3Al2O3.2SiO2）/silicon carbide （SIC） coatings were deposited on C/C composite s...Carbon-carbon composite （C/C） materials are prone to severe oxidation and volatilization problems. To address these issues, mullite （3Al2O3.2SiO2）/silicon carbide （SIC） coatings were deposited on C/C composite substrates characterized into high and low densities. The coatings were applied by a two-step approach： pack cementation and silica sol based slurry coating processes. The relationship between the microstructure of 3Al2O3·2SiO2/SiC coatings and C/C substrates during isothermal oxidation cycle at 1 500 ℃ was investigated using X-ray diffractometer （XRD） and scanning electron microscope （SEM） mounted with energy dispersive spectrometer （EDS）. The results indicate that the density of the substrates has a marked effect on the coatings. Dense, thick and well-bonded coatings are obtained in the high density substrate. After 106 h of isothermal oxidation, the high density substrate with 3Al2O3-2SiO2/SiC coating offers effective protection as compared to low density substrate suffering recession.展开更多
In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of S...In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.展开更多
A multi-layer coating for carbon-carbon composites with a Si-W outer layer,a SiC barrier layer and a SiC transition layer is prepared by the combination of siliconiza-tion, CVD and liquid reaction method. The effect o...A multi-layer coating for carbon-carbon composites with a Si-W outer layer,a SiC barrier layer and a SiC transition layer is prepared by the combination of siliconiza-tion, CVD and liquid reaction method. The effect of temperature on the oxidation protec-tion life from 1600 to 17OOC is investigated. The thickness of the oxide film on thecoating surface is measured through SEM and EMPA. A concept of critical oxide filmthickness and a critical oxidation protection time is put forward, and, based on it, the re-lation of the critical time with temperature is analyzed. The re8ults show that the relationof the critical oxidation protection time with temperature found by the experiments is fullyidentical with that calcu1ated based on the critical thickness- The physical significance andthe effect factors of the critical oxide film thickness are discussed.展开更多
The oxidation behavior and damage mechanism of modifiers and compounds of many types of ceramic coatings were investigated experimentally. A MoSi 2/SiC coating was produced by infiltration process. The oxidation beha...The oxidation behavior and damage mechanism of modifiers and compounds of many types of ceramic coatings were investigated experimentally. A MoSi 2/SiC coating was produced by infiltration process. The oxidation behavior of the coated C/C composites was studied at various temperatures below 1650℃. The oxidation results showed that the MoSi 2/SiC coating for thermal protection of C/C composites has high oxidation resistance at temperature up to 1650℃. In the present work, a new model of an oxidation protective, self sealing multi layer coating system was proposed for C/C composites. The multi layer coating possessing the self sealing property was obtained by pack cementation and infiltration process. The protection coating system for C/C composites consists of an inner layer of SiC and an outer layer of porous refractory oxides filled by modified SiO 2 glass. Isothermal and cyclic thermal oxidation tests showed the multi layer coating was capable of protecting the C/C composites in an oxidizing atmosphere at temperature up to 1800℃.展开更多
A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure ...A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.展开更多
Al specimens were covered with TiO2 film by sol-gel dip-coating and then anodized in ammonium adipate solution.The structure,composition and capacitance properties of the anodic oxide film were investigated by transmi...Al specimens were covered with TiO2 film by sol-gel dip-coating and then anodized in ammonium adipate solution.The structure,composition and capacitance properties of the anodic oxide film were investigated by transmission electron microscopy (TEM),Auger electron spectroscopy (AES),X-ray diffractometry (XRD) and electrochemical impedance spectroscopy (EIS).It was found that an anodic oxide film with a dual-layer structure formed between TiO2 coating and Al substrate.The film consisted of an inner Al2O3 layer and an outer Ti-Al composite oxide layer.The thickness of layers varied with the number of times of sol-gel dip-coating.The capacitance of anodic oxide films formed on coated specimens was at most 80% higher than that without TiO2.In film formation mechanism,it was claimed that the formation of composite oxide film was mainly affected by the structure of micro-pores network in TiO2 coating which had an influence on Al3+ and O2? ions transport during the anodizing.展开更多
Ablation characteristics and mechanism at high temperature for TaC coatings on carbon-carbon composites were investigated by ablation experiments with low power laser and oxyacetylene flame. The results show that the ...Ablation characteristics and mechanism at high temperature for TaC coatings on carbon-carbon composites were investigated by ablation experiments with low power laser and oxyacetylene flame. The results show that the TaC coating is decomposed at the initial stage of laser ablation in atmosphere, and free carbon diffused to the surface, then oxidized to the melt including carbon, oxygen and tantalum. With the increase of ablation time, the melt is oxidized to low valent tantalum-oxide and Ta2O5 is formed finally. During the melt cooling, needle-like crystals of Ta2O5 are precipitated. Between the melt and TaC coating, there exists a diffusion transition layer with thickness of 1-2 μm. The transition layer consists of fine crystals and pores including carbon, oxygen and tantalum. The oxyacetylene flame ablation at 2 300 ℃ results in the rapid oxidation of TaC and formation of protective liquid films of tantalum oxide on the coating surface, where the liquid film can fill up the cracks and cover the coating. In such case, the oxidation mechanism of TaC is converted to the oxygen solution and diffusion control mechanism.展开更多
In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase com...In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on acti...The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on active anodic oxide film and the structure and properties of the composite coating were studied by several surface and electrochemical techniques.The results showed that Ag nanograins with an average size of 10 nm were embedded into the anodic oxide film with pores of 0.1−2μm.Ag nanoparticles provided a catalytic site for the deposition of Ni-B alloy,and the Ni crystal nucleus was first grown in horizontal mode and then in cylindrical mode.The corrosion potential of the composite coating increased by 1.37 V and the corrosion current reduced two orders of magnitude due to the subsequent deposition of Ni-P alloy.The high corrosion resistance was attributed to the misaligning of these micro defects in the three different layers and the amorphous structure of the Ni-P alloy in the outer layer.These findings provide a new idea for electroless nickel plating on anodic oxide film.展开更多
The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2,4 and 6 g/l h...The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2,4 and 6 g/l have been investigated.It has been established by SEM,EDS,and XPS that ZrO_(2)/SiO_(2)nanoparticles successfully were incorporated into the coatings.Micro-Raman spectroscopy showed the presence of ZrO_(2)in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg_(2)SiO_(4) in tetrahedral configuration uniformly distributed in the outer part of coatings.Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEOlayer(from 2.4×10^(–7)A/cm^(2) for base PEO layer to 0.7×10^(–7)A/cm^(2) for coatings with nanoparticles).It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness(this parameter was increased from 2.1±0.3 GPa to 3.1±0.4 GPa)and wearproof(the wear was reduced from(4.3±0.4)×10^(–5)mm^(3)/(N×m)to(3.5±0.2)×10^(–5)mm^(3)/(N×m)).展开更多
基金Project(2006CB600908) supported by the National Basic Research Program of China
文摘Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD) alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 ℃ was compared. The results show that the C/C-SiC substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of many bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense SiC layer and porous Si-Mo layer. Dense SiC layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating.
基金Project(2011CB605805) supported by the National Basic Research Program of ChinaProject(51021063) supported by the Creative Research Group of National Natural Science Foundation of China
文摘Carbon-carbon composite （C/C） materials are prone to severe oxidation and volatilization problems. To address these issues, mullite （3Al2O3.2SiO2）/silicon carbide （SIC） coatings were deposited on C/C composite substrates characterized into high and low densities. The coatings were applied by a two-step approach： pack cementation and silica sol based slurry coating processes. The relationship between the microstructure of 3Al2O3·2SiO2/SiC coatings and C/C substrates during isothermal oxidation cycle at 1 500 ℃ was investigated using X-ray diffractometer （XRD） and scanning electron microscope （SEM） mounted with energy dispersive spectrometer （EDS）. The results indicate that the density of the substrates has a marked effect on the coatings. Dense, thick and well-bonded coatings are obtained in the high density substrate. After 106 h of isothermal oxidation, the high density substrate with 3Al2O3-2SiO2/SiC coating offers effective protection as compared to low density substrate suffering recession.
基金This work was financially supported by the National Natural Science Foundation of China for Distinguished Young Scholars (No. 50225210) the Foundation of Aeronautic Science of China (No. 03H53044).
文摘In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.
文摘A multi-layer coating for carbon-carbon composites with a Si-W outer layer,a SiC barrier layer and a SiC transition layer is prepared by the combination of siliconiza-tion, CVD and liquid reaction method. The effect of temperature on the oxidation protec-tion life from 1600 to 17OOC is investigated. The thickness of the oxide film on thecoating surface is measured through SEM and EMPA. A concept of critical oxide filmthickness and a critical oxidation protection time is put forward, and, based on it, the re-lation of the critical time with temperature is analyzed. The re8ults show that the relationof the critical oxidation protection time with temperature found by the experiments is fullyidentical with that calcu1ated based on the critical thickness- The physical significance andthe effect factors of the critical oxide film thickness are discussed.
文摘The oxidation behavior and damage mechanism of modifiers and compounds of many types of ceramic coatings were investigated experimentally. A MoSi 2/SiC coating was produced by infiltration process. The oxidation behavior of the coated C/C composites was studied at various temperatures below 1650℃. The oxidation results showed that the MoSi 2/SiC coating for thermal protection of C/C composites has high oxidation resistance at temperature up to 1650℃. In the present work, a new model of an oxidation protective, self sealing multi layer coating system was proposed for C/C composites. The multi layer coating possessing the self sealing property was obtained by pack cementation and infiltration process. The protection coating system for C/C composites consists of an inner layer of SiC and an outer layer of porous refractory oxides filled by modified SiO 2 glass. Isothermal and cyclic thermal oxidation tests showed the multi layer coating was capable of protecting the C/C composites in an oxidizing atmosphere at temperature up to 1800℃.
文摘A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.
文摘Al specimens were covered with TiO2 film by sol-gel dip-coating and then anodized in ammonium adipate solution.The structure,composition and capacitance properties of the anodic oxide film were investigated by transmission electron microscopy (TEM),Auger electron spectroscopy (AES),X-ray diffractometry (XRD) and electrochemical impedance spectroscopy (EIS).It was found that an anodic oxide film with a dual-layer structure formed between TiO2 coating and Al substrate.The film consisted of an inner Al2O3 layer and an outer Ti-Al composite oxide layer.The thickness of layers varied with the number of times of sol-gel dip-coating.The capacitance of anodic oxide films formed on coated specimens was at most 80% higher than that without TiO2.In film formation mechanism,it was claimed that the formation of composite oxide film was mainly affected by the structure of micro-pores network in TiO2 coating which had an influence on Al3+ and O2? ions transport during the anodizing.
基金Project(2007AA03Z110) supported by the National Hi-tech Research and Development Program of ChinaProject(50721003) supported by the National Natural Science Foundation of China+2 种基金Project(20070420822) supported by China Postdoctoral Science FoundationProject(2007RS4027) supported by the Postdoctoral Science Foundation of Hunan Province, ChinaProject(2007) supported by the Postdoctoral Science Foundation of Central South University, China
文摘Ablation characteristics and mechanism at high temperature for TaC coatings on carbon-carbon composites were investigated by ablation experiments with low power laser and oxyacetylene flame. The results show that the TaC coating is decomposed at the initial stage of laser ablation in atmosphere, and free carbon diffused to the surface, then oxidized to the melt including carbon, oxygen and tantalum. With the increase of ablation time, the melt is oxidized to low valent tantalum-oxide and Ta2O5 is formed finally. During the melt cooling, needle-like crystals of Ta2O5 are precipitated. Between the melt and TaC coating, there exists a diffusion transition layer with thickness of 1-2 μm. The transition layer consists of fine crystals and pores including carbon, oxygen and tantalum. The oxyacetylene flame ablation at 2 300 ℃ results in the rapid oxidation of TaC and formation of protective liquid films of tantalum oxide on the coating surface, where the liquid film can fill up the cracks and cover the coating. In such case, the oxidation mechanism of TaC is converted to the oxygen solution and diffusion control mechanism.
基金supported by the Major State Basic Research and Development Program of China (No.2006CB600908)
文摘In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.
基金Project(5227010679)supported by the National Natural Science Foundation of China。
文摘The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on active anodic oxide film and the structure and properties of the composite coating were studied by several surface and electrochemical techniques.The results showed that Ag nanograins with an average size of 10 nm were embedded into the anodic oxide film with pores of 0.1−2μm.Ag nanoparticles provided a catalytic site for the deposition of Ni-B alloy,and the Ni crystal nucleus was first grown in horizontal mode and then in cylindrical mode.The corrosion potential of the composite coating increased by 1.37 V and the corrosion current reduced two orders of magnitude due to the subsequent deposition of Ni-P alloy.The high corrosion resistance was attributed to the misaligning of these micro defects in the three different layers and the amorphous structure of the Ni-P alloy in the outer layer.These findings provide a new idea for electroless nickel plating on anodic oxide film.
基金supported within the frames of the Grant of the Russian Science Foundation, project No. 20-73-00280carried out within the framework of the Grant of the Russian Science Foundation, project No. 20-13-00130collected under the government assignments from Ministry of Science and Higher Education of the Russian Federation (project no. 0265-2019-0001)。
文摘The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2,4 and 6 g/l have been investigated.It has been established by SEM,EDS,and XPS that ZrO_(2)/SiO_(2)nanoparticles successfully were incorporated into the coatings.Micro-Raman spectroscopy showed the presence of ZrO_(2)in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg_(2)SiO_(4) in tetrahedral configuration uniformly distributed in the outer part of coatings.Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEOlayer(from 2.4×10^(–7)A/cm^(2) for base PEO layer to 0.7×10^(–7)A/cm^(2) for coatings with nanoparticles).It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness(this parameter was increased from 2.1±0.3 GPa to 3.1±0.4 GPa)and wearproof(the wear was reduced from(4.3±0.4)×10^(–5)mm^(3)/(N×m)to(3.5±0.2)×10^(–5)mm^(3)/(N×m)).
