This article investigates the low-temperature formation of aluminide coatings on a Ni-base superalloy by pack cementation process. The pack cemented coatings characteristic of high density and homogeneity possess a tw...This article investigates the low-temperature formation of aluminide coatings on a Ni-base superalloy by pack cementation process. The pack cemented coatings characteristic of high density and homogeneity possess a two-layer structure. The top layer mainly consists of Al3Ni2 and Al3Ni,while the bottom layer of Al3Ni2. Great efforts are made to elucidate the effects of different experimental parameters on the microstructure and the constituent distribution of the coatings. The results show that all the parameters exclusive of the pack activator （NH4Cl） content produce effect on the coating thickness,but do not on the microstructure and the constituent distribution. The pack activator （NH4Cl） content affects neither the coating thickness nor structure and constituent distribution. The parabolic relationship between the coating thickness and the deposition time suggests that the process is diffusion-controlled. Furthermore,the article demonstrates a linear relationship between the coating thickness and the re-ciprocal deposition temperature.展开更多
Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies i...Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies indicated that the diffusion of Al-bearing gases through the pack is the rate-controlling step in this process.The activation energy of 161.8 kJ/mol was calculated for this step.In addition,the mass gains of the aluminized samples were predicted using the partial pressures of gases in the pack and those adjacent to the samples surface.The predicted values are in good agreement wim the experimental measurements at 950 ℃ but are higher than those measured at 1025 and 1100 ℃.展开更多
A series of low-temperature phase transitions of sodium aluminate solutions were studied by differential scanning calorimetry (DSC) and Raman spectroscopy. The results indicate that NaOH concentration is a primary imp...A series of low-temperature phase transitions of sodium aluminate solutions were studied by differential scanning calorimetry (DSC) and Raman spectroscopy. The results indicate that NaOH concentration is a primary impact factor for the binary eutectic point and ice melting temperature of sodium aluminate solutions with low NaOH concentration. In addition, the phase transition process of sodium aluminate solutions with low NaOH concentration from 123.15 to 283.15 K is divided into four steps: non-crystal to crystal, ternary eutectic reaction, binary eutectic reaction and ice melt. The projection phase diagram of NaOH-Al(OH)3-H2O system at low temperature was plotted, in which the ternary eutectic temperature for sodium aluminate solutions is 183.15 K.展开更多
In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by...In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques. Results show that the thickness of coating layer increases with increasing aluminizing temperature. The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate. In comparison with the steel substrate, the corrosion current density Ico^r of the Fe-AI coatings is always lower than that of substrate, about 1/38 or 1/33 after 2 h immersion, and 1/3 or 1/6 for 720 h immersion. As can be seen from the weight loss curve, the Fe-AI coatings show less loss than that of the substrate within 30-day immersion. The corrosion products formed on the surface of the coatings include oxides of Al, Mg, Fe and Ca, and pitting defect has also been found. The Fe-Al coating with higher content of Fe2Al5 has better corrosion resistance.展开更多
Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the micro...Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.展开更多
The halide-activated pack cementation method is utilized to deposit aluminide coat- ings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy. The addition of...The halide-activated pack cementation method is utilized to deposit aluminide coat- ings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy. The addition of a small amount of Nb or Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the solid-state division of Al through the formation of stable TiAl3 layer. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has better toughness than the TiAl3 formed on the non-alloyed TiAl. The reason for better toughness of the coating formed on TiAl is that partial TiAl3 with tetragonal structure was changed to high symmetry cubic L12 structure since Nb or Cr was dissolved into TiAl3. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has much better oxidation resistance than the TiAl3 layer formed on the non-alloyed TiAl. It is attributed to change in the crystal structure of TiAl3 from the brittle tetragonal DO22 to the ductile cubic L12 by addition of small amount of Nb or Cr.展开更多
Aluminum diffusion coatings are often prepared by a pack aluminization technique, which is a specific variety of chemical vapor deposition (CVD) method. The coating process takes place in a bed containing a mixed powd...Aluminum diffusion coatings are often prepared by a pack aluminization technique, which is a specific variety of chemical vapor deposition (CVD) method. The coating process takes place in a bed containing a mixed powder that serves as a source of the coatings forming element. The phase composition of the diffusion layer obtained depends on the activity of the Al during the pack aluminization processing. In this work, the proportion of Al to special additive powder in the pack and the treatment temperature are adjusted to achieve the desired surface composition of aluminized layer. The aluminized 20 plain carbon steel and HK40 austenitic steel were investigated by optical microscopy (OM) , X-ray diffraction (XRD) and microsclerometer. The results showed that the desired FeAl, Fe3Al and NiAl were respectively formed on the 20 plain carbon steel and HK40 austenitic steel, and the aluminides FeAl3, Fe2Al5 or Ni2Al3, NiAl3 could be inhibited.展开更多
The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the...The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25-250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the Ni Al phase is formed. It is also found that the Ni2Al3 phase completely turns into Ni Al phase after oxidizing treatment for 100 h and above. The Ni Al coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.展开更多
A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2S...A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2SO4/K2SO4（3：1） or Na2SO4/NaCl（3：1） salts at 900 °C in static air are evaluated as well as the aluminide coating.The results indicate that compared with the aluminide coating,the anti-corrosion properties of the Cr-modified aluminide coating in the both salts are improved,which should be attributed to the beneficial effect of the Cr in the coating.The corrosion mechanism of the Cr-modified aluminide coating,especially the role of Cr in the mixture salt corrosion,is discussed.展开更多
Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results...Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients in β-NiAI phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometric β-NiAI phase, the interdiffusion coefficients in β-NiAI phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of β-NiAI phase.展开更多
A method was presented to prepare aluminide coatings on metals by combining the pack aluminizing with the ball impact process. This technique applied mechanical vibration to a retort, which was loaded with pack-alumin...A method was presented to prepare aluminide coatings on metals by combining the pack aluminizing with the ball impact process. This technique applied mechanical vibration to a retort, which was loaded with pack-aluminizing powder, specimens and alloy balls. Pack aluminizing was carried out with repeated ball impact, which accelerated chemical reactions and atomic diffusion. Aluminide coatings were formed at a relatively lower temperature (below 600 ℃) and in a shorter treatment time, compared with the conventional pack aluminizing. The effects of the operation temperature and the treatment time on the formation of the coatings were analysed. The SEM, EDS and XRD analysis results show that the aluminide coatings appear to be homogeneous, with a high density and free of porosity, and have excellent adherence to the substrate. The coatings mainly consist of Al-rich phases such as η-Fe2Al5, θ-FeAl3 and ?CrAl5. Oxidation resistance was studied by high-temperature tests. The formation mechanism of the Al-coatings was also investigated. This technique provides a new approach for industrial diffusion coatings with great energy and time savings.展开更多
Present-day Liþstorage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability.Herein,based on a Ca2þsubstituted Mg_(2)Nb_(34)O_(87) anod...Present-day Liþstorage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability.Herein,based on a Ca2þsubstituted Mg_(2)Nb_(34)O_(87) anode material,we demonstrate that decreasing the ionic packing factor is a two-fold strategy to enhance the low-temperature electrochemical kinetics and high-temperature cyclic stability.The resulting Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) shows the smallest ionic packing factor among Wadsley–Roth niobate materials.Compared with Mg_(2)Nb_(34)O_(87),Mg1.5Ca0.5Nb_(34)O_(87) delivers a 1.6 times faster Liþdiffusivity at-20℃,leading to 56%larger reversible capacity and 1.5 times higher rate capability.Furthermore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) exhibits an 11%smaller maximum unit-cell volume expansion upon lithiation at 60℃,resulting in better cyclic stability;at 10C after 500 cycles,it has a 7.1%higher capacity retention,and its reversible capacity at 10C is 57%larger.Therefore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) is an allclimate anode material capable of working at harsh temperatures,even when its particle sizes are in the order of micrometers.展开更多
文摘This article investigates the low-temperature formation of aluminide coatings on a Ni-base superalloy by pack cementation process. The pack cemented coatings characteristic of high density and homogeneity possess a two-layer structure. The top layer mainly consists of Al3Ni2 and Al3Ni,while the bottom layer of Al3Ni2. Great efforts are made to elucidate the effects of different experimental parameters on the microstructure and the constituent distribution of the coatings. The results show that all the parameters exclusive of the pack activator （NH4Cl） content produce effect on the coating thickness,but do not on the microstructure and the constituent distribution. The pack activator （NH4Cl） content affects neither the coating thickness nor structure and constituent distribution. The parabolic relationship between the coating thickness and the deposition time suggests that the process is diffusion-controlled. Furthermore,the article demonstrates a linear relationship between the coating thickness and the re-ciprocal deposition temperature.
文摘Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies indicated that the diffusion of Al-bearing gases through the pack is the rate-controlling step in this process.The activation energy of 161.8 kJ/mol was calculated for this step.In addition,the mass gains of the aluminized samples were predicted using the partial pressures of gases in the pack and those adjacent to the samples surface.The predicted values are in good agreement wim the experimental measurements at 950 ℃ but are higher than those measured at 1025 and 1100 ℃.
基金Project(51374251)supported by the National Natural Science Foundation of China
文摘A series of low-temperature phase transitions of sodium aluminate solutions were studied by differential scanning calorimetry (DSC) and Raman spectroscopy. The results indicate that NaOH concentration is a primary impact factor for the binary eutectic point and ice melting temperature of sodium aluminate solutions with low NaOH concentration. In addition, the phase transition process of sodium aluminate solutions with low NaOH concentration from 123.15 to 283.15 K is divided into four steps: non-crystal to crystal, ternary eutectic reaction, binary eutectic reaction and ice melt. The projection phase diagram of NaOH-Al(OH)3-H2O system at low temperature was plotted, in which the ternary eutectic temperature for sodium aluminate solutions is 183.15 K.
基金supported by the Foundation of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology (No. ASMA 201403)Cooperative Innovation Fund of Jiangsu Province (No. BY 2014004-09)
文摘In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques. Results show that the thickness of coating layer increases with increasing aluminizing temperature. The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate. In comparison with the steel substrate, the corrosion current density Ico^r of the Fe-AI coatings is always lower than that of substrate, about 1/38 or 1/33 after 2 h immersion, and 1/3 or 1/6 for 720 h immersion. As can be seen from the weight loss curve, the Fe-AI coatings show less loss than that of the substrate within 30-day immersion. The corrosion products formed on the surface of the coatings include oxides of Al, Mg, Fe and Ca, and pitting defect has also been found. The Fe-Al coating with higher content of Fe2Al5 has better corrosion resistance.
文摘Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.
基金The National Natural Science Foundation of ChinaThe Korea Science and Engineering Foundation
文摘The halide-activated pack cementation method is utilized to deposit aluminide coat- ings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy. The addition of a small amount of Nb or Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the solid-state division of Al through the formation of stable TiAl3 layer. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has better toughness than the TiAl3 formed on the non-alloyed TiAl. The reason for better toughness of the coating formed on TiAl is that partial TiAl3 with tetragonal structure was changed to high symmetry cubic L12 structure since Nb or Cr was dissolved into TiAl3. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has much better oxidation resistance than the TiAl3 layer formed on the non-alloyed TiAl. It is attributed to change in the crystal structure of TiAl3 from the brittle tetragonal DO22 to the ductile cubic L12 by addition of small amount of Nb or Cr.
基金supported by Nano-meter Research Program of Shanghai Commission of Science and Technology under the contract No.0211nm093
文摘Aluminum diffusion coatings are often prepared by a pack aluminization technique, which is a specific variety of chemical vapor deposition (CVD) method. The coating process takes place in a bed containing a mixed powder that serves as a source of the coatings forming element. The phase composition of the diffusion layer obtained depends on the activity of the Al during the pack aluminization processing. In this work, the proportion of Al to special additive powder in the pack and the treatment temperature are adjusted to achieve the desired surface composition of aluminized layer. The aluminized 20 plain carbon steel and HK40 austenitic steel were investigated by optical microscopy (OM) , X-ray diffraction (XRD) and microsclerometer. The results showed that the desired FeAl, Fe3Al and NiAl were respectively formed on the 20 plain carbon steel and HK40 austenitic steel, and the aluminides FeAl3, Fe2Al5 or Ni2Al3, NiAl3 could be inhibited.
基金Projects(CKJB201205,QKJB201202,YJK201307)supported by the Nanjing Institute of Technology,China
文摘The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25-250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the Ni Al phase is formed. It is also found that the Ni2Al3 phase completely turns into Ni Al phase after oxidizing treatment for 100 h and above. The Ni Al coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.
基金financially supported by the National Natural Science Foundation of China (No.51001106)National Basic Research Program of China (No.2012CB625100)
文摘A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2SO4/K2SO4（3：1） or Na2SO4/NaCl（3：1） salts at 900 °C in static air are evaluated as well as the aluminide coating.The results indicate that compared with the aluminide coating,the anti-corrosion properties of the Cr-modified aluminide coating in the both salts are improved,which should be attributed to the beneficial effect of the Cr in the coating.The corrosion mechanism of the Cr-modified aluminide coating,especially the role of Cr in the mixture salt corrosion,is discussed.
文摘Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients in β-NiAI phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometric β-NiAI phase, the interdiffusion coefficients in β-NiAI phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of β-NiAI phase.
基金Project(50271010) supported by the National Natural Science Foundation of China
文摘A method was presented to prepare aluminide coatings on metals by combining the pack aluminizing with the ball impact process. This technique applied mechanical vibration to a retort, which was loaded with pack-aluminizing powder, specimens and alloy balls. Pack aluminizing was carried out with repeated ball impact, which accelerated chemical reactions and atomic diffusion. Aluminide coatings were formed at a relatively lower temperature (below 600 ℃) and in a shorter treatment time, compared with the conventional pack aluminizing. The effects of the operation temperature and the treatment time on the formation of the coatings were analysed. The SEM, EDS and XRD analysis results show that the aluminide coatings appear to be homogeneous, with a high density and free of porosity, and have excellent adherence to the substrate. The coatings mainly consist of Al-rich phases such as η-Fe2Al5, θ-FeAl3 and ?CrAl5. Oxidation resistance was studied by high-temperature tests. The formation mechanism of the Al-coatings was also investigated. This technique provides a new approach for industrial diffusion coatings with great energy and time savings.
基金supported by the National Natural Science Foundation of China (51762014)Key Research Project of Natural Science in Universities of Anhui Province (KJ2020A0749)Excellent Young Talents Foundation in Universities of Anhui Province (gxyq2021223).
文摘Present-day Liþstorage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability.Herein,based on a Ca2þsubstituted Mg_(2)Nb_(34)O_(87) anode material,we demonstrate that decreasing the ionic packing factor is a two-fold strategy to enhance the low-temperature electrochemical kinetics and high-temperature cyclic stability.The resulting Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) shows the smallest ionic packing factor among Wadsley–Roth niobate materials.Compared with Mg_(2)Nb_(34)O_(87),Mg1.5Ca0.5Nb_(34)O_(87) delivers a 1.6 times faster Liþdiffusivity at-20℃,leading to 56%larger reversible capacity and 1.5 times higher rate capability.Furthermore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) exhibits an 11%smaller maximum unit-cell volume expansion upon lithiation at 60℃,resulting in better cyclic stability;at 10C after 500 cycles,it has a 7.1%higher capacity retention,and its reversible capacity at 10C is 57%larger.Therefore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) is an allclimate anode material capable of working at harsh temperatures,even when its particle sizes are in the order of micrometers.
