The halide activated pack cementation method is utilized to deposit aluminide and chromium modified aluminide coatings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing kinetic...The halide activated pack cementation method is utilized to deposit aluminide and chromium modified aluminide coatings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing kinetics as well as on the study of formation of chromium modified aluminide coating. The addition of a small amount of Nb and Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the reaction rate of active Al atoms with substrate through grain refinement as well as by increasing the solid state diffusion of Al through the formation of stable TiAl 3 layer. Cr and Al are simultaneously co deposited by diffusion into K 5 alloy, by a single step, pack cementation process. The morphologies of the coating formed on K 5 substrate, i.e., an external layer with L1 2 structure and an underlying interdiffusion zone, are presented. The mechanism for the formation of Cr modified aluminide coating is discussed.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
This study aims to investigate the feasibility of forming iron aluminide coatings on a commercial 9Cr-lMo (wt.%) alloy steel by pack cementation at 650 °C in an attempt to improve its high temperature oxidation r...This study aims to investigate the feasibility of forming iron aluminide coatings on a commercial 9Cr-lMo (wt.%) alloy steel by pack cementation at 650 °C in an attempt to improve its high temperature oxidation resistance. Pack powders containing Al, A12O3 and a series of halide salts were used to carry out the coating deposition experiments, which enabled identification of the most suitable activator for the pack aluminising process at the intended temperature. The effect of pack aluminium content on the growth kinetics and microstructure of the coatings was then studied by keeping deposition conditions and pack activator content constant while increasing the pack aluminium content from 1.4 wt.% to 6 wt.%. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques were used to analyse the phases and microstructures of the coatings formed and to determine depth profiles of coating elements in the coating layer. Oxidation resistance of the coating was studied at 650 °C in air by intermittent weight measurement at room temperature. It was observed that the coating could substantially enhance the oxidation resistance of the steel under these testing conditions, which was attributed to the capability of the iron aluminide phases to form alumina scale on the coating surface through preferential Al oxidation.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
In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy（SEM）, energy dispersive s...In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD） were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on Ti Al alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant（k） ranged from 1.53 mg^2/（cm^4·h^2） to 2.3 mg^2/（cm^4·h^2）. Activation energy（Q） for the process was calculated as 109 k J/mol, determined by Arrhenius＇ equation： k = k0 exp[–Q/（RT）].展开更多
Up to now, the aluminide coatings used to protect industrial components at high temperature and corrosive environments have been modified by Pt, Cr, Si and Ni. In this investigation, aluminide coatings were modified b...Up to now, the aluminide coatings used to protect industrial components at high temperature and corrosive environments have been modified by Pt, Cr, Si and Ni. In this investigation, aluminide coatings were modified by titanium and the microstructural feature and formation mechanism were evaluated. The coatings were formed on a Ni-based superalloy(IN738LC) by a two stage process including titanizing at first and aluminizing thereafter. Pack cementation titanizing performed at temperatures 950° C and 1050° C in several mixtures of Ti, A12O3 and NH^Cl. At the second stage, aluminum diffused into surface of the specimens by an industrial aluminizing process known as Elcoatl01(4 hrs at 1050° C). The modified coatings were characterized by means of standard optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-Ray diffraction methods. The results show that Ti in the coatings is mainly present in the form of TiNi and Al67Cr8Ti25. Titanium modified coatings grew with a mechanism similar to simple aluminizing; this includes inward diffusion of Al from the pack to the substrate and then outward diffusion of Ni from the substrate to the coating. The advantages and characteristics of this two-stage modified coating is discussed and the process parameters are proposed to obtain a coating of optimum microstructure.展开更多
In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modified with silicon addition and the microstructural features and formation mechani...In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modified with silicon addition and the microstructural features and formation mechanism were evaluated. The coating on the nickel-based superalloy IN738LC was carried out by a two stage process including siliconizing at first and aluminizing thereafter. Pack cementation siliconizing performed at 950C for 2, 4 and 6 hours in several powder mixtures of Si, A12O3 and NHiCl, then aluminum was diffused into the surface of the specimens by an industrial aluminizing process. The modified coatings were characterized by means of standard metallography, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction methods. The results show that Si in the coatings mainly presents in the form of secondary phases including Cr3Si, Mo5Si3 and Nii6Ti6Si7, well distributed within the NiAl matrix. The advantages of this two stage modified coating is discussed.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
文摘The halide activated pack cementation method is utilized to deposit aluminide and chromium modified aluminide coatings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing kinetics as well as on the study of formation of chromium modified aluminide coating. The addition of a small amount of Nb and Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the reaction rate of active Al atoms with substrate through grain refinement as well as by increasing the solid state diffusion of Al through the formation of stable TiAl 3 layer. Cr and Al are simultaneously co deposited by diffusion into K 5 alloy, by a single step, pack cementation process. The morphologies of the coating formed on K 5 substrate, i.e., an external layer with L1 2 structure and an underlying interdiffusion zone, are presented. The mechanism for the formation of Cr modified aluminide coating is discussed.
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The authors wish to thank the European Commission for funding this research under the SUPERCOAT programme contract ENK5-CT-2002-00608(SUPERCOAT).
文摘This study aims to investigate the feasibility of forming iron aluminide coatings on a commercial 9Cr-lMo (wt.%) alloy steel by pack cementation at 650 °C in an attempt to improve its high temperature oxidation resistance. Pack powders containing Al, A12O3 and a series of halide salts were used to carry out the coating deposition experiments, which enabled identification of the most suitable activator for the pack aluminising process at the intended temperature. The effect of pack aluminium content on the growth kinetics and microstructure of the coatings was then studied by keeping deposition conditions and pack activator content constant while increasing the pack aluminium content from 1.4 wt.% to 6 wt.%. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques were used to analyse the phases and microstructures of the coatings formed and to determine depth profiles of coating elements in the coating layer. Oxidation resistance of the coating was studied at 650 °C in air by intermittent weight measurement at room temperature. It was observed that the coating could substantially enhance the oxidation resistance of the steel under these testing conditions, which was attributed to the capability of the iron aluminide phases to form alumina scale on the coating surface through preferential Al oxidation.
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Funded by the Natural Science Program for Basic Research in Key Areas of Shaanxi Province(2014JZ012)
文摘In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD） were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on Ti Al alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant（k） ranged from 1.53 mg^2/（cm^4·h^2） to 2.3 mg^2/（cm^4·h^2）. Activation energy（Q） for the process was calculated as 109 k J/mol, determined by Arrhenius＇ equation： k = k0 exp[–Q/（RT）].
基金The authors thank Isfahan University of technology for help with OM,SEM,and XRD.Special thank to Dr.F.Shahriari for his instruction and kindly cooperation.
文摘Up to now, the aluminide coatings used to protect industrial components at high temperature and corrosive environments have been modified by Pt, Cr, Si and Ni. In this investigation, aluminide coatings were modified by titanium and the microstructural feature and formation mechanism were evaluated. The coatings were formed on a Ni-based superalloy(IN738LC) by a two stage process including titanizing at first and aluminizing thereafter. Pack cementation titanizing performed at temperatures 950° C and 1050° C in several mixtures of Ti, A12O3 and NH^Cl. At the second stage, aluminum diffused into surface of the specimens by an industrial aluminizing process known as Elcoatl01(4 hrs at 1050° C). The modified coatings were characterized by means of standard optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-Ray diffraction methods. The results show that Ti in the coatings is mainly present in the form of TiNi and Al67Cr8Ti25. Titanium modified coatings grew with a mechanism similar to simple aluminizing; this includes inward diffusion of Al from the pack to the substrate and then outward diffusion of Ni from the substrate to the coating. The advantages and characteristics of this two-stage modified coating is discussed and the process parameters are proposed to obtain a coating of optimum microstructure.
基金The authors appreciate Isfahan University of Technology for financial support.
文摘In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modified with silicon addition and the microstructural features and formation mechanism were evaluated. The coating on the nickel-based superalloy IN738LC was carried out by a two stage process including siliconizing at first and aluminizing thereafter. Pack cementation siliconizing performed at 950C for 2, 4 and 6 hours in several powder mixtures of Si, A12O3 and NHiCl, then aluminum was diffused into the surface of the specimens by an industrial aluminizing process. The modified coatings were characterized by means of standard metallography, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction methods. The results show that Si in the coatings mainly presents in the form of secondary phases including Cr3Si, Mo5Si3 and Nii6Ti6Si7, well distributed within the NiAl matrix. The advantages of this two stage modified coating is discussed.
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.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51971205)Shenzhen Science and Technology Innovation Program,China(JCYJ20190807154005593)the Fundamental Research Funds for the Central Universities,China(19lgpy20).
基金Natural Science Foundation of Shandong Province(ZR2019MEE107)Project of Shandong Provincial Department of Transportation(2020B88)Graduate Science and Technology Innovation Project of Shandong Jiaotong University(2023YK106,2023YK109)。
