In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot co...In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.展开更多
The NiCrAlY+ZrO2 thermal barrier coating was prepared on the surface of TiAl alloy by plasma spraying technique. The microstructure and phase structure were analyzed using scanning electron microscopy(SEM) and X-ray d...The NiCrAlY+ZrO2 thermal barrier coating was prepared on the surface of TiAl alloy by plasma spraying technique. The microstructure and phase structure were analyzed using scanning electron microscopy(SEM) and X-ray diffractometry(XRD). The high temperature oxidation resistance of the plasma sprayed samples at 850℃ was investigated. The results show that the bonding between thermal barrier coating and substrate is very good. Surface hardness of TiAl alloy is improved too. The microhardness of the coating surface is about HV 900 after the oxidation test at 850 ℃ . The oxidation resistance of the samples is improved remarkably.展开更多
In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstruc...In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstructures, phase constitutions and oxidation behavior of these coatings were studied. The results show that the coating prepared by co-depositing Si?Y at 1080 °C for 5 h has a multiple layer structure: a superficial zone consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3, an out layer consisting of (Ti,Nb)Si2, a middle layer consisting of (Ti,Nb)5Si4 and (Ti,Nb)5Si3, and aγ-TiAl inner layer. Co-deposition temperature imposes strong influences on the coating structure. The coating prepared by Si?Y co-depositing at 1080 °C for 5 h shows relatively good oxidation resistance at 1000 °C in air, and the oxidation rate constant of the coating is about two orders of magnitude lower than that of the bare TiAl alloy.展开更多
Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures a...Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures and compositions were analyzed by SEM,EDX and XRD.The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test,respectively.The results show that the MAO coatings consist of WO3,Ti2O3,graphite and Al2O3 besides Al2TiO5 and Al2SiO5.With additives in the electrolyte,the working voltage at the micro-arc discharge stage decreases,and the ceramic coating gets smoother and more compact.The corrosion current density of MAO coating is much lower than that of TiAl substrate.It can be reduced from 9.81×10-8A/cm 2to 3.02×10-10A/cm 2 .The MAO coatings composed of hard Al2O3,WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy.The wear rate is-3.27×10-7g/(N·m).展开更多
The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr3C2 coating with intermediate layer. Ni-Zn-Al2O3 coatings as interlaye...The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr3C2 coating with intermediate layer. Ni-Zn-Al2O3 coatings as interlayers were prepared by low pressure cold spray（LPCS） between NiCr-Cr3C2 cermet coatings to form a sandwich structure to enhance the corrosion resistance properties. The tribological properties were examined using the UMT-3 fricition and wear tester by line-contact reciprocating sliding under dry and salt spray one week corrosion. The morphology, element distribution, and phase compositions of the coating and worn sufaces were analyzed by using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction respectively. The corrosion behavior of the coating was studied by the open-circuit potential, the electrochemical impedance spectroscopy, potentiodynamic polarization, and salt spray corrosion methods. It is found that the sandwich structured coating has better corrosion resistance than the single layer coating. The results show that under dry wear conditions, the wear mechanism is abrasive and adhesive wear, whereas under salt spray corrosion conditions it becomes corrosion wear. The friction coefficient of the sandwich structured coating after salt spray corrosion is slightly lower than the dry friction coefficient, but the weight of the wear loss is lower than that under dry condition.展开更多
Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler...Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler tube steel, FeCrAl, NiCrTi, Ni50Cr and NiCrAlMoFe-Cr 3C 2 coatings, which are widely used at present for protection of boiler tubes. Meanwhile,the influence of sealer on the hot corrosion resistance of various coatings and the mechanisms of coating corrosion were explored.展开更多
The effect of coatings(Y_2O_3, Zr O_2 and Al_2O_3) on the interfacial reaction of Ti Al alloys was studied with molecular dynamics. The binding energy of coatings and the diffusion process of oxygen in the melt were s...The effect of coatings(Y_2O_3, Zr O_2 and Al_2O_3) on the interfacial reaction of Ti Al alloys was studied with molecular dynamics. The binding energy of coatings and the diffusion process of oxygen in the melt were simulated, and then the simulation results were compared with the experimental results. The simulation results indicate that for each of the three simulated coatings, inordinate interfacial reactions have occurred between the coating and the melt. The binding energy results show that Y_2O_3 has the best stability and is the most difficult to break down. Zr O_2 has the greatest decomposition energy and is the easiest to break down in the melt. Besides, the molecular dynamics indicate that the diffusion coefficient of the oxygen atom in Al_2O_3 is larger than that in the other two coatings, indicating that oxygen diffusion in Al_2O_3 is the fastest at a given temperature. The experimental results show that the oxygen concentration of the melt with Al_2O_3 coating is the highest, and the oxygen diffusion is of similar magnitude to the simulation values, from which the conclusion can be obtained that the oxygen concentration is significantly influenced by the coating materials.展开更多
C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl com...C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl composites were also prepared under the same processing condition for comparision. Both kinds of the composites were thermally exposed in vacuum at 800 and 900℃ for different durations in order to study thermal stability of the interfacial zone. With the aids of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）, the interracial microstructures of the composites were investigated. The results reveal that, although adding the Mo coating, the interfacial reaction product of the SiCf/C/Mo/TiAl composite is the same with that of the SiCf/C/TiA1 composite, which is TiC/Ti2AlC between the coating and the matrix. However, C/Mo duplex coating is more efficient in hindering interfacial reaction than C single coating at 900 ℃ and below. In addition, a new layer of interfacial reaction product was found between Ti2AlC and the matrix after 900 ℃, 200 h thermal exposure, which is rich in V and close to the chemical composition of B2 phase.展开更多
Effect of a sputtered Co-30Cr-5Al microcrystalline coating on oxidation resistance of intermetallic compound TiAl and oxidation behavior of the bare TiAl were investigated at 900—1000℃ in static air.The oxidation ki...Effect of a sputtered Co-30Cr-5Al microcrystalline coating on oxidation resistance of intermetallic compound TiAl and oxidation behavior of the bare TiAl were investigated at 900—1000℃ in static air.The oxidation kinetics for the TiAl alloy seems to approximately follow a linear rate law.Poor oxidation resistance of TiAl is due to the formation of the mixed Al_2O_3+TiO_2 scale which is loosely packed and easily spalled off.but not of dense and adherent pure Al_2O_3.A sputtered Co-30Cr-5Al coating,30 μm thickness,can remarkably improve the oxidation resistance of TiAl owing to the formation of adherent Al_2O_3 protective scale.However,many Kirkendall voids were formed between coating and substrate.展开更多
In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment,Si-Al-Y coatings were fabricated by pack cementation process at 1050℃for 4 h.Corrosion behaviors...In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment,Si-Al-Y coatings were fabricated by pack cementation process at 1050℃for 4 h.Corrosion behaviors of the TiAl alloy with and without Si-Al-Y coatings are compared to illustrate the factors and corresponding mechanism in molten salt environment of 25 wt%K2SO4 and 75 wt%Na2SO4 at 900°C.The obtained Si-Al-Y coating was mainly composed of a TiSi2 outer layer,a(Ti,X)5Si4 and(Ti,X)5Si3(X represents Nb or Cr element)middle layer,a TiAl2 inner layer and a Al-rich inter-diffusion zone.The inter-phase selective corrosion containing corrosion pits extending alongα2 phase from lamellar interfaces in hot corrosion tested TiAl alloy was observed.However,by being coated with Si-Al-Y coating,the hot corrosion performance of TiAl alloy was improved remarkably.展开更多
基金supported by Corporate Talent Fund Program of Zhengzhou Research Institute of Mechanical Engineering Co.,Ltd.(No.201SJ2023013)the Faculty of Materials and Manufacturing,Beijing University of Technology.
文摘In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.
基金Project(20061D0500500151) supported by Beijing Excellent Talent Nurture and Sponsor Project
文摘The NiCrAlY+ZrO2 thermal barrier coating was prepared on the surface of TiAl alloy by plasma spraying technique. The microstructure and phase structure were analyzed using scanning electron microscopy(SEM) and X-ray diffractometry(XRD). The high temperature oxidation resistance of the plasma sprayed samples at 850℃ was investigated. The results show that the bonding between thermal barrier coating and substrate is very good. Surface hardness of TiAl alloy is improved too. The microhardness of the coating surface is about HV 900 after the oxidation test at 850 ℃ . The oxidation resistance of the samples is improved remarkably.
基金Project(2014JZ012)supported by the Natural Science Program for Basic Research in Key Areas of Shaanxi Province,China
文摘In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstructures, phase constitutions and oxidation behavior of these coatings were studied. The results show that the coating prepared by co-depositing Si?Y at 1080 °C for 5 h has a multiple layer structure: a superficial zone consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3, an out layer consisting of (Ti,Nb)Si2, a middle layer consisting of (Ti,Nb)5Si4 and (Ti,Nb)5Si3, and aγ-TiAl inner layer. Co-deposition temperature imposes strong influences on the coating structure. The coating prepared by Si?Y co-depositing at 1080 °C for 5 h shows relatively good oxidation resistance at 1000 °C in air, and the oxidation rate constant of the coating is about two orders of magnitude lower than that of the bare TiAl alloy.
基金Project(2006KG03) supported by the Science and Technology Program of Shannxi Province, China
文摘Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures and compositions were analyzed by SEM,EDX and XRD.The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test,respectively.The results show that the MAO coatings consist of WO3,Ti2O3,graphite and Al2O3 besides Al2TiO5 and Al2SiO5.With additives in the electrolyte,the working voltage at the micro-arc discharge stage decreases,and the ceramic coating gets smoother and more compact.The corrosion current density of MAO coating is much lower than that of TiAl substrate.It can be reduced from 9.81×10-8A/cm 2to 3.02×10-10A/cm 2 .The MAO coatings composed of hard Al2O3,WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy.The wear rate is-3.27×10-7g/(N·m).
基金Funded by the High-Tech Research and Development Program of China(No.2012AA09A203)the Fundmental Research Funds for the Central Universities(No.15CX06061A)the Postgraduate Innovation Project of China University of Petroleum(East China)(No.YCXJ2016059)
文摘The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr3C2 coating with intermediate layer. Ni-Zn-Al2O3 coatings as interlayers were prepared by low pressure cold spray（LPCS） between NiCr-Cr3C2 cermet coatings to form a sandwich structure to enhance the corrosion resistance properties. The tribological properties were examined using the UMT-3 fricition and wear tester by line-contact reciprocating sliding under dry and salt spray one week corrosion. The morphology, element distribution, and phase compositions of the coating and worn sufaces were analyzed by using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction respectively. The corrosion behavior of the coating was studied by the open-circuit potential, the electrochemical impedance spectroscopy, potentiodynamic polarization, and salt spray corrosion methods. It is found that the sandwich structured coating has better corrosion resistance than the single layer coating. The results show that under dry wear conditions, the wear mechanism is abrasive and adhesive wear, whereas under salt spray corrosion conditions it becomes corrosion wear. The friction coefficient of the sandwich structured coating after salt spray corrosion is slightly lower than the dry friction coefficient, but the weight of the wear loss is lower than that under dry condition.
文摘Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler tube steel, FeCrAl, NiCrTi, Ni50Cr and NiCrAlMoFe-Cr 3C 2 coatings, which are widely used at present for protection of boiler tubes. Meanwhile,the influence of sealer on the hot corrosion resistance of various coatings and the mechanisms of coating corrosion were explored.
基金Projects(52161009,51961003)supported by the National Natural Science Foundation of ChinaProject(2022AAC03224)supported by the Natural Science Foundation of Ningxia,ChinaProject(XAB2022YW07)supported by the West Light Foundation of the Chinese Academy of Science。
基金financially supported by the National Natural Science Foundation of China(No.51304198)the Natural Science Foundation of Jiangsu Province,China(Nos.2013106,20141134 and 2014028-08)
文摘The effect of coatings(Y_2O_3, Zr O_2 and Al_2O_3) on the interfacial reaction of Ti Al alloys was studied with molecular dynamics. The binding energy of coatings and the diffusion process of oxygen in the melt were simulated, and then the simulation results were compared with the experimental results. The simulation results indicate that for each of the three simulated coatings, inordinate interfacial reactions have occurred between the coating and the melt. The binding energy results show that Y_2O_3 has the best stability and is the most difficult to break down. Zr O_2 has the greatest decomposition energy and is the easiest to break down in the melt. Besides, the molecular dynamics indicate that the diffusion coefficient of the oxygen atom in Al_2O_3 is larger than that in the other two coatings, indicating that oxygen diffusion in Al_2O_3 is the fastest at a given temperature. The experimental results show that the oxygen concentration of the melt with Al_2O_3 coating is the highest, and the oxygen diffusion is of similar magnitude to the simulation values, from which the conclusion can be obtained that the oxygen concentration is significantly influenced by the coating materials.
基金Projects(51201134,51271147)supported by the National Natural Science Foundation of ChinaProject(2015JM5181)supported by the Natural Science Foundation of Shaanxi Province,China+1 种基金Project(115-QP-2014)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject(3102014JCQ01023)supported by the Fundamental Research Funds for the Central Universities,China
文摘C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl composites were also prepared under the same processing condition for comparision. Both kinds of the composites were thermally exposed in vacuum at 800 and 900℃ for different durations in order to study thermal stability of the interfacial zone. With the aids of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）, the interracial microstructures of the composites were investigated. The results reveal that, although adding the Mo coating, the interfacial reaction product of the SiCf/C/Mo/TiAl composite is the same with that of the SiCf/C/TiA1 composite, which is TiC/Ti2AlC between the coating and the matrix. However, C/Mo duplex coating is more efficient in hindering interfacial reaction than C single coating at 900 ℃ and below. In addition, a new layer of interfacial reaction product was found between Ti2AlC and the matrix after 900 ℃, 200 h thermal exposure, which is rich in V and close to the chemical composition of B2 phase.
文摘Effect of a sputtered Co-30Cr-5Al microcrystalline coating on oxidation resistance of intermetallic compound TiAl and oxidation behavior of the bare TiAl were investigated at 900—1000℃ in static air.The oxidation kinetics for the TiAl alloy seems to approximately follow a linear rate law.Poor oxidation resistance of TiAl is due to the formation of the mixed Al_2O_3+TiO_2 scale which is loosely packed and easily spalled off.but not of dense and adherent pure Al_2O_3.A sputtered Co-30Cr-5Al coating,30 μm thickness,can remarkably improve the oxidation resistance of TiAl owing to the formation of adherent Al_2O_3 protective scale.However,many Kirkendall voids were formed between coating and substrate.
基金Project(2020AAC02025)supported by the Natural Science Foundation of Ningxia Province,ChinaProject(51961003)supported by the National Natural Science Foundation of China+1 种基金Project(TJGC2019040)supported by the Ningxia Youth Talents Supporting Program,ChinaProject(2020xyzc103)supported by the Foundation of North Minzu University,China。
文摘In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment,Si-Al-Y coatings were fabricated by pack cementation process at 1050℃for 4 h.Corrosion behaviors of the TiAl alloy with and without Si-Al-Y coatings are compared to illustrate the factors and corresponding mechanism in molten salt environment of 25 wt%K2SO4 and 75 wt%Na2SO4 at 900°C.The obtained Si-Al-Y coating was mainly composed of a TiSi2 outer layer,a(Ti,X)5Si4 and(Ti,X)5Si3(X represents Nb or Cr element)middle layer,a TiAl2 inner layer and a Al-rich inter-diffusion zone.The inter-phase selective corrosion containing corrosion pits extending alongα2 phase from lamellar interfaces in hot corrosion tested TiAl alloy was observed.However,by being coated with Si-Al-Y coating,the hot corrosion performance of TiAl alloy was improved remarkably.
