Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the...Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the oxidation resistance of the electrodeposited Ni-La2O3/CeO2 composites in air at 1000 °C was studied. The results indicate that, compared with the electrodeposited Ni-film, Ni-La2O3/CeO2 composites exhibit a superior oxidation resistance due to the codeposited La2O3 or CeO2 particles blocking the outward diffusion of nickel. Moreover, compared with nanoparticles, La2O3 or CeO2 microparticles have stronger effect because La2O3 or CeO2 microparticles also act as a diffusion barrier layer at the onset of oxidation.展开更多
Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）...Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）.Effects of different fillers on the isothermal and cyclic oxidation resistance of chromizing coating in air at 850 ℃ were comparably investigated.Microstructure results show that the addition of CeO2 into the filler significantly retards the grain growth of the chromizing coating.Oxidation results indicate that the chromizing coating using CeO2 as filler exhibits somewhat increased oxidation resistance than the normal chromizmg coating,while the chromizing coating using Al2O3＋CeO2 as filler exhibits much better oxidation resistance.The effects of different fillers on the oxidation behaviors were discussed in detail.展开更多
Ni3Al coatings with and without Y2O3 particles were developed by annealing the electrodeposited Ni-Al composite coatings with and without Y2O3 particles at 800 °C for 3 h. The microstructures and cyclic oxidation...Ni3Al coatings with and without Y2O3 particles were developed by annealing the electrodeposited Ni-Al composite coatings with and without Y2O3 particles at 800 °C for 3 h. The microstructures and cyclic oxidation performances of the produced Ni3Al coatings were comparatively investigated, with the emphasis on the effect of Y2O3. SEM/EDAX and TEM characterizations showed that the dispersion of Y2O3 refines the grains. Oxidation at 900 °C for 100 h showed that the addition of Y2O3 significantly improved the cyclic oxidation resistance of Ni3Al coating. The effect of Y2O3 on the microstructure and the oxidation of the Ni3Al coating were discussed in detail.展开更多
By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline...By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.展开更多
Ni-based superalloys added with comparably higher concentrations of single-doped Hf and co-doped Hf/Y are prepared by vacuum induction melting(VIM).The oxidation properties up to 300 h at 900℃,1000℃,and 1100℃ are i...Ni-based superalloys added with comparably higher concentrations of single-doped Hf and co-doped Hf/Y are prepared by vacuum induction melting(VIM).The oxidation properties up to 300 h at 900℃,1000℃,and 1100℃ are investigated.The undoped alloy exhibited a minimum oxidation rate at 900℃ and 1000℃.The co-doped alloy showed a higher oxidation rate;however,it possesses better scale adhesion,and no spallation occurs.Hf-doped alloy showed a lower oxidation rate and better scale adhesion at 900℃ and 1000℃,but exhibited a shorter lifetime at 1100℃.The spallation of the Hf-doped alloy is attributed to the precipitation of the HfO2 in and beneath the oxide scale.The spallation in the undoped alloy is accredited to the thermal expansion mismatch between the growing oxide scale and superalloy substrate.Incorporating two reactive elements(REs)in alloy minimized the precipitation of RE oxide in the oxide scale,diminished internal oxidation in the alloy,and decreased oxide scale spallation.展开更多
B2 FeA1 intermetallic compounds modified with reactive elements （REs） including Sc and Y were fabricated by vacuum arc-melting, and the isothermal oxidation behavior of the RE-doped alloys at 1373 K was investigated...B2 FeA1 intermetallic compounds modified with reactive elements （REs） including Sc and Y were fabricated by vacuum arc-melting, and the isothermal oxidation behavior of the RE-doped alloys at 1373 K was investigated. Both Sc and Y single-doping significantly decrease the alumina film growth rate of the alloys. The alumina film growth rate of Sc＋ Y co-doped alloy even further reduces compared to that of the Sc and Y single-doped alloys. The synergistic effect produced by Sc＋ Y codoping on the growth behavior of alumina was discussed. It could be anticipated that the combined additions of Sc and Y which have matched chemical properties might decrease the alumina film growth rate more effectively and provide FeA1 alloys with enhanced oxidation resistance.展开更多
In order to clarify the effects of reactive element Y on the properties of Si-B co-deposition coating on Mo substrate, the Si-B-Y2O3 and Si-B-Y co-deposition coatings were prepared at 1300 ℃ for 5 h by using the pack...In order to clarify the effects of reactive element Y on the properties of Si-B co-deposition coating on Mo substrate, the Si-B-Y2O3 and Si-B-Y co-deposition coatings were prepared at 1300 ℃ for 5 h by using the pack mixtures 16Si-4B-xY2O3/Y- 4NaF-（76–x）Al2O3 （wt.%,x=0, 0.5, 1, 2, 4, 8）. X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and wavelength dis-persive spectroscopy （WDS） techniques were used to analyze the structure and oxidation behavior of these coatings. The results re-vealed that the Si-B-Y2O3 and Si-B-Y co-deposition coatings had the same structure with that of the Si-B co-deposition coating. However, Y was incorporated into these coatings and the thicknesses of these coatings were thicker than that of the Si-B co-deposition coating. In addition, the Si-B-Y co-deposition coating demonstrated better cyclic oxidation resistance than the Si-B co-deposition coating at 1100 ℃. The modifying mechanism of Y on the Si-B co-deposition coating was discussed.展开更多
β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-...β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-PVD）. Transient oxidation behavior of the coatings is investigated. At 1 200 ℃, only stable α-Al2O3 phase is observed on the 0.05 at% doped coating, whereas the phase transfomlation from θ-Al2O3 to α-Al2O3 occurs in the 0.5 at% Dy doped coating during 1 h oxidation. At 1 100 ℃, all the coatings reveal the transient transformation of θ-α in the early 15 min and the transformation for the 0.05 at% Dy doped coating is completed within 45 min, much earlier than that for the 0.5 at% Dy doped coating. Overdoping of Dy retards the transformation of θ-α. The undoped and overdoped coatings reveal the whisker structure of θ-Al2O3 even after 20 h oxidation at 1 100 ℃, while the 0.05 at% Dy coating reveals typical granulated structure of α-Al2O3.展开更多
The Cr-/Si-modified Ni Al Hf coatings were produced on single-crystal（SC） superalloy N5 by electron beam physical vapor deposition（EB-PVD）. The cyclic oxidation behavior of the coatings at 1100 °C was investi...The Cr-/Si-modified Ni Al Hf coatings were produced on single-crystal（SC） superalloy N5 by electron beam physical vapor deposition（EB-PVD）. The cyclic oxidation behavior of the coatings at 1100 °C was investigated. The microstructures of the oxide scales grown on the coatings were characterized by scanning electron microscope（SEM） with energy-dispersive X-ray spectrum（EDX）,electron probe micro-analyzer（EPMA） and X-ray diffraction（XRD）. The effects of Cr and Si on the cyclic oxidation behavior of the Ni Al Hf coatings were discussed. The addition of Si to the Ni Al Hf Cr coating not only reduces the oxidation rate but also enhances the oxide scale adherence.Owing to the addition of Si in the coating, the segregation of Cr and Mo beneath the oxide scale is effectively avoided,which contributes to enhancing oxide scale adherence.展开更多
Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray ...Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electron probe microanalyzer （EPMA）. The oxidation resistance of the steel is improved by CeO2 coating, though the improvement is not remarkable. Ce-rich oxide band is located at the interface of the inner equiaxed layer and the outer columnar layer after oxidation, which is not consistent with the original surface. The results show that outward iron transport is blocked by the Ce-rich band. A new oxide nucleating and growing site （reaction front） is induced at the inner surface of the Ce rich band.展开更多
Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on t...Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystallineβ-NiAl,severe-scale spallation is observed forβ-NiAl-0.05Hf single-crystal alloy,especially in dry atmosphere.It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale-substrate interface,which promotes the conditions required for reactive element effect.Once the reactive element effect of Hf does not work,its strong affinity with oxygen will accelerate the process of high-temperature oxidation.However,the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance ofβ-NiAl single crystal,resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere.In addition,interfacial cavities are observed in dry and humid atmospheres,which may eventually result in the spallation of the oxide scale.展开更多
Oxide pegging is a widely accepted mechanistic model explaining the reactive element effect on the improved adherence of scale.However,previous models for the oxide peg formation process have not considered the effect...Oxide pegging is a widely accepted mechanistic model explaining the reactive element effect on the improved adherence of scale.However,previous models for the oxide peg formation process have not considered the effects of more than one active element added into the alloy during the peg formation.This study proposes a new model of oxide peg formation and growth for the doping of two reactive elements in an alloy(the precipitated Y and solid solute Ti).Different amounts of Ti and Y were added to a Co Ni Cr Al alloy,and the characteristics of the resulting oxide pegs,such as their linear density,size,and forming process,are obtained by examining alloy samples subjected to an isothermal oxidation operation at a temperature of 1150℃.It is found that the amount of Y determines the density of the oxide pegs,and Ti does not form a Ti-rich oxide core if a Y-rich oxide exists in the sample.In samples with the same Y content,the oxide pegs primarily grow in length,and with increased Ti content,they grow along the b-phase boundary and into the alloy.Based on these results,a three-step model for oxide peg formation and growth is conceived.展开更多
This research presents a thorough assessment of the cyclic oxidation characteristics of Y-and Hf-doped NiCoCrAlTaRe superalloy bond coatings in a pure steam atmosphere,emphasizing the distinct influences of reactive e...This research presents a thorough assessment of the cyclic oxidation characteristics of Y-and Hf-doped NiCoCrAlTaRe superalloy bond coatings in a pure steam atmosphere,emphasizing the distinct influences of reactive elements (Y and Hf) and refractory elements (Ta and Re)on the growth mechanisms of thermally grown oxide(TGO).The findings indicate that,in contrast to air conditions,elevated levels of water vapor significantly diminish the oxidation resistance of the bond coatings,leading to considerable porosity defects in both the central and lower regions of the TGO.Furthermore,this environment hinders the development of the"peg"structure at the TGO/metal interface,thereby accelerating the premature delamination of the coating.Additionally,the presence of doped elements such as Hf,Ta,and Y leads to their segregation at the Al_(2)O_(3)grain boundaries within the TGO,creating grain boundary structures characterized by a high density of defects.This defective architecture promotes the inward diffusion of water molecules at elevatedtemperatures,causing hydrogen atoms generated from oxidation and reduction reactions at the TGO/metal interface to become entrapped within the Al_(2)O_(3)lattice at the base of the TGO,rather than escaping efficiently.Ultimately,this phenomenon contributes to the formation of internal porosity defects during the oxidation of TGO in a steam environment.展开更多
基金Project(GC13A113)supported by the Technology Research and Development Program of Heilongjiang Provincial Science and Technology DepartmentProject(12511469)supported by Heilongjiang Provincial Science and Technology Department
文摘Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the oxidation resistance of the electrodeposited Ni-La2O3/CeO2 composites in air at 1000 °C was studied. The results indicate that, compared with the electrodeposited Ni-film, Ni-La2O3/CeO2 composites exhibit a superior oxidation resistance due to the codeposited La2O3 or CeO2 particles blocking the outward diffusion of nickel. Moreover, compared with nanoparticles, La2O3 or CeO2 microparticles have stronger effect because La2O3 or CeO2 microparticles also act as a diffusion barrier layer at the onset of oxidation.
基金Project (11551419) supported by Scientific Research Fund of Heilongjiang Provincial Education DepartmentProject (12511469) supported by Heilongjiang Provincial Science and Technology Department
文摘Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al2O3,Al2O3＋CeO2 and CeO2 acting as filler,respectively,at a greatly decreased temperature（700 ℃）.Effects of different fillers on the isothermal and cyclic oxidation resistance of chromizing coating in air at 850 ℃ were comparably investigated.Microstructure results show that the addition of CeO2 into the filler significantly retards the grain growth of the chromizing coating.Oxidation results indicate that the chromizing coating using CeO2 as filler exhibits somewhat increased oxidation resistance than the normal chromizmg coating,while the chromizing coating using Al2O3＋CeO2 as filler exhibits much better oxidation resistance.The effects of different fillers on the oxidation behaviors were discussed in detail.
基金Project (11531319) supported by Scientific Research Fund of Heilongjiang Provincial Education Department, China
文摘Ni3Al coatings with and without Y2O3 particles were developed by annealing the electrodeposited Ni-Al composite coatings with and without Y2O3 particles at 800 °C for 3 h. The microstructures and cyclic oxidation performances of the produced Ni3Al coatings were comparatively investigated, with the emphasis on the effect of Y2O3. SEM/EDAX and TEM characterizations showed that the dispersion of Y2O3 refines the grains. Oxidation at 900 °C for 100 h showed that the addition of Y2O3 significantly improved the cyclic oxidation resistance of Ni3Al coating. The effect of Y2O3 on the microstructure and the oxidation of the Ni3Al coating were discussed in detail.
基金Project(11531319)supported by Scientific Research Fund of Heilongjiang Provincial Education Department,China
文摘By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.
基金funded by the National Natural Science Foundation of China under Grant No 51971214.
文摘Ni-based superalloys added with comparably higher concentrations of single-doped Hf and co-doped Hf/Y are prepared by vacuum induction melting(VIM).The oxidation properties up to 300 h at 900℃,1000℃,and 1100℃ are investigated.The undoped alloy exhibited a minimum oxidation rate at 900℃ and 1000℃.The co-doped alloy showed a higher oxidation rate;however,it possesses better scale adhesion,and no spallation occurs.Hf-doped alloy showed a lower oxidation rate and better scale adhesion at 900℃ and 1000℃,but exhibited a shorter lifetime at 1100℃.The spallation of the Hf-doped alloy is attributed to the precipitation of the HfO2 in and beneath the oxide scale.The spallation in the undoped alloy is accredited to the thermal expansion mismatch between the growing oxide scale and superalloy substrate.Incorporating two reactive elements(REs)in alloy minimized the precipitation of RE oxide in the oxide scale,diminished internal oxidation in the alloy,and decreased oxide scale spallation.
基金financially supported by the Basic Research Program of State Grid (No.GCB17201500188)
文摘B2 FeA1 intermetallic compounds modified with reactive elements （REs） including Sc and Y were fabricated by vacuum arc-melting, and the isothermal oxidation behavior of the RE-doped alloys at 1373 K was investigated. Both Sc and Y single-doping significantly decrease the alumina film growth rate of the alloys. The alumina film growth rate of Sc＋ Y co-doped alloy even further reduces compared to that of the Sc and Y single-doped alloys. The synergistic effect produced by Sc＋ Y codoping on the growth behavior of alumina was discussed. It could be anticipated that the combined additions of Sc and Y which have matched chemical properties might decrease the alumina film growth rate more effectively and provide FeA1 alloys with enhanced oxidation resistance.
基金Project supported by the National Natural Science Foundation of China(51401032)the Fundamental Research Funds for the Central Universities from Chang'an University(310831161012)the Fund of the State Key Laboratory of Solidification Processing in NWPU(SKLSP201216)
文摘In order to clarify the effects of reactive element Y on the properties of Si-B co-deposition coating on Mo substrate, the Si-B-Y2O3 and Si-B-Y co-deposition coatings were prepared at 1300 ℃ for 5 h by using the pack mixtures 16Si-4B-xY2O3/Y- 4NaF-（76–x）Al2O3 （wt.%,x=0, 0.5, 1, 2, 4, 8）. X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and wavelength dis-persive spectroscopy （WDS） techniques were used to analyze the structure and oxidation behavior of these coatings. The results re-vealed that the Si-B-Y2O3 and Si-B-Y co-deposition coatings had the same structure with that of the Si-B co-deposition coating. However, Y was incorporated into these coatings and the thicknesses of these coatings were thicker than that of the Si-B co-deposition coating. In addition, the Si-B-Y co-deposition coating demonstrated better cyclic oxidation resistance than the Si-B co-deposition coating at 1100 ℃. The modifying mechanism of Y on the Si-B co-deposition coating was discussed.
基金National Natural Science Foundation of China （50771009, 50731001） National Basic Research Program of China （2010CB631200） Research Fund for the Doctoral Program of Higher Education of China （20070006017）
文摘β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-PVD）. Transient oxidation behavior of the coatings is investigated. At 1 200 ℃, only stable α-Al2O3 phase is observed on the 0.05 at% doped coating, whereas the phase transfomlation from θ-Al2O3 to α-Al2O3 occurs in the 0.5 at% Dy doped coating during 1 h oxidation. At 1 100 ℃, all the coatings reveal the transient transformation of θ-α in the early 15 min and the transformation for the 0.05 at% Dy doped coating is completed within 45 min, much earlier than that for the 0.5 at% Dy doped coating. Overdoping of Dy retards the transformation of θ-α. The undoped and overdoped coatings reveal the whisker structure of θ-Al2O3 even after 20 h oxidation at 1 100 ℃, while the 0.05 at% Dy coating reveals typical granulated structure of α-Al2O3.
基金financially supported by the National Basic Research Program of China (Nos. 2012CB625100 and 2010CB631200)the National Natural Science Foundation of China (No. 51231001)
文摘The Cr-/Si-modified Ni Al Hf coatings were produced on single-crystal（SC） superalloy N5 by electron beam physical vapor deposition（EB-PVD）. The cyclic oxidation behavior of the coatings at 1100 °C was investigated. The microstructures of the oxide scales grown on the coatings were characterized by scanning electron microscope（SEM） with energy-dispersive X-ray spectrum（EDX）,electron probe micro-analyzer（EPMA） and X-ray diffraction（XRD）. The effects of Cr and Si on the cyclic oxidation behavior of the Ni Al Hf coatings were discussed. The addition of Si to the Ni Al Hf Cr coating not only reduces the oxidation rate but also enhances the oxide scale adherence.Owing to the addition of Si in the coating, the segregation of Cr and Mo beneath the oxide scale is effectively avoided,which contributes to enhancing oxide scale adherence.
基金Project(2007A-47) supported by Shandong Electric Power Corporation,China
文摘Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electron probe microanalyzer （EPMA）. The oxidation resistance of the steel is improved by CeO2 coating, though the improvement is not remarkable. Ce-rich oxide band is located at the interface of the inner equiaxed layer and the outer columnar layer after oxidation, which is not consistent with the original surface. The results show that outward iron transport is blocked by the Ce-rich band. A new oxide nucleating and growing site （reaction front） is induced at the inner surface of the Ce rich band.
基金financially supported by the China Postdoctoral Science Foundation(Nos.2016M600028,2017T100023)。
文摘Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystallineβ-NiAl,severe-scale spallation is observed forβ-NiAl-0.05Hf single-crystal alloy,especially in dry atmosphere.It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale-substrate interface,which promotes the conditions required for reactive element effect.Once the reactive element effect of Hf does not work,its strong affinity with oxygen will accelerate the process of high-temperature oxidation.However,the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance ofβ-NiAl single crystal,resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere.In addition,interfacial cavities are observed in dry and humid atmospheres,which may eventually result in the spallation of the oxide scale.
基金financially supported by Tsinghua University Initiative Scientific Research Program and the National Magnetic Confinement Fusion Energy Research Project of China(No.2015GB118001)。
文摘Oxide pegging is a widely accepted mechanistic model explaining the reactive element effect on the improved adherence of scale.However,previous models for the oxide peg formation process have not considered the effects of more than one active element added into the alloy during the peg formation.This study proposes a new model of oxide peg formation and growth for the doping of two reactive elements in an alloy(the precipitated Y and solid solute Ti).Different amounts of Ti and Y were added to a Co Ni Cr Al alloy,and the characteristics of the resulting oxide pegs,such as their linear density,size,and forming process,are obtained by examining alloy samples subjected to an isothermal oxidation operation at a temperature of 1150℃.It is found that the amount of Y determines the density of the oxide pegs,and Ti does not form a Ti-rich oxide core if a Y-rich oxide exists in the sample.In samples with the same Y content,the oxide pegs primarily grow in length,and with increased Ti content,they grow along the b-phase boundary and into the alloy.Based on these results,a three-step model for oxide peg formation and growth is conceived.
基金financially supported by the National Key R&D Program of China(No.2023YFB3711200)the National Natural Science Foundation of China(No.U21A2044)the Science Center for Gas Turbine Project(No.P2022-B-IV-008-001)
文摘This research presents a thorough assessment of the cyclic oxidation characteristics of Y-and Hf-doped NiCoCrAlTaRe superalloy bond coatings in a pure steam atmosphere,emphasizing the distinct influences of reactive elements (Y and Hf) and refractory elements (Ta and Re)on the growth mechanisms of thermally grown oxide(TGO).The findings indicate that,in contrast to air conditions,elevated levels of water vapor significantly diminish the oxidation resistance of the bond coatings,leading to considerable porosity defects in both the central and lower regions of the TGO.Furthermore,this environment hinders the development of the"peg"structure at the TGO/metal interface,thereby accelerating the premature delamination of the coating.Additionally,the presence of doped elements such as Hf,Ta,and Y leads to their segregation at the Al_(2)O_(3)grain boundaries within the TGO,creating grain boundary structures characterized by a high density of defects.This defective architecture promotes the inward diffusion of water molecules at elevatedtemperatures,causing hydrogen atoms generated from oxidation and reduction reactions at the TGO/metal interface to become entrapped within the Al_(2)O_(3)lattice at the base of the TGO,rather than escaping efficiently.Ultimately,this phenomenon contributes to the formation of internal porosity defects during the oxidation of TGO in a steam environment.
