High-entropy pyrochlore-type structures based on rare-earth zirconates are successfully produced by conventional solid-state reaction method. Six rare-earth oxides(La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, and Y2O3) and ZrO2...High-entropy pyrochlore-type structures based on rare-earth zirconates are successfully produced by conventional solid-state reaction method. Six rare-earth oxides(La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, and Y2O3) and ZrO2 are used as the raw powders. Five out of the six rare-earth oxides with equimolar ratio and ZrO2 are mixed and sintered at different temperatures for investigating the reaction process. The results demonstrate that the high-entropy pyrochlores(5RE1/5)2 Zr2O7 have been formed after heated at 1000 ℃. The(5RE1/5)2Zr2O7 are highly sintering resistant and possess excellent thermal stability. The thermal conductivities of the(5RE1/5)2Zr2O7 high-entropy ceramics are below 1 W·m–1·K–1 in the temperature range of 300–1200 ℃. The(5RE1/5)2Zr2O7 can be potential thermal barrier coating materials.展开更多
High-entropy oxides(HEOs)are widely researched as potential materials for thermal barrier coatings(TBCs).However,the relatively low thermal expansion coefficient(TEC)of those materials severely restricts their practic...High-entropy oxides(HEOs)are widely researched as potential materials for thermal barrier coatings(TBCs).However,the relatively low thermal expansion coefficient(TEC)of those materials severely restricts their practical application.In order to improve the poor thermal expansion property and further reduce the thermal conductivity,high-entropy(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))_(2)Ce_(2)O_(7) is designed and synthesized in this work.The as-prepared multicomponent material is formed in a simple disordered fluorite structure due to the high-entropy stabilization effect.Notably,it exhibits a much higher TEC of approximately 12.0×10^(−6) K^(−1) compared with those of other high-entropy oxides reported in the field of TBCs.Besides,it presents prominent thermal insulation behavior with a low intrinsic thermal conductivity of 0.92 W·m^(−1)·K^(−1) at 1400℃,which can be explained by the existence of high concentration oxygen vacancies and highly disordered arrangement of multicomponent cations in the unique high-entropy configuration.Through high-temperature in-situ X-ray diffraction(XRD)measurement,this material shows excellent phase stability up to 1400℃.Benefiting from the solid solution strengthening effect,it shows a higher hardness of 8.72 GPa than the corresponding single component compounds.The superior thermo-physical performance above enables(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))_(2)Ce_(2)O_(7) a promising TBC material.展开更多
HfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics.X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy are employed to decide the crystal structur...HfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics.X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy are employed to decide the crystal structure.Scanning electronic microscopy is utilized to detect the influence of HfO2 alloying effect on microstructure.Current paper indicates that the same numbers of Ta5+and Ho3+ions of HoTaO4 are substituted by Hf4+cations,and it is defined as alloying effect.No crystal structural transition is introduced by HfO2 alloying effect,and circular pores are produced in HoTaO4.HfO2 alloying effect is efficient in decreasing thermal conductivity of HoTaO4 and it is contributed to the differences of ionic radius and atomic weight between Hf4+ions and host cations(Ta5+and Ho3+).The least experimental thermal conductivity is 0.8 W·K–1·m–1 at 900℃,which is detected in 6 and 9 mol%-HfO2 HoTaO4 ceramics.The results imply that HfO2–HoTaO4 ceramics are promising thermal barrier coatings(TBCs)due to their extraordinary thermal insulation performance.展开更多
A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4mol.% yttria stabilized zirconia(4YSZ, hereafter) top coat was fabricated on a second generation Ni-base superalloy. T...A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4mol.% yttria stabilized zirconia(4YSZ, hereafter) top coat was fabricated on a second generation Ni-base superalloy. Thermal cycling behavior of NiCoCrAlY-4 YSZ thermal barrier coatings(TBCs) with and without Pt modification was evaluated in ambient air at 1100?C up to 1000 cycles, aiming to investigate the effect of Pt on formation of thermally grown oxide(TGO) and oxidation resistance. Results indicated that a dual layered TGO, which consisted of top(Ni,Co)(Cr,Al)_2O_4 spinel and underlying α-Al_2O_3, was formed at the NiCoCrAlY/4 YSZ interface with thickness of 8.4μm, accompanying with visible cracks at the interface. In contrast, a single-layer and adherent α-Al_2O_3 scale with thickness of 5.6μm was formed at the interface of Pt-modified NiCoCrAlY and 4 YSZ top coating. The modification of Pt on NiCoCrAlY favored the exclusive formation of α-Al_2O_3 and the reduction of TGO growth rate, and thus could effectively improve overall oxidation performance and extend service life of TBCs. Oxidation and degradation mechanisms of the TBCs with/without Pt-modification were discussed.展开更多
Chemical doping is a normal strategy to tune thermal expansion coefficient(TEC)of ceramics in engineering applications,but the resultant TEC values usually follow Vegard’s law,as doping does not modify the nature of ...Chemical doping is a normal strategy to tune thermal expansion coefficient(TEC)of ceramics in engineering applications,but the resultant TEC values usually follow Vegard’s law,as doping does not modify the nature of chemical bonding in ceramics and its anharmonicity.In this paper,we report abnormal TEC behavior in(Nd_(1−x)Dy_(x))_(2)Zr_(2)O_(7) ceramics,where the TEC values remarkably exceed the values predicted by Vegard’s law and even exceed the values obtained for two constituents Nd_(2)Zr_(2)O_(7) and Dy_(2)Zr_(2)O_(7).In addition to a reduction in lattice energy with an increasing molar fraction of Dy(x)value,we attribute the additional increase in the TEC to the high concentration of Dy dopants in a pyrochlore(P)region,which can soften low-lying optical phonon modes and induce strongly avoided crossing with acoustic phonon branches and enhanced anharmonicity.We believe that this finding can provide a new route to break through the restriction imposed by the conventional Vegard’s law on the TEC values and bring new opportunities for thermal barrier coatings(TBCs)or ceramic/metal composites towards realizing minimized thermal mismatch and prolonged service life during thermal cycling.展开更多
基金Financial support from the National Natural Science Foundation of China (Nos. 51532009, 51602324, and 51872405) are gratefully acknowledged.
文摘High-entropy pyrochlore-type structures based on rare-earth zirconates are successfully produced by conventional solid-state reaction method. Six rare-earth oxides(La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, and Y2O3) and ZrO2 are used as the raw powders. Five out of the six rare-earth oxides with equimolar ratio and ZrO2 are mixed and sintered at different temperatures for investigating the reaction process. The results demonstrate that the high-entropy pyrochlores(5RE1/5)2 Zr2O7 have been formed after heated at 1000 ℃. The(5RE1/5)2Zr2O7 are highly sintering resistant and possess excellent thermal stability. The thermal conductivities of the(5RE1/5)2Zr2O7 high-entropy ceramics are below 1 W·m–1·K–1 in the temperature range of 300–1200 ℃. The(5RE1/5)2Zr2O7 can be potential thermal barrier coating materials.
基金This research was financially supported by Youth Innovation Promotion Association(No.2014378)for Chinese Academy of Sciences.The authors are grateful to the constructive comments of the reviewers.
文摘High-entropy oxides(HEOs)are widely researched as potential materials for thermal barrier coatings(TBCs).However,the relatively low thermal expansion coefficient(TEC)of those materials severely restricts their practical application.In order to improve the poor thermal expansion property and further reduce the thermal conductivity,high-entropy(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))_(2)Ce_(2)O_(7) is designed and synthesized in this work.The as-prepared multicomponent material is formed in a simple disordered fluorite structure due to the high-entropy stabilization effect.Notably,it exhibits a much higher TEC of approximately 12.0×10^(−6) K^(−1) compared with those of other high-entropy oxides reported in the field of TBCs.Besides,it presents prominent thermal insulation behavior with a low intrinsic thermal conductivity of 0.92 W·m^(−1)·K^(−1) at 1400℃,which can be explained by the existence of high concentration oxygen vacancies and highly disordered arrangement of multicomponent cations in the unique high-entropy configuration.Through high-temperature in-situ X-ray diffraction(XRD)measurement,this material shows excellent phase stability up to 1400℃.Benefiting from the solid solution strengthening effect,it shows a higher hardness of 8.72 GPa than the corresponding single component compounds.The superior thermo-physical performance above enables(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))_(2)Ce_(2)O_(7) a promising TBC material.
基金support of the National Natural Science Foundation of China(No.51762028)Materials Genome Engineering of Rare and Precious Metal of Yunnan Province(No.2018ZE019).
文摘HfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics.X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy are employed to decide the crystal structure.Scanning electronic microscopy is utilized to detect the influence of HfO2 alloying effect on microstructure.Current paper indicates that the same numbers of Ta5+and Ho3+ions of HoTaO4 are substituted by Hf4+cations,and it is defined as alloying effect.No crystal structural transition is introduced by HfO2 alloying effect,and circular pores are produced in HoTaO4.HfO2 alloying effect is efficient in decreasing thermal conductivity of HoTaO4 and it is contributed to the differences of ionic radius and atomic weight between Hf4+ions and host cations(Ta5+and Ho3+).The least experimental thermal conductivity is 0.8 W·K–1·m–1 at 900℃,which is detected in 6 and 9 mol%-HfO2 HoTaO4 ceramics.The results imply that HfO2–HoTaO4 ceramics are promising thermal barrier coatings(TBCs)due to their extraordinary thermal insulation performance.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51,671,202 and 51,301,184)the Defense Industrial Technology Development Program(Grant No. JCKY2016404C001)sponsored by the "Liaoning BaiQianWan Talents" Program
文摘A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4mol.% yttria stabilized zirconia(4YSZ, hereafter) top coat was fabricated on a second generation Ni-base superalloy. Thermal cycling behavior of NiCoCrAlY-4 YSZ thermal barrier coatings(TBCs) with and without Pt modification was evaluated in ambient air at 1100?C up to 1000 cycles, aiming to investigate the effect of Pt on formation of thermally grown oxide(TGO) and oxidation resistance. Results indicated that a dual layered TGO, which consisted of top(Ni,Co)(Cr,Al)_2O_4 spinel and underlying α-Al_2O_3, was formed at the NiCoCrAlY/4 YSZ interface with thickness of 8.4μm, accompanying with visible cracks at the interface. In contrast, a single-layer and adherent α-Al_2O_3 scale with thickness of 5.6μm was formed at the interface of Pt-modified NiCoCrAlY and 4 YSZ top coating. The modification of Pt on NiCoCrAlY favored the exclusive formation of α-Al_2O_3 and the reduction of TGO growth rate, and thus could effectively improve overall oxidation performance and extend service life of TBCs. Oxidation and degradation mechanisms of the TBCs with/without Pt-modification were discussed.
基金supported by the National Natural Science Foundation of China(No.52022042)the National Key R&D Program of China(No.2021YFB3702300)National Science and Technology Major Project(No.J2019-VII-0008-0148).
文摘Chemical doping is a normal strategy to tune thermal expansion coefficient(TEC)of ceramics in engineering applications,but the resultant TEC values usually follow Vegard’s law,as doping does not modify the nature of chemical bonding in ceramics and its anharmonicity.In this paper,we report abnormal TEC behavior in(Nd_(1−x)Dy_(x))_(2)Zr_(2)O_(7) ceramics,where the TEC values remarkably exceed the values predicted by Vegard’s law and even exceed the values obtained for two constituents Nd_(2)Zr_(2)O_(7) and Dy_(2)Zr_(2)O_(7).In addition to a reduction in lattice energy with an increasing molar fraction of Dy(x)value,we attribute the additional increase in the TEC to the high concentration of Dy dopants in a pyrochlore(P)region,which can soften low-lying optical phonon modes and induce strongly avoided crossing with acoustic phonon branches and enhanced anharmonicity.We believe that this finding can provide a new route to break through the restriction imposed by the conventional Vegard’s law on the TEC values and bring new opportunities for thermal barrier coatings(TBCs)or ceramic/metal composites towards realizing minimized thermal mismatch and prolonged service life during thermal cycling.
