The commonly-employed material for thermal barrier coatings(TBCs)is 7 wt.%Y2O3 ZrO2(7YSZ),generally deposited by electron beam-physical vapor deposition(EB-PVD).Due to the increasing demand for higher operating temper...The commonly-employed material for thermal barrier coatings(TBCs)is 7 wt.%Y2O3 ZrO2(7YSZ),generally deposited by electron beam-physical vapor deposition(EB-PVD).Due to the increasing demand for higher operating temperature in aero-derivative gas turbines,a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs,which is induced by the microstructure degradation,sintering and spallation after the deposition of infiltrated siliceous mineral(consisting of calcium magnesium aluminum silicate(CaO MgO Al2O3 SiO2,i.e.,CMAS)).A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present.The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs,followed by performing vacuum heat treatment of the Al-deposited TBCs.During the heat treatment,the molten Al reacted with ZrO2 to formα-Al2O3 overlay that effectively hindered CMAS infiltration.Moreover,the Al film could evaporate and re-nucleate,leading to the generation of Al2O3 nanowires,which further restrained the moving of molten CMAS.展开更多
The corrosion resistance characteristics of RE-rich RE_(50)Ta_(x)Zr_(50-x)O_(175+0.5x)oxides in RE_(2)Zr_(2)O_(7)-RETaO_(4)systems to calcium-magnesium-alumino-silicate(CMAS)at 1300°C,and the influence of RE^(3+)...The corrosion resistance characteristics of RE-rich RE_(50)Ta_(x)Zr_(50-x)O_(175+0.5x)oxides in RE_(2)Zr_(2)O_(7)-RETaO_(4)systems to calcium-magnesium-alumino-silicate(CMAS)at 1300°C,and the influence of RE^(3+)and Ta^(5+)on chemical reactions and reactive crystallization of CMAS melts were investigated.The results show that following the thermochemical reactions,apatite,pyrochlore,reprecipitated fluorite and residual Yb(Y)TaO4phases were the predominant reaction products.Formation abilities of apatite and pyrochlore were found to be proportional to the ionic radius of RE^(3+).The increase of Ta^(5+)amount can decrease the number of available RE^(3+)to form apatite.Moreover,the resistance characteristic to CMAS corrosion in RE_(50)Ta_(x)Zr_(50-x)O_(175+0.5x)systems was decided by the combined action of apatite and pyrochlore phases.The cohesive mixture of apatite and pyrochlore phases can generate a dense layer near the reaction front,which had a positive effect on suppressing CMAS infiltration.The ability of the fluorite+RETaO4two-phase field was determined to be sufficient to mitigate CMAS corrosion.展开更多
Exploring superior calcium-magnesium-aluminosilicate(CMAS)corrosion resistance is crucial for highentropy rare-earth monosilicates(HEREMs)as the next-generation environmental barrier coating(EBC)materials.However,rela...Exploring superior calcium-magnesium-aluminosilicate(CMAS)corrosion resistance is crucial for highentropy rare-earth monosilicates(HEREMs)as the next-generation environmental barrier coating(EBC)materials.However,related studies are rarely reported.This work presents the exploration of HEREMs with remarkable CMAS corrosion resistance by engineering their compositions.The equimolar 3-to-9 cation high-entropy rare-earth monosilicate(3-9HEREM)specimens were initially prepared using a pressure-less sintering technique;subsequently,their resistance to CMAS corrosion was evaluated at temperatures up to 1600C.The results demonstrate that the 5HEREM specimens possess the best CMAS corrosion resistance among all the as-fabricated specimens,surpassing other reported EBC materials.Such remarkable CMAS corrosion resistance results from the generation of a dense apatite protective layer originating from its low dissolution rate at elevated temperatures.展开更多
Failure of thermal barrier coatings(TBCs)can reduce the safety of aero-engines.Predicting the lifetime of TBCs on turbine blades under real service conditions is challenging due to the complex multiscale computation r...Failure of thermal barrier coatings(TBCs)can reduce the safety of aero-engines.Predicting the lifetime of TBCs on turbine blades under real service conditions is challenging due to the complex multiscale computation required and the chemo-thermomechanically coupled mechanisms involved.This paper proposes a multiscale deep-learning method for TBC failure prediction under typical thermal shock conditions involving calcium-magnesium-alumina-silicate(CMAS)corrosion.A microscale model is used to describe local stress and damage with consideration of the TBC microstructure and CMAS infiltration and corrosion mechanisms.A deep learning network is developed to reveal the effect of microscale corrosion on TBC lifetime.The modeled spalling mechanism and area are consistent with the experimental results,with the predicted lifetime being within 20%of that observed.This work provides an effective method for predicting the lifetime of TBCs under real service conditions.展开更多
Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-bas...Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-based ceramics.RE2Si2O7(RE=rare earth)has been widely recognized as one of the most promising candidates for environmental barrier coatings due to its good water vapor corrosion resistance.However,the relatively high thermal conductivity and poor resistance to CMAS corrosion have limited its practical application.Inspired by the high entropy effect,in this work,a novel rare earth disilicate(Lu_(_(1/7))Yb_(_(1/7))Sc_(_(1/7))Er_(_(1/7))Y_(_(1/7))Ho_(_(1/7))Dy_(_(1/7)))2Si2O7((7RE_(_(1/7)))2Si2O7)has been designed and synthesized by a solid reaction process.(7RE_(_(1/7)))2Si2O7 showed a low thermal conductivity of 1.81 W·m^(−1)·K^(−1)at 1273 K.Furthermore,the thermal expansion coefficient of(7RE_(_(1/7)))_(2)Si_(2)O_(7)(4.07×10^(−6)℃^(−1)from room temperature(RT)to 1400℃)is close to that of the SiC-based ceramic matrix composites(SiC-CMCs)((4.5–5.5)×10^(−6)℃^(−1)).Additionally,(7RE_(_(1/7)))2Si2O7 exhibited excellent resistance to CMAS corrosion.When exposed to CMAS at 1300℃for 48 h,the reaction layer thickness was 22μm.The improved performance of(7RE_(_(1/7)))2Si2O7 highlights its potential as a promising candidate for thermal/environmental barrier coatings.展开更多
Laser glazing to produce a modified layer on the surface of thermal barrier coatings(TBCs)is a promising method to alleviate calcium-magnesium-alumina-silicate(CMAS)attacks to coatings.In this study,finite element ana...Laser glazing to produce a modified layer on the surface of thermal barrier coatings(TBCs)is a promising method to alleviate calcium-magnesium-alumina-silicate(CMAS)attacks to coatings.In this study,finite element analysis is carried out to investigate the temperature field and stress distribution of TBCs after the laser glazing process and the modified TBCs after CMAS corrosion.Results revealed that along the direction of laser scanning,the principal stress was in a tensile state,which increased along the direction of the laser spot movement;while perpendicular to the laser scanning direction,the maximum principal stress appeared at the interface between the glazed layer and the unmodified coating,where could be a potential danger zone for crack initiation and coating spallation.For the modified TBCs with CMAS attack,in regions that are located in the range of 0–6 mm along the radial direction,the radial stress and maximum principal stress were high(~1094 MPa),and the coating edge had complex shear stress state;as a result,these areas were easy to crack.展开更多
Calcium-magnesium-alumino-silicate(CMAS)corrosion is a critical factor which causes the failure of thermal barrier coating(TBC).CMAS attack significantly alters the temperature and stress fields in TBC,resulting in th...Calcium-magnesium-alumino-silicate(CMAS)corrosion is a critical factor which causes the failure of thermal barrier coating(TBC).CMAS attack significantly alters the temperature and stress fields in TBC,resulting in their delamination or spallation.In this work,the evolution process of TBC prepared by suspension plasma spraying(SPS)under CMAS attack is investigated.The CMAS corrosion leads to the formation of the reaction layer and subsequent bending of TBC.Based on the observations,a corrosion model is proposed to describe the generation and evolution of the reaction layer and bending of TBC.Then,numerical simulations are performed to investigate the corrosion process of free-standing TBC and the complete TBC system under CMAS attack.The corrosion model constructs a bridge for connecting two numerical models.The results show that the CMAS corrosion has a significant influence on the stress field,such as the peak stress,whereas it has little influence on the steady-state temperature field.The peak of stress increases with holding time,which increases the risk of the rupture of TBC.The Mises stress increases nonlinearly along the thick direction of the reaction layer.Furthermore,in the traditional failure zone,such as the interface of the top coat and bond coat,the stress obviously changes during CMAS corrosion.展开更多
Calcium–magnesium–alumina–silicate(CMAS)corrosion is a serious threat to thermal barrier coatings(TBCs).Ti_(2)AlC has been proven to be a potential protection layer material for TBCs to resist CMAS corrosion.In thi...Calcium–magnesium–alumina–silicate(CMAS)corrosion is a serious threat to thermal barrier coatings(TBCs).Ti_(2)AlC has been proven to be a potential protection layer material for TBCs to resist CMAS corrosion.In this study,the effects of the pellet surface roughness and temperature on the microstructure of the pre-oxidation layer and CMAS corrosion behavior of Ti_(2)AlC were investigated.The results revealed that pre-oxidation produced inner Al_(2)O_(3)layer and outer TiO_(2)clusters on the pellet surfaces.The content of TiO_(2)decreased with decreasing pellet surface roughness and increased along with the pre-oxidation temperature.The thickness of Al_(2)O_(3)layer is also positively related to the pre-oxidation temperature.The Ti_(2)AlC pellets pre-oxidized at 1050℃could effectively resist CMAS corrosion by promoting the crystallization of anorthite(CaAl_(2)Si_(2)O_(8))from the CMAS melt rapidly,and the resistance effectiveness increased with the pellet surface roughness.Additionally,the CMAS layer mainly spalled off at the interface of CaAl_(2)Si_(2)O_(8)/Al_(2)O_(3)layer after thermal cycling tests coupled with CMAS corrosion.The Al_(2)O_(3)layer grown on the rough interface could combine with the pellets tightly during thermal cycling tests,which was attributed to obstruction of the rough interface to crack propagation.展开更多
Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of...Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.展开更多
In this research,a novel method for regulating components in RE_(2)SiO_(5)/RE_(2)Si_(2)O_(7)multiphase silicates was developed,combining the benefits of a suitable thermal expansion coefficient(CTE)and outstanding cor...In this research,a novel method for regulating components in RE_(2)SiO_(5)/RE_(2)Si_(2)O_(7)multiphase silicates was developed,combining the benefits of a suitable thermal expansion coefficient(CTE)and outstanding corrosion resistance against calcium–magnesium–alumino–silicate(CMAS).This approach enhanced the overall thermophysical properties.Additionally,the results from the CMAS corrosion resistance test indicated that(Lu_(1/3)Yb_(1/3)Tm_(1/3))_(2)SiO_(5)/(Lu_(1/3)Yb_(1/3)Tm_(1/3))_(2)Si_(2)O_(7)and(Lu_(1/4)Yb_(1/4)Tm_(1/4)Er_(1/4))_(2)SiO_(5)/(Lu_(1/4)Yb_(1/4)Tm_(1/4)Er_(1/4))_(2)Si_(2)O_(7)exhibited exceptional resistance to CMAS penetration,even at temperatures up to 1500℃.To comprehend the corrosion mechanism of CMAS on these silicates,we introduced a reaction–diffusion model,which involved observing the changes in the interface between the corrosion product layer and the silicate block.This was achieved using electron backscatter diffraction(EBSD).These findings lay a theoretical basis for selecting rare earth elements in RE_(2)SiO_(5)/RE_(2)Si_(2)O_(7)multiphase silicates based on the radii of different rare earth cations.展开更多
Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–sil...Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate(CMAS)melt corrosion at high service temperatures,which impedes their practical application.In this work,we developed a series of REAlO_(3)/RE_(2)Zr_(2)O_(7)(RE=La,Nd,Sm,Eu,Gd,and Dy)composites with a eutectic composition that not only significantly enhanced the fracture toughness by more than 40%relative to that of RE_(2)Zr_(2)O_(7)but also exhibited improved resistance to CMAS corrosion.The increase in toughness arises from multiple mechanisms,such as ferroelastic toughening,fine-grain strengthening,and residual stress toughening,all of which trigger more crack defects and energy consumption.Additionally,the CMAS penetration depth of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites is approximately 36%lower than that of RE_(2)Zr_(2)O_(7).Al–O constituents in composites can capture CaO,SiO_(2),and MgO in CMAS melts and increase their viscosity,resulting in enhanced CMAS corrosion resistance.The thermophysical properties of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites were also investigated,and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7–8 wt%Y_(2)O_(3)partially stabilized ZrO2(YSZ),indicating their potential as TBC materials.展开更多
Xenotime rare-earth(RE)phosphates are emerging as promising materials for environmental barrier coatings(EBCs)for SiC-based ceramic-matrix composites(CMCs)because of their close coefficients of thermal expansion(CTEs)...Xenotime rare-earth(RE)phosphates are emerging as promising materials for environmental barrier coatings(EBCs)for SiC-based ceramic-matrix composites(CMCs)because of their close coefficients of thermal expansion(CTEs)and resistance to calcium-magnesium-alumina-silicate(CMAS)corrosion.In this work,high-entropy(HE)(Sc_(0.2)Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2))PO_(4) and five single-component REPO4(RE=Sc,Lu,Yb,Er,and Y)compounds were synthesized,and their stability,thermal properties,and CMAS corrosion resistance were investigated.The CTE values of four REPO_(4) compounds(RE=Lu,Yb,Er,and Y;~(5.6-6)×10^(−6)℃^(−1))are close to those of SiC-CMC((4.5-5.5)×10^(−6)℃^(−1)),whereas ScPO_(4)(6.98×10^(−6)℃^(−1))and HE(5RE_(0.2))PO_(4)(6.39×10^(−6)℃^(−1))have slightly higher values in the temperature range of 200-1300℃.HE phosphate has the lowest thermal conductivity due to its size and mass disorder.Systematic CMAS corrosion tests at 1300℃ for 5,45,and 96 h revealed that all RE phosphates formed a continuous and dense reaction layer predominantly composed of Ca_(8)MgRE(PO_(4))_(7),effectively impeding CMAS penetration.Additionally,REPO_(4) with smaller RE³−cations displays a slower reaction rate and reduced corrosion kinetics,as evidenced by the smaller thickness of the reaction layer.A larger negative difference in the optical basicity(OB)value between REPO_(4) and CMAS signifies greater corrosion resistance.A mechanistic understanding of CMAS corrosion and elucidation of the effects of critical parameters such as the ionic mass and ionic radius of RE elements on their thermal properties and CMAS corrosion kinetics are useful for the development of novel xenotime-type phosphates as EBCs for SiC-CMCs.展开更多
Rare earth(RE)silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines.However,calcium-magnesium-alumina-silicate(CMAS)corrosion becomes much more serious ...Rare earth(RE)silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines.However,calcium-magnesium-alumina-silicate(CMAS)corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature.Therefore,it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures.Herein,the interaction between RE_(2)SiO_(5) and CMAS up to 1500℃was investigated by a novel high temperature in-situ observation method.High temperature promotes the growth of the main reaction product(Ca_(2)RE_(8)(SiO_(4))6O_(2))fast along the[001]direction,and the precipitation of short and horizontally distributed Ca_(2)RE_(8)(SiO_(4))6O_(2) grains was accelerated during the cooling process.The increased temperature increases the solubility of RE elements,decreases the viscosity of CMAS,and thus elevates the corrosion reaction rate,making RE_(2)SiO_(5) fast interaction with CMAS and less affected by RE element species.展开更多
基金Project(2017YFB0306100) supported by the National Key Research&Development Plan of ChinaProjects(51801034,51771059) supported by the National Natural Science Foundation of China+3 种基金Projects(2018GDASCX-0949,2018GDASCX-0950,2017GDASCX-0111) supported by the Guangdong Academy of Sciences,ChinaProjects(2017B090916002,2017A070701027) supported by the Guangdong Technical Research Program,ChinaProjects(2016A030312015,2017A030310315) supported by the Natural Science Foundation of Guangdong Province,ChinaProjects(201605131008557,201707010385) supported by the Technical Research Program of Guangzhou City,China
文摘The commonly-employed material for thermal barrier coatings(TBCs)is 7 wt.%Y2O3 ZrO2(7YSZ),generally deposited by electron beam-physical vapor deposition(EB-PVD).Due to the increasing demand for higher operating temperature in aero-derivative gas turbines,a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs,which is induced by the microstructure degradation,sintering and spallation after the deposition of infiltrated siliceous mineral(consisting of calcium magnesium aluminum silicate(CaO MgO Al2O3 SiO2,i.e.,CMAS)).A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present.The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs,followed by performing vacuum heat treatment of the Al-deposited TBCs.During the heat treatment,the molten Al reacted with ZrO2 to formα-Al2O3 overlay that effectively hindered CMAS infiltration.Moreover,the Al film could evaporate and re-nucleate,leading to the generation of Al2O3 nanowires,which further restrained the moving of molten CMAS.
基金supported by the National Natural Science Foundation of China(No.51801170)the National Postdoctoral Program for Innovative Talents,China(No.BX20180265)+2 种基金the Natural Science Foundation of Hunan Province,China(No.2019JJ50570)the China Postdoctoral Science Foundation(No.2019M652786)the Research Initiation Project of Xiangtan University,China(No.18QDZ24)。
文摘The corrosion resistance characteristics of RE-rich RE_(50)Ta_(x)Zr_(50-x)O_(175+0.5x)oxides in RE_(2)Zr_(2)O_(7)-RETaO_(4)systems to calcium-magnesium-alumino-silicate(CMAS)at 1300°C,and the influence of RE^(3+)and Ta^(5+)on chemical reactions and reactive crystallization of CMAS melts were investigated.The results show that following the thermochemical reactions,apatite,pyrochlore,reprecipitated fluorite and residual Yb(Y)TaO4phases were the predominant reaction products.Formation abilities of apatite and pyrochlore were found to be proportional to the ionic radius of RE^(3+).The increase of Ta^(5+)amount can decrease the number of available RE^(3+)to form apatite.Moreover,the resistance characteristic to CMAS corrosion in RE_(50)Ta_(x)Zr_(50-x)O_(175+0.5x)systems was decided by the combined action of apatite and pyrochlore phases.The cohesive mixture of apatite and pyrochlore phases can generate a dense layer near the reaction front,which had a positive effect on suppressing CMAS infiltration.The ability of the fluorite+RETaO4two-phase field was determined to be sufficient to mitigate CMAS corrosion.
基金the National Key Research and Development Program of China(No.2022YFB3708600)the National Natural Science Foundation of China(No.52122204).
文摘Exploring superior calcium-magnesium-aluminosilicate(CMAS)corrosion resistance is crucial for highentropy rare-earth monosilicates(HEREMs)as the next-generation environmental barrier coating(EBC)materials.However,related studies are rarely reported.This work presents the exploration of HEREMs with remarkable CMAS corrosion resistance by engineering their compositions.The equimolar 3-to-9 cation high-entropy rare-earth monosilicate(3-9HEREM)specimens were initially prepared using a pressure-less sintering technique;subsequently,their resistance to CMAS corrosion was evaluated at temperatures up to 1600C.The results demonstrate that the 5HEREM specimens possess the best CMAS corrosion resistance among all the as-fabricated specimens,surpassing other reported EBC materials.Such remarkable CMAS corrosion resistance results from the generation of a dense apatite protective layer originating from its low dissolution rate at elevated temperatures.
基金supported by the National Natural Science Foundation of China(Grant No.12202507)the China Postdoctoral Science Foundation(Grant No.2023M732738)+3 种基金the National Natural Science Foundation of China(Grant No.11890684)the Hunan Provincial Natural Science Foundation(Grant No.2022JJ40118)the National Science and Technology Major Project(Grant No.J2022-V-0003-0029)the Fundamental Research Funds for the Central Universities(Grant No.QTZX23014).
文摘Failure of thermal barrier coatings(TBCs)can reduce the safety of aero-engines.Predicting the lifetime of TBCs on turbine blades under real service conditions is challenging due to the complex multiscale computation required and the chemo-thermomechanically coupled mechanisms involved.This paper proposes a multiscale deep-learning method for TBC failure prediction under typical thermal shock conditions involving calcium-magnesium-alumina-silicate(CMAS)corrosion.A microscale model is used to describe local stress and damage with consideration of the TBC microstructure and CMAS infiltration and corrosion mechanisms.A deep learning network is developed to reveal the effect of microscale corrosion on TBC lifetime.The modeled spalling mechanism and area are consistent with the experimental results,with the predicted lifetime being within 20%of that observed.This work provides an effective method for predicting the lifetime of TBCs under real service conditions.
基金the National Key R&D Program of China(No.2022YFE0121200)the National Natural Science Foundation of China(Nos.52371052 and 52073029).
文摘Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-based ceramics.RE2Si2O7(RE=rare earth)has been widely recognized as one of the most promising candidates for environmental barrier coatings due to its good water vapor corrosion resistance.However,the relatively high thermal conductivity and poor resistance to CMAS corrosion have limited its practical application.Inspired by the high entropy effect,in this work,a novel rare earth disilicate(Lu_(_(1/7))Yb_(_(1/7))Sc_(_(1/7))Er_(_(1/7))Y_(_(1/7))Ho_(_(1/7))Dy_(_(1/7)))2Si2O7((7RE_(_(1/7)))2Si2O7)has been designed and synthesized by a solid reaction process.(7RE_(_(1/7)))2Si2O7 showed a low thermal conductivity of 1.81 W·m^(−1)·K^(−1)at 1273 K.Furthermore,the thermal expansion coefficient of(7RE_(_(1/7)))_(2)Si_(2)O_(7)(4.07×10^(−6)℃^(−1)from room temperature(RT)to 1400℃)is close to that of the SiC-based ceramic matrix composites(SiC-CMCs)((4.5–5.5)×10^(−6)℃^(−1)).Additionally,(7RE_(_(1/7)))2Si2O7 exhibited excellent resistance to CMAS corrosion.When exposed to CMAS at 1300℃for 48 h,the reaction layer thickness was 22μm.The improved performance of(7RE_(_(1/7)))2Si2O7 highlights its potential as a promising candidate for thermal/environmental barrier coatings.
基金financially supported by the National Natural Science Foundation of China(No.51971156)
文摘Laser glazing to produce a modified layer on the surface of thermal barrier coatings(TBCs)is a promising method to alleviate calcium-magnesium-alumina-silicate(CMAS)attacks to coatings.In this study,finite element analysis is carried out to investigate the temperature field and stress distribution of TBCs after the laser glazing process and the modified TBCs after CMAS corrosion.Results revealed that along the direction of laser scanning,the principal stress was in a tensile state,which increased along the direction of the laser spot movement;while perpendicular to the laser scanning direction,the maximum principal stress appeared at the interface between the glazed layer and the unmodified coating,where could be a potential danger zone for crack initiation and coating spallation.For the modified TBCs with CMAS attack,in regions that are located in the range of 0–6 mm along the radial direction,the radial stress and maximum principal stress were high(~1094 MPa),and the coating edge had complex shear stress state;as a result,these areas were easy to crack.
基金This study is supported by the National Natural Science Foundation of China(Nos.1171101165 and 11902240).
文摘Calcium-magnesium-alumino-silicate(CMAS)corrosion is a critical factor which causes the failure of thermal barrier coating(TBC).CMAS attack significantly alters the temperature and stress fields in TBC,resulting in their delamination or spallation.In this work,the evolution process of TBC prepared by suspension plasma spraying(SPS)under CMAS attack is investigated.The CMAS corrosion leads to the formation of the reaction layer and subsequent bending of TBC.Based on the observations,a corrosion model is proposed to describe the generation and evolution of the reaction layer and bending of TBC.Then,numerical simulations are performed to investigate the corrosion process of free-standing TBC and the complete TBC system under CMAS attack.The corrosion model constructs a bridge for connecting two numerical models.The results show that the CMAS corrosion has a significant influence on the stress field,such as the peak stress,whereas it has little influence on the steady-state temperature field.The peak of stress increases with holding time,which increases the risk of the rupture of TBC.The Mises stress increases nonlinearly along the thick direction of the reaction layer.Furthermore,in the traditional failure zone,such as the interface of the top coat and bond coat,the stress obviously changes during CMAS corrosion.
基金This research is sponsored by the National Natural Science Foundation of China(Grant No.51971156).
文摘Calcium–magnesium–alumina–silicate(CMAS)corrosion is a serious threat to thermal barrier coatings(TBCs).Ti_(2)AlC has been proven to be a potential protection layer material for TBCs to resist CMAS corrosion.In this study,the effects of the pellet surface roughness and temperature on the microstructure of the pre-oxidation layer and CMAS corrosion behavior of Ti_(2)AlC were investigated.The results revealed that pre-oxidation produced inner Al_(2)O_(3)layer and outer TiO_(2)clusters on the pellet surfaces.The content of TiO_(2)decreased with decreasing pellet surface roughness and increased along with the pre-oxidation temperature.The thickness of Al_(2)O_(3)layer is also positively related to the pre-oxidation temperature.The Ti_(2)AlC pellets pre-oxidized at 1050℃could effectively resist CMAS corrosion by promoting the crystallization of anorthite(CaAl_(2)Si_(2)O_(8))from the CMAS melt rapidly,and the resistance effectiveness increased with the pellet surface roughness.Additionally,the CMAS layer mainly spalled off at the interface of CaAl_(2)Si_(2)O_(8)/Al_(2)O_(3)layer after thermal cycling tests coupled with CMAS corrosion.The Al_(2)O_(3)layer grown on the rough interface could combine with the pellets tightly during thermal cycling tests,which was attributed to obstruction of the rough interface to crack propagation.
基金supported by the National Natural Science Foundation for Young Scientists of China(Grant No.51802213)Program of Applied Basic Research Program of Shanxi Province(Grant No.201901D211118)Key R&D Program of Shanxi Province(Grant No.202102030201006).
文摘Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.
基金supported by the National Key R&D Program of China(No.2023YFF0719800).
文摘In this research,a novel method for regulating components in RE_(2)SiO_(5)/RE_(2)Si_(2)O_(7)multiphase silicates was developed,combining the benefits of a suitable thermal expansion coefficient(CTE)and outstanding corrosion resistance against calcium–magnesium–alumino–silicate(CMAS).This approach enhanced the overall thermophysical properties.Additionally,the results from the CMAS corrosion resistance test indicated that(Lu_(1/3)Yb_(1/3)Tm_(1/3))_(2)SiO_(5)/(Lu_(1/3)Yb_(1/3)Tm_(1/3))_(2)Si_(2)O_(7)and(Lu_(1/4)Yb_(1/4)Tm_(1/4)Er_(1/4))_(2)SiO_(5)/(Lu_(1/4)Yb_(1/4)Tm_(1/4)Er_(1/4))_(2)Si_(2)O_(7)exhibited exceptional resistance to CMAS penetration,even at temperatures up to 1500℃.To comprehend the corrosion mechanism of CMAS on these silicates,we introduced a reaction–diffusion model,which involved observing the changes in the interface between the corrosion product layer and the silicate block.This was achieved using electron backscatter diffraction(EBSD).These findings lay a theoretical basis for selecting rare earth elements in RE_(2)SiO_(5)/RE_(2)Si_(2)O_(7)multiphase silicates based on the radii of different rare earth cations.
基金supported by the National Key R&D Program of China(No.2021YFB3702300)the National Natural Science Foundation of China(No.52022042)+2 种基金the Project of the Science Center for Gas Turbine(No.HT-P2022-DB-Ⅳ-002-001)the National Science and Technology Major Project(No.J2019-Ⅶ−0008-0148)the Research on the Development and Preparation of Thermal Barrier Coating Materials on New Generation of Heavy-duty Gas Turbines(No.UGTC-HT-WXKT-2022-032).
文摘Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate(CMAS)melt corrosion at high service temperatures,which impedes their practical application.In this work,we developed a series of REAlO_(3)/RE_(2)Zr_(2)O_(7)(RE=La,Nd,Sm,Eu,Gd,and Dy)composites with a eutectic composition that not only significantly enhanced the fracture toughness by more than 40%relative to that of RE_(2)Zr_(2)O_(7)but also exhibited improved resistance to CMAS corrosion.The increase in toughness arises from multiple mechanisms,such as ferroelastic toughening,fine-grain strengthening,and residual stress toughening,all of which trigger more crack defects and energy consumption.Additionally,the CMAS penetration depth of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites is approximately 36%lower than that of RE_(2)Zr_(2)O_(7).Al–O constituents in composites can capture CaO,SiO_(2),and MgO in CMAS melts and increase their viscosity,resulting in enhanced CMAS corrosion resistance.The thermophysical properties of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites were also investigated,and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7–8 wt%Y_(2)O_(3)partially stabilized ZrO2(YSZ),indicating their potential as TBC materials.
基金supported as part of the DMREF:Machine Learning Accelerated Design and Discovery of Rare-earth Phosphates as Next Generation Environmental Barrier Coatings,a standard Grant funded by the Division of Materials Research,National Science Foundation under Award DMREF-2119423.
文摘Xenotime rare-earth(RE)phosphates are emerging as promising materials for environmental barrier coatings(EBCs)for SiC-based ceramic-matrix composites(CMCs)because of their close coefficients of thermal expansion(CTEs)and resistance to calcium-magnesium-alumina-silicate(CMAS)corrosion.In this work,high-entropy(HE)(Sc_(0.2)Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2))PO_(4) and five single-component REPO4(RE=Sc,Lu,Yb,Er,and Y)compounds were synthesized,and their stability,thermal properties,and CMAS corrosion resistance were investigated.The CTE values of four REPO_(4) compounds(RE=Lu,Yb,Er,and Y;~(5.6-6)×10^(−6)℃^(−1))are close to those of SiC-CMC((4.5-5.5)×10^(−6)℃^(−1)),whereas ScPO_(4)(6.98×10^(−6)℃^(−1))and HE(5RE_(0.2))PO_(4)(6.39×10^(−6)℃^(−1))have slightly higher values in the temperature range of 200-1300℃.HE phosphate has the lowest thermal conductivity due to its size and mass disorder.Systematic CMAS corrosion tests at 1300℃ for 5,45,and 96 h revealed that all RE phosphates formed a continuous and dense reaction layer predominantly composed of Ca_(8)MgRE(PO_(4))_(7),effectively impeding CMAS penetration.Additionally,REPO_(4) with smaller RE³−cations displays a slower reaction rate and reduced corrosion kinetics,as evidenced by the smaller thickness of the reaction layer.A larger negative difference in the optical basicity(OB)value between REPO_(4) and CMAS signifies greater corrosion resistance.A mechanistic understanding of CMAS corrosion and elucidation of the effects of critical parameters such as the ionic mass and ionic radius of RE elements on their thermal properties and CMAS corrosion kinetics are useful for the development of novel xenotime-type phosphates as EBCs for SiC-CMCs.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.52202078 and 52202126)Guangdong Basic and Applied Basic Research Foundation for Distinguished Young Scholars(Grant No.2021B1515020083)+1 种基金Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2021A1515110293 and 2022A1515012201)Shenzhen Science and Technology Program(Grant Nos.202206193000001 and 20220818183014003).
文摘Rare earth(RE)silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines.However,calcium-magnesium-alumina-silicate(CMAS)corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature.Therefore,it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures.Herein,the interaction between RE_(2)SiO_(5) and CMAS up to 1500℃was investigated by a novel high temperature in-situ observation method.High temperature promotes the growth of the main reaction product(Ca_(2)RE_(8)(SiO_(4))6O_(2))fast along the[001]direction,and the precipitation of short and horizontally distributed Ca_(2)RE_(8)(SiO_(4))6O_(2) grains was accelerated during the cooling process.The increased temperature increases the solubility of RE elements,decreases the viscosity of CMAS,and thus elevates the corrosion reaction rate,making RE_(2)SiO_(5) fast interaction with CMAS and less affected by RE element species.
