An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The micros...An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The microstructure of the coating annealed at 1300 ℃ and its high-temperature oxidation behavior at 1350 ℃ were investigated. The significant mass loss of silica during the plasma spray process led to the formation of Yb2SiO5 and Yb2O3 binary phases in the top-coat. Eutectics of Yb2SiO5 and Yb2O3 were precipitated in the top-coat, and channel cracks were formed in the top-coat after 20 h annealing because of the mismatch between the coefficients of thermal expansion(CTEs) of Yb2SiO5 and the SiC substrate. The EBC effectively improved the oxidation resistance of the CMC substrate. The channel cracks in the Yb2SiO5 top-coat provided inward diffusion channels for oxygen and led to the formation of oxidation delamination cracks in the bond coat, finally resulting in spallation failure of the coating after 80 h oxidation.展开更多
The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ce...The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate material for advanced TBCs/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability, and calcium–magnesium–alumino–silicate (CMAS) resistance. Most feedstock powder used for medium/high-entropy TBCs/EBCs is prepared via traditional spray drying, which cannot fully exploit the advantages of multicomponent ceramics. The density, sphericity, inner structure, and flowability of feedstock powder affect their melting state during the thermal spraying process, which strongly affects the microstructure and properties of the deposited coatings. Therefore, the deposited coatings exhibit phase segregation, amorphous phases, and microstructure defects owing to unpredictable variations in feedstock powder with random morphologies and structures. Here, the structure and properties of feedstock powder prepared by state-of-the-art granulation technologies and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powder and the manufacturing accuracy of the deposited coating. This review aims to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing TBCs/EBCs.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
Thermal/environmental barrier coatings(T/EBCs)systems are regarded as potential solutions to address the degradation challenges of ceramic matrix composites(CMCs)under extreme temperatures in aeroengine applications.R...Thermal/environmental barrier coatings(T/EBCs)systems are regarded as potential solutions to address the degradation challenges of ceramic matrix composites(CMCs)under extreme temperatures in aeroengine applications.Rare-earth hafnates are recognized as promising candidates for the top-layer materials of T/EBCs.In this work,Yb_(4)Hf_(3)O_(12)/Yb_(2)Si_(2)O_(7)/Si and Yb_(4)Hf_(3)O_(12)/Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si T/EBCs systems were designed and fabricated via plasma spraying,and their isothermal oxidation and water-quenching thermal shock behaviors at 1500°C were systematically evaluated.The results revealed that the T/EBCs system incorporating a Yb_(4)Hf_(3)O_(12)top layer exhibited excellent high-temperature performance and maintained its structural integrity at 1500°C.Compared with the tri-layer system,the four-layer system demonstrated better oxidation and thermal shock resistance,which was attributed primarily to the incorporation of the Yb_(2)SiO_(5)interlayer,which effectively enhanced the interfacial stability and mitigated the thermal expansion coefficient mismatch between adjacent layers,and reduced the stress fluctuations at the coating edges and interfaces.In a tri-layer system,the spallation of the top layer can be identified as an important failure mechanism.However,for both multilayer systems,the reduction in the Si bond layer emerged as a critical factor contributing to their high-temperature degradation.展开更多
The protective effectiveness of environmental barrier coatings(EBCs)for SiC-based composites is limited by the thickening and phase transformation of the SiO_(2)scale,known as thermally grown oxide(TGO).In this study,...The protective effectiveness of environmental barrier coatings(EBCs)for SiC-based composites is limited by the thickening and phase transformation of the SiO_(2)scale,known as thermally grown oxide(TGO).In this study,a tri-layered TGO scale,comprising cristobalite,Hf-doped SiO_(2)glass,and particle-reinforced Hf-Si-O glass,was formed during the oxidation of MoSi_(2)/HfO_(2)duplex EBCs.The incorporation of gradient Hf doping and HfO_(2)/HfSiO_(4)particle reinforcement effectively suppressed the crystallization and phase transition of SiO_(2)and mitigated the internal stress within the EBCs,generating a crack-blocking effect.This effect prevented the scale of the TGOs from further channel crack propagation,enabling the SiC substrate with no detectable corrosion after 200 h of exposure at 1500℃in steam,even when the TGOs thickness reached 24.5μm.This work presents a novel strategy to simultaneously extend the service lifetime and enhance the high-temperature capability of EBCs through the tailored design of TGO composition and structure.展开更多
The unique multilayer, multiscale structure of teakwood results in excellent mechanical and long-term environmental stability, providing inspiration for the biomimetic design of environmental barrier coating (EBC) str...The unique multilayer, multiscale structure of teakwood results in excellent mechanical and long-term environmental stability, providing inspiration for the biomimetic design of environmental barrier coating (EBC) structures. However, achieving the desired biomimetic structure control in high-temperature plasma spraying is a challenging task that requires new technological breakthroughs. In this study, a multiscale nano Yb_(2)Si_(2)O_(7)–Yb_(2)SiO_(5) (YbDS–YbMS) composite EBC with a teakwood-like lamellar structure was realized via a novel alternating vapor/liquid phase deposition method involving plasma spraying-physical vapor deposition (PS-PVD). Volatilized waste SiO_(2) from Yb_(2)Si_(2)O_(7) (YbDS) was reused and deposited on the coating surface during the spraying process, where a regularly arranged multilayer structure was formed in the coating by the alternate deposition of gaseous SiO_(2) and droplet YbDS. In addition, SiO_(2) on the coated surface formed nanoclusters and dome-shaped nanocrystals via homogeneous and heterogeneous nucleation, respectively, and some of them gradually formed a continuous nanofilm as the arc current increased. The deposited SiO_(2) reacted in situ with the decomposed phase YbMS in the coating to form YbDS, preserving its multiscale nanostructure after heat treatment and enabling the preparation of the YbDS–YbMS composite coating. This work provides a new design strategy and method for the preparation of coatings using YbDS and other spray powders with similar decomposition and volatilization characteristics during the plasma spraying process.展开更多
Environmental barrier coatings(EBCs)effectively protect the ceramic matrix composites(CMCs)from harsh engine environments,especially steam and molten salts.However,open pores inevitably formed during the deposition pr...Environmental barrier coatings(EBCs)effectively protect the ceramic matrix composites(CMCs)from harsh engine environments,especially steam and molten salts.However,open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives,and lead to premature failure of EBCs.This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings.These results showed that it was difficult for aluminum to infiltrate spontaneously,but with the increase of external gas pressure and internal vacuum simultaneously,the molten aluminum obviously moved forward,and finally stopped infiltrating at a depth of a specific geometry.Based on the wrinkled zigzag pore model,a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established.The infiltration results confirmed this relationship,indicating that for a given coating,a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.展开更多
The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for su...The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for surfacemodification using aluminum is proposed.The oxidation performance was examined in a 50 vol%H_(2)O-50 vol%O_(2)environment at 1350℃for up to 300 h.The results indicate that a dense ytterbium aluminum garnet(YbAG)layer wasformed after modification,decreasing the porosity by 80%.Due to the elimination of fast diffusion channels and the lowoxygen permeability of YbAG,aluminum modification significantly reduced the growth rate of SiO_(2)-TGO by nearly twoorders of magnitude.Consequently,its thickness decreased by more than 70%after 300 h of exposure.A diffusioncontrolled oxidation mechanism indicates that the modified dense surface is equivalent to an initial SiO_(2)layer with a specificthickness,causing a shift in the oxidation time and increasing the oxidation resistance.This research provides valuableinsights for designing Si-based EBC with improved lifetimes.展开更多
Aero-engine is a key part of aircraft,the operating temperature of which is being pushed to unprecedented levels for higher engine efficiency and performance.To accomplish higher gas-inlet temperature of aero-engines,...Aero-engine is a key part of aircraft,the operating temperature of which is being pushed to unprecedented levels for higher engine efficiency and performance.To accomplish higher gas-inlet temperature of aero-engines,applying thermal barrier coatings(TBCs)on hot-section metallic components,or even replacing some of the metallic components in aero-engines with ceramic-matrix composites(CMCs)and applying environmental-barrier coatings(EBCs)on them,are effective methods and have been widely accepted.On the other hand,increasing aero-engines operating temperature causes the aircraft more easily be detected,thus stealth coatings are necessary for engines.Except the hottest part in aero-engines,other parts may not need TBCs or EBCs due to the relatively low operating temperature,but they still need protection from oxidation and corrosion.Hence,corrosion-resistant coatings are essential.In this paper,the latest progress of the above high-temperature protective coatings,i.e.,TBCs,EBCs,stealth coatings and corrosion-resistant coatings is reviewed,mainly including their materials,fabrication technologies and performance.In addition,due to the harsh operating environment,these protective coatings face many threats such as calcia-magnesia-aluminosilicates(CMAS)attack,causing premature failure of the coatings,which is also concerned in this paper.The work would provide a comprehensive understanding on the high-temperature protective coatings in aero-engines and guidance for developing advanced protective coatings for next-generation aero-engines.展开更多
The development of Si-HfO_(2)/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)environmental barrier coatings(EBCs)aims to improve the operational temperature and longevity of ceramic matrix composites(CMCs)in turbine environments.Neve...The development of Si-HfO_(2)/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)environmental barrier coatings(EBCs)aims to improve the operational temperature and longevity of ceramic matrix composites(CMCs)in turbine environments.Nevertheless,several critical questions remain unanswered,including the oxidation mechanism of Si-HfO_(2)bond coating,the compatibility of its mixed thermally grown oxide(m-TGO)with adjacent layers during thermal cycling,and the evolution pattern of vertical mud-cracks that impact the overall performance in service.Using plasma spraying physical vapor deposition(PS-PVD),we fabricated these EBCs on a CMC substrate,and thermal cycling tests at 1400,1450,and 1500℃ revealed that their durability reached 200 h.m-TGO growth followed a parabolic model,with the oxygen diffusion activation energy being 133.69 kJ/mol between 1400 and 1450℃ and 101.47 kJ/mol from 1450 to 1500℃,emphasizing that the transport of molecular oxygen is key to controlling the oxidation of m-TGO in this EBC system.Although residual stresses and stored elastic strain energy build up between m-TGO and adjacent layers,especially around the cristobalite phase transition temperature,causing interlaminar crack formation in later thermal cycles,the stored elastic strain energy remains lower than that of the silicon oxide-thermally grown oxide(SiO_(2)-TGO)formed in Si bond coating system.In addition to[110]dislocations,(001)twinning and interaction zones between twinning and dislocations were discovered for the first time,driving the bifurcation of mud cracks.Notably,controlling the mud-crack density is vital for protection of Yb_(2)SiO_(5)layer,as bifurcated mud-crack tips may converge with adjacent mud-cracks.展开更多
Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor...Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor and CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS).Nevertheless,a relatively high thermal conductivity(κ)of the REPO_(4) becomes the bottleneck for their practical applications.In this work,novel xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO4(HE(7RE_(1/7))PO_(4))has been designed and synthesized for the first time to solve this issue.HE(7RE_(1/7))PO_(4) with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750℃and good chemical compatibility with SiO_(2) up to 1400℃.In addition,the thermal expansion coefficient(TEC)of HE(7RE_(1/7))PO_(4)(5.96×10^(−6)℃^(−1) from room temperature(RT)to 900℃)is close to that of the SiC-CMCs.What is more,the thermal conductivities of HE(7RE_(1/7))PO_(4)(from 4.38 W·m^(−1)·K^(−1) at 100℃to 2.25 W·m^(−1)·K^(−1) at 1300℃)are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m^(−1)·K^(−1).These results suggest that HE(7RE_(1/7))PO_(4) has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.展开更多
The search for new materials with reliable molten calcium-magnesium-alumino-silicate(CMAS)resistance at elevated temperatures is important for the development of advanced aeroengines.In the present study,a novel Y_(4)...The search for new materials with reliable molten calcium-magnesium-alumino-silicate(CMAS)resistance at elevated temperatures is important for the development of advanced aeroengines.In the present study,a novel Y_(4)Al_(2)O_(9)(YAM)/Y_(2)O_(3)composite was designed and fabricated from dense samples via the hot-pressing method.The interactions and mechanisms between the Y_(4)Al_(2)O_(9)/Y_(2)O_(3)composite and CMAS at 1300 and 1500℃for durations of 1,4,25,and 50 h were thoroughly explored.The results revealed that Y_(4)Al_(2)O_(9)/Y_(2)O_(3)exhibited substantial resistance to CMAS infiltration at both temperatures,without notable grain-boundary penetration by CMAS glass.More importantly,the incorporation of reaction-active components in the composite accelerated the consumption of molten CMAS constituents and reduced their corrosive activity,which is recognized as the crucial principle for the composition design of anti-CMAS materials.This work provides valuable insights that can guide the design of the composition and advancement of superior CMAS-resistant materials.展开更多
Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ce...Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics.Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance.However,the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application.Inspired by the high entropy effect,a novel rare earth monosilicate solid solution(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)was designed to improve the overall performance.The as-synthesized(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)shows very low thermal conductivity(1.07 W·m-1·K-1 at 600℃).Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties.The thermal expansion coefficient of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)can be decreased to(4.0–5.9)×10^(-6)K^(-1)due to severe lattice distortion and chemical bonding variation,which matches well with that of SiC((4.5–5.5)×10^(-6)K^(-1)).In addition,(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)presents good resistance to CMAS corrosion.The improved performance of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)highlights it as a promising environmental barrier coating candidate.展开更多
Environmental barrier coating(EBC)materials that are resistant against molten calcia-magnesia-aluminosilicate(CMAS)corrosion are urgently required.Elerein,multicomponent rare-earth(RE)disilicate((Yb_(0.2)Y_(0.2)Lu_(0....Environmental barrier coating(EBC)materials that are resistant against molten calcia-magnesia-aluminosilicate(CMAS)corrosion are urgently required.Elerein,multicomponent rare-earth(RE)disilicate((Yb_(0.2)Y_(0.2)Lu_(0.2)Sc_(0.2)Gd_(0.2))_(2)Si_(2)O_(7),(5RE)_(2)Si_(2)O_(7))was investigated with regard to its CMAS interaction behavior at 1400°C.Compared with the individual RE disilicates,the(5RE)2Si2C>7 material exhibited improved resistance against CMAS attack.The dominant process involved in the interaction of(5RE)_(2)Si_(2)O_(7)with CMAS was reaction-recrystallization.A dense and continuous reaction layer protected the substrate from rapid corrosion at high temperatures.The results demonstrated that multicomponent strategy of RE species in disilicate can provide a new perspective in the development of promising EBC materials with improved corrosion resistance.展开更多
The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO_(2)scale.In this study,Si-HfO_(2)dual-state duplex composite materials are proposed to ...The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO_(2)scale.In this study,Si-HfO_(2)dual-state duplex composite materials are proposed to address this issue by partially forming HfSiO_(4)and minimizing the SiO_(2)content.The as-prepared composite exhibited a structure comprising discrete HfO_(2)“bricks”embedded in a continuous Si“mortar”,while the oxidized state transformed into discrete HfSiO_(4)“bricks”within continuous thin SiO_(2)“mortars”.The results indicate that continuous thin SiO_(2)contributes to reducing the oxidation rate to a level comparable to that of pure Si,and discrete HfSiO_(4)particles aid in relieving phase transition-induced stress and inhibiting crack propagation,thereby enhancing oxidation and cracking resistance simultaneously.Consequently,the composite with 20 mol%HfO_(2)and a mean particle size of~500 nm at 1370℃exhibited a service lifetime 10 times greater than that of pure Si.This research provides valuable insights for designing Si-based bond coatings with improved service lifetime.展开更多
High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of vario...High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE^(3+) ions ( r¯(RE^(3+))). The nine pyrosilicates with a small r¯(RE^(3+)) preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of r¯(RE^(3+)). The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.展开更多
Effective manipulations of thermal expansion and conductivity are significant for improving operational performances of protective coatings,thermoelectric,and radiators.This work uncovers determinant mechanisms of the...Effective manipulations of thermal expansion and conductivity are significant for improving operational performances of protective coatings,thermoelectric,and radiators.This work uncovers determinant mechanisms of the thermal expansion and conductivity of symbiotic ScTaO_(4)/SmTaO_(4) composites as thermal/environmental barrier coatings(T/EBCs),and we consider the effects of interface stress and thermal resistance.The weak bonding and interface stress among composite grains manipulate coefficient of thermal expansion(CTE)stretching from 6.4×10^(−6) to 10.7×10^(−6) K^(−1) at 1300℃,which gets close to that of substrates in T/EBC systems.The multiscale effects,including phonon scattering at the interface,mitigation of the phonon speed(vp),and lattice point defects,synergistically depress phonon thermal transports,and we estimate the proportions of different parts.The interface thermal resistance(R)reduces the thermal conductivity(k)by depressing phonon speed and scattering phonons because of different acoustic properties and weak bonding between symbiotic ScTaO_(4) and SmTaO_(4) ceramics in the composites.This study proves that CTE of tantalates can be artificially regulated to match those of different substrates to expand their applications,and the uncovered multiscale effects can be used to manipulate thermal transports of various materials.展开更多
Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fract...Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fractions to tailor their performance.In this work,the key material parameters(e.g.,ionic size and ionic size disorder)and the elements governing their thermal‒mechanical properties and resistance against calcium‒magnesium‒aluminosilicate(CMAS)corrosion were elucidated.The thermal conductivities of multicomponent rare-earth phosphates correlate well with cation size disorder,but no clear trend is identified for the coefficient of thermal expansion(CTE).Er-containing compositions display low CTEs and high fracture toughness.Rapid formation of a dense interfacial layer occurs for most CAMS corrosion-resistant compositions when tested at 1300°C,e.g.,(Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2)Gd_(0.2))PO_(4) and(Lu_(0.2)Yb_(0.2)Er_(0.2)Dy_(0.2)Gd_(0.2))PO_(4).These multicomponent phosphates also display the least recession upon molten CMAS attack at 1400°C without significant volumetric swelling,which is superior to their single-component counterparts and state-of-the-art EBCs based on rare-earth disilicates.In contrast,Sc-containing multicomponent phosphates display inferior performance against CMAS corrosion and penetration.A mechanistic understanding and understanding of the kinetics of the interfacial interaction at higher temperatures,as well as the key parameters governing their thermomechanical properties and CMAS corrosion,are valuable for designing data-driven materials of multicomponent phosphates for EBC applications.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
Thermal/environmental barrier coatings(T/EBCs)are used to protect hot-section superalloys and/or ceramic matrix composite components from hot corrosion and oxidation;however,the majority of T/EBCs exhibit extremely hi...Thermal/environmental barrier coatings(T/EBCs)are used to protect hot-section superalloys and/or ceramic matrix composite components from hot corrosion and oxidation;however,the majority of T/EBCs exhibit extremely high thermal and ionic conductivities.Here,we obtain a novel rare-earth tantalate with excellent oxygen and thermal insulation via a high-entropy strategy.The high-entropy component(8RE_(1/8))TaO_(4)(RE=rare earth),which is designed by large size disorder and mass disorder,has been reassembled into a stabilized monoclinic structure.(8RE_(1/8))TaO_(4)had 30.0%–31.1%and 59.2%–67.5%lower intrinsic thermal conductivity than single-RE RETaO_(4)and 8(Y_(2)O_(3)–ZrO_(2))8YSZ at 1200℃,respectively,and exhibited lower intrinsic thermal conductivity across the entire temperature range of 100–1200℃.This is the result of strong scattering by the phonon–phonon,grain boundary,domain boundary,dislocation,and vacancy defects.The ionic conductivity of(8RE_(1/8))TaO_(4)is 3712–29,667 times lower than that of 8YSZ at 900℃,benefiting from the strong Ta–O bonding strength,low concentration of mobile oxygen vacancies and severe lattice distortions that impede carrier transport.Moreover,(8RE_(1/8))TaO_(4)had superior high-temperature stability and excellent mechanical properties.Analysis of above results demonstrates that(8RE_(1/8))TaO_(4)is a promising candidate for T/EBCs.展开更多
基金sponsored by the National Natural Science Foundation of China (NSFC) under grant Nos. 51590894, 51425102, and 51231001
文摘An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The microstructure of the coating annealed at 1300 ℃ and its high-temperature oxidation behavior at 1350 ℃ were investigated. The significant mass loss of silica during the plasma spray process led to the formation of Yb2SiO5 and Yb2O3 binary phases in the top-coat. Eutectics of Yb2SiO5 and Yb2O3 were precipitated in the top-coat, and channel cracks were formed in the top-coat after 20 h annealing because of the mismatch between the coefficients of thermal expansion(CTEs) of Yb2SiO5 and the SiC substrate. The EBC effectively improved the oxidation resistance of the CMC substrate. The channel cracks in the Yb2SiO5 top-coat provided inward diffusion channels for oxygen and led to the formation of oxidation delamination cracks in the bond coat, finally resulting in spallation failure of the coating after 80 h oxidation.
基金supported by the Shanghai Pujiang Program(No.2022PJD033)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(No.SL2022MS013)the Key R&D Program of Zhejiang(No.2024SSYS0085).
文摘The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate material for advanced TBCs/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability, and calcium–magnesium–alumino–silicate (CMAS) resistance. Most feedstock powder used for medium/high-entropy TBCs/EBCs is prepared via traditional spray drying, which cannot fully exploit the advantages of multicomponent ceramics. The density, sphericity, inner structure, and flowability of feedstock powder affect their melting state during the thermal spraying process, which strongly affects the microstructure and properties of the deposited coatings. Therefore, the deposited coatings exhibit phase segregation, amorphous phases, and microstructure defects owing to unpredictable variations in feedstock powder with random morphologies and structures. Here, the structure and properties of feedstock powder prepared by state-of-the-art granulation technologies and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powder and the manufacturing accuracy of the deposited coating. This review aims to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing TBCs/EBCs.
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sponsored by the National Natural Science Foundation of China(No.52202075).
文摘Thermal/environmental barrier coatings(T/EBCs)systems are regarded as potential solutions to address the degradation challenges of ceramic matrix composites(CMCs)under extreme temperatures in aeroengine applications.Rare-earth hafnates are recognized as promising candidates for the top-layer materials of T/EBCs.In this work,Yb_(4)Hf_(3)O_(12)/Yb_(2)Si_(2)O_(7)/Si and Yb_(4)Hf_(3)O_(12)/Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si T/EBCs systems were designed and fabricated via plasma spraying,and their isothermal oxidation and water-quenching thermal shock behaviors at 1500°C were systematically evaluated.The results revealed that the T/EBCs system incorporating a Yb_(4)Hf_(3)O_(12)top layer exhibited excellent high-temperature performance and maintained its structural integrity at 1500°C.Compared with the tri-layer system,the four-layer system demonstrated better oxidation and thermal shock resistance,which was attributed primarily to the incorporation of the Yb_(2)SiO_(5)interlayer,which effectively enhanced the interfacial stability and mitigated the thermal expansion coefficient mismatch between adjacent layers,and reduced the stress fluctuations at the coating edges and interfaces.In a tri-layer system,the spallation of the top layer can be identified as an important failure mechanism.However,for both multilayer systems,the reduction in the Si bond layer emerged as a critical factor contributing to their high-temperature degradation.
基金supported by the Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory(No.2023-JCJQ-LB-071-01-01).
文摘The protective effectiveness of environmental barrier coatings(EBCs)for SiC-based composites is limited by the thickening and phase transformation of the SiO_(2)scale,known as thermally grown oxide(TGO).In this study,a tri-layered TGO scale,comprising cristobalite,Hf-doped SiO_(2)glass,and particle-reinforced Hf-Si-O glass,was formed during the oxidation of MoSi_(2)/HfO_(2)duplex EBCs.The incorporation of gradient Hf doping and HfO_(2)/HfSiO_(4)particle reinforcement effectively suppressed the crystallization and phase transition of SiO_(2)and mitigated the internal stress within the EBCs,generating a crack-blocking effect.This effect prevented the scale of the TGOs from further channel crack propagation,enabling the SiC substrate with no detectable corrosion after 200 h of exposure at 1500℃in steam,even when the TGOs thickness reached 24.5μm.This work presents a novel strategy to simultaneously extend the service lifetime and enhance the high-temperature capability of EBCs through the tailored design of TGO composition and structure.
基金support from the National Natural Science Foundation of China(Nos.52322104,52172067,and 92160202)the Natural Science Foundation of Guangdong Province(No.2021B1515020038)+2 种基金the Guangdong Special Support Program(No.2019BT02C629)the Guangdong Provincial Science and Technology Program(No.2023A0505010017)the Science Center for Gas Turbine Project(No.P2023-C-IV-002-001).
文摘The unique multilayer, multiscale structure of teakwood results in excellent mechanical and long-term environmental stability, providing inspiration for the biomimetic design of environmental barrier coating (EBC) structures. However, achieving the desired biomimetic structure control in high-temperature plasma spraying is a challenging task that requires new technological breakthroughs. In this study, a multiscale nano Yb_(2)Si_(2)O_(7)–Yb_(2)SiO_(5) (YbDS–YbMS) composite EBC with a teakwood-like lamellar structure was realized via a novel alternating vapor/liquid phase deposition method involving plasma spraying-physical vapor deposition (PS-PVD). Volatilized waste SiO_(2) from Yb_(2)Si_(2)O_(7) (YbDS) was reused and deposited on the coating surface during the spraying process, where a regularly arranged multilayer structure was formed in the coating by the alternate deposition of gaseous SiO_(2) and droplet YbDS. In addition, SiO_(2) on the coated surface formed nanoclusters and dome-shaped nanocrystals via homogeneous and heterogeneous nucleation, respectively, and some of them gradually formed a continuous nanofilm as the arc current increased. The deposited SiO_(2) reacted in situ with the decomposed phase YbMS in the coating to form YbDS, preserving its multiscale nanostructure after heat treatment and enabling the preparation of the YbDS–YbMS composite coating. This work provides a new design strategy and method for the preparation of coatings using YbDS and other spray powders with similar decomposition and volatilization characteristics during the plasma spraying process.
基金supported by the National Natural Science Foundation of China(No.51901175)the Guangdong Province Outstanding Youth Foundation(No.2021B1515020038)+3 种基金the Guangzhou Technical Research Program(No.201906010015)the Industry University Research Project funded by Aero Engine Corporation of China(No.HFZL2019CXY015)the Postdoctoral Research Foundation of China(Nos.2020T130499 and 2019M653602)the National Program for Support of Top-notch Young Professionals.
文摘Environmental barrier coatings(EBCs)effectively protect the ceramic matrix composites(CMCs)from harsh engine environments,especially steam and molten salts.However,open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives,and lead to premature failure of EBCs.This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings.These results showed that it was difficult for aluminum to infiltrate spontaneously,but with the increase of external gas pressure and internal vacuum simultaneously,the molten aluminum obviously moved forward,and finally stopped infiltrating at a depth of a specific geometry.Based on the wrinkled zigzag pore model,a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established.The infiltration results confirmed this relationship,indicating that for a given coating,a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.
基金supported by the Postdoctoral Innovative Talent Support Program(No.BX2021238)the National Natural Science Foundation of China(Nos.U22A20110 and 52301102).
文摘The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for surfacemodification using aluminum is proposed.The oxidation performance was examined in a 50 vol%H_(2)O-50 vol%O_(2)environment at 1350℃for up to 300 h.The results indicate that a dense ytterbium aluminum garnet(YbAG)layer wasformed after modification,decreasing the porosity by 80%.Due to the elimination of fast diffusion channels and the lowoxygen permeability of YbAG,aluminum modification significantly reduced the growth rate of SiO_(2)-TGO by nearly twoorders of magnitude.Consequently,its thickness decreased by more than 70%after 300 h of exposure.A diffusioncontrolled oxidation mechanism indicates that the modified dense surface is equivalent to an initial SiO_(2)layer with a specificthickness,causing a shift in the oxidation time and increasing the oxidation resistance.This research provides valuableinsights for designing Si-based EBC with improved lifetimes.
文摘Aero-engine is a key part of aircraft,the operating temperature of which is being pushed to unprecedented levels for higher engine efficiency and performance.To accomplish higher gas-inlet temperature of aero-engines,applying thermal barrier coatings(TBCs)on hot-section metallic components,or even replacing some of the metallic components in aero-engines with ceramic-matrix composites(CMCs)and applying environmental-barrier coatings(EBCs)on them,are effective methods and have been widely accepted.On the other hand,increasing aero-engines operating temperature causes the aircraft more easily be detected,thus stealth coatings are necessary for engines.Except the hottest part in aero-engines,other parts may not need TBCs or EBCs due to the relatively low operating temperature,but they still need protection from oxidation and corrosion.Hence,corrosion-resistant coatings are essential.In this paper,the latest progress of the above high-temperature protective coatings,i.e.,TBCs,EBCs,stealth coatings and corrosion-resistant coatings is reviewed,mainly including their materials,fabrication technologies and performance.In addition,due to the harsh operating environment,these protective coatings face many threats such as calcia-magnesia-aluminosilicates(CMAS)attack,causing premature failure of the coatings,which is also concerned in this paper.The work would provide a comprehensive understanding on the high-temperature protective coatings in aero-engines and guidance for developing advanced protective coatings for next-generation aero-engines.
基金support from the National Major Science and Technology Projects of China(No.Y2022-1II-0004-0013)the National Natural Science Foundation of China(No.52272065),and the Program of the China Scholarships Council(No.202206830106)+1 种基金performed at the Hefei Advanced Computing Center.Moreover,we appreciate eceshi(www.eceshi.com)for SEM-FIB analysiswe acknowledge the Center for Microscopy and Analysis at Nanjing University of Aeronautics and Astronautics for SEMEDS analysis.
文摘The development of Si-HfO_(2)/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)environmental barrier coatings(EBCs)aims to improve the operational temperature and longevity of ceramic matrix composites(CMCs)in turbine environments.Nevertheless,several critical questions remain unanswered,including the oxidation mechanism of Si-HfO_(2)bond coating,the compatibility of its mixed thermally grown oxide(m-TGO)with adjacent layers during thermal cycling,and the evolution pattern of vertical mud-cracks that impact the overall performance in service.Using plasma spraying physical vapor deposition(PS-PVD),we fabricated these EBCs on a CMC substrate,and thermal cycling tests at 1400,1450,and 1500℃ revealed that their durability reached 200 h.m-TGO growth followed a parabolic model,with the oxygen diffusion activation energy being 133.69 kJ/mol between 1400 and 1450℃ and 101.47 kJ/mol from 1450 to 1500℃,emphasizing that the transport of molecular oxygen is key to controlling the oxidation of m-TGO in this EBC system.Although residual stresses and stored elastic strain energy build up between m-TGO and adjacent layers,especially around the cristobalite phase transition temperature,causing interlaminar crack formation in later thermal cycles,the stored elastic strain energy remains lower than that of the silicon oxide-thermally grown oxide(SiO_(2)-TGO)formed in Si bond coating system.In addition to[110]dislocations,(001)twinning and interaction zones between twinning and dislocations were discovered for the first time,driving the bifurcation of mud cracks.Notably,controlling the mud-crack density is vital for protection of Yb_(2)SiO_(5)layer,as bifurcated mud-crack tips may converge with adjacent mud-cracks.
基金supported by the National Key R&D Program of China(No.2021YFB3701404)the National Science Fund for Distinguished Young Scholars(No.52025041)the National Natural Science Foundation of China(Nos.51904021 and 52174294).
文摘Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor and CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS).Nevertheless,a relatively high thermal conductivity(κ)of the REPO_(4) becomes the bottleneck for their practical applications.In this work,novel xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO4(HE(7RE_(1/7))PO_(4))has been designed and synthesized for the first time to solve this issue.HE(7RE_(1/7))PO_(4) with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750℃and good chemical compatibility with SiO_(2) up to 1400℃.In addition,the thermal expansion coefficient(TEC)of HE(7RE_(1/7))PO_(4)(5.96×10^(−6)℃^(−1) from room temperature(RT)to 900℃)is close to that of the SiC-CMCs.What is more,the thermal conductivities of HE(7RE_(1/7))PO_(4)(from 4.38 W·m^(−1)·K^(−1) at 100℃to 2.25 W·m^(−1)·K^(−1) at 1300℃)are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m^(−1)·K^(−1).These results suggest that HE(7RE_(1/7))PO_(4) has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.
基金supported by the National Key R&D Program of China(No.2024YFB3714503)the National Natural Science Foundation of China(Nos.52130204 and U21A2063)+1 种基金the LiaoNing Revitalization Talents Program(No.XLYC2203090)the International Partnership Program of the Chinese Academy of Sciences(No.172GJHZ2022094FN).
文摘The search for new materials with reliable molten calcium-magnesium-alumino-silicate(CMAS)resistance at elevated temperatures is important for the development of advanced aeroengines.In the present study,a novel Y_(4)Al_(2)O_(9)(YAM)/Y_(2)O_(3)composite was designed and fabricated from dense samples via the hot-pressing method.The interactions and mechanisms between the Y_(4)Al_(2)O_(9)/Y_(2)O_(3)composite and CMAS at 1300 and 1500℃for durations of 1,4,25,and 50 h were thoroughly explored.The results revealed that Y_(4)Al_(2)O_(9)/Y_(2)O_(3)exhibited substantial resistance to CMAS infiltration at both temperatures,without notable grain-boundary penetration by CMAS glass.More importantly,the incorporation of reaction-active components in the composite accelerated the consumption of molten CMAS constituents and reduced their corrosive activity,which is recognized as the crucial principle for the composition design of anti-CMAS materials.This work provides valuable insights that can guide the design of the composition and advancement of superior CMAS-resistant materials.
基金This work was financially supported by Guangdong Basic and Applied Basic Research Foundation for Distinguished Young Scholars(Grant No.2021B1515020083)Guang Dong Basic and Applied Basic Research Foundation for Young Scholars(Grant No.21201910240002803)+1 种基金Shenzhen Science and Technology Program(Grant Nos.GXWD20201231165807008,20200831172254001)Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.2021qntd10).
文摘Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics.Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance.However,the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application.Inspired by the high entropy effect,a novel rare earth monosilicate solid solution(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)was designed to improve the overall performance.The as-synthesized(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)shows very low thermal conductivity(1.07 W·m-1·K-1 at 600℃).Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties.The thermal expansion coefficient of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)can be decreased to(4.0–5.9)×10^(-6)K^(-1)due to severe lattice distortion and chemical bonding variation,which matches well with that of SiC((4.5–5.5)×10^(-6)K^(-1)).In addition,(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)presents good resistance to CMAS corrosion.The improved performance of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)highlights it as a promising environmental barrier coating candidate.
基金supported by the National Natural Science Foundation of China(Grant Nos.51972027 and 51902260).
文摘Environmental barrier coating(EBC)materials that are resistant against molten calcia-magnesia-aluminosilicate(CMAS)corrosion are urgently required.Elerein,multicomponent rare-earth(RE)disilicate((Yb_(0.2)Y_(0.2)Lu_(0.2)Sc_(0.2)Gd_(0.2))_(2)Si_(2)O_(7),(5RE)_(2)Si_(2)O_(7))was investigated with regard to its CMAS interaction behavior at 1400°C.Compared with the individual RE disilicates,the(5RE)2Si2C>7 material exhibited improved resistance against CMAS attack.The dominant process involved in the interaction of(5RE)_(2)Si_(2)O_(7)with CMAS was reaction-recrystallization.A dense and continuous reaction layer protected the substrate from rapid corrosion at high temperatures.The results demonstrated that multicomponent strategy of RE species in disilicate can provide a new perspective in the development of promising EBC materials with improved corrosion resistance.
基金This study is supported by the Postdoctoral Innovative Talent Support Program(No.BX2021238)the National Natural Science Foundation of China(No.U22A20110)the Natural Science Foundation of Suzhou(No.SYG202103).
文摘The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO_(2)scale.In this study,Si-HfO_(2)dual-state duplex composite materials are proposed to address this issue by partially forming HfSiO_(4)and minimizing the SiO_(2)content.The as-prepared composite exhibited a structure comprising discrete HfO_(2)“bricks”embedded in a continuous Si“mortar”,while the oxidized state transformed into discrete HfSiO_(4)“bricks”within continuous thin SiO_(2)“mortars”.The results indicate that continuous thin SiO_(2)contributes to reducing the oxidation rate to a level comparable to that of pure Si,and discrete HfSiO_(4)particles aid in relieving phase transition-induced stress and inhibiting crack propagation,thereby enhancing oxidation and cracking resistance simultaneously.Consequently,the composite with 20 mol%HfO_(2)and a mean particle size of~500 nm at 1370℃exhibited a service lifetime 10 times greater than that of pure Si.This research provides valuable insights for designing Si-based bond coatings with improved service lifetime.
基金supported by the Instrument and Equipment Development,Chinese Academy of Sciences(YJKYYQ20210030)Shanghai Science and Technology Innovation Action Plan(21142201100).
文摘High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE^(3+) ions ( r¯(RE^(3+))). The nine pyrosilicates with a small r¯(RE^(3+)) preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of r¯(RE^(3+)). The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.
基金Thanks for the supports from the National Natural Science Foundation of China(No.91960103)National Key Research and Development Program of China(No.2022YFB3708600)+1 种基金the Rare and Precious Metals Material Genetic Engineering Project of Yunnan Province(No.202102AB080019-1)the Top Innovative Talents of Graduate Students of Kunming University of Science and Technology。
文摘Effective manipulations of thermal expansion and conductivity are significant for improving operational performances of protective coatings,thermoelectric,and radiators.This work uncovers determinant mechanisms of the thermal expansion and conductivity of symbiotic ScTaO_(4)/SmTaO_(4) composites as thermal/environmental barrier coatings(T/EBCs),and we consider the effects of interface stress and thermal resistance.The weak bonding and interface stress among composite grains manipulate coefficient of thermal expansion(CTE)stretching from 6.4×10^(−6) to 10.7×10^(−6) K^(−1) at 1300℃,which gets close to that of substrates in T/EBC systems.The multiscale effects,including phonon scattering at the interface,mitigation of the phonon speed(vp),and lattice point defects,synergistically depress phonon thermal transports,and we estimate the proportions of different parts.The interface thermal resistance(R)reduces the thermal conductivity(k)by depressing phonon speed and scattering phonons because of different acoustic properties and weak bonding between symbiotic ScTaO_(4) and SmTaO_(4) ceramics in the composites.This study proves that CTE of tantalates can be artificially regulated to match those of different substrates to expand their applications,and the uncovered multiscale effects can be used to manipulate thermal transports of various 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Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fractions to tailor their performance.In this work,the key material parameters(e.g.,ionic size and ionic size disorder)and the elements governing their thermal‒mechanical properties and resistance against calcium‒magnesium‒aluminosilicate(CMAS)corrosion were elucidated.The thermal conductivities of multicomponent rare-earth phosphates correlate well with cation size disorder,but no clear trend is identified for the coefficient of thermal expansion(CTE).Er-containing compositions display low CTEs and high fracture toughness.Rapid formation of a dense interfacial layer occurs for most CAMS corrosion-resistant compositions when tested at 1300°C,e.g.,(Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2)Gd_(0.2))PO_(4) and(Lu_(0.2)Yb_(0.2)Er_(0.2)Dy_(0.2)Gd_(0.2))PO_(4).These multicomponent phosphates also display the least recession upon molten CMAS attack at 1400°C without significant volumetric swelling,which is superior to their single-component counterparts and state-of-the-art EBCs based on rare-earth disilicates.In contrast,Sc-containing multicomponent phosphates display inferior performance against CMAS corrosion and penetration.A mechanistic understanding and understanding of the kinetics of the interfacial interaction at higher temperatures,as well as the key parameters governing their thermomechanical properties and CMAS corrosion,are valuable for designing data-driven materials of multicomponent phosphates for EBC applications.
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 Natural Science Foundation of China(No.52402077)the Open Project of Shaanxi Laboratory(No.2021SXSYS-01-05)+1 种基金the Open Project of Yunnan Precious Metals Laboratory(No.YPML-2023050240)the Yunnan Fundamental Research Projects(Nos.202201BE070001-008,202201AT070192,and 202101BE070001-011).
文摘Thermal/environmental barrier coatings(T/EBCs)are used to protect hot-section superalloys and/or ceramic matrix composite components from hot corrosion and oxidation;however,the majority of T/EBCs exhibit extremely high thermal and ionic conductivities.Here,we obtain a novel rare-earth tantalate with excellent oxygen and thermal insulation via a high-entropy strategy.The high-entropy component(8RE_(1/8))TaO_(4)(RE=rare earth),which is designed by large size disorder and mass disorder,has been reassembled into a stabilized monoclinic structure.(8RE_(1/8))TaO_(4)had 30.0%–31.1%and 59.2%–67.5%lower intrinsic thermal conductivity than single-RE RETaO_(4)and 8(Y_(2)O_(3)–ZrO_(2))8YSZ at 1200℃,respectively,and exhibited lower intrinsic thermal conductivity across the entire temperature range of 100–1200℃.This is the result of strong scattering by the phonon–phonon,grain boundary,domain boundary,dislocation,and vacancy defects.The ionic conductivity of(8RE_(1/8))TaO_(4)is 3712–29,667 times lower than that of 8YSZ at 900℃,benefiting from the strong Ta–O bonding strength,low concentration of mobile oxygen vacancies and severe lattice distortions that impede carrier transport.Moreover,(8RE_(1/8))TaO_(4)had superior high-temperature stability and excellent mechanical properties.Analysis of above results demonstrates that(8RE_(1/8))TaO_(4)is a promising candidate for T/EBCs.
