Utilizing self-propagating high-temperature synthesis(SHS) reactive spraying technology,the feeding self-combustion agglomerated particles composed of Ti,B4C and C powders,TiC-TiB2 multi-phase ceramic coatings were pr...Utilizing self-propagating high-temperature synthesis(SHS) reactive spraying technology,the feeding self-combustion agglomerated particles composed of Ti,B4C and C powders,TiC-TiB2 multi-phase ceramic coatings were prepared on the steel substrates. Orthogonal experiment was carried out to optimize the spraying parameters. The phase component and microstructure of the coating fabricated at the optimized parameters were studied by XRD and SEM. The reactive mechanism in flying agglomerated particles was discussed. The optimized conditions,spraying distance of 220 mm,powders delivering gas pressure of 0.3 MPa and preheating temperature of 240 ℃ to sprayed particles,were obtained from orthogonal experiment. For the coating,porosity of 2.5% and HV 1 595 are achieved under the optimized parameters. The coatings are mainly composed of TiC0.3N0.7,TiB2 and a little TiO2. The SEM analysis shows the morphology of TiC0.3N0.7 matrix in which the fine granular TiB2 crystals evenly disperse. It is concluded that,as solo reactive units,the agglomerated particles would finally form into the coatings after going through four successive stages in the flame,which are,respectively,pregnant reaction,flight combustion,collision and structure transformation and solidification. The solid diffusion and dissolution-precipitation are the two mechanisms to control the synthesis reaction.展开更多
Thermal barrier coatings(TBCs)can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat....Thermal barrier coatings(TBCs)can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat.However,the continuous pursuit of a higher operating temperature leads to degradation,delamination,and premature failure of the top coat.Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems.In this paper,the latest progress of some new ceramic materials is first reviewed.Then,a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth,ceramic sintering,erosion,and calcium–magnesium–aluminium–silicate(CMAS)molten salt corrosion.Finally,new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar,columnar,and nanostructure inclusions.The latest developments of ceramic top coat will be presented in terms of material selection,structural design,and failure mechanism,and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance,better thermal insulation,and longer lifetime.展开更多
Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of ...Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.展开更多
Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The pr...Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The procedure of chemical combustion and structure transformation, reactive mechanism, and solidifying behavior during spaying were emphasized. Reactants which influenced on SHS spraying was discussed. SHS reactive spraying processes were studied. Mechanical properties of the coatings were tested.展开更多
Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivi...Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia(YSZ).However,the low Vickers hardness and toughness are the main shortcomings of RE;TaO-and REjNbOr that limit their applications as TBC materials.To increase the hardness,high entropy(Yu3Ybu3Er/3)sTaOr,(Y13YbnErns)NbO,and(Sm1/6Eu1/6Y 1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study.These high entropy ceramics exhibit high Vickers hardness(10.912.0 GPa),close thermal expansion coefficients to that of single-principal-component RE3TaO,and RE;NbO,(7.9×10^-6-10.8×10-6 C-1 at room temperature),good phase stability,and good chemical compatibility with thermally grown Al2O3,which make them promising for applications as candidate TBC materials.展开更多
基金Project (50672130) supported by the National Natural Science Foundation of China
文摘Utilizing self-propagating high-temperature synthesis(SHS) reactive spraying technology,the feeding self-combustion agglomerated particles composed of Ti,B4C and C powders,TiC-TiB2 multi-phase ceramic coatings were prepared on the steel substrates. Orthogonal experiment was carried out to optimize the spraying parameters. The phase component and microstructure of the coating fabricated at the optimized parameters were studied by XRD and SEM. The reactive mechanism in flying agglomerated particles was discussed. The optimized conditions,spraying distance of 220 mm,powders delivering gas pressure of 0.3 MPa and preheating temperature of 240 ℃ to sprayed particles,were obtained from orthogonal experiment. For the coating,porosity of 2.5% and HV 1 595 are achieved under the optimized parameters. The coatings are mainly composed of TiC0.3N0.7,TiB2 and a little TiO2. The SEM analysis shows the morphology of TiC0.3N0.7 matrix in which the fine granular TiB2 crystals evenly disperse. It is concluded that,as solo reactive units,the agglomerated particles would finally form into the coatings after going through four successive stages in the flame,which are,respectively,pregnant reaction,flight combustion,collision and structure transformation and solidification. The solid diffusion and dissolution-precipitation are the two mechanisms to control the synthesis reaction.
文摘Thermal barrier coatings(TBCs)can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat.However,the continuous pursuit of a higher operating temperature leads to degradation,delamination,and premature failure of the top coat.Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems.In this paper,the latest progress of some new ceramic materials is first reviewed.Then,a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth,ceramic sintering,erosion,and calcium–magnesium–aluminium–silicate(CMAS)molten salt corrosion.Finally,new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar,columnar,and nanostructure inclusions.The latest developments of ceramic top coat will be presented in terms of material selection,structural design,and failure mechanism,and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance,better thermal insulation,and longer lifetime.
文摘Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.
基金Supported by national natural science fund of P.R.China,No.50272084.
文摘Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The procedure of chemical combustion and structure transformation, reactive mechanism, and solidifying behavior during spaying were emphasized. Reactants which influenced on SHS spraying was discussed. SHS reactive spraying processes were studied. Mechanical properties of the coatings were tested.
基金This study was financially supported by the National Natural Science Foundation of China(Nos.51672064 and 51972089).
文摘Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia(YSZ).However,the low Vickers hardness and toughness are the main shortcomings of RE;TaO-and REjNbOr that limit their applications as TBC materials.To increase the hardness,high entropy(Yu3Ybu3Er/3)sTaOr,(Y13YbnErns)NbO,and(Sm1/6Eu1/6Y 1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study.These high entropy ceramics exhibit high Vickers hardness(10.912.0 GPa),close thermal expansion coefficients to that of single-principal-component RE3TaO,and RE;NbO,(7.9×10^-6-10.8×10-6 C-1 at room temperature),good phase stability,and good chemical compatibility with thermally grown Al2O3,which make them promising for applications as candidate TBC materials.
