WO2015030674A1 - Procédé de traitement d'un revêtement formant barrière thermique - Google Patents

Procédé de traitement d'un revêtement formant barrière thermique Download PDF

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Publication number
WO2015030674A1
WO2015030674A1 PCT/SG2014/000380 SG2014000380W WO2015030674A1 WO 2015030674 A1 WO2015030674 A1 WO 2015030674A1 SG 2014000380 W SG2014000380 W SG 2014000380W WO 2015030674 A1 WO2015030674 A1 WO 2015030674A1
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WIPO (PCT)
Prior art keywords
thermal barrier
barrier coating
substance
alloy substrate
thermal
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PCT/SG2014/000380
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English (en)
Inventor
Shi Jie WANG
Thiam Min Brian ONG
Wee Kwong Na
Li Teck KOH
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Agency For Science, Technology And Research
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Priority to SG11201601451XA priority Critical patent/SG11201601451XA/en
Priority to US14/915,463 priority patent/US20160208371A1/en
Publication of WO2015030674A1 publication Critical patent/WO2015030674A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
    • C23C4/134—Plasma spraying
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/18—After-treatment
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
    • F01D5/288—Protective coatings for blades
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Definitions

  • the present invention generally relates to method of treating a thermal barrier coating.
  • the present invention also relates to a system for treating a thermal barrier coating .
  • thermal barrier coatings are widely used in both industrial gas turbine and aircraft engines. Thermal barrier coatings facilitate a quantum leap' in turbine inlet temperature (up to 170°C) by providing thermal insulation to hot section metallic components. Thermal barrier coatings, besides facilitating such a tremendous increase in turbine inlet temperature, also protect the load bearing structural alloys of combustion turbines from extreme environment (high temperature, high pressure, corrosion) and have become the materials system of choice for improved efficiency and performance of gas turbine engines. These thermal barrier coating systems are usually made up of a triple layer structure, consisting of yttria-stabilized zirconia acting as the thermal barrier coatings; thermally grown oxide; and bond coat. Thermal barrier coating systems are highly employed for the use of protection from surrounding hot gases by temperature regulation and the prevention of oxidation and corrosion. A schematic drawing showing a typical thermal barrier coating system is provided in Fig. 1.
  • thermal barrier coatings are increasingly susceptible to calcium- magnesium-almino silicate attack which fills up voids in the thermal barrier coating layer. Due to the coefficient of thermal expansion mismatch between the super alloy and the thermal barrier coating layer, these voids are specially introduced into the thermal barrier coating layer to increase the strain tolerance and served as areas for stress relaxation. The ingestion of calcium-magnesium- almino silicate into the thermal barrier coating layer during service fills up these voids, leading to the buildup of stress after many hours of service.
  • melt ingression into the porous yttria-stabilized zirconia topcoat should be completely suppressed.
  • a method for treating a substance having a thermal barrier coating in contact with an alloy substrate comprising the step of irradiating the thermal barrier coating while the alloy substrate is maintained at a substantially constant temperature .
  • the method may be able to substantially decrease the amount of particulate matter (such as calcium-magnesium-almino-silicate) penetration into the thermal barrier coating. This may extend the useful lifetime and reduce the service and maintenance costs for coated parts.
  • the structure of the thermal barrier coating may not change significantly after irradiation treatment.
  • the thermal barrier layer may not suffer from cracks .
  • the method may ensure uniform heating of the thermal barrier coating layer only, without heating the underlying alloy substrate portion. This can avoid overheating of the underlying alloy substrate and thereby prevent reduction in its mechanical and thermal properties.
  • the method may be able to selectively heat up the thermal barrier coating only.
  • the method may increase the hardness of the thermal barrier coating.
  • the method may increase the density of the thermal barrier coating. This may result in a graded density where the thermal barrier coating is denser than the underlying layer (such as the thermally grown oxide layer or the bond coat) . This may avoid the need to employ an additional step of depositing a denser thermal barrier coating on top of a porous one which could be complicated and possess a larger coefficient of thermal expansion mismatch and lower strain tolerance due to the denser structure. This leads to a decrease in the time and temperature required for densification of the thermal barrier coating as compared to conventional furnace annealing .
  • a system for treating a substance having a thermal barrier coating in contact with an alloy substrate comprising an enclosed chamber for receiving the substance, the enclosed chamber comprising heating means and radiation generating components.
  • the system may allow for selective heating of the thermal barrier coating only.
  • both the underlying alloy substrate portion and the thermal barrier coating may be heated to different temperatures accordingly to match their coefficient of thermal expansion mismatch as only the thermal barrier coating is affected by radiation while the alloy substrate portion is not. Hence, this may ensure that the stress due to coefficient of thermal expansion mismatch between the thermal barrier coating and alloy substrate is minimized.
  • a substance comprising an alloy substrate in contact with a radiation treated thermal barrier coating.
  • the quality of the thermal barrier coating may be enhanced to substantially resist penetration of particulate matter such as calcium- magnesium-almino-silicate particles.
  • the hardness of the thermal barrier coating may be higher than a conventional thermal barrier coating that is not subjected to radiation treatment.
  • the density of the thermal barrier coating may be higher (that is, less porous) than a conventional thermal barrier coating that is not subjected to radiation treatment.
  • first substance when referring to the interaction between a first substance and a second substance can refer to a direct contact (in which the first substance is physically in contact with the second substance without any intervening layer) or can refer to an indirect contact (in which the first substance is not physically in contact with the second substance due to the presence - of an intervening layer (s) between the first substance and the second substance) .
  • first substance is an alloy substrate and the second substance is a thermal barrier coating
  • the intervening layer (s) between the alloy substrate and the thermal barrier coating can include one or more of a bond coat or a thermally grown oxide layer.
  • the first substance is a microwave absorber
  • the microwave absorber can be in contact with a thermal barrier coating (now the second substance) .
  • radiation source is to be interpreted broadly to include any electromagnetic waves that are capable of heating a substance.
  • the terms “irradiating”, “radiating”, or grammatical variants thereof, refer to a process of subjecting electromagnetic waves to a substance, leading to the absorption of electromagnetic waves which are then converted to thermal energy.
  • substantially constant temperature is to be interpreted broadly to refer to a temperature that does not deviate significantly from a set value along the course of time. Minor deviations from the set value (such as up to 5% of the set value) as well as fluctuations above or below the set value are permissible such that the general trend of the temperature can be viewed as stable in the vicinity of or at the set value.
  • the term "about”, in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/ - 1% of the stated value, and even more typically +/- 0.5% of the stated value.
  • range format may be disclosed in a range format. It should be understoodthat the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6 , from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range .
  • the method comprises the step of irradiating the thermal barrier coating while the alloy substrate is maintained at a substantially constant temperature .
  • the method may increase the resistance of the thermal barrier coating to ingress or penetration by particulate matter.
  • the method may include a method for increasing the resistance of a thermal barrier coating to ingress or penetration by particulate matter.
  • the method may increase the hardness of the thermal barrier coating.
  • the method may include a method for increasing the hardness of a thermal barrier coating.
  • the method may decrease the porosity of the thermal barrier coating.
  • the method may include a method for decreasing the porosity of a thermal barrier coating.
  • the method may include a method for increasing the density of a thermal barrier coating.
  • the thermal barrier coating may comprise any chemical composition known in the art for thermal barrier coatings. These include various ceramic materials such as zirconia (Zr0 2 ) , yttria (Y 2 O 3 , yttrium oxide), magnesia (MgO, magnesium oxide) , ceria (Ce0 2 , cerium oxide) , ln 2 0 3 (indium oxide, india) , La 2 0 3 (lanthanum oxide, lanthana) , Pr 2 0 3 (praesodymium oxide, praesodymia) , Nd 2 0 3 (neodymium oxide, neodymia) , Sm 2 0 3 (samarium oxide, samaria) , Eu 2 0 3 (europium oxide, europia) , Gd0 3 (gadolinium oxide, gadolinia) , Tb 2 0 3 (terbium oxide, terbia) , Dy 2 0 3 (dy
  • the thermal barrier coating may comprise zirconias stabilized by a metal oxide selected from yttria, dysprosia, erbia, europia, gadolinia, neodymia, praseodymia, urania, and hafnia and combinations thereof.
  • the thermal barrier coating may comprise an yttria- stabilized-zirconia wherein the yttria is in an amount of six to eight weight percent yttria based on the total weight of the yttria-stabilized-zirconia .
  • the yttria- stabilized-zirconia may be 7YSZ, which has high temperature durability, low thermal conductivity, and relative ease of deposition.
  • the composition of the thermal barrier coating may affect the uptake of the electromagnetic waves during irradiation.
  • the alloy substrate may be a nickel, cobalt, titanium, aluminium and/or iron based alloy.
  • the alloy may be a high temperature super alloy.
  • Exemplary super alloys may be selected from the group consisting of Hastelloy, Inconel (for example IN100, IN600, IN713) , PWA 1480, Waspaloy, Rene alloys (for example Rene 41, Rene 80, Rene 95, Rene N5) , Haynes alloys, Incoloy, MP98T, TMS alloys, Nimonic 80A and CMSX (for example CMSX-4 or CMSX- 2 ) single crystal alloys.
  • the thermal barrier coating may be in direct contact with the alloy substrate.
  • the thermal barrier coating may be in indirect contact with the alloy substrate such that there is at least one intervening layer between the thermal barrier coating and the alloy substrate.
  • the intervening layer may include a thermally grown oxide layer and/or a bond coat.
  • the thermally grown oxide layer may be due to the oxidation of the bond coat and may include oxides of aluminium, nickel chromium, magnesium, or combinations thereof.
  • the thermally grown oxide layer may comprise Al 2 0 3 , Ni (Al , Cr) 2 0 4 , NiO, (Cr,Al) 2 0 3 or MgAl 2 0 4 .
  • the thermally grown oxide layer may be a single layer or multi- layer.
  • the bond coat may comprise any composition known in the art for adhering a thermal barrier coating to an alloy substrate.
  • the bond coat may comprise metallic oxidation-resistant materials such as MCrAlY alloy powders, where M represents a metal such as iron, nickel, platinum or cobalt.
  • M may be various metal aluminides such as nickel aluminide and platinum aluminide .
  • the thermal barrier coating may be a combination of a pure thermal barrier coating of a percentage thereof comprising a metallic component in the form of a MCrAlY ranging from 0 to 50%.
  • the thermal barrier coating and bond coat may comprise one or more layers formed by known coating methods that include, but are not limited to plasma spraying (for example, air plasma spraying or vacuum plasma spraying) , or other thermal spraying deposition methods (for example, high velocity oxy-fuel spraying, detonation spraying, or wire spraying) , chemical vapor deposition, or physical vapor deposition (for example electron beam physical vapor deposition) .
  • plasma spraying for example, air plasma spraying or vacuum plasma spraying
  • other thermal spraying deposition methods for example, high velocity oxy-fuel spraying, detonation spraying, or wire spraying
  • chemical vapor deposition for example, chemical vapor deposition, or physical vapor deposition (for example electron beam physical vapor deposition) .
  • the thermal barrier coating and bond coat may have any thickness.
  • Exemplary thickness of the thermal barrier coating may be selected from about 0.004 to about 0.200 inches.
  • the bond coat may have a thickness in the range of from about 25 to about 495 micrometers (about 1 to about 19.5 mils).
  • Bond coats deposited by physical vapour deposition techniques such as electron beam physical vapor deposition may have a thickness in the range of about 25 to about 76 micrometers (about 1 to about 3 mils) .
  • Bond coats deposited by plasma spray techniques such as air plasma spraying may have a thickness in the range of from about 76 to about 381 micrometers (about 3 to about 15 mils) .
  • the thickness of the thermal barrier coating may affect the uptake of electromagnetic waves.
  • the porosity of the thermal barrier coating (before irradiation) may be at least about 2% to about 20%, about 2% to about 5%, about 2% to about 10%, about 2% to about 15%, about 5% to about 20%, about 10% to about 20%, about 15% .to about 20%, or about 15% (measured using optical microscopy) .
  • the porosity of the thermal barrier coating may affect the uptake of electromagnetic waves.
  • the thermal barrier coating may be irradiated with electromagnetic waves such as radio waves, microwaves, infrared, ultraviolet, X-rays or gamma rays.
  • the electromagnetic wave may be microwaves.
  • the two main mechanisms of microwave heating are dipolar polarization and conduction mechanism.
  • Dipolar polarization is a process by which heat is generated in polar molecules .
  • the oscillating nature of the electromagnetic field results in the movement of the polar molecules as they try to align in phase with the field.
  • the inter-molecular forces experienced by the polar molecules effectively prevent such alignment, resulting in the random movement of the polar molecules and generating heat.
  • Conduction mechanisms result in the generation of heat due to resistance to an electric current.
  • the oscillating nature of the electromagnetic field causes oscillation of the electrons or ions in a conductor such that an electric current is generated.
  • the internal resistance faced by the electric current results in the generation of heat. Accordingly, the microwaves may be used to produce high temperatures uniformly inside a material as compared to conventional heating means which may result in heating only the external surfaces of a material .
  • the microwaves may be applied at a power in the range of about 30 W to about 180 kW, about 30 W to about 150 kW, about 30 W to about 120 kW, about 30 W to about 100 kW, about 30 W to about 50 kW, about 30 W to about 25 kW, about 30 to about 15 kW, about 30 W to about 10 kW, about 30 to about 5 kW, about 30 to about 2 kW, about 30 W to about 1200 W, about 50 to about 180 KW, about 2kW to about 180 KW, about 5kW to about 180 KW, about 10 kW to about 180 KW, about 15kW to about 180 KW, about 25kW to about 180 KW, about 50kW to about 180 KW, about lOOkW to about 180 KW, about 120kW to about 180 KW or about 150kW to about 180 KW.
  • Typical frequencies of microwaves may be in the range of about 300 MHz to about 300 GHz. This range may be divided into the ultra-high frequency range of 0.3 to 3 GHz, the super high frequency range of 3 to 30 GHz and the extremely high frequency range of 30 to 300 GHz.
  • Common sources of microwaves are microwave ovens that emit microwave radiation at a frequency of about 0.915, 2.45, or 5.8 GHz.
  • the microwaves may be applied with a frequency in the range selected from the group consisting of ; about 0.3 GHz to about 300 GHz, about 0.3 GHz to about 200 GHz, about 0.3 GHz to about 100 GHz, about 0.3 GHz to about 50 GHz, about 0.3 GHz to about 10 GHz, about 0.3 GHz to about 5.8 GHz, about 0.3 GHz to about 2.45 GHz, about 0.3 GHz to about 0.915 GHz or about 0.3 GHz to about 0.9 GHz .
  • the microwave heating may be conducted for a period of time that is dependent on the composition and thickness of the thermal barrier coating.
  • the time may be in the range of about 1 minute to about ' 5 hours, about 15 minutes to about 5 hours, about 30 minutes to about 5 hours, about 1 hour to about 5 hours, about 2 hours to about 5 hours, about 3 hours to about 5 hours, about 4 hours to about 5 hours, about 1 minute to about 15 minutes, about 1 minute to about 30 minutes, about 1 minute to about 1 hour, about 1 minute to about 2 hours, about 1 minute to about 3 hours or about 1 minute to about 4 hours.
  • the microwave heating may be carried out at a pulse repetition frequency where the pulses per second is in the range of about 10 to about 200, about 10 to about 50, about 10 to about 100, about 10 to about 150, about 50 to about 200, about 100 to about 200, or about 150 to about 200.
  • the microwave heating may be carried out at a temperature in the range of about 25°C to about 1500°C, about 25°C to about 50°C, about 25°C to about 100°C, about 25°C to about 250°C, about 25°C to about 500°C, about 25°C to about 750°C, about 25°C to about 1000°C, about 25°C to about 1250°C, about 50°C to about 1500°C, about 100°C to about 1500°C, about 250°C to about 1500°C, about 500°C to about 1500°C, about 750°C to about 1500°C, about 1000°C to about 1500°C or about 1250°C to about 1500°C.
  • the method may comprise the step of contacting the thermal barrier coating with a microwave absorber.
  • the microwave absorber may be a high temperature material .
  • the microwave absorber may be a carbon-based absorber or composites thereof .
  • the microwave absorber may be selected from silicon carbide (SiC, including Al 2 0 3 -SiC, MgO-SiC, AlN-SiC or BeO-SiC) , carbon black, activated carbon, carbon nanotubes, carbon nanofibers or multiwall carbon nanotube (MWCNT) .
  • the microwave absorber may be placed in contact with the thermal barrier coating such that the heated up microwave absorber can heat up the thermal barrier layer efficiently. Hence, the microwave absorber may aid in increasing the uptake of electromagnetic waves such as microwave by the thermal barrier coating.
  • microwave absorber in order to increase the uptake of electromagnetic waves by the thermal barrier coating, higher frequency, higher temperature or higher power of radiation may also be used.
  • the method may comprise the step of the alloy substrate in a receptacle that is a thermal insulator.
  • the thermal insulator may be selected from the group consisting of ceramics, glass and plastics (such as polyethylene terephthalate (PET) , high density polyethylene (HDPE) , low density polyethylene (LDPE) or polypropylene) .
  • PET polyethylene terephthalate
  • HDPE high density polyethylene
  • LDPE low density polyethylene
  • the receptacle may aid in reducing conduction losses through the alloy substrate so that the thermal barrier layer can be heated up efficiently.
  • the receptacle may isolate the alloy substrate to prevent charging and sparking.
  • the receptacle may also aid to contain the electromagnetic waves within the receptacle.
  • the method may comprise the step of pre-heating the substance before the irradiating step.
  • the alloy substrate may be pre-heated to a desired temperature and kept at that temperature as the thermal barrier coating is irradiated.
  • the alloy substrate may be placed in the receptacle to maintain the temperature of the alloy substrate at a substantially constant temperature (which is the pre-heating temperature) .
  • the alloy substrate and the thermal barrier coating may be kept at different temperatures during irradiation to match their coefficient of thermal expansions. This may aid in minimizing stress due to coefficient of thermal expansion mismatch.
  • the pre-heating temperature may be selected from about 25°C to about 900°C, about 25°C to about 50°C, about 25°C to ' about 75°C, about 25°C to about 100°C, about 25°C to about 300°C, about 25°C to about 500°C, about 25°C to about 700°C, about 50°C to about 900°C, about 75°C to about 900°C, about 100°C to about 900°C, about 300°C to about 900°C, about 500°C to about 900°C or about 700°C to about 900°C.
  • Pre-heating may aid to remove water vapour so as to prevent charging and sparking.
  • pre-heating may aid to enhance the uptake of electromagnetic waves by the thermal barrier coating.
  • the system comprises an enclosed chamber for receiving the substance, the enclosed chamber comprising heating means and radiation generating components.
  • the system further comprises a receptacle for receiving the substance.
  • the receptacle may be a thermal insulator as mentioned above.
  • the heating means of the system may pre-heat the enclosed chamber and/or substance to a desired temperature, as mentioned above.
  • the radiation generating components may be a magnetron tube for generating electromagnetic waves such as microwaves .
  • the substance comprises an alloy substrate in contact with a radiation treated thermal barrier coating.
  • the thermal barrier coating of the substance may have a hardness of more than 5 GPa.
  • the hardness of the thermal barrier coating of the substance may be selected from the range of about 5 to about 10 GPa, about 5.5 to about 8.5 GPa, or about 6 to about 9 GPa.
  • the thermal barrier coating of the substance may have a surface that is substantially resistant to ingress of particulate matter.
  • the particulate matter may be calcium- magnesium-alumino-silicate particles .
  • the thermal barrier coating of the substance may have a porosity that is less than 15%, or less than 12%, less than 11%, less than 10%, less than 9%, or about 9% to about 11%.
  • the thermal barrier coating may have an improvement in one or more properties such as improved hardness, increased resistance to ingress or penetration of particulate matter or decreased porosity.
  • Fig. 1 is a schematic diagram showing different sections of a typical thermal barrier coating system and the temperature drop across the turbine blade to the thermal barrier coating.
  • Fig. 2a is a photograph showing the side view of a hybrid microwave furnace used in the Examples below.
  • Fig. 2b is a photograph showing a top view of the experimental setup.
  • Fig. 3 is a graph showing the coefficient of thermal expansion values as a function of temperature for the various layers present in a thermal barrier coating system.
  • Fig. 4a is a scanning electron microscopy (SEM) image at a scale of 100 ⁇ showing a typical thermal barrier coating layer acting as the control.
  • Fig. 4b is a SEM image at a scale of 100 ⁇ showing the microwave treated thermal barrier coating layer of Example 1.
  • Fig. 5a is a graph showing the modulus of the thermal barrier coating layer before and after microwave treatment.
  • Fig. 5b is a graph showing the hardness of the thermal barrier coating layer before and after microwave treatment.
  • Fig. 6 is a series of energy dispersive X-ray spectroscopy mapping of untreated (A) and microwave treated thermal barrier coating samples at 1000°C for 1 hour (B) , 1000°C for 2 hours (C) and at 1200°C for 1 hour (D) .
  • Fig. 7 is a series of SEM images showing the microstructures of the untreated (A) and thermally treated (B) super alloy processed according to Comparative Example 1.
  • Fig. 8 is a graph showing the modulus of samples thermally treated at 500°C, 700°C and 900°C. The circled data showed that the modulus decreased at the temperature of 900°C. Examples
  • super alloy substrates with precoated thermal barrier coatings were subjected to microwave treatment in a hybrid microwave furnace operating at 2.45GHz to modify their near surface properties.
  • the super alloy substrate is an original Base Material Hastelloy X material coated with 8% Yittria Stablised-Zirconia as the thermal barrier coating.
  • Fig. 2a is a photograph showing the side view of the hybrid microwave furnace while Fig. 2b is another photograph showing the top view of the experimental setup.
  • the super alloy substrate with the precoated thermal barrier coating was placed inside a ceramic crucible and covered with a piece of silicon carbide.
  • the ceramic crucible reduced conduction losses through the metallic super alloy so that the thermal barrier coating can be heated up efficiently.
  • the ceramic crucible functioned to isolate the metallic super alloy from the microwaves to prevent charging and sparking.
  • the silicon carbide functions as a good and efficient microwave absorber to allow for efficient heating up of the thermal barrier coating layer.
  • Silicon carbide was chosen because it is a high temperature material which does not diffuse easily. By placing the silicon carbide on top of the thermal barrier coating layer, the heated up silicon carbide can be used to heat up the underlying thermal barrier coating layer. This then mitigates the conduction losses through the super alloy substrate.
  • the hybrid microwave furnace consists of heating elements and microwave generating components.
  • the heating elements heat up the furnace (as well as the sample) to remove water vapour in order to prevent charging and sparking as well as enhance the uptake of the microwaves in the thermal barrier coating layer.
  • the furnace is then maintained at an elevated temperature of about 900°C.
  • Microwave power is then applied to heat the thermal barrier coating at a temperature of 1100°C for 2 hours.
  • Fig. 3 is a representative graph (obtained from Sheffler, K. D. and Gupta, D. K. (1988) Current status and future trends in turbine application of thermal barrier coatings. J. Eng.
  • the microwave treated thermal barrier coating sample was then characterized by SEM, modulus and hardness determination and thermal cycling.
  • Fig. 4a is a SEM image showing a control (untreated) thermal barrier coating layer with homogeneous distribution of splats and pores while Fig. 4b is a SEM image showing the microwave treated thermal barrier coating layer in which a denser thermal barrier coating layer was stacked on top of a less dense one.
  • YSZ refers to yttria-stabilized zirconia
  • TGO refers to thermally grown oxide
  • BC refers to bond coat. This showed that there was a change in the porosity in the thermal barrier coating after the microwave treatment.
  • the porosity of the microwave thermal barrier coating layer was about 9% to about 11%.
  • Fig. 5a shows the modulus of the thermal barrier coating layer before and after microwave treatment
  • Fig. 5b shows the hardness of the thermal barrier coating layer before (where the hardness is 4.6 GPa) and after (where the hardness is about 5.5 to about 8.5 GPa) microwave treatment.
  • the modulus and hardness of the thermal barrier coating layer increased.
  • the modulus and hardness also increased with increasing treatment temperature and time. Comparing Fig. 4a and Fig. 4b with Fig. 5a, it can be seen that the change in the porosity of the microwave treated thermal barrier coating sample did not affect the modulus significantly. Thus, it can be assumed that the amount of- strain tolerance remains similar.
  • a conventional furnace was used to thermally treat a sample having both the thermal barrier coating layer and the underlying super alloy substrate as those in Example 1.
  • the heating temperature used was 900°C.
  • Fig. 7 shows the morphologies of the control and thermally treated nickel superalloy.
  • the thermally treated nickel superalloy had more crystallized structure as well as lower modulus values. This will reduce its mechanical and thermal performance and will affect its service life significantly.
  • Fig. 8 shows the modulus of samples heated to 500°C, 700°C and 900°C. A decrease in the modulus accompanied a change in the microstructure at the heating temperature of 900°C.
  • Different layers such as the thermal barrier coating layer and the superalloy are made of different materials. Hence, they possess different properties such as different coefficient of thermal expansion values.
  • the use of a conventional furnace would heat up both the thermal barrier coating layer and the underlying superalloy substrate.
  • additional stress are present due to the coefficient of thermal expansion mismatch between the superalloy and the thermal barrier coating layer when both layers are cooled after heating up to the same temperature inside the conventional furnace.
  • mere thermal treatment suffers from a number of disadvantages.
  • the disclosed method may be used to treat thermal barrier coatings for turbines, engines and related parts such as aircraft gas turbines, industrial gas turbines, turbine blades, turbine vanes, high pressure turbine duct segment, combustion engine, rocket engine, rocket engine parts, combustors and high pressure shrouds.
  • the disclosed method may decrease the amount of calcium-magnesium-almino silicate penetration into a treated thermal barrier coating. This may aid in improving the hardness of the coating and extend the useful lifetime with reduction in service and maintenance costs .
  • the structure of the thermal barrier coating may not change significantly after microwave treatment.
  • the disclosed method may ensure that the thermal barrier coating is heated up uniformly without heating the super alloy substrate.
  • the disclosed method may result in selective heating of the coating since it is possible to selectively heat the coating to a temperature that is different from that on the super alloy substrate. This may ensure that the stress due to coefficient of thermal expansion mismatch between the layers is minimized.
  • the disclosed method may cause densification of the coating to a desired thickness or may be used to produce a graded density in the coating. Hence, this may avoid the need for an additional step of depositing a denser thermal barrier coating layer on top of a porous one, which can be complicated and possesses a larger coefficient of thermal expansion mismatch and lower strain tolerance due to the denser structure.
  • the disclosed method may result in decreased time and temperature required for densification of the coating as compared to conventional furnace heating. This may lead to savings in cost ⁇

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  • Physics & Mathematics (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

L'invention concerne un procédé de traitement d'une substance comportant un revêtement formant barrière thermique en contact avec un substrat en alliage, qui comprend l'étape d'irradiation du revêtement formant barrière thermique alors que le substrat en alliage est maintenu à une température sensiblement constante. L'invention concerne aussi un système de traitement d'une substance comportant un revêtement formant barrière thermique en contact avec un substrat en alliage. L'invention concerne une substance comportant un substrat en alliage en contact avec un revêtement formant barrière thermique traité par des rayonnements.
PCT/SG2014/000380 2013-08-27 2014-08-13 Procédé de traitement d'un revêtement formant barrière thermique WO2015030674A1 (fr)

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SG11201601451XA SG11201601451XA (en) 2013-08-27 2014-08-13 A method of treating a thermal barrier coating
US14/915,463 US20160208371A1 (en) 2013-08-27 2014-08-13 Method of treating a thermal barrier coating

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