WO2006061431A2 - A method of protecting a component against hot corrosion - Google Patents

A method of protecting a component against hot corrosion Download PDF

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Publication number
WO2006061431A2
WO2006061431A2 PCT/EP2005/056643 EP2005056643W WO2006061431A2 WO 2006061431 A2 WO2006061431 A2 WO 2006061431A2 EP 2005056643 W EP2005056643 W EP 2005056643W WO 2006061431 A2 WO2006061431 A2 WO 2006061431A2
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WO
WIPO (PCT)
Prior art keywords
coating
component
weight
chromium
aluminium
Prior art date
Application number
PCT/EP2005/056643
Other languages
German (de)
French (fr)
Other versions
WO2006061431A3 (en
Inventor
Paul Box
Mick Whitehurst
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Priority to US11/792,629 priority Critical patent/US20070264126A1/en
Priority to EP05818992A priority patent/EP1819906A2/en
Publication of WO2006061431A2 publication Critical patent/WO2006061431A2/en
Publication of WO2006061431A3 publication Critical patent/WO2006061431A3/en

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Classifications

    • 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
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/04—Diffusion into selected surface areas, e.g. using masks
    • 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
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/06—Solid state diffusion of only metal elements or silicon into metallic material surfaces using gases
    • C23C10/16—Solid state diffusion of only metal elements or silicon into metallic material surfaces using gases more than one element being diffused in more than one step
    • 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
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
    • C23C10/52—Embedding in a powder mixture, i.e. pack cementation more than one element being diffused in one step
    • C23C10/54—Diffusion of at least chromium
    • C23C10/56—Diffusion of at least chromium and at least aluminium
    • 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
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
    • C23C10/58—Embedding in a powder mixture, i.e. pack cementation more than one element being diffused in more than one step
    • 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
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/60—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
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/007—Preventing corrosion
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/90—Coating; Surface treatment
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2300/00—Materials; Properties thereof
    • F05D2300/60—Properties or characteristics given to material by treatment or manufacturing
    • F05D2300/611—Coating

Definitions

  • This invention relates to a method of protecting a component against hot corrosion.
  • the invention finds particular application in the protection against hot corrosion of a gas turbine engine rotor blade.
  • chromium provides excellent protection against so called Type I and Type II hot corrosion.
  • diffusion coatings produced by the diffusion of chromium and aluminium into the alloy substrate have long been used to provide this protection.
  • a method of protecting a component against hot corrosion comprising the steps: (a) applying a chromium diffusion coating to the component; and (b) applying a further coating to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component.
  • the selected regions are regions not subject to higher physical stress in the subsequent use of the component .
  • the further coating comprises an aluminium diffusion coating.
  • the further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two.
  • the further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two, and the method further comprises the step (c) applying an aluminium diffusion coating to the selected regions coated with the MCrAlY overlay coating.
  • the MCrAlY overlay coating applied in step (b) suitably comprises: 30 to 70 weight % Nickel; 30 to 50 weight % Cobalt; 15 to 25 weight % Chromium; 5 to 15 weight % Aluminium; and up to 1 weight %
  • the MCrAlY overlay coating applied in step (b) may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium.
  • the chromium diffusion coating applied in step (a) suitably comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.
  • Methods according to the present invention find particular application in the protection against hot corrosion of nickel based superalloy components.
  • Methods according to the present invention find particular application in the protection against hot corrosion of gas turbine engine rotor blades.
  • the present invention also extends to components protected against hot corrosion by means of a method according to the present invention.
  • Fig 1 shows a gas turbine engine rotor blade and the coating of this blade using a first method in accordance with the present invention
  • Fig 2 is a view of a side of the rotor blade of Fig 1 hidden in Fig 1 but to be seen when looking from the right in Fig 1;
  • Fig 3 shows a gas turbine engine rotor blade and the coating of this blade using a second method in accordance with the present invention
  • Fig 4 is a view of a side of the rotor blade of Fig 3 hidden in Fig 3 but to be seen when looking from the right in Fig 3;
  • Fig 5 shows a gas turbine engine rotor blade and the coating of this blade using a third method in accordance with the present invention.
  • Fig 6 is a view of a side of the rotor blade of Fig 5 hidden in Fig 5 but to be seen when looking from the right in Fig 5.
  • the rotor blade coated is a nickel based superalloy rotor blade.
  • the rotor blade may be produced by conventional or directionally solidified (including single crystal) casting techniques. Typical alloys are MarM247, IN6203 and CMSX-4.
  • the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) .
  • the blade includes an internal cooling passage 9 which commences as shown in Fig 1, loops within the blade, and exits (exit not shown) via the top side of shroud part 1.
  • chromised i.e. chromium is diffused into the surfaces.
  • This diffusion is achieved by any suitable method, e.g. pack cementation or chemical vapour deposition (CVD) .
  • CVD chemical vapour deposition
  • the layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick.
  • an aluminium diffusion coating is applied to all external surfaces of the blade above dotted line M. This diffusion is again achieved by any suitable method, e.g. pack cementation or CVD. Masking is employed below dotted line M to prevent stray aluminium depositing below this line.
  • a chromium modified aluminide coating results on all external surfaces of the blade above dotted line M.
  • the so called outer beta layer of the chromium modified aluminide coating should typically contain 15 to 30 weight % aluminium and 5 to 15 weight % chromium.
  • the total thickness of the chromium modified aluminide coating, including inter-diffusion zone, should typically be 25 to 100 microns.
  • the blade is heat treated to ensure that it maintains its optimum mechanical properties.
  • the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) .
  • the blade includes an internal cooling passage 9 which commences as shown in Fig 3, loops within the blade, and exits (exit not shown) via the top side of shroud part 1.
  • all surfaces of all parts of the blade, including internal cooling passage 9 are chromised, i.e. chromium is diffused into the surfaces. This diffusion is achieved by any suitable method, e.g. pack cementation or CVD. This results in a surface layer rich in chromium.
  • the layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick.
  • an MCrAlY overlay coating (where M is Ni or Co or a combination of the two) is applied to the following parts of the blade: outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5.
  • the coating suitably comprises 30 to 70 weight % Nickel, 30 to 50 weight % Cobalt, 15 to 25 weight % Chromium, 5 to 15 weight % Aluminium, and up to 1 weight % Yttrium.
  • the coating may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium.
  • the coating is applied by any suitable method, e.g.
  • thermal spray techniques such as vacuum plasma spraying (VPS) , low pressure plasma spraying (LPPS) , and high velocity ox-fuel spraying (HVOF) , or by electroplating.
  • VPS vacuum plasma spraying
  • LPPS low pressure plasma spraying
  • HVOF high velocity ox-fuel spraying
  • Masking is employed to ensure that MCrAlY is not deposited on the remainder of platform part 5 below top face 11, and on root part 7.
  • outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5 are chromised plus have an overlay coating of MCrAlY, whereas the remainder of platform part 5 below top face 11, root part 7, and internal cooling passage 9 are chromised only.
  • the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) .
  • the blade includes an internal cooling passage 9 which commences as shown in Fig 5, loops within the blade, and exits (exit not shown) via the top side of shroud part 1.
  • chromised i.e. chromium is diffused into the surfaces. This diffusion is achieved by any suitable method, e.g. pack cementation or CVD. This results in a surface layer rich in chromium. The layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick.
  • an MCrAlY overlay coating (where M is Ni or Co or a combination of the two) is applied to the following parts of the blade: outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5.
  • the coating suitably comprises 30 to 70 weight % Nickel, 30 to 50 weight % Cobalt, 15 to 25 weight % Chromium, 5 to 15 weight % Aluminium, and up to 1 weight % Yttrium.
  • the coating may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium.
  • the coating is applied by any suitable method, e.g. by thermal spray techniques such as VPS, LPPS, and HVOF, or by electroplating. Masking is employed to ensure that MCrAlY is not deposited on the remainder of platform part 5 below top face 11, and on root part 7.
  • those parts of the blade to which the MCrAlY overlay coating was applied are over-aluminised, i.e. an aluminium diffusion coating is applied to these parts.
  • the diffusion is achieved by any suitable method, e.g. pack cementation or CVD.
  • Masking is employed to ensure that stray aluminium is not deposited on the remainder of platform part 5 below top face 11, and on root part 7.
  • the result of the over- aluminisation should be that the outer surface of the MCrAlY overlay coating has an aluminium content of typically 15 to 30 weight %.
  • the total thickness of the over-aluminised MCrAlY coating, including inter-diffusion zone, should typically be 100 to 200 microns.
  • outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5 are chromised plus have an overlay coating of MCrAlY, which MCrAlY overlay coating has been over-aluminised, whereas the remainder of platform part 5 below top face 11, root part 7, and internal cooling passage 9 are chromised only.
  • the application of further coating (s) in addition to the initial chromium diffusion coating is restricted to regions of the rotor blade not subject to higher physical stress in use of the blade.
  • the diffused aluminium coating is restricted to all external surfaces above dotted line M.
  • the MCrAlY overlay coating is restricted to outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5.
  • the MCrAlY overlay coating plus over- aluminisation is restricted to outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Resistance Heating (AREA)

Abstract

A method of protecting a component against hot corrosion comprising the Steps: (a) applying a chromium diffusion coating to the component; and (b) applying a further coating to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component.

Description

A method of protecting a component against hot corrosion
This invention relates to a method of protecting a component against hot corrosion.
The invention finds particular application in the protection against hot corrosion of a gas turbine engine rotor blade.
It is known that chromium provides excellent protection against so called Type I and Type II hot corrosion. In this regard, diffusion coatings produced by the diffusion of chromium and aluminium into the alloy substrate have long been used to provide this protection. MCrAlY overlay coatings
(where M is Ni or Co or a combination of the two) have been used as an alternative to diffusion coatings at higher temperatures to protect against oxidation. The use of diffused chromium alone (chromising) is known to provide excellent protection against relatively low temperature Type
II hot corrosion, and further to be strain tolerant (to have no effect on the fatigue properties of the substrate) .
According to the present invention there is provided a method of protecting a component against hot corrosion comprising the steps: (a) applying a chromium diffusion coating to the component; and (b) applying a further coating to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component. Preferably, the selected regions are regions not subject to higher physical stress in the subsequent use of the component .
In a first method according to the present invention described below, the further coating comprises an aluminium diffusion coating.
In a second method according to the present invention described below, the further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two.
In a third method according to the present invention described below, the further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two, and the method further comprises the step (c) applying an aluminium diffusion coating to the selected regions coated with the MCrAlY overlay coating.
In the second and third methods the MCrAlY overlay coating applied in step (b) suitably comprises: 30 to 70 weight % Nickel; 30 to 50 weight % Cobalt; 15 to 25 weight % Chromium; 5 to 15 weight % Aluminium; and up to 1 weight %
Yttrium.
In the second and third methods the MCrAlY overlay coating applied in step (b) may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium. The chromium diffusion coating applied in step (a) suitably comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.
Methods according to the present invention find particular application in the protection against hot corrosion of nickel based superalloy components.
Methods according to the present invention find particular application in the protection against hot corrosion of gas turbine engine rotor blades. The present invention also extends to components protected against hot corrosion by means of a method according to the present invention.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig 1 shows a gas turbine engine rotor blade and the coating of this blade using a first method in accordance with the present invention;
Fig 2 is a view of a side of the rotor blade of Fig 1 hidden in Fig 1 but to be seen when looking from the right in Fig 1;
Fig 3 shows a gas turbine engine rotor blade and the coating of this blade using a second method in accordance with the present invention; Fig 4 is a view of a side of the rotor blade of Fig 3 hidden in Fig 3 but to be seen when looking from the right in Fig 3;
Fig 5 shows a gas turbine engine rotor blade and the coating of this blade using a third method in accordance with the present invention; and
Fig 6 is a view of a side of the rotor blade of Fig 5 hidden in Fig 5 but to be seen when looking from the right in Fig 5. In each of the first to third methods the rotor blade coated is a nickel based superalloy rotor blade. The rotor blade may be produced by conventional or directionally solidified (including single crystal) casting techniques. Typical alloys are MarM247, IN6203 and CMSX-4. Referring to Figs 1 and 2, the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) . The blade includes an internal cooling passage 9 which commences as shown in Fig 1, loops within the blade, and exits (exit not shown) via the top side of shroud part 1.
In a first stage of the first method, all surfaces of all parts of the blade, including internal cooling passage 9, are chromised, i.e. chromium is diffused into the surfaces. This diffusion is achieved by any suitable method, e.g. pack cementation or chemical vapour deposition (CVD) . This results in a surface layer rich in chromium. The layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick. In a second stage of the first method, an aluminium diffusion coating is applied to all external surfaces of the blade above dotted line M. This diffusion is again achieved by any suitable method, e.g. pack cementation or CVD. Masking is employed below dotted line M to prevent stray aluminium depositing below this line. If such stray depositing does occur, this is acceptable between dotted lines M and S, but not below dotted line S, i.e. not on the so called fir tree root of root part 7. Thus, a chromium modified aluminide coating results on all external surfaces of the blade above dotted line M. The so called outer beta layer of the chromium modified aluminide coating should typically contain 15 to 30 weight % aluminium and 5 to 15 weight % chromium. The total thickness of the chromium modified aluminide coating, including inter-diffusion zone, should typically be 25 to 100 microns.
Finally, the blade is heat treated to ensure that it maintains its optimum mechanical properties.
It is to be noted that in the final blade, all external surfaces above dotted line M are chromised plus aluminised, whereas all external surfaces below dotted line M and internal cooling passage 9 are chromised only.
Referring to Figs 3 and 4, the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) . The blade includes an internal cooling passage 9 which commences as shown in Fig 3, loops within the blade, and exits (exit not shown) via the top side of shroud part 1. In a first stage of the second method, all surfaces of all parts of the blade, including internal cooling passage 9, are chromised, i.e. chromium is diffused into the surfaces. This diffusion is achieved by any suitable method, e.g. pack cementation or CVD. This results in a surface layer rich in chromium. The layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick.
In a second stage of the second method, an MCrAlY overlay coating (where M is Ni or Co or a combination of the two) is applied to the following parts of the blade: outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5. The coating suitably comprises 30 to 70 weight % Nickel, 30 to 50 weight % Cobalt, 15 to 25 weight % Chromium, 5 to 15 weight % Aluminium, and up to 1 weight % Yttrium. The coating may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium. The coating is applied by any suitable method, e.g. by thermal spray techniques such as vacuum plasma spraying (VPS) , low pressure plasma spraying (LPPS) , and high velocity ox-fuel spraying (HVOF) , or by electroplating. Masking is employed to ensure that MCrAlY is not deposited on the remainder of platform part 5 below top face 11, and on root part 7.
Finally, the blade is heat treated to ensure that it maintains its optimum mechanical properties. It is to be noted that in the final blade, outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5 are chromised plus have an overlay coating of MCrAlY, whereas the remainder of platform part 5 below top face 11, root part 7, and internal cooling passage 9 are chromised only.
Referring to Figs 5 and 6, the blade coated comprises an outer shroud part 1 (above dotted line A) , an aerofoil part 3 (between dotted lines A and B) , a platform part 5 (between dotted lines B and C) , and a root part 7 (below dotted line C) . The blade includes an internal cooling passage 9 which commences as shown in Fig 5, loops within the blade, and exits (exit not shown) via the top side of shroud part 1.
In a first stage of the third method, all surfaces of all parts of the blade, including internal cooling passage 9, are chromised, i.e. chromium is diffused into the surfaces. This diffusion is achieved by any suitable method, e.g. pack cementation or CVD. This results in a surface layer rich in chromium. The layer should typically contain 15 to 30 weight % chromium and be 5 to 25 microns thick. In a second stage of the third method, an MCrAlY overlay coating (where M is Ni or Co or a combination of the two) is applied to the following parts of the blade: outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5. The coating suitably comprises 30 to 70 weight % Nickel, 30 to 50 weight % Cobalt, 15 to 25 weight % Chromium, 5 to 15 weight % Aluminium, and up to 1 weight % Yttrium. The coating may additionally include one or more elements selected from the group consisting of rhenium, silicon and hafnium. The coating is applied by any suitable method, e.g. by thermal spray techniques such as VPS, LPPS, and HVOF, or by electroplating. Masking is employed to ensure that MCrAlY is not deposited on the remainder of platform part 5 below top face 11, and on root part 7.
In a third stage of the third method, those parts of the blade to which the MCrAlY overlay coating was applied (outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5) are over-aluminised, i.e. an aluminium diffusion coating is applied to these parts. The diffusion is achieved by any suitable method, e.g. pack cementation or CVD. Masking is employed to ensure that stray aluminium is not deposited on the remainder of platform part 5 below top face 11, and on root part 7. The result of the over- aluminisation should be that the outer surface of the MCrAlY overlay coating has an aluminium content of typically 15 to 30 weight %. The total thickness of the over-aluminised MCrAlY coating, including inter-diffusion zone, should typically be 100 to 200 microns.
Finally, the blade is heat treated to ensure that it maintains its optimum mechanical properties. It is to be noted that in the final blade, outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5 are chromised plus have an overlay coating of MCrAlY, which MCrAlY overlay coating has been over-aluminised, whereas the remainder of platform part 5 below top face 11, root part 7, and internal cooling passage 9 are chromised only.
It is to be appreciated that in the above described first to third methods the application of further coating (s) in addition to the initial chromium diffusion coating is restricted to regions of the rotor blade not subject to higher physical stress in use of the blade. In the first method, the diffused aluminium coating is restricted to all external surfaces above dotted line M. In the second method, the MCrAlY overlay coating is restricted to outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5. In the third method, the MCrAlY overlay coating plus over- aluminisation is restricted to outer shroud part 1, aerofoil part 3, and the top face 11 of platform part 5. This restriction ensures that those regions of the blade that are subject to higher physical stress are coated with a chromium diffusion coating alone which is strain tolerant, and that the strain tolerance of this coating is not degraded by the application of further coating (s) . The purpose of the application of the further coating (s) is to provide additional protection against hot corrosion. The approach taken therefore with regard to the application of the further coating (s) is as follows. It is first determined where on the blade there will be a region of relatively high temperature. Further coating (s) are then applied to this region provided it is not also a region that will experience higher physical stress.

Claims

Claims :
1. A method of protecting a component against hot corrosion comprising the steps: (a) applying a chromium diffusion coating to the component; and (b) applying a further coating to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component .
2. A method according to claim 1 wherein said selected regions are regions not subject to higher physical stress in said subsequent use of the component.
3. A method according to claim 1 or claim 2 wherein said further coating comprises an aluminium diffusion coating.
4. A method according to claim 1 or claim 2 wherein said further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two.
5. A method according to claim 4 further comprising the step (c) applying an aluminium diffusion coating to said selected regions coated with said MCrAlY overlay coating.
6. A method according to claim 4 or claim 5 wherein said MCrAlY overlay coating applied in step (b) comprises: 30 to
70 weight % Nickel; 30 to 50 weight % Cobalt; 15 to 25 weight % Chromium; 5 to 15 weight % Aluminium; and up to 1 weight % Yttrium.
7. A method according to claim 4 or claim 5 or claim 6 wherein said MCrAlY overlay coating applied in step (b) additionally includes one or more elements selected from the group consisting of rhenium, silicon and hafnium.
8. A method according to any one of the preceding claims wherein said chromium diffusion coating applied in step (a) comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.
9. A method according to any one of the preceding claims wherein said component is a nickel based superalloy component .
10. A method according to any one of the preceding claims wherein said component is a gas turbine engine rotor blade.
11. A component having a coating to protect against hot corrosion, the coating comprising: a chromium diffusion coating; and a further coating applied to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component.
12. A component according to claim 11 wherein said selected regions are regions not subject to higher physical stress in said subsequent use of the component.
13. A component according to claim 11 or claim 12 wherein said further coating comprises an aluminium diffusion coating.
14. A component according to claim 11 or claim 12 wherein said further coating comprises an MCrAlY overlay coating, where M is Ni or Co or a combination of the two.
15. A component according to claim 14 wherein said coating to protect against hot corrosion further comprises an aluminium diffusion coating applied to said selected regions coated with said MCrAlY overlay coating.
16. A component according to claim 14 or claim 15 wherein said MCrAlY overlay coating comprises: 30 to 70 weight % Nickel; 30 to 50 weight % Cobalt; 15 to 25 weight % Chromium; 5 to 15 weight % Aluminium; and up to 1 weight % Yttrium.
17. A component according to claim 14 or claim 15 or claim 16 wherein said MCrAlY overlay coating additionally includes one or more elements selected from the group consisting of rhenium, silicon and hafnium.
18. A component according to any one of claims 11 to 17 wherein said chromium diffusion coating comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.
19. A component according to any one of claims 11 to 18 wherein the component is a nickel based superalloy component.
20. A component according to any one of claims 11 to 19 wherein the component is a gas turbine engine rotor blade.
PCT/EP2005/056643 2004-12-11 2005-12-09 A method of protecting a component against hot corrosion WO2006061431A2 (en)

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GB0427155A GB2421032A (en) 2004-12-11 2004-12-11 A method of protecting a component against hot corrosion

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US20070264126A1 (en) 2007-11-15
GB2421032A (en) 2006-06-14

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