EP1144708A2 - Method for coating hollow bodies - Google Patents

Method for coating hollow bodies

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Publication number
EP1144708A2
EP1144708A2 EP99967878A EP99967878A EP1144708A2 EP 1144708 A2 EP1144708 A2 EP 1144708A2 EP 99967878 A EP99967878 A EP 99967878A EP 99967878 A EP99967878 A EP 99967878A EP 1144708 A2 EP1144708 A2 EP 1144708A2
Authority
EP
European Patent Office
Prior art keywords
powder
metal
donor
coating
particle size
Prior art date
Legal status (The legal status 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 status listed.)
Granted
Application number
EP99967878A
Other languages
German (de)
French (fr)
Other versions
EP1144708A3 (en
EP1144708B1 (en
Inventor
Horst Pillhöfer
Andreas Fritsch
Thomas Dautl
Guido Schesny
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MTU Aero Engines AG
Original Assignee
MTU Aero Engines GmbH
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Publication date
Application filed by MTU Aero Engines GmbH filed Critical MTU Aero Engines GmbH
Publication of EP1144708A2 publication Critical patent/EP1144708A2/en
Publication of EP1144708A3 publication Critical patent/EP1144708A3/en
Application granted granted Critical
Publication of EP1144708B1 publication Critical patent/EP1144708B1/en
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Expired - Lifetime legal-status Critical Current

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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
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/30—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes using a layer of powder or paste on the surface
    • 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
    • C23C24/00—Coating starting from inorganic powder
    • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat

Definitions

  • the invention relates to a method for coating hollow bodies, in which a powder mixture of a metal donor powder, an inert filling powder and an activator powder is provided, the powder mixture with an inner surface of the body to be coated, e.g. made of a Ni, Co or Fe-based alloy, is brought into contact and heated.
  • a powder mixture of a metal donor powder, an inert filling powder and an activator powder is provided, the powder mixture with an inner surface of the body to be coated, e.g. made of a Ni, Co or Fe-based alloy, is brought into contact and heated.
  • the known processes for diffusion coating components made of heat-resistant alloys, such as Ni, Co or Fe-based alloys include the so-called powder packing processes.
  • powder packing processes Such a method is disclosed in US Pat. No. 3,667,985, in which the component surfaces to be coated are brought into contact and heated with a donor powder made of titanium and aluminum, to which an inert filler material and a halogen salt activator are mixed.
  • a powder packing method is known from US Pat. No. 3,958,047, in which the metallic component is brought into contact with a donor powder containing aluminum and chromium and is diffusion-coated with heating.
  • the achievable inner layer thicknesses are also limited here because the coating gas or the donor metal gas becomes impoverished on its way through the cavities of the component and a layer thickness gradient arises over the length of the cavity. Because the layer thickness of the outer coating is higher than that of the inner coating due to the process, the service life of the components is limited due to the thinner inner coating.
  • DE 30 33 074 A1 discloses a method for diffusion coating the inner surface of cavities, in which a metallic workpiece with an aluminizing diffusion powder mixture composed of 15% aluminum powder with a particle size of 40 ⁇ m and 85% alumina powder with a particle size of approximately 200 to 300 ⁇ m and an NH-CL powder can be coated.
  • US Pat. No. 5,208,071 discloses a method for aluminizing a ferritic component with an aluminum oxide slip and subsequent heat treatment, the slip consisting of at least 10% by weight of chromium, at least 10% by weight of inert filler material, at least 12% by weight of water Binder and a halogen activator and the coated ferritic component finally heat is treated.
  • the use of a slip differs significantly from a powder pack coating process.
  • the composition of the coating powder can comprise 10 to 60% chromium powder, 0.1 to 20% chromium halide and aluminum oxide.
  • the problem on which the present invention is based is to improve a powder packing process of the type described in the introduction in such a way that the layer thicknesses of the inner coating are sufficiently large even in the case of cavities with relatively complicated geometries.
  • the solution to this problem is characterized according to the invention in that the inert filling powder is provided with an average or average particle size which is approximately the same size as the average particle size of the metal donor powder.
  • the advantage is that, with such a choice of particle sizes, the specific density can be increased without the powder mixture clumping, for example due to an excessive proportion of the metal donor powder. It is also ensured that there is no early depletion of the donor metal.
  • a powder mixture is free-flowing and finds its way into narrow edges of inner cavities to be coated. Hollow bodies such as guide and rotor blades of gas turbines made of heat-resistant Ni, Co or Fe-based alloys can be coated.
  • the layer thicknesses of the inner coating also lie in narrow edges or gusset areas of the cavities in the range of 50 to 110 ⁇ m and thus ensure the function of the inner coating as an oxidation and corrosion protection layer.
  • the metal donor powder and the inert filling powder are provided with an average particle size of greater than 40 ⁇ m, as a result of which the coating gas can be permeated well by the bed of the powder mixture.
  • the powder mixture is preferably provided with a proportion of the metal donor powder of 10 to 25% by weight in order to prevent the powder mixture from clumping together and to ensure good permeation through the bed.
  • an alloy with a proportion of the donor metal of 20 to 80% by weight is provided as the metal donor powder, so that a sufficiently thick layer thickness is ensured due to the high proportion of donor metal.
  • a mixture of an alloy with a donor metal content of 40 to 70% by weight and an alloy with a donor metal content of 30 to 50% by weight is provided as the metal donor powder, so that the depletion of the metal donor in the two Alloys gradually, that is with a time delay.
  • the metal donor powder and the inert filling powder can be provided with an average or average particle size of 150 ⁇ m.
  • Such a powder mixture is free-flowing and fills the cavities with the inner surfaces to be coated due to an advantageous specific bulk density.
  • the hollow body is a hollow turbine guide vane of a gas turbine, which is provided with an oxidation and corrosion protection layer.
  • the cavity has a length of approximately 160 mm. Its inner surfaces are spaced between 2 and 6 mm and converge at two opposite end sections.
  • a powder mixture of approximately 20% by weight of metal donor powder and approximately 80% by weight of inert filler powder is provided to coat the inner surfaces of the guide vanes.
  • AlCr is selected as the metal donor powder and AI2O3 as the inert filler powder.
  • the melting point of AlCr is at least about 100 ° C above the coating temperature of about 800 ° C - 1200 ° C, so that no diffusion bonding of the metal particles to one another or clumping occurs.
  • the proportion of an activator powder is about 3% by weight, with AIF3, i.e. a halide compound is selected.
  • AIF3 i.e. a halide compound is selected.
  • a connection for the activator powder comes e.g. also consider CrC.
  • Such a connection must have a low vapor pressure at the coating temperature so that it remains intact during the entire coating process.
  • a halide compound of the donor metal here aluminum, is used to avoid agglomeration due to a chemical reaction of the halogen with the donor metal.
  • the average particle size of the inert filling powder is 100 ⁇ m and is significantly larger than the particle size of the metal donor powder, which is 60 ⁇ m.
  • the proportion of aluminum, i.e. of the metal dispenser, on the metal dispenser powder is 50% by weight.
  • the powder mixture provided in this way is filled into the cavity of the guide vanes for coating the inner surfaces.
  • the subsequent coating is carried out at 1080 ° C and a holding time of 6 h, the outer coating, i.e. the coating of the outer surfaces of the guide vane can be carried out simultaneously in a one-step process using a conventional powder packing process or by a gas diffusion coating process.
  • The.AI content in the layer is between 30 and 35% by weight in the inner coating deposited in this way.
  • an inert filler powder (A Oa) with an average particle size of approximately 100 ⁇ m is selected, which makes up approximately 80% by weight of the powder mixture.
  • AIF 3 with about 3% by weight of a powder mixture is selected and mixed as the activator powder.
  • the metal donor powder which makes up about 20% by weight of the powder mixture, consists of two fractions.
  • the first fraction is an alloy of AlCr, in which the proportion of aluminum is 50% by weight.
  • the proportion of the donor metal, aluminum is lower in the second fraction and is 30% by weight.
  • the Al content in the inner layers is 24 to 28% by weight.
  • the inner layer thicknesses are between 65 and 105 ⁇ m and thus significantly higher than the layer thicknesses that can be achieved with conventional (powder pack) processes.
  • the hollow body is a hollow turbine guide vane of a gas turbine, which is provided with an oxidation and corrosion protection layer by means of a powder pack coating process.
  • the elongated cavity is about 180 mm long.
  • the inner surfaces are spaced between 2 and 6 mm and converge at two opposite, longitudinal end sections.
  • a powder mixture of approximately 15% by weight of metal donor powder and just below 85% by weight of inert filler powder is provided.
  • the proportion of the metal donor powder can range from 10 to 25% by weight, depending on the application.
  • the metal donor powder is AlCr and the inert filler powder is AI2O3.
  • a halogen compound such as AIF 3 is used as the activator powder.
  • the activator powder is thus a halide compound of the donor metal AI.
  • the average particle size of the inert filling powder is approximately the same size as the average particle size of the metal donor powder and is 150 ⁇ m.
  • the proportion of the donor metal AI in the metal donor powder, which is an alloy, is 50% by weight.
  • the specific density of such a powder pack mixture is not high because of a high proportion of the metal donor powder, but because of the selected particle size distribution. With this pouring of the powder pack mixture, there is sufficient permeation of the coating gases originating from the halide compound.
  • the powder mixture thus provided is filled into its cavity.
  • the bed is easy to pour and also has access to the narrow edges of the cavity.
  • the subsequent coating takes place at 1080 ° C and a holding time of 6 h. It can be used simultaneously with the outer coating, i.e. the coating of the outer surface of the turbine guide vane, which can be carried out by a conventional powder packing process or by a gas diffusion coating process. In general, the coating is carried out simultaneously on several turbine guide vanes.
  • the Al content in the inner coating deposited in this way is between 30 and 35% by weight and therefore in a very advantageous range, i.e. it occurs e.g. B. no embrittlement of the layer.
  • the layer thicknesses are also in the narrow edges or gusset area of the cavities in the range from 60 to 110 ⁇ m, so that the function of the inner coating as protection against oxidation and corrosion is ensured.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Powder Metallurgy (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Paints Or Removers (AREA)

Abstract

The invention relates to a method for coating hollow bodies in which a powder mixture is prepared that is comprised of a metal dispensing powder, of an inert charging powder, and of an activator powder consisting of a metal halogenide. The powder mixture is brought into contact with an inner surface of the hollow body to be coated and is heated. In order to increase the thicknesses of the inner layer, the inert charging powder is prepared with an average particle size which is approximately the same size as the average particle size of the metal dispensing powder.

Description

Verfahren zum Beschichten von Hohlkörpern Process for coating hollow bodies
Die Erfindung betrifft ein Verfahren zum Beschichten von Hohlkörpern, bei dem eine Pulvermischung aus einem Metallspenderpulver, einem inerten Füllpulver und einem Aktivatorpulver bereitgestellt wird, die Pulvermischung mit einer zu beschichtenden inneren Oberfläche des Körpers, z.B. aus einer Ni-, Co- oder Fe-Basislegierung, in Kontakt gebracht und erwärmt wird.The invention relates to a method for coating hollow bodies, in which a powder mixture of a metal donor powder, an inert filling powder and an activator powder is provided, the powder mixture with an inner surface of the body to be coated, e.g. made of a Ni, Co or Fe-based alloy, is brought into contact and heated.
Zu den bekannten Verfahren zum Diffusionsbeschichten von Bauteilen aus warmfe- sten Legierungen, wie Ni-, Co- oder Fe-Basislegierungen, gehören die sog. Pulverpackverfahren. Ein derartiges Verfahren wird in der US 3,667,985 offenbart, bei dem die zu beschichtenden Bauteiloberflächen mit einem Spenderpulver aus Titan und Aluminium, dem ein inertes Füllmaterial sowie ein Halogensalz-Aktivator zugemischt wird, in Kontakt gebracht und erhitzt wird. Aus der US 3,958,047 ist ein Pulverpack- verfahren bekannt, bei dem das metallische Bauteil mit einem Aluminium und Chrom enthaltenden Spenderpulver in Kontakt gebracht und unter Erhitzen diffusionsbeschichtet wird.The known processes for diffusion coating components made of heat-resistant alloys, such as Ni, Co or Fe-based alloys, include the so-called powder packing processes. Such a method is disclosed in US Pat. No. 3,667,985, in which the component surfaces to be coated are brought into contact and heated with a donor powder made of titanium and aluminum, to which an inert filler material and a halogen salt activator are mixed. A powder packing method is known from US Pat. No. 3,958,047, in which the metallic component is brought into contact with a donor powder containing aluminum and chromium and is diffusion-coated with heating.
Diese Verfahren eignen sich insbesondere zur Beschichtung der Außenoberflächen metallischer Bauteile, wobei Schichtdicken zwischen 50 und 100 μm erzielt werden. Beim Beschichten von inneren Oberflächen treten jedoch verfahrensimmanente Nachteile auf, so daß die erreichbaren Innenschichtdicken bei relativ komplizierten Geometrien mit engen Spalten, Winkeln oder Hinterschneidungen begrenzt und unzureichend sind und im allgemeinen unter 30 μm liegen. Problematisch ist dabei, daß die Spenderpulver lediglich eine geringe Fließfähigkeit besitzen und die Hohlräume unvollständig füllen. Zudem läßt sich das Spenderpulver nach dem Beschichten nur schwer und nicht rückstandsfrei aus den Hohlräumen entfernen und sintert an den Oberflächen an.These methods are particularly suitable for coating the outer surfaces of metallic components, layer thicknesses between 50 and 100 μm being achieved. When coating inner surfaces, however, there are disadvantages inherent in the process, so that the achievable inner layer thicknesses are limited and inadequate in the case of relatively complicated geometries with narrow gaps, angles or undercuts and are generally below 30 μm. The problem here is that the donor powder has only a low fluidity and incompletely fill the cavities. In addition, the donor powder is difficult to remove from the cavities after coating and does not leave any residue and sinters on the surfaces.
Die genannten Nachteile der Pulverpackverfahren lassen sich zum Teil durch sog. Gasdiffusionsbeschichtungsverfahren umgehen. Ein solches Verfahren ist aus der US 4, 148,275 bekannt, bei dem eine z.B. Aluminium enthaltende Pulvermischung in einer ersten Kammer und die zu beschichtenden, metallischen Bauteile in einer zwei- ten Kammer eines Behälters angeordnet sind. Das Beschichtungsgas wird durch Erhitzen des Pulvers erzeugt und lagert sich unter Einsatz eines Trägergases an den äußeren und inneren Oberflächen der zu beschichtenden Bauteile ab. Die Gasdiffusi- onsbeschichtungsverfahren besitzen jedoch den Nachteil, daß die Vorrichtungen zur Durchführung des Verfahrens, wie z.B. zur Zwangsführung der Beschichtungsgase, im Vergleich zu jenen für die Pulverpackverfahren komplex und teuer sind. Darüber hinaus sind auch hier die erreichbaren Innenschichtdicken begrenzt, weil das Beschichtungsgas bzw. das Spendermetallgas auf seinem Weg durch die Hohlräume des Bauteils verarmt und ein Schichtdickengradient über die Länge des Hohlraums entsteht. Weil die Schichtdicke der Außenbeschichtung verfahrensbedingt über jener der Innenbeschichtung liegt, ist die Lebensdauer der Bauteile infolge der dünneren Innenbeschichtung begrenzt.The mentioned disadvantages of the powder packing process can be partly avoided by so-called gas diffusion coating processes. Such a method is known from US Pat. No. 4,148,275, in which a powder mixture containing, for example, aluminum in a first chamber and the metallic components to be coated in a two th chamber of a container are arranged. The coating gas is generated by heating the powder and is deposited on the outer and inner surfaces of the components to be coated using a carrier gas. However, the gas diffusion coating processes have the disadvantage that the devices for carrying out the process, such as for example the forced guidance of the coating gases, are complex and expensive in comparison with those for the powder packing process. In addition, the achievable inner layer thicknesses are also limited here because the coating gas or the donor metal gas becomes impoverished on its way through the cavities of the component and a layer thickness gradient arises over the length of the cavity. Because the layer thickness of the outer coating is higher than that of the inner coating due to the process, the service life of the components is limited due to the thinner inner coating.
Aus der US 4,208,453 ist ein Verfahren zum Diffusionsbeschichten der Innen- und Außenflächen von Bauteilen, wie Gasturbinenschaufeln, bekannt, bei dem eine Pulvermischung aus 10 % Chrom-Spenderpulver mit einer Partikelgröße von 10 bis 20 μm und 90 % Aluminiumoxid-Granulat mit einer Partikelgröße von 100 bis 300 μm besteht. Zudem wird ein Metallhalogenid als Aktivator hinzugefügt. Die Offenbarung beschäftigt sich nicht mit Maßnahmen zur Erhöhung der Schichtdicke in Hohlräumen mit komplizierten Geometrien.From US 4,208,453 a method for diffusion coating the inner and outer surfaces of components, such as gas turbine blades, is known, in which a powder mixture of 10% chromium donor powder with a particle size of 10 to 20 μm and 90% aluminum oxide granules with a particle size of 100 to 300 μm. A metal halide is also added as an activator. The disclosure is not concerned with measures to increase the layer thickness in cavities with complicated geometries.
Die DE 30 33 074 A1 offenbart ein Verfahren zur Diffusionsbeschichtung der Innenfläche von Hohlräumen, bei dem ein metallisches Werkstück mit einem aluminisie- renden Diffusionspulvergemisch aus 15 % Aluminiumpulver mit einer Teilchengröße von 40 μm und 85 % Tonerdepulver mit einer Teilchengröße von etwa 200 bis 300 μm sowie einem NH-CL-Pulver beschichtet werden kann.DE 30 33 074 A1 discloses a method for diffusion coating the inner surface of cavities, in which a metallic workpiece with an aluminizing diffusion powder mixture composed of 15% aluminum powder with a particle size of 40 μm and 85% alumina powder with a particle size of approximately 200 to 300 μm and an NH-CL powder can be coated.
Die US 5,208,071 offenbart ein Verfahren zum Aluminisieren eines ferritischen Bauteils mit einem Aluminiumoxid-Schlicker und anschließender Wärmebehandlung, wobei der Schlicker aus wenigstens 10 Gew.-% Chrom, wenigstens 10 Gew.-% inertem Füllmaterial, wenigstens 12 Gew.-% Wasser, einem Binder sowie einem Halogenaktivator besteht und das beschichtete ferritische Bauteil abschließend wärme- behandelt wird. Die Verwendung eines Schlickers unterscheidet sich verfahrenstechnisch deutlich von einem Pulverpackbeschichtungsverfahren.US Pat. No. 5,208,071 discloses a method for aluminizing a ferritic component with an aluminum oxide slip and subsequent heat treatment, the slip consisting of at least 10% by weight of chromium, at least 10% by weight of inert filler material, at least 12% by weight of water Binder and a halogen activator and the coated ferritic component finally heat is treated. In terms of process technology, the use of a slip differs significantly from a powder pack coating process.
Aus der GB 2 109 822 A ist ein Metalldiffusionsverfahren bekannt, mit dem Diffusi- onsbeschichtungen schneller als beim Pulverpackverfahren hergestellt werden können, wobei das Beschichtungspulver locker vorliegt und mit mechanischen Mitteln während der Erwärmung mit dem zu beschichtenden Bauteil, insbesondere auch mit dessen innerer Oberfläche, in Kontakt gehalten wird. Die Zusammensetzung des Beschichtungspulvers kann 10 bis 60 % Chrompulver, 0, 1 bis 20 % um Chromhalo- genid und Aluminiumoxid umfassen.From GB 2 109 822 A a metal diffusion process is known with which diffusion coatings can be produced faster than with the powder packing process, the coating powder being loose and with mechanical means during heating with the component to be coated, in particular also with its inner surface. is kept in contact. The composition of the coating powder can comprise 10 to 60% chromium powder, 0.1 to 20% chromium halide and aluminum oxide.
Das der vorliegenden Erfindung zugrunde liegende Problem besteht darin, ein Pulverpackverfahren der eingangs beschriebenen Gattung so zu verbessern, daß die Schichtdicken der Innenbeschichtung auch bei Hohlräumen mit verhältnismäßig komplizierten Geometrien ausreichend groß sind.The problem on which the present invention is based is to improve a powder packing process of the type described in the introduction in such a way that the layer thicknesses of the inner coating are sufficiently large even in the case of cavities with relatively complicated geometries.
Die Lösung dieses Problems ist erfindungsgemäß dadurch gekennzeichnet, daß das inerte Füllpulver mit einer durchschnittlichen bzw. mittleren Partikelgröße, die ungefähr gleich groß wie die mittlere Partikelgröße des Metallspenderpulvers ist, bereit- gestellt wird.The solution to this problem is characterized according to the invention in that the inert filling powder is provided with an average or average particle size which is approximately the same size as the average particle size of the metal donor powder.
Der Vorteil besteht darin, daß sich bei einer derartigen Wahl der Partikelgrößen die spezifische Dichte erhöhen läßt, ohne daß ein Verklumpen der Pulvermischung, z.B. aufgrund eines zu hohen Anteils des Metallspenderpulvers, auftritt. Ebenso ist ge- währleistet, dass kein frühzeitiges Verarmen des Spendermetalls auftritt. Eine derartige Pulvermischung ist gut rieselfähig und findet Zugang in engen Kanten von zu beschichtenden inneren Hohlräumen. Es lassen sich Hohlkörper, wie Leit- und Laufschaufeln von Gasturbinen aus warmfesten Ni-, Co- oder Fe-Basislegierungen, beschichten. Die Schichtdicken der Innenbeschichtung liegen auch in engen Kanten oder Zwickelbereichen der Hohlräume im Bereich von 50 bis 1 10 μm und gewährleisten somit die Funktion der Innenbeschichtung als Oxidations- und Korrosionsschutzschicht. In einer bevorzugten Ausgestaltung wird das Metallspenderpulver und das inerte Füllpulver mit einer durchschnittlichen Partikelgröße von größer als 40 μm bereitgestellt, wodurch eine gute Permeation des Beschichtungsgases durch die Schüttung der Pulvermischung erfolgen kann.The advantage is that, with such a choice of particle sizes, the specific density can be increased without the powder mixture clumping, for example due to an excessive proportion of the metal donor powder. It is also ensured that there is no early depletion of the donor metal. Such a powder mixture is free-flowing and finds its way into narrow edges of inner cavities to be coated. Hollow bodies such as guide and rotor blades of gas turbines made of heat-resistant Ni, Co or Fe-based alloys can be coated. The layer thicknesses of the inner coating also lie in narrow edges or gusset areas of the cavities in the range of 50 to 110 μm and thus ensure the function of the inner coating as an oxidation and corrosion protection layer. In a preferred embodiment, the metal donor powder and the inert filling powder are provided with an average particle size of greater than 40 μm, as a result of which the coating gas can be permeated well by the bed of the powder mixture.
Bevorzugt wird die Pulvermischung mit einem Anteil des Metallspenderpulvers von 10 bis 25 Gew.-% bereitgestellt, um das Verklumpen der Pulvermischung zu vermeiden und eine gute Permeation durch die Schüttung zu gewährleisten.The powder mixture is preferably provided with a proportion of the metal donor powder of 10 to 25% by weight in order to prevent the powder mixture from clumping together and to ensure good permeation through the bed.
Es ist des weiteren zweckmäßig, daß als Metallspenderpulver eine Legierung mit einem Anteil des Spendermetalls von 20 bis 80 Gew.-% bereitgestellt wird, damit aufgrund des hohen Spendermetallanteils eine ausreichend starke Schichtdicke gewährleistet ist.It is furthermore expedient that an alloy with a proportion of the donor metal of 20 to 80% by weight is provided as the metal donor powder, so that a sufficiently thick layer thickness is ensured due to the high proportion of donor metal.
Es kann vorteilhaft sein, daß als Metallspenderpulver eine Mischung aus einer Legierung mit einem Spendermetallanteil von 40 bis 70 Gew.-% und einer Legierung mit einem Spendermetallanteil von 30 bis 50 Gew.-% bereitgestellt wird, so daß die Verarmung des Metallspenders in den beiden Legierungen schrittweise, d.h. mit zeitlicher Verzögerung, erfolgt.It can be advantageous that a mixture of an alloy with a donor metal content of 40 to 70% by weight and an alloy with a donor metal content of 30 to 50% by weight is provided as the metal donor powder, so that the depletion of the metal donor in the two Alloys gradually, that is with a time delay.
Das Metallspenderpulver und das inerte Füllpulver können mit einer durchschnittlichen bzw. mittleren Partikelgröße von 150 μm bereitgestellt werden. Eine derartige Pulvermischung ist gut rieselfähig und füllt die Hohlräume mit den zu beschichtenden Innenoberflächen aufgrund einer vorteilhaften spezifischen Schüttdichte gut aus. Zudem erfolgt eine gute Permeation des Beschichtungsgases durch die Schüttung der Pulvermischung.The metal donor powder and the inert filling powder can be provided with an average or average particle size of 150 μm. Such a powder mixture is free-flowing and fills the cavities with the inner surfaces to be coated due to an advantageous specific bulk density. In addition, there is good permeation of the coating gas by pouring the powder mixture.
Weitere Ausgestaltungen der Erfindung sind in den Unteransprüchen beschrieben.Further refinements of the invention are described in the subclaims.
Im folgenden wird die Erfindung anhand von Beispielen näher erläutert.The invention is explained in more detail below with the aid of examples.
In einem ersten Beispiel ist der Hohlkörper einer hohle Turbinen-Leitschaufel einer Gasturbine, die mit einer Oxidations- und Korrosionsschutzschicht versehen wird. Der Hohlraum besitzt eine Länge von etwa 160 mm. Seine inneren Oberflächen sind zwischen 2 und 6 mm beabstandet und laufen an zwei gegenüberliegenden Endabschnitten zusammen. Zur Beschichtung der inneren Oberflächen der Leitschaufeln wird eine Pulvermischung aus etwa 20 Gew.- Metallspenderpulver und etwa 80- Gew.-% inertem Füllpulver bereitgestellt. Als Metallspenderpulver wird AlCr und als inertes Füllpulver AI2O3 gewählt. Der Schmelzpunkt von AlCr liegt wenigstens etwa 100 °C über der Beschichtungstemperatur von etwa 800 °C - 1200 °C, so daß kein Diffusionsverbinden der Metallpartikel untereinander bzw. ein Verklumpen auftritt.In a first example, the hollow body is a hollow turbine guide vane of a gas turbine, which is provided with an oxidation and corrosion protection layer. The cavity has a length of approximately 160 mm. Its inner surfaces are spaced between 2 and 6 mm and converge at two opposite end sections. A powder mixture of approximately 20% by weight of metal donor powder and approximately 80% by weight of inert filler powder is provided to coat the inner surfaces of the guide vanes. AlCr is selected as the metal donor powder and AI2O3 as the inert filler powder. The melting point of AlCr is at least about 100 ° C above the coating temperature of about 800 ° C - 1200 ° C, so that no diffusion bonding of the metal particles to one another or clumping occurs.
Der Anteil eines Aktivatorpulvers beträgt etwa 3 Gew.- , wobei AIF3, d.h. eine Halo- genidverbindung, gewählt wird. Als Verbindung für das Aktivatorpulver kommt z.B. auch CrC in Betracht. Eine solche Verbindung muß einen niedrigen Dampfdruck bei der Beschichtungstemperatur aufweisen, damit sie während des gesamten Beschich- tungsprozesses erhalten bleibt. Zudem wird eine Halogenidverbindung des Spen- dermetalls, hier Aluminium, eingesetzt, um eine Agglomeration infolge einer chemischen Reaktion des Halogens mit dem Spendermetall zu vermeiden.The proportion of an activator powder is about 3% by weight, with AIF3, i.e. a halide compound is selected. As a connection for the activator powder comes e.g. also consider CrC. Such a connection must have a low vapor pressure at the coating temperature so that it remains intact during the entire coating process. In addition, a halide compound of the donor metal, here aluminum, is used to avoid agglomeration due to a chemical reaction of the halogen with the donor metal.
Die durchschnittliche Partikelgröße des inerten Füllpulvers beträgt 100 μm und ist deutlich größer als die Partikelgröße des Metallspenderpulvers, die 60 μm beträgt. Der Anteil von Aluminium, d.h. des Metallspenders, an dem Metallspenderpulver beträgt 50 Gew.-%.The average particle size of the inert filling powder is 100 μm and is significantly larger than the particle size of the metal donor powder, which is 60 μm. The proportion of aluminum, i.e. of the metal dispenser, on the metal dispenser powder is 50% by weight.
Die so bereitgestellte Pulvermischung wird in den Hohlraum der Leitschaufeln zur Beschichtung der inneren Oberflächen eingefüllt. Die anschließende Beschichtung erfolgt bei 1080 °C und einer Haltezeit von 6 h, wobei die Außenbeschichtung, d.h. die Beschichtung der äußeren Oberflächen der Leitschaufel, gleichzeitig in einem Einstufenprozeß mit einem herkömmlichen Pulverpackverfahren oder auch durch ein Gasdiffusionsbeschichtungsverfahren erfolgen kann.The powder mixture provided in this way is filled into the cavity of the guide vanes for coating the inner surfaces. The subsequent coating is carried out at 1080 ° C and a holding time of 6 h, the outer coating, i.e. the coating of the outer surfaces of the guide vane can be carried out simultaneously in a one-step process using a conventional powder packing process or by a gas diffusion coating process.
Der.AI-Gehalt in der Schicht liegt bei der auf diese Weise abgeschiedenen Innenbeschichtung zwischen 30 und 35 Gew.- . Bei einem zweiten Beispiel wird wieder ein inertes Füllpulver (A Oa) mit einer dur- schnittlichen Partikelgröße von etwa 100 μm gewählt, das etwa 80 Gew.-% der Pulvermischung ausmacht. Als Aktivatorpulver wird AIF3 mit etwa 3 Gew.-% eine Pulvermischung gewählt und zugemischt.The.AI content in the layer is between 30 and 35% by weight in the inner coating deposited in this way. In a second example, an inert filler powder (A Oa) with an average particle size of approximately 100 μm is selected, which makes up approximately 80% by weight of the powder mixture. AIF 3 with about 3% by weight of a powder mixture is selected and mixed as the activator powder.
Im Unterschied zu Beispiel 1 besteht das Metallspenderpulver, das einen Anteil von etwa 20 Gew.-% an der Pulvermischung ausmacht, aus zwei Fraktionen. Die erste Fraktion ist eine Legierung aus AlCr, bei der der Anteil von Aluminium 50 Gew.-% beträgt. In der zweiten Fraktion ist der Anteil des Spendermetalls, Aluminium, gerin- ger und beträgt 30 Gew.-%. Mit dieser Maßnahme läßt sich der Beschichtungsprozeß in der Weise optimieren, daß zunächst die Fraktion mit dem geringeren AI-Gehalt verarmt, der Beschichtungsprozeß jedoch durch die Fraktion mit dem größeren AI- Gehalt fortgesetzt wird. Auf diese Weise läßt sich die Duktilität der Schichten auf den inneren Oberflächen der Leitschaufel vergrößern.In contrast to Example 1, the metal donor powder, which makes up about 20% by weight of the powder mixture, consists of two fractions. The first fraction is an alloy of AlCr, in which the proportion of aluminum is 50% by weight. The proportion of the donor metal, aluminum, is lower in the second fraction and is 30% by weight. With this measure, the coating process can be optimized in such a way that the fraction with the lower Al content is initially depleted, but the coating process is continued by the fraction with the higher Al content. In this way, the ductility of the layers on the inner surfaces of the guide vane can be increased.
Der AI-Gehalt in den inneren Schichten beträgt 24 bis 28 Gew.-%. Die Innenschichtdicken liegen zwischen 65 und 105 μm und damit deutlich über den mit herkömmlichen (Pulverpack-)Verfahren erzielbaren Schichtdicken.The Al content in the inner layers is 24 to 28% by weight. The inner layer thicknesses are between 65 and 105 μm and thus significantly higher than the layer thicknesses that can be achieved with conventional (powder pack) processes.
In einem dritten Beispiel ist der Hohlkörper eine hohle Turbinen-Leitschaufel einer Gasturbine, die mittels eines Pulverpackbeschichtungsverfahrens mit einer Oxida- tions- und Korrosionsschutzschicht versehen wird. Der längliche Hohlraum ist etwa 180 mm lang. Die inneren Oberflächen sind zwischen 2 und 6 mm beabstandet und laufen an zwei gegenüberliegenden, längsseitigen Endabschnitten zusammen. Zur Beschichtung der inneren Oberfläche der Leitschaufel wird eine Pulvermischung aus etwa 15 Gew.-% Metallspenderpulver und knapp unter 85 Gew.-% inertem Füllpulver bereitgestellt. Der Anteil des Metallspenderpulvers kann je nach Einsatzfall im Bereich von 10 bis 25 Gew.-% liegen. Das Metallspenderpulver ist AlCr und das inerte Füllpulver ist AI2O3. Als Aktivatorpulver wird eine Halogenverbindung wie AIF3 einge- setzt, dessen Anteil etwa 3 Gew.-% beträgt. Das Aktivatorpulver ist somit einer Halo- genidverbindung des Spendermetalls AI. Die mittlere Partikelgröße des inerten Füllpulvers ist ungefähr gleich groß wie die mittlere Partikelgröße des Metallspenderpulvers und beträgt 150 μm. Der Anteil des Spendermetalls AI an dem Metallspenderpulver, das eine Legierung ist, beträgt 50 Gew.-%. Die spezifische Dichte einer derartigen Pulverpackmischung ist nicht aufgrund eines hohen Anteils des Metallspenderpulvers, sondern aufgrund der gewählten Partikelgrößenverteilung hoch. Bei dieser Schüttung der Pulverpackmischung erfolgt eine ausreichend Permeation der aus der Halogenidverbindung stammenden Beschichtungsgase.In a third example, the hollow body is a hollow turbine guide vane of a gas turbine, which is provided with an oxidation and corrosion protection layer by means of a powder pack coating process. The elongated cavity is about 180 mm long. The inner surfaces are spaced between 2 and 6 mm and converge at two opposite, longitudinal end sections. To coat the inner surface of the guide vane, a powder mixture of approximately 15% by weight of metal donor powder and just below 85% by weight of inert filler powder is provided. The proportion of the metal donor powder can range from 10 to 25% by weight, depending on the application. The metal donor powder is AlCr and the inert filler powder is AI2O3. A halogen compound such as AIF 3 , the proportion of which is about 3% by weight, is used as the activator powder. The activator powder is thus a halide compound of the donor metal AI. The average particle size of the inert filling powder is approximately the same size as the average particle size of the metal donor powder and is 150 μm. The proportion of the donor metal AI in the metal donor powder, which is an alloy, is 50% by weight. The specific density of such a powder pack mixture is not high because of a high proportion of the metal donor powder, but because of the selected particle size distribution. With this pouring of the powder pack mixture, there is sufficient permeation of the coating gases originating from the halide compound.
Für die Beschichtung der inneren Oberfläche der Turbinen-Leitschaufel wird die so bereitgestellte Pulvermischung in deren Hohlraum eingefüllt. Bei der gewählten Partikelgrößenverteilung des inerten Füllpulvers und des Metallspenderpulvers ist die Schüttung gut rieselfähig und findet auch Zugang zu den engen Kanten des Hohlraums. Die anschließende Beschichtung erfolgt bei 1080°C und einer Haltezeit von 6 h. Sie kann gleichzeitig mit der Außenbeschichtung, d.h. der Beschichtung der äußeren Oberfläche der Turbinen-Leitschaufel, die nach einem herkömmlichen Pulverpackverfahren oder auch durch ein Gasdiffusionsbeschichtungsverfahren erfolgen kann, durchgeführt werden. Im allgemeinen wird die Beschichtung bei mehreren Turbinen-Leitschaufeln gleichzeitig durchgeführt.For the coating of the inner surface of the turbine guide vane, the powder mixture thus provided is filled into its cavity. With the chosen particle size distribution of the inert filling powder and the metal donor powder, the bed is easy to pour and also has access to the narrow edges of the cavity. The subsequent coating takes place at 1080 ° C and a holding time of 6 h. It can be used simultaneously with the outer coating, i.e. the coating of the outer surface of the turbine guide vane, which can be carried out by a conventional powder packing process or by a gas diffusion coating process. In general, the coating is carried out simultaneously on several turbine guide vanes.
Der AI-Gehalt in der auf diese Weise abgeschiedenen Innenbeschichtung liegt zwischen 30 und 35 Gew.-% und mithin in einem sehr vorteilhaften Bereich, d.h. es tritt z. B. keine Versprödung der Schicht auf.The Al content in the inner coating deposited in this way is between 30 and 35% by weight and therefore in a very advantageous range, i.e. it occurs e.g. B. no embrittlement of the layer.
Die Schichtdicken liegen auch in engen Kanten oder Zwickelbereich der Hohläume im Bereich von 60 bis 1 10 μm, so daß die Funktion der Innenbeschichtung als Oxida- tions- und Korrosionsschutz gewährleistet ist. The layer thicknesses are also in the narrow edges or gusset area of the cavities in the range from 60 to 110 μm, so that the function of the inner coating as protection against oxidation and corrosion is ensured.

Claims

Patentansprüche claims
1. Verfahren zum Beschichten von Hohlkörpern, bei dem eine Pulvermischung aus einem Metallspenderpulver, einem inerten Füllpulver und einem Aktivatorpulver aus einem Metallhalogenid bereitgestellt wird, die Pulvermischung mit einer zu beschichtenden, inneren Oberfläche des Hohlkörpers in Kontakt gebracht und erwärmt wird, dadurch gekennzeichnet, daß das inerte Füllpulver mit einer mittleren Partikelgröße, die ungefähr gleich groß wie die mittlere Partikelgröße des Metallspenderpulvers ist, bereitgestellt wird.1. A method for coating hollow bodies, in which a powder mixture of a metal donor powder, an inert filler powder and an activator powder made of a metal halide is provided, the powder mixture is brought into contact with an inner surface of the hollow body to be coated and heated, characterized in that the inert filling powder is provided with an average particle size which is approximately the same size as the average particle size of the metal donor powder.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daß das Metallspenderpulver und das inerte Füllpulver mit einer durchschnittlichen Partikelgröße von gößer als 40 μm bereitgestellt werden.2. The method according to claim 1, characterized in that the metal donor powder and the inert filler powder are provided with an average particle size of greater than 40 microns.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß eine Pulvermischung mit einem Anteil des Metallspenderpulvers von 10 bis 25 Gew.-% bereitgestellt wird.3. The method according to claim 1 or 2, characterized in that a powder mixture is provided with a proportion of the metal donor powder of 10 to 25 wt .-%.
4. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekenn- zeichnet, daß als Metallspenderpulver eine Legierung mit einem Anteil des Spendermetalls von 20 bis 80 Gew.-% bereitgestellt wird.4. The method according to one or more of the preceding claims, characterized in that an alloy with a proportion of the donor metal of 20 to 80 wt .-% is provided as the metal donor powder.
5. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekennzeichnet, daß als Metallspenderpuiver eine Mischung aus einer Legierung mit ei- nem Spendermetallanteil von 40 bis 70 Gew.- und einer Legierung mit einem5. The method according to one or more of the preceding claims, characterized in that a mixture of an alloy with a donor metal content of 40 to 70 wt .-% and an alloy with a as a metal dispenser powder
Spendermetallanteil von 30 bis 50 Gew.-% bereitgestellt wird.Donor metal content of 30 to 50 wt .-% is provided.
6. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekennzeichnet, daß eine Pulvermischung mit einem Aktivatorpulveranteil von 2 bis 5 Gew.-% bereitgestellt wird. 6. The method according to one or more of the preceding claims, characterized in that a powder mixture with an activator powder content of 2 to 5 wt .-% is provided.
7. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekenn¬ zeichnet, daß für das Aktivatorpulver ein Metallhalogenid des Spendermetalls ausgewählt wird.Characterized 7. The method according to one or more of the preceding claims, characterized ¬ marked in that the donor metal is selected for the activator powder a metal halide.
8. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekennzeichnet, daß als Spendermetallpulver AlCr ausgewählt wird.8. The method according to one or more of the preceding claims, characterized in that AlCr is selected as the donor metal powder.
9. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekennzeichnet, daß als inertes Füllpulver AIΛausgewählt wird.9. The method according to one or more of the preceding claims, characterized in that AIΛ is selected as the inert filling powder.
10. Verfahren nach einem oder mehreren der vorherigen Ansprüche, dadurch gekennzeichnet, daß die Pulvermischung auf eine Beschichtungstemperatur von 800 °C bis 1200 °C erwärmt wird.10. The method according to one or more of the preceding claims, characterized in that the powder mixture is heated to a coating temperature of 800 ° C to 1200 ° C.
1 1. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Metallspenderpulver und das interte Füllpulver mit einer mitteleren Partikelgröße von etwa 150 μm bereitgestellt werden. 1 1. The method according to one or more of the preceding claims, characterized in that the metal donor powder and the interte filling powder are provided with an average particle size of about 150 microns.
EP99967878A 1998-12-10 1999-12-09 Method for coating hollow bodies Expired - Lifetime EP1144708B1 (en)

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DE19856901A DE19856901C2 (en) 1998-12-10 1998-12-10 Process for coating hollow bodies
PCT/DE1999/003942 WO2000034547A2 (en) 1998-12-10 1999-12-09 Method for coating hollow bodies

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DE59904502D1 (en) 2003-04-10
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