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EP1471162A1 - Process for obtaining a flexo-adaptive thermal barrier coating - Google Patents

Process for obtaining a flexo-adaptive thermal barrier coating Download PDF

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Publication number
EP1471162A1
EP1471162A1 EP04290944A EP04290944A EP1471162A1 EP 1471162 A1 EP1471162 A1 EP 1471162A1 EP 04290944 A EP04290944 A EP 04290944A EP 04290944 A EP04290944 A EP 04290944A EP 1471162 A1 EP1471162 A1 EP 1471162A1
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EP
European Patent Office
Prior art keywords
torch
blade
ceramic layer
thermal barrier
layer
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EP04290944A
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German (de)
French (fr)
Inventor
Per Bengtsson
Laurent Dudon
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Safran Aircraft Engines SAS
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SNECMA Moteurs SA
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Publication of EP1471162A1 publication Critical patent/EP1471162A1/en
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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
    • C23C4/18—After-treatment
    • 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
    • C23C4/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • 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

Definitions

  • the invention relates to flexo-adaptive thermal barriers, that is to say to thermal barriers with sufficient flexibility to adapt to deformation of the substrate, whether of mechanical or dilatometric origin under the effect of a thermal gradient.
  • the invention relates more particularly to a method economical to obtain such barriers by thermal spraying.
  • substantially tangential directions will be called “horizontal” on the surface of the part on which the thermal barrier is applied.
  • the thermal barriers thus obtained by plasma projection are therefore reserved for fixed parts not subjected to thermal shocks such as combustion chambers.
  • the ceramic layer is of the order of 0.3mm and its lifespan is perfectly in this case.
  • thermal barrier having a cohesion of material high and a grip of the most resistant.
  • a first problem to be solved is to improve the resistance to flaking of the barriers. thermal.
  • a second problem to solve is to reduce the cost of developing a barrier thermal.
  • a thermal barrier in order to be resistant to both thermal stresses high at the surface of the substrate and at high mechanical stresses thereof, and by the same to answer the first problem posed, must be flexible in the directions tangential to the surface it covers. To this end, it is necessary to introduce vertical cracks from the surface of the thermal barrier to the substrate or the undercoat, that is to say crossing the entire ceramic layer.
  • the invention provides a process for obtaining a flexo-adpative thermal barrier, the thermal barrier comprising a ceramic layer (44) with a thickness at least equal to 80 ⁇ m, deposited on a substrate (40) covered with a sublayer (42), the ceramic layer (44) being deposited by thermal spraying using a torch (30) called "plasma arc", the operation of the torch being defined by the power of the torch , the material flow, the distance from the torch to the workpiece (10) to be coated and the speed of movement of the torch relative to the workpiece.
  • a torch (30) called "plasma arc"
  • Such a method is remarkable in that it consists in depositing, directly on the underlay and in a single pass, the ceramic layer while maintaining a projection distance between 20mm and 90mm, the speed of movement of the torch being between 2mm / s and 10mm / s, the material flow being between 2mm / s and 10mm / s and the arc intensity of the torch being between 500A and 800A, so as to obtain after cooling , at least 2 substantially vertical cracks per millimeter and crossing the entire ceramic layer.
  • the power of the torch being adjusted to a high value and the ceramic layer produced in a single pass, the new drops of molten material arrive on material still very hot, which causes an excellent bond by welding between the ceramic grains in the vertical direction.
  • This is favored by the choice of the speed of movement of the torch as low as possible, preferably between 2mm / s and 10mm / s.
  • the temperature at the location of the deposit is high, which makes it possible to obtain a dense microstructure with a number of horizontal micro cracks, reduced delaminations and pores, and better cohesion of the material. Projection in a single pass is an important parameter directly affecting the resistance to flaking of the thermal barrier.
  • the cohesion between the different layers of material deposited on each pass is lower than within the same layer.
  • a horizontal crack can then be initiated between two layers, which is detrimental for the behavior of the thermal barrier.
  • the ceramic layer thus formed under the jet being very hot, its cooling in contact with ambient air, when the jet has moved, causes a significant vertical thermal gradient, this gradient promoting the formation of cracks at the surface of the ceramic layer, these cracks then propagating vertically to the sub-layer, thus passing through the entire ceramic layer.
  • the inventors have observed that these two phenomena appear simultaneously. With too low a power, the cracks are spaced, very irregular and the vertical connections between the grains of material are poor.
  • the inventors By increasing the power of the torch, the cracks are more dense and homogeneous and the vertical connections between the grains are simultaneously improved. With sufficient power, that is to say sufficiently large to obtain a crack density at least equal to the claimed value, the inventors obtain a thermal barrier having a satisfactory flaking resistance up to a thickness of the ceramic layer of 250 ⁇ m, the optimal quality being however between 100 ⁇ m and 150 ⁇ m. Note that the power of the torch appropriate to obtain this result depends on many parameters such as the ceramic used heat dissipation in the room, the powder flow, the width of the jet, the coefficient of loss of the torch, etc. Note also that those skilled in the art will however limit the power of the torch so as not to cause excessive heating which could cause the melting of the substrate or an inadmissible alteration of its granular structure.
  • the dimensions of the cracks, as well as the number of cracks per mm, depend on the thickness of the deposit The thicker the deposit, the larger the cracks and their number per mm low.
  • the thickness of the ceramic layer obtained in a single pass is obviously function of material flow, distance from torch to workpiece and speed of displacement of the torch, i.e. of the jet, relative to the workpiece, as well as of the torch loss coefficient. So the thickness of the ceramic layer increases with the flow of material, but this thickness decreases when the distance or the speed increases. Those skilled in the art will experimentally define these parameters at case by case depending on the material at its disposal.
  • Figure 1 illustrates the deposition of the ceramic layer with a plasma torch.
  • Figure 2 is a sectional micrograph of the thermal barrier thus obtained.
  • Figure 3 is a micrograph of the surface of the thermal barrier.
  • the part to be coated with a thermal barrier is a turbine blade 10 made of superalloy nickel base with directed solidification.
  • the thermal barrier comprises an underlay of McrAIY covered by a ceramic layer of 125 ⁇ m in ZrO 2 zircon with 8% of ytrin Y 2 O 3 .
  • the blade 12 of the blade 10 is covered with a sub-layer of McrAIY deposited according to the usual procedures.
  • the blade 10 is then held by its foot 14 on a rotating assembly 20 capable of rotate the dawn on its axis 16, i.e. on itself in the direction of the length, the blade 12 being presented in front of a plasma torch 30, the jet of which will be referenced 32
  • the plasma torch 32 is here the F4 model marketed by the company whose the company name is Sultzer Metco.
  • the torch is placed 50mm from the blade 10, the blade 10 then being rotated on its axis 16.
  • THE torch 30 is put into operation and the jet 32 first touches the vertex 18a of dawn 10 and gradually moves towards foot 14 to reach the other end 18b of the blade 12 and thus form on the surface of the blade 10 a ceramic layer 44 having the shape of a helix with contiguous turns.
  • Jet 32 is moves on the surface of the blade 12 at a resulting speed of 6mm / s.
  • Powder flow is 70g / mm, and the power of the torch is obtained with an arc intensity of 700A
  • the torch setting is said to be "hot", the temperature of the deposit is 550 ° C. this temperature being measured on the surface of the deposit just after the passage of the jet 32 and 10mm behind the jet
  • FIG. 40, 42 and 44 are respectively referenced the substrate, the sub-layer and the ceramic layer thus obtained.
  • the cracks are referenced 50.
  • the cracks 50 are substantially vertical, that is to say substantially perpendicular to the substrate 40.
  • the two edges of the cracks 50 may be parallel or open towards the surface or towards the under-layer 42.
  • the characteristic primordial of the cracks 50 is that they travel from the surface to the under-layer 42, crossing the entire thickness of the ceramic layer 44, as illustrated in the micrograph.
  • the cracks 50 form a locally irregular but statistically homogeneous and anisotropic network, these cracks 50 providing the thermal barrier with the flexibility required in a tangential plane to the substrate 40.
  • the density of cracks is defined as being the average number of cracks per millimeter cutting any geometric line.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Coating By Spraying Or Casting (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)

Abstract

The production of a flexi-adaptive thermal barrier, incorporating a ceramic layer (44) deposited on a substrate (40) covered with a sub-layer (42), consists of depositing the ceramic layer by thermal spraying with a plasma arc torch. The ceramic layer is deposited directly on the sub-layer in a single pass. The torch is regulated to provide a ceramic layer with a thickness of at least 80 Micro so that after cooling at least two essentially vertical fissures, traversing through the whole thickness of the ceramic layer, are introduced.

Description

Domaine technique de l'inventionTechnical field of the invention

L'invention se rapporte aux barrières thermiques flexo-adaptives, c'est à dire aux barrières thermiques présentant une flexibilité suffisante pour s'adapter aux déformations du substrat, qu'elle soient d'origine mécaniques ou dilatométriques sous l'effet d'un gradient thermique. L'invention se rapporte plus particulièrement à un procédé économique pour obtenir de telles barrières par projection thermique.The invention relates to flexo-adaptive thermal barriers, that is to say to thermal barriers with sufficient flexibility to adapt to deformation of the substrate, whether of mechanical or dilatometric origin under the effect of a thermal gradient. The invention relates more particularly to a method economical to obtain such barriers by thermal spraying.

Etat de la technique et problème poséState of the art and problem posed

Aujourd'hui, les pièces de turbomachine exposées au flux chaud de gaz de combustion sont réalisées en super-alliages résistant aux hautes températures et protégées de la chaleur et de la corrosion par un revêtement appelé barrière thermique.
Une barrière thermique est constituée aujourd'hui habituellement par :

  • une sous-couche alumineuse de NiPtAl ou de McrAlY (M = Fe, Ni, Co et NiCo) formant un obstacle chimique à l'oxydation et à la corrosion ;
  • une couche de céramique ZrO2-Y O thermiquement isolante.
Today, the turbomachine parts exposed to the hot flow of combustion gases are made of superalloys resistant to high temperatures and protected from heat and corrosion by a coating called a thermal barrier.
Today a thermal barrier is usually made up of:
  • an aluminous sublayer of NiPtAl or McrAlY (M = Fe, Ni, Co and NiCo) forming a chemical obstacle to oxidation and corrosion;
  • a layer of thermally insulating ZrO 2 -YO ceramic.

Dans ce qui suit et par commodité de langage, on appellera "verticale" la direction sensiblement perpendiculaire à la surface de la pièce sur laquelle on applique la barrière thermique.In what follows and for convenience of language, we will call "vertical" the direction substantially perpendicular to the surface of the part on which the barrier is applied thermal.

De la même manière, on appellera "horizontale" les directions sensiblement tangentielles à la surface de la pièce sur laquelle on applique la barrière thermique.In the same way, the substantially tangential directions will be called "horizontal" on the surface of the part on which the thermal barrier is applied.

La couche de céramique est traditionnellement déposée en plusieurs passes par projection thermique, par exemple avec une torche à arc plasma. A chaque passe, on dépose une couche élémentaire de céramique dont l'épaisseur est habituellement comprise entre 5µm et 40µm, le nombre de couches élémentaires ainsi appliquées définissant l'épaisseur totale du revêtement. Cette façon de procéder permet :

  • de mieux contrôler l'épaisseur du revêtement ;
  • de réduire l'échauffement de la barrière thermique et d'éviter ainsi les fissurations et l'écaillage du revêtement lors de son refroidissement.
The ceramic layer is traditionally deposited in several passes by thermal spraying, for example with a plasma arc torch. At each pass, an elementary layer of ceramic is deposited, the thickness of which is usually between 5 μm and 40 μm, the number of elementary layers thus applied defining the total thickness of the coating. This way of proceeding allows:
  • better control the thickness of the coating;
  • reduce the heating of the thermal barrier and thus avoid cracking and spalling of the coating when it cools.

Ce procédé présente cependant deux inconvénients :

  • La couche de céramique est peu flexible selon les directions tangentielles à la surface de la pièce. Par conséquent, les barrières thermiques ainsi obtenues résistent mal aux chocs thermiques importants, par exemple au niveau des aubes de turbines, ces barrières thermiques s'écaillant et se détachant assez rapidement.
  • Les liaisons verticales entre les couches élémentaires sont imparfaites car elles sont assurées par les micro soudures se formant lorsque les gouttelettes de céramique en fusion arrivent sur la céramique précédemment déposée et partiellement refroidie. De ce fait, les couches élémentaires de céramique constituant de telles barrières thermiques tendent à se séparer sous l'effet des chocs thermiques, ce qui provoque également l'écaillage de la barrière thermique.
This process has two drawbacks, however:
  • The ceramic layer is not very flexible in the directions tangential to the surface of the part. Consequently, the thermal barriers thus obtained are poorly resistant to significant thermal shocks, for example at the level of the turbine blades, these thermal barriers flaking off and coming off fairly quickly.
  • The vertical connections between the elementary layers are imperfect because they are provided by micro-welds which form when the droplets of molten ceramic arrive on the previously deposited and partially cooled ceramic. Therefore, the elementary ceramic layers constituting such thermal barriers tend to separate under the effect of thermal shock, which also causes flaking of the thermal barrier.

Les barrières thermiques ainsi obtenues par projection plasma sont donc réservées aux pièces fixes ne subissant pas de chocs thermiques telles les chambres de combustion. La couche de céramique est de l'ordre de 0,3mm et sa durée de vie est parfaitement maítrisée dans ce cas.The thermal barriers thus obtained by plasma projection are therefore reserved for fixed parts not subjected to thermal shocks such as combustion chambers. The ceramic layer is of the order of 0.3mm and its lifespan is perfectly in this case.

Afin de mieux protéger les chambres de combustion des turboréacteurs contre le chaleur, des barrières thermiques épaisses, c'est à dire dont l'épaisseur est supérieure à 1 mm, projetées par plasma furent développées Pour cette application, il état nécessaire d'introduire des fissures verticales dans l'épaisseur du dépôt céramique, afin de rendre le dépôt flexible dans les directions horizontales, c'est à dire tangentielles à la surface de la pièce. Sans ce réseau de fissures unidirectionnelles, les contraintes thermiques en bordure du dépôt seraient trop élevées, et il en résulterait un écaillage de la barrière thermique pendant son exploitation.In order to better protect the combustion chambers of turbojets against heat, thick thermal barriers, that is to say whose thickness is greater than 1 mm, projected by plasma were developed For this application, it is necessary to introduce vertical cracks in the thickness of the ceramic deposit, in order to make the flexible deposit in horizontal directions, i.e. tangential to the surface of the room. Without this network of unidirectional cracks, the thermal stresses in edge of the repository would be too high, and the barrier would flake during operation.

On connaít à ce titre le brevet US 5,073,433 selon lequel la couche de céramique est déposée par projection thermique en plusieurs passes successives, chaque passe déposant une couche de matière de l'ordre de 5µm, chaque passe étant suivie d'un refroidissement afin de former des fissures verticales.
Un tel procédé présente cependant deux inconvénients :

  • Le revêtement en plusieurs passes séparées par une étape de refroidissement entraíne un coût supplémentaire,
  • Ce procédé présente l'inconvénient habituel des revêtements multicouches précédemment décrits, à savoir des liaisons imparfaites par micro soudures entre les couches élémentaires favorisant la séparation de ces couches élémentaires et l'écaillage de la barrière thermique. Cet inconvénient est aggravé par le refroidissement du dépôt effectué entre chaque couche élémentaire.
We know in this regard US Patent 5,073,433 according to which the ceramic layer is deposited by thermal spraying in several successive passes, each pass depositing a layer of material of the order of 5 μm, each pass being followed by cooling in order to form vertical cracks.
However, such a method has two drawbacks:
  • Coating in several passes separated by a cooling step involves an additional cost,
  • This method has the usual drawback of the previously described multilayer coatings, namely imperfect connections by micro-welds between the elementary layers promoting the separation of these elementary layers and the flaking of the thermal barrier. This drawback is aggravated by the cooling of the deposit made between each elementary layer.

On connaít également par le brevet US 6,306,517 un procédé d'application d'une barrière thermique en couches minces par projection plasma, la liaison entre les couches étant améliorée par la germination colonnaire des grains qui peuvent ainsi devenir communs à plusieurs couches. Avec un tel procédé malheureusement, la germination se fait également latéralement ce qui réduit la flexibilité de la barrière thermique.We also know from US Patent 6,306,517 a method of applying a barrier thermal in thin layers by plasma spraying, the connection between the layers being improved by the columnar germination of the grains which can thus become common to several layers. Unfortunately, with such a process, germination takes place also laterally which reduces the flexibility of the thermal barrier.

On connaít aujourd'hui un procédé de dépôt dit "en phase vapeur" et plus particulièrement le EBPVD (Electron Beam Physical Vapour Deposition). La couche céramique obtenue se présente sous al forme de fines colonnes verticales adjacentes liées par leur base à la sous-couche. A titre indicatif, ce s colonnes ont un diamètre de l'ordre de 5µm. Untel procédé donne des barrières thermiques d'excellente qualité présentant un bonne flexibilité horizontale et de bonnes liaisons verticales et résistant par conséquent bien aux chocs thermiques.
Un tel procédé présente cependant deux inconvénients :

  • Il est lent et coûteux ,
  • La barrière thermique conserve malgré tout une durée de vie limitée, car les gaz de combustion chauds et corrosifs atteignent la sous-couche par les espaces réduits mais très nombreux entre les colonnes, la corrosion progressive de la sous-couche provoquant se destruction et l'écaillage de la barrière thermique.
We know today a so-called "vapor phase" deposition process and more particularly the EBPVD (Electron Beam Physical Vapor Deposition). The ceramic layer obtained is in the form of thin adjacent vertical columns linked by their base to the sub-layer. As an indication, these columns have a diameter of the order of 5 μm. Such a process gives thermal barriers of excellent quality with good horizontal flexibility and good vertical bonds and therefore resistant to thermal shock.
However, such a method has two drawbacks:
  • It is slow and expensive,
  • The thermal barrier nevertheless retains a limited lifespan, because the hot and corrosive combustion gases reach the underlay by the reduced but very numerous spaces between the columns, the progressive corrosion of the underlay causing destruction and the flaking of the thermal barrier.

A noter que d'une manière plus générale, la sensibilité à l'écaillage d'une barrière thermique augmente dans les parties en saillie de la pièce présentant un faible rayon de courbure, donc plus particulièrement avec les petites pièces telles les aubes de turbine.Note that more generally, the sensitivity to flaking of a barrier thermal increases in the projecting parts of the part having a small radius of curvature, therefore more particularly with small parts such as turbine blades.

Par ailleurs afin d'avoir une barrière thermique la moins sensible possible à l'écaillage, il faut chercher à obtenir une barrière thermique présentant une cohésion de matière élevée et un accrochage des plus résistants.Furthermore, in order to have the least sensitive thermal barrier possible to chipping, it must seek to obtain a thermal barrier having a cohesion of material high and a grip of the most resistant.

Un premier problème à résoudre est d'améliorer la résistance à l'écaillage des barrières thermiques. A first problem to be solved is to improve the resistance to flaking of the barriers. thermal.

Un second problème à résoudre est de réduire le coût d'élaboration d'un barrière thermique.A second problem to solve is to reduce the cost of developing a barrier thermal.

Exposé de l'inventionStatement of the invention

Une barrière thermique, afin d'être résistante à la fois aux sollicitations thermiques élevées en surface du substrat et aux sollicitations mécaniques importantes de celui-ci, et par la même de répondre au premier problème posé, doit être souple dans les directions tangentielles à la surface qu'elle recouvre. A cet effet, il est nécessaire d'introduire des fissures verticales allant de la surface de la barrière thermique jusqu'au substrat ou à la sous-couche, c'est à dire traversant toute la couche de céramique.A thermal barrier, in order to be resistant to both thermal stresses high at the surface of the substrate and at high mechanical stresses thereof, and by the same to answer the first problem posed, must be flexible in the directions tangential to the surface it covers. To this end, it is necessary to introduce vertical cracks from the surface of the thermal barrier to the substrate or the undercoat, that is to say crossing the entire ceramic layer.

L'invention propose un procédé d'obtention d'une barrière thermique flexo-adpative, la barrière thermique comportant une couche de céramique (44) d'une épaisseur au moins égale à 80µm, déposée sur un substrat (40) recouvert d'une sous-couche (42), la couche de céramique (44) étant déposée par projection thermique à l'aide d'une torche (30) dite "à arc plasma", le fonctionnement de la torche étant défini par la puissance de la torche, le débit de matière, la distance de la torche à la pièce (10) à revêtir et la vitesse de déplacement de la torche par rapport à la pièce.
Un tel procédé est remarquable en ce que qu'il consiste à déposer, directement sur la sous-couche et en une seule et unique passe, la couche de céramique en maintenant une distance de projection comprise entre 20mm et 90mm, la vitesse de déplacement de la torche étant comprise entre 2mm/s et 10mm/s, le débit de matière étant compris entre 2mm/s et 10mm/s et l'intensité d'arc de la torche étant comprise entre 500A et 800A, de façon à obtenir après refroidissement, au moins 2 fissures sensiblement verticales par millimètre et traversant toute la couche de céramique.The invention provides a process for obtaining a flexo-adpative thermal barrier, the thermal barrier comprising a ceramic layer (44) with a thickness at least equal to 80 μm, deposited on a substrate (40) covered with a sublayer (42), the ceramic layer (44) being deposited by thermal spraying using a torch (30) called "plasma arc", the operation of the torch being defined by the power of the torch , the material flow, the distance from the torch to the workpiece (10) to be coated and the speed of movement of the torch relative to the workpiece.
Such a method is remarkable in that it consists in depositing, directly on the underlay and in a single pass, the ceramic layer while maintaining a projection distance between 20mm and 90mm, the speed of movement of the torch being between 2mm / s and 10mm / s, the material flow being between 2mm / s and 10mm / s and the arc intensity of the torch being between 500A and 800A, so as to obtain after cooling , at least 2 substantially vertical cracks per millimeter and crossing the entire ceramic layer.

On comprend que la puissance de la torche étant réglée à une valeur élevée et la couche de céramique produite en seule passe, les nouvelles gouttes de matière en fusion arrivent sur de la matière encore très chaude, ce qui provoque une excellente liaison par soudure entre les grains de céramique dans la direction verticale. Ceci est favorisé par le choix d'une vitesse de déplacement de la torche la plus réduite possible, préférentiellement comprise entre 2mm/s et 10mm/s. Ainsi, la température à l'endroit du dépôt est élevée ce qui permet d'obtenir une microstructure dense avec un nombre micro fissures horizontales, délaminations et pores réduits, et une meilleure cohésion de la matière. La projection en une seule passe est un paramètre important intervenant directement sur la résistance à l'écaillage de la barrière thermique. En effet, si l'on projette la matière en plusieurs passes, la cohésion entre les différentes couches de matière déposée à chaque passe est moins élevée qu'au sein d'une même couche. Une fissure horizontale peut alors s'initier entre deux couches, ce qui est préjudiciable pour la tenue de la barrière thermique.
Par ailleurs, la couche de céramique ainsi formée sous le jet étant très chaude, son refroidissement au contact de l'air ambiant, lorsque le jet s'est déplacé, provoque un gradient thermique vertical important, ce gradient favorisant la formation de fissures à la surface de la couche de céramique, ces fissures se propageant ensuite verticalement jusqu'à la sous-couche, traversant ainsi toute la couche de céramique.
Les inventeurs ont constaté que ces deux phénomènes apparaissent simultanément. Avec une puissance trop faible, les fissures sont espacées, très irrégulières et les liaisons verticales entre les grains de matière sont médiocres. En augmentant la puissance de la torche, les fissures sont plus denses et homogènes et les liaisons verticales entre les grains sont simultanément améliorées. Avec une puissance suffisante, c'est à dire suffisamment importante pour obtenir une densité de fissures au moins égale à la valeur revendiquée, les inventeurs obtiennent une barrière thermique présentant une résistance à l'écaillage satisfaisante jusqu'à une épaisseur de la couche de céramique de 250µm, la qualité optimale se situant cependant entre 100µm et 150µm. A noter que la puissance de la torche appropriée pour obtenir ce résultat dépend de nombreux paramètres tels que la céramique utilisée la dissipation thermique dans la pièce, le débit de poudre, la largeur du jet, le coefficient de déperdition de la torche, etc
A noter également que l'homme du métier limitera toutefois la puissance de la torche pour ne pas provoquer un échauffement excessif risquant d'entraíner la fusion du substrat ou une altération non admissible de sa structure granulaire.It is understood that the power of the torch being adjusted to a high value and the ceramic layer produced in a single pass, the new drops of molten material arrive on material still very hot, which causes an excellent bond by welding between the ceramic grains in the vertical direction. This is favored by the choice of the speed of movement of the torch as low as possible, preferably between 2mm / s and 10mm / s. Thus, the temperature at the location of the deposit is high, which makes it possible to obtain a dense microstructure with a number of horizontal micro cracks, reduced delaminations and pores, and better cohesion of the material. Projection in a single pass is an important parameter directly affecting the resistance to flaking of the thermal barrier. Indeed, if the material is projected in several passes, the cohesion between the different layers of material deposited on each pass is lower than within the same layer. A horizontal crack can then be initiated between two layers, which is detrimental for the behavior of the thermal barrier.
Furthermore, the ceramic layer thus formed under the jet being very hot, its cooling in contact with ambient air, when the jet has moved, causes a significant vertical thermal gradient, this gradient promoting the formation of cracks at the surface of the ceramic layer, these cracks then propagating vertically to the sub-layer, thus passing through the entire ceramic layer.
The inventors have observed that these two phenomena appear simultaneously. With too low a power, the cracks are spaced, very irregular and the vertical connections between the grains of material are poor. By increasing the power of the torch, the cracks are more dense and homogeneous and the vertical connections between the grains are simultaneously improved. With sufficient power, that is to say sufficiently large to obtain a crack density at least equal to the claimed value, the inventors obtain a thermal barrier having a satisfactory flaking resistance up to a thickness of the ceramic layer of 250µm, the optimal quality being however between 100µm and 150µm. Note that the power of the torch appropriate to obtain this result depends on many parameters such as the ceramic used heat dissipation in the room, the powder flow, the width of the jet, the coefficient of loss of the torch, etc.
Note also that those skilled in the art will however limit the power of the torch so as not to cause excessive heating which could cause the melting of the substrate or an inadmissible alteration of its granular structure.

Les dimensions des fissures, ainsi que le nombre de fissures par mm, dépendent de l'épaisseur du dépôt Plus le dépôt est épais, plus les fissures sont larges et leur nombre par mm faible.The dimensions of the cracks, as well as the number of cracks per mm, depend on the thickness of the deposit The thicker the deposit, the larger the cracks and their number per mm low.

L'épaisseur de la couche de céramique obtenue en une seule passe est évidemment fonction du débit de matière, de la distance de la torche à la pièce et de la vitesse de déplacement de la torche, c'est à dire du jet, par rapport à la pièce, ainsi que du coefficient de déperdition de la torche. Ainsi l'épaisseur de la couche de céramique augmente avec le débit de matière, mais cette épaisseur diminue lorsque la distance ou la vitesse augmentent. L'homme du métier définira expérimentalement ces paramètres au cas par cas en fonction du matériel dont il dispose. The thickness of the ceramic layer obtained in a single pass is obviously function of material flow, distance from torch to workpiece and speed of displacement of the torch, i.e. of the jet, relative to the workpiece, as well as of the torch loss coefficient. So the thickness of the ceramic layer increases with the flow of material, but this thickness decreases when the distance or the speed increases. Those skilled in the art will experimentally define these parameters at case by case depending on the material at its disposal.

L'invention propose également d'appliquer le présent procédé à une aube de turboréacteur comportant une pale et un pied, la couche de céramique étant appliquée sur la pale.
Un tel procédé est remarquable en ce qu'il consiste :

  • a. à maintenir le pied (14) de l'aube (10) par un outillage (20) pivotant à une vitesse de rotation V selon son axe géométrique (16),
  • b à exposer la pale (12) au jet (32) d'une torche (30) susceptible d'un déplacement relatif D1 parallèle à l'axe géométrique (16) et d'un déplacement relatif D2 perpendiculaire à l'axe géométrique (16) ;
  • c. à effectuer la projection de céramique en un seul déplacement du jet (32) depuis l'une des extrémités (18a, 18b) jusqu'à son autre extrémité(18b, 18a) de la pale, l'aube (10) étant mise en rotation selon l'axe géométrique (16), la torche (30) étant déplacée selon D2 pour rester à une distance constante de la surface de la pale (12), la torche (30) étant déplacée suivant D1 pour former à la surface de la pale (12) une couche de céramique (44) en spirale de pas égal à la largeur du jet (32).
    • The invention also proposes to apply the present method to a turbojet blade comprising a blade and a foot, the ceramic layer being applied to the blade.
    Such a process is remarkable in that it consists:
  • at. maintaining the foot (14) of the blade (10) by a tool (20) pivoting at a speed of rotation V along its geometric axis (16),
  • b exposing the blade (12) to the jet (32) of a torch (30) capable of a relative displacement D1 parallel to the geometric axis (16) and of a relative displacement D2 perpendicular to the geometric axis ( 16);
  • vs. performing the ceramic projection in a single movement of the jet (32) from one of the ends (18a, 18b) to its other end (18b, 18a) of the blade, the blade (10) being brought into rotation along the geometric axis (16), the torch (30) being moved along D2 to remain at a constant distance from the surface of the blade (12), the torch (30) being moved along D1 to form on the surface of the blade (12) a ceramic layer (44) in a spiral with a pitch equal to the width of the jet (32).

    • Description des figuresDescription of the figures

    L'invention sera mieux comprise et les avantages qu'elle procure apparaítront plus clairement au vu d'un exemple détaillé de mise en oeuvre du procédé et des figures annexées.The invention will be better understood and the advantages it provides will appear more clearly in view of a detailed example of implementation of the method and of the figures attached.

    La figure 1 illustre le dépôt de la couche de céramique avec une torche plasma.Figure 1 illustrates the deposition of the ceramic layer with a plasma torch.

    La figure 2 est une micrographie en coupe de la barrière thermique ainsi obtenue.Figure 2 is a sectional micrograph of the thermal barrier thus obtained.

    La figure 3 est une micrographie de la surface de la barrière thermique.Figure 3 is a micrograph of the surface of the thermal barrier.

    Description détailléedetailed description

    On se reportera en premier lieu à la figure 1.We will first refer to Figure 1.

    La pièce à revêtir d'une barrière thermique est une aube 10 de turbine en superalliage base nickel à solidification dirigée. La barrière thermique comporte une sous-couche de McrAIY recouverte par une couche de céramique de 125µm en zircon ZrO2 avec 8% d'ytrine Y2O3. The part to be coated with a thermal barrier is a turbine blade 10 made of superalloy nickel base with directed solidification. The thermal barrier comprises an underlay of McrAIY covered by a ceramic layer of 125 μm in ZrO 2 zircon with 8% of ytrin Y 2 O 3 .

    La pale 12 de l'aube 10 est recouverte d'une sous-couche de McrAIY déposée selon les procédés habituels.The blade 12 of the blade 10 is covered with a sub-layer of McrAIY deposited according to the usual procedures.

    L'aube 10 est ensuite tenue par son pied 14 sur un montage 20 tournant susceptible de faire tourner l'aube sur son axe 16, c'est à dire sur elle-même dans le sens de la longueur, la pale 12 étant présentée devant une torche plasma 30 dont le jet sera référencé 32 La torche plasma 32 est ici le modèle F4 commercialisé par la société dont la raison sociale est Sultzer Metco.The blade 10 is then held by its foot 14 on a rotating assembly 20 capable of rotate the dawn on its axis 16, i.e. on itself in the direction of the length, the blade 12 being presented in front of a plasma torch 30, the jet of which will be referenced 32 The plasma torch 32 is here the F4 model marketed by the company whose the company name is Sultzer Metco.

    La torche est placée à 50mm de l'aube 10, l'aube 10 étant ensuite mise en rotation sur son axe 16. LA torche 30 est mise en fonctionnement et le jet 32 touche d'abord le sommet 18a de l'aube 10 et se déplace progressivement vers le pied 14 pour atteindre l'autre extrémité 18b de la pale 12 et pour former ainsi à la surface de l'aube 10 une couche de céramique 44 ayant la forme d'une hélice à spires jointives. Le jet 32 se déplace à la surface de la pale 12 à une vitesse résultante de 6mm/s. Le débit de poudre est de 70g/mm, et la puissance de la torche est obtenue avec une intensité d'arc de 700A Le réglage de la torche est dit "chaud", la température du dépôt est de 550°C, cette température étant mesurée à la surface du dépôt juste après le passage du jet 32 et à 10mm en arrière du jetThe torch is placed 50mm from the blade 10, the blade 10 then being rotated on its axis 16. THE torch 30 is put into operation and the jet 32 first touches the vertex 18a of dawn 10 and gradually moves towards foot 14 to reach the other end 18b of the blade 12 and thus form on the surface of the blade 10 a ceramic layer 44 having the shape of a helix with contiguous turns. Jet 32 is moves on the surface of the blade 12 at a resulting speed of 6mm / s. Powder flow is 70g / mm, and the power of the torch is obtained with an arc intensity of 700A The torch setting is said to be "hot", the temperature of the deposit is 550 ° C. this temperature being measured on the surface of the deposit just after the passage of the jet 32 and 10mm behind the jet

    On se reportera maintenant à la figure 2.
    Sont référencés 40, 42 et 44 respectivement le substrat, la sous-couche et la couche de céramique ainsi obtenue. Les fissures sont référencées 50. Sur cette micrographie, on compte 4,8 fissures par millimètre dont la distance moyenne est de 200µm. Comme le montre la micrographie, les fissures 50 sont sensiblement verticales, c'est à dire sensiblement perpendiculaires au substrat 40. Les deux bords des fissures 50 peuvent être parallèles ou s'ouvrir vers la surface ou vers la sous-couche 42. La caractéristique primordiale des fissures 50 est qu'elles cheminent de la surface vers la sous-couche 42, en traversant toute l'épaisseur de la couche de céramique 44, comme illustré sur la micrographie.    We will now refer to Figure 2.
    40, 42 and 44 are respectively referenced the substrate, the sub-layer and the ceramic layer thus obtained. The cracks are referenced 50. On this micrograph, there are 4.8 cracks per millimeter, the average distance of which is 200 μm. As the micrograph shows, the cracks 50 are substantially vertical, that is to say substantially perpendicular to the substrate 40. The two edges of the cracks 50 may be parallel or open towards the surface or towards the under-layer 42. The characteristic primordial of the cracks 50 is that they travel from the surface to the under-layer 42, crossing the entire thickness of the ceramic layer 44, as illustrated in the micrograph.

    On se reportera maintenant à la figure 3.
    On voit sur cette micrographie que les fissures 50 forment un réseau localement irrégulier mais statistiquement homogène et anisotrope, ces fissures 50 apportant à la barrière thermique la flexibilité requise suivant un plan tangentiel au substrat 40. Le densité de fissures est définie comme étant le nombre moyen de fissures par millimètre coupant un droite géométrique quelconque.    We will now refer to Figure 3.
    We see on this micrograph that the cracks 50 form a locally irregular but statistically homogeneous and anisotropic network, these cracks 50 providing the thermal barrier with the flexibility required in a tangential plane to the substrate 40. The density of cracks is defined as being the average number of cracks per millimeter cutting any geometric line.

    Claims (2)

    Procédé d'obtention d'une barrière thermique flexo-adaptive, la barrière thermique comportant une couche de céramique (44) d'une épaisseur au moins égale à 80µm, déposée sur un substrat (40) recouvert d'une sous-couche (42), la couche de céramique (44) étant déposée par projection thermique à l'aide d'une torche (30) dite "à arc plasma", le fonctionnement de la torche étant défini par la puissance de la torche, le débit de matière, la distance de la torche à la pièce (10) à revêtir et la vitesse de déplacement de la torche par rapport à la pièce
    caractérisé en ce qu'il consiste à déposer, directement sur la sous-couche et en une seule et unique passe, la couche de céramique en maintenant une distance de projection comprise entre 20mm et 90mm, la vitesse de déplacement de la torche étant comprise entre 2mm/s et 10mm/s, le débit de matière étant compris entre 2mm/s et 10mm/s et l'intensité d'arc de la torche étant comprise entre 500A et 800A, de façon à obtenir après refroidissement, au moins 2 fissures sensiblement verticales par millimètre et traversant toute la couche de céramique.    Method for obtaining a flexo-adaptive thermal barrier, the thermal barrier comprising a ceramic layer (44) with a thickness at least equal to 80 μm, deposited on a substrate (40) covered with an undercoat (42 ), the ceramic layer (44) being deposited by thermal spraying using a torch (30) called "plasma arc", the operation of the torch being defined by the power of the torch, the material flow , the distance from the torch to the workpiece (10) to be coated and the speed of movement of the torch relative to the workpiece
    characterized in that it consists of depositing, directly on the sub-layer and in a single pass, the ceramic layer while maintaining a projection distance between 20mm and 90mm, the speed of movement of the torch being between 2mm / s and 10mm / s, the material flow being between 2mm / s and 10mm / s and the arc intensity of the torch being between 500A and 800A, so as to obtain, after cooling, at least 2 cracks substantially vertical per millimeter and passing through the entire ceramic layer.         Procédé selon la revendication 1, la pièce (10) étant une aube d'axe géométrique (16) comportant une pale (12) et un pied (14), la couche de céramique (44) étant appliquée sur la pale (12),
    caractérisé en ce qu'il consiste : a. à maintenir le pied (14) de l'aube (10) par un outillage (20) pivotant à une vitesse de rotation V selon son axe géométrique (16), b. à exposer la pale (12) au jet (32) d'une torche (30) susceptible d'un déplacement relatif D1 parallèle à l'axe géométrique (16) et d'un déplacement relatif D2 perpendiculaire à l'axe géométrique (16) ; c. à effectuer la projection de céramique en un seul déplacement du jet (32) depuis l'une des extrémités (18a, 18b) jusqu'à son autre extrémité(18b, 18a) de la pale, l'aube (10) étant mise en rotation selon l'axe géométrique (16), la torche (30) étant déplacée selon D2 pour rester à une distance constante de la surface de la pale (12), la torche (30) étant déplacée suivant D1 pour former à la surface de la pale (12) une couche de céramique (44) en spirale de pas égal à la largeur du jet (32).     Method according to claim 1, the part (10) being a vane with a geometric axis (16) comprising a blade (12) and a foot (14), the ceramic layer (44) being applied to the blade (12),
    characterized in that it consists: at. maintaining the foot (14) of the blade (10) by a tool (20) pivoting at a speed of rotation V along its geometric axis (16), b. exposing the blade (12) to the jet (32) of a torch (30) capable of a relative displacement D1 parallel to the geometric axis (16) and of a relative displacement D2 perpendicular to the geometric axis (16 ); vs. performing the ceramic projection in a single movement of the jet (32) from one of the ends (18a, 18b) to its other end (18b, 18a) of the blade, the blade (10) being brought into rotation along the geometric axis (16), the torch (30) being moved along D2 to remain at a constant distance from the surface of the blade (12), the torch (30) being moved along D1 to form on the surface of the blade (12) a ceramic layer (44) in a spiral with a pitch equal to the width of the jet (32).
    EP04290944A 2003-04-25 2004-04-09 Process for obtaining a flexo-adaptive thermal barrier coating Withdrawn EP1471162A1 (en)

    Applications Claiming Priority (2)

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    FR0305086 2003-04-25

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    WO2012004525A1 (en) 2010-07-06 2012-01-12 Snecma Thermal barrier for turbine blades, having a columnar structure with spaced-apart columns

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    EP1862568A1 (en) 2006-05-30 2007-12-05 Siemens Aktiengesellschaft Thermal barrier coating with tungsten-bronze structure
    FR3013360B1 (en) 2013-11-19 2015-12-04 Snecma INTEGRATED SINTERING PROCESS FOR MICROFILERATION AND EROSION PROTECTION OF THERMAL BARRIERS

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    FR2854166B1 (en) 2007-02-09

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