FR2522543A1 - PROCESS FOR APPLYING A COMPOSITE MATERIAL COATING ON PARTS - Google Patents

Abstract

A THERMAL INSULATION COATING 2 IS MADE OF A COMPOSITE MATERIAL IN THE FORM OF LOW THERMAL CONDUCTIVITY OXIDE PARTICLES 3 BONDED IN BINDER, COMPACT AND FIXED TO THE SURFACE OF A PART 1 BY HOT ISOSTATIC COMPRESSION. THERE ARE SEVERAL TYPES OF THIS COATING: ONE OF THEM IS IN THE FORM OF PARTICLES OF AN OXIDE SUCH AS ZIRCONIA, WIRED IN A METAL BOND SUCH AS AN ALLOY OF CHROME, ALUMINUM AND YTTRIUM CONTAINING COBALT AND OR NICKEL. IN ANOTHER TYPE, THE BINDER IS A CERAMIC MATERIAL, SUCH AS ZIRCONIUM SILICATE, WHICH IS DUCTILE AT HIGH TEMPERATURES. THEN A METAL LAYER IS NEEDED, FOR EXAMPLE AN ALLOY OF THE MCRALY TYPE, BETWEEN THE COATING AND THE SURFACE OF THE PART.

Description

The present invention relates to a coating of

  composite material and a method for applying this coating

on an article.

  Composite materials, including ceramic materials or glasses, are used as thermal insulation coatings on parts such as blades and

  discs of gas turbine rotors to reduce the speed

  the amount of ambient heat entering it

  these. As they are traditionally applied, it

  that is to say by means of a flame sprayer, these re-

  clothes are porous and the tiny air pockets em-

  they contain considerably improve their thermal insulation properties On the other hand, they decrease their density, so that they resist erosion less well and adhere relatively poorly to the metallic support.

  Similar problems arise with regard to

  identifies the adhesion of other composite coatings, such as

  that the abrasive coatings Sou susceptible to abrasion ap-

  plied on rotor blades and gas turbine housings and used to reduce the effects of contact with

  friction between the blade heads and the housings.

  The object of the invention is therefore to provide a process

  dice of application of a coating of composite material on an article by which this coating adheres securely to the support while retaining the properties required of it. To this end, the method according to the invention consists in mixing a ceramic material in the form of particles with a binder and in compacting the mixture on a surface of 1 '

  article by hot isostatic pressure.

  The ceramic material may have a lower thermal conductivity than that of the material from which I 'is made.

  article and binder can be made of metal or glass.

  The resulting mixture is applied to the article as a coating and the article thus coated is then subjected

  at hot isostatic pressure to compact the re-

  garment and fix it on the item.

  The ceramic particles are preferably oxide particles, but other forms of ceramic can be used, for example a nitride, or a mixed oxide, for example magnesium zirconate or a silicate of

  magnesium, according to the required properties of the coating.

  It is preferable that the ceramic particles

  are spherical and that, in particular in the case of a coating

  thermal insulation, these spherical particles

are hollow.

  In an embodiment of the coating according to I '

  invention, intended in particular to serve as thermal insulation

  that the binder is metallic, preferably an alloy

  resistant to high temperatures and corrosion,

  oxide particles ensuring a decrease in conductivity

  thermal life of the composite coating, while the ma-

  metallic trice, compacted on the surface of the article by hot isostatic compression, forms a diffusion bond with the metallic support, bond which

  provides good adhesion The metal matrix acts

  a flexible layer between the oxide, a material with a low coefficient of thermal expansion, and the support material, and its composition is chosen, inter alia, so that it contributes to mitigating the effects of the difference

  between the respective thermal expansions of the two ma-

materials.

  As examples of oxides with low thermal conductivity,

  mique, we can cite zirconia, alumina and silica,

  and, for these oxides, we will preferably choose zirco-

  ne, because it has the lowest thermal conductivity. It will be understood that zirconia requires the presence

  stabilizers, so that throughout the pre-

  Please remember, any reference to zirconia should be understood

  taken as referring to stabilized zirconia.

  The metal binder is preferably an alloy, the composition of which also depends on the environment in which it will have to work. In the environment specific to a gas turbine, properties such as resistance to oxidation or to corrosion. in general are almost always required, so that the composi-

  preferred coating nations would be a nickel-

  aluminum for resistance to oxidation or one of the al-

  chrome-alumium-yttrium bonding, with cobalt or nickel,

  for corrosion resistance in general.

  In another embodiment of the coating,

  lon the invention, the binder used is a non-metal binder-

  ductile liquefaction, for example a vitreous ceramic, such as zirconium silicate This decreases even more

  the thermal conductivity of the outer layer in eli-

  undermining the presence of a metal, a material which is very good conductor, but may require the addition of an intermediate layer to produce good adhesion with the

metal support.

  The thickness of the coating obviously depends on the use for which it is intended. When it must serve as a heat shield, this thickness can be of the order

  from 0.250 to 0.508 mm On the other hand, the coatings susceptible to

  erosion or abrasive coatings, for example on rotor blade heads, are usually a little thicker, and their thickness can be between

0.508 and 1.016 mm approximately.

  In a form of execution still different from 1 '

  invention, a light shield can be applied to the head

  te of a rotor blade, shielding which is sufficiently

  but to be brought by machining to a specific shape.

  The term "coating" should be interpreted as

encompassing such shielding.

  In any case, the invention will be well understood from 1 '

  using the following description, with reference to the drawing

  schematic annexed, representing, by way of nonlimiting examples, several embodiments of this coating: FIG. 1 represents a portion of a gas turbine blade provided with a coating according to the invention; Fig 2 shows part of a turbine blade

  gas provided with another embodiment of the coating

  lon the invention; Fig 3 is an enlarged reproduction of a micro-

  spelling of a coating according to the invention comprising mainly

  mainly spherical ceramic particles and fixed

to a metal support.

  As shown in the figures, a turbine blade 1

  gas fired with a composite coating 2, which acts as a heat shield and is made up of particles

  of zirconia 2 embedded in a binder made of nickel-aluminum alloy

  minimum. This composite coating is applied in the form

  of a suspension, in one or more layers, by spraying

  rization, soaking or any other appropriate method A-

  after drying, another nickel coating is applied to the surface by electroplating This additional coating provides an outer layer which is waterproof

  to gases and transmits pressure during compression

  Isostatic hot heat which takes place later and its composition or the method followed for its application do not form an essential part of the invention It can be applied, for example, by plasma spraying

  or by vapor deposition, or it may have the form

  me of a tightly fitting metal bag, which is welded and in which we made the vacuum In fact, we can substitute a coating of glass, provided that

  there is no possibility of interaction with the coating

composite.

  Once this additional coating has been applied

  folded, the part is placed in a container and it is subjected to hot isostatic pressure to bind the

metal support coating.

  Hot isostatic compression is an operation

  tion known per se and it will not be described in detail in the present specification. It suffices to know that during

  this operation the turbine blade is subjected to a pressure

  sion between 151,700 and 379,250 Pa approximately, at a temperature above 8000 C. When possible, the hot isostatic compression operation can be combined with a heat treatment which may be necessary.

  to reduce the overall manufacturing cost of the

  be provided with the coating, since the treatments

  Thermal events of this type generally take place at temperatures

  erasures between 8000 C and 13000 C.

  Once the hot isostatic compression ends

  born, the additional metallic or other coating is removed by any suitable method, for example

  by chemical attack, to expose the coating

  thermal insulation now compacted.

  In this embodiment of the invention, the re-

  garment adheres directly to the metal support thanks to a diffusion bonding provided by the metal binder, which is chosen for its resistance to oxidation or corrosion at high temperatures as well as for its thermal expansion properties In place of the binder nickel-aluminum alloy which has just been described, we

  can use any other traditional binder

  resistant to corrosion, for example one of the aluminum binders

  bond known under the general name of M Cr Al Y, in which Cr, Al and Y are the symbols of chromium, aluminum and yttrium and M can be cobalt,

nickel or a mixture of the two.

  The incorporation of a metal binder in the thermal insulation coating reduces the effectiveness of the latter

  because of the thermal conductivity of the metal.

  However, the con-

  thermal ductivity of the coating using parts

  spherical and hollow ceramic cules using

  spherical particles, we have a lot of control

  tighter shot on the density of the coating There is a maximum volume of spheres that can be contained in

  a given fixed volume and, using different

  spheres of spheres, the density of the coating can be graduated

  so as to place the maximum volume of metal near the surface of the article and the maximum volume of ceramic near the external face of the coating The maximum volume of ceramic in the mixture is of the order of 70%

  authors of the invention have found that a mixture of spheres

  Zirconia hollow resins correctly to a cobaltchrome-aluminum-yttrium alloy binder and to a support

nickel-based alloy.

  The thickness of the thermal insulation coating

  present must obviously be chosen so as to give

  an optimal result for the conditions in which this re-

  garment is subject, but you can usually use u-

  thickness between 0.254 and 0.508 mm Being given

  born as the greatest possible decrease in conductivity

  thermal speed, which requires a thick coating, and the greatest possible lightness, which requires a coating

  thin, are two conflicting requirements, it will be necessary

  may proceed by successive approximations to

  complete thickness and optimal properties.

  If we can reach a maximum volume of ceramic spheres such that they all touch each other, it

  may be possible to extract some or ex-

  milk all of the coating to leave spaces for

air in this one.

  In the alternative embodiment shown in FIG. 2, an entirely non-metallic coating 10 is

  applied to dawn and grip is improved by the u

  use of an intermediate coating 11 between the

  che thermal insulation and metal support.

  Since the hot isostatic compression gives a dense coating, there is no longer in the latter

  no flexibility that allows it to absorb the stresses

  your created by the temperature differences from one place to another In this coating variant, it is therefore planned to drown the oxide material in a binder

  ductile to absorb these thermal stresses.

  The thermal insulation coating is, in this case, a composite material formed by particles of zirconia 12, which may be hollow spheres, and a binder

  with zirconium silicate, which is very ductile at times

high peratures.

  To improve grip and reduce the diffi-

  due to differences in thermal expansion, a

  intermediate layer 11, preferably a metallic layer

  that formed from one of the above-mentioned alloy compositions M Cr Al Y

  tees, -ekt applied to the support This metallic layer

  that intermediate forms a flexible zone between the coating

  ment and the support and it provides corrosion resistance.

  Where the coating must be susceptible to erosion

  or be abrasive, the shape of the particles is pre-

  irregular and not spherical ference and thickness

  can reach 1.016 mm The ceramic material for a re-

  abrasive clothing is preferably alumina or si-

  magnesium licate having the formula Mg O 25 i O 2.

  Once the oxide material is trapped in the binder, whether or not the bond between them remains

  intact may not matter.

  We can see in Figure 3 that the metal part of the composite coating (light areas) has absorbed everywhere between the ceramic particles (dark areas)

  and forms a good bond with the support (large par-

clear tie).

  Although the invention has been described in relation to-

  With gas turbine blades, it is clear that it can

  also apply to other rooms in which a re-

  thermal or other clothing is currently being used or may be used in the future As an example of

  another use, one can quote that of coating of insola-

  thermal tion for fuel chamber liners

  tion in gas turbines We can also cite the re-

  clothing for piston engine valves.

  The invention is not limited to the use of coatings

  thin mats The composite coating material can be

  be light if using ceramic particles of

  low density and especially if it is hollow spheres

  Similarly, the metal binder provides very good adhesion to a support when it is bonded to it by pressure.

hot isostatic.

  The invention which has just been described therefore embraces for example the fixing of a light and thick coating, which can reach, for example a thickness of 6.35 mm, on the head of a rotor blade i with aerodynamic profile, under the shape of a bloe which has an extra thickness

  allowing to be brought by machining to the form of a shield

  dage dawn The term coating is therefore used here

in a very broad sense.

Claims (17)

CLAIMS -   1. Method for applying a composite coating   site on an article, characterized in that it consists of   mix with a binder a ceramic material in the state of   and compact the mixture on a surface of this   article by hot isostatic pressure.   2. Method according to claim 1, characterized   in that the ceramic particles have a spherical shape   risk. 3 Method according to claim 2, characterized in that the ceramic particles are hollow spheres.   4. Method according to any one of the claims   above, characterized in that the binder is a metallic powder.   5. Method according to claim 4, characterized   in that the binder is an alloy of nickel and aluminum.   6. Method according to claim 4, characterized in that the binder is an alloy of chromium, of aluminum   and yttrium containing cobalt and / or nickel.   7. Method according to claim 1, characterized in that the binder is a ceramic material which is more   ductile than that of particles at a high temperature.   8. Method according to claim 7, characterized   in that the binder is zirconium silicate.   9. Method according to any one of the claims   1 to 6, characterized in that the particles of this   ramic are made of a material chosen from a group   formed of zirconia, alumina, silica and si-   magnesium licate having the formula Mg O 25 i O 2.   10. Method according to claim 1, characterized in that it consists in mixing hollow spheres of zirconia with a binder consisting of a powder of nickel or of cobalt-based alloy, in applying this mixture to the surface of the article and attach it to this surface by hot isostatic pressure.   11. Article provided with a composite coating, character-   that this coating is applied according to the   process according to any one of the preceding claims   teeth. 12. Article according to claim 11, characterized in that the coating is a thermal insulation coating.   13. Article according to claim 11, character-   dried in that the coating is an abrasive coating.   14. Article according to claim 11, character-   dried in that the coating is a coating susceptible to erosion.   15. Article according to claim 11, character-   is that the coating is a light coating which   is then brought by machining to the requested shape.   16 Article according to any one of the claims   tions II to 15, characterized in that the article is a   airfoil blade (1) for gas turbine.   17. Article according to any one of the claims   tions 13 to 15, characterized in that it is a rotor blade with an aerodynamic profile for a gas turbine and in that   that the coating is applied to the dawn head.