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
  • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
  • C23C10/52—Embedding in a powder mixture, i.e. pack cementation more than one element being diffused in one step
• • 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
  • C23C10/02—Pretreatment of the material to be coated
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12528—Semiconductor component

Definitions

• the invention relates to formation on a metal substrate.
• an aluminide type protective coating incorporating at least one reactive element.
• the field of application of the invention is that of production or repair of metal parts which, due to their use at high temperatures and in an oxidizing environment, must be provided with a protective coating.
• the invention is particularly, but not exclusively, applicable to parts of gas turbines, in particular parts of parts turbojet engines.
• Parts exposed to these temperatures are usually made of refractory metallic alloy, or superalloy, nickel-based or cobalt.
• aluminide type coatings which allow in particular the development of a protective alumina film on their surface, are commonly used.
• Aluminum cementation is the most common technique commonly used to form aluminide type coatings. This technique usually involves placing the metal substrate in a closed enclosure containing a cement and to bring the assembly to a temperature generally between 900 ° C and 1150 ° C.
• the aluminide type coatings can be used alone, or in combination with an external barrier coating thermal such as a ceramic coating.
• the aluminide type coating constitutes a bonding layer between the substrate and the external coating, the attachment of the latter being favored by the presence of the alumina film forming an adhesion layer.
• aluminide alumina film In order to increase the service life of the generator aluminide alumina film and limit deterioration of the latter by flaking it is known to incorporate in the aluminide type coating at least one reactive element usually chosen from the group consisting of zirconium, yttrium, hafnium and lanthanides.
• Such a reactive element reinforces the barrier function of diffusion towards elements of the metallic substrate susceptible affect the alumina film, and therefore promotes the integrity and persistence of this one.
• the presence of the reactive element also results in a decrease in the rate of oxidation of the metal substrate and by a prevention of highly undesirable segregation of sulfur to interface with an external ceramic coating.
• a first type of known process consists in combining or associating separately the reactive element with one or more constituents of the coating and to form it by a process of physical deposition on the metallic substrate.
• a second type of known process consists in forming a aluminum coating incorporating a reactive element by chemical deposition in the gas phase (CVD).
• CVD gas phase
• a heat treatment allows reduction of oxide by aluminum.
• a third known type of process uses the technique of aluminization, but by modifying it by incorporating the reactive element in the cement.
• the object of the invention is to propose a method making it possible to simple and economical way the formation of a type coating aluminide incorporating at least one reactive element, on a substrate metallic.
• the supply of the reactive element in the form of an oxide powder of this element makes it possible to avoid difficulties in handling the powder of reactive element.
• the contribution of the reactive element to the surface of the metal substrate can be produced by coating with a composition containing the powder mixed with a liquid, or by spraying such a composition, or by projection of the powder on the substrate so that it becomes encrusted on its surface, or by electrophoresis.
• the method according to the invention is remarkable in that, in despite the provision of the reactive element in powder form, a aluminide type coating is obtained having a microstructure and a effectiveness quite comparable to that of similar coatings of the prior art, while the method of implementing the method turns out particularly advantageous.
• the reactive element is also brought as close as possible to the substrate. metallic, which optimizes the yield between mass of reactive element putting into play and doping of the coating thus produced.
• the method makes it possible to bring the reactive element in localized regions of the substrate surface, for example at to repair a protective coating, which is not possible with the prior art methods in which the reactive element is deposited in the gas phase or incorporated into a cement.
• the aluminide type coating can be formed by aluminization after addition of the reactive element to the surface of the substrate. No changes to known aluminization processes, except possibly the duration, is not necessary, which constitutes another another advantage of the process.
• the aluminide type coating can be formed by deposition of coating components after addition of the reactive element on the surface of the substrate, and heat treatment to react the constituents between them.
• the surface of the metal substrate at least aluminum in powder form and one then forms the aluminide type coating by heat treatment.
• the reactive element and the aluminum can be brought to the surface of the substrate by coating or spraying with a liquid composition comprising a powder of the reactive element in oxide form, a aluminum powder and a binder, the coating or spraying being carried out advantageously in superimposed layers to reach a thickness depending on that of the desired aluminide type coating.
• one carries out in in addition to the surface of the substrate a deposit of at least one metal chosen from the group consisting of platinum, palladium, rhodium and ruthenium.
• the aluminide type coating formed by the process according to the invention can be used alone, or as a barrier underlay thermal, an external ceramic coating then being formed which anchors on an alumina film generated at the interface between the coating of aluminide type and external ceramic coating.
• the invention also relates to metallic substrates, in particular gas turbine parts made of superalloy, fitted with aluminide type as obtained by the above process.
• the process according to the invention is intended more particularly, but not only to the production of protective coatings of the type aluminide on metallic substrates in superalloy, in particular in nickel or cobalt-based superalloy, such as metallic substrates parts of gas turbines, in particular parts of turbojets.
• At least one element reagent to be present in the aluminide type coating is brought to the surface of the substrate, prior to the formation of the coating, in the form of an oxide powder of the reactive element.
• the reactive element is preferably chosen from zirconium, yttrium, hafnium and lanthanides.
• the deposition in the form of oxide powder makes it possible to avoid difficulties in handling these reactive elements in contact with air.
• a first technique consists in preparing a composition containing powder and liquid and coating the surface of the substrate metallic, or a selected part of this surface with this composition.
• the liquid used is for example a resin, possibly added with a solvent which, after possible polymerization of the resin, allows to fix the powder on the surface.
• the coating can be very conventionally performed with a brush.
• composition containing the powder and a liquid can be sprayed onto the surface or onto a selected part of it.
• Another usable technique is to spray the powder alone on the surface of the substrate, or on a selected part thereof.
• the projection is carried out by giving the powder particles a sufficient energy for them to become encrusted on the surface of the substrate.
• Yet another technique is to deposit the powder in the substrate surface by electrophoresis. This is a good technique known per se, a brief description of which can be found in the document FR 96 15257 already cited.
• a possible initial step in the process can consist in the formation on the surface of the substrate of a coating in one precious metal chosen from platinum, palladium, rhodium and ruthenium.
• a metallic coating can be carried out by sputtering or by electrolytic deposition, a diffusion heat treatment is then often carried out.
• a platinum group metal coating could be produced after the active element oxide powder has been added to the surface of the substrate.
• the next step in the process is to form the coating of aluminide type.
• a conventional process is implemented aluminization by cementation.
• Case hardening in pack with contact between a case hardening powder and the substrate consists in burying the latter in a powder containing (i) an aluminum alloy, generally a chromium-aluminum alloy, (ii) an inert constituent, such as alumina, to avoid sintering, and (iii) a halogenated activator (for example NH 4 Cl, NH 4 F, AlF 3 , NaF, NaCl, ...) which allows the transport of the metal to be deposited between the cement and the substrate.
• the whole is brought to a temperature of, for example, between 900 ° C. and 1150 ° C. in an oven.
• Case hardening can also be carried out without contact with the substrate, the cement being placed apart in the furnace.
• the halogenated activator can be incorporated into the cement or be brought separately in the oven.
• the reactive element oxide previously brought to the surface of the substrate can be at least partially reduced.
• the oxide is dispersed in a resin, the latter is degraded quickly by the halides formed by the activating element and by the heat.
• Thermochemical reactions occur between halides, cement, reactive element oxide and the metal alloy of substrate which allow the formation of the aluminide coating and the dispersion of the reactive element within the aluminide coating formed.
• a nickel-based superalloy substrate With a nickel-based superalloy substrate, a nickel aluminide containing the reactive element.
• Processes other than aluminization can be used to form the aluminide type coating.
• constituents of the desired coating on the substrate by physical gas deposition process, such as sputtering cathodic or plasma projection, or chemical deposition processes in the gas phase from gaseous precursors. These processes are known in themselves. We could for example refer to the documents GB 2 005 729, US 5 741 604 and US 5 494 704. The deposit of the constituents can be made in alternating overlapping layers.
• a treatment thermal provides the desired aluminide with reduction any oxide previously brought to the surface of the substrate and dispersion of the reactive element released within the coating.
• a mixed deposit of powder of reactive element oxide and aluminum powder is produced on the surface of the metal substrate.
• the deposit can be made by coating or spraying with a composition containing the oxide powder, the aluminum powder and an inorganic or organic binder, such as a resin possibly diluted in a solvent.
• Several overlapping layers are formed according to the thickness of the coating to be produced.
• a heat treatment is then carried out at a temperature of preferably between 800 ° C and 1100 ° C to allow the formation of a aluminide by diffusion from the metal substrate, and the dispersion of the reactive element within the coating.
• the metal substrate can be used with the only coating aluminide forming a protective coating against corrosion and oxidation at high temperatures.
• an external coating in ceramic for example zirconia, yttrium oxide or zirconia yttria.
• This external coating obtained by a physical deposition process such as, for example, sputtering, thermal spraying, evaporation under an electron beam, constitutes a thermal barrier.
• the aluminide type intermediate coating then in particular has a bonding layer function allowing, via a developed alumina film on its surface, the attachment of the external ceramic coating.
• a nickel-based superalloy metal substrate was provided a coating of nickel aluminide doped with zirconium in the way next.
• a zirconia powder of average particle size equal to 14 ⁇ m was mixed with a liquid acrylate resin at a rate of 1 part by weight of powder for 8 parts by weight of resin. The mixture was applied to the substrate by coating with a brush then the resin been polymerized by UV exposure.
• Non-contact cementation aluminization was then carried out by placing the substrate in an oven in the presence of a cement and an activator.
• the cement was composed of 30% by weight of aluminum and 70% by weight of chromium, and the activator used was NH 4 Cl.
• the aluminization was carried out at a temperature of approximately 1100 ° C. for a period of 4 h 30 min approximately.
• the acrylate resin was rapidly degraded by the halides formed and the heat, while the zirconia was reduced.
• a nickel-based superalloy substrate was thus obtained with a nickel aluminide coating containing 0.9% by mass of zirconium.
• a nickel-based superalloy metal substrate was subjected to sandblasting with a zirconia powder identical to that of Example 1.
• the sanding allowed the inlay and the surface deposition of the substrate of zirconia particles.
• a contactless cementation aluminization was then carried out as in Example 1.
• the nickel aluminide obtained has a zirconium content of a few hundred ppm, as well as a fine dispersion of alumina particles with a particle size of less than one micron.
• a nickel-based superalloy metal substrate was coated with several layers of aluminizing paint.
• This painting was consisting of the dispersion in an inorganic binder of a mixture of zirconia powder, aluminum powder and silicon powder in respective weight proportions of 8%, 82% and 10%.
• the layers were formed by spraying paint and deposited successively with intermediate air drying supplemented by a steaming at 90 ° C for 30 min. The number of layers was chosen in depending on the thickness of the desired aluminide coating.
• the metal substrate was then placed in an oven to undergo a heat treatment at 1000 ° C under a neutral atmosphere (argon).
• a nickel aluminide coating was obtained by diffusion in which of the zirconium was dispersed.
• the deposition of reactive element oxide by coating or spraying is advantageous in that it makes it possible to form this deposit on only part of the surface of the metal substrate. We then chooses the most exposed critical parts of the substrate, or the parts of the substrate that require repair of the coating aluminide type and any external ceramic coating.
• the method can be implemented so similar with yttrium oxide powder, oxide powder hafnium, lanthanide oxide powder, or a mixture of two or more of these powders.

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