US-12623277-B2 - Method for coating a refractory alloy part, and the part thus coated

US12623277B2US 12623277 B2US12623277 B2US 12623277B2US-12623277-B2

Abstract

A method includes coating of one or more zones of the refractory alloy part, using a treatment composition including one or more types of preceramic polymer, a solvent and one or more active fillers, and heat treating the coated refractory alloy part, the heat treatment allowing to partially convert the preceramic polymer to form a ceramic layer, the active filler forming on a surface of the refractory alloy part, one or more ternary alloys and forming a continuous layer between the surface of the refractory alloy part and the ceramic layer obtained by conversion. The heat treatment forms a continuous layer of the ternary alloy. The treatment composition includes, relative to the total weight of the treatment composition, a weight proportion of between 40% and 66% of the one or more active fillers, and an active filler/preceramic polymer weight ratio is greater than or equal to 2.

Inventors

Mathieu SOULIER
Richard Laucournet
Jacky Bancillon
Alexandre MONTANI
Mirna BECHELANY
VIRGINIE JAQUET
AMAR SABOUNDJI

Assignees

SAFRAN
COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

Dates

Publication Date: 20260512
Application Date: 20220530
Priority Date: 20210601

Claims (16)

1 . A method for coating a refractory alloy part, comprising: coating of at least one portion of the refractory alloy part, using a treatment composition comprising at least one type of preceramic polymer, a solvent and at least one active filler, heat treating the refractory alloy part coated with the treatment composition, the heat treatment allowing to at least partially convert the preceramic polymer to form a ceramic layer, the active filler being chosen to form, by solid or liquid diffusion, on a surface of the refractory alloy part, at least one alloy which is at least ternary resulting from a co-reactivity of the active filler with the refractory alloy part and the preceramic polymer, the at least ternary alloy forming a continuous layer between the surface of the refractory alloy part and the ceramic layer obtained by conversion, wherein the heat treatment is carried out so as to form a continuous layer of the at least ternary alloy, wherein the treatment composition comprises, relative to the total weight of the treatment composition, a weight proportion of between 40% and 66% of at least one active filler, and wherein an active filler/preceramic polymer weight ratio is greater than or equal to 2.
2 . The method according to claim 1 , wherein the treatment composition comprises, relative to the total weight of the treatment composition, the weight proportion of between 45% and 60% of at least one active filler and wherein the active filler/preceramic polymer weight ratio is comprised between 2 and 3.
3 . The method according to claim 1 , wherein said treatment composition comprises, relative to the total weight of the treatment composition, the weight proportion of between 55% and 60% of at least one active filler, and wherein the active filler/preceramic polymer weight ratio is comprised between 2 and 2.5.
4 . The method according to claim 1 , wherein the at least one active filler is selected from silicon powder, aluminum powder, iron powder, copper powder, cobalt powder, nickel powder, lanthanum powder, germanium powder, zirconium powder, chromium powder, titanium powder, hafnium powder, lanthanum powder and rhenium powder.
5 . The method according to claim 1 , wherein the preceramic polymer is selected from siloxanes, polysiloxanes which are converted into silica (SiO 2 ) or silicon oxycarbide (Si—O—C) by pyrolysis, polysilazanes or polycarbosilanes.
6 . The method according to claim 1 , wherein the treatment composition further comprises passive fillers, configured to modulate a thermal expansion coefficient of the at least ternary alloy layer, so as to have a difference between a thermal expansion coefficient of the refractory alloy part and the thermal expansion coefficient of the at least ternary alloy layer less than 3.10 −6 K −1 .
7 . The method according to claim 1 , wherein the coating comprises at least one first coating step and one second consecutive coating step, and the heat treatment comprises at least one heat treatment step carried out between the first coating step and the second consecutive coating step, the heat treatment step being a crosslinking step for crosslinking the preceramic polymer(s), configured to generate an infusible polymer network capable of withstanding subsequent pyrolysis steps, the second consecutive coating step being applied to obtain a thicker treatment composition layer.
8 . The method according to claim 7 , wherein the treatment composition used during the second consecutive coating step has a viscosity lower than a viscosity of the treatment composition used during the first coating step.
9 . The method according to one of claims 7 , wherein the crosslinking step is carried out in the presence of air at a temperature greater than or equal to a highest crosslinking temperature among the different crosslinking temperatures of the different species of preceramic polymer of the treatment solution.
10 . The method according to claim 1 , wherein the heat treating comprises: crosslinking at a first temperature configured to evaporate the solvent and thus accelerate the crosslinking, performing a conversion carried out at a second temperature, higher than the first, configured to convert the preceramic polymer into ceramic and eliminate the organic species, so as to obtain a ceramic having an amorphous structure, and structuring carried out at a third temperature, higher than the second temperature, configured to convert the ceramic with an amorphous structure into ceramic having a crystalline structure.
11 . The method according to claim 1 , wherein the heat treating is carried out under a controlled atmosphere so as to avoid oxidation of the refractory alloy part, while having an oxygen partial pressure sufficient to ensure the conversion of the preceramic polymer into oxycarbide ceramic or oxide ceramic.
12 . The method according to claim 1 , wherein the ceramic layer obtained by conversion is removed after the heat treatment, by mechanical or chemical action to leave only the at least ternary alloy layer.
13 . A refractory alloy part, obtained by the coating method according to claim 1 , wherein the refractory alloy part is coated with a continuous layer of at least one alloy which is at least ternary and which results from the co-reactivity of the active filler with the refractory alloy part and the preceramic polymer, and with a ceramic layer, and the continuous layer of at least one alloy which is at least ternary being disposed between the refractory alloy part and the ceramic layer.
14 . The refractory alloy part according to claim 13 , wherein the refractory alloy part is a foundry core made of refractory alloy.
15 . The refractory alloy part according to claim 13 , wherein the refractory alloy part is based on molybdenum.
16 . The method according to claim 1 , wherein the refractory alloy part is based on molybdenum.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a National Stage of International Application No. PCT/FR2022/051021 filed May 30, 2022, claiming priority based on French Patent Application No. 2105756 filed Jun. 1, 2021, the contents of each of which being incorporated by reference herein in their entireties. FIELD OF THE INVENTION The invention lies in the field of protective coatings for refractory alloy parts subject to oxidation, for example foundry cores. The present invention relates more precisely to a method for coating a refractory alloy part and to a part of refractory alloy coated with such a protective coating. STATE OF THE ART During a foundry manufacturing method, foundry cores are conventionally disposed in foundry molds, prior to the injection of the liquid metal, so as to produce one or more cavities or recesses in the mechanical elements which will be produced during this manufacturing method. These foundry cores are conventionally made of refractory ceramics. It is also known to use foundry cores made of refractory alloys to replace or complement the ceramic cores conventionally used. These refractory alloy materials, typically molybdenum alloys, must be coated with a protective layer to preserve their mechanical features, particularly when they are subjected to very high temperatures encountered for example during the manufacturing processes of superalloy blades for turbomachines. In the case of lost wax foundry methods, shells of refractory material are made around a wax model of the mechanical element to be produced, so as to form a mold of the model of this mechanical element. The wax is then evacuated into an autoclave under steam. Finally, the shell is heated to be consolidated, in order to produce an imprint of the external shape of the mechanical element to be produced. A core can be disposed initially in the wax model and be present before the casting of the material constituting the mechanical element to be produced, the core defining the internal shape of this mechanical element. In the case of producing turbomachine blades, typically superalloy turbine blades, by a lost wax casting method, the consolidation of the blade shell is carried out in air, at a temperature greater than 1000° C. Consequently, significant oxidation phenomena may be encountered, particularly for the refractory metal which constitutes a portion of the core or the complete core. Molybdenum, for example, when uncoated, reacts with oxygen from 400° C., to form molybdenum dioxide (MoO2) up to 650° C., then molybdenum trioxide beyond 650° C., molybdenum trioxide being very volatile. The oxidation rate of molybdenum follows a known linear increase between 400° C. and 650° C., then an exponential increase beyond and up to 1700° C. It is also known to use for the production of a foundry core, a molybdenum-based alloy including zirconium and titanium (known under the name TZM alloy), which has a mechanical resistance greater than molybdenum at ambient temperature, which makes it more easily machinable. However, TZM is known to oxidize from 540° C. and the oxidation becomes exponential from 790° C. with rapid volatilization of TZM. This very significant oxidation of molybdenum or TZM parts leads to a significant weight loss, and a rapid degradation of their mechanical properties. In addition, after the consolidation of the shell in air, the superalloy used for the manufacture of the mechanical element (for example a turbomachine blade) is melted and cast under vacuum into the shell. Then it comes into contact with the refractory alloy which constitutes the core. This casting step, carried out under vacuum, at a temperature above 1500° C., results in particular in diffusion phenomena of superalloy elements in the refractory alloy of the core. An inter-diffusion of the elements of the refractory alloy of the core towards the superalloy of the mechanical element to be manufactured can lead to a modification of the mechanical properties of the superalloy, and therefore lead to a degradation of the performance of the mechanical element obtained. It is therefore desirable to protect these refractory alloy parts with a protective coating. For this purpose, it is known to produce preceramic polymer coatings for protection against oxidation of metal parts made of refractory alloy. “Preceramic polymers” means polymers which, after pyrolysis, are converted into ceramic. The “preceramic polymer” route is a synthesis method allowing the manufacture of homogeneous ceramics of high chemical purity. Due to control of the viscoelastic properties and the composition at the atomic scale of the polymers, it is in particular possible to generate ceramics of the desired shape and composition. The best-known classes of ceramics obtained by this chemical route are the binary systems Si3N4, SiC, BN and AlN, the ternary systems SiCN, SiCO and BCN, as well as the quaternary systems SiCNO, SiBCN, SiBCO, SiAlCN and SiAlCO. The use