REVESTIMENTO MULTICAMADAS PARA PEÇAS METÁLICAS DE ALTO ESTRESSE

Abstract

The multilayer coating (100) for a metal piece (10), in particular a turbomachinery component, more in particular a turbomachinery impeller, comprising a first layer (20) which is applied on at least a portion of the metal piece (10) and which has a hydrogen diffusion coefficient of less than 10-7 m2 / s even when subjected to stress (the hydrogen diffusion coefficient being measured through a hydrogen permeation test), and a second layer (30) which is applied on top of the first layer (20) and which is exposed to a process fluid comprising hydrogen. The second layer (30) comprises an oxide chosen between: aluminum oxide (Al2O3), titanium dioxide (TiO2) and silicon dioxide (SiO2). The first and the second layer (20) and (30) may be applied according to various depositing process techniques at temperature below 500 °C.

Description

1 / 9 Multilayer coating for high-stress metal parts. DESCRIPTION TECHNICAL FIELD

[0001] The matter disclosed in this document relates to a multilayer coating for a metal part, particularly in a turbomachine component, more particularly a turbomachine impeller, and a method for preventing hydrogen diffusion in a metal part, particularly in a turbomachine component, more particularly a turbomachine impeller. FUNDAMENTALS OF THE TECHNIQUE

[0002] Hydrogen (=H2) turbomachine components, especially rotating parts, are typically made of materials that are easily subject to embrittlement in case of direct contact with hydrogen. In fact, hydrogen is a small molecule that can also split into atomic hydrogen. Hydrogen atoms can enter (i.e., diffuse) into small cavities in the metal structure and settle there, increasing the risk of cracking in the material.

[0003] In order to prevent corrosion and / or improve the strength of a metal part, a protective coating can be applied to the surface of the metal part. However, traditional coatings have disadvantages when applied to rotating components, particularly impellers: in fact, the complex geometry of the part makes the coating process particularly challenging. Furthermore, the base material, particularly high-strength steel, of high-speed rotating components cannot be coated at high temperatures (i.e., temperatures >500°C) so as not to affect the metallic microstructure of the base material. In addition, the high rotational speeds of the impeller during operational use cause high stress on the metal part, causing it to stretch. Therefore, due to imperfect coating and / or cracking of the coating (which may not withstand the Petition 870250085423, dated 09 / 22 / 2025, page 15 / 101 2 / 9 stretching of the part), portions of the metal surface can be exposed to hydrogen, thus allowing hydrogen to diffuse into the part.

[0004] Therefore, to process a fluid comprising hydrogen (eventually a fluid comprising 100% hydrogen), it would be desirable to have an efficient hydrogen diffusion barrier, in particular deposited at a temperature below 500°C (in order not to affect the microgeometry of the part) and resistant to stress and deformation during operation, to prevent metal parts from becoming brittle, particularly in the case of high deformation caused by centrifugal speeds of rotating parts. SUMMARY

[0005] According to one aspect, the matter disclosed in this document relates to a multilayer coating for a metal part, in particular a turbomachine component, more specifically a turbomachine impeller, comprising a first layer that is applied to at least a portion of the metal part and that has a hydrogen diffusion coefficient of less than 10⁻⁷ m² / s even when subjected to stress (the hydrogen diffusion coefficient being measured by means of a hydrogen permeation test) and a second layer that is applied on top of the first layer and that is exposed to a process fluid comprising hydrogen. The second layer comprises an oxide chosen from: aluminum oxide (Al₂O₃), titanium dioxide (TiO₂) and silicon dioxide (SiO₂). The first layer and the second layer are applied at a temperature below 500°C.

[0006] According to another aspect, the matter disclosed in this document refers to a method for preventing hydrogen diffusion in a metal part, in particular in a turbomachine component, more specifically a turbomachine impeller, comprising the steps of: a. Apply a first layer to at least a portion of the metal part using a technique chosen from: spraying, physical vapor deposition (PVD), and chemical vapor deposition (CVD), the first layer being made of a low hydrogen permeability primer, and Petition 870250085423, dated 09 / 22 / 2025, page 16 / 101 3 / 9 b. Apply a second layer over the first layer, the second layer being made of a second material that is anti-oxidation and / or anti-corrosion and / or anti-erosion, the application of step a and the application of step b being carried out at a temperature below 500°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A fuller understanding of the disclosed embodiments of the invention and of many of the advantages associated therewith will be readily obtained as a better understanding is gained by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein:

[0008] Fig. 1 shows a simplified diagram of an embodiment of an innovative multilayer coating for a metal part,

[0009] Fig. 2 shows a flowchart of an innovative method for preventing hydrogen diffusion in a metal part, and

[0010] Fig. 3 shows an embodiment of an impeller that may comprise the innovative multilayer coating of Fig. 1. DETAILED DESCRIPTION OF THE MODALITIES

[0011] In one aspect, the matter disclosed in this document relates to a hydrogen diffusion barrier to be provided on a metal part that is subject to high stresses, such as, for example, a turbomachine impeller rotating at high speed. The hydrogen diffusion barrier is made of a two-layer coating in which the first layer is applied directly to the metal impeller and prevents most hydrogen diffusion even when subjected to stress, i.e., during impeller operation and / or after impeller operation, due to its ability to follow the deformation of the metallic substrate without showing cracks. The second layer is applied over the first layer and comprises an oxide chosen from: aluminum oxide (Al2O3), titanium dioxide (TiO2) and silicon dioxide (SiO2). The second layer may also have a diffusion coefficient of Petition 870250085423, dated 09 / 22 / 2025, page 17 / 101 4 / 9 very low hydrogen when uninterrupted (i.e., cracked), but also has low resistance to deformation, and is therefore frequently subject to cracking which affects the overall hydrogen diffusion coefficient. The second layer prevents corrosion and / or oxidation and / or uniform erosion of the base material of the metal part. Therefore, the synergistic cooperation between the first and second layers generates an innovative hydrogen diffusion barrier that is more efficient in preventing hydrogen diffusion than what is known in the prior art.

[0012] According to another aspect, the matter disclosed in this document refers to a method for providing a hydrogen diffusion barrier in a metal impeller even when subjected to stress, i.e., during impeller operation and / or after impeller operation, by applying a first protective layer to the metal impeller to prevent hydrogen diffusion and applying a second protective layer over the first protective layer to prevent corrosion and / or oxidation and / or uniform erosion of the first protective layer. The application of the first and second layers is carried out at temperatures below 500°C, so that the geometry (micro and / or macro) of the metal impeller is not modified.

[0013] Reference will now be made in detail to the modalities of the revelation, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the revelation and should not be interpreted as a limitation of the revelation. Indeed, it will be evident to those skilled in the art that various modifications and variations can be made to the present revelation without departing from the scope or spirit of the revelation. In the following description, similar reference numbers are used for the illustration of the figures of the modalities to indicate elements that perform the same or similar functions. Furthermore, for the sake of clarity of illustration, some references may not be repeated in all figures.

[0014] Fig. 1 shows an exemplary piece of multilayer coating 100. The multilayer coating 100 is configured Petition 870250085423, dated 09 / 22 / 2025, page 18 / 101 5 / 9 to be applied to a metal part 10, in particular a turbomachine component, more particularly a turbomachine impeller.

[0015] The multilayer coating 100 is particularly advantageous for protecting the metal part 10 when processing a fluid comprising hydrogen. In fact, as will be evident from the following, the multilayer coating 100 is particularly advantageous for protecting high-stress parts of a turbomachine from hydrogen diffusion and maintaining the hydrogen diffusion protection characteristic also against oxidation and / or corrosion and / or erosion.

[0016] Turbomachine impellers are typically subjected to temperatures up to 250°C due to the temperature of the working fluid (i.e., the fluid to be processed by the turbomachine impeller) and high stress due to the high rotational speed of the turbomachine impeller (i.e., the turbomachine impeller materials are subjected to stretching due to centrifugal force caused by the rotational speed).

[0017] According to the example shown in Fig. 1, coating 100 includes two layers 20 and 30: a first layer 20 is applied to at least a portion of the metal part 10, preferably over the entire surface of the metal part 10, and the second layer 30 is configured to be applied over the first layer 20, preferably over the entire surface of the first layer 20. In order to create an efficient hydrogen diffusion barrier, the first layer 20 has a hydrogen diffusion coefficient of less than 10⁻⁷ m² / s, even when stressed, and the second layer 30 comprises an oxide chosen from: aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), and silicon dioxide (SiO₂), such that the overall hydrogen diffusion coefficient of coating 100 (i.e., through the first and second layers) is less than 10⁻⁹ m² / s.

[0018] It should be noted that the hydrogen diffusion coefficient is advantageously measured through a hydrogen permeation test, in particular according to ASTM G148-97(2018). In particular, the hydrogen diffusion coefficient is obtained from the Arrhenius equation: Petition 870250085423, dated 09 / 22 / 2025, page 19 / 101 6 / 9 D(T)=DO e -[E / R x T] where, - D(T): diffusion coefficient [m2 / s], - DO: the diffusion coefficient when the temperature reaches infinity [m2 / s], - E: the activation energy for diffusion [Joule / Mol], - (R) Universal gas constant (8.314 [Joule / Mol*Kelvin]).

[0019] The Applicant has studied that various combinations of first and second layers 20 and 30 having the above-mentioned characteristics create an efficient hydrogen diffusion barrier for the metal part 10 to be protected.

[0020] Furthermore, the Applicant studied a multilayer coating 100 in which the first layer 20 and the second layer 30 can be applied at a temperature below 500°C, so that the metal part 10 is not affected by geometric deformations and / or the microstructure of the metal part 10 is not affected.

[0021] Advantageously, the first layer 20 has a thickness greater than 25 pm, particularly in a range of 25-150 pm, preferably in a range of 50-100 pm.

[0022] According to a first example, the first layer 20 may comprise an aluminum-based material, that is, a material having a composition of at least 50% aluminum. According to a second example, the first layer 20 may comprise chromium nitride. According to a third example, the first layer 20 may comprise tungsten carbide, in particular tungsten carbide added with cobalt or cobalt-chromium. Various other configurations are possible without departing from the scope of the present disclosure.

[0023] Furthermore, as will be explained further below, the first and second layers 20 and 30 can be applied to the metal part 10 according to various deposition process techniques, depending, for example, on the geometry. Petition 870250085423, dated 09 / 22 / 2025, page 20 / 101 7 / 9 of the metal part 10 and / or of the first layer material 20 and / or of the second layer material 30.

[0024] As already explained, the multilayer coating 100 can be exposed to a process fluid comprising hydrogen, in particular the second layer 30 is configured to be exposed to a flow comprising hydrogen. Advantageously, the second layer 30 is a non-porous material, for example, a material exhibiting a porosity value below 0.05%, possibly equal to 0%, according to the mercury porosimetry method or image analysis in the section. It should be noted that, in any case, the second layer 30 may exhibit defects, especially when subjected to high stress in operation, in particular structural defects; however, typically, structural defects result in local damage that increases the hydrogen diffusion coefficient but does not compromise the overall functionality of the layer. More advantageously, the second layer has a thickness greater than 3 µm, particularly in a range of 3-25 µm, preferably in a range of 5-15 µm.

[0025] It should be noted that the above-mentioned characteristics of the second layer 30, in particular the low porosity (possibly zero) and thickness of the second layer 30, make the second layer 30 particularly suitable for preventing oxidation and / or corrosion and / or erosion of the first layer 20 (if necessary).

[0026] According to another aspect, the matter disclosed in this document relates to a turbomachine component, in particular a turbomachine impeller, more specifically a metal turbomachine impeller comprising a multilayer coating as explained above (see the exemplary impeller shown in Fig. 3).

[0027] The multilayer coating covers at least a portion of the turbomachine component, preferably the entire surface of the turbomachine component, in order to prevent hydrogen diffusion into the component, thus advantageously avoiding the embrittlement of the turbomachine component caused by hydrogen diffusion into the materials when the Petition 870250085423, dated 09 / 22 / 2025, page 21 / 101 The 8 / 9 component must be exposed to a flow comprising hydrogen, particularly when the turbomachine impeller is configured to process (i.e., compress or expand) a fluid comprising hydrogen (possibly a fluid comprising 100% hydrogen).

[0028] According to another aspect, the matter disclosed in this document refers to an innovative method 200 for preventing hydrogen diffusion in a metal part, in particular a turbomachine component, more specifically a turbomachine impeller. In general, the innovative method 200 comprises the following steps a and b: a. Apply a first layer to at least a portion of the metal part using a technique chosen from: spraying, dipping, physical vapor deposition (=PVD) and chemical vapor deposition (=CVD), the first layer being made of a first material with low hydrogen permeability, even when subjected to stress, and b. Apply 220 a second layer over the first layer, the second layer being made of a second material that is anti-oxidation and / or anti-corrosion and / or anti-erosion, the application 210 of step a and the application 220 of step b being carried out at a temperature below 500°C.

[0029] As already explained, the first layer is made of a material that has a hydrogen diffusion coefficient of less than 10⁻⁷ m² / s, even when subjected to stress, resulting, therefore, in a layer that is of low hydrogen permeability. In particular, the innovative method aims to prevent the embrittlement of metal parts caused by hydrogen diffusion in the materials when the metal part must be exposed to a flow comprising hydrogen, in particular when the metal part is a turbomachine impeller configured to process (i.e., compress or expand) a fluid comprising hydrogen (possibly a fluid comprising 100% hydrogen).

[0030] According to step a of the innovative method 200, the first layer can be applied to at least a portion of the metal part, of Petition 870250085423, dated 09 / 22 / 2025, page 22 / 101 9 / 9 preference across the entire surface of the metal part, according to various deposition process techniques.

[0031] As already explained, the first layer can be applied by spraying the first material onto the surface of the metal part (spray deposition) or by immersing the metal part in a bath coating (dip coating or immersion coating) or by vaporizing the first material, typically in a vacuum, and depositing it onto the surface of the metal part (physical vapor deposition or PVD) or by depositing the first material onto the surface of the metal part by chemical reaction in a gas (chemical vapor deposition or CVD) or by depositing the first material onto the surface of the metal part by chemical reaction in a gas using electrical energy to generate plasma useful for providing energy to carry out the chemical reaction (plasma-assisted chemical vapor deposition or PACVD).

[0032] It should be noted that chemical vapor deposition can be carried out at both high and low temperatures; advantageously, the first layer is applied using low-temperature chemical vapor deposition, in particular at a temperature in the range of 0-350 °C.

[0033] Advantageously, the second layer is applied using chemical vapor deposition using electrical energy to generate useful plasma to provide energy to carry out the chemical reaction (e.g., plasma-assisted chemical vapor deposition or PACVD or plasma-intensified chemical vapor deposition or PECVD or induction plasma-intensified chemical vapor deposition or IPECVD). In other words, the second layer is applied using one of these low-temperature chemical vapor deposition methods, in particular to avoid damaging (in particular burning) the first layer already applied to the metal part.

[0034] According to a preferred embodiment, low-temperature chemical vapor deposition is carried out at a temperature in the range of 0-350 °C. According to a preferred embodiment, low-temperature chemical vapor deposition is carried out at a pressure in the range of 0-1 bar. Petition 870250085423, dated 09 / 22 / 2025, page 23 / 101

Claims

1 / 3 CLAIMS 1. Multilayer coating (100) for a metal part (10), in particular a turbomachine component, more particularly a turbomachine impeller, characterized in that the coating (100) comprises: - a first layer (20) to be applied to at least a portion of the metal part (10), wherein the first layer (20) has a hydrogen diffusion coefficient of less than 10⁻⁷ m² / s even when subjected to stress, the hydrogen diffusion coefficient being measured by means of a hydrogen permeation test; - a second layer (30) to be applied to the first layer (20), the second layer (30) comprising an oxide chosen from: aluminum oxide (Al2O3), titanium dioxide (TiO2) and silicon dioxide (SiO2), wherein the second layer (30) is configured to be exposed to a process fluid comprising hydrogen, wherein the first layer (20) and the second layer (30) are applied at a temperature below 500°C.

2. Multilayer coating (100), according to claim 1, characterized in that the second layer (30) is configured to prevent oxidation.

3. Multilayer coating (100), according to claim 1, characterized in that the second layer (30) is configured to prevent corrosion.

4. Multilayer coating (100), according to claim 1, characterized in that the second layer (30) is configured to prevent erosion.

5. Multilayer coating (100), according to claim 1, characterized in that the second layer (30) has a thickness in the range of 3-15 pm.

6. Multilayer coating (100), according to claim 1, characterized in that the first layer (20) comprises an aluminum-based material. Petition 870250085423, dated 22 / 09 / 2025, page 24 / 101 2 / 3 7. Multilayer coating (100), according to claim 1, characterized in that the first layer (20) comprises chromium nitride.

8. Multilayer coating (100), according to claim 1, characterized in that the first layer (20) comprises tungsten carbide, in particular tungsten carbide added with cobalt or cobalt-chromium.

9. Method (200) for preventing hydrogen diffusion in a metal part, in particular a turbomachine component, more particularly a turbomachine impeller, the method (200) characterized by comprising the steps of: a. applying (210) a first layer to at least a portion of the metal part using a technique chosen from: spraying, immersion, physical vapor deposition (PVD) and chemical vapor deposition (CVD), the first layer being made of a first material of low hydrogen permeability, even when subjected to stress, and b. applying (220) a second layer to the first layer, the second layer being made of a second material being anti-oxidation and / or anti-corrosion and / or anti-erosion, wherein the application (210) of step a and the application (220) of step b are carried out at a temperature below 500°C.

10. Method (200), according to claim 9, characterized in that the second layer is applied using chemical vapor deposition (CVD).

11. Method (200), according to claim 10, characterized in that the second layer is applied using low-temperature chemical vapor deposition, in particular plasma-assisted chemical vapor deposition (PACVD) or plasma-enhanced chemical vapor deposition (PECVD) or induction plasma-enhanced chemical vapor deposition (IPECVD), in particular temperature in the range of 0 to 350°C.

12. Turbomachine component, in particular a turbomachine impeller (300), characterized by comprising a multi-layer coating according to claim 1, wherein the multi-layer coating covers at least a portion of the turbomachine component.

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