Multi-layer coating for high-stress metal parts

Abstract

A multilayer coating (100) for a metal piece (10), in particular a turbomachine component, more particularly a turbomachine impeller, comprises: a first layer (20) applied on at least a portion of the metal piece (10) and having a hydrogen diffusion coefficient (measured by a hydrogen permeation test) of less than 10 <-7 > m2 / s even when subjected to stress; and a second layer (30) applied on top of the first layer (20) and exposed to a process fluid comprising hydrogen. The second layer (30) includes an oxide selected between aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2). The first layer (20) and the second layer (30) may be applied at temperatures less than 500 DEG C according to various deposition process techniques.

Description

[0001] Description TECHNICAL FIELD

[0002] The subject matter disclosed herein relates to a multilayer coating for a metal piece, in particular a turbomachine component, more particularly a turbomachine impeller, and a method for preventing hydrogen diffusion in a metal piece, in particular a turbomachine component, more particularly a turbomachine impeller. BACKGROUND

[0003] Turbomachine components, especially rotating components, for hydrogen (= H2) treatment are generally made of materials that are susceptible to embrittlement in direct contact with hydrogen. Indeed, hydrogen is a small molecule that can also split into atomic hydrogen. Hydrogen atoms can enter, i.e. diffuse, into the small cavities of the metal structure and settle there, thereby increasing the risk of crack formation in the material.

[0004] To prevent corrosion of the metal piece and / or to improve its corrosion resistance, a protective coating can be applied on the surface of the metal piece. However, when applied on rotating components, in particular impellers, conventional coatings have the following drawbacks: indeed, the complex geometry of the workpiece makes the coating process particularly challenging. In addition, the base material of high rotation speed components, in particular high-strength steel, cannot be coated at high temperature, i.e. temperature > 500°C, so as not to affect the metal microstructure of the base material. Furthermore, the high rotation speed of the impeller during operational use results in high strain in the metal piece, thereby stretching it. Thus, due to imperfect coating and / or cracking of the coating, which can not resist the stretching of the workpiece, parts of the metal surface can be exposed to hydrogen, thereby allowing hydrogen to diffuse within the workpiece.

[0005] Therefore, to treat fluids containing hydrogen, eventually fluids containing 100% hydrogen, it is desirable to have an efficient hydrogen diffusion barrier, in particular deposited at a temperature lower than 500°C, so as not to affect the microgeometry of the workpiece, and resistant to stress and strain during operation, to prevent embrittlement of the metal piece, in particular in the case of high strain induced by the centrifugal speed of the rotating component. SUMMARY

[0006] According to one aspect, the subject matter disclosed herein relates to a multilayer coating for a metal piece, in particular a turbomachine component, more particularly a turbomachine impeller, the multilayer coating comprising: a first layer applied on at least a portion of the metal piece and having a thickness of less than 10 -7 m 2The first and second layers are applied at a temperature below 500°C.

[0007] According to another aspect, the subject matter disclosed herein relates to a method for preventing hydrogen diffusion in a metal part, in particular a turbomachine component, more particularly a turbomachine impeller, comprising the following steps:

[0008] a. applying a first layer on at least a portion of the metal part using a technique selected between: spraying, physical vapor deposition (PVD) and chemical vapor deposition (CVD), the first layer being made of a first material having low hydrogen permeability, and

[0009] b. applying a second layer on the first layer, the second layer being made of a second material that is resistant to oxidation and / or corrosion and / or erosion,

[0010] The application of step "a" and the application of step "b" are performed at a temperature below 500°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A more complete appreciation thereof will be readily obtained as the disclosed embodiments of the present invention and many of its attendant advantages become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0012] Figure 1 A simplified diagram showing an embodiment of an innovative multilayer coating for metal parts,

[0013] Figure 2 A flow chart illustrating an innovative method for preventing hydrogen diffusion in a metal part, and

[0014] Figure 3 Shows that it can include Figure 1 Implementation of the innovative multi-layer coating for the impeller. DETAILED DESCRIPTION

[0015] According to one aspect, the subject matter disclosed herein relates to a hydrogen diffusion barrier to be provided on a metal piece subject to high stresses, such as a blade of a turbomachine rotating at high rotational speed. The hydrogen diffusion barrier is made of two layers of coating, wherein the first layer is applied directly on the metal blade and prevents most of the hydrogen diffusion even when subject to stresses, i.e. during and / or after operation of the blade, thanks to the ability to follow the deformation of the metal substrate without significant cracking. The second layer is applied on the first layer and comprises an oxide selected between: aluminum oxide (AI2O3), titanium dioxide (TiO2) and silicon dioxide (SiO2). The second layer can still have a very low hydrogen diffusion coefficient without interruption, i.e. cracking, but also has a low strain resistance, thus often subject to cracking affecting the overall hydrogen diffusion coefficient. The second layer prevents even the corrosion and / or oxidation and / or erosion of the base material of the metal piece. Thus, the synergy between the first and second layers results in an innovative hydrogen diffusion barrier more efficient in preventing hydrogen diffusion than known in the prior art.

[0016] According to another aspect, the subject matter disclosed herein relates to a method of providing a hydrogen diffusion barrier on a metal blade even when subject to stresses, i.e. during and / or after operation of the blade, by applying a first protective layer on the metal blade to prevent hydrogen diffusion and a second protective layer on the first protective layer to prevent uniform corrosion and / or oxidation and / or erosion of the first protective layer. The application of the first and second layers is performed at a temperature lower than 500°C so that the (micro- and / or macro-) geometry of the metal blade is not altered.

[0017] Reference will now be made in detail to implementations of the present disclosure, examples of which are illustrated in the accompanying drawings. The examples and drawings are provided to illustrate the present disclosure and are not intended to limit the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or spirit of the present disclosure. In the following description, like reference numbers are used to illustrate the drawings of the implementations to indicate elements that perform the same or similar functions. Furthermore, some references can not be repeated in all the drawings for the sake of clarity.

[0018] In Figure 1 An exemplary multilayer coating 100 piece is shown. The multilayer coating 100 is configured to be applied on a metal piece 10, in particular a turbomachinery component, more particularly a turbomachinery blade.

[0019] The multilayer coating 100 is particularly advantageous for protecting the metal piece 10 when handling fluids containing hydrogen. Indeed, as will become apparent from hereafter, the multilayer coating 100 is particularly advantageous for protecting high-stress components of a turbomachine from hydrogen diffusion and for maintaining the hydrogen diffusion protection properties also from oxidation and / or corrosion and / or erosion.

[0020] Due to the temperature of the working fluid, i.e. the fluid to be handled by the turbomachine impeller, the turbomachine impeller is usually subjected to temperatures up to 250°C and, due to the high rotation speed of the turbomachine impeller, the turbomachine impeller is subjected to high strains, i.e. the material of the turbomachine impeller is subjected to stretching due to the centrifugal forces induced by the rotation speed.

[0021] According to Figure 1 The coating 100 comprises, according to the example shown, two layers 20 and 30: a first layer 20 is applied on at least a portion of the metal piece 10, preferably on the entire surface of the metal piece 10, and a second layer 30 is configured to be applied on the first layer 20, preferably on the entire surface of the first layer 20. In order to create an effective hydrogen diffusion barrier, the first layer 20 has a hydrogen diffusion coefficient less than 10 -7 m 2 / s, even under stress, and the second layer 30 comprises an oxide selected between: aluminum oxide (AI2O3), titanium dioxide (TiO2) and silicon dioxide (SiO2), so that the total hydrogen diffusion coefficient of the coating 100, i.e. through both the first and the second layer, is less than 10 -9 m 2 / s.

[0022] It is noted that the hydrogen diffusion coefficient is advantageously measured by hydrogen permeation test, in particular according to ASTM G148-97 (2018). In particular, the hydrogen diffusion coefficient is obtained by the Arrhenius equation:

[0023] D(T) = D0 e-[E / R x T]

[0024] wherein:

[0025] - D(T): diffusion coefficient [m2 / s],

[0026] - D0: diffusion coefficient when temperature reaches infinity [m2 / s],

[0027] - E: diffusion activation energy [Joule / mole],

[0028] - R: universal gas constant (8.314 [Joule / mole Kelvin]).

[0029] The Applicant has studied various combinations of the first layer 20 and of the second layer 30 having the above-mentioned properties to generate an effective hydrogen diffusion barrier for the metal piece 10 to be protected.

[0030] Furthermore, the Applicant has studied a multilayer coating 100 in which the first layer 20 and the second layer 30 can be applied at temperatures lower than 500°C, so that the metal piece 10 is not affected by geometric deformations and / or the microstructure of the metal piece 10 is not affected.

[0031] Advantageously, the first layer 20 has a thickness higher than 25 pm, in particular in the range 25 pm - 150 pm, preferably in the range 50 pm - 100 pm.

[0032] According to a first example, the first layer 20 can comprise an aluminum-based material, i.e. a material having a composition of at least 50% aluminum. According to a second example, the first layer 20 can comprise chromium nitride. According to a third example, the first layer 20 can comprise tungsten carbide, in particular tungsten carbide added with cobalt or cobalt-chromium. However, many other embodiments are possible without departing from the scope of the present disclosure.

[0033] Furthermore, as will be better explained hereinafter, the first layer 20 and the second layer 30 can be applied on the metal piece 10 according to various deposition process techniques, depending for example on the geometry of the metal piece 10 and / or on the material of the first layer 20 and / or on the material of the second layer 30.

[0034] As already explained, the multilayer coating 100 can be exposed to process fluids containing hydrogen, in particular the second layer 30 is configured to be exposed to a flow containing hydrogen. Advantageously, the second layer 30 is a non-porous material, for example a material presenting a porosity value lower than 0.05%, eventually equal to 0%, according to the mercury porosimetry method or cross-section image analysis. It is noted that in any case, especially when subjected to high stresses in operation, the second layer 30 can present defects, in particular structural defects; however, generally, the structural defects cause local damages which increase the hydrogen diffusion coefficient, but do not compromise the overall functionality of the layer. More advantageously, the second layer has a thickness higher than 3 pm, in particular in the range 3 pm - 25 pm, preferably in the range 5 pm - 15 pm.

[0035] It is noted that the above-mentioned properties of the second layer 30, in particular the low (eventually zero) porosity and the thickness of the second layer 30, make the second layer 30 particularly suitable to avoid oxidation and / or corrosion and / or erosion of the first layer 20, if required.

[0036] According to another aspect, the subject-matter disclosed herein relates to a turbomachinery component, in particular a turbomachinery blade, more particularly a metal turbomachinery blade, comprising a multilayer coating as explained above (seeFigure 3 the exemplary impeller shown).

[0037] The multi-layer coating covers at least a portion of the turbomachinery component, preferably the entire surface of the turbomachinery component, in order to prevent hydrogen diffusion in the component, thus advantageously preventing embrittlement of the turbomachinery component caused by hydrogen diffusion in the material when the component should be exposed to a flow containing hydrogen, in particular when the turbomachinery impeller is configured to handle, i.e. compress or expand, a fluid containing hydrogen, eventually a fluid containing 100% hydrogen.

[0038] According to another aspect, the subject matter disclosed herein relates to an innovative method 200 for preventing hydrogen diffusion in a metal piece, in particular a turbomachinery component, more particularly a turbomachinery impeller. In general terms, the innovative method 200 comprises the following steps "a" and "b":

[0039] a. applying 210 a first layer on at least a portion of the metal piece using a technique selected between: spraying, immersion, physical vapor deposition (= PVD) and chemical vapor deposition (= CVD), the first layer being made of a first material having a low hydrogen permeability even when subjected to stress, and

[0040] b. applying 220 a second layer on the first layer, the second layer being made of a second material being resistant to oxidation and / or corrosion and / or erosion,

[0041] The application 210 of step "a" and the application 220 of step "b" are performed at a temperature lower than 500°C.

[0042] As already explained, the first layer is made of a material having a hydrogen diffusion coefficient lower than 10 -7 m 2 / s even when subjected to stress, thus resulting in a layer having a low hydrogen permeability. In particular, the innovative method aims at preventing embrittlement of the metal piece caused by hydrogen diffusion in the material when the metal piece should be exposed to a flow containing hydrogen, in particular when the metal piece is a turbomachinery impeller configured to handle, i.e. compress or expand, a fluid containing hydrogen, eventually a fluid containing 100% hydrogen.

[0043] According to step "a" of the innovative method 200, the first layer can be applied on at least a portion of the metal piece, preferably on the entire surface of the metal piece, according to various deposition process techniques.

[0044] As already explained, the first layer can be applied by spraying the first material on the surface of the metal piece ("spray deposition"), or by dipping the metal piece in a bath of paint ("dip coating" or "dip painting"), or by evaporating the first material in vacuum and depositing it on the surface of the metal piece ("physical vapor deposition" or "PVD"), or by chemical reaction in a gas to deposit the first material on the surface of the metal piece ("chemical vapor deposition" or "CVD"), or by chemical reaction in a gas using plasma generated by electrical energy that can be used to supply energy to carry out the chemical reaction ("plasma- assisted chemical vapor deposition" or "PACVD").

[0045] It is noted that chemical vapor deposition can be carried out at high and low temperatures; advantageously, the first layer is applied using low-temperature chemical vapor deposition, in particular at a temperature of 0°C-350°C.

[0046] Advantageously, the second layer is applied using chemical vapor deposition using plasma generated by electrical energy that can be used to supply energy to carry out the chemical reaction (e.g. "plasma-assisted chemical vapor deposition" or "PACVD" or "plasma-enhanced chemical vapor deposition" or "PECVD" or "inductively coupled plasma-enhanced chemical vapor deposition" or "IPECVD"). In other words, the second layer is applied using one of those low-temperature chemical vapor depositions, in particular to avoid damaging (in particular burning) the first layer that has already been applied on the metal piece.

[0047] According to a preferred embodiment, the low-temperature chemical vapor deposition is carried out at a temperature of 0°C-350°C. According to a preferred embodiment, the low-temperature chemical vapor deposition is carried out at a pressure of 0 bar-1 bar.

Claims

1. Multilayer coating (100) for a metal piece (10), in particular a turbomachinery component, more particularly a turbomachinery impeller, said coating (100) comprising: - a first layer (20) to be applied on at least a portion of said metal piece (10), said first layer (20) having a hydrogen diffusion coefficient, measured by hydrogen permeation test, of less than 10 -7 m 2 / s, even when subjected to stress; - a second layer (30) to be applied on said first layer (20), said second layer (30) comprising an oxide selected between: aluminum oxide (AI2O3), titanium dioxide (T1O2) and silicon dioxide (S1O2), wherein said second layer (30) is configured to be exposed to a process fluid comprising hydrogen, wherein said first layer (20) and said second layer (30) are applied at a temperature lower than 500°C.

2. Multilayer coating (100) according to claim 1, wherein said second layer (30) is configured to avoid oxidation.

3. Multilayer coating (100) according to claim 1, wherein said second layer (30) is configured to avoid corrosion.

4. Multilayer coating (100) according to claim 1, wherein said second layer (30) is configured to avoid erosion.

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

6. Multilayer coating (100) according to claim 1, wherein said first layer (20) comprises an aluminum-based material.

7. Multilayer coating (100) according to claim 1, wherein said first layer (20) comprises chromium nitride.

8. Multilayer coating (100) according to claim 1, wherein said 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 piece, in particular a turbomachinery component, more particularly a turbomachinery impeller, said method (200) comprising the steps of: a. applying (210) a first layer on at least a portion of said metal piece using a technique selected between: spraying, immersion, physical vapor deposition (PVD) and chemical vapor deposition (CVD), said first layer being made of a first material having a low hydrogen permeability even when subjected to stress, and b. applying (220) a second layer on said first layer, said second layer being made of a second material resistant to oxidation and / or corrosion and / or erosion, wherein said application (210) of step "a" and said application (220) of step "b" are performed at a temperature lower than 500°C.

10. Method (200) according to claim 9, wherein said second layer is applied using chemical vapor deposition (CVD).

11. Method (200) according to claim 10, wherein said 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 inductive plasma-enhanced chemical vapor deposition (IPECVD), in particular at a temperature in the range 0°C - 350°C.

12. A turbomachine component, in particular a turbomachine wheel (300), comprising a multilayer coating according to claim 1, wherein the multilayer coating covers at least a portion of the turbomachine component.

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