Apparatus and method for depositing thick metal nitride coatings via a supercritical fluid path

Abstract

The present invention relates to a device (100) for depositing thick metal nitrides on a sample (104) by a supercritical fluid route, comprising: - a first outer shell (110) forming a first closed volume (V1); - a second outer shell (120) which is placed in the first outer shell and is delimited by an inner wall (102) permeable to electromagnetic radiation, forming a second closed volume (V2) intended to contain a fluid under supercritical conditions; - a dielectric heat transfer fluid circulating around the second outer shell in the first volume; - a sample holder (105) present in the second volume; - an induction heater (103) surrounding the second outer shell; - inlets (150, 151) for introducing a fluid and at least one precursor material into the second outer shell; and an outlet (152) for purifying the second volume.

Description

Technical Field

[0001] The present invention relates to the general field of metal nitride coatings, and more particularly to thick coatings (greater than 1 μm) of metal nitrides, and even more particularly, the present invention relates to an apparatus and a method for depositing thick metal nitride coatings by supercritical fluid deposition. Background Art

[0002] Currently, industrialists have praised hard chromium-based coatings formed with chromium IV produced by chemical and electrolytic synthesis because they are simple to produce, inexpensive, and allow covering many applications. However, due to new regulations regarding the protection of human health and the environment, they are doomed to disappear.

[0003] To replace these coatings and / or manufacturing methods, coatings based on tungsten carbide, steel, or cermet produced by plasma torch technology have been proposed. Nevertheless, they do not allow the production of thick coatings, particularly because of the degradation of the friction characteristics of the coatings and the formation of cracks.

[0004] Techniques of autocatalytic nickel plating or electrolytic nickel deposition have also been proposed, but they are expensive, and the coatings obtained have little corrosion resistance and / or degrade with temperature. Vapor deposition techniques are also not suitable because they do not allow the production of thick coatings and do not allow coating parts with complex geometries (i.e., non-planar). In addition, the required precursors are often dangerous, and the materials on which the coatings are deposited need to withstand temperatures above 700 °C.

[0005] Therefore, there is a desire to have an apparatus and a method for depositing a metal nitride coating with a thickness greater than 1 μm in order to coat parts with complex geometries and obtain a coating with good mechanical, chemical, and tribological properties that can withstand thermal aging, and the deposition method must also cause little harm to the operator and the environment. Summary of the Invention

[0006] The present invention relates to an apparatus for depositing a metal nitride having a thickness greater than or equal to 1 μm on a sample by supercritical fluid, the apparatus comprising:

[0007] - a first housing defined by an outer wall forming a first enclosed volume;

[0008] - a second housing defined by an inner wall forming a second enclosed volume, the second housing being placed in the first housing and intended to contain a fluid under supercritical conditions, and the material of the inner wall being permeable to electromagnetic radiation;

[0009] - a heat transfer dielectric fluid circulating in a first volume surrounding the second housing;

[0010] - A sample holder, which is present in the second volume and is configured to support the sample;

[0011] - An induction heating device, which is placed in the first housing and surrounds the second housing so as to be able to heat the sample placed on the sample holder;

[0012] - An inlet, which is configured to introduce a fluid into the second volume;

[0013] - An inlet, which is configured to introduce at least one precursor material into the second volume; and

[0014] - At least one outlet, which is configured to purify the second volume.

[0015] In the present invention, the fluid under supercritical conditions is a supercritical fluid, that is, a fluid at a temperature and pressure under supercritical conditions.

[0016] The device of the present invention allows the formation of a thick coating (greater than 1 μm) of metal nitride on a flat sample or on a sample with a complex geometry, while reducing the mechanical stress that partly causes delamination. In addition, metal nitrides, such as titanium nitride TiN and tantalum nitride TaN, can replace hard chromium and are thus more suitable for different aviation applications, such as engine or landing gear applications.

[0017] The induction heating device allows only the sample to be heated while keeping the temperatures on the inner and outer walls lower than the temperature of the sample. In fact, the fact that the inner wall is permeable to electromagnetic radiation allows avoiding inductive coupling with these walls and keeping them at a temperature colder than the temperature of the sample in order to control the convective movement inside the second housing. Therefore, the formation of metal nitride on the inner wall of the device is avoided, which saves reagents, such as precursor materials.

[0018] Induction heating also allows for a better yield than resistance heating, because it also allows heating the entire surface of a sample with a complex geometry in a faster and more uniform manner, or alternatively by limiting the maximum heating to a thickness close to the final surface of the part.

[0019] When the pressure and temperature conditions are met, the fluid under supercritical conditions (referred to as supercritical fluid) present in the second volume will promote convection inside the second housing to obtain heterogeneous nucleation, formation kinetics, and growth of metal nitride deposition on the sample surface, and the amounts of the reagents provided are significant and controllable.

[0020] According to a specific feature of the present invention, the material of the inner wall is ceramic. Most ceramics are permeable to electromagnetic radiation, so ceramics are excellent candidates for forming the inner wall.

[0021] According to another specific feature of the present invention, the first and second outer casings are closed by two caps made of 316L stainless steel.

[0022] Another object of the present invention is a method for depositing a metal nitride having a thickness greater than or equal to 1 μm on a sample by means of a supercritical fluid implemented by the device of the present invention, the method comprising at least the following steps:

[0023] - Placing the sample on a sample holder;

[0024] - Heating the sample by induction and heating the second volume by means of a dielectric heat transfer fluid;

[0025] - Introducing each precursor material and fluid into the second volume so that the precursor material and fluid react under supercritical conditions to form a metal nitride on the surface of the sample and grow the metal nitride formed on the surface of the sample; and

[0026] - Cooling and then depressurizing the second volume.

[0027] The method of the present invention implemented by the device of the present invention allows for the production of a thick deposit (greater than 1 μm) of metal nitride on a sample that can have a complex geometry, that is to say, a non-planar geometry.

[0028] According to one embodiment of the present invention, each precursor material and fluid is introduced into the second volume while the temperature of the sample is greater than or equal to 100 °C and the temperature of the inner wall is greater than or equal to 70 °C throughout the entire duration of the formation and growth of the metal nitride on the surface of the sample.

[0029] This allows for deposition in a semi - continuous or continuous mode, that is to say, the deposition increases as the precursor material and fluid are added and react under supercritical conditions in the second outer casing. This semi - continuous or continuous mode allows for precise control and regulation of the deposition and amount of the precursor material and fluid introduced, in order to better control the kinetics of the formation and growth of the metal nitride on the surface of the sample.

[0030] According to another embodiment of the present invention, each precursor material and fluid is introduced into the second volume when the temperature and pressure in the second volume are respectively greater than or equal to the critical temperature and pressure of the introduced fluid, and no precursor material and fluid are introduced during the growth of the metal nitride on the surface of the sample.

[0031] This allows for deposition in a closed mode.

[0032] According to a specific feature of the present invention, the sample is made of steel, or of a metal alloy, or of a conductive ceramic, or of a conductive polymer.

[0033] According to another specific feature of the present invention, the precursor material is an organometallic titanium or an organometallic tantalum. The advantage of using these precursor materials is to form a titanium nitride or tantalum nitride coating on the sample. In addition, these precursor materials are not very dangerous for the operator and are not very toxic.

[0034] According to another specific feature of the present invention, the fluid introduced into the second volume includes ammonia. Then, ammonia is used both as a nitrogen source and as a reducing agent for the precursor material containing the titanium or tantalum precursor.

[0035] According to another specific feature of the present invention, during the formation and growth of the metal nitride on the surface of the sample, the temperature of the inner wall is included between 90 °C and 200 °C.

[0036] According to another specific feature of the present invention, during the formation and growth of the metal nitride on its surface, the sample is heated to reach a temperature included between 100 °C and 800 °C.

[0037] According to another specific feature of the present invention, during the formation and growth of the metal nitride on the surface of the sample, in the second volume, the temperature is included between 90 °C and 800 °C, and the pressure is included between 1 MPa and 25 MPa, for example between 10 MPa and 25 MPa.

[0038] According to another specific feature of the present invention, the duration of the method is included between 1 minute and 60 minutes.

[0039] According to another specific feature of the present invention, the duration of the method is greater than 60 minutes. This allows increasing the thickness of the metal nitride formed on the surface of the sample. Description of the Drawings

[0040] With reference to the accompanying drawings, other features and advantages of the present invention will become apparent from the description given below, which illustrate embodiments of the implementation without any limiting features.

[0041] Figure 1 schematically and partially shows a cross-sectional view of a deposition apparatus according to the present invention.

[0042] Figure 2 schematically shows the steps of a deposition method according to an embodiment of the present invention.

[0043] Figure 3 schematically shows the steps of a deposition method according to an embodiment of the present invention. Detailed Description of the Invention

[0044] Throughout the specification, a supercritical fluid or a fluid under supercritical conditions is a fluid at a temperature and pressure under supercritical conditions.

[0045] FIG. 1 schematically and partially shows a cross-sectional view of a device according to the present invention.

[0046] Device 100 allows the deposition of a metal nitride coating on a sample 104. Device 100 includes a first outer casing 110 defined by an outer wall 101 forming a first enclosed volume V1. It also includes a second outer casing 120 defined by an inner wall 102 forming a second enclosed volume V2. The second outer casing 120 is included within the first outer casing 110.

[0047] A heat transfer fluid is placed in the first volume V1 and thus circulates around the second outer casing 120.

[0048] The second outer casing 120 is adapted to receive a supercritical fluid and is subjected to a temperature and pressure above the critical temperature and pressure of the supercritical fluid.

[0049] Device 100 also includes an inlet 150 capable of introducing a fluid into the second volume V2, which fluid will be a supercritical fluid and will thus be subjected to supercritical pressure and temperature conditions. It also includes an inlet 151 capable of introducing a precursor material into this same volume V2.

[0050] An outlet 152 is also present in device 100 to purify the second volume V2 and thus allow the continuous operation of deposition device 100.

[0051] A sample holder 105 is placed in the second outer casing 120 to support the sample 104 on which the coating is deposited. Preferably, the sample holder 105 is placed in the second outer casing 120 such that the sample 104 is held at the center of the inductor forming the induction heater 103. Preferably, the sample holder 105 has a shape that allows the sample 104 to be supported with a minimum number of contact points in order to coat the maximum possible surface of the sample with the deposited metal nitride coating and to limit interference in the induced convective flow. Preferably, the sample holder 105 is made of a material that limits heat loss, which is for example made of a material that is not thermally conductive and not electrically conductive.

[0052] The induction heater 103 is placed in the first outer casing 110 and surrounds the second outer casing 120. Inductive heating allows the sample 104 to be heated by restricting the heating of the precursor material present in the second volume V2.

[0053] In order not to interfere with the heating of the sample 104 by induction, the inner wall 102 is permeable to electromagnetic radiation. For example, they are made of ceramic. The ceramic used can be boron nitride, aluminum nitride, alumina or silicon nitride. These embodiments of dense and non-porous ceramics allow the inner wall 102 to have excellent mechanical strength and thus withstand the pressure present in the second volume V2.

[0054] In order not to reduce the induction yield, the heat transfer fluid present in the first volume V1 is dielectric. For example, the heat transfer fluid can be synthetic oil, air or even nitrogen.

[0055] According to a particular feature of the invention, O-rings 130, 131, 132 and 133 can be present at the ends of the two housings 110 and 120 in order to ensure the tightness of the two housings 110, 120. For example, these seals 130 to 132 are made of ethylene-propylene-diene monomer (EPDM) or of Kalrez 6375.

[0056] According to another particular feature of the invention, covers 140 and 141 can be present at the ends of the two housings 110 and 120 in order to close them. Advantageously, only one of the two covers 140 and 141 is movable. For example, these covers can be made of steel, and more particularly of 316L steel.

[0057] Figure 2 shows the steps of a method for depositing a thick metal nitride coating according to an embodiment of the invention, in particular for a method of depositing a coating in semi-continuous mode.

[0058] In a first step 201, the sample on which it is desired to form a metal nitride coating is placed on a sample holder in the second housing.

[0059] Then, in the next step 202, the sample is heated by induction using an induction heating device. In this step, the second volume is also heated by means of a dielectric heat transfer fluid.

[0060] Then, once the temperature of the sample T 样品 reaches at least 100 °C and the temperature of the inner wall T 壁 reaches at least 70 °C, the introduction of the precursor material and the fluid into the second housing is started (step 203). Then, the introduced fluid will be subjected to supercritical conditions in the second housing.

[0061] During the introduction of the precursor material and the fluid, the sample and the second volume continue to be heated by induction. This allows the supercritical conditions necessary for the formation of the metal nitride on the sample surface of the introduced fluid to be reached near the sample.

[0062] Thus, the precursor material and the introduced fluid react under supercritical conditions to form a metal nitride on the sample surface by chemical reaction of the seeds (step 204). During the entire period of formation and growth of the metal nitride on the sample surface, the precursor material and the fluid are introduced into the second housing. Thus, the formation of the metal nitride on the sample surface occurs in semi-open or continuous mode. This allows the amount of precursor material and fluid to be adjusted as the metal nitride layer grows.

[0063] When the growth of the continuous layer of metal nitride is complete, i.e., when the thickness of the metal nitride is reached, the second enclosure is cooled (step 205) before decompressing the second enclosure.

[0064] Figure 3 shows the steps of a method for depositing a thick metal nitride coating according to another embodiment of the present invention, particularly for depositing the coating in a closed mode.

[0065] In a first step 301, a sample on which a metal nitride coating is desired to be formed is placed on a sample holder in the second enclosure.

[0066] Then, in the next step 302, the sample is heated by induction using an induction heating device. In this step, the second volume is also heated by means of a dielectric heat transfer fluid.

[0067] Once the temperature and pressure (T, P) inside the second enclosure 第二容积 reach at least the critical temperature and pressure (T, P) of the fluid to be introduced c , the precursor material and the fluid, which will thus be placed under supercritical conditions, are introduced into the second enclosure (step 303).

[0068] Then, the precursor material and the supercritical fluid will react, and metal nitride will be formed on the sample surface through a chemical reaction of the seeds, so as to form a continuous layer that will grow throughout the reaction duration. During this reaction step 304, no precursor material or fluid is added. The formation of metal nitride on the sample surface occurs in a closed mode.

[0069] When the growth of the continuous layer of metal nitride is complete, i.e., when all the precursor material has reacted, the second enclosure is cooled (step 305) before decompressing the second enclosure.

[0070] Irrespective of the embodiment, the sample can be made of steel, can be made of a metal alloy, or can be made of a conductive ceramic or a conductive polymer.

[0071] Irrespective of the embodiment, the precursor material can be a halide or an organometal. The precursor material can particularly be a titanium organometal or a tantalum organometal, such as titanium tetrakis(dimethylamido) TDMAT or titanium tetrakis(diethylamido) TDEAT. Thus, for example, with a titanium organometal as the precursor, a titanium nitride coating can be formed on the surface of the sample; or a tantalum nitride coating can be formed with a tantalum organometal as the precursor material.

[0072] Irrespective of the embodiment, the supercritical fluid, i.e., the fluid introduced into the second enclosure, may comprise ammonia, ethanol, methanol, carbon dioxide, dinitrogen, argon, alkanes, toluene or a mixture of these fluids. If the precursor material is TDMAT or TDEAT, ammonia is preferably selected as the supercritical fluid because these precursors have good solubility in this medium and the reducing properties of ammonia allow obtaining the stoichiometry of the desired nitride.

[0073] In the case of the method described with reference to Figure 3, if ammonia is selected as the supercritical fluid, the precursor material and ammonia are introduced into the second enclosure (step 303) when the temperature reaches at least 132.3 °C and the pressure 11.3 MPa, these thresholds corresponding to the critical temperature and pressure values of ammonia.

[0074] Irrespective of the embodiment, during the formation and growth of the metal nitride on the sample, the temperature of the inner wall may vary between 90 °C and 200 °C (step 204 or 304).

[0075] Irrespective of the embodiment, during step 204 or 304, the temperature of the sample may vary between 100 °C and 800 °C.

[0076] Irrespective of the embodiment, during step 204 or 304, the temperature of the supercritical fluid, and thus of the second volume, may vary between 90 °C and 800 °C in the vicinity of the sample.

[0077] Irrespective of the embodiment, during step 204 or 304, the pressure in the second volume may vary between 1 MPa and 25 MPa, for example between 10 MPa and 25 MPa.

[0078] Irrespective of the embodiment, the method of the invention may last between 1 minute and 60 minutes, or even longer if necessary, depending on the desired thickness of the metal nitride deposition.

[0079] Whether in semi-open or continuous mode (method described with reference to Figure 2) or in closed mode (method described with reference to Figure 3), the method according to the invention allows obtaining a continuous, dense and uniform metal nitride coating on the surface of a sample that may have a complex three-dimensional geometry, i.e., non-planar.

[0080] The expression "comprising between... and..." must be understood as including these limit values.

Claims

1. An apparatus for depositing a metal nitride having a thickness greater than or equal to 1 μm on a sample by a supercritical fluid, comprising: - A first outer shell defined by an outer wall forming a first enclosed volume; - A second outer shell defined by an inner wall forming a second enclosed volume, the second outer shell being placed in the first outer shell and being adapted to contain a fluid under supercritical conditions, and the material of the inner wall being permeable to electromagnetic radiation; - A heat-transfer dielectric fluid circulating in the first volume around the second outer shell; - A sample holder present in the second volume and configured to support the sample; - An induction heating device placed in the first outer shell and surrounding the second outer shell so as to be able to heat the sample placed on the sample holder; - An inlet configured to introduce a fluid into the second volume; - An inlet configured to introduce at least one precursor material into the second volume; And - At least one outlet configured to purify the second volume.

2. The device according to claim 1, wherein, The material of the inner wall is ceramic.

3. The apparatus according to claim 1, wherein, The first outer shell and the second outer shell are closed by two caps made of 316L stainless steel.

4. A method for depositing a metal nitride having a thickness greater than or equal to 1 μm on a sample by a supercritical fluid, implemented by the apparatus according to claim 1, the method comprising at least the following steps: - Placing the sample on the sample holder; - Heating the sample by induction and heating the second volume by a dielectric heat-transfer fluid; - Introducing each precursor material and the fluid into the second volume so that the precursor material and the fluid react under supercritical conditions to form a metal nitride on the surface of the sample and to grow the metal nitride formed on the surface of the sample; And - Cooling the second volume and then depressurizing the second volume.

5. The method according to claim 4, wherein Throughout the duration of the formation and growth of the metal nitride on the surface of the sample, each precursor material and the fluid are introduced into the second volume when the temperature of the sample is greater than or equal to 100°C and the temperature of the inner wall is greater than or equal to 70°C.

6. The method according to claim 4, wherein Each precursor material and the fluid are introduced into the second volume when the temperature and pressure in the second volume are respectively greater than or equal to the critical temperature and pressure of the supercritical fluid, and no precursor material and supercritical fluid are introduced during the growth of the metal nitride on the surface of the sample.

7. The method according to claim 4, wherein The sample is made of steel, or a metal alloy or a conductive ceramic or a conductive polymer.

8. The method according to claim 4, wherein The precursor material is a titanium organometal or a tantalum organometal.

9. The method according to claim 4, wherein The fluid introduced into the second volume includes ammonia.

10. The method according to claim 4, wherein, During the formation and growth of the metal nitride on the surface of the sample, the temperature of the inner wall is included between 90°C and 200°C.

11. The method according to claim 4, wherein During the formation and growth of the metal nitride on its surface, the sample is heated to reach a temperature included between 100°C and 800°C.

12. The method according to claim 4, wherein During the formation and growth of the metal nitride on the surface of the sample, in the second volume, the temperature is included between 90°C and 800°C and the pressure is included between 10 MPa and 25 MPa.

13. The method according to claim 4, wherein During the formation and growth of the metal nitride on the surface of the sample, in the second volume, the temperature is included between 90°C and 800°C and the pressure is included between 1 MPa and 25 MPa.

14. The method according to claim 4, wherein, The duration of the method is included between 1 minute and 60 minutes.

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