Method for forming a coating by chemical vapour deposition

Abstract

A method of depositing a coating by a chemical vapor deposition method in a reactor, the method comprising: forming a bond coating on a surface of the substrate (20), from a precursor comprising silicon, and inserting a Lewis acid into the reactor when forming the bond coating.

Description

Description Title of the invention: method of forming a coating by chemical vapor deposition Technical Field

[0001] This disclosure relates to the field of coatings and more particularly to that of processes for forming coatings by chemical vapor deposition (or CVD), in particular for protecting ceramic-based substrates from aggressive environments. Prior art

[0002] Ceramic matrix composite (CMC) materials, and in particular those based on carbide (generally called SiC / SiC) have been proposed for numerous applications, and in particular for the production of gas turbine parts, such as blades and nozzles. Indeed, thanks to their heat-resistant properties, these materials make it possible to reduce or even eliminate the cooling traditionally used in metal turbine parts based on nickel and / or cobalt, while allowing an increase in operating temperatures.

[0003] However, in the corrosive environment of a turbine, SiC / SiC CMCs can be subject to oxidation resulting in the formation of silicon oxide, and the volatilization of this silicon oxide under the effect of water vapor. Thus, for applications at intermediate temperatures (between 800°C and 1400°C) in an environment rich in oxygen and water vapor, the application of a protective coating is recommended on ceramic matrix composite parts.

[0004] For this, the protective coating may typically comprise a barrier coating or environmental barrier coating (EBC), for example based on silicate of rare earth and, between the substrate and the barrier coating, a bond coating, for example silicon-based, to ensure adhesion of the barrier coating to the substrate. The oxidation of the silicon in the bond coating can also form an intermediate layer of silica, called thermal growth oxide (TGO), between the bond coating and the barrier coating.

[0005] The deposition of such a primer coating on a substrate can be carried out by a CVD process, in a suitable reactor, comprising a reaction chamber. Typically, EBCs can be obtained from halogenosilane precursors, such as for example HSiCl3. This type of precursor is preferred because it makes it possible to obtain primer coatings having satisfactory properties in terms of substrate protection.

[0006] However, this type of precursor is likely to form pyrophoric species, which are deposited on the reactor walls. These species are flammable in air, or even explosive. They represent a significant risk for an operator who must open the reactor to clean the pipes downstream of the reaction chamber. These risks are a considerable obstacle to the industrialization of the coating deposition process, and therefore, more generally, to the industrialization of SiC / SiC parts for application in a turbomachine.

[0007] There is therefore a need to improve the process to compensate, at least in part, for these aforementioned defects. Statement of the invention

[0008] The present disclosure relates to a method of depositing a coating by a chemical vapor deposition method in a reactor, the method comprising forming a primer coating on a surface of a substrate, from a precursor comprising silicon, and inserting a Lewis acid into the reactor during formation of the primer coating.

[0009] The inventors were able to empirically observe that the introduction of a Lewis acid during the formation of the bonding coating makes it possible to reduce - or even eliminate the formation of pyrophoric species downstream of the reaction chamber. Thus, the safety of the process is greatly improved.

[0010] In addition, such a secure process is simpler to industrialize because risk control makes it possible to considerably simplify the implementation of the process for the operator.

[0011] In some embodiments, the reactor comprises a hot chamber having an upstream and a downstream and configured to receive a substrate, an inlet channel connected to the upstream of the hot chamber configured to convey gases into the hot chamber; an outlet channel connected to the downstream of the hot chamber configured to evacuate gases from the hot chamber.

[0012] More generally, the species resulting from the reaction at the outlet of the hot chamber are designated under the name of “effluent gases”

[0013] The use of such a device facilitates the implementation of the process.

[0014] In some embodiments, the reactor includes a secondary inlet channel connected downstream of the hot chamber, and wherein Lewis acid is introduced into the reactor through the secondary inlet channel.

[0015] Thus, the insertion of Lewis acid does not disturb the formation of the bonding coating. It therefore becomes possible to inhibit the formation of pyrophoric species without modifying the bonding coating deposition conditions.

[0016] In some embodiments, the Lewis acid is introduced upstream of the hot chamber, together with the precursor comprising silicon.

[0017] Thus, it is possible to dope the bonding coating. For example, the bonding coating can be doped with boron. Such a coating can, depending on the application, have advantages, such as improved creep resistance.

[0018] In some embodiments, the flow rate of Lewis Acid in the reactor is greater than or equal to 1 sccm, preferably greater than or equal to 5 sccm, even more preferably greater than 10 sccm.

[0019] It is recalled that the sccm unit designates a flow rate expressed in "standard cubic centimeters per minute", which measures a flow rate of a fluid in cubic centimeters per minute, flowing under standard temperature and pressure conditions.

[0020] In this configuration, the inhibition of the formation of pyrophoric species is improved. Generally, the higher the Lewis acid flow rate, the more the formation of pyrophoric species is inhibited.

[0021] In some embodiments, the Lewis acid is one of BX3 or AlX3, where X is halogen.

[0022] The use of these Lewis acids is particularly suitable for the present process. In particular, these chemical species react optimally with precursors comprising silicon, which increases the inhibition of the formation of pyrophoric species.

[0023] The above-mentioned features and advantages, as well as others, will become apparent from the following detailed description of examples of embodiments of the device and the proposed method. This detailed description refers to the attached drawings. Brief description of the drawings

[0024] The attached drawings are schematic and are intended primarily to illustrate the principles of the presentation.

[0025] [Fig.1] Figure 1 schematically represents a method of forming a coating by chemical vapor deposition according to one embodiment of the invention.

[0026] [Fig.2] Figure 2 schematically represents a chemical vapor deposition reactor according to a first embodiment.

[0027] [Fig.3] Figure 3 schematically represents a chemical vapor deposition reactor according to a second embodiment.

[0028] [Fig.4] Figure 4 is a graph showing the evolution of the concentration of certain chemical species in the reactor as a function of the flow rate of BCl3 introduced into said reactor. Description of the embodiments

[0029] In order to make the disclosure more concrete, an example of a device is described in detail below, with reference to the attached drawings. It is recalled that the invention is not limited to this example.

[0030] Figure 1 schematically represents a method of forming a coating by chemical vapor deposition according to one embodiment of the invention. The method comprises the formation of a primer coating E1 and the formation of a barrier coating E2.

[0031] By way of non-limiting example, the formation of the barrier coating E2 is carried out by thermal spraying or by electrophoresis. A layer of A2Si2O7 where A is for example Re, Yb or Y, can be deposited in this way.

[0032] The formation of the bonding coating is carried out by a chemical vapor deposition (CVD) process.

[0033] Figure 2 schematically represents a reactor 10 capable of forming the bonding coating by CVD on a substrate 20. The reactor 10 comprises an inlet channel 101 placed upstream of a hot chamber 103 and an outlet channel 105 placed downstream of the hot chamber 103. In addition, the reactor 10 comprises a casing 104 attached to the outlet channel 105.

[0034] Furthermore, the formation of the bonding coating E1 comprises on the one hand the insertion E1' of a precursor comprising silicon into the reactor 10 and on the other hand the insertion E1'' of a Lewis acid into the reactor 10. Advantageously, the insertions of the precursor and the Lewis acid into the reactor are simultaneous.

[0035] With reference to Figure 2, the Lewis acid can be introduced upstream of the hot chamber 103, together with the precursor comprising silicon. Under these circumstances, the bonding coating can be doped with an element of the Lewis acid. For example, if the Lewis acid is BCl3, the bonding coating can be doped with boron.

[0036] Alternatively, with reference to FIG. 3, a reactor 10 according to a second embodiment may comprise a secondary inlet channel 107 connected downstream of the hot chamber. In these circumstances, the Lewis acid is introduced into the reactor 10 through the secondary inlet channel 107.

[0037] By way of non-limiting example, the precursor may be an organosilicon precursor such as HSiCl3. The Lewis acid may be, for example, BCl3, BF3 or AlCl3.

[0038] [Essays and examples]

[0039] In order to highlight the role of Lewis acid in inhibiting the formation of pyrophoric species, several processes were carried out in the reactor of Figure 2.

[0040] For each of these tests, the temperature of the hot chamber was set at 1000°C, the pressure was set at 5kPa and a flow rate of 66 sccm of HSiCl3 was imposed between the inlet channel 101 and the outlet channel 105. Three different tests were carried out, in which there was a respective flow rate of 0 sccm, 1 sccm and 10 sccm of BCl3 between the inlet channel 101 and the outlet channel 105. At the end of each test, the casing 104 was observed to measure the deposit of pyrophoric species, which is weighed.

[0041] For the control test at 0 sccm of BCl3, pyrophoric species were deposited on the casing 104. The mass of the pyrophoric species deposit is of the order of a gram. The opening of the reactor 10 is accompanied by a release of HCl.

[0042] For the 1 sccm BCl3 test, the deposition of pyrophoric species on the casing 104 is low, or even non-existent. The mass of the pyrophoric species deposit is of the order of 0.01g.

[0043] For the 10 sccm BCl3 test, the deposition of pyrophoric species on the 104 housing is very low, or even non-existent. The mass of the pyrophoric species deposit is less than 0.01g.

[0044] It is therefore concluded that BCl3 inhibits the formation of pyrophoric species.

[0045] BCl3, and more generally Lewis acids, therefore appear to interfere in the process of formation of polysilanes at the origin of the formation of pyrophoric species.

[0046] As a reminder, the temperature of the hot chamber 103 in operation makes it possible to stabilize species that are not stable at room temperature. Thus, the use of precursors comprising silicon can cause silicon to appear in a singlet state, comprising a non-bonding doublet. In the example of the precursor HSiCl3, SiCl2 can be formed.

[0047] Under these circumstances, the following polymerization reaction occurs within the hot chamber 103.

[0048] [Chem 1]

[0049] ^^^ ^^ ^^^^ ^^ ^^ − ^^^^^ ^^ ^^^^ ^^ + ^^^^ ^ → ^^^ ^^ ^^^^ ^^ ^^ − ^^^^ ^ − ^^^^^ ^^ ^^^^ ^^

[0050] Silicon in the singlet state then acts as a Lewis base.

[0051] Without wishing to be bound by any theory, the inventors assume that the addition of a Lewis acid, for example BCl3, in the reactor 10 allows a new chemical reaction which competes with the polymerization reaction.

[0052] [Chem 2]

[0053] ^^^^ ^ + ^^^^ ^ → ^^ ^ ^⋯^^^^ ^

[0054] This reaction creates an adduct that is able to dissociate at low temperatures to reform species such as SiHCl3, SiH2Cl2, or HBCl2. These species are easier for the operator to handle and can be simply removed by suction during the reaction cycle.

[0055] Other reaction hypotheses can be considered. For example, it is conceivable that the presence of BCl3 opens other reaction pathways to SiCl2. Indeed, SiCl2 can react directly with BCl3 to form SiCl3BCl2. This reaction can, in a similar way, compete with the SiCl2 polymerization reactions mentioned above. In such circumstances, observation would show that in this case, the formation of light boron species is favorable compared to heavier polymeric species.

[0056] Furthermore, in the presence of excess hydrogen (which is the case in the present reactor), BCl3 is reduced to BHCl2 at around 800°C. Thus, it is conceivable that other reactions with BHCl2, similar to those possible with BCl3, lead to species such as SiCl3BHCl, the presence of which has been observed. In all circumstances, such a mechanism provides for the formation of the same gaseous species, which are not deposited on the walls of the reactor.

[0057] Figure 4 represents the evolution of the concentration of certain chemical species at the outlet of reactor 10 as a function of the flow rate of BCl3 introduced into said reactor 10. These measurements were carried out under the same conditions as the tests discussed previously.

[0058] It is observed that the introduction of BCl3 into reactor 10, even at low flow rate, promotes the formation of the species SiHCl3, SiH2Cl2 or HBCl2, mentioned above, which seems to confirm that there is indeed competition between the formation of gaseous species and polymerization, thereby inhibiting the formation of pyrophoric species.

[0059] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0060] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device.

Claims

Claims

1. A method of depositing a coating by a chemical vapor deposition method in a reactor, the method comprising: forming a primer coating on a surface of a substrate (20), from a precursor comprising silicon, and inserting a Lewis acid into the reactor during the formation of the primer coating.

2. The method of claim 1, wherein the reactor comprises: a hot chamber having an upstream and a downstream and configured to receive the substrate, an inlet channel connected to the upstream of the hot chamber configured to convey gases into the hot chamber; an outlet channel connected to the downstream of the hot chamber configured to evacuate gases from the hot chamber.

3. The method of claim 2, wherein the reactor comprises a secondary inlet channel connected downstream of the hot chamber, and wherein the Lewis acid is introduced into the reactor through the secondary inlet channel.

4. The method of claim 1 or 2, wherein the Lewis acid is introduced upstream of the hot chamber, together with the precursor comprising silicon.

5. The method of one of claims 1 to 4, wherein the flow rate of Lewis acid in the reactor is greater than or equal to 1 sccm, preferably greater than or equal to 5 sccm, even more preferably greater than 10 sccm.

6. The method of one of claims 1 to 5, wherein the Lewis acid is one of BX3 or AlX3, where X is a halogen.

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