FR2736361A1 - Low friction carbon@-silicon@-hydrogen@ complex thin film - produced by plasma-CVD e.g. on metal pinion or bearing part. - Google Patents

Abstract

A novel, low friction coefft., chemically stable, complex thin film, based on carbon, silicon and hydrogen, contains 30 wt.% hydrogen and has C : Si atomic ratio 1.4-3.3, pref. 2.4-2.5. Also claimed is a very low friction coefft. pt. having a substrate consisting of a material unaffected by heating at 500-600 [deg]C and which has surface coating of the above complex thin film, pref. with an intermediate nitrided, carburised or carbonitrided layer between the substrate and the surface coating. Further claimed is a process for coating a substrate with the complex thin film by microwave plasma-enhanced CVD.

Description

THIN LAYER COMPLEX, PIECE WITH LOW COEFFICIENT OF
FRICTION COATED WITH SUCH A LAYER AND METHOD OF
ACHIEVING SUCH A PIECE.

DESCRIPTION
Technical area
The invention mainly relates to a complex thin layer, chemically stable and having a low coefficient of friction, based on carbon, silicon and hydrogen.

 The invention also relates to a very low friction part comprising a substrate of any material, such as an alloy of iron or titanium, unaltered by a temperature rise between about 5000C and about 6000C, and a coating of surface constituted by such a complex thin layer.

 In addition, the invention also relates to a method for producing a surface coating, in the form of such a complex thin layer, on a substrate, by microwave vapor-activated chemical vapor deposition.

 The low coefficient of friction of the complex thin film according to the invention, as well as its chemical stability makes it possible to envisage its use in many industrial fields, since parts in contact are called to move one another. relative to each other either continuously or intermittently. Thus and only by way of example, the invention can in particular be used to make gearing or rolling parts.

State of the art
In general, it is customary to modify the surface properties of a part by a surface treatment, in order to adapt this part to the intended applications.

 A well-known technique for performing such a surface treatment consists in depositing a coating on the surface of the parts by chemical deposition from a vapor phase. This technique consists in placing the part in a vacuum chamber and providing on the surface of this part the constituent elements of the material in which it is desired to effect the coating, by means of a reactive gas phase.

 When the chemical vapor deposition is activated by a plasma such as a microwave plasma, it becomes possible to deposit polyatomic combinations at low temperature. This makes it possible to maintain the entirety of the mass properties of the substrates that one wishes to cover.

 When the chemical vapor deposition is activated by a plasma, the latter can be obtained by a microwave system or by a radiofrequency system. In all cases, a reactive gas, also called "precursor", is injected, alone or in mixture, into the chamber and forms a plasma which facilitates the deposition on the part of the atoms initially contained in the reactive gas.

Various studies have shown the influence of temperature on the nature, the morphology and the microstructure of the layers deposited on the part according to this technique. In this connection, we can cite the study by F. Demichelis et al. "Hydrogen diffusion and related defects in hydrogenated amorphous silicon carbide" in the journal "Journal of Non-Crystalline
Solids, 128: 133-138 (1991), and the study of HYLU et al., "Effects of temperature and biostructure of plasma deposited amorphous silicon carbide" in the Journal of Applied Physics, 72, 5, pages 2054 to 2056 (1992), which show that below a critical deposition temperature, atoms initially contained in the reactive gas, such as hydrogen, chlorine and oxygen can remain trapped in the deposited layers and play a detrimental role vis-à-vis the desired properties.
US-A-4 981 071, which shows that the temperature has a significant influence on the microstructure of the deposited layers.

 US-A-4 981 071 teaches the possibility of using a plasma-enhanced chemical vapor deposition process to obtain a coating which contains both carbon and silicon from reactive gas mixtures. containing silicon, carbon and hydrogen.

 US-A-5,061,514, EP-A-0 448 227, US-A-5,011,706 and FR-A-2,584,098 also propose using the plasma-activated chemical vapor deposition technique to realize deposits containing amorphous silicon carbide. These documents generally relate to applications in the electronic field and cite the abrasion resistance and corrosion properties of the coatings obtained.

 US-A-5 198 285 also relates to the production of a complex thin layer, based on carbon, silicon and hydrogen, by plasma-enhanced chemical vapor deposition. More specifically, the composition of the coating obtained, which is characterized in particular by the presence of 70 to 90% of carbon atoms in the total composition of the coating outside of hydrogen, has a very low coefficient of friction, of about 0.04 to 0.05.

However, the process used to make the deposit imposes the presence of 30 to 50% of hydrogen atoms.

This high percentage of hydrogen leads to a relatively poor chemical coating stability, especially when the temperature rises. It is therefore to be expected that the initial properties of the coating, particularly its friction characteristics, will be relatively quickly lost, especially when the coating is to be used in a corrosive external environment and / or in the absence of a lubricant. liquid.

 In US-A-5,370,912, the microwave plasma-enhanced chemical vapor deposition technique is used to deposit a diamond film on a substrate. More specifically, the substrate is placed in an enclosure whose upper partition is movable and in which microwaves are emitted by a coaxial antenna whose penetration length is adjustable. The reactive gases, consisting of a mixture of hydrogen and methane, are introduced into the chamber by an annular injector placed around the substrate, substantially at the same level as the latter. The heating of the substrate, at a temperature preferably between 950 ° C. and 11 ° C., is provided directly by the plasma and by a block of graphite on which the substrate rests, this graphite block being itself heated by the plasma more rapidly than the substrate.

 In this document US-A-5 370 912, the nature of the substrate is not specified. It is clear that the temperature of about 1000 ° C reached during the deposition renders the process described practically inapplicable to a substrate capable of degrading at such a temperature, that is to say, in particular to a substrate made of alloy based on iron or titanium.

 Despite the crucial role played by the temperature during deposition, as well as with regard to the nature, morphology and microstructure of the deposited layers as regards the maintenance of the integrity of the substrate, it appears that none of the prior art plasma-enhanced chemical vapor deposition techniques independently provide satisfactory control of microwave power and substrate temperature.

 Furthermore, none of the existing techniques makes it possible to deposit on a substrate a complex thin layer based on carbon, silicon and hydrogen having both a low coefficient of friction, good mechanical characteristics (especially hardness) and a chemically stable structure capable of keeping its friction properties in a corrosive atmosphere and when the temperature rises.

Presentation of the invention
The invention firstly relates to a complex thin layer based on carbon, silicon and hydrogen, having both a low coefficient of friction and a chemical stability ensuring the maintenance of its properties under corrosion and temperature.

 The second object of the invention is a low friction part comprising a substrate provided with a surface coating consisting of a complex thin layer having the above properties.

 In addition, the third object of the invention is a method for producing on a substrate a surface coating in the form of a complex thin film having the above characteristics, by chemical vapor deposition activated by a microporous plasma. waves.

 According to the invention, the first of these objects is achieved by means of a complex thin layer, chemically stable, with a low coefficient of friction, based on carbon, silicon and hydrogen, characterized in that it comprises less than 30% of hydrogen atoms and a C / Si ratio, between the number C of carbon atom and the number Si of silicon atoms, of between about 1.4 and about 3.3.

 In this complex thin layer, the C / Si ratio is preferably between about 2.4 and about 2.5.

 According to the invention, the second object is achieved by means of a very low friction part, comprising a substrate of a material which is not altered when heated to a temperature of between about 5000C and about 600 ° C and a surface coating covering this substrate, characterized in that the surface coating is a complex thin film as defined above.

 Preferably, the part further comprises a nitrided, carburized or carbonitrided intermediate layer interposed between the substrate and the surface coating.

According to the invention, the third object is achieved by means of a process for producing a surface coating, in the form of a complex, chemically stable, low-friction, carbon-based, thin layer of silicon and hydrogen, on a substrate of a material which is not altered when heated to a temperature between about 500 ° C and about 6000 ° C by chemical vapor deposition, activated by a microwave plasma, characterized in that it comprises the following successive steps - placing the substrate on a support, in a
enclosure having a density plasma area
maximum, called the active zone, in a first re
of the enclosure outside the active zone
and inside a dump area fit to tale
to establish a plasma - establishment of a primary vacuum within
the enclosure; stripping of the substrate by injection of a deca gas
page, establishment of a plasma of this gas, in the
discharge zone, and separate heating of the substrate to
a regulated temperature of between about 5000C
and about 600 ° C; deposition of said coating by injection of a reactive gas
in a second area of the enclosure located between
the substrate and the active zone, or in a limited area
trophe of this active zone, turned to the subs
said reactive gas comprising a compound which is unique to
tetrahedral silicon environment, so that
replace the plasma of the stripping gas with a plasma of
reactive gas while maintaining the heating of the subs
treated at said regulated temperature; and - interruption of the injection of the reactive gas and cooling
substrate degradation, after a duration of injection
predetermined, corresponding to a desired thickness
coating.

 The stripping gas is advantageously argon, to which may be added hydrogen.

 Moreover, the reactive gas advantageously comprises tetramethylsilane mixed with argon.

Alternatively, this reactive gas may also contain hydrogen.

 In particular in order to improve the adhesion of the complex thin film to the substrate, the method according to the invention preferably comprises, between the steps of etching and deposition of the coating, a step of producing an intermediate layer by injection of a pretreatment gas in the second chamber region, said pretreatment gas containing the nitrogen element and / or the carbon element so as to substitute a pretreatment gas plasma for the stripping gas plasma. It is important to observe that the intermediate layer is then made in the chamber used for pickling and depositing the coating, virtually without interruption.

 In a preferred embodiment of the process, the pretreatment gas comprises at most about 20% nitrogen and / or methane, mixed with argon.

 The active zone may in particular be a microwave cavity located in a waveguide connected to a microwave generator that operates at a frequency of 2.45 GHz and whose power is set between about 150 W and about 500 W.

 The injection rate of the reactive gas during the deposition of the coating is preferably between about 0.01 I / h and about 0.3 I / h.

 Furthermore, the injection flow rate of the pickling gas during pickling of the substrate is preferably between about 0.5 l / h and about 10 l / h.

 In addition, the primary vacuum established inside the chamber advantageously corresponds to a pressure of between about 0.5 torr and about 2 torr.

Brief description of the drawings
We will now describe, by way of nonlimiting example, preferred embodiments of the invention, with reference to the accompanying drawings, in which:
- Figure 1 is a schematic view of a chemical vapor deposition installation activated by a microwave plasma, may be used for carrying out the deposition method according to the invention; and
- Figure 2 is an enlarged view showing the part of the installation of Figure 1 surrounding the substrate.

Detailed presentation of embodiments.

 The production, in accordance with the invention, of a complex, chemically stable, low-coefficient of friction layer, by chemical vapor deposition, activated by a microwave plasma, on a substrate made of a material such as an alloy based on iron or titanium, is obtained by means of an installation such as that which will now be described with reference to FIG.

 This installation comprises a sealed enclosure 10 which internally delimits a reaction chamber 11. In the embodiment shown, the enclosure 10 is a tubular enclosure of substantially vertical axis. Such an enclosure is particularly suitable for the manufacture of small parts. For larger pieces, the enclosure 10 may take a different geometry, especially in its upper half whose diameter may be substantially larger than in its lower half.

 In the top of its lower half, the enclosure 10 passes through a horizontal waveguide 12, a first end of which is connected to a variable power microwave generator 14. The microwaves produced by the generator 14 are conveyed by the waveguide 12 to a shorting piston 16 placed at the opposite end of the waveguide. The power reflected on this short-circuit piston is measured by a device 18 placed in the waveguide 12 at the output of the generator 14. A device 20 placed in the waveguide 12 immediately downstream of the device 18 of FIG. measurement of the reflected power, adjusts the impedance. The region of the reaction chamber 11 located in the waveguide 12 defines a microwave cavity corresponding to the shaded area 22 in FIG. 1. The microwave cavity 22 defines an active zone, in which the plasma has a maximum density.

 The waveguide 12 makes it possible to convey to the reaction chamber 11, in the form of surface waves, the energy necessary for the creation and maintenance of a stable discharge in the reaction chamber.

This stable discharge extends on both sides of the microwave cavity 22 to a height which depends on a certain number of parameters such as the power of the microwave generator 14, the pressure prevailing in the reaction chamber , the flow of gas injected, etc.

 In order to adjust the pressure in the sealed enclosure 10 to the desired value, the enclosure is connected to a vacuum system 24 such as a primary pump, by means of a pipe 26 opening, for example, in the top of the reaction chamber 11. The pressure established in the chamber 10 by the vacuum system 24 corresponds to a primary vacuum whose value, preferably between 0.5 torr and 2 torr, is measured and monitored by means of a device 26 mounted in branch on the pipe 26. In addition, a liquid nitrogen trap 30 is placed in this pipe 26 between the enclosure 10 and the branch on which is connected the device 28 for measuring and controlling the pressure.

 A support 32, on which is fixed the substrate 34 to be coated is mounted in the lower part of the upper half of the enclosure 10, by means of a mechanism schematically illustrated at 36 in Figure 1.

The mechanism 36 connects the support 32 to the ground and incorporates, outside the enclosure 10, a device 38 for measuring temperature. It is important to observe that the support 32 on which the substrate 34 to be coated is mounted is in a first region of the enclosure 10, located outside the microwave cavity 22 and within the suitable discharge zone. to contain the plasma, when the microwave generator 14 is in operation.

 The positioning of the substrate 34 to be coated outside the microwave cavity 22 makes it possible to separately ensure the heating of the substrate at a controlled temperature of between about 5000.degree. C. and about 600.degree. C., by means of separate heating means provided for this purpose. .

In the embodiment illustrated in FIG. 1, these separate heating means comprise an induction coil 40 placed coaxially around the enclosure 10, at the level of the substrate 34. This induction coil 40 is electrically connected to a generator 42 of frequency 10 KHz. it should be noted that, in a variant, and particularly in the case where the upper half of the enclosure 10 is of larger diameter, the induction coil 40 may be placed inside the enclosure 10 or replaced by another heating system such as an electrical resistance integrated in the support 32.

 In addition to the various components that have just been described, the installation illustrated in FIG. 1 comprises means making it possible to inject into the chamber 10 different gases necessary for the implementation of the method and in particular for the formation of the complex thin layer desired on the substrate 34.

 In the embodiment shown, these gas injection means mainly comprise an injection tube 44 which passes through the bottom of the enclosure 10 and travels along the vertical axis of the latter to open into a second region of the enclosure located between the substrate 34 and the microwave cavity 22 or in a zone adjacent to this cavity facing the substrate 34. Outside the enclosure 10, the tube 44 is connected to a flow meter system 46 allowing adjust the flow rate of the injected gas at will. This flowmetering system 46 is itself connected to a feed tube 48 of reactive gas or precursor, to a pickling gas feed tube 50 and, if appropriate, to a supply tube 52 for the feed gas. pretreatment.

The reactive gas or precursor injected by the feed tube 48 is a single organosilicon compound with a tetrahedral silicon environment. This compound is preferably tetramethylsilane
If (CH 3) 4 (usually designated by the abbreviation "TMS") Alternatively, it is also possible to use tetraethylsilane Si (C2Hs) 4 (usually designated by the abbreviation "TES") or any derivative of the TMS or TES obtained respectively by substitution of one or two ethyl or methyl groups in particular with hydrogen or with chlorine. The choice of TMS is based on the fact that it is a known compound, liquid, with high vapor pressure, easily handled and fairly stable in air.

 Moreover, the etching gas injected by the tube 50 is advantageously argon and the pretreatment gas injected by the tube 52 may in particular be hydrogen or nitrogen.

 It should be noted that the injection tube 44 may be replaced by any other injection means such as a ring-shaped or grid-shaped system comprising a plurality of injection nozzles, in particular in the case where the substrate to be coated is relatively large. This other injection means remains, however, placed in the second region of the enclosure defined above and must not obscure the discharge in which the substrate 34 is placed.

 Moreover, when the substrate to be coated is relatively large, it may also be necessary to provide a relative displacement between the injection system of the reactive gas such as the tube 44 and the support 32. For this purpose, the mechanism 38 supporting the support 32 may take a more complex shape than that shown schematically in Figure 1 and incorporate, for example, at least one motor providing a displacement of the support 32 in translation and / or rotation. Such arrangements are well known to those skilled in the art and will not be described in more detail.

 As has been shown on a larger scale in FIG. 2, the installation furthermore comprises a second plasmagene stripping gas injection tube 54 opening directly into the bottom of the enclosure 10. This second tube 54 is directly connected to the stripping gas injection tube 50 via the flow meter system 46, since the same gas (usually argon) is preferably used as stripping gas and carrier gas.

 The installation that has just been described makes it possible to coat a substrate 34, made of an unaltered material when heated between 5000.degree. C. and 6000.degree. C., with a complex, chemically stable, low-friction layer based on carbon, silicon and hydrogen, thanks to the use of a single reactive gas chosen from the group defined above. The coating, obtained by chemical vapor deposition activated by a microwave plasma, has the desired characteristics of mechanical strength and friction, particularly thanks to the placement of the substrate 34 in a first region of the enclosure for the separate heating. of this substrate at a controlled temperature, and thanks to the injection of the reactive gas in a second region of the enclosure which allows this reactive gas not to stay in the cavity for too long. This last characteristic makes it possible to avoid dissociation too much of the reactive gas and ensures, therefore, a good control of the nature, morphology and microstructure of the deposited layers. In other words, the mode of injection of the reactive gas ensures a moderate activation of this gas and allows a stability of the discharge with a minimum of deposition on the walls.

While allowing to work in an inexpensive primary vacuum, it also allows a high deposition rate and an optimal adhesion to the substrate and hardness.

 For the implementation of the invention, use is advantageously made of a microwave generator 14 delivering microwaves at a frequency of 2.45 GHz.

The power of the generator 14 is advantageously set between 150 W and 500 W, for example at a value of 350 W.

 As illustrated more precisely in FIG. 2, the upper end of the tube 44 through which the reactive gas is introduced into the chamber 10, can open into a zone bordering the microwave cavity 22 facing the substrate 34, or between the substrate 34 and this microwave cavity 22. This positioning is characterized by the distance b between the upper limit of the microwave cavity 22 of the end of the tube 44, parallel to the vertical axis common to the tube 44 and the enclosure 10, positively counted upward. By using TMS as a reactive gas and under the conditions of pressure, flow rates and microwaves power given elsewhere, this distance b is advantageously between about -1 cm and about 5.5 cm.

 In a comparable manner, the positioning of the substrate 34 outside the microwave cavity 22 and inside the discharge zone capable of containing the plasma may be characterized by the distance from which the end of the opening tube 44 separates. in the chamber 10 of the face of the substrate 34 facing this tube, along the vertical axis common to the tube 44 and the chamber 10, positively counted upwardly.

By using TMS as a reactive gas and under the conditions of pressure, flow rates and microwaves power otherwise given, this distance is advantageously between about 1 cm and about 6 cm.

Under these conditions, the Applicant has established that it is possible to form, on a substrate of a material such as an alloy based on iron or titanium, a surface coating consisting of a complex thin layer, chemically stable, having a low coefficient of friction and satisfactory mechanical characteristics allowing the prolonged use of such a coating on friction parts, dry or in the presence of a lubricant, even in the presence of a corrosive atmosphere. This coating is characterized by a ratio C between the number C of atoms of
If carbon and the number Si of relatively high silicon atoms, between about 1.4 and about 3.3 and preferably between about 2.4 and about 2.5. It is also characterized by a percentage of The low hydrogen content of the coating gives it high stability over time and makes it insensitive to a corrosive environment as well as to a high ambient temperature.

 The implementation of the installation described above with reference to FIGS. 1 and 2 will now be described in order to illustrate the conditions for obtaining such a coating.

 After having placed the substrate 34 to be coated on the support 32 and introduced this assembly into the enclosure 10, the operator begins by evacuating the enclosure.

 The operator then introduces argon in the chamber 10 through the tube 54, for example at a flow rate of 5 I / h, while adjusting the pressure inside the chamber to the desired value for the setting process, for example about 1 torr. This operation, schematized by the rectangle Ar in Figure 2, lasts approximately 10 min.

 When the desired pressure and argon flow conditions are reached, the operator actuates the microwave generator 14 at the desired power, for example 250 W. Thus, in the discharge zone of the enclosure 10 corresponding to the previously established pressure and flow rate, a purplish-violet argon plasma characteristic.

 The operator then activates the heating of the substrate 34 by means of the induction coil 40. The temperature of the substrate is thus raised to the desired value, between about 500 ° C. and about 6000 ° C.

 When all these conditions are established, the surface of the substrate is stripped. The duration of this stripping is about 10 minutes.

This stripping operation provides a clean surface, free of contamination harmful to the adhesion of the deposit. It should be noted that the argon which constitutes the stripping gas in the embodiment described can be replaced by any other ionizable gas which promotes desorption by the substrate as a result of the formation of volatile species. Thus, under otherwise identical conditions, the gas used during the etching may consist of a mixture of hydrogen and argon.

 This stripping step is advantageously followed by a step during which an intermediate layer is produced on the substrate, in order to form on the latter a diffusion layer or a layer which precipitates phases which may or may not have a common element. with the subsequent realization.

It should be noted, however, that this step of producing an intermediate layer on the substrate is optional and can therefore be omitted in the case of the manufacture of certain parts.

 When it is desired to carry out the production of an intermediate layer on the surface of the substrate 34, the operating conditions generally remain unchanged and the passage at this stage simply results in stopping the injection of argon by the tube 54. and by introducing a pretreatment gas through the tube 44. This pretreatment gas can in particular comprise at most about 20% of nitrogen and / or methane, mixed with argon which then serves as a carrier gas. More generally, the pretreatment gas may be any pure or mixed gas containing the nitrogen element and / or the carbon element. A nitrided, carburized or carbonitrided diffusion layer is thus rapidly produced on the surface of the substrate 34. By way of example, a nitrided diffusion layer 60 μm thick is obtained in 5 min at a pressure of 0.5 torr with a total flow rate of 5.1 l / h of a gaseous mixture of argon and nitrogen comprising 1.7% nitrogen, the substrate being maintained at a temperature of 5500C. This intermediate layer considerably improves the adhesion of the subsequent complex layer based on carbon and silicon, since the thickness thereof can be quadrupled compared to the case of a coating deposited directly on the substrate. It should be noted that the reduction of at least one of the factors that constitute the nitrogen flow rate, the pretreatment time and the substrate temperature makes it possible to obtain only a diffusion layer.

 This step of producing an intermediate layer is illustrated by the rectangle Ar + N2 in FIG.

 Following this step of producing an intermediate layer or following the pickling step if the step of producing an intermediate layer has been omitted, the operator proceeds to deposit the coating formed by the layer thin complex defined above, still without leaving the substrate of the enclosure 10 and, generally, without changing the operating conditions such as the temperature, pressure and power of the microwave generator.

 The deposition of the coating is obtained by stopping the injection of the pretreatment gas through the tube 44 and injecting through this tube the reactive gas. As already indicated, this reactive gas is advantageously constituted by tetramethylsilane, mixed with argon in variable proportions depending on the characteristics of the coating that is desired to achieve. The injection of the mixture may especially be carried out at a flow rate of approximately 0.5 l / h. This step is illustrated by the rectangle Ar + TMS in FIG. 2. Its duration is directly proportional to the thickness of the layer that it is desired to form on the substrate 34. The operating conditions make it possible to ensure particularly rapid deposition. characterized by a deposition rate of about 20 μm / h. A layer of about 5 μm can be deposited in about 15 minutes.

 It should be noted that hydrogen can be added to the reactive gas during this step, for example at a flow rate of between about 1 I / h and 3 I / h. As will be seen in more detail below, this supply of hydrogen in the reactive gas is beneficial with respect to the hardness of the deposited layer but reduces the deposition rate and tends to increase the coefficient of friction.

 The treatment of the substrate is completed by stopping the arrival of the reactive gas and cooling the room. This cooling can be performed either simply by cutting the inductive heating and microwave power, or by gradually decreasing the heating power if slower cooling is desired.

 Various samples were made using this method and then tested to accurately determine the characteristics of the coating obtained and the influence of various factors on these characteristics. These factors relate in particular to the temperature of the substrate, the duration of the treatment, the distance from, the presence of hydrogen in the carrier gas, the use of a pretreatment by nitriding and the addition of hydrogen in the reactive gas. The tests also made it possible to control the resistance of salt spray coatings.

 In a first series of tests, aimed at studying the influence of the substrate temperature on the friction properties of the films produced according to the process described above, samples in the form of 2 mm thick discs and 16 mm in diameter were made of 35 CD4 steel and NCDV14 steel. More specifically, the process according to the invention was carried out without pretreatment and without adding hydrogen to the reactive gas, under the operating conditions indicated in Table 1.

TABLE 1

<tb><SEP> parameter <SEP> notation <SEP> value <SEP> (s) <SEP>
<tb> temperature <SEP> of <SEP> Ts <SEP> 500, <SEP> 550 <SEP> and <SEP> 600 "C <SEP>
<tb> substrate
<tb> distance <SEP> cavity- <SEP> d <SEP> -1 <SEP> cm
<tb> output <SEP> TMS
<tb> distance <SEP> output <SEP> from <SEP> 5 <SEP> cm
<tb> TMS-substrate
<tb> pressure <SEP> P <SEP> 0.5 <SEP> torr
<tb> power <SEP> W <SEP> 350 <SEP> W
<tb> flow rate <SEP> of <SEP> TMS <SEP> D (TMS) <SEP> 0.05 <SEP> lh- <SEP>
<tb> flow rate <SEP> lower <SEP> D (Ar) <SEP> 5 <SEP> lh- <SEP>
<tb> argon
<tb> flow rate <SEP> internal <SEP> Di (Ar) <SEP> 0.5 <SEP> lh- <SEP>
<tb><SEP> argon <SEP>
<Tb>
Under these conditions, four samples were made while maintaining the substrate at a temperature of 5000C (sample 1a), 550C (sample 1b) and 600C (samples 1c and 1d). It should be noted that in the case of sample 1d, the distances d and data in table 1 have been modified, to become respectively 5.5 cm for d and 4.5 cm for d '.

The coatings obtained on these different samples were analyzed by ray diffraction
X. A broad peak around the position of the peak 111 of ss-SiC was obtained, characterizing a nanocrystallized structure. The samples were then analyzed by electron spectroscopy or ESCA ("Electron Spectroscopy for Chemical Analysis"). The thickness, hardness and Young's modulus of the layers were also measured respectively by the ball imprint method and instrumented nanoindentation (tests under 10 mN, 50mN and 100 mN). The results are shown in Table 2.

TABLE 2

<tb><SEP> sample <SEP> the <SEP> lb <SEP> lc <SEP> ld
<tb><SEP> (500C) <SEP> (550C) <SEP> (600C) <SEP> (600C)
<tb> thickness <SEP> (lux) <SEP> 3,6i0,5 <SEP> 3,6i0,5 <SEP> 1,8i0,2 <SEP> 3i0,4
<tb> composition <SEP> (c / si) <SEP> 2.1 <SEP> 2.2 <SEP> 2.38 <SEP> 2
<tb> hardness <SEP> (GPa) <SEP> 13.5i0.5 <SEP> 15.8il, 5 <SEP> 17 # 1.5 <SEP><SEP> 16.3i0.5
<tb> module <SEP> Young <SEP> (GPa) <SEP> 122 + 4 <SEP> 134 # 10 <SEP><SEP> ~ SE> 137,5i4 <SEP> 132i5 <SEP>
<Tb>
The films obtained on the four samples tested are carbon surplus, hard and deposited with relatively high growth rates (from 7.2 .mu.m to 1 to 14.4 .mu.mh -1).

The hydrogen content of samples 1a and 1c was measured by nuclear analysis. More precisely, the nuclear analysis gives the number of hydrogen atoms per cm3 (respectively 3.1022 at.H / cm3 and 2.1022 at.H / cm3 for the samples 1a and 1c).
This measurement is then converted taking into account element content and density. The measured content is 25% for sample 1a and 15% for sample 1c. It can therefore be estimated that a hydrogen content at most equal to about 30% is obtained in all cases.

 The coatings of samples 1a to 1d were then subjected to a friction test by applying on their surface a 10 mm radius antagonist either in the form of a 35NCD16 steel cylinder or in the form of a 100C6 steel ball, with a normal 3 N and / or 14 N and moving this antagonist on the surface at a linear velocity of 0.02 + 4.10-3 m / sec. The coefficients of friction obtained, together with some remarks relating to the wear are reported in Table 3.

TABLE 3

exch. <SEP> antagonist <SEP> distance <SEP> load <SEP> coeff. <SEP> of <SEP> remarks
<tb> (m) <SEP> (N) <SEP> friction
<tb> 1a <SEP> cylinder <SEP> 485 <SEP> 14 <SEP> 0.14 # 0.02 <SEP> wear <SEP> very <SEP> low <SEP> (0.5 m)
<tb> 35NCD16
<tb> 1b <SEP> cylinder <SEP> 485 <SEP> 14 <SEP> 0.095 # 5.10-3 <SEP> wear <SEP> very <SEP> low <SEP> (0.4 <SEP> m)
<tb> 35NCD16
<tb> 1c <SEP> cylinder <SEP> 485 <SEP> 3 <SEP> 0.55 + 5.10-3 <SEP> wear <SEP> very <SEP> low <SEP> (0.2 <SEP> m)
<tb> 35NCD16 <SEP> width <SEP> of <SEP> trace <SEP>: <SEP> 160 <SEP> m
<tb> 1c <SEP> cylinder <SEP> 485 <SEP> 14 <SEP> 0.065 # 5.10-3 <SEP> wear <SEP> very <SEP> low <SEP> (0.15 <SEP> m)
<tb> 35NCD16
<tb> 1c <SEP> cylinder <SEP> 80 <SEP> 3 <SEP> 0.072 # 0.014 <SEP> wear <SEP> very <SEP> low
<tb> 35NCD16 <SEP> width <SEP> of <SEP> trace <SEP>#<SEP> 150 <SEP> m
<tb> 1c <SEP> ball <SEP> 80 <SEP> 3 <SEP> 0.08 # 0.02 <SEP> wear <SEP> very <SEP> low
<tb> 100C6 <SEP> width <SEP> of <SEP> trace <SEP>#<SEP> 150 <SEP> m
<tb> 1d <SEP> ball <SEP> 80 <SEP> 3 <SEP> 0.065 # 0.018 <SEP> low <SEP> wear
<tb> 100C6 <SEP> width <SEP> of <SEP> trace <SEP>#<SEP> 300 <SEP> m
<Tb>
The behavior of the different coatings, developed between 5000C and 600 ° C is very good, although there is a certain increase in the coefficient of friction when the manufacturing temperature decreases.We measure very low coefficients of friction associated with traces Shallow wear (the substrate is not reached) An increase in the load as well as a variation in the nature of the antagonist or the experimentation time (total distance traveled) do not change in any way. significant this behavior.

 The coefficients of friction obtained are comparable for processing conditions such that d + d 'are between about 6 cm and about 10 cm, provided that the sample is sufficiently far from the microwave cavity (so as to decouple power and temperature) and not too far from the reactive gas outlet (<5 cm) and provided that this gas is not injected upstream of the cavity.

 For comparison, samples in the form of discs of the same dimensions as samples 1a-1d and samples 1f and 1g in the form of a rectangular wafer 0.5 mm thick, 30 mm long and 5 mm thick. The widths were made at 400 ° C. under the same conditions as those set forth elsewhere in Table 1. In the case of samples 1f and 1g, the values of d and d were respectively 5.5 cm and 1 cm.

 The properties of the deposited layers comparable to those of the samples given in Table 2 are shown in Table 4.

TABLE 4

<tb><SEP> sample <SEP> 1st <SEP> (400C) <SEP> 1f <SEP> (400C) <SEP> 1g <SEP> (400C)
<tb><SEP> disks <SEP> platelet <SEP> 1 <SEP> platelet <SEP> 2
<tb> composition <SEP> 2.63 # 0.05 <SEP><SEP> 1.66 <SEP> 1.66
<tb> (C / Si)
<tb> hardness <SEP> (GPa) <SEP> 5.9 # 0.1 <SEP><SEP> 11.8 # 0.4 <SEP><SEP> 11.5 # 0.3
<tb> module <SEP> of Young <SEP> 55i1 <SEP> 88i4 <SEP> 89i5 <SEP>
<tb> (GPa)
<Tb>
The comparison of the properties of the layers deposited on the samples 1f and 1g with those of the layers deposited on the samples shows that the deposition rate, the hardness and the Young's modulus increase when the distance separating the output of the reactive gas from the substrate decreases. Friction tests were carried out on the samples 1a, 1f and 1g under the conditions similar to those of the tests carried out on the samples la to id (Table 3). The coefficients of friction thus measured are given in Table 5.

TABLE 5

exch. <SEP> antagonist <SEP> distance <SEP> load <SEP> coeff. <SEP> of <SEP> remarks
<tb> (m) <SEP> (N) <SEP> friction
<tb> 1e <SEP> cylinder <SEP> 485 <SEP> 3 <SEP> 0.35 # 0.15 <SEP> wear = 1 <SEP> m
<tb> 35NCD16 <SEP> width <SEP> of <SEP> trace # 350 <SEP> m
<tb> 1f <SEP> cylinder <SEP> 80 <SEP> 3 <SEP> 0,4 # 0,1 <SEP> similar <SEP> wear
<tb> 35NCD16 <SEP> width # 450 <SEP> m
<tb> 1g <SEP> ball <SEP> 80 <SEP> 3 <SEP> 0.3 # 0.1 <SEP> same <SEP> remarks
<tb> 100C6
<Tb>
A comparison of Table 5 with the
Table 3 shows immediately that the coefficients of friction of the samples made at 4000C are relatively higher than those of the samples made at a higher temperature. In addition, a very important dispersion was measured, as well as a local detachment in the traces, although that the applied load is always low (3N) in the case of samples 1 to 1g.

 This first series of tests therefore shows that the deposition temperature must necessarily be maintained between about 5000C and about 6000C so that the coefficient of friction of the deposited layer remains low.

 In a second series of tests, the layer-substrate adhesion of samples made without pretreatment, such as sample 1c, was compared with the adhesion of samples obtained interposing between the stripping step of substrate and the step of producing the complex thin film pretreatment with nitrogen or with hydrogen.

 More specifically, after argon plasma etching for about 10 minutes, a sample 2b was made by injecting hydrogen into the gas phase for about 10 minutes and a 2C sample by injecting nitrogen into the phase. gaseous for about 5 min, before making the TMS injection deposition. In both cases, the deposition was carried out after stopping the arrival of the pretreatment gases, adjusted the temperature, and then injected the TMS, under conditions identical to those previously set out in Table 1, except for the temperature.

Finally, after stopping the arrival of the TMS, the samples were cooled under argon flow. Pretreatment conditions are given in Table 6.

TABLE 6

<tb> sample <SEP> gas <SEP> of <SEP> pre- <SEP> flow <SEP> temperature <SEP> of <SEP> duration
<tb><SEP> treatment <SEP> (lh-1) <SEP><SEP> treatment <SEP><0c><SEP>("C)<SEP> (min) <SEP>
<tb><SEP> 2b <SEP> H <SEP><SEP> 3 <SEP> 400 <SEP> 10
<tb><SEP> 2c <SEP> N2 <SEP> 0.1 <SEP> 550 <SEP> 5
<Tb>
The sample 1a, made at 400 ° C without pretreatment, was then compared to these samples 2b and 2c.

 Regarding sample 1c, it shows poor adhesion and flaking at the edge of the trace is very important. On acoustic emission spectra, it is very difficult to measure the critical load Lc. Optical measurements made it possible to fix the critical load Lc at about 3.5 N.

The peeling of the film for a load equal to this critical load is abrupt, with a very clear deposit-substrate transition which has been demonstrated by spectroscopic analysis by energy dispersion.
With regard to acoustic emission spectra, the critical load Lc of the sample is greater than or equal to 6N.

 The same measurements made on the sample 2b show that pretreatment with hydrogen clearly improves the adhesion. Thus, the emission spectra show that the critical load Lc is greater than or equal to 11 N. In addition, the detachment of the deposit is essentially carried out at the edge of the trace, in the form of scales of small dimensions. There is deposit down to the bottom of the trace, which confirms a clear difference of behavior compared to the sample.

Finally, the measurements made on the sample 2c show that pretreatment with nitrogen considerably improves the mechanical strength of the coatings. The critical load Lc has a value ~ 19.2 +
1.6 N.

 A sample 2d, also comparable to the sample 2c, was made with a pretreatment of nitrogen at a rate substantially higher than in the case of the sample 2c, this flow rate being fixed at 1 I / h.

This sample made it possible to show that a nitrogen pretreatment with a too high nitrogen flow rate on the contrary plays a detrimental role as regards the mechanical strength of the coatings. Thus, in the case of this sample 2d, the same tests led to a very large edge flaking which starts at a very low load on the acoustic emission spectra. It is difficult to measure the critical load Lc because it grows gradually almost from the beginning. Nevertheless, this critical load is very low.

 An X-ray diffraction spectrum was performed on samples 2c and 2d and revealed the presence of Fe2-3N and Fe4N phases. Examination of a section confirmed the presence of a combination layer in both cases, about 3 μm thick. A nanoindentation profile was made and revealed the existence of a diffusion layer with a thickness of about 40 to 60 μm. These experiments show that the applicant has successfully deposited a combination layer to increase the attachment and that the composition of this layer is essential.

A third series of tests was carried out to control the corrosion resistance of the layers obtained. During this third series of tests, a sample 3a was made at 600 ° C from a 35CD4 steel plate, and at 5500C, samples 3b and 3c on silicon wafers of 0, 5 mm thick and 16 mm side.In addition, the conditions of preparation of the coatings were identical to those which are exposed in the
Table 1.

These different samples 3a to 3c have been exposed in a corrosive atmosphere (salt spray) for varying times. Friction tests were then carried out on these samples using a 35NCD16 steel cylinder antagonist, under conditions otherwise similar to those previously discussed with regard to the tests carried out on the samples ld. The results of these tests are shown in Table 7. TABLE 7

exch. <SEP> time <SEP> distance <SEP> load <SEP> coeff. <SEP> of <SEP> notes
<tb> Exposure <SEP> (m) <SEP> (N) <SEP> Friction
<tb> (h)
<tb> 3a <SEP> 8 <SEP> 80 <SEP> 3 <SEP> 0.08 # 0.01 <SEP> low <SEP> wear
<tb> width <SEP> trace # 150 m
<tb> 3b <SEP> 0 <SEP> 485 <SEP> 14 <SEP> 0.13 # 0.02 <SEP> wear <SEP> very <SEP> low
<tb> (0.5 m)
<tb> 3c <SEP> 24 <SEP> 485 <SEP> 14 <SEP> 0.13 # 0.02 <SEP> wear <SEP> very <SEP> low
<tb> (0.5 m)
<Tb>
In the case of samples 3a produced from 35CD4 steel discs, the very good coefficient of friction reported in Table 7 reveals a good stability of this coefficient after exposure in a corrosive atmosphere.

 This good corrosion behavior is confirmed by the deposits made on silicon substrates (samples 3b, 3c and 3d), which were developed under the same conditions and on which the friction tests show unequivocally that the coatings are inert in corrosive atmosphere.

 Another series of tests was performed by varying the injection rate of the reactive gas to increase the deposition rate. The deposition conditions were otherwise identical to those set forth in Table 1. Samples 4a, 4b and 4c were made at 600 ° C and samples 4d and 4e at 550 ° C, with a TMS flow of about 0 ° C. , 2 I / h. The different coating thicknesses obtained by varying the duration of the treatment are shown in Table 8.

TABLE 8

<tb> sample <SEP> At <SEP> (min) <SEP> e <SEP> (pm) <SEP>
<tb><SEP> 4a <SEP> 10 <SEP> 3.5i0.5 <SEP>
<tb><SEP> 4b <SEP> 20 <SEP> 6.5i0.5 <SEP>
<tb><SEP> 4c <SEP> 30 <SEP> 10in, 5 <SEP>
<tb><SEP> 4d <SEP> 20 <SEP> 6,8i0,6 <SEP>
<tb><SEP> 4th <SEP> 30 <SEP> 10,80,7 <SEP>
<Tb>
This table shows that the growth of the thickness over time is linear.

 Friction tests were also performed on samples 4b, 4d and 4e, using as a counter-actor a 10 mm radius steel cylinder 35NCD16 applied to the coating surface with a normal load of 14 N and moved onto this surface. at a linear velocity of 0.02 + 4.10-3 m / sec over a total distance of 485 m. The coefficients of friction thus measured are given in Table 9.

TABLE 9

<tb> sample <SEP> coeff. <SEP> of <SEP> remarks
<tb><SEP> rubbing
<tb><SEP> 4b <SEP> 0.19 # 0.05 <SEP><SEP> wear <SEP>#<SEP> 2.5 m
<tb><SEP> 4d <SEP> 0.13 # 0.02 <SEP><SEP> wear <SEP>#<SEP> 1 m
<tb><SEP> 4th <SEP> 0.16 # 0.04 <SEP><SEP> wear <SEP> t <SEP> lum <SEP>
<Tb>
These results show that an increase in the deposition rate was achieved by increasing the flow rate of the precursor (up to 21.6 μm / h) while maintaining a low coefficient of friction when the deposition temperature is below 600 C. In addition, a comparison of Tables 3 and 9 shows that the coefficient of friction increases slightly with the flow rate of the reactive gas, regardless of the deposition temperature.

 In a final series of tests, the effect of a hydrogen supply in the reactive gas of TMS and argon was studied. For this purpose, samples 5a-5e were made under the deposition conditions shown in Table 10.

TABLE 10

Parameters <SEP> constant <SEP>: <SEP> P = 0.5 <SEP> Torr <SEP>;<SEP># t = 15 <SEP> min <SEP>;<SEP> D (TMS) = 0.05 <SEP> lh-1 <SEP>;<SEP> DT (Ar) = 5.5 <SEP> lh-1
<tb> sample <SEP> substrate <SEP> Ts <SEP> (C) <SEP> d <SEP> (cm) <SEP> from <SEP> (cm) <SEP> D (H2) <SEP> W <SEP> (watt)
<tb> (lh-1)
<tb> 5a <SEP> platelet <SEP> 400 <SEP> 5.5 <SEP> 1 <SEP> 0 <SEP> 350
<tb> 5b <SEP> disk <SEP> 400 <SEP> 5.5 <SEP> 1 <SEP> 1 <SEP> 350
<tb> 5c <SEP> disk <SEP> 400 <SEP> 5.5 <SEP> 1 <SEP> 2 <SEP> 350
<tb> 5d <SEP> disk <SEP> 400 <SEP> 5.5 <SEP> 1 <SEP> 3 <SEP> 350
<tb> 5th <SEP> disk <SEP> 400 <SEP> 5.5 <SEP> 1 <SEP> 5 <SEP> 500
<Tb>
Sample 5a was obtained from a NCDV14 rectangular steel wafer having a thickness of 0.5 mm, a length of 30 mm and a width of 5 mm. Samples 5b to 5e were made from a CD4 steel disc 2 mm thick and 16 mm in diameter.

 The characteristics of these different samples were measured in the same way as in the previous tests, to determine the thickness of the coating, its composition, its hardness and its Young's modulus. The results of these measurements are given in Table 11.

TABLE 11

<tb> ech. <SEP> e <SEP> (m) <SEP> C / If <SEP> H (GPa) <SEP> E (GPa)
<tb> 5a <SEP> 9.8 <SEP> 1.7 <SEP> 11.30.7 <SEP> 89 # 2) <SEP>
<tb> 5b <SEP> 7.4 <SEP> 1.6 <SEP> 14.70.5 <SEP> 122 # 5 <SEP>
<tb> 5c <SEP> 4.7 <SEP> 1.6 <SEP> 16.5i0.9 <SEP> 155 # 5 <SEP>
<tb> 5d <SEP> 3 <SEP> 1.6 <SEP> 17.9i0.2 <SEP> 147 # 3 <SEP>
<tb> 5th <SEP> 4.5 <SEP> 1.1 <SEP> 22.5 # 1.5 <SEP><SEP> 188 # 15
<Tb>
This Table shows that a supply of hydrogen in the reactive gas results in a decrease in the thickness of the coating and in an increase in its hardness and the Young's modulus. A significant variation in the ratio only occurs for the flow of hy-
If it's the highest. For this same flow, an increase in the microwave power was necessary, so as to compensate for the decrease in the volume of the discharge attributable to the energy consumption by hydrogen. This mechanism is also responsible for reducing the thickness of the deposit as soon as the substrate is at the edge of the discharge zone.

Friction tests were also performed on samples 5a and 5e. These tests were carried out using a steel cylinder 35NCD16 of 10 mm radius in the case of the sample 5e and by means of a steel ball 100C6 of 10 mm radius in the case of the sample 5a. In the latter case, the normal charge on the ball was 3 N while the load on the cylinder in the case of the 5e sample was 14 N. In all cases, the linear velocity was 0.02 + 4.10-3 m / sec, the total distance traveled being 80m for sample 5a and 485m for sample 5e. The coefficients of friction obtained are indicated in the
Table 12.

TABLE 12

<tb> sample <SEP> coefficient <SEP> of <SEP> remarks
<tb><SEP> rubbing
<tb><SEP> 5a <SEP> 0.4i0.1 <SEP> results <SEP> discussed
<tb><SEP> 0,30,1 <SEP> in <SEP><SEP> table <SEP> 5
<tb><SEP> 5th <SEP> 0.5 + 0.1 <SEP> important <SEP> wear
<tb><SEP>(><SEP> 3 <SEP> Mm) <SEP>
<Tb>
Tables 11 and 12 show that a supply of hydrogen in the reactive gas leads to a high growth of hardness and Young's modulus, reduces the fragility of the layers at 400 ° C. (no detachment was observed in the traces of wear) but disrupts the friction properties.

 Finally, a deposit was also made on a TA6V titanium alloy substrate, under conditions identical to those which led to the production of the sample 1b.

 Scratch tests carried out on sample 1b and on this sample in TA6V showed a critical load Lc <6 N in the first case and Lc> 6 N in the second case. The deposition performed on a TA6V substrate has the same priorities as the deposition performed on a steel substrate.

 In conclusion, the applicant has demonstrated that it is possible to produce a complex, chemically stable, low-friction layer based on carbon, silicon and hydrogen on a substrate made of a material such as a an iron-based or titanium-based alloy, by microwave-activated chemical vapor deposition by precisely positioning the substrate and injecting the reactive gas into the chamber, with respect to the microwave cavity and using a particular reactive gas or precursor. The positioning of the substrate makes it possible in particular to control its temperature independently of the microwave power used, in order to give this temperature an optimum value for the desired characteristics.

 The Applicant has also established that such a coating can be made particularly rapidly and by simply establishing a primary vacuum in the reaction chamber, without the need to exit the substrate of this chamber at any time during the various stages. necessary to deposit.

 Finally, the applicant has shown that pretreatment with nitrogen and / or methane carried out under precise conditions substantially improves the adhesion of the coating without significantly affecting its friction properties.

Claims (15)

 1. Thin layer complex, chemically stable, low coefficient of friction, based on carbon, silicon and hydrogen, characterized in that it comprises less than 30% of hydrogen atoms and a ratio C / If, between the number C of carbon atom and the number Si of silicon atoms, between about 1.4 and about 3.3.  2. complex thin layer according to claim 1, characterized in that the C / Si ratio is between about 2.4 and about 2.5.  A very low friction part, comprising a substrate of a material which is not tampered with when heated to a temperature of from about 5000 ° C. to about 6000 ° C. and a surface coating covering said substrate, characterized by the fact that the surface coating is a complex thin film according to any one of claims 1 and 2.  4. Part according to claim 3, characterized in that it further comprises a nitrided intermediate layer, carburized or carbonitrided, interposed between the substrate and the surface coating.  5. A process for producing a surface coating in the form of a complex, chemically stable, low-friction layer based on carbon, silicon and hydrogen on a substrate (34) in a material which is not altered when heated to a temperature of between about 5000C and about 6000C, by chemical vapor deposition, activated by a microwave plasma, characterized in that it comprises the successive steps following - placing the substrate (34) on a support (32),  in an enclosure (10) having a plasma zone  maximum density, called the active zone (22), in  a first region of the enclosure located outside of  the active zone and within a zone of  discharge capable of containing a plasma - establishment of a primary vacuum within  the enclosure; stripping of the substrate by injection of a deca gas  page, establishment of a plasma of this gas, in the  discharge zone, and separate heating of the substrate to  a regulated temperature of between about 5000C  and about 6000C - deposition of said coating by injection of a reactive gas  in a second area of the enclosure located between  the substrate and the active zone, or in a limited area  trophe of this active zone, turned to the subs  said reactive gas comprising a compound which is unique to  tetrahedral silicon environment, so that  replace the plasma of the stripping gas with a plasma of  reactive gas while maintaining the heating of the subs  treated at said regulated temperature; and - interruption of the injection of the reactive gas and cooling  substrate degradation, after a duration of injection  predetermined, corresponding to a desired thickness  coating.  6. Method according to claim 5, characterized in that the stripping gas is argon.  7. Method according to claim 6, characterized in that the stripping gas also contains hydrogen.  8. Process according to any one of claims 5 to 7, characterized in that the reactive gas comprises tetramethylsilane mixed with argon.  9. Process according to claim 8, characterized in that the reactive gas also contains hydrogen.  10. Method according to any one of claims 5 to 9, characterized in that it further comprises, between the steps of etching and deposition of the coating, a step of producing an intermediate layer by injection of a pre-treatment gas in the second region of the enclosure, the pretreatment gas containing the nitrogen element and / or the carbon element, so as to substitute a pretreatment gas plasma for the pickling gas plasma.  11. The method of claim 10, characterized in that the pretreatment gas comprises at most about 20% nitrogen and / or methane, mixed with argon.  12. Method according to any one of claims 5 to 11, characterized in that the active area is a localized microwave cavity is formed in a waveguide connected to a microwave generator working at a frequency of 2 , 45 GHz and whose power is set between about 150 W and about 500 W.  13. Method according to any one of claims 4 to 12, characterized in that, during the deposition of the coating, the reactive gas is injected at a flow rate of between about 0.01 I / h and about 0.3 I / h. h.  14. A method according to any one of claims 4 to 13, characterized in that during the pickling of the substrate, the etching gas is injected at a flow rate of between about 0.5 I / h and about 10 I / h.  15. Method according to any one of claims 5 to 14, characterized in that the primary vacuum established inside the enclosure advantageously corresponds to a pressure between about 0.5 torr and about 2 torr.