FR3029813B1 - METHOD FOR MANUFACTURING MICROSTRUCTURE COATING - Google Patents

Abstract

The invention relates to a method for producing a microstructured coating on a substrate, which comprises a step of spraying molten particles having a diameter of between 0.05 μm and 5 μm onto the substrate (20), the projection being carried out by at least one plasma torch (51, 52), which is displaced relative to the substrate (20), the displacement parameters and / or the flow rate of the particles projected by the plasma torches (51, 52) being variable as a function of the position of the plasma torches (51, 52), providing a variable thickness of the coating formed by the particles, at different points of the substrate (20). The invention also relates to a wall having a coating obtained by this method.

Description

Process for producing a microstmctorate coating

THE FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a microstuctured coating on a wall, and in particular on an outer wall of an aircraft. The invention also relates to a wall having such a microstructured coating.

.2., PRIOR ART

To improve the performance of an aircraft, and in particular to reduce fuel consumption, it seeks to reduce its aerodynamic drag. To reduce this drag, it is known to form on part of the outer wall of the aircraft, for example a part of the wing or fuselage elements, a microstructure usually called "shark skin", or designated by the English term. "Ribiet".

A microstructure, in the sense of the presence demand, is constituted by a set of reliefs repeating on a surface, whose depth is generally between 10 and 60 microns, and whose geometry is optimized to meet a specific objective.

A "shark skin" type microstructure, or "ribiet", has ribs substantially parallel to each other, the ridge lines of the ribs being oriented in the direction of flow of a fluid on the surface, for example the direction of flow. flow of air on the outer wall of an aircraft. These ribs have, in cross section, the form of sawtooth. Such a microstructure is known for example from documents EP 2 729 363 or EP 1 283 163. Several ways of producing such microstructures on a wall are known. It is in particular known to stick, on the wall, a plastic film having grooves of a few hundredths of a millimeter in depth, the ribs being formed between two successive grooves. According to another known embodiment, grooves of a few hundredths of a millimeter are machined on a metal wall, so as to produce the microstructure.

The walls having such microstructures have characteristics enabling them to reduce their aerodynamic drag, when they are subjected to a flow of air flowing in the direction of the ribs. However, this reduction of the aerodynamic drag is effective only if the ribs have precise shapes. It is particularly important, to ensure this efficiency, that the crest lines of the ribs are sufficiently elongated.

Known processes for manufacturing microstructures make it possible to obtain such ridge lines. However, there is a need to improve these manufacturing processes, to obtain microstructures having a better resistance to erosion, especially when the walls having microstructures are subjected to the friction of air, water and water. dust, in order to guarantee the long-term performance of the microstructures and the corresponding decrease in the aerodynamic drag of the wall.

There is therefore a need for microstructured walls whose microstructures have an increased resistance to erosion, and a method for making such walls. The object of the present invention is in particular to provide a method of manufacturing microstructured walls satisfying this need.

3. SUMMARY OF THE INVENTION

These objectives, as well as others which will become more clearly apparent thereafter, are achieved by a method of manufacturing a microstructured coating on a substrate, which comprises a step of spraying molten particles having a diameter. between 0.05 μm and 5 μm on the substrate, the projection being carried out by at least one plasma torch which is displaced relative to the substrate, the displacement parameters and / or the flow rate of particles projected by said plasma torch or torches being variables depending on the position of the plasma torch or torches, ensuring a variable thickness of the coating formed by said particles, at different points of the substrate. It is thus possible to obtain a microstructure coating having a very precisely controlled geometry, which has a surface state rendering it insensitive to erosion.

According to an advantageous embodiment, the variable thickness is achieved by the projection, on at least a portion of the surface of the substrate, of at least two successive layers of molten particles, the number of projected particle layers being variable in different points of the substrate.

According to another advantageous embodiment, the variable thickness is achieved by the projection of at least one layer of molten particles whose thickness is variable at different points of the substrate.

Advantageously, the method uses a robot that controls the position, the orientation and the flow rate of each of the plasma torches projecting particles onto the substrate.

According to an advantageous embodiment, the projection step comprises: - the projection of a first layer of particles, of substantially uniform thickness at any point of the substrate, then - the projection, over this first layer, of a plurality of other layers of particles, the number and / or thickness of which are different at different points of the substrate.

According to an advantageous embodiment, the projection step comprises: the projection of layers of particles, the number and / or thickness of which are different at different points of the substrate, then - projection over the particle layers preceding of at least one outer layer of particles, of substantially uniform thickness at any point of the substrate.

Advantageously, the method comprises, prior to the projection step, a step of measuring the geometry of the surface of the substrate and a step of calculating the thickness and / or the number of particle layers to be projected at different points of said substrate.

Preferably, the particles projected during the projection step comprise metal oxide particles.

Advantageously, the method comprises, prior to the projection step, a step of dispersing the particles to be projected in a sol-gel compound. Advantageously, the particles projected during the projection step comprise zirconia particles.

Advantageously, the particles projected during the projection step comprise particles of titanium dioxide.

The present invention also relates to a wall, comprising a substrate covered by a coating, this coating is a microstructured coating obtained by the method described above.

Advantageously, the coating has an average thickness of between 0.01 mm and 0.25 mm.

Advantageously, the coating shows, on its surface, a microstructure forming ribs substantially parallel to each other.

Advantageously, the ribs have a height of between 10 μm and 60 μm.

4- LIST OF FIGURES Other features and advantages will become apparent from the following description of the invention, description given by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a diagrammatic representation, in perspective , a wall having microritic structures; - Figure 2 is a schematic sectional view of a wall having a microstructured coating of the "riblet" type made according to one embodiment of the invention; FIG. 3 is a schematic perspective view of the wall of FIG. 2; FIG. 4 is a diagrammatic sectional view showing the wall of FIG. 2 during the manufacture of the microstructured coating; FIG. 5 is a diagrammatic sectional view of a wall adapted to receive a microstructured coating, according to another embodiment of the invention; FIG. 6 is a diagrammatic sectional view of the wall of FIG. microstructured type "ribiet"; FIG. 7 is a diagrammatic sectional view of a detail of a wall having a "ribiet" microstructured coating made according to another embodiment of the invention; - Figure 8 is a schematic representation of the device for the projection of the coating layers on a substrate, according to one embodiment of the invention. 5 DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 represents in perspective a portion of a wall 1 having a "ribiet" type microstructure. This microstructure has a plurality of ribs 11, 12, 13, 14 and 15 extending substantially parallel to each other. In a conventional manner, each of these ribs has a height of the order of 50 μm. In the example shown, the ridge lines 110, 120, 130, 140 and 150 of the ribs are represented as the intersections of the planes formed by the flanks of each rib. These ridge lines are thus very acute. As is known to those skilled in the art, a wall 1 having ribs 11, 12, 13, 14 and 15 with sufficiently sharp ridge lines 110, 120, 130, 140 and 150 generates a relatively low aerodynamic drag when subjected to a flow of air or fluid flowing in the direction of the ribs.

In reality, the ridge lines obtained by the known methods do not present exactly this theoretical form, but a shape approaching it. This shape may slightly change during the life of the wall 1, in particular under the effect of the erosion of the air or the flow of fluid to which the wall 1 is subjected,

In the embodiments which are presented hereinafter, substrates are covered by microstructured coatings forming a wall having microstructures which may be of the "ribiet" type. The substrate may for example consist of a plate such as a metal sheet or a plate made of composite material. The microstructured coatings, the thickness of which is preferably between 0.01 mm and 0.25 mm, are obtained by the projection on the substrate, by a plasma torch, of fine particles, with a diameter of between 0.05 μm and 5 pm. Preferably, these particles are projected in the form of a plurality of successive layers of particles, together forming the coating. The use of fine particles to form the coating makes it possible to adjust the thickness of this coating very precisely. Indeed, the particles having a size much smaller than the thickness of the coating, it is necessary to project a large number to obtain the final coating. The coating is then obtained in a progressive manner, which allows a very good control of its thickness, and therefore the geometry of the microstructures.

Moreover, the use of fine particles makes it possible to obtain a surface state of the coating which is very homogeneous, which limits the risk of erosion and avoids the fixing on the wall of dirt or water.

According to a preferred embodiment shown schematically in Figure 8, the projection of the particles on the substrate is made by an atmospheric plasma beam, consisting of ionized gas in which are included the particles to be sprayed. As shown in FIG. 8, the plasma torch 81 forms a plasma beam 810. Particles 83 are introduced into this plasma beam 810 via a nozzle 82. In the plasma beam 810, these particles 83 are heated until they are melted and are projected. to the substrate 80. In some cases, these particles may also undergo chemical transformations in this plasma beam 810, in particular due to heat. In contact with the surface of the substrate 80, the particles 83 solidify therein to form a coating layer 830. By way of example, in one embodiment of the invention, the plasma temperature is of the order of 200 to 14000 ° K, the plasma jet speed is between 50 and 2500 m / s, and the particles move in the plasma at a speed between 20 and 400 m / s. The distance between the plasma torch and the substrate to be coated is of the order of 25 cm.

The particles projected by the plasma on the substrate are heated at very high temperature, of the order of thousands of degrees, for a very short time, of the order of a thousandth of a second. This rise in temperature can have consequences on the cohesion of the projected particles, or generate chemical reactions in these particles. The small dimensions of these particles prevent the occurrence of an unacceptable heating of the substrate during the impact of hot particles.

According to a preferred embodiment, the particles used for the manufacture of the coating are previously dispersed in a liquid to form a sol-gel compound which is itself inserted into the beam of the plasma torch. The use of such a sol-gel process allows a good particle size distribution of the particles to be sprayed.

As shown in FIG. 8, a compound 820 of the sol-gel type, contained in a container 821, can be fed to the nozzle 82 via a pipe 822, so as to be introduced into the plasma beam 810. Advantageously, the nozzle introduces a precise flow rate of sol-gel compound, in order to control at each instant the amount of particles deposited by the plasma beam. Several nozzles may be provided, for the same plasma beam, so as to introduce simultaneously or successively several types of particles in the plasma, in desired proportion,

The formation of such a sol-gel type compound containing fine particles, and the introduction of this sol-gel type compound into a plasma beam for projecting the particles onto a substrate to form a thin layer of coating are described in particular by WO2006 / 043006 and WO2007 / 122256.

Preferably, the particles projected by the plasma beam to form the coating layers are particles of metal oxides. The use of such particles makes it possible to manufacture a resistive layer which has good resistance to erosion, which allows the microstructures to maintain a long lasting aerodynamic performance.

More specifically, the choice of particles used can be made between several types of particles, depending on the desired properties for the coating. Each layer can be composed of a single type of particles or of several types of mixed particles. Moreover, some of the particle layers may be porous so as to allow interpenetration between the particles forming successive layers. Such interpenetration can allow an optimization of the final properties sought.

Thus, according to a preferred embodiment of the invention, the first layers deposited on the substrate may be anchoring sub-layers made of polymers blocking corrosion. According to one variant, the plasma torches can generate metal oxides on a metal substrate enabling adhesion of the subsequent layers.

On the outer layers of the coating, it is advantageous to use zirconia-based layers. This material has a high wear resistance, and provides a coating having good wear resistance. The degree of porosity of these layers can be chosen to allow the penetration of particles offering particular properties to the coating. Thus, a layer based on zirconia, offering good mechanical performance of impact resistance and erosion, can also have properties resulting from the presence of other particles.

Among these particles, the titanium dioxide particles can bring a self-cleaning character to the coating. The photo-catalytic properties of this material, in combination with a source of ultraviolet, allows the permanent transformation of organic elements such as debris associated with mosquito impacts or any other organic element. Ultraviolet lights can be of natural origin or projected on the wall by a suitable projector.

According to another possible embodiment, a self-cleaning character can be provided by the projection of piezoelectric ceramic particles. Under the effect of a current, these ceramics vibrate, generate surface waves and allow delamination and cleaning of the walls, ensuring an improvement in the aesthetics and durability of aerodynamic performance of the wall.

According to yet another possible embodiment, the projection of organometallic particles makes it possible to give the coating a super-hydrophobic character, notably reducing the risk of ice formation on the wall.

The implementation of such particles or combinations of particles, to obtain a coating having particular properties, is described in particular in WO2006 / 043006 and WO2007 / 122256.

The movements of the torch, or torches projecting the coating layers, are preferably controlled by a robot that moves the torch or torches so as to make a number of particle projections at each point of the substrate. This robot, by moving the torch relative to the substrate, makes it possible to control the distance between the torch and the substrate, which is generally less than 25 cm. The robot can also realize, with one or more torches, the projection of a plurality of successive layers on the wall, by varying, if necessary, the orientation of the torches. It can in particular ensure a positioning of the torch, at a suitable distance relative to the substrate and with a suitable angle, to ensure the homogeneous projection of the coating layers on a substrate that may have a complex non-planar shape.

This robot can, for example, drive a train of torches each having different orientations and flow rates.

This robot can also actuate, cut or modulate the particle feed of the nozzles introducing the particles into the plasma beams of the torches. Thus, this robot allows the torch, as it passes through each point of the wall of the substrate, to deposit a layer of particles of desired thickness, or do not deposit any particle, when the particle supply is interrupted. This embodiment allows a layer of particles to be deposited on certain areas of the wall, and not on certain other areas. It also makes it possible to vary the thickness of the same layer of particles, as a function of the zones of the wall. This embodiment thus makes it possible to effectively control the geometry of the coating.

Advantageously, the robot can be combined with a real-time control means of the coating deposition conditions, such as a camera.

FIGS. 2 and 3 schematically represent a wall 2 which is covered, according to a first embodiment of the invention, with a microstructured coating forming a plurality of ribs 21, 22, 23 and 24. In this embodiment, the wall 2 is formed on the basis of a substrate 20 consisting of a flat plate. This substrate may for example be constituted by a metal sheet, for example aluminum, or by a plate made of composite material. It is advantageously completely covered by a first layer 201 of coating, which may for example be a tie layer allowing good adhesion of the following layers.

In this embodiment, each of the ribs 21, 22, 23 and 24 is formed by a plurality of coating layers stacked on each other, each new layer having a width smaller than the previous layer so that the stack of layers has a pyramidal shape. The set of coating layers thus forms the microstructured coating, comprising the ribs 21, 22, 23 and 24.

FIG. 4 diagrammatically shows the projection of the particles forming the microstructured coating on the substrate 20, according to a possible embodiment of the invention, in order to form the wall 2 represented by FIGS. 2 and 3.

According to this embodiment, the projection of the coating layers on the substrate 20 is made by a plurality of torches 51 and 52, each projecting a directional jet, respectively 510 and 520, of particles on the substrate 20. In this embodiment , the two plasma torches 51 and 52 move from left to right, projecting each of the particles to form a coating layer. Each of these torches thus deposited on the wall a separate layer of particles. It can be seen in FIG. 4 that the first layer 201 and the two following layers of particles forming the base of the ribs 21, 22, 23 and 24 have been deposited before the passage of the plasma torches 51 and 52. Thus, a second layer 211, 221, 231 and 241 respectively have been deposited on the first layer 201, to form the base, respectively, of the rib 21, 22, 23 and 24. A third layer, respectively 212, 222, 232 and 242 has been deposited, respectively, on the second layer, respectively 211, 221, 231 and 241. The torches 51 and 52 deposit, respectively, the fourth and fifth layers. More specifically, in FIG. 4, the torch 51 has deposited the fourth layer 213 on the layer 212, the fourth layer 223 on the layer 222, and is depositing the fourth layer 233 on the layer 232. The torch 52 has deposited the fifth layer 214 on the layer 213, and is in the process of depositing the fifth layer 224 on the layer 223. The succession of layers deposited on each other by the torches thus makes it possible to form the controlled geometry of the grooves represented by the Figures 2 and 3.

Of course, the invention can be implemented with a larger number of torches than those shown in FIG. 4. It can also be implemented with a single torch making several passes so as to produce the different layers of the microstructure. .

As a result, the microstructure of the wall 2 is composed of a large number of successive layers, preferably greater than ten layers. Since the quantity of particles deposited in each layer can be determined precisely, it is possible to produce layers having a very precise thickness. It is thus possible to control the geometry of the microstructure, by adapting the number of layers.

Figures 5 and 6 show the implementation of another possible embodiment of the invention. FIG. 5 represents, in continuous lines, a substrate 30 on which a microstructured coating must be deposited, so as to produce the wall 3 comprising ribs whose desired shape is represented in dotted lines. In this embodiment, the substrate 30 is not flat, but has reliefs 310, 320, 330 and 340 for forming the leader of the ribs. These reliefs can be obtained, for example, with one of the known methods for the formation of "ribiet" type microstructures.

The method according to this embodiment comprises a preliminary step which consists in making an accurate measurement of the surface of the substrate 30, in order to measure the precise dimensions of the reliefs 310, 320, 330 and 340. This measurement can for example be performed by scanning systematically the surface by the beam of a laser range finder. Another step is to calculate, based on these measurements, using a computer-adapted adapted software, the number and / or the thickness of coating layers to be deposited at each point of the substrate 30 in order to producing a coating having the desired microstructure, which is shown in dashed lines in FIG. 5. Finally, in the following steps, these coating layers are deposited on the substrate 30 to form the microstructured coating which is shown in FIG. different layers of coating are stacked on each other, each layer adapting to the shape of the layer on which it is deposited, to form ribs, respectively 31, 32, 33 and 34, on the reliefs, 310, 320, 330 and 340, respectively, of the substrate 30.

In the embodiment shown, the coating layers comprise a first layer 301, which is continuous on the substrate and which may for example be a tie layer allowing good adhesion of the following layers. The coating layers also include a last layer 302, which is also continuous and covers all other layers. This last layer 302 is advantageously a layer having characteristics making it suitable for ensuring the surface state of the coating, and in particular its resistance to erosion.

Figure 7 shows the implementation of another possible embodiment of the invention. In this embodiment, a plurality of coating layers, referenced 411 to 419, have been deposited on a substrate 40 to form a microstructured coating. Each of the coating layers 411 to 419 has a variable thickness depending on the areas. Thus, in areas 401 and 402 of the coating, each of these layers has a minimum thickness, so that the coating formed of these layers has a minimum thickness.

In the zone between these zones 401 and 402, the thickness of the layers of the coating increases progressively to a maximum thickness value, then progressively decreases to a minimum thickness value. This variation of the thickness of a coating layer can be obtained by varying the quantity and / or size of the particles introduced into the plasma beam, and / or by varying the speed of displacement of the plasma beam on the substrate. In the embodiment shown, the thickness of all the layers is identical, at a given point of the substrate. As a result, the stack of coating layers having a large thickness forms a relief 41 in the coating, which makes it possible to form a microstructure in the coating. Those skilled in the art will of course be able to imagine other solutions for projecting particles that, by varying the thickness and / or position of each layer, provide a microstructure in the coating.

Thus, the method according to the invention makes it possible to obtain a wall, for example a metal or composite wall of an aircraft exterior, which is covered with a microstructured coating that may comprise grooves or reliefs with a height of 10. at 60 microns. These reliefs can be formed very precisely, with a tolerance of 0.8 to 3 microns, and have a very smooth surface and having good erosion resistance, ensuring the durability of the microstructure over time. This coating may also have characteristics enabling it to limit the effects of contamination (for example by mosquitoes, or dust, resistance to chemical attack and mechanical stress), and providing an aesthetic effect through a consistent and durable coloring .

Such a structure thus makes it possible to respond to the various stresses experienced by a wall element of an aircraft, among which: resistance to environmental conditions, and especially to atmospheric conditions; compatibility with various non-planar shapes, the coating being able to be deposited in various directions; - The aerodynamic performance of the coating, the coating may have microstructures reducing the drag generated by a fluid flow; - the aesthetic conditions relating to the outer surfaces of aircraft.

In the embodiments shown, the microstructured coatings obtained form ribs of substantially triangular section. Of course, the skilled person can easily implement this process for the manufacture of microstructures of different types.

Claims (8)

A method for producing a microstructured coating on a substrate (20, 30, 40, 80), characterized in that it comprises a step of measuring the geometry of the surface of said substrate (20, 30, 40, 80}; a step of calculating the thickness and / or number of the layers (201, 211, 212, 411, 412 ...) of particles to be projected at different points of said substrate (20, 30, 40, 80); a step of dispersing the particles to be projected in a sol-gel compound (820); a step of projecting particles (83) in fusion, comprising metal oxide particles and having a diameter of between 0.05 and pm and 5 pm on said substrate (20, 30, 40, 80), said projection being carried out by at least one plasma torch (81, 51, 52), which is displaced with respect to said substrate (20, 30, 40, 80 ), the displacement parameters and / or the flow rate of particles (83) projected by the at least one plasma torch (81, 51, 52) being variable as a function of the p ositioning said at least one plasma torch (81, 51, 52), providing a variable thickness of the coating formed by said particles (83), at different points of the substrate (20, 30, 40, 80). 2. Method according to claim 1, characterized in that said variable thickness is achieved by the projection, on at least a portion of the surface of said substrate, of at least two layers (201, 211, 212, ..., 411 , 412 ...} successive particles (83) melt, the number of layers (201, 211, 212, ..., 411, 412.,.) Of projected particles (83) being variable at different points of the substrate . 3. Method according to any one of claims 2 and 3 characterized in that said variable thickness is achieved by the projection of at least one layer of molten particles whose thickness is variable at different points of the substrate. 4. Method according to any one of the preceding claims, characterized in that it implements a robot that controls the position, the orientation and the flow rate of each of the plasma torches (81, 51, 52) projecting particles ( 83) on the substrate (20, 30, 40, 80). 5. Method according to any one of the preceding claims, characterized in that said projecting step comprises: the projection of a first layer (201, 301) of particles, of substantially uniform thickness at any point of said substrate (20); , 30, 40, 80) and then projecting, over said first layer, a plurality of other layers (211, 212, ..) of particles, of which Se number and / or thickness are different. at different points of the substrate (20, 30, 40, 80). 6. Method according to any one of the preceding claims, characterized in that said projection step comprises: the projection of layers of particles, the number and / or thickness of which are different at different points of the substrate (20, 30, 40, 80), and then projection over the preceding particle layers of at least one outer layer (302) of particles, of substantially uniform thickness at any point of said substrate. 7. Method according to any one of claims 1 to 6, characterized in that the particles (83) projected during said projection step comprise zirconia particles. 8. Method according to any one of claims 1 to 7, characterized in that the particles (83) projected in said projection step comprise titanium dioxide particles.