Method for depositing a metal coating by thermal spraying and mixture for implementing such a method

Abstract

The invention relates to a method (100) for depositing a metal coating (R) by thermal spraying, which method comprises the following sequential steps: - providing a surface (S) to be coated (110), a tank (2) for a mixture and a metal spraying device (1) connected to the tank, the mixture comprising ellipsoidal metal particles (PMe) and ellipsoidal mineral particles (PMi) having a hardness that is greater than a hardness of the surface and a melting point that is strictly greater than the melting point of the metal particles; - heating the mixture (120) to a temperature below the melting point of the metal particles via neutral gas so as to obtain partially softened and ductile metal particles; - spraying the mixture (130) through the nozzle (20) so as to form a jet of material in the direction of the surface and to form the metal coating on this surface.

Description

[0001] METHOD FOR DEPOSITING A METAL COATING BY THERMAL SPRAYING AND MIXTURE FOR IMPLEMENTING SUCH A METHOD

[0002] Technical field of the invention

[0003] The invention relates to the technical field of methods for depositing a metal coating by thermal spraying. The metal spraying method may in particular be a Cold Spray method.

[0004] Technical background

[0005] Thermal spraying is widely used in the aeronautics industry for the repair of components that have suffered wear during operation. The process is implemented using a spraying device equipped with a heating element and a spray nozzle, which respectively heat and spray metal particles in powder form at high speed onto the surface to be coated. Among the various thermal spraying technologies, the Cold Spray process stands out from other thermal spraying processes by the possibility of carrying out a coating at low pressure and low temperature. In this respect, aluminum is particularly suitable for this process due to its low melting point and high ductility.

[0006] In prior art Cold Spray processes, some metal particles to be sprayed remain blocked at the bore of the spray nozzle at the time of their spraying, which causes fouling and finally clogging of the spray nozzle ("Barrel loading and finally barrel clogging" in English). This phenomenon is even more pronounced when the metal used has a low melting point. It is therefore very recurrent in thermal spraying processes using aluminum-based mixtures, a material particularly used in the aeronautical field for the repair of parts that have undergone wear. This phenomenon is detrimental to the efficiency of the process since the quantity of powder to be sprayed is all the more reduced as the deposit formed in the bore of the spray nozzle is significant until the system is completely stopped.Under these conditions, it is also very difficult to control the thickness of the coating deposited on the spray surface during coating deposition.

[0007] In order to overcome this problem, it has been proposed to add an angular mineral filler, also in powder form, to the metal powder in order to clean the nozzle bore by friction / erosion at the same time as the material is projected onto the projection surface. Conventionally, this mineral filler is based on silicon carbide (SiC) or alumina (AI2O3). However, these mineral fillers generate a large number of defects in the coating obtained due to their acute angles / sharp edges. In particular, it has been found that they promote rupture under load due to their size and geometry, that they generate unusual erosion of the organs of the metal projection device, of the metal particles themselves and of the surface located opposite the coating deposited by friction between said coating and said surface.Furthermore, a high proportion of mineral filler was also observed in the coating obtained, a proportion varying from 40% to 50% by mass for a mixture of particles comprising between 40% and 60% mineral filler. The presence of mineral filler in such proportions greatly affects the quality of the coating obtained since the coating obtained corresponds more to a ceramic-metal composite than to a metal.

[0008] Document US 2019 / 355891 A1 discloses a method for depositing a coating of a polycrystalline material, in particular a semiconductor material, but does not relate to the deposition of a metal coating. Documents EP 3 348 670 A1, US 8 114 474 B1, CN 111 364 036 A and US 2010 / 187119 A1 disclose methods for depositing metal coatings. However, none of these documents addresses the aforementioned problems and none of these documents discloses a mixture containing other types of particles than metal particles.

[0009] Thus, although this solution makes it possible to solve the problem of clogging of the bore of the projection nozzle, it raises numerous other problems to which the inventors of the present invention have responded by the invention in question.

[0010] The invention aims to overcome at least some of the aforementioned problems.

[0011] Summary of the invention

[0012] The invention proposes for this purpose a method of depositing a metallic coating by thermal spraying, the method comprising the following steps, in this order:

[0013] - providing a surface to be coated, a reservoir for a mixture and a metal spraying device connected to the reservoir, the spraying device comprising a heating element and a spraying nozzle, the mixture comprising metal particles, mineral particles of substantially ellipsoidal shape, and an inert gas, the mineral particles having a hardness index greater than a hardness index of the surface to be coated, and a melting point strictly greater than the melting point of the metal particles, heating the mixture to a temperature lower than the melting point of the metal particles, by means of the inert gas, so as to obtain partially softened and ductile metal particles, spraying the heated mixture through the nozzle so as to form a jet of material towards a surface to be coated and to form the metal coating on this surface.

[0014] The method according to the invention makes it possible to solve the problem of clogging of the bore of the projection nozzle while retaining mechanical properties close to those of the metal alone, the premature erosion of the components of the projection device, of the metal particles useful for the deposition, and the erosion of the surface opposing the deposited coating. Indeed, the use of mineral particles of substantially ellipsoidal shape makes it possible to promote the rebound of the mineral particles on the surfaces in contact with said particles. The erosion phenomena previously described are therefore significantly reduced. The components of the projection device brought into contact with the mixture therefore have a longer service life, as do the opposing surfaces in contact with the coating obtained. The integrity of the metal particles to be projected is also better preserved.

[0015] Furthermore, the method according to the invention makes it possible to substantially improve the quality of the coating obtained. Indeed, when the mineral particles collide with the surface to be coated, they have a greater tendency to bounce off it due to their substantially ellipsoidal shape which promotes point contact and their hardness index, which is higher than the hardness index of the surface to be coated. This allows them not to systematically break on contact with the surface or to insert themselves into the coating produced but to bounce back on contact with this surface. The proportion of mineral particles in the metallic coating obtained is therefore significantly reduced.

[0016] Furthermore, since the melting point of the mineral particles is higher than the melting point of the metal particles, when the mixture is heated to a temperature lower than the melting point of the metal particles, a mixture is obtained in which the metal particles are softened and very ductile and, concomitantly, in which the mineral particles are preserved in their original form.

[0017] According to various characteristics of the invention which may be taken together or separately: the mineral particles are solid; the mixture comprises between 5% and 30% of mineral particles, the mixture comprises between 10% and 15% of mineral particles, an average diameter of the mineral particles does not differ by more than 60% from an average diameter of the metal particles; an average diameter of the mineral particles does not differ by more than 40% from an average diameter of the metal particles; the mineral particles have a hardness index higher than the hardness index of the metal particles; the mineral particles are made of glass; the metal particles are made of aluminum; the metal particles are made of an aluminum-based alloy;

[0018] - the method comprises a preliminary step consisting of degreasing the projection surface;

[0019] - during the projection stage, the heated mixture is projected onto the projection surface at a speed between 200 m / s and 1200 m / s;

[0020] - the steps of the method are repeated several times depending on the desired coating thickness; wherein the melting point of the metal particles differs by at least 100°C from the melting point of the mineral particles, preferably differs by at least 150°C and more preferably by at least 250°C; the average density of the mineral particles of the mixture does not differ by more than 40% from the average density of the metal particles of the mixture, preferably it does not differ by more than 20% from an average density of the metal particles;

[0021] - during the heating step, the mixture of particles is heated to a temperature between 50% of the melting point of the metal particles and 95% of the melting point of said metal particles.

[0022] The invention further relates to a mixture intended for the manufacture or repair of a functional part for an aircraft by the method as previously described, the mixture comprising metallic particles, ellipsoidal mineral particles, and a neutral gas, the mineral particles having a hardness index greater than a hardness index of the surface to be coated, and a melting point greater than the melting point of the metallic particles.

[0023] Brief description of the figures

[0024] Other objects, characteristics and advantages of the invention will appear more clearly in the description which follows, made with reference to the appended figures, in which:

[0025] - Figure 1 is a schematic view of a method for depositing a metal coating by thermal spraying according to an exemplary embodiment of the invention; - Figure 2 is a schematic side view of an assembly according to an embodiment of the invention;

[0026] - Figure 3 is a microscope image of an aluminum deposit comprising 15% of alumina-based mineral particles produced by a deposition process according to the prior art;

[0027] - figure 4a is a microscope image of an aluminum deposit made by the deposition method according to the invention;

[0028] - Figure 4b is a close-up view of the image shown in Figure 4a, in which a glass-based mineral particle can be distinguished;

[0029] - figure 5 schematically illustrates a metallic particle and a mineral particle;

[0030] - Figure 6 is a SEM (Scanning Electron Microscope) view of an example of mineral particles used (glass particles).

[0031] Detailed description of the invention

[0032] With reference to Figure 1, the invention relates to a method 100 for depositing a metal coating by thermal spraying. The thermal spraying method used in the context of the invention may be a Cold Spray method. As indicated in the introductory part of this description, this method is distinguished from other thermal spraying methods by the possibility of carrying out a coating at low pressure and at low temperature.

[0033] The deposition method 100 according to the invention is implemented by means of a projection device 1 comprising at least one heating element 10 and a projection nozzle 20 and comprises the following steps:

[0034] - providing a surface S to be coated 110, a tank 2 for a mixture and the metal projection device 1, the projection device being connected to the tank,

[0035] - heating the mixture 120 to a temperature below the melting point of the PMe metal particles by means of the neutral gas, so as to obtain partially softened and ductile metal particles,

[0036] - projecting the heated mixture 130 through the nozzle 20 so as to form a jet of material towards the surface S to be coated and to form the metallic coating on this surface.

[0037] In the following, we will return in more detail to the different steps of the deposition method 100 according to the invention. The heating element 10 makes it possible to heat the particles contained in the reservoir 2 by means of the neutral gas. The mixture comprising the particles is intended to be projected onto the surface S to be coated in order to form a metallic coating. This metallic coating is used in particular to repair components that have undergone wear in operation but it can have other uses. In the context of the invention, these components are essentially components of an aircraft but this is not mandatory, the components being able to be any component requiring a coating by metallic deposition. In principle, the metallic coating R to be deposited can therefore be made of the same material as the component on which it is intended to be deposited but this is not mandatory.In the context of the invention, the surface S to be coated designates both the surface of the component (or more generally of the part) and the surface of the metal coating being formed.

[0038] The heating element 10 may be any heat source enabling the mixture to be brought to the desired temperature by means of the neutral gas. Preferably, the heating element 10 has reduced dimensions in order to have a compact and handy projection device 1. The heating element 10 does not necessarily need to be in or in the immediate vicinity of, i.e. attached to, the tank 2 comprising the mixture. Indeed, what is important is to have appropriate exposure of the mixture to the heat emitted by the heating element 10.

[0039] Thus, according to the exemplary embodiment illustrated in Figure 2, the reservoir 2 is separated from the projection device 1. The advantage of such a configuration is to have a reservoir with a larger capacity, that is to say having a higher internal storage volume. In addition, the internal volume of the projection device 1 can advantageously have smaller dimensions, which makes it possible to have a more compact projection device 1. In this configuration, the reservoir 2 can be connected to the projection device 1 by a conduit 11 for conveying the mixture. In this regard, the projection device 1 can be equipped with an internal cavity (not visible) and a supply orifice 12, connected to this internal cavity, which makes it possible to receive the mixture coming from the conduit 11 and to convey it to the internal cavity. Once it is in the internal cavity, the heating element 10 is configured to heat the mixture.

[0040] The tank 2 is not necessarily separated from the projection device 1 as illustrated in figure 2. The tank 2 can in fact be fixed on an external wall of the projection device 1.

[0041] The heating element 10 is preferably adjacent to the internal cavity in order to allow efficient heating of the mixture. Indeed, the closer the heating element 10 is to the internal cavity, the faster the heating of the mixture. As previously indicated, the mixture comprises metal particles PMe and mineral particles PMi. The mixture of particles may advantageously comprise a neutral gas by means of which the metal particles PMe and the mineral particles PMi are heated. The term "neutral gas" has the conventional meaning attributed to it in the field of chemistry.

[0042] The metal particles PMe are the metal precursor for the metal coating to be deposited on the surface S to be coated while the mineral particles PMi are intended for cleaning the projection nozzle 20. Thus, the mineral particles are not intended to enter into the composition of the coating obtained even if, in practice, it is not possible to obtain a coating completely free of mineral particles. We will return to this in more detail later in this description.

[0043] The metal particles PMe must be softened in order to form a homogeneous coating on the surface S to be coated due to the impact speed of the metal particles which leads to their crushing. Conversely, the structure of the mineral particles PMi must be preserved so that they produce a sufficient friction force when they pass through a bore of the projection nozzle 20. In this regard, in the context of the invention, the mineral particles have a melting point strictly higher than the melting point of the metal particles, which makes it possible, during a step 120 of the method 100 according to the invention, to heat the mixture to a temperature lower than the melting point of the metal particles and therefore lower than the melting point of the mineral particles, so as to obtain a mixture in which the metal particles are partially softened and ductile and in which the mineral particles PMi are intact.This makes it possible to achieve both a uniform metal coating and effective cleaning of the spray nozzle bore.

[0044] As previously stated, the particle mixture is heated to a temperature below the melting point of the metal particles and therefore below the melting point of the mineral particles. More specifically, the particle mixture can be heated to a temperature between 50% of the melting point of the metal particles and 95% of the melting point of said metal particles depending on the ductility of the material from which these metal particles are made. The more ductile the material from which the metal particles are made, the lower the heating temperature of the particle mixture can be. Thus, heating the particle mixture to a temperature representing 95% of the melting point of the metal particles is preferable for materials with low ductility.

[0045] For example, when the metal particles are made from pure aluminum, the particle mixture can be sprayed at 300°C even though the melting point of pure aluminum is close to 650°C. When the metal particles are made from an aluminum alloy, for example a 7XXX series alloy, the particle mixture can be heated to 600°C to be sprayed onto the surface S to be coated. The choice of the heating temperature of the particle mixture is a compromise between softening of the material and spraying efficiency.

[0046] Preferably, the melting point of the metal particles differs by at least 100°C from the melting point of the mineral particles, more preferably by at least 150°C and even more preferably by at least 250°C. This facilitates the choice of the heating temperature during the heating step 120 and makes it possible to reduce the edge effects on the structure of the mineral particles when the melting point of the mineral particles is too close to that of the metal particles. The consequences of the melting of the mineral particles would be numerous since, on the one hand, the cleaning of the bore of the projection nozzle 20 would be ineffective and, on the other hand, the proportion of the mineral in the final coating would be very high, which is not desirable.In practice, the melting point of metal particles and that of mineral particles depend respectively on the nature of the metal and mineral chosen, so that the temperature difference between these two melting points depends above all on the choice of material previously made.

[0047] Once the mixture has been heated during step 120, the spray nozzle 20 makes it possible to form a jet of material towards the surface S to be coated and thus makes it possible to form the coating layer R on this surface. In this regard, it advantageously comprises an outlet orifice 21 and a bore connecting the internal cavity to this outlet orifice 21.

[0048] According to an alternative embodiment, the heating element 10 is located in the immediate vicinity of the projection nozzle 20 so that at least the portion of the mixture intended to be projected comprises partially softened metal particles PMe. It is therefore not necessary to wait for the entire mixture to be heated to begin projection of the portion of the mixture already heated. Still according to this alternative embodiment, the internal cavity may be formed of several compartments. The internal cavity may comprise at least one proximal compartment of the heating element 10 which is intended to contain the portion of the mixture comprising the partially softened metal particles and, in addition, comprise at least one distal compartment of the heating element 10 which connects the conveying orifice 12 to the proximal compartment capable of receiving the other portion of the mixture, i.e. the portion of the mixture which is not heated or which is almost not or only slightly heated.

[0049] According to a particularly advantageous embodiment variant, the heating element 10 and the projection nozzle 20 form a single part. According to this embodiment variant, the part functions as an acceleration nozzle which makes it possible both to heat the mixture and to project this mixture so as to form a jet of material in the direction of the surface S to be coated. The use of an acceleration nozzle is also advantageous in that it makes it possible to further improve the compactness of the projection device 1 as well as the impact speed of the particles and therefore the compactness of the layer produced. Other configurations within the reach of those skilled in the art are conceivable provided that they allow the implementation of the heating step 120 and the projection step 130 according to the invention.

[0050] According to the invention, the mineral particles PMI have a substantially ellipsoidal shape and a hardness index greater than the hardness index of the surface S to be coated. The shape of the mineral particles, namely ellipsoidal, and their hardness index as previously defined, produce a synergistic effect making a large portion of the mineral particles capable of rebounding on the surface S to be coated when they are projected onto said surface by the projection device 1. Indeed, their substantially ellipsoidal shape (see figure 6) makes it possible to form with the surface S to be coated an ellipsoid / plane point contact characterized by the existence of a force originating from the point of contact, for direction the straight line perpendicular to the tangent to the surface S to be coated at this point and having for direction the opposite direction of movement of the particles at the moment of entering into collision with the surface.According to a preferred embodiment, the PMi mineral particles are spherical in shape.

[0051] Incidentally, unlike known metal coatings which contain between 40% and 50% of mineral particles for 40% to 60% by mass of mineral particles in the initial particle mixture, the metal coating of the invention contains only 1% to 2% for an initial proportion of 15% to 30%. The proportion of PMi mineral particles in the metal coating obtained is therefore significantly reduced in comparison with what is conventionally obtained in processes using angular mineral particles. The inventors of the present invention therefore take advantage of the high rebound elasticity (coefficient of restitution between 0.5 and 1) of the PMi mineral particles as presently disclosed to solve both the problem of bore clogging and that of the high proportion of minerals in the coating.Indeed, when mineral particles are present in high proportion in the R coating obtained, this leads to a coating corresponding more to a ceramic-metal composite than to a metallic coating.

[0052] However, a ceramic-metal composite coating has mechanical properties that are very different from those of a metallic coating, particularly a quasi-pure coating, made with the same metal and having the same thickness. The ceramic-metal composite coating is in fact more fragile than a metallic coating, which can be detrimental to the use to which it must be put. Figure 3 illustrates a coating obtained by a process according to the prior art. The coating was obtained in particular by carrying out a Cold Spray thermal projection deposition process of a mixture comprising aluminum particles and 15% of angular mineral particles of alumina (AI2O3). In Figure 3, a large number of black areas corresponding to irregular grains of alumina can be seen. These irregular grains can have a deleterious effect when rubbing against an opposing surface and a destructive effect on the coating by erosion during its formation.The resulting coating consists of aluminum and 25% alumina particles, which corresponds to a ceramic-metal composite coating.

[0053] On the contrary, in Figure 4a which illustrates a metallic coating R in aluminum obtained by the deposition process 100 according to the invention, the black areas are almost non-existent. This coating was obtained by spraying a mixture comprising aluminum particles and 15% of ellipsoidal glass PMi mineral particles. The proportions of mineral particles in the initial mixture are therefore the same as for the coating in Figure 3. Figure 4a highlights an almost “pure” metallic microstructure. The metallic coating R obtained by the process 100 of the invention is therefore of much better quality than those of the prior art since it is more “pure”. It should be noted that Figures 3 and 4a were captured at the same magnification scale, which allows them to be compared. Figure 4b allows an intact PMi mineral particle to be visualized in the metallic coating R.

[0054] As mentioned in the introduction to this description, obtaining a metallic coating with low proportions of PMi mineral particles makes it possible to reduce the phenomenon of rupture under load generally observed in the presence of very angular defects. In addition, the phenomenon of erosion of the metallic coating observed during the formation of the coating is considerably limited since the hammering of the coating surface is considerably reduced. This makes it possible to increase the projection efficiency, i.e. to obtain a ratio of the quantity of projected material to the quantity of material present in the final coating that is superior. In addition, the significant reduction in mineral filler in the R coating reduces its abrasive nature and therefore makes it possible to significantly reduce the deterioration, i.e. the wear, of the surface opposing the R coating by friction.The coating can therefore be used in a greater number of applications than those previously envisaged. Very advantageously, the PMi mineral particles are solid. This makes it possible to reduce the number of mineral particles that break when they are projected onto the surface S to be coated at very high speeds. Indeed, during the projection step 130, the heated mixture can be projected onto the surface S to be coated at a speed of between 200 m / s and 1200 m / s. The speed of the PMi mineral particles at the nozzle outlet can therefore be very high. At speeds close to 1200 m / s, even if the hardness index of the PMi mineral particles is higher than that of the surface S to be coated, a certain number of particles can break by colliding with the surface (surface of the component or surface of the metal coating being formed).However, this phenomenon generates material breakages which increase the proportion of mineral particles in the resulting R coating. The fact that the PMi mineral particles are solid reduces, or even prevents, impact breakages which can be observed, for example, when the mineral particles are hollow at high speed.

[0055] According to another particular implementation of the method according to the invention, the initial mixture (provided during step 110), comprises between 5% and 30% of mineral particles PMi, preferably between 10% and 15% of mineral particles. 5% is the minimum proportion of mineral particles in the mixture which makes it possible to obtain sufficient unblocking of the bore of the projection nozzle 20. The proportion of mineral particles in the mixture must not exceed 30% in order to obtain a heated mixture of appropriate viscosity for projection and adequate filling of the surface by the metal. When the proportion of mineral particles PMi in the mixture is between 10% and 15%, continuous cleaning of the bore is obtained while having a heated mixture of appropriate viscosity for the formation of a good quality coating. The optimal proportion of mineral particles can vary depending on the nature of the mineral from which the particles are made.

[0056] According to a particular implementation of the method according to the invention, the average diameter of the mineral particles PMi does not differ by more than 60% from an average diameter of the metal particles PMe, preferably it does not differ by more than 40% from an average diameter of the metal particles. This makes it possible to have good consistency of the output speed in the jet of material leaving the projection nozzle 20. Better consistency is obtained when the dimensions of the mineral particles PMi and the metal particles PMe are similar, namely when the average diameter of the mineral particles PMi does not differ by more than 20% from an average diameter of the metal particles PMe. Figure 5 illustrates a metal particle PMe with a diameter d eand a mineral particle PMi of diameter dj. As illustrated, if the metal particles PMe can have any shape, the mineral particles PMi are substantially ellipsoidal. It should therefore be understood that the term "diameter" has, in the context of the invention, the broad meaning and designates the greatest distance between two points of the same particle.

[0057] Similarly, the particle density also makes it possible to improve the velocity cohesion at the nozzle outlet when the average density of the mineral particles PMi does not differ by more than 40% from the average density of the metal particles PMe, preferably it does not differ by more than 20% from an average density of the metal particles PMe. These particular implementations can be combined with those previously described.

[0058] According to a particular implementation of the method according to the invention, the mineral particles have a hardness index greater than or equal to the hardness index of the metal particles. In the context of the present invention, the hardness index is measured according to the Mohs scale, a scale typically used to classify materials according to their hardness. The ellipsoidal mineral particles are thus well suited to the deposition method of the invention for most surfaces used in the aeronautics industry. This particular implementation can be combined with those previously described.

[0059] Preferably, the material from which the metal particles are made has a hardness index similar to that of the material from which the surface S to be coated is made. Indeed, the metal particles can advantageously be made of the same material as the material of the surface to be coated. For example, a mixture of particles comprising metal particles made of 7XXX aluminum could be projected onto a 7XXX substrate. That being said, the projected mixture of particles is heated and therefore has a softening greater than that of the substrate.

[0060] In this regard, it is advantageous for the PMi mineral particles to be made of glass when the surface S to be coated is made of aluminum. Indeed, the glass particles have, in this particular implementation, a hardness index substantially equal to 5 on the Mohs scale which on the one hand ensures sufficient rigidity to avoid breaking on contact with the surfaces of the aluminum components and on the other hand which gives them a high coefficient of restitution (close to 1), i.e. a high elasticity on rebound, considering ellipsoidal glass particles.

[0061] At this point, it should be noted that it is indeed the ellipsoidal shape of the particles in combination with an appropriate choice of material - in this example glass - in terms of hardness that makes it possible to obtain this high coefficient of restitution. A low-mineral metallic coating (i.e. comprising 1% to 5% of mineral particles) cannot be obtained using non-ellipsoidal mineral particles made of glass. For example, with prior art deposition processes comprising barely 5% by mass of non-ellipsoidal silicon carbide (SiC) particles in the initial mixture, 30% of mineral particles are obtained in the final coating even though the silicon carbide has a hardness index greater than or equal to 9 on the Mohs scale.Thus, the implementation of the deposition method 100 according to the invention with a mixture comprising mineral particles having a high hardness index compared to that of the surface S to be coated is not sufficient to obtain a mineral-poor metallic coating if said mineral particles are angular.

[0062] Similarly, having mineral particles PMi of substantially ellipsoidal shape without these particles having a hardness index higher than the hardness index of the surface S to be coated is not sufficient to obtain a mineral-poor metallic coating even if this makes it possible to clean the projection nozzle 20. Indeed, as described previously, this will result in the mineral particles breaking when they are projected onto the surface S to be coated. Let us recall that during a thermal projection deposition process, the particles are projected at speeds of between 200 m / s and 1200 m / s. The particles therefore move at a very high speed.

[0063] According to a particularly advantageous implementation of the method according to the invention, the mixture comprises PMe metallic particles made of aluminum. Thermal spraying, in particular by Cold Spray, of PMe metallic particles made of aluminum is particularly suitable for this Cold Spray process due to the low melting point of aluminum. However, it should be emphasized that aluminum-based alloys can also be used, as well as any metal and any metal alloy whose melting point is lower than or equal to the temperatures used in Cold Spray deposition processes. These temperatures are generally at most 600°C.

[0064] Depending on the coating thickness required to repair the surface S to be coated, it may be necessary to repeat steps 110 to 130 several times. In particular, it may be necessary to repeat steps 120 to 130 several times. If the amount of the mixture in the internal cavity of the spraying device 1 is sufficient, it is indeed not necessary to repeat this step.

[0065] The surface S to be coated may further undergo preliminary treatments in order to improve the adhesion of the coating R to said surface. Thus, in an exemplary implementation of the deposition method 100 of the invention, a step 105 may be provided consisting of degreasing the surface S to be coated prior to the step 110 of providing the surface S to be coated, the reservoir 2 and the projection device 1. Other surface treatments such as polishing or even material removal may also be envisaged to carry out the repair of the worn surface. In this regard, it should be noted that the surface S to be coated is not necessarily flat as illustrated in the figures. It may also have any other shape, the shape typically being that of the component or part on which the invention is implemented.

[0066] The invention further relates to an assembly for depositing a metal coating by thermal spraying according to the method 100 as previously described, said assembly comprising the tank 2 for a mixture and the metal spraying device 1 connected to the tank, the spraying device 1 comprising the heating element 10 and the spraying nozzle 20.

[0067] The invention further relates to a mixture intended for the manufacture or repair of a functional part for an aircraft by the method as previously described, the mixture comprising the metal particles PMe and the mineral particles PMi of ellipsoidal shape, the mineral particles having a hardness index greater than a hardness index of the projection surface, and a melting point greater than the melting point of the metal particles.

[0068] The configurations shown in the figures cited are only possible examples, in no way limiting, of the invention which on the contrary encompasses the design variants within the reach of those skilled in the art.

Claims

CLAIMS 1. Method (100) of depositing a metallic coating (R) by thermal spraying, the method comprising the following steps, in this order: - providing a surface (S) to be coated (110), a reservoir (2) for a mixture and a metal spraying device (1) connected to the reservoir (2), the spraying device (1) comprising a heating element (10) and a spraying nozzle (20), the mixture comprising metal particles (PMe), ellipsoidal mineral particles (PMi) and a neutral gas, the mineral particles having a hardness index greater than a hardness index of the surface (S) to be coated, and a melting point strictly greater than the melting point of the metal particles (PMe), - heating the mixture (120) to a temperature below the melting point of the metal particles (PMe) by means of the neutral gas, so as to obtain partially softened and ductile metal particles, - projecting the heated mixture through the nozzle (20) so as to form a jet of material towards a surface (S) to be coated and to form the metallic coating (R) on this surface.

2. Method (100) according to claim 1, in which the mineral particles (PMi) are solid.

3. Method (100) according to any one of the preceding claims, wherein the mixture comprises between 5%m and 30%m of mineral particles (PMi), preferably between 10%m and 15%m of mineral particles.

4. Method (100) according to any one of the preceding claims, wherein an average diameter of the mineral particles (PMi) does not differ by more than 60% from an average diameter of the metal particles (PMe), preferably not by more than 40% from an average diameter of the metal particles (PMe).

5. A method (100) according to any preceding claim, wherein the mineral particles have a hardness index greater than the hardness index of the metal particles.

6. Method (100) according to any one of the preceding claims, wherein the mineral particles (PMi) are made of glass.

7. Method (100) according to any one of the preceding claims, in which the metal particles (PMe) are made from aluminum and / or an aluminum-based alloy.

8. Method (100) according to any one of the preceding claims, comprising a prior step (105) consisting of degreasing the surface (S) to be coated.

9. Method (100) according to any one of the preceding claims, wherein, during the projection step (130), the partially melted mixture is projected onto the projection surface at a speed of between 200 m / s and 1200 m / s.

10. Method (100) according to any one of the preceding claims, in which steps (110) to (130) are repeated several times depending on the desired metal coating thickness (R).

11. Method (100) according to any one of the preceding claims, wherein the melting point of the metal particles (PMe) differs by at least 100°C from the melting point of the mineral particles (Pmi), preferably differs by at least 150°C and more preferably by at least 250°C.

12. Method (100) according to any one of the preceding claims, wherein the average density of the mineral particles (Pmi) of the mixture does not differ by more than 40% from the average density of the metal particles (PMe) of the mixture, preferably it does not differ by more than 20% from an average density of the metal particles (PMe).

13. Method (100) according to any one of the preceding claims, wherein, during the heating step (120), the mixture of particles is heated to a temperature between 50% of the melting point of the metal particles (PMe) and 95% of the melting point of said metal particles (PMe).

14. Mixture intended for the manufacture or repair of a functional part for an aircraft by the method of claims 1 to 13, the mixture comprising metallic particles (PMe), mineral particles (PMi) of ellipsoidal shape, and a neutral gas, the mineral particles (PMi) having a hardness index greater than a hardness index of the surface (S) to be coated, and a melting point greater than the melting point of the metallic particles.

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