Method for manufacturing a part comprising a metal substrate covered with a protective layer

Abstract

One aspect of the invention relates to a method for manufacturing a part (1) comprising a metal substrate (Sub) at least partially covered with a finished protective layer (Rf), the method including the following steps: a first step (A) of preparing an initial surface to produce a rough surface, without sandblasting, comprising a sub-step of shot-blasting an initial surface of the substrate to obtain a roughness of the rough surface having an overall height of the roughness profile of the surface Rt of between 10 µm and 15 µm and a sub-step of cleaning the rough surface (Sub); a second step (B) of forming, by spraying a powder mixture containing submicron metal carbide grains according to a HVOF thermal spraying method, on the cleaned rough surface (S2), a rough coating layer (Rb), to a thickness of between 95 μm and 120 μm; and a third finishing step (D) by polishing the surface of said rough coating layer (S2) formed from the powder mixture so as to form the finished protective layer (Rf) having a thickness of between 75 μm and 100 μm, thus forming a polished surface (S3) having a roughness of less than 0.2 μm.

Description

DESCRIPTION TITLE: Method for manufacturing a part comprising a metallic substrate covered with a protective layer TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of a method for manufacturing parts, such as aeronautical parts, comprising a substrate at least partially coated with a protective layer protecting this substrate.

[0002] The present invention relates to a method for manufacturing a part comprising a metallic substrate at least partially covered with a protective layer. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] We know, for example, of manufacturing processes for parts involving the application, via a metal bath, of a layer of hard chrome coating to a metallic substrate, serving both to protect this substrate and to give it a functional roughness.

[0004] It is known to produce the hard chrome coating layer in an electrolytic cell in the presence of chromic acid based on hexavalent chromium (Cr(VI)). Hexavalent chromium is harmful to humans and the environment, and is classified as CMR (Carcinogenic, Mutagenic, and Harmful to Reproduction).

[0005] The aim is therefore to eliminate the use of hexavalent chromium, which is harmful to health and the environment.

[0006] A process for manufacturing a part with a thermal spray coating of the HVOF (High Velocity Oxygen Fuel) type on a substrate with a thickness between 30 µm and 50 µm is known, notably from document EP2956564 B1 or document FR3002239 of the same patent family. This process includes a first step of preparing the substrate surface by sandblasting, in order to increase its surface roughness Ra by approximately 0.6 to 1.6 µm. The process then includes a step of forming the coating layer by HVOF spraying a powder mixture containing WC-type metal carbide grains and a Co- and Cr-carbide binder onto the prepared substrate. These carbide grains have dimensions The thickness of the coating layer is strictly less than 1 µm and preferably in the range of 450 nm + / - 50 nm, with a final coating layer thickness of less than 50 µm. The process then includes a surface finishing step by polishing the coating layer to ensure its roughness Ra is less than 1.6 µm, thus achieving the required dimensions and surface finish. These coatings provide corrosion resistance of approximately 500 hours in salt spray and reduce the risk of failure / delamination of the layer on the substrate. However, this solution is insufficient because the aviation industry requires improved corrosion resistance while also maintaining resistance to flaking compared to previous methods.Indeed, the corrosion test in the field of aviation currently consists of 1000 hours in salt spray, and it has been shown that corrosion resistance is not systematic, particularly on a cylindrical substrate.

[0007] Furthermore, the sandblasting step in this solution is costly and has an environmental impact. The sandblasting step increases the substrate roughness and consequently increases the surface roughness profile Rt (Rt > 20 µm). The overall surface roughness profile height Rt corresponds to the sum of the height Zp of the highest profile peak and the depth Zv of the deepest valley of the profile, within a section of length L measured relative to a mean line of the profile. In other words, it is the greatest difference between the highest peak and the deepest valley.

[0008] Furthermore, this document describes that it was previously known to deposit a coating layer, obtained with grains of several micrometers, having a thickness greater than 75 pm and then to rectify it (removing at least 50 pm for the rectification).

[0009] There is a need to reduce the manufacturing cost of this process while maintaining corrosion resistance, particularly for thin coating thicknesses (<100 pm) in the finished state of this manufacturing process.

[0010] The invention presented here therefore relates to the improvement of this process of producing deposits by HVOF. SUMMARY OF THE INVENTION

[0011] It was observed internally, without publication, that by impregnating a coating layer before polishing with an organic impregnating agent, the coating layer could have a finished thickness of less than 80 µm while meeting the criteria for corrosion resistance and flaking by avoiding the sandblasting step.

[0012] It was also noted internally, without publication, that by applying a coating layer as in document EP2956564 but with a finished thickness of 55 pm, there was still a corrosion problem in the 1000-hour corrosion test.

[0013] However, this impregnation step is an additional step and therefore a constraint in terms of cost and time, as well as from a health, safety and environmental point of view.

[0014] The invention offers a solution improving the process described in document EP2956564 B1, since it eliminates a surface sandblasting step before thermal spray coating and without adding an impregnation step while having superior corrosion resistance by passing the 1000-hour corrosion test.

[0015] One aspect of the invention relates to a method for manufacturing a part comprising a metallic substrate at least partially covered with a finished protective layer, the method comprising successively: a first preparation step without surface modification by sandblasting, comprising a substep of shot blasting an initial surface to obtain a roughness of the raw surface having an overall surface roughness profile height Rt of between 10 pm and 15 pm and a substep of cleaning the raw surface of the raw substrate, a second forming step by projecting a powder mixture containing submicron metallic carbide grains according to a high liquid pressure HVOF type thermal spraying process, onto the cleaned raw surface having its prepared roughness,a rough coating layer with a thickness between 95µm and 125µm, a third finishing step by polishing the surface of said rough coating layer made from the powdered mixture in such a way, to form the finished protective layer forming a polished surface having a roughness Ra less than 0.2pm, the finished protective layer having a thickness between 75 pm and 100 pm.

[0016] Surprisingly, by depositing a finished protective layer thicker than 75 µm, without adding any impregnation, onto a cleaned (prepared) raw substrate surface with a roughness of the raw surface having an overall surface roughness profile height (Rt) between 10 µm and 15 µm, by shot blasting only during preparation, the finished coating layer thicker than 75 µm adheres and does not peel off (unlike the prior art of document FR3002239 involving a sandblasting step on the substrate and a thinner layer). In other words, the invention does not include a sandblasting step but does include a shot blasting step. Shot blasting is a technique consisting of projecting metallic shot onto the surface of an object to perform a surface treatment, the purpose of which is to improve the appearance of the part.Shot blasting also allows for the sealing of microscopic cracks (invisible to the naked eye) that, over time, cause leaks due to internal pressure. This provides an additional guarantee against corrosion. Shot blasting, known to modify the surface structure and therefore the appearance of the object or part, allows for a greater surface roughness (Ra having a lower value) and a smaller overall surface roughness profile height Rt (here between 10 µm and 15 µm) than a sandblasting step (Rt > 20 µm), which is known for removing impurities to ensure compatibility with the adhesion of a powder or liquid coating or paint. Thus, it is surprising that using only shot blasting instead of or without sandblasting to add a coating layer allows for a thicker coating layer (finished layer greater than 75 pm) that adheres and does not peel off.In addition, because the layer is thicker, this improves corrosion resistance and thus allows it to withstand the 1000-hour corrosion test.

[0017] By initial substrate surface, we mean a surface without any change in roughness at the end of substrate manufacturing, whether by molding or machining (i.e., the initial surface has not undergone any treatment, for example, sandblasting).

[0018] By cleaned raw surface, we mean the initial surface which has undergone the preparation stage, i.e. shot blasting of the initial surface and cleaning.

[0019] By prepared surface, we mean in the following description the raw cleaned surface (preparation by shot peening of prestress according to PCS-2300 on the initial surface to achieve Ra between 0.6 and 1.6pm and cleaning).

[0020] By raw coating layer made from the powder mixture, we mean that the layer is made up of 100% material from the powder mixture and therefore does not contain any added material such as an organic impregnator.

[0021] Submicron metallic carbide means that the metallic carbide grains each have a dimension strictly less than 1 pm (submicron carbides).

[0022] HVOF thermal process refers to the thermal process known by the English name (High Velocity Oxygen-Fuel), which is a high-speed thermal process using liquid fuel (kerosene).

[0023] The invention provides a substrate with optimized raw coating thickness without increasing surface roughness through sandblasting, while simultaneously improving corrosion resistance. This allows for optimization of the powder mixture quantity, eliminating the need for a roughness modification step or an impregnation step with an organic impregnating agent, and improving corrosion resistance compared to prior art solutions. In other words, the solution eliminates costly additional steps, such as substrate preparation by sandblasting directly onto an initial surface, or after shot blasting or impregnation.

[0024] The raw thickness, ranging from 95 µm to 120 µm, is due in particular to a manufacturing tolerance in the high-speed liquid fuel (kerosene) thermal spraying process (HVOF), but also to the amount of shrinkage required during polishing to obtain a finished surface with a roughness Ra < 0.2 µm, as well as a manufacturing tolerance for part assembly. Given that the aim is to use as few submicron metal carbide grains as possible for environmental and cost reasons, while maintaining good corrosion resistance, the applicant surprisingly and unexpectedly observed that by adding 25 µm to the finished thickness of the polished surface using the process of the invention (without sandblasting) (corresponding to the coating layer thickness between 75 pm and 100 pm with a polished surface having a roughness Ra less than 0.2 pm) compared to the solution of patent FR3002239 and that mentioned in its prior art, allows to pass saline tests of 1000 hours, i.e. to double the corrosion resistance compared to the solution of patent FR3002239 and that mentioned in its prior art.

[0025] The projection step according to the invention deposits a layer thickness equal to the dimensioned thickness plus an additional thickness removed by polishing. Indeed, the polishing step removes a thickness strictly less than 30 µm (specifically between 20 and 25 µm), whereas grinding removes at least 50 µm to account for roughness as well as geometric defects of the part. Thus, after polishing, the raw coating layer thickness, by removing a maximum of 30 µm, results in a thickness between 75 µm and 100 µm and a roughness of less than 0.2 µm. Naturally, the dimensions and manufacturing tolerances of the raw substrate will be adjusted according to the manufacturing tolerances of the finished part (substrate tolerance + finished protective layer tolerance).

[0026] In conclusion, surprisingly, and contrary to what is indicated in document FR3002239, it is possible to achieve a coating thickness exceeding 75 µm without the sandblasting step (since sandblasting results in a roughness where the overall roughness profile height Rt of the raw surface is greater than 20 µm). Having a final roughness of less than 0.2 µm, and a layer formed with submicron metallic carbide grains, with a finished thickness between 75 µm and 100 µm, also eliminates coating delamination problems. Furthermore, by adding only 25 to 50 µm more coating layer than specified in document FR3002239, corrosion resistance is doubled.

[0027] Furthermore, in the prior art, it was necessary to prepare the initial or rough (after shot blasting) surface of the substrate by sandblasting to increase surface roughness and thus increase the adhesion surface of the coating layer. Here, thanks to the invention, since the protective layer is compact, it has been found that the level of mechanical adhesion of the protective layer to the cleaned rough surface of the substrate to be coated is sufficient without increasing the risk of delamination. Thus The invention allows such a substrate to clean only its raw surface comprising an overall surface roughness profile height Rt between 10 pm and 15 pm and not to modify its surface as in the prior art, by sandblasting.

[0028] In addition to the characteristics mentioned in the preceding paragraph, the process according to one aspect of the invention may have one or more complementary characteristics from among the following, considered individually or in all technically possible combinations:

[0029] According to one embodiment, the liquid fuel is kerosene.

[0030] According to one method, only the HVOF type thermal spraying process is at high pressure. This type of HVOF allows for higher particle velocities, which ensures good adhesion of small particles to the substrate.

[0031] According to one embodiment, the manufacturing process of a part includes a pre-stage of manufacturing the substrate, before the preparation stage consisting of machining a substrate forming an initial surface.

[0032] According to another embodiment, the manufacturing process of a part includes a pre-stage of substrate manufacturing, before the preparation stage, including demolding of a substrate forming an initial surface.

[0033] According to one embodiment, the process consists of a pre-stage of substrate manufacturing and successively the first stage, the second stage and the third stage.

[0034] By consisting of the pre-stage and the three successive stages mentioned previously we mean without other stages, that is to say without a stage of rectification, or sandblasting, or addition of material in the layer, for example without impregnation of organic impregnating agent.

[0035] In one embodiment, the substrate cleaning substep results in a raw surface free of dirt or grease. This cleaning substep can be a simple degreasing process, reducing the cost and time of such an operation. The preparation step improves the adhesion of submicron grains to form the raw coating deposit layer.

[0036] According to an example of the preceding embodiment, the cleaning substep is solely a degreasing step to obtain a degreased raw surface and in that the preparation step consists solely of the shot blasting substep and the cleaning substep, it improves the adhesion of submicron grains to form the coating deposition layer.

[0037] In one embodiment, the metallic carbide grains each have a size strictly less than 1 µm (submicron carbides) and are predominantly in the range of 400 to 800 nm in average grain size. Grains of this size allow for the application, via the HVOF spraying process, of a compact coating layer that adheres to a substrate surface with a prepared roughness between 0.6 and 1.6 µm. Furthermore, polishing the surface of the coating layer formed by grains of this size, whose as-sprayed deposit has a roughness Ra~ 3-5 µm, down to a roughness of 0.2 µm, provides corrosion resistance. This also reduces the spraying time required to create the finished protective layer and thus the mass of the as-sprayed coating layer.

[0038] In addition, the thickness of the coating layer has a resistance to delamination under stress (also called "spalling" >>) significantly greater than the requirements in the field of the invention and the fact that it is not thicker than 100 pm reduces the forces transmitted by the coating-substrate interface.

[0039] Another unclaimed aspect of the invention relates to a part comprising a metallic substrate and a finished protective layer, obtained according to the manufacturing process of the first aspect of the invention with or without the various features described in the preceding paragraphs.

[0040] Another unclaimed aspect of the invention relates to a part comprising a metallic substrate and a finished protective layer made of a powder mixture containing submicron metallic carbide grains deposited by an HVOF type spraying process, the finished protective layer being deposited on a rough surface of the substrate having a roughness prepared by shot peening to obtain a rough surface having a prepared roughness Ra between 0.6 and 1.6pm, and comprising a polished surface having a roughness of less than 0.2pm.

[0041] Such a part has a lower production cost than a part produced using the process described in document EP2956564 B1 while having better corrosion resistance.

[0042] According to one embodiment, the polished surface is intended to be subjected to fretting and / or doweling. (by doweling we mean the forces subjected to a cylindrical part of a shaft, generally its end, pivoting in or on a part that holds it (clevis, bearing, flange, bushing)).

[0043] According to an example of this embodiment, the part is a pivot point or axle in the aeronautical field.

[0044] According to one embodiment, the polished surface is intended to be subjected to pivoting functions (for example an axle) as well as dynamic sealing functions (for example a sliding rod).

[0045] In one embodiment, the polished surface is intended to be subjected to static and / or dynamic sealing zones. For example, the part is a sliding rod.

[0046] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0047] The figures are presented for illustrative purposes only and are in no way limiting to the invention.

[0048] [Fig. 1 a] represents a schematic representation of a cross-section of a part comprising a substrate having a rough surface.

[0049] [Fig. 1 b] represents a schematic representation of a cross-section of a part comprising a raw coating layer on a cleaned and prepared raw substrate surface.

[0050] [Fig. 1c] represents a schematic representation of a cross-section of a part including a finished protective layer on the substrate.

[0051] [Fig. 2] shows a schematic representation of the manufacturing process.

[0052] [Fig. 3] schematically shows a sample that has undergone a corrosion test in a saline atmosphere comprising a polished surface according to the invention and a protective surface polished according to the prior art. DETAILED DESCRIPTION

[0053] The figures are presented for illustrative purposes only and are in no way limiting to the invention.

[0054] As previously stated, the manufacturing process according to the invention is preferably used to produce a part 1, an enlargement of a section of which is schematically represented in Figure 1c.

[0055] In particular, part 1 is used in the aeronautical field.

[0056] Part 1 in section shown in figure 1c includes a partially shown metallic substrate Sub and a finished protective layer Rf comprising a polished surface S3.

[0057] Figure 2 represents a flowchart of a manufacturing process for part 1.

[0058] Part 1 is generally machined to present at least a portion of a cylindrical surface in the case of a rod, which could be a pivot point, an axle, or a sliding rod of a lander. This cylindrical portion is hereafter referred to as the substrate Sub. The finished protective layer Rf is therefore annular and, in this instance, designed to operate in static and / or dynamic sealing areas. For example, the finished protective layer Rf is designed to withstand seal friction to allow the rod to slide relative to a lander shaft, or to be subjected to fretting and / or doweling, for example, for a pivot point or axle.

[0059] The finished protective layer Rf must provide both corrosion protection for the part, a seal between the polished surface S3 of the finished protective layer Rf and another part, for example the barrel, to limit the risk of hydraulic fluid leaks, resistance to wear under pressure, and resistance to "spalling," also called spalling tests, with alternating tensile and compressive movements with a load ratio of R=-1.

[0060] Note that the Sub substrate is a metallic alloy of the steel or titanium type.

[0061] In the following example, we are looking for a finished part 1 with a cylinder of diameter 13mm whose total manufacturing tolerance (substrate + polishing finish) is + or - 0.4 pm.

[0062] The manufacturing of the Sub substrate here, for example, involves machining on a lathe to obtain a diameter of 12.82mm with a manufacturing tolerance.

[0063] As shown in Figure 2, the manufacturing process for part 1 includes a preparation step A of an initial rough surface S1 of the substrate Sub, to obtain a prepared initial rough surface S1n to be covered by the finished protective layer rf. Figure 1a shows a cross-section of the substrate Sub, including its initial rough surface S1, and the prepared rough surface S1n is referenced in Figure 1c and in Figure 1b, which represents part 1, including the prepared rough surface S1n covered with a rough coating layer Rb. In this example, the preparation step A includes a degreasing substep and a shot blasting substep. The preparation step A therefore modifies the roughness of the initial surface, resulting in a rough surface S1 of the substrate, by shot blasting, which is then cleaned. The cleaned rough surface S1n has therefore not undergone sandblasting or grinding.

[0064] The shot peening substep of the initial surface yields a rough surface with an overall surface roughness profile height Rt, as shown in Figure 1a, between 10 µm and 15 µm, unlike sandblasting, which produces a roughness profile with an overall height Rt exceeding 20 µm. This shot peening method also yields a prepared roughness Ra between 0.6 and 1.6 µm.

[0065] In this example, the cleaning substep is simply a degreasing of the initial raw surface S1 of the substrate, resulting in a cleaned raw surface S1n with a roughness Ra identical to that of the raw surface S1, for example, 1.6 pm. Surface roughness can be measured, for example, according to standards such as ISA3274-1997, ISO 4287-1997, ISO 4288-1996, and ISO 11562.

[0066] The manufacturing process for part 1 comprises, after preparation step A, a step B of forming a rough coating layer Rb onto the cleaned (prepared) rough surface S1n, in this case degreased, of the substrate Sub, by HVOF-type spraying of a powder mixture containing submicron-sized metallic carbide grains. Figure 1b shows a cross-section of part 1 including the substrate Sub and the rough coating layer Rb deposited on the cleaned surface. S1 n. The rough coating layer Rb includes a rough coating surface S2 visible in this figure 1 b.

[0067] In particular, in this example, the grains have dimensions strictly less than 1 µm, and the maximum thickness (Epmax) of the resulting Rb coating layer is between 95 and 120 µm; for example, in this instance, the thickness is between 100 and 110 µm. The thickness of the Rb coating layer varies according to the manufacturing tolerances of the coating layer, thus allowing a polishing finishing step (C), described later, to remove no more than 30 µm of the coating layer thickness, in this case, a maximum of 22 µm. This powder mixture contains metal carbide grains embedded in a binder, in this case, WC tungsten carbide embedded in cobalt (Co) and chromium (Cr). The cobalt (Co) acts as a binder, and the chromium (Cr) provides protection against oxidation.

[0068] In this example, the powder mixture is in the form of agglomerates / aggregates with powder particles of approximately 20-30 µm. Deposition by the HVOF process results in a stack of molten, metal-matrix ceramic powder particles. These ceramic powder particles are strictly smaller than 1 µm to form a maximum coating thickness of less than 120 µm and greater than 95 µm. The agglomerates are typically formed by sintering to create bridges between the carbide and the binder material. This sintering is generally performed in a furnace to melt the binder without decarburizing the metal carbide grains.

[0069] Ideally, the WC metal carbide grains present in this powder mixture are calibrated to have a size strictly less than 1 pm, and preferably in the order of 400 to 800 nm in average particle size.

[0070] It is noted that the present invention can be implemented with other types of chemical compositions containing at least one metal carbide and at least one binder. Examples of possible compositions include WCCo, which can be in the form of a mixture of 83% WC and 17% Co, or a mixture of 88% WC and 12% Co, or WCCoCr.

[0071] Since the raw Rb coating layer, and the powder agglomerates / aggregates have a small particle size, the resulting surface roughness of The raw coating S2 of the raw coating layer Rb in this example is on the order of 3pm immediately after spraying.

[0072] The manufacturing process for part 1 includes, directly after the forming step B, a third finishing step involving polishing the raw coating surface S2 to form the polished surface S3 with a roughness Ra of less than 0.2 µm, until part 1 is obtained with the desired diameter, for example, 13 mm, corresponding to a radius of 6.5 mm. The finished protective layer Rf has a thickness between 75 µm and 100 µm. In this example, the thickness of the finished protective layer Rf is between 88 and 92 µm due to the tolerances in the substrate manufacturing Sub and the tolerances in the polishing finishing step.

[0073] The third finishing stage by polishing is therefore formed on the raw coating surface S2, removing a part Rrp from the raw coating layer Rb thus forming the finished protective layer Rf having a thickness between 88 and 92 pm.

[0074] The raw Rb coating surface is porous, comprising in this example (depending on the type of powder) pores with diameters ranging from 0.3 pm to 0.04 pm, and 80% predominantly between 0.25 and 0.1 pm. The median pore diameter is 0.2 pm per pore, with a porosity of 0.04 mL / g.

[0075] As previously mentioned, the raw coating layer Rb has a surface roughness Ra of S2, here Ra of S2 = 3 pm, of the same order of magnitude as the surface roughness Ra of S1, here in this example 2 pm. The third finishing step, polishing C of the raw surface S2, ensures that the roughness Ra of the polished surface S3 of the finished protective layer Rf is less than 0.2 pm. Polishing can, for example, be carried out with a diamond belt.

[0076] The polishing step of the raw coating layer Rb reduces its thickness until a specific part dimension is achieved, in this case a cylinder with a diameter of 13 mm and a manufacturing tolerance of ±0.4 µm. Specifically, the polishing step reduces the thickness of the raw coating layer Rb by removing a portion Rrp from the raw coating layer, which has a thickness between 12 and 18 µm. The finished protective layer Rf thus has a thickness between 88 and 92 µm in this example, with a roughness Ra of 0.2 µm, allowing for a part diameter of 13 mm (substrate: 12.82 mm with a tolerance of ±0.4 µm). of + or - 4pm + (2 times (radii) the thickness of the coating layer 88 and 92 pm) + or - 0.4 pm.

[0077] The polishing of the raw surface S2 by removing a thickness of a portion Rrp of the raw coating layer Rb until the finished protective layer Rf is formed, until a roughness Ra of less than 0.2 pm is obtained, thus having a polished surface 53 to be subjected to static and / or dynamic sealing zones while having corrosion resistance.

[0078] It should be noted that traditionally, a rectification step of the coating layer is required to obtain a given layer geometry and surface finish. However, rectifying an annular layer formed on a straight cylindrical section necessitates a significant layer thickness to ensure that, after rectification, a minimum layer thickness is maintained on the substrate.

[0079] By eliminating the annular layer grinding step, the process according to the invention makes it possible to directly obtain the desired layer thickness without having to grind the coating layer of the part, thus eliminating the risk of grinding defects (grinding a cylindrical annular layer frequently leads, due to uncertainties in the positioning of the part on the grinding machine, to the appearance of excessively thin layers, which are difficult to detect and can promote premature corrosion of the substrate). The invention eliminates this risk of having a locally excessively thin, undetectable layer.

[0080] Figure 3 schematically represents a test specimen 2 comprising on the left a polished surface S3 of the finished protective layer rf formed like part 1 according to the process of the invention, and on the right a surface of the coating layer 54 comprising a maximum thickness of 50 pm with a roughness Ra of 1.6 pm.

[0081] Specimen 2 was tested for corrosion resistance; the test was carried out under a saline atmosphere (salt spray) according to ASTM B117.

[0082] Test tube 2' and 2" corresponds to test tube 2 after 1000h under saline atmosphere.

[0083] It can thus be seen that the surface S3 of the part according to the invention, with a minimum deposit thickness of 75 µm of test specimen 2, shows no trace of pitting (left part) even after 1000 µm of exposure to salt spray. Whereas The surface S4 having a thin coating layer (right part) is attacked: first with pitting traces 9 then with a generalized development of corrosion 90.

[0084] Furthermore, a wear resistance test was performed on a part 1 obtained using the process of the invention. This part has a cylindrical area with a diameter of 10 mm, comprising the surface S3, on which a bronze ring (AMS4590) is mounted, with grease present. The wear test comprises a first phase of 500 cycles of pressure exerted by the ring on the surface S3 under 50 MPa, followed by a second phase of 500 cycles under 100 MPa, and a final phase of 4,000 cycles under 200 MPa, at a frequency of 0.1 Hz. The coefficient of friction and the wear rate (measured by the external diameter of the shaft and the internal diameter of the ring) are recorded every 500 cycles, and the grease is renewed each time. The test showed that part 1 obtained with the process of the invention includes a similar level of wear resistance performance compared to that produced according to the process of document EP2956564 B1.

[0085] The manufacturing process of the invention therefore makes it possible to obtain a part that is cheaper than according to the process of document EP2956564 B1 while comprising a metallic substrate Sub at least partially covered with a finished protective layer rf having similar wear resistance and better corrosion resistance.

[0086] Furthermore, and surprisingly, starting with a substrate that was only cleaned without altering its roughness by sandblasting during the preparation stage, unlike the substrate that underwent sandblasting or grinding during the preparation stage in document EP2956564 B1, it is observed that in the invention the protective layer remains adhered to the raw surface, which has a roughness of the raw surface with an overall surface roughness profile height Rt between 10 µm and 15 µm. Moreover, due to the increased thickness of the coating layer, the finished substrate of the invention is more resistant to corrosion than the coating layer of document EP2956564 B1, i.e., one with a thickness of less than 50 µm and a roughness Ra of 1.6 µm.

[0087] In addition, a spalling test, also called a spalling resistance test, i.e., no loss of adhesion between the deposited finished protective layer Rf and the substrate Sub of a test specimen, was carried out with alternating movements tensile and compressive testing with a load ratio of R=-1 was performed on samples with a finished protective layer Rf of 10 µm thickness in the finished state. The test showed that a part comprising a metallic substrate Sub at least partially covered with a finished protective layer Rf obtained according to the manufacturing process of the invention exhibits spalling resistance under 1140 MPa, 1250 MPa, and 1300 MPa for a thickness of 100 µm.

[0088] Finally, following the same principle as the spalling test, fatigue tests were performed on a part 1 obtained using the process of the invention. These tests consist of alternating tensile and compressive movements under a load ratio R=0.1. The results obtained showed that the reduction previously defined for this type of deposition / testing is still met in the aeronautical field.

[0089] Thanks to all these characteristics, the process of the invention makes it possible to obtain a finished part that is lighter, less expensive and of at least the same level of performance while keeping intact the characteristics necessary for a good seal between part 1 and another part.

[0090] It should be noted that the carbide grains used may be of a different type of metallic carbide than tungsten carbide and the bonding materials may be of materials other than Chromium and Cobalt.

[0091] Unless otherwise specified, the same element appearing on different figures has a unique reference.

Claims

DEMANDS

1. A method for manufacturing a part (1) comprising a metallic substrate (Sub) at least partially covered with a finished protective layer (Rf), the method comprising successively: - a first preparation step (A) without modification of the surface by sandblasting, comprising a sub-step of shot blasting an initial surface of the substrate to obtain a roughness of the raw surface having an overall height of surface roughness profile Rt between 10 pm and 15 pm and a sub-step of cleaning the raw surface (Sub), - a second formation step (B), by projecting a powder mixture containing submicron metallic carbide grains according to a high liquid pressure HVOF type thermal spraying process, onto the cleaned raw surface (S2) having its roughness prepared, of a raw coating layer (Rb), with a thickness between 95pm and 125pm, - a third finishing step by polishing (D) on the surface of said rough coating layer (S2) formed from the powder mixture so as to form the finished protective layer (Rf) forming a polished surface (S3) having a roughness Ra less than 0.2pm, the finished protective layer (Rf) having a thickness between 75 pm and 100 pm.

2. A method according to claim 1, comprising a pre-step of manufacturing the substrate (Sub), before the preparation step (A), consisting of machining a substrate forming an initial surface (S1).

3. A method according to claim 1 or 2, wherein the cleaning substep of the preparation step (A) is solely a degreasing step to obtain a degreased raw surface (S2).

4. A method according to any one of the preceding claims wherein the metallic carbide grains are predominantly of the order of 400 to 800nm ​​in average particle size.

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