Method of manufacturing a part comprising a metal substrate covered with a protective layer and a part manufactured according to this method

Abstract

Method for manufacturing a part comprising a metal substrate covered with a protective layer and a part manufactured according to this method 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 protective layer (Pro), comprising steps of: preparation (A) of a surface to be covered, of the substrate (Sub) formation (B) by projection, according to a HVOF type projection method, of a coating layer (Rev), on the prepared surface (S1), this coating layer (Rev) being formed by the projection of a powder mixture containing submicron metal carbide grains, a step of impregnation (C) of the coating layer (Rev) with an organic impregnant (Io) forming together an impregnated layer,a finishing step by polishing (D) at least one surface of said impregnated layer imp to form a protective layer pro having a polished surface S3 having a roughness Ra less than 0.2μm or less than 0.1μm depending on the applications. Figure to be published with the abstract: Figure 2,

Description

Title of the invention: Method for manufacturing a part comprising a metal substrate covered with a protective layer and a part manufactured according to this method TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of a method of 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 metal substrate at least partially covered with a protective layer and a part manufactured according to this method. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] For example, methods are known for manufacturing parts comprising the application to a metal substrate, via a metal bath, of a layer of hard chrome coating, 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] We are therefore seeking to eliminate the use of hexavalent chromium which is harmful to health and the environment.

[0006] Known in particular from document EP2956564 B1 or from document FR3002239 of the same patent family is a method for manufacturing a part having a coating layer by HVOF type spraying on a substrate. This method comprises a first step of preparation by sandblasting of a surface to be covered of the substrate, so as to increase its surface roughness Ra. The method then comprises a step of forming the coating layer by HVOF type spraying, of a powder mixture containing WC type metal carbide grains and a binder of this carbide in Co and Cr on the prepared substrate. These carbide grains have dimensions strictly less than 1 pm and in particular less than 450 nm + / - 50 nm and the thickness of the coating layer thus formed is less than 50 pm. Then, the method comprises a step of finishing the surface of said coating layer so as to obtain the required dimension and surface condition in the plan.These deposits provide corrosion resistance of around 500 hours in salt spray and a reduction in the risk of rupture / detachment of the layer formed on the substrate.

[0007] There is a need to reduce the manufacturing cost of this process and to improve the corrosion resistance, particularly for low coating thicknesses (<80 μm) of this manufacturing process.

[0008] The invention presented here therefore relates to the improvement of this method of producing deposits by HVOF. Summary of the invention

[0009] The invention provides a solution improving the method described in document EP2956564 B1, by adding an impregnation step.

[0010] One aspect of the invention relates to a method of manufacturing a part comprising a metal substrate at least partially covered with a protective layer, the method comprising steps of: • preparation of a surface to be covered with the substrate; • formation by projection of a powder mixture containing submicron metal carbide grains according to an HVOF type projection process, on the prepared surface of the substrate, of a coating layer, • characterized in that it further comprises after the formation step: • a step of impregnating the coating layer with an organic impregnant, together forming an impregnated layer, • a finishing step by polishing at least one surface of said impregnated layer so as to form the protective layer comprising a polished surface having a roughness Ra of less than 0.2 pm.

[0011] Thanks to the invention, the step of impregnation with an organic impregnant makes it possible to reduce the thickness of the coating layer compared to a coating layer described in the prior art while improving the level of corrosion resistance. Indeed, the organic impregnant will enter the pores of the coating layer, fill them and thus form with the coating layer a more compact protective layer than a coating layer without impregnation. The organic impregnant can enter completely into the coating layer up to the surface of the substrate, thus forming the compact protective layer making it possible to attach a prepared substrate surface which can only be cleaned by degreasing (unlike the solution described in document FR3002239).It is therefore possible to reduce the necessary thickness of the coating layer as in document FR3002239 while having better corrosion protection, in particular for thin protective layers (< 80 pm).

[0012] Furthermore, in the prior art described in document EP2956564 B1, it was necessary to prepare the surface of the substrate by sandblasting to increase the roughness of the surface and thus increase the adhesion surface of the coating layer. Here, thanks to the invention, the protective layer being more compact, the level of mechanical adhesion of the protective layer on the substrate to be coated can be reduced without increasing the risk of detachment. Thus the invention allows such a substrate to be only degreased and not sandblasted.

[0013] In addition to the characteristics which have just been mentioned in the preceding paragraph, the method according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations:

[0014] According to one embodiment, the organic impregnant is based on a Dimethacrylate Ester comprising a fluidity to enter the pores of the coating layer having a diameter of between 0.03 pm and 0.3 pm. Such an organic impregnant makes it possible to have a fluidity allowing it to penetrate into the pores of the coating layer. The microporosities of the coating layer are thus filled thanks to the low viscosity of the Dimethacrylate Ester which can fill pores having a diameter of between 0.03 pm and 0.3 pm.

[0015] According to one embodiment, the organic impregnant may be based on a Dimethacrylate Ester or an epoxy or even based on an alcohol comprising a fluidity to enter the pores of the coating layer having a diameter of between 0.03 pm and 0.3 pm.

[0016] According to one embodiment, the preparation step is a step of cleaning a substrate to obtain a prepared surface free of dirt or grease, with a roughness Ra of less than 2 pm. The preparation step may in fact be solely a cleaning, in particular a degreasing simplifying and reducing the cost and time of such a method. The step of impregnating the coating layer with an organic impregnant makes it possible to carry out the formation step by spraying the powder mixture containing metal carbide grains onto a substrate having a roughness Ra of less than 2 pm when it is cleaned, unlike the prior art of document FR3002239 involving a sandblasting step on the substrate. The preparation step may therefore be solely a degreasing step.

[0017] According to an example of the preceding embodiment, the preparation step is only a degreasing step to obtain a degreased prepared surface.

[0018] According to one embodiment, the metal carbide grains each have a dimension strictly less than 1 pm (submicron carbides) and the maximum thickness of the coating layer thus formed is less than 100 pm, for example between 70 and 90 pm. The submicron carbide grain powder allows a reduction in the risk of rupture / detachment of the protective layer formed on the substrate while having an improved level of protection against corrosion compared to to that of patent EP2956564 B1 due to the impregnant. In addition, this allows a reduction in the projection time required to produce the coating layer and thus a reduction in the mass of the coating layer thus formed.

[0019] Furthermore, reducing the thickness of the coating layer improves resistance to detachment under stress (also called "spalling") and reduces the forces transmitted by the coating-substrate interface.

[0020] According to one embodiment, the step of impregnating the coating is carried out with a brush by dipping the brush into a container of organic impregnant and applying it to the surface of the coating layer.

[0021] According to one embodiment, the step of impregnating the coating comprises a sub-step of polymerizing the impregnant on the coating layer before the finishing step.

[0022] Another aspect of the invention relates to a part obtained by the method according to the invention, with or without the different possible combinations of the characteristics previously described.

[0023] Another aspect of the invention relates to a part comprising a metal substrate and a protective layer at least partially covering the substrate, made of submicron metal carbide impregnated with an organic impregnant and comprising a polished surface having a roughness of less than 0.1 qm or 0.2 qm. The surface is polished having a roughness of less than 0.1 qm or 0.2 qm depending on the uses of the part.

[0024] Such a part has a lower production cost than a part according to the method described in document EP2956564 B1 while having at least the same level of corrosion resistance.

[0025] According to one embodiment, the polished surface is intended to be subjected to fretting and / or journaling. (journaling means the forces subjected to a cylindrical part of an axis, generally its end, pivoting in or on a part which holds it (yoke, bearing, flange, bearing)).

[0026] According to an example of this embodiment, the part is a hinge pin or an axle in the aeronautical field.

[0027] According to one embodiment, the polished surface is intended to be subjected to the static and / or dynamic sealing zones. For example, the part is a sliding rod.

[0028] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0029] The figures are presented for information purposes only and in no way limit the invention.

[0030] [Fig.1a] represents a schematic representation of a section of a part comprising a coating layer on a substrate.

[0031] [Fig.lb] represents a schematic representation of a section of a part comprising an impregnated layer on the substrate.

[0032] [Fig.lb]] represents a schematic representation of a section of a part comprising a protective layer on the substrate.

[0033] [Fig.2] shows a schematic representation of the manufacturing process.

[0034] [Fig.3] schematically shows a sample having undergone a corrosion test in a saline atmosphere comprising a polished surface according to the invention and a polished protective surface according to the prior art. DETAILED DESCRIPTION

[0035] The figures are presented for information purposes only and in no way limit the invention.

[0036] As indicated previously, the manufacturing method according to the invention is preferably used to produce a part 1 of which an enlargement of a section is shown schematically in [Fig. 1c].

[0037] In particular, part 1 is used in the aeronautical field.

[0038] The sectional part 1 shown in [Fig. 1c] comprises a metal substrate Sub partially shown and a Pro protective layer including a polished S3 surface.

[0039] [Fig.2] represents a flowchart of a manufacturing process for part 1.

[0040] Part 1 is generally produced by machining to present at least one portion of a cylindrical surface in the case of a rod, which can be a hinge pin, an axle or even a sliding rod of a landing gear. This cylindrical portion is hereinafter called the Sub substrate. The Pro protective layer is therefore annular and in this case intended to operate in static and / or dynamic sealing zones. For example, the Pro protective layer is intended to undergo joint friction to allow the rod to slide relative to a barrel of the landing gear or is intended to be subjected to fretting and / or journaling, for example for a hinge pin or an axle.

[0041] The protective layer Pro must provide both protection against corrosion of the part, sealing between the surface of the protective layer 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 flaking tests with alternating tensile and compression movements with a load ratio of R=-1.

[0042] It is noted that the substrate Sub is a metal alloy of the steel or titanium type.

[0043] As seen in [Fig.2], the manufacturing process of part 1 comprises a preparation step A of a surface SI to be covered, of the substrate Sub, to obtain a prepared surface SL In this case, in this example the preparation step is a degreasing step and therefore does not require sanding or sanding. Of course, according to another example and for reasons other than cost reduction, roughness can also be modified at the substrate preparation stage, for example by sanding.

[0044] In this case, in this example, the substrate preparation step is only a cleaning, degreasing of the substrate having on its cleaned SI surface for example a roughness Ra less than 2qm for example 1.9 qm. The roughness of a surface can for example be measured according to the standards ISA3274-1997, ISO 4287-1997, ISO 4288-1996, ISO 11562.

[0045] The method for manufacturing the part 1 comprises, after the preparation step A, a step B of forming a coating layer Rev, on the surface SI, in this case degreased, of the substrate Sub, by HVOF type projection, of a powder mixture containing submicron metal carbide grains. [Fig. 1a] represents a section of the part 1 comprising the substrate sub and the coating layer Rev deposited on the surface SL

[0046] In particular, in this example the grains have dimensions strictly less than Ipm and the thickness Epmax of the coating layer Rev thus formed is in this example less than 90 pm, for example between 70 and 90 pm. This powder mixture contains grains of metal carbide coated in a binder, in this case tungsten carbide WC coated in cobalt Co and chromium Cr. The cobalt Co serves as a binder and the chromium Cr serves as protection against oxidation.

[0047] In this example, this powder mixture is in the form of agglomerates / aggregates with a particle size of less than 50qm and preferably less than 30qm to form a maximum coating layer of less than 90qm and greater than 70qm. The agglomerates are generally produced by sintering to create bridges between the carbide and the binder material. This sintering is generally carried out with a furnace to melt the binder without decarburizing the metal carbide grains.

[0048] Ideally, the WC metal carbide grains present in this powder mixture are calibrated to have a size strictly less than Ipm, and preferably of the order of 400 to 800nm ​​in average particle size.

[0049] 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. Among examples of possible compositions, there may be WCCo which can be in the form of a mixture of 83% WC and 17% Co or in the form of a mixture of 88% WC and 12% Co or WCCoCr.

[0050] Since the Rev coating layer is thin, and the powder agglomerates / aggregates have a small particle size, the resulting roughness at the surface S2 of the Rev coating layer in this example is of the order of 3 pm immediately after projection.

[0051] The method for manufacturing the part 1 comprises, after the forming step B, a step C of impregnation of the coating layer Rev with an organic impregnant lo, together forming an impregnated layer lmp.

[0052] [Fig. 1b] represents the part 1 in section with the impregnated layer lmp comprising the coating layer Rev impregnated with the organic impregnant lo.

[0053] The organic impregnant lo may be based on dimethacrylate ester, epoxy, alcohol, etc. and must have sufficient fluidity to enter the pores of the coating layer Rev. Indeed, the impregnant must be able to penetrate the coating layer via the network of open pores which, in this example, represents 10% of the porosity of the coating layer with a median pore diameter of the order of 0.20 μm.

[0054] Thus the impregnation step can therefore be carried out by brushing the surface S2 of the coating layer Rev with the organic impregnant lo, for example with a brush.

[0055] The impregnation step C comprises a sub-step of waiting for polymerization of the impregnant forming the impregnated layer lmp comprising an impregnated surface S2'.

[0056] As previously stated, the coating layer Rev has a roughness Ra of the surface S2, here Ra of S2 = 3 pm of the same order of magnitude as the roughness Ra of the surface SI, here in this example of 2 pm. In addition, the impregnated layer lmp of organic impregnant merges with the coating layer Rev which does not generate additional roughness hence Ra of the impregnated surface S2' of the impregnated layer lmp identical to Ra of S2. Indeed, the pores of the coating layer Rev are filled by the organic impregnant which has a low viscosity to penetrate all pore sizes, even the smallest (from 0.03 pm to 0.3 pm) and therefore does not remain on the surface S2 of the coating layer Rev.

[0057] The method further comprises a finishing step by polishing D of the surface S2' of said impregnated layer lmp so as to ensure that the roughness Ra of the polished surface S3 of the protective layer Pro is less than 0.1 pm or less than 0.2 pm depending on the intended applications. The polishing can for example be carried out using a diamond strip.

[0058] The step of polishing the impregnated layer lmp reduces the thickness of this layer until the protective layer Pro is obtained having its polished surface S3. In this case, the step of polishing the impregnated layer lmp reduces the thickness of this layer by approximately 20 μm. The impregnated layer lmp having in this example a thickness of less than 90 μm, for example between 70 and 90 μm. The protective layer Pro therefore comprises a thickness, measured between the polished surface S3 and the surface SI, between a minimum thickness Epmin of 50 μm and a maximum thickness Epmax of 70 μm.

[0059] Indeed, a simple polishing of the protective surface S2' makes it possible to obtain a roughness Ra of less than 0.1 pm or less than 0.2 pm, thus allowing the polished surface S3 to be subjected to the static and / or dynamic sealing zones.

[0060] It should be noted that traditionally, a step of grinding the coating layer is required to obtain a given layer geometry and layer surface condition. However, grinding an annular layer formed on a straight cylindrical portion requires providing a significant layer thickness to ensure that after grinding, a minimum layer thickness is maintained on the substrate.

[0061] By eliminating the step of grinding the annular layer, the method according to the invention makes it possible to directly obtain the desired layer thickness without having to grind the part, thus eliminating the risk of the appearance of grinding defects (The grinding of a cylindrical annular layer frequently leads, due to uncertainties in positioning the part on the grinding machine, to the appearance of zones of layer that are too thin, difficult to detect and likely to promote premature corrosion of the substrate). The invention makes it possible to eliminate this risk of having a locally too thin layer that cannot be detected.

[0062] [Fig. 3] schematically represents a test piece 2 comprising on the left a polished surface S3 of the protective layer Pro formed like the part 1 according to the method of the invention, and on the right a surface of the coating layer S2, that is to say without the impregnation step C.

[0063] Test piece 2 was tested for corrosion resistance, the test carried out was under saline atmosphere (salt fog) according to ASTM B117.

[0064] Test piece 2' corresponds to test piece 2 after 1000 hours under saline atmosphere.

[0065] It can thus be seen that the surface S3 of the impregnated part of the test piece 2 does not show any trace of pitting (left part) even after 1,000 hours of exposure to the salt spray. Whereas the surface S2 of the non-impregnated part (right part) is attacked: first with traces of pitting 9 and then with a generalized development of corrosion 90.

[0066] In addition, a wear resistance test was carried out on a part 1 obtained with the method of the invention having a cylindrical zone with a diameter of 10 mm comprising the surface S3 and on which is mounted a bronze ring (AMS4590), with the presence of grease. The wear test comprises a first phase of 500 cycles of pressure of the ring on the surface S3 under 50 MPa then a second phase of 500 cycles under 100 MPa and a last phase with 4,000 cycles under 200 MPa, and a frequency of 0.1 Hz. The coefficient of friction and the wear rate (measurement of the external diameter of the axis and the internal diameter of the ring) are recorded every 500 cycles, and each time the grease is renewed. The test showed that the part 1 obtained with the method of the invention comprises a performance level of similar wear resistance compared to that achieved according to the method of document EP2956564B1.

[0067] The manufacturing method of the invention therefore makes it possible to obtain a less expensive part than according to the method of document EP2956564 B1 while comprising a metal substrate Sub at least partially covered with a protective layer Pro having similar wear resistance.

[0068] Furthermore, surprisingly, starting from a substrate that has only been cleaned without modifying its roughness in the preparation step, unlike the substrate that has undergone a sanding or sanding step in the preparation step in document EP2956564 B1, it is found that in the invention the protective layer resists at least the same level of wear and corrosion as the coating layer of this document EP2956564 B1, i.e. without impregnation.

[0069] In addition, a spalling test, also called spalling resistance, i.e. no loss of adhesion between the deposit of the protective layer Pro and the substrate Sub of a test piece, was carried out, with an alternation of tensile and compression movement with a load ratio of R=-1, on samples with a protective layer Pro with a thickness of 80 μm in the finished state. The test showed that a part comprising a metal substrate Sub at least partially covered with a protective layer Pro obtained according to the manufacturing method of the invention has a spalling resistance of 1140 MPa, 1250 MPa and 1300 MPa for 80 μm of thickness.

[0070] Finally, on the same principle as the chipping test, fatigue tests were carried out on a part 1 obtained with the method of the invention. These tests consist of alternating tensile and compression movements under a load ratio R=0.1. The results obtained showed that the reduction defined in the past for this type of deposit / test is still respected in the aeronautics field.

[0071] Thanks to all these characteristics, the method 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 retaining intact the characteristics necessary for good sealing between the part 1 and another part.

[0072] It should be noted that the carbide grains used may be in a type of metal carbide other than tungsten carbide and the binding materials may be in materials other than Chromium and Cobalt.

[0073] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

Claims

1. Method for manufacturing a part (1) comprising a metal substrate (Sub) at least partially covered with a protective layer (Pro), the method comprising steps of: - preparing (A) a surface to be covered of the substrate (Sub); in which the preparation step (A) is a step of cleaning a substrate (Sub) to obtain a prepared surface (SI) free of dirt or grease, with a roughness Ra less than 2 pm, - forming (B), by spraying a powder mixture containing submicron metal carbide grains according to an HVOF type spraying process, on the prepared surface (SI) of the substrate, a coating layer (Rev),in which the grains of metal carbide each have a dimension strictly less than Ipm (submicron carbides) and the maximum thickness (Ep max) of the coating layer (Rev) thus formed being less than 100pm characterized in that it further comprises after the formation step (B): • a step of impregnation (C) of the coating layer (Rev) with an organic impregnant (lo) together forming an impregnated layer (lmp), • a step of finishing by polishing (D) at least one surface (S2') of said impregnated layer (lmp), so as to form the protective layer (Pro) comprising a polished surface (S3) having a roughness Ra less than 0.2pm.,

2. Method according to claim 1, in which the organic impregnant (io) is based on a Dimethacrylate Ester, or an epoxy or an alcohol comprising a fluidity to enter the pores of the coating layer (Rev) having a diameter between 0.03pm and 0.3pm.

3. A method according to claim 1 or 2 wherein the preparation step (A) is only a degreasing step to obtain a degreased prepared surface (SI).

4. A method according to any preceding claim in wherein the impregnation step (C) of the coating is carried out with a brush by dipping the brush into a container of organic impregnant and applying it to the surface of the coating layer.

5. Method according to any one of the preceding claims in which the step of impregnating (C) the coating comprises a sub-step of polymerizing the impregnant on the coating layer (Rev) before the finishing step.

6. Part (1) comprising a metal substrate and a protective layer (Pro) at least partially covering the substrate, made of submicron metal carbide impregnated with an organic impregnant and comprising a polished surface (S3) having a roughness of less than 0.1 pm or less than 0.2 pm.

7. Part (1) according to the preceding claim, in which the polished surface (S3) is intended to be subjected to fretting and / or spinning.

8. Part (1) according to the preceding claim, in which the part (1) is a hinge pin or an axle in the aeronautical field.

9. Part (1) according to one of claims 6 to 8, in which the polished surface (S3) is intended to be subjected to the static and / or dynamic sealing zones.

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