FR2883574A1 - "THERMAL PROJECTION DEPOSITION METHOD OF ANTI-WEAR COATING" - Google Patents

Abstract

AC-HVAF type thermal spray deposition method of an anti-wear coating on a mechanical part, said coating being made of copper base alloy comprising from 30% to 42% of nickel, by mass, and from 4% to 6% indium, by mass.

Description

2883574 i

  The subject of the invention is a thermal spraying method for depositing an anti-wear coating on a mechanical part and, more particularly, a gas turbine engine part made of titanium or titanium alloy such as a fan blade or a fan blade. turbomachine compressor.

  Blower or compressor blades are a good example of parts subject to wear during turbine operation. These vanes are embedded by their feet in grooves of suitable shape, formed on the periphery of rotating disks, hereinafter referred to as compressor disks or blower.

  During operation of the turbojet engine, the blade roots move in said grooves under the effect of centrifugal force and vibrations. The shape of the blade roots is adjusted to that of the grooves to allow such relative movements. The surfaces of the blade roots which abut against the edge of said grooves, under the effect of the centrifugal force, undergo significant compressive stresses (which are generally cyclic). These constraints combined with the vibratory movement damage and wear said surfaces. The observed wear is all the more important that the blade roots and the discs of the blower or the compressor are made of titanium or titanium alloy. Indeed, the coefficient of friction titanium / titanium is quite high.

  To protect the blade roots, it is known to use anti-wear coatings which are copper-nickel alloys (CuNi), copper-aluminum alloys (CuAI) or even copper-nickel-indium alloys (CuNiIn). It is generally preferred to use the latter type of alloy (CuNiIn) because it has better mechanical properties at high temperatures.

  To deposit these alloys on the blade roots, one usually uses a thermal projection method called plasma projection. This method can be implemented using a plasma gun such as that described in US application 3,145,287. Plasma spraying involves bringing alloy powder to a plasma torch producing a gas jet at a very high temperature: more than 2,000 C. The particle projection speed is, for its part, between 100 and 400 m / s.

  The microstructure of the plasma spray deposited coating, however, has a very high porosity and oxidation, which affect the mechanical properties of the coating. In addition, this coating adheres poorly on titanium or its alloys. Thus, in practice, there is rapid peeling of the coating that poorly withstands the stresses to which it is subjected during operation of the turbine.

  A second type of thermal spraying is also used for depositing anti-wear coatings: the HVOF type thermal spray for High Velocity Oxy Fuel, which consists of taking advantage of the combustion of oxygen and a combustible gas such as the propane, propylene, hydrogen, or methylacetylene propadiene, for heating and propelling grains of alloy powder melted at a very high speed. The temperatures reached with this process are between 1500 and 2000 C and the projection speeds between 300 and 700 m / s. An example of HVOF projection nickel base alloy deposition is described in US patent application 5,518,683.

  Although the lifetime of the deposits obtained with a HVOF process is better than that of the deposits made by plasma spraying, there is nevertheless a rapid peeling of the coating under normal operating conditions of the turbomachine.

  The object of the invention is to propose a new deposition process making it possible to deposit anti-wear coatings which are more resistant to the stresses to which they are subjected than the coatings obtained by the existing processes.

  To achieve this object, the subject of the invention is a method of depositing by thermal spraying an anti-wear coating on a mechanical part, characterized in that said coating is deposited by thermal spraying of the so-called AC-HVAF type, for Activated Combustion High Velocity Air Fuel.

  The thermal projection type called AC-HVAF is a known technique which has the main difference with the projection HVOF mentioned above, the use of a mixture of air and a combustible gas such as propane (instead of a mixture of oxygen and gas) that is burned to heat and propel an alloy powder at a very high speed. With the projection AC-HVAF, the projection speed of the fused alloy particles is substantially between 600 and 800 m / s and the temperatures reached vary between 800 and 1500 C.

  The temperatures reached during an AC-HVAF type projection are lower than those reached during a HVOF or plasma type projection.

  This limits the oxidation of the projected particles.

  In addition, the projection speeds that can be obtained with the AC-HVAF process are higher than the speeds obtained by plasma or HVOF projection. Thus, the time between the moment when the particles are projected and the one where they reach the part to be coated, during which the particles are particularly sensitive to oxidation, is decreased. This again results in a reduction in the oxidation of the coating.

  In addition, the high kinetic energy of the particles projected onto the part to be coated allows, on the one hand, a better attachment of these particles on this part and, on the other hand, to obtain a more compact coating which has a porosity less than that obtained with the methods used until now. In particular, the structure of the coating obtained is unitary and non-lamellar.

  The reduction of the porosity and the quantity of oxide in the coating does not result in a concrete reduction of the number of potential failure initiators in the microstructure of the coating. This results in a better resistance to mechanical stresses and more particularly to compressive stresses to which the coating is subjected. Since, moreover, the coating is more compact and adheres better to the part which it covers, it is practically seen that the flaking problems occur less rapidly during operation of the gas turbine, and that the lifetime of the coating of the invention is much better than that of known coatings.

  Finally, the thermal projection AC-HVAF is by nature a more economical method than the plasma projection.

  Advantageously, said coating is a copper base alloy comprising from 30% to 42% of nickel, by weight, and from 2% to 8% of indium, by weight.

  Advantageously still, it is possible to use for said copper base alloy coating comprising from 34% to 38% of nickel, by weight, and from 4% to 6% of indium, by mass.

  As already pointed out, CuNiln coatings are interesting coatings because they are mechanically very resistant to high temperatures.

  In its research aimed at improving the service life of anti-wear coatings of this type, the Applicant Company found that the melting temperatures of CuNiln alloys were much lower than the temperatures reached during a plasma spraying, and lower than those reached during a HVOF type projection. On the contrary, the temperatures attained by an AC-HVAF projection appear to be of the same order as the melting temperatures of said CuNiln alloy. Thus, it is found that using the AC-HVAF process, it is possible to melt a CuNiln alloy avoiding unnecessary oxidation, linked to too high temperatures. The ACHVAF process is therefore particularly suitable for depositing CuNiIn coatings.

  Advantageously, a layer of lubricating varnish comprising, for example, molybdenum disulphide (MoS2) and an organic resin is deposited on the CuNiln anti-wear coating after it has been deposited. Indeed, CuNiln coatings have a high roughness and it is recommended to cover it with a layer of varnish with a low coefficient of friction, to promote sliding and limit wear. The CuNiln coating and lubricant layer gives completely satisfactory results in terms of protection of the part and durability of the coating.

  Although the only example of a part cited herein is a titanium compressor or turbine engine fan blade, it is clear that the process of the invention can be used to coat any type of part, be it or not in titanium or in one of its alloys. For example, the method can be used to coat at least one of two gas turbine parts, whatever they are, that may be in contact with each other.

  The invention and its advantages will be better understood on reading the following detailed description of embodiments of the invention given as non-limiting examples. The description refers to the appended figures in which: FIG. 1 is a comparative graph; FIG. 2 is a micrograph of a CuNiln coating deposited by AC-HVAF projection according to the process of the invention; FIG. 3 is a micrograph of a CuNiln coating deposited by plasma spraying; FIG. 4 schematizes a device making it possible to simulate the stresses exerted on a blade root of a fan in service; and FIG. 5 is a graph showing a cycle of variation of the pulling force exerted on a fan blade root in use as a function of time.

  The graph of FIG. 1 represents on the abscissa the projection speeds in m / s and on the ordinate the C projection temperatures obtained with different thermal projection methods. On this graph are plotted temperature and velocity ranges, plasma, HVOF and AC-HVAF projections. Furthermore, the range of melting temperatures of a copper base alloy, such as the CuNiln alloy, is shown.

  It can be seen from this diagram that, in accordance with what has been previously described, the temperatures attained in AC-HVAF projection are adapted to the melting range of the CuNiln alloy used according to the invention, and make it possible to melt these alloys without overheating. unnecessary that would promote oxidation. Furthermore, it can be seen that higher projection speeds can be obtained by the AC-HVAF projection.

  We will now describe an example of implementation of the method according to the invention, according to which a CuNiln alloy has been deposited on a piece of titanium alloy of the TA6V type. The operating conditions were as follows: Device used: AC-HVAF torch model SB-500 marketed by Uniquecoat Technologies.

  Powder used: Composition: CuNiln alloy comprising 36% by weight of Ni, 5% by weight of In, and a balance of Cu; Particle size: 11 to 45 microns; Torch loading: 8kg / h; Carrier gas: nitrogen.

  Torch operating parameters: Gas: propane; Air pressure: 85 psi; Pressure 1, Propane: 74 psi Propane Pressure 2 (0): 38 psi; Carrier gas pressure: 41 psi; Distance: 150 to 165 mm; Coating Deposition Rate: 45 microns per pass.

  Information about the coated part: Preparation: sanding with aluminum oxide particles of average size equal to 300 microns; Initial temperature: 29 C; Temperature variation: 50 to 95 C.

  The thickness of the deposited coating was 165 microns but greater thicknesses could have been obtained without particular difficulty. The porosity of the coating measured was less than 1%.

  The micrograph of FIG. 2 was made on the CuNiln coating deposited by AC-HVAF according to the invention, while the micrograph of FIG. 3 was made on a CuNiln coating obtained by plasma spraying.

  The oxides and porosities appear as black spots among the coating layer 2 deposited on the substrate 1.

  It is clear that the presence of oxides and porosities is less in the coating of FIG. 2 than in that of FIG. 3. Moreover, it can be seen that the coating of FIG. 2 has a compact and unitary microstructure while that that of the coating of Figure 3 is lamellar. Therefore the coating deposited with the process of the invention is less conducive to delamination (and therefore to flaking) than that obtained by plasma spraying. In the end, the microstructure of the coating of FIG. 2 is mechanically more resistant.

  To simulate the mechanical stresses at which a fan blade is subjected in use, a device similar to that of FIG. 3 has been made in which a mechanical part 10 which replaces the blade is mounted at its foot 14 inside. a groove 15 defined between two uprights 16a and 16b held in position between two jaws 18. The assembly thus produced is similar to a dovetail assembly. The uprights 16a and 16b here replace the fan disk. The foot 14 of the part 10 has two surfaces 14a and 14b in contact with the uprights 16a and 16b. A cyclic traction force F was exerted on the workpiece 10.

  The evolution of the force F as a function of time is represented in FIG.

  The behavior of a coating: CuNiln deposited by ACHVAF projection according to the invention was tested for 30,000 traction cycles. After 30,000 cycles, no flaking and no wear were observed. With a plasma sprayed CuNiln coating, flaking appears between 15,000 and 19,000 cycles.

  This test illustrates the significant improvement in terms of coating life, which the invention makes it possible to obtain

Claims (7)

  1. A method of thermal spraying an antiwear coating on a mechanical part, characterized in that said coating is deposited by thermal spraying type AC-HVAF.   2. Method according to claim 1, characterized in that said coating is copper base alloy comprising 30% to 42% nickel, by mass, and 2% to 8% indium, by mass.   3. Method according to claim 2, characterized in that said coating is copper base alloy comprising 34% to 38% nickel, by mass, and 4% to 6% indium, by mass.   4. Method according to claim 3, characterized in that said coating is copper base alloy comprises 36% nickel, by mass, 5% indium, by mass.   5. Method according to any one of the preceding claims, characterized in that said mechanical part to be coated is a piece of titanium or titanium alloy.   6. Method according to any one of the preceding claims, characterized in that said coating is deposited on at least one of two pieces of gas turbine, which may be in contact with each other.   7. Method according to any one of the preceding claims, characterized in that said coating is deposited on a blade root of a fan or compressor of a turbomachine, and / or the disk of the fan or the compressor in which said blade root is recessed. i0