EP3899081B1 - Method for manufacturing a core - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the field of manufacturing the leading edge for Organic Matrix Composite (OMC) fan blades.

STATE OF THE ART

It is recalled that a blade conventionally has a leading edge and a trailing edge. The leading edge corresponds to the anterior part of the airfoil which faces the airflow and which divides the airflow into a lower surface flow and an upper surface flow, and a trailing edge which corresponds to the rear part of the airfoil. In the environment of a turbomachine, of an aircraft, it is possible for solid debris to be caught in a flow of air circulating in the turbomachine. This debris will then strike the leading edge of a blade and risk damaging it. Consequently, it is customary to reinforce the leading edge of the blades. This technical arrangement is all the more important in the case of a CMO blade. Indeed, the composite material may poorly resist perforation.

It is for example known from the prior art to have a CMO fan blade having a titanium leading edge.

The document FR1051992 describes a known method of manufacturing such a blade. This method takes place as follows: two sheets, intrados and extrados, formed, are shaped, via a hot isostatic compaction operation, around a refractory alloy core whose geometry corresponds to the internal geometry of the desired leading edge . After shaping, the core, which is a reusable tool, is removed and the leading edge is machined only on its outer surfaces to obtain the final geometry of the part.

This method makes it possible to control the internal shape of the cavity of the leading edge, which is a replica of the blade on which the leading edge will be placed, thus making it possible to do no re-machining of the internal cavity of the leading edge. In addition, this technique makes it possible to control and facilitate final machining operations thanks to the presence of the internal core which makes it possible both to stiffen the assembly and to have integrated dimensional references which makes it possible to avoid having recourse , as for the other techniques, to complex machining tools. Thus, these different arrangements induce a significant reduction in the cost of the manufacturing range due to the reuse of the cores, then considered as tools.

• Le noyau doit être indéformable dans la gamme thermomécanique de fabrication du bord d'attaque afin d'assurer la forme de la cavité interne du bord d'attaque
• Le noyau ne doit permettre aucune réaction chimique entre son matériau et le matériau du bord d'attaque
• Le noyau ne doit permettre aucune adhérence ou collage entre son matériau et le matériau du bord d'attaque

For this so-called core shaping technique, the latter must have three main characteristics in relation to the fact that the shaping step is carried out via a thermomechanical cycle at high temperature, of the order of 800 - 1000°C, during which, the core is in contact with the titanium leading edge elements for several hours:

• The core must be non-deformable within the thermomechanical manufacturing range of the leading edge in order to ensure the shape of the internal cavity of the leading edge
• The core must not allow any chemical reaction between its material and the material of the leading edge
• The core must not allow any adhesion or sticking between its material and the material of the leading edge

The first characteristic, linked to the choice of core material, makes it possible not to have to machine the internal cavity of the leading edge.

The second avoids or minimizes the chemical decontamination of the surfaces of the internal cavity of the leading edge.

The third completely conditions the reuse of the nuclei and therefore the economic viability of this technique.

The last two features are related and require special kernel processing. Indeed, the metal alloys selected for the core are nickel-based or cobalt-based alloys in order to be sufficiently rigid not to deform during high-temperature shaping cycles. However, this type of alloy brought into contact at high temperature with the titanium alloys of the part are reactive with each other and form solid solutions or intermetallic compounds, which leads at best to contamination of the titanium alloy, to worse a prohibitive bonding between nickel / cobalt and titanium.

It is therefore essential to carry out a treatment adapted to the core to avoid contamination and sticking.

A technical solution consists of inserting an anti-diffusion barrier between the two metal alloys in contact, namely the nickel or cobalt base alloy of the core and the titanium alloy of the leading edge, which will undergo thermomechanical treatment at high temperature for many hours.

To do this, a method described by the document EN 1653221 is the realization of a nitriding or nitro-carburizing of the core in nickel or cobalt base. This treatment generates a superficial layer rich in nitrogen and carbon of a few tens of microns on the surface of the core ensuring the role of anti-diffusion barrier.

However, tests carried out on a scale using this technique have revealed deficiencies in the effectiveness of the anti-diffusion barrier generated by the nitriding or carbo-nitriding of the nickel- or cobalt-based core. Traces of contamination are observed on the internal areas of the titanium leading edge and degradation of the nitrided layer of the core is observable from the first compaction cycle, very strongly compromising the ability to reuse the core and therefore the model many times. economics of technology.

Additionally, the document FR2463191 discloses a nickel base alloy substrate coated with a layer of a cobalt base alloy.

DISCLOSURE OF THE INVENTION

• (a) fourniture d'un noyau initial en alliage base nickel,
• (b) projection thermique sur le noyau initial d'une couche d'un alliage base cobalt,

In this context, the objective of the present invention is to provide a process for the manufacture of a core for the production of a leading edge of a fan blade, which meets the three criteria set out above: thermomechanical non-deformability, chemical neutrality vis-à-vis the leading edge and lack of adhesion to the leading edge. According to a first aspect, the invention proposes a process for manufacturing a core for the production of a leading edge of a fan blade, characterized in that it comprises the steps of:

• (a) supply of an initial nickel base alloy core,
• (b) thermal spraying on the initial core of a layer of a cobalt base alloy,

according to claim 1. In a particularly advantageous manner, the thermal spraying of this type of alloy, resistant to hot friction, provides a chemical inertia which makes it possible to produce an anti-diffusion barrier between the nickel base alloy core and sheets titanium used for the manufacture of the fan blade. Thus, this process makes it possible to cover the core with a layer guaranteeing thermomechanical stability, protecting against chemical contamination and avoiding any adhesion of the blade parts to the core.

The cobalt base alloy may include carbon.

The cobalt base alloy comprises, as a mass percentage, between 26% and 32% molybdenum, between 7% and 20% chromium, between 1% and 5% silicon and less than 1% carbon.

The layer can have a hardness between 40 and 65 HRC.

The deposited layer may have a thickness of between 100 microns and 2 millimeters, preferably 500 microns.

Step (b) can be performed using a method selected from: supersonic flame spraying, blown arc plasma spraying or plasma torch deposition.

The method may also comprise, following step (b) of thermal spraying, a step (c) of heat treatment of the layer, carried out between 800 and 1000°C.

The method may further comprise, following step (b) of thermal spraying, a step (d) of machining by rectification.

The method may further comprise, following step (b) of thermal spraying, a step (e) of heat treatment in air, comprising a first stage of thirty minutes at a temperature between 300° C. and 400° C. C, a second stage of thirty minutes at a temperature between 500°C and 700°C, a third stage of thirty minutes at a temperature between 800°C and 1000°C, and cooling in ambient air, for oxidize the layer. According to a second aspect, the invention proposes a nickel base alloy core according to claim 8.

DESCRIPTION OF FIGURES

• La figure 1 est une vue en coupe, microscopique de la surface d'un noyau selon l'invention.
• La figure 2 est un schéma bloc d'un procédé selon l'invention.

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

• The figure 1 is a sectional, microscopic view of the surface of a core according to the invention.
• The figure 2 is a block diagram of a method according to the invention.

In all the figures, similar elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION Manufacturing process

• (a) fourniture d'un noyau initial 11 en alliage base nickel,
• (b) projection thermique sur le noyau initial 11 d'une couche 12 d'un alliage base cobalt, selon la revendication 1.

According to a first aspect, the invention relates to a process for manufacturing a core 1 for the production of a leading edge of a fan blade, the process essentially comprises the steps of:

• (a) supply of an initial core 11 of nickel base alloy,
• (b) thermal spraying on the initial core 11 of a layer 12 of a cobalt base alloy, according to claim 1.

Step (a) of supplying the initial core can be carried out by machining a nickel-based alloy block to obtain the initial core 11.

Then, the initial core 11 can be sandblasted (step (a1)) to increase the roughness of its outer surface. This arrangement advantageously facilitates the attachment of the layer 12 projected in step (b).

Finally, the initial core 11 can be cleaned and degreased (step (a2)). This step makes it possible to guarantee a surface state, of the initial core 11, that is optimal for the next step (b) of projection.

As stated above, the - next - step (b) consists of the thermal spraying on the initial core 11 of a layer 12 of a cobalt-based alloy, comprising chromium and at least one element among tungsten and/or molybdenum.

It is specified that tungsten, molybdenum and chromium may be present in the form of carbide.

Furthermore molybdenum can be used in an intermetallic mixture. It is recalled that an intermetallic mixture is a mixture comprising at least one metalloid. Metalloids being chemical elements whose properties are intermediate between those of metals and non-metals, or are a combination of these properties. The metalloids are the following elements: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Astate. In this case, the metalloid preferentially used in combination with molybdenum is silicon.

According to the invention, the cobalt-based alloy comprises, as a mass percentage, between 26% and 32% molybdenum, between 7% and 20% chromium, between 1% and 5% silicon and less than 1% carbon.

Preferably, the cobalt base alloy may comprise 29% molybdenum, 8.5% chromium, 2.6% silicon and less than 0.08% carbon.

Alternatively, the cobalt base alloy may comprise 28% molybdenum, 18% chromium, 3.4% silicon and less than 0.08% carbon.

Thus, in a particularly advantageous manner, the thermal spraying of these types of alloys, resistant to hot friction, provides a chemical inertia which makes it possible to produce an anti-diffusion barrier between the initial core 11 made of nickel base alloy and metal sheets. titanium used for the manufacture of the fan blade.

According to a first preferred technical arrangement, the thermal spraying can be carried out by supersonic flame, according to a so-called “High Velocity Oxy-Fuel” (HVOF) method or according to a so-called “High Velocity Air-Fuel” (HVAF) method. The HVOF method is particularly preferred because it consists of spraying the cobalt base alloy at very high speed with a moderate temperature, which generates very little porosity in the layer 12 deposited.

According to another technical arrangement, the layer can be sprayed by blown arc plasma. This method leads to a porous layer but having a good mechanical grip on the surface of the core. This method can optionally consider vacuum pumping during projection.

According to another technical arrangement, the layer can be deposited by a plasma torch according to the so-called “Plasma Transferred Arc” (PTA) method. This method makes it possible to obtain a layer 12 that is thicker, more compact and metallurgically bonded to the substrate than with the methods previously described, which will then be taken up in machining.

Following the deposition of layer 12 by thermal spraying, the method may comprise a step (c) of heat treatment of layer 12, carried out between 800°C and 1000°C. Preferably, step (c) is carried out between 850°C and 900°C. This heat treatment makes it possible to relax the internal stresses induced by the deposition of the layer 12, in the previous step.

Then, the method can comprise a step (d) of rectification to reduce a thickness of the layer 12. Following this step, the layer 12 can have a thickness comprised between 100 and 500 microns. This step can also be used as a practical check of deposit adhesion.

After the rectification step, the method may comprise a step (e) of heat treatment in air, comprising a first stage of thirty minutes at a temperature between 300° C. and 400° C., a second stage of thirty minutes at a temperature of between 500° C. and 700° C., a third stage of thirty minutes at a temperature of between 800° C. and 1000° C., and cooling in ambient air.

Preferably, step (e) may comprise a first plateau of thirty minutes at 350° C., then a second plateau of thirty minutes at 650° C., then a third plateau of thirty minutes at 900° C., followed by cooling to Ambiant air.

Step (e), called passivation, makes it possible to oxidize the layer 12 on the surface, which makes it possible to reduce the risks of chemical interaction between the layer 12 and the material used to manufacture the blade (most often titanium ).

At the end of this manufacturing process, the layer 12 can have a hardness of between 35 and 65 HRC, preferably between 45 and 55 HRC. It is specified that the hardness is expressed and measured according to the so-called Rockwell test, using an indenter on which is applied an initial load and then an additional load. The hardness being measured by comparing the depth of penetration of the indenter during the application of the initial load and during the application of the additional load. For the HRC scale, In this case, the test is carried out with an indenter consisting of a diamond cone of circular section with a rounded spherical tip of 0.2 millimeters. In addition, the initial load applied is 98N and the total load (corresponding to the initial load plus the additional load) is 1471.5N. One HRC hardness unit corresponds to a penetration of 0.002 millimeters.

For thicknesses less than 400 microns, the HR15N scale is preferred because the initial load applied is only 29N and the total load (corresponding to the initial load plus the additional load) is only 147.1N.

It is also possible to use the Vickers (HV) method. The test is then carried out with an indenter consisting of a square-based diamond pyramid. The hardness being determined by measuring the two diagonals of the indentation. The load is adapted to the thickness of the layer: 5 to 10 kilograms for thicknesses ≤ 400 microns and 20 to 30 kilograms maximum for thicknesses greater than 400 microns.

In these last two cases (HR15N and HV) the HRC value is deduced from the conversion tables expressed in the current ISO and ASTM standards.

Thus, this process makes it possible to cover the initial core 11 with a layer 12 guaranteeing thermomechanical stability, protecting against chemical contamination and avoiding any adhesion of the blade parts to the core.

Core

According to a second aspect, the invention relates to a core 1 of nickel-based alloy obtained by a method according to the invention. The core 1 has a layer 12 composed of a cobalt base alloy according to claim 8.

Claims (8)

1. A process for manufacturing a core (1) for the production of a leading edge of a fan blade, characterized in that it comprises the steps of:

   (a) providing an initial core (11) of a nickel-based alloy,

   (b) thermally spraying a layer of a cobalt-based alloy, comprising between 26% and 32% molybdenum, between 7% and 20% chromium, between 1% and 5% silicon, and less than 1% carbon in percentage by weight, onto the initial core(12).
2. The process as claimed in any claim 1, wherein the layer (12) has a hardness comprised between 40 and 65 HRC.
3. The process as claimed in claim 1 or claim 2, wherein the deposited layer (12) has a thickness comprised between 100 microns and 2 millimeters, preferably 500 microns.
4. The process as claimed in any one of claims 1 to 3, wherein step (b) is performed using a method selected from: supersonic flame spraying, blown arc plasma spraying or plasma torch deposition.
5. The process as claimed in any one of claims 1 to 4 further comprising, following the thermal spraying step (b), a step (c) of heat treatment of the layer (12), carried out between 800 and 1000°C.
6. The process as claimed in any one of claims 1 to 5 further comprising, following the thermal spraying step (b), a grinding step (d).
7. The process as claimed in any one of claims 1 to 6, further comprising, following the thermal spraying step (b), a heat treatment step (e) in air, comprising a first stage of thirty minutes at a temperature comprised between 300°C and 400°C, a second stage of thirty minutes at a temperature comprised between 500°C and 700°C, a third stage of thirty minutes at a temperature comprised between 800°C and 1000°C, and cooling in ambient air, to oxidize the layer (12).
8. A nickel-based alloy core obtained from an initial core (12) of a nickel-based alloy, said core having a layer (12) composed of a cobalt-based alloy comprising, in percentage by weight, between 26% and 32% of molybdenum, between 7% and 20% of chromium, between 1% and 5% of silicon and less than 1% of carbon.

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