CORE FOR HIGH-TEMPERATURE SHAPING OF A METAL PART AND MANUFACTURING PROCESS

Abstract

A metal core for hot-shaping a metal part made out of titanium-based alloy. The metal core presents on an outside surface that is to come into contact with the metal part, a layer of material enriched in metallic carbonitride. The metal core includes an alloy based on nickel or on cobalt, and the nickel- or cobalt-based alloy includes chromium, molybdenum, and/or titanium. A method of fabricating and regenerating the metal core, and also a method of fabricating a metal part using the metal core, are disclosed.

Claims

1. A metal core for hot-shaping a metal part made out of titanium-based alloy, wherein the metal core comprises an alloy based on nickel or on cobalt, in that the nickel- or cobalt-based alloy includes chromium, molybdenum, and/or titanium, and wherein the metal core also presents on an outside surface that is to come into contact with the metal part, a layer comprising a material that is enriched in metallic carbonitride relative to said alloy.

2. The metal core according to claim 1, wherein the layer of material enriched in metallic carbonitride comprises a first layer and a second layer, the first layer having a greater concentration of metallic nitride than the second layer, and the second layer being separated from the outside surface of the metal core by the first layer.

3. The metal core according to claim 1, wherein the layer of material enriched in metallic carbonitride presents a thickness of at least 20 m, preferably of at least 30 m.

4. A fabrication method for fabricating a metal core according to claim 1, comprising: fabricating the metal core; and carbonitriding the outside surface of the metal core in such a manner as to obtain a layer of material enriched in metallic carbonitride.

5. The fabrication method according to claim 4, wherein the outside surface of the metal core is carbonitrided by forming a plasma of carbon and of nitrogen.

6. A regeneration method for regenerating a metal core according to claim 1, said method comprising a step of carbonitriding the outside surface of the metal core so as to obtain a new layer of material enriched in metallic carbonitride.

7. The regeneration method according to claim 6, wherein, prior to the new step of carbonitriding the outside surface of the metal core, a step is performed of using heat treatment to eliminate the layer of material enriched in metallic carbonitride.

8. A shaping method for hot-shaping a metal part made out of titanium-based alloy, the method comprising: positioning the metal part around a metal core according to claim 1; hot-shaping the metal part around the metal core; and extracting the metal core.

9. The shaping method according to claim 8, wherein the metal part is a leading edge shield of a rotary blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention can be well understood and its advantages appear better on reading the following detailed description of an embodiment given by way of non-limiting example. The description refers to the accompanying drawings, in which:

[0036] FIG. 1 is a diagrammatic perspective view of a bypass jet engine;

[0037] FIG. 2 is a diagrammatic perspective view of a rotary blade of the fan of the FIG. 1 jet engine;

[0038] FIG. 3 is a diagrammatic perspective view of a shield for the leading edge of the FIG. 2 blade;

[0039] FIG. 4 is a cross-section view on plane IV-IV of the FIG. 3 shield;

[0040] FIGS. 5A to 5E show successive steps in a method of fabricating the FIG. 4 shield;

[0041] FIG. 6 is an enlarged section view of a metal core; and

[0042] FIGS. 7A and 7B are graphs showing respectively the concentrations of carbon and of nitrogen starting from the surface of the metal core.

DETAILED DESCRIPTION OF THE INVENTION

[0043] FIG. 1 shows a bypass jet engine 1 having a gas generator unit 2 and a fan 3. The fan 3 has a plurality of rotary blades 4 arranged radially around a central axis X and aerodynamically profiled in such a way as to impel air when they rotate. Thus, as shown in FIG. 2, each blade 4 presents a leading edge 5, a trailing edge 6, a suction side 7, and a pressure side 8.

[0044] In normal operation, the relative air flow is directed substantially towards the leading edge 5 of each blade 4. Thus, the leading edge 5 is particularly exposed to impacts. In particular when the blade 4 has a body 9 made out of composite material, in particular out of fiber-reinforced polymer-matrix material, it is therefore appropriate to protect the leading edge 5 with a shield 10 incorporated in each blade.

[0045] FIGS. 3 and 4 show this shield 10, which presents a pressure side fin 11, a suction side fin 12, and a thicker central section 13 that is to be placed astride the leading edge of the blade 4 and interconnecting the pressure side fin 11 and the suction side fin 12. The pressure- and suction-side fins 11 and 12 serve to position the shield 10 on the blade 4. The shield 10 is made mainly out of metal, and more specifically out of titanium-based alloy, e.g. such as TA6V (Ti-6Al-4V). The shield 10 is thus an example of a metal part 10 made of titanium-based alloy.

[0046] As can be seen in FIGS. 3 and 4, the shape of this shield 10 is rather complex, which, in combination with the high performance materials typically used for this part, can make it expensive and difficult to fabricate, in particular when the core traditionally used for hot-shaping the leading edge can be used only one or two times.

[0047] The metal core 20 is obtained by forming the core by carbonitriding an outside surface 23 of the metal core 20. Such carbonitriding can be performed in particular by forming a plasma of carbon and nitrogen, also referred to as ion carbonitriding or plasma carbonitriding. This reaction technique serves to cause carbon and nitrogen to diffuse in depth into the metal core 20 and to create at the surface 23 of the metal core 20 a layer 24 of material that is enriched in metallic carbonitride. As can be seen in FIG. 6, a metal core 20 is thus obtained that presents on its outside surface 23 a layer 24 made of material that is enriched in metallic carbonitride. Under the layer 24 of metallic carbonitride enriched material, there can be found the composition 25 of the nickel- or cobalt-based alloy used for forming the metal core 20 prior to the carbonitriding treatment.

[0048] As shown in FIG. 6, the layer 24 of material enriched in metallic carbonitride may comprise a first layer 26 and a second layer 27, the first layer 26 having a greater concentration of metallic nitride than the second layer 27, and the second layer 27 being separated from the outside surface 23 of the metal core 20 by the first layer 26.

[0049] FIGS. 7A and 7B show the concentrations respectively of carbon and of nitrogen going from the outside surface 23 of the metal core 20 towards the inside of the metal core 20 substantially perpendicularly to its outside surface 23, with this being done for various different nickel- or cobalt-based alloys (referenced A-D). It can be seen that nitrogen is present above all in the first layer 26 and that its concentration falls off quite quickly on going towards the inside of the metal core 20. With the exception of alloy A, the concentration of carbon is generally lower in the first layer 26 and tends to increase in the second layer 27 prior to decreasing once more on reaching the nickel- or cobalt-based alloy 25 used for making the metal core 20, prior to the carbonitriding treatment.

[0050] It can be understood that the concentrations of carbon and of nitrogen in the first and second layers 26 and 27 vary in continuous manner. The layer 24 of material enriched in metallic carbonitride thus comprises metallic nitrides, metallic carbides, and/or metallic carbonitride. Nevertheless, since the first layer 26 has a higher concentration of nitrogen than the second layer 27, its concentration of metallic nitride (in the form of nitride and/or of material based on carbonitride) is higher than that of the second layer 27.

[0051] By way of example, the ion carbonitriding may be performed at 500 C. for 150 hours (h). These conditions make it possible to obtain a layer of material enriched in carbonitride having thickness lying in the range 20 m to 30 m. It is also possible to envisage performing ion carbonitriding at 720 C. for 150 h.

[0052] After being subjected to a plurality of hot-shaping thermal cycles, the layer 24 of material enriched in carbonitride might become damaged. The layer 24 of material enriched in metallic carbonitride on the metal core 20 can then be enriched by performing a new step of carbonitriding the metal core 20. This produces a new layer 24 of material in metallic carbonitride.

[0053] The new step of carbonitriding the metal core 20 can be performed directly on the metal core 20 having its layer 24 of material enriched in metallic carbonitride that has become damaged, or it is also possible to perform heat treatment at a temperature higher than the hot-shaping temperature in order to remove the damaged layer 24 of material enriched in metallic carbonitride and then perform a new step of carbonitriding the outside surface 23 of the metal core 20.

[0054] It is thus possible to reuse the metal core 20 and to subject it to a plurality of hot-shaping cycles. The number of hot-shaping cycles to which the metal core 20 is subjected can thus be increased.

[0055] The method of hot-shaping a metal part 10 made of titanium-based alloy around the metal core 20 is shown in FIGS. 5A to 5E. It comprises steps of positioning the metal part around the core 20 (FIGS. 5A and 5B), of hot-shaping the metal part 10 around the metal core (FIG. 5C), and of extracting the metal core from the metal part 10 (FIGS. 5D and 5E). In this example, it should be observed that after hot-shaping, the metal part is cut (FIG. 5D) so as to make it possible to extract the core 20 (FIG. 5E). A leading edge shield 10 is thus obtained that can be positioned on and attached to the leading edge of the blade.

[0056] It should be observed that the method of hot-shaping the metal part 10 does not include a step of machining the surface of the leading edge 5 that is to be put into contact with the blade.

[0057] Specifically, during the hot-shaping step there is no sticking and/or chemical reaction between the metal core 20 and the metal part 10, since the metal part 10 is in contact with the layer 24 of material enriched in metallic carbonitride, and not with the nickel- or cobalt-based alloy 25 forming the metal core.

[0058] Furthermore, the layer 24 of material enriched in metallic carbonitride is chemically and physically inert relative to the metal part 10. As a result of its dispersion of carbides and nitrides, this layer 24 forms a diffusion barrier between the alloy of the metal core 20 and the titanium-based alloy of the metal part 10. This serves to limit contamination of the metal part 10 made of titanium-based alloy by elements from the nickel- or cobalt-based alloy of the metal core 20.

[0059] This shaping method may include steps of fabricating the metal core 20 or steps of regenerating the metal core 20, as described above.

[0060] Although the present invention is described with reference to a specific embodiment, it is clear that various modifications and changes may be made to those embodiments without going beyond the general ambit of the invention as defined by the claims. For example, the invention is not limited to leading edge shields for rotary blades. Specifically, the metal core and the fabrication and regeneration methods can be used for fabricating any other metal part made of titanium-based alloy by hot-shaping around a metal core as defined. In addition, individual characteristics of the various embodiments mentioned may be combined in additional embodiments. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.