Composite reinforcing insert and manufacturing method

Abstract

A composite reinforcement insert includes a strand formed by a central fiber made of ceramic material surrounded by filaments of metal alloy helically wound around the central fiber, and a metal reinforcement layer covering the strand.

Claims

1. A composite reinforcing insert comprising: a strand consisting of a central fibre made of a ceramic material surrounded by metal alloy filaments wound spirally around the central fibre, and a metal reinforcing layer coating the strand.

2. The composite reinforcing insert according to claim 1, wherein the strand comprises N filaments, where N is greater than or equal to 6.

3. The composite reinforcing insert according to claim 1, wherein the central fibre is made of silicon carbide.

4. The composite reinforcing insert according to claim 1, wherein the filaments are made of an alloy based on titanium, nickel or aluminium.

5. The composite reinforcing insert according to claim 1, wherein the reinforcing layer is made from the same material as a basic material forming the filaments.

6. A turbomachine part comprising a composite reinforcing insert including a strand consisting of a central fibre made of a ceramic material surrounded by metal alloy filaments wound spirally around the central fibre, and a metal reinforcing layer coating the strand.

7. A method of making a reinforcing insert from a central ceramic fibre, the method comprising: stranding metal alloy filaments around the central fibre so as to form a strand, and coating the strand with a protective metal layer.

8. The method according to claim 7, wherein the coating includes dipping the strand into a liquid metal bath in levitation fusion, the liquid metal in levitation fusion containing a filler with the same material as a basic material of the filaments.

9. The method according to claim 7, further comprising fixing the filaments by spot welds.

10. The method according to claim 7, further comprising, between the stranding and the coating, coating the strand with an oxidation-resistant protective layer.

11. The composite reinforcing insert according to claim 2, wherein N is equal to 7, 19 or 37.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other characteristics and advantages of the invention will become clear after reading the detailed description given with reference to the appended figures that illustrate:

(2) FIG. 1, a sectional view of a ceramic filament;

(3) FIG. 2, a sectional view of a ceramic fibre surrounded by metal alloy filaments;

(4) FIG. 3, a perspective view of three strands;

(5) FIG. 4, a strand coated with a reinforcing layer;

(6) FIG. 5 shows the variation of the ratio of the radius of metal filaments and the radius of the fibre, and the Vf obtained as a function of the number of filaments for single layer constructions.

(7) Identical or similar elements are identified by identical references on all figures, to improve clarity.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

(8) A method of making a reinforcing insert according to one embodiment of the invention is described with reference to FIGS. 1 to 4. The reinforcing insert is made from a ceramic central fibre 1. This central fibre 1 is made from silicon carbide. The method includes a first step (a) to make a strand by winding metal alloy filaments 2 around the central fibre 1. The filaments are preferably made from a metal alloy based on titanium, nickel or aluminium. The filaments are wound spirally around the central fibre so as to form a spiral around the central fibre. Depending on the ratio Vf, the strand may comprise more or less filaments 2. The number Vf is defined as the ratio between the areas of the central fibre and the metal filaments. For example, a 140 ?m diameter central fibre 1 has a cross-section of 15400 ?m.sup.2. A strand with ten 70 ?m diameter filaments has 10 cross-sections of 3850 ?m.sup.2 giving a total of 38500+15400=53900 ?m.sup.2. Therefore, the area ratio Vf is equal to 15400?53900?100=29%.

(9) The strand usually comprises N filaments where N is greater than or equal to 6. The filaments 2 are arranged in concentric layers around central fibre 1. The diameter of the central fibre 1 and the diameter of filaments 2 may vary as a function of the required ratio Vf between the percentage of silicon carbide fibre and the percentage of strand material. The dimensional relations are:
sin(180?/N)=RS/(R1+R2)Vf=R1.sup.?2/(R1.sup.?2+N*R2.sup.?2)

(10) where R1=radius of the ceramic fibre, R2 radius of the metal filament N=number of metal filaments

(11) The variation of the number Vf as a function of the number of filaments in the case of single layer stranding is shown in FIG. 5, together with the variation of the ratio R2/R1 as a function of the number of filaments around the periphery.

(12) For example, a 140 ?m diameter silicon carbide fibre surrounded by seven 107 ?m diameter filaments and coated with a 3 ?m protective layer, has a percentage of silicon carbide SiC fibre equal to 20%.

(13) During the stranding operation of metal alloy filaments around the central fibre 1, it is essential that the central fibre should be free to move without generating any radii of curvature less than 20 mm to avoid damaging the central fibre. To achieve this, the pulleys used to wind the central fibre during the stranding operation must be sufficiently large to avoid generating radii of curvature in the central fibre less than 20 mm.

(14) If the strand is subject to swelling phenomena around the central fibre, then small weld spots of the filaments may be made in line with the stranding machine. A laser welding or electron beam technique can be used.

(15) Moreover, when the filaments 2 are made from metal alloys sensitive to oxidation, the method may include a step (c) in which the strand is coated with a protective layer. For example, when the metal alloy used for the filaments 2 is based on aluminium, the protective layer may be a copper nanolayer. This protective layer disappears during the next step.

(16) The method then includes a step (c) in which the strand is coated with a metal reinforcing layer 3. To achieve this, the strand is dipped into a liquid metal bath in levitation fusion with a filler of the same material as the filaments wound spirally around the central fibre 1. Thus, when the filaments 2 are made from a titanium-based alloy, the filler of the liquid metal bath preferably contains titanium. Similarly, when the filaments 2 are made from an aluminium-based metal alloy, the filler preferably contains aluminium. Strand coating methods using a liquid metal bath are known in prior art. For example, such methods are described in documents EP 0 931 846 or EP 1 995 342. The filaments 2 are not entirely remelted during the coating step. When this coating step (c) is finished, the strand is coated with a metal reinforcing layer 3. This reinforcing layer 3 is continuous.

(17) The method then comprises a solidification step of the reinforcing insert, during which the reinforcing insert becomes rigid.

(18) The result obtained is thus a reinforcing insert according to one embodiment of the invention comprising: a strand comprising: a ceramic central fibre 1; metal alloy filaments 2 surrounding the central fibre 1 so as to form a spiral around the central fibre; a metal alloy reinforcing layer 3 coating the strand.

(19) The reinforcing insert thus obtained is easy to manufacture and is very strong. Furthermore, its composition can easily be modified.

(20) The reinforcing insert thus obtained can then be used to reinforce parts, particularly in the aeronautic field. To achieve this, the reinforcing insert can subsequently be formed by winding around a part for a turbomachine, and particularly around a turbomachine casing or a disk. The reinforcing insert is placed in the part to be reinforced. The assembly thus obtained can then be compacted by hot isostatic compression. The result is a fully compact composite part.

(21) Naturally, the invention is not limited to the embodiments described with reference to the figures, and variants could be envisaged without going outside the scope of the invention.