METAL MATRIX COMPOSITES

Abstract

A method of forming a metal matrix composite component comprises: providing a body defining a mould cavity; covering a first surface of the mould cavity with a first reinforcement material; restraining the first reinforcement material relative to the body to restrict movement of the first reinforcement material in the mould cavity; adding a second reinforcement material to the mould cavity, the second reinforcement material being in contact with the first reinforcement material; adding molten metal to the mould cavity such that the first reinforcement material and the second reinforcement material become embedded in a continuous metal matrix when the molten metal solidifies.

Claims

1. A method of forming a metal matrix composite component, comprising: providing a body defining a mould cavity; covering a first surface of the mould cavity with a first reinforcement material; restraining the first reinforcement material relative to the body to restrict movement of the first reinforcement material in the mould cavity; adding a second reinforcement material to the mould cavity, the second reinforcement material being in contact with the first reinforcement material; adding molten metal to the mould cavity such that the first reinforcement material and the second reinforcement material become embedded in a continuous metal matrix when the molten metal solidifies.

2. A method according to claim 1, in which the first reinforcement material has a planar profile.

3. A method according to claim 2, in which the first reinforcement material comprises inter-engaging fibres which are entangled, entwined or woven into a sheet-like structure.

4. A method according to claim 2, in which the first reinforcement material comprises at least one elongate member, such as a filament or a braid, wrapped around a former to form a raft-like structure.

5. A method according to claim 2, in which the planar profile of the first reinforcement material has a thickness of at least 1 mm.

6. A method according to claim 1, in which restraining the first reinforcement material relative to the body comprises bonding the first reinforcement material to the body, for example with an adhesive.

7. A method according to claim 1, in which restraining the first reinforcement material relative to the body comprises clamping the first reinforcement material between a first part of the body and a second part of the body.

8. A method according to claim 1, in which restraining the first reinforcement material relative to the body comprises placing the first reinforcement material under tension in the mould cavity.

9. A method according to claim 1, in which the second reinforcement material comprises hollow or porous particles, e.g. ceramic particles.

10. A method according to claim 1, further comprising covering a second surface of the mould cavity with a third reinforcement material.

11. A method according to claim 10, in which the second surface of the mould cavity is opposite the first surface of the mould cavity.

12. A method according to claim 10, in which the third reinforcement material is in contact with the second reinforcement material.

13. A method according to claim 10, further comprising restraining the third reinforcement material relative to the body to restrict movement of the third reinforcement material in the mould cavity.

14. A method according to claim 10, in which the third reinforcement material is the same as the first reinforcement material.

15. A method according to claim 1, further comprising removing a solidified metal matrix composite structure from the mould cavity and cutting the metal matrix composite component from the solidified metal matrix composite structure such that the first reinforcement material is adjacent one external surface of the metal matrix composite component.

16. A metal matrix composite component comprising a body with an external surface, the body having a surface region adjacent the external surface and a core region spaced from the external surface by the surface region, with a metal matrix extending continuously through the surface region and the core region, wherein the surface region comprises a reinforcement material embedded in the metal matrix, and the core region has a density which is less than that of the surface region.

17. A metal matrix composite component according to claim 16, in which the reinforcement material comprises inter-engaging fibres which are entangled, entwined or woven into a sheet-like structure.

18. A metal matrix composite component according to claim 16, in which the reinforcement material comprises at least one elongate member, such as a filament or a braid, with lengths thereof arranged side-by-side to form a raft-like structure.

19. A metal matrix composite component according to claim 16, in which the reinforcement material has a thickness of at least 1 mm, perhaps at least 1.5 mm, and possibly even at least 2 mm, with the thickness being measured transverse to the external surface and towards the core region.

20. A metal matrix composite component according to claim 16, in which the core region comprises hollow or porous particles, e.g. ceramic particles.

21. A metal matrix composite component according to claim 16, in which the core region has a space frame structure, comprising struts with channels therebetween.

22. A metal matrix composite component according to claim 16, in which the body has a second surface region adjacent the external surface, the second surface region being spaced from the aforementioned surface region by the core region, the second surface region comprising a further reinforcement material embedded in the metal matrix.

23. A metal matrix composite component according to claim 16, further comprising a member protruding from either the surface region or the core region of the body, the member comprising a metal.

24. A metal matrix composite component according to claim 23, in which the member further comprises fibre reinforcement.

25. A metal matrix composite component according to claim 23, in which the member is integrally formed with the metal matrix of the body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] An embodiment of the invention will now be described with reference to the accompanying drawings in which:

[0024] FIG. 1 shows schematically a cross-sectional view of a metal matrix composite component made in accordance with the present invention;

[0025] FIG. 2 is a flowchart illustrating schematically a method embodying the present invention of forming the metal matrix composite component of FIG. 1;

[0026] FIG. 3 illustrates schematically some of the parts used in the method of FIG. 2;

[0027] FIG. 4 illustrates schematically an alternative form of parts used in FIG. 3; and

[0028] FIGS. 5A-5B are perspective illustrations of a kinematic linkage embodying the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT

[0029] FIG. 1 illustrates schematically a cross-sectional view of a metal matrix composite component 10 made in accordance with an embodiment of the present invention. The metal matrix composite component 10 is a multi-phase product comprising a core region 12 sandwiched between a pair of skin regions 14, 16. A single metal matrix 18 extends continuously through the core region 12 and skin regions 14, 16. The core region 12 is a metal matrix syntactic foam and comprises hollow or porous particles 20 embedded in the metal matrix 18. The skin regions 14, 16 comprise woven fibre sheets 22 also embedded in the metal matrix 18.

[0030] FIG. 2 is a flowchart illustrating schematically a method 100 embodying the present invention of manufacturing the metal matrix composite component 10 of FIG. 1, and FIG. 3 illustrates schematically some of the parts used in the method 100. The method 100 comprises the step 102 of providing a body 200 defining at least part of a mould cavity 202. The next step 104 comprises covering a first surface 204 of the mould cavity 202 with a first reinforcement material 206 which is in the form of a woven sheet of ceramic fibres 208, and which is larger than the body 200. At step 106, the first reinforcement material 206 is restrained relative to the body 200, using adhesive to bond the fibrous woven sheet 208 to the body 200. Alternatively, or additionally, the woven sheet of ceramic fibres 208 may be placed under tension by pulling a pair of opposing peripheral edges 210 of the woven sheet of ceramic fibres 208 which overlap the body 200.

[0031] The method further comprises the step 108 of adding a second reinforcement material 212 in the form of hollow or porous ceramic particles 214 to the mould cavity 202, on top of the first reinforcement material 206. The ceramic particles occupy a high volume fraction of available space, perhaps 40-60% per unit volume. The next step 110 comprises covering a second surface 216 of the mould cavity 202, opposite the first surface 204, with a third reinforcement material 220, which may also be in the form of a woven sheet 222 of ceramic fibres. The third reinforcement material 220 is in contact with the ceramic particles 214 of the second reinforcement material 212, and is restrained at step 112 relative to the body 200 in the same way as the first reinforcement material 206. The resulting assemblage or “cassette” is clamped between a pair of plates or within a net shape cavity and heated prior to molten metal being forced under pressure into the mould cavity 202 at step 114, to infiltrate and embed the first, second and third reinforcement materials in a continuous metal matrix.

[0032] FIG. 4 illustrates an alternative way in which the first and third reinforcement materials 206 and 220 are formed from a continuous fibre 300 (monofilament or multifilament) wrapped tightly around the body 200 which acts as open frame former. As the continuous fibre 300 is wrapped around the body 200, the first and second surfaces 204 and 216 of the mould cavity 202 are covered simultaneously. Each surface 204 and 216 is covered by parts of the continuous fibre 300, which are aligned and side-by-side in a raft-like structure. A small gap 302 is left uncovered by the continuous fibre 300 at one end of the body 200 so that the second reinforcement material 212 may be added to and fill the mould cavity 202. As before, the resulting assemblage or “cassette” is clamped between a pair of plates and heated prior to molten metal being forced under pressure into the mould cavity 202, to infiltrate and embed the first, second and third reinforcement materials in a continuous metal matrix. The metal matrix composite component 10 may be cut out from the body 200 once the metal has solidified.

[0033] Advanced liquid pressure forming nay be used to infiltrate the reinforcement materials 206, 212, 220, although other liquid metal infiltration processes could be utilised including, but not limited to, direct or indirect squeeze casting. If the second reinforcement material 212 comprises hollow spheres (e.g. formed from glass), a low pressure processes could be utilised. An important part of the infiltration process is presenting a quiescent melt front to construction and designing the casting process so that directional solidification is achieved so to prevent porosity in the core or skin. The assembled cassette is thus preheated to above the liquidus of the molten metal used to form the matrix. This could be done in-situ or external to the casting machine die. If external, this is then moved into the casting machine die and the liquid metal poured into the die. If using primary aluminium, the casting temperature range could be between 700 to 820° C. The same levels of superheat could be applied to any aluminium alloy or other low melting point metal (and its alloys).

[0034] If using fibre outer layers with syntactic core a suitable pressure is applied after pouring so not to “crush” or damage the hollow spheres. This would typically be within the range of 5 to 25 MPa metal pressure. For other reinforcement cores, much higher pressure could be used, up to 450 MPa metal pressure (and all ranges in between to suit the core and skin combination). Pressure is generally modified to suit the material, with higher pressure used to create “higher strength” (but higher density) materials. Lower pressure is used where very low density, high modulus materials are required (such as syntactic foams & foam cores). The density of these materials can be as low as 1.6 g/cc—if using hollow spheres core, continuous fibre skins and aluminium matrix, but lower densities could be achieved by changing to matrix to a lower density metal such as magnesium.

[0035] The cassette is held at pressure during solidification before ejection from the die. Cooling could be ambient or quenched. After ejecting from the die and cooling, depending on the cassette design, the material can either be removed from the cassette (if using net shape) or extracted so that the cassette is removed and that none of the extended fibres form part of the final material. It is anticipated that some final machining will be required.

[0036] The thickness of the core region 12 and skin regions 14 and 16 can be tailored to suit a specific need, as can the matrix, with temperatures and pressure modified to suit. It is also possible to design the cassette so that metal rich surfaces are present if a coating or polished surface is required. The outer skin could be a single fibre type or could be a co-mingle, or in the case of woven or tape layup a multilayer stack, consisting of different fibres. This would be utilised if a surface ply or different surface finish was required to the “load bearing” fibre in the skin region(s) 14 and 16. In the case of a net shape cassette, the skin regions may additionally include short fibre, whisker or particle reinforcement, although there would likely be some mixing of these with the second reinforcement material 212 at the interface between the core region 12 and skin regions 14 and 16.

[0037] FIGS. 5A and 5B illustrate schematically two embodiments of a metal matrix composite component (a kinematic linkage) 400, each comprising a body 402 with an external surface 404. The body 402 has a surface region 406 adjacent the external surface 404, and a core region 408 spaced from the external surface by the surface region 406, in a direction perpendicular to the external surface 404. The body 402 comprises a metal matrix 410 extending continuously through the surface region 406 and the core region 408, infiltrating a reinforcement material (not shown) in the surface region 406. The core region 408 has a density which is less (e.g. at least 10% less) than that of the surface region 406. In the case of FIG. 5A, the core region 408 is a metal matrix syntactic foam, with hollow or porous particles embedded in the metal matrix. In the case of FIG. 5B, the core region 108 includes integrally formed struts 410 with open channels 412 therebetween and which extend through the body 402 parallel to the surface region 406. The struts 410 and open channels 412 space the surface region 406 from an opposing surface region 414.

[0038] In FIGS. 5A and 5B, the reinforcement material may include a continuous fibre(s) wound around opposing end lugs 420,422 of the body 402, with adjacent lengths of fibre aligned side-by-side in a single orientation to form a raft-like structure. Woven plies of fibres may also be included to enhance transverse and shear properties of the metal matrix composite component 400. Also in FIGS. 5A and 5B, the metal matrix composite component 400 has an upper lug 424 protruding from the surface region 406, and which is integrally formed with the metal matrix of the body 402.