Fibre reinforced metal-matrix composite

Abstract: A metal matrix composite includes a plurality of fibres having an average diameter of about eight micrometers with a coating, and a metal or alloy distributed with said fibres, a fibres-to-metal or alloy ratio has a range is has a range of about 9:1 to less than about 1:1.

Description: The present invention relates generally to metal-matrix composites, and more particularly, to a metal-matrix composite suitable for rapid prototyping. In the automotive industry, it is desirable to bring a product to market in a short amount of time. This reduces the overall cost of the vehicle. One manner in which automakers have reduced product development time is by using rapid prototyping and tooling methods such as stereolithography. Stereolithography or other rapid prototyping systems in conjunction with a computer aided design system can be used to form a prototype part based upon drawings generated by the CAD system. One drawback to parts developed in known rapid prototyping systems is that the techniques use layers of paper and plastic or plastic powders to construct the parts. As a result, the part can only be used in low-temperature prototype environment. Also, additional processing must take place in order to make metal dies. It would therefore be desirable to provide a rapid prototyping system that forms parts having a higher melting point than those known rapid prototyping systems. This allows the part to be used under higher temperature processing such as the formation of metal dies. In one aspect of the invention as given in claim 1, a metal-matrix composite comprises a plurality of carbon fibres having an average diameter of about eight micrometers with a coating, and an Sn alloy distributed with said fibres, a fibres to alloy ratio by volume has a range of about 9:1 to about 7:1 A method of forming a part may include the steps of forming said composite material by mixing a molten metal or alloy with a bundle of fibres; heating the composite material to a melting point of the composite material to form a molten material; dispensing the molten material at least at said melting point into a shape of a part; and solidifying the molten material. The present invention provides suitable metal-matrix composites for use in rapid prototyping systems. The metal-matrix composites have higher melting temperatures than materials used in prior known rapid prototyping systems. One advantage of the invention is that by eliminating additional processing in prototypes, the cost and time of producing a product is reduced. The present invention is described with respect to a metal-matrix composite for use in a rapid prototyping system. However, the metal-matrix composite of the present invention may also be suitable for other applications both inside and outside of the automotive industry. For example, the aerospace industry may also benefit from the metal-matrix composite. Metal-matrix composites are metals or alloys strengthened with tiny inclusions of another material which inhibit crack growth and increase performance. The metal is a Sn alloy reinforced with carbon fibre or fibres. The carbon fibres may be continuous or discrete fibres. The preferred aspect ratio of discrete fibres is greater than 10:1. Carbon fibres having a diameter of about eight micrometers have been used. Preferably, the carbon fibres have a coating to increase wetability. The coatings are formed from Ni, Au and/or In. The thickness of the coating preferably ranges from about 0.3 micrometers to 1.5 micrometers. The metal-matrix is a Sn alloy that has a melting temperature above 130°C but below 300°C. The composition of the metal is preferably eutectic or near-eutectic. Alloys of Sn include the mixture of Ag, Sb, Cu, Zn, Bi. Fe, Co, In, Ni, or Pb. Preferred compositions include by weight Ag from 0 to 5%, Sb from 0 to 7%, Cu from 0 to 5%, Zn from 0 to 15%, Bi from 0 to 60 %, In from 0 to 60%, Fe, Co, Ni from 0 to 1%, and Pb from 0 to 50%. Suitable compositions include Sn-3.5 Ag, Sn-5 Sb, Sn-0.7 Cu, Sn-9 Zn, Sn-58 Bi, or Sn-62 Pb. For many applications, however, the lead alloy may not be preferred due to its lead content. The ratio of fibre to metal by volume is between about nine and about seven. A goal of the present invention is to have comparable, equal or better stiffness yield strength mechanical strength than pure aluminium and aluminium alloys. Pure aluminium has a tensile of 90 MPa. Sn alloy has a tensile strength of 30 MPa. A composite material formed according to the present invention using a continuous fibre and an alloy with 63% Sn and 37% Pb was formed having a tensile strength of 270 MPa. Using non-woven carbon fibre and the same alloy, a tensile strength of 95 MPa has been achieved. Another desirable feature of the composite of the present invention is the melting temperature. Known rapid prototyping systems have processing temperatures around 280°C. The present invention has a melting temperature below a desired 250°C. One composite material had a melting temperature below 230°C. In contrast, aluminium and its alloys have a melting temperature near or above 600°C. so processing temperatures are typically above 650°C. To form the composite material, a capillary flow may be used to flow the molten metal alloy into the bundle of fibres. The molten metal flows into the gaps between the fibres to form the composite. Little or no pressure has to be used. A flux may be used to first wet the fibres before applying the molten Sn alloy. The wetting process may be manual or may be performed by dipping the fibres into the flux material. An automatic system feeding the fibre into the flux bath then drawing them out is also contemplated. Another method for applying flux to the fibres is dispensing the metal flux directly onto the fibres. A squeegee may be used to remove excess molten material from the fibre bundle. To form a rapid prototype part, the composite material is deposited into the desired shape by rapid prototyping system. Typically, such systems use an XYZ co-ordinate system for directing movement. The composite material of the present invention is particularly suitable for rapid prototyping because the composite material solidifies within seconds to form a solid structure. Another manner for manufacturing the composite material is vacuum infiltration with pressurised molten Sn-based alloy.

Claims: A metal matrix composite suitable for rapid prototyping comprising: a plurality of carbon fibres having an average diameter of 8 micrometers, a coating selected from the group Ni, Au, and In substantially surrounding said plurality of carbon fibres, and an Sn alloy distributed around said carbon fibres and said coating, said carbon fibres to Sn alloy ratio of the metal matrix composite is between 9:1 to 7:1 by volume. A metal matrix composite as recited in claim 1, wherein the metal matrix has a melting temperature below 280 degrees Celsius. A metal matrix composite as recited in claim 2, wherein the metal matrix composite has a melting temperature between 230 and 280 degrees Celsius. A metal matrix composite as claimed in any one of the preceding claims, wherein said coating has a thickness between 0.3 micrometers and 1.5 micrometers. A metal matrix composite as claimed in any one of the preceding claims, wherein each of said plurality of carbon fibres has an aspect ratio of greater than 10:1. A metal matrix composite as claimed in any one of the preceding claims, wherein the alloying metal of said Sn alloy is selected from the group consisting of Ag, Sb, Cu, Zn, Bi, and Pb.

Inventors: BLAIR HOWARD DOUGLAS, PAN TSUNG-YU, SHAIKH FURQAN ZAFAR, BLAIR, HOWARD DOUGLAS, PAN, TSUNG-YU, SHAIKH, FURQAN ZAFAR
Applicants: FORD GLOBAL TECH LLC, FORD GLOBAL TECHNOLOGIES, LLC
Application year: 2000
Main classification: C22C49
IPC codes: C22C47, C22C49