Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Patent
1998-09-01
2000-10-10
Meeks, Timothy
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
4272555, 118724, 118726, 118730, C23C 1456, C23C 1424
Patent
active
061299510
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus for coating monofilaments of ceramic reinforcing materials such as silicon carbide with a predetermined thickness of matrix metal by a process of physical vapour deposition. Subsequently, the coated reinforcement may be consolidated into a metal matrix composite material having a controlled fibre spacing.
2. Discussion of Prior Art
Fibre reinforced metal matrix composites offer combinations of strength, stiffness and elevated temperature performance which are unattainable with conventional structural materials. As a result, they are currently under consideration for a wide range of applications in aerospace technology.
Typical matrix materials include titanium, aluminium or their alloys. Especially preferred are alloys of these elements which are capable of undergoing superplastic deformation.
Hitherto, the use of titanium as a matrix material has been largely confined to solid state processes undertaken at relatively low temperatures (1000.degree. C.) because of the high chemical reactivity of titanium. One well-known technique is the so-called "foil-fibre" method in which alternate layers of metal foils and ceramic fibres are hot pressed together to give a fully dense product. This process is reasonably successful for flat products, but problems sometimes arise due to incompatibility between the foil and the reinforcement. In addition, some movement of the fibres is inevitable, possibly leading to touching fibres and local inhomogeneity in the structure. A variant of the foil-fibre method uses alloy powders mixed with an organic binder and rolled into a cloth as an alternative to the metal foil. This alternative method suffers from the same risks of fibre movement but allows a greater variety of matrix materials to be used by mixing of powders.
SUMMARY OF THE INVENTION
The method of pre-coating by physical vapour deposition used in the present invention provides a matrix coating on each fibre of sufficient thickness and uniformity that the desired matrix volume fraction is achieved in the finished composite. There is no need for any further matrix material to be added during the consolidation stage. In addition, fibre spacing in the finished product is predetermined by the thickness of the matrix coating. Inadvertent movement of the fibres does not affect their spacing. Another advantage of the pre-coating method is that the ceramic fibre is protected from damage, both during handling and also whilst undergoing consolidation.
It is known to produce metal matrix composite materials from titanium alloy and long fibre reinforcements by a process which involves laying together the reinforcement fibres and thin foils of the matrix alloy. These are then consolidated under conditions which cause superplastic flow within the matrix material and subsequent diffusion bonding. This known method has two major disadvantages. Firstly, it is limited by the choice of matrix alloys because foils are not necessarily available with the desired composition. Secondly, control of fibre spacing is not easily achievable across the full range of fibre/matrix volume ratios that might be desired.
It is also known to use liquid metal infiltration for the production of certain types of long fibre metal matrix materials. Unfortunately, this is unsuitable for composites with a titanium or titanium alloy matrix because of the high reactivity of liquid titanium. As a result of this reactivity, undesirable reactions take place between the matrix material and the reinforcement during the infiltration stage.
In Japanese Patent Application No. 63-56625, a continuous vapour coating apparatus is described which is said to be suitable for coating either fibres or films. The specification gives no information about the nature of the coating material, but the apparatus includes a reversing reel which turns the fibre (or film) over for its return pass through the coating station. No provision is made for presenting intermediate aspects of the fibr
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patent: 5660923 (1997-08-01), Bieler et al.
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Chandrasekaran Lakshman
Ward-Close Charles M.
Chen Bret
Meeks Timothy
The Secretary of State for Defence in Her Britannic Majesty's Go
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