Coating processes – Nonuniform coating – Mask or stencil utilized
Patent
1995-11-30
1997-11-11
Bareford, Katherine A.
Coating processes
Nonuniform coating
Mask or stencil utilized
427287, 427294, 4274301, B05D 118, B05D 132
Patent
active
056861443
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This is a national stage application of PCT/FR95/00431, filed Apr. 5, 1995.
The present invention concerns protecting carbon-containing composite material brake disks against oxidation.
BACKGROUND OF THE INVENTION
Carbon-containing composite material brake disks are well known and are used in particular in the brakes of aircraft and racing vehicles. They have the advantage of offering good tribological characteristics up to relatively high temperatures, and they have excellent mechanical strength for a specific gravity which is far lower than that of conventional solid disks, in particular metal disks.
Of the carbon-containing composite materials used for the manufacture of brake disks, a carbon-carbon composite material is currently the most popular. It comprises a reinforcing piece, or preform, constituted by carbon fibers, for example in the form of superimposed layers of carbon fabric which may be bound together by needling, the reinforcing piece being densified by a carbon matrix. However, other carbon-containing composite materials have been suggested for use in a brake disk, in particular materials reinforced with carbon fibers and having a ceramic matrix (for example silicon carbide) or a mixed carbon and ceramic matrix, also materials which are reinforced with ceramic fibers and which have a ceramic matrix, with the interposition of a matching or interphase layer of pyrolytic carbon between the fibers and the matrix.
A brake disk essentially comprises two zones: a first zone constituted by its friction face(s) and a second zone constituted by that which does not constitute the friction face. In the first zone, the tribological characteristics of the material constituting the disk are the most important. The second zone mainly corresponds to the portion of the disk which carries out the mechanical functions of fixing the disk and stress recovery. It is essential to maintain the integrity of the material constituting the disk in the second zone. Further, in the case of brake disks made of carbon-containing composite material, effective oxidation protection must be provided in the second zone, since the disks normally heat up in use to a temperature which falls within the carbon oxidation range, i.e., a temperature of more than 350.degree. C. In the absence of any oxidation protection, the disappearance of carbon in the zone in the disks which carries out a mechanical function will change its mechanical properties, and could lead to the fixing or stress recovery portions breaking. Weight loss in carbon-carbon composite material disks caused by the oxidation of carbon makes this obvious. This is the case also when the carbon is present only in the reinforcing fibers, due to the role played by the fibers as regards the mechanical properties of the material, and when the carbon is present only in a pyrolytic carbon interphase between the fibers and the matrix, the interphase being essential to the mechanical properties, as described in European patent EP-A-0 172 082.
Regardless of the method of manufacture of the composite material--impregnation of a fibrous preform with a liquid composition containing a matrix precursor (for example, a resin) followed by transformation of the precursor by heat treatment, or densification of a fibrous preform by a matrix deposited in the core of the preform by chemical vapor infiltration--the material produced has residual open pore space throughout its volume.
Protecting carbon-containing composite materials which have such pore space against oxidation, and also protecting porous solid carbon or graphite against oxidation, has given rise to a great deal of prior art.
In general, oxidation protection is in the form of a layer of refractory material such as a carbide, nitride, boride or oxide. The layer can be self-healing or it can be completed by a layer with such a property. Self-healing materials which are in current use are glass-containing compositions, the term "self-healing" here meaning the ability of a material, by becoming viscous in
REFERENCES:
patent: 3850669 (1974-11-01), Mino et al.
patent: 4454193 (1984-06-01), Block
patent: 4550034 (1985-10-01), Shimrock et al.
Delaval Rodolphe
Laxague Michel
Palavit Gerard
Rey Jacques
Thebault Jacques
Bareford Katherine A.
Societe Europeenne de Propulsion
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