Coating processes – Coating by vapor – gas – or smoke – Carbon or carbide coating
Patent
1996-06-14
1998-04-14
Beck, Shrive
Coating processes
Coating by vapor, gas, or smoke
Carbon or carbide coating
4272551, 4272552, 427589, C23C 1632
Patent
active
057389080
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to densifying porous substrates by chemical vapor infiltration of silicon carbide.
A field of the invention is that of making parts out of thermostructural composite material having a matrix that is made at least in part out of silicon carbide. Such parts are suitable for use, in particular, in aviation, or in space, or in the field of friction because they have mechanical properties which make them suitable for constituting structural elements and because they have the ability to conserve said properties at high temperatures.
BACKGROUND OF THE INVENTION
The manufacture of thermostructural composite material parts generally comprises making a substrate or preform out of refractory fibers, in particular carbon fibers or ceramic fibers, and densifying the preform with the matrix-constituting material.
Methods of densifying a porous substrate with a silicon carbide matrix are well known.
The invention relates to the method of densification by chemical vapor infiltration. In this method, the substrate to be densified is placed in an infiltration chamber. A reactive gas generally comprising a mixture of methyltrichlorosilane (MTS) and hydrogen is admired into the chamber. The temperature and pressure conditions are adjusted so as to enable the gas to diffuse into the pores of the substrate right into the core thereof and form a deposit of silicon carbide by decomposition of MTS in the presence of hydrogen which acts as a reducing agent: ##STR1##
Chemical vapor infiltration requires special control of operating conditions to enable the substrate to be densified right into its core in a manner that is as uniform and as complete as possible. Under poorly controlled conditions, there is a risk of a solid deposit forming on the surface, thereby rapidly obstructing the internal pores of the substrate and preventing any further densification of the core. The implementation of chemical vapor infiltration is thus different from the implementation of chemical vapor deposition methods as are used for forming surface coatings.
Various chemical vapor infiltration methods are known, in particular temperature gradient and/or pressure gradient methods, and also the constant temperature and constant pressure method.
With the temperature and/or pressure gradient methods, temperature and/or pressure differences are established between the surfaces of the substrate that are exposed to the reactive gas and the internal portions of the substrate remote from the exposed surfaces, which differences favor formation of the matrix initially in the internal portions of the substrate. Densification progresses towards the exposed surfaces, thereby achieving a result that is relatively uniform.
The temperature gradient method is implemented by heating the substrate either indirectly by causing the internal surfaces of the substrate to come into contact with an induction core that is heated by induction, or else by direct inductive coupling when the nature of the substrate makes that possible. The application of that method is limited to substrates that are simple in shape.
The pressure gradient method requires a forced flow to be established through the substrate and therefore requires equipment that matches the shape thereof.
Unfortunately, the duration of chemical vapor infiltration cycles as performed on an industrial scale makes it necessary to use a method that makes it possible to densify a plurality of substrates simultaneously inside the same chamber, which substrates may be of various or complex shapes.
Under such circumstances, the constant temperature and pressure method is used, and attempts are made to adjust the temperature and the pressure within the enclosure to optimum values for ensuring that densification takes place as uniformly as possible right into the core of substrates of various shapes and thicknesses, with this occurring throughout the working volume of the chamber.
One such chemical vapor infiltration method for infiltrating silicon carbide is described in d
REFERENCES:
patent: 4823734 (1989-04-01), Christin
patent: 5362228 (1994-11-01), Vaudel
patent: 5382453 (1995-01-01), Mason
"Safety Procedures Used During the Manufacturing of Amorphous Silicon Solar Cells", C.R. Dickson, Solar Cells, vol. 19, No. 3-4, Jan. 1987, pp. 189-201.
Charvet Jean-Luc
Delperier Bernard
Minet Jacky
Rey Jacques
Robin-Brosse Christian
Beck Shrive
Meeks Timothy
Societe Europeenne de Propulsion
LandOfFree
Method of densifying porous substrates by chemical vapor infiltr does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of densifying porous substrates by chemical vapor infiltr, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of densifying porous substrates by chemical vapor infiltr will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-632977