Protecting composite material parts against oxidation

#The invention relates to applying a protective coating against oxidation on thermostructural composite material parts containing carbon or some other material that is sensitive to oxidation at high temperature, such as boron nitride.

#Thermostructural composite materials are characterized by their mechanical properties which make them suitable for constituting structural parts, and by their ability to conserve these mechanical properties at high temperature. They are constituted by fiber reinforcement densified with a matrix of refractory material which fills the pores in the fiber reinforcement, at least in part. The materials constituting the fiber reinforcement and the matrix are typically selected from carbon and ceramics. Examples of thermostructural composite materials are carbon/carbon (C/C) composites, and ceramic matrix composites (CMCs) such as carbon fiber reinforcement with a silicon carbide matrix (C/SiC) or carbon fiber reinforcement with a matrix comprising a mixture of carbon and silicon carbide (C/C—SiC), or indeed a C/C composite silicided by being caused to react with Si (C/C—SiC—Si).

#Thermostructural composite materials very frequently contain carbon, whether constituting the fibers, constituting at least part of the matrix, or indeed constituting an interphase coat formed on the fibers to provide them with adequate bonding with the matrix. Thus, whenever such parts are used in an oxidizing atmosphere and at a temperature above 350° C., protection against oxidation is essential in order to avoid rapid deterioration of parts made out of such composite materials. This also applies when boron nitride (BN) is used as an interphase component between ceramic fibers and matrix.

#The invention will be better understood on reading the following detailed description given by way of non-limiting indication. Reference is made to the accompanying drawings, in which:

#FIG. 1 is a flow chart showing the successive steps in forming a coating for providing protection against oxidation in an implementation of the invention; and

#FIGS. 2 to 4 are graphs showing how protective coatings as obtained in accordance with the invention withstand dry and wet oxidizing atmospheres at temperatures of 1000° C. or 1200° C.

#The invention is described below in its application to protecting C/C composite material parts against oxidation, in particular parts constituting the diverging portions of rocket engine nozzles and friction parts such as airplane brake disks.

#Nevertheless, as mentioned above, the invention can be applied to any composite material containing carbon, or any other material that is sensitive to oxidation, in particular CMCs having carbon fiber reinforcement or presenting a carbon interphase or a boron nitride (BN) interphase between the reinforcing fibers and the ceramic matrix made of SiC, for example.

#A first step 10 of the method consists in preparing the composition for application to the surface of the part that is to be protected.