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Method of producing carbon fiber reinforced ceramic matrix composites

The present invention relates to a method of producing carbon fiber reinforced ceramic matrix composites, maintaining excellent mechanical strength at high temperature as well as having excellent properties in corrosion resistance, thermal resistance, friction and abrasion under a severe environment, such as heat, chemical erosion, etc.

Fiber reinforced ceramic matrix composites are lightweight materials having excellent mechanical and thermal properties at high temperature. With these properties, fiber reinforced ceramic matrix composites are applicable to friction and abrasion materials, such as brake disks, and pads for aircraft or ground transport means, and also to ultrahigh thermal resistant materials, such as ceramic engines, and rocket nozzle parts, which require mechanical strength, corrosion resistance, and thermal resistance. Fiber reinforced ceramic matrix composites have been studied to overcome the drawbacks to monolithic ceramics, such as brittle failure, or the like, and they can be produced by filling the pores of a preform made of carbon fibers or silicon carbide fibers with thermal resistant materials, such as pyrolytic carbon, silicon carbide, or boron nitride.

Up to now, fiber reinforced ceramic matrix composites have been produced with a variety of manufacturing processes, however, in most cases, they cause mechanical and/or chemical impact damages to fibers during the manufacturing processes. To solve such a problem, ceramic matrix composites are produced by injecting precursors in a gas state into a porous fiber preform having low density, and then pyrolyzing it for the deposition of ceramic matrix-phase. Such a process is called chemical vapor in-filtration, and the matrix-phase is infiltrated under a low temperature and pressure condition during this manufacturing process to solve the problem causing damage to fibers, which has been created when producing conventional ceramic matrix composites.

In this process, however, high-priced raw materials and manufacturing equipment are employed, its manufacturing process is complicated, and lots of process time more than several hundred hours is required, and therefore its application is extremely restricted to high-tech industries, such as aerospace, or the like.

Rather than the chemical vapor infiltration process using raw materials in a gas state, a process of producing carbon fiber reinforced ceramic matrix composites by in-filtrating liquid-phase silicon into a porous carbon preform has been developed.

As described in U.S. Pat. No. 6,308,808, U.S. Pat. No. 6,358,565, and U.S. Pat. No. 5,942,064 owned by Walter Krenkel et al., a mixture including carbon fibers that have been cut out, liquid-phase phenol, and carbon powder, is molded under a high temperature and pressure condition, and then a thermal treatment process at high temperature is performed to produce a carbon fiber reinforced carbon composite. The produced carbon fiber reinforced carbon composite is infiltrated with liquid-phase silicon to produce a carbon fiber reinforced ceramic matrix composite, and it is applicable to brake disks for ground vehicles and thermal resistance materials in the field of aerospace.

As described above, however, the carbon fiber reinforced resin composite produced by mixing with liquid-phase carbon precursors is more effective than existing chemical vapor infiltration processes in terms of manufacturing cost, but it is difficult to prevent the reaction of liquid-phase silicon against carbon fibers due to some difficulties in forming a uniform carbon fiber protective layer, and thereby rapidly reducing mechanical properties of carbon fiber reinforced ceramic matrix composites. To solve such a problem, as disclosed in Korean Patent Application No. 1999-7008146, as well as U.S. Pat. No. 6,079,525, U.S. Pat. No. 6,030,913, and U.S. Pat. No. 6,231,791, the carbon fiber reinforced ceramic matrix composite is produced by iterative impregnation of liquid organic binders or by changing the composition of the mixture, but it is impossible to prevent the reduction in mechanical properties caused by carbon fiber erosion and to improve friction and abrasion characteristics at high temperature.

As a different process from the above, as disclosed in U.S. Pat. No. 6,221,475 and Korean Patent Application No. 1999-7003211, a preform made of weaved carbon fibers is deposited with pyrolytic carbon by means of an isothermal/isobaric chemical vapor infiltration (ICVI) process, and then a densification process is performed on carbon precursors by means of a liquid-phase infiltration method to produce a carbon fiber reinforced ceramic matrix composite. This process has remarkably improved an aspect of fiber protection, but it is difficult to produce carbon fiber reinforced ceramic matrix composites having a complicated shape due to difficulty in combining different carbon fiber reinforced ceramic matrix composites into a structured body. In particular, the manufacturing process is complicated and required more than several hundred hours for the manufacturing time, and therefore it caused an increase in the manufacturing cost.

Examining the overall problems related to the production technologies of carbon fiber reinforced ceramic matrix composites in most cases a process of producing a carbon fiber reinforced carbon composite that is employed for producing carbon fiber reinforced ceramic matrix composites still has some difficulties in terms of its production cost and technologies. For example, conventional chemical vapor in-filtration process has excellent characteristics as a fiber protective layer; but it is not adequate for producing carbon fiber reinforced carbon composites due to its high-cost raw materials and manufacturing process difficulties. Furthermore, when carbon fiber reinforced resin composites are produced by performing an infiltration process of organic binders containing carbon component, it is known that iterative infiltration processes are required, and the effect is reduced in an aspect of fiber protection.

The present invention is devised to solve the aforementioned problems, and it is an object of the invention to provide a method of producing carbon fiber reinforced ceramic matrix composites for improving thermal and mechanical properties of the carbon fiber reinforced ceramic matrix composites and for providing a solution to the problems due to its high manufacturing cost and processes as described above, by improving the method of producing starting material and a carbon fiber reinforced carbon composite, which are required for producing the carbon fiber reinforced ceramic matrix composites.

To solve the above problems, a method of producing carbon fiber reinforced ceramic matrix composites is provided by the inventors to simplify the manufacturing process by employing a carbon felt preform having a sandwich structure or a carbon fiber mixture as starting material, and to produce carbon fiber reinforced carbon composites having a uniform fiber protective layer with a rapid and low cost process by applying a rapid thermal gradient chemical vapor infiltration process as well as employing a liquid-phase silicon infiltration process.

To achieve the aforementioned object, a method of producing carbon fiber reinforced ceramic matrix (C/C—SiC) composites according to the present invention comprises the steps of: producing a carbon fiber reinforced resin composite that is molded with a mixture in which carbon fibers and polymer precursors containing carbon are mixed; producing a carbon fiber reinforced carbon composite by depositing pyrolytic carbon during a rapid thermal gradient chemical vapor infiltration process while increasing the deposition speed in a direction from the inside to the outside by performing a thermal treatment on said carbon fiber reinforced resin composite at high temperature; and infiltrating liquid-phase silicon into the pores of said carbon fiber reinforced carbon composite.

Moreover, it is preferable that the mixture includes 10-60 wt % of the carbon fibers, and 30-60 wt % of the polymer precursors containing carbon.

Further, it is preferable that the mixture includes less than 30 wt % silicon carbide powder, and less than 30 wt % carbon powder.

Further, it is preferable that the carbon fiber reinforced resin composite is stacked with the mixture and carbon fabrics alternately.

Further, it is preferable that the green body is formed with a first surface layer for preventing carbon fibers from reacting with silicon by means of the mixture that has been mixed during the mixing process, and the first surface layer is formed with a ceramic matrix layer including silicon carbide and silicon by chemically reacting with the liquid-phase silicon in the step of infiltrating the liquid-phase silicon.

Further, it is preferable that the green body undergoes a thermal treatment in a range of 900-2,200° C. under inert gas atmosphere, and then a pyrolytic carbon matrix layer as a second surface layer is deposited on the first surface layer in a deposition step through the rapid thermal gradient chemical vapor infiltration process.

Further, it is preferable that the deposition step by the rapid thermal gradient chemical vapor infiltration process is performed in a range of pyrolytic reaction temperatures 700-1,200° C. and reaction pressures 188-1,130 torr using hydro-carbon gas.