DE4016052C2 - - Google Patents

Description

The invention relates to a method for producing a ceramic fiber composite material, the fibers made of C or SiC or SiO ₂ or Al ₂ O ₃ or Si ₃ N ₄ or Al ₂ O ₃ .SiO ₂ .B ₂ O ₃ or mixtures or compounds thereof consist.

In GB 21 19 777 A there are ceramic molded parts made of fiber composite materials described, which contain inorganic fibers, and the matrix of one preceramic material, namely a silane or siloxane by means of Vernet tion and pyrolysis is produced.

EP 03 46 192 A1 describes the production of a matrix from a Mi Development of a polymer and a powder for an inorganic fiber holding composite ceramics known. State of the art (DE 37 24 580 A1) also the use of coated fibers in composite materials made of sili cium carbide fibers in a silicon nitride matrix.  

Efforts have been made for years by installing Fibers in a ceramic matrix the damage tolerance of the composite material and at the same time the positive properties of the monolithi ceramics. The use of carbon fiber reinforced sili cium carbide (C / SiC) or silicon carbide fiber reinforced silicon carbide for the Space as thermal shields and structural materials are knows. These are structural components and parts of rocket engines as well "nozzle flaps" for use in military jet engines. That here used manufacturing principle of the deposition of the matrix from the gas phase (CVI) requires very long process times and therefore high costs. For the civilian Such parts cannot therefore be used economically in aircraft construction.

The invention has for its object to develop a ceramic composite material which, in addition to resistance to high temperatures (≧ 500 ° C), resistance to corrosion and resistance to oxidation and an increased fracture toughness compared to monolithic ceramics. Pipes with the lowest possible specific density (<2.5 g / cm ³ ) should also be able to be produced in series from the composite material.

The object is achieved by the teaching of the main claim and of the subclaims solved.

The manufacture of products such as B. tubes, from continuous fiber reinforced Ceramics are analogous to the production of fiber-reinforced plastics either by a process in which the thread is immersed in an immersion bath impregnated with a slip and then placed on a winding core or via lamination of soaked tissues. According to the invention  the slip from a dissolved Si polymer (e.g. silazane, silane or silo xan) and a ceramic powder whose rheological properties are based on the winding parameters and the thread characteristics are coordinated. The kera Mix powder serves as a lean agent to help reduce the shrinkage of the matrix the subsequent temperature treatment.

The finished wound or laminated part can be placed in an autoclave high pressure (e.g. 1.5 MPa) and temperature increase (e.g. 200 to 450 ° C) be networked. Networking via chemical auxiliaries (e.g. boric acid) is also possible at room temperature with suitable Si polymers. To the impression is ceramized at temperatures <500 ° C (e.g. by pyrolysis). The polymer becomes viscous in the autoclave and thus fills the Gaps and pores in the workpiece. With networking, it will Polymer solid.

Pyrolysis causes organic groups to split off and a ceramic product to form, predominantly SiC from silanes, carbosilanes and vinylsilanes, Si ₃ N ₄ from silazanes and SiC with SiO ₂ from siloxanes. The pyrolysis product connects the powder particles of the slip and the fibers. Pyrolysis under pressure brings a slight improvement in the ceramic yield, but hardly justifies the increased outlay on equipment. The pyrolysis can be carried out without the use of expensive molds and without warping the structural parts.

As an alternative to direct shaping on the winding core, the prepreg can be used can also be removed from the core after drying. The dried ones Parts can be made flexible again by adding solvents Molded parts are laminated before they are cured and pyrolyzed.  

The molded parts are dimensionally stable after curing.

The ceramic end product is easy to machine and if it can required to be provided with a ceramic coating.

Depending on the pyrolysis temperature and the selected Si polymer, resistance of the ceramic molded part to temperatures of more than 1400 ° C. can be achieved. The molded part has a low specific weight (<2.5 g / cm ³ ), can be machined, for example, by turning, milling, sawing, drilling and self-supporting.

The matrix is resistant to oxidation. When using more resistant to oxidation Fibers (SiC or oxidic fibers) do not require additional protection against oxidation agile. The material is highly tolerant of damage, even the heaviest Damage remains local.

The bending strength is more than 100 MPa.

The chemical composition of the fibers and the matrix is chosen so that corrosion resistance is guaranteed.

The advantages of the invention lie in the low specific weight of the ceramic component (<2.5 g / cm ³ ) and the high temperature resistance, oxidation resistance and thermal shock resistance. In addition, there is the significantly reduced thermal conductivity of the ceramic composite material, which can lead to a reduction in the amount of insulating material used to date and thus contributes to further weight savings.

Compared to other known methods of producing ceramic ver Bund materials (e.g. CVI of fiber fabrics) has the procedure shown here significant advantages in terms of the price of the raw materials and the  Manufacturing time and manufacturing costs.

An embodiment of the invention is explained below.

According to the teaching of the claims, pipes were of a maximum Diameter of 300 mm and a length of 420 mm for a wall 1.5 mm thick. The dimensions are not subject to any principle len restrictions. Investigations of the flexural strength of the fiber reinforcement ceramics gave values of <300 MPa for unidirectional fabrics as well <150 MPa for bidirectional fabrics. With unidirectionally reinforced bending pro Average strengths of 400 MPa were used at a test temperature of 1100 ° C enough. Tests on fabrics that correspond in structure to the pipe wall, are currently running.

Oxidation tests up to 700 ° C with a cyclical course show the necessity of an additional oxidation protection for the C-fiber. With fibers resistant to oxidation (e.g. SiO ₂ , Al ₂ O ₃ , Al ₂ O ₃ × SiO ₂ × B ₂ O ₃ , SiC), an oxidation resistance up to 400 h could be demonstrated, especially in the temperature range up to 1100 ° C. Long-term stability of several 1000 h is very likely and is currently being tested.

A possible application of the subject matter of the invention is as an exhaust pipe in the engines of commercial aircraft or engines of motor vehicles. Another application is the guidance of hot engine gases to the Purpose of defrosting vulnerable areas in manned and unmanned areas missiles. In addition to hot gases, hot and corrosive rivers can also occur liquids in these tubes.

Claims (5)

1. A process for producing a ceramic fiber composite material, wherein the fibers of C, or SiC, or SiO ₂ or Al ₂ O ₃ or Si ₃ N ₄ or Al ₂ O ₃ · SiO ₂ · B ₂ O ₃ or mixtures or compounds consist thereof, characterized characterized in that the ceramic matrix is formed from a preceramic Si polymer by means of crosslinking and pyrolysis, and that the fibers or a fabric formed therefrom with an inorganic coating of C or SiC or TiC or TiN are inserted into the composite material in one or more layers be brought. 2. The method according to claim 1, characterized in that as Si Polymer is a silane, carbosilane, vinylsilane, silazane or siloxane or a compound or a mixture thereof is used. 3. The method according to claim 1 to 2, characterized in that a ceramic powder made of glass or SiO ₂ or SiC or Si ₃ N ₄ or BN or Al ₂ O ₃ or mixtures or compounds of these substances is added to the Si polymer. 4. The method according to claims 1 to 3, characterized in that the fibers or fabrics with the mixture of Si polymer and powder ("Slip") are soaked. 5. Use of manufactured according to the method of claims 1 to 4 products as hot gas pipes for engines.