DE4102909A1 - WORKPIECES MADE OF FIBER REINFORCED CERAMIC - Google Patents

Description

The invention relates to workpieces made of fiber-reinforced ceramic, best hend from at least two put together and surrounded with matrix material fiber fabric made of ceramic material and a manufacturing process development of such workpieces.

Workpieces of this type are bonded in particular at high temperatures which applications are used. So far, such fiber-reinforced Kera Microfabricated parts made from a woven fabric or type of storage (structure) from one Fiber material stacked on top of each other and impregnated with SiC matrix. Here who the structures such as B. canvas, satin or satin fabric or just plain Directionally designed fibers for stacking used in fiber materials Carbon or SiC fibers. With the choice of fiber structure for a ge given material combination of fibers and matrix the mechanical properties properties of the workpiece.

By using a certain type of fabric or wrapping layers Construction according to the state of the art, the properties of the component (Tensile strength, compressive strength, rigidity and their directional dependencies) in set narrow limits. It has thus been found that such construction share many applications with complex requirements, e.g. B. as a lightweight construction workpiece with load-bearing function is not sufficient.

The invention has for its object workpieces of the aforementioned Way to develop that can be realized with a wide range of properties.

The object is achieved with the features of claim 1.

The fiber composite ceramics according to the invention are characterized in that they are made up of different fiber structures and as a whole with one Ceramic matrix are impregnated.  

By structuring and combining different fiber fabrics The properties compared to composite materials are stacked in the same way fiber impregnated with SiC matrix with uniform, uniform improved according to structure type or expanded to a larger area of application. Another advantage of using different fiber structures within of a ceramic component lies in the considerably enlarged structural shape freedom for the component. This allows the properties of a component Made of fiber-reinforced ceramic in an optimal way to meet the requirements be adjusted. For example, by combining dense tissue areas with voluminous but wide-meshed fiber structures a balanced ratio of strength and rigidity with minimized weight light. The invention thus serves to improve the properties of fiber stronger ceramics, especially for applications in lightweight construction techniques.

The invention extends to a method for producing workpieces, which is characterized by the measures according to claim 2.

Depending on the intended use, the fiber structures can be a combination tion of canvas, satin, polar or non-woven Structures or fabrics with unoriented fibers (felts) or oriented Fibers (e.g. winding structures or UD laminates) exist. The individual structure Tur elements (fiber fabrics) can have different surface densities and consist of different fiber materials (carbon, silicon carbide, Silicon carbonitride, aluminum oxide, mullite). The selection and arrangement of the respective fiber structures depend on the requirements at the intended Use or function (gas tightness, strength).

The fiber structure composites can not only in one dimension in sandwich structure, but also laterally in the other two dimensions be structured.

Impregnation processes are suitable according to the invention for the construction of the ceramic matrix using a fluid phase. The gas phase infiltration and / or the impregnation of liquid substances, pure or in solution, which as Precursors for a ceramic matrix can be preferred metho the.  

According to a further embodiment of the invention, the fiber structure is bund in a preliminary stage for fixing the fibers with a polymer material as pure liquid substance or soaked in solution, which by subsequent thermi hardened treatment and then pyrolyzed. The amount of entered gene polymer material is chosen so that the fiber strands bridges, however do not completely verify the pore spaces in the fiber bundles and between the strands be closed. This creates a firm connection between the fiber structure elements without the subsequent impregnation with the matrix material is significantly impaired. The determination has become the control parameter for this the pressure drop with gas flow proven.

The invention is described in more detail with reference to a simple quaderörmi gene component or workpiece 10 shown in FIG. 1. As shown in the two cross-sectional areas 11 and 12 , the workpiece 10 consists of different structures. These structures initially consist of different fiber layers 13 to 17 stacked in the z direction. The two outer layers 13 , 17 and the middle layer 15 extend through the entire surface, while the intermediate layer 14 in the y direction has three structures 14 a to c and the intermediate layer 16 in the x direction has two structures 16 a, 16 b has.

The different structures are characterized by the type of binding of the fibers. For example, the continuous layers 13 , 15 , 17 fabrics of different or the same type (canvas, atlas etc.), the fiber fabric 14 a can be a felt, the fabrics 14 b and 16 b made of UD fiber layers of different orientations (x or . y direction) exist and the two fiber fabrics 16 a and 14 c can be fiber wool of different densities.

Further change parameters are the fiber material and the matrix material like the density or porosity of a clutch. These can also be used arbitrarily combine. The choice of both the fiber structure, their distribution as the materials also depend on the specific application.

A layer 13 to 17 can consist of a fiber fabric or a stack of fiber fabrics. When producing geometrically irregular workpieces, the correspondingly cut fiber fabrics are preferably placed in a mold.

After the fiber fabric has been folded together, the fiber structure formed impregnated as a whole with the selected matrix material and then Burnt to eat.

It has proven to be advantageous if the fibers within the composite before Impregnation process can be fixed using a material. This is particularly suitable special a polymer material, which as a pure liquid substance or in solution in the Compound entered and hardened by subsequent thermal treatment and finally pyrolyzed.

What type of polymer is used to fix the fiber body depends on the conditions under which the resulting component is used should be det. For applications with an operating temperature below approximately 400 ° C are organic resins such as B. epoxy, phenol, imide or thermo plastic can be used. They are thermally treated in amorphous Koh transferred lenstoff, which causes the structural consolidation. For operating temperature Ren above about 400 ° C in air in the same way a silicon-containing Polymer from the compound classes polycarbosilane, polysilazane or polysiloxane used, because from the thermal treatment an amorphous, but oxidation resistant product - i. w. from SiC - arises. In order for a balanced ratio of solidification and remaining porosity optimal amount adjust the matrix, the polymer can in an aprotic Lö solvents such as hexane can be used in solution.

The fiber structure fixed by the pre-impregnation and thermal treatment in the composite is filled with the matrix by chemical gas phase infiltration (CVI). In particular aluminum oxide (Al ₂ O ₃ ) from aluminum chloride (AlCl ₃ ) and carbon dioxide (CO ₂ ) in a hydrogen stream, silicon carbide (SiC) from trichloromethylsilane (CH ₃ -SiCl ₃ ) in a H ₂ stream and silicon nitride (Si ₃ N ₄ ) Silicon fluoride (SiF ₄ ) and ammonia (NH ₃ ) can advantageously be introduced as a matrix into the fiber structure using this process. With denser fiber structures, such as z. B. are favorable to achieve dense surfaces, the best results were with the Gradi entenverfahren (described in: WV Kotlenski "A Review of CVD Carbon Infil tration of Porous Substrates", 16th Natl. SAMPE Conf., 1971, p.257 ff) achieved, which is based on a controlled flow through the fiber body.

As an alternative to the CVI method, the matrix was impregnated with a liquid phase and subsequent thermal treatment for drying and firing entered into the fibrous body.

The raw materials used for liquid phase impregnation differ in their chemical nature, depending on which matrix material is needed. The impregnation is carried out with a polysilazane to produce a matrix of SiC. An Al ₂ O ₃ matrix is produced using the so-called sol-gel process from aluminum tri-tertiary butylate by controlled hydrolysis and subsequent drying and sintering.

For the production of oxide matrices, Al ₂ O ₃ or mullite, instead of the sol-gel process, attempts have also been made to impregnate aqueous suspensions of very fine oxide powders with grain sizes of approximately 0.1 micrometers in fiber templates. However, a noticeable accumulation of the solid was found in the zones near the surface. In addition, hardly any matrix material has penetrated into the interstices between the individual fibers of the fiber bundle. A bridging of the fiber interstices by matrix material is required in order to achieve the load transfer in the composite material and thus its mechanical strength.

Figs. 2 to 4 show scanning and light microscopy images of manufactured according to the invention, exemplary material samples.

Fig. 2 shows a cross section in 15 times magnification and Fig. 3 is a plan view of a first sample 20 , which consisted of a wide-mesh multi-layer fabric 21 and a densely stacked laminate 22 of 2D fabrics, each of SiC fibers, combined and by CVl had been infiltrated with a SiC matrix. While the denser layer 22 in this composite construction ensures strength, the braced, open fabric 21 additionally provides rigidity with low weight.

Fig. 4 shows in 50x magnification a cross section of a sample 30 produced according to Example 2, which consists of a stack of fiber fabric in linen structure 31 and felt layers 32 made of SiC fibers. 33 denotes the remaining porosity.

With the methods recognized as advantageous, test components were made of fiber reinforced ceramics. The principle of the invention was thus Combination of different fiber assembly forms in workpieces and that with achieved setting of their properties after the introduction of the matrix guided. Such exemplary embodiments are described below and the optimal adaptation of the component properties to the application requirements explained by the component structure according to the invention.

example 1

One as a structural component in the engine inlet of a high speed aircraft intended component with a box-like shape was made of coal Fiber-reinforced SiC ceramic manufactured with the following structure:

A so-called carbon spacer fabric tailored to the final shape fibers, which formed a cuboid box and two inner had continuous webs parallel to the longitudinal edge and in a multi-layered web weaving structure was carried out, was clamped on a support structure. Thereon fabric layers of carbon fibers were laid, with layers varying blended with canvas and satin fabrics. The interposing of well drapable satin fabric served to size the interlaminar hollow to minimize space and to distribute the lead as evenly as possible to achieve porosity in the composite.

The fabric structure was impregnated with a silicon-containing polymer, namely a mixture of polymeric silazanes, which had been prepared from methyldichlorohydrogensilane (CH ₃ SiHCl ₂ ) and vinyltrichlorosilane (CH ₂ CHSiCl ₃ ) with ammonia (NH ₃ ) as crosslinking agent. By curing the polymer and subsequent pyrolysis to SiC, a box-shaped fiber preform was obtained in which the fiber layers were so firmly connected that it was self-supporting and could be installed in a CVI system. The gas phase infiltration of SiC was carried out in a gradient process using a gas stream (methyltrichlorosilane in H ₂ ) with a maximum temperature of 11 50 ° C.

This principle of construction, combined with the manufacturing method described, resulted in Result in a component with an optimal ratio of strength and  Stiffness to his weight. The necessary for the aerodynamic load che component strength was due to the tightly infiltrated outer layers with about 45 vol% fiber content and the torsional rigidity due to the inner webs made of egg an open-pore C / SiC composite with multi-layer fabric with an average achieved fiber content of 20 to 25% in the volume unit.

Example 2

SiC fiber fabric in a linen structure, cut into a disk shape, was stacked with thin felt layers made of short SiC fibers and thick short fiber mats as cover layers on both sides and installed under pressure in perforated graphite plates in a CVI system. The disc-shaped fiber body was infiltrated with SiC matrix using the gradient method. In the short fiber intermediate and top layers, the prevailing flow conditions in gas phase infiltration caused a much stronger matrix growth than in the fabric layers, so that a significantly higher matrix: fiber ratio could be set here than in the fabric layers (see Fig. 4). Since the short fibers 32 were pressed by the pressing substantially into the non-filled spaces 33 of the fiber strands of the adjacent fabric layers 31 , an overall high compression during infiltration could be achieved. After processing, the composite component was tested as a brake disc. Its suitability for this application is the result of the selected fiber structure and is determined by the high pressure and shear strength achieved in connection with the thermal shock resistance of the SiC / SiC material and its friction properties.

Example 3

In the tape winding process, a fiber preform in the form of an elongated cylinder was produced from Al ₂ O ₃ fibers in a crosswise diagonal orientation with respect to the cylinder axis. With the layered fabric structure, a wall thickness of 2.5 mm was set. The fiber body was stabilized as in Example 1 by impregnation of a polysilazane mixture and its pyrolysis to form nitrogen-containing SiC. The gas phase infiltration of SiC matrix was also carried out analogously to Example 1.

When trying to use the fiber composite ceramic tube produced in this way as a can in one Using canned liquid pumps became an inadequate seal  speed of the material compared to the passage of liquid. In another Embodiments were made in the same manner as in Example 2, thin short intermediate layers and a short fiber top layer in the otherwise similar herge provided component introduced. The effect of the short fibers was also in a ver strong matrix entry in the respective layers. In another treatment the remaining fine porosity was replaced by a simple one Post impregnation of Si polymer and its pyrolysis to SiC completely ver closed. In a test run of the pipe in a canned pump, the Media tightness determined.

Example 4

For the production of a shaft protection sleeve for use in a pump for cor Roding and wearing media became a cylindrical fiber body SiC fiber strands diagonally crosswise to the longitudinal axis up to a wall thickness of 1.5 mm and three top layers wrapped in circumferential orientation. The ge supported The fiber body was infiltrated with a SiC matrix using CV1. On the outside The cylinder surface was then a mixture of SiC powder with a medium Grain size of 0.2 micrometers and a Si polymer with a thickness of approx. 0.5 mm applied. It became dense by thermal treatment Cover layer formed from SiC-bonded SiC by grinding and polishing was brought to the required surface quality.

This ceramic composite component had an optimal characteristic for the application shaft combination with maximum wear resistance and surface density, combined with the best possible fracture toughness for ceramic components and thus damage tolerance.

In a corresponding way, only in reverse of the layer sequence, so that the inner Surface of the cylindrical tube sealed with the fiber-free SiC layer was a cylindrical liner for a mold filling device (filling book se) a plastic injection molding machine. The component proved itself under the complex operational loads, such as high filling pressure and wear-and-tear media um and temperature changes.

Claims (6)

1. Workpieces made of fiber-reinforced ceramic, consisting of at least two fiber gels placed against one another and surrounded by a matrix material, made of ceramic material, characterized in that the fiber layers ( 13-17 ) have different structures and / or consist of different materials. 2. A process for the production of workpieces according to claim 1, wherein fiber scrims made of ceramic material and folded into a fiber composite, impregnated with a ceramic matrix and fired who, characterized in that fiber scrims ( 13-17 ) with differen chen structures and / or used from different materials and folded, impregnated and burned to a fiber structure composite ( 12 ). 3. The method according to claim 2, characterized in that the fiber structure ( 10 ) is impregnated by liquid phase infiltration or by chemical gas phase infiltration with the matrix material. 4. The method according to claim 2 or 3, characterized in that the fiber composite structure ( 10 ) is impregnated with liquid polymer material and thermally treated before the impregnation process. 5. The method according to claim 4, characterized in that the liquid Polymer material is used in pure liquid form or as a solution. 6. The method according to claim 3, characterized in that the fiber structurally soaked with a lot of polymer material that just enough to bridge the fiber strands, but pore spaces not closed.