Preparation method of integrally-formed ceramic matrix composite hollow guide blade

Abstract

The invention discloses a preparation method of an integrally-formed ceramic matrix composite hollow guide vane, the hollow guide vane comprises an upper margin plate, a vane body and a lower margin plate, a hollow guide vane preform is obtained by weaving carbon fibers or silicon carbide fibers, and the fiber interweaving density at the joint of the vane body and the lower margin plate is larger than that at other positions; the method comprises the following steps: preparing a mold based on a hollow guide blade preform, fastening and shaping to obtain a tool, impregnating, cracking and depositing a silicon carbide matrix through a precursor to fill pores among fiber bundles for a certain time, dismounting the tool, and continuously impregnating, cracking and depositing the silicon carbide matrix through the precursor; according to the manufacturing method, continuous and complete fibers at the junctions of the blade body and the upper and lower edge plates are achieved, matrix densification is achieved, the overall strength is effectively improved, the risks of cracking and gas leakage are reduced, tools do not need to be replaced in the manufacturing process, the manufacturing complexity can be greatly reduced, and the manufacturing cost is reduced. The processing period is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of high-pressure turbine guide blades of aircraft engines, and more particularly to a method for preparing an integrally formed ceramic-based composite hollow guide blade. Background Art

[0002] As an important component inside an aircraft engine, the turbine guide vanes can convert part of the thermal energy of high-temperature combustion gas into kinetic energy, while ensuring that the direction of the airflow meets the working requirements. Due to their direct contact with the combustion chamber outlet combustion gas, they must withstand extreme environmental tests such as high temperature, oxidation, thermal fatigue and impact loads during service. With the development of modern aircraft engines towards high thrust-to-weight ratio and high efficiency, the average temperature of the turbine inlet of engines with a thrust-to-weight ratio of 15 to 20 in the future will exceed 2200K. Traditional high-temperature alloy guide vanes have basically reached their operating temperature limit. Ceramic-based composites, with their low density (only 1 / 3-1 / 4 of that of high-temperature alloys), excellent corrosion resistance, oxidation resistance, thermal shock resistance and high-temperature mechanical properties, can withstand more extreme environmental tests while achieving an overall lightweight design of the structure. They are considered to be ideal candidate materials for the hot end components of the next generation of aircraft engines.

[0003] The turbine guide vanes consist of multiple complex structures, including the upper edge plate, the lower edge plate, and the blade body. The upper and lower edge plates need to be equipped with high-precision mounting edges to achieve reliable connection with the turbine casing, while the blade body is designed as a hollow structure with a cooling cavity to achieve efficient heat dissipation through internal cooling airflow. Due to the complex weaving process of the integrated blade components and the difficulty in finalizing the shape during the deposition densification process, the existing engineering field generally adopts a semi-integrated guide vane design scheme, which replaces the material on the basis of the metal guide vane structure: the blade body adopts ceramic-based composite materials, and the upper and lower edge plates still adopt high-temperature alloys. Due to the large difference in thermal expansion coefficient and elastic modulus between ceramic-based composite materials and high-temperature alloys, the thermal stress concentration generated under thermal cycling loads will cause microcracks to initiate and expand in the components at the joints, resulting in damage to the joints, limiting actual engineering applications.

[0004] At present, there are few studies on the integrated molding of ceramic matrix composite guide blades, which mainly use a split preparation process to avoid the problem of thermal stress concentration caused by excessive differences in the thermal expansion coefficients of the materials. For example, the Chinese patent (application number 202311627077.7) mentions a method for preparing a ceramic matrix composite multi-cavity structure high-pressure turbine guide blade. First, the upper edge plate component preform, the lower edge plate component preform and the blade body preform are prepared; each preform is separately shaped, interface deposited, and the matrix densified; finally, the various components are assembled online, put into the furnace for deposition, and processed to obtain the turbine guide blade. However, the blade and the edge plate are connected by composite pins, the fiber continuity is poor, and the strength of the assembly is low; at the same time, due to the complexity of the overall preparation process, multiple deposition processes, preform shape processing and tooling replacement are required, and the mass production cost is high. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing an integrally formed ceramic-based composite hollow guide blade, so as to solve the problems existing in the existing split preparation process, such as low strength at the connection between the blade body and the edge plate, complex preparation process, and high cost; at the same time, based on a large number of previous preparation process explorations and high-temperature mechanical properties test results, the interface deposition and matrix densification processes are optimized to obtain guide blades with high strength and long service life.

[0006] The present invention provides a method for preparing an integrally formed hollow guide vane made of ceramic-based composite materials. The blade structure comprises a blade body component and upper and lower edge plates disposed on either side of the blade body component. The blade body is a thin-walled, curved structure, the inner side of which forms a closed-loop cooling cavity. Except for the leading and trailing edges, where the blade body has a uniform thickness, both the upper and lower edge plates have mounting edges.

[0007] The method comprises the following preparation steps:

[0008] First, a preliminary experiment was carried out to obtain high-density specimens with excellent high-temperature mechanical properties by optimizing the chemical vapor deposition and precursor impregnation and cracking process parameters, and to determine the blade preparation process.

[0009] Then, a method for preparing an integrated hollow guide vane made of ceramic-based composite material is carried out according to the process. The hollow guide vane includes at least a blade body and upper and lower edge plates. The hollow guide vane preform is woven using carbon fiber or silicon carbide fiber. The fiber interweaving density at the intersection of the blade body and the upper and lower edge plates is greater than that at other locations.

[0010] Based on the preform, molds of high-temperature resistant materials are prepared and fixed tightly to obtain a tooling. After depositing the interface layer, two stages of precursor impregnation and cracking are carried out to deposit a silicon carbide matrix to fill the pores between the fiber bundles. The first stage of deposition is first carried out with the tooling, and then the tooling is removed, and the second stage of deposition of the silicon carbide matrix is continued through precursor impregnation and cracking. After the two stages of deposition are completed, chemical vapor infiltration is used to deposit silicon carbide to fill the pores between the single fibers in the fiber bundle.

[0011] Furthermore, the preform is woven by carbon fiber or silicon carbide fiber, and the preform structure is 2.5D.

[0012] Furthermore, during the braiding preparation process of the hollow guide blade preform, a machining allowance is reserved based on the dimensional changes and machining accuracy occurring during the densification process.

[0013] Furthermore, the machining allowance is determined according to the curvature of the blade surface, with a 0.2-0.4 mm allowance reserved for the blade back with positive curvature and a 0.3-0.5 mm allowance reserved for the blade base with negative curvature.

[0014] Furthermore, a 0.3-0.5mm margin is reserved for the upper and lower edge plates, and a 1-2mm thickness margin is reserved for the installation edge.

[0015] Furthermore, the blade body, upper edge plate and lower edge plate have a thickness of 3-4 mm.

[0016] Furthermore, the blade body is a thin-walled curved structure, the inner side of the curved structure forms a cooling cavity with a closed-loop structure, the upper edge plate and the lower edge plate have mounting edges, and the hollow guide blade preform is obtained by weaving using a metal core mold, and the high-temperature resistant material is high-purity graphite with a carbon content of >99.99%.

[0017] Furthermore, each mold includes a core mold of high-temperature resistant material, an outer mold 1, an outer mold 2, an upper mold and a lower mold.

[0018] Furthermore, the outer mold 1, outer mold 2, upper mold and lower mold all have a plurality of vent holes and limit holes perpendicular to the molding surface.

[0019] Furthermore, the diameter of the vent hole of the shaping mold is 2-4 mm; the diameter of the limit hole is 8-12 mm;

[0020] Furthermore, outer mold one and outer mold two are U-shaped structures, and the preform blade part is clamped between outer mold one, outer mold two and the core mold, and outer mold one and outer mold two are fastened; the U-shaped extension parts of outer mold one and outer mold two are matched with the lower edge of the upper mold and the upper edge of the lower mold, and the upper mold and the lower mold are fastened to complete the shaping of the hollow guide blade preform.

[0021] Furthermore, the wall thickness of the outer mold 1 and the outer mold 2 is 20-30 mm, and the wall thickness of the upper mold and the lower mold is 15-40 mm;

[0022] Furthermore, the outer mold 1 and the outer mold 2, the upper mold and the lower mold are fixed with bolts / nuts, and the material thereof is C / C composite material.

[0023] Furthermore, the interface layer types include pyrolytic carbon (PyC) interface, (PyC / SiC) n Multilayer composite interface and boron nitride (BN) interface.

[0024] Furthermore, an interface layer of desired thickness is deposited by chemical vapor infiltration process.

[0025] Furthermore, when the silicon carbide substrate is deposited by the precursor impregnation and cracking process, the tooling is removed when the weight gain rate of the first stage deposition drops to 8%.

[0026] Furthermore, after the tooling was removed, the weight gain rate of the second stage of deposition was reduced to below 1%.

[0027] Furthermore, the fibers at the junction of the blade body and the upper and lower edge plates are interwoven using an angle interlocking weaving method, with the warp yarns bending and interweaving multiple layers of weft yarns in the thickness direction to form interlayer reinforcement; the junction of the blade body and the upper and lower edge plates is a right-angle weaving structure with a warp density of 5-7 strands / cm and a weft density of 3-5 strands / cm.

[0028] Furthermore, chemical vapor infiltration and deposition of silicon carbide are used to fill the pores between the filaments in the fiber bundle, thereby achieving complete densification of the blades; finally, the blades are machined to obtain turbine guide blades with high dimensional accuracy.

[0029] Furthermore, a ceramic-based composite hollow guide vane is prepared using the method.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention is a method for preparing an integrally formed hollow guide blade of a ceramic-based composite material. This forming method can achieve the continuity and integrity of the fibers at the junction of the blade body and the upper and lower edge plates, so that the various structures of the preform can complete interface deposition and matrix densification under the same preparation environment, effectively improving the overall strength of the guide blade and reducing the risk of cracking and air leakage. Compared with the split preparation, the preparation process does not require the replacement of tooling, can greatly reduce the complexity of preparation, and shorten the processing cycle. Different from the matrix densification process in the existing patents, the present invention adopts the preparation process parameters optimized by pre-experimentation, and the precursor impregnation and cracking process is combined with the chemical vapor infiltration process technology to improve the density of the component. The prepared hollow guide blade of the ceramic-based composite material was found to have no obvious holes after industrial CT inspection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of a ceramic-based composite guide blade in an embodiment of the present invention.

[0033] Figure 2 This is a physical picture of the metal core mold used for weaving the hollow guide blade preform of the present invention.

[0034] Figure 3 It is a schematic diagram of the tooling used for shaping the hollow guide blades of ceramic-based composite materials according to the present invention. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0036] like Figure 1 As shown, a ceramic matrix composite hollow guide blade structure includes an upper edge plate 1, a blade body 2, and a lower edge plate 3 arranged in sequence. The upper edge plate 1 has mounting edges 11 and 12, the lower edge plate 3 has mounting edges 31 and 32, and the blade body 2 has a closed-loop cooling cavity 22 inside.

[0037] like Figure 2 As shown, a metal core mold is prepared with reference to the internal cavity dimensions, and both ends of the metal core mold are extended to facilitate subsequent demolding. A hollow guide vane preform is obtained by weaving carbon fibers onto the metal core mold using an angle interlocking weaving method. The warp yarns are bent and interwoven with multiple layers of weft yarns in the thickness direction to form interlayer reinforcement. In view of the right-angle weaving structure at the junction of the blade body and the edge plate in the preform, the yarns are tightly interwoven in the intersection area, with a warp density of 5-7 yarns / cm and a weft density of 3-5 yarns / cm. This not only has excellent load-bearing capacity but also avoids the difficulty of deposition caused by overly dense yarns.

[0038] like Figure 3 As shown, with the cooling cavity 22 of the blade body as a reference, a core mold 4 is prepared, with the blade back as a reference, an outer mold 1 5 is prepared, with the blade basin as a reference, an outer mold 2 6 is prepared, with the upper edge plate as a reference, an upper mold 7 is prepared, and with the lower edge plate as a reference, a lower mold 8 is prepared; the upper mold and the lower mold are respectively provided with openings matching the upper and lower mounting edges;

[0039] The blade body of the hollow guide blade preform is clamped between the core mold, the first outer mold, and the second outer mold and fixed with C / C bolts / nuts. The upper edge plate is fitted with the upper mold curved surface, and the lower edge plate is fitted with the lower mold curved surface. The mounting edge is placed in the openings of the upper and lower molds. The upper and lower molds are also fixed with C / C bolts / nuts to complete the shaping of the hollow guide blade preform.

[0040] The hollow guide vane preform with tooling is deposited on the interface by chemical vapor infiltration process. The interface layer type can be pyrolytic carbon (PyC) interface, (PyC+SiC) n Multilayer composite interface and BN interface.

[0041] 1) The specific deposition process of the PyC interface is as follows: under a pressure of 3000-8000Pa, the temperature is raised to 900-1200°C, and after holding it for 1-2 hours, a mixture of natural gas and propane gas is introduced. After deposition for 15-25 hours, the mixture is held for another hour and then cooled to room temperature. Among them, the flow ratio of natural gas to propane gas is 1:4-8, and the final weight gain rate must reach more than 10%.

[0042] 2)(PyC+SiC) n The specific deposition process of the multi-layer composite interface is as follows: the pyrolytic carbon interface deposition process remains unchanged, and the deposition time is adjusted according to the designed thickness. Then, under a pressure of 4000-8000Pa, the temperature is raised to 900-1200°C. After keeping warm for 1-2 hours, a mixed gas of trichloromethylsilane, hydrogen and argon is introduced. Among them, the flow ratio of trichloromethylsilane, hydrogen and argon is 1:8-12:8-12. The deposition time can be adjusted independently, and the temperature is lowered to room temperature after the insulation is completed.

[0043] 3) The specific deposition process of the BN interface is as follows: under a pressure of 50-1000 Pa, the temperature is raised to 650-1000°C, and after keeping the temperature for 1-2 hours, a mixed gas of argon, hydrogen, ammonia and boron trichloride gas is introduced. After deposition for 10-20 hours, the temperature is kept for another hour and then cooled to room temperature. Among them, the flow ratio of argon, hydrogen, ammonia and boron trichloride gas is 1:2-4:2-4:4-8, and the final weight gain rate must reach more than 10%;

[0044] The pores in the guide vane preform can be divided into two types: pores between fiber bundles and pores between individual filaments within the fiber bundles. Densification of the preform using a precursor impregnation and pyrolysis process produces a matrix that can effectively fill the pores between the fiber bundles. However, due to the small size of the pores between the individual filaments within the fiber bundles, the precursor solution is difficult to penetrate. To obtain a highly densified ceramic-based composite guide vane, the present invention uses a precursor impregnation and pyrolysis process combined with chemical vapor infiltration technology for densification, selecting silicon carbide as the matrix. The specific densification process is as follows:

[0045] The guide vane preform is impregnated using a vacuum impregnation process, using a polycarbosilane / xylene solution. To fully fill the small pores within the preform and minimize the production cycle, the initial polycarbosilane concentration in the precursor impregnation solution was 20-30%. Once the single-pass weight gain rate drops below 8%, the polycarbosilane concentration is increased to 30-50%. The preform is first placed in a vacuum impregnation apparatus, evacuated, and then the precursor solution is added. The vacuum impregnation process is maintained for 0.5-1 hour, followed by impregnation at atmospheric pressure for 1-3 hours.

[0046] After impregnation, the impregnated preform is taken out and placed in an oven to dry at 120°C for 5 hours;

[0047] The dried guide blade blank is placed in a high-temperature cracking furnace for cracking and deposition. During the first stage of cracking and deposition, the blade is placed in a graphite tooling to prevent deformation during the cracking process. Under vacuum conditions, the temperature is first raised to 300°C for 90 minutes; then the temperature is raised to 1100°C at a rate of 2-4°C / min and maintained in vacuum for 1 hour; after the insulation process is completed, it is cooled with the furnace. When the single weight gain rate is less than 8%, a large amount of silicon carbide matrix has been filled between the preform fiber bundles during the previous precursor impregnation and cracking process, which has played a shaping role. The graphite tooling can be removed and the second stage of deposition can begin. Since there is no tooling, the second stage of deposition can significantly improve the densification efficiency. The above impregnation-drying-cracking process is repeated until the single weight gain rate is less than 1%.

[0048] The chemical vapor infiltration densification stage can quickly fill the tiny pores between the single filaments in the fiber bundle. The specific deposition process is as follows: the preform is heated to 1100°C under a pressure of 2000-5000Pa. After keeping warm for 1 hour, a mixed gas of trichloromethylsilane, hydrogen and argon is introduced. After deposition for 50 hours, the mixture is cooled to room temperature; the flow ratio of trichloromethylsilane: hydrogen: argon is 1:10-15:10-15.

[0049] (8) The hollow guide vanes are precisely measured using the machine tool’s on-machine detection technology, allowing the on-machine status of the stator to be acquired in real time. Based on the measurement data acquired on-machine, digital removal processing of complex curved surface components can be quickly and accurately achieved, resulting in high-dimensional precision hollow guide vanes made of ceramic-based composite materials.

[0050] The above applications are only some embodiments of the present application. For those skilled in the art, without departing from the inventive concept of the present application, several modifications and improvements can be made, which all fall within the scope of protection of the present application.

Claims

1. A method for preparing an integrally formed ceramic-based composite hollow guide vane, characterized in that: The hollow guide blade comprises at least a blade body and upper and lower edge plates. The hollow guide blade preform is woven with carbon fiber or silicon carbide fiber. The fiber interweaving density at the intersection of the blade body and the upper and lower edge plates is greater than that at other positions. Based on the preform, molds of high-temperature resistant materials are prepared and fixed tightly to obtain a tooling. After depositing the interface layer, two stages of precursor impregnation and cracking are carried out to deposit a silicon carbide matrix to fill the pores between the fiber bundles. The first stage of deposition is first carried out with the tooling, and then the tooling is removed, and the second stage of deposition of the silicon carbide matrix is continued through precursor impregnation and cracking. After the two stages of deposition are completed, chemical vapor infiltration is used to deposit silicon carbide to fill the pores between the single fibers in the fiber bundle.

2. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 1, characterized in that: During the weaving preparation process of the hollow guide blade preform, a processing allowance is reserved based on the dimensional changes and processing accuracy occurring during the densification process.

3. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 2, characterized in that: The machining allowance is determined according to the curvature of the blade surface. A 0.2-0.4 mm allowance is reserved for the blade back with positive curvature, and a 0.3-0.5 mm allowance is reserved for the blade base with negative curvature.

4. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 3, characterized in that: The blade body is a thin-walled curved surface structure, and the inner side of the curved surface structure forms a cooling cavity with a closed-loop structure. The upper edge plate and the lower edge plate have mounting edges. The hollow guide blade preform is woven using a metal core mold, and the high-temperature resistant material is high-purity graphite with a carbon content of >99.99%.

5. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 4, characterized in that: Each mold comprises a core mold made of high temperature resistant material, an outer mold 1, an outer mold 2, an upper mold and a lower mold.

6. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 1, characterized in that: When the silicon carbide substrate is deposited by the precursor impregnation and cracking process, the tooling is removed when the weight gain rate of the first stage deposition drops to 8%.

7. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 6, characterized in that: After the tooling was removed, the second stage of deposition was to reduce the weight gain to below 1%.

8. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to claim 1, characterized in that: The fibers at the junction of the blade body and the upper and lower edge plates are interwoven using an angle interlocking weaving method. The warp yarns are bent in the thickness direction and interspersed with multiple layers of weft yarns to form interlayer reinforcement. The junction of the blade body and the upper and lower edge plates is a right-angle weaving structure with a warp density of 5-7 strands / cm and a weft density of 3-5 strands / cm.

9. The method for preparing an integrally formed ceramic matrix composite hollow guide vane according to any one of claims 1 to 8, characterized in that: After chemical vapor infiltration and deposition of silicon carbide to fill the pores between the filaments in the fiber bundle, the blades are machined to obtain turbine guide blades with high dimensional accuracy.

10. A hollow guide vane made of ceramic matrix composite material prepared by the method according to any one of claims 1 to 9.

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