A precursor gel-cured high solids fiber reinforced ceramic core and method of making the same

Abstract

The application provides a precursor gel solidified high solid phase fiber reinforced ceramic core and a preparation method thereof, and belongs to the technical field of preparation of ceramic cores for investment casting. The ceramic core comprises a ceramic matrix and a reinforcing structure, the reinforcing structure is covered on the ceramic matrix, and the reinforcing structure is supported and reinforced by fibers. The application adopts an organic silicon precursor gel, the conversion solid phase rate of which can reach 60%, and the normal temperature viscosity of the precursor is equivalent to that of a wax liquid; under the condition that the slurry volume solid phase rate is the same, the final solid phase rate after conversion can be increased by 20%.

Description

Technical Field

[0001] This invention relates to the field of ceramic core preparation technology for investment casting, and particularly to a precursor gel-cured high-solids fiber-reinforced ceramic core and its preparation method. Background Technology

[0002] With the rapid increase in demand for aero-engines and gas turbines, breakthroughs have been achieved in the manufacturing technology of hollow high-temperature alloy single-crystal turbine blades. Some domestically produced hollow blades have already been widely used in engines. However, the manufacturing process of hollow turbine blades still faces key technical challenges such as low core quality pass rates and unstable performance. In traditional blade manufacturing, deformation, misalignment, and core leakage in the ceramic core lead to a defect rate exceeding 60%, particularly pronounced in the manufacturing of large-size gas turbine blades. The long waxing, curing, and sintering times for ceramic cores, along with the difficulty in controlling process parameters and temperature, make it challenging to determine the patterns and causes of deformation, shrinkage cavities, and cracks. Therefore, how to manufacture high-quality ceramic cores has become a major bottleneck in the hollow blade industry.

[0003] Investment casting is a near-net-shape forming technology widely used in the aerospace field. It can not only produce precision parts with complex shapes but also achieve integrated casting of composite structures. It is widely used in the manufacture of complex heat-resistant components such as heat-resistant parts for aerospace engines and key hot-end components for automobiles. With technological iterations in forming processes, mold design, and material systems, investment casting has achieved stable production of products with larger dimensions, higher precision, thinner walls, and superior mechanical properties. For investment castings with complex internal cavity structures, ceramic cores are required as the forming core, whose core function is to form the internal cavity contour of the hollow casting. During the high-temperature molten metal pouring, filling, and solidification process, the ceramic core must withstand the static pressure, impact loads, and high-temperature thermal effects of the molten metal, which places stringent requirements on its key properties such as high-temperature mechanical strength, high-temperature dimensional stability, and thermal shock resistance.

[0004] Therefore, it is of great significance to provide a precursor gel-cured high-solid-phase fiber-reinforced ceramic core and its preparation method that can improve the strength of ceramic cores, reduce deformation and defects, simplify the preparation process, and shorten the preparation time. Summary of the Invention

[0005] The purpose of this invention is to provide a precursor gel-cured high-solid-phase fiber-reinforced ceramic core and its preparation method, in order to solve the problems of low yield, easy deformation, core deviation, and core leakage in existing ceramic core preparation methods, which lead to a high failure rate of hollow turbine blades. At the same time, the traditional preparation process has long wax injection, curing and sintering times, and the process parameters and temperature are difficult to control, making it difficult to avoid technical problems such as deformation, shrinkage cavities and cracks.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a precursor gel-cured high-solids fiber-reinforced ceramic core, the ceramic core comprising a ceramic matrix and a reinforcing structure, the reinforcing structure covering the ceramic matrix and being reinforced by fiber support.

[0007] Furthermore, the fiber comprises zirconium fiber, with a fiber length of 500~1000μm and a fiber diameter of 8~12μm.

[0008] The present invention also provides a method for preparing the precursor gel-cured high-solids fiber-reinforced ceramic core, comprising the following steps: 1) Mix the precursor gel with ceramic powder to make a slurry, then evenly lay fibers on the slurry, and repeat the process of laying slurry and laying fibers to form a multi-layer composite structure. 2) The multi-layer composite structure is subjected to high-pressure molding vibration molding to obtain a ceramic core blank; 3) After demolding the ceramic core blank, it is calcined to obtain a precursor gel-cured high-solid-phase fiber-reinforced ceramic core.

[0009] Furthermore, the precursor gel is a liquid silicone resin.

[0010] Furthermore, the volume ratio of the precursor gel to the ceramic powder is 2~4:6~8.

[0011] Furthermore, in the steps of repeatedly laying the slurry and laying the fiber, the number of times the slurry is laid is 4 to 6.

[0012] Furthermore, the pressure of the high-pressure molding vibration forming is 35~45MPa.

[0013] Furthermore, the heating rate of the calcination is 4~6℃ / min, the calcination temperature is 900~1300℃, and the calcination time is 1~5h.

[0014] The beneficial effects of this invention are: 1) This invention uses organosilicon precursor gel, which has a conversion solids rate of up to 60%, and the room temperature viscosity of the precursor is comparable to that of wax liquid; under the same slurry volume solids rate, the final solids rate after conversion can be increased by 20%.

[0015] 2) This invention eliminates the thermal debinding step by gradually converting the precursor through heating, which greatly improves the preparation efficiency. At the same time, no liquid phase is formed during the heating and conversion of the precursor, which can avoid debinding deformation and reduce or even eliminate the use of sintering aids, thereby reducing sintering deformation.

[0016] 3) The present invention reduces the molding and curing temperature to room temperature and the curing time is adjustable and controllable; by spreading ceramic fibers on the surface of a plastic thin layer and then repeatedly stacking and pressing the plastic process, a three-dimensional network ceramic plastic blank with high fiber solid content and uniform distribution is formed, and then a three-dimensional precision molding is achieved by using a high pressure molding vibration process. Attached Figure Description

[0017] Figure 1 This is a bar chart showing the flexural strength of the precursor gel-cured high solid phase fiber reinforced ceramic core under different calcination temperatures and times according to the present invention. Detailed Implementation

[0018] The present invention provides a precursor gel-cured high-solids fiber-reinforced ceramic core, the ceramic core comprising a ceramic matrix and a reinforcing structure, the reinforcing structure covering the ceramic matrix and being reinforced by fiber support.

[0019] In this invention, the fiber comprises zirconium fiber, the length of which is 500-1000 μm, preferably 600-900 μm, and more preferably 700-800 μm; the diameter of which is 8-12 μm, preferably 9-11 μm, and more preferably 10 μm.

[0020] The present invention also provides a method for preparing the precursor gel-cured high-solids fiber-reinforced ceramic core, comprising the following steps: 1) Mix the precursor gel with ceramic powder to make a slurry, then evenly lay fibers on the slurry, and repeat the process of laying slurry and laying fibers to form a multi-layer composite structure. 2) The multi-layer composite structure is subjected to high-pressure molding vibration molding to obtain a ceramic core blank; 3) After demolding the ceramic core blank, it is calcined to obtain a precursor gel-cured high-solid-phase fiber-reinforced ceramic core.

[0021] In this invention, the precursor gel is a liquid silicone resin.

[0022] In this invention, the volume ratio of the precursor gel to the ceramic powder is 2~4:6~8, preferably 2.5~3.5:6.5~7.5, and more preferably 3:7.

[0023] In this invention, the steps of repeatedly laying slurry and laying fibers are performed 4 to 6 times, preferably 5 times.

[0024] In this invention, a mixed solution of water and alcohol is used to treat the surface of the fibers to remove surface dust and enhance the surface activity of the fibers. The fibers are then dried and packed into sealed bags. A blower is used to slowly blow air into the transparent bag to evenly disperse the zirconium fibers in the sealed bag and prevent them from clumping together.

[0025] In this invention, the alcohol purity is 99%.

[0026] In this invention, the volume ratio of water to alcohol is 7:3.

[0027] In this invention, the drying process of the fiber is natural drying or low-temperature drying; The low-temperature drying is performed at a low temperature of 60°C in a drying oven.

[0028] In this invention, before laying the fibers, the dried fibers are placed in a sealed bag and blown slowly with a hair dryer to disperse them evenly; when laying the fibers, the "rain method" is used to allow the fibers to fall naturally and spread evenly on the surface of the slurry.

[0029] In this invention, the pressure of the high-pressure molding vibration forming is 35~45MPa, preferably 37~43MPa, and more preferably 40MPa.

[0030] In this invention, the heating rate of the calcination is 4~6℃ / min, preferably 4.5~5.5℃ / min, and more preferably 5℃ / min; the calcination temperature is 900~1300℃, preferably 950~1250℃, and more preferably 1000~1200℃; the calcination time is 1~5h, preferably 1.5~4h, and more preferably 2~3h.

[0031] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1

[0033] Zirconium fibers with a length of 800 μm and a diameter of 10 μm were soaked in a mixed solution of water and 99% alcohol with a volume ratio of 7:3. This removed surface dust and improved the surface activity of the fibers. The fibers were then placed in a drying oven and dried at a low temperature of 60°C. After drying, they were placed in a large transparent sealed bag. A regular hair dryer was used to gently blow air into the sealed bag to evenly disperse the zirconium fibers and prevent them from clumping together. The solution was then ready for use. The organosilicon precursor (liquid silicone resin) and ceramic powder in a volume ratio of 3:7 were stirred and mixed at room temperature to obtain a slurry. The viscosity of the slurry at room temperature was comparable to that of the wax liquid used for investment casting. Pour the slurry into a resin mold and place it on a vibrating bed to vibrate it evenly. The vibration amplitude of the vibrating bed is 20mm. Use the "rain method" to let the evenly dispersed zirconium fibers in the sealed bag fall naturally and spread evenly on top of the slurry to form a thin fiber layer structure. Continue to slowly spread a small amount of slurry on top of the fiber layer and turn on the vibrating bed to vibrate it so that the slurry covers the fiber layer. Repeat the spreading process 5 times to form a multi-layer composite structure. The multi-layer composite structure, along with the resin mold, is placed on a high-pressure molding vibratory bed. It is first vibrated and then pressed at a pressure of 40 MPa to further press the slurry and zirconium fiber into a three-dimensional network ceramic core blank. After demolding, the ceramic core blank was placed in a drying room with 48% humidity and 21°C and left to stand for 12 hours. The ceramic core blank was then placed in a mortar and calcined in an inert atmosphere. The temperature was increased to 900°C at a rate of 5°C / min and held for 2 hours. The core was then cooled to room temperature in the furnace to obtain a precursor gel-cured high-solid-phase fiber-reinforced ceramic core.

[0034] Example 2

[0035] Compared with Example 1, the difference is that the roasting temperature in Example 2 is 1200℃ and the roasting time is 2h.

[0036] Example 3

[0037] Compared with Example 1, the difference is that the roasting temperature in Example 3 is 1200℃ and the roasting time is 3h.

[0038] Example 4

[0039] Compared with Example 1, the difference is that the roasting temperature in Example 4 is 1200℃ and the roasting time is 5h.

[0040] The flexural strength of the precursor gel-cured high-solid-phase fiber-reinforced ceramic cores prepared in Examples 1-4 was tested, and the test results were obtained by... Figure 1 As shown. By Figure 1 It can be seen that, under different calcination temperatures and calcination times, the precursor gel-cured high-solid-phase fiber-reinforced ceramic cores exhibit different flexural strengths after calcination, with the final maximum flexural strength being 8.41 MPa. This indicates that the core preparation process of the present invention can fully meet the specifications of conventional cores.

[0041] As can be seen from the above embodiments, the present invention provides a precursor gel-cured high-solids fiber-reinforced ceramic core and its preparation method. The ceramic core includes a ceramic matrix and a reinforcing structure, wherein the reinforcing structure covers the ceramic matrix and is supported and strengthened by fibers. The present invention uses an organosilicon precursor gel, which can achieve a conversion solids rate of up to 60%, and the room temperature viscosity of the precursor is comparable to that of wax liquid; under the same slurry volume solids rate, the final solids rate after conversion can be increased by 20%.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A precursor gel-cured high-solids fiber-reinforced ceramic core, characterized in that, The ceramic core includes a ceramic matrix and a reinforcing structure, the reinforcing structure covering the ceramic matrix and being reinforced by fiber support.

2. The precursor gel-cured high-solids fiber-reinforced ceramic core according to claim 1, characterized in that, The fiber comprises zirconium fiber, with a length of 500~1000μm and a diameter of 8~12μm.

3. A method for preparing a precursor gel-cured high-solids fiber-reinforced ceramic core as described in claim 1 or 2, characterized in that, Includes the following steps: 1) The precursor gel is mixed with ceramic powder to form a slurry, and then fibers are evenly laid on the slurry. The process of laying slurry and fibers is repeated to form a multi-layer composite structure. 2) The multi-layer composite structure is subjected to high-pressure molding vibration molding to obtain a ceramic core blank; 3) After demolding the ceramic core blank, it is calcined to obtain a precursor gel-cured high-solid-phase fiber-reinforced ceramic core.

4. The method for preparing a precursor gel-cured high-solid-phase fiber-reinforced ceramic core according to claim 3, characterized in that, The precursor gel is a liquid silicone resin.

5. The method for preparing a precursor gel-cured high-solids fiber-reinforced ceramic core according to claim 4, characterized in that, The volume ratio of the precursor gel to the ceramic powder is 2~4:6~8.

6. The method for preparing the precursor gel-cured high-solids fiber-reinforced ceramic core according to claim 4 or 5, characterized in that, In the steps of repeatedly laying slurry and fiber, the number of times the slurry is laid is 4 to 6.

7. The method for preparing the precursor gel-cured high-solid-phase fiber-reinforced ceramic core according to claim 5, characterized in that, The pressure of the high-pressure molding vibration forming is 35~45MPa.

8. The method for preparing a precursor gel-cured high-solids fiber-reinforced ceramic core according to claim 6, characterized in that, The calcination heating rate is 4~6℃ / min, the calcination temperature is 900~1300℃, and the calcination time is 1~5h.

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