CN105367105A - Method for preparing thick-walled ceramic-matrix composite material through mechanical processing assisted CVI (Chemical Vapor Infiltration) - Google Patents

Abstract

The invention relates to a mechanical processing-assisted CVI method for preparing a ceramic matrix composite material thick-walled part (≥5mm), comprising the following steps: depositing an interface layer on a prefabricated body in a graphite furnace; densifying the prefabricated body by chemical vapor infiltration treatment, the relative density of the preform reaches 20% to 65%, and the preform is taken out; the preform is processed with micropores by mechanical processing, so as to dredge the transmission channel of the gaseous precursor; and the ceramic matrix composite material is obtained by cyclic deposition. The advantages of this process: (1) It improves the pore structure of the prefabricated body itself, reduces the density gradient of the composite material, and effectively solves the problem of uneven density of ceramic matrix composite material thick-walled parts (≥5mm); (2) improves (3) Improve the densification speed and shorten the preparation cycle.

Description

Method for preparing thick-walled ceramic matrix composites by machining-assisted CVI

technical field

The invention belongs to the field of CVI preparation of ceramic matrix composite materials, and in particular relates to a method for preparing thick-walled ceramic matrix composite materials with mechanical processing assisted CVI. The gaseous precursor diffusion channel inside the preform enables the formation of multi-scale mass transfer channels in the porous body: intra-bundle holes, inter-bundle holes and processing holes, thereby improving the compactness and density of ceramic matrix composite thick-walled parts (≥5mm). Density uniformity to achieve high density and high strength preparation of ceramic matrix composites.

Background technique

Ceramic matrix composites can meet the requirements of long life below 1650°C, limited life below 20000°C, and instantaneous life below 2800°C. Thermal systems, cruise missile engines, liquid and solid rocket engines and other weapons and equipment fields have broad prospects for promotion and application, and have great market potential in civil fields such as turbine gas power plants and nuclear power reactors.

The chemical vapor infiltration (CVI) method is currently the only commercialized manufacturing method for the manufacture of complex braided toughened CMC. It has strong adaptability and is applicable to all inorganic non-metallic materials in principle. This method can avoid damage to fibers caused by high temperature, and facilitates the manufacture of large, thin-walled, and complex near-net shape components. However, for thick-walled products (wall thickness ≥ 5mm), since the mass transfer of gaseous precursors in the porous body mainly depends on diffusion in this process, there is a certain density gradient in the component along the direction of gas diffusion, resulting in The pores of the preform are closed prematurely and the gas source is cut off to transmit to the interior of the preform, resulting in the "bottleneck effect" of the blockage of the mass transfer channel to the internal pores, so that the preform has more than 30% residual pores, forming a typical hollow sandwich structure, which seriously affects Mechanical properties and engineering applications of composite materials. How to increase the density of the composite material, the deposition rate of the matrix as much as possible and reduce the density gradient inside the material has become one of the key issues that need to be solved urgently in the preparation of CMC-SiC composite materials, especially in the development and application of composite materials with a wall thickness ≥ 5mm.

In order to solve the above problems, in US Pat. No. 5,411,763, when the thermal gradient CVI method is used to prepare porous structure composite materials, the uniformity of densification can be effectively improved, but the gas transmission is slow, and the densification rate of the material is limited. U.S. Patent US5900297 discloses a method for preparing porous structure composite materials by the pressure gradient CVI method. Using the pressure gradient CVI technology, the densification process of the material can be effectively completed in a short period of time, but this method has high requirements for equipment. , The operation is difficult, and it is not suitable for mass production. In US Patent 4580524, the FCVI method is used to prepare ceramic matrix composites, which can effectively shorten the densification process and improve the density uniformity. However, the heating of each area in the preform mainly depends on heat conduction, resulting in insufficient densification of the cold surface of the preform. In the German patent DE4142261, the isothermal pressure gradient CVI process is used to prepare porous structure composite materials, which effectively improves the gas transmission capacity, but there is still the problem of uneven densification. The document "Microwave Heated Chemical Vapor Infiltration: Densification Mechanism of SiC _{f /SiC Composites. David Jaglin, Jon Binner, and Bala Vaidhyanathan. The American Ceramic Society, 2006, 9: 2710-2717" proposed the use of microwave pyrolysis to densify SiC f /} SiC composites, which can be used within 24 hours. The average density of the composite material reaches 50%, and the center density of the composite material reaches 73%, which speeds up the densification rate of the preform and improves the density uniformity. However, the process requires high equipment and is still in the experimental stage.

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a method for the preparation of thick-walled ceramic matrix composites with mechanical processing assisted CVI, which provides a simple process, low cost and can effectively reduce the thickness of ceramic matrix composites (wall thickness ≥ 5mm) density gradient, a chemical vapor infiltration preparation method that improves its compactness and mechanical properties.

Technical solutions

A method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI, characterized in that the steps are as follows:

Step 1: Place the formed thick-walled reinforced fiber preform in a chemical vapor infiltration furnace, and prepare a ceramic interface layer by the CVI method;

Step 2: Depositing a ceramic matrix by chemical vapor infiltration method to densify the fiber prefabricated body, and the relative density reaches 35% to 65%;

Step 3: Uniformly process small holes on the fiber preform, and the hole distance is ≥ 2 times the aperture; increase the diffusion channel of the gaseous precursor inside the preform;

Step 4: The processed composite material is further densified by depositing a matrix by a chemical vapor infiltration method, and the relative density reaches more than 90%.

The small holes in step 3 are: round holes with a diameter of 0.5-5 mm, square holes with a side length of 0.5-5 mm, or small holes of other shapes with an outline size of 0.5-5 mm.

The hole machining method of the small hole is: drilling, reaming, turning, boring, water cutting hole or wire cutting hole.

The structure of the thick-walled reinforced fiber preform is: 1-dimensional, 2-dimensional, 2.5-dimensional or 3-dimensional.

The preparation method of the thick-walled reinforcing fiber preform is: lamination, weaving or needle punching.

The fibers are high-temperature ceramic fibers.

The fiber is: boron fiber, silicon carbide fiber or oxide fiber.

The ceramic interface layer is pyrolytic carbon or boron nitride.

The thick wall of the thick-walled reinforced fiber preform is ≥ 5 mm.

Beneficial effect

The invention proposes a method for preparing thick-walled ceramic matrix composite materials assisted by mechanical processing through CVI, which is a chemical vapor infiltration method assisted by mechanical processing. When the SiC matrix is deposited by the chemical vapor infiltration method so that the relative density of the preform reaches 30% to 70%, mechanical processing equipment is used to process small holes in the ceramic matrix composite material (wall thickness ≥ 5mm), so that the inside of the preform is formed: holes in the bundle , inter-bundle pores and multi-scale mass transfer channels of processing pores, thereby adjusting the pore structure of the preform itself, clearing the transmission channel of the gaseous precursor, and then densifying the preform until the density is greater than 2.0kg/cm ³ , specifically The steps are shown in Figure (1):

The beneficial effect of the present invention is: when preparing the ceramic matrix composite material (wall thickness ≥ 5mm), the intervention of machining small hole technology helps to form multi-scale gas-phase mass transfer channels in the deposition process, and improves the internal diffusion environment of fiber bundles. Fill the pores caused by the CVI bottleneck process, reduce the density gradient of the preform, improve the compactness of the composite material, and improve the strength and toughness of the composite material. Compared with the C/SiC composite material in the prior art, the bending strength of the composite material prepared by this process method has increased, as shown in Fig. 4 . When the mechanical opening density is 1.69%, the density of the prepared composite material is 2.1-2.3g/cm ³ , and the bending strength at room temperature is 330-400MPa; when the mechanical opening density is 3.38%, the density of the prepared composite material is 2.0-2.2 g/cm ³ , and the bending strength at room temperature is 340-420 MPa.

Description of drawings

Fig. 1: Flow chart of the inventive method

Figure 2: Diameter and layout of mechanically processed micro-holes

Figure 3: SEM morphology of the holes and the edges of the machined micro-holes

Fig. 4: The flexural strength diagram of the composite material prepared by the embodiment

detailed description

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

The technical scheme of the present invention: when the SiC matrix is deposited by chemical vapor infiltration to make the relative density of the preform reach 30% to 70%, mechanical processing equipment is used to process small holes on the ceramic matrix composite material (wall thickness ≥ 5mm), so that the inside of the preform Formation: multi-scale mass transfer channels of intra-bundle holes, inter-bundle holes and processing holes, thereby adjusting the pore structure of the preform itself, dredging the transmission channel of the gaseous precursor, and then densifying the preform until the density is greater than 2.0kg / ^cm3

Step 1, preparation of fiber prefabricated body: After two-dimensional sequential lamination of 1K carbon fibers, the reinforcing fibers are punctured along the thickness direction with a suture distance of 3mm×3mm to obtain a carbon fiber prefabricated body with a volume fraction of about 40-42%.

Step 2, Deposit the pyrolytic carbon interface layer by chemical vapor infiltration method: place the carbon fiber preform in a high-temperature vacuum furnace, the deposition temperature is 800-1000°C, the atmosphere pressure is 0.2KPa, the flow rate of Ar is 300ml/min, and the flow rate of propylene is 30ml/min. Cool down naturally after 45-60 hours.

Step 3, deposition of SiC substrate by chemical vapor infiltration method: deposition at 1000-1100°C, atmosphere pressure 2KPa, Ar flow rate 300ml/min, H ₂ flow rate 200ml/min, MTS is brought into the high-temperature deposition furnace by bubbling, H ₂ The molar mass ratio to MTS is 10:1, and the temperature is naturally lowered after 180-230 hours of deposition to form a C/SiC composite material.

Step 4, machining micro-hole diameter and arrangement Figure 2 and its SEM appearance between the holes and around the holes are shown in Figure 3: the diameter of the holes is 0.5-3mm, the mechanical holes are evenly distributed on the hole surface of the material, the holes The hole density is 1-8% for the distance ≥ 2 times the hole diameter.

Step 5, densifying the C/SiC composite material by chemical vapor infiltration until the density of the C/SiC composite material is greater than 2.0 kg/cm ³ .

Example 1:

Step 1, preparing two-dimensional laminated carbon cloth preforms in two heats, the specific process is:

(1) Select T300-1K carbon fiber, weave it into a two-dimensional plain weave, and after stacking 77 layers, use 1K carbon fiber to connect with needles along the thickness direction with a stitching distance of 3mm×3mm, and stitch the laminated layers together to obtain the volume density A carbon fiber preform of 0.70 g/cm ³ and a carbon fiber volume fraction of 40.0% to 42.0%.

(2) Clamp the carbon fiber preform with a graphite mold, place it in a vacuum furnace at 1800°C for 3 hours of degumming and pretreatment, and then use CVI to deposit the pyrolytic carbon interface layer (PyC) on the obtained fiber preform. The preparation process of the PyC interface phase is as follows: deposition temperature 900°C, atmospheric pressure 0.2KPa, propylene flow rate 30ml/min, Ar flow rate 300ml/min, and natural cooling after deposition for 50-60h. The above process was repeated 2 times.

(3) Deposit the SiC matrix on the heat-treated C/SiC composite material by the CVI method. Place the carbon fiber preform in a high-temperature vacuum furnace, and the specific preparation process of the SiC matrix phase is as follows: deposition at 1100 °C, atmosphere pressure at 2KPa, _H2 flow at 200ml/min, Ar flow at 300ml/min, and MTS is brought into the In the high-temperature deposition furnace, the molar mass ratio of _H2 to MTS is 10:1, and the temperature is naturally lowered after 200-230 hours of deposition. The above process is repeated ⁴ times, and the graphite mold is removed to finally obtain C/ SiC composite materials.

(4) Machining small holes. The C/SiC composite material was soaked in alcohol and ultrasonically cleaned for 15 minutes to remove impurities such as dust and oil on the surface, and finally dried in an oven to prepare a C/SiC sample. Place the sample on the processing platform, select a suitable drill bit, clamp the drill bit, adjust the cutting speed of machining, the position and height of the bed, drill the pilot hole in the center and process the sample layer by layer to prepare the fiber prefabricated body for uniform processing 0.5 ~ 5mm round hole, hole spacing ≥ 2 times the hole diameter, small hole opening density is 1.69%;

(5) Repeat the process described in step (3) to densify the C/SiC composite material until the density of the sample is above 2.0 kg/cm ³ .

(6) The volume density of the C/SiC composite material prepared in this example is 2.2g/cm ³ _. , and the bending strength is 345MPa after testing by SANSCMT4304 electronic universal testing machine.

Example 2:

Step 1, preparing two-dimensional laminated carbon cloth preforms in two heats, the specific process is:

(1) Select T300-1K carbon fiber, weave it into a two-dimensional plain weave, and after superimposing 77 layers, use 1K carbon fiber to stitch and connect along the thickness direction with a stitching distance of 3mm×3mm, and stitch the laminated layers together to obtain the volume density A carbon fiber preform of 0.70 g/cm ³ and a carbon fiber volume fraction of 40.0% to 42.0%.

(2) Clamp the carbon fiber preform with a graphite fixture, place it in a vacuum furnace at 1800°C for 3 hours of degumming and pretreatment, and then deposit PyC on the obtained fiber preform by CVI. The preparation process of the PyC interface phase is as follows: deposition temperature 920°C, atmospheric pressure 0.23KPa, propylene flow rate 32ml/min, Ar flow rate 310ml/min, natural cooling after deposition for 50-60h. The above process was repeated 2 times.

(3) Deposit the SiC matrix on the heat-treated C/SiC composite material by the CVI method. Place the carbon fiber preform in a high-temperature vacuum furnace. The specific preparation process of the SiC matrix phase is as follows: deposition at 1200°C, atmosphere pressure at 2.2KPa, _H2 flow rate at 210ml/min, Ar flow rate at 305ml/min, and MTS with MTS by bubbling. Into a high-temperature deposition furnace, the molar mass ratio of H ₂ to MTS is 10:1, and the temperature is naturally lowered after 200-230 hours of deposition. The above process is repeated 4 times, and finally a C/SiC composite material with a bulk density of 1.7g/cm ³ is obtained.

(4) Machining small holes. The C/SiC composite material was soaked in alcohol and ultrasonically cleaned for 15 minutes to remove impurities such as dust and oil on the surface, and finally dried in an oven to prepare a C/SiC sample. Place the sample on the processing platform, select a suitable drill bit, clamp the drill bit, adjust the cutting speed of machining, the position and height of the bed, drill the pilot hole in the center and process the sample layer by layer to prepare the fiber prefabricated body for uniform processing For square holes with a side length of 0.5-5mm, the hole spacing is ≥2 times the hole diameter, and the small hole opening density is 1.69%.

(5) Repeat the process described in step (3) to densify the C/SiC composite material until the density of the sample is above 2.0 kg/cm ³ .

The volume density of the C/SiC composite material prepared in this embodiment is 2.1 g/cm ³ , and the bending strength is 330 MPa after being tested by a SANSCMT4304 electronic universal testing machine.

Claims (9)

1. A method for mechanically processing assisted CVI to prepare thick-walled ceramic matrix composites, characterized in that the steps are as follows: Step 1: Place the formed thick-walled reinforced fiber preform in a chemical vapor infiltration furnace, and prepare a ceramic interface layer by the CVI method; Step 2: Depositing a ceramic matrix by chemical vapor infiltration method to densify the fiber prefabricated body, and the relative density reaches 35% to 65%; Step 3: Uniformly process small holes on the fiber preform, and the hole distance is ≥ 2 times the aperture; increase the diffusion channel of the gaseous precursor inside the preform; Step 4: The processed composite material is further densified by depositing a matrix by a chemical vapor infiltration method, and the relative density reaches more than 90%. 2. The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1, characterized in that: the small hole in the step 3 is: a round hole with a diameter of 0.5-5 mm and a side length of 0.5-5 mm Square holes or small holes of other shapes with an outline size of 0.5-5 mm. 3. The method for preparing thick-walled ceramic matrix composites according to claim 1 or 2, characterized in that: the machining hole method of the small hole is: drilling, reaming, lathing, boring , water cutting holes or wire cutting holes. 4. The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1, characterized in that: the structure of the thick-walled reinforced fiber preform is: 1-dimensional, 2-dimensional, 2.5-dimensional or 3-dimensional. 5. The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1 or 3, characterized in that: the preparation method of the thick-walled reinforced fiber preform is: lamination, weaving or needle punching. 6 . The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1 , characterized in that: the fibers are high-temperature ceramic fibers. 7 . The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1 , wherein the fibers are: boron fibers, silicon carbide fibers or oxide fibers. 8. The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted CVI according to claim 1, characterized in that: the ceramic interface layer is pyrolytic carbon or boron nitride. 9. The method for preparing thick-walled ceramic matrix composites with mechanical processing assisted by CVI according to claim 1 or 5, characterized in that: the thick-wall of the thick-walled reinforced fiber preform is ≥ 5 mm.