A forming method for improving the density of ceramic fiber reinforced ceramic matrix composite

Abstract

The application discloses a forming method for improving the compactness of ceramic fiber reinforced ceramic matrix composite, and belongs to the technical field of composite material preparation. The method selects a specific precursor mixture as an impregnation matrix material, and then is combined with a high-temperature pressure sintering process to regulate and control process parameters in different composite stages, so that the problem of uneven distribution of the matrix formed by the cracking of polysilazane in the existing process is maximally solved, internal defects of the material are reduced, the compactness of the composite material can be improved to about 70%, the damage degree of the fiber is reduced by reducing the composite times, the fiber can play a better reinforcing and toughening effect, the mechanical properties such as tensile and bending of the composite material are effectively improved, and finally high-performance silicon nitride fiber reinforced silicon nitride composite material can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of composite material preparation, in particular to a molding method for improving the density of ceramic fiber reinforced ceramic matrix composite materials. Background Art

[0002] As new aircraft advance toward higher Mach speeds and longer flight distances, demands are rising for high-performance wave-transmitting and heat-resistant components, including high-temperature resistance, wave transmission, and load-bearing performance. These components must withstand greater loads and aerodynamic thermal shock in harsher operating environments, operate at temperatures exceeding 1400°C, and meet high wave-transmission requirements. Ceramic materials, due to their excellent high-temperature resistance, heat resistance, high strength, and superior electrical properties, are often the preferred choice for high-temperature, wave-transmitting components in aerospace applications. Among wave-transmitting materials, traditional quartz ceramics have a low operating temperature, with a long-term non-ablative temperature not exceeding 1000°C, making them unable to meet the high Mach number requirements of high-speed aircraft. Alumina ceramics have poor electrical properties, such as dielectric constant and dielectric loss, making them incapable of meeting the wave-transmitting requirements of components in high-temperature environments. Silicon nitride ceramics offer excellent high-temperature resistance and electrical properties, but inherent drawbacks such as brittleness limit their reliability.

[0003] Further research has revealed that ceramic fiber-reinforced ceramic matrix composites, due to their fiber-enhancing and toughening effects, significantly improve material reliability, making them a promising choice for high-temperature resistant and wave-transparent components. Silicon nitride fiber-reinforced silicon nitride composites, with their excellent dielectric properties, exceptional high-temperature resistance, and high mechanical reliability, have become ideal high-temperature resistant and wave-transparent ceramic materials for high-speed aircraft.

[0004] Silicon nitride fiber-reinforced silicon nitride composites primarily refer to ceramic composites with silicon nitride fibers as the reinforcing fibers and a silicon nitride matrix. Further research on silicon nitride fibers has revealed that they possess excellent thermal shock resistance and room-temperature / high-temperature mechanical properties. Furthermore, they can be used at temperatures exceeding 1400°C in an inert atmosphere. Their electrical properties, such as dielectric constant and dielectric loss, are moderate, demonstrating excellent load-bearing and wave-transmitting properties. Therefore, silicon nitride composites prepared with a silicon nitride matrix possess excellent high-temperature mechanical properties, stable electrical properties, and ablation resistance, making them ideal materials for high-temperature, wave-transmitting components in future aircraft.

[0005] Currently, the precursor impregnation and pyrolysis (PIP) process is primarily used to prepare silicon nitride fiber-reinforced silicon nitride composites. This process involves weaving silicon nitride fibers into a fiber preform, which is then thoroughly impregnated with a polysilazane organic precursor. The precursor-impregnated preform undergoes crosslinking and curing at a specific temperature. The preform, containing the precursor-cured product, is then placed in a high-temperature sintering furnace for a high-temperature pyrolysis reaction. The pyrolysis reaction converts the organic precursor into a ceramic matrix, which is then densified. Repeated impregnation, curing, and pyrolysis of the ceramic precursor ultimately produce the silicon nitride fiber-reinforced silicon nitride composite. Examples include CN112010654A, CN104261850A, and CN115636681A.

[0006] The silicon nitride precursor (i.e., polysilazane) used in the PIP process is generally highly viscous and has poor fluidity. This results in uneven distribution of the precursor within the fiber preform after impregnation and curing. Furthermore, the ceramic yield of the precursor-cured product is low (generally less than 70%). Furthermore, the cracking process releases small gas molecules, creating pores that further reduce the density of the composite material, resulting in a poor overall density improvement achieved with a single pass. Currently, due to process and precursor limitations, such composites can only be prepared through multiple impregnation and curing steps of the composite precursor. However, even this approach has limited effects on increasing the density of the composite and improving the uniformity within the matrix, and the porosity of the final product can still be as high as over 45%. Multiple rounds of cracking and compounding also reduce the strength of the fiber preform, significantly reducing the mechanical properties, heat resistance, and dielectric properties of the composite material, making it impossible to achieve an ideal high-temperature resistant and wave-transparent composite material.

[0007] In order to solve the technical problems in the preparation of silicon nitride fiber reinforced silicon nitride composites by the PIP process, multiple rounds of high-temperature cracking process aggravate fiber damage, low yield of polysilazane ceramics, and poor internal uniformity of the matrix after cracking, which lead to low density and poor performance of the composite materials. It is necessary to innovate the composite process of silicon nitride fiber reinforced silicon nitride composites. Summary of the Invention

[0008] To address the technical problems existing in the prior art, the present invention provides a molding method for improving the density of ceramic fiber-reinforced ceramic matrix composites. By combining the precursor impregnation and curing process with a high-temperature pressure sintering process and selecting an optimized matrix, the present invention maximizes the solution to the problem of uneven matrix distribution formed by the cracking of polysilazane in the existing process, reduces internal defects in the material, and increases the density of the composite material to approximately 70%.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] In one aspect, the present invention provides a molding method for improving the density of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0011] (1) Preparation of silicon nitride fiber preform: placing a preform formed by weaving silicon nitride fibers into a mold required for impregnation; the weaving is three-dimensional weaving, and the volume content of the fibers in the fiber preform is 35-50%;

[0012] (2) Immersing the prepared polysilazane precursor mixture into the mold in step (1) by vacuum suction, ensuring that the liquid level is above the surface of the fiber preform;

[0013] The precursor mixture is composed of the following components in percentage by weight: 60-90 wt% of polysilazane; 10-40 wt% of powder; the powder is a mixture of silicon nitride powder and yttrium oxide powder, wherein the amount of yttrium oxide powder is 4-6 wt% of the total mass of the powder; the particle size of the silicon nitride powder is 100-500 nm, and the particle size of the yttrium oxide powder is 50-200 nm;

[0014] (3) The mold in step (2) is then placed in a hot pressing sintering furnace, the temperature is raised to 180-200°C, and the temperature is kept under a nitrogen atmosphere for 2-4 hours to ensure that the polysilazane in the precursor mixture is completely cured;

[0015] (4) Then, pressurize the mold in the hot pressing sintering furnace in step (3) with an initial pressure of 0.5 MPa to ensure that the pressure head in the furnace is in contact with the sample. After 2 hours, continue to heat it to 600-700 °C and keep it at this temperature for 2-4 hours.

[0016] (5) The hot pressing sintering furnace in step (4) is then pressurized to ensure that the pressure applied to the mold reaches 30-60 MPa;

[0017] (6) The hot pressing sintering furnace in step (5) is then heated to 1200-1400°C after 2-3 hours, kept at this temperature for 2-6 hours, and the pressure is maintained. After the end of the heat preservation, the temperature is lowered to 1000°C and the pressure is released, and the pressure is released to normal pressure within 10 minutes;

[0018] (7) The hot pressing sintering furnace in step (6) is then cooled to below 100°C, the furnace is opened and samples are taken to obtain silicon nitride fiber reinforced silicon nitride composite materials, thus completing the entire composite process.

[0019] On the other hand, the present invention also provides a ceramic fiber reinforced ceramic matrix composite material prepared by the above method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention proposes a new densification molding composite process for silicon nitride fiber reinforced silicon nitride composite materials. By innovatively combining the precursor impregnation and curing process with the high-temperature pressure sintering process, selecting an optimized matrix, and regulating the process parameters of different composite stages, the problem of uneven matrix distribution formed by the cracking of polysilazane in the existing process is maximized, the internal defects of the material are reduced, the density of the composite material is increased to about 70%, and the degree of damage to the fiber is reduced by reducing the number of composites, so that the fiber can exert a better reinforcement and toughening effect, effectively improving the tensile and bending mechanical properties of the composite material, and ultimately obtaining a high-performance silicon nitride fiber reinforced silicon nitride composite material.

[0022] On the basis of reducing the number of composite times, the present invention further improves the density of the composite material and the uniform distribution of the matrix by combining the precursor impregnation and curing process with the high-temperature pressure sintering process, thereby obtaining a high-performance silicon nitride fiber reinforced silicon nitride high-temperature resistant and wave-transparent composite material.

[0023] This method combines a silicon nitride fiber preform impregnated with a polysilazane precursor mixture into a high-temperature hot-pressing sintering furnace for curing and pyrolysis, allowing the fiber reinforcement and matrix to be combined in a single hot-pressing sintering process. Compared to the traditional PIP process, this avoids repeated precursor impregnation and reduces damage to the silicon nitride fibers from multiple rounds of high-temperature pyrolysis. This significantly shortens the production cycle and reduces production costs, making it more suitable for industrial production.

[0024] The impregnant used in the present invention is a composite impregnation phase formed by mixing a polysilazane precursor, a silicon nitride powder matrix, and an yttrium oxide sintering aid. Compared with the low yield of single polysilazane ceramics, there will be a large amount of mass loss during the cracking and compounding process, which will produce a large number of pore defects after a single compounding. Adding silicon nitride powder to the impregnant can greatly improve the impregnation efficiency and impregnation weight gain, reduce the pore content generated during the cracking of the precursor, and effectively improve the final density of the composite material. Compared with the single polysilazane precursor impregnation compounding, the impregnation efficiency is increased by more than 50% by impregnation with a mixture of polysilazane and silicon nitride powder, and the final density of the material is increased by 20~50%. In the presence of yttrium oxide sintering aid, the sintering temperature of the silicon nitride powder can be significantly reduced, thereby obtaining a sintered and dense silicon nitride matrix at a relatively low temperature in the range of 1200~1400℃ while ensuring that the silicon nitride fiber is not damaged.

[0025] The sintering process proposed in the present invention is an innovatively designed process. Compared with the traditional hot-pressing sintering process, the process steps proposed in the present invention are significantly innovative. By first curing the precursor at 180-200°C in a hot-pressing sintering furnace, and then directly raising the temperature to 600-700°C in the furnace, at this temperature, the polysilazane precursor solidified material will begin to crack and form a powdered silicon nitride matrix. At this time, a pressurization operation is performed. Since the fiber preform is a monolithic structure, it can still maintain its integrity under high pressure. The powdered matrix formed by the initial cracking will have a certain fluidity under high pressure, so that the powdered matrix will diffuse evenly and fully into the complete silicon nitride fiber preform, reducing the number and size of pore defects in the composite material, and maximizing the solution to the problem of uneven matrix distribution formed by the cracking of polysilazane in the existing PIP process. When the temperature is further raised to 1200-1400°C, under pressure, the cured polysilazane product continuously decomposes into powder and flows evenly into the interior of the preform. Under the action of high temperature, high pressure, and the yttrium oxide sintering aid, the silicon nitride powder undergoes liquid-phase sintering, promoting the densification and sintering of the silicon nitride, thus completing the composite process. Furthermore, the sintering temperature is below 1400°C, which does not affect the state and performance of the silicon nitride fibers themselves. Ultimately, the novel preparation process proposed in this invention effectively improves the internal uniformity and density of the composite material, significantly enhancing its overall properties, including mechanical properties and heat resistance, ultimately achieving the successful preparation of a high-performance silicon nitride fiber-reinforced silicon nitride high-temperature resistant and wave-transparent composite material. This process is an innovative design based on this type of material to address the technical challenges of low density, poor internal uniformity, and low strength of composite materials used in the PIP process.

[0026] The new composite method for preparing composite materials, described in this invention, features a relatively simple process, easy operation, and minimal equipment requirements. This invention significantly enhances the feasibility of industrialized preparation of silicon nitride fiber-reinforced silicon nitride composites, effectively improving the composite's overall properties, including density, mechanical properties, and thermal performance. This advances the subsequent development of silicon nitride fiber-reinforced silicon nitride composites and high-temperature-resistant, wave-transparent materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a CT detection image after the flat plate component is reassembled in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0029] In the present invention, the materials used are all commercially available unless otherwise specified.

[0030] The present invention provides a molding method for improving the density of ceramic fiber reinforced ceramic matrix composite materials, and specific embodiments are as follows.

[0031] Example 1

[0032] A molding method for improving the density of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0033] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0034] (2) Weighing 900 g of polysilazane, 95 g of silicon nitride powder, and 5 g of yttrium oxide powder, and thoroughly mixing them by ball milling, to prepare an impregnation mixture of polysilazane precursor (90 wt%), silicon nitride powder, and yttrium oxide powder; then, vacuum-suctioning the prepared mixed impregnation mixture into the mold containing the fiber preform in step (1), ensuring that the liquid level is above the upper surface of the fiber preform;

[0035] (3) The mold containing the silicon nitride fiber preform impregnated with the precursor mixture obtained in step (2) is then placed in a hot pressing sintering furnace, the temperature is raised to 180° C., and the heat is maintained for 4 hours under a nitrogen atmosphere to ensure that the polysilazane in the precursor mixture is completely cured;

[0036] (4) Then, the mold in the hot pressing sintering furnace in step (3) was pressurized with an initial pressure of 0.5 MPa to ensure that the pressing head was in contact with the sample. After 2 hours, the temperature was raised to 600 °C and kept at this temperature for 3 hours.

[0037] (5) The mold in the hot pressing sintering furnace in step (4) is then pressurized to 30 MPa;

[0038] (6) The hot pressing sintering furnace in step (5) was then heated to 1400°C in 2 hours, kept at this temperature for 5 hours, and maintained at a pressure of 30 MPa. The temperature was then lowered to 1000°C and the pressure was released to atmospheric pressure within 10 minutes.

[0039] (7) The hot pressing sintering furnace in step (6) was then cooled to 80°C and the furnace was opened for sampling.

[0040] Example 2

[0041] A molding method for improving the density of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0042] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0043] (2) Weighing 700 g of polysilazane, 285 g of silicon nitride powder, and 15 g of yttrium oxide powder, and thoroughly mixing them by ball milling, to prepare an impregnation mixture of polysilazane precursor (70 wt%), silicon nitride powder, and yttrium oxide powder; then, vacuum-suctioning the prepared mixed impregnation mixture into the mold containing the fiber preform in step (1), ensuring that the liquid level is above the upper surface of the fiber preform;

[0044] (3) The mold containing the silicon nitride fiber preform impregnated with the precursor mixture obtained in step (2) is then placed in a hot pressing sintering furnace, the temperature is raised to 200° C., and the heat is maintained for 3 hours under a nitrogen atmosphere to ensure that the polysilazane in the precursor mixture is completely cured;

[0045] (4) Then, the mold in the hot pressing sintering furnace in step (3) was pressurized with an initial pressure of 0.5 MPa to ensure that the pressing head was in contact with the sample. After 2 hours, the temperature was raised to 700 °C and kept at this temperature for 4 hours.

[0046] (5) The mold in the hot pressing sintering furnace in step (4) is then pressurized to 60 MPa;

[0047] (6) The hot pressing sintering furnace in step (5) was then heated to 1300°C in 2 hours, kept at this temperature for 6 hours, and maintained at a pressure of 60 MPa. The temperature was then lowered to 1000°C and the pressure was released to atmospheric pressure within 10 minutes.

[0048] (7) The hot pressing sintering furnace in step (6) was then cooled to 90°C and the furnace was opened for sampling.

[0049] Example 3

[0050] A molding method for improving the density of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0051] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0052] (2) Weighing 800 g of polysilazane, 190 g of silicon nitride powder, and 10 g of yttrium oxide powder, and thoroughly mixing them by ball milling, to prepare an impregnation mixture of polysilazane precursor (80 wt%), silicon nitride powder, and yttrium oxide powder; then, vacuum-suctioning the prepared mixed impregnation mixture into the mold containing the fiber preform in step (1), ensuring that the liquid level is above the upper surface of the fiber preform;

[0053] (3) The mold containing the silicon nitride fiber preform impregnated with the precursor mixture obtained in step (2) is then placed in a hot pressing sintering furnace, the temperature is raised to 190° C., and the heat is maintained for 2 hours under a nitrogen atmosphere to ensure that the polysilazane in the precursor mixture is completely cured;

[0054] (4) Then, the mold in the hot pressing sintering furnace in step (3) was pressurized with an initial pressure of 0.5 MPa to ensure that the pressing head was in contact with the sample. After 2 hours, the temperature was further increased to 650°C and kept at this temperature for 2 hours.

[0055] (5) The mold in the hot pressing sintering furnace in step (4) is then pressurized to 50 MPa;

[0056] (6) The hot pressing sintering furnace in step (5) was then heated to 1200°C in 2 hours, kept at this temperature for 4 hours, and maintained at a pressure of 50 MPa. The temperature was then lowered to 1000°C and the pressure was released to atmospheric pressure within 10 minutes.

[0057] (7) The hot pressing sintering furnace in step (6) was then cooled to 80°C and the furnace was opened for sampling.

[0058] In order to further illustrate the beneficial effects of the present invention, the following comparative examples are constructed.

[0059] Comparative Example 1

[0060] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0061] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0062] (2) The polysilazane precursor is impregnated into the fiber preform by vacuum inhalation impregnation method, and the mold containing the fiber preform fully impregnated with polysilazane is heated to 180°C and kept warm for 4 hours under nitrogen atmosphere to ensure that the precursor is completely cured;

[0063] (3) The fiber preform with the polysilazane cured product in step (2) is then taken out and placed in a high-temperature cracking furnace, treated at 1400°C in an ammonia atmosphere for 5 hours, and then taken out after cooling. At this time, a complete polysilazane impregnation-curing-cracking process is completed;

[0064] (4) Steps (2) and (3) were then repeated. After the fourth compounding process was completed, the compounding weight gain was 3.7 wt%, and the compounding was completed.

[0065] The raw materials and cracking process temperature parameters for preparing the silicon nitride fiber reinforced silicon nitride composite material used in Comparative Example 1 are similar to those in Example 1. However, Comparative Example 1 adopts a traditional PIP composite process, and the impregnant is a single polysilazane precursor. The number of composites is increased by 3 times compared with Example 1.

[0066] Comparative Example 2

[0067] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0068] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0069] (2) The polysilazane precursor is impregnated into the fiber preform by vacuum inhalation impregnation method, and the mold containing the fiber preform fully impregnated with polysilazane is heated to 200°C and kept warm for 3 hours under nitrogen atmosphere to ensure that the precursor is completely cured;

[0070] (3) The fiber preform with the polysilazane cured product in step (2) is then taken out and placed in a high-temperature cracking furnace, treated at 1300°C in an ammonia atmosphere for 6 hours, and then taken out after cooling. At this time, a complete polysilazane impregnation-curing-cracking process is completed;

[0071] (4) Steps (2) and (3) were then repeated. After the fifth compounding process was completed, the compounding weight gain was 1.9 wt%, and the compounding was completed.

[0072] The raw materials and cracking process temperature parameters for preparing the silicon nitride fiber reinforced silicon nitride composite material used in Comparative Example 2 are similar to those in Example 2. However, Comparative Example 2 adopts a traditional PIP composite process, and the impregnant is a single polysilazane precursor. The number of composites is increased by 4 times compared with Example 2.

[0073] Comparative Example 3

[0074] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0075] (1) Silicon nitride fibers were processed into fiber preforms with a fiber volume content of 43% by three-dimensional weaving;

[0076] (2) The polysilazane precursor is impregnated into the fiber preform by vacuum inhalation impregnation method, and the mold containing the fiber preform fully impregnated with polysilazane is heated to 190°C and kept warm for 2 hours under nitrogen atmosphere to ensure that the precursor is completely cured;

[0077] (3) The fiber preform with the polysilazane cured product in step (2) is then taken out and placed in a high-temperature cracking furnace, treated at 1200°C in an ammonia atmosphere for 4 hours, and taken out after cooling. At this time, a complete polysilazane impregnation-curing-cracking process is completed;

[0078] (4) Steps (2) and (3) were then repeated. After the fourth compounding process was completed, the compounding weight gain was 3.1 wt%, and the compounding was completed.

[0079] The raw materials and pyrolysis process temperature parameters for preparing the silicon nitride fiber reinforced silicon nitride composite material used in Comparative Example 3 are similar to those in Example 3, while Comparative Example 3 adopts the traditional PIP composite process, and the impregnant is a single polysilazane precursor, and the number of composites is increased by 3 times compared with Example 3.

[0080] Comparative Example 4

[0081] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0082] (1)-(3) are the same as in Example 1;

[0083] (4) The fiber preform with the polysilazane cured product in step (3) is then taken out and placed in a high-temperature cracking furnace. It is treated in an ammonia atmosphere at 1400°C for 5 hours and then taken out after cooling. At this time, a complete polysilazane impregnation-curing-cracking process is completed and the composite is completed.

[0084] Comparative Example 5

[0085] The precursor mixture of this comparative example includes 500 g of polysilazane, 475 g of silicon nitride powder and 25 g of yttrium oxide powder, and the other conditions are the same as those in Example 1.

[0086] Comparative Example 6

[0087] In the precursor mixture of this comparative example, silicon nitride powder was omitted, and the other conditions were the same as those in Example 1.

[0088] Comparative Example 7

[0089] In the precursor mixture of this comparative example, yttrium oxide powder was omitted, and other conditions were the same as those in Example 1.

[0090] Comparative Example 8

[0091] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0092] (1)-(3) are the same as in Example 1;

[0093] (4) The mold in the hot pressing sintering furnace in step (3) is then pressurized to 30 MPa;

[0094] (5) The hot pressing sintering furnace in step (4) was then heated to 1400°C in 2 hours, kept at this temperature for 5 hours, and maintained at a pressure of 40 MPa. The temperature was then lowered to 1000°C and the pressure was released, and the pressure was released to normal pressure within 10 minutes.

[0095] (6) The hot pressing sintering furnace in step (5) is then cooled to 80°C and the furnace is opened for sampling.

[0096] Comparative Example 9

[0097] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0098] (1)-(4) are the same as in Example 1;

[0099] (5) The hot pressing sintering furnace in step (4) is then heated to 1400°C over 2 hours, kept at this temperature for 5 hours, and then depressurized to normal pressure after the end of the heat preservation;

[0100] (6) The hot pressing sintering furnace in step (5) is then cooled to 80°C and the furnace is opened for sampling.

[0101] The inventors tested the properties of the composite materials prepared in the above examples and comparative examples according to the GJB873-2015 Test Method for Tensile Properties of Continuous Fiber-Reinforced Ceramic Matrix Composites at Room Temperature and ASTM C1341-2006 Standard Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites. The results are shown in Figure 1 and Table 1-2.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the density of the composite material prepared by the method of the present invention is increased by 13-22% compared with the conventional impregnation-cracking method, and the tensile strength and flexural strength are increased by 24.6-57.1% and 38.1-69.8%, respectively. The composite material obtained by the method of the present invention is tested by CT ( Figure 1 ), showing that the internal structure of the material is relatively uniform and dense. The composite materials obtained in Comparative Examples 1-3 have uneven internal structures and poor density compared to Examples 1-3.

[0105] This method prepares a composite by placing a silicon nitride fiber preform impregnated with a precursor mixture into a high-temperature hot-pressing sintering furnace for a curing-pyrolysis integrated sintering process. The fiber reinforcement and matrix are combined in a single sintering process. Compared to the traditional PIP process, this significantly shortens the material production cycle, reducing production costs. Furthermore, the reduced number of composites reduces damage to the fiber reinforcement. This combined effect significantly improves the composite's mechanical properties, such as tensile and flexural strength. This allows the preparation of a high-performance silicon nitride fiber-reinforced silicon nitride high-temperature-resistant and wave-transparent composite material, which is of great significance for the subsequent development of high-temperature-resistant and wave-transparent functional ceramic materials.

[0106] Table 2

[0107]

[0108] As shown in Table 2, in Comparative Example 4, only silicon nitride powder is added to improve the efficiency of single impregnation composite, but it has little effect on the density, tensile strength and flexural strength of the composite material. In Comparative Example 5, there is too much powder and the viscosity of the precursor mixture is high, resulting in a small amount of matrix immersed in the preform during the impregnation process, resulting in a poor single composite densification effect, and the viscosity is too high, resulting in a very uneven distribution of the matrix inside the preform. In Comparative Example 6, without the addition of silicon nitride powder, the composite material obtained by single composite has a low degree of densification and poor mechanical properties. In Comparative Example 7, the sintering aid is omitted, and the silicon nitride powder has a low degree of densification at low temperature, and the density is slightly lower than that of Example 1, and the flexural strength also decreases significantly. In Comparative Example 8, the prepolymer remains solid after curing and is highly brittle. Direct application of high pressure before cleaving into powder causes cracking, which can cause the fiber preform to break during cracking, leading to a sharp drop in tensile strength. However, since the internal matrix content does not change much, the density is acceptable and has certain bending strength, but the uniformity is very poor. In Comparative Example 9, the high pressure process is omitted. In this case, the pressure has little effect on the fluidity of the cleaved powder, resulting in low matrix composite efficiency and internal unevenness and low density.

[0109] In summary, the present invention combines the precursor impregnation and curing process with the high-temperature pressure sintering process, selects an optimized impregnation matrix material, and regulates the process parameters of different composite stages based on the characteristics of the matrix material. This maximizes the solution to the problem of uneven matrix distribution formed by the cracking of polysilazane in the existing process, reduces internal defects in the material, and significantly improves the unevenness and density of the composite material.

[0110] The above is a preferred embodiment of the present invention. For ordinary technicians in this technical field, making several improvements and modifications without departing from the principles of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A molding method for improving the density of ceramic fiber reinforced ceramic matrix composite materials, characterized in that: include: (1) placing a fiber preform formed by weaving silicon nitride fibers into a mold required for impregnation; (2) Add the precursor mixture into the mold in step (1), ensuring that the liquid level is above the upper surface of the fiber preform; The precursor mixture is composed of the following components in percentage by weight: 60-90 wt% of polysilazane; 10-40% of powder; the powder is a mixture of silicon nitride powder and yttrium oxide powder; wherein the amount of yttrium oxide powder is 4-6 wt% of the total mass of the powder; (3) The mold in step (2) is then placed in a hot pressing sintering furnace, and the temperature is increased to completely solidify the precursor mixture; (4) The mold in the hot pressing sintering furnace of step (3) is then pressurized to 0.5 MPa for 2 hours, and then the temperature is continuously raised to 600-700°C and kept at this temperature for 2-4 hours; (5) The hot pressing sintering furnace in step (4) is then pressurized to ensure that the pressure applied to the mold reaches 30-60 MPa; (6) The hot pressing sintering furnace in step (5) is then heated to 1200-1400°C within 2-3 hours, and the pressure is maintained for 2-6 hours. The temperature is then lowered to 1000°C and the pressure is released to atmospheric pressure within 10 minutes. (7) The hot pressing sintering furnace in step (6) is then cooled to below 100° C., the furnace is opened and samples are taken to obtain a silicon nitride fiber reinforced silicon nitride composite material.

2. The method according to claim 1, characterized in that In the step (1), the weaving is three-dimensional weaving, and the volume content of the fiber in the fiber preform is 35-50%.

3. The method according to claim 2, characterized in that The particle size of the silicon nitride powder is 100-500 nm, and the particle size of the yttrium oxide powder is 50-200 nm.

4. The method according to claim 1, wherein In the step (3), the temperature is 180-200° C. and the temperature is kept under nitrogen atmosphere for 2-4 hours.

5. A ceramic fiber reinforced ceramic matrix composite material prepared by the method according to any one of claims 1 to 4.

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