A molding method for improving the density of fiber reinforced ceramic matrix composites

Abstract

The application discloses a forming method for improving the density of fiber reinforced ceramic matrix composites, 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 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 uneven degree of the composite material and the density are greatly improved, 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-boron-nitrogen fiber reinforced silicon-boron-nitrogen composite material can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material preparation, in particular to a forming method for improving the density of fiber reinforced ceramic matrix composite materials. BACKGROUND

[0002] With the development of various new aircraft towards higher Mach flying speed and long flying distance, higher demands are put forward for the high-temperature-resistant, wave-transparent, load-bearing and other properties of the wave-transparent heat-resistant components thereof, which are required to withstand greater load and aerodynamic thermal shock in a more severe working environment, with a working temperature of up to 1600℃ or above, and to meet the requirements of high wave-transparent characteristics. Ceramic materials are often the preferred choice for high-temperature-resistant wave-transparent components of aircraft in the aerospace field due to their good high-temperature resistance, heat resistance, high strength and excellent electrical properties. In wave-transparent materials, the service temperature of traditional quartz ceramic materials is low, and the long-time non-ablation temperature does not exceed 1000℃, which cannot meet the use requirements of high-Mach aircraft. The electrical properties such as dielectric constant and dielectric loss of alumina ceramic are poor, which cannot meet the use requirements of wave-transparent components in high-temperature environments. Silicon nitride ceramic has excellent high-temperature resistance and electrical properties, but the inherent brittleness and other shortcomings of ceramic materials limit its reliability.

[0003] Further research has found that ceramic fiber reinforced ceramic matrix composite materials have greatly improved material reliability due to the reinforcing and toughening effect of fibers, and stand out in the selection of high-temperature-resistant wave-transparent components. Among them, silicon boron nitride fiber reinforced silicon boron nitride composite material has become an ideal high-speed aircraft high-temperature-resistant wave-transparent ceramic material due to its excellent dielectric properties, excellent high-temperature resistance and high mechanical reliability.

[0004] Silicon boron nitride fiber reinforced silicon boron nitride composite material mainly refers to ceramic composite material with silicon boron nitride fiber as reinforcing fiber and silicon boron nitride as matrix. Further research on silicon boron nitride fiber has found that silicon boron nitride fiber has the advantages of Si3N4 and BN materials, with excellent properties such as oxidation resistance, high-temperature strength and modulus retention rate, high-temperature wave-transparent and ablation resistance. In addition, due to the addition of boron element, the temperature resistance of silicon boron nitride material is improved, so that its service temperature in inert atmosphere can reach 1600℃ or above compared with silicon nitride fiber, and the corresponding composite material has good high-temperature mechanical properties, stable electrical properties and ablation resistance. Therefore, silicon boron nitride composite material prepared by silicon boron nitride matrix composite has good high-temperature resistance, stable electrical properties and ablation resistance, and is an ideal material for high-temperature-resistant wave-transparent components of future aircraft.

[0005] At present, due to the novelty of the material, there are few reports on silicon boron nitride fiber reinforced silicon boron nitride composite materials. Investigation found that this kind of material is mainly prepared by precursor impregnation and pyrolysis (PIP for short) process. The process is to weave silicon boron nitride fibers into a fiber preform, then fully impregnate the preform in polysilazane organic precursor, and then cross-link and cure the preform impregnated with the precursor at a certain temperature. Then put the preform with the cured precursor into a high temperature sintering furnace for high temperature pyrolysis reaction treatment. Through the pyrolysis reaction of the organic precursor, the ceramic matrix is converted into the ceramic matrix, and then the preform is densified. Through the repeated impregnation, curing and pyrolysis steps of the ceramic precursor, silicon boron nitride fiber reinforced silicon boron nitride composite material is finally prepared. For example, CN112010654A, CN104261850A, CN115636681A and the like.

[0006] The silicon boron nitride precursor (i.e. polysilazane) used in the PIP process generally has high viscosity and poor flowability, which leads to uneven distribution of the cured precursor inside the fiber preform after the precursor is impregnated into the preform. More importantly, the ceramic yield of the cured precursor is not high (generally less than 60%), and small molecule gases are released during the pyrolysis process, which further reduces the density of the composite material, resulting in poor improvement of the overall density of the composite material in a single process. Due to the limitations of the process and the precursor, this type of composite material can only be prepared by multiple impregnation and curing processes of the composite precursor. However, even so, the improvement of the density and the uniformity of the matrix inside the composite material is still limited, and the porosity of the final product can still be as high as more than 50%. Multiple pyrolysis and composite processes also reduce the strength of the fiber preform. In this case, the mechanical properties, heat resistance and dielectric properties of the composite material are greatly reduced, so that the ideal high-temperature resistant wave-transparent composite material cannot be obtained.

[0007] In view of the technical problems of the PIP process for preparing silicon boron nitride fiber reinforced silicon boron nitride composite material, such as the fiber damage caused by multiple high temperature pyrolysis processes, the low ceramic yield of polysilazane, the poor uniformity of the matrix after pyrolysis, and the low density and poor performance of the composite material, the composite process of the silicon boron nitride fiber reinforced silicon boron nitride composite material needs to be innovatively designed. SUMMARY

[0008] To solve the technical problems in the prior art, the present application provides a molding method for improving the density of fiber reinforced ceramic matrix composite material. The present application combines the precursor impregnation and curing process with high temperature pressure sintering process, and selects an optimally designed matrix, which maximizes the problem of uneven distribution of the matrix formed by the pyrolysis of polysilazane in the existing process, reduces the internal defects of the material, and improves the density of the composite material to about 70%.

[0009] To solve the above technical problems, the present application provides technical solutions as follows:

[0010] In one aspect, the present application provides a forming method for improving the density of fiber reinforced ceramic matrix composites, comprising:

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

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

[0013] The precursor mixture is prepared by uniformly dispersing powder in polysilazane precursor, and the precursor mixture is composed of the following mass percentage components: polysilazane 70-90wt%; powder 10-30%;

[0014] The powder is a mixture of silicon nitride powder, boron nitride powder and yttrium oxide powder, the mass ratio of silicon nitride powder and boron nitride powder is 1-2.2:1, and the mass of yttrium oxide powder is 10wt% of the total content of the powder; the particle size of the silicon nitride powder is 100-500nm, the particle size of the boron nitride powder is 0.8-2μm; the particle size of the yttrium oxide powder is 50-200nm;

[0015] (3) Then put the mold containing the silicon boron nitride fiber preform impregnated with the precursor mixture obtained in step (2) into a hot-pressing sintering furnace, raise the temperature to 220-260℃, and keep the temperature for 6-8h under nitrogen atmosphere, to ensure that the polysilazane in the precursor mixture is completely cured;

[0016] (4) Then pressurize the mold in the hot-pressing sintering furnace in step (3), give an initial pressure of 0.5MPa, ensure that the pressure head in the furnace contacts the sample, continue to raise the temperature to 700-800℃ after 2 hours, and keep the temperature for 4-6h;

[0017] (5) Then raise the pressure of the hot-pressing sintering furnace in step (4), to ensure that the pressure applied to the mold reaches 40-60MPa;

[0018] (6) Then raise the temperature of the hot-pressing sintering furnace in step (5), raise the temperature to 1300-1500℃ after 2-3 hours, keep the temperature for 6-8 hours and maintain the pressure, and after the temperature keeping is completed, lower the temperature to 1000℃ and start pressure relief, and the pressure is relieved to normal pressure within 10 minutes;

[0019] (7) Then lower the temperature of the hot-pressing sintering furnace in step (6) to below 100℃, open the furnace and take out the sample, to obtain a silicon boron nitride fiber reinforced silicon boron nitride composite material, and complete the entire composite process.

[0020] In another aspect, the present application also provides a ceramic fiber reinforced ceramic matrix composite prepared by the above method.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The present application proposes a new composite process for densification of silicon-boron-nitrogen fiber reinforced silicon-boron-nitrogen composite material, which combines the precursor impregnation and curing process with high-temperature pressure sintering process by innovative selection, and selects an optimized matrix to control the process parameters in different composite stages, thereby maximizing the problem of uneven distribution of the matrix formed by the cracking of polysilazane in the existing process, reducing the internal defects of the material, and improving the density of the composite material to about 70%, and reducing the number of compounding to reduce the damage to the fiber, so that the fiber can play a better reinforcing and toughening effect, effectively improve the mechanical properties such as tensile and bending of the composite material, and finally obtain high-performance silicon-boron-nitrogen fiber reinforced silicon-boron-nitrogen composite material.

[0023] On the basis of reducing the number of compounding, the present application further improves the density of the composite material and the uniform distribution degree of the matrix, thereby obtaining high-performance silicon-boron-nitrogen fiber reinforced silicon-boron-nitrogen high-temperature wave-transparent composite material.

[0024] In the present application, the silicon-boron-nitrogen fiber preform impregnated with the polysilazane precursor mixture is placed in a high-temperature hot-pressing sintering furnace for integrated sintering and compounding, and the fiber reinforcement and the matrix can complete material compounding through one hot-pressing sintering process, compared with the traditional PIP process, the repeated impregnation process of the precursor is avoided, the damage of polysilazane fiber caused by multiple high-temperature cracking is reduced, the production cycle is greatly shortened, the production cost is greatly reduced, and the industrial production is more beneficial.

[0025] In the present application, the impregnant is a composite impregnated phase formed by mixing polysilazane precursor, silicon nitride powder, boron nitride powder matrix and yttria sintering aid. The single polysilazane ceramic has a low yield, and a large amount of mass loss will occur in the cracking and compounding process, thereby a large amount of pore defects will be generated after single compounding. The addition of silicon nitride powder and boron nitride powder in the impregnant can greatly improve the impregnation efficiency and impregnation weight gain, reduce the pore content generated in the cracking of the precursor, and effectively improve the final density of the composite material. Compared with the single polysilazane precursor impregnation, the use of polysilazane and silicon nitride powder and boron nitride powder mixture for impregnation improves the impregnation efficiency by more than 40%, and the final density of the material is improved by 30-50%. In the presence of yttria sintering aid, the sintering temperature of silicon nitride and boron nitride powder can be obviously reduced, so that at a lower temperature in the range of 1300-1500 DEG C, the silicon-boron-nitrogen fiber is not damaged, and a sintered and dense silicon-boron-nitrogen matrix is obtained.

[0026] The sintering process of the present application is an innovative process, and compared with the traditional hot-pressing sintering process, the process steps of the present application have obvious innovation. In the hot-pressing sintering furnace, first, the precursor is solidified and formed at 220-260℃, then the temperature in the furnace is directly raised to 700-800℃, at this temperature, the polyborosilazane precursor solidification will begin to crack and form a powder-like silicon boron nitride matrix, at this time, the pressure operation is carried out, the fiber preform is still able to ensure its integrity under high pressure due to its overall structure, while the powder matrix formed by the initial cracking will have a certain fluidity under high pressure, so that the powder matrix will uniformly diffuse into the complete silicon boron nitride fiber preform, reducing the number and size of internal pore defects of the composite material, and maximizing the problem of uneven distribution of the matrix formed by the cracking of polyborosilazane in the existing PIP process. Continue to raise the temperature to 1300-1500℃, at this time, under the action of pressure, the product of the borosilazane solidification continues to crack into powder and uniformly flows into the preform, and under the action of high temperature and high pressure, silicon nitride powder and boron nitride powder will form a silicon boron nitride composite ceramic, and due to the presence of yttria sintering aid, the densification sintering of the silicon boron nitride composite ceramic will be further promoted to complete the composite densification process, and the sintering temperature is lower than 1500℃, which will not affect the state and performance of the silicon boron nitride fiber, finally, under the promotion of the preparation new process of the present application, the internal uniformity and density of the composite material are effectively improved, the comprehensive performance such as the mechanical properties and heat resistance of the composite material is greatly improved, and finally the smooth preparation of high-performance silicon boron nitride fiber reinforced silicon boron nitride high-temperature wave-transparent composite material is realized. This process is an innovative design for the technical problems of low density, poor internal uniformity and low strength of the composite material in the PIP process.

[0027] Meanwhile, the present application relates to a new composite method in the preparation process of the composite material, the process is relatively simple, easy to operate and master, and has no harsh requirements for the equipment. The present application greatly improves the feasibility of the industrial preparation of the silicon boron nitride fiber reinforced silicon boron nitride composite material, effectively improves the density, force, heat and other comprehensive performance of the composite material, and has a promoting significance for the follow-up development of the silicon boron nitride fiber reinforced silicon boron nitride composite material and high-temperature wave-transparent material. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a CT detection image of the flat plate member composite completed by the present application embodiment 1. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail in combination with the drawings and specific embodiments.

[0030] In the present application, the materials used are commercially available if not otherwise specified.

[0031] The application provides a forming method for improving the density of a fiber-reinforced ceramic matrix composite material, and the specific implementation is as follows.

[0032] Example 1

[0033] A forming method for improving the density of a fiber-reinforced ceramic matrix composite material, comprising:

[0034] (1) processing silicon-boron-nitrogen fibers into a fiber preform with a fiber volume content of 41% by means of three-dimensional weaving;

[0035] (2) weighing 700g of polysilazane, 180g of silicon nitride powder, 90g of boron nitride powder and 30g of yttrium oxide powder, and mixing them by ball milling to prepare an impregnation mixture of polysilazane (70wt%), silicon nitride powder, boron nitride powder and yttrium oxide powder; then, the prepared mixed impregnation is sucked into the mold containing the fiber preform in step (1) by vacuum suction, so as to ensure that the liquid surface is higher than the upper surface of the fiber preform;

[0036] (3) then, the mold containing the silicon-boron-nitrogen fiber preform impregnated with the mixed precursor in step (2) is placed into a hot-pressing sintering furnace, the temperature is raised to 220℃, and the temperature is kept for 6h under a nitrogen atmosphere, so as to ensure that the polysilazane in the mixed precursor is completely solidified;

[0037] (4) then, the mold in the hot-pressing sintering furnace in step (3) is subjected to a pressing operation, an initial pressure of 0.5MPa is given, the pressure head is kept in contact with the sample for 2h, and then the temperature is continuously raised to 700℃, and the temperature is kept for 4h;

[0038] (5) then, the mold in the hot-pressing sintering furnace in step (4) is subjected to a pressing operation, and the pressure is raised to 40MPa;

[0039] (6) then, the hot-pressing sintering furnace in step (5) is subjected to a temperature raising operation, the temperature is raised to 1300℃ in 2h, the temperature is kept for 6h, and the pressure is kept at 40MPa, then the temperature is lowered to 1000℃, and the pressure is released to normal pressure in 10min;

[0040] (7) then, the hot-pressing sintering furnace in step (6) is cooled to 80℃, and the sample is taken out.

[0041] Example 2

[0042] A forming method for improving the density of a fiber-reinforced ceramic matrix composite material, comprising:

[0043] (1) processing silicon-boron-nitrogen fibers into a fiber preform with a fiber volume content of 41% by means of three-dimensional weaving;

[0044] (2) Weigh 800g of polysilazane, 90g of silicon nitride powder, 90g of boron nitride powder and 20g of yttrium oxide powder, and mix them thoroughly by ball milling to prepare an impregnation mixture of polysilazane (80wt%), silicon nitride powder, boron nitride powder and yttrium oxide powder; then the prepared mixed impregnation is introduced into the mold containing the fiber preform in step (1) by vacuum suction to ensure that the liquid level is above the upper surface of the fiber preform;

[0045] (3) Then, the mold containing the silicon-boron-nitrogen fiber preform impregnated with the precursor mixture obtained in step (2) is placed in a hot-pressing sintering furnace, the temperature is raised to 260℃, and the furnace is kept at this temperature for 8h under a nitrogen atmosphere to ensure that the polysilazane in the precursor mixture is completely cured;

[0046] (4) Then, the mold in the hot-pressing sintering furnace in step (3) is subjected to a pressing operation, an initial pressure of 0.5MPa is applied, the pressure head is brought into contact with the sample, and the temperature is kept at 800℃ for 6h;

[0047] (5) Then, the mold in the hot-pressing sintering furnace in step (4) is subjected to a pressing operation, and the pressure is raised to 60MPa;

[0048] (6) Then, the hot-pressing sintering furnace in step (5) is subjected to a temperature raising operation, the temperature is raised to 1500℃ in 2h, and the furnace is kept at this temperature for 8h under a pressure of 60MPa, and then the temperature is lowered to 1000℃ to start pressure relief, and the pressure is relieved to normal pressure within 10min;

[0049] (7) Then, the hot-pressing sintering furnace in step (6) is cooled to 90℃, and the sample is taken out.

[0050] Example 3

[0051] A forming method for improving the density of fiber-reinforced ceramic matrix composites, comprising:

[0052] (1) A silicon-boron-nitrogen fiber is processed into a fiber preform with a fiber volume content of 41% by three-dimensional weaving;

[0053] (2) Weigh 800g of polysilazane, 90g of silicon nitride powder, 90g of boron nitride powder and 20g of yttrium oxide powder, and mix them thoroughly by ball milling to prepare an impregnation mixture of polysilazane (80wt%), silicon nitride powder, boron nitride powder and yttrium oxide powder; then the prepared mixed impregnation is introduced into the mold containing the fiber preform in step (1) by vacuum suction to ensure that the liquid level is above the upper surface of the fiber preform;

[0054] (3) then the mold with the silicon-boron-nitrogen fiber preform soaked with the precursor mixture obtained in step (2) is put into a hot-pressing sintering furnace, the temperature is raised to 230℃, and the temperature is kept for 7 hours under a nitrogen atmosphere, so as to ensure that the polysilazane in the precursor mixture is completely cured;

[0055] (4) then the mold in the hot-pressing sintering furnace in step (3) is subjected to a pressing operation, an initial pressure of 0.5 MPa is given, the pressure head is kept in contact with the sample for 2 hours, and then the temperature is continuously raised to 750℃, and the temperature is kept for 5 hours;

[0056] (5) then the mold in the hot-pressing sintering furnace in step (4) is subjected to a pressing operation, and the pressure is raised to 50 MPa;

[0057] (6) then the hot-pressing sintering furnace in step (5) is subjected to a temperature raising operation, the temperature is raised to 1400℃ in 2 hours, the temperature is kept for 7 hours, and the pressure is kept at 50 MPa, and then the temperature is lowered to 1000℃, and the pressure is released to normal pressure in 10 minutes;

[0058] (7) then the hot-pressing sintering furnace in step (6) is cooled to 70℃, and the sample is taken out.

[0059] Example 4

[0060] In step (2) of this example, the precursor mixture is: 700 g of polysilazane, 185.6 g of silicon nitride powder, 84.4 g of boron nitride powder, and 30 g of yttrium oxide powder, and the remaining conditions are the same as in Example 1.

[0061] In order to further illustrate the beneficial effects of the present application, the following comparative examples are constructed.

[0062] Comparative Example 1

[0063] A method for preparing a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0064] (1) a silicon-boron-nitrogen fiber is processed into a fiber preform with a fiber volume content of 41% by three-dimensional weaving;

[0065] (2) a polysilazane precursor is used to impregnate the fiber preform by vacuum suction impregnation, a mold with the fiber preform impregnated with the polysilazane is raised to a temperature of 220℃, and the temperature is kept for 6 hours under a nitrogen atmosphere, so as to ensure that the precursor is completely cured;

[0066] (3) then the fiber preform with the cured polysilazane in step (2) is taken out and put into a high-temperature pyrolysis furnace, and is treated at 1300℃ under an ammonia atmosphere for 6 hours, and is taken out after cooling, at this time, a complete polysilazane impregnation-curing-pyrolysis process is completed;

[0067] (4) Then continue to repeat step (2) and step (3), after completing the fifth compounding process, the composite weight gain is 3.3wt%, and the compounding is completed;

[0068] The raw materials and pyrolysis process temperature parameters used in the preparation of the ceramic fiber reinforced ceramic matrix composite material of Comparative Example 1 are similar to those of Example 1, while Comparative Example 1 adopts a traditional PIP compounding process, and the impregnant is a single polysilazane precursor, and the compounding times are increased by 4 times compared with Example 1.

[0069] Comparative Example 2

[0070] A preparation method of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0071] (1) The silicon-boron-nitrogen fibers are processed into a fiber preform with a fiber volume content of 41% by three-dimensional weaving;

[0072] (2) The polysilazane precursor is impregnated into the fiber preform by vacuum suction impregnation method, the mold containing the fiber preform fully impregnated with the polysilazane is raised to a temperature of 260°C, and is kept at 260°C for 8 hours in a nitrogen atmosphere to ensure complete curing of the precursor;

[0073] (3) Then the fiber preform with the cured polysilazane in step (2) is taken out and placed in a high-temperature pyrolysis furnace, and is treated at 1500°C in an ammonia atmosphere for 8 hours, and is taken out after cooling down, at this time, a complete polysilazane impregnation-curing-pyrolysis process is completed;

[0074] (4) Then continue to repeat step (2) and step (3), after completing the sixth compounding process, the composite weight gain is 1.6wt%, and the compounding is completed;

[0075] The raw materials and pyrolysis process temperature parameters used in the preparation of the ceramic fiber reinforced ceramic matrix composite material of Comparative Example 2 are similar to those of Example 2, while Comparative Example 2 adopts a traditional PIP compounding process, and the impregnant is a single polysilazane precursor, and the compounding times are increased by 5 times compared with Example 2.

[0076] Comparative Example 3

[0077] A preparation method of a ceramic fiber reinforced ceramic matrix composite material, comprising:

[0078] (1) The silicon-boron-nitrogen fibers are processed into a fiber preform with a fiber volume content of 41% by three-dimensional weaving;

[0079] (2) The polysilazane precursor is impregnated into the fiber preform by vacuum suction impregnation method, the mold containing the fiber preform fully impregnated with the polysilazane is raised to a temperature of 230°C, and is kept at 230°C for 7 hours in a nitrogen atmosphere to ensure complete curing of the precursor;

[0080] (3) Then the fiber preform with polyborosilazane cured product in step (2) is taken out and put into a high-temperature pyrolysis furnace, treated at 1400°C in an ammonia atmosphere for 7 hours, and taken out after cooling, at which time one complete polyborosilazane impregnation-curing-pyrolysis process is completed;

[0081] (4) Then steps (2) and (3) are continuously repeated, and after the fifth composite process is completed, the composite weight gain is 2.7 wt%, and the composite process is completed.

[0082] The raw materials and pyrolysis process temperature parameters used in Comparative Example 3 for preparing the ceramic fiber reinforced ceramic matrix composite are similar to those in Example 3, but Comparative Example 3 uses a traditional PIP composite process, and the impregnant is a single polyborosilazane precursor, and the number of composite processes is increased by 4 compared to Example 3.

[0083] Comparative Example 4

[0084] A method for preparing a ceramic fiber reinforced ceramic matrix composite, comprising:

[0085] (1)-(3) are the same as in Example 1.

[0086] (4) Then the fiber preform with polyborosilazane cured product in step (3) is taken out and put into a high-temperature pyrolysis furnace, treated at 1300°C in an ammonia atmosphere for 6 hours, and taken out after cooling, at which time one complete polyborosilazane impregnation-curing-pyrolysis process is completed, and the composite process is completed.

[0087] Comparative Example 5

[0088] In the precursor mixture of this comparative example, 600 g of polyborosilazane, 240 g of silicon nitride powder, 120 g of boron nitride powder, and 40 g of yttrium oxide powder are used, and the remaining conditions are the same as in Example 1.

[0089] Comparative Example 6

[0090] In the precursor mixture of this comparative example, the silicon nitride powder is omitted, and the remaining conditions are the same as in Example 1.

[0091] Comparative Example 7

[0092] In the precursor mixture of this comparative example, the yttrium oxide powder is omitted, and the remaining conditions are the same as in Example 1.

[0093] Comparative Example 8

[0094] In the precursor mixture of this comparative example, the silicon nitride powder is replaced with an equal amount of boron nitride powder, and the remaining conditions are the same as in Example 1.

[0095] Comparative Example 9

[0096] In the precursor mixture of the present comparative example, boron nitride powder is replaced by an equal amount of silicon nitride powder, and the rest of the conditions are the same as in Example 1.

[0097] Comparative Example 10

[0098] In step (2) of the present comparative example, the precursor mixture is: 700 g of polyborosilazane, 90 g of silicon nitride powder, 180 g of boron nitride powder, and 30 g of yttrium oxide powder, and the rest of the conditions are the same as in Example 1.

[0099] Comparative Example 11

[0100] A method for preparing a ceramic fiber-reinforced ceramic matrix composite material, comprising:

[0101] (1)-(3) are the same as in Example 1;

[0102] (4) Then, a pressurizing operation is performed on the mold in the hot-pressing sintering furnace in step (3), and the pressure is raised to 40 MPa;

[0103] (5) Then, a temperature-raising operation is performed on the hot-pressing sintering furnace in step (4), and the temperature is raised to 1300℃ in 2 hours, and the temperature is kept for 6 hours, and then the pressure is released to normal pressure after the temperature-keeping is finished;

[0104] (6) Then, the hot-pressing sintering furnace in step (5) is cooled to 80℃, and the furnace is opened to take samples.

[0105] Comparative Example 12

[0106] A method for preparing a ceramic fiber-reinforced ceramic matrix composite material, comprising:

[0107] (1)-(4) are the same as in Example 1;

[0108] (5) Then, a temperature-raising operation is performed on the hot-pressing sintering furnace in step (4), and the temperature is raised to 1300℃ in 2 hours, and the temperature is kept for 6 hours, and then the pressure is released to normal pressure after the temperature-keeping is finished;

[0109] (6) Then, the hot-pressing sintering furnace in step (5) is cooled to 80℃, and the furnace is opened to take samples.

[0110] The inventors have tested the performance of the materials prepared in the above examples and comparative examples, and the testing standards are based on GJB873-2015 Continuous Fiber Reinforced Ceramic Matrix Composites Tensile Properties Test Method, ASTM C1341-2006 Standard Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites; the results are shown in Figure 1 and Tables 1-2.

[0111] Table 1

[0112]

[0113] As shown in Table 1, the density of the composite material prepared by the method of the present application is increased by more than 10% than that prepared by the conventional impregnation-pyrolysis method, the tensile strength and the bending strength are increased by more than 35% and more than 18%, respectively, and the composite material obtained by the method of the present application is detected by CT to show that the internal structure of the material is relatively uniform and dense, while the internal structure of the composite material obtained in Comparative Examples 1-3 is not uniform and has poor compactness.

[0114] In the present application, the silicon-boron-nitrogen fiber preform impregnated with the precursor mixture is placed in a high-temperature hot-pressing sintering furnace for solidification-pyrolysis integrated sintering and composite preparation, and the fiber reinforced phase and the matrix can be combined through a one-time sintering process, which greatly shortens the material production cycle and reduces the production cost compared with the traditional PIP process, and the reduction of the number of material compounding reduces the damage to the fiber reinforced phase. Under the comprehensive action, the mechanical properties such as tensile strength and bending strength of the composite material are greatly improved, the preparation of high-performance silicon-boron-nitrogen fiber reinforced silicon-boron-nitrogen high-temperature resistant wave-transparent composite material is realized, which has important significance for the subsequent development of high-temperature resistant wave-transparent materials.

[0115] Table 2

[0116]

[0117] From Table 2, in the comparative example 4, only powder is added, which improves the single impregnation composite efficiency, but has little effect on the densification, tensile strength and bending strength of the composite material. In the comparative example 5, the powder is too much, and the viscosity of the precursor mixture is high, which leads to less matrix being immersed into the preform during the impregnation process, resulting in poor single composite densification effect, and the high viscosity leads to uneven distribution of the matrix in the preform. In the comparative example 6, without adding silicon nitride powder, the single composite obtained has low densification degree and poor mechanical properties. In the comparative example 7, the sintering aid is omitted, the powder has low densification at low temperature, and the densification degree is slightly lower than that of the example 1, and the bending strength also decreases significantly. In the comparative example 8, the silicon nitride powder is replaced by boron nitride powder, and the sintering temperature of pure boron nitride is too high, and the composite material prepared under the conditions of the comparative example 8 has low densification degree. In the comparative example 9, the boron nitride powder is replaced by silicon nitride powder, and there is no boron nitride, and the silicon nitride and boron nitride cannot form a silicon-boron-nitrogen matrix, which has little effect on the densification and room temperature performance, but the addition of boron element is lacking, and the temperature resistance of the material is affected, so the material performance is reduced in high temperature environment. In the comparative example 10, the amount of each substance in the powder is changed, resulting in excessive boron nitride, and after the formation of the silicon-boron-nitrogen matrix, the remaining boron nitride has low densification. In the comparative example 11, the prepolymer remains in a solid state after curing, which has high brittleness, and when high pressure is applied directly without cracking, the fiber preform will be pulled apart, resulting in a sharp decrease in tensile strength, but the internal matrix content changes little, so the densification is acceptable, and the bending strength is good, but the uniformity is poor. In the comparative example 12, the high pressure process is omitted, and at this time the pressure has little effect on the fluidity of the powder after cracking, resulting in low composite efficiency and low internal uniformity.

[0118] In summary, the present application combines the precursor impregnation and curing process with the high temperature pressure sintering process, and selects an optimized design of the impregnation matrix material, adjusts the process parameters in different composite stages according to the characteristics of the matrix material, and maximizes the problem of uneven distribution of the matrix formed by the cracking of polyborosilazane in the existing process, reduces the internal defects of the material, and greatly improves the uniformity and densification of the composite material.

[0119] The above describes the preferred embodiments of the present application, and those skilled in the art can make some improvements and refinements without departing from the principles of the present application, which should be considered as the protection scope of the present application.

Claims

1. A forming method for improving the density of a fiber-reinforced ceramic matrix composite material, characterized in that, The method comprises the following steps: (1) placing a fiber preform formed by weaving silicon-boron-nitrogen fibers into a mold required for impregnation; (2) adding a precursor mixture into the mold in step (1), ensuring that the liquid surface is above the upper surface of the fiber preform; the precursor mixture is composed of the following components by mass percentage: 70-90wt% of polysilazane; 10-30wt% of powder; the powder is a mixture of silicon nitride powder, boron nitride powder and yttrium oxide powder, the mass ratio of the silicon nitride powder and the boron nitride powder is 1-2.2:1, and the mass of the yttrium oxide powder accounts for 10wt% of the total content of the powder; (3) subsequently placing the mold in step (2) into a hot-pressing sintering furnace, increasing the temperature to completely solidify the precursor mixture; (4) subsequently applying pressure to the mold in the hot-pressing sintering furnace in step (3), maintaining the pressure at 0.5MPa for 2 hours, then continuously increasing the temperature to 700-800℃ and maintaining the temperature for 4-6h; (5) subsequently increasing the pressure of the hot-pressing sintering furnace in step (4) to ensure that the pressure applied to the mold reaches 40-60MPa; (6) subsequently increasing the temperature of the hot-pressing sintering furnace in step (5) to 1300-1500℃ within 2-3 hours, maintaining the pressure and the temperature for 6-8 hours, then decreasing the temperature to 1000℃ to start pressure relief, and decreasing the pressure to normal pressure within 10 minutes; (7) subsequently decreasing the temperature of the hot-pressing sintering furnace in step (6) to below 100℃, opening the furnace to take samples, and obtaining a silicon-boron-nitrogen fiber reinforced silicon-boron-nitrogen composite material.

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

3. The method of claim 2, wherein, The particle size of the silicon nitride powder is 100-500nm, the particle size of the boron nitride powder is 0.8-2μm, and the particle size of the yttrium oxide powder is 50-200nm.

4. The method of claim 1, wherein, In step (3), the temperature is 220-260℃, and the temperature is maintained in a nitrogen atmosphere for 6-8h.

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

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