Method for reducing residual stress of carbon ceramic composite material by low-pressure-high-pressure step silicon infiltration

Abstract

The application discloses the technical field of carbon ceramic composite material preparation, and particularly discloses a method for reducing residual stress of carbon ceramic composite material through low-pressure-high-pressure stepwise silicon infiltration, which is especially suitable for industrial production of high-performance carbon ceramic brake discs. The method comprises the following steps: under the protection of an inert atmosphere, a shallow silicon deposition buffer layer is formed in the pores of a preformed porous carbon matrix at a low pressure of 1-5 kPa and a temperature of 1400-1500 DEG C, heat preservation is carried out for 1-3 hours, then the temperature is rapidly increased to a high pressure of 30-60 kPa, and silicon elements are guided to penetrate deeply, and heat preservation is carried out for 2-4 hours. The silicon deposition dynamics is controlled through stepwise pressure, so that the residual stress is reduced from more than 150 MPa in a conventional process to less than 80 MPa, the material density is simultaneously realized, the porosity is less than 5%, the shear strength is improved by about 18%, and the thermal shock cycle life is improved by more than 30%, and the synergistic optimization is realized. Moreover, the method can be implemented on a traditional silicon infiltration equipment, the cost is controllable, and the method is suitable for the production of carbon ceramic parts in high-end braking fields such as aviation and new energy vehicles.

Description

Technical Field

[0001] This invention relates to the field of carbon-ceramic composite materials technology, and specifically to a method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepwise silicon infiltration. Background Technology

[0002] Carbon fiber reinforced silicon carbide ceramic matrix composites (carbon-ceramic composites) have become core materials for high-end braking systems (such as aircraft brake discs and new energy vehicle brake discs) due to their high specific strength, excellent high-temperature stability, and friction properties. In their preparation, the silicon infiltration process is a key step in forming the silicon carbide reinforcing phase, achieving material densification through the reaction of molten silicon with the carbon matrix.

[0003] In existing technologies, conventional silicon infiltration processes employ constant-pressure, high-temperature silicon infiltration, where silicon vapor is introduced under a fixed pressure, allowing silicon to permeate into the pores of the carbon matrix and react to form silicon carbide. However, this process has a fundamental flaw: the silicon vapor deposits rapidly and unevenly within the pores, easily leading to localized stress concentrations in the silicon-infiltrated layer, with measured residual stresses often exceeding 150 MPa. This high residual stress stems from two aspects:

[0004] Firstly, there is the volume expansion during the reaction of silicon and carbon to form silicon carbide (silicon density 2.33 g / cm³). 3 Silicon carbide density 3.21 g / cm³ 3 (volume expansion of approximately 37%)

[0005] Secondly, there is a significant difference in the coefficients of thermal expansion among silicon, carbon, and silicon carbide (silicon: 2.6 × 10⁻⁶). -6 / ℃, Carbon: 1.0×10 -6 / ℃, Silicon carbide: 4.3×10 -6 / ℃), which generates superimposed thermal stress during the cooling process.

[0006] High residual stress can directly induce the initiation and propagation of microcracks within the material, leading to a shortened fatigue life and decreased thermal shock resistance of the brake disc during service, severely impacting braking reliability. To mitigate this problem, existing technologies attempt to employ subsequent heat treatment (such as annealing at 1200-1300℃) or machining (such as surface stress relief grooves), but these methods have significant limitations: heat treatment requires additional energy and may cause coarsening of silicon carbide grains, while machining can damage the surface integrity of the material and increase process costs; neither of these methods can fundamentally solve the stress concentration problem.

[0007] Further research shows that the core contradiction of the existing constant pressure process lies in the difficulty of balancing "rapid penetration" and "uniform deposition": low pressure is conducive to silicon vapor diffusion, but it is easy to cause incomplete densification due to insufficient deposition; high pressure can promote deep penetration, but it will cause "silicon blockage" due to premature closure of pore entrances, which will aggravate local stress. Summary of the Invention

[0008] To address the aforementioned technical problems, this application resolves the core contradiction of existing constant pressure processes, which lies in the difficulty of simultaneously achieving "rapid penetration" and "uniform deposition".

[0009] To achieve the above objectives, the technical solution adopted in this application is as follows: the core is to realize the gradient deposition of silicon vapor in the pores of the carbon matrix through a step-by-step pressure control of "low-pressure pre-buffering - high-pressure densification". The specific steps are as follows:

[0010] Pretreatment: The pre-formed porous carbon matrix (such as biomass-derived carbon or petroleum coke-based porous carbon) is placed in a silicon infiltration furnace, and the vacuum is drawn to below 0.1 kPa. An inert gas (such as argon) is introduced as a protective atmosphere to remove air and impurity gases from the furnace.

[0011] Low-pressure silicon infiltration stage: Under inert atmosphere protection, the furnace pressure is adjusted to 1–5 kPa (preferably 1 kPa), the temperature is raised to 1400–1500℃, silicon vapor is introduced and held at this temperature for 1–3 hours. In this stage, the diffusion rate of silicon vapor is controlled by the low-pressure environment, so that silicon elements form a low-density, loose silicon deposition buffer layer at the pore inlet and shallow region of the carbon matrix, providing a stress buffer interface for subsequent high-pressure silicon infiltration.

[0012] High-pressure silicon infiltration stage: Maintaining the above temperature, rapidly increase the furnace pressure to 30–60 kPa (preferably 50 kPa), continue to introduce silicon vapor and hold for 2–4 hours. The high-pressure environment enhances the driving force of the silicon vapor, allowing silicon elements to penetrate directionally into the depths of the carbon matrix pores under the guidance of the buffer layer formed in the low-pressure stage, achieving full filling and densification of the pores, and ultimately obtaining a carbon-ceramic composite material with low residual stress.

[0013] The method described in this invention is particularly suitable for the preparation of high-performance carbon ceramic brake discs (such as aircraft brake discs and new energy vehicle brake discs). It can adjust low-pressure / high-pressure parameters (such as pressure value and heat preservation time) according to the application scenario of the brake disc (such as load-bearing strength and service temperature) to achieve targeted optimization.

[0014] The core flaw of existing constant-pressure silicon infiltration processes lies in the contradiction caused by the "single pressure": low pressure, while facilitating silicon vapor diffusion, results in insufficient densification; high pressure, while promoting infiltration, easily leads to "silicon blockage" due to rapid closure of pore inlets, causing localized stress concentration. This invention fundamentally solves this contradiction through a stepped pressure design, the core mechanism of which is as follows:

[0015] The "stress relief" function of the low-pressure buffer layer: Under low pressure (1–5 kPa), the partial pressure of silicon vapor is low, the deposition rate is slow, and the silicon deposition layer formed in the shallow layer of carbon matrix pores has low density and high toughness. This buffer layer can be regarded as an "elastic transition zone" that can absorb the impact energy of silicon vapor during subsequent high-pressure silicon infiltration, prevent the pore inlet from being blocked due to rapid silicon accumulation, and reduce "stress concentration caused by local blockage" from the source.

[0016] The "homogenization" effect of high-pressure gradient deposition: Under high pressure (30–60 kPa), the driving force of silicon vapor is enhanced, but due to the guidance of the buffer layer, silicon elements no longer fill randomly, but instead permeate in a gradient along the pore depth direction. This ordered deposition makes the formation and volume expansion process of silicon carbide phase more uniform, reduces the interfacial stress caused by local phase transformation differences and thermal expansion mismatch, and ultimately achieves a significant reduction in residual stress.

[0017] Coordinated control of temperature and pressure: The temperature is maintained at 1400–1500℃ throughout the process (the melting and reactive temperature range of silicon) to ensure that silicon is in a vapor state and can react with carbon (Si+C→SiC); while the stepwise control of pressure precisely controls the diffusion kinetics of silicon, so that the "reaction-deposition-densification" process is carried out simultaneously, avoiding the superposition of secondary stress caused by temperature fluctuations.

[0018] The technical solution provided by this invention has the following advantages compared with the prior art:

[0019] 1. This invention constructs a unique stress relief mechanism through phased control of "low-pressure-high-pressure stepped silicon infiltration": the low-density silicon deposition buffer layer formed in the low-pressure stage can buffer the impact of silicon vapor in the subsequent high-pressure stage, preventing premature closure of the pore inlets; in the high-pressure stage, silicon elements are deposited along the pore gradient under the guidance of the buffer layer, reducing the interface stress concentration caused by abrupt volume changes and thermal expansion mismatch. Actual results show that the residual stress is reduced from over 150 MPa in conventional processes to below 80 MPa, directly inhibiting the initiation and propagation of microcracks, and solving the core problem that existing constant-pressure processes cannot simultaneously address infiltration and stress.

[0020] 2. The stepped pressure design of this invention reduces stress while ensuring sufficient silicon penetration: low pressure initially fills shallow pores, while high pressure achieves deep densification, keeping the material porosity stably below 5%. Simultaneously, the gradient-deposited silicon carbide phase is more uniformly distributed, improving interfacial bonding strength and increasing brake disc shear strength by approximately 18% and thermal shock cycle life by over 30%. Compared to the existing approach of "sacrificing performance for stress relief," this invention achieves a synergistic effect of "stress reduction" and "performance improvement," breaking through the performance bottlenecks of traditional processes.

[0021] 3. The stepped pressure control of this invention can be directly implemented on a traditional silicon infiltration furnace without the need for additional complex equipment. It can be achieved simply by adjusting the partial pressure of the inert atmosphere and the rhythm of silicon vapor introduction, reducing the adaptation cost to existing production lines by more than 40%. Compared with the cost increase (approximately 20-30%) caused by "additional heat treatment / machining" in the prior art, this invention significantly improves the economics of the process and is more conducive to industrial promotion.

[0022] 4. This invention addresses the different scenarios of aviation brake discs (requiring high stress and long life) and new energy vehicle brake discs (requiring high frequency and low cost). It achieves precise adaptation by adjusting low-pressure / high-pressure parameters (such as pressure and holding time): in the aviation field, it uses 1kPa low-pressure + 50kPa high-pressure parameters to ensure extremely low stress (80MPa) and high density; in the new energy vehicle field, it uses 1.5kPa low-pressure + 40kPa high-pressure parameters to balance efficiency and cost under slightly higher stress (85MPa), solving the problem that a single process cannot meet the needs of different braking scenarios.

[0023] 5. The essential difference between this invention and conventional constant-pressure silicon diffusion processes and subsequent stress relief methods lies in the fact that it does not rely on "post-treatment" (such as heat treatment or machining), but rather suppresses the generation of residual stress from the source through "process control"; it utilizes pressure gradients to achieve "directional deposition" of silicon, rather than disordered filling, thus balancing material densification (porosity < 5%) and stress control (residual stress ≤ 80 MPa); the process is simple and can be directly implemented on traditional silicon diffusion equipment without the need for additional complex devices, solving the problems of "process complexity and high cost" in existing technologies. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] In the description of this application, it should be noted that the use of terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships commonly used when the product is in use. These terms are used solely for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the use of terms such as "first" and "second" in the description of this application is only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] Furthermore, the use of terms such as "horizontal" and "vertical" in the description of this application does not imply that the component is required to be absolutely horizontal or suspended, but rather that it may be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but rather that it may be slightly tilted.

[0031] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0032] like Figure 1 As shown, a method for reducing residual stress in carbon-ceramic composites by low-pressure-high-pressure stepped silica infiltration includes the following steps:

[0033] Step 1: Place the preformed porous carbon matrix in a silicon diffusion furnace. Under the protection of an inert atmosphere, control the furnace pressure to 1-5 kPa and the temperature to 1400-1500℃. Hold the temperature for 1-3 hours to carry out low-pressure silicon diffusion, so that silicon vapor can form a shallow preliminary infiltration in the pores of the carbon matrix, and obtain an intermediate product with a low-density silicon deposition buffer layer.

[0034] Step 2: Under the temperature conditions of Step 1, the gas pressure inside the furnace is rapidly increased to 30-60 kPa and held for 2-4 hours to perform high-pressure silicon infiltration, so that silicon elements can deeply penetrate into the pores of the carbon matrix under the guidance of the buffer layer, completing the pore filling and obtaining a carbon-ceramic composite material with reduced residual stress.

[0035] The carbon-ceramic composite material is a silicon carbide particle-reinforced ceramic matrix composite material (for example, the existing mature silicon carbide particle-reinforced alumina (Al2O3) ceramic matrix composite material (SiC / Al2O3), silicon carbide particle-reinforced zirconium oxide (ZrO2) ceramic matrix composite material (SiC / ZrO2) or silicon carbide particle-reinforced silicon nitride (Si3N4) ceramic matrix composite material (SiC / Si3N4)).

[0036] In step 1, the inert atmosphere is argon.

[0037] In step 1, the gas pressure inside the furnace is controlled at 1 kPa.

[0038] In step 1, the heat preservation time is 2 hours.

[0039] In step 1, before performing low-pressure silicon diffusion, the silicon diffusion furnace is first evacuated to below 0.1 kPa, and then an inert gas is introduced.

[0040] In step 2, the gas pressure inside the furnace is increased to 50 kPa.

[0041] In step 2, the heat preservation time is 3 hours.

[0042] The preformed porous carbon matrix is ​​an existing porous carbon matrix used to prepare brake discs. The existing porous carbon matrix used to prepare brake discs can be biomass-derived carbon or petroleum coke-based porous carbon.

[0043] The brake disc is an aviation brake disc or a new energy vehicle brake disc.

[0044] Example 1:

[0045] Preparation of carbon-ceramic composite materials for aircraft brake discs (for high-stress control applications)

[0046] 1. Raw materials and equipment

[0047] Preformed porous carbon matrix: Petroleum coke-based porous carbon (porosity 25%, density 1.5 g / cm³) 3It is made of carbon fiber reinforced resin carbon through carbonization, and its size is φ380mm×50mm (standard size of aviation brake disc);

[0048] Silicon diffusion furnace: Traditional medium-frequency induction silicon diffusion furnace (adjustable gas pressure range 0-100kPa, temperature accuracy ±5℃);

[0049] Protective gas: High-purity argon (99.99% purity);

[0050] Silicon source: Industrial-grade polycrystalline silicon (99.5% purity, particle size 5-10mm).

[0051] 2. Stepped silicon infiltration process

[0052] Pretreatment: Place the carbon matrix in the center of the silicon diffusion furnace chamber, close the furnace door and evacuate to 0.1 kPa to remove air from the furnace; introduce argon gas to 0.5 kPa, and repeat the evacuation-purging process 3 times to ensure that there are no oxidizing gases remaining in the furnace.

[0053] Low-pressure silicon infiltration stage:

[0054] The heating rate is controlled at 10℃ / min, and the temperature is raised to 1450℃ (the melting and reactive temperature of silicon, to ensure a stable silicon vapor generation rate).

[0055] Adjust the partial pressure of argon gas to 1 kPa (preferred parameter; experiments have verified that silicon vapor diffuses smoothly under this pressure, forming a uniform buffer layer), and simultaneously turn on the silicon source heating device to allow silicon vapor to be introduced into the furnace at a rate of 0.5 g / min.

[0056] After holding at this temperature for 2 hours (determined by orthogonal experiments: within the range of 1-3 hours, 2 hours is sufficient to form an effective buffer layer while avoiding pore blockage caused by excessive deposition), silicon vapor forms a low-density silicon deposition layer (density approximately 2.0 g / cm³) in the shallow pores (depth 0.5-1 mm) of the carbon matrix. 3 ).

[0057] High-pressure silicon infiltration stage:

[0058] Maintaining a constant temperature of 1450℃, the partial pressure of argon gas is increased to 50 kPa within 5 minutes using a rapid gas replenishment device (preferred parameter, at which pressure the driving force of silicon vapor is sufficient to achieve deep penetration and avoid stress fluctuations caused by a sudden increase in pressure).

[0059] The silicon vapor injection rate is maintained at 0.5 g / min, and the temperature is maintained for 3 hours (ensuring that the area with a pore depth > 5 mm is fully filled). At this time, silicon elements are deposited along the pore gradient under the guidance of the low-pressure buffer layer and react with carbon to form silicon carbide.

[0060] Cooling stage: Turn off the silicon source, stop heating, and maintain an argon atmosphere to cool naturally to room temperature (cooling rate < 5℃ / min, to avoid secondary stress caused by sudden temperature changes).

[0061] 3. Performance test results and analysis

[0062] Residual stress: Detected by X-ray diffraction (Cu target, 2θ = 35.6°), the result was 80 MPa, which is 47% lower than that of the conventional constant pressure process (150 MPa);

[0063] Density: 2.55 g / cm³ 3 The porosity is 4.2% (<5%), which meets the densification requirements for aviation brake discs;

[0064] Mechanical properties: Shear strength 320MPa, an improvement of 18.5% compared to conventional process (270MPa);

[0065] Thermal shock performance: After 99 cycles of 800℃ to room temperature, no visible cracks were found, and the thermal shock cycle life was improved by 33% compared with the conventional process (75 cycles).

[0066] Mechanism of action: The buffer layer formed by the 1kPa low pressure effectively absorbs the silicon vapor impact of the 50kPa high pressure stage, preventing the pore inlet from closing (SEM observation shows no local silicon accumulation at the interface); gradient deposition makes the silicon carbide phase distribution uniform (EDS elemental surface scan shows that the Si element increases in a gradient along the pore depth), reducing stress concentration caused by abrupt volume changes.

[0067] Example 2:

[0068] Preparation of carbon-ceramic composite materials for brake discs in new energy vehicles (cost-performance balance scenario)

[0069] 1. Raw materials and equipment

[0070] Pre-formed porous carbon matrix: Biomass-derived carbon (prepared from coconut shells through carbonization and activation, with a porosity of 28% and a density of 1.4 g / cm³). 3 The dimensions are φ320mm×35mm (standard size for brake discs in new energy vehicles);

[0071] The equipment and silicon source are the same as in Example 1, with an emphasis on cost control (shortening the heat preservation time to reduce energy consumption).

[0072] 2. Stepped silicon infiltration process

[0073] Pretreatment: Same as in Example 1, evacuate to 0.1 kPa and then purge with argon gas for protection.

[0074] Low-pressure silicon infiltration stage:

[0075] The temperature was increased to 1420°C (slightly lower than in Example 1 to reduce energy consumption), and the partial pressure of argon was adjusted to 1.5 kPa (slightly higher than the preferred value to accelerate shallow deposition and shorten the time).

[0076] The silicon vapor is introduced at a rate of 0.6 g / min and kept at a temperature for 1.5 hours (balancing efficiency and buffer layer quality) to form a shallow silicon deposition buffer layer.

[0077] High-pressure silicon infiltration stage:

[0078] The temperature was maintained and increased to 1480°C (to compensate for the slightly lower temperature during the low-pressure stage and ensure deep reaction activity), and the argon partial pressure was increased to 40 kPa (lower than in Example 1, to reduce the pressure load on the equipment);

[0079] The silicon vapor was introduced at a rate of 0.6 g / min and kept at that temperature for 2.5 hours to achieve deep penetration.

[0080] Cooling stage: Same as in Example 1, allow to cool naturally to room temperature.

[0081] 3. Performance test results and analysis

[0082] Residual stress: 85MPa, which meets the requirements for use of brake discs in new energy vehicles (allowable stress ≤100MPa);

[0083] Density: 2.50 g / cm³ 3 Porosity 4.8%;

[0084] Shear strength: 305 MPa, an improvement of 17.3% compared to conventional process (260 MPa);

[0085] Production cost: 15% lower than Example 1 (shorter insulation time and lower high pressure value), and 20% lower than conventional process (eliminating subsequent stress treatment process).

[0086] Mechanism of action: By matching the parameters of "slightly higher low pressure + shorter time" and "slightly lower high pressure + temperature compensation", the core advantages of stepped pressure are retained while controlling costs - the buffer layer relieves stress and gradient deposition ensures densification, thus achieving a balance between cost and performance.

[0087] Comparative example (conventional constant voltage silicon infiltration process)

[0088] Using the same pre-formed porous carbon matrix and equipment as in Example 1, but employing constant pressure silicon infiltration:

[0089] Process parameters: Argon partial pressure 30 kPa (common pressure in conventional processes), temperature 1450℃, holding time 5 hours (total time same as in Example 1);

[0090] Test results: residual stress 155 MPa, porosity 5.5% (insufficient densification), shear strength 270 MPa, thermal shock cycle life 75 cycles.

[0091] Comparative analysis: Conventional constant pressure processes, due to the single pressure, cause silicon vapor to accumulate rapidly at the pore inlet, forming "silicon blockage" (SEM shows that the silicon content at the pore inlet is 3 times that inside), resulting in localized stress concentration; at the same time, the deep pores are poorly densified due to insufficient silicon penetration, ultimately resulting in overall performance inferior to the present invention.

[0092] Example 3:

[0093] Preparation of carbon-ceramic composite materials for high-speed rail brake discs (high-frequency, high-temperature braking scenarios)

[0094] 1. Characteristics of application scenarios

[0095] High-speed rail brake discs need to withstand high-frequency friction and high temperatures (instantaneous temperatures can reach 600-800℃) during braking at speeds of 350km / h. This requires materials with extremely low residual stress (to avoid thermal fatigue cracking), high density (to resist thermal shock), and excellent high-temperature stability.

[0096] 2. Raw materials and process parameters

[0097] Preformed porous carbon matrix: petroleum coke-based carbon / carbon fiber composite matrix (carbon fiber volume fraction 30%, improving high temperature creep resistance), porosity 22% (low porosity to meet high frequency braking requirements), size φ420mm×60mm.

[0098] Silicon infiltration furnace: Industrial silicon infiltration furnace with precise temperature control module (temperature fluctuation ≤ ±3℃);

[0099] Low-pressure silicon infiltration stage:

[0100] Inert atmosphere: Argon (99.999% purity, to reduce impurities affecting high-temperature performance);

[0101] Pressure: 2 kPa (slightly higher than in aviation scenarios, balancing buffer layer density and high-temperature stability);

[0102] Temperature: 1480℃ (to enhance silicon vapor activity and meet the permeation requirements of low-porosity matrices);

[0103] Insulation time: 2.5 hours (to ensure that a sufficient buffer layer is formed in the shallow layer of the low-porosity matrix);

[0104] Silicon vapor inlet rate: 0.7 g / min (to accelerate deposition to match low porosity).

[0105] High-pressure silicon infiltration stage:

[0106] Pressure: 60 kPa (maximum preferred value, enhancing the driving force for deep penetration into low-porosity matrices);

[0107] Temperature: 1500℃ (maintaining high temperature ensures complete deep reaction);

[0108] Insulation time: 3.5 hours (extended time to ensure pore filling depth > 8mm);

[0109] Silicon vapor introduction rate: 0.7 g / min.

[0110] 3. Performance test results

[0111] Residual stress: 75 MPa (X-ray diffraction method, 53% lower than the conventional process of 160 MPa);

[0112] Density: 2.60 g / cm³ 3 Porosity 3.8% (low porosity improves heat conduction efficiency);

[0113] High-temperature mechanical properties: Shear strength retention rate of 90% at 800℃ (compared to only 75% with conventional processes);

[0114] Thermal fatigue performance: After 200 cycles of 600℃→room temperature cycling test, no cracks were generated (microcracks appeared after 120 cycles in conventional process);

[0115] Friction and wear: Wear rate 0.8×10 -6 mm 3 / (N·m)(Conventional process 1.2×10 -6 mm 3 / (N·m)), wear resistance is improved by 33%.

[0116] 4. Mechanism Analysis

[0117] Low-porosity matrices require higher silicon vapor driving force (60 kPa high pressure) to achieve deep penetration, while the buffer layer formed under 2 kPa low pressure has a slightly higher density (2.1 g / cm³). 3 It is adapted to the structural stability requirements under high frequency and high temperature conditions;

[0118] The high temperature of 1480-1500℃ ensures a more complete reaction between silicon and carbon, resulting in finer silicon carbide grains (average particle size of 2μm, compared to 3.5μm in conventional processes), thus improving high-temperature creep resistance.

[0119] Gradient-deposited silicon carbide phases exhibit more uniform thermal expansion at high temperatures, avoiding stress concentration caused by localized overheating and meeting the stringent requirements of high-frequency braking in high-speed trains.

[0120] Example 4:

[0121] Preparation of carbon-ceramic composite materials for heavy-duty truck brake discs (heavy-load, low-frequency braking scenario)

[0122] 1. Characteristics of application scenarios

[0123] Braking for heavy-duty trucks (load capacity over 50 tons) requires low-frequency heavy loads as the core requirement. Materials need to have high load-bearing strength and low manufacturing cost. The requirements for residual stress are slightly more lenient (≤90MPa), but wear resistance and process economy must be emphasized.

[0124] 2. Raw materials and process parameters

[0125] Preformed porous carbon matrix: biomass-derived carbon (rice husk-based, cost reduced by 20% compared to petroleum coke-based), porosity 30% (high porosity improves silicon penetration efficiency), size φ400mm×45mm;

[0126] Silicon diffusion furnace: Economic industrial silicon diffusion furnace (pressure control accuracy ±1kPa);

[0127] Low-pressure silicon infiltration stage:

[0128] Inert atmosphere: Nitrogen (replaces argon, reducing gas costs);

[0129] Pressure: 5 kPa (maximum low pressure value, to accelerate shallow deposition and shorten time);

[0130] Temperature: 1400℃ (minimum temperature threshold, balancing energy consumption and reaction activity);

[0131] Insulation time: 1 hour (shortest insulation time, suitable for rapid filling of high porosity matrices);

[0132] Silicon vapor introduction rate: 0.8 g / min (high rate matching high porosity).

[0133] High-pressure silicon infiltration stage:

[0134] Pressure: 30 kPa (minimum high pressure value, to reduce equipment pressure load);

[0135] Temperature: 1400℃ (maintain low temperature to reduce energy consumption);

[0136] Insulation time: 2 hours (to complete the filling of the high-porosity matrix in a short time);

[0137] Silicon vapor introduction rate: 0.8 g / min.

[0138] 3. Performance test results

[0139] Residual stress: 88MPa (meets the requirement of ≤90MPa);

[0140] Density: 2.45 g / cm³ 3Porosity 4.9%;

[0141] Mechanical properties: Shear strength 290MPa (meets heavy-load braking requirements);

[0142] Wear resistance: After 100,000 simulated braking tests, the wear amount is reduced by 25% compared with conventional processes;

[0143] Production cost: 30% lower than Example 1 (biomass matrix + nitrogen protection + short heat preservation time).

[0144] 4. Mechanism Analysis

[0145] The 5kPa low pressure is matched with the high porosity matrix to quickly form a buffer layer (which can cover the pore inlet in 1 hour) to avoid silicon blockage during the high pressure stage.

[0146] The combination of 30kPa low pressure and 1400℃ low temperature significantly reduces energy consumption while ensuring basic penetration, making it suitable for the low-cost requirements of heavy-duty trucks.

[0147] Although the nitrogen atmosphere slightly reduces the purity of silicon vapor, the more open pore structure of the biomass carbon matrix offsets the effects of impurities, achieving a balance between performance and cost.

[0148] Summary of Parameters and Scenario Adaptability in Implementation Examples

[0149]

[0150]

[0151] The key innovation of this invention lies in the fact that the parameter differences in different scenarios are not randomly adjusted, but rather based on a synergistic logic of "porosity-pressure-temperature-time"—low-porosity matrices (aviation / high-speed rail) require higher pressure and longer time to ensure permeation, while high-porosity matrices (heavy-duty trucks) can shorten the time through high and low pressure values; high-temperature scenarios (high-speed rail) require increased temperature to maintain reactivity, while low-cost scenarios (heavy-duty trucks) can reduce temperature by sacrificing some performance to control costs. This precise adaptability further demonstrates the inventiveness of this invention, rather than simply listing parameters.

[0152] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration, characterized in that: Includes the following steps: Step 1: Place the pre-formed porous carbon matrix in a silicon infiltration furnace. Before low-pressure silicon infiltration, evacuate the furnace to below 0.1 kPa, then introduce inert gas. Under the protection of the inert atmosphere, control the furnace pressure to 1-5 kPa and the temperature to 1400-1500℃, and hold for 1-3 hours to perform low-pressure silicon infiltration. This allows silicon vapor to form a shallow initial infiltration within the pores of the carbon matrix, resulting in an intermediate product with a low-density silicon deposition buffer layer. Step 2: Under the temperature conditions of Step 1, increase the furnace pressure to 30-60 kPa within 5 minutes and hold for 2-4 hours to perform high-pressure silicon infiltration. This allows silicon elements to deeply penetrate into the pores of the carbon matrix under the guidance of the buffer layer, completing the pore filling and obtaining a carbon-ceramic composite material with reduced residual stress.

2. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: In step 1, the inert atmosphere is argon.

3. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: In step 1, the gas pressure inside the furnace is controlled at 1 kPa.

4. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: In step 1, the heat preservation time is 2 hours.

5. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: In step 2, the gas pressure inside the furnace is increased to 50 kPa.

6. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: In step 2, the heat preservation time is 3 hours.

7. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 1, characterized in that: The preformed porous carbon matrix is ​​an existing porous carbon matrix used to prepare brake discs.

8. The method for reducing residual stress in carbon-ceramic composite materials by low-pressure-high-pressure stepped silica infiltration according to claim 7, characterized in that: The brake disc is an aviation brake disc or a new energy vehicle brake disc.

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