Low-defect degreasing process for photocuring silicon nitride ceramic green body

Abstract

The invention relates to the technical field of advanced ceramic additive manufacturing control, in particular to a low-defect degreasing process for a light-cured silicon nitride ceramic green body, which comprises the following steps: S1, obtaining the same organic system of the light-cured silicon nitride ceramic green body to be degreased, carrying out thermal analysis, obtaining a mass loss rate TG-DSC curve, and determining the peak temperature Tp of a main decomposition peak; s2, respectively setting a thermal insulation platform, a pre-peak platform temperature T1 and a post-peak platform temperature T2 before and after the main decomposition peak; s3, the degreasing temperature range is divided into at least three stages with T1 and T2 as nodes, the heating rate is set, and degreasing is completed; according to the method, the main decomposition peak of the organic system is identified through thermal analysis, and the main decomposition peak temperature zone is converted into a controllable gas release process of pre-release before peak and emptying after peak from single high-risk concentrated gas release, so that the occurrence probability of defects such as swelling, layering and cracking is reduced, and the degreasing stability and the finished product consistency are improved.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic additive manufacturing control technology, and in particular to a low-defect degreasing process for photocurable silicon nitride ceramic green bodies. Background Technology

[0002] Silicon nitride ceramics are widely used in aerospace, weaponry, high-temperature structural components, and high-end industrial equipment due to their high strength, high hardness, high temperature resistance, corrosion resistance, and excellent overall reliability. With the increasing demand for lightweight components and functional integration, the fabrication of complex silicon nitride ceramic green bodies using photopolymer additive manufacturing (DLP / SLA, etc.) has become an important technological approach. This approach typically involves dispersing silicon nitride powder and sintering aids in a photopolymerizable resin system, followed by debinding and sintering to obtain dense ceramic products.

[0003] However, compared with traditional pressed / slurry-cast green bodies, photocured silicon nitride green bodies generally have high organic content, poor initial pore connectivity, and significant structural anisotropy. Simultaneously, complex irregular structures, ribs, thickness transitions, free boundaries, lattice / honeycomb structures, and areas with large wall thicknesses exhibit significant uneven heat and mass transfer during debinding. During the debinding stage, the organic binder softens and decomposes upon heating, generating a large amount of volatile gases and decomposition products. If the gas generation rate is too high within a specific temperature range, the exhaust channels are not fully established, or the exhaust capacity is insufficient, it can easily lead to internal pressure accumulation and local stress concentration within the green body, resulting in defects such as bulging, delamination, cracking, local collapse, and edge warping. These defects not only reduce the debinding pass rate but can also be further amplified during subsequent sintering into problems such as through cracks, pore aggregation, or excessive deformation, severely restricting the engineering fabrication of large-size complex components.

[0004] In existing technologies, to reduce the risk of degreasing defects, methods such as slowing down the heating rate, setting up a heat preservation platform, staged atmosphere switching, powder bed embedding support, and solvent extraction pre-degreasing are commonly used to slow down the gas release rate and promote product discharge. However, in practical applications, the degreasing process still faces the following shortcomings:

[0005] (1) Narrow process window and sensitive to structure: The same curve shows significant differences in defect performance under different wall thicknesses and different rib / transition geometry, resulting in insufficient reproducibility and scale-up stability;

[0006] (2) The main decomposition temperature zone is a high risk: Organic systems often experience concentrated cracking and gas release in a certain main decomposition temperature zone. If only a single heat preservation platform or a single slow heating strategy is used, cracking and delamination may still occur due to excessively high internal pressure peaks.

[0007] (3) It is difficult to balance cycle and quality: In order to pursue safety, an overly conservative long cycle and low speed degreasing is often adopted. Although it can reduce the risk to a certain extent, it is inefficient and energy-intensive. Moreover, in mass production, it may still cause defect fluctuations due to formula fluctuations, furnace loading differences and changes in exhaust conditions.

[0008] (4) Insufficient conversion of thermal analysis to process: Although thermogravimetric / differential thermal analysis can reveal the decomposition behavior characteristics of organic systems, there is still a lack of universal and parameterizable control strategies on how to effectively convert the main decomposition characteristics into more robust temperature range design so that the gas release and exhaust capabilities are matched.

[0009] Therefore, there is an urgent need for a degreasing process for photocurable silicon nitride ceramic green bodies that can control the gas release process and reduce risks in the main gas release temperature range, so as to improve degreasing stability and product consistency. Summary of the Invention

[0010] This invention proposes a low-defect degreasing process for photocurable silicon nitride ceramic green bodies. By identifying the main decomposition peak of the organic system through thermal analysis, the temperature range of the main decomposition peak is transformed from "single high-risk concentrated gas release" to a controllable gas release process of "pre-release before peak + post-emptying after peak", thereby reducing the probability of defects such as bulging, delamination and cracking, and improving the degreasing stability and product consistency.

[0011] The present invention adopts the following technical solution:

[0012] A low-defect debinding process for photocurable silicon nitride ceramic green bodies, comprising:

[0013] S1. Perform thermal analysis on the same organic system as the photocurable silicon nitride ceramic green body to be degreased, obtain the mass loss rate TG-DSC curve and determine the peak temperature Tp of the main decomposition peak;

[0014] S2. Set up insulation platforms before and after the main decomposition peak, with the platform temperature before the peak being T1 and the platform temperature after the peak being T2.

[0015] S3. Divide the degreasing temperature range into at least three stages with T1 and T2 as nodes, and set the heating rate for each stage to complete the degreasing process.

[0016] Preferably, the peak temperature Tp of the main decomposition peak in S1 is determined by the temperature corresponding to the maximum weight loss rate of the TG curve, or by a combination of the maximum TG peak and the characteristic peak of DSC.

[0017] Preferably, in S2,

[0018] T1 = Tp - ΔT1;

[0019] T2 = Tp + ΔT2;

[0020] ΔT1 and ΔT2 are positive values.

[0021] Preferably, ΔT1 and ΔT2 are between 10 and 60°C, and more preferably between 20 and 40°C.

[0022] Preferably, in S3, the stage from room temperature to T1 is as follows: the temperature is increased at a rate v1 and held at T1 for t1, which is used for the release of low molecular weight volatiles, weak bond breaking products, and the establishment of pore connectivity; the stage from T1 to T2 is as follows: the temperature is increased at a lower rate v2 through the main gas release sensitive zone and held at T2 for t2, which is used for the cracking of residual polymers and the clearing of coking / residual organic matter, and the suppression of internal pressure spikes; the stage from T2 to the final temperature Tf is as follows: the temperature is increased at a rate v3 to the final degreasing temperature Tf and held at t3, which completes deep degreasing and stable removal of residual volatiles.

[0023] Preferably, the heating rate in S3 satisfies v2≤v1 and v2≤v3, so as to reduce the amount of gas released per unit time in the main release temperature zone and weaken the internal pressure peak.

[0024] Preferably, v1 is 0.2–3℃ / min, v2 is 0.05–1℃ / min, and v3 is 0.2–3℃ / min.

[0025] Preferably, t1 is 0.5-10h, t2 is 0.5-12h, and t3 is 0.5-8h.

[0026] Preferably, in step S3, the degreasing inert atmosphere, vacuum, or a combination of inert atmosphere and vacuum are controlled, and the gas flow rate, furnace pressure, or exhaust capacity are adjusted to match the gas generation rate inside the green billet with the exhaust capacity.

[0027] Preferably, an exhaust strategy of alternating between vacuum and inert gas, pulse extraction, or flow step is implemented in the T1 to T2 stage to improve exhaust efficiency and reduce internal pressure peak.

[0028] Preferably, when the characteristic wall thickness of the green body increases or there are rib intersections and thickness transition structures, v2 is reduced and / or t1 and t2 are increased to enhance the degreasing stability of large wall thickness and complex structures.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] 1. Reduce the peak pressure in the main gas release zone: Through the dual-platform design of "pre-release before peak + post-emptying", the centralized gas release process is decentralized and peak-shaving is achieved, which significantly reduces the risk of bulging and internal cracking.

[0031] 2. Promote channel connectivity and smooth exhaust: Prioritize the establishment of exhaust channels in the pre-peak platform to improve permeability, making it easier for subsequent main cracking products to be discharged and reducing stratification and local collapse.

[0032] 3. Improve adaptability to complex structures and thick walls: To address the uneven heat / mass transfer issues in areas such as rib intersections, thickness transition zones, and free boundaries, a more stable degreasing process is achieved through the coordinated control of v2 and plateau time, reducing structural sensitivity.

[0033] 4. The process is parameterizable, reproducible, and easy to scale up: The temperature range is constructed with Tp and ΔT1 / ΔT2 as the core parameters, which reduces the dependence on experience and improves the reproducibility and engineering scale-up feasibility of different batches and equipment conditions.

[0034] 5. Balancing efficiency and safety window: Compared to the conservative approach of simply reducing the overall heating rate, this invention only targets the high-risk temperature range with "peak shaving and controlled release", which helps to shorten the overall cycle and reduce energy consumption fluctuations while ensuring safety. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a process for degreasing photocurable silicon nitride ceramics based on a dual-platform approach before and after the main decomposition peak.

[0036] Figure 2 This is a schematic diagram of the temperature range for dual-platform degreasing;

[0037] Figure 3 This is an example implementation of the TG-DSC curve;

[0038] Figure 4 This is a picture showing the results of the defatting process. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] This application addresses the problems existing in the debinding process of photocurable silicon nitride ceramic green bodies, such as high peak pressure in the main release temperature zone, delayed pore establishment, sensitivity to process due to complex structures such as thick / thin / ribbed materials, and poor defect reproducibility. This invention proposes a low-defect debinding process for photocurable silicon nitride ceramic green bodies. This process identifies the main decomposition peak of the organic system through thermal analysis and transforms the main decomposition peak temperature zone from "single high-risk concentrated gas release" to a controllable gas release process of "pre-peak pre-release + post-peak clearing", thereby reducing the probability of defects such as bulging, delamination, and cracking, and improving the debinding stability and consistency of thick-walled and complex irregularly shaped components.

[0041] Reference Figure 1-2 A low-defect debinding process for photocurable silicon nitride ceramic green bodies, comprising the following steps:

[0042] S1. Main decomposition peak identification and parameter modeling

[0043] Thermal analysis (TG-DSC) was performed on the organic system used in the photocurable silicon nitride ceramic green body to obtain the mass loss rate curve and determine the peak temperature Tp of the main decomposition peak.

[0044] S2, Dual-platform setup before and after the main decomposition peak

[0045] Two insulation platforms were set up near the main decomposition peak:

[0046] Pre-peak plateau: T1 = Tp - ΔT1;

[0047] Post-peak plateau: T2 = Tp + ΔT2;

[0048] Where ΔT1 and ΔT2 are positive values, ranging from 10 to 60℃, with a preferred range of 20 to 40℃;

[0049] S3, Segmented heating and heat preservation coordinated control

[0050] The defatting temperature range is divided into at least three stages, and the heating rate is set for each stage:

[0051] From room temperature to T1: The temperature is increased at a rate of v1 and held at T1 for the release of low-molecular-weight volatiles, weak bond breaking products, and the establishment of pore connectivity; From T1 to T2: The temperature is increased at a lower rate of v2 through the main gas release sensitive zone and held at T2 for the cracking of residual polymers and the clearing of coking / residual organic matter, suppressing internal pressure spikes; From T2 to the final temperature Tf: The temperature is increased at a rate of v3 to the final degreasing temperature Tf and held at t3 to complete deep degreasing and stabilize and remove residual volatiles.

[0052] S4, Atmosphere and Exhaust Capability Matching

[0053] The degreasing process is usually carried out under inert atmosphere and vacuum conditions, and the gas generation rate inside the billet is matched with the exhaust capacity by regulating the atmosphere flow rate, furnace pressure or exhaust strategy. Optionally, the degreasing atmosphere can be appropriately changed in the T1 to T2 stage, such as by introducing vacuum or inert gas, to improve exhaust efficiency and reduce the peak internal pressure.

[0054] In S2, the peak temperature Tp of the main decomposition peak is determined by the temperature corresponding to the maximum weight loss rate of the TG curve, or by the joint determination of the maximum TG peak and the DSC characteristic peak.

[0055] In S4, the heating rate satisfies v2≤v1 and v2≤v3, so that the gas release per unit time in the main gas release temperature zone is reduced and the internal pressure peak is weakened.

[0056] The speeds are v1 (0.2–3℃ / min), v2 (0.05–1℃ / min), and v3 (0.2–3℃ / min).

[0057] The t1 is 0.5–10 h, the t2 is 0.5–12 h, and the t3 is 0.5–8 h.

[0058] In S4, an exhaust strategy is implemented in the T1 to T2 stages, which involves alternating between vacuum and inert gas, pulse extraction, or flow stepping, to improve exhaust efficiency and reduce internal pressure peaks.

[0059] It also includes thickness / structure adaptive parameter tuning

[0060] For components with large characteristic wall thickness or high-risk structures such as rib intersections, thickness transitions, and free boundaries, strategies such as reducing v2 and extending t1 / t2 are adopted, or parameter adjustment relationships are established based on wall thickness to enhance process robustness.

[0061] This invention is not only applicable to silicon nitride powder systems, but can also be extended to debinding scenarios of photocurable ceramic green bodies containing different sintering aids, organic systems or different geometric scales without changing the basic idea of ​​"dual platforms before and after the main decomposition peak + segmented speed control + exhaust matching". It has good versatility and engineering application value.

[0062] Reference Figure 3-4 For example:

[0063] To better illustrate the process of this application, a detailed explanation is provided using a photopolymerization additive manufacturing (DLP / SLA) process to prepare a silicon nitride ceramic green body. The green body's solid phase is silicon nitride powder, and the sintering aids are alumina and yttrium oxide. These are mixed with a photopolymerizable organic system to obtain a ceramic slurry, which is then cured by exposure to form the green body. Furthermore, this green body is a thick-walled / complex structural component with thick-thin transitions and ribbed areas.

[0064] Step 1: Determination of the main decomposition peak Tp

[0065] Samples of the "powder-organic system" with the same formulation as the above-mentioned green body were subjected to TG-DSC testing. The peak temperature Tp of the main decomposition peak was determined by the maximum weight loss rate peak of DTG or the main characteristic peak of DSC. Figure 3 The TG-DSC curve indicates that Tp ≈ 410℃.

[0066] Step 2: Setting the temperature point on both platforms

[0067] Set up two plateaus before and after the main decomposition peak at ΔT1=30℃ and ΔT2=30℃:

[0068] Peak plateau temperature: T1 = Tp − 30℃ = 380℃;

[0069] Post-peak plateau temperature: T2 = Tp + 30℃ = 440℃;

[0070] Step 3: Degreasing, loading, and atmosphere setup

[0071] The green billets are placed in the sagger. Nitrogen gas is continuously introduced to degrease the furnace and a stable exhaust condition is maintained (about 2-3 L / min). The furnace is kept under normal or slightly positive pressure exhaust conditions.

[0072] Step 4: Specific degreasing procedure

[0073] Perform the operation according to the following temperature range (where 380℃ and 440℃ are the core dual platforms of this invention):

[0074] (1) Room temperature → 200℃: Increase temperature by 1.0℃ / min, and keep warm at 200℃ for 1 hour;

[0075] (2) 200℃→250℃: Increase the temperature by 0.5℃ / min and keep it at 250℃ for 2 hours. This stage is the pre-discharge stage of volatiles before entering significant weight loss.

[0076] (3) 250℃→T1(380℃): Temperature rises at 0.3℃ / min, and T1 is kept warm for t1=4h; This section is the pre-peak release stage: establishing an exhaust channel and reducing the risk of internal pressure in the subsequent peak area;

[0077] (4) T1 (380℃) → T2 (440℃): Heat up at 0.2℃ / min, keep warm at T2 for t2=6h; This segment is the main decomposition stage: the chemical bonds of the polymer main chain break, which leads to rapid cracking and gas release. The decomposition of the main peak weakens the internal pressure and the risk of delamination cracking.

[0078] (5) T2 (440℃) → 600℃: Increase temperature at 0.5℃ / min and hold at 600℃ for 2 hours; this stage is for deep degreasing to remove residual volatiles;

[0079] (6) Cool the furnace to room temperature to obtain a degreased blank.

[0080] When the characteristic wall thickness is ≥20mm or there is obvious rib intersection or thickness transition, the heating rate in step (4) should be reduced to 0.1~0.2℃ / min, or t1 and t2 should be extended by 2~4h each to further improve the degreasing robustness.

[0081] Step 5: Specific degreasing procedure

[0082] Using the aforementioned photocurable silicon nitride ceramic samples, after setting a dual-platform degreasing process based on Tp≈410℃, the degreased blanks showed intact appearance, without bulging, delamination, or through cracks; a focused inspection of free boundaries, rib intersection areas, and thickness transition zones revealed no obvious degreasing defects. Figure 4 As shown, this provides a stable, defect-free green body foundation for subsequent sintering.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-defect debinding process for photocurable silicon nitride ceramic green bodies, characterized in that: include S1. Perform thermal analysis on the same organic system as the photocurable silicon nitride ceramic green body to be degreased, obtain the mass loss rate TG-DSC curve and determine the peak temperature Tp of the main decomposition peak; S2. Set up insulation platforms before and after the main decomposition peak, with the platform temperature before the peak being T1 and the platform temperature after the peak being T2. S3. Divide the degreasing temperature range into at least three stages with T1 and T2 as nodes, and set the heating rate for each stage to complete the degreasing process.

2. The low-defect degreasing process according to claim 1, characterized in that: The peak temperature Tp of the main decomposition peak in S1 is determined by the temperature corresponding to the maximum weight loss rate of the TG curve, or by a combination of the maximum TG peak and the characteristic peak of DSC.

3. The low-defect degreasing process according to claim 1, characterized in that: In S2, T1 = Tp - ΔT1; T2 = Tp + ΔT2; ΔT1 and ΔT2 are positive values.

4. The low-defect degreasing process according to claim 1, characterized in that: In S3, From room temperature to T1 stage: The temperature is increased at a rate of v1 and held at T1 for t1, which is used for the release of low molecular weight volatilization, weak bond breaking products and the establishment of pore connectivity. T1 to T2 stage: Pass through the main gas release sensitive zone at a low heating rate v2, and hold at T2 for residual polymer cracking and clearing of coke / residual organic matter, suppressing internal pressure spikes; T2 to final temperature Tf stage: Heat to the final degreasing temperature Tf at a heating rate v3 and hold at t3 to complete deep degreasing and stabilize and remove residual volatiles.

5. The low-defect degreasing process according to claim 4, characterized in that: In S3, the heating rate satisfies v2≤v1 and v2≤v3, so that the gas release per unit time in the main release temperature zone is reduced and the internal pressure peak is weakened.

6. The low-defect degreasing process according to claim 5, characterized in that: The speeds are v1 (0.2–3℃ / min), v2 (0.05–1℃ / min), and v3 (0.2–3℃ / min).

7. The low-defect degreasing process according to claim 4, characterized in that: The t1 is 0.5–10 h, the t2 is 0.5–12 h, and the t3 is 0.5–8 h.

8. The low-defect degreasing process according to claim 4, characterized in that: In S3, the degreasing inert atmosphere, vacuum, or a combination of inert atmosphere and vacuum are controlled, and the gas flow rate, furnace pressure, or exhaust capacity are adjusted to match the gas generation rate and exhaust capacity inside the green billet.

9. The low-defect degreasing process according to claim 8, characterized in that: During the T1 to T2 phase, an exhaust strategy is implemented that alternates between vacuum and inert gas, pulsed extraction, or flow stepping to improve exhaust efficiency and reduce internal pressure peaks.

10. The low-defect degreasing process according to claim 4, characterized in that: When the characteristic wall thickness of the green body increases or there are rib intersections and thickness transition structures, v2 is reduced and / or t1 and t2 are increased to enhance the degreasing stability of large wall thickness and complex structures.

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