Staged controlled atmosphere degreasing and sintering method for copper metal parts

Abstract

The invention discloses a staged controlled atmosphere degreasing and sintering method for a copper metal part, which is realized by adopting a gradient temperature sintering strategy and comprises the following steps: selecting nano copper powder with the particle size of 450-550nm as a raw material of a green body and polyurethane acrylate resin as a low-temperature degreasing binder for 3D printing, by constructing a four-stage gradient sintering process (green body degreasing-framework pre-sintering-high-temperature densification-grain regulation), collaborative regulation of a temperature field and material transport is realized, and finally a sintered product with excellent density and geometric integrity is obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material preparation technology, specifically to a staged controlled atmosphere degreasing and sintering method for copper metal parts. Background Technology

[0002] As the manufacturing industry moves towards higher precision and intelligence, precision copper metal parts, with their excellent electrical and thermal conductivity, wear resistance, and machinability, have become core components for maintaining the normal operation of aerospace electronic devices, electronic control systems, and other equipment. These parts support and promote the miniaturization, high reliability, and high performance of modern electronic equipment, and have broad application prospects in cutting-edge fields such as high-end equipment and aerospace.

[0003] Existing sintering processes for copper metal parts mainly include: compression molding, cold isostatic pressing (CIP), powder injection molding (MIM), and binder jet 3D printing. In the field of precision micro-copper metal part manufacturing, MIM and binder jet 3D printing technologies have greater technological advantages. However, MIM technology requires high-pressure injection to inject a mixture of metal powder and binder into a mold, which presents challenges such as high equipment investment and short mold lifespan. During high-pressure injection, the fluidity of the slurry within the mold is limited by the complexity of the component. For example, parts with special structures such as deep holes, undercuts, or thin walls are prone to incomplete microstructure filling and dimensional inaccuracies due to gravity collapse during high-temperature sintering.

[0004] Binder jetting 3D printing technology prepares green bodies through layer-by-layer powder laying and selective binder jetting. Leveraging the advantages of moldless forming, this technology enables low-cost, high-precision molding of precision micro-components using 3D models processed through finite element analysis and topology optimization. It possesses significant technological advantages and industrial application potential in the mass production of irregularly shaped precision parts. However, compared to MIM (Metal Injection Molding) processes, the green bodies obtained by binder jetting 3D printing do not undergo a high-pressure densification process, resulting in a significantly lower initial density than injection-molded green bodies. This leads to a substantial increase in the difficulty of controlling the material densification behavior during subsequent sintering. Therefore, a more precise sintering process control method is urgently needed to address this technological bottleneck.

[0005] Based on the above problems, this invention proposes an integrated "degreasing-sintering" sintering process, which provides an effective technical solution for the manufacturing of precision copper metal parts. Summary of the Invention

[0006] The purpose of this invention is to provide a staged controlled atmosphere degreasing and sintering method for copper metal parts. This process is achieved by using a gradient temperature sintering strategy: that is, by constructing a four-stage gradient sintering process (green degreasing - pre-sintered skeleton - high-temperature densification - grain control), the temperature field and material transport are synergistically controlled, and finally sintered products with excellent density and geometric integrity are obtained.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a staged controlled atmosphere debinding and sintering method for copper metal parts, comprising the following steps: (1) Preparation of copper-based green body: Select nano copper powder with a particle size of 450-550nm, use polyurethane acrylate resin as low-temperature degreasing binder for 3D printing spraying, place the green body under ultraviolet light of 365-405nm for curing for 10-30min, place it on a vibration table, vibrate at a frequency of 50-100Hz for 3-5min, use dry compressed air with a pressure of 0.1-0.3MPa at a flow rate of 10-20L / min to blow away uncured copper powder, and obtain copper-based green body; (2) Degreasing of green billet: Place the copper-based green billet into a crucible and then into a tube furnace. Vacuum the furnace, introduce argon gas, and then degrease it by heating. The heating method is to raise the temperature from room temperature to 175-185℃ at a heating rate of 4-6℃ / min, and then raise it to the degreasing temperature of 450-505℃ at a heating rate of 1.0-3.5℃ / min, and hold it for 3-5 hours. (3) Pre-skeleton sintering: Heat to 800-900℃ at a heating rate of 1.0-3.5℃ / min and hold for 1.5-2.0h; (4) Densification: Heat to the sintering temperature of 970-1060℃ at a heating rate of 1.0-3.5℃ / min, while simultaneously introducing low-concentration reducing gases H2 and Ar, and hold for 2-3 hours; (5) Grain control: Cool the temperature in the furnace to 870-980℃ at a cooling rate of 2.5-5.5℃ / min, hold for 1-2.5h, and then cool to room temperature with the furnace to obtain copper-based sintered parts.

[0008] In step (1) above, the particle size of the nano copper powder is 500 nm, and the amount of polyurethane acrylate resin used is 15 to 25% of the weight of the copper-based green body.

[0009] In step (1) above, the amount of polyurethane acrylate resin used is 15% of the weight of the copper-based green body.

[0010] In the aforementioned step (2), the green blank is degreased: the copper-based green blank is placed in a crucible and then placed in a tube furnace, vacuumed, and argon gas is introduced, and then degreased by heating. The purity of the argon gas is ≥99.99%. The heating method is to raise the temperature from room temperature to 180°C at a heating rate of 5°C / min, and then raise it to the degreasing temperature of 450°C at a heating rate of 1.5~3°C / min, and hold it for 5 hours.

[0011] In the aforementioned step (3), pre-skeleton sintering: the temperature is raised to 900°C at a heating rate of 1.5 to 3°C / min and held for 2 hours to pre-sinter the green blank, forming a partial sintering neck, so that the green blank is initially densified.

[0012] In the aforementioned step (4), densification is carried out by heating to a sintering temperature of 1000°C at a heating rate of 1.5 to 3°C / min, while simultaneously introducing low-concentration reducing gases H2 and Ar, and holding for 3 hours; the volume ratio of H2 to Ar is 5:95.

[0013] In the aforementioned step (5), grain control: the temperature inside the furnace is cooled to 950°C at a cooling rate of 3-5°C / min, and held for 2 hours. The temperature gradient difference is used to gradually release the stress between the surface layer and the core to avoid sudden cooling cracking. The furnace is cooled to room temperature and taken out of the furnace at a cooling rate of 1.5-4°C / min to obtain copper-based sintered parts.

[0014] Specifically, in the aforementioned step (5), grain control: the temperature inside the furnace is rapidly cooled to 900-950°C at a rate of 3-5°C / min, and held for 1-2 hours. The temperature gradient difference is used to gradually release the stress between the surface layer and the core, avoiding sudden cooling cracking. The furnace is cooled to room temperature and removed from the furnace at a cooling rate of 2-3°C / min to obtain copper-based sintered parts.

[0015] Compared with the prior art, the present invention has the following advantages: Compared with sintered parts prepared by existing technologies, the parts prepared by this invention have a relative density >90%, a volume deformation rate <10%, significantly reduced production time, and significantly lower mass production costs. It achieves synergistic optimization of high efficiency, low energy consumption, and precision forming. Its main advantages are as follows: 1. By selecting a specific binder system, complete decomposition of the binder can be achieved during the debinding and sintering process at 450–500℃ (see...). Figure 2The TGA curves show that PUA rapidly undergoes thermal decomposition within the 450–500℃ temperature range, providing a scientific basis for selecting the degreasing temperature. In the innovative four-step gradient sintering process: firstly, degreasing and holding are performed at 450–500℃, ensuring a high-cleanliness environment for the sintered body by introducing high-purity argon gas and dynamically removing waste gas from the furnace; then, heating to the 800–900℃ range, which is the transition zone from low-temperature sintering to medium-temperature sintering, where atomic diffusion is mainly surface diffusion, can form a stable initial sintering neck structure, while also preventing copper recrystallization due to the temperature being lower than that of copper. The critical point is effectively avoided to prevent grain coarsening, and a three-dimensional skeleton support system is constructed simultaneously to prevent subsequent high-temperature collapse. Then, the temperature is raised to the range of 1000-1060℃ (the high-efficiency solid-state sintering temperature range, 92%-98% of the melting point) and the main sintering stage approaches the melting point of copper (1083℃). With the help of a low-concentration reducing atmosphere, the densification degree of the material is significantly improved. Finally, it is rapidly cooled to the range of 900-950℃ and short-term heat preservation for 1-2 hours is carried out to control the grain boundaries, induce the grain boundary slip mechanism to release residual stress, and effectively suppress abnormal grain growth caused by Ostwald ripening.

[0016] 2. This invention innovatively constructs a four-step temperature gradient: selecting the debinding temperature (450–500℃) based on the thermal decomposition characteristics of the binder; using the diffusion behavior of copper as the core (pre-sintering 800–900℃, densification 1000–1060℃); and finally achieving a closed loop of precise microstructure control (stress release and grain optimization 900–950℃). This process chain forms a complete technical closed loop from organic matter removal to metal densification and final microstructure optimization.

[0017] 3. Dynamic atmosphere control: High-purity argon is used for protection during the degreasing stage, and low-concentration reducing gas is switched during the high-temperature sintering stage to balance the discharge of binder decomposition products and the inhibition of metal surface oxidation, thus creating conditions that promote metallurgical bonding.

[0018] 4. This invention is easy to operate, the process is simple and controllable, and it can realize large-scale industrial production. The copper-based parts obtained can have a relative density of up to 95, a deformation rate of <5%, and uniform grain size, making them suitable for high thermal and electrical conductivity components in precision electronic components. Attached Figure Description

[0019] Figure 1 The heat treatment process designed for this patent; Figure 2 The thermal decomposition curve of PUA adhesive; Figure 3 The image shows the surface morphology of the sintered sample obtained in Example 1. Figure 4 The image shows the surface morphology of the sintered sample obtained in Example 2. Figure 5The surface morphology of the sintered sample obtained in Comparative Example 1 is shown in the image (a is a sintered sample with the appearance features of the Temple of Heaven building; b is a sintered sample with gear features). Figure 6 The surface morphology of the sintered sample obtained in Comparative Example 2 is shown in the figure. Figure 7 The EDS spectrum of Example 1; Figure 8 The EDS spectrum of Example 2; Figure 9 The EDS spectrum is shown in Comparative Example 1; Figure 10 The image shown is the EDS spectrum of Comparative Example 2. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention will be further described below with reference to the embodiments. The embodiments are merely further supplements and explanations of the present invention, and are not intended to limit the invention.

[0021] Example 1: 1. Preparation of copper-based green body: Nano copper powder (particle size 500nm) is selected for green body binder jet 3D printing. The green body binder is polyurethane acrylate resin. The slurry composition is 85% nano copper powder and 15% polyurethane acrylate resin. After curing under 365nm ultraviolet light for 30min, it is placed on a vibration table and vibrated at a frequency of 100Hz for 4min. Dry compressed air with a pressure of 0.1MPa is used to blow it at a flow rate of 10L / min for 5min to remove uncured copper powder, thus obtaining the copper-based green body.

[0022] 2. Degreasing of green blanks: Place the copper-based green blanks into a crucible and put them into a tube furnace. After evacuation, introduce high-purity argon gas and heat to 180°C at room temperature at 5°C / min. Then heat to the degreasing temperature of 480°C at 1.5-3°C / min and hold for 5 hours to ensure that the binder is completely removed.

[0023] 3. Pre-skeleton sintering: Heat to 900℃ at 1.5~3℃ / min and hold for 2h to form a uniform sintering neck, enhance the structural strength of the green body and avoid subsequent high-temperature deformation; 4. Densification: Continue to raise the temperature to 1000℃ at a rate of 1.5-3℃ / min and hold for 3 hours for further high-temperature densification sintering. At the same time, introduce a low-concentration reducing gas with a volume ratio of 5%H2+95%Ar until sampling is performed. This can promote metallurgical bonding between particles and increase density. 5. Grain control: The temperature is lowered to 950℃ at a rate of 3–5℃ / min, held for 2 hours to eliminate thermal stress accumulated during sintering and optimize microstructure uniformity; the grains are then cooled to room temperature in the furnace before being removed from the furnace, yielding the desired grain size. Figure 3The copper metal sintered part shown.

[0024] The sample has a density of 95%, a volume deformation rate of <5%, and uniform grain size, making it suitable for high thermal and electrical conductivity components in precision electronic devices.

[0025] Depend on Figure 3 As can be seen from the macroscopic surface morphology results of the sintered samples in Example 1, the samples can maintain the designed microstructure after sintering, and no obvious defects are observed on the surface. EDS analysis confirmed that the samples were not contaminated by impurities.

[0026] Example 2: Preparation of copper-based green body: Nano copper powder (particle size 500nm) was selected for green body binder jet 3D printing. The green body binder was polyurethane acrylate resin. The slurry composition was 80% nano copper powder and 20% polyurethane acrylate resin. After curing under 405nm ultraviolet light for 10min, it was placed on a vibration table and vibrated at a frequency of 50Hz for 4min. Dry compressed air with a pressure of 0.3MPa was used to blow it for 10min at a flow rate of 20L / min to remove uncured copper powder, thus obtaining the copper-based green body.

[0027] 2. Degreasing of green billets: Place the copper-based green billets into a crucible and put it into a tube furnace. After evacuation, introduce high-purity argon gas and heat to 480℃ at room temperature at a rate of 1.5-3℃ / min. Hold at this temperature for 4 hours to ensure low-residue degreasing.

[0028] 3. Pre-skeleton sintering: Heat to 850℃ at 1.5~3℃ / min and hold for 2h to initially form a sintering neck and stabilize the geometry of the green body; 4. Densification: Continue to heat to 1060℃ at 1.5~3℃ / min and hold for 2.5h for further high-temperature densification sintering. At the same time, introduce gas with a volume ratio of 10%H2+90%Ar until sampling. Use high temperature to promote atomic diffusion and achieve deep densification. 5. Grain control: The temperature is lowered to 920℃ at a rate of 3–5℃ / min and held for 1.5 hours to inhibit excessive grain growth and improve material toughness; the material is then cooled to room temperature in the furnace before being removed from the furnace, yielding the desired result. Figure 4 The copper metal sintered part shown.

[0029] The sample has a density of 96.2%, a volume deformation rate of <10%, and uniform grain size, making it suitable for high thermal and electrical conductivity components in mechanical transmission parts and precision electronic components that require high strength and wear resistance.

[0030] Depend on Figure 4 As can be seen from the microstructure of the sintered sample in Example 2, the sample surface structure is robust and dense, and EDS analysis further confirms the uniformity of element distribution.

[0031] To facilitate comparison of the technical advantages of this invention, two counterexamples are listed below, with specific comparative explanations.

[0032] Comparative Example 1: Preparation of copper-based green body: The same nano-copper powder (particle size 500nm) as in Example 1 was selected for green body binder jet 3D printing. The binder was polyvinyl alcohol resin (such as PVA-205), which is a water-soluble polymer with a decomposition temperature range of 200-350℃. The decomposition process involves multi-stage weight loss (hydroxyl dehydration occurs at 200-250℃, and main chain cleavage occurs at 250-350℃). The decomposition products contain a large amount of hydrocarbons. The slurry composition was consistent with that in Example 1. After curing under 365nm ultraviolet light for 30min, it was placed on a vibration table and vibrated at a frequency of 100Hz for 4min. Dry compressed air with a pressure of 0.1MPa was used to purge at a flow rate of 10L / min for 5min to remove uncured copper powder, thus obtaining the copper-based green body.

[0033] 2. Degreasing of green billets: Place the copper-based green billets in a crucible and put them into a tube furnace. After evacuation, argon gas is introduced and the temperature is raised from room temperature to 180°C at a rate of 5°C / min. Then, the temperature is raised to the degreasing temperature of 480°C at a rate of 1.5 to 3°C / min and held for 5 hours to fully degrease. 3. Pre-skeleton sintering: The temperature is raised to 800℃ at a heating rate of 1.5~3℃ / min and held for 1h to pre-sinter the green body, forming a partial sintering neck, so that the green body is initially densified. 4. Densification: The temperature is increased to 1050℃ at a heating rate of 1.5~3℃ / min and held for 2h for further high-temperature densification sintering. At the same time, a low-concentration reducing gas with a volume ratio of 5%H2+95%Ar is introduced until the sample is taken. This can prevent metal oxidation and promote densification of the green body. 5. Grain control: The furnace temperature is reduced to 900℃ at a rate of 3-5℃ / min, held for 1 hour to release thermal stress and homogenize the morphology; the grains are then cooled to room temperature in the furnace and removed from the furnace to obtain the following: Figure 5 The copper metal sintered part shown.

[0034] Depend on Figure 5 As can be seen, the surface morphology of the sintered samples in Comparative Example 1, where Figure a) and Figure b) are sintered samples with architectural features of the Temple of Heaven and gear features respectively, both have obvious defects such as black deposits and cracks on the surface. The use of different types of binders resulted in high impurity content and a density of less than 80% in the samples, as shown by EDS analysis, which led to a significant reduction in mechanical properties.

[0035] Differences from Example 1: Although the selected PVA-205 has a lower lower limit of decomposition temperature (200℃) than PUA resin, the decomposition process is "incomplete": under the condition of holding at 500℃ for 3 hours, the residual carbon chains after the main chain breaks (due to the strong hydrogen bonding between hydroxyl groups in the PVA molecular chain, it is easy to form difficult-to-decompose carbides at low temperatures) cannot be completely removed, resulting in black carbon impurities remaining in the green body. These residual carbons form a brittle phase (CuC2) with copper during subsequent high-temperature sintering, destroying the metallurgical bonding between particles, resulting in a density of only 78% (95% in Example 1).

[0036] Comparative Example 2: 1. Preparation of copper-based green body: Nano copper powder (particle size 500nm) is selected for green body binder jet 3D printing. The binder is polyurethane acrylate resin. The slurry composition is 80% metal and 20% organic. After curing under 405nm ultraviolet light for 10min, it is placed on a vibration table and vibrated at a frequency of 50Hz for 4min. Dry compressed air with a pressure of 0.3MPa is used to blow it for 10min at a flow rate of 20L / min to remove uncured copper powder, thus obtaining the copper-based green body.

[0037] 2. Degreasing of green billets: Place the copper-based green billets into a crucible and put it into a tube furnace. After evacuation, introduce high-purity argon gas and heat to 480℃ at room temperature at a rate of 1.5-3℃ / min. Hold at this temperature for 4 hours to ensure low-residue degreasing.

[0038] 3. Pre-skeleton sintering: Heat to 750℃ at 1.5~3℃ / min and hold for 1h to initially form a sintering neck and stabilize the geometry of the green body; 4. Densification: Continue to heat to 1060℃ at 1.5~3℃ / min and hold for 3h for further high-temperature densification sintering. At the same time, introduce gas with a volume ratio of 10%H2+90%Ar until sampling. Use high temperature to promote atomic diffusion and achieve deep densification. 5. Grain control: The temperature is lowered to 920℃ at a rate of 3–5℃ / min, and held for 1.5 hours to inhibit excessive grain growth and improve material toughness; the material is then cooled to room temperature in the furnace before being removed from the furnace, yielding the desired result. Figure 6 The copper metal sintered part shown.

[0039] Depend on Figure 6 As can be seen from the morphology of the sintered sample in Comparative Example 2, local areas of the sample showed shrinkage and collapse, resulting in a loss of structural integrity. EDS analysis results showed that the sample had a high impurity content and a density of less than 75%, and its performance was far inferior to that of the samples in the examples.

[0040] Differences from Example 2: The sample of Comparative Example 2 had insufficient sintering temperature and time for the pre-skeleton, resulting in insufficient diffusion kinetic energy of copper atoms. The amount of sintered neck formed was only about 75% of that of Example 2, which could not form an effective structural support. This led to local gravity collapse deformation during high-temperature sintering, resulting in structural failure and performance indicators that did not meet practical requirements. This highlights the criticality of the pre-sintering stage in the four-step segmented sintering process of this invention for the sintering and forming of copper metal parts.

[0041] Depend on Figure 7-10 As can be seen from the comparative analysis, the elemental distribution of Example 1 is more uniform, and the impurity content is significantly lower, verifying that different types of binders have a significant impact on the purity of the sintered sample. The spectrum of Example 2 shows clear elemental peaks, while the spectrum of the control group shows disordered peak shapes. This result demonstrates that under different debinding or sintering temperatures and times, the complete volatilization of the binder and the sintering process have a controlling effect on the evolution of the sample's microstructure.

Claims

1. A staged controlled atmosphere degreasing and sintering method for copper metal parts, characterized in that: Includes the following steps: (1) Preparation of copper-based green body: Select nano copper powder with a particle size of 450-550nm, use polyurethane acrylate resin as low-temperature degreasing binder for 3D printing spraying, place the green body under ultraviolet light of 365-405nm for curing for 10-30min, place it on a vibration table, vibrate at a frequency of 50-100Hz for 3-5min, use dry compressed air with a pressure of 0.1-0.3MPa at a flow rate of 10-20L / min to blow away uncured copper powder, and obtain copper-based green body; (2) Degreasing of green billet: Place the copper-based green billet into a crucible and then into a tube furnace. Vacuum the furnace, introduce argon gas, and then degrease it by heating. The heating method is to raise the temperature from room temperature to 175-185℃ at a heating rate of 4-6℃ / min, and then raise it to the degreasing temperature of 450-505℃ at a heating rate of 1.0-3.5℃ / min, and hold it for 3-5 hours. (3) Pre-skeleton sintering: Heat to 800-900℃ at a heating rate of 1.0-3.5℃ / min and hold for 1.5-2.0h; (4) Densification: Heat to the sintering temperature of 970-1060℃ at a heating rate of 1.0-3.5℃ / min, while simultaneously introducing low-concentration reducing gases H2 and Ar, and hold for 2-3 hours; (5) Grain control: Cool the temperature in the furnace to 870-980℃ at a cooling rate of 2.5-5.5℃ / min, hold for 1-2.5h, and then cool to room temperature with the furnace to obtain copper-based sintered parts.

2. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (1), the particle size of the nano copper powder is 500 nm, and the amount of polyurethane acrylate resin used is 15-25% of the weight of the copper-based green body.

3. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 2, characterized in that: In step (1), the amount of polyurethane acrylate resin used is 15% of the weight of the copper-based green body.

4. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (2), the green blank is degreased: the copper-based green blank is placed in a crucible and then placed in a tube furnace, vacuumed, and argon gas is introduced. The argon gas is heated to degrease, and the purity of the argon gas is ≥99.99%. The heating method is to raise the temperature from room temperature to 180°C at a heating rate of 5°C / min, and then raise the temperature to the degreasing temperature of 450°C at a heating rate of 1.5~3°C / min, and hold for 5 hours.

5. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (3), pre-skeleton sintering: the temperature is raised to 900°C at a heating rate of 1.5 to 3°C / min and held for 2 hours to pre-sinter the green blank, forming a partial sintering neck, so that the green blank is initially densified.

6. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (4), densification is carried out by heating to a sintering temperature of 1000℃ at a heating rate of 1.5 to 3℃ / min, while simultaneously introducing low-concentration reducing gases H2 and Ar, and holding for 3 hours; the volume ratio of H2 to Ar is 5:

95.

7. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (5), grain control: the temperature inside the furnace is cooled to 950°C at a cooling rate of 3-5°C / min, and held for 2 hours. The temperature gradient difference is used to gradually release the stress between the surface layer and the core to avoid sudden cooling cracking. The furnace is cooled to room temperature and taken out of the furnace at a cooling rate of 1.5-4°C / min to obtain copper-based sintered parts.

8. The staged controlled atmosphere degreasing and sintering method for copper metal parts as described in claim 1, characterized in that: In step (5), grain control: the temperature inside the furnace is rapidly cooled to 900-950°C at a rate of 3-5°C / min, and held for 1-2 hours. The temperature gradient difference is used to gradually release the stress between the surface layer and the core to avoid sudden cooling cracking. The furnace is cooled to room temperature and taken out of the furnace at a cooling rate of 2-3°C / min to obtain copper-based sintered parts.

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