Surface-modified copper metal powder as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of additive manufacturing, and relates to surface modified copper metal powder and a preparation method and application thereof. According to the method, the oxidation process is accurately controlled, so that an oxidation layer which is uniform and appropriate in thickness is formed on the surface of the copper metal powder, the oxidation layer can effectively change the interaction mechanism of the powder to laser, the laser absorptivity of the powder is improved by 30%-50% compared with that of a non-oxidation state, and the utilization efficiency of laser energy is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and relates to a surface-modified copper metal powder, a preparation method thereof, and an application thereof. Background Art

[0002] In additive manufacturing, especially in processes such as laser powder bed fusion (LPBF), the absorption rate of powder materials to laser is crucial. Additive manufacturing technology, also known as 3D printing, represents a revolution in the manufacturing industry because it allows the creation of complex-shaped components by adding materials layer by layer, rather than the traditional subtractive manufacturing method. This method not only reduces material waste but also enables the production of structures that are difficult to achieve by traditional methods. However, in this innovative manufacturing process, the material properties used have a direct impact on the quality and performance of the final product, especially for the laser powder bed fusion process.

[0003] Due to their excellent thermal conductivity, electrical conductivity, and corrosion resistance, pure copper and copper alloys have a wide range of application requirements in many fields such as electrical engineering, aerospace, automotive manufacturing, medical devices, and consumer electronics. These properties make copper-based materials an ideal choice for high-performance applications. However, when it comes to additive manufacturing using laser powder bed fusion, traditional pure copper or copper alloy powders have a low absorption rate for common red laser wavelengths in the untreated state. This is because copper has a high reflectivity, especially at room temperature, and strongly reflects light in the visible and near-infrared regions, which results in difficult effective coupling of laser energy into the powder material.

[0004] During the printing process, a low absorption rate means that more laser energy is reflected rather than used to heat and melt the powder. As a result, the energy utilization efficiency is not high, and problems such as unstable molten pools are likely to occur. The instability of the molten pool will further affect the forming accuracy, cause dimensional deviations, and may lead to internal defects such as pores, cracks, and incomplete fusion. These problems seriously affect the printing quality and limit the application range of copper-based materials in additive manufacturing.

[0005] The patent application document (CN117858776A) discloses a pure copper or copper alloy powder for additive manufacturing. The pure copper or copper alloy powder is formed with an oxide coating film, wherein the oxide coating film contains carbon, and the ratio of oxygen concentration to carbon concentration (oxygen concentration / carbon concentration) is 5 or less. The processing technology is complex, and the process window is relatively narrow, resulting in poor performance stability of the copper alloy. Summary of the Invention

[0006] The object of the present invention is to address the above problems existing in the prior art, and propose a method for preparing a surface-modified copper metal powder, which forms a specific oxide layer on the surface of the copper metal powder, thereby significantly increasing the laser absorption rate, and further greatly improving the additive manufacturing printing quality, and the surface copper oxide layer has a minimal impact on the internal components of the powder, ensuring that the original properties of the material are not damaged.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A method for preparing a surface-modified copper metal powder, the method comprising the following steps: S1. Place the copper metal powder in a vacuum, then introduce oxygen, and perform a heating treatment; S2. When the reflectivity of the copper metal powder drops below 60%, stop introducing oxygen, and then perform a cooling treatment; S3. Finally, obtain the surface-modified copper metal powder through an air flow dispersion treatment.

[0009] In the above method for preparing a surface-modified copper metal powder, the copper metal powder is a powder of pure copper or a copper alloy.

[0010] In the above method for preparing a surface-modified copper metal powder, the median particle size of the copper metal powder is 10 - 100 μm. By controlling the median particle size of the copper metal powder to be 10 - 100 μm, the present invention provides a relatively large specific surface area, but is not too fine to cause excessive oxidation. Such a particle size range enables the oxidation process to be carried out under controlled conditions, that is, while achieving the required reflectivity, the copper powder will not be overly oxidized to affect its subsequent application performance, and can be better separated under the action of air flow, avoiding adhesion between particles and further improving the quality of the powder. It can be seen that by controlling the particle size of the copper metal powder, the present invention not only reduces the possibility of agglomeration, thereby improving the processing efficiency and the consistency of the finished product; but also greatly improves the spreadability of the copper metal powder, which is crucial for constructing high-quality printed parts because it affects the dimensional accuracy and surface finish of the final product.

[0011] In the above method for preparing a surface-modified copper metal powder, the oxygen introduction rate in step S1 is 0.1 - 1 L / min. The present invention needs to strictly control the oxygen concentration. The oxygen introduction rate in step S1 is precisely controlled within 0.1 - 1 L / min. If the oxygen introduction rate is too high, the oxidation reaction will be too intense, resulting in the oxide film thickness exceeding the expected range. This will not only change the physical and chemical properties of the surface of the copper metal powder but also affect the forming quality of the material and the performance of the final product during the additive manufacturing process. On the contrary, if the oxygen concentration is too low, it may lead to insufficient oxidation, and the formed oxide film is too thin to provide the required surface modification effect, which is also not conducive to subsequent processing and applications. By controlling the oxygen introduction rate within the range of 0.1 - 1 L / min, the present invention can ensure the formation of a uniform, dense, and moderately deep copper oxide layer while avoiding problems of over-oxidation or under-oxidation. This precise regulation ensures that the oxide layer is limited to the surface of the powder particles and does not significantly affect the internal composition and original properties of the powder, thereby maintaining key properties such as the electrical conductivity, thermal conductivity, and mechanical strength of the material.

[0012] In the above method for preparing a surface-modified copper metal powder, the heat treatment is specifically heating up to 100 - 300 °C at a rate of 1 - 5 °C / min. The present invention uses a heating rate of 1 - 5 °C / min to ensure uniform heating of the entire powder sample, avoiding local overheating or non-uniform oxidation caused by rapid heating. The slow and stable heating process helps to promote the full reaction between oxygen and the copper metal powder, while preventing an increase in internal stress of the material or other adverse effects caused by sudden temperature changes. Secondly, setting the final temperature at 100 to 300 °C is based on precise control of the oxidation degree. Within this temperature range, it can effectively promote a moderate oxidation reaction on the surface of the copper metal powder to form a uniform and dense copper oxide film. This oxide film can not only improve the surface properties of the powder, such as enhancing its fluidity and spreading property, but also increase the bonding strength between the powder and the substrate material during the subsequent additive manufacturing process. By strictly controlling the maximum temperature not exceeding 300 °C, the present invention can effectively avoid the occurrence of the "over-burning" phenomenon. Too high a temperature may lead to over-oxidation, resulting in an overly thick oxide layer with a loose structure, and may even cause unnecessary fusion or deformation between the copper metal powder particles, which will seriously affect the quality and performance of the final product.

[0013] In the above method for preparing a surface-modified copper metal powder, the reflectance in step S2 is detected in real time by a spectral analyzer, and the detection wavelength is 400 - 1400 nm.

[0014] Preferably, the oxygen introduction is stopped when the reflectance drops to 50 - 58%.

[0015] In the above method for preparing a surface-modified copper metal powder, the cooling treatment in step S2 is to cool to room temperature at a rate of 2-10 °C / min.

[0016] The present invention realizes a slight oxidation treatment on the powder surface through a special oxidation environment. In this process, high-purity oxygen is slowly introduced at a rate of 0.1-1 L / min, and the temperature is gradually increased to 100-300 °C at a rate of 1-5 °C / min to promote selective slight oxidation on the powder surface. A high-precision spectroscopic analyzer is used to monitor in real time the reflectivity of the powder to a specific laser wavelength within the red light band. When the detected reflectivity drops between 50% and 58%, the oxygen supply is immediately stopped, indicating that the ideal oxide layer thickness has been reached. Subsequently, the temperature is reduced back to room temperature at a rate of 2-10 °C / min to ensure that the whole process is completed under controlled conditions. This method can form a uniform, dense and extremely shallow copper oxide layer on the surface of powder particles, while minimizing the impact on the internal composition and properties of the powder and maintaining the original excellent characteristics of the material, which is very suitable for advanced manufacturing processes such as additive manufacturing and thermal spraying to improve the quality and reliability of the final product.

[0017] After a large number of microstructure analysis and detection, the oxidation treatment method of the present invention ensures that the treated copper metal powder (including pure copper and copper alloys) has a very small deviation in elemental composition and content compared with the original powder. After the oxidation treatment, the internal copper content remains above 99.5%, almost completely retaining the purity of the original material. For copper alloy powders containing multiple alloying elements, the content fluctuations of each alloying element are strictly controlled within ±0.5%, ensuring the consistency and stability of the alloy composition. This high level of composition control is achieved by precisely adjusting the oxygen introduction rate, temperature increase rate in the oxidation environment and real-time monitoring of the reflectivity change. The precise regulation of these parameters confines the oxide layer only to the surface of the powder particles, forming a uniform and dense oxide layer with minimal impact on the interior of the powder.

[0018] The core advantage of the present invention is that it can effectively protect the original thermal conductivity, electrical conductivity and other key physical properties of the material from being damaged. Traditional oxidation treatment methods often lead to changes in the internal composition of the material, thereby affecting these important properties. In contrast, the present invention avoids changes in the internal structure by restricting the oxidation reaction to occur only on the powder surface, thus ensuring the preservation of the original properties of the material.

[0019] This technological breakthrough provides a solid guarantee for the use of copper metal powder in high-end application fields. Whether it is components requiring high electrical conductivity in the electronics industry or parts requiring good thermal conductivity in the aerospace field, the powder treated by this method can meet the stringent application requirements and ensure the reliability of product quality and performance.

[0020] In the above method for preparing a surface-modified copper metal powder, the gas flow dispersion treatment rotates and disperses the copper metal powder at a gas flow rate of 0.5 - 2 m / s.

[0021] Preferably, the gas flow dispersion treatment is carried out in air or oxygen.

[0022] The present invention adopts a gentle and efficient gas flow dispersion technology mainly using a rotary disperser to ensure that the powder maintains good fluidity on the premise of obtaining uniform surface modification. Specifically, by setting the gas flow rate to 0.5 - 2 m / s, this appropriate speed range can effectively break the adhesion between particles caused by the formation of the surface oxide layer without damaging the fragile oxide layer. The rotary disperser further enhances the dispersion effect. It works synergistically through mechanical force and aerodynamic principles, enabling the oxidized copper powder to regain excellent fluidity and spreadability, which is crucial for subsequent processing steps (such as powder laying in additive manufacturing).

[0023] Preferably, the prepared copper metal powder needs to be sealed and packaged. The sealed packaging not only prevents further oxidation caused by contact with external oxygen but also avoids the problem of moisture intrusion and dampness. This step is particularly crucial for maintaining the chemical stability and physical properties of the powder, ensuring that when these powders are put into additive manufacturing or other precision manufacturing processes, their performance remains stable and reliable, meeting the strict requirements of high-end application fields.

[0024] The present invention also provides a surface-modified copper metal powder prepared by the above preparation method.

[0025] The present invention also provides an application of the above surface-modified copper metal powder in laser additive manufacturing.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. By precisely controlling the oxidation process, the present invention forms a uniform and appropriately thick oxide layer on the surface of the copper metal powder. This oxide layer can effectively change the interaction mechanism between the powder and the laser, increasing the laser absorption rate of the powder by 30% - 50% compared to the unoxidized state, greatly improving the utilization efficiency of laser energy.

[0028] 2. The surface oxide layer in the copper metal powder prepared by the present invention has little influence on the internal composition of the powder, which not only ensures that the original good thermal conductivity, electrical conductivity and other properties of the material are not damaged by the oxidation treatment, but also makes the comprehensive performance of the printed parts equivalent to that of the products printed with the original powder during the subsequent additive manufacturing process. Moreover, on the basis of improving the forming quality due to the increased absorption rate, its application potential is further expanded. For example, it is widely used in fields with strict requirements for material properties such as the heat dissipation structure of electronic devices and precision electrical connectors.

[0029] 3. When the copper metal powder prepared by the present invention is used in the additive manufacturing process, the high absorption rate brings about the formation of a stable molten pool, and the size of the molten pool is more uniform, which can effectively reduce defects such as pores, cracks, and lack of fusion. As a result, the density of the printed parts is increased by 20 - 50%, the dimensional accuracy error is controlled within the range of ±0.1 - 0.3 mm, and the surface roughness is reduced by 30% - 60%, greatly improving the printing quality and meeting the strict requirements for copper-based parts in the high-end manufacturing field.

[0030] 4. The copper metal powder of the present invention is applicable to a variety of mainstream additive manufacturing processes, such as laser powder bed fusion (LPBF), electron beam melting (EBM), etc. Without large-scale modification of the existing equipment, only fine-tuning of the process parameters according to the increase in the powder absorption rate is required to achieve high-efficiency and high-quality printing, reducing the technical application threshold and having broad market promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the equipment for preparing the surface-modified copper metal powder in Example 1: 1. Oxygen cylinder; 2. Flow valve; 3. Transparent test window; 4. Oven; 5. Pure copper powder; 6. Vacuum pump.

[0032] Figure 2 Reflectivity curve graphs of the original copper metal powder and the finally prepared copper metal powder during the process of preparing the surface-modified copper metal powder in Example 2.

[0033] Figure 3 Comparison chart of the surface colors of the copper alloy powder after being treated in the manner of Example 2 (oxygen passing treatment) and Comparative Example 1 (non-oxygen passing treatment).

[0034] Figure 4 Optical microscope photos (uncorroded) of the SLM formed specimens of the copper alloy powder after being treated in the manner of Example 2 (oxygen passing treatment) and Comparative Example 1 (non-oxygen passing treatment). DETAILED DESCRIPTION OF THE INVENTION

[0035] The following are specific examples of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these examples. Example 1

[0036] S1. As shown in Figure 1 , first place 100 g of pure copper powder with a median particle size of 30 μm in an oven, and then evacuate it;

[0037] S2. Then introduce oxygen at a rate of 0.3 L / min, and at the same time heat it up to 250 °C at a rate of 2 °C / min;

[0038] S3. Use a portable spectral analyzer to monitor the reflectivity of the pure copper powder at a laser wavelength of 1080 nm in real time. When the reflectivity drops to 58%, stop introducing oxygen and cool it down to room temperature at a rate of 5 °C / min;

[0039] S4. Finally, rotate and disperse it at an air flow rate of 1 m / s to obtain copper metal powder. Example 2

[0040] S1. First place 100 g of pure copper powder with a median particle size of 50 μm in an oven, and then evacuate it;

[0041] S2. Then introduce oxygen at a rate of 0.5 L / min, and at the same time heat it up to 200 °C at a rate of 2 °C / min;

[0042] S3. Use a portable spectral analyzer to monitor the reflectivity of the pure copper powder at a laser wavelength of 1080 nm in real time. When the reflectivity drops to 57%, stop introducing oxygen and cool it down to room temperature at a rate of 5 °C / min;

[0043] S4. Finally, rotate and disperse it at an air flow rate of 1 m / s to obtain copper metal powder.

[0044] Figure 2 It is a graph showing the reflectivity of the original copper metal powder and the finally prepared copper metal powder during the preparation of the surface-modified copper metal powder in Example 2. It can be seen from the figure that the red light reflectivity of the copper alloy has decreased from 63% to 57%, and the utilization rate of the red light laser energy has increased by more than 10%. Example 3

[0045] The difference from Example 1 is only that the median particle size of the pure copper powder in step S1 is 1 μm. Example 4

[0046] The difference from Example 1 is only that the median particle size of the pure copper powder in step S1 is 150 μm. Example 5

[0047] The difference from Example 1 is only that the oxygen introduction rate is 2 L / min. Example 6

[0048] The difference from Example 1 is only that the oxygen inlet rate is 0.01 L / min. Example 7

[0049] The difference from Example 1 is only that the temperature increase in step S2 is 50°C. Example 8

[0050] The difference from Example 1 is only that the temperature increase in step S2 is 350°C. Comparative Example 1

[0051] The difference from Example 1 is only that no oxygen is introduced. Comparative Example 2

[0052] The difference from Example 1 is only that when the reflectivity of the copper metal powder drops to 75%, the oxygen inlet is stopped. Comparative Example 3

[0053] The difference from Example 1 is only that no stepwise temperature increase treatment is carried out, and the reaction is directly carried out at 200°C.

[0054] The copper metal powders prepared in Examples 1 - 8 and Comparative Examples 1 - 3 were used to print copper specimens on a laser powder bed fusion device, and the laser power requirements remained unchanged during the printing process (power 300 W, scanning speed 1200 m / s, layer thickness 40 μm).

[0055] Table 1: Performance test results of copper specimens prepared using the copper metal powders of Examples 1 - 8 and Comparative Examples 1 - 3

[0056] Figure 3 Comparison chart of the surface colors of copper alloy powders after being treated in the manner of Example 2 (oxygen - passing treatment) and Comparative Example 1 (non - oxygen - passing treatment). The surface color of the copper alloy powder after oxygen - passing treatment is dark and has obvious granularity; while the color of the non - oxygen - passing treated powder is brighter, which indicates that the oxygen - passing treatment has a significant impact on the surface properties of the copper alloy powder. Due to the oxidation reaction between oxygen and copper, the chemical composition and physical properties of the powder surface are changed.

[0057] Figure 4Optical microscope photos of copper alloy powder SLM formed samples after treatment in Example 2 (oxygen treatment) and Comparative Example 1 (no oxygen treatment). As can be seen from the figure, there are more pores and defects inside the test block without oxygen treatment, and the surface appears to be relatively rough; the test block formed by the copper alloy powder after oxygen treatment has a denser microstructure, significantly reduced pores, and a more uniform and smoother surface. The density of the test block formed by the powder after oxygen treatment is higher (99.2%), while the density of the test block formed by the powder without oxygen treatment is lower (92%), which shows that the oxygen treatment not only changes the color and reflectivity of the powder surface, but also significantly improves the density of the powder after forming, reduces the internal pores, and thus may improve the mechanical properties and physical properties of the material.

[0058] It can be seen from the above results that the copper metal powder prepared by the present invention is used in the additive manufacturing process, and the high absorption rate brings about a stable molten pool formation, and the molten pool size is more uniform, which can effectively reduce defects such as pores, cracks, and unfused parts, so that the thermal conductivity of the printed parts is increased by 20-50%, and the density is increased to 99.4%, which greatly improves the printing quality and meets the stringent requirements of the high-end manufacturing field for copper-based components.

[0059] The parts of the embodiments herein that are not exhaustive of the midpoint values ​​of the technical scope claimed for protection by the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope claimed for protection by the present invention; at the same time, in all the listed or unlisted embodiments of the scheme of the present invention, each parameter in the same embodiment merely represents an example of its technical solution (i.e., a feasible solution), and there is no strict coordination and limitation relationship between the parameters, wherein the parameters can be replaced with each other without violating the axioms and the claims of the present invention, unless otherwise stated.

[0060] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical schemes composed of any combination of the above technical features. The above is a specific implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0061] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for preparing a surface-modified copper metal powder, characterized in that: The method comprises the following steps: S1, placing copper metal powder in a vacuum, then introducing oxygen, and performing a temperature treatment; S2. When the reflectivity of the copper metal powder drops below 60%, stop introducing oxygen and then perform a cooling treatment; S3. Finally, the copper metal powder with surface modification is obtained by air flow dispersion treatment.

2. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The copper metal powder is a powder of pure copper or a copper alloy.

3. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The median particle size of the copper metal powder is 10-100 μm.

4. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The oxygen introduction rate in step S1 is 0.1-1 L / min.

5. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The temperature increase treatment is specifically to increase the temperature to 100-300° C. at a rate of 1-5° C. / min.

6. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: In step S2, the reflectivity is detected in real time by a spectrum analyzer, and the detection wavelength is 400-1400nm.

7. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The cooling process in step S2 is to cool the temperature to room temperature at a rate of 2-10°C / min.

8. The method for preparing a surface-modified copper metal powder according to claim 1, characterized in that: The air flow dispersion treatment rotates and disperses the copper metal powder at an air flow speed of 0.5-2m / s.

9. A surface-modified copper metal powder, characterized in that: The copper metal powder is prepared by the preparation method according to claim 1.

10. Use of the surface-modified copper metal powder according to claim 9 in laser additive manufacturing.

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