Preparation method of tungsten-coated copper powder and method for preparing high-density and high-conductivity copper device through powder 3D printing

Abstract

The invention discloses a preparation method of tungsten-coated copper powder and a method for preparing a high-density and high-conductivity copper device through 3D printing of the powder. Specifically, the surface of spherical pure copper powder is coated with tungsten metal particles with high laser absorptivity by combining a sol-gel method with a chemical vapor reduction technology, so that the laser absorption capacity of the copper powder is improved, and the problems that a device prepared through copper powder 3D printing is poor in forming capacity, low in density and poor in performance are solved. The tungsten-coated copper powder has the advantages that the laser absorptivity is high, the sphericity degree is high, powder laying is not affected, tungsten coating is uniform, and the content is controllable. Compared with surface modified copper powder or copper alloy powder used in traditional 3D printing, a device printed by the copper powder coated with the nano tungsten particles has the advantages of being high in density and excellent in electric conduction and heat conduction performance. The invention provides a feasible method for designing high-complexity and high-performance copper-based electric conduction and heat conduction devices through 3D printing.

Description

Technical Field

[0001] The present invention belongs to the field of metal material preparation, and particularly relates to a method for preparing tungsten-coated copper powder and a method for 3D printing high-density and high-conductivity copper devices using the powder. Background Art

[0002] Copper is widely used in the fields of electricity and thermal management due to its excellent electrical and thermal conductivity. In recent years, the concept of geometric structure design and optimization has been proposed to increase the surface area of copper devices to reduce energy loss and maximize the working efficiency of the devices. Laser powder bed fusion is a 3D printing technology that selectively melts metal powder layer by layer using a laser to stack and form metal parts. Due to its advantages such as high raw material utilization rate, short production cycle, and integrated forming of complex structures, it is an ideal method for manufacturing geometrically complex copper-based devices. However, due to the extremely high laser reflectivity of copper, there are problems of poor forming quality and low density in printing copper devices. This seriously deteriorates the electrical conductivity, thermal conductivity, and mechanical properties of the devices, making the printed devices unusable.

[0003] Currently used alloy powders such as CuZn, CuCrZr, CuNiSi, etc. and copper powders surface-modified with elements such as Sn, Co, Ni, etc. have relatively low laser reflectivity and can achieve printing of high-density samples. However, during the printing process with a high cooling rate, the added alloying elements often exist in the copper matrix in the form of supersaturated solid solutions. This leads to lattice distortion of copper, seriously hindering the transmission of internal electrons, thereby significantly reducing the electrical and thermal conductivity of copper. In order to prevent the addition of alloying elements from affecting the copper lattice parameters, insoluble ceramic particles and carbon materials are coated on the copper surface to improve the printability of the copper powder. However, under high-energy lasers, ceramic particles and carbon materials are extremely prone to decomposition and ablation, which results in limited improvement in the density of the printed samples. Therefore, it is necessary to seek a new high-laser-absorbing enhancer to modify copper powder so that copper parts can retain the excellent electrical and thermal conductivity of copper while achieving high-density printing.

[0004] On the one hand, tungsten (W) has extremely high melting and boiling points, which enables it to be non-volatile under high-energy lasers and ensures efficient energy absorption. On the other hand, the characteristics of immiscibility and non-reactivity with copper mean that its addition will not affect the lattice parameters of copper. In addition, tungsten also has relatively high electrical and thermal conductivities. Therefore, choosing tungsten as the laser absorption modification phase is expected to achieve the printing and preparation of highly dense and highly conductive copper devices. However, due to the significant difference in the melting points of tungsten and copper, it is difficult to incorporate tungsten into copper powder through conventional alloying methods. At the same time, mechanical mixing methods are also not suitable for preparing the required Cu-W composite powder. Because during the mixing process, not only is it difficult to achieve compositional homogenization of tungsten, but the sphericity and fluidity of copper powder are also easily damaged. Therefore, there is an urgent need to develop a uniform tungsten-modified copper powder that can significantly improve the laser absorption rate of the powder while ensuring the sphericity and fluidity of the copper powder, in order to achieve the high density and high conductivity of 3D printed copper devices. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing tungsten-coated copper powder and a method for 3D printing and preparing a high-density and high-conductivity copper device using this powder in view of the above-mentioned deficiencies of the prior art. This method uses the sol-gel method combined with chemical vapor reduction technology to prepare a tungsten particle surface-modified copper composite powder and performs 3D printing to prepare a high-density and high-conductivity copper device. The tungsten-coated copper powder has the advantages of high laser absorption rate, high sphericity without affecting powder spreading, and controllable tungsten coating content. The tungsten-coated copper powder significantly improves the forming ability of printed samples, and the printed device has the advantages of few defects, high electrical and thermal conductivity, and high mechanical properties. The present invention solves the problems of high laser reflectivity of copper powder during 3D printing, low forming ability of printed devices, and poor performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing tungsten-coated copper powder, the method comprising:

[0008] 1) Preparing tungsten salt-coated copper composite powder by sol-gel method:

[0009] Dissolve tungsten salt, adjust the pH value of the solution, then pour in copper powder and stir. After stirring, evaporate the mixed suspension to dryness to obtain tungsten salt-coated copper composite powder;

[0010] 2) Preparing tungsten oxide-coated copper composite powder by high-temperature calcination:

[0011] Put the tungsten salt-coated copper composite powder obtained in step 1) into an atmosphere furnace, introduce an inert gas, raise the furnace temperature to a preset temperature, maintain for a period of time, then stop heating and cool to room temperature, and close the gas to obtain tungsten oxide copper composite powder;

[0012] 3) Preparation of copper spherical powder with surface-modified tungsten by gas-phase reduction method:

[0013] Put the tungsten oxide copper composite powder obtained in step 2) into an atmosphere furnace, raise the furnace body temperature to the reduction temperature, and introduce inert gas and reducing gas according to the preset ratio to reduce the composite powder. After the reaction is completed, cool it to room temperature and close the gas to obtain tungsten-coated copper powder.

[0014] A method for preparing a high-density and high-conductivity copper device by 3D printing of tungsten-coated copper powder, the method comprising:

[0015] In the control computer of the selective laser melting forming machine, set the parameters of selective laser melting forming, and solidify the tungsten surface-modified copper powder layer by layer on the substrate to finally obtain the corresponding formed metal part.

[0016] Preferably, the tungsten salt in step 1) is ammonium paratungstate and ammonium metatungstate. This preferred tungsten salt can be dissolved, will not introduce other metal impurities to deteriorate the performance of copper, and is easily decomposed into tungsten oxide at high temperature.

[0017] Preferably, the mass ratio of tungsten to copper powder in the tungsten salt in step 1) is (0.1 - 5):100. This mass ratio of tungsten to copper powder in the preferred tungsten salt is used to precisely control the mass ratio of tungsten coated on the copper powder surface.

[0018] Preferably, the pH value of the solution in step 1) is 2 - 10. This preferred pH value is used to control the morphology of the coated W.

[0019] Preferably, the preset temperature of the calcination system in step 2) is 400 - 600 °C, and the reaction time is 30 - 240 min. This preferred calcination process parameter ensures that the tungsten salt is fully decomposed to form tungsten oxide during calcination.

[0020] Preferably, the inert gas in step 2) is a gas that does not react with the powder raw material. The inert gas includes one or several of nitrogen and argon, and the gas flow rate is 100 - 2000 mL / min or more. This preferred gas and flow rate ensure that the gas after the decomposition of the tungsten salt can be quickly removed and prevent copper from being oxidized during calcination.

[0021] Preferably, the preset temperature of the reduction system in step 3) is 700 - 800 °C, and the reaction time is 30 - 240 min or more. This preferred temperature ensures that the oxide is completely reduced, prevents the oxygen element from affecting the performance of the subsequent printed device, and avoids sintering of copper during reduction, which affects the subsequent printing.

[0022] Preferably, the reducing gas in step 3) is hydrogen with a flow rate of 100 - 2000 mL / min. This preferred hydrogen is conducive to reducing tungsten oxide to pure tungsten; this preferred gas ratio ensures that the oxide is reduced in a short time and can quickly carry away the generated water vapor.

[0023] Preferably, the process parameters of laser powder bed fusion are a laser power of 300 - 500 W, a scanning speed of 300 - 1500 mm / s, a processing layer thickness of 0.02 - 0.05 mm, and a scanning spacing of 0.05 - 0.15 mm. These preferred 3D printing process parameters ensure the effective fusion of tungsten-modified copper powder and are conducive to the preparation of highly dense and highly conductive copper devices.

[0024] The present invention proposes a method for preparing tungsten-coated copper powder and a method for 3D printing highly dense and highly conductive copper devices using this powder. The sol-gel method combined with chemical vapor reduction technology is proposed to prepare spherical copper powder coated with tungsten particles. The coated tungsten particles are characterized by small size and highly uniform distribution, and a small amount of coated tungsten can significantly reduce the laser reflectivity of copper powder. Compared with traditional alloy, ceramic, and carbon material laser absorption enhancers, the introduced tungsten will neither volatilize under high-energy laser to limit the improvement of the density of printed devices, nor dissolve into the substrate to induce lattice distortion of copper, resulting in the decline of the electrical and thermal conductivity of copper. Therefore, the use of tungsten-modified copper powder realizes the simultaneous improvement of the density and conductivity of 3D printed copper devices. The density and conductivity of the printed copper devices are much higher than those of the printed devices modified with other laser absorption enhancer powders. This method effectively solves the problems of poor 3D printing forming ability, low density, and unqualified performance of copper powder with high laser reflectivity, and has the advantages of simple process, short process flow, low cost, and easy large-scale production. Description of the Drawings

[0025] Figure 1 SEM image of tungsten surface-modified copper powder in Example 1 of the present invention;

[0026] Figure 2 High-magnification SEM image of tungsten surface-modified copper powder in Example 1 of the present invention;

[0027] Figure 3 Cross-sectional light microscope image of the printed part of tungsten surface-modified copper powder in Example 1 of the present invention;

[0028] Figure 4 High-magnification SEM image of tungsten surface-modified copper powder in Example 2 of the present invention;

[0029] Figure 5 SEM image of tungsten surface-modified copper powder in Example 3 of the present invention;

[0030] Figure 6This is the cross-sectional optical microscope image of the tungsten surface-modified copper powder printed part in Example 4 of the present invention. Detailed implementation manners

[0031] To make the objectives, technical solutions, implementation details and advantages of the present invention clearer and more understandable, the following further detailed description of the present invention is provided in conjunction with four specific embodiments and with reference to the accompanying drawings. It should not be regarded as the protection scope of the present invention. For some non-substantive modifications that do not deviate from the concept of the present invention, they all fall within the scope of the rights protection of the present invention.

[0032] Specifically, a preparation method of tungsten-coated copper powder and a method for 3D printing a high-density and high-conductivity copper device using the powder are proposed. Sol-gel method combined with chemical vapor reduction technology is used to prepare tungsten particle surface-modified spherical copper powder. The coated tungsten particles have the characteristics of small size and highly uniform distribution. A small amount of coated tungsten can significantly reduce the laser reflectivity, and remarkably improve the printing densification and the conductivity of the parts.

[0033] Example 1

[0034] A preparation method of tungsten-coated copper powder and a method for 3D printing a high-density and high-conductivity copper device using the powder include the following steps:

[0035] 1) Preparation of tungsten salt-coated copper composite powder by sol-gel method: Dissolve 1.4 g of ammonium paratungstate in 20 mL of deionized water, adjust the pH of the solution to 7, then pour in 99 g of spherical pure copper powder with a particle size of 15 - 53 μm and perform magnetic stirring at a rotation speed of 300 rpm for 180 min. After the stirring ends, evaporate the mixed suspension to dryness in a water bath at 60 °C to obtain tungsten salt-coated copper composite powder;

[0036] 2) Preparation of tungsten oxide-coated copper composite powder by high-temperature calcination: Put the tungsten salt-coated copper composite powder obtained in step 1) into a horizontal furnace, introduce argon at a flow rate of 200 mL / min, raise the furnace temperature to 500 °C, keep it for 120 min, then stop heating and cool to room temperature, and close the gas to obtain tungsten oxide copper composite powder;

[0037] 3) Preparation of tungsten surface-modified copper spherical powder by chemical vapor reduction method: Put the tungsten oxide copper composite powder obtained in step 2) into a horizontal furnace, introduce argon and hydrogen with a flow rate of 200 mL / min each, raise the furnace temperature to 750 °C and reduce for 60 min, then cool to room temperature and close the gas to obtain 1.0 wt.% tungsten surface-modified copper spherical powder;

[0038] 4) Preparation of 3D printed high-conductivity copper devices with tungsten surface modified copper powder: In the control computer of the selective laser melting forming machine, the laser power of the selective laser melting forming is set to 425 W, the scanning speed is 500 mm / s, the processing layer thickness is 0.03 mm, and the scanning interval is 0.1 mm. The tungsten surface modified high laser reflectivity copper powder obtained in step 3) is solidified layer by layer on the substrate to finally obtain the corresponding formed metal parts.

[0039] Figure 1 This is a SEM image of the tungsten surface-modified copper powder in Example 1. The copper powder has good sphericity and W particles are evenly distributed on the surface.

[0040] Figure 2 This is a high-magnification SEM image of the tungsten surface-modified copper powder in Example 1. The tungsten particles coated on the surface of the powder have the characteristics of small particle size and highly uniform distribution. The uniformly coated tungsten particles reduce the laser reflectivity of the powder from 82.7% to 35.8%.

[0041] Figure 3 This is a cross-sectional optical microscopy image of a part printed with tungsten surface modified copper powder in Example 1 of the present invention. It can be seen from the figure that the unmelted copper powder disappears and the internal pores are significantly reduced, indicating that the density of the printed sample reaches more than 99% and the conductivity reaches more than 95% IACS, which is much higher than the performance of other laser absorption enhancer modified powder printing devices, which fully proves that coating with highly stable and inert tungsten is conducive to the printing preparation of highly densified and highly conductive copper.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is that the tungsten salt in Example 1 is replaced by ammonium metatungstate from ammonium paratungstate, and the pH of the solution is adjusted to 2, which is used to verify that the morphology of W can be effectively controlled by pH control;

[0044] Figure 4 This is a high-magnification SEM image of the tungsten surface-modified copper powder in Example 2. As shown in the figure, the change of tungsten salt will not seriously affect the uniformity of the coated W, and the morphology of the coated W can be regulated by the pH of the solution.

[0045] Through the laser reflectivity test of W-coated copper powder and the density and conductivity of the printed samples, its laser reflectivity dropped to 41.9%, the density increased to 98.5%, and the conductivity was 92.5% IACS, which is still significantly better than the conductivity of other modified phase copper powder printed samples.

[0046] Example 3

[0047] The difference between Example 3 and Example 1 is as follows: the calcination temperature in Example 1 is increased to 600 °C and the holding time is increased to 240 min; the reduction temperature is increased to 800 °C and the holding time is increased to 180 min.

[0048] Figure 5 Figure 4 is the SEM image of the tungsten surface-modified copper powder in Example 3. W particles are evenly distributed on the surface. However, increasing the calcination, reduction temperature and time may induce sintering of some copper powder. Through the measurement of the laser reflectivity of the W-coated copper powder, the density and performance of the printed samples were tested. Its laser reflectivity decreased to 38.7%, the density increased to 98.9%, and the conductivity was 93.5% IACS, which was still significantly better than the conductivity of the printed samples of other modified-phase copper powders.

[0049] Example 4

[0050] The difference between Example 4 and Example 1 is as follows: the laser power in Example 1 is decreased to 350 W, the scanning speed is increased to 800 mm / s, and the scanning spacing is 0.12 mm, which is used to study the influence of scanning parameters on the density and performance of tungsten-modified powder printing.

[0051] Figure 6 Figure 5 is the cross-sectional optical microscope image of the tungsten surface-modified pure copper powder printed part in Example 4. As can be seen from the figure, by changing the scanning parameters and reducing the scanning energy density, the printed sample has a density of more than 98% and a conductivity of 92% IACS, indicating that the tungsten surface-modified pure copper powder can eliminate the unmelted copper powder and improve the printing densification of copper powder under a wide range of scanning parameters.

[0052] The laser reflectivity of the copper powder before and after tungsten surface modification in Examples 1-3 is shown in Table 1.

[0053] Table 1 Laser reflectivity results of pure copper powder and tungsten-modified copper powder

[0054] Original powder laser reflectivity (%) Tungsten surface modified powder laser reflectivity (%) Example 1 82.7 35.8 Example 2 82.7 41.9 Example 3 82.7 38.7

[0055] The density and conductivity of the printed samples using the copper powder after tungsten surface modification in Examples 1-4 are shown in Table 2.

[0056] Table 2 Density and conductivity of printed devices using tungsten-modified copper powder

[0057] Relative density (%) Conductivity (% IACS) Example 1 99.5 95.6 Example 2 98.5 92.5 Example 3 98.9 93.5 Example 4 98.0 92.0

[0058] The upper and lower limit values and interval values of the process parameters (such as temperature, time, etc.) of the present invention can all implement the present method, and the examples are not listed one by one here.

[0059] All the content not detailed in the present invention can adopt the conventional technical knowledge in the field.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing tungsten-coated copper powder, the method comprises: 1) Preparing tungsten salt-coated copper composite powder by sol-gel method: Dissolve tungsten salt, adjust the pH value of the solution, then pour in copper powder and stir. After stirring, evaporate the mixed suspension to dryness to obtain tungsten salt-coated copper composite powder; 2) Preparing tungsten oxide-coated copper composite powder by high-temperature calcination: Put the tungsten salt-coated copper composite powder obtained in step 1) into an atmosphere furnace, introduce an inert gas, raise the furnace body temperature to a preset temperature, keep it for a period of time, then stop heating and cool to room temperature to obtain tungsten oxide copper composite powder; 3) Preparing tungsten surface-modified copper spherical powder by chemical vapor reduction method: Put the tungsten oxide copper composite powder obtained in step 2) into an atmosphere furnace, raise the furnace body temperature to the reduction temperature, and introduce an inert gas and a reducing gas according to a preset ratio to reduce the composite powder. After the reaction, cool to room temperature to obtain tungsten-coated copper powder.

2. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the tungsten salt in step 1) is ammonium paratungstate and ammonium metatungstate.

3. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the mass ratio of tungsten in the tungsten salt in step 1) to the mass of copper powder is (0.1 - 5):

100.

4. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the pH value of the solution in step 1) is 2 - 10.

5. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the preset temperature of the calcination system in step 2) is 400 - 600 °C, and the reaction time is 30 - 240 min.

6. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the inert gas in step 2) includes one or two of nitrogen and argon, and the gas flow rate is 100 - 2000 mL / min.

7. The method for preparing tungsten-coated copper powder according to claim 1, characterized in that the preset temperature of the reduction system in step 3) is 700 - 800 °C, and the reaction time is 30 - 240 min; the reducing gas is hydrogen.

8. A method for preparing a high-density and high-conductivity copper device by 3D printing tungsten-coated copper powder, the method comprises: Set the parameters of selective laser melting forming, and solidify the tungsten-coated copper powder layer by layer on the substrate to finally obtain the corresponding formed metal part.

9. The method for preparing a high-density and high-conductivity copper device by 3D printing tungsten-coated copper powder according to claim 8, characterized in that the parameters of the selective laser melting forming are that the laser power is 300 - 500 W, the scanning speed is 300 - 1000 mm / s, the processing layer thickness is 0.02 - 0.05 mm, and the scanning spacing is 0.05 - 0.15 mm.

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