Preparation method of tungsten-copper composite material with uniform structure
Uniform tungsten powder was prepared by ball milling, air classification, and vacuum melting, which solved the problem of non-uniform microstructure in tungsten-copper alloys, improved the density and electrical conductivity of the material, and enhanced processing accuracy and utilization.
Patent Information
- Application Number
- CN202410630978.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-21
- Publication Date
- 2025-11-21
AI Technical Summary
In existing methods for preparing tungsten-copper alloys, the non-uniformity of tungsten powder particles leads to uneven microstructure, affecting the density and electrical conductivity of the material. Furthermore, conventional methods are prone to producing pores and grain coarsening.
Tungsten powder with narrow particle size distribution and good dispersibility was prepared by ball milling and air classification, combined with low-temperature reduction and vacuum melting infiltration. Stearic acid was used as a binder, and the degreasing and pre-sintering temperatures were controlled to ensure the uniformity of the tungsten skeleton pores. Copper melting infiltration was carried out in a vacuum environment.
This study improved the uniformity and density of the tungsten-copper alloy, increased its electrical conductivity, reduced copper enrichment and tungsten skeleton closure, and improved the processing accuracy and utilization rate of the material.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of composite material preparation, and specifically relates to a method for preparing a tungsten-copper alloy with uniform microstructure. Background Technology
[0002] Tungsten-copper alloys are widely used as high-voltage contact materials, thermal conductive materials, and functionally graded materials due to their high electrical and thermal conductivity combined with good mechanical properties. Tungsten particles, dispersed as a reinforcing phase in the matrix, significantly reduce the coefficient of thermal expansion of tungsten-copper composites. Particle size influences the size of tungsten grains in the matrix to some extent. Generally, smaller tungsten powder particle size results in finer grains and higher strength in the prepared tungsten-copper alloy. However, finer tungsten grains also lead to increased grain boundaries, reducing the connectivity of the copper phase and consequently decreasing the overall electrical conductivity of the tungsten-copper alloy. Therefore, using uniform tungsten powder helps improve the material's electrical conductivity.
[0003] Tungsten-copper composites are commonly used to prepare processed electrodes, therefore, the uniformity of the material's microstructure significantly affects the electrode's processing accuracy. Electrodes with uniform microstructure have high surface finish and are beneficial for improving material utilization. Commonly used methods for preparing tungsten-copper alloys include high-temperature liquid-phase sintering, activated liquid-phase sintering, and melt infiltration. Liquid-phase sintering tends to generate gas during the sintering process, forming pores in the composite material and thus reducing its density. Numerous studies have also shown that liquid-phase sintered tungsten-copper alloys have lower density. High-temperature sintering of fine tungsten powder easily produces porosity and segregation, and low-temperature sintering is more prone to grain coarsening. Tungsten-copper alloys prepared by melt infiltration generally have higher density than those prepared by liquid-phase sintering.
[0004] The melt infiltration method comprises two parts: degreasing and pre-sintering of the tungsten framework and melt infiltration of copper. During the pre-sintering stage, tungsten powder diffuses to form a tungsten framework with a certain strength. Therefore, the porosity of the tungsten framework plays a decisive role in the uniformity of the microstructure of the tungsten-copper composite material. Improving the uniformity of the tungsten powder and the dispersibility of the powder during molding are key to improving the porosity of the tungsten framework. Summary of the Invention
[0005] This invention employs a melt infiltration method to prepare tungsten-copper alloys. Commercially available tungsten powder has poor particle uniformity and exhibits slight agglomeration, which is detrimental to improving the microstructure uniformity of the tungsten-copper alloy. Therefore, to obtain tungsten powder with uniform particle size, the raw material needs to be ball-milled first. The ball-milling time should not be too long to avoid particle breakage during the milling process, which would generate a large amount of fine tungsten powder and introduce a large number of impurity elements. After ball milling, the tungsten powder is classified into five particle size distribution ranges: 50nm-1μm, 1-3μm, 3-5μm, 5-8μm, and 8-12μm.
[0006] To avoid the slight oxidation of tungsten powder during ball milling and classification affecting the copper melting process, the classified tungsten powder is reduced with dry hydrogen at low temperature for a period of time. The reduction time should not be too long, and the reduction temperature should be below 500℃ to prevent the tungsten powder from agglomerating during the reduction process.
[0007] To ensure the tungsten powder particles adhere together, a binder needs to be added. This invention uses stearic acid as the binder. A certain mass fraction of stearic acid is dissolved in a small amount of alcohol. After the stearic acid is completely dissolved, it is mixed with the tungsten powder to form a paste and then ultrasonically treated. After ultrasonic treatment, the mixture is placed in a vacuum drying oven and dried at low temperature for a period of time. The dried tungsten powder is prone to significant agglomeration. To reduce agglomeration, the tungsten powder is ground in a mortar for 10 minutes and then sieved to obtain the final tungsten powder.
[0008] A certain mass of tungsten powder is weighed and placed in a mold to press into a blank. The size of the blank is controlled by the mold. The pressed tungsten skeleton undergoes degreasing and pre-sintering treatment. The degreasing temperature depends on the decomposition temperature of stearic acid, and the degreasing time should be slightly longer than the empirically established time. To avoid oxidation of the tungsten powder during degreasing and pre-sintering, hydrogen is used as the degreasing atmosphere. The pre-sintering temperature and holding time are the same as in practical experience.
[0009] The higher the copper melting temperature and the lower the copper viscosity, the better the copper melting process. However, the tungsten framework is prone to sintering at high temperatures, which can lead to the closure of some finer pores. Therefore, the copper melting temperature should not be too high or too low. To avoid the influence of gases on the melting process, tungsten and copper are placed in a tube furnace and a vacuum is applied.
[0010] The technical solution of this invention is as follows: This invention employs tungsten powder ball milling, airflow classification, and low-temperature pre-reduction to reduce the particle size distribution range of tungsten powder, and uses vacuum melting infiltration to promote copper infiltration. The specific steps are as follows: (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a low speed for a period of time; (2) The tungsten powder after ball milling was subjected to multiple airflow classification processes, and the resulting tungsten powder was divided into five particle size distribution ranges; (3) Reduce the graded tungsten powder at low temperature for a period of time; (4) Weigh a certain percentage of stearic acid and dissolve it in a small amount of alcohol. Mix the tungsten powder with the alcohol solution and sonicate. (5) After the ultrasonic tungsten powder is dried, it is ground and sieved to obtain tungsten powder for pressing. (6) After the tungsten powder is pressed into a billet, it is placed in a tube furnace for degreasing and pre-sintering; (7) Place the tungsten skeleton in a tube furnace and place the copper block on the tungsten skeleton for high-temperature copper infiltration.
[0011] Furthermore, the ball milling time in step (1) should not be too long to avoid the particles from breaking during the ball milling process, generating a large amount of fine tungsten powder and introducing a large amount of impurity elements. The ball milling method is dry milling, so if the ball mill speed is too fast, it will easily cause slight oxidation of the tungsten powder.
[0012] Furthermore, in step (2), to improve the utilization rate of tungsten powder, a dry classifier is used to perform multiple airflow classifications on the tungsten powder, dividing the tungsten powder into multiple particle size ranges. The classifier speed is 1400 r / min. The tungsten powder after airflow classification should be dispersed and have a narrow particle size distribution.
[0013] Furthermore, in step (3), to avoid the slight oxidation of tungsten powder during ball milling and classification affecting the copper melting process, the classified tungsten powder is reduced by passing dry hydrogen through it at a low temperature for a period of time. The reduction time should not be too long, and the reduction temperature should be below 500℃ to avoid the tungsten powder from agglomerating during the reduction process.
[0014] Furthermore, in step (4), the amount of alcohol should not be excessive to avoid a gradient distribution of stearic acid concentration during the drying process.
[0015] Furthermore, in step (5), due to the presence of the binder, the tungsten powder is prone to agglomeration, which is not conducive to the uniformity of pores in the pressed blank. Therefore, the tungsten powder needs to be ball-milled and sieved.
[0016] Furthermore, a high pre-sintering temperature in step (6) can easily cause some fine pores to close due to sintering, so the sintering temperature should not be too high. The degreasing temperature should be higher than the decomposition temperature of stearic acid, and the holding time should be longer. The degreasing atmosphere is hydrogen, which can prevent the tungsten skeleton from being oxidized while further reducing the tungsten skeleton.
[0017] Furthermore, the melting temperature in step (7) should be higher than 1200℃. If the temperature is too low, the copper infiltration rate will be too slow and it will be difficult to penetrate into small pores, thus reducing the density of the tungsten copper alloy.
[0018] The key to this invention is to obtain tungsten powder with a narrow particle size distribution and good dispersibility. Specifically, it is obtained through air classification and ball milling. The ball milling process plays a role in de-agglomeration, fully crushing the soft agglomerated particles in the tungsten powder without further breaking the larger tungsten powder particles. In order to improve the utilization rate of tungsten powder, the tungsten powder is divided into multiple particle size ranges.
[0019] This invention uses stearic acid as a binder, which is low-cost. Since the decomposition products of stearic acid are gaseous, they will not introduce impurities into the tungsten framework. The decomposition temperature of stearic acid is above 300℃, and the hydrogen flow rate should be relatively high during degreasing to avoid excessive impurity atmosphere content inhibiting the decomposition of stearic acid. Attached Figure Description
[0020] Figure 1The 3-5μm tungsten powder of this invention is obtained after ball milling and air classification; Figure 2 This is a schematic diagram of the microstructure of the tungsten-copper alloy prepared in Example 1 of the present invention; Figure 3 This is a schematic diagram of the microstructure of the tungsten-copper alloy prepared in Example 2 of the present invention; Figure 4 The image shows a scanned image of the tungsten-copper alloy prepared in Comparative Example 1 of this invention. Detailed Implementation
[0021] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.
[0022] The experimental materials used in this invention include commercially available 5μm tungsten powder, stearic acid, anhydrous ethanol, etc., and the sintering atmosphere of the samples is hydrogen. Example
[0023] A method for preparing a uniformly structured tungsten-copper composite material involves obtaining uniformly dispersed tungsten powder through ball milling and air classification, and then preparing the tungsten-copper composite material by degreasing followed by copper infiltration using a melt infiltration method.
[0024] (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a speed of 200 r / min for 25 min; (2) The tungsten powder after ball milling was subjected to multiple air classification processes. The classifier was rotated at 1400 r / min and the resulting tungsten powder was divided into five particle size distribution ranges. Tungsten powder with a particle size of 1-3 μm was taken. (3) Reduce the graded tungsten powder at 450℃ for 2 hours with a hydrogen flow rate of 200 ml / min; Tungsten powder after ball milling, classification, and low-temperature reduction, such as Figure 1 As shown, tungsten powder exhibits good dispersibility and a narrow particle size distribution. Example
[0025] A method for preparing a uniformly structured tungsten-copper composite material involves obtaining uniformly dispersed tungsten powder through ball milling and air classification, and then preparing the tungsten-copper composite material by degreasing followed by copper infiltration using a melt infiltration method.
[0026] (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a speed of 200 r / min for 25 min; (2) The tungsten powder after ball milling was subjected to multiple air classification processes. The classifier was rotated at 1400 r / min and the resulting tungsten powder was divided into five particle size distribution ranges. Tungsten powder with a particle size of 1-3 μm was taken. (3) Reduce the graded tungsten powder at 450℃ for 2 hours with a hydrogen flow rate of 200 ml / min; (4) Weigh out 1.5% stearic acid and dissolve it in a small amount of alcohol. Mix the tungsten powder with the alcohol solution and sonicate for 20 minutes. (5) After the ultrasonic tungsten powder is dried at 55°C for 1.5h, it is ground and sieved to obtain tungsten powder for pressing. (6) After pressing the tungsten powder into blanks, they are placed in a tube furnace for degreasing and pre-sintering. The degreasing process includes holding at 340℃ for 90 min, holding at 440℃ for 100 min, and holding at 580℃ for 40 min. The pre-sintering process is holding at 1250℃ for 2 h. (7) Place the tungsten skeleton in a tube furnace and place the copper block on the tungsten skeleton. Keep it at 1300℃ for 3 hours with a hydrogen flow rate of 100ml / min.
[0027] The tungsten-copper alloy obtained in Example 2 was polished and its performance was tested, such as... Figure 2 As shown, the tungsten-copper alloy has a density of 98.5% and an electrical conductivity of 45% IACS. The microstructure of the tungsten-copper alloy is uniformly distributed, with no obvious copper enrichment or closure of the tungsten skeleton. Example
[0028] (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a speed of 200 r / min for 25 min; (2) The tungsten powder after ball milling was subjected to multiple air classification processes. The classifier was rotated at 1400 r / min and the resulting tungsten powder was divided into five particle size distribution ranges. Tungsten powder with a particle size of 3-5 μm was taken. (3) Reduce the graded tungsten powder at 450℃ for 2 hours with a hydrogen flow rate of 200 ml / min; (4) Weigh out 1.5% stearic acid and dissolve it in a small amount of alcohol. Mix the tungsten powder with the alcohol solution and sonicate for 20 minutes. (5) After the ultrasonic tungsten powder is dried at 55°C for 1.5h, it is ground and sieved to obtain tungsten powder for pressing. (6) After pressing the tungsten powder into blanks, they are placed in a tube furnace for degreasing and pre-sintering. The degreasing process includes holding at 340℃ for 90 min, holding at 440℃ for 100 min, and holding at 580℃ for 40 min. The pre-sintering process is holding at 1250℃ for 2 h. (7) Place the tungsten skeleton in a tube furnace and place the copper block on the tungsten skeleton. Keep it at 1300℃ for 3 hours with a hydrogen flow rate of 100ml / min.
[0029] The tungsten-copper alloy obtained in Example 3 was polished and its performance was tested, such as... Figure 3 As shown, the tungsten-copper alloy has a density of 98.8% and an electrical conductivity of 47.4% IACS. The microstructure of the tungsten-copper alloy is uniformly distributed, with no obvious copper enrichment or closure of the tungsten skeleton.
[0030] Comparative Example 1 (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a speed of 200 r / min for 25 min; (2) Reduce the ball-milled tungsten powder at 450℃ for 2 hours with a hydrogen flow rate of 200 ml / min; (3) Weigh out 1.5% stearic acid and dissolve it in a small amount of alcohol. Mix the tungsten powder with the alcohol solution and sonicate for 20 minutes. (4) After the ultrasonic tungsten powder is dried at 55°C for 1.5h, it is ground and sieved to obtain tungsten powder for pressing. (5) After the tungsten powder is pressed into a billet, it is placed in a tube furnace for degreasing and pre-sintering. The degreasing process includes holding at 340℃ for 90 min, holding at 440℃ for 100 min, and holding at 580℃ for 40 min. The pre-sintering process is holding at 1250℃ for 2 h. (6) Place the tungsten skeleton in a tube furnace and place the copper block on the tungsten skeleton. Keep it at 1300℃ for 3 hours with a hydrogen flow rate of 100ml / min.
[0031] The tungsten-copper alloy obtained in Example 1 will be polished and its performance tested, such as... Figure 3 As shown, the tungsten-copper alloy has a density of 97.8% and an electrical conductivity of 41.4% IACS. The microstructure of the tungsten-copper alloy is uneven, with obvious copper enrichment and tungsten skeleton closure.
Claims
1. A method for preparing a tungsten-copper composite material with uniform structure, characterized in that, The specific steps are as follows: (1) Place the raw tungsten powder in a ball mill jar and ball mill it at a low speed for a period of time; (2) The tungsten powder after ball milling was subjected to multiple airflow classification processes, and the resulting tungsten powder was divided into five particle size distribution ranges; (3) Reduce the graded tungsten powder at low temperature for a period of time; (4) Weigh a certain percentage of stearic acid and dissolve it in a small amount of alcohol. Mix the tungsten powder with the alcohol solution and sonicate. (5) After the ultrasonic tungsten powder is dried, it is ground and sieved to obtain tungsten powder for pressing. (6) After the tungsten powder is pressed into a billet, it is placed in a tube furnace for degreasing and pre-sintering; (7) Place the tungsten skeleton in a tube furnace and place the copper block on the tungsten skeleton for high-temperature copper infiltration.
2. The preparation method according to claim 1, characterized in that, Step (1) The ball mill speed is 150-250 r / min and the ball milling time is 25 min.
3. The preparation method according to claim 1, characterized in that, Step (2) The classifier speed is 1400 r / min.
4. The preparation method according to claim 1, characterized in that, Step (3) The reduction temperature is 350-500℃, the reduction time is 1-3h, and the hydrogen flow rate is 100-200ml / min.
5. The preparation method according to claim 1, characterized in that, Step (4) The stearic acid content is 1-1.5%.
6. The preparation method according to claim 1, characterized in that, Step (6) Degreasing process includes holding at 300-360℃ for 50-80 min, holding at 400-480℃ for 80-100 min, holding at 580-650℃ for 30-60 min, and the pre-sintering temperature is 1200-1400℃. The holding time is 1.5-2.5 h.
7. The preparation method according to claim 1, characterized in that, Step (7) The melting and infiltration temperature is 1250-1350℃, and the holding time is 1.5-3h.