Ag-W composite spherical powder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metal composite material preparation, in particular to Ag-W composite spherical powder and a preparation method and application thereof. The preparation method comprises the following steps: mixing a silver source compound, a tungsten source compound, a binder, a dispersant and water, and performing wet ball milling to obtain suspension slurry; the mass ratio of Ag in the silver source compound to W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder; carrying out spray granulation on the suspension slurry to obtain spherical precursor particles; sequentially performing degreasing, in-situ reduction sintering and liquid-phase sintering on the spherical precursor particles to obtain the Ag-W composite spherical powder, the temperature of the liquid phase sintering is 980 to 1160 DEG C. The prepared Ag-W composite spherical powder is uniform in component, high in sphericity degree, high in density and excellent in flowability, and is particularly suitable for laser 3D printing.

Description

Technical Field

[0001] This invention relates to the field of metal composite material preparation technology, and in particular to an Ag-W composite spherical powder, its preparation method, and its application. Background Technology

[0002] Silver (Ag) is highly sought after for its excellent electrical and thermal conductivity, while tungsten (W) is valued for its high melting point, high hardness, and low coefficient of thermal expansion. Composite materials combining these two materials are in high demand in fields such as electrical contacts, electronic packaging materials, and high-temperature components. Laser 3D printing technology offers unprecedented possibilities for manufacturing Ag-W parts with complex geometries, but the successful application of this technology heavily depends on the quality of the powder raw materials.

[0003] Currently, mechanical ball milling is the main method for preparing Ag-W composite powders. This method has significant drawbacks: First, the large density difference between Ag and W makes them prone to segregation during powder feeding and spreading in 3D printing, leading to uneven composition and properties in the printed parts. Second, W powder has high hardness and irregular shape, making it difficult to mix uniformly with soft Ag powder; the W phase easily agglomerates, severely affecting the electrical and thermal conductivity and mechanical properties of the composite material. Finally, mechanically mixed powders have poor flowability, limiting the stability of the printing process and the accuracy of the formed parts.

[0004] To address these issues, researchers attempted to prepare spherical powders using a combination of spray granulation and sintering. Compared to mechanical mixing, the spherical powders prepared by directly spray granulating Ag and W powders followed by sintering exhibited significantly improved compositional uniformity, but were still not ideal. Furthermore, because W powder is difficult to deform and densify during sintering, and Ag and W are immiscible, traditional solid-state sintering methods lack sufficient kinetics, resulting in spherical powders with numerous internal pores and insufficient density (prone to defects such as spatter and pores during laser printing). Simultaneously, a hollow structure forms on the powder surface, reducing the sphericity and flowability of the powder. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an Ag-W composite spherical powder, its preparation method, and its applications. The Ag-W composite spherical powder prepared by this invention has uniform composition, high sphericity, high density, and excellent flowability, making it particularly suitable for laser 3D printing.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing Ag-W composite spherical powder, comprising the following steps: The silver source compound, tungsten source compound, binder, dispersant and water are mixed and then wet ball milled to obtain a suspension slurry; the mass ratio of Ag in the silver source compound and W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder; The suspension slurry was spray-granulated to obtain spherical precursor particles; The spherical precursor particles were sequentially degreased, subjected to in-situ reduction sintering, and liquid phase sintering to obtain the Ag-W composite spherical powder; the liquid phase sintering temperature was 980~1160℃.

[0007] Preferably, the in-situ reduction sintering temperature is 700~900℃, and the holding time is 0.5~2h; the in-situ reduction sintering is carried out in a hydrogen-containing atmosphere, and the volume fraction of hydrogen is 5~20%.

[0008] Preferably, the silver source compound includes silver oxide and / or silver carbonate; the tungsten source compound includes tungsten trioxide and / or ammonium paratungstate.

[0009] Preferably, the degreasing temperature is 350~500℃, and the holding time is 0.5~2h; the degreasing is carried out under a protective atmosphere.

[0010] Preferably, the holding time for liquid phase sintering is 0.5 to 2 hours; the liquid phase sintering is carried out under an inert atmosphere.

[0011] Preferably, the mass of the binder is 4-8% of the total mass of the silver source compound and the tungsten source compound; the mass of the dispersant is 0.5-1.5% of the total mass of the suspension slurry; and the solid content of the suspension slurry is 40-60 wt%.

[0012] Preferably, the conditions for wet ball milling include: a ball-to-material mass ratio of 6:1 to 10:1, a rotation speed of 180 to 250 rpm, and a milling time of 10 to 15 hours.

[0013] Preferably, the conditions for spray granulation include: an air inlet temperature of 160~250℃, an air outlet temperature of 90~110℃, and an atomizer speed of 18000~28000rpm.

[0014] The present invention provides Ag-W composite spherical powder prepared by the preparation method described above, which is composed of a continuous Ag matrix and a W reinforcing phase dispersed therein; the sphericity of the Ag-W composite spherical powder is not less than 0.9, the Hall flow rate is less than 25s / 50g, and the tap density of the Ag-W composite spherical powder is greater than 90% of its theoretical density.

[0015] This invention provides the application of the Ag-W composite spherical powder described above in laser 3D printing.

[0016] This invention provides a method for preparing Ag-W composite spherical powder, comprising the following steps: mixing a silver source compound, a tungsten source compound, a binder, a dispersant, and water, and then wet ball milling to obtain a suspension slurry; the mass ratio of Ag in the silver source compound to W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder; spray granulating the suspension slurry to obtain spherical precursor particles; and sequentially subjecting the spherical precursor particles to degreasing, in-situ reduction sintering, and liquid-phase sintering to obtain the Ag-W composite spherical powder; the liquid-phase sintering temperature is 980~1160℃.

[0017] This invention abandons the traditional physical mixing method and innovatively uses silver and tungsten source compounds as precursors. Through wet ball milling, the silver and tungsten source compounds are first uniformly mixed at the nanoscale. Then, after in-situ reduction sintering, Ag and W are formed, achieving atomic-level uniform mixing. This fundamentally solves the problems of W phase agglomeration and macroscopic segregation, resulting in Ag-W composite spherical powder with uniform composition. This invention utilizes the liquid-phase sintering effect of Ag to greatly promote the densification process, yielding spherical powders that are internally dense, have a smooth surface, and good flowability.

[0018] The results of the embodiments show that the Ag-W composite spherical powder prepared by the present invention consists of a continuous Ag matrix and a W reinforcing phase uniformly dispersed therein; the sphericity of the Ag-W composite spherical powder is not less than 0.9, the Hall flow rate is less than 25 s / 50 g, and the tap density of the Ag-W composite spherical powder is greater than 90% of its theoretical density. The Ag-W composite spherical powder prepared by the present invention has a uniform composition, and its sphericity, flowability, and tap density all meet or exceed the stringent requirements for powder materials in high-end metal 3D printing, laying a material foundation for printing high-density, high-performance Ag-W composite material parts.

[0019] Furthermore, the preparation method provided by this invention is highly versatile, with controllable parameters at each stage, and is highly compatible with existing ceramic and metal powder preparation equipment, thus possessing the potential for large-scale industrial production. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the preparation method of the present invention; Figure 2 The X-ray diffraction pattern of the Ag-W composite spherical powder prepared in Example 1; Figure 3 Scanning electron microscope image of the Ag-W composite spherical powder prepared in Example 1. Detailed Implementation

[0021] This invention provides a method for preparing Ag-W composite spherical powder, comprising the following steps: The silver source compound, tungsten source compound, binder, dispersant and water are mixed and then wet ball milled to obtain a suspension slurry; the mass ratio of Ag in the silver source compound and W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder; The suspension slurry was spray-granulated to obtain spherical precursor particles; The spherical precursor particles were sequentially degreased, subjected to in-situ reduction sintering, and liquid phase sintering to obtain the Ag-W composite spherical powder; the liquid phase sintering temperature was 980~1160℃.

[0022] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0023] This invention involves mixing a silver source compound, a tungsten source compound, a binder, a dispersant, and water, followed by wet ball milling to obtain a suspension slurry.

[0024] In this invention, the silver source compound preferably includes silver oxide (Ag₂O) and / or silver carbonate (Ag₂CO₃), more preferably Ag₂CO₃; the tungsten source compound preferably includes tungsten trioxide (WO₃) and / or ammonium paratungstate (AMT), more preferably AMT. This invention most preferably uses Ag₂CO₃ and AMT in combination. When Ag₂CO₃ and AMT are used in combination, this invention utilizes their decomposition temperature and product characteristics (i.e., during degreasing, Ag₂CO₃ decomposes into Ag₂O and CO₂, and AMT decomposes into WO₃, NH₃, and H₂O, with gas escape creating a porous structure) to create a highly active, large specific surface area reaction precursor before reduction, making the reduction reaction more complete and efficient, further optimizing the microstructure and properties of the powder. Specifically, it mainly optimizes the "compositional uniformity," "internal density," and "sphericity and flowability" of the prepared Ag-W composite spherical powder. The Ag-W composite spherical powder prepared by the present invention using the preferred precursor combination has the following optimized microstructure characteristics: the W reinforcing phase is dispersed in a continuous Ag matrix at a finer and more uniform nanoscale, and the porosity inside the powder is extremely low, with almost no closed pores.

[0025] In this invention, the mass ratio of Ag in the silver source compound and W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder. In this invention, the target mass content of Ag in the Ag-W composite powder is preferably 20-80%, and in specific embodiments it can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%, with the balance being W.

[0026] In this invention, the binder preferably comprises one or more of polyvinyl butyral (PVB), stearic acid, and polyethylene glycol (PEG); the mass of the binder is preferably 4-8% of the total mass of the silver-source compound and the tungsten-source compound, and in specific embodiments, it can be 4%, 5%, 6%, 7%, or 8%. In this invention, the dispersant preferably comprises ammonium polyacrylate and / or ammonium citrate; the mass of the dispersant is preferably 0.5-1.5% of the total mass of the suspension slurry, and in specific embodiments, it can be 0.5%, 0.8%, 1.0%, 1.2%, or 1.5%. In this invention, the function of the dispersant is to promote the uniform dispersion of the silver-source compound and the tungsten-source compound in the slurry.

[0027] In this invention, the amount of water used preferably satisfies the requirement that the solid content of the suspension slurry is 40-60 wt%. In specific embodiments, the solid content of the suspension slurry can be 40%, 45%, 50%, 55%, or 60%.

[0028] In this invention, the preferred conditions for wet ball milling include: a ball-to-material mass ratio of 6:1 to 10:1, a rotational speed of 180 to 250 rpm, and a milling time of 10 to 15 hours. In specific embodiments, the ball-to-material mass ratio can be 6:1, 7:1, 8:1, 9:1, or 10:1; the rotational speed can be 180, 200, 220, 230, or 250 rpm; and the milling time can be 10, 11, 12, 13, 14, or 15 hours. This invention preferably uses a planetary ball mill for the wet ball milling. In specific embodiments, zirconia balls are used as the grinding media. This invention achieves uniform mixing of silver-source compounds and tungsten-source compounds at the nanoscale through wet ball milling.

[0029] After obtaining the suspension slurry, the present invention performs spray granulation on the suspension slurry to obtain spherical precursor particles. In the present invention, the preferred conditions for spray granulation include: an inlet temperature of 160~250℃, an outlet temperature of 90~110℃, and an atomizer speed of 18000~28000rpm; in specific embodiments, the inlet temperature can be 160, 180, 200, 220, 230 or 250℃, the outlet temperature can be 90, 100 or 110℃, and the atomizer speed can be 18000, 20000, 22000, 24000, 26000 or 28000rpm.

[0030] After obtaining spherical precursor particles, the present invention sequentially degreases, performs in-situ reduction sintering and liquid phase sintering on the spherical precursor particles to obtain the Ag-W composite spherical powder.

[0031] In this invention, the degreasing temperature is preferably 350~500℃, and in specific embodiments, it can be 350, 400, 450, or 500℃; the holding time for degreasing is preferably 0.5~2h, and in specific embodiments, it can be 0.5, 1, 1.5, or 2h; the rate of heating to the degreasing temperature is preferably 4~6℃ / min, and in specific embodiments, it can be 5℃ / min. In this invention, the degreasing is preferably carried out under a protective atmosphere; the protective atmosphere is preferably a vacuum atmosphere or provided by a flowing inert gas; the inert gas can specifically be argon or nitrogen. This invention removes binders and residual moisture during the degreasing process. When Ag2CO3 is used as the silver source compound and AMT is used as the tungsten source compound, Ag2CO3 will decompose into Ag2O and CO2 during degreasing, and AMT will decompose into WO3, NH3, and H2O.

[0032] After the degreasing is completed, the present invention heats up (referred to as the first heating) to the temperature for in-situ reduction sintering and performs in-situ reduction sintering.

[0033] The first heating rate is preferably 4~6℃ / min, and in a specific embodiment it can be 5℃ / min. In this invention, the in-situ reduction sintering temperature is preferably 700~900℃, and in a specific embodiment it can be 700, 750, 800, 850 or 900℃; the holding time of the in-situ reduction sintering is preferably 0.5~2h, and in a specific embodiment it can be 0.5, 1, 1.5 or 2h; the in-situ reduction sintering is preferably carried out in a hydrogen-containing atmosphere, more preferably in a hydrogen-argon mixture; the volume fraction of hydrogen in the hydrogen-containing atmosphere is preferably 5~20%, and in a specific embodiment it can be 5%, 10%, 15% or 20%. In the in-situ reduction sintering process of this invention, the silver source and tungsten source are reduced to Ag and W. This invention first achieves uniform mixing of silver source compound and tungsten source compound at the nanoscale through wet ball milling combined with spray granulation, and then achieves uniform mixing at the atomic level through in-situ reduction sintering, which greatly improves the uniformity of microstructure of Ag-W composite spherical powder.

[0034] After completing the in-situ reduction sintering, the present invention raises the temperature (referred to as the second temperature rise) to the temperature for liquid phase sintering and performs liquid phase sintering.

[0035] In this invention, the second heating rate is preferably 2~4℃ / min, and in a specific embodiment, it can be 3℃ / min; the liquid phase sintering temperature is 980~1160℃, and in a specific embodiment, it can be 980, 1000, 1050, 1100, 1130, or 1160℃; the liquid phase sintering holding time is preferably 0.5~2h, and in a specific embodiment, it can be 0.5, 1, 1.5, or 2h; the liquid phase sintering is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere or an argon atmosphere. This invention utilizes the liquid phase sintering effect of Ag to greatly promote the densification process, resulting in spherical powders that are internally dense, have a smooth surface, and good flowability.

[0036] After the liquid phase sintering is completed, the present invention preferably cools the powder to room temperature in the furnace to obtain Ag-W composite spherical powder.

[0037] Those skilled in the art can also sieve and grade Ag-W composite spherical powder according to actual particle size requirements to obtain Ag-W composite spherical powder with the target particle size. For example, an air classifier can be used to process Ag-W composite spherical powder after liquid phase sintering to accurately screen out finished Ag-W composite spherical powder with a particle size range of 15~53μm.

[0038] Figure 1 This is a process flow diagram of the preparation method of the present invention. Figure 1 As shown, in this invention, a silver source compound, a tungsten source compound, a binder, a dispersant, and water are mixed and then wet-milled to obtain a suspension slurry; the suspension slurry is then spray-granulated to obtain spherical precursor particles; the spherical precursor particles are then subjected to debinding, in-situ reduction sintering, and liquid-phase sintering (i.e.,...) Figure 1 The Ag-W composite spherical powder is obtained by degreasing and in-situ reduction sintering. It can also be further sieved and graded according to the particle size requirements to obtain Ag-W composite spherical powder with the target particle size.

[0039] The present invention provides Ag-W composite spherical powder prepared by the preparation method described above, which is composed of a continuous Ag matrix and a W reinforcing phase dispersed therein; the sphericity of the Ag-W composite spherical powder is not less than 0.9, the Hall flow rate is less than 25s / 50g, and the tap density of the Ag-W composite spherical powder is greater than 90% of its theoretical density.

[0040] In this invention, the W-reinforcing phase is uniformly dispersed in the Ag continuous matrix.

[0041] The Ag-W composite spherical powder prepared by this invention has uniform composition, high sphericity, high density and excellent flowability, and is particularly suitable for laser 3D printing.

[0042] This invention provides the application of the Ag-W composite spherical powder described above in laser 3D printing. This invention does not specify any particular laser 3D printing method; it can be selective laser melting (SLM) or laser cladding deposition (LCD).

[0043] The Ag-W composite spherical powder, its preparation method, and its application provided by the present invention will be described in detail below with reference to the embodiments. However, these should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 This embodiment aims to prepare Ag-W composite spherical powder with a silver content of 70wt% and a tungsten content of 30wt%. The specific preparation method is as follows: First, the precursor slurry was prepared: Ag₂O and WO₃ powders were accurately weighed as raw materials and mixed according to an elemental mass ratio of Ag:W = 70:30. Then, 6% by weight of polyvinyl butyral (PVB) was added as a binder, and 1% by weight of ammonium polyacrylate as a dispersant. An appropriate amount of deionized water was added to adjust the slurry solid content to 50%. The mixture was placed in a planetary ball mill, using zirconia balls as the grinding media (ball-to-material mass ratio controlled at 8:1), and continuously ball-milled at 200 rpm for 12 hours to obtain a highly uniform and stable precursor suspension slurry. Next, spray drying granulation was performed: the obtained slurry was conveyed to a spray drying tower, with the inlet temperature set to 200℃, the outlet temperature to 100℃, and the atomizing disc speed adjusted to 22000 rpm, thereby obtaining Ag₂O-WO₃ composite precursor particles with good sphericity. Then, debinding and in-situ reduction sintering were performed: the precursor particles were placed in an atmosphere sintering furnace and first heated to 400°C at a heating rate of 5°C / min under flowing argon protection, and held for 1 hour to thoroughly remove the binder and residual moisture; subsequently, a hydrogen-argon mixture with a hydrogen gas fraction of 10% was introduced into the furnace, and heating continued at the same heating rate to 800°C, and held at this temperature for 1 hour to ensure that Ag₂O and WO₃ were completely reduced to metallic Ag and W; finally, the atmosphere was switched back to pure argon, and the temperature was increased to 1050°C at a rate of 3°C / min for liquid-phase sintering, held for 1 hour, and then cooled to room temperature with the furnace, utilizing the liquid phase of Ag to promote the final densification and spheroidization of the powder. Finally, sieving and grading were performed: the sintered powder was processed using an airflow classifier to accurately screen out finished Ag-W composite spherical powder with a particle size range of 15~53μm.

[0045] The Ag-W composite spherical powder prepared in Example 1 was characterized by XRD, and the results are shown in the figure. Figure 2 .Depend on Figure 2 It can be seen that the composite powder is phase-pure, consisting only of Ag and W phases. Scanning electron microscopy observation of the Ag-W composite spherical powder yielded the following results: Figure 3 ,Depend on Figure 3 It can be seen that the powder has good sphericity, the tungsten phase is uniformly dispersed in the silver matrix, the powder sphericity is tested to reach 0.92, the Hall flow rate is 23s / 50g, the flowability is good, and the tap density of the Ag-W composite spherical powder is 95% of its theoretical density.

[0046] Example 2 This embodiment demonstrates the preparation of Ag-W composite spherical powder with a silver-to-tungsten mass ratio of 1:1 (i.e., Ag-50wt%W) using a preferred raw material combination. The specific preparation method is as follows: Precursor slurry preparation: Ag₂CO₃ and secondary AMT were selected as reactants to achieve better decomposition and reduction kinetics. After weighing the raw materials according to the target ratio, 5% stearic acid (by mass) was added as a binder, and 1% ammonium polyacrylate was added as a dispersant. Deionized water was added to adjust the solid content to 50%. The mixture was then ball-milled in a planetary ball mill at a ball-to-material ratio of 8:1 and a speed of 200 rpm for 12 hours to form a uniform slurry. The spray drying granulation process parameters were the same as in Example 1. In the debinding and in-situ reduction sintering stages, the program settings have specific considerations: First, under an argon atmosphere, the temperature is raised to 480℃ at 3℃ / min and held for 1.5h. During this stage, the binder is removed, and Ag2CO3 decomposes into Ag2O and CO2, while AMT decomposes into WO3, NH3, and H2O. The escaping gases create a porous structure, which is then filled during subsequent liquid-phase sintering. Next, an argon-hydrogen mixture containing 15% hydrogen by volume is introduced, and the temperature is raised to 750℃ at 5℃ / min and held for 1.5h, fully utilizing the high activity of the precursor to achieve low-temperature, thorough in-situ reduction. Finally, under argon protection, the temperature is raised to 1080℃ for liquid-phase sintering, held for 1h, and then cooled with the furnace. After sintering, the powder undergoes airflow classification to obtain finished Ag-W composite spherical powder with a diameter of 15~53μm.

[0047] Performance tests show that the Ag-W composite spherical powder has a sphericity of up to 0.95 and a Hall flow rate of 20 s / 50 g. Microstructure analysis shows that its tungsten phase distribution is finer and more uniform, and the powder tap density is significantly improved. The tap density of the Ag-W composite spherical powder is 96.2% of its theoretical density, which verifies the synergistic advantages of the Ag2CO3 and AMT combination.

[0048] Comparative Example 1 This comparative example uses a traditional mechanical-physical mixing method to prepare Ag-30wt%W composite powder.

[0049] First, commercially available micron-sized spherical silver powder and irregularly shaped tungsten powder were selected as raw materials and accurately weighed according to a mass ratio of Ag:W = 70:30. The weighed raw materials were placed in a three-dimensional mixer and continuously mixed at 45 rpm for 4 hours to ensure the uniformity of physical mixing. After mixing, the properties of the resulting powder were characterized. The test results showed that the Hall flow rate of the mechanically mixed powder was 49 s / 50 g, indicating poor flowability. Scanning electron microscopy revealed obvious component segregation regions in the powder, uneven distribution of the silver and tungsten phases, and tungsten particles exhibiting settling and agglomeration due to their higher density.

[0050] Comparative Example 1 demonstrates that simple physical mixing cannot solve the problem of uniform composite between metals with large density differences, and cannot obtain spherical powder that meets the requirements of laser 3D printing.

[0051] Comparative Example 2 This comparative example uses the same precursor raw materials (Ag₂O and WO₃) and slurry preparation process as Example 1 of this invention, but only solid-state sintering is performed in the sintering stage, without utilizing the liquid-phase sintering effect of silver. The specific process is as follows: Precursor slurry is prepared according to the same formulation and ball milling parameters as in Example 1, and spherical precursor particles are obtained using the same spray drying process. Subsequently, the precursor particles are placed in a sintering furnace and heated directly to 900°C at a rate of 10°C / min under an argon-hydrogen mixed gas (10% H₂) atmosphere and held for 2 hours to complete the reduction of the oxides. This temperature is lower than the melting point of silver (961.78°C), therefore the entire process is solid-state sintering. After sintering, the powder is air-separated to obtain a finished product with a particle size of 15~53 μm. Performance testing shows that although the obtained powder has better compositional uniformity than the mechanical mixing method, its sphericity is only 0.78, and the Hall flow rate is 38 s / 50 g. More importantly, scanning electron microscopy revealed that the cross-section of the powder contained a large number of pores, and the degree of densification was much lower than that of the powder in Example 1 that had undergone liquid phase sintering. The tap density of the Ag-W composite spherical powder was 82% of its theoretical density.

[0052] Comparative Example 2 demonstrates that even with the same precursor, omitting the key liquid phase sintering step cannot yield high-density, high-sphericity, high-quality 3D printing powder, highlighting the necessity of the liquid phase sintering step in this invention.

[0053] Comparative Example 3 This comparative example adopts another common improvement approach in the current technology, that is, directly using commercial silver powder and tungsten powder for spray granulation and sintering, rather than the compound precursor route adopted in this invention.

[0054] The specific process is as follows: Commercially available micron-sized spherical silver powder and irregularly shaped tungsten powder were selected as raw materials and mixed at an Ag:W mass ratio of 70:30. A mixed slurry with a solid content of 50wt% was prepared using the same binder (PVB, 6%), dispersant (ammonium polyacrylate, 1%), deionized water, and ball milling process as in Example 1 (ball-to-particle ratio 8:1, 200 rpm). Subsequently, spherical precursor particles were obtained using the exact same spray granulation parameters as in Example 1 (inlet temperature 200°C, outlet temperature 100°C, atomizer speed 22000 rpm). The precursor particles were placed in an atmosphere sintering furnace. First, they were heated to 400℃ at 5℃ / min and held for 1 hour under an argon atmosphere for degreasing. Then, under pure argon protection, they were directly heated to 1100℃ (above the melting point of silver) at 5℃ / min and held for 1 hour to achieve densification through the liquid phase of Ag. Finally, they were cooled with the furnace and obtained as finished powder with a particle size of 15~53μm through airflow classification.

[0055] Performance testing showed that although the Ag-W composite powder obtained in Comparative Example 3 achieved a spherical morphology through spray granulation, its overall performance was unsatisfactory: the sphericity was only 0.85, the Hall flow rate was 32 s / 50 g, and the flowability was generally poor. More importantly, since the starting materials were physically mixed metal powders, the density difference during spray drying resulted in microscopic component segregation that could not be fundamentally resolved. Furthermore, the rigid W powder particles severely hindered the flow of molten Ag and pore filling during sintering, resulting in limited densification. Its tap density as a percentage of theoretical density was only 83.7%, significantly lower than that of Example 1 (95%) and Example 2 (96.2%).

[0056] Comparative Example 3 demonstrates that even with spray granulation and high-temperature liquid phase sintering, the traditional physical mixing method for metal powders still cannot overcome the fundamental defects of uneven W phase distribution and difficulty in densification. This illustrates the unique advantages of the present invention in achieving highly uniform composition and extremely dense structure by using a compound precursor combined with the "in-situ reduction + liquid phase sintering" strategy.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing Ag-W composite spherical powder, characterized in that, Includes the following steps: The silver source compound, tungsten source compound, binder, dispersant and water are mixed and then wet ball milled to obtain a suspension slurry; the mass ratio of Ag in the silver source compound and W in the tungsten source compound is the same as the target mass ratio of Ag to W in the Ag-W composite powder; The suspension slurry was spray-granulated to obtain spherical precursor particles; The spherical precursor particles were sequentially degreased, subjected to in-situ reduction sintering, and liquid phase sintering to obtain the Ag-W composite spherical powder; the liquid phase sintering temperature was 980~1160℃.

2. The preparation method according to claim 1, characterized in that, The in-situ reduction sintering temperature is 700~900℃, and the holding time is 0.5~2h; the in-situ reduction sintering is carried out in a hydrogen-containing atmosphere, with a hydrogen volume fraction of 5~20%.

3. The preparation method according to claim 1, characterized in that, The silver source compound includes silver oxide and / or silver carbonate; the tungsten source compound includes tungsten trioxide and / or ammonium paratungstate.

4. The preparation method according to claim 1, characterized in that, The degreasing temperature is 350~500℃, and the holding time is 0.5~2h; the degreasing is carried out under a protective atmosphere.

5. The preparation method according to claim 1, characterized in that, The holding time for liquid phase sintering is 0.5 to 2 hours; the liquid phase sintering is carried out under an inert atmosphere.

6. The preparation method according to claim 1, characterized in that, The mass of the binder is 4-8% of the total mass of the silver source compound and the tungsten source compound; the mass of the dispersant is 0.5-1.5% of the total mass of the suspension slurry; and the solid content of the suspension slurry is 40-60 wt%.

7. The preparation method according to claim 1, characterized in that, The conditions for wet ball milling include: a ball-to-material mass ratio of 6:1 to 10:1, a rotation speed of 180 to 250 rpm, and a milling time of 10 to 15 hours.

8. The preparation method according to claim 1, characterized in that, The conditions for spray granulation include: an air inlet temperature of 160~250℃, an air outlet temperature of 90~110℃, and an atomizer speed of 18000~28000rpm.

9. The Ag-W composite spherical powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It is composed of a continuous Ag matrix and a W-reinforcing phase dispersed therein; the sphericity of the Ag-W composite spherical powder is not less than 0.9, the Hall flow rate is less than 25s / 50g, and the tap density of the Ag-W composite spherical powder is greater than 90% of its theoretical density.

10. The application of the Ag-W composite spherical powder according to claim 9 in laser 3D printing.

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