Low-cost preparation method of WC-Co alloy

Abstract

The invention discloses a low-cost preparation method of a WC-Co alloy, and belongs to the technical field of hard alloys. The method comprises the following steps: mixing tungsten carbide powder and cobalt powder through wet grinding, and drying to obtain mixed powder; the mixed powder is dispersed in an additive aqueous solution, and WC-Co water-based slurry with the solid phase content being 89 wt%-92 wt% is prepared; carrying out printing molding on the obtained slurry at room temperature by adopting a direct writing type 3D printer to obtain a WC-Co composite material green body; and then the green body is subjected to degreasing and sintering treatment, and the WC-Co alloy is obtained. A water-based system is adopted, the using amount of a dispersing agent is small, the slurry is green and environmentally friendly, the prepared slurry has the high solid phase content and the good rheological property and is suitable for direct-writing 3D printing, the density of the obtained WC-Co alloy is larger than 98%, and the Vickers hardness is higher than 1800 HV30; and the process is simple, the equipment and raw material cost is low, efficient forming of the WC-Co alloy component in the complex shape can be achieved, and the method has good application prospects in the field of hard alloy additive manufacturing.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide, and more specifically to a low-cost preparation method for WC-Co alloy. Background Technology

[0002] Cemented carbide, with its excellent mechanical and wear-resistant properties, is widely used in machining, mining, aerospace, and other fields. Traditional cemented carbide forming processes are mature, but when manufacturing complex structural parts, they suffer from high mold design and manufacturing costs, cumbersome and difficult subsequent precision machining processes, and significant material waste, making it difficult to meet the demand for efficient and low-cost manufacturing of complex components. The rise of additive manufacturing technology has provided a new path for the preparation of complex cemented carbide components, enabling moldless direct forming and effectively solving the aforementioned drawbacks of traditional forming processes. Currently, additive manufacturing of WC-Co alloys mainly falls into two technical routes: one is powder melting technology based on hot forming. This technology, due to the rapid heating and cooling phenomenon during forming, has a large temperature gradient, which easily introduces defects such as brittle phases, porosity, and cracks into the formed parts, affecting product quality. At the same time, this technology requires large equipment investment, consumes a lot of energy, and has low powder utilization, further increasing manufacturing costs. Another type is the forming-debinding-sintering technology based on cold forming. Among them, the direct-write forming process has become an important development direction for WC-Co alloy additive manufacturing because it does not require powder spreading, has a relatively simple equipment structure, and low cost. Furthermore, it can produce high-density cemented carbide products after subsequent debinding and sintering. The core challenge of this technology lies in preparing a slurry that meets the requirements of direct-write forming. It must simultaneously possess high solid content, good stability, and suitable fluidity to ensure forming accuracy and subsequent sintering quality.

[0003] Currently, the slurries used in forming-debinding-sintering technology are mostly organic solvent systems. These slurries have problems such as high toxicity, pungent odor, and environmental unfriendliness. Moreover, organic solvents are expensive, which is not conducive to large-scale production. To solve these problems, related research has turned to the development of water-based slurries. However, existing water-based slurries usually require the addition of more than 1.9 wt% dispersant to optimize rheological properties, resulting in a still high slurry preparation cost. This makes it difficult to achieve low-cost, large-scale preparation of WC-Co alloys, thus limiting the widespread application of this technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing WC-Co alloy preparation and slurry preparation technologies, and to provide a low-cost preparation method for WC-Co alloys. The aim is to obtain a WC-Co water-based slurry with both good rheological properties and high solid content (≥89wt%), while achieving efficient and low-cost preparation of WC-Co alloys, and ensuring that the WC-Co alloys obtained after 3D printing and sintering have excellent density and hardness properties.

[0005] To achieve its objectives, the present invention employs the following technical solution: A low-cost method for preparing WC-Co alloys includes the following steps: (1) Preparation of WC-Co water-based slurry: Tungsten carbide powder and cobalt powder are wet-milled and mixed, and then dried to obtain mixed powder; the mixed powder is then dispersed in an aqueous solution of additives to prepare a WC-Co water-based slurry with a solid content of 89wt%-92wt%; (2) 3D printing: At room temperature, the WC-Co water-based slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite material green body of the desired shape; (3) Degreasing and sintering: The WC-Co composite material green blank is degreased and sintered to obtain WC-Co alloy.

[0006] As a preferred option, in step (1), the mass percentage of tungsten carbide powder to cobalt powder is 80%~96%:20%~4%.

[0007] As a preferred option, in step (1), anhydrous ethanol is used as the medium for wet grinding, and the wet grinding mixing time is 10~12h.

[0008] As a preferred option, in step (1), the drying temperature is 60~80℃ and the time is 8~10h.

[0009] As a preferred embodiment, the additive aqueous solution in step (1) is a mixed aqueous solution of ammonium citrate (AC) and polyethylene glycol (PEG), wherein the mass ratio of ammonium citrate to polyethylene glycol is 1~5:1, and the total mass percentage of ammonium citrate and polyethylene glycol in WC-Co water-based slurry is 1~1.2wt%.

[0010] As a preferred embodiment, in step (1), the mixed powder is dispersed in an aqueous solution of additives at room temperature.

[0011] The present invention further provides a WC-Co alloy prepared by the above preparation method.

[0012] Compared with the prior art, the beneficial effects of the present invention are reflected in: (1) The preparation method of the present invention uses green and environmentally friendly AC+PEG aqueous solution as a dispersion system. The amount of dispersant is small and the preparation process is environmentally friendly and pollution-free. At the same time, the dispersion system can make the mixed powder uniformly dispersed. The prepared WC-Co water-based slurry takes into account both high solid content and good fluidity. Its viscosity can be controlled at 7000mPa·s and below, which can meet the forming requirements of direct writing 3D printing process.

[0013] (2) The present invention effectively improves the solid content of WC-Co water-based slurry for direct writing 3D printing, increasing it to 89wt% or more, solving the problem that the existing water-based slurry has a low solid content and is difficult to meet the requirements of high-precision forming.

[0014] (3) The WC-Co alloy prepared by the method of the present invention has a density of over 98% and a Vickers hardness of over 1800 HV. 30 It possesses excellent mechanical properties and can meet the performance requirements of cemented carbide components in the industrial field. Attached Figure Description

[0015] Figure 1 The viscosity variation trend of WC-Co water-based slurry prepared in Examples 1-4 of this invention at different rotation speeds is shown in the figure. Figure 2 The graph shows the trend of the electrokinetic potential (zeta potential) of the WC-Co water-based slurry prepared in Example 4 of the present invention under different standing times. Figure 3 This is a picture of the WC-Co water-based slurry prepared in Example 4 of the present invention after being printed by a direct-write 3D printer; Figure 4 This is a microhardness indentation metallographic image of the WC-Co alloy prepared in Example 4 of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] The specific conditions of the traditional debinding-sintering process used in the following examples are as follows: Degreasing: Under a nitrogen atmosphere, the temperature is increased to 80°C at a rate of 5°C / min and held for 30 minutes, then increased to 400°C at a rate of 5°C / min and held for 30 minutes. The nitrogen flow rate is controlled at 150 mL / min.

[0018] Sintering: Under a nitrogen atmosphere, the temperature is increased to 1000℃ at a rate of 5℃ / min and held for 10 minutes, then increased to 1450℃ at a rate of 3℃ / min and held for 120 minutes. The nitrogen flow rate is controlled at 100 ml / min.

[0019] Example 1 A low-cost method for preparing WC-Co alloys includes the following steps: (1) Preparation of WC-Co water-based slurry: According to the mass ratio of tungsten carbide to cobalt of 92%:8%, tungsten carbide powder and cobalt powder were weighed and wet-milled with anhydrous ethanol as the medium for 12 hours. After thorough mixing, the powder was placed in a 70°C oven to dry for 10 hours and cooled to room temperature for later use. Then, 0.5961g of ammonium citrate (AC) and 0.5961g of polyethylene glycol (PEG) were weighed and dissolved in 9.7363g of deionized water to prepare a mixed aqueous solution with a mass ratio of AC to PEG of 1:1. The solution was left to stand at room temperature for later use. Finally, at room temperature, 88.4216g of the dried mixed powder was dispersed in the above AC+PEG mixed aqueous solution to prepare a WC-Co water-based slurry with a solid content of 89wt%.

[0020] (2) 3D printing: At room temperature, the WC-Co water-based slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite green body of the desired shape.

[0021] (3) Degreasing and sintering: The WC-Co composite material green blank obtained in step (2) is processed by traditional degreasing-sintering process to obtain WC-Co alloy.

[0022] Example 2 A low-cost method for preparing WC-Co alloys includes the following steps: (1) Preparation of WC-Co water-based slurry: According to the mass ratio of tungsten carbide to cobalt of 92%:8%, tungsten carbide powder and cobalt powder were weighed and wet-milled with anhydrous ethanol as the medium for 12 hours. After thorough mixing, the powder was placed in a 70°C oven to dry for 10 hours and cooled to room temperature for later use. Then, 1.0351g of ammonium citrate (AC) and 0.2072g of polyethylene glycol (PEG) were weighed and dissolved in 10.1495g of deionized water to prepare a mixed aqueous solution with a mass ratio of AC to PEG of 5:1. The solution was left to stand at room temperature for later use. Finally, at room temperature, 92.1418g of the dried mixed powder was dispersed in the above AC+PEG mixed aqueous solution to prepare a WC-Co mixed slurry with a solid content of 89wt%.

[0023] (2) 3D printing: At room temperature, the WC-Co mixed slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite green body of the desired shape.

[0024] (3) Degreasing and sintering: The WC-Co composite material green blank obtained in step (2) is processed by traditional degreasing-sintering process to obtain WC-Co alloy.

[0025] Example 3 A low-cost method for preparing WC-Co alloys includes the following steps: (1) Preparation of WC-Co water-based slurry: According to the mass ratio of tungsten carbide to cobalt of 92%:8%, tungsten carbide powder and cobalt powder were weighed and wet-milled with anhydrous ethanol as the medium for 12 hours. After thorough mixing, the powder was placed in a 70°C oven to dry for 10 hours and cooled to room temperature for later use. Then, 0.8103g of ammonium citrate (AC) and 0.8103g of polyethylene glycol (PEG) were weighed and dissolved in 9.1831g of deionized water to prepare a mixed aqueous solution with a mass ratio of AC to PEG of 1:1. The solution was left to stand at room temperature for later use. Finally, at room temperature, 124.2415g of the dried mixed powder was dispersed in the above AC+PEG mixed aqueous solution to prepare a WC-Co water-based slurry with a solid content of 92wt%.

[0026] (2) 3D printing: At room temperature, the WC-Co water-based slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite green body of the desired shape.

[0027] (3) Degreasing and sintering: The WC-Co composite material green blank obtained in step (2) is processed by traditional degreasing-sintering process to obtain WC-Co alloy.

[0028] Example 4 A low-cost method for preparing WC-Co alloys includes the following steps: (1) Preparation of WC-Co water-based slurry: Tungsten carbide powder and cobalt powder were weighed according to the mass ratio of tungsten carbide to cobalt of 92%:8%, and wet-milled and mixed with anhydrous ethanol as the medium for 12 hours. After thorough mixing, the powder was placed in a 70°C oven to dry for 10 hours and cooled to room temperature for later use. Then, a certain amount of 1.3751g ammonium citrate (AC) and 0.2750g polyethylene glycol (PEG) were weighed and dissolved in 9.3509g deionized water to prepare a mixed aqueous solution with a mass ratio of AC to PEG of 5:1. The solution was left to stand at room temperature for later use. Finally, at room temperature, 126.5123g of the dried mixed powder was dispersed in the above AC+PEG mixed aqueous solution to prepare a WC-Co water-based slurry with a solid content of 92wt%.

[0029] (2) 3D printing: At room temperature, the WC-Co water-based slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite green body of the desired shape.

[0030] (3) Degreasing and sintering: The WC-Co composite material green blank obtained in step (2) is processed by traditional degreasing-sintering process to obtain WC-Co alloy.

[0031] Figure 1The graphs show the viscosity trends of the WC-Co water-based slurries prepared in Examples 1-4 at different rotation speeds. As can be seen from the graphs, the slurries in each example exhibit significant shear-thinning characteristics: the viscosity decreases significantly with increasing rotation speed. This characteristic allows the slurry to maintain good flowability during extrusion and rapidly recover high viscosity after deposition to maintain shape accuracy during direct-write 3D printing, meeting the process requirements of direct-write forming. Among them, Example 4 (92wt% solid content, AC:PEG=5:1) exhibits moderate viscosity at low rotation speeds, excellent flowability at high rotation speeds, and superior overall rheological properties.

[0032] Figure 2 The figure shows the zeta potential variation trend of the WC-Co water-based slurry (92 wt.% solid content) prepared in Example 4 at different standing times. The figure shows that the zeta potential of the slurry remained consistently between approximately -32 mV and -42 mV within a standing time of 0–72 h, exhibiting a high absolute value and small variation. This indicates that the slurry maintains good dispersion stability even after prolonged standing, and is not prone to aggregation or sedimentation, thus ensuring a continuous and stable 3D printing process.

[0033] Figure 3 The image shows a gear component printed using a direct-write 3D printer after the WC-Co water-based slurry prepared in Example 4 was used. As can be seen in the image, the printed gear has a clear outline and complete tooth shape, with no obvious collapse or deformation, demonstrating that the slurry prepared in this invention has good formability and structural fidelity, enabling the direct forming of complex cemented carbide components.

[0034] Figure 4 This is a microhardness indentation metallographic image of the WC-Co alloy prepared in Example 4. The indentation edges are clear and free of obvious cracks, indicating a dense internal structure and uniform mechanical properties. Combined with performance test data, the alloy has a density exceeding 98% and a Vickers hardness higher than 1800 HV. 30 This meets the application requirements of cemented carbide in the industrial field.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost preparation method for WC-Co alloys, characterized in that, Includes the following steps: (1) Preparation of WC-Co water-based slurry: Tungsten carbide powder and cobalt powder are wet-milled and mixed, and then dried to obtain a mixed powder; the mixed powder is then dispersed in an additive aqueous solution to prepare a WC-Co water-based slurry with a solid content of 89wt%-92wt%; the additive aqueous solution is a mixed aqueous solution of ammonium citrate and polyethylene glycol, wherein the mass ratio of ammonium citrate to polyethylene glycol is 1~5:1, and the total mass percentage of ammonium citrate and polyethylene glycol in the WC-Co water-based slurry is 1~1.2wt%; (2) 3D printing: At room temperature, the WC-Co water-based slurry prepared in step (1) is printed using a direct-write 3D printer to obtain a WC-Co composite material green body of the desired shape; (3) Degreasing and sintering: The WC-Co composite material green blank is degreased and sintered to obtain WC-Co alloy.

2. The low-cost preparation method of WC-Co alloy according to claim 1, characterized in that: In step (1), the mass percentage of tungsten carbide powder to cobalt powder is 80%~96%:20%~4%.

3. The low-cost preparation method of WC-Co alloy according to claim 1, characterized in that: In step (1), anhydrous ethanol is used as the medium for wet milling, and the wet milling time is 10~12h.

4. The low-cost preparation method of WC-Co alloy according to claim 1, characterized in that: In step (1), the drying temperature is 60~80℃ and the time is 8~10h.

5. The low-cost preparation method of WC-Co alloy according to claim 1, characterized in that: In step (1), the mixed powder is dispersed in an aqueous solution of additives at room temperature.

6. A WC-Co alloy, characterized in that: The WC-Co alloy is prepared by any one of the low-cost preparation methods according to claims 1-6.

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