A cobalt-low cemented carbide preparation process based on high-entropy alloy

Abstract

The application discloses a preparation process of low-cobalt hard alloy based on high-entropy alloy, which reduces the cobalt content to less than 1%, controls the number of cobalt pools to improve the wear resistance of the alloy, and utilizes the multi-component structure of the high-entropy alloy to cooperate with the water bath drying process and the plasma sintering and hot pressing process with high temperature, so that each element is uniformly dispersed in the hard alloy, and the sintered hard alloy has strong mechanical properties. The sintering process of high-temperature pressing by discharging plasma is adopted, the alloy dispersion strengthening mechanism is utilized to improve the performance of the alloy, the micropore problem of the alloy can be well solved, and the density is higher and better than that of conventional pressing; the high-entropy alloy contains Cr, Ni and Ti elements, and has better high-temperature resistance, corrosion resistance and wear resistance. The hard alloy prepared by the above process has excellent polishing performance and wear resistance, and has high fracture toughness.

Description

Technical Field

[0001] This invention relates to the preparation of cemented carbide, specifically a low-cobalt cemented carbide preparation process based on high-entropy alloys. Background Technology

[0002] Cemented carbide is a composite material made by sintering metal carbides, mainly composed of a hardening phase and a binder phase. Tungsten carbide-based cemented carbides use cobalt as the binder phase and have the advantages of high hardness, high wear resistance, and high elastic modulus, and are widely used in cutting tools, stamping drill bits, etc. Cobalt powder is a very important raw material in the production process of cemented carbide. However, due to the high price of cobalt powder and its radioactivity, which is harmful to the human body, research and development of sintering processes for low-cobalt cemented carbides has begun in the current technology field.

[0003] The distribution of cobalt in cemented carbide greatly affects its performance. Currently, the cobalt content of low-cobalt alloys on the domestic market needs to be controlled between 2.5% and 3.0%. If the cobalt content is further reduced, it will not be able to play a role in binding the hardened phase grains.

[0004] Conventional sintering uses graphite heating elements for heating and sintering, transferring heat through thermal radiation. However, this results in uneven temperature distribution and unstable sintering performance. Conventional techniques involve ordinary pressing followed by low-pressure sintering, which often leads to defects in cemented carbides such as micropores and cobalt pools, degrading the alloy's performance. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a process for preparing low-cobalt cemented carbide based on high-entropy alloys, characterized by comprising the following steps:

[0006] S1. Tungsten carbide powder and high-entropy alloy powder are added to a ball mill in a weight ratio of 98:2 to 99:1; the high-entropy alloy powder contains five elements: Co, Cr, Ni, Ti, and W.

[0007] S2. Add wet grinding media to the ball mill and rotate the ball mill to dry the slurry obtained by wet grinding in a water bath.

[0008] S3. Sift the dried product to make powder;

[0009] S4. The powder prepared in S3 is subjected to discharge plasma pressing sintering and then cooled.

[0010] Furthermore, the molar ratio of Co, Cr, and Ni in the high-entropy alloy is between 0.9 and 1.0.

[0011] Furthermore, the step of discharge plasma pressing and sintering includes placing the powder made of S3 in a graphite mold, sintering it using a discharge plasma device under a pressure of 30-55 MPa, controlling the sintering temperature at 1600-1750°C, and holding it at that temperature for 5-10 minutes.

[0012] Furthermore, in the ball milling process of S2, the wet grinding media is alcohol with a concentration of not less than 99%, which is added to the ball mill at a solid-liquid ratio of 300-330 ml / kg and a ball-to-material ratio of 4:1-5:1.

[0013] Furthermore, the ball mill speed is 40-50 r / min, and the ball milling time is 60-84 h.

[0014] Furthermore, in the S2 water bath drying process, the water bath temperature is 90-95°C, and the drying time lasts for 4-5 hours.

[0015] Furthermore, the particle size of the tungsten carbide powder is 0.10-0.25 μm.

[0016] This invention provides a process for preparing low-cobalt cemented carbide based on high-entropy alloys. Tungsten carbide powder is mixed with high-entropy alloy powder, and then hot-pressed and sintered using a spark plasma device to prepare a high-hardness low-cobalt cemented carbide.

[0017] The principle of this invention is to reduce the cobalt content to less than 1%, thereby controlling the number of cobalt pools, and to utilize the stable multi-component structure of high-entropy alloys, combined with a high-temperature water bath drying process and a plasma sintering hot pressing process, so that each element is uniformly dispersed in the cemented carbide, and the sintered cemented carbide has strong mechanical properties.

[0018] This invention employs a high-temperature sintering process using spark plasma pressing, leveraging the alloy dispersion strengthening mechanism to improve alloy properties. This effectively addresses the microporosity problem of the alloy, resulting in higher and better density compared to conventional pressing. The high-entropy alloy contains Cr, Ni, and Ti elements, exhibiting superior high-temperature resistance, corrosion resistance, and wear resistance. The cemented carbide prepared using this process possesses excellent polishing properties and wear resistance, as well as high fracture toughness. Attached Figure Description

[0019] Figure 1 This is a surface polishing diagram of Example 1, with a scale bar of 200 μm;

[0020] Figure 2 This is a metallographic micrograph of Example 1, with a scale bar of 10 μm;

[0021] Figure 3 This is a surface polishing diagram of Comparative Example 1, with a scale bar of 200 μm;

[0022] Figure 4 This is a metallographic micrograph of Comparative Example 3, with a scale bar of 10 μm;

[0023] Figure 5 This is a metallographic micrograph of Comparative Example 4, with a scale bar of 10 μm. Detailed Implementation

[0024] The purpose of this invention is to provide a low-cobalt cemented carbide preparation process, using tungsten carbide as the hard phase and a high-entropy alloy instead of cobalt as the binder phase in conventional techniques. The high-entropy alloy is composed of five elements: Co, Cr, Ni, Ti, and W, with a mass ratio of tungsten carbide to high-entropy alloy of 98:2-99:1. The principle of this invention is to reduce the cobalt content to less than 1%, thereby controlling the number of cobalt pools. Adding Cr, Ni, and Ti elements to the alloy increases the high-temperature resistance, corrosion resistance, and wear resistance of the low-cobalt cemented carbide. The multi-component structure of the high-entropy alloy ensures uniform dispersion of the alloying elements. Combined with a high-temperature water bath drying process and a plasma sintering hot pressing process, the sintered cemented carbide exhibits strong mechanical properties.

[0025] Example 1 describes a process for preparing low-cobalt cemented carbide based on the above principle, including the following steps:

[0026] Tungsten carbide powder with a particle size of 0.10 μm and high-entropy alloy powder were added to a ball mill at a weight ratio of 98:2; the molar ratio of Co, Cr, Ni, Ti, and W in the high-entropy alloy was 1:1:1:0.5:0.8. Wet grinding media were added to the ball mill for rotary ball milling, and the slurry obtained from the wet milling was dried. The dried product was then vibrated and sieved to form powder, which was then loaded into a mold and sintered using spark plasma pressing to finally obtain the desired low-cobalt cemented carbide.

[0027] The wet grinding media is alcohol with a concentration of not less than 99%, which is added to the ball mill at a solid-liquid ratio of 300 ml / kg and a ball-to-material ratio of 4:1; the ball mill speed is 40 r / min and the ball milling time is 60 h.

[0028] The wet abrasive slurry is dried using a water bath at 90°-95°C, which can maintain uniform temperature dispersion and the drying time lasts for 4-5 hours.

[0029] The sintering temperature of spark plasma sintering is 1600-1750°C, with a holding time of 5-10 minutes and a sintering pressure of 30-55 MPa. Compared with conventional techniques that rely on radiation for convection and heat transfer, spark plasma sintering has the advantage of high heat utilization. Pressing the alloy at high temperatures effectively solves the micropore problem. Furthermore, the rapid heating and short sintering time of spark plasma sintering prevent the oxidation of cobalt.

[0030] Example 2: The same wet milling, water bath drying, sieving and granulation, and spark plasma pressing sintering processes as Example 1 were used. The difference was that the ratio of tungsten carbide powder to high-entropy alloy powder added to the ball mill was 98.5:1.5, the molar ratio of Co, Cr, Ni, Ti, and W in the high-entropy alloy was 0.9:1:1:0.5:0.6, and the particle size of the tungsten carbide powder was 0.15 μm. In the wet milling process, the wet milling media was added at a solid-liquid ratio of 300 ml / kg and a ball-to-material ratio of 4:1. The ball mill speed was 40 r / min, and the ball milling time was 60 h.

[0031] Example 3: The same wet milling, water bath drying, sieving and granulation, and spark plasma pressing sintering processes as Example 1 were used. The difference was that the ratio of tungsten carbide powder to high-entropy alloy powder added to the ball mill was 99:1.0, the molar ratio of Co, Cr, Ni, Ti and W in the high-entropy alloy was 1:0.9:1:0.7:0.4, and the particle size of the tungsten carbide powder was 0.20 μm. In the wet milling process, the wet milling media was added at a solid-liquid ratio of 320 ml / kg and a ball-to-material ratio of 5:1. The ball mill speed was 46 r / min, and the ball milling time was 76 h.

[0032] Example 4: The same wet milling, water bath drying, sieving and granulation, and spark plasma pressing sintering processes as Example 1 were used. The difference was that the ratio of tungsten carbide powder to high-entropy alloy powder added to the ball mill was 98.3:1.7, 1:1:0.9:0.7:0.4, and the particle size of the tungsten carbide powder was 0.25 μm. In the wet milling process, the wet milling media was added at a solid-liquid ratio of 330 ml / kg and a ball-to-material ratio of 4.8:1. The ball mill speed was 50 r / min, and the ball milling time was 84 h.

[0033] Comparative Example 1: The raw material used was a conventional low-cobalt alloy containing cobalt, nickel, and tungsten carbide in a mass ratio of 2.5:0.5:97, with a tungsten carbide particle size of 0.6 μm. The above raw materials were added to a ball mill containing 2 parts by mass of paraffin powder. Wet grinding media were added to the ball mill for rotary ball milling, and the slurry obtained from wet milling was spray-dried and granulated. After molding in a mold, it was sintered under low pressure.

[0034] The wet grinding media is alcohol with a concentration of not less than 99%, which is added to the ball mill at a solid-liquid ratio of 320 ml / kg and a ball-to-material ratio of 4:1; the ball mill speed is 50 r / min, the ball milling time is 70 h; the sintering temperature is 1390-1400℃, and the sintering pressure is 5-9 MPa.

[0035] Comparative Example 2: The raw materials used were the same as those used in Comparative Example 1, with the difference being that the sintering temperature was increased to 1700-1800℃.

[0036] Comparative Example 3: 0.2 μm ultrafine WC powder, Co powder, Cr powder, Ni powder, Ti powder, and W powder were added to a ball mill in a weight ratio of 98:0.5:0.5:0.5:0.2:0.3, and ball milling, hot water drying, granulation, and spark plasma pressing sintering were performed according to the parameters of Example 1.

[0037] Comparative Example 4: The same proportion of ultrafine WC powder and high-entropy alloy powder as in Example 1 were added to a ball mill containing 2 parts by weight of paraffin powder, and ball milling, spray drying, granulation and low-pressure sintering were carried out according to the parameters and steps of Comparative Example 1.

[0038] The cemented carbides obtained in Examples 1-3 and Comparative Examples 1-3 were tested for the following properties:

[0039] 1. Observe the surface of cemented carbide under a high-magnification metallographic microscope, determine the maximum size of the alloy grinding pores, and evaluate the grain size of cemented carbide by comparison with metallographic images.

[0040] 2. The hardness of cemented carbide under a 10kg load was determined using a Vickers hardness tester;

[0041] 3. After the above-mentioned cemented carbide is shaped, it is placed into a molding test machine. The molding object is a glass lens. The quality of the glass lens is checked under a molding pressure of 5kN, and the molding process is repeated. When the quality of the molded lens is unqualified, the molding object needs to be repaired or replaced. The total number of molding times before repair is the number of single molding times.

[0042] 4. Test the coefficient of thermal expansion of the molded product using a thermal expansion meter at 700°C.

[0043] The performance test results of Examples 1-4 and Comparative Examples 1-3 are shown in the table below:

[0044]

[0045] The data in the table shows that the performance of the embodiments is relatively stable, all achieving a hardness of approximately HV102600, which is a significant improvement compared to the comparative example, meeting the requirements of existing technology. Figure 1 and Figure 2 As shown, the alloy surface has no visible micropores under a 200µm microscope. At the same time, due to the cobalt content of less than 1%, it is not easy to aggregate and form cobalt pools, which brings about a significant improvement in mechanical properties and alloy life.

[0046] Porosity is a crucial evaluation indicator for cemented carbide, significantly impacting its strength and machinability. Minimizing porosity is essential during cemented carbide processing. Comparative Example 1 reflects the traditional sintering approach, controlling the cobalt powder content to approximately 2.5%-3% and sintering the molded alloy powder at a relatively low pressure within a specified sintering temperature to reduce porosity. While the porosity of the cemented carbide in Comparative Example 1 meets expectations, the difficulty in controlling the uniform distribution of cobalt and the molding density in conventional techniques means that cobalt pools and micropores still exist in the cemented carbide.

[0047] Conventional negative pressure dewaxing processes can lead to incomplete dewaxing and residual wax pores. Improper density control during pressing can also result in residual porosity in the alloy. Furthermore, uneven cobalt distribution creates cobalt pools, resulting in poor alloy polishing performance and failing to meet the precision production requirements of molds. (See attached image) Figure 3 The metallographic micrographs shown indicate that cobalt was not evenly distributed to form a cobalt pool, which greatly affected the lifespan of the alloy. The number of single molding cycles under 5kN conditions was only around 200. The measured coefficient of thermal expansion also showed that the alloy in Comparative Example 1 had poor thermal stability.

[0048] Comparative Example 2 increased the sintering temperature compared to Comparative Example 1. Due to the volatilization of cobalt at high temperatures and the excessively high sintering temperature, a certain amount of porosity was formed inside the alloy. Although the thermal expansion system was slightly lower than that of Comparative Example 1, the hardness of the alloy decreased significantly, and therefore it is not used in existing technologies. At the same time, since the cobalt content is between 2.5% and 3%, spark plasma hot pressing cannot be used for sintering. A relatively large amount of binder phase would be squeezed out during the sintering process, causing the pressing mold to be scrapped due to sticking.

[0049] Combination Figure 4 Comparative Example 3 has similar raw material composition and processing technology to Example 1, the difference being that Comparative Example 3 uses multiple single-element powders mechanically added to the ball mill. Since the cobalt powder content is less than 1%, it is difficult to form a cobalt pool; however, during ball milling, the elements are difficult to distribute evenly, failing to form a dense structure, and the alloy surface still produces many pores. This also results in the alloy hardness and alloy life not being significantly improved compared to conventional methods.

[0050] The raw material composition of Comparative Example 4 was the same as that of Example 1, with the addition of tungsten carbide and high-entropy alloy powder. The sintering process employed conventional techniques of spray drying and low-pressure sintering. Figure 5 As shown, the alloy exhibits a large number of visible pores, and its lifespan and hardness are lower than those of Comparative Example 1, which was processed using conventional techniques. This is because under the conditions of thermal radiation sintering, heat utilization is low, and it is difficult for low-cobalt-content alloys to form a highly dense structure.

[0051] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A process for preparing low-cobalt cemented carbide based on high-entropy alloys, characterized in that: It includes the following steps: S1. Tungsten carbide powder and high-entropy alloy powder are added to a ball mill in a weight ratio of 98:2 to 99:1; the high-entropy alloy powder is composed of five elements: Co, Cr, Ni, Ti, and W, wherein the molar ratio of each element Co, Cr, and Ni is between 0.9 and 1.

0. S2. Add wet grinding media to the ball mill and rotate the ball mill to dry the slurry obtained by wet grinding in a water bath. S3. Sift the dried product to make powder; S4. Perform spark plasma pressing sintering on the powder prepared in S3 and cool it; the spark plasma pressing sintering step includes placing the powder prepared in S3 in a graphite mold, using a spark plasma device to sinter it under a pressure of 30-55 MPa, controlling the sintering temperature at 1600-1750°C, and holding it at that temperature for 5-10 minutes.

2. The low-cobalt cemented carbide preparation process based on high-entropy alloys as described in claim 1, characterized in that: In the S2 ball milling process, the wet grinding media is alcohol with a concentration of not less than 99%, which is added to the ball mill at a solid-liquid ratio of 300-330 ml / kg and a ball-to-material ratio of 4:1-5:

1.

3. The low-cobalt cemented carbide preparation process based on high-entropy alloys as described in claim 2, characterized in that: The ball mill speed is 40-50 r / min, and the ball milling time is 60-84 h.

4. The low-cobalt cemented carbide preparation process based on high-entropy alloys as described in claim 1, characterized in that: In the S2 water bath drying process, the water bath temperature is 90-95°C, and the drying time lasts for 4-5 hours.

5. The low-cobalt cemented carbide preparation process based on high-entropy alloys as described in claim 1, characterized in that: The tungsten carbide powder has a particle size of 0.10-0.25 μm.

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