A precise pretreatment method of wc-co alloy powder suitable for non-uniform twin structure

Abstract

The application discloses a WC-Co alloy powder precision pretreatment method suitable for non-uniform twin crystal structure and belongs to the technical field of hard alloy material preparation. The method comprises the following steps: preparing mixed powder 1 by wet grinding of coarse-grained WC powder and cobalt powder with alcohol; preparing mixed powder 2 by pre-sintering of fine-grained WC powder and cobalt powder at 700-800 DEG C; three-dimensionally mixing the mixed powder 1 and the mixed powder 2 according to a mass ratio of (7-8):(2-3) to obtain mixed material 3; adding the mixed material 3 into a composite mixed solution composed of oleic acid, paraffin and alcohol, and stirring the solution in a water bath to obtain dark gray slurry; drying, crushing and sieving the slurry, and then performing compression molding to obtain non-uniform twin crystal hard alloy after sintering. The method provided by the application effectively solves the problems of agglomeration, cobalt segregation and green body layering in the pretreatment of twin crystal structure powder, and improves the consistency and stability of alloy performance.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide material preparation technology, and in particular to a precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures. Background Technology

[0002] WC-Co cemented carbide, with its excellent hardness, wear resistance, and mechanical stability, has become a core industrial material in metal processing, mining, and other fields. Among them, the bicrystalline non-uniform structure is a key technological direction for overcoming the contradiction between hardness and toughness in traditional WC-Co alloys.

[0003] However, in existing manufacturing processes, the technical shortcomings of the powder pretreatment stage have become a core bottleneck restricting the full realization of the properties of the bicrystalline structure. Firstly, the fine-grained WC required for the bicrystalline structure has a large specific surface area and high surface energy, making it prone to forming tight hard agglomerates due to intermolecular van der Waals forces. Existing pretreatment processes mostly use single-acid dispersion or conventional mechanical stirring, lacking targeted anti-agglomeration control methods. This leads to the formation of hard agglomerates between fine-grained WC particles, destroying the powder uniformity and consequently affecting the uniformity of the sintered structure and the overall performance of the alloy. Secondly, existing pretreatment processes have not formed a synergistic system adapted to the bicrystalline structure. Some processes directly mix solid paraffin with the powder without first dissolving the paraffin in a solvent to form a homogeneous solution, resulting in paraffin agglomeration on the powder surface and a high delamination rate during cold pressing. Furthermore, the drying stage often uses natural drying or high-temperature rapid drying. Natural drying is time-consuming and prone to powder settling and forming hard agglomerates, while high-temperature drying causes premature melting and loss of paraffin, losing its binding and molding-aiding effects. The aforementioned problems ultimately lead to large performance fluctuations in the bicrystalline structure, making it difficult to meet the requirements of industrial mass production for product consistency and stability.

[0004] Therefore, it is necessary to develop a precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures, so as to provide key technical support for the industrial preparation of high-performance non-uniform bicrystalline WC-Co cemented carbide. Summary of the Invention

[0005] To address the bottlenecks in existing technologies, such as hard agglomeration of fine-grained WC, uneven distribution of forming agents, and difficulty in synergistic performance of bicrystalline structures, this invention provides a precise pretreatment method for WC-Co alloy powder adapted to bicrystalline non-uniform structures. This method first involves low-temperature pre-calcination of a mixture of fine-grained WC and high-cobalt powder, allowing cobalt to form a uniform coating layer on the surface of the fine-grained WC through solid-phase diffusion, thereby suppressing van der Waals hard agglomeration of the fine-grained WC. Based on this, a three-dimensional mixture of coarse-grained WC-low-cobalt powder and fine-grained WC-high-cobalt pre-calcined powder is performed at a specific mass ratio to achieve a gradient cobalt distribution with low cobalt in the coarse-grained region and high cobalt in the fine-grained region, ensuring both the toughness of the coarse-grained framework and the hardness enhancement of the fine-grained structure. Finally, the mixed powder is wetted using a ternary composite liquid of oleic acid, paraffin wax, and alcohol under controlled-temperature water bath conditions, allowing paraffin wax to uniformly coat the powder surface in solution form. Temperature-controlled drying is then performed to prevent paraffin wax loss, completely resolving the problem of green body delamination. Therefore, this pretreatment method is fully adapted to the special requirements of non-uniform bicrystalline structures for powder dispersibility, cobalt phase distribution uniformity, and molding quality.

[0006] The technical solution of the present invention is as follows: A precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures, characterized by comprising the following steps: Step 1: Add coarse WC powder and cobalt powder to a ball mill, add dispersing media and ball mill to obtain a mixed slurry. After drying the slurry, obtain mixture 1. Step 2: After mixing fine-grained WC powder and cobalt powder evenly, pre-calcination is performed to obtain mixture 2; Step 3: Add mixed powder 1 and mixed powder 2 into the three-dimensional mixer and mix to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture of oleic acid, paraffin and alcohol, then heat and stir in a water bath to obtain a dark gray slurry; Step 5: Dry the slurry obtained in Step 4, crush it into powder and sieve it to obtain pretreated mixed powder; press the pretreated mixed powder into shape, and then sinter it through a preset sintering process to finally obtain a non-uniform bicrystalline hard alloy.

[0007] Preferably, in step 1, the particle size of the coarse-grained WC powder is 10-30 μm; the particle size of the cobalt powder is 1.0-3.0 μm; and the amount of cobalt powder added is 6-8% of the total mass of the coarse-grained WC powder and the cobalt powder.

[0008] Preferably, in step 1, the amount of the dispersion medium added is 40-60% of the total mass of coarse-grained WC powder and cobalt powder, and the dispersion medium is 96-98 vol% alcohol.

[0009] Preferably, in step 1, the ball mill rotation speed is 250-300 r / min, the time is 5-6 h, and the ball-to-material ratio is (3-5):1.

[0010] Preferably, in step 2, the particle size of the fine-grained WC powder is 0.5-1 μm; the particle size of the cobalt powder is 1.0-3.0 μm; and the amount of cobalt powder added is 10-12% of the total mass of the fine-grained WC powder and the cobalt powder.

[0011] Preferably, in step 2, the pre-firing temperature is 700-800℃ and the pre-firing time is 2-3 hours.

[0012] Further explanation of the present invention: In step 2, after mixing fine-grained WC powder with a higher content of cobalt powder, a pre-calcination treatment is performed at 700-800°C for 2-3 hours. This temperature is lower than the melting point of cobalt and the liquid-phase sintering temperature of the WC-Co alloy. At this temperature, cobalt diffuses on the surface in solid form and forms a thin and uniform coating layer on the surface of the fine-grained WC particles, achieving weak bonding between particles and forming a loose aggregate structure. This can stabilize the dispersion state of fine-grained WC without generating dense agglomerates. This loose aggregate has a certain structural strength, which can resist van der Waals forces in subsequent mixing and stirring processes, preventing the fine-grained WC from hard agglomerating again. At the same time, the pre-calcination process can clean the particle interface and generate a small amount of interfacial diffusion, improving the interfacial bonding strength between WC and the cobalt phase during subsequent sintering and reducing the generation of sintering defects. In addition, the cobalt phase is uniformly attached to the surface of the fine-grained WC, which can effectively suppress the segregation of cobalt powder in subsequent processes and provide a structural basis for the uniform distribution of the cobalt phase in the bicrystalline system. If this pre-firing step is omitted, the fine-grained WC will exhibit severe hard agglomeration, and the cobalt phase distribution will be severely uneven, resulting in a significant decrease in the alloy's hardness and bending strength.

[0013] Preferably, in step 3, the mixed powder 1 and mixed powder 2 are added to the three-dimensional mixer in a mass ratio of (7-8):(2-3) and mixed; the rotation speed of the three-dimensional mixer is 40-60Hz and the mixing time is 22-25h.

[0014] Regarding a further explanation of the present invention, in step 3, mixed powder 1 and mixed powder 2 are added to a three-dimensional mixer at a mass ratio of (7-8):(2-3). This ratio is based on a multi-dimensional design considering the synergistic effect of bicrystalline structure particle size, the gradient distribution of the cobalt phase, the densification during molding and sintering, and the balance of mechanical properties. The coarse-grained WC content of 70-80% serves as a tough skeleton to ensure the fracture toughness and impact resistance of the alloy, avoiding excessive fine-grained content which could lead to increased brittleness. The fine-grained WC content of 20-30% serves as a hardness-enhancing phase, improving hardness and wear resistance without sacrificing toughness. A content exceeding 30% will damage the coarse-grained skeleton, leading to a decrease in flexural strength, while a content below 20% will result in insufficient strengthening effect. Simultaneously, the low cobalt content of mixed powder 1 and the high cobalt content of mixed powder 2, through this ratio, control the overall cobalt content at 6.8-9.6%, forming a gradient distribution of high cobalt in the fine-grained region and low cobalt in the coarse-grained region. The high cobalt in the fine-grained region compensates for the brittleness defect of the fine grains, while the low cobalt in the coarse-grained region ensures rigidity. Furthermore, the coarse grains are fully filled by the fine grains to form a dense packing structure. The gradient cobalt phase generates a liquid phase flow gradient driving force during sintering, which promotes densification and reduces porosity. When the proportion of fine grains is too low, the hardness strengthening effect is insufficient and the twinning structure characteristics are not obvious. When the gradient cobalt design is removed, the expected twinning structure cannot be formed, and the alloy properties deteriorate significantly.

[0015] Preferably, in step 4, the ratio of the mixture 3 to the composite mixture is that for every 100g of mixture 3, a composite mixture consisting of 0.2mL of oleic acid, 2g of paraffin wax, and 60mL of alcohol is added.

[0016] Preferably, in step 4, the water bath temperature is 65-70℃, and the mixing time is 3-4 hours.

[0017] Preferably, in step 5, the drying temperature is 80-90℃ and the drying time is 4-5 hours; after drying, the product is crushed into powder and passed through a 40-80 mesh sieve.

[0018] Further explanation of this invention addresses the problem of agglomeration and green body delamination caused by the direct addition of solid paraffin in existing technologies. This invention first dissolves paraffin in alcohol and adds oleic acid as a surfactant to form a uniform composite mixture (based on 3 parts per 100g of mixture: 0.2mL oleic acid, 2g paraffin, and 60mL alcohol). The mixture is stirred in a water bath at 65-70℃ for 3-4 hours, allowing the paraffin to uniformly penetrate and coat the powder surface in solution form. The oleic acid reduces the surface tension of the paraffin and improves wettability, forming a uniform dark gray slurry. Subsequently, the mixture is dried at a controlled temperature of 80-90℃ for 4-5 hours, slowly evaporating the alcohol. This prevents the paraffin from melting and flowing away due to high temperatures and avoids powder settling and hard agglomeration caused by natural drying. If this composite mixture treatment is omitted, fine-grained WC will agglomerate again, significantly reducing alloy properties; if the water bath temperature is too low, the paraffin will not dissolve sufficiently, leading to delamination and cracking in the green body.

[0019] Preferably, in step 5, the alloy is further subjected to a preset sintering process and vacuum sintered at 1400-1450℃ for 1-3 hours to finally obtain a non-uniform bicrystalline cemented carbide.

[0020] Preferably, the non-uniform bicrystalline cemented carbide has a Vickers hardness HV20 ≥ 1390 and a bending strength ≥ 2885 MPa.

[0021] The present invention has the following beneficial effects: 1. Compared with existing technologies, this invention pre-calcines the fine-grained WC and high-cobalt mixed powder at 700-800℃. Cobalt diffuses into the fine-grained WC surface to form a uniform coating layer and loose aggregates, effectively resisting hard agglomeration caused by van der Waals forces. This ensures the fine-grained WC maintains good dispersion during subsequent mixing, stirring, and molding processes. Simultaneously, the uniform adhesion of the cobalt phase to the fine-grained WC surface fundamentally suppresses cobalt powder segregation, providing a reliable structural basis for the gradient distribution of low cobalt in the coarse-grained region and high cobalt in the fine-grained region within the bicrystalline system, ensuring the consistency of the alloy microstructure and the stability of its properties.

[0022] 2. Compared to existing technologies, this invention achieves a gradient cobalt distribution by mixing coarse-grained WC-low-cobalt mixed powder and fine-grained WC-high-cobalt pre-calcined powder in a three-dimensional manner at a mass ratio of (7-8):(2-3), resulting in a low-cobalt cobalt distribution in the coarse-grained region and a high-cobalt distribution in the fine-grained region, with the overall cobalt content controlled between 6.8% and 9.6%. The coarse-grained WC, comprising 70-80%, forms a continuous toughness skeleton, while the fine-grained WC, comprising 20-30%, acts as a hardness-reinforcing phase, uniformly filling the gaps between the coarse grains. This synergistic effect allows the alloy to maintain high hardness while also possessing excellent bending strength. Furthermore, the oleic acid-paraffin-alcohol ternary composite mixture, combined with temperature-controlled water bath treatment and temperature-controlled drying, ensures that the paraffin wax uniformly coats the powder surface in solution form, completely avoiding the green body delamination problem caused by solid paraffin wax agglomeration. This improves molding quality and process stability, further ensuring the consistency of alloy performance. The method provided by this invention results in stable alloy performance with minimal deviation and high process adaptability, meeting the requirements for product consistency in industrial mass production and possessing promising industrial development prospects. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 The image shows the metallographic structure of the non-uniform bicrystalline cemented carbide obtained in Example 1 of this invention. Figure 2 The image shows the metallographic structure of the non-uniform bicrystalline cemented carbide obtained in Example 2 of this invention. Figure 3 This is a metallographic image of the non-uniform bicrystalline cemented carbide obtained in Example 3 of the present invention; Figure 4 The image shows the metallographic structure of the WC-Co cemented carbide obtained in Comparative Example 1 of this invention. Figure 5 This is a 1500X magnified metallographic image of the WC-Co cemented carbide obtained in Comparative Example 1 of the present invention. Figure 6 The metallographic image is of the WC-Co cemented carbide obtained in Comparative Example 2 of this invention. Figure 7 The metallographic image is of the WC-Co cemented carbide obtained in Comparative Example 3 of this invention. Figure 8 The metallographic image is of the WC-Co cemented carbide obtained in Comparative Example 5 of this invention. Figure 9 The metallographic image is of the WC-Co cemented carbide obtained in Comparative Example 6 of this invention. Figure 10 This is a metallographic image of the WC-Co cemented carbide obtained in Comparative Example 7 of the present invention.

[0025] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures, comprising the following steps: Step 1: Add coarse WC powder and cobalt powder to a ball mill, add dispersing media and ball mill to obtain a mixed slurry. After drying the slurry, obtain mixture 1. Step 2: After mixing fine-grained WC powder and cobalt powder evenly, pre-calcination is performed to obtain mixture 2; Step 3: Add mixed powder 1 and mixed powder 2 into the three-dimensional mixer and mix to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture of oleic acid, paraffin and alcohol, then heat and stir in a water bath to obtain a dark gray slurry; Step 5: Dry the slurry obtained in Step 4, crush it into powder and sieve it to obtain pretreated mixed powder; press the pretreated mixed powder into shape, and then sinter it through a preset sintering process to finally obtain a non-uniform bicrystalline hard alloy.

[0028] Preferably, in step 1, the particle size of the coarse-grained WC powder is 10-30 μm; the particle size of the cobalt powder is 1.0-3.0 μm; and the amount of cobalt powder added is 6-8% of the total mass of the coarse-grained WC powder and the cobalt powder.

[0029] Specifically, the particle size of the coarse-grained WC powder can be any one of 10μm, 15μm, 20μm, 25μm, 30μm or a range between two of these; the particle size of the cobalt powder can be any one of 1.0μm, 1.5μm, 2μm, 2.5μm, 3μm or a range between two of these; and the amount of cobalt powder added can be any one of 6%, 6.5%, 7%, 7.5%, 8% of the total mass of the coarse-grained WC powder and the cobalt powder or a range between two of these.

[0030] Preferably, in step 1, the amount of the dispersion medium added is 40-60% of the total mass of coarse-grained WC powder and cobalt powder, and the dispersion medium is 96-98 vol% alcohol.

[0031] Preferably, in step 1, the ball mill rotation speed is 250-300 r / min, the time is 5-6 h, and the ball-to-material ratio is (3-5):1.

[0032] Specifically, the rotational speed of the ball mill can be any one of 250 r / min, 260 r / min, 270 r / min, 280 r / min, 290 r / min, 300 r / min or a range between two of them; the time can be any one of 5 h, 5.5 h, 6 h or a range between two of them; and the ball-to-material ratio can be any one of 3:1, 4:1, 5:1 or a range between two of them.

[0033] Preferably, in step 2, the particle size of the fine-grained WC powder is 0.5-1 μm; the particle size of the cobalt powder is 1.0-3.0 μm; and the amount of cobalt powder added is 10-12% of the total mass of the fine-grained WC powder and the cobalt powder.

[0034] Specifically, the particle size of the fine-grained WC powder can be any one of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, or a range between two of these; the particle size of the cobalt powder can be any one of 1.0μm, 1.5μm, 2μm, 2.5μm, 3μm, or a range between two of these; and the amount of cobalt powder added can be any one of 10%, 10.5%, 11%, 11.5%, 12% of the total mass of the coarse-grained WC powder and the cobalt powder, or a range between two of these.

[0035] Preferably, in step 2, the pre-firing temperature is 700-800℃ and the pre-firing time is 2-3 hours.

[0036] Specifically, the pre-firing temperature can be any one of 700℃, 720℃, 740℃, 750℃, 760℃, 780℃, 800℃ or a range between two; the pre-firing time can be any one of 2h, 2.5h, 3h or a range between two.

[0037] Preferably, in step 3, the mixed powder 1 and mixed powder 2 are added to the three-dimensional mixer in a mass ratio of (7-8):(2-3) and mixed; the rotation speed of the three-dimensional mixer is 40-60Hz and the mixing time is 22-25h.

[0038] Specifically, the mixed powder 1 and mixed powder 2 can be added to the three-dimensional mixer in a mass ratio of 7:3, 7.5:2.5, 8:2 or a range between the two; the rotational speed of the three-dimensional mixer can be any one of 40Hz, 45Hz, 50Hz, 55Hz, 60Hz or a range between the two; and the mixing time can be any one of 22h, 23h, 24h, 25h or a range between the two.

[0039] Preferably, in step 4, the ratio of the mixture 3 to the composite mixture is that for every 100g of mixture 3, a composite mixture consisting of 0.2mL of oleic acid, 2g of paraffin wax, and 60mL of alcohol is added.

[0040] Preferably, in step 4, the water bath temperature is 65-70℃, and the mixing time is 3-4 hours.

[0041] Specifically, the water bath temperature can be any one of 65℃, 66℃, 67℃, 68℃, 69℃, 70℃ or a range between two of them; the mixing and stirring time can be any one of 3h, 3.5h, 4h or a range between two of them.

[0042] Preferably, in step 5, the drying temperature is 80-90℃ and the drying time is 4-5 hours; after drying, the product is crushed into powder and passed through a 40-80 mesh sieve.

[0043] Specifically, the drying temperature can be any one of 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, 90℃ or a range between two of them; the drying time can be any one of 4h, 4.5h, 5h or a range between two of them.

[0044] Preferably, in step 5, the alloy is further subjected to a preset sintering process and vacuum sintered at 1400-1450℃ for 1-3 hours to finally obtain a non-uniform bicrystalline cemented carbide.

[0045] Preferably, the non-uniform bicrystalline cemented carbide has a Vickers hardness HV20 ≥ 1390 and a bending strength ≥ 2885 MPa.

[0046] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0047] Example 1 A precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures includes the following steps: Step 1: Add coarse-grained WC powder with a particle size of 10μm and cobalt powder with a particle size of 1μm into a ball mill, add 96 vol% alcohol, and ball mill for 5 hours at a speed of 250 r / min. The amount of alcohol added is 40% of the total mass of coarse-grained WC powder and cobalt powder, and the ball-to-powder ratio is 3:1 to obtain a mixed slurry. After drying the slurry, obtain mixture 1, in which the amount of cobalt powder added is 6% of the total mass of coarse-grained WC powder and cobalt powder. Step 2: Mix 0.5μm fine-grained WC powder and 1μm cobalt powder evenly, and then pre-calcine at 700℃ for 2 hours to obtain mixture 2, wherein the amount of cobalt powder added is 10% of the total mass of fine-grained WC powder and cobalt powder; Step 3: Add mixed powder 1 and mixed powder 2 to the three-dimensional mixer at a mass ratio of 7:3 and mix for 22 hours at a speed of 40Hz to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture of oleic acid, paraffin and alcohol. For every 100g of mixture 3, add 0.2mL of oleic acid, 2g of paraffin and 60mL of alcohol. Mix and stir in a water bath at 65℃ for 3 hours to obtain a dark gray slurry. Step 5: Dry the slurry obtained in Step 4 at 80°C for 4 hours. After drying, crush it into powder and pass it through a 40-mesh sieve to obtain pretreated mixed powder. Press the pretreated mixed powder into shape and then vacuum sinter it at 1430°C for 2 hours using a preset sintering process to finally obtain a non-uniform bicrystalline cemented carbide.

[0048] Metallographic analysis, hardness testing, and bending strength testing were performed on the non-uniform bicrystalline cemented carbide prepared in this embodiment. The test results showed that the Vickers hardness (HV20) of the non-uniform bicrystalline cemented carbide was 1413, and the bending strength (TRS) was 2823 MPa. The metallographic image of the non-uniform bicrystalline cemented carbide is shown below. Figure 1 As shown, by Figure 1 It can be seen that the coarse-grained WC and fine-grained WC are evenly distributed, with no obvious agglomeration or segregation. The coarse-grained WC forms a continuous tough skeleton, while the fine-grained WC is evenly filled in the gaps between the coarse grains, forming a dense, non-uniform bicrystal structure. The cobalt phase is continuously distributed and has no segregation defects, resulting in good consistency in the microstructure.

[0049] Example 2 A precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures includes the following steps: Step 1: Add coarse-grained WC powder with a particle size of 20μm and cobalt powder with a particle size of 2μm into a ball mill, add 97 vol% alcohol, and ball mill for 5.5 h at a speed of 275 r / min. The amount of alcohol added is 50% of the total mass of coarse-grained WC powder and cobalt powder, and the ball-to-powder ratio is 4:1 to obtain a mixed slurry. After drying the slurry, we obtain mixture 1, in which the amount of cobalt powder added is 7% of the total mass of coarse-grained WC powder and cobalt powder. Step 2: After uniformly mixing 0.75μm fine-grained WC powder and 2μm cobalt powder, pre-calcining at 750℃ for 2.5h to obtain mixture 2, wherein the amount of cobalt powder added is 11% of the total mass of fine-grained WC powder and cobalt powder; Step 3: Add mixed powder 1 and mixed powder 2 to the three-dimensional mixer at a mass ratio of 7.5:2.5 and mix for 23.5 hours at a speed of 50Hz to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture of oleic acid, paraffin and alcohol. For every 100g of mixture 3, add 0.2mL of oleic acid, 2g of paraffin and 60mL of alcohol. Mix and stir in a water bath at 67℃ for 3.5h to obtain a dark gray slurry. Step 5: Dry the slurry obtained in Step 4 at 85°C for 4.5 hours. After drying, crush it into powder and pass it through a 60-mesh sieve to obtain pretreated mixed powder. Press the pretreated mixed powder into shape and then vacuum sinter it at 1430°C for 2 hours using a preset sintering process to finally obtain a non-uniform bicrystalline cemented carbide.

[0050] Metallographic analysis, hardness testing, and bending strength testing were performed on the non-uniform bicrystalline cemented carbide prepared in this embodiment. The test results showed that the Vickers hardness (HV20) of the non-uniform bicrystalline cemented carbide was 1398, and the bending strength (TRS) was 2885 MPa. The metallographic image of the non-uniform bicrystalline cemented carbide is shown below. Figure 2 As shown, by Figure 2 It can be seen that the coarse-grained WC and fine-grained WC are evenly distributed, with no obvious agglomeration or segregation. The coarse-grained WC forms a continuous tough skeleton, while the fine-grained WC is evenly filled in the gaps between the coarse grains, forming a dense, non-uniform bicrystal structure. The cobalt phase is continuously distributed and has no segregation defects, resulting in good consistency in the microstructure.

[0051] Example 3 A precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures includes the following steps: Step 1: Add coarse-grained WC powder with a particle size of 30μm and cobalt powder with a particle size of 3μm into a ball mill, add 98 vol% alcohol, and ball mill for 6 hours at a speed of 300 r / min. The amount of alcohol added is 60% of the total mass of coarse-grained WC powder and cobalt powder, and the ball-to-powder ratio is 5:1 to obtain a mixed slurry. After drying the slurry, obtain mixture 1, in which the amount of cobalt powder added is 8% of the total mass of coarse-grained WC powder and cobalt powder. Step 2: Mix 1μm fine-grained WC powder and 3μm cobalt powder evenly, and then pre-calcine at 800℃ for 3 hours to obtain mixture 2, wherein the amount of cobalt powder added is 12% of the total mass of fine-grained WC powder and cobalt powder; Step 3: Add mixed powder 1 and mixed powder 2 into a three-dimensional mixer at a mass ratio of 8:2 and mix for 25 hours at a speed of 60Hz to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture composed of oleic acid, paraffin and alcohol. For every 100g of mixture 3, add 0.2mL of oleic acid, 2g of paraffin and 60mL of alcohol. Mix and stir in a water bath at 70℃ for 4 hours to obtain a dark gray slurry. Step 5: Dry the slurry obtained in Step 4 at 90°C for 5 hours. After drying, crush it into powder and pass it through an 80-mesh sieve to obtain pretreated mixed powder. Press the pretreated mixed powder into shape and then vacuum sinter it at 1430°C for 2 hours using a preset sintering process to finally obtain a non-uniform bicrystalline cemented carbide.

[0052] Metallographic analysis, hardness testing, and bending strength testing were performed on the non-uniform bicrystalline cemented carbide prepared in this embodiment. The test results showed that the Vickers hardness (HV20) of the non-uniform bicrystalline cemented carbide was 1390, and the bending strength (TRS) was 2933 MPa. The metallographic image of the non-uniform bicrystalline cemented carbide is shown below. Figure 3 As shown, by Figure 3 It can be seen that the coarse-grained WC and fine-grained WC are evenly distributed, with no obvious agglomeration or segregation. The coarse-grained WC forms a continuous tough skeleton, while the fine-grained WC is evenly filled in the gaps between the coarse grains, forming a dense, non-uniform bicrystal structure. The cobalt phase is continuously distributed and has no segregation defects, resulting in good consistency in the microstructure.

[0053] Comparative Example 1 A method for preparing WC-Co cemented carbide differs from Example 1 only in step 2, which is as follows: After mixing fine WC powder with a particle size of 0.5μm with cobalt powder with a particle size of 1μm evenly, mixture 2 is prepared, wherein the amount of cobalt powder added is 10% of the total mass of fine WC powder and cobalt powder.

[0054] Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 985, and the bending strength (TRS) was 1865 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 4 and Figure 5 As shown in (1500X magnification), by Figure 4 and Figure 5 It can be seen that the metallographic structure shows severe agglomeration of fine-grained WC and uneven distribution of the cobalt phase.

[0055] Comparative Example 2 A method for preparing WC-Co cemented carbide differs from Example 1 only in the mass ratio of mixed powder 1 to mixed powder 2 in step 3. In this comparative example, the mass ratio of mixed powder 1 to mixed powder 2 in step 3 is 9:1.

[0056] Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 1098, and the bending strength (TRS) was 2042 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 6 As shown, by Figure 6 Metallographic observation shows that the proportion of fine-grained WC is too low, the hardness strengthening effect is insufficient, and the twinning structure characteristics are not obvious.

[0057] Comparative Example 3 A method for preparing WC-Co cemented carbide differs from Example 1 only in the ball milling time in step 1. In this comparative example, the ball milling time in step 1 is 3 hours. Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 892, and the bending strength (TRS) was 1650 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 7 As shown, by Figure 7 Metallographic observation shows that the cobalt phase is severely aggregated, and the coarse-grained WC is unevenly mixed with the cobalt powder.

[0058] Comparative Example 4 A method for preparing WC-Co cemented carbide differs from Example 1 only in the water bath temperature in step 4. In this comparative example, the water bath temperature in step 4 is 50°C.

[0059] The WC-Co cemented carbide finally prepared using this comparative method exhibited delamination and cracking.

[0060] Comparative Example 5 A method for preparing WC-Co cemented carbide includes the following steps: Step 1: Add coarse-grained WC powder with a particle size of 10μm and cobalt powder with a particle size of 1μm into a ball mill, add 96 vol% alcohol, and ball mill for 5 hours at a speed of 250 r / min. The amount of alcohol added is 40% of the total mass of coarse-grained WC powder and cobalt powder, and the ball-to-powder ratio is 3:1 to obtain a mixed slurry. After drying the slurry, obtain mixture 1, in which the amount of cobalt powder added is 6% of the total mass of coarse-grained WC powder and cobalt powder. Step 2: Mix 0.5μm fine-grained WC powder and 1μm cobalt powder evenly, and then pre-calcine at 700℃ for 2 hours to obtain mixture 2, wherein the amount of cobalt powder added is 10% of the total mass of fine-grained WC powder and cobalt powder; Step 3: Add mixed powder 1 and mixed powder 2 to the three-dimensional mixer at a mass ratio of 7:3 and mix for 24 hours at a speed of 50Hz to obtain mixed material 3; Step 4: Take 100g of the mixture and pass it through a 40-mesh sieve to obtain pretreated mixture powder; press the pretreated mixture powder into shape, and then vacuum sinter it at 1430℃ for 2 hours using a preset sintering process to finally obtain WC-Co cemented carbide.

[0061] Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 958, and the bending strength (TRS) was 1820 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 8 As shown, by Figure 8 Metallographic observation shows that fine-grained WC aggregates.

[0062] Comparative Example 6 A method for preparing WC-Co cemented carbide differs from Example 1 only in step 3, which is as follows: Mix powder 1 and mixed powder 2 at a mass ratio of 7:3 until they are evenly mixed to obtain mixture 3.

[0063] Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 945, and the bending strength was 1795 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 9 As shown, by Figure 9 Metallographic observation shows that fine-grained WC exhibits localized agglomeration, and the mixing of coarse and fine-grained WC is uneven, with a disordered distribution of the twin crystal structure.

[0064] Comparative Example 7 A method for preparing WC-Co cemented carbide differs from Example 1 only in that the amount of cobalt powder added in step 1 is 8% of the total mass of coarse-grained WC powder and cobalt powder; and the amount of cobalt powder added in step 2 is 8% of the total mass of fine-grained WC powder and cobalt powder; the remaining operations are the same as in Example 1.

[0065] Metallographic analysis, hardness testing, and bending strength testing were performed on the WC-Co cemented carbide prepared in this comparative example. The test results showed that the Vickers hardness (HV20) of the WC-Co cemented carbide was 1125, and the bending strength (TRS) was 2150 MPa. The metallographic image of the WC-Co cemented carbide is shown below. Figure 10 As shown, by Figure 10 Metallographic observation shows no obvious twinning structure.

[0066] In summary, this invention provides a precise pretreatment method for WC-Co alloy powder adapted to non-uniform bicrystalline structures. This method involves low-temperature pre-calcination of a mixture of fine-grained WC and high-cobalt powder, forming a uniform cobalt coating layer on the surface of the fine-grained WC, effectively suppressing hard agglomeration of the fine-grained WC. By three-dimensionally mixing coarse-grained WC-low-cobalt mixed powder and fine-grained WC-high-cobalt pre-calcined powder in a specific ratio, a gradient distribution of low cobalt in the coarse-grained region and high cobalt in the fine-grained region is achieved, balancing the hardness and strength of the alloy. The use of a temperature-controlled water bath treatment with an oleic acid-paraffin-alcohol ternary composite solution solves the problem of green blank delamination caused by paraffin agglomeration, improving the forming quality. The combined use of these techniques fully adapts this pretreatment method to the specific requirements of non-uniform bicrystalline structures for powder dispersibility, cobalt phase uniformity, and forming quality, providing reliable technical support for the industrial preparation of high-performance non-uniform bicrystalline WC-Co cemented carbides. The method provided by this invention makes the alloy properties stable and with small deviations, and has high process adaptability, meeting the requirements of industrial mass production for product consistency, and has good industrial development prospects.

[0067] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for precise pretreatment of WC-Co alloy powder adapted to non-uniform bicrystalline structures, characterized in that, Includes the following steps: Step 1: Add coarse WC powder and cobalt powder to a ball mill, add dispersing media and ball mill to obtain a mixed slurry. After drying the slurry, obtain mixture 1. Step 2: After mixing fine-grained WC powder and cobalt powder evenly, pre-calcination is performed to obtain mixture 2; Step 3: Add mixed powder 1 and mixed powder 2 into the three-dimensional mixer and mix to obtain mixed material 3; Step 4: Add mixture 3 to the composite mixture of oleic acid, paraffin and alcohol, then heat and stir in a water bath to obtain a dark gray slurry; Step 5: Dry the slurry obtained in Step 4, crush it into powder and sieve it to obtain pretreated mixed powder; press the pretreated mixed powder into shape, and then sinter it through a preset sintering process to finally obtain a non-uniform bicrystalline hard alloy.

2. The method according to claim 1, characterized in that, In step 1, the particle size of the coarse-grained WC powder is 10-30 μm; the particle size of the cobalt powder is 1.0-3.0 μm, and the amount of cobalt powder added is 6-8% of the total mass of the coarse-grained WC powder and the cobalt powder.

3. The method according to claim 1, characterized in that, In step 1, the ball mill rotates at a speed of 250-300 r / min for 5-6 h, and the ball-to-material ratio is (3-5):

1.

4. The method according to claim 1, characterized in that, In step 2, the particle size of the fine-grained WC powder is 0.5-1 μm; the particle size of the cobalt powder is 1.0-3.0 μm, and the amount of cobalt powder added is 10-12% of the total mass of the fine-grained WC powder and the cobalt powder.

5. The method according to claim 1, characterized in that, In step 2, the pre-firing temperature is 700-800℃ and the pre-firing time is 2-3h.

6. The method according to claim 1, characterized in that, In step 3, the mixed powder 1 and mixed powder 2 are added to the three-dimensional mixer at a mass ratio of (7-8):(2-3) and mixed. The rotation speed of the three-dimensional mixer is 40-60Hz and the mixing time is 22-25h.

7. The method according to claim 1, characterized in that, In step 4, the ratio of the mixture 3 to the composite mixture is that for every 100g of mixture 3, a composite mixture consisting of 0.2mL of oleic acid, 2g of paraffin wax and 60mL of alcohol is added.

8. The method according to claim 1, characterized in that, In step 4, the water bath temperature is 65-70℃, and the mixing time is 3-4 hours.

9. The method according to claim 1, characterized in that, In step 5, the drying temperature is 80-90℃ and the drying time is 4-5 hours; after drying, the product is crushed into powder and passed through a 40-80 mesh sieve.

10. The method according to claim 1, characterized in that, The non-uniform bicrystalline cemented carbide has a Vickers hardness HV20 ≥ 1390 and a bending strength ≥ 2885 MPa.

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