A high cobalt ultrafine cemented carbide and a method for preparing the same

Abstract

The application belongs to the technical field of hard alloy, and particularly relates to a high-cobalt superfine hard alloy and a preparation method thereof. The preparation method comprises the following steps: S1, obtaining tungsten carbide powder, cobalt powder, vanadium carbide powder and chromium carbide powder, performing first ultrasonic cell disruption on the tungsten carbide powder to obtain first mixed material, performing second ultrasonic cell disruption on the vanadium carbide powder to obtain second mixed material, and adding the second mixed material into the first mixed material to perform third ultrasonic cell disruption to obtain third mixed material; performing centrifugal spraying on the third mixed material to obtain WC-VC composite powder; S2, performing first ball milling on the cobalt powder and the chromium carbide powder to obtain first slurry; performing second ball milling on the WC-VC composite powder to obtain second slurry; adding the first slurry into the second slurry to perform third ball milling to obtain third slurry; S3, performing drying, pressing and sintering on the third slurry to obtain the high-cobalt superfine hard alloy. The high-cobalt superfine hard alloy with excellent performance is prepared through VC coating and Cr3C2 pre-solid solution.

Description

Technical Field

[0001] This application belongs to the field of cemented carbide technology, specifically relating to a high-cobalt ultrafine cemented carbide and its preparation method. Background Technology

[0002] WC-Co based cemented carbide is a composite material composed of a WC hard phase and a Co binder phase. Due to its excellent combination of hardness, wear resistance, and toughness, it has been widely used in key industrial fields such as machining, mining, and mold manufacturing. With the development of modern manufacturing towards higher precision and efficiency, and the widespread application of difficult-to-machine materials (such as high-strength steel and composite materials), more stringent requirements are being placed on the comprehensive mechanical properties of cemented carbide.

[0003] Studies have shown that ultrafine WC grain cemented carbides possess high hardness and wear resistance; while increasing the Co binder phase content can further enhance the alloy's fracture toughness and bending strength. Therefore, high-cobalt ultrafine cemented carbides (generally defined as those with a Co content ≥10wt%) combine ultra-high hardness with excellent toughness, making them irreplaceable in high-end cutting tools and wear-resistant components for extreme working conditions, and thus becoming one of the current research hotspots in cemented carbide materials.

[0004] However, the preparation process of high-cobalt ultrafine cemented carbide faces many technical bottlenecks. The core challenge lies in how to effectively control the abnormal growth of ultrafine WC grains while ensuring the densification of the alloy. Due to the extremely high surface energy and lattice distortion energy of ultrafine WC powder, energy is easily released during sintering, leading to rapid grain growth. Especially in the low-temperature sintering stage (800℃-1280℃), severe early grain growth behavior occurs, making it difficult to maintain the ultrafine grain structure.

[0005] Existing techniques involve first preparing cobalt-based solid solution powder, then reducing oxides such as V₂O₅ and Cr₂O₃ to inhibitors dissolved in the cobalt phase, followed by mixing with WC powder and ball milling and sintering to obtain ultrafine high-cobalt cemented carbide. However, this method easily introduces impurities during the reduction of V₂O₅ and Cr₂O₃ oxides, affecting subsequent densification during sintering. Furthermore, the introduction of oxides and the reduction process makes it difficult to control carbon content, complicates the process, and easily leads to decarburization defects, thus affecting the quality of the cemented carbide.

[0006] Therefore, there is an urgent need for a method to enhance the inhibition effect by using dual inhibitors combined with a special new preparation process, thereby preparing high-performance, high-cobalt, ultrafine cemented carbide. Summary of the Invention

[0007] To solve the above-mentioned technical problems, this application provides a method for preparing high-cobalt ultrafine cemented carbide, comprising the following steps: S1, obtaining tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder; adding the tungsten carbide powder to deionized water for a first ultrasonic cell disruption to obtain a first mixture; adding the vanadium carbide powder to deionized water for a second ultrasonic cell disruption to obtain a second mixture; adding the second mixture to the first mixture for a third ultrasonic cell disruption to obtain a third mixture; centrifuging and spraying the third mixture to obtain WC-VC composite powder; S2, adding the cobalt powder and the chromium carbide powder to alcohol for a first ball milling to obtain a first slurry; adding the WC-VC composite powder to alcohol for a second ball milling to obtain a second slurry; adding the first slurry to the second slurry for a third ball milling to obtain a third slurry; S3, drying, pressing, and sintering the third slurry to obtain high-cobalt ultrafine cemented carbide.

[0008] As a preferred embodiment of the preparation method of high cobalt ultrafine cemented carbide described in this application, in step S1, the particle size of the tungsten carbide powder is 0.2-0.4µm, and the particle size of the cobalt powder is <1.0µm; the mass ratio of the tungsten carbide powder, the cobalt powder, the vanadium carbide powder, and the chromium carbide powder is (82.9-86.6):(12-15):(0.4-0.6):(1.0-1.5).

[0009] In a preferred embodiment of the preparation method of high-cobalt ultrafine cemented carbide described in this application, in step S1, the power of the first ultrasonic cell disruption is 260-360W, the duty cycle of the first ultrasonic cell disruption is 0.3-0.5, and the time of the first ultrasonic cell disruption is 3-5min; the power of the second ultrasonic cell disruption is 260-360W, the duty cycle of the second ultrasonic cell disruption is 0.3-0.5, and the time of the second ultrasonic cell disruption is 3-5min; the power of the third ultrasonic cell disruption is 260-360W, the duty cycle of the third ultrasonic cell disruption is 0.3-0.5, and the time of the third ultrasonic cell disruption is 3-5min.

[0010] As a preferred embodiment of the preparation method of high cobalt ultrafine cemented carbide described in this application, in step S1, the rotation speed of the centrifugal spray is 7000-8000 r / min, and the temperature of the centrifugal spray is 120-135℃.

[0011] In a preferred embodiment of the preparation method of high cobalt ultrafine cemented carbide described in this application, in step S1, the size of the WC-VC composite powder is 0.2-0.4µm.

[0012] In a preferred embodiment of the preparation method of high-cobalt ultrafine cemented carbide described in this application, in step S2, the ball-to-material ratio of the first ball mill is (8-10):1, the ball milling time is 48-64 h, and the rotation speed of the first ball mill is 250-350 r / min; the ball-to-material ratio of the second ball mill is (2-5):1, the ball milling time is 3-5 h, and the rotation speed of the second ball mill is 150-200 r / min; the ball-to-material ratio of the third ball mill is (5-8):1, the ball milling time is 8-12 h, and the rotation speed of the third ball mill is 250-350 r / min.

[0013] In a preferred embodiment of the preparation method of high cobalt ultrafine cemented carbide described in this application, in step S3, the sintering temperature is 1410-1430℃ and the sintering holding time is 1-2h.

[0014] This application also provides a high-cobalt ultrafine cemented carbide, which is prepared using the above-described method for preparing high-cobalt ultrafine cemented carbide.

[0015] As a preferred embodiment of the high-cobalt ultrafine cemented carbide described in this application, the high-cobalt ultrafine cemented carbide has an average grain size of 200-300 nm, a uniform microstructure, and a density ≥99.5%.

[0016] As a preferred embodiment of the high-cobalt ultrafine cemented carbide described in this application, the high-cobalt ultrafine cemented carbide has a hardness HRA ≥ 91.5 and a fracture toughness ≥ 10 MPa·m. 1 / 2 ; Bending strength ≥ 4000 MPa.

[0017] The beneficial effects of this application are as follows: This application provides a high-cobalt ultrafine cemented carbide and its preparation method. This application prepares a high-cobalt ultrafine cemented carbide with excellent performance through VC coating and Cr3C2 presolution. The cemented carbide prepared by this method has fine grains, no abnormally large particles, and a uniform distribution of the cobalt phase, exhibiting excellent performance. This application utilizes the strong shearing, impact, and cavitation effects of a cell disruptor to fully deagglomerate and ultrafine VC aggregates, significantly improving particle surface energy. Due to the high lattice matching degree and low interfacial energy between WC and VC, ultrafine VC particles spontaneously adsorb and uniformly spread on the surface of WC particles under the influence of interfacial affinity and electrostatic adsorption, forming a continuous and dense nanoscale thin coating layer. This achieves atomic-scale uniform dispersion of VC on the WC surface, laying the structural foundation for grain boundary pinning during subsequent ball milling and sintering processes.

[0018] In this application, the WC-VC composite powder particles, after ultrasonic agitation, are fully activated and uniformly dispersed, exhibiting high sintering activity. Cr3C2 / Co, after pre-ball milling, can form a stable reinforcing structure within the binder phase. Excessive temperature or prolonged holding time can easily lead to abnormal growth of WC grains and excessive solid solution of the VC and Cr3C2 inhibitory phases, damaging the ultrafine grain structure. Conversely, insufficient temperature or short holding time results in inadequate densification, residual porosity, and difficulty in achieving optimal performance. Under conditions of 1410-1430℃ / 1-2h, the high activity of the powder can be fully utilized to achieve rapid densification, while simultaneously enabling VC and Cr3C2 to synergistically stabilize and pin grain boundaries, maintaining a uniform ultrafine grain structure even in a high-cobalt system. Ultimately, this leads to a comprehensive improvement in the alloy's hardness, bending strength, and fracture toughness.

[0019] This application utilizes a pre-formed WC-VC composite powder to form a uniform coating film on the particle surface, which exhibits a significant synergistic effect with the pre-dissolved Cr3C2 Co binder phase during sintering. The VC film improves the wetting and spreading behavior of the Co liquid phase, promoting densification. Simultaneously, the segregation of VC at WC grain boundaries and the solid solution and enrichment of Cr3C2 in the Co phase create a dual grain boundary pinning effect, synergistically inhibiting abnormal WC grain growth and stabilizing the ultrafine-grained structure. Furthermore, the two components form a reinforcing transition layer at the interface, enhancing the interfacial bonding flexural strength and jointly suppressing decarburization and defect phase formation. Ultimately, this results in a synergistic improvement in density, fineness, and overall mechanical properties of the high-cobalt ultrafine-grained cemented carbide.

[0020] This method employs the synergistic effect of VC and Cr3C2 to effectively inhibit grain growth and improve alloy performance. Firstly, ultrasonic pulverization and activation are used to uniformly disperse the inhibitor around WC. Crushing and activating WC and VC first facilitates the uniform dispersion of VC around WC, increasing the formation of a thin film of V on the WC basal surface and inhibiting the diffusion of W and C atoms. Lower inhibitor dosages can achieve the same growth inhibition effect as conventional methods. Then, high-energy ball milling and dissolution of Co and Cr3C2 increases the solid solution content of Cr3C2 in Co, inhibiting the dissolution and precipitation growth of WC. Finally, the mixture is ball-milled, pressed, and sintered to prepare a high-performance high-cobalt ultrafine cemented carbide. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 The image shows the morphology of the high-cobalt ultrafine cemented carbide prepared in Example 1 of this application. Figure 2 The image shows the morphology of the high-cobalt ultrafine cemented carbide prepared in Comparative Example 1 of this application. Figure 3 This is a morphology diagram of the high-cobalt ultrafine cemented carbide prepared in Comparative Example 3 of this application.

[0023] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0024] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] This application provides a method for preparing high-cobalt ultrafine cemented carbide, comprising the following steps: S1. Obtain tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder; add the tungsten carbide powder to deionized water for first ultrasonic cell disruption to obtain a first mixture; add the vanadium carbide powder to deionized water for second ultrasonic cell disruption to obtain a second mixture; add the second mixture to the first mixture for third ultrasonic cell disruption to obtain a third mixture; centrifuge and spray the third mixture to obtain WC-VC composite powder. The tungsten carbide powder has a particle size of 0.2-0.4µm, and the cobalt powder has a particle size of <1.0µm; the mass ratio of the tungsten carbide powder, the cobalt powder, the vanadium carbide powder, and the chromium carbide powder is (82.9-86.6):(12-15):(0.4-0.6):(1.0-1.5). The power of the first ultrasonic cell disruption is 260-360W, the duty cycle is 0.3-0.5, and the disruption time is 3-5 minutes; the power of the second ultrasonic cell disruption is 260-360W, the duty cycle is 0.3-0.5, and the disruption time is 3-5 minutes; the power of the third ultrasonic cell disruption is 260-360W, the duty cycle is 0.3-0.5, and the disruption time is 3-5 minutes; the rotation speed of the centrifugal spray is 7000-8000 r / min, and the temperature of the centrifugal spray is 120-135℃. The size of the WC-VC composite powder is 0.2-0.4µm; S2. The cobalt powder and the chromium carbide powder are added to alcohol and subjected to a first ball milling to obtain a first slurry; the WC-VC composite powder is added to alcohol and subjected to a second ball milling to obtain a second slurry; the first slurry is added to the second slurry and subjected to a third ball milling to obtain a third slurry; The ball-to-material ratio of the first ball mill is (8-10):1, the milling time is 48-64 hours, and the rotation speed is 250-350 r / min; the ball-to-material ratio of the second ball mill is (2-5):1, the milling time is 3-5 hours, and the rotation speed is 150-200 r / min; the ball-to-material ratio of the third ball mill is (5-8):1, the milling time is 8-12 hours, and the rotation speed is 250-350 r / min. S3. The third slurry is dried, pressed, and sintered to obtain a high-cobalt ultrafine cemented carbide. The sintering temperature is 1410-1430℃, and the sintering holding time is 1-2h. Specifically, the sintering temperature is any one of 1410℃, 1415℃, 1420℃, 1425℃, and 1430℃, or any two of them.

[0026] This application also provides a high-cobalt ultrafine cemented carbide, comprising: an average grain size of 200-300 nm, a uniform microstructure, and a density ≥99.5%. The high-cobalt ultrafine cemented carbide has a hardness HRA ≥91.5 and a fracture toughness ≥10 MPa·m. 1 / 2 ; Bending strength ≥ 4000 MPa.

[0027] The technical solution of this application will be further described below with reference to specific embodiments.

[0028] Example 1 A method for preparing a high-cobalt ultrafine cemented carbide, the method comprising the following steps: S1. Obtain tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder. Add tungsten carbide powder to deionized water and perform a first ultrasonic cell disruption to obtain a first mixture. Add vanadium carbide powder to deionized water and perform a second ultrasonic cell disruption to obtain a second mixture. Add the second mixture to the first mixture and perform a third ultrasonic cell disruption to obtain a third mixture. Centrifuge and spray the third mixture to obtain WC-VC composite powder. The particle size of tungsten carbide powder is 0.3µm, and the particle size of cobalt powder is <1.0µm; the mass ratio of tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder is 84.4:14:0.4:1.2. The power of the first ultrasonic cell disruption was 320W, the duty cycle was 0.4, and the disruption time was 4 minutes; the power of the second ultrasonic cell disruption was 320W, the duty cycle was 0.4, and the disruption time was 4 minutes; the power of the third ultrasonic cell disruption was 320W, the duty cycle was 0.4, and the disruption time was 4 minutes; the centrifugal spray speed was 7500 r / min, the centrifugal spray temperature was 130℃; the size of the WC-VC composite powder was 0.3µm; S2. Cobalt powder and chromium carbide powder are added to alcohol and ball-milled for the first time to obtain a first slurry; WC-VC composite powder is added to alcohol and ball-milled for the second time to obtain a second slurry; the first slurry is added to the second slurry and ball-milled for the third time to obtain a third slurry; The ball-to-material ratio of the first ball mill is 9:1, the milling time is 56 hours, and the rotation speed is 300 r / min; the ball-to-material ratio of the second ball mill is 4:1, the milling time is 4 hours, and the rotation speed is 175 r / min; the ball-to-material ratio of the third ball mill is 6:1, the milling time is 10 hours, and the rotation speed is 300 r / min. S3. The third slurry is dried, pressed, and sintered to obtain a high-cobalt ultrafine cemented carbide. The sintering temperature was 1420℃, and the sintering holding time was 1.5h.

[0029] The prepared high-cobalt ultrafine cemented carbide was tested, and the results are as follows: Please refer to [link / reference needed]. Figure 1 , Figure 1 This image shows the morphology of the high-cobalt ultrafine cemented carbide prepared in Example 1 of this application. The high-cobalt ultrafine cemented carbide has an average grain size of 232 nm, a uniform microstructure, and a density of 99.8%. The high-cobalt ultrafine cemented carbide has a hardness (HRA) of 91.5 and a fracture toughness of 10.48 MPa·m. 1 / 2 The flexural strength is 4085 MPa.

[0030] Example 2 A method for preparing a high-cobalt ultrafine cemented carbide, the method comprising the following steps: S1. Obtain tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder. Add tungsten carbide powder to deionized water and perform a first ultrasonic cell disruption to obtain a first mixture. Add vanadium carbide powder to deionized water and perform a second ultrasonic cell disruption to obtain a second mixture. Add the second mixture to the first mixture and perform a third ultrasonic cell disruption to obtain a third mixture. Centrifuge and spray the third mixture to obtain WC-VC composite powder. The particle size of tungsten carbide powder is 0.2µm, and the particle size of cobalt powder is <1.0µm; the mass ratio of tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder is 82.9:15:0.6:1.5. The power of the first ultrasonic cell disruption was 260W, the duty cycle was 0.3, and the disruption time was 3 minutes; the power of the second ultrasonic cell disruption was 260W, the duty cycle was 0.3, and the disruption time was 3 minutes; the power of the third ultrasonic cell disruption was 260W, the duty cycle was 0.3, and the disruption time was 3 minutes; the centrifugal spray speed was 7000 r / min, the centrifugal spray temperature was 120℃; the size of the WC-VC composite powder was 0.2µm; S2. Cobalt powder and chromium carbide powder are added to alcohol and ball-milled for the first time to obtain a first slurry; WC-VC composite powder is added to alcohol and ball-milled for the second time to obtain a second slurry; the first slurry is added to the second slurry and ball-milled for the third time to obtain a third slurry; The ball-to-material ratio for the first ball mill is 8:1, the milling time is 48 hours, and the mill speed is 250 r / min; the ball-to-material ratio for the second ball mill is 2:1, the milling time is 3 hours, and the mill speed is 150 r / min; the ball-to-material ratio for the third ball mill is 5:1, the milling time is 8 hours, and the mill speed is 250 r / min. S3. The third slurry is dried, pressed, and sintered to obtain a high-cobalt ultrafine cemented carbide. The sintering temperature was 1410℃, and the sintering holding time was 2 hours.

[0031] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 265 nm, with a uniform microstructure and a density of 99.7%. The hardness (HRA) of the high-cobalt ultrafine cemented carbide was 91.8, and the fracture toughness was 10.21 MPa·m. 1 / 2 The flexural strength is 4250 MPa.

[0032] Example 3 A method for preparing a high-cobalt ultrafine cemented carbide, the method comprising the following steps: S1. Obtain tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder. Add tungsten carbide powder to deionized water and perform a first ultrasonic cell disruption to obtain a first mixture. Add vanadium carbide powder to deionized water and perform a second ultrasonic cell disruption to obtain a second mixture. Add the second mixture to the first mixture and perform a third ultrasonic cell disruption to obtain a third mixture. Centrifuge and spray the third mixture to obtain WC-VC composite powder. The particle size of tungsten carbide powder is 0.4µm, and the particle size of cobalt powder is <1.0µm; the mass ratio of tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder is 86.6:12:0.4:1.0. The power of the first ultrasonic cell disruption was 360W, the duty cycle was 0.5, and the disruption time was 5 minutes; the power of the second ultrasonic cell disruption was 360W, the duty cycle was 0.5, and the disruption time was 5 minutes; the power of the third ultrasonic cell disruption was 360W, the duty cycle was 0.5, and the disruption time was 5 minutes; the centrifugal spray speed was 8000 r / min, the centrifugal spray temperature was 135℃; the size of the WC-VC composite powder was 0.4µm; S2. Cobalt powder and chromium carbide powder are added to alcohol and ball-milled for the first time to obtain a first slurry; WC-VC composite powder is added to alcohol and ball-milled for the second time to obtain a second slurry; the first slurry is added to the second slurry and ball-milled for the third time to obtain a third slurry; The ball-to-material ratio of the first ball mill was 10:1, the milling time was 64 hours, and the rotation speed was 350 r / min; the ball-to-material ratio of the second ball mill was 5:1, the milling time was 5 hours, and the rotation speed was 200 r / min; the ball-to-material ratio of the third ball mill was 8:1, the milling time was 12 hours, and the rotation speed was 350 r / min. S3. The third slurry is dried, pressed, and sintered to obtain a high-cobalt ultrafine cemented carbide. The sintering temperature was 1430℃, and the sintering holding time was 1 hour.

[0033] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 248 nm, with a uniform microstructure and a density of 99.8%. The hardness (HRA) of the high-cobalt ultrafine cemented carbide was 91.6, and the fracture toughness was 10.33 MPa·m. 1 / 2 The flexural strength is 4120 MPa.

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is that steps S1 and S2 are omitted. Instead, tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder are directly mixed and ball-milled to obtain the third slurry. All other steps are the same as in Example 1.

[0035] The prepared high-cobalt ultrafine cemented carbide was tested, and the results are as follows: Please refer to [link / reference needed]. Figure 2 , Figure 2This image shows the morphology of the high-cobalt ultrafine cemented carbide prepared in Comparative Example 1 of this application. The average grain size of the high-cobalt ultrafine cemented carbide is 523 nm, and its microstructure contains abnormally large grains with a density of 99.1%. The high-cobalt ultrafine cemented carbide has a hardness of HRA 90.2 and a fracture toughness of 9.85 MPa·m. 1 / 2 Flexural strength 2584MPa.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S2, cobalt powder, chromium carbide powder and WC-VC composite powder are mixed and ball-milled to obtain a third slurry. All other steps are the same as in Example 1.

[0037] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 552 nm, the microstructure contained abnormally large grains, and the density was 99.2%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.1 and a fracture toughness of 9.66 MPa·m. 1 / 2 Flexural strength 3265MPa.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S1, tungsten carbide powder and vanadium carbide powder are mixed, ball-milled, and dried to obtain WC-VC composite powder. All other steps are the same as in Example 1.

[0039] The prepared high-cobalt ultrafine cemented carbide was tested, and the results are as follows: Please refer to [link / reference needed]. Figure 3 , Figure 3 This image shows the morphology of the high-cobalt ultrafine cemented carbide prepared in Comparative Example 3 of this application. The average grain size of the high-cobalt ultrafine cemented carbide is 364 nm, and its microstructure contains abnormally large grains and exhibits inhibitor aggregation, with a density of 98.9%. The high-cobalt ultrafine cemented carbide has a hardness of HRA 90.2 and a fracture toughness of 9.31 MPa·m. 1 / 2 Flexural strength 2846MPa.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that the sintering temperature in step S3 is 1450°C, while the other steps are the same as in Example 1.

[0041] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 531 nm, the microstructure contained abnormally large grains, and the density was 99.2%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.6 and a fracture toughness of 9.67 MPa·m. 1 / 2 Flexural strength 3361MPa.

[0042] Comparative Example 5 The difference between this comparative example and Example 1 is that the sintering temperature in step S3 is 1380°C, while the other steps are the same as in Example 1.

[0043] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 324 nm, the microstructure contained a large number of pores, and the density was 97.8%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 89.8 and a fracture toughness of 9.12 MPa·m. 1 / 2 Flexural strength 2318MPa.

[0044] Comparative Example 6 The difference between this comparative example and Example 1 is that the mass ratio of tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder in step S1 is 83.2:14:1:1.8. All other steps are the same as in Example 1.

[0045] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 364 nm, the microstructure contained abnormally large grains and exhibited inhibitor aggregation, and the density was 99.1%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.7 and a fracture toughness of 9.67 MPa·m. 1 / 2 Flexural strength 2591MPa.

[0046] Comparative Example 7 The difference between this comparative example and Example 1 is that the mass ratio of tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder in step S1 is 85:14:0.2:0.8. All other steps are the same as in Example 1.

[0047] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 586 nm, the microstructure contained abnormally large grains, and the density was 99.3%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.2 and a fracture toughness of 9.65 MPa·m. 1 / 2 Flexural strength 3621MPa.

[0048] Comparative Example 8 The difference between this comparative example and Example 1 is that in step S1, the power of the first ultrasonic cell disruption is 500W, and the duty cycle of the first ultrasonic cell disruption is 0.6; the power of the second ultrasonic cell disruption is 500W, and the duty cycle of the second ultrasonic cell disruption is 0.6; the power of the third ultrasonic cell disruption is 500W, and the duty cycle of the third ultrasonic cell disruption is 0.6; all other steps are the same as in Example 1.

[0049] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 436 nm, the microstructure contained abnormally large grains, and the density was 99.0%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 91.0 and a fracture toughness of 9.38 MPa·m. 1 / 2 Flexural strength 2894MPa.

[0050] Comparative Example 9 The difference between this comparative example and Example 1 is that in step S1, the power of the first ultrasonic cell disruption is 200W, and the duty cycle of the first ultrasonic cell disruption is 0.2; the power of the second ultrasonic cell disruption is 200W, and the duty cycle of the second ultrasonic cell disruption is 0.2; the power of the third ultrasonic cell disruption is 200W, and the duty cycle of the third ultrasonic cell disruption is 0.2; all other steps are the same as in Example 1.

[0051] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 465 nm, the microstructure contained abnormally large grains, and the density was 99.1%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.9 and a fracture toughness of 9.14 MPa·m. 1 / 2 Flexural strength 2267MPa.

[0052] Comparative Example 10 The difference between this comparative example and Example 1 is that the ball-to-material ratio of the second ball mill in step S2 is 8:1, the ball milling time of the second ball mill is 10 hours, and the rotation speed of the second ball mill is 300 r / min; all other steps are the same as in Example 1.

[0053] The prepared high-cobalt ultrafine cemented carbide was tested, and the results showed that the average grain size of the high-cobalt ultrafine cemented carbide was 482 nm, the microstructure contained abnormally large grains, and the density was 99.2%. The high-cobalt ultrafine cemented carbide had a hardness of HRA 90.8 and a fracture toughness of 9.76 MPa·m. 1 / 2 Flexural strength 3169MPa.

[0054] A comparison of the performance data of the above embodiments and comparative examples shows that: Example 1, in conjunction with Comparative Example 1, shows that because the stepwise pretreatment of VC coating and Cr3C2 presolidation was omitted, the VC / Cr3C2 double grain boundary pinning effect could not be formed during sintering, resulting in abnormal growth of WC grains and a significant decrease in the bending strength of the alloy.

[0055] Example 1, in conjunction with Comparative Example 2, shows that because Co and Cr3C2 were not pre-ball-milled separately, Cr3C2 was not sufficiently dissolved in the binder phase. Furthermore, excessive ball milling of the WC-VC composite powder would destroy the already formed VC coating layer, weaken the inhibitory effect on WC dissolution and precipitation, and cause significant grain coarsening and reduced mechanical properties.

[0056] Example 1, combined with Comparative Example 3, shows that because ordinary ball milling was used instead of ultrasonic crushing to prepare WC-VC composite powder, the VC agglomerates failed to be fully depolymerized and uniformly coated at the nanoscale. During sintering, inhibitor aggregation and insufficient local pinning occurred, resulting in abnormal grain growth and performance deterioration.

[0057] Example 1, in conjunction with Comparative Example 4, shows that excessively high sintering temperatures lead to excessive solid solution or thermal instability failure of the VC and Cr3C2 inhibitory phases, weakening the pinning effect and causing WC grains to grow rapidly, resulting in a decrease in both hardness and strength.

[0058] Example 1, in conjunction with Comparative Example 5, shows that because the sintering temperature is too low, the liquid phase generation is insufficient and the densification driving force is not enough, resulting in more pores remaining inside the alloy, and the bending strength is severely degraded due to the low density.

[0059] Example 1, in conjunction with Comparative Example 6, shows that excessive addition of VC and Cr3C2 leads to the aggregation of excessive inhibitors at grain boundaries, forming brittle phases, causing uneven pinning and local stress concentration, resulting in abnormal grain growth and reduced toughness and strength.

[0060] Example 1, in conjunction with Comparative Example 7, shows that because the addition of VC and Cr3C2 is too low, there are insufficient effective pinning points at the grain boundaries, which cannot suppress the rapid migration and merging of WC grains, resulting in significant grain coarsening and a substantial decrease in hardness.

[0061] Example 1, in conjunction with Comparative Example 8, shows that excessive ultrasonic power and duty cycle lead to excessive energy input, which may cause secondary agglomeration of VC particles or damage to the coating layer, resulting in uneven pinning and decreased density during sintering, and grain coarsening.

[0062] Example 1, in conjunction with Comparative Example 9, shows that because the ultrasonic power and duty cycle are too low, the shearing and cavitation effects are insufficient, the VC agglomerates are not fully depolymerized, and it is difficult to form a continuous coating on the WC surface, resulting in weak pinning effect and grain growth, and a comprehensive decline in performance.

[0063] Example 1, in conjunction with Comparative Example 10, shows that excessive ball milling of the WC-VC composite powder in the second stage caused high-energy mechanical force to peel off the VC nano-coating layer that had formed on the WC surface, causing the VC to re-agglomerate, lose its precise grain boundary pinning ability, and result in abnormal grain growth and reduced strength.

[0064] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing a high-cobalt ultrafine cemented carbide, characterized in that, Includes the following steps: S1. Obtain tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder; add the tungsten carbide powder to deionized water for first ultrasonic cell disruption to obtain a first mixture; add the vanadium carbide powder to deionized water for second ultrasonic cell disruption to obtain a second mixture; add the second mixture to the first mixture for third ultrasonic cell disruption to obtain a third mixture; centrifuge and spray the third mixture to obtain WC-VC composite powder. S2. The cobalt powder and the chromium carbide powder are added to alcohol and subjected to a first ball milling to obtain a first slurry; the WC-VC composite powder is added to alcohol and subjected to a second ball milling to obtain a second slurry; the first slurry is added to the second slurry and subjected to a third ball milling to obtain a third slurry; S3. The third slurry is dried, pressed, and sintered to obtain a high-cobalt ultrafine cemented carbide.

2. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S1, the particle size of the tungsten carbide powder is 0.2-0.4µm, and the particle size of the cobalt powder is <1.0µm; the mass ratio of the tungsten carbide powder, the cobalt powder, the vanadium carbide powder, and the chromium carbide powder is (82.9-86.6):(12-15):(0.4-0.6):(1.0-1.5).

3. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S1, the power of the first ultrasonic cell disruption is 260-360W, the duty cycle of the first ultrasonic cell disruption is 0.3-0.5, and the disruption time is 3-5 minutes; the power of the second ultrasonic cell disruption is 260-360W, the duty cycle of the second ultrasonic cell disruption is 0.3-0.5, and the disruption time is 3-5 minutes; the power of the third ultrasonic cell disruption is 260-360W, the duty cycle of the third ultrasonic cell disruption is 0.3-0.5, and the disruption time is 3-5 minutes.

4. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S1, the rotation speed of the centrifugal spray is 7000-8000 r / min, and the temperature of the centrifugal spray is 120-135℃.

5. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S1, the size of the WC-VC composite powder is 0.2-0.4µm.

6. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S2, the ball-to-material ratio of the first ball mill is (8-10):1, the milling time is 48-64 hours, and the rotation speed is 250-350 r / min; the ball-to-material ratio of the second ball mill is (2-5):1, the milling time is 3-5 hours, and the rotation speed is 150-200 r / min; the ball-to-material ratio of the third ball mill is (5-8):1, the milling time is 8-12 hours, and the rotation speed is 250-350 r / min.

7. The method for preparing a high-cobalt ultrafine cemented carbide according to claim 1, characterized in that, In step S3, the sintering temperature is 1410-1430℃, and the sintering holding time is 1-2h.

8. A high-cobalt ultrafine cemented carbide, characterized in that, It is prepared by the preparation method of a high cobalt ultrafine cemented carbide according to any one of claims 1-7.

9. The high-cobalt ultrafine cemented carbide according to claim 8, characterized in that, The high-cobalt ultrafine cemented carbide has an average grain size of 200-300 nm, a uniform microstructure, and a density of ≥99.5%.

10. A high-cobalt ultrafine cemented carbide according to claim 8, characterized in that, The high-cobalt ultrafine cemented carbide has a hardness HRA≥91.5 and a fracture toughness≥10MPa·m. 1 / 2 ; Bending strength ≥ 4000 MPa.

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