High-toughness ultrafine-grained wc-co cemented carbide and method for producing the same

Abstract

The application belongs to the technical field of powder metallurgy materials, and particularly relates to a high-strength and high-toughness ultrafine-grain WC-Co hard alloy and a preparation method thereof. The preparation method comprises the following steps: S1, obtaining ultrafine-grain tungsten carbide powder, nanocrystalline tungsten carbide powder, cobalt powder and grain inhibitor as raw materials, performing ultrasonic dispersion, vacuum reduction and spray drying on the ultrafine-grain tungsten carbide powder and the nanocrystalline tungsten carbide powder to obtain composite tungsten carbide powder; S2, mixing the cobalt powder and the grain inhibitor, performing first ball milling to obtain first mixture, mixing the first mixture and the composite tungsten carbide powder, performing second ball milling to obtain second mixture, and performing third ball milling on the second mixture to obtain third mixture; and S3, drying, pressing, sintering and cooling the third mixture to obtain the hard alloy. The application can ensure high hardness and significantly improve the fracture toughness and bending strength of the material by optimizing the ball milling process and the sintering process and adopting a new dispersant and a grain inhibitor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of powder metallurgy materials, and particularly relates to a high-strength and high-toughness ultrafine-grain WC-Co hard alloy and a preparation method thereof. BACKGROUND

[0002] As "industrial teeth", the performance of WC-Co hard alloy depends on the synergistic control of WC grain size and binder phase distribution. The traditional hard alloy has a typical "hardness-toughness" trade-off contradiction: when the WC content increases, the hardness and wear resistance increase but the toughness significantly decreases; and increasing the Co binder phase content can improve the toughness but leads to a decrease in hardness. This performance paradox seriously limits the application of hard alloy in the cutting field of difficult-to-machine materials such as aerospace high-temperature alloys.

[0003] Ultrafine-grain (WC grain size ≤0.6 µm) WC-Co hard alloy has the characteristics of high hardness and strength, which is mainly realized by the Hall-Petch effect to synergistically improve the strength and toughness, and the ultrafine WC grains also promote the diffusion of the Co phase, making it uniformly distributed, thereby improving the overall performance of the hard alloy. The hardness can reach 1900-2100 HV20, and the room-temperature toughness reaches 20 MPa·m 1 / 2 Above.

[0004] However, in actual production, industrial production faces the following technical bottlenecks:

[0005] Powder quality control: ultrafine WC powder (FSSS ≤0.5 µm) has a lower carbonization temperature, which can cause incomplete development of WC particles, and there may be cracks and pores on the surface, and the specific surface area is large (BET 2.5-3.5 m 2 / g), the oxygen content is high (1.5-2 times that of conventional powder), and it is easy to agglomerate, resulting in uneven dispersion of WC-Co;

[0006] Grain growth: long-time ball milling increases the activation energy of WC, making the sintering activity of ultrafine WC high, and abnormal growth (some grains grow to 3 µm) occurs easily above 1300℃. If the addition amount of traditional VC / Cr3C2 inhibitor is more than 1.0%, brittle phases are easily precipitated, affecting the performance of the alloy.

[0007] The prior art realizes grain refinement to 190 nm by adding 0.1-0.5% rare earth oxides (Pr6O 11 / Nd2O3), but does not solve the problem of surface defects of ultrafine WC powder; and the prior art uses two-stage grinding to improve mixing uniformity, but does not involve the synergistic effect of rare earth and traditional inhibitors. Therefore, developing an integrated process that combines powder defect repair, grain synergistic inhibition and low-stress ball milling is the key to preparing high-strength and high-toughness ultrafine-grain hard alloy. SUMMARY

[0008] To solve the above-mentioned technical problems, this application provides a method for preparing high-strength and tough ultrafine-grained WC-Co cemented carbide, comprising the following steps: S1, obtaining tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials, wherein the tungsten carbide powder includes ultrafine-grained tungsten carbide powder and nanocrystalline tungsten carbide powder, and obtaining composite tungsten carbide powder by ultrasonic dispersion, vacuum reduction, and spray drying of the ultrafine-grained tungsten carbide powder and the nanocrystalline tungsten carbide powder; S2, mixing the cobalt powder and the grain inhibitor and performing a first ball milling to obtain a first mixture, mixing the first mixture and the composite tungsten carbide powder and performing a second ball milling to obtain a second mixture, and performing a third ball milling to obtain a third mixture; S3, drying, pressing, sintering, and cooling the third mixture to obtain cemented carbide, wherein the sintering includes dewaxing, pre-sintering, a first sintering, and a second sintering.

[0009] As a preferred embodiment of the preparation method of high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, in step S1, the particle size of the ultrafine-grained tungsten carbide powder is 0.3-0.5µm, and the particle size of the nanocrystalline tungsten carbide powder is 45-55nm. By mass percentage, the proportions of the tungsten carbide powder, the cobalt powder, and the grain inhibitor in the raw materials are 92.0%-86.5%, 7.2%-12.0%, and 0.8%-1.5%, respectively, and the mass ratio of the ultrafine-grained tungsten carbide powder to the nanocrystalline tungsten carbide powder is (90-95):(10-5).

[0010] As a preferred embodiment of the preparation method of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, the ultrasonic dispersion in step S1 is specifically as follows: the ultrafine-grained tungsten carbide powder and an alcohol solution containing polyvinylpyrrolidone are mixed and then subjected to a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture; the first ultrasonic dispersion mixture, the nanocrystalline tungsten carbide powder, and polyethylene glycol are mixed and then subjected to a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The ultrasonic power of the first ultrasonic dispersion is 700-800W, the rotation speed of the first ultrasonic dispersion is 200-300rpm, and the time of the first ultrasonic dispersion is 30-60min; the ultrasonic power of the second ultrasonic dispersion is 500-600W, the rotation speed of the second ultrasonic dispersion is 200-300rpm, and the time of the second ultrasonic dispersion is 90-120min.

[0011] As a preferred embodiment of the preparation method of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, in step S1, the content of polyvinylpyrrolidone in the alcohol solution is 0.1-0.3 wt%, the liquid-to-solid ratio of the alcohol solution to the tungsten carbide powder is (0.3-0.5) L:1 kg, the mass ratio of polyethylene glycol to the tungsten carbide powder is 0.3-0.6 wt%, and the oxygen content of the composite tungsten carbide powder is ≤0.15 wt%.

[0012] As a preferred embodiment of the preparation method of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, step S2 further includes: adding myristic acid, oleic acid, alcohol, and paraffin during the first ball milling process; the grinding media of the first ball mill, the second ball mill, and the third ball mill are cemented carbide balls, which include: Ø8-12mm cemented carbide balls, Ø6-8mm cemented carbide balls, and Ø4-6mm cemented carbide balls, and the mass ratio of the three is (10-20):(50-60):(40-20); the ball-to-material ratio of the first ball mill, the second ball mill, and the third ball mill is (3-5):1; and the myristic acid and the raw material... The mass ratio of oleic acid to the raw material is 0.3-0.6 wt%, the mass ratio of oleic acid to the raw material is 0.3-0.5 wt%, the liquid-solid ratio of ethanol to the raw material is (0.3-0.5) L:1kg, the mass ratio of paraffin wax to the raw material is 1.5-2.5 wt%, the first ball milling, the second ball milling, and the third ball milling are carried out under an argon atmosphere, the rotation speed of the first ball milling is 40-50 rpm, the first ball milling time is 1-3 h, the rotation speed of the second ball milling is 20-30 rpm, the second ball milling time is 20-24 h, the rotation speed of the third ball milling is 30-35 rpm, and the third ball milling time is 1-2 h.

[0013] As a preferred embodiment of the preparation method of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, in step S3, the dewaxing method specifically involves heating to 280-300℃ at a heating rate of 1.0-1.2℃ / min under a vacuum of 100-200Pa and holding for 30-90min; the pre-sintering method involves heating to 1350-1375℃ at a heating rate of 2-5℃ / min and holding for 10-20min; the first sintering method specifically involves heating at 1-3℃ / min under a N2 pressure of 40-60mbar. The heating rate is raised to 1400-1450℃ and held for 20-30 minutes; the second sintering method is as follows: under N2 pressure of 40-60 mbar, the temperature is lowered to 1100-1200℃ at a cooling rate of 5-7℃ / min, and then raised from 1100-1200℃ to 1350-1375℃ at a heating rate of 2-5℃ / min and held for 10-20 minutes, and the cooling-heating-holding process in the second sintering is repeated 1-3 times; the cooling method is pressurized cooling, and the pressure of the pressurized cooling is 50-70 bar.

[0014] As a preferred embodiment of the preparation method of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, in step S1, the grain inhibitor includes Cr3C2, VC and rare earth oxides, and the mass ratio of Cr3C2, VC and rare earth oxides is (0.5-0.9):(0.2-0.4):(0.1-0.3); the rare earth oxides include one or more oxides of yttrium, ytterbium, gadolinium, praseodymium, lutetium and neodymium.

[0015] This application also provides a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, which is prepared using the above-described method for preparing high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide.

[0016] As a preferred embodiment of the high-strength and tough ultrafine-grained WC-Co cemented carbide described in this application, the average grain size of WC in the cemented carbide is ≤0.4µm, and the coefficient of variation K of the average grain size of WC in the cemented carbide is ≤0.52.

[0017] As a preferred embodiment of the high-strength and high-toughness ultrafine-grained WC-Co cemented carbide described in this application, the cemented carbide has a Vickers hardness ≥ 2000 HV20, a bending strength ≥ 4650 MPa, and a fracture toughness ≥ 11.5 MPa·m. 1 / 2 The relative density of the cemented carbide is ≥99.5%.

[0018] The beneficial effects of this application are as follows:

[0019] This application provides a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide and its preparation method. By optimizing the ball milling and sintering process parameters, this application significantly improves the size uniformity of WC grains; and by employing a novel dispersant, it achieves a highly uniform distribution of the Co phase and grain inhibitors in the alloy microstructure. Furthermore, the combined action of multiple grain inhibitors, through synergistic grain refinement and grain boundary pinning effects, effectively inhibits abnormal grain growth and strengthens grain boundaries, thereby significantly improving the fracture toughness and bending strength of the material while maintaining high hardness. The specific beneficial effects of this application are as follows:

[0020] 1. Nano WC Surface Repair Mechanism: This application adopts a method of premixing ultrafine WC and nano WC, and using a vacuum reduction step to reduce the oxygen content. Nano WC preferentially dissolves in the early stage of sintering (1100-1200℃) (the solubility is 1.8 times that of ultrafine WC). The surface cracks and pores of ultrafine WC are filled through "dissolution-precipitation". At the same time, a multi-stage liquid phase sintering process is adopted to further extend the process, which improves the integrity of WC particles by 40%. Furthermore, the second sintering temperature is lower than the first sintering temperature, which reduces the probability of abnormal grain growth.

[0021] 2. Novel dispersant: The mixed addition of myristic acid and oleic acid in this application can form a three-dimensional barrier on the surface of WC-Co particles. Through the steric hindrance effect, it can effectively prevent the aggregation of WC-Co particles, increase the uniformity of WC-Co in cemented carbide, and improve the performance of cemented carbide.

[0022] 3. Rare Earth-Carbide Synergistic Inhibition: This application utilizes rare earth-carbide synergistic inhibition of WC grain growth, VC / Cr3C2 to inhibit WC dissolution and precipitation, and rare earth oxides to agglomerate at the WC / Co interface to form a nano-dispersed phase, which synergistically refines the grains. At the same time, rare earth oxides, VC, and Cr3C2 can also form a "composite pinning" effect, inhibiting grain boundary migration and hindering crack propagation. The amount of Cr3C2 inhibitor added is reduced by 30% compared to that of a single inhibitor. In addition, rare earth elements can also increase the proportion of plastic phase in the binder phase and purify grain boundaries, thereby improving fracture toughness and bending strength.

[0023] 4. Three-stage flexible ball milling process: This application introduces a three-stage flexible ball milling process, with inert gas protection throughout to prevent powder oxidation. In the first stage, Co and grain inhibitors are pre-milled at high intensity to ensure initial uniform dispersion of Co and the inhibitors, preventing uneven mixing of the inhibitors and WC and resulting in localized additive aggregation. In the second stage, WC is added followed by flexible ball milling to reduce milling intensity, decrease grain breakage, lower the powder surface activation energy, and reduce abnormal grain growth during sintering. The third stage employs short-duration, low-to-medium intensity activation to perform final mixing and homogenization of the powder, moderately increasing the surface activation energy and significantly improving the powder's sintering activity, which is beneficial for subsequent densification and interfacial bonding during sintering.

[0024] 5. The prepared cemented carbide has a Vickers hardness ≥2000HV20, a bending strength ≥4650MPa, and a fracture toughness ≥11.5MPa·m. 1 / 2 Relative density ≥99.5%. Detailed Implementation

[0025] 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.

[0026] This application provides a method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, comprising the following steps:

[0027] S1. Obtain tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials. The tungsten carbide powder includes ultrafine tungsten carbide powder and nanocrystalline tungsten carbide powder. After ultrasonic dispersion, vacuum reduction, and spray drying of the ultrafine tungsten carbide powder and the nanocrystalline tungsten carbide powder, composite tungsten carbide powder is obtained.

[0028] The ultrafine crystalline tungsten carbide powder has a particle size of 0.3-0.5µm, and the nanocrystalline tungsten carbide powder has a particle size of 45-55nm. By mass percentage, the proportions of the tungsten carbide powder, the cobalt powder, and the grain inhibitor in the raw materials are 92.0%-86.5%, 7.2%-12.0%, and 0.8%-1.5%, respectively. The mass ratio of the ultrafine crystalline tungsten carbide powder to the nanocrystalline tungsten carbide powder is (90-95):(10-5).

[0029] The ultrasonic dispersion method specifically involves: mixing the ultrafine crystalline tungsten carbide powder and an alcohol solution containing polyvinylpyrrolidone, followed by a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture; then mixing the first ultrasonic dispersion mixture, the nanocrystalline tungsten carbide powder, and polyethylene glycol, followed by a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The ultrasonic power of the first ultrasonic dispersion is 700-800W, the rotation speed of the first ultrasonic dispersion is 200-300rpm, and the time of the first ultrasonic dispersion is 30-60min. The ultrasonic power of the second ultrasonic dispersion is 500-600W, the rotation speed of the second ultrasonic dispersion is 200-300rpm, and the time of the second ultrasonic dispersion is 90-120min.

[0030] The content of polyvinylpyrrolidone in the alcohol solution is 0.1-0.3 wt%, the liquid-to-solid ratio of the alcohol solution to the tungsten carbide powder is (0.3-0.5) L:1 kg, the mass ratio of polyethylene glycol to the tungsten carbide powder is 0.3-0.6 wt%, and the oxygen content of the composite tungsten carbide powder is ≤0.15 wt%.

[0031] The grain inhibitor comprises Cr3C2, VC, and rare earth oxides, wherein the mass ratio of Cr3C2, VC, and rare earth oxides is (0.5-0.9):(0.2-0.4):(0.1-0.3); the rare earth oxides comprise one or more oxides of yttrium, ytterbium, gadolinium, praseodymium, lutetium, and neodymium.

[0032] S2. The cobalt powder and the grain inhibitor are mixed and then subjected to a first ball milling to obtain a first mixture. The first mixture and the composite tungsten carbide powder are mixed and then subjected to a second ball milling to obtain a second mixture. The second mixture is then subjected to a third ball milling to obtain a third mixture.

[0033] Myristic acid, oleic acid, alcohol, and paraffin are added during the first ball milling process. The grinding media of the first, second, and third ball mills are cemented carbide balls, which include Ø8-12mm cemented carbide balls, Ø6-8mm cemented carbide balls, and Ø4-6mm cemented carbide balls, with a mass ratio of (10-20):(50-60):(40-20). The ball-to-material ratio of the first, second, and third ball mills is (3-5):1. The mass ratio of myristic acid to the raw material is 0.3-0.6wt%, and the mass ratio of oleic acid to the raw material is... The mass ratio of the raw materials is 0.3-0.5 wt%, the liquid-solid ratio of the alcohol to the raw materials is (0.3-0.5) L:1kg, the mass ratio of the paraffin wax to the raw materials is 1.5-2.5 wt%, the first ball milling, the second ball milling, and the third ball milling are carried out under an argon atmosphere, the rotation speed of the first ball milling is 40-50 rpm, the first ball milling time is 1-3h, the rotation speed of the second ball milling is 20-30 rpm, the second ball milling time is 20-24h, the rotation speed of the third ball milling is 30-35 rpm, and the third ball milling time is 1-2h;

[0034] S3. The third mixture is dried, pressed, sintered and cooled to obtain a cemented carbide. The sintering includes dewaxing, pre-sintering, first sintering and second sintering.

[0035] The dewaxing method specifically involves heating to 280-300℃ at a heating rate of 1.0-1.2℃ / min under a vacuum of 100-200Pa and holding for 30-90 minutes; the pre-sintering method involves heating to 1350-1375℃ at a heating rate of 2-5℃ / min and holding for 10-20 minutes; the first sintering method specifically involves heating to 1400-1450℃ at a heating rate of 1-3℃ / min under a N2 pressure of 40-60mbar and holding for 20 minutes. -30min; the second sintering method is as follows: under N2 pressure of 40-60mbar, the temperature is lowered to 1100-1200℃ at a cooling rate of 5-7℃ / min, and then raised from 1100-1200℃ to 1350-1375℃ at a heating rate of 2-5℃ / min and held for 10-20min, and the cooling-heating-holding process in the second sintering is repeated 1-3 times; the cooling method is pressurized cooling, and the pressure of the pressurized cooling is 50-70bar.

[0036] The technical solution of this application will be further described below with reference to specific embodiments.

[0037] Example 1

[0038] A method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, the method comprising the following steps:

[0039] S1. Obtain tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials. The tungsten carbide powder includes ultrafine tungsten carbide powder and nanocrystalline tungsten carbide powder. The ultrafine tungsten carbide powder and an alcohol solution containing polyvinylpyrrolidone (PVP, molecular weight 10000, the content of polyvinylpyrrolidone in the alcohol solution is 0.2wt%) are mixed and subjected to a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture. The first ultrasonic dispersion mixture, nanocrystalline tungsten carbide powder, and polyethylene glycol (the mass ratio of polyethylene glycol to tungsten carbide powder is 0.45wt%) are mixed and subjected to a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The second ultrasonic dispersion mixture is subjected to vacuum reduction and spray drying to obtain composite tungsten carbide powder.

[0040] The raw materials, by mass percentage, contain 90% tungsten carbide powder, 9% cobalt powder, and 1.0% grain inhibitors, with a mass ratio of ultrafine tungsten carbide powder to nanocrystalline tungsten carbide powder of 92:8. The grain inhibitors include Cr3C2, VC, and Y2O3, with a mass ratio of Cr3C2, VC, and Y2O3 of 0.6:0.3:0.2. The ultrafine tungsten carbide powder has a particle size of 0.4µm, and the nanocrystalline tungsten carbide powder has a particle size of 50nm. The liquid-to-solid ratio of the alcohol solution to the tungsten carbide powder is 0.4L / kg. The ultrasonic power for the first ultrasonic dispersion is 750W, the rotation speed is 250rpm, and the dispersion time is 45min. The ultrasonic power for the second ultrasonic dispersion is 550W, the rotation speed is 250rpm, and the dispersion time is 105min. The oxygen content of the composite tungsten carbide powder is 0.15wt%.

[0041] S2. Cobalt powder, grain inhibitor, myristic acid (myristic acid to raw material mass ratio of 0.45wt%), oleic acid (oleic acid to raw material mass ratio of 0.4wt%), ethanol (ethanol to raw material liquid-solid ratio of 0.4L / kg), and paraffin wax (paraffin wax to raw material mass ratio of 2wt%) are mixed and then subjected to a first ball mill to obtain a first mixture. The first mixture is then mixed with composite tungsten carbide powder and subjected to a second ball mill to obtain a second mixture. The second mixture is then subjected to a third ball mill to obtain a third mixture. The first ball milling, the second ball milling, and the third ball milling are described in detail. The grinding media for the third ball mill is cemented carbide balls, with a ball-to-material ratio of 4:1. The cemented carbide balls include Ø10mm cemented carbide balls, Ø8mm cemented carbide balls, and Ø6mm cemented carbide balls, and the mass ratio of the three is 15:55:30. The first, second, and third ball mills are carried out under an argon atmosphere. The rotation speed of the first ball mill is 45 rpm, and the milling time is 2 hours. The rotation speed of the second ball mill is 25 rpm, and the milling time is 22 hours. The rotation speed of the third ball mill is 32 rpm, and the milling time is 1.5 hours.

[0042] S3. The third mixture is dried, pressed, sintered, and cooled to obtain cemented carbide. Sintering includes dewaxing, pre-sintering, first sintering, and second sintering. The dewaxing method is as follows: heating to 290℃ at a heating rate of 1.1℃ / min under a vacuum of 150Pa and holding for 60min; pre-sintering is heating to 1360℃ at a heating rate of 3.5℃ / min and holding for 15min; the first sintering method is as follows: heating to 1425℃ at a heating rate of 2℃ / min under a N2 pressure of 50mbar and holding for 25min; the second sintering method is as follows: cooling to 1150℃ at a cooling rate of 6℃ / min under a N2 pressure of 50mbar and then heating to 1360℃ at a heating rate of 3.5℃ / min and holding for 15min. The cooling-heating-holding process is repeated twice in the second sintering; the cooling method is pressurized cooling at a pressure of 60bar.

[0043] The properties of the cemented carbide prepared in Example 1 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.38 µm, the coefficient of variation K was 0.52, the hardness of the cemented carbide was 2150 HV20, and the fracture toughness was 13.5 MPa·m. 1 / 2 It has a flexural strength of 5050 MPa and a relative density of 99.8%.

[0044] Example 2

[0045] A method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, the method comprising the following steps:

[0046] S1. Obtain tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials. The tungsten carbide powder includes ultrafine crystalline tungsten carbide powder and nanocrystalline tungsten carbide powder. The ultrafine crystalline tungsten carbide powder and an alcohol solution containing polyvinylpyrrolidone (PVP, molecular weight 10000, the content of polyvinylpyrrolidone in the alcohol solution is 0.1wt%) are mixed and subjected to a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture. The first ultrasonic dispersion mixture, nanocrystalline tungsten carbide powder, and polyethylene glycol (the mass ratio of polyethylene glycol to tungsten carbide powder is 0.3wt%) are mixed and subjected to a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The second ultrasonic dispersion mixture is subjected to vacuum reduction and spray drying to obtain composite tungsten carbide powder.

[0047] The raw materials, by mass percentage, contain 92% tungsten carbide powder, 7.2% cobalt powder, and 0.8% grain inhibitors, with a mass ratio of 90:10 between ultrafine tungsten carbide powder and nanocrystalline tungsten carbide powder. The grain inhibitors include Cr3C2, VC, and Y2O3, with a mass ratio of 0.5:0.2:0.1. The ultrafine tungsten carbide powder has a particle size of 0.3µm, and the nanocrystalline tungsten carbide powder has a particle size of 45nm. The liquid-to-solid ratio of the alcohol solution to the tungsten carbide powder is 0.3L / kg. The ultrasonic power for the first ultrasonic dispersion is 700W, the rotation speed is 200rpm, and the dispersion time is 30min. The ultrasonic power for the second ultrasonic dispersion is 500W, the rotation speed is 200rpm, and the dispersion time is 90min. The oxygen content of the composite tungsten carbide powder is 0.1wt%.

[0048] S2. Cobalt powder, grain inhibitor, myristic acid (myristic acid to raw material mass ratio of 0.3wt%), oleic acid (oleic acid to raw material mass ratio of 0.3wt%), ethanol (ethanol to raw material liquid-solid ratio of 0.3L / kg), and paraffin wax (paraffin wax to raw material mass ratio of 1.5wt%) are mixed and then subjected to a first ball mill to obtain a first mixture. The first mixture is then mixed with composite tungsten carbide powder and subjected to a second ball mill to obtain a second mixture. The second mixture is then subjected to a third ball mill to obtain a third mixture. The first ball milling, the second ball milling... The grinding media for the first, second, and third ball mills are cemented carbide balls, with a ball-to-material ratio of 3:1. The cemented carbide balls include Ø10mm, Ø8mm, and Ø6mm cemented carbide balls, and their mass ratio is 10:50:40. The first, second, and third ball mills are conducted under an argon atmosphere. The rotation speed of the first ball mill is 40 rpm, and the milling time is 1 hour. The rotation speed of the second ball mill is 20 rpm, and the milling time is 20 hours. The rotation speed of the third ball mill is 30 rpm, and the milling time is 1 hour.

[0049] S3. The third mixture is dried, pressed, sintered, and cooled to obtain cemented carbide. Sintering includes dewaxing, pre-sintering, first sintering, and second sintering. The dewaxing method is as follows: heating to 280℃ at a heating rate of 1.0℃ / min under a vacuum of 100Pa and holding for 30min; pre-sintering is heating to 1350℃ at a heating rate of 2℃ / min and holding for 10min; the first sintering method is as follows: heating to 1400℃ at a heating rate of 1℃ / min under a N2 pressure of 40mbar and holding for 20min; the second sintering method is as follows: cooling to 1200℃ at a cooling rate of 5℃ / min under a N2 pressure of 40mbar and then heating to 1350℃ at a heating rate of 2℃ / min and holding for 10min. The cooling-heating-holding process is repeated once in the second sintering; the cooling method is pressurized cooling at a pressure of 70bar.

[0050] The properties of the cemented carbide prepared in Example 2 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.37 µm, the coefficient of variation K was 0.50, the hardness of the cemented carbide was 2360 HV20, and the fracture toughness was 11.7 MPa·m. 1 / 2 It has a flexural strength of 4850 MPa and a relative density of 99.7%.

[0051] Example 3

[0052] A method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, the method comprising the following steps:

[0053] S1. Obtain tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials. The tungsten carbide powder includes ultrafine tungsten carbide powder and nanocrystalline tungsten carbide powder. The ultrafine tungsten carbide powder and an alcohol solution containing polyvinylpyrrolidone (PVP, molecular weight 10000, the content of polyvinylpyrrolidone in the alcohol solution is 0.3wt%) are mixed and subjected to a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture. The first ultrasonic dispersion mixture, nanocrystalline tungsten carbide powder, and polyethylene glycol (the mass ratio of polyethylene glycol to tungsten carbide powder is 0.6wt%) are mixed and subjected to a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The second ultrasonic dispersion mixture is subjected to vacuum reduction and spray drying to obtain composite tungsten carbide powder.

[0054] The raw materials, by mass percentage, comprise 86.5% tungsten carbide powder, 12% cobalt powder, and 1.5% grain inhibitors, respectively; the mass ratio of ultrafine tungsten carbide powder to nanocrystalline tungsten carbide powder is 95:5; the grain inhibitors include Cr3C2, VC, and Y2O3, with a mass ratio of Cr3C2, VC, and Y2O3 of 0.9:0.4:0.3; the particle size of the ultrafine tungsten carbide powder is 0.5µm, the particle size of the nanocrystalline tungsten carbide powder is 55nm, the liquid-solid ratio of the alcohol solution to the tungsten carbide powder is 0.5L / kg, the ultrasonic power of the first ultrasonic dispersion is 800W, the rotation speed of the first ultrasonic dispersion is 300rpm, and the time of the first ultrasonic dispersion is 60min, the ultrasonic power of the second ultrasonic dispersion is 600W, the rotation speed of the second ultrasonic dispersion is 300rpm, and the time of the second ultrasonic dispersion is 120min, and the oxygen content of the composite tungsten carbide powder is 0.14wt%.

[0055] S2. Cobalt powder, grain inhibitor, myristic acid (myristic acid to raw material mass ratio of 0.6 wt%), oleic acid (oleic acid to raw material mass ratio of 0.5 wt%), ethanol (ethanol to raw material liquid-solid ratio of 0.5 L / kg), and paraffin wax (paraffin wax to raw material mass ratio of 2.5 wt%) are mixed and then subjected to a first ball mill to obtain a first mixture. The first mixture is then mixed with composite tungsten carbide powder and subjected to a second ball mill to obtain a second mixture. The second mixture is then subjected to a third ball mill to obtain a third mixture. The first ball milling, the second ball milling... The grinding media for the first, second, and third ball mills are cemented carbide balls, with a ball-to-material ratio of 5:1. The cemented carbide balls include Ø10mm, Ø8mm, and Ø6mm cemented carbide balls, and their mass ratio is 20:60:20. The first, second, and third ball mills are carried out under an argon atmosphere. The rotation speed of the first ball mill is 50 rpm, and the milling time is 3 hours. The rotation speed of the second ball mill is 30 rpm, and the milling time is 24 hours. The rotation speed of the third ball mill is 35 rpm, and the milling time is 2 hours.

[0056] S3. The third mixture is dried, pressed, sintered, and cooled to obtain cemented carbide. Sintering includes dewaxing, pre-sintering, first sintering, and second sintering. The dewaxing method is as follows: heating to 300℃ at a heating rate of 1.2℃ / min under a vacuum of 200Pa and holding for 90min; pre-sintering is heating to 1375℃ at a heating rate of 5℃ / min and holding for 20min; the first sintering method is as follows: heating to 1450℃ at a heating rate of 3℃ / min under a N2 pressure of 60mbar and holding for 30min; the second sintering method is as follows: cooling to 1100℃ at a cooling rate of 7℃ / min under a N2 pressure of 60mbar and then heating to 1375℃ at a heating rate of 5℃ / min and holding for 20min. The cooling-heating-holding process is repeated 3 times in the second sintering; the cooling method is pressurized cooling at a pressure of 50bar.

[0057] The properties of the cemented carbide prepared in Example 3 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.39 µm, the coefficient of variation K was 0.51, the hardness of the cemented carbide was 2000 HV20, and the fracture toughness was 16 MPa·m. 1 / 2 It has a flexural strength of 4650 MPa and a relative density of 99.9%.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 2 is that in step S1, the tungsten carbide powder does not contain nanocrystalline tungsten carbide powder, the grain inhibitor is Cr3C2, and the tungsten carbide powder is not ultrasonically dispersed and mixed; in step S2, all raw materials are mixed and ball-milled once, and the novel dispersant myristic acid is not added during the ball milling process. The ball milling speed is 45 rpm and the time is 30 h; in step S3, the second sintering is not performed, and the first sintering is held at a temperature of 60 min. All other steps are the same as in Example 2.

[0060] The properties of the cemented carbide prepared in Comparative Example 1 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.54 µm, the coefficient of variation K was 0.64, the hardness was 1560 HV20, and the fracture toughness was 7.7 MPa·m. 1 / 2 It has a flexural strength of 2450 MPa and a relative density of 98.9%.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 3 is that the tungsten carbide powder in step S1 does not contain nanocrystalline tungsten carbide powder, and the tungsten carbide powder is not ultrasonically dispersed and mixed. All other steps are the same as in Example 3.

[0063] The properties of the cemented carbide prepared in Comparative Example 2 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.43 µm, the coefficient of variation K was 0.63, the hardness was 1750 HV20, and the fracture toughness was 11.4 MPa·m. 1 / 2 It has a flexural strength of 3700MPa and a relative density of 99.5%.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 3 is that in step S2, all raw materials are mixed and ball-milled once, and the novel dispersant myristic acid is not added during the ball milling process. The ball milling speed is 45 rpm and the time is 30 h. All other steps are the same as in Example 3.

[0066] The properties of the cemented carbide prepared in Comparative Example 3 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.65 µm, the coefficient of variation K was 0.66, the hardness was 1660 HV20, and the fracture toughness was 9.4 MPa·m. 1 / 2 It has a flexural strength of 2750 MPa and a relative density of 99.4%.

[0067] Comparative Example 4

[0068] The difference between this comparative example and Example 1 is that a second sintering is not performed in step S3, and the first sintering is held at a temperature of 60 minutes. All other steps are the same as in Example 1.

[0069] The properties of the cemented carbide prepared in Comparative Example 4 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.44 µm, the coefficient of variation K was 0.64, the hardness was 1620 HV20, and the fracture toughness was 8.2 MPa·m. 1 / 2 It has a flexural strength of 3250 MPa and a relative density of 99.4%.

[0070] Comparative Example 5

[0071] The difference between this comparative example and Example 1 is that the raw material in step S1 does not contain crystallization inhibitors, while the other steps are the same as in Example 1.

[0072] The properties of the cemented carbide prepared in Comparative Example 5 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.74 µm, the coefficient of variation K was 0.70, the hardness was 1580 HV20, and the fracture toughness was 12 MPa·m. 1 / 2 It has a flexural strength of 2350 MPa and a relative density of 99.0%.

[0073] Comparative Example 6

[0074] The difference between this comparative example and Example 2 is that in step S1, the ultrasonic power of the first ultrasonic dispersion is 400W and the time is 20min; the ultrasonic power of the second ultrasonic dispersion is 300W and the time is 60min; all other steps are the same as in Example 2.

[0075] The properties of the cemented carbide prepared in Comparative Example 6 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.53 µm, the coefficient of variation K was 0.62, the hardness was 1770 HV20, and the fracture toughness was 12.4 MPa·m. 1 / 2 It has a flexural strength of 3800MPa and a relative density of 99.4%.

[0076] Comparative Example 7

[0077] The difference between this comparative example and Example 1 is that the cooling-heating-holding process in the second sintering is not repeated in step S3; all other steps are the same as in Example 1.

[0078] The properties of the cemented carbide prepared in Comparative Example 7 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.33 µm, the coefficient of variation K was 0.72, the hardness was 2110 HV20, and the fracture toughness was 11.1 MPa·m. 1 / 2 It has a flexural strength of 4100MPa and a relative density of 99.3%.

[0079] Comparative Example 8

[0080] The difference between this comparative example and Example 1 is that the cooling-heating-holding process in the second sintering in step S3 is repeated 4 times; all other steps are the same as in Example 1.

[0081] The properties of the cemented carbide prepared in Comparative Example 8 were tested. The results showed that the average grain size of WC in the cemented carbide was 0.63 µm, the coefficient of variation K was 0.66, the hardness was 1850 HV20, and the fracture toughness was 14.1 MPa·m. 1 / 2 It has a flexural strength of 3900MPa and a relative density of 99.3%.

[0082] As shown in Table 1, Table 1 presents the mechanical properties of the cemented carbides prepared in each embodiment and comparative example.

[0083] Table 1

[0084]

[0085] A comparison of the performance data from the above examples and comparative examples shows that: Example 2 compared to Comparative Example 1 indicates that when nanocrystalline tungsten carbide powder is not added to the raw materials, and the grain inhibitor lacks VC and rare earth oxides, and when ultrasonic dispersion and mixing of the tungsten carbide powder are not performed, the novel dispersant myristic acid is not added during ball milling, and a three-stage ball milling process and a second sintering process are not used, the tungsten carbide particles are more prone to agglomeration, resulting in insufficient sintering activity and difficulty in effectively refining the grains. This leads to a significant decrease in the hardness, fracture toughness, and bending strength of the resulting cemented carbide, resulting in the worst overall mechanical properties. The comparison between Example 3 and Comparative Example 2 shows that if the raw materials do not contain nanocrystalline tungsten carbide powder and the tungsten carbide powder is not ultrasonically dispersed and mixed, the uniformity of the composite powder decreases, leading to an enhanced tendency for WC grain growth during sintering, thereby reducing the overall mechanical properties of the cemented carbide. The comparison between Example 3 and Comparative Example 3 shows that the absence of the novel dispersant myristic acid and the lack of a three-stage ball milling process during the ball milling stage increases the degree of WC agglomeration, resulting in insufficient powder mixing uniformity and consequently reducing the mechanical properties of the final sintered cemented carbide. The comparison table between Example 1 and Comparative Example 4 is also relevant. Note: If the second sintering process is not used, especially without the cooling-heating-holding sequence control, the WC grains cannot be fully rearranged and densified, resulting in an uneven sintered structure and a decrease in the mechanical properties of the cemented carbide. A comparison between Example 1 and Comparative Example 5 shows that the lack of grain inhibitors in the raw materials causes significant growth of WC grains, an increase in coarse grains in the microstructure, and brittle fracture as the main characteristic of the material, exhibiting performance degradation such as reduced hardness and weakened bending strength. A comparison between Example 2 and Comparative Example 6 shows that insufficient ultrasonic dispersion time and power lead to inadequate powder dispersion and uneven composite powder. The uniformity of the sintered structure leads to non-dense sintered structure and uneven grain size, ultimately resulting in a decrease in the performance of the cemented carbide. The comparison between Example 1 and Comparative Example 7 shows that if the cooling-heating-holding process in the second sintering is not repeated, the control of WC grains is insufficient, the microstructure rearrangement is inadequate, and the grain growth is incomplete and uneven, thereby reducing the mechanical properties of the cemented carbide. The comparison between Example 1 and Comparative Example 8 shows that if the number of cycles in the second sintering is too high, the WC grains will overgrow, the proportion of coarse grains will increase, the microstructure uniformity of the cemented carbide will deteriorate, and the performance will decrease.

[0086] In summary, by rationally combining nanocrystalline WC, optimizing ultrasonic dispersion conditions, using grain inhibitors, introducing myristic acid dispersants, employing three-stage ball milling, and precisely controlling the number of cycles in the second sintering, the powder uniformity and sintering structure can be significantly improved, thereby increasing the hardness, fracture toughness, and bending strength of cemented carbide and achieving excellent comprehensive performance.

[0087] This application provides a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide and its preparation method. By optimizing the ball milling and sintering process parameters, the size uniformity of WC grains is significantly improved. Furthermore, a novel dispersant is used to achieve a highly uniform distribution of the Co phase and grain inhibitors in the alloy microstructure. In addition, the combined action of multiple grain inhibitors, through synergistic grain refinement and grain boundary pinning effects, effectively inhibits abnormal grain growth and strengthens grain boundaries, thereby significantly improving the fracture toughness and bending strength of the material while maintaining high hardness. The specific beneficial effects of this application are as follows:

[0088] 1. Nano WC Surface Repair Mechanism: This application adopts a method of premixing ultrafine WC and nano WC, and using a vacuum reduction step to reduce the oxygen content. Nano WC preferentially dissolves in the early stage of sintering (1100-1200℃) (the solubility is 1.8 times that of ultrafine WC). The surface cracks and pores of ultrafine WC are filled through "dissolution-precipitation". At the same time, a multi-stage liquid phase sintering process is adopted to further extend the process, which improves the integrity of WC particles by 40%. Furthermore, the second sintering temperature is lower than the first sintering temperature, which reduces the probability of abnormal grain growth.

[0089] 2. Novel dispersant: The mixed addition of myristic acid and oleic acid in this application can form a three-dimensional barrier on the surface of WC-Co particles. Through the steric hindrance effect, it can effectively prevent the aggregation of WC-Co particles, increase the uniformity of WC-Co in cemented carbide, and improve the performance of cemented carbide.

[0090] 3. Rare Earth-Carbide Synergistic Inhibition: This application utilizes rare earth-carbide synergistic inhibition of WC grain growth, VC / Cr3C2 to inhibit WC dissolution and precipitation, and rare earth oxides to agglomerate at the WC / Co interface to form a nano-dispersed phase, which synergistically refines the grains. At the same time, rare earth oxides, VC, and Cr3C2 can also form a "composite pinning" effect, inhibiting grain boundary migration and hindering crack propagation. The amount of Cr3C2 inhibitor added is reduced by 30% compared to that of a single inhibitor. In addition, rare earth elements can also increase the proportion of plastic phase in the binder phase and purify grain boundaries, thereby improving fracture toughness and bending strength.

[0091] 4. Three-stage flexible ball milling process: This application introduces a three-stage flexible ball milling process, with inert gas protection throughout to prevent powder oxidation. In the first stage, Co and grain inhibitors are pre-milled at high intensity to ensure initial uniform dispersion of Co and the inhibitors, preventing uneven mixing of the inhibitors and WC and resulting in localized additive aggregation. In the second stage, WC is added followed by flexible ball milling to reduce milling intensity, decrease grain breakage, lower the powder surface activation energy, and reduce abnormal grain growth during sintering. The third stage employs short-duration, low-to-medium intensity activation to perform final mixing and homogenization of the powder, moderately increasing the surface activation energy and significantly improving the powder's sintering activity, which is beneficial for subsequent densification and interfacial bonding during sintering.

[0092] 5. The prepared cemented carbide has a Vickers hardness ≥2000HV20, a bending strength ≥4650MPa, and a fracture toughness ≥11.5MPa·m. 1 / 2 Relative density ≥99.5%.

[0093] 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-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, characterized in that, Includes the following steps: S1. Obtain tungsten carbide powder, cobalt powder, and grain inhibitor as raw materials. The tungsten carbide powder includes ultrafine tungsten carbide powder and nanocrystalline tungsten carbide powder. After ultrasonic dispersion, vacuum reduction, and spray drying of the ultrafine tungsten carbide powder and the nanocrystalline tungsten carbide powder, composite tungsten carbide powder is obtained. S2. The cobalt powder and the grain inhibitor are mixed and then subjected to a first ball milling to obtain a first mixture. The first mixture and the composite tungsten carbide powder are mixed and then subjected to a second ball milling to obtain a second mixture. The second mixture is then subjected to a third ball milling to obtain a third mixture. S3. The third mixture is dried, pressed, sintered and cooled to obtain a cemented carbide. The sintering includes dewaxing, pre-sintering, first sintering and second sintering. In step S1, the particle size of the ultrafine crystalline tungsten carbide powder is 0.3-0.5µm, and the particle size of the nanocrystalline tungsten carbide powder is 45-55nm. By mass percentage, the proportions of the tungsten carbide powder, the cobalt powder, and the grain inhibitor in the raw materials are 92.0%-86.5%, 7.2%-12.0%, and 0.8%-1.5%, respectively. The mass ratio of the ultrafine crystalline tungsten carbide powder to the nanocrystalline tungsten carbide powder is (90-95):(10-5).

2. The method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, The ultrasonic dispersion method in step S1 is as follows: the ultrafine crystalline tungsten carbide powder and the alcohol solution containing polyvinylpyrrolidone are mixed and then subjected to a first ultrasonic dispersion to obtain a first ultrasonic dispersion mixture. The first ultrasonic dispersion mixture, the nanocrystalline tungsten carbide powder, and polyethylene glycol are mixed and then subjected to a second ultrasonic dispersion to obtain a second ultrasonic dispersion mixture. The ultrasonic power of the first ultrasonic dispersion is 700-800W, the rotation speed of the first ultrasonic dispersion is 200-300rpm, and the time of the first ultrasonic dispersion is 30-60min. The ultrasonic power of the second ultrasonic dispersion is 500-600W, the rotation speed of the second ultrasonic dispersion is 200-300rpm, and the time of the second ultrasonic dispersion is 90-120min.

3. The method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 2, characterized in that, In step S1, the content of polyvinylpyrrolidone in the alcohol solution is 0.1-0.3 wt%, the liquid-solid ratio of the alcohol solution to the tungsten carbide powder is (0.3-0.5) L:1 kg, the mass ratio of polyethylene glycol to the tungsten carbide powder is 0.3-0.6 wt%, and the oxygen content of the composite tungsten carbide powder is ≤0.15 wt%.

4. The method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, Step S2 further includes: adding myristic acid, oleic acid, alcohol, and paraffin during the first ball milling process; the grinding media of the first, second, and third ball mills are cemented carbide balls, which include: Ø8-12mm cemented carbide balls, Ø6-8mm cemented carbide balls, and Ø4-6mm cemented carbide balls, with a mass ratio of (10-20):(50-60):(40-20); the ball-to-material ratio of the first, second, and third ball mills is (3-5):1; the mass ratio of myristic acid to the raw material is 0.3-0.6wt%; and the oil... The mass ratio of acid to the raw material is 0.3-0.5 wt%, the liquid-to-solid ratio of alcohol to the raw material is (0.3-0.5) L:1 kg, the mass ratio of paraffin to the raw material is 1.5-2.5 wt%, the first ball milling, the second ball milling, and the third ball milling are carried out under an argon atmosphere, the rotation speed of the first ball milling is 40-50 rpm, the first ball milling time is 1-3 h, the rotation speed of the second ball milling is 20-30 rpm, the second ball milling time is 20-24 h, the rotation speed of the third ball milling is 30-35 rpm, and the third ball milling time is 1-2 h.

5. The method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, In step S3, the dewaxing method specifically involves heating to 280-300℃ at a heating rate of 1.0-1.2℃ / min under a vacuum of 100-200Pa and holding for 30-90 minutes; the pre-sintering method involves heating to 1350-1375℃ at a heating rate of 2-5℃ / min and holding for 10-20 minutes; the first sintering method specifically involves heating to 1400-1450℃ at a heating rate of 1-3℃ / min under a N2 pressure of 40-60mbar. The second sintering process involves holding the temperature for 20-30 minutes. Specifically, the second sintering process is as follows: under a N2 pressure of 40-60 mbar, the temperature is lowered to 1100-1200℃ at a rate of 5-7℃ / min, and then raised from 1100-1200℃ to 1350-1375℃ at a rate of 2-5℃ / min, and the holding temperature is maintained for 10-20 minutes. The cooling-raising-holding process in the second sintering process is repeated 1-3 times. The cooling method is pressurized cooling, and the pressure of the pressurized cooling is 50-70 bar.

6. The method for preparing a high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, In step S1, the grain inhibitor includes Cr3C2, VC and rare earth oxides, and the mass ratio of Cr3C2, VC and rare earth oxides is (0.5-0.9):(0.2-0.4):(0.1-0.3); the rare earth oxides include one or more oxides of yttrium, ytterbium, gadolinium, praseodymium, lutetium and neodymium.

7. A high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide, characterized in that, It is prepared by the preparation method of a high-strength and tough ultrafine-grained WC-Co cemented carbide according to any one of claims 1-6.

8. The high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 7, characterized in that, The average grain size of WC in the cemented carbide is ≤0.4µm, and the coefficient of variation K of the average grain size of WC in the cemented carbide is ≤0.

52.

9. A high-strength, high-toughness, ultrafine-grained WC-Co cemented carbide according to claim 7, characterized in that, The cemented carbide has a Vickers hardness ≥2000HV20, a bending strength ≥4650MPa, and a fracture toughness ≥11.5MPa·m. 1 / 2 The relative density of the cemented carbide is ≥99.5%.

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