Ultrafine grain wc-co cemented carbide and method for producing the same

Abstract

This invention belongs to the technical field of powder metallurgy cemented carbide materials, specifically relating to an ultrafine-grained WC-Co cemented carbide and its preparation method. The cemented carbide comprises ultrafine tungsten carbide powder, cobalt carbonyl powder, vanadium-chromium-tantalum-niobium-zirconium composite carbide, a cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and graphite powder. During preparation, the components are mixed with anhydrous ethanol and polyethylene glycol and ball-milled. The mixture is then dried, sieved, pressed, cold isostatically pressed, vacuum degreased, pre-sintered, liquid-phase sintered, and pressure sintered to obtain the finished product. This invention inhibits grain growth through the composite carbide and improves interfacial bonding through the oxygen vacancy interface phase, resulting in cemented carbide with high hardness, high wear resistance, and good toughness.

Description

Technical Field

[0001] This invention belongs to the technical field of powder metallurgy cemented carbide materials, specifically relating to an ultrafine-grained WC-Co cemented carbide and its preparation method. Background Technology

[0002] Cemented carbide is a type of powder metallurgy material prepared with refractory metal carbides as the hard phase and metallic cobalt or similar materials as the binder phase. It possesses characteristics such as high hardness, good wear resistance, strong heat resistance, and high compressive strength, and is widely used in cutting tools, wear-resistant parts, mining tools, mold processing, and precision manufacturing. With the development of high-speed machining, cutting of difficult-to-machine materials, and precision forming technologies, traditional medium-coarse grained cemented carbides can no longer simultaneously meet the comprehensive requirements of high hardness, high wear resistance, and good toughness. Ultrafine grained tungsten carbide-cobalt cemented carbides, due to their small grain size, uniform distribution of the hard phase, and excellent material strength and wear resistance, are gradually becoming an important development direction for high-performance cemented carbides.

[0003] Existing ultrafine-grained tungsten carbide cobalt cemented carbide is typically prepared by ball milling, pressing, degreasing, and sintering fine-grained tungsten carbide powder and carbonyl cobalt powder. Due to the high surface energy of ultrafine tungsten carbide powder, it is prone to dissolution, migration, and re-precipitation during sintering heating and liquid-phase sintering, leading to rapid tungsten carbide grain growth, and even localized abnormal growth. This results in decreased material hardness, poor microstructure uniformity, and reduced wear resistance during service. To suppress grain growth, existing technologies often incorporate carbides such as vanadium, chromium, tantalum, and niobium as grain growth inhibitors. However, single inhibitors suffer from uneven dispersion, interfacial segregation, excessive precipitation, or a single inhibition stage during sintering. This can easily lead to decreased continuity of the binder phase, increased brittle phases, or weakened interfacial bonding, making it difficult to maintain high hardness while simultaneously ensuring bending strength and fracture toughness.

[0004] Furthermore, the performance of ultrafine-grained tungsten carbide cobalt cemented carbide depends not only on the tungsten carbide grain size but also on the wettability of the cobalt binder phase, the interfacial bonding state between the hard phase and the binder phase, the oxygen impurity content, and the carbon potential stability during sintering. While existing technologies can improve the microstructure by adjusting graphite content, optimizing the sintering process, or adding conventional rare earth oxides, these methods have limited effectiveness in removing interfacial oxygen impurities, promoting uniform spread of the binder phase, and stabilizing grain boundaries, making it difficult to achieve synergistic regulation of grain growth inhibition and interfacial strengthening. Therefore, there is an urgent need for an ultrafine-grained tungsten carbide cobalt cemented carbide and its preparation method that can utilize multi-component composite carbides to inhibit tungsten carbide grain growth and combine a rare earth zirconium-based oxygen vacancy interfacial phase to improve interfacial bonding and microstructure uniformity, in order to solve the problem of the difficulty in coordinating the improvement of hardness, wear resistance, and toughness in existing materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an ultrafine-grained WC-Co cemented carbide and its preparation method.

[0006] In a first aspect, the present invention provides an ultrafine-grained WC-Co cemented carbide comprising the following components in parts by weight: 86.20-91.80 parts of ultrafine tungsten carbide powder, 7.20-11.50 parts of cobalt carbonyl powder, 0.40-1.60 parts of vanadium-chromium-tantalum-niobium-zirconium composite carbide, 0.05-0.35 parts of cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase, and 0.02-0.20 parts of graphite powder.

[0007] A second aspect of the present invention provides a method for preparing the aforementioned ultrafine-grained WC-Co cemented carbide, comprising the following steps:

[0008] S1. Under argon protection, ultrafine tungsten carbide powder, cobalt carbonyl powder, vanadium-chromium-tantalum-niobium-zirconium composite carbide, cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and graphite powder are added to 70-130 parts of anhydrous ethanol, and 0.60-1.50 parts of polyethylene glycol 6000 are added. The mixture is ball-milled to obtain WC-Co composite slurry. The WC-Co composite slurry is dried and sieved to obtain composite granulated powder.

[0009] S2. The composite granulated powder is loaded into a mold and pressed to obtain a green body; the green body is cold isostatically pressed to obtain a pressed green body; the pressed green body is placed in a vacuum degreasing and sintering furnace for vacuum degreasing and pre-sintering, followed by liquid phase sintering, argon gas is introduced, pressure sintering is applied, and then it is cooled.

[0010] In this invention, during the preparation of ultrafine-grained WC-Co cemented carbide, ultrafine tungsten carbide powder serves as the source of the hard phase, cobalt carbonyl powder as the source of the binder phase, vanadium-chromium-tantalum-niobium-zirconium composite carbide as a grain growth inhibitor, cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase as an interface control component, graphite powder as a carbon potential regulating component, anhydrous ethanol as the ball milling medium, and polyethylene glycol 6000 as a forming auxiliary component. During ball milling under argon protection, the ultrafine tungsten carbide powder, cobalt carbonyl powder, vanadium-chromium-tantalum-niobium-zirconium composite carbide, cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and graphite powder are thoroughly mixed. The vanadium-chromium-tantalum-niobium-zirconium composite carbide is distributed between the ultrafine tungsten carbide powder particles, the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase is dispersed in the contact area between the hard and binder phases, and the graphite powder is uniformly distributed in the composite powder. Polyethylene glycol 6000 improves the forming adaptability of the composite slurry. The composite granulated powder obtained after drying and sieving is pressed and cold isostatically pressed to form a compact. During vacuum degreasing, polyethylene glycol 6000 is gradually discharged, and pre-sintering causes the powder particles to form a preliminary bond. During liquid-phase sintering, cobalt carbonyl powder forms a liquid-phase binder phase and wets the ultrafine tungsten carbide powder. The ultrafine tungsten carbide powder undergoes limited dissolution and re-precipitation. The vanadium and chromium carbide components in the vanadium-chromium-tantalum-niobium-zirconium composite carbide are enriched near the interface between the hard phase and the binder phase. The tantalum, niobium, and zirconium carbide components maintain a high-temperature stable pinning effect, which together reduces the dissolution and re-precipitation rate of the ultrafine tungsten carbide powder particles and inhibits abnormal grain growth. The cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase improves the spreading state of the liquid-phase binder phase relative to the hard phase by adsorbing interfacial oxygen impurities through oxygen vacancies. Graphite powder maintains the carbon potential stability during sintering. After argon gas is introduced and pressure sintering is performed, the residual porosity is reduced. After cooling, an ultrafine-grained WC-Co cemented carbide with uniform structure and enhanced interfacial bonding is formed.

[0011] According to a preferred embodiment of the present invention, in step S1, the ball milling time is 36-72 hours.

[0012] According to a preferred embodiment of the present invention, in step S2, the temperature of liquid phase sintering is 1360-1420°C.

[0013] According to a preferred embodiment of the present invention, the method for preparing the vanadium-chromium-tantalum-niobium-zirconium composite carbide includes:

[0014] A1. By weight, 12.0-18.0 parts of tantalum pentoxide, 8.0-14.0 parts of niobium pentoxide, 3.0-8.0 parts of nano-zirconium dioxide powder, 8.0-14.0 parts of acetylene black, 6.0-12.0 parts of thermosetting phenolic resin, and 100-160 parts of anhydrous ethanol are mixed and ball-milled under argon protection to obtain a composite slurry. The composite slurry is dried, crushed, and sieved to obtain a tantalum-niobium-zirconium carbothermic reduction precursor. The tantalum-niobium-zirconium carbothermic reduction precursor is placed in an argon atmosphere for carbothermic reduction and cooled to obtain tantalum-niobium-zirconium composite carbide powder.

[0015] A2. Mix 9.0-11.0 parts of tantalum-niobium-zirconium composite carbide powder, 0.8-1.8 parts of vanadium pentoxide, 0.6-1.6 parts of chromium trioxide, 2.0-5.0 parts of glucose, 1.0-3.0 parts of thermosetting phenolic resin, 0.1-0.5 parts of polyvinylpyrrolidone, and 60-100 parts of anhydrous ethanol. Ball mill under argon protection to obtain vanadium-chromium coated composite slurry. After drying, place the vanadium-chromium coated composite slurry in an argon atmosphere for secondary carbothermic reduction, followed by cooling, cleaning, drying, pulverizing, and sieving.

[0016] In this invention, during the preparation of the vanadium-chromium-tantalum-niobium-zirconium composite carbide, tantalum pentoxide, niobium pentoxide, and nano-zirconium dioxide powder are used as the sources of tantalum, niobium, and zirconium, respectively; acetylene black and thermosetting phenolic resin are used as the carbon source; and anhydrous ethanol is used as the dispersion medium. Ball milling thoroughly refines and uniformly contacts the tantalum pentoxide, niobium pentoxide, nano-zirconium dioxide powder, acetylene black, and thermosetting phenolic resin. After drying, crushing, and sieving, a tantalum-niobium-zirconium carbothermic reduction precursor is obtained. When the tantalum-niobium-zirconium carbothermic reduction precursor is heated in an argon atmosphere, the thermosetting phenolic resin first undergoes pyrolysis and carbonization. The residual carbon and acetylene black together form a dispersed carbon source. This dispersed carbon source coats the tantalum pentoxide, niobium pentoxide, and nano-zirconium dioxide powder particles, shortening the distance of the oxide deoxidation and carbonization reaction. During carbothermal reduction, tantalum pentoxide and niobium pentoxide gradually lose oxygen and react with a dispersed carbon source to form tantalum carbide components and niobium carbide components. Nano-zirconia powder reacts with the dispersed carbon source under high-temperature carbothermal reduction conditions to form zirconium carbide components. The tantalum, niobium, and zirconium carbide components then combine to obtain tantalum-niobium-zirconia composite carbide powder. Subsequently, the tantalum-niobium-zirconia composite carbide powder is ball-milled with vanadium pentoxide, chromium trioxide, glucose, thermosetting phenolic resin, polyvinylpyrrolidone, and anhydrous ethanol. Polyvinylpyrrolidone improves the powder's dispersibility and coating uniformity. Glucose and thermosetting phenolic resin are converted into finely dispersed carbon sources during drying and secondary carbothermal reduction, causing vanadium pentoxide and chromium trioxide to undergo reduction carbonization on the surface of the tantalum-niobium-zirconia composite carbide powder, forming vanadium and chromium-containing carbide components. After cooling, washing, drying, pulverizing, and sieving, vanadium-chromium-tantalum-niobium-zirconia composite carbide is obtained.

[0017] According to a preferred embodiment of the present invention, in step A1, the ball milling time is 18-30 h and the carbothermic reduction temperature is 1550-1700 °C.

[0018] According to a preferred embodiment of the present invention, in step A2, the temperature of the secondary carbothermal reduction is 1220-1280°C, and the time of the secondary carbothermal reduction is 1.5-3.0h.

[0019] According to a preferred embodiment of the present invention, the method for preparing the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase includes:

[0020] B1. By weight, dissolve 2.0-4.0 parts of lanthanum nitrate hexahydrate, 1.0-3.0 parts of yttrium nitrate hexahydrate, 2.0-4.5 parts of cerium nitrate hexahydrate, and 3.0-6.0 parts of zirconium nitrate dihydrate in 60-100 parts of deionized water to obtain a mixed salt solution; add 6.0-12.0 parts of citric acid monohydrate and 4.0-8.0 parts of ethylene glycol to the mixed salt solution, adjust the pH to 6.0-7.0, stir the reaction, and obtain a complex sol; dry the complex sol, perform gel combustion, and grind it to obtain the cerium-zirconium-lanthanum-yttrium composite oxide precursor powder;

[0021] B2. The cerium-zirconium-lanthanum-yttrium composite oxide precursor powder was calcined in an air atmosphere to obtain the cerium-zirconium-lanthanum-yttrium composite oxide; the cerium-zirconium-lanthanum-yttrium composite oxide was then subjected to reduction treatment in a mixed atmosphere of hydrogen and nitrogen, followed by cooling, ball milling, drying, and sieving.

[0022] In this invention, during the preparation of the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, lanthanum nitrate hexahydrate, yttrium nitrate hexahydrate, cerium nitrate hexahydrate, and zirconium oxynitrate dihydrate are used as sources of lanthanum, yttrium, cerium, and zirconium, respectively. Deionized water is used as the dissolving medium, and citric acid monohydrate and ethylene glycol are used as complexing and gel-forming components. After dissolving, lanthanum nitrate hexahydrate, yttrium nitrate hexahydrate, cerium nitrate hexahydrate, and zirconium oxynitrate dihydrate form a homogeneous mixed salt solution. Citric acid monohydrate complexes with lanthanum, yttrium, cerium, and zirconium ions, ensuring uniform dispersion of different metal ions in the mixed salt solution. Ethylene glycol participates in the formation of the complex network, gradually transforming the system into a stable complex sol. After drying, the complexed sol forms a gel containing metal complexes and organic components. During gel combustion, the nitrate component provides oxidation, while citric acid monohydrate and ethylene glycol decompose as combustion components. The exothermic combustion promotes the transformation of lanthanum, yttrium, cerium, and zirconium components into loose composite oxide precursors. After grinding, cerium-zirconium-lanthanum-yttrium composite oxide precursor powder is obtained. When the cerium-zirconium-lanthanum-yttrium composite oxide precursor powder is calcined in air, residual organic components are further removed, and cerium, zirconium, lanthanum, and yttrium oxides form a uniform composite structure, yielding cerium-zirconium-lanthanum-yttrium composite oxides. When the cerium-zirconium-lanthanum-yttrium composite oxide is subjected to reduction treatment in a mixed atmosphere of hydrogen and nitrogen, the cerium component undergoes a partial valence state transformation accompanied by lattice oxygen desorption, forming oxygen vacancies. After the lanthanum and yttrium components enter the composite oxide lattice, they generate charge-compensating defects, further promoting the formation of oxygen vacancies. The zirconium component helps stabilize the composite oxide lattice and inhibit particle agglomeration, making the oxygen vacancy distribution more uniform. After cooling, ball milling, drying, and sieving, the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase is obtained.

[0023] According to a preferred embodiment of the present invention, in step B1, the temperature of the stirring reaction is 70-85°C, and the stirring reaction time is 2-4 hours.

[0024] According to a preferred embodiment of the present invention, in step B2, the temperature of the reduction treatment is 550-700°C, and the time of the reduction treatment is 1-3 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) This invention uses ultrafine tungsten carbide powder and carbonyl cobalt powder as the main components, and adds vanadium-chromium-tantalum-niobium-zirconium composite carbide, cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase and graphite powder. The vanadium-chromium-tantalum-niobium-zirconium composite carbide can be distributed between ultrafine tungsten carbide powder particles and near their interfaces during sintering, which can inhibit grain migration and growth, reduce local abnormal growth, keep the alloy structure fine and uniform, and thus improve the hardness and wear resistance of the material.

[0027] (2) The cerium-zirconium-lanthanum-yttrium oxygen vacancy interfacial phase can act on the bonding region formed by ultrafine tungsten carbide powder and cobalt carbonyl powder. Its oxygen vacancy structure is conducive to adsorbing interfacial oxygen impurities, reducing the influence of interfacial defects on the spreading of the bonding phase, and making the bonding phase formed by cobalt carbonyl powder more uniformly distributed around the ultrafine tungsten carbide powder. This effect can improve the interfacial bonding state, reduce local bonding phase aggregation, weak bonding areas and micropore defects, and improve the crack resistance and reliability of the material.

[0028] (3) Graphite powder can regulate the carbon potential during sintering, reducing the risk of decarburization phase formation and abnormal precipitation of free carbon; anhydrous ethanol is beneficial for the full dispersion of each component during ball milling, and polyethylene glycol 6000 is beneficial for the pressing and forming of composite granulated powder. After vacuum degreasing, pre-sintering, liquid phase sintering and pressure sintering, the compaction degree of the pressed blank is improved, and finally an ultrafine-grained WC-Co cemented carbide with uniform structure, good interfacial bonding, and high hardness, wear resistance and toughness is obtained. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing ultrafine-grained WC-Co cemented carbide, the steps of which include:

[0032] S1. Under argon protection, 89.00g of ultrafine tungsten carbide powder, 9.35g of cobalt carbonyl powder, 1.00g of vanadium-chromium-tantalum-niobium-zirconium composite carbide, 0.20g of cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and 0.11g of graphite powder were added to 100g of anhydrous ethanol, along with 1.05g of polyethylene glycol 6000 and cemented carbide grinding balls. The ball-to-material mass ratio was 6:1. After sealing, argon gas was introduced three times for purging, and the mixture was ball-milled for 54h under argon protection to obtain WC-Co composite slurry. The WC-Co composite slurry was then vacuum-dried at 80℃ for 10h. After drying, it was sieved through a 100-mesh sieve to obtain composite granulated powder.

[0033] S2. The composite granulated powder is loaded into a mold and pressed at 150 MPa to obtain a green body. The green body is then cold isostatically pressed at 200 MPa for 3 minutes to obtain a pressed green body. The pressed green body is placed in a vacuum degreasing and sintering furnace and vacuum degreasing and pre-sintering are performed under a vacuum degree not exceeding 10 Pa. The vacuum degreasing temperature is 500℃ and the vacuum degreasing time is 2 hours. The pre-sintering temperature is 1000℃ and the pre-sintering time is 1 hour. Subsequently, liquid phase sintering is performed at 1390℃, argon gas is introduced, and pressure sintering is carried out at 6 MPa for 60 minutes. The mixture is then cooled to 25℃ to obtain an ultrafine-grained WC-Co cemented carbide.

[0034] Preparation steps of vanadium-chromium-tantalum-niobium-zirconium composite carbides:

[0035] A1. 15.0g tantalum pentoxide, 11.0g niobium pentoxide, 5.5g nano-zirconium dioxide powder, 11.0g acetylene black, 9.0g thermosetting phenolic resin, and 130g anhydrous ethanol were added to a ball mill jar, along with cemented carbide grinding balls at a mass ratio of 6:1. After sealing, argon gas was introduced three times for purging, and the mixture was ball-milled for 24 hours under argon protection to obtain a composite slurry. The composite slurry was transferred to a drying tray and vacuum-dried at 80℃ for 10 hours to allow the anhydrous ethanol to evaporate, resulting in a dried block. The dried block was crushed and sieved through a 100-mesh sieve to obtain a tantalum-niobium-zirconium carbothermic reduction precursor. The tantalum-niobium-zirconium carbothermic reduction precursor was placed in a graphite boat, which was then placed in a tube furnace. Argon gas was introduced to maintain a protective atmosphere, and carbothermic reduction was performed at 1625℃ for 3 hours. Subsequently, the mixture was cooled to 25℃ in an argon atmosphere to obtain tantalum-niobium-zirconium composite carbide powder.

[0036] A2. Add 10.0g of tantalum-niobium-zirconium composite carbide powder, 1.3g of vanadium pentoxide, 1.1g of chromium trioxide, 3.5g of glucose, 2.0g of thermosetting phenolic resin, 0.3g of polyvinylpyrrolidone, and 80g of anhydrous ethanol to a ball mill jar. Add cemented carbide grinding balls at a ball-to-material mass ratio of 6:1. After sealing, purge with argon gas three times and ball mill for 18 hours under argon protection to obtain a vanadium-chromium coated composite slurry. Transfer the vanadium-chromium coated composite slurry to a drying tray and vacuum dry at 80℃. After 10 hours, a dry powder was obtained. The dry powder was placed in a graphite boat, which was then placed in a tube furnace. Argon gas was introduced to maintain a protective atmosphere, and a secondary carbothermal reduction was carried out at 1250℃ for 2.25 hours. Subsequently, the powder was cooled to 25℃ in an argon atmosphere to obtain a secondary carbothermal reduced powder. The secondary carbothermal reduced powder was washed three times with anhydrous ethanol. After each washing, the powder was centrifuged and the precipitate was collected. The precipitate was vacuum dried at 80℃ for 8 hours, pulverized, and sieved through a 200-mesh sieve to obtain a vanadium-chromium-tantalum-niobium-zirconium composite carbide.

[0037] Preparation steps of the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase:

[0038] B1. Add 3.0g of lanthanum nitrate hexahydrate, 2.0g of yttrium nitrate hexahydrate, 3.25g of cerium nitrate hexahydrate and 4.5g of zirconium nitrate dihydrate to 80g of deionized water and stir at 25℃ for 30min until completely dissolved to obtain a mixed salt solution; add 9.0g of citric acid monohydrate and 6.0g of ethylene glycol to the mixed salt solution, adjust the pH to 6.5 with ammonia water, and stir at 77.5℃ for 3h to obtain a complex sol; dry the complex sol at 105℃ for 8h to obtain a dry gel; place the dry gel in a heat-resistant container and perform gel combustion in an air atmosphere; after combustion, cool to 25℃ and grind the combustion product for 30min to obtain cerium-zirconium-lanthanum-yttrium composite oxide precursor powder;

[0039] B2. The cerium-zirconium-lanthanum-yttrium composite oxide precursor powder was placed in an alumina boat, which was then placed in a furnace and calcined at 600°C for 2 hours in air. After cooling to 25°C, the cerium-zirconium-lanthanum-yttrium composite oxide was obtained. The cerium-zirconium-lanthanum-yttrium composite oxide was placed in a tube furnace and a mixed atmosphere of hydrogen and nitrogen was introduced, with a hydrogen integral of 5% and a nitrogen integral of 95%. It was reduced at 625°C for 2 hours, and then cooled to 25°C in a nitrogen atmosphere to obtain the reduced powder. The reduced powder was ball-milled in anhydrous ethanol for 4 hours at a ball-to-powder mass ratio of 5:1. After ball milling, it was vacuum dried at 80°C for 8 hours and then sieved through a 200-mesh sieve to obtain the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase.

[0040] Example 2

[0041] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing an ultrafine-grained WC-Co cemented carbide, the steps of which include:

[0042] S1. Under argon protection, 86.20g of ultrafine tungsten carbide powder, 7.20g of cobalt carbonyl powder, 0.40g of vanadium-chromium-tantalum-niobium-zirconium composite carbide, 0.05g of cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and 0.02g of graphite powder were added to 70g of anhydrous ethanol, along with 0.60g of polyethylene glycol 6000. The mixture was ball-milled for 36h to obtain a WC-Co composite slurry. The WC-Co composite slurry was dried at 80℃ for 10h, and then sieved to obtain composite granulated powder.

[0043] S2. The composite granulated powder is loaded into a mold and pressed at 150 MPa to obtain a green body. The green body is then cold isostatically pressed at 200 MPa for 3 minutes to obtain a pressed green body. The pressed green body is placed in a vacuum degreasing and sintering furnace and vacuum degreasing and pre-sintering are performed under a vacuum degree not exceeding 10 Pa. Subsequently, liquid phase sintering is performed at 1360℃, argon gas is introduced, and pressure sintering is performed at 6 MPa for 60 minutes. The mixture is then cooled to 25℃ to obtain an ultrafine-grained WC-Co cemented carbide.

[0044] Preparation steps of vanadium-chromium-tantalum-niobium-zirconium composite carbides:

[0045] A1. 12.0g tantalum pentoxide, 8.0g niobium pentoxide, 3.0g nano-zirconium dioxide powder, 8.0g acetylene black, 6.0g thermosetting phenolic resin and 100g anhydrous ethanol were added to a ball mill jar and ball milled for 18h under argon protection to obtain a composite slurry. The composite slurry was placed in a vacuum drying oven and dried at 80℃ for 10h. After drying, it was crushed and sieved to obtain a tantalum-niobium-zirconium carbothermic reduction precursor. The tantalum-niobium-zirconium carbothermic reduction precursor was placed in a graphite boat, and the graphite boat was placed in a tube furnace. The temperature was raised to 1550℃ in an argon atmosphere for carbothermic reduction for 3h, and then cooled to 25℃ in an argon atmosphere to obtain tantalum-niobium-zirconium composite carbide powder.

[0046] A2. 9.0g of tantalum-niobium-zirconium composite carbide powder, 0.8g of vanadium pentoxide, 0.6g of chromium trioxide, 2.0g of glucose, 1.0g of thermosetting phenolic resin, 0.1g of polyvinylpyrrolidone, and 60g of anhydrous ethanol were added to a ball mill jar and ball-milled for 18 hours under argon protection to obtain a vanadium-chromium coated composite slurry. The vanadium-chromium coated composite slurry was placed in a vacuum drying oven and dried at 80℃ for 10 hours. After drying, it was placed in a graphite boat, which was then placed in a tube furnace and heated to 1220℃ in an argon atmosphere for a secondary carbothermic reduction for 1.5 hours. Subsequently, it was cooled to 25℃ in an argon atmosphere, washed three times with anhydrous ethanol, dried at 80℃ for 8 hours, pulverized, and sieved to obtain the vanadium-chromium-tantalum-niobium-zirconium composite carbide.

[0047] Preparation steps of the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase:

[0048] B1. Add 2.0g of lanthanum nitrate hexahydrate, 1.0g of yttrium nitrate hexahydrate, 2.0g of cerium nitrate hexahydrate and 3.0g of zirconium nitrate dihydrate to 60g of deionized water and stir at 25°C until completely dissolved to obtain a mixed salt solution; add 6.0g of citric acid monohydrate and 4.0g of ethylene glycol to the mixed salt solution, adjust the pH to 6.0, and stir at 70°C for 2h to obtain a complex sol; dry the complex sol at 105°C for 8h, then perform gel combustion, cool the combustion product to 25°C and grind for 30min to obtain cerium-zirconium-lanthanum-yttrium composite oxide precursor powder;

[0049] B2. The precursor powder of cerium-zirconium-lanthanum-yttrium composite oxide was placed in an alumina boat, and the alumina boat was placed in a furnace and calcined at 600°C for 2 hours in an air atmosphere to obtain cerium-zirconium-lanthanum-yttrium composite oxide. The cerium-zirconium-lanthanum-yttrium composite oxide was placed in a tube furnace and reduced at 550°C for 1 hour in a mixed atmosphere of hydrogen and nitrogen. Then it was cooled to 25°C in a nitrogen atmosphere, ball-milled for 4 hours, dried at 80°C for 8 hours, and sieved to obtain the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase.

[0050] Example 3

[0051] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing an ultrafine-grained WC-Co cemented carbide, the steps of which include:

[0052] S1. Under argon protection, 91.80g of ultrafine tungsten carbide powder, 11.50g of cobalt carbonyl powder, 1.60g of vanadium-chromium-tantalum-niobium-zirconium composite carbide, 0.35g of cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and 0.20g of graphite powder were added to 130g of anhydrous ethanol, along with 1.50g of polyethylene glycol 6000. The mixture was ball-milled for 72h to obtain a WC-Co composite slurry. The WC-Co composite slurry was dried at 80℃ for 10h, and then sieved to obtain composite granulated powder.

[0053] S2. The composite granulated powder is loaded into a mold and pressed at 150 MPa to obtain a green body. The green body is then cold isostatically pressed at 200 MPa for 3 minutes to obtain a pressed green body. The pressed green body is placed in a vacuum degreasing and sintering furnace and vacuum degreasing and pre-sintering are performed under a vacuum degree not exceeding 10 Pa. Subsequently, liquid phase sintering is performed at 1420℃, argon gas is introduced, and pressure sintering is performed at 6 MPa for 60 minutes. The mixture is then cooled to 25℃ to obtain an ultrafine-grained WC-Co cemented carbide.

[0054] Preparation steps of vanadium-chromium-tantalum-niobium-zirconium composite carbides:

[0055] A1. 18.0g tantalum pentoxide, 14.0g niobium pentoxide, 8.0g nano-zirconium dioxide powder, 14.0g acetylene black, 12.0g thermosetting phenolic resin and 160g anhydrous ethanol were added to a ball mill jar and ball milled for 30h under argon protection to obtain a composite slurry. The composite slurry was placed in a vacuum drying oven and dried at 80℃ for 10h. After drying, it was crushed and sieved to obtain a tantalum-niobium-zirconium carbothermic reduction precursor. The tantalum-niobium-zirconium carbothermic reduction precursor was placed in a graphite boat, and the graphite boat was placed in a tube furnace. The temperature was raised to 1700℃ in an argon atmosphere for carbothermic reduction for 3h, and then cooled to 25℃ in an argon atmosphere to obtain tantalum-niobium-zirconium composite carbide powder.

[0056] A2. 11.0g of tantalum-niobium-zirconium composite carbide powder, 1.8g of vanadium pentoxide, 1.6g of chromium trioxide, 5.0g of glucose, 3.0g of thermosetting phenolic resin, 0.5g of polyvinylpyrrolidone, and 100g of anhydrous ethanol were added to a ball mill jar and ball milled for 18h under argon protection to obtain vanadium-chromium coated composite slurry. The vanadium-chromium coated composite slurry was placed in a vacuum drying oven and dried at 80℃ for 10h. After drying, it was placed in a graphite boat and placed in a tube furnace. The furnace was heated to 1280℃ in an argon atmosphere for a second carbothermic reduction for 3.0h. Then it was cooled to 25℃ in an argon atmosphere, washed three times with anhydrous ethanol, dried at 80℃ for 8h, pulverized, and sieved to obtain vanadium-chromium-tantalum-niobium-zirconium composite carbide.

[0057] Preparation steps of the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase:

[0058] B1. Add 4.0 g of lanthanum nitrate hexahydrate, 3.0 g of yttrium nitrate hexahydrate, 4.5 g of cerium nitrate hexahydrate and 6.0 g of zirconium nitrate dihydrate to 100 g of deionized water and stir at 25 °C until completely dissolved to obtain a mixed salt solution. Add 12.0 g of citric acid monohydrate and 8.0 g of ethylene glycol to the mixed salt solution, adjust the pH to 7.0, and stir at 85 °C for 4 h to obtain a complex sol. Dry the complex sol at 105 °C for 8 h, then perform gel combustion. After cooling the combustion product to 25 °C, grind it for 30 min to obtain the cerium-zirconium-lanthanum-yttrium composite oxide precursor powder.

[0059] B2. The cerium-zirconium-lanthanum-yttrium composite oxide precursor powder was placed in an alumina boat, and the alumina boat was placed in a furnace and calcined at 600°C for 2 hours in an air atmosphere to obtain the cerium-zirconium-lanthanum-yttrium composite oxide. The cerium-zirconium-lanthanum-yttrium composite oxide was placed in a tube furnace and reduced at 700°C for 3 hours in a mixed atmosphere of hydrogen and nitrogen. Then it was cooled to 25°C in a nitrogen atmosphere, ball-milled for 4 hours, dried at 80°C for 8 hours, and sieved to obtain the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that no vanadium-chromium-tantalum-niobium-zirconium composite carbide was prepared or added; otherwise, it is the same as Example 1.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that no cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase is prepared and no cerium-zirconium-lanthanum-yttrium-oxygen-vacancy phase is added; otherwise, it is the same as Example 1.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that the vanadium-chromium-tantalum-niobium-zirconium composite carbide and the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase are not prepared or added; otherwise, they are the same as in Example 1.

[0066] The properties of the ultrafine-grained WC-Co cemented carbides obtained in Examples 1-3 and Comparative Examples 1-3 were tested.

[0067] The ultrafine-grained WC-Co cemented carbide samples prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. At least 5 parallel samples were taken for each group of samples. Before the test, the sample surface was subjected to coarse grinding, fine grinding and polishing in sequence, and then dried at 80°C for 2 hours after being cleaned with anhydrous ethanol. The average value of all test results was taken as the average value of the parallel samples.

[0068] For relative density testing, the sample is processed into a block-shaped specimen with a smooth surface and no obvious gaps. The mass of the dried sample in air is weighed, and then the sample is completely immersed in deionized water at 25°C. After removing the air bubbles attached to the surface, the suspended mass is weighed, and the actual density of the sample is calculated. The theoretical density is calculated based on the ratio of ultrafine tungsten carbide powder, carbonyl cobalt powder, vanadium-chromium-tantalum-niobium-zirconium composite carbide, cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase, and graphite powder. The relative density is then obtained by the ratio of the actual density to the theoretical density, and the result is expressed as a percentage (%).

[0069] During the average grain size test, the sample was cut and mounted, and polished to a mirror finish using a diamond grinding wheel and diamond polishing fluid. The polished surface was then etched to expose the grain boundaries. The microstructure was observed under a scanning electron microscope. At least five fields of view were randomly selected for each sample, and at least 100 grains formed after the sintering of ultrafine tungsten carbide powder were counted in each field of view. The grain size was calculated using the truncation method and the average value was taken. The result is expressed in nm.

[0070] During hardness testing, the polished sample was fixed on the Vickers hardness tester stage and held under a load of 294N for 15s. Five indentations were tested for each sample. The center-to-center distance between adjacent indentations was not less than three times the length of the diagonal of the indentation. Data with abnormal crack propagation, edge chipping, or incomplete indentations were discarded, and the average value was taken. The result is expressed as HV30.

[0071] During the flexural strength test, the sample is processed into a long strip specimen. Each surface of the specimen is finely ground and the edge burrs are removed. The test is conducted using a 3-point bending loading method with a span of 20 mm and a loading speed of 0.5 mm / min. The loading direction is perpendicular to the wide surface of the specimen. The maximum load at fracture is recorded, and the flexural strength is calculated based on the specimen width, thickness, span, and fracture load. The results are expressed in MPa.

[0072] For fracture toughness testing, samples were polished to a mirror finish and then cracks were prepared using the Vickers indentation method. A load of 294 N was applied for 15 seconds, and the diagonal length of the indentation and the length of the crack extending from the corner of the indentation were measured. Five effective indentations with clear crack morphology and no edge chipping were selected from each sample. Fracture toughness was calculated based on hardness, indentation size, and crack length. The results are expressed in MPa·m. 1 / 2 express.

[0073] For wear rate testing, the samples were machined into planar specimens with uniform surface roughness. After cleaning and drying with anhydrous ethanol, they were fixed on a reciprocating friction and wear test bench and tested under dry friction conditions: a load of 30 N, a sliding speed of 0.10 m / s, and a wear time of 60 min. After the test, the wear debris on the sample surface was removed. The cross-sectional area and length of the wear track were measured using a three-dimensional profilometer, and the wear volume was calculated. The wear rate was then calculated as the ratio of the wear volume to the product of the load and the sliding distance. The results are expressed in mm. 3 ·N -1 ·m -1 express.

[0074] The performance test data above are shown in Table 1.

[0075] Table 1: Performance Test Results

[0076]

[0077] The test results in Table 1 clearly show that the relative densities of Examples 1-3 are 99.5-99.7%, which are all higher than those of Comparative Example 1 (98.9%), Comparative Example 2 (99.1%), and Comparative Example 3 (98.4%). This indicates that the simultaneous addition of vanadium-chromium-tantalum-niobium-zirconium composite carbide and cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase improves the sintering densification of ultrafine-grained WC-Co cemented carbide and reduces porosity defects.

[0078] The average grain size of Examples 1-3 was 230-285 nm, which was significantly lower than 465 nm of Comparative Example 1 and 620 nm of Comparative Example 3, and also lower than 310 nm of Comparative Example 2. This indicates that the vanadium-chromium-tantalum-niobium-zirconium composite carbide can effectively suppress the dissolution, migration and re-precipitation of ultrafine tungsten carbide powder during liquid phase sintering, and solve the problem of abnormal grain growth in existing ultrafine-grained cemented carbide.

[0079] The hardness of Examples 1-3 was 1935-2060 HV30, significantly higher than that of Comparative Example 1 (1765 HV30), Comparative Example 2 (1900 HV30), and Comparative Example 3 (1640 HV30), and the wear rate was only 1.8 × 10⁻⁶. -6 -2.3×10 -6 mm 3 ·N -1 ·m -1 This is lower than the 5.6 × 10⁻⁶ of Comparative Example 1. -6 mm 3 ·N -1 ·m -1 Comparative Example 2: 3.8 × 10 -6 mm 3 ·N -1 ·m -1 And 8.4 × 10⁻⁶ in Comparative Example 3 - 6 mm 3 ·N -1 ·m -1 This indicates that grain refinement and the pinning effect of composite carbides improve the hardness and wear resistance of the material.

[0080] The flexural strength of Examples 1-3 is 3970-4210 MPa, and the fracture toughness is 10.8-11.4 MPa·m. 1 / 2 Both were higher than the 3455 MPa and 8.9 MPa·m of Comparative Example 2. 1 / 2 And Comparative Example 3: 3180 MPa and 8.2 MPa·m 1 / 2 This indicates that the cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase can improve the interfacial bonding between the hard phase and the binder phase, and reduce the adverse effects of interfacial oxygen impurities and weak bonding regions on crack propagation.

[0081] Comparative Example 1, without the addition of vanadium-chromium-tantalum-niobium-zirconium composite carbide, showed increased grain size and decreased hardness and wear resistance. Comparative Example 2, without the addition of cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, showed decreased bending strength and fracture toughness. Comparative Example 3, lacking both vanadium-chromium-tantalum-niobium-zirconium composite carbide and cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, exhibited the worst performance across all aspects. This demonstrates that the present invention, through the synergistic effect of vanadium-chromium-tantalum-niobium-zirconium composite carbide and cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, solves the technical problems of difficult-to-control grain growth, insufficient sintering density, weak interfacial bonding, and difficulty in simultaneously achieving hardness, wear resistance, and toughness in existing ultrafine-grained WC-Co cemented carbide.

Claims

1. An ultrafine-grained WC-Co cemented carbide, characterized in that, The composition includes the following components in parts by weight: 86.20-91.80 parts of ultrafine tungsten carbide powder, 7.20-11.50 parts of cobalt carbonyl powder, 0.40-1.60 parts of vanadium-chromium-tantalum-niobium-zirconium composite carbide, 0.05-0.35 parts of cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase, and 0.02-0.20 parts of graphite powder.

2. A method for preparing ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that the step... include: S1. Under argon protection, ultrafine tungsten carbide powder, cobalt carbonyl powder, vanadium-chromium-tantalum-niobium-zirconium composite carbide, cerium-zirconium-lanthanum-yttrium oxygen vacancy interface phase, and graphite powder are added to 70-130 parts of anhydrous ethanol, and 0.60-1.50 parts of polyethylene glycol 6000 are added. The mixture is ball-milled to obtain WC-Co composite slurry. The WC-Co composite slurry is dried and sieved to obtain composite granulated powder. S2. The composite granulated powder is loaded into a mold and pressed to obtain a green body; the green body is cold isostatically pressed to obtain a pressed green body; the pressed green body is placed in a vacuum degreasing and sintering furnace for vacuum degreasing and pre-sintering, followed by liquid phase sintering, argon gas is introduced, pressure sintering is applied, and then it is cooled.

3. The method for preparing ultrafine-grained WC-Co cemented carbide according to claim 2, characterized in that, In step S1, the ball milling time is 36-72 hours.

4. The method for preparing ultrafine-grained WC-Co cemented carbide according to claim 2, characterized in that, In step S2, the temperature of liquid phase sintering is 1360-1420℃.

5. The ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, The preparation method of the vanadium-chromium-tantalum-niobium-zirconium composite carbide includes: A1. By weight, 12.0-18.0 parts of tantalum pentoxide, 8.0-14.0 parts of niobium pentoxide, 3.0-8.0 parts of nano-zirconium dioxide powder, 8.0-14.0 parts of acetylene black, 6.0-12.0 parts of thermosetting phenolic resin, and 100-160 parts of anhydrous ethanol are mixed and ball-milled under argon protection to obtain a composite slurry. The composite slurry is dried, crushed, and sieved to obtain a tantalum-niobium-zirconium carbothermic reduction precursor. The tantalum-niobium-zirconium carbothermic reduction precursor is placed in an argon atmosphere for carbothermic reduction and cooled to obtain tantalum-niobium-zirconium composite carbide powder. A2. Mix 9.0-11.0 parts of tantalum-niobium-zirconium composite carbide powder, 0.8-1.8 parts of vanadium pentoxide, 0.6-1.6 parts of chromium trioxide, 2.0-5.0 parts of glucose, 1.0-3.0 parts of thermosetting phenolic resin, 0.1-0.5 parts of polyvinylpyrrolidone, and 60-100 parts of anhydrous ethanol. Ball mill under argon protection to obtain vanadium-chromium coated composite slurry. After drying, place the vanadium-chromium coated composite slurry in an argon atmosphere for secondary carbothermic reduction, followed by cooling, cleaning, drying, pulverizing, and sieving.

6. The ultrafine-grained WC-Co cemented carbide according to claim 5, characterized in that, In step A1, the ball milling time is 18-30 hours, and the carbothermic reduction temperature is 1550-1700℃.

7. The ultrafine-grained WC-Co cemented carbide according to claim 5, characterized in that, In step A2, the temperature of the secondary carbothermal reduction is 1220-1280℃, and the time of the secondary carbothermal reduction is 1.5-3.0h.

8. The ultrafine-grained WC-Co cemented carbide according to claim 1, characterized in that, The preparation method of the cerium-zirconium-lanthanum-yttrium oxygen-vacancy interface phase includes: B1. By weight, dissolve 2.0-4.0 parts of lanthanum nitrate hexahydrate, 1.0-3.0 parts of yttrium nitrate hexahydrate, 2.0-4.5 parts of cerium nitrate hexahydrate, and 3.0-6.0 parts of zirconium nitrate dihydrate in 60-100 parts of deionized water to obtain a mixed salt solution; add 6.0-12.0 parts of citric acid monohydrate and 4.0-8.0 parts of ethylene glycol to the mixed salt solution, adjust the pH to 6.0-7.0, stir the reaction, and obtain a complex sol; dry the complex sol, perform gel combustion, and grind it to obtain the cerium-zirconium-lanthanum-yttrium composite oxide precursor powder; B2. The cerium-zirconium-lanthanum-yttrium composite oxide precursor powder was calcined in an air atmosphere to obtain the cerium-zirconium-lanthanum-yttrium composite oxide; the cerium-zirconium-lanthanum-yttrium composite oxide was then subjected to reduction treatment in a mixed atmosphere of hydrogen and nitrogen, followed by cooling, ball milling, drying, and sieving.

9. The ultrafine-grained WC-Co cemented carbide according to claim 8, characterized in that, In step B1, the temperature of the stirring reaction is 70-85℃, and the stirring reaction time is 2-4 hours.

10. The ultrafine-grained WC-Co cemented carbide according to claim 8, characterized in that, In step B2, the reduction treatment temperature is 550-700℃, and the reduction treatment time is 1-3h.

Images