A method for preparing high-density, cobalt-free nano-tungsten carbide cemented carbide.

Abstract

This invention discloses a method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide, belonging to the field of cemented carbide technology. The preparation method includes the following steps: aluminum powder, copper powder, manganese powder, molybdenum powder, and titanium powder are mixed and then subjected to a first ball milling process to obtain high-entropy alloy powder; nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide, and yttrium oxide are mixed and then subjected to a second ball milling process to obtain composite powder; paraffin wax, stearic acid, ethylene-vinyl acetate copolymer, and low-density polyethylene are mixed to obtain a binder; the composite powder and binder are kneaded to obtain a compound; the compound is extruded to obtain a green body; the green body is subsequently subjected to solvent degreasing and hot degreasing treatments to obtain a degreased green body; the degreased green body is rapidly hot-pressed and sintered to obtain the high-density cobalt-free nano-tungsten carbide cemented carbide. Through the above scheme, this invention prepares a high-density cobalt-free nano-tungsten carbide cemented carbide with good density, hardness, and oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide technology, specifically to a method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide. Background Technology

[0002] Cemented carbide, due to its excellent hardness, wear resistance, and high-temperature performance, is widely used in cutting tools, molds, wear-resistant parts, and other fields. Traditional cemented carbide is usually prepared using powder metallurgy processes, with tungsten carbide (WC) as the hard phase and metals such as cobalt (Co) or nickel (Ni) as the binder phase. However, with the continuous improvement of industrial requirements for material performance, especially the increasing demand for cobalt-free cemented carbide, traditional cemented carbide is gradually showing its limitations in certain applications.

[0003] Cobalt-free tungsten carbide cemented carbide has attracted attention due to its unique environmental advantages and corrosion resistance, but its preparation process faces many challenges. For example, the cobalt-free system requires extremely high temperatures during sintering, which places higher demands on equipment and processes. Furthermore, under high-temperature conditions, nano-tungsten carbide particles are prone to abnormal grain growth, affecting the material's microstructure and overall properties. To maintain the excellent properties of tungsten carbide, the temperature gradient and holding time during sintering must be strictly controlled to prevent excessive grain growth. Although spark plasma sintering technology can solve some of these problems, its high equipment cost and complex process parameters limit its large-scale application.

[0004] Patent CN109692955A discloses a method for preparing pure tungsten carbide cemented carbide. Combining discharge plasma sintering with specific sintering processes, the entire sintering cycle is controlled within 40-60 minutes, ensuring the tungsten carbide grains maintain their initial state, resulting in a high-density pure tungsten carbide cemented carbide material. This method uses micron-sized tungsten carbide powder as a single-component phase for sintering, without adding any metal binders or non-metallic additives. The resulting tungsten carbide cemented carbide has a density of approximately 99%, a density of approximately 15.4 g / cm³, a Vickers hardness of 2600-2700 HV, a flexural strength of 1400-1500 MPa, and a compressive strength of 8000 MPa. However, while the cemented carbide prepared by this method has high density and hardness, the lack of a binder phase may lead to insufficient toughness, and the high equipment requirements limit its widespread application. Summary of the Invention

[0005] Existing technologies for preparing cobalt-free nano-tungsten carbide cemented carbides still have certain shortcomings in terms of grain refinement and densification control, grain growth suppression during high-temperature sintering, and performance optimization in cobalt-free systems. Therefore, this invention provides a method for preparing highly dense cobalt-free nano-tungsten carbide cemented carbides, optimizing grain distribution and density, and improving material properties to meet the demands of modern industry for high-performance cemented carbides. Specifically, the technical solution of this invention includes the following steps:

[0006] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide, the method comprising the following steps:

[0007] Aluminum powder, copper powder, manganese powder, molybdenum powder and titanium powder are mixed and then subjected to a first ball milling process with grinding balls at a ball-to-material ratio of 10:1 to obtain high-entropy alloy powder.

[0008] Nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide and yttrium oxide are mixed and then subjected to a second ball milling process with grinding balls at a ball-to-material ratio of 8:1 to obtain composite powder.

[0009] An adhesive is obtained by mixing paraffin wax, stearic acid, ethylene-vinyl acetate copolymer, and low-density polyethylene.

[0010] The composite powder and binder are intensively mixed to obtain a compound, which is then extruded to obtain a green body. The green body is then subjected to solvent degreasing and thermal degreasing treatments to obtain a degreased green body.

[0011] The high-density cobalt-free nano-tungsten carbide cemented carbide was obtained by rapid hot pressing and sintering of the degreased blank.

[0012] Furthermore, the weight ratio of the aluminum powder, copper powder, manganese powder, molybdenum powder, and titanium powder is 1.25–1.45: 6.25–6.45: 5.4–5.6: 9.5–9.7: 4.7–4.9.

[0013] Furthermore, the conditions for the first ball milling treatment include a ball milling speed of 300 r / min and a ball milling time of 18–22 h.

[0014] Furthermore, the weight ratio of the nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide, and yttrium oxide is 80–84:11–13:1.1–1.3:0.5–0.7:0.9–1.1:3.4–3.6:1.4–1.6.

[0015] Furthermore, the conditions for the second ball milling treatment include a ball milling speed of 210–250 r / min and a ball milling time of 14–16 h.

[0016] Furthermore, the weight ratio of paraffin wax, stearic acid, ethylene-vinyl acetate copolymer and low-density polyethylene is 36-40:9-10:13-15:23-25.

[0017] Furthermore, the weight ratio of the composite powder to the binder is 100:8.5 to 9.5.

[0018] Furthermore, the mixing conditions include a mixing temperature of 120–125°C and a mixing time of 40–60 min.

[0019] Furthermore, the extrusion molding conditions include an extrusion temperature of 90–100°C and an extrusion pressure of 45–55 MPa.

[0020] Furthermore, the conditions for solvent degreasing include hexane as the degreasing solvent, a degreasing temperature of 40–50°C, and a degreasing time of 24–26 h.

[0021] Furthermore, the conditions for heat degreasing include first heating to 80°C and holding for 30 minutes, then heating to 200°C and holding for 60 minutes, then heating to 350°C and holding for 120 minutes, and finally heating to 450°C and holding for 90 minutes.

[0022] Furthermore, the conditions for rapid hot pressing sintering include a sintering temperature of 1700–1800°C, a sintering time of 60–80 min, an axial pressure of 30–50 MPa, and a DC electric field of 80 V / cm.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) In this invention, five metal powders, Al, Cu, Mn, Mo and Ti, are formed into a high-entropy alloy through high-energy mechanical alloying during ball milling. Nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide and yttrium oxide are mixed to obtain a composite powder. The composite powder and binder are mixed and then subjected to intensive mixing, degreasing and electric field-assisted rapid hot pressing sintering to obtain a high-density cobalt-free nano-tungsten carbide hard alloy.

[0025] (2) In this invention, high-entropy alloy replaces traditional cobalt and forms a uniform distribution during ball milling. The solid solution strengthening effect of multi-principal alloy significantly improves the high-temperature stability of the binder phase. The interface between nano-tungsten carbide and high-entropy alloy is well wetted through two-stage ball milling. Combined with the grain boundary pinning of tantalum carbide and vanadium carbide and the bridging toughening of carbon nanotubes, grain growth is inhibited in a synergistic manner, and the final grain size is stabilized at the nanoscale, laying the structural foundation for ultra-high hardness. Lanthanum oxide and yttrium oxide purify the grain boundaries and reduce the oxygen impurity content during sintering. On the other hand, they form a rare earth segregation layer, which hinders grain boundary migration and enhances the interfacial bonding force. In synergy with electric field-assisted rapid hot pressing sintering, nanoparticle coarsening is inhibited and densification is achieved. The high-entropy effect of the high-entropy alloy binder phase delays the oxidation diffusion of elements. The densified structure blocks oxygen permeation channels. Rare earth oxides form a protective oxide film on the surface. In addition, the stress matching design of multi-scale reinforcing phases, such as carbides, carbon nanotubes, and rare earth elements, with the nano-tungsten carbide matrix ensures high hardness while avoiding brittle fracture, achieving an ideal balance between hardness and toughness. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0028] Example 1:

[0029] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0030] 1.25 parts by weight of aluminum powder, 6.25 parts by weight of copper powder, 5.4 parts by weight of manganese powder, 9.5 parts by weight of molybdenum powder and 4.7 parts by weight of titanium powder were mixed and loaded into a planetary ball mill jar with grinding balls at a ball-to-material ratio of 10:1. 20 parts by weight of anhydrous ethanol were added, and the mixture was ball-milled for 18 hours at a speed of 200 r / min in an argon-protected environment to obtain high-entropy alloy powder.

[0031] 80 parts by weight of nano-tungsten carbide powder, 11 parts by weight of high-entropy alloy powder, 1.1 parts by weight of tantalum carbide powder, 0.5 parts by weight of vanadium carbide powder, 0.9 parts by weight of carbon nanotubes, 3.4 parts by weight of lanthanum oxide and 1.4 parts by weight of yttrium oxide were mixed and loaded into a ball mill jar with grinding balls at a ball-to-material ratio of 8:1. Then 150 parts by weight of heptane were added. After a second ball milling treatment at 210 r / min for 14 h in an argon-protected environment, the composite powder was obtained by vacuum drying at 80 °C and passing through a 200-mesh sieve.

[0032] 36 parts by weight of paraffin wax were placed in a stainless steel container and heated to 68°C. Then, 9 parts by weight of stearic acid were added and stirred at 500 r / min for 10 min to obtain a premix. The mixture was then heated to 100°C and 13 parts by weight of ethylene-vinyl acetate copolymer were added and stirred at 50 r / min for 15 min. The mixture was then heated to 118°C and 23 parts by weight of low-density polyethylene were added and stirred for 30 min to obtain an adhesive.

[0033] 100 parts by weight of composite powder and 8.5 parts by weight of binder are placed in an internal mixer and heated to 120°C. The mixture is then internally mixed at 50 r / min for 40 min to obtain the compound.

[0034] The compound was placed in an extrusion cylinder and preheated at 90°C for 30 minutes. It was then extruded at a pressure of 45 MPa to obtain a green body. The green body was immersed in n-hexane at a liquid-to-solid ratio of 10:1 and degreased at 40°C for 24 hours. Then, under argon protection, the temperature was first raised to 80°C and held for 30 minutes, then raised to 200°C and held for 60 minutes, then raised to 350°C and held for 120 minutes, and finally raised to 450°C and held for 90 minutes. The degreased green body was obtained after the above thermal degreasing treatment.

[0035] The degreased preform was placed in a graphite mold and then placed in a rapid hot pressing sintering furnace. Argon gas was introduced to purge the air, and the temperature was raised to 1700℃ at a heating rate of 250℃ / min and held at that temperature for 60 min. An axial pressure of 30 MPa was applied and an 80 V / cm DC electric field was turned on. The vacuum / argon atmosphere was switched every 3 min to remove volatile impurities. The temperature was lowered to 1000℃ at a cooling rate of 80℃ / min, and the sample was transferred to a nitrogen-filled glove box by a robotic arm. The sample was then cooled to room temperature at a rate of 100℃ / min. Nitrogen protection was maintained throughout the process to prevent oxidation and produce a high-density cobalt-free nano-tungsten carbide cemented carbide.

[0036] Example 2:

[0037] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0038] 1.30 parts by weight of aluminum powder, 6.30 parts by weight of copper powder, 5.45 parts by weight of manganese powder, 9.55 parts by weight of molybdenum powder and 4.75 parts by weight of titanium powder were mixed and loaded into a planetary ball mill jar with grinding balls at a ball-to-material ratio of 10:1. 20 parts by weight of anhydrous ethanol were added, and the mixture was ball-milled for 19 hours at a speed of 220 r / min in an argon-protected environment to obtain high-entropy alloy powder.

[0039] 81 parts by weight of nano-tungsten carbide powder, 11.5 parts by weight of high-entropy alloy powder, 1.15 parts by weight of tantalum carbide powder, 0.55 parts by weight of vanadium carbide powder, 0.95 parts by weight of carbon nanotubes, 3.45 parts by weight of lanthanum oxide and 1.45 parts by weight of yttrium oxide were mixed and loaded into a ball mill jar with grinding balls at a ball-to-material ratio of 8:1. Then 150 parts by weight of heptane were added. After ball milling at 220 r / min for 14.5 h in an argon-protected environment, the mixture was dried under vacuum at 80 °C and passed through a 200-mesh sieve to obtain composite powder.

[0040] 37 parts by weight of paraffin wax were placed in a stainless steel container and heated to 69°C. Then, 9.2 parts by weight of stearic acid were added, and the mixture was stirred at 500 r / min for 10 min to obtain a premix. The mixture was then heated to 101°C and 13.5 parts by weight of ethylene-vinyl acetate copolymer were added. The mixture was stirred at 50 r / min for 15 min. The mixture was then heated to 119°C and 23.5 parts by weight of low-density polyethylene were added. The mixture was stirred for 30 min to obtain an adhesive.

[0041] 100 parts by weight of composite powder and 8.7 parts by weight of binder were placed in an internal mixer and heated to 121°C. The mixture was then internally mixed at 50 r / min for 45 min to obtain the compound.

[0042] The compound was placed in an extrusion cylinder and preheated at 92°C for 30 min. It was then extruded at a pressure of 47 MPa to obtain a green body. The green body was immersed in n-hexane at a liquid-to-solid ratio of 10:1 and degreased at 42°C for 24.5 h. Then, under argon protection, the temperature was first raised to 80°C and held for 30 min, then raised to 200°C and held for 60 min, then raised to 350°C and held for 120 min, and finally raised to 450°C and held for 90 min. The degreased green body was obtained by the above thermal degreasing treatment.

[0043] The degreased preform was placed in a graphite mold and then placed in a rapid hot pressing sintering furnace. Argon gas was introduced to purge the air, and the temperature was raised to 1720℃ at a heating rate of 250℃ / min and held at that temperature for 65 min. An axial pressure of 35MPa was applied and an 80V / cm DC electric field was turned on. The vacuum / argon atmosphere was switched every 3 min to remove volatile impurities. The temperature was lowered to 1000℃ at a cooling rate of 80℃ / min, and the sample was transferred to a nitrogen-filled glove box by a robotic arm. The sample was then cooled to room temperature at a rate of 100℃ / min. Nitrogen protection was maintained throughout the process to prevent oxidation and produce a high-density, cobalt-free nano-tungsten carbide cemented carbide.

[0044] Example 3:

[0045] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0046] 1.35 parts by weight of aluminum powder, 6.35 parts by weight of copper powder, 5.50 parts by weight of manganese powder, 9.60 parts by weight of molybdenum powder and 4.80 parts by weight of titanium powder were mixed and loaded into a planetary ball mill jar with grinding balls at a ball-to-material ratio of 10:1. 20 parts by weight of anhydrous ethanol were added, and the mixture was ball-milled for 20 hours at a speed of 250 r / min in an argon-protected environment to obtain high-entropy alloy powder.

[0047] 82 parts by weight of nano-tungsten carbide powder, 12 parts by weight of high-entropy alloy powder, 1.2 parts by weight of tantalum carbide powder, 0.6 parts by weight of vanadium carbide powder, 1.0 parts by weight of carbon nanotubes, 3.5 parts by weight of lanthanum oxide and 1.5 parts by weight of yttrium oxide were mixed and loaded into a ball mill jar with grinding balls at a ball-to-material ratio of 8:1. Then 150 parts by weight of heptane were added. After ball milling at 220 r / min for 15 h in an argon-protected environment, the mixture was vacuum dried at 80 °C and passed through a 200-mesh sieve to obtain composite powder.

[0048] 38 parts by weight of paraffin wax were placed in a stainless steel container and heated to 70°C. Then, 9.5 parts by weight of stearic acid were added and stirred at 500 r / min for 10 min to obtain a premix. The mixture was then heated to 102°C and 14 parts by weight of ethylene-vinyl acetate copolymer were added and stirred at 50 r / min for 15 min. The mixture was then heated to 120°C and 24 parts by weight of low-density polyethylene were added and stirred for 30 min to obtain an adhesive.

[0049] 100 parts by weight of composite powder and 9 parts by weight of binder are placed in an internal mixer and heated to 122°C. The mixture is then internally mixed at 50 r / min for 50 min to obtain the compound.

[0050] The compound was placed in an extrusion cylinder and preheated at 95°C for 30 min. It was then extruded at a pressure of 50 MPa to obtain a green body. The green body was immersed in n-hexane at a liquid-to-solid ratio of 10:1 and degreased at 45°C for 25 h. Then, under argon protection, the temperature was first raised to 80°C and held for 30 min, then raised to 200°C and held for 60 min, then raised to 350°C and held for 120 min, and finally raised to 450°C and held for 90 min. The degreased green body was obtained after the above thermal degreasing treatment.

[0051] The degreased preform was placed in a graphite mold and then placed in a rapid hot pressing sintering furnace. Argon gas was introduced to purge the air, and the temperature was raised to 1750℃ at a heating rate of 250℃ / min and held at that temperature for 70 min. An axial pressure of 40 MPa was applied and an 80 V / cm DC electric field was turned on. The vacuum / argon atmosphere was switched every 3 min to remove volatile impurities. The temperature was lowered to 1000℃ at a cooling rate of 80℃ / min, and the sample was transferred to a nitrogen-filled glove box by a robotic arm. The sample was then cooled to room temperature at a rate of 100℃ / min. Nitrogen protection was maintained throughout the process to prevent oxidation and produce a high-density, cobalt-free nano-tungsten carbide cemented carbide.

[0052] Example 4:

[0053] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0054] 1.40 parts by weight of aluminum powder, 6.40 parts by weight of copper powder, 5.55 parts by weight of manganese powder, 9.665 parts by weight of molybdenum powder and 4.85 parts by weight of titanium powder were mixed and loaded into a planetary ball mill jar with grinding balls at a ball-to-material ratio of 10:1. 20 parts by weight of anhydrous ethanol were added, and the mixture was ball-milled for 21 hours at a speed of 270 r / min in an argon-protected environment to obtain high-entropy alloy powder.

[0055] 83 parts by weight of nano-tungsten carbide powder, 12.5 parts by weight of high-entropy alloy powder, 1.25 parts by weight of tantalum carbide powder, 0.65 parts by weight of vanadium carbide powder, 1.05 parts by weight of carbon nanotubes, 3.55 parts by weight of lanthanum oxide and 1.55 parts by weight of yttrium oxide were mixed and loaded into a ball mill jar with grinding balls at a ball-to-material ratio of 8:1. Then 150 parts by weight of heptane were added. After ball milling at 240 r / min for 15.5 h in an argon-protected environment, the mixture was dried under vacuum at 80 °C and passed through a 200-mesh sieve to obtain composite powder.

[0056] 39 parts by weight of paraffin wax were placed in a stainless steel container and heated to 71°C. Then, 9.7 parts by weight of stearic acid were added, and the mixture was stirred at 500 r / min for 10 min to obtain a premix. The mixture was then heated to 103°C and 14.5 parts by weight of ethylene-vinyl acetate copolymer were added. The mixture was stirred at 50 r / min for 15 min. The mixture was then heated to 121°C and 24.5 parts by weight of low-density polyethylene were added. The mixture was stirred for 30 min to obtain an adhesive.

[0057] 100 parts by weight of composite powder and 9.2 parts by weight of binder were placed in an internal mixer and heated to 123°C. The mixture was then internally mixed at 50 r / min for 55 min to obtain the compound.

[0058] The compound was placed in an extrusion cylinder and preheated at 97°C for 30 min. It was then extruded at a pressure of 52 MPa to obtain a green body. The green body was immersed in n-hexane at a liquid-to-solid ratio of 10:1 and degreased at 47°C for 25.5 h. Then, under argon protection, the temperature was first raised to 80°C and held for 30 min, then raised to 200°C and held for 60 min, then raised to 350°C and held for 120 min, and finally raised to 450°C and held for 90 min. The degreased green body was obtained by the above thermal degreasing treatment.

[0059] The degreased preform was placed in a graphite mold and then placed in a rapid hot pressing sintering furnace. Argon gas was introduced to purge the air, and the temperature was raised to 1770℃ at a heating rate of 250℃ / min and held at that temperature for 75 min. An axial pressure of 45MPa was applied and an 80V / cm DC electric field was turned on. The vacuum / argon atmosphere was switched every 3 min to remove volatile impurities. The temperature was lowered to 1000℃ at a cooling rate of 80℃ / min, and the sample was transferred to a nitrogen-filled glove box by a robotic arm. The sample was then cooled to room temperature at a rate of 100℃ / min. Nitrogen protection was maintained throughout the process to prevent oxidation and produce a high-density cobalt-free nano-tungsten carbide cemented carbide.

[0060] Example 5:

[0061] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0062] 1.45 parts by weight of aluminum powder, 6.45 parts by weight of copper powder, 5.6 parts by weight of manganese powder, 9.7 parts by weight of molybdenum powder and 4.9 parts by weight of titanium powder were mixed and loaded into a planetary ball mill jar with grinding balls at a ball-to-material ratio of 10:1. 20 parts by weight of anhydrous ethanol were added, and the mixture was ball-milled for 22 hours at a speed of 300 r / min in an argon-protected environment to obtain high-entropy alloy powder.

[0063] 84 parts by weight of nano-tungsten carbide powder, 13 parts by weight of high-entropy alloy powder, 1.3 parts by weight of tantalum carbide powder, 0.7 parts by weight of vanadium carbide powder, 1.1 parts by weight of carbon nanotubes, 3.6 parts by weight of lanthanum oxide and 1.6 parts by weight of yttrium oxide were mixed and loaded into a ball mill jar with grinding balls at a ball-to-material ratio of 8:1. Then 150 parts by weight of heptane were added. After a second ball milling treatment at 250 r / min for 16 h in an argon-protected environment, the composite powder was obtained by vacuum drying at 80 °C and passing through a 200-mesh sieve.

[0064] 40 parts by weight of paraffin wax were placed in a stainless steel container and heated to 72°C. Then, 10 parts by weight of stearic acid were added, and the mixture was stirred at 500 r / min for 10 min to obtain a premix. The mixture was then heated to 105°C and 15 parts by weight of ethylene-vinyl acetate copolymer were added. The mixture was stirred at 50 r / min for 15 min. The mixture was then heated to 122°C and 25 parts by weight of low-density polyethylene were added. The mixture was stirred for 30 min to obtain an adhesive.

[0065] 100 parts by weight of composite powder and 9.5 parts by weight of binder were placed in an internal mixer and heated to 125°C and internally mixed at 50 r / min for 60 min to obtain a compound.

[0066] The compound was placed in an extrusion cylinder and preheated at 100°C for 30 minutes. It was then extruded at a pressure of 55 MPa to obtain a green body. The green body was immersed in n-hexane at a liquid-to-solid ratio of 10:1 and degreased at 50°C for 26 hours. Then, under argon protection, the temperature was raised to 80°C and held for 30 minutes, then raised to 200°C and held for 60 minutes, then raised to 350°C and held for 120 minutes, and finally raised to 450°C and held for 90 minutes. The degreased green body was obtained by the above thermal degreasing treatment.

[0067] The degreased preform was placed in a graphite mold and then placed in a rapid hot pressing sintering furnace. Argon gas was introduced to purge the air, and the temperature was raised to 1800℃ at a heating rate of 250℃ / min and held at that temperature for 80 min. An axial pressure of 50 MPa was applied and an 80 V / cm DC electric field was turned on. The vacuum / argon atmosphere was switched every 3 min to remove volatile impurities. The temperature was lowered to 1000℃ at a cooling rate of 80℃ / min, and the sample was transferred to a nitrogen-filled glove box by a robotic arm. The sample was then cooled to room temperature at a rate of 100℃ / min. Nitrogen protection was maintained throughout the process to prevent oxidation and produce a high-density cobalt-free nano-tungsten carbide cemented carbide.

[0068] Comparative Example 1:

[0069] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0070] The high-entropy alloy powder in Example 5 was replaced with nickel powder, and all other operations were the same as in Example 5.

[0071] Comparative Example 2:

[0072] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0073] Lanthanum oxide and yttrium oxide were removed from Example 5, while other operations remained the same as in Example 5.

[0074] Comparative Example 3:

[0075] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0076] Remove the 80V / cm DC electric field from Example 5, and keep all other operations the same as in Example 5.

[0077] Comparative Example 4:

[0078] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0079] Remove tantalum carbide and vanadium carbide from Example 5, and keep all other operations the same as in Example 5.

[0080] Comparative Example 5:

[0081] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0082] The carbon nanotubes in Example 5 were used, and all other operations were kept the same as in Example 5.

[0083] Comparative Example 6:

[0084] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0085] Replace 13 parts by weight of high-entropy alloy powder in Example 5 with 20 parts by weight of high-entropy alloy powder, and keep all other operations the same as in Example 5.

[0086] Comparative Example 7:

[0087] A method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide includes the following steps:

[0088] In Example 5, 13 parts by weight of high-entropy alloy powder were replaced with 5 parts by weight of high-entropy alloy powder, and other operations were kept the same as in Example 5.

[0089] Performance testing:

[0090] Density test: The Archimedes displacement method was used for measurement, referring to the test method in GB / T 3850-2015.

[0091] Hardness test: Refer to the test method in GB / T 7997-2014, use a Vickers hardness tester to measure on the polished sample surface, and apply a load of 30 kg;

[0092] Bending strength: Refer to the test method in GB / T 3851-2015. Place the specimen on two supports and apply a load to the middle of the specimen with a loading head until it breaks. Record the maximum load and calculate the bending strength based on the specimen size and the maximum load.

[0093] Antioxidant performance test: Standard-sized samples (e.g., 5mm × 5mm × 2mm) are placed in a TGA furnace and heated to 1000℃ at a heating rate of 5℃ / min under air atmosphere, and then held at 800℃ for 5 hours. The mass gain of the samples over time is continuously measured to evaluate their antioxidant capacity. The lower the percentage of oxidation weight gain, the better the antioxidant properties of the material.

[0094] The test results are shown in Table 1.

[0095] Table 1. Performance Testing

[0096]

[0097]

[0098] The test results in Table 1 show that the high-density cobalt-free tungsten carbide cemented carbides prepared in Examples 1-5 of this invention have good density and mechanical properties, while the high-density cobalt-free tungsten carbide cemented carbides prepared in Comparative Examples 1-7 have reduced properties.

[0099] The reason for the performance degradation in Comparative Example 1 may be that the high-entropy alloy powder was replaced with nickel powder, resulting in the material lacking the multi-element synergistic strengthening effect of high-entropy alloy, such as the solid solution strengthening and anti-oxidation effect of aluminum, copper, manganese, molybdenum and titanium; the single component of nickel powder cannot effectively inhibit grain growth or promote densification, so the grain size increases, the density decreases, the hardness and bending strength decrease significantly, and the oxidation weight gain also increases, indicating the deterioration of the anti-oxidation performance;

[0100] The reason for the performance degradation of Comparative Example 2 may be that after removing lanthanum oxide and yttrium oxide, the rare earth oxides lost their role as grain growth inhibitors and sintering aids; the grains grew abnormally during the sintering process, and although the density was 99.30%, the hardness and bending strength were reduced, and the oxidation weight gain increased, reflecting the weakening of grain boundaries and the decrease in oxidation resistance.

[0101] The reason for the performance degradation of Comparative Example 3 may be that the removal of the 80V / cm DC electric field makes it impossible to effectively remove volatile impurities and promote particle rearrangement during the sintering process; the impurity residue leads to an increase in internal defects, a decrease in density, an increase in grain size, a decrease in hardness and flexural strength, and an increase in oxidation weight gain, which may be due to the impurities accelerating oxidation corrosion.

[0102] The reason for the performance degradation in Comparative Example 4 may be the removal of tantalum carbide and vanadium carbide, which reduces the hard phase component and leads to a decline in mechanical properties. As nanoscale reinforcing phases, tantalum carbide and vanadium carbide can pin grain boundaries and improve high-temperature stability. After their absence, the material softens significantly, the bending strength decreases, the grain size increases, the density decreases, and the oxidation weight gain increases.

[0103] The reason for the performance degradation in Comparative Example 5 may be the removal of carbon nanotubes, which weakens the toughness and strength enhancement mechanism of the material. Carbon nanotubes can bridge cracks and improve conductivity. After removal, stress concentration is aggravated, density is reduced, bending strength is significantly reduced, and oxidation weight gain is increased.

[0104] The reason for the performance degradation of Comparative Example 6 may be that the high-entropy alloy powder dilutes the hard phase too much. Excessive high-entropy alloy interferes with the uniformity of the tungsten carbide matrix, causing compositional segregation and grain coarsening. The increase in grain size, decrease in density, and increase in oxidation weight gain may be due to the accelerated oxidation caused by structural inhomogeneity.

[0105] The performance degradation of Comparative Example 7 may be due to insufficient high-entropy alloy powder. The insufficient alloy amount cannot provide enough bonding and densification driving force. The reduced density, increased grain size, decreased hardness and flexural strength, and increased oxidation weight gain reflect that the increased porosity and weakened oxidation resistance may be due to insufficient bonding.

[0106] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for producing a high-density cobalt-free nanocrystalline tungsten carbide hard alloy, characterized by, The preparation method includes the following steps: Aluminum powder, copper powder, manganese powder, molybdenum powder and titanium powder are mixed and then subjected to a first ball milling process with grinding balls at a ball-to-material ratio of 10:1 to obtain high-entropy alloy powder. Nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide and yttrium oxide are mixed and then subjected to a second ball milling process with grinding balls at a ball-to-material ratio of 8:1 to obtain composite powder. An adhesive is obtained by mixing paraffin wax, stearic acid, ethylene-vinyl acetate copolymer, and low-density polyethylene. The composite powder and binder are intensively mixed to obtain a compound, which is then extruded to obtain a green body. The green body is then subjected to solvent degreasing and thermal degreasing treatments to obtain a degreased green body. The high-density cobalt-free nano-tungsten carbide cemented carbide was obtained by rapid hot pressing and sintering of the degreased preform. The weight ratio of the aluminum powder, copper powder, manganese powder, molybdenum powder, and titanium powder is 1.25~1.45: 6.25~6.45: 5.4~5.6: 9.5~9.7: 4.7~4.9; The weight ratio of the nano-tungsten carbide powder, high-entropy alloy powder, tantalum carbide powder, vanadium carbide powder, carbon nanotubes, lanthanum oxide, and yttrium oxide is 80~84:11~13:1.1~1.3:0.5~0.7:0.9~1.1:3.4~3.6:1.4~1.

6.

2. The method of claim 1, wherein the high-density cobalt-free nanocrystalline tungsten carbide hard alloy is prepared by the steps of: The weight ratio of paraffin, stearic acid, ethylene-vinyl acetate copolymer and low-density polyethylene is 36~40:9~10:13~15:23~25. ​ 3. The preparation method for high-density cobalt-free nano-tungsten carbide cemented carbide as described in claim 1, characterized in that, The weight ratio of the composite powder to the binder is 100:8.5~9.

5.

4. The preparation method for high-density cobalt-free nano-tungsten carbide cemented carbide as described in claim 1, characterized in that, The conditions for intensive mixing include a mixing temperature of 120~125℃ and a mixing time of 40~60min.

5. The method for preparing high-density cobalt-free nano-tungsten carbide cemented carbide as described in claim 1, characterized in that, The solvent degreasing conditions include hexane as the degreasing solvent, a degreasing temperature of 40-50°C, and a degreasing time of 24-26 hours.

6. The preparation method for high-density cobalt-free nano-tungsten carbide cemented carbide as described in claim 1, characterized in that, The conditions for heat degreasing include first heating to 80°C and holding for 30 minutes, then heating to 200°C and holding for 60 minutes, then heating to 350°C and holding for 120 minutes, and finally heating to 450°C and holding for 90 minutes.

7. The preparation method for high-density cobalt-free nano-tungsten carbide cemented carbide as described in claim 1, characterized in that, The conditions for rapid hot pressing sintering include a sintering temperature of 1700~1800℃, a sintering time of 60~80min, an axial pressure of 30~50MPa, and a DC electric field of 80V / cm.

8. A high-density, cobalt-free, nano-tungsten carbide cemented carbide, characterized in that, It is prepared by any one of the preparation methods for preparing high-density cobalt-free nano-tungsten carbide cemented carbide as described in claims 1 to 7.

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