A twinned and dispersion-strengthened WC-Ni based cemented carbide and its preparation method

Abstract

The present invention discloses a twinned and dispersion-strengthened WC-Ni-based cemented carbide and its preparation method. The alloy is composed of a hard phase component WC, a bonding metal Ni, and supersaturated composite grain growth inhibitors Cr3C2 and VC. The WC hard phase in the alloy is composed of irregular grains with an average grain size of less than 0.5 μm and dispersed small plate-like grains. The typical morphological characteristics of the fine plate-like WC grains in the polished cross-section of the alloy are long strips with an average length of less than 2.2 μm and an average width of less than 0.5 μm. Nano-dispersed phases exist in the Ni-based bonding phase solid solution matrix in the alloy. The present invention uses unsaturated carbon nano-WC powder as raw material, and through ultrafine grain strengthening of the hard phase, strengthening of dispersed fine plate-like crystals, and nano-dispersed phase strengthening of the bonding phase, the alloy is given high hardness, high toughness, and high strength.

Description

Technical Field

[0001] The invention relates to a twinned and dispersion-strengthened WC-Ni based hard alloy and a preparation method thereof, and belongs to the fields of low-carbon clean energy and high-performance hard new materials. Background Art

[0002] Nuclear energy is an important component of low-carbon clean energy. The nuclear main pump is a key component to maintain the safe operation of the nuclear reactor. The key components of the nuclear main pump mechanical seal are made of WC-Ni based cemented carbide.

[0003] The Vickers hardness of Ni and Co is 784MPa and 1784MPa respectively, and the stacking fault energy, which is negatively correlated with the work hardening ability and crack growth resistance, is 125mJ / m 2 and 20mJ / m 2 Therefore, compared to WC-Co cemented carbide, it is more difficult to improve the mechanical properties of pure WC-Ni cemented carbide, such as hardness, strength, and toughness. Due to its obvious advantages in particle size and purity, carbonyl Ni powder is the best choice for the preparation of Ni-containing hard materials. However, due to its rough surface, it is difficult to be evenly dispersed during the wet grinding mixture preparation process, which easily leads to the aggregation of bonding phases in the alloy microstructure.

[0004] Grain refinement is an important means of improving alloy strength, hardness, and wear resistance. The liquidus phase of WC-Ni ternary alloys is 40-70°C higher than that of WC-Co ternary alloys. During liquid-phase sintering, the vapor pressure of Ni is significantly higher than that of Co. Consequently, during sintering, the driving force for WC grain growth in WC-Ni-based alloys is significantly increased, and Ni evaporates more easily, making it difficult to obtain WC-Ni-based alloys with fine WC grains and a uniform microstructure. The flexural strength of conventional pure WC-Ni cemented carbides is typically less than 2300 MPa. Under conditions of identical WC grain size and binder metal content, the Rockwell hardness (HRA) of WC-Ni-based cemented carbides is more than 0.5 lower than that of WC-Co alloys. Consequently, the comprehensive performance of WC-Ni ternary alloys cannot meet the stringent requirements for strength, toughness, wear resistance, and performance stability required by extreme service conditions, such as those found in nuclear main pump mechanical seals.

[0005] Chinese patent CN101205584A, "A High-Hardness, High-Strength, Low-Cost Non-Magnetic Cemented Carbide," discloses an alloy composition of 80-90 parts WC, 5-20 parts Ni, 0.5-5 parts chromium carbide, 0.1-0.5 parts vanadium carbide, and 0.1-0.5 parts molybdenum carbide. The WC grain size in the alloy is 1.8-2.4 μm, which falls within the medium-coarse alloy grain size range. The alloy prepared in this patent has a porosity as high as A06 and B06. High porosity can cause abnormal failure of key mechanical seal components in nuclear main pumps, seriously affecting the safe operation of the equipment. Summary of the Invention

[0006] An object of the present invention is to provide a twinned and dispersion strengthened WC-Ni based cemented carbide which can be used as a key component of a nuclear main pump mechanical seal.

[0007] In order to achieve the above object, the present invention is a twinned and dispersion-strengthened WC-Ni based cemented carbide, which is composed of a hard phase component WC, a bonding metal Ni and a composite grain growth inhibitor; the composite grain growth inhibitor is Cr3C2 and VC; the mass fraction of the bonding metal Ni in the alloy is 6.0-13.0%; the mass ratio of the grain growth inhibitor Cr3C2 to Ni is 12.0-25.0%, the mass ratio of VC to Ni is 3.0-4.0%, and the total amount of the composite grain growth inhibitor added exceeds the room temperature condition. The WC hard phase in the WC-Ni based cemented carbide is composed of irregular grains with an average grain size of less than 0.5 μm and dispersed small plate-like grains, and the typical morphological feature of the small plate-like WC grains in the polished cross-section of the alloy is long strips with an average length of less than 2.2 μm and an average width of less than 0.5 μm; the bonding phase is a Ni-based solid solution formed by the solid solution of alloy components W, Cr, V and C in the bonding metal Ni during the alloy sintering process, and a nano-dispersed phase exists in the Ni-based solid solution.

[0008] Preferably, the twinned and dispersion-strengthened WC-Ni based cemented carbide of the present invention is composed of a hard phase component WC, a bonding metal Ni and a supersaturated composite grain growth inhibitor.

[0009] Preferably, the total amount of the composite grain growth inhibitor added has significantly exceeded its solid solubility in the binder phase at room temperature.

[0010] Another object of the present invention is to provide a method for preparing twinned and dispersion strengthened WC-Ni based cemented carbide.

[0011] To achieve the above object, the raw materials of the present invention include: nano-scale unsaturated carbon WC powder with an average particle size of less than 120 nm in specific surface area, carbonyl Ni powder with a Fisher's particle size of less than 1.2 μm, and Cr3C2 powder and VC powder with a Fisher's particle size of less than 1.2 μm; the total carbon content of the unsaturated carbon WC powder is less than 6.12%. The preparation process includes:

[0012] A. Batching and dry premixing: Nano-scale unsaturated carbon WC powder having a total carbon content of less than 6.12% and an average specific surface area particle size of less than 120 nm, carbonyl nickel powder having a Fisher's particle size of less than 1.2 μm, and Cr3C2 powder and VC powder each having a Fisher's particle size of less than 1.2 μm are batched so that the mass fraction of Ni in the raw material powder is 6.0-13.0%, the mass ratio of Cr3C2 to Ni is 12.0-25.0%, and the mass ratio of VC to Ni is 3.0-4.0%. The prepared raw material powders are then dry premixed under an Ar gas protective atmosphere for 1-2 hours to form a premix;

[0013] B. Wet grinding: Wet grinding WC-Ni based cemented carbide grinding balls, premix and composite forming agent in a wet grinding medium for at least 60 hours, preferably 60 to 72 hours, wherein the mass ratio of cemented carbide grinding balls to premix is ​​4:1 to 6:1, and the amount of composite forming agent added is 2.2 to 2.4% of the total mass fraction of the powder;

[0014] C. Drying and granulating the mixture: using spray drying granulation or vacuum drying and mechanical granulation technology to prepare the wet-milled mixture into a mixture with an average particle size of less than 150 μm;

[0015] D. Forming: Press the granulated mixture into shape according to the shape and size of the product;

[0016] E. Forming agent removal and sintering: a. Remove the forming agent from the green compact; b. After the forming agent is removed, perform vacuum sintering in a pressure sintering furnace. When the sintering furnace temperature rises to 1250-1300°C, introduce high-purity argon gas to increase the pressure in the sintering furnace to 8-10 kPa and maintain the temperature for 60-80 minutes; c. When the sintering furnace temperature rises to 1410-1430°C, increase the amount of high-purity argon gas in the sintering furnace to increase the pressure in the sintering furnace to 5-8 MPa. a. Maintain the pressure in the sintering furnace at 5-8 MPa, continue to raise the temperature to 1430-1450°C, and hold for 15-20 minutes. e. Continue to maintain the pressure in the sintering furnace at 5-8 MPa, reduce the temperature at a rate of 10-20°C / min to 1410-1430°C, and hold for 80-120 minutes. f. Reduce the furnace temperature to 1000-1100°C within 5-10 minutes. g. Cool the furnace to a product discharge temperature of less than 70°C.

[0017] F. Low temperature tempering: The tempering temperature is 400-450℃, the tempering time is 5-8 hours, and it is carried out under a protective atmosphere.

[0018] The wet grinding in step B is carried out in a drum ball mill.

[0019] The average grain size of the WC hard phase in the WC-Ni based cemented carbide grinding ball in step B is less than 0.8 μm, and Ni is used as the single bonding metal.

[0020] The wet grinding medium in step B is a mixed solution of alcohol and hexane; wherein the volume proportion of hexane in the wet grinding medium mixed solution is 5-10%.

[0021] In step B, the composite forming agent is composed of polyethylene glycol, paraffin wax and stearic acid, wherein the mass proportions of polyethylene glycol, paraffin wax and stearic acid in the composite forming agent are 20-30%, 60-70% and 10-15% respectively, and the total amount of the three is 100%.

[0022] The protective atmosphere in step F is vacuum or high-purity argon or high-purity nitrogen inert gas.

[0023] Through research, the inventors have discovered that under the conditions of multiple coupled factors, the alloy of the present invention will be accompanied by the following phenomena during the sintering process: W2C reacts with Ni to form carbides containing W and Ni (η phase), and then the η phase decomposes in situ into Ni and active WC; W atoms in the active sites of the original WC preferentially dissolve in Ni; through the dynamic behavior of dissolution and precipitation of W atoms in Ni, active WC grains and WC grains with prominent lattice distortion effects grow anisotropically, leading to the formation of plate-like WC grains; by regulating the amount of active WC obtained by the in situ decomposition of the η phase, the number of active sites in the original WC, the type of grain growth inhibitor and the amount of grain growth inhibitor added, it is possible to effectively regulate the self-consistent behavior of the dispersion distribution of plate-like WC grains and their grain refinement. The multiple factors include: (1) the presence and amount of W2C in unsaturated carbon WC that does not reach the theoretical carbon content; (2) the WC nanosize effect; (3) the WC lattice distortion effect caused by long-term intensive wet grinding for more than 60 hours; and (4) the synergistic behavior of the alloy components W, Cr, and V dissolved in Ni during liquid phase sintering.

[0024] The present invention is based on basic data such as the extremely poor solubility of alloy grain growth inhibitors Cr and V atoms in Ni under high-temperature sintering conditions higher than the eutectic temperature of the alloy system and the solubility of Cr and V atoms in Ni under room temperature conditions, as well as the change in the solubility of alloy components in Ni under the coexistence of W, Cr and V. The addition amount of Cr3C2 and VC composite grain growth inhibitors that matches the alloy preparation process is designed; through the composition control and pressure control sintering of the alloy system, the eutectic temperature of the alloy system and the sintering temperature required for full densification are significantly reduced, thereby enhancing the inhibitory effect on WC grain growth in the alloy and significantly inhibiting the evaporation behavior of Ni during the sintering process; through rapid cooling at the sintering temperature, the formation of the supersaturated Cr3C2 and VC composite grain growth inhibitor third phase is inhibited; by The addition of a high content of corrosion-resistant promoting component Cr3C2, which causes less damage to the alloy's toughness, strengthens the alloy's grain growth inhibition effect and significantly improves the alloy's wear resistance; by regulating the environment for the in-situ formation of WC plate grains, the three-dimensional scale of the plate grains is effectively refined and the crystal integrity is effectively guaranteed, significantly improving the intrinsic strength and wear resistance of the plate-like WC grains; based on the comprehensive strengthening effect of the hardness anisotropy of the plate-like WC grains and their effective hindrance to crack propagation, the alloy's hardness and fracture toughness are simultaneously improved, solving the contradiction of the inverted relationship between hardness and toughness in traditional alloys; through low-temperature tempering, the internal stress formed by rapid cooling is reduced, and the in-situ precipitation and self-consistent recombination of supersaturated solid solution atoms in the Ni-based bonding phase form a nano-dispersed phase reinforcement, thereby improving the hardness of the bonding phase and the hardness of the alloy.

[0025] The present invention adopts alcohol and hexane mixed wet grinding medium and polyethylene glycol, paraffin and stearic acid composite forming agent, which helps to achieve efficient dissolution of the forming agent, improve the wet grinding crushing and wet grinding dispersion efficiency, and effectively solve the problem of difficult forming of nano powders.

[0026] The present invention achieves high crystalline integrity intrinsic strengthening through fine grain strengthening of WC hard phase, plate-like crystal dispersion strengthening and self-consistent orderly growth in the alloy, and achieves high strength of the alloy and simultaneous improvement of alloy hardness and toughness through nano-dispersed phase strengthening in the nickel-based bonding phase. The alloy has a maximum bending strength of 3945MPa and a Vickers hardness HV30 of 2060kgf / mm 2 , Palmqvist fracture toughness K IC The maximum value can reach 10.81MPa·m 1 / 2 It can better meet the stringent requirements of the mechanical seal on the nuclear main pump for the strength, hardness, wear resistance, fracture toughness and performance stability of WC-Ni based cemented carbide material components. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is a scanning electron microscope photograph of the microstructure of the WC-10.0Ni-1.2Cr3C2-0.4VC alloy in Example 1.

[0028] Figure 2 This is a metallographic photograph of the microstructural defects of the WC-10.0Ni-1.2Cr3C2-0.4VC alloy prepared in Comparative Example 1 without dry premixing, with the mixture directly wet-milled for 50 hours, and without low-temperature tempering.

[0029] Figure 3 This is a scanning electron microscope photograph of the microstructure of the WC-6.0Ni-0.72Cr3C2-0.24VC alloy prepared in Comparative Example 2 using saturated carbon WC powder raw material with a total carbon content of 6.14%.

[0030] Figure 4 This is a scanning electron microscope photograph of the Cr3C2 third phase in the microstructure of the WC-13.0Ni-3.25Cr3C2-0.39VC alloy prepared in Comparative Example 3 without rapid cooling and directly cooled from the sintering temperature.

[0031] Figure 5 This is a metallographic photograph of large cracks in the WC-13.0Ni-3.25Cr3C2-0.39VC alloy prepared in Comparative Example 5 using a single alcohol medium and a single polyethylene glycol forming agent accounting for 2.2% of the total mass of the mixture. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0033] Example 1

[0034] The experimental raw materials are as follows: specific surface area is 3.99g / cm 3 , unsaturated carbon WC powder with a specific surface area average particle size of 96nm and a total carbon content of 6.08%, carbonyl Ni powder with a Fisher particle size of 1.1μm, Cr3C2 powder with a Fisher particle size of 0.8μm, and VC powder with a Fisher particle size of 1.0μm. The preparation process is as follows:

[0035] A. Batching and Dry Premixing: The above raw material powders were batched so that the mass fraction of Ni in the raw material powders was 10%, the mass ratio of Cr3C2 to Ni was 12%, and the mass ratio of VC to Ni was 4%. The prepared raw material powders were poured into a dry mixing device, filled with Ar gas, and dry premixed for 1.5 hours under an Ar gas protective atmosphere to form a premix.

[0036] B. Wet milling: Using a drum-type ball mill and WC-8Ni-based carbide grinding balls with an average WC grain size of 0.7 μm, with a mass ratio of grinding balls to premix of 4:1, the grinding balls, the premix obtained in step A, a composite forming agent consisting of polyethylene glycol, paraffin wax, and stearic acid accounting for 2.3% of the total mass of the mixture, and a mixed wet milling medium of alcohol and hexane were added to a ball mill barrel. The wet milling time was 72 hours. The mass proportions of polyethylene glycol, paraffin wax, and stearic acid in the composite forming agent were 20%, 70%, and 10%, respectively, and the volume proportion of hexane in the wet milling medium mixed solution was 5%.

[0037] C. Drying and granulating the mixture: using spray drying to granulate the wet-milled mixture into a mixture with an average particle size of less than 150 μm;

[0038] D. Forming: According to the shape and size of the product, the granulated mixture is pressed into shape by molding process;

[0039] E. Forming agent removal and sintering: Forming agent removal and sintering are carried out in a 6MPa pressure sintering furnace. The forming agent is removed according to a conventional forming agent removal process. After the forming agent is removed, vacuum sintering is carried out in the furnace. When the sintering furnace temperature rises to 1250°C, high-purity argon is introduced to increase the pressure in the sintering furnace to 9kPa and the temperature is maintained for 60 minutes. When the temperature in the sintering furnace rises to 1420°C, the high-purity argon loading in the sintering furnace is increased to increase the pressure in the sintering furnace to 5.6MPa. The pressure in the sintering furnace is maintained at 5.6MPa, and the temperature is continued to be raised to 1440°C and maintained for 15 minutes. The pressure in the sintering furnace is continued to be maintained at 5.6MPa, and the temperature is lowered at a rate of 15°C / minute to 1420°C and maintained for 100 minutes. The furnace temperature is then lowered to 1000°C within 8 minutes. The product is then cooled to a product discharge temperature of less than 70°C.

[0040] F. Low temperature tempering: Tempering is carried out in a vacuum furnace at a tempering temperature of 400°C for 7 hours.

[0041] Microstructural examination was conducted in accordance with GB / T 3488.4-2022 "Metallographic determination of cemented carbide microstructure - Part 4: Metallographic determination of porosity, uncombined carbon defects and decarburized phases". The results showed that the alloy porosity was <A02, B00, indicating a fully densified state, with no decarburized or carburized phases in the alloy. Scanning electron microscope observation of the microstructure of the alloy after etching with standard metallographic reagents showed that the alloy had a homogeneous structure of a WC hard phase and a Ni-based solid solution bonding phase. Figure 1Electron microscopic measurements were conducted using the average intercept method in accordance with GB / T 3488.2-2018, "Metallographic Determination of Cemented Carbide Microstructure - Part 2: Measurement of WC Grain Size." The results show that the WC hard phase in the alloy is composed of irregularly shaped grains with an average grain size of 0.3 μm and dispersed small plate-like grains. The elongated WC grains have an average length of 1.6 μm and an average width of 0.3 μm. Transmission electron microscopy observations and analysis reveal the presence of uniformly distributed nano-dispersed phases containing W, Cr, and V within the alloy's binder phase.

[0042] Example 2

[0043] The experimental raw materials are as follows: specific surface area is 3.47g / cm 3 , unsaturated carbon WC powder with an average particle size of 110nm and a total carbon content of 6.11%, carbonyl Ni powder with a Fisher particle size of 1.1μm, Cr3C2 powder with a Fisher particle size of 0.8μm, and VC powder with a Fisher particle size of 1.0μm. The preparation process is as follows:

[0044] A. Batching and Dry Premixing: The raw material powders described above were batched so that the mass fraction of Ni in the raw material powders was 6%, the mass ratio of Cr3C2 to Ni was 18%, and the mass ratio of VC to Ni was 3.5%. The prepared raw material powders were poured into a dry mixing device, filled with Ar gas, and dry premixed for 1 hour under an Ar gas protective atmosphere to form a premix.

[0045] B. Wet milling: Using a drum-type ball mill and WC-8Ni-based carbide grinding balls with an average WC grain size of 0.7 μm, with a mass ratio of grinding balls to premix of 6:1, the grinding balls, the premix obtained in step A, a composite forming agent consisting of polyethylene glycol, paraffin wax, and stearic acid accounting for 2.4% of the total mass of the mixture, and a mixed wet milling medium of alcohol and hexane were added to a ball mill barrel for 60 hours. The mass proportions of polyethylene glycol, paraffin wax, and stearic acid in the composite forming agent were 25%, 60%, and 15%, respectively, and the volume proportion of hexane in the wet milling medium mixed solution was 8%;

[0046] C. Drying and granulating the mixture: preparing the wet-milled mixture into a mixture with an average particle size of less than 150 μm by vacuum drying and mechanical granulation;

[0047] D. Forming: According to the shape and size of the product, the granulated mixture is pressed into shape by molding process;

[0048] E. Forming agent removal and sintering: Forming agent removal and sintering are carried out in a 10 MPa pressure sintering furnace. The forming agent is removed according to a conventional forming agent removal process. After the forming agent is removed, vacuum sintering is carried out in the furnace. When the sintering furnace temperature rises to 1300°C, high-purity argon is introduced to increase the pressure in the sintering furnace to 8 kPa and the temperature is maintained for 80 minutes. When the temperature in the sintering furnace rises to 1430°C, the high-purity argon loading in the sintering furnace is increased to increase the pressure in the sintering furnace to 8 MPa. The pressure in the sintering furnace is maintained at 8 MPa, and the temperature is continued to be raised to 1450°C and maintained for 20 minutes. The pressure in the sintering furnace is continued to be maintained at 8 MPa, and the temperature is lowered at a rate of 20°C / minute to 1430°C and maintained for 120 minutes. The furnace temperature is lowered to 1100°C within 10 minutes. The product is then cooled to a product discharge temperature of less than 70°C.

[0049] F. Low temperature tempering: Tempering is carried out in a high-purity argon atmosphere, and the tempering temperature is kept at 450℃ for 5 hours.

[0050] Testing according to the relevant standards described in Example 1 revealed that the alloy had a porosity of <A02, B00, indicating a fully densified state, with no decarburized or carburized phases present. Scanning electron microscopic observation of the alloy's microstructure after etching with standard metallographic reagents revealed a homogeneous structure consisting of a WC hard phase and a Ni-based solid solution binder phase. The WC hard phase consisted of irregularly shaped grains with an average grain size of 0.3 μm and dispersed small plate-like grains. The elongated WC grains had an average length of 1.7 μm and an average width of 0.4 μm. Transmission electron microscopy and analysis revealed the presence of uniformly distributed nano-dispersed phases containing W, Cr, and V within the binder phase.

[0051] Example 3

[0052] The experimental raw materials are as follows: specific surface area is 3.90g / cm 3 , unsaturated carbon WC powder with a specific surface area average particle size of 98nm and a total carbon content of 6.05%, carbonyl Ni powder with a Fisher particle size of 1.1μm, Cr3C2 powder with a Fisher particle size of 0.8μm, and VC powder with a Fisher particle size of 1.0μm. The preparation process is as follows:

[0053] A. Batching and Dry Premixing: The raw material powders described above were batched so that the mass fraction of Ni in the raw material powders was 13%, the mass ratio of Cr3C2 to Ni was 25%, and the mass ratio of VC to Ni was 3%. The prepared raw material powders were poured into a dry mixing device, filled with Ar gas, and dry premixed for 2 hours under an Ar gas protective atmosphere to form a premix.

[0054] B. Wet milling: Using a drum-type ball mill and WC-8Ni-based carbide grinding balls with an average WC grain size of 0.7 μm, with a mass ratio of grinding balls to premix of 5:1, the grinding balls, the premix obtained in step A, a composite forming agent consisting of polyethylene glycol, paraffin wax, and stearic acid accounting for 2.2% of the total mass of the mixture, and a wet milling medium mixed with alcohol and hexane were added to a ball mill barrel. The wet milling time was 68 hours. The mass proportions of polyethylene glycol, paraffin wax, and stearic acid in the composite forming agent were 30%, 60%, and 10%, respectively, and the volume proportion of hexane in the wet milling medium mixed solution was 10%.

[0055] C. Drying and granulating the mixture: preparing the wet-milled mixture into a mixture with an average particle size of less than 150 μm by vacuum drying and mechanical granulation;

[0056] D. Forming: According to the shape and size of the product, the granulated mixture is pressed into shape by molding process;

[0057] E. Forming agent removal and sintering: Forming agent removal and sintering are carried out in a 6MPa pressure sintering furnace, and the forming agent is removed according to a conventional forming agent removal process. After the forming agent is removed, vacuum sintering is carried out in the furnace. When the sintering furnace temperature rises to 1250°C, high-purity argon is introduced to increase the pressure in the sintering furnace to 10kPa and the temperature is maintained for 70 minutes. When the temperature in the sintering furnace rises to 1410°C, the high-purity argon loading in the sintering furnace is increased to increase the pressure in the sintering furnace to 5MPa. The pressure in the sintering furnace is maintained at 5MPa, and the temperature is continued to be raised to 1430°C and maintained for 20 minutes. The pressure in the sintering furnace is continued to be maintained at 5MPa, and the temperature is lowered at a rate of 20°C / minute to 1410°C and maintained for 80 minutes. The furnace temperature is lowered to 1000°C within 5 minutes, and the product is cooled to a temperature of less than 70°C at which it can be discharged from the furnace.

[0058] F. Low temperature tempering: Tempering is carried out in a high-purity nitrogen atmosphere, and the tempering temperature is kept at 400°C for 8 hours.

[0059] Testing according to the relevant standards described in Example 1 revealed that the alloy had a porosity of <A02, B00, indicating a fully densified state, with no decarburized or carburized phases present. Scanning electron microscopic observation of the alloy's microstructure after etching with standard metallographic reagents revealed a homogeneous structure consisting of a WC hard phase and a Ni-based solid solution binder phase. The WC hard phase consisted of irregularly shaped grains with an average grain size of 0.3 μm and dispersed small plate-like grains. The elongated WC grains had an average length of 1.7 μm and an average width of 0.4 μm. Transmission electron microscopy and analysis revealed the presence of uniformly distributed nano-dispersed phases containing W, Cr, and V within the binder phase.

[0060] Comparative Example 1

[0061] The raw materials and alloy composition ratios used in the experiment were the same as those in Example 1. Except that dry premixing was not used, the direct wet grinding time of the mixture was 50 hours, and low-temperature tempering was not used, the other preparation process parameters were the same as those in Example 1. The metallographic observation and analysis results showed that the alloy had obvious defects of bonding phase aggregation and coarse WC grain agglomeration, and the WC grain inclusion was relatively coarse, as shown in Figure 1. Figure 2 Scanning electron microscopy (SEM) observations of the alloy's microstructure after etching with standard metallographic reagents revealed a very small number of WC grains with distinct plate-like characteristics. Transmission electron microscopy and analysis revealed no nano-dispersed phases within the alloy's binder phase.

[0062] Comparative Example 2

[0063] The WC raw material used in the experiment has a specific surface area of ​​3.86 g / cm 3 , saturated carbon WC powder with an average specific surface area particle size of 99nm and a total carbon content of 6.14%, and the other raw materials are the same as in Examples 1 to 3. The alloy composition ratio is: the mass fraction of Ni in the raw material powder is 6%, the mass ratio of Cr3C2 to Ni is 12%, and the mass ratio of VC to Ni is 4%; the preparation process parameters of the alloy are the same as in Example 2. The results of scanning electron microscopy observation and analysis show that the alloy has a two-phase homogeneous structure of WC hard phase and Ni-based solid solution bonding phase. The average grain size of the WC hard phase in the alloy is 0.3μm, and WC grains with obvious plate-like crystal characteristics are rare. Figure 3 .

[0064] Comparative Example 3

[0065] The experimental raw materials and alloy composition ratios were the same as those in Example 3; except that rapid cooling was not used during sintering, and the alloy was directly cooled from the sintering temperature, the other preparation process parameters were the same as those in Example 3. Scanning electron microscopy and energy spectrum analysis showed that the WC hard phase in the alloy was composed of ultrafine and nano-grains with irregular morphology and dispersed small plate-like grains; in addition to the WC hard phase and Ni-based solid solution bonding phase, some Cr3C2 was found in the alloy as an independent third phase. Figure 4 The arrow in the middle indicates the location. Transmission electron microscopy observation and analysis results show that no nano-dispersed phase is observed in the alloy bonding phase.

[0066] Comparative Example 4

[0067] Except that the mass ratio of Cr3C2 to Ni was 10.0%, the raw materials, the Ni content of the binder metal in the alloy, the mass ratio of VC to Ni, and the alloy preparation process were the same as in Example 3. Transmission electron microscopy observation and analysis results showed that no nano-dispersed phase was observed in the binder phase of the alloy.

[0068] Comparative Example 5

[0069] The ratio of raw materials and alloy components used in the experiment was the same as that in Example 3; except for the use of a single alcohol medium and a single polyethylene glycol forming agent accounting for 2.2% of the total mass of the mixture, the other preparation process parameters were the same as those in Example 3. The molded green compacts were tested and found to have delamination and cracking defects. The green compacts with the above defects were sintered in the same furnace as the green compacts in Example 3, and obvious large cracks were still observed under the metallographic microscope, as shown in FIG. Figure 5 .

[0070] The alloys prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested for their flexural strength (TRS), Vickers hardness (HV30) and Palmqvist fracture toughness (K) using GB / T 3851-2015 "Determination of Transverse Fracture Strength of Cemented Carbide" (selecting Type B specimen), GB / T 7997-2014 "Test Method for Vickers Hardness of Cemented Carbide" (selecting a 30 kg load) and GB / T 33819-2017 "Babbitt Toughness Test for Cemented Carbide". Ic ), the test results are shown in Table 1.

[0071] Table 1 Test results of alloy properties in Examples and Comparative Examples

[0072]

Claims

1. A twinned and dispersion-strengthened WC-Ni based cemented carbide, characterized by: The alloy is composed of a hard phase component WC, a bonding metal Ni and a composite grain growth inhibitor; the composite grain growth inhibitor is Cr3C2 and VC; the mass fraction of the bonding metal Ni in the alloy is 6.0-13.0%; the mass ratio of the grain growth inhibitor Cr3C2 to Ni is 12.0-25.0%, the mass ratio of VC to Ni is 3.0-4.0%, and the total amount of the composite grain growth inhibitor added exceeds its solid solubility in the bonding phase at room temperature; the WC hard phase in the WC-Ni based cemented carbide is composed of a morphology of an average grain size of less than 0.5 μm. The alloy is composed of irregular grains and dispersed small plate-like grains, wherein the typical morphology of the small plate-like WC grains in the polished cross-section of the alloy is long strips with an average length of less than 2.2 μm and an average width of less than 0.5 μm; the bonding phase is a Ni-based solid solution formed by the solid solution of alloy components W, Cr, V and C in the bonding metal Ni during the alloy sintering process, and a nano-dispersed phase exists in the Ni-based solid solution; the raw materials used include: nano-scale unsaturated carbon WC powder with an average particle size of less than 120 nm in specific surface area, and the unsaturated carbon WC powder is WC powder with a total carbon content of less than 6.12%.

2. A method for preparing the twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 1, characterized in that: The raw materials used include: nano-scale unsaturated carbon WC powder with an average particle size of less than 120nm in specific surface area, carbonyl Ni powder with a Fisher particle size of less than 1.2μm, and Cr3C2 powder and VC powder with a Fisher particle size of less than 1.2μm; the total carbon content of the unsaturated carbon WC powder is less than 6.12%. The preparation process includes: A. Batching and dry premixing: Nano-scale unsaturated carbon WC powder with a total carbon content of less than 6.12% and an average specific surface area particle size of less than 120 nm, carbonyl nickel powder with a Fisher's particle size of less than 1.2 μm, and Cr3C2 powder and VC powder, both with a Fisher's particle size of less than 1.2 μm, are batched such that the mass fraction of Ni in the raw material powder is 6.0-13.0%, the mass ratio of Cr3C2 to Ni is 12.0-25.0%, and the mass ratio of VC to Ni is 3.0-4.0%. The prepared raw material powders are then dry premixed under an Ar gas protective atmosphere for 1-2 hours to form a premix. B. Wet Grinding: Wet grind WC-Ni based cemented carbide grinding balls, premix, and composite forming agent in a wet grinding medium for at least 60 hours, wherein the mass ratio of cemented carbide grinding balls to premix is ​​4:1 to 6:1, and the amount of composite forming agent added is 2.2 to 2.4% of the total mass fraction of the powder; C. Drying and granulating the mixture: using spray drying granulation or vacuum drying and mechanical granulation technology to prepare the wet-milled mixture into a mixture with an average particle size of less than 150 μm; D. Forming: Press the granulated mixture into shape according to the shape and size of the product; E. Forming Agent Removal and Sintering: a. Remove the forming agent from the compact; b. After removing the forming agent, perform vacuum sintering in a pressure sintering furnace. When the sintering furnace temperature reaches 1250-1300°C, introduce high-purity argon gas to raise the furnace pressure to 8-10 kPa and maintain this temperature for 60-80 minutes; c. When the sintering furnace temperature reaches 1410-1430°C, increase the high-purity argon gas loading to raise the furnace pressure to 5-8 MPa; d. Maintain the furnace pressure at 5-8 MPa and continue to raise the temperature to 1430-1450°C and maintain this temperature for 15-20 minutes; e. Continue to maintain the furnace pressure at 5-8 MPa and reduce the temperature at a rate of 10-20°C / minute to 1410-1430°C and maintain this temperature for 80-120 minutes; f. Lower the furnace temperature to 1000-1100°C within 5-10 minutes; g. Cool the product to a temperature below 70°C before it leaves the furnace; F. Low temperature tempering: The tempering temperature is 400~450℃, the tempering time is 5~8 hours, and it is carried out under a protective atmosphere.

3. The method for preparing twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 2, characterized in that: The wet grinding in step B is carried out in a drum ball mill.

4. The method for preparing twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 2, characterized in that: The average grain size of the WC hard phase in the WC-Ni based cemented carbide grinding ball is less than 0.8 μm, and Ni is used as a single bonding metal.

5. The method for preparing twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 2, characterized in that: The wet grinding medium in step B is a mixed solution of alcohol and hexane; wherein the volume proportion of hexane in the wet grinding medium mixed solution is 5-10%.

6. The method for preparing twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 2, characterized in that: The composite forming agent described in step B is composed of polyethylene glycol, paraffin and stearic acid, wherein the mass proportions of polyethylene glycol, paraffin and stearic acid in the composite forming agent are 20-30%, 60-70% and 10-15% respectively, and the total amount of the three is 100%.

7. The method for preparing twinned and dispersion-strengthened WC-Ni based cemented carbide according to claim 2, characterized in that: The protective atmosphere in step F is vacuum or high-purity argon or high-purity nitrogen inert gas.

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