WC-Ni3Al hard alloy strengthened and toughened by adding coating phase and preparation method of WC-Ni3Al hard alloy

Abstract

The invention belongs to the technical field of hard alloy preparation, and discloses a WC-Ni3Al hard alloy strengthened and toughened by adding a coating phase and a preparation method of the WC-Ni3Al hard alloy. According to the mass fraction, a hard phase is 84.7%-94.98% of WC, a binding phase is 5%-15% of Ni3Al, and a reinforcing phase is 0.01%-0.15% of hexagonal boron nitride coated with multiple layers of graphene and 0.01%-0.2% of B. After the multi-layer graphene powder and the hexagonal boron nitride are combined, the formed hexagonal boron nitride coated with the multi-layer graphene can generate nanoscale pores in the hard alloy, the nanoscale pores can absorb energy needed for generating fracture toughness, and the fracture toughness of the WC-Ni3Al hard alloy is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of cemented carbide preparation, and specifically relates to a WC-Ni 3 Al cemented carbide and preparation method thereof. Background Art

[0002] WC cemented carbide is widely used in cutting tools, mining equipment, metallurgy and engineering machinery wear-resistant parts due to its high hardness, high wear resistance and high toughness. With the increase in the application range of WC-based cemented carbide tools, cutting processing has also put forward more and higher performance requirements for them. Many researchers have developed a series of new cemented carbide tools with high toughness and high wear resistance by adjusting WC grain size, optimizing binder phase composition, surface coating and functional gradient design. Intermetallic compound Ni 3 Al has excellent properties such as high temperature resistance, corrosion resistance and low density, and has great potential as a high-temperature structural material. It is considered to be an excellent material for a new type of cemented carbide binder. 3 Cemented carbide with Al as the binder phase still has the disadvantages of insufficient fracture toughness and easy failure of the material, so it is necessary to 3 Al cemented carbide is used for toughness.

[0003] Chinese patent application document CN105907997A discloses an in-situ self-generated Al 2 O 3 Toughened WC-Ni 3 Al composite material and preparation method thereof, the method directly adds strengthening phase to WC-Ni 3 Al cemented carbide is strengthened and toughened, but the improvement of the fracture toughness performance of cemented carbide is limited. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings and defects mentioned in the above background technology and provide a WC-Ni 3 Al cemented carbide and preparation method thereof.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A WC-Ni reinforced with coating phase 3 Al cemented carbide, by mass fraction, has a hard phase of 84.7%~94.98% WC and a bonding phase of 5%~15% Ni 3 Al, the reinforcement phase is 0.01%~0.15% multilayer graphene-coated hexagonal boron nitride and 0.01%~0.2% B.

[0006] The WC-Ni 3 Al cemented carbide, further, the number of layers of the multilayer graphene is 3 to 10; the hexagonal boron nitride coated with the multilayer graphene is obtained by wet ball milling multilayer graphene powder and hexagonal boron nitride powder at a mass ratio of 3 to 7:1.

[0007] Multilayer graphene (MLG) and hexagonal boron nitride (h-BN) have the effects of reducing friction and resisting wear at different temperature stages due to their unique physical and chemical properties. However, MLG exhibits excellent interfacial compatibility with the tungsten carbide (WC) matrix, while the interfacial bonding performance between h-BN and WC is poor. The present invention uses a multilayer graphene-coated hexagonal boron nitride (h-BN@MLG) core-shell structure material prepared by a coating process to induce the formation of uniformly distributed nanoscale pores in WC cemented carbide. This unique microstructure design can significantly improve the fracture toughness of the alloy while maintaining the hardness of the material.

[0008] Based on a general inventive concept, the present invention also provides a WC-Ni reinforced with a coating phase. 3 The preparation method of Al cemented carbide comprises the following steps: (1) wet-ball milling, drying, and crushing the multilayer graphene powder and hexagonal boron nitride powder after ultrasonic dispersion to obtain multilayer graphene-coated hexagonal boron nitride powder, i.e., h-BN@MLG powder; (2) The h-BN@MLG powder, WC powder, and Ni 3 Al powder, B powder and paraffin wax chips were wet ball milled, dried, crushed and sieved in a vacuum environment to obtain WC-Ni 3 Al-Bh-BN@MLG powder; (3) The WC-Ni obtained in step (2) 3 Al-Bh-BN@MLG powder was pressed into shape to obtain a molded sample; (4) placing the molded sample obtained in step (3) into a vacuum sintering furnace, heating and keeping the temperature under vacuum for a period of time, stopping the heating and maintaining the vacuum in the furnace until the pre-sintered sample is obtained after cooling; (5) The pre-sintered sample obtained in step (4) is placed in a microwave sintering furnace, subjected to microwave heating and heat preservation in a nitrogen environment, and then cooled to obtain the pre-sintered sample.

[0009] The above preparation method further comprises the following steps: in step (1), the mass ratio of the multilayer graphene to the hexagonal boron nitride is 3-7:1; the number of layers of the multilayer graphene is 3-10, the diameter of the flakes is 5 μm-50 μm, and the thickness is 3 nm-10 nm; the hexagonal boron nitride is a spherical granular powder, and the diameter of a single flake is 100 nm-500 nm.

[0010] Furthermore, the conditions for wet ball milling in step (1) are as follows: the milling is carried out in a carbide ball mill, the organic solvent used for the ball milling is anhydrous ethanol, the grinding balls are carbide grinding balls, the grinding ball diameter is 1-10 mm, the ball-to-material mass ratio is 20-30:1, the ball mill speed is 300 r / min-400 r / min, and the ball milling time is 40 h-55 h.

[0011] Furthermore, in step (2), the particle size of the WC powder is 200nm~1μm, and the Ni 3 The particle size of the Al powder is 200nm~1μm, and the particle size of the B powder is 200nm~1μm; the drying temperature is 70~80°C, and the mesh number of the standard sieve is 70 mesh~300 mesh.

[0012] Furthermore, the conditions for wet ball milling in step (2) are as follows: the process is carried out in a carbide ball mill with a vacuum of ≤1Pa, the organic solvent is anhydrous ethanol, the grinding balls are carbide grinding balls, the grinding balls are arranged in a number ratio of 1:2~3:4~9 according to the diameter specification of 10mm:5mm:2mm, the ball-to-material mass ratio is 3~5:1, the ball mill speed is 250r / min~350r / min, and the ball milling time is 20h~30h.

[0013] Furthermore, in step (3), the pressing pressure is 280 MPa to 300 MPa, and the holding time is 2 min to 10 min.

[0014] Furthermore, in step (4), the vacuum sintering furnace is evacuated to ≤0.1 Pa and maintained there, and the molded sample is heated to 400~650°C at a heating rate of 6°C / min~10°C / min and kept warm for 20~80 minutes.

[0015] Furthermore, in step (5), the microwave frequency of the microwave sintering furnace is 2.45 GHZ, and the nitrogen pressure filled is 300 Pa~800 Pa; microwave heating is performed to a temperature of 1380°C~1550°C and kept warm for 10 min~20 min, wherein the heating rate in the room temperature~350°C stage is 20°C / min~35°C / min, the heating rate in the 350°C~1250°C stage is 10°C / min~20°C / min, and the heating rate in the 1250°C~1550°C stage is 5°C / min~10°C / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. WC-Ni of the present invention 3 In Al cemented carbide, multilayer graphene powder and hexagonal boron nitride have the effect of reducing friction and wearing resistance at different temperature stages, which can improve the WC-Ni 3 Al cemented carbide has good wear resistance; multilayer graphene powder and hexagonal boron nitride also have very good thermal conductivity, which can improve the thermal conductivity of WC-Ni 3 The thermal conductivity of Al cemented carbide material promotes uniform temperature distribution during microwave sintering; after the multilayer graphene powder and hexagonal boron nitride are combined, the multilayer graphene-coated hexagonal boron nitride can produce nano-scale pores in the cemented carbide. These nano-scale pores can absorb the energy required for fracture toughness, greatly improving the WC-Ni 3 Fracture toughness of Al cemented carbide.

[0017] 2. WC-Ni of the present invention 3 In Al cemented carbide, graphene is distributed on Ni 3 Al can isolate hexagonal boron nitride from direct contact with WC and pinning with WC, avoid the problem of poor wettability between hexagonal boron nitride and WC, hinder the movement of WC grains when bending occurs, and help improve the overall wettability, hardness and strength of the alloy.

[0018] 3. WC-Ni of the present invention 3 In Al cemented carbide, the B element can cause the Ni bonding phase to 3 Al produces lattice distortion, achieving the effect of solid solution strengthening, which can effectively improve the WC-Ni 3 The strength of Al cemented carbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 TEM image of the coated phase h-BN@MLG prepared in Example 4.

[0021] Figure 2 The WC-Ni reinforced coating prepared in Example 4 3 Surface TEM image of Al cemented carbide.

[0022] Figure 3The WC-Ni reinforced coating prepared in Example 4 3 BSE image of the surface morphology of Al cemented carbide.

[0023] Figure 4 The WC-Ni reinforced coating prepared in Example 4 3 SEM image of the fracture morphology of Al cemented carbide.

[0024] Figure 5 The WC-Ni reinforced coating prepared in Example 4 3 SEM image of indentation test of Al cemented carbide. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] In the present invention, MLG represents multilayer graphene, and h-BN represents hexagonal boron nitride.

[0029] The present invention is further described in detail below in conjunction with examples (Table 1), but the embodiments of the present invention are not limited thereto.

[0030] Table 1: WC-Ni in the examples 3 Composition of Al cemented carbide

[0031] Embodiment 1: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: (1) Weigh the ultrasonically dispersed MLG and h-BN powders in a mass fraction ratio of 5:1. Take the preparation of 20g composite powder as an example, use a precision balance to weigh 16.67g MLG and 3.33g h-BN respectively. The number of graphene layers is 3-10, the diameter of the flakes is 5μm-50μm, and the thickness is 3nm-10nm. The h-BN is a granular powder with a single flake diameter of 100nm-500nm. Then pour the powder into a cemented carbide ball mill, add cemented carbide grinding balls, wherein the mass ratio of cemented carbide grinding balls to composite powder is 20:1, and then add anhydrous ethanol to 3 / 4 of the volume of the ball mill. The mill is rotated at 400r / min and ball milled for 48h. After the ball milling is completed, the powder is dried in a drying oven at 80℃, and the dried powder is crushed in a stainless steel mortar to obtain graphene-coated hexagonal boron nitride powder, i.e., h-BN@MLG powder. (2) According to the mass fraction of 84.7% WC and 15% Ni 3 Al, 0.15% h-BN@MLG and 0.15% B were weighed as raw material powders, and then 3% of the total mass of the raw materials was weighed as paraffin chips (sintering aid), and all were poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol were added, and the loaded ball mill was tightly covered. The mass ratio of cemented carbide grinding balls to composite powders was 5:1, and the grinding balls were configured in a ratio of 1:2:4 with a diameter of 10mm:5mm:2mm. The speed was 250r / min, and the ball milling was performed for 24h; then the ball-milled mixture was poured into a stainless steel plate, placed in a drying oven and dried at 80°C, and then the dried material was poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder; (3) Weigh 9 g of the WC-Ni prepared in step (2) 3 The Al-Bh-BN@MLG powder was loaded into a molding die and pressed at a pressure of 300 MPa by a press machine. After holding the pressure for 2 minutes, the mold was unloaded to obtain a molded sample. (4) Place the molded sample in a vacuum sintering furnace, evacuate the vacuum sintering furnace to ≤1Pa and maintain it, then heat the molded sample to 550℃ at a heating rate of 8℃ / min and keep it at that temperature for 1h, pre-sinter to remove the molding agent paraffin, then turn off the heating system and maintain the vacuum in the furnace, keep the cooling water circulating, and let the sample cool to room temperature with the furnace; (5) The molded sample obtained after pre-sintering is placed in a microwave sintering furnace with a microwave frequency of 2.45 GHZ. The microwave sintering furnace is evacuated to a vacuum of ≤1 Pa, and then 600 Pa of nitrogen is introduced. The water circulation is turned on, and the microwave heating system is started to heat the sample to 1500 ° C and keep it warm for 15 minutes. The heating rate from room temperature to 350 ° C is 30 ° C / min, the heating rate from 350 ° C to 1250 ° C is 15 ° C / min, and the heating rate from 1250 ° C to 1550 ° C is 8 ° C / min. Then the microwave heating system is turned off, the water circulation is maintained, and the sample is cooled to room temperature with the furnace. In this way, WC-Ni with a strengthened and toughened coating phase is prepared. 3 Al cemented carbide.

[0032] The WC-Ni hardness tester, universal material mechanical testing machine and high-speed reciprocating friction testing machine (grinding ball material Gcr15) were used to measure the 3 The hardness, toughness, strength and friction coefficient of Al cemented carbide. 3 The hardness of Al cemented carbide is 1050HV and the fracture toughness is 22MPa·mm 1 / 2 , the bending strength is 853MPa and the average friction coefficient is 0.76.

[0033] Embodiment 2: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 87.3% WC, 12.5% ​​Ni 3 Al, 0.1% h-BN@MLG and 0.1% B are weighed as raw material powders, and then 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), all of which are poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol are added, and the ball mill filled with materials is tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball milling is performed for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0034] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1125HV and the fracture toughness is 18.5MPa·mm 1 / 2, the bending strength is 1095MPa and the average friction coefficient is 0.65.

[0035] Embodiment 3: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 89.85% WC, 10% Ni 3 Al, 0.05% h-BN@MLG and 0.1% B were weighed as raw material powders, and then 3% paraffin chips (sintering aid) of the total weight of the raw materials were weighed, and all were poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol were added, and the loaded ball mill was tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders was 5:1, and the grinding balls were configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed was 250r / min, and the ball milling was performed for 24h; then the ball-milled mixture was poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material was poured into a stainless steel mortar for crushing, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0036] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1382HV and the fracture toughness is 76.5MPa·mm 1 / 2 , the bending strength is 1195MPa and the average friction coefficient is 0.36.

[0037] Embodiment 4: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 89.8% WC, 10% Ni 3Al, 0.1% h-BN@MLG and 0.1% B are weighed as raw material powders, and then 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), all of which are poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol are added, and the ball mill filled with materials is tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball milling is performed for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0038] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1399HV and the fracture toughness is 93.5MPa·mm 1 / 2 , the bending strength is 1387MPa and the average friction coefficient is 0.28.

[0039] Depend on Figure 1-5 It can be seen that the h-BN@MLG composite powder ( Figure 1 ) is introduced into WC-Ni 3 After Al-based cemented carbide system, a uniformly distributed nanoscale pore structure can be formed in situ ( Figure 2 ). This material significantly improves the WC-Ni 3 Fracture toughness of Al-based cemented carbide. Microstructural analysis shows that the surface of the alloy ( Figure 3 ) and fracture morphology ( Figure 4 ) showed good compactness, and no obvious pore defects were observed. At the same time, the indentation test ( Figure 5 ) further showed that its crack propagation resistance was significantly enhanced.

[0040] Compared with other embodiments, when the mass fraction of the bonding phase is 10% and the mass fraction of the coating phase is 0.1%, the relative density, hardness and strength performance of the alloy are optimal, and the improvement of the fracture toughness effect is most obvious at this time.

[0041] Embodiment 5: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 89.75% WC, 10% Ni 3Al, 0.15% h-BN@MLG and 0.1% B are weighed as raw material powders, and then 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), all of which are poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol are added, and the loaded ball mill is tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball milling is performed for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0042] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1386HV and the fracture toughness is 88.9MPa·mm 1 / 2 , the bending strength is 1295MPa and the average friction coefficient is 0.33.

[0043] Embodiment 6: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 92.3% WC, 7.5% Ni 3 Al, 0.1% h-BN@MLG and 0.1% B are weighed as raw material powders, and then 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), all of which are poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol are added, and the ball mill filled with materials is tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball milling is performed for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0044] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1475HV and the fracture toughness is 24.3MPa·mm 1 / 2 , the bending strength is 1451MPa and the average friction coefficient is 0.26.

[0045] Embodiment 7: A WC-Ni reinforced with coating phase 3 The preparation method of Al cemented carbide comprises the following steps: Steps (1), (3), (4), and (5) are the same as those in Example 1, except that step (2) is as follows: According to the mass fraction of 94.98% WC, 5% Ni 3 Al, 0.01% h-BN@MLG and 0.01% B are weighed as raw material powders, and then 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), all of which are poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol are added, and the ball mill filled with materials is tightly covered, wherein the mass ratio of cemented carbide grinding balls to composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball milling is performed for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar for crushing, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN@MLG powder.

[0046] The WC-Ni coating obtained in this embodiment has a strong and tough coating. 3 The hardness of Al cemented carbide is 1605HV and the fracture toughness is 13.6MPa·mm 1 / 2 , the bending strength is 1497MPa and the average friction coefficient is 0.36.

[0047] Comparative Example 1: A WC-Ni reinforced by adding MLG and h-BN 3 The preparation method of Al cemented carbide comprises the following steps: (1) According to the mass fraction of 89.78% WC and 10% Ni 3Al, 0.1% MLG, 0.02% h-BN and 0.1% B were weighed as raw material powders. The number of graphene layers is 3 to 10, the diameter of the flakes is 5um to 50um, and the thickness is 3nm to 10nm. The h-BN is a granular powder with a single flake diameter of 100nm to 500nm. Then, 3% of the total mass of the raw materials is weighed as paraffin chips (sintering aid), and all are poured into a cemented carbide ball mill. After adding cemented carbide grinding balls and 3 / 4 of anhydrous ethanol, the loaded ball mill is tightly covered. The mass ratio of cemented carbide grinding balls to composite powder is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4. The speed is 250r / min and the ball mill is milled for 24h. Then, the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven and dried at 80°C, and the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-Bh-BN / MLG powder; (2) Weigh 9 g of the WC-Ni prepared in step (2) 3 The Al-Bh-BN / MLG powder was loaded into a molding die, and a press was used to press the powder under a pressure of 300 MPa. After the pressure was maintained for 2 minutes, the powder was released from the mold to obtain a molding sample. (3) Same as step (4) of embodiment (1); (4) Same as step (5) of embodiment (1); The WC-Ni 3 The hardness of Al cemented carbide is 1405HV and the fracture toughness is 12.7MPa·mm 1 / 2 , the bending strength is 1375MPa and the average friction coefficient is 0.37.

[0048] Comparative Example 2: A WC-Ni reinforced with MLG 3 The preparation method of Al cemented carbide comprises the following steps: (1) According to the mass fraction of 89.8% WC and 10% Ni 3Al, 0.1% MLG and 0.1% B were weighed as raw material powders. The number of graphene layers was 3 to 10, the diameter of the flakes was 5um to 50um, and the thickness was 3nm to 10nm. Then 3% of the total mass of the raw materials was weighed as paraffin chips (sintering aids), all of which were poured into a cemented carbide ball mill, and cemented carbide grinding balls and 3 / 4 of anhydrous ethanol were added to cover the loaded ball mill tightly. The mass ratio of cemented carbide grinding balls to composite powders was 5:1, and the grinding balls were configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4. The speed was 250r / min and the ball milling was performed for 24h. Then the ball-milled mixture was poured into a stainless steel plate, placed in a drying oven and dried at 80°C, and the dried material was poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3 Al-B-MLG powder; (2) Weigh 9 g of the WC-Ni prepared in step (2) 3 Al-B-MLG powder was loaded into a molding die, and a press was used to press the mold at a pressure of 300 MPa. After holding the pressure for 2 minutes, the mold was unloaded to obtain a molded sample. (3) Same as step (4) of embodiment (1); (4) Same as step (5) of embodiment (1); The WC-Ni 3 The hardness of Al cemented carbide is 1387HV and the fracture toughness is 13.3MPa·mm 1 / 2 , the bending strength is 1383MPa and the average friction coefficient is 0.32.

[0049] Comparative Example 3: A WC-Ni reinforced by adding h-BN 3 The preparation method of Al cemented carbide comprises the following steps: (1) According to the mass fraction of 89.88% WC and 10% Ni 3 Al, 0.02% h-BN and 0.1% B are weighed as raw material powders. Among them, h-BN is a granular powder with a single piece diameter of 100nm~500nm. Then weigh 3% of the total mass of the raw materials as paraffin chips (sintering aid), pour all of them into the cemented carbide ball mill, add cemented carbide grinding balls and 3 / 4 of the can of anhydrous ethanol, and then cover the loaded ball mill tightly. The mass ratio of cemented carbide grinding balls and composite powders is 5:1, and the grinding balls are configured in a ratio of 10mm:5mm:2mm in diameter and 1:2:4; the speed is 250r / min, and the ball mill is used for 24h; then the ball-milled mixture is poured into a stainless steel plate, placed in a drying oven for drying at 80°C, and then the dried material is poured into a stainless steel mortar and crushed, and sieved with a 100-mesh standard sieve to obtain WC-Ni 3Al-Bh-BN powder; (2) Weigh 9 g of the WC-Ni prepared in step (2) 3 The Al-Bh-BN powder was loaded into a molding die, and a press was used to press the powder under a pressure of 300 MPa. After the pressure was maintained for 2 minutes, the powder was released from the mold to obtain a molded sample. (3) Same as step (4) of embodiment (1); (4) Same as step (5) of embodiment (1); The WC-Ni 3 The hardness of Al cemented carbide is 1334HV and the fracture toughness is 11.6MPa·mm 1 / 2 , the bending strength is 1279MPa and the average friction coefficient is 0.65.

Claims

1. A WC-Ni3Al hard alloy with a coating phase added to strengthen the toughness, characterized in that: By mass fraction, the hard phase is 84.7% to 94.98% of WC, the bonding phase is 5% to 15% of Ni3Al, the reinforcing phase is 0.01% to 0.15% of hexagonal boron nitride coated with multilayer graphene and 0.01% to 0.2% of B; the number of layers of the multilayer graphene is 3 to 10; the hexagonal boron nitride coated with multilayer graphene is obtained by wet ball milling multilayer graphene powder and hexagonal boron nitride powder at a mass ratio of 3 to 7:

1.

2. A method for preparing WC-Ni3Al cemented carbide with added coating phase for toughening as claimed in claim 1, characterized in that: The steps include: (1) wet-ball milling, drying, and crushing the multilayer graphene powder and hexagonal boron nitride powder after ultrasonic dispersion to obtain multilayer graphene-coated hexagonal boron nitride powder, i.e., h-BN@MLG powder; (2) wet-ball milling the h-BN@MLG powder, WC powder, Ni3Al powder, B powder and paraffin chips obtained in step (1) in a vacuum environment, drying, crushing and sieving to obtain WC-Ni3Al-Bh-BN@MLG powder; (3) pressing the WC-Ni3Al-Bh-BN@MLG powder obtained in step (2) to obtain a molded sample; (4) placing the molded sample obtained in step (3) into a vacuum sintering furnace, heating and keeping the temperature under vacuum, stopping heating and maintaining the vacuum in the furnace until cooling to obtain a pre-sintered sample; (5) The pre-sintered sample obtained in step (4) is placed in a microwave sintering furnace, subjected to microwave heating and heat preservation in a nitrogen environment, and then cooled to obtain the pre-sintered sample.

3. The preparation method according to claim 2, characterized in that: In step (1), the mass ratio of the multilayer graphene to hexagonal boron nitride is 3-7:1; the number of layers of the multilayer graphene is 3-10, the diameter of the flakes is 5 μm-50 μm, and the thickness is 3 nm-10 nm; the hexagonal boron nitride is a spherical granular powder, and the diameter of a single flake is 100 nm-500 nm.

4. The preparation method according to claim 2, characterized in that: The conditions for wet ball milling in step (1) are as follows: the milling is carried out in a carbide ball mill, the organic solvent used for the ball milling is anhydrous ethanol, the grinding balls are carbide grinding balls, the grinding ball diameter is 1-10 mm, the ball-to-material mass ratio is 20-30:1, the ball mill speed is 300 r / min-400 r / min, and the ball milling time is 40 h-55 h.

5. The preparation method according to claim 2, characterized in that: In step (2), the particle size of the WC powder is 200nm~1μm, the particle size of the Ni3Al powder is 200nm~1μm, and the particle size of the B powder is 200nm~1μm; the drying temperature is 70~80℃, and the mesh size of the standard sieve is 70 mesh~300 mesh.

6. The preparation method according to claim 2, characterized in that: The conditions for wet ball milling in step (2) are as follows: the milling is carried out in a carbide ball mill with a vacuum of ≤1Pa, the organic solvent is anhydrous ethanol, the grinding balls are carbide grinding balls, the grinding balls are arranged in a number ratio of 1:2~3:4~9 according to the diameter specification of 10mm:5mm:2mm, the ball-to-material mass ratio is 3~5:1, the ball mill speed is 250r / min~350r / min, and the ball milling time is 20h~30h.

7. The preparation method according to claim 2, characterized in that: In step (3), the pressing pressure is 280 MPa to 300 MPa, and the holding time is 2 min to 10 min.

8. The preparation method according to claim 2, characterized in that: In step (4), the vacuum sintering furnace is evacuated to ≤0.1 Pa and maintained, and the molded sample is heated to 400~650℃ at a heating rate of 6℃ / min~10℃ / min and kept warm for 20~80min.

9. The preparation method according to any one of claims 2 to 8, characterized in that In step (5), the microwave frequency of the microwave sintering furnace is 2.45 GHZ, and the nitrogen pressure filled is 300 Pa~800 Pa; microwave heating is performed to a temperature of 1380°C~1550°C and kept warm for 10 min~20 min, wherein the heating rate in the stage from room temperature to 350°C is 20°C / min~35°C / min, the heating rate in the stage from 350°C to 1250°C is 10°C / min~20°C / min, and the heating rate in the stage from 1250°C to 1550°C is 5°C / min~10°C / min.

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