Graphene-reinforced high-toughness WC-Co-based hard alloy and preparation method thereof

Abstract

The invention discloses a graphene reinforced ultra-fine grain WC-Co-based hard alloy which is characterized by comprising the following components in percentage by mass: 10% of Co, 0-0.3% of Gr and the balance of WC powder, and a preparation method of the graphene reinforced ultra-fine grain WC-Co-based hard alloy comprises the following steps: 1, preparing graphene oxide; (2) preparation of WC-Co-Gr composite powder; and thirdly, the WC-Co-Gr hard alloy material is sintered. The self-prepared graphene is added through a wet chemical method, so that the toughness of the hard alloy is effectively improved; gr is added to promote fine grain strengthening, strengthen hardness and increase corrosion resistance, and 10% Co is matched to fully fill pores of WC grains, so that the hard alloy has high compactness; and the ball milling time, the rotating speed and the ball-to-material ratio are controlled in the ball milling process, so that the hardness and the fracture toughness of the hard alloy are effectively improved, the service life of the hard alloy in a severe environment is prolonged, and the risk and the cost caused by damage of hard alloy parts are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of tungsten-based cemented carbide, and relates to an ultrafine-grained WC-Co-based cemented carbide and a preparation method thereof, and more specifically, to a graphene-enhanced ultrafine-grained WC-Co-based cemented carbide and a preparation method thereof. Background Art

[0002] Cemented carbide is a multiphase composite material, mainly composed of refractory metal compounds with high hardness and high elastic modulus (such as WC, MoC, TaC, TiC, NbC, etc.) as the matrix, supplemented by transition metals (such as Co, Zr, Ni, Fe, etc.) or their alloys as binders. This material is usually prepared by powder metallurgy and is one of the most important and typical materials in the field of powder metallurgy. Cemented carbide is highly favored for its unique properties, including extremely high hardness, excellent wear resistance, good strength and toughness, excellent heat resistance and corrosion resistance. It is particularly worth mentioning that even under high temperature conditions, cemented carbide can still maintain its high hardness and wear resistance. Specifically, even in a high temperature environment of 500°C, its performance will hardly change; and at 1000°C, it can still show a high hardness. Based on these characteristics, cemented carbide is widely used in many fields such as metal cutting, metal forming tools, mining, oil drilling, national defense and military industry, and stone and wood cutting. Among them, tungsten-cobalt cemented carbide (such as WC-Co) is particularly suitable for the manufacture of rock drilling tools, cutting tools and wear-resistant tools due to its higher hardness, toughness and excellent wear resistance.

[0003] With the continuous changes in the production environment and the continuous improvement of performance requirements, the performance of traditional WC-Co cemented carbide is increasingly unable to meet the actual production needs of today, and cemented carbide is prone to wear and fracture during use, which greatly affects the normal progress of the entire project. It is mainly reflected in the following aspects: (1) When traditional WC-Co cemented carbide is used to cut high-strength alloy steel, ceramics and other high-hardness materials, the tool is prone to excessive wear and edge deformation, affecting the processing accuracy and efficiency; (2) In some heavy-load cutting or high-impact processing occasions, the strength of traditional WC-Co cemented carbide is difficult to withstand large cutting forces and impact forces, which easily leads to tool fracture and damage, increasing production costs and processing cycles; (3) Although WC-Co cemented carbide has a certain toughness, in some complex working conditions, such as intermittent cutting, thin-walled parts processing, etc., its insufficient toughness will become prominent, and it is easy to produce cracks or even chipping, reducing the service life of the tool and processing quality. Therefore, it is very important to develop a new preparation method to improve the comprehensive mechanical properties of cemented carbide. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a graphene (Gr) enhanced ultrafine-grained WC-Co based cemented carbide and a preparation method thereof, which can make the graphene evenly distributed in the cemented carbide powder and make the grain size of the finished product after sintering be about 400nm, so that the hardness and fracture toughness of the WC-Co based cemented carbide material are significantly improved.

[0005] The technical solution of the present invention: A graphene-enhanced ultrafine-grained WC-Co-based hard alloy, wherein the characteristic components are composed of Co: 10wt%, Gr: 0-0.3wt% and the balance being WC powder in terms of mass percentage.

[0006] A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide comprises the following steps: 1. Preparation of Graphene Oxide (GO) Immerse the dry three-necked flask in a low-temperature reaction bath and pour graphite powder and NaNO into one of the ports of the flask. 3 , slowly pour concentrated sulfuric acid from the other port, slowly stir until the temperature in the flask stabilizes, and while stirring, add KMnO 4 Pour the mixture into a three-necked flask very slowly in three small portions. After the reaction is complete, soak the flask in cold water to cool it down. Then, pour in excess H 2 O 2 The solution turns golden yellow, and the pH value of the solution is brought close to 7 by dialysis to obtain a GO solution. A portion of the GO solution is freeze-dried to obtain a GO solid. The GO solid is placed in an iron box, sealed, and placed in a high-temperature furnace for heating and reduction to finally obtain Gr. 2. Preparation of WC-Co-Gr composite powder WC powder, Co powder and grinding balls are placed in a ball mill, soaked with an appropriate amount of anhydrous ethanol, and after ensuring that the liquid level covers the powder and the grinding balls, the ball mill is placed in a glove box to evacuate, and then argon is introduced, the ball mill is sealed and taken out, and then the ball mill is wet-milled and mixed in a planetary ball mill for several hours, and Gr is dispersed in anhydrous ethanol at a ratio of 1 mg / mL using a magnetic stirring pot, and then the dispersed Gr solution is placed in the ball mill and continued to be ball-milled for several hours, and the ball-milled mixed powder slurry is placed in a blast drying oven to dry and sieve to obtain WC-Co-Gr composite powder; 3. Sintering of WC-Co-Gr cemented carbide materials The composite powder obtained in step 2 is placed in a graphite mold for pre-compression, and then placed in a spark plasma sintering furnace (SPS) for sintering. The temperature is first raised to 600°C and kept for 3 minutes, and then raised to 1250°C and kept for 5 minutes. After keeping warm, the powder is cooled in the furnace to obtain a WC-Co-Gr cemented carbide material.

[0007] Preferably, in step 1, the temperature is maintained at -5°C before the reaction, and after reacting for 30 minutes, the temperature is adjusted to 35°C and stirring is continued for 6 hours.

[0008] Preferably, when reducing graphene in step 1, the temperature in the furnace is 1050° C. and the time is 30 seconds.

[0009] Preferably, in step 2, the ball milling mixing is carried out for 20 hours, the ball-to-material ratio is 6:1, the grinding balls are a mixture of two small balls of φ7mm and φ8mm, wherein the mixing ratio of the two small balls of φ7mm and φ8mm is 8:1, the rotation speed is 300r / min, and the ball milling is carried out using a carbide ball mill and grinding balls.

[0010] Preferably, after adding Gr in step 2, ball milling is continued for 4 hours at a rotation speed of 120 r / min.

[0011] Preferably, in step 2, the product is dried in a forced air drying oven at 80° C. for 5 hours and the sieve mesh is 100 mesh.

[0012] Preferably, the pre-pressing pressure in step three is 10 MPa.

[0013] Preferably, in step three, the sintering heating rate before 600°C is 60°C / min, the heating rate when sintering from 600°C to 1250°C is 100°C / min, and the sintering pressure is 40MPa. The beneficial effects of the present invention are as follows: the present invention adds self-prepared graphene by a wet chemical method, and the graphene is evenly distributed at the grain boundaries of WC and Co grains during the sintering process, thereby achieving mechanical strengthening to prevent crack fracture at the grain boundaries and effectively improving the toughness of the cemented carbide; the addition of Gr can also refine the grains to a certain extent and improve the interface, thereby promoting fine grain strengthening, strengthening hardness, and increasing corrosion resistance, and the pores of the WC grains are fully filled with 10% Co, so that the cemented carbide has high density and avoids the performance degradation caused by internal defects; in addition, the ball milling time, rotation speed, and ball-to-material ratio are controlled in the ball milling process, so that the final sample composition is uniform, and the grain size is stabilized at about 400nm, thereby effectively improving the hardness and fracture toughness of the cemented carbide, and the hardness of the WC-Co-Gr cemented carbide prepared by the present invention can reach 1925.60kg / mm 2 , the fracture toughness reached 12.88MPa·m 1 / 2 Compared with traditional WC-Co cemented carbide (hardness 1793.43kg / mm 2 , fracture toughness 10.65MPa·m 1 / 2 ) has been significantly improved, thereby increasing the service life of cemented carbide in harsh environments and reducing the risks and costs caused by damage to cemented carbide parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a microscopic morphology of the graphene (Gr) material prepared by the present invention; Figure 2 This is a microscopic morphology of the WC-Co-Gr cemented carbide composite material in Example 2; Figure 3 This is the microscopic morphology of the WC-Co cemented carbide composite material in the comparative example. DETAILED DESCRIPTION

[0015] Below, in conjunction with the accompanying drawings and specific embodiments, the present invention is further described. It should be noted that, under the premise of no conflict, the embodiments described below or the technical features can be arbitrarily combined to form new embodiments. The specific techniques or conditions not specified in the embodiments are carried out according to the techniques or conditions described in the literature in this field, and the reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased on the market.

[0016] The mass percentages of the components in the following embodiments are respectively: Example 1: Co: 10wt%, Gr: 0.1wt%, the balance is WC; Example 2: Co: 10wt%, Gr: 0.2wt%, the balance is WC; Example 3: Co: 10wt%, Gr: 0.3wt%, the balance is WC; Comparative example: Co: 10wt%, Gr: 0wt%, and the balance WC.

[0017] The graphene is prepared as follows: Preparation of graphene oxide (GO): Immerse a dry three-necked flask in a low-temperature reaction bath at -5°C, and pour 5g of graphite powder and 2.5g of NaNO into one of the ports of the flask. 3 , slowly pour 150mL of concentrated sulfuric acid from the other port and stir slowly until the temperature in the flask stabilizes at -5°C; weigh 15g KMnO 4 , pour into the three-necked flask very slowly in three small portions while stirring. After reacting for 30 minutes, adjust the temperature to 35°C and continue stirring for 6 hours. After the reaction is complete, soak the flask in cold water to cool it down, then pour in excess H 2 O 2 Until the solution turns golden yellow, the pH value of the solution is brought close to 7 by dialysis to obtain GO solution. A portion of the GO solution is freeze-dried to obtain GO solid. The GO solid is placed in an iron box, sealed, and placed in a high-temperature furnace for heating and reduction. When reducing graphene, the furnace temperature is 1050°C and the time is 30s, and Gr is finally obtained.

[0018] Example 1 A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide, which uses WC powder, Co powder and Gr powder as raw materials, and sequentially performs batching, ball milling, drying, extrusion molding and pressure sintering to obtain the obtained product, specifically: According to the composition ratio of this embodiment, WC, Co and Gr are placed in a ball mill, and grinding balls are placed in the ball mill according to the ball-to-material ratio of 6:1, wherein the mixing ratio of φ7 mm and φ8 mm small balls is 8:1, anhydrous ethanol is added to cover the materials in the ball mill, and the ball mill is placed in a glove box, argon gas is introduced and sealed; The ball mill was placed on a planetary ball mill for 20 h at a speed of 300 r / min. Use a magnetic stirring pot to disperse Gr in anhydrous ethanol at a ratio of 1 mg / mL, then put the dispersed Gr solution into a ball mill and continue ball milling for 4 hours at a speed of 120 r / min; The ball-milled slurry was placed in a blast drying oven for drying and sieving, wherein the drying temperature was 80°C, the drying time was 5 hours, and the sieving mesh number was 100 meshes, thereby obtaining WC-Co-Gr composite powder; The obtained WC-Co-Gr composite powder was loaded into a graphite mold and pre-pressed using a hydraulic press at a pressing pressure of 10 MPa. The pressed mold was placed in a spark plasma sintering furnace (SPS) for sintering. The first stage heating rate was 60℃ / min, the temperature was raised to 600℃ and kept for 3min, the second stage heating rate was 100℃ / min and then raised to 1250℃ and kept for 5min. After the insulation, it was cooled in the furnace to obtain a WC-Co-Gr cemented carbide composite material.

[0019] In this embodiment, the Vickers hardness and fracture toughness of the sintered WC-Co-Gr cemented carbide composite material are 1856.77 kg / mm 2 and 10.91MPa·m 1 / 2 .

[0020] Example 2 A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide, which uses WC powder, Co powder and Gr powder as raw materials, and sequentially performs batching, ball milling, drying, extrusion molding and pressure sintering to obtain the obtained product, specifically: According to the composition ratio of this embodiment, WC, Co and Gr are placed in a ball mill, and grinding balls are placed in the ball mill according to the ball-to-material ratio of 6:1, wherein the mixing ratio of φ7 mm and φ8 mm small balls is 8:1, anhydrous ethanol is added to cover the materials in the ball mill, and the ball mill is placed in a glove box, argon gas is introduced and sealed; The ball mill was placed on a planetary ball mill for 20 h at a speed of 300 r / min. Use a magnetic stirring pot to disperse Gr in anhydrous ethanol at a ratio of 1 mg / mL, then put the dispersed Gr solution into a ball mill and continue ball milling for 4 hours at a speed of 120 r / min; The ball-milled slurry was placed in a blast drying oven for drying and sieving, wherein the drying temperature was 80°C, the drying time was 5 hours, and the sieving mesh number was 100 meshes, thereby obtaining WC-Co-Gr composite powder; The obtained WC-Co-Gr composite powder was loaded into a graphite mold and pre-pressed using a hydraulic press at a pressing pressure of 10 MPa. The pressed mold was placed in a spark plasma sintering furnace (SPS) for sintering. The first stage heating rate was 60℃ / min, the temperature was raised to 600℃ and kept for 3min, the second stage heating rate was 100℃ / min and then raised to 1250℃ and kept for 5min. After the insulation, it was cooled in the furnace to obtain a WC-Co-Gr cemented carbide composite material.

[0021] In this embodiment, the Vickers hardness and fracture toughness of the sintered WC-Co-Gr cemented carbide composite material are 1925.60 kg / mm 2 and 12.88MPa·m 1 / 2 .

[0022] Example 3 A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide, which uses WC powder, Co powder and Gr powder as raw materials, and sequentially performs batching, ball milling, drying, extrusion molding and pressure sintering to obtain the obtained product, specifically: According to the composition ratio of this embodiment, WC, Co and Gr are placed in a ball mill, and grinding balls are placed in the ball mill according to the ball-to-material ratio of 6:1, wherein the mixing ratio of φ7 mm and φ8 mm small balls is 8:1, anhydrous ethanol is added to cover the materials in the ball mill, and the ball mill is placed in a glove box, argon gas is introduced and sealed; The ball mill was placed on a planetary ball mill for 20 h at a speed of 300 r / min. Use a magnetic stirring pot to disperse Gr in anhydrous ethanol at a ratio of 1 mg / mL, then put the dispersed Gr solution into a ball mill and continue ball milling for 4 hours at a speed of 120 r / min; The ball-milled slurry was placed in a blast drying oven for drying and sieving, wherein the drying temperature was 80°C, the drying time was 5 hours, and the sieving mesh number was 100 meshes, thereby obtaining WC-Co-Gr composite powder; The obtained WC-Co-Gr composite powder was loaded into a graphite mold and pre-pressed using a hydraulic press at a pressing pressure of 10 MPa. The pressed mold was placed in a spark plasma sintering furnace (SPS) for sintering. The first stage heating rate was 60℃ / min, the temperature was raised to 600℃ and kept for 3min, the second stage heating rate was 100℃ / min and then raised to 1250℃ and kept for 5min. After the insulation, it was cooled in the furnace to obtain a WC-Co-Gr cemented carbide composite material.

[0023] In this embodiment, the Vickers hardness and fracture toughness of the sintered WC-Co-Gr cemented carbide composite material are 1704.29 kg / mm 2 and 12.07MPa·m 1 / 2 .

[0024] Comparative Example (without Gr added) A method for preparing ultrafine-grained WC-Co based cemented carbide, using WC powder and Co powder as raw materials, and sequentially performing batching, ball milling, drying, extrusion molding and pressure sintering to obtain the ultrafine-grained WC-Co based cemented carbide, specifically comprising: According to the composition ratio of this embodiment, WC and Co are placed in a ball mill, and grinding balls are placed in the ball mill according to a ball-to-material ratio of 6:1, wherein the mixing ratio of φ7 mm and φ8 mm small balls is 8:1, anhydrous ethanol is added to cover the materials in the ball mill, and the ball mill is placed in a glove box, argon gas is introduced, and the ball mill is sealed; The ball mill was placed on a planetary ball mill for 24 h at a speed of 300 r / min. The ball-milled slurry was placed in a blast drying oven for drying and sieving, wherein the drying temperature was 80°C, the drying time was 5 hours, and the sieving mesh number was 100 meshes, thereby obtaining WC-Co composite powder; The obtained WC-Co composite powder was loaded into a graphite mold and pre-pressed using a hydraulic press at a pressing pressure of 10 MPa. The pressed mold was placed in a spark plasma sintering furnace (SPS) for sintering. The first stage heating rate was 60℃ / min, the temperature was raised to 600℃ and kept for 3min, the second stage heating rate was 100℃ / min and then raised to 1250℃ and kept for 5min. After the insulation, it was cooled in the furnace to obtain a WC-Co-Gr cemented carbide composite material.

[0025] In this embodiment, the Vickers hardness and fracture toughness of the sintered WC-Co cemented carbide composite material are 1793.43 kg / mm 2 and 10.65MPa·m 1 / 2 .

[0026] Figure 1This is the microscopic morphology of the self-prepared Gr material, which is a thin sheet with a diameter of 3~5μm.

[0027] Depend on Figure 2 It can be seen that the WC grains in the WC-Co-Gr cemented carbide prepared in Example 2 are evenly distributed, without abnormally grown grains and pores. After adding Gr, the grains are more uniform than those in the comparative example. Under the same corrosion time, the corrosion resistance is stronger after adding Gr.

[0028] Depend on Figure 3 It can be seen that the WC grains in the WC-Co cemented carbide prepared in the comparative example are evenly distributed without the presence of pores, and some grains have a slight abnormal growth phenomenon.

[0029] The performance of the hard alloy composite materials obtained in Examples 1 to 3 and the comparative example was tested, and the test results are shown in Table 1: Table 1 Performance test results of Examples 1 to 3 and Comparative Examples It can be seen from Table 1 that with the increase of Gr addition, the Vickers hardness of the prepared cemented carbide composite material first increases and then decreases, but the fracture toughness is improved. Due to the high hardness of the ultrafine-grained cemented carbide itself, the fracture toughness of the material can be improved after adding a small amount of Gr. Considering the hardness and fracture toughness of the material, when the Gr addition is 0.2%, the comprehensive performance of the cemented carbide is the best, and the Vickers hardness reaches 1925.60kg / mm 2 , the fracture toughness reached 12.88MPa·m 1 / 2 Compared with traditional WC-Co cemented carbide (hardness 1793.43kg / mm 2 , fracture toughness 10.65MPa·m 1 / 2 ), the cemented carbide of the present application is more suitable for rock drilling tools, cutting tools and wear-resistant tools working in harsh service environments. It maintains the long life of the components while ensuring production efficiency, which is of great significance to the research on cemented carbide.

[0030] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A graphene-enhanced ultrafine-grained WC-Co based cemented carbide, characterized in that: Its characteristic components are as follows according to mass percentage: Co: 10wt%, Gr: 0-0.3wt%, and the balance is WC powder.

2. A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide as claimed in claim 1, characterized in that: The steps include:

1. Preparation of Graphene Oxide (GO) Immerse a dry three-necked flask in a low-temperature reaction bath, pour graphite powder and NaNO3 from one of the ports of the flask, pour concentrated sulfuric acid slowly from the other port, and stir slowly until the temperature in the flask is stable. While stirring, pour KMnO4 into the three-necked flask in small amounts three times and very slowly. After the reaction is completed, soak the flask in cold water to cool it down, then pour excess H2O2 while stirring until the solution turns golden yellow, dialyze the solution to a pH value close to 7, and obtain a GO solution. Take a portion of the GO solution and freeze-dry it to obtain a GO solid. Place the GO solid in an iron box and seal it, then put it in a high-temperature furnace for heating and reduction, and finally obtain Gr; 2. Preparation of WC-Co-Gr composite powder WC powder, Co powder and grinding balls are placed in a ball mill, soaked with an appropriate amount of anhydrous ethanol, and after ensuring that the liquid level covers the powder and the grinding balls, the ball mill is placed in a glove box to evacuate, and then argon is introduced, the ball mill is sealed and taken out, and then the ball mill is wet-milled and mixed in a planetary ball mill for several hours, and Gr is dispersed in anhydrous ethanol at a ratio of 1 mg / mL using a magnetic stirring pot, and then the dispersed Gr solution is placed in the ball mill and continued to be ball-milled for several hours, and the ball-milled mixed powder slurry is placed in a blast drying oven to dry and sieve to obtain WC-Co-Gr composite powder; 3. Sintering of WC-Co-Gr cemented carbide materials The composite powder obtained in step 2 is placed in a graphite mold for pre-compression, and then placed in a spark plasma sintering furnace (SPS) for sintering. The temperature is first raised to 600°C and kept for 3 minutes, and then raised to 1250°C and kept for 5 minutes. After keeping warm, the powder is cooled in the furnace to obtain a WC-Co-Gr cemented carbide material.

3. The method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide according to claim 1, characterized in that: In the step 1, the temperature was maintained at -5°C before the reaction. After reacting for 30 min, the temperature was adjusted to 35°C and stirring was continued for 6 h.

4. The method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide according to claim 1, characterized in that: When reducing graphene in step 1, the temperature in the furnace is 1050° C. and the time is 30 seconds.

5. The method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide according to claim 1, characterized in that: In the step 2, the ball milling is performed for 20 hours, the ball-to-material ratio is 6:1, the grinding balls are a mixture of two small balls of φ7 mm and φ8 mm, wherein the mixing ratio of the two small balls of φ7 mm and φ8 mm is 8:1, the rotation speed is 300 r / min, and the ball milling is performed using a carbide ball mill and grinding balls.

6. A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide as claimed in claim 1, characterized in that: After adding Gr in step 2, the ball milling was continued for 4 hours at a rotation speed of 120 r / min.

7. A method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide as claimed in claim 1, characterized in that: The step 2 is dried in a forced air drying oven at 80° C. for 5 h and sieved with a mesh size of 100 meshes.

8. The method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide according to claim 1, characterized in that: The pre-pressing pressure in step 3 is 10 MPa.

9. The method for preparing a graphene-enhanced ultrafine-grained WC-Co based cemented carbide according to claim 1, characterized in that: In the step 3, the heating rate of sintering before 600°C is 60°C / min, the heating rate of sintering from 600°C to 1250°C is 100°C / min, and the sintering pressure is 40MPa.

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