Gradient-structure hard alloy ball tooth suitable for dry rock breaking and preparation method

Abstract

The invention provides a hard alloy ball tooth of a gradient structure suitable for dry rock breaking and a preparation method, the hard alloy ball tooth is of an N-layer gradient structure, and raw materials of the gradient structure comprise WC powder, Co powder and graphene powder; in the N-layer gradient structure, the volume fraction of the WC powder and the volume fraction of the graphene powder are equal or increased layer by layer from the inner layer to the outer layer, and the volume fraction of the Co powder is equal or decreased layer by layer from the inner layer to the outer layer; in the outermost layer of the N-layer gradient structure, the volume fraction of the WC powder and the volume fraction of the graphene powder are both larger than the volume fraction of the Co powder; and the thickness of each layer in the N layers of gradient structures is greater than or equal to 0.1 mm. According to the hard alloy ball tooth, the mechanical property of the hard alloy ball tooth is improved, the hard alloy ball tooth has high hardness and high toughness, the hard alloy ball tooth is endowed with more excellent heat dissipation performance, the rock breaking efficiency is improved to a great extent, and the service life of a product is prolonged to a great extent.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and relates to cemented carbide ball teeth, specifically to a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking and its preparation method. Background Technology

[0002] Cemented carbide is a composite material prepared by powder metallurgy, using refractory metal compounds as the matrix and transition metals as the binder phase. It possesses strong comprehensive properties, including high hardness, high strength, high wear resistance, and chemical stability. In recent years, with the development of mining, energy extraction, and major infrastructure construction, the demand for mining products such as cemented carbide drill bits has been increasing both domestically and internationally. In working environments such as coal mines where dry rock breaking is required, the drill bit is subjected to multiple stresses, including tension and compression, placing high demands on its hardness and impact toughness. Furthermore, it faces challenges such as excessively high temperatures and inadequate heat dissipation, which can lead to drill bit failure. Therefore, it is necessary to develop cemented carbide ball teeth that combine high hardness and high toughness with efficient heat dissipation to address the problems encountered in dry rock breaking.

[0003] Gradient-structured cemented carbide ball teeth exhibit a gradient distribution of cobalt in their microstructure. Due to the higher WC content on the surface, they possess high hardness and good wear resistance, while the cobalt content increases further towards the interior of the cemented carbide ball tooth, resulting in excellent toughness. During rock drilling, the cemented carbide ball teeth can withstand higher loads before failure, effectively resolving the contradiction between toughness and wear resistance, thus attracting widespread attention. However, currently, the preparation of gradient-structured cemented carbide ball teeth mainly relies on carburizing methods. Popular processes include carburizing with carbon-deficient alloys and carburizing with low-carbon alloys. However, both methods have significant drawbacks. The core technology of the carbon-deficient method is the control of the distribution of the η phase, which carries significant risks to process stability and repeatability. The low-carbon method depends on precise control of process equipment. Therefore, developing a new method for preparing gradient-structured cemented carbide ball teeth is of great significance for improving the application of gradient cemented carbide ball teeth. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking and its preparation method, thereby solving the technical problem that it is difficult to simultaneously improve the stability of the process and reduce the harshness of the reaction conditions when preparing cemented carbide ball teeth with a gradient structure for dry rock breaking.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0006] A cemented carbide ball tooth with a gradient structure suitable for dry rock breaking, wherein the cemented carbide ball tooth has an N-layer gradient structure, and the raw materials of the gradient structure include WC powder, Co powder and graphene powder.

[0007] In the N-layer gradient structure, the volume fractions of WC powder and graphene powder are equal or increase from the inner layer to the outer layer, while the volume fraction of Co powder is equal or decreases from the inner layer to the outer layer. In the outermost layer of the N-layer gradient structure, the volume fractions of both WC powder and graphene powder are greater than the volume fraction of Co powder.

[0008] The thickness of each layer in the N-layer gradient structure is greater than or equal to 0.1 mm.

[0009] The present invention also has the following technical features.

[0010] Specifically, N is greater than or equal to 4; the total thickness of the N-layer gradient structure is 0.4 to 25 mm.

[0011] Specifically, the WC powder has an average particle size of 0.5–2.0 μm; the Co powder has an average particle size of 0.3–1.5 μm; and the graphene powder has an average particle size of 0.2–1.0 μm.

[0012] The present invention also provides a method for preparing a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking, as described above, the method specifically including the following steps.

[0013] Step 1, Ingredients and Mixing:

[0014] WC powder, Co powder and graphene powder are mixed, then placed in a mixer and mixed with binder and water. After being mixed evenly, a set of mixtures is obtained. N sets of mixtures with different ratios are prepared by the same method.

[0015] Step 2, Model Building: A 3D model of the N-layer gradient structure of the cemented carbide ball teeth is created in the computer. Then, the printing parameters of the 3D model are set and imported into the slurry direct writing molding 3D printer to obtain the slurry direct writing molding 3D printer after setting.

[0016] Step 3, print the green blank: The N mixtures obtained in step one are used as printing materials, and the slurry direct-write molding 3D printer with the settings obtained in step two is used for printing to obtain N green bodies with different ratios.

[0017] Step 4, Remove Adhesive: The N groups of green blanks with different proportions obtained in step three are placed in a degreasing furnace. The heating rate, holding temperature and holding time are set, and then hydrogen reduction is performed to remove the binder, resulting in N degreased sheets.

[0018] Step 5, two-step vacuum sintering: According to the design layer number and sequence, the N degreased thin sheets obtained in step four are assembled into the sintering mold from the innermost layer to the outermost layer, and two-step vacuum sintering is performed. After sintering, the mold is cooled with the furnace to obtain N-layer gradient structure cemented carbide spherical teeth.

[0019] Specifically, in step one, the solid content of the N groups of mixtures is 45-75 wt%; In step one, the total mass of the WC powder, Co powder, and graphene powder is in a mass ratio of (4-9):1 to the binder.

[0020] Specifically, in step one, the volume fraction ratio of WC powder:Co powder:graphene powder is (60-90%):(2-30%):(0-10%).

[0021] Specifically, in step one, the binder in each of the N groups of mixtures is made of the following components by mass: 15-25% guar gum, 5-15% polyphenylene ether, 3-10% dodecyltrimethylammonium chloride, and the balance is styrene-based thermoplastic elastomer, with the sum of the mass parts of the components being 100%.

[0022] Specifically, in step two, the printing parameters are: printing speed of 10-350 mm / s, printing layer thickness of 0.1-0.5 mm, printing temperature of 100-380℃, and nozzle temperature of 100-260℃.

[0023] Specifically, in step four, the hydrogen reduction debinding process involves debinding in a degreasing furnace purged with hydrogen using a stepped heating and holding method. The specific steps of the stepped heating and holding debinding method are as follows: heating from room temperature to 80℃ to 150℃ at a heating rate of 4 to 7℃ / min, holding for 0.5 to 1 hour; then heating to 230℃ to 290℃ at a heating rate of 3 to 8℃ / min, holding for 2 to 2.5 hours; then heating to 380℃ to 420℃ at a heating rate of 2.5 to 4℃ / min, holding for 1 to 1.5 hours; and finally heating to 580℃ to 650℃ at a heating rate of 2 to 3℃ / min, holding for 1.5 to 2 hours.

[0024] Specifically, in step five, the two-step vacuum sintering process is as follows: First, the sintering mold assembled with N degreased thin sheets is placed in a vacuum sintering furnace, using nitrogen as the pressure medium. The first step is to heat the sample to 750–1150°C and hold it for sintering for 30–90 minutes, with a sintering pressure of 1–15 MPa. After the sintered sample cools down, the second step of sintering is carried out. The sintering temperature of the second step is 1250–1500°C, the sintering pressure is 1–15 MPa, and the sintering time is 30–70 minutes.

[0025] Compared with the prior art, the present invention has the following technical effects.

[0026] (I) In the cemented carbide ball teeth of the present invention, the volume fractions of WC powder and graphene powder are equal or increase from the inner layer to the outer layer, while the volume fraction of Co powder is equal or decreases from the inner layer to the outer layer. By utilizing the changes in the volume fractions of the three raw materials, the mechanical properties of the cemented carbide ball teeth are improved, and they have both high hardness and high toughness. They also give the cemented carbide ball teeth better heat dissipation, which effectively solves the problem of cemented carbide ball teeth breaking due to slow heat dissipation caused by high temperature in dry rock breaking environment, and greatly improves rock breaking efficiency and product life.

[0027] (II) In this invention, slurry direct writing molding 3D printing is used, which can accurately print the designed gradient structure layer, control the layer thickness, and ensure that the raw materials in each gradient layer are uniform, thereby optimizing the performance of the cemented carbide ball teeth of the gradient structure. At the same time, it can also improve production efficiency and reduce production costs. The two-step vacuum sintering process ensures the formation of the gradient structure and ensures that the presence of graphene powder does not affect the density of the product.

[0028] (III) The gradient structure of the carbide ball teeth in this invention has good heat dissipation, making it particularly suitable for use in working environments such as coal mines that require dry rock breaking. It also has the special properties of high surface hardness and high internal toughness, which greatly improves the drilling efficiency of drilling tools and extends their service life. It specifically solves the drilling needs of mining in arid areas and drilling operations in urban buildings.

[0029] (IV) In this invention, graphene powder, as an auxiliary binder, does not affect the compactness of the cemented carbide ball teeth. Furthermore, due to the good thermal conductivity of graphene, graphene is added to each gradient layer and uniformly distributed through 3D printing technology, ensuring continuous and uniform energy transfer. This results in cemented carbide ball teeth with good heat dissipation, without affecting the mechanical properties of the cemented carbide ball teeth, thus improving their service life. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the 8-layer gradient structure of the cemented carbide ball tooth prepared in Example 2 of the present invention.

[0031] The specific content of the present invention will be further described in detail below with reference to the embodiments. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, all equipment, raw materials and methods in this invention are commonly used in the art and are known in the prior art. For example, the mixer is a known mixer, the degreasing furnace is a known degreasing furnace, the WC powder is a known WC powder, the Co powder is a known Co powder, the graphene powder is a known graphene powder, and the water is preferably a known deionized water.

[0033] In this invention, room temperature refers to the ambient temperature during the production process, which is typically within the range of 20±10℃.

[0034] In this invention, the guar gum used is a commonly known guar gum in the art, with a number-average molecular weight of 250,000. The polyphenylene ether used is a commonly known polyphenylene ether in the art, with a number-average molecular weight of 50,000. The styrene-based thermoplastic elastomer used is a styrene-isoprene-styrene copolymer, with a number-average molecular weight of 10,000.

[0035] Following the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of the present invention fall within the protection scope of the present invention.

[0036] Example 1: This embodiment provides a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking. The cemented carbide ball tooth has a 4-layer gradient structure, i.e., N = 4, with each layer having a thickness of 0.3 mm, and the total thickness of the 4-layer gradient structure is 1.2 mm. The raw materials for each layer in the gradient structure include WC powder, Co powder, and graphene powder; the average particle size of WC powder (i.e., tungsten carbide powder) is 0.8 μm; the average particle size of Co powder (i.e., cobalt powder) is 0.8 μm; and the average particle size of graphene powder is 0.8 μm.

[0037] In this embodiment, N equals 4, which is more than the number of gradient layers compared to the prior art. This is mainly because the thickness of each layer in the gradient structure of the cemented carbide ball teeth in this embodiment is relatively thin. Therefore, multiple layers can be densely stacked by combining degreasing and two-step vacuum sintering, thereby ensuring that graphene can be continuously distributed in each gradient layer. This can greatly improve the heat dissipation of the cemented carbide ball teeth, and the gradient change of Co content can maintain the continuity and uniformity of impact load transmission in each layer without abrupt changes. If N is less than 4, it is not possible to effectively buffer the impact load, which can easily cause the cemented carbide ball teeth to break.

[0038] In this embodiment, the thickness of each layer in the cemented carbide ball tooth is 0.3 mm, and the total thickness of the four-layer gradient structure is 1.2 mm. This is mainly because the cemented carbide ball tooth needs to maintain both good wear resistance and impact resistance, thus requiring control of the thickness of each layer in the gradient structure. If the thickness of a single layer in the gradient structure is too small, the hardness of the cemented carbide ball tooth will decrease and the buffering capacity of the inner layer will also decrease during application, resulting in a significant reduction in its effectiveness. If the thickness of each layer in the gradient structure is too large, on the one hand, it limits the number of gradient layers, leading to a decrease in the buffering performance of the cemented carbide ball tooth; on the other hand, it will cause difficulties in subsequent degreasing and two-step vacuum sintering, resulting in a decrease in the interfacial bonding force of each layer in the gradient structure.

[0039] In this embodiment of the cemented carbide ball teeth, WC powder is the hard phase; within the scope of the present invention, if the volume fraction of WC powder is higher, the cemented carbide ball teeth exhibit high hardness; while when the volume fraction of Co powder increases, the cemented carbide ball teeth exhibit high toughness; if the amount of graphene powder increases, the cemented carbide ball teeth exhibit high heat dissipation.

[0040] In this embodiment, if the average particle size of WC powder and Co powder is too large, severe agglomeration will occur during the preparation of the mixture, making printing impossible.

[0041] This embodiment also provides a method for preparing a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking, which specifically includes the following steps: Step 1, Ingredients and Mixing: WC powder, Co powder, and graphene powder were mixed, then placed in a mixer and mixed with binder and water. After stirring evenly, a mixture was obtained. Four mixtures with different proportions were prepared using the same method. Each mixture is a layer of the gradient structure of cemented carbide ball teeth. The solid content of all four mixtures was 60 wt%. During the preparation of each mixture, the total mass ratio of WC powder, Co powder, and graphene powder to binder was 6:1.

[0042] In each of the four mixtures, the binder is composed of the following components by mass: 20% guar gum, 15% polyphenylene ether, 5% dodecyltrimethylammonium chloride, and the balance being a styrene-based thermoplastic elastomer. The sum of the mass parts of the components is 100%.

[0043] The gradient structure, from the outermost layer to the innermost layer, has the following raw material ratios during preparation: The volume fraction ratio of WC powder:Co powder:graphene powder is 85%:5%:10%.

[0044] The second layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 82%, 10%, and 8%.

[0045] The volume fraction ratio of WC powder:Co powder:graphene powder is 79%:15%:6%.

[0046] The fourth layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 76%, 20%, and 4%.

[0047] Step 2, Model Building: A 3D model of a 4-layer gradient structure of cemented carbide ball teeth was created in the computer. Then, the printing parameters of the 3D model were set and imported into the slurry direct writing molding 3D printer to obtain the slurry direct writing molding 3D printer after setting. The specific printing parameters are: printing speed of 50mm / s, printing layer thickness of 0.3mm, printing temperature of 110℃, and nozzle temperature of 230℃.

[0048] In this embodiment, the method for creating the 3D model in the computer adopts a method known and commonly used in the art, and the method for setting the printing parameters of the 3D model and the method for importing the 3D model after setting the printing parameters into the slurry direct writing molding 3D printer also adopt a method known and commonly used in the art.

[0049] Step 3, print the green blank: The four mixtures obtained in step one were used as printing materials, and the slurry direct-write molding 3D printer with the settings obtained in step two was used for printing to obtain four green bodies with different ratios.

[0050] In this embodiment, the printing method of the slurry direct-write molding 3D printer adopts a method commonly known in the art.

[0051] In this embodiment, by combining 3D printing technology and powder metallurgy, the designed gradient structure layers can be precisely printed, and the thickness of each gradient structure layer can be precisely controlled. Traditional powder spreading processes cannot control the uniformity of materials at this thickness. Therefore, the number of gradient layers in this invention can be as large as possible while ensuring the total thickness of the cemented carbide ball teeth, thereby achieving a slow change in the content of Co powder and graphene powder, reducing the difficulty of bonding between gradient layers, and the addition of graphene powder does not affect the density of the cemented carbide ball teeth, thus further improving the performance of the cemented carbide ball teeth.

[0052] Step 4, Remove Adhesive: The four groups of green blanks with different proportions obtained in step three were placed in a degreasing furnace. Degreasing was performed in the furnace, which was purged with hydrogen, using a stepped heating and holding method. The specific steps of the stepped heating and holding degreasing were as follows: the temperature was increased from room temperature to 120℃ at a rate of 6℃ / min and held for 0.5 hours; then increased to 270℃ at a rate of 4℃ / min and held for 2 hours; then increased to 420℃ at a rate of 3℃ / min and held for 1 hour; finally, the temperature was increased to 620℃ at a rate of 2℃ / min and held for 2 hours. After hydrogen reduction and debinding, four degreased sheets were obtained.

[0053] In this embodiment, a stepped heating and heat preservation degreasing method (degreasing is the removal of binder) is adopted. This method is mainly based on the difference in the pyrolysis temperature range of different components in the binder, which can effectively ensure the integrity of the green body and the removal of binder from the green body, thus avoiding degreasing defects.

[0054] Step 5, two-step vacuum sintering: According to the designed number of layers and sequence, the four degreased sheets obtained in step four were assembled into a sintering mold from the innermost layer to the outermost layer, and then subjected to two-step vacuum sintering. The specific process of the two-step vacuum sintering is as follows: First, the sintering mold with the four degreased sheets was placed in a vacuum sintering furnace, using nitrogen as the pressure medium. The first step was to heat the mold to 950℃ and hold it for 60 minutes, with a sintering pressure of 10 MPa. After the sintered sample cooled, the second step of sintering was carried out. The sintering temperature of the second step was 1400℃, the sintering pressure was 10 MPa, and the sintering time was 60 minutes. After sintering, the mold was cooled with the furnace to obtain a four-layer gradient structure of cemented carbide spherical teeth.

[0055] In this embodiment, the sintering mold is a commonly used sintering mold known in the art, and the vacuum sintering furnace is a commonly used vacuum sintering furnace known in the art.

[0056] The two-step vacuum sintering process used in this embodiment can greatly eliminate internal excess pores under high pressure during the first sintering step because the temperature does not reach the liquefaction temperature of Co. This greatly helps to ensure the gradient structure by preventing Co from migrating after liquefaction during the second high-temperature sintering step. The second high-temperature vacuum sintering can greatly eliminate internal pores, and because excess large pores were eliminated in the first step, liquid Co cannot migrate, ensuring the formation of the gradient structure. Furthermore, the carbon content of the cemented carbide spherical teeth can be corrected by adjusting the atmosphere in the vacuum sintering furnace, and the η phase in the cemented carbide spherical teeth structure can be eliminated.

[0057] The performance of the obtained four-layer gradient structure cemented carbide ball teeth was tested. The impact toughness of the cemented carbide ball teeth was measured using a pendulum impact testing machine, and the measured impact toughness was 8.8 J / cm. 2 Compared to traditional cemented carbide ball teeth, the impact toughness is improved by 15% to 30%. The bending strength of the four-layer gradient structure cemented carbide ball teeth was tested using the three-point bending test method, and the bending strength was measured to be 3560 MPa, showing a significant improvement. The hardness of the four-layer gradient structure cemented carbide ball teeth was measured using a Vickers hardness tester, and its Vickers hardness was measured to be 1856 HV, which is also higher than that of traditional cemented carbide ball teeth. Performance test results show that the four-layer gradient structure cemented carbide ball teeth obtained using the preparation method in this embodiment possess both excellent high hardness and high toughness.

[0058] In this embodiment, the conventional cemented carbide ball teeth are cemented carbide ball teeth prepared using conventional methods known in the art. The pendulum impact testing machine and the impact resistance testing method use equipment and testing methods known in the art; the three-point bending test uses the three-point bending test method known in the art; the Vickers hardness tester and the hardness testing method use equipment and testing methods known in the art.

[0059] Example 2: This embodiment provides a graded-structure cemented carbide ball tooth suitable for dry rock breaking, such as... Figure 1 As shown, the cemented carbide ball tooth has an 8-layer gradient structure, i.e., N = 8, with each layer having a thickness of 0.3 mm, and the total thickness of the 8-layer gradient structure is 2.4 mm. The raw materials for each layer in the gradient structure include WC powder, Co powder, and graphene powder; the average particle size of the WC powder is 1.2 μm; the average particle size of the Co powder is 1.2 μm; and the average particle size of the graphene powder is 1.2 μm.

[0060] This embodiment also provides a method for preparing a gradient structure of cemented carbide ball teeth suitable for dry rock breaking. This method is basically the same as the preparation method in Example 1, except that: N in this embodiment is 8; in step one, the total mass ratio of WC powder, Co powder, and graphene powder to the binder is 4:1; in step two, the nozzle temperature is 220℃; in step five, the first step is to heat to 1050℃ and hold for sintering for 65 minutes at a sintering pressure of 12 MPa; the second step is to sinter at 1450℃ at a sintering pressure of 12 MPa for 65 minutes; in step one of this embodiment, the raw material ratios of the mixture in each layer of the gradient structure from the outermost layer to the innermost layer during preparation are as follows: Layer 1: The volume fraction ratio of WC powder:Co powder:graphene powder is 90%:2%:8%; Layer 2: The volume fraction ratio of WC powder:Co powder:graphene powder is 89%:4%:7%; The volume fraction ratio of WC powder:Co powder:graphene powder is 88%:6%:6%; The fourth layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 87%, 8%, and 5%. Layer 5: The volume fraction ratio of WC powder:Co powder:graphene powder is 86%:10%:4%; Layer 6: The volume fraction ratio of WC powder:Co powder:graphene powder is 85%:12%:3%; Layer 7: The volume fraction ratio of WC powder: Co powder: graphene powder is 84%:14%:2%; Layer 8: The volume fraction ratio of WC powder: Co powder: graphene powder is 83%: 16%: 1%.

[0061] The performance of the obtained 8-layer gradient structure cemented carbide ball teeth was tested. The impact toughness of the cemented carbide ball teeth was measured using a pendulum impact testing machine, and the measured impact toughness was 9.8 J / cm. 2 Compared to traditional cemented carbide ball teeth, the impact toughness is improved by 15% to 30%. The bending strength of the 8-layer gradient structure cemented carbide ball teeth was tested using the three-point bending test method, and the measured bending strength was 4007 MPa, showing a significant improvement. The hardness of the 8-layer gradient structure cemented carbide ball teeth was measured using a Vickers hardness tester, and its Vickers hardness was 1892 HV, which is also higher than that of traditional cemented carbide ball teeth. Performance test results show that the 8-layer gradient structure cemented carbide ball teeth obtained using the preparation method in this embodiment possess both good high hardness and high toughness properties. Furthermore, compared to the 4-layer gradient structure cemented carbide ball teeth in Example 1, it can be seen that as the number of layers in the gradient structure increases, the bending strength and Vickers hardness of the corresponding cemented carbide ball teeth can be further enhanced.

[0062] Example 3: This embodiment provides a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking. The cemented carbide ball tooth has a 12-layer gradient structure, i.e., N = 12, with each layer having a thickness of 0.1 mm, and the total thickness of the 12-layer gradient structure is 1.2 mm. The raw materials for each layer in the gradient structure include WC powder, Co powder, and graphene powder; the average particle size of the WC powder is 1.4 μm; the average particle size of the Co powder is 1.4 μm; and the average particle size of the graphene powder is 1.4 μm.

[0063] This embodiment also provides a method for preparing a gradient structure of cemented carbide ball teeth suitable for dry rock breaking. This method is basically the same as the preparation method in Example 1, except that: N in this embodiment is 12; in step one, the total mass ratio of WC powder, Co powder, and graphene powder to the binder is 8:1; in step two, the printing layer thickness is 0.1 mm; in step four, the temperature is increased from room temperature to 150°C at a rate of 7°C / min, then increased to 290°C at a rate of 8°C / min, and finally increased to 650°C at a rate of 3°C / min; in step five, the first step is to heat to 1150°C and hold for sintering for 70 min at a sintering pressure of 15 MPa; the second step is to sinter at a temperature of 1500°C, a sintering pressure of 15 MPa, and a sintering time of 70 min; in step one of this embodiment, the raw material ratios of the mixture in each layer of the gradient structure from the outermost layer to the innermost layer during preparation are as follows: Layer 1: The volume fraction ratio of WC powder:Co powder:graphene powder is 87%:3%:10%; The second layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 86%, 4%, and 10%. The third layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 85%:5%:10%. Layer 4: The volume fraction ratio of WC powder:Co powder:graphene powder is 85%:7%:8%; Layer 5: The volume fraction ratio of WC powder:Co powder:graphene powder is 84%:8%:8%; Layer 6: The volume fraction ratio of WC powder:Co powder:graphene powder is 83%:9%:8%; Layer 7: The volume fraction ratio of WC powder: Co powder: graphene powder is 83%:11%:6%; Layer 8: The volume fraction ratio of WC powder: Co powder: graphene powder is 82%:12%:6%; Layer 9: The volume fraction ratio of WC powder: Co powder: graphene powder is 81%:13%:6%; Layer 10: The volume fraction ratio of WC powder:Co powder:graphene powder is 81%:15%:4%; Layer 11: The volume fraction ratio of WC powder:Co powder:graphene powder is 80%:16%:4%; The volume fraction of WC powder, Co powder, and graphene powder in the 12th layer is 79%, 17%, and 4%, respectively.

[0064] The performance of the obtained 12-layer gradient structure cemented carbide ball teeth was tested. The impact toughness of the cemented carbide ball teeth was measured using a pendulum impact testing machine, and the measured impact toughness was 10.8 J / cm. 2 Compared to traditional cemented carbide ball teeth, the impact toughness is improved by 15% to 30%. The bending strength of the 12-layer gradient structure cemented carbide ball teeth was tested using the three-point bending test method, and the bending strength was measured to be 4309 MPa, showing a significant improvement. The hardness of the 12-layer gradient structure cemented carbide ball teeth was measured using a Vickers hardness tester, and its Vickers hardness was measured to be 1879 HV, which is also higher than that of traditional cemented carbide ball teeth. Performance test results show that the 12-layer gradient structure cemented carbide ball teeth obtained using the preparation method in this embodiment possess both excellent high hardness and high toughness.

[0065] Comparative Example 1: This comparative example provides a method for preparing cemented carbide ball teeth, which is basically the same as the preparation method in Example 1, except that N in this comparative example is 3, the gradient structure is from the outermost layer to the innermost layer, and the raw material ratios of the mixture in each layer during preparation are as follows: Layer 1: The volume fraction ratio of WC powder:Co powder:graphene powder is 90%:2%:8%; The second layer consists of WC powder, Co powder, and graphene powder in a volume fraction ratio of 85%, 10%, and 5%. The volume fraction ratio of WC powder:Co powder:graphene powder is 80%:19%:1%.

[0066] This comparative example also provides a cemented carbide ball tooth, which is prepared using the same method as the cemented carbide ball tooth in this comparative example.

[0067] Because the number of gradient layers in the cemented carbide ball teeth prepared in this comparative example is relatively small, it cannot effectively buffer and transfer impact loads. The impact toughness of the cemented carbide ball teeth with a 4-layer gradient structure prepared in Example 1 and those prepared in this comparative example were tested under the same working conditions. The results showed that the impact toughness of the cemented carbide ball teeth prepared in this comparative example was 8.0 J / cm². 2The heat dissipation is much smaller than that of the 4-layer gradient structure cemented carbide ball teeth prepared in Example 1; at the same time, due to the large range of graphene content in each layer, the heat dissipation is also much lower than that of the 4-layer gradient structure cemented carbide ball teeth prepared in Example 1.

[0068] Comparative Example 2: This comparative example provides a cemented carbide ball tooth, which is a cemented carbide ball tooth (without gradient layer structure) made from commercially available YG3 cemented carbide (i.e., made from 97wt% WC powder and 3wt% Co powder) using a commonly known 3D printing method in the art.

[0069] The impact toughness of the YG3 cemented carbide ball teeth in this comparative example was tested using a pendulum impact testing machine, and the measured impact toughness was 8.2 J / cm. 2 The bending strength was tested using the three-point bending test method, and the bending strength was measured to be 1200MPa. The hardness of the YG3 cemented carbide ball tooth was tested to be 91.0HRA, which is equivalent to a Vickers hardness of 1300HV.

[0070] Comparative Example 3: This comparative example provides a method for preparing cemented carbide ball teeth, which is basically the same as the preparation method in Example 3, except that: the thickness of each layer of the N-layer gradient structure in this comparative example is 1.5 mm, that is, the printing layer thickness is 1.5 mm, and the total thickness of the 12-layer gradient structure is 18 mm.

[0071] This comparative example also provides a cemented carbide ball tooth, which is prepared using the same method as the cemented carbide ball tooth in this comparative example.

[0072] Because the thickness of each layer of the cemented carbide ball tooth prepared in this comparative example is relatively large, its effect on the transmission of impact load is poor, resulting in abrupt changes in force. The impact toughness of the 12-layer gradient structure cemented carbide ball tooth prepared in Example 3 and the cemented carbide ball tooth in this comparative example were tested under the same working conditions. The results showed that the impact toughness of the cemented carbide ball tooth prepared in Comparative Example 3 was 6.8 J / cm². 2 The thickness of the gradient layer is much smaller than that of the cemented carbide ball teeth prepared in Example 3. An excessively thick gradient layer can easily lead to the loss of the advantage of gradient transfer of impact loads. Furthermore, an excessively thick gradient layer is difficult to ensure its density during sintering, and the joint may experience strength loss.

Claims

1. A type of hard alloy ball tooth with a gradient structure suitable for dry rock breaking, characterized in that, The structure of the cemented carbide ball teeth is an N-layer gradient structure, and the raw materials of the gradient structure include WC powder, Co powder and graphene powder; In the N-layer gradient structure, the volume fractions of WC powder and graphene powder are equal or increase from the inner layer to the outer layer, while the volume fraction of Co powder is equal or decreases from the inner layer to the outer layer. In the outermost layer of the N-layer gradient structure, the volume fractions of both WC powder and graphene powder are greater than the volume fraction of Co powder. The thickness of each layer in the N-layer gradient structure is greater than or equal to 0.1 mm.

2. The cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 1, characterized in that, The N is greater than or equal to 4; the total thickness of the N-layer gradient structure is 0.4 to 25 mm.

3. The cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 1, characterized in that, The WC powder has an average particle size of 0.5–2.0 μm; the Co powder has an average particle size of 0.3–1.5 μm; and the graphene powder has an average particle size of 0.2–1.0 μm.

4. A method for preparing a cemented carbide ball tooth with a gradient structure suitable for dry rock breaking as described in any one of claims 1 to 3, characterized in that, The method specifically includes the following steps: Step 1, Ingredients and Mixing: WC powder, Co powder and graphene powder are mixed, then placed in a mixer and a binder and water are added and stirred. After stirring evenly, a set of mixtures is obtained. N sets of mixtures with different proportions are prepared using the same method. Step 2, Model Building: A 3D model of the N-layer gradient structure of the cemented carbide ball teeth is created in the computer. Then, the printing parameters of the 3D model are set and imported into the slurry direct writing molding 3D printer to obtain the slurry direct writing molding 3D printer after setting. Step 3, print the green blank: The N sets of mixtures obtained in step one are used as printing materials, and printed using the slurry direct writing molding 3D printer set in step two, to obtain N sets of green bodies with different ratios. Step 4, Remove Adhesive: The N groups of green blanks with different proportions obtained in step three are placed in a degreasing furnace. The heating rate, holding temperature and holding time are set, and then hydrogen reduction is performed to remove the binder, resulting in N degreased sheets. Step 5, Two-step vacuum sintering: According to the design layer number and sequence, the N degreased thin sheets obtained in step four are assembled into the sintering mold from the innermost layer to the outermost layer, and two-step vacuum sintering is performed. After sintering, the mold is cooled with the furnace to obtain N-layer gradient structure cemented carbide spherical teeth.

5. The method for preparing cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step one, the solid content of the N groups of mixtures is 45-75 wt%. In step one, the total mass of the WC powder, Co powder, and graphene powder is in a mass ratio of (4-9):1 with that of the binder.

6. The cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step one, the volume fraction ratio of WC powder:Co powder:graphene powder is (60-90%):(2-30%):(0-10%).

7. The method for preparing cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step one, the binder in each of the N groups of mixtures is made of the following components by mass: 15-25% guar gum, 5-15% polyphenylene ether, 3-10% dodecyltrimethylammonium chloride, and the balance is styrene-based thermoplastic elastomer, and the sum of the mass parts of the components is 100%.

8. The method for preparing cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step two, the printing parameters are as follows: printing speed of 10-350 mm / s, printing layer thickness of 0.1-0.5 mm, printing temperature of 100-380℃, and nozzle temperature of 100-260℃.

9. The method for preparing cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step four, the process of hydrogen reduction to remove the binder involves degreasing in a degreasing furnace purged with hydrogen using a stepped heating and holding method. The specific steps of the stepped heating and holding degreasing method are as follows: heating from room temperature to 80℃ to 150℃ at a heating rate of 4 to 7℃ / min, holding for 0.5 to 1 hour; then heating to 230℃ to 290℃ at a heating rate of 3 to 8℃ / min, holding for 2 to 2.5 hours; then heating to 380℃ to 420℃ at a heating rate of 2.5 to 4℃ / min, holding for 1 to 1.5 hours; and finally heating to 580℃ to 650℃ at a heating rate of 2 to 3℃ / min, holding for 1.5 to 2 hours.

10. The method for preparing cemented carbide ball teeth with a gradient structure suitable for dry rock breaking as described in claim 4, characterized in that, In step five, the specific process of the two-step vacuum sintering is as follows: First, the sintering mold assembled with N degreased thin sheets is placed in a vacuum sintering furnace, using nitrogen as the pressure medium. The first step is to heat the sample to 750-1150℃ and hold it for sintering for 30-90 minutes, with a sintering pressure of 1-15 MPa. After the sintered sample cools down, the second step of sintering is carried out. The sintering temperature of the second step is 1250-1500℃, the sintering pressure is 1-15 MPa, and the sintering time is 30-70 minutes.

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