Polycrystalline diamond spherical tooth with functional gradient structure and preparation method of polycrystalline diamond spherical tooth

Abstract

The invention provides a polycrystalline diamond spherical tooth with a functional gradient structure and a preparation method of the polycrystalline diamond spherical tooth. The polycrystalline diamond spherical tooth is divided into a hard alloy substrate, a connecting layer and a polycrystalline diamond layer from bottom to top; the content of the polycrystalline diamond in the connecting layer is gradually increased, and the content of the hard alloy is gradually decreased; according to the polycrystalline diamond spherical tooth, a 3D printing mode is adopted, diamond micro-powder slurry and WC-Co pre-alloyed powder slurry are put into two feeding ports of a 3D printer correspondingly, the two kinds of slurry enter a mixing cavity independently or in different proportions, then a spherical tooth green body is obtained through extrusion printing of a nozzle, the spherical tooth green body is firstly subjected to compression molding to obtain a spherical tooth pressed blank, and then the spherical tooth pressed blank is subjected to hot pressing to obtain the polycrystalline diamond spherical tooth. The polycrystalline diamond spherical tooth prepared by the preparation method disclosed by the invention has excellent wear resistance and high efficiency, and has important application prospects and economic benefits in construction of underground tunnels, mine drilling and the like.

Description

Technical Field

[0001] The present invention belongs to the field of construction machinery, and particularly relates to a polycrystalline diamond button with a functionally graded structure and a preparation method thereof. Background Art

[0002] At present, buttons are widely used in geological exploration, coal mining, oil extraction, etc., which improves work efficiency. There are many types of button materials. In the past, high-speed steel was used, and currently, most are made of cemented carbide, and some use diamond composite buttons. High-speed steel has withdrawn from the stage due to its insufficient wear resistance and short service life, and has been replaced by cemented carbide buttons, which have high hardness and strong wear resistance and are suitable for cutting operations under general geological conditions. However, due to the complexity and inhomogeneity of underground rock formations, traditional cemented carbide buttons are prone to problems such as uneven wear and short service life when facing different geological conditions, resulting in frequent tool replacement, increasing construction costs and reducing construction efficiency.

[0003] The emergence of diamond composite buttons is to cope with the exploration of harder rock formations, which can improve the bit life and work efficiency. However, diamond composite buttons are based on cemented carbide, with a layer of polycrystalline diamond composite layer compounded on it. Most of them are still cemented carbide. Due to the large difference in thermal expansion coefficients between diamond and cemented carbide, the polycrystalline diamond layer is prone to peeling at the boundary between the two materials during the working process. The key reason is that there is an interface with a sudden change in physical properties between the cemented carbide substrate and the polycrystalline diamond layer. Such a sudden change in material composition often leads to obvious local stress concentration, resulting in easy damage at this mutation interface. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a polycrystalline diamond button with a functionally graded structure. The polycrystalline diamond button provided by the present invention has a gradually changing structure with controllable composition, significantly increasing wear resistance and improving service life and work efficiency.

[0005] The second object of the present invention is to provide a preparation method for a polycrystalline diamond button with a functionally graded structure. The preparation method of the present invention is simple and controllable, and suitable for industrial production.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A polycrystalline diamond button with a functionally graded structure of the present invention, the polycrystalline diamond button is divided into a cemented carbide substrate, a bonding layer, and a polycrystalline diamond layer from bottom to top;

[0008] The bonding layer is composed of diamond and cemented carbide, and along the direction from the cemented carbide substrate to the polycrystalline diamond layer, the content of polycrystalline diamond increases in sequence, and the content of cemented carbide decreases in sequence;

[0009] The connecting layer is selected from a multi-layer gradient transition layer or a continuous gradient transition layer.

[0010] For the polycrystalline diamond button bit with a functionally graded structure provided by the present invention, the substrate part is made of cemented carbide, which is used to provide the structural support and strength of the button bit; the upper part is covered with polycrystalline diamond, which is used to increase the cutting performance and wear resistance of the button bit; and the connecting layer has a functional gradient, so that the material properties change with the change of the composition or structure of the material, forming a functionally graded material with performance change characteristics. This can not only significantly relieve the residual thermal stress inside the diamond-cemented carbide composite material, but also change the stress distribution state inside the composite sheet, improve the interfacial bonding strength between the cemented carbide and the polycrystalline diamond, and can also improve the drilling speed and service life of the button bit.

[0011] In a preferred embodiment, both the cemented carbide substrate and the cemented carbide in the connecting layer are WC-Co alloys, and in the WC-Co alloy, the mass fraction of Co is 8%-13%.

[0012] In a preferred embodiment, the top of the polycrystalline diamond layer is spherical.

[0013] In a preferred embodiment, the thickness of the connecting layer is 0.4-7 mm, preferably 6-7 mm, and the thickness of the polycrystalline diamond layer is 4-9 mm, preferably 8-9 mm. Controlling the thickness of the connecting layer within the above range can provide the optimal performance of the polycrystalline diamond button bit ultimately.

[0014] In a preferred embodiment, the multi-layer gradient transition layer is n layers, where n is 4-12 layers, preferably 6-10, and more preferably 8.

[0015] In a preferred embodiment, in the multi-layer gradient transition layer, the volume fraction of polycrystalline diamond in the top layer is 75-95%, preferably 90-95%, and then from the second top layer to the bottom layer, the volume fraction decreases by 5-20% for each layer. The volume fraction of cemented carbide in the top layer is 5-25%, preferably 5-10%, and then from the second top layer to the bottom layer, the volume fraction increases by 5-20% for each layer.

[0016] The inventor found that by adopting the connecting layer with the above gradient composition, it is finally possible to avoid the formation of intermetallic compounds, eliminate the sharp gradient interface, realize the smooth transition of the material structure and elements, and further reduce the thermal stress, so that the performance of the final shield machine cutter is optimal and the best.

[0017] In a further preferred embodiment, the decreasing amplitude gradient increases from the second top layer to the bottom layer, and the increasing amplitude gradient increases from the second top layer to the bottom layer.

[0018] Further preferably, in the multi-layer gradient transition layer, from the bottom layer to the top layer, the volume fractions of polycrystalline diamond are 15%, 25%, 35%, 50%, 60%, 75%, 85%, 90% in sequence, and the volume fractions of cemented carbide are 85%, 75%, 65%, 50%, 40%, 25%, 15%, 10% in sequence. When the connecting layer is 8 layers and the composition gradient is controlled under this preferred condition, firstly, it can effectively avoid intermetallic compounds, improve the connection strength between polycrystalline diamond and cemented carbide, and form a good combination of strength and toughness between the materials on both sides of the interface; secondly, it can transition to eliminate the sharp gradient interface, realize the smooth transition of material structure and elements, and thus reduce the thermal stress; thirdly, when the polycrystalline diamond button is applied to cut rocks with a Mohs hardness of 3-5, the performance is optimal.

[0019] Further preferably, in the multi-layer gradient transition layer, from the bottom layer to the top layer, the volume fractions of polycrystalline diamond are 20%, 40%, 60%, 70%, 80%, 85%, 90%, 95% in sequence, and the volume fractions of cemented carbide are 80%, 60%, 40%, 30%, 20%, 15%, 10%, 5% in sequence. When the connecting layer is 8 layers and the composition gradient is controlled under this preferred condition, firstly, it can effectively avoid intermetallic compounds, improve the connection strength between polycrystalline diamond and cemented carbide, and form a good combination of strength and toughness between the materials on both sides of the interface; secondly, it can transition to eliminate the sharp gradient interface, realize the smooth transition of material structure and elements, and thus reduce the thermal stress; thirdly, when the polycrystalline diamond button is applied to cut rocks with a Mohs hardness of 6-8, the performance is optimal.

[0020] Further preferably, the multi-layer gradient transition layer is a gradually convex arched structure, and the radius of curvature decreases layer by layer from bottom to top. The height of the arch top of any upper layer increases by 0.1-0.3 mm compared with the adjacent lower layer. The inventor found that the arched structure further disperses the stress concentration, optimizes the interlayer bonding strength. At the same time, compared with the flat layer, the arched layer greatly enhances the anti-lateral impact ability, has higher wear resistance and anti-impact ability, especially for the lateral impact force, which can effectively extend the tool life, reduce energy consumption, and improve the operation efficiency.

[0021] In the preferred solution, in the continuous gradient transition layer, the content of cemented carbide in the continuous gradient transition layer decreases from 100% to 0, and the content of diamond increases from 0 to 100%.

[0022] The present invention also provides a method for preparing a polycrystalline diamond button with a functionally gradient structure. Diamond micropowder and WC-Co pre-alloy powder are respectively mixed with deionized water and additives to obtain diamond micropowder slurry and WC-Co pre-alloy powder slurry. Then, the diamond micropowder slurry and WC-Co pre-alloy powder slurry are respectively placed into two feeding ports of a 3D printer. According to the model of the connecting layer, the feeding speeds of the two slurries are controlled by the feeding system, so that the two slurries enter the mixing chamber separately or in different proportions, and then are extruded through a nozzle for printing to obtain a button green body. The button green body is first compacted to obtain a button compact, and the button compact is sintered at ultra-high temperature and high pressure to obtain the polycrystalline diamond button.

[0023] In a preferred embodiment, before preparing the mixed powder, a polycrystalline diamond layer model, a connecting layer model, and a cemented carbide substrate model are established in a computer three-dimensional modeling software, and the model files are stored in STL format. Then, these files are cut by a slicing software to make the thickness of each slice layer processable, and the final sliced file is imported into the 3D printer. Then, the two slurries are respectively placed into the feeding ports of the printer, the equipment is started, and printing is carried out to obtain the product.

[0024] In the actual operation process, when the connecting layer is a multi-layer gradient transition layer, when printing the connecting layer, through the formula of the connecting layer, the two slurries are mixed in a certain proportion into the mixing chamber according to the formulas of different layers to obtain the components in the corresponding layer. When the connecting layer is a continuous gradient transition layer, when printing the connecting layer, the proportion of the two slurries continuously changes in a gradient manner into the mixing chamber.

[0025] Further preferably, when the connecting layer is a multi-layer gradient transition layer, the optimal composition of the connecting layer is determined by a phase diagram calculation software (CALPHAD). In the present invention, through a large number of experiments, the optimal composition formula of the polycrystalline diamond button suitable for rocks with a Mohs hardness of 3-5 is obtained. For other rocks with uncommon hardness, the optimal composition of the connecting layer can be determined by calculation using the phase diagram calculation software based on the above range of the connecting layer and the formula suitable for rocks with a Mohs hardness of 3-5.

[0026] Preferably, the additive comprises guar gum, polyvinyl alcohol, polyacrylamide, sodium hexametaphosphate, phenylboronic acid, ethylenediaminetetraacetic acid, glycerol, and tripropylene glycol. In the diamond micropowder slurry and WC-Co pre-alloy powder slurry, the mass fraction of guar gum is 1-2.5%, the mass fraction of glycerol is 1.5-2%, the mass fraction of sodium hexametaphosphate is 0.1-0.2%, the mass fraction of polyvinyl alcohol (PVA) is 1-2%, the mass fraction of polyacrylamide (PAM) is 0.1-0.3%, the mass fraction of phenylboronic acid (PBA) is 1-3%, the mass fraction of ethylenediaminetetraacetic acid (EDTA) is 0.05-0.1%, and the mass fraction of tripropylene glycol (TPG) is 1-3%.

[0027] In the present invention, for the same additive, on the one hand, it is more conducive to the mixing of the slurry in the bonding layer, and on the other hand, it can ensure the consistency of subsequent sintering and improve the quality of the composite material. However, since the ball teeth provided by the present invention are compared with other conventional teeth, due to the top of the polycrystalline diamond layer being hemispherical, the net forming difficulty is much greater. To ensure the more stable shape of the ball teeth, accelerate the curing speed, improve the fluidity and ensure the manufacturing accuracy, the present invention uses guar gum as the binder, tripropylene glycol as the plasticizer, and polyvinyl alcohol (PVA) as the thickener. Among them, guar gum increases the slurry adhesiveness and adjusts the thixotropy. Polyvinyl alcohol (PVA) can increase the viscosity of the slurry, improve the fluidity and shape retention during printing. And tripropylene glycol (TPG) can reduce the viscosity of the material and enhance its fluidity. Under the synergy of guar gum, tripropylene glycol, and polyvinyl alcohol, the slurry can have appropriate viscosity, better fluidity and shape retention, which helps to better control the thickness and stability of each layer and ensure the precise shape during the printing process. In addition, glycerol is added as a lubricant to further improve the slurry fluidity. The addition of polyacrylamide (PAM) can effectively adjust the rheological properties of the slurry, make it have better fluidity during the printing process, and quickly return to its original state after printing to maintain the shape stability. In addition, sodium hexametaphosphate and ethylenediaminetetraacetic acid (EDTA) are added simultaneously as dispersants, which helps to evenly distribute the solid particles in the slurry, prevent particle aggregation, improve the stability and printing accuracy of the slurry. Finally, phenylboronic acid (PBA) is added as a curing accelerator, which can significantly accelerate the curing speed of the slurry, reduce the drying time of the printing layer, and thus improve the printing efficiency and shape accuracy. Under the synergy of the above components, not only can an additive that can be simultaneously adapted to diamond micropowder and WC-Co pre-alloy powder be identified, but finally the slurry has strong thixotropy, good fluidity, excellent stability, and curing performance, ensuring the printing accuracy.

[0028] Preferably, the solid content of the diamond micropowder slurry and WC-Co pre-alloy powder slurry is 55-60 wt%.

[0029] In a preferred embodiment, the process parameters for printing are as follows: the nozzle diameter of the printing device used is 1 - 1.5 mm, the layer height is 0.2 - 0.35 mm, the extrusion rate is 12 - 20 mm / s, and the extrusion flow rate is 100 - 130%.

[0030] Further preferably, when printing the connection layer and the diamond layer, the layer height of each layer is controlled to increase by 0.025 - 0.05 mm compared to the next lower layer, and the length of each layer is controlled to increase by 0.25 - 1 mm compared to the next lower layer. Each of the above-mentioned layers refers to the layers for which the layer height is controlled during printing. The upper part of its base is arc-shaped and protrudes outward, with a shape similar to a hillock. This unique structural design requires precise control of the thickness and length of each layer during the production of the functionally graded structure transition layer and the polycrystalline diamond (PDC) part.

[0031] In the present invention, since the provided button bits are such that the pressure received at each point is different, the pressure in the middle region is the largest and concentrated, the pressure around is smaller, and the middle part is the area that first receives the pressure. During the preparation process of the present invention, by gradually increasing the thickness and length of each layer from bottom to top, it is ensured that the bonding between layers is firm and the morphology is stable.

[0032] In the present invention, the button bit green body dried to constant weight is placed in a high-temperature and high-pressure resistant metal mold for preliminary compaction and shaping to ensure the accuracy and uniformity of the spherical shape.

[0033] In a preferred embodiment, the pressure for ultra-high temperature and high-pressure sintering is 5 - 7.5 GPa, the temperature for ultra-high temperature and high-pressure sintering is 1400 - 1600 °C, and the time for ultra-high temperature and high-pressure sintering is 600 - 800 s.

[0034] Beneficial effects

[0035] For the polycrystalline diamond button bit with a functionally graded structure provided by the present invention, the base part is made of cemented carbide, which is used to provide the structural support and strength of the tool; the upper part is covered with polycrystalline diamond, which is used to increase the cutting performance and wear resistance of the tool; and the connection layer has a functional gradient, such that the material properties change with the change of the material composition or structure, forming a functionally graded material with performance change characteristics. This can not only improve the interfacial bonding strength between the cemented carbide and the polycrystalline diamond, but also adjust the functionally graded layer according to the hardness of the rock being drilled, thereby improving the drilling speed and service life of the button bit.

[0036] The inventors found that during the production of polycrystalline diamond inserts, there are still problems such as the formation of intermetallic compounds, the mismatch of thermal physical parameters, and the change of dilution rate between materials. For intermetallic compounds, for inserts used for general rocks, the present invention determines specific ratios to avoid intermetallic compounds. For tools used for rocks with other hardness, in terms of the organization regulation of intermetallic compounds, the present invention searches for the optimal path in different composition spaces through thermodynamic model simulation or thermodynamic phase diagram software to construct a gradient transition path, determines the best composition design of the functionally graded material, and thus effectively avoids intermetallic compounds, improves the connection strength between polycrystalline diamond and cemented carbide, and forms a good combination of strength and toughness between the materials on both sides of the interface.

[0037] Regarding thermal residual stress, when the thermal residual stress reaches a certain value, it often causes various mechanical failures. Optimizing the volume fraction of the functionally graded material can effectively reduce the thermal residual stress. For inserts used for general rocks, the present invention also determines specific ratios to eliminate sharp gradient interfaces through transition, realize the smooth transition of material organization and elements, and thus reduce thermal stress. The dilution rate is a key parameter in the manufacturing process of the functionally graded material, which involves the mixing degree and composition ratio of different materials in the transition layer. In the regulation of the dilution rate, on the one hand, it is necessary to control the material components of the transition layer on both sides of the bonding interface. When manufacturing the functionally graded material, one material needs to be gradually "diluted" into another material to achieve a smooth composition transition. On the other hand, for different transition layer materials, the present invention optimizes different process parameters. During the manufacturing process, different process parameters (such as temperature, pressure, cooling rate, etc.) need to be controlled to affect the diffusion and mixing behavior of the materials, thereby affecting the dilution rate and ensuring the reliability and performance of the entire gradient structure. The combination of these two aspects realizes the regulation of the dilution rate.

[0038] During the preparation process, on the one hand, the present invention prepares a slurry with strong thixotropy, good fluidity, excellent stability, and curing performance to ensure the printing accuracy. On the other hand, when printing the connection layer and the diamond layer, by gradually increasing the thickness and length of each layer from top to bottom: it ensures that the bonding between layers is firm and the morphology is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1Schematic diagram of the polycrystalline diamond button bit with a functionally graded structure according to the present invention; in the figure, 1: cemented carbide substrate, 2: bonding layer, 3: polycrystalline diamond layer.

[0041] Figure 2 Schematic diagram of the composition of the polycrystalline diamond button bit with a functionally graded structure according to the present invention.

[0042] Figure 3 Schematic diagram of the polycrystalline diamond button bit with a multi-layer gradient transition layer in the shape of a gradually protruding arched structure according to the present invention. Detailed implementation manners

[0043] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed in the following specification.

[0044] Embodiment 1

[0045] The present embodiment provides the preparation of a polycrystalline diamond button bit for cutting rocks with a Mohs hardness of 3-5 (including limestone, sandstone and some igneous rocks):

[0046] The polycrystalline diamond button bit is composed of three parts: a polycrystalline diamond layer, an eight-layer polycrystalline diamond / cemented carbide composite gradient layer, and a cemented carbide substrate. In the polycrystalline diamond layer, the volume fraction of diamond is 100%. The cemented carbide substrate layer uses WC-13wt%Co (YG13) alloy powder, and its composition ratio is WC 87%, Co 13%. In the eight-layer gradient layer, the volume contents of YG13 are 15%, 25%, 35%, 50%, 60%, 75%, 85%, 90% respectively, and the corresponding volume contents of polycrystalline diamond are 85%, 75%, 65%, 50%, 40%, 25%, 15%, 10% respectively.

[0047] Among them, the height of the polycrystalline diamond layer is 9 mm, the total height of the eight-layer intermediate gradient layer is 7 mm, and the total height of the cemented carbide substrate layer is 12 mm.

[0048] The specific preparation process is as follows:

[0049] (1) Select an appropriate amount of diamond micropowder and YG13 pre-alloy powder;

[0050] (2) Add 2.5% guar gum, 1.5% glycerol, 0.15% sodium hexametaphosphate, 2% polyvinyl alcohol, 0.3% polyacrylamide, 1% phenylboric acid, 3% tripropylene glycol, 0.05% ethylenediaminetetraacetic acid to diamond micropowder, YG13 pre-alloyed powder, and YG13 and diamond mixed powder prepared according to each gradient requirement, and an appropriate amount of deionized water, mix thoroughly, place in a planetary ball mill for high-speed ball milling, mix evenly, and prepare a slurry with a solid content of 55%;

[0051] (3) Use computer 3D modeling software to build a model of a functionally gradient structured polycrystalline diamond composite sheet, including a polycrystalline diamond layer, eight intermediate connection layers, and a cemented carbide layer model, and store the model file in STL format. Use slicing software to slice the model file so that the thickness of each layer can be processed, and import the slice files into the corresponding slurry direct writing 3D printing equipment;

[0052] (4) Diamond micropowder slurry and WC-Co pre-alloyed powder slurry are placed in two feed ports of the 3D printer respectively. According to the model of the connecting layer, the feeding speed of the two slurries is controlled by the feeding system so that the two slurries enter the mixing chamber separately or in different proportions, and then the slurries mixed in proportion are extruded through the nozzle for printing. The working parameters of the 3D printing equipment are set as follows: nozzle diameter 1.5 mm, layer height 0.35 mm, extrusion rate 20 mm / s, flow rate 100%, and the equipment is started to print. When controlling the printing of the connecting layer and the diamond layer, the thickness of each layer is controlled to increase by 0.05-0.1 mm compared with the next layer, and the length of each layer is controlled to increase by 0.1-0.5 mm compared with the next layer.

[0053] (5) The green body dried to constant weight is placed in a high temperature and high pressure resistant metal round cup for compaction and then placed in a six-sided hydraulic press, the pressure is increased to 6.0 GPa, the temperature is increased to 1500°C, the pressure and temperature are maintained for 800 seconds, the heating is stopped, the pressure is reduced, and after the equipment temperature reaches room temperature and the pressure drops to standard atmospheric pressure, it is taken out from the six-sided hydraulic press to obtain a polycrystalline diamond ball tooth.

[0054] Application Examples

[0055] The polycrystalline diamond ball teeth prepared in the above Example 1 are used to cut rock (limestone) with a Mohs hardness of 3-5. During the drilling process, the cutting efficiency is significantly higher than that of traditional carbide teeth. The average drilling speed is 0.45 meters per minute, while the average drilling speed of traditional carbide teeth is 0.15 meters per minute. When the total drilling depth reaches 180 meters, the tool wear rate is only 0.015 mm / m.

[0056] When the total drilling depth of traditional cemented carbide cutters is only 45 meters, the wear rate is 0.07 mm / m, and the cutters show multiple fracture phenomena. This indicates that the service life of polycrystalline diamond button bits is 4 times that of traditional cutters, while significantly reducing the wear rate.

[0057] This is because the gradient design of polycrystalline diamond button bits effectively disperses the stress concentration during the cutting process, reduces the local stress peak value of polycrystalline diamond button bits, and significantly improves the impact resistance. Polycrystalline diamond button bits can better absorb the impact energy, prevent brittle failure, and keep the tool stable under high-stress conditions. The energy consumption of the polycrystalline diamond button bits provided in Example 1 of the present invention is reduced by about 20%, showing higher drilling efficiency and longer service life.

[0058] Generally speaking, polycrystalline diamond button bits are significantly superior to traditional cemented carbide cutters when cutting medium-hard rocks, with higher wear resistance and impact resistance, which can effectively extend the tool life, reduce energy consumption, and improve the operation efficiency.

[0059] Example 2

[0060] This example provides the preparation of a gradient structure tool for cutting rocks with Mohs hardness of 6-8 (including limestone, sandstone, and some igneous rocks):

[0061] Establish a model

[0062] 1. Use computer 3D modeling software to establish a functional gradient structure cutter tooth model. The model should include a diamond layer, eight intermediate gradient layers, and a cemented carbide substrate layer. Among them, the height of the polycrystalline diamond layer is 8 mm, the total height of the eight intermediate gradient layers is 6 mm, and the total height of the cemented carbide substrate layer is 11 mm.

[0063] 2. Use a thermodynamic model simulation or a thermodynamic phase diagram calculation software (CALPHAD) to determine the optimal composition design of the functional gradient material according to the design requirements, and store the model file in STL format. The Mohs hardness of general rocks is between 3-5. When encountering rocks with higher hardness (Mohs hardness between 6-8), the composition gradient content needs to be adjusted according to the actual drilling needs. The best results obtained through simulation and calculation are as follows: in the eight gradient layers, the volume contents of YG13 are 20%, 40%, 60%, 70%, 80%, 85%, 90%, and 95% respectively, and the corresponding volume contents of polycrystalline diamond are 80%, 60%, 40%, 30%, 20%, 15%, 10%, and 5% respectively.

[0064] 3. Use slicing software to slice the model file so that the thickness of each slice is suitable for processing. Import the sliced files into the corresponding slurry direct writing 3D printing equipment respectively.

[0065] Prepare the slurry

[0066] 1. Select an appropriate amount of diamond micropowder and YG13 pre-alloy powder;

[0067] 2. Add diamond micropowder, YG13 pre-alloy powder, and YG13 and diamond mixed powder configured according to each gradient requirement to 2% guar gum, 2.5% glycerol, 0.1% sodium hexametaphosphate, 2% polyvinyl alcohol, 0.1% polyacrylamide, 3% phenylboric acid, 2% tripropylene glycol, and 0.1% ethylenediaminetetraacetic acid respectively. Supplement other slurries and an appropriate amount of deionized water, mix well, place in a planetary ball mill, and perform high-speed ball milling to mix evenly to make a slurry with a solid content of 55%;

[0068] Preparation of button bit green body by 3D printing

[0069] 1. Put the diamond micropowder slurry and WC-Co pre-alloy powder slurry into two feeding ports of a 3D printer respectively. According to the model of the connecting layer, control the feeding speed of the two slurries through the feeding system, so that the two slurries enter the mixing chamber alone or in different proportions, and then extrude the proportionally mixed slurry through the nozzle for printing. Set the working parameters of the 3D printing equipment: nozzle diameter 1.5 mm, layer height 0.35 mm, extrusion rate 20 mm / s, flow rate 100%. When controlling the printing of the connecting layer and the diamond layer, control the thickness of each layer to increase by 0.05 - 0.1 mm compared with the next layer, and the length of each layer to increase by 0.1 - 0.5 Mm compared with the next layer.

[0070] Compaction and sintering

[0071] 1. Put the button bit green body dried to constant weight into a high-temperature and high-pressure metal mold for preliminary compaction and forming to ensure the accuracy and uniformity of the sphere.

[0072] 2. Then put the mold into a six-sided hydraulic press, raise the pressure to 6.0 GPa, raise the temperature to 1500 °C, and maintain the pressure and temperature for 800 seconds.

[0073] 3. Stop heating and gradually reduce the pressure. After the temperature of the equipment drops to room temperature and the pressure returns to standard atmospheric pressure, take out the product from the six-sided hydraulic press.

[0074] Final machining

[0075] 1. The button bits taken out from the six-sided hydraulic press undergo necessary finishing processes such as grinding and polishing to ensure that the surface finish and dimensional accuracy of the button bits meet the design requirements.

[0076] Quality inspection and application

[0077] 2. Conduct quality inspection on the prepared functionally graded material button bits to ensure that all performance indicators of the button bits meet the design requirements.

[0078] When the optimized gradient structure tool drills rocks with a higher hardness (between Mohs hardness 5 and 8), its average drilling speed is 0.4 meters per minute. When the total drilling depth reaches 180 meters, the tool wear rate is only 0.015 mm / m.

[0079] Example 3

[0080] Other conditions are the same as those in Example 1, except that 4 intermediate gradient layers are set. The volume contents of YG13 in each gradient layer are 15%, 35%, 55%, and 75% respectively, and the corresponding volume contents of diamond in each gradient layer are 85%, 65%, 45%, and 25% respectively. When the tool with this structure cuts rocks with a Mohs hardness of 3 - 5, although it also shows certain wear resistance, due to only four gradient layers being set and the gradient transition being relatively less, the overall performance is slightly inferior to that of Example 1. Its impact resistance and stress distribution uniformity are reduced compared to Example 1. The tool life is shortened by about 15%, the overall wear resistance is reduced, and under high-load cutting conditions, the wear rate of the tool is relatively high, resulting in an increased replacement frequency.

[0081] Example 4

[0082] Other conditions are the same as those in Example 1, except that in the eight gradient layers, the volume contents of YG13 are 15%, 25%, 35%, 50%, 60%, 70%, 85%, and 90% respectively, and the corresponding volume contents of polycrystalline diamond are 85%, 75%, 65%, 50%, 40%, 30%, 15%, and 10% respectively. Due to the adjustment of the ratio of YG13 and diamond in the gradient layer of the tool in this example, the transition of the material is more uniform, effectively improving the impact resistance and wear resistance of the tool. However, compared with Example 1, there are more layers with an increased volume content of YG13, making the transition between the cemented carbide matrix and the diamond layer too smooth, resulting in a slight decrease in the stability of the tool during high-speed drilling. Overall, the tool life is shortened by about 5% compared to Example 1, and its performance under high-load cutting conditions is slightly worse, but it can still meet the cutting requirements of medium-hard rocks.

[0083] Example 5

[0084] Other conditions are the same as those in the example, except that the connecting layer is a continuous gradient transition layer, and in the continuous gradient transition layer, the content of cemented carbide decreases from 100% to 0, and the content of diamond increases from 0 to 100%.

[0085] The polycrystalline diamond button bits prepared in Example 5 above are used to cut rocks (limestone) with a Mohs hardness of 3-5. During the drilling process, the cutting efficiency is significantly higher than that of traditional cemented carbide button bits. The average drilling speed is 0.5 meters per minute, while the average drilling speed of traditional cemented carbide button bits is 0.15 meters per minute. When the total drilling depth reaches 180 meters, the tool wear rate is only 0.015 mm / m

[0086] Example 6: Polycrystalline diamond button bits with an arched transition layer structure

[0087] This example provides the preparation of polycrystalline diamond button bits for cutting rocks (including limestone, sandstone, and some igneous rocks) with a Mohs hardness of 3-5. Other conditions are the same as in Example 1, except that the transition layer is designed as a gradually convex arched structure.

[0088] Among them, the height direction of the arched layer is consistent with the axial direction of the button bit. The height of the top of each arch increases by 0.1-0.3 mm compared to the adjacent lower layer, and the radius of curvature of the arch decreases layer by layer from the lower layer to the upper layer. The total thickness of the connection layer and the diamond volume fraction are the same as in Example 1.

[0089] The specific preparation process is as follows:

[0090] (1) Select an appropriate amount of diamond micropowder and YG13 pre-alloy powder;

[0091] (2) Add diamond micropowder, YG13 pre-alloy powder, and YG13 and diamond mixed powder configured according to each gradient requirement to 2.5% guar gum, 1.5% glycerol, 0.15% sodium hexametaphosphate, 2% polyvinyl alcohol, 0.3% polyacrylamide, 1% phenylboric acid, 3% tripropylene glycol, and 0.05% ethylenediaminetetraacetic acid. And an appropriate amount of deionized water, mix well, and place it in a planetary ball mill for high-speed ball milling to make a slurry with a solid content of 55%;

[0092] (3) Use computer three-dimensional modeling software to establish a model of a functionally graded polycrystalline diamond composite sheet with a continuous layer in the shape of an arch, including a polycrystalline diamond layer, eight intermediate connection layer models, and a cemented carbide layer model, and store the model file in STL format. Use slicing software to slice the model file so that the thickness of each layer can be processed, and import the sliced files into the corresponding slurry direct writing 3D printing equipment respectively;

[0093] (4) Put the diamond micropowder slurry and the WC-Co pre-alloy powder slurry into two feeding ports of a 3D printer respectively. According to the model of the connecting layer, control the feeding speeds of the two slurries through the feeding system, so that the two slurries enter the mixing chamber separately or in different proportions, and then extrude the proportionally mixed slurry through the nozzle for printing. Adjust the 3D printing path: the nozzle moves along an arched trajectory, and set the working parameters of the 3D printing equipment: nozzle diameter 1.5 mm, layer height 0.3 mm, extrusion rate reduced to 15 - 18 mm / s, and flow rate increased to 110 - 120% to ensure the dense filling of the arched structure. Start the equipment for printing. When controlling the printing of the connecting layer and the diamond layer, control the thickness of each layer to increase by 0.05 - 0.1 mm compared with the next layer, and the length of each layer to increase by 0.1 - 0.3 mm compared with the next layer.

[0094] (5) After the green body is dried, use a customized arc-shaped mold for pressing to keep the stability of the arched structure. Then put it into a six-sided hydraulic press, raise the pressure to 6.0 GPa, raise the temperature to 1500 °C, maintain the pressure and temperature for 800 seconds, stop heating, reduce the pressure, and after the equipment temperature reaches room temperature and the pressure drops to standard atmospheric pressure, take it out from the six-sided hydraulic press to obtain polycrystalline diamond button bits.

[0095] Application Example

[0096] Cut the arched transition layer polycrystalline diamond button bits prepared in Example 6 above on rocks (limestone) with a Mohs hardness of 3 - 5. During the drilling process, the cutting efficiency is higher than that of the polycrystalline diamond button bits in Example 1, with an increase of about 20%. The average drilling speed is 0.48 meters per minute, the tool wear rate is reduced to 0.012 mm / m, and there is no interface spalling phenomenon.

[0097] The polycrystalline diamond button bits obtained in Example 6 have a greater improvement compared with Example 1 because the arched structure further disperses the stress concentration, optimizes the interlayer bonding strength, and at the same time, the arched layer significantly enhances the anti-lateral impact ability compared with the flat layer. The polycrystalline diamond button bits provided in Example 6 of the present invention show higher drilling efficiency and longer service life.

[0098] Generally speaking, the continuous layer design of the arch is further significantly improved on the basis of the original design, with higher wear resistance and anti-impact ability, especially the lateral impact force, which can effectively extend the tool life, reduce energy consumption, and improve the operation efficiency.

[0099] Comparative Example 1

[0100] Other conditions are the same as those in Example 1, except that in the WC-Co alloy, the mass fraction of Co is 15%. The tool in this comparative example performs worse than that in Example 1 when cutting rocks with a Mohs hardness of 3-5. Since the mass fraction of Co in the cemented carbide matrix is increased to 15%, the toughness of the tool increases to some extent, but the overall hardness and wear resistance decrease. Compared with Example 1, the impact resistance of the tool is slightly improved, but its wear resistance decreases by about 20%, and plastic deformation is likely to occur under high load conditions, weakening the tool.

[0101] Comparative Example 2

[0102] Other conditions are the same as those in Example 1, except that the additive in the slurry does not contain polyacrylamide and other components remain unchanged. The same 3D printing equipment is used for printing, and finally, it is solidified and formed according to the pressing and sintering conditions consistent with those in Example 1 to obtain polycrystalline diamond inserts. However, when actually cutting rocks with a Mohs hardness of 3-5 (such as limestone), the polycrystalline diamond inserts without polyacrylamide show obvious performance disadvantages. First, the drilling speed drops significantly. The average drilling speed of the comparative example is 0.32 meters per minute, which is about 28% less than 0.45 meters per minute in Example 1. When the total drilling depth reaches 120 meters, the wear rate of the tool is 0.05 mm / m, which is significantly higher than 0.015 mm / m in Example 1. During the cutting process, local cracks and chipping occur many times on the tool in the comparative example. Especially when cutting rocks with higher hardness, the fracture frequency of the tool is much higher than that in Example 1. In addition, due to the lack of polyacrylamide, the rheology of the slurry is poor, resulting in poor interlayer bonding quality during the 3D printing process. The local stress distribution of the polycrystalline diamond inserts is uneven during the cutting process, thereby generating stress concentration, and the impact resistance also decreases significantly. This not only affects the overall stability of the tool but also increases its energy consumption by about 15%, further reducing the cutting efficiency. The comparative example without the rheology modifier polyacrylamide is inferior to Example 1 in terms of cutting performance, wear resistance, and impact resistance. As a key rheology regulator, the absence of polyacrylamide leads to a decline in printing quality, ultimately affecting the service life and operation efficiency of the finished tool.

[0103] Comparative Example 3

[0104] Other conditions are the same as those in Example 1, except that the diameter of the 3D printing nozzle is changed from 1.5 mm to 4.5 mm, and other process parameters such as layer height, extrusion rate, flow rate, etc. remain unchanged. In this comparative example, during the actual preparation process, the surface quality and accuracy of the printed green body are significantly lower than those in Example 1. Due to the increase in nozzle diameter, the accuracy of the printed layer decreases significantly, resulting in a rough and uneven surface of the printed green body, and the connection between layers is not as tight as that in Example 1. This rough surface not only affects the densification of subsequent sintering and forming, but also increases the stress concentration area of the green body in a high-temperature and high-pressure environment, greatly reducing the mechanical properties of the finished polycrystalline diamond button bit. Due to the uneven stress distribution caused by the rough surface of the printed green body, local chipping and crack propagation occur during the cutting process of the tool, and the impact resistance is also poor. The increased nozzle diameter also affects the uniformity of the material between printed layers, the deposition accuracy of the material decreases, resulting in a less smooth transition of the gradient layer structure, and the interlayer bonding is not as dense as that in Example 1. Due to the uneven material distribution, the problem of local stress concentration is more serious, and the tool is prone to early failure during the cutting process, further shortening the service life.

[0105] The above embodiments are only for illustrating the present invention, rather than limiting the present invention. Those skilled in the relevant technical fields can also make various transformations or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the scope of the present invention, which should be defined by each claim.

Claims

1. A polycrystalline diamond ball tooth with a functional gradient structure, characterized in that: The polycrystalline diamond ball teeth are divided into a cemented carbide base, a connecting layer, and a polycrystalline diamond layer from bottom to top; The connecting layer is composed of diamond and cemented carbide, wherein the content of polycrystalline diamond increases successively and the content of cemented carbide decreases successively along the direction from the cemented carbide substrate to the polycrystalline diamond layer; The connecting layer is selected from a multi-layer gradient transition layer or a continuous gradient transition layer.

2. The polycrystalline diamond ball tooth with a functional gradient structure according to claim 1, characterized in that: The cemented carbide in the cemented carbide substrate and the connecting layer are both WC-Co alloys, and the mass fraction of Co in the WC-Co alloy is 8%-13%; The top of the polycrystalline diamond layer is spherical; The thickness of the transition layer is 0.4-7 mm, and the thickness of the polycrystalline diamond layer is 4-9 mm.

3. The polycrystalline diamond ball tooth with a functional gradient structure according to claim 1 or 2, characterized in that: The multi-layer gradient transition layer is n layers, and n is 4-12 layers; In the multi-layer gradient transition layer, the volume fraction of polycrystalline diamond in the top layer is 75-95%, and then from the second top layer to the bottom layer, the volume fraction decreases by 5-20% per layer, and the volume fraction of cemented carbide in the top layer is 5-25%, and then from the second top layer to the bottom layer, the volume fraction increases by 5-20% per layer; In the continuous gradient transition layer, the content of cemented carbide in the continuous gradient transition layer decreases from 100% to 0, and the content of diamond increases from 0 to 100%.

4. The polycrystalline diamond ball tooth with a functional gradient structure according to claim 3, characterized in that: The multi-layer gradient transition layer is a gradually convex arched structure, the radius of curvature decreases layer by layer from bottom to top, and the height of the arch of any upper layer increases by 0.1-0.3mm compared with the adjacent lower layer.

5. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to any one of claims 1 to 4, characterized in that: Diamond micropowder and WC-Co pre-alloyed powder are mixed with deionized water and additives to obtain diamond micropowder slurry and WC-Co pre-alloyed powder slurry respectively; then the diamond micropowder slurry and WC-Co pre-alloyed powder slurry are put into two feed ports of the 3D printer respectively, and the feeding speed of the two slurries is controlled by the feeding system according to the model of the connecting layer, so that the two slurries enter the mixing chamber separately or in different proportions, and then extruded and printed through the nozzle to obtain a ball tooth green body, the ball tooth green body is first pressed to obtain a ball tooth compact, and the knife tooth compact is sintered at ultra-high temperature and high pressure to obtain a polycrystalline diamond ball tooth.

6. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to claim 5, characterized in that: Before preparing the diamond micropowder slurry and the WC-Co pre-alloyed powder slurry, a polycrystalline diamond layer model, a connecting layer model and a cemented carbide substrate model are first established in a computer three-dimensional modeling software, and the model files are stored in the STL format. These files are then cut using slicing software to make the thickness of each layer machinable, and the final slicing file is imported into a 3D printer; then the two slurries are respectively placed in the feed port of the printer, the device is started, and printing is completed.

7. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to claim 5, characterized in that: The additive comprises guar gum, polyvinyl alcohol, polyacrylamide, sodium hexametaphosphate, phenylboric acid, ethylenediaminetetraacetic acid, glycerol and tripropylene glycol. In the diamond micropowder slurry and the WC-Co pre-alloyed powder slurry, the mass fraction of guar gum is 1-2.5%, the mass fraction of glycerol is 1.5-2%, the mass fraction of sodium hexametaphosphate is 0.1-0.2%, the mass fraction of polyvinyl alcohol is 1-2%, the mass fraction of polyacrylamide is 0.1-0.3%, the mass fraction of phenylboric acid is 1-3%, the mass fraction of ethylenediaminetetraacetic acid is 0.05-0.1%, and the mass fraction of tripropylene glycol is 1-3%.

8. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to claim 5, characterized in that: The solid contents of the diamond micropowder slurry and the WC-Co pre-alloyed powder slurry are both 55-60wt%.

9. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to claim 5, characterized in that: The printing process parameters are as follows: the nozzle diameter of the printing equipment used is 1-1.5 mm, the layer height is 0.2-0.35 mm, the extrusion rate is 12-20 mm / s, and the extrusion flow rate is 100-130%; when printing the connecting layer and the diamond layer, the layer height of each layer is controlled to increase by 0.025-0.05 mm compared with the next layer, and the length of each layer is controlled to increase by 0.25-1 mm compared with the next layer.

10. The method for preparing a polycrystalline diamond ball tooth with a functional gradient structure according to claim 5, characterized in that: The pressure of the ultra-high temperature and high pressure sintering is 5-7.5 GPa, the temperature of the ultra-high temperature and high pressure sintering is 1400-1600° C., and the time of the ultra-high temperature and high pressure sintering is 600-800 seconds.

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