A method for evaluating the tableting index of cemented carbide powder based on the discrete element method.

Abstract

This invention provides a method for evaluating the pressing index of cemented carbide powder based on the discrete element method (DEM), relating to the fields of powder metallurgy forming and numerical simulation technology. The invention constructs a discrete element bonded particle model by obtaining the basic physical property parameters characterizing the powder particles of the cemented carbide powder to be evaluated. Bonding bonds are established between contacting particle pairs in the DEM model, and the contact parameters of these bonds are obtained after calibration and verification. Based on the calibrated and verified bond contact parameters, a discrete element pressing model is constructed on the DEM bonded particle model to simulate the powder filling and pressing process, resulting in a compact model. The tensile strength and impact hardness of the compact model are then subjected to discrete element numerical simulations to calculate the pressing index evaluation index. Based on the pressing index evaluation index, the pressing performance of the cemented carbide powder to be evaluated and the presence of crack risk during the pressing process are assessed.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy forming and numerical simulation technology, and more specifically, to a method for evaluating the pressing index of cemented carbide powder based on the discrete element method. Background Technology

[0002] Currently, cemented carbide is typically prepared using powder metallurgy, and its forming quality largely depends on the densification behavior and structural integrity of the powder during the pressing process. Due to the high hardness, brittleness, and complex interparticle bonding of cemented carbide powder, problems such as cracking, delamination, and springback deformation easily occur during pressing, affecting the dimensional stability of the compact and subsequent sintering performance. Therefore, accurately evaluating the pressing performance of cemented carbide powder is one of the key technical issues in cemented carbide preparation. Research on the forming performance of cemented carbide powder mainly relies on macroscopic mechanical indicators such as pressing density, forming strength, and flexural strength. While these indicators can reflect the densification effect of the powder under specific pressure, they are insufficient to comprehensively describe the microscopic characteristics such as interparticle bonding, plastic deformation, and fracture behavior during pressing. Furthermore, differences in particle size distribution, surface properties, and flowability between different batches of powder lead to significant data dispersion, making it difficult to achieve quantitative and standardized comparisons using traditional testing methods.

[0003] The tableting index theory was initially applied in the pharmaceutical field to evaluate the compressibility and forming stability of particulate materials during tableting. It typically includes indices such as the Bonding Index (BI), Brittle Fracture Index (BFI), and Strain Index (SI). This theory establishes three dimensionless parameters using measurements of impact hardness (P) and tensile strength. Particle bonding, elastic aftereffects, and brittle fracture tendency are quantified into BI, SI, and BFI, thus enabling a systematic evaluation of powder tableting performance. However, existing tableting index evaluation methods mainly rely on actual tableting experiments, and their application is primarily limited to organic particles or low-strength powders. A systematic evaluation method applicable to high-hardness, brittle powder systems such as cemented carbide has not yet been developed. The Discrete Element Method (DEM), as an important numerical method for studying the mechanical behavior of particulate materials, has been widely used in the simulation analysis of powder filling, compaction, and failure processes. By introducing the Bonded-Particle Model (BPM), the stress, bonding, and fracture behavior between particles can be described at a mesoscale. However, existing discrete element method (DEM) studies mostly focus on density distribution, stress evolution, or local damage characteristics during the pressing process. They lack a systematic approach that combines simulation results with forming performance indicators that can be used for engineering evaluation, making it difficult to achieve quantitative comparison and prediction of powder forming performance.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] This invention provides a method for evaluating the index of cemented carbide powder compression based on the discrete element method, in order to improve at least one of the above-mentioned technical problems.

[0006] This invention provides a method for evaluating the tableting index of cemented carbide powder based on the discrete element method, comprising the following steps:

[0007] S1: Obtain the basic physical property parameters on the cemented carbide powder to be evaluated, which can characterize the powder particle features, and construct a discrete element binder particle model based on the basic physical property parameters; The basic physical properties include particle size distribution, particle shape, and particle morphology; the particle size distribution is determined by at least one of laser particle size analyzer, sieving, or image analysis; the particle shape is determined by particle size analyzer; and the particle morphology is obtained by scanning electron microscopy or optical microscopy. The construction of the discrete element bonding particle model includes the following steps: S11: Based on the particle size distribution and particle density in the basic physical property parameters, a spherical particle system is generated in the discrete element software, and the geometry of the cemented carbide powder to be evaluated is equivalently approximated as spherical particles. S12: Set the coarsening coefficient K, and use the coarsening strategy to enlarge the size of the spherical particles by a factor of K, while maintaining the distribution characteristics proportional to the experimental particle size distribution, to obtain the discrete element bonded particle model. Preferably, the coarsening coefficient K=5.

[0008] S2: In the discrete element bonded particle model, bonding bonds are established between the particle pairs that are in contact with each other. The bonding bond contact parameters are obtained after calibration and verification. The calibration and verification of the bonding bond contact parameters are performed using the mechanical properties measured by actual uniaxial compression tests and three-point bending tests as target values, and specifically include the following steps: S21: Determine the initial range of values ​​for the bonding bond contact parameters through single-factor experiments; S22: Within the initial value range, using the bonding bond contact parameter as the variable to be calibrated, a virtual test scheme is constructed through the response surface methodology, and multiple sets of discrete element virtual uniaxial compression tests are executed to obtain the corresponding macroscopic mechanical response. S23: Establish the mathematical mapping relationship between the bonding bond contact parameters and the macroscopic mechanical response; S24: Using the mechanical properties measured by the actual uniaxial compression test as the target value, the bonding bond contact parameters are inverted and calibrated through the mathematical mapping relationship to obtain the calibrated bonding bond contact parameters; S25: Compare the results of the discrete element virtual uniaxial compression test with the results of the actual uniaxial compression test. When the error between the two is less than the preset allowable range, the effectiveness of the calibrated bond contact parameters is preliminarily verified; otherwise, adjust the parameters and repeat steps S21 to S24. S26: Construct a three-point bending discrete element virtual test model based on the calibrated bond contact parameters, and compare the three-point bending virtual test results with the corresponding actual three-point bending test results for verification. When the three-point bending virtual test results are consistent with the actual three-point bending test results or the error is within the allowable range, the calibrated bond contact parameters are confirmed to be valid; otherwise, repeat steps S21 to S25. Preferably, the bonding bond contact parameters include at least normal stiffness per unit area, tangential stiffness per unit area, normal critical force, and tangential critical force.

[0009] S3: Based on the calibrated and verified bonding bond contact parameters, a discrete element compression molding model is constructed on the basis of the discrete element bonding particle model to simulate the powder filling and compression molding process, and a compact model is obtained. The specific steps for obtaining the compact model include: S31: Construct a mold geometry model for compact preparation, wherein the mold geometry model is a cuboid structure with an internal cavity for accommodating powder particles; S32: The discrete element pressing model is filled into the cavity of the mold geometry model, and the pressing simulation is performed by loading the top pressure head to obtain the pressing model; Preferably, the overall geometric model of the mold is a cuboid structure, including a blank-free pressing model and a pressing model with holes, wherein the pressing model with holes has a through hole at the center of the pressing.

[0010] S4: Perform discrete element numerical simulation of tensile strength and impact hardness on the compact model, calculate the compaction index evaluation index, which includes at least one of bonding index, strain index and brittle fracture index, and evaluate the pressing performance of the cemented carbide powder to be evaluated and whether there is a risk of cracking in the cemented carbide powder to be evaluated during the pressing process based on the compaction index evaluation index.

[0011] Furthermore, the tableting index evaluation indicators include the tableting index BI, the strain index SI, and the brittle fracture index BFI; The process of obtaining the tablet compression index evaluation index includes: S41: Perform a Brazilian splitting test on the non-porous compact model and record the peak load at which the non-porous compact model is destroyed. Calculate the tensile strength of the non-porous compact model. : ; In the formula, The length of the non-porous compact model, The thickness of the non-porous blank model; S42: Perform a discrete element virtual impact hardness test on the non-porous compact model, establish a spherical impactor, and allow the spherical impactor to fall freely under gravity and impact the surface of the non-porous compact model. Record the rebound height of the spherical impactor. Radius of the dent after impact a Calculate impact hardness : ; In the formula, The mass of the spherical impactor is... The initial height of the spherical impactor. The radius of the spherical impactor; It is the gravitational constant. Pi; S43: Perform a Brazilian splitting discrete element virtual test on the perforated compact model and record the peak load at failure of the perforated compact model. Calculate the tensile strength of the perforated compact model. : ; In the formula, The length of the perforated blank mold, The thickness of the perforated blank model; S44: Based on the tensile strength of the non-porous compact model and the tensile strength of the perforated blank model The binding index BI, strain index SI, and brittle fracture index BFI were calculated respectively. The formula for calculating the composite index BI is as follows: ; The formula for calculating the strain index SI is as follows: ; The formula for calculating the brittle fracture index (BFI) is as follows: .

[0012] When the brittle fracture index BFI > 0.8, the cemented carbide powder to be evaluated is determined to have a tendency to brittle fracture during pressing or subsequent processing, and there is a risk of crack formation. When the brittle fracture index BFI < 0.2, it is determined that the overall crack resistance of the cemented carbide powder to be evaluated is strong, and the possibility of cracks occurring during pressing or subsequent processing is small. When the brittle fracture index BFI satisfies 0.2 ≤ BFI ≤ 0.8, a comprehensive judgment is made in conjunction with the binding index BI. When the bonding index BI < 0.005, the cemented carbide powder to be evaluated has insufficient energy absorption capacity under impact load, and the cemented carbide powder to be evaluated still has the risk of cracking; when the bonding index BI ≥ ​​0.005, it is determined that the cemented carbide powder to be evaluated has good impact deformation resistance, and the possibility of cracking is significantly reduced. When the brittle fracture index BFI or the bonding index BI are in the same judgment range, the smaller the strain index SI, the smaller the elastic aftereffect of the cemented carbide powder to be evaluated during the pressing and subsequent processing, and the less likely the compact is to crack due to elastic recovery during the unloading process.

[0013] By adopting the above technical solution, the present invention can achieve the following technical effects: By combining the discrete element method with the compression index theory, three evaluation indices—bonding index (BI), strain index (SI), and brittle fracture index (BFI)—were established to address the high hardness and brittleness of cemented carbide powder. Through quantitative analysis of these three indices, the bonding strength, strain uniformity, and crack resistance of cemented carbide powder can be systematically evaluated. This overcomes the technical shortcomings of traditional methods that rely solely on macroscopic mechanical indicators such as compression density and forming strength, which cannot comprehensively describe the powder compression forming performance. It accurately assesses the risk of cracking in the compact before powder compression, providing a scientific basis for optimizing compression process parameters. Attached Figure Description

[0014] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some specific embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating a method for evaluating the index of cemented carbide powder tablets based on the discrete element method.

[0016] Figure 2 This is a flowchart illustrating the calibration and verification process for bonding bond parameters.

[0017] Figure 3 These are the particle size distribution and morphology diagrams of the four powders in Example 2: (a) A3; (b) A4; (c) B2; (d) B3.

[0018] Figure 4 The comparison between the DEM virtual simulation results and the actual experimental results of A3 powder under uniaxial compression and three-point bending loading conditions in Example 2 is as follows: (a) under uniaxial compression loading conditions; (b) under three-point bending loading conditions.

[0019] Figure 5 This is a schematic diagram of the compact model.

[0020] Figure 6 These are simulation cloud diagrams of the tensile strength of four non-porous compact models in Example 2 under DEM numerical simulation: (a) A3; (b) A4; (c) B2; (d) B3.

[0021] Figure 7 Here are schematic diagrams of the impact hardness discrete element numerical simulation process and dent calculation model in Example 2: (a) Impact hardness discrete element numerical simulation process; (b) Schematic diagram of dent calculation model.

[0022] Figure 8The maximum springback height h of the spherical impactor in Example 2 during the springback stage of the four non-porous compact models is... x Schematic diagram.

[0023] Figure 9 These are typical destruction morphology evolution cloud maps of the four perforated compact models in Example 2 under DEM numerical simulation: (a) A3; (b) A4; (c) B2; (d) B3. Detailed Implementation

[0024] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0025] Example 1 Please see Figure 1 The first embodiment of the present invention provides a method for evaluating the tableting index of cemented carbide powder based on the discrete element method, comprising the following steps: S1: Obtain the basic physical property parameters on the cemented carbide powder to be evaluated, which can characterize the powder particle features, and construct a discrete element binder particle model based on the basic physical property parameters; The basic physical properties include particle size distribution, particle shape, and particle morphology; the particle size distribution is determined by at least one of laser particle size analyzer, sieving, or image analysis; the particle shape is determined by particle size analyzer; and the particle morphology is obtained by scanning electron microscopy or optical microscopy. The construction of the discrete element bonding particle model includes the following steps: S11: Based on the particle size distribution and particle density in the basic physical property parameters, a spherical particle system is generated in the discrete element software, and the geometry of the cemented carbide powder to be evaluated is equivalently approximated as spherical particles. S12: Set the coarsening coefficient K, and use the coarsening strategy to enlarge the size of the spherical particles by a factor of K, while maintaining the distribution characteristics proportional to the experimental particle size distribution, to obtain the discrete element bonded particle model. Preferably, the coarsening coefficient K=5, but it should be understood that the coarsening coefficient K can also be set according to actual needs, such as 3, 7, etc., and these schemes are all within the protection scope of the present invention. S2: In the discrete element bonded particle model, bonding bonds are established between the particle pairs that are in contact with each other. The bonding bond contact parameters are obtained after calibration and verification. The calibration and verification of the bonding bond contact parameters are performed using the mechanical properties measured by actual uniaxial compression tests and three-point bending tests as target values, and specifically include the following steps: S21: Determine the initial range of values ​​for the bonding bond contact parameters through single-factor experiments; S22: Within the initial value range, using the bonding bond contact parameter as the variable to be calibrated, a virtual test scheme is constructed through the response surface methodology, and multiple sets of discrete element virtual uniaxial compression tests are executed to obtain the corresponding macroscopic mechanical response. S23: Establish the mathematical mapping relationship between the bonding bond contact parameters and the macroscopic mechanical response; S24: Using the mechanical properties measured by the actual uniaxial compression test as the target value, the bonding bond contact parameters are inverted and calibrated through the mathematical mapping relationship to obtain the calibrated bonding bond contact parameters; S25: Compare the results of the discrete element virtual uniaxial compression test with the results of the actual uniaxial compression test. When the error between the two is less than the preset allowable range, the effectiveness of the calibrated bond contact parameters is preliminarily verified; otherwise, adjust the parameters and repeat steps S21 to S24. S26: Construct a three-point bending discrete element virtual test model based on the calibrated bond contact parameters, and compare the three-point bending virtual test results with the corresponding actual three-point bending test results for verification. When the three-point bending virtual test results are consistent with the actual three-point bending test results or the error is within the allowable range, the calibrated bond contact parameters are confirmed to be valid; otherwise, repeat steps S21 to S25. Preferably, the bonding bond contact parameters include at least normal stiffness per unit area, tangential stiffness per unit area, normal critical force, and tangential critical force.

[0026] S3: Based on the calibrated and verified bonding bond contact parameters, a discrete element compression molding model is constructed on the basis of the discrete element bonding particle model to simulate the powder filling and compression molding process, and a compact model is obtained. The specific steps for obtaining the compact model include: S31: Construct a mold geometry model for compact preparation, wherein the mold geometry model is a cuboid structure with an internal cavity for accommodating powder particles; S32: The discrete element pressing model is filled into the cavity of the mold geometry model, and the pressing simulation is performed by loading the top pressure head to obtain the pressing model; Preferably, the overall geometric model of the mold is a cuboid structure, including a blank-free compact model and a compact model with holes, wherein the compact model with holes has a through hole at the center of the compact; The perforated compact model has an additional cylindrical spacer structure inside the cavity. The diameter and height of the spacer structure are smaller than the perforated compact model, and it extends through the compact model along its height. During the pressing process, the spacer structure provides localized spatial constraint for the powder particles, creating a through-hole with a diameter of approximately 1 mm at the center of the compact model after it is formed. By adding or removing the spacer structure, a comparative fabrication of a non-perforated compact model and a perforated compact model can be achieved.

[0027] S4: Perform discrete element numerical simulation of tensile strength and impact hardness on the compact model, calculate the compaction index evaluation index, which includes at least one of bonding index, strain index and brittle fracture index, and evaluate the pressing performance of the cemented carbide powder to be evaluated and whether there is a risk of cracking in the cemented carbide powder to be evaluated during the pressing process based on the compaction index evaluation index.

[0028] Furthermore, the tableting index evaluation indicators include the tableting index BI, the strain index SI, and the brittle fracture index BFI; The process of obtaining the tablet compression index evaluation index includes: S41: Perform a Brazilian splitting test on the non-porous compact model and record the peak load at which the non-porous compact model is destroyed. Calculate the tensile strength of the non-porous compact model. : ; In the formula, The length of the non-porous compact model, The thickness of the non-porous blank model; As an optional implementation, the Brazilian splitting test can be performed as follows: In discrete element simulation, a non-porous compact model is placed between two parallel rigid plates. A pressure head drives the upper plate at a constant speed, applying radial compression to the model until failure, while simultaneously recording the peak load. During loading, the rigid plates move along a direction perpendicular to the length of the compact and remain in contact with the specimen surface at all times. The macroscopic failure criterion for the specimen is defined as: large-scale breakage of the interparticle bonds, causing the non-porous compact model to split into two parts along the loading axis.

[0029] S42: Perform a discrete element virtual impact hardness test on the non-porous compact model, establish a spherical impactor, and allow the spherical impactor to fall freely under gravity and impact the surface of the non-porous compact model. Record the rebound height of the spherical impactor. Radius of the dent after impact a Calculate impact hardness : ; In the formula, The mass of the spherical impactor is... The initial height of the spherical impactor. The radius of the spherical impactor; It is the gravitational constant. Pi; S43: Perform a Brazilian splitting discrete element virtual test on the perforated compact model and record the peak load at failure of the perforated compact model. Calculate the tensile strength of the perforated compact model. : ; In the formula, The length of the perforated blank mold, The thickness of the perforated blank model; The Brazilian split discrete element virtual experiment reference S41.

[0030] S44: Based on the tensile strength of the non-porous compact model and the tensile strength of the perforated blank model The binding index BI, strain index SI, and brittle fracture index BFI were calculated respectively. The formula for calculating the composite index BI is as follows: ; The formula for calculating the strain index SI is as follows: ; The formula for calculating the brittle fracture index (BFI) is as follows: .

[0031] When the brittle fracture index BFI > 0.8, the cemented carbide powder to be evaluated is determined to have a tendency to brittle fracture during pressing or subsequent processing, and there is a risk of crack formation. When the brittle fracture index BFI < 0.2, it is determined that the overall crack resistance of the cemented carbide powder to be evaluated is strong, and the possibility of cracks occurring during pressing or subsequent processing is small. When the brittle fracture index BFI satisfies 0.2 ≤ BFI ≤ 0.8, a comprehensive judgment is made in conjunction with the binding index BI. When the bonding index BI < 0.005, the cemented carbide powder to be evaluated has insufficient energy absorption capacity under impact load, and the cemented carbide powder to be evaluated still has the risk of cracking; when the bonding index BI ≥ ​​0.005, it is determined that the cemented carbide powder to be evaluated has good impact deformation resistance, and the possibility of cracking is significantly reduced. When the brittle fracture index BFI or the bonding index BI are in the same judgment range, the smaller the strain index SI, the smaller the elastic aftereffect of the cemented carbide powder to be evaluated during the pressing and subsequent processing, and the less likely the compact is to crack due to elastic recovery during the unloading process.

[0032] Compared with the prior art, the present invention has the following beneficial effects: By introducing a pressing index evaluation system based on the discrete element method, the forming performance that is difficult to be directly characterized during the pressing and forming process of cemented carbide powder is transformed into a quantifiable evaluation index, thereby realizing the quantitative analysis of the crack sensitivity and forming stability of the pressed blank. Discrete element simulation is used to predict the pressing process of cemented carbide powder under evaluation, which significantly reduces the reliance on a large number of physical pressing experiments, shortens the evaluation cycle, reduces material consumption and experimental costs, and improves R&D efficiency. By combining the tableting index evaluation index with discrete element simulation, high-precision prediction of the pressing performance of cemented carbide powder to be evaluated was achieved. It can rapidly evaluate cemented carbide powders of different batches, particle size distributions, and bonding properties, providing a scientific basis for powder screening, formulation design, and process parameter optimization.

[0033] Example 2 Referring to Example 1, Example 2 will use a specific cemented carbide powder as an example to describe the present invention in detail for the purpose of facilitating understanding of the present invention.

[0034] In this embodiment, the raw materials used are four high-purity RTP (Ready-to-Press) powders from different batches containing different forming agents, named A3, A4, B2, and B3, respectively. The main chemical component of the powder is tungsten carbide (WC), with a purity of not less than 99.5% and an impurity content of less than 0.2%.

[0035] S1: Obtain the basic physical properties of the four high-purity RTP powders that characterize the powder particles. Use a particle shape and size analyzer to test the particle shape and size of the four high-purity powders. Use a Microtrac Retsch CAMSIZER X2 particle shape and size analyzer to obtain the particle size distribution and shape parameters of the four high-purity RTP powders. (See reference...) Figure 3In the figure, (a) is A3, (b) is A4, (c) is B2, and (d) is B3. The particle morphology of the four high-purity RTP powders was further tested and characterized. The morphological characteristics and surface structure information of the four high-purity RTP powders were obtained by microscopic imaging.

[0036] A spherical particle system was generated in discrete element software, and the geometry of the four high-purity RTP powders was approximated as spherical particles. By setting the coarsening coefficient K=5, the size of the spherical particles is magnified by 5 times using a coarsening strategy, while maintaining the distribution characteristics proportional to the experimental particle size distribution, thus obtaining a discrete element bonded particle model.

[0037] S2: Establish adhesive bonds between the particle pairs that are in contact with each other in the discrete element bonded particle model; S21: Determine the initial range of values ​​for the bonding bond contact parameters through single-factor experiments; The bonding bond contact parameters include normal stiffness per unit area (NSPUA), tangential stiffness per unit area (SSPUA), critical normal stress (CNS), and critical tangential stress (CSS).

[0038] S22: Within the initial value range, using the bonding bond contact parameter as the variable to be calibrated, a discrete element virtual test scheme is constructed using the Box-Behnken experimental design method, and multiple sets of discrete element virtual tests are executed to obtain the corresponding macroscopic mechanical response; S23: Establish the mathematical mapping relationship between the bonding bond contact parameters and the macroscopic mechanical response; S24: Using the mechanical properties measured by the actual uniaxial compression test as the target value, the bonding bond contact parameters are inverted and calibrated through the mathematical mapping relationship to obtain the calibrated bonding bond contact parameters; S25: Compare the results of the discrete element virtual uniaxial compression test with the results of the actual uniaxial compression test; S26: Construct a three-point bending discrete element virtual test model based on the calibrated bond contact parameters, and compare and verify the results of the three-point bending virtual test with the corresponding actual three-point bending test results.

[0039] See Figure 4 (a) shows the comparison between the virtual simulation results of DEM and the actual experimental results of A3 under uniaxial compression loading conditions; (b) shows the comparison between the virtual simulation results of DEM and the actual experimental results of A3 under three-point bending loading conditions. The virtual simulation results of DEM and the actual experimental results show good consistency, and their relative errors are within acceptable range, indicating that the calibrated bond contact parameters have high accuracy and reliability. The calibration and verification process for the bonding parameters of the remaining powders A4, B2, and B3 is the same as that for A3.

[0040] S3: Based on the calibrated and verified bonding bond contact parameters, construct a discrete element compression molding model on the basis of the discrete element bonded particle model.

[0041] See Figure 5 , Figure 5 (a) and Figure 5 (b) shows the mold geometry structure for preparing non-porous and porous compacts, respectively. Both mold geometry structures are cuboid in shape and have the same external dimensions, with a length, width and height of 38 mm, 38 mm and 15 mm, respectively. The mold has a cavity inside to accommodate powder particles, so as to fill and bond the powder particles during the pressing process, thereby forming a compact structure.

[0042] The mold geometry of the perforated compact model includes an additional cylindrical spacer structure inside the cavity. This spacer structure has a diameter of 1 mm and a height of 15 mm, extending through the compact model along its height. During the pressing process, this spacer structure provides localized spatial constraint for the powder particles, resulting in a through-hole with a diameter of approximately 1 mm at the center of the compact model after it has been formed.

[0043] The discrete element pressing model is filled into the cavity of the mold geometry model, and pressing simulation is performed by loading with a top pressure head to obtain a blank model without holes and a blank model with holes, respectively.

[0044] S4: Perform a Brazilian splitting test on the non-porous compact model, see [reference]. Figure 6 In the figure, (a) is A3, (b) is A4, (c) is B2, and (d) is B3. The main crack of the non-porous compact model extends along the central axis of the compact and forms typical radial secondary cracks at the edge. The peak load when the non-porous compact model is destroyed is recorded. Calculate the tensile strength of the non-porous compact model. : ; In the formula, The length of the non-porous compact model, The thickness of the non-porous blank model; The tensile strength of the non-porous compact model calculated according to the above formula is as follows: Table 1. Peak load and tensile strength of four types of high-purity RTP powder non-porous compacts at the time of failure.

[0045] S42: See also Figure 7 A discrete element method (DEM) virtual impact hardness test was performed on the non-porous compact model. A spherical impactor was established, and the spherical impactor was allowed to fall freely under gravity and impact the surface of the non-porous compact model. This process included a falling phase, an impact phase, and a rebound phase, completely reproducing the entire process of the spherical impactor falling freely under gravity, making instantaneous contact with the compact and undergoing plastic deformation, and then rebounding. Figure 7 (a) in the figure represents the discrete element numerical simulation process for impact hardness. Figure 7 (b) in the diagram is a schematic diagram of the dent calculation model. The distance between the initial point of the spherical impactor's fall and the bottom of the indentation. The height of the spherical impactor within the non-porous compact mold. This refers to the initial height of the spherical impactor. (See also...) Figure 8 Record the rebound height of the spherical impactor. Radius of the dent after impact a Calculate impact hardness : ; In the formula, The mass of the spherical impactor is... The radius of the spherical impactor; It is the gravitational constant. Pi; The impact hardness of the non-porous compact model calculated according to the above formula is as follows: Table 2 Impact Hardness of Non-porous Compacts of Four Types of High-Purity RTP Powders

[0046] S43: Perform a Brazilian splitting discrete element virtual experiment on the perforated compact model. (See below) Figure 9 Figure (a) represents A3, (b) represents A4, (c) represents B2, and (d) represents B3, illustrating the typical failure morphology evolution of the porous compact models of the four high-purity RTP powders under DEM numerical simulation. Microcracks first initiate in the central pore region during the initial loading stage (approximately 0.05 s), then rapidly propagate radially, quickly penetrating to both sides to form macroscopic fracture zones. The simulation results further reveal that the crack propagation process undergoes three stages: "microcrack initiation—local connection—rapid propagation," ultimately forming a typical brittle fracture zone penetrating along the loading axis. The peak load at failure of the porous compact model is recorded. Calculate the tensile strength of the perforated compact model. : ; The tensile strength of the perforated compact model calculated according to the above formula is as follows: Table 3 Loads and tensile strengths of perforated compacts of four types of high-purity RTP powders at the time of failure.

[0047] S44: Based on the tensile strength of the non-porous compact model and the tensile strength of the perforated blank model The binding index BI, strain index SI, and brittle fracture index BFI were calculated respectively; the results are summarized in Table 4.

[0048] The formula for calculating the composite index BI is as follows: ; The formula for calculating the strain index SI is as follows: ; The formula for calculating the brittle fracture index (BFI) is as follows: ; The results of calculating the tablet compression index evaluation index using the above formula are as follows: Table 4 Evaluation Indicators of Compactation Index for Four Types of High-Purity RTP Powder Compactors

[0049] According to the calculation results, overall, since the BFI values ​​of the four high-purity RTP powders are all less than 0.2, it indicates that the four high-purity RTP powders are structurally stable and not easily brittle during pressing or subsequent processing. A comparative analysis of the bonding index BI and strain index SI of four high-purity RTP powders showed that the bonding index BI of A3 was 0.0086, which is greater than 0.005 and is the largest among the four batches of powders. This indicates that A3 has the strongest bonding ability among the four high-purity RTP powders. At the same time, A3 has the lowest strain index SI, indicating that A3 has a smaller elastic aftereffect and is less likely to crack due to elastic recovery during the unloading process of the compact. Therefore, A3 has the best overall forming performance. In comparison, the bonding indices BI of A4, B2, and B3 are all less than 0.005, indicating that their particle bonding ability is weaker than that of A3. Among them, the strain index SI of B3 is the highest among the four high-purity RTP powders, indicating that B3 has the most obvious elastic aftereffect. During the unloading process, the compact is most prone to cracking due to the release of elastic strain. Therefore, B3 has relatively poor forming stability. Furthermore, B2 has a higher bonding index (BI) than A4 and a lower strain index (SI) than A4, indicating that B2 not only has better interparticle bonding ability than A4, but also has a weaker elastic aftereffect. Therefore, compared with A4, B2 is less likely to crack after pressing, and its overall forming performance is relatively better.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating a cemented carbide powder tablet pressing index based on a discrete element method, characterized by, Includes the following steps: S1: Obtain the basic physical property parameters on the cemented carbide powder to be evaluated, which can characterize the powder particle features, and construct a discrete element model of the bonded particles based on the basic physical property parameters; S2: In the discrete element bonded particle model, bonding bonds are established between the particle pairs that are in contact with each other. The bonding bond contact parameters are obtained after calibration and verification. S3: Based on the calibrated and verified bonding bond contact parameters, a discrete element compression molding model is constructed on the basis of the discrete element bonding particle model to simulate the powder filling and compression molding process, and a compact model is obtained. S4: Perform discrete element numerical simulation of tensile strength and impact hardness on the compact model, calculate the compaction index evaluation index, which includes at least one of bonding index, strain index and brittle fracture index, and evaluate the pressing performance of the cemented carbide powder to be evaluated and whether there is a risk of cracking in the cemented carbide powder to be evaluated during the pressing process based on the compaction index evaluation index.

2. The method for evaluating the tabletting index of cemented carbide powder based on the discrete element method according to claim 1, characterized in that, The basic physical properties in S1 include particle size distribution, particle shape, and particle morphology; the particle size distribution is determined by at least one of laser particle size analyzer, sieving, or image analysis; the particle shape is determined by particle size analyzer; and the particle morphology is obtained by scanning electron microscopy or optical microscopy.

3. The method according to claim 2, wherein, The construction of the discrete element bonded particle model in S1 includes the following steps: S11: Based on the particle size distribution and particle density in the basic physical property parameters, the particle shape of the cemented carbide powder to be evaluated is approximated as spherical particles, and a spherical particle system is generated in the discrete element software. S12: Set the coarsening coefficient K, and use the coarsening strategy to enlarge the size of the spherical particles by a factor of K, while maintaining the distribution characteristics proportional to the experimental particle size distribution, to obtain the discrete element bonded particle model.

4. The method according to claim 3, wherein, The coarsening coefficient K=5.

5. The method according to claim 1, wherein, The calibration and verification of the bonding bond contact parameters are performed using the mechanical properties measured by actual uniaxial compression tests and three-point bending tests as target values, and specifically include the following steps: S21: Determine the initial range of values ​​for the bonding bond contact parameters through single-factor experiments; S22: Within the initial value range, using the bonding bond contact parameter as the variable to be calibrated, a virtual test scheme is constructed through the response surface methodology, and multiple sets of discrete element virtual uniaxial compression tests are executed to obtain the corresponding macroscopic mechanical response. S23: Establish the mathematical mapping relationship between the bonding bond contact parameters and the macroscopic mechanical response; S24: Using the mechanical properties measured by the actual uniaxial compression test as the target value, the bonding bond contact parameters are inverted and calibrated through the mathematical mapping relationship to obtain the calibrated bonding bond contact parameters; S25: Compare the results of the discrete element virtual uniaxial compression test with the results of the actual uniaxial compression test. When the error between the two is less than the preset allowable range, the effectiveness of the calibrated bond contact parameters is preliminarily verified; otherwise, adjust the parameters and repeat steps S21 to S24. S26: Construct a three-point bending discrete element virtual test model based on the calibrated bond contact parameters, and compare and verify the three-point bending virtual test results with the corresponding actual three-point bending test results. When the three-point bending virtual test results are consistent with the actual three-point bending test results or the error is within the allowable range, the calibrated bond contact parameters are confirmed to be valid; otherwise, repeat steps S21 to S25.

6. The method according to claim 5, wherein the method is characterized by, The bond contact parameters in S2 include normal stiffness per unit area, tangential stiffness per unit area, normal critical force, and tangential critical force.

7. The method according to claim 3, wherein the method is characterized by, Obtaining the billet model in S3 specifically includes: S31: Construct a mold geometry model for compact preparation, wherein the mold geometry model is a cuboid structure with an internal cavity for accommodating powder particles; S32: The discrete element pressing model is filled into the cavity of the mold geometry model, and the pressing simulation is performed by loading the top pressure head to obtain the pressing model.

8. The method according to claim 7, wherein the method is characterized by, The overall geometric model of the mold is a cuboid structure, including a blank-free pressing model and a pressing model with holes. The pressing model with holes has a through hole in the center of the pressing.

9. The method according to claim 8, wherein the method is characterized by, The tablet compression index evaluation indicators in S4 include the tablet compression index BI, strain index SI, and brittle fracture index BFI. The process of obtaining the tablet compression index evaluation indicators includes: S41: performing a Brazilian split test on the green body model without pores, recording the peak load at which the green body model without pores is destroyed , calculating the tensile strength of the green body model without pores : ； wherein L is the length of the non-porous green compact model, T is the thickness of the non-porous green compact model; S42: performing an impact hardness discrete element virtual test on the non-porous compacting model, establishing a spherical impact body, making the spherical impact body free fall under the action of gravity to impact the surface of the non-porous compacting model, and recording the rebound height of the spherical impact body , the indentation radius after impact a , calculating the impact hardness : ； In the formula, The mass of the spherical impactor is... The initial height of the spherical impactor. The radius of the spherical impactor; It is the gravitational constant. Pi; S43: Perform a Brazilian splitting discrete element virtual test on the perforated compact model and record the peak load at failure of the perforated compact model. Calculate the tensile strength of the perforated compact model. : ； In the formula, The length of the perforated blank mold, The thickness of the perforated blank model; S44: Based on the tensile strength of the non-porous compact model and the tensile strength of the perforated blank model The binding index BI, strain index SI, and brittle fracture index BFI were calculated respectively. The formula for calculating the composite index BI is as follows: ； The formula for calculating the strain index SI is as follows: ； The formula for calculating the brittle fracture index (BFI) is as follows: 。 10. The method for evaluating the pressing index of cemented carbide powder based on the discrete element method according to claim 9, characterized in that, The specific evaluation principles in S4 are as follows: When the brittle fracture index BFI > 0.8, it is determined that the cemented carbide powder to be evaluated has a tendency to brittle fracture during pressing or subsequent processing, and there is a risk of crack formation. When the brittle fracture index BFI < 0.2, it is determined that the overall crack resistance of the cemented carbide powder to be evaluated is strong, and the possibility of cracks occurring during pressing or subsequent processing is small. When the brittle fracture index BFI satisfies 0.2 ≤ BFI ≤ 0.8, a comprehensive judgment is made in conjunction with the binding index BI. When the bonding index BI < 0.005, the cemented carbide powder to be evaluated has insufficient energy absorption capacity under impact load, and the cemented carbide powder to be evaluated still has the risk of cracking; when the bonding index BI ≥ ​​0.005, it is determined that the cemented carbide powder to be evaluated has good impact deformation resistance, and the possibility of cracking is significantly reduced. When the brittle fracture index BFI or the bonding index BI are in the same judgment range, the smaller the strain index SI, the smaller the elastic aftereffect of the cemented carbide powder to be evaluated during the pressing and subsequent processing, and the less likely the compact is to crack due to elastic recovery during the unloading process.

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