A method for analyzing hydrogen explosion process mechanism of recycled neodymium-iron-boron material

Abstract

This invention relates to a method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials, belonging to the field of simulation technology for rare earth permanent magnet material processing and advanced manufacturing. The method includes: constructing a simplified recycled NdFeB model; establishing a multiphysics numerical model based on the recycled NdFeB model by coupling rare earth diffusion, chemical field, temperature field, stress field, and phase field; solving the multiphysics numerical model to obtain the trends in hydrogen absorption rate and amount, stress and elastic strain energy changes, and phase field evolution data of the NdFeB material during the hydrogen explosion process. This invention can quantitatively simulate, visualize, analyze, and predict the multi-field coupling evolution behavior and final fragmentation effect within the material during the hydrogen explosion process.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material processing and advanced manufacturing simulation technology, specifically involving a method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials. Background Technology

[0002] The rare earth elements Nd, Pr, and Dy contained in neodymium iron boron (NdFeB) are critical strategic resources. Due to the highly concentrated global supply chain and significant risks, the development of efficient and controllable regeneration technologies is of great strategic importance. Among the various NdFeB regeneration technologies, the hydrogen explosion (HD) process has become the key step with the greatest industrial potential because it can rapidly pulverize waste magnets under mild conditions and obtain fine powder suitable for resintering.

[0003] However, the hydrogen penetration depth is difficult to monitor in real time during the hydrogen explosion process, and existing technologies cannot directly measure the internal stress distribution. Microcrack initiation is often only detected after particle breakage, making real-time monitoring and precise control of the hydrogen absorption and breakage process difficult. If the NdFeB hydrogen explosion process is ineffective, it will not only lead to insufficient material crack formation, decreased production efficiency, increased manufacturing costs such as electricity, gas, and labor, but also force a longer production cycle. Simultaneously, insufficient hydrogen explosion increases the newly formed surface area of ​​the powder, making it easier to adsorb and introduce impurity elements such as CON, accelerating the consumption of useful elements such as Re, ultimately causing a decrease in magnetic properties. Therefore, exploring the diffusion behavior, reaction process, stress field distribution, and crack initiation and propagation mechanism of hydrogen within NdFeB alloys is crucial for clarifying the influence of various factors on hydrogen absorption efficiency and crack propagation. This can improve the multiphysics coupling theory and hydrogen-induced damage model, and provide a theoretical basis for optimizing hydrogen explosion process parameters, thereby promoting precise control of the hydrogen explosion process and improving the recovery rate of rare earth resources and the performance stability of regenerated magnets.

[0004] Existing research methods are mostly limited to experimental observation of post-fragmentation products or use simplified models that only consider a single physical process, failing to truly reflect the complex nature of the multi-field coupling effects of chemistry, thermodynamics, and mechanics during hydrogen explosion. Therefore, developing an intrinsic mechanism analysis method that can deeply integrate and quantitatively analyze these coupled processes is urgently needed for achieving precise process design and intelligent optimization. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the background technology by providing a method for analyzing the hydrogen explosion process mechanism of regenerated NdFeB materials. This method is a numerical simulation method for the hydrogen absorption process of NdFeB in the hydrogen explosion process based on COMSOL multi-physics coupling. This method can not only simulate the hydrogen absorption changes of the NdFeB main phase and the NdFeB-rich phase with hydrogen, but also show the stress changes and volume expansion caused by the hydrogenation reaction, as well as the crack formation and propagation when the elastic strain energy reaches the limit that the material can withstand. This overcomes the core defects of the existing technology, such as unclear understanding of the internal mechanism of NdFeB hydrogen explosion process and reliance on experience-based trial and error in process development. It provides a method that can quantitatively simulate, visualize, analyze, and predict the multi-field coupling evolution behavior and final fragmentation effect inside the material during the hydrogen explosion process.

[0006] To achieve the above objectives, the technical solution of the present invention is: a method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials, comprising:

[0007] S1. Construct a simplified model for regenerated NdFeB;

[0008] S2. Based on the regenerated NdFeB model, a multiphysics numerical model is established by coupling rare material diffusion, chemical field, temperature field, stress field and phase field;

[0009] S3. Solve the multiphysics numerical model to obtain the trends of hydrogen absorption rate and amount, stress and elastic strain energy changes, and phase field evolution data of NdFeB material during the hydrogen explosion process.

[0010] Further, step S1 includes:

[0011] S11. A three-dimensional geometric model of the regenerated NdFeB model is constructed using three-dimensional modeling software. The model consists of a main phase and a NdFeB-rich phase.

[0012] S12. Set material properties for the three-dimensional geometric model of the regenerated NdFeB model, and set the main phase region and the NdFeB-rich phase region.

[0013] Furthermore, in step S2, the process of coupling multiple physics fields includes:

[0014] S21. Set up a rare substance transfer interface;

[0015] S22. Add a chemical reaction interface and couple it with the dilute substance transfer interface;

[0016] S23. Through the temperature interface, correct the heat transfer behavior and reaction between the object and the outside world, resulting in heat changes;

[0017] S24. Couple the chemical field with the stress field to correct the volume expansion of the object caused by the reaction of neodymium iron boron with hydrogen.

[0018] S25. Introduce the phase field method and couple it with the stress field to simulate the formation and propagation of cracks.

[0019] Furthermore, in step S21, in the rare substance transfer interface, an external hydrogen pressure is simulated by setting a concentration interface, and Fick's second law is used to describe the diffusion process of hydrogen in NdFeB. The governing equation is expressed as:

[0020]

[0021] Where c is the hydrogen concentration, D is the hydrogen diffusion coefficient, and D = 1 mm / s.

[0022] Furthermore, in step S22, a reaction is added in the chemical field. Within the Nd-rich phase reaction domain of the regenerated NdFeB model, the chemical reaction formula for the reaction of Nd and H2 to generate NdH3 is set as: 2Nd + 3H2 → 2NdH3; In the main phase reaction domain of the regenerated NdFeB model, a reaction formula for Nd2Fe... 14 The chemical reaction formula for the reaction of B and H2 to produce NdFeBH2 is: Nd2Fe 14 B + H₂ → Nd₂Fe 14 BH2;

[0023] Define Nd2Fe in the reaction domain 14 The initial concentrations of B and Nd were determined, and H2 was not present inside the neodymium iron boron at the beginning. Then, the H2 was continuously increased at the beginning of the simulation, and the diffusion rate was obtained by calculating Fick's second law.

[0024] The reaction rate is expressed using the Arrhenius expression:

[0025]

[0026] In the formula The activation energy of the reaction. For frequency factors, For hydrogen concentration, It is the thermodynamic temperature.

[0027] Furthermore, in step S24, the coupling between the stress field and the chemical field is achieved through a constitutive relation, the expression of which is:

[0028]

[0029] Where σ is stress, C is the elastic tensor, and ε is the total strain. ch ϕ represents the intrinsic strain caused by the hydrogenation reaction, and g(ϕ) is the energy degradation function related to the phase field damage variable ϕ.

[0030] Specifically, in step S24, at the solid mechanics interface, a damage-degraded linear elastic constitutive relation is used to correlate stress and strain through the following formula:

[0031] First, the stress field satisfies the equilibrium equations:

[0032]

[0033] It is the force acting on each unit volume within the material, and stress and strain satisfy the linear elastic degenerate constitutive relation:

[0034]

[0035] In the formula Let be the energy degradation function, representing the decrease in material stiffness as the degree of damage increases, and let be a constant to ensure numerical stability. This is the intrinsic strain caused by the hydrogenation reaction.

[0036] Furthermore, in step S25, the evolution of the phase field variables is controlled by the brittle fracture theory based on the AT-2 model, and its governing equation is:

[0037]

[0038] Among them, G C ϕ represents the fracture toughness, l represents the phase field characteristic length, H represents the historical state variable, which characterizes the maximum elastic strain energy driving force that the material has ever withstood, and ϕ represents the phase field damage variable.

[0039] Specifically, in step S25, the phase-field interface simulates crack propagation after the material reaches its bearing limit based on the elastic strain energy provided by the solid mechanics interface. The specific equations are as follows:

[0040] The elastic strain energy density of a material is defined as:

[0041]

[0042] In the formula For the total strain tensor, For intrinsic chemical strain tensor, Let be the elastic stiffness tensor.

[0043] It will be decomposed into its tensioning part. + and compression section The tensioning component is defined as the sole driving force for crack propagation:

[0044]

[0045] In the formula For hydrogen concentration, based on the brittle fracture theory of the AT-2 model, the evolution of phase field variables (ranging from 0 to 1, representing no damage and complete fracture, respectively) is controlled by the following equation:

[0046]

[0047] In the formula Let H be the fracture toughness and l be the characteristic length of the phase field. The former term describes the dissipation of crack surface energy, and the latter term represents crack propagation driven by strain energy. As H continuously increases, the damage variable ϕ continuously increases and forms a crack penetration.

[0048] Further, step S3 includes:

[0049] S31. A free tetrahedral mesh is used to generate a mesh for the entire regenerated NdFeB model. Then, an adaptive mesh is used to refine the NdFeB model in the NdFeB-rich phase region. A boundary layer mesh is used between the main phase region and the NdFeB-rich phase region of the regenerated NdFeB model.

[0050] S32. The regenerated NdFeB model is simulated and solved using the computational coupling equations to obtain the hydrogen absorption rate and amount, stress and elastic strain energy variation curves, stress distribution and crack propagation evolution.

[0051] Furthermore, in step S3, simulation results are used to analyze the main stages and underlying mechanisms from hydrogen absorption to crack formation and propagation, which is crucial for achieving precise process design and intelligent optimization.

[0052] The present invention also provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the program is executed by a processor, it implements the steps of the above-described method for analyzing the hydrogen explosion process mechanism of regenerated NdFeB materials.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. By establishing a multiphysics model that closely corresponds to physical reality, abstract internal processes (such as hydrogen diffusion, phase transition, and stress generation) are transformed into quantifiable and visualized data. This makes process optimization no longer a blind experiment, but a scientific prediction based on a deep understanding of the internal mechanisms, greatly improving the accuracy and foresight of research and development.

[0055] 2. It can dynamically and in three dimensions display, in the form of cloud maps and curves, where the internal stress of the material concentrates and where cracks are most likely to initiate every second during a hydrogen explosion. This "process visualization" capability provides a powerful tool for understanding and controlling the material's fracture behavior from its root cause.

[0056] 3. The core innovation lies in strong coupling. It accurately captures the series of chain reactions: "exothermic chemical reaction → local temperature increase → change in hydrogen diffusion rate → combined effect of phase change volume expansion and thermal expansion → generation of complex internal stress." This comprehensive and dynamic coupling analysis is far closer to the real physical process than single-physics-field or decoupled analysis methods, and therefore the prediction results are more reliable. Attached Figure Description

[0057] Figure 1 This is a flowchart of the method of the present invention.

[0058] Figure 2 This is a three-dimensional geometric model of a regenerated NdFeB model.

[0059] Figure 3 This is a graph showing the changes in the hydrogen absorption-crack propagation curve.

[0060] Figure 4 This represents the stress field distribution during the hydrogenation process.

[0061] Figure 5 The images show the crack propagation at different time points. Detailed Implementation

[0062] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0063] This invention provides a method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials, including:

[0064] S1. Construct a simplified model for regenerated NdFeB;

[0065] S2. Based on the regenerated NdFeB model, a multiphysics numerical model is established by coupling rare material diffusion, chemical field, temperature field, stress field and phase field;

[0066] S3. Solve the multiphysics numerical model to obtain the trends of hydrogen absorption rate and amount, stress and elastic strain energy changes, and phase field evolution data of NdFeB material during the hydrogen explosion process.

[0067] The following is a detailed implementation process of the present invention.

[0068] like Figure 1 , 2 As shown, this invention provides a method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials, simulating the hydrogen explosion process of NdFeB under normal process conditions. The specific process is as follows:

[0069] Establish a physical field model:

[0070] Upon entering the initial page of the COMSOL software, select "Model-oriented" for new creation, choose three-dimensional space dimension, and select rare matter transport, chemical reaction, solid temperature, solid mechanics, solid phase field, and transient study for the physical field.

[0071] 1) Establish a geometric model:

[0072] Import the model from the geometry model page;

[0073] 2) Set material parameters: Click on the completed two-dimensional geometric model to set the material parameters of the main phase and the neodymium-rich phase, which mainly include: density, Poisson's ratio, Young's modulus, coefficient of thermal expansion, enthalpy of reaction, etc.

[0074] 3) Set initial values, domain, and boundary conditions:

[0075] In a rare-matter transport field, transport properties are set, with the diffusion coefficients of the main phase and the neodymium-rich phase set separately. Both are set according to Fick's second law, and the concentration boundary is set on the surface of the neodymium iron boron geometric model. The hydrogen pressure is converted into concentration using the ideal gas law.

[0076] A chemical reaction is added to the neodymium-rich reaction zone: 2Nd + 3H₂ → 2NdH 3， The chemical reaction formula in the main phase reaction domain is Nd2Fe 14 B + H₂ → Nd₂Fe 14 BH2, set the reaction rate, check the option to give the reaction rate constant using the Arrhenius expression, and couple H2 to the dilute substance transfer interface at the initial amount of substance position.

[0077] The temperature interface establishes the heat generated by the chemical reaction, and the neodymium iron boron exchanges heat with the external temperature, defining the initial temperature as 298K.

[0078] At the interface between solid mechanics and solid phase field, the damage driving force and crack characteristic length of the main phase and the Nd:cium-rich phase are defined in the multiphysics field after coupling the two. Solid mechanics uses domain expansion to set the hydrogenation expansion of the main phase and the Nd:cium-rich phase. Damage and expansion need to be set separately.

[0079] Mesh generation: A free tetrahedral mesh is used, followed by adaptive meshing for mesh refinement. A boundary layer mesh is used at the boundary between the principal phase and the neodymium-rich phase.

[0080] Solution calculation: The solver uses transient calculation. At the physics field interface, select rare matter transport, chemistry, solid heat transfer, solid mechanics, and solid phase field. In multiphysics coupling, select thermal expansion 1, thermal expansion 2, phase field damage 1, and phase field damage 2.

[0081] The above-described embodiments of the operation construction can be obtained Figure 3 The graph showing the changes in the hydrogen absorption-crack propagation curve. Figure 4 Stress field distribution during hydrogenation process, Figure 5 The crack propagation diagrams at different time points show that this model transforms complex physicochemical processes into intuitive dynamic images, clearly revealing the complete chain of preferential hydrogen diffusion along grain boundaries, stress concentration caused by local volume expansion, and ultimately, crack propagation along grain boundaries.

[0082] This invention utilizes COMSOL software for 3D modeling. By simplifying the model to simulate the hydrogen absorption process of NdFeB, it can quantitatively calculate stress values, hydrogen concentrations, and crack formation and propagation at different times and locations, providing crucial data support for establishing a kinetic model of the hydrogen explosion process. Furthermore, by rapidly adjusting parameters such as hydrogen pressure, temperature, and alloy microstructure within the model, its impact on the fracture effect can be predicted cost-effectively and efficiently, identifying the optimal process window and significantly shortening the research and development cycle.

[0083] The present invention also provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the program is executed by a processor, it implements the steps of the above-described method for analyzing the hydrogen explosion process mechanism of regenerated NdFeB materials.

[0084] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials, characterized in that, include: S1. Construct a simplified model for regenerated NdFeB; S2. Based on the regenerated NdFeB model, a multiphysics numerical model is established by coupling rare material diffusion, chemical field, temperature field, stress field and phase field; S3. Solve the multiphysics numerical model to obtain the trends of hydrogen absorption rate and amount, stress and elastic strain energy changes, and phase field evolution data of NdFeB material during the hydrogen explosion process.

2. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 1, characterized in that, Step S1 includes: S11. A three-dimensional geometric model of the regenerated NdFeB model is constructed using three-dimensional modeling software. The model consists of a main phase and a NdFeB-rich phase. S12. Set material properties for the three-dimensional geometric model of the regenerated NdFeB model, and set the main phase region and the NdFeB-rich phase region.

3. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 1, characterized in that, In step S2, the process of coupling multiple physics fields includes: S21. Set up a rare substance transfer interface; S22. Add a chemical reaction interface and couple it with the dilute substance transfer interface; S23. Through the temperature interface, correct the heat transfer behavior and reaction between the object and the outside world, resulting in heat changes; S24. Couple the chemical field with the stress field to correct the volume expansion of the object caused by the reaction of neodymium iron boron with hydrogen. S25. Introduce the phase field method and couple it with the stress field to simulate the formation and propagation of cracks.

4. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 3, characterized in that, In step S21, in the rare substance transfer interface, the external hydrogen pressure is simulated by setting a concentration interface, and Fick's second law is used to describe the diffusion process of hydrogen in NdFeB. The governing equation is expressed as: Where c is the hydrogen concentration and D is the hydrogen diffusion coefficient.

5. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 3, characterized in that, In step S22, a reaction is added to the chemical field. Within the Nd-rich phase reaction domain of the regenerated NdFeB model, the chemical reaction formula for the reaction of Nd and H2 to generate NdH3 is set as: 2Nd + 3H2 → 2NdH3. In the main phase reaction domain of the regenerated NdFeB model, a reaction formula for Nd2Fe... 14 The chemical reaction formula for the reaction of B and H2 to produce NdFeBH2 is: Nd2Fe 14 B + H₂ → Nd₂Fe 14 BH2; Define Nd2Fe in the reaction domain 14 The initial concentrations of B and Nd were determined, and H2 was not present inside the neodymium iron boron at the beginning. Then, the H2 was continuously increased at the beginning of the simulation, and the diffusion rate was obtained by calculating Fick's second law. The reaction rate is expressed using the Arrhenius expression: In the formula The activation energy of the reaction. For frequency factors, For hydrogen concentration, It is the thermodynamic temperature.

6. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 3, characterized in that, In step S24, the coupling between the stress field and the chemical field is achieved through a constitutive relation, the expression of which is: Where σ is stress, C is the elastic tensor, and ε is the total strain. ch ϕ represents the intrinsic strain caused by the hydrogenation reaction, and g(ϕ) is the energy degradation function related to the phase field damage variable ϕ.

7. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 3, characterized in that, In step S25, the evolution of the phase field variables is controlled by the brittle fracture theory based on the AT-2 model, and its governing equation is: Among them, G C ϕ represents the fracture toughness, l represents the phase field characteristic length, H represents the historical state variable, which characterizes the maximum elastic strain energy driving force that the material has ever withstood, and ϕ represents the phase field damage variable.

8. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 1, characterized in that, Step S3 includes: S31. A free tetrahedral mesh is used to generate a mesh for the entire regenerated NdFeB model. Then, an adaptive mesh is used to refine the NdFeB model in the NdFeB-rich phase region. A boundary layer mesh is used between the main phase region and the NdFeB-rich phase region of the regenerated NdFeB model. S32. The regenerated NdFeB model is simulated and solved using the computational coupling equations to obtain the hydrogen absorption rate and amount, stress and elastic strain energy variation curves, stress distribution and crack propagation evolution.

9. The method for analyzing the hydrogen explosion process mechanism of recycled NdFeB materials according to claim 1, characterized in that, In step S3, simulation results are used to analyze the main stages and underlying mechanisms from hydrogen absorption to crack formation and propagation, which is crucial for achieving precise process design and intelligent optimization.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method for analyzing the hydrogen explosion process mechanism of regenerated NdFeB materials as described in any one of claims 1 to 9.

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