Optimization design method for dehydrogenation control die in yttrium hydride sintering process

Abstract

The invention discloses an optimization design method for a dehydrogenation control mold in the yttrium hydride sintering process. The optimization design method comprises the steps that a heat-fluid-solid multi-physics field coupling model in the yttrium hydride sintering process and a thermal dehydrogenation kinetic equation based on yttrium hydride are established. According to the method, a traditional experience trial and error method is abandoned, the hydrogen generation rate and pressure accumulation curve in the sintering process can be accurately calculated by establishing the thermal-fluid-solid multi-physics field coupling model based on the thermal dehydrogenation kinetic equation, quantitative data support is provided for mold design, the hydrogen implosion risk is avoided from the source, and the mold design efficiency is improved. By introducing density gradient distribution, surface roughness, effective air permeability coefficient and other key parameters and adopting variable wall thickness design to be matched with a micro-stress release structure, the functional gradient characteristic that the mold is strong in outside and transparent in inside is achieved, the structural strength of the mold at high temperature and high pressure is guaranteed, the exhaust efficiency is maximized, and the service life of the mold is prolonged. The contradiction between exhaust and pressure bearing is effectively solved, and the requirements of workers are met.

Description

Technical Field

[0001] This invention relates to the field of yttrium hydride sintering technology, specifically to an optimized design method for a dehydrogenation control mold during the yttrium hydride sintering process. Background Technology

[0002] Yttrium hydride, an important rare-earth metal hydride, is widely used in advanced ceramics, functional coatings, and energy storage due to its unique optical properties, high hydrogen storage capacity, and potential as a moderator and shielding material in the nuclear industry. In the preparation process of yttrium hydride materials, sintering is a crucial step that determines its final density, phase structure, and optical / mechanical properties. However, during the sintering heating process, yttrium hydride undergoes a thermal dehydrogenation reaction, a strongly endothermic process accompanied by the generation of a large amount of gas.

[0003] In existing yttrium hydride sintering technologies, graphite molds or refractory metal molds are typically used for hot pressing sintering under vacuum or a protective atmosphere. However, the following technical problems exist: First, the contradiction between hydrogen emission from inside the mold and structural strength is difficult to reconcile. Yttrium hydride dehydrogenates at an extremely rapid rate within a specific temperature range (typically 400℃~800℃), generating a large amount of hydrogen gas in a short time. If the mold density is too high, the permeability will be poor, leading to a sharp increase in the hydrogen partial pressure inside the mold. When the pressure exceeds the critical decomposition pressure of yttrium hydride or the mold's withstand limit, it will cause product delamination, blistering, or even mold bursting. On the other hand, if the mold density is reduced to allow for venting, it will result in insufficient high-temperature strength of the mold, leading to plastic deformation under thermocompression stress.

[0004] Second, there is a lack of precise design theory based on multiphysics coupling. Traditional mold design mainly relies on rules of thumb and has not established a "thermal-fluid-solid" multiphysics coupling model. Because it is impossible to accurately calculate the hydrogen generation rate and pressure accumulation curve inside the mold during the sintering heating process, the design of the exhaust channel is somewhat arbitrary. Especially in variable wall thickness and complex geometries, hydrogen is prone to accumulate in dead corners or stress concentration areas, forming local high-pressure zones and triggering microcrack propagation.

[0005] Third, there is a lack of design considerations regarding mold surface characteristics and microstructure. Existing molds often have smooth inner walls or simple machined textures, failing to consider the impact of surface roughness on hydrogen boundary layer flow. Furthermore, stress concentration easily occurs in the rounded corner transition areas and bottom connection areas of the mold due to mismatched coefficients of thermal expansion and gas pressure impacts. Traditional molds lack targeted "micro-stress relief structures" (such as micropores and microgroove arrays), making them prone to fatigue cracking under repeated thermal shocks and shortening mold life. Summary of the Invention

[0006] To address the aforementioned technical problems, this paper provides an optimized design method for a dehydrogenation control mold during yttrium hydride sintering. This technical solution resolves the issues raised in the background section.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for optimizing the design of a mold for controlling dehydrogenation during yttrium hydride sintering includes: A thermal-fluid-solid multiphysics coupling model for the sintering process of yttrium hydride was established. Based on the thermal dehydrogenation kinetic equation of yttrium hydride, the hydrogen generation rate and pressure accumulation curve inside the mold during the sintering heating process were calculated. Based on the pressure accumulation curve, the key optimization parameters of the mold are determined. The key optimization parameters include the density gradient distribution of the mold body, the surface roughness of the inner wall of the mold, and the effective air permeability coefficient of the mold. Based on the key optimization parameters, a three-dimensional structural design model of the mold is generated, wherein the mold body adopts a variable wall thickness design and a micro-stress relief structure is set in the stress concentration area. The topology optimization algorithm is used to iteratively calculate the three-dimensional structural design model. The optimal mold geometry is obtained with the constraint that the maximum hydrogen partial pressure inside the mold does not exceed the critical pressure for the decomposition of yttrium hydride and the Von Mises stress of the mold is less than the yield strength of the material. The mold is manufactured according to the optimal mold geometry and applied to the sintering process of yttrium hydride material.

[0008] Preferably, the specific steps for establishing the thermo-fluid-solid multiphysics coupling model of the yttrium hydride sintering process include: Thermogravimetric analysis data of yttrium hydride at different heating rates were obtained, and a thermal dehydrogenation kinetic equation was constructed based on the Arrhenius equation. The specific expression is as follows: ; in, For dehydrogenation conversion rate, For time, Pre-exponential factor, As the apparent activation energy, For molar gas constant, Thermodynamic temperature The reaction order is [number]. The aforementioned kinetic equations were imported into multiphysics simulation software as internal heat source and mass source terms. Darcy's law was used to describe the hydrogen permeation behavior in the mold pores, and the hydrogen generation rate at any point inside the mold during the sintering heating process was calculated. With pressure accumulation curve .

[0009] Preferably, the specific logic for determining the density gradient distribution of the mold body based on the pressure accumulation curve is as follows: Define the density distribution function ρ(r) of the mold body from the inner cavity surface to the outer wall, such that it satisfies a nonlinear decreasing relationship: ; in, Radial coordinates, The inner radius is 1. The outer radius of the mold, For the density at the outer wall, ≥98%, The density at the inner wall is 85%-92%. The gradient exponent is (1.5≤k≤3.0). This design allows the inner wall of the mold to have a high permeability for rapid hydrogen removal, while the outer wall maintains high density to provide structural support, thus balancing venting efficiency and mold strength.

[0010] Preferably, the surface roughness of the inner wall of the mold The optimization criteria are: Based on fluid lubrication theory and boundary layer separation characteristics, the arithmetic mean deviation of the microscopic surface profile of the mold inner wall is set. It is within the range of 0.8μm-3.2μm; Calculating slip lengths under different roughnesses using fluid-structure interaction interface algorithms Satisfying the relation: ; in, This is the slip coefficient, with a value ranging from 0.01 to 0.05. The dynamic viscosity of hydrogen. For wall shear stress, The density of hydrogen gas; By controlling Within a specific range, the laminar sublayer of the hydrogen boundary layer is disrupted by microscale turbulence, promoting the diffusion of hydrogen at the interface to the outside of the mold, while avoiding yttrium hydride surface sticking to the mold due to excessive roughness.

[0011] Preferably, the design method of the micro-stress relief structure includes: In the rounded corner transition area and bottom connection area of ​​the mold body, an array of micro-holes or micro-grooves are prepared by laser micromachining or electrical discharge machining as a micro-stress relief structure. The geometric parameters of the microstructure are defined to satisfy the stress streamline deflection criterion, and the micropore depth h and pore spacing d satisfy: ; in, The mold wall thickness for this area; By introducing microstructures, the local stress concentration factor Kt is reduced to below 1.5, as calculated by the following formula: ; in, The maximum principal stress at the edge of the microstructure. The nominal stress is the stress without microstructure, ensuring that under thermal shock, microcracks preferentially initiate at the microstructure and self-limit their propagation, preventing the overall mold from cracking.

[0012] Preferably, the objective function and constraints for iterative calculation using the topology optimization algorithm are specifically as follows: Establish a dual objective function that minimizes mold structural compliance (strain energy) and maximizes air permeability: ; in, , These are the weighting coefficients. , These are the stress tensor and the strain tensor, respectively. This represents the hydrogen flux through the inner wall. For mold domain, For the inner wall boundary; The constraints include the partial pressure of hydrogen in the sovereign term. and Von Mises stress In addition, thermal fatigue cumulative damage constraints are introduced; ; in, In order to accommodate temperature differences and stress amplitude The number of loops below, This represents the number of failure cycles under the corresponding operating condition. The moving asymptote method (MMA) or the cone model trust region method (CONM) is used for iteration until the objective function converges.

[0013] Preferably, the effective air permeability coefficient of the mold The method for determining is as follows ; in, For the local porosity of the mold, This is the Kozeny constant, with a value of 5 ± 0.5. Specific surface area Pore ​​connectivity correction factor (0 < ≤1); In the variable wall thickness design region, the sintering process parameters are adjusted to achieve... The venting flow rate varies in a gradient to ensure that the overall venting flow rate of the mold remains constant at the peak of the dehydrogenation rate. satisfy: ; in, For effective exhaust area, This is the length of the exhaust path. The maximum volumetric flow rate for hydrogen production is given, with a safety factor of 1.2.

[0014] Preferably, the process of obtaining the optimal mold geometry includes a multi-scale simulation verification step: Based on macroscopic topology optimization, representative volume element (RVE) with the largest stress concentration is selected for mesoscopic crystal plasticity finite element analysis; Establish the hydrogen concentration-stress coupled diffusion equation: ; in, For hydrogen atom concentration, Where is the diffusion coefficient. Let be the partial molar volume of hydrogen. It is the hydrostatic pressure; This equation is used to predict the sensitive region for hydrogen-induced hysteresis cracking. This information is then fed back into the macroscopic model to refine the micro-stress release structure density in the corresponding region until the hydrogen concentration accumulation factor is reached. .

[0015] Preferably, the selection of the mold material and the design of the composite structure satisfy the following: The mold matrix material is selected from refractory metals or ceramic matrix composites with high thermal conductivity and high strength. Must meet: ; in, The exothermic power density of the yttrium hydride dehydrogenation reaction. The inner radius is 1. For mold height, The maximum permissible mold wall temperature; A porous functional gradient coating is sprayed or inlaid on the inner surface of the mold. The coating material is nano-sized tungsten powder or graphene-reinforced ceramic, and its air permeability is... It needs to be 1-2 orders of magnitude higher than the matrix, and its coefficient of thermal expansion must be... Must meet: ; To prevent the coating from peeling off during repeated thermal cycling, in which is the coefficient of thermal expansion of the matrix.

[0016] Preferably, the temperature control strategy for applying the optimized mold to the sintering process is as follows: Based on the optimal air permeability curve of the mold, a segmented variable heating rate sintering process was developed. In the main dehydrogenation reaction zone (temperature) - heating rate Strictly controlled by the rate of increase of internal pressure in the mold, satisfying the inequality: ; in, As the initial pressure, For dehydrogenation enthalpy change, Yttrium hydride charge density, This refers to the volume of the charge. During the heat preservation stage, air is evacuated using a vacuum pump or an inert protective gas is introduced to create a pressure difference between the inside and outside of the mold. By maintaining the pressure between 0.1 and 0.5 MPa, the pressure difference driving force is used to assist the hydrogen gas to be discharged through the mold pores, thereby achieving the densification sintering of yttrium hydride.

[0017] Compared with the prior art, the present invention provides an optimized design method for dehydrogenation control molds during yttrium hydride sintering, which has the following beneficial effects: This invention abandons the traditional trial-and-error method and establishes a thermo-fluid-solid multi-physics coupling model based on the thermal dehydrogenation kinetic equation. This model can accurately calculate the hydrogen generation rate and pressure accumulation curve during the sintering process, providing quantitative data support for mold design and avoiding the risk of hydrogen explosion from the source. By introducing key parameters such as density gradient distribution, surface roughness and effective permeability coefficient, and adopting a variable wall thickness design combined with a micro-stress release structure, the functional gradient characteristics of the mold, which is "strong on the outside and permeable on the inside", are realized. This design ensures the structural strength of the mold under high temperature and pressure while maximizing venting efficiency, effectively resolving the contradiction between venting and pressure bearing. Utilizing a topology optimization algorithm, iterative optimization is performed with hydrogen partial pressure and Von Mises stress as hard constraints to automatically generate the optimal geometric configuration. This design significantly reduces the peak stress in stress concentration areas, preventing the mold from cracking under thermal shock. At the same time, it ensures smooth exhaust of internal hydrogen, preventing the hydrogen partial pressure from exceeding the decomposition critical pressure. Furthermore, applying the optimized mold to the sintering process effectively suppresses defects such as product layer cracking and blistering caused by thermal dehydrogenation, significantly improving the density, phase structure uniformity, and overall performance of yttrium hydride materials, greatly increasing the sintering yield and extending the mold's service life. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the method flow for S101-S105 in this invention; Figure 2 This is a schematic diagram of the method flow for S201-S202 in this invention; Figure 3 This is a schematic diagram of the method flow of S301-S303 in this invention; Figure 4 This is a schematic diagram of the method flow for S401-S403 in this invention; Figure 5 This is a schematic diagram of the method flow for S501-S503 in this invention. Detailed Implementation

[0019] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0020] Example 1 Please refer to Figure 1 As shown, a method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering includes: S101. Establish a thermal-fluid-solid multiphysics coupling model for the sintering process of yttrium hydride. Based on the thermal dehydrogenation kinetic equation of yttrium hydride, calculate the hydrogen generation rate and pressure accumulation curve inside the mold during the sintering heating process. S102. Based on the pressure accumulation curve, determine the key optimization parameters of the mold. The key optimization parameters include the density gradient distribution of the mold body, the surface roughness of the inner wall of the mold, and the effective air permeability coefficient of the mold. S103. Based on key optimization parameters, generate a three-dimensional structural design model of the mold, wherein the mold body adopts a variable wall thickness design and a micro-stress relief structure is set in the stress concentration area. S104. Using the topology optimization algorithm, iterative calculations are performed on the three-dimensional structural design model. The optimal mold geometry is obtained under the constraints that the maximum hydrogen partial pressure inside the mold does not exceed the critical pressure for the decomposition of yttrium hydride and the Von Mises stress of the mold is less than the yield strength of the material. S105. Manufacture a mold according to the optimal mold geometry and apply it to the sintering process of yttrium hydride material.

[0021] As will be understood by those skilled in the art, this invention abandons the traditional trial-and-error method and establishes a thermo-fluid-solid multi-physics coupling model based on the thermal dehydrogenation kinetic equation. This model can accurately calculate the hydrogen generation rate and pressure accumulation curve during the sintering process, providing quantitative data support for mold design and avoiding the risk of hydrogen explosion from the source. By introducing key parameters such as density gradient distribution, surface roughness, and effective permeability coefficient, and by adopting a variable wall thickness design combined with a micro-stress release structure, the functional gradient characteristics of the mold, which is "strong on the outside and permeable on the inside," are achieved. This design ensures the structural strength of the mold under high temperature and pressure while maximizing venting efficiency, effectively resolving the contradiction between venting and pressure bearing. Utilizing a topology optimization algorithm, iterative optimization is performed with hydrogen partial pressure and Von Mises stress as hard constraints to automatically generate the optimal geometric configuration. This design significantly reduces the peak stress in stress concentration areas, preventing the mold from cracking under thermal shock. At the same time, it ensures smooth exhaust of internal hydrogen, preventing the hydrogen partial pressure from exceeding the decomposition critical pressure. Furthermore, applying the optimized mold to the sintering process effectively suppresses defects such as product layer cracking and blistering caused by thermal dehydrogenation, significantly improving the density, phase structure uniformity, and overall performance of yttrium hydride materials, greatly increasing the sintering yield and extending the mold's service life.

[0022] Please refer to Figure 2 As shown, the specific steps for establishing a thermal-fluid-solid multiphysics coupling model of the yttrium hydride sintering process include: S201. Obtain thermogravimetric analysis data of yttrium hydride at different heating rates, and construct a thermal dehydrogenation kinetic equation based on the Arrhenius equation. The specific expression is as follows: ; in, For dehydrogenation conversion rate, For time, Pre-exponential factor, As the apparent activation energy, For molar gas constant, Thermodynamic temperature The reaction order is [number]. S202. The kinetic equations are imported into multiphysics simulation software as internal heat source and mass source terms. Darcy's law is used to describe the percolation behavior of hydrogen in the mold pores, and the hydrogen generation rate at any point inside the mold during the sintering heating process is calculated. With pressure accumulation curve .

[0023] The specific logic for determining the density gradient distribution of the mold body based on the pressure accumulation curve is as follows: Define the density distribution function ρ(r) of the mold body from the inner cavity surface to the outer wall, such that it satisfies a nonlinear decreasing relationship: ; in, Radial coordinates, The inner radius is 1. The outer radius of the mold, For the density at the outer wall, ≥98%, The density at the inner wall is 85%-92%. The gradient exponent is (1.5≤k≤3.0). This design allows the inner wall of the mold to have a high permeability for rapid hydrogen removal, while the outer wall maintains high density to provide structural support, thus balancing venting efficiency and mold strength.

[0024] Please refer to Figure 3 As shown, the surface roughness of the inner wall of the mold The optimization criteria are: S301. Based on fluid lubrication theory and boundary layer separation characteristics, the arithmetic mean deviation of the microscopic surface profile of the mold inner wall is set. It is within the range of 0.8μm-3.2μm; S302. Calculate the slip length under different roughnesses using a fluid-structure interaction interface algorithm. Satisfying the relation: ; in, This is the slip coefficient, with a value ranging from 0.01 to 0.05. The dynamic viscosity of hydrogen. For wall shear stress, The density of hydrogen gas; S303, via control Within a specific range, the laminar sublayer of the hydrogen boundary layer is disrupted by microscale turbulence, promoting the diffusion of hydrogen at the interface to the outside of the mold, while avoiding yttrium hydride surface sticking to the mold due to excessive roughness.

[0025] Please refer to Figure 4 As shown, the design method for micro-stress relief structures includes: S401. In the rounded corner transition area and bottom connection area of ​​the mold body, an array of micro-holes or micro-grooves are prepared by laser micromachining or electrical discharge machining as a micro-stress relief structure. S402. Define the geometric parameters of the microstructure to satisfy the stress streamline deflection criterion, and the micropore depth h and pore spacing d satisfy: ; in, The mold wall thickness for this area; S403. By introducing microstructures, the local stress concentration factor Kt is reduced to below 1.5. The calculation formula is as follows: ; in, The maximum principal stress at the edge of the microstructure. The nominal stress is the stress without microstructure, ensuring that under thermal shock, microcracks preferentially initiate at the microstructure and self-limit their propagation, preventing the overall mold from cracking.

[0026] The objective function and constraints for iterative calculation using the topology optimization algorithm are as follows: Establish a dual objective function that minimizes mold structural compliance (strain energy) and maximizes air permeability: ; in, , These are the weighting coefficients. , These are the stress tensor and the strain tensor, respectively. This represents the hydrogen flux through the inner wall. For mold domain, For the inner wall boundary; The constraints include the partial pressure of hydrogen in the sovereign term. and Von Mises stress In addition, thermal fatigue cumulative damage constraints are introduced; ; in, In order to accommodate temperature differences and stress amplitude The number of loops below, This represents the number of failure cycles under the corresponding operating condition. The moving asymptote method (MMA) or the cone model trust region method (CONM) is used for iteration until the objective function converges.

[0027] Effective air permeability coefficient of mold The method for determining is as follows ; in, For the local porosity of the mold, This is the Kozeny constant, with a value of 5 ± 0.5. Specific surface area Pore ​​connectivity correction factor (0 < ≤1); In the variable wall thickness design region, the sintering process parameters are adjusted to achieve... The venting flow rate varies in a gradient to ensure that the overall venting flow rate of the mold remains constant at the peak of the dehydrogenation rate. satisfy: ; in, For effective exhaust area, This is the length of the exhaust path. The maximum volumetric flow rate for hydrogen production is given, with a safety factor of 1.2.

[0028] Please refer to Figure 5 As shown, the process of obtaining the optimal mold geometry includes multi-scale simulation verification steps: S501. Based on macroscopic topology optimization, the representative volume element (RVE) with the largest stress concentration is selected for mesoscopic crystal plasticity finite element analysis. S502. Establish the hydrogen concentration-stress coupled diffusion equation: ; in, For hydrogen atom concentration, Where is the diffusion coefficient. Let be the partial molar volume of hydrogen. It is the hydrostatic pressure; S503. The equation is used to predict the sensitive region for hydrogen-induced hysteresis cracking. This information is then fed back into the macroscopic model to refine the micro-stress release structure density in the corresponding region until the hydrogen concentration accumulation factor is reached. .

[0029] The selection of mold materials and the design of composite structures meet the following requirements: The mold matrix material is selected from refractory metals or ceramic matrix composites with high thermal conductivity and high strength. Must meet: ; in, The exothermic power density of the yttrium hydride dehydrogenation reaction. The inner radius is 1. For mold height, The maximum permissible mold wall temperature; A porous functional gradient coating is sprayed or inlaid on the inner surface of the mold. The coating material is nano-sized tungsten powder or graphene-reinforced ceramic, and its air permeability is... It needs to be 1-2 orders of magnitude higher than the matrix, and its coefficient of thermal expansion must be... Must meet: ; To prevent the coating from peeling off during repeated thermal cycling, in which is the coefficient of thermal expansion of the matrix.

[0030] The optimized mold is used in the sintering process for temperature control as follows: Based on the optimal air permeability curve of the mold, a segmented variable heating rate sintering process was developed. In the main dehydrogenation reaction zone (temperature) - heating rate Strictly controlled by the rate of increase of internal pressure in the mold, satisfying the inequality: ; in, As the initial pressure, For dehydrogenation enthalpy change, Yttrium hydride charge density, This refers to the volume of the charge. During the heat preservation stage, air is evacuated using a vacuum pump or an inert protective gas is introduced to create a pressure difference between the inside and outside of the mold. By maintaining the pressure between 0.1 and 0.5 MPa, the pressure difference driving force is used to assist the hydrogen gas to be discharged through the mold pores, thereby achieving the densification sintering of yttrium hydride.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for optimizing the design of a mold for controlling dehydrogenation during yttrium hydride sintering, characterized in that, include: A thermal-fluid-solid multiphysics coupling model for the sintering process of yttrium hydride was established. Based on the thermal dehydrogenation kinetic equation of yttrium hydride, the hydrogen generation rate and pressure accumulation curve inside the mold during the sintering heating process were calculated. Based on the pressure accumulation curve, the key optimization parameters of the mold are determined. The key optimization parameters include the density gradient distribution of the mold body, the surface roughness of the inner wall of the mold, and the effective air permeability coefficient of the mold. Based on the key optimization parameters, a three-dimensional structural design model of the mold is generated, wherein the mold body adopts a variable wall thickness design and a micro-stress relief structure is set in the stress concentration area. The topology optimization algorithm is used to iteratively calculate the three-dimensional structural design model. The optimal mold geometry is obtained with the constraint that the maximum hydrogen partial pressure inside the mold does not exceed the critical pressure for the decomposition of yttrium hydride and the Von Mises stress of the mold is less than the yield strength of the material. The mold is manufactured according to the optimal mold geometry and applied to the sintering process of yttrium hydride material.

2. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering as described in claim 1, characterized in that, The specific steps for establishing the thermo-fluid-solid multiphysics coupling model of the yttrium hydride sintering process include: Thermogravimetric analysis data of yttrium hydride at different heating rates were obtained, and a thermal dehydrogenation kinetic equation was constructed based on the Arrhenius equation. The specific expression is as follows: ； in, For dehydrogenation conversion rate, For time, Pre-exponential factor, As the apparent activation energy, For molar gas constant, Thermodynamic temperature The reaction order is [number]. The aforementioned kinetic equations were imported into multiphysics simulation software as internal heat source and mass source terms. Darcy's law was used to describe the hydrogen permeation behavior in the mold pores, and the hydrogen generation rate at any point inside the mold during the sintering heating process was calculated. With pressure accumulation curve .

3. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 2, characterized in that, The specific logic for determining the density gradient distribution of the mold body based on the pressure accumulation curve is as follows: Define the density distribution function ρ(r) of the mold body from the inner cavity surface to the outer wall, such that it satisfies a nonlinear decreasing relationship: ； in, Radial coordinates, The inner radius is 1. The outer radius of the mold, For the density at the outer wall, ≥98%, The density at the inner wall is 85%-92%. The gradient exponent is (1.5≤k≤3.0). This design allows the inner wall of the mold to have a high permeability for rapid hydrogen removal, while the outer wall maintains high density to provide structural support, thus balancing venting efficiency and mold strength.

4. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 3, characterized in that, Surface roughness of the inner wall of the mold The optimization criteria are: Based on fluid lubrication theory and boundary layer separation characteristics, the arithmetic mean deviation of the microscopic surface profile of the mold inner wall is set. It is within the range of 0.8μm-3.2μm; Calculating slip lengths under different roughnesses using fluid-structure interaction interface algorithms Satisfying the relation: ； in, This is the slip coefficient, with a value ranging from 0.01 to 0.

05. The dynamic viscosity of hydrogen. For wall shear stress, The density of hydrogen gas; By controlling Within a specific range, the laminar sublayer of the hydrogen boundary layer is disrupted by microscale turbulence, promoting the diffusion of hydrogen at the interface to the outside of the mold, while avoiding yttrium hydride surface sticking to the mold due to excessive roughness.

5. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 4, characterized in that, The design method for the micro-stress relief structure includes: In the rounded corner transition area and bottom connection area of ​​the mold body, an array of micro-holes or micro-grooves are prepared by laser micromachining or electrical discharge machining as a micro-stress relief structure. The geometric parameters of the microstructure are defined to satisfy the stress streamline deflection criterion, and the micropore depth h and pore spacing d satisfy: ； in, The mold wall thickness for this area; By introducing microstructures, the local stress concentration factor Kt is reduced to below 1.5, as calculated by the following formula: ； in, The maximum principal stress at the edge of the microstructure. The nominal stress is the stress without microstructure, ensuring that under thermal shock, microcracks preferentially initiate at the microstructure and self-limit their propagation, preventing the overall mold from cracking.

6. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 5, characterized in that, The objective function and constraints for iterative calculation using the topology optimization algorithm are as follows: Establish a dual objective function that minimizes mold structural compliance (strain energy) and maximizes air permeability: ； in, , These are the weighting coefficients. , These are the stress tensor and the strain tensor, respectively. This represents the hydrogen flux through the inner wall. For mold domain, For the inner wall boundary; The constraints include the partial pressure of hydrogen in the sovereign term. and Von Mises stress In addition, thermal fatigue cumulative damage constraints are introduced; ； in, In order to accommodate temperature differences and stress amplitude The number of loops below, This represents the number of failure cycles under the corresponding operating condition. The moving asymptote method (MMA) or the cone model trust region method (CONM) is used for iteration until the objective function converges.

7. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 6, characterized in that, The effective air permeability coefficient of the mold The method for determining is as follows ； in, For the local porosity of the mold, This is the Kozeny constant, with a value of 5 ± 0.

5. Specific surface area Pore ​​connectivity correction factor (0 < ≤1); In the variable wall thickness design region, the sintering process parameters are adjusted to achieve... The venting flow rate varies in a gradient to ensure that the overall venting flow rate of the mold remains constant at the peak of the dehydrogenation rate. satisfy: ； in, For effective exhaust area, This is the length of the exhaust path. The maximum volumetric flow rate for hydrogen production is given, with a safety factor of 1.

2.

8. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 7, characterized in that, The process of obtaining the optimal mold geometry includes a multi-scale simulation verification step: Based on macroscopic topology optimization, representative volume element (RVE) with the largest stress concentration is selected for mesoscopic crystal plasticity finite element analysis; Establish the hydrogen concentration-stress coupled diffusion equation: ； in, For hydrogen atom concentration, Where is the diffusion coefficient. Let be the partial molar volume of hydrogen. It is the hydrostatic pressure; This equation is used to predict the sensitive region for hydrogen-induced hysteresis cracking. This information is then fed back into the macroscopic model to refine the micro-stress release structure density in the corresponding region until the hydrogen concentration accumulation factor is reached. .

9. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 8, characterized in that, The selection of mold materials and the design of the composite structure satisfy the following: The mold matrix material is selected from refractory metals or ceramic matrix composites with high thermal conductivity and high strength. Must meet: ； in, The exothermic power density of the yttrium hydride dehydrogenation reaction. The inner radius is 1. For mold height, The maximum permissible mold wall temperature; A porous functional gradient coating is sprayed or inlaid on the inner surface of the mold. The coating material is nano-sized tungsten powder or graphene-reinforced ceramic, and its air permeability is... It needs to be 1-2 orders of magnitude higher than the matrix, and its coefficient of thermal expansion must be... Must meet: ； To prevent the coating from peeling off during repeated thermal cycling, in which is the coefficient of thermal expansion of the matrix.

10. The method for optimizing the design of a dehydrogenation control mold during yttrium hydride sintering according to claim 9, characterized in that, The temperature control strategy for applying the optimized mold to the sintering process is as follows: Based on the optimal air permeability curve of the mold, a segmented variable heating rate sintering process was developed. In the main dehydrogenation reaction zone (temperature) - heating rate Strictly controlled by the rate of increase of internal pressure in the mold, satisfying the inequality: ； in, As the initial pressure, For dehydrogenation enthalpy change, Yttrium hydride charge density, This refers to the volume of the charge. During the heat preservation stage, air is evacuated using a vacuum pump or an inert protective gas is introduced to create a pressure difference between the inside and outside of the mold. By maintaining the pressure between 0.1 and 0.5 MPa, the pressure difference driving force is used to assist the hydrogen gas to be discharged through the mold pores, thereby achieving the densification sintering of yttrium hydride.

Images