Creep property prediction method of ODS steel under high temperature and high irradiation conditions

Abstract

The invention relates to a method for predicting the creep performance of oxide dispersion strengthened (ODS) steel under high temperature and high irradiation conditions. A complex crystal plasticity constitutive model is developed to accurately predict the performance of ODS steel in terms of irradiation hardening and creep behavior, which incorporates the spatial distribution of voids and oxides. This developed model is highly consistent with experimental data at different temperatures and irradiation doses, demonstrating its strong robustness. As the irradiation dose increases, the yield stress of irradiated ODS steel also increases. The yield strength of ODS steel shows a linear relationship with the irradiation dose, which initially increases with the increase of irradiation dose and then decreases. The void size steadily increases, while the void spacing initially decreases and then increases. Therefore, the void hardening effect gradually weakens after the initial enhancement. In contrast, as the irradiation temperature increases, the yield strength decreases due to the expansion of the void spacing at higher temperatures. The creep rate of irradiated ODS steel is nonlinearly related to the irradiation dose. ODS steel irradiated at low or high doses has relatively poor creep performance and exhibits a higher creep rate under low applied stress. In contrast, at moderate doses, the creep performance is better due to the small number of irradiated voids and high strength of oxide particles. And spherical voids exhibit better creep resistance, and the void spacing has a more significant impact on the creep performance than the void size. At low and high doses, the creep performance decreases as the irradiation temperature increases, and in addition, at lower doses, the effect of irradiation temperature on creep performance is not as significant as at higher doses. This invention provides an efficient theoretical method for accurately evaluating the irradiation performance of ODS steel under complex environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of creep performance prediction under high temperature and high irradiation environment, and in particular to a crystal plasticity model, a cavity hardening theory caused by irradiation, an oxide dispersion strengthening theory and a creep rate calculation model related to a threshold stress, to establish a hardening and creep theory model with unified parameters to realize accurate prediction of the creep performance of oxide dispersion strengthened (ODS) steel under different irradiation doses and irradiation temperatures. BACKGROUND

[0002] The fourth generation of fission reactors needs to operate in an environment of high temperature coolant, high neutron flux and long-term high creep load. Therefore, they require structural materials with excellent mechanical properties, thermal stability and long-term creep performance. Oxide dispersion strengthened (ODS) steel, due to its excellent mechanical strength, significant microstructure stability at high temperatures and resistance to creep deformation, has become a strong contender for the fourth generation reactor. The high density of oxide particles in the matrix plays a key role in imparting these extraordinary properties. Through effective dislocations and grain boundaries, these tiny particles help to stabilize the structure and enhance the overall strength of the material.

[0003] Neutron irradiation and ion implantation are both experimental techniques used to evaluate the radiation resistance of ODS steel. Ion implantation offers several advantages, including lower cost, shorter irradiation time, and the ability to provide non-radioactive samples, facilitating post-implantation inspection in standard preparation laboratories. This has led to a large number of studies on ODS steel using ion implantation. ODS alloys containing 0.5% Y2O3 were subjected to neutron irradiation at temperatures of 250°C, 350°C and 450°C up to 16.2 dpa. The level and characteristics of the observed radiation damage were found to be significantly influenced by the irradiation temperature and the ODS particle distribution. A zirconium-doped nanocrystalline 14YWTZ ODS steel, consisting of a ferritic matrix with an average grain size of 50 nanometers and a high density of oxide nano precipitates with an average diameter of 3.3 nanometers. The ODS steel has an abnormally high sink strength of about 3 x 10 16 m -2 of helium atoms. While ODS steel is known for its favorable characteristics, there have been reports that ODS steel with lower oxide particle density can exhibit higher levels of irradiation hardening and transition to a brittle-plastic state after low-temperature irradiation compared to traditional RAFM steels.

[0004] The present application analyzes the irradiation hardening and creep behavior of ODS steel at high temperatures and doses, analyzes the effects of temperature and dose on irradiation hardening and creep rate, and discusses the creep mechanism of ODS steel. SUMMARY

[0005] The present application is based on experimental data combined with consideration of irradiation-induced void evolution, oxide particle evolution, through the crystal plasticity model and the creep rate analysis model related to the threshold stress, to establish a unified parameterized hardening and creep model; combined with the spatial distribution of voids and oxides, the model is used to accurately predict the irradiation hardening and creep behavior of ODS steel, and to realize the quantitative analysis of the creep rate under different irradiation doses and different irradiation temperatures. At the same time, by adjusting the irradiation dose and irradiation temperature, the creep rate and threshold stress of ODS steel under specific conditions are obtained, and the design guidance of ODS steel is realized.

[0006] The technical scheme of the present application is:

[0007] The material parameters of the ODS steel used are determined, including the related parameters of the physical parameters of the elements. The material used in the present application is ODS steel containing 14.9Cr-1.92W-0.34Y2O3(wt%) and 14Cr-3W-0.3Y2O3(wt%), and the performance prediction of other ODS steels. The void / helium bubble size in the ODS steel under different irradiation environments is shown in the following table:

[0008] Table 1 Helium bubble parameters in the matrix of 15Cr-ODS steel and 15Cr-ODS steel after irradiation.

[0009]

[0010] Table 2 Void parameters in ODS steel under different irradiation doses.

[0011]

[0012] Table 3 Oxide particle parameters in ODS steel under different irradiation doses.

[0013] Table 4 Void parameters in ODS steel under different irradiation temperatures.

[0014]

[0015] In the classical crystal plasticity theory, the deformation of the crystal is described by the deformation gradient and the velocity gradient:

[0016] F = F e · F p

[0017]

[0018] Wherein “e” and “p” represent the elastic and plastic parts, respectively, represents the deformation gradient. Plastic deformation is mainly caused by dislocation slip, therefore, the plastic part of the velocity gradient is composed of the accumulated shear rate of twelve slip systems:

[0019]

[0020] where N s is the total number of slip systems. is the Schmid factor, s a represents the dislocation slip direction, n a represents the normal direction of dislocation slip. is the reference plastic strain rate, m represents the strain rate sensitivity coefficient, τ a = σ : R a represents the local shear stress, σ is the Cauchy stress. is the critical fraction of shear stress, the defects induced under high temperature and intense irradiation are mainly considered as voids.

[0021] Therefore, the critical fraction of shear stress is expressed as

[0022]

[0023] where is the solid solution strengthening, is the dislocation strengthening, is the grain strengthening, is the void strengthening, is the oxide dispersion strengthening. By considering the interaction and behavior of individual grains, the stress-strain relationship of polycrystalline materials is characterized by using the self-consistent plasticity method.

[0024] The solid solution structure, dislocations, grain size, voids and oxide particles have a strengthening effect on the mechanical properties of the material by impeding the movement of dislocations. The solid solution strengthening is expressed as

[0025]

[0026] where k i represents the hardening coefficient, X i is the atomic content, for the substitutional solid solution Z = 3 / 4, k Cr = 9.95 MPa / at% 3 / 4 and k W = 75.79 MPa / at% 3 / 4 , m is the Taylor factor. The dislocation strengthening is expressed as

[0027]

[0028] where h nis the dislocation strengthening coefficient, which increases with plastic strain, the Mecking and Kocks model captures the change in dislocation density due to multiplication and annihilation

[0029]

[0030] where is the reference plastic shear rate, k1 is a multiplication factor, is the annihilation coefficient, the relationship between the two coefficients is

[0031]

[0032] where is the loading strain rate, is the reference strain rate, D α is the drag stress, g α is the normalized activation energy, k is the Boltzmann constant, χ is the interaction parameter. The grain strengthening is expressed as

[0033]

[0034] where k hp is the Hall-Petch coefficient, k hp = 0.2Gb 1 / 2 , d is the average grain size. The effectiveness of voids in impeding dislocations is closely related to the shape, the critical shear stress for spherical voids is expressed as

[0035]

[0036] where L represents the void spacing, is the harmonic mean size, D is the void diameter, Ψ is the fitting coefficient. For cubic voids, the cross-sectional shape of dislocations and voids is different. The cross-sectional shape includes triangle and hexagon. The overall contribution of voids to the critical shear stress is expressed as

[0037]

[0038] where, the impeding effect of the triangular section is expressed as The impeding effect of the hexagonal interface is Oxide particles also have a strengthening effect on the mechanical properties of materials by impeding dislocation movement, the main mechanisms of oxide particle strengthening are the shear strengthening mechanism τ cutting , the Orowan bypass strengthening mechanism τ orowan and the climb mechanism τ climb . Their expressions are

[0039]

[0040] τ = min(τ climb ,τ orowan ,τ cutting )

[0041] where A and B are constant parameters, D is the spatial particle diameter, L is the interparticle spacing, r a is the dislocation core radius, which is assumed to be the magnitude of the Burgers vector. ε is the misfit strain, which is calculated as ε = b / 4r, where r is the radius of the oxide particle and can be obtained experimentally. τ represents the minimum stress of the three interaction mechanisms. This assumption does not accurately reflect the physical model. Although the slip plane of the dislocation remains fixed in the matrix, the precipitates are randomly distributed. In addition, even particles of the same size exhibit different dislocation bypass mechanisms. Therefore, the critical fraction shear stress contribution of the spatial distribution probability model is represented as:

[0042]

[0043] where and represent the climb, cutting, and bypass strengthening mechanisms, respectively. Therefore, by integrating the probabilistic nature and spatial distribution of the interaction between dislocations and particles, a refined model of oxide particle strengthening is established. This new approach explains the random distribution of precipitates and the different mechanisms of dislocation bypassing the same size particles. Therefore, the critical fraction shear stress contribution is represented as

[0044] The threshold stress coupled can be considered as the coupled creep resistance of voids and oxide particles in the irradiation environment. Considering the irradiation-induced void evolution theory and the creep rate equation of the oxide dispersion strengthening theory, the unified equation is represented as:

[0045]

[0046] τ L is the dislocation line tension, τ L = Gb 2 . G is the shear modulus, G = 84 - 16 / (e 448 / T - 1), b is the Burgers vector. c L is the strain hardening parameter, σ app is the applied stress, σ D is the threshold stress, and α is an empirical constant. N is the dislocation mobility related to stress and temperature, which is described by:

[0047]

[0048] D osd represents the pre-exponential factor, k B is the Boltzmann constant, and Q sd represents the activation energy for self-diffusion, Rg R is the gas constant m The threshold stress is related to the intrinsic properties of voids and oxide particles and shows its effectiveness in impeding dislocation motion, which can be expressed as

[0049]

[0050] Finally, the calculated results are processed and analyzed, which can obtain the comparison between the model and the experimental data, and predict the creep rate under different irradiation doses and irradiation temperatures.

[0051] Advantages

[0052] A complex crystal plasticity constitutive model is developed to accurately predict the performance of ODS steels in terms of irradiation hardening and creep behavior, which incorporates the spatial distribution of voids and oxides. The developed model is highly consistent with the experimental data at different temperatures and irradiation doses, showing its strong robustness. With the increase of irradiation dose, the yield stress of irradiated ODS steel also increases. The yield strength of ODS steel shows a linear relationship with the irradiation dose, which increases initially and then decreases. The void size increases steadily, while the void spacing decreases initially and then increases. Therefore, the void hardening effect is gradually weakened after the initial enhancement. On the contrary, the yield strength decreases with the increase of irradiation temperature, which is due to the expansion of void spacing at higher temperatures. The creep rate of irradiated ODS steel is nonlinearly related to the irradiation dose. The creep performance of ODS steel irradiated at low or high doses is relatively poor, and shows a higher creep rate under low applied stress. On the contrary, at moderate doses, the creep performance is better due to the small number of irradiated voids and high strength of oxide particles. And spherical voids show better creep resistance, and the influence of void spacing on creep performance is more significant than that of void size. At low and high doses, the creep performance decreases with the increase of irradiation temperature, and in addition, the influence of irradiation temperature on the creep performance is not as obvious as at higher doses at lower doses. This work provides an efficient theoretical method for accurately evaluating the irradiation performance of ODS steels under complex environments. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 (a) is the contribution of various strengthening mechanisms to the yield strength of ODS steel before and after irradiation, (b) is the comparison of the irradiation yield strength increment calculated by the current model and the experimental results.

[0054] Figure 2 (a) is the curve of the diameter of voids and oxide particles changing with irradiation dose; (b) is the curve of the void spacing and the density of oxide particles changing with irradiation dose.

[0055] Figure 3 (a) is how the creep behavior of ODS steel changes with the change of irradiation dose at a temperature of 823K; (b) the effect of cavity spacing on the creep behavior of ODS steel is studied when the constant cavity size is 5 nanometers, and the cavity spacing is 30 nanometers, 50 nanometers and 70 nanometers respectively; (c) the effect of cavity size on the creep behavior of ODS steel is discussed when the cavity spacing is 50 nanometers, and the spherical cavity diameter is 5 nanometers, 10 nanometers and 15 nanometers respectively, and the cubic cavity edge length is 5 nanometers, 10 nanometers and 15 nanometers respectively.

[0056] Figure 4 is the creep performance prediction of ODS steel at different irradiation temperatures in 100dpa and 500dpa environments respectively. DETAILED DESCRIPTION

[0057] The helium bubble data in Table 1 and the creep data of ODS steel in different irradiation environments are combined to verify the robustness of the model. Figure 1 (a) gives the contribution of various strengthening mechanisms to the yield strength of ODS steel before and after irradiation, and (b) compares the irradiation yield strength increment calculated by the current model with the experimental results. Figure 1 (b) compares the irradiation yield strength increment calculated by the current model with the experimental results.

[0058] Further elaboration of the technical scheme, the present application is not limited to the following examples, as long as the design idea of using the present application is within the scope of protection of the present application.

[0059] Oxide dispersion strengthening refers to adding a certain amount of thermodynamically stable oxide in a high-temperature alloy, so that the oxide dispersion phase insoluble in the matrix is formed by dispersing in the matrix; The new phase hinders the movement of dislocations in the alloy, and plays a strengthening role on the mechanical properties of the material. The distribution evolution of irradiation-induced cavities and oxide particles changes with the change of irradiation and irradiation temperature, and the creep performance prediction of the material in different irradiation environments can be realized based on the microstructure data and theoretical model.

[0060] Specific steps: collect ODS steel experimental data to obtain material parameters involved in the method of the present application, as shown in Table 2.

[0061] Table 5 Material parameters.

[0062]

[0063] The robustness of the model is verified by comparing the model-calculated yield strength increment of ODS steel at different irradiation temperatures with the experimental yield strength increment. Then the distribution evolution data of cavities and oxide particles under different irradiation doses are collected to obtain Figure 2 According to the creep data of ODS steel in different irradiation environments, the model is verified by comparing the model-calculated yield strength increment of ODS steel at different irradiation temperatures with the experimental yield strength increment. Then the distribution evolution data of cavities and oxide particles under different irradiation doses are collected to obtainFigure 2 , obtain the threshold stress and the creep rate change curve of the cavity and the oxide particle contribution under 100-390 dpa, and realize the creep performance prediction of the ODS steel under different irradiation doses (appendix Figure 3 a) According to the cavity evolution law, the influence of different cavity shapes, cavity diameters and cavity spacings on the creep performance is explored (appendix Figure 3 a, b), so as to guide the alloy design in the future. Collect the cavity data in the ODS steel under different irradiation temperatures, obtain the threshold stress and the creep rate change curve of the cavity and the oxide particle contribution under different temperatures, and realize the creep performance prediction of the ODS steel under different irradiation temperatures (appendix Figure 4 ).

[0064] Therefore, the present application has good analysis precision on the creep rate of the ODS steel under the irradiation environment, can effectively predict the anti-creep performance of the material under different irradiation doses and irradiation temperatures, and provides a reliable theoretical model for analyzing the micro-defect evolution and anti-creep performance of the ODS steel under the irradiation environment.

Claims

1. A method for predicting the creep properties of oxide-dispersion-strengthened steels under high-temperature and high-irradiation conditions, combining a crystal plasticity model, radiation-induced void evolution theory, oxide dispersion strengthening theory based on oxide particle size and spatial distribution, and a creep rate analysis model, is characterized by: The strengthening effect of void evolution in oxide-dispersion-strengthened steel under high-temperature and high-irradiation environments was considered, including changes in void size and shape. Voids in the material are generated when the matrix is ​​exposed to the irradiation environment. Dislocations, grain size, and solid solution strengthening are the material hardening mechanisms before irradiation. A unified parameterized hardening and creep model was established using a crystal plasticity model and a creep rate analysis model related to threshold stress. Combining the spatial distribution of voids and oxides can accurately predict the radiation hardening and creep behavior of oxide-dispersion-strengthened steel, enabling quantitative analysis of creep rates at different irradiation doses and temperatures. At the same time, by adjusting the irradiation dose and irradiation temperature, the creep rate and threshold stress of oxide-dispersion-strengthened steel under specific conditions can be obtained, providing design guidance for oxide-dispersion-strengthened steel. The specific processing steps are as follows: Determine the basic material parameters required in the model and collect relevant physical parameters of related materials; The coupled threshold stress can be regarded as the coupled creep resistance of voids and oxide particles under irradiation. Considering the theory of irradiation-induced void evolution and the theory of oxide dispersion strengthening, the unified equation for the creep rate of oxide dispersion strengthened steel is expressed as: in, τ L is the dislocation line tension, τ L =Gb 2 ; G is the shear modulus, G = 84-16 / (e 448 / T -1); b is the Burgers vector, M is the Taylor factor, c L is the strain hardening parameter, σ app is the applied stress, σ D is the threshold stress, α is an empirical constant; N is the dislocation mobility that is stress- and temperature-dependent and is described by the following equation: Among them, D osd represents the pre-exponential factor, k B is the Boltzmann constant, Q sd represents the activation energy of self-diffusion, R g is the gas constant, R m represents the tensile strength at room temperature; the threshold stress is related to the intrinsic properties of voids and oxide particles, indicating their effectiveness in preventing dislocation motion and can be expressed as The critical partial shear stress of a spherical cavity is expressed as Where L represents the hole spacing, is the harmonic mean size, D is the void diameter, Ψ is the fitting coefficient; for cubic voids, the cross-sectional shapes of dislocations and voids are different; cross-sectional shapes include triangles and hexagons; the total contribution of voids to the critical partial shear stress is expressed as The obstruction of the triangular cross section is expressed as The hindrance of the hexagonal interface is Oxide particles also have a strengthening effect on the mechanical properties of materials by hindering dislocation movement. The main mechanism of oxide particle strengthening is the cutting strengthening mechanism τ cutting 、Orowan bypasses the reinforcement mechanism τ orowan and the climbing mechanism τ climb ; Their expressions are τ=min(τ climb ,t orowan ,t cutting ) Among them, A and B are constant parameters, D o is the diameter of the spatial particle, L o is the interparticle distance, r a is the dislocation core radius, assumed to be the magnitude of the Burgers vector; ε is the misfit strain, calculated as ε = b / 4r, where r is the radius of the oxide particle and can be obtained experimentally; τ represents the minimum stress for the three interaction mechanisms; this assumption does not accurately reflect the physical model; although the slip plane of the dislocation remains fixed in the matrix, the precipitates are randomly distributed; moreover, even particles of the same size can exhibit different dislocation bypassing mechanisms; therefore, the critical partial shear stress contribution of the spatially distributed probabilistic model is expressed as: in and represent the climb strengthening, shear strengthening, and bypass strengthening mechanisms, respectively. Therefore, a refined model of oxide particle strengthening is established by integrating the probabilistic nature and spatial distribution of the interaction between dislocations and particles. This accounts for the random distribution of precipitates and the different mechanisms by which dislocations bypass particles of the same size. Therefore, the critical partial shear stress contribution is expressed as The critical shear and stress are constructed within the framework of the crystal plasticity model and all known microstructural strengthening mechanisms are considered. In classical crystal plasticity theory, the deformation of a crystal is described by deformation gradients and velocity gradients: in, is the deformation gradient due to the elasticity of the material, It is the deformation gradient caused by the plasticity of the material. and are the elastic velocity gradient and the plastic velocity gradient, represents the time derivative of the deformation gradient; plastic deformation is mainly caused by dislocation slip, so the plastic part of the velocity gradient is composed of the cumulative shear rate of the twelve slip systems: Among them, N s is the total number of slip systems; is the Schmid factor, where represents the dislocation slip direction, represents the normal direction of dislocation slip; is the reference plastic strain rate, m represents the strain rate sensitivity coefficient, represents the local shear stress, is the Cauchy stress; is the critical partial shear stress. The defects induced by high temperature and strong irradiation are mainly considered as voids. Therefore, the critical partial shear stress is expressed as in, represents solid solution strengthening, represents dislocation strengthening, For grain strengthening, is the critical partial shear stress of the void, is the critical partial shear stress of the oxide particles; the self-consistent plasticity method is used to characterize the stress-strain relationship of polycrystalline materials by considering the interaction and behavior of individual grains; Solid solution structure, dislocations, grain size, voids, and oxide particles have a strengthening effect on the mechanical properties of materials by hindering dislocation motion; solid solution strengthening is expressed as Among them, k i represents the hardening coefficient, X i is the atomic content, for substitutional solid solution Z = 3 / 4; dislocation strengthening is expressed as Among them, h n is the dislocation strengthening coefficient; as the plastic strain increases, the Mecking and Kocks model captures the change in dislocation density due to proliferation and annihilation in, represents the reference plastic shear rate, is the loading strain rate, k1 is the multiplication factor, is the annihilation coefficient, and the relationship between the two coefficients is in, is the reference strain rate, D α is the drag stress, g α is the normalized activation energy, χ is the interaction parameter; grain strengthening is expressed as Among them, k hp is the Hall-Petch coefficient, k hp =0.2Gb 1 / 2 ; d is the grain size.

2. The method for predicting creep properties of oxide dispersion strengthened steel under high temperature and high irradiation environment according to claim 1, characterized in that The inherent parameters of the material and existing experimental data are used to accurately calculate the creep rate and threshold stress of the involved void evolution, strength and creep rate models under different irradiation doses and irradiation temperatures.

3. The method for predicting creep properties of oxide dispersion strengthened steel in a high temperature and high irradiation environment according to claim 1, characterized in that: Determine the effective material parameters; the materials used are 14.9Cr-1.92W-0.34Y2O3 and 14Cr-3W-0.3Y2O3 steels, the content of each component is expressed in mass percentage, and the performance of other steels is predicted.

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