阅读说明：本技术 一种辐照缺陷和纳米相协同演化的相场模拟方法 (Phase field simulation method for irradiation defect and nanophase co-evolution ) 是由 李永胜 严正伟 于 2020-06-28 设计创作，主要内容包括：本发明为一种辐照缺陷和纳米相协同演化的相场模拟方法。通过合金热力学自由能来表征系统的演变；建立辐照缺陷–合金体系的总自由能；创建辐照缺陷和纳米相共同演化的相场方程,实现辐照下合金缺陷和纳米相演化的模拟与表征；分析辐照温度和缺陷浓度变化条件下的缺陷和纳米相微观组织形貌的变化,得出辐照下缺陷和纳米析出相的演变规律；同时分析缺陷和纳米相的体积分数变化,得出不同辐照温度和缺陷浓度对缺陷和纳米相的形成及演化动力学的影响规律；本发明提供了一种辐照缺陷和纳米相协同演化的相场模拟方法,能够获得辐照下缺陷和相分解之间的相互作用关系,为辐照下合金材料的设计和服役安全提供指导。(The invention relates to a phase field simulation method for irradiation defect and nanophase co-evolution. The evolution of the system is characterized by the thermodynamic free energy of the alloy; establishing total free energy of an irradiation defect-alloy system; establishing a phase field equation of irradiation defect and nanophase co-evolution, and realizing simulation and characterization of alloy defect and nanophase evolution under irradiation; analyzing the defects under the condition of changing the irradiation temperature and the defect concentration and the change of the shape of the nanophase microstructure to obtain the evolution law of the defects and nanophase precipitated phases under irradiation; analyzing the volume fraction change of the defects and the nanophase simultaneously to obtain the influence rule of different irradiation temperatures and defect concentrations on the formation and evolution dynamics of the defects and the nanophase; the invention provides a phase field simulation method for irradiation defect and nanophase co-evolution, which can obtain the interaction relation between irradiation defect and phase decomposition and provide guidance for the design and service safety of an irradiated alloy material.)

1. A phase field simulation method for irradiation defect and nanophase co-evolution is characterized by comprising the following steps:

(1) performing thermodynamic description of defects and a nanophase system by using thermodynamic free energy of the alloy;

(2) solving chemical free energy and elastic energy of the defects and the nanophase system under irradiation according to thermodynamic description;

(3) establishing a phase field kinetic equation of defect and nanophase evolution under irradiation based on a Chan-Hilliard diffusion equation;

(4) and simulating the tissue morphology and component evolution of the defects and the nanophase under different irradiation conditions according to the input variables, and analyzing the influence of the defects on the phase decomposition kinetic law under different irradiation conditions.

2. The irradiation defect and nanophase co-evolution phase field simulation method according to claim 1, wherein the thermodynamic description in step (1) comprises: the chemical free energy, elastic energy and gradient energy of the system are as follows:

where F is the total free energy of the system, F_chemIs the chemical free energy of the alloy, V_mIs the molar volume of the alloy, i represents the alloying element, c_iIs the atomic fraction of the element i, c_VAnd c_IAtomic fraction, k, divided into vacancies and interstitial atoms_j(j ═ I, V, I) is the gradient energy coefficient, f_elasIs the elastic energy density.

3. The method for simulating the phase field of irradiation defect and nanophase co-evolution of claim 1, wherein the formation energy and concentration of the defect are coupled into the chemical free energy of the system, and the chemical free energy in step (2) can be expressed as:

whereinAndrespectively being empty spaces and gapsThe energy of formation of the atoms,gibbs free energy of element i, k represents an alloying element, c_kIs the atomic fraction of the element k, L_ikIs an interatomic interaction parameter.

4. The method for simulating the phase field of irradiation defect and nanophase co-evolution of claim 1, wherein the inhomogeneous defect and strain induced components are coupled into the intrinsic strain, and the elastic energy density in step (2) can be expressed as follows:

wherein C is_ijklIn order to be the modulus of elasticity,

wherein₀，_V0And are and_I0the elastic strain and the lattice expansion coefficient generated by the non-uniform components and the introduction of the vacancy and the interstitial atoms_klIn relation to displacement, the expression is:

by coupling defect-related quantities into chemical free energy and elastic energy, it is convenient to describe the evolution of defects and their effect on phase decomposition using the phase-field method.

5. The method for simulating the phase field of irradiation defect and nanophase cooperative evolution according to claim 1, wherein the kinetic equation of irradiation defect and nanophase cooperative evolution described in the step (3) is:

where M is the chemical mobility of the alloy, M_j(j ═ V, I) is the vacancy and interstitial atom mobility, ξ_j(j ═ I, V, I) is the thermodynamic fluctuation, P_j(j ═ V, I) and S_j(j ═ V, I) is the generation rate and annihilation rate of defects, respectively, R_VIIs the merging rate of defects; and (3) solving a kinetic evolution equation by using a semi-implicit Fourier spectrum algorithm in phase field simulation calculation to obtain a relation between components and time and space positions, completing the morphological characteristics of the defects and the nano-phase tissues under different irradiation conditions in the step (4) through quantitative analysis, and simultaneously searching the influence rule of the defects on the phase decomposition kinetics.

Technical Field

The invention relates to the technical field of microstructure control under irradiation of metal materials, in particular to a phase field simulation method for irradiation defect and nanophase co-evolution.

Background

In the nuclear field, under high temperature and irradiation, atoms in the nuclear reactor structural material leave the original lattice positions to form vacancies and interstitial atoms, the existence of the defects promotes the precipitation of nanophase, and the increase of brittleness and hardness of the alloy caused by dislocation movement is prevented, so that the service life of the material is reduced. Therefore, the research on the defects and the evolution of the nanophase under the irradiation is particularly important for the safe use of the alloy.

The current research shows that the irradiation temperature and the irradiation dose mainly have the influence factors on the metallographic transformation caused by irradiation, and the increase of the irradiation temperature enhances the migration effect of defects and the atomic diffusion effect, thereby promoting the nanophase transformation. The increase of the irradiation dose promotes the enhancement of the cascade effect, the increase of the number of defects provides a channel for the diffusion of atoms, the diffusion of atoms is accelerated, and the phase decomposition is accelerated. Therefore, the irradiation dose and the irradiation temperature promote the phase decomposition by enhancing the defect effect, but the kinetic influence rule of the defect on the nanophase evolution under irradiation is not clear.

At present, most simulation researches only aim at the defect under irradiation or single evolution of the nanophase, the researches on the defect under irradiation and the synergistic evolution of the nanophase are lacked at present, and the defect can be simplified into the same element variable in phase-field method simulation to simulate the synergistic evolution of the defect and the nanophase. Meanwhile, the phase-field method can be used for research to overcome the defects of long experimental period, high cost, single research object and difficulty in real-time observation. Therefore, it is very advantageous and necessary to utilize the phase field simulation means to study the defect and the nanophase co-evolution under irradiation.

Disclosure of Invention

The technical problem solved by the invention is to provide a phase field simulation method for irradiation defect and nanophase co-evolution, and solve the problem that the existing research method cannot research the defect and nanophase simultaneously.

The technical scheme for realizing the purpose of the invention is as follows:

a phase field simulation method for irradiation defect and nanophase co-evolution comprises the following steps:

(1) performing thermodynamic description of defects and a nanophase system by using thermodynamic free energy of the alloy;

(2) solving chemical free energy and elastic energy of the defects and the nanophase system under irradiation according to thermodynamic description;

(3) establishing a phase field kinetic equation of defect and nanophase evolution under irradiation based on a Chan-Hilliard diffusion equation;

(4) and simulating the tissue morphology and component evolution of the defects and the nanophase under different irradiation conditions according to the input variables, and analyzing the influence of the defects on the phase decomposition kinetic law under different irradiation conditions.

The specific contents are as follows:

the thermodynamics in (1) are described according to the thermodynamic characteristics of the alloy, and mainly comprise: the chemical free energy, elastic energy and gradient energy of the system are as follows:

where F is the total free energy of the system, F_chemIs the chemical free energy of the alloy, V_mIs the molar volume of the alloy, i represents the alloying element, c_iIs the atomic fraction of the element i, c_VAnd c_IAtomic fraction, k, divided into vacancies and interstitial atoms_j(j ═ I, V, I) is the gradient energy coefficient, f_elasIs the elastic energy density.

In the present invention, the formation energy of defects and the concentration thereof are coupled to the chemical free energy of the system, and the chemical free energy in (2) is expressed as:

whereinAndrespectively forming energy for the vacancy and the interstitial atom,gibbs free energy of element i, k represents an alloying element, c_kIs the atomic fraction of the element k, L_ikIs an interatomic interaction parameter.

In the present invention, the non-uniformity of defect and strain-induced components is coupled into the intrinsic strain, and the elastic energy density in (2) can be expressed as follows:

wherein C is_ijklIn order to be the modulus of elasticity,the specific formula for intrinsic strain is:

wherein₀，_V0And are and_I0the elastic strain and the lattice expansion coefficient generated by the non-uniform components and the introduction of the vacancy and the interstitial atoms_klIn relation to displacement, the expression is:

by coupling defect-related quantities into chemical free energy and elastic energy, it is convenient to describe the evolution of defects and their effect on phase decomposition using the phase-field method.

The kinetic equation for the cooperative evolution of irradiation defects and nanophase described in step (3) of the present invention can be expressed as:

where M is the chemical mobility of the alloy, M_j(j ═ V, I) is the vacancy and interstitial atom mobility, ξ_j(j ═ I, V, I) is the thermodynamic fluctuation, P_j(j ═ V, I) and S_j(j ═ V, I) is the generation rate and annihilation rate of defects, respectively, R_VIIs the merging rate of defects. And (3) solving a kinetic evolution equation by using a semi-implicit Fourier spectrum algorithm in phase field simulation calculation to obtain the relation between components and time and space positions, completing the morphological characteristics of the defects and the nano-phase tissues under different irradiation conditions in the step (4) through quantitative analysis, and simultaneously searching the influence rule of the defects on the phase decomposition kinetics.

Compared with the prior art, the invention has the following remarkable advantages:

(1) the method enables the irradiation point defects and the nanophase to be captured simultaneously by coupling the formation energy and the concentration of the defects into the free energy of the system, makes up the limitation that the existing simulation method can only research a single factor, and provides a specific and effective method for the research of the alloy irradiation effect;

(2) the method considers the nature of crystal defects while changing the nano-phase, establishes a kinetic equation of the collaborative evolution of vacancy and interstitial defects and the nano-phase through a Chan-Hilliard diffusion equation, obtains a phase field simulation method of the joint evolution of irradiation defects and the nano-phase, and can better analyze the influence of different irradiation conditions on the evolution of the defects and the nano-phase and the mutual influence between the defects and the nano-phase.

Drawings

FIG. 1 is a microstructure of alpha' phase, vacancies, and interstitial atoms in an Fe-35 at.% Cr alloy with an irradiation temperature of 750K and an initial defect concentration of 10^-5The irradiation times t are 44, 52 and 482, respectively.

FIG. 2 is a microstructure of alpha' phase, vacancies, and interstitial atoms in a Fe-35 at.% Cr alloy at different irradiation temperatures, 710K, 730K, and 760K, respectively, with an initial defect concentration of 10^-5When irradiatedThe time t is 382.

FIG. 3 is a graph of the alpha' phase volume fraction in Fe-35 at.% Cr as a function of time for different initial defect concentrations, 0 and 10^-7、10^-5And 10^-4The irradiation temperature was 750K.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention, they are further illustrated by way of example in the accompanying drawings.

The invention relates to a phase field simulation method for irradiation defect and nanophase co-evolution, which comprises the following steps:

(1) performing thermodynamic description of defects and a nanophase system by using thermodynamic free energy of the alloy;

(2) solving chemical free energy and elastic energy of the defects and the nanophase system under irradiation according to thermodynamic description;

(3) establishing a phase field kinetic equation of defect and nanophase evolution under irradiation based on a Chan-Hilliard diffusion equation;

(4) and simulating the tissue morphology and component evolution of the defects and the nanophase under different irradiation conditions according to the input variables, and analyzing the influence of the defects on the phase decomposition kinetic law under different irradiation conditions.

Taking Fe-Cr alloy as an example.

In the step (1), the thermodynamic description of the Fe-Cr alloy comprises chemical free energy, elastic energy and gradient energy of a system, and the specific formula is as follows:

where F is the total free energy of the system, F_chemIs the chemical free energy of the alloy, V_mIs the molar volume of the alloy, i represents the alloying element, c_iIs the atomic fraction of the element i, c_VAnd c_IAtomic fraction, k, divided into vacancies and interstitial atoms_j(j ═ I, V, I) is the gradient energy coefficient, f_elasIs the elastic energy density.

Coupling the formation energy of the defects and the concentration thereof into the chemical free energy of the system, the chemical free energy of the Fe-Cr alloy in step (2) can be expressed as:

(i＝Fe,Cr；k＝Fe,Cr；i≠k)

wherein

And

respectively forming energy for the vacancy and the interstitial atom,

gibbs free energy of element i, k represents an alloying element, c_kIs the atomic fraction of the element k, L_ikIs an interatomic interaction parameter.

The elastic energy density of the Fe-Cr alloy in step (2) can be expressed as follows, coupling the inhomogeneity of the defect and strain induced components into the intrinsic strain:

wherein C is_ijklIn order to be the modulus of elasticity,the specific formula for intrinsic strain is:

wherein₀，_V0And are and_I0the elastic strain and the lattice expansion coefficient generated by the non-uniform components and the introduction of the vacancy and the interstitial atoms_klIn relation to displacement, the expression is:

in the step (3), the kinetic equation of the irradiation defect and the phase collaborative evolution of the Fe-Cr alloy can be expressed as follows:

the chemical mobility of an alloy in which M is Fe — Cr can be expressed as M ═ c_CrM_Fe+(1-c_Cr)M_Cr]c_Cr(1-c_Cr)，M_j(j ═ V, I) is the vacancy and interstitial atom mobilities, and from the kinetic equation it is known that defects and atoms can establish an intrinsic relationship by mobility, whereas the vacancy diffusion mechanism indicates that atoms complete their migration by exchange with vacancies, and therefore the phase field equation is theoretically true. Xi_j(j ═ I, V, I) is the thermodynamic fluctuation, P_j(j ═ V, I) and S_j(j ═ V, I) is the generation rate and annihilation rate of defects, respectively, R_VIThe introduction of the rate makes the phase-field method more practical for the merging rate of defects. And solving a kinetic evolution equation by using a semi-implicit Fourier spectrum algorithm in the simulation calculation process.

Step (4), setting the initial component of the Fe-Cr alloy as c_Cr0.35, initial concentration range of vacancies and interstitials of 10^-7～10^-4The irradiation temperature range is 710-760K, and the calculation grid size is 128 delta x^*×128△y^*And drawing a microstructure evolution diagram of the Fe-Cr alloy under different irradiation conditions according to the numerical value obtained by the simulation calculation.

FIG. 1 is a microstructure of alpha' phase, vacancies, and interstitial atoms in an Fe-35 at.% Cr alloy with an irradiation temperature of 750K and an initial defect concentration of 10^-5The irradiation times t are 44, 52 and 482, respectively. From the figure canIt is known that as the irradiation time is prolonged, the α' phase starts to accumulate at a high defect concentration, while the defects gradually accumulate from the middle toward the phase boundary, forming a defect ring between the two phases. This is because in the vacancy diffusion mechanism, atoms are easily exchanged with vacancies and then complete their migration, so that a large number of vacancies generated by irradiation can promote phase decomposition.

FIG. 2 is a microstructure of alpha' phase, vacancies, and interstitial atoms in a Fe-35 at.% Cr alloy at different irradiation temperatures, 710K, 730K, and 760K, respectively, with an initial defect concentration of 10^-5The irradiation time t is 382. As can be seen from the figure, as the irradiation temperature increases, the α' phase grows larger and coarsens more, the particles grow larger, and the defects also gradually gather from the initial positions toward the boundaries and form loops.

FIG. 3 is a graph of the alpha' phase volume fraction in Fe-35 at.% Cr as a function of time for different initial defect concentrations, 0 and 10^-7、10^-5And 10^-4The irradiation temperature is 750K; as can be seen from the graph, as the defect concentration increases, the time at which the volume fraction of the α' phase starts to change advances, the phase decomposition time advances, and the phase transition is promoted.

In general, both the irradiation temperature and the defect concentration promote phase decomposition, and the higher the temperature the stronger the effect. The method can be used as a theoretical reference for designing and applying the nuclear reactor structural material under irradiation, and the structural performance of the alloy is optimized according to the theoretical reference.

The foregoing is a detailed description of the preferred embodiments and principles of the present invention, and variations in the specific embodiments that may be made by those skilled in the art based on the teachings herein are considered to be within the scope of the present invention.