阅读说明：本技术 一种高氮钢高温钎焊过程中Fe-Cu、Fe-Ni二元体系分子动力学扩散模拟方法 (Molecular dynamics diffusion simulation method for Fe-Cu and Fe-Ni binary system in high-nitrogen steel high-temperature brazing process ) 是由 何鹏 张墅野 王星星 于 2020-07-07 设计创作，主要内容包括：一种高氮钢高温钎焊过程中Fe-Cu、Fe-Ni二元体系分子动力学扩散模拟方法。本发明属于高氮奥氏体不锈钢钎焊领域。本发明为了在原子尺度上探索高氮钢钎焊过程中钎料中的基体元素Cu、Ni与母材基体元素Fe的扩散机制,从而研究钎焊工艺对高氮钢性能的影响。该方法具体为：一：采用Lammps软件建立扩散体系模型；二：使体系弛豫,施加原子间作用力和周期性边界条件,使体系中原子扩散至达到热力学平衡状态；三：分析与评估二元体系中原子的扩散过程与扩散能力。本发明采用分子动力学的方法,在原子尺度上探索钎焊过程中钎料中的元素与母材基体元素的扩散机制。对原子势能进行分析,并计算均方位移MSD、扩散系数等,进而比较Fe-Cu、Fe-Ni中元素的扩散能力。(A molecular dynamics diffusion simulation method of a Fe-Cu and Fe-Ni binary system in the high-nitrogen steel high-temperature brazing process. The invention belongs to the field of high-nitrogen austenitic stainless steel brazing. The invention aims to explore the diffusion mechanism of matrix elements Cu and Ni and base matrix element Fe in the brazing filler metal in the high-nitrogen steel brazing process on the atomic scale, thereby researching the influence of the brazing process on the performance of the high-nitrogen steel. The method specifically comprises the following steps: firstly, the method comprises the following steps: establishing a diffusion system model by using Lammps software; II, secondly: relaxing the system, applying interatomic force and periodic boundary conditions, and diffusing atoms in the system until a thermodynamic equilibrium state is reached; thirdly, the method comprises the following steps: and analyzing and evaluating the diffusion process and the diffusion capacity of atoms in a binary system. The invention adopts a molecular dynamics method to explore the diffusion mechanism of elements in the brazing filler metal and base material matrix elements in the brazing process on an atomic scale. And analyzing the atomic potential energy, calculating the mean square displacement MSD, the diffusion coefficient and the like, and further comparing the diffusion capacity of the elements in Fe-Cu and Fe-Ni.)

1. A molecular dynamics diffusion simulation method of a Fe-Cu and Fe-Ni binary system in a high-nitrogen steel high-temperature brazing process is characterized by comprising the following steps:

the method comprises the following steps: establishing a diffusion system model by adopting Lammps software, and determining the number of atoms, the interatomic force and the periodic boundary conditions in a binary system of Fe-Cu and Fe-Ni;

step two: relaxing the system, and after the system is balanced, under the condition of keeping the temperature, the pressure and the number of atoms of the system unchanged, applying the interatomic acting force and the periodic boundary condition in the first step in the three directions of the x axis, the y axis and the z axis to diffuse the atoms in the system until the thermodynamic equilibrium state is reached;

step three: and calculating the mean square displacement and diffusion coefficient of atomic diffusion in the binary system from the initial state to the thermodynamic equilibrium state, and analyzing and evaluating the diffusion process and diffusion capacity of atoms in the binary system of Fe-Cu and Fe-Ni.

2. The method for simulating molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein in the step one, a model is established according to the actual atomic size ratio according to the difference of atomic radii in the binary system.

3. The method for simulating molecular dynamics diffusion of a binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of high-nitrogen steel according to claim 1, wherein the diffusion system model in the first step is specifically as follows: in the directions of x, y and z, 10 repeated cells are respectively established to form a super cell, the number of atoms in the whole system is 3892, and the distance between crystals of the two atoms is 0.1 nm.

4. The method for simulating molecular dynamics diffusion of the binary system Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as recited in claim 1, wherein the interatomic force in the first step is determined by using an EAM potential function.

5. The simulation method for molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein in the step one, the lattice constant of Cu atoms in the binary system of Fe-Cu and Fe-Ni is 3.61492505nm, the lattice constant of Fe atoms is 2.85532463nm, and the lattice constant of Ni atoms is 3.506486 nm.

6. The simulation method for molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein in the second step, the system is relaxed by 10 ps.

7. The method for simulating molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel according to claim 1, wherein in the second step, the temperature of the system is 850-1050 ℃, and the pressure of the system is 0.1 MPa.

8. The simulation method for molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein in the second step, atoms in the system are diffused for 0ps to 600 ps.

9. The simulation method for molecular dynamics diffusion of the binary system of Fe-Cu and Fe-Ni in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein in the second step, atoms in the system are diffused for 200ps to 400 ps.

10. The method for simulating the molecular dynamics diffusion of the Fe-Cu and Fe-Ni binary system in the high-temperature brazing process of the high-nitrogen steel as claimed in claim 1, wherein the diffusion coefficients of Fe atoms in the Fe-Cu binary system at 850 ℃, 950 ℃ and 1050 ℃ in the third step are 2.12 × 10 respectively^-9m²/s、2.97×10^-9m²S and 3.55 × 10^-9m²(ii) a diffusion coefficient of 2.062 × 10 at 850 ℃, 950 ℃ and 1050 ℃ for Cu atoms, respectively^-9m²/s、2.753×10^-9m²S and 3.457 × 10^-9m²The diffusion coefficients of Fe atoms in the Fe-Ni binary system at 850 ℃, 950 ℃ and 1050 ℃ are respectively 4.73 × 10^-10m²/s、7.63×10^-10m²S and 11.7 × 10^-10m²The diffusion coefficients of Ni atoms at 850 deg.C, 950 deg.C and 1050 deg.C were 4.53 × 10^-10m²/s、7.33×10^-10m²S and 10.92 × 10^-10m²/s。

Technical Field

The invention belongs to the field of high-nitrogen austenitic stainless steel brazing; in particular to a molecular dynamics diffusion simulation method of a Fe-Cu and Fe-Ni binary system in the high-temperature brazing process of high-nitrogen steel.

Background

With respect to the definition of high nitrogen steel, it is currently widely believed that steel having a nitrogen content (mass%) of more than 0.4% in an austenitic matrix or more than 0.08% in a ferritic matrix is called high nitrogen steel, and due to the shortage of nickel resources in the period of shivering, many scholars propose to austenitize the structure with nitrogen element instead of nickel element, nitrogen element is more easily dissolved in solid solution than carbon element in austenite, and precipitation of carbide can be reduced, and the strength and corrosion resistance of steel can be improved. With the development of high nitrogen steel, some outstanding advantages of the steel grade, such as high strength, good toughness, good process performance and excellent corrosion resistance, are found. By replacing nickel element with nitrogen element, the steel grade has good economical efficiency and improved biocompatibility. Therefore, the high-nitrogen steel is widely applied to the fields of electric power, ships, ocean engineering, military equipment, medical instruments and the like at present.

In application, high nitrogen steel is mainly used as a structural member, and is required to have high bearing capacity and high impact resistance in electric power, ships and military equipment. Therefore, in these fields, a fusion welding method such as laser welding or telephone welding is often used as a weak link in the welded joint. In the field of medical instruments and the like, the bearing capacity and impact resistance of high-nitrogen steel as medical austenitic stainless steel are not the first criteria, and the corrosion resistance is rather the key point of the requirements in this respect.

The high nitrogen steel studied by us has better weldability as austenitic stainless steel, and the diffusion phenomenon is accompanied when the brazing filler metal wets the base metal in the brazing process, and the diffusion process is continued in the subsequent process. The AgCuNi brazing filler metal is used for carrying out vacuum brazing on high-nitrogen steel, and mutual diffusion among elements can occur at the interface of a base metal and the brazing filler metal in the brazing process. And the exploration of the diffusion mechanism of the matrix elements Cu and Ni and the matrix element Fe in the brazing filler metal in the high-nitrogen steel brazing process on the atomic scale is particularly important.

Disclosure of Invention

The invention provides a molecular dynamics diffusion simulation method of a binary system of Fe-Cu and Fe-Ni in a high-temperature brazing process of high-nitrogen steel, which aims to explore a diffusion mechanism of matrix elements Cu and Ni and matrix element Fe in a brazing filler metal in the high-nitrogen steel brazing process on an atomic scale so as to research the influence of a brazing process on the performance of the high-nitrogen steel.

The molecular dynamics diffusion simulation method of the Fe-Cu and Fe-Ni binary system in the high-temperature brazing process of the high-nitrogen steel is carried out according to the following steps:

the method comprises the following steps: establishing a diffusion system model by adopting Lammps software, and determining the number of atoms, the interatomic force and the periodic boundary conditions in a binary system of Fe-Cu and Fe-Ni;

step two: relaxing the system, and after the system is balanced, under the condition of keeping the temperature, the pressure and the number of atoms of the system unchanged, applying the interatomic acting force and the periodic boundary condition in the first step in the three directions of the x axis, the y axis and the z axis to diffuse the atoms in the system until the thermodynamic equilibrium state is reached;

step three: and calculating the mean square displacement and diffusion coefficient of atomic diffusion in the binary system in the process of the system from the initial state to the thermodynamic equilibrium state, and analyzing and evaluating the diffusion process and diffusion capacity of the atoms in the binary system.

And further limiting, in the step one, establishing a model according to the proportion of the actual size of atoms according to the difference of the radii of the atoms in the binary system.

Further limiting, in the step one, the diffusion system model specifically includes: in the directions of x, y and z, 10 repeated cells are respectively established to form a super cell, the number of atoms in the whole system is 3892, and the distance between crystals of the two atoms is 0.1 nm.

Further defined, the interatomic force of step one is determined using an EAM potential function.

Further limiting, in the binary system of Fe-Cu and Fe-Ni in the first step, the lattice constant of Cu atoms is 3.61492505nm, the lattice constant of Fe atoms is 2.85532463nm, and the lattice constant of Ni atoms is 3.506486 nm.

Further limiting, in the second step, the system is relaxed by 10 ps.

Further limiting, in the second step, the temperature of the system is 850-1050 ℃, and the pressure of the system is 0.1 MPa.

Further limiting, in the second step, the atoms in the system are diffused for 0ps to 600 ps.

Further limiting, in the second step, the atoms in the system are diffused for 200ps to 400 ps.

Further limit, the diffusion coefficients of Fe atoms in the Fe-Cu binary system in the third step are respectively 2.12 × 10 at 850 ℃, 950 ℃ and 1050 DEG C^-9m²/s、2.97×10^-9m²S and 3.55 × 10^-9m²(ii) a diffusion coefficient of 2.062 × 10 at 850 ℃, 950 ℃ and 1050 ℃ for Cu atoms, respectively^-9m²/s、2.753×10^-9m²S and 3.457 × 10^{- 9}m²The diffusion coefficients of Fe atoms in the Fe-Ni binary system at 850 ℃, 950 ℃ and 1050 ℃ are respectively 4.73 × 10^-10m²/s、7.63×10^-10m²S and 11.7 × 10^-10m²The diffusion coefficients of Ni atoms at 850 deg.C, 950 deg.C and 1050 deg.C were 4.53 × 10^-10m²/s、7.33×10^-10m²S and 10.92 × 10^-10m²/s。

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

1) the invention adopts a molecular dynamics method to explore the diffusion mechanism of elements in the brazing filler metal and base material matrix elements in the brazing process on an atomic scale. And (2) performing molecular dynamics simulation by using Lammps aiming at a high-nitrogen steel matrix element Fe and two elements of Cu and Ni in the brazing filler metal, respectively simulating the atomic diffusion processes of a Fe-Cu binary system and a Fe-Ni binary system, analyzing the atomic potential energy of the Fe-Cu binary system and the Fe-Ni binary system, calculating the mean square displacement MSD, the diffusion coefficient and the like, and further comparing the diffusion capacities of the elements in the Fe-Cu binary system and the Fe-Ni binary system.

2) According to the simulation method disclosed by the invention, obvious interatomic interdiffusion occurs in the Fe-Cu binary system at the temperature range of 850-1050 ℃. The thickness of the Fe-Cu diffusion region increases with the diffusion time, and only interdiffusion between elements occurs during the process, and no mesophase is generated. During the diffusion process, more Fe atoms diffuse into the Cu lattice, while only a few Cu atoms diffuse into the Fe lattice. During the diffusion process, the potential energy of Fe atoms is greater than that of Cu atoms, and is more unstable, and the absolute value of their atomic potential energy becomes larger as the temperature rises. The mean square displacement MSD of the diffusion of the two is obtained through simulation, the diffusion coefficient is further calculated, and the higher the temperature is, the larger the diffusion coefficients of Fe and Cu are, and the stronger the diffusion capability is. Under the same temperature, the diffusion coefficient of Fe is larger than that of Cu, which shows that the diffusion capability of Fe is stronger than that of Cu.

3) According to the simulation method disclosed by the invention, the Fe-Ni binary system generates obvious interatomic mutual diffusion at the temperature range of 850-1050 ℃, and the diffusion area is increased along with the increase of time. Meanwhile, unlike Fe-Cu diffusion, a plateau region with a reduced slope appears on an atomic concentration curve in Fe-Ni diffusion, which shows that a new phase is formed at the same time of the diffusion process and is presumed to be an intermediate phase of FeNi and FeNi 3. In the diffusion process, the potential energy of the Fe atom is larger than that of the Ni atom, and the Fe atom is more unstable. Similarly, more Fe atoms are diffused into Ni crystal lattices in the diffusion process, and the mean square displacement and the diffusion coefficient are calculated to find that the higher the temperature is, the larger the diffusion coefficients of Fe and Ni are, and the stronger the diffusion capability is. At the same temperature, the diffusion coefficient of Fe is larger than that of Ni, which shows that the diffusion capability of Fe is stronger than that of Ni.

Drawings

FIG. 1 is a diagram of an atomic diffusion model for 0ps diffusion at 850 deg.C according to one embodiment;

FIG. 2 is a diagram of an atomic diffusion model for diffusion at 850 ℃ for 200ps according to one embodiment;

FIG. 3 is a diagram of an atomic diffusion model for diffusion at 850 ℃ for 400ps according to one embodiment;

FIG. 4 is a diagram of an atomic diffusion model for 600ps diffusion at 850 deg.C according to one embodiment;

FIG. 5 is a graph of atomic concentration along the Z direction for 0ps diffusion at 850 deg.C, according to one embodiment;

FIG. 6 is a graph of atomic concentration along the Z direction for a diffusion of 200ps at 850 deg.C according to one embodiment;

FIG. 7 is a graph of atomic concentration along the Z direction for a diffusion of 400ps at 850 deg.C, in accordance with one embodiment;

FIG. 8 is a graph of atomic concentration along the Z direction for a diffusion of 600ps at 850 deg.C, in accordance with one embodiment;

FIG. 9 is a schematic diagram of the atomic potential at 600ps at 850 deg.C according to one embodiment;

FIG. 10 is a schematic diagram of the atomic potential at 600ps at 950 ℃ in accordance with one embodiment;

FIG. 11 is a schematic diagram of the atomic potential at 1050 deg.C for 600ps according to one embodiment;

FIG. 12 is a MSD plot of Fe atoms at different temperatures according to embodiments;

FIG. 13 is a MSD plot of Cu atoms at different temperatures according to embodiments;

FIG. 14 is a graph of Fe-Cu diffusion coefficient versus temperature for one embodiment;

FIG. 15 is a model diagram of atomic diffusion at 850 ℃ for 0ps diffusion according to the second embodiment;

FIG. 16 is a diagram of an atomic diffusion model for diffusion at 850 ℃ for 200ps according to an embodiment;

FIG. 17 is a diagram of an atomic diffusion model for diffusion at 850 ℃ for 400ps according to an embodiment;

FIG. 18 is a model diagram of atomic diffusion at 850 ℃ for 600ps diffusion according to the second embodiment;

FIG. 19 is a graph of atomic concentration along the Z direction for diffusion of 0ps at 850 deg.C for the second embodiment;

FIG. 20 is a graph of atomic concentration along the Z direction for a diffusion of 200ps at 850 deg.C for the second embodiment;

FIG. 21 is a graph of atomic concentration along the Z direction for a diffusion of 400ps at 850 deg.C according to example two;

FIG. 22 is a graph of atomic concentration along the Z direction for a diffusion of 600ps at 850 deg.C for the second embodiment;

FIG. 23 is a schematic diagram of the atomic potential at 600ps at 850 deg.C for the second embodiment;

FIG. 24 is a schematic diagram of the atomic potential at 600ps at 950 ℃ in accordance with one embodiment;

FIG. 25 is a schematic diagram of the atomic potential at 600ps at 1050 deg.C for one embodiment;

FIG. 26 is a MSD plot of Fe atoms at different temperatures according to example two;

FIG. 27 is a MSD plot of Ni atoms at different temperatures according to example two;

FIG. 28 is a graph of the diffusion coefficient of Fe-Ni versus temperature for an embodiment;

Detailed Description