Method for simulating the effect of irradiation on the crack propagation process of silicon carbide

Abstract

The application provides a method for simulating the influence of irradiation on the crack propagation process of silicon carbide, which comprises the following steps: NPT relaxation is performed on a supercell of silicon carbide; a Si atom is randomly selected as a primary off-lattice atom, and the Si atom is given a kinetic energy of 10 keV, so that the Si atom collides with surrounding atoms; the collided atom continues to collide with surrounding atoms in a cascade collision process; the cascade collision process is repeated 300 times to form an irradiation structure after cascade superposition; two crack forms are designed; for each crack, firstly, NPT relaxation is performed on the system, and then uniaxial tensile strain is applied in the direction perpendicular to the plane of the crack. The influence of irradiation on the crack propagation process of silicon carbide is simulated by using LAMMPS software based on a molecular dynamics method, and it is found that the fracture form of the irradiated silicon carbide is still brittle fracture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of computational simulation of materials, and in particular to a method for simulating the influence of irradiation on the crack propagation process of silicon carbide. BACKGROUND

[0002] Due to its inherent advantages (including low activation energy, high temperature resistance, low neutron absorption cross section, and radiation resistance), SiC / SiC composite materials (CMCs, SiC Ceramic Matrix Composites) are considered as one of the excellent candidate cladding and structural materials for future nuclear fusion and fission reactors, and are applied to the prospective research of accident tolerant fuel (ATF, Accident Tolerant Fuels) cladding materials. Based on the successful development of nuclear-grade silicon carbide fibers and multi-layer structure composite cladding tubes, people have carried out ex-core performance research on SiC / SiC composite materials from multiple angles such as basic size, mechanics, thermal conductivity, air tightness, micro characterization, simulation calculation, and gradually carried out in-core irradiation verification experiments of SiC / SiC composite cladding tubes and fuel assemblies, in order to promote the early realization of the engineering application of the material.

[0003] Considering the harsh service environment inside the reactor, the changes of SiC / SiC composite materials after irradiation in mechanics, creep, endurance, thermal conductivity coefficient, etc. need to be studied in depth. Due to the long period and high cost of in-core irradiation experiments, people carry out calculation and evaluation work on the in-core service performance of SiC / SiC composite materials through simulation and theoretical calculation methods. However, the changes of SiC-based materials at atomic scale caused by neutron irradiation, the mechanism of crack initiation and its influence on the mechanical properties of the material are not clear. SUMMARY

[0004] The present application aims to at least partially solve one of the technical problems in the related art.

[0005] To this end, the present application aims to provide a method for simulating the influence of irradiation on the crack propagation process of silicon carbide. The LAMMPS software based on molecular dynamics method is used to simulate the influence of irradiation on the crack propagation process of 3C-SiC. After irradiation, the fracture form of silicon carbide is still brittle fracture. With the increase of cascade superposition times, the tensile strength of silicon carbide containing

[001] (010) cracks shows a large fluctuation, while the elongation shows a gradually increasing trend in the fluctuation process; the tensile strength of silicon carbide containing [11-2] (111) cracks gradually decreases in the fluctuation, while the elongation gradually increases in the fluctuation.

[0006] To achieve the above-mentioned purpose, the method for simulating the influence of irradiation on the crack propagation process of silicon carbide provided by the present application comprises:

[0007] NPT relaxation is performed on the supercell of 3C-SiC;

[0008] A Si atom is randomly selected as a primary knock-on atom, and a kinetic energy of 10 keV is given to the primary knock-on atom to make it collide with surrounding atoms, and the collided atom continues to collide with surrounding atoms, which is a process of cascade collision;

[0009] The process of cascade collision is repeated 300 times to form an irradiated structure after cascade superposition;

[0010] Two crack forms of

[001] (010) and [11-2] (111) are designed, and for each crack, first, NPT relaxation is performed on the system, and then uniaxial tensile strain is applied in the direction perpendicular to the plane where the crack is located.

[0011] Further, the cascade superposition process is performed on the silicon carbide material at a temperature of 573K.

[0012] Further, the entire system in the process of cascade collision is run under NVT ensemble for 11.2ps.

[0013] Further, the running period consists of three stages: running for 0.2ps at a step of 0.001fs, running for 1ps at a step of 0.01fs, and running for 10ps at a step of 1fs.

[0014] Further, the process of cascade collision adopts the Tersoff potential with zbl correction.

[0015] Further, the temperature at which the system is first relaxed for each crack is 573K.

[0016] Further, the stretching process adopts NVT ensemble, and the strain rate is 1e-4 / ps.

[0017] Further, the

[001] (010) crack propagation adopts a 3C-SiC supercell structure of 45x45x40 to simulate the crack propagation process of the (010) surface of the material after irradiation.

[0018] Further, the [11-2] (111) crack propagation adopts a 3C-SiC supercell structure of 30x20x10 to simulate the crack propagation process of the (111) surface of the material after irradiation.

[0019] Further, the crack is generated by removing atoms in the central region to form a (010) surface or a (111) surface crack after cascade superposition of the irradiated structure.

[0020] Additional aspects and advantages of the application will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following and / or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0021] The foregoing and / or additional aspects and advantages of the present application are achieved by providing a method for simulating the effect of irradiation on the crack propagation process of silicon carbide, which comprises the following steps:

[0022] Figure 1 is a flowchart of the method for simulating the effect of irradiation on the crack propagation process of silicon carbide of the present application;

[0023] Figure 2 is a stress-strain curve of two crack tensile processes of the present application;

[0024] Figure 3 is a fracture process of the crack of

[001] (010) of the present application;

[0025] Figure 4 is a fracture process of the crack of [11-2] (111) of the present application;

[0026] Figure 5 is a stress-strain curve in the crack propagation process of SiC

[001] (010) before and after irradiation of the present application;

[0027] Figure 6 is the effect of irradiation on the strength of

[001] (010) crack of the present application;

[0028] Figure 7 is the change of the microstructure of the material before and after the crack propagation of

[001] (010) at each cascade superposition number of the present application;

[0029] Figure 8 is a stress-strain curve in the crack propagation process of SiC [11-2] (111) before and after irradiation of the present application;

[0030] Figure 9 is the effect of irradiation on the strength of [11-2] (111) crack of the present application;

[0031] Figure 10 is the change of the microstructure of the material before and after the crack propagation of [11-2] (111) at each cascade superposition number of the present application. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described below in detail with reference to examples shown in the attached drawings, wherein the same or similar numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary only, and are for the purpose of explanation only, and are not to be taken as limiting of the present application. On the contrary, the embodiments of the present application include all modifications, variations, and alternatives falling within the spirit and the scope of the appended claims.

[0033] The present application simulates the irradiation and crack propagation process of 3C-SiC by using LAMMPS software. The cascade superposition process of silicon carbide material at 573K temperature is simulated, and the crack is designed after irradiation and uniaxial tension is carried out, as shown in Figure 1 The specific method process is as follows:

[0034] Step 1: NPT relaxation is carried out on the supercell of silicon carbide.

[0035] Step 2: randomly select Si atom as primary knock-on atom (PKA), give PKA 10keV kinetic energy, let it collide with surrounding atoms, and the collided atoms continue to collide with surrounding atoms, which is the cascade collision process.

[0036] In detail, the whole system runs under NVT ensemble for 11.2ps in the cascade collision process, which consists of three stages, i.e. running for 0.2ps with a step of 0.001fs, running for 1ps with a step of 0.01fs, and running for 10ps with a step of 1fs. The zbl modified Tersoff potential is used in the cascade collision process.

[0037] Step 3: repeat the cascade collision process for 300 times to form the irradiated structure after cascade superposition;

[0038] Step 4: design two crack forms of

[001] (010) and [11-2](111), for each crack, first carry out NPT relaxation of the system at a temperature of 573K. Then apply uniaxial tension strain in the direction perpendicular to the plane where the crack is located, the stretching process adopts NVT ensemble, and the strain rate is 1e-4 / ps. The interatomic potential between Si and C in the stretching process is selected as the modified Tersoff potential.

[0039] To validate the above simulation method, in some embodiments, a through crack is generated on a periodic slab. Consider

[001] (010) and [11-2] (111) cracks (crack tip direction and the plane where the crack lies). The length of the slab Lx, Ly and Lz is about 30 nm x 30 nm x 2 nm. The crack is generated by removing atoms in the center region, and the area of the removed region is 0.3Lx x rc, where rc=0.3 nm is the cutoff radius of Si-Si. To eliminate the normal stress, the initial structure is relaxed at a temperature of 0.1 K for 10,000 fs, and the temperature is controlled by velocity scaling. The time step is set to 1 fs. Then a strain increment of Δεyy=1.0 x 10-7 is applied to each MD step. During the stretching process, the length of the slab Lx and Lz is fixed, and the temperature is also controlled at 0.1 K. After the MD simulation ends, the stress component σyy in the stretching direction is obtained, and the stress-strain curve is plotted. The stress-strain curves of the

[001] (010) and [11-2] (111) crack extension processes are calculated as shown in Figure 2 . The microstructure before and after the crack is shown as Figure 3 and Figure 4 By observing the stress-strain curves during the

[001] (010) and [11-2] (111) crack extension processes, and the changes in the microstructure of the two types of crack extension processes, it is found that although the tensile strengths of the two types are not much different, the crack extension methods are very different. In terms of tensile strength, the maximum stress during crack extension is calculated to be 35.2 GPa and 36.1 GPa, respectively. In terms of crack extension method, the

[001] (010) type crack continues to extend along the crack tip direction until it breaks, while the [11-2] (111) type crack extends after a 45° deflection at the crack tip until it breaks.

[0040] It needs to be noted that the

[001] (010) and [11-2] (111) crack extensions before and after irradiation in the present application need to be detailed.

[0041] In some embodiments, the

[001] (010) crack extension before and after irradiation is as follows:

[0042] The present application designs a 45x45x40 3C-SiC supercell structure to simulate the crack propagation process on the (010) surface of the material after irradiation. The whole system adopts a periodic boundary structure, containing a total of 324000 atoms, and the lengths of Lx, Ly, and Lz in the three directions are 19.6 nm, 19.6 nm, and 8.7 nm, respectively. The supercell is simulated for the irradiation cascade superposition process at 573K. The cascade superposition process is composed of multiple cascade collision processes. A Si atom is randomly selected as a primary knock-on atom (PKA) in the cascade collision process, and the PKA is given a kinetic energy of 10 keV. The PKA then collides with the surrounding atoms, and the cascade collision time is 11.2 ps. The cascade collision process adopts a canonical (NVT) ensemble, that is, the number of atoms, volume, and temperature of the system remain unchanged. After 300 times of cascade collision process superposition, the irradiation damage structure is obtained. The irradiated structure generates a crack on the (010) surface by removing atoms in the central region, and the area of the removed region is 0.3Lx x rc, where rc=0.3 nm. The present application slices the irradiation damage structure in the Lz (

[001] ) direction, and selects the left and right slices to simulate the crack propagation process. The present application applies a uniaxial tensile strain in the

[010] direction, and the strain rate is 1e-4 / ps. The stress-strain curves of SiC materials before and after irradiation and after multiple PKA cascade collisions are as shown in From the stress-strain curve, it can be seen that the failure of SiC after irradiation is always in a brittle fracture mode. Figure 5

[0043] It can be seen that after multiple cascade superposition, the present application simulates the crack propagation process under different numbers of cascade collisions, and obtains the change of tensile strength and elongation with the number of cascade collisions as shown in Figure 6 From the figure, it can be seen that after about 50 times of cascade superposition, the strength of the crack-containing silicon carbide appears a large fluctuation, and the elongation shows a gradually increasing trend in the fluctuation process. By observing the microstructure of the crack propagation process before and after irradiation, the present application finds that the form of crack propagation is still cleavage fracture. The increase in elongation before fracture indicates that the plasticity of the silicon carbide material increases. The present application then analyzes the change of the microstructure of the material under different numbers of cascade superposition. The microstructure before and after crack propagation and the stress distribution of the atoms are as shown in Figure 7

[0044] In some embodiments, the [11-2] (111) crack propagation before and after irradiation is as follows:

[0045] ​​The 3C-SiC supercell structure of 30x20x10 is designed with [-110],

[111] and [11-2] as the base vector to simulate the crack propagation process on the (111) surface of the material after irradiation. The whole system adopts a periodic boundary structure and contains 288000 atoms. The lengths of Lx, Ly and Lz in the three directions are 18.5 nm, 15.1 nm and 10.7 nm respectively. The simulation of the irradiation cascade superposition process is consistent with the above method. The irradiation damage structure after 300 times of cascade superposition at 573 K is finally generated. The crack on the (111) surface is generated by removing atoms in the central region, and the area of the removed region is 0.3Lx x rc, where rc=0.3 nm. The irradiation damage structure is sliced in the Lz ([11-2]) direction, and the left and right slices are simulated for crack propagation. The uniaxial tensile strain is applied in the

[111] direction, and the strain rate is 1e-4 / ps. The stress-strain curves of SiC materials without irradiation and after multiple PKA cascade collisions are as shown in Figure 8 From the stress-strain curve, it can be seen that the failure of SiC after irradiation is in the form of brittle fracture.

[0046] After multiple cascade superposition processes, the crack propagation process under different cascade collision times is simulated, and the changes of tensile strength and elongation with the number of cascade collisions are as shown in Figure 9 With the increase of the number of cascade superposition, the tensile strength of the crack-containing silicon carbide gradually decreases in the fluctuation, and the elongation gradually increases in the fluctuation. The changes of the microstructure of the material under different cascade superposition times are analyzed. The microstructure before and after crack propagation and the stress distribution on the atoms are as shown in Figure 10 From the figure, it can be seen that stress concentration phenomenon appears near the crack tip, and the crack usually expands along the direction of maximum stress, and the stress is released after the crack propagation.

[0047] By observing the change of microstructure, it is found that there is stress concentration phenomenon before the crack propagation. With the increase of irradiation dose, the tensile strength of silicon carbide containing

[001] (010) cracks fluctuates greatly, and the elongation increases; the tensile strength of silicon carbide containing [11-2] (111) cracks decreases, and the elongation increases. The tensile strength reflects the stress change of the overall structure, and the elongation reflects the stress change of the local region atoms. Before irradiation, the tensile strength of

[001] (010) cracks and [11-2] (111) cracks is not much different. The change of tensile strength after irradiation should be consistent with the change of the strength of the structure without cracks, that is, it decreases with the increase of the number of cascade superposition. When cracks appear in the material, the uncertainty caused by irradiation defects increases because silicon carbide is a brittle material, so the tensile strength fluctuates greatly. In addition, because the number of internal defects of SiC increases after irradiation, the deformation of the local region increases during the tensile process, and the stress that the atoms can withstand also increases, so the elongation increases. The increase of elongation of the two cracks after irradiation indicates that the plasticity of the crack tip increases.

[0048] In summary, the present application simulates the effect of irradiation on the crack propagation process of 3C-SiC by using molecular dynamics method. The present application simulates the cascade collision of silicon carbide after irradiation and the cascade superposition process formed by multiple cascade collisions, and designs cracks in the structure before and after irradiation and uniaxial tension. The present application designs two crack forms of

[001] (010) and [11-2] (111). It is found that the cracking form of silicon carbide before and after irradiation is brittle fracture. With the increase of the number of cascade superposition, the tensile strength of silicon carbide containing

[001] (010) cracks fluctuates greatly, while the elongation gradually increases in the fluctuation process; the tensile strength of silicon carbide containing [11-2] (111) cracks gradually decreases in the fluctuation, while the elongation gradually increases in the fluctuation. The present application observes the change of microstructure of crack propagation process before and after irradiation, and finds that the defects of the system increase after irradiation, the local deformation increases, and the stress that the atoms can withstand also increases.

[0049] It should be noted that in the description of the present application, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance. In addition, in the description of the present application, the meaning of "multiple" is two or more, unless otherwise specified.

[0050] Any procedural or methodological descriptions in flow charts or otherwise described herein can be understood to represent modules, segments, or portions of code that include executable instructions for implementing the logic functions or procedures described, and the scope of preferred embodiments of the present application includes additional implementations in which the functions can be performed in an order different from that shown or discussed, including substantially simultaneously, or in reverse order, as will be understood by those having ordinary skill in the art to which embodiments of the present application pertain.

[0051] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in an appropriate manner.

[0052] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary, and are not to be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements, and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method of simulating the effect of irradiation on the crack growth process in silicon carbide, characterized in that, Comprising: NPT relaxation of the 3C-SiC supercell; Randomly select a Si atom as the primary knock-on atom, give the primary knock-on atom a kinetic energy of 10 keV, let it collide with the surrounding atoms, and the collided atoms continue to collide with the surrounding atoms, which is the process of cascade collision; Repeat the cascade collision process 300 times to form the irradiated structure after cascade superposition; Design two crack forms [001](010) and [11-2](111), for each crack, first relax the system by NPT, then apply uniaxial tensile strain in the direction perpendicular to the plane where the crack is located.

2. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1, wherein, The cascade superposition process of the 3C-SiC material is carried out at a temperature of 573 K.

3. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 2, wherein, The entire system runs under NVT ensemble during the cascade collision process for 11.2 ps.

4. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 3, wherein, The running period consists of three stages: running for 0.2 ps with a step size of 0.001 fs, running for 1 ps with a step size of 0.01 fs, and running for 10 ps with a step size of 1 fs.

5. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1, wherein, The cascade collision process uses the zbl modified Tersoff potential.

6. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1, wherein, The temperature of the system relaxation by NPT for each crack is 573 K.

7. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1 wherein, The stretching process uses NVT ensemble, and the strain rate is 1e-4 / ps.

8. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1, wherein, The [001](010) crack propagation uses a 3C-SiC supercell structure of 45×45×40 to simulate the crack propagation process of the (010) surface of the material after irradiation.

9. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1 wherein, The [11-2](111) crack propagation uses a 3C-SiC supercell structure of 30×20×10 to simulate the crack propagation process of the (111) surface of the material after irradiation.

10. The method of simulating the effect of irradiation on the crack growth process in silicon carbide of claim 1 wherein, The crack is generated by removing atoms in the central region to form a (010) surface or a (111) surface crack after cascade superposition of the irradiated structure.

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