Molecular dynamics based irradiation and simulation mechanical testing method for amorphous carbon thin films

Abstract

The application provides a method for irradiation and simulation mechanical test of amorphous carbon film based on molecular dynamics, and belongs to the technical field of irradiation and simulation mechanical test of amorphous carbon film, and comprises the following steps: constructing a molecular dynamics simulation model of amorphous carbon film; relaxing the obtained model through an NPT system to ensure that the model reaches a stable structure state; using a large-scale parallel simulator LAMMPS to simulate the model after relaxation under different irradiation doses to obtain irradiation simulation results; according to the model after irradiation, using the large-scale parallel simulator LAMMPS again to simulate the constant force nanoindentation of the amorphous carbon film to obtain nanoindentation simulation results; and using OVITO to respectively visualize and analyze the structure defects of the irradiation simulation results and the nanoindentation simulation results to evaluate the influence of different irradiation doses on the structure and mechanical properties of the amorphous carbon film. The application provides an effective technical means for studying the behavior of the amorphous carbon film under irradiation conditions.

Description

Technical Field

[0001] This invention relates to the field of irradiation and simulated mechanical testing technology for amorphous carbon thin films, and in particular to a method for irradiation and simulated mechanical testing of amorphous carbon thin films based on molecular dynamics. Background Technology

[0002] Nuclear energy, as a highly efficient and clean energy source, possesses unique advantages and development potential in reducing coal consumption, decreasing greenhouse gas emissions, and alleviating energy transmission pressures, playing a vital role in achieving comprehensive, coordinated, and sustainable economic development in my country. Currently, fusion reactors operate in high-flux radiation environments, and the installation and support components, remote control systems, and large heating antennas are the three major components requiring solid lubrication protection. During reactor operation, the lubrication protective film must withstand not only friction and wear from prolonged mechanical movement but also high-dose radiation, placing higher demands on the solid lubrication films coated on moving parts. Therefore, understanding and mastering the radiation damage behavior of solid lubrication films under nuclear irradiation environments and enhancing their resistance to radiation damage is of great significance for the design, safety, and stable operation of advanced nuclear energy systems.

[0003] Amorphous carbon (aC) films, a commonly used solid lubricant, have potential applications in harsh nuclear environments. They are amorphous carbon materials composed of a mixture of sp3 and sp2 hybrid carbons. The mixed bond structure gives them both the anti-friction properties of graphite and the mechanical properties of diamond. Currently, they are widely used in precision machinery, medicine, automotive, and micro / nano manufacturing. However, a deep understanding of their irradiation damage mechanisms is lacking. Comprehensive research into the formation and evolution of irradiation defects, energy transfer during irradiation, and the interactions between incident and matrix atoms is crucial for a deeper understanding of the underlying mechanisms of irradiation damage in materials. Due to limitations in time and space scales, experimentally characterizing these detailed processes presents significant challenges.

[0004] Nanoindentation is a material mechanical property characterization technique. This technique is primarily used to measure the hardness, elastic modulus, and other mechanical properties of materials, and is particularly suitable for characterizing micro-regions and thin film materials. Due to the extremely small scale of nanoindentations, existing experimental methods struggle to provide detailed and effective observation of the material deformation process induced by nanoindentation.

[0005] Molecular dynamics simulations can analyze materials on spatial scales of angstroms and time scales of picoseconds. Many researchers have used molecular dynamics simulations to study irradiation processes, but research on amorphous carbon thin films is extremely limited. While many studies have investigated nanoindentation processes, these primarily focus on constant-depth indentation simulations on flat surfaces. Irradiation causes surface bulging, making it difficult to find a reference plane for traditional constant-depth indentation.

[0006] Therefore, research on irradiation simulation of amorphous carbon and molecular dynamics simulation of constant force nanoindentation after irradiation urgently needs to be filled and improved. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a molecular dynamics-based method for irradiating and simulating the mechanical testing of amorphous carbon thin films, providing an effective technical means for studying the behavior of amorphous carbon thin films under irradiation conditions.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] A molecular dynamics-based method for irradiating and simulating the mechanical properties of amorphous carbon thin films includes the following steps:

[0010] Based on actual amorphous carbon thin film models, a molecular dynamics simulation model of amorphous carbon thin films is constructed.

[0011] The molecular dynamics simulation model of the amorphous carbon thin film was relaxed using the NPT system to ensure that the model reached a stable structural state.

[0012] The molecular dynamics simulation model of relaxed amorphous carbon thin films under different irradiation doses was simulated using the large-scale parallel simulator LAMMPS, and the irradiation simulation results were obtained.

[0013] Based on the molecular dynamics simulation model of the irradiated amorphous carbon thin film, the constant force nanoindentation simulation of the amorphous carbon thin film was performed again using the large-scale parallel simulator LAMMPS, and the nanoindentation simulation results were obtained.

[0014] The irradiation simulation results and nanoindentation simulation results were visualized and structural defect analyzed using OVITO to evaluate the effects of different irradiation doses on the structure and mechanical properties of amorphous carbon thin films.

[0015] Preferably, the molecular dynamics simulation model of the amorphous carbon thin film is an amorphous structure with a density of 3.2 g / cm³. 3 .

[0016] Preferably, the molecular dynamics simulation model of the amorphous carbon thin film is relaxed using an NPT system, including: placing the molecular dynamics simulation model of the amorphous carbon thin film in the NPT system for a 50ps relaxation process to adjust the system temperature to 300K, thereby obtaining a model with a stable structural state to ensure the accuracy and reliability of subsequent simulations.

[0017] Preferably, the molecular dynamics simulation model of the relaxed amorphous carbon thin film is simulated under different irradiation doses using the large-scale parallel simulator LAMMPS, including: in the simulation process, the incident atom is set to a carbon atom, and the incident kinetic energy of the carbon atom is 4 keV.

[0018] Preferably, in the process of visualizing and analyzing the irradiation simulation results and nanoindentation simulation results using OVITO, the analysis of the irradiation simulation results includes:

[0019] Using OVITO's analysis tools, the atomic positions on the surface of amorphous carbon thin films were statistically analyzed and the coordinate information of the atoms was extracted. Then, by comparing the changes in the height of the atoms on the surface of amorphous carbon thin films before and after irradiation, the changes in the surface roughness of amorphous carbon thin films caused by irradiation were calculated.

[0020] Using the coordination number analysis function of OVITO, the distribution of carbon atoms inside the kinetic simulation model of amorphous carbon thin films was statistically analyzed. Then, the changes in the hybridization state of carbon atoms inside the amorphous carbon thin films before and after irradiation were compared to determine the changes in the hybridization of carbon atoms inside the amorphous thin films caused by irradiation.

[0021] Using the Voronoi analysis function in OVITO, Voronoi polyhedra around each atom inside the amorphous carbon film were generated, and the types and numbers of Voronoi polyhedra were counted to determine the changes in Voronoi polyhedra during irradiation.

[0022] Preferably, in the process of visualizing and analyzing the irradiation simulation results and nanoindentation simulation results using OVITO, the analysis of the nanoindentation simulation results includes:

[0023] First, the effect of irradiation on the elastic modulus of amorphous carbon films was calculated through the elastic loading stage; then, the effect of irradiation on the hardness of amorphous carbon films was calculated through the holding load stage; finally, the changes in the elastic modulus and hardness of amorphous carbon films before and after irradiation were analyzed using OVITO to determine the effect of irradiation on the mechanical properties of amorphous carbon films.

[0024] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0025] (1) This invention enables quantitative analysis of structural changes in amorphous carbon thin films: by changing the roughness, internal atomic hybridization and Voronoi polyhedron number, the evolution of the structure of amorphous carbon thin films during irradiation is accurately reflected.

[0026] (2) The present invention also realizes the evaluation of the mechanical properties of amorphous carbon thin films: by using the change in hardness to quantify the influence of irradiation on the mechanical properties of amorphous carbon thin films, a basis for evaluating the radiation resistance of materials is provided.

[0027] (3) This invention uses LAMMPS to perform large-scale molecular dynamics simulations, which can handle complex atomic interactions, improve simulation accuracy and efficiency, and provide an effective technical means for studying the behavior of amorphous carbon thin films under irradiation conditions.

[0028] (4) This invention also enables the visualization analysis of amorphous carbon thin films: through the OVITO visualization analysis tool, complex simulation data is presented intuitively, helping researchers to understand the material behavior and performance changes more deeply. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart of the molecular dynamics-based method for irradiating and simulating the mechanical testing of amorphous carbon thin films provided by the present invention;

[0031] Figure 2 A molecular dynamics simulation model diagram of the irradiation process of amorphous carbon film provided for this invention;

[0032] Figure 3 The root mean square roughness histogram of the upper surface of the amorphous carbon film under different irradiation doses provided by the present invention;

[0033] Figure 4 The hybridization transition curves inside the amorphous carbon film under different irradiation doses provided by the present invention;

[0034] Figure 5 Line graph showing the transformation of the number of Voronoi polyhedra inside the amorphous carbon film under different irradiation doses provided by the present invention;

[0035] Figure 6 A schematic diagram of the molecular dynamics simulation model of constant force nanoindentation after irradiation of amorphous carbon film provided by the present invention;

[0036] Figure 7 This invention provides molecular dynamics simulation data of constant-force nanoindentation on amorphous carbon films subjected to different irradiation doses; wherein, Figure 7 (a) is a force-displacement curve of constant force nanoindentation. Figure 7 (b) is a bar chart showing the average indentation depth of the indenter under the same load. Figure 7 (c) is a bar chart of the average pressure of the indenter under the same load.

[0037] Figure 8 The bar chart shows the hardness variation of the amorphous carbon film under different irradiation doses provided by this invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] To make the objectives, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1

[0041] like Figure 1 As shown, this invention provides a method for irradiating and simulating the mechanical properties of amorphous carbon thin films based on molecular dynamics, comprising the following steps:

[0042] Step 100: Construct a molecular dynamics simulation model of amorphous carbon thin films based on actual amorphous carbon thin film models;

[0043] Step 200: Relax the molecular dynamics simulation model of the amorphous carbon thin film using the NPT system to ensure that the model reaches a stable structural state;

[0044] Step 300: The molecular dynamics simulation model of the relaxed amorphous carbon thin film was simulated under different irradiation doses using the large-scale parallel simulator LAMMPS to obtain the irradiation simulation results;

[0045] Step 400: Based on the molecular dynamics simulation model of the irradiated amorphous carbon film, the nanoindentation simulation of the amorphous carbon film is performed again using the large-scale parallel simulator LAMMPS to obtain the constant force nanoindentation simulation results.

[0046] Step 500: Visualize and analyze the irradiation simulation results and nanoindentation simulation results using OVITO to evaluate the effects of different irradiation doses on the structure and mechanical properties of amorphous carbon thin films.

[0047] In the above, the molecular dynamics simulation model of the amorphous carbon thin film is an amorphous structure with a density of 3.2 g / cm³. 3 Secondly, the molecular dynamics simulation model of the amorphous carbon thin film was relaxed using an NPT system. This included placing the molecular dynamics simulation model of the amorphous carbon thin film in the NPT system for a 50 ps relaxation process to adjust the system temperature to 300 K, thereby obtaining a model with a stable structural state to ensure the accuracy and reliability of subsequent simulations. Additionally, the relaxed molecular dynamics simulation model of the amorphous carbon thin film was simulated under different irradiation doses using the large-scale parallel simulator LAMMPS, including: referencing... Figure 2 In the simulation, the incident atom is set to a carbon atom, and the incident kinetic energy of the carbon atom is 4 keV.

[0048] In step 500, during the analysis of the irradiation simulation results, the unirradiated model is selected and denoted as the R0 model, such as... Figure 2 As shown, the irradiation process is as follows: The established amorphous carbon thin film model, R0, is imported. A carbon atom is then created in a 50 Å x 50 Å region above the amorphous carbon thin film and given an initial downward kinetic energy of 4 keV. The film is then incident on an NVE system, with sufficient time for cascaded collisions to allow the model to reach a stable state. After the collisions, the system temperature is controlled at 300 K using the Berendsen method, and the irradiation is repeated 300 times. Models irradiated 100, 200, and 300 times are named R100, R200, and R300, respectively, for subsequent analysis. The subsequent analysis process is as follows:

[0049] Using OVITO's analysis tools, the atomic positions on the surface of amorphous carbon thin films were statistically analyzed and their coordinate information extracted. Then, by comparing the changes in atomic heights before and after irradiation, the changes in surface roughness caused by irradiation were calculated. Figure 3 As shown, the surface roughness of the upper surface of the R0-R300 model after irradiation can be observed, thus indicating that the model surface becomes rougher as the irradiation dose increases.

[0050] Using OVITO's coordination number analysis function, the distribution of carbon atoms within the kinetic simulation model of amorphous carbon thin films was statistically analyzed. Then, the changes in the hybridization state of carbon atoms within the amorphous carbon thin films before and after irradiation were compared to determine the changes in carbon atom hybridization caused by irradiation within the amorphous thin films. (Refer to...) Figure 4As shown, the hybridization transformation of atoms after irradiation can be observed. If the distance between two atoms is less than or equal to 1.85 Å, the two atoms are considered bonded; if an atom has four bonds, it is considered sp3 hybridization; if an atom has three bonds, it is considered sp2 hybridization; and if an atom has two bonds, it is considered sp1 hybridization. Figure 4 In the results shown, the original model was dominated by sp2, accounting for about 68%-69%, and irradiation can convert sp3 into sp2 and sp1.

[0051] Using the Voronoi analysis function in OVITO, Voronoi polyhedra surrounding each atom within the amorphous carbon thin film were generated. The types and numbers of these Voronoi polyhedra were then statistically analyzed to determine the changes in Voronoi polyhedra during irradiation. (Refer to...) Figure 5 As shown, the transformation of the facet number of Voronoi polyhedra after irradiation is illustrated. The atomic arrangement of amorphous structures can be statistically analyzed using the Voronoi mosaic method. In the four models provided, Voronoi polyhedra exhibit a preferred distribution, with 15-17 faces being the most prevalent. However, as the irradiation dose increases, the proportion of 15-17 faces gradually decreases in the models, while the proportion of polyhedra with more than 20 faces (or less than 14 faces) increases, indicating a gradual weakening of the preferred distribution trend. This is also clearly evident in the Gaussian fitting results, where the abscissa of the Gaussian peak in the four models remains almost constant, but the peak value decreases with increasing irradiation dose.

[0052] Additionally, in step 500, refer to Figure 6As shown, this diagram illustrates constant-force nanoindentation. The leftmost image shows the internal layering of the model, which consists of three types of atoms: boundary atoms, isothermal layer atoms, and Newtonian layer atoms. During nanoindentation, the fixed layer atoms remain stationary, holding the model in place to support the entire system. The initial temperature of the model is chosen to be 300K. During molecular dynamics simulations, the isothermal layer is kept at a constant temperature of 300K for heat dissipation using a velocity rescaling method. The motion of the Newtonian layer atoms obeys the classical Newton's second law. A diamond indenter with a radius of 20 angstroms is positioned sufficiently far from the model below to avoid interaction between the initial indenter and the model. The logic of constant-force nanoindentation for the above content is as follows: Import the amorphous carbon thin film model to be tested, input the force required for holding the load, then create a diamond indenter with a radius of 20 angstroms in the center above the amorphous carbon thin film, and keep the fixed layer of the amorphous carbon thin film model stationary. The indenter is pressed down at a speed of 0.2 angstroms / picosecond, and the pressure is checked every 0.01 picoseconds to see if the input holding force has been reached. If not, the pressure continues to be pressed down; if it has been reached, the input holding force is applied to the indenter, holding the load for 100 picoseconds, and then the indenter is lifted up at a speed of 0.2 angstroms / picosecond to complete the unloading. The process of analyzing the nanoindentation simulation results based on the above content includes:

[0053] First, the effect of irradiation on the elastic modulus of amorphous carbon films was calculated using the elastic loading stage; then, the effect of irradiation on the hardness of amorphous carbon films was calculated using the holding load stage; finally, the changes in the elastic modulus and hardness of amorphous carbon films before and after irradiation were analyzed using OVITO to determine the impact of irradiation on the mechanical properties of amorphous carbon films. (Refer to...) Figure 7 (a) Figure 7 (b) and Figure 7 (c) It can be observed that as the irradiation dose increases, the indenter penetrates deeper into the substrate, while the indentation force remains at 0.7 μN, demonstrating the feasibility of the constant-force nanoindentation simulation method. Finally, refer to... Figure 8 It can be observed that as the irradiation dose gradually increases, the hardness of the amorphous carbon film gradually decreases, thus proving the feasibility of the method provided in this embodiment.

[0054] Therefore, compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] (1) This invention enables quantitative analysis of structural changes in amorphous carbon thin films: by changing the roughness, internal atomic hybridization and Voronoi polyhedron number, the evolution of the structure of amorphous carbon thin films during irradiation is accurately reflected.

[0056] (2) The present invention also realizes the evaluation of the mechanical properties of amorphous carbon thin films: by using the change in hardness to quantify the influence of irradiation on the mechanical properties of amorphous carbon thin films, a basis for evaluating the radiation resistance of materials is provided.

[0057] (3) This invention uses LAMMPS to perform large-scale molecular dynamics simulations, which can handle complex atomic interactions, improve simulation accuracy and efficiency, and provide an effective technical means for studying the behavior of amorphous carbon thin films under irradiation conditions.

[0058] (4) This invention also enables the visualization analysis of amorphous carbon thin films: through the OVITO visualization analysis tool, complex simulation data is presented intuitively, helping researchers to understand the material behavior and performance changes more deeply.

[0059] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for irradiating and simulating the mechanical properties of amorphous carbon thin films based on molecular dynamics, characterized in that, Includes the following steps: Based on actual amorphous carbon thin film models, a molecular dynamics simulation model of amorphous carbon thin films is constructed. The molecular dynamics simulation model of the amorphous carbon thin film was relaxed using the NPT system to ensure that the model reached a stable structural state. The molecular dynamics simulation model of relaxed amorphous carbon thin films under different irradiation doses was simulated using the large-scale parallel simulator LAMMPS. The simulation included setting the incident atom as a carbon atom with an incident kinetic energy of 4 keV to obtain the irradiation simulation results. Based on the molecular dynamics simulation model of the irradiated amorphous carbon thin film, the constant force nanoindentation simulation of the amorphous carbon thin film was performed again using the large-scale parallel simulator LAMMPS, and the nanoindentation simulation results were obtained. The irradiation simulation results and nanoindentation simulation results were visualized and structural defect analyzed using OVITO to evaluate the effects of different irradiation doses on the structure and mechanical properties of amorphous carbon thin films. The process of analyzing the irradiation simulation results includes: Using OVITO's analysis tools, the atomic positions on the surface of amorphous carbon thin films were statistically analyzed and the coordinate information of the atoms was extracted. Then, by comparing the changes in the height of the atoms on the surface of amorphous carbon thin films before and after irradiation, the changes in the surface roughness of amorphous carbon thin films caused by irradiation were calculated. Using the coordination number analysis function of OVITO, the distribution of carbon atoms inside the kinetic simulation model of amorphous carbon thin films was statistically analyzed. Then, the changes in the hybridization state of carbon atoms inside the amorphous carbon thin films before and after irradiation were compared to determine the changes in the hybridization of carbon atoms inside the amorphous thin films caused by irradiation. Using the Voronoi analysis function in OVITO, Voronoi polyhedra around each atom inside the amorphous carbon film were generated, and the types and numbers of Voronoi polyhedra were counted to determine the changes in Voronoi polyhedra during irradiation. The process of analyzing the results of nanoindentation simulation includes: First, the effect of irradiation on the elastic modulus of amorphous carbon films was calculated through the elastic loading stage; then, the effect of irradiation on the hardness of amorphous carbon films was calculated through the holding load stage; finally, the changes in the elastic modulus and hardness of amorphous carbon films before and after irradiation were analyzed using OVITO to determine the effect of irradiation on the mechanical properties of amorphous carbon films.

2. The method for irradiating and simulating the mechanical properties of amorphous carbon thin films based on molecular dynamics according to claim 1, characterized in that, The molecular dynamics simulation model of the amorphous carbon thin film shows an amorphous structure with a density of 3.2 g / cm³. 3 .

3. The method for irradiating and simulating the mechanical properties of amorphous carbon thin films based on molecular dynamics according to claim 1, characterized in that, The molecular dynamics simulation model of the amorphous carbon thin film is relaxed using an NPT system, including placing the molecular dynamics simulation model of the amorphous carbon thin film in the NPT system for a 50 ps relaxation process to adjust the system temperature to 300 K, thereby obtaining a model with a stable structural state to ensure the accuracy and reliability of subsequent simulations.

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