High-entropy alloy stacking fault energy prediction method based on atom preferential occupation

Abstract

The invention relates to a high-entropy alloy stacking fault energy prediction method based on atom preferred occupancy, which comprises the following steps: firstly, calculating the occupancy fraction (SOFs) of high-entropy alloy atoms on sublattices, and constructing an atom occupancy ordered structure model of a high-entropy alloy according to the structure information; carrying out structure optimization and section cutting on the built unit cell model, shearing the cut (1 < 1 >) surface, and carrying out cell expansion and vacuum layer translation adding operation by increasing the number of atomic layers, so as to build a slip plane structure model without fault generation; secondly, constructing a structure model of each fault slip plane through translation; finally, the total energy of the high-entropy alloy is calculated based on the density function theory, and then the stacking fault energy of the high-entropy alloy is predicted. According to the method, the atom distribution structure model for predicting the fault energy of the high-entropy alloy can be reasonably constructed, and then the fault energy of the high-entropy alloy can be accurately calculated.

Description

Technical Field

[0001] The invention relates to the technical field of alloy design, and in particular to a method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy. Background Art

[0002] High entropy alloy (HEAs) is a new alloy design concept. It is an alloy composed of three or more metal elements with equimolar or nearly equimolar components. Its phase structure is relatively simple. The main phase structure is FCC, BCC or HCP solid solution. Some systems also contain a small amount of other alloy phases. Some scholars also call high entropy alloys with three main elements medium entropy alloys. More scholars are increasingly inclined to use multi-main element alloys or alloys with complex components to express this field. From one aspect, it also shows that high entropy alloys are a new field that is constantly being recognized and deepened. As a new concept, in order to respect the first creation, this application uses high entropy alloys to refer to this complex multi-main element alloy. There are many high entropy alloy systems and a large space for alloy components. Many high entropy alloys have one or more unique physical, mechanical or chemical properties, such as high strength, high corrosion resistance, high temperature stability, good plasticity or catalytic activity. High entropy alloys have opened up a new field of metal material research, and even led to the research and development of high entropy ceramics and high entropy optoelectronic functional materials. The research, development and application space is unlimited, so it has attracted widespread attention and research in the field of materials science. However, due to the huge composition space, the relationship between "composition-heat treatment process-microstructure-performance" of high entropy alloys is intricate, so it is necessary to conduct systematic and in-depth exploration of high entropy alloys with different alloy compositions. In the era of rapid development of AI for Science, predictions based on reasonable theoretical models are particularly needed to accelerate the research and development of such emerging materials.

[0003] Generalized Stacking Fault Energy (GSFE) refers to the total energy difference between a crystal material with complete stacking faults and the original structure without stacking faults per unit area along a certain crystal direction. It is an important physical quantity used to describe the plastic deformation mechanism of crystal materials and is closely related to the mechanical properties of the FCC metal deformation mechanism. The changes at different stacking fault planes are also different. Although the values ​​of intrinsic stacking fault energy (ISFE), extrinsic fault energy (ESFE), unstable stacking fault energy (USFE) and unstable twinning energy (UTE) in the generalized stacking fault energy can be measured by high-resolution transmission electron microscopy TEM or XRD, due to the complexity of experimental technology and difficulty in analysis, it is a feasible way to accurately predict the stacking fault energy by building a theoretical model and then compare different materials. The GSFE of FCC high entropy alloys is closely related to the alloy composition and microstructure. Tian et al. found that high SFE (>45mJ / m 2 ) leads to perfect dislocation sliding and shear banding in the SFE range of 20-40 mJ / m 2 The TWIP mechanism is obvious in the steel, and the low SFE induces martensitic transformation, showing the transformation induced plasticity effect (TRIP). Hyun Seok Oh et al. showed that the negative intrinsic stacking fault energy and the presence of atomic and nanoscale barriers in Co-rich FCC_CoCrNi are essential for promoting fault plasticity and suppressing deformation-induced transformation plasticity. By analyzing the generalized stacking fault energy image, the dislocation slip, twinning tendency and martensitic transformation of FCC metals can be predicted.

[0004] On the other hand, it is well known that in order to obtain accurate calculation results, it is necessary to reasonably construct a calculation model for the stacking fault energy of high entropy alloys. A lot of research has been done on the first-principles calculation of the stacking fault energy of high entropy alloys. Ding Jun et al. theoretically calculated the stacking fault energy of FCC_CoCrNi high entropy alloys and found that the chemical short-range order phenomenon affects the stacking fault energy of this system, and the stacking fault energy can be regulated by the atomic position. However, all current calculation models ignore the actual atomic occupancy ordering behavior in high entropy alloys. The structural model of random atomic distribution used by predecessors leads to inaccurate calculation results of stacking fault energy, which may have a certain impact on the derivation results of dislocation slip and twinning tendency. Wu Jian et al. found that the stacking fault energy of different clusters is different. For example, the shear strain generated by the CoCr cluster is the highest and the unstable stacking fault energy is the lowest. In high-entropy alloys, due to the differences in the types of constituent atoms and the differences between the sublattice structures, alloying elements inevitably have preferential occupancy (i.e., occupancy preference), that is, it is not a completely random structure. There are strong or weak short-range order and long-range order behaviors in high-entropy alloys, which depends on the specific high-entropy alloy system and heat treatment process conditions. In an academic paper published in 2022 by Wu Bo et al. on the reasonable model and prediction method of atomic distribution in high-entropy alloys, the occupancy preference of atoms in high-entropy alloys was elaborated in detail. For example, in FCC_CoCrFeNi high-entropy alloys, Ni atoms only occupy the 1a sublattice (vertex position), while Co, Cr and Fe atoms mainly occupy the 3c sublattice (face-centered position). Previous first-principles calculation models for stacking fault energy of high-entropy alloys, whether CPA modeling or SQS modeling methods, all assumed that alloy atoms were randomly dissolved, which is unreasonable and the prediction results are inaccurate. Therefore, the construction of the structural model required for the calculation of stacking fault energy of high-entropy alloys must take into account the actual atomic preferential occupation behavior (i.e., the tendency of site ordering) in high-entropy alloys. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting the stacking fault energy of high entropy alloys based on atomic preferential occupancy, which is conducive to rationally constructing an atomic distribution structure model for predicting the stacking fault energy of high entropy alloys, and then accurately calculating the stacking fault energy of high entropy alloys.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy, comprising the following steps:

[0007] Step S1: Calculate the site occupation fraction (SOFs) of the high entropy alloy atoms on the sublattice according to the crystallographic structure information of the high entropy alloy and the thermodynamic principle of the alloy;

[0008] Step S2: Based on the prototype structure of the alloy phase, a supercell is constructed using a first-principles calculation toolkit, and based on the occupancy fraction calculated in step S1, various types of atoms in the high-entropy alloy are randomly distributed on various types of sublattices according to the occupancy fraction according to the sublattice type, and then various sublattices are nested to form an overall high-entropy alloy structure, and a high-entropy alloy occupancy ordered structure model is constructed to obtain a model file POSCAR;

[0009] Step S3: Based on the obtained high entropy alloy site-ordered structure model file POSCAR, the volume of the crystal structure is first optimized through the VASP calculation software package; on this basis, the volume, shape and atomic position are globally optimized to obtain the highest total energy and most stable high entropy alloy site-ordered structure model;

[0010] Step S4: cutting the high entropy alloy site-ordered structure model after structural optimization, transforming the coordinate system in the specified direction, and adding a vacuum layer of set thickness to obtain the slip plane structure model when no stacking fault occurs in the stacking fault energy calculation; calculating by VASP software package to obtain the total energy E0 of the high entropy alloy slip plane structure model when no stacking fault occurs in the equilibrium state;

[0011] Step S5: according to the set shearing route, a partial atomic layer of the slip plane structure model without stacking fault is translated to obtain a stacking fault slip plane structure model;

[0012] Step S6: After constructing the stacking fault slip plane structure model, the slip plane (111) of the model is fixed, and its atoms are allowed to relax freely in the

[111] direction. The total energy E of the high entropy alloy corresponding to the stacking fault in the equilibrium state is calculated by the VASP software package. d ;

[0013] Step S7: Total energy E of the slip surface structure model after stacking fault occurs d The difference between the total energy E0 of the slip plane structure model without stacking fault and the ratio of the stacking fault area A is the required stacking fault energy γ d ;

[0014] Step S8: Calculate the stacking fault energy on different shear paths, and then draw a generalized stacking fault energy image with the unit length of the Burgers vector displaced in the [11-2] slip direction as the abscissa and the stacking fault energy as the ordinate;

[0015] Step S9: predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

[0016] Furthermore, for the site-ordered structural models of high entropy alloys with different physical phase structures, including high entropy alloys with FCC, BCC and HCP structures, the modeling steps and calculation prediction steps of the structural models required for stacking fault energy prediction are the same.

[0017] Furthermore, for the FCC_CoCrNi high entropy alloy, a double sublattice model of the L12 structure with AuCu3 as the prototype is established to characterize the atomic distribution model of the high entropy alloy, and then the structural model required for stacking fault energy prediction is established to calculate and predict the stacking fault energy.

[0018] Further, for FCC_CoCrNi high entropy alloy, the step S2 is specifically:

[0019] The unit cell of FCC_CoCrNi high entropy alloy is based on the ordered face-centered cubic FCC_L1 2— AuCu3 prototype structure, build 2×2×2 supercell, distribute the occupancy configuration of high entropy alloy atoms based on the occupancy fraction, and obtain the high entropy alloy occupancy ordered structure model containing 32 atoms;

[0020] The step S3 is specifically as follows:

[0021] The first-principles calculation software package VASP based on density functional theory was used to optimize the high-entropy alloy site-ordered structural model in steps. The K-space point grid was selected as 5×5×5. The volume relaxation was performed first. On this basis, the volume, shape and atomic position were relaxed at the same time to obtain the high-entropy alloy site-ordered structural model data after crystal structure optimization, that is, the state with the lowest total energy and the most stable crystal structure.

[0022] Furthermore, the step S4 is specifically as follows:

[0023] Materials Studio and VESTA crystal structure visualization software were used together to section the FCC_CoCrNi high entropy alloy site-ordered structure model after crystal structure optimization, and the slip plane (111) was selected. The (111) plane after sectioning was sheared and the number of atomic layers was increased to establish a slip plane structure model with 8 atoms per layer and a total of 9 atomic layers without stacking faults. A high vacuum layer eliminates the effect of structural mirroring; the supercell size and vacuum layer height of the structural model required for stacking fault energy prediction are determined in combination with the available computing resources. Because stacking fault energy calculation involves a large amount of calculation, it is necessary to ensure a balance between calculation accuracy and efficiency.

[0024] Furthermore, the step S5 is specifically as follows:

[0025] Step S51: fix the 1st to 6th atomic layers of the slip plane structure model without stacking fault, apply shear stress to the 7th to 9th atomic layers in the [11-2] direction, and move them by a unit Burgers vector length This displacement process is divided into 10 small sections, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each section;

[0026] Step S52: fix the 1st to 7th atomic layers of the slip surface structure model after the unit Burgers vector is moved, and apply shear stress to the 8th to 9th atomic layers in the [11-2] direction to move the unit Burgers vector. Vector length, this displacement process is divided into 10 small segments, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each segment;

[0027] Furthermore, the step S6 is specifically as follows:

[0028] When calculating the total energy of each slip plane structure model, the x-axis and y-axis of the atomic coordinates of the slip plane structure model are fixed, and the atoms are relaxed along the z-axis, i.e., the

[111] direction, to obtain the total energy of the slip plane structure model after the stacking fault occurs in the equilibrium state, and then the total energy of the remaining slip plane structure models is calculated respectively.

[0029] Furthermore, the step S7 is specifically as follows:

[0030]

[0031] Where E0 is the total energy of a perfect crystal structure, E d is the total energy of the crystal structure containing defects, A is the total defect area, γ d is the generalized stacking fault energy.

[0032] Furthermore, the step S8 is specifically as follows:

[0033] After calculating the stacking fault energy on different shear paths, the generalized stacking fault energy image is plotted with the unit length of the Burgers vector displaced in the [11-2] direction as the horizontal coordinate and the stacking fault energy as the vertical coordinate.

[0034] Furthermore, the step S9 is specifically as follows:

[0035] The unstable stacking fault energy γ obtained according to the prediction usf , intrinsic stacking fault energy γ isf , unstable twin energy γ utf and extrinsic stacking fault energy γ esf size, and further predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

[0036] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides a method for predicting stacking fault energy of high entropy alloys based on preferential atomic occupancy. Different from the quasi-random model with unreasonable assumptions of the SQS and CPA methods, the present invention takes into account the actual occupancy ordering behavior of atoms on the sublattice, and calculates the precise occupancy fraction based on the thermodynamic principles of alloys, thereby rationally distributing alloy atoms in the high entropy alloy, further constructing the high entropy alloy structure required for stacking fault energy prediction, and finally accurately calculating the stacking fault energy of the high entropy alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 1 is a schematic diagram of constructing POSCAR of a site-ordered 2×2×2 supercell of a FCC_CoCrNi high entropy alloy in an embodiment of the present invention;

[0038] Figure 2 In the embodiment of the present invention, the FCC_CoCrNi high entropy alloy supercell is cut along the (111) plane, and a new spatial rectangular coordinate system is established with [11-2], [1-10] and

[111] directions as new x-axis, y-axis and z-axis directions, and further shearing operation is performed to increase the number of atomic layers, and then adding After the vacuum layer, a slip plane structure model with 9 layers, 8 atoms in each layer, and a total of 72 atoms without stacking faults was obtained;

[0039] Figure 3 is a schematic diagram of a visualization process of establishing a structural model required for prediction of different stacking fault energies in an embodiment of the present invention;

[0040] Figure 4 It is the generalized stacking fault energy (GSFE) image of the FCC_CoCrNi high entropy alloy in the embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0042] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0043] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] This embodiment provides a method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy, comprising the following steps:

[0045] Step S1: Calculate the site occupation fraction (SOFs) of the high entropy alloy atoms on the sublattice according to the crystallographic structure information of the high entropy alloy and the thermodynamic principle of the alloy;

[0046] Step S2: Based on the prototype structure of the alloy phase, a supercell is constructed using a first-principles calculation toolkit, and based on the occupancy fraction calculated in step S1, various types of atoms in the high-entropy alloy are randomly distributed on various types of sublattices according to the occupancy fraction according to the sublattice type, and then various sublattices are nested to form an overall high-entropy alloy structure, and a high-entropy alloy occupancy ordered structure model is constructed to obtain a model file POSCAR;

[0047] Step S3: Based on the obtained high entropy alloy site-ordered structure model file POSCAR, the volume of the crystal structure is first optimized through the VASP calculation software package; on this basis, the volume, shape and atomic position are globally optimized to obtain the highest total energy and most stable high entropy alloy site-ordered structure model;

[0048] Step S4: cutting the high entropy alloy site-ordered structure model after structural optimization, transforming the coordinate system in the specified direction, and adding a vacuum layer of set thickness to obtain the slip plane structure model when no stacking fault occurs in the stacking fault energy calculation; calculating by VASP software package to obtain the total energy E0 of the high entropy alloy slip plane structure model when no stacking fault occurs in the equilibrium state;

[0049] Step S5: according to the set shearing route, a partial atomic layer of the slip plane structure model without stacking fault is translated to obtain a stacking fault slip plane structure model;

[0050] Step S6: After constructing the stacking fault slip plane structure model, the slip plane (111) of the model is fixed, and its atoms are allowed to relax freely in the

[111] direction. The total energy E of the high entropy alloy corresponding to the stacking fault in the equilibrium state is calculated by the VASP software package. d ;

[0051] Step S7: Total energy E of the slip surface structure model after stacking fault occurs d The difference between the total energy E0 of the slip plane structure model without stacking fault and the ratio of the stacking fault area A is the required stacking fault energy γ d ;

[0052] Step S8: Calculate the stacking fault energy on different shear paths, and then draw a generalized stacking fault energy image with the unit length of the Burgers vector displaced in the [11-2] slip direction as the abscissa and the stacking fault energy as the ordinate;

[0053] Step S9: predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

[0054] The modeling steps and calculation prediction steps of the structural model required for stacking fault energy prediction of high entropy alloys with different phase structures, such as FCC, BCC and HCP structures, are similar. In this embodiment, FCC_CoCrNi high entropy alloy is taken as an example to establish a double sublattice model of L12 structure with AuCu3 as the prototype to characterize the atomic distribution model of high entropy alloy, and then establish the structural model required for stacking fault energy prediction, and calculate and predict the stacking fault energy.

[0055] This embodiment takes FCC_CoCrNi high entropy alloy as an example to calculate the occupancy fraction under thermodynamic equilibrium at different heat treatment temperatures. The occupancy fraction data corresponding to the heat treatment temperature of concern to the researcher is selected to build a high entropy alloy atomic distribution model. Subsequent calculations simulate structural relaxation, build the structural model required for stacking fault energy prediction, and calculate the predicted stacking fault energy, which is equivalent to the high entropy alloy being heat treated at a specified temperature to reach equilibrium, and then the structure at high temperature is quenched to a low temperature, retaining its high temperature atomic configuration. Therefore, this embodiment performs atomic occupancy ordering modeling based on the occupancy fraction at a certain high temperature, and obtains the FCC_CoCrNi high entropy alloy occupancy ordering structural model and corresponding stacking fault energy data.

[0056] The present invention takes FCC_CoCrNi high entropy alloy as an example. In this embodiment, the step S2 is specifically as follows:

[0057] The unit cell of FCC_CoCrNi high entropy alloy is based on the ordered face-centered cubic FCC_L1 2— AuCu3 prototype structure, building a 2×2×2 supercell, and distributing the occupancy configuration of high entropy alloy atoms based on the occupancy fraction to obtain a high entropy alloy site-ordered structure model containing 32 atoms.

[0058] In this embodiment, step S3 is specifically as follows:

[0059] The first-principles calculation software package VASP based on density functional theory was used to optimize the high-entropy alloy site-ordered structural model in steps (also known as relaxation). The K-space point grid was selected as 5×5×5, and volume relaxation was performed first (i.e., only volume optimization, the optimization mode ISIF=7 in the INCAR file, the maximum number of ion relaxation steps NSW=10, and the energy convergence accuracy was set to EDIFF=1E-5eV). On this basis, the volume, shape and atomic position were relaxed at the same time (i.e., global optimization, ISIF=3, NSW=20, EDIFF=1E-5eV in the INCAR file) to obtain the high-entropy alloy site-ordered structural model data after crystal structure optimization, that is, the state with the lowest total energy and the most stable crystal structure.

[0060] In this embodiment, step S4 is specifically as follows:

[0061] Materials Studio and VESTA crystal structure visualization software were used together to section the FCC_CoCrNi high entropy alloy site-ordered structure model after crystal structure optimization, and the slip plane (111) was selected. The (111) plane after sectioning was sheared and the number of atomic layers was increased to establish a slip plane structure model with 8 atoms per layer and a total of 9 atomic layers without stacking faults. The vacuum layer with a high height eliminates the effect of the structural mirror image. In theory, the vacuum layer is infinite, but it leads to infinite computational effort and cannot be calculated. The supercell size and vacuum layer height of the structural model required for stacking fault energy prediction are determined in combination with the available computing resources. Because the stacking fault energy calculation involves a large amount of computation, it is necessary to ensure a balance between computational accuracy and efficiency.

[0062] In this embodiment, step S5 is specifically as follows:

[0063] Step S51: fix the 1st to 6th atomic layers of the slip plane structure model without stacking fault, apply shear stress to the 7th to 9th atomic layers in the [11-2] direction, and move them by a unit Burgers vector length This displacement process is divided into 10 small sections, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each section;

[0064] Step S52: fix the 1st to 7th atomic layers of the slip surface structure model after the unit Burgers vector is moved, and apply shear stress to the 8th to 9th atomic layers in the [1 1 -2] direction to move the unit Burgers vector. Vector length, this displacement process is divided into 10 small segments, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each segment;

[0065] Step S51 and step S52 are both obtained by a one-click command of the script program.

[0066] In this embodiment, the self-developed script program one-key command processing program script Script-to-Creat-HEAs-SFE-model.py is as follows.

[0067]

[0068]

[0069] In this embodiment, step S6 is specifically as follows:

[0070] When calculating the total energy of each slip plane structure model, the x-axis and y-axis of the atomic coordinates of the slip plane structure model are fixed, and the atoms are relaxed along the z-axis, i.e., the

[111] direction, to obtain the total energy of the slip plane structure model after the stacking fault occurs in the equilibrium state, and then the total energy of the remaining slip plane structure models is calculated respectively.

[0071] In this embodiment, step S7 is specifically as follows:

[0072]

[0073] Where E0 is the total energy of a perfect crystal structure, E d is the total energy of the crystal structure containing defects, A is the total defect area, γ d is the generalized stacking fault energy.

[0074] In this embodiment, step S8 is specifically as follows:

[0075] After calculating the stacking fault energy on different shear paths, the generalized stacking fault energy image is plotted with the unit length of the Burgers vector displaced in the [11-2] direction as the horizontal coordinate and the stacking fault energy as the vertical coordinate.

[0076] In this embodiment, step S9 is specifically as follows:

[0077] The unstable stacking fault energy γ obtained according to the prediction usf , intrinsic stacking fault energy γ isf , unstable twin energy γ utf and extrinsic stacking fault energy γ esf The size can be further used to predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

[0078] The generalized stacking fault slip plane structure model constructed in this embodiment surpasses the completely disordered random model structure that is commonly used in academia but is not reasonable. Because the patent of this invention takes into account the ordering of the actual atomic occupancy, it can more reasonably and accurately reflect the influence of the long-range and short-range order of atomic occupancy on the stacking fault energy of the system.

[0079] The implementation of this embodiment is further described in detail below in conjunction with the accompanying drawings.

[0080] This embodiment takes FCC_CoCrNi high entropy alloy as an example to provide a method for making and calculating a structural model required for stacking fault energy prediction of a site-occupied ordered high entropy alloy, including the following specific steps:

[0081] Step S1: First, according to the alloy thermodynamic principles and crystallographic structure information, based on the established end group thermodynamic database, the site occupation fractions (SOFs) of different types of atoms in the FCC sublattice under different heat treatment conditions are obtained by Thermo-Calc or Pandat.

[0082] Step S2: Based on computing resources, a supercell of appropriate size is constructed for the L12 prototype structure AuCu3 of the ordered FCC. Further, based on the predicted site occupancy fractions (SOFs), the atoms are randomly distributed on the sublattice according to the site occupancy fractions, and then the sublattices are nested to form the overall high entropy alloy structure. A high entropy alloy site occupancy ordering structure model is constructed; the supercell size here is 2×2×2, with a total of 32 atoms, such as Figure 1 shown.

[0083] Step S3: The crystal structure is optimized (also called relaxation, i.e., relax) in steps by using the first-principles calculation software package VASP based on density functional theory. First, the volume is relaxed (the optimization mode ISIF in the INCAR file is ISIF=7, the maximum number of ion relaxation steps NSW=10, and the energy convergence accuracy is set to EDIFF=1E-5eV). On this basis, the volume, shape, and atomic position are relaxed simultaneously (ISIF=3, NSW=20, EDIFF=1E-5eV in the INCAR file). The high entropy alloy site-ordered structure model after crystal structure optimization is obtained. Slight lattice distortion occurs, which can be ignored. Therefore, the high entropy alloy is still regarded as a face-centered cubic structure with a lattice constant of a.

[0084] Step S4: The optimized FCC_CoCrNi high entropy alloy site-ordered structure model is cut along the (111) plane of the original coordinate axis through the joint use of Materials Studio and VESTA crystal structure visualization software, and the directions of the x, y and z axes are redefined as [11-2], [1-10] and

[111] , respectively, to establish a new spatial rectangular coordinate system atomic distribution model as shown in FIG. Figure 2 As shown in (a); further shearing operation, increasing the number of atomic layers, and then adding The vacuum layer is set to obtain a slip plane structure model without stacking faults. The number of atomic layers in the new crystal structure is set to 9, with 8 atoms in each layer, a total of 72 atoms, and the size of the vacuum layer is set to like Figure 2 As shown in (b).

[0085] Step S5: As we all know, the FCC unit cell has three different stacking orders on the (111) crystal plane, which are marked as ABC, such as Figure 3 As shown. The arrangement of the 9 layers of atoms in the FCC unit cell on the (111) plane is ABCABCABC. First, the 1st to 6th atomic layers are fixed, and the 7th to 9th atomic layers are subjected to shear stress in the [11-2] direction. The unstable stacking fault (USF) energy slip surface structure model was established, and the arrangement of the atomic layers became BCA|ABCABC. Based on the established unstable stacking fault (USF) energy slip surface structure model, the same method was used to continue to apply shear stress to the 7th to 9th atomic layers and move them in the direction of [11-2]. The intrinsic stacking fault (ISF) energy slip plane structure model is obtained, and the atomic layer arrangement at this time becomes CAB|ABCABC; further, based on the established intrinsic stacking fault (ISF) energy slip plane structure model, the 1st to 7th atomic layers are fixed, and the 8th to 9th atomic layers are subjected to shear stress in the [11-2] direction in the same way, and the atomic layers are moved. The unstable twin (UTF) energy slip surface structure model is obtained; finally, based on the established unstable twin (UTF) energy slip surface structure model, the 1st to 7th atomic layers are fixed, and the 8th to 9th atomic layers continue to be applied with shear stress in the same way, moving in the direction of 11-2]. The extrinsic stacking fault (ESF) energy slip plane structure model is obtained, and the atomic layer arrangement at this time is BC|B|ABCABC.

[0086] Figure 3 Schematic diagram of the visualization process of the structural model required for the prediction of different stacking fault energies in this embodiment, wherein (a) is the intrinsic stacking fault structure and (b) is the extrinsic stacking fault structure. Figure 3The projection diagram of the stacking fault slip plane structure model along the [1-10] direction is shown. This process per unit length is divided into 10 steps, and a crystal structure file POSCAR is created for calculation.

[0087] Step S6: Use the VASP first-principle calculation software package to calculate the total energy of each high entropy alloy structure model. First, calculate the total energy E0 of the slip surface structure model when no stacking fault occurs, and then calculate the total energy E0 of the stacking fault slip surface structure model (i.e., the high entropy alloy after a certain shear deformation). d .

[0088] Step S7: The total energy E of each stacking fault slip surface structure model d The difference between the total energy E0 of the slip surface structure model when no stacking fault occurs and the ratio of the total energy E0 to the stacking fault area A is the required stacking fault energy γ. d The classic formula for calculating stacking fault energy is as shown in the above equation (1);

[0089] Step S8: After calculating the stacking fault energy on different shear paths, the generalized stacking fault energy image is plotted with the unit length of the Burgers vector displaced in the [11-2] direction as the abscissa and the stacking fault energy as the ordinate, as shown in Figure 4 In this FCC_CoCrNi high entropy alloy embodiment, the unstable stacking fault energy γ usf and intrinsic stacking fault energy γ isf The values ​​are: 307.19mJ / m 2 and -84.51mJ / m 2 Different from the irrational modeling methods of random distribution adopted by EMTO-CPA and SQS, the present invention constructs the structural model required for stacking fault energy prediction based on the FCC_CoCrNi high entropy alloy structure with actual site ordering behavior.

[0090] Step S9: According to the predicted unstable stacking fault energy γ usf , intrinsic stacking fault energy γ isf , unstable twin energy γ utf and extrinsic stacking fault energy γ esf The size can be further used to predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

[0091] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy, characterized in that: The following steps are involved: Step S1: Calculate the site occupation fraction (SOFs) of the high entropy alloy atoms on the sublattice according to the crystallographic structure information of the high entropy alloy and the thermodynamic principle of the alloy; Step S2: Based on the prototype structure of the alloy phase, a supercell is constructed using a first-principles calculation toolkit, and based on the occupancy fraction calculated in step S1, various types of atoms in the high-entropy alloy are randomly distributed on various types of sublattices according to the occupancy fraction according to the sublattice type, and then various sublattices are nested to form an overall high-entropy alloy structure, and a high-entropy alloy occupancy ordered structure model is constructed to obtain a model file POSCAR; Step S3: Based on the obtained high entropy alloy site-ordered structure model file POSCAR, the volume of the crystal structure is first optimized through the VASP calculation software package; on this basis, the volume, shape and atomic position are globally optimized to obtain the highest total energy and most stable high entropy alloy site-ordered structure model; Step S4: cutting the high entropy alloy site-ordered structure model after structural optimization, transforming the coordinate system in the specified direction, and adding a vacuum layer of set thickness to obtain the slip plane structure model when no stacking fault occurs in the stacking fault energy calculation; calculating by VASP software package to obtain the total energy E0 of the high entropy alloy slip plane structure model when no stacking fault occurs in the equilibrium state; Step S5: according to the set shearing route, a partial atomic layer of the slip plane structure model without stacking fault is translated to obtain a stacking fault slip plane structure model; Step S6: After constructing the stacking fault slip plane structure model, the slip plane (111) of the model is fixed, and its atoms are allowed to relax freely in the [111] direction. The total energy E of the high entropy alloy corresponding to the stacking fault in the equilibrium state is calculated by the VASP software package. d ; Step S7: Total energy E of the slip surface structure model after stacking fault occurs d The difference between the total energy E0 of the slip plane structure model without stacking fault and the ratio of the stacking fault area A is the required stacking fault energy γ d ; Step S8: Calculate the stacking fault energy on different shear paths, and then draw a generalized stacking fault energy image with the unit length of the Burgers vector displaced in the [11-2] slip direction as the abscissa and the stacking fault energy as the ordinate; Step S9: predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

2. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The site-ordered structural models of high entropy alloys with different phase structures, including high entropy alloys with FCC, BCC and HCP structures, have the same modeling steps and calculation prediction steps as those required for stacking fault energy prediction.

3. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: For FCC_CoCrNi high entropy alloy, a double sublattice model of L12 structure with AuCu3 as the prototype is established to characterize the atomic distribution model of the high entropy alloy, and then the structural model required for stacking fault energy prediction is established to calculate and predict the stacking fault energy.

4. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: For FCC_CoCrNi high entropy alloy, the step S2 is specifically as follows: The unit cell of FCC_CoCrNi high entropy alloy is based on the ordered face-centered cubic FCC_L1 2— AuCu3 prototype structure, build 2×2×2 supercell, distribute the site-occupancy configuration of high entropy alloy atoms based on the site-occupancy fraction, and obtain a high entropy alloy site-occupancy ordered structure model containing 32 atoms; The step S3 is specifically as follows: The first-principles calculation software package VASP based on density functional theory was used to optimize the high-entropy alloy site-ordered structural model in steps. The K-space point grid was selected as 5×5×5. The volume relaxation was performed first. On this basis, the volume, shape and atomic position were relaxed at the same time to obtain the high-entropy alloy site-ordered structural model data after crystal structure optimization, that is, the state with the lowest total energy and the most stable crystal structure.

5. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S4 is specifically as follows: Materials Studio and VESTA crystal structure visualization software were used together to section the FCC_CoCrNi high entropy alloy site-ordered structure model after crystal structure optimization, and the slip plane (111) was selected. The (111) plane after sectioning was sheared and the number of atomic layers was increased to establish a slip plane structure model with 8 atoms per layer and a total of 9 atomic layers without stacking faults. A high vacuum layer eliminates the effect of structural mirroring; the supercell size and vacuum layer height of the structural model required for stacking fault energy prediction are determined in combination with the available computing resources. Because stacking fault energy calculation involves a large amount of calculation, it is necessary to ensure a balance between calculation accuracy and efficiency.

6. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S5 is specifically as follows: Step S51: fix the 1st to 6th atomic layers of the slip plane structure model without stacking fault, apply shear stress to the 7th to 9th atomic layers in the [11-2] direction, and move them by a unit Burgers vector length This displacement process is divided into 10 small sections, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each section; Step S52: fix the 1st to 7th atomic layers of the slip surface structure model after the unit Burgers vector is moved, and apply shear stress to the 8th to 9th atomic layers in the [11-2] direction to move the unit Burgers vector. Vector length, this displacement process is divided into 10 small segments, and a corresponding stacking fault slip surface structure model POSCAR is obtained for each segment.

7. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S6 is specifically as follows: When calculating the total energy of each slip plane structure model, the x-axis and y-axis of the atomic coordinates of the slip plane structure model are fixed, and the atoms are relaxed along the z-axis, i.e., the [111] direction, to obtain the total energy of the slip plane structure model after the stacking fault occurs in the equilibrium state, and then the total energy of the remaining slip plane structure models is calculated respectively.

8. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S7 is specifically as follows: Where E0 is the total energy of a perfect crystal structure, E d is the total energy of the crystal structure containing defects, A is the total defect area, γ d is the generalized stacking fault energy.

9. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S8 is specifically as follows: After calculating the stacking fault energy on different shear paths, the generalized stacking fault energy image is plotted with the unit length of the Burgers vector displaced in the [11-2] direction as the horizontal coordinate and the stacking fault energy as the vertical coordinate.

10. The method for predicting stacking fault energy of high entropy alloys based on atomic preferential occupancy according to claim 1, characterized in that: The step S9 is specifically as follows: The unstable stacking fault energy γ obtained according to the prediction usf , intrinsic stacking fault energy γ isf , unstable twin energy γ utf and extrinsic stacking fault energy γ esf size, and further predict whether the plastic deformation of the crystal is dominated by twinning or dislocation slip.

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