Theoretical design method for improving chromizing rate of alloy, alloy and preparation method thereof

Abstract

This invention discloses a theoretical design method and its application for improving the chromium diffusion rate of alloys by adding rare earth elements. The theoretical design method includes: classifying rare earth elements according to their differences in properties and selecting specific elements; constructing phase diagram thermodynamic data for the Cr-C-X-RE system based on phase diagram calculation methods, at least calculating the equilibrium phase diagram and the Gibbs free energy curves of the liquid phase, face-centered cubic phase, and first carbide phase for initial screening; calculating the changes in the diffusion barrier and diffusion coefficient of Cr and C elements before and after RE treatment using first-principles calculations; simulating the influence of rare earth elements on the stability of the oxide film on the substrate surface using molecular dynamics simulations; and confirming the rare earth elements based on the changes and influence patterns. By using the integrated computational materials engineering design approach of this invention to screen reasonable rare earth elements, the goal of prioritizing theoretical design can be achieved, resulting in time and cost savings.

Description

Technical Field

[0001] This invention relates to the field of materials research methods and technology, and in particular to a theoretical design method for improving the chromium infiltration rate of alloys, alloys and their preparation methods. Background Technology

[0002] Under normal conditions, alloy failures often originate from the surface. Surface strengthening techniques can alter the composition, microstructure, and composition of the alloy surface to some extent, extending its service life and reducing costs. Surface chromium infiltration is a common method for alloy surface strengthening, improving the hardness, strength, corrosion resistance, and high-temperature resistance of the substrate. Chromium not only readily exhibits high solid solubility with iron, titanium, and nickel, but can even form continuous solid solutions. Furthermore, it readily combines with trace amounts of carbon in the matrix to form a surface carbide layer. This carbide layer not only improves the strength and hardness of the substrate to some extent but can also be combined with subsequent nitriding treatments to further strengthen the alloy's surface.

[0003] The catalytic and modifying effects of rare earth elements in chromium diffusion have been widely accepted in industry. Rare earth elements often have larger atomic radii than other alloying elements (about 40% larger than iron). After diffusion, they cause lattice distortion in the substrate, leading to the enrichment of interstitial atoms in the distorted regions, which become nucleation sites for carbides and nitrides, ultimately forming a compound layer. Different rare earth elements differ in atomic radius, melting point, and stable structure, thus their promoting effects during chromium diffusion also vary.

[0004] Adding rare earth elements can increase the chromium infiltration rate, but this process is closely related to the selection of rare earth elements and the design of corresponding process parameters. However, there is no rigorous and reliable design and selection approach in the current technology, so the selection of rare earth elements has drawbacks such as long time and high cost. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a theoretical design method, an alloy and its preparation method for improving the chromium diffusion rate of alloys.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides a theoretical design method for improving the chromium infiltration rate of alloys by adding rare earth elements, comprising:

[0008] 1) Based on the differences in the characteristics of rare earth elements, classify rare earth elements and select a specific element from each category;

[0009] 2) Construct phase diagram thermodynamic data of the Cr-CX-RE system based on phase diagram calculation method, where X is the main element of the alloy base material and RE is the specified element, and at least calculate the equilibrium phase diagram and Gibbs free energy curves of the liquid phase, face-centered cubic phase and the first carbide phase to achieve the initial screening of rare earth elements.

[0010] 3) Construct the first structural model of the body-centered cubic phase, the second carbide phase and the selected compound phase that may appear in the alloy during the chromium diffusion process, and obtain the changes in the diffusion energy barrier and diffusion coefficient of Cr and C elements before and after the RE action through first-principles calculations.

[0011] 4) Construct a second structural model consisting of the face-centered cubic alloy matrix and its surface oxide film, and simulate the influence of rare earth elements on the stability of the oxide film on the surface of the substrate through molecular dynamics.

[0012] 5) Based on the changes discovered in step (3) and the influence patterns discovered in step (4), the required rare earth elements are identified.

[0013] Secondly, the present invention also provides a method for improving the chromium diffusion rate of an alloy, comprising:

[0014] The above method is used to design a rare earth element-doped alloy material system, and then the alloy is prepared and chromium is applied to the surface based on the designed material system.

[0015] Thirdly, the present invention also provides an alloy prepared by the above-described preparation method.

[0016] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0017] This invention provides a theoretical design method for improving the chromium diffusion rate of alloys by adding rare earth elements. The method categorizes the added elements based on their different properties. Next, it acquires the thermodynamic database of the Cr-CX-RE system and uses phase diagram calculations to calculate the equilibrium phase diagram and Gibbs free energy curves for the liquid phase, face-centered cubic phase, and carbide phase, thus initially screening the rare earth elements. Subsequently, first-principles calculations are used to obtain the changes in the diffusion barrier and diffusion coefficient of Cr and C elements. Finally, molecular dynamics simulations are used to study the influence of surface rare earth elements on the stability of the oxide film. By using the integrated computational materials engineering design approach of this invention to screen appropriate rare earth elements, the goal of theoretical design first can be achieved, resulting in time and cost savings.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the technical concept of the theoretical design method provided in a typical embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram illustrating the melting point, steady-state structure, phase transition behavior, and other characteristics of various rare earth elements provided in a typical embodiment of the present invention.

[0021] Figure 3 This is a typical embodiment of the present invention, showing the isothermal cross section and the change in the phase fraction of the precipitated phase before and after the action of rare earth element La.

[0022] Figure 4 This is a diagram showing the change in chemical potential of element C in a face-centered cubic phase caused by the infiltration of element Cr, provided in a typical embodiment of the present invention.

[0023] Figure 5 This is a typical embodiment of the invention that provides the diffusion barrier of Cr atoms in the body-centered cubic phase and carbide phase;

[0024] Figure 6 This is another typical embodiment of the present invention, showing isothermal cross-sectional diagrams containing Mo and Mn elements;

[0025] Figure 7 This is another typical embodiment of the present invention, showing the root mean square displacement diagram of C atoms in the Bcc and σ phases;

[0026] Figure 8 This is a phase fraction diagram showing the content of the σ phase in the infiltration agent according to the Mo / Cr ratio, provided in another typical embodiment of the present invention. Detailed Implementation

[0027] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0030] Adding rare earth elements can increase the chromium diffusion rate, but this process is closely related to the selection of rare earth element types and the design of corresponding process parameters, and a rigorous and reliable design and selection approach has not yet been established. This invention provides a theoretical design method for increasing the chromium diffusion rate of alloys by adding rare earth elements, which can achieve the selection of rare earth element types and the design of corresponding process parameters to improve the surface chromium diffusion rate of steel.

[0031] In this invention, a theoretical design method for improving the chromium infiltration rate of alloys by adding rare earth elements is proposed by combining the characteristics of rare earth elements with phase diagram calculations, first-principles calculations and molecular dynamics simulations, so as to screen rare earth elements.

[0032] See Figure 1 Based on the above technical concept, embodiments of the present invention provide a theoretical design method for improving the chromium infiltration rate of alloys by adding rare earth elements, comprising the following steps:

[0033] 1) Based on the differences in the characteristics of rare earth elements, classify rare earth elements and select a specific element from each category.

[0034] 2) Construct phase diagram thermodynamic data of the Cr-CX-RE system based on phase diagram calculation method, where X is the main element of the alloy base material and RE is the specified element, and at least calculate the equilibrium phase diagram and Gibbs free energy curves of the liquid phase, face-centered cubic phase and the first carbide phase to achieve the initial screening of rare earth elements.

[0035] 3) Construct the first structural model of the body-centered cubic phase, the second carbide phase and the selected compound phase that may appear in the alloy during the chromium diffusion process, and obtain the changes in the diffusion barrier and diffusion coefficient of Cr and C elements before and after the RE action through first-principles calculations.

[0036] 4) Construct a second structural model consisting of the face-centered cubic alloy matrix and its surface oxide film, and simulate the influence of rare earth elements on the stability of the oxide film on the surface of the substrate through molecular dynamics.

[0037] 5) Based on the changes discovered in step (3) and the influence patterns discovered in step (4), the required rare earth elements are identified.

[0038] The rare earth element classification design criteria in this invention are the first step in this work. Based on this, theoretical calculation methods such as phase diagram calculations, first-principles calculations, and molecular dynamics simulations jointly serve to screen rare earth element types and design process parameters. These methods are respectively used to obtain phase diagrams and Gibbs free energies, screen rare earth element types, determine elemental composition, design process parameters, and simulate the chromium infiltration process. By organically combining multiple theoretical methods, the rare earth infiltration process can be analyzed and reproduced, which is of great significance for the design and development of rare earth elements that can significantly improve the chromium infiltration rate.

[0039] The alloys mentioned can be various alloys that can be strengthened by chromium diffusion, such as low-carbon steel, high-carbon steel, high-temperature alloys, and titanium alloys. The specific content shown in the embodiments of the present invention is only an example of a typical solution and is not a limitation on the scope of protection of the present invention. That is, any type of alloy that can be strengthened by chromium diffusion can be calculated and screened by the method or model provided by the present invention, and is not limited to the several alloys exemplified in the embodiments of the present invention.

[0040] In some implementations, the properties of the rare earth element include atomic radius, melting point, and stable structure.

[0041] In some implementation schemes, the criteria for classifying rare earth elements include: variations in atomic radius, bimodal effect, number of 4f electrons, and standard state crystal structure.

[0042] In some implementations, the rules for classifying and selecting the specified elements using the criteria specifically include: classifying elements based on 1) the standard state crystal structure being a close-packed hexagonal structure or a non-close-packed hexagonal structure; and 2) the bimodal effect caused by the abrupt change in atomic radius due to the half-filling or full-filling of the 4f electron shell. Then, a rare earth element can be randomly specified in each category for subsequent calculations and screening.

[0043] As a typical application example, in step 1) above, there are 17 rare earth elements. To make the design process more rigorous, it is first necessary to classify the rare earth elements according to their differences in elemental properties. This method can reduce redundant research work. The main classification design criteria are as follows:

[0044] Rule 1: Changes in atomic radius. Except for Sc and Y, the lanthanides exhibit "lanthanide contraction," meaning their atomic and ionic radii gradually decrease with increasing atomic number. Atomic radius contraction is relatively slow, with the difference in radius between adjacent atoms being only about 1 pm, while ionic radius contraction is much more pronounced.

[0045] Criterion 2: "Bimodal Effect". The atomic radii of lanthanides do not decrease monotonically; instead, they exhibit a peak at Eu and Yb and a valley at Ce, a phenomenon known as the "bimodal effect". Besides atomic radius, this effect also occurs in atomic volume, density, the coefficient of thermal expansion, the third ionization energy, the sum of the first three ionization energies, electronegativity, and the melting and boiling points of some compounds, thus significantly influencing the selection of rare earth elements.

[0046] Criterion 3: Number of 4f electrons. Lanthanides contain unfilled f electron orbitals. Due to complex collective electron correlation effects and continuously adjustable electron correlation strengths, this type of system is of significant research importance and relatively complex to calculate. Following Hund's rule, compared to other rare earth elements, elements like Ce, Eu, and Yb, whose equivalent orbitals are completely empty, half-filled, or fully filled, have relatively stable electronic states.

[0047] Criterion 4: Standard state crystal structures of rare earth elements. The standard state crystal structures of different rare earth elements differ, which is also reflected in other physicochemical properties of the elements.

[0048] The above classification design criteria are an important basis for the classification of rare earth elements. Based on these criteria, elements such as Y (Hcp), La (Dhcp), Ce (Fcc: face-centered cubic, the same below; completely empty), Eu (Bcc: body-centered cubic, the same below; half-filled), Dy (Hcp), and Yb (Fcc, completely filled) can be selected, thereby greatly reducing redundant research work and improving research efficiency.

[0049] In some implementations, the correlation and energy competition relationships of the liquid phase, the first carbide phase, and the face-centered cubic phase of the alloy with temperature are obtained based on the calculated phase diagram and the Gibbs free energy curves of the liquid phase, the first carbide phase, and the face-centered cubic phase.

[0050] In some implementation schemes, step 2) specifically includes the following steps:

[0051] The equilibrium phase diagram and Gibbs free energy curves of the liquid phase, face-centered cubic phase, and first carbide phase are calculated using phase diagram calculation methods. Based on the phase diagram calculation results, the correlation coefficients and energy competition relationships among the liquid phase, face-centered cubic phase, and first carbide phase as a function of temperature are obtained, enabling preliminary screening of rare earth elements. For example, in 316 stainless steel, X represents elements such as Fe, Mo, and Ni.

[0052] As some typical application examples, in step 2), the phase diagram calculation involves using a thermodynamic database to calculate the thermodynamic properties of the Cr-CX-RE system and the relationship between alloy composition, temperature, and phase composition. The phase diagram calculation software used in this invention can be, for example, Thermo-Calc and Pandat, which can directly calculate the correlation coefficient, phase fraction, and enthalpy of formation at a specific composition point at a specific temperature, thereby obtaining the equilibrium phase diagram and the Gibbs free energy curves of the liquid phase, face-centered cubic phase, and carbide phase. The main steps can be as follows:

[0053] Step 1: Based on literature reports and parameter optimization, obtain a thermodynamic database of the system containing the above rare earth elements. Calculate the phase diagram of the Cr-CX-RE system using the phase diagram calculation software Thermo-Calc and Pandat to obtain the changes in phase relationship, null reaction temperature, and liquidus line caused by changes in the type and content of rare earth elements.

[0054] Step 2: Based on Step 1, calculate the Gibbs free energy curves of the liquid phase, face-centered cubic phase, and carbide phase to perform preliminary screening of rare earth elements.

[0055] In some embodiments, in step 3), the second carbide phase includes the Cr7C3 phase, and the selected compound phase includes the σ phase.

[0056] In some implementations, step 3) specifically includes the following steps:

[0057] The first structural model of the body-centered cubic phase, the Cr7C3 phase, and the σ phase was constructed, and the simulation results were obtained.

[0058] Based on the simulation results, at least the root mean square displacement of Cr element versus time can be obtained.

[0059] The changing parameters are calculated based on the relationship between the root mean square displacement and time.

[0060] As some typical application examples, in step 3), based on quantum mechanics theory and combined with first-principles calculation methods, the interaction between electron clouds between atoms is studied to obtain various properties of the material without inputting any external parameters. The changes in diffusion barriers and diffusion coefficients of Cr and C elements before and after the addition of rare earth elements are calculated using first-principles calculations. As an example, the specific steps are as follows: First, construct the structures of a body-centered cubic phase, a Cr7C3 phase, and a σ phase, where the body-centered cubic phase can use a 3×3×3 supercell; in the CI-NEB calculation, the maximum electron step number and the maximum ion step number are preferably set to 60, the total energy convergence criterion is preferably set to less than or equal to 1×10⁻³ eV / cell, and the single-atom force convergence criterion is preferably less than or equal to 0.1 eV / Å; in the AIMD simulation, the simulation temperature is preferably set to 1000℃, and the simulation results are processed to obtain the relationship between the root mean square displacement (MSD) and time; finally, the changes in diffusion behavior with and without rare earth elements are calculated as the basis for the design method.

[0061] In this invention, the vacancy diffusion path of Cr atoms is first constructed using VESTA software to establish a vacancy model before and after diffusion. Then, VTST software is used to insert four points to determine the diffusion path. Finally, the diffusion barrier changes of Cr atoms in the body-centered cubic phase and the carbide phase are calculated.

[0062] In this invention, the root-mean-square displacement and time satisfy Einstein's diffusion theory, i.e., they exhibit a priori relationship. Furthermore, according to Einstein's diffusion theory, the diffusion coefficient, time, and root-mean-square displacement have the following relationship:

[0063]

[0064] In the formula, D is the diffusion coefficient, N is the number of atoms (in some simulations, only the diffusion of one C atom can be considered, so N is taken as 1), n ​​is the dimension (in this invention, C atom diffusion occurs in all three spatial dimensions, so n is taken as 3), and t is time. Finally, the formulas actually used in some typical application examples of this invention are as follows:

[0065]

[0066] In some implementations, step 4) specifically includes:

[0067] A multilayer model comprising a face-centered cubic substrate, an oxide film on its surface, and preliminary screening elements on the substrate surface was constructed as the second structural model. The activation process of the oxide film was simulated using molecular dynamics to obtain the influence of rare earth elements on the stability of the oxide film.

[0068] For example, a multi-layer model can be constructed first based on VESTA software to simplify the simulation of real-world conditions. This multi-layer model should include a bottom face-centered cubic matrix, an oxide film at the interface, and surface rare earth atoms. At the same time, the interaction interfaces between atoms in each layer should be optimized, and molecular dynamics simulations should be performed on the surface oxide film change process to study the influence of different rare earth elements on the oxide film activation process.

[0069] This invention also provides a method for improving the chromium diffusion rate of an alloy, comprising: designing a rare earth element-doped alloy material system using the theoretical design method described in any of the above embodiments, and then preparing the alloy based on the designed material system and performing surface chromium diffusion.

[0070] The present invention also provides an alloy, particularly a stainless steel alloy, which is prepared by the above-described preparation method.

[0071] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0072] Example 1

[0073] This embodiment uses rare earth metal La as an example to illustrate the entire theoretical design method.

[0074] (1) Based on the differences in the characteristics of rare earth (RE) elements, the added elements are classified according to atomic radius, melting point, steady-state structure, etc. (see Figure 2 The design work is carried out by selecting specific elements from each category. This example uses this selection method to select the elements Y, La, Ce, Eu, Dy, and Yb as representatives, as shown in Table 1.

[0075] Table 1. Selected Specified Elements in Example 1

[0076]

[0077] (2) Phase diagram data and thermodynamic parameters from the literature were integrated, and then a phase diagram thermodynamic database of the C-Cr-Fe-Mo-Ni-La multi-component system was constructed based on the CALPHAD method. The calculations were performed using the software Thermo-Calc and Pandat, as shown in the appendix. Figure 3 The phase diagrams of the C-Cr-Fe-Mo-Ni pentagonal system and the C-Cr-Fe-Mo-Ni-La hexaagonal system are shown. Under isothermal and isobaric conditions, the correlations of the liquid phase, face-centered cubic phase, and carbide phase in the equilibrium phase diagram with the change of Cr element content in the chromium-diffused layer are compared. The calculation results are shown in Table 2.

[0078] Table 2. Correlation coefficients of the liquid phase, face-centered cubic phase, and carbide phase in the equilibrium phase diagram calculated in Example 1.

[0079]

[0080] By calculating the change in the chemical potential of C element after Cr element infiltration into the matrix material as the Cr element content in the Fcc phase increases, the results can be obtained as shown in the attached figure. Figure 4 The graph shows that this process reduces the chemical potential of carbon (C) at the surface, causing C to diffuse uphill and form a carbide layer of varying thickness on the surface. Software calculations show that when a small amount of rare earth element (La) diffuses into the matrix material, it lowers the temperature at which the material in the corresponding region reaches the liquid phase, promoting the diffusion of chromium (Cr).

[0081] (3) The transition states and diffusion barriers of Cr atoms diffusing in Bcc and carbide structures with vacancies were calculated using the CI-NEB method built into VASP. First, the initial and final states of diffusion were determined, and corresponding CONTCAR files were generated after structural relaxation. Then, the VTST software was used to find the transition states along the diffusion path between the two states, and four intermediate state files were linearly inserted. Finally, the files were executed to calculate the diffusion barriers, as shown in the attached figure. Figure 5 The changes in energy barrier were obtained with and without rare earth elements (La).

[0082] (4) A multilayer model containing the underlying Fcc matrix, the Cr2O3 and Fe2O3 oxide films at the interface and the rare earth atoms on the surface was constructed using VESTA software. Then, structural relaxation was performed, and the specific values ​​of parameters such as the layer height and crystal plane index of each layer were selected according to the stability of the structure. Finally, a reasonable model was constructed, and molecular dynamics simulation was performed on the change process of the surface oxide film to study the influence of different rare earth elements on the activation process of the oxide film.

[0083] Based on theoretical calculations, using La as a chromating agent increases the chromium-impregnated layer thickness by 10% to 20% compared to samples without rare earth elements, under the same chromating time and temperature conditions. Traditionally, using a trial-and-error method to test and characterize each rare earth element individually requires at least 2000 hours, while this theoretically calculated approach can reduce the overall time by 20%.

[0084] Example 2

[0085] This embodiment expands upon Embodiment 1, and, under the premise of the same research approach, uses other trace alloying elements as examples to illustrate the entire theoretical design method.

[0086] (1) By analyzing typical Fe-based or Ni-based alloys, phase diagram data and thermodynamic parameters from the literature were integrated. Subsequently, a phase diagram thermodynamic database of the C-Cr-Fe-Mo-Mn-Ni multi-component system was constructed based on the CALPHAD method. The calculations were performed using the software Thermo-Calc and Pandat, as shown in the attached figure. Figure 6 The Cr-Fe-Mo-Ni and Cr-Fe-Mn-Ni quaternary phase diagrams shown compare the changes in the equilibrium phase region from the Fe- and Ni-rich side toward the chromium-diffused layer under isothermal and isobaric conditions. When Mo (2.0 wt.%) is applied to this system, a σ phase is generated, while when Mn (1.0 wt.%) is applied to this system, the generation of the σ phase is significantly suppressed.

[0087] (2) A C atom is randomly placed into the supercell of the constructed Bcc and other compound phases (taking the σ phase as an example here), and AIMD simulation is performed at 1000 °C. The calculated XDATCAR file is then post-processed to calculate the displacement of the C atom relative to the previous step. Statistical analysis is then performed to obtain the relationship between the root mean square displacement and time. Subsequently, the diffusion coefficient, time, and root mean square displacement relationship described in the invention are used for data processing to obtain the diffusion coefficient of the C atom in different structures, such as... Figure 7 As shown, the diffusion coefficient of C atoms in the Bcc phase is significantly greater than that in the σ phase, thus causing a difference in the thickness of the surface carbide layer. Subsequently, combined with the influence of the diffusion barrier of Cr element in the carbide phase in Example 1, the influence of different phase structures on the chromium diffusion process was determined, thereby establishing the relationship between composition, diffusion layer structure, and chromium diffusion rate. It can be seen that the σ phase can significantly increase the diffusion layer thickness, thereby improving the chromium diffusion efficiency.

[0088] (3) A multilayer model containing the underlying Fcc matrix, Cr2O3 and Fe2O3 oxide films at the interface, and Mo atoms was constructed using VESTA software. Then, structural relaxation was performed. Based on the stability of the structure, the specific values ​​of parameters such as the layer height and crystal plane index of each layer were selected. Finally, a reasonable model was constructed, and molecular dynamics simulation was performed on the surface oxide film change process to study the influence of different alloying elements on the oxide film activation process.

[0089] (4) Based on the first two steps, further calculate the phase diagram, replace the pure Cr side with the specified Cr / Mo ratio, and calculate the change in the σ phase fraction along the path, such as... Figure 8 As shown, when the Mo / Cr ratio is between 10% and 25%, the content of the σ phase can be increased from about 15% to more than 25%.

[0090] Based on theoretical calculations, using Mo powder as a chromizing agent additive, under the same chromizing time and temperature conditions, it is expected to increase the content of the σ phase by more than 50%, thereby improving chromizing efficiency. The research approach proposed in this invention can shorten the overall research and development time by 20%.

[0091] Based on the above test results, it is clear that the theoretical design method for improving the chromium diffusion rate of alloys by adding rare earth elements provided by this invention involves classifying the added elements according to their different characteristics; secondly, obtaining the thermodynamic database of the Cr-CX-RE system, and using phase diagram calculation methods to calculate the equilibrium phase diagram and the Gibbs free energy curves of the liquid phase, Fcc, and carbide phases to initially screen the rare earth elements; subsequently, obtaining the changes in the diffusion barrier and diffusion coefficient of Cr and C elements through first-principles calculations; and finally, studying the influence of surface rare earth elements on the stability of the oxide film through molecular dynamics simulations. By using the integrated computational materials engineering comprehensive design approach of this invention to screen reasonable rare earth elements, the goal of theoretical design first can be achieved, resulting in time and cost savings.

[0092] The present invention also provides a computer device, the computer device including a processor and a memory, the memory storing at least one instruction, the at least one instruction being loaded and executed by the processor to perform the operations performed in the aforementioned theoretical design method for increasing the chromium infiltration rate of alloys by adding rare earth elements.

[0093] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0094] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A theoretical design method for improving the chromium infiltration rate of alloys by adding rare earth elements, characterized in that, include: 1) Based on the differences in the characteristics of rare earth elements, classify rare earth elements and select a specific element from each category; 2) Construct phase diagram thermodynamic data of the Cr-CX-RE system based on phase diagram calculation method, where X is the main element of the alloy base material and RE is the specified element, and at least calculate the equilibrium phase diagram and Gibbs free energy curves of the liquid phase, face-centered cubic phase and the first carbide phase to achieve the initial screening of rare earth elements. 3) Construct the first structural model of the body-centered cubic phase, the second carbide phase and the selected compound phase that may appear in the alloy during the chromium diffusion process, and obtain the changes in the diffusion energy barrier and diffusion coefficient of Cr and C elements before and after the RE action through first-principles calculations. 4) Construct a second structural model consisting of the face-centered cubic alloy matrix and its surface oxide film, and simulate the influence of rare earth elements on the stability of the oxide film on the surface of the substrate through molecular dynamics. 5) Based on the changes discovered in step (3) and the influence patterns discovered in step (4), the required rare earth elements are identified.

2. The theoretical design method according to claim 1, characterized in that, In step 1), the characteristics of the rare earth elements include atomic radius, melting point, and stable structure; And / or, the criteria for classifying rare earth elements include: atomic radius variation, bimodal effect, number of 4f electrons, and standard state crystal structure.

3. The theoretical design method according to claim 2, characterized in that, The rules for classifying and selecting the specified elements using the criteria specifically include: classifying elements based on 1) the standard state crystal structure being either close-packed hexagonal or non-close-packed hexagonal; and 2) the bimodal effect caused by abrupt changes in atomic radius due to half-filling or full-filling of the 4f electron shell, and then randomly assigning a rare earth element in each category.

4. The theoretical design method according to claim 1, characterized in that, Step (2) specifically includes: using the phase diagram calculation method to calculate the equilibrium phase diagram and the Gibbs free energy curves of the liquid phase, face-centered cubic phase and the first carbide phase, and at least based on the phase diagram calculation results, obtaining the correlation coefficient and energy competition relationship between the liquid phase, face-centered cubic phase and the first carbide phase as a function of temperature, and performing preliminary screening of rare earth elements to achieve preliminary screening of rare earth elements.

5. The theoretical design method according to claim 4, characterized in that, The phase diagram calculation method specifically includes: The thermodynamic database of the Cr-CX-RE system is obtained, and the phase diagram is calculated using phase diagram calculation software to obtain the phase relationship, zero-variable reaction temperature and liquidus change caused by changes in the types and contents of the rare earth elements. Here, X represents the main element of the alloy and RE represents the specified element. Based on the aforementioned phase relationship, zero-variable reaction temperature, and liquidus line changes, calculate the Gibbs free energy curves for the liquid phase, face-centered cubic phase, and first carbide phase.

6. The theoretical design method according to claim 1, characterized in that, In step 3), the second carbide phase includes the Cr7C3 phase, and the selected compound phase includes the σ phase.

7. The theoretical design method according to claim 6, characterized in that, Step 3) specifically includes: The first structural model of the body-centered cubic phase, the Cr7C3 phase, and the σ phase was constructed, and the simulation results were obtained. Based on the simulation results, at least the root mean square displacement of Cr element versus time should be obtained. The change is calculated based on the relationship between the root mean square displacement and time.

8. The theoretical design method according to claim 1, characterized in that, Step 4) specifically includes: A multilayer model comprising a face-centered cubic matrix, an oxide film on its surface, and primary screening elements on the surface of the matrix is ​​constructed as the second structural model. The activation process of the oxide film was simulated using molecular dynamics to obtain the results of the influence of rare earth elements on the stability of the oxide film.

9. A method for preparing an alloy with improved chromium infiltration rate, characterized in that, include: The alloy-doped rare earth element material system is designed using the theoretical design method of any one of claims 1-8, and then the alloy is prepared and chromium is applied to the surface based on the designed material system.

10. An alloy, characterized in that, It is prepared by the method of claim 9.

Images