Material Design Method and Application of Cr-N Protective Coating

Abstract

The present invention discloses a material design method and its application for a Cr-N protective coating. The material design method includes: obtaining the total energy of adding M element to the Cr₂N phase and the total energy of adding it to the CrN phase by using the first-principles calculation method, and then calculating the formation enthalpy Hf according to the formation enthalpy calculation formula; calculating the free energies of the two phases based on the formation enthalpy Hf; calculating the phase diagram by using the phase diagram calculation method according to the free energies of the two phases; selecting the system with the lowest formation temperature of the Cr₂N phase, so as to determine the optimal M element. The method of the present invention uses a multi-dimensional material design method to reduce the formation temperature of the Cr₂N strengthening phase. Compared with the experimental method, the method provided by the present invention combines the first-principles calculation and the phase diagram calculation, and can quickly determine the addition of the M element, achieving the effect of halving both time and cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of material research methods, and particularly relates to a material design method and application of a Cr-N protective coating. Background Art

[0002] The Cr-N protective coating has excellent high-temperature resistance, corrosion resistance and wear resistance, and is a good high-temperature structural material, hard tool material and surface protective material. At the same time, it also has excellent thermal conductivity and electrical conductivity, so it has a wide range of applications in many industrial fields.

[0003] For example, a Cr-N coating is often plated on the surface of the piston ring of an automobile engine to improve the wear resistance of the piston ring and extend the service life of the engine. There are two phases, CrN and Cr2N, in the Cr-N coating. Compared with the CrN phase, the Cr2N phase has higher hardness, better toughness and more excellent corrosion resistance. Therefore, when preparing the Cr-N protective coating, it is often desired to increase the content of the Cr2N strengthening phase in the coating. However, since the CrN phase is more thermodynamically stable than the Cr2N phase, a higher preparation temperature (usually > 1000 °C) is required to generate the Cr2N phase using conventional preparation methods.

[0004] Attached Figure 2 The shown Cr-N phase diagram well reflects the thermodynamic stability relationship between the CrN phase and the Cr2N phase. The CrN phase has good thermodynamic stability below 1044 °C, while the Cr2N phase has better thermodynamic stability above 1044 °C.

[0005] In order to simplify the preparation process of the Cr-N protective coating and increase the phase fraction of the Cr2N strengthening phase, it is necessary to develop a new material design method to reduce the formation temperature of the Cr2N strengthening phase. It is a feasible method to add a suitable element M (M can be one of Ti, Al, V, Mo, Co, Ni, Fe, Cr) to dissolve in the Cr2N phase to improve its thermal stability performance. However, how to select a suitable element to add from among many candidate elements M is a problem that remains to be solved at present. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a material design method and application of a Cr-N protective coating.

[0007] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a material design method of a Cr-N protective coating, the Cr-N protective coating includes a CrN phase and a Cr2N strengthening phase, and the material design method includes:

[0009] (1) Use the first-principles calculation method to obtain the total energy E0((CrM)2N) of the addition of element M to the Cr2N phase and the total energy E0((CrM)N) of the addition of element M to the CrN phase, and then calculate the formation enthalpies H of the (CrM)2N phase and the (CrM)N phase according to the formation enthalpy calculation formula. f ;

[0010] (2) Calculate the Gibbs free energies of the (CrM)2N phase and the (CrM)N phase based on the formation enthalpy H. f ;

[0011] (3) According to the Gibbs free energies of the (CrM)2N and (CrM)N phases, use the CALPHAD phase diagram calculation method to calculate the phase diagram of the Cr-M-N system.

[0012] (4) Analyze the formation temperature of the Cr2N phase through the melting point of the CrN phase in the phase diagram, and select the system with the lowest formation temperature of the Cr2N phase, so as to determine the optimal element M.

[0013] In a second aspect, the present invention also provides a use of the above material design method in the production of Cr-N protective coatings.

[0014] In a third aspect, the present invention also provides a preparation method of a Cr-N protective coating, including:

[0015] Design the material system of the Cr-N protective coating by using the above method, and then prepare the Cr-N protective coating according to the designed material system.

[0016] In a fourth aspect, the present invention also provides a Cr-N protective coating prepared by the above method.

[0017] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0018] The method of the present invention uses a multi-dimensional material design method to reduce the formation temperature of the Cr2N strengthening phase. Compared with the experimental method, the method provided by the present invention combines the first-principles calculation and the phase diagram calculation to quickly determine the addition of element M, achieving the effect of halving both time and cost.

[0019] The above description is only an overview of the technical solutions of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it according to the content of the specification, the following takes the preferred embodiments of the present invention and combines detailed drawings to illustrate as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic flow chart of the material design method provided by a typical embodiment of the present invention;

[0021] Figure 2 is the existing Cr-N binary phase diagram in the background art of the present invention;

[0022] Figure 3 is the calculated Cr-Fe-N ternary phase diagram provided for a typical embodiment of the present invention;

[0023] Figure 4 is the calculated Cr-Mo-N ternary phase diagram provided for a typical embodiment of the present invention;

[0024] Figure 5 is the XRD test pattern of the CrN x protective coating provided for a typical embodiment of the present invention. Detailed implementation manners

[0025] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The following will further explain the technical solution, its implementation process, principle, etc.

[0026] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those described herein, and thus, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0027] Moreover, relational terms such as "first" and "second" are only used to distinguish one component or method step with the same name from another, and do not necessarily require or imply any actual relationship or order between these components or method steps.

[0028] See Figure 1 , an embodiment of the present invention provides a material design method for a Cr-N protective coating, the Cr-N protective coating includes a CrN phase and a Cr2N strengthening phase, and the material design method includes the following steps:

[0029] (1) Use the first-principles calculation method to obtain the total energy E0((CrM)2N) of the M element added to the Cr2N phase and the total energy E0((CrM)N) added to the CrN phase, and then calculate the formation enthalpy H of the (CrM)2N phase and the (CrM)N phase according to the formation enthalpy calculation formula f .

[0030] (2) Calculate the Gibbs free energy of the (CrM)2N phase and the (CrM)N phase based on the formation enthalpy H f .

[0031] (3) Calculate the phase diagram of the Cr-M-N system using the CALPHAD phase diagram calculation method based on the Gibbs free energies of the (CrM)2N and (CrM)N phases.

[0032] (4) Analyze the formation temperature of the Cr2N phase from the melting point of the CrN phase in the phase diagram, and select the system with the lowest formation temperature of the Cr2N phase to determine the optimal M element.

[0033] In some embodiments, the candidate M elements may include any one of Ti, Al, V, Mo, Co, Ni, Fe, and Cr.

[0034] In some embodiments, the enthalpy calculation formula in step (1) may be:

[0035] H f = E0 - E(Cr) - E(M) - E(N) to calculate the formation enthalpies of the (CrM)2N and (CrM)N phases,

[0036] where E(Cr), E(M), and E(N) are the total energies of the standard states of elements Cr, M, and N, respectively.

[0037] In some embodiments, step (2) may include:

[0038] Using the formula to calculate the Gibbs free energies of the (CrM)2N and (CrM)N phases.

[0039] where are the Gibbs free energies of elements N, M, and Cr in the reference state, respectively, is the contribution of the standard mixing entropy to the energy.

[0040] In some embodiments, the contribution of the standard mixing entropy to the energy can be specifically calculated using the following formula:

[0041] x is the mole fraction of each component, i.e., x1 is the mole fraction of element Cr, x2 is the mole fraction of element M, R is the molar gas constant, and T is the temperature.

[0042] In some embodiments, step (2) may include: initially selecting M elements that can make the Gibbs free energy of the (CrM)2N phase less than the Gibbs free energy of the (CrM)N phase by comparing the magnitudes of the Gibbs free energies; and step (3) includes: calculating the phase diagram of the Cr-M-N system using the CALPHAD phase diagram calculation method based on the Gibbs free energies of the (CrM)2N and (CrM)N phases corresponding to the initially selected M elements.

[0043] In some embodiments, step (3) may specifically include the following steps:

[0044] a. Write the Gibbs free energies of the (CrM)2N phase and the (CrM)N phase into the thermodynamic database.

[0045] b. Use CALPHAD phase diagram calculation software to read the thermodynamic database.

[0046] c. Set the composition of each element and the calculation boundary conditions.

[0047] d. Calculate the phase diagram of the Cr-M-N system.

[0048] In some embodiments, the phase diagram calculation software includes Pandat.

[0049] In some embodiments, step 6) specifically includes the following steps:

[0050] Obtain the formation temperature of the (CrM)2N phase corresponding to each M element based on the Cr-M-N system phase diagram of each M element in the preliminary screening element set.

[0051] Select the M element with the lowest formation temperature of the (CrM)2N phase as the optimal M element.

[0052] As some typical application examples, the material design method described in the above embodiments can be specifically implemented through the following technical solutions:

[0053] (1) Use the first-principles calculation method to obtain the total energies E0((CrM)2N) and E0(CrMO) of adding the M element (M is one of Ti, Al, V, Mo, Co, Ni, Fe, Cr) to the Cr2N phase and the CrN phase, and use the formation enthalpy calculation formula:

[0054] H f = E0 - E(Cr) - E(M) - E(N)

[0055] Calculate the formation enthalpies of the (CrM)2N and (CrM)N phases.

[0056] (2) Substitute the formation enthalpy Hf into the key formula:

[0057]

[0058] Calculate the Gibbs free energies of the (CrM)2N and (CrM)N phases (Gibbs free energy, the same below); compare the magnitudes of the Gibbs free energies of the (CrM)2N and (CrM)N phases, and preliminarily screen out the feasible M elements to be added (i.e., the above-mentioned preliminary screening element set).

[0059] (3) Using the CALPHAD phase diagram calculation method, the phase diagram of the Cr-M-N system is calculated based on the Gibbs free energies of the (CrM)2N and (CrM)N phases;

[0060] (4) By analyzing the melting point of the CrN phase in the phase diagram, the formation temperature of the Cr2N phase is obtained, the system with the lowest formation temperature of the Cr2N phase is selected, and the optimal M element to be designed and added is determined.

[0061] In the method of the present invention, the first-principles calculation method and the CALPHAD phase diagram calculation jointly serve to screen the M addition element and reduce the formation temperature of the Cr2N phase.

[0062] In step (1), the formation enthalpies of the M element added to the Cr2N phase and the CrN phase are calculated. The first-principles calculation method is based on density functional theory. Without any external parameter input, by studying the interaction of the electron clouds between atoms, various properties of the material can be obtained, which is a commonly used material property calculation method. Through this method, the total energy E0 of the material can be calculated, and then the formation enthalpy calculation formula:

[0063] H f = E0 - E(Cr) - E(M) - E(N)

[0064] The formation enthalpies of the (CrM)2N and (CrM)N phases are calculated, where E(Cr), E(M), and E(N) are the total energies of the standard states of the elements Cr, M, and N, respectively.

[0065] In step (2), the formation enthalpy Hf is brought into

[0066]

[0067] to calculate the Gibbs free energies of the (CrM)2N and (CrM)N phases, where and are the Gibbs free energies of the elements N, M, and Cr in the reference state, respectively, is the contribution of the standard mixing entropy to the energy.

[0068] where x1 is the mole fraction of the element Cr, x2 is the mole fraction of the element M, R is the molar gas constant, and T is the temperature.

[0069] In step (3), the CALPHAD phase diagram calculation uses a thermodynamic database to calculate the thermodynamic properties of the Cr-M-N system and the relationships among alloy composition, temperature, and phase composition. The CALPHAD phase diagram calculation software used in the present invention is preferably Pandat, which can calculate the "composition-temperature-phase" relationship of a certain composition of the Cr-M-N system.

[0070] The main steps are:

[0071] Step 1: Write the Gibbs free energy of (CrM)2N and (CrM)N phases into the thermodynamic database TDB file;

[0072] Step 2: Use Pandat software to read the TDB thermodynamic database;

[0073] Step 3: Set the composition of each element and the calculation boundary conditions;

[0074] Step 4: Calculate the phase diagram of the Cr-MN system.

[0075] Continue to see Figure 1 In the above implementation schemes, the first-principles calculations are a theoretical analysis method based on density functional theory, which uses only five basic physical constants: electron mass m0, original charge e, Planck constant h, speed of light c, Boltzmann constant k b Without relying on any empirical parameters, the state and properties of the microscopic system can be reasonably predicted. The basic principle of the first-principles calculation method is to solve the Kohn-Sham equation of density functional theory: F[ρ] = <Φ|T+V|Φ> through the pseudopotential method to obtain the total energy and charge density spatial distribution of the multi-electron system. In the present invention, the formation enthalpy Hf of the Cr2N phase of the solid solution M element is calculated using first-principles methods and is brought into the CALPHAD phase diagram calculation as an input parameter.

[0076] The essence of the CALPHAD phase diagram calculation method is to construct thermodynamic models of each phase in the target system based on their structural and thermodynamic information. Combining mathematical and physical analysis, these models are expressed in Gibbs free energy. Phase diagrams are then calculated using the Gibbs free energy common tangent rule and phase equilibrium conditions. The parameters to be optimized for each phase's thermodynamic model can be obtained using relevant computational software based on experimental data. Phase diagrams and their thermodynamic information for multicomponent systems are obtained by rationally extrapolating the thermodynamic parameters of low-component systems (generally binary and ternary systems) or by adding a small number of multicomponent parameters.

[0077] In order to combine first-principles calculations with CALPHAD phase diagram calculations to jointly serve the purpose of screening out the appropriate M element addition to reduce the formation temperature of the Cr2N strengthening phase, this paper proposes the key formula for calculating the energy of (CrM)2N and (CrM)N phases: The formation enthalpy H obtained by first-principles calculation fSubstituting into this formula can calculate the Gibbs free energies of the corresponding (CrM)2N and (CrM)N phases. The Gibbs free energies of the (CrM)2N and (CrM)N phases calculated by the key formula can be directly compared to obtain their relative thermodynamic stabilities, which serves as the preliminary screening process for the selection of element M. In addition, the Gibbs free energy can be directly input into the CALPHAD phase diagram calculation. Thus, the barrier between the first-principles calculation and the CALPHAD phase diagram calculation is broken, enabling the two calculation methods to jointly serve the design method of the present invention.

[0078] Based on the above principle, the present invention uses first-principles calculation to calculate the enthalpies of formation of the Cr2N phase and the CrN phase with added element M, and calculates the Gibbs free energies of the (CrM)2N and (CrM)N phases through the enthalpies of formation using the key formula. Then, the Gibbs free energy is taken as an input parameter and brought into the CALPHAD calculation to obtain the phase diagram of the Cr-M-N system. The formation temperature of the Cr2N phase is analyzed from the melting point of the CrN phase in the phase diagram. The material design method proposed by the present invention can avoid the blind experimental process and add element M in a targeted manner to achieve the goal of reducing the formation temperature of the Cr2N phase.

[0079] The embodiment of the present invention also provides the use of the material design method in any of the above embodiments in the preparation of a Cr-N protective coating.

[0080] The embodiment of the present invention also provides a preparation method of a Cr-N protective coating, including:

[0081] Design the material system of the Cr-N protective coating by the above method, and then prepare the Cr-N protective coating according to the designed material system.

[0082] The embodiment of the present invention also provides a Cr-N protective coating prepared by the above preparation method.

[0083] The technical solution of the present invention will be further described in detail below through several embodiments in combination with the drawings. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0084] Example 1

[0085] This example provides a material design method for reducing the formation temperature of the Cr2N strengthening phase in a Cr-N x protective coating, specifically including the following steps:

[0086] (1) The total energy and the enthalpy of formation H of the Cr2N and CrN phases when element M (where M is one of Ti, Al, V, Mo, Co, Ni, Fe, Cr) is added are calculated using the first-principles Vienna ab initio simulation package (VASP) software based on density functional theory. f . The projector augmented wave pseudopotential is used to describe the interaction between electrons and ions, and the generalized gradient approximation based on the Perdew - Burke - Ernzerhof functional is used to describe the interaction between electrons. The plane wave cutoff energy is set to 400 eV. The calculation uses a primitive cell containing 48 atoms, and the structure optimization is all fully relaxed optimization. The boundary conditions set for the calculation are: the optimization accuracy is that the energy and force of the atoms converge to 10 -4 eV and 0.01 The formula for calculating the enthalpy of formation is used:

[0087] H f = E0 - E(Cr) - E(M) - E(N) to calculate the enthalpy of formation of the (CrM)2N and (CrM)N phases.

[0088] The calculation results are shown in Table 1.

[0089] Table 1 Calculation results of the enthalpy of formation of each M element

[0090]

[0091] (2) Substitute the enthalpy of formation Hf calculated in Table 1 into

[0092] to calculate the Gibbs free energy (T = 1000 °C) of the (CrM)2N and (CrM)N phases. The calculation results of the Gibbs free energy are shown in Table 2.

[0093] Table 2 Calculation results of the Gibbs free energy of each M element

[0094] Add element M <![CDATA[G((CrM)2N)]]> G((CrM)N) Ti -73717 -94521 Al -82350 -117879 V -93653 -123326 Mo -113717 -101256 Co -179328 -207803 Ni -93008 -141146 Fe -89786 -73180 Cr -55680 -80644

[0095] (3) By comparing the data in Table 2, it is found that when Fe and Mo are added to the CrN phase and the Cr2N phase, the Gibbs free energy of Cr2N is lower than that of the CrN phase, indicating that the addition of Fe and Mo improves the thermodynamic stability of Cr2N. The Gibbs free energy data of the CrN phase and the Cr2N phase added with Fe and Mo are substituted into the CALPHAD phase diagram calculation. The boundary conditions for the phase diagram calculation of Cr-Fe-N and Cr-Mo-N are set as follows: temperature 0 - 2000 °C; the molar percentages of Fe and Mo are set to 5 at%, the molar percentage of Cr varies from 0 - 90 at%, and the total molar percentage of each element is controlled to be 100 at%, thereby determining the molar percentage of N; the calculation pressure is set to one atmosphere (about 100000 Pa). The calculated phase diagrams of Cr-Fe-N shown in Appendix Figure 3 and Cr-Mo-N shown in Appendix Figure 4 are obtained.

[0096] (4) Analyzing the phase diagrams, it can be seen that after adding 5 at% of Fe and Mo to the Cr-N system, the melting points of the CrN phase both decrease. The addition of Fe reduces the melting point of the CrN phase by 8 °C, while the addition of Mo reduces the melting point of the CrN phase by 73 °C. This shows that after adding Mo, the lowest formation temperature of the Cr2N phase decreases from the original 1044 °C to 971 °C. Therefore, the element Mo is used as the designed additive element, and its addition amount is determined to be 5 at%.

[0097] (5) Using the solid powder method, Mo powder and Cr powder are coated on the surface of stainless steel, and then Cr infiltration treatment is carried out under vacuum conditions at 980 °C for 15 - 18 hours. A CrN x protective coating mainly composed of Cr2N is successfully obtained, as shown in Appendix Figure 5 . The mechanical properties of the prepared CrN x coating are tested using a nanoindentation instrument. The CrN x protective coating prepared in this example reaches a hardness value of 20 - 25 GPa and an elastic modulus of 220 - 286 GPa, which is higher than the typical hardness value of 12 - 19 GPa of the CrN x coating without the Cr2N phase.

[0098] In this example, the time-consuming of the first-principles calculation process in step (1) depends on the number of calculator cores. Taking a typical 64-core calculator as an example, the time used is about 2 hours; the typical time-consuming for calculating the phase diagram in step (3) is about 0.5 hours; step (5) includes a nitriding experiment, which takes 15 - 18 hours, and corresponding material X-ray diffraction characterization and performance testing experiments, which take 1.5 - 3.5 hours. The total time-consuming of this example is 19 - 24 hours.

[0099] Comparative Example 1

[0100] Design of CrN protective coating using experimental trial and error method, including the following steps: x

[0101] (1) Using the solid powder method, coat Ti powder and Cr powder on the surface of stainless steel, and then carry out Cr infiltration treatment under vacuum conditions at 980 °C for 15 - 18 hours to prepare the CrN protective coating. Characterize the phase composition of the prepared CrN coating using X-ray diffraction, and test the mechanical properties of the CrN protective coating using a nanoindentation instrument. x x x

[0102] (2) Using the same method as in step (1), coat Al powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0103] (3) Using the same method as in step (1), coat V powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0104] (4) Using the same method as in step (1), coat Mo powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0105] (5) Using the same method as in step (1), coat Co powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0106] (6) Using the same method as in step (1), coat Ni powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0107] (7) Using the same method as in step (1), coat Fe powder and Cr powder on the surface of stainless steel to prepare the CrN protective coating, and correspondingly characterize the phase composition and mechanical properties of the coating. x

[0108] (8) Compare the Cr2N phase content and its mechanical properties in the CrN coatings prepared in steps (1 - 8) to determine the optimal element addition. x

[0109] ​​​​​​​​​​​In this comparative example, steps (1-7) include 7 nitriding experiments, which take 105 to 126 hours, and corresponding material X-ray diffraction characterization and performance test experiments, which take 10.5 to 24.5 hours. The total time consumed in this comparative example is 115.5 to 150.5 hours.

[0110] It should be understood that the above embodiments are only used to illustrate the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A material design method for a Cr-N protective coating, the Cr-N protective coating comprising a CrN phase and a Cr2N strengthening phase, characterized in that, The described material design method includes: (1) The total energy E0((CrM)2N) of the M element added to the Cr2N phase and the total energy E0((CrM)N) of the M element added to the CrN phase are obtained using the first-principles calculation method, and then the enthalpies of formation H of the (CrM)2N phase and the (CrM)N phase are calculated according to the enthalpy of formation calculation formula f ; The enthalpy calculation formula is as follows: ; where E(Cr), E(M), and E(N) are the total energies of the standard states of elements Cr, M, and N, respectively; (2) Using the formula ; to calculate the Gibbs free energies of the (CrM)2N and (CrM)N phases; Among them , , are the Gibbs free energies of elements N, M, and Cr in the reference state respectively, is the contribution of the standard mixing entropy to the energy, and the contribution of the standard mixing entropy to the energy is calculated by the following formula: ； where x is the mole fraction of each component, x1 is the mole fraction of element Cr, x2 is the mole fraction of element M, R is the molar gas constant, and T is the temperature; By comparing the magnitudes of the Gibbs free energies, initially select the M element that can make the Gibbs free energy of the (CrM)2N phase less than the Gibbs free energy of the (CrM)N phase; (3) Based on the Gibbs free energies of the (CrM)2N and (CrM)N phases corresponding to the initially selected M element, use the CALPHAD phase diagram calculation method to calculate the phase diagram of the Cr-M-N system; (4) Analyze the formation temperature of the Cr2N phase through the melting point of the CrN phase in the phase diagram, and select the system with the lowest formation temperature of the Cr2N phase, thereby determining the optimal M element.

2. The material design method according to claim 1, characterized in that The described M element includes one of Ti, Al, V, Mo, Co, Ni, Fe, and Cr.

3. The material design method according to claim 1, wherein Step (3) specifically includes: a. Write the Gibbs free energies of the (CrM)2N and (CrM)N phases into the thermodynamic database; b. Use the CALPHAD phase diagram calculation software to read the thermodynamic database; c. Set the composition of each element and the calculation temperature boundary conditions; d. Calculate the phase diagram of the Cr-M-N system.

4. Use of the method according to any one of claims 1 - 3 in the preparation of a Cr-N protective coating.

5. A method for preparing a Cr-N protective coating, characterized in that, It includes: Design the material system of the Cr-N protective coating by using the method according to any one of claims 1 - 3, and then prepare the Cr-N protective coating based on the designed material system.

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