A method for preparing a dual-layer protective coating with self-repairing characteristics

Abstract

The application discloses a preparation method of a double-layer protective coating with a self-repairing feature, and aims at solving the problems of low bonding strength of a high-entropy alloy coating and a base body and difficulty in maintaining long-time service stability. The preparation method comprises the following steps: (1) base body pretreatment; (2) calculating the average atomic radius difference, VEC, mixing entropy and mixing enthalpy of a high-entropy alloy multi-element system, and mixing and ball milling corresponding single-element powders; (3) adopting a high-energy beam deposition process to perform cladding deposition on the mixed metal powders; (4) polishing, polishing and cleaning the high-entropy alloy coating; and (5) adopting an oxidation process or a nitriding process to form an oxidation layer or a nitriding layer on the high-entropy alloy coating in situ. The double-layer protective coating with the self-repairing feature has the double-layer protection of the high-entropy alloy coating with excellent corrosion resistance and the in-situ oxidation / nitriding layer, wherein the high-entropy alloy coating is designed to utilize the dilution of the base body to form stable intermetallic compounds and improve the matching of the coating and the base body.

Description

Technical Field

[0001] This invention belongs to the field of composite coating technology, specifically relating to a method for preparing a double-layer protective coating with self-healing characteristics. Background Technology

[0002] Surface technology has significant applications in improving the surface performance of components. High-entropy alloy coatings, due to their four major effects, have a broader application prospect compared to traditional protective coatings. For example, the mature AlCoCrFeNi eutectic high-entropy coating has been initially applied to cutting tools and other equipment. The excellent corrosion resistance and other properties of high-entropy alloy coatings have been applied in many fields and components. However, in application exploration, it has been found that due to the difference in thermophysical properties between the coating and the substrate, problems such as poor coating formability, complex phases, and low bonding strength lead to peeling. This makes it difficult to maintain long-term service stability in increasingly harsh working environments. Therefore, it is urgent to optimize the long-term service performance of the coating through structural design while ensuring a good bond between the substrate and the high-entropy alloy coating. Summary of the Invention

[0003] The purpose of this invention is to solve the problem that the bonding strength between high-entropy alloy coatings and the substrate is low, making it difficult to maintain long-term service stability, and to propose a method for preparing a double-layer protective coating with self-healing characteristics.

[0004] The method for preparing the self-healing double-layer protective coating of the present invention is carried out according to the following steps:

[0005] 1. The substrate surface is successively ground, polished, and cleaned to obtain the pretreated substrate;

[0006] 2. Analyze the metallic elements in the matrix, select one element with a metallic element content of not less than 30% or the element with the highest metallic element content as the additive element, and select 2 to 6 elements from the easily oxidized / nitrided elements as alloying elements. Use the additive elements and alloying elements to form a high-entropy alloy multi-component system. Then calculate the average atomic radius difference δ, VEC (valence electron concentration), ΔSmix (mixing entropy), and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system (including matrix elements and easily oxidized / nitrided elements). Make the average atomic radius difference δ ≤ 15%, 6.7 (e / a) ≤ VEC ≤ 8 (e / a), 12 J / (mol·K) ≤ ΔSmix ≤ 17.5 J / (mol·K) and -22 kJ / mol ≤ ΔHmix ≤ 7 kJ / mol;

[0007] The powders of the added elements and alloying elements are put together into a high-energy ball mill for ball milling to obtain a mixed powder.

[0008] 3. The mixed powder is coated on the pretreated substrate surface, and the mixed metal powder is clad and deposited using a high-energy beam deposition process to form a high-entropy alloy coating.

[0009] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0010] 5. An oxide layer is formed in situ on the high-entropy alloy coating by an oxidation process, or a nitriding layer is formed in situ by a nitriding process, thereby obtaining a double-layer protective coating with self-healing characteristics.

[0011] The easily oxidized / nitrided elements mentioned in step two are Cr, Fe, Al, Si, Co, Ni, Zr and Ti;

[0012] The oxidation process in step five is either a high-temperature oxidation process or a micro-arc oxidation process, and the nitriding process is either ion nitriding or carbonitriding.

[0013] The self-healing double-layer protective coating of this invention consists of a high-entropy alloy coating as the bottom layer and an in-situ oxidation / nitriding layer as the top layer. The high-entropy alloy coating exhibits excellent corrosion resistance and high-temperature resistance, and all selected elements are easily oxidized / nitrided, with the internal structure of the coating being intermetallic compounds. The in-situ oxidation / nitriding layer is formed by pre-oxidation / nitriding catalysis on the surface of the high-entropy alloy coating.

[0014] The self-healing dual-layer protective coating provided by this invention features a high-entropy alloy coating with excellent corrosion resistance and an in-situ oxide / nitride layer. The high-entropy alloy coating is designed to utilize substrate dilution to form stable intermetallic compounds, solving the problem of insufficient coating-substrate compatibility. Simultaneously, due to the presence of the in-situ oxide / nitride layer, a negative oxygen / nitrogen concentration gradient exists in an oxygen-rich environment, resulting in stronger stability. Furthermore, due to the self-oxidation / nitride properties of the selected elements in the high-entropy alloy, self-healing can be achieved in an oxygen / nitrogen-rich environment, exhibiting superior protective performance. The preparation method of this coating is reliable, efficient, and ensures stable and controllable coating structure and dimensions.

[0015] The self-healing double-layer protective coating described in this invention can be prepared on the surface of medium- and high-temperature components, such as nuclear power plant loop pipes and hot-end components. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation process of the self-healing double-layer protective coating of the present invention;

[0017] Figure 2 The image shows the phase structure of the high-entropy alloy coating obtained in Example 1 (TEM image).

[0018] Figure 3This is a schematic diagram of the self-healing process of the double-layer protective coating with self-healing features of the present invention;

[0019] Figure 4 The figure shows the phase structure analysis of the self-healing double-layer protective coating (high-entropy alloy coating) prepared in Example 1. In the figure, (a) is the microstructure of the ZrNbCrAlFe coating; (b) is the elemental distribution of the ZrNbCrAlFe coating; (c) is the high-magnification microstructure of the ZrNbCrAlFe coating; and (d) is the phase structure of the ZrNbCrAlFe coating.

[0020] Figure 5 A cross-sectional view of the self-healing double-layer protective coating prepared in Example 1;

[0021] Figure 6 The elemental distribution diagram of the self-healing double-layer protective coating prepared in Example 1;

[0022] Figure 7 The phase structure analysis diagram is shown for the self-healing double-layer protective coating prepared in Example 2.

[0023] Figure 8 This is a cross-sectional view of the in-situ oxide layer in the double-layer protective coating with self-healing characteristics in Example 2;

[0024] Figure 9 The elemental distribution diagram shows the self-healing double-layer protective coating prepared in Example 2.

[0025] Figure 10 This is a cross-sectional view of the in-situ oxide layer in the self-healing double-layer protective coating prepared in Example 3;

[0026] Figure 11 The elemental distribution diagram shows the self-healing double-layer protective coating prepared in Example 3.

[0027] Figure 12 The figure shows the phase structure analysis of the self-healing double-layer protective coating prepared in Example 4. (a-f) shows the elemental distribution of the FeCoCrAlNi coating; (g) shows the line scan distribution of each element in the FeCoCrAlNi coating; (h) shows the TEM microstructure of the FeCoCrAlNi coating; and (i-j) shows the FCC and BCC phase diffraction spots of the FeCoCrAlNi coating.

[0028] Figure 13 This is a cross-sectional view of the in-situ nitrided layer of the self-healing double-layer protective coating prepared in Example 4;

[0029] Figure 14 The elemental distribution diagram shows the self-healing double-layer protective coating prepared in Example 4. Detailed Implementation

[0030] Specific Implementation Method 1: The preparation method of the self-healing double-layer protective coating in this implementation method is carried out according to the following steps:

[0031] 1. The substrate surface is successively ground, polished, and cleaned to obtain the pretreated substrate;

[0032] 2. Analyze the metallic elements in the matrix, select one element with a metallic element content of not less than 30% or the element with the highest metallic element content as the additive element, and select 2 to 6 elements from the easily oxidized / nitrided elements as alloying elements. Use the additive elements and alloying elements to form a high-entropy alloy multi-component system. Then calculate the average atomic radius difference δ, VEC (valence electron concentration), ΔSmix (mixing entropy), and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system (including matrix elements and easily oxidized / nitrided elements). Make the average atomic radius difference δ ≤ 15%, 6.7 (e / a) ≤ VEC ≤ 8 (e / a), 12 J / (mol·K) ≤ ΔSmix ≤ 17.5 J / (mol·K) and -22 kJ / mol ≤ ΔHmix ≤ 7 kJ / mol;

[0033] The powders of the added elements and alloying elements are put together into a high-energy ball mill for ball milling to obtain a mixed powder.

[0034] 3. The mixed powder is coated on the pretreated substrate surface, and the mixed metal powder is clad and deposited using a high-energy beam deposition process to form a high-entropy alloy coating.

[0035] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0036] 5. An oxide layer is formed in situ on the high-entropy alloy coating by an oxidation process, or a nitriding layer is formed in situ by a nitriding process, thereby obtaining a double-layer protective coating with self-healing characteristics.

[0037] The easily oxidized / nitrided elements mentioned in step two are Cr, Fe, Al, Si, Co, Ni, Zr and Ti;

[0038] The oxidation process in step five is either a high-temperature oxidation process or a micro-arc oxidation process, and the nitriding process is either ion nitriding or carbonitriding.

[0039] In step one of this embodiment, when calculating the average atomic radius difference δ, VEC (valence electron concentration), ΔSmix, and ΔHmix of the high-entropy alloy multi-element system, the molar concentration of the added elements is selected to be between 15% and 35%.

[0040] In step two of this embodiment, various elemental powders are selected according to the molar concentration ratio of the added elements and alloying elements in the high-entropy alloy multi-element system, and then placed in a high-energy ball mill for ball milling.

[0041] In this embodiment, when the phase structure in the high-entropy alloy coating in step three is three or more, two to three metal elemental powders are selected from easily oxidized / nitrided metals in step two; when the phase structure in the high-entropy alloy coating in step three is three or fewer, three to six metal elemental powders are selected from easily oxidized / nitrided metals in step two to avoid overly complex structures.

[0042] This embodiment provides a method for preparing a double-layer protective coating with self-healing characteristics. A high-entropy alloy coating is prepared on the substrate surface as the bottom layer using high-energy beam deposition technology. Since the elements selected in the high-entropy alloy coating are prone to oxidation / nitridation, an in-situ oxidation / nitridation layer can be formed on the surface of the high-entropy alloy coating through pre-oxidation / nitridation catalysis. When the in-situ oxidation / nitridation layer cracks, the high-entropy alloy coating reacts with oxygen again to form an oxidation / nitridation layer, thus achieving a self-healing effect.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the formula for calculating the average atomic radius difference δ of the high-entropy alloy multi-component system in step two is as follows:

[0044]

[0045] Where C i r represents the molar percentage of each element (i) in a high-entropy alloy multi-component system. i Let be the atomic radius, and r be the average atomic radius of all elements in the high-entropy alloy multi-element system.

[0046] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the calculation formula for VEC of the high-entropy alloy multi-component system in step two is as follows:

[0047]

[0048] Where C i Let (i) represent the molar percentage of each element (i) in the high-entropy alloy multi-component system, (VEC). i denoted as valence electron concentration of each element (i) in a high-entropy alloy multi-component system.

[0049] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the particle size of the mixed metal powder in step two is 45-80 μm.

[0050] The purpose of limiting the powder particle size in this embodiment is to make the sizes closer together, which is conducive to the mutual solid solution of elements and the formation of stable structures (including single solid solutions and intermetallic compounds).

[0051] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the laser power is controlled to be 1000-1500W in the high-energy beam deposition process in step 3.

[0052] This embodiment limits the deposition power, which can ensure a high energy density and facilitates the full integration of matrix elements and alloying elements.

[0053] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the deposition rate in step three of the high-energy beam deposition process is controlled to be 10-15 mm / s.

[0054] This embodiment limits the deposition rate, which can ensure a high energy density and facilitates the full integration of matrix elements and alloying elements.

[0055] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the thickness of the high-entropy alloy coating in step three is 400–800 μm.

[0056] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that the thickness of the oxide layer or nitriding layer in step five is 20 to 50 μm.

[0057] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the high-temperature oxidation process involves placing the substrate with a high-entropy alloy coating into a high-temperature furnace and performing high-temperature oxidation treatment at a temperature of 600–800°C in an air or oxygen atmosphere.

[0058] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the ion nitriding process involves applying an 800V voltage between the substrate with a high-entropy alloy coating and the furnace body of a vacuum furnace, using pure ammonia as the gas source, and nitriding for 5 to 6 hours at a nitriding temperature of 520°C and a gas pressure of 350Pa.

[0059] Example 1: The preparation method of the self-healing double-layer protective coating in this example is carried out according to the following steps:

[0060] 1. The surface of the zirconium alloy substrate is successively ground, polished, and cleaned to obtain the pretreated substrate;

[0061] II. The main metallic element composition of the matrix is ​​Zr. Four elemental powders of Nb, Fe, Cr and Al are selected from easily oxidized / nitrided elements as alloying elements. A high-entropy alloy multi-component system is composed of Zr and alloying elements Nb, Fe, Cr and Al. The atomic radius difference δ, VEC (valence electron concentration), ΔSmix (mixing entropy) and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system are calculated to make the average atomic radius difference δ ≤ 15%, 6.7 (e / a) ≤ VEC ≤ 8 (e / a), 12 J / (mol·K) ≤ ΔSmix ≤ 17.5 J / (mol·K) and -22 kJ / mol ≤ ΔHmix ≤ 7 kJ / mol.

[0062] The formula for calculating the atomic radius difference δ is as follows:

[0063]

[0064] Where C i r represents the molar percentage of each element (i) in a high-entropy alloy multi-component system. i Let be the atomic radius, and r be the average atomic radius of all elements in the high-entropy alloy multi-element system;

[0065] The formula for calculating ΔHmix (enthalpy of mixing) is as follows:

[0066]

[0067] Where ΔH mix It is the enthalpy of mixture, Ω ij It is the enthalpy of mixture of an alloy (between two elements), C i and C j This represents the molar percentage of different elements;

[0068] ΔS mix The calculation formula is as follows:

[0069]

[0070] Where ΔS mix It is the entropy of mixing, R is the gas constant, and C i denoted as the molar percentage of each element (i) in a high-entropy alloy multi-component system;

[0071] The formula for calculating VEC (valence electron concentration) is as follows:

[0072]

[0073] Where C i Let (i) represent the molar percentage of each element (i) in the high-entropy alloy multi-component system, (VEC). iLet represent the valence electron concentration of each element (i) in the high-entropy alloy multi-component system;

[0074] The relevant calculation results for the high-entropy alloy multi-component system in this embodiment are as follows: the average atomic radius difference is 9.02%, VEC = 6.71e / a, ΔSmix = 13.92mol / K, and ΔHmix = -17.64mol / K, which meet the requirements.

[0075] The Zr, Nb, Fe, Cr, and Al elemental powders were ball-milled in a high-energy ball mill according to a molar ratio of 10:8:50:16:16 to obtain mixed metal powders with a particle size of 80-100 μm.

[0076] 3. The mixed metal powder is coated on the pretreated substrate surface, and the mixed metal powder is clad deposited using a high energy beam deposition process. The laser power is controlled at 1200W and the deposition rate is 10mm / s to form a high entropy alloy coating.

[0077] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0078] 5. The substrate with the high-entropy alloy coating is placed in a high-temperature furnace and treated at 600°C for 80 hours in an air atmosphere to form an oxide layer in situ on the high-entropy alloy coating. After the temperature of the high-temperature furnace drops to room temperature, a double-layer protective coating with self-healing characteristics is obtained.

[0079] The self-healing double-layer protective coating obtained in this embodiment has a bottom layer of ZrNbCrAlFe high-entropy alloy coating, where Zr and Nb are elements found in the zirconium alloy matrix. The coating thickness is 800 μm, forming an intermetallic compound Zr(Fe,Cr)2 with a bonding strength of 95 MPa. The in-situ oxide layer thickness is 35–45 μm. The phase structure analysis diagram of the high-entropy alloy coating is shown below. Figure 4 As shown, the cross-sectional view of the in-situ oxide layer is as follows: Figure 5 As shown, the elemental distribution diagram of the double-layer protective coating is as follows: Figure 6 As shown. Combined with Figures 4-6 It can be seen that a double-layer protective coating was prepared with ZrNbCrAlFe as the bottom layer and an in-situ oxide layer as the surface layer.

[0080] Example 2: The preparation method of the self-healing double-layer protective coating in this example is carried out according to the following steps:

[0081] 1. The zirconium alloy surface is successively ground, polished, and cleaned to obtain the pretreated substrate;

[0082] II. The main metallic element composition of the matrix is ​​Zr. Four elemental powders of Nb, Cr, Si and Al are selected from easily oxidized / nitrided elements as alloying elements. A high-entropy alloy multi-component system is composed of Zr and alloying elements Nb, Si, Cr and Al. The atomic radius difference, VEC (valence electron concentration), ΔSmix (mixing entropy) and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system are calculated to make the average atomic radius difference δ≤15%, 6.7(e / a)≤VEC≤8(e / a), 12J / (mol·K)≤ΔSmix≤17.5J / (mol·K) and -22kJ / mol≤ΔHmix≤7kJ / mol;

[0083] The atomic radius difference, VEC (valence electron concentration), ΔSmix (mixing entropy), and ΔHmix (mixing enthalpy) of a high-entropy alloy multi-component system are calculated using the following formulas:

[0084]

[0085]

[0086] The relevant calculation results for the high-entropy alloy multi-component system in this embodiment are as follows: the average atomic radius difference is 10.12%, VEC = 7.01e / a, ΔSmix = 12.77mol / K, and ΔHmix = -14.34mol / K, which meet the requirements.

[0087] The elemental powders of Zr, Nb, Cr, Al and Si were ball-milled in a high-energy ball mill according to the molar ratio of Zr, Nb, Cr, Al and Si of 20:8:25:33:14 to obtain mixed metal powder with a particle size of 80 to 100 μm.

[0088] 3. The mixed powder is coated on the pretreated substrate surface, and the mixed metal powder is clad and deposited using a high-energy beam deposition process. The laser power is controlled at 1000W and the deposition rate is 15mm / s to form a high-entropy alloy coating.

[0089] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0090] 5. The substrate with the high-entropy alloy coating is placed in a high-temperature furnace and treated at 650°C for 20 hours in an air atmosphere to form an oxide layer in situ on the high-entropy alloy coating. After the temperature of the high-temperature furnace drops to room temperature, a double-layer protective coating with self-healing characteristics is obtained.

[0091] The self-healing double-layer protective coating obtained in this embodiment has a bottom layer of ZrNbCrAlSi high-entropy alloy coating with a thickness of 750 μm, forming two intermetallic compounds, Zr(Ai,Si) and Zr2Cr, with a bonding strength of 98 MPa. The in-situ oxide layer thickness is 35–45 μm. The phase structure analysis of the high-entropy alloy coating is as follows: Figure 7 As shown, the in-situ oxidation cross-sectional diagram is as follows: Figure 8 As shown, the elemental distribution diagram of the double-layer protective coating is as follows: Figure 9 As shown, combined with Figures 7-9 It can be seen that a double-layer protective coating with a bottom layer of ZrNbCrAlSi and a surface layer of in-situ oxide was prepared.

[0092] Example 3: The preparation method of the self-healing double-layer protective coating in this example is carried out according to the following steps:

[0093] 1. The zirconium alloy surface is successively ground, polished, and cleaned to obtain the pretreated substrate;

[0094] II. The main metallic component of the matrix is ​​Zr. Four elemental powders of Nb, Cr, Si and Al were selected from easily oxidized / nitrided elements as alloying elements. A high-entropy alloy multi-component system was formed by adding Zr and alloying elements Nb, Cr, Si and Al. The atomic radius difference, VEC (valence electron concentration), ΔSmix (mixing entropy) and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system were calculated to make the average atomic radius difference δ≤15%, 6.7(e / a)≤VEC≤8(e / a), 12J / (mol·K)≤ΔSmix≤17.5J / (mol·K) and -22kJ / mol≤ΔHmix≤7kJ / mol;

[0095] Calculate using the following formula:

[0096]

[0097]

[0098] The relevant calculation results for the high-entropy alloy multi-component system in this embodiment are as follows: the average atomic radius difference is 14.12%, VEC = 7.82e / a, ΔSmix = 14.97mol / K, and ΔHmix = -20.09mol / K, which meet the requirements.

[0099] The elemental powders of Zr, Nb, Cr, Al and Si were ball-milled in a high-energy ball mill according to the molar ratio of Zr, Nb, Cr, Al and Si of 20:8:25:33:14 to obtain mixed metal powders with a particle size of 60 to 100 μm.

[0100] 3. The mixed powder is coated on the pretreated substrate surface, and the mixed metal powder is clad and deposited using a high-energy beam deposition process. The laser power is controlled at 1000W and the deposition rate is 15mm / s to form a high-entropy alloy coating.

[0101] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0102] 5. Place the substrate with the high-entropy alloy coating in the electrolyte and use a micro-arc oxidation process with a pulsed power supply. The electrolyte is a mixed solution of 20 g / L Na2O·nSiO2, 8 g / L KF, and 2 g / L NaOH. The pulse frequency is 700 Hz with a duty cycle of 20%. The positive voltage is controlled at 100 V and the negative voltage at 10 V for 1-5 min; the positive voltage is controlled at 150 V and the negative voltage at 10 V for 5-13 min; the positive voltage is controlled at 350 V and the negative voltage at 10 V for 13-15 min; and the positive voltage is controlled at 350 V and the negative voltage at 10 V for 15-20 min. The total oxidation time is 20 min. An oxide layer is formed in situ on the high-entropy alloy coating. After the high-temperature furnace temperature drops to room temperature, a double-layer protective coating with self-healing characteristics is obtained.

[0103] The self-healing double-layer protective coating obtained in this embodiment has a bottom layer of ZrNbCrAlSi high-entropy alloy coating with a thickness of 750 μm, forming two intermetallic compounds, Zr(Ai,Si) and Zr2Cr, with a bonding strength of 98 MPa. The in-situ oxide layer thickness is 1–2 μm. The phase structure of the high-entropy alloy coating is the same as that of the bottom layer. Figure 7 Consistent, in-situ oxidation cross-sectional diagram as follows Figure 10 As shown, the elemental distribution diagram of the double-layer protective coating is as follows: Figure 11 As shown, combined with Figures 7-11 It can be seen that a double-layer protective coating with a bottom layer of ZrNbCrAlSi and a surface layer of in-situ oxide was prepared.

[0104] Example 4: The preparation method of the self-healing double-layer protective coating in this example is carried out according to the following steps:

[0105] 1. Grinding, polishing and cleaning the surface of 20Cr stainless steel in sequence to obtain the pretreated substrate;

[0106] II. The main metallic component of the matrix is ​​Fe. Four elemental powders of Co, Cr, Al and Ni were selected from easily oxidized / nitrided elements as alloying elements. A high-entropy alloy multi-component system was formed by adding Fe and alloying elements Co, Cr, Al and Ni. The atomic radius difference, VEC (valence electron concentration), ΔSmix (mixing entropy) and ΔHmix (mixing enthalpy) of the high-entropy alloy multi-component system were calculated to make the average atomic radius difference δ≤15%, 6.7(e / a)≤VEC≤8(e / a), 12J / (mol·K)≤ΔSmix≤17.5J / (mol·K) and -22kJ / mol≤ΔHmix≤7kJ / mol;

[0107] Calculate using the following formula:

[0108]

[0109]

[0110] The relevant calculation results for the high-entropy alloy multi-component system in this embodiment are as follows: the average atomic radius difference is 8.12%, VEC = 6.94e / a, ΔSmix = 13.97mol / K, and ΔHmix = -7.31mol / K, which meet the requirements.

[0111] Fe, Co, Cr, Al and Ni elemental powders were ball-milled in a high-energy ball mill according to a molar ratio of 1:1:1:1:1 to obtain mixed metal powders with a particle size of 60-80 μm.

[0112] 3. The mixed metal powder is coated on the pretreated substrate surface, and the mixed metal powder is clad deposited using a high energy beam deposition process. The laser power is controlled at 1000W and the deposition rate is 15mm / s to form a high entropy alloy coating.

[0113] 4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating;

[0114] 5. An in-situ nitriding layer was prepared on the surface of a high-entropy alloy coating using an ion nitriding process. The vacuum degree was 0.8 Pa, the nitriding temperature was 520 °C, the nitriding time was 6 h, the gas pressure was 350 Pa, the voltage was 800 V, the DC power supply was 10 A, and the AC power supply was 25 A, thereby obtaining a double-layer protective coating with self-healing characteristics.

[0115] The self-healing double-layer protective coating obtained in this embodiment has a bottom layer of FeCoCrAlNi high-entropy alloy coating with a thickness of 1800 μm, forming two phase structures: FCC phase and BCC phase, with a bonding strength of 98 MPa and an in-situ oxide layer thickness of 3 μm. The phase structure of the high-entropy alloy coating is as follows: Figure 12 As shown, the in-situ oxidation cross-sectional diagram is as follows: Figure 13 As shown, the elemental distribution diagram of the double-layer protective coating is as follows: Figure 14 As shown, combined with Figures 12-14 It can be seen that a double-layer protective coating was prepared with FeCoCrAlNi as the bottom layer and an in-situ nitrided layer as the top layer.

Claims

1. A method for preparing a double-layer protective coating with self-healing characteristics, characterized in that... The preparation method of this self-healing double-layer protective coating is carried out according to the following steps:

1. The substrate surface is successively ground, polished, and cleaned to obtain the pretreated substrate; 2. Analyze the metallic elements in the matrix, select one element with a metallic element content of not less than 30% or the element with the highest metallic element content as the additive element, and select 2 to 6 elements from the easily oxidized elements as alloying elements. Use the additive elements and alloying elements to form a high-entropy alloy multi-component system. Then calculate the average atomic radius difference δ, VEC, ΔSmix and ΔHmix of the high-entropy alloy multi-component system, so that the average atomic radius difference δ of the high-entropy alloy multi-component system is ≤15%, 6.7(e / a)≤VEC≤8(e / a), 12J / (mol·K)≤ΔSmix≤17.5 J / (mol·K) and -22 kJ / mol≤ΔHmix≤7 kJ / mol; The powders of the added elements and alloying elements are put together into a high-energy ball mill for ball milling to obtain a mixed powder.

3. The mixed powder is coated on the pretreated substrate surface, and the mixed metal powder is clad and deposited using a high-energy beam deposition process to form a high-entropy alloy coating.

4. The high-entropy alloy coating is successively ground, polished and cleaned to obtain a substrate with the high-entropy alloy coating; 5. An oxide layer is formed in situ on the high-entropy alloy coating using an oxidation process, thereby obtaining a double-layer protective coating with self-healing characteristics; The easily oxidizable elements mentioned in step two are Cr, Fe, Al, Si, Co, Ni, Zr, and Ti; The oxidation process in step five is a high-temperature oxidation process or a micro-arc oxidation process. The high-temperature oxidation process involves placing the substrate with a high-entropy alloy coating into a high-temperature furnace and performing high-temperature oxidation treatment at a temperature of 600~800°C in an air atmosphere or an oxygen atmosphere.

2. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... The formula for calculating the average atomic radius difference δ of the high-entropy alloy multi-component system in step two is as follows: Where C i r represents the molar percentage of each element in a high-entropy alloy multi-component system. i Where is the atomic radius. is the average atomic radius of all elements in a high-entropy alloy multi-element system.

3. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... The formula for calculating the VEC of the high-entropy alloy multi-component system in step two is as follows: Where C i The molar percentage of each element in a high-entropy alloy multi-component system is given by (VEC). i This represents the valence electron concentration of each element in a high-entropy alloy multi-element system.

4. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... In step two, the particle size of the mixed metal powder is 45~80μm.

5. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... In step three, the laser power is controlled to be 1000~1500W during the high-energy beam deposition process.

6. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... In step three, the deposition rate is controlled at 10~15 mm / s during the high-energy beam deposition process.

7. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... In step three, the thickness of the high-entropy alloy coating is 400~800μm.

8. The method for preparing the self-healing double-layer protective coating according to claim 1, characterized in that... The thickness of the oxide layer in step five is 20~50μm.

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