Method for producing a feal coating on a stainless steel surface

Abstract

The present application relates to the technical field of FeAl coating preparation, and particularly relates to a FeAl coating preparation method for a stainless steel surface, which comprises the following steps: determining an overlapping laying strategy of Fe foil and Al foil based on a configuration index of the FeAl coating to form a multilayer preform; determining whether the prepared multilayer preform is qualified based on a layer combination index of the multilayer preform; performing first reaction heat treatment on the qualified multilayer preform, and determining a heating rate of second reaction heat treatment based on a uniformity index; determining a switching amount of a hydrogen-argon mixed gas containing YCl3 vapor in a protective atmosphere of second reaction heat treatment based on a spatial coincidence degree; determining a cerium element immersion time in molten salt treatment based on a grain boundary strengthening index; determining whether the low-temperature resistance of the FeAl coating is qualified based on a low-temperature cracking index of the FeAl coating; and determining to adjust the cerium element immersion time in the next batch of preparation process based on unqualified low-temperature resistance of the FeAl coating. The present application improves the performance consistency of the FeAl coating.

Description

Technical Field

[0001] This invention relates to the field of FeAl coating preparation technology, and more particularly to a method for preparing FeAl coating on stainless steel surfaces. Background Technology

[0002] With the rapid development of high-end equipment manufacturing, stainless steel components are increasingly used in harsh conditions such as high temperature and corrosion, placing higher demands on the performance of their surface protective coatings. FeAl intermetallic compound coatings, due to their excellent high-temperature oxidation resistance, good corrosion resistance, and relatively low cost, are considered one of the ideal candidate materials for stainless steel surface modification. However, in actual preparation, the comprehensive performance of FeAl coatings, especially their resistance to low-temperature cracking, is often constrained by factors such as precursor structure design, heat treatment process parameters, and the uniformity of strengthening element distribution.

[0003] Traditional FeAl coating preparation methods, such as hot pressing-reactive sintering, thermal spraying, or laser cladding, can achieve initial coating formation, but they struggle to precisely control the diffusion reaction process of Fe and Al elements and the interfacial bonding state. These methods typically lack systematic optimization of the component ratios and layup strategies for multilayer preforms, leading to defects such as component segregation, porosity, and poor interfacial bonding within the coating. Furthermore, during the heat treatment stage, fixed heating patterns cannot adapt to the actual needs of preforms with varying homogeneity, easily causing reactive stress concentration and microcrack initiation, reducing the integrity and reliability of the coating.

[0004] Chinese Patent Publication No. CN105463444A discloses a method for preparing a corrosion-resistant FeAl intermetallic compound-based composite structure coating, applicable to fields such as materials processing, metallurgy, power, machinery, and chemical engineering. This method uses readily available and inexpensive Fe, Al, and ceramic particles as raw materials. Alloy powder is prepared by ball milling, deposited onto a substrate using cold spraying, and then heat-treated to form a FeAl intermetallic compound-based composite structure coating. Under certain oxygen partial pressure conditions, a uniform and dense Al2O3 film is formed on its surface. The composite structure coating prepared by this method, based on FeAl intermetallic compounds, possesses good high-temperature wear resistance and Zn(Al) corrosion resistance. The uniform and dense Al2O3 film on the surface contributes to the coating's excellent corrosion resistance, low metal molten wettability, and superior wear resistance. This coating has broad application prospects in industries such as steel galvanizing where it comes into contact with liquid metals.

[0005] Therefore, the method for preparing the corrosion-resistant FeAl intermetallic compound-based composite coating has the following problems:

[0006] 1. The inherent layered structure of thermal spraying contains unbonded interfaces and pores. Although subsequent heat treatment can enhance the bonding between particles through atomic diffusion, it is difficult to guarantee that all internal pores, especially those penetrating into the substrate or coating, will be completely "healed". In the harsh molten zinc environment, these pores become rapid channels for liquid metal to penetrate. Once the penetrating molten zinc comes into contact with the internal FeAl phase, it will directly cause corrosion, leading to the disintegration of the coating from the inside.

[0007] 2. Relying on the surface-generated α-Al₂O₃ film as a protective barrier, however, the oxide film is formed on the surface of an already formed coating that may contain microscopic defects. The bond between the film and the coating substrate is mainly chemical bonding, lacking strong mechanical anchoring. When the coating is subjected to thermal shock or mechanical stress, the oxide film is very easy to peel off from the inherent layered interfaces or pores and other weak points, causing the protective function to be lost instantly. Summary of the Invention

[0008] Therefore, the present invention provides a method for preparing FeAl coating on stainless steel surface to overcome the problems of uncontrolled coating microstructure, poor performance consistency and insufficient resistance to low-temperature cracking caused by the mismatch between the initial quality fluctuation of the preform and the immobilization heat treatment process in the prior art.

[0009] To achieve the above objectives, the present invention provides a method for preparing a FeAl coating on a stainless steel surface, comprising:

[0010] The overlapping layup strategy of Fe foil and Al foil is determined based on the comparison results of the configuration index of FeAl coating and the preset configuration index to form a multilayer preform.

[0011] The quality of the prepared multi-layer preform is determined based on the embryo layer bonding index of the multi-layer preform.

[0012] The qualified multilayer preform is subjected to a first reaction heat treatment, and the propagation speed of the ultrasonic guided wave after the first reaction heat treatment is obtained to determine the uniformity index of the multilayer preform. The heating rate of the second reaction heat treatment is determined based on the comparison result between the uniformity index and the preset uniformity index.

[0013] The temperature anomaly region and defect region in the second reaction heat treatment process are obtained, and the spatial overlap is determined based on the temperature anomaly region and the defect region to determine the amount of hydrogen-argon mixture gas containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment.

[0014] Based on the standard deviation coefficient of yttrium element distribution in the coating section after the second reaction heat treatment, the grain boundary strengthening index is determined to obtain the cerium immersion time in the molten salt treatment.

[0015] The low-temperature cracking index of the FeAl coating after molten salt treatment was obtained and compared with the low-temperature cracking index of the preset FeAl coating to determine whether the low-temperature resistance of the FeAl coating is qualified.

[0016] Based on the fact that the FeAl coating failed to meet the low-temperature resistance requirements, the cerium impregnation time in the next batch preparation process was adjusted.

[0017] The first reaction heat treatment involves heating to 600°C at a rate of 10°C / min under argon protection and holding at that temperature for 120 minutes. The second reaction heat treatment involves heating to 900°C at a first heating rate of 5°C / min or a second heating rate of 2°C / min, switching the protective atmosphere to a hydrogen-argon mixture containing YCl3 vapor, and continuing to heat to 1100°C and holding at that temperature for 180 minutes.

[0018] Furthermore, based on the fact that the configuration index of the FeAl coating is greater than or equal to a preset configuration index, a first overlapping layup strategy is determined to be adopted; based on the fact that the configuration index of the FeAl coating is less than the preset configuration index, a second overlapping layup strategy is determined to be adopted; wherein,

[0019] The first overlapping layup strategy is to symmetrically alternate between Fe and single-layer Al foil, and the second overlapping layup strategy is to alternate between Fe and double-layer Al foil. The configuration index is the ratio of the number of Fe atoms to the number of Al atoms in the target FeAl coating.

[0020] Furthermore, based on the embryo layer binding index being greater than or equal to a preset embryo layer binding index, the multi-layer prefabricated embryo is determined to be qualified, wherein...

[0021] The embryo layer bonding index is the product of the ratio of the measured interface wave impedance to the preset interface wave impedance and the weighting coefficient A, plus the product of 1 and the difference between the average interface porosity and the weighting coefficient A.

[0022] Furthermore, the process of determining the heating rate of the second reaction heat treatment includes:

[0023] Compare the uniformity index with the preset uniformity index;

[0024] Based on the uniformity index being greater than or equal to the preset uniformity index, the heating rate of the second reaction heat treatment is determined as the first heating rate.

[0025] Based on the fact that the uniformity index is less than a preset uniformity index, the heating rate of the second reaction heat treatment is determined as the second heating rate, wherein...

[0026] The first heating rate is 5℃ / min, the second heating rate is 2℃ / min, and the uniformity index is the ratio of the average propagation velocity of the ultrasonic longitudinal wave to the standard deviation of the propagation velocity of the ultrasonic longitudinal wave.

[0027] Furthermore, the process of determining the amount of hydrogen-argon mixture containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment includes:

[0028] Compare the spatial overlap with the preset spatial overlap.

[0029] Based on the spatial overlap being greater than or equal to the preset spatial overlap, the injection rate of the hydrogen-argon mixture containing YCl3 vapor is determined as the first injection rate.

[0030] Based on the fact that the spatial overlap is less than the preset spatial overlap, the injection rate of the hydrogen-argon mixture containing YCl3 vapor is determined to be the second injection rate, wherein...

[0031] The first inlet flow rate is a YCl3 carrier gas flow rate of 0.5 L / min, the second inlet flow rate is a YCl3 carrier gas flow rate of 1.0 L / min, the spatial overlap is the ratio of the overlapping area of ​​the temperature anomaly region and the defect region to the total area of ​​the defect region, the temperature anomaly region is a continuous region where the surface temperature of the preform deviates from the average surface temperature of the preform by ±25°C when the furnace temperature reaches 900°C, and the defect region is a region where the attenuation of the laser ultrasonic signal exceeds 35% of the average attenuation.

[0032] Furthermore, the process of determining the cerium immersion time during molten salt treatment includes:

[0033] The grain boundary strengthening index is compared with the preset grain boundary strengthening index;

[0034] Based on the grain boundary strengthening index being greater than or equal to the preset grain boundary strengthening index, the cerium immersion time in the molten salt treatment is determined as the first immersion time.

[0035] Based on the fact that the grain boundary strengthening index is less than the preset grain boundary strengthening index, the cerium immersion time in the molten salt treatment is determined to be the second immersion time, wherein...

[0036] The first impregnation time is 4 hours, the second impregnation time is 6 hours, and the grain boundary strengthening index is the ratio of 1 to 1 plus the standard deviation coefficient, where the standard deviation coefficient is the ratio of the standard deviation value of the yttrium surface distribution data to the average value of the yttrium surface distribution data.

[0037] Furthermore, based on the fact that the low-temperature cracking index of the FeAl coating is less than the preset low-temperature cracking index of the FeAl coating, the low-temperature resistance of the FeAl coating is determined to be unqualified.

[0038] The low-temperature cracking index is the ratio of 1 to the result of 1 plus the microcrack density, where the microcrack density is the average number of microcracks per unit area in different fields of view.

[0039] Furthermore, in response to the unsatisfactory low-temperature resistance of the FeAl coating, based on the deviation value being less than or equal to a preset deviation threshold, the elemental cerium impregnation time of the next batch preparation process is increased by a first adjustment coefficient; based on the deviation value being greater than the preset deviation threshold, the elemental cerium impregnation time of the next batch preparation process is increased by a second adjustment coefficient, wherein the deviation value is the difference between the preset low-temperature cracking index of the FeAl coating and the measured low-temperature cracking index of the FeAl coating.

[0040] Compared with existing technologies, the advantages of this invention are as follows: This invention ensures the precursor component ratio by matching the Fe / Al foil overlap strategy with the configuration index, avoiding incomplete intermetallic compound formation due to aluminum content fluctuations; it effectively eliminates preforms with interface bonding defects by quantitatively screening the preforms through the preform bonding index, preventing the transmission of inherent defects to subsequent processes; it adaptively adjusts the heating rate of the second reaction heat treatment using the uniformity index measured by ultrasonic guided waves, ensuring precise matching between the heat treatment intensity and the actual state of the preform, avoiding both insufficient reaction and suppressing the generation of overheat stress cracks; it intelligently determines the amount of rare earth yttrium introduced into the gas phase based on the spatial overlap between the temperature field and the defect field, achieving targeted repair of strengthening elements in high-risk areas and balanced enhancement of overall performance; finally, through the synergistic effect of the grain boundary strengthening index and the low-temperature cracking index, a prediction-feedback mechanism for cerium impregnation time is constructed, enabling continuous iterative optimization of the coating's low-temperature resistance performance in practice.

[0041] Furthermore, this invention achieves proactive design and precise pre-setting of precursor component ratios based on the dynamic matching of the Fe and Al foil overlapping layup strategy with the target Fe / Al atomic ratio. When the target component corresponds to a higher Fe / Al atomic ratio, the first overlapping layup strategy is adopted to ensure the kinetic balance of Fe and Al elements during the diffusion reaction process; when the target component corresponds to a lower Fe / Al atomic ratio, the second overlapping layup strategy is activated, directly achieving the required element ratio through physical structure design. This end-to-end layup mechanism ensures the stoichiometric accuracy of the multilayer preform, avoiding incomplete formation of intermetallic compounds or precipitation of impurity phases due to improper initial component ratios, laying a solid foundation for obtaining a FeAl coating with accurate composition, stable phase structure, and dense microstructure.

[0042] Furthermore, this invention uses the embryo layer bonding index to determine the quantitative quality assessment and access control of multi-layer preforms. By combining ultrasonic and metallographic analysis, it comprehensively reflects the acoustic bonding state and microscopic physical defects of the internal interface of the preform. The embryo layer bonding index establishes a clear and quantitative qualification standard for the preform quality, effectively screening out preforms with congenital defects such as poor interface bonding and pores, preventing them from entering subsequent high-temperature processes and causing coating cracking, peeling and other failure risks, thereby improving the process yield and coating reliability.

[0043] Furthermore, this invention adaptively determines the second reaction heat treatment heating rate based on the uniformity index of the preform, achieving a precise match between the heat treatment intensity and the initial state of the material. Preforms with high uniformity have uniform internal diffusion channels and stress distribution, and can use the first heating rate to fully realize their performance potential and improve efficiency; preforms with poor uniformity use the second heating rate, effectively mitigating the risk of reaction stress concentration and crack initiation that may be caused by internal inhomogeneity.

[0044] Furthermore, this invention utilizes the spatial overlap between the temperature field and the defect field to jointly determine the vapor-phase introduction strategy of rare-earth yttrium, achieving targeted delivery and efficient utilization of strengthening elements. High spatial overlap indicates that defects are mainly concentrated in the high-temperature region, a high-risk area for potential failure due to intense reactions and stress concentration. Using a lower flow rate for precise repair avoids waste of rare-earth elements and embrittlement caused by localized overdoping. Low spatial overlap indicates that defects are widely distributed in the preform or are not significantly related to the temperature field, suggesting the need for global grain boundary strengthening. Therefore, a higher flow rate is used to ensure overall performance. This "on-demand allocation" intelligent doping technology improves the strengthening efficiency and economy of Y elements, providing key technical support for obtaining FeAl coatings with excellent high-temperature stability and toughness.

[0045] Furthermore, this invention uses the grain boundary strengthening index to proactively determine the cerium impregnation time, constructing a precision control link for coordinated optimization of upstream and downstream processes. The grain boundary strengthening index robustly reflects the uniformity of Y element distribution and its initial strengthening effect on grain boundaries. A high index indicates uniform Y distribution and excellent grain boundary condition, allowing for supplementary strengthening with Ce element using a shorter impregnation time; a low index indicates uneven Y distribution and insufficient initial strengthening, requiring a longer Ce treatment for deep strengthening and grain boundary purification. This improves the overall performance of the coating, especially the consistency and reliability of low-temperature toughness.

[0046] Furthermore, this invention determines the adjustment range of cerium immersion time by comparing the deviation value of the low-temperature cracking index of the FeAl coating with the preset low-temperature cracking index of the FeAl coating and the preset deviation threshold. This graded adjustment strategy can adapt to raw material fluctuations, equipment status changes, etc., drive the coating quality to be iteratively optimized in actual production, and ultimately achieve a steady improvement in product qualification rate and performance consistency. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the steps of the method for preparing a FeAl coating on a stainless steel surface according to an embodiment of the present invention.

[0048] Figure 2 This is a logic diagram for determining whether a multi-layer preform is qualified in an embodiment of the present invention;

[0049] Figure 3 A logic diagram for determining the amount of hydrogen-argon mixture containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment in an embodiment of the present invention.

[0050] Figure 4 This is a logic diagram for determining whether the low-temperature resistance of the FeAl coating is qualified in an embodiment of the present invention. Detailed Implementation

[0051] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0052] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0053] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0054] Please see Figure 1 As shown, it is a flowchart of the steps of the method for preparing FeAl coating on stainless steel surface according to an embodiment of the present invention.

[0055] A flowchart illustrating the steps of a method for preparing a FeAl coating on a stainless steel surface according to an embodiment of the present invention includes:

[0056] The overlapping layup strategy of Fe foil and Al foil is determined based on the comparison results of the configuration index of FeAl coating and the preset configuration index to form a multilayer preform.

[0057] The quality of the prepared multi-layer preform is determined based on the embryo layer bonding index of the multi-layer preform.

[0058] The qualified multilayer preform is subjected to a first reaction heat treatment, and the propagation speed of the ultrasonic guided wave after the first reaction heat treatment is obtained to determine the uniformity index of the multilayer preform. The heating rate of the second reaction heat treatment is determined based on the comparison result between the uniformity index and the preset uniformity index.

[0059] The temperature anomaly region and defect region in the second reaction heat treatment process are obtained, and the spatial overlap is determined based on the temperature anomaly region and the defect region to determine the amount of hydrogen-argon mixture gas containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment.

[0060] Based on the standard deviation coefficient of yttrium element distribution in the coating section after the second reaction heat treatment, the grain boundary strengthening index is determined to obtain the cerium immersion time in the molten salt treatment.

[0061] The low-temperature cracking index of the FeAl coating after molten salt treatment was obtained and compared with the low-temperature cracking index of the preset FeAl coating to determine whether the low-temperature resistance of the FeAl coating is qualified.

[0062] Based on the fact that the FeAl coating failed to meet the low-temperature resistance requirements, the cerium impregnation time in the next batch preparation process was adjusted.

[0063] The first reaction heat treatment involves heating to 600°C at a rate of 10°C / min under argon protection and holding at that temperature for 120 minutes. The second reaction heat treatment involves heating to 900°C at a first heating rate of 5°C / min or a second heating rate of 2°C / min, switching the protective atmosphere to a hydrogen-argon mixture containing YCl3 vapor, and continuing to heat to 1100°C and holding at that temperature for 180 minutes.

[0064] In this embodiment of the invention, the initial thicknesses of the Fe foil and Al foil are 50 μm and 20 μm, respectively, and the purity of both is not less than 99.5%. Before laying, each foil is ultrasonically cleaned for 15 minutes with acetone and anhydrous ethanol in sequence to remove surface oil and oxides, and then dried in a vacuum drying oven at 80°C for 30 minutes for later use.

[0065] Specifically, this invention ensures the precursor component ratio by matching the Fe / Al foil overlap strategy with the configuration index, avoiding incomplete formation of intermetallic compounds due to fluctuations in aluminum content; it quantitatively screens the preforms using the preform bonding index, effectively eliminating preforms with interface bonding defects and preventing the transmission of inherent defects to subsequent processes; it adaptively adjusts the heating rate of the second reaction heat treatment using the uniformity index measured by ultrasonic guided waves, ensuring precise matching between the heat treatment intensity and the actual state of the preform, avoiding both insufficient reaction and suppressing the generation of overheat stress cracks; it intelligently determines the amount of rare earth yttrium introduced into the gas phase based on the spatial overlap between the temperature field and the defect field, achieving targeted repair of strengthening elements in high-risk areas and balanced enhancement of overall performance; finally, through the synergistic effect of the grain boundary strengthening index and the low-temperature cracking index, it constructs a prediction-feedback mechanism for cerium impregnation time, enabling continuous iterative optimization of the coating's low-temperature resistance performance in practice.

[0066] Specifically, the overlapping layup strategy of Fe foil and Al foil is determined based on the comparison results of the configuration index of FeAl coating and the preset configuration index to form a multilayer preform.

[0067] If the configuration index of the FeAl coating is greater than or equal to the preset configuration index, then the first overlapping layup strategy is determined to be adopted.

[0068] If the configuration index of the FeAl coating is less than the preset configuration index, then the second overlapping layup strategy is adopted.

[0069] In this embodiment of the invention, the configuration index is the atomic ratio of Fe to Al in the target FeAl coating, that is, the ratio of the number of Fe atoms to the number of Al atoms in the target FeAl coating. The preset configuration parameter has a value range of [0.8, 1.2], preferably set to 1.0, that is, the Fe:Al atomic ratio is from 0.8:1 to 1.2:1. However, the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs.

[0070] In this embodiment of the invention, the calculation of the configuration index aims to determine the component ratio of the target FeAl coating to ensure the formation of a single, uniform intermetallic compound layer. The formation of FeAl intermetallic compounds is a typical solid-state diffusion reaction. The phase composition and crystal structure of the coating depend on the initial atomic ratio of Fe and Al. If the ratio is inappropriate, it will lead to the formation of non-target impurity phases. These impurity phases often have different hardness, brittleness, and thermal expansion coefficients than the main phase, and will become stress concentration sources and performance weaknesses inside the coating.

[0071] Understandably, when the configuration index is greater than or equal to the preset configuration index, the composition of the target FeAl coating is biased towards the Fe-rich side. Employing the first overlapping layup strategy, this microscopically ensures that each Al layer has sufficient adjacent Fe layers for diffusion, preventing localized Al excess and the formation of a brittle Al-rich phase. When the configuration index is less than the preset configuration index, the composition of the target FeAl coating is biased towards the Al-rich side, providing a sufficient Al source in its physical structure. This compensates for the higher diffusion rate and potential volatilization loss of Al elements at high temperatures, maintaining the target Al content even after prolonged heat treatment, resulting in a single, uniform intermetallic compound layer.

[0072] In this embodiment of the invention, the first overlapping layup strategy is a symmetrical alternating layup of Fe / Al / Fe / Al… with a total of 40 layers. The second overlapping layup strategy is to increase the proportion of Al foil and adopt the Fe / (Al) / Fe / (Al)… pattern, where (Al) represents a double layer of Al foil, increasing the total number of layers to 60.

[0073] In this embodiment of the invention, the formation process of the multilayer preform is as follows: after the Fe foil and Al foil are laid, they are hot-pressed and kept at 150 MPa and 200°C for 60 minutes, so that the Fe foil and Al foil are initially combined through diffusion and plastic deformation.

[0074] Specifically, this invention achieves proactive design and precise pre-setting of precursor component ratios based on the dynamic matching of Fe and Al foil overlapping layup strategy with the target Fe / Al atomic ratio. When the target component corresponds to a higher Fe / Al atomic ratio, a first overlapping layup strategy is adopted to ensure the kinetic balance of Fe and Al elements during the diffusion reaction process; when the target component corresponds to a lower Fe / Al atomic ratio, a second overlapping layup strategy is activated, directly achieving the required element ratio through physical structure design. This end-to-end layup mechanism ensures the stoichiometric accuracy of the multilayer preform, avoiding incomplete formation of intermetallic compounds or precipitation of impurity phases due to improper initial component ratios, laying a solid foundation for obtaining a FeAl coating with accurate composition, stable phase structure, and dense microstructure.

[0075] Please see Figure 2 As shown, it is a logic diagram for determining whether a multi-layer preform is qualified according to an embodiment of the present invention.

[0076] Specifically, the quality of the prepared multi-layer preform is determined based on the embryo layer bonding index of the multi-layer preform.

[0077] If the embryo layer binding index is greater than or equal to the preset embryo layer binding index, then the multi-layer prefabricated embryo is determined to be qualified.

[0078] If the embryo layer binding index is less than the preset embryo layer binding index, then the multi-layer prefabricated embryo is determined to be unqualified.

[0079] In this embodiment of the invention, the process of determining the layer bonding index is as follows: the interfacial impedance is measured by an ultrasonic flaw detector, and the average interfacial porosity is calculated by metallographic observation. The calculation is performed using the formula: Layer bonding index = A × (Measured interfacial impedance / Preset interfacial impedance) + B × (1 - Average interfacial porosity), where A and B are weighting coefficients, and A + B = 1. The values ​​of the weighting coefficients A and B are both in the range of [0.4, 0.6], preferably A = 0.5 and B = 0.5. The average value of ultrasonic measurements at multiple preset standard measurement points on the surface of the preform to be tested is taken as the measured interfacial impedance. The value range of the preset interfacial impedance is [15, 45]MRayl, and the value range of the preset layer bonding index is [0.85, 1.0], preferably set to 0.90. However, the above values ​​are not limited to these values, and those skilled in the art can adjust them according to actual needs. Unqualified multi-layer preforms need to be disassembled, re-cleaned, and then hot-pressed.

[0080] In this embodiment of the invention, the interfaces between the FeAl coatings in the multilayered preform formed by hot pressing are not completely metallurgically bonded, and may contain microscopic pores, uncontacted areas, or oxide films. These interface defects can become obstacles to uniform interdiffusion of Fe and Al and pathways for crack initiation and propagation during subsequent high-temperature reaction heat treatment. They are also prone to cracking under exothermic reaction or thermal stress. The calculation of the preform bonding index aims to combine the mechanical bonding state and geometric integrity of the interface, reflecting the microscopic interface quality of the FeAl coating.

[0081] Specifically, this invention uses the embryo layer bonding index to determine the quantitative quality assessment and access control of multi-layer preforms. By combining ultrasonic and metallographic analysis, it comprehensively reflects the acoustic bonding state and microscopic physical defects of the internal interface of the preform. The embryo layer bonding index establishes a clear and quantitative qualification standard for the preform quality, effectively screening out preforms with congenital defects such as poor interface bonding and pores, preventing them from entering subsequent high-temperature processes and causing coating cracking, peeling and other failure risks, thereby improving the process yield and coating reliability.

[0082] Specifically, qualified multilayer preforms are subjected to a first reaction heat treatment, and the propagation speed of ultrasonic guided waves after the first reaction heat treatment is obtained to determine the uniformity index of the multilayer preforms. The heating rate of the second reaction heat treatment is determined based on the comparison result between the uniformity index and the preset uniformity index.

[0083] If the uniformity index is greater than or equal to the preset uniformity index, then the heating rate of the second reaction heat treatment is determined to be the first heating rate.

[0084] If the uniformity index is less than the preset uniformity index, then the heating rate of the second reaction heat treatment is determined as the second heating rate.

[0085] In this embodiment of the invention, the first reaction heat treatment process is to raise the temperature to 600°C at 10°C / min under argon protection and hold it for 120 minutes. This process aims to achieve the initial interdiffusion of Fe and Al elements to form a preliminary Fe-Al intermetallic compound, laying the foundation for the subsequent high-temperature reaction.

[0086] In this embodiment of the invention, the purpose of calculating the uniformity index is to perform ultrasonic guided wave detection on the multilayer preform after the first reaction heat treatment, and to obtain a quantitative index characterizing the uniformity of the internal structure of the preform by measuring the propagation speed of the ultrasonic longitudinal wave at different positions of the preform.

[0087] It is understandable that the uniformity index is used to guide the selection of the heating rate for the second reaction heat treatment. If the uniformity index is high, it indicates that the preform has a sufficient reaction and a homogeneous structure, and a faster heating rate can be used to improve efficiency. If the uniformity index is low, it indicates that there are areas of uneven reaction or concentrated defects in the preform, and a slower heating rate should be used to avoid thermal stress concentration that could lead to cracks, thus suppressing coating defects caused by internal inhomogeneity.

[0088] In this embodiment of the invention, immediately after the first reaction heat treatment, the preform is tested using a pulsed ultrasonic guided wave instrument (frequency 5MHz). 25 points are selected on the surface of the preform in a 5×5 grid to measure the propagation speed of the ultrasonic longitudinal wave, and the average value and standard deviation of the ultrasonic longitudinal wave propagation speed are calculated. The uniformity index of the multilayer preform is obtained by the formula being the ratio of the average value of the ultrasonic longitudinal wave propagation speed to the standard deviation of the ultrasonic longitudinal wave propagation speed. The preset uniformity index ranges from [80, 120], preferably set to 110, but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs.

[0089] In this embodiment of the invention, the first heating rate is 5°C / min, and the second heating rate is 2°C / min.

[0090] Specifically, this invention adaptively determines the second reaction heat treatment heating rate based on the uniformity index of the preform, achieving a precise match between the heat treatment intensity and the initial state of the material. Preforms with high uniformity have uniform internal diffusion channels and stress distribution, and can use the first heating rate to fully utilize their performance potential and improve efficiency; preforms with poor uniformity use the second heating rate, effectively mitigating the risk of reaction stress concentration and crack initiation that may be caused by internal inhomogeneity.

[0091] Please see Figure 3 As shown, it is a logic diagram for determining the amount of hydrogen-argon mixture containing YCl3 vapor to switch the protective atmosphere of the second reaction heat treatment environment to the amount of gas introduced in an embodiment of the present invention.

[0092] Specifically, the temperature anomaly region and defect region in the second reaction heat treatment process are obtained, and the spatial overlap is determined based on the temperature anomaly region and the defect region to determine the amount of hydrogen-argon mixture gas containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment.

[0093] If the spatial overlap is greater than or equal to the preset spatial overlap, the amount of hydrogen-argon mixture containing YCl3 vapor is determined as the first amount of gas introduced.

[0094] If the spatial overlap is less than the preset spatial overlap, then the amount of hydrogen-argon mixture containing YCl3 vapor is determined to be the second injection amount.

[0095] In this embodiment of the invention, the second reaction heat treatment is carried out under the protection of hydrogen and argon, with a first heating rate of 5℃ / min or a second heating rate of 2℃ / min to 900℃. The protective atmosphere is then switched to a hydrogen-argon mixture containing YCl3 vapor and the temperature is further increased to 1100℃ and held for 180 minutes. The surface temperature field of the preform is monitored in real time by a high-temperature resistant infrared thermal imager (sampling frequency 10Hz) installed on the observation window of the furnace wall. The evolution of internal defects is detected online using a laser ultrasonic scanning system (resolution 50μm). When the furnace temperature reaches 900℃, temperature abnormality areas and defect areas are identified. Temperature abnormality areas are defined as continuous areas where the surface temperature of the preform deviates from the average surface temperature of the preform by ±25℃ when the furnace temperature reaches 900℃. Defect areas are defined as areas where the laser ultrasonic signal attenuation exceeds 35% of the average attenuation.

[0096] In this embodiment of the invention, the spatial overlap is the ratio of the overlapping area of ​​the temperature anomaly region and the defect region to the total area of ​​the defect region. The preset spatial overlap range is [0.6, 0.8], preferably set to 0.7, but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs.

[0097] In this embodiment of the invention, the first inlet flow rate is a YCl3 carrier gas flow rate of 0.5 L / min, and the second inlet flow rate is a YCl3 carrier gas flow rate of 1.0 L / min.

[0098] In this embodiment of the invention, the mixing ratio of the hydrogen-argon mixture containing YCl3 vapor is as follows: a mixture of 5% H2 and 95% Ar by volume is used as the carrier gas and is introduced into a YCl3 evaporator at a constant temperature of 150±5℃ at a flow rate of 0.5 L / min or 1.0 L / min. At this temperature, YCl3 produces stable saturated vapor, making the outflowing carrier gas a hydrogen-argon mixture saturated with YCl3.

[0099] In this embodiment of the invention, the protective atmosphere of hydrogen and argon in the second reaction heat treatment environment is switched to a hydrogen-argon mixture containing YCl3 vapor, which is generated by a YCl3 evaporator maintained at 150°C. When the furnace temperature is raised to 900°C, the atmosphere is switched, and the temperature is further raised to 1100°C at either the first or second heating rate and held for 180 minutes to allow Fe and Al to fully react and form a FeAl coating. At the same time, Y element enters the coating through gas phase transport and segregates at the grain boundaries, achieving grain boundary strengthening.

[0100] Specifically, this invention uses the spatial overlap between the temperature field and the defect field to jointly determine the gas-phase introduction strategy of rare-earth yttrium, achieving targeted delivery and efficient utilization of strengthening elements. High spatial overlap indicates that defects are mainly concentrated in the high-temperature region, a high-risk area for potential failure due to intense reactions and stress concentration. Using a lower flow rate for precise repair avoids waste of rare-earth elements and embrittlement caused by localized overdoping. Low spatial overlap indicates that defects are widely distributed in the preform or are not closely related to the temperature field, suggesting the need for global grain boundary strengthening. Therefore, a higher flow rate is used to ensure overall performance. This "on-demand allocation" intelligent doping technology improves the strengthening efficiency and economy of Y element, providing key technical support for obtaining FeAl coatings with excellent high-temperature stability and toughness.

[0101] Specifically, the grain boundary strengthening index is determined based on the standard deviation coefficient of the yttrium element distribution in the coating section after the second reaction heat treatment to obtain the cerium element immersion time in the molten salt treatment;

[0102] If the grain boundary strengthening index is greater than or equal to the preset grain boundary strengthening index, then the cerium immersion time in the molten salt treatment is determined as the first immersion time.

[0103] If the grain boundary strengthening index is less than the preset grain boundary strengthening index, then the cerium immersion time in the molten salt treatment is determined to be the second immersion time.

[0104] In this embodiment of the invention, when the grain boundary strengthening index is greater than or equal to the preset grain boundary strengthening index, it indicates that the Y element has achieved uniform distribution and preliminary grain boundary strengthening. At this time, 4 hours of immersion can ensure that the Ce element fully penetrates into the grain boundary, achieves impurity purification and supplementary strengthening, while avoiding over-treatment that leads to the formation of brittle phases. When the grain boundary strengthening index is less than the preset grain boundary strengthening index, it means that the Y element is unevenly distributed or the grain boundary strengthening is insufficient. The immersion time needs to be extended to 6 hours so that the Ce element can more fully cover the weak grain boundary, deeply purify impurities and enhance the grain boundary bonding force. Thus, targeted repair and strengthening of the grain boundary state can be achieved without excessively affecting the performance of the coating substrate.

[0105] In this embodiment of the invention, the process of determining the grain boundary strengthening index is as follows: after the second reaction heat treatment is completed, a sample is cut from the coating, and after mounting and polishing, an electron probe microanalyzer is used to analyze the surface distribution of yttrium in the coating cross section to obtain the surface distribution data of yttrium. The average value and standard deviation of the surface distribution data of yttrium are calculated. The standard deviation coefficient is the ratio of the standard deviation of the surface distribution data of yttrium to the average value of the surface distribution data of yttrium. The grain boundary strengthening index is obtained by 1 / (1+standard deviation coefficient). The preset grain boundary strengthening index has a value range of [0.75, 0.95], preferably set to 0.85, but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs.

[0106] In this embodiment of the invention, the purpose of calculating the grain boundary strengthening index is to perform yttrium element surface distribution analysis on the coating cross section after the second reaction heat treatment, so as to evaluate the uniformity of yttrium element distribution in the coating and its preliminary strengthening effect on grain boundaries.

[0107] Understandably, the grain boundary strengthening index is used to determine the immersion time of cerium in subsequent molten salt treatment: a high grain boundary strengthening index indicates that the yttrium is evenly distributed and the grain boundary is in good condition, so a shorter immersion time can be used for supplementary strengthening; a low index indicates that the yttrium is unevenly distributed or the strengthening is insufficient, so the immersion time needs to be extended to achieve deep grain boundary repair and purification.

[0108] In this embodiment of the invention, the NaCl-KCl-NaF-5wt%CeCl3 mixed molten salt is composed of the following components by mass fraction: NaCl 42.75wt%, KCl 42.75wt%, NaF 9.5wt%, CeCl 35wt%. After the powders of each component are mixed evenly, they are placed in a crucible, melted at 900℃ and kept at that temperature for 1 hour to form a homogeneous molten salt bath for impregnation treatment.

[0109] In this embodiment of the invention, the coated sample that has undergone the second reaction heat treatment is immersed in a mixed molten salt of NaCl-KCl-NaF-5wt%CeCl3 at 900℃, and the first immersion time is 4 hours and the second immersion time is 6 hours. After the treatment is completed, the sample is cooled in air and then ultrasonically cleaned in boiled deionized water for 10 minutes to completely remove residual salt on the surface.

[0110] Specifically, this invention uses the grain boundary strengthening index to proactively determine the cerium impregnation time, constructing a precision control link for coordinated optimization of upstream and downstream processes. The grain boundary strengthening index robustly reflects the uniformity of Y element distribution and its initial strengthening effect on grain boundaries. A high index indicates uniform Y distribution and excellent grain boundary condition, allowing for supplementary strengthening with Ce element using a shorter impregnation time; a low index suggests uneven Y distribution and insufficient initial strengthening, requiring a longer Ce treatment for deep strengthening and grain boundary purification. This improves the overall performance of the coating, especially the consistency and reliability of its low-temperature toughness.

[0111] Please see Figure 4 As shown, it is a logic diagram for determining whether the low-temperature resistance of the FeAl coating is qualified according to an embodiment of the present invention.

[0112] Specifically, the low-temperature cracking index of the FeAl coating after molten salt treatment is obtained and compared with the preset low-temperature cracking index of the FeAl coating to determine whether the low-temperature resistance of the FeAl coating is qualified.

[0113] If the low-temperature cracking index of the FeAl coating is greater than or equal to the preset low-temperature cracking index of the FeAl coating, then the low-temperature resistance of the FeAl coating is deemed qualified.

[0114] If the low-temperature cracking index of the FeAl coating is less than the preset low-temperature cracking index of the FeAl coating, then the low-temperature resistance of the FeAl coating is determined to be unqualified.

[0115] In this embodiment of the invention, the process for determining the low-temperature cracking index of the FeAl coating involves placing the molten salt-treated coating sample in a liquid nitrogen (-196°C) environment for cryogenic treatment for 30 minutes, removing it and allowing it to return to room temperature, observing the coating surface under a scanning electron microscope (SEM), counting the number of microcracks per unit area (mm²), and counting at least 5 different fields of view, each field having an area of ​​not less than 0.5 mm². 2 The number of microcracks with a length exceeding 1 μm is calculated, and the average value is taken as the microcrack density (unit: cracks / mm²). The low-temperature cracking index of FeAl coating is calculated using the formula: FeAl coating low-temperature cracking index = 1 / (microcrack density + 1). The closer the index is to 1, the better the coating's resistance to low-temperature cracking.

[0116] In this embodiment of the invention, the purpose of calculating the low-temperature cracking index is to quantitatively evaluate the crack resistance performance of the FeAl coating under extreme low-temperature environments by subjecting the FeAl coating after molten salt treatment to liquid nitrogen cryogenic treatment. The low-temperature cracking index is used for the quality judgment of the final FeAl coating's low-temperature resistance and process iteration optimization.

[0117] In this embodiment of the invention, the preset low-temperature cracking index of the FeAl coating is in the range of [0.85, 0.95], preferably set to 0.90, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0118] Specifically, the cerium impregnation time in the next batch preparation process is adjusted based on the fact that the FeAl coating fails to meet the low-temperature resistance requirements.

[0119] If the deviation value is less than or equal to the preset deviation threshold, then the immersion time of cerium in the next batch preparation process is increased to the corresponding value by the first adjustment coefficient of 1.10.

[0120] If the deviation value is greater than the preset deviation threshold, the cerium immersion time in the next batch preparation process will be increased to the corresponding value by the second adjustment coefficient of 1.20.

[0121] In this embodiment of the invention, the deviation value is the difference between the preset low-temperature cracking index of the FeAl coating and the measured low-temperature cracking index of the FeAl coating, and the preset deviation threshold value ranges from [0.02, 0.06], preferably set to 0.04.

[0122] Specifically, this invention determines the adjustment range of cerium immersion time by comparing the deviation value of the low-temperature cracking index of the FeAl coating with the preset low-temperature cracking index of the FeAl coating and the preset deviation threshold. This graded adjustment strategy can adapt to raw material fluctuations, equipment status changes, etc., drive the coating quality to be iteratively optimized in actual production, and ultimately achieve a steady improvement in product qualification rate and performance consistency.

[0123] The substrate is 304 stainless steel (100mm×100mm×3mm), and the raw materials are Fe foil (50μm, 99.8%) and Al foil (20μm, 99.5%). Example 1

[0124] (1) Laying and embryo screening: Based on the preset configuration index of 1.0, the first overlapping laying strategy is adopted, with a total of 40 layers. After laying, the embryo is formed by hot pressing at 150MPa and 200℃ for 60 minutes. The embryo layer binding index is calculated by formula to be 1.05 to determine that the embryo is qualified.

[0125] (2) Heat treatment: The qualified embryos are heated to 600°C at 10°C / min under argon protection and held for 120 minutes. The uniformity index is 112.4, which indicates that the embryos have excellent uniformity.

[0126] Under a 5% H2 + 95% Ar atmosphere, the second reaction heat treatment was carried out at the first heating rate. The process was monitored in real time by a high-temperature resistant infrared thermal imager (sampling frequency 10 Hz) and a laser ultrasonic scanning system (resolution 50 μm). When the furnace temperature reached 900℃, the area of ​​the temperature anomaly region was measured to be 3.8 mm², the total area of ​​the defect region was 8.5 mm², the overlapping area was 2.9 mm², and the calculated spatial overlap was 0.34. The second injection rate was then used to continue heating to 1100℃ and holding for 180 minutes.

[0127] (3) Molten salt treatment: After heat treatment, samples were taken and polished. The surface distribution of yttrium was analyzed by an electron probe microanalyzer (accelerating voltage 15kV, beam current 20nA). The average value was 2.35wt%, the standard deviation was 0.41wt%, the standard deviation coefficient was 0.174, and the grain boundary strengthening index was 0.851. The samples were treated in NaCl-KCl-NaF-5wt%CeCl3 molten salt at 900℃ for the first immersion time, followed by air cooling and cleaning.

[0128] Comparative Example 1

[0129] (1) Laying and hot pressing: Fe / Al is used for alternating laying, with a total of 40 layers. Then, it is hot pressed at 150MPa and 200℃ for 60 minutes. If no macroscopic cracks are observed in the preform, it is considered qualified and proceeds to the next process.

[0130] (2) Heat treatment: Under argon protection, the temperature is increased to 600℃ at 10℃ / min and held for 120 minutes. Under a 5%H2+95%Ar atmosphere, the temperature is increased to 1100℃ at a fixed rate of 5℃ / min. When the furnace temperature reaches 900℃, YCl3 carrier gas is introduced at a flow rate of 1.0L / min until the temperature is held at 1100℃ for 180 minutes.

[0131] (3) Molten salt treatment: After the sample was taken out of the furnace at 1100℃, it was fixed and immersed in NaCl-KCl-NaF-5wt%CeCl3 molten salt at 900℃ for 5 hours, followed by air cooling and cleaning.

[0132] Table 1 Test Items and Results

[0133] ,

[0134] In this embodiment of the invention, the mechanical and protective properties of Example 1 are significantly improved, with a microhardness reaching 575 HV. 0.3 Comparison with 385HV in Comparison Example 1 0.3 The bonding strength was improved by approximately 49%, reaching 62 MPa, which is about 29% higher than the 48 MPa of Comparative Example 1. This is attributed to the fact that the present invention eliminates weak bonding regions at the interface through screening by the layer bonding index and regulates the stress distribution and phase formation process through gradient heat treatment guided by the uniformity index. After deep cryogenic shock at -196℃, the microcrack density of Example 1 was as low as 0.05 cracks / mm², which is 82% lower than the 0.28 cracks / mm² of Comparative Example 1. This proves that the cerium impregnation strategy based on the grain boundary strengthening index, combined with the targeted strengthening of yttrium in the early stage, significantly enhances the grain boundary bonding force and toughness. In the high-temperature oxidation experiment at 900℃, the oxidation weight gain of Example 1 was only 0.52 mg / cm², which is 58% lower than the 1.25 mg / cm² of Comparative Example 1. This confirms that the rare earth yttrium targeted doping based on spatial overlap decision effectively promotes the formation of a dense and well-adhesive Al2O3 protective film, verifying the effectiveness of the multi-index linkage regulation of the present invention in improving the overall performance of FeAl coating.

[0135] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a FeAl coating on a stainless steel surface, characterized in that, include: The overlapping layup strategy of Fe foil and Al foil is determined based on the comparison results of the configuration index of FeAl coating and the preset configuration index to form a multilayer preform. The quality of the prepared multi-layer preform is determined based on the embryo layer bonding index of the multi-layer preform. The qualified multilayer preform is subjected to a first reaction heat treatment, and the propagation speed of the ultrasonic guided wave after the first reaction heat treatment is obtained to determine the uniformity index of the multilayer preform. The heating rate of the second reaction heat treatment is determined based on the comparison result between the uniformity index and the preset uniformity index. The temperature anomaly region and defect region in the second reaction heat treatment process are obtained, and the spatial overlap is determined based on the temperature anomaly region and the defect region to determine the amount of hydrogen-argon mixture gas containing YCl3 vapor to be introduced into the protective atmosphere of the second reaction heat treatment environment. Based on the standard deviation coefficient of yttrium element distribution in the coating section after the second reaction heat treatment, the grain boundary strengthening index is determined to obtain the cerium immersion time in the molten salt treatment. The low-temperature cracking index of the FeAl coating after molten salt treatment was obtained and compared with the low-temperature cracking index of the preset FeAl coating to determine whether the low-temperature resistance of the FeAl coating is qualified. Based on the fact that the FeAl coating failed to meet the low-temperature resistance requirements, the cerium impregnation time in the next batch preparation process was adjusted. The first reaction heat treatment involves heating to 600°C at a rate of 10°C / min under argon protection and holding at that temperature for 120 minutes. The second reaction heat treatment involves heating to 900°C at a rate of 5°C / min or 2°C / min under hydrogen and argon protection, then switching the protective atmosphere to a hydrogen-argon mixture containing YCl3 vapor and continuing to heat to 1100°C, holding at that temperature for 180 minutes. The configuration index is the ratio of the number of Fe atoms to the number of Al atoms in the target FeAl coating; The embryo layer bonding index = A × (measured interface wave impedance / preset interface wave impedance) + B × (1 - average interface porosity), where A and B are weighting coefficients, and A + B = 1. The uniformity index is the ratio of the average propagation velocity of the ultrasonic longitudinal wave to the standard deviation of the propagation velocity of the ultrasonic longitudinal wave. The grain boundary strengthening index is the ratio of 1 to the result of 1 plus the standard deviation coefficient, where the standard deviation coefficient is the ratio of the standard deviation value of the surface distribution data of yttrium to the average value of the surface distribution data of yttrium. The abnormal temperature region is a continuous area where the surface temperature of the preform deviates from the average surface temperature of the preform by ±25°C when the furnace temperature reaches 900°C. The defective area is the region where the attenuation of the laser ultrasonic signal exceeds 35% of the average attenuation. The low-temperature cracking index is the ratio of 1 to the result of 1 plus the microcrack density, where the microcrack density is the average number of microcracks per unit area in different fields of view.

2. The method for preparing FeAl coating on stainless steel surface according to claim 1, characterized in that, If the configuration index of the FeAl coating is greater than or equal to a preset configuration index, a first overlapping layup strategy is adopted; if the configuration index of the FeAl coating is less than the preset configuration index, a second overlapping layup strategy is adopted. The first overlapping layup strategy is to symmetrically alternate between Fe and single-layer Al foil, and the second overlapping layup strategy is to alternate between Fe and double-layer Al foil.

3. The method for preparing FeAl coating on stainless steel surface according to claim 1, characterized in that, Based on the embryo layer binding index being greater than or equal to the preset embryo layer binding index, the multi-layer prefabricated embryo is determined to be qualified.

4. The method for preparing FeAl coating on stainless steel surface according to claim 1, characterized in that, The process of determining the heating rate of the second reaction heat treatment includes: Compare the uniformity index with the preset uniformity index; Based on the uniformity index being greater than or equal to the preset uniformity index, the heating rate of the second reaction heat treatment is determined as the first heating rate. Based on the fact that the uniformity index is less than a preset uniformity index, the heating rate of the second reaction heat treatment is determined as the second heating rate, wherein... The first heating rate is 5℃ / min, and the second heating rate is 2℃ / min.

5. The method for preparing FeAl coating on stainless steel surface according to claim 1, characterized in that, The process of determining the amount of hydrogen-argon mixture containing YCl3 vapor introduced into the protective atmosphere of the second reaction heat treatment environment includes: Compare the spatial overlap with the preset spatial overlap. Based on the spatial overlap being greater than or equal to the preset spatial overlap, the injection rate of the hydrogen-argon mixture containing YCl3 vapor is determined as the first injection rate. Based on the fact that the spatial overlap is less than the preset spatial overlap, the injection rate of the hydrogen-argon mixture containing YCl3 vapor is determined to be the second injection rate, wherein... The first inlet flow rate is a YCl3 carrier gas flow rate of 0.5 L / min, the second inlet flow rate is a YCl3 carrier gas flow rate of 1.0 L / min, and the spatial overlap is the ratio of the overlapping area of ​​the temperature anomaly region and the defect region to the total area of ​​the defect region.

6. The method for preparing a FeAl coating on a stainless steel surface according to claim 1, characterized in that, The process of determining the cerium immersion time in molten salt treatment includes: The grain boundary strengthening index is compared with the preset grain boundary strengthening index; Based on the grain boundary strengthening index being greater than or equal to the preset grain boundary strengthening index, the cerium immersion time in the molten salt treatment is determined as the first immersion time. Based on the fact that the grain boundary strengthening index is less than the preset grain boundary strengthening index, the cerium immersion time in the molten salt treatment is determined to be the second immersion time, wherein... The first immersion time is 4 hours, and the second immersion time is 6 hours.

7. The method for preparing a FeAl coating on a stainless steel surface according to claim 1, characterized in that, The low-temperature cracking index of the FeAl coating is determined to be less than the preset low-temperature cracking index of the FeAl coating, indicating that the low-temperature resistance of the FeAl coating is unqualified.

8. The method for preparing FeAl coating on stainless steel surface according to claim 1, characterized in that, In response to the failure of the FeAl coating to meet the low-temperature resistance requirements, based on the deviation value being less than or equal to a preset deviation threshold, the elemental cerium impregnation time for the next batch preparation process is increased by a first adjustment factor. Based on the deviation value being greater than a preset deviation threshold, the cerium impregnation time for the next batch of preparation process is increased by a second adjustment coefficient, wherein the deviation value is the difference between the preset low-temperature cracking index of the FeAl coating and the measured low-temperature cracking index of the FeAl coating.

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