Method for preparing ceramic coating on stainless steel surface, stainless steel connector and application thereof

Abstract

This invention relates to the field of ceramicization technology for metal surfaces, specifically to a method for preparing ceramic coatings on stainless steel surfaces, an adhesive, and their applications. The method includes: S1, preparing multi-layered ceramic coating green bodies on a stainless steel surface, wherein each green body is subjected to warm isostatic pressing after preparation to obtain a ceramic green body, wherein the ceramic green body is composed of multiple green body layers stacked sequentially; S2, decarburizing the ceramic green body, then performing a primary sintering under a nitrogen or inert gas atmosphere and hot isostatic pressing, followed by a secondary sintering under oxygen-permeable conditions. This invention, through dual improvements in preparation process and composition, prepares ceramic coatings with high bonding strength, high uniformity, and high density on stainless steel surfaces, suitable for large-scale industrial application.

Description

Technical fields:

[0001] This invention relates to the field of ceramicization technology for metal surfaces, specifically to a method for preparing a ceramic coating on a stainless steel surface, a stainless steel connector, and its applications. Background technology:

[0002] With the development of modern science and technology, industrial production places increasingly higher demands on material performance. Metal alloys possess high strength, good toughness, and thermal conductivity at high temperatures, but their oxidation resistance is poor, limiting their use at high temperatures. Ceramic materials, on the other hand, exhibit excellent high-temperature oxidation resistance and wear resistance. Therefore, uniformly coating various functional ceramics onto the surface of a base metal (or alloy) to form a composite material combines the excellent physical and mechanical properties of the metal (or alloy) with the advantages of ceramic materials, such as heat resistance, wear resistance, corrosion resistance, superconductivity, and bioactivity. Consequently, this topic has attracted significant attention from scientists and engineers worldwide, becoming a new research hotspot.

[0003] However, in actual use, ceramic coatings may peel off and / or corrode the substrate due to problems such as high porosity, poor bonding strength with the substrate, and uneven coating with leakage points. Therefore, how to prepare ceramic coatings with uniform coating, high bonding strength with the substrate, and good density has become the focus of current research.

[0004] CN110981554A discloses a method for preparing a metal-ceramic coating, comprising the following steps: grinding the surface of a substrate, cleaning, degreasing and drying the ceramic substrate, and preparing an intermediate layer slurry; spraying the intermediate layer coating onto the surface of the ceramic substrate, sintering the ceramic substrate surface coated with the intermediate layer in a central control furnace to obtain a uniform and dense transition layer; preparing a surface coating; spraying the surface slurry onto the ceramic surface, and sintering the ceramic substrate surface coated with the transition layer in a vacuum furnace to obtain a uniform and dense metal-ceramic outer layer.

[0005] CN109665824A discloses a wear-resistant ceramic coating applied to a metal surface, comprising: a metal substrate and a ceramic composite metal coating, wherein the metal substrate is an iron metal substrate, and the ceramic composite metal coating is a coating prepared from a ceramic composite metal material composed of clay, alumina and quartz, wherein the mass percentages of each ceramic composite metal material are: clay 30%-40%, alumina 10%-15%, and quartz 50%-55%; firstly, the ceramic composite metal materials are prepared into a ceramic composite metal coating, then the ceramic composite metal coating is poured onto the surface of the iron metal substrate using a flow coating method, and then dried and fired to form the ceramic composite metal coating.

[0006] The above method optimizes coating performance by adjusting the coating forming process, thereby improving the coating's effectiveness. However, this simple process improvement, especially the direct coating and sintering method, results in coatings with poor uniformity. During drying and sintering, the coating is prone to peeling or cracking, ultimately affecting the yield and performance of the sintered product. Summary of the Invention:

[0007] The purpose of this invention is to overcome the problem that the density and uniformity of ceramic coatings in the prior art need to be improved, and to provide a method for preparing ceramic coatings on stainless steel surfaces, stainless steel connectors and their applications.

[0008] To achieve the above objectives, one objective of the present invention is to provide a method for preparing a ceramic coating on a stainless steel surface, the method comprising:

[0009] S1. A multi-layer ceramic-coated green body is prepared on the surface of stainless steel. Each green body is subjected to warm isostatic pressing after preparation to obtain a ceramic green body. The ceramic green body is composed of multiple green body layers stacked sequentially.

[0010] S2. The ceramic green body is decarburized, then sintered under hot isostatic pressing in a nitrogen or inert gas atmosphere, and then sintered under oxygen conditions.

[0011] A second objective of this invention is to provide a stainless steel connector, comprising a stainless steel substrate and a ceramic coating covering the surface of the stainless steel substrate, wherein the ceramic coating is prepared according to the aforementioned method.

[0012] A third objective of this invention is to provide the application of the aforementioned stainless steel connector in solid oxide fuel cells.

[0013] Through the above technical solution, the present invention has the following technical effects:

[0014] (1) The present invention uses a multi-layer preparation method to obtain a coated green blank. Each layer is subjected to warm isostatic pressing after preparation, which improves the thickness uniformity of the coating and the bonding strength between the coating and the substrate, and avoids the green blank peeling and warping caused by the thick thickness of the green blank formed in one step.

[0015] (2) In this invention, low carbon alcohol is added to the raw materials as an additional solvent to reduce the overall viscosity of the system, avoid the inability to form due to excessive viscosity of the slurry, and prevent the green body from cracking again due to insufficient binder dosage. Low carbon alcohol itself is volatile, so it will not introduce excessive carbon into the system, causing an increase in coating porosity.

[0016] (3) The present invention can increase the temperature of the initial sintering by hot isostatic pressing under nitrogen or inert gas atmosphere, thereby increasing the density of the coating. Finally, oxygen treatment can be carried out to allow the reduced coating to continue to oxidize, thus avoiding the failure of the ceramic coating.

[0017] (4) This invention prepares a ceramic coating with high bonding strength, high uniformity and high density on the surface of stainless steel through dual improvements in preparation process and composition, which is suitable for large-scale industrial promotion. Attached image description:

[0018] Figure 1 A process flow diagram for preparing a ceramic coating on a stainless steel surface;

[0019] Figure 2 The results of the tensile test on the coated sample of Example 2 are shown.

[0020] Figure 3 Metallographic photograph of the green sample from Example 3;

[0021] Figure 4 SEM images of the green sample from Example 3 (left) and the green sample from Comparative Example 1 (right);

[0022] Figure 5 The XRD patterns are of the coated samples of Example 3 and Comparative Example 10. Detailed implementation method:

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] In this invention, the sintering temperature of ceramic powder refers to the temperature at which the ceramic powder reaches the state of minimum pore size, maximum shrinkage, highest product density, best performance, or becomes a solid aggregate through sintering.

[0026] The process flow diagram for preparing ceramic coatings on stainless steel surfaces is as follows: Figure 1 As shown, the present invention provides a method for preparing a ceramic coating on a stainless steel surface, the method comprising:

[0027] S1. A multi-layer ceramic-coated green body is prepared on the surface of stainless steel. Each green body is subjected to warm isostatic pressing after preparation to obtain a ceramic green body. The ceramic green body is composed of multiple green body layers stacked sequentially.

[0028] S2. The ceramic green body is decarburized, then sintered under hot isostatic pressing in a nitrogen or inert gas atmosphere, and then sintered under oxygen conditions.

[0029] In this invention, the methods for preparing the ceramic coating green body include, but are not limited to, screen printing, dip-coating, sol-gel, spin coating, ultrasonic atomization spraying, electrostatic spraying, and cold spraying.

[0030] In this invention, the thickness of each green body layer should not exceed 30 μm. Otherwise, excessively thick green bodies will cause uneven heating of the coating during the heating process, leading to peeling and warping, and reducing the yield of the finished green body. However, it should not be too thin either, as this would increase the number of cold spraying operations and increase production costs. Preferably, the thickness of the green body layer is 15-25 μm. Preferably, the thickness of the ceramic green body is 30-50 μm. To save costs, the number of ceramic green body layers is 2-4.

[0031] In this invention, the pressure of each warm isostatic pressing (WIP) should be as high as possible, while the temperature of the WIP process should be controlled within a suitable range. Excessive temperature can cause undried slurry inside the ceramic green body to volatilize to the surface, resulting in the green body sticking to and detaching from the packaging bag. Conversely, if the WIP temperature is too low, the green body cannot fully soften and densify under low temperature and high pressure, resulting in a coating with high porosity and reduced bonding strength with the substrate after sintering. Preferably, the WIP process includes: a pressure of 20-60 MPa, a temperature of 50-80°C, and a time of 1-10 minutes.

[0032] In this invention, if the decarburization temperature is too low or the time is too short, decarburization may be incomplete; if the decarburization temperature is too high or the time is too long, the substrate may be over-oxidized during the decarburization process, leading to coating failure. Preferably, the decarburization process includes: a temperature of 400-600℃ and a time of 30-90 minutes.

[0033] This invention improves the density of the coating and the bonding strength between the coating and the substrate by performing a primary sintering under hot isostatic pressing (HIP) followed by a secondary sintering under oxygen-permeable conditions. Performing the primary sintering under HIP, and adjusting the primary sintering temperature according to the sintering temperature of the ceramic powder, can improve the density of the coating. Preferably, the primary sintering process includes: a temperature 100-150°C higher than the sintering temperature of the ceramic powder, a time of 1-4 hours, and a sintering pressure of 40-80 MPa, preferably 60-80 MPa. For example, when the sintering temperature of the ceramic powder is 900°C, the primary sintering temperature can be 1000-1050°C; when the sintering temperature of the ceramic powder is 1000°C, the primary sintering temperature can be 1100-1150°C.

[0034] Furthermore, since the initial sintering is carried out under an inert gas or nitrogen atmosphere and hot isostatic pressing (HIP), the oxygen partial pressure in the environment is very low during HIP. This inevitably leads to the loss of oxygen from the ceramic coating, resulting in the reduction of the ceramic coating. This results in a large number of vacancies and defects within the ceramic coating, which in turn reduces the density and bonding strength of the coating. Secondary sintering under oxygen-rich conditions can oxidize the reduced ceramic. Additionally, if the secondary sintering temperature is too low or the time is too short, oxygen may not diffuse sufficiently within the ceramic coating, resulting in incomplete oxygenation. Preferably, the secondary sintering process includes: an oxygen flow rate of 100-300 mL / min, a temperature of 500-800 °C, and a time of 1-5 h.

[0035] The inventors of this invention also unexpectedly discovered that adding additional low-carbon alcohols to the ceramic slurry can improve the uniformity of the coating. Preferably, the ceramic slurry comprises, by weight, the following components: 30-50 parts ceramic powder, 35-45 parts terpineol, 2-5 parts ethyl cellulose, 30-50 parts low-carbon alcohol, 1-3 parts sodium dodecylbenzenesulfonate, and 0.5-2.5 parts polyether defoamer.

[0036] Preferably, the viscosity of the ceramic slurry is 300-1500 cp.

[0037] Preferably, the sintering temperature of the ceramic powder is not higher than 1000℃; if the sintering temperature of the ceramic powder is too high, the forming temperature of the ceramic on the metal surface will increase, causing thermal deformation of the substrate, or even damage by high temperature.

[0038] Preferably, the lower alcohol is selected from at least one of methanol, ethanol, n-propanol and isopropanol.

[0039] Preferably, the ceramic powder is selected from at least one of strontium lanthanum manganate powder, manganese cobaltate powder, lanthanum cobaltate powder, and copper manganate powder. Preferably, the particle size D50 of the ceramic powder is 20-60 nm.

[0040] The present invention also provides a stainless steel connector, comprising a stainless steel substrate and a ceramic coating covering the surface of the stainless steel substrate, the ceramic coating being prepared according to the aforementioned method.

[0041] The present invention also provides the application of the stainless steel connector in solid oxide fuel cells (SOFCs), particularly in intermediate temperature solid oxide fuel cells.

[0042] The present invention will be described in detail below through embodiments.

[0043] Test method:

[0044] 1. Thickness uniformity test:

[0045] The coating thickness uniformity was tested according to GB / T 6462-2005. Specifically, the thickness of the coating cross-section was measured using metallographic microscopy, the thickness range was calculated, and then the thickness uniformity was calculated based on the thickness. The formula for calculating thickness uniformity is as follows:

[0046]

[0047] Among them, X max X represents the maximum thickness in μm. min ε represents the minimum thickness in μm; ε indicates thickness uniformity in %; the smaller the ε value, the higher the thickness uniformity of the coating.

[0048] 2. Bond strength test:

[0049] Tensile tests are performed according to the method of GB / T228.1-2010. In the tensile test, the maximum tensile stress that the specimen experiences until it breaks is called the tensile strength (i.e., bond strength).

[0050] 3. Porosity test:

[0051] a. The sample to be tested is inlaid in metallography and polished on a metallographic polishing machine (the standard is that there are no obvious scratches in the area to be tested when observed under a metallographic microscope).

[0052] b. Take metallographic photographs of the polished sample, with the photographed area being the area to be tested (500X);

[0053] c. Use Image Pro Plus software to test the porosity of metallographic photographs.

[0054] 4. Greenware yield test:

[0055] The green blank yield test is the ratio of qualified products (without surface cracks or warping defects) to the total number of green blanks.

[0056] 5. Sintering yield test:

[0057] The sintering yield test is the ratio of qualified products (no cracks in the surface coating, no powder shedding, and no impurities detected by XRD) to the total number of products in the sintering process.

[0058] Example 1

[0059] A method for preparing a ceramic coating on a stainless steel surface includes the following steps:

[0060] Step S1:

[0061] The slurry was prepared according to the following weight ratio: 30 parts of lanthanum strontium manganate powder (LSM, sintering temperature of 960℃, D50 of 20nm), 35 parts of terpineol, 2 parts of ethyl cellulose, 40 parts of ethanol, 1 part of sodium dodecylbenzene sulfonate, and 0.5 parts of polyether defoamer were mixed and ball-milled to obtain ceramic slurry. The ball milling method was horizontal ball milling, the ball milling time was 20min, the ball milling speed was 100rpm, and the viscosity of the ceramic slurry after ball milling was 300cp.

[0062] The stainless steel substrate was sandblasted, and the average surface roughness Ra of the metal substrate after sandblasting was 5μm.

[0063] Step S2:

[0064] Ceramic slurry was screen-printed onto the surface of a stainless steel substrate and dried at 70°C to obtain a first green layer with a thickness of 15μm.

[0065] The stainless steel substrate covered with the first green layer was subjected to warm isostatic pressing to obtain a first warm isostatic pressing sample. The processing pressure was 20 MPa, the processing temperature was 50 °C, and the holding time was 1 min.

[0066] A ceramic slurry was screen-printed twice on the surface of a sample subjected to isostatic pressing. After drying, a second green body layer with a thickness of 15 μm was obtained. At this time, the total thickness of the ceramic green body on the stainless steel surface was 30 μm.

[0067] The sample covered with the second green layer was subjected to warm isostatic pressing to obtain a secondary warm isostatic pressing sample. The processing pressure was 20 MPa, the processing temperature was 50 °C, and the holding time was 1 min.

[0068] Step S3:

[0069] The secondary isostatically pressed sample was placed in a muffle furnace for decarburization treatment at a temperature of 400℃ for 30 minutes.

[0070] In an argon atmosphere, the decarburized sample was sintered under hot isostatic pressing (HIP) conditions at a temperature of 1100℃, a holding time of 1 h, and a sintering pressure of 40 MPa.

[0071] The vacuum-sintered sample was sintered under oxygen-permeable conditions at a temperature of 500℃ for 1 hour with an oxygen flow rate of 100 mL / min.

[0072] The performance data of the coating in this embodiment are shown in Table 1.

[0073] Example 2

[0074] A method for preparing a ceramic coating on a stainless steel surface includes the following steps:

[0075] Step S1:

[0076] The slurry was prepared according to the following weight ratio: 50 parts of lanthanum strontium manganate powder (LSM, sintering temperature of 980℃, D50 of 60nm), 45 parts of terpineol, 5 parts of ethyl cellulose, 30 parts of ethanol, 3 parts of sodium dodecylbenzene sulfonate, and 2.5 parts of polyether defoamer were mixed and ball-milled to obtain ceramic slurry. The ball milling method was horizontal ball milling, the ball milling time was 50min, the ball milling speed was 150rpm, and the viscosity of the ceramic slurry after ball milling was 1500cp.

[0077] The stainless steel substrate was sandblasted, and the average surface roughness Ra of the metal substrate after sandblasting was 15μm.

[0078] Step S2:

[0079] Ceramic slurry was cold-sprayed onto the surface of a stainless steel substrate and dried to obtain a first green layer with a thickness of 25 μm.

[0080] The stainless steel substrate covered with the first green layer was subjected to warm isostatic pressing to obtain a first warm isostatic pressing sample. The processing pressure was 60 MPa, the processing temperature was 80℃, and the holding time was 10 min.

[0081] A second green body with a thickness of 25 μm was obtained by cold spraying ceramic slurry onto the surface of a sample subjected to isostatic pressing and drying. At this time, the total thickness of the ceramic green body on the stainless steel surface was 50 μm.

[0082] The sample covered with the second green layer was subjected to warm isostatic pressing to obtain a secondary warm isostatic pressing sample. The processing pressure was 60 MPa, the processing temperature was 80 °C, and the holding time was 10 min.

[0083] Step S3:

[0084] The secondary isostatically pressed sample was placed in a muffle furnace for decarburization treatment at a temperature of 600℃ for 90 minutes.

[0085] In an argon atmosphere, the decarburized sample was sintered under hot isostatic pressing (HIP) conditions at a temperature of 1130℃, a holding time of 4h, and a sintering pressure of 60MPa.

[0086] The vacuum-sintered sample was sintered under oxygen-permeable conditions at a temperature of 800℃ for 5 hours, with an oxygen flow rate of 300 mL / min.

[0087] The performance data of the coating in this embodiment are shown in Table 1.

[0088] Figure 2 The results are from the tensile test of the coated sample in Example 2.

[0089] Example 3

[0090] A method for preparing a ceramic coating on a stainless steel surface includes the following steps:

[0091] Step S1:

[0092] The slurry was prepared according to the following weight ratio: 40 parts of lanthanum strontium manganate powder (LSM, sintering temperature of 960℃, D50 of 20nm), 40 parts of terpineol, 3 parts of ethyl cellulose, 50 parts of ethanol, 2 parts of sodium dodecylbenzene sulfonate, and 1.5 parts of polyether defoamer were mixed and ball-milled to obtain ceramic slurry. The ball milling method was horizontal ball milling, the ball milling time was 30min, the ball milling speed was 120rpm, and the viscosity of the ceramic slurry after ball milling was 1000cp.

[0093] The stainless steel substrate was sandblasted, and the average surface roughness Ra of the metal substrate after sandblasting was 10 μm.

[0094] Step S2:

[0095] Ceramic slurry was cold-sprayed onto the surface of a stainless steel substrate and dried to obtain a first green layer with a thickness of 20 μm.

[0096] The stainless steel substrate covered with the first green layer was subjected to warm isostatic pressing to obtain a first warm isostatic pressing sample. The processing pressure was 40 MPa, the processing temperature was 60 °C, and the holding time was 5 min.

[0097] A second green body with a thickness of 20 μm was obtained by cold spraying ceramic slurry onto the surface of a sample subjected to isostatic pressing and drying. At this time, the total thickness of the ceramic green body on the stainless steel surface was 40 μm.

[0098] The sample covered with the second green layer was subjected to warm isostatic pressing to obtain a secondary warm isostatic pressing sample. The processing pressure was 40 MPa, the processing temperature was 60 °C, and the holding time was 5 min.

[0099] Step S3:

[0100] The secondary isostatically pressed sample was placed in a muffle furnace for decarburization treatment at a temperature of 500℃ for 60 minutes.

[0101] In an argon atmosphere, the decarburized sample was sintered under hot isostatic pressing at a temperature of 1080℃ for 3 hours and a pressure of 80MPa.

[0102] The vacuum-sintered sample was sintered under oxygen-permeable conditions at a temperature of 600℃ for 3 hours, with an oxygen flow rate of 200 mL / min.

[0103] The performance data of the coating in this embodiment are shown in Table 1.

[0104] Figure 3 Metallographic photographs of the green sample from Example 3. Figure 3 As can be seen, the coating thickness of the green blank has good uniformity.

[0105] Comparative Example 1

[0106] The method of Example 3 is the same, except that the ceramic slurry does not contain ethanol; that is, the composition of the slurry is as follows: 40 parts of strontium lanthanum manganate powder, 90 parts of terpineol, 3 parts of ethyl cellulose, 2 parts of sodium dodecylbenzene sulfonate, and 1.5 parts of polyether defoamer; the performance data of the coating in this comparative example are shown in Table 1.

[0107] Figure 4 SEM images of the green sample from Example 3 (left) and Comparative Example 1 (right) are shown. Figure 4 As can be seen, when ethanol is not added as a solvent, the viscosity of the slurry increases, and the coating green body will crack and warp after drying.

[0108] As shown in Table 1, compared with Example 3, the coating thickness uniformity and density of Comparative Example 1 are worse. The possible reason is that after not using ethanol as a solvent, the overall viscosity of the system increases, which makes it difficult to form during the green body forming process. Some slurry clumps, resulting in a decrease in uniformity and an increase in defects.

[0109] Comparative Example 2

[0110] The method of Example 3 is the same, except that the sintering temperature of the lanthanum strontium manganate powder (particle size of 2 μm) is different. In this comparative example, the sintering temperature of the lanthanum strontium manganate powder is 1200℃.

[0111] The performance data of the coating in this comparative example are shown in Table 1.

[0112] As shown in Table 1, compared with Example 3, the tensile strength and density of the coating obtained in Comparative Example 2 were significantly reduced. This indicates that when the sintering temperature of the lanthanum strontium manganate powder is increased without correspondingly increasing the sintering temperature of the sample under vacuum conditions, the original sintering temperature is insufficient to densify the coating, ultimately resulting in a decrease in the density and strength of the coating.

[0113] Comparative Example 3

[0114] The method is the same as in Example 3, except that a ceramic green layer with a thickness of 40 μm is directly cold-sprayed onto a stainless steel substrate in one step.

[0115] Step S2:

[0116] Ceramic slurry was cold-sprayed onto the surface of a stainless steel substrate and dried to obtain a green layer with a thickness of 40 μm.

[0117] The stainless steel substrate covered with the green blank layer was subjected to warm isostatic pressing to obtain a warm isostatic pressing sample. The processing pressure was 40 MPa, the processing temperature was 60 °C, and the holding time was 5 min.

[0118] The performance data of the coating in this comparative example are shown in Table 1.

[0119] As shown in Table 1, the thickness uniformity of Comparative Example 3 is significantly worse than that of Example 3, exceeding 10%. This indicates that the uniformity of coating thickness cannot be guaranteed after only one green forming and isostatic pressing.

[0120] Comparative Example 4

[0121] The method is the same as in Example 3, except that the ceramic green body is not subjected to warm isostatic pressing.

[0122] Step S2:

[0123] Ceramic slurry was cold-sprayed onto the surface of a stainless steel substrate and dried to obtain a first green layer with a thickness of 20 μm.

[0124] A second green layer with a thickness of 20 μm is obtained by cold spraying ceramic slurry onto the surface of a stainless steel substrate covered with the first green layer and drying it. At this time, the total thickness of the ceramic green layer on the stainless steel surface is 40 μm.

[0125] The performance data of the coating in this comparative example are shown in Table 1.

[0126] As shown in Table 1, compared to Example 3, the coating obtained in Comparative Example 4 exhibited significantly worse thickness uniformity, bonding strength with the substrate, density, and green blank yield. This indicates that when isostatic pressing is not performed on the green blank, multiple cold spraying processes can actually degrade the coating performance.

[0127] Comparative Example 5

[0128] The method is the same as in Example 3, except that the temperature for isostatic pressing is 40°C.

[0129] The performance data of the coating in this comparative example are shown in Table 1.

[0130] As shown in Table 1, compared with Example 3, the coating density and green yield of Comparative Example 5 were significantly reduced. This indicates that when the temperature of warm isostatic pressing is lowered, the green body cannot be sufficiently softened and densified under low temperature and high pressure, resulting in a higher porosity of the coating after sintering, and a decrease in both bonding strength and yield.

[0131] Comparative Example 6

[0132] The method is the same as in Example 3, except that the thickness of the first green body layer and the second green body layer is 40 μm, and the total thickness of the ceramic green body is 80 μm.

[0133] The performance data of the coating in this comparative example are shown in Table 1.

[0134] As shown in Table 1, compared with Example 3, the thickness uniformity, density and green yield of Comparative Example 6 were significantly reduced. The reason for this problem is similar to that of Comparative Example 4. Increasing the coating thickness of the green blank will lead to an increase in coating defects, which in turn will lead to the deterioration of subsequent performance.

[0135] Comparative Example 7

[0136] The method is the same as in Example 3, except that the decarburization temperature is 700°C.

[0137] The performance data of the coating in this comparative example are shown in Table 1.

[0138] As shown in Table 1, the bonding strength between the coating and the substrate obtained in Comparative Example 7 decreased significantly compared to Example 3. This indicates that increasing the decarburization temperature will cause oxidation of the substrate, but increasing the decarburization temperature will not affect the ceramic itself. This is because the ceramic itself is an oxide and is difficult to be affected by oxygen in the air. However, after the substrate is oxidized, a loose oxide layer is formed, which in turn leads to a decrease in the bonding strength between the coating and the substrate.

[0139] Comparative Example 8

[0140] The method is the same as in Example 3, except that the oxygenation temperature is 900°C and the oxygen flow rate is 400 mL / min during the oxygenation process.

[0141] The performance data of the coating in this comparative example are shown in Table 1.

[0142] As shown in Table 1, the bonding strength between the coating and the substrate in Comparative Example 8 was significantly lower than that in Example 3. This indicates that increasing the oxygenation temperature causes oxidation of the substrate, which in turn reduces the bonding strength between the coating and the substrate.

[0143] Comparative Example 9

[0144] The method is the same as in Example 3, except that the sample obtained from the decarburization treatment is sintered directly under oxygen-bearing conditions.

[0145] Step S3:

[0146] The secondary isostatically pressed sample was placed in a muffle furnace for decarburization treatment at a temperature of 500℃ for 60 minutes.

[0147] The decarburized sample was sintered under oxygen-permeable conditions at a temperature of 1120℃ for 3 hours, with an oxygen flow rate of 200 mL / min.

[0148] The performance data of the coating in this comparative example are shown in Table 1.

[0149] As shown in Table 1, direct high-temperature sintering under oxygen-bearing conditions will cause the substrate to be damaged and melt together with the coating, resulting in complete coating failure.

[0150] Comparative Example 10

[0151] The method of Example 3 is the same, except that the sample obtained by decarburization is sintered only under vacuum conditions.

[0152] Step S3:

[0153] The secondary isostatically pressed sample was placed in a muffle furnace for decarburization treatment at a temperature of 500℃ for 60 minutes.

[0154] In an argon atmosphere, the decarburized sample was sintered under hot isostatic pressing at a temperature of 1080℃ for 3 hours and a pressure of 80MPa.

[0155] The performance data of the coating in this comparative example are shown in Table 1.

[0156] Figure 5 The XRD patterns of the coating samples of Example 3 and Comparative Example 10 show that when oxygenation is not performed, the LSM peak in the obtained coating is weak and a large number of impurity peaks appear, indicating that the coating obtained by vacuum sintering contains other impurities besides LSM.

[0157] As shown in Table 1, the bonding strength between the coating and the substrate obtained in Comparative Example 10 is reduced compared to Example 3. The possible reason is that when oxygenation is not performed, there are a large number of vacancies and defects inside the coating, which will lead to a decrease in the density and strength of the coating.

[0158] Comparative Example 11

[0159] The method is the same as in Example 3, except that the oxygenation temperature is 400°C.

[0160] The performance data of the coating in this comparative example are shown in Table 1.

[0161] As shown in Table 1, compared with Example 3, the density of the coating and substrate obtained in Comparative Example 11 decreased, indicating that when the oxygenation temperature was reduced, the temperature at which oxygen could diffuse sufficiently in the coating was not reached, resulting in incomplete oxygenation and a higher porosity of the coating.

[0162] Table 1

[0163]

[0164]

[0165] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a ceramic coating on a stainless steel surface, characterized in that, The method includes: S1. A multi-layer ceramic coating green body is prepared by cold spraying ceramic slurry on a stainless steel surface. Each green body is subjected to warm isostatic pressing after preparation to obtain a ceramic green body. The ceramic green body is composed of multiple green body layers stacked sequentially. The temperature isostatic pressing process includes: a pressure of 20-60 MPa, a temperature of 50-80°C, and a time of 1-10 min; The thickness of the green layer is 15-25 μm; The ceramic slurry comprises the following components: 30-50 parts ceramic powder, 35-45 parts terpineol, 2-5 parts ethyl cellulose, 30-50 parts low-carbon alcohol, 1-3 parts sodium dodecylbenzene sulfonate, and 0.5-2.5 parts polyether defoamer. The sintering temperature of the ceramic powder is not higher than 1000℃; S2. The ceramic green body is decarburized, then sintered under hot isostatic pressing in a nitrogen or inert gas atmosphere, and then sintered under oxygen conditions. The decarbonization process includes: a temperature of 400-600℃ and a time of 30-90 minutes; The initial sintering process includes: a sintering temperature 100-150°C higher than the sintering temperature of the ceramic powder, a sintering time of 1-4 hours, and a sintering pressure of 40-80 MPa. The secondary sintering process includes: an oxygen flow rate of 100-300 mL / min, a temperature of 500-800℃, and a time of 1-5 h.

2. The method according to claim 1, characterized in that, The thickness of the ceramic green body is 30-50 μm.

3. The method according to claim 2, characterized in that, The ceramic slurry is cold-sprayed 2-4 times.

4. The method according to any one of claims 1-3, characterized in that, The viscosity of the ceramic slurry is 300-1500 cp.

5. The method according to claim 4, characterized in that, The ceramic powder is selected from at least one of strontium lanthanum manganate powder, manganese cobaltate powder, lanthanum cobaltate powder, and copper manganate powder.

6. The method according to claim 5, characterized in that, The particle size D50 of the ceramic powder is 20-60 nm.

7. A stainless steel connector comprising a stainless steel substrate and a ceramic coating covering the surface of the stainless steel substrate, wherein the ceramic coating is prepared by the method according to any one of claims 1-6.

8. The application of the stainless steel connector according to claim 7 in a solid oxide fuel cell.

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