Aluminide protective coating with Cr3Si diffusion barrier introduced in advance and preparation method of aluminide protective coating

Abstract

The invention relates to the technical field of high-temperature protective coatings, and discloses an aluminide protective coating with a Cr3Si diffusion barrier introduced in advance and a preparation method of the aluminide protective coating. The aluminide protective coating comprises a Cr-rich layer, a Cr3Si diffusion barrier layer and an aluminide layer which are sequentially arranged on the surface of the base material before thermal diffusion is completed; and the content of Cr atoms in the Cr-rich layer is not less than 90 at.%. According to the aluminide protective coating disclosed by the invention, element interdiffusion between the aluminide layer and the base material can be effectively prevented, and the aluminide protective coating has relatively good stability and stripping resistance at high temperature, so that a relatively good protective effect can be kept in a long-term service period.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature protective coatings, and in particular to an aluminide protective coating with a Cr3Si diffusion barrier pre-introduced therein and a preparation method thereof. Background Art

[0002] Aluminide protective coatings have the advantages of low cost and simple preparation process, and are often widely used as high-temperature protective materials in modern industrial systems. In the context of large-scale application of supercritical unit technology, the microstructural evolution and life prediction methods of aluminide protective coatings in service environments of 500-700°C are increasingly receiving attention. Currently, commonly used methods for preparing aluminide protective coatings include slurry aluminizing, hot-dip aluminizing, chemical vapor deposition, and electrochemical deposition. These methods each have their own advantages and disadvantages in practical applications, but in general, they are based on the mutual diffusion of elements between the coating raw material and the substrate, ultimately forming a coating layer of a certain thickness composed of one or more aluminides.

[0003] During actual service, interdiffusion of elements between the aluminide protective coating and the base alloy can easily occur, leading to changes in the coating's composition and structure. This reduces the amount of aluminum in the coating, weakening its protective effect and making it difficult to maintain adequate antioxidant and corrosion resistance. Currently, research on aluminide protective coatings primarily focuses on optimizing the coating's composition to enhance its protective effectiveness (e.g., patent CN118773602A), while less research has focused on reducing interdiffusion between the coating and the base alloy. Summary of the Invention

[0004] To address the technical problem of elemental interdiffusion between aluminide protective coatings and substrate alloys, which weakens the coating's protective properties, the present invention provides an aluminide protective coating pre-introduced with a Cr3Si diffusion barrier and a method for preparing the coating. The aluminide protective coating of the present invention effectively prevents elemental interdiffusion between the aluminide layer and the substrate, and exhibits excellent stability and spalling resistance at high temperatures, thereby maintaining effective protective performance over long periods of service.

[0005] The specific technical solutions of the present invention are: In a first aspect, the present invention provides an aluminide protective coating with a pre-introduced Cr3Si diffusion barrier, wherein the aluminide protective coating comprises a Cr-rich layer, a Cr3Si diffusion barrier layer, and an aluminide layer sequentially arranged on the surface of a substrate before thermal diffusion is completed; the content of Cr atoms in the Cr-rich layer is not less than 90 at.%.

[0006] After thermal diffusion of the aluminide protective coating of the present invention (during the preparation of the aluminide protective coating, elements undergo interlayer diffusion through high-temperature treatment), a diffusion barrier primarily composed of the Cr3Si phase exists between the aluminide layer and the substrate. (The "Cr3Si diffusion barrier layer" and "Cr3Si diffusion barrier" referred to in the present invention do not mean that the layer or diffusion barrier is entirely composed of the Cr3Si phase, but rather refers to a diffusion barrier layer primarily composed of the Cr3Si phase.) Using the Cr3Si phase as the primary diffusion barrier material, the calculated enthalpy of formation of Cr3Si is negative from a thermodynamic perspective, indicating good thermodynamic stability. From a crystallographic perspective, Cr3Si has a very stable crystal structure, containing three tetrahedral interstices and four triangular basal bipyramid interstices. However, only the tetrahedral interstices and the largest bipyramid positions are preferential sites for interstitial atoms. Interstitial atoms, including oxygen atoms, can only diffuse to adjacent tetrahedral or bipyramid positions. This means that elemental diffusion requires greater energy, thereby inhibiting interdiffusion of elements. Therefore, the Cr3Si diffusion barrier layer in the present invention can effectively prevent the mutual diffusion of elements between the aluminide layer and the substrate, thereby enabling the aluminide layer to maintain a good protective effect during long-term service.

[0007] In addition, if a Cr3Si diffusion barrier layer is formed directly on the surface of the substrate, although it can significantly hinder the elemental interdiffusion between the aluminide layer and the Cr-rich layer, the high stability of Cr3Si makes it difficult for it to effectively diffuse with the substrate during the coating preparation process, resulting in too low a bonding strength between the Cr3Si diffusion barrier layer and the substrate. To solve this problem, the present invention sets a Cr-rich layer between the substrate and the Cr3Si diffusion barrier layer. Since the Cr element has a high solubility in the alloy substrate, the Cr-rich layer can diffuse with the substrate during the thermal diffusion process, thereby enhancing the bonding strength between the two. At the same time, the Cr-rich layer and the Cr3Si diffusion barrier layer have similar elemental compositions. During the thermal diffusion process, the Cr-rich layer and the Cr3Si diffusion barrier layer can also diffuse with each other, ultimately forming a uniform Cr3Si diffusion barrier. In this way, after the thermal diffusion is completed, the Cr-rich layer can improve the bonding strength between the substrate and the Cr3Si diffusion barrier and reduce interface defects, thereby improving the stability and anti-stripping properties of the aluminide protective coating when serving in a high-temperature environment, enabling it to maintain a good protective effect for a long time.

[0008] Preferably, the aluminide protective coating further comprises a CrAl layer before completing thermal diffusion, and the CrAl layer is provided between the Cr3Si diffusion barrier layer and the aluminide layer.

[0009] During the thermal diffusion treatment, the CrAl layer can decompose and undergo element diffusion with the Cr3Si diffusion barrier layer and the aluminide layer, thereby forming a stronger bonding interface between the Cr3Si diffusion barrier layer and the aluminide layer, further improving the stability and spalling resistance of the aluminide protective coating at high temperatures, so that it can maintain a good protective effect during long-term service.

[0010] Preferably, the Cr3Si diffusion barrier layer comprises Cr and Si in an atomic ratio of 2.5 to 4.0:1.

[0011] In the Cr3Si diffusion barrier layer, when the ratio of the number of Cr and Si atoms is less than 2.5:1, there will be more Cr5Si in the layer. 3、 When the atomic ratio of Cr to Si is greater than 4.0:1, Cr-rich phases such as σ-CrFe will appear in the layer, while Cr3Si phase will be less. In both cases, the diffusion barrier formed will weaken the effect of preventing element interdiffusion between the aluminide layer and the substrate, or the bonding strength will be insufficient, thus shortening the service life of the aluminide protective coating.

[0012] Preferably, the raw material of the Cr-rich layer is Cr, or Cr and Si.

[0013] Preferably, the aluminide layer includes Al element, and may be doped with a small amount of one or more of Pt element, Si element and Cr element as a modifying element.

[0014] Preferably, the thickness of the Cr-rich layer is less than 1 μm, the thickness of the Cr3Si diffusion barrier layer is 1-2 μm, and the thickness of the aluminide layer is 30-60 μm.

[0015] Preferably, the thickness of the CrAl layer is less than 1 μm.

[0016] The thickness of the Cr-rich layer and the CrAl layer is relatively small, and they will fully diffuse with their adjacent layers (substrate, Cr3Si diffusion barrier layer, and aluminide layer) during the thermal diffusion process. In the aluminide protective coating formed after the thermal diffusion treatment, the diffusion phase between the substrate and the aluminide layer is relatively uniform, with the Cr3Si phase being the main phase.

[0017] Preferably, the substrate is an Fe-containing alloy.

[0018] In the present invention, the formation of the Cr3Si diffusion barrier does not depend on the substrate and is therefore not limited by the elemental composition of the substrate.

[0019] Furthermore, the Fe-containing alloy is austenitic stainless steel or ferritic stainless steel.

[0020] In a second aspect, the present invention provides a method for preparing the aluminide protective coating, comprising the following steps: sequentially preparing a Cr-rich layer, a Cr3Si diffusion barrier layer and an aluminide layer on the surface of a substrate, and allowing the elements to fully diffuse between the layers through thermal diffusion treatment.

[0021] Preferably, after preparing the Cr3Si diffusion barrier layer, a CrAl layer is first prepared on the surface of the Cr3Si diffusion barrier layer, and then an aluminide layer is prepared on the surface of the CrAl layer.

[0022] Preferably, the thermal diffusion treatment includes the following process: after preparing the Cr3Si diffusion barrier layer, performing hot isostatic pressing in an inert atmosphere; after preparing the aluminide layer, performing heat treatment at 700-1100°C for 0.5-3h in an inert atmosphere.

[0023] Furthermore, the temperature of the hot isostatic pressing treatment is 900-1000° C., and the pressure is 100-130 MPa.

[0024] Preferably, the method for preparing the Cr-rich layer is to use a Cr target for magnetron sputtering, or to use a Cr target and a Si target for magnetron sputtering.

[0025] Preferably, the method for preparing the Cr3Si diffusion barrier layer is to use a Cr target and a Si target for magnetron sputtering.

[0026] Preferably, the method for preparing the CrAl layer is magnetron sputtering using a CrAl alloy target.

[0027] Preferably, the method for preparing the aluminide layer is a slurry aluminizing process or a plasma spraying process.

[0028] Furthermore, the slurry aluminizing process includes the following steps: preparing a slurry by combining aluminum powder, silicon powder, aluminum oxide and a binder solution, and curing the slurry after coating to obtain an aluminide layer.

[0029] Furthermore, the plasma spraying process is to use AlSi alloy powder for spraying.

[0030] Preferably, before preparing the Cr-rich layer, the surface of the substrate is first ground, sandblasted, cleaned and dried.

[0031] Compared with the prior art, the present invention has the following advantages: (1) In the aluminide protective coating of the present invention, Cr3Si phase is used as the diffusion barrier material, which can utilize its good thermodynamic stability and special crystal structure to prevent the mutual diffusion of elements between the substrate and the aluminide layer, thereby extending the service life of the aluminide protective coating and enabling it to maintain a good protective effect during long-term service.

[0032] (2) In the aluminide protective coating of the present invention, by providing a Cr-rich layer and a CrAl layer, the bonding strength between the Cr3Si diffusion barrier and the substrate, and between the high Cr3Si diffusion barrier and the aluminide layer can be improved after thermal diffusion is completed, thereby improving the stability and anti-stripping property of the aluminide protective coating at high temperatures, which is beneficial for it to maintain good protective performance during long-term service. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the embodiments.

[0034] Overall embodiment An aluminide protective coating with a pre-introduced Cr3Si diffusion barrier, the aluminide protective coating comprising a Cr-rich layer, a Cr3Si diffusion barrier layer, and an aluminide layer sequentially arranged on the surface of a substrate before thermal diffusion is completed; the content of Cr atoms in the Cr-rich layer is not less than 90 at.%.

[0035] In some specific embodiments, the Cr3Si diffusion barrier layer includes Cr and Si in an atomic ratio of 2.5 to 4.0:1.

[0036] In some specific embodiments, the raw material of the Cr-rich layer is Cr, or Cr and Si.

[0037] In some specific embodiments, the aluminide protective coating further comprises a CrAl layer before thermal diffusion is completed, and the CrAl layer is disposed between the Cr3Si diffusion barrier layer and the aluminide layer.

[0038] In some specific embodiments, the thickness of the Cr-rich layer is less than 1 μm, the thickness of the Cr3Si diffusion barrier layer is 1-2 μm, the thickness of the CrAl layer is less than 1 μm, and the thickness of the aluminide layer is 30-60 μm.

[0039] In some embodiments, the substrate is an Fe-containing alloy, including but not limited to austenitic stainless steel or ferritic stainless steel.

[0040] In a second aspect, the present invention provides a method for preparing the aluminide protective coating, comprising the following steps: sequentially preparing a Cr-rich layer, a Cr3Si diffusion barrier layer and an aluminide layer on the surface of a substrate, and allowing the elements to fully diffuse between the layers through thermal diffusion treatment.

[0041] In some specific embodiments, before forming the Cr-rich layer, the substrate surface is first ground, sandblasted, cleaned, and dried.

[0042] In some specific embodiments, after preparing the Cr3Si diffusion barrier layer, a CrAl layer is first prepared on the surface of the Cr3Si diffusion barrier layer, and then an aluminide layer is prepared on the surface of the CrAl layer.

[0043] In some specific embodiments, the thermal diffusion treatment includes the following steps: after forming the Cr3Si diffusion barrier layer, performing hot isostatic pressing in an inert atmosphere; and after forming the aluminide layer, performing heat treatment in an inert atmosphere at 700-1100°C for 0.5-3 hours. Optionally or preferably, the hot isostatic pressing temperature is 900-1000°C and the pressure is 100-130 MPa.

[0044] In some specific embodiments, the method for preparing the Cr-rich layer is to use a Cr target for magnetron sputtering, or to use a Cr target and a Si target for magnetron sputtering.

[0045] In some specific embodiments, the method for preparing the Cr3Si diffusion barrier layer is to use a Cr target and a Si target for magnetron sputtering.

[0046] In some specific embodiments, the CrAl layer is prepared by magnetron sputtering using a CrAl alloy target.

[0047] The aluminide layer in the present invention can be any conventional aluminide layer used as a high-temperature protective material, and may also contain modifying elements such as Pt, Si, and Cr, without specific limitations in the present invention. The aluminide layer can be prepared using conventional methods, such as a slurry aluminizing process, where aluminum powder, silicon powder, aluminum oxide, and a binder solution are prepared into a slurry, which is then coated and cured to produce the aluminide layer. Alternatively, a plasma spraying process can be used, where AlSi alloy powder is sprayed. The composition and preparation method of the aluminide layer are not specifically limited in the present invention. Specific embodiments The present invention is described below by way of specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, any changes and advantages that can be imagined by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used herein are conventional in the art and can be obtained from conventional commercial sources. The methods used herein are conventional in the art, unless otherwise specified.

[0050] Example 1 The substrate in this embodiment is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0051] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 20 min. After magnetron sputtering, a 0.3±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0052] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 180 W power for the Si target, and 80 min deposition time, while all other parameters remained unchanged. After magnetron sputtering, a 1.7 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average atomic ratio of 3:1 for Cr to Si.

[0053] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0054] S5: Deposition of CrAl layer The sample obtained after step S4 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -100 V, and the deposition time was 20 min. After magnetron sputtering, a CrAl layer with a thickness of 0.3 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0055] S6: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. After completing step S5, apply the slurry to the surface of the CrAl layer of the sample and heat-treat at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0056] S7: Heat treatment The sample after step S6 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0057] Example 2 The substrate in this embodiment is P91 ferritic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment The P91 ferritic stainless steel plate was cut into sheet specimens with a size of 50×50×5mm using a wire cutting machine, and then polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then subjected to alumina sandblasting. It was then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, it was placed in a drying oven at 120°C to obtain the pretreated substrate sample.

[0058] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 40 min. After magnetron sputtering, a 0.8±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0059] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 180 W power for the Si target, and a deposition time of 60 minutes. All other parameters remained unchanged. After magnetron sputtering, a 1.2 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average Cr to Si atomic ratio of 3:1.

[0060] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0061] S5: Deposition of CrAl layer The sample obtained after step S4 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -100 V, and the deposition time was 30 min. After magnetron sputtering, a CrAl layer with a thickness of 0.8 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0062] S6: Spraying aluminide layer After completing step S5, the sample was sprayed with AlSi alloy powder (Si content: 20 at.%) on the surface of the CrAl layer. The spraying parameters were set as follows: voltage 46 V, current 680 A, argon 45 L / min, hydrogen 1 L / min, gun standoff 180 mm, and powder feed rate 7 L / min. After spraying, an aluminide layer with a thickness of 50 ± 10 μm was formed on the surface of the CrAl layer.

[0063] S7: Heat treatment The sample after step S6 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0064] Example 3 The substrate in this embodiment is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0065] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3Pa, the substrate bias voltage was set to -150 V, and the deposition time was 20 min. After magnetron sputtering, a 0.3±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0066] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 120 W power for the Si target, and 80 min deposition time, while all other parameters remained unchanged. After magnetron sputtering, a 1.6 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average Cr to Si atomic ratio of 4:1.

[0067] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0068] S5: Deposition of CrAl layer The sample obtained after step S4 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -100 V, and the deposition time was 20 min. After magnetron sputtering, a CrAl layer with a thickness of 0.3 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0069] S6: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. After completing step S5, apply the slurry to the surface of the CrAl layer of the sample and heat-treat at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0070] S7: Heat treatment The sample after step S6 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0071] Comparative Example 1 The only difference between this comparative example and Example 1 is that in this comparative example, an aluminide layer is directly coated on the surface of the pretreated substrate (i.e., steps S2 to S5 are not performed). Specifically, the substrate in this comparative example is 304H austenitic stainless steel, and the aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0072] S2: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. The slurry is applied to the surface of the substrate sample pretreated in step S1. The sample is then placed in a 300°C environment for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40 ± 10 μm.

[0073] S3: Heat treatment The sample after step S2 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0074] Comparative Example 2 The only difference between this comparative example and Example 2 is that in this comparative example, an aluminide layer is directly coated on the surface of the pretreated substrate (i.e., steps S2 to S5 are not performed). Specifically, the substrate in this comparative example is P91 ferritic stainless steel, and the aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment The P91 ferritic stainless steel plate was cut into sheet specimens with a size of 50×50×5mm using a wire cutting machine, and then polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then subjected to alumina sandblasting. It was then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, it was placed in a drying oven at 120°C to obtain the pretreated substrate sample.

[0075] S2: Spraying aluminide layer The substrate sample pretreated in step S1 was sprayed with AlSi alloy powder (Si content: 20 at.%). The spraying parameters were as follows: voltage 46 V, current 680 A, argon 45 L / min, hydrogen 1 L / min, gun standoff 180 mm, and powder feed rate 7 L / min. After spraying, an aluminide layer with a thickness of 50 ± 10 μm was formed on the surface of the CrAl layer.

[0076] S3: Heat treatment The sample after step S2 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0077] Comparative Example 3 The only difference between this comparative example and Example 1 is that no Cr-rich layer is deposited in this comparative example (i.e., step S2 is not performed). Specifically, the substrate in this comparative example is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0078] S2: Deposition of Cr3Si diffusion barrier layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 180 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 80 min. After magnetron sputtering, a Cr3Si diffusion barrier layer with a thickness of 1.7 ± 0.2 μm was formed on the surface of the Cr-rich layer, in which the average atomic ratio of Cr to Si was 3:1.

[0079] S3: Hot isostatic pressing The sample obtained after completing step S2 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0080] S4: Deposition of CrAl layer The sample obtained after step S3 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -100 V, and the deposition time was 20 min. After magnetron sputtering, a CrAl layer with a thickness of 0.3 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0081] S5: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. After completing step S4, apply the slurry to the surface of the CrAl layer of the sample and heat-treat at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0082] S6: Heat treatment The sample after step S5 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain an aluminide protective coating.

[0083] Comparative Example 4 The only difference between this embodiment and embodiment 1 is that no CrAl layer is deposited in this embodiment (i.e., step S5 is not performed). Specifically, the substrate in this embodiment is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0084] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 20 min. After magnetron sputtering, a 0.3±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0085] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 180 W power for the Si target, and 80 min deposition time, while all other parameters remained unchanged. After magnetron sputtering, a 1.7 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average atomic ratio of 3:1 for Cr to Si.

[0086] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0087] S5: Apply an aluminide layer using the following raw materials by mass: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. Mix the aluminum powder, silicon powder, and alumina filler, then add the phosphate solution binder and stir to form a slurry. Apply the slurry to the Cr3Si diffusion barrier surface of the sample after step S4. Heat the sample at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0088] S6: Heat treatment The sample after step S5 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0089] Comparative Example 5 The only difference between this comparative example and Example 1 is that in step S3, the average atomic ratio of Cr to Si at each location within the Cr3Si diffusion barrier layer formed in this comparative example is 1.5:1. Specifically, the substrate in this comparative example is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0090] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 20 min. After magnetron sputtering, a 0.3±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0091] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 300 W power for the Si target, and 80 min deposition time, while all other parameters remained unchanged. After magnetron sputtering, a 1.7 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average Cr to Si atomic ratio of 1.5:1.

[0092] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0093] S5: Deposition of CrAl layer The sample obtained after step S4 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -100 V, and the deposition time was 20 min. After magnetron sputtering, a CrAl layer with a thickness of 0.3 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0094] S6: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. After completing step S5, apply the slurry to the surface of the CrAl layer of the sample and heat-treat at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0095] S7: Heat treatment The sample after step S6 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0096] Comparative Example 6 The only difference between this comparative example and Example 3 is that in step S3, the average atomic ratio of Cr to Si at each location within the Cr3Si diffusion barrier layer formed in this comparative example is 5:1. Specifically, the substrate in this comparative example is 304H austenitic stainless steel, and an aluminide protective coating is prepared on its surface by the following steps: S1: Substrate pretreatment After using a wire cutting machine to cut the 304H austenitic stainless steel plate into sheet samples with a size of 50×50×5mm, they were polished with 150#, 400#, and 800# SiC sandpaper in sequence, and then sandblasted with aluminum oxide. They were then placed in ethanol and acetone solutions in sequence and ultrasonically cleaned for 10 minutes each time. After cleaning, they were placed in a drying oven at 120°C to obtain the pretreated substrate samples.

[0097] S2: Deposition of Cr-rich layer The substrate sample pretreated in step S1 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: Cr target and Si target were used, with the power of the two targets being 200 W and 60 W respectively, and the vacuum degree in the instrument was maintained at 10 -3 Pa, the substrate bias voltage was set to -150 V, and the deposition time was 20 min. After magnetron sputtering, a 0.3±0.1 μm thick Cr-rich layer was formed on the substrate surface, in which the Cr atomic content was 95±1 at.%.

[0098] S3: Deposition of Cr3Si diffusion barrier layer After completing step S2, the magnetron sputtering parameters were adjusted as follows: 200 W power for the Cr target, 100 W power for the Si target, and 80 min deposition time, while all other parameters remained unchanged. After magnetron sputtering, a 1.7 ± 0.2 μm thick Cr3Si diffusion barrier layer formed on the surface of the Cr-rich layer, with an average Cr to Si atomic ratio of 5.0:1.

[0099] S4: Hot isostatic pressing The sample obtained after completing step S3 is placed in a hot isostatic press, set the temperature to 900°C and the pressure to 120 MPa, and kept warm for 2 hours in an argon atmosphere. It is then cooled with the furnace and taken out. The obtained sample consists of the substrate and the Cr3Si diffusion barrier on its surface.

[0100] S5: Deposition of CrAl layer The sample obtained after step S4 was placed in a magnetron sputtering instrument and magnetron sputtering was performed under the following conditions: a CrAl alloy target (the ratio of Cr to Al atoms was 1:1) was used, and the vacuum degree in the instrument was maintained at 10 -3Pa, the substrate bias voltage was set to -100 V, and the deposition time was 20 min. After magnetron sputtering, a CrAl layer with a thickness of 0.3 ± 0.1 μm was formed on the surface of the Cr3Si diffusion barrier.

[0101] S6: Coating of aluminide layer The following raw materials, by mass percentage, are prepared: 20% aluminum powder, 10% silicon powder, 25% alumina filler, and 45% phosphate solution binder. After mixing the aluminum powder, silicon powder, and alumina filler, add the phosphate solution binder and stir to form a slurry. After completing step S5, apply the slurry to the surface of the CrAl layer of the sample and heat-treat at 300°C for 30 minutes to allow the slurry to solidify, forming an aluminide layer with a thickness of 40±10μm.

[0102] S7: Heat treatment The sample after step S6 was placed in a nitrogen atmosphere at 950° C. and heat treated for 90 minutes to obtain a sample with an aluminide protective coating on the surface.

[0103] Test Case To compare the performance advantages of the aluminide protective coatings designed in this patent, which incorporate a pre-introduced Cr3Si diffusion barrier, Table 1 shows the long-term protective effectiveness of samples coated with aluminide coatings prepared in Example 1, Example 2, and Comparative Examples 1 and 2, respectively. The samples were tested in air at 650°C for long-term protection, measuring and comparing the changes in Al content within the coatings after varying service times. Table 2 shows the interfacial bonding strength of the coatings prepared in Example 1 and Comparative Examples 3-6, as well as the phase composition of the resulting diffusion barriers.

[0104] Table 1 Al content (at.%) of aluminide protective coating after thermal exposure in air at 650°C Table 2 Interface bonding strength and diffusion barrier composition of aluminide protective coating and stainless steel substrate Combining the above test results with relevant theories, the effects of the embodiments and comparative examples are described as follows: (1) In terms of long-term protective effect, the Al element reduction rate inside the aluminide protective coating of Example 1 is significantly lower than that of Comparative Example 1, and the Al element reduction rate inside the aluminide protective coating of Example 2 is significantly lower than that of Comparative Example 2. The reason for this is that: in Examples 1 and 2, a diffusion barrier mainly composed of Cr3Si phase is pre-introduced between the aluminide layer and the substrate. The calculated result of the formation enthalpy of Cr3Si is negative, which has good thermodynamic stability. In addition, Cr3Si has a very stable crystal structure, containing 3 tetrahedral interspaces and 4 triangular base bipyramid interspaces, but only the tetrahedral interspaces and the largest bipyramid positions are the preferential sites for interstitial atoms. Interstitial atoms, including oxygen atoms, can only diffuse to adjacent tetrahedral or bipyramid positions, which means that element diffusion requires more energy. Therefore, the diffusion barrier mainly composed of Cr3Si phase can effectively prevent element interdiffusion between the aluminide layer and the substrate. However, in Comparative Examples 1 and 2, no Cr3Si diffusion barrier layer is pre-introduced. Large-scale element interdiffusion occurs between the substrate and the aluminide layer, the Al content inside the coating decreases rapidly, and the service life is greatly reduced.

[0105] (2) Compared with Comparative Example 3, the bonding strength between the aluminide protective coating of Example 1 and the stainless steel substrate is higher. The reason for this is that: in Comparative Example 3, the Cr3Si diffusion barrier layer is directly prepared on the surface of the substrate. The high stability of Cr3Si makes it difficult for it to effectively diffuse with the substrate, resulting in too low bonding strength between the Cr3Si diffusion barrier layer and the substrate and the presence of many interface defects; while in Example 1, a Cr-rich layer is provided between the substrate and the Cr3Si diffusion barrier layer. During the thermal diffusion treatment, the Cr-rich layer can diffuse well with the substrate and the Cr3Si diffusion barrier layer, ultimately forming a uniform Cr3Si diffusion barrier, which can improve the bonding strength between the Cr3Si diffusion barrier and the substrate and reduce interface defects.

[0106] (3) Compared with Comparative Example 4, the bonding strength between the aluminide protective coating of Example 1 and the stainless steel substrate is higher. The reason for this is that: in Example 4, the aluminide layer is directly prepared on the surface of the Cr3Si diffusion barrier layer. Since it is difficult for effective diffusion to occur between the two layers, the interlayer bonding strength is low and interface defects are easily formed; while in Example 1, a CrAl layer is first prepared on the surface of the Cr3Si diffusion barrier layer, and then an aluminide layer is prepared on the surface of the CrAl layer. During the thermal diffusion treatment, the CrAl layer can decompose and undergo element diffusion with the Cr3Si diffusion barrier layer and the aluminide layer, thereby forming a stronger bonding interface between the Cr3Si diffusion barrier layer and the aluminide layer, reducing the interface defects between the two.

[0107] (5) The bonding strength between the aluminide protective coatings of Examples 1 and 3 and the stainless steel substrate is higher than that of Comparative Examples 5 and 6. The reason for this is that the unique crystal structure of Cr3Si can effectively prevent the mutual diffusion of elements. When the atomic ratio of Cr to Si is too small (Comparative Example 5), more Si-rich phases such as Cr5Si3 will be present in the diffusion barrier layer. When the atomic ratio of Cr to Si is too large (Comparative Example 6), Cr-rich phases such as σ-CrFe will appear in the diffusion barrier layer. Both of these situations will reduce the bonding strength between the coating and the substrate.

[0108] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. An aluminide protective coating with a pre-introduced Cr3Si diffusion barrier, characterized in that: The aluminide protective coating comprises a Cr-rich layer, a Cr3Si diffusion barrier layer and an aluminide layer sequentially arranged on the surface of the substrate before completing thermal diffusion; the content of Cr atoms in the Cr-rich layer is not less than 90 at.%.

2. The aluminide protective coating according to claim 1, characterized in that The aluminide protective coating further comprises a CrAl layer before completing thermal diffusion, and the CrAl layer is arranged between the Cr3Si diffusion barrier layer and the aluminide layer.

3. The aluminide protective coating according to claim 1, characterized in that The Cr3Si diffusion barrier layer includes Cr and Si in an atomic ratio of 2.5 to 4.0:

1.

4. The aluminide protective coating according to claim 1, characterized in that The raw material of the Cr-rich layer is Cr, or Cr and Si.

5. The aluminide protective coating according to claim 1, characterized in that The thickness of the Cr-rich layer is less than 1 μm, the thickness of the Cr3Si diffusion barrier layer is 1-2 μm, and the thickness of the aluminide layer is 30-60 μm.

6. The aluminide protective coating according to claim 2, characterized in that The thickness of the CrAl layer is less than 1 μm.

7. The aluminide protective coating according to claim 1, characterized in that The substrate is an Fe-containing alloy.

8. A method for preparing the aluminide protective coating according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: sequentially preparing a Cr-rich layer, a Cr3Si diffusion barrier layer and an aluminide layer on the surface of a substrate, and performing thermal diffusion treatment to allow elements to fully diffuse between the layers.

9. The preparation method according to claim 8, characterized in that After preparing the Cr3Si diffusion barrier layer, a CrAl layer is firstly prepared on the surface of the Cr3Si diffusion barrier layer, and then an aluminide layer is prepared on the surface of the CrAl layer.

10. The preparation method according to claim 8 or 9, characterized in that: The thermal diffusion treatment includes the following processes: before preparing the aluminide layer, performing hot isostatic pressing in an inert atmosphere; after preparing the aluminide layer, performing heat treatment at 700-1100° C. for 0.5-3 h in an inert atmosphere.

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