Iron-based amorphous composite coating, method for preparing same, and use thereof

Abstract

The application provides an iron-based amorphous composite coating and a preparation method and application thereof, and relates to the technical field of amorphous coatings.The chemical composition of the iron-based amorphous composite coating provided by the application comprises an FeCrMo amorphous coating and Cr3C2 particles dispersed in the FeCrMo amorphous coating; the mass content of the Cr3C2 particles in the iron-based amorphous composite coating is 3-10%.The FeCrMo amorphous coating provided by the application has high hardness, high wear resistance and excellent corrosion resistance, does not contain toxic substances, has low cost, and has good mechanical properties of a metal matrix and excellent properties of an amorphous alloy.The hardness, wear resistance and corrosion resistance of the iron-based amorphous composite coating are significantly improved by adding 3-10% Cr3C2 particles as a reinforcing phase, the Cr3C2 particles having high hardness, chemical stability and corrosion resistance, and the iron-based amorphous composite coating can prolong the service life of the metal matrix under high load and harsh working conditions as a protective layer.

Description

Technical Field

[0001] The present invention relates to the technical field of amorphous coatings, and in particular to an iron-based amorphous composite coating and a preparation method and application thereof. Background Art

[0002] Due to their special atomic structure, amorphous alloys have many excellent physical, chemical, and mechanical properties. For example, their strength reaches 2-5GPa, their Vickers hardness reaches 7GPa, and their elastic limit is as high as 2%, all of which are several times that of crystalline alloys. They also have excellent wear and corrosion resistance. However, their critical size is relatively small, and they are currently mainly used as wear-resistant coatings for large transformer cores and large oil drilling equipment. Among the many amorphous systems, Fe-based amorphous coatings have the best strength, hardness, and wear resistance. However, with the development of industry, single Fe-based amorphous coatings can no longer meet the industry's increasingly demanding performance requirements for coatings.

[0003] Compared to traditional iron-based amorphous alloy coatings, iron-based amorphous composite coatings significantly improve hardness, wear resistance, and strength by introducing a reinforcing phase material. The increased bonding strength with the substrate reduces the likelihood of spalling, extending their service life in harsh marine environments. Furthermore, compared to traditional and costly coating materials, iron-based amorphous alloy composite coatings are not only inexpensive but also environmentally friendly, significantly mitigating risks to the environment and human health.

[0004] The preparation methods of iron-based amorphous composite coatings mainly include arc spraying, plasma spraying, explosion spraying, supersonic flame spraying, etc. Among them, supersonic flame spraying has the following advantages: (1) the spraying powder is heated to a high temperature state by a high-speed airflow and rapidly cooled to form a high-density amorphous structure, reducing the porosity of the coating; (2) supersonic flame spraying can achieve uniform spraying in a large area, can be sprayed on the surface of parts with various complex shapes, and the coating quality is more stable and reliable; (3) supersonic flame spraying is more efficient and can be completed in a short time, saving time and cost and improving production efficiency. For example, the prior art discloses a NiCr-Cr3C2 coating prepared by supersonic flame spraying. The NiCr-Cr3C2 coating has a dense structure, low porosity, and a friction coefficient of 0.5 to 0.7. However, the wear resistance of the above-mentioned NiCr-Cr3C2 coating is not good enough, which limits its application. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide an iron-based amorphous composite coating and its preparation method and application. The iron-based amorphous composite coating prepared by the present invention has excellent wear resistance.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides an iron-based amorphous composite coating, the chemical composition of which includes a FeCrMo amorphous coating and Cr3C2 particles dispersed in the FeCrMo amorphous coating; the mass content of the Cr3C2 particles in the iron-based amorphous composite coating is 3-10%.

[0008] Preferably, the chemical composition of the FeCrMo amorphous coating includes, in terms of mass percentage, Cr 25-27%, Mo 16-18%, C 2.0-2.5%, B 2.0-2.2%, and Fe 50.3-55%.

[0009] Preferably, the thickness of the iron-based amorphous composite coating is 200-400 μm.

[0010] The present invention also provides a method for preparing the iron-based amorphous composite coating described in the above technical solution, comprising the following steps: using a mixed powder to perform supersonic flame spraying on the surface of a metal substrate to form an iron-based amorphous composite coating; the mixed powder includes FeCrMo amorphous powder and Cr3C2 particles, and the mass content of Cr3C2 particles in the mixed powder is 3 to 10%.

[0011] Preferably, the particle size of the FeCrMo amorphous powder is 15 to 53 μm.

[0012] Preferably, the particle size of the Cr3C2 particles is 35-55 μm.

[0013] Preferably, the supersonic flame spraying adopts high-speed air fuel technology, and the process conditions include: oxygen flow rate 1500-2200SCFH, spraying distance 250-350mm, fuel flow rate 5-8GPH, powder feeding rate 30-40g / min, and carrier gas flow rate 10-15L / min.

[0014] Preferably, the fuel for supersonic flame spraying includes one or more of kerosene, propylene, natural gas and liquefied petroleum gas.

[0015] Preferably, the metal substrate is sandblasted and then preheated before use.

[0016] The present invention also provides the use of the iron-based amorphous composite coating described in the above technical solution or the iron-based amorphous composite coating prepared by the preparation method described in the above technical solution as a protective layer.

[0017] Compared to other amorphous alloy systems, the FeCrMo amorphous coating provided by the present invention has high hardness, high wear resistance, and superior corrosion resistance, and can effectively resist erosion by corrosive media such as acids and alkalis. The FeCrMo iron-based amorphous coating does not contain toxic substances, thus avoiding serious environmental pollution. The research of FeCrMo iron-based amorphous coating has low cost and can simultaneously take into account the good mechanical properties of the metal substrate and the excellent properties of the amorphous alloy. Cr3C2 particles are ceramic particles with excellent hardness, chemical stability, and corrosion resistance. The present invention successfully improves the porosity of the coating cross-section and surface by adding 3-10wt% of Cr3C2 particles as a reinforcing phase to the FeCrMo amorphous coating, resulting in fewer pores and a more dense internal structure, significantly improving the hardness, wear resistance, and corrosion resistance of the iron-based amorphous composite coating. The iron-based amorphous composite coating (FeCrMo·Cr3C2) provided by the present invention, as a protective layer, can extend the service life of the metal substrate, especially the metal substrate under high load and harsh working conditions (such as pump and valve components used in corrosive environments), and reduce its maintenance and replacement frequency. As shown in the test results of the embodiment, the hardness of the FeCrMo iron-based amorphous coating without the addition of Cr3C2 particles is 800HV, the friction coefficient is about 0.7, and the self-corrosion potential is -916.89V; while the iron-based amorphous composite coating containing 6wt% Cr3C2 particles has a microhardness of 962.7HV, a friction coefficient reduced to about 0.2933, and a self-corrosion potential of -466.82V, indicating that the addition of Cr3C2 particles significantly enhances the hardness, wear resistance and corrosion resistance of the iron-based amorphous composite coating.

[0018] The present invention utilizes a supersonic flame spraying method to prepare an iron-based amorphous composite coating on the surface of a metal substrate. The coating exhibits a well-melted surface, a small amount of pores, a dense internal structure, and contains a Cr3C2 phase. The amorphous ratio is above 70%, and the iron-based amorphous composite coating exhibits a strong bond with the metal substrate and is not easily detached. Furthermore, the preparation method provided by the present invention is simple in process, operation, and cost, making it suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : This is the SEM image of the X8-FeCrMoCB amorphous powder used in Examples 1 to 4 and Comparative Example 1;

[0020] Figure 2 is an SEM image of the Cr3C2 particles used in Examples 1 to 4;

[0021] Figure 3 This is a photo of the iron-based amorphous composite coating prepared in Example 1 before grinding and polishing;

[0022] Figure 4XRD patterns of the iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4;

[0023] Figure 5 These are SEM images of the polished surfaces of the iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4, wherein (a) has a content of 3%, (b) has a content of 4.5%, (c) has a content of 6%, and (d) has a content of 7.5%;

[0024] Figure 6 Cross-sectional SEM images of iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4, wherein (a) has a content of 3%, (b) has a content of 4.5%, (c) has a content of 6%, and (d) has a content of 7.5%;

[0025] Figure 7 BSE image (a) and EDS images (b-g) of the pores in the iron-based amorphous composite coating prepared in Example 4;

[0026] Figure 8 BSE image (a) and EDS images (b-g) of Cr3C2 particles in the iron-based amorphous composite coating prepared in Example 4;

[0027] Figure 9 Microhardness diagrams of the iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4;

[0028] Figure 10 The friction coefficient of the iron-based amorphous composite coating with different Cr3C2 contents prepared in Examples 1 to 4 changes with time;

[0029] Figure 11 Wear quality diagrams of iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4;

[0030] Figure 12 The microstructures of the iron-based amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4 after wear, wherein (a) content is 3%, (b) content is 4.5%, (c) content is 6%, and (d) content is 7.5%;

[0031] Figure 13 This is an EDS elemental analysis diagram of the surface characteristic area of ​​the iron-based amorphous composite coating prepared in Example 4;

[0032] Figure 14 Surface profiles of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1 to 4 after friction and wear, obtained using a laser confocal microscope and white light interferometer, where (a) has a 3% content, (b) has a 4.5% content, (c) has a 6% content, and (d) has a 7.5% content.

[0033] Figure 15 OCP curves of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4;

[0034] Figure 16 Polarization curves of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 and Comparative Example 1;

[0035] Figure 17 Nyquist plots of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 and Comparative Example 1, and the inset is a schematic diagram of the equivalent circuit of the coating.

[0036] Figure 18 A schematic diagram of the packaging of the iron-based amorphous composite coating sample;

[0037] Figure 19 A graph of the weight loss statistics of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 after 15 days of immersion;

[0038] Figure 20 SEM images of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 after 1 day (a1-a4), 7 days (b1-b4), 15 days (c1-c4) of immersion, and after removing the corrosion products after 15 days of immersion (d1-d4), a1, a2, a3 and a4 have a content of 3%, b1, b2, b3 and b4 have a content of 4.5%, c1, c2, c3 and c4 have a content of 6%, and d1, d2, d3 and d4 have a content of 7%;

[0039] Figure 21 An EDS image of the iron-based amorphous composite coating prepared in Example 4 at the corrosion product site;

[0040] Figure 22 An XRD pattern of the iron-based amorphous composite coating prepared in Example 4 after corrosion in simulated seawater;

[0041] Figure 23 Polarization curves of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 and Comparative Example 1 after 15 days of immersion;

[0042] Figure 24 Nyquist plots of the iron-based amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1-4 and Comparative Example 1 after 15 days of immersion, and the inset is a schematic diagram of the equivalent circuit of the coating. DETAILED DESCRIPTION

[0043] The application provides an iron-based amorphous composite coating, which has a chemical composition comprising an FeCrMo amorphous coating and Cr3C2 particles dispersed in the FeCrMo amorphous coating; the content of the Cr3C2 particles in the iron-based amorphous composite coating is 3-10 wt%.

[0044] In the application, the mass content of the Cr3C2 particles in the iron-based amorphous composite coating is 3-10%, and in specific embodiments, can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%. In the application, the particle size of the Cr3C2 particles is preferably 35-55 μm.

[0045] The Cr3C2 particles have very high hardness and excellent wear resistance, and the hardness is between 1800-2200 HV, which can effectively resist external wear and scratches. When the Cr3C2 particles exist in the iron-based amorphous composite coating, the Cr3C2 particles can form a hard protective layer to block the wear of external substances on the iron-based amorphous composite coating, thereby prolonging the service life of the iron-based amorphous composite coating. The melting point of the Cr3C2 particles is 1890°C, which exhibits excellent stability and heat resistance in a high-temperature environment, which makes the Cr3C2 particles very suitable for use in high-temperature working conditions, such as aerospace, energy and petrochemical industries. In addition, the Cr3C2 particles have excellent crack resistance, and the Cr3C2 particles can effectively avoid the cracking problem of the coating, because the hardness of the Cr3C2 particles is very large, when the crack encounters the Cr3C2 particles, the high hardness of the particles can well hinder the further expansion of the crack, thereby slowing down the crack propagation speed, effectively resisting the propagation of the crack, which can improve the crack resistance of the coating. The Cr3C2 particles exhibit good chemical stability in various chemical media, and can resist corrosion and chemical erosion, which makes the Cr3C2 particles can be used in coatings to protect the substrates working in harsh environments (such as in acid and alkali corrosion or corrosive gas). The application adds Cr3C2 particles as a reinforcing phase in the FeCrMo amorphous coating, and controls the addition amount of the Cr3C2 particles, so that the iron-based amorphous composite coating has excellent wear resistance, hardness and corrosion resistance.

[0046] In the present invention, the chemical composition of the FeCrMo amorphous coating preferably includes, by weight percentage, Cr25-27%, Mo 16-18%, C 2.0-2.5%, B 2.0-2.2%, and Fe 50.3-55%. Compared with amorphous alloys of other systems, the FeCrMo amorphous coating provided by the present invention has high hardness, high wear resistance and better corrosion resistance, and can very well resist the erosion of corrosive media such as acids and alkalis. The excellent corrosion resistance of the FeCrMo amorphous alloy is due to the chromium oxide film on the surface of the alloy. The oxide film isolates the metal from the corrosive environment. There is no lattice mismatch between the surface oxide film and the amorphous alloy, and the oxide film can achieve stress-free growth. Compared with the surface of the crystalline alloy, the surface oxide film of the amorphous alloy is more uniform and has a better protective effect on the base metal. Due to the unique properties of the FeCrMo amorphous alloy, it can be used as a protective coating with corrosion resistance, high hardness and wear resistance, and it avoids the disadvantage of being limited to low-latitude shapes in practical applications.

[0047] In the present invention, the thickness of the iron-based amorphous composite coating is preferably 200-400 μm, and in specific embodiments may be 200 μm, 250 μm, 300 μm, 350 μm or 400 μm.

[0048] The present invention also provides a method for preparing the iron-based amorphous composite coating described in the above technical solution, comprising the following steps: using a mixed powder to perform supersonic flame spraying on the surface of a metal substrate to form an iron-based amorphous composite coating; the mixed powder includes FeCrMo amorphous powder and Cr3C2 particles, and the mass content of Cr3C2 particles in the mixed powder is 3 to 10%.

[0049] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0050] In the present invention, the chemical composition of the FeCrMo amorphous powder is the same as the chemical composition of the FeCrMo amorphous coating, and will not be repeated here. In the present invention, the particle size of the FeCrMo amorphous powder is preferably 15 to 53 μm; the shape of the FeCrMo amorphous powder is preferably spherical. The FeCrMo amorphous powder of the above-mentioned particle size used in the present invention has good fluidity, uniform particle size and good sphericity, which can effectively reduce the friction and interlocking phenomenon between particles, thereby greatly improving the fluidity during the spraying process; and the FeCrMo amorphous powder can pass through the nozzle smoothly, and achieve uniform spraying during the supersonic flame spraying process, ensuring that the coating is uniform and of good quality.

[0051] In the present invention, the particle size of the Cr3C2 particles is preferably 35 to 55 μm. The particle size of the FeCrMo amorphous powder used in the present invention is 15 to 53 μm, and the particle size of the Cr3C2 particles is 35 to 55 μm. The particle size of the Cr3C2 particles matches that of the FeCrMo amorphous powder. This particle size matching advantage helps promote good mixing of the reinforcing phase Cr3C2 particles and the FeCrMo amorphous powder, prevents separation or uneven deposition of the Cr3C2 particles, and further facilitates the formation of a uniform iron-based amorphous composite coating during the supersonic flame spraying process. Moreover, the matching particle size of the two also improves the density and bonding strength of the iron-based amorphous composite coating, thereby improving the overall performance and durability of the iron-based amorphous composite coating.

[0052] In the present invention, the mixed powder is preferably dried before use. The drying temperature is preferably 40-60°C, and in specific embodiments, it can be 40°C, 45°C, 50°C, 55°C, or 60°C. The drying time is preferably 20-40 minutes, and in specific embodiments, it can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes. Drying the mixed powder in the present invention can significantly reduce its water content, thereby improving the fluidity of the mixed powder. This not only improves the dispersibility of the mixed powder during the spraying process, but also reduces particle agglomeration caused by moisture. Good fluidity is the basis for achieving a uniform coating and good adhesion, thereby ensuring the overall performance and durability of the coating.

[0053] In the present invention, the metal substrate is preferably made of 304 stainless steel, 316 stainless steel, aluminum alloy, nickel-based alloy, or copper-based alloy; the nickel-based alloy preferably includes an Inconel series nickel-based alloy. In the present invention, the metal substrate is preferably sandblasted and preheated before use. In the present invention, the metal substrate is preferably first cleaned, polished, and then cleaned again before sandblasting.

[0054] In the present invention, the solvent used in the first cleaning preferably includes acetone and / or ethanol, and the purpose of the cleaning is to remove grease and impurities.

[0055] In the present invention, the polishing is preferably performed using sandpaper with a mesh size of 60 to 600. In a specific embodiment, sandpaper with a mesh size of 60, 120, 400, and 600 can be used in sequence for polishing. The present invention polishes the surface of the metal substrate, which helps to improve the adhesion and surface quality of the iron-based amorphous composite coating. Among them, polishing with 60-mesh sandpaper can quickly remove the oxide layer and surface impurities; polishing with 120-mesh sandpaper can further smooth the surface, reduce roughness, and remove larger scratches; using 400-mesh sandpaper can remove minor defects and enhance surface smoothness; using 600-mesh sandpaper for fine polishing can effectively remove tiny particles and oxides to ensure uniform adhesion of the coating. Although polishing with 800 mesh and above can further improve smoothness, polishing with 600 mesh is sufficient to meet the coating adhesion requirements. Therefore, reasonable polishing conditions are conducive to achieving a balance between coating performance and reducing process complexity to achieve optimal coating quality and efficiency.

[0056] In the present invention, the solvent used in the second cleaning preferably includes one or more of ethanol, methanol and isopropanol; the second cleaning is preferably ultrasonic cleaning; the frequency of the ultrasonic cleaning is preferably 20-40kHz, and in specific embodiments, it can be 20kHz, 25kHz, 30kHz, 35kHz or 40kHz; the power of the ultrasonic cleaning is preferably 100-200W, and in specific embodiments, it can be 100W, 120W, 140W, 150W, 160W, 180W or 200W. The present invention controls the frequency range of ultrasonic cleaning to 20-40kHz, which can generate sufficient cavitation effect, quickly form and collapse microbubbles, thereby effectively removing surface dirt and impurities, and ensuring the best cleaning effect on the metal surface; frequencies below 20kHz may cause excessive mechanical stress and damage the substrate surface, and frequencies above 40kHz, although the cleaning effect is more delicate, may not be sufficient to remove heavy dirt. Therefore, this frequency range achieves a good balance between cleaning effect and material safety. By controlling the power of ultrasonic cleaning to be within the range of 100 to 200 W, the present invention can ensure the cavitation effect during the ultrasonic cleaning process while avoiding overheating or deformation of the substrate caused by excessive power. By controlling the frequency and power range of ultrasonic cleaning, the cleaning effect can be significantly improved, ensuring that the surface of the cleaned metal substrate meets the quality standards required for preparing the coating.

[0057] In the present invention, the process conditions of the sandblasting preferably include: the sandblasting medium is Al2O3, the particle size of the sandblasting medium is 50-120 mesh, and in a specific embodiment, it can be 50 mesh, 60 mesh, 70 mesh, 80 mesh, 90 mesh, 100 mesh, 110 mesh or 120 mesh; the sandblasting pressure is 0.2-0.6 MPa, and in a specific embodiment, it can be 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or 0.6 MPa; the distance between the nozzle and the metal substrate is 150-300 mm, and in a specific embodiment, the distance between the nozzle and the metal substrate is 150-300 mm. The sandblasting time is 5 to 15 minutes, and in a specific embodiment, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes. The present invention adopts a 50 to 120 mesh sandblasting medium, which can achieve good cutting ability and appropriate surface roughness; by controlling the sandblasting pressure to 0.2 to 0.6 MPa, it is beneficial to the uniformity of the sandblasting effect; by controlling the distance between the nozzle and the metal substrate to 150 to 300 mm, it is beneficial to obtain an ideal sandblasting intensity and coverage effect; by controlling the surface roughness, it is helpful to enhance the adhesion between the iron-based amorphous composite coating and the metal substrate. The above parameters ensure the effectiveness of the sandblasting process and provide a good foundation for the subsequent supersonic flame spraying. The present invention can prevent excessive differences in thermal expansion of the metal substrate by sandblasting, thereby improving the bonding strength between the iron-based amorphous composite coating and the metal substrate, thereby preventing the iron-based amorphous composite coating from peeling or cracking.

[0058] In the present invention, the supersonic flame spraying is preferably completed within 30 minutes after the sandblasting is completed to avoid secondary oxidation or contamination of the metal substrate surface.

[0059] In the present invention, the temperature of the preheated metal substrate is preferably 150-250°C, and in specific embodiments, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C. The present invention controls the preheated temperature to 150-250°C, which helps reduce the stress generated by the difference in thermal expansion coefficient between the substrate and the coating during the supersonic flame spraying process, thereby effectively improving the adhesion and density of the coating. It can also ensure a good melting state on the coating surface and reduce porosity defects, ultimately improving the overall performance of the coating. Too low a temperature (below 150°C) may not effectively relieve the stress caused by the thermal expansion difference; while too high a temperature (above 250°C) may cause excessive thermal deformation of the metal substrate or a decrease in coating adhesion. Therefore, a preheating temperature of 150-250°C is an ideal choice, which is conducive to optimizing the coating quality and overall performance.

[0060] The present invention preferably uses high velocity air fuel (HVAF) technology for supersonic flame spraying. HVAF technology uses a high-speed air and fuel mixture to spray the coating. Compared with traditional thermal spraying methods, the present invention uses HVAF technology for supersonic flame spraying, which can achieve higher spraying speeds and better coating density, thereby improving the overall mechanical properties and wear resistance of the iron-based amorphous composite coating.

[0061] In the present invention, the process conditions of the supersonic flame spraying preferably include: an oxygen flow rate of 1500-2200 SCFH, which can be 1500 SCFH, 1600 SCFH, 1700 SCFH, 1800 SCFH, 1900 SCFH, 2000 SCFH, 2100 SCFH or 2200 SCFH in a specific embodiment; a spraying distance of 250-350 mm, which can be 250 mm, 260 mm, 270 mm, 280 mm, 290 mm, 300 mm, 310 mm, 320 mm, 330 mm, 340 mm or 350 mm in a specific embodiment; a fuel flow rate of 5-8 GPH, which can be 5 GPH, 5.5 GPH, 6 GPH, 6.5 GPH in a specific embodiment. H, 7GPH, 7.5GPH or 8GPH; the fuel preferably includes one or more of kerosene, propylene, natural gas and liquefied petroleum gas; the powder feeding rate is 30-40g / min, and in specific embodiments it can be 30g / min, 31g / min, 32g / min, 33g / min, 34g / min, 35g / min, 36g / min, 37g / min, 38g / min, 39g / min or 40g / min; the carrier gas flow rate is 10-15L / min, and in specific embodiments it can be 10L / min, 11L / min, 12L / min, 13L / min, 14L / min or 15L / min; the carrier gas preferably includes nitrogen, argon, helium, air or hydrogen. In the present invention, the carrier gas is mainly used to provide the fluidity and aerodynamic force required for supersonic flame spraying; among them, nitrogen has a low cost; the low density and high thermal conductivity of helium help to improve the spraying speed and the density of the coating; argon can remain stable at high temperatures and can effectively prevent oxidation, thereby improving the quality of the coating. Its cost and density are between nitrogen and helium; air has a low cost and is easy to obtain, but in some applications it may cause oxidation of the coating, thereby affecting performance; although hydrogen has high thermal conductivity, due to its flammable and explosive properties, it must be used under strictly controlled conditions to ensure safety. Among the fuels used in the present invention, kerosene has a relatively high combustion temperature and can provide sufficient heat to rapidly heat the coating material to a molten state. This helps improve the density and adhesion of the coating, particularly when preparing an iron-based amorphous composite coating, thereby improving the coating's high quality and good hardness, wear resistance, and corrosion resistance. Kerosene produces fewer oxides during combustion, reducing oxidation of the coating and substrate, thereby ensuring the purity and quality of the coating. Kerosene has high volatility and good combustion efficiency, which can prevent overheating and deformation of the substrate while ensuring the accuracy and density of the coating. Kerosene's high combustion efficiency and stable heat release result in a faster cooling rate for the coating, effectively reducing pores and defects in the coating and further improving the coating's density, hardness, and corrosion resistance. The combustion process also produces fewer pollutants.Propylene has a low combustion temperature and high combustion efficiency, which can improve coating density, reduce porosity formation, and enhance hardness and wear resistance. Natural gas generates relatively stable heat during combustion and, when mixed with air, produces low pollutant emissions. For applications requiring high coating quality, natural gas also helps control oxidation reactions during the spraying process. Liquefied petroleum gas has a high calorific value and good volatility. It is commonly used in HVAF spraying to improve spray speed and coating density. LPG also performs well in temperature control, making it suitable for large-scale coating preparation. The present invention, when conducted under the aforementioned conditions, effectively improves the hardness, wear resistance, and corrosion resistance of the iron-based amorphous composite coating.

[0062] After the supersonic flame spraying, the present invention preferably also includes polishing the formed iron-based amorphous composite coating after grinding to obtain a smooth iron-based amorphous composite coating. In the present invention, the grinding is preferably performed using 60 to 3000 mesh sandpaper for grinding. In a specific embodiment, it can be performed by sequentially using 60 mesh, 120 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1500 mesh, 2000 mesh and 3000 mesh sandpaper for grinding. The present invention is polished under the above conditions, and it is possible to remove rough layers and uneven parts, improve the grinding effect, and then improve the quality of the iron-based amorphous composite coating. The present invention uses sandpaper from coarse to fine to grind, which can effectively remove the defects on the surface of the iron-based amorphous composite coating and avoid producing excessive scratches at each stage. Among them, using 60-grit and 120-grit sandpaper can effectively remove larger defects, using 400-grit and 600-grit sandpaper can improve the smoothness and fineness of the surface, using 800-grit and 1000-grit sandpaper for detailed sanding to make the surface smoother, and using 1500-grit, 2000-grit, and 3000-grit sandpaper for sanding can achieve the final smooth effect and thus achieve the ideal gloss. This step-by-step sanding method not only improves processing efficiency, but also significantly improves surface quality, providing better adhesion for subsequent painting or bonding.

[0063] The present invention also provides the use of the iron-based amorphous composite coating described in the above technical solution or the iron-based amorphous composite coating prepared by the preparation method described in the above technical solution as a protective layer. In the present invention, the iron-based amorphous composite coating is preferably used as a protective layer in the electronics, materials, engineering, aerospace, energy, petrochemical, or marine fields, and more preferably as a protective layer for pump and valve components.

[0064] Compared with amorphous alloys of other systems, the FeCrMo amorphous coating provided by the present invention has high hardness, high wear resistance and better corrosion resistance, and can very well resist the erosion of corrosive media such as acids and alkalis; the FeCrMo iron-based amorphous coating does not contain toxic substances, thereby avoiding serious pollution to the environment; the research on the FeCrMo iron-based amorphous coating has a low cost and can simultaneously take into account the good mechanical properties of the metal substrate and the excellent properties of the amorphous alloy. Cr3C2 particles are ceramic particles with excellent hardness, chemical stability and corrosion resistance. The present invention successfully improves the porosity of the coating cross section and surface by adding 3 to 10 wt% of Cr3C2 particles as a reinforcing phase to the FeCrMo amorphous coating, with fewer pores and a denser internal structure, significantly improving the hardness, wear resistance and corrosion resistance of the iron-based amorphous composite coating. The iron-based amorphous composite coating provided by the present invention serves as a protective layer and can extend the service life of the metal substrate, especially the metal substrate under high load and harsh working conditions (such as pump valve components used in corrosive environments), and reduce the frequency of its maintenance and replacement.

[0065] The iron-based amorphous composite coating provided by the present invention is a corrosion-resistant coating that exhibits excellent corrosion resistance in marine environments and other highly corrosive media, can effectively protect mechanical parts from corrosion damage, significantly extend the service life of equipment, reduce maintenance costs and downtime, and can be widely used in the fields of ships, offshore platforms and marine structures. Due to the high hardness of the iron-based amorphous composite coating and the uniform dispersion of Cr3C2 particles, the iron-based amorphous composite coating also exhibits excellent performance in wear resistance. The coating can significantly reduce the wear rate of mechanical parts under high friction and high pressure conditions, and is particularly suitable for key parts such as bearings and gears. The performance of the iron-based amorphous composite coating under high temperature conditions is also outstanding. Thanks to the strengthening effect of Cr3C2 particles, it can maintain good wear resistance and corrosion resistance at higher temperatures. Therefore, the coating has important application value in the surface protection of equipment such as gas turbines, heat exchangers and furnace walls in high-temperature working environments. These applications not only require the coating to have high hardness, but also need to maintain its chemical stability and mechanical strength at extreme temperatures, further demonstrating the wide applicability and technical advantages of the coating.

[0066] In order to further illustrate the present invention, the iron-based amorphous composite coating provided by the present invention, its preparation method and application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present invention.

[0067] In the following examples and comparative examples, the chemical composition of the X8-FeCrMoCB amorphous powder is, by mass percentage, Cr 25-27%, Mo 16-18%, C 2.0-2.5%, B 2.0-2.2%, and Fe as the balance, with a particle size of 15-53 μm. Figure 1 The SEM image of the X8-FeCrMoCB amorphous powder shows good sphericity. The particle size of the Cr3C2 (ceramic particles) is 35-55 μm, and the purity is 99.1%. Figure 2 This is the SEM image of Cr3C2 particles. It can be seen from the figure that the Cr3C2 particles are spherical and the particle size is about 35 to 55 μm.

[0068] Example 1

[0069] The X8-FeCrMoCB amorphous powder and Cr3C2 particles were dried at 50° C. for 30 minutes to obtain a mixed powder, wherein the mass content of the Cr3C2 particles was 3%.

[0070] A 304 stainless steel substrate (50 mm × 25 mm × 7.5 mm) was cleaned with acetone, polished with 60-, 120-, 400-, and 600-grit sandpaper, ultrasonically cleaned with anhydrous ethanol at 20-40 kHz and 100-200 W, and sandblasted to obtain a sandblasted substrate. The sandblasted substrate was preheated to 200° C. to obtain a preheated substrate. The sandblasting process parameters were as follows: 50-120 mesh Al2O3 as the sandblasting medium, 0.2-0.6 MPa as the sandblasting pressure, 150-300 mm as the sandblasting distance, 5-15 min as the sandblasting time, and a surface roughness (Ra) of 1.0-3.0 μm as the sandblasted substrate.

[0071] The mixed powder was sprayed onto the preheated substrate surface using supersonic flame spraying to form an amorphous composite coating. The HVOF process parameters were: HVAF technology, an oxygen flow rate of 1850 SCFH, a spray distance of 300 mm, a kerosene flow rate of 6.5 GPH, a powder feed rate of 35 g / min, and a carrier gas N2 flow rate of 13 L / min.

[0072] Figure 3 This is a physical picture of the amorphous composite coating prepared in Example 1 before grinding and polishing. It can be seen from the figure that the coating surface is uniform gray. Since it has not undergone subsequent grinding treatment, the surface retains the natural texture during the spraying process. Overall, the coating exhibits excellent uniformity and complete coverage. The coating surface presents a relatively rough feature, and no obvious cracks or peeling are observed, indicating that the spraying process has high stability and strong coating adhesion, and can provide reliable surface protection performance in practical applications.

[0073] The substrate containing the amorphous composite coating was cut into blocks of 12.5 mm × 12.5 mm × 7.5 mm. The surface and cross-section of the iron-based amorphous composite coating were polished using 60-mesh, 120-mesh, 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1500-mesh, 2000-mesh, and 3000-mesh sandpapers in sequence, and then polished to facilitate subsequent microstructural analysis, performance evaluation, and electrochemical testing.

[0074] Examples 2 to 4

[0075] An iron-based amorphous composite coating was prepared according to the method of Example 1, the only difference from Example 1 being that the mass contents of Cr3C2 particles in the mixed powder were 4.5%, 6% and 7.5% respectively.

[0076] Comparative Example 1

[0077] The FeCrMo iron-based amorphous composite coating was prepared according to the method of Example 1, with the only difference from Example 1 being that the mixed powder was replaced with X8-FeCrMoCB amorphous powder, and the mass content of Cr3C2 particles was 0%.

[0078] Test Example 1

[0079] The material structure and mechanical properties of the iron-based amorphous composite coatings prepared in Examples 1 to 4 and Comparative Example 1 were analyzed and tested.

[0080] (1) Organizational structure analysis test

[0081] (1.1) X-ray diffractometer analysis (XRD)

[0082] Figure 4 XRD patterns of amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4. Within the 35-40° range, the coatings exhibit diffuse scattering peaks characteristic of the amorphous phase, indicating that coatings with different Cr3C2 particle contents are primarily amorphous. PDF card comparison revealed that the diffraction peaks of Cr3C2 and Fe3C are superimposed on the amorphous peak. The appearance of Fe3C may be due to the small amount of crystallization of the amorphous phase caused by the high temperature and high pressure during the supersonic flame spraying process. Further calculations revealed that the amorphous ratios of the amorphous coatings with 3%, 4.5%, 6%, and 7.5% Cr3C2 ceramic particles added were 76.81%, 75.45%, 74.23%, and 70.75%, respectively.

[0083] (1.2) Scanning electron microscopy (SEM) analysis

[0084] Figure 5SEM images of the polished top surface of the amorphous composite coatings with different Cr3C2 contents prepared in Examples 1-4, wherein a content 3%, b content 4.5%, c content 6%, d content 7.5%. As can be seen from the figure, with the gradual increase of the content of Cr3C2 particles from 3% to 6%, the number of pores in the coating shows a trend of gradual decrease, and when the content of particles reaches 7.5%, the number of pores in the coating slightly increases. This may be because in the range of gradually increasing the content of Cr3C2 particles from 3% to 6%, after sufficient mixing before spraying, the Cr3C2 particles can be uniformly distributed in the coating alloy powder, so that the Cr3C2 particles are more easily filled in the pores during the spraying process, reducing the formation of pores; when the content reaches 7.5%, too many Cr3C2 particles can cause accumulation between particles, leading to an increase in the number of pores in the coating; in addition, due to the high melting point of Cr3C2 particles, too high Cr3C2 particle content can also increase the melting point of the alloy powder, resulting in poor flowability of the molten alloy during the spraying process, making it difficult for Cr3C2 particles to fully fill the pores, which can also lead to an increase in the number of pores in the coating.

[0085] Figure 6 SEM images of the cross-section of the amorphous composite coatings with different Cr3C2 contents prepared in Examples 1-4, wherein (a) content 3%, (b) content 4.5%, (c) content 6%, (d) content 7.5%. The thickness of all coatings is maintained between 200-400 μm. As can be seen from the figure, the bonding between all coatings and 304 stainless steel substrate is good, and no cracking of the coating and substrate is observed, which indicates that the amorphous composite coatings with different particle contents prepared exhibit excellent performance in structural integrity and coating-substrate bonding, providing a good foundation for future applications in mechanical properties and corrosion resistance.

[0086] (1.3) Coating microstructure characterization - pore and particle morphology change and element distribution analysis (BSE and EDS)

[0087] Figure 7 BSE image (a) and EDS images (b-g) of the pores in the amorphous composite coating (Cr3C2 content 7.5%) prepared in Example 4, the black position is the pore, and after EDS element analysis of the coating surface, it is found that the pore area is mainly O and C elements.

[0088] Figure 8BSE image (a) and EDS images (b-g) of the Cr3C2 particles in the amorphous composite coating (Cr3C2 content of 7.5%) prepared in Example 4. As can be seen from the EDS image, the white areas are concentrated with higher concentrations of Cr and C elements, indicating that these areas are mainly composed of Cr3C2 particles. The gray areas are mainly composed of other elements in the coating. More importantly, image analysis reveals that the morphology of the Cr3C2 particles has undergone significant changes during the spraying process, gradually splitting from the original large particles into multiple smaller particles. This phenomenon can be clearly observed in the image. Analysis of the cause of this change may be related to the high temperature and high pressure environment of supersonic flame spraying. During the spraying process, under the action of strong airflow and thermal energy, the morphology of the Cr3C2 particles has split. This may be due to the difference in thermal expansion between the particles and the stress caused by particle collisions during the spraying process, which causes the originally larger Cr3C2 particles to crack and disperse. This phenomenon may have a certain impact on the overall structure and properties of the coating, especially the mechanical properties and corrosion resistance of the coating.

[0089] according to Figure 7 and Figure 8 The results of elemental analysis show that O and C elements are aggregated in the pores of the coating. This is because the unique structure of the pores provides more surface area for oxidation, thereby increasing the possibility of oxidation. Especially during the supersonic flame spraying process, the high temperature, high pressure and oxygen-rich atmosphere may trigger an oxidation reaction on the coating surface, leading to the aggregation of oxygen elements. In particular, there is a difference in oxygen concentration in the pores during the spraying process. This difference may cause the oxidation reaction around the pores to be more intense.

[0090] (2) Mechanical properties test

[0091] Mechanical property testing is crucial in studying iron-based amorphous composite coatings with varying Cr3C2 particle content. These tests assess the impact of Cr3C2 particle content on the coating's strength, hardness, toughness, and wear resistance. This data helps determine the optimal particle content, thereby optimizing the coating's overall performance and enhancing its durability and reliability in practical applications. Systematic testing and analysis provide a scientific basis for improving coating design and enhancing application performance.

[0092] (2.1) Hardness test

[0093] The microhardness of the cross-section of the 304 stainless steel substrate and its iron-based amorphous composite coating was measured using an HV-1000 Vickers microhardness tester. During the test, the applied load was 0.05 kg and the holding time was 15 seconds. During the test, a measuring point was set every 50 μm in the parallel and vertical directions at the interface between the coating and the substrate. Each set of measurements contained five data points, and at least three sets of measurements were performed. The average of the three sets of data was finally taken as the microhardness value of the coating and the 304 stainless steel substrate.

[0094] Figure 9 The microhardness diagrams of amorphous composite coatings with different Cr3C2 contents prepared in Examples 1 to 4 are shown. As can be seen from the figure, the average hardness of the amorphous composite coating is approximately two to three times that of the 304 stainless steel substrate. This phenomenon is mainly attributed to the unique advantages of amorphous alloys. Due to the long-range disorder of amorphous materials, they are less likely to slip when subjected to stress, and thus exhibit higher hardness than the substrate. As the Cr3C2 particle content increases from 3% to 6%, the hardness of the coating shows an overall upward trend. However, when the particle content continues to increase to 7.5%, the coating hardness begins to decrease. When the Cr3C2 particle content is 6%, the coating microhardness reaches a maximum of 962.7 HV. The reason for this change is that the hardness of the coating is mainly affected by the porosity. The pores will cause local stress concentration inside the material, thereby reducing the overall hardness. In particular, when subjected to external stress, the pores may become crack initiation points, further reducing the hardness of the material.

[0095] The hardness change trend of the joint is that when the particle content increases from 3% to 6%, the hardness of the joint also shows an upward trend, and then begins to decrease. It is also when the Cr3C2 particle content is 6% that the microhardness of the joint reaches a maximum value of 532.4HV. The occurrence of this phenomenon is directly related to the bonding quality of the above-mentioned coating and substrate. The better the bonding quality, the less likely stress concentration will occur, thereby achieving a higher hardness. In general, the microhardness of the joint is about 500HV, which is also higher than the microhardness of 304 stainless steel (about 300HV).

[0096] In addition, the hardness of the 304 stainless steel substrate within 50 microns of the joint is slightly improved. This phenomenon is mainly attributed to the influence of high temperature on the microstructure of the substrate surface during the spraying process. High temperature treatment may lead to grain refinement on the substrate surface and induce local phase transformation (such as transformation of ferrite or martensite). These phase transformations usually significantly change the crystal structure of the substrate, thereby improving the hardness and mechanical properties of this area to a certain extent.

[0097] (2.2) Friction and wear test

[0098] The friction and wear characteristics of the amorphous composite coating were tested using an MSR-2T electrochemical reciprocating friction and wear tester. Prior to measurement, the amorphous composite coating was inlaid with polyethylene resin. The MSR-2T electrochemical reciprocating friction and wear tester simulates actual working conditions by performing high-frequency reciprocating friction between the coating and the friction pair. The experimental parameters were set as a load of 6 N, a friction path of 5 mm, a rotation speed of 270 rpm, and a wear time of 24 min. The friction pair consisted of a 3 mm diameter Al2O3 ceramic ball. Following the experiment, the sample was ultrasonically cleaned with ethanol and observed and analyzed using confocal microscopy and scanning electron microscopy (SEM). Subsequently, the surface of the worn coating was measured using a CHOTEST white-light interferometer. This instrument accurately depicts the micromorphology, wear state, and deformation characteristics of the material surface after the friction and wear experiment. The wear loss was calculated based on the change in coating mass loss before and after the friction and wear experiment.

[0099] Figure 10 The following graph shows the time-dependent variation of the friction coefficient for amorphous composite coatings with varying Cr3C2 content prepared in Examples 1 to 4. The graph shows similar trends in the friction coefficient for coatings with varying Cr3C2 particle contents. This is due to the initial stage of friction, when point contact occurs. This point contact friction has a smaller contact area and bears greater local pressure, resulting in an upward trend in the friction coefficient. Subsequently, point contact transitions to surface contact, where the contact surface gradually increases relative to point contact friction, resulting in a more even distribution of pressure. The friction process then enters a stable phase, and the friction coefficient also tends to stabilize.

[0100] The average friction coefficient of the coating with a 3% Cr3C2 particle content was 0.6906, which decreased to 0.5543 for the coating with a 4.5% Cr3C2 particle content and significantly decreased to 0.2933 for the coating with a 6% Cr3C2 particle content. The friction coefficient of the coating with a 7.5% Cr3C2 particle content increased again to 0.4449. Generally speaking, a lower friction coefficient reflects better wear resistance because the friction coefficient directly affects the amount of friction the surface is subjected to during contact. The smaller the friction coefficient, the smaller the friction force. Smaller friction can reduce surface wear and damage, thereby improving the wear resistance of the coating. However, the friction coefficient is not the only indicator reflecting the wear resistance of the coating, so the wear quality of the coating was also measured and analyzed.

[0101] Figure 11Wear mass plots of the amorphous composite coatings with different Cr3C2 contents prepared in Examples 1-4. As can be seen from the figure, under the same friction and wear conditions, the coating with 3% Cr3C2 particles shows the largest wear mass, about 0.153 g, while the coating with 4.5% Cr3C2 particles slightly decreases to about 0.144 g, and with the increase of the Cr3C2 particle content, the wear mass of the coatings with 6% and 7.5% Cr3C2 particles decreases to about 0.123 g and 0.132 g, respectively; by comparing the wear mass, it can be concluded that the amorphous composite coating with 6% Cr3C2 particles has the best wear resistance under the same friction conditions.

[0102] Figure 12 Microstructure images of the amorphous composite coatings with different Cr3C2 contents prepared in Examples 1-4 after wear, wherein (a) 3% content, (b) 4.5% content, (c) 6% content, and (d) 7.5% content. As can be seen from the figure, after the friction and wear test, the coating surface appears areas with no obvious changes, rough areas, and bright particles. This phenomenon is mainly caused by the strong friction of the Al2O3 ceramic ball friction pair. During the friction and wear process, the coating is subjected to a large mechanical stress, and due to some unavoidable defects in thermal spraying, stress concentration will occur locally, and the previously polished smooth coating surface may become no longer smooth, and even peeling off to expose the substrate surface. High frequency contact and local stress concentration cause dynamic changes in the coating surface, and the formation of bright particles is mainly due to the friction process, when the friction pair reciprocally wears on the coating, the extrusion effect promotes the generation of these particles, and these bright particles indicate that the material has undergone local plastic deformation, and the stress concentration in the extrusion area also affects the service life of the coating, and in subsequent use, there will be more serious stress concentration, thereby reducing the service life of the coating; in comparison, the rough areas have more stress concentration points due to surface irregularities and defects, which leads to more serious stress concentration, so these areas bear more stress; and the areas with no obvious changes have relatively good surface state due to lighter stress concentration and smaller mechanical stress, although the bright particles can also cause significant stress concentration, but the number of concentration points is small, and compared with the rough areas, the stress concentration effect is relatively light; therefore, the less bright particles and rough areas observed by SEM, the better the wear resistance of the coating is in general.

[0103] Figure 13The EDS elemental analysis results of the surface characteristic areas of the iron-based amorphous composite coating prepared in Example 4. As can be seen from the figure, carbon elements show a significant aggregation phenomenon in the rough areas and bright particles. Especially under high stress conditions, local areas will generate higher temperatures due to stress concentration and frictional heat accumulation during friction or wear. In this high-temperature environment, the diffusivity of carbon is significantly enhanced, thereby promoting the aggregation of carbon elements in high-stress and high-temperature areas (such as extrusion areas and rough areas). The concentration of carbon elements in these areas is relatively high. As mentioned above, bright particles appear in areas that have undergone local plastic deformation. Their strong reflective properties make these particles appear high-brightness in SEM images. This phenomenon is closely related to the surface morphology. The raised surface areas can reflect more secondary electrons and therefore show a strong brightness. When analyzing the micromorphology of the worn area, although SEM can provide certain information, SEM images alone are not sufficient to fully evaluate the surface changes after wear. In order to gain a deeper understanding of the surface morphology changes during wear, the measurement of the worn surface profile using a laser confocal microscope and white light interferometer can provide more accurate three-dimensional surface data. This analysis method that combines SEM with interferometry technology is very helpful in revealing the microscopic mechanism of coating wear and provides a more scientific basis for further optimizing the wear resistance of the coating.

[0104] Figure 14 These are surface profiles of amorphous composite coatings prepared in Examples 1-4 with varying Cr3C2 particle contents, obtained using a laser confocal microscope and white light interferometer, after friction and wear. (a) 3% content, (b) 4.5% content, (c) 6% content, and (d) 7.5% content. The figures show that the wear marks on the surface of the iron-based amorphous composite coating with a 6% Cr3C2 particle content are shallower and narrower than those on the coatings with other Cr3C2 particle contents, indicating that it experienced milder wear. In contrast, the wear marks on the surface of the composite coating with a 3% Cr3C2 particle content are deeper and wider, indicating that it experienced more significant wear.

[0105] In summary, the present invention successfully prepared amorphous composite coatings with different Cr3C2 particle contents by supersonic flame spraying technology under a series of fixed process parameters, and studied and analyzed the porosity, microstructure and microhardness of coatings with different Cr3C2 particle contents. At the same time, the influence mechanism of Cr3C2 particles on the hardness and porosity of the coatings was analyzed, and the following conclusions were drawn:

[0106] (1) The iron-based amorphous composite coatings with different Cr3C2 particle contents prepared by supersonic flame spraying have a good surface melting state, a small amount of pores, and a relatively dense internal structure. They contain both Cr3C2 phase and Fe3C phase, and the amorphous ratio is above 70%.

[0107] (2) By adding Cr3C2 particles, the porosity of the coating cross section and surface was successfully improved. When the amount of Cr3C2 particles added increased to 6%, the number of pores on the coating surface first decreased, but when the amount of Cr3C2 particles added increased to 7.5%, the number of pores increased instead.

[0108] (3) The presence of Cr3C2 particles increases the hardness of the coating. When the Cr3C2 particle addition is 6%, the coating has the highest microhardness of about 962.7HV, which is about three times the hardness of the 304 stainless steel substrate. The hardness of the joint is about 500HV.

[0109] (4) The wear morphology of the coating is mainly composed of two areas: a rough peeling area and a relatively smooth area. In the friction and wear experiment, it was found that when the content of Cr3C2 particles in the coating reached 6%, the peeling phenomenon was significantly reduced. The coating with a 6% Cr3C2 particle content showed the best wear resistance.

[0110] Test Example 2

[0111] Electrochemical performance test of the Fe-based amorphous composite coating and the FeCrMo iron-based amorphous composite coating prepared in Comparative Example 1

[0112] The corrosion behavior of amorphous composite coatings containing different contents of Cr3C2 particles in simulated seawater was analyzed through electrochemical tests and immersion experiments. At the same time, the corrosion protection performance of these coatings on 304 stainless steel was detected and evaluated. The corrosion mechanism of the coatings in simulated seawater was explored by characterizing the surface products of the coatings after immersion.

[0113] (1) Electrochemical experiments

[0114] The corrosion resistance of the iron-based amorphous composite coating in simulated seawater was evaluated using a CS350M electrochemical workstation. The experiment adopted a standard three-electrode system, in which the Ag / AgCl electrode was used as the reference electrode, the platinum electrode was used as the auxiliary electrode, and the working electrode was the iron-based amorphous composite coating. The corrosive solution was simulated seawater at room temperature, and the simulated seawater composition was: NaCl 24.420 g / L, MgCl 2 5.16 g / L, Na2SO4 4.002 g / L, CaCl 2 1.017 g / L, and KCl 0.693 g / L.

[0115] The test process is as follows: first, the open circuit potential (OCP) is measured, the sample is immersed in simulated seawater for 1800s, and after the open circuit potential is stable, the electrochemical impedance spectroscopy test is performed. The electrochemical impedance spectroscopy test covers a frequency range of 10 -2 ~10 5Hz, with a sinusoidal perturbation amplitude of 10 mV (relative to the open-circuit potential). Potentiodynamic polarization testing was then performed with a potential sweep range of -1 V to 1 V and a scan rate of 0.5 mV / s. Electrochemical impedance spectroscopy data were fitted and analyzed using CS Studio 6 software included with the CS350M electrochemical workstation, while polarization curves were processed using the Tafel linear extrapolation method.

[0116] (1.1) Open circuit potential test analysis

[0117] In order to study the corrosion resistance of iron-based amorphous composite coatings with different Cr3C2 particle contents and analyze and compare the corrosion resistance of the coatings, amorphous composite coatings with different Cr3C2 particle contents were selected and immersed in simulated seawater for 1800s. The open circuit potential (OCP) curves of different amorphous composite coatings were measured by electrochemical workstation.

[0118] Figure 15 The OCP curves of amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1 to 4 are shown. The results show that the open circuit potential of the coating with a Cr3C2 particle content of 6% is greater than that of the coating with a Cr3C2 particle content of 7.5%, followed by 4.5% and 3%. A higher open circuit potential indicates that the coating has a lower corrosion tendency. This is because a high open circuit potential means that charge transfer in the system is relatively difficult, the charge transfer reaction is relatively slow, and it has stronger electrochemical stability. The OCP curve only provides static information of the open circuit potential and cannot fully represent the corrosion resistance of the coating. The OCP curve can only preliminarily determine, predict, and evaluate the corrosion resistance of the coating. The corrosion resistance of the coating is also affected by other factors, such as the composition, structure, and bonding strength of the coating, so dynamic potential polarization testing and impedance testing are also necessary.

[0119] (1.2) Potentiodynamic polarization test analysis

[0120] Figure 16 Polarization curves of iron-based amorphous composite coatings with different Cr3C2 particle contents (0%, 3%, 4.5%, 6%, and 7.5%) prepared in Examples 1 to 4 and Comparative Example 1. The self-corrosion current density (Icorr) and self-corrosion potential (Ecorr) of the amorphous composite coatings with different Cr3C2 particle contents were obtained by Tafel linear extrapolation. The relevant data are shown in Table 1.

[0121] Table 1 Polarization curve fitting parameters of Fe-based amorphous composite coatings with different Cr3C2 particle contents

[0122] Depend on Figure 16As can be seen from Table 1, the self-corrosion current density of the coating is basically stable at around 100 at different particle contents, without significant changes; in contrast, the self-corrosion potential shows different trends: the self-corrosion potential of the coating with 6% Cr3C2 particle content is greater than that of the coating with 7.5% Cr3C2 particle content, followed by 4.5% and 3%, which indicates that in simulated seawater, the coating with 6% Cr3C2 particle content has the smallest corrosion tendency and the best corrosion resistance.

[0123] This is because the self-corrosion potential reflects the potential when the coating reaches equilibrium with its electrochemical system. A high self-corrosion potential indicates that the coating is more inclined to be in a more stable state. A high self-corrosion potential means that it is easier for a stable oxide film or other protective layer to form on the coating surface, which can slow down the erosion of the corrosive medium on the material, thereby reducing the corrosion rate. On the other hand, a high self-corrosion potential also means that the electrochemical reaction rate of the coating is slower, the electron transfer and ion transport reactions are relatively less, and the corrosion tendency is smaller. That is, in a corrosive environment, the coating can maintain minimal corrosion tendency and optimal corrosion resistance.

[0124] (1.3) Electrochemical impedance spectroscopy test analysis

[0125] Electrochemical impedance spectroscopy (EIS) is a commonly used analytical method in studying the chemical corrosion failure system of coatings. It is as important as the potentiodynamic polarization test analysis. -2 Hz to 10 -5 The EIS test results are obtained by performing a sinusoidal wave perturbation with an amplitude of 10mV in the frequency range of Hz. Through EIS, the response data of the electrochemical system to the electrical signal, such as the impedance modulus and phase angle, can be obtained. Among them, the Nyquist plot is widely used to visualize EIS data. The Nyquist plot can intuitively display the EIS data on a plane, thereby presenting the response characteristics of the impedance.

[0126] In the Nyquist plot, the radius of the capacitance arc is considered to be an important metric characteristic for characterizing the corrosion resistance of the material. A larger capacitance arc radius means better corrosion resistance, because the increase in the capacitance arc radius represents an increase in the charge transfer resistance of the electrochemical system, which slows down the electrochemical reaction and improves the stability of the electrochemical system, thereby reflecting better corrosion resistance of the coating.

[0127] Figure 17Nyquist plots and schematic diagrams of the coating equivalent circuits for amorphous composite coatings with different Cr3C2 particle contents (0%, 3%, 4.5%, 6% and 7.5%) prepared in Examples 1 to 4 and Comparative Example 1 (inset). In the Nyquist plot, the horizontal axis Z' (real impedance) reflects the resistive behavior of the electrochemical system, which is mainly related to the conductivity of the coating and the stability of the interfacial reaction. The larger the Z' value, the greater the resistance encountered when the current flows in the system, which in turn indicates the resistive characteristics of the coating; the vertical axis Z" (imaginary impedance) reflects the reactive behavior of the system, reflecting the charge transfer and energy storage characteristics. A larger Z" value usually means a stronger charge transfer resistance or a significant capacitance effect, revealing the electrochemical reaction kinetics of the coating; through a comprehensive analysis of the real and imaginary impedances, the corrosion resistance of the coating and its electrochemical stability can be effectively evaluated. In addition, the experimental results show that the coating containing 6% Cr3C2 particles has a larger capacitance arc radius, which is better than the coating containing 7.5% Cr3C2 particles, which exhibits a lower capacitance arc radius. The other coatings containing 4.5% and 3% Cr3C2 particles also showed similar trends, which were highly consistent with the results of potentiodynamic polarization test and open circuit potential test, further verifying the effect of different Cr3C2 particle contents on the electrochemical properties of the coatings.

[0128] To further analyze the EIS experimental data, the coating impedance spectrum was fitted, and an equivalent circuit based on a realistic physical model was designed. In this simulation circuit, R1 represents the resistance of the simulated seawater, R2 represents the charge transfer resistance, and CPE represents the capacitance between the pores and cracks and the simulated seawater. The results are shown in Table 2.

[0129] Table 2 Fitting results of components in the equivalent circuit

[0130]

[0131]

[0132] Table 2 shows that the solution resistance R1 varied within a range of about 10 during the experiment, with little fluctuation. This indicates that the simulated seawater solution conditions were relatively stable during the test. In addition, the value of the resistance R2 reflects the resistance to charge transfer on the sample surface. The coating with a 6% Cr3C2 particle content exhibited the largest R2 value, indicating that the electrochemical system of this coating had the most significant charge transfer resistance. The introduction of Cr3C2 particles effectively inhibited the progress of the electrochemical reaction, enhanced the stability of the electrochemical system, and thus significantly improved the corrosion resistance of the coating.

[0133] By simulating seawater as the electrolyte, the coatings with different Cr3C2 particle contents were subjected to open circuit potential test, potentiodynamic polarization test and electrochemical impedance spectroscopy test at room temperature. The three test results all showed that the coating with 6% Cr3C2 particle content showed the best corrosion resistance. This performance was attributed to the low porosity of the coating. According to the EDS analysis results in Test Example 1, oxygen elements had accumulated around the pores of the coating during the spraying process, which means that these porous areas had undergone local oxidation during spraying. The areas that were oxidized first became the core of corrosion because they had partially lost their original amorphous structure, weakening their protective performance. Therefore, electrochemical reactions usually occurred preferentially in these oxidized areas. , forming the core of coating corrosion; in addition, in the simulated seawater environment, oxidation reaction is one of the main processes of metal corrosion. The special structure of the pores provides more surface area, which in turn increases the site of oxidation reaction. The small potential difference formed inside and outside the pores will trigger local electrochemical reactions, which usually occur first in the pores and their surroundings to form a corrosion core. Once a corrosion core is formed in the pores and their surroundings, if it is long-term corrosion, the corrosion products produced will diffuse and aggregate in the pores and their surroundings. The generated oxide corrosion products will aggravate local corrosion, which will not only weaken the protective performance of the coating, but may also cause acidification or alkalization of the local environment, further aggravating the overall corrosion process. The accumulation of these corrosion products will weaken the mechanical strength and protective ability of the coating, leading to cracking and peeling.

[0134] (2) Immersion test

[0135] The surface of pumps and valves is likely to be in a seawater environment for a long time and is susceptible to long-term corrosion. Therefore, studying long-term corrosion under simulated seawater conditions can help engineers better understand the corrosion resistance of materials, and hopefully help with material selection and the design of protective measures.

[0136] Before testing, the amorphous composite coating was embedded with polyethylene resin to ensure that only the coating portion was in contact with the simulated seawater. Figure 18 Schematic diagram of the packaging of the amorphous composite coating sample. The amorphous composite coating was immersed in simulated seawater for 1, 7, and 15 days, with fresh simulated seawater replaced daily. Electrochemical testing was performed on the sample immersed for 15 days to evaluate its corrosion performance.

[0137] The coating area and simulated seawater are 1cm 2 :50mL was immersed in simulated seawater and placed in a constant temperature water bath at room temperature for immersion experiments, with coating samples with different Cr3C2 particle contents as comparisons.

[0138] (2.1) Weightlessness test

[0139] Before each coating is immersed, the test surface must be ground and polished, and then ultrasonically cleaned with anhydrous ethanol to remove impurities on the coating surface. During the immersion process, the simulated seawater is replaced every 24 hours. After being taken out, it is ultrasonically cleaned in a chromic acid solution for 15 minutes, and then cleaned with anhydrous ethanol and quickly dried with a hair dryer before the weight loss test is carried out.

[0140] Figure 19 The weight loss statistics of amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1 to 4 after immersion for 15 days show that when the immersion time reaches 15 days, the coating containing 6% Cr3C2 particles has the smallest weight loss of 5.2 mg, which is lower than that of coatings with other particle contents. Specifically, the coating with 7.5% Cr3C2 particle content loses the most, followed by coatings with 4.5% and 3% content. According to the porosity analysis of Test Example 1, the coating with 6% Cr3C2 particle content has the lowest porosity, which may be one of the important factors for its smaller weight loss and better corrosion resistance. Lower porosity means fewer pores inside the coating, making it difficult for seawater to penetrate into the lower layer of the coating, reducing the chance of corrosion. In contrast, coatings with higher porosity may be more easily invaded by seawater, resulting in more serious corrosion.

[0141] (2.2) Corrosion morphology analysis after long-term corrosion

[0142] In order to better observe the micro-corrosion changes of amorphous composite coatings with different Cr3C2 particle contents after immersion in simulated seawater for 15 days, the coatings were immersed in simulated seawater for 1 day, 7 days and 15 days, and their micro-surface morphologies were photographed using SEM.

[0143] Figure 20SEM images of the amorphous composite coatings with different Cr3C2 particle contents prepared in Examples 1 to 4 after immersion for 1 day, 7 days, and 15 days, as well as SEM images after removal of corrosion products; a1, b1, c1, and d1 are for 1 day immersion, and the particle contents are 3%, 4.5%, 6%, and 7.5%, respectively; a2, b2, c2, and d2 are for 7 days immersion, and the particle contents are 3%, 4.5%, 6%, and 7.5%, respectively; a3, b3, c3, and d3 are for 15 days immersion, and the particle contents are 3%, 4.5%, 6%, and 7.5%, respectively; a4, b4, c4, and d4 are for removal of corrosion products after 15 days immersion, and the particle contents are 3%, 4.5%, 6%, and 7.5%, respectively. As can be seen from the figure, after immersion for 1 day, the coating surface remained flat and basically unchanged; after immersion for 7 days, a small amount of pitting pits appeared on the coating surface, but no obvious corrosion products were seen. The formation of these pitting pits was mainly due to the local corrosion effect of simulated seawater, and the absence of corrosion products may be due to the short time, resulting in corrosion products not yet beginning to accumulate on the surface; after immersion for 15 days, the corrosion products generated at this time were granular and aggregated together. The formation of this granular corrosion product is due to the gradual deposition of corrosion products on the surface during the point chemical reaction process, and forming uneven precipitation over time, which eventually crystallizes into granular form.

[0144] To further investigate the corrosion morphology, 180 g / L chromic acid solution was mixed with coatings containing varying amounts of Cr3C2 particles in a beaker and cleaned using an ultrasonic cleaner to better remove corrosion products. As shown in the figure, as the immersion time reached the 15th day, the pitting area gradually increased and expanded, revealing distinct pitting and deeper pores. This phenomenon is consistent with the analysis results in Section 2.1, indicating that the accumulation of corrosion products exacerbates the corrosion process.

[0145] (2.3) Corrosion product analysis

[0146] SEM observations showed that a thin layer of corrosion products covered the surface of the coating after the coating was immersed in simulated seawater for 15 days, and EDS analysis was performed on these corrosion products. Figure 21This is an EDS image of the corrosion products in the amorphous composite coating (Cr3C2 content 7.5%) prepared in Example 4. The results show that the corrosion products are mainly iron oxides. Corrosion products are mainly concentrated in areas with low chromium content, while they are less common in areas with high chromium content. This is due to the excellent corrosion resistance of chromium, which can form a stable passivation film on the metal surface, effectively preventing further corrosion. In addition, the chemical stability of chromium carbide enables it to perform well in simulated seawater environments and is not prone to significant chemical reactions, thus having strong resistance to chloride ion corrosion. Similarly, corrosion products mainly appear in areas with low molybdenum content, while they are less common in areas with high molybdenum content. This is because molybdenum also has strong corrosion resistance, especially in chloride environments, and it can significantly improve the corrosion resistance of iron-based alloys. In areas with high molybdenum content, the presence of molybdenum effectively prevents the intrusion of corrosive media, thereby reducing the formation of corrosion products.

[0147] It is important to note that the Cr3C2 particles exhibit no significant corrosion behavior during the corrosion process. Their improved corrosion resistance primarily stems from their improved microstructure. Increasing the Cr3C2 particle content reduces the porosity of the coating surface, effectively reducing the penetration of corrosive media and enhancing overall corrosion resistance. Therefore, the corrosion resistance of the coating depends not only on the chemical stability of the particles but also on their distribution and the coating's microstructure.

[0148] Through EDS analysis of the corrosion products, it can be found that the corrosion products are mainly composed of iron and oxygen elements. In order to further determine the specific composition of the corrosion products, XRD analysis is performed on the samples. Figure 22 The XRD image of the amorphous composite coating (Cr3C2 content 7.5%) prepared in Example 4 after corrosion in simulated seawater shows that the sample has a diffraction peak of Fe2O3, which indicates that in the simulated seawater environment, an oxidation reaction occurred in the iron-based amorphous alloy coating, and Fe2O3 was the main corrosion product, while other corrosion products were not clearly shown in the XRD spectrum.

[0149] (2.4) Potentiodynamic polarization test analysis after long-term corrosion

[0150] To further explore the performance of the two composite coatings during the corrosion failure process, a 15-day full immersion experiment was conducted in a simulated seawater environment. Polarization curves of coatings with different particle contents were measured using an electrochemical workstation, and the corrosion process of the coatings was further explained using AC impedance spectroscopy. It is important to note that open-circuit voltage testing is not usually performed after corrosion. As mentioned above, open-circuit voltage can only provide a preliminary prediction and assessment of the corrosion resistance of the coating. Once metal corrosion occurs, the corrosion products will change the chemical properties and electrochemical behavior of the metal surface, which is likely to interfere with the open-circuit voltage test results, thereby affecting the accuracy and reliability of the test, resulting in inaccurate test results that cannot truly reflect the actual situation.

[0151] Figure 23 Polarization curves of amorphous composite coatings prepared in Examples 1-4 and Comparative Example 1 with varying Cr3C2 particle contents (0%, 3%, 4.5%, 6%, and 7.5%) after 15 days of immersion. Tafel extrapolation was used to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr) of the coatings with varying Cr3C2 particle contents. See Table 3 for details.

[0152] Table 3 Polarization curve fitting parameters of amorphous composite coatings with different Cr3C2 particle contents after immersion for 15 days

[0153] Depend on Figure 23 As can be seen from Table 3, the corrosion current density of the coatings with different Cr3C2 particle contents is basically stable at around 100, with no significant change. In addition, the corrosion potential has a basically consistent trend before and after 15 days of immersion. According to Tables 1 and 3, after 15 days of immersion, the corrosion potential has decreased, but the corrosion potential of the coating with 6% Cr3C2 particle content is still the highest, showing the smallest corrosion tendency and the best corrosion resistance.

[0154] (2.5) Impedance spectrum test analysis after long-term corrosion

[0155] Figure 24 Nyquist plots of amorphous composite coatings prepared in Examples 1-4 and Comparative Example 1 with varying Cr3C2 particle contents (0%, 3%, 4.5%, 6%, and 7.5%) after 15 days of immersion. The inset is a schematic diagram of the coating's equivalent circuit. The plot shows that the coating with 6% Cr3C2 particle content has the highest capacitance arc radius, followed by 7.5%, 4.5%, and 3%, which is consistent with the potentiodynamic polarization test analysis results in (1.2).

[0156] Continue to analyze the EIS experimental data in depth and fit the coating impedance spectrum, such as Figure 24As shown in the simulation circuit, Table 4 shows the fitting results of each component in the equivalent circuit of the coating impedance spectrum after immersion for 15 days. By observing Table 4, it can be found that the solution resistance R1 also fluctuates slightly during the experiment, and the coating with 6% Cr3C2 particle content shows the largest R2 value.

[0157] Table 4 Fitting results of components in the equivalent circuit of the coating impedance spectrum after immersion for 15 days

[0158]

[0159] A 15-day full immersion experiment was carried out in a simulated seawater environment. The coatings with different Cr3C2 particle contents were subjected to potentiodynamic polarization tests and electrochemical impedance spectroscopy tests at room temperature. The test results showed that after 15 days of full immersion, the coating with 6% Cr3C2 particle content still exhibited the best corrosion resistance. This phenomenon was also attributed to the low porosity of the coating, but the accumulation of corrosion products should also be considered. The pores are channels for simulated seawater to penetrate into the surface of the substrate, and the dense coating effectively blocks this penetration, inhibits the electrochemical corrosion reaction, thereby reducing the corrosion rate and reducing the accumulation of corrosion products. Especially in the long-term corrosion process, the accumulation of corrosion products is more important, and these corrosion products usually accelerate the corrosion rate. It is hoped that this conclusion can provide some valuable help for the design and optimization of iron-based amorphous alloy coatings to cope with long-term corrosion in marine environments.

[0160] In summary, the corrosion resistance and corrosion process of amorphous composite coatings with different Cr3C2 particle contents in simulated seawater were studied by electrochemical corrosion. The following conclusions were drawn:

[0161] (1) By using simulated seawater as the electrolyte, the coatings with different Cr3C2 particle contents were subjected to open circuit potential test, potentiodynamic polarization test and electrochemical impedance spectroscopy test at room temperature. The three test results all showed that the coating with 6% Cr3C2 particle content exhibited the best corrosion resistance, which was attributed to the low porosity of the coating.

[0162] (2) After being fully immersed for 15 days, the coatings with different Cr3C2 particle contents were subjected to potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The coating with 6% Cr3C2 particle content still showed the best corrosion resistance.

[0163] (3) In the immersion experiment, scanning electron microscopy revealed that the surface remained flat on the first day. On the seventh day of immersion, pitting began to appear on the surface, but no corrosion products were found. After 15 days of immersion, corrosion products appeared on the surface, and after removing these corrosion products, it was found that obvious pitting and cracks had formed on the surface. EDS analysis and XRD analysis confirmed that these corrosion products were mainly Fe2O3.

[0164] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An iron-based amorphous composite coating, characterized in that: The chemical composition includes an FeCrMo amorphous coating and Cr3C2 particles dispersed in the FeCrMo amorphous coating; the mass content of the Cr3C2 particles in the iron-based amorphous composite coating is 3-10%; Calculated by mass percentage, the chemical composition of the FeCrMo amorphous coating includes: Cr 25-27%, Mo 16-18%, C 2.0-2.5%, B 2.0-2.2%, and Fe 50.3-55%.

2. The iron-based amorphous composite coating according to claim 1, characterized in that: The thickness of the iron-based amorphous composite coating is 200-400 μm.

3. The method for preparing the iron-based amorphous composite coating according to any one of claims 1 to 2, characterized in that: The following steps are involved: A mixed powder is used to perform supersonic flame spraying on the surface of a metal substrate to form an iron-based amorphous composite coating; the mixed powder includes FeCrMo amorphous powder and Cr3C2 particles, and the mass content of the Cr3C2 particles in the mixed powder is 3-10%.

4. The preparation method according to claim 3, characterized in that The particle size of the FeCrMo amorphous powder is 15-53 μm.

5. The preparation method according to claim 3, characterized in that The particle size of the Cr3C2 particles is 35-55 μm.

6. The preparation method according to any one of claims 3 to 5, characterized in that The supersonic flame spraying adopts high-velocity air fuel technology, and the process conditions include: oxygen flow rate of 1500~2200SCFH, spraying distance of 250~350mm, fuel flow rate of 5~8GPH, powder feeding rate of 30~40g / min, and carrier gas flow rate of 10~15L / min.

7. The preparation method according to claim 6, characterized in that The fuel for the supersonic flame spraying includes one or more of kerosene, propylene, natural gas and liquefied petroleum gas.

8. The preparation method according to claim 3, characterized in that The metal substrate is sandblasted and then preheated before use.

9. Use of the iron-based amorphous composite coating according to any one of claims 1 to 2 or the iron-based amorphous composite coating prepared by the preparation method according to any one of claims 3 to 8 as a protective layer.

Images