Multi-principal alloy coatings for mitigating marine biofouling and their preparation methods

Abstract

This invention discloses a multi-principal alloy coating for mitigating marine biofouling and its preparation method, belonging to the technical field of thermal spray coatings and their preparation methods. The powder used to prepare the coating is a pre-alloyed powder prepared by inert gas atomization. Its chemical composition, by weight percentage, is: Cr: 10%-30%, Ni: 8%-22%, Mo: 1%-10%, Cu: 5%-30%, Nb: 0.1%-0.7%, C: ≤0.3%, Si: ≤1.0%, Mn: ≤2.0%, P: ≤0.05%, S: ≤0.03%, with the balance being Fe; the weight ratio of Cu to Nb ranges from 10 to 290. This multi-principal alloy coating achieves an antibacterial rate of 99.9% against Pseudomonas aeruginosa and Bacillus vinifera within 6 hours; and inhibits the adhesion behavior of marine algal fouling organisms within 7 days, with a fouling coverage ratio of less than 5%.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal spray coatings and their preparation methods, specifically relating to a multi-principal alloy coating that can mitigate marine biofouling. This coating is prepared using supersonic flame spraying technology and applied to the surface of marine engineering equipment that is in full contact with the marine environment. Background Technology

[0002] In the field of marine engineering, the problem of marine biofouling caused by unnecessary biological attachment on equipment surfaces not only seriously harms the marine economy and ecosystems but also significantly reduces the performance and safety of marine engineering equipment. Currently, the main methods for marine biofouling control include mechanical cleaning, seawater electrolysis, chemical agents, and antifouling coatings. Among these, antifouling coatings have become the preferred method for solving marine biofouling problems due to their economic efficiency and high effectiveness. However, existing industrial antifouling coatings mainly rely on organic copolymers, which exhibit insufficient mechanical properties during service, and the excessive release of antifouling agents poses a potential pollution risk to the marine environment, necessitating urgent solutions.

[0003] To overcome the limitations of organic-based antifouling coatings in terms of environmental friendliness, bonding strength, and service life, researchers have developed metal-based antifouling coatings containing antifouling agents. Metal coatings not only significantly improve the bonding strength, mechanical properties, and service life of the coating, but also reduce its toxicity. Currently, the most widely studied metal-based antifouling coatings mainly include Cu-Ag, Cu-Ti, Cu-Ni, and Cu-stainless steel composite coatings. However, existing Cu / X antifouling system coatings still face the problem of uncontrollable release of antifouling agents. This is because traditional metal coating preparation usually employs a powder mixing process, and the physical bonding between different metals can easily lead to significant anode-cathode separation, thereby accelerating the corrosion performance of the coating and making it less stable than a single metal during service. Therefore, the design of the metal antifouling component system and the innovation of powder preparation methods have become key directions for the development of novel antifouling coatings. Furthermore, there is a wide range of preparation technologies for metal coatings, mainly including cold spraying, thermal spraying, and electroplating. Among these, thermal spraying technology, with its wide material adaptability, high efficiency, and minimal thermal impact on the substrate, has become the preferred option.

[0004] Against this backdrop, innovations in three aspects—the preparation method of metal coating powder, the composition design, and the coating preparation process—are expected to provide new ideas for the development of antifouling coatings and offer practical solutions for improving the environmental friendliness of coatings. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-principal alloy coating capable of mitigating marine biofouling and its preparation method. The main technical feature of this invention is the use of a pre-alloyed multi-principal alloy powder as the powder for spraying. By adding copper (Cu) and niobium (Nb) to the powder, the multi-principal alloy coating possesses strong corrosion resistance while mitigating biofouling on the surface of marine engineering equipment. The multi-principal alloy coating achieves a 99.9% antibacterial rate against typical marine fouling symbiotic bacteria (such as *Pseudomonas aeruginosa* and *Bacillus vivax*) within 6 hours. Within 7 days, it inhibits the adhesion of marine algae fouling organisms, resulting in a fouling coverage ratio of less than 5%. The corrosion current density of the multi-principal alloy coating in the service environment is 50 nA / cm². 2 -300nA / cm 2 Multi-principal alloy coatings can be widely applied to the surfaces of marine engineering metal equipment, such as jacket legs in offshore platforms, propeller blades in ships, impellers and pump casings of seawater pumps, etc.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] This invention discloses a multi-principal alloy coating for mitigating marine biofouling. The powder used to prepare the coating is a pre-alloyed powder prepared by an inert gas atomization method. The chemical composition of the pre-alloyed powder, by weight percentage, is: Cr: 10%-30%, Ni: 8%-22%, Mo: 1%-10%, Cu: 5%-30%, Nb: 0.1%-0.7%, C: ≤0.3%, Si: ≤1.0%, Mn: ≤2.0%, P: ≤0.05%, S: ≤0.03%, with the balance being Fe.

[0008] Furthermore, the chemical composition of the pre-alloyed powder is as follows: Cr: 18%-25%, Ni: 10%-20%, Mo: 3%-8%, Cu: 10%-25%, Nb: 0.2%-0.5%, C: ≤0.3%, Si: ≤1.0%, Mn: ≤2.0%, P: ≤0.05%, S: ≤0.03%, with the balance being Fe.

[0009] Furthermore, in the chemical composition of the pre-alloyed powder, the weight ratio of Cu to Nb ranges from 10 to 290. Even further, the weight ratio of Cu to Nb ranges from 22 to 120.

[0010] Further, the pre-alloyed powder has a particle size distribution D50 value of 10.0 μm-75.0 μm. Even further, the pre-alloyed powder has a particle size distribution D50 value of 25.0 μm-53.0 μm.

[0011] The present invention discloses a method for preparing a multi-principal element alloy coating with the function of mitigating marine biofouling, comprising pretreatment of the substrate surface before spraying, including sandblasting the substrate surface. After pretreatment, the multi-principal element alloy coating is prepared by spraying the substrate surface using supersonic flame spraying technology.

[0012] Furthermore, the substrate surface is sandblasted using white corundum abrasive, with a compressed air pressure of 0.5MPa-0.6MPa and a blasting distance of 100mm-150mm. After sandblasting, the surface roughness of the substrate is Ra 3.0μm-3.5μm. The substrate surface is then cleaned with acetone.

[0013] Furthermore, a supersonic flame spraying device is used to spray the working layer. The process parameters are as follows: kerosene flow rate of 5.0 GPH-7.0 GPH, oxygen flow rate of 1600 SCFH-2200 SCFH, nitrogen flow rate of powder feeding gas of 20 SCFH-30 SCFH, powder feeding rate of 20 g / min-60 g / min, spraying distance of 300 mm-500 mm, number of coating layers of 15-25 layers, and coating thickness of 350 μm-500 μm. Furthermore, the supersonic flame spraying process parameters are as follows: kerosene flow rate of 6.0 GPH-6.8 GPH, oxygen flow rate of 1850 SCFH-2100 SCFH, nitrogen flow rate of powder feed gas of 22 SCFH-26 SCFH, powder feed rate of 30 g / min-50 g / min, spraying distance of 350 mm-400 mm, number of coating layers of 18-22, and coating thickness of 400 μm-450 μm.

[0014] In the multi-principal alloy coating system involved in this invention, Cu and Nb are crucial alloying elements, essential prerequisites for ensuring the coating's inhibitory effect against marine biofouling. Regarding Cu, this invention precisely designs its addition amount to exceed the solid solution limit of Cu in the multi-principal alloy. In this way, supersaturated Cu exists in the coating matrix as a precipitated phase. This special form creates conditions for the release of copper ions, thereby achieving the antifouling purpose. The addition of Nb is equally significant. Nb acts as a coating layer for copper-rich precipitates in the coating. Precise control of its addition amount effectively regulates the release rate of copper ions. A schematic diagram illustrating the role and effect of Cu and Nb in the multi-principal alloy coating is shown below. Figure 1 This initiative is significant, as it can substantially reduce the potential harm that antifouling coatings may cause to the marine environment. A deeper examination at the microscopic level reveals that the release of copper ions involves a dynamic conversion between monovalent and divalent copper ions. Simultaneously, the metabolic processes of microorganisms in the marine environment produce reactive oxygen species (ROS) with weak oxidizing properties, such as superoxide anion radicals (O2).- The copper ions react with hydrogen peroxide (H₂O₂). At this point, monovalent copper ions undergo the classic Fenton reaction with H₂O₂, generating highly oxidizing reactive oxygen species (ROS), such as hydroxyl radicals (•OH). These highly oxidizing ROS can effectively inhibit biofilm formation, thereby preventing biofouling. A significant feature of this invention is that the antifouling coating does not rely solely on the toxicity of copper ions to achieve its antifouling effect. Instead, it cleverly uses the addition of Nb to precisely control the conversion process of copper ions to different valence states. Specifically, the addition of Nb effectively slows down the conversion rate of monovalent copper ions to divalent copper ions. During the release of copper ions, more monovalent copper ions are retained to participate in the formation of highly oxidizing ROS. These highly oxidizing ROS can damage biological cells, thereby fundamentally inhibiting biofouling. This unique antifouling mechanism has a dual advantage. On the one hand, it effectively reduces the excessive release of copper ions, lowering the risk of damage to the marine ecological environment; on the other hand, it fully utilizes the catalytic effect of monovalent copper ions and achieves efficient control of microbial biofilms and biofouling through ROS-mediated pathways, providing a more environmentally friendly and efficient solution for pollution prevention in the field of marine engineering.

[0015] The beneficial effects of this invention are:

[0016] 1. This invention achieves control over the microstructure of the coating by using pre-alloyed powder for coating preparation, avoids the occurrence of galvanic corrosion between different mixed metals, and improves the corrosion resistance of the coating.

[0017] 2. This invention, by adding Cu and Nb elements, enables the coating to effectively mitigate the formation of marine biofouling. By controlling the transformation process of different valence states of copper ions, the catalytic process of ROS is accelerated, and the expression level of ROS is increased. This achieves the reduction of copper ion release rate while effectively inhibiting marine biofouling. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the role and effect of Cu and Nb in multi-principal element alloy coatings in this invention. Detailed Implementation

[0019] Based on the content of this invention, the technical solution of this invention is further illustrated through specific embodiments. The following embodiments are only for the purpose of helping to understand this invention and are not intended to limit the invention. The powder information used in the embodiments and comparative examples is shown in Table 1, and the supersonic flame spraying process parameters are shown in Table 2. In the implementation of this invention, 316L stainless steel for marine engineering is selected.

[0020] A method for preparing a multi-principal element alloy coating to mitigate marine biofouling is described below:

[0021] (1) Pretreatment of substrate material: The stainless steel surface was sandblasted. The sandblasting abrasive was white corundum sand. The sandblasting compressed air pressure was set to 0.55MPa and the sandblasting distance was set to 135mm. The surface roughness of the sample after sandblasting was Ra3.3μm. After sandblasting, the substrate surface was cleaned with acetone and dried for later use.

[0022] (2) Preparation of supersonic flame spray coating: First, pre-alloyed powder is prepared by inert gas atomization method. The powder information is shown in Table 1. Then, the pre-alloyed powder is put into the powder feeder. During spraying, the spray gun is kept perpendicular to the sample. The coating is prepared according to the spraying process parameters in Table 2.

[0023] Table 1. Basic information on the powders used for preparing multi-principal element alloy coatings in the examples and comparative examples:

[0024]

[0025] Table 2. Process parameter settings for the preparation of multi-principal element alloy coatings in the examples and comparative examples:

[0026]

[0027] 1. Antibacterial performance test:

[0028] According to the GB / T 2591-2003 standard "Test Methods and Antibacterial Effects of Antibacterial Plastics", the antibacterial properties of the multi-principal alloy coatings shown in Tables 1 and 2 were quantitatively tested. Two typical marine biofouling bacteria were selected for the test: Pseudomonas aeruginosa (…). Pseudomonas aeruginosa Gram-negative bacteria) and Bacillus viminalis ( Bacillus vietnamensis (Gram-positive bacteria), the coating was co-cultured with the bacteria for 6 hours, and the bacterial concentration for co-culture was set at (1~2)×10 8 CFU / mL. The results of the antibacterial performance test are shown in Table 3. Among them, the control material used for the antibacterial performance test was uncoated 316L stainless steel. The antibacterial rate was calculated by the formula: Antibacterial rate (%) = [(Number of viable bacteria on the surface of 316L stainless steel - Number of viable bacteria on the surface of multi-principal element alloy coating) / Number of viable bacteria on the surface of 316L stainless steel] × 100%.

[0029] 2. Biofouling inhibition performance test:

[0030] The antifouling performance of multi-principal element alloy coatings was evaluated using a dynamic antifouling performance evaluation system for simulated marine environments, developed in-house. The dynamic antifouling evaluation system rigorously controlled light intensity, light cycle, water temperature, water quality, and room temperature. By adjusting the parameters of the downlights, the system simulated the sunlight intensity in actual marine environments. The parameter settings are as follows:

[0031] 7:00-10:00, pure white, 20w; 10:00-13:00, pure white, 40w; 13:00-16:00, pure white, 50w; 16:00-19:00, pure white, 30w; 19:00-22:00, pure white, 10w; 22:00-7:00 off.

[0032] Regarding water temperature, based on the annual average water temperature in the South China Sea environment, the water temperature and room temperature were both set at 27℃. Water quality was controlled using a multi-stage filtration system. Substrate samples coated with a multi-principal alloy coating were embedded in molds containing epoxy resin, ensuring the coating surface was exposed. The exposed coating was then completely immersed in a dynamic antifouling evaluation system for 7 days. The coating was photographed using a fluorescence microscope to analyze the fouling adhesion on the coating surface after co-cultivation. ImageJ software was used to quantitatively analyze the degree of fouling coverage on the sample surface and calculate the biofouling coverage rate. The test results are shown in Table 3.

[0033] 3. Corrosion resistance test:

[0034] The coating was immersed in artificial seawater solution, and the potentiodynamic polarization curves of the coatings in the embodiments and comparative examples of the present invention were measured to obtain the corrosion current density of the coating. i corr The test results are shown in Table 3.

[0035] Table 3. Process parameter settings for the preparation of multi-principal element alloy coatings in the examples and comparative examples:

[0036]

[0037] As can be seen from the results in Table 3, the multi-principal element alloy coatings of Examples 1-8 of the present invention exhibit effective antibacterial properties. Furthermore, they effectively inhibit the adhesion of biofouling, ensuring that the coverage rate during the cultivation period does not exceed 5%. In addition, the corrosion resistance of the coating is an important indicator of its service life in engineering applications; the examples... i corr Value at 50 nA / cm 2 -300nA / cm 2 Within the specified range, it meets the requirements of this invention. Therefore, the appropriate setting of powder particle size distribution, powder composition, and supersonic flame spraying process parameters are key factors for this invention to obtain an effective multi-principal element alloy coating.

[0038] Supersonic flame spraying places strict requirements on the particle size distribution of the selected powder, as this can affect the corrosion resistance of the coating. A low D50 value indicates finer powder particles and a significantly increased specific surface area. During supersonic flame spraying, fine particles are prone to agglomeration. These agglomerated particles, during flight and deposition, create numerous voids and defects within the coating, making it difficult to form a dense structure. This loose structure provides channels for corrosive media to penetrate the coating and contact the substrate, leading to a decrease in corrosion resistance (Comparative Example 1) and a reduced service life. Conversely, a high D50 value, besides increasing the coating's porosity, also results in uneven composition and structure, with significant differences in particle size at different locations, leading to inconsistent coating performance and consequently reduced corrosion resistance (Comparative Example 2).

[0039] The amount of Cu added in multi-principal alloy coatings that mitigate marine biofouling has a significant impact on their antibacterial and antifouling effects. Too little Cu results in ineffective antibacterial and antifouling performance (Comparative Example 3). Too much Cu leads to an increase in the content of precipitated phases, which reduces the coating's corrosion resistance and thus affects its service life (Comparative Example 4).

[0040] The addition of nitrogen (Nb) effectively controls the release rate of copper ions, improving corrosion resistance and avoiding the environmental impact and service life effects of Cu release. It also effectively slows down the conversion rate of monovalent to divalent copper ions, retaining more monovalent copper ions to participate in the formation of highly oxidizing reactive oxygen species (ROS). Insufficient Nb content results in insignificant improvement in corrosion resistance; even with the addition of copper within the limits specified in this invention, the antibacterial and antifouling properties cannot be guaranteed to meet the effectiveness requirements of this invention (Comparative Example 5). Excessive Nb content significantly improves corrosion resistance but simultaneously inhibits copper ion release and valence conversion, thus reducing the antibacterial and antifouling properties of the coating (Comparative Example 6).

[0041] Furthermore, in the pre-alloyed powder, Nb acts as a core-shell structure for the copper-rich precipitate, restricting its release process. Therefore, the addition ratio of Cu and Nb needs to be limited. Even if the addition amounts of Cu and Nb are within the specified range, it cannot be guaranteed that the coating will exhibit excellent antibacterial and antifouling properties while also possessing good corrosion resistance. When the Cu / Nb ratio is too low, it indicates that the encapsulation of the copper-rich phase by Nb is increased, thus restricting the release process of copper ions, and the coating exhibits poor antibacterial and antifouling properties (Comparative Example 7). However, when the Cu / Nb ratio is too high, it indicates that the encapsulation of the copper-rich phase by Nb in the coating is weakened, the corrosion resistance of the coating decreases, and the lifespan of the coating is reduced (Comparative Example 8).

[0042] For the preparation of multi-principal element alloy coatings, the composition and particle size of the pre-alloyed powder are factors affecting the coating performance. On the other hand, the process parameters of supersonic flame spraying also affect the coating's antibacterial, antifouling, and corrosion resistance properties. When the kerosene flow rate is too low during supersonic flame spraying, the coating's microstructure becomes loose, reducing its corrosion resistance (Comparative Example 9). When the kerosene flow rate is too high during supersonic flame spraying, incomplete combustion can occur, leading to defects such as porosity and inclusions in the coating, reducing its density and corrosion resistance (Comparative Example 10).

[0043] In supersonic flame spraying, insufficient oxygen flow can lead to incomplete combustion of the pre-alloyed powder, resulting in decreased coating density, increased porosity, and reduced corrosion resistance (Comparative Example 11). Conversely, excessive oxygen flow can cause over-oxidation of the metal powder, leading to the consumption of Cu in the coating and thus reducing its antibacterial and antifouling properties (Comparative Example 12).

[0044] In supersonic flame spraying, nitrogen flow rate plays a crucial role. When the nitrogen flow rate is too low, the deposition rate of powder ejected from the spray gun reaching the substrate surface decreases significantly. This change directly leads to poor coating density, resulting in more pores and defects within the coating. This deterioration of the coating structure significantly reduces its corrosion resistance, thus severely impacting the coating's service life (Comparative Example 13). Conversely, if the nitrogen flow rate is too high, the high-speed nitrogen flow causes the sprayed particles to violently impact the substrate surface at high speeds. This high-speed impact generates significant residual stress within the coating. The presence of residual stress greatly reduces the coating's stability, making it more prone to cracking and deformation during actual use, and less able to effectively resist external corrosion (Comparative Example 14).

[0045] In supersonic flame spraying, an insufficient powder feed rate can lead to discontinuous coatings due to inadequate powder supply. This reduces the bonding strength between powder particles, resulting in gaps and affecting the coating's corrosion resistance (Comparative Example 15). Conversely, an excessively high powder feed rate prevents sufficient heating and acceleration of the powder, causing some powder to deposit onto the substrate before complete melting. This increases the coating's porosity and reduces its corrosion resistance (Comparative Example 16).

[0046] Furthermore, the distance between the spray gun and the substrate during the spraying process also affects the coating quality. If the spraying distance is too short, the particles will have excessive kinetic energy when they reach the substrate, which may cause impact damage. At the same time, the close distance between the spray gun and the substrate leads to concentrated heat on the substrate, making it prone to deformation. This increases the surface roughness of the coating, increases the internal stress of the coating, and causes defects such as cracks, thereby reducing the corrosion resistance of the coating (Comparative Example 17). If the spraying distance is too long, the powder particles will have a longer time to exchange heat with the surrounding gas during flight, resulting in a decrease in temperature and velocity. When they reach the substrate, their kinetic and thermal energy will be insufficient, leading to a decrease in the density of the coating and affecting its corrosion resistance (Comparative Example 18).

[0047] The final coating preparation also needs to consider the limitation of the number of coating layers. If the number of coating layers is too low, the coating will be thin and easily damaged under harsh working conditions. Moreover, a thin coating cannot effectively protect the substrate, resulting in reduced corrosion resistance (Comparative Example 19). If the number of coating layers is too high, the internal stress will cause problems such as cracking and peeling of the coating, which will reduce the corrosion resistance of the coating (Comparative Example 20).

[0048] The results of the above examples and comparative examples show that only when the amount of Cu and Nb added, the D50 size of the pre-alloyed powder, and the supersonic flame spraying process parameters are within a certain appropriate range, and they work together, can the multi-principal alloy coating have the effect of mitigating marine biofouling and have a good service life.

[0049] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A multi-principal element alloy coating for mitigating marine biofouling, characterized in that, The powder used to prepare the coating is a pre-alloyed powder prepared by inert gas atomization. The chemical composition of this pre-alloyed powder, by weight percentage, is: Cr: 18%-25%, Ni: 10%-20%, Mo: 3%-8%, Cu: 10%-25%, Nb: 0.2%-0.5%, C: ≤0.3%, Si: ≤1.0%, Mn: ≤2.0%, P: ≤0.05%, S: ≤0.03%, with the balance being Fe. The weight ratio of Cu to Nb is between 22 and 120. The particle size distribution (D50) of the pre-alloyed powder is 10.0 μm-75.0 μm. The preparation method of this multi-principal alloy coating for mitigating marine biofouling includes pretreatment of the substrate surface before spraying, including sandblasting the substrate surface. After pretreatment, a multi-principal element alloy coating was prepared by spraying the substrate surface using supersonic flame spraying technology. The supersonic flame spraying process parameters were as follows: kerosene flow rate of 5.0 GPH-7.0 GPH, oxygen flow rate of 1600 SCFH-2200 SCFH, nitrogen flow rate of powder feed gas of 20 SCFH-30 SCFH, powder feed rate of 20 g / min-60 g / min, spraying distance of 300 mm-500 mm, 15-25 coating layers, and a coating thickness of 350 μm-500 μm. This multi-principal alloy coating, designed to mitigate marine biofouling, achieved a 99.9% antibacterial rate against *Pseudomonas aeruginosa* and *Bacillus vivax* within 6 hours; and within 7 days, it inhibited the adhesion of marine algae, reducing the fouling coverage to less than 5%. The corrosion current density of this multi-principal alloy coating in the service environment was 50 nA / cm². 2 -300nA / cm 2 .

2. The multi-principal alloy coating for mitigating marine biofouling according to claim 1, characterized in that, The pre-alloyed powder has a particle size distribution D50 value of 25.0 μm-53.0 μm.

3. The multi-principal alloy coating for mitigating marine biofouling according to claim 1, characterized in that, The substrate surface is sandblasted with white corundum abrasive, the pressure of the compressed air is 0.5MPa-0.6MPa, the sandblasting distance is 100mm-150mm, and the surface roughness of the substrate after sandblasting is Ra 3.0μm-3.5μm. The substrate surface is then cleaned with acetone.

4. The multi-principal alloy coating for mitigating marine biofouling according to claim 1, characterized in that, The supersonic flame spraying process parameters are as follows: kerosene flow rate of 6.0 GPH-6.8 GPH, oxygen flow rate of 1850 SCFH-2100 SCFH, nitrogen flow rate of powder feed gas of 22 SCFH-26 SCFH, powder feed rate of 30 g / min-50 g / min, spraying distance of 350 mm-400 mm, number of coating layers of 18-22, and coating thickness of 400 μm-450 μm.

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