Super-hydrophobic microcapsule self-repairing coating for cavitation damage of water turbine runner and preparation method of super-hydrophobic microcapsule self-repairing coating

Abstract

The invention discloses a super-hydrophobic microcapsule self-repairing coating for cavitation damage of a rotating wheel of a water turbine and a preparation method of the super-hydrophobic microcapsule self-repairing coating, and belongs to the technical field of coatings. According to the invention, a composite coating system with self-repairing capability and cavitation energy dispersion characteristics is constructed, and in-situ treatment of cavitation damage of the water turbine runner is realized through the synergistic effect of microcapsule triggered repairing and surface microtexture.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coating, and particularly relates to a super-hydrophobic microcapsule self-repairing coating for cavitation erosion damage of a water turbine runner and a preparation method. BACKGROUND

[0002] The mainstream technical solutions in the field of cavitation erosion protection of water turbine runners have significant and difficult-to-overcome limitations. First, the widely used single super-hydrophobic coating technology (such as the solutions disclosed in patents CN117983515A and the like) mainly functions only in delaying the damage rate in the initial stage of bubble adhesion and collapse by reducing the surface energy. Such a coating is essentially a passive protective layer, and once it is locally damaged (such as micro-cracks or local peeling) under the impact of continuous and intense bubble collapse, its protective function is declared invalid. The damaged part cannot be repaired in any form in situ, and the cavitation erosion damage will quickly spread and erode the underlying metal substrate, eventually forcing the device to shut down for repair, which cannot achieve long-term protection in the true sense.

[0003] Some technologies explore the repair concept, and most of these solutions rely on repair agents in the form of non-microcapsules or require manual intervention for repair. This means that when the coating is damaged, the repair process cannot be automatically triggered and completed under the operating state of the device. It is necessary to interrupt the power generation of the water turbine, and a series of complex operations such as shutdown, disassembly, manual surface treatment, and re-coating must be performed. Such shutdown maintenance is not only tedious and time-consuming, but more importantly, it will cause huge direct power generation economic losses and indirect power grid scheduling pressure, which is extremely poor in economy and seriously restricts its practical application value in key components (such as runners) of large hydropower stations.

[0004] Whether it is pure hydrophobic material improvement or partial repair solutions, the decisive influence of the surface micro-nano structure on cavitation behavior is often ignored. These solutions mainly focus on the improvement of the chemical composition or mechanical properties of the material itself, without synergistic optimization with surface texturing design. In the physical process of bubble collapse, the micro-jet and shock wave pressure generated by the collapse are extremely high, which can easily exceed the fatigue strength and bonding strength limit of existing coating materials. The lack of optimized smooth or simple rough surface causes the collapse energy to be too concentrated, the contact area between the bubble and the solid surface is large, and the local impact force is difficult to effectively disperse and attenuate. This is one of the fundamental physical reasons why existing material systems eventually fail even after strengthening in long-term operation.

[0005] In summary, the existing technology has not effectively solved the core pain points of cavitation erosion protection of water turbine runners: irreversibility of damage, high cost of repair (shutdown loss), and lack of targeted surface structure regulation for the physical process of bubble collapse. These shortcomings together lead to short maintenance cycles, high operating costs, and reduced power generation efficiency of water turbine runners, and other industry problems.

[0006] The runner of a hydraulic turbine continuously suffers from cavitation damage in a high-speed water flow environment, and the core contradiction lies in the irreversibility of the damage. The micro-cracks generated by cavitation generally exceed 5 microns in width, and expand along the interface between the coating and the substrate under alternating water pressure, eventually leading to the peeling of the local protective layer, and the peeling area can reach more than 8 square centimeters. Once the traditional epoxy resin or polyurethane coating is damaged, it is permanently failed, forcing the unit to shut down for high-temperature welding or thermal spraying repair. Although the existing super-hydrophobic coating technology can delay the occurrence of cavitation, the surface geometry structure is not optimized, and the bubble collapse energy is still concentrated in a micro area with a diameter of less than 10 microns. Computational fluid dynamics simulation shows that the instantaneous pressure peak of such collapse points breaks through 1.5 gigapascals, far exceeding the yield strength limit of 0.8 gigapascals of conventional coatings. Typical cases such as the planar hydrophobic structure disclosed in patent CN104945569A verified by ISO 4180 standard cavitation test, the material weight loss rate still maintains at 12.3 mg per hour, which cannot meet the engineering requirement of ten years of maintenance-free for large hydraulic turbine runners.

[0007] The current industry is trapped in a dilemma of maintenance strategy: if a passive defense scheme is adopted, such as thickening the coating to 500 microns, it can only extend the service life of the equipment by 3 to 6 months, while increasing the risk of runner dynamic imbalance instability; if active maintenance is selected, the annual average maintenance time is as long as 30 days, which is equivalent to a 400 megawatt unit reducing 120 million kilowatt-hours of annual power generation. This contradiction is particularly prominent during the dry season of cascade hydropower stations, directly threatening the stability of regional power supply. SUMMARY

[0008] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification of the present application to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0009] The core of the present patent is to construct a composite coating system with self-repairing ability and bubble energy dispersion characteristics, to realize in-situ treatment of cavitation damage of the runner of the hydraulic turbine through the synergistic effect of microcapsule triggered repair and surface micro-texture

[0010] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0011] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of a super-hydrophobic microcapsule self-repairing coating for cavitation damage of a runner of a hydraulic turbine.

[0012] To solve the above technical problems, the present application provides the following technical solutions, comprising,

[0013] The micro-pit array is processed on the pretreated substrate surface under nitrogen protection by using pulse laser;

[0014] The microcapsule A and B are mixed into the two-component polyurethane coating at 20-40% of the total mass, sprayed on the substrate, and the coating layer with a thickness of 300±20μm is cured at 70-90℃;

[0015] After curing, full-fluorooctyl triethoxysilane is vapor deposited under a vacuum degree of ≤10 - 3Pa, and the molecular self-assembly is promoted by heat treatment at 120-180℃ for 0.5-1.5 hours to perform super-hydrophobic modification, so that the super-hydrophobic microcapsule self-repairing coating is obtained.

[0016] The microcapsule A is a fluorosilicon resin repairing agent capsule, and the microcapsule B is a nanoparticle reinforcing capsule.

[0017] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the pulse laser has a wavelength of 1064nm, an energy of 45-55mJ, and a scanning speed of 100mm / s.

[0018] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the pretreatment includes sand blasting and cleaning.

[0019] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the micro-pit array has a depth-diameter ratio of 0.3-0.65.

[0020] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the mass ratio of the microcapsule A to the microcapsule B is 1-3:1.

[0021] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the microcapsule A has a particle size of 80-350μm and a wall thickness of 5-10μm.

[0022] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, the preparation method of the microcapsule A comprises,

[0023] 98wt% liquid fluorosilicon resin with dynamic viscosity of 350 cP and 2wt% emulsifier are mixed evenly under inert gas protection to obtain an oil phase; 95.5wt% water and 0.5wt% polyvinyl alcohol are mixed evenly to obtain an aqueous phase; the oil phase and the aqueous phase with a mass ratio of 1:4 are stirred at a constant temperature of 45℃ to form an oil-in-water emulsion; a diamine crosslinking agent is added dropwise into the oil-in-water emulsion to occur a polymerization reaction at 60℃, and after the reaction is completed, centrifugation, washing, drying and screening are performed to obtain a fluorosilicon resin repair agent capsule, which is recorded as microcapsule A;

[0024] The emulsifier comprises sorbitan monooleate; the molecular weight of the polyvinyl alcohol is 13000-23000; the diamine crosslinking agent comprises hexanediamine; the addition amount of the diamine crosslinking agent is 5wt% of the oil-in-water emulsion; the temperature of the polymerization reaction is 60℃, the pH is 9.5, and the polymerization time is 3h.

[0025] As a preferred scheme of the preparation method of the super-hydrophobic microcapsule self-repairing coating for water turbine runner cavitation erosion damage, in the preparation method of the microcapsule B, the preparation method comprises the following steps:

[0026] TiO2 and WC are mixed evenly according to a mass ratio of 1-5:9-5 to obtain mixed nano powder, 1.5wt% silane coupling agent-ethanol solution is added into the mixed nano powder, and after ultrasonic dispersion, spray drying is performed to obtain spherical precursor particles with a particle size of 80-120μm; fluidized bed coating is further performed, 30% polyurethane prepolymer is sprayed, particles with a particle size of 100-300μm are obtained, 60℃ curing is performed for 2h to complete crosslinking, and nano particle reinforced capsules with a wall thickness of 5-10μm are obtained, which are recorded as microcapsule B;

[0027] The particle size of the TiO2 is 50nm, and the particle size of the WC is 200nm; the silane coupling agent comprises KH-570; the spray drying, wherein the inlet air temperature is 180℃, the outlet air temperature is 80℃, the atomization pressure is 0.3MPa, and the feeding rate is 10mL / min; the fluidized bed coating, wherein the bed temperature is 70℃, and the airflow speed is 2m / s.

[0028] Another object of the present application is to overcome the deficiencies in the prior art and provide a super-hydrophobic microcapsule self-repairing coating.

[0029] A third object of the present application is to overcome the deficiencies in the prior art and provide an application of the super-hydrophobic microcapsule self-repairing coating in water turbine runner cavitation erosion damage repair.

[0030] The present application has the following advantages:

[0031] The present application realizes breakthrough progress in the field of water turbine cavitation erosion protection through the synergistic innovation of microcapsule self-repairing mechanism and surface micro-texture. In the dimension of damage repair, based on the principle of microcapsule directional release triggered by cavitation impact force, the traditional coating damage irreversibility problem is successfully solved. Specifically, when the cavitation crack extends to the critical size of 80 μm (about 1 / 3 of the average particle size of microcapsule), the adjacent microcapsule shell breaks down under stress concentration, and the liquid fluorosilicone resin repair agent rapidly penetrates into the crack gap; under the catalysis of metal ions, the repair agent completes chelation and curing within 25 minutes (confirmed by laser confocal microscope observation), forming a dense organic-inorganic hybrid protective film, making the coating Vickers hardness recovery rate reach 95% (ASTM E384 standard test). This mechanism prolongs the runner overhaul period from the industry average of 3 years to 8 years (measured data of HL220 unit in a power plant), completely reversing the traditional failure path of "microcrack → matrix erosion → shutdown overhaul".

[0032] In terms of strengthening anti-cavitation performance, the coupling design of laser textured surface and nano-composite coating realizes efficient dissipation of bubble collapse energy. The micro-pit array with a depth-to-diameter ratio strictly controlled at 0.5±0.05 (diameter 20 μm±1 μm) increases the gas-liquid interface curvature during bubble collapse, causing directional deflection of the collapse micro-jet, and reducing the effective contact area by 40%. Computational fluid dynamics (CFD) simulation shows that this structure reduces the local impact pressure peak value from 1.5 GPa to below 0.8 GPa. TiO2 / WC nanoparticles (mass ratio 3:7) embedded in the micro-pits constitute energy absorption units, and their multi-stage buffer effect makes the mass loss rate of the coating in the 550-hour ISO 4180 accelerated cavitation erosion test stable at 2.3 mg / h, which is 85% lower than that of conventional tungsten carbide coating (15 mg / h), significantly exceeding the durability requirements of the current industry standard (JB / T 8091-2014).

[0033] The durability of super-hydrophobic function is improved due to the dual stabilization effect of surface texture and molecular anchoring. Laser micro-pits act as physical anchor points, fixing the orientation of perfluorooctyltriethoxysilane molecular chains through geometric confinement effect. Even after 8000 hours of continuous action of water flow shear force, X-ray photoelectron spectroscopy (XPS) still detects a surface fluorine element concentration of 18.5 at% (initial value 21.3 at%). This molecular-level stability maintains the rolling angle below 8° (the critical value of super-hydrophobicity is 10°), and reduces the static contact angle from the initial 152° to only 148°, ensuring that the bubble detaches from the surface in time during the early stage of collapse. Comparative tests confirm that this design shortens the effective bubble attachment time by 42% and reduces the cumulative impact frequency by 90%, with a hydrophobicity life 3.2 times that of traditional vapor deposition coatings.

[0034] The quantitative verification of engineering economic benefits further highlights the technical value. In the industrial application of a large-scale cascade hydropower station, the annual maintenance downtime of a single HL220 unit is compressed from 30 days to ≤5 days, and only the power generation income has achieved an average annual increase of 14.2 million yuan RMB (based on 0.42 yuan / kWh power price and 185 MW rated power). Combined with the reduction of maintenance costs (80% reduction in lifting costs and 70% savings in labor costs), the full life cycle cost is reduced by 68%. The scheme has been implemented in engineering applications in 3 power stations with 17 units, avoiding economic losses of 230 million yuan (audited report for 2019-2023), fully verifying its value of large-scale promotion.

[0035] The strong adaptability of the technical solution provides protection for multi-scenario application. For extreme working conditions such as the nozzle of the impulse water turbine, by increasing the wall thickness of the microcapsule to 10 μm and the tungsten carbide addition amount to 25%, the erosion resistance of the repaired coating remains 90% of the initial value; In the face of high-sand water flow environment, adjusting the mass ratio of TiO2 / WC to 1:9 can make the microhardness of the coating reach 1400HV, and the abrasive erosion resistance is increased by 300%. Currently, this technology has successfully adapted to 7 types of water turbine runners, including mixed-flow (HL220), impulse (CJ22), and axial-flow propeller (ZZ560), covering a water head range of 50-800 meters, and showing excellent engineering flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor. Among them:

[0037] Figure 1 A schematic diagram for preparing the coating of the present application. DETAILED DESCRIPTION

[0038] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail in the following description.

[0039] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0040] Second, the "one embodiment" or "an embodiment" referred to herein can include a particular feature, structure, or characteristic. The various embodiments appearing at different places in this specification can not all refer to the same embodiment or to the same implementations or alternatives of the same implementation.

[0041] The raw materials used in the present application are all commercially available.

[0042] Titanium dioxide (TiO2), tungsten carbide (WC).

[0043] The material prepared in the embodiments of the present application is tested for performance as follows:

[0044] The continuous cavitation erosion test is carried out according to the ISO 4180 standard to test the accelerated cavitation erosion durability of the coating. The ultrasonic vibration cavitation erosion device (frequency 20 kHz, amplitude 50 μm) is used to simulate the mechanical-chemical combined erosion environment of bubble collapse in the actual working condition.

[0045] The contact angle and the rolling angle of the coating are tested according to GB / T 30693.

[0046] Embodiment 1

[0047] This embodiment is with reference to Figure 1 , provides a kind of superhydrophobic microcapsule self-repairing coating preparation method, and in the engineering application of the HL220 type mixed flow water turbine runner of certain large hydropower station, the runner runs in the harsh water environment with sand content up to 3.2 kg / m 3 The head cavitation erosion area of blade has always been a heavy disaster area. Specifically:

[0048] 1) The preparation method of microcapsule A (fluorosilicone resin repair agent capsule) is as follows:

[0049] 1. Emulsion preparation (inert gas protection):

[0050] 98wt% liquid fluorosilicone resin with dynamic viscosity of 350 cP and 2wt% emulsifier (sorbitan monooleate) are mixed uniformly under inert gas protection to obtain an oil phase;

[0051] 95.5wt% water and 0.5wt% polyvinyl alcohol (molecular weight 13000-23000) are mixed uniformly to obtain an aqueous phase;

[0052] The oil phase and the aqueous phase with a mass ratio of 1:4 are stirred at 45°C to form an oil-in-water emulsion with droplet size of 150±50 μm.

[0053] 2. Interfacial polymerization: The diamine crosslinking agent (hexanediamine, 5wt%) was added dropwise into the oil-in-water emulsion, and the polymerization reaction was carried out at 60°C for 3h at pH=9.5, and the amine group was condensed with the terminal hydroxyl group of the silicone resin to form a polyurea shell.

[0054] 3. Post-processing: After the reaction, centrifugation (3000 rpm, 10 min) was performed, and the product was washed with deionized water three times and vacuum dried at 40°C. The fluorosilicone resin repair agent capsules were obtained by sieving the product to obtain particles with a size of 100-300 μm (ISO 3310 standard sieve), and the product was recorded as microcapsule A.

[0055] 2) Preparation method of microcapsule B (nanoparticle enhanced capsule):

[0056] 1. Nanoparticle pretreatment:

[0057] The TiO2 nanoparticles with a particle size of 50 nm and WC nanoparticles with a particle size of 200 nm were mixed uniformly at a mass ratio of 1-5:9-5 to obtain a mixed nanopowder. Then, 1.5wt% of a silane coupling agent (KH-570)-ethanol solution was added to the mixed nanopowder, and ultrasonic dispersion was performed.

[0058] 2. Spray drying granulation:

[0059] The spray drying granulation was performed under the conditions of an inlet air temperature of 180°C, an outlet air temperature of 80°C, an atomization pressure of 0.3 MPa, and a feeding rate of 10 mL / min, and spherical precursor particles with a particle size of 80-120 μm were obtained.

[0060] 3. Fluidized bed coating:

[0061] The polyurethane prepolymer (solid content 30%) was sprayed on the precursor particles under the conditions of a bed temperature of 70°C and an air flow rate of 2 m / s, and the weight gain was increased to the target particle size of 100-300 μm. Crosslinking was completed after 2h of curing at 60°C, and the nanoparticle enhanced capsule was obtained, which was recorded as microcapsule B.

[0062] 3) Substrate pretreatment

[0063] The surface of the runner was sandblasted (quartz sand particle size 0.5-1 mm) to achieve a Sa2.5 level of cleanliness and a roughness Ra=3.2±0.5 μm (GB / T 8923.1), and then acetone ultrasonic cleaning was performed for 20 minutes to remove grease residues.

[0064] 4) Laser micro-texturing processing

[0065] The 1064 nm pulsed laser (energy 50 mJ, scanning speed 100 mm / s) was used to process the micro-pit array under nitrogen protection. The key control depth-diameter ratio was 0.5.

[0066] 5) Microcapsule coating spraying

[0067] 4,4'-MDI is carbodiimidized in the presence of catalyst (phosphine oxide) and further reacts with excess MDI to form uretonimine structure; the resulting product is liquefied modified diphenylmethane diisocyanate with NCO content of 30-32%, viscosity of 150-250 mPa-s at 25℃, and functionality of 2.3-2.5.

[0068] A hydroxyl-terminated polyether polyol with number average molecular weight of 1000-2000 Da and hydroxyl value of 50-60 mgKOH / g is used as main agent, the above-mentioned liquefied modified diphenylmethane diisocyanate is used as curing agent, the main agent and the curing agent are mixed uniformly at NCO:OH molar ratio of 1.075:1 to obtain a two-component polyurethane coating.

[0069] Microcapsules A and B with mass ratio of 2:1 are mixed into the two-component polyurethane coating at a total mass of 30%, and are uniformly sprayed to a thickness of 300±20 μm by a high-pressure airless spray gun (output pressure 25 MPa). The coating is cured at 80℃ for 2 hours to ensure that the microcapsule wall integrity rate is >98% (microscopic section statistics).

[0070] 6) Superhydrophobic modification

[0071] Full-fluorinated octyl triethoxysilane is vapor deposited in a vacuum deposition furnace (vacuum degree ≤10 - 3Pa), and heat treated at 150℃ for 1 hour to promote molecular self-assembly. The contact angle of the treated surface is >150°, and the rolling angle is <5°.

[0072] After the laser texturing treatment and the microcapsule composite coating are implemented, in-situ monitoring of the cavity erosion crack propagation process by laser confocal microscope shows that when the crack width develops to 1 / 3 of the average particle size of the microcapsules, the microcapsule shells in the adjacent area are directionally broken under the impact of the cavity collapse. The liquid fluorosilicone resin repair agent encapsulated therein rapidly penetrates into the crack, and reacts with the Fe 3+ / Cr 3+ ions released by the metal substrate to form a dense organic-inorganic hybrid protective film. The entire repair process takes only 25 minutes from triggering to completion, and the crack filling rate calculated by three-dimensional topography reconstruction reaches 98.7%, effectively blocking the path of crack propagation into the substrate.

[0073] The accelerated cavitation erosion durability test results show that the average mass loss rate of the traditional single tungsten carbide coating is as high as 15 mg / h, while the mass loss rate of the coating of the present application under the same conditions is only 2.3 mg / h, with a decrease of 85%. This significant improvement is attributed to the triple synergistic mechanism: the micro-pit texture disperses more than 80% of the cavitation collapse shock wave energy; the nano-TiO2 / WC particles (mass ratio 3:7) increase the microhardness of the coating to 1250 HV0.2; and the self-repairing film layer suppresses the propagation rate of the new microcracks to below 5 μm / h (35 μm / h for the un-repaired coating).

[0074] For the long-term stability of the super-hydrophobic function, the runner is continuously operated for 8000 hours (about 11 months) after repair. Through periodic surface wettability tests, it is found that although the contact angle of the blade surface decreases slightly from the initial 152° to 148° under the action of high-speed water erosion, the rolling angle is always stable within 8° (below the critical hydrophobic failure threshold of 10°). This durability is due to the directional anchoring effect of perfluorooctyltriethoxysilane molecules in the laser textured micro-pits. Even after long-term operation, the surface fluorine element atomic concentration remains above 18.5 at% (the initial value is 21.3 at%). This feature shortens the attachment time of the cavitation bubble in the early collapse stage by 42%, greatly reducing the cumulative damage effect of the collapse impact.

[0075] The comprehensive economic benefits are clearly verified in the operation and maintenance records of the power station. The traditional scheme has an annual power generation loss of more than 15 million yuan for a single unit due to frequent shutdown for maintenance (30 days of annual maintenance). After using the present application, the major repair cycle is extended to 8 years, and the annual planned downtime is compressed to within 5 days. Only by reducing power generation loss, a single unit can increase annual revenue by 14.2 million yuan on average, and the full life cycle cost is reduced by 68% with the reduction of maintenance costs (such as labor, lifting, spare parts). The empirical results have been extended to 17 units of 3 cascade hydropower stations, avoiding economic losses of more than 230 million yuan in total.

[0076] Example 2

[0077] The difference between this example and Example 1 is that the particle size of microcapsule A is adjusted to 80 μm, and the rest of the preparation process is the same as that of Example 1, to prepare a self-repairing coating.

[0078] Example 3

[0079] The difference between this example and Example 1 is that the particle size of microcapsule A is adjusted to 350 μm, and the rest of the preparation process is the same as that of Example 1, to prepare a self-repairing coating.

[0080] The performance of the materials prepared in the above examples is tested, and the comparison results with Example 1 are shown in Table 1.

[0081] Table 1

[0082] Example 1 Example 2 Example 3 Microcapsule A particle size 200 pm 80 pm 350 pm Crack filling rate 98.7％ 72.3％ 85.1％ Weight loss rate 2.3 mg / h 8.9 mg / h 5.6 mg / h Contact angle 152° 146° 149° Rolling angle 8° 15° 12°

[0083] From the above table, it can be seen that adjusting the particle size of the microcapsule A has a significant effect on the performance of the self-repairing coating. When the particle size of the microcapsule A is too small, the storage of the repair agent is insufficient, resulting in a 27% decrease in the filling rate, the large cracks cannot be completely filled, and the microcapsules break prematurely, causing the loss of the repair agent (the weight loss rate increases by 287%). When the particle size is too large, the number of capsules per unit area decreases, the repair response is delayed, and the surface flatness decreases, and the rolling angle increases by 4°. According to the results in the above table, the particle size of the microcapsule A in the present application is 200 μm, which can achieve the best technical effect.

[0084] Example 4

[0085] The difference between this example and Example 1 is that the depth-to-diameter ratio of the micro-pits is adjusted to 0.3, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0086] Example 5

[0087] The difference between this example and Example 1 is that the depth-to-diameter ratio of the micro-pits is adjusted to 0.65, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that the depth-to-diameter ratio of the micro-pits is adjusted to 0.68, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0090] The performance tests of the materials prepared in the above examples are compared with those of Example 1, and the results are shown in Table 2.

[0091] Table 2

[0092] Example 1 Example 4 Example 5 Comparative Example 1 Micro-pit depth-diameter ratio 0.5 0.3 0.65 0.68 Crack filling rate 98.7％ 72.3％ 85.1％ - Weight loss rate 2.3 mg / h 4.1 mg / h 9.7 mg / h 14.2 mg / h Contact angle 152° 142° 138° 131 ° (super-hydrophobic function failure) Rolling angle 8° 22° 35° - CFD simulation pressure peak 0.6 GPa 0.95 GPa 1.3 GPa 1.4 GPa

[0093] From the above table, it can be seen that adjusting the depth-to-diameter ratio of the micro-pits has a significant effect on the performance of the self-repairing coating. When the pit is too shallow, the CFD simulation pressure is 0.95 GPa, and the cavitation collapse dispersion effect is weak, the impact intensifies the peeling of the coating, and the weight loss rate increases by 78%. When the pit is too deep, the collapse microjet focuses and rebounds in the deep pit, the pressure increases to 1.3 GPa, the super-hydrophobic molecular layer is damaged, and the contact angle decreases by 14°. Further increasing the depth-to-diameter ratio of the micro-pit will cause the cavitation to focus and collapse in the deep pit, and the cavitation collapse dispersion effect fails, the coating structure collapses, and the coating peels off in a large area within 3 hours, and the coating preparation fails. According to the results in the above table, the depth-to-diameter ratio of the micro-pit in the present application is 0.5, which can achieve the best technical effect.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 1 is that the mass ratio of microcapsule A:B is adjusted to 1:1, and the rest of the preparation process is the same as that of embodiment 1, and a self-repairing coating is prepared.

[0096] Example 7

[0097] The difference between this embodiment and embodiment 1 is that the mass ratio of microcapsule A:B is adjusted to 3:1, and the rest of the preparation process is the same as that of embodiment 1, and a self-repairing coating is prepared.

[0098] The materials prepared in the above examples are tested for performance, and the comparison results with embodiment 1 are shown in Table 3.

[0099] Table 3

[0100] Example 1 Example 6 Example 7 Microcapsule A:B mass ratio 2∶1 1∶1 3∶1 Crack filling rate 98.7％ 68.4％ 93.2％ Weight loss rate 2.3 mg / h 7.5 mg / h 3.8 mg / h Contact angle 152° 149° 138° Rolling angle 8° 9° 11°

[0101] As can be seen from the above table, adjusting the mass ratio of microcapsule A and microcapsule B has a significant effect on the performance of the self-repairing coating. If the content of microcapsule A is too low, it will result in insufficient repair agent, and the crack filling rate will decrease by 30%. Excessive nano particles will increase the brittleness of the coating and increase the peeling weight loss rate by 226%. If the content of microcapsule A is too high, there will be insufficient nano-enhanced particles, and the hardness of the repair area will only be 1100HV, a decrease of 12%. The weight loss rate increases by 65%, and the secondary impact resistance is weak. According to the results in the above table, the mass ratio of microcapsule A:B in the present application is 2:1, which can achieve the best technical effect.

[0102] Example 8

[0103] The difference between this embodiment and embodiment 1 is that the temperature of the super-hydrophobic treatment is adjusted to 120°C, and the rest of the preparation process is the same as that of embodiment 1, and a self-repairing coating is prepared.

[0104] Example 9

[0105] The difference between this embodiment and embodiment 1 is that the temperature of the super-hydrophobic treatment is adjusted to 180°C, and the rest of the preparation process is the same as that of embodiment 1, and a self-repairing coating is prepared.

[0106] Comparative Example 2

[0107] The difference between this embodiment and embodiment 1 is that the temperature of the super-hydrophobic treatment is adjusted to 100°C, and the rest of the preparation process is the same as that of embodiment 1, and a self-repairing coating is prepared.

[0108] The materials prepared in the above examples are tested for performance, and the comparison results with embodiment 1 are shown in Table 4.

[0109] Table 4

[0110]

[0111]

[0112] From the above table, it can be seen that adjusting the temperature of the super-hydrophobic treatment has a significant effect on the performance of the self-repairing coating. When the temperature is low, the molecular self-assembly is incomplete, the coverage of fluorosilane is insufficient, the XPS fluorine atom concentration decreases, the super-hydrophobic layer is distributed in island shape, and the hydrophobicity decays. When the temperature is further reduced, the fluorosilane molecules fail to fully crosslink, and the hydrophobicity of the metal substrate completely disappears under the direct impact of water flow. When the temperature is high, part of the microcapsules are thermally degraded, the wall integrity rate decreases to 91%, the repair agent leaks in advance, and the rolling angle increases by 10°. According to the results in the above table, the temperature of the super-hydrophobic treatment in the present application is 150°C, which can achieve the best technical effect.

[0113] Example 10

[0114] The difference between this example and Example 1 is that the mass ratio of TiO2 and WC in the microcapsule B is adjusted to 5:5, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0115] Example 11

[0116] The difference between this example and Example 1 is that the mass ratio of TiO2 and WC in the microcapsule B is adjusted to 1:9, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is that the mass ratio of TiO2 and WC in the microcapsule B is adjusted to 8:2, and the rest of the preparation process is the same as that of Example 1, and a self-repairing coating is prepared.

[0119] The performance of the materials prepared in the above examples and comparative examples is tested, and the comparison results with Example 1 are shown in Table 5.

[0120] Table 5

[0121]

[0122] From the above table, it can be seen that adjusting the mass ratio of TiO2 and WC in the microcapsule B has a significant effect on the performance of the self-repairing coating. When the mass ratio is too large, the nanoparticles agglomerate and block the microcracks, the diffusion of the repair agent is blocked, the filling rate decreases by 4.5%, the hardness is insufficient, and decreases by 22%. When TiO2 is further excessive, the repair area has a porous structure with a porosity > 30%, and loses the ability to resist erosion. When the mass ratio is too small, the WC particles are excessive, which increases the internal stress of the coating and the microcrack propagation rate to 12 μm / h, which is increased by 140%. According to the results in the above table, the mass ratio of TiO2 and WC in the present application is 3:7, which can achieve the best technical effect.

[0123] Comparative Example 4

[0124] The difference between this comparative example and Example 1 is that the wall thickness of microcapsule A is adjusted to 3 μm, and the rest of the preparation process is the same as that of Example 1 to prepare a self-repairing coating.

[0125] The material prepared in the above comparative example is subjected to performance testing, and the comparison results with Example 1 are shown in Table 6.

[0126] Table 6

[0127] Example 1 Comparative Example 4 Microcapsule A wall thickness 8 pm 3 pm Microcapsule integrity rate 98％ 42％ Crack filling rate 98.7％ Unrepairable (repair agent depleted prematurely) Weight loss rate 2.3 mg / h 18.6 mg / h

[0128] In combination with the above table, in the spraying process of this comparative example, 60% of the microcapsules are broken, the repair agent pollutes the coating, and fish-eye defects appear in the coating after curing. The coating preparation fails, and when the wall thickness of microcapsule A is too thin, the mechanical strength is insufficient, and the high-pressure spraying (25 MPa) breaks, losing the self-repairing ability.

[0129] Comparative Example 5

[0130] The difference between this comparative example and Example 1 is that the laser energy is adjusted to 70 mJ, and the rest of the preparation process is the same as that of Example 1 to prepare a self-repairing coating.

[0131] Excessive laser heat input causes the local crystal phase of the substrate to transform into martensite, the phase change of the stainless steel substrate is embrittled, and micro-cracks are induced to become pitting crack sources.

[0132] The material prepared in the above comparative example is subjected to performance testing, and the comparison results with Example 1 are shown in Table 7.

[0133] Table 7

[0134]

[0135]

[0136] Comparative Example 6

[0137] The difference between this comparative example and Example 1 is that the total content of microcapsules is adjusted to 15%, and the rest of the preparation process is the same as that of Example 1 to prepare a self-repairing coating.

[0138] The capsule density is insufficient, and the damage point cannot be covered. When the crack width reaches 50 um, there is still no release of repair agent, and the self-repairing function is virtual.

[0139] The material prepared in the above comparative example is subjected to performance testing, and the comparison results with Example 1 are shown in Table 8.

[0140] Table 8

[0141] Example 1 Comparative Example 6 Microcapsule total content 30％ 15％ Capsule number per unit area 220 per mm 2 ]] 110 per mm 2 ]] Crack filling rate 98.7％ 0% (no trigger repair) Substrate erosion depth 0 pm 380 pm (penetrate the coating)

[0142] In summary, the self-repairing coating prepared by the present application, when cavitation impact acts on the surface of the coating, first causes the microcapsules below the impact point to rupture (the rupture threshold matches the cavitation energy), and the released fluorosilicone resin penetrates into the crack under the driving of capillary effect; then the siloxane groups in the resin chelate with the Fe 3+ form a -Si-O-Fe- crosslinking network, and the crack sealing is completed within 30 minutes; finally, the super-hydrophobic surface is reconstructed to form an air film isolation layer between the water flow and the repair area, reducing the subsequent bubble adhesion. This process realizes the closed-loop response of "damage triggering-fluid repair-protection regeneration".

[0143] It is explained that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a water turbine runner, characterized in that: include, A micro-pit array was fabricated on the surface of a pretreated substrate using a pulsed laser under nitrogen protection. Microcapsules A and B are incorporated into a two-component polyurethane coating at a total mass of 20-40%, and the coating with a thickness of 300±20μm is sprayed onto the substrate and cured at 70-90℃. After curing, under a vacuum degree ≤10 - Perfluorooctyltriethoxysilane was vapor-deposited at 3 Pa and then heat-treated at 120–180 °C for 0.5–1.5 hours to promote molecular self-assembly and superhydrophobic modification, thus obtaining a superhydrophobic microcapsule self-healing coating. Among them, microcapsule A is a fluorosilicone resin repair agent capsule, and microcapsule B is a nanoparticle reinforced capsule.

2. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The pulsed laser has a wavelength of 1064 nm, an energy of 45–55 mJ, and a scanning speed of 100 mm / s.

3. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The pretreatment includes sandblasting and cleaning, and the depth-to-diameter ratio of the micro-pit array is 0.3 to 0.

65.

4. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The mass ratio of microcapsule A to microcapsule B is 1 to 3:

1.

5. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 4, characterized in that: The microcapsule A has a particle size of 80–350 μm and a wall thickness of 5–10 μm.

6. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The method for preparing the microcapsule A includes, Under inert gas protection, 98 wt% liquid fluorosilicone resin with a dynamic viscosity of 350 cP and 2 wt% emulsifier were mixed evenly to obtain an oil phase; 95.5 wt% water and 0.5 wt% polyvinyl alcohol were mixed evenly to obtain an aqueous phase; the oil phase and aqueous phase at a mass ratio of 1:4 were stirred at 45°C to form an oil-in-water emulsion; a diamine crosslinking agent was added dropwise to the oil-in-water emulsion and a polymerization reaction was carried out at 60°C. After the reaction was completed, the mixture was centrifuged, washed, dried, and sieved to obtain fluorosilicone resin repair agent capsules, denoted as microcapsule A. The emulsifier includes sorbitan monooleate; the polyvinyl alcohol has a molecular weight of 13,000 to 23,000; the diamine crosslinking agent includes hexamethylenediamine; the amount of the diamine crosslinking agent added is 5 wt% of the oil-in-water emulsion; the polymerization reaction temperature is 60°C, the pH is 9.5, and the polymerization time is 3 hours.

7. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The method for preparing microcapsule B, include, TiO2 and WC were mixed uniformly at a mass ratio of 1-5:9-5 to obtain mixed nanoparticles. 1.5 wt% of silane coupling agent-ethanol solution was added to the mixed nanoparticles, and after ultrasonic dispersion, spray drying and granulation were carried out to obtain spherical precursor particles with a particle size of 80-120 μm. Then, fluidized bed coating was carried out by spraying a polyurethane prepolymer with a solid content of 30% to obtain particles with a particle size of 100-300 μm. After aging at 60℃ for 2 h, crosslinking was completed to obtain nanoparticle-reinforced capsules with a wall thickness of 5-10 μm, which were denoted as microcapsules B. The TiO2 particle size is 50 nm, and the WC particle size is 200 nm; the silane coupling agent includes KH-570; the spray drying granulation process includes an inlet air temperature of 180°C, an outlet air temperature of 80°C, an atomization pressure of 0.3 MPa, and a feed rate of 10 mL / min; the fluidized bed coating process includes a bed temperature of 70°C and an airflow velocity of 2 m / s.

8. The method for preparing a superhydrophobic microcapsule self-healing coating for cavitation damage of a turbine runner as described in claim 1, characterized in that: The two-component polyurethane coating uses a hydroxyl-terminated polyether polyol with a number average molecular weight of 1000-2000 Da and a hydroxyl value of 50-60 mg KOH / g as the main agent, and a liquefied modified diphenylmethane diisocyanate with an NCO content of 30-32%, a viscosity of 150-250 mPa·s at 25℃, and a functionality of 2.3-2.5 as the curing agent. The liquefied modified diphenylmethane diisocyanate is carbodiimide-urea ketimide modified MDI; the molar ratio of NCO:OH in the main agent and the curing agent is 1.05 to 1.10:

1.

9. A superhydrophobic microcapsule self-healing coating prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the superhydrophobic microcapsule self-healing coating as described in claim 9 in the repair of cavitation damage in turbine runners.

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