Friction-induced piezoelectric effect-based long-acting lubrication-corrosion prevention integrated coating and preparation method thereof

Abstract

The invention discloses a friction-induced piezoelectric effect-based long-acting lubrication-corrosion prevention integrated coating and a preparation method thereof, and solves the bottleneck problems of accelerated degradation of tribological properties and insufficient long-acting service life of the existing bonding solid lubrication coating in a salt spray corrosion environment. The specific technical scheme is as follows: polyamide-imide (PAI) is taken as a matrix, a polyamide-imide / polyvinylidene fluoride (PVDF) binary composite resin matrix is constructed, barium titanate (BTO) piezoelectric nano-particles subjected to surface modification by a silane coupling agent and graphene are doped, and polytetrafluoroethylene (PTFE) micro-particles are added. Through the mechanical energy-electric energy conversion effect in the friction process, the BTO / PVDF composite phase generates piezoelectric potential under the action of contact stress, a three-dimensional electric field network is formed in the coating, the electric field generates directional repulsive action on electronegative corrosion ions such as Cl and the like, and corrosion medium permeation is delayed.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional coating materials, and particularly relates to a long-lasting lubrication-anti-corrosion integrated coating based on tribo-induced piezoelectric effect and a preparation method thereof, which is applicable to the surface protection and lubrication functions of mechanical components in corrosive environments. Background Art

[0002] For traditional solid lubricating coatings (such as molybdenum disulfide-containing and polytetrafluoroethylene-based coatings), in order to balance lubricating performance and load-carrying capacity, the coating thickness generally does not exceed 30 μm. Due to the limited coating thickness, its ability to isolate corrosive media is insufficient. In particular, small-sized corrosive ions such as Cl - (atomic radius about 0.181 nm) can easily penetrate the coating and cause corrosion. And it has been clearly pointed out in ASTM G119-09 "Standard Guide for Determining Synergism Between Wear and Corrosion" that the frictional behavior in corrosive media poses a more severe test for solid lubricating coatings. The coupled damage effect of corrosion and friction is greater than the simple sum of corrosion and wear, resulting in a serious reduction in the service life of the coating. In order to improve the service life of solid lubricating coatings in corrosive media, the current design and preparation of coatings mainly proceed from the following aspects. One is to improve the densification of coating materials (CN112521836B, CN202411220714.3) to achieve physical isolation of corrosive media. The second is to add corrosion inhibitors to the coating (CN202410601066.X, CN202211506367.1), and the corrosion inhibitor is released by the coating through frictional movement, thereby delaying the erosion of the corrosive media on the metal substrate. The third is to prepare superhydrophobic coating materials (CN109232964B), and use the low surface energy of the material surface and interface to block the infiltration of corrosive media. Although the above methods can improve the service performance and life of the coating within a certain range, there are still great limitations. Improving the densification of the coating not only requires high requirements for the material itself, but also has high requirements for the processability. There are problems with strong targeting and poor controllability of slow release in the doping of corrosion inhibitors. Although the superhydrophobic coating can achieve the surface characteristics of a high contact angle, it is difficult to balance mechanical strength and tribological performance. In addition, most of the above methods are limited by equipment. The friction test and salt spray test are carried out independently, and the actual performance under the coupled corrosion and friction conditions has not been verified. Therefore, considering the actual application situation, it is necessary to develop a coating with both anti-corrosion and lubrication functions and a preparation method thereof under the coupled corrosion and friction conditions. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide a long-lasting lubrication-anti-corrosion integrated coating based on the friction-induced piezoelectric effect and a preparation method thereof. By constructing a composite lubricating coating containing piezoelectric materials, the piezoelectric electric field generated during the friction process is used to actively repel negatively charged corrosion media such as Cl - and other negatively charged corrosion media, realizing the synergistic protection of lubrication and anti-corrosion from passive isolation to dynamic electric field defense.

[0004] I. Preparation of a long-lasting lubrication-anti-corrosion integrated coating based on the friction-induced piezoelectric effect 1) Surface modification of barium titanate nanoparticles: Add a silane coupling agent to a mixed solvent of anhydrous ethanol and deionized water, and dropwise add glacial acetic acid to adjust the pH value to 4.0 - 4.5; then add barium titanate nanoparticles, heat and stir at 60 - 70 °C for 2 - 3 h. After the reaction, centrifuge and wash multiple times, and vacuum dry the barium titanate precipitate to obtain surface-modified barium titanate nanoparticles. Perform Fourier transform infrared spectroscopy on the modified barium titanate, and the spectrum is as Figure 1 shown. 3340 cm -1 , 2860 cm -1 , 1080 cm -1 , 553 cm -1 correspond to the O-H stretching vibration peak, C-H stretching vibration peak, Si-O-Ba vibration peak, and Ti-O stretching vibration peak respectively. The appearance of the above group peaks indicates the successful modification of barium titanate; The silane coupling agent is KH560, and the dosage of the silane coupling agent is 4.0 - 6.0% of the mass of barium titanate nanoparticles; The mass ratio of anhydrous ethanol to deionized water is 8:1 - 10:1; 2) Preparation of the coating: Add the surface-modified barium titanate nanoparticles obtained in step 1) and PVDF resin to a stone mortar, and grind until the particle sizes of barium titanate and PVDF resin are less than 2 μm. Then add graphene and a dispersant, and grind and mix evenly; then blend the obtained mixed particles of BTO / PVDF / graphene together with PAI and PTFE resin particles in an organic solvent, and shear and disperse evenly to obtain the required coating; The organic solvent is at least one of N-methylpyrrolidone or N,N-dimethylacetamide; the dispersant is BYK-192 wetting dispersant; The main component contents in the coating are 30.0 wt% - 40.0 wt% of PAI, 20.0 wt% - 30.0 wt% of PVDF, 0.5 wt% - 1.0 wt% of surface-modified BTO, 5.0 wt% - 10.0 wt% of PTFE, and 0.1 wt% - 0.5 wt% of graphene; 3) Preparation of the coating: The coating obtained in step 2) is coated onto the conductive metal substrate by spraying, drop coating, spin coating or blade coating, cured and then placed in the middle of a parallel plate capacitor, and an electric field is applied for polarization until the absolute value of the coating in the quasi-static d33 / d31 measuring instrument is ≥ 0.5.

[0005] The coating curing process is curing at 150 °C for 2 h and then at 250 °C for 1 h, and the thickness of the prepared coating is 10 - 30 μm; The internal electric field strength of the parallel plate capacitor is set to 6 - 7 kV / mm, and the sample polarization time is 25 - 30 min.

[0006] In the present invention, by constructing a tribo-induced piezoelectric lubricating coating, an internal normal electric field is generated inside the coating during the friction process. Under the action of the electric field force, negatively charged ions (such as Cl-) in the corrosive medium are repelled, delaying the penetration of the corrosive medium into the coating interior, reducing the performance degradation of the coating caused by the intrusion of the corrosive medium, and at the same time increasing the time for the corrosive medium to reach the metal matrix; on the other hand, through the externally directed electric field generated by tribo-induction, the diffusion of cations generated by the corrosion at the coating / substrate interface is resisted by the electric field, causing cation accumulation at the interface, thereby inhibiting the occurrence of the corrosion reaction and prolonging the service life of the coating. The mechanism of action is as Figure 2 shown. Based on the above idea, the present invention uses a polyamideimide (PAI) / polyvinylidene fluoride (PVDF) binary composite resin matrix to construct a high-strength and tough hydrophobic material system. The surface of barium titanate (BTO) piezoelectric nanoparticles is modified by a silane coupling agent to reduce the agglomeration ratio of the nanoparticles and improve the dispersion of BTO in the coating; the generation of the β-phase in the PVDF material is enhanced by doping with BTO, enhancing the piezoelectric effect of the coating; by adding a small amount of graphene sheets, a three-dimensional electric field network is formed by graphene, BTO and PVDF in the coating, further enhancing the piezoelectric effect of the coating; by adding polytetrafluoroethylene (PTFE) micron particles, the porosity of the coating is enhanced and the friction coefficient of the coating is greatly reduced.

[0007] II. Performance of the long-term lubrication-anti-corrosion integrated coating based on the tribo-induced piezoelectric effect Salt spray atmospheric friction and wear test: The tested specimen is clamped onto a salt spray atmospheric friction and wear testing machine, the salt spray concentration is adjusted to 85% RH, the conditions of the friction testing machine are a load of 5 N, a reciprocating frequency of 5 Hz, and a full amplitude of 5 mm, and the test duration is 2 h. The test results are as Figure 4 shown. After a 4-hour salt spray friction test, the friction coefficient is still not greater than 0.14, the friction coefficient is less than that of the same type of lubricating coating, and the coating life is greater than that of the same type of lubricating coating.

[0008] In summary, the present invention constructs a composite lubricating coating containing piezoelectric materials, and utilizes the piezoelectric electric field generated during the friction process to actively repel negatively charged corrosion media such as Cl⁻, realizing the synergistic protection of lubrication and anti-corrosion from passive isolation to dynamic electric field defense. The coating uses polyamideimide (PAI) / polyvinylidene fluoride (PVDF) as a binary composite matrix, endowing the resin phase of the coating with toughness, hydrophobicity, and piezoelectric properties; and doping barium titanate (BTO) piezoelectric nanoparticles and graphene surface-modified with silane coupling agent to enhance the piezoelectric effect and load-bearing capacity of the coating; by adding micron-sized polytetrafluoroethylene particles, the lubricating performance and hydrophobic performance of the coating are further enhanced. Utilizing the mechanical energy-electric energy conversion effect during the friction process, the BTO / PVDF composite phase generates a piezoelectric potential under the action of contact stress, forming a three-dimensional electric field network inside the coating. This electric field has a directional repelling effect on negatively charged corrosion ions such as Cl⁻, delays the medium penetration rate, curbs the deterioration speed of the lubricating coating, and extends the service life of the solid lubricating coating. It realizes the technological innovation from "passive isolation" to "active defense", providing a new idea for the design and preparation of lubrication and anti-corrosion integrated coatings. Description of the Drawings

[0009] Figure 1 It is the Fourier infrared spectrum diagram of the modified barium titanate nanoparticles of the present invention.

[0010] Figure 2 It is the lubrication mechanism diagram of the coating prepared by the present invention.

[0011] Figure 3 It is the polarization schematic diagram of the coating prepared by the present invention.

[0012] Figure 4 It is the variation law diagram of the friction coefficient of the coating prepared by the present invention tested in a salt spray friction testing machine for 4 hours. Detailed Embodiments

[0013] The preparation method and performance of the present invention will be further described below through specific examples.

[0014] Example 1 1. Material Preparation Resins: Polyamideimide (PAI), non-volatile content 23.4%; Polyvinylidene fluoride (PVDF), non-volatile content 20%; Fillers: BaTiO3 nanoparticles, particle size 200 nm; Polytetrafluoroethylene (PTFE) particles, particle size 2 μm; Graphene, sheet diameter 8 - 20 μm, 5 - 10 layers; Solvents: N-methylpyrrolidone (NMP), analytical pure, purity 99%; N,N-dimethylacetamide (DMAc), analytical pure, purity 99%; Auxiliaries: BYK-192 wetting and dispersing agent from BYK, Germany.

[0015] 2. Synthesis of Coating 1) Take 18 g of absolute ethanol and 2 g of deionized water, add them to a three-necked flask, and adjust the pH value to 4.5 by dropping glacial acetic acid; add 0.5 g of silane coupling agent KH560 and stir evenly; add 10 g of nano-barium titanate (particle size 100 nm) particles, heat at 60 °C and stir for 2 h; after the reaction is completed, centrifuge the barium titanate nanoparticles at a high speed of 10,000 rpm for 2 min; remove the supernatant of barium titanate, add 20 mL of absolute ethanol, stir evenly, and centrifuge again. Repeat this process three times; put the barium titanate precipitate into a vacuum oven and keep it at 100 °C for 6 h; 2) Take 0.45 g of dried BTO and 12.50 g of PVDF into a stone mortar and grind for 20 min until the particle diameter is less than 2 μm; then add 0.05 g of graphene and 0.010 g of BYK-192 dispersant and grind for 10 min; add 17.09 g of PAI, 3.00 g of PTFE, 8.45 g of DMAc, and 8.45 g of NMP, and disperse at a high speed of 8000 rpm for 5 min. The coating synthesis is completed.

[0016] 3. Preparation of Coating Take a 304 stainless steel test piece, perform surface sandblasting treatment, and clean it with acetone. Adopt the coating process method to spray the coating onto the 304 stainless steel test piece. The spraying pressure is 0.15 MPa, and the spraying is carried out in a small amount and multiple times. The coating thickness is 20 μm. After spraying, put the test piece into a high-temperature oven for curing, keep it at 150 °C for two hours and then at 250 °C for one hour; Perform electric field polarization on the cured coating. Connect the positive pole of the DC power supply to the metal matrix of the test piece, and the negative pole to a metal plate. The metal plate is placed parallel to the coating surface. The metal matrix and the metal plate form a parallel plate capacitor, as Figure 3 shown. Adjust the DC power supply voltage to 0.12 kV and keep it for 30 min; Finally, place the electrically polarized sample on a quasi-static d33 / d31 measuring instrument. Select the d33 measurement range. The metal matrix is in contact with the lower end of the holding clamp below, and the coating is in contact with the upper end of the holding clamp. Turn on the measuring instrument for testing, and the test result is -0.8 pC / N.

[0017] 4. Salt Spray Corrosion Friction Test Salt spray atmospheric friction and wear test: Clamp the tested sample onto a salt spray atmospheric friction and wear testing machine, adjust the salt spray concentration to 85% RH, and the conditions of the friction testing machine are a load of 5 N, a reciprocating frequency of 5 Hz, and a full amplitude of 5 mm. The test duration is 2 h. After 4 h of salt spray friction test, the friction coefficient is still not greater than 0.14. The test results are as Figure 4 shown. Figure 4Friction tests were conducted on different PAI-based bonded solid lubricating coatings under salt spray atmosphere. Among them, the blue curve represents the PAI / MoS2 coating, the red curve represents the PAI / graphite coating, and the green curve represents the PAI / PTFE coating. By comparing the friction coefficients and coating lifetimes, it can be seen that the coating of the present invention has stable performance, the friction coefficient is less than that of similar lubricating coatings, and the coating lifetime is higher than that of similar lubricating coatings.

Claims

1. A preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect, characterized in that It includes the following steps: 1) Surface modification of barium titanate nanoparticles: Add a silane coupling agent into a mixed solvent of absolute ethanol and deionized water, and dropwise add glacial acetic acid to adjust the pH value to 4.0 - 4.5; then add barium titanate nanoparticles, heat and stir at 60 - 70 °C for 2 - 3 h. After the reaction, centrifuge and wash multiple times, and vacuum dry the barium titanate precipitate to obtain surface-modified barium titanate nanoparticles; 2) Preparation of the coating: Add the surface-modified barium titanate nanoparticles obtained in step 1) and PVDF resin into a stone mortar, grind until the particle sizes of barium titanate and PVDF resin are less than 2 μm, then add graphene and a dispersant, and grind and mix evenly; then blend the obtained BTO / PVDF / graphene mixed particles together with PAI and PTFE resin particles in an organic solvent, and shear and disperse evenly to obtain the required coating; 3) Preparation of the coating: Coating the coating obtained in step 2) onto a conductive metal substrate by spraying, drop coating, spin coating or knife coating, cure it and place it in the middle of a parallel plate capacitor, apply an electric field for polarization until the absolute value of the coating in a quasi-static d33 / d31 measuring instrument ≥ 0.

5.

2. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect according to claim 1, characterized in that, In step 1), the silane coupling agent is KH560, and the dosage of the silane coupling agent is 4.0 - 6.0% of the mass of the barium titanate nanoparticles.

3. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect according to claim 1, characterized in that, In step 1), the mass ratio of the absolute ethanol to the deionized water is 8:1 - 10:

1.

4. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect as described in claim 1, characterized in that, In step 2), the organic solvent is at least one of N-methylpyrrolidone or N,N-dimethylacetamide, and the dispersant is BYK-192 wetting dispersant.

5. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect according to claim 1, characterized in that, In step 2), the main component contents in the coating are 30.0 wt% - 40.0 wt% of PAI, 20.0 wt% - 30.0 wt% of PVDF, 0.5 wt% - 1.0 wt% of surface-modified barium titanate nanoparticles, 5.0 wt% - 10.0 wt% of PTFE, and 0.1 wt% - 0.5 wt% of graphene.

6. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect as described in claim 1, characterized in that, In step 3), the thickness of the prepared coating is 10 - 30 μm.

7. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect according to claim 1, characterized in that, In step 3), the coating curing process is curing at 150 °C for 2 h and then curing at 250 °C for 1 h.

8. The preparation method of a long-acting lubrication and anti-corrosion integrated coating based on the tribo-induced piezoelectric effect according to claim 1, characterized in that, In step 3), the internal electric field strength of the parallel plate capacitor is set to 6 - 7 kV / mm, and the sample polarization time is 25 - 30 min.

9. A long-lasting lubrication-anti-corrosion integrated coating based on the friction-induced piezoelectric effect prepared by the method according to claim 1.

Images