An ultra-low friction carbon-based multi-layer composite coating on the rubber surface and its construction method

Abstract

The present invention discloses a carbon-based multi-layer composite coating with ultra-low friction on the rubber surface. The coating is obtained by sequentially depositing a carbon film and a metal layer on the surface of a rubber substrate through magnetron sputtering technology, then alternately depositing a MXene-based and other two-dimensional material multi-layer coating on the surface of the metal layer by an electrochemical method, and finally through oil immersion treatment. The outermost layer of the obtained carbon-based multi-layer composite coating is a porous two-dimensional material layer, and there are a large number of micron-sized oil storage pores in the layer structure. During the friction process, the lubricating oil in the micron-sized pores is released due to the repeated extrusion of the frictional contact stress on the surface layer of the coating, and the solid-liquid composite ultra-low friction characteristics are achieved through the synergistic effect with the two-dimensional material. At the same time, the porous structure of the two-dimensional material is similar to a sponge and can serve as a lubricating oil storage device, continuously providing lubricating oil for the friction interface to ensure the stability and durability of the ultra-low friction characteristics.

Description

Technical Field

[0001] The present invention relates to a carbon-based multi-layer composite coating with ultra-low friction on the surface of rubber and a preparation method thereof, and particularly relates to the construction of an alternating multi-layer composite coating of a carbon thin film / metal layer / MXene-based and other two-dimensional materials on the surface of rubber for the preparation of movable seals, belonging to the fields of solid lubrication materials and tribology. Background Art

[0002] The sealing failure of seals is one of the key common technical problems in the sealing systems of mechanical equipment. When rubber mates with metal, the friction coefficient is extremely high (µ>1). The frictional heat generated by high friction easily causes the rubber seal to soften and quickly wear out, resulting in the leakage of high-pressure sealing medium from the damaged part and sealing failure, affecting the safe and reliable operation of the equipment. Therefore, to solve the problem of wear failure of rubber seals, it is necessary to start from reducing friction.

[0003] Carbon thin films have excellent properties such as low adhesion characteristics when paired with steel, low deposition temperature (deposition temperature ≤ 100°C, which will not cause fatal damage to the nitrile rubber matrix), controllable composition and mechanical strength, variable structures (such as multi-micro-nano structures, multi-element doping, etc.), and low friction and wear. Therefore, they are ideal coatings for achieving low friction on the surface of rubber. Although traditional carbon thin films can effectively reduce the friction of rubber, the friction coefficient is still relatively high (≥0.2), and it is difficult to fundamentally solve the problem of wear failure of rubber sealing materials.

[0004] The friction of carbon thin films on the surface of rubber mainly includes adhesive friction and hysteresis friction. Adhesive friction stems from the continuous formation and destruction of adhesion points between rubber and the mating surface, and hysteresis friction results from the slow response of rubber to stretch away from the hard surface when sliding relative to the hard surface. However, during the friction process, the friction coefficient of the thin film gradually increases, while its hysteresis friction effect gradually weakens, indicating that the friction coefficient of the carbon thin film on the surface of rubber mainly depends on the adhesive effect at the friction interface. Therefore, how to reduce the adhesive effect at the friction interface of the thin film is the key to achieving the super-slippery characteristics of rubber seals. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon-based composite coating that can achieve the super-slippery characteristics of the rubber surface from the perspective of reducing the adhesive effect at the friction interface of the thin film, aiming at the defect that the friction coefficient of the existing carbon thin film on the rubber surface is still relatively high.

[0006] I. Preparation of the Carbon-based Multi-layer Composite Coating with Ultra-low Friction on the Surface of Rubber

[0007] The carbon-based multi-layer composite coating with ultra-low friction on the surface of rubber in the present invention is obtained by sequentially depositing a carbon-based thin film and a metal layer on the surface of a rubber substrate through magnetron sputtering technology, then alternately depositing a multi-layer coating of MXene-based and other two-dimensional materials on the surface of the metal layer by an electrochemical method, and finally through oil immersion treatment.

[0008] The rubber substrate is one of nitrile rubber, hydrogenated nitrile rubber, ethylene propylene diene monomer rubber and silicone rubber, and its surface roughness is ≤ 150 nm.

[0009] The carbon-based film is a Ta-C film without hydrogen and an a-C:H film with hydrogen. The thickness of the carbon film is 1-2 μm.

[0010] The metal layer is one of copper, aluminum and tungsten.

[0011] The construction method of alternately depositing MXene-based and other two-dimensional material multi-layer coatings on the surface of the metal layer by electrochemistry includes the following steps:

[0012] ① Add MXene-based two-dimensional materials and positively charged polymers into an ethanol aqueous solution, and ultrasonically stir and mix them to obtain solution A respectively. Add other two-dimensional materials and positively charged polymers into an ethanol aqueous solution, and ultrasonically stir and mix them to obtain solution B;

[0013] ② Use the rubber / carbon film / metal layer sample as the negative electrode and the graphite sheet as the positive electrode. First deposit the MXene layer in solution A, and then deposit other two-dimensional material layers in solution B. Repeat several times as needed and then dry.

[0014] In the step ①, the MXene-based two-dimensional material is one of titanium-based, vanadium-based and molybdenum-based MXenes, and the other two-dimensional materials are one or several of graphene-based, boron nitride and transition metal dichalcogenide-based two-dimensional materials.

[0015] In the step ①, the positively charged polymer is one of chitosan, urea and polydopamine (PDA).

[0016] In the step ①, the mass ratio of the MXene-based two-dimensional material to the positively charged polymer is 2:3-3:2, and the mass ratio of the other two-dimensional material to the positively charged polymer is 2:3-3:2; the ultrasonic time is 30-50 min, the stirring time is 2-4 hours, and the stirring speed is 300-500 rpm.

[0017] In the step ②, the number of layers of the MXene-based and other two-dimensional materials is 4-8 layers, and the thickness of each layer is 100-200 nm. The electrochemically deposited voltage is 30-60 V.

[0018] During the oil immersion treatment, the lubricating oil is one or several of animal and plant lubricating oils, petroleum lubricating oils and synthetic lubricating oils, and the oil immersion time of the sample is 20-40 minutes.

[0019] Figure 1 This is a schematic diagram of the preparation of the alternately multi-layer two-dimensional material composite coating on the surface of the rubber / carbon film / metal layer of the present invention. Figure 2Schematic diagram of the ultra-low friction carbon-based multi-layer composite coating structure on the rubber surface of the present invention. The outermost layer of the carbon-based multi-layer composite coating designed by the present invention is a porous two-dimensional material layer, and there are a large number of oil-storing micro-holes in this layer structure. During the friction process, the surface layer of the coating is repeatedly squeezed by the friction contact stress, causing the lubricating oil in the micro-holes to be released, and realizing the ultra-low friction characteristics of the coating through the synergistic effect with the two-dimensional material. At the same time, the porous structure of the two-dimensional material is similar to a sponge body and can be used as a lubricating oil storage device to continuously provide lubricating oil for the friction interface, ensuring the stability and durability of the ultra-low friction characteristics.

[0020] II. Friction performance evaluation of the ultra-low friction carbon-based multi-layer composite coating on the rubber surface

[0021] The tribological performance of the ultra-low friction carbon-based multi-layer composite coating of the present invention was evaluated using a friction and wear tester. The specific friction conditions were: ball-on-disk rotation mode, normal load of 1 - 15 N, friction pair was a φ6 mm GCr15 steel ball, and the test environment was an atmospheric environment. The test results showed that the friction coefficient of the conventional carbon film was relatively high (≥0.15), while the friction coefficient of the carbon-based composite coating of the present invention was significantly reduced (≤0.01), which can be used to prepare rubber dynamic seals.

[0022] In summary, the present invention successively deposits a carbon film and a metal layer on the surface of a rubber substrate by magnetron sputtering technology, then alternately deposits MXene-based and other two-dimensional material multi-layer coatings on the surface of the metal layer by an electrochemical method, and finally obtains an ultra-low friction composite coating through oil immersion treatment. The outermost layer of this carbon-based multi-layer composite coating is a porous two-dimensional material layer, and there are a large number of oil-storing micro-holes in this layer structure. During the friction process, the surface layer of the coating is repeatedly squeezed by the friction contact stress, causing the lubricating oil in the micro-holes to be released, and realizing the solid-liquid composite ultra-low friction characteristics through the synergistic effect with the two-dimensional material. At the same time, the porous structure of the two-dimensional material is similar to a sponge body and can be used as a lubricating oil storage device to continuously provide lubricating oil for the friction interface, ensuring the stability and durability of the ultra-low friction characteristics. It effectively reduces the adhesion effect at the friction interface of the film, overcomes the limitation that it is difficult to achieve ultra-low friction on the soft surface of rubber simply relying on a hard carbon-based film, can be applied to a variety of complex working conditions, and is easy to realize large-area industrial application. Description of the drawings

[0023] Figure 1 Schematic diagram for the preparation of the alternating multi-layer two-dimensional material composite coating on the rubber / carbon film / metal layer surface of the present invention;

[0024] Figure 2 Schematic diagram of the ultra-low friction carbon-based multi-layer composite coating structure on the rubber surface of the present invention. Detailed implementation manners

[0025] The construction method and friction performance of the ultra-low friction carbon-based multi-layer composite lubricating coating on the rubber surface of the present invention will be further described below through specific embodiments.

[0026] Example 1

[0027] (1) Cut a 300×300×2 mm black nitrile rubber sheet (surface finish Ra < 150 nm) into 30×30 mm rubber sheets, soak them in a 60°C soap aqueous solution and ultrasonically clean for 30 min to remove the grease and dirt on the rubber surface; then take them out and soak them in 90-95°C distilled water and ultrasonically clean for 30 min to remove the possible remaining soap aqueous solution; finally, dry them with dry nitrogen and then place them in a drying oven at 100°C for another 20 min to evaporate the remaining moisture on the rubber surface. The above process is repeated 5 times; 2 (2) After the rubber is cooled to room temperature, place it in a magnetron sputtering vacuum chamber. Close the vacuum chamber door and pump the vacuum to ≤1.0×10

[0028] Pa. Introduce nitrogen with a flow rate of 200 sccm into the vacuum chamber, and the chamber pressure is 4 Pa; turn on the high-power pulsed bias power supply, and use nitrogen plasma to bombard the rubber, where the bias voltage is -700 V, the duty cycle is 55%, the frequency is 60 KHz, and the treatment time is 35 min. Then pump out the nitrogen completely, and then introduce 300 sccm argon, adjust the pulsed bias voltage to -1200 V, and bombard and clean for 25 min under other conditions unchanged; –3 (3) After the bombardment, immediately introduce argon, turn on the graphite target sputtering power supply, adjust the target-substrate distance to 10 cm, the target current to 3 A, the argon flow rate to 45 sccm, the substrate bias voltage to -700 V, the pressure to 1.0 Pa, the duty cycle to 40%, the frequency to 60 KHz, and the deposition time to 60 min; after the deposition of the Ta-C film is completed, rotate the sample holder to the opposite side of the metal aluminum target, and the deposition time is 5 min under other conditions unchanged; after the deposition is completed, wait for the temperature in the vacuum chamber to cool to room temperature and take out the sample for use;

[0029] (4) Add 60 mg of chitosan to 45 mL of ethanol solution and mix evenly, then slowly add 60 mg of Ti3C2 MXene nanosheets, ultrasonically for 30 minutes and then stir at a speed of 300 rpm for 2.5 hours to obtain solution A. Add 75 mg of chitosan to 60 mL of ethanol solution and mix evenly, then slowly add 45 mg of graphene nanosheets, ultrasonically for 40 minutes and then stir at a speed of 400 rpm for 3 hours to obtain solution B.

[0030] (5) Slowly add solution B dropwise to solution A while stirring at a speed of 500 rpm, and continue to stir for 1.5 hours to obtain a homogeneous mixture C.

[0031] (5) Using a graphite sheet as the positive electrode and the previously prepared rubber / carbon film / aluminum layer sample as the negative electrode, first deposit at a deposition voltage of 30 V in solution A for 40 seconds, then transfer the electrode to solution B and deposit at a deposition voltage of 45 V for 30 seconds. Repeat this process 2 times to obtain a 4-layer alternating multi-layer coating; after the deposition is completed, dry the sample.

[0032] (6) Immerse the above-deposited sample in vegetable oil for about 20 minutes, then take it out and dry the surface with a lint-free cloth to obtain the ultra-low friction carbon-based multi-layer composite coating sample of the present invention. The friction coefficient of this carbon-based composite coating sample in the atmospheric environment is as low as 0.008.

[0033] Example 2

[0034] (1) Use silicone rubber (the surface finish of the silicone rubber Ra < 100 nm), and the pre-cleaning steps are the same as in Example 1;

[0035] (2) The same as in Example 1;

[0036] (3) After the bombardment ends, immediately introduce argon, turn on the graphite target sputtering power supply, adjust the target-substrate distance to 10 cm, the target current to 3 A, the argon flow rate to 45 sccm, the flow ratio of Ar / CH4 to 1.5:1, the substrate bias voltage to -700 V, the gas pressure to 1.0 Pa, the duty cycle to 40%, the frequency to 60 KHz, and the deposition time to 90 min; after the deposition of the a-C:H film is completed, rotate the sample holder to the opposite side of the copper target, and keep other conditions unchanged with a deposition time of 5 min; after the deposition is completed, wait for the temperature in the vacuum chamber to cool to room temperature and then take out the sample for use;

[0037] (4) Add 85 mg of chitosan to 60 mL of ethanol solution and mix evenly, then slowly add 45 mg of V2C MXene nanosheets, ultrasonicate for 45 minutes and then stir at a speed of 500 rpm for 3.5 hours to obtain solution A. Add 75 mg of urea to 55 mL of ethanol solution and mix evenly, then slowly add 40 mg of molybdenum disulfide nanosheets, ultrasonicate for 50 minutes and then stir at a speed of 500 rpm for 4 hours to obtain solution B.

[0038] (5) Using a graphite sheet as the positive electrode and the previously prepared rubber / carbon film / copper layer sample as the negative electrode, first deposit at a deposition voltage of 45 V in solution A for 40 seconds, then transfer the electrode to solution B and deposit at a deposition voltage of 60 V for 30 seconds. Repeat this process 3 times to obtain a 6-layer alternating multi-layer coating; after the deposition is completed, dry the sample for standby.

[0039] (6) Immerse the above-deposited sample in synthetic lubricating oil for about 30 minutes, then take it out and dry the surface with a lint-free cloth to obtain the ultra-low friction carbon-based multi-layer composite coating sample of the present invention. The friction coefficient of this carbon-based composite coating sample in the atmospheric environment is as low as 0.006.

Claims

1. A carbon-based multi-layer composite coating with ultra-low friction on the rubber surface is obtained by sequentially depositing a carbon-based thin film and a metal layer on the surface of a rubber substrate through magnetron sputtering technology, then alternately depositing MXene-based two-dimensional materials and other two-dimensional materials on the surface of the metal layer by an electrochemical method to form a multi-layer coating, and finally through oil immersion treatment; wherein, The metal layer is one of copper, aluminum, and tungsten metal layers, the MXene-based two-dimensional material is one of titanium-based, vanadium-based, and molybdenum-based MXenes; the other two-dimensional materials are one or more of graphene-based, boron nitride, and transition metal dichalcogenide-based two-dimensional materials.

2. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 1, wherein: The rubber substrate is one of nitrile rubber, hydrogenated nitrile rubber, ethylene propylene diene monomer rubber, and silicone rubber, and its surface roughness ≤ 150 nm.

3. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 1, characterized in that: The carbon-based film is a Ta-C film without hydrogen and an a-C:H film with hydrogen.

4. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 1, wherein: The construction method of alternately depositing a multi-layer coating of MXene-based two-dimensional materials and other two-dimensional materials on the surface of the metal layer by an electrochemical method includes the following steps: ① Add the MXene-based two-dimensional material and the positively charged polymer into an ethanol aqueous solution, and ultrasonically stir and mix to obtain solution A; add the other two-dimensional material and the positively charged polymer into an ethanol aqueous solution, and ultrasonically stir and mix to obtain solution B; ② Use the rubber / carbon film / metal layer sample as the negative electrode and the graphite sheet as the positive electrode; First deposit the MXene layer in solution A, then deposit the other two-dimensional material layer in solution B, alternately deposit multiple times, and then dry.

5. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 4, characterized in that: In step ①, the positively charged polymer is one of chitosan, urea, and acrylate.

6. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 4, wherein: In step ①, the mass ratio of the MXene-based two-dimensional material to the positively charged polymer is 2:3 - 3:2, and the mass ratio of the other two-dimensional material to the positively charged polymer is 2:3 - 3:2; the ultrasonic time is 30 - 50 min, the stirring time is 2 - 4 hours, and the stirring speed is 300 - 500 rpm.

7. The ultra-low friction carbon-based multi-layer composite coating on the rubber surface according to claim 4, characterized in that: In step ②, the total number of layers of the MXene-based and other two-dimensional materials is 4 - 8 layers, and the thickness of each layer is 100 - 200 nm; the electrochemical deposition voltage is 30 - 60 V.

8. The ultra-low friction carbon-based multi-layer composite coating on a rubber surface according to claim 1, characterized in that: The lubricating oil used for the oil immersion treatment is one or several of animal and plant lubricating oils, petroleum lubricating oils, and synthetic lubricating oils, and the oil immersion time is 20 - 40 minutes.

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