Oil-based lubricant and lubrication method for diamond-like carbon film

Abstract

The present invention provides an oil-based lubricant and a method for lubricating a diamond-like carbon (DLC) film. The oil-based lubricant comprises a base lubricating oil and a lubricating additive having ester and hydroxyl groups, and comprising a lactate compound and / or a salicylate compound. The present invention also provides a method for lubricating a DLC film, wherein the DLC film is lubricated with a lubricant comprising the oil-based lubricant. The oil-based lubricant can achieve an ultra-low coefficient of friction and wear rate on the DLC film, improving the lubrication efficiency and service life of the DLC film, and exhibits excellent lubrication performance and a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the technical field of lubricants, and in particular to an oil-based lubricant and a lubricating method for a diamond-like carbon film. Background Art

[0002] Friction and wear are ubiquitous in moving mechanical systems. Statistics show that friction and wear consume approximately one-third of the world's primary energy and cause nearly 80% of mechanical component failures. Furthermore, over 50% of serious mechanical equipment accidents are caused by lubrication failure or excessive wear. The energy and economic losses caused by friction and wear are significant. Therefore, research into lubrication and friction reduction technologies to improve the friction state of mechanical systems, reduce friction, and control wear is crucial for improving resource utilization and reducing material consumption.

[0003] Diamond-like carbon (DLC) films are widely used in the field of tribology due to their excellent properties such as wear resistance, low friction, and chemical stability.

[0004] Currently, ultra-low friction can be achieved on DLC under vacuum or nitrogen conditions, but friction cannot be effectively reduced in atmospheric conditions. To address this issue, using liquid lubricants to lubricate DLC can reduce the friction coefficient in atmospheric conditions. For example, when using traditional lubricants such as polyalphaolefin (PAO) to lubricate DLC, the friction coefficient is reduced compared to dry friction conditions, but the absolute value of the friction coefficient is still large.

[0005] Currently, using traditional lubricants to lubricate DLC results in a high coefficient of friction, making efficient lubrication difficult. In oil-based lubrication systems, traditional lubricants such as polyalphaolefins (PAO) exhibit relatively high coefficients of friction for DLC. Even additives such as molybdenum dialkyldithiocarboxylate (MoDTC) or zinc dialkyldithiophosphate (ZDDP) are unable to effectively reduce friction and wear rates. Summary of the Invention

[0006] In order to solve the above problems, the present invention aims to provide an oil-based lubricant and a method for lubricating a diamond-like carbon film. The oil-based lubricant has good lubrication performance and a wide range of applications.

[0007] In order to achieve the above object, the present invention provides an oil-based lubricant, which includes a base lubricating oil and a lubricating additive, wherein the molecules of the lubricating additive have an ester group and a hydroxyl group, and the lubricating additive includes a lactate compound and / or a salicylate compound.

[0008] In the aforementioned oil-based lubricant, the ester and hydroxyl groups contained in the lubricating additive can undergo a tribochemical reaction with the diamond-like carbon film to form a friction reaction film, thereby effectively reducing the friction coefficient and wear rate of the diamond-like carbon film. Specifically, the lubricating additive can form a chemical adsorption film with the diamond-like carbon film through the ester group, and the hydroxyl groups in the lubricating additive can form a hydrated sheath-like structure through hydrogen bonding, effectively reducing the friction coefficient. Compared to conventional PAO-based lubricants or oleic acid, the present invention, by adding a lubricating additive with a specific molecular structure to the PAO base oil or oleic acid, can reduce the friction coefficient of the diamond-like carbon film by over 40%.

[0009] In the above-mentioned oil-based lubricant, the lubricating additive can be dissolved in an oil phase solvent. The lactate compound can specifically include one or a combination of two or more of cetyl lactate, butyl lactate, and leaf lactate. The salicylate compound can include ethyl salicylate.

[0010] In the above-mentioned oil-based lubricant, the base lubricant includes a PAO (polyalphaolefin) base oil and / or oleic acid. Accordingly, the oil-based lubricant is an oil-based lubricant with a PAO base oil and / or oleic acid as a base dispersion. The lubricating additive is soluble in the above-mentioned base lubricant to form a uniform system.

[0011] In the above oil-based lubricants, the oleic acid is compatible with the diamond-like carbon film, and mixing the oleic acid with lactate compounds (such as hexadecyl lactate, butyl lactate, etc.) can achieve better lubrication and friction reduction effects.

[0012] In the above-mentioned oil-based lubricants, the PAO base oil may specifically include PAO6 base oil and / or PAO2 base oil, etc.

[0013] According to a specific embodiment of the present invention, the combination of the lubricating additive and the base lubricating oil in the oil-based lubricant includes but is not limited to the following: a combination of hexadecyl lactate and PAO6 base oil; a combination of ethyl salicylate and PAO2 base oil; a combination of leaf lactate and PAO6 base oil; a combination of hexadecyl lactate and oleic acid; a combination of butyl lactate and oleic acid.

[0014] In the above-mentioned oil-based lubricant, the lubricating additive comprises 0.5 wt% to 30 wt% of the oil-based lubricant, for example, 0.5 wt%, 1 wt%, 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or other specific values, as well as ranges having any two of these specific values ​​as endpoints. By controlling the proportion of the lubricating additive in the liquid lubricant, the overall performance of the liquid lubricant can be adjusted to achieve a relative balance between price and lubrication efficiency.

[0015] In the above-mentioned oil-based lubricant, the mass percentage of the lubricating additive in the oil-based lubricant can be further adjusted according to the specific type of lubricating additive. Specifically, the ethyl salicylate has a benzene ring and has a high solubility in the base lubricating oil. The mass percentage of ethyl salicylate in the oil-based lubricant can be controlled to be 0.5wt%-30wt%, for example, 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints. The mass proportion of the lactic acid ester compound in the oil-based lubricant can be controlled to be 0.5wt%-20wt%, 0.5wt%-15wt%, for example, the mass proportion of hexadecyl lactate in the oil-based lubricant can be controlled to be 0.5wt%-2wt%, specifically 0.5wt%, 1wt%, 1.5wt%, 2wt% and other specific values, and ranges with any two of the above specific values ​​as endpoints, and further controlled to be 0.5wt%-20wt%; the mass proportion of butyl lactate in the oil-based lubricant (especially the oil-based lubricant with PAO6 as the base oil) can be controlled to be 0.5wt%-20wt%, specifically 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt%, 15wt%, 20wt% and other specific values, and ranges with any two of the above specific values ​​as endpoints, and further controlled to be 0.5wt%-15wt% or 0.5wt%-10wt% or 10wt%-15wt%. The mass proportion of the leaf lactate in the oil-based lubricant can be 0.5wt%-15wt%, specifically 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt%, 15wt%, 20wt% and other specific values, as well as ranges with any two of the above specific values ​​as endpoints, and can be further controlled to be 0.5wt%-15wt% or 0.5wt%-10wt% or 10wt%-15wt%.

[0016] The present invention also provides a method for lubricating a diamond-like film, wherein the method uses a lubricant to lubricate the diamond-like film, and the lubricant includes the above-mentioned oil-based lubricant provided by the present invention.

[0017] In a specific embodiment of the present invention, the diamond-like carbon film has both sp 3 Hybridized CC single bond, also contains graphite sp 2 Hybridized C-C bonds. Accordingly, the diamond-like carbon film has a high hardness close to that of diamond (10GPa-60GPa) and has lubricating and friction-reducing properties similar to graphite. By changing the sp 3 Hybridization and sp 2The hybridization ratio can regulate its mechanical properties such as hardness. The specific means of regulation can be doping, such as doping metal elements, non-metal elements, etc. into the diamond-like carbon film.

[0018] In the above lubrication method, the diamond-like film may include a non-doped diamond-like film and / or a doped diamond-like film.

[0019] In the above lubrication method, the undoped diamond-like film may specifically include an amorphous carbon film, etc.; the doped diamond-like film may specifically include a metal-doped diamond-like film and / or a non-metallic element-doped diamond-like film, etc.

[0020] In some specific embodiments, the non-metal-doped diamond-like carbon film comprises a silicon-doped diamond-like carbon film (or DLC-Si film). Specifically, the silicon-doped diamond-like carbon film has a silicon content by mass (i.e., the percentage by mass of silicon in the silicon-doped diamond-like carbon film) of 1% to 10%, and may include, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and other specific values, as well as ranges with any two of these values ​​as endpoints. Silicon doping can form stronger C-Si bonds in the diamond-like carbon film, thereby improving the strength of the diamond-like carbon film.

[0021] In some specific embodiments, the metal-doped diamond-like film includes a chromium-doped diamond-like film. Specifically, the mass content of chromium in the chromium-doped diamond-like film (i.e., the mass proportion of chromium in the chromium-doped diamond-like film) is generally 1%-10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0022] In specific embodiments of the present invention, the surface of the diamond-like carbon film typically contains CO single bonds and C=O double bonds formed by oxidation. During certain manufacturing processes, C-H single bonds may form on the film surface due to specific processing. These CO single bonds, C=O double bonds, and C-H single bonds can react with lubricating additives. During friction, the C=O double bonds may break and form bonds with ester or hydroxyl groups in the lubricating additive, while the C-H single bonds may break and adsorb to the ester or hydroxyl groups in the lubricating additive.

[0023] In the above lubrication method, the material paired with the diamond-like film includes one or a combination of two or more of the group consisting of diamond-like film, carbon steel, alloy steel, and silicon nitride. A friction pair is a friction system formed by two contacting objects generating friction, and the paired material refers to the two objects in the friction pair that rub against each other.

[0024] In some specific embodiments, the diamond-like carbon film can form a friction pair with bearing steel (eg, GCr15).

[0025] In the above-mentioned lubrication method, prior to lubrication, the diamond-like carbon (DLC) film may be deposited on the surface of a substrate material for lubrication. The substrate material may include one or a combination of two or more of silicon wafers, carbon steel, and alloy steel. If the DLC film to be lubricated is a metal-doped or non-metallic DLC film, the DLC film may be first deposited on the substrate surface, and then the metal or non-metallic material may be doped into the DLC film to form a doped DLC film. In some specific embodiments, a transition layer may be applied to the substrate surface before the film is deposited, ensuring that the subsequent film fully covers the substrate surface and maintains the integrity of the film. The material of the substrate generally has no significant effect on the film's lubrication performance.

[0026] According to a specific embodiment of the present invention, the lubrication treatment can be to apply an oil-based lubricant to the surface of the diamond-like film. In some specific embodiments, the relative amount of the oil-based lubricant and the diamond-like film can be: 2 The surface of the diamond-like carbon film can be lubricated with 10μL-15μL of oil-based lubricant.

[0027] According to a specific embodiment of the present invention, when lubricating the friction pair including the diamond-like film, the contact surface of the diamond-like film and its counterpart material can be lubricated with an oil-based lubricant. The amount of the oil-based lubricant can be: 2 Apply 10μL-15μL of oil-based lubricant to the contact surface.

[0028] According to a specific embodiment of the present invention, the lubrication method may specifically include:

[0029] (1) Depositing a diamond-like carbon film on the surface of a substrate material;

[0030] (2) An oil-based lubricant is applied to the surface of the deposited diamond-like carbon film for lubrication.

[0031] The beneficial effects of the present invention include:

[0032] 1. The oil-based lubricant provided by the present invention can be used for lubrication of silicon-doped diamond-like carbon (DLC) films. By lubricating the DLC-Si film with the oil-based lubricant, an ultra-low friction coefficient and wear rate can be achieved on the DLC film, thereby improving the lubrication efficiency and service life of the DLC film. Compared with direct lubrication with PAO base oil or oleic acid, lubrication with the oil-based lubricant of the present invention can reduce the friction coefficient by more than 40%.

[0033] 2. The oil-based lubricant provided by the present invention is universal, easy to use, convenient to operate, and has a wide range of applications. It is of great significance for promoting the in-depth application of diamond-like carbon films in tribology. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The curves of the change of friction coefficient over time after the friction pair is lubricated with hexadecyl lactate / PAO6 oil-based lubricant and PAO6 base oil in Example 1 are shown.

[0035] Figure 2 This is a curve showing the change in friction coefficient over time when the friction pair is lubricated for one hour using hexadecyl lactate / PAO6 oil-based lubricant in Example 1.

[0036] Figure 3 The curves of the change of friction coefficient over time after the friction pair is lubricated with hexadecyl lactate / PAO6 oil-based lubricant, PAO6 base oil, and oleic acid in Example 2 are shown.

[0037] Figure 4 This is a wear test diagram of the wear spot after the tribological test in Example 2.

[0038] Figure 5 These are curves showing the change in friction coefficient over time after the friction pair is lubricated with hexadecyl lactate / PAO6 oil-based lubricant and ethanol monostearate / PAO6 oil-based lubricant in Example 3.

[0039] Figure 6 The curves of the change in friction coefficient over time after the friction pair is lubricated with ethyl salicylate / PAO2 oil-based lubricant, salicylic acid / PAO2 oil-based lubricant, and PAO2 base oil in Example 4 are shown.

[0040] Figure 7 This is a curve showing the change in friction coefficient over time after the friction pair is lubricated with lactic acid / ethylene glycol lubricant and ethyl lactate / ethylene glycol lubricant in Test Example 1.

[0041] Figure 8 These are the corrosion test results of the lactic acid / ethylene glycol lubricant and the ethyl lactate / ethylene glycol lubricant in Test Example 1.

[0042] Figure 9 This is a curve showing the change of friction coefficient over time after lubrication of the friction pair by the leaf alcohol lactate / PAO6 oil-based lubricant in Example 5.

[0043] Figure 10 This is a curve showing the change in friction coefficient over time after the friction pair is lubricated with hexadecyl lactate / PAO6 oil-based lubricant and octyl lactate / PAO6 oil-based lubricant in Example 6.

[0044] Figure 11 This is a curve showing the change in friction coefficient over time after the friction pair is lubricated with different concentrations of cetyl lactate / PAO6 oil-based lubricants in Example 7.

[0045] Figure 12 These are the results of the variable load tribological test of the cetyl lactate / PAO6 oil-based lubricant in Test Example 2.

[0046] Figure 13 These are the tribological test results of cetyl lactate / PAO6 oil-based lubricant lubricating different friction pair materials in Test Example 2. DETAILED DESCRIPTION

[0047] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0048] The DLC-Si film used in the following experiments has a C content of 95.63% by mass and a Si content of 4.37% by mass, which are the analysis results of an X-ray photoelectron spectroscopy (XPS) experiment.

[0049] In the following experiments, the method of lubricating the friction pair with lubricant is to apply the lubricant to the contact surface of the two mating materials in the friction pair. 2 The contact surface was coated with 15 μL of lubricant for lubrication; in other experiments, 1×1 cm 2 The contact surface was lubricated by applying 10 μL of lubricant.

[0050] Example 1

[0051] This embodiment provides an oil-based lubricant comprising a PAO6 base oil and cetyl lactate. The cetyl lactate accounts for 1 wt% of the oil-based lubricant, with the remainder being the PAO6 base oil. This is referred to as cetyl lactate / PAO6 oil-based lubricant.

[0052] This embodiment also provides a method for lubricating a diamond-like carbon film.

[0053] Among them, the preparation method of diamond-like carbon film includes: using silicon wafer as the base material, forming an amorphous carbon film (aC) with a thickness of about 1 μm on the surface of the base material by chemical deposition, and doping Si into the amorphous carbon film to obtain a silicon-doped diamond-like carbon film (DLC-Si).

[0054] The friction pair composed of the above DLC-Si and bearing steel (GCr15 steel) was used as the lubrication object. The contact surface (1×1 cm2 ) Apply 10 μL of oil-based lubricant to complete the lubrication treatment.

[0055] Pure PAO6 base oil was used as a control oil-based lubricant.

[0056] The tribological tests were conducted on the two oil-based lubricants mentioned above. The test conditions were as follows: the DLC-Si / bearing steel friction pair was lubricated with the two oil-based lubricants respectively, the tribological tests were conducted at room temperature and 60% RH, a bearing steel ball with a diameter of 10 mm, a rotation speed of 300 rpm, a rotation radius of 4 mm, and a normal load of 10 N. The results are shown in Figure 2. Figure 1 shown. Figure 1 The “PAO6” in the table is the test result of pure PAO6 base oil, and the “cetyl lactate” is the test result of cetyl lactate / PAO6 oil-based lubricant.

[0057] from Figure 1 As can be seen, the coefficient of friction (COF) for DLC-Si lubricated with a cetyl lactate / PAO6 base oil is 0.04, while the COF for lubricating with PAO6 alone without cetyl lactate is 0.07. Compared to pure PAO6 base oil, the COF reduction achieved with PAO6 lubricant containing cetyl lactate is over 40%.

[0058] Figure 2 The friction coefficient of the DLC-Si / bearing steel friction pair was tested with hexadecyl lactate / PAO6 oil-based lubricant for one hour. The test conditions were room temperature and 20% RH. The bearing steel ball with a diameter of 10 mm was used, the rotation speed was 300 rpm, the rotation radius was 4 mm, and the normal load was 10 N. Figure 2 It can be seen that the friction pair lubricated with the oil-based lubricant containing hexadecyl lactate can maintain a low friction coefficient within 1 hour, thereby increasing the service life of the friction pair.

[0059] Example 2

[0060] This embodiment provides an oil-based lubricant, which includes PAO6 base oil and cetyl lactate, wherein the cetyl lactate accounts for 1 wt% of the oil-based lubricant by weight, with the remainder being PAO6 base oil.

[0061] The oil-based lubricant, PAO6 base oil and pure oleic acid of this embodiment are used to lubricate the DLC-Si / bearing steel friction pair respectively, and the lubrication method is the same as that of Example 1.

[0062] The tribological test was carried out on the friction pair after lubrication. The test parameters were: room temperature, air humidity 60% RH, a bearing steel ball with a diameter of 10 mm, a rotation speed of 500 rpm, a rotation radius of 4 mm, and an applied normal load of 10 N. The results are as follows: Figure 3 shown.

[0063] from Figure 3 It can be seen that the minimum friction coefficient of pure PAO6 base oil is 0.06. The oil-based lubricant with cetyl lactate added provided in this embodiment has an even lower friction coefficient under the same conditions, reaching below 0.03. Compared with the minimum friction coefficient of pure PAO6 base oil, it is reduced by about 50%, and has a lubricating effect comparable to that of pure oleic acid, thus having a better friction-reducing effect.

[0064] The wear rate of DLC-Si after the friction test was calculated by observing the size of the wear spot under an optical microscope and then calculating the wear rate based on the spherical cap volume. The surface state and area of ​​the wear spot can be found in Figure 4 The wear volume of the wear spot lubricated with pure PAO6 base oil is calculated to be 118728.91 μm 3 The wear volume of the wear spot after lubrication with the oil-based lubricant in this embodiment is 194161.76μm 3 Compared with pure PAO6 base oil lubrication, the wear volume can be reduced by 38.85% when lubricated with the oil-based lubricant of this embodiment, indicating that adding the lubricating additive used in the present invention to the base oil can significantly reduce wear during the friction process and has a friction-reducing effect.

[0065] Example 3

[0066] This embodiment provides an oil-based lubricant composed of a lubricating additive and a lubricating base oil.

[0067] The lubricating additives are cetyl lactate and ethylene glycol monostearate, respectively; the lubricating base oil is PAO6 base oil; and the mass proportion of the lubricating additives in the oil-based lubricant is 1 wt %. These are denoted as cetyl lactate / PAO6 oil-based lubricant and ethylene glycol monostearate / PAO6 oil-based lubricant, respectively.

[0068] The friction pairs used for the test consisted of DLC-Si and bearing steel. The friction pairs were lubricated with the above-mentioned oil-based lubricants and then tribological tests were carried out.

[0069] The tribological test conditions are: room temperature, air humidity 60% RH, using a bearing steel ball with a diameter of 10mm, a rotation speed of 500rpm, a rotation radius of 4mm, and an applied normal load of 10N; the results are as follows Figure 5As shown, the experimental time of the sample with hexadecyl lactate as the lubricating additive is 1 hour, and the experimental time of the sample with ethylene glycol monostearate as the lubricating additive is 0.5 hour.

[0070] from Figure 5 It can be seen that the friction coefficient of the oil-based lubricant containing ethylene glycol monostearate is around 0.05, while the friction coefficient of the oil-based lubricant containing the alkyl ester of cetyl lactate is even lower, reaching 0.02-0.03, a 60% decrease in the friction coefficient of the oil-based lubricant containing ethylene glycol monostearate. This indicates that cetyl lactate, which contains both hydroxyl and ester groups, has a better lubricating effect than ethylene glycol monostearate, which contains only ester groups but no hydroxyl groups.

[0071] Example 4

[0072] This embodiment provides an oil-based lubricant composed of PAO2 base oil and ethyl salicylate. The ethyl salicylate accounts for 10 wt% of the oil-based lubricant, with the remainder being PAO2 base oil. This is referred to as an ethyl salicylate / PAO2 oil-based lubricant.

[0073] An oil-based lubricant obtained by replacing the ethyl salicylate with an equal amount of salicylic acid was used as a control sample and was designated as a salicylic acid / PAO2 oil-based lubricant.

[0074] Pure PAO2 base oil was used as the oil-based lubricant as another control sample.

[0075] The friction pairs used in the test were composed of DLC-Si and bearing steel, and the three oil-based lubricants mentioned above were used to lubricate the friction pairs. The tribological test parameters were as follows: room temperature, air humidity 60% RH, a bearing steel ball with a diameter of 10 mm, a rotation speed of 500 rpm, a rotation radius of 4 mm, and an applied normal load of 10 N. The results are shown in Figure 2. Figure 6 shown.

[0076] from Figure 6 It can be seen that, compared with the lubrication performance of PAO2 base oil alone, the addition of salicylic acid to the oil-based lubricant did not significantly improve the lubrication performance, while the addition of ethyl salicylate to the oil-based lubricant significantly enhanced the lubrication performance. This experimental result shows that for aromatic compounds, selecting molecules containing both ester and hydroxyl groups as oil-based lubricants can effectively improve the tribological performance of lubricants.

[0077] Test Example 1

[0078] This test example provides a comparative experiment on the lubricating effects of ethyl lactate and lactic acid.

[0079] Ethyl lactate was dissolved in ethylene glycol as a lubricating additive to obtain a lubricant, wherein the mass proportion of ethyl lactate in the lubricant was 20 wt %. This was recorded as an ethyl lactate / ethylene glycol lubricant.

[0080] A lubricant obtained by dissolving an equal amount of lactic acid in ethylene glycol instead of the above-mentioned ethyl lactate is called a lactic acid / ethylene glycol lubricant.

[0081] Using DLC-Si and bearing steel as the friction pair, the two lubricants were used to lubricate the friction pair. Tribological experiments were then conducted using the following parameters: room temperature, 60% humidity, a 10mm diameter bearing steel ball, a rotation speed of 500rpm, a rotation radius of 4mm, and a normal load of 10N. See the test results for details. Figure 7 .

[0082] from Figure 7 It can be seen that the ethyl lactate / ethylene glycol lubricant has a lower friction coefficient than the lactic acid / ethylene glycol lubricant. The only difference between ethyl lactate and lactic acid is that ethyl lactate contains both ester and hydroxyl groups, while lactic acid only contains hydroxyl groups. This shows that, given the same base solvent, using compounds with both hydroxyl and ester groups as additives can effectively improve lubrication compared to molecules with only hydroxyl groups.

[0083] This test also provides corrosion tests for ethyl lactate lubricants and lactic acid. Bearing steel was immersed in a lactic acid / ethylene glycol lubricant (LA) and an ethyl lactate / ethylene glycol lubricant (EL+EG) consisting of ethyl lactate and ethylene glycol, respectively. The lactic acid and ethyl lactate accounted for 20% by weight of the lactic acid / ethylene glycol lubricant, respectively. Figure 8 Figure 1 is the test results, where Figure a is a photograph of steel immersed in lactic acid / ethylene glycol lubricant and ethyl lactate / ethylene glycol lubricant for 2 days; Figure b is a photograph of steel immersed in lactic acid / ethylene glycol lubricant and ethyl lactate / ethylene glycol lubricant for 4 days; Figure c is a microscopic photograph of steel immersed in lactic acid / ethylene glycol lubricant for 4 days; Figure d is a microscopic photograph of steel immersed in ethyl lactate / ethylene glycol lubricant for 4 days.

[0084] from Figure 8 It can be seen that the steel surface immersed in the lactic acid / ethylene glycol lubricant shows obvious corrosion, while the steel surface immersed in the ethyl lactate / ethylene glycol lubricant is smoother and less corroded. These results show that compared to using lactic acid as a lubricant additive, using esterified lactic acid (lactate) as an additive not only improves lubrication but also reduces corrosion to the friction pair materials.

[0085] Example 5

[0086] This embodiment provides an oil-based lubricant comprising leaf lactate and PAO6 base oil. The leaf lactate comprises 10 wt% of the oil-based lubricant, with the remainder being PAO6 base oil. This is referred to as a leaf lactate / PAO6 oil-based lubricant.

[0087] A tribological test was performed on the oil-based lubricant of this embodiment, and the friction pair used in the test consisted of DLC-Si and bearing steel.

[0088] The tribological test process is as follows: the friction pair is lubricated with the oil-based lubricant of this embodiment, the room temperature and air humidity are 60% RH, a bearing steel ball with a diameter of 10 mm is used, the rotation speed is 500 rpm, the rotation radius is 4 mm, and the normal load is 10 N. The results are as follows Figure 9 As shown. Figure 9 It can be seen that using leaf lactate as a lubricant additive can improve the lubrication effect of PAO base oil, with the friction coefficient as low as around 0.06. This result shows that compounds with hydroxyl and ester groups added to base oil have a good friction-reducing effect.

[0089] Will Figures 5 to 9 The combined results show that, compared to compounds containing only hydroxyl groups but no ester groups (salicylic acid) and compounds containing only ester groups but no hydroxyl groups (ethanol monostearate), using aromatic compounds (ethyl salicylate) and aliphatic compounds (cetyl lactate, leaf lactate) containing both ester and hydroxyl groups as lubricant additives can effectively improve the lubrication properties of PAO base oils and reduce the friction coefficient. Furthermore, compared to compounds containing only hydroxyl groups, especially acidic compounds (lactic acid), using ester compounds containing both hydroxyl and ester groups can avoid corrosion of friction pair materials, thereby extending the life of the friction pair.

[0090] Example 6

[0091] This embodiment provides an oil-based lubricant composed of a lubricating additive and a lubricating base oil.

[0092] The lubricating additives were cetyl lactate and octyl lactate, respectively, and the oil-based lubricants were all PAO6 base oils. The lubricating additives accounted for 1 wt% of the oil-based lubricants, respectively, as cetyl lactate / PAO6 oil-based lubricants and octyl lactate / PAO6 oil-based lubricants.

[0093] The friction pair used for the test consisted of DLC-Si and bearing steel. The friction pair was lubricated with the above oil-based lubricant and tribological tests were carried out.

[0094] The tribological test conditions are: room temperature, air humidity 60% RH, using a bearing steel ball with a diameter of 10mm, a rotation speed of 800rpm, a rotation radius of 4mm, and an applied normal load of 10N; the results are as follows Figure 10 shown.

[0095] from Figure 10 As can be seen, the friction coefficient of the oil-based lubricant containing octyl lactate reaches 0.10-0.12, while the friction coefficient of the oil-based lubricant containing the alkyl ester of cetyl lactate is lower, reaching below 0.04 and even around 0.02. This represents a 60%-83% reduction in the friction coefficient of the oil-based lubricant containing octyl lactate. These results demonstrate that the lubrication effect of oil-based lubricants can be adjusted by adjusting the carbon number of lactate esters.

[0096] Example 7

[0097] This embodiment provides oil-based lubricants with different concentrations. The oil-based lubricants are composed of cetyl lactate and PAO6 base oil. The mass proportions of cetyl lactate in the oil-based lubricants are 0.5 wt%, 1 wt%, and 2 wt%, respectively.

[0098] Using DLC-Si and bearing steel as the friction pair, the friction pair was lubricated with the above oil-based lubricant, and then the tribological test was conducted using the following parameters: room temperature, air humidity 60% RH, a bearing steel ball with a diameter of 10mm, a rotation speed of 500rpm, a rotation radius of 4mm, and an applied normal load of 10N. The test results are shown in Figure 11 .

[0099] from Figure 11 The results show that when the concentration of cetyl lactate is between 0.5wt% and 1wt%, the coefficient of friction (COF) remains low, essentially below 0.07. When the concentration rises to 1.5wt%, the COF rises to 0.08-0.10. These results demonstrate that the lubricating properties of oil-based lubricants can be controlled by adjusting the ratio of lubricating additives to the lubricating oil.

[0100] Those skilled in the art will understand that, due to the influence of the production batches of friction pair materials, especially the manufacturing process of diamond-like carbon films, the absolute values ​​of the friction coefficients measured in tribological experiments of different batches of the same lubricant sample (such as oil-based lubricant, pure PAO base oil) will be different, but the tribological change trends and amplitudes measured in tribological experiments of different batches of the same lubricant sample are consistent.

[0101] Test Example 2

[0102] This test case provides a tribological test with variable load.

[0103] The oil-based lubricant used in the experiment consisted of cetyl lactate and PAO6 base oil, with cetyl lactate accounting for 1 wt%. The friction pair used in the experiment consisted of DLC-Si and bearing steel.

[0104] The friction pair was lubricated with 15 μL of the above oil-based lubricant and tribological tests were conducted using the following parameters: room temperature, 60% humidity, a 10 mm diameter bearing steel ball, a rotation speed of 500 rpm, a rotation radius of 4 mm, and normal loads of 3 N, 5 N, and 10 N, respectively. Figure 12 .

[0105] from Figure 12 It can be seen that the oil-based lubricant provided by the present invention has a low friction coefficient under different load conditions. In particular, when the load is 5N and 10N, the lubricating effect of the oil-based lubricant is more obvious, and the friction coefficient can reach below 0.06 or even below 0.05.

[0106] Test Example 3

[0107] This test case provides a tribological experiment of variable friction pair materials.

[0108] Bearing steel (GCr15 steel), SiO2, Si3N4, and Al2O3 are paired with DLC-Si to form friction pair materials steel / DLC-Si, SiO2 / DLC-Si, Si3N4 / DLC-Si, and Al2O3 / DLC-Si, respectively. Friction pair materials (steel / steel) formed by bearing steel and bearing steel are also provided.

[0109] An oil-based lubricant was prepared by mixing cetyl lactate with PAO6 base oil, wherein the mass proportion of cetyl lactate was 1.5 wt %. The oil-based lubricant was used to lubricate the friction pair materials respectively.

[0110] The test parameters are: room temperature, air humidity 60% RH, bearing steel ball with a diameter of 10mm, rotation speed of 500rpm, rotation radius of 4mm, and applied normal loads of 3N, 5N, and 10N respectively. Figure 13 .

[0111] from Figure 13 It can be seen that when using the same lubricant, the composition of the friction pair material has a significant impact on the lubrication effect: compared with SiO2, Si3N4, and Al2O3, the friction pair composed of bearing steel and DLC-Si has the lowest friction coefficient and the best lubrication effect.

[0112] In summary, the oil-based lubricant of the present invention can reduce the friction coefficient of the diamond-like carbon film to 0.03-0.04, or even to 0.02-0.03. Compared with pure PAO base oil, the oil-based lubricant with lubricating additives can reduce the friction coefficient by more than 40%, reduce wear, and significantly increase the service life.

Claims

1. A method for lubricating a diamond-like carbon film, wherein the method lubricates the diamond-like carbon film with a lubricant, wherein the lubricant comprises an oil-based lubricant; The oil-based lubricant includes a base lubricant and a lubricating additive. The molecules of the lubricating additive have an ester group and a hydroxyl group. The lubricating additive includes a lactate compound and / or a salicylate compound. The lactate compound includes one or a combination of two or more of butyl lactate, leaf lactate, and hexadecyl lactate. The salicylate compound includes ethyl salicylate. The mass proportion of the lubricating additive in the oil-based lubricant is 0.5wt%-30wt%. The base lubricant includes a PAO base oil and / or oleic acid.

2. The lubrication method according to claim 1, wherein: The PAO base oil includes PAO6 base oil and / or PAO2 base oil.

3. The lubrication method according to claim 1, wherein: The diamond-like film includes an undoped diamond-like film and / or a doped diamond-like film.

4. The lubrication method according to claim 3, wherein: The doped diamond-like film includes a metal-doped diamond-like film and / or a non-metallic element-doped diamond-like film.

5. The lubrication method according to claim 4, wherein: The diamond-like carbon film doped with non-metallic elements includes a diamond-like carbon film doped with silicon.

6. The lubrication method according to claim 5, wherein: In the silicon-doped diamond-like carbon film, the mass content of silicon is 1%-10%.

7. The lubrication method according to claim 4, wherein: The metal-doped diamond-like carbon film includes a chromium-doped diamond-like carbon film.

8. The lubrication method according to claim 7, wherein: In the chromium-doped diamond-like carbon film, the mass content of chromium is 1%-10%.

9. The lubrication method according to claim 1, wherein: The material used in conjunction with the diamond-like film includes one or a combination of two or more of the following: diamond-like film, carbon steel, alloy steel, and silicon nitride.

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