An ultralow friction system and its applications

Abstract

This invention provides an ultra-low friction system and its application, using a room-temperature ionic liquid as a lubricant and polyimide as a friction component. Its mating component is any one of GCr15 steel, silicon nitride (Si3N4), silicon carbide (SiC), or zirconium dioxide (ZrO2), achieving a friction coefficient of up to 0.001 during system sliding, resulting in an ultra-low friction phenomenon.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lubricating materials, and particularly relates to an ultralow-friction system and application thereof. BACKGROUND

[0002] Friction is a physical phenomenon occurring between moving surfaces. The microscopic friction surface is composed of many micro-convex peaks and valleys. During the contact movement, the surface of the object will be damaged, i.e. wear. The wear will accelerate the damage of mechanical parts and shorten the service life. Good lubrication is an important means to reduce friction and wear. About 30% of the global energy consumption is related to friction, so it is very important to reduce the friction and wear between mechanical parts through effective lubrication means. The design and development of new lubrication systems have always been a hot issue of common concern in the academic and industrial circles. As a new field of tribology, ultralow-friction behavior gradually enters the field of vision, and the design and construction of ultralow-friction system are particularly valued by people.

[0003] Ultralow friction refers to the friction behavior with a friction coefficient reaching the order of magnitude of 0.001 or less. Hirano et al. first proposed this ultralow friction phenomenon and calculated through theoretical derivation that the friction force between two completely clean and atomically smooth crystal surfaces in non-conformal contact may be zero. The generation of ultralow friction means that the loss caused by friction will be greatly reduced, but absolute ultralow friction is only an ideal state, which can only gradually approach this ideal state. Ultralow friction can be generally divided into two categories, namely solid ultralow friction and liquid ultralow friction. Solid ultralow friction is to use powder, film or solid composite material as lubricating medium to make the lubrication state of two relative motion surfaces in ultralow friction. At present, most of the materials that can realize solid ultralow friction are two-dimensional materials with layered or sheet structure, such as some single elements, sulfides, nitrides, fluorides and part of selenides. The interlayer interaction of such solid material structure is very weak and can realize non-conformal contact, which provides the necessary conditions for realizing solid ultralow friction. At present, the lubrication mechanism of two-dimensional materials mainly includes surface non-conformal contact, weak interaction and coulomb repulsion. Compared with solid ultralow friction, liquid ultralow friction has less restrictions and can realize ultralow friction under macroscopic conditions.

[0004] Polyimide (PI) is a class of organic polymers containing imide bonds, typically polymerized from diamines and dianhydrides. The aromatic heterocyclic structure of the main molecular chain of polyimide materials is highly stable, exhibiting excellent heat resistance. Even under extreme conditions such as high temperature, high pressure, or high speed operation, it retains excellent friction-reducing and wear-resistant properties, making it one of the most thermally stable polymers to date. Due to its excellent tribological properties, it is often used as a self-lubricating material. Compared to dry friction, water lubrication and oil lubrication generally result in lower coefficients of friction and wear rates for polyimides. Given the excellent properties of polyimide, it is also frequently used in basic industries to manufacture bearings, such as as the main bearing material in hybrid friction pairs to prevent seizing in moving mechanisms, aiming to achieve high precision, high performance, low noise, and long lifespan in bearings. Composite bearings using polyimide as the friction element can have various choices for their mating materials, such as metals or ceramics.

[0005] GCr15 steel is also a very typical bearing material. It refers to high-carbon chromium bearing steel, whose main components are carbon, chromium, manganese, silicon, tungsten, and other elements. It is a bearing steel with excellent comprehensive performance. After quenching and tempering, GCr15 steel has high and uniform hardness, high wear resistance, high contact fatigue strength, and good hot workability, making it a high-performance bearing material. GCr15 steel is widely used in the manufacture of molds, precision measuring tools, and other mechanical parts requiring high wear resistance, high elastic limit, and high contact fatigue strength. It is also commonly used in the manufacture of steel balls, rollers, and bushings on the drive shafts of high-speed and / or heavy-duty equipment such as internal combustion engines, electric locomotives, machine tools, tractors, rolling mill equipment, drilling rigs, railway vehicles, and mining machinery.

[0006] Hybrid ceramic bearings are a typical example of the widespread application of engineering ceramics in the industrial field and have received high attention from many countries. Hybrid ceramic bearings generate less heat through friction, especially at high speeds, which helps extend bearing life and reduces the intervals between lubrication media additions, significantly reducing downtime losses and increased maintenance costs associated with bearing repairs. Simultaneously, the small elastic deformation of ceramics ensures good operational accuracy of machine tools using hybrid ceramic bearings. Silicon nitride, silicon carbide, and zirconium dioxide are common ceramic bearing materials. Silicon nitride has an octahedral structure and is an atomic crystal: the two vertices are Si, the four N atoms are the four points on the central plane of the octahedron, and the center of the plane formed by these four N atoms is the third Si atom. Each Si atom is connected to four N atoms, and each N atom is connected to three silicon atoms; there are no connections between N, N, and N atoms. Silicon nitride is an important structural ceramic material with high hardness, lubricity, wear resistance, oxidation resistance, and stable performance at high and low temperatures, and is commonly used in bearing manufacturing. Silicon carbide crystal structures are divided into hexagonal or rhombohedral α-SiC and cubic β-SiC (called cubic silicon carbide). Silicon carbide ceramics possess high hardness and excellent high-temperature strength, wear resistance, chemical corrosion resistance, and thermal shock resistance. As a high-temperature wear-resistant structural material, it has found increasingly widespread applications, such as in various mechanical seals and high-temperature structural components. Furthermore, as a material, silicon carbide has better flexibility than silicon nitride, while silicon nitride exhibits better wear resistance. Zirconia has three crystal forms: monoclinic below 1373 K, tetragonal between 1373 and 2173 K, and cubic above 2173 K. Its chemically inert properties, high melting point, high resistivity, high refractive index, and low coefficient of thermal expansion make it an important high-temperature and corrosion-resistant material.

[0007] In ionic compounds, the interaction force between cations and anions is called the Coulomb force. Its magnitude depends on the charge quantity and radius of the cations and anions; the larger the ionic radius, the smaller the Coulomb force, and the lower the melting point of the compound. If the cations and anions of an ionic compound are very large, the structure becomes loose, and the interionic force is low, resulting in a melting point close to room temperature. Despite this, ionic liquids still possess good electrical conductivity. Currently, ionic liquids are widely studied as lubricating media in the field of tribology. Furthermore, ionic liquids, as lubricant components, undergo hydration ionization in polyol aqueous solutions. Combined with the surface polishing and self-healing effects of hydroxylated boron nitride nanosheets, macroscopic ultra-low friction behavior of the liquid at the steel / steel interface under point-to-point contact under high loads and high speeds has been achieved.

[0008] In recent years, to reduce greenhouse gas emissions and improve the global ecological environment, countries around the world have vigorously promoted the development of the new energy vehicle industry, with electric vehicles being a key focus. The most critical component of an electric vehicle is the motor, and motor bearings are crucial parts of the motor. With changing operating conditions, the stability and durability of bearings are major issues that electric vehicles must address, and electrolytic corrosion is a problem that motor bearings must be carefully considered. Using conductive lubricating media to solve bearing electrolytic corrosion problems offers advantages such as simple design, minimal optimization modifications, low cost, and efficient reduction of shaft voltage.

[0009] Although polyimide, GCr15 steel, silicon nitride, silicon carbide, or zirconium dioxide are widely used in the mechanical field, no ultra-low friction phenomenon or technical application has yet been found when ionic liquids are used alone as lubricants. Summary of the Invention

[0010] To address the shortcomings of the existing technologies, this invention provides an ultra-low friction system and its application, achieving a friction coefficient down to the order of 0.001 and generating ultra-low friction phenomena.

[0011] The technical solution provided by this invention is an ultra-low friction system, wherein the ultra-low friction system uses room temperature ionic liquid as lubricant and GCr15 steel / polyimide, silicon nitride / polyimide, silicon carbide / polyimide or zirconium dioxide / polyimide as friction pairs.

[0012] Furthermore, the room temperature ionic liquid is selected from ionic liquids that are in a liquid state at room temperature (20°C).

[0013] Furthermore, the polyimide is a PMDA (pyromellitic dianhydride)-ODA (4,4'-oxybisbenzenamine) type polyimide.

[0014] The application of room temperature ionic liquids in ultra-low friction systems involves using room temperature ionic liquids as lubricants and GCr15 steel / polyimide, silicon nitride / polyimide, silicon carbide / polyimide, or zirconium dioxide / polyimide as friction pairs to form ultra-low friction systems.

[0015] Furthermore, the room-temperature ionic liquid is selected from either 1-hexyl-3-methylimidazolium chloride or 1-hexyl-3-methylimidazolium tetrafluoroborate.

[0016] Furthermore, using room-temperature ionic liquids as lubricants for mechanical components, polyimide is paired with any one of GCr15 steel, silicon nitride, silicon carbide, or zirconium dioxide to form the material of the mechanical components. In this case, the room-temperature ionic liquid acts as the lubricating medium, resulting in ultra-low friction behavior in the friction system.

[0017] Ionic liquids are liquids composed entirely of ions. Substances composed of free ions that are liquid at or near room temperature are called room-temperature ionic liquids. In existing technologies, the super-lubricating phenomenon of ionic liquids is due to the hydration and ionization of the ionic liquid as a lubricant component in a polyol aqueous solution system, combined with the surface polishing and self-healing effects of nanomaterials. This invention uses a pure room-temperature ionic liquid as a lubricant, eliminating the need for water. When GCr15 steel / polyimide, silicon nitride / polyimide, silicon carbide / polyimide, or zirconium dioxide / polyimide are used as friction pairs, it achieves ultra-low friction behavior, avoiding problems such as corrosion caused by moisture affecting the service life of mechanical parts. Simultaneously, ionic liquids possess excellent electrical and tribological properties, making them potential as conductive lubricating media in motor bearings. Attached Figure Description

[0018] Figure 1 This is the molecular structural formula of the PMDA-ODA type polyimide material used in this invention;

[0019] Figures 2-(a), 2-(b), and 2-(c) show the changes in point-to-surface contact friction coefficients over time when the ionic liquid 1-hexyl-3-methylimidazolium chloride is used to lubricate GCr15 / PI (PMDA-ODA), Si3N4 / PI (PMDA-ODA), and ZrO2 / PI (PMDA-ODA) pairs, respectively.

[0020] Figures 3-(a), 3-(b), 3-(c), and 3-(d) show the changes in point-to-surface contact friction coefficients over time when the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate is used to lubricate GCr15 / PI (PMDA-ODA), Si3N4 / PI (PMDA-ODA), SiC / PI (PMDA-ODA), and ZrO2 / PI (PMDA-ODA) pairs, respectively.

[0021] Figure 4 This is a graph showing the change of friction coefficient over time at different rotational speeds in point-to-surface contact of the GCr15 / PI (PMDA-ODA) pair lubricated with the ionic liquid 1-hexyl-3-methylimidazolium chloride.

[0022] Figure 5 This is a graph showing the change of the point-to-surface contact friction coefficient over 10 hours in the SiC / PI (PMDA-ODA) pair lubricated by the ionic liquid 1-hexyl-3-methylimidazolium chloride of this invention.

[0023] Figure 6 This is a graph showing the change of friction coefficient over time in point-to-surface contact under different loads when using the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate to lubricate Si3N4 / PI (PMDA-ODA) pair.

[0024] Figure 7 This is a graph showing the change of the point-to-surface contact friction coefficient over 10 hours when the Si3N4 / PI (PMDA-ODA) pair is lubricated with the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate. Detailed Implementation

[0025] The technical solutions of the present invention will now be clearly and completely described in conjunction with specific embodiments and accompanying drawings.

[0026] In the following examples, a UTM-3 micro-friction testing machine (Brück, Germany) was used for micro-friction testing. During the test, the test temperature was 25°C. A test ball (4.76 mm in diameter, made of GCr15 steel, silicon nitride, silicon carbide, or zirconium dioxide) was used as the static specimen. PMDA-ODA type polyimide material was attached to a fixed disk as the rotating disk specimen, rotating clockwise at a corresponding speed. The radius of the annular friction path was 8.5 mm. The test load was applied perpendicularly through the centerline of the ball specimen, and the test was conducted in a point-to-surface contact mode. With the appropriate load applied, 0.1-0.2 mL of lubricant was added dropwise between the test ball and the PMDA-ODA type polyimide material. During the test, the coefficient of friction (COF) was automatically recorded by the computer, and then the average coefficient of friction was calculated by software.

[0027] Example 1

[0028] Using the ionic liquid 1-hexyl-3-methylimidazolium chloride (C 10 H 19 ClN2 was used as a lubricant in the motion system of GCr15 / PI (PMDA-ODA), Si3N4 / PI (PMDA-ODA), and ZrO2 / PI (PMDA-ODA) pairs. Under a 5N load, the friction coefficient was tested at 200 rpm clockwise in a point-to-surface contact manner for three cycles of 3600 s each on different friction pairs. The variation of the friction coefficient over time is shown in Figure 2, where the 5N-C... 10 H 19 ClN2-GCr15 / PI(PMDA-ODA) / 200rpm-1 represents the coefficient of friction versus time during the first cycle of rotation at 200rpm with 1-hexyl-3-methylimidazolium chloride lubrication and the GCr15 / PI(PMDA-ODA) pair under a 5N load. 10 H 19 ClN2-GCr15 / PI(PMDA-ODA) / 200rpm-2,5N-C 10 H 19ClN2-Si3N4 / PI(PMDA-ODA) / 200rpm-1, etc., and so on.

[0029] The average friction coefficient for each running cycle of the process is recorded in Table 1. The friction systems using the ionic liquid 1-hexyl-3-methylimidazolium chloride as lubricant were all in an ultra-low friction state during the test.

[0030] Table 1. Average coefficients of friction for different friction pair systems lubricated with 1-hexyl-3-methylimidazolium chloride under a load of 5 N and a rotation speed of 200 rpm.

[0031]

[0032] Example 2

[0033] Using the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate (C 10 H 19 Tribological tests were conducted on GCr15 / PI (PMDA-ODA), Si3N4 / PI (PMDA-ODA), SiC / PI (PMDA-ODA), and ZrO2 / PI (PMDA-ODA) pairs using BF4N2 as a lubricant, with other test conditions the same as in Example 1. The friction coefficient of the system as a function of time is shown in Figure 3. The average friction coefficient for each running cycle of this process is recorded in Table 2. The friction systems using the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate as lubricant all exhibited ultra-low friction during the test.

[0034] Table 2. Average coefficients of friction for different friction pair systems lubricated with 1-hexyl-3-methylimidazolium tetrafluoroborate under a load of 5 N and a rotation speed of 200 rpm.

[0035]

[0036] Example 3

[0037] Under a load of 5 N, using 1-hexyl-3-methylimidazolium chloride as a lubricant, several cycles of testing were conducted on the same GCr15 / PI (PMDA-ODA) friction pair in a point-to-surface contact manner. The initial speed was 50 rpm, each cycle lasted 3600 s, and the speed was increased by 50 rpm in each subsequent cycle until it reached 300 rpm. The results of the friction coefficient versus speed and time curve of the system with 1-hexyl-3-methylimidazolium chloride as the lubricant are shown below. Figure 4 As shown in Table 3, the average friction coefficient of this process is recorded. Throughout this process, the system remains in an ultra-low friction state.

[0038] Table 3 shows the average coefficient of friction for the GCr15 / PI (PMDA-ODA) system lubricated with 1-hexyl-3-methylimidazolium chloride as the friction pair under a load of 5 N and different rotational speeds.

[0039]

[0040] Example 4

[0041] With a load of 5 N and a rotational speed of 200 rpm, using 1-hexyl-3-methylimidazolium chloride as a lubricant, a long-term wear test of 3600 s for 10 cycles was conducted on the same SiC / PI (PMDA-ODA) friction pair. The results of the friction coefficient change over 10 hours with 1-hexyl-3-methylimidazolium chloride as the lubricant are shown below. Figure 5 As shown, the friction coefficient of the system is less than 0.01, and the system is in an ultra-low friction state throughout the test time.

[0042] Table 4 shows the average coefficient of friction for a SiC / PI (PMDA-ODA) system lubricated with 1-hexyl-3-methylimidazolium chloride as the friction pair under a load of 5 N and a speed of 200 rpm.

[0043]

[0044] Example 5

[0045] Using 1-hexyl-3-methylimidazolium tetrafluoroborate as a lubricant, and rotating at 200 rpm, a multi-cycle test was conducted on a Si3N4 / PI (PMDA-ODA) friction pair in a point-to-surface contact manner. The initial load was 5 N, and each cycle lasted 3600 s. The load was increased by 10 N in each subsequent cycle until the polyimide film reached its load-bearing capacity and ruptured (the polyimide film ruptured at a load of 55 N). The friction coefficient as a function of load in point-to-surface contact with 1-hexyl-3-methylimidazolium tetrafluoroborate as the lubricant is shown in the figure below. Figure 6 As shown in Table 5, the average friction coefficient of this process is recorded. The friction coefficient is on the order of 0.001 throughout the process, indicating that the friction system is in an ultra-low friction state.

[0046] Table 5. Average coefficient of friction for Si3N4 / PI (PMDA-ODA) systems lubricated with 1-hexyl-3-methylimidazolium tetrafluoroborate as the friction pair at 200 rpm under different loads.

[0047]

[0048] Example 6

[0049] Using 1-hexyl-3-methylimidazolium tetrafluoroborate as a lubricant, a long-term wear test of 3600 s for 10 cycles was conducted on the same Si3N4 / PI (PMDA-ODA) friction pair at a rotational speed of 200 rpm and a load of 5 N. The results of the friction coefficient change over 10 hours with 1-hexyl-3-methylimidazolium tetrafluoroborate as the lubricant are shown below. Figure 7 As shown in Table 6, the friction coefficient of the system is less than 0.01, and the system is in an ultra-low friction state during the test time.

[0050] Table 6 shows the average coefficient of friction for a Si3N4 / PI (PMDA-ODA) system lubricated with 1-hexyl-3-methylimidazolium tetrafluoroborate as the friction pair at a rotational speed of 200 rpm and a load of 5 N.

[0051]

[0052]

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An ultra-low friction system, characterized by: The super low friction system is that room temperature ionic liquid is used as lubricant, PMDA-ODA type polyimide is used as friction part, and the counter part of the polyimide is any one of silicon nitride, silicon carbide or zirconium dioxide.

2. Use of a room temperature ionic liquid in an ultra-low friction system, characterized in that: The super low friction system is that room temperature ionic liquid is used as lubricant, PMDA-ODA type polyimide is used as friction part, and the counter part of the polyimide is any one of silicon nitride, silicon carbide or zirconium dioxide.

3. Use of a room temperature ionic liquid according to claim 2 in an ultra-low friction system, characterized in that: The super low friction system is that room temperature ionic liquid is used as lubricant, PMDA-ODA type polyimide is used as friction part, and the counter part of the polyimide is any one of silicon nitride, silicon carbide or zirconium dioxide.

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