Film formation method and lubricating oil composition

Abstract

A method of forming a coating film according to the present invention forms a coating film on a sliding surface of a sliding member, the method of forming a coating film comprising: a first contact step of bringing tungsten disulfide into contact with the sliding surface by supplying a lubricating oil composition containing the tungsten disulfide to the sliding surface; and a second contact step of bringing a silane compound, which is a dialkoxysilane, a trialkoxysilane, a tetraalkoxysilane, or a polymer or copolymer thereof, into contact with the sliding surface.

Description

Technical Field

[0001] This invention relates to a coating formation method for sliding components and a lubricating oil composition.

[0002] This application claims priority based on Japanese Patent Application No. 2021-145702, filed on September 7, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Mechanical components such as rolling bearings or gears have sliding parts that bear repeated loads. The sliding surfaces formed on these sliding parts are in a rolling lubrication state and have a finite fatigue life under surface pressure conditions exceeding the fatigue limit under repeated loads. The design life is set considering this finite fatigue life and also taking into account a safety factor. However, for example, in cases where the lubrication condition of the component deteriorates, or scratches or rust form on the sliding surfaces due to foreign matter, or a higher-than-expected load is applied, there is a concern that damage may occur within a shorter time than the set fatigue life. When damage such as surface roughness, cracking, or peeling occurs on the sliding surfaces, it can cause failure, or the damage may progress to spalling, thus requiring replacement of the component.

[0004] When damage occurs on the sliding surface, measures to suppress spalling without replacing the parts can include changing the lubricating oil, removing wear powder or peeling fragments by rinsing, or limiting operating conditions.

[0005] The inventors have proposed a method that first uses a surface protective oil containing lubricating oil and silane compounds to form a coating on a sliding surface based on the reaction of silane compounds, and then uses this coating to cover the damaged area, thereby inhibiting the development of damage (Patent Document 1).

[0006] Previous technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-164595 Summary of the Invention

[0009] The technical problem to be solved by the invention

[0010] The method described in Patent Document 1 has the advantage of being able to suppress the development of damage through a simple method, but further improvement in the suppression effect is required.

[0011] In view of the above, the object of the present invention is to further improve the suppression of damage generated in the sliding surface of the sliding component.

[0012] means for solving technical problems

[0013] To achieve the above objectives, one aspect of the coating forming method according to the present invention involves forming a coating on the sliding surface of a sliding component. The coating forming method comprises: a first contact step, wherein a lubricating oil composition containing tungsten disulfide is supplied to the sliding surface, thereby bringing the tungsten disulfide into contact with the sliding surface; and a second contact step, wherein a dialkoxysilane, a trialkoxysilane, a tetrakoxysilane, or a silane compound as a polymer or copolymer thereof is brought into contact with the sliding surface.

[0014] Furthermore, one embodiment of the lubricating oil composition involved in this invention comprises: a lubricating base oil; tungsten disulfide; and a lubricating oil composition comprising a dialkoxysilane, a trialkoxysilane, a tetrakoxysilane, or a silane compound as a polymer or copolymer thereof, wherein the concentration of the tungsten disulfide in the lubricating oil composition is 0.01 to 5% by mass, and the mass ratio of the silane compound to the tungsten disulfide is 0.3 to 0.5.

[0015] Invention Effects

[0016] According to one aspect of the coating forming method of the present invention, a coating is formed covering the sliding surface of the sliding member, thereby suppressing cracking of the sliding surface and suppressing the development of cracks even if cracks occur on the sliding surface, thereby extending the peeling life.

[0017] Furthermore, by forming a coating on the sliding surface using the lubricating oil composition involved in this invention, cracking and crack development on the sliding surface can be suppressed, thereby extending the peeling life. Attached Figure Description

[0018] Figure 1 This is a process diagram of a coating formation method according to one embodiment.

[0019] Figure 2 This is a schematic cross-sectional view showing the cross-section of the sliding component that has been coated by the above-described coating forming method.

[0020] Figure 3A This is a schematic cross-sectional view illustrating the behavior of cracking when the additive enters the crack formed on the sliding surface through the above-mentioned coating method.

[0021] Figure 3B This is a line graph showing the stress amplitude generated around the crack when the additive enters the crack through the above-mentioned coating formation method.

[0022] Figure 4 This is a schematic diagram illustrating the reaction of forming a coating on a sliding surface in a coating forming method according to one embodiment.

[0023] Figure 5This is a schematic diagram illustrating the reaction of forming a coating on a sliding surface in a coating forming method according to one embodiment.

[0024] Figure 6 This is a schematic diagram illustrating the reaction of forming a coating on a sliding surface in a coating forming method according to one embodiment.

[0025] Figure 7 This is a process diagram of a coating formation method according to one embodiment.

[0026] Figure 8 This is a process diagram of a coating formation method according to one embodiment.

[0027] Figure 9 It is a line graph showing the relationship between the concentration of silane compounds added to the lubricating base oil and the kinematic viscosity of the gear oil.

[0028] Figure 10 This is a graph showing the time until peeling occurs for each test case involved in the comparative examples and several embodiments.

[0029] Figure 11A The image shows a real photograph of a sliding surface that has developed cracks.

[0030] Figure 11B This is a graph showing the analytical results of tungsten disulfide and silane compounds contained in the cracks.

[0031] Figure 12A This is a schematic cross-sectional view showing the behavior of the additive, which is used as a comparative example, in the area surrounding the crack when it does not enter the crack.

[0032] Figure 12B This is a line graph showing the stress amplitude generated in the area surrounding the crack when the additive used as a comparative example did not enter the crack. Detailed Implementation

[0033] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. The dimensions, materials, shapes, and relative arrangements of the structural components described or illustrated in these embodiments are not intended to limit the scope of the present invention, but are merely illustrative examples.

[0034] For example, expressions such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" that indicate relative or absolute configuration not only indicate such configuration in a strict sense, but also indicate a state of relative displacement by an angle or distance with tolerance or to the extent that the same function can be obtained.

[0035] For example, expressions such as "same," "equal," and "homogeneous" that indicate things are in the same state not only mean that they are the same in a strict sense, but also that there are differences in the degree to which they can achieve the same function.

[0036] For example, the descriptions of shapes such as quadrilaterals and cylinders not only refer to quadrilaterals and cylinders in a strict geometric sense, but also include shapes with concave and convex parts, chamfers, etc., within the range where the same effect can be obtained.

[0037] On the other hand, the expression "possessing," "setting up," "including," "containing," or "having" a constituent element is not an exclusive expression that excludes the existence of other constituent elements.

[0038] Figure 12A This is a schematic cross-sectional view of a sliding component 100 in a mechanical component such as a rolling bearing or gear, which bears repeated loads. Figure 12A The sliding surface 100a of the sliding member 100 shown is a conventional sliding surface 100a that has not implemented the coating formation method involved in the present invention, and shows a state in which cracks Cr are generated due to repeated loads L from the sliding member 102. Figure 12B This is a line graph representing the amplitude of the repetitive stress σ generated in the crack periphery region due to the repetitive load L borne by the sliding component 102. When the mechanical component is a rolling bearing, the sliding component 100 is, for example, a race (inner ring, outer ring), and the sliding component 102 is a rolling element.

[0039] Figure 12A The conventional sliding surface 100a, as shown, experiences high oil film pressure inside the crack Cr due to the sliding of the opposing sliding component 102 through the opening of the crack Cr, and the area surrounding the crack is subjected to a large repetitive load L. In this figure, the dashed line Cri represents the position of the crack Cr on the sliding surface 100a before it bears the load from the opposing sliding component 102. The crack Cr elastically deforms to the position of the solid line Cro due to the load borne by the opposing sliding component 102.

[0040] exist Figure 12B In the diagram, the horizontal axis represents time, tb represents the time period before the opposing sliding component 102 passes through the crack Cr, and ta represents the time period after the opposing sliding component 102 passes through the crack Cr. When the opposing sliding component 102 passes through the opening of the crack Cr, the area surrounding the crack undergoes elastic deformation, thereby generating a large-amplitude repetitive stress σ in the area surrounding the crack in the sliding component 100. There is a concern that this repetitive stress σ may accelerate the development of the crack Cr.

[0041] Figure 1 This is a process diagram illustrating one embodiment of the coating formation method according to the present invention. Figure 2This is a schematic cross-sectional view of the sliding surface 100a of the sliding member 100 in which the coating forming method is implemented.

[0042] exist Figure 1 In the first contact step S10, a lubricating oil composition containing at least tungsten disulfide as the lubricating base oil is supplied to the sliding surface 100a. This brings the tungsten disulfide into contact with the sliding surface 100a. Furthermore, in the second contact step S12, a dialkoxysilane, a trialkoxysilane, a tetrakoxysilane, or a silane compound as a polymer or copolymer thereof is brought into contact with the sliding surface 100a.

[0043] Therefore, as Figure 2 As shown, the components contained in the silane compound and lubricating oil composition react with the components constituting the sliding surface 100a to form a tungsten disulfide-containing coating f on the sliding component 100. This coating f protects the sliding surface 100a, thereby suppressing damage to the sliding surface 100a. Furthermore, in the event of initial damage to the sliding surface 100a, large-diameter, high-density, and high-hardness tungsten disulfide particles enter the cracks Cr formed due to the initial damage. These tungsten disulfide particles entering the cracks Cr suppress the oil film pressure generated by the opposing sliding component 102 passing through the opening of the cracks Cr, and suppress elastic deformation in the crack periphery region caused by repeated loads L borne by the opposing sliding component 102, thereby reducing the stress amplitude σ generated in the crack periphery region. The silane compound forms the coating f and acts as an adhesive that bonds the particles together and retains them within the cracks Cr. Through the synergistic effect of these two additives, the spalling life from initial damage leading to spalling can be extended.

[0044] In one embodiment, the tungsten disulfide and silane compound are composed of nanoparticles with a particle size of less than 1 μm. These nanoparticles have, for example, a particle size of 1 to several hundred nm. Thus, due to their small particle size, they can easily enter the cracked Cr, thereby increasing the filling rate of these particles within the cracked Cr.

[0045] The particle size of silane compound nanoparticles is smaller than that of tungsten disulfide nanoparticles. Therefore, it is easier to surround large-diameter tungsten disulfide nanoparticles with small-diameter silane compound nanoparticles inside cracked Cr, thereby improving the adhesive effect of silane compounds.

[0046] exist Figure 2 In this context, the larger particles are tungsten disulfide nanoparticles (Pn), while particles smaller than Pn represent silane compound nanoparticles (Ps). For example, the particle size of Pn nanoparticles is approximately 100 times that of Ps silane compound nanoparticles.

[0047] Figure 3A This is a schematic cross-sectional view illustrating the behavior of the cracked Cr when nanoparticles Pn and Ps enter the cracked Cr in the above embodiment. The surrounding region of the cracked Cr where nanoparticles Pn and Ps have entered is shown in the diagram. Figure 12A The elastic deformation shown is suppressed. Figure 3B It shows Figure 3A The stress amplitude σ generated in the surrounding region of the cracked Cr shown. Figure 3A and Figure 3B In the embodiments shown, such as Figure 12A and Figure 12B As shown, compared with the case where no coating f is formed and no tungsten disulfide and silane compound particles enter the interior of the cracked Cr, the elastic deformation of the cracked Cr is suppressed, and the stress amplitude σ generated in the surrounding area of ​​the crack is also smaller.

[0048] The lubricating base oil contained in the lubricating oil composition is an oil, such as mineral oil, polyalphaolefin, polyol ester, etc. Furthermore, the viscosity grade is preferably VG32 to VG680.

[0049] As described above, the silane compound may be a dialkoxysilane, a trialkoxysilane, a tetrakoxysilane, or a polymer or copolymer thereof. When the silane compound is a polymer or copolymer, the number of monomers is preferably 5 or less. The two or more alkoxy groups in the silane compound may be the same or different. The number of carbon atoms in the alkoxy groups is preferably 1 to 3. When the silane compound is a dialkoxysilane or a trialkoxysilane, one or two hydrogen atoms or any functional group other than alkoxy groups are bonded to the silicon atoms of the silane compound.

[0050] The mechanism by which a coating f is formed on the sliding surface 100a through a reaction between a silane compound and the components constituting the sliding surface 100a will be explained below. Here, the case where tetraethoxysilane ((C2H5O)4Si) is used as the silane compound will be explained. The coating f is formed on the sliding surface 100a by hydrolyzing and polycondensing the silane compound contained in the lubricating oil composition while the lubricating oil composition is in contact with the sliding surface 100a.

[0051] That is, such as Figure 4 As shown, lubricating oil composition 1 comprises silane compound 10 (here, tetraethoxysilane (C2H5O)4Si) and water (H2O). The water is added as water or an impurity contained in lubricating oil composition 1. Silane compound 10 reacts with water to undergo hydrolysis. For example... Figure 5As shown, silane compound 10 is hydrolyzed into substance 10A and substance 10B. Substance 10A is a substance containing Si and OH groups, with the Si and OH groups bonded together. Substance 10A is tetrasilanol (Si(OH)4). Substance 10B is an organic compound obtained by removing substance 10A from silane compound 10 and water; it is ethanol (C2H5OH). Furthermore, in... Figure 4 and Figure 5 For ease of explanation, only one instance of silane compound 10 and water are described in the text, but in reality, multiple instances exist.

[0052] Here, as Figure 4 and Figure 5 As shown, the sliding member 100 is capped with an OH group. That is, the sliding member 100 has a sliding surface 100a made of a metal oxide (in this case, Fe2O3). 3、 It is formed from iron oxides such as Fe3O4, and is therefore capped by OH groups. In other words, OH groups are present on the sliding surface 100a of the sliding component 100. The first substance 10A here is a tetrasilanol, which is an unstable substance and readily reacts. Therefore, the first substance 10A reacts with the OH groups on the sliding surface 100a to undergo condensation polymerization, which is a dehydration condensation polymerization, such as... Figure 6 As shown, siloxane bonds (bonding of Si and O groups) are generated. That is, the OH groups bonded to the Si groups contained in the first substance 10A undergo dehydration polycondensation, and the Si groups bond to the Fe contained in the sliding member 100 via the O groups. Therefore, a coating f containing Si and O is formed on the sliding surface 100a of the sliding member 100.

[0053] Furthermore, the first substance 10A also undergoes dehydration condensation polymerization with other substances 10A. In other words, the hydrolyzed silane compounds 10 also undergo dehydration condensation polymerization with each other. That is, the Si groups of the first substance 10A are also bonded to the Si groups of other substances 10A via O groups. Therefore, the coating f is formed to include bonds between multiple Si groups and O groups, with the Si groups bonded to the Fe of component A via O groups, and forming a structure in which the Si groups are bonded to each other via O groups. Therefore, the coating f can be formed into a thick film. In addition, Figure 6 The structure (chemical composition) of the coating f in the example is that it may also be bonded with Si groups.

[0054] In one implementation, such as Figure 7 As shown, the second contact step S12 is performed after the first contact step S10, and the lubricating oil composition used in the first contact step S10 does not contain silane compounds.

[0055] In this embodiment, after the first contact step S10, in which tungsten disulfide contacts the sliding surface 100a, the second contact step S12, in which the silane compound contacts the sliding surface 100a, occurs. Therefore, the tungsten disulfide contacts the sliding surface 100a before the silane compound. Consequently, large-sized tungsten disulfide particles with high density and high hardness can enter the cracked Cr without being hindered by silane compound particles. Therefore, as... Figure 2 As shown, by introducing a sufficient amount of tungsten disulfide particles into the cracked Cr, the oil film pressure generated by the sliding component 102, such as the rolling element, through the cracked Cr can be prevented from acting on the interior of the crack. Furthermore, it can suppress elastic deformation in the area surrounding the crack, thereby reducing the stress amplitude σ generated in the area surrounding the crack. Thus, the crack development suppression effect can be improved, significantly extending the spalling life of the sliding component 100.

[0056] In the embodiments described later, test 3 is equivalent to this implementation.

[0057] In this embodiment, in the second contact step S12 where the silane compound comes into contact with the sliding surface 100a, the silane compound may be made to come into direct contact with the sliding surface 100a without being mixed with the lubricating base oil, for example by coating.

[0058] Furthermore, in another method, a first lubricating base oil containing tungsten disulfide and a second lubricating base oil containing a silane compound can be prepared separately, and in the second contact step S12, the second lubricating base oil is supplied to the sliding surface 100a.

[0059] Figure 8 This is a process diagram of a coating formation method according to another embodiment. In this embodiment, the lubricating oil composition contains, in addition to tungsten disulfide, a silane compound, such as... Figure 8 As shown, the first contact step S10 and the second contact step S12 are performed simultaneously.

[0060] According to this embodiment, by simultaneously performing the first contact step S10 and the second contact step S12, tungsten disulfide and silane compound simultaneously come into contact with the sliding surface 100a, thus enabling the coating formation method to be implemented in one step.

[0061] In the embodiments described later, test 2 is equivalent to this implementation.

[0062] One embodiment of the lubricating oil composition comprises: a lubricating base oil; tungsten disulfide; and a silane compound comprising a dialkoxysilane, a trimekoxysilane, a tetrakoxysilane, or a polymer or copolymer thereof, wherein the concentration of tungsten disulfide in the lubricating oil composition is 0.01 to 5% by mass, and the mass ratio of the silane compound to tungsten disulfide is 0.3 to 0.5.

[0063] Regarding the concentration of tungsten disulfide, it is believed that the aforementioned effects cannot be achieved unless tungsten disulfide is present in the lubricating oil composition at a certain concentration. Therefore, 0.01% by mass is set as the minimum concentration, referring to the concentration of typical lubricating oil compositions. On the other hand, the higher the concentration of tungsten disulfide in the lubricating oil composition, the greater the concern about sedimentation or clogging of the lubricating oil filter. Therefore, 5% by mass is set as the maximum concentration.

[0064] If the role of silane compounds in the lubricating oil composition is considered as an adhesive effect to bind tungsten disulfide particles together, then the concentration of silane compounds depends on the concentration of tungsten disulfide in the lubricating oil composition. Based on this, the mass ratio of silane compounds to tungsten disulfide is calculated as follows.

[0065] For example, the concentration of tungsten disulfide in the lubricating oil composition is set to 2% by mass, and the density of tungsten disulfide is 7.5 g / cm³. 3 Therefore, the volume of 2g of tungsten disulfide is 0.26cm³. 3 If the average particle size of tungsten disulfide is set to 0.2 μm, then 2 g of tungsten disulfide will contain 6.2 × 10⁻⁶ particles. 13 The total surface area of ​​these tungsten disulfide particles is 7.8 × 10⁻⁶. 4 cm 2 For tungsten disulfide particles to adhere to each other, assuming a minimum 0.1 μm layer of silane compound is required on the surface of the tungsten disulfide particles, the necessary volume of the silane compound becomes 7.8 × 10⁻⁶. 4 cm 2 ×0.00001cm (0.1μm)=0.78cm 3 The density of silane compounds is approximately 1 g / cm³. 3 Relative to 2% by mass of tungsten disulfide, the required concentration of the silane compound is 0.78% by mass. Therefore, the mass ratio of the silane compound to tungsten disulfide is 0.78 ÷ 2 = 0.39. It is speculated that a value of 0.3 to 0.5, with a margin above and below this value, is used as a center, and the above-mentioned effect is obtained within this range.

[0066] According to this embodiment, by using a lubricating oil composition containing tungsten disulfide and a silane compound in the above-described proportions to form a coating f on the sliding surface 100a, the sliding surface 100a can be protected and the generation of initial damage can be suppressed. Furthermore, even if damage such as cracking occurs, a coating f capable of inhibiting its development can be formed. Moreover, since the concentration of tungsten disulfide is 5% by mass or less, there are no concerns about the sedimentation of tungsten disulfide particles or clogging of the lubricating oil filter. In the embodiments described later, the lubricating oil composition according to this embodiment was used in Test 2.

[0067] Next, the kinematic viscosity of a lubricating oil composition using gear oil as the base lubricant and in which tungsten disulfide and silane compounds are added was investigated. Tungsten disulfide has a higher kinematic viscosity than gear oil, therefore, the addition of tungsten disulfide does not result in a decrease in viscosity. On the other hand, silane compounds have low viscosity; adding silane compounds to gear oil raises concerns about a decrease in kinematic viscosity.

[0068] Figure 9 This indicates the relationship between the concentration of silane compounds and the kinematic viscosity (40°C) of the lubricating oil composition when 2% by mass of tungsten disulfide is added to the gear oil, and further silane compounds are added. The gear oil is VG320, using the ISO VG320 standard range (kinematic viscosity 320 mmHg). 2 Gear oil with viscosity ±10% (s / s). If 2.3% by mass of silane compound is added, the viscosity drops to the lower limit of ISO VG320 standard, 288 mm. 2 / s( Figure 9 The values ​​indicated by the dashed lines in the figure are used to determine the maximum amount of silane compound to be added (2.3% by mass). Furthermore, the kinematic viscosity of the mixture varies depending on the type of silane compound, therefore the maximum concentration for each silane compound needs to be calculated or measured.

[0069] In production Figure 9 At that time, materials having the kinematic viscosity shown in Table 1 were used as materials constituting the lubricating oil composition.

[0070] [Table 1]

[0071] Table 1

[0072]

[0073] (Example)

[0074] Next, a thrust roller bearing with initial damage in its rollers was used as the test specimen, and tests were conducted in the following order to confirm the life extension effect from initial damage to spalling.

[0075] (a) Using a thrust needle roller bearing of type AXK1103, a surface pressure of 1.3 GPa is applied to the roller to induce initial damage in the roller.

[0076] (b) Rollers with initial damage were used as test samples, and three tests (Tests 1–3) were conducted. VG320 gear oil was used as the base lubricant. The additives were tungsten disulfide nanoparticles (2% by mass, 200 nm particle size) and silane compound nanoparticles (1.4% by mass and ethyl silicate 40 with a particle size of 2 nm), both of which were added to the base lubricant. In Test 1, a baseline test was conducted in the base lubricant without mixing these additives. In Tests 2 and 3, the effect of extending spalling life by mixing the additives was verified. In Test 2, tungsten disulfide nanoparticles (additive A) and ethyl silicate 40 (additive B) were added simultaneously. In Test 3, additive A was added first, followed by additive B after a certain time. Additive A and additive B have different particle sizes, with additive A being approximately 100 times larger. Therefore, it was considered that if added simultaneously, the smaller particle size of additive B would preferentially enter the cracked Cr, potentially resulting in a lower filling rate of additive A.

[0077] (c) An experiment was conducted to investigate the lifespan of the roller from the initial damage to the point of spalling by applying a surface pressure of 21 GPa to the roller.

[0078] [Table 2]

[0079] Table 2 Experimental conditions

[0080] project Test 1 Test 2 Test 3 Lubricating base oil VG320 gear oil VG320 gear oil VG320 gear oil Additive A × ○ ○ Additive B × ○ ○ When to add additives × Add at the same time Add B after A.

[0081] ○ With additives × Without additives

[0082] The lifetime ratios for Tests 2 and 3, calculated based on the time it took for the spalling to occur in Test 1, are shown below. Figure 10 Compared to Test 1, the lifetime extension rates of Tests 2 and 3, which incorporated the additive, were 1.6 times and 5.6 times, respectively. Furthermore, comparing Test 2 and Test 3, Test 3, which had a different additive incorporation time, showed a more significant increase in peel life. The compositional analysis results of the internal cracks after the Test 3 experiment are shown below. Figure 11A and Figure 11B middle. Figure 11A This is a diagram showing the formation of a cracked sliding surface. Figure 11B It means Figure 11A The figure shows the analytical results of tungsten disulfide and silane compounds contained in the cracks generated in region R of the sliding surface. Both additives A and B showed silane compounds entering the crack interior, thus verifying the reliability of the lifespan extension mechanism caused by additive entry into the cracks. Furthermore, the difference in lifespan extension effects due to different additive incorporation times indicates that incorporation time is also a parameter related to the extension effect on spalling lifespan.

[0083] The main reason for the difference in the extension effect of exfoliation lifetime in Tests 2 and 3, which were added at different times, is presumably due to the difference in the filling rate of tungsten disulfide nanoparticles. In Test 2, it is believed that by adding additives A and B at the same time, additive B, with its smaller particle size and coarser structure compared to additive A, entered preferentially, thus reducing the filling rate of additive A. In Test 3, it is believed that because additive A, with its larger particle size, was added first, it entered the cracks first, and the subsequently added additive B entered by filling the gaps, thereby increasing the density of additives within the cracks and further extending the exfoliation lifetime.

[0084] The contents described in the above embodiments can be understood as follows, for example.

[0085] 1) A coating forming method according to one aspect forms a coating (f) on a sliding surface (100a) of a sliding member (100), the coating forming method comprising: a first contact step (S10), wherein a lubricating oil composition containing tungsten disulfide is supplied to the sliding surface (100a) to bring the tungsten disulfide into contact with the sliding surface (100a); and a second contact step (S12), wherein a dialkoxysilane, a trialkoxysilane, a tetrakoxysilane, or a silane compound as a polymer or copolymer thereof is brought into contact with the sliding surface.

[0086] According to this structure, the following effects are achieved: the tungsten disulfide particles penetrate the crack (Cr), suppressing the oil film pressure generated by the sliding component (102) on the opposite side from acting inside the crack (Cr), and reducing the stress amplitude (σ) generated in the crack periphery by suppressing elastic deformation. Furthermore, the silane compound forms a coating (f) on the sliding surface (100a) and acts as a binder, binding the tungsten disulfide and silane compound particles (Pn, Ps) together and retaining them within the crack. Through the synergistic effect of these two additives, the spalling life from initial damage to spalling can be extended.

[0087] 2) In a coating formation method according to the method described in 1), the lubricating oil composition does not contain the silane compound, and the second contact step (S12) is performed after the first contact step (S10).

[0088] According to this structure, after the first contact step (S10) in which tungsten disulfide contacts the sliding surface (100a), a second contact step (S12) in which a silane compound contacts the sliding surface (100a) occurs, thus the tungsten disulfide contacts the sliding surface (100a) before the silane compound. Therefore, the large-sized, high-density, and high-hardness tungsten disulfide particles enter the crack (Cr) without being hindered by the silane compound particles, and then the silane compound enters by filling the gaps, thereby increasing the density within the crack (Cr). This significantly extends the spalling life of the sliding component (100).

[0089] 3) In another method of coating formation, the lubricating oil composition contains the silane compound in addition to the tungsten disulfide, and the first contact step (S10) and the second contact step (S12) are performed simultaneously.

[0090] Based on this structure, the first contact step (S10) of contacting tungsten disulfide with the sliding surface (100a) and the second contact step (S12) of contacting the silane compound with the sliding surface (100a) are performed simultaneously, thus simplifying the implementation of the coating formation method.

[0091] 4) The lubricating oil composition according to one method comprises: a lubricating base oil; tungsten disulfide; and a dialkoxysilane, a trimekoxysilane, a tetrakoxysilane, or a silane compound as a polymer or copolymer thereof, wherein the concentration of the tungsten disulfide in the lubricating oil composition is 0.01 to 5% by mass, and the mass ratio of the silane compound to the tungsten disulfide is 0.3 to 0.5.

[0092] According to this structure, tungsten disulfide and silane compounds having concentrations and mass ratios within the aforementioned numerical ranges are contained in the lubricating oil composition, thus enabling the formation of a coating on the sliding surface (100a) that inhibits damage development. Furthermore, since the concentration of tungsten disulfide is 5% by mass or less relative to the lubricating oil composition, there are no concerns about tungsten disulfide particle sedimentation or clogging of the lubricating oil filter.

[0093] Symbol Explanation

[0094] 1-Lubricating oil composition, 10-Silane compound, 100-Sliding part, 100a-Sliding surface, 102-Opposite sliding part, Cr(Cri, Cro)-Crack, L-Repetitive load, Pn-Tungsten disulfide nanoparticles, Ps-Silane compound nanoparticles, f-Coating.

Claims

1. A film formation method of forming a film on a sliding surface of a sliding member, the film formation method comprising: a first contact step of bringing a lubricating oil composition containing tungsten disulfide into contact with the sliding surface by supplying the lubricating oil composition to the sliding surface; and a second contact step of bringing a silane compound of a dialkoxysilane, a trialkoxysilane, a tetraalkoxysilane, or a polymer or copolymer thereof into contact with the sliding surface, the lubricating oil composition not containing the silane compound, the second contact step being performed after the first contact step, the tungsten disulfide and the silane compound being composed of nanoparticles having a particle diameter of less than 1 μm, the particle diameter of the nanoparticles of the silane compound being smaller than the particle diameter of the nanoparticles of the tungsten disulfide. ​ ​ ​ ​ ​

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