Solid lubrication film, slide member, and method of manufacturing solid lubrication film

Abstract

To provide a solid lubrication film having an improved friction coefficient.SOLUTION: A solid lubrication film 300 includes a layer containing metal oxide. An arithmetical average height of a surface of the layer containing the metal oxide is less than 12 nm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a solid lubricant coating, a sliding member, and a method for producing a solid lubricant coating. [Background technology]

[0002] One way to save energy is to reduce the frictional force of sliding members. For the purpose of reducing friction, it is known to form a coating made of a solid lubricant (solid lubricant coating) on ​​the surface of the sliding member. The following Patent Documents 1 and 2 disclose a zinc oxide coating as a solid lubricant coating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 039264 [Patent Document 2] International Publication No. 2016 / 190375 Summary of the Invention [Problem to be solved by the invention]

[0004] The friction coefficient of a solid lubricating coating can usually increase over time when it is oxidized by oxygen in the air or oil. In order to suppress such an increase in the friction coefficient over time, it is desirable for the solid lubricating coating to contain a metal oxide. It is desirable for a solid lubricating coating that contains a metal oxide to have a small friction coefficient. Therefore, there is a demand for a solid lubricating coating having an improved friction coefficient, a sliding member having such a solid lubricating coating, and a method for producing a solid lubricating coating. [Means for solving the problem]

[0005] A solid lubricating coating according to one embodiment has a layer containing a metal oxide, and the arithmetic mean height of the surface of the layer is less than 12 nm.

[0006] A slide member according to one embodiment has the above-described solid lubricant coating and a substrate on which the solid lubricant coating is formed.

[0007] A method for producing a solid lubricant coating according to one embodiment includes a film-forming step of forming a metal oxide layer on a substrate, and the method includes at least one of forming the metal oxide layer in an oxygen-containing atmosphere at any timing during the film-forming step and exposing the metal oxide layer to an oxygen-containing atmosphere after the film-forming step. Effect of the Invention

[0008] According to the above aspects, it is possible to provide a solid lubricant coating having a low coefficient of friction, a method for producing the solid lubricant coating, and a sliding member having the solid lubricant coating. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an example of a sliding member having a solid lubricant coating formed thereon according to the first embodiment. [Diagram 2] FIG. 2 shows laser microscope photographs of the surfaces of the substrates in Examples 1 and 2 and Reference Example 1 after the reciprocating friction test. [Diagram 3] FIG. 3 is a graph showing the measurement results of the friction coefficients of the surfaces of the substrates in Examples 1 and 2 and Reference Example 1 during a reciprocating friction test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described with reference to the drawings. In the following drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and the ratios of dimensions may differ from the actual ones.

[0011] A slide member according to one embodiment will now be described. Fig. 1 is a schematic diagram showing an example of a slide member on which a solid lubricant coating according to a first embodiment is formed.

[0012] The sliding member 100 may have a substrate 200 and a solid lubricant coating 300. The solid lubricant coating 300 is formed on the substrate 200.

[0013] The material constituting the substrate 200 is not particularly limited, and may be, for example, a metal material. The material constituting the substrate 200 may contain, for example, at least one element belonging to groups 3 to 14. Preferably, the material constituting the substrate 200 may contain at least one element belonging to groups 3 to 11.

[0014] More preferably, the material constituting the substrate 200 contains at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, and Cu. Even more preferably, the material constituting the substrate 200 contains Fe. Such a material may be, for example, iron or an alloy containing iron.

[0015] 1, the solid lubricant coating 300 may have an underlayer 310 facing the substrate 200 and a surface layer 320 facing the opposite side to the substrate 200. However, it should be noted that the underlayer 310 and the surface layer 320 do not have to be separated by a clear boundary.

[0016] The solid lubricant coating 300 can be formed by a film formation technique such as sputtering. In this case, the base layer 310 and the surface layer 320 of the solid lubricant coating 300 may be layers formed under different film formation conditions.

[0017] Although not shown, the solid lubricating coating 300 may include a layer formed, for example, under different deposition conditions between the underlayer 310 and the surface layer 320. Alternatively to the embodiment shown in Fig. 1, the underlayer 310 and the surface layer 320 may be composed of the same layer that is indistinguishable from each other. In other words, the solid lubricating coating 300 may be composed of a single layer formed under the same deposition conditions.

[0018] The solid lubricating coating 300 has a layer containing a metal oxide. Each of the underlayer 310 and the surface layer 320 may have a layer containing a metal oxide. The metal oxide preferably contains at least one selected from the group consisting of Ag2O, Al2O3, Bi2O3, CaO, Ce2O3, Cr2O3, CrO, CrO3, Cu2O, CuO, Fe2O3, Fe3O4, FeO, In2O3, Li2O, MgO, MnO, Nb2O5, NiO, Sb2O3, Sb2O5, SiO2, SnO2, Ta2O5, TiO2, WO3, ZnO, and ZrO2. More preferably, the metal oxide contains ZnO.

[0019] When the solid lubricating coating 300 has at least two layers, an underlayer 310 and a surface layer 320, the thickness of the underlayer 310 may be, for example, 10 nm to 100 nm or less, or 20 nm to 80 nm or less. Similarly, the thickness of the surface layer 320 may be, for example, 500 nm to 4500 nm or less, or 800 nm to 3000 nm or less.

[0020] The Vickers hardness of the surface of the solid lubricating coating 300, i.e., the layer containing a metal oxide, is, for example, greater than Hv605. The Vickers hardness of the surface of the solid lubricating coating 300 may be preferably Hv610 or more, more preferably Hv615 or more, and even more preferably Hv619 or more. It is believed that the high Vickers hardness of the surface of the solid lubricating coating 300 improves the durability of the solid lubricating coating 300.

[0021] The Vickers hardness of the surface of the solid lubricant coating 300, ie, the layer containing a metal oxide, is not particularly limited, and may be, for example, Hv2000 or less, Hv1800 or less, Hv1600 or less, or Hv1400 or less.

[0022] The arithmetic mean height (Sa) of the surface of the solid lubricant coating 300, i.e., the layer containing the metal oxide, is, for example, less than 12 nm. The arithmetic mean height of the surface of the solid lubricant coating 300 is preferably 11 nm or less, more preferably 10 nm or less, and even more preferably 9 nm or less. It is believed that a small arithmetic mean height of the surface of the solid lubricant coating 300 reduces the friction coefficient of the solid lubricant coating 300 and improves the durability of the solid lubricant coating 300.

[0023] There is no particular restriction on the lower limit of the arithmetic mean height of the surface of the solid lubricating coating 300. The lower limit of the arithmetic mean height of the surface of the solid lubricating coating 300 may be, for example, 0 nm, 0.1 nm, or 2 nm. The arithmetic mean height of the surface of the solid lubricating coating 300 may be within a range that combines any of the above upper and lower limits.

[0024] The solid lubricant coating 300 can be formed by any film formation technique capable of forming a metal oxide film on a substrate (film formation step). One example of such a film formation technique is a sputtering film formation method. A preferred method for producing the solid lubricant coating 300 will now be described.

[0025] First, a target material that is the basis for forming the solid lubricant coating 300 is prepared. The target material may be a metal or metal oxide that forms the metal oxide that constitutes the main component of the solid lubricant coating 300. The types of metal elements that form the metal oxide are as described above. Preferably, the target material may be a material made of the metal oxide that constitutes the main component of the solid lubricant coating 300. If the metal oxide that constitutes the main component of the solid lubricant coating 300 is ZnO, the target material is preferably made of Zn or ZnO, and more preferably made of ZnO. If the target material is a metal oxide, oxygen atoms are also scattered by sputtering the target material, making it easier to form a metal oxide layer as a solid lubricant coating.

[0026] As described above, when forming at least two layers, the base layer 310 and the surface layer 320, each layer can be formed by sputtering the same target material. The base layer 310 and the surface layer 320 may be formed under different film formation conditions or under the same film formation conditions.

[0027] Preferably, at any timing in the film formation step, a metal oxide is sputtered as a target material in an atmosphere containing oxygen. For example, when forming at least one of the underlayer 310 and the surface layer 320, the sputtering of the target material is preferably performed in an atmosphere containing oxygen. In one example, the underlayer 310 may be formed by sputtering a target material in an atmosphere containing oxygen. Alternatively or in addition, the surface layer 320 may be formed by sputtering a target material in an atmosphere containing oxygen.

[0028] More preferably, the metal oxide is sputtered as a target material in an oxygen-containing atmosphere at all times during the film formation step. For example, both the underlayer 310 and the surface layer 320 may be formed by sputtering a target material in an oxygen-containing atmosphere.

[0029] It is believed that sputtering deposition in an oxygen-containing atmosphere reduces oxygen defects in the deposited metal oxide layer. The reduction in oxygen defects is believed to make the crystal structure of the deposited metal oxide layer more stable, improving the hardness of the metal oxide layer. The increased hardness of the metal oxide layer can improve the durability of the solid lubricating coating.

[0030] Furthermore, it is believed that the surface roughness (arithmetic mean height) of the surface of the formed metal oxide layer decreases due to the reduction in oxygen defects in the formed metal oxide layer.

[0031] Furthermore, it is believed that by performing sputtering in an atmosphere containing oxygen, the energy of oxygen ions in the atmosphere increases, causing the surface of the solid lubricant coating to be ashed, thereby reducing the surface roughness of the solid lubricant coating. From this perspective, it is preferable to sputter the target material in an atmosphere containing oxygen at least during deposition of the surface layer 320.

[0032] It is believed that a decrease in the arithmetic mean height of a solid lubricant coating can result in a decrease in the dynamic friction coefficient of the solid lubricant coating.

[0033] The oxygen-containing atmosphere during sputtering may be, for example, a mixed gas of oxygen gas and a rare gas. The rare gas may be helium gas, neon gas, argon gas, or a mixed gas thereof. The oxygen partial pressure ratio of the oxygen-containing atmosphere is not particularly limited as long as the desired thickness of the mixed layer can be realized. The oxygen partial pressure ratio in the oxygen atmosphere may be, for example, 1.5% or more, 3% or more, 5% or more, 8% or more, or 10% or more.

[0034] The upper limit of the oxygen partial pressure ratio in the oxygen-containing atmosphere is not particularly limited. The oxygen partial pressure ratio in the oxygen atmosphere may be, for example, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less.

[0035] Preferably, in the film formation step, the target material is a metal oxide, and sputtering is performed in an atmosphere containing oxygen at least at some timing during film formation. In this case, more oxygen atoms than the number of oxygen atoms contained in the metal oxide may be scattered toward the substrate at the start of film formation. Therefore, oxygen defects in the formed metal oxide layer may be further reduced.

[0036] It is believed that instead of sputtering under an oxygen-containing atmosphere, exposing the metal oxide layer to an oxygen-containing atmosphere after the deposition step can also reduce oxygen defects in the deposited metal oxide layer.

[0037] For example, an annealing treatment in an oxygen atmosphere, an oxygen plasma treatment, an ozone treatment, and / or an immersion treatment in an oxidizing solution may be performed on the metal oxide layer after the deposition step.

[0038] Furthermore, from the viewpoint of reducing the surface roughness of the solid lubricating coating, the following treatments may be carried out instead of or in addition to the above methods. For example, before and / or after the film-forming step, a treatment may be carried out to reduce the roughness of the substrate surface and / or the surface of the solid lubricating coating by polishing, wet etching, or the like.

[0039] [Example 1] A solid lubricant coating according to Example 1 will be described. In Example 1, a zinc oxide coating is provided on a substrate as a solid lubricant coating. The substrate is soft iron (SPCC). As shown in FIG. 1, the zinc oxide coating includes an underlayer 310 and a surface layer 320. The underlayer and surface layer of the zinc oxide coating were formed by a sputtering deposition method using an "Intervac-type sputtering device SIH-300 manufactured by ULVAC, Inc." The target material was zinc oxide.

[0040] In Example 1, the deposition gas used for depositing the underlayer of the zinc oxide coating was a mixture of 80% argon partial pressure and 20% oxygen partial pressure (see Table 1). In Example 1, the deposition gas used for depositing the surface layer was argon, which contained substantially no oxygen. The flow rate of the deposition gas was 50 ml / min. The deposition temperature was 25° C., and the deposition pressure was 0.5 Pa. The discharge power used for depositing the underlayer was 224 W, and the discharge power used for depositing the surface layer was 2236 W. The film thickness of the underlayer was 60 nm, and the film thickness of the surface layer was 1700 nm. The above-mentioned film thicknesses were measured by spectroscopic ellipsometry (the same applies below).

[0041] [Example 2] The solid lubricant coating according to Example 2 will be described. In Example 2, a zinc oxide coating is provided on a substrate as a solid lubricant coating. The zinc oxide coating according to Example 2 was formed under the same conditions as Example 1, except for the composition of the deposition gas when depositing the surface layer and the thickness of the surface layer (see Table 1). The deposition gas when depositing the surface layer of the zinc oxide coating was a mixture of 80% argon partial pressure and 20% oxygen partial pressure. The thickness of the surface layer was 1100 nm.

[0042] [Example 3] A solid lubricant coating according to Example 3 will be described. In Example 3, a zinc oxide coating is provided on a substrate as a solid lubricant coating. The substrate is soft iron (SPCC). The zinc oxide coating includes only an underlayer 310. The underlayer of the zinc oxide coating was formed by a sputtering deposition method using an "Intervac-type sputtering device SIH-300 manufactured by ULVAC, Inc." The target material was zinc oxide. In Example 3, the deposition gas used for depositing the underlayer of the zinc oxide coating was a mixture of 80% argon partial pressure and 20% oxygen partial pressure (see Table 1). The flow rate of the deposition gas was 50 ml / min. The deposition temperature was 25° C., and the deposition pressure was 0.5 Pa. The discharge power used for depositing the underlayer was 224 W, and the discharge power used for depositing the surface layer was 2236 W. The thickness of the underlayer was 35 nm.

[0043] [Reference example 1] The solid lubricant coating according to Reference Example 1 will be described. In Reference Example 1, a zinc oxide coating is provided on a substrate as a solid lubricant coating. The zinc oxide coating according to Reference Example 1 was formed under the same conditions as in Example 1, except for the components of the deposition gas used when depositing the underlayer. In Reference Example 1, the deposition gas used when depositing the underlayer and surface layer was argon, and contained substantially no oxygen (see Table 1). In Reference Example 1, the thickness of the underlayer was 60 nm, and the thickness of the surface layer was 1700 nm.

[0044] (Table 1) TIFF2024127140000002.tif36165

[0045] [Vickers hardness] The Vickers hardness of the zinc oxide coatings according to Reference Example 1 and each of the Examples was measured. The Vickers hardness was measured by the nanoindentation method (ISO14577) using an "ENT-1100a" manufactured by Elionix. The indenter used to measure the Vickers hardness was a Berkovich (triangular pyramid). The indenter was pressed against the zinc oxide coating with a load of 12.5 mN at a temperature of 28°C. The Vickers hardness (kgf / mm 2 ) is obtained. The Vickers hardness was determined by averaging the values ​​from 10 measurements. The measured Vickers hardness values ​​are shown in Table 1 above.

[0046] From Table 1, it can be seen that the Vickers hardness of the zinc oxide coating increases when the deposition gas contains oxygen. From the viewpoint of increasing the Vickers hardness of the zinc oxide coating, it is sufficient that the deposition gas contains oxygen during the deposition of either the underlayer or the surface layer. To obtain a higher Vickers hardness, it is sufficient that the deposition gas contains oxygen during the deposition of both the underlayer and the surface layer.

[0047] [Surface roughness: arithmetic mean height (Sa)] The arithmetic mean height (Sa) was measured for Reference Example 1 and each Example. The arithmetic mean height was measured using an atomic force microscope (AFM: "E-sweep" manufactured by SII Corporation). The measurement area of ​​the zinc oxide coating is a square area of ​​5 μm × 5 μm. The arithmetic mean height is measured in accordance with ISO25178. The arithmetic mean height is calculated by averaging the absolute value of the difference between the average plane of the surface and the height of each measurement point.

[0048] From Table 1, it can be seen that the arithmetic mean height of the zinc oxide film is reduced by the deposition gas containing oxygen. From the viewpoint of reducing the arithmetic mean height of the zinc oxide film, it is sufficient that the deposition gas contains oxygen during the deposition of either the underlayer or the surface layer. To further reduce the arithmetic mean height, it is sufficient that the deposition gas contains oxygen during the deposition of both the underlayer and the surface layer.

[0049] [Kinematic friction coefficient] A reciprocating friction test was conducted on the sliding members having the zinc oxide coatings according to Examples 1 and 2 and Reference Example 1. In the reciprocating friction test, a ball made of steel (SUJ-2) having a diameter of 0.5 inches was moved back and forth on the surface of the substrate on which the zinc oxide coating was formed ("Friction and Wear Tester" Type: 40, manufactured by Shinto Scientific Co., Ltd.). Here, the reciprocating friction test was conducted with machine oil applied on the zinc oxide coating.

[0050] The steel ball was pressed against the substrate with a load of 3 kgf and moved back and forth on the substrate. The temperature during the test was room temperature. The stroke width of the steel ball was 20 mm, and the stroke speed was 10 mm / s. The steel ball was moved back and forth on a sliding member 100 having a zinc oxide coating. The values ​​of the dynamic friction coefficients shown in Table 1 are the arithmetic average values ​​of the dynamic friction coefficients measured at 100 points when the steel ball was moved back and forth 100 times.

[0051] Fig. 2 shows laser microscope photographs of the surfaces of the substrates in Examples 1 and 2 and Reference Example 1 after the reciprocating friction test. Fig. 2 shows that the zinc oxide coatings in Examples 1 and 2 hardly peeled off even after the reciprocating friction test. In contrast, the zinc oxide coating in Reference Example 1 partially peeled off after the reciprocating friction test. This result shows that the durability of the zinc oxide coatings in Examples 1 and 2 is improved.

[0052] Fig. 3 is a graph showing the measurement results of the friction coefficient of the surface of the substrate in Examples 1 and 2 and Reference Example 1 during the reciprocating friction test. From Fig. 3, it can be seen that in Examples 1 and 2, the friction coefficient is stable even if the number of sliding movements of the steel ball increases. In contrast, in Reference Example 1, the dynamic friction coefficient increases rapidly around the 20th sliding movement, reaching approximately 0.16. This is a value close to the dynamic friction coefficient of the substrate, and it is considered that the zinc oxide coating in Reference Example 1 peels off significantly around the 20th sliding movement.

[0053] Thus, it is found that the zinc oxide coatings of Examples 1 and 2 have higher durability than the zinc oxide coating of Reference Example 1. This is believed to be because the zinc oxide coatings of Examples 1 and 2 have higher Vickers hardness.

[0054] From this perspective, it is believed that if the Vickers hardness of the zinc oxide coating is greater than Hv605, a zinc oxide coating having higher durability than the zinc oxide coating of Reference Example 1 can be provided.

[0055] In fact, when a similar reciprocating friction test was performed on the zinc oxide coating of Example 3, the dynamic friction coefficient of the zinc oxide coating was stable, even after 100 sliding cycles, as in Examples 1 and 2 (see Table 1). This means that the zinc oxide coatings of Examples 1 to 3 have higher durability than the zinc oxide coating of Reference Example 1.

[0056] Furthermore, referring to Reference Example 1 and Examples 1 and 2, it can be seen that the dynamic friction coefficient decreases as the arithmetic mean height decreases. In this way, the friction coefficient of the zinc oxide coating can be further reduced. From this perspective, it is considered that if the arithmetic mean height of the zinc oxide coating is smaller than 12 nm, it is possible to provide a zinc oxide coating having a dynamic friction coefficient lower than that of the zinc oxide coating in Reference Example 1.

[0057] As described above, the contents of the present invention have been disclosed through the embodiments and examples, but the descriptions and drawings forming part of this disclosure should not be understood as limiting the present invention. From this disclosure, various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art. Therefore, the technical scope of the present invention is defined only by the invention-specific matters related to the appropriate claims from the above description. [Explanation of symbols]

[0058] 100 Sliding member 200 Base material 300 Solid lubricant coating

Claims

1. having a layer containing a metal oxide, a solid lubricating film in which an arithmetic mean height of a surface of the layer is less than 12 nm.

2. The metal oxide is Ag ２ O, Al ２ O ３ 、Bi ２ O ３ 、CaO, Ce ２ O ３ 、Cr ２ O ３ 、CrO, CrO ３ 、Cu ２ O, CuO, Fe ２ O ３ 、Fe ３ O ４ 、FeO, In ２ O ３ 、Li ２ O, MgO, MnO, Nb ２ O ５ 、NiO, Sb ２ O ３ 、Sb ２ O ５ 、SiO ２ 、SnO ２ 、Ta ２ O ５ 、TiO ２ 、WO ３ 、ZnO, and ZrO ２ The solid lubricating coating according to claim 1, comprising at least one selected from the group consisting of

3. The solid lubricating film according to claim 1, wherein the metal oxide contains ZnO.

4. a solid lubricating film according to any one of claims 1 to 3, and a base material on which the solid lubricating film is formed, a sliding member.

5. The sliding member according to claim 4, wherein the base material contains at least one element belonging to groups 3 to 14.

6. A method for manufacturing a solid lubricating film according to any one of claims 1 to 3, having a film-forming step of forming a layer of a metal oxide on a base material, performing film formation in an atmosphere containing oxygen at any timing in the film-forming step, and exposing the layer of the metal oxide to an atmosphere containing oxygen after the film-forming step, a method for manufacturing a solid lubricating film including at least one of them.

7. The method for manufacturing a solid lubricating film according to claim 6, including sputtering a metal oxide as a target material in an atmosphere containing oxygen at any timing in the film-forming step.

8. The method for manufacturing a solid lubricating film according to claim 6, including sputtering a metal oxide as a target material in an atmosphere containing oxygen at all timings in the film-forming step.

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