Sliding member and method for manufacturing the same

Abstract

To provide a technology that enables improved wear resistance in sliding members formed from self-lubricating molybdenum sulfide compared to conventional methods. [Solution] The sliding member (10) has a base material (11) and a solid lubricating film (12). The solid lubricating film is provided so as to cover the base material. The solid lubricating film is composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio S / Mo of 1.33 or less. Such a solid lubricating film can be produced by atomic layer deposition using an organic material having tertiary butyl groups as a sulfur-containing raw material.

Description

Technical Field

[0001] The present disclosure relates to a sliding member and a method for manufacturing the same.

Background Art

[0002] Sliding members formed of molybdenum disulfide having self-lubricating properties have been variously known in the past. For example, the sliding member described in Patent Document 1 has a base material and a sliding layer formed on at least the sliding surface side of the base material and containing molybdenum disulfide. The sliding layer is composed of a first sliding layer formed on the base material and a second sliding layer laminated on the first sliding layer. The first sliding layer contains 10 at% or less of a metal element and / or a compound of a metal element when the total is 100 at%. The metal element is at least one of Ti, Cr, W, Zr, and V. The second sliding layer does not contain such a metal element and / or a compound of a metal element.

[0003] By containing a metal element or a compound of a metal element, a decrease in the strength of the first sliding layer and peeling from the base material are suppressed. Since the second sliding layer does not contain a metal element or a compound of a metal element, it is a soft layer having a lower hardness than the first sliding layer. Therefore, it shows high conformity to a mating member during sliding.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As is well known, molybdenum sulfide has a layered crystalline structure along the (001) plane, and delamination is prone to occur along this plane. Therefore, for example, if the (001) plane is oriented perpendicular to the load direction, delamination will occur, while if it is oriented in the direction of the load, delamination can be suppressed. However, in sliding layers, the (001) planes are usually oriented in random directions, making it difficult to align them completely in the same direction, and thus difficult to sufficiently suppress delamination. Furthermore, if the load and sliding are not in the same direction, frictional force is applied in the sliding direction, so even if delamination in the load direction is suppressed, delamination will occur in the sliding direction.

[0006] This disclosure has been made in view of the circumstances illustrated above. Specifically, this disclosure provides, for example, a technology that makes it possible to improve the wear resistance of sliding members formed of self-lubricating molybdenum sulfide compared to conventional methods. [Means for solving the problem]

[0007] The sliding member (10) described in claim 1 is Base material (11) and A solid lubricating film (12) is provided so as to cover the substrate, It has, The solid lubricating film is composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio (S / Mo) of 1.33 or less. The manufacturing method described in claim 5 is a manufacturing method for a sliding member described in claim 1, comprising a process or procedure for forming the solid lubricating film by atomic layer deposition using an organic material having a tertiary butyl group as a sulfur-containing raw material.

[0008] In addition, each element in the application documents may be denoted by a reference numeral in parentheses. In this case, the reference numeral is merely an example of the correspondence between the element and the specific configuration described in the embodiments described later. Therefore, this disclosure is not limited in any way by the inclusion of reference numerals. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing a schematic configuration of a sliding member according to one embodiment of the present disclosure. [Figure 2] Figure 1 shows a cross-sectional TEM image of the area near the interface between the aluminum oxide film and the solid lubricant film in the configuration shown. [Figure 3] This is a cross-sectional TEM image of the area near the interface between the aluminum oxide film and the solid lubricant film in the comparative example. [Figure 4] This graph shows the change in the coefficient of friction over time in the comparative example. [Figure 5] This graph shows the sliding cross-sectional profile in the comparative example. [Figure 6] This graph shows how the coefficient of friction changes over time in the example. [Figure 7] This graph shows the sliding cross-sectional profile in the example. [Figure 8] This graph shows a comparison of the X-ray diffraction intensity patterns between the example and the comparative example. [Figure 9] This graph shows the relationship between the sulfur-to-molybdenum ratio (S / Mo) and the carbon concentration. [Figure 10] This graph shows the relationship between adhesion strength and carbon concentration in solid lubricant films. [Figure 11] This graph shows the dependence of carbon concentration in solid lubricating films on the film deposition temperature. [Modes for carrying out the invention]

[0010] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as appropriate. Note that the following embodiments, their modifications, and the descriptions of the drawings related thereto are schematic or simplified for the purpose of briefly explaining the content of the present disclosure, and the content of the present disclosure is not limited thereby. Needless to say, the description of the drawings and the specific device configuration actually manufactured and sold do not necessarily match. That is, unless the applicant explicitly limits it during the application process of this application, the present disclosure should not be construed in a limited manner by the description of the drawings and the description of the configuration, its functions, or operations described below corresponding thereto.

[0011] (Embodiment: Configuration) Hereinafter, with reference to FIG. 1, the schematic configuration of the sliding member 10 according to an embodiment of the present disclosure will be described. As shown in FIG. 1, the sliding member 10 has a base material 11 and a solid lubricating film 12 provided so as to cover the base material 11.

[0012] For simplicity of illustration and description, a right-handed XYZ coordinate system as shown in FIG. 1 is set. Here, the Z-axis direction is referred to as the "height direction", and any direction in the XY plane is referred to as the "in-plane direction". In the present embodiment, the sliding member 10 has a structure in which the base material 11 and the solid lubricating film 12 are laminated in the height direction.

[0013] The base material 11 is formed of a metal material such as a steel material, for example, bearing steel such as SUJ2. In the present embodiment, the base material 11 has a plate-like or disk-like shape having a plate thickness direction in the height direction. And a solid lubricating film 12 is formed on a coating surface 111 which is one surface in the plate thickness direction of the base material 11. The coating surface 111 is formed in a planar shape extending in the in-plane direction.

[0014] In this embodiment, the base material 11 has an aluminum oxide film 112 on the coating surface 111 side, which is the outermost surface thereof. That is, the coating surface 111 is provided as the outer surface of the aluminum oxide film 112, which is the outermost layer of the base material 11. The aluminum oxide film 112 is formed in a thin film shape having a film thickness direction in the height direction. And the solid lubricating film 12 is formed on the aluminum oxide film 112.

[0015] The solid lubricating film 12 is a self-lubricating film mainly composed of molybdenum sulfide, and is formed with a constant film thickness so as to have a film thickness direction in the height direction. That is, the sliding surface 121 of the sliding member 10 is provided as the surface of the solid lubricating film 12.

[0016] Here, in this embodiment, the solid lubricating film 12 is composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio S / Mo of 1.33 or less. Specifically, the solid lubricating film 12 contains 11 atomic% or more of carbon. And as is clear from the cross-sectional TEM photograph shown in FIG. 2, the solid lubricating film 12 has an amorphous structure.

[0017] (Effect) Hereinafter, the wear resistance performance exhibited by the sliding member 10 according to this embodiment will be described using examples and comparative examples.

[0018] In an environment where lubricating oil cannot be used, such as a vacuum, hydrogen atmosphere, or corrosive atmosphere, a sliding element formed of self-lubricating molybdenum sulfide is used. Here, as is well known, molybdenum disulfide (that is, MoS2) has a layered structure along the (001) plane in the hexagonal crystal system in the crystalline state, and there is a problem that it is easily peeled due to the weak bond by van der Waals force between layers and wear due to sliding is likely to occur.

[0019] In this regard, for example, peeling occurs when the (001) plane is oriented perpendicular to the load direction, while peeling can be suppressed when it is oriented in the load direction. Therefore, a measure to improve wear resistance by controlling the surface orientation can be considered.

[0020] Figure 3 is a cross-sectional TEM image of comparative example film 130, a typical molybdenum disulfide film, formed using a well-known film deposition method by atomic layer deposition. As shown by the white dotted line in Figure 3, the (001) planes are oriented in random directions, making it difficult to align them completely in the same direction, and thus difficult to sufficiently suppress delamination. Furthermore, if the load and sliding are not in the same direction, frictional force is applied in the sliding direction, so even if delamination in the load direction is suppressed, delamination will occur in the sliding direction.

[0021] Figure 4 shows the time evolution of the sliding characteristics when a normal molybdenum disulfide film is formed on the surfaces of the ball and the disk, and the ball is moved back and forth a predetermined distance in a constant reciprocating direction while being pressed against each other. In Figure 4, the vertical axis μ represents the coefficient of friction. Figure 5 shows the cross-sectional profile of the disk side in this case. In Figure 5, the vertical axis D represents the wear depth. In the comparative example using a normal molybdenum disulfide film, the coefficient of friction was unstable as shown in Figure 4, and significant wear occurred as shown in Figure 5.

[0022] On the other hand, attempts have been made to amorphousize molybdenum sulfide films by adding Ti. However, adding a Ti addition step to the manufacturing process leads to increased complexity of the manufacturing line and higher manufacturing costs, and a large amount of Ti (for example, 20 atomic percent or more) is required to amorphousize the film.

[0023] Here, as is well known, molybdenum sulfide has a layered structure in which sulfur atoms are regularly arranged above and below the molybdenum atoms such that the content ratio S / Mo = 2. Furthermore, in the crystal arrangement of the (001) plane viewed from a direction perpendicular to the layering direction, there are three sulfur atoms adjacent to each molybdenum atom. Therefore, by reducing the content ratio S / Mo to 1.33 or less, one of the three adjacent sulfur atoms will be missing.

[0024] Therefore, as a result of diligent research, the inventor devised a method to amorphousize the molybdenum sulfide film by disrupting its periodicity and inhibiting the formation of a layered structure by mixing carbon into the molybdenum sulfide to create the aforementioned defects. Specifically, it was found that the solid lubricating film 12 according to this embodiment can be obtained by depositing a film using an organic material having tertiary butyl groups as the S raw material in atomic layer deposition.

[0025] Figures 6 and 7 show the time evolution of sliding characteristics and the cross-sectional profile of the disk side, respectively, when using a molybdenum sulfide film with a carbon content of 11 atomic percent in the example. In Figure 6, the vertical axis μ represents the coefficient of friction. In Figure 7, the vertical axis D represents the wear depth. As shown in Figures 6 and 7, according to the example, the coefficient of friction stabilized at a low value, and the amount of wear was also significantly suppressed.

[0026] Figure 8 shows the results of X-ray diffraction measurements using CuKα rays for an example in which the carbon content of molybdenum sulfide was 11 atomic percent and a comparative example in which the carbon content was 8.5 atomic percent. Atomic percent is also expressed as at%. In the figure, the vertical axis I represents the diffraction intensity, the horizontal axis θ represents the diffraction angle, and the dashed vertical line represents the incident angle of 7.189° corresponding to the (002) plane.

[0027] As shown in Figure 8, the comparative example clearly has a 7.189° reflection peak, whereas the example does not have such a peak. Note that "not having" a 7.189° reflection peak includes "substantially not having" one, i.e., only having a background-level reflection peak.

[0028] Figure 9 shows the relationship between carbon content and content ratio S / Mo. As is clear from the results in Figures 6 to 9, by setting the carbon content to 11 atomic percent or more, the content ratio S / Mo can be set to 1.33 or less, which makes it possible to amorphousize the molybdenum sulfide film. Figure 10 shows the relationship between adhesion strength and carbon concentration in the solid lubricating film. In Figure 10, the vertical axis S represents adhesion strength. As shown in Figure 10, by setting the carbon content to 11 atomic percent or more, the adhesion strength of the solid lubricating film 12 is significantly improved.

[0029] (Manufacturing method) The manufacturing method of the sliding member 10 according to this embodiment will be described in detail below. The sliding member 10 is obtained by forming a solid lubricant film 12 on a substrate 11 by atomic layer deposition.

[0030] Atomic layer deposition (ADD) allows for the formation of films by alternately supplying raw materials of each constituent element and allowing each atom to adsorb and react. For example, bister-thar-butyliminovisdimethylaminomolybdenum can be used as the Mo raw material. For example, diter-thar-butyldisulfide can be used as the S raw material.

[0031] The tertiary butyl group has a structure in which three methyl groups protrude from a carbon atom. Therefore, steric hindrance is likely to occur, inhibiting the adsorption of adjacent raw materials. Thus, by inhibiting the approach of adjacent sulfur atoms through adsorption while the tertiary butyl group remains, the S / Mo content ratio can be reduced. As a result, by forming the solid lubricant film 12 at a temperature below the decomposition temperature of the organic raw material, the above-mentioned good wear resistance can be obtained.

[0032] Figure 11 shows the relationship between film deposition temperature and carbon content. As shown in Figure 11, by setting the film deposition temperature to 300°C or below, which is the decomposition temperature, the carbon content can be set to 11 atomic percent or more.

[0033] In this embodiment, a solid lubricating film 12 is formed on an aluminum oxide film 112 provided on the outermost surface, the coated surface 111, of the substrate 11. By forming the film on the aluminum oxide film 112, the reaction between iron and sulfur during film formation is effectively suppressed, making it possible to effectively control the content ratio S / Mo.

[0034] (modified version) This disclosure is not limited to the embodiments described above. Therefore, the embodiments can be modified as appropriate. Representative modifications are described below. In the following description of modifications, the differences from the embodiments will be mainly described. In addition, parts that are the same or equivalent to each other in the embodiments and modifications are denoted by the same reference numerals. Therefore, in the following description of modifications, with respect to components that have the same reference numerals as in the embodiments, the descriptions in the embodiments can be appropriately referenced unless there is a technical inconsistency or additional explanation to be provided.

[0035] There are no particular limitations on the shape or structure of the sliding member 10. For example, the base material 11 may be cylindrical or spherical. In other words, the sliding surface 121 may be curved.

[0036] It goes without saying that the elements constituting the above embodiments are not necessarily essential unless explicitly stated to be particularly essential or considered to be fundamentally essential. Furthermore, when numerical values ​​such as the number, quantity, or range of components are mentioned, this disclosure is not limited to those specific numerical values ​​unless explicitly stated to be particularly essential or considered to be fundamentally limited to those specific numerical values. Similarly, when the shape, orientation, positional relationship, etc., of components are mentioned, this disclosure is not limited to those shape, orientation, positional relationship, etc., unless explicitly stated to be particularly essential or considered to be fundamentally limited to those specific shape, orientation, positional relationship, etc.

[0037] Modifications are not limited to the examples given above. That is, for example, multiple embodiments other than those exemplified above can be combined with each other, as long as they do not technically contradict each other. Similarly, multiple modifications can be combined with each other, as long as they do not technically contradict each other.

[0038] (Disclosure perspective) As is evident from the above description of embodiments and modifications, this specification discloses at least the following: [First point of view] A sliding member (10), Base material (11) and A solid lubricating film (12) is provided so as to cover the substrate, It has, The solid lubricating film is composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio (S / Mo) of 1.33 or less. Sliding member. [Second perspective] The amount of carbon contained in the molybdenum sulfide constituting the solid lubricating film is 11 atomic percent or more. A sliding member as described in the first aspect. [Third perspective] The solid lubricating film does not have a reflection peak at an incident angle of 7.189° in X-ray diffraction measurements using CuKα rays. A sliding member as described in the first or second viewpoint. [Fourth perspective] The solid lubricating film is formed on an aluminum oxide film (112) provided on the outermost surface (111) of the substrate. A sliding member described in any one of the first to third viewpoints. [Fifth perspective] A method for manufacturing a sliding member as described in any one of the first to fourth viewpoints, The solid lubricating film is fabricated by atomic layer deposition using an organic material having a tertiary butyl group as a sulfur-containing raw material. A method for manufacturing a sliding member. [Sixth perspective] The solid lubricating film is formed at a temperature below the decomposition temperature of the organic material. A method for manufacturing a sliding member as described in the fifth aspect. [Explanation of Symbols]

[0039] 10 Sliding member 11 Base material 111 Coating surface (outermost surface of the substrate) 112 Aluminum oxide coating 12 Solid lubricant film 121 Sliding surface

Claims

1. A sliding member (10), Base material (11) and A solid lubricating film (12) is provided so as to cover the substrate, It has, The solid lubricating film is composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio (S / Mo) of 1.33 or less. Sliding member.

2. The amount of carbon contained in the molybdenum sulfide constituting the solid lubricating film is 11 atomic percent or more. The sliding member according to claim 1.

3. The solid lubricating film does not have a reflection peak at an incident angle of 7.189° in X-ray diffraction measurements using CuKα rays. The sliding member according to claim 1 or 2.

4. The solid lubricating film is formed on an aluminum oxide film (112) provided on the outermost surface (111) of the substrate. The sliding member according to claim 1 or 2.

5. A method for manufacturing a sliding member (10) having a base material (11) and a solid lubricating film (12) provided to cover the base material and composed of molybdenum sulfide with a sulfur-to-molybdenum content ratio S / Mo of 1.33 or less, The solid lubricating film is fabricated by atomic layer deposition using an organic material having a tertiary butyl group as a sulfur-containing raw material. A method for manufacturing a sliding member.

6. The solid lubricating film is formed at a temperature below the decomposition temperature of the organic material. A method for manufacturing a sliding member according to claim 5.

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