Sliding member

Abstract

A sliding member (10) is provided with: a bearing alloy layer (12); and a first DLC layer (11) provided on a sliding side of the bearing alloy layer (12) with respect to the mating member. The first DLC layer (11) is formed of a DLC containing a preset additive element, and a high-concentration section (21) in which the concentration of the additive element is high and a low-concentration section (22) in which the concentration of the additive element is lower than that of the high-concentration section (21) are alternately formed in a direction perpendicular to the thickness direction.

Description

[0001] Cross Reference to Related Applications

[0002] This application is based on Japanese Patent Application No. 2023-073393 filed on April 27, 2023, and the content of the application is incorporated herein by reference. TECHNICAL FIELD

[0003] The present embodiment relates to a sliding member. BACKGROUND

[0004] In the past, as a sliding member for a bearing, a sliding member in which a DLC (Diamond Like Carbon) layer is formed on the most surface that slides against a mating member is known (Patent Literature 1). The sliding member in which the DLC layer is formed has a reduced coefficient of friction with the mating member. Therefore, the sliding member in which the DLC layer is formed has a characteristic of reducing the frequency of occurrence of seizure. On the other hand, the DLC layer is very hard and is not easily worn or deformed. Therefore, there is a problem in that it is difficult to expect that the sliding member having the DLC layer and the mating member secure the oil film gap by shape running-in. In addition, there is a problem in that when peeling occurs due to the brittleness of the DLC layer, the coefficient of friction locally increases and the seizure resistance is reduced.

[0005] In the case of Patent Literature 1, the DLC layer is provided with a starting portion that intentionally causes separation. The DLC layer is separated from the starting portion as a starting point, and thus the DLC layer is deformed with the base material, and the purpose of improving the shape running-in property is achieved. However, the performance required of the sliding member is higher, and the sliding conditions of the sliding member and the mating member become more severe. Therefore, more subtle separation of the DLC layer is required.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: Japanese Patent Application Publication No. 2019-143802 SUMMARY

[0009] Problems to be Solved by the Invention

[0010] Therefore, an object of the present application is to provide a sliding member that can achieve more subtle separation of a DLC layer, further improvement of shape running-in, and further improvement of seizure resistance resulting therefrom.

[0011] Means for Solving the Problems

[0012] The sliding member of one embodiment has a bearing alloy layer, and a first DLC layer provided on a sliding side of the bearing alloy layer with respect to a mating member. The first DLC layer is formed of DLC containing a predetermined additive element, a high-concentration portion in which the concentration of the additive element is high, and a low-concentration portion in which the concentration of the additive element is lower than in the high-concentration portion are alternately formed in a direction perpendicular to a thickness direction.

[0013] In this way, in the sliding member of one embodiment, the first DLC layer has the high-concentration portion and the low-concentration portion formed by the concentration of the additive element being high and low, respectively, in the direction perpendicular to the thickness direction. That is, the first DLC layer of the sliding member of one embodiment has the high-concentration portion and the low-concentration portion alternately formed at the atomic level. Thus, the first DLC layer is caused to separate from the start of the strength variation portion caused by the concentration of the additive element being high and low. Thus, the first DLC layer can separate more finely, shape adaptation is further improved, and further improvement of seizure resistance can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic view of a cross section of Figure 2

[0015] Figure 2 is a schematic view of the sliding member of one embodiment as viewed from an axial end portion;

[0016] Figure 3 is a schematic view of a cross section of another embodiment of the sliding member of one embodiment;

[0017] Figure 4 is a schematic view of a main portion of the sliding member of one embodiment;

[0018] Figure 5 is a schematic view of an interface formed in the sliding member of one embodiment as viewed in the direction of the arrow V shown in Figure 4

[0019] Figure 6 is a schematic view for explaining the structure of the first DLC layer of the sliding member of one embodiment;

[0020] Figure 7 is a schematic view of a cross section of another embodiment of the sliding member of one embodiment;

[0021] Figure 8 is a summary view of conditions of a seizure test;

[0022] Figure 9 is a schematic view of contact of the first DLC layer with the mating member in the sliding member of one embodiment; ​​

[0023] Figure 10 This is a schematic diagram illustrating the break-in process resulting from the contact between the first DLC layer in the sliding member and the mating part in one embodiment.

[0024] Figure 11 This is a schematic diagram illustrating the running-in state of the first DLC layer in a sliding member of one embodiment, as viewed from the axial end.

[0025] Figure 12 This is a schematic diagram illustrating an embodiment of a sliding member. Detailed Implementation

[0026] The following describes an embodiment of the sliding member based on the accompanying drawings.

[0027] like Figure 1 and Figure 2 As shown, the sliding member 10 has a first DLC layer 11 and a bearing alloy layer 12. The first DLC layer 11 is disposed on the sliding side of the bearing alloy layer 12 relative to the mating member. The first DLC layer 11 is laminated on the bearing alloy layer 12 and bonded to it. The bearing alloy layer 12 is formed of an alloy such as Cu or Al. Alternatively, the sliding member 10 may also have a backing metal layer 13 formed of Fe, steel, etc. The first DLC layer 11 has a sliding surface 14 formed on the opposite side from the bearing alloy layer 12, which slides relative to the mating member. The hardness of the first DLC layer 11 based on Vickers hardness (HV) is 250HV to 1500HV. This reduces the aggression of the first DLC layer 11 on the mating member.

[0028] The first DLC layer 11 includes pre-defined additive elements. These additive elements are selected from one or more carbide-forming elements, such as W, Co, Zr, Ta, Nb, V, Ti, Cr, Si, Ni, and Mo. The first DLC layer 11 contains 1 vol% to 60 vol% of these additive elements. Therefore, the first DLC layer 11 is prone to shape fitting. Furthermore, as... Figure 3 As shown, in addition to the first DLC layer 11 and the bearing alloy layer 12, the sliding member 10 may also have an intermediate layer 15. The intermediate layer 15 is disposed between the first DLC layer 11 and the bearing alloy layer 12. The intermediate layer 15 is formed of one or more elements selected from W, Co, Zr, Ta, Nb, V, Ti, Cr, Si, Ni, and Mo, similar to the added elements. Figure 1 As shown, the end of the first DLC layer 11 on the bearing alloy layer 12 side forms the interface 16. Furthermore, as... Figure 3As shown, in the case of the sliding member 10 having an intermediate layer 15, the end of the first DLC layer 11 on the intermediate layer 15 side forms an interface 16. Hereinafter, in this specification, the term "forming interface 16" refers to the end face of the first DLC layer 11 on the bearing alloy layer 12 side and the end face of the first DLC layer 11 on the intermediate layer 15 side.

[0029] like Figure 4 and Figure 5 As shown, the first DLC layer 11 has a high-concentration portion 21, a low-concentration portion 22, and a core portion 23. The concentrations of the added elements contained in the first DLC layer 11 differ between the high-concentration portion 21 and the low-concentration portion 22. These high-concentration portions 21 and low-concentration portions 22 are formed alternately in a direction perpendicular to the thickness direction, that is, in the plane direction forming the interface 16, in other words, along the direction of the sliding surface 14.

[0030] In the high-concentration section 21, the concentration of the added element is 1 vol% to 60 vol%, while in the low-concentration section 22, the concentration of the added element is 0.5 vol% to 59 vol%. Therefore, the first DLC layer 11 can reduce its impact on sliding performance and facilitate shape-fitting. The high-concentration section 21 is a region where the concentration of the added element is relatively higher than that of the low-concentration section 22. For the high-concentration section 21 and the low-concentration section 22, the concentration of the added element at their boundary does not change significantly. That is, as... Figure 4 As schematically shown, the concentration of the added element changes continuously at the boundary between the high-concentration section 21 and the low-concentration section 22. Figure 4 In this diagram, for ease of understanding, the high-concentration portion 21, where the added element concentration is high, is schematically represented by a dark color, while the low-concentration portion 22 is represented by a light color. Furthermore, the high-concentration portion 21 does not necessarily have to be formed as a distinct columnar shape in the thickness direction of the first DLC layer 11. That is, the high-concentration portion 21 can also be formed in a three-dimensional hemispherical region centered on the core portion 23. Thus, even when the high-concentration portion 21 is formed in three dimensions, low-concentration portions 22 exist between adjacent high-concentration portions 21. Additionally, it is preferable that the concentration difference between the region with the highest added element concentration in the high-concentration portion 21 and the region with the lowest added element concentration in the low-concentration portion 22 of the first DLC layer 11 is 1 vol% or more. By forming such a concentration difference, the first DLC layer 11 can facilitate separation and easily achieve shape fitting.

[0031] A core portion 23 is provided on the bearing alloy layer 12 side of the first DLC layer 11. When the first DLC layer 11 and the bearing alloy layer 12 are directly laminated, the core portion 23 is provided at the formation interface 16 at the end of the bearing alloy layer 12 side of the first DLC layer 11. Furthermore, when an intermediate layer 15 is provided, the core portion 23 is provided at the formation interface 16 at the end of the intermediate layer 15 side of the first DLC layer 11. The core portion 23 is provided corresponding to the high-concentration portion 21 of the first DLC layer 11. That is, the core portion 23 is located at the end of each bearing alloy layer 12 side in the high-concentration portion 21 of the first DLC layer 11. The core portion 23 is a region in the first DLC layer 11 where the concentration of the added element is high. In this case, it is preferable that the concentration of the added element in the core portion 23 is 60% or more. The region of the first DLC layer 11, excluding the added element, is composed of aC:H. Additionally, in Figure 4 In the diagram, for ease of understanding, the core 23 is schematically represented in white. The concentration of the added element also varies continuously between this high-concentration section 21 and the core 23.

[0032] like Figure 6 As shown, the outer diameter 'a' of the core 23 is set to 1 nm ≤ a ≤ 125 nm. Based on this outer diameter 'a', the shortest interval 'Da' between the cores 23 is 2a ≤ Da ≤ 8a. For example... Figure 1 , Figure 4 as well as Figure 6 As shown, the spacing Da of the core portions 23 corresponds to the shortest distance between the centers of adjacent core portions 23 on a cross-section in the thickness direction of the first DLC layer 11. Therefore, the shortest spacing Da of the core portions 23 can be set to approximately a few nm to several hundred nm, which is significantly smaller than before. Furthermore, as... Figure 4 The construction of the first DLC layer 11 shown is in Figure 1 The same pattern is also formed on the cross-section in the X direction of the arrow.

[0033] like Figure 5 As shown, the core portions 23 are arranged approximately evenly at the formation interface 16 at the end of the bearing alloy layer 12 side, which serves as the first DLC layer 11. These core portions 23 are formed by additive elements at the formation interface 16 before the first DLC layer 11 is formed by sputtering. At this time, the additive elements forming the core portions 23 are arranged approximately regularly with a spacing Da related to the outer diameter a of the core portions 23, based on their own interactions and the sputtering conditions.

[0034] like Figure 6As shown, based on the outer diameter a of the core portion 23, the interval Db between the high-concentration portion 21 and the adjacent high-concentration portion 21 is preferably Db=2a. In this case, the interval Db can also be in the range of approximately 2a≤Db≤8a. Similarly, based on the outer diameter a of the core portion 23, the interval Dc between the low-concentration portion 22 and the adjacent low-concentration portion 22 is preferably Dc=2a. In this case, the interval Dc can also be in the range of approximately 2a≤Dc≤8a. By sputtering the carbon (C) forming the first DLC layer 11 together with the additive elements, the high-concentration portion 21 and the core portion 23 are grown from the formation interface 16 in the thickness direction of the first DLC layer 11. That is, the high-concentration portion 21 is formed extending from the core portion 23 to the side opposite to the bearing alloy layer 12. Furthermore, between the high-concentration portions 21 formed corresponding to the core portion 23, low-concentration portions 22 with a lower concentration of additive elements than the high-concentration portions 21 are formed.

[0035] like Figure 4 As shown, at the boundary between the high-concentration section 21 and the low-concentration section 22, the concentration of the added element changes continuously, rather than changing significantly at the boundary between the high-concentration section 21 and the low-concentration section 22. Therefore, the intervals Db and Dc are defined and calculated as follows. First, the center point of the core 23 forming the interface 16 is extracted. A circular region is defined along the interface 16 with a radius of 1 / 4 of the interval Da from this center point. The width of this region, that is, the length of the portion equivalent to the diameter of the circular region centered at the center point, is defined as the interval Dc. Then, the region enclosed by the already defined interval Dc is defined as the interval Db.

[0036] By providing an intermediate layer 15 between the first DLC layer 11 and the bearing alloy layer 12, the adhesion of the additive elements formed from the interface 16 to the intermediate layer 15 is improved. Specifically, the intermediate layer 15 is preferably formed of an element that is the same as or has high material commonality with the additive element. By selecting elements in this manner to form the intermediate layer 15, the core 23 is easily formed in the intermediate layer 15, and adhesion to the intermediate layer 15 is improved. Preferably, the intermediate layer 15 is formed with a thickness of approximately 0.1 μm to 1 μm. This reliably ensures the adhesion between the first DLC layer 11 and the bearing alloy layer 12.

[0037] like Figure 7As shown, the sliding member 10 can further have a second DLC layer 30. The second DLC layer 30 is layered on the sliding side of the first DLC layer 11, that is, the face of the first DLC layer 11 opposite to the bearing alloy layer 12. The second DLC layer 30 is formed of DLC as with the first DLC layer 11. The concentration of the additive element of the second DLC layer 30 is set to be lower than the concentration of the additive element contained in the entirety of the first DLC layer 11. That is, the second DLC layer 30 is lower in the concentration of the additive element than the first DLC layer 11 as the layering target, and the concentration of the additive element is set to be 0 to 20 vol%. By setting the concentration of the additive element of the second DLC layer 30 in this way, the second DLC layer 30 can reduce the aggressiveness against the mating member, and the difference in hardness from the first DLC layer 11 can be easily adjusted. Further, when the thickness of the first DLC layer 11 is T1 and the thickness of the second DLC layer 30 is T2, T1 > T2. In this way, the second DLC layer 30 is formed thinner than the first DLC layer 11. The hardness of the second DLC layer 30 is preferably set to be 250 HV to 1500 HV. In this case, it is more preferable that the difference in hardness between the first DLC layer 11 and the second DLC layer 30 be 100 HV or less. Thereby, the aggressiveness of the second DLC layer 30 against the mating member can be reduced. The concentration of the additive element in the first DLC layer 11, the high-concentration portion 21, the low-concentration portion 22, and the second DLC layer 30 is measured using an electron probe microanalyzer (EPMA) on the cross section of the sliding member 10. The concentration of the additive element of the entirety of the first DLC layer 11 is calculated by averaging the concentration of the additive element of the high-concentration portion 21 and the concentration of the additive element of the low-concentration portion 22.

[0038] Next, an example of the manufacturing method of the sliding member 10 will be described.

[0039] The first DLC layer 11 is formed using the sputtering device in the above-described manner. The material for forming the bearing alloy layer 12 is housed in the chamber. The inside of the chamber in which the material is housed is depressurized to, for example, 1.0 x 10 -3 After the depressurization, the material is subjected to a pretreatment using, for example, an inert gas. When the pretreatment is completed, the nucleus portion 23 is formed on the surface of the bearing alloy layer 12 as the interface 16. The intermediate layer 15 can also be formed on the surface of the bearing alloy layer 12 before the formation of the nucleus portion 23. The intermediate layer 15 is formed by separately sputtering the additive element on the surface of the bearing alloy layer 12. By performing sputtering for a short time of several minutes or so, the nucleus portion 23 is formed on the interface 16. At this time, due to the interaction of the additive elements, the DLC layer 11 is formed on the nucleus portion 23. Figure 6As shown, the core portions 23 are formed at substantially equal intervals Da corresponding to the outer diameter a of the core portions 23 at the interface 16. The outer diameter a and the interval Da of these core portions 23 can be controlled by the sputtering time, the bias voltage, the target used, and the pressure in the chamber, and the like. In particular, the outer diameter a and the interval Da are controlled by the pressure in the chamber.

[0040] The material forming the core portions 23 forms the first DLC layer 11. The first DLC layer 11 is formed by sputtering for a sufficiently long time compared to the formation of the core portions 23. Further, the thickness of the film formation per unit time is set to be larger when forming the first DLC layer 11 than when forming the core portions 23. When forming the first DLC layer 11, the second DLC layer 30 can be formed as needed. The thickness of the film formation per unit time is set to be smaller when forming the second DLC layer 30 than the first DLC layer 11.

[0041] By the above steps, the sliding member 10 is formed. In addition, the above description is one example of the manufacturing method, but the manufacturing method in which the first DLC layer 11 forms the high concentration portion 21 and the low concentration portion 22 is not limited to the above description.

[0042] Hereinafter, regarding the effects of the sliding member 10 of the present embodiment, the evaluation based on the examples and the comparative examples is described. The examples and the comparative examples are evaluated based on the bite test. The bite test is performed according to the conditions shown in Figure 8 The examples and the comparative examples of the sliding member 10 shaped to be halved are used in the bite test. In the bite test, the conditions shown in Figure 8 are applied, and Figure 9 and Figure 10 The maximum surface pressure at which no bite occurs is measured when the shaft-shaped fitting member 40 composed of S55C is slid in the abnormal contact state.

[0043] As shown in Figure 9 , when the sliding member 10 is caused to slide with the fitting member 40 in the abnormal contact state, the bearing alloy layer 12 of the sliding member 10 is deformed as shown in Figure 10 by the force applied by the fitting member 40. At this time, the first DLC layer 11 of the sliding member 10 of the present embodiment is caused to separate from the part where the strength varies due to the concentration of the added elements. That is, in the first DLC layer 11, the high concentration portion 21 and the low concentration portion 22 in which the concentration of the added elements differs are alternately formed, and thus a local difference in strength occurs at a fine interval. Due to this, the first DLC layer 11 is caused to separate finely from the part where the strength difference occurs. Therefore, the first DLC layer 11 that is destroyed finely like the sliding member 10 of the present embodiment is caused to separate from the part where the strength difference occurs. Figure 10 and Figure 11The first DLC layer 11 deforms as the bearing alloy layer 12 deforms as shown. As a result, even in the case of abnormal contact with the mating member 40, the sliding member 10 easily follows the deformation of the bearing alloy layer 12, and an improvement in seizure resistance can be achieved.

[0044] As shown in Figure 12 Examples 1 to 15 are examples in which the first DLC layer 11 is directly layered on the bearing alloy layer 12 without the intermediate layer 15. Examples 16 to 24 are examples in which the intermediate layer 15 is provided between the first DLC layer 11 and the bearing alloy layer 12. Examples 18 to 24 are examples in which the second DLC layer 30 is provided in addition to the first DLC layer 11.

[0045] On the other hand, Comparative Examples 1 and 2 are examples in which the first DLC layer 11 containing the additive element is provided on the bearing alloy layer 12, but the concentration distribution of the additive element in the first DLC layer 11 is not formed. That is, in Comparative Examples 1 and 2, the high-concentration portion 21 and the low-concentration portion 22 are not formed in the first DLC layer 11. Comparative Examples 3 and 4 are examples in which the intermediate layer 15 is provided between the first DLC layer 11 and the bearing alloy layer 12. The first DLC layer 11 in Comparative Examples 3 and 4 does not contain the additive element.

[0046] It is known that these Examples 1 to 24 improve the seizure resistance compared to Comparative Examples 1 to 4. That is, the first DLC layer 11 in which the high-concentration portion 21 and the low-concentration portion 22 are alternately formed as in Examples 1 to 24 promotes failure at the low-concentration portion 22 where the concentration of the additive element is low when stress is applied due to abnormal contact. Therefore, the first DLC layer 11 improves the followability to the deformation of the bearing alloy layer 12. As a result, the seizure resistance of the sliding member 10 is improved. Further, it is known from Examples 1 to 13 that the kind of the additive element and the combination of the additive elements contained in the first DLC layer 11 do not affect the seizure resistance.

[0047] It is known from Examples 12 to 24 that the smaller the interval Da of the core portion 23, the higher the seizure resistance. When the interval Da of the core portion 23 is made small, the interval Db of the high-concentration portion 21 and the interval Dc of the low-concentration portion 22 are of course also made small. Therefore, in the first DLC layer 11, as the interval Da of the core portion 23 is made small, more subtle failure is promoted. Therefore, the first DLC layer 11 further improves the followability to the deformation of the bearing alloy layer 12. As a result, the seizure resistance of the sliding member 10 is improved.

[0048] As is clear from Embodiment 15 and Embodiment 16, Embodiment 16 provided with the intermediate layer 15 can improve the seizure resistance. The intermediate layer 15 contributes to improving the adhesion of the nucleus portion 23 that is a starting point of growth of the high concentration portion 21. That is, the intermediate layer 15 is formed of an element having the same or approximately the same properties as the added element added in the first DLC layer 11, and has high affinity with the nucleus portion 23. Therefore, by forming the intermediate layer 15, it is possible to improve the adhesion of the first DLC layer 11 to the bearing alloy layer 12. As a result, the first DLC layer 11 is less likely to separate from the bearing alloy layer 12, and the seizure resistance of the sliding member 10 is further improved.

[0049] As is clear from Embodiments 17 to 24 provided with the second DLC layer 30, it is possible to further improve the seizure resistance. The second DLC layer 30 contributes to reducing the contact resistance of the sliding member 10 with the mating member 40, particularly at the initial stage of sliding with respect to the mating member 40. Therefore, by providing the second DLC layer 30, it is possible to reduce the damage in the sliding of the sliding member 10 with the mating member 40, and further improve the seizure resistance of the sliding member 10. In this case, as is clear from Embodiments 21 to 24 where T1 > T2, it is possible to further promote the separation of the first DLC layer 11 from the bearing alloy layer 12 as the bearing alloy layer 12 deforms. As a result, it is possible to achieve further improvement of the seizure resistance. In addition, as is clear from Embodiment 24 where the difference in hardness between the first DLC layer 11 and the second DLC layer 30 is 100 HV or less, it is possible to further improve the seizure resistance. As such, by reducing the difference in hardness between the first DLC layer 11 and the second DLC layer 30, it is possible to improve the adhesion of the first DLC layer 11 to the second DLC layer 30. As a result, it is possible to achieve further improvement of the seizure resistance.

[0050] The present application described above is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Claims

1. A sliding member comprising: a bearing alloy layer; and a first DLC layer disposed on the sliding side of the bearing alloy layer relative to a mating member, wherein, The first DLC layer is formed by a DLC containing pre-defined added elements. The high-concentration portion, where the concentration of the added element is high, and the low-concentration portion, where the concentration of the added element is lower than that of the high-concentration portion, are alternately formed in a direction perpendicular to the thickness direction.

2. The sliding member according to claim 1, further comprising: A core portion is disposed on the bearing alloy layer side of the first DLC layer, corresponding to the high-concentration portion, wherein the concentration of the added element in the core portion is higher than that in the high-concentration portion.

3. The sliding member according to claim 2, wherein, The outer diameter 'a' of the core is 1 nm ≤ a ≤ 125 nm. In a cross-section perpendicular to the thickness direction of the first DLC layer, the spacing Da between adjacent core portions is 2a≤Da≤8a.

4. The sliding member according to any one of claims 1 to 3, wherein, The added element is one or more of the elements that form carbides.

5. The sliding member according to claim 4, wherein, The added element is selected from one or more of W, Co, Zr, Ta, Nb, V, Ti, Cr, Si, Ni, and Mo.

6. The sliding member according to claim 1, further comprising: An intermediate layer, disposed between the bearing alloy layer and the first DLC layer, is formed of one or more elements selected from W, Co, Zr, Ta, Nb, V, Ti, Cr, Si, Ni, and Mo.

7. The sliding member according to claim 6, further comprising: The second DLC layer, disposed on the sliding side of the first DLC layer, is composed of DLC in which the concentration of the added element is lower than the concentration of the added element contained in the entire first DLC layer.

8. The sliding member according to claim 7, wherein, The thickness T1 of the first DLC layer and the thickness T2 of the second DLC layer are T1 > T2.

9. The sliding member according to claim 7, wherein, The hardness difference between the first DLC layer and the second DLC layer is less than 100 HV.

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