Sliding member

Abstract

To provide a sliding member in which a DLC layer is separated even finer, conformity to the shape is improved, and seizure resistance is thus improved.SOLUTION: A sliding member 10 comprises a bearing alloy layer 12, and a first DLC layer 11 provided on a sliding side of the bearing alloy layer 12 with a mating material. The first DLC layer 11 is formed of DLC containing a preset additive element, and high concentration parts 21 having a high concentration of the additive element and low concentration parts 22 having a lower concentration of the additive element than the high concentration part 21 are alternately formed in a direction perpendicular to a thickness direction.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present embodiment relates to a sliding member. [Background technology]

[0002] Conventionally, a sliding member used in a bearing is known to have a DLC (Diamond Like Carbon) layer formed on the outermost surface that slides against a counter material (Patent Document 1). A sliding member on which a DLC layer is formed has a reduced coefficient of friction with the counter material. Therefore, a sliding member on which a DLC layer is formed has a characteristic that the frequency of occurrence of seizure is reduced. On the other hand, since the DLC layer is very hard, it is difficult to cause wear or deformation. Therefore, there is a problem that it is difficult to expect oil clearance due to conformity between the sliding member having a DLC layer and the counter material. In addition, if peeling occurs due to the brittleness of the DLC layer, it will lead to a local increase in the coefficient of friction and a decrease in seizure resistance.

[0003] In the case of Patent Document 1, the DLC layer is provided with a cause part that is the cause of intentional separation. The DLC layer separates from the cause part, and the DLC layer deforms to follow the base material, improving the conformability of the shape. However, the performance required for the sliding member is increasing, and the sliding conditions between the sliding member and the counter member are becoming more severe. Therefore, there is a demand for even finer separation of the DLC layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-143802 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide a sliding member in which the DLC layer is separated even finer, the conformity to the shape is improved, and the seizure resistance is accordingly improved. [Means for solving the problem]

[0006] A sliding member according to one embodiment includes a bearing alloy layer and a first DLC layer provided on the sliding side of the bearing alloy layer with respect to a mating material, the first DLC layer being formed of DLC containing a preset additive element, and high concentration portions having a high concentration of the additive element and low concentration portions having a lower concentration of the additive element than the high concentration portions being alternately formed in a direction perpendicular to the thickness direction.

[0007] Thus, in the slide member according to one embodiment, the first DLC layer has high concentration parts and low concentration parts formed by the concentration of the added element in a direction perpendicular to the thickness direction. That is, in the first DLC layer of the slide member according to one embodiment, high concentration parts and low concentration parts are alternately formed at the atomic level. Therefore, separation of the first DLC layer is promoted starting from the strength change part caused by the concentration of the added element. Therefore, the first DLC layer is separated more finely, the conformity of the shape can be further improved, and the seizure resistance can be further improved. [Brief description of the drawings]

[0008] [Figure 1] Schematic diagram showing a cross section taken along line II in FIG. 2. [Diagram 2] FIG. 2 is a schematic diagram of a sliding member according to an embodiment, viewed from an end in an axial direction; [Diagram 3] FIG. 13 is a schematic cross-sectional view of another embodiment of the sliding member according to the embodiment; [Figure 4] FIG. 1 is a schematic diagram showing a main part of a sliding member according to an embodiment; [Diagram 5] 5 is a schematic diagram showing a forming interface of a slide member according to one embodiment as viewed from the direction of arrow V shown in FIG. [Figure 6] FIG. 2 is a schematic diagram illustrating a structure of a first DLC layer of a slide member according to an embodiment; [Figure 7] FIG. 13 is a schematic cross-sectional view of another embodiment of the sliding member according to the embodiment; [Figure 8] Schematic diagram showing the conditions of the seizure test [Figure 9] FIG. 2 is a schematic diagram showing contact between a first DLC layer and a counter material in a slide member according to an embodiment. [Figure 10] FIG. 1 is a schematic diagram showing conformity caused by contact between a first DLC layer and a counter material in a sliding member according to an embodiment; [Figure 11] FIG. 1 is a schematic diagram showing conformation caused by contact between a first DLC layer and a counter material in a slide member according to an embodiment, as viewed from an end in the axial direction; [Figure 12] FIG. 1 is a schematic diagram illustrating an example of a sliding member according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the sliding member will be described with reference to the drawings. As shown in FIG. 1 and FIG. 2, the sliding member 10 includes a first DLC layer 11 and a bearing alloy layer 12. The first DLC layer 11 is provided on the side of the bearing alloy layer 12 that slides with a counter material. The first DLC layer 11 is laminated on the bearing alloy layer 12 and is bonded to the bearing alloy layer 12. The bearing alloy layer 12 is formed of, for example, a Cu-based or Al-based alloy. The sliding member 10 may include a backing layer 13 formed of Fe, steel, or the like. The first DLC layer 11 forms a sliding surface 14 that slides with the counter material on the side opposite to the bearing alloy layer 12. The first DLC layer 11 has a hardness based on Vickers hardness (HV) of 250HV to 1500HV. This reduces the attacking power of the first DLC layer 11 against the counter material.

[0010] The first DLC layer 11 contains a preset additive element. The additive element is one or more elements selected from elements that form carbides, 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 the additive element as a whole. This makes it easier for the first DLC layer 11 to conform to the shape. Furthermore, as shown in FIG. 3, the slide member 10 may include an intermediate layer 15 in addition to the first DLC layer 11 and the bearing alloy layer 12. The intermediate layer 15 is provided 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 additive element. As shown in FIG. 1, the end of the first DLC layer 11 on the bearing alloy layer 12 side is a formation interface 16. 3, in the case of slide member 10 having intermediate layer 15, the end portion of first DLC layer 11 on the intermediate layer 15 side is formation interface 16. Hereinafter, when the term formation interface 16 is referred to in this specification, it refers to the end face of first DLC layer 11 on the bearing alloy layer 12 side and the end face of first DLC layer 11 on the intermediate layer 15 side.

[0011] 4 and 5, the first DLC layer 11 includes a high concentration portion 21, a low concentration portion 22, and a core portion 23. The high concentration portion 21 and the low concentration portion 22 differ in the concentration of the additive element contained in the first DLC layer 11. The high concentration portion 21 and the low concentration portion 22 are alternately formed in a direction perpendicular to the thickness direction, that is, in the planar direction of the formation interface 16, in other words, in the direction along the sliding surface 14.

[0012] The high concentration portion 21 has a concentration of the additive element of 1 vol% to 60 vol%, and the low concentration portion 22 has a concentration of the additive element of 0.5 vol% to 59 vol%. This reduces the influence on the sliding performance of the first DLC layer 11, while facilitating shape conformity. The high concentration portion 21 is a region in which the concentration of the additive element is relatively higher than that of the low concentration portion 22. The concentration of the additive element does not change clearly at the boundary between the high concentration portion 21 and the low concentration portion 22. That is, as shown in FIG. 4, the concentration of the additive element changes continuously at the boundary between the high concentration portion 21 and the low concentration portion 22. In FIG. 4, the high concentration portion 21 having a high concentration of the additive element is shown in a dark color, and the low concentration portion 22 is shown in a light color, for ease of understanding. The high concentration portion 21 does not necessarily have to be formed in a clear columnar shape in the thickness direction of the first DLC layer 11. That is, the high concentration portions 21 may be formed in a three-dimensional hemispherical range centered on the core portion 23. Even when the high concentration portions 21 are formed three-dimensionally, the low concentration portions 22 exist between adjacent high concentration portions 21. In the first DLC layer 11, the concentration difference between the region with the highest concentration of the additive element in the high concentration portions 21 and the region with the lowest concentration of the additive element in the low concentration portions 22 is preferably 1 vol% or more. By forming such a concentration difference, separation of the first DLC layer 11 is promoted, and shape conformity is more likely to occur.

[0013] The core 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 23 is provided at the formation interface 16, which is the end of the first DLC layer 11 on the bearing alloy layer 12 side. When the intermediate layer 15 is provided, the core 23 is provided at the formation interface 16, which is the end of the first DLC layer 11 on the intermediate layer 15 side. The core 23 is provided corresponding to the high concentration portion 21 of the first DLC layer 11. That is, the core 23 is located at the end of the high concentration portion 21 of the first DLC layer 11 on the bearing alloy layer 12 side. The core 23 is a region in the first DLC layer 11 where the concentration of the additive element is high. In this case, the concentration of the additive element in the core 23 is preferably 60% or more. The region of the first DLC layer 11 other than the additive element is composed of aC:H. 4, for ease of understanding, the core portion 23 is shown in white. The concentration of the additive element also changes continuously between the high concentration portion 21 and the core portion 23.

[0014] As shown in FIG. 6, the outer diameter a of the core 23 is set to 1 nm≦a≦125 nm. Based on the outer diameter a of the core 23, the shortest distance Da between the cores 23 is 2a≦Da≦8a. The distance Da between the cores 23 corresponds to the shortest distance to the center of adjacent cores 23 in the cross section of the thickness direction of the first DLC layer 11 as shown in FIG. 1, FIG. 4 and FIG. 6. For this reason, the shortest distance Da between the cores 23 is set to about several nm to several hundred nm, which is sufficiently small compared to the conventional method. The structure of the first DLC layer 11 as shown in FIG. 4 is also formed in the cross section in the direction of the arrow X in FIG. 1.

[0015] 5, the cores 23 are arranged generally evenly at the formation interface 16, which is the end of the first DLC layer 11 on the bearing alloy layer 12 side. The cores 23 are formed at the formation interface 16 by the additive elements when only the additive elements are sputtered prior to the formation of the first DLC layer 11 by sputtering. At this time, the additive elements forming the cores 23 are arranged generally regularly while maintaining an interval Da that correlates with the outer diameter a of the cores 23, based on their own interactions and the sputtering conditions.

[0016] As shown in FIG. 6, the high concentration portion 21 is preferably spaced apart from another adjacent high concentration portion 21 by about Db=2a, based on the outer diameter a of the core portion 23. In this case, the distance Db may be in the range of about 2a≦Db≦8a. Similarly, the low concentration portion 22 is preferably spaced apart from another adjacent low concentration portion 22 by about Dc=2a, based on the outer diameter a of the core portion 23. In this case, the distance Dc may be in the range of about 2a≦Dc≦8a. The high concentration portion 21 grows from the formation interface 16 in the thickness direction of the first DLC layer 11 in correspondence with the core portion 23 by sputtering carbon (C) forming the first DLC layer 11 together with the additive element. That is, the high concentration portion 21 is formed by extending from the core portion 23 to the opposite side to the bearing alloy layer 12. In addition, between the high concentration portions 21 formed in correspondence with the core portion 23, low concentration portions 22 having a lower concentration of the additive element than the high concentration portions 21 are formed.

[0017] As shown in FIG. 4, the concentration of the additive element changes continuously at the boundary between the high concentration portion 21 and the low concentration portion 22, and the concentration of the additive element does not change clearly at the boundary between the high concentration portion 21 and the low concentration portion 22. Therefore, the intervals Db and Dc are defined and calculated as follows. First, the center point of the core portion 23 at the formation interface 16 is extracted. From this center point, a circular region is defined along the formation interface 16 with a radius of 1 / 4 of the interval Da. The width of this region, that is, the length of the part corresponding to the diameter of the circular region centered on the center point, is defined as the interval Dc. Then, the region sandwiched between the defined intervals Dc is defined as the interval Db.

[0018] By providing intermediate layer 15 between first DLC layer 11 and bearing alloy layer 12, the additional element growing from formation interface 16 is more firmly fixed to intermediate layer 15. In other words, intermediate layer 15 is preferably formed of an element that is the same as the additional element or has a high material commonality with the additional element. By forming intermediate layer 15 by selecting an element in this way, core portion 23 is more easily formed in intermediate layer 15, and the fixation to intermediate layer 15 is also improved. Intermediate layer 15 is preferably formed to a thickness of about 0.1 μm to 1 μm. This ensures that the adhesive strength between first DLC layer 11 and bearing alloy layer 12 is secured.

[0019] The sliding member 10 may further include a second DLC layer 30 as shown in FIG. 7. The second DLC layer 30 is laminated on the sliding side of the first DLC layer 11, that is, on the surface of the first DLC layer 11 opposite to the bearing alloy layer 12. The second DLC layer 30 is formed of DLC like the first DLC layer 11. The second DLC layer 30 has a lower concentration of additive elements than the concentration of additive elements contained in the entire first DLC layer 11. That is, the second DLC layer 30 has a lower concentration of additive elements than the first DLC layer 11 to be laminated thereon, and the concentration of additive elements is set to 0 to 20 vol%. By setting the concentration of additive elements of the second DLC layer 30 in this manner, the second DLC layer 30 can reduce the aggressiveness of the second DLC layer 30 to the counter material and can easily adjust the difference in hardness with the first DLC layer 11. In addition, 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 250HV to 1500HV. In this case, it is more preferable that the difference in hardness between the first DLC layer 11 and the second DLC layer 30 is 100HV or less. This reduces the attacking power of the second DLC layer 30 against the counter material. The concentrations of the additive elements in the first DLC layer 11, the high concentration portion 21, the low concentration portion 22, and the second DLC layer 30 are measured from the cross section of the sliding member 10 using an electron probe microanalyzer (EPMA). The concentration of the additive element in the entire first DLC layer 11 is calculated by averaging the concentration of the additive element in the high concentration portion 21 and the concentration of the additive element in the low concentration portion 22.

[0020] Next, an example of a method for manufacturing the slide member 10 will be described. The first DLC layer 11 is formed using a sputtering device as described above. The material on which the bearing alloy layer 12 is formed is contained in a chamber. The chamber containing the material has an internal volume of, for example, 1.0×10 -3The pressure is reduced to 1 Pa or less. After the pressure reduction, the material is pretreated, for example, using an inert gas. When the pretreatment is completed, a core 23 is formed on the surface of the bearing alloy layer 12 that will become the formation interface 16. Prior to the formation of this core 23, an intermediate layer 15 may be formed on the surface of the bearing alloy layer 12. The intermediate layer 15 is formed by sputtering an additive element alone on the surface of the bearing alloy layer 12. The core 23 is formed on the formation interface 16 by performing a short sputtering process of about several minutes. At this time, the core 23 is formed on the formation interface 16 approximately uniformly at an interval Da according to the outer diameter a of the core 23 as shown in FIG. 6 due to the interaction of the additive elements. The outer diameter a and the interval Da of these cores 23 are controlled, for example, by the time required for sputtering, the bias voltage, the target used, and the pressure in the chamber. The outer diameter a and the interval Da are controlled, in particular, by the pressure in the chamber.

[0021] The material on which the core portion 23 is formed is used to form 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 portion 23. Furthermore, when forming the first DLC layer 11, the thickness of the film formed per unit time is set to be larger than that of the formation of the core portion 23. After the first DLC layer 11 is formed, the second DLC layer 30 is formed as necessary. When forming the second DLC layer 30, the thickness of the film formed per unit time is set to be smaller than that of the first DLC layer 11. The above procedure forms the slide member 10. Note that the above disclosure is merely an example of a manufacturing method, and the manufacturing method for forming the high concentration portion 21 and the low concentration portion 22 in the first DLC layer 11 is not limited to the above disclosure.

[0022] The operation of the sliding member 10 of this embodiment will be described below based on verification of examples and comparative examples. The examples and comparative examples were evaluated based on a seizure test. The seizure test was performed under the conditions shown in FIG. 8. The sliding members 10 of the examples and comparative examples, which were formed into a half-split shape, were used in the seizure test. In the seizure test, the maximum contact pressure at which seizure did not occur was measured when the sliding member 10 was caused to slide against a shaft-shaped mating member 40 made of S55C with improper contact based on the conditions shown in FIG. 8, as shown in FIG. 9 and FIG. 10.

[0023] When the sliding member 10 and the counter member 40 are caused to slide with an incorrect contact as shown in FIG. 9, the bearing alloy layer 12 of the sliding member 10 is deformed as shown in FIG. 10 by the force applied from the counter member 40. At this time, the first DLC layer 11 of the sliding member 10 according to this embodiment is promoted to separate from the portion where the strength changes due to the concentration of the added element. That is, the first DLC layer 11 is formed with alternating high concentration portions 21 and low concentration portions 22 having different concentrations of the added element, so that a partial difference in strength occurs in a minute sense. As a result, the first DLC layer 11 is promoted to separate finely from the portion where the strength differs. Therefore, the first DLC layer 11, which is finely broken as in the sliding member 10 according to this embodiment, is deformed following the deformation of the bearing alloy layer 12 as shown in FIG. 10 and FIG. 11. As a result, even if the sliding member 10 comes into improper contact with the mating member 40, it is possible for the sliding member 10 to easily follow the deformation of the bearing alloy layer 12, thereby improving the seizure resistance.

[0024] 12, Examples 1 to 15 are examples in which the first DLC layer 11 is laminated directly on the bearing alloy layer 12, and no intermediate layer 15 is provided. Examples 16 to 24 are examples in which an 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 a second DLC layer 30 is provided in addition to the first DLC layer 11.

[0025] On the other hand, Comparative Example 1 and Comparative Example 2 are examples in which a first DLC layer 11 containing an additive element is provided in the bearing alloy layer 12, but a concentration distribution of the additive element is not formed in the first DLC layer 11. That is, in Comparative Example 1 and Comparative Example 2, high concentration portions 21 and low concentration portions 22 are not formed in the first DLC layer 11. Comparative Example 3 and Comparative Example 4 are examples in which an intermediate layer 15 is provided between the first DLC layer 11 and the bearing alloy layer 12. The first DLC layer 11 in Comparative Example 3 and Comparative Example 4 does not contain an additive element.

[0026] It is seen that the seizure resistance of Examples 1 to 24 is improved compared to Comparative Examples 1 to 4. That is, in the first DLC layer 11 in which the high concentration parts 21 and the low concentration parts 22 are alternately formed as in Examples 1 to 24, when stress due to improper contact is applied, destruction is promoted in the low concentration parts 22 in which the concentration of the additive element is low. Therefore, the first DLC layer 11 is improved in its ability to follow the deformation of the bearing alloy layer 12. As a result, the seizure resistance of the slide member 10 is improved. Moreover, according to Examples 1 to 13, it is seen that the type and combination of the additive elements contained in the first DLC layer 11 do not affect the seizure resistance.

[0027] It can be seen from Examples 12 to 24 that the smaller the spacing Da of the core portion 23, the more improved the seizure resistance. When the spacing Da of the core portion 23 becomes smaller, the spacing Db of the high concentration portion 21 and the spacing Dc of the low concentration portion 22 naturally become smaller. Therefore, in the first DLC layer 11, the smaller the spacing Da of the core portion 23, the more microscopic fracture is promoted. Therefore, the first DLC layer 11 has improved ability to follow the deformation of the bearing alloy layer 12. As a result, the seizure resistance of the slide member 10 is improved.

[0028] According to Examples 15 and 16, it is found that Example 16, in which intermediate layer 15 is provided, has improved seizure resistance. Intermediate layer 15 contributes to improving the fixation of nuclei 23, which are the starting points for the growth of high-concentration portion 21. That is, intermediate layer 15 is formed of an element having the same or similar properties as the additive element added to first DLC layer 11, and has high affinity with nuclei 23. Therefore, by forming intermediate layer 15, the adhesive strength between first DLC layer 11 and bearing alloy layer 12 is increased. As a result, detachment of first DLC layer 11 from bearing alloy layer 12 is reduced, and the seizure resistance of slide member 10 is further improved.

[0029] It is seen that the seizure resistance is further improved in Examples 17 to 24 in which the second DLC layer 30 is provided. The second DLC layer 30 contributes to reducing the contact resistance between the sliding member 10 and the mating member 40, especially in the early stage of sliding with the mating member 40. Therefore, by providing the second DLC layer 30, damage during sliding between the sliding member 10 and the mating member 40 is reduced, and the seizure resistance of the sliding member 10 is further improved. In this case, it is seen that the seizure resistance is further improved in Examples 21 to 24 in which T1>T2. In this way, by making T1>T2, separation of the first DLC layer 11 that follows the deformation of the bearing alloy layer 12 is further promoted. As a result, the seizure resistance can be further improved. In addition, it is seen that the seizure resistance is further improved in Example 24 in which the difference in hardness between the first DLC layer 11 and the second DLC layer 30 is 100HV or less. In this way, by reducing the difference in hardness between the first DLC layer 11 and the second DLC layer 30, the adhesive strength between the first DLC layer 11 and the second DLC layer 30 is improved. As a result, the seizure resistance can be further improved.

[0030] The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist of the invention. [Explanation of symbols]

[0031] In the drawing, 10 denotes a sliding member, 11 denotes a first DLC layer, 12 denotes a bearing alloy layer, 15 denotes an intermediate layer, 21 denotes a high concentration portion, 22 denotes a low concentration portion, 23 denotes a core portion, and 30 denotes a second DLC layer.

Claims

1. A sliding member comprising a bearing alloy layer and a first DLC layer provided on a sliding side of the bearing alloy layer with a counter material, The first DLC layer is It is formed of DLC containing a preset additive element, a high concentration portion having a high concentration of the additive element and a low concentration portion having a lower concentration of the additive element than the high concentration portion are alternately formed in a direction perpendicular to the thickness direction; Sliding member.

2. a core portion provided on the bearing alloy layer side of the first DLC layer in correspondence with the high concentration portion, the core portion having a higher concentration of the additive element than the high concentration portion; The sliding member according to claim 1.

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

4. The additive element is one or more elements that form carbides. The sliding member according to claim 1 .

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

6. Further comprising an intermediate layer provided between the bearing alloy layer and the first DLC layer and formed of one or more elements selected from the group consisting of W, Co, Zr, Ta, Nb, V, Ti, Cr, Si, Ni, and Mo. The sliding member according to claim 1.

7. a second DLC layer provided on a sliding side of the first DLC layer and made of DLC having a lower concentration of the additive element than a concentration of the additive element contained in the entire first DLC layer; The sliding member according to claim 6.

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

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

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