Sliding member

Abstract

The present invention provides a sliding member having a covering layer capable of preventing delamination between layers and achieving good fatigue resistance. The sliding member has a covering layer formed of an alloy coating film of Bi and Sb, and a Bi-Sb oxide is formed on the surface of the covering layer.

Description

Technical Field

[0001] The present invention relates to a sliding member having a covering layer with an alloy coating of Bi and Sb. Background Art

[0002] Conventionally, a sliding member having a covering layer made of Bi has been known. For example, in Patent Document 1, a technique for improving the sinter resistance by forming bismuth oxide on the surface of the covering layer is disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 6087684 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] However, when the sliding member of Patent Document 1 is used in engine oil, oxidation occurs and the thickness of bismuth oxide becomes thick. Since bismuth oxide is hard and brittle, if there is a large amount of bismuth oxide in the covering layer, the bismuth oxide falls off from the covering layer during use and the fatigue resistance decreases.

[0008] The present invention has been made in view of the above problems, and an object thereof is to improve the fatigue resistance.

[0009] Means for Solving the Problems

[0010] In order to achieve the above object, the sliding member is a sliding member having a covering layer formed of an alloy coating of Bi and Sb, and a Bi-Sb oxide is formed on the surface of the covering layer.

[0011] The ability of the Bi-Sb oxide to resist brittle fracture is stronger than that of bismuth oxide. In addition, since the Bi-Sb oxide exists on the surface of the covering layer, the generation and growth of bismuth oxide can be prevented. Therefore, the Bi-Sb oxide formed on the surface of the covering layer can prevent the bismuth oxide from falling off and the like, and improve the fatigue resistance of the sliding member. Brief Description of the Drawings

[0012] Figure 1 It is a perspective view of the sliding member according to an embodiment of the present invention.

[0013] Figure 2 It is an explanatory diagram of a fatigue test.

[0014] Figure 3 It is a graph of the fatigue area ratio. Detailed Description of the Invention

[0015] Here, the embodiments of the present invention will be described in the following order.

[0016] (1-1) Structure of the sliding member:

[0017] (1-2) Manufacturing method of the sliding member:

[0018] (2) Experimental results:

[0019] (3) Other embodiments:

[0020] (1-1) Structure of the sliding member:

[0021] Figure 1 FIG. 18 is a perspective view of a sliding member 1 according to an embodiment of the present invention. The sliding member 1 includes a backing 10, a lining 11, and a coating layer 12. The sliding member 1 is a metal member having a semi-segmented shape formed by bisecting a hollow cylinder in the diameter direction, and the cross section is a semi-circular arc shape. By combining two sliding members 1 into a cylindrical shape, a sliding bearing A is formed. The sliding bearing A axially supports a cylindrical object shaft 2 (the crankshaft of an engine) through a hollow portion formed inside. The outer diameter of the object shaft 2 is formed slightly smaller than the inner diameter of the sliding bearing A. Lubricating oil (engine oil) is supplied to the gap between the outer peripheral surface of the object shaft 2 and the inner peripheral surface of the sliding bearing A. At this time, the outer peripheral surface of the object shaft 2 slides on the inner peripheral surface of the sliding bearing A.

[0022] The sliding member 1 has a structure in which the backing 10, the lining 11, an intermediate layer 13, and the coating layer 12 are laminated in order from far to near from the center of curvature. Therefore, the backing 10 constitutes the outermost layer of the sliding member 1, and the coating layer 12 constitutes the innermost layer of the sliding member 1. The backing 10, the lining 11, the intermediate layer 13, and the coating layer 12 each have a constant thickness in the circumferential direction. The thickness of the backing 10 is, for example, 1.5 mm, the thickness of the lining 11 is, for example, 0.2 mm to 0.3 mm, the thickness of the intermediate layer 13 is, for example, 1.0 to 7.0 μm, and the thickness of the coating layer 12 is, for example, 3 to 20 μm. Twice the radius of the surface on the center-of-curvature side of the coating layer 12 (the inner diameter of the sliding member 1) is, for example, 55 mm. The width of the sliding bearing A is, for example, 19 mm. Hereinafter, the inner side refers to the center-of-curvature side of the sliding member 1, and the outer side refers to the side opposite to the center of curvature of the sliding member 1. The inner surface of the coating layer 12 constitutes the sliding surface of the object shaft 2.

[0023] In the present embodiment, the backing 10 is formed of, for example, a steel containing 0.15% by mass of C, 0.06% by mass of Mn, and the balance being Fe. In addition, the backing 10 may be formed of a material capable of supporting the load from the object shaft 2 via the lining 11 and the coating layer 12, and does not necessarily have to be formed of steel.

[0024] The lining 11 is a layer laminated on the inner side of the backing 10 and constitutes the base layer. In the present embodiment, the lining 11 is made of a Cu alloy. There is no limitation on the elements contained in the lining 11. For example, an example of the lining 11 made of a Cu-Bi alloy can be cited. Of course, elements other than Cu and Bi can also be added. For example, the lining 11 can be made of a Cu alloy containing 5% by mass of Bi, 5% by mass of Sn, 5% by mass of Ni, and the balance being Cu respectively. In addition, the lining 11 can be made of a Cu alloy containing 3% by mass of Bi, 3% by mass of In, and the balance being Cu respectively.

[0025] Furthermore, the lining 11 can be an alloy other than a Cu alloy, such as an Al alloy. The elements added to the Al alloy can also be assumed to be various elements. For example, Sn, Si, Mg, etc. can be cited. More specifically, for example, the lining 11 can be made of an Al alloy containing 7% by mass of Sn, 3% by mass of Si, and the balance being Al respectively. In addition, the lining 11 can be made of an Al alloy containing 3% by mass of Mg, and the balance being Al.

[0026] Of course, the presence or absence and concentration of these elements are just an example, and inevitable impurities can also be contained. The inevitable impurities in the lining 11 are Mg, Ti, B, Pb, Cr, etc., and can be assumed to be impurities mixed in refining or waste materials, etc. The content of the inevitable impurities in the lining 11 is, for example, 0.5% by mass or less in total.

[0027] The intermediate layer 13 can be omitted or can be provided for various functions. For example, in the structure where the lining 11 is made of a Cu alloy, if an intermediate layer 13 mainly composed of Ag is formed between the covering layer 12 and the lining 11, the amount of Cu diffusing from the lining 11 to the covering layer 12 can be reduced, and the possibility of reducing fatigue resistance can be lowered. In addition, the intermediate layer mainly composed of Ag can be, for example, pure Ag, or Ag-Sn, etc. In the latter case, a composition with a Sn concentration of, for example, 20% by mass can be cited.

[0028] The intermediate layer 13 can be composed of multiple layers. For example, the following structures can be cited: in the structure where the lining is an Al alloy, a first intermediate layer mainly composed of Cu is formed on the lining 11, and a second intermediate layer mainly composed of Ag is formed between the first intermediate layer and the covering layer 12. According to these structures, the first intermediate layer can be, for example, a structure of pure Cu. The second intermediate layer can be, for example, pure Ag, or Ag-Sn, etc. In the latter case, a composition with a Sn concentration of, for example, 20% by mass can be cited. Of course, the structure of the intermediate layer is not limited to these examples. For example, it can be a structure such as: a first intermediate layer mainly composed of Ag is formed on various linings, and a second intermediate layer mainly composed of Ag-Sn is formed between the first intermediate layer and the covering layer 12.

[0029] According to the above configuration, the amount of Cu diffusing from the Cu in the first intermediate layer to the covering layer 12 can be reduced by the second intermediate layer mainly composed of Ag, and the possibility of reducing fatigue resistance can be decreased. In addition, by forming the first intermediate layer with Cu, the possibility of delamination occurring between the second intermediate layer and the lining 11 can be reduced. Further, the intermediate layer 13 may contain inevitable impurities. The content of the inevitable impurities in the intermediate layer 13 is, for example, 0.5% by mass or less in total.

[0030] The covering layer 12 is a layer laminated on the inner surface of the lining 11. The covering layer 12 is an alloy coating film of Bi and Sb, and a Bi-Sb oxide is formed on the surface. Further, the covering layer 12 may contain inevitable impurities. The content of the inevitable impurities in the covering layer 12 is, for example, 0.5% by mass or less in total.

[0031] According to the above configuration, for example, a sliding member can be formed by the covering layer 12 with a thickness of 8 to 20 μm, the intermediate layer 13 composed of Ag-Sn with a thickness of 2 μm, the lining 11 composed of a Cu alloy with a thickness of 0.2 mm, and the backing 10 with a thickness of 1.5 mm. In addition, for example, a sliding member can be formed by the covering layer 12 with a thickness of 3 to 10 μm, the second intermediate layer with a thickness of 3 to 6 μm, the first intermediate layer with a thickness of 1 μm, the lining 11 composed of an Al alloy with a thickness of 0.3 mm, and the backing 10 with a thickness of 1.5 mm.

[0032] (1-2) Manufacturing method of the sliding member:

[0033] A Bi-Sb oxide is formed on the surface of the covering layer 12 according to the present embodiment. The covering layer 12 is formed by oxidizing an alloy coating film of Bi and Sb. Here, an example of the manufacturing method of the sliding member will be described by taking the lining 11 as a Cu alloy containing Sn, Ni, and Bi and the intermediate layer 13 as Ag-Sn as an example. In the position example of the manufacturing method of the sliding member, first, a flat plate of low-carbon steel having the same thickness as the backing 10 is prepared.

[0034] Next, powders of the materials constituting the lining 11 are scattered on the flat plate formed of low-carbon steel. Specifically, for example, powders of Cu, Sn, Ni, and Bi are scattered on the flat plate of low-carbon steel so as to be the mass ratio of each component in the above-mentioned lining 11. In the lining 11, it is sufficient to satisfy the mass ratio of each component, and alloy powders such as Cu-Sn, Cu-Ni, and Cu-Bi may also be scattered on the flat plate of low-carbon steel. The particle size of the powders can be adjusted to 150 μm or less, for example, using a test sieve (JIS Z8801).

[0035] Next, a flat plate of low-carbon steel and the powder scattered on the flat plate are sintered. The sintering temperature is controlled to be 700 to 1000 °C, and sintering is carried out in an inert atmosphere. After sintering, it is cooled. In addition, the lining 11 does not necessarily have to be formed by sintering, and can also be formed by casting or the like. If the cooling is completed, a Cu alloy layer is formed on the flat plate of low-carbon steel.

[0036] Next, the low-carbon steel formed with the Cu alloy layer is stamped into a shape obtained by bisecting a hollow cylinder in the diameter direction. At this time, stamping is performed so that the outer diameter of the low-carbon steel is the same as the outer diameter of the sliding member 1.

[0037] Next, the surface of the Cu alloy layer formed on the backing 10 is machined by cutting. At this time, the cutting amount is controlled so that the thickness of the Cu alloy layer formed on the backing 10 is the same as that of the lining 11. Thus, the lining 11 is formed by the Cu alloy layer after machining. The machining by cutting is performed, for example, by setting a lathe provided with a cutting tool material formed of sintered diamond.

[0038] Next, Ag and Sn are laminated on the surface of the lining 11 by electroplating in an amount of, for example, 2 μm in thickness to form an intermediate layer 13. In addition, here, the concentrations of Ag and Sn formed as the intermediate layer 13 can be adjusted by adjusting the metal ion concentration in the plating bath.

[0039] Next, Bi and Sb are laminated on the surface of the intermediate layer 13 by electroplating in an amount of, for example, 8 to 20 μm in thickness. The steps of electroplating are as follows, for example. First, the surface of the intermediate layer 13 is washed with water. Further, the surface of the intermediate layer 13 is pickled to remove unnecessary oxides from the surface of the intermediate layer 13. After that, the surface of the intermediate layer 13 is washed with water again.

[0040] If the above pretreatment is completed, a current is supplied to the lining 11 immersed in the plating bath to perform electroplating. The bath composition is, for example, a bath composition of a plating bath containing 150 g / L of methanesulfonic acid, 20 g / L of bismuth methanesulfonate, and 25 g / L of an organic surfactant. In the above plating bath, pure Sb is dissolved in an amount of, for example, 1.0 g / L by electrolysis. The bath temperature of the plating bath is 30 °C. Further, the current supplied to the lining 11 is a direct current, and its current density is 2.0 A / dm 2 。

[0041] In addition, in the plating bath, for example, methanesulfonic acid can be adjusted between 0 and 250 g / L, bismuth methanesulfonate can be adjusted between 5 and 40 g / L, the amount of dissolved Sb can be adjusted between 0.3 and 1.5 g / L, and the organic surfactant can be adjusted between 0.5 and 50 g / L. Additionally, the bath temperature of the plating bath can be adjusted to 20 - 50°C, and the current density of the current supplied to the lining 11 can be adjusted to 0.5 - 7.5 A / dm 2 Adjustment. The concentration of Sb in the coating layer 12 can be increased by increasing the ionic concentration of Sb in the plating bath.

[0042] As described above, after electroplating, water washing and drying are performed. Subsequently, an oxide film is formed on the surface of the coating layer 12. As methods for forming the oxide film, various techniques can be cited. For example, it can be achieved by an oxidation treatment in which, after electroplating, water washing, and drying, the product is immersed in paraffin oil containing 1000 ppm of an organic peroxide (such as methyl ethyl ketone peroxide, cumene hydroperoxide, etc.) and heated at 150°C for 50 hours. Additionally, the oxidation treatment can also be carried out by heating the electroplated, water-washed, and dried product at 200°C for 50 hours in an atmospheric atmosphere.

[0043] In addition, in the case where the lining 11 is an Al alloy, for example, by injecting the molten material of the lining 11 into a mold and pulling the molten material of the lining 11 from the opening of the mold in the casting direction, a continuous casting plate of the lining 11 is formed. Further, cold rolling is performed until the continuous casting plate of the lining 11 reaches the thickness of the lining 11. Further, by also performing cold rolling on the low-carbon steel plate of the backing 10, a rolled plate in which the continuous casting plate of the lining 11 and the low-carbon steel plate of the backing 10 are pressed together is formed.

[0044] Furthermore, the intermediate layer 13 is formed by electroplating or the like. In the case where the intermediate layer 13 is composed of a first intermediate layer and a second intermediate layer, for example, by electroplating Cu in an amount of a thickness such as 1 μm and laminating it on the surface of the lining 11, the first intermediate layer is formed. Additionally, by electroplating Ag or the like in an amount of a thickness such as 3 - 6 μm and laminating it on the surface of the first intermediate layer, the second intermediate layer is formed.

[0045] (2) Experimental results:

[0046] As described above, if an oxide film is formed on the surface of the coating layer 12, the sliding member 1 is completed. Further, if two sliding members 1 are combined in a cylindrical shape, a sliding bearing is formed. In the above sliding member 1, it is sufficient that both Bi and Sb are present in the coating layer 12 (both are more than 0 mass%), and the Sb concentration is arbitrary.

[0047] [Table 1]

[0048]

[0049] [Table 2]

[0050]

[0051] Table 1 and Table 2 are diagrams showing the main components at each depth of the covering layer 12 for multiple examples and comparative examples with different Sb concentrations (mass concentrations). In addition, in Examples 1 to 6 and Comparative Examples 1 to 6 of Table 1, the lining 11 is a 200-μm Cu alloy containing Sn, Ni, and Bi, the intermediate layer 13 is a 2-μm layer of Ag-Sn, and the covering layer 12 is a 15-μm layer. In Examples 7 to 12 and Comparative Examples 7 to 12, the lining 11 is a 300-μm Al alloy containing Sn and Si, the intermediate layer 13 is a 4-μm layer of Ag, and the covering layer 12 is a 15-μm layer. In Example 13 and Comparative Example 13, the lining 11 is a 300-μm Al alloy containing Sn and Si, the intermediate layer 13 is a first intermediate layer of 1-μm Cu and a second intermediate layer of 5-μm Ag, and the covering layer 12 is a 15-μm layer. Additionally, oxidation treatment was carried out in paraffin oil in the examples, but no oxidation treatment was carried out in the comparative examples.

[0052] In Examples 1 to 6 and Examples 7 to 12, the Sb concentration is 2.0 mass% to 12.0 mass%, and in Comparative Examples 1 to 6 and Comparative Examples 7 to 12, the Sb concentration is 2.0 mass% to 12.0 mass%. In Example 13 and Comparative Example 13, the Sb concentration is 5.0 mass%. In addition, the concentration of Sb in the covering layer 12 can be adjusted by increasing or decreasing the Sb concentration in the plating bath for electroplating.

[0053] In Table 1 and Table 2, the main components at each depth position starting from the outermost surface of the covering layer 12 are shown. That is, the main components when the depths of the respective samples are 0 μm (outermost surface), 0.01 μm, 0.05 μm, 0.1 μm, 1 μm, and 3 μm are shown.

[0054] In addition, the main components at each depth position are measured by a scanning X-ray photoelectron spectroscopy analyzer (PHI X-tool manufactured by ULVAC-PHI). That is, measurement regions are set at positions with depths of 0 μm, 0.01 μm, 0.05 μm, 0.1 μm, 1 μm, and 3 μm in the depth direction of the coating layer 12, and X-ray photoelectron spectroscopy analysis is performed. In addition, the size and shape of the measurement region are a square with a side length of 2 mm. The components present in the measurement region are determined from the binding energies obtained from the measurement regions at each depth, and the abundance ratios of the components are quantified from the peak areas. Then, the components with an abundance ratio above the threshold are determined as the main components. In addition, the main components can be defined by various methods. For example, the N (N is an integer of 1 or more) compounds with the abundance ratios from large to small can be used as the main components. Alternatively, the compounds with an abundance ratio above the threshold and up to the top N in terms of abundance ratio can be used as the main components. In either case, the compound with the highest abundance ratio is the main component.

[0055] For example, in all of Examples 1 to 13, the outermost main component is a Bi-Sb oxide (Bi-Sb-O). In all of these Examples 1 to 13, at least on the outermost surface, the abundance ratio of the Bi-Sb-O compound is larger than the abundance ratios of other compounds and elemental metals. In Examples 1 to 13, a Bi-Sb oxide is formed as the main component over the entire sliding surface between the coating layer 12 and the object shaft 2. On the other hand, in all of Comparative Examples 1 to 13, the outermost main component is not an oxide.

[0056] The Bi-Sb oxide is a compound with very high stability. Therefore, by having the Bi-Sb oxide on the outermost surface, the coating layer 12 can be protected. Accordingly, the fatigue resistance of Examples 1 to 13 in which the Bi-Sb oxide is present on the outermost surface is higher than that of Comparative Examples 1 to 13 in which the Bi-Sb oxide is not present on the outermost surface. In Table 1, the results of the fatigue tests performed on the sliding members of Examples 1 to 13 and Comparative Examples 1 to 13 are shown as the fatigue area ratio (%). Figure 3 It is a graph showing the fatigue area ratio (%). In addition, in Figure 3 , the horizontal axis is the Sb concentration in the coating layer 12, and Examples 1 to 6 are plotted as black circles, Examples 7 to 12 are plotted as black squares, and Example 13 is plotted as a black triangle. Comparative Examples 1 to 6 are plotted as white circles, Comparative Examples 7 to 12 are plotted as white squares, and Comparative Example 13 is plotted as a white triangle.

[0057] The fatigue area ratio is measured through the following steps. Figure 2 It is an explanatory diagram of the fatigue test. First, as Figure 2As shown, a connecting rod R having cylindrical through-holes formed at both ends in the length direction is prepared, and a test shaft H (shaded) is shaft-supported through the through-hole at one end.

[0058] In addition, a coating layer 12 (black) similar to the sliding member 1 is formed on the inner peripheral surface of the through-hole of the connecting rod R that shaft-supports the test shaft H. The test shaft H is shaft-supported on both outer sides of the connecting rod R in the axial direction of the test shaft H, and the test shaft H is rotated at a sliding speed of 6.6 m / s. The sliding speed refers to the relative speed between the surface of the coating layer 12 and the test shaft H. The end of the connecting rod R on the side opposite to the test shaft H is connected to a moving body F that reciprocates in the length direction of the connecting rod R, and the reciprocating load of the moving body F is 100 MPa. In addition, engine oil at about 140 °C is supplied between the connecting rod R and the test shaft H.

[0059] By maintaining the above state for 100 hours, a fatigue test of the coating layer 12 was carried out. Then, after the fatigue test, the inner surface (sliding surface) of the coating layer 12 was photographed from a position on a straight line orthogonal to the surface with the straight line as the principal optical axis, and an evaluation image that became the image obtained by the photographing was obtained. Then, the damaged part of the surface of the coating layer 12 reflected in the evaluation image was observed and determined with a binocular microscope (magnifying glass), and the fatigue area ratio was measured as a percentage of the value obtained by dividing the damaged part area, which is the area of the damaged part, by the entire area of the surface of the coating layer 12 reflected in the evaluation image.

[0060] If based on Table 1, Table 2, and Figure 3 When comparing samples with the same Sb concentration (for example, Example 1 and Comparative Example 1), at all Sb concentrations, the fatigue area ratios of Examples 1 to 6 having Bi-Sb oxide on the outermost surface are smaller than those of Comparative Examples 1 to 6. The fatigue area ratios of Examples 7 to 12 are smaller than those of Comparative Examples 7 to 12. The fatigue area ratio of Example 13 is smaller than that of Comparative Example 13. Therefore, it can be said that the sliding member 1 having Bi-Sb oxide has higher fatigue resistance than the sliding member without Bi-Sb oxide.

[0061] In addition, if Bi-Sb oxide exists on the outermost surface as in Examples 1 to 13, the possibility of oxidation of elements existing in a part deeper than the outermost surface can be reduced. Therefore, in the coating layer 12, the formation and growth of bismuth oxide (Bi2O3) as the main component can be prevented.

[0062] That is, since bismuth oxide is brittle, if it is formed in the covering layer 12, bismuth oxide may peel off during the use of the sliding member. However, if a Bi-Sb oxide exists on the outermost surface as in Examples 1 to 13, it is possible to prevent bismuth in a region deeper than the outermost surface from being oxidized to form bismuth oxide. Therefore, in Examples 1 to 13, it is considered that preventing the formation of bismuth oxide also contributes to the improvement of fatigue resistance. In Examples 1 to 13, the Sb concentration is 2.0 mass% to 12.0 mass%. However, if a Bi-Sb oxide exists on the surface at any Sb concentration within this concentration range, the fatigue area ratio is smaller than the case where no Bi-Sb oxide exists. Therefore, it is considered that at any concentration of Sb more than 0 mass% in the covering layer 12, a Bi-Sb oxide is formed and the fatigue resistance is improved.

[0063] In addition, if one wants to obtain the sliding member 1 in which the fatigue area ratio in the above fatigue test becomes a specific value range, the Sb concentration in the covering layer 12 can be controlled. For example, when it is desired to make the fatigue area ratio 11% or less, it is preferable that the Sb concentration in the covering layer 12 is 3.0 mass% or more and 10.0 mass% or less.

[0064] Furthermore, in Examples 2 to 6 and Examples 8 to 13, directly below the layer mainly composed of a Bi-Sb oxide, the main components are a Bi-Sb oxide and antimony oxide (Sb2O3). For example, in Example 2, a Bi-Sb oxide exists as the main component in the surface layer, and at a depth of 0.1 μm directly below it, the main components are a Bi-Sb oxide and antimony oxide (Sb2O3). Then, if it is 1 μm deeper, no oxide is observed, and Bi and Sb exist as the main components. Thus, in Examples 2 to 6 and Examples 8 to 13, oxides other than Bi-Sb-O are also generated at deeper positions in the covering layer 12. However, when comparing Bi and Sb, since Sb is more easily oxidized, more antimony oxide is formed than bismuth oxide. Therefore, the formation of bismuth oxide is suppressed, and bismuth oxide does not exist as the main component (as the compound with the largest existence ratio or the second largest compound), and the fatigue resistance is improved.

[0065] Therefore, it is possible to prevent the sliding member from becoming brittle by bismuth oxide. Thus, even if the Sb concentration is low, if a Bi-Sb oxide is formed on the outermost surface, this Bi-Sb oxide can protect the surface, prevent the formation of bismuth oxide, and improve the fatigue resistance. On the other hand, for a sliding member with an Sb concentration of 0 in the covering layer 12, for example, even when the covering layer 12 is made of Bi or made of Bi-Cu, Bi-Sn, etc., and the other layers are the same as those in Examples 1 to 13 and the sliding member is oxidized, it is difficult to protect the outermost surface by the oxide.

[0066] That is, when the Sb-free coating layer 12 is oxidized, bismuth oxide (Bi2O3) is formed on the outermost surface. Then, when the fatigue test is performed on the sample with bismuth oxide formed on the outermost surface, a fatigue area ratio of more than 20% is obtained. That is, the sliding member with bismuth oxide formed on the outermost surface has reduced fatigue resistance compared to the example due to the peeling off of brittle bismuth oxide and other reasons. In the example, Bi-Sb oxide is formed on the outermost surface, suppressing the generation and peeling off of bismuth oxide. Therefore, Bi can be maintained in the coating layer 12 for a long time, and the high adhesion brought by the soft Bi can be provided by itself for a long time.

[0067] In Examples 1 to 6, Examples 7 to 12, and Example 13, the intermediate layer 13 and the lining 11 are different. That is, the intermediate layer 13 of Examples 1 to 6 is composed of Ag-Sn. The intermediate layer 13 of Examples 7 to 12 is composed of Ag. The intermediate layer of Example 13 is composed of a first intermediate layer (Cu) and a second intermediate layer (Ag). If these examples are compared, the main components in the coating layer 12 are the same, and the fatigue area ratios are also very close. Further, if Comparative Examples 1 to 6, Comparative Examples 7 to 12, and Comparative Example 13 are compared, the fatigue-resistant area of the example is smaller. Therefore, it can be considered that the improvement of the fatigue-resistant area brought by forming Bi-Sb oxide on the outermost surface of the coating layer 12 composed of Bi and Sb can be achieved without relying on the compositions of the intermediate layer 13 and the lining 11.

[0068] In addition, the main components at each depth position from the outermost surface shown in Table 1 are the results measured for the sliding member before the fatigue test. On the other hand, the main components were also measured after the fatigue test. As a result, in both Examples 1 to 13 and Comparative Examples 1 to 13, no change in the main components at each depth position was observed. That is, in the outermost surfaces of Comparative Examples 1 to 13, even after the fatigue test, no oxide was formed as the main component. Therefore, in a state where oxidation treatment is not actively performed as in Comparative Examples 1 to 13, it is difficult to form Bi-Sb oxide uniformly on the entire outermost surface during the general use of the sliding member 1. On the other hand, if oxidation treatment is actively performed as in Examples 1 to 13, Bi-Sb oxide is formed uniformly on the entire outermost surface.

[0069] In Comparative Examples 1 to 13, even though it is very difficult to form Bi-Sb oxide on the outermost surface during normal use, since Bi-Sb oxide is not formed on the outermost surface in these Comparative Examples 1 to 13, Bi is locally oxidized and bismuth oxide can be generated. If bismuth oxide is generated, since this bismuth oxide is brittle, the fatigue resistance is reduced due to the peeling off of this bismuth oxide, etc. Therefore, as in Examples 1 to 13, by performing pre-oxidation treatment to form Bi-Sb oxide on the entire outermost surface, the fatigue resistance can be surely improved.

[0070] (3) Other embodiments:

[0071] In the above embodiment, the sliding member 1 constituting the sliding bearing A for axially supporting the crankshaft of the engine is exemplified, but the sliding bearing A for other uses can be formed according to the sliding member 1 of the present invention. For example, a radial bearing such as a gear bushing, a piston pin bushing, or a hub bushing for a transmission can be formed by the sliding member 1 of the present invention. Further, the sliding member of the present invention can be a thrust bearing, can be various washers, or can be a swash plate for an automotive air-conditioning compressor.

[0072] In addition, the base of the lining 11 is not limited to Cu alloy or Al alloy, and the material of the base can be selected according to the hardness of the object shaft 2. In addition, the back lining 10 is not essential and can be omitted.

[0073] Explanation of reference numerals

[0074] 1: Sliding member;

[0075] 2: Object shaft;

[0076] 10: Back lining;

[0077] 11: Lining;

[0078] 12: Cover layer;

[0079] 13: Intermediate layer;

[0080] A: Bearing;

[0081] F: Moving body;

[0082] H: Test shaft;

[0083] R: Connecting rod.

Claims

1. A sliding member having a covering layer formed of an alloy coating of Bi and Sb, wherein, Bi-Sb oxide is formed on the surface of the covering layer. The Bi-Sb oxide is the compound with the highest existence ratio on the outermost surface of the covering layer.

2. The sliding member according to claim 1, wherein, The concentration of Sb in the covering layer is 2.0 mass% or more and 12.0 mass% or less.

3. The sliding member according to claim 1, wherein, The concentration of Sb in the covering layer is 3.0 mass% or more and 10.0 mass% or less.

4. The sliding member according to any one of claims 1 to 3, wherein, Antimony oxide is formed directly below the Bi-Sb oxide in the depth direction of the covering layer.

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