Bearing Alloy, Sliding Member, Internal Combustion Engine, And Motor Vehicle

Abstract

A bearing alloy according to one embodiment includes 5.5 to 10 mass % of Sn; 2 to 7 mass % of Ni; 1 to 5 mass % of Bi; 0 to 0.3 mass % of Ag; and the balance consists essentially of Cu and unavoidable impurities.

Claims

1. An alloy for a sliding member, the alloy comprising: 5.5 to 10 mass % of Sn; 2 to 7 mass % of Ni; 1 to 5 mass % of Bi; 0 to 0.3 mass % of Ag; and the balance consisting essentially of Cu and unavoidable impurities.

2. The alloy for a sliding member according to claim 1, wherein the area ratio of NiSn intermetallic compound in the cross section is 0.4% or more.

3. The alloy for a sliding member according to claim 1, wherein in the cross section, Bi grains having an area of 30 m.sup.2 or more and Bi grains having an area of 5 m.sup.2 or less coexist.

4. The alloy for a sliding member according to claim 3, wherein the ratio of the number of Bi grains having the area of 5 m or less to the total number of Bi grains observed in the cross section is 50% or more.

5. The alloy for a sliding member according to claim 3, wherein in an area with a radius of 25 m whose center is located at the center of Bi grains having an area of 30 m.sup.2 or more, the ratio of specific Bi grains to the total number of Bi grains is 50% or more, the specific Bi grains being Bi grains having an area of 5 .sup.2 or less.

6. A sliding member comprising: a lining layer formed of an alloy for a sliding member according to claim 1; and a resin coating layer or a metal plating layer formed on the lining layer.

7. An internal combustion engine comprising the sliding member according to claim 6.

8. A motor vehicle comprising an internal combustion engine according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows an external appearance of a thrust sliding member according to an embodiment.

[0017] FIG. 2 is an example of a cross-sectional photograph of an alloy for a sliding member according to an embodiment.

[0018] FIG. 3 shows a schematic view of a cross-sectional structure of an alloy for a sliding member.

[0019] FIG. 4 shows effects of Sn and Ni on the characteristics of the alloy.

[0020] FIG. 5 is a flowchart illustrating a method of manufacturing a sliding member according to an embodiment.

[0021] FIG. 6 is a graph showing the relationship between the area ratio of the NiSn phase and the abrasion depth.

[0022] FIG. 7 is a graph showing the relationship between the area ratio of the NiSn phase and the frictional coefficient.

DETAILED DESCRIPTION

1. Composition

[0023] FIG. 1 shows an external appearance of a sliding member according to an embodiment. Here, a half bearing is illustrated as an example of a sliding member. The sliding member includes a layer formed of an alloy for the sliding member according to an embodiment. The alloy for the sliding member is a Cu-based alloy (copper alloy). The Cu-based alloy is a so-called CuSnNiBiAg alloy and includes (A) Sn, (B) Ni, (C) Bi, and (D) Ag. The remainder is composed of Cu and unavoidable impurities. The unavoidable impurities include, for example, at least one of Al, Fe, Mg, Ti, B, Pb, and Cr. The unavoidable impurities are incorporated, for example, in smelting or scrap. The content of unavoidable impurities is, for example, 1.0 mass % or less in total amount.

[0024] FIG. 2 is an example of a cross-sectional photograph of an alloy for a sliding member according to an embodiment. These images are 500 images obtained by SEM-EDX (using JSM-6610A manufactured by Nippon Electronics Co., Ltd.). The image at the left of the figure is a secondary electron image (SEI), and the distribution of Cu, Sn, Ni, Bi, and Ag elements is shown in this order from left to right. From these figures, it can be seen that Sn and Ni are divided into a solid solution in Cu and an intermetallic compound of NiSn. The composition of the sample in this photograph is as follows. Other components are not included or are unavoidable impurities.

TABLE-US-00001 TABLE 1 Cu Sn Ni Bi Ag Sample 1 Bal. 8.5 3.0 4.2 0.19 Sample 2 Bal. 6.6 4.6 3.1 0.11 Sample 3 Bal. 5.4 6 2.1 0.02 in mass %

[0025] The content of each component is preferably as follows.

[0026] (A) Sn: 5 to 10 mass %. More preferably, the content is 5 to 8.5 mass %.

[0027] (B) Ni: 2 to 7 mass %. It is more preferable that the content is 3 to 6 mass %.

[0028] (C) Bi: 1 to 5 mass %. It is more preferable that the content is 2 to 4.5 mass %.

[0029] (D) Ag: 0 to 0.3 mass %. It is more preferable that the content is 0.01 to 0.2 mass %. Here, 5 to 10 mass % means 5 mass % or more and 10 mass % or less.

[0030] FIG. 3 shows a schematic diagram of a cross-sectional structure of an alloy for a sliding member. In the cross-sectional structure of the alloy for a sliding member, Bi grains having a relatively large size (specifically, an area of 30 m or more .sup.2) and Bi grains having a relatively small size (specifically, an area of 5 m or less .sup.2) coexist (or are mixed). Specifically, the ratio of the number of small Bi grains to the total number of Bi grains observed on the observation surface (150 m in length250 m in width) is 50% or more, and preferably 60% or more.

[0031] Table 2 shows the results of measurement of the ratio of the number of small Bi grains for Samples 1 to 3. For the measurement, the same apparatus as that used for the image analysis in the experimental example described later was used. Sample 4 is a comparative example, and the composition thereof is Cu-4Sn-6.5Bi.

TABLE-US-00002 TABLE 2 Ratio (%) of Ratio (%) of Ratio (%) of small Bi grain middle Bi grain large Bi grain (less than 5 m.sup.2) (5 to 30 m.sup.2) (more than 30 m.sup.2) Sample 1 62.3 22.3 15.3 Sample 2 85.0 10.0 5.0 Sample 3 68.6 21.1 10.3 Sample 4 38.5 22.2 39.3

[0032] As can be seen from the results, in each of Samples 1 to 3, the proportion of Bi grains smaller than that in Sample 4, which is a comparative example, was higher, 40% or more, and in detail, 60% or more. The proportion of large Bi grains was 30% or less, more specifically 20% or less, and even 16% or less. The area of the Bi grains in this measurement is calculated by image analysis software, which calculation will be described later.

[0033] In addition, from another viewpoint, the small Bi grains are distributed in many areas around the large Bi grains. Specifically, in an area having a radius of 25 m from the center of the large Bi grains, the ratio occupied by the small Bi grains is 50% or more on average, and is preferably 60% or more.

[0034] Table 3 shows the results of measuring the ratio of the number of Bi grains in an area having a radius of 25 m from the center of the large Bi grains for Samples 1 to 4. For the measurement, the same apparatus as that used for the image analysis in the experimental example described later was used. Although a plurality of large Bi grains exist in the observation region, an area having a radius of 25 m was set for each of the large Bi grains, and the results were averaged for all the large Bi grains after the Bi grains in the area were measured.

TABLE-US-00003 TABLE 3 Ratio (%) of Ratio (%) of Ratio (%) of small Bi grain middle Bi grain large Bi grain (less than 5 m.sup.2) (5 to 30 m.sup.2) (more than 30 m.sup.2) in the area in the area in the area Sample 1 69.3 13.1 17.6 Sample 2 84.7 7.3 8.0 Sample 3 68.1 18.7 13.3 Sample 4 31.3 24.7 44.0

[0035] As can be seen from the results, in each of Samples 1 to 3, the proportion of Bi grains smaller than that in Sample 4, which is a comparative example, was higher, 40% or more, and more specifically, 60% or more. The proportion of large Bi grains was 30% or less, more specifically 20% or less, and further 18% or less. Further, in contrast to the results shown in Table 2, the ratio of the number of medium Bi grains in the area is smaller than the ratio of the number of medium Bi grains in the entire observation region. Conversely, the ratio of the number of large Bi grains in the area is greater than the ratio of the number of large Bi grains in the entire observation region.

[0036] Bi is a soft and self-lubricating material. The distribution of Bi grains having a small diameter as well as Bi grains having a large diameter expands the range of contact with Bi grains on the opposite shaft, resulting in lower friction compared to a case in which only Bi grains having a large diameter exist. The low friction provides the effects of improved seizure resistance and improved wear resistance. Since Bi is soft, the strength of the entire material may be lowered. However, as compared with the example in which only large granular Bi is distributed, the reduction in strength of the entire material is smaller when large granular Bi and small granular Bi are mixed. When this material is used for a sliding member, for example, a bearing, an effect of suppressing reduction in fatigue resistance can be obtained.

[0037] FIG. 4 is a diagram showing the influence of Sn and Ni on the characteristics of the alloy. Here, the content of Sn was 0 mass % or 4.5 mass %, and the content of Ni was 0 mass % or 7 mass %. Compositions other than Sn and Ni were 3 mass % of Bi, 0.07 mass % of Ag, and the balance was Cu. With respect to the coefficient of friction, the amount of wear, the amount of corrosion, and the Rockwell hardness, the characteristics were improved in the example including at least one of Sn and Ni as compared with the example including no Sn or Ni. In particular, examples containing both Sn and Ni showed further improvement in properties compared to examples containing only either Sn or Ni. With respect to the friction coefficient, the wear amount, the corrosion amount, and the hardness, the improvement effect was higher in the example containing only Sn than in the example containing only Ni.

2. Manufacturing Method

[0038] FIG. 5 is a flowchart illustrating a method of manufacturing a sliding member using an alloy for a sliding member according to an embodiment. In step S1, a raw material powder of a copper alloy is prepared. In this embodiment, CuSnNiBiAg alloy powder is used. In addition to or instead of this, a mixture of elemental metal powders may be used. In step S2, the raw material powder is sprayed onto the backing metal. In step S3, primary sintering is performed. The primary sintering is carried out under conditions of a temperature of 850 C. and a retention time of 10 minutes in a hydrogen reduction atmosphere. After primary sintering, rolling (step S4) is performed, followed by secondary sintering (step S5). The secondary sintering is carried out under the same conditions as those of the primary sintering. The workpiece after the secondary sintering has a belt shape, and is wound up, for example, on a roll and subjected to the next step. In step S6, the alloy material is processed into a desired shape to obtain a sliding member.

[0039] The sliding member thus obtained is, for example, a half bearing. This half bearing is used, for example, as a so-called main bearing in an internal combustion engine of a motor vehicle. In addition, in the related art, there is an example in which a Cu-based alloy containing In is used as an alloy for a sliding member, but In has a relatively high cost, and there have been cases in which cost has become a problem. However, since the alloy for a sliding member according to the present embodiment does not contain In in the component (In-free), the cost can be kept low as compared with the example in which In is contained.

3. Embodiment

[0040] The inventors of the present application produced specimens of sliding members under various conditions, and evaluated the wear resistance and the coefficient of friction of these specimens. First, the compositions of the alloys used in the produced test pieces and the area ratio of the NiSn phase (NiSn intermetallic compound phase) in the cross-sectional structure are as shown in Table 4. The area ratio of the NiSn phase in the cross-sectional structure was measured by the following methods. First, a cross section was photographed by SEM-EDX (using JSM-6610A manufactured by Nippon Electronics Corporation) at an optical magnification of 300, and image data of an observed image was obtained. This image data was input to an image analyzer (LUZEX_AP manufactured by Nireko Corporation), and the area of the phase present in the observed image was measured. As shown in FIG. 2, in the cross-sectional structure of the alloys for a sliding member, the relatively thin-colored layers relative to the matrices are NiSn phases.

TABLE-US-00004 TABLE 4 Ni-Sn area abrasion ratio depth frictional Cu Sn Ni Bi Ag (%) (mm) coefficient Experimental Bal. 5.1 6.0 1.8 0.01 0.3 9.7 0.113 Example 1 Experimental Bal. 9.0 3.1 3.8 0.14 0.7 8.6 0.092 Example 1 Experimental Bal. 8.9 6.2 4.0 0.14 1.9 8.0 0.098 Example 1 Experimental Bal. 8.1 6.0 1.9 0.01 0.9 7.5 0.11 Example 1 Experimental Bal. 5.8 1.1 2.7 0.09 0.1 11.5 0.163 Example 1 Experimental Bal. 10.0 6.1 2.1 0.29 1.5 8.0 0.1 Example 1 Experimental Bal. 8.0 5.3 1.6 0.21 0.4 8.7 0.125 Example 1

[0041] FIG. 6 is a graph showing the relationship between the area ratio of the NiSn phase and the abrasion depth. The conditions of the abrasion test are as follows.

[0042] Test: block on ring

[0043] Load: 90 N

[0044] Rotating speed: 0.5 m/s

[0045] Time: 30 minutes

[0046] Oil type: paraffin oil

[0047] Oil temperature: room temperature

[0048] According to the experimental results, while the amount of wear is large while the area ratio of the NiSn phase is low, the amount of wear decreases as the area ratio of the NiSn phase increases, and the area ratio stabilizes at low levels from about 0.8% or more. From this result, the area ratio of the NiSn intermetallic compound in the cross section is preferably 0.4% or more, and more preferably 0.8% or more.

[0049] FIG. 7 is a graph showing the relationship between the area ratio of the NiSn phase and the frictional coefficient. According to the experimental results, while the friction coefficient is large when the area ratio of the NiSn phase is low, the friction coefficient decreases as the area ratio of the NiSn phase increases, and the area ratio stabilizes at levels lower than about 1.5%. From this result, the area ratio of the NiSn intermetallic compound in the cross section is preferably 0.4% or more, and more preferably 1.5% or more. As a result of decreasing the coefficient of friction in this manner, when this material is used for a sliding member, for example, a bearing, effects of a suppressed rise in temperature at the time of high load and improved seizure resistance can be obtained.