Sliding material

Abstract

Disclosed is a sliding material containing 0.5 to 15 mass % of Sn, 0.2 to 10 mass % of Ni, 0.4 to 10 volume % of hard particles, and the balance being essentially Cu. The hard particles are of one or more selected from the group consisting of WC, W2C, Mo2C, W, and Mo. A grain size of the Cu—Sn—Ni matrix is set to be not more than 0.070 mm.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a sliding material consisting of a Cu-based alloy, particularly to a sliding material excellent in corrosion resistance and fatigue resistance.

[0002] A Cu—Sn—Pb-based alloy bearing has heretofore been used as a sliding material of a Cu-based alloy in a bush, thrust washer, and the like. However, for the bearings in use under high-temperature environment, such as a piston bush used at a small end of a connecting rod, there has been a problem of corrosion by a lubricant, and there has been also a problem of fatigue resistance to large variations of load. To improve this, an attempt has been made to improve corrosion and fatigue resistances with utilization of a Cu—Sn—Ni-based or Cu—Sn—Ni—Pb-based material in which Ni is added by reducing or without Pb. However, in recent years, the piston bush of an internal combustion engine has been increasingly used under the high-temperature environment, and the problem of corrosion has not completely been solved by such improvement.

BRIEF SUMMARY OF THE INVENTION

[0003] The present invention has been made taking the above background into consideration, and an object thereof is to provide a sliding material in which a Cu-based alloy is used and which is excellent in corrosion and fatigue resistances.

[0004] While, in general, a sliding material of a Cu-based alloy has been manufactured by sintering, but the present inventors have found that with addition of a certain type of hard particles (particles of WC, W2C, Mo2C, W, Mo) to a Cu—Sn—Ni alloy, growth of crystal grains is inhibited in a final process of sintering resulting in that the alloy has fine crystal grains. It has been found also that by grain refining, strength is improved, fatigue resistance becomes excellent, and corrosion by a lubricant is particularly effectively prevented.

[0005] Thus, according to the present invention, there is provided a sliding material comprising: 0.5 to 15 mass % of Sn; 0.2 to 10 mass % of Ni; 0.4 to 10 volume % of hard particles; and the balance being essentially Cu, wherein the hard particles are of one or more selected from the group consisting of WC, W2C, Mo2C, W, and Mo and a grain size of the matrix of a Cu—Sn—Ni base is set to be not more than 0.070 mm. The grain size is determined in accordance with a method for estimating average grain size of wrought copper and copper-alloys which is defined in JIS H 0501.

[0006] In this case, with regard to an average particle size of the hard particles, that of WC, W2C, or Mo2C is preferably 0.1 to 10 &mgr;m, and that of W or Mo is 1 to 25 &mgr;m.

[0007] According to one feature of the present invention, the sliding material may contain not more than 40 mass % in total of one or more selected from the group of Fe, Al, Mn, Co, Zn, Si and P.

[0008] According to another feature of the present invention, the sliding material may contain not more than 10 volume % in total of one or more selected from the group consisting of MoS2, WS2, h-BN and graphite.

[0009] According to a still another feature of the present invention, the sliding material may contain not more than 10 mass % in total of Bi and/or Pb.

[0010] Herein below, there will be provided a description of reasons for the above specified features.

[0011] (1) Sn: 0.5 to 15 mass %

[0012] Sn strengthens the Cu alloy matrix, and improves fatigue resistance property. If the Sn content is less than 0.5 mass %, it is impossible to obtain an improvement effect of strengthening the Cu alloy matrix. When the Sn content exceeds 15 mass %, a lot of Cu—Sn compounds are formed resulting in that the alloy becomes brittle.

[0013] (2) Ni: 0.2 to 10 mass %

[0014] Ni is dissolved in the Cu alloy matrix to improve it in the corrosion resistance property, the fatigue resistance property and mechanical strength. If the Ni content is less than 0.2 mass %, it is impossible to obtain an improvement effect of the corrosion resistance property and mechanical strength of the Cu alloy matrix. When the Ni content exceeds 10 mass %, the Cu alloy matrix becomes too hard and is not preferable as the sliding material.

[0015] (3) Hard Particles: WC, W2C, Mo2C, W and Mo

[0016] Since these hard particles have good wettability with the Cu alloy matrix, the alloy strength is not deteriorated and no void is formed in the alloy. Thus, penetration of the lubricant into the Cu alloy matrix is prevented resulting in improved corrosion resistance property.

[0017] (4) Hard Particles: 0.4 to 10 Volume %

[0018] If a content rate of the hard particles is less than 0.4 volume %, it is impossible to obtain a grain refining effect of the Cu alloy matrix resulting in no improvement effect of the corrosion resistance property. When the content rate exceeds 10 volume %, a mating material will be attacked by the alloy too intensively resulting in inferior anti-seizure property of the alloy.

[0019] (5) Grain Size of Cu—Sn—Ni Alloy Matrix: not more than 0.070 mm

[0020] In the case where the grain size of the Cu—Sn—Ni alloy matrix (i.e. the Cu alloy matrix) exceeds 0.070 mm, the improvement effect of the corrosion resistance property can not be obtained.

[0021] (6) Size of Hard Particles of WC, W2C, Mo2C: 0.1 to 10 &mgr;m

[0022] In the case where the particle size of WC, W2C and Mo2C is less than 0.1 &mgr;m, the hard particles are too fine, and poor in the refining effect of crystal grains resulting in that the improvement effect of the corrosion resistance property can not be obtained. On the other hand, if the particle size exceeds 10 &mgr;m, they attack the mating material too strongly resulting in deteriorated anti-seizure property. In this case, the particles are not dispersed uniformly resulting in an inferior refining effect of crystal grains.

[0023] (7) Size of Hard Particles W, Mo: 1 to 25 &mgr;m

[0024] In the case where the particle size of W and Mo is less than 1 &mgr;m, they are too fine, and poor in the refining effect of crystal grains resulting in that the improvement effect of the corrosion resistance property can not be obtained. On the other hand, if the particle size exceeds 25 &mgr;m, they attack the mating material too strongly resulting in deteriorated anti-seizure property. In this case, the particles are not dispersed uniformly resulting in an inferior refining effect of crystal grains.

[0025] (8) Fe, Al, Mn, Co, Zn, Si, and P: not more than 40 mass % in total

[0026] These strengthen the Cu alloy matrix to improve the fatigue resistance property. If the content of those exceeds 40 mass %, they do not contribute to improvement of the fatigue resistance property.

[0027] (9) MoS2, WS2, h-BN, graphite: not more than 10 volume % in total

[0028] These are solid lubricating materials. An additive of those further improves anti-seizure and wear resistance properties. If the total content of those exceeds 10 volume %, the alloy strength is reduced.

[0029] (10) Bi, Pb: not more than 10 mass % in total

[0030] These are dispersed in the Cu alloy matrix to form a soft phase resulting in improved embeddability and anti-seizure property. If the content of those exceeds 10 mass %, the strength of the Cu alloy matrix is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a sectional view of a bush showing one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Herein below there will be described one embodiment in which the present invention is applied to a piston pin bush mounted on a small end of a connecting rod. A piston pin bush 1 is of a so-called wrapped bush. It is configured such that, as shown in FIG. 1, an inner peripheral surface of a back metal 2 made of a thin steel plate is provided with a bearing alloy layer 4 as a sliding material according to the present invention via a Cu plating layer 3 for improving adhesiveness.

[0033] The bearing alloy layer 4 is made of a sintered Cu alloy, and has a chemical composition defined in the claims as represented by Invention Examples 1 to 11 described later. That is, the bearing alloy layer 4 comprises 0.5 to 15 mass % of Sn, 0.2 to 10 mass % of Ni, 0.4 to 10 volume % of hard particles, and the balance being essentially of Cu. The hard particles are of one or more selected from the group of WC, W2C, Mo2C, W and Mo. The grain size of a Cu—Sn—Ni matrix is not more than 0.070 mm.

[0034] In this case, preferably an average particle size of WC, W2C and Mo2C is 0.1 to 10 &mgr;m, and preferably that of W and Mo is 1 to 25 &mgr;m. Further, the bearing alloy may contain not more than 40 mass % in total of one or more selected from the group of Fe, Al, Mn, Co, Zn, Si, and P. It may contain also not more than 10 mass % in total of Bi and/or Pb. It may contain also not more than 10 volume % in total of one or more selected from the group of MoS2, WS2, h-BN, and graphite.

[0035] Here, there will be briefly described a manufacturing method of the bush 1. First, a Cu alloy powder having a given composition and hard particles are mixed in a mixer to obtain a predetermined rate. The Cu alloy powder may be of a Cu—Sn—Ni alloy, Cu—Sn—Ni—Zn alloy and so on. In the mixing process, the Cu alloy powder comprises not less than 90 mass % of particles having a particle size of not more than 75 &mgr;m and not less than 60 mass % of particles having a particle size of not more than 45 &mgr;m in order to uniformly mix with the hard particles.

[0036] Subsequently, the powder mixture is spread onto a 1.3 mm thick steel strip (the back metal 2) previously provided with the Cu plating layer 3, subsequently heated for a first sintering at 800 to 950° C. for about 15 minutes in a reducing atmosphere. Thereafter, the processed material is rolled to compact the bearing alloy layer. Further processes of sintering and rolling are repeated in order to compact the bearing alloy layer, whereby a bimetal is obtained, which has a total thickness of about 1.6 mm and an about 0.4 mm thickness of the bearing alloy layer.

[0037] In the manufacturing process of the bimetal, a sintering temperature in the finally performed sintering process was set at not higher than 920° C. in order to inhibit the growth of crystal grains. The temperature of not higher than 920° C. is a temperature at which no liquid phase is generated in the Cu—Sn—Ni matrix. A specimen of comparative Example 3 was processed at a final sintering temperature of 970° C., which was used in the tests described below. The bimetal was machined and formed to be a cylindrical shape, and finally coated with an overlay layer 5 so that the bush 1 was manufactured.

[0038] With regard to the invention examples and the comparative examples having chemical compositions shown in Table 1, the present inventors measured the grain sizes of those Cu alloys, and conducted a corrosion, seizure and fatigue tests in order to confirm advantages of embodiments of the invention.

[0039] The grain size of the respective Cu alloy was measured in accordance with a method for estimating average grain size for wrought copper and copper-alloys which is defined in JIS H 0501. The corrosion test was conducted in a lubricating oil with regard to a respective specimen, having a total thickness of 1.5 mm (including 0.3 mm of the bearing alloy layer thickness), a width of 25 mm and a length of 50 mm, which was produced from the bimetal. The seizure test was conducted with regard to a respective specimen bush having a total thickness of 1.5 mm (including 0.3 mm thickness of the bearing alloy layer), an inner diameter of 20 mm, and a width of 15 mm. And the fatigue test was conducted with regard to a cylindrical bearing which was prepared by mating two semi-circular bearings each having a total thickness of 1.5 mm (including 0.3 mm thickness of the bearing alloy layer). Conditions of the tests are shown in Tables 2 to 4. 1 TABLE 1 Chemical composition Cu Sn Ni Hard particles (vol %) No. mass % mass % mass % Mo2C WC Mo W others Invention 1 bal. 10 8 8 — — — Example 2 bal. 0.8 0.3 0.5 — — — 3 bal. 6 3 0.5 — — — 4 bal. 6 3 1.5 — — — 5 bal. 6 3 9.5 — — — 6 bal. 6 3 — 1.5 — — 7 bal. 6 3 — — 1.5 — 8 bal. 6 3 — — — 1.5 — 9 bal. 6 3 1.5 — — — Bi 3 mass % 10 bal. 6 3 1.5 — — — Graphite 1 vol % 11 bal. 6 3 1.5 — — — Zn 20 mass % Comparative 1 bal. 6 3 — — — — Example 2 bal. 10 — 3 — — — 3 bal. — 3 3 — — — 4 bal. 6 3 1.5 — — — Al2O3 1.5 vol % 5 bal. 6 3 1.5 — — — SiC 1.5 vol % Size Corrosion depth Specific load when Crystal grains at grain seizure occurred Occurrence of mm boundaries &mgr;m MPa fatigue 0.015 4 18 no 0.065 35 15 no 0.055 6 27 no 0.025 6 27 no 0.010 1 15 no 0.025 6 24 no 0.045 12 24 no 0.045 10 27 no 0.015 30 30 no 0.025 45 30 no 0.025 4 12 no 0.095 80 9 no 0.006 110 15 no 0.080 90 6 no 0.050 125 12 yes 0.050 130 12 yes In Comparative Example 3, a final sintering temperature of 970° C. was used.

[0040] 2 TABLE 2 Item Conditions Size of specimen Width 25 mm × Length 50 mm Used oil CD grade for diesel, Fresh Test temp. 150° C. Test time 100 hours

[0041] 3 TABLE 3 Item Conditions Bearing inner diameter &phgr;20 mm Bearing width 15 mm Peripheral speed 1.0 m/sec Lubricant SAE #10 Shaft material JIS S55C as quenched Shaft roughness Rmax 1.0 &mgr;m or less

[0042] 4 TABLE 4 Item Conditions Surface load 120 MPa Test time 20 hours Speed 9 m/sec Lubricant SAE #30 Lubrication pressure 0.49 MPa Test temp. 100° C. Partner material JIS S55C Hardened Partner material roughness Rmax 1.0 &mgr;m or less

[0043] In the seizure test, the surface load was increased step-by-step in increments of 5 MPa and held under operation at each increment of surface load for 10 minutes, wherein a bearing surface load one-step lower than an actual bearing surface load, when a back surface temperature of the bearing exceeds 200° C. or when a driving current of a motor for driving a rotary shaft exhibited an abnormal value, was regarded as a maximum specific load without seizure. In the fatigue test, the respective semi-circular bearing was exposed to a sliding-contact state under a predetermined load. After the test, the respective test specimen was checked to confirm whether or not fatigue occurred in the bearing alloy.

[0044] As is apparent from Table 1, in comparison with Comparative Examples 1 to 5, Invention Examples 1 to 11 are significantly excellent in corrosion resistance property, and exhibit similar or excellent results with regard to anti-seizure and fatigue resistance properties.

[0045] Herein below, there will be described the grain size of the Cu alloy matrix, constituent elements of the Cu alloy matrix, and type of the hard particles and test result of corrosion resistance property.

[0046] (1) As is apparent from Table 1, Invention Examples 1 to 11 are substantially the same as Comparative Examples 2,4 and 5 in the point that the grain size of the Cu alloy matrix is not more than 0.070 mm.

[0047] (2) In Invention Examples 1 to 11, the Cu alloy matrix is of the Cu—Sn—Ni system (Invention Examples 1 to 10 are of Cu—Sn—Ni, and Invention Example 11 is of Cu—Sn—Ni—Zn), and Mo2C, WC, Mo and W are used as the hard particles.

[0048] (3) On the other hand, in Comparative Example 1, the Cu alloy matrix is of the Cu—Sn—Ni system, but does not contain the hard particles.

[0049] (4) In Comparative Examples 2 and 3, Mo2C is used as the hard particles, but the Cu alloy matrix does not contain Ni and Sn.

[0050] (5) In Comparative Examples 4 and 5, the Cu alloy matrix is of the Cu—Sn—Ni system, and Al2O3, SiC are used as the hard particles in addition to Mo2C.

[0051] (6) Additionally, Invention Examples 1 to 11 are excellent than Comparative Examples 1 to 5 in corrosion resistance property.

[0052] (7) It can be seen from the above that for the Cu alloy matrix of the Cu—Sn—Ni system having the grain size not more than 0.070 mm and containing Mo2C, WC, Mo and W, the corrosion resistance property is improved.

[0053] It should be noted that the present invention is not limited to the above-described embodiment with reference to the drawing, and can be expanded or varied as follows.

[0054] The hard particles may be W2C.

[0055] The hard particles may also contain two or more selected from W2C, Mo2C, WC, Mo and W.

[0056] The present invention is not limited to the bush for the piston pin disposed in the small end of the connecting rod, and may also be applied to a main bearing of an internal combustion engine constituted as the semi-circular bearing.

Claims

1. A sliding material comprising 0.5 to 15 mass % of Sn, 0.2 to 10 mass % of Ni, 0.4 to 10 volume % of hard particles, and the balance being essentially Cu, wherein the hard particles are one or more selected from the group of WC, W2C, Mo2C, W and Mo, and wherein a grain size of the matrix of the sliding material is not larger than 0.070 mm, the matrix being of a Cu—Sn—Ni alloy.

2. A sliding material according to claim 1, wherein:

when the hard particles are of WC, W2C or Mo2C, an average particle size thereof is 0.1 to 10 &mgr;m, and

when the hard particles are of W or Mo, an average particle size thereof is 1 to 25 &mgr;m.

3. A sliding material according to claim 1, which further comprises 40 mass % in total of one or more selected from the group of Fe, Al, Mn, Co, Zn, Si and P.

4. A sliding material according to claim 2, which further comprises 40 mass % in total of one or more selected from the group of Fe, Al, Mn, Co, Zn, Si and P.

5. A sliding material according to claim 1, which further comprises not more than 10 volume % in total of one or more selected from the group of MoS2, WS2, h-BN and graphite.

6. A sliding material according to claim 2, which further comprises not more than 10 volume % in total of one or more selected from the group of MoS2, WS2, h-BN and graphite.

7. A sliding material according to claim 3, which further comprises not more than 10 volume % in total of one or more selected from the group of MoS2, WS2, h-BN and graphite.

8. A sliding material according to claim 4, which further comprises not more than 10 volume % in total of one or more selected from the group of MoS2, WS2, h-BN and graphite.

9. A sliding material according to claim 1, which further comprises not more than 10 mass % in total of Bi and/or Pb.

10. A sliding material according to claim 2, which further comprises not more than 10 mass % in total of Bi and/or Pb.

11. A sliding material according to claim 3, which further comprises not more than 10 mass % in total of Bi and/or Pb.

12. A sliding material according to claim 4, which further comprises not more than 10 mass % in total of Bi and/or Pb.

13. A sliding material according to claim 5, which further comprises not more than 10 mass % in total of Bi and/or Pb.

14. A sliding material according to claim 6, which further comprises not more than 10 mass % in total of Bi and/or Pb.

15. A sliding material according to claim 7, which further comprises not more than 10 mass % in total of Bi and/or Pb.

16. A sliding material according to claim 8, which further comprises not more than 10 mass % in total of Bi and/or Pb.