GB2375801A

GB2375801A - Multi-layered sliding material of tin-copper

Info

Publication number: GB2375801A
Application number: GB0206056A
Authority: GB
Inventors: Hideo Tsuji; Hideo Ishikawa; Takayuki Shibayama
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 2001-04-09
Filing date: 2002-03-14
Publication date: 2002-11-27
Anticipated expiration: 2022-03-14
Also published as: GB0206056D0; JP3754315B2; JP2002310158A; GB2375801B

Abstract

A multi-layer sliding material comprising a bearing alloy layer (2) and a tin base overlayer (6) of tin-copper series provided thereon through an intermediate layer (3), the tin base overlayer comprising a plurality of layers (4, 5) having different copper content, among which the lowest layer (4) in contact with the intermediate layer (3) contains 5 to 20% by per cent of copper and has a thickness of 1 to 3 žm. This prevents reduction in the copper content in the surface layer of the overlayer due to diffusion of copper for a long time and can maintain a good anti-seizure property without losing the conformability. The intermediate layer can be of Nickel, Iron or Cobolt and of 0.5-3 žm thickness. The upper layer (5) can have 0.5 to 10% of copper. The alloy layer (2) can be a Copper or Aluminium base alloy. The upper layer (5) can have up to 5% of Zinc, Indium, Antimony or Silver.

Description

237580 1

- 1 - MULTI-LAYERED SLIDING MATERIAL

BACKGROUND OF THE INVENTION

The present invention relates to a multi-

layered sliding material, which comprises a copper base or aluminum base bearing alloy layer and a tin base 5 overlayer of tin-copper series provided thereon through an intermediate layer.

In the fields of automobiles, agricultural

machinery and industrial machinery, plain bearings comprising a steel back metal and a copper base or 10 aluminum base bearing alloy are often used. To improve the conformability or the foreign matter embeddability, an overlayer is often provided on the surface of the bearing alloy layer.

It is well known to use a lead base alloy as 15 the overlayer, but to overcome the problem of global environment or improve the corrosion resistance, tin base alloys are nowadays often used. The plain bearing with the tin base overlayer is provided with, for example, a nickel plating layer as an intermediate 20 layer between the bearing alloy layer and the over-

layer. The nickel plating layer is provided to enhance the bondability of the tin base overlayer in case of an aluminum base bearing alloy, and to prevent diffusion of tin from the tin base overlayer into the bearing 25 alloy.

However, in case the overlayer is composed of tin base alloy of tincopper series, copper in the overlayer diffuses into the nickel plating layer under the thermal influence, when used at elevated tempera 5 Lures for a long time, resulting in reduction in the copper content of the overlayer and consequent lowering of fatigue resistance and anti-seizure property. To prevent diffusion of the copper from the overlayer into the nickel plating layer, JP-A-2000-64085 discloses 10 that the intermediate layer must be composed of a 1-3 Am thick nickel layer and a 2-10 Am thick nickel-tin layer deposited thereon.

In the structure of the intermediate layer disclosed in JP-A-2000-64085, the nickel layer as a 15 lower layer is hard, and the nickel-tin layer as an upper layer is much harder. When the overlayer is worn out during the use for a considerably long time, the hard nickel-tin layer or nickel layer will be exposed to the surface. The nickel-tin layer or the nickel 20 layer is considerably thick, for example, 3-13 pun in total, and is too hard to be worn out, resulting in worse conformability and a high possibility of seizure.

SUMMARY OF THE INVENTION

An object of the present invention is to 25 improve the disadvantages of the prior art and to

provide a multi-layered sliding material capable of preventing reduction in the copper content in the

3 - surface layer of the tin base overlayer due to the diffusion of copper as much as possible without making larger the thickness of the intermediate layer formed between the tin base overlayer and the bearing alloy.

5 The present invention provides a multi layered sliding material, which comprises a bearing alloy layer and a tin base overlayer of tin-copper series provided thereon through an intermediate layer, the tin base overlayer comprising a plurality of layers 10 having different copper contents, among which the lowest layer in contact with the intermediate layer contains 5 to 20% by mass of copper and has a thickness of 1 to 3 m.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view of a multi layer sliding material according to an embodiment of the present invention.

Fig. 2 is a graph showing results of thermal diffusion tests.

20 Fig. 3 is a graph showing results of seizure tests. Fig. 4 is a graph showing results of fatigue tests. DETAILED DESCRIPTION OF THE INVENTION

25 The present multi-layered sliding material comprises a bearing alloy layer and a tin base

- 4 overlayer of tin-copper series provided thereon through an intermediate layer, the tin base overlayer compris-

ing a plurality of layers having different copper contents, among which the lowest layer in contact with 5 the intermediate layer contains 5 to 20 by mass of copper and has a thickness of 1 to 3 m.

The bearing alloy layer can be composed of ordinary copper base alloy or aluminum base alloy. The copper base or aluminum base bearing alloy has distin 10 guished bearing properties under high loads and at high speed revolutions and thus is particularly suitable for plain bearings for engines in the fields of auto-

mobiles, agricultural machinery and industrial machinery. Any of bronze base and lead bronze base 15 alloys can be used as the copper base alloy. As the aluminum base alloy, those containing at least one of zinc, tin, lead, etc. to form a soft phase can be used, and copper, magnesium, etc. can be also contained as reinforcing elements and chromium, silicon, etc. can be 20 also used to improve the fatigue resistance.

Between the copper base or aluminum base bearing alloy layer and the tin base overlayer of tin-

copper series an intermediate layer is provided to prevent diffusion of tin from the tin base overlayer 25 into the bearing alloy layer or improve the bondability of the tin base overlayer to the bearing alloy layer.

The intermediate layer can be composed of any one of nickel, iron and cobalt, and the thickness is prefer

- 5 - ably 0.5 to 3 m.

When the sliding material is used at elevated temperatures, copper diffuses from the tin base over-

layer into the intermediate layer. According to the 5 present invention, the lowest layer of the tin base overlayer has a relatively high copper content, and thus diffusion of copper from the tin base overlayer into the intermediate layer starts from the lowest layer of the tin base overlayer. That is, reduction in 10 the copper content of the uppermost layer of the tin base overlayer in contact with the counter member is less. The intermediate layer can be made not so thick and can maintain a distinguished anti-seizure property without losing the conformability, even if the tin base 15 overlayer is worn out to expose the intermediate layer to the surface.

The copper content in the uppermost layer of the tin base overlayer is preferably 0.5 to 10% by mass. 20 The uppermost layer of the tin base overlayer can contain not more than 5% by mass of at least one of zinc, indium, antimony and silver in sum total.

Reasons why the aforementioned proportions and thicknesses are selected will be as follows: 25 (1) Copper content in the lowest layer of the tin base overlayer: 5 to 20% by mass.

Below 5% by mass of copper, the prevention of copper diffusion from the uppermost layer of the tin

- 6 base overlayer tends to be less effective, whereas above 20% by weight of copper the fatigue resistance tends to be lowered.

Thickness of the lowest layer of the tin base 5 overlayer is 1 to 3 m. Below 1 m, prevention of copper diffusion from the uppermost layer tends to be less effective, whereas above 3 am the fatigue resist-

ance tends to be lowered.

(2) Copper content in the uppermost layer of 10 the tin base overlayer: preferably 0.5 to 10% by mass.

Tin matrix plays an important role in corrosion resistance, conformability and foreign matter embeddability, and copper can enhance the strength of the tin matrix and improve the anti-seizure property, 15 fatigue resistance and wear resistance. Below 0.5% by mass, copper tends to be less effective, whereas above 10% by mass the anti-seizure property and fatigue resistance tend to be lowered.

Thickness of the uppermost layer of the tin 20 base overlayer is preferably 10 to 40 m. Below 10 Am the conformability and foreign matter embeddability tend to be lowered, whereas above 40 Em the fatigue resistance tends to be lowered.

(3) Contents of at least one of zinc, 25 indium, antimony and silver in the uppermost layer of the tin base overlayer: preferably not more than 5% by mass in sum total.

These elements can improve the anti-seizure

property and wear resistance of the uppermost layer of the tin base overlayer. Above 5% by mass the uppermost layer tends to be too hard, and the conformability and foreign matter embeddability tend to be lowered.

5 (4) Intermediate layer: preferably any of nickel, iron and cobalt.

Nickel, iron and cobalt can prevent diffusion of tin from the tin base overlayer into the bearing alloy layer in case of copper base bearing alloy or 10 enhance the bondability of the tin base overlayer to the bearing alloy layer in case of aluminum base bear-

ing alloy.

Thickness of the intermediate layer is preferably 0.5 to 3 m. Below 0.5 am, neither good dam 15 effect nor good bondability will be obtained, whereas above 3 Am the anti-seizure property after the tin base overlayer is worn out tends to be lowered.

The present invention will be described below, referring to Examples and Drawings.

20 Examples 1 to 10 and Comparative Examples 1 to 7 Bimetal was made as a bearing material by sintering and rolling a copper base bearing alloy comprising 23% by mass of lead and 3.5% by mass of tin, the balance being copper, onto a steel plate. The 25 resulting bimetal was press formed into a 1.5 mm-thick half bearing, which was further machined to desired dimensions. Then, a 1.5 M-thick nickel layer was formed on the inner surface of the half bearing by

8 - electroplating and thereafter a tin bese alloy compris-

ing components as shown in Table 1 as Lower Layer was electroplated onto the nickel layer except Comparative Examples Nos. 1 to 4, and a tin base alloy comprising 5 components as shown in Table 1 as Upper Layer was further electroplated onto the lower layer. As to Comparative Examples Nos. 1 to 4, the tin base alloy comprising components as shown in Table 1 as Upper layer was electroplated to a thickness of 15 Em onto 10 the nickel layer only as a single layer.

In Example Nos. 1 to 10 and Comparative Example Nos. 5 to 7, test pieces in structures each comprising back steel layer 1, copper base bearing alloy layer 2 formed on said back steel layer 1, 15 intermediate layer 3 consisting of a nickel plating layer formed on said bearing alloy layer 2 and tin base overlayer 6 consisting of two layrs, i.e. lower layer 4 and upper layer 5 having different copper contents formed on said intermediate layer 3, as shown in Fig. 1 20 were obtained by the aforementioned procedure. In Comparative Examples Nos. 1 to 4, test pieces in structures comprising a back steel layer, a copper base bearing alloy layer formed on said back steel layer and a single tin base overlayer formed on the bearing alloy 25 layer through an intermediate layer consisting of a nickel plating layer, though not shown in the drawing, were obtained.

- 9 Table 1

Tin base overlayer Test piece Upper layer Lower layer Classifi- Component (mass %) Thick- Component Thick _ ness (mass %)ness cation No. Sn Cu In Ag Sb Am Sn Cu Am 1 Balance 4.2 _ 15 Balance 5.2 1 2.. 4.1 _ 15.. 1

3 " 4.3 3.1 15 " 19.1 1

4.. 4.2 15.. 2

Example 5 ' 3.9 2.0 15.. 19.5 2 6.. 8.1 _ 15.. 5.1 2

7.. 8.2 _ 15.. 9.9 2

8.. 7.9 2.1 15.. 2

9.. 7.9 15.. 5.2 3

_ 10.. 8.1 15 1 " 19.7 3

1.. 0.3 = = - 15 - =

Compara- 2 | " | 4.1 _ 15 j - - _ tive 3 " | 8 1 15 1 - _ Example 4 1 " |13.1 _ 15 | - I 5 1.' 1 4.1 _ I 15 |Balance| 10.1 0.5 6 1 " 1 4 2 15 " 10.2 5

7 '' 3.9 = 1 15 I 23.5

Test pieces of Examples Nos. 1 to 10 and Comparative Examples Nos. 1 to 7 were subjected to a thermal diffusion test, a seizure test and a fatigue test. 5 Thermal diffusion test was carried out to investigate copper content in the upper layer of the tin base overlayer each after keeping the heated state

- 10 at 130 C for 300 hours and after keeping that state for 1,000 hours.

Seizure test was carried out by using a preheated lubricating oil of VG22 at 100 C, rotating 5 the counter member at 3,600 rpm by a motor and giving a load under surface pressure at 10 MPa thereto by reduc-

ing a flow rate of the lubricating oil to 150 cc/mint after a running-in under no load for one hour, then increasing the surface pressure 5 MPa by 5 MPa, while 10 running under each surface pressure for 10 minutes to determine the bearing surface pressure when the temper-

ature of the bearing back exceeded 200 C or the driving current of the motor for driving the counter member exceeded the predetermined value as a seizure surface 15 pressure. The seizure test was carried out twice each for test pieces not subjected to said thermal diffusion and for those subjected to thermal diffusion at 130 C for l,OOO hours.

Fatigue test was carried out by using a 20 preheated lubricating oil of SAE20 at 100 C, rotating the counter member at 3250 rpm and giving a load under surface pressure of 50 MPa thereto to run for 20 hours after a running-in under no load for 30 minutes, thereby evaluating a degree of fatigue. Evaluation is 25 given by the following 5 classes of fatigue evaluation ranking. As in the seizure test, the fatigue test was carried out twice each for test pieces not subjected to thermal diffusion and for those subjected to thermal

- 11 diffusion at 130 C for 1,000 hours.

5: No cracking is observed at all.

4: Cracking is observed not visually, but microscopically. 5 3: Cracking is visually observable, but not discriminately. 2: Cracking is visually observable.

1: Not less than 50% of cracking is visually observable in terms of bearing projection 10 area.

Results of the thermal diffusion test of Examples Nos. 1, 3, 9 and 10 and Comparative Examples Nos. 2, 3 and 5 are graphically shown in Fig. 2.

Results of the seizure test and fatigue test thereof 15 are also graphically shown in Fig. 3 and Fig. 4, respectively, where unhatched portions each at the tops in histogramic columns show deviations each in the two test results.

As is apparent from Figs. 2 to 4, the copper 20 content of the surface layer of the tin base overlayer is less reduced by thermal diffusion of copper in Examples Nos. 1 to 10 embodying the tin base overlayer consisting of two layers, i.e. an upper layer and a lower layer, where the lower layer contains 5 to 20% by 25 mass of copper than that in Comparative Examples Nos. 1 to 4 showing the absence of a lower layer. That is, Examples Nos. 1 to 10 show distinguished anti-seizure property and fatigue resistance even after the thermal

- 12 diffusion test at 130 C for 1,000 hours.

Comparative Examples Nos. 5 to 7 show a tin base overlayer consisting of two layers, i.e. an upper layer and a lower layer. Comparative Example 7 shows a 5 low fatigue resistance, because the copper content in the lower layer of the tin base overlayer is as high as 23.5% by mass before the thermal diffusion test. When the copper content in the lower layer of the tin base overlayer is lower, the effect on prevention of the 10 upper layer from copper diffusion is lowered, whereas when higher an adverse effect on the fatigue resistance is produced. Thus, the copper content in the lower layer of the tin base overlayer is preferably 5 to 20% by mass.

15 Comparative Example No. 5 shows that the lower layer of the tin base overlayer is as thin as 0.5 m, so that the effect on prevention of the upper layer from copper diffusion is lower. That is, the copper content in the upper layer was initially 4.1% by 20 weight, but was considerably reduced to, for example, 2.1% by mass after the thermal diffusion test for 300 hours and 0.9% by mass after the thermal diffusion test for 1,000 hours. As a result, the anti-seizure property and the fatigue resistance were lowered after 25 the thermal diffusion test for 1,000 hours. Compara-

tive Example No. 6, on the other hand, shows that the lower layer of the tin base overlayer is as thick as 5 m, the fatigue resistance is poor even before the

- 13 -

thermal diffusion test. It can be seen from the fore-

going facts that when the lower layer of the tin base overlayer has a smaller thickness, the effect on prevention of the upper layer from copper diffusion 5 will be lowered, whereas when it has a larger thick-

ness, the fatigue resistance will be lowered. Thus, the thickness of the lower layer of the tin base overlayer is preferably 1 to 3 m.

Reduction in the copper content of the upper 10 layer can be suppressed by making the tin base over-

layer consist of two layers, i.e. an upper layer and a lower layer, and also making the lower layer have a copper content of 5 to 20% by mass and a thickness of 1 to 3 m, and as a result the thickness of the nickel 15 plating layer as an intermediate layer can be made smaller (e.g. 1.5 Em in Examples Nos. 1 to 10). Thus, when the overlayer is worn out to expose the inter-

mediate layer to the surface, the intermediate layer will be worn out for a relatively short time, thereby 20 reducing chances of seizure due to contact of the counter member with the hard nickel intermediate layer.

The foregoing Examples and those as shown in the drawings should not be construed to be restrictive of the present invention, and the present invention 25 should be construed to include the following modifica-

tion and alterations.

The intermediate layer is made not only of nickel, but also of iron or cobalt.

- 14 The copper content in upper layer 5 of tin base overlayer 6 may be higher than that in lower layer 4. Tin base overlayer 6 may consist not only of 5 two layers but also of three or more layers. In that case, it is preferable that the copper content is made lower in the direction from the lowest layer towards the uppermost layer, but so long as the copper content of the lowest layer is 5 to 20% by mass, the copper 10 content of upper layers above the lowest layer may be higher or lower.

The uppermost layer of the tin base overlayer may contain not more than 5% by mass of inorganic particles to improve the wear resistance.

Claims

WHAT I S CLAIMED I S:

1. A multi-layered sliding material, which comprises a bearing alloy layer and a tin base over layer of tin-copper series provided thereon through an intermediate layer, the tin base overlayer comprising a plurality of layers having different copper contents, among which the lowest layer in contact with the intermediate layer contains 5 to 20% by mass of copper and has a thickness of 1 to 3 m.

2. A multi-layered sliding material according to Claim 1, wherein the copper content in the uppermost

layer of the tin base overlayer is 0.5 to 10% by mass.

3. A multi-layered sliding material according to Claim 1 or 2, wherein the uppermost layr of the tin base overlayer contains not more than 5% by mass of at least one of zinc, indium, antimony and silver.

4. A multi-layered sliding material according to any one of Claims 1 to 3, wherein the intermediate layer is composed of any one of nickel, iron and cobalt, and has a thickness of 0.5 to 3 m.

5. A multi-layered sliding material according to any one of Claims 1 to 4, wherein the bearing alloy layer is composed of a copper base alloy or an aluminum base alloy.

6. A multi-layered sliding material substantially as hereinbefore described with reference to and as shown in the accompanying drawings.