U.S. patent application number 17/070032 was filed with the patent office on 2021-02-11 for sliding member and sliding bearing.
This patent application is currently assigned to TAIHO KOGYO CO., LTD.. The applicant listed for this patent is TAIHO KOGYO CO., LTD.. Invention is credited to Shigeyuki SUGA.
Application Number | 20210040988 17/070032 |
Document ID | / |
Family ID | 1000005164272 |
Filed Date | 2021-02-11 |
United States Patent
Application |
20210040988 |
Kind Code |
A1 |
SUGA; Shigeyuki |
February 11, 2021 |
SLIDING MEMBER AND SLIDING BEARING
Abstract
Provided are a sliding member and a sliding bearing which can
improve the fatigue resistance. A sliding member having a base
layer and a coating layer laminated on the base layer, in which the
coating layer contains Bi or Sn as a first metal element, a second
metal element which is harder than the first metal element and
forms an intermetallic compound with the first metal element, C,
and unavoidable impurities.
Inventors: |
SUGA; Shigeyuki;
(Toyota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIHO KOGYO CO., LTD. |
Toyota-shi |
|
JP |
|
|
Assignee: |
TAIHO KOGYO CO., LTD.
Toyota-shi
JP
|
Family ID: |
1000005164272 |
Appl. No.: |
17/070032 |
Filed: |
October 14, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16318907 |
Jan 18, 2019 |
|
|
|
PCT/JP2018/024804 |
Jun 29, 2018 |
|
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17070032 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 12/00 20130101;
F16C 33/12 20130101; F16C 2204/18 20130101; F16C 33/14 20130101;
C22C 13/00 20130101; F16C 2204/12 20130101 |
International
Class: |
F16C 33/12 20060101
F16C033/12; C22C 12/00 20060101 C22C012/00; C22C 13/00 20060101
C22C013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 2017 |
JP |
2017-141581 |
Aug 4, 2017 |
JP |
2017-151239 |
Claims
1. A sliding member comprising a base layer and a coating layer
laminated on the base layer, wherein the coating layer contains: Sn
as a first metal element; a second metal element that is harder
than the first metal element and forms an intermetallic compound
with the first metal element; 0.015 wt % or more and 0.100 wt % or
less of C; and unavoidable impurities.
2. A sliding bearing comprising a base layer and a coating layer
laminated on the base layer, wherein the coating layer contains: Sn
as a first metal element; a second metal element that is harder
than the first metal element and forms an intermetallic compound
with the first metal element; 0.015 wt % or more and 0.100 wt % or
less of C; and unavoidable impurities.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional Application of U.S.
application Ser. No. 16/318,907 filed Jan. 18, 2019, which is a
National Stage of International Application No. PCT/JP2018/024804
filed Jun. 29, 2018, claiming priority based on Japanese Patent
Application No. 2017-141581 filed Jul. 21, 2017, and Japanese
Patent Application No. 2017-151239 filed Aug. 4, 2017.
[0002] The present invention relates to a sliding member and a
sliding bearing in which a counterpart member slides on a sliding
surface.
BACKGROUND ART
[0003] An overlay layer containing Cu as an essential element and
formed of a Bi alloy containing at least one of Sn and In is known
(see Patent Literature 1). Patent Literature 1 describes that the
fatigue resistance is improved by incorporating Cu and Sn or In in
the Bi alloy. Also, a tin-based overlay in which Cu is added to Sn
which is a soft metal is known (see Patent Literature 2). In Patent
Literature 2, the improvement of wear resistance and fatigue
resistance is attempted by adding Cu as a strengthening element to
Sn.
CITATIONS LIST
Patent Literature
[0004] Patent Literature 1: JP 2004-353042 A
[0005] Patent Literature 2: JP 2002-310158 A
SUMMARY OF INVENTION
Technical Problems
[0006] However, when Cu is contained in the Bi alloy, as disclosed
in Patent Literature 1, there is a problem that the fatigue
resistance is rather lowered. This problem arises because, when
thermal load is applied to the overlay layer, a hard intermetallic
compound is generated by Bi and Cu so that cracks are easily
generated at an interface between the hard intermetallic compound
and soft Bi. In particular, the coarsening of the intermetallic
compound easily develops cracks in the overlay layer, resulting in
considerable deterioration in fatigue resistance. Further, when
thermal load is applied, for example, at the time of using the
tin-based overlay of Patent Literature 2, there is a problem of
decrease in fatigue resistance. When thermal load is applied to the
tin-based overlay of Patent Literature 1, a hard intermetallic
compound is formed by Sn and Cu. Then, an interface is formed
between the hard intermetallic compound and soft Sn, across which
the hardness is greatly different, and fatigue cracks are easily
generated at the interface. Furthermore, fatigue cracks are
developed at the interface between the intermetallic compound and
Sn, thereby lowering the fatigue resistance.
[0007] The present invention has been made in view of the above
problems, and it is an object of the present invention to provide a
technique capable of realizing the improvement in fatigue
resistance of an overlay.
Solutions to Problems
[0008] In order to attain the above object, the present invention
provides a sliding member and a sliding bearing. The sliding member
has a base layer and a coating layer laminated on the base layer,
and the coating layer contains Bi as a first metal element, a
second metal element which is harder than the first metal element
and forms an intermetallic compound with the first metal element,
0.010 wt % or more and 0.080 wt % or less of C, and unavoidable
impurities.
[0009] In the above structure, even when an intermetallic compound
is formed by the first metal element and the second metal element
upon application of thermal load, an appropriate amount of C serves
as a diffusion barrier, thereby making it possible to reduce the
possibility of coarsening of the intermetallic compound. Therefore,
the interface between soft Bi and the hard intermetallic compound
can be kept small. Therefore, even if fatigue cracks are generated
at the interface between soft Bi and the hard intermetallic
compound, it is possible to reduce the possibility of considerable
development of the fatigue cracks and to improve the fatigue
resistance.
[0010] Incidentally, by setting the content of C to 0.010 wt % or
more, the coarsening of the intermetallic compound can be
suppressed. The content of C is more desirably set to 0.020 wt % or
more. Further, by setting the content of C to 0.080 wt % or less,
the embrittlement of the coating layer can be suppressed. The
content of C is more desirably set to 0.060 wt % or less. The
second metal element may be any element that is harder than Bi and
forms an intermetallic compound with Bi, and examples thereof may
include Ag, Sb, and Ni. The content of the second metal element may
be 0.5 wt % or more and 5.0 wt % or less, and may be desirably 1.0
wt % or more and 3.0 wt % or less. Bi as the first metal element
constitutes the balance except the second metal element, C, and
unavoidable impurities.
[0011] In order to attain the above object, the present invention
provides a sliding member and a sliding bearing. The sliding member
has a base layer and a coating layer laminated on the base layer,
and the coating layer contains Sn as a first metal element, a
second metal element which is harder than the first metal element
and forms an intermetallic compound with the first metal element,
0.015 wt % or more and 0.100 wt % or less of C, and unavoidable
impurities.
[0012] In the above structure, even when an intermetallic compound
is formed by the first metal element and the second metal element
upon application of thermal load, an appropriate amount of C serves
as a diffusion barrier, thereby making it possible to reduce the
possibility of coarsening of the intermetallic compound. Therefore,
the interface between soft Sn and the hard intermetallic compound
can be kept small. Therefore, even if fatigue cracks are generated
at the interface between soft Sn and the hard intermetallic
compound, it is possible to reduce the possibility of considerable
development of the fatigue cracks and to improve the fatigue
resistance.
[0013] Incidentally, by setting the content of C to 0.015 wt % or
more, the coarsening of the intermetallic compound can be
suppressed. The content of C is more desirably set to 0.02 wt % or
more. Also, by setting the content of C to 0.100 wt % or less, the
embrittlement of the coating layer can be suppressed. The content
of C is more desirably set to 0.075 wt % or less. The second metal
element may be any element that is harder than Sn and forms an
intermetallic compound with Sn, and examples thereof may include
Ag, Sb, and Ni. The second metal element may be 0.5 wt % or more
and 10.0 wt % or less, and may be desirably 1.0 wt % or more and
5.0 wt % or less. Sn as the first metal element constitutes the
balance except the second metal, C, and unavoidable impurities.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a perspective view of a sliding member according
to an embodiment of the present invention.
[0015] FIG. 2 is an explanatory diagram of a fatigue test.
[0016] FIG. 3 is a graph of the carbon concentration and the
fatigue damage area rate in an overlay of a first embodiment.
[0017] FIG. 4 is a graph of the carbon concentration and the
fatigue damage area rate in an overlay of a second embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
[0018] Embodiments of the present invention will be described in
the following order.
[0019] (1) First embodiment:
[0020] (1-1) Structure of sliding member:
[0021] (1-2) Measurement method:
[0022] (1-3) Method for manufacturing sliding member:
[0023] (2) Experimental result:
[0024] (3) Second embodiment:
[0025] (4) Other Embodiments:
(1) First Embodiment
[0026] (1-1) Structure of Sliding Member:
[0027] FIG. 1 is a perspective view of a sliding member 1 according
to the first embodiment of the present invention. The sliding
member 1 includes a back metal 10, a lining 11, and an overlay 12.
The sliding member 1 is a half-shaped metallic member obtained by
dividing a hollow cylinder into two equal parts in a diametrical
direction, and has a semicircular arc shape in cross section. By
combining the two sliding members 1 so as to form a cylindrical
shape, a sliding bearing A is formed. The sliding bearing A bears a
columnar counter shaft 2 (crankshaft of an engine) in a hollow
portion formed therein. The outer diameter of the counter shaft 2
is formed to be slightly smaller than the inner diameter of the
sliding bearing A. A lubricating oil (engine oil) is supplied to a
gap formed between the outer peripheral surface of the counter
shaft 2 and the inner peripheral surface of the sliding bearing A.
At that time, the outer peripheral surface of the counter shaft 2
slides on the inner peripheral surface of the sliding bearing
A.
[0028] The sliding member 1 has a structure in which the back metal
10, the lining 11, and the overlay 12 are laminated in an order of
being distant from the center of curvature. Therefore, the back
metal 10 constitutes the outermost layer of the sliding member 1,
and the overlay 12 constitutes the innermost layer of the sliding
member 1. The back metal 10, the lining 11, and the overlay 12 each
have a constant thickness in the circumferential direction. The
thickness of the back metal 10 is 1.8 mm, the thickness of the
lining 11 is 0.2 mm, and the thickness of the overlay 12 is 10
.mu.m. Twice the radius of the surface on the curvature center side
of the overlay 12 (the inner diameter of the sliding member 1) is
73 mm. Hereinafter, the term "inner side" means the curvature
center side of the sliding member 1, and the term "outer side"
means the side opposite to the center of curvature of the sliding
member 1. The inner surface of the overlay 12 constitutes the
sliding surface for the counter shaft 2.
[0029] The back metal 10 is formed of steel containing 0.15 wt % of
C, 0.06 wt % of Mn, and the balance Fe. It suffices that the back
metal 10 is formed of a material that can support the load from the
counter shaft 2 via the lining 11 and the overlay 12, and the back
metal 10 may not necessarily be formed of steel.
[0030] The lining 11 is a layer laminated on the inner side of the
back metal 10 and constitutes the base layer of the present
invention. The lining 11 contains 10 wt % of Sn, 8 wt % of Bi, and
the balance consisting of Cu and unavoidable impurities. The
unavoidable impurities of the lining 11 are Mg, Ti, B, Pb, Cr, and
the like, and are impurities mixed in refining or scrapping. The
content of the unavoidable impurities in the lining 11 is 1.0 wt %
or less in total. The lining 11 is not limited to that having the
above-described composition, and may be formed of an Al alloy in
which the total amount of one or more of Bi, Sn, In, and Ni, and
unavoidable impurities is 25 wt % or less. Furthermore, the lining
11 may be formed of a Cu alloy. For example, the lining 11 may be
formed of a Cu alloy in which the total amount of one or more of
Sn, Si, Zn, Mg, Cr, Zr, Ni, and V, and unavoidable impurities is 25
wt % or less.
[0031] The overlay 12 is a layer laminated on the inner surface of
the lining 11 and constitutes the coating layer of the present
invention. In the overlay 12, the coating layer contains Bi as a
first metal element, Ni as a second metal element forming an
intermetallic compound with the first metal element, C, and
unavoidable impurities. In the overlay 12 of the present
embodiment, the content of Ni is 2.0 wt %, the content of C is 0.03
wt %, the total content of the unavoidable impurities is 1.0 wt %
or less, and the balance is Bi.
[0032] A fatigue test piece (connecting rod R) having an overlay 12
similar to that of the above-explained sliding member 1 was
prepared, and its fatigue damage area rate was measured. As a
result, the fatigue damage area rate was 2.0%, which was good. In a
fatigue test which will be described later, even when an
intermetallic compound is formed by the first metal element and the
second metal element upon application of thermal load, an
appropriate amount of C serves as a diffusion barrier, thereby
making it possible to reduce the possibility of coarsening of the
intermetallic compound. In the present embodiment, Bi.sub.3Ni and
the like are precipitated as intermetallic compounds in the overlay
12, but C serves as a diffusion barrier and can suppress coarsening
of Bi.sub.3Ni and the like. As a result, the interface between soft
Bi and the hard intermetallic compound can be kept small.
Therefore, even if fatigue cracks are generated at the interface
between soft Bi and the hard intermetallic compound, it is possible
to reduce the possibility of considerable development of the
fatigue cracks and to improve the fatigue resistance.
[0033] (1-2) Measurement Method:
[0034] The fatigue damage area rate was measured by the following
procedure. First, as shown in FIG. 2, a connecting rod R having
cylindrical through holes formed at both ends in the longitudinal
direction was prepared, and a test shaft H (hatching) was borne in
the through hole at one end. An overlay 12 (black) similar to that
of the sliding member 1 was formed on the inner peripheral surface
of the through hole for bearing the test shaft H formed in the
connecting rod R. The test shaft H was borne on both outer sides of
the connecting rod R in the axial direction of the test shaft H,
and the test shaft H was rotated so that a sliding speed was kept
at 6.6 m/sec. The sliding speed is a relative speed between the
surface of the overlay 12 and the test shaft H. The end portion of
the connecting rod R on the side opposite to the test shaft H was
connected to a moving body F reciprocating in the length direction
of the connecting rod R, and the reciprocating load of the moving
body F was set to 57 MPa. Also, engine oil at 120.degree. C. was
fed between the connecting rod R and the test shaft H.
[0035] By continuing the above state for 50 hours, the fatigue test
of the overlay 12 was carried out. After the fatigue test, the
inner surface (sliding surface) of the overlay 12 was photographed
from a position on a straight line orthogonal to the surface in
such a manner that the straight line served as the main optical
axis. So, the taken image was used as an evaluation image. Then,
the damaged portion in the surface of the overlay 12 reflected in
the evaluation image was observed with a binocular (magnifying
glass) and identified. The percentage of a value obtained by
dividing the area of the damaged portion, which was the area of the
damaged portion, by the area of the entire surface of the overlay
12 reflected in the evaluation image was measured as the fatigue
damage area rate.
[0036] Each of the numerical values shown in the above embodiment
was measured by the following method. The mass of the elements
constituting each of the layers of the sliding member 1 was
measured by an ICP emission spectroscopic analyzer (ICPS-8100
manufactured by Shimadzu Corporation). However, the concentration
of carbon in the overlay 12 was measured by a high-frequency
induction heating furnace combustion infrared absorption method
(carbon amount analysis method for steel according to JIS G
1211).
[0037] The thickness of each of the layers was measured by the
following procedures. First, the vertical cross section in the
axial direction of the sliding member 1 was polished with a cross
section polisher (IB-09010CP manufactured by JEOL Ltd.). Image data
of an observation image (backscattered electron image) was obtained
by photographing the cross section of the sliding member 1 with an
electron microscope (JSM-6610A manufactured by JEOL Ltd.) at a
magnification of 7000 times. Then, the film thickness was measured
by analyzing the observation image with an image analyzer (Luzex AP
manufactured by NIRECO).
[0038] (1-3) Method for Manufacturing Sliding Member:
[0039] First, a flat plate of low carbon steel having the same
thickness as the back metal 10 was prepared.
[0040] Next, powder of a material constituting the lining 11 was
scattered on the flat plate formed of low carbon steel.
Specifically, Cu powder, Bi powder and Sn powder were scattered on
the flat plate of low carbon steel so as to attain the mass ratio
among the respective components in the lining 11 described above.
It suffices that the mass ratio among the respective components in
the lining 11 can be satisfied, and alloy powder such as Cu--Bi or
Cu--Sn may be scattered on the flat plate of low carbon steel. The
particle sizes of the powders were adjusted to 150 .mu.m or less by
a test sieve (JIS Z 8801).
[0041] Next, the flat plate of low carbon steel and the powders
sprayed on the flat plate were sintered. The sintering temperature
was controlled to 700 to 1000.degree. C., and the sintering was
performed in an inert atmosphere. After the sintering, the sintered
flat plate was cooled. The lining 11 may not necessarily be formed
by sintering, and may be formed by casting or the like.
[0042] After completion of the cooling, a Cu alloy layer is formed
on the flat plate of low carbon steel. The Cu alloy layer contains
soft Bi particles precipitated during the cooling.
[0043] Next, the low carbon steel having a Cu alloy layer formed
thereon was pressed so as to have a shape obtained by dividing a
hollow cylinder into two equal parts in diameter. At this time, the
pressing process was performed so that the outer diameter of the
low carbon steel matched with the outer diameter of the sliding
member 1.
[0044] Next, the surface of the Cu alloy layer formed on the back
metal 10 was cut. At this time, the cutting amount was controlled
so that the thickness of the Cu alloy layer formed on the back
metal 10 was the same as that of the lining 11. Thereby, the lining
11 can be formed by the Cu alloy layer after the cutting process.
The cutting process was carried out by a lathe with a cutting tool
material made, for example, of sintered diamond set. The surface of
the lining 11 after the cutting process constitutes the interface
between the lining 11 and the overlay 12.
[0045] Next, Bi was laminated by a thickness of 10 .mu.m on the
surface of the lining 11 by electroplating, whereby the overlay 12
was formed. The electroplating procedures were as follows. First,
the surface of the lining 11 was washed with water. Further,
unnecessary oxides were removed from the surface of the lining 11
by pickling the surface of the lining 11. Thereafter, the surface
of the lining 11 was again washed with water.
[0046] Upon completion of the above pretreatment, electroplating
was performed by supplying a current to the lining 11 immersed in a
plating bath. The bath composition of the plating bath contained
organic Bi sulfonate: 20 g/l (Bi concentration), Ni nitrate: 1 g/l
(Ni concentration), organic surfactant: 20 ml/l, and organic
sulfonic acid: 100 g/l. As the organic surfactant, a polyethylene
glycol solution was used. The bath temperature of the plating bath
was set to 30.degree. C. Further, the current to be supplied to the
lining 11 was a direct current, and the current density was set to
3.0 A/dm.sup.2. After completion of the electroplating, water
washing and drying were carried out.
[0047] When the sliding member 1 was completed as described above,
the sliding bearing A was formed by combining the two sliding
members 1 in a cylindrical shape, and attached to the engine.
[0048] (2) Experimental Result:
[0049] Example 1 in which the concentration of the organic
surfactant was changed to 5 ml/l, Example 2 in which the
concentration of the organic surfactant was changed to 10 ml/l,
Example 3 (first embodiment) in which the concentration of the
organic surfactant was 20 ml/l, Example 4 in which the
concentration of the organic surfactant was changed to 40 ml/l, and
Comparative Example 1 in which the concentration of the organic
surfactant was changed to 80 ml/l, in the same electroplating as
that of the first embodiment, were prepared. Further, Comparative
Example 2 in which electroplating was performed in a plating bath
of sulfuric acid bath (Bi nitrate: 30 g/l (Bi concentration), Ni
nitrate: 2 g/l (Ni concentration), sulfuric acid: 100 g/l) was
prepared.
TABLE-US-00001 TABLE 1 Organic Carbon Fatigue damage surfactant
concentration area rate [ml/l] [wt %] [%] Example 1 20 0.01 8
Example 2 10 0.015 6 Example 3 20 0.03 2 (First embodiment) Example
4 40 0.08 6 Comparative 80 0.18 25 Example 1 Comparative 0 0.005 18
Example 2 (Sulfuric acid bath)
[0050] Table 1 shows the carbon concentration and the fatigue
damage area rate in the overlay 12 in Examples 1 to 4 and
Comparative Examples 1 and 2, respectively. The carbon
concentration and the fatigue damage area rate were measured by the
same methods as those in the first embodiment. As indicated in
Table 1, it was possible to increase the concentration of carbon in
the overlay 12 by increasing the concentration of the organic
surfactant in the plating bath. Further, as in Comparative Example
2, by using a plating bath containing no organic substance, the
concentration of carbon in the overlay 12 could be made almost
zero.
[0051] FIG. 3 is a graph showing the relationship between the
carbon concentration and the fatigue damage area rate. As shown in
the figure, it was found that better fatigue resistance was
exhibited as the carbon concentration was higher in the carbon
concentration range of 0.03 wt % or less. It is considered that the
coarsening of Cu.sub.6Bi.sub.5 and Cu.sub.3Bi could be suppressed
effectively as the carbon concentration was increased. It was found
that better fatigue resistance was exhibited as the carbon
concentration was lower in the carbon concentration range of more
than 0.03 wt %. It is considered that the embrittlement of the
overlay 12 due to C could be suppressed more as the carbon
concentration was lower.
[0052] In addition, as shown by hatching in the graph of FIG. 3, it
was found to be desirable to set the content of C to 0.010 wt % or
more and 0.080 wt % or less. More desirably, the C content is 0.02
wt % or more and 0.060 wt % or less.
(3) Second Embodiment
[0053] The second embodiment is identical with the first embodiment
in terms of the structure other than the overlay 12. Hereinafter,
the overlay 12 of the second embodiment will be described. The
overlay 12 of the second embodiment is also a layer laminated on
the inner surface of the lining 11 and constitutes the coating
layer of the present invention. In the overlay 12 of the second
embodiment, the coating layer contains Sn as a first metal element,
Cu as a second metal element forming an intermetallic compound with
the first metal element, C, and unavoidable impurities. In the
overlay 12 of the second embodiment, the content of Cu is 3.0 wt %,
the content of C is 0.05 wt %, the total content of the unavoidable
impurities is 1.0 wt % or less, and the balance is Sn.
[0054] A fatigue test piece (connecting rod R) having the
above-explained overlay 12 of the second embodiment was prepared,
and its fatigue damage area rate was measured. As a result, the
fatigue damage area rate was 3.0%, which was good. In a fatigue
test, even when an intermetallic compound is formed by the first
metal element and the second metal element upon application of
thermal load, an appropriate amount of C serves as a diffusion
barrier, thereby making it possible to reduce the possibility of
coarsening of the intermetallic compound. In the second embodiment,
Cu.sub.6Sn.sub.5 and Cu.sub.3Sn are precipitated as intermetallic
compounds in the overlay 12, but C serves as a diffusion bather and
can suppress the coarsening of Cu.sub.6Sn.sub.5 and Cu.sub.3Sn. As
a result, the interface between soft Sn and the hard intermetallic
compound can be kept small. Therefore, even if fatigue cracks are
generated at the interface between soft Sn and the hard
intermetallic compound, it is possible to reduce the possibility of
considerable development of the fatigue cracks and to improve the
fatigue resistance.
[0055] Next, Sn was laminated by a thickness of 10 .mu.m on the
surface of the lining 11 by electroplating, whereby the overlay 12
of the second embodiment was formed. The electroplating procedures
were as follows. First, the surface of the lining 11 was washed
with water. Further, unnecessary oxides were removed from the
surface of the lining 11 by pickling the surface of the lining 11.
Thereafter, the surface of the lining 11 was again washed with
water.
[0056] Upon completion of the above pretreatment, electroplating
was performed by supplying a current to the lining 11 immersed in a
plating bath. The bath composition of the plating bath contained
stannous nitrate: 28 g/l (Sn concentration), copper sulfate: 3 g/l
(Cu concentration), inorganic ammonium salt: 100 g/l, and organic
carboxylic acid: 80 g/l. The bath temperature of the plating bath
was set to 30.degree. C. Further, the current to be supplied to the
lining 11 was a direct current, and the current density was set to
2.0 A/dm.sup.2. After completion of the electroplating, water
washing and drying were carried out.
[0057] Example 5 in which the concentration of the organic
carboxylic acid was changed to 20 g/l, Example 6 in which the
concentration of the organic carboxylic acid was changed to 40 g/l,
Example 7 (second embodiment) in which the concentration of the
organic carboxylic acid was changed to 80 g/l, Example 8 in which
the concentration of the organic carboxylic acid was changed to 100
g/l, and Comparative Example 3 in which the concentration of the
organic carboxylic acid was changed to 200 g/l, in the same
electroplating as that of the second embodiment, were prepared.
Further, Comparative Example 4 in which electroplating was
performed in a plating bath of borofluoride bath (tin borofluoride,
copper borofluoride) was prepared.
TABLE-US-00002 TABLE 2 Organic Carbon Fatigue damage carboxylic
acid concentration area rate [ml/l] [wt %] [%] Example 5 20 0.015 8
Example 6 40 0.02 5 Example 7 80 0.05 3 (Second embodiment) Example
8 100 0.1 7 Comparative 200 0.5 21 Example 3 Comparative 0 0.005 15
Example 4 (Borofluoride bath)
[0058] Table 2 shows the carbon concentration and the fatigue
damage area rate in the overlay 12 in Examples 5 to 7 and
Comparative Examples 3 and 4, respectively. The carbon
concentration and the fatigue damage area rate were measured by the
same methods as those in the first embodiment. As indicated in
Table 2, it was possible to increase the concentration of carbon in
the overlay 12 by increasing the concentration of the organic
carboxylic acid in the plating bath. Further, as in Comparative
Example 4, by using a plating bath containing no organic substance,
the concentration of carbon in the overlay 12 could be made almost
zero.
[0059] FIG. 4 is a graph showing the relationship between the
carbon concentration and the fatigue damage area rate in the second
embodiment. As shown in the figure, it was found that better
fatigue resistance was exhibited as the carbon concentration was
higher in the carbon concentration range of 0.05 wt % or less. It
is considered that the coarsening of Cu.sub.6Sn.sub.5 and
Cu.sub.3Sn could be suppressed effectively as the carbon
concentration was increased. It was found that better fatigue
resistance was exhibited as the carbon concentration was lower in
the carbon concentration range of more than 0.05 wt %. It is
considered that the embrittlement of the overlay 12 due to C could
be suppressed more as the carbon concentration was lower.
[0060] In addition, as shown by hatching in the graph of FIG. 4, it
was found to be desirable to set the content of C to 0.015 wt % or
more and 0.100 wt % or less. Further, it is more desirable to set
the C content to 0.02 wt % or more and 0.075 wt % or less.
(4) Other Embodiments
[0061] In the above embodiment, Cu was employed as the second metal
element, but other elements (Ag, Sb, Ni, Au, and the like) harder
than Bi (for example, having higher Mohs hardness) may be adopted
as the second metal element. In addition, the formation of the
intermetallic compound is not necessarily limited to that during
use of the sliding member 1. For example, before use of the sliding
member 1, the precipitation of the intermetallic compound may be
completed by preliminary heat treatment. Also in this case, the
coarsening of the intermetallic compound can be suppressed by an
appropriate amount of C.
[0062] Further, an intermediate layer may be inserted between the
lining 11 and the overlay 12. The intermediate layer is desirably
formed of a material capable of suppressing diffusion of the
elements of the lining 11 into the overlay 12, and may be formed of
Cu, for example. The carbon concentration of the overlay 12 may not
necessarily be adjusted by the carbon concentration in the plating
bath of electroplating, and the method for forming the overlay 12
is not limited to the electroplating. For example, the overlay 12
may be formed by sputtering or vapor deposition, and the carbon
concentration may be adjusted during sputtering or vapor
deposition. Further, after formation of the overlay 12 having a low
carbon concentration, the carbon concentration may be increased by
diffusion or the like.
[0063] In the above embodiment, the sliding members 1 constituting
the sliding bearing A for bearing the crankshaft of an engine have
been illustrated, but a sliding bearing A for another purpose may
be formed by the sliding members 1 of the present invention. For
example, a radial bearing such as a transmission gear bush or a
piston pin bush/boss bush may be formed by the sliding member 1 of
the present invention. Furthermore, the sliding member of the
present invention may be used in thrust bearings, various washers,
or swash plates for car air-conditioner compressors. Further, the
matrix of the lining 11 is not limited to the Cu alloy, and it
suffices that the material of the matrix is selected according to
the hardness of the counter shaft 2. Also, the back metal 10 is not
essential and may not be used.
REFERENCE SIGNS LIST
[0064] 1 Sliding member
[0065] 2 Counter shaft
[0066] 10 Back metal
[0067] 11 Lining
[0068] 12 Overlay
[0069] A Bearing
[0070] F Moving body
[0071] H Test shaft
[0072] R Connecting rod
* * * * *