U.S. patent application number 09/749442 was filed with the patent office on 2001-09-13 for copper alloy sliding material.
Invention is credited to Inaba, Takashi, Kawakami, Naohisa, Kurimoto, Satoru, Sakai, Kenji, Shibayama, Takayuki, Yamamoto, Koichi.
Application Number | 20010021353 09/749442 |
Document ID | / |
Family ID | 18575129 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021353 |
Kind Code |
A1 |
Sakai, Kenji ; et
al. |
September 13, 2001 |
Copper alloy sliding material
Abstract
Disclosed is a copper alloy sliding material comprising 0.5 to
15 mass % Sn and 0.1 to 10 vol % of hard particles consisting of
one or more selected from WC, W.sub.2C and Mo.sub.2C. The hard
particles have preferably an average particle size of 0.1 to 10
.mu.m, whereby they are dispersed in the copper alloy matrix so as
to make the sliding-contact surface uneven, from which the hard
particles protrude partially. The sliding material comprises an
amount or a total amount of not more than 40 mass % of one or more
selected from Ni, Ag, Fe, Al, Zn, Mn, Co, Si and P, an amount or a
total amount of not more than 10 mass % of Bi and/or Pb, and/or an
amount or a total amount of not more than 10 vol % of a solid
lubricant comprising BN, graphite, MoS.sub.2 and/or WS.sub.2.
Inventors: |
Sakai, Kenji; (Nagoya,
JP) ; Kawakami, Naohisa; (Nagoya, JP) ;
Kurimoto, Satoru; (Nagoya, JP) ; Inaba, Takashi;
(Nagoya, JP) ; Yamamoto, Koichi; (Nagoya, JP)
; Shibayama, Takayuki; (Nagoya, JP) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Family ID: |
18575129 |
Appl. No.: |
09/749442 |
Filed: |
December 28, 2000 |
Current U.S.
Class: |
420/470 |
Current CPC
Class: |
F16C 2204/12 20130101;
C22C 32/0089 20130101; Y10T 428/12007 20150115; C22C 32/0052
20130101; C22C 9/00 20130101; C22C 9/02 20130101; F16C 33/121
20130101 |
Class at
Publication: |
420/470 |
International
Class: |
C22C 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 2000 |
JP |
2000-053798 |
Claims
What is claimed is:
1. A copper alloy sliding material comprising 0.5 to 15 mass % Sn
and 0.1 to 10 vol % of hard particles consisting of one or more
selected from WC, W.sub.2C and Mo.sub.2C.
2. A copper alloy sliding material according to claim 1, wherein
the hard particles have an average particle size of 0.1 to 10
.mu.m.
3. A copper alloy sliding material according to claim 1, which
further comprises an amount or a total amount of not more than 40
mass % of one or more selected from Ni, Ag, Fe, Al, Zn, Mn, Co, Si
and P (phosphorous).
4. A copper alloy sliding material according to claim 2, which
further comprises an amount or a total amount of not more than 40
mass % of one or more selected from Ni, Ag, Fe, Al, Zn, Mn, Co, Si
and P (phosphorous).
5. A copper alloy sliding material according to claim 1, which
further comprises an amount or a total amount of not more than 10
mass % of Bi and/or Pb.
6. A copper alloy sliding material according to claim 2, which
further comprises an amount or a total amount of not more than 10
mass % of Bi and/or Pb.
7. A copper alloy sliding material according to claim 3, which
further comprises an amount or a total amount of not more than 10
mass % of Bi and/or Pb.
8. A copper alloy sliding material according to claim 4, which
further comprises an amount or a total amount of not more than 10
mass % of Bi and/or Pb.
9. A copper alloy sliding material according to claim 1, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
10. A copper alloy sliding material according to claim 2, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
11. A copper alloy sliding material according to claim 3, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
12. A copper alloy sliding material according to claim 4, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
13. A copper alloy sliding material according to claim 5, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
14. A copper alloy sliding material according to claim 6, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
15. A copper alloy sliding material according to claim 7, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
16. A copper alloy sliding material according to claim 8, which
further comprises an amount or a total amount of not more than 10
vol % of a solid lubricant comprising BN, graphite, MoS.sub.2
and/or WS.sub.2.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a copper alloy sliding
material, more particularly to the copper alloy sliding material
which is suitable to a sintering alloy bearing including a plain
bearing.
[0003] 2. Brief Description of the Art
[0004] In general, the Kelmet alloy (i.e. a Cu--Pb system or a
Cu--Sn--Pb system) is used for a copper alloy sliding material, for
example a sintering copper alloy for plain bearings. It has been
known that the Kelmet material has excellent anti-seizure property
and exhibits good sliding property under a hydrodynamic lubrication
condition by virtue of a much content of Pb (i.e. about 20 mass %).
Recently, however, it has been desired for various metal materials
not to contain Pb as far as possible from the view point of
protecting the environment.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention has been developed under the above
background and is aimed to provide the copper alloy sliding
material which can ensure a high performance of anti-seizure
property while reducing the Pb content.
[0006] With regard to the copper alloy sliding material, there may
be an idea of dispersing hard particles in the copper based matrix
(e.g. Cu--Sn), the hard particles being much harder than the
matrix. In general, the hard particles may be of a metal system
material such as Mo or W, or of a ceramic system material such as
SiO.sub.2, Al.sub.2O.sub.3 or SiC.
[0007] In this case, the following function or effects can be
expected:
[0008] (1) Since the hard particles much harder than the copper
based matrix are dispersed on the surface (i.e. sliding-contact
surface), the copper alloy sliding material will have good
sliding-contact property and excellent wear resistance.
[0009] (2) The hard particles will protrude from the surface so as
to form recessions with relation to the matrix, so that the oil
retaining property and anti-seizure property will be improved.
[0010] (3) The hard particles will make the surface of a mating
shaft smooth to improve the anti-seizure property.
[0011] (4) Although there is a fear that the copper based matrix
will partially move to the surface of the mating shaft (usually,
steel) due to adhesion to deteriorate the anti-seizure property,
the hard particles will shave off adhesives of the copper alloy
from the mating shaft to contribute to improvement of the
anti-seizure property and a long life of the mating shaft.
[0012] However, because the metal system hard particles consisting
of Mo or W have a lower hardness (which is not more than 500 of
Vickers Hardness) than the ceramic system hard particles, they are
inferior in the effect of shaving off adhesives of the copper alloy
from the mating shaft. There is also a problem that metals such as
Mo or W are comparatively adhesive to steel (Fe) of the mating
shaft as compared with ceramics because of the metal to metal
sliding-contact. In contrast, the ceramic system hard particles
such as SiO.sub.2, Al.sub.2O.sub.3 or SiC are excellent in the
effect of shaving off adhesives of the copper alloy from the mating
shaft because of higher hardness (for example, 600 to 700 of
Vickers Hardness) than the mating shaft and do not adhere to the
mating shaft because they are hard to form intermetallic compounds
with metals such as steel (Fe).
[0013] However, in the case where the ceramic system hard particles
such as SiO.sub.2, Al.sub.2O.sub.3 or SiC are selected, there have
been a problem that, when the sliding contact material receives a
dynamic load, since the protruded hard particles support the load,
cracks arise at the interface between the copper system matrix and
the hard particles due to shear stress arisen at the interface
resulting in a phenomenon of falling-off of the hard particles from
the copper system matrix. If such falling-off of the hard particles
occurs, the abrasive wear arises resulting in deterioration of
anti-seizure property. Further, when such falling-off of hard
particles arises, voids (or recessions) are produced to become
trigger points of fatigue due to stress concentration resulting in
deteriorated fatigue resistance. The factor that hard particles
such as SiO.sub.2, Al.sub.2O.sub.3 or SiC are liable to fall off
from the matrix will reside in low wettability by copper (or a
copper alloy).
[0014] Thus, the present inventors practiced various experiments
and researches in order to solve the falling-off problem of the
hard particles while ensuring the effect in virtue of the hard
particles, whereby it has been confirmed that the wettability of
the hard particles by the copper alloy matrix is improved to make
them hard to leave from the matrix by using WC, W.sub.2C and/or
Mo.sub.2C as the hard particles instead of usual SiO.sub.2,
Al.sub.2O.sub.3 or SiC, consequently the present invention has been
achieved.
[0015] The invention copper alloy sliding material comprises 0.5 to
15 mass % Sn and 0.1 to 10 vol % of hard particles consisting of
one or more selected from WC, W.sub.2C and Mo.sub.2C. The content
of the hard particles is defined not with the mass percent but with
the volume percent, being more proper than the former unit which
varies with the specific gravity of the hard particles, because a
volume of the hard particles is important with regard to the
function thereof. This is the same in the case of a solid lubricant
mentioned below.
[0016] According to the copper alloy sliding material in which the
hard particles with a high hardness are dispersed, excellent
anti-seizure and fatigue resistance properties can be obtained
while reducing the Pb amount. Since the hard particles consisting
of one or more selected from WC, W.sub.2C and Mo.sub.2C have a high
hardness (i.e. not less than 1300 of Vickers Hardness), they are
excellent in the effect of shaving off adhesives of the copper
alloy from the mating shaft and do not adhere to the mating shaft
because they are hard to form intermetallic compounds with metals
such as steel (Fe). Further, the hard particles consisting of one
or more selected from WC, W.sub.2C and Mo.sub.2C have good
wettability by the copper alloy contrasting with SiO.sub.2,
Al.sub.2O.sub.3 or SiC, so that it is possible to prevent them to
fall off from the copper alloy matrix.
[0017] The defined amount of Sn being 0.5 to 0.15 mass % can
strengthen the copper alloy matrix to improve the fatigue
resistance. If the Sn amount is less than 0.5 mass %, there can not
be seen the effect of strengthening the copper alloy matrix. If the
Sn amount exceeds 15 mass %, a much amount of Cu--Sn system
intermetallic compounds is produced to become brittle
disadvantageously.
[0018] The amount of the hard particles are required to be 0.1 to
10 volume %. If it is less than 0.1 volume %, the desired
improvement in anti-seizure and wear resistance properties can not
be obtained. If it exceeds 10 volume %, the strength is
deteriorated to be lower fatigue resistance and an attacking
intensity of the hard particles against the mating shaft becomes
too great, so that there can not be seen the improvement effect of
anti-seizure and wear resistance properties. More preferably, the
amount of the hard particles is 0.5 to 5 volume %.
[0019] The hard particles have preferably an average particle size
of 0.1 to 10 .mu.m. If the average particle size is less than 0.1
.mu.m, the hard particles are too fine, so that there can not be
appeared improvement of anti-seizure and wear resistance properties
as an elemental hard particle. If the average particle size exceeds
10 .mu.m, an attacking intensity of the hard particles against the
mating shaft increases resulting in deterioration of workability
including machinability. More preferably, the average particle size
is within a range of 1 to 5 .mu.m.
[0020] The copper alloy may comprise an amount or a total amount of
not more than 40 mass % of one or more selected from Ni, Ag, Fe,
Al, Zn, Mn, Co, Si and P (phosphorous). The alloying element(s)
strengthens the copper alloy matrix to improve the fatigue
resistance of the copper alloy. If the amount of the alloying
element(s) exceeds 40 mass %, the copper alloy matrix becomes too
hard to apply the alloy material to bearings. Therefore, the amount
or the total amount of the alloying element(s) is preferably not
more than 40 mass %.
[0021] The copper alloy may also comprise an amount or a total
amount of not more than 10 mass % of Bi and/or Pb. In this case, a
soft Bi and/or Pb phase is formed in the copper alloy matrix to
improve conformability, foreign substance embeddability and
anti-seizure property of the copper alloy. If the amount of Bi
and/or Pb exceeds 10 mass %, the strength of the copper alloy is
deteriorated. Therefore, the amount of Bi and/or Pb is suitably not
more than 10 mass %. With regard to Pb, while its amount is
desirably as small as possible (for example, zero percent), it is
possible to achieve the object of the invention, which is to fully
reduce the Pb content in the copper alloy relative to the
conventional the Kelmet alloy (comprising about 20 mass % Pb), by
the defined amount of Pb.
[0022] The copper alloy may also comprise an amount or a total
amount of not more than 10 vol % of a solid lubricant comprising
BN, graphite, MoS.sub.2 and/or WS.sub.2. The solid lubricant can
improve the self lubrication property of the copper alloy, so that
the anti-seizure and wear resistance properties of the copper alloy
can be further improved. If the amount of the solid lubricant
exceeds 10 vol %, the strength of the copper alloy is deteriorated.
Thus, the amount of the solid lubricant is properly of not more
than 10 vol %.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic cross-sectional view around the inner
surface of a plain bearing as one embodiment of the invention;
[0024] FIG. 2 is a cross-sectional view showing a structure of a
plain bearing according to the invention;
[0025] FIG. 3 is a graph which shows results of a seizure test on
Invention and Comparative Examples; and
[0026] FIG. 4 is a graph which shows results of a fatigue test on
Invention and Comparative Examples.
BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT
INVENTION
[0027] Herein below, referring to the drawings, an embodiment of
the invention will be described with respect to a plain
bearing.
[0028] FIG. 2 shows schematically a structure of plain bearing 1
according to the invention. The plain bearing 1 is a so-called
hemi-circular bearing half, a pair of which are combined
cylindrically in use. The plain bearing 1 consists of a back metal
2 made of a thin steel plate, a copper alloy sliding material layer
4 of the invention, which is provided on the inner surface of the
back metal 2 optionally via a copper plating layer 3 as a bonding
layer, and an overlay layer 5 which is provided on the copper alloy
sliding material layer 4 and made of a soft metal or resin.
[0029] The copper alloy sliding material layer 4 is of a copper
system sintering alloy having a chemical composition as defined in
the claims, for example, those of invention examples 1 to 9
described hereafter. Namely, the copper alloy sliding material
layer 4 has a chemical composition of 0.5 to 15 mass % Sn and 0.1
to 10 vol % of hard particles consisting of one or more selected
from WC, W.sub.2C and Mo.sub.2C. The hard particles have an average
particle size of 0.1 to 10 .mu.m.
[0030] Preferably, the copper alloy sliding material layer 4
comprises an amount or a total amount of not more than 40 mass % of
one or more selected from Ni, Ag, Fe, Al, Zn, Mn, Co, Si and P. It
may also comprise an amount or a total amount of not more than 10
mass % of Bi and/or Pb. It may also comprise an amount or a total
amount of not more than 10 vol % of a solid lubricant comprising BN
(especially, h-BN), graphite, MoS.sub.2 and/or WS.sub.2.
[0031] Here, a brief description will described on a method of
producing the plain bearing 1.
[0032] (1) First, a copper alloy powder (Cu--Sn), having a
predetermined chemical composition, and hard particles are mixed in
a mixing machine so as to have a predetermined proportion (i.e. 0.1
to 10 vol % of the hard particles). Preferably, the copper alloy
powder consists of particles each having a particle size of not
more than 250 .mu.m. The copper alloy powder may comprise also an
alloying element(s) in a predetermined proportion, which is one or
more of Ni, Ag, Fe, Al, Zn, Mn, Co, Si and P, and/or one or more of
Bi and Pb. The copper alloy powder may comprise also a
predetermined amount of BN, graphite, MoS.sub.2 and/or WS.sub.2 in
addition to the hard particles. Further, the copper alloy powder is
not always required to be of a previously alloyed powder but may be
a mixture of powders each consists of an alloying element.
[0033] (2) Next, the thus prepared powder mixture is spread
uniformly on a steel plate (i.e. a back metal 2) being provided
with a copper plating layer 3 thereon and having a thickness of 1.3
mm, for example. The steel plate with the powder mixture is heated
to 800 to 920.degree. C. of temperature for about 15 minutes in a
reduction atmosphere in order to perform a first sintering
treatment. The sintered steel plate is subjected to rolling. In
order to further increase the density of the sintered layer on the
steel plate, a further process of desired times of sintering and
subsequent rolling is repeated, so that a bimetal plate, which
consists of the steel plate (back metal 2) and the sintered copper
alloy layer (i.e. the copper alloy sliding material layer 4) and in
which the sintered copper alloy layer is 0.4 mm thick and the total
thickness is 1.6 mm, for example, can be obtained. The bimetal
plate is subjected to a machine working thereby shearing to a
predetermined measurement, bending to a hemi-circular shape and
finish-machining its surface. Thereafter, an overlay layer is
provided on the sintered copper alloy layer whereby the plain
bearing 1 produced.
[0034] Referring to FIG. 1 which is a schematic cross-sectional
view around the inner surface of the plain bearing 1 while omitting
the overlay layer 5, there are dispersed hard particles 7,
consisting of WC, W.sub.2C and/or Mo.sub.2C and having a high
hardness (i.e. not less than 1300 of Vickers Hardness), in the
copper alloy matrix 6. Microscopically looking at the inner surface
state of the plain bearing 1, the hard particles 7 protrude from
the surface (i.e. the sliding surface) so as to form an uneven
surface with respect to the copper alloy matrix 6.
[0035] While the thus structured plain bearing 1 supports the
mating shaft 8 of a crank shaft of motor vehicle engines, for
example, on its inner surface, the partially protruded hard
particles 7 of the copper alloy sliding material layer 4 receive
the load from the mating shaft 8. Further, while lubricant oil is
supplied to the sliding-contact surface of the bearing, recessions
at the uneven surface, which are present under the relationship
between the protruded hard particles 7 and the copper alloy matrix
6, act as oil reservoirs to improve the oil retaining capacity of
the plain bearing 1.
EXPERIMENT
[0036] In order to inspect and confirm the effectiveness of the
copper alloy sliding material layer 4, the inventors performed a
seizure test and a fatigue test for examining anti-seizure property
and fatigue resistance with regard to specimen materials of
Invention Example Nos. 1 to 9 and Comparative Example Nos. 1 to 4
of which chemical compositions are shown in following Table 1.
1 TABLE 1 COMPONENTS *H.P. mass % volume % Size No Cu Sn Ni Bi Pb
Gr. H.P. (.mu.m) INVENTION 1 Bal. 10 -- -- -- -- WC: 1.5 1.5 2 Bal.
6 1.5 -- -- -- WC: 2 1.5 3 Bal. 6 7 -- -- -- WC: 1 5 4 Bal. 6 -- --
-- -- Mo.sub.2C: 1 2 5 Bal. 2 3 -- -- -- Mo.sub.2C: 2 2 6 Bal. 2 --
5 -- -- WC: 5 5 7 Bal. 2 -- -- -- -- WC1.5 1.5 8 Bal. 10 3 -- -- --
WC: 7 5 9 Bal. 10 -- -- -- 1.5 Mo.sub.2C: 4 4 COMPARATIVE EXAMPLE 1
Bal. 3.5 -- -- 23 -- -- -- 2 Bal. 6 1.5 -- -- -- WC: 15 1.5 3 Bal.
6 -- -- -- -- -- -- 4 Bal. 6 -- -- -- -- Al.sub.2O.sub.3: 1 2
*Note: "H.P. Size" means "an average particle size of hard
particles".
[0037] The seizure test was carried out as follows.
[0038] Bearings were prepared by the same process as that of the
bearing 1 shown in FIG. 2, of which copper alloy sliding material
layers have the chemical compositions of Invention Example Nos. 1
to 9 and Comparative Example Nos. 1 to 4, respectively. However,
the respective bearing was not provided with an overlay layer in
order to clearly confirm characteristics of the copper alloy
sliding material layer.
[0039] A rotary shaft, which was driven by an electric motor, was
supported by the respective bearing.
TEST CONDITIONS
[0040] At first a running-in operation was conducted for 60
minutes.
[0041] Thereafter, the bearing load was increased step-by-step from
a given initial bearing load in such a manner that 5 MPa was
accumulated every 10 minutes.
[0042] Continuously rotating the rotary shaft and increasing the
bearing load as stated above, a bearing load just prior to the
bearing load, when the temperature of the bearing back surface
exceeded 220.degree. C. or there arose an abnormal driving current
of the electric motor which drives the shaft, was determined as a
maximum specific load without seizure.
[0043] Other test conditions are shown in following Table 2.
2TABLE 2 ITEM CONDITION SHAFT DIAMETER 53 mm BEARING WIDTH 13 mm
PERIPHERAL SPEED OF SHAFT 10 m/second LUBRICANT OIL SAE #20 OIL
SUPPLY AMOUNT 12.5 ml/minute MATERIAL OF SHAFT JIS S55C as quenched
SHAFT SURFACE ROUGHNESS Rmax: not more than 1.0 .mu.m
[0044] The fatigue test was carried out as follows.
[0045] Bimetal plates were prepared by the same process as afore
mentioned, of which copper alloy sliding material layers have the
chemical compositions of Invention Example Nos. 1 to 9 and
Comparative Example Nos. 1 to 4, respectively. A back metal was
removed from the respective bimetal plate by machining to obtain a
specimen.
[0046] A testing load was exerted on the thus obtained every
specimen under room temperature to examine fatigue property. The
testing load was increased step-by-step from an initial load of 50
MPa in such a manner that 10 MPa was accumulated at every increase
of load. Applying the testing load cyclically and sine-curvedly
50,000 times to the respective specimen at every testing load
level, a testing load value when there arose a crack in the
specimen was determined as the fatigue rupture load.
[0047] FIGS. 3 and 4 show the results of the seizure test and the
fatigue test, respectively.
[0048] A consideration on the test results will be provided
below.
[0049] First, comparing Comparative Example No. 1, which is of the
Kelmet material comprising a lot of Pb which has been generally
used in conventional plain bearings, with the other Examples which
comprise WC and/or Mo.sub.2C of the hard particles 7, with regard
to the anti-seizure property (i.e. the maximum specific load
without seizure), the all Invention Example Nos. 1 to 9 are
generally the same or superior than Comparative Example No. 1. With
regard to the fatigue rupture load, the all Invention Examples 1 to
9 are significantly improved as compared with Comparative Example
No. 1. Regarding the anti-seizure property, Comparative Example No.
3 is notably inferior than Invention Example No. 4, the former
comprising substantially the same chemical composition as that of
the latter except for the component of the hard particles 7.
[0050] From the results, it is believed that the high anti-seizure
property could be obtained because the hard particles 7, having a
high hardness and being dispersed in the copper alloy matrix 6,
well acted with respect to the anti-seizure property. The following
four points could be raised as functions of the hard particles
7.
[0051] (1) By virtue of the hard particles 7 having a high hardness
present at the surface (i.e. the sliding-contact surface) of the
copper alloy sliding material layer 4, the sliding-contact property
of the plain bearing is improved so as to have excellent wear
resistance property.
[0052] (2) By virtue of the hard particles 7 partially protruded
from the surface of the copper alloy sliding material layer 4,
recessions at the surface, which are present under the relationship
between the protruded hard particles 7 and the copper alloy matrix
6, act as oil reservoirs to improve the oil retaining capacity
resulting in improved anti-seizure property of the plain bearing
1.
[0053] (3) The hard particles 7 make the surface of the mating
shaft smooth so as to improve the anti-seizure property.
[0054] (4) Although there is a fear that the copper alloy matrix 6
will partially move to the surface of the mating shaft (usually,
steel) 8 due to adhesion to deteriorate the anti-seizure property,
the hard particles 7 shave off adhesives of the copper alloy from
the mating shaft 8 to contribute to improvement of the anti-seizure
property and a long life of the mating shaft 8. Because of a high
hardness (i.e. not less than 1300 of Vickers Hardness), the ceramic
system hard particles 7 of WC, W.sub.2C and/or Mo.sub.2C have
excellent performance of shaving off adhesions of the copper alloy
from the mating shaft 8. Also there is not adhesion with the mating
shaft 8 because the ceramic system hard particles are hard to form
an intermetallic compound with steel (or Fe).
[0055] Comparing Comparative Example No. 2 with Invention Example
No. 2 both of which contain the hard particles (WC), Comparative
Example No. 2, which comprises 15 vol % of the hard particles, is
extremely inferior in both of the anti-seizure and fatigue
resistance properties than Invention Example No. 2 which comprises
2 vol % of the hard particles. It is noted also that Comparative
Example No. 2 is inferior in the anti-seizure and fatigue
resistance properties than all Invention Examples.
[0056] This will be because a too much amount of the hard particles
7 makes the copper alloy to have low strength so as to be
deteriorated in fatigue resistance property and to have too great
attacking intensity against the mating shaft 8 resulting in that
the hard particles is no more effective for improving the
anti-seizure and wear resistance properties. According to a
research by the present inventors, a proper amount of the hard
particles 7 is within a range of 0.1 to 10 vol %, more preferably
0.5 to 5 vol %.
[0057] Comparing Comparative Example No. 4, which contains the
ceramic system hard particles of Al.sub.2O.sub.3, with Invention
Example No. 4 which comprises the same metal base (i.e. the copper
alloy matrix 6) with the former Example and the hard particles of
Mo.sub.2C, the former is extremely inferior in the anti-seizure and
fatigue resistance properties than the latter.
[0058] This will be because, in the case where the ceramic system
hard particles such as SiO.sub.2, Al.sub.2O.sub.3 or SiC are
selected, there is a problem that, when the sliding contact
material receives a dynamic load, since Al.sub.2O.sub.3 has low
wettability by copper (or a copper alloy), cracks are liable to
arise at the interface between the copper system matrix and the
hard particles due to shear stress arisen at the interface
resulting in a phenomenon of falling off of the hard particles from
the copper system matrix. If such falling off of the hard particles
occurs, the abrasive wear arises resulting in deterioration of
anti-seizure property, and furthermore when such separation of hard
particles arises, voids (or recessions) are produced to become
trigger points of fatigue due to stress concentration resulting in
deteriorated fatigue resistance. In contrast, the hard particles 7
of WC and Mo.sub.2C being contained in Invention Examples are hard
to fall off from the copper alloy matrix 6 because of good
wettability by a copper alloy.
[0059] Reviewing the Invention Examples, Example No. 3 containing 7
mass % of Ni has the highest fatigue resistance property. This will
be because the copper alloy matrix 6 was strengthened by Ni
dissolved therein. Example No. 6 containing 5 mass % of Bi has high
anti-seizure property. This will be because a soft Bi phase was
formed in the copper alloy matrix 6 so as to improve the
conformability, foreign substance embeddability and anti-seizure
property.
[0060] As will be apparent from the above, according to the
invention copper alloy sliding material, it is possible to ensure a
high performance of the anti-seizure and fatigue resistance
properties while reducing the Pb content. Consequently, the high
utility copper alloy sliding material can be provided as an
alternative of the conventional Kelmet material.
[0061] While the copper alloy sliding materials of the embodiment
Invention Examples do not comprise Pb, the invention material may
comprise a small amount of Pb (i.e. not more than 10 mass %). Even
in this case, it is possible to achieve the object of fully
reducing the Pb amount as compared with the conventional Kelmet
material (comprising about 20 mass % Pb). The hard particles may be
a combination of two or more of WC, W.sub.2C and Mo.sub.2C. The
present invention can be practiced under various modifications or
alternatives within a scope of the claim definition, more
specifically, the invention copper alloy sliding material can be
applied to not only plain bearings but also various types of
sliding material.
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