U.S. patent application number 09/959817 was filed with the patent office on 2002-12-26 for sliding member.
Invention is credited to Omiya, Takao, Onoda, Motonobu, Takamura, Hiroyuki.
Application Number | 20020197504 09/959817 |
Document ID | / |
Family ID | 18498224 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197504 |
Kind Code |
A1 |
Takamura, Hiroyuki ; et
al. |
December 26, 2002 |
Sliding member
Abstract
The present invention provides a sliding member, of which the
surface cavities do not disappear even after progress of wear of
the sliding surface, which permits maintenance of a satisfactory
seizure resistance, and has better seizure resistance, wear
resistance and strength properties than in a sliding member having
a porous chrome plating layer formed thereon in the conventional
art. The sliding member of the invention has a laminated hard Cr
plating layer comprising a plurality of hard Cr plating layers
laminated on the sliding surface. Micro-cracks are formed on each
hard Cr plating layer surface, and the micro-cracks of each hard Cr
plating layer form micro-pores independent in the film-forming
direction. On the cross-section of the laminated hard Cr plating
layer, the porosity should be within a range of from 0.5 to
4.5%.
Inventors: |
Takamura, Hiroyuki;
(Tochigi-ken, JP) ; Omiya, Takao; (Tochigi-ken,
JP) ; Onoda, Motonobu; (Saitama-ken, JP) |
Correspondence
Address: |
Parkhurst & Wendel
Suite 210
1421 Prince Street
Alexandria
VA
22314-2805
US
|
Family ID: |
18498224 |
Appl. No.: |
09/959817 |
Filed: |
November 8, 2001 |
PCT Filed: |
December 26, 2000 |
PCT NO: |
PCT/JP00/09235 |
Current U.S.
Class: |
428/636 ;
205/113; 428/666; 428/667; 428/935 |
Current CPC
Class: |
Y10T 428/12854 20150115;
C25D 3/04 20130101; C25D 5/625 20200801; C23C 28/023 20130101; Y10T
428/12847 20150115; C25D 7/10 20130101; C23C 26/00 20130101; Y10T
428/12639 20150115; C25D 5/14 20130101; C25D 5/623 20200801; C25D
5/18 20130101 |
Class at
Publication: |
428/636 ;
428/666; 428/667; 428/935; 205/113 |
International
Class: |
C25D 005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1999 |
JP |
11/371144 |
Claims
1. A sliding member having a laminated hard Cr plating layer
comprising a plurality of hard Cr plating layers laminated on a
sliding surface, micro-cracks being formed on the surface of each
hard Cr plating layer, the micro-cracks of each hard Cr plating
layer forming independent micro-pores in the film forming
direction; wherein porosity on a cross-section of said laminated
hard Cr plating layer is within a range of from 0.5 to 4.5%.
2. A sliding member according to claim 1, wherein porosity on the
surface of said hard Cr plating layer is within a range of from 0.5
to 30%, and the number of micro-cracks on said surface is within a
range of from 50 to 1,200 cracks/10 mm.
3. A sliding member according to claim 1 or 2, wherein the
thickness per layer of said hard Cr plating layer is within a range
of from 0.1 to 60 .mu.m.
4. A sliding member having a laminated hard Cr plating layer
comprising a plurality of hard Cr plating layers laminated on a
sliding surface, micro-cracks being formed on the surface of each
hard Cr plating layer, the micro-cracks of each hard Cr plating
layer forming independent micro-pores in the film forming
direction; wherein porosity on the surface of said hard Cr plating
layer is within a range of from 0.5 to 5.0%, and the number of
micro-cracks on said surface is within a range of from 50 to 1,200
cracks/10 mm.
5. A sliding member according to claim 4, wherein the thickness per
layer of said hard Cr plating layer is within a range of from 0.1
to 60 .mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sliding member comprising
a lamination of a plurality of hard Cr plating layers on a sliding
surface. More particularly, the invention relates to a sliding
member suitably applicable to a piston ring for an internal
combustion engine.
BACKGROUND ART
[0002] Along with the recent tendency toward a lighter weight and a
higher output of internal combustion engines, the quality
requirement is increasing for sliding members such as piston rings.
It is the conventional practice for these sliding members such as
piston rings for internal combustion engines to apply a wear
resistant surface treatment through, for example, hard Cr plating
or nitriding to the sliding surface as means for improving
durability. Among others, the nitriding treatment, which gives an
excellent wear resistance, attracts the general attention as being
suitable as a surface treatment for sliding members including
piston rings used under severe operating conditions, and is widely
used in practice.
[0003] However, the nitriding treatment, while being excellent in
resultant wear resistance, is not always sufficient for seizure
resistance (scarfing resistance): there may occur an abnormal wear
when used under severe operating conditions. Improvement has
therefore been demanded. A conventional hard chrome plating layer
(hereinafter referred to as a "hard Cr plating layer" as required),
having a slightly higher seizure resistance (scarfing resistance)
as compared with the nitriding treatment, is not always sufficient
in wear resistance. There has therefore been a demand for
improvement in applications under severe operating conditions.
[0004] In these respects, porous chrome plating having fine
cavities on the surface serving as lubricant oil sumps formed on
the conventional hard Cr plating layer was studied for improving
seizure resistance and wear resistance, and the result is actually
applied in some cases.
[0005] In the conventional porous chrome plating, however, cavities
are present only on the surface, and cavities effective for
improving sliding properties are not existent in the interior of
the plating layer. When applying grinding or when the sliding
surface is worn out, a solid portion not containing cavities on the
surface of the plating layer is exposed, leading to deterioration
of seizure resistance or wear resistance.
DISCLOSURE OF INVENTION
[0006] The present invention was achieved in view of the
aforementioned problems, and has a main object to provide a sliding
member in which surface cavities do not disappear even after
grinding or in progress of wear of the sliding surface, seizure
resistance and wear resistance can be maintained at a satisfactory
level, and seizure resistance, wear resistance and strength are
higher than in the conventional sliding member having a porous
chrome plating layer formed thereon.
[0007] To achieve the aforementioned object, the sliding member of
the invention as recited in claim 1 has a laminated hard Cr plating
layer comprising a plurality of hard Cr plating layers laminated on
a sliding surface, micro-cracks being formed on the surface of each
hard Cr plating layer, the micro-cracks of each hard Cr plating
layer forming independent micro-pores in the film forming
direction; wherein porosity on a cross-section of the laminated
hard Cr plating layer is within a range of from 0.5 to 4.5%.
[0008] In the invention, a plurality of hard Cr plating layers
having micro-cracks formed on the surface thereof are laminated,
and micro-cracks in each layer form independent micro-pores in the
film forming direction. When micro-cracks disappear along with
progress of wear, therefore, another micro-cracks immediately
appear on the surface. Even when grinding is applied or after a
long use in service, therefore, there always exist micro-cracks
serving as lubricant oil sumps on the surface. No problem is
therefore posed in seizure resistance or wear resistance. The
porosity on the cross-section of this laminated hard Cr plating
layer is within a range of from 0.5 to 4.5%, resulting in a sliding
member satisfactory seizure resistance, wear resistance and
strength.
[0009] In the sliding member of claim 1 of the invention, the
porosity on the surface of the hard Cr plating layer is within a
range of from 0.5 to 30%, and the number of micro-cracks on the
surface is within a range of from 50 to 1,200 cracks/10 mm.
[0010] According to the invention, by limiting the porosity and the
number of micro-cracks within the above-mentioned ranges, it is
possible to obtain a laminated hard Cr plating layer satisfying the
seizure resistance, wear resistance and strength requirements, as
in the case of above-mentioned porosity on the cross-section.
Because many micro-cracks are formed on the hard chrome plating
layer, seizure resistance or wear resistance never poses
problems.
[0011] In the sliding member according to claim 1 or 2 of the
invention, as recited in claim 3, the thickness per layer of the
hard Cr plating layer should preferably be within a range of from
0.1 to 60 .mu.m.
[0012] In the invention, when the thickness is smaller than 0.1
.mu.m, it is necessary to laminate many hard Cr plating layers in
order to obtain a laminated hard Cr plating layer having a
necessary thickness, and this may result in a cost problem. When
the thickness is over 60 .mu.m, after disappearance of micro-cracks
by wear, the thickness before appearance of -micro-cracks of the
next layer becomes too large, and in the meantime, problems may be
encountered in seizure resistance or wear resistance.
[0013] To achieve the aforementioned object, the invention provides
a sliding member having a laminated hard Cr plating layer
comprising a plurality of hard Cr plating layers laminated on a
sliding surface, micro-cracks being formed on the surface of each
hard Cr plating layer, the micro-cracks of each hard Cr plating
layer forming independent micro-pores in the film forming
direction; wherein porosity of the surface of the hard Cr plating
layer is within a range of from 0.5 to 5.0%, and the number of
micro-cracks on the surface is within a range of from 50 to 1,200
cracks/10 mm.
[0014] In the invention, a plurality of hard Cr plating layers thus
having micro-cracks on the surface thereof are laminated, and
micro-cracks in each layer form independent micro-pores in the film
forming direction. Even when micro-cracks disappear along with
progress of wear, new micro-cracks appear on the surface
immediately. When applying grinding or using for a long period of
time, therefore, presence of micro-cracks serving as lubricant oil
sumps always on the surface makes the sliding member free from any
problem in seizure resistance or wear resistance. The porosity of
the surface resulting from the micro-cracks on the surface of each
hard Cr plating layer is within a range of from 0.5 to 5.0%, and
the number of these micro-cracks is within a range of from 50 to
1,200 cracks/10 mm. Cracks on the surface of the hard Cr plating
layer in the invention therefore largely comprise many
micro-cracks. Since many micro-cracks are formed on the surface of
the hard Cr plating layer, no problem is caused in seizure
resistance or wear resistance, although the porosity of the surface
based on the micro-cracks is within a relatively low range of from
0.5 to 5.0%. Because the porosity on the surface is on such a low
level, and cracks are fine in size, strength-related properties
such as peeling resistance of the hard Cr plating layer are
considerably improved. The present invention have these features is
particularly suitably applicable to uses in which the total
thickness of the laminated hard Cr plating layer is relatively
small as in piston rings of automobile.
[0015] In the sliding member of the invention according to claim 4,
as recited in claim 5 of the invention, the thickness per layer of
the hard Cr plating layer should preferably be within a range of
from 0.1 to 60 .mu.m.
[0016] When the thickness is smaller than 0.1 .mu.m in the
invention, it is necessary to laminate many hard Cr plating layers
for the purpose of obtaining a laminated hard Cr plating layer
having a necessary thickness, and this may pose a cost problem.
When the thickness is larger than 60 .mu.m, the thickness becomes
excessively large during the period from disappearance of
micro-cracks by wear to appearance of micro-cracks on the next
layer, during which a problem may be encountered in seizure
resistance or wear resistance
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a surface photo illustrating typical micro-cracks
formed on the surface of each hard Cr plating layer;
[0018] FIG. 2 is a sectional photo illustrating typical lamination
of hard Cr plating layers laminated on the surface of a substrate
having an Rz of 3 .mu.m;
[0019] FIG. 3 is a sectional photo illustrating typical lamination
of hard Cr plating layers laminated on the surface of a substrate
having an Rz of 20 .mu.m; and
[0020] FIG. 4 is a schematic descriptive view illustrating an
improved tester of an NPR type impact tester (a quantitative tester
of plating adhesion disclosed in Japanese examined Patent
Publication No. 36-19046).
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] The sliding member of the present invention will now be
described in detail.
[0022] A first feature of the sliding member of the invention is
that the sliding member has a laminated hard Cr plating layer
comprising a lamination of a plurality of hard Cr plating layers on
a sliding surface; micro-cracks are formed on the surface of each
hard Cr plating layer; and the micro-cracks of each hard Cr plating
layer have micro-pores independent in the film-forming
direction.
[0023] As shown in FIG. 1, the sliding member of the invention
comprises a lamination of the hard Cr plating layers having
micro-cracks on the surfaces thereof. Therefore, for example, in
the case of a sliding member having only a single hard Cr plating
layer on the sliding surface, wear causes most of micro-cracks to
disappear in a short period of time, thus posing a problem of a
decrease in seizure resistance and wear resistance. In the
invention, however, a plurality of hard Cr plating layers having
such micro-cracks on the surfaces thereof are laminated so that,
even when the portion of the surfaces containing micro-cracks
disappears as a result of wear or working, micro-cracks (forming
micro-pores independent in the film-forming direction) appear on
the next surfaces, thus permitting maintenance of satisfactory
seizure resistance and wear resistance for a long period of
time.
[0024] In the invention, the thickness per layer of the hard Cr
plating layer should preferably be within a range of from 0.1 to 60
.mu.m. In the case where the entire laminated hard Cr layer should
have a relatively small total thickness, as in the automotive
piston ring, the thickness per layer of the hard Cr plating layer
should preferably be within a range of from 0.1 to 15 .mu.m, or
more preferably, from 2 to 15 .mu.m. In the case where the total
thickness of the entire laminated hard Cr plating layer is
relatively large as in a marine piston ring, the thickness per
layer of the hard Cr plating layer should preferably be within a
range of from 15 to 60 .mu.m, or more preferably, from 15 to 40
.mu.m.
[0025] When the thickness per layer of the hard Cr plating layer is
smaller than the aforementioned range, it is necessary to laminate
many layers when forming a laminated hard Cr plating layer having a
prescribed thickness. This is not desirable because of the
possibility of posing a cost problem and since a small thickness of
each layer may cause a problem in strength of each layer. When the
thickness is larger than the aforementioned range, on the other
hand, it would take a long period of time from disappearance of
most of the micro-cracks to appearance of micro-cracks on the
surface of the next layer. A larger thickness is not desirable
because of the possibility of posing a seizure resistance
problem.
[0026] In the invention, the surface portion of the substrate
should preferably be flat. The substrate surface may have fine
irregularities to some extent, and after lamination of hard Cr
plating layers thereon in a prescribed number, smoothed by wrapping
or the like. Presence of such fine irregularities on the substrate
surface causes irregularities also in all the hard Cr plating
layers. This reduces the possibility of disappearance of fine
cracks in a stroke upon progress of wear, and this may improve
seizure resistance. As shown in FIGS. 2 and 3, the hard Cr plating
layer of the invention laminated by a method described later is
observed, varying with plating conditions, to have fine cavities
over the entire area in the thickness direction formed thereon. A
solid portion free from fine cavities is therefore hard to appear.
As a result, a substrate surface even with irregularities within a
range of Rz (ten-point average roughness) of from 0.3 to 20 .mu.m
is suitably applicable. In a use in which the total thickness of
the laminated hard Cr plating layer as a whole is relatively small
as in an automotive piston ring, Rz of the substrate surface should
preferably be within a range of from 0.3 to 3.0 .mu.m. In a use in
which the total length of the entire laminated hard Cr plating
layer is relatively large as in a marine piston ring, Rz of the
substrate surface should preferably be within a range of from 1 to
20 .mu.m.
[0027] The number of laminated hard Cr plating layers in the
sliding member of the invention is the result of division of the
necessary thickness of the hard Cr plating layers by the thickness
of the individual layers, to be appropriately selected in response
to the circumstances of application of the sliding member. The
generally applicable number of layers is within a range of from
about 5 to 30 layers, or more preferably, from 8 to 20 layers. A
number of laminated layers larger than the aforementioned range
requires more time and labor to conduct hard Cr plating, and this
may cause a cost problem. When the number of laminated layers is
smaller than the range shown, on the other hand, an increase in the
thickness of the individual layers is generally expected, so that
seizure resistance may be deteriorated.
[0028] A second feature of the sliding member of the invention is
that the porosity on a cross-section of the laminated hard Cr
plating layer is within a range of from 0.5 to 4.5%.
[0029] In general, in a porous chrome plating layer used as a
sliding surface, when ignoring seizure resistance and wear
resistance problems, the number of cavities such as cracks present
on the surface should be the smallest possible, considering
properties related with strength by the porous chrome plating layer
itself such as peeling resistance. Particularly, under severe
service conditions as in a sliding member for marine applications,
strength-related properties become more important. When seizure
resistance and wear resistance problems cannot be ignored, however,
there occurs a serious problem in that reduction of the number of
micro-cracks of the porous chrome plating layer results in
deterioration of seizure resistance and wear resistance. Therefore,
the number of micro-cracks in this porous chrome plating layer is
an important factor for satisfying property requirements of
strength, seizure resistance and wear resistance. In the present
invention, the number of micro-cracks in this hard Cr plating layer
was evaluated in terms of the porosity on a cross-section of the
laminated hard Cr plating layer and possibility was found to
maintain satisfactory strength properties, seizure resistance and
wear resistance as described above by limiting the porosity on the
cross-section of the laminated hard Cr plating layer within a range
of from 0.5 to 4.5%.
[0030] It is necessary, as described above, to limit the porosity
on the cross-section of the laminated hard Cr plating layer of the
invention within a range of from 0.5 to 4.5%. With a porosity on
the cross-section of under 0.5%, seizure resistance and wear
resistance are low. A porosity on the cross-section of over 4.5%
leads to a decrease in strength, causing breakage and cracks.
[0031] The term the porosity on a cross-section of the laminated
hard Cr plating layer as used in the invention (also referred to as
the "porous degree") shall mean a value determined by first
applying polishing to the cross-section by use of water-proof
polishing sheets of paper in a sequence of #180, #240, #320, #600,
#800, and then #1000, then applying buffing by use of alumina
having a particle size of up to 1 .mu.m for 20 seconds, finally
applying buffing by use of alumina having a particle size of up to
0.1 .mu.m for seven seconds, and analyzing the cross-section by
means of an image analyzer.
[0032] This definition is adopted because it is experimentally
revealed that the value of porosity measured on the cross-section
of the laminated hard Cr plating layer varies with the sample
polishing conditions and time, and the necessity arises to set
constant polishing conditions. The porosity on the cross-section of
the laminated hard Cr plating layer in the invention means a
porosity after polishing as described in the above-mentioned
definition in all cases.
[0033] In the invention, furthermore, the porosity on the surface
of the laminated hard Cr plating layer should preferably be within
a range of from 0.5 to 30%, and the number of micro-cracks on this
surface should preferably be within a range of from 50 to 1,200
cracks/10 mm.
[0034] A porosity on the surface of under 0.5% leads to poorer
seizure resistance or wear resistance, and a porosity on the
surface of over 30% causes a decrease in strength and production of
breakage and cracks. In this case, in a use in which the total
thickness of the entire laminated hard Cr plating layer is
relatively small as in an automotive piston ring, the porosity
should preferably be within a range of from 0.5 to 5.0%, or more
preferably, from 2.0 to 4.5%. In a use in which the total thickness
of the entire laminated hard Cr plating layer is relatively large
as in a marine piston ring, the porosity should preferably be
within a range of from 5 to 30%, or more preferably, from 10 to
20%. By limiting the number of micro-cracks on the surface within
the above-mentioned range, many micro-cracks are formed on the hard
chrome plating layer. No seizure resistance or wear resistance
problem is therefore encountered.
[0035] In the above case where the surface porosity is within a
range of from 0.5 to 30 % and the number of micro-cracks is within
a range of from 50 to 1,200 cracks/10 mm, the formed micro-cracks
have a width within a range of from 0.42 to 2.5 .mu.m. In the case
with a surface porosity of from 0.5 to 5.0% and a number of
micro-cracks of from 50 to 1,200 cracks/10 mm, the width is from
0.42 to 1.0 .mu.m. A surface porosity of from 5.0 to 30% and a
number of micro-cracks of from 50 to 1,200 cracks/10 mm result in a
width within a range of from 1.0 to 2.5 .mu.m.
[0036] In the sliding member of the invention, particularly, in the
sliding member in uses in which the total thickness of the entire
laminated hard Cr plating layer is relatively small as in an
automotive piston ring, as described above, it is possible to
achieve the object of the invention by specifying the surface
porosity (also referred as the surface area ratio) based on
micro-cracks on the surface and the number of micro-cracks without
the need to clearly specify the porosity on the cross-section. More
specifically, as recited in claim 4 of the invention, it is
possible to achieve the object by limiting the surface porosity
based on micro-cracks formed on the surface of each hard Cr plating
layer within a range of from 0.5 to 5.0%, and the number of the
micro-cracks within a range of from 1,200 cracks/10 mm.
[0037] As in the aforementioned second feature, when the problems
of seizure resistance and wear resistance are disregarded in a
porous chrome plating layer used generally as a sliding surface,
the number of cavities such as cracks present on the surface should
preferably be the smallest possible in terms of strength-related
properties of the porous chrome plating layer itself including
peeling resistance. Since seizure resistance and wear resistance
are important properties, however, cavities are provided so that
cracks are formed, for example, through an inverse current
treatment on the surface of the hard Cr plating layer, and a
prescribed porosity (surface area ratio) is achieved even when
allowing a decrease in strength in the plating layer itself such as
peeling resistance to some extent.
[0038] In an aspect of the invention, as recited in claim 4, new
findings were obtained that, by causing micro-cracks to serve as
such surface cavities, no problem was posed in seizure resistance
or wear resistance even with a porosity based on a smaller number
of cavities than in an usual case. This aspect of the invention has
a marked feature in that it is intended to improve strength of the
plating layer itself such as peeling resistance without causing a
decrease in seizure resistance or wear resistance.
[0039] These micro-cracks are such that, as described above, in the
case where the porosity of the surface based on surface
micro-cracks of each hard Cr plating layer is within a range of
from 0.5 to 5.0%, the number of micro-cracks is within a range of
from 50 to 1,200 cracks/10 mm, or more preferably, that in the case
where the porosity is within a range of from 2.0 to 4.5%, the
number of micro-cracks is within a range of from 150 to 800
cracks/10 mm. In the case with a surface porosity within a range of
from 0.5 to 5.0% and a number of micro-cracks within a range of
from 50 to 1,200 cracks/10 mm, the width of the formed cracks is
within a range of from 0.42 to 1.0 .mu.m.
[0040] The sliding member of the invention described above is
manufactured by repeating a hard Cr plating step and an etching
step including an inverse current treatment prescribed times by use
of a Cr plating bath on a substrate, and laminating hard Cr plating
layers. By forming hard Cr plating layers one on top of the others
as described above, an excellent adhesion between plating layers
can be obtained. A hard Cr plating layer having a porosity on the
cross-section or the surface as shown in the invention is obtained
by adjusting conditions for the plating step and conditions for the
etching step including the inverse current treatment.
[0041] The present invention is not limited to the aforementioned
embodiments. These embodiments are only examples, and any sliding
members having substantially the same configuration and providing
the same advantages as in the technical idea recited in the claims
of the invention are included in the technical scope of the
invention.
EXAMPLES
[0042] The present invention will be described in detail by means
of examples and comparative examples.
Example 1
[0043] A silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
1.5 g/L. and NaSiF.sub.6: 5 g/L) held constantly at 60.degree. C.
was used as a chrome plating bath. First, the substrate surface was
subjected to an inverse current treatment as an activation
treatment at a current density of 60 A/dm.sup.2 for 30 seconds
(inverse current treatment 1). Then, a positive current treatment
was applied at a current density of 60 A/dm.sup.2 for 17 minutes
(positive current treatment 1). Then, an inverse current treatment
was carried out at a current density of 60 A/dm.sup.2 for 60
seconds (inverse current treatment 2). The positive current
treatment 1 and the inverse current treatment 2 were repeated 17
times so as to achieve a predetermined plating thickness, thereby
forming a laminated hard Cr plating layer used in the sliding
member of the invention.
[0044] The resultant laminated hard Cr plating layer had a
thickness per layer of about 10 .mu.m and a total thickness of
about 170 .mu.m as a laminated hard Cr plating layer. The surface
porosity based on micro-cracks on the surface was about 3.0%, and
the number of micro-cracks was about 600 cracks/10 mm. Measurement
of the sectional porosity in this state showed a porosity of about
3.0%.
Example 2
[0045] A silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
1.5 g/L, and NaSiF.sub.6: 1 g/L) held constantly at 65.degree. C.
was used as a chrome plating bath. First, the substrate surface was
subjected to an inverse current treatment as an activation
treatment at a current density of 60 A/dm.sup.2 for 30 seconds
(inverse current treatment 1). Then, a positive current treatment
was applied at a current density of 60 A/dm.sup.2 for 18 minutes
(positive current treatment 1). Then, an inverse current treatment
was conducted at a current density of 60 A/dm.sup.2 for 60 seconds
(inverse current treatment 2). The positive current treatment 1 and
the inverse current treatment 2 were repeated 17 times so as to
achieve a predetermined plating thickness, thereby forming a
laminated hard Cr plating layer used in the sliding member of the
invention.
[0046] The resultant laminated hard Cr plating layer had a
thickness per layer of about 10 .mu.m and a total thickness of
about 170 .mu.m as a laminated hard Cr plating layer. The surface
porosity based on micro-cracks on the surface was about 0.5%, and
the number of micro-cracks was about 50 cracks/10 mm. Measurement
of the sectional porosity in this state showed a porosity of about
0.5%.
Example 3
[0047] A silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
1.5g/L. and NaSiF.sub.6: 8 g/L) held constantly at 50.degree. C.
was used as a chrome plating bath. First, the substrate surface was
subjected to an inverse current treatment as an activation
treatment at a current density of 60 A/dm.sup.2 for 30 seconds
(inverse current treatment 1). Then, a positive current treatment
was applied at a current density of 60 A/dm.sup.2 for 16 minutes
(positive current treatment 1). Then, an inverse current treatment
was carried out at a current density of 60 A/dm.sup.2 for 60
seconds (inverse current treatment 2). The positive current
treatment 1 and the inverse current treatment 2 were repeated 17
times so as to achieve a predetermined plating thickness, thereby
forming a laminated hard Cr plating layer used in the sliding
member of the invention.
[0048] The resultant laminated hard Cr plating layer had a
thickness per layer of about 10 .mu.m and a total thickness of
about 170 .mu.m as a laminated hard Cr plating layer. The surface
porosity based on micro-cracks on the surface was about 4.5%, and
the number of micro-cracks was about 1,200 cracks/10 mm.
Measurement of the sectional porosity in this state showed a
porosity of about 4.5%.
Example 4
[0049] A plating bath (CrO.sub.3: 256.7 g/L, trivalent chromium:
3.47 g/L, H.sub.2SO.sub.4: 3.00 .mu.L, and iron: 9.20 g/L) held at
a temperature within a range of from 56 to 58.degree. C. was used
as a chrome plating bath. First, the substrate surface was
subjected to a positive current treatment at a current density of
30 A/dm.sup.2 for 110 minutes (positive current treatment 1). Then,
an inverse current treatment was carried out at a current density
of 30 A/dm.sup.2 for three minutes (inverse current treatment 1).
Then, a positive current treatment was conducted at a current
density of 30 A/dm.sup.2 for 80 minutes (positive current treatment
2). In addition, an inverse current treatment was applied at a
current density of 30 A/dm.sup.2 for three minutes (inverse current
treatment 1). The positive current treatment 2 and the inverse
current treatment 1 were repeated 11 times, thereby forming a
sliding member having a hard Cr plating layer laminated on a
sliding surface.
[0050] In the resultant laminated hard Cr plating layer, a first
layer, had a thickness of about 50 .mu.m, and a second and
subsequent layers had a thickness of about 30 .mu.m per layer. The
thus obtained laminated hard Cr plating layer had a thickness of
about 410 .mu.m. The sectional porosity was measured by polishing a
cross-section of this laminated hard Cr plating layer by the
aforementioned method, a porosity was 2.1%. The surface porosity
measured as above gave a porosity of about 15%.
Comparative Example 1
[0051] A silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
2.5 g/L, and NaSiF.sub.6: 8 g/L) kept at a constant temperature of
55.degree. C. was used as a chrome plating bath. First, a substrate
was electrolytically polished, with the substrate as an anode and
an opposite electrode comprising a tin-lead alloy as a cathode, by
applying a selective uniform current corresponding to 60 A/dm.sup.2
from a current controlling power source for a minute to
electrolytically eluting the substrate surface. Then, the anode and
the cathode were rapidly reversed, and a selective uniform current
of 60 A/dm.sup.2 was applied from the current controlling power
source until precipitation of a hard Cr plating layer having a
prescribed thickness.
[0052] A conventional single-layer chrome plating layer
continuously formed was obtained.
Comparative Example 2
[0053] A silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
2.5 g/L, and NaSiF.sub.6: 8 g/L) kept at a constant temperature of
55.degree. C. was used as a chrome plating bath. First, a substrate
was electrolytically polished, with the substrate as an anode and
an opposite electrode comprising a tin-lead alloy as a cathode, by
applying a selective uniform current corresponding to 60 A/dm.sup.2
from a current controlling power source for a minute to
electrolytically eluting the substrate surface. Then, the anode and
the cathode were rapidly reversed, and a selective uniform current
corresponding to 60 A/dm.sup.2 was applied from the current
controlling power source for 17 minutes to cause precipitation of a
single hard Cr plating layer having a prescribed thickness. Then,
the cathode and the anode were rapidly reversed again, and a
selective uniform current corresponding to 60 A/dm.sup.2 was
applied from the current controlling power source for a minute to
electrolytically elute the surface of the precipitated hard Cr
plating layer. Then, the above-mentioned precipitation step and
electrolytic elution step were continuously repeated until
precipitation of a Cr plating layer having a prescribed thickness,
and the process was completed by a precipitation step.
[0054] Thus, there was obtained a conventional chrome plating layer
having a multi-layer structure in which hard Cr plating layers were
formed into a thickness per layer of 10 .mu.m, and micro-cracks
were independently formed without continuation between two adjacent
layers.
Comparative Example 3
[0055] A plating bath prepared by adding ceramic particles (size
within a range of from 0.05 to 1.0 .mu.m; degree of suspension: 100
g/L) to a silicofluoride bath (CrO.sub.3: 250 g/L, H.sub.2SO.sub.4:
2.5 g/L, and NaSiF.sub.6: 8 g/L) kept at a constant temperature of
55.degree. C. was used. Plating was performed while stirring the
bath by aeration. First, a substrate was electrolytically polished
by applying a selective uniform current of 60 A/dm.sup.2 by a
current controlling power source for a minute with the substrate as
an anode and an opposite electrode comprising a tin-lead alloy as a
cathode and electrolytically eluting the substrate surface. Then,
the anode and the cathode were rapidly reversed, and a selective
uniform current corresponding to 60 A/dm.sup.2 was applied from the
current controlling power source for 17 minutes to cause
precipitation of a single hard Cr plating layer having a prescribed
thickness. Then, the cathode and the anode were rapidly reversed
again, and a selective uniform current corresponding to 60
A/dm.sup.2 was applied from the current controlling power source
for a minute, and the surface of a precipitated hard Cr plating
layer was electrolytically eluted. Then, the above-mentioned
precipitation step and electrolytic eluting step were continuously
repeated until precipitation of a Cr plating layer having a
prescribed thickness, finally ending the process by the
precipitation step.
[0056] In each of the Cr plating layers composing the Cr plating
film having the multi-layer structure, a conventional Cr plating
film retaining ceramic particles (size: 0.05 to 1.0 .mu.m) in pores
of chrome plating micro-cracks was obtained.
[0057] (Test Method and Test Conditions)
[0058] The thus obtained Cr plating layers, serving as examples 1
to 4 and comparative examples 1 to 3 were subjected to a wear test,
a scarfing test and a peeling resistance test. Test conditions were
as follows:
[0059] 1. Wear Test
[0060] Tester and Method:
[0061] An Amsler type wear tester was used. The wear test was
carried out by immersing substantially a half of the rotary piece
into oil, bringing a fixing piece into contact therewith, and
applying a load onto it.
[0062] Counterpart material: FC25 (HRB 98)
[0063] Lubricant: Turbine oil (#100)
[0064] Oil temperature: 80.degree. C.
[0065] Circumferential speed: 1 m/sec (478 rpm)
[0066] Load: 80 kg
[0067] Time: 7 hr
[0068] Measurement of amount of wear: The amount of wear (.mu.m)
was measured in terms of a step profile by use of a roughness
meter.
[0069] 2. Scarfing Test
[0070] Tester and Method:
[0071] An Amsler type wear tester was used. The test was carried
out by coating an oil in a certain amount onto the rotary piece,
and then, applying a load up to occurrence of scarf.
[0072] Counterpart material: FC25 (HRB 98)
[0073] Lubricant: No.2 Spindle oil
[0074] Oil temperature: Letting it run its natural cause
[0075] Circumferential speed: 1 m/sec (478 rpm)
[0076] Load and time: Load was increased continuously and
straightly at a rate of 5 kg/min up to occurrence of scarf. The
load at which a signal indicating seizure by scarf was evaluated as
scarfing load.
[0077] 3. Peeling Resistance Test
[0078] Tester:
[0079] An improved tester (see FIG. 4) of NPR type impact tester
(Japanese Unexamined Patent Publication No. 36-19046: Quantitative
Tester of Plating Adhesion) was used.
[0080] Method:
[0081] An impact energy of 43.1 mJ (44 kg/mm) per run was applied
to the film surface, and the peeling resistance was evaluated in
terms of the number of runs up to occurrence of peeling.
[0082] Presence of Peeling:
[0083] Presence of peeling was observed and evaluated by enlarging
the surface to 15 magnifications.
[0084] (Test Result)
[0085] The wear resistance was evaluated by assuming the amount of
wear for the test piece of Example 1 to be 1.00, by means of the
amount of wear for the other test pieces (Examples 2 to 4 and
Comparative Examples 1 to 3) as a wear index relative to the test
piece of Example 1. The test result is shown in Table 1. In Table
1, a smaller wear index than 1.00 suggests a smaller amount of
wear.
[0086] The seizure resistance was evaluated by assuming the amount
of seizure causing load for the test piece in Example 1 to be 1.00,
by means of the amount of seizure causing load for the other test
pieces (Examples 2 to 4 and Comparative Examples 1 to 3) as a
seizure resistance index relative to the test piece of Example 1.
The result is shown in Table 1. In Table 1, a larger seizure
resistance index than 1.00 corresponds to a larger seizure causing
load, suggesting a more excellent seizure resistance.
[0087] The peeling resistance was evaluated by assuming the number
of occurrences of peeling for the test piece of Example 1 to be
1.00, and comparing the same to the number of occurrences of
peeling for the other test pieces (Examples 2 to 4 and Comparative
Examples 1 to 3) as the peeling resistance index relative to the
test piece of Example 1. The result is shown in Table 1. In Table
1, a peeling resistance index smaller than 1.00 suggests that
peeling occurred in a number of runs smaller than that for the test
pieces of Example 1, revealing a poorer peeling resistance.
[0088] As is evident from Table 1, according to a comprehensive
evaluation of the three above-mentioned kinds of test results, the
test pieces of Examples 1 to 4 are confirmed to be superior to the
test pieces of Comparative Examples 1 to 3. These properties were
determined as a result of the comprehensive evaluation because, on
a commercial equipment, a single poor property may lead to a
defective result even when the other two properties are excellent.
Determination was therefore made through comprehensive evaluation
of the lowest property.
1 TABLE 1 Surface Number of Sectional porosity porosity cracks/10
mm Wear index Example 1 3.0% 3.0% ab. 600 cracks 1.00 .largecircle.
Example 2 0.5% 0.5% ab. 50 cracks 0.97 .circleincircle. Example 3
4.5% 4.5% ab. 1200 cracks 0.99 .largecircle. Example 4 2.1% 15% ab.
800 cracks 1.00 .largecircle. Comparative Single-layer film -- --
1.11 X Example 1 Comparative Multi-layer film 40% ab. 1000 cracks
0.96 .circleincircle. Example 2 10.0% Comparative Multi-layer film
20% ab. 1200 cracks 1.53 X Example 3 sealing ceramics (volume
ratio: 6.0%) Seizure resistance Peeling resistance Comprehensive
index index evaluation Example 1 1.00 .largecircle. 1.00
.largecircle. Reference .largecircle. Example 2 0.95 .largecircle.
1.20 .circleincircle. .largecircle. Example 3 1.05 .largecircle.
0.98 .largecircle. .largecircle. Example 4 1.00 .largecircle. 1.00
.largecircle. .largecircle. Comparative 0.83 X 0.95 .DELTA. X
Example 1 Comparative 1.08 .circleincircle. 0.90 X X Example 2
Comparative 1.16 .circleincircle. 0.85 X X Example 3 Note)
.circleincircle.: Excellent, .largecircle.: Equivalent, .DELTA.:
Fair, X: Inferior
INDUSTRIAL APPLICABILITY
[0089] As described above, the sliding member of the present
invention has the following features: the sliding member has a
laminated hard Cr plating layer comprising a plurality of hard Cr
plating layers on the sliding surface thereof; micro-cracks are
formed on the surface of each hard Cr plating layer; and the
micro-cracks of each hard Cr plating layer form fine pores
independent in the film-forming direction. The sliding member of
the invention is characterized in that the porosity on a
cross-section of the laminated hard Cr plating layer is within a
range of from 0.5 to 4.5%. It is thus possible to obtain a sliding
number excellent in strength properties, seizure resistance and
wear resistance. The sliding member thus obtained is suitably
applicable to automotive piston rings and marine piston rings
exposed to severe service conditions such as a high-output engine
and an engine used at high temperatures and a high load.
[0090] The entire disclosure of Japanese Patent Application No.
11-371144 filed on Dec. 27, 1999, including the specification,
claims, drawings and summary is incorporated herein by reference
its entirety.
* * * * *