U.S. patent application number 11/667033 was filed with the patent office on 2008-04-24 for method for electrolytically depositing a ceramic coating on a metal, electrolyte for such electrolytic ceramic coating method, and metal member.
Invention is credited to Yoshihiro Ikeda, Kazuhiko Mori, Mitsuhiro Okuhata, Masatoshi Yamashita, Nobuaki Yoshioka.
Application Number | 20080093223 11/667033 |
Document ID | / |
Family ID | 35462930 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080093223 |
Kind Code |
A1 |
Yoshioka; Nobuaki ; et
al. |
April 24, 2008 |
Method for electrolytically depositing a ceramic coating on a
metal, electrolyte for such electrolytic ceramic coating method,
and metal member
Abstract
A method of electrolytic ceramic coating for metals, in which
there can be obtained a coating film that even when it is thin,
exhibits high hardness, excellent abrasion resistance and excellent
toughness and that even when applied to a slide material without
polishing, has low offensiveness to the mate material. As such a
method, there is provided a method of electrolytic ceramic coating
for metals, comprising carrying out electrolysis with the use of a
metal as a positive electrode in an electrolyte containing a
zirconium compound so that a ceramic coating is formed on the
surface of the metal.
Inventors: |
Yoshioka; Nobuaki;
(Kanagawa, JP) ; Mori; Kazuhiko; (Kanagawa,
JP) ; Okuhata; Mitsuhiro; (Osaka, JP) ;
Yamashita; Masatoshi; (Kanagawa, JP) ; Ikeda;
Yoshihiro; (Kanagawa, JP) |
Correspondence
Address: |
FLYNN THIEL BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1631
US
|
Family ID: |
35462930 |
Appl. No.: |
11/667033 |
Filed: |
August 5, 2005 |
PCT Filed: |
August 5, 2005 |
PCT NO: |
PCT/JP05/14412 |
371 Date: |
May 3, 2007 |
Current U.S.
Class: |
205/322 |
Current CPC
Class: |
C25D 11/04 20130101;
C04B 2235/449 20130101; C04B 35/119 20130101; C04B 2235/3244
20130101; C04B 2235/765 20130101; C04B 2235/442 20130101; C04B
2235/76 20130101; C25D 11/024 20130101; C04B 2235/762 20130101;
C04B 2235/80 20130101; C25D 7/10 20130101; C04B 2235/447 20130101;
C04B 35/4885 20130101; C25D 11/30 20130101; C25D 11/26 20130101;
C04B 2235/44 20130101; C04B 2235/5445 20130101; C04B 2235/96
20130101; C04B 2235/3201 20130101; C04B 2235/963 20130101; C04B
2235/786 20130101; C25D 11/026 20130101; C04B 2235/3217
20130101 |
Class at
Publication: |
205/322 |
International
Class: |
C25D 11/00 20060101
C25D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2004 |
JP |
2004-321919 |
Claims
1. A method for electrolytically depositing a ceramic coating on a
metal wherein an electrolytic treatment is conducted by using the
metal as an anode in an electrolyte containing a zirconium compound
to thereby form a ceramic coating on a surface of the metal.
2. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the zirconium compound is a
water soluble zirconium compound.
3. The method for electrolytically depositing a ceramic coating on
a metal according to claim 2 wherein the water soluble zirconium
compound is a zirconium carbonate compound.
4. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolyte is at a pH of
at least 8.0.
5. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolyte further
contains a water soluble phosphorus compound.
6. The method for electrolytically depositing a ceramic coating on
a metal according to claim 5 wherein the water soluble phosphorus
compound is a condensed phosphate.
7. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolyte further
contains an ion and/or an oxide of at least one metal selected from
the group consisting of titanium, yttrium, calcium, magnesium,
scandium, and cerium.
8. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolyte further
contains poorly soluble particles of at least one member selected
from the group consisting of oxide, hydroxide, phosphate, and
carbonate.
9. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolytic treatment is
carried out by a direct current electrolysis or a bipolar
electrolysis using a voltage waveform in which an AC component is
superposed on a DC component.
10. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolytic treatment is
conducted by using a voltage waveform in which at least one pulse
wave selected from the group consisting of rectangular wave, sine
wave, and triangular wave having a duty ratio of up to 0.5 is
superposed on a DC or AC component.
11. The method for electrolytically depositing a ceramic coating on
a metal according to claim 9 wherein the maximum value of the
voltage waveform is at least 400 V.
12. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the electrolytic treatment is
conducted under glow discharge and/or arc discharge caused on the
surface of the metal used as the anode.
13. The method for electrolytically depositing a ceramic coating on
a metal according to claim 1 wherein the metal is a valve metal or
its alloy.
14. An electrolyte for use in electrolytic deposition of a ceramic
coating on a metal, containing water, a zirconium compound, and at
least one member selected from the group consisting of alkali metal
ion, ammonium ion, and organic alkali.
15. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the zirconium
compound is a water soluble zirconium compound.
16. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 15 wherein the water soluble
zirconium compound is a zirconium carbonate compound.
17. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the electrolyte is
at a pH of at least 8.0.
18. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the electrolyte
further contains a water soluble phosphorus compound.
19. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 18 wherein the water soluble
phosphorus compound is a condensed phosphate.
20. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the electrolyte
further contains an ion and/or an oxide of at least one metal
selected from the group consisting of titanium, yttrium, calcium,
magnesium, scandium, and cerium.
21. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the electrolyte
further contains poorly soluble particles of at least one member
selected from the group consisting of oxide, hydroxide, phosphate,
and carbonate.
22. The electrolyte for use in electrolytic deposition of a ceramic
coating on a metal according to claim 14 wherein the electrolyte is
used for electrolytically depositing a ceramic coating on a valve
metal or its alloy.
23. A metal member comprising a metal substrate and a hard coating
on the metal substrate, wherein: the hard coating comprises an
amorphous layer which is composed of an amorphous oxide containing
a metal element constituting the metal substrate and zirconium, and
zirconium oxide microcrystals dispersed in the amorphous oxide.
24. A metal member comprising a metal substrate and a hard coating
on the metal substrate, wherein: the hard coating comprises a
crystalline layer on the metal substrate and an amorphous layer on
the crystalline layer, with the crystalline layer containing
crystals of oxide of a metal element constituting the metal
substrate, and the amorphous layer being composed of an amorphous
oxide containing the metal element constituting the metal substrate
and zirconium, and zirconium oxide microcrystals dispersed in the
amorphous oxide.
25. The metal member according to claim 24 wherein the crystalline
layer further contains zirconium oxide microcrystals dispersed
along a grain boundary and/or in a grain of the crystals of oxide
of the metal element constituting the metal substrate.
26. The metal member according to claim 23 wherein concentration
distribution of the zirconium in the hard coating is such that the
zirconium concentration gradually reduces from the surface of the
hard coating toward the metal substrate.
27. The metal member according to claim 23 wherein, when the hard
coating is analyzed by X ray diffractometry, relative peak
intensity on (111) plane of tetragonal zirconium oxide and/or cubic
zirconium oxide is equal to or higher than relative peak intensity
of the main peak of the oxide of the metal element constituting the
metal substrate.
28. The metal member according to claim 23 wherein, when the hard
coating is analyzed by X ray diffractometry, proportion of volume
of monoclinic zirconium oxide to the total of volume of the
tetragonal zirconium oxide and/or the cubic zirconium oxide and
volume of the monoclinic zirconium oxide is up to 0.5.
29. The metal member according to claim 23 wherein microcrystals of
the tetragonal zirconium oxide and/or the cubic zirconium oxide
have an average grain diameter of 0.25 to 500 nm.
30. The metal member according to claim 23 wherein a phosphorus
oxide is present on the surface of the hard coating and/or at the
interface of the hard coating with the metal substrate.
31. The metal member according to claim 23 wherein the hard coating
further contains at least one element selected from the group
consisting of yttrium, calcium, cerium, scandium, magnesium, and
titanium.
32. The metal member according to claim 23 wherein the metal
element constituting the metal substrate is a valve metal or its
alloy.
33. A metal member according to produced by the method for
electrolytically depositing a ceramic coating on a metal according
to claim 1.
Description
TECHNICAL FIELD
[0001] This invention relates to a method for forming a ceramic
coating on the surface of a metal by conducting electrolysis, and
an electrolyte for electrolytically depositing a ceramic coating on
a metal well adapted for such method. This invention also relates
to a metal member having a hard coating.
BACKGROUND ART
[0002] When a sliding member is produced from a light metal such as
aluminum alloy, the sliding part of the sliding member is generally
covered with a hard coating formed by anodization, electric
plating, vapor deposition, or the like to thereby provide the
sliding member with wear resistance. The anodization used in
providing a valve metal such as aluminum with wear resistant
coating is excellent in the covering power of the coating and in
the reduced environmental stress since it does not use chromium,
nickel, and the like, and accordingly, such method is widely
adopted.
[0003] Among such anodized coatings, the anodized coating having
improved wear resistance is called a hard anodized coating, and
such hard anodized coating is generally formed by low temperature
method. In this low temperature method, the anodization is
conducted in an electrolytic bath containing sulfuric acid as its
main component at a bath temperature of up to 10.degree. C. In
addition, the anodization is conducted in the low temperature
method at a relatively high current density of 3 to 5 A/dm.sup.2
compared to other anodization methods, and the hard anodized
coating obtained by the low temperature method typically has a
Vickers hardness of 300 to 500 Hv, and the coating is of a higher
denseness compared to other anodized coatings.
[0004] Hard anodized coatings are currently used, for example, in
the sliding part of aluminum alloy machine parts, and with the
increase in the severity of the sliding conditions, further
improvement in the wear resistance is awaited. In the meanwhile,
hard anodized coatings of a high denseness involve a problem in
that they are hard to form on an aluminum die cast alloy.
[0005] Another known method for forming a coating having a high
surface hardness is anode spark discharge method wherein the
coating is formed by using a spark discharge (see, for example,
Patent Documents 1 to 3). In the conventional anode spark discharge
methods, alkali metal silicate, alkali metal hydroxide, and oxygen
acid catalyst have been used for the electrolyte.
[0006] Patent Documents 1 and 3 disclose a method wherein the
treatment using a voltage as high as 600 V or higher is performed
to produce a super-hard coating containing .alpha.-alumina as its
chief component. The coating obtained by such method has an
extremely high hardness as represented by the Vickers hardness in
excess of 1500 Hv. In addition, while the maximum thickness of the
coating which can be produced by the anodization using an ordinary
alkaline electrolyte is approximately 10 .mu.m, the thickness of
the coating produced by such method can be as thick as 100 .mu.m or
more. Accordingly, a coating having improved wear resistance,
corrosion resistance, and the like could be realized by increasing
the thickness of the coating.
[0007] Other anode spark discharge methods have also been
disclosed. Patent Documents 4 to 6 disclose methods using an
electrolyte having a composition substantially the same as that of
Patent Document 3 with a special current waveform to form a coating
on the surface of a substrate at an efficiency higher than that of
Patent Document 3.
[0008] Patent Document 7 discloses an anode spark discharge method
in which smoothness, hardness, and coating speed have been improved
by using not only silicate but also lithium ion and sodium or
potassium ion.
PATENT DOCUMENT 1: JP 2002-508454 A
PATENT DOCUMENT 2: U.S. Pat. No. 4,082,626
PATENT DOCUMENT 3: U.S. Pat. No. 5,616,229
PATENT DOCUMENT 4: JP 58-17278 B
PATENT DOCUMENT 5: JP 59-28636 B
PATENT DOCUMENT 6: JP 59-28637 B
PATENT DOCUMENT 7: JP 9-310184 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] However, the coatings obtained by the conventional anode
spark discharge methods described in Patent Documents 1 to 3 have a
high surface roughness and a high hardness with low tenacity, and
use of such coating for a sliding member without polishing results
in the wear and scratches in the counterpart member, or
equivalently, such coating has high likeliness of attacking the
counterpart member. Accordingly, the coatings obtained by the
conventional anode spark discharge methods cannot be used for a
sliding member unless polished. In addition, polishing of such
coating is difficult due to the extremely high hardness.
[0010] In the meanwhile, a large amount of electricity is consumed
in the production of the coating, and the electricity is also
required for the cooling of the electrolyte. Accordingly, the cost
of the electricity is very high, and production of an excessively
thick coating is economically disadvantageous. In such view,
reduction in the thickness of the coating is highly desirable.
[0011] However, while reduction in the thickness contributes to the
reduction in the surface roughness, the thin coating formed is
likely to become destroyed in the course of sliding.
[0012] The methods described in Patent Documents 4 to 6 suffer from
poor hardness of the resulting coating as well as low coating
speed.
[0013] The method described in Patent Document 7 cannot realize the
hardness and the wear resistance of the level equivalent to the
coating obtained by the method described in Patent Document 3.
[0014] In view of the situation as described above, an object of
the present invention is to provide a method for electrolytically
depositing a ceramic coating on a metal which is capable of
producing a coating having an excellent hardness, wear resistance
and excellent tenacity despite its reduced thickness and less
likeliness of attacking the counterpart member even if used for a
sliding member without polishing. Another object of the present
invention is to provide an electrolyte used in such method.
[0015] A further object of the present invention is to provide a
metal member having excellent wear resistance and sliding
properties.
Means to Solve the Problems
[0016] In order to realize the objects as described above, the
inventors of the present invention made an extensive study and
found that, when the electrolysis is conducted by using a metal as
an anode in an electrolyte containing a zirconium compound, the
coating formed on the surface of the metal will have excellent
hardness, wear resistance and excellent tenacity despite its
reduced thickness and its reduced thickness and less likeliness of
attacking the counterpart member even if used for a sliding member
without polishing. The method for electrolytically depositing a
ceramic coating on a metal of the present invention and the
electrolyte for use in electrolytic deposition of a ceramic coating
on a metal of the present invention have been completed on the
basis of such findings.
[0017] In the extensive study for realizing the objects as
described above, the inventors of the present invention also found
that, when a hard coating is provided on a metal substrate so that
the hard coating comprises a continuous phase of an amorphous oxide
containing the metal element that constitutes the metal substrate
and zirconium and a dispersed phase of zirconium oxide
microcrystals which are dispersed in the continuous phase, the
metal member obtained will have excellent hardness, excellent wear
resistance and sliding properties, excellent tenacity, and less
likeliness of attacking the counterpart member even if used as a
sliding member without polishing, and that such hard coating can be
formed by conducting anode electrolysis or bipolar electrolysis in
an electrolyte containing a zirconium compound. The metal member of
the present invention has been completed on the basis of such
findings.
[0018] Accordingly, the present invention provides the following
(1) to (33).
[0019] (1) A method for electrolytically depositing a ceramic
coating on a metal wherein an electrolytic treatment is conducted
by using the metal as an anode in an electrolyte containing a
zirconium compound to thereby form a ceramic coating on the surface
of the metal.
[0020] (2) The method for electrolytically depositing a ceramic
coating on a metal according to the above (1) wherein the zirconium
compound is a water soluble zirconium compound.
[0021] (3) The method for electrolytically depositing a ceramic
coating on a metal according to the above (2) wherein the water
soluble zirconium compound is a zirconium carbonate compound.
[0022] (4) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (3)
wherein the electrolyte is at a pH of at least 8.0.
[0023] (5) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (4)
wherein the electrolyte further contains a water soluble phosphorus
compound.
[0024] (6) The method for electrolytically depositing a ceramic
coating on a metal according to the above (5) wherein the water
soluble phosphorus compound is a condensed phosphate.
[0025] (7) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (6)
wherein the electrolyte further contains an ion and/or an oxide of
at least one metal selected from the group consisting of titanium,
yttrium, calcium, magnesium, scandium, and cerium.
[0026] (8) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (7)
wherein the electrolyte further contains poorly soluble particles
of at least one member selected from the group consisting of oxide,
hydroxide, phosphate, and carbonate.
[0027] (9) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (8)
wherein the electrolytic treatment is carried out by a direct
current electrolysis or a bipolar electrolysis using a voltage
waveform in which an AC component is superposed on a DC
component.
[0028] (10) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (8)
wherein the electrolytic treatment is conducted by using a voltage
waveform in which at least one pulse wave selected from the group
consisting of rectangular wave, sine wave, and triangular wave
having a duty ratio of up to 0.5 is superposed on a DC or AC
component.
[0029] (11) The method for electrolytically depositing a ceramic
coating on a metal according to the above (9) or (10) wherein the
maximum value of the voltage waveform is at least 400 V.
[0030] (12) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (11)
wherein the electrolytic treatment is conducted under(with) glow
discharge and/or arc discharge caused on the surface of the metal
used as the anode.
[0031] (13) The method for electrolytically depositing a ceramic
coating on a metal according to any one of the above (1) to (12)
wherein the metal is a valve metal or its alloy.
[0032] (14) An electrolyte for use in electrolytic deposition of a
ceramic coating on a metal, containing water, a zirconium compound,
and at least one member selected from the group consisting of
alkali metal ion, ammonium ion, and organic alkali.
[0033] (15) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to the above (14) wherein the
zirconium compound is a water soluble zirconium compound.
[0034] (16) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to the above (15) wherein the
water soluble zirconium compound is a zirconium carbonate
compound.
[0035] (17) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to any one of the above (14)
to (16) wherein the electrolyte is at a pH of at least 8.0.
[0036] (18) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to any one of the above (14)
to (17) wherein the electrolyte further contains a water soluble
phosphorus compound.
[0037] (19) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to the above (18) wherein the
water soluble phosphorus compound is a condensed phosphate.
[0038] (20) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to any one of the above (14)
to (19) wherein the electrolyte further contains an ion and/or an
oxide of at least one metal selected from the group consisting of
titanium, yttrium, calcium, magnesium, scandium, and cerium.
[0039] (21) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to any one of the above (14)
to (20) wherein the electrolyte further contains poorly soluble
particles of at least one member selected from the group consisting
of oxide, hydroxide, phosphate, and carbonate.
[0040] (22) The electrolyte for use in electrolytic deposition of a
ceramic coating on a metal according to any one of the above (14)
to (21) wherein the electrolyte is used for electrolytically
depositing a ceramic coating on a valve metal or its alloy.
[0041] (23) A metal member comprising a metal substrate and a hard
coating on the metal substrate, wherein:
[0042] the hard coating comprises an amorphous layer which is
composed of an amorphous oxide containing a metal element
constituting the metal substrate and zirconium, and zirconium oxide
microcrystals dispersed in the amorphous oxide.
[0043] (24) A metal member comprising a metal substrate and a hard
coating on the metal substrate, wherein:
[0044] the hard coating comprises a crystalline layer on the metal
substrate and an amorphous layer on the crystalline layer, with the
crystalline layer containing crystals of oxide of a metal element
constituting the metal substrate, and the amorphous layer being
composed of an amorphous oxide containing the metal element
constituting the metal substrate and zirconium, and zirconium oxide
microcrystals dispersed in the amorphous oxide.
[0045] (25) The metal member according to the above (24) wherein
the crystalline layer further contains zirconium oxide
microcrystals dispersed along a grain boundary and/or in a grain of
the crystals of oxide of the metal element constituting the metal
substrate.
[0046] (26) The metal member according to any one of the above (23)
to (25) wherein the concentration distribution of the zirconium in
the hard coating is such that the zirconium concentration gradually
reduces from the surface of the hard coating toward the metal
substrate.
[0047] (27) The metal member according to any one of the above (23)
to (26) wherein, when the hard coating is analyzed by X ray
diffractometry, the relative peak intensity on (111) plane of
tetragonal zirconium oxide and/or cubic zirconium oxide is equal to
or higher than the relative peak intensity of the main peak of the
oxide of the metal element constituting the metal substrate.
[0048] (28) The metal member according to any one of the above (23)
to (27) wherein, when the hard coating is analyzed by X ray
diffractometry, the proportion of the volume of monoclinic
zirconium oxide to the total of the volume of the tetragonal
zirconium oxide and/or the cubic zirconium oxide and the volume of
the monoclinic zirconium oxide is up to 0.5.
[0049] (29) The metal member according to any one of the above (23)
to (28) wherein microcrystals of the tetragonal zirconium oxide
and/or the cubic zirconium oxide have an average grain diameter of
0.25 to 500 nm.
[0050] (30) The metal member according to any one of the above (23)
to (29) wherein a phosphorus oxide is present on the surface of the
hard coating and/or at the interface of the hard coating with the
metal substrate.
[0051] (31) The metal member according to any one of the above (23)
to (30) wherein the hard coating further contains at least one
element selected from the group consisting of yttrium, calcium,
cerium, scandium, magnesium, and titanium.
[0052] (32) The metal member according to any one of the above (23)
to (31) wherein the metal element constituting the metal substrate
is a valve metal element or a metal element used in a valve metal
alloy.
[0053] (33) The metal member according to any one of the above (23)
to (32) produced by the method for electrolytically depositing a
ceramic coating on a metal according to any one of the above (1) to
(13).
EFFECTS OF THE INVENTION
[0054] The method of the invention for electrolytically depositing
a ceramic coating on a metal is capable of forming an excellent
coating on the surface of a metal which could not be realized by
the conventional anodization such as anode spark discharge. The
coating formed has excellent hardness and wear resistance as well
as excellent tenacity despite its reduced thickness and even if
used for a sliding member without polishing, it hardly attack the
counterpart member.
[0055] The metal member of the present invention is a metal member
which could not be realized by the conventional anodization such as
hard anodization and anode spark discharge, or surface hardening
such as adhesion of a sintered ceramic plate on the metal surface.
The metal member of the invention has excellent hardness, excellent
wear resistance and sliding properties, excellent tenacity, and
even if used as a sliding member without polishing, it hardly
attack the counterpart member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a graph showing voltage waveform and current
density used in Example 1.
[0057] FIG. 2 is a graph showing voltage waveform and current
density used in Example 8.
[0058] FIG. 3 is an optical micrograph (at a magnification of 500)
of the cross-section of the coating obtained in Example 1.
[0059] FIG. 4 is an optical micrograph (at a magnification of 100)
of the coating obtained in Comparative Example 2 along the sliding
track after the friction wear test.
[0060] FIG. 5(A) is a graph showing the X ray diffraction pattern
for the coating obtained in Example 1, and FIG. 5(B) is a graph
showing the X ray diffraction pattern for the coating obtained in
Comparative Example 1.
[0061] FIG. 6 is a conceptual diagram of the metal member of the
present invention. FIG. 6(A) shows a metal member comprising a
metal substrate and a hard coating on the metal substrate, in which
the hard coating comprises an amorphous layer. FIG. 6(B) shows a
metal member comprising a metal substrate and a hard coating on the
metal substrate, in which the hard coating comprises a crystalline
layer and an amorphous layer.
[0062] FIG. 7(A) is a micrograph of the amorphous layer in the
coating of the metal member produced in Example 14. FIG. 7(B) is a
micrograph of the crystalline layer in the coating formed in
Example 14.
[0063] FIG. 8(A) is an electron diffractogram at the location "a"
in FIG. 7(A). FIG. 8(B) is an electron diffractogram at the
location "b" in FIG. 7(A).
[0064] FIG. 9(A) is a graph showing the result of the qualitative
analysis in depth direction obtained by glow discharge optical
emission spectroscopy for the coating of the metal member produced
in Example 16. FIG. 9(B) is a graph showing the result of the
qualitative analysis in depth direction obtained by glow discharge
optical emission spectroscopy for the coating of the metal member
produced in Example 18.
[0065] FIGS. 10(A) to 10(F) are graphs showing the X ray
diffraction patterns for the coatings of the metal members obtained
in Examples 14, 17, 18, 19, 21 and 22, respectively.
[0066] FIGS. 11(A) to 11(C) are graphs showing the X ray
diffraction patterns for the coatings of the metal members obtained
in Comparative Examples 5, 7 and 8, respectively.
LEGEND
[0067] 1: coating [0068] 2: aluminum plate [0069] 3: aluminum that
became exposed in the friction wear test [0070] 10, 20: metal
member [0071] 12, 22: metal substrate [0072] 14, 24: hard coating
[0073] 16, 26: amorphous oxide [0074] 18, 28, 34: zirconium oxide
microcrystal [0075] 30: crystalline layer [0076] 32: metal oxide
crystal
BEST MODE FOR CARRYING OUT THE INVENTION
[0077] Next, the method for electrolytically depositing a ceramic
coating on a metal, the electrolyte for use in electrolytic
deposition of a ceramic coating on a metal, and the metal member of
the present invention are described in detail. First, the method
for electrolytically depositing a ceramic coating on a metal and
the electrolyte for use in electrolytic deposition of a ceramic
coating on a metal of the present invention are described.
[0078] The method for electrolytically depositing a ceramic coating
on a metal of the present invention is a method in which an
electrolytic treatment is conducted by using the metal as an anode
in an electrolyte containing a zirconium compound to thereby form
the ceramic coating on the metal surface.
[0079] The metal used in the electrolytic ceramic coating method of
the present invention is not particularly limited. The metal,
however, is preferably a valve metal or its alloy, on which an
oxidized coating can be formed by electrolysis. More specifically,
the metal is preferably at least one member selected from the group
consisting of aluminum, magnesium, titanium, niobium, and alloys
thereof.
[0080] The present invention is not limited to the case in which
the metal is the matrix of a member, and the metal may be a coating
such as a plated, or vapor deposited coating.
[0081] No particular pretreatment is necessary in forming the
coating on the metal. However, in one preferable embodiment, the
metal surface is preliminarily cleaned by degreasing, etching, or
the like.
[0082] The electrolyte used in the electrolytic ceramic coating
method of the present invention is not particularly limited as long
as it is an electrolyte containing a zirconium compound. The
electrolyte, however, is preferably the electrolyte of the present
invention containing water, a zirconium compound, and at least one
member selected from the group consisting of alkali metal ion,
ammonium ion, and organic alkali. For example, a preferable
electrolyte contains water, a zirconium compound, and an alkali
metal ion and/or an ammonium ion.
[0083] While the zirconium compound is not particularly limited,
the zirconium compound is preferably a water soluble zirconium
compound since use of such water soluble zirconium compound enables
production of a coating having a dense structure.
[0084] For the same reason, when the electrolyte contains two or
more zirconium compounds, at least one of the zirconium compounds
is preferably a water soluble zirconium compound, and more
preferably, all of the zirconium compounds are water soluble
zirconium compounds.
[0085] The non-limiting examples of the water soluble zirconium
compound include zirconium salts of an organic acid such as
zirconium acetate, zirconium formate, and zirconium lactate;
zirconium complex salts such as zirconium ammonium carbonate,
zirconium potassium carbonate, zirconium ammonium acetate,
zirconium sodium oxalate, zirconium ammonium citrate, zirconium
ammonium lactate, and zirconium ammonium glycolate.
[0086] Among these, the preferred are the zirconium carbonate
compounds represented by the chemical formula
M.sub.2ZrO(CO.sub.3).sub.2 (M representing ammonium or alkali
metal) because such compounds dissolve in an alkaline electrolyte
and exist in a stable manner. Exemplary zirconium carbonate
compounds include zirconium ammonium carbonate, and zirconium
potassium carbonate.
[0087] Use of zirconium hydroxide as the zirconium compound is also
preferable.
[0088] Content of the zirconium compound in the electrolyte is
preferably 0.0001 to 5 mol/L, and more preferably 0.001 to 0.5
mol/L in terms of zirconium.
[0089] Preferably, the electrolyte further contains a water soluble
phosphorus compound. The water soluble phosphorus compound has the
action of reducing surface roughness of the coating and improving
the stability of the electrolyte.
[0090] While the water soluble phosphorus compound is not
particularly limited, it is preferably a condensed phosphate or an
organic phosphonate. Among others, the preferred is the condensed
phosphate, and the more preferable is use of a pyrophosphate or a
tripolyphosphate, which has chelating ability, and hence, is
capable of stably retaining zirconium in the electrolyte without
precipitation, and which also has alkaline buffering action to
stabilize the pH and enable easy control of the pH.
[0091] Content of the phosphorus compound in the electrolyte is
preferably 0.0001 to 1 mol/L, and more preferably 0.001 to 0.1
mol/L in terms of phosphorus.
[0092] When the electrolyte contains a condensed phosphate and/or
an organic phosphonate, a phosphorus compound such as
orthophosphate, hypophosphite, or phosphite may be used at a
content ratio (molar ratio) of up to 0.5 in relation to the
condensed phosphate and the organic phosphonate.
[0093] The electrolyte may further contain a peroxo compound such
as aqueous hydrogen peroxide. Content of such peroxo compound in
the electrolyte is preferably in the range of 0.001 to 1 mol/L.
[0094] The electrolyte may further contain an yttrium compound, a
calcium compound, a titanium compound, a magnesium compound, a
scandium compound, a cerium compound, and the like. Exemplary
yttrium compounds include yttrium nitrate and yttrium oxide.
Exemplary calcium compounds include calcium tartarate and calcium
oxide. Exemplary titanium compounds include peroxotitanic acid
compound and titanium oxide. Exemplary magnesium compounds include
magnesium carbonate, magnesium phosphate, magnesium hydroxide, and
magnesium oxide. Exemplary scandium compounds include scandium
carbonate, scandium phosphate, and scandium oxide. Exemplary cerium
compounds include cerium chloride, cerium hydroxide, cerium
acetate, cerium carbonate, and cerium oxide.
[0095] More specifically, in one preferred embodiment of the
present invention, the electrolyte contains the ion and/or an oxide
of at least one metal selected from the group consisting of
titanium, yttrium, calcium, magnesium, scandium, and cerium.
[0096] Inclusion of such compound in the electrolyte is believed to
improve mechanical properties of the coating. In particular,
inclusion of an yttrium compound or a calcium compound is believed
to cause formation of partially stabilized zirconium which results
in the improvement of the mechanical properties of the coating.
[0097] Such compound is preferably used at a content ratio of about
0.001 to 0.3, and more preferably about 0.005 to 0.1 in relation to
the zirconium compound.
[0098] In addition, a lanthanoid compound may be incorporated in
the electrolyte for similar purposes.
[0099] In another preferable embodiment of the present invention,
the electrolyte further contains poorly soluble particles of at
least one member selected from the group consisting of oxide,
hydroxide, phosphate, and carbonate. Inclusion of such poorly
soluble particles results in the faster formation of the coating,
and hence, reduced time required for the coating treatment.
[0100] The metal or semi-metal used in such oxide, hydroxide,
phosphate or carbonate is not particularly limited.
[0101] Examples of the poorly soluble particles include particles
of zirconium oxide (zirconia), titanium oxide, iron oxide, tin
oxide, silicon oxide (for example, silica sol), and cerium oxide;
zirconium hydroxide, titanium hydroxide, and magnesium hydroxide;
zirconium phosphate, titanium phosphate, calcium phosphate, zinc
phosphate, and manganese phosphate; and calcium carbonate.
[0102] Among these, the preferred is zirconium oxide, and the more
preferred are cubic zirconium dioxide and tetragonal zirconium
dioxide.
[0103] The poorly soluble particles preferably have a particle
diameter of up to 1 .mu.m, and more preferably up to 0.3 .mu.m.
Dispersion of the particles in the electrolyte is facilitated when
the particle diameter is within such range.
[0104] Content of the poorly soluble particles in the electrolyte
is not particularly limited. The content, however, is preferably in
the range of 0.3 to 300 g/L.
[0105] The electrolyte of the present invention contains at least
one member selected from the group consisting of alkali metal ion,
ammonium ion, and organic alkali.
[0106] For example, the electrolyte of the present invention may be
an electrolyte prepared by dissolving or dispersing any of the
zirconium-containing sodium salts, potassium salts and ammonium
salts as above in water. In that case, at least some of the sodium
salt, potassium salt, or ammonium salt may be replaced with an
organic alkali.
[0107] The electrolyte may also contain sodium salts such as sodium
hydroxide, various types of sodium silicate, various types of
sodium phosphate, various types of sodium borate, and various types
of sodium citrate; potassium salts such as potassium hydroxide,
various types of potassium silicate, various types of potassium
phosphate, various types of potassium borate, and various types of
potassium citrate; and ammonium salts such as ammonium hydroxide,
various types of ammonium silicate, various types of ammonium
phosphate, various types of ammonium borate, and various types of
ammonium citrate.
[0108] Concentration of the alkali metal ion and/or ammonium ion in
the electrolyte is preferably 0.001 to 5 mol/L, and more preferably
0.01 to 0.5 mol/L.
[0109] Examples of the organic alkali which may be used to replace
the alkali metal salt or the ammonium salt include quaternary
ammonium salts such as tetraalkylammonium hydroxide (for example,
tetramethylammonium hydroxide) and trimethyl-2-hydroxyethylammonium
hydroxide; and organic amines such as trimethylamine, alkanolamine,
and ethylenediamine.
[0110] The electrolyte is preferably at a pH of at least 8.0, more
preferably at a pH of at least 9.0, but the electrolyte is
preferably at a pH of up to 13.5. When the pH is in such range, the
coating can be formed at an improved efficiency, and a relatively
reduced amount of the metal used as the anode will be
dissolved.
[0111] Such alkaline electrolyte is prepared suitably by, for
example, including an alkali metal hydroxide such as potassium
hydroxide, sodium hydroxide, or lithium hydroxide in the
electrolyte.
[0112] The electrolyte is not particularly limited for its
temperature. The electrolyte, however, is typically used at 10 to
60.degree. C. A temperature in such range is advantageous in view
of economy, and will bring about a reduced dissolution of the metal
used as the anode.
[0113] The electrolyte is not particularly limited for its
production method, and the electrolyte may be produced by
dissolving or dispersing the components as described above in a
solvent. The solvent is preferably water while the solvent is not
particularly limited.
[0114] In the method for electrolytically depositing a ceramic
coating on a metal of the present invention, the electrolytic
treatment is conducted in the electrolyte as described above,
whereupon the metal as described above is used as the anode.
[0115] The method used for the electrolytic treatment is not
particularly limited, and exemplary methods include direct current
electrolysis, bipolar electrolysis, and pulse electrolysis. Among
these, the preferred are bipolar electrolysis and pulse
electrolysis since the electrolytic treatment is preferably
conducted at a relatively high voltage as will be described later.
Use of the direct current electrolysis is economically
disadvantageous because of the boiling of the electrolyte.
[0116] In the bipolar electrolysis, the voltage waveform used
preferably has an AC component superposed on a DC component.
[0117] In the pulse electrolysis, it is preferable to use the
voltage waveform in which at least one pulse wave selected from the
group consisting of rectangular wave, sine wave, and triangular
wave having a duty ratio of up to 0.5 is superposed on a DC or AC
component.
[0118] The conditions for the electrolytic treatment may be
adequately selected depending on the metal and the electrolyte to
be used. For example, when the electrolytic treatment (anodization)
is carried out by bipolar electrolysis or pulse electrolysis in an
alkaline electrolyte using aluminum as the anode, the voltage
waveform preferably has a maximum value (peak voltage) of 300 to
800 V, and more preferably 400 to 800 V, and the current density at
the positive peak is preferably 1 to 250 A/dm.sup.2, and more
preferably 20 to 150 A/dm.sup.2 Spark discharge is facilitated when
the voltage waveform has a maximum value of at least 300 V, and in
particular, at least 400 V.
[0119] Surface roughness of the coating will not be excessively
high when the voltage waveform has a minimum value of up to 800
V.
[0120] When the current density at the positive peak is at least 1
A/dm.sup.2, formation of the coating proceeds at a faster rate, and
oxidation of the aluminum and crystallization of the zirconium
oxide are facilitated. When the current density at the positive
peak is up to 250 A/dm.sup.2, the surface roughness of the coating
can be reduced to a sufficient degree.
[0121] The electrolytic treatment is preferably conducted under the
glow discharge and/or the arc discharge (spark discharge) from the
metal. Such discharge stages can be confirmed by visually observing
the surface of the anode metal during the treatment. Glow discharge
is the phenomenon associated with the weak continuous light
surrounding the entire surface, and arc discharge is the phenomenon
associated with intermittent or local sparks. The glow discharge
and the arc discharge may occur at once or separately. The
temperature in the ark (spark) is said to be at least 1000.degree.
C., and this facilitates crystallization and deposition of the
zirconium in the electrolyte.
[0122] The electrolytic bath may be cooled in order to keep the
electrolyte temperature within the range as described above. Such
cooling of the electrolytic bath is conducted in one preferred
embodiment of the present invention.
[0123] The electrolytic treatment can be conducted for any period
of time chosen in order to realize the desired coating thickness.
It is generally preferred that the treatment time is 1 to 45
minutes, especially 5 to 30 minutes.
[0124] The electrolyzing apparatus to be used for the electrolytic
treatment is not particularly limited, and any apparatus known in
the art can be used as desired.
[0125] The coating obtained by the method for electrolytically
depositing a ceramic coating on a metal of the present invention is
not particularly limited for its thickness, and any thickness can
be selected depending on the intended use of the coating. In
general, the thickness is preferably 0.01 to 500 .mu.m, and more
preferably 0.5 to 50 .mu.m. When the thickness is in such range,
the resulting coating will exhibit improved impact resistance, and
the time required for the electrolytic treatment will not be so
long as to detract from the economic advantage.
[0126] In the present invention, a ceramic coating is formed on the
surface of the metal as described above by conducting the
electrolytic treatment as described above.
[0127] The mechanism of ceramic coating formation is not fully
clear. However, it is conceived that, when the oxidized coating is
formed on the metal by the electrolytic treatment, the zirconium in
the electrolyte crystallizes as zirconium oxide to become
incorporated in the coating, that is to say, a composite coating
which contains an oxide of the metal used as the anode and an oxide
of the zirconium is formed.
[0128] This ceramic coating preferably contains tetragonal
zirconium oxide and/or cubic zirconium oxide as in the case of the
coating obtained in Example 1 (see FIG. 5).
[0129] When a stress is applied to the tetragonal zirconium oxide
(density, 6.10 g/cm.sup.3), the tetragonal zirconium oxide
typically transforms to the monoclinic zirconium oxide (density,
5.56 g/cm.sup.3) at the end of the crack for stress relaxation.
Because of such mechanism, zirconium oxide exhibits high tenacity
despite its ceramic entity.
[0130] The cubic zirconium oxide is readily produced by
incorporating calcium oxide, cerium oxide, or yttrium oxide, and
the stabilized zirconia and/or partly stabilized zirconia produced
exhibits high tenacity.
[0131] As described above, the ceramic coating formed by the
present invention preferably contains the tetragonal zirconium
oxide and/or the cubic zirconium oxide, and this is considered to
result in the coating which is improved not only in hardness but
also tenacity. For a substance in the form of a thin film, no
convenient measurement for tenacity has been known yet, and
therefore, the coating may be evaluated for its tenacity by
evaluating ductility, which is one element of the tenacity.
[0132] The method for electrolytically depositing a ceramic coating
on a metal of the present invention can be used for any desired
application. For example, when an extremely hard ceramic coating is
formed on the surface of a metal such as aluminum or magnesium
having a low hardness, the metal can suitably be used for a sliding
member which could not be made of such soft metal, or a member
which is required to have a hardness higher than the conventional
anodized coating (for example, hard anodized aluminum coating). The
ceramic coating is preferable because it is less likely to damage
the counterpart member even if used for a sliding member without
polishing.
[0133] The ceramic coating produced by the method for
electrolytically depositing a ceramic coating on a metal of the
present invention is also useful as a protective coating of various
members. Since the ceramic coating produced by the method for
electrolytically depositing a ceramic coating on a metal of the
present invention contains zirconium oxide, it is excellent in such
properties as heat resistance, heat shock resistance, and corrosion
resistance. Accordingly, the ceramic coating is well adapted for
the application to a furnace material for a shaft furnace, a
chamber inner wall of a semiconductor production equipment, and the
like.
[0134] Next, the metal member of the present invention is
described.
[0135] First aspect of the metal member of the present invention is
a metal member comprising a metal substrate and a hard coating on
the metal substrate, in which the hard coating comprises an
amorphous layer which is composed of an amorphous oxide containing
a metal element constituting the metal substrate and zirconium, and
zirconium oxide microcrystals dispersed in the amorphous oxide.
[0136] Second aspect of the metal member of the present invention
is a metal member comprising a metal substrate and a hard coating
on the metal substrate, in which the hard coating comprises a
crystalline layer on the metal substrate and an amorphous layer on
the crystalline layer, and in which the crystalline layer contains
crystals of oxide of a metal element constituting the metal
substrate, and the amorphous layer is composed of an amorphous
oxide containing the metal element constituting the metal substrate
and zirconium, and zirconium oxide microcrystals dispersed in the
amorphous oxide.
[0137] The metal member according to the first aspect of the
present invention is different from the metal member according to
the second aspect of the present invention in that the crystalline
layer is absent in the hard coating. These metal members share
other features, and accordingly, the metal members are described
together.
[0138] FIG. 6 is a conceptual diagram of the metal member of the
present invention. FIG. 6(A) shows a metal member comprising a
metal substrate and a hard coating on the metal substrate, in which
the hard coating comprises an amorphous layer according to the
first aspect of the present invention. FIG. 6(B) shows a metal
member comprising a metal substrate and a hard coating on the metal
substrate, in which the hard coating comprises a crystalline layer
and an amorphous layer according to the second aspect of the
present invention.
[0139] A metal member 10 according to the first aspect of the
present invention shown in FIG. 6(A) comprises a metal substrate 12
and a hard coating on the metal substrate 12. The hard coating
comprises an amorphous layer 14 which is composed of an amorphous
oxide 16 containing a metal element constituting the metal
substrate 12 and zirconium, and zirconium oxide microcrystals 18
dispersed in the amorphous oxide.
[0140] A metal member 20 according to the second aspect of the
present invention shown in FIG. 6(B) comprises a metal substrate 22
and a hard coating on the metal substrate 22. The hard coating
comprises a crystalline layer 30 on the metal substrate 22 and an
amorphous layer 24 on the crystalline layer 30. The crystalline
layer contains crystals 32 of oxide of a metal element constituting
the metal substrate 22, and the amorphous layer is composed of an
amorphous oxide 26 containing the metal element constituting the
metal substrate 22 and zirconium, and zirconium oxide microcrystals
28 dispersed in the amorphous oxide.
[0141] In the second aspect of the present invention, it is
preferable that the crystalline layer 30 further contains zirconium
oxide microcrystals 34 dispersed along a grain boundary and/or in a
grain of the crystals 32 of the oxide of the metal element
constituting the metal substrate 22 as shown in FIG. 6(B).
[0142] In the second aspect of the present invention, part of the
crystalline layer may be left uncovered with the amorphous layer,
and the uncovered part of the crystalline layer may remain
exposed.
[0143] The metal substrate used in the metal member of the present
invention is preferably a substrate comprising a valve metal or its
alloy. Examples of the valve metal include aluminum, titanium,
niobium, magnesium, and tantalum.
[0144] Among others, the substrate comprising at least one member
selected from the group consisting of aluminum, titanium,
magnesium, and alloys thereof is preferred. Use of such substrate
facilitates formation of a hard coating by anode electrolysis or
bipolar electrolysis.
[0145] The present invention is not limited to the case in which
the metal is the matrix of a member, and the metal may be a coating
such as a plated, or vapor deposited coating.
[0146] The amorphous layer is a layer which is composed of an
amorphous oxide containing the metal element constituting the metal
substrate and zirconium, and zirconium oxide microcrystals
dispersed in the amorphous oxide.
[0147] The amorphous oxide is an oxide in amorphous
(non-crystalline) state, and it contains the metal element
constituting the metal substrate and zirconium. For example, when
the aluminum is the metal element constituting the metal substrate,
that is to say, the metal substrate is made of aluminum or its
alloy, the amorphous oxide contains aluminum and zirconium.
[0148] The zirconium oxide microcrystals are micro grains of
zirconium oxide crystal. The zirconium oxide microcrystals in the
amorphous layer preferably have a grain diameter of 0.1 to 1000
nm.
[0149] When the zirconium oxide microcrystals have an excessively
small grain diameter, the hard coating is likely to have a reduced
hardness and wear resistance. When the grain diameter is
excessively large, the coating will have an increased likeliness of
attacking the counterpart member and the amorphous layer is likely
to decrease in strength.
[0150] The shape of the zirconium oxide microcrystals is not
particularly limited, and exemplary shapes include sphere shape,
needle shape, and plate shape. When the zirconium oxide
microcrystals are not spherical, the minor axis is preferably 0.25
to 250 nm and the major axis is preferably 1 to 500 nm for the same
reason as described above.
[0151] The zirconium oxide microcrystals are preferably tetragonal
zirconium oxide and/or cubic zirconium oxide, as will be described
later. In such a case, the zirconium oxide microcrystals preferably
have an average grain diameter of 0.25 to 500 nm.
[0152] The zirconium oxide microcrystals are not particularly
limited for their state of dispersion. Preferably, at least one
zirconium oxide microcrystal, and more preferably 10.sup.2 to
10.sup.4 zirconium oxide microcrystals per cubic micrometer of the
amorphous layer are present in the layer.
[0153] The crystalline layer is a layer containing the crystals of
an oxide of the metal element constituting the metal substrate as
above (hereinafter also referred to as "oxide of the substrate
metal"). For example, when the aluminum is the metal element
constituting the metal substrate, that is to say, the metal
substrate is made of aluminum or its alloy, the crystals are
aluminum oxide crystals. In such a case, the crystals are
preferably cubic aluminum oxide because, when the metal member
according to the second aspect of the present invention is used as
a sliding member, rhombohedral aluminum oxide present in the hard
coating in a large amount will result in an increased likeliness of
attacking the counterpart member.
[0154] The crystals of the oxide of the substrate metal preferably
have a grain diameter of up to 10 .mu.m, and more preferably up to
3 .mu.m. When the grain diameter is excessively large, voids (gaps)
are likely to be formed in the crystalline layer, and the layer is
likely to be destroyed from the periphery of such voids upon
sliding.
[0155] As described above, it is preferable that the crystalline
layer further contains zirconium oxide microcrystals dispersed
along a grain boundary and/or in a grain of the crystals of the
oxide of the metal element constituting the metal substrate.
[0156] The zirconium oxide microcrystals in the crystalline layer
is not particularly limited for its grain diameter when they are
present along the grain boundary of the crystals of the oxide of
the substrate metal. However, when they are present in the grains
of the crystals of the oxide of the substrate metal, the grain
diameter is preferably 0.1 to 250 nm, and more preferably 1 to 50
nm.
[0157] In the crystalline layer, the crystals of the oxide of the
substrate metal preferably have a grain diameter reducing from the
interface with the metal substrate toward the interface with the
amorphous layer because the hard coating will then have a
remarkably improved wear resistance, impact resistance, and
adhesion to the metal substrate.
[0158] The shape of the zirconium oxide microcrystals is not
particularly limited, and exemplary shapes include sphere shape,
needle, shape, and plate shape. When the zirconium oxide
microcrystals are in needle shape, the major axis is preferably
within the range as defined above.
[0159] The zirconium oxide microcrystals are preferably tetragonal
zirconium oxide and/or cubic zirconium oxide, as will be described
later. In such a case, the zirconium oxide microcrystals preferably
have an average grain diameter of 0.1 to 250 nm.
[0160] The zirconium oxide microcrystals are not particularly
limited for their state of dispersion. Preferably, 10.sup.2 to
10.sup.6 zirconium oxide microcrystals per cubic micrometer of the
crystalline layer are included in the layer.
[0161] In the metal members according to the first and second
aspects of the present invention, the concentration distribution of
the zirconium in the hard coating is preferably such that the
zirconium concentration gradually reduces from the surface of the
hard coating toward the metal substrate. While an abrupt change in
physical properties at the interface between a hard coating and a
metal substrate invites stress concentration at the interface and
sometimes causes the peeling and destroying of the coating, the
concentration distribution as described above will well prevent
such peeling or destroying.
[0162] In the metal members according to the first and second
aspects of the present invention, the zirconium oxide microcrystals
in the hard coating are preferably tetragonal crystals and/or cubic
crystals. When the zirconium oxide having crystallized into the
tetragonal crystals and/or the cubic crystals with excellent
mechanical properties is included in the hard coating, stress
relaxation will occur under mechanical deformation or heat, and the
hard coating will have a remarkably improved wear resistance.
[0163] In the metal members according to the first and second
aspects of the present invention, when the hard coating is analyzed
by X ray diffractometry, the relative peak intensity on (111) plane
of the tetragonal zirconium oxide and/or cubic zirconium oxide is
preferably equal to or higher than the relative peak intensity of
the main peak of the oxide of the substrate metal. The zirconium
oxide microcrystals will then have a sufficiently improved degree
of crystallization, resulting in improved impact resistance and
wear resistance of the hard coating.
[0164] In the metal members according to the first and second
aspect of the present invention, when the hard coating is analyzed
by X ray diffractometry, the proportion (V.sub.m) of the volume of
monoclinic zirconium oxide to the total of the volume of the
tetragonal zirconium oxide and/or the cubic zirconium oxide and the
volume of the monoclinic zirconium oxide is preferably up to 0.5,
and more preferably up to 0.3. When the V.sub.m is within such
range, the stress relaxation under stress by the monoclinic
crystals will be less reduced, and the hard coating will have
improved impact resistance and wear resistance.
[0165] The V.sub.m is calculated from the X ray diffraction
intensity by the following equation:
V.sub.m={I(-111).sub.m+I(111).sub.m}/{I(-111).sub.m+I(111).sub.m+I(111).s-
ub.tc} (1)
[0166] V.sub.m: proportion of the volume of the monoclinic
zirconium oxide to the total of the volume of the tetragonal
zirconium oxide and/or the cubic zirconium oxide and the volume of
the monoclinic zirconium oxide.
[0167] I(111).sub.tc: relative peak intensity on (111) plane of the
tetragonal zirconium oxide and/or the cubic zirconium oxide.
[0168] I(-111).sub.m: relative peak intensity on (-111) plane of
the monoclinic zirconium oxide.
[0169] I(111).sub.m: relative peak intensity on (111) plane of the
monoclinic zirconium oxide.
[0170] The peak on (111) plane of the tetragonal zirconium oxide is
difficult to distinguish from the peak on (111) plane of the cubic
zirconium oxide, so that the relative intensities of these peaks
are to be employed as the I(111).sub.tc without discrimination.
[0171] In one preferred embodiment, the hard coating further
contains at least one element selected from the group consisting of
yttrium, calcium, cerium, scandium, magnesium, and titanium. It is
preferable in particular that such element is included in the
interior or in the vicinity of the zirconium oxide
microcrystals.
[0172] Yttrium, calcium, cerium, scandium, and magnesium each have
the action of stabilizing the tetragonal and/or cubic crystal state
of the zirconium oxide. Titanium has the action of improving
mechanical properties such as flexural strength of the hard
coating.
[0173] Such element is preferably contained at a content ratio of
up to 0.1 in relation to the zirconium.
[0174] In addition, such element is preferably present in the form
of an oxide.
[0175] Preferably, the hard coating further contains a phosphorus
oxide so that the hard coating may have an improved initial contact
property in the sliding.
[0176] The phosphorus oxide may be crystalline or amorphous, and
examples of such phosphorus oxide include phosphorus oxides such as
diphosphorus pentoxide; phosphates such as zirconium phosphate,
zirconium potassium phosphate, zirconium sodium phosphate,
zirconium silicophosphate, aluminum phosphate, titanium phosphate,
magnesium phosphate, calcium phosphate, and cerium phosphate; and
polyphosphates such as zirconium pyrophosphate, aluminum
pyrophosphate, calcium pyrophosphate, zirconium polyphosphate, and
aluminum tripolyphosphate.
[0177] The phosphorus oxide is incorporated in the hard coating at
a content of preferably up to 15% by weight, and more preferably
0.1 to 5% by weight in terms of P.sub.2O.sub.5 in relation to the
entire coating. When the content is within such range, the coating
will have an improved hardness with a reduced surface
roughness.
[0178] The hard coating is not particularly limited for its
thickness, and any thickness can be selected depending on the
intended use of the resulting member. In general, the thickness is
preferably 0.01 to 500 .mu.m, and more preferably 0.5 to 50 .mu.m.
When the thickness is in such range, the resulting coating will
exhibit improved impact resistance, and the time required for the
electrolytic treatment will not be so long as to detract from the
economic advantage.
[0179] In the second aspect of the present invention, the ratio of
the thickness of the crystalline layer to the thickness of the hard
coating (namely, total of the thickness of the amorphous layer and
the thickness of the crystalline layer) is preferably 0.01 to 0.95,
and more preferably 0.1 to 0.9. When the thickness ratio is within
such range, the amorphous layer will have a sufficient thickness,
and the hard coating will have an improved contact property.
[0180] The surface of the hard coating preferably has a center line
average roughness of 0.01 to 10 .mu.m, more preferably 0.1 to 3
.mu.m. When the center line average roughness is within such range,
a higher oil retention and a lower surface roughness are attained
concurrently, and the likeliness of attacking the counterpart
member can thus be reduced.
[0181] The method used for producing the metal member of the
present invention is not particularly limited. For instance, the
metal member can be produced by conducting electrolysis such as
direct current electrolysis, bipolar electrolysis and pulse
electrolysis using the metal substrate as an anode.
[0182] Before the electrolysis, the metal substrate is preferably
degreased for removal of oil components on the surface of the metal
substrate. The metal substrate may optionally be pickled for
removal of oxide film formed on the surface of the metal
substrate.
[0183] The electrolysis is preferably conducted under spark
discharge (arc discharge) and/or glow discharge by using a high
voltage with the peak voltage of 300 V or higher.
[0184] The surface of the metal substrate is hardened (by the
formation of the hard coating) by the temporal and local melting
and solidifying of the surface during the spark discharge.
[0185] The temperature of the surface upon melting is said to be at
least 1000.degree. C., and the formation of the amorphous oxide is
facilitated because the surface is quenched by the electrolyte
simultaneously with the intake of the oxygen generated at the
anode.
[0186] The electrolysis is preferably carried out by bipolar
electrolysis or pulse electrolysis since high current density
arises during the spark discharge. Use of a DC voltage is not
preferable because the electrolyte is likely to boil due to the
excessively high current density to result in the formation of
voids in the hard coating.
[0187] The current density is preferably 1 to 250 A/dm.sup.2, and
more preferably 20 to 150 A/dm.sup.2 at its peak. When the current
density is within such range, formation of the hard coating
proceeds at a sufficiently fast rate, and crystallization of the
zirconium oxide is facilitated, and also, the surface roughness of
the coating is hardly increased.
[0188] The electrolysis is preferably conducted by using an
electrolyte containing water and a zirconium compound, and more
preferably, by using the above-mentioned electrolyte for use in
electrolytic deposition of a ceramic coating on a metal according
to the present invention which contains water, a zirconium
compound, and at least one member selected from the group
consisting of alkali metal ion, ammonium ion, and organic
alkali.
[0189] When such electrolyte is used, zirconium is incorporated in
the hard coating, and as a consequence, growth of the crystal
grains of the oxide of the substrate metal is suppressed, and
formation of a dense surface structure is facilitated. By the
incorporation of the zirconium oxide in the form of microcrystals
of tetragonal zirconium oxide and/or cubic zirconium oxide in the
hard coating, the fracture toughness and other mechanical
properties of the hard coating are improved.
[0190] Use of the method for electrolytically depositing a ceramic
coating on a metal of the present invention is particularly
preferable.
[0191] The difference between the metal member according to the
first aspect of the present invention and the metal member
according to the second aspect of the present invention is the
presence of the crystalline layer in the hard coating of the latter
metal member. Formation of the crystalline layer can be achieved or
prevented by appropriately setting such conditions as the voltage
for electrolysis and the zirconium concentration of the
electrolyte.
[0192] For example, the crystalline layer is more likely to be
formed at a higher voltage presumably because of the increase in
the thermal energy under the spark discharge associated with the
increase in the current density. More specifically, the crystalline
layer is likely to be formed when the maximum voltage value is 600
V or higher.
[0193] Also, the crystalline layer is more likely to be formed at a
lower zirconium concentration presumably because the
crystallization of the oxide of the metal substrate is suppressed
by the zirconium. More specifically, the crystalline layer is
likely to be formed when the zirconium concentration of the
electrolyte is 0.015 mol/L or less.
[0194] The mechanism of the dispersion of the zirconium oxide
microcrystals in the amorphous oxide (and in the amorphous layer
and the crystalline layer in some cases of the second aspect of the
present invention) is not yet clear. However, the excessive
increase in the size of the zirconium oxide microcrystals is
believed to be suppressed because of a short discharging time upon
spark discharge and so forth in the order of several microseconds,
and the presence of the metal element constituting the metal
substrate that has dissolved in the electrolyte.
[0195] The metal member of the present invention is not
particularly limited for its application. For example, even if a
metal member is produced by using a metal substrate made of a soft
metal such as aluminum or magnesium, such member can be used for
the sliding member for which the conventional metal member produced
by using such soft metal could not be used. Exemplary applications
include interior surface of an aluminum engine cylinder, a piston,
a shaft, parts of a rotary compressor, parts of a pump, an aluminum
wheel, a propeller, an agitation blade, a valve, a cum, a shaft,
and a wire.
[0196] The metal member of the present invention can also be used
for the purpose of protecting various members. In particular, the
metal member of the present invention is excellent in such
properties as heat resistance, heat shock resistance, and corrosion
resistance since the hard coating contains oxide of zirconium.
Accordingly, the metal member is well adapted for the application
to a furnace material for a shaft furnace, a chamber inner wall of
a semiconductor production equipment, and the like.
EXAMPLES
[0197] Next, the present invention is described in further detail
by referring to the Examples which by no means limit the scope of
the present invention.
<A. Examples of the Method for Electrolytically Depositing a
Ceramic Coating on a Metal According to the Present
Invention>
1. Electrolytic Treatment
Example 1
[0198] Electrolytic treatment was conducted for 10 minutes by
bipolar electrolysis using an aluminum plate (a plate of JIS 1000)
having a surface area of 0.12 dm.sup.2 for the anode and a
stainless steel plate for the cathode to thereby deposit a coating
on the aluminum plate. When the anode surface was observed during
the electrolytic treatment, light emission by spark discharge and
glow discharge was recognized.
[0199] The electrolyte used was an electrolyte (pH 11.7) prepared
by adding 0.01 mol/L of zirconium potassium carbonate, 0.015 mol/L
of sodium pyrophosphate, and 0.036 mol/L of potassium hydroxide to
water.
[0200] The voltage waveform used was the one having a frequency of
60 Hz comprising an AC component at 300 V superposed with a DC
component having an effective value of 300V. The voltage used had
the maximum value of about 720 V and the minimum value of about
-120 V. The current density had a positive peak of about 150
A/dm.sup.2 and a negative peak of about 70 A/dm.sup.2. The voltage
waveform and the current density of this Example are shown in the
graph of FIG. 1.
Example 2
[0201] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 11.8
prepared by adding 0.01 mol/L of zirconium potassium carbonate and
0.036 mol/L of potassium hydroxide to water. When the anode surface
was observed during the electrolytic treatment, light emission by
spark discharge and glow discharge was recognized.
Example 3
[0202] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 11.6
prepared by adding 0.01 mol/L of zirconium potassium carbonate,
0.015 mol/L of sodium pyrophosphate, 0.036 mol/L of potassium
hydroxide, and 0.02 mol/L of hydrogen peroxide to water. When the
anode surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
Example 4
[0203] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.7
prepared by adding 0.01 mol/L of zirconium hydroxide, 0.015 mol/L
of sodium pyrophosphate, and 0.036 mol/L of potassium hydroxide to
water. When the anode surface was observed during the electrolytic
treatment, light emission by spark discharge and glow discharge was
recognized.
Example 5
[0204] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 8.9
prepared by adding 0.01 mol/L of zirconium acetate, 0.01 mol/L of
sodium citrate dihydrate, and 0.009 mol/L of potassium hydroxide to
water, and the electrolytic treatment was conducted for 20 minutes.
When the anode surface was observed during the electrolytic
treatment, light emission by spark discharge and glow discharge was
recognized.
Example 6
[0205] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.1
prepared by adding 0.01 mol/L of zirconium acetate, 0.01 mol/L of
sodium citrate dihydrate, and 0.036 mol/L of potassium hydroxide to
water. When the anode surface was observed during the electrolytic
treatment, light emission by spark discharge and glow discharge was
recognized.
Example 7
[0206] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the voltage waveform used was the one having a
frequency of 60 Hz comprising a DC component at 250 V superposed
with an AC component having an effective value of 250 V, and the
voltage used had a maximum value of about 600 V and a minimum value
of about -100V. When the anode surface was observed during the
electrolytic treatment, light emission by spark discharge and glow
discharge was recognized.
Example 8
[0207] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolytic treatment was conducted by pulse
electrolysis using a voltage waveform comprising a DC component at
300 V superposed with a pulse wave having an amplitude of 420 V.
The voltage values were the same as those of Example 1, with a
maximum value of about 720 V and a minimum value of about -120 V.
When the anode surface was observed during the electrolytic
treatment, light emission by spark discharge and glow discharge was
recognized. The voltage waveform and the current density of this
Example are shown in the graph of FIG. 2.
Example 9
[0208] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 11.4
prepared by adding 0.01 mol/L of zirconium potassium carbonate,
0.0001 mol/L of yttrium oxide, 0.015 mol/L of sodium pyrophosphate,
and 0.025 mol/L of sodium hydroxide to water. When the anode
surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
Example 10
[0209] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on a magnesium alloy plate
except that a magnesium alloy plate (a plate of JIS AZ91D) having a
surface area of 0.12 dm.sup.2 was used for the anode, and the
electrolyte used was the one having a pH of 13.0 prepared by adding
0.05 mol/L of stabilized zirconia (poorly soluble particles having
a particle size about 0.3 .mu.m), 0.01 mol/L of peroxotitanic acid
(prepared by dissolving hydrated titanium oxide gel in aqueous
hydrogen peroxide), 0.015 mol/L of sodium pyrophosphate, and 0.130
mol/L of sodium hydroxide to water. When the anode surface was
observed during the electrolytic treatment, light emission by spark
discharge and glow discharge was recognized.
Example 11
[0210] The electrolytic treatment was conducted by repeating the
procedure of Example 10 to form a coating on the magnesium alloy
plate except that the electrolyte used was the one having a pH of
12.8 prepared by adding 0.01 mol/L of zirconium acetate, 0.05 mol/L
of calcium carbonate (poorly soluble particles having a particle
size of about 0.6 .mu.m), 0.015 mol/L of sodium pyrophosphate, and
0.150 mol/L of potassium hydroxide to water, and the electrolytic
treatment was conducted by using a voltage waveform having a
frequency of 60 Hz comprising a DC component at 250 V superposed
with an AC component having an effective value of 250 V, and the
voltage having a maximum value of about 600 V and a minimum value
of about -100 V. When the anode surface was observed during the
electrolytic treatment, light emission by spark discharge and glow
discharge was recognized.
Example 12
[0211] The electrolytic treatment was conducted by repeating the
procedure of Example 11 to form a coating on a titanium alloy plate
except that a titanium alloy plate (a plate of JIS 60, i.e., the so
called 6-4 alloy plate) having a surface area of 0.12 dm.sup.2 was
used for the anode, and the electrolyte used was the one having a
pH of 10.5 prepared by adding 0.01 mol/L of zirconium potassium
carbonate, 0.05 mol/L of hydrogen peroxide, 0.03 mol/L of anatase
titanium dioxide (poorly soluble particles having a particle size
of about 0.15 .mu.m), 0.015 mol/L of sodium pyrophosphate, and
0.010 mol/L of tetramethylammonium hydroxide (TMAH) to water. When
the anode surface was observed during the electrolytic treatment,
light emission by spark discharge and glow discharge was
recognized.
Example 13
[0212] The electrolytic treatment was conducted by repeating the
procedure of Example 11 to form a coating on the magnesium alloy
plate except that the electrolyte used was the one having a pH of
12.5 prepared by adding 0.01 mol/L of zirconium potassium
carbonate, 0.01 mol/L of silica sol (poorly soluble particles
having a particle size of about 0.05 .mu.m), 0.002 mol/L of cerium
dioxide (poorly soluble particles having a particle size of about
0.2 .mu.m), 0.015 mol/L of sodium pyrophosphate, and 0.100 mol/L of
potassium hydroxide to water. When the anode surface was observed
during the electrolytic treatment, light emission by spark
discharge and glow discharge was recognized.
Comparative Example 1
[0213] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.5
prepared by adding 0.01 mol/L of sodium metasilicate nonahydrate,
0.015 mol/L of sodium pyrophosphate, and 0.036 mol/L of potassium
hydroxide to water, and the current density had a positive peak of
about 200 A/dm.sup.2 and a negative peak of about 100 A/dm.sup.2.
When the anode surface was observed during the electrolytic
treatment, light emission by spark discharge and glow discharge was
recognized.
Comparative Example 2
[0214] The electrolytic treatment was conducted by repeating the
procedure of Example 8 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.5
prepared by adding 0.01 mol/L of sodium metasilicate nonahydrate,
0.015 mol/L of sodium pyrophosphate, and 0.036 mol/L of potassium
hydroxide to water. When the anode surface was observed during the
electrolytic treatment, light emission by spark discharge and glow
discharge was recognized.
Comparative Example 3
[0215] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.7
prepared by adding 0.015 mol/L of sodium pyrophosphate and 0.036
mol/L of potassium hydroxide to water, and the current density had
a positive peak of about 200 A/dm.sup.2 and a negative peak of
about 100 A/dm.sup.2. When the anode surface was observed during
the electrolytic treatment, light emission by spark discharge and
glow discharge was recognized.
Comparative Example 4
[0216] The electrolytic treatment was conducted by repeating the
procedure of Example 1 to form a coating on the aluminum plate
except that the electrolyte used was the one having a pH of 12.7
prepared by adding 0.015 mol/L of sodium pyrophosphate and 0.036
mol/L of potassium hydroxide to water, the voltage waveform used
was the one having a frequency of 60 Hz comprising DC component at
200 V superposed with AC component at an effective value of 100V,
and the voltage used had the maximum value of about 340 V and the
minimum value of about 60 V. When the anode surface was observed
during the electrolytic treatment, no light emission by either
spark discharge or glow discharge was not recognized.
2. Evaluation of the Coating
[0217] The coatings prepared in Examples 1 to 13 and Comparative
Examples 1 to 4 were evaluated for the following items.
(1) Observation of the Cross-Section of the Coating
[0218] The cross-section of the coating obtained in Example 1 was
observed under a metallurgical microscope (manufactured by Olympus
Corporation). The aluminum plate having the coating formed on its
surface produced in Example 1 was cut to expose the cross-section,
and after impregnating the surface of the cross-section with a
resin and curing the resin, the surface was polished to prepare a
cross-section for observation. A micrograph was taken at a
magnification of 500.
[0219] The results are shown in FIG. 3 which is an optical
micrograph (taken at a magnification of 500) of the cross-section
of the coating produced in Example 1. FIG. 3 confirms that a
coating 1 had been formed on the surface of the aluminum plate 2 in
Example 1.
(2) Thickness of the Coating
[0220] The coatings produced in Examples 1 to 13 and Comparative
Examples 1 to 4 were measured for their thickness by eddy current
coating thickness tester (manufactured by Kett Electric
Laboratory).
[0221] The results are shown in Table 1.
(3) Ten Point Average Roughness
[0222] Each ten point average roughness of the surface of the
coatings obtained in Examples 1 to 13 and Comparative Examples 1 to
4 was measured by a surface texture and contour measuring
instruments (manufactured by Tokyo Seimitsu Co., Ltd.).
[0223] The results are shown in Table 1.
(4) Vickers Hardness
[0224] Each Vickers hardness of the surface of the coatings
obtained in Examples 1 to 13 and Comparative Examples 1 to 4 was
measured by a microhardness tester (manufactured by Akashi
Corporation) by applying a load of 25 g.
[0225] The results are shown in Table 1. The hardness could not be
measured in Comparative Examples 3 and 4 because the coatings were
destroyed in the measurement.
(5) Nanoindentation
[0226] The coatings obtained in Examples 1 to 13 and Comparative
Examples 1 to 4 were subjected to nanoindentation by a micro
surface material property evaluation system (manufactured by Akashi
Corporation), and the indentation depth was plotted in relation to
the load, and maximum indentation depth and degree of plastic
deformation were determined from this curve to evaluate ductility.
The nanoindentation was performed under the conditions of the test
load of 10 g, indentation speed of 10 .mu.m/s, retention time of 1
second, and unloading time of 10 seconds.
[0227] The results are shown in Table 1. Since no drastic change in
the slope was found in the load curve of the indentation depth vs
load in all coatings, it was estimated that the coating was not
destroyed.
(6) Friction Wear Test
[0228] Friction wear test was conducted for the coatings obtained
in Examples 1 to 13 and Comparative Examples 1 to 4 by using a
reciprocal sliding surface property tester (manufactured by Shinto
Scientific Co., Ltd.) to measure coefficient of friction and worn
area of the counterpart member. In the friction wear test, a ball
of SUJ2 steel having a diameter of 10 mm was used for the
counterpart member. The friction wear test was conducted by using
no lubricant under the load of 200 g, slide speed of 1500 mm/min,
and number of reciprocal sliding of 100. The coating after the
friction wear test was visually inspected to evaluate wear
resistance of the coating.
[0229] The results are shown in Table 1. In Table 1, the sample
exhibiting no wear in the coating was evaluated "pass", and the
sample with worn coating was evaluated "fail".
[0230] In Comparative Example 2, initial coefficient of friction
was 0.20 to 0.25. However, the coefficient of friction increased to
the level of 0.30 to 0.35 when the number of reciprocal sliding
reached 80 to 100. At this stage, the aluminum matrix became
exposed along the sliding track of the coating, indicating the wear
of the coating (see FIG. 4, which is an optical micrograph at a
magnification of 100 of the coating obtained in Comparative Example
2 along the sliding track after the friction wear test). This
indicates that the increase in the coefficient of friction is
caused by the cohesion of metals by the contact of the aluminum
with the ball of SUJ2 steel.
[0231] In Comparative Example 3, the initial coefficient of
friction was 0.25 to 0.30. However, the coefficient of friction
increased to the level of 0.50 to 0.60 when the number of
reciprocal sliding exceeded 50. At this stage, the aluminum matrix
became exposed along the sliding track of the coating, indicating
the wear of the coating.
[0232] In Comparative Example 4, the initial coefficient of
friction was 0.20 to 0.25. However, the coefficient of friction
increased to the level of 0.80 to 0.90 when the number of
reciprocal sliding exceeded 10. At this stage, the aluminum matrix
became exposed along the sliding track of the coating, indicating
the wear of the coating. The worn area of the counterpart member
could not be measured because the aluminum adhered to the top part
of the ball.
(7) X Ray Diffraction
[0233] The coatings obtained in Example 1 and Comparative Example 1
were evaluated by X ray diffractometry. The X ray diffractometry
was conducted by thin film method on a X ray diffractometer
(manufactured by Philips).
[0234] The results are shown in FIG. 5. FIG. 5(A) is a graph
showing the X ray diffraction pattern for the coating obtained in
Example 1, and FIG. 5(B) is a graph showing the X ray diffraction
pattern for the coating obtained in Comparative Example 1.
[0235] FIG. 5(A) indicates that the coating formed in Example 1
contained tetragonal zirconium oxide, rhombohedral aluminum oxide,
and zirconium potassium phosphate. FIG. 5(B) indicates that the
coating obtained in Comparative Example 1 contained rhombohedral
aluminum oxide as its main component. TABLE-US-00001 TABLE 1
Evaluation Ten Ductility Coat- point Max. Wear of Electrolyte
composition ing average inden- Plastic counter- Zr P Voltage thick-
rough- Hard- tation defor- Wear part or or Alkali Max. Min. ness
ness ness depth mation Coefficient Resis- material Si O (mol/L)
Wave-form (V) (V) (.mu.m) (.mu.m) (Hv) (.mu.m) (.mu.m) of friction
tance (mm.sup.2) Ex. 1 Zr-1 P 0.036 (KOH) DC + sin 720 -120 30 24
>1500 1.07 0.64 0.15-0.20 Pass 1.6 Ex. 2 Zr-1 -- 0.036 (KOH) DC
+ sin 720 -120 35 45 >1500 0.99 0.55 0.30-0.35 Pass 2.3 Ex. 3
Zr-1 P 0.036 (KOH) DC + sin 720 -120 32 27 >1500 1.02 0.61
0.175-0.225 Pass 1.7 Ex. 4 Zr-2 P 0.036 (KOH) DC + sin 720 -120 30
21 >1500 0.68 0.27 0.20-0.25 Pass 2.1 Ex. 5 Zr-3 O 0.036 (KOH)
DC + sin 720 -120 15 8.5 >1500 0.67 0.23 0.20-0.25 Pass 1.0 Ex.
6 Zr-3 O 0.036 (KOH) DC + sin 720 -120 20 11 >1500 0.75 0.33
0.20-0.25 Pass 1.2 Ex. 7 Zr-1 P 0.036 (KOH) DC + sin 600 -100 15 11
>1500 0.61 0.22 0.175-0.225 Pass 1.7 Ex. 8 Zr-1 P 0.036 (KOH) DC
+ 720 -120 13 7.7 >1500 0.72 0.44 0.15-0.20 Pass 1.0 pulse Ex. 9
Zr-1 P 0.025 (NaOH) DC + sin 720 -120 15 7.0 >1500 0.75 0.41
0.15-0.20 Pass 1.3 Ex. 10 Zr-4 P 0.130 (NaOH) DC + sin 720 -120 21
12 800-1200 0.93 0.50 0.15-0.20 Pass 1.2 Ex. 11 Zr-3 P 0.150 (KOH)
DC + sin 600 -100 25 8.0 800-1200 0.96 0.51 0.20-0.25 Pass 1.1 Ex.
12 Zr-1 P 0.010 (TMAH) DC + sin 600 -100 22 15 800-1200 0.85 0.42
0.20-0.25 Pass 0.9 Ex. 13 Zr-1 P 0.100 (KOH) DC + sin 600 -100 18
13 800-1200 0.80 0.39 0.20-0.25 Pass 1.1 Comp. Si-1 P 0.036 (KOH)
DC + sin 720 -120 35 32 >1500 0.57 0.18 0.275-0.325 Pass 2.7 Ex.
1 Comp. Si-1 P 0.036 (KOH) DC + 720 -120 12 8.2 >1500 0.54 0.17
0.30-0.35 Fail 1.0 Ex. 2 pulse Comp. -- P 0.036 (KOH) DC + sin 720
-120 19 9.8 -- 0.54 0.15 0.50-0.60 Fail 1.3 Ex. 3 Comp. -- P 0.036
(KOH) DC + sin 340 60 1.8 6.6 -- 2.06 1.91 0.80-0.90 Fail -- Ex.
4
[0236] The abbreviations used in Table 1 are as described
below.
[0237] Zr-1: zirconium potassium carbonate (water soluble), 0.01
mol/L
[0238] Zr-2: zirconium hydroxide (poorly soluble particles having a
particle size of about 0.1 .mu.m), 0.01 mol/L
[0239] Zr-3: zirconium acetate (water soluble), 0.01 mol/L
[0240] Zr-4: stabilized zirconia (poorly soluble particles having a
particle size of about 0.3 .mu.m), 0.05 mol/L
[0241] Si-1: sodium metasilicate nonahydrate, 0.01 mol/L
[0242] P: sodium pyrophosphate, 0.015 mol/L
[0243] Q: sodium citrate dihydrate, 0.01 mol/L
[0244] DC+sin: voltage waveform comprising a direct current
superposed with a sine wave
[0245] DC+pulse: voltage waveform comprising a direct current
superposed with a pulse wave
[0246] As demonstrated in Table 1, the coatings of Examples 1 to 13
obtained by the electrolytic treatment using the electrolyte for
electrolytic deposition of a ceramic coating on a metal of the
present invention exhibited high hardness, excellent wear
resistance, and reduced attack on the counterpart member.
[0247] In contrast, when an electrolyte containing a silicon
compound was used instead of the electrolyte containing a zirconium
compound, the resulting article exhibited increased attack to the
counterpart member (Comparative Example 1) or low wear resistance
(Comparative Example 2). When an electrolyte containing neither the
zirconium compound nor the silicon compound was used, the resulting
article had inferior hardness at both high voltage (Comparative
Example 3) and low voltage (Comparative Example 4).
<B. Examples of the Metal Member of the Present
Invention>
1. Electrolytic Treatment
Example 14
[0248] Electrolytic treatment was conducted for 10 minutes by
bipolar electrolysis using an aluminum plate (a plate of JIS 1000)
having a surface area of 0.12 dm.sup.2 for the anode and a
stainless steel plate for the cathode to thereby produce a metal
member having a coating deposited on the aluminum plate. When the
anode surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
[0249] The electrolyte used was an electrolyte (pH 11.2) prepared
by adding 0.01 mol/L of zirconium potassium carbonate, 0.005 mol/L
of sodium pyrophosphate, and 0.025 mol/L of potassium hydroxide to
water.
[0250] The voltage waveform used was the one having a frequency of
60 Hz comprising an AC component at 300 V superposed with a DC
component having an effective value of 300V. The voltage used had a
maximum value of about 720 V and a minimum value of about -120 V.
The current density had a positive peak of about 125 A/dm.sup.2 and
a negative peak of about 60 A/dm.sup.2.
Example 15
[0251] The electrolytic treatment was conducted by repeating the
procedure of Example 14 except that the electrolyte used was the
one having a pH of 10.8 prepared by adding 0.015 mol/L of zirconium
acetate, 0.02 mol/L of sodium citrate dihydrate, and 0.020 mol/L of
potassium hydroxide to water to thereby produce a metal member
having a coating deposited on the aluminum plate. When the anode
surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
Example 16
[0252] The electrolytic treatment was conducted by repeating the
procedure of Example 14 except that the electrolytic treatment was
conducted by pulse electrolysis using a voltage waveform comprising
a DC component at 300 V superposed with a pulse wave having an
amplitude of 420 V to thereby produce a metal member having a
coating deposited on the aluminum plate. The voltage values were
the same as those of Example 14, with the maximum value of about
720 V and the minimum value of about -120 V. When the anode surface
was observed during the electrolytic treatment, light emission by
spark discharge and glow discharge was recognized.
Example 17
[0253] Electrolytic treatment was conducted for 5 minutes by an
anode electrolysis using an aluminum alloy plate (a plate of JIS
6000) having a surface area of 0.5 dm.sup.2 for the anode and a
stainless steel plate for the cathode to thereby produce a metal
member having a coating deposited on the aluminum alloy plate. When
the anode surface was observed during the electrolytic treatment,
light emission by spark discharge and glow discharge was
recognized.
[0254] The electrolyte used was an electrolyte (pH 10.0) prepared
by adding 0.05 mol/L of zirconium potassium carbonate, and 0.05
mol/L of sodium pyrophosphate to water.
[0255] The voltage waveform used was a sine wave having a frequency
60 Hz which had been subjected to half-wave rectification. The
voltage used had a maximum value of about 500 V. The current
density had a positive peak of about 70 A/dm.sup.2.
Example 18
[0256] The electrolytic treatment was conducted by repeating the
procedure of Example 17 except that an aluminum die cast alloy
plate (a plate of JIS ADC12) having a surface area of 0.52 dm.sup.2
was used for the anode with the stainless steel plate used for the
cathode, and the electrolytic treatment was conducted by anode
electrolysis for 15 minutes to thereby produce a metal member
having a coating deposited on the aluminum die cast plate. When the
anode surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
Example 19
[0257] The electrolytic treatment was conducted by repeating the
procedure of Example 17 except that a titanium alloy plate (a plate
of JIS 60, i.e., the so called 6-4 alloy plate) having a surface
area of 0.48 dm.sup.2 was used for the anode with the cathode
stainless steel plate used for the cathode, and the electrolytic
treatment was conducted by anode electrolysis for 5 minutes to
thereby produce a metal member having a coating deposited on the
titanium alloy plate. When the anode surface was observed during
the electrolytic treatment, no light emission by either spark
discharge or glow discharge was recognized.
Example 20
[0258] The electrolytic treatment was conducted by repeating the
procedure of Example 19 except that the electrolytic treatment was
conducted for 20 minutes to thereby produce a metal member having a
coating deposited on the titanium alloy plate. When the anode
surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
Example 21
[0259] Electrolytic treatment was conducted for 10 minutes by anode
electrolysis using an aluminum alloy plate (a plate of JIS 1000)
having a surface area of 0.35 dm.sup.2 for the anode and a
stainless steel plate for the cathode to thereby produce a metal
member having a coating deposited on the aluminum alloy plate. When
the anode surface was observed during the electrolytic treatment,
light emission by spark discharge and glow discharge was
recognized.
[0260] The electrolyte used was an electrolyte (pH 9.5) prepared by
adding 0.18 mol/L of zirconium potassium carbonate, 0.015 mol/L of
sodium pyrophosphate, and 0.036 mol/L of potassium hydroxide to
water.
[0261] The voltage waveform used was a sine wave having a frequency
60 Hz which had been subjected to half-wave rectification. The
voltage used had a maximum value of about 600 V. The current
density had a positive peak of about 120 A/dm.sup.2.
Example 22
[0262] Electrolytic treatment was conducted for 10 minutes by anode
electrolysis using a magnesium alloy plate (a plate of JIS AZ91D)
having a surface area of 0.4 dm.sup.2 for the anode and a stainless
steel plate for the cathode to thereby produce a metal member
having a coating deposited on the magnesium alloy plate. When the
anode surface was observed during the electrolytic treatment, light
emission by spark discharge and glow discharge was recognized.
[0263] The electrolyte used was an electrolyte (pH 13.0) prepared
by adding 0.01 mol/L of zirconium potassium carbonate, 0.015 mol/L
of sodium pyrophosphate, and 0.130 mol/L of potassium hydroxide to
water.
[0264] The voltage waveform used was a sine wave having a frequency
60 Hz which had been subjected to half-wave rectification. The
voltage used had a maximum value of about 500 V. The current
density had a positive peak of about 100 A/dm.sup.2.
Comparative Example 5
[0265] The electrolytic treatment was conducted by repeating the
procedure of Example 14 except that the electrolyte used was the
one having a pH of 12.8 prepared by adding 0.013 mol/L of sodium
metasilicate nonahydrate, 0.010 mol/L of sodium pyrophosphate, and
0.036 mol/L of potassium hydroxide to water to thereby produce a
metal member having a coating deposited on the aluminum plate. When
the anode surface was observed during the electrolytic treatment,
light emission by spark discharge and glow discharge was
recognized.
Comparative Example 6
[0266] The electrolytic treatment was conducted by repeating the
procedure of Example 16 except that the electrolyte used was the
one having a pH of 12.8 prepared by adding 0.013 mol/L of sodium
metasilicate nonahydrate, 0.010 mol/L of sodium pyrophosphate, and
0.036 mol/L of potassium hydroxide to water to thereby produce a
metal member having a coating deposited on the aluminum plate. When
the anode surface was observed during the electrolytic treatment,
light emission by spark discharge and glow discharge was
recognized.
Comparative Example 7
[0267] The electrolytic treatment was conducted by repeating the
procedure of Example 14 except that the electrolyte used was the
one having a pH of 13.0 prepared by adding 0.015 mol/L of sodium
pyrophosphate and 0.030 mol/L of potassium hydroxide to water to
thereby produce a metal member having a coating deposited on the
aluminum plate. When the anode surface was observed during the
electrolytic treatment, light emission by spark discharge and glow
discharge was recognized.
2. Test Sample
Comparative Example 8
[0268] A commercially available metal member which is made of an
aluminum alloy (JIS 6000) having a hard anodized aluminum coating
deposited thereon was used for the test sample of Comparative
Example 4.
Comparative Example 9
[0269] A commercially available metal member which is an aluminum
die cast alloy plate (a plate of JIS ADC12) having a hard anodized
aluminum coating deposited thereon was used for the test sample of
Comparative Example 5.
3. Evaluation of the Coating
[0270] The metal members produced in Examples 14 to 22 and
Comparative Examples 5 to 9 were evaluated for the following
items.
(1) Observation of the Cross-Section of the Coating Deposited on
the Metal Member
[0271] A thin slice of the metal member produced in Example 14 was
prepared. The cross-section of the coating that became exposed was
observed under a field emission transmission electron microscope
(manufactured by Hitachi, Ltd.).
[0272] The results are shown in FIG. 7. FIG. 7(A) is a micrograph
of the amorphous layer in the coating of the metal member produced
in Example 14, and FIG. 7(B) is a micrograph of the crystalline
layer in the coating of the metal member produced in Example
14.
[0273] As demonstrated in FIG. 7(A), zirconium oxide microcrystals
are dispersed in the amorphous oxide in the amorphous layer, and as
demonstrated in FIG. 7(B), zirconium oxide microcrystals are
dispersed in the crystalline oxide in the crystalline layer.
[0274] The metal members produced in Examples 15 to 22 were also
observed in the similar procedure, and the results were similar for
these metal members.
(2) Electron Diffraction Analysis and Energy-Dispersive X Ray
Spectroscopic Analysis
[0275] Electron diffraction analysis was conducted for locations
"a" and "b" in the micrograph of the amorphous layer in the coating
of the metal member produced in Example 14 shown in FIG. 7(A).
[0276] The results are shown in FIG. 8. FIG. 8(A) is the electron
diffractogram at the location "a" in FIG. 7(A), and FIG. 8(B) is
the electron diffractogram at the location "b" in FIG. 7(A).
[0277] Energy-dispersive X ray spectroscopic analysis was conducted
for locations "a" and "b" in the same micrograph to identify the
substance at these locations. It was then found that the substance
at location "a" was an amorphous oxide containing zirconium and
aluminum, and the substance at location "b" was cubic zirconium
oxide.
(3) Glow Discharge Optical Emission Spectroscopic Analysis
[0278] The coatings obtained in Examples 16 and 18 were evaluated
by qualitative analysis in the depth direction by using a glow
discharge optical emission spectrometer (manufactured by HORIBA,
Ltd.).
[0279] The results are shown in FIG. 9. FIG. 9(A) is the graph
showing the result of the qualitative analysis in depth direction
obtained by glow discharge optical emission spectroscopy for the
coating of the metal member produced in Example 16, and FIG. 9(B)
is the graph showing the result of the qualitative analysis in
depth direction obtained by glow discharge optical emission
spectroscopy for the coating of the metal member produced in
Example 18.
[0280] As demonstrated in FIGS. 9(A) and 9(B), elemental zirconium
exhibited concentration gradient gradually decreasing in the depth
direction toward the interface between the coating and the metal
substrate.
(4) X Ray Diffraction
[0281] The coatings obtained in Examples 14 to 22 and Comparative
Examples 5 to 9 were evaluated by X ray diffractometry. The X ray
diffractometry was conducted by thin film method on an X ray
diffractometer (manufactured by Philips).
[0282] The results are shown in FIGS. 10 and 11 and Table 2. FIGS.
10(A), 10(B), 10(C), 10(D), 10(E), and 10(F) are respectively
graphs showing the X ray diffraction pattern for the coatings of
the metal members obtained in Examples 14, 17, 18, 19, 21, and 22,
and FIGS. 11(A), 11(B), and 11(C) are respectively graphs showing
the X ray diffraction pattern for the coatings of the metal members
obtained in Comparative Examples 5, 7, and 8.
[0283] As demonstrated in FIGS. 10(A) to 10(F), all of the coatings
formed in Examples 14, 17, 18, 19, 21, and 22 contained cubic
zirconium oxide and/or tetragonal zirconium oxide.
[0284] In addition, FIG. 10(A) reveals that, in the X ray
diffraction pattern of the coating of the Example 14, relative peak
intensity of (111) plane of tetragonal zirconium oxide and/or cubic
zirconium oxide is higher than relative peak intensity of the main
peak of the alumina. FIG. 10(D) reveals that, in the X ray
diffraction pattern of the coating of Example 19, relative peak
intensity of (111) plane of tetragonal zirconium oxide and/or cubic
zirconium oxide is higher than relative peak intensity of the main
peak of the titanium oxide.
[0285] Furthermore, FIG. 10(E) reveals that monoclinic zirconium
oxide is present in the coating of Example 21, and that proportion
(V.sub.m) of volume of the monoclinic zirconium oxide in relation
to the total of the volume of the tetragonal zirconium oxide and/or
the cubic zirconium oxide and the volume of the monoclinic
zirconium oxide is 0.3 to 0.4.
[0286] For Examples 14 to 22, each proportion (V.sub.m) of the
volume of the monoclinic zirconium oxide in relation to the total
of the volume of the tetragonal zirconium oxide and/or the cubic
zirconium oxide and the volume of the monoclinic zirconium oxide
calculated from the X ray diffraction pattern by the equation (1)
is shown in Table 2.
[0287] As demonstrated in FIGS. 11(A) and 11(B), all of the
coatings formed in Comparative Examples 5 and 7 contain
rhombohedral alumina. As evident from FIG. 11(C), in the case of
the coating formed in Comparative Example 8, peaks other than the
peak of the metal element constituting the metal substrate were not
recognized.
(5) Thickness of the Coating
[0288] The coatings produced in Examples 14 to 22 and Comparative
Examples 5 to 9 were measured for their thickness by eddy current
coating thickness tester (manufactured by Kett Electric
Laboratory).
[0289] The results are shown in Table 2.
(6) Centerline Average Roughness
[0290] The surface of the coatings produced in Examples 14 to 22
and Comparative Examples 5 to 9 were measured for the center line
average roughness by a surface texture and contour measuring
instruments (manufactured by Tokyo Seimitsu Co., Ltd.).
[0291] The results are shown in Table 2.
(7) Vickers Hardness
[0292] Each Vickers hardness of the surface of the coatings
obtained in Examples 14 to 22 and Comparative Examples 5 to 9 was
measured by a microhardness tester (manufactured by Akashi
Corporation) by applying a load of 10 g.
[0293] The results are shown in Table 2. The hardness could not be
measured in Comparative Examples 4 and 6 because the coating was
destroyed in the measurement.
(8) Friction Wear Test
[0294] Friction wear test was conducted for the coatings obtained
in Examples 14 to 22 and Comparative Examples 5 to 9 using a
reciprocal sliding surface property tester (manufactured by Shinto
Scientific Co., Ltd.) to measure coefficient of friction and worn
area of the counterpart member. In the friction wear test, a ball
of SUJ2 steel having a diameter of 10 mm was used for the
counterpart member. The friction wear test was conducted by using
no lubricant under the load of 200 g, slide speed of 1500 mm/min,
and number of reciprocal sliding of 500. The coating after the
friction wear test was measured for the wear depth by a surface
texture and contour measuring instruments.
[0295] The results are shown in Table 2.
[0296] In Comparative Example 6, initial coefficient of friction
was 0.25 to 0.3. However, the coefficient of friction increased to
the level of 0.50 to 0.60 when the number of reciprocal sliding
reached 400 to 500.
[0297] In Comparative Example 7, initial coefficient of friction
was 0.30 to 0.35. However, the coefficient of friction increased to
the level of 0.50 to 0.60 when the number of reciprocal sliding
reached 400 to 500.
[0298] In Comparative Example 8, the coefficient of friction
increased to the level of 0.80 to 0.90 and the wear depth became
3.0 .mu.m when the number of reciprocal sliding reached
approximately 100.
[0299] In Comparative Example 9, the coefficient of friction
increased to the level of 0.80 to 0.90 and the wear depth became
2.5 .mu.m when the number of reciprocal sliding reached
approximately 100.
[0300] As demonstrated in Table 2, each coating of Examples 14 to
22 had a coefficient of friction smaller than that of Comparative
Examples 5 to 9. When the coatings with similar center line average
roughness were compared for the wear area of their counterpart
member, the coatings of the Examples of the present invention
exhibited smaller values compared to those of the Comparative
Examples.
[0301] [Table 2] TABLE-US-00002 TABLE 2 Wear area Electro- of Wear
depth lyte Coating Center line counterpart of the composi-
thickness Average Coefficient member coating tion (.mu.m) roughness
(.mu.m) Hardness (Hv) V.sub.m of friction (mm.sup.2) (.mu.m) Ex. 14
Zr 30 2.10 >1500 .ltoreq.0.1 0.20-0.25 1.60 0.0 Ex. 15 Zr 20
1.23 >1500 .ltoreq.0.1 0.20-0.25 0.95 0.0 Ex. 16 Zr 14 0.98
>1500 .ltoreq.0.1 0.20-0.25 0.83 0.0 Ex. 17 Zr 4 0.54 --
.ltoreq.0.1 0.15-0.20 0.19 0.0 Ex. 18 Zr 6 0.60 800-900 .ltoreq.0.1
0.15-0.20 0.14 0.0 Ex. 19 Zr 3 0.30 -- .ltoreq.0.1 0.25-0.30 0.15
0.0 Ex. 20 Zr 27 2.06 500-700 0.4-0.5 0.20-0.25 0.28 0.0 Ex. 21 Zr
17 1.40 800-1000 0.3-0.4 0.25-0.30 1.10 0.0 Ex. 22 Zr 15 1.10
800-1000 .ltoreq.0.1 0.20-0.25 0.45 0.0 Comp. Si 35 4.50 >1500
-- 0.30-0.40 3.57 0.0 Ex. 5 Comp. Si 12 1.19 >1500 -- 0.50-0.60
2.03 0.0 Ex. 6 Comp. -- 11 1.33 >1500 -- 0.50-0.60 2.15 0.0 Ex.
7 Comp. -- 10 1.22 300-500 -- 0.80-0.90 0.69 3.0 Ex. 8 Comp. -- 9
0.74 300-400 -- 0.80-0.90 0.45 2.5 Ex. 9
[0302] As demonstrated in Table 2, the metal members of the present
invention (Examples 14 to 22) have excellent wear resistance and
sliding properties.
* * * * *