EP0668375B1 - Process for forming composite galvanic coatings of hard chromium with a disperse phase, and wear-resistant coating formed thereby - Google Patents
Process for forming composite galvanic coatings of hard chromium with a disperse phase, and wear-resistant coating formed thereby Download PDFInfo
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- EP0668375B1 EP0668375B1 EP95102258A EP95102258A EP0668375B1 EP 0668375 B1 EP0668375 B1 EP 0668375B1 EP 95102258 A EP95102258 A EP 95102258A EP 95102258 A EP95102258 A EP 95102258A EP 0668375 B1 EP0668375 B1 EP 0668375B1
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- Prior art keywords
- microcracks
- layer
- particles
- matrix
- chromium
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- 239000011651 chromium Substances 0.000 title claims description 49
- 229910052804 chromium Inorganic materials 0.000 title claims description 41
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 title claims description 40
- 238000000576 coating method Methods 0.000 title claims description 40
- 239000011248 coating agent Substances 0.000 title claims description 31
- 238000000034 method Methods 0.000 title claims description 21
- 239000002131 composite material Substances 0.000 title claims description 5
- 239000002245 particle Substances 0.000 claims description 41
- 239000011159 matrix material Substances 0.000 claims description 34
- 239000000758 substrate Substances 0.000 claims description 19
- 238000000151 deposition Methods 0.000 claims description 16
- 229910052755 nonmetal Inorganic materials 0.000 claims description 15
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 9
- 238000007747 plating Methods 0.000 claims description 8
- 239000000725 suspension Substances 0.000 claims description 7
- 230000008021 deposition Effects 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 4
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims description 4
- 229910010271 silicon carbide Inorganic materials 0.000 claims description 4
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 claims description 3
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 claims description 3
- 229910052580 B4C Inorganic materials 0.000 claims description 2
- 229910052582 BN Inorganic materials 0.000 claims description 2
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 claims description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 2
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 2
- INAHAJYZKVIDIZ-UHFFFAOYSA-N boron carbide Chemical compound B12B3B4C32B41 INAHAJYZKVIDIZ-UHFFFAOYSA-N 0.000 claims description 2
- UFGZSIPAQKLCGR-UHFFFAOYSA-N chromium carbide Chemical compound [Cr]#C[Cr]C#[Cr] UFGZSIPAQKLCGR-UHFFFAOYSA-N 0.000 claims description 2
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 claims description 2
- 229910003460 diamond Inorganic materials 0.000 claims description 2
- 239000010432 diamond Substances 0.000 claims description 2
- 238000009826 distribution Methods 0.000 claims description 2
- 229910002804 graphite Inorganic materials 0.000 claims description 2
- 239000010439 graphite Substances 0.000 claims description 2
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 2
- 229910003470 tongbaite Inorganic materials 0.000 claims description 2
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 claims description 2
- 238000005260 corrosion Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 239000002270 dispersing agent Substances 0.000 description 4
- 229910001018 Cast iron Inorganic materials 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000005315 distribution function Methods 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000007749 high velocity oxygen fuel spraying Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000013011 mating Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 230000003134 recirculating effect Effects 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
- C25D15/02—Combined electrolytic and electrophoretic processes with charged materials
Definitions
- the present invention relates to a process for forming, on a substrate, a composite hard chromium coating comprising a disperse phase consisting of nonmetal particles; and to a wear-resistant coating formed using such a process and particularly suitable for mechanical components subjected to high-temperature chafing, such as internal combustion engine piston rings and components.
- US Patent n. 4,846,940 relates to galvanic hard chromium coatings characterized by a Cr matrix with a large number of micro- and macrocracks combined with a disperse phase, in the matrix, consisting of hard particles embedded in the micro- and macrocracks of the matrix.
- Such coatings are formed by means of a galvanic electrodeposition process characterized by comprising a current inversion step, i.e. by alternately switching the substrate from cathode to anode potential and vice versa.
- Such coatings present a small amount of incorporated hydrogen, a large number of even relatively large cracks, and a large number of particle inclusions in the cracks, which make them highly susceptible to corrosion. Moreover, depositing the coating by inverting the polarity of the electrodes poses practical problems which complicate the fabrication process.
- a process for forming, on a substrate, a composite hard chromium coating comprising a disperse phase and particularly suitable for mechanical components subjected to high-temperature chafing comprising the step of galvanically depositing at least one layer of hard chromium in a chromium plating bath of the type forming microcracks and in which is dispersed in suspension a predetermined concentration of given sized particles of a nonmetal insoluble in the bath; characterized in that, in the course of said deposition step, the substrate is maintained permanently at cathode potential; and a pulsating cathode current, varying cyclically in time between a minimum and maximum value, is supplied to achieve a chromium layer comprising a matrix with microcracks of a given distribution, and a disperse phase consisting of said nonmetal particles, some of which are included in the microcracks, and some of which are directly embedded in the matrix, said chromium plat
- This provides for achieving a so-called "disperse chromium" coating comprising a Cr matrix containing dispersing agents, which is extremely hard (over 1,000 Vickers), includes dispersing agents in the form of nonmetal particles of hard materials such as oxides, carbides and nitrides of very low thermal conductivity and high thermal stability, and which, combined with a low hydrogen content, presents a high degree of thermal stability characterized by a reduced loss in hardness alongside an increase in temperature, and a small amount of incorporated hydrogen in the Cr matrix.
- variation of the cathode current may be achieved easily using known facilities, and fully automatically by means of appropriate programming, thus enabling troublefree, low-cost formation of the coating according to the present invention.
- the above deposition step is preferably preceded by the step of depositing on the substrate a continuous hard chromium base layer with substantially no microcracks or porosity, which covers the whole of the substrate, and which is formed, preferably to a thickness of roughly 50 ⁇ m, by galvanically depositing chromium in a chromium plating bath of the type forming no microcracks and containing no particles in suspension.
- a number of said "disperse" layers comprising a microcracked Cr matrix and including hard particles are then deposited successively on the continuous base layer.
- the substrate-coating interface thus presents a fairly thick layer (in relation to the total thickness of the coating, which is roughly 500 ⁇ m) with absolutely no cracks or dispersing agent particles (at least none detectable by standard metallographic techniques), and which prevents the microcracks in the upper layers of the coating from propagating towards the substrate, thus ensuring absolute protection of the substrate and greatly enhancing the corrosion resistance of both the substrate and the coating.
- the cathode current is supplied according to a cycle comprising the following steps:
- the cathode current is varied in a square wave pattern; and in said first and third steps, it is varied in steps.
- the "disperse chromium" layers are therefore formed with the microcracks of one layer offset, depthwise of the coating, in relation to those of the adjacent "disperse” layers, so that any depthwise propagation of the microcracks in one layer (due to mechanical stress in the layer) is prevented from being transmitted to those of the adjacent underlying layer, thus preventing the formation of macrocracks as in galvanic Cr coatings formed using known processes.
- This provides for obtaining a much more stable coating, and for further improving the corrosion resistance of the substrate, without, however, affecting the in-service lubricant collecting and distribution function of the microcracks.
- nonmetal dispersing agent particles substantially consisting of oxides (e.g. aluminium oxide - Al 2 O 3 ) and/or carbides (tungsten, chromium, silicon, boron) and/or nitrides (silicon, boron), i.e. extremely hard compounds, and both included inside the microcracks and embedded directly in the chromium matrix, provides for obtaining a coating which is extremely resistant to wear caused by abrasion or adhesion typical of high-temperature, mutually sliding metal surfaces.
- oxides e.g. aluminium oxide - Al 2 O 3
- carbides tungsten, chromium, silicon, boron
- nitrides silicon, boron
- the coating according to the present invention therefore comprises a layer comprising a microcracked hard chromium matrix and a disperse phase, in the matrix, consisting of a number of particles of a nonmetal material; a first number of said particles being included in the microcracks of the matrix, and a second number of said particles being embedded directly in parts of the matrix with no microcracks; characterized in that it comprises a first hard chromium layer with substantially no microcracks or porosity and without said particles; and, deposited on the first layer, a number of said layers comprising a microcracked matrix and a disperse phase consisting of said particles; the superimposed layers, deposited on the first layer, presenting the microcracks offset depthwise in relation to those of the adjacent layers.
- the first layer presents a thickness of at least 50 ⁇ m; the width of the microcracks, measured parallel to the layer, is at least 1 ⁇ m; the density of the microcracks ranges from 100 to 300 per centimeter; and the size of the nonmetal particles embedded in the matrix ranges from 0.1 to 20 ⁇ m.
- cylinder liners such as the piston rings of four- and two-stroke engines or piston pumps
- the cylinder liners are normally made of lamellar, nodular or vermicular cast iron, either natural or hardened (e.g. laser quenched) or nitrided (e.g. using the TENIFER (registered trade mark) process or similar), or present surfaces with hot spray coatings such as FK1008 formed using the HVOF process (both registered trade marks).
- Number 1 in Figure 1 indicates a wear-resistant coating formed according to the present invention on a substrate 2, e.g. any known mechanical component made of cast iron.
- Coating 1 comprises a first layer 3, preferably no more than 50 ⁇ m deep, formed of hard Cr, and characterized by being continuous, i.e. by presenting no detectable microcracks or porosity, and no inclusions of any sort.
- layer 3 On top of layer 3, there are deposited a given number (four in the example) of substantially identical layers 5a, 5b, 5c, 5d, each comprising a hard chromium matrix 6 in which are formed a number of microcracks 7 extending radially depthwise of layer 5 towards substrate 2, and a disperse phase in matrix 6 and consisting of a number of particles 8 of any hard nonmetal material.
- a first number of particles 8 is included in microcracks 7 of matrix 6, and a second number of particles 8 is embedded directly inside parts of matrix 6 with no microcracks 7; and the microcracks 7 of layers 5 deposited on first layer 3 are offset depthwise in relation to those of the adjacent layers 5.
- microcracks 7 of layer 5b extend depthwise towards underlying layer 5a and substantially towards the portions between microcracks 7 of layer 5a, i.e. towards matrix 6 portions of layer 5a presenting no microcracks.
- the microcracks 7 of each layer 5 present a "spiderweb" pattern along the interface surface 9 of each layer 5, as shown in Figure 5.
- the width of the microcracks, measured parallel to each layer 5, is at least 1 ⁇ m; the microcrack density measured at surfaces 9 ranges from 100 to 300 microcracks per centimeter of surface; and the size of nonmetal particles 8 ranges from 0.1 to 20 ⁇ m.
- a coating as described above may be formed electrolytically; layer 3 being formed by galvanically depositing Cr in known manner using any known chromium plating bath of the type resulting in no microcracks and containing no particles in suspension, or operating accordingly with a bath containing particles in suspension; and layers 5 being formed using known chromium plating baths of the type for forming microcracks and containing particles 8 in suspension.
- a further precaution to ensure layer 3 presents no microcracks is to limit its thickness, and to use such operating parameters (current cycles and density, etc.) as to limit the formation of stress within the layer due to excessive energy supply.
- the baths for forming layers 5 and containing particles 8 in suspension are preferably agitated at all times, e.g. by means of mechanical, fluidodynamics, energetic agitators, or by air injection.
- the nonmetal particles 8 included in the coating must be insoluble in the baths which present a chromic acid, sulphuric acid and catalyst base, are maintained at a temperature of about 55°C, and present a 20 to 400 gr/liter concentration of particles 8 (ranging in size between 0.1 and 20 micron).
- Particles 8 therefore consist of one or more materials in the group comprising: tungsten carbide, silicon carbide, chromium carbide, aluminium oxide, silicon nitride, boron carbide, diamond, graphite, hexagonal boron nitride.
- Each layer 5 may of course include particles 8 all of the same material or of different materials, and likewise from one layer to another.
- the cathode current supply cycle comprises the following steps:
- a bath with the following composition is prepared: CrO 3 250.0 gr/lt; FeSiF 6 1.5 gr/lt; H 2 SO 4 2.5 gr/lt SiC 50.0 gr/lt;
- Lead anodes and a cathode consisting of rings of lamellar cast iron are immersed in the bath, and a chromium coating is deposited, agitating the bath by recirculating roughly 300 lt/min and injecting air at roughly 5 bar pressure, and operating with a potential difference of 15 volts and a continuous cathode current of a mean density of 70 A per square decimeter, which is varied during deposition according to the following cycle:
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electroplating Methods And Accessories (AREA)
Description
The present invention relates to a process for
forming, on a substrate, a composite hard chromium
coating comprising a disperse phase consisting of
nonmetal particles; and to a wear-resistant coating
formed using such a process and particularly suitable
for mechanical components subjected to high-temperature
chafing, such as internal combustion engine piston rings
and components.
US Patent n. 4,846,940 relates to galvanic hard
chromium coatings characterized by a Cr matrix with a
large number of micro- and macrocracks combined with a
disperse phase, in the matrix, consisting of hard
particles embedded in the micro- and macrocracks of the
matrix. Such coatings are formed by means of a galvanic
electrodeposition process characterized by comprising a
current inversion step, i.e. by alternately switching
the substrate from cathode to anode potential and vice
versa.
Such coatings present a small amount of
incorporated hydrogen, a large number of even relatively
large cracks, and a large number of particle inclusions
in the cracks, which make them highly susceptible to
corrosion. Moreover, depositing the coating by inverting
the polarity of the electrodes poses practical problems
which complicate the fabrication process.
It is an object of the present invention to
provide a process for forming hard chromium coatings
comprising at least one layer with a microcracked matrix
and a disperse phase, and which is both straightforward
and economical while at the same time providing for good
quality coatings characterized by a small amount of
incorporated hydrogen. It is a further object of the
present invention to provide a composite hard chromium
coating of good quality and strength, which remains
extremely hard even at high temperature, and which is
highly resistant to corrosion and wear both of itself
and the mating part.
According to the present invention, there is
provided a process for forming, on a substrate, a
composite hard chromium coating comprising a disperse
phase and particularly suitable for mechanical
components subjected to high-temperature chafing; the
process comprising the step of galvanically depositing
at least one layer of hard chromium in a chromium
plating bath of the type forming microcracks and in
which is dispersed in suspension a predetermined
concentration of given sized particles of a nonmetal
insoluble in the bath;
characterized in that, in the course of said deposition step, the substrate is maintained permanently at cathode potential; and a pulsating cathode current, varying cyclically in time between a minimum and maximum value, is supplied to achieve a chromium layer comprising a matrix with microcracks of a given distribution, and a disperse phase consisting of said nonmetal particles, some of which are included in the microcracks, and some of which are directly embedded in the matrix, said chromium plating bath is a chromic acid based bath, containing in solution prevalently hexavalent chromium.
characterized in that, in the course of said deposition step, the substrate is maintained permanently at cathode potential; and a pulsating cathode current, varying cyclically in time between a minimum and maximum value, is supplied to achieve a chromium layer comprising a matrix with microcracks of a given distribution, and a disperse phase consisting of said nonmetal particles, some of which are included in the microcracks, and some of which are directly embedded in the matrix, said chromium plating bath is a chromic acid based bath, containing in solution prevalently hexavalent chromium.
This provides for achieving a so-called "disperse
chromium" coating comprising a Cr matrix containing
dispersing agents, which is extremely hard (over 1,000
Vickers), includes dispersing agents in the form of
nonmetal particles of hard materials such as oxides,
carbides and nitrides of very low thermal conductivity
and high thermal stability, and which, combined with a
low hydrogen content, presents a high degree of thermal
stability characterized by a reduced loss in hardness
alongside an increase in temperature, and a small amount
of incorporated hydrogen in the Cr matrix. Moreover,
variation of the cathode current may be achieved easily
using known facilities, and fully automatically by means
of appropriate programming, thus enabling troublefree,
low-cost formation of the coating according to the
present invention.
The above deposition step is preferably preceded
by the step of depositing on the substrate a continuous
hard chromium base layer with substantially no
microcracks or porosity, which covers the whole of the
substrate, and which is formed, preferably to a
thickness of roughly 50 µm, by galvanically depositing
chromium in a chromium plating bath of the type forming
no microcracks and containing no particles in
suspension. A number of said "disperse" layers
comprising a microcracked Cr matrix and including hard
particles are then deposited successively on the
continuous base layer.
The substrate-coating interface thus presents a
fairly thick layer (in relation to the total thickness
of the coating, which is roughly 500 µm) with absolutely
no cracks or dispersing agent particles (at least none
detectable by standard metallographic techniques), and
which prevents the microcracks in the upper layers of
the coating from propagating towards the substrate, thus
ensuring absolute protection of the substrate and
greatly enhancing the corrosion resistance of both the
substrate and the coating.
When galvanically depositing each said hard
chromium layer comprising a microcracked matrix and a
disperse phase consisting of said particles embedded in
the layer, the cathode current is supplied according to
a cycle comprising the following steps:
- a first step wherein the cathode current is brought to and maintained for a first predetermined time at a first threshold value other than zero;
- a second step, superimposed on the first, wherein the cathode current is varied alternately, in a wave pattern and for a second predetermined time, between said first threshold value and a second threshold value higher than the first; and
- a third step wherein the cathode current is zeroed and maintained at zero for a third predetermined time.
More specifically, in said second step, the
cathode current is varied in a square wave pattern; and
in said first and third steps, it is varied in steps.
The "disperse chromium" layers are therefore
formed with the microcracks of one layer offset,
depthwise of the coating, in relation to those of the
adjacent "disperse" layers, so that any depthwise
propagation of the microcracks in one layer (due to
mechanical stress in the layer) is prevented from being
transmitted to those of the adjacent underlying layer,
thus preventing the formation of macrocracks as in
galvanic Cr coatings formed using known processes. This
provides for obtaining a much more stable coating, and
for further improving the corrosion resistance of the
substrate, without, however, affecting the in-service
lubricant collecting and distribution function of the
microcracks.
Finally, the presence of nonmetal dispersing agent
particles substantially consisting of oxides (e.g.
aluminium oxide - Al2O3) and/or carbides (tungsten,
chromium, silicon, boron) and/or nitrides (silicon,
boron), i.e. extremely hard compounds, and both included
inside the microcracks and embedded directly in the
chromium matrix, provides for obtaining a coating which
is extremely resistant to wear caused by abrasion or
adhesion typical of high-temperature, mutually sliding
metal surfaces.
The coating according to the present invention
therefore comprises a layer comprising a microcracked
hard chromium matrix and a disperse phase, in the
matrix, consisting of a number of particles of a
nonmetal material; a first
number of said particles being included in the
microcracks of the matrix, and a second number of
said particles being embedded directly in parts of the
matrix with no microcracks; characterized in that it
comprises a first hard chromium layer with
substantially no microcracks or porosity and without
said particles; and, deposited on the first layer, a
number of said layers comprising a microcracked matrix
and a disperse phase consisting of said particles;
the superimposed layers, deposited on the first layer,
presenting the microcracks offset depthwise in relation
to those of the adjacent layers. Preferably, the
first layer presents a thickness of at least 50 µm; the width of the
microcracks, measured parallel to the layer, is at
least 1 µm; the density of the microcracks ranges from
100 to 300 per centimeter; and the size of the nonmetal
particles embedded in the matrix ranges from 0.1 to 20
µm.
The favourable tribological properties of such
coatings make them particularly suitable for sliding
components cooperating with cylinder liners, such as the
piston rings of four- and two-stroke engines or piston
pumps, wherein the cylinder liners are normally made of
lamellar, nodular or vermicular cast iron, either
natural or hardened (e.g. laser quenched) or nitrided
(e.g. using the TENIFER (registered trade mark) process
or similar), or present surfaces with hot spray coatings
such as FK1008 formed using the HVOF process (both
registered trade marks).
A number of non-limiting embodiments of the
present invention will be described by way of example
with reference to the accompanying Figures, in which:
Number 1 in Figure 1 indicates a wear-resistant
coating formed according to the present invention on a
substrate 2, e.g. any known mechanical component made of
cast iron. Coating 1 comprises a first layer 3,
preferably no more than 50 µm deep, formed of hard Cr,
and characterized by being continuous, i.e. by
presenting no detectable microcracks or porosity, and no
inclusions of any sort. On top of layer 3, there are
deposited a given number (four in the example) of
substantially identical layers 5a, 5b, 5c, 5d, each
comprising a hard chromium matrix 6 in which are formed
a number of microcracks 7 extending radially depthwise
of layer 5 towards substrate 2, and a disperse phase in
matrix 6 and consisting of a number of particles 8 of
any hard nonmetal material.
According to the present invention, and as shown
clearly, albeit schematically, in Figure 1, a first
number of particles 8 is included in microcracks 7 of
matrix 6, and a second number of particles 8 is embedded
directly inside parts of matrix 6 with no microcracks 7;
and the microcracks 7 of layers 5 deposited on first
layer 3 are offset depthwise in relation to those of the
adjacent layers 5. For example, as shown in the Figure 1
section, microcracks 7 of layer 5b extend depthwise
towards underlying layer 5a and substantially towards
the portions between microcracks 7 of layer 5a, i.e.
towards matrix 6 portions of layer 5a presenting no
microcracks. When viewed from above, the microcracks 7
of each layer 5 present a "spiderweb" pattern along the
interface surface 9 of each layer 5, as shown in Figure
5.
According to the present invention, the width of
the microcracks, measured parallel to each layer 5, is
at least 1 µm; the microcrack density measured at
surfaces 9 ranges from 100 to 300 microcracks per
centimeter of surface; and the size of nonmetal
particles 8 ranges from 0.1 to 20 µm.
According to the present invention, a coating as
described above may be formed electrolytically; layer 3
being formed by galvanically depositing Cr in known
manner using any known chromium plating bath of the type
resulting in no microcracks and containing no particles
in suspension, or operating accordingly with a bath
containing particles in suspension; and layers 5 being
formed using known chromium plating baths of the type
for forming microcracks and containing particles 8 in
suspension. A further precaution to ensure layer 3
presents no microcracks is to limit its thickness, and
to use such operating parameters (current cycles and
density, etc.) as to limit the formation of stress
within the layer due to excessive energy supply.
According to the present invention, to achieve the
above characteristics of layers 5 (particles 8 included
both inside the microcracks and directly in the matrix,
and microcracks offset between one layer and another),
when depositing the layer on to the substrate (or
underlying layer 5), substrate 2 is maintained
permanently at cathode potential, and a pulsating
cathode current varying cyclically in time between a
minimum and maximum value is supplied. Also, the baths
for forming layers 5 and containing particles 8 in
suspension are preferably agitated at all times, e.g. by
means of mechanical, fluidodynamics, energetic
agitators, or by air injection.
The nonmetal particles 8 included in the coating
must be insoluble in the baths which present a chromic
acid, sulphuric acid and catalyst base, are maintained
at a temperature of about 55°C, and present a 20 to 400
gr/liter concentration of particles 8 (ranging in size
between 0.1 and 20 micron). Particles 8 therefore
consist of one or more materials in the group
comprising: tungsten carbide, silicon carbide, chromium
carbide, aluminium oxide, silicon nitride, boron
carbide, diamond, graphite, hexagonal boron nitride.
Each layer 5 may of course include particles 8 all of
the same material or of different materials, and
likewise from one layer to another.
The cathode current supply cycle comprises the
following steps:
- a first step wherein the cathode current is increased in steps to a first threshold value other than zero (roughly 70 amps per square decimeter) and maintained at that value for a first predetermined time ranging from 10 to 60 seconds;
- a second step, superimposed on the first, wherein the cathode current is varied alternately, in a square wave pattern, between the first threshold value and a second threshold value higher than the first; in particular, using a pulse amplitude of 0.2-0.5 times the first threshold value, i.e. 0.2-0.5 x 70 = 14-35 A/dm2, and an oscillation period of 0.01 to 1 second; and for a time ranging from 10 to 60 seconds;
- a third step wherein the cathode current is zeroed in steps and maintained at zero for a third predetermined time ranging from 0.03 to 60 seconds.
The following is a non-limiting embodiment by way
of example of the present invention.
Using a 1500 lt tank, a bath with the following
composition is prepared:
| CrO3 | 250.0 gr/lt; | FeSiF6 | 1.5 gr/lt; |
| H2SO4 | 2.5 gr/lt | SiC | 50.0 gr/lt; |
Lead anodes and a cathode consisting of rings of
lamellar cast iron are immersed in the bath, and a
chromium coating is deposited, agitating the bath by
recirculating roughly 300 lt/min and injecting air at
roughly 5 bar pressure, and operating with a potential
difference of 15 volts and a continuous cathode current
of a mean density of 70 A per square decimeter, which is
varied during deposition according to the following
cycle:
- a first step wherein the cathode current is increased in steps from zero to 70 A/dm2 and maintained at that value for 20 seconds;
- a second step, superimposed on the first, wherein the cathode current is oscillated in a square wave pattern with a bandwidth of 18 A/dm2 and a frequency of 16 Hz for the same time of 20 seconds;
- a third step wherein the cathode current is zeroed in steps and maintained at zero for 0.03 seconds;
- repetition of the cycle from the beginning.
This eventually produces the coating shown in the
Figure 4 section, which presents excellent adherence at
the coating-substrate interface. The Figure 3 photograph
(enlarged 625 times) of the unetched coating, and the
similar top plan view in Figure 5 show the
characteristics of the coating: good adherence, low
microcrack density, and inclusion of silicon carbide
particles both inside and outside the cracks. This is
confirmed by EDS analysis (Figure 6) of specimen pieces,
which shows the typical Cr and Si peaks of a spot
analysis of the matrix far from the cracks.
Claims (10)
- A process for forming, on a substrate, a composite hard chromium coating comprising a disperse phase and particularly suitable for mechanical components subjected to high-temperature chafing; the process comprising the step of galvanically depositing at least one layer of hard chromium in a chromium plating bath of the type forming microcracks and in which is dispersed in suspension a predetermined concentration of given sized particles of a nonmetal insoluble in the bath;
characterized in that, in combination:(i)- in the course of said deposition step, the substrate is maintained permanently at cathode potential; and a pulsating cathode current, varying cyclically in time between a minimum and maximum value, is supplied to achieve a chromium layer comprising a matrix with microcracks of a given distribution, and a disperse phase consisting of said nonmetal particles, some of which are included in the microcracks, and some of which are directly embedded in the matrix;(ii)- said chromium plating bath is a chromic acid based bath, containing in solution prevalently hexavalent chromium. - A process as claimed in Claim 1, characterized in that said deposition step is preceded by the step of depositing on the substrate a continuous hard chromium base layer with substantially no microcracks or porosity and which covers the whole of the substrate; said base layer being formed by galvanically depositing chromium in a chromium plating bath of the type forming no microcracks.
- A process as claimed in Claim 2, characterized in that, on said base layer, there are deposited galvanically a number of said hard chromium layers, each comprising a microcracked matrix and a disperse phase; said layers being so formed that the microcracks of each layer are offset depthwise in relation to the microcracks of the adjacent layers.
- A process as claimed in one of the foregoing Claims, characterized in that said nonmetal particles insoluble in the bath consist of one or more materials in the group comprising: tungsten carbide, silicon carbide, chromium carbide, aluminium oxide, silicon nitride, boron carbide, diamond, graphite, and hexagonal boron nitride.
- A process as claimed in one of the foregoing Claims, characterized in that, during the step of galvanically depositing each said hard chromium layer comprising a microcracked matrix and a disperse phase consisting of said particles embedded in the layer, the cathode current is supplied in a cycle comprising the following steps:a first step wherein the cathode current is brought to and maintained for a first predetermined time at a first threshold value other than zero;a second step, superimposed on the first, wherein the cathode current is varied alternately, in a wave pattern and for a second predetermined time, between said first threshold value and a second threshold value higher than the first; anda third step wherein the cathode current is zeroed and maintained at zero for a third predetermined time.
- A process as claimed in Claim 5, characterized in that, in said second step, the cathode current is varied in a square wave pattern; and in said first and third steps, the cathode current is varied in steps.
- A wear-resistant hard chromium coating, characterized in that it is formed using the process as claimed in one of the foregoing Claims from 1 to 6, so as to present a relatively low hydrogen content
- A wear-resistant hard chromium coating formed electrolytically, comprising a layer in turn comprising a microcracked hard chromium matrix and a disperse phase, in the matrix, consisting of a number of particles of a nonmetal material, and particularly suitable for mechanical components subjected to high-temperature chafing; a first number of said particles being included in the microcracks of the matrix, and a second number of said particles being embedded directly in parts of the matrix with no microcracks;
characterized in that, in combination:(i)- it comprises a first hard chromium layer with substantially no microcracks or porosity and without said particles; and, deposited on said first layer, a number of said layers comprising a microcracked matrix and a disperse phase consisting of said particles;(ii)- the microcracks of said layers deposited on the first layer being provided offset depthwise in relation to the microcracks of the adjacent layers. - A wear-resistant hard chromium coating as claimed in Claim 8, characterized in that the first layer presents a thickness of at least 50 µm.
- A wear-resistant hard chromium coating as claimed in Claim 8 or 9, characterized in that the width of the microcracks, measured parallel to the layer, is at least 1 µm; the density of the microcracks ranges from 100 to 300 microcracks per centimeter; and the size of said nonmetal particles ranges from 0.1 to 20 µm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT94TO000101A IT1267394B1 (en) | 1994-02-18 | 1994-02-18 | PROCEDURE FOR THE PRODUCTION OF HARD CHROME COMPOSITE GALVANIC FINISHINGS WITH A DISPERSED PHASE AND ANTI-WEAR FINISHING MADE WITH |
| ITTO940101 | 1994-02-18 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0668375A1 EP0668375A1 (en) | 1995-08-23 |
| EP0668375B1 true EP0668375B1 (en) | 1999-01-13 |
Family
ID=11412164
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP95102258A Expired - Lifetime EP0668375B1 (en) | 1994-02-18 | 1995-02-17 | Process for forming composite galvanic coatings of hard chromium with a disperse phase, and wear-resistant coating formed thereby |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0668375B1 (en) |
| DE (1) | DE69507172T2 (en) |
| IT (1) | IT1267394B1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19931829A1 (en) * | 1999-07-08 | 2001-01-18 | Federal Mogul Burscheid Gmbh | Galvanic hard chrome layer |
| DE102007050811A1 (en) * | 2007-10-24 | 2009-04-30 | Robert Bosch Gmbh | Wear protection layer and method for its production |
| CN1764745B (en) * | 2004-01-30 | 2012-01-11 | 株式会社理研 | Composite chromium plating film and sliding member having the same and method for manufacture thereof |
| KR101589892B1 (en) | 2008-04-04 | 2016-01-27 | 페데랄-모굴 부르샤이트 게엠베하 | Structured chrome solid particle layer and method for the production thereof |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0841413B1 (en) * | 1996-11-11 | 2001-09-26 | Teikoku Piston Ring Co., LTd. | Composite chromium plating film and sliding member covered thereof |
| US6054225A (en) † | 1996-11-11 | 2000-04-25 | Teikoku Piston Ring Co., Ltd. | Composite chromium plating film and sliding member covered thereof |
| DE19745811C2 (en) * | 1997-10-16 | 2002-06-13 | Federal Mogul Burscheid Gmbh | Electroplated hard chrome layer, use and method for the production thereof |
| SE514700C2 (en) * | 1999-03-19 | 2001-04-02 | Daros Holding Ab | Electrolytic coating of a substrate with a ceramic chrome layer, ceramic chrome layer and piston ring |
| US20020197504A1 (en) * | 1999-12-27 | 2002-12-26 | Hiroyuki Takamura | Sliding member |
| JP4059621B2 (en) * | 2000-09-29 | 2008-03-12 | 日本ピストンリング株式会社 | Chromium plating sliding member and manufacturing method thereof |
| SE521471C2 (en) | 2001-03-27 | 2003-11-04 | Koncentra Holding Ab | Piston ring and coating on a piston ring comprising a composite material of a ceramic and an intermetallic compound |
| DE10255853A1 (en) | 2002-11-29 | 2004-06-17 | Federal-Mogul Burscheid Gmbh | Manufacture of structured hard chrome layers |
| DE102004019370B3 (en) | 2004-04-21 | 2005-09-01 | Federal-Mogul Burscheid Gmbh | Production of optionally coated structurized hard chrome layer, used e.g. for decoration, protection or functional coating on printing roller or stamping, embossing or deep drawing tool uses aliphatic sulfonic acid in acid plating bath |
| DE102005023627B4 (en) * | 2005-05-21 | 2010-05-06 | Federal-Mogul Burscheid Gmbh | Steel Kolbe ring |
| DE102007037778A1 (en) * | 2007-08-10 | 2009-02-12 | Mahle International Gmbh | Hard chrome layer, coated substrate and tribological system |
| CN103403229B (en) | 2010-12-27 | 2016-05-25 | 日本活塞环株式会社 | Composite chrome plating overlay film and use the slide unit of this overlay film |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3531410A1 (en) * | 1985-09-03 | 1987-03-05 | Goetze Ag | GALVANIC HARD CHROME LAYER |
| DE3933896C1 (en) * | 1989-10-11 | 1990-10-11 | Lpw-Chemie Gmbh, 4040 Neuss, De |
-
1994
- 1994-02-18 IT IT94TO000101A patent/IT1267394B1/en active IP Right Grant
-
1995
- 1995-02-17 DE DE69507172T patent/DE69507172T2/en not_active Expired - Fee Related
- 1995-02-17 EP EP95102258A patent/EP0668375B1/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19931829A1 (en) * | 1999-07-08 | 2001-01-18 | Federal Mogul Burscheid Gmbh | Galvanic hard chrome layer |
| CN1764745B (en) * | 2004-01-30 | 2012-01-11 | 株式会社理研 | Composite chromium plating film and sliding member having the same and method for manufacture thereof |
| DE102007050811A1 (en) * | 2007-10-24 | 2009-04-30 | Robert Bosch Gmbh | Wear protection layer and method for its production |
| KR101589892B1 (en) | 2008-04-04 | 2016-01-27 | 페데랄-모굴 부르샤이트 게엠베하 | Structured chrome solid particle layer and method for the production thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1267394B1 (en) | 1997-02-05 |
| ITTO940101A1 (en) | 1995-08-18 |
| ITTO940101A0 (en) | 1994-02-18 |
| DE69507172T2 (en) | 1999-07-22 |
| EP0668375A1 (en) | 1995-08-23 |
| DE69507172D1 (en) | 1999-02-25 |
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