U.S. patent application number 13/517697 was filed with the patent office on 2012-10-25 for process for deposition of amorphous carbon.
Invention is credited to Clark V. Cooper, Michael F. Mullen.
Application Number | 20120267238 13/517697 |
Document ID | / |
Family ID | 36778382 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120267238 |
Kind Code |
A1 |
Cooper; Clark V. ; et
al. |
October 25, 2012 |
PROCESS FOR DEPOSITION OF AMORPHOUS CARBON
Abstract
A method for increasing oil-out survivability in a mechanical
system having a plurality of components each having a least one
surface, includes placing at least one of the plurality of
components into a vacuum chamber having at least one broad-beam ion
gun; supplying an inert gas to the broad-beam ion gun; accelerating
the ionized inert gas to high kinetic energy; cleaning the surface
of the component with the ionized and accelerated inert gas;
supplying a hydrocarbon gas having at least 25 wt % acetylene to
the broad-beam ion gun; ionizing the hydrocarbon gas; accelerating
the ionized hydrocarbon gas to high kinetic energy; and directing
the ionized and accelerated hydrocarbon gas to the surface of the
component at a temperature of about 300.degree. F. or less to
deposit a carbon-based coating thereon.
Inventors: |
Cooper; Clark V.;
(Arlington, VA) ; Mullen; Michael F.; (Cheshire,
CT) |
Family ID: |
36778382 |
Appl. No.: |
13/517697 |
Filed: |
June 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12084604 |
May 6, 2008 |
8222189 |
|
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13517697 |
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Current U.S.
Class: |
204/192.11 |
Current CPC
Class: |
C23C 14/0605
20130101 |
Class at
Publication: |
204/192.11 |
International
Class: |
C23C 14/46 20060101
C23C014/46 |
Claims
1. A method for increasing oil-out survivability in a mechanical
system having a plurality of components each having a least one
surface, comprising the following steps: placing at least one of
said plurality of components into a vacuum chamber having at least
one broad-beam ion gun therein; supplying an inert gas to said at
least one broad-beam ion gun; accelerating said ionized inert gas
to high kinetic energy; cleaning said at least one surface of said
at least one of said plurality of components with said ionized and
accelerated inert gas; supplying a hydrocarbon gas having at least
25 wt % acetylene to said at least one broad-beam ion gun; ionizing
said hydrocarbon gas; accelerating said ionized hydrocarbon gas to
high kinetic energy; and directing said ionized and accelerated
hydrocarbon gas to said at least one surface of said at least one
of said plurality of components at a temperature about 300.degree.
F. or less to deposit a carbon-based coating thereon.
2. The method of claim 1, wherein said hydrocarbon gas has at least
50 wt % acetylene.
3. The method of claim 1, further comprising depositing an
intermediate, adherence-promoting layer onto said at least one
surface of said at least one of said plurality of components prior
to said deposit of said carbon-based coating.
4. The method of claim 3, wherein said intermediate,
adherence-promoting layer includes a transition metal selected from
Periodic Table column IB, IIB, IIIB, VIIB or VIIIB.
5. The method of claim 3, wherein the adherence-promoting
intermediate coating layer includes non-stoichiometric silicon
carbide.
6. The method of claim 3, wherein the adherence-promoting
intermediate coating layer includes silicon and nitrogen.
7. The method of claim 3, wherein the adherence-promoting
intermediate coating layer includes aluminum.
8. The method of claim 1, wherein the carbon-based coating has a
coefficient of friction of less than about 0.5, an atomic hydrogen
content of about 5% to about 25%, and an abrasive wear rate of 10-5
m3 m-1N-1 or less.
9. The method of claim 1, wherein the carbon-based coating has a
hardness of about 10 giga Pascals or more.
10. The method of claim 1, wherein said at least one of said
plurality of components is selected from the group consisting of
iron, aluminum, alloys of the foregoing, and silicon.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present disclosure is a divisional of the U.S. patent
application Ser. No. 12/084,604, filed on May 6, 2008, and is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a dynamic contact surface having a
carbon-based coating. The invention further relates to a mechanical
system that has a contact surface with a carbon-based coating
thereon. The invention still further relates to a process for
making the dynamic contact surface.
[0004] 2. Description of the Prior Art
[0005] Some current helicopter designs utilize a cylindrical
roller/split angular contact ball bearing combination bearing
assembly as the production bearing assemblies for power
transmission subsystems, e.g., the main transmission gearbox. The
cylindrical rollers, contact ball bearings, the cages, and the
inner and outer rings, including the raceways of such bearing
assemblies, are typically formed from iron alloys. Iron alloys
currently employed include Pyrowear 53, a surface-carburized steel
manufactured by Carpenter Technology, and AISI 52100 steel.
[0006] A desirable design feature for helicopter power transmission
gearboxes is the ability to maintain flight operations for sixty
minutes (albeit at reduced power levels sufficient only to sustain
level flight operations) under an "oil-out" condition, i.e., if the
flow of lubricating/cooling oil to the transmission gearbox is
lost. Current production bearing assemblies are not able to provide
the foregoing design feature.
[0007] One approach to provide the desired design feature for
oil-out conditions is to substitute ceramic functional components
for the iron alloy functional components in production bearing
assemblies to reduce contact friction. Another approach is to
employ various coatings to the functional components in production
bearing assemblies to reduce contact friction. The latter approach
is exemplified in U.S. Pat. No. 5,482,602. Neither of the foregoing
approaches provide a reduced level of contact friction sufficient
to provide the desired design feature.
[0008] It would be further desirable to have a dynamic contact
surface having a carbon-based coating exhibiting superior hardness
and low frictional resistance. It would be further desirable to
have a mechanical system having a contact surface(s) with a
carbon-based coating exhibiting superior hardness and low
frictional resistance. It would still be further desirable to have
a process for depositing such a carbon-based coating on a contact
surface. It would yet be further desirable to have a helicopter
transmission that is able to function for an extended period of
time under oil-out conditions.
SUMMARY OF THE INVENTION
[0009] According to an exemplary aspect of the present disclosure,
a method for increasing oil-out survivability in a mechanical
system having a plurality of components each having a least one
surface, includes placing at least one of the plurality of
components into a vacuum chamber having at least one broad-beam ion
gun; supplying an inert gas to the broad-beam ion gun; accelerating
the ionized inert gas to high kinetic energy; cleaning the surface
of the component with the ionized and accelerated inert gas;
supplying a hydrocarbon gas having at least 25 wt % acetylene to
the broad-beam ion gun; ionizing the hydrocarbon gas; accelerating
the ionized hydrocarbon gas to high kinetic energy; and directing
the ionized and accelerated hydrocarbon gas to the surface of the
component at a temperature of about 300.degree. F. or less to
deposit a carbon-based coating thereon.
[0010] In a further non-limiting example, the hydrocarbon gas has
at least 50 wt % acetylene.
[0011] A further non-limiting example of any of the foregoing
examples includes depositing an intermediate, adherence-promoting
layer onto said at least one surface of said at least one of said
plurality of components prior to said deposit of said carbon-based
coating.
[0012] In a further non-limiting example of any of the foregoing
examples, the intermediate, adherence-promoting layer includes a
transition metal selected from Periodic Table column IB, IIB, IIIB,
VIIB or VIIIB.
[0013] In a further non-limiting example of any of the foregoing
examples, the adherence-promoting intermediate coating layer
includes non-stoichiometric silicon carbide.
[0014] In a further non-limiting example of any of the foregoing
examples, the adherence-promoting intermediate coating layer
includes silicon and nitrogen.
[0015] In a further non-limiting example of any of the foregoing
examples, the adherence-promoting intermediate coating layer
includes aluminum.
[0016] In a further non-limiting example of any of the foregoing
examples, the carbon-based coating has a coefficient of friction of
less than about 0.5, an atomic hydrogen content of about 5% to
about 25%, and an abrasive wear rate of 10.sup.-5 m.sup.3
m.sup.-1N.sup.-1 or less.
[0017] In a further non-limiting example of any of the foregoing
examples, the carbon-based coating has a hardness of about 10 giga
Pascals or more.
[0018] In a further non-limiting example of any of the foregoing
examples, the at least one of said plurality of components is
selected from the group consisting of iron, aluminum, alloys of the
foregoing, and silicon.
DESCRIPTION OF THE FIGURES
[0019] FIG. 1 illustrates an exemplary schematic embodiment of an
apparatus for implementing broad-beam ion deposition coating
methods according to the present invention wherein a carbon-based
layer or coating is deposited indirectly or directly on the dynamic
surface of an article.
[0020] FIG. 2 illustrates another exemplary schematic embodiment of
an apparatus for implementing broad-beam ion deposition coating
methods according to the present invention wherein a carbon-based
layer or coating is deposited indirectly or directly on the dynamic
surface of an article.
[0021] FIG. 3 is a partial cross-sectional view depicting a
carbon-based coating indirectly deposited on an interface layer
deposited on the dynamic surface of an article.
[0022] FIG. 4 is a partial cross-sectional view depicting a
carbon-based coating directly deposited on the dynamic surface of
an article.
[0023] FIG. 5 is a process flow chart for one broad-beam ion
deposition coating method according to the present invention
illustrating the steps for depositing a DLC coating indirectly on a
dynamic surface of an article that exhibits adherence
difficulties.
[0024] FIG. 6 depicts optional substeps for the broad-beam ion
deposition coating method of FIG. 5 or 7.
[0025] FIG. 7 is a process flow chart for another broad-beam ion
deposition coating method according to the present invention
illustrating the steps for depositing a DLC coating directly on a
dynamic surface of an article that does not exhibit adherence
difficulties.
[0026] FIG. 8 is a partial cross-sectional view of a cylindrical
roller/split angular contact ball bearing combination bearing
assembly as an exemplary application for the broad-beam ion
deposition coating methods according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] It was surprisingly found that there could be a dynamic
contact surface exhibiting superior hardness, low frictional
resistance, and a low abrasive wear rate. It was further
surprisingly found that there could be a mechanical component
having a contact surface(s) exhibiting superior hardness, low
frictional resistance, and a low abrasive wear rate. It was
surprisingly found that there could be a process for depositing a
carbon-based coating to form such a contact surface. It was
surprisingly found that there could be a helicopter transmission
that is able to function for an extended period of time under
oil-out conditions.
[0028] Contact surfaces coated with the carbon according to the
process of the present invention exhibit a lower proportion of
atomic hydrogen therein than carbon-based coatings made with
processes different than that of the present invention. The
carbon-based coatings made with the process of the present
invention exhibit an atomic hydrogen content of about 5% to about
25%, or more preferably about 5% to about 20%, or even more
preferably about 5% to about 15%, atomic mole percent.
[0029] The reduced atomic hydrogen content of the carbon-based
coatings affords one or more of the following performance
advantages: superior hardness, low frictional resistance, and low
abrasive wear rate. A coated contact surface has a coefficient of
friction of about 0.5 or less, preferably about 0.2 or less, and
most preferably about 0.1 or less. A contact surface has a hardness
of about 10 giga Pascals or more, preferably about 12 giga Pascals
or more, and most preferably about 15 giga Pascals or more. A
contact surface has a abrasive wear rate of about 10N.sup.-1 or
less, more preferably about 10.sup.-1 m.sup.3m.sup.-1 N.sup.-1 or
less, and most preferably about 10.sup.-14 m.sup.-3m.sup.-1N.sup.-1
or less.
[0030] An important feature in coating contact surfaces is the use
of broad beam ion deposition. Another important feature is the use
of acetylene as the ion-generating gas.
[0031] Broad-beam ion deposition is a coating process that may be
considered to be a hybrid CVD-PVD method. It is related to chemical
vapor deposition (CVD) in that the hydrocarbon source gas is
supplied to and dissociated by an ionizing filament that is an
element within the Kaufman ion source. Similarly, it is related to
physical vapor deposition (PVD) processes in that ionized species
are accelerated with significant kinetic energy to clean both
targets and substrates as well as to sputter-deposit atomically
clean target material onto atomically clean substrate surfaces.
Specifically, the sequential steps for performing broad-beam ion
deposition include (1) abrasive and/or solvent cleaning of the
substrate, (2) inserting the cleaned substrate into a suitable
deposition chamber, (3) evacuating the deposition chamber to a
predetermined base pressure, (4) ion-sputter conditioning the
substrate and target surfaces, (5) sputter-depositing an
intermediate, adherence-promoting layer onto the substrate surface,
and (6) depositing a carbon-based coating on the interface layer of
the substrate surface.
[0032] Step (1) of the above-described process entails macroscopic
conditioning of the substrate surface by mechanical and/or chemical
techniques. Step (4), ion-sputter conditioning of the target and
substrate surfaces, is accomplished by ionizing an inert gas to
form an ion beam that has a predetermined beam current density and
accelerating energy and directing the ion beam onto the dynamic
surface. Deposition of an intermediate layer, step (5), is achieved
by ionizing a gas, typically an inert gas such as argon (Ar) or
helium (He) to form an ion beam, having a predetermined beam
current density and accelerating energy, and directing the ion beam
onto a target to dislodge atoms therefrom. After sputter cleaning
the target and substrate surfaces to render them atomically clean,
the dislodged target atoms are collected on the substrate surface
to form the intermediate, adherence-promoting layer. The
predetermined beam current density for ion sputtering conditioning
and interface layer deposition is within the range of about 1.5
mA/cm.sup.2 to about 3.5 mA/cm.sup.2, and preferably about 2.5
mA/cm.sup.2. The predetermined accelerating energy for ion
sputtering conditioning and interface layer deposition is within
the range of about 0.7 keV to about 1.5 keV, and preferably about
1.0 keV. The thickness of the interface layer is within the range
of about 50 to about 500 nm, and preferably within the range of
about 100 nm to about 150 nm.
[0033] The carbon-based coating is deposited on the interface layer
by ionizing a carbon-based gas, which contains acetylene, to form
an ion beam having a predetermined beam current density and a
predetermined accelerating energy and directing the ion beam for
deposition of carbon ions on the intermediate, adherence-promoting
layer for the deposition of the outer carbon-based coating. The
predetermined beam current density for depositing the carbon-based
coating on the intermediate layer is within the range of about 1.5
mA/cm.sup.2 to about 3.5 mA/cm.sup.2, and preferably about 2.5
mA/cm.sup.2. The predetermined accelerating energy for depositing
the carbon-based coating on the interface layer is within the range
of about 200 eV to about 1000 eV, and preferably within the range
of about 450 eV to about 700 eV, and more preferably about 450 eV.
The thickness of carbon-based coatings deposited utilizing the
broad-beam ion deposition coating methods according to the present
invention have a thickness within the range of about 500 nm to
about 2000 nm, and preferably within the range of about 700 nm to
about 1500 nm.
[0034] The process of the present invention employs a precursor
hydrocarbon or carbonaceous gas. The gas is preferably composed
partially or entirely of acetylene. The gas is preferably composed
of at least 25 wt %, more preferably at least 50 wt %, and most
preferably at least 75 wt % of acetylene based on the total weight
of the hydrocarbon content of the gas. Other useful hydrocarbons
that may be used in combination with acetylene are methane, ethane,
propane, and the like.
[0035] FIG. 1 is schematic representation of one exemplary
embodiment of an apparatus 100 for implementing broad-beam ion
deposition coating methods 10 or 10' according to the present
invention wherein a carbon-based coating is deposited indirectly or
directly on one or more dynamic surfaces of an article. FIG. 2 is
another exemplary embodiment of an apparatus 100' for implementing
the broad-beam ion deposition coating methods 10 or 10' according
to the present invention wherein a carbon-based coating is
deposited indirectly or directly on one or more dynamic surfaces of
an article. The apparatuses 100 and 100' are configured to
implement the broad-beam ion deposition processes described
hereinbelow, a hybrid physical vapor deposition-chemical vapor
deposition (PVD-CVD) process wherein the generated plasma cloud is
proximal to the broad-beam ion gun(s), i.e., distal from the
dynamic surface of the article to be coated.
[0036] The apparatus 100 of FIG. 1 includes a deposition chamber
102, a broad-beam ion gun 104 that is operative to generate an ion
beam 104B, a vacuum means 106, e.g., a vacuum line 108 and a vacuum
pump 110, fluidically interconnected to the deposition chamber 102
and operative for evacuating the deposition chamber, a gas supply
means 112, e.g., gas line(s) 114 and one or more gas sources 116,
fluidically interconnected to the broad-beam ion gun 104 and the
deposition chamber 102 for supplying gas thereto, and a target 118.
For the broad-beam ion deposition coating methods described
hereinbelow, the gas line 114 may be alternately fluidically
interconnected to a first gas source 116A, e.g., argon, helium, and
a carbon-based gas source 116M, e.g., acetylene and methane
(alternatively, each individual gas source 116A, 116M may be
fluidically interconnected to the broad-beam ion gun 104 and the
deposition chamber 102 utilizing individual dedicated gas lines
112). The apparatus 100' of FIG. 2 includes the deposition chamber
102, first and second broad-beam ion guns 104-1, 104-2 operative to
generate ion beams 104B-1, 104B2 for steps 22 and 24, respectively,
a vacuum means 106, individual gas supply means 112-1, 112-2 for
the respective broad-beam ion guns 104-1, 104-2, and the deposition
chamber 102, the target 118, and a shutter 119.
[0037] The broad-beam ion gun 104, the vacuum means 106, and the
gas supply means 112 are schematically represented inasmuch as such
systems are conventional and of the type generally known to those
skilled in the art. For example, the broad-beam ion gun 104 is
typically a Kaufman-type broad-beam ion gun (see, e.g. FIG. 7 and
the corresponding disclosure in the specification in U.S. Pat. No.
4,793,908) which is operative to ionize a supplied gas (utilizing a
hot filament such that the generated plasma is adjacent the ion gun
104 and not the surface to be carbon coated) to generate an ion
beam and which may be precisely regulated to accelerate the
resultant ion beam at a predetermined beam current density and a
predetermined accelerating energy. Since such systems are
conventional and generally known to those skilled in the art, a
detailed description of the mechanical and functional
characteristics thereof is not included herein.
[0038] Also exemplarily illustrated in FIGS. 1 and 2 is an article
120 to have deposited thereon a carbon-based coating, with one
dynamic surface 120S thereof positioned within the deposition
chamber 102 for coating by means of the broad-beam ion deposition
coating methods 10, 10' described hereinbelow. The term "article"
as used herein encompasses various types of engineering mechanical
devices and/or manufacturing tooling having one or more surfaces
thereof engaged in interactive rolling and/or sliding frictional
contact with countersurfaces of the same device, a complementary
mechanical device, or a workpiece. The interactive contact surfaces
of such mechanical devices and/or manufacturing tooling are defined
herein as dynamic surfaces. Such dynamic surfaces are subject to
mechanical degradation due to interactive sliding and/or rolling
frictional contact, and are therefore, prime candidates for
carbon-based coatings. Depending upon the complexity of the
structural configuration of a given article, the article may have
one or more distinct dynamic surfaces. As used herein, the term
"dynamic surface" encompasses all dynamic surfaces of an article to
be coated utilizing one of the broad-beam ion deposition coating
methods 10 or 10' according to the present invention. By way of
illustration only, which is not intended to be limiting, specific
applications for the broad-beam ion deposition coating methods 10
or 10' according to the present invention include depositing
carbon-based coatings on the inner and outer raceways (each raceway
comprises a single continuous dynamic surface) of a cylindrical
roller/split angular contact ball bearing combination bearing
assembly (the roller/bearing combination and races are in
predominately rolling frictional contact), depositing carbon-based
coatings on the teeth (each face surface of each gear tooth
comprises a single continuous dynamic surface) of a helicopter main
transmission gear (the interacting gear teeth are in both rolling
and sliding frictional contact), and depositing carbon-based
coatings on the annular microstructures (the flank and land
surfaces of each annular microstructure comprise a single dynamic
surface) of a rolling die (tool) utilized to form detailed heat
transfer surfaces in a copper sheeting workpiece which is
subsequently utilized to fabricate heat exchanger tubing for air
conditioners (the flank, land surfaces of the annular
microstructures engage the workpiece in both sliding frictional
contact (85-80% of total contact) and rolling frictional contact
(15-20% of total contact). A representative non-limiting bearing
assembly is identified by the numeral 150 and is shown in FIG. 8.
Assembly 150 has an inner raceway 152 and an outer raceway 154,
respectively. Assembly 150 also has an inner ring 156 and an outer
ring 158, respectively. Assembly 150 also has an inner raceway 160
and an outer raceway 162, respectively. Assembly 150 also has cages
164 and a rolling element 166, respectively.
[0039] Broad-beam ion deposition coating methods 10, 10' according
to the present invention for depositing a carbon-based coating
indirectly or directly on a dynamic surface 120S are described in
the following paragraphs. The specific broad-beam ion deposition
coating method 10 or 10' utilized to deposit a carbon-based coating
on a dynamic surface 120S depends upon the material composition of
the dynamic surface 120S of the article 120 to be coated. The
dynamic surfaces of articles formed of certain material
compositions may exhibit adherence difficulties with respect to
carbon-based coatings directly deposited thereon. For example, the
dynamic surfaces of articles formed from iron, iron-based alloys,
titanium, and titanium-based alloys may exhibit adherence
difficulties. Carbon ions deposited directly on the dynamic
surfaces of such articles generally exhibit poor bonding with the
dynamic surfaces or no growth. The factors which contribute to this
phenomenon are not well understood, but one contributing factor may
be deposited-carbon diffusion. That is, carbon ions deposited
directly on the dynamic surface diffuse into the article, i.e.,
migrate away from the near-surface region of the dynamic surface.
Deposited-carbon diffusion and other factors (defined herein as
"adherence difficulties") adversely affect the characteristics,
especially the adhesion characteristics, of carbon-based coating
deposited directly on the dynamic surface of such articles. It has
been determined that such articles often require an interface layer
122 (see FIG. 1C), i.e., a layer deposited directly on the dynamic
surface 120S of the article 120, prior to deposition of the
carbon-based coating. The carbon-based coating 124 is subsequently
deposited on the interface layer 122, i.e., the carbon-based
coating is indirectly deposited on the dynamic surface of the
article.
[0040] The interface layer 122 is formed from a material
composition that exhibits good adhesion characteristics with both
the dynamic surface 120S and subsequently deposited carbon-based
coating 124 as a result of broad-beam ion deposition, and is
operative to effectively limit deposited-carbon diffusion into the
article during carbon ion deposition, thereby ensuring enhanced
adhesion characteristics for the subsequently deposited
carbon-based coating. For example, acceptable material compositions
for the interface layer 122 for iron, iron-based alloys, titanium,
and titanium-based alloys include silicon, molybdenum, compounds
based upon these and similar transition metals (columns IIIA-VIIIA,
IB, and IIB of the periodic table), including, for example,
chromium (Cr), nickel (Ni), aluminum (Al), silicon (Si), solid
solutions or compounds containing silicon and carbon (SiC,
stoichiometric or non-stoichiometric; crystalline or amorphous),
solid solutions or compounds containing silicon and nitrogen, and
other transition metals, metalloids, and transition-metal solid
solutions or compounds.
[0041] The preliminary conditioning step involves one or more
substeps that entail macroscopic physical, chemical, and/or
electro-chemical conditioning of the dynamic surface 120S for
broad-beam ion deposition of the interface layer or the
carbon-based coating. Depending upon the structural and functional
characteristics required for the dynamic surface 120S, a mechanical
conditioning substep 12A may be utilized to mechanically prepare
the dynamic surface 120S. For example, the dynamic surface 120S may
be mechanically polished or machine-ground, to enhance the surface
finish thereof for the broad-beam ion deposition of the interface
layer or the carbon-based coating. Further, the dynamic surface
120S may be chemically and/or electro-chemically cleaned in a
substep 12B to remove contaminants therefrom by chemical reaction.
For example, substep 12B may entail degreasing the dynamic surface
120S by washing thereof utilizing one or more solvents. The
solvents utilized in substep 12B depend upon the nature of the
contaminants to be removed, and the selection of such solvent(s) is
within the general knowledge of one skilled in the art. Typically,
organic solvents are utilized in substep 12B.
[0042] The inserting step comprises placing the article 120 within
the deposition chamber 102 and spatially orientating the dynamic
surface 120S of the article 120 with respect to the trajectory of
the ion beam 104B generated by the broad-beam ion gun 104 to
achieve a predetermined trajectory angle .theta.) (see, e.g., FIG.
1) therebetween. Preferably, the dynamic surface 120S is positioned
orthogonal to the ion beam 104B, i.e., trajectory angle .theta.=90
degrees (see FIG. 1), as this spatial orientation ensures the best
adhesion characteristics for broad-beam ion deposition of the
carbon-based coating and the optimal deposition rate. Depending
upon the complexity of the structural configuration of dynamic
surface 120S of the article 120, however, the ion beam 104B may be
non-orthogonally orientated, i.e., angled such that the trajectory
angle (.theta.)<90 degrees, with respect to the dynamic surface
120S to ensure the requisite coating of the dynamic surface 120S.
For example, one application for the broad-beam ion deposition
coating methods 10, 10' according to the present invention involves
depositing a carbon-based coating on the dynamic surface of a
rolling die to enhance the functional characteristics thereof,
e.g., increased hardness, increased wear resistance, and
particularly to provide high lubricity which eliminates the need to
use contaminating lubricants during the forming process since the
high lubricity of a carbon-coated tool significantly reduces
metal-particulate-forming forces. The rolling die must be spatially
orientated at a specific trajectory angle .theta.<90 degrees.
For dynamic surfaces 120S having a complex configuration, e.g., the
rolling die, it may be necessary to reposition the dynamic surface
120S one or more times (or continually) to ensure complete coating
thereof by ion beam deposition according to the methods 10, 10' of
the present invention.
[0043] The deposition chamber 102 is evacuated in step 16 utilizing
the vacuum means (vacuum line 106, vacuum source 108) which is
fluidically interconnected to the deposition chamber 102. For
depositing carbon-based coatings on the working surfaces 120S of
the articles 120 described hereinbelow utilizing the broad-beam ion
deposition coating methods 10, 10' according to the present
invention, the deposition chamber 102 is evacuated to a base
pressure equal to or less than 3.times.10.sup.-5 torr. In preparing
carbon-coated Pyrowear 53 test specimens as described hereinbelow
in further detail, the deposition chamber 102 was evacuated to a
base pressure of about 2.5.times.10.sup.-5 torr.
[0044] The dynamic surface 120S is microscopically conditioned in
the deposition chamber 102 as a precursor to implementing the
broad-beam ion deposition coating method 10 or 10' according to the
present invention. Ion sputtering is utilized for the microscopic
conditioning of step 18 to eliminate unwanted residue remaining
after the preliminary conditioning step 12, e.g., oxides and/or
contaminants that are not amenable to mechanical conditioning
and/or are not soluble in solvents. In addition, ion sputtering
microscopically roughens the dynamic surface 120S to facilitate
subsequent ion deposition of the interface layer 122 (or the
carbon-based coating 124 in the broad-beam ion deposition coating
method 10' described hereinbelow). With respect to FIG. 1, a
sputtering gas such as argon is introduced into the broad-beam ion
gun 104 utilizing the gas supply means 112 (line 114, gas source
116A) where ionization thereof is effected by means of the broad
beam ion gun 104 to form Ar+. The Ar+ ions in the form of the ion
beam 104B are accelerated toward the dynamic surface 120S by the
broad-beam ion gun 104 where the impact energy thereof effectuates
sputter cleaning of the dynamic surface 120S. With respect to FIG.
2, the broad-beam ion gun 104-2 is utilized for ion sputter
conditioning, with the article 120 rotated so that the dynamic
surface 120S thereof is perpendicular to the ion beam 104B-2. The
apparatus 100' of FIG. 2 provides the further capability for ion
sputtering conditioning of the target 118 prior to step 22
utilizing the broad-beam ion gun 104-1. If the target 118 is ion
sputtering conditioned, the shutter 119 is operative to shield the
dynamic surface 120S from any ions dislodged during the target
conditioning procedure. For the described broad-beam ion deposition
coating methods 10, 10' according to the present invention, the
broad-beam ion gun 104 utilizes an accelerating energy within the
range of about 0.7 keV to about 1.5 keV, and preferably about 1.0
keV, and a beam current density within the range of about 1.5
mA/cm.sup.2 to about 3.5 mA/cm.sup.2, and preferably about 2.5
mA/cm.sup.2. The dynamic surface 120S is conditioned for a
predetermined period of time, the time period being dependent,
inter alia, on the acceleration energy and the beam current density
of the ion beam 104B, and the configurational complexity of the
dynamic surface 120S. By way of example, the period for ion
sputtering conditioning of the Pyrowear 53 test specimens was
approximately 300 seconds. In addition to argon gas (which is
inexpensive and works reasonably well), other inert gases such as
helium may be utilized to form ions for the ion sputtering
conditioning of step 18.
[0045] An interface layer 122 (see FIG. 3) is deposited on the
dynamic surface 120S in step 20. A gas such as argon (Ar) is
supplied to the broad-beam ion gun 104 (the broad-beam ion gun
104-1 of FIG. 2) by means of the gas supply means 112 (the gas
supply means 112-1). The supplied gas is ionized to form the ion
beam 104B (the ion beam 104B-1) and accelerated towards the target
118 by the broad-beam ion gun 104 (broad-beam ion gun 104-1). The
accelerating energy for step 20 is within the range of about 0.7
keV to about 1.5 keV, and preferably about 1.0 keV, and a beam
current density within the range of about 1.5 mA/cm.sup.2 to about
3.5 mA/cm.sup.2, and preferably about 2.5 mA/cm.sup.2.
[0046] The target 118 is fabricated from a material composition
that exhibits good adhesion characteristics with both the material
composition of the dynamic surface 120S and the subsequently
deposited carbon-based coating 124, and that inhibits carbon ion
diffusion. As disclosed hereinabove, acceptable material
compositions for the target 118 for the dynamic surfaces 120S of
articles 120 fabricated from iron, iron-based alloys, titanium, and
titanium-based alloys include silicon, molybdenum, compounds and
solid solutions based upon these and similar transition metals
(columns IIIA-VIIIA, IB, and IIB of the periodic table), including,
for example, chromium, aluminum, and silicon. The target 118 is
interposed between the broad-beam ion gun 104 (the broad-beam ion
gun 104-1) and the dynamic surface 120S, i.e., in the trajectory of
the ion beam 104B (ion beam 104B-1), so that the accelerated ions
comprising the ion beam 104B (ion beam 104B-1) impact the target
118. The impact energy of the accelerated ions is sufficient to
dislodge atoms from the target 118, the dislodged atoms being
subsequently deposited on the dynamic surface 120S to form the
interface layer 122. The interface layer 122 is operative to
provide an effective diffusion barrier for the carbon ions to be
deposited in step 22 to form the carbon-based coating. The
interface layer 122 formed in step 20 should have a thickness
sufficient to inhibit deposited-carbon diffusion. It has been
determined that interface layers 122 having a thickness within the
range of about 100 nm to about 150 nm satisfactorily inhibit
deposited-carbon diffusion. Subsequent to the deposition of the
interface layer 122 on the dynamic surface 120S, the target 118 of
the apparatus 100 is removed from the trajectory of the ion beam
104B generated by the broad-beam ion gun 104.
[0047] The material composition of the target 118 and the partial
pressure of gases in the deposition chamber 102 in combination
determine the composition of the interface layer 122 deposited on
the dynamic surface 120S. For example, the target 118 may be
fabricated from silicon (Si) to form a silicon interface layer 122
on the dynamic surface 120S that is operative to inhibit
deposited-carbon diffusion where the dynamic surface 120S of the
article 120 is fabricated from material composition such as iron,
iron-based alloys, titanium, or titanium-based alloys. If argon gas
is supplied to the broad-beam ion gun 104 (broad-beam ion gun
104-1) in step 20, Ar+ ions are accelerated therefrom to impact the
Si target 118 with sufficient impact energy to dislodge Si atoms
from the Si target 118, the dislodged Si atoms possessing
sufficient impact energy to be deposited on the dynamic surface
120S to form an interface layer 122 of elemental silicon (Si). If
acetylene gas at a predetermined partial pressure is present in the
deposition chamber 102 during sputtering of the silicon target 118
by Ar+ ions, the dislodged Si atoms combine with the acetylene gas
molecules in the deposition chamber 102 and are deposited on the
dynamic surface 120S to form an interface layer 122 of amorphous
silicon-carbon-hydrogen, i.e., a-Si:C:H, on the dynamic surface
120S. In fabricating the Pyrowear 53 test specimens described
hereinbelow, acetylene gas at a predetermined partial pressure of
about 1.5.times.10.sup.-4 torr was present in the deposition
chamber 102. Broader ranges of acetylene gas partial pressures are
possible, such as about 1.5.times.10.sup.-5 to about
1.times.10.sup.-3 torr. A partial pressure of 1.5.times.10.sup.-4
torr is preferred.
[0048] Carbon-based coating 124 is deposited on the interface layer
122. As a general rule, the deposition of the carbon-based coating
124 is more sensitive to process parameters, i.e., accelerating
energy, beam current density, than the deposition of the interface
layer 122. A carbon-based gas (as used herein, a carbon-based gas
is a gas that provides carbon ions (C+) when dissociated or
ionized, e.g., a hydrocarbon gas such as acetylene (C.sub.2H.sub.2)
and methane (CH.sub.4) or a gas that produces hydrocarbons as a
result of decomposition or reaction) is supplied to the broad-beam
ion gun 104 (broad-beam ion gun 104-2) by the gas supply means 112
(gas supply means 112-2) and ionized by the broad-beam ion gun 104
(broad-beam ion gun 104-2) to provide, inter alia, a supply of
carbon ions (C+). Where acetylene is utilized as the supply gas,
the resulting carbon ions (C+) and hydrogen ions (H+) comprising
the ion beam 104B (ion beam 104B-2) are accelerated toward the
dynamic surface 120S by the broad-beam ion gun 104 (broad-beam ion
gun 104-2). The carbon ions (C+) deposited on the interface layer
122 form the carbon-based coating 124 for the dynamic surface 120S.
It will be appreciated that hydrogen ions (H+) are also deposited
on the interface layer 122. Secondary ion mass spectrometry (SIMS)
was employed to estimate the concentration of hydrogen incorporated
in carbon-based coatings 124 deposited on a dynamic surface 120S
utilizing one of the broad-beam ion deposition coating methods 10,
10' according to the present invention. SIMS results indicate that
the concentration of hydrogen in such carbon-based coatings 124, in
which methane (CH.sub.4) is used as the carbonaceous (hydrocarbon)
source gas is approximately 30 atomic percent; conversely,
carbon-based coatings synthesized according to the present
invention, in which acetylene (C.sub.2H.sub.2) is used as the
source gas, incorporate hydrogen in a concentration of about 5-25
atomic percent.
[0049] The accelerating energy for step 22 should be within the
range of about 200 eV to about 1000 eV, and preferably within the
range of about 450 eV to about 700 eV, and more preferably about
450 eV. If the accelerating energy provided by the broad-beam ion
gun 104 is too high, i.e., >about 1000 eV, the impact energy of
the ions deposited onto the dynamic surface 120S will cause
resputtering. That is, previously deposited ions will be ejected
from the dynamic surface 120S by the impact energy of incoming
ions, i.e., the high impact energy thereof. If the accelerating
energy provided by the broad-beam ion gun 104 is too low, i.e.,
<about 200 eV, the interface layer formed by the deposited ions
exhibits poor adhesion characteristics due to the low impact energy
of the deposited ions. The beam current density of the generated
ion beam 104B (ion beam 104B-2) should be within the range of about
1.5 mA/cm.sup.2 to about 3.5 mA/cm.sup.2, and preferably about 2.5
mA/cm.sup.2.
[0050] The specific thickness of the carbon-based coating 124 is
determined in part by the load forces to which the carbon-coated
dynamic surface 120S is to be subjected to and in part by the type
of frictional contact to which the carbon-coated dynamic surface
120s is to be subjected to. It has been determined that when the
dynamic surface 120S is subjected to pure rolling frictional
contact, e.g., cylindrical roller bearings, the most effective
thickness for the carbon-based coating 124 is less than the
carbon-coating thickness required when the dynamic surface 120S is
subjected exclusively to sliding frictional contact. Pragmatically,
however, most dynamic surfaces 120S will be subjected to an
admixture of rolling and sliding frictional contact, and therefore
the thickness requirement for the carbon-based coating 124 will be
within the range defined between pure sliding frictional contact
and pure rolling frictional contact. For example, the rolling die
described hereinbelow is subject to about 15-20% sliding frictional
contact and about 85-80% rolling frictional contact. It has been
determined that carbon-based coatings 122 having a thickness within
the range of about 500 nm to about 2000 nm, and preferably within
the range of about 700 nm to about 1500 nm, are sufficient for most
engineering device and manufacturing tooling applications.
[0051] "Oil-out survivability" is defined to be the ability of a
component within a mechanical system or the entire mechanical
system itself, to survive and continue to operate (execute its
intended function) in the event that the supply of lubricant is
interrupted or compromised. Such conditions include, but are not
limited to, diminished lubricant supply caused by accelerations
during aircraft maneuvers; failure of components that comprise the
lubrication system, including but not limited to the oil pump;
ballistic damage to the mechanical system housing or other
components within the system caused by arms fire or explosion;
mis-assembly of components within the mechanical system or the
entire mechanical system; and failure of components within other
systems or failure of other entire systems, resulting in
degradation or disruption of the lubrication system or the
lubricant, such as but not limited to lubricant dilution with fuel,
hydraulic fluid, and the like.
[0052] "Inert gas" is defined to be any member or plurality of
members of group 18 (group 8A) elements of the periodic table,
including argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon
(Xe), and radon (Rn).
[0053] "Carbon-based coating" is defined to be a coating that is
deposited by means of a physical (PVD) or chemical (CVD) vapor
deposition process, or a hybrid PVD-CVD process, in which carbon is
the major constituent (element). Carbon shall constitute the
"major" element in the event that it comprises 50 atomic percent or
more of all constituents. The "carbon-based coating" may be
crystalline or amorphous or contain structures and other
characteristics of both crystalline and amorphous phases.
[0054] "Adherence-promoting intermediate coating layer" is defined
to be any coating that lies between the component substrate and the
carbon-based coating that increases the level of adherence or
adhesion between the carbon-based coating and the component
substrate. Examples include, but are not limited to, chromium (Cr),
nickel (Ni), aluminum (Al), silicon (Si), solid solutions or
compounds containing silicon and carbon (SiC, stoichiometric or
non-stoichiometric; crystalline or amorphous), solid solutions or
compounds containing silicon and nitrogen, and other transition
metals, metalloids, and transition-metal solid solutions and
compounds.
[0055] Other teachings regarding useful techniques for broad beam
ion deposition are disclosed in U.S. Pat. No. 5,482,602, which is
incorporated herein in its entirety.
[0056] The following are examples of the present invention. The
examples are illustrative of the invention and not to be construed
as limiting.
EXAMPLES
Comparative Example 1
[0057] A carbon-based coating was deposited via broad-beam ion
deposition onto steel substrates using dissociated acetylene
(C.sub.2H.sub.2) at a temperature of about 120.degree. C. A
comparative carbon-based coating was likewise deposited using
dissociated methane at a temperature of about 100.degree. C. The
coatings were tested for nanoindentation (ultralow-load
indentation) to measure the hardness and indentation modulus.
Hardness and indentation modulus were measured with a Nanoindenter
XP (MTS Nano Instruments Co.)
[0058] The acetylene-derived coating exhibited far superior to
hardness and indentation elastic modulus to the methane-derived
coating. The acetylene-derived coating exhibited a hardness and
indentation elastic modulus of 23.6 and 206 GPa, respectively.
These values exceeded those of the methane-derived coating by
multiples of 3.1 and 3.5 times greater, respectively.
Example 2
[0059] To demonstrate the efficacy of the broad-beam ion deposition
coating method, several test specimens composed of the Pyrowear 53
(Carpenter Technology) alloy had a-C:H coatings of different
thicknesses deposited thereon via the broad-beam ion deposition
method taught in U.S. Pat. No. 5,482,602. The Pyrowear 53 test
specimens were first mechanically polished and then thoroughly
degreased in organic solvents. The prepared Pyrowear 53 test
specimens were introduced into the broad-beam, ion-deposition
chamber in such a manner that the functional surfaces thereof were
orthogonal to the ion beam generated by the broad-beam ion gun. The
deposition chamber was evacuated to a base pressure of
approximately 2.5.times.10.sup.-5 torr, and the Pyrowear 53 test
specimens were ion-sputter cleaned with Ar.sup.+ at an accelerating
energy of about 1.0 keV and a beam current density of 2.5
mA/cm.sup.2. Since Pyrowear 53 is an iron-based alloy, it is
subject to adherence difficulties. Therefore, an interface layer
composed of Si or amorphous hydrogenated silicon carbide (a-Si:C)
was deposited to the sputter-cleaned test specimens to a thickness
of approximately 100 nm. While methane (CH.sub.2) gas was taught as
the preferred precursor carbonaceous or hydrocarbon gas in U.S.
Pat. No. 5,482,602, additional research conducted since its
issuance has demonstrated that a-C:H coating possessing superior
qualities may be achieved through the use of acetylene (ethene,
C.sub.2H.sub.2) as the precursor hydrocarbon or carbonaceous source
gas. Accordingly, C.sub.2H.sub.2 was utilized as the hydrocarbon
precursor gas for the deposition of a-C:H coatings in the thickness
range from approximately 700 to 1500 nm onto the Si or a-SiC
interface layer of the Pyrowear 53 test specimens. The accelerating
energy for the deposition of the a-C:H coating layer was 450 eV,
and the current density of the ion beam was 2.5 mA/cm.sup.2. As
noted above, U.S. Pat. No. 5,482,602 teaches, as a preferred
embodiment, the use of C.sub.2H.sub.2 as the hydrocarbon precursor
source gas for deposition of the a-C:H coating; however, based on
more recent research results by the applicants, a preferred
embodiment for the present invention includes the use of
C.sub.2H.sub.2 as the precursor source gas, as the properties of
the resulting coating have been observed to be superior to those
that resulted from the use of CH.sub.4.
[0060] The a-C:H-coated Pyrowear 53 specimens were subsequently
subjected to 50,000 specimen rotations in unlubricated sliding
frictional contact, to simulate operation in an oil-starved
condition, against countersurfaces of several different types of
uncoated counterbodies, including the surface-carburized iron
alloy, Pyrowear 53, Norton/Cerbec's NBD 200 hot-pressed
Si.sub.3N.sub.4, and the through-hardened steel alloy, AISI M50.
Experimental results indicate that the a-C:H-coated Pyrowear 53
specimens have a coefficient of friction that is significantly
lower than that of the uncoated specimen by a factor of nearly
10.times., even though the a-C:H-coated Pyrowear 53 specimens were
subjected to a higher contact stress. In addition, the wear rate of
the a-C:H-coated Pyrowear 53 test specimens was lower than the
standard Pyrowear 53 specimen by a factor of 700.times., receding
at the end of 50,000 specimen rotations less than 1 .mu.m and
approximately 500 .mu.m for the coated and uncoated components,
respectively. A slight wear track was detected in the a-C:H-coated
Pyrowear 53 test specimens, but no detectable wear scars were
observed in the uncoated counterbodies up to 500.times.
magnification, indicating that frictional contact between an
uncoated surface with an a-C:H-coated surface causes no perceptible
degradation to the uncoated surface.
[0061] To further demonstrate the efficacy of the broad-beam ion
deposition coating methods for depositing a a-C:H coating on the
surface of bearing assemblies for helicopter main transmission
gearboxes, rig testing of several bearing assemblies in an
oil-starved condition was conducted. The tested bearing assemblies
included a baseline cylindrical roller/split angular contact ball
bearing combination bearing assembly as exemplarily illustrated in
FIG. 8, an SB-1231 bearing assembly, wherein the functional
components thereof are fabricated of Pyrowear 53, a modified
baseline bearing assembly having monolithic, hot pressed
Si.sub.3N.sub.4 rolling elements substituted for the Pyrowear 53
roller bearing elements, and a modified baseline bearing assembly
having a-C:H-coated inner and outer raceways utilizing the
broad-beam ion deposition coating method described above. While
only the inner and outer raceways of the a-C:H-modified bearing
assembly were a-C:H coated for rig testing, one skilled in the art
will appreciate that, alternatively, the cylindrical rollers and
split angular contact ball bearings may be a-C:H coated, or that
both the inner and outer raceways and the rollers and ball bearings
may be a-C:H coated.
[0062] Rig testing protocol involved heating the lubricating oil
flow of approximately 0.6 gallons/minute to a nominal bearing
assembly operating temperature of approximately 121.degree. C.
(250.degree. F.) while subjecting the running bearing assembly,
operating at a rotational speed of 14,400 RPM, to partial loading
(about 2250-2750 lbs). Following thermal stabilization of the
lubricating oil at the nominal operating temperature, the oil flow
was terminated and the lubricating oil was drained from the gearbox
to simulate an oil-out (oil-starved) condition.
[0063] As noted above, the baseline, uncoated bearing assembly
failed after only 120 seconds of operation in the oil-out
condition. The modified baseline bearing assembly incorporating
Si.sub.3N.sub.4 roller bearing elements exhibited a time-to-failure
of approximately minutes, nonetheless failing the 60-minutes DoD
(Department of Defense) requirement. The failures of the baseline
bearing assembly and the ceramic-modified bearing assembly were
attended by thermal instabilities within the power transmission
subsystem. The a-C:H-modified bearing assembly, in contrast,
operated successfully for a full 60 minutes in an oil-out
condition. Following the application of test conditions for
approximately 292 seconds, the lubricating oil flow was terminated,
at which point the temperature of the a-C:H-modified bearing
assembly began to rise. The highest temperature achieved by the
a-C:H-modified bearing assembly was approximately 243.degree. C.
(470.degree. F.). While this is higher than the nominal bearing
assembly operating temperature of approximately 121.degree. C.
(250.degree. F.), such a temperature is within acceptable limits
for a bearing assembly operating in a helicopter main transmission
gearbox.
[0064] While the foregoing examples illustrate the efficacy and
superiority of an a-C:H coating deposited on a cylindrical
roller/split angular contact ball bearing combination bearing
assembly utilizing the broad-beam ion deposition coating method,
one skilled in the art will appreciate that the methods described
herein have utility for depositing a-C:H coatings to other types of
bearing assemblies. For example, the broad-beam ion deposition
coating methods according to the present invention have utility for
depositing a-C:H coatings to one or more contact surfaces of other
types of bearing assemblies having utility in helicopter
applications; examples include a cylindrical roller bearing
assembly having a spherical thrust shoulder, a high speed tapered
roller bearing assembly, and a single row, angular contact
spherical roller bearing assembly. One skilled in the art will also
appreciate that the broad-beam ion deposition coating methods
according to the present invention are not limited to bearing
assemblies utilized in helicopter applications. The broad-beam ion
deposition coating methods according to the present invention also
have utility for depositing a-C:H coatings on the dynamic or
functional surfaces of bearing assemblies having utility in other
diverse applications.
[0065] It should be understood that the foregoing description is
only illustrative of the present invention. Various alternatives
and modifications can be devised by those skilled in the art
without departing from the invention. Accordingly, the present
invention is intended to embrace all such alternatives,
modifications and variances that fall within the scope of the
appended claims.
* * * * *