U.S. patent application number 15/993932 was filed with the patent office on 2019-12-05 for coatings containing nickel-tungsten plating layers and methods for the production thereof.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. The applicant listed for this patent is HONEYWELL INTERNATIONAL INC.. Invention is credited to Gangmin Cao, Ersan Ilgar, Jingkang Lv, James Piascik.
Application Number | 20190368065 15/993932 |
Document ID | / |
Family ID | 66677039 |
Filed Date | 2019-12-05 |
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United States Patent
Application |
20190368065 |
Kind Code |
A1 |
Cao; Gangmin ; et
al. |
December 5, 2019 |
COATINGS CONTAINING NICKEL-TUNGSTEN PLATING LAYERS AND METHODS FOR
THE PRODUCTION THEREOF
Abstract
Coatings containing nickel-tungsten (NiW) plating layers are
provided, as are methods for forming coatings and NiW plating
layers over metallic components. In embodiments, the method
includes preparing a plating bath containing a tungsten (W) ion
source; inserting at least one consumable nickel (Ni) electrode and
at least a portion of the metallic component into the plating bath;
and, afterwards, electrodepositing a NiW plating layer over the
component surface by energizing the at least one consumable Ni
electrode as an anode and the metallic component as a cathode to
attract Ni ions and W ions to the component surface. An amount of
anode corrosion accelerant in the plating bath is controlled to
balance Ni dissolution at the anode to Ni deposition at cathode, as
considered in conjunction with any additional Ni ion sources within
the plating bath, to achieve a desired composition of the
electrodeposited NiW layer.
Inventors: |
Cao; Gangmin; (Shanghai,
CN) ; Piascik; James; (Randolph, NJ) ; Lv;
Jingkang; (Shanghai, CN) ; Ilgar; Ersan;
(Morristown, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HONEYWELL INTERNATIONAL INC. |
Morris Plains |
NJ |
US |
|
|
Assignee: |
HONEYWELL INTERNATIONAL
INC.
Morris Plains
NJ
|
Family ID: |
66677039 |
Appl. No.: |
15/993932 |
Filed: |
May 31, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 21/12 20130101;
C25D 5/48 20130101; C25D 3/562 20130101; C25D 21/14 20130101; C25D
17/12 20130101 |
International
Class: |
C25D 3/56 20060101
C25D003/56; C25D 17/12 20060101 C25D017/12; C25D 21/12 20060101
C25D021/12 |
Claims
1. A method for forming a coating over a component surface of a
metallic component, the method comprising: preparing a plating bath
containing a tungsten (W) ion source; inserting at least one
consumable nickel (Ni) electrode and at least a portion of the
metallic component into the plating bath; after insertion of the at
least one Ni electrode and the component surface into the plating
bath, electrodepositing a nickel-tungsten (NiW) plating layer over
the component surface by energizing the at least one consumable Ni
electrode as an anode and the metallic component as a cathode to
attract Ni ions and W ions to the component surface; and
controlling an amount of anode corrosion accelerant in the plating
bath to balance Ni dissolution at the anode to Ni deposition at
cathode, considered in conjunction with any additional Ni ion
sources within the plating bath, to achieve a desired composition
of the electrodeposited NiW layer.
2. The method of claim 1 further comprising selecting the anode
corrosion accelerant to comprise chloride.
3. The method of claim 2 further comprising adding the chloride to
the plating bath as at least one of the group consisting of nickel
chloride, sodium chloride, and hydrochloric acid.
4. The method of claim 2 further comprising maintaining the anode
corrosion accelerant in a range between about 0.0002 to about 0.01
moles chloride per liter of plating bath solution during the
electrodeposition process.
5. The method of claim 4 wherein maintaining comprises maintaining
the anode corrosion accelerant in a range between 0.0008 to about
0.0025 moles chloride per liter of plating bath solution during the
electrodeposition process.
6. The method of claim 1 further comprising preparing the plating
bath to further contain ammonium hydroxide ions in a concentration
range of about 1.0 to about 2.0 moles per liter of plating bath
solution.
7. The method of claim 6 wherein the plating bath is prepared to
further contain ammonium hydroxide ions in a concentration range of
1.3 to 2.7 moles per liter of plating bath solution.
8. The method of claim 1 further comprising formulating the plating
bath and controlling process parameters during electrodeposition of
the NiW plating layer such that Ni ions are present within the
plating bath in a concentration range of about 0.085 to about 0.307
moles per liter of plating bath solution.
9. The method of claim 8 wherein formulating comprises formulating
the plating bath and controlling process parameters during
electrodeposition of the NiW plating layer such that Ni ions are
present within the plating bath in a concentration range of 0.187
to 0.230 moles per liter of plating bath solution.
10. The method of claim 1 further comprising selecting the at least
one consumable Ni electrode to comprise consumable Ni pellets.
11. The method of claim 10 further comprising repeatedly adding
fresh consumable Ni pellets to the plating bath as the
electroplating process progresses to maintain a ratio between a
cumulative surface area of the consumable Ni pellets and a surface
area of the contact surface within a predetermined range.
12. The method of claim 1 wherein energizing comprises energizing
the at least one consumable Ni electrode and the metallic component
at a current density between 1 and 5 ampere per decimeter
squared.
13. The method of claim 1 further comprising formulating the
plating bath to further contain citric acid in a quantity ranging
from 90 to 150 grams per liter of the plating bath.
14. The method of claim 1 wherein the metallic component comprises
a connector terminal having a contact resistance, wherein
electrodepositing comprises electrodepositing the NiW plating layer
directly onto the component surface, and wherein the method further
comprises depositing at least one gold layer directly onto the NiW
plating layer to decrease the contact resistance of the connector
terminal.
15. The method of claim 1 further comprising selecting the target W
content of the NiW plating to range from about 25% to about 35% by
weight.
16. A method for forming a coating over a component surface of a
metallic component, the method comprising: preparing a plating bath
solution to comprise: about 0.0002 to about 0.01 moles of an anode
corrosion accelerant per liter of the plating bath solution; and a
tungsten (W) ion source; inserting at least one consumable nickel
(Ni) electrode and at least a portion of the metallic component
into the plating bath; and energizing the at least one consumable
Ni electrode as an anode and the metallic component as a cathode to
electrodeposit a nickel-tungsten (NiW) plating layer over the
component surface.
17. The method of claim 16 further comprising selecting the anode
corrosion accelerant to comprise chloride.
18. The method of claim 16 further comprising forming the NiW
plating layer to consist essentially of: between 25% and 35% W by
weight; and the remainder Ni.
19. The method of claim 16 wherein preparing comprises preparing
the plating bath solution to further contain ammonium hydroxide
ions in a concentration range between about 1.0 to about 2.0 moles
per liter of the plating bath solution.
20. A coating formed over a metallic component having a component
surface, the coating comprising: an electrodeposited
nickel-tungsten (NiW) plating layer formed over and in contact with
the component surface, the electrodeposited NiW plating layer
comprising: at least 50% Ni by weight; and between 25% and 35% W by
weight; and at least one gold (Au) layer formed over and in contact
with the electrodeposited NiW plating layer, the at least one Au
layer having a thickness less than a thickness of the NiW plating
layer.
Description
TECHNICAL FIELD
[0001] The following disclosure relates generally to coatings
formed over articles of manufacture and, more particularly, to
coatings and methods for producing coatings, which contain or
consist of nickel-tungsten plating layers, over metallic
components.
ABBREVIATIONS
[0002] Abbreviations appearing relatively infrequently in this
document are defined upon initial usage, while abbreviations
appearing more frequently in this document are defined below.
[0003] Au--Gold; [0004] Cu--Copper; [0005] Ni--Nickel; [0006]
NiW--Nickel-tungsten; and [0007] W--Tungsten.
BACKGROUND
[0008] In high performance applications, Au plating layers are
often electrodeposited over surfaces of electrical connectors to
minimize resistance between points of contact. For example, in the
case pin-and-socket electrical connectors, Au plating layers may be
formed over the terminals (pins) of the male connector and over the
terminals (sockets) of the female connector to decrease contact
resistance across the connectors when joined. In certain instances,
a barrier layer composed of essentially pure, electroplated Ni may
be provided between the outer Au plating layer and the connector
terminal body. The provision of the pure Ni plating layer may serve
as a barrier layer, which reduces diffusion of the Au plating layer
into the terminal body, which may be composed of a less costly,
electrically-conductive metal or alloy, such as Cu. The Ni plating
layer may also increase the wear resistance of the coated connector
terminal and protect the connector terminal from corrosion or other
chemical degradation, which may otherwise occur over time.
[0009] While providing the above-noted benefits, pure Ni plating
layers remain limited in multiple respects. Often, the enhancements
to wear and corrosion resistance achieved by incorporating a pure
Ni plating layer into a particular coating system are modest.
Further, while relatively straightforward and well-established, the
plating processes utilized to electrodeposit pure Ni plating layers
are likewise associated with various drawbacks. For example, Ni
electrodeposition processes are often prone to relatively
pronounced pH swings and the accumulation of undesired chemical
species, such as sulfates (SO.sub.4) and sodium (Na), within the
plating bath. The accumulation of such undesired chemical species
tends to limit bath performance and lifespan, which, in turn,
increases material and processing costs. As a yet further
limitation, conventional Ni electrodeposition processes often
achieve relatively sluggish deposition rates (e.g., on the order of
0.23 milliinch (mil) per hour) and may thus require several hours
to deposit Ni plating layers to even moderate thicknesses.
[0010] There thus exists a continued demand for methods for
electrodepositing Ni-containing layers having enhanced wear and
corrosion resistance properties, while also possessing
nanocrystalline structures lacking microcracks and other structural
defects. More generally, there exists an ongoing demand for methods
by which coatings containing nanocrystalline Ni-containing barrier
layers can be fabricated, whether the Ni-containing layer is
provided as a standalone protection solution (e.g., to provide
enhanced wear resistance on sliding surfaces) or is instead
combined with other materials layers (e.g., one or more Au plating
layers) to form a coating system over surfaces of metallic
articles, such as the contact surfaces of electrical connectors.
Other desirable features and characteristics of embodiments of the
present invention will become apparent from the subsequent Detailed
Description and the appended Claims, taken in conjunction with the
accompanying drawings and the foregoing Background.
BRIEF SUMMARY
[0011] Coatings containing NiW plating layers are provided, as are
methods for forming coatings and NiW plating layers over metallic
components. In various embodiments, the method includes the steps
or processes of preparing a plating bath containing a W ion source;
inserting at least one consumable Ni electrode and at least a
portion of the metallic component into the plating bath; and, after
insertion of the at least one Ni electrode and the component
surface into the plating bath, electrodepositing a NiW plating
layer over the component surface by energizing the at least one
consumable Ni electrode as an anode and the metallic component as a
cathode to attract Ni ions and W ions to the component surface. An
amount of anode corrosion accelerant in the plating bath is
controlled to balance Ni dissolution at the anode to Ni deposition
at cathode, as considered in conjunction with any additional Ni ion
sources within the plating bath, to achieve a desired composition
of the electrodeposited NiW layer.
[0012] In other embodiments, the coating formation method includes
the step or process of preparing a plating bath solution to
contain: (i) about 0.0002 to about 0.01 moles of an anode corrosion
accelerant, such as chloride, per liter of the plating bath
solution; and (ii) a W ion source. At least one consumable Ni
electrode and at least a portion of the metallic component is
inserted into the plating bath. The at least one consumable Ni
electrode is then energized as an anode, while the metallic
component is concurrently energized as a cathode to electrodeposit
a NiW plating layer over the component surface. In certain
embodiments, the NiW plating layer may be formed to consist
essentially of between 25% and 35% W by weight, with the remainder
Ni. In other embodiments, the plating bath solution may be prepared
to further contain ammonium hydroxide ions in a concentration range
between about 1.0 to about 2.0 moles per liter of the plating bath
solution.
[0013] Coatings or coating systems are further provided, which are
formed over selected surfaces of metallic components. In
embodiments, the coating includes an electrodeposited NiW plating
layer, which is formed over and in contact with the component
surface. The electrodeposited NiW plating layer contains at least
50% Ni by weight, as well as between 25% and 35% W by weight. At
least one Au layer is formed over and contacts the electrodeposited
NiW plating layer, with the at least one Au layer having a
thickness less than a thickness of the NiW plating layer. In at
least some implementations, the electrodeposited NiW plating layer
consists essentially of about 30% W by weight, with the reminder
Ni.
[0014] Various additional examples, aspects, and other useful
features of embodiments of the present disclosure will also become
apparent to one of ordinary skill in the relevant industry given
the additional description provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] At least one example of the present invention will
hereinafter be described in conjunction with the following figures,
wherein like numerals denote like elements, and:
[0016] FIG. 1 is a flowchart of a method for producing a coating
including or consisting of a NiW plating layer formed over selected
surfaces of a metallic component, such as the terminals of an
electrical connector or the sliding surfaces of a high temperature
(e.g., engine) component, as illustrated in accordance with an
exemplary embodiment of the present disclosure;
[0017] FIG. 2 is a schematic of an exemplary NiW plating apparatus,
which can be utilized to electrodeposit an NiW plating layer over
selected surfaces of a metallic component, when carrying-out the
method of FIG. 1;
[0018] FIG. 3 is a simplified cross-sectional view of a limited
region of an exemplary coating containing an NiW plating layer and
an Au topcoat, which are formed over an underlying metallic
component and which can be produced pursuant to the method of FIG.
1 in an exemplary embodiment; and
[0019] FIG. 4 is an isometric view of a female electrical connector
and the pins of a mating male electrical connector (the remainder
of which is not shown for clarity), both of which contain terminals
over which the disclosed coatings are usefully formed.
[0020] For simplicity and clarity of illustration, descriptions and
details of well-known features and techniques may be omitted to
avoid unnecessarily obscuring the exemplary and non-limiting
embodiments of the invention described in the subsequent Detailed
Description. It should further be understood that features or
elements appearing in the accompanying figures are not necessarily
drawn to scale unless otherwise stated.
DETAILED DESCRIPTION
[0021] The following Detailed Description is merely exemplary in
nature and is not intended to limit the invention or the
application and uses of the invention. The term "exemplary," as
appearing throughout this document, is synonymous with the term
"example" and is utilized repeatedly below to emphasize that the
description appearing in the following section merely provides
multiple non-limiting examples of the invention and should not be
construed to restrict the scope of the invention, as set-out in the
Claims, in any respect. As further appearing herein, statements
indicating that a first layer is "formed over," "formed on,"
"deposited over," or "deposited on" a second layer, surface, or
body do not require that that the first layer is directly bonded to
and intimately contacts the second layer, surface, or body unless
otherwise expressly stated by, for example, stating the first layer
is "formed directly on," "deposited directly on," "is formed in
contact with," or "contacts" the second layer, surface, or
body.
Definitions
[0022] The following definitions apply throughout this document.
Those terms not expressly defined here or elsewhere in this
document are assigned their ordinary meaning in the relevant
technical field.
[0023] Coating--One or more layers of material formed over a
component surface. This term encompasses the more specific term
"coating system" defined below.
[0024] Coating System--A coating structure containing at least two
material layers having varying compositions, such as one or more Au
layers joined to a component body by an intervening NiW plating
layer.
[0025] Component--Any article of manufacture over which a coating
can be formed. This term is synonymous with or encompasses similar
terms including "substrate," "part," and "workpiece."
[0026] Electrical Connector--Any component or structure utilized to
provide an a current- or signal-carrying electrical connection
between two points or nodes including wirebonds and mating
connector devices, such as male (e.g., pin), female (e.g., socket),
and hybrid (e.g., pin and socket) connectors.
[0027] Gold (Au) Topcoat--One or more layers predominately composed
of Au by weight and formed over an NiW plating layer.
[0028] Nickel (Ni) Barrier Layer--A layer composed essentially of
pure Ni by weight and deterring unfavorable chemical reactions with
an underlying material layer, component, or body of material.
[0029] Nickel-tungsten (NiW) plating layer--A layer composed
predominately of Ni and W by weight and deterring unfavorable
chemical reactions with an underlying material layer, component, or
body of material.
[0030] Ni Pellets--Discrete bodies or pieces of material, such as
shot, predominately composed of Ni by weight, regardless of shape
or size.
Overview
[0031] As discussed briefly in the foregoing BACKGROUND, pure Ni
plating layers are beneficially electrodeposited on selected
surfaces of metallic components to improve wear properties and to
prevent undesired chemical degradation, such as corrosion, of the
underlying component or substrate. As a more specific example, pure
Ni plating layers are usefully formed on contact surfaces of high
performance electrical connectors over which Au topcoats are
further deposited to lower contact resistance. In other instances,
pure Ni plating layers may be formed over sliding surfaces,
particularly over the sliding surfaces of high temperature
components, to provide enhanced wear resistance. However, as
further discussed above, pure Ni plating layers remain limited in
certain respects and, in many instances, provide only modest
improvements in the wear and corrosion properties of the coating
system. Additionally, the plating processes utilized to
electrodeposit pure Ni plating layers are often hampered by various
constraints, such as bath instabilities, poor bath life longevity,
relatively sluggish deposition rates, and correspondingly high
process and material costs.
[0032] Relative to pure Ni plating layers, NiW plating layers can
potentially provide greater enhancement to the wear and corrosion
resistance properties of a coating or coating system. The plating
processes utilized to electrodeposit NiW plating layers are,
however, considerably more complex than those utilized to
electrodeposit pure Ni. This is due, at least in part, to
difficulties encountered when attempting to deposit a (typically
binary) alloy having a specific fractional composition of W to Ni.
Further, NiW electrodeposition processes are also typically prone
to the accumulation of plating bath impurities, which can result in
rough deposits leading to microcrack formation and propagation.
Once formed, microcracks can detract from the intended
functionality of the NiW plating layer to serve a physical shield
against undesired chemical reactions with the underlying component,
in applications in which the NiW plating layer is utilized as a
barrier layer. Specifically, such microcracks can lead to greater
diffusion of outer material layers (e.g., an Au topcoat), if
present, into the parent material of the underlying component or
substrate. Still other challenges are also encountered when
electrodepositing NiW plating layers. For example, if Ni ions are
supplied to the plating bath in the form of a Ni-containing sulfate
chemical additive, the gradual build-up of sulfates can occur over
time thereby greatly reducing bath life and raising the cost of the
NiW electrodeposition process. Similarly, if not deposited onto the
plated component at a sufficiently controlled rate, an abundance of
Ni ions can develop within the plating bath. Eventually, the
plating bath may saturate with Ni ions, which may necessitate
partial dumping of the plating bath and refilling with plating bath
solution lacking Ni. This again prolongs, complicates, and adds
cost to the NiW electrodeposition process.
[0033] To overcome many, if not all of the aforementioned
challenges, the following provides improved processes for forming
coatings and coatings systems containing NiW plating layers.
Embodiments of the below-described NiW electrodeposition process
reduce or eliminate the accumulation of sulfates and other
undesired chemical species within the plating bath to significantly
extend bath life and lower material costs. This is accomplished, in
part, through the incorporation of consumable or dissolvable Ni
electrodes into the NiW electrodeposition process, rather than
utilizing inert (e.g., platinum-coated titanium) anodes as
conventionally practiced in the context of pure Ni plating
processes. Embodiments of the plating bath solution further contain
at least one chemical serving as an anode corrosion accelerant,
such as chloride, which promotes the controlled dissolution of the
consumable Ni electrodes into the plating bath. The anode corrosion
accelerant is maintained in the plating bath in a carefully
controlled amount or fraction, which is sufficient to prevent scale
build-up over the surfaces of the Ni electrodes, while further
limiting dissolution of the Ni electrodes to a rate substantially
equivalent to the rate of N ion deposition onto the component
surfaces subject to plating.
[0034] In various embodiments, the controlled amount of anode
corrosion accelerant added to and generally maintained within the
NiW plating bath may be determined utilizing different approaches.
In one approach, the amount of anode corrosion accelerant is
determined based upon a target W content of the NiW plating layer,
as well as an estimated cumulative surface area of the Ni
electrodes submerged in the plating bath and energized as anodes
during the NiW electrodeposition process. As the electrodeposition
process progresses and the Ni electrodes dwindle in size, new or
fresh Ni electrodes may be repeatedly introduced into the plating
bath to maintain the cumulative surface area of Ni electrodes and
plated surface area of the metallic component surface within a
predetermined range or desired relationship. This may be
accomplished by, for example, providing the Ni electrodes as
consumable Ni pellets or shot, which are retained within an inert
mesh basket or other container and which are replenished
periodically during the NiW electrodeposition process.
[0035] Through the usage of consumable Ni electrodes and tailored
amounts of at least one anode corrosion accelerant, the gradual
accumulation of undesired chemical species, such as sulfates,
within the plating bath can be reduced or eliminated. Bath life is
prolonged as a result, potentially to near infinite lifespans.
Further, as compared to inert anodes, the consumable Ni electrodes
utilized in the NiW electroplating process can be energized at
reduced voltages, utilizing either a Direct Current (DC) or
Alternating Current (AC) power source, to minimize oxygen evolution
and carbonate production during the electroplating process. This,
again, extends useful bath life and reduces processing costs.
Finally, as a yet further benefit, embodiments of the
below-described plating process can boost mas transfer within the
plating bath diffusion zone to achieve deposition rates
well-exceeding those attained by conventional Ni plating processes.
Process efficiency is thus improved, while costs are reduced. These
and other benefits may be further enhanced by formulating the
plating bath to contain tailored amounts of additional constituents
serving as chelating or structuring agents, such as ammonium
hydroxide (NH.sub.4OH) and/or other organic acids; and controlling
other plating process parameters during the plating process, as
further discussed below. Exemplary embodiments of a coating
formation method including the electrodeposition of NiW plating
layers will now be described in conjunction with FIG. 1.
[0036] Examples of Methods for Forming Coatings and Coating Systems
Including Niw Plating Layers
[0037] FIG. 1 is a flowchart of an exemplary coating formation
method 10 for forming a coating or coating system including NiW
plating layers over metallic components, such as the terminals of
high performance electrical connectors or the sliding surfaces of a
high temperature (e.g., engine) component, as illustrated in
accordance with an exemplary embodiment of the present disclosure.
As a point of emphasis, a given coating or coating system may
contain and, perhaps, may consist of a single NiW plating layer,
which may be deposited over a metallic component. In certain
applications, the NiW plating layer is beneficially deposited over
the sliding surface of a metallic component, typically (although
non-essentially) a metallic component utilized in a high
temperature operating environment, such as a valve part or other
component contained in an internal combustion or gas turbine
engine. In other applications, the NiW plating layer may be
combined with additional material layers to yield a multi-layer
coating system. For example, and as further discussed below in
conjunction with FIG. 3, one or more Au topcoat layers may be
formed over the NiW plating layer when the plated component is the
terminal of an electrical connector. Various other coatings and
coating systems can be formed pursuant to method 10, as
appropriately modified to suit a particular application or usage,
providing that the coating or coating system consists of or
includes at least one NiW plating layer as described below.
[0038] In the example of FIG. 1, coating formation method 10
includes a number of process steps identified as STEPS 12, 14, 16,
18, 20, 22, with STEPS 14, 16, 18 performed pursuant to an
overarching NiW plating sub-process identified as "PROCESS BLOCK
24." Depending upon the particular manner in which coating
formation method 10 is implemented, each illustrated process step
(STEPS 12, 14, 16, 18, 20, 22) may entail a single process or
multiple sub-processes. Further, the steps shown in FIG. 1 and
described below are offered by way of non-limiting example only. In
alternative embodiments of method 10, additional process steps may
be performed, certain steps may be omitted, and/or the illustrated
steps may be performed in varying sequences. For example, in
further implementations, STEP 20 of method 10 may be omitted or
modified such that the NiW plating layer is left as a standalone
protection solution (e.g., as wear protection for sliding surfaces)
or, instead, overlaid by one or more additional material layers
other than an Au topcoat in the completed coating system.
[0039] For ease of description, coating formation method 10 is
principally described below as carried-out to form a coating or
multi-layer coating system over selected surfaces of a single
metallic component. This notwithstanding, it will be appreciated
that any practical number of metallic components may be processed
in parallel to form coatings or coating systems over selected
surfaces of a plurality of components in accordance with the
below-described process steps. For example, in the case of smaller
(e.g., stamped) metallic components, such as the terminals of an
electrical connector, a reel-to-reel plating process can be
utilized to from coatings or coating systems a connected series of
parts or components, such as stamped pins or sockets, which are
passed through the below-described NiW plating bath and other
processing stages for large scale production.
[0040] With continued reference to FIG. 1, coating formation method
10 commences at STEP 12 during which the metallic component or
components to be coated are obtained; e.g., by purchase from a
third party supplier or by independent fabrication. The surfaces of
the metallic component or components targeted for electrodeposition
of the NiW plating layer are further prepared during STEP 12. In
embodiments, surface preparation may involve degreasing or
otherwise cleaning the targeted component surfaces. For example, if
desired, surface oxides may be removed from the component surfaces
utilizing a sulfuric acid dip or similar process. Grinding,
polishing, lapping, and/or other such mechanical operations can
further be performed, as appropriate, to improve surface finish
prior to NiW plating layer electrodeposition. Finally, any
component surfaces not desirably coated with the NiW plating layer
may be masked during STEP 12.
[0041] Coating formation method 10 next advances to PROCESS BLOCK
24. During PROCESS BLOCK 24, at least one NiW plating layer is
electrodeposited over the targeted component surfaces. As indicated
at STEP 14, the NiW electrodeposition process involves formulating
or preparing the plating bath solution to possess a chemistry
suitable for electrodeposition of the NiW plating layer having a
desired composition and other characteristics, such as a desired
morphology. Generally, the formulation of the NiW plating bath will
depend, at least in part, on the target W content of the NiW
plating layer. As the W content of the NiW plating layer will vary
among embodiments, so too will the composition of the NiW plating
bath. However, by way of example, the target W content of the NiW
plating layer may range from about 15% and 45% by weight,
preferably from about 25% to about 35% by weight, and more
preferably may be substantially equivalent to 30% by weight. In
other embodiments, the W content of the NiW plating layer may be
greater than or lesser than the aforementioned ranges.
[0042] In accordance with embodiments of the present disclosure,
the NiW plating bath is formulated such that an amount of anode
corrosion accelerant in the plating bath is controlled to balance
the amount of Ni dissolution at the anode (the energized consumable
Ni electrodes) to the amount of Ni deposition at cathode (the
plated part), combined with any additional Ni ion source within the
plating bath, to achieve a desired composition of the NiW layer. In
many embodiments, the plating bath will not contain any additional
Ni ion source such that anode corrosion accelerant concentration is
tailored to achieve Ni dissolution at the anode relative to the Ni
deposition at cathode to arrive at the desired composition of the
NiW layer. However, in other embodiments, the Ni dissolution at the
anode may be purposefully undershot with additional Ni ions
introduced in the form of a chemical additive, such as Ni sulfate,
to allow greater flexibility in adjusting chemistry during the
electrodeposition process. In such embodiments, bath life may still
be extended as a relatively small or reduced amount of the Ni
sulfate (or other Ni-containing chemical) may be added to the
plating bath.
[0043] In embodiments, the anode corrosion accelerant can include
or assume the form of chloride. The chloride can be added as a
chloride-containing agent or chemical, such as nickel chloride
(NiCl.sub.2), ammonia chloride (NH.sub.4Cl), or sodium chloride
(NaCl). Ideally, the amount of anode corrosion accelerant is
carefully tailored in relation to the other constituents of the NiW
plating bath and to prevent scale build-up over the surfaces of the
Ni electrodes, while further limiting dissolution of the Ni
electrodes to a rate substantially equivalent to the rate of N ion
deposition onto the component surfaces subject to plating. The
amount of anode corrosion accelerant added to the plating bath may
be determined based, at least in part, on the target W content of
the NiW plating layer and a cumulative surface area of the
consumable Ni electrodes. As a result, the amount of anode
corrosion accelerant added to and generally maintained within the
NiW plating bath will vary amongst different implementations of
method 10. This notwithstanding, and by way of non-limiting example
only, the chloride range in the plating bath ranges between about
0.0002 and about 0.01 moles per liter (mol/liter); and, more
preferably, between 0.0008 and 0.0025 mol/liter. The foregoing
exemplary molarity ranges apply when chloride is selected as the
anode corrosion accelerant or as at least one of the anode
corrosion accelerants, if multiple accelerant types are utilized.
In other implementations, a different type of anode corrosion
accelerant may be utilized or chloride may be employed as the anode
corrosion accelerant, but in a concentration greater than or less
than the aforementioned ranges.
[0044] The controlled amount of anode corrosion accelerant
introduced into and maintained in the NiW plating above may thus be
defined, in part, based upon the desired Ni ion concentration in
the bath. Other process parameters (e.g., voltages, temperatures,
agitation intensities, etc.) and whether a supplemental Ni ion
source (e.g., a Ni-containing chemical additive) is present within
the bath will also impact the N ion concentration within the bath.
As with the various other constituents of the NiW plating bath, the
Ni ion concentration will vary among different implementations of
method 10. However, by way of example, the Ni ion concentration
within the NiW plating bath may be maintained through the NiW
electrodeposition process in a range between about 5 grams and
about 18 grams Ni per liter of plating bath solution; or, stated
differently, between about 0.085 to about 0.307 mol/liter. In a
more specific example, the Ni ion concentration within the NiW
plating bath may be maintained in a range between about 11 and
about 13.5 grams per liter; or between about 0.187 to about 0.230
mol/liter.
[0045] In addition to the anode corrosion accelerant, the NiW
plating bath also contains at least one W ion source. The W ion
source is conveniently provided as a water-soluble additive
containing W, such as sodium tungstate dihydrate
(Na.sub.2WO.sub.4.2H.sub.2O). Additionally, the plating bath will
further contain a liquid carrier, such as an aqueous or
alcohol-based solvent. The plating bath chemistry may also be
formulated to include other ingredients or constituents including
chelating agents and pH balancing agents; e.g., in one embodiment,
a complex of an organic acid, such as citric acid
(C.sub.6H.sub.8O.sub.7) and ammonia (NH.sub.3) may be provided
within the bath (e.g., added in solution as NH.sub.4OH) to serve as
a chelating or structuring agent. With respect to the NH.sub.3
additive, in particular, this additive may contribute ammonium
hydroxide (OH--) ions when reacted in the plating bath, which are
highly effectively in service as chelating agents. In one
embodiment, adequate NH.sub.3 (or another OH-- donor) is introduced
into the plating bath to provide ammonium hydroxide (OH--) ions in
the range of about 1.0 to about 2.0 mol/liter; and, more
preferably, in the range of 1.3 to 1.7 mol/litter. Finally, as
noted above, the NiW plating bath will also contain a Ni ion source
in the form of the consumable NiW electrodes; although the
possibility that the NiW plating bath can be formulated to contain
another Ni ion source, such as a Ni sulfate or other chemical
species, in addition to the Ni ion electrodes is not precluded.
Various other bath formulations are also possible.
[0046] At STEP 16, the consumable Ni electrodes and metallic
components are inserted into the NiW plating bath, whether by
inserting the Ni electrodes and the metallic component into the
plating bath or by first positioning the at least one electrode and
the component in a vessel and subsequently filling the vessel with
plating bath solution. The Ni electrodes are then energized as
anodes and the metallic components are energized as cathodes to
carry-out the NiW electrodeposition process and thereby deposit the
NiW plating layer over the selected component surfaces. The
consumable Ni electrodes can generally be energized at reduced
voltages, whether utilizing a Direct Current (DC) or Alternating
Current (A/C) power source, to minimize oxygen evolution and
carbonate production within the plating bath. Advantageously, the
usage of soluble Ni anodes generally enables reduced anode voltages
to lower decomposition products and thereby prolong bath life. In
one embodiment, the at least one consumable Ni electrode and the
metallic component are energized at a current density (e.g., a
direct current density) between 1 and 5 ampere per decimeter
squared.
[0047] Various parameters are controlled during the NiW
electrodeposition process. Bath agitation may be applied and, in
embodiments, may range from about 100 to about 1000 revolutions per
minute (RPM). The temperature and pH level of the plating bath may
also be monitored and controlled. In one implementation, bath
chemistry is formulated to maintain NiW plating bath at a pH
between about 5 and about 9 and, more preferably, a pH of about
7.+-.1 through the electroplating process. In other instances, the
pH level of the plating bath may be greater or less than the
aforementioned range. As the plating process progress and the Ni
electrodes dwindle in size, new or fresh Ni electrodes may be
repeatedly introduced into the plating bath to maintain the
cumulative surface area of Ni electrodes and plated surface area of
the metallic component surface within a predetermined range or
desired relationship. This may be accomplished by, for example,
providing the Ni electrodes as consumable Ni pellets or shot, which
are retained within an inert mesh basket or other container and
which are replenished periodically during the NiW electrodeposition
process, as further described below in conjunction with FIG. 2.
[0048] FIG. 2 is a schematic of an exemplary NiW plating apparatus
26, which can be utilized to electrodeposit an NiW plating layer 30
over surfaces of a metallic component 32 during PROCESS BLOCK 24 of
coating formation method 10 (FIG. 1). As schematically depicted in
FIG. 2, plating apparatus 26 includes a vessel 34 retaining a
plating bath solution 36. Metallic component 32 is electrically
connected, either directly or indirectly (e.g., through an
intervening bracket or fixture) to a negative terminal of power
source 38 by a first electrical connection 40. The positive
terminal of power source 38 is further connected, either directly
or indirectly, to one or more consumable Ni electrodes by a second
electrical connection 42. In the illustrated example, specifically,
power source 38 is electrically coupled to a mesh basket 44
composed of an inert electrically-conductive material, such as
titanium. Ni shot 46 is held within mesh basket 44 and is energize
when with the application of a controlled voltage across mesh
basket 44 and metallic component 32. As Ni shot 46 dissolves during
the plating process, new or fresh Ni shot 46 may be added to mesh
basket 44, as indicated in FIG. 2 by arrow 48. Certain variations
in the cumulative surface area of consumable Ni shot 46 (the
anodes) will occur, with the surface area-to-volume ratio
increasing as the pieces of shot decrease in size. However, by
repeatedly adding fresh consumable Ni pellets 46 to NiW plating
bath 36 as the electroplating process progresses, a ratio between a
cumulative surface area of the consumable Ni pellets and a surface
area of the component surface can be maintained within a
predetermined range. In embodiments, Ni pellets 46 may be added and
process parameters controlled to maintain a Ni ion concentration
within the above-described molarity ranges (between about 0.085 to
about 0.307 mol/liter; and, perhaps, between about 0.187 to about
0.230 mol/liter) throughout a majority and, perhaps, the
substantial entirety of the electroplating process.
[0049] Returning once again to FIG. 1, coating formation method 10
next progresses to STEP 20 (if performed) during which an Au
topcoat is formed over the newly-deposited NiW plating layer. When
formed, the Au topcoat will often have a thickness less than the
thickness of the NiW plating layer; e.g., in embodiments, the Au
topcoat may have a thickness ranging from 0.381 micron (.mu.m) to
1.016 .mu.m, while the NiW plating layer will often have a
thickness ranging between 1.27 .mu.m and 5.08 .mu.m. In this
regard, and as noted above, the provision of a microcrystalline,
essentially microcrack-free NiW plating layer may allow the
thickness the Au topcoat to be appreciably reduced for cost
savings. In other high performance applications, the thickness of
the Au topcoat may approach or potentially exceed that of the NiW
plating layer. For example, when the coating is formed over the
terminals of an electrical connector deployed onboard a spacecraft
or aircraft, the Au topcoat may range between 2.54 .mu.m and 5.08
.mu.m, with the NiW plating layer having a thickness as specified
above. In still further implementations, the NiW plating layer
and/or the Au topcoat may be thickener or thinner than the
aforementioned ranges; or STEP 20 of method 10 may be omitted. The
provision of such an essentially microcrack-free NiW plating layer
may also serve as an effective barrier layer for preventing
undesired diffusion of Au topcoat (or other overlying material
layer) into the substrate in at least some realizations of method
10.
[0050] Finally, at STEP 22 of coating formation method 10 (FIG. 1),
zero or more additional processing steps are performed to complete
fabrication of the coating or coating system. This may include
machining (e.g., lapping, polishing, and/or grinding) of the
newly-deposited Au topcoat to achieve a desired surface finish
and/or dimensional tolerance. Heat treatment can also be performed
for densification or other purposes. Coating formation method 10
then concludes and can be repeated, as needed, an iterative basis
to further form similar or identical coatings or coating systems
over other metallic components. In other implementations of method
10, and as previously indicated, STEPS 20, 22 may not be performed
such that the NiW plating layer electrodeposited during PROCESS
BLOCK 24 serves as a standalone protection solution; e.g., as may
be useful when the NiW plating layer is deposited onto a sliding
surface or other contact surface for enhanced wear resistance.
Alternatively, other coating layer or coating systems may be formed
over the NiW plating layer in still further embodiments, such as a
environmental barrier coating and/or thermal barrier coating.
[0051] FIG. 3 is a simplified cross-sectional view of a limited
region of a coating system 52, which is formed over an underlying
metallic component 54 and which may be produced pursuant to coating
formation method 10 in accordance with an exemplary embodiment of
the present disclosure. In this example, coating system 52 includes
an Au topcoat 56 and an electrodeposited NiW plating layer 58,
which is formed between Au topcoat 56 and metallic component 54.
Specifically, NiW plating layer 58 is formed over and in contact
with component surface 60 of metallic component 54. Au topcoat 56
is, in turn, formed over and in contact with outer surface 62 of
NiW plating layer 58. As indicated in FIG. 3 by dashed line 64, Au
topcoat 56 can be formed as two (or more) layers. In various
implementations, Au topcoat 56 is formed to include a first or base
Au layer 66, which is plated directly onto NiW plating layer 58;
and a second or outer Au layer 68, which is plated directly onto
base Au layer 66. Such an arrangement may be beneficial when Au
topcoat 56 is desirably formed to have a relatively high thickness
and is utilized within a high performance application, such as a
spaceborne or an airborne connector. In such embodiments, base Au
layer 66 may be formed as relatively thin strike plating layer
(e.g., a layer having a thickness equal to or less than 1 .mu.m) to
enhance adhesion between NiW plating layer 58 and the thicker outer
Au layer 68. Wear testing has shown that coating systems similar or
identical to coating system 52 perform comparably and, in certain
cases, outperform conventional coating systems containing pure Ni
plating layers in useful life cycle limits.
[0052] Turning lastly to FIG. 4, there is shown an isometric view
of a female electrical connector 70 and a number of pins 72, which
may be included in a non-illustrated mating male electrical
connector. Pins 72 engage into sockets 74 when the non-illustrated
male electrical connector is plugged into female electrical
connector 70. To decrease contact resistance across the electrical
interface formed between each pin 72 and its mating socket 74, the
above-described coatings or coating systems (e.g., coating system
52 shown in FIG. 3) may be formed over the outer contact surfaces
of pins 72 and/or over the inner contact surfaces of sockets 70. In
this particular example, female electrical connector 70 is of the
type deployed onboard spacecraft and aircraft and, thus, a coating
having a relatively thick Au topcoat may be formed over the
interior of sockets 74 and over pins 72 of the mating male
electrical connector. The provision of the NiW plating layer, as
previously noted, may further enhance the wear and corrosion
resistance properties of sockets 74 and pins 72, as may be desired
in such applications to satisfy stringent mission requirements in
certain instances. The example of FIG. 4 notwithstanding, it is
again emphasized that the coatings or coating systems described
herein can be formed over any type of metallic article or
component, without limitation.
CONCLUSION
[0053] There has thus been provided describes processes for
depositing NiW plating layers in an essentially crack-free,
nanocrystalline state. Additionally, embodiments of the plating
process minimize, if not eliminate the accumulation of sulfates and
undesired chemical species within the plating bath to greatly
extend bath life. By virtue of its nanocrystalline microcrack-free
morphology, the NiW plating layer provides excellent shielding of
undesired chemical reactions between the Au topcoat (when present)
and the underlying substrate material or component body, as is
beneficial when the NiW plating layer is utilized as a barrier
layer. This, in turn, may allow the thickness of the Au topcoat to
be reduced for cost savings, while maintaining coating system
performance at desired levels in embodiments in which the NiW
plating layer is included in a coating system further containing
such an Au topcoat. Alternatively, in such embodiments, the NiW
plating layer may be utilized to enhance coating system
performance, while leaving the thickness of the Au topcoat
unchanged. This latter approach may be preferable in high
performance application, as in the case of electrical connectors
deployed onboard aircraft or spacecraft. Generally, the NiW plating
layer may help improve oxidation, corrosion, and/or wear resistance
of the plated part in certain instances. This material system is
beneficially utilized to coat current-carrying electronic
structures, such as electrical terminals or connectors. Examples of
current-carrying electronic structures include wirebonds, as well
as larger mating interconnect structures or devices, such as male
(e.g., pin) and female (e.g., socket) connectors. In yet other
embodiments, the NiW plating layer may be utilized in isolation or,
perhaps, with other types of material layers to provide other
performance enhancements, such as increasing sliding surface wear
resistance.
[0054] Terms such as "comprise," "include," "have," and variations
thereof are utilized herein to denote non-exclusive inclusions.
Such terms may thus be utilized in describing processes, articles,
apparatuses, and the like that include one or more named steps or
elements, but may further include additional unnamed steps or
elements. While at least one exemplary embodiment has been
presented in the foregoing Detailed Description, it should be
appreciated that a vast number of variations exist. It should also
be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing Detailed Description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. Various changes may be made
in the function and arrangement of elements described in an
exemplary embodiment without departing from the scope of the
invention as set-forth in the appended Claims.
* * * * *