U.S. patent application number 13/932188 was filed with the patent office on 2015-01-01 for coated articles and methods comprising a rhodium layer.
This patent application is currently assigned to Xtalic Corporation. The applicant listed for this patent is Xtalic Corporation. Invention is credited to John Cahalen, Trevor Goodrich, Alan C. Lund, Christopher A. Schuh.
Application Number | 20150004434 13/932188 |
Document ID | / |
Family ID | 52115877 |
Filed Date | 2015-01-01 |
United States Patent
Application |
20150004434 |
Kind Code |
A1 |
Goodrich; Trevor ; et
al. |
January 1, 2015 |
COATED ARTICLES AND METHODS COMPRISING A RHODIUM LAYER
Abstract
Coated articles and methods for applying coatings including a
rhodium layer are described. In some cases, the coating can exhibit
desirable properties and characteristics such as durability,
corrosion resistance, and high conductivity. The articles may be
coated, for example, using an electrodeposition process.
Inventors: |
Goodrich; Trevor; (Ashland,
MA) ; Cahalen; John; (Somerville, MA) ; Lund;
Alan C.; (Ashland, MA) ; Schuh; Christopher A.;
(Wayland, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xtalic Corporation |
Marlborough |
MA |
US |
|
|
Assignee: |
Xtalic Corporation
Marlborough
MA
|
Family ID: |
52115877 |
Appl. No.: |
13/932188 |
Filed: |
July 1, 2013 |
Current U.S.
Class: |
428/670 ;
205/170; 205/176; 205/181 |
Current CPC
Class: |
C25D 3/12 20130101; C25D
3/50 20130101; C25D 5/10 20130101; Y10T 428/12875 20150115; C25D
5/12 20130101 |
Class at
Publication: |
428/670 ;
205/176; 205/181; 205/170 |
International
Class: |
C25D 5/12 20060101
C25D005/12 |
Claims
1. An article comprising: a base material; a barrier layer formed
on the base material; a metal layer formed on the barrier layer;
and a Rh layer formed on the metal layer and having a thickness
between about 1 microinch and about 5 microinches.
2. The article of claim 1, wherein the barrier layer comprises
silver.
3. The article of claim 2, wherein the barrier layer comprises a
silver-based alloy.
4. The article of claim 1, wherein the barrier layer comprises
nickel.
5. The article of claim 4, wherein the barrier layer comprises a
nickel-based alloy.
6. The article of claim 5, wherein the nickel-based alloy further
comprises tungsten and/or molybdenum.
7. The article of claim 5, wherein the nickel-based alloy further
comprises phosphorous.
8. The article of claim 5, wherein the nickel-based alloy further
comprises cobalt.
9. The article of claim 5, wherein the nickel-based alloy further
comprises palladium.
10. The article of claim 1, wherein the barrier layer comprises
palladium.
11. The article of claim 1, wherein the barrier layer has a
nanocrystalline grain size.
12. The article of claim 1, wherein the metal layer has a
nanocrystalline grain size.
13. The article of claim 1, wherein the metal layer comprises a
metal selected from the group consisting of Au, Ru, Os, Rh, Ir, Pd,
Pt, and Ag.
14. The article of claim 1, wherein the metal layer comprises a
silver-based alloy.
15. The article of claim 1, wherein the metal layer comprises a
silver-based alloy and the barrier layer comprises a nickel-based
alloy.
16. The article of claim 1, wherein the metal layer comprises a
silver-based alloy further comprising molybdenum and/or tungsten
and the barrier layer comprises a nickel-based alloy further
comprising molybdenum and/or tungsten.
17. The article of claim 1, wherein the metal layer comprises a
silver-tungsten alloy and the barrier layer comprises a
nickel-tungsten alloy.
18. The article of claim 1, wherein the Rh layer is formed directly
on the metal layer.
19. The article of claim 1, wherein the Rh layer is
electrodeposited.
20. The article of claim 1, wherein the Rh layer has a
nanocrystalline grain size.
21. The article of claim 1, wherein the base material comprises a
conductive metal.
22. A method comprising electrodepositing a barrier layer on a base
material; electrodepositing a metal layer on the barrier layer; and
electrodepositing a Rh layer on the metal layer, wherein the Rh
layer has a thickness between about 1 microinch and about 5
microinches.
23-42. (canceled)
Description
FIELD OF INVENTION
[0001] The present invention generally relates to coated articles
comprising a rhodium layer and related methods. In some
embodiments, the articles are coated using an electrodeposition
process.
BACKGROUND OF INVENTION
[0002] Many types of coatings may be applied on a base material.
Electrodeposition is a common technique for depositing such
coatings. Electrodeposition generally involves applying a voltage
to a base material placed in an electrodeposition bath to reduce
metal ionic species within the bath which deposit on the base
material in the form of a metal, or metal alloy, coating. The
voltage may be applied between an anode and a cathode using a power
supply. At least one of the anode or cathode may serve as the base
material to be coated. In some electrodeposition processes, the
voltage may be applied as a complex waveform such as in pulse
plating, alternating current plating, or reverse-pulse plating.
[0003] A variety of metal and metal alloy coatings may be deposited
using electrodeposition. For example, metal alloy coatings can be
based on two or more transition metals including Ni, W, Fe, Co,
amongst others.
[0004] Corrosion processes, in general, can affect the structure
and composition of an electroplated coating that is exposed to the
corrosive environment. For example, corrosion can involve direct
dissolution of atoms from the surface of the coating, a change in
surface chemistry of the coating through selective dissolution or
de-alloying, or a change in surface chemistry and structure of the
coating through, e.g., oxidation or the formation of a passive
film. Some of these processes may change the topography, texture,
properties, or appearance of the coating. For example, spotting
and/or tarnishing of the coating may occur. Such effects may be
undesirable, especially when the coating is applied at least in
part to improve electrical conductivity since these effects can
increase the resistance of the coating.
SUMMARY OF INVENTION
[0005] Coated articles comprising a rhodium layer and related
methods are provided.
[0006] In some embodiments, articles are provided. In some
embodiments, an article comprises a base material, a barrier layer
formed on the base material, a metal layer formed on the barrier
layer, and a Rh layer formed on the metal layer and having a
thickness between about 1 microinch and about 5 microinches.
[0007] In some embodiments, methods are provided. In some
embodiments, a method comprises electrodepositing a barrier layer
on a base material; electrodepositing a metal layer on the barrier
layer; and electrodepositing a Rh layer on the metal layer, wherein
the Rh layer has a thickness between about 1 microinch and about 5
microinches.
[0008] Other aspects, embodiments, and features of the invention
will become apparent from the following detailed description when
considered in conjunction with the accompanying drawings. The
accompanying figures are schematic and are not intended to be drawn
to scale. For purposes of clarity, not every component is labeled
in every figure, nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. All
patent applications and patents incorporated herein by reference
are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will
control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a coated article, according to some
embodiments.
DETAILED DESCRIPTION
[0010] Coated articles comprising a rhodium layer and methods for
applying coatings are described. The article may include a base
material and a multi-layer coating formed thereon. In some
embodiments, the coating includes a base material, a barrier layer
formed on the base material, a metal layer formed on the barrier
material, and a rhodium layer formed on the metal layer. In some
cases, the barrier layer comprises an alloy (e.g., nickel alloy,
silver alloy) and the metal layer comprises a precious metal (e.g.,
Ru, Rh, Os, Ir, Pd, Pt, Ag, and/or Au). In some cases, the coating
may be applied using an electrodeposition process. The coating can
exhibit desirable properties and characteristics such as
durability, corrosion resistance, and high conductivity, which may
be beneficial, for example, in electrical applications.
[0011] FIG. 1 shows an article 10 according to a non-limiting
embodiment. The article has coating 20 formed on a base material
30. The coating may comprise barrier layer 40 formed on the base
material, metal layer 50 formed on the barrier layer, and rhodium
layer 60 formed on the metal layer. Each layer may be applied using
a suitable process, as described in more detail below. It should be
understood that the coating may include more than three layers.
However, in some embodiments, the coating may only include three
layers, as shown.
[0012] The inventors have discovered that formation of a rhodium
layer on a metal layer results in articles with desired properties
as compared to articles formed comprising only the metal layer. For
example, the presence of a metal layer and a rhodium layer on an
article as compared to only a metal layer leads to improved
coloration (e.g., desired shade/tone, color stability over time,
etc.), improved durability, and/or improved corrosion
resistance.
[0013] In some embodiments, the rhodium layer has a thickness
greater than about 1 microinch. In some cases, the rhodium layer
has a thickness between about 1 microinch and about 5 microinches.
The inventors have discovered that coated articles comprising a
rhodium layer having a thickness less than about 1 microinch or
greater than about 5 microinches can result in inferior
performance. For example, rhodium layers having a thickness less
than 1 microinch may provide incomplete coverage of the metal layer
which can affect the overall coating appearance (e.g., may affect
the color stability overtime), wear performance, and/or corrosion
resistance. For example, rhodium layers having a thickness greater
than 5 microinches can have highly stressed and/or cracked deposits
which can affect the coating appearance and/or wear
performance.
[0014] In some embodiments, the barrier layer comprises one or more
metals. The barrier layer is generally comprised of a layer that is
conductive. In some cases, the barrier layer comprises a material
that has some corrosion resistance to the conditions under which
the article is to be employed. In some cases, the barrier layer
acts as a diffusion barrier between the base material and
subsequent layers of material. In some cases, the barrier layer
comprises nickel or consists essentially of nickel. In some cases,
the barrier layer comprises silver or consists essentially of
silver. In some cases, the barrier layer comprises palladium or
consists essentially of palladium. In some cases, the barrier layer
comprises a metal alloy. In some cases, alloys that comprise nickel
(e.g., nickel-tungsten alloys) or silver (e.g., silver, tungsten,
and/or molybdenum) are preferred.
[0015] In some embodiments, the barrier layer comprises a nickel
alloy (i.e., nickel-based alloys). Nickel alloys are known in the
art. For example, see U.S. Publication No. 2011/0008646 by Cahalen
et al., filed Jul. 10, 2009, and U.S. Publication No. 2012/0328904
by Baskin et al., filed Jun. 22, 2012, each herein incorporated by
reference. In some cases, the nickel-alloy further comprises
tungsten and/or molybdenum (e.g., a nickel-tungsten alloy, a
nickel-molybdenum alloy, a nickel-tungsten-molybdenum alloy). Other
nickel alloys may also be employed. For example, the nickel alloy
may further comprise cobalt, phosphorus, and/or palladium. In some
cases, the weight percent of nickel in the alloy may be between
25-75 weight percent; and, in some cases, between 50 and 70 weight
percent. In these cases, the remainder of the alloy may be tungsten
and/or molybdenum. Other weight percentages outside of this range
may be used as well. For example, in some embodiments and for
certain applications, the weight percent of tungsten in the alloy
may be greater than or equal to 10 weight percent; in some cases,
greater than or equal to 14 weight percent; in some cases, greater
than or equal to 15 weight percent; and, in some cases greater than
or equal to 20 weight percent. In some cases, the total weight
percentage of tungsten in the alloy is less than or equal to 35
weight percent; in some cases, the total weight percentage of
tungsten in the alloy is less than or equal to 30 weight percent;
in some cases, the total weight percentage of tungsten in the alloy
is less than or equal to 28 weight percent; and, the total weight
percentage of tungsten in the alloy is less than or equal to 25
weight percent.
[0016] In some embodiments, the barrier layer comprises a silver
alloy (i.e., silver-based alloys). Such alloys may also comprise
tungsten and/or molybdenum. Silver alloys are known in the art, for
example, see U.S. Publication No. 2011/0223442 by Dadvand et al.,
filed Mar. 12, 2010, herein incorporated by reference. In some
embodiments, the barrier layer comprises a silver-tungsten alloy.
Other silver alloys may also be employed. In some cases, the atomic
percent of tungsten and/or molybdenum in the alloy may be between
0.1 atomic percent and 50 atomic percent; and, in some cases,
between 0.1 atomic percent and 20 atomic percent, the remainder
being silver. In some embodiments, the atomic percent of tungsten
and/or molybdenum in the alloy may be at least 0.1 atomic percent,
at least 1 atomic percent, at least 1.5 atomic percent, at least 5
atomic percent, at least 10 atomic percent, or at least 20 atomic
percent, the remainder being silver. Other atomic percentages
outside of this range may be used as well.
[0017] The barrier layer may have a thickness suitable for a
particular application. For example, the barrier layer thickness
may be greater than about 1 microinch (e.g., between about 1
microinch and about 250 microinches, between about 1 microinch and
about 200 microinches, between about 1 microinch and about 150
microinches, between about 1 microinch and about 100 microinches,
between about 1 microinch and 50 microinches); in some cases,
greater than about 5 microinches (e.g., between about 5 microinches
and about 100 microinches, between about 5 microinches and 50
microinches); greater than about 25 microinches (e.g., between
about 25 microinches and about 100 microinches, between about 1
microinch and 50 microinches). It should be understood that other
barrier layer thicknesses may also be suitable. Thickness may be
measured by techniques known to those in the art.
[0018] In some embodiments, it may be preferable for the barrier
layer to be formed directly on the base material. Such embodiments
may be preferred over certain prior art constructions that utilize
a layer between the barrier layer and the base material because the
absence of such an intervening layer can save on overall material
costs. Though, it should be understood that in other embodiments,
one or more layers may be formed between the barrier layer and the
base material.
[0019] The metal layer may comprise one or more precious metals.
Examples of suitable precious metals include Ru, Rh, Os, Ir, Pd,
Pt, Ag, and/or Au. In some embodiments, the precious metal is
selected from the group consisting Ru, Os, Ir, Pd, Pt, Ag, and Au,
or combinations thereof. Gold may be preferred in some embodiments.
In some embodiments, the metal layer consists essentially of one
precious metal. In some embodiments, it may be preferable that the
metal layer is free of tin. In some cases, the precious metal is
not rhodium. In other cases, the metal layer may comprise an alloy
that includes at least one precious metal and at least one other
metal. The other metal may be selected from Ni, W, Fe, B, S, Co,
Mo, Cu, Cr, Zn, and Sn, amongst others.
[0020] In some embodiments, the metal layer comprises a silver
alloy (i.e., silver-based alloys). Such alloys may also comprise
tungsten and/or molybdenum. Silver alloys are known in the art, for
example, see U.S. Publication No. 2011/0223442 by Dadvand et al.,
filed Mar. 12, 2010, herein incorporated by reference. In some
embodiments, the barrier layer comprises a silver-tungsten alloy.
Other silver alloys may also be employed. In some cases, the atomic
percent of tungsten and/or molybdenum in the alloy may be between
0.1 atomic percent and 50 atomic percent; and, in some cases,
between 0.1 atomic percent and 20 atomic percent, the remainder
being silver. In some embodiments, the atomic percent of tungsten
and/or molybdenum in the alloy may be at least 0.1 atomic percent,
at least 1 atomic percent, at least 1.5 atomic percent, at least 5
atomic percent, at least 10 atomic percent, or at least 20 atomic
percent, the remainder being silver. Other atomic percentages
outside of this range may be used as well.
[0021] In some embodiments, the metal layer comprises a
silver-based alloy and the barrier layer comprises a nickel-based
alloy. In some cases, the metal layer comprises a silver-based
alloy further comprising molybdenum and/or tungsten and the barrier
layer comprises a nickel-based alloy further comprising molybdenum
and/or tungsten. In some cases, the metal layer comprises a
silver-tungsten alloy and the barrier layer comprises a
nickel-tungsten alloy.
[0022] The metal layer may have any suitable thickness. It may be
advantageous for the metal layer to be thin, for example, to save
on material costs. For example, the metal layer thickness may be
less than 30 microinches (e.g., between about 1 microinch and about
30 microinches; in some cases, between about 5 microinches and
about 30 microinches); in some cases the metal layer thickness may
be less than 20 microinches (e.g., between about 1 microinch and
about 20 microinches; in some cases, between about 5 microinches
and about 20 microinches); and, in some cases, the metal layer
thickness may be less than 10 microinches (e.g., between about 1
microinch and about 10 microinches; in some cases, between about 5
microinches and about 10 microinches). It should be understood that
other metal layer thicknesses may also be suitable.
[0023] In some embodiments, it may preferable for the metal layer
to be formed directly on the barrier material. Such embodiments may
be preferred over certain prior art constructions that utilize a
layer between the metal layer and the barrier material because the
absence of such an intervening layer can save on overall material
costs. Though, it should be understood that in other embodiments,
one or more layers may be formed between the metal layer and the
barrier material.
[0024] The metal layer may cover the entire barrier layer. However,
it should be understood that in other embodiments, the metal layer
covers only part of the barrier layer. In some cases, the metal
layer covers at least 50% of the surface area of the barrier layer;
in other cases, at least 75% of the surface area of the barrier
layer. In some cases, an element from the barrier layer may be
incorporated within the metal layer and/or an element from the
metal layer may be incorporated into the barrier layer.
[0025] In some cases, the coating (e.g., the barrier layer, rhodium
layer, and/or the metal layer) may have a particular
microstructure. For example, at least a portion of the coating may
have a nanocrystalline microstructure. As used herein, a
"nanocrystalline" structure refers to a structure in which the
number-average size of crystalline grains is less than one micron.
The number-average size of the crystalline grains provides equal
statistical weight to each grain and is calculated as the sum of
all spherical equivalent grain diameters divided by the total
number of grains in a representative volume of the body. The
number-average size of crystalline grains may, in some embodiments,
be less than 100 nm (e.g., 1 nm to 100 nm). In some embodiments, at
least a portion of the coating may have an amorphous structure. As
known in the art, an amorphous structure is a non-crystalline
structure characterized by having no long range symmetry in the
atomic positions. Examples of amorphous structures include glass,
or glass-like structures. Some embodiments may provide coatings
having a nanocrystalline structure throughout essentially the
entire coating. Some embodiments may provide coatings having an
amorphous structure throughout essentially the entire coating.
[0026] In some embodiments, the coating may comprise various
portions having different microstructures. For example, the barrier
layer may have a different microstructure than the metal layer
and/or the rhodium layer. The coating may include, for example, one
or more portions having a nanocrystalline structure and one or more
portions having an amorphous structure. In one set of embodiments,
the coating comprises nanocrystalline grains and other portions
which exhibit an amorphous structure. In some cases, the coating,
or a portion thereof (i.e., a portion of the barrier layer, a
portion of the metal layer, a portion of the rhodium layer, or a
portion of two of the layers, or all three of the layers), may
comprise a portion having crystal grains, a majority of which have
a grain size greater than one micron in diameter. In some
embodiments, the coating may include other structures or phases,
alone or in combination with a nanocrystalline portion or an
amorphous portion. Those of ordinary skill in the art would be able
to select other structures or phases suitable for use in the
context of the invention.
[0027] Advantageously, the coating (i.e., the barrier layer, the
metal layer, the rhodium layer, or two of the layers, or all three
of the layers) may be substantially free of elements or compounds
having a high toxicity or other disadvantages. In some instances,
it may also be advantageous for the coating to be substantially
free of elements or compounds that are deposited using species that
have a high toxicity or other disadvantages. For example, in some
cases, the coating is free of chromium (e.g., chromium oxide),
which is often deposited using chromium ionic species that are
toxic (e.g., Cr.sup.6+). Such coating may provide various
processing, health, and environmental advantages over certain
previous coatings.
[0028] In some embodiments, metal, non-metal, and/or metalloid
materials, salts, etc. (e.g., phosphate or a redox mediator such as
potassium ferricyanide, or fragment thereof) may be incorporated
into the coating.
[0029] The composition of the coatings, or portions or layers
thereof, may be characterized using suitable techniques known in
the art, such as Auger electron spectroscopy (AES), X-ray
photoelectron spectroscopy (XPS), etc. For example, AES and/or XPS
may be used to characterize the chemical composition of the surface
of the coating.
[0030] Base material 30 may be coated to form coated articles, as
described above. In some cases, the base material may comprise an
electrically conductive material, such as a metal, metal alloy,
intermetallic material, or the like. Suitable base materials
include steel, copper, aluminum, brass, bronze, nickel, polymers
with conductive surfaces and/or surface treatments, transparent
conductive oxides, amongst others. In some embodiments, copper base
materials are preferred.
[0031] In some embodiments, a lubricant layer may be formed as an
upper portion of the coating. The lubricant layer may comprise, for
example, an organic material, a self-assembled monolayer, carbon
nanotubes, and the like. In some cases, the presence of a lubricant
layer reduces the coefficient of friction of the coating as
compared to a substantially similar coating but which does not
include the lubricant layer. The lubricant layer may be formed of
any suitable material, for example halogen-containing organic
lubricant, a polyphenyl-containing organic lubricant, or a
polyether-containing lubricant. In one embodiment, the lubricant
layer is formed of a halogen-containing organic lubricant. Specific
non-limiting examples of lubricants include Evabrite.TM. (Enthone),
Au lube (AMP), NyeTact.RTM. 570H (Nye Lubricants), FS-5 (Gabriel
Performance Products), S-30 (Gabriel Performance Products), and
MS-383H (Miller-Stephenson). Another non-limiting example of a
lubricant is chlorotrifluoroethylene. In some cases, the lubricant
layer comprises a monolayer formed on the surface of the coating.
In some cases, the lubricant may be as described in U.S.
Publication No. 2012/0118755 to Dadvand et al., filed Sep. 14, 2011
or U.S. Publication No. 2012/0121925 by Trenkle et al., filed Sep.
14, 2011, herein incorporated by reference.
[0032] Those of ordinary skill in the art will be aware of suitable
methods for forming a lubricant layer on a coating. For example, in
some embodiments, an article comprising the coating may exposed
(e.g., dipped into) to the lubricant (e.g., optionally in a
solution), and the article may then be allowed to dry, thereby
forming the lubricant layer on the upper portion of the
coating.
[0033] In some embodiments, an article comprising a lubricant layer
formed on coating may have a reduced coefficient of friction as
compared to a substantially similar article which does not comprise
the lubricant layer. In some cases, the article having the
lubricant layer has a co-efficient of friction which is at least
two times less, at least three times less, at least four times
less, at least five times less, or at least ten times less than an
article which not having the lubricant layer.
[0034] In some cases, an article having a lubricant layer may have
better wear durability as compared to a substantially similar
article which does not have a lubricant layer. Those of ordinary
skill in the art will be aware of suitable methods to determine the
wear durability of a material (e.g., ball-on-plate-type
reciprocating friction abrasion test, wherein the ball and plate
both are coated with a layer of the alloy, and optionally the
lubricant layer). For example, in some embodiments, minimal or no
wear-through may be observed for an article comprising a
silver-based alloy and a lubricant layer over 50 cycles, 100
cycles, 250 cycles, 500 cycles, or 1000 cycles, with a 100 g
applied load, wherein a substantially similar article which does
not comprise the lubricant layer may show substantial or complete
wear-through.
[0035] The articles can be used in a variety of applications
including electrical applications such as electrical connectors
(e.g., plug-type). The coating can impart desirable characteristics
to an article, such as durability, corrosion resistance, and
improved electrical conductivity. These properties can be
particularly advantageous for articles in electrical applications
such as electrical connectors, which may experience rubbing or
abrasive stress upon connection to and/or disconnection from an
electrical circuit that can damage or otherwise reduce the
conductivity of a conductive layer on the article. Non-limiting
examples of electrical connectors include infrared connectors, USB
connectors, battery chargers, battery contacts, automotive
electrical connectors, etc. In some embodiments, the presence of
the first layer of a coating may provide at least some of the
durability and corrosion resistance properties to the coating. In
some embodiments, the coating may impart decorative qualities.
[0036] The coatings described herein may impart advantageous
properties to an article, such as an electrical connector. In some
embodiments, the coating, or layer of the coating, may have a low
electrical resistivity. For example, the electrical resistivity may
be less than 100 microohm-centimeters, less than 50
microohm-centimeters, less than 10 microohm-centimeters, or less
than 2 microohm-centimeters.
[0037] The coating or layer of the coating may have a hardness of
at least 1 GPa, at least 1.5 GPa, at least 2 GPa, at least 2.5 GPa,
or at least 3 GPa. Those of ordinary skill in the art would readily
be able to measure these properties.
[0038] Coating 20 may be formed using an electrodeposition process.
Electrodeposition generally involves the deposition of a material
(e.g., electroplate) on a substrate by contacting the substrate
with an electrodeposition bath and flowing electrical current
between two electrodes through the electrodeposition bath, i.e.,
due to a difference in electrical potential between the two
electrodes. For example, methods described herein may involve
providing an anode, a cathode, an electrodeposition bath (also
known as an electrodeposition fluid) associated with (e.g., in
contact with) the anode and cathode, and a power supply connected
to the anode and cathode. In some cases, the power supply may be
driven to generate a waveform for producing a coating, as described
more fully below.
[0039] Generally, the barrier layer, the metal layer, and the
rhodium layer of the coating may be applied using separate
electrodeposition baths. In some cases, individual articles may be
connected such that they can be sequentially exposed to separate
electrodeposition baths, for example in a reel-to-reel process. For
instance, articles may be connected to a common conductive
substrate (e.g., a strip). In some embodiments, each of the
electrodeposition baths may be associated with separate anodes and
the interconnected individual articles may be commonly connected to
a cathode.
[0040] The electrodeposition process(es) may be modulated by
varying the potential that is applied between the electrodes (e.g.,
potential control or voltage control), or by varying the current or
current density that is allowed to flow (e.g., current or current
density control). In some embodiments, the coating may be formed
(e.g., electrodeposited) using direct current (DC) plating, pulsed
current plating, reverse pulse current plating, or combinations
thereof. In some embodiments, reverse pulse plating may be
preferred, for example, to form the barrier layer (e.g.,
nickel-tungsten alloy). Pulses, oscillations, and/or other
variations in voltage, potential, current, and/or current density,
may also be incorporated during the electrodeposition process, as
described more fully below. For example, pulses of controlled
voltage may be alternated with pulses of controlled current or
current density. In general, during an electrodeposition process an
electrical potential may exist on the substrate (e.g., base
material) to be coated, and changes in applied voltage, current, or
current density may result in changes to the electrical potential
on the substrate. In some cases, the electrodeposition process may
include the use waveforms comprising one or more segments, wherein
each segment involves a particular set of electrodeposition
conditions (e.g., current density, current duration,
electrodeposition bath temperature, etc.), as described more fully
below.
[0041] Some embodiments of the invention involve electrodeposition
methods wherein the grain size of electrodeposited materials (e.g.,
metals, alloys, and the like) may be controlled. In some
embodiments, selection of a particular coating (e.g., electroplate)
composition, such as the composition of an alloy deposit, may
provide a coating having a desired grain size. In some embodiments,
electrodeposition methods (e.g., electrodeposition conditions)
described herein may be selected to produce a particular
composition, thereby controlling the grain size of the deposited
material. The methods of the invention may utilize certain aspects
of methods described in U.S. Patent Publication No. 2006/02722949,
entitled "Method for Producing Alloy Deposits and Controlling the
Nanostructure Thereof using Negative Current Pulsing
Electro-deposition, and Articles Incorporating Such Deposits" and
U.S. application Ser. No. 12/120,564, entitled "Coated Articles and
Related Methods," filed May 14, 2008, which are incorporated herein
by reference in their entirety. Aspects of other electrodeposition
methods may also be suitable including those described in U.S.
Patent Publication No. 2006/0154084 and U.S. application Ser. No.
11/985,569, entitled "Methods for Tailoring the Surface Topography
of a Nanocrystalline or Amorphous Metal or Alloy and Articles
Formed by Such Methods," filed Nov. 15, 2007, which are
incorporated herein by reference in their entireties. In some
embodiments, a nickel-based alloy and/or metal coating may be
electrodeposited according to the methods described in U.S.
Publication No. 2011/0008646 by Cahalen et al., filed Jul. 10,
2009, and/or U.S. Publication No. 2012/0328904 by Baskin et al.,
filed Jun. 22, 2012, each herein incorporated by reference. In some
embodiments, a silver-based alloy and/or metal coating may be
electrodeposited according to the methods described in U.S.
Publication No. 2011/0223442 by Dadvand et al., filed Mar. 12,
2010, herein incorporated by reference.
[0042] In some embodiments, a coating, or portion thereof, may be
electrodeposited using direct current (DC) plating. For example, a
substrate (e.g., electrode) may be positioned in contact with
(e.g., immersed within) an electrodeposition bath comprising one or
more species to be deposited on the substrate. A constant, steady
electrical current may be passed through the electrodeposition bath
to produce a coating, or portion thereof, on the substrate. In some
embodiments, the potential that is applied between the electrodes
(e.g., potential control or voltage control) and/or the current or
current density that is allowed to flow (e.g., current or current
density control) may be varied. For example, pulses, oscillations,
and/or other variations in voltage, potential, current, and/or
current density, may be incorporated during the electrodeposition
process. In some embodiments, pulses of controlled voltage may be
alternated with pulses of controlled current or current density. In
some embodiments, the coating may be formed (e.g.,
electrodeposited) using pulsed current electrodeposition, reverse
pulse current electrodeposition, or combinations thereof.
[0043] In some cases, a bipolar waveform may be used, comprising at
least one forward pulse and at least one reverse pulse, i.e., a
"reverse pulse sequence." As noted above, the electrodeposition
baths described herein are particularly well suited for depositing
coatings using complex waveforms such as reverse pulse sequences.
In some embodiments, the at least one reverse pulse immediately
follows the at least one forward pulse. In some embodiments, the at
least one forward pulse immediately follows the at least one
reverse pulse. In some cases, the bipolar waveform includes
multiple forward pulses and reverse pulses. Some embodiments may
include a bipolar waveform comprising multiple forward pulses and
reverse pulses, each pulse having a specific current density and
duration. In some cases, the use of a reverse pulse sequence may
allow for modulation of composition and/or grain size of the
coating that is produced.
[0044] A coating may be applied using an electrodeposition process
at a current density of at least 0.001 A/cm.sup.2, at least 0.01
A/cm.sup.2, or at least 0.02 A/cm.sup.2. Current densities outside
these ranges may be used as well. In some cases, a direct current
is employed having a direct current density of greater than about
10 mA/cm.sup.2, greater than about 15 mA/cm.sup.2, greater than
about 20 mA/cm.sup.2, greater than about 30 mA/cm.sup.2, or greater
than about 50 mA/cm.sup.2.
[0045] For current which is applied in pulses, the frequency may be
any suitable frequency (e.g., between 0.1 Hertz and about 100 Hz).
Similarly, the voltage may be any suitable voltage (e.g., between
about 0.1 V and about 1 V).
[0046] The deposition rate of the coating may be controlled. In
some instances, the deposition rate may be at least 0.1
microns/minute, at least 0.3 microns/minute, at least 1
micron/minute, or at least 3 microns/minute. Deposition rates
outside these ranges may be used as well.
[0047] Those of ordinary skill in the art would recognize that the
electrodeposition processes described herein are distinguishable
from electroless processes which primarily, or entirely, use
chemical reducing agents to deposit the coating, rather than an
applied voltage. The electrodeposition baths described herein may
be substantially free of chemical reducing agents that would
deposit coatings, for example, in the absence of an applied
voltage.
[0048] The electrodeposition processes use suitable
electrodeposition baths. Such baths typically include species that
may be deposited on a substrate (e.g., electrode) upon application
of a current. For example, an electrodeposition bath comprising one
or more metal species (e.g., metals, salts, other metal sources)
may be used in the electrodeposition of a coating comprising a
metal (e.g., an alloy). In some cases, the electrochemical bath
comprises nickel species (e.g., nickel sulfate) and tungsten
species (e.g., sodium tungstate) and may be useful in the formation
of, for example, nickel-tungsten alloy coatings.
[0049] Typically, the electrodeposition baths comprise an aqueous
fluid carrier (e.g., water). However, it should be understood that
other fluid carriers may be used in the context of the invention,
including, but not limited to, molten salts, cryogenic solvents,
alcohol baths, and the like. Those of ordinary skill in the art
would be able to select suitable fluid carriers for use in
electrodeposition baths. The pH of the electrodeposition bath can
be from about 2.0 to 12.0. In some cases, the electrodeposition
bath may be selected to have a pH from about 7.0-9.0. In some
cases, the electrodeposition bath may have a pH from about 7.6 to
8.4, or, in some cases, from about 7.9 to 8.1. However, it should
be understood that the pH may be outside the above-noted ranges.
The pH of the bath may be adjusted using any suitable agent known
to those of ordinary skill in the art. In some embodiments, the pH
of the bath is adjusted using a base, such as a hydroxide salt
(e.g., potassium hydroxide). In some embodiments, the pH of the
bath is adjusted using an acid (e.g., nitric acid).
[0050] The electrodeposition baths may include other additives,
such as wetting agents, complexing agents, brightening or leveling
agents, and the like. Those of ordinary skill in the art would be
able to select appropriate additives for use in a particular
application.
[0051] In some embodiments, the electrodeposition bath may comprise
at least one complexing agent (i.e., a complexing agent or mixture
of complexing agents). A complexing agent refers to any species
which can coordinate with the ions contained in the solution. In
some embodiments, a complexing agent or mixture of complexing
agents may permit codeposition of at least two elements.
[0052] In some cases, the baths may include at least one wetting
agent. A wetting agent refers to any species capable of reducing
the surface tension of the electrodeposition bath and/or increasing
the ability of gas bubbles to detach from surfaces in the bath. For
example, the substrate may comprise a hydrophilic surface, and the
wetting agent may enhance the compatibility (e.g., wettability) of
the bath relative to the substrate. In some cases, the wetting
agent may also reduce the number of defects within the metal
coating that is produced. The wetting agent may comprise an organic
species, an inorganic species, an organometallic species, or
combinations thereof. In some embodiments, the wetting agent may be
selected to exhibit compatibility (e.g., solubility) with the
electrodeposition bath and components thereof.
[0053] In some embodiments, the baths may include at least one
brightening agent. The brightening agent may be any species that,
when included in the baths described herein, improves the
brightness and/or smoothness of the electrodeposited coating
produced. In some cases, the brightening agent is a neutral
species. In some cases, the brightening agent comprises a charged
species (e.g., a positively charged ion, a negatively charged
ion).
[0054] Those of ordinary skill in the art would be able to select
the appropriate combination of ionic species, wetting agent,
complexing agent and/or other additives (e.g., brightening agents)
suitable for use in a particular application. Generally, the
additives in a bath are compatible with electrodeposition
processes, i.e., a bath may be suitable for electrodeposition
processes. One of ordinary skill in the art would be able to
recognize a bath that is suitable for electrodeposition processes
Likewise, one of ordinary skill in the art would be able to
recognize additives that, when added to a bath, would make the bath
not suitable for electrodeposition processes.
[0055] In some cases, the operating range for the electrodeposition
baths described herein is 5-100.degree. C., 10-70.degree. C.,
10-30.degree. C., 25-80.degree. C., or, in some cases,
40-70.degree. C. In some cases, the temperature is less than
80.degree. C. However, it should be understood that other
temperature ranges may also be suitable.
[0056] Methods of the invention may be advantageous in that
coatings having various compositions may be readily produced by a
single electrodeposition step. For example, a coating comprising a
layered composition, graded composition, etc., may be produced in a
single electrodeposition bath and in a single deposition step by
selecting a waveform having the appropriate segments. The coated
articles may exhibit enhanced corrosion resistance and surface
properties.
[0057] It should be understood that other techniques may be used to
produce coatings as described herein, including vapor-phase
processes, sputtering, physical vapor deposition, chemical vapor
deposition, thermal oxidation, ion implantation, spray coating,
powder-based processes, slurry-based processes, etc.
[0058] In some embodiments, the invention provides coated articles
that are capable of resisting corrosion, and/or protecting an
underlying substrate material from corrosion, in one or more
potential corrosive environments. Examples of such corrosive
environments include, but are not limited to, aqueous solutions,
acid solutions, alkaline or basic solutions, or combinations
thereof. For example, coated articles described herein may be
resistant to corrosion upon exposure to (e.g., contact with,
immersion within, etc.) a corrosive environment, such as a
corrosive liquid, vapor, or humid environment.
[0059] The corrosion resistance of coated articles may be assessed
using tests such as ASTM B845, entitled "Standard Guide for Mixed
Flowing Gas (MFG) Tests for Electrical Contacts" following the
Class IIa protocol, may also be used to assess the corrosion
resistance of coated articles. This test outline a procedure in
which coated substrate samples are exposed to a corrosive
atmosphere (e.g., a mixture of NO.sub.2, H.sub.2S, Cl.sub.2, and
SO.sub.2). The mixture of flowing gas can comprise 200+/-50 ppb of
NO.sub.2, 10+/-5 ppb of H.sub.2S, 10+/-3 ppb of Cl.sub.2, and
100+/-20 ppb SO.sub.2. The temperature and relative humidity may
also be controlled. For example, the temperature may be
30+/-1.degree. C., and the relative humidity may be 70+/-2%.
[0060] The exposure time of an article to a gas or gas mixture can
be variable, and is generally specified by the end user of the
product or coating being tested. For example, the exposure time may
be at least 30 minutes, at least 2 hours, at least 1 day, at least
5 days, or at least 40 days. After a prescribed amount of exposure
time, the sample is examined (e.g., visually by human eye and/or
instrumentally as described below) for signs of change to the
surface appearance and/or electrical conductivity resulting from
corrosion and/or spotting. The test results can be reported using a
simple pass/fail approach after the exposure time.
[0061] The coating subjected to the test conditions discussed above
may be evaluated, for example, by measuring the change in the
appearance of the coating. For instance, a critical surface area
fraction may be specified, along with a specified time. If, after
testing for the specified time, the fraction of the surface area of
the coating that changes in appearance resulting from corrosion is
below the specified critical value, the result is considered
passing. If more than the critical fraction of surface area has
changed in appearance resulting from corrosion, then the result is
considered failing. For example, the extent of corrosive spotting
may be determined. The extent of spotting may be quantified by
determining the number density and/or area density of spots after a
specified time. For example, the number density may be determined
counting the number of spots per unit area (e.g., spots/cm.sup.2).
The spot area density can be evaluated by measuring the fraction of
the surface area occupied by the spots, where, for example, an area
density equal to unity indicates that 100% of the surface area is
spotted, an area density equal to 0.5 indicates that 50% of the
surface area is spotted, and an area density equal to 0 indicates
that none of the surface area is spotted.
[0062] In some cases, the coated article that is exposed to a mixed
flowing gas according to ASTM B845, protocol Class IIa, for 5 days
has a spotting area density of less than 0.10; in some cases, less
than 0.05; and, in some cases, 0. In some embodiments, the coated
article exposed to these conditions has a number density of spots
of less than 3 spots/cm.sup.2; in some embodiments, less than 2
spots/cm.sup.2; and, in some embodiments, 0 spots/cm.sup.2. It
should be understood that spotting area densities and the number
density of spots may be outside the above-noted ranges.
[0063] The low-level contact resistance of a sample may be
determined before and/or after exposure to a corrosive environment
for a set period of time according to one of the tests described
above. In some embodiments, the low-level contact resistance may be
determined according to specification EIA 364, test procedure 23.
Generally, the contact resistivity of a sample may be measured by
contacting the sample under a specified load and current with a
measurement probe having a defined cross-sectional area of contact
with the sample. For example, the low-level contact resistance may
be measured under a load of 25 g, 50g, 150 g, 200 g, etc.
Generally, the low-level contact resistance decreases as the load
increases.
[0064] A threshold low-level contact resistance value may be set
where measurement of a low-level contact resistance value for a
sample above the threshold indicates that the sample failed the
test. For example, the threshold low-level contact resistance value
under a load of 25 g after 5 days exposure to mixed flowing gas
according to ASTM B845, protocol Class IIa, may be greater than 1
mOhm, greater than 10 mOhm, greater than 100 mOhm, or greater than
1000 mOhm. It should be understood that other threshold low-level
contact resistance values may be achieved.
[0065] In some embodiments, a coated article has reduced low-level
contact resistance. Reduced low-level contact resistance may be
useful for articles used in electrical applications such as
electrical connectors. In some cases, an article may have a
low-level contact resistance under a load of 25 g of less than
about 100 mOhm; in some cases, less than about 10 mOhm; in some
cases, less than about 5 mOhm; and, in some cases, less than about
1 mOhm. It should be understood that the article may have a
low-level contact resistance outside this range as well. It should
also be understood that the cross-sectional area of contact by the
measurement probe may affect the value of the measured low-level
contact resistance.
[0066] Durability of the coated articles may also be tested. In
some embodiments, durability tests may be performed in conjunction
with the corrosion tests discussed above and/or contact resistance
measurements. A durability test may comprise rubbing the surface of
a coated article with an object for a period of time and then
visually inspecting the coating for damage and/or measuring the
contact resistance of the coating. In one non-limiting example of a
durability test, a counterbody may be held against the surface of a
coated article at a set load and the coated article may be
reciprocated such that the counterbody rubs against the surface of
the coated article. For example, the counterbody may be held
against the surface of a coated article at a load of 50 g. The
duration of the reciprocal motion may be measured, for example, by
the number of cycles per unit time per unit time. For instance, the
reciprocal motion may be carried out for 500 seconds at a rate of 1
cycle per second. In some embodiments, durability may be measured
before and/or after subjection of an article to a corrosion test as
discussed in more detail above. The contact resistance of the
coating may be measured as described above. In some cases, the
coating may be visually inspected for wear tracks. The wear tracks
may, in some embodiments, be analyzed by measuring the width of
exposed base material between the wear tracks after a specific
number of cycles under a specific load. In some instances, the
analysis may be a "pass/fail" test, where a threshold width of
exposed base material between wear tracks is set such that the
presence of a width of exposed base material above the threshold
indicates the article failed the test.
[0067] The following examples should not be considered to be
limiting but illustrative of certain features of the invention.
EXAMPLES
[0068] All base materials for the following examples were cleaned
and activated prior to electroplating using standard practices
which would be familiar to one of ordinary skill in the art. The
base material for all samples provided in the examples was Cu alloy
7025. Summaries of the example coatings and their performance
metrics are shown in Tables 1 and 2.
[0069] Nanocrystalline NiW alloy deposits in the following examples
were produced using a pulsed waveform and suitable bath chemistry
operating at 60.degree. C.
[0070] Nickel deposits in the following examples were produced
using a DC current and nickel sulfamate plating chemistry operating
at 60.degree. C. and pH 3.8. The bath comprised Ni sulfamate at
431-533 g/L, NiCl.sub.2-6H.sub.2O at 14-21 g/L, and boric acid at
40-50 g/L.
[0071] Nanocrystalline AgW alloy deposits in the following examples
were produced using a DC current and suitable bath chemistry
operating at 50.degree. C.
[0072] Rhodium deposits in the following examples were produced
using a DC current and rhodium sulfate plating chemistry at
50.degree. C. and pH 2.0. The bath comprised rhodium sulfate at 10
g/L rhodium metal and an organic brightening agent.
[0073] MFG class IIA testing refers to Mixed Flowing Gas test
environment class IIA (ASTM B845).
[0074] Heat and humidity testing refers to a heat and humidity test
conducted in an environmental chamber which maintains the
temperature at 85.degree. C. and the relative humidity at 85% RH
using distilled water.
[0075] Dry heat testing refers to a dry heat test conducted in a
constant temperature oven maintained at 150.degree. C. for 1000
hours.
[0076] Neutral salt spray testing (NSST) refers to a neutral salt
spray test conducted in an environmental chamber with a 5% sodium
chloride salt fog per the ASTM B-117 standard test procedure.
Example 1
[0077] A series of flat coupons were cleaned, activated, and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy, and 80 microinches of a nanocrystalline AgW alloy. The set
of coupons was subjected to each of the tests shown in Table 2. The
results on these tests showed some level of discoloration or
corrosion in all cases.
Example 2
[0078] A series of flat coupons were cleaned, activated, and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy, 80 microinches of a nanocrystalline AgW alloy, and 0.5
microinches of rhodium. The set of coupons was subjected to each of
the tests shown in Table 2. The results on these tests showed some
level of discoloration or corrosion distributed across the coupons
in all cases.
Example 3
[0079] A series of flat coupons were cleaned, activated, and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy, 80 microinches of a nanocrystalline AgW alloy, and 1.5
microinches of rhodium. The set of coupons was subjected to each of
the tests shown in Table 2. The result on the MFG test showed
slight discoloration distributed across the coupons. The other test
conditions showed no evidence of discoloration or corrosion.
Example 4
[0080] A series of flat coupons were cleaned, activated, and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy, 80 microinches of a nanocrystalline AgW alloy, and 3
microinches of rhodium. The set of coupons was subjected to each of
the tests shown in Table 2. The results on the tests showed no
evidence or discoloration or corrosion.
Example 5
[0081] A series of flat coupons were cleaned, activated and
subsequently plated with 40 microinches of nickel, 80 microinches
of a nanocrystalline AgW alloy, and 3 microinches of rhodium. The
set of coupons was subjected to each of the tests shown in Table 2.
The results on the tests showed no evidence or discoloration or
corrosion.
Example 6
[0082] A series of flat coupons were cleaned, activated and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy, 80 microinches of a nanocrystalline AgW alloy, and 5
microinches of rhodium. The set of coupons was subjected to each of
the tests shown in Table 2. The results on the tests showed no
evidence or discoloration or corrosion.
Example 7
[0083] A series of flat coupons were cleaned, activated, and
subsequently plated with 40 microinches of a nanocrystalline NiW
alloy deposit, 80 microinches of a nanocrystalline AgW alloy
deposit, and 10 microinches of rhodium. The set of coupons was
subjected to the MFG and NSST tests shown in Table 2. The results
on the tests showed localized corrosion. SEM/EDS inspection of
samples prior to testing showed stress cracks in the Rhodium
deposit.
TABLE-US-00001 TABLE 1 List of examples Rh AgW Alloy NiW Alloy
Nickel Thickness Thickness Thickness Thickness Example (microinch)
(microinch) (microinches) (microinches) 1 0 80 40 -- 2 0.5 80 40 --
3 1.5 80 40 -- 4 3 80 40 -- 5 3 80 -- 60 6 5 80 40 -- 7 10 80 40
--
TABLE-US-00002 TABLE 2 Example performance Heat and MFG Class
Humidity NSST Examples IIA 5 days (5 days) (96 hours) Dry Heat 1
Discoloration Corrosion Corrosion Discoloration 2 Discoloration
Corrosion Corrosion Discoloration 3 Minor PASS PASS PASS
discoloration 4 PASS PASS PASS PASS 5 PASS PASS PASS PASS 6 PASS
PASS PASS PASS 7 Localized Not tested Localized Not tested
discoloration corrosion
* * * * *