U.S. patent application number 17/367278 was filed with the patent office on 2021-10-28 for cobalt chrome etching process.
This patent application is currently assigned to Tech Met, Inc.. The applicant listed for this patent is Tech Met, Inc.. Invention is credited to Daniel Schutzer, Michael VIDRA.
Application Number | 20210332483 17/367278 |
Document ID | / |
Family ID | 1000005697637 |
Filed Date | 2021-10-28 |
United States Patent
Application |
20210332483 |
Kind Code |
A1 |
VIDRA; Michael ; et
al. |
October 28, 2021 |
COBALT CHROME ETCHING PROCESS
Abstract
Compositions and methods for etching cobalt chromium alloys are
disclosed. The compositions generally include at least two mineral
acids, certain component metals of the alloy to be etched, and
optionally iron (Fe). For example, when etching a cobalt chromium
molybdenum alloy, the component metals may include chromium (Cr),
molybdenum (Mo), and optionally, cobalt (Co). The at least two
mineral acids may include hydrochloric acid (HCl), nitric acid
(HNO.sub.3), and hydrofluoric acid (HF). The methods provide for
etching an entire surface of a substrate or etching a surface of a
substrate in a pattern using selective coating patterns and/or
coating removal. Thus, unlimited patterns, as well as etch depths
and variations in etch depths are achievable using the compositions
and methods disclosed. Moreover, the compositions and methods
provide cobalt chrome surfaces having very low surface roughness
(Ra) that are useful in the aerospace industry.
Inventors: |
VIDRA; Michael; (Export,
PA) ; Schutzer; Daniel; (Irwin, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tech Met, Inc. |
Glassport |
PA |
US |
|
|
Assignee: |
Tech Met, Inc.
Glassport
PA
|
Family ID: |
1000005697637 |
Appl. No.: |
17/367278 |
Filed: |
July 2, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16715530 |
Dec 16, 2019 |
11053595 |
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17367278 |
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62892744 |
Aug 28, 2019 |
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62779545 |
Dec 14, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23F 1/28 20130101; C09K
13/08 20130101; C09K 13/12 20130101 |
International
Class: |
C23F 1/28 20060101
C23F001/28; C09K 13/12 20060101 C09K013/12; C09K 13/08 20060101
C09K013/08 |
Claims
1. A composition for etching a cobalt chromium alloy, the
composition comprising: at least two mineral acids selected from
the groups consisting of hydrochloric acid (HCl), nitric acid
(HNO.sub.3), sulfuric acid (H.sub.2SO.sub.4), and hydrofluoric acid
(HF); and component metals of the cobalt chromium alloy, the
component metals comprising at least 0.2 g/l chromium (Cr) and at
least 0.1 g/l molybdenum (Mo), wherein the composition etches
cobalt chromium alloys at a rate of 0.1 to 1.0 mil/minute.
2. The composition according to claim 1, wherein the component
metals comprise at least 3.0 g/l Cr and at least 0.5 g/l Mo.
3. The composition of claim 1, comprising HCl, HF, and HNO.sub.3,
wherein the HCl is included at 1N-10N.
4. The composition of claim 1, comprising HCl, HF, and HNO.sub.3,
wherein the HNO.sub.3 is included at 0.05N-2.0N.
5. The composition of claim 1, comprising HCl, HF, and HNO.sub.3,
wherein the HF is included at 0.1N-2.0N.
6. The composition of claim 1, comprising: 1N-10N HCl; 0.05N-2.0N
HNO.sub.3; and 0.1N-2.0N HF.
7. The composition of claim 1, further comprising: 0.1-400 g/l Iron
(Fe), or 0.1-400 g/l cobalt (Co), or 0.1-400 g/l Fe and 0.1-400 g/l
Co.
8. The composition of claim 1, wherein the component metals
comprise cobalt (Co), Cr, and Mo provided in a native ratio of each
metal in the cobalt chromium alloy to be etched.
9. The composition of claim 8, wherein a total amount of the
component metals Co, Cr, and Mo in the composition does not exceed
400 g/l.
10. The composition of claim 8, comprising: 7-355 g/l Co; 3.0-170
g/l Cr; 0.5-40 g/l Mo; and optionally 0.1 to 400 g/l Iron (Fe).
11. The composition of claim 1, comprising: 2N-8N HCl; 0.05N-1.1N
HNO.sub.3; 0.4N-1.3N HF; 50-225 g/l Iron (Fe); 3.0-170 g/l Cr; and
0.5-40 g/l Mo.
12. The composition of claim 11, further comprising: 7-355 g/l
cobalt (Co).
13. The composition of claim 1, comprising: 1N-10N hydrochloric
acid (HCl); 0.05N-2.0N nitric acid (HNO.sub.3); 0.1N-2.0N
hydrofluoric acid (HF). 0.5-355 g/l cobalt (Co); 0.2-170 g/l
chromium (Cr); 0.1-40 g/l molybdenum (Mo); and optionally 0.1 to
400 g/l Iron (Fe).
14. The composition of claim 13, wherein a total amount of the
component metals Co, Cr, and Mo in the composition does not exceed
400 g/l.
15. A method for etching a cobalt chromium alloy work-piece, the
method comprising: contacting at least one surface of the
work-piece with a chemical etching composition according to claim
1, wherein the contacting step is carried out at a temperature of
20.degree. C. to 150.degree. C. for a time period of 1 minute to
200 minutes, and wherein the composition etches a surface of the
cobalt chromium alloy work-piece at a rate of 0.1 to 1.0
mil/minute.
16. The method of claim 15, further comprising, before the step of
contacting the work-piece with the chemical etching composition:
activating the at least one surface of the work-piece with an
activation solution comprising a 10% to 100% (v/v) aqueous solution
of a mineral acid.
17. The method of claim 15, wherein the contacting step is carried
out within 120 seconds of the activating step.
18. A work-piece formed by additive manufacturing using a powdered
cobalt chromium alloy, the work piece comprising an etched surface
that is substantially free of grains of the powdered cobalt
chromium alloy, has a surface roughness (R.sub.a) of less than 200
win, and no directional surface scratches.
19. A work-piece formed of a cobalt chromium alloy having a surface
with a surface roughness (R.sub.a) of less than 200 win, no
directional surface scratches, and absent cobalt chromium alloy
particles.
20. The work-piece of claim 19, wherein the surface roughness
(R.sub.a) is less than 100 win, and the work-piece forms at least a
portion of a component part of an aerospace vehicle.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
U.S. patent application Ser. No. 16/715,530 filed Dec. 16, 2019,
now U.S. Pat. No. 11,053,595, which claims priority to U.S.
Provisional Patent Application Ser. No. 62/779,545 filed Dec. 14,
2018, and U.S. Provisional Patent Application Ser. No. 62/892,744
filed Aug. 28, 2019, all of which are incorporated herein by
reference in their entirety.
TECHNICAL FIELD
[0002] This present disclosure pertains generally to compositions
for the controlled etching of cobalt chromium-based alloys and
methods of use thereof to etch cobalt chromes.
BACKGROUND
[0003] Cobalt chromium alloys, commonly referred to as
Cobalt-Chrome (CoCr), are generally corrosion resistant and
extremely hard. These outstanding properties result from the
crystallographic nature of cobalt, the strengthening effect of
chromium and other alloying elements, the formation of extremely
hard carbides, and the corrosion resistance imparted by chromium.
These qualities make CoCr alloys desirable in industrial, medical
and technical fields. It also makes the alloys very difficult to
chemically mill or chemically machine, by which we mean to
intentionally corrode or etch the material in a predictable and
controlled manner.
[0004] In several fields where CoCr is used, it is desirable to
obtain as smooth a surface condition as practical, without
excessive removal of material. This is particularly true with
respect to aerospace applications, where the target is to prepare a
surface for dye penetrant or other inspections, to improve air flow
patterns and characteristics, and to improve long term fatigue
performance.
[0005] Abrasive flow smoothing or machining has historically been
used for smoothing of cobalt chromium alloys. In such a process, a
highly viscous fluid comprising an abrasive material is forced over
surfaces and through internal passageways of a work-piece to polish
those surfaces and passageways. The viscosity of the fluid, and
often highly intricate system of piping connections needed to
direct the fluid through the passageways of the work-piece make
this process slow and expensive. Moreover, every unique work-piece
typically requires a uniquely designed system of piping
connections, adding to the expense of the process.
[0006] Certain chemistries have been shown to provide a relatively
smooth surface while only removing small amounts of material
through chemical attack, most notably, a mixture of concentrated
hydrogen peroxide and concentrated hydrochloric acid. These methods
are suitable only for superficial removal of material as the
mixture is volatile, depletes quickly, and suffers from aggressive
metal-ion driven decomposition of the peroxide. Further, this
solution commonly results in significant intergranular attack (IGA)
of the CoCr materials.
[0007] Accordingly, a controlled means of reliably and predictably
removing material from CoCr alloys through chemical machining is
desired, and would find application in several different fields,
including medical, aerospace, and specialty industrial. Moreover,
means to remove material from CoCr alloys in order to impart a
particular surface roughness or microscopic surface profile for
enhanced or accelerated bio-integration, or a particular surface
smoothness for aerospace applications that may improve air flow
patterns and characteristics and/or enhance dye penetrant or other
inspections is desired. Means to remove material from CoCr alloys
in order to reduce weight of a part, remove 3D printed support
structures, and improve long term fatigue performance, among other
applications is also desired.
SUMMARY
[0008] To meet these and other needs, the present disclosure
provides compositions useful for controlled chemical etching of
cobalt chromium alloys, and methods of their use to provide
surfaces having finely tunable characteristics, such as smooth
surfaces useful in the aerospace industry.
[0009] Disclosed herein are compositions for etching a cobalt
chromium alloy, such as a cobalt chromium molybdenum alloy, cobalt
chromium tungsten nickel alloy, cobalt nickel chromium molybdenum
alloy, or the like. The compositions generally comprise at least
two mineral acids and certain component metals of the alloy to be
etched. For example, when etching a cobalt chromium molybdenum
alloy, the metals may include chromium (Cr), molybdenum (Mo), and
optionally, cobalt (Co). The composition may comprise at least 0.2
g/l Cr, such as at least 3 g/l Cr, and at least 0.1 g/l Mo, such as
at least 0.5 g/l Mo. According to certain aspects, the composition
may also comprise iron, such as up to 400 g/l iron (Fe), and Co,
such as up to 400 g/l Co. Exemplary compositions include at least
two mineral acids and 0.2-400 g/l Cr, 0.1-400 g/l Mo, 0-400 g/l Co,
and 0-400 g/l Fe.
[0010] According to certain aspects, the component metals may be
included in amounts that mimic the ratio they are included in the
metal alloy (i.e., the native ratio of metals in the alloy). For
example, when the alloy is a cobalt chromium molybdenum alloy, the
component metals may be provided at about 63-68 wt. % Co, 27-30 wt.
% Cr, and 5-7 wt. % Mo, based on the total weight of the alloy.
[0011] According to certain aspects, the at least two mineral acids
may be selected from hydrochloric acid (HCl), nitric acid
(HNO.sub.3), sulfuric acid (H.sub.2SO.sub.4), iodic acid
(HIO.sub.3), and hydrofluoric acid (HF). According to certain
aspects, the at least two mineral acids may comprise HCl,
HNO.sub.3, and HF. For example, the composition may comprise 1-10N
HCl, 0.05-2.0N HNO.sub.3, and 0.1-2.0N HF. According to certain
aspects, the composition may be an aqueous solution.
[0012] The alloy material may be etched on one or more surfaces by
contacting the alloy material (e.g., surface of or all of a
work-piece) with any of the chemical etching compositions disclosed
herein. Before the work-piece can be etched with the chemical
etching compositions of disclosed herein, the work-piece may
require an activation step. An exemplary activation step includes
exposing the surface of the work-piece that is to be etched to a
mineral acid such as a 10% to 100% solution of concentrated
hydrochloric acid (v/v; dilution with an aqueous buffer or water).
The surface may be exposed to the mineral acid at a range of
temperatures, such as room temperature, wherein higher temperatures
require lower concentrations of the mineral acid. The alloy
material may be exposed to the mineral acid by submersion or
spraying.
[0013] Immediately after activation, such as within 120 seconds, or
within 60 seconds, or within 30 seconds, the work-piece may be
exposed to the chemical etching compositions as described herein
below. According to certain aspects, the work-piece may still be
"wet" with the activation solution (i.e., mineral acid such as the
10%-100% dilution of hydrochloric acid).
[0014] After the surface of the work-piece is activated, it may be
etched by contact with the chemical etching compositions, which may
include dipping or submersing the work-piece in the composition, or
spraying, rolling, or brushing the composition onto one or more
surfaces of the work-piece.
[0015] Thus, the present disclosure also includes methods for
etching an alloy material. According to certain aspects, one method
may include preparing one of the chemical etching compositions
described above, activating the alloy material (e.g., a work-piece)
with a mineral acid, and contacting the alloy material with the
chemical etching composition. According to certain aspects, the
step of contacting with the chemical etching composition may be
carried out immediately after the activation step, such as before
the alloy material dries (i.e., from exposure to the mineral acid),
or within 30 seconds after exposure to the mineral acid. According
to certain aspects the alloy material and/or the chemical
composition may be agitated during contact.
[0016] According to certain aspects, the alloy material may be
contacted with the chemical etching composition at a temperature of
from about 20.degree. C. to about 150.degree. C., such as from
about 30.degree. C. to about 105.degree. C., or from about
40.degree. C. to about 100.degree. C., or from about 50.degree. C.
to about 100.degree. C., or from about 60.degree. C. to about
100.degree. C. According to yet further aspects, the alloy material
may be contacted with the chemical etching composition at a
temperature of from about 65.degree. C. to about 95.degree. C.,
such as from about 80.degree. C. to about 95.degree. C., such as
from about 82.degree. C. to about 88.degree. C., or from about
88.degree. C. to about 91.degree. C. Further, the alloy material
may be agitated in the chemical etching composition. Further yet,
the alloy material may be contacted with the chemical etching
composition for an unlimited time period based on the desired depth
of etch.
[0017] The present disclosure further includes methods for etching
a patterned design in a metal alloy. The method may comprise
applying a coating which resists chemical etchants to at least a
portion of the metal alloy, removing a portion of the coating to
form a patterned design in the coating, and applying a chemical
etching composition. The chemical etching composition, and the
times and temperatures used for exposure of the alloy material to
the chemical etching composition may be as disclosed hereinabove.
Moreover, prior to etching, the alloy material may be activated as
described hereinabove, such as before etching, or even before
application of the coating material (i.e., before patterning). The
method may further comprise stripping the coating from the metal
alloy after the patterned etching is complete. The metal alloy may
form all or a portion of a work-piece, including parts of the
work-piece or a coating thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A and 1B show micrographs of a native cobalt-chromium
alloy surface and an etched cobalt-chromium alloy surface,
respectively, using etching compositions in accordance with certain
aspects of the present disclosure.
[0019] FIGS. 2A-2F show micrographs of cobalt-chromium alloy
surfaces, where FIGS. 2A and 2B are 150.times. and 1000.times.
magnifications, respectively, of a native alloy surface; FIGS. 2C
and 2D are 150.times. and 1000.times. magnifications, respectively,
of a surface etched to 2 mil (50 micron) depth using etching
compositions in accordance with certain aspects of the present
disclosure; and FIGS. 2E and 2F are 150.times. and 1000.times.
magnifications, respectively, of a surface etched to 12 mil (300
micron) depth using etching compositions in accordance with certain
aspects of the present disclosure.
[0020] 3A-3C show micrographs of a cross-section of a
cobalt-chromium-molybdenum alloy surface etched with various
chemistries according to certain aspects of the present disclosure,
with a 5 mil (127 micron) scale bar.
DETAILED DESCRIPTION
[0021] In the following description, the present invention is set
forth in the context of various alternative embodiments and
implementations involving chemical compositions for the selective
removal of surface materials from a cobalt chrome alloy (i.e.,
chemical etching compositions), methods of their use, and surfaces
etched using these compositions and methods.
[0022] Various aspects of the chemical etching compositions,
methods, and surfaces disclosed herein may be illustrated by
describing components that are coupled, attached, and/or joined
together. As used herein, the terms "coupled", "attached", and/or
"joined" are interchangeably recited to indicate either a direct
connection between two components or method steps or, where
appropriate, an indirect connection to one another through
intervening or intermediate components or steps. In contrast, when
a component is referred to as being "directly coupled", "directly
attached", and/or "directly joined" to another component, there are
no intervening elements shown in said examples. Moreover, when a
method step is indicated to directly precede another step, there
are no intervening steps.
[0023] Various aspects of the chemical etching compositions,
methods, and surfaces disclosed herein may be described and
illustrated with reference to one or more exemplary
implementations. As used herein, the term "exemplary" means
"serving as an example, instance, or illustration," and should not
necessarily be construed as preferred or advantageous over other
variations of the compositions or methods disclosed herein.
"Optional" or "optionally" means that the subsequently described
component, event, or circumstance may or may not occur, and that
the description includes instances where the component in included
or the event occurs and instances where the component is not
included or the event does not occur. In addition, the word
"comprising" as used herein means "including, but not limited
to".
[0024] It must also be noted that as used herein and in the
appended claims, the singular forms "a", "an", and "the" include
the plural reference unless the context clearly dictates otherwise.
Thus, reference to "a" composition, "an" alloy, or "the" metal, may
be a reference to one or more of these or any other component as
disclosed herein.
[0025] Moreover, other than in any operating examples, or where
otherwise indicated, all numbers expressing, for example,
quantities of ingredients used in the specification and claims are
to be understood as being modified in all instances by the term
"about". Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
appended claims are approximations that may vary depending upon the
desired properties to be obtained by the presently disclosed
compositions and methods. At the very least, and not as an attempt
to limit the application of the doctrine of equivalents to the
scope of the claims, each numerical parameter should at least be
construed in light of the number of reported significant digits and
by applying ordinary rounding techniques.
[0026] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the present disclosure are
approximations, the numerical values set forth in the specific
examples are reported as precisely as possible. Any numerical
value, however, inherently contains certain errors necessarily
resulting from the standard variation found in their respective
testing measurements.
[0027] "Substantially free", as used herein, is understood to mean
inclusive of only trace amounts of a component or constituent.
Thus, a surface substantially free of particles may be understood
to mean only trace amounts of particles on the surface. "Trace
amounts" are those quantitative levels of a component or
constituent that are barely detectable and provide no benefit to
the functional properties of the subject composition, process, or
articles formed therefrom. For example, a trace amount may
constitute 1.0 wt. %, 0.5 wt. %, 0.1 wt. %, 0.05 wt. %, or even
0.01 wt. % of a surface or a constituent. "Totally free", as used
herein, is understood to mean completely free of a surface or
constituent.
[0028] Unless defined otherwise, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
ordinary skill in the art.
[0029] The chemical etching compositions disclosed herein provide a
means for performing a subtractive process on a substrate, i.e.,
chemical etching, also referred to as chemical machining or
milling. Chemical etching may comprise, for example, exposure of
select surfaces of an object or work-piece, or the entire
work-piece, to the chemical etching compositions disclosed herein
for a period of time sufficient to remove a portion of the surface
to a desired depth.
[0030] Chemical Etching Compositions
[0031] The chemical etching compositions include at least two
mineral acids. A mineral acid is an inorganic acid derived from one
or more inorganic compounds. All mineral acids release hydrogen
ions when dissolved in water. Suitable examples of mineral acids
include, but are not limited to, hydrochloric acid (HCl), nitric
acid (HNO.sub.3), phosphoric acid (H.sub.3PO.sub.4), sulfuric acid
(H.sub.2SO.sub.4), hydrofluoric acid (HF), iodic acid (HIO.sub.3),
and hydrobromic acid (HBr).
[0032] The at least two mineral acids in the chemical etching
composition may be selected from hydrochloric acid (HCl), nitric
acid (HNO.sub.3), sulfuric acid (H.sub.2SO.sub.4), iodic acid
(HIO.sub.3), and hydrofluoric acid (HF). According to certain
aspects, the chemical etching composition comprises hydrochloric
acid (HCl), nitric acid (HNO.sub.3), and hydrofluoric acid
(HF).
[0033] The chemical etching compositions may comprise at least 1N
hydrochloric acid (HCl), such as at least 1.5N HCl, or at least
2.0N, or at least 2.5N, or at least 3.0N, or at least 3.5N, or at
least 4.0N, or at least 4.5N, or at least 5.0N, or at least 5.5N,
or at least 6.0N, or at least 6.5N, or at least 7.0N HCl. The
chemical etching compositions may comprise up to 10N HCl, such as
up to 9.5N, or up to 9.0N, or up to 8.5N, or up to 8.0N, or up to
7.5N, or up to 7.0N, or up to 6.5N, or up to 6.0N, or up to 5.5N,
or up to 5.0N HCl. The chemical etching compositions may comprise
HCl in any combination of upper and lower limits listed herein,
such as, for example, from 1N to 10N, or from 2N to 8N, or from 2N
to 7.5N, or from 3N to 7.5N, or from 3N to 8.0N, or from 2N to
6.0N, or from 3N to 6.0N, etc.
[0034] The chemical etching compositions may comprise at least
0.05N nitric acid (HNO.sub.3), such as at least 0.1N HNO.sub.3, or
at least 0.2N, or at least 0.3N, or at least 0.4N, or at least
0.5N, or at least 0.6N, or at least 0.7N, or at least 0.8N, or at
least 0.9N, or at least 1.0N, or at least 1.1N, or at least 1.2N,
or at least 1.3N, or at least 1.4N, or at least 1.5N HNO.sub.3. The
chemical etching compositions may comprise up to 2.0N HNO.sub.3,
such as up to 1.9N, or up to 1.8N, or up to 1.7N, or up to 1.6N, or
up to 1.5N, or up to 1.4N, or up to 1.3N, or up to 1.2N, or up to
1.1N, or up to 1.0N, or up to 0.9N, or up to 0.8N HNO.sub.3. The
chemical etching compositions may comprise HNO.sub.3 in any
combination of upper and lower limits listed herein, such as, for
example, from 0.05N to 2N, or from 0.05N to 0.8N, or from 0.1N to
0.6N, or from 0.2N to 0.6N, etc.
[0035] The chemical etching compositions may comprise at least 0.1N
hydrofluoric acid (HF), such as at least 0.2N HF, or at least 0.3N,
or at least 0.4N, or at least 0.5N, or at least 0.6N, or at least
0.7N, or at least 0.8N, or at least 0.9N, or at least 1.0N, or at
least 1.1N, or at least 1.2N, or at least 1.3N, or at least 1.4N,
or at least 1.5N, or at least 1.6N HF. The chemical etching
compositions may comprise up to 2.0N HF, such as up to 1.9N, or up
to 1.8N, or up to 1.7N, or up to 1.6N, or up to 1.5N, or up to
1.4N, or up to 1.3N, or up to 1.2N, or up to 1.1N, or up to 1.0N,
or up to 0.9N, or up to 0.8N, or up to 0.7N HF. The chemical
etching compositions may comprise HF in any combination of upper
and lower limits listed herein, such as, for example, from 0.1N to
2N, or from 0.2N to 1.3N, or from 0.3N to 1.0N, or from 0.4N to
1.0N, etc.
[0036] The chemical etching composition may comprise 1N to 10N
hydrochloric acid (HCl), 0.05N to 2.0N nitric acid (HNO.sub.3), and
0.1N to 2.0N hydrofluoric acid (HF). For example, the chemical
etching compositions may comprise 2N to 8N HCl, 0.05N to 0.8N
HNO.sub.3, and 0.2N to 1.3N HF.
[0037] The chemical etching compositions also comprise component
metals of the metal alloy to be etched. For example, the chemical
etching composition may comprise chromium (Cr) and molybdenum (Mo)
for use in etching a cobalt chrome work-piece formed of a cobalt
chromium molybdenum alloy such as ASTM F75, F799, or F1357. As
additional examples, the chemical etching composition may comprise
chromium (Cr), molybdenum (Mo), and nickel (Ni) for use in etching
a cobalt chrome work-piece formed of a cobalt nickel chromium
molybdenum alloy such as ASTM F562, or chromium (Cr), nickel (Ni),
and tungsten (W) for use in etching a cobalt chrome work-piece
formed of a cobalt chromium tungsten nickel alloy such as ASTM
F90.
[0038] Accordingly, the chemical etching compositions disclosed
herein generally comprise at least 0.1 g/l molybdenum (Mo), such as
at least 0.5 g/l Mo, or at least 1 g/l, or at least 2 g/l, or at
least 3 g/l, or at least 4 g/l Mo. The chemical etching
compositions disclosed herein generally comprise up to 400 g/l Mo,
such as up to 350 g/l, or up to 300 g/l, or up to 200 g/l, or up to
100 g/l, or up to 50 g/l. The chemical etching compositions may
comprise Mo in any combination of upper and lower limits listed
herein, such as, for example, from 0.1 g/l to 400 g/l, such as from
0.1 g/l to 300 g/l, or from 0.1 g/l to 200 g/l, or from 0.1 g/l to
100 g/l Mo, etc.
[0039] The chemical etching composition may comprise at least 0.2
g/l chromium (Cr), such as at least 1 g/l Cr, or at least 2 g/l, or
at least 3 g/l, or at least 4 g/l, or at least 5 g/l, or at least 6
g/l, or at least 7 g/l, or at least 8 g/l, or at least 9 g/l. The
chemical etching compositions may comprise up to 400 g/l Cr, such
as up to 350 g/l Cr, or up to 300 g/l, or up to 250 g/l, or up to
200 g/l, or up to 150 g/l, or up to 100 g/l, or up to 50 g/l, or up
to 20 g/l. The chemical etching compositions may comprise Cr in any
combination of upper and lower limits listed herein, such as, for
example, from 0.2 g/l to 400 g/l, such as from 0.2 g/l to 300 g/l,
or from 0.2 g/l to 200 g/l, or from 0.2 g/l to 100 g/l Cr, etc.
[0040] The chemical etching compositions may optionally comprise
cobalt (Co). According to certain aspects, the chemical etching
composition comprises no Co, or at least 0.1 g/l, or at least 1
g/l, or at least 2 g/l, or at least 4 g/l, or at least 6 g/l, or at
least 8 g/l, or at least 10 g/l, or at least 15 g/l, or at least 20
g/l Co. According to certain other aspects, the chemical etching
composition comprises up to 400 g/l Co, such as up to 350 g/l Co,
or up to 300 g/l, or up to 250 g/l, or up to 200 g/l, or up to 150
g/l, or up to 100 g/l, or up to 50 g/l, or up to 20 g/l Co. When Co
is included, the chemical etching compositions may comprise Co in
any combination of upper and lower limits listed herein, such as,
for example, from 0.1 g/l to 400 g/l, such as from 2 g/l to 300
g/l, or from 2 g/l to 50 g/l, or from 4 g/l to 20 g/l Cr, etc.
[0041] The chemical etching compositions may optionally comprise
iron (Fe). Without being tied to one theory, it is believed that
the addition of iron to the chemical etching composition may help
to stabilize the reaction rate of the composition. Accordingly, the
chemical etching compositions may comprise at least 10 g/l iron
(Fe), such as at least 20 g/l Fe, or at least 30 g/l, or at least
50 g/l, or at least 70 g/l, or at least 90 g/l, or at least 110
g/l, or at least 130 g/l, or at least 150 g/l, or at least 170 g/l,
or at least 200 g/l Fe. The chemical etching compositions may
comprise up to 400 g/l Fe, such as up to 350 g/l Fe, or up to 300
g/l, or up to 250 g/l, or up to 200 g/l, or up to 150 g/l, or up to
100 g/l, or up to 50 g/l, or up to 20 g/l Fe. When Fe is included,
the chemical etching compositions may comprise Fe in any
combination of upper and lower limits listed herein, such as, for
example, from 0.1 g/l to 400 g/l Fe, such as from 2 g/l to 225 g/l
Fe, or from 20 g/l to 50 g/l, or from 50 g/l to 225 g/l Fe,
etc.
[0042] The present inventors have discovered that for a composition
where all acids are within the concentration ranges previously
discussed, and the component metals chromium and molybdenum are
present, with or without the presence of cobalt and/or iron, the
composition is capable of etching a cobalt chrome surface. The
absence of Mo, in particular, abolishes the compositions ability to
etch cobalt chromium surfaces.
[0043] Thus, the chemical etching composition may comprise at least
two mineral acids, and low to moderate concentrations of certain
component metals of the alloy to be etched. For example, the
composition may comprise any two or more of the mineral acids
listed herein, at least 0.2 g/l chromium (Cr); at least 0.1 g/l
molybdenum (Mo); and optionally cobalt (Co) when the alloy to be
etched is a cobalt chromium molybdenum alloy. The composition may
further comprise up to 400 g/l iron (Fe), such as 50-225 g/l Fe, or
100-300 g/l Fe, or 125-200 g/l Fe, or 50-100 g/l Fe. According to
certain aspects, a total content of the component metals of the
alloy to be etched may not be greater than 20 g/l, or 30 g/l, or 40
g/l, or 50 g/l, or 100 g/l, or 200 g/l, or 300 g/l, or 400 g/l.
[0044] The chemical etching composition may comprise at least two
mineral acids, and high concentrations of certain component metals
of the alloy to be etched. For example, the composition may
comprise any two or more of the mineral acids listed herein, and at
least 0.5 g/l Co, such as about 0.5-355 g/l Co; at least 0.2 g/l
Cr, such as about 0.2-170 g/l chromium (Cr); and at least 0.1 g/l
molybdenum (Mo), such as about 0.1-40 g/l Mo when the alloy to be
etched is a cobalt chromium molybdenum alloy. The composition may
be substantially free of, or totally free of, iron. According to
certain aspects, a total content of the component metals of the
alloy to be etched may not be greater than 20 g/l, or 30 g/l, or 40
g/l, or 50 g/l, or 100 g/l, or 200 g/l, or 300 g/l, or 400 g/l.
[0045] According to certain aspects, the component metals may be
included in amounts that mimic the ratio in which they are included
in the metal alloy. For example, when the alloy is a cobalt
chromium molybdenum alloy, such as ASTM F75, the component metals
may be provided as about 63-68 wt. % Co, 27-30 wt. % Cr, and 5-7
wt. % Mo, based on the total weight of the alloy; or when the alloy
is a cobalt nickel chromium molybdenum alloy, such as ASTM F562,
the component metals may be provided as about 35 wt. % Co, about 35
wt. % Ni, about 20 wt. % Cr, and about 10 wt. % Mo, based on the
total weight of the alloy. While certain examples of alloys and
their component metal ratios have been provided herein as examples,
other alloys of cobalt chrome are within the scope of the presently
disclosed invention. One of ordinary skill in the art would know
the ratio of the component metals in certain other alloys and be
able to understand the ratios in which they would be provided
according to the description of the invention provided in this
disclosure.
[0046] The chemical etching composition may be an aqueous
composition. As such, the mineral acids and component metals may be
dissolved into an aqueous medium, such as water or another aqueous
buffer.
[0047] According to certain aspects, the work-piece may be etched
on one or more surfaces by contacting the work-piece with any of
the chemical etching compositions disclosed herein. According to
certain aspects, the alloy material may be etched on one or more
surfaces by contacting the alloy with any of the chemical etching
compositions disclosed herein.
[0048] Surface Activation
[0049] Before the work-piece or alloy can be etched with the
chemical etching compositions disclosed herein, the work-piece or
alloy may require an activation step. An exemplary activation step
includes exposing the surface of the work-piece to be etched to a
mineral acid, such as a 10% to 100% (v/v) aqueous solution of the
mineral acid. An exemplary activation solution includes a 10% to
100% aqueous solution of concentrated hydrochloric acid and/or
hydrofluoric acid (v/v; dilution with an aqueous buffer or water).
The surface may be exposed to the mineral acid at a range of
temperatures, such as room temperature or above, wherein higher
temperatures require lower concentrations of the mineral acid. The
work-piece may be exposed to the mineral acid by submersion or
spraying.
[0050] According to certain aspects, certain alloys, e.g., wrought
and/or forged cobalt chromium alloys, may benefit from activation
with a mixture of concentrated hydrogen peroxide (50%
H.sub.2O.sub.2) and concentrated hydrochloric acid (fuming
hydrochloric acid; 37%). For example, according to certain aspects,
the activation composition may comprise at least 25% (v/v) hydrogen
peroxide and at least 25% concentrated hydrochloric acid. The
surface may be exposed to the mixture at a range of temperatures,
such as room temperature or above, wherein higher temperatures
require lower concentrations of the mineral acid. The work-piece
may be exposed to the mixture by submersion or spraying.
[0051] As indicated hereinabove, such chemistry is generally only
suitable for superficial removal of material. However, as used in
the presently disclosed methods, the activation step is not
employed to etch the alloy surface but rather to activate the alloy
surface for etching with the novel compositions disclosed herein.
Moreover, any intergranular attack (IGA) of the CoCr materials that
may be incurred by this activation step would be removed by the
subsequent more substantial etching compositions and methods that
follow the activation step.
[0052] Immediately after activation, such as within 120 seconds,
the work-piece may be exposed to the chemical etching compositions
as described herein below. According to certain aspects, the
work-piece may still be "wet" with the activation solution (i.e.,
mineral acid such as the 10%-100% dilution of hydrochloric
acid).
[0053] After the surface of the work-piece is activated, it may be
etched by contact with the chemical etching compositions, which may
include dipping or submersing the work-piece in the composition, or
spraying, rolling, or brushing the composition onto one or more
surfaces of the work-piece.
[0054] Etching Methods
[0055] The present disclosure provides methods for etching an alloy
material of a work-piece. According to certain aspects, one method
may include preparing one of the chemical etching compositions
described above and contacting the alloy material with the chemical
etching composition.
[0056] According to certain aspects, another method may include
preparing one of the chemical etching compositions described above,
activating the alloy material with a mineral acid or mixture of a
mineral acid and hydrogen peroxide, and contacting the alloy
material with the chemical etching composition. According to
certain aspects, the step of contacting with the chemical etching
composition may be carried out immediately after the activation
step, such as before the alloy material dries, or within 120
seconds after activation (i.e., 120 seconds from exposure to the
mineral acid), or within 90 seconds after activation, or within 60
seconds after activation, or within 30 seconds after
activation.
[0057] Contacting the work-piece with the chemical etching
compositions may include dipping or submersing the work-piece in
the composition, or spraying, rolling, or brushing the composition
onto one or more surfaces of the work-piece.
[0058] For example, the work-piece to be etched may be attached to
a fixture resistant to the chemical etching composition and both
the work-piece and at least a portion of the fixture may be
submerged in the chemical etching composition for a specified time
(e.g., the part is suspended over/in the chemical etching
composition).
[0059] The present inventors have found that it may be preferred to
position the surfaces to be etched horizontally, such as facing
upward in the composition, or vertically depending on the targeted
surface characteristics. The gaseous byproducts of the etch
reaction move directly upwards and away from the surface when that
surface is etched horizontally, and do not otherwise affect the
process. When the surface to be etched is positioned vertically,
bubbles may travel along the vertical surface and influence the
etch rate through localized microcirculation and its effects on the
replenishment of unreacted chemistry to the target surface. In such
ways, surface geometry may be manipulated by adjusting the angle of
the parts (with respect to horizontal) during processing.
[0060] Accordingly, the work-piece may be etched on one or more
surfaces by positioning the work-piece at an angle within the
chemical etching composition. Exemplary angles include 0.degree.
with respect to the surface of the "bath" containing the chemical
etching composition (i.e., horizontal facing upward), to 90.degree.
with respect to the surface of the bath (i.e., vertical), to
180.degree. with respect to the surface of the bath (i.e.,
horizontal facing downward), or any angle therebetween.
[0061] Alternatively, the work-piece may be moved or agitated
within the etching composition (e.g., in the bath) to provide
circulation of the etching composition thereabout, and/or the
etching composition may be moved or circulated within the bath
(e.g., stirred or recirculated).
[0062] Yet still, the work-piece may placed into a drum filled with
the chemical etching composition, and the drum may be rotated.
Additional substrate, such as inert plastic beads or pieces, may be
added to the drum to cushion the parts during rotation.
[0063] Accordingly, the chemical etching step may include agitating
the work-piece in the chemical etching composition. The chemical
etching step may include recirculating the etching composition,
wherein the recirculating may include circulation of the original
chemical etching composition (i.e., etching composition
applied/used at start of method), or circulation of the original
chemical etching composition with additional new, unused chemical
etching composition. The chemical etching step may include exchange
of used chemical etching composition after a certain amount of etch
time for new, unused chemical etching composition.
[0064] The chemical etching step may further include heating the
work-piece and/or the chemical etching composition to a temperature
in a range of from about 20.degree. C. to about 150.degree. C.,
such as from about 30.degree. C. to about 105.degree. C., or from
about 40.degree. C. to about 100.degree. C., or from about
50.degree. C. to about 100.degree. C., or from about 60.degree. C.
to about 100.degree. C., or from about 65.degree. C. to about
95.degree. C., or from about 80.degree. C. to about 95.degree. C.,
or from about 82.degree. C. to about 88.degree. C., or from
88.degree. C. to about 91.degree. C. The alloy material may be
contacted with the chemical etching composition at a temperature in
a range of from about 20.degree. C. to about 150.degree. C., such
as from about 30.degree. C. to about 105.degree. C., or from about
40.degree. C. to about 100.degree. C., or from about 50.degree. C.
to about 100.degree. C., or from about 60.degree. C. to about
100.degree. C., or from about 65.degree. C. to about 95.degree. C.,
or from about 80.degree. C. to about 95.degree. C., or from about
82.degree. C. to about 88.degree. C., or from 88.degree. C. to
about 91.degree. C.
[0065] The alloy material may be contacted with the chemical
etching composition for an unlimited time period based on the
desired depth of etch. Etching starts as soon as the alloy material
is exposed to the chemical etching composition and may proceed
until the desired depth of etching is achieved. As such, the alloy
material may be contacted with the chemical etching compositions
from greater than 0 seconds to greater than several hours or days.
According to certain aspects, the alloy material may be exposed to,
such as agitated within, the chemical etching composition for a
time of from 1 to 1000 minutes, such as from 2 to 200 minutes, or
from 5 to 50 minutes.
[0066] The chemical etching compositions and methods disclosed
herein may be used to remove portions or all of a surface of a
work-piece to a desired depth. Moreover, the compositions and
methods disclosed herein provide removal of the material without
significant intergranular attack (IGA).
[0067] The compositions and methods disclosed herein also provide
means to remove artifacts of manufacture, such as support
structures formed during 3D manufacture of the work-piece, or
islands left behind during laser manufacture of a work-piece, or to
reduce debris from the work-piece surfaces, such as artifacts of
the additive manufacturing process, e.g., powder, particles,
granules, etc. that were not completely melted or completely
sintered during the additive building. Debris may also include
external debris such as dirt or other artifacts of handling.
[0068] The present inventors have found that the removal of surface
material using the compositions and methods disclosed herein are
predictable and repeatable. Unlike other alloys, however, once the
material is removed with certain compositions disclosed herein, the
etched surface of the alloy may form an extremely stable passive
surface layer that may inhibit further etching without a suitable
chemical or electrochemical re-activation of the surface, such as
the activation step disclosed above, or disruption of the surface
layer (e.g., by a mechanical means such as grit-blasting). Because
of this, processing in certain of the compositions disclosed herein
may be most easily and economically performed with full targeted
removal taking place all in one step.
[0069] Cobalt Alloys
[0070] The compositions and methods disclosed herein are suitable
for all types of Cobalt-Chromium-Molybdenum based alloys including
cast, forged, machined, and other products with formulations such
as, but not limited to, ASTM F75 (Standard Specification for
Cobalt-28Chromium-6Molybdenum Alloy Casting and Casting Alloy for
Surgical Implants), ASTM F799 (Standard Specification for
Cobalt-28Chromium-6Molybdenum Alloy Forgings for Surgical
Implants), and ASTM F1537 (Standard Specification for
Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants).
[0071] This composition is also suitable for Cobalt-Chromium alloys
containing Nickel such as ASTM F90 (Standard Specification for
Wrought Cobalt-20Chromium-15Tungsten-10Nickel Alloy for Surgical
Implant Applications) and ASTM F562 (Standard Specification for
Wrought 35Cobalt-35Nickel-20Chromium-10Molybdenum Alloy for
Surgical Implant Applications).
[0072] Pattern Generation
[0073] Specific portions of a work-piece may be etched, such as in
a pattern. Those portions that are to remain un-etched may be
protected from the chemical etching composition using a masking
material. Masking materials may include at least coatings applied
to the surfaces to be protected, such as coatings resistant to the
chemical etching composition. The exposed, non-masked surfaces may
then be chemically etched by exposure to the chemical etching
compositions disclosed herein.
[0074] Coatings resistant to the chemical etching composition, and
the activation solution (mineral acid) may be applied by any means
known in the art, such as at least dipping, pouring, spraying,
brushing, or rolling. Exemplary coatings resistant to the chemical
etching compositions disclosed herein include, for example,
maskants from AC Products, such as ADCOAT AC-818.
[0075] Depending on the solids content of the selected coating,
multiple applications of the coating may be necessary, allowing for
sufficient drying time between applications. The coatings used are
generally customized to protect the object from the selected
etchant while avoiding any harm to the underlying material of the
object.
[0076] After each application, the coating may be allowed to cure
in a manner which prevents damage to the preceding application,
and/or which does not inhibit future applications. The term "cure",
as used in connection with a cured coating, means that at least a
portion of the components that form the coating are polymerized,
cross-linked, or dried to form a hardened film. Curing or drying
reactions to form the hardened film may be carried out under
ambient conditions, or may be carried out at elevated temperatures,
pressures, or in the presence of various gases. For example, the
coating may comprise a solvent which may be evaporated to dry or
cure the coating. The solvent evaporation may be accelerated by
vacuum removal coupled with fresh air or inert gas supply.
Depending upon the nature of the chosen coating, heat sources may
be used to accelerate drying. Further, for certain coating
chemistries, additional processing steps (imaging, hardening,
fixing, etc.) may be necessary to make the coating fully resistant
to the targeted etching composition.
[0077] The coating may be applied in a pattern that exposes the
regions of the work-piece to be etched and covers the regions to be
protected. Alternatively, the coating may be patterned to remove
those regions of the coating that are to be etched on the
work-piece. Such removal may be via mechanical scribing and
peeling, or by laser ablation, wherein a laser is utilized to
remove or ablate the coating in specific regions or patterns. In
both cases, a thickness of the coating may be matched to the
characteristics of the scribing or laser ablation equipment. In
general, the thinnest application that allows for full protection
during the chemical etching step is desired, as thinner coatings
require less drying time, less coating material, lower laser
intensities, and less time stripping the coating after etching is
complete. Moreover, for laser ablation processes, colorants or
other additives may be added to the coating to improve the ablation
process. The colorants and/or additives may be matched to the
specific laser type and wavelength.
[0078] For work-pieces that are to be patterned using a
photoresist, the photoresist may be applied to the surface of the
work-piece. Photoresist is a photosensitive coating that changes
properties when exposed to light, either gaining or losing
resistance to attack by an etchant or solvent in the areas exposed
to electromagnetic radiation, most commonly in the UV light
spectrum. The thickness and properties of the photoresist (e.g.,
positive or negative photoresist) may be matched to the equipment
used for exposure of the pattern onto the photoresist.
[0079] While several methods for coating the surface of the
work-piece have been described herein, other methods known in the
art are within the scope of the present disclosure. Furthermore,
more than one coating layer may be applied to the surface of the
work-piece, wherein each coating layer may vary in thickness and
identity of the coating material. As previously indicated,
selection of the specific coating thickness and coating material
may depend on at least the method of pattern generation to be used
in future steps of the process.
[0080] The term "pattern generation" generally describes various
methods and implementations used to remove a portion of the coating
from the surface of the work-piece according to a specific pattern
or design. The pattern may be preset or programmed into a computer
(e.g., translated from CAD drawings) which directs the movements of
the various devices used to remove the portion of coating and
movements of the work-piece, either together or individually.
[0081] The patterned work-piece, whether produced through laser
ablation, mechanical scribing and peeling, or by a photo resist
process may be exposed to the chemical etching composition using
any of dipping, rolling, brushing, or spraying. As indicated
hereinabove, if the work-piece is contacted with the chemical
etching composition in a bath, the work-piece may be agitated while
in the bath, or alternatively, the chemical etching composition may
be provided as a flow of material (e.g., the work-piece may be
positioned in a stream of the chemical etching composition).
[0082] When an activation step is included prior to the chemical
etch, the patterned surface may be activated, such as with any of
the chemistries disclosed hereinabove. Alternatively, the surface
may be activated prior to patterning using any of the methods
discussed herein (patterned coating, coating having portions
removed, or photoresist).
[0083] Moreover, either or both of the work-piece and the chemical
etching composition may be heated to a temperature in a range of
from about 20.degree. C. to about 150.degree. C., such as from
about 30.degree. C. to about 105.degree. C., or from about
40.degree. C. to about 100.degree. C., or from about 50.degree. C.
to about 100.degree. C., or from about 60.degree. C. to about
100.degree. C., or from about 65.degree. C. to about 95.degree. C.,
or from about 80.degree. C. to about 95.degree. C., or from about
82.degree. C. to about 88.degree. C., or from 88.degree. C. to
about 91.degree. C.
[0084] Once etching is complete, the work-piece may be rinsed clean
of all residual etchant and placed in a bath of stripping solution
(a solvent matched to the coatings) to remove all remaining coating
material. Alternatively, a wet blast process consisting of a
high-pressure spray of a solution could be used in place of the
stripping solution to mechanically remove the coating from the
object. After the remaining coating is removed ("stripping"), the
work-piece may be thoroughly washed and dried.
[0085] Chemical Etch Characteristics
[0086] The amount of material removed by the chemical etching
composition, i.e., the depth of the etch, is unlimited and may
depend on the amount of exposure time to the chemical etching
composition and changes in the chemistry of the composition, e.g.,
after long exposure times. Such changes can include at least a
reduction in the acid content, an increase in the component metals
content, or any combination thereof.
[0087] The rate of etching, i.e., rate of material removal, may
depend on a combination of the proportion of chemical components to
one another, the temperature, and/or amount of agitation of the
work-piece in the chemical etching composition. For example,
according to certain aspects of the presently disclosed methods, a
sample of cobalt chrome may be etched at a rate of 0.1 to 1
mil/minute in the presently disclosed chemical etching
compositions, such as 0.3 to 1 mil/minutes, or about 0.5
mil/minute, when exposed at room temperature.
[0088] The etched surfaces may display a surface roughness, or Ra,
that is at least 25% less than the native, un-etched surface, such
as a surface roughness that is at least 40% less, or at least 50%
less, or at least 60% less, or at least 70% less, or at least 80%
less, or even at least 90% less than the native, un-etched surface.
Surface roughness is quantified by the deviations in the direction
of the normal vector of a real surface from its ideal form. If
these deviations are large, the surface is rough; if they are
small, the surface is smooth. Cobalt chrome surfaces etched using
the compositions and methods disclosed herein may have a surface
roughness (Ra) that is less than 200 .mu.-in, or less than 150
.mu.-in, or even less than 100 .mu.-in (less than 5 .mu.m, 3.8
.mu.m, or 2.5 .mu.m, respectively).
[0089] One unique and unexpected quality of the present chemical
etching compositions and methods of use is that the final surface,
after the chemical etching is completed, does not include any
directionally oriented etch markings or "scratches". As discussed
above, prior art methods for smoothing surfaces on alloys such as
those disclosed herein include abrasive flow machining or
smoothing. Such methods force a viscous liquid comprising abrasive
material past the surface to be smoothed at high flow rates. The
directionality of the flow of abrasive material leads to
directionally oriented scratches or marks. Thus, while this process
may provide smooth surfaces, albeit at increased time and cost
compared to the presently disclosed compositions and methods, the
surfaces include directionally oriented marks.
[0090] It should be noted that the low surface roughness (Ra),
indicative of a smooth surface, provided by the present
compositions and methods is different from the "depth of etch"
described herein, where longer etch times may remove greater
amounts of the metal surface (i.e., greater depth of the etch).
Longer etch times may be useful to remove artifacts of manufacture,
such as support structures formed during 3D manufacture of the body
implantable device, or islands left behind during laser manufacture
of a body implantable device, or to reduce debris from the body
implantable device surfaces, such as artifacts of the additive
manufacturing process, e.g., powder, particles, granules, etc.,
that were not completely melted or completely sintered during the
additive building. Debris may also include external debris such as
dirt or other artifacts of handling. However, as discussed in the
examples section below, a smooth surface may achievable and
maintained over various depths of etching.
[0091] Another unique and unexpected quality of certain of the
present chemical etching compositions and methods of use is that
the final surface, after the chemical etching is completed, may be
a passivated surface. That is, it is generally not possible to
perform the etching process a subsequent time. Alternate
chemistries, such as the activation chemistries disclosed
hereinabove, and/or mechanical polishing or abrasion may be used to
expose more of the underlying surface (i.e., non-passivated
surface) in preparation for a subsequent round of chemical etching
using the chemical etching compositions disclosed herein.
[0092] Passivation may be useful to achieve complex patterning of a
surface, where certain areas that are protected during a first
round of etching, may be uncoated and etched during a second round
of etching to a depth different than the depth of etching achieved
during the first round of etching. Such a process may be used to
achieve any number of varied depths in a substrate over any number
of coating and etching processes. In addition, the resultant
surface may be expected to exhibit an even higher degree of
corrosion resistance at elevated temperatures that the pre etch
base alloy.
[0093] Moreover, the present inventors have found that the chemical
etching compositions and methods of use thereof provide for
unlimited chemical etching or milling of the surface (e.g., depth,
total area, etc.) in a single etching process.
[0094] This stable surface layer, when present, may be beneficial
for enhanced corrosion potential beyond that of standard
cobalt-chrome-moly surfaces, and further reduce toxicity beyond
standard alloys when implanted as in an orthopedic device.
EXAMPLES
[0095] The following examples provide formulations that may be used
to etch various cobalt chromium alloys. Before each of the chemical
etching steps listed in these examples, the alloy material may be
activated. Exemplary activation steps that form part of the
presently disclosed methods include exposure of the alloy material
to a mineral acid just prior to exposure to the chemical etching
compositions, such as by submerging or spraying the alloy material
with the mineral acid just prior to exposure to the chemical
etching compositions disclosed herein. For example, the work-piece
may be dipped in or sprayed with a 10% to 100% (v/v) aqueous
solution of hydrochloric acid and within several minutes, such as
less than 120 seconds, or less than 60 seconds, or even within 30
seconds, exposed to one of the chemical etching solutions as
detailed below in Examples I-IV. While the activation solution is
specifically indicated herein to comprise hydrochloric acid, other
mineral acids or mixtures thereof would provide substantially the
same results. Additionally, certain alloys, such as forged cobalt
chromium alloys, may benefit from different activation solutions,
such as mixtures of concentrated hydrochloric acid and hydrogen
peroxide.
[0096] Because it is preferred to expose the work-piece to the
chemical etching composition within a short time after exposure to
the activation solution, such as when the work-piece is still wet
with the activation solution, it may be beneficial to apply any
coatings or patterning before the activation step. As such, if the
work-piece is to be patterned, such as by including of a coating to
protect certain portions or surfaces of the work-piece, that
coating may be applied before the surface is activated and/or
etched.
[0097] Provided below are several exemplary chemical etching
compositions according to certain aspects of the presently
disclosed invention. The compositions were formulated using the
following components: acids--31% (w/w) HCl, 67% (w/w) HNO.sub.3,
49% (w/w) HF; and metal salts--Iron (III) chloride anhydrous
(FeCl.sub.3), Cobalt (II) chloride hexahydrate
(CoCl.sub.2.6H.sub.2O), Chromium (III) chloride hexahydrate
(CrCl.sub.3.6H.sub.2O), and Molybdenum (V) chloride anhydrous
(MoCl.sub.5).
[0098] Temperature ranges for the solutions in these tables are
from about 20.degree. C. to about 150.degree. C., such as typically
from about 50.degree. C. to about 95.degree. C. Exposure times for
the substrate in the chemical etching compositions shown are
greater than 0 seconds up to several hours or days, typically from
about 5 minutes to about 50 minutes.
TABLE-US-00001 TABLE 1 Component Etching Composition Metals A B C
Cr 10 g/l 10 g/l 3 g/l Mo 0 g/l 10 g/l 0.5 g/l Co 10 g/l 10 g/l 0
g/l Fe 50 g/l 50 g/l 0 g/l Etch Rate.sup.1 0.sup.2 0.33 mils/min
0.25 mils/min Cobalt chromium coupons were exposed to compositions
A and B at 180.degree. F. for 10 minutes, and to composition C at
195.degree. F. for 20 minutes. Each of compositions A-C comprise
4.7N HCl, 0.4N HNO.sub.3, and 0.8N HF. .sup.1Measured by weight
difference of metal coupon before and after etching .sup.2No
measurable removal after 10 minutes at 180.degree. F.
Example I
[0099] Compositions comprising the presently disclosed mineral
acids and minimal amounts of various combinations of CoCr component
metals were formulated and used to etch CoCr coupons. The results
shown in Table 1 demonstrate that compositions absent certain
metals are not capable of etching a cobalt chromium surface.
Specifically, shown in Table 1 are compositions comprising a
mixture of mineral acids (HCl, HNO.sub.3, and HF) and various
amounts of component metals of the alloy to be etched. The
composition absent molybdenum (composition A) failed to etch a
cobalt chromium surface, while compositions comprising at least
chromium and molybdenum (compositions B and C) etched at rates of
0.1 to 1 mil/minute.
Example II
[0100] An exemplary chemical etching composition for the chemical
dissolution of CoCr alloys according to certain aspects of the
present disclosure include constituents and amounts as shown in
Table II.
[0101] While CoCr can be etched at many (or all) combinations of
chemistry within the ranges listed in Table II, at the preferred
set-point conditions, uniform removal of material at up to 0.015
inches and beyond is achieved with no measurable IGA, making it a
suitable composition for flight-critical aerospace components.
TABLE-US-00002 TABLE II Set-Point at start of Component Range
etching Iron (Fe) 0-400 g/l 115 g/l Cobalt (Co) 0-400 g/l 0.2 g/l
Chromium (Cr) 0.2-400 g/l 3.3 g/l Molybdenum (Mo) 0.1-400 g/l 1.2
g/l Hydrochloric Acid (HCl) 1-10N 4.0N Nitric Acid (HNO.sub.3)
0.05-2.0N 0.5N Hydrofluoric Acid (HF) 0.1-2.0N 1.0N
Example III
[0102] An exemplary inventive high-iron composition for etching
CoCr alloys is shown in Table III. This composition was found to
provide surface roughness (R.sub.a) improvements from a starting
condition of approximately 400 .mu.-in (about 10 micrometer, .mu.m)
to a finished condition of approximately 125 .mu.-in (about 3
.mu.m), with a surface material removal of 0.005 inches.
TABLE-US-00003 TABLE III Set-Point at start of Component Range
etching Iron (Fe) 50-400 g/l 175 g/l Cobalt (Co) 0-400 g/l 5 g/l
Chromium (Cr) 0.2-400 g/l 3 g/l Molybdenum (Mo) 0.1-400 g/l 0.5 g/l
Hydrochloric Acid (HCl) 1-10N 4.5N Nitric Acid (HNO.sub.3)
0.05-2.0N 0.11N Hydrofluoric Acid (HF) 0.1-2.0N 0.9N
Example IV
[0103] An exemplary inventive iron-free, high-metals composition
for etching CoCr alloys is shown in Table IV. The composition was
found to provide surface roughness (R.sub.a) improvements from a
starting condition of approximately 250 .mu.-in (about 6.4 .mu.m)
to a finished condition of approximately 70 .mu.-in (less than 2
.mu.m), with a surface material removal of 0.005 inches.
[0104] The high metals chemical etching composition shown in Table
IV provides a ratio of metals in solution that is at or near the
ratio of the elemental components in the starting alloy, cobalt
chromium molybdenum ASTM F75, and resulted in dramatic improvement
in surface condition. Thus, the present inventors have found that
increased metal concentrations improve the surface roughness, i.e.,
provides a smoother surface, exponentially up to the point of
saturation. Higher concentrations were found to decrease the rate
of etch (i.e., as the metals concentrations rise, the rate of
etching will begin to decrease, potentially making the processing
of parts at or near full saturation impractical from a processing
time standpoint).
TABLE-US-00004 TABLE IV Set-Point at start of Component Range
etching Iron (Fe) 0 g/l 0 g/l Cobalt (Co) 0-400 g/l 81.7 g/l
Chromium (Cr) 0.2-400 g/l 35.8 g/l Molybdenum (Mo) 0.1-400 g/l 7.5
g/l Hydrochloric Acid (HCl) 1-10N 4.5N Nitric Acid (HNO.sub.3)
0.05-2.0N 0.11N Hydrofluoric Acid (HF) 0.1-2.0N 0.9N
[0105] The high metals chemical etching composition shown in Table
IV provides a ratio of metals in solution that is at or near the
ratio of the elemental components in the starting alloy, cobalt
chromium molybdenum ASTM F75, and resulted in dramatic improvement
in surface condition. Thus, the present inventors have found that
increased metal concentrations improve the surface roughness, i.e.,
provides a smoother surface, exponentially up to the point of
saturation. Higher concentrations were found to decrease the rate
of etch (i.e., as the metals concentrations rise, the rate of
etching will begin to decrease, potentially making the processing
of parts at or near full saturation impractical from a processing
time standpoint).
Example V
[0106] An exemplary inventive composition comprising component
metals in their native ratios for etching a cobalt chrome surface
is shown in Table V. The total metals component of the etching
solution is 180 g/l.
[0107] The solution was heated to 180.degree. F. (82.2.degree. C.)
and the activated substrate was added to the solution, which was
maintained at a temperature of 173.degree. F. to 177.degree. F.
(78.degree. C. to 80.5.degree. C.). The high metals chemical etch
composition shown in Table V provides a ratio of metals in solution
that is at or near the ratio of the elemental components in the
starting alloy, cobalt chromium molybdenum ASTM F75.
TABLE-US-00005 TABLE V Component Range Set-Point Iron (Fe) 0-400
g/l 30 g/l Cobalt (Co) 0-400 g/l 180 g/l total Chromium (Cr)
0.2-400 g/l component metals.sup..dagger-dbl. Molybdenum (Mo)
0.1-400 g/l Hydrochloric Acid (HCl) 1-10N 5.9N Nitric Acid
(HNO.sub.3) 0.05-2.0N 0.15N Hydrofluoric Acid (HF) 0.1-2.0N 0.72N
.sup..dagger-dbl.For a cobalt-molybdenum-chromium alloy, the
composition includes: 117.6 g/l Co, 51.6 g/l Cr, and 10.8 g/l
Mo.
Example VI
[0108] An exemplary inventive composition comprising component
metals in their native ratios for etching a cobalt chrome surface
is shown in Table VI. The total metals component of the etching
solution is 120 g/l.
[0109] The solution was heated to 180.degree. F. (82.2.degree. C.)
and the activated substrate was added to the solution, which was
maintained at a temperature of 173.degree. F. to 177.degree. F.
(78.degree. C. to 80.5.degree. C.). The high metals chemical etch
composition shown in Table VI provides a ratio of metals in
solution that is at or near the ratio of the elemental components
in the starting alloy, cobalt chromium molybdenum ASTM F75.
TABLE-US-00006 TABLE VI Component Range Set-Point Iron (Fe) 0-400
g/l 20 g/l Cobalt (Co) 0-400 g/l 120 g/l total Chromium (Cr)
0.2-400 g/l component metals.sup..dagger-dbl. Molybdenum (Mo)
0.1-400 g/l Hydrochloric Acid (HCl) 1-10N 7.1N Nitric Acid
(HNO.sub.3) 0.05-2.0N 0.156N Hydrofluoric Acid (HF) 0.1-2.0N 0.723N
.sup..dagger-dbl.For a cobalt-molybdenum-chromium alloy, the
composition includes: 78.4 g/l Co, 34.4 g/l Cr, and 7.2 g/l Mo.
Example VII
[0110] An exemplary inventive composition comprising component
metals in their native ratios for etching a cobalt chrome surface
is shown in Table VI. The total metals component of the etching
solution is 120 g/l.
TABLE-US-00007 TABLE VII Component Range Set-Point Iron (Fe) 0-400
g/l 80 g/l Cobalt (Co) 0-400 g/l 120 g/l total Chromium (Cr)
0.2-400 g/l component metals.sup..dagger-dbl. Molybdenum (Mo)
0.1-400 g/l Hydrochloric Acid (HCl) 1-10N 7.1N Nitric Acid
(HNO.sub.3) 0.05-2.0N 0.156N Hydrofluoric Acid (HF) 0.1-2.0N 0.723N
.sup..dagger-dbl.For a cobalt-molybdenum-chromium alloy, the
composition includes: 78.4 g/l Co, 34.4 g/l Cr, and 7.2 g/l Mo.
[0111] The solution was heated to 180.degree. F. (82.2.degree. C.)
and the activated substrate was added to the solution, which was
maintained at a temperature of 173.degree. F. to 177.degree. F.
(78.degree. C. to 80.5.degree. C.). The high metals chemical etch
composition shown in Table VII provides a ratio of metals in
solution that is at or near the ratio of the elemental components
in the starting alloy, cobalt chromium molybdenum ASTM F75.
[0112] Superior surface results with increasing metals at the
ratios native to the original alloy is an important finding as it
provides a processing composition that does not require the
addition of non-native metals or metal salts. That is, the
composition can be concentrated in metals for improved surface
finish simply by etching more material while maintaining the
appropriate acid concentrations. This greatly aids process control
(i.e., the metals will always drift towards the alloy
concentrations with increased usage) and eliminates the need for
non-native metals addition, namely iron salts, which represents
substantial processing costs in a production setting (e.g., iron
solutions need to be made in an inert environment to prevent
oxidization of the iron; iron solutions are generally
expensive).
[0113] It should be noted that nitric acid concentrations are
relatively low for these compositions as high metals may lead to
rapid breakdown of the nitric acid when that acid is present in
higher concentrations.
[0114] As indicated, the chemical etching compositions of the
present disclosure provide uniform material removal of up to
0.015'' and beyond with no measurable IGA, making them suitable
compositions for etching flight critical aerospace components.
[0115] Exemplary aerospace or aircraft components that may benefit
from the compositions and methods disclosed herein include at least
aircraft skin and fuselage skin and architectural trims. For
example, according to certain aspects, the alloys etched by the
compositions and methods presently disclosed may for a component,
in part or wholly, of an aerospace vehicle. As such, the component
may be an aerospace component attachable or forming part of an
aerospace vehicle or device.
[0116] Shown in FIGS. 1A and 1B are micrographs of a native
cobalt-chromium alloy surface and an etched cobalt-chromium alloy
surface, respectively, using the presently disclosed etching
compositions and methods. Typical cobalt chrome surfaces or
products are forming using additive manufacturing methods, which
includes deposition and sintering of powdered cobalt chromium alloy
powders. As is evident from FIG. 1A, the native cobalt-chromium
alloy surface comprises grains or particles, such as from the
additive manufacturing process, while the etched cobalt-chromium
alloy surface (FIG. 1B) is substantially absent such particles, and
further shows no directional surface scratches or markings (i.e.,
no extended grooves).
[0117] Shown in FIGS. 2A-2F are micrographs of an unetched native
cobalt chromium alloy at 150.times. and 1000.times. magnification
(FIGS. 2A and 2B, respectively) compared with a cobalt chromium
alloy surface that has been etched with a composition according to
the present disclosure, with 2 mil surface removed (50 microns
removed shown at 150.times. and 1000.times. magnification in FIGS.
2C and 2D, respectively) and with 12 mil surface removed (300
microns removed shown at 150.times. and 1000.times. magnification
in FIGS. 2E and 2F, respectively). Note that the native surface
includes deep crevices into which the dye may fill or adhere in a
dye penetrant test, while the surfaces etched using the methods and
compositions disclosed herein lack these crevices.
[0118] Micrographs of cross-sections of surfaces etched using the
compositions and methods disclosed herein are shown in FIGS. 3A-3C,
wherein the smoother surface of FIG. 3A was obtained with an
etching composition comprising higher concentrations of the
component metals of the metal alloy. Note that none of the
exemplary surfaces show directional surface scratches or markings
(i.e., no extended grooves).
[0119] Aspects of the Invention
[0120] The present disclosure provides the following aspects:
[0121] Aspect 1: A composition for etching a cobalt chromium alloy,
the composition comprising: at least two mineral acids; certain or
all of the main component metals of the cobalt chromium alloy; and
optionally iron (Fe).
[0122] Aspect 2: The composition according to aspect 1, wherein the
composition comprises: at least two mineral acids; chromium (Cr);
molybdenum (Mo); optionally Fe; and optionally, cobalt (Co).
[0123] Aspect 3: The composition according to aspects 1 or 2,
wherein the at least two mineral acids are selected from
hydrochloric acid (HCl), nitric acid (HNO.sub.3), sulfuric acid
(H.sub.2SO.sub.4), and hydrofluoric acid (HF).
[0124] Aspect 4: The composition according to any one of aspects 1
to 3, wherein the at least two mineral acids comprise HCl,
HNO.sub.3, and HF.
[0125] Aspect 5: The composition according to any one of aspects 1
to 4, comprising: 1N-10N HCl; and/or 0.05N-2.0N HNO.sub.3; and/or
0.1N-2.0N HF.
[0126] Aspect 6: The composition according to any one of aspects 1
to 5, comprising: at least 0.2 Cr; at least 0.1 molybdenum Mo;
0-400 Iron (Fe); and 0-400 cobalt (Co).
[0127] Aspect 7: The composition according to any one of aspects 1
to 6, comprising: 0.5-355 cobalt (Co); 0.2-170 chromium (Cr); and
0.1-40 molybdenum (Mo).
[0128] Aspect 8: The composition according to any one of aspects 1
to 7, wherein the Co, Cr, and Mo are provided in a ratio that is
the same as a native ratio of each metal in the cobalt chromium
alloy.
[0129] Aspect 9: The composition according to any one of aspects 1
to 8, a total amount of the component metals Co, Cr, and Mo in the
composition does not exceed 400 g/l.
[0130] Aspect 10: The composition according to any one of aspects 1
to 9, wherein the composition etches cobalt chromium alloys at a
rate of 0.1 to 1.0 mil/minute.
[0131] Aspect 11: A method for etching an alloy material, the
method comprising: preparing an aqueous chemical etching
composition according to any one of aspects 1 to 10; and contacting
the alloy material with the aqueous chemical etching
composition.
[0132] Aspect 12: The method according to aspect 11, further
comprising, before the step of contacting the alloy material with
the aqueous chemical etching composition, activating the alloy
material to be etched with an activation solution.
[0133] Aspect 13: The method according to aspect 12, wherein the
activating step is carried out immediately before the contacting
step, such as within 120 seconds, or within 60 seconds, or within
30 seconds.
[0134] Aspect 14: The method according to aspects 12 or 13, wherein
the activation solution comprises a concentrated mineral acid, such
as a 10% to 100% aqueous solution of hydrochloric acid or
hydrofluoric acid (v/v), or a mixture of concentrated mineral acid
and hydrogen peroxide, such as concentrated hydrochloric acid and
hydrogen peroxide.
[0135] Aspect 15: The method according to any one of aspects 11 to
14, wherein the contacting step is carried out at a temperature of
from about 20.degree. C. to about 150.degree. C., such as
30.degree. C. to 105.degree. C.
[0136] Aspect 16: The method according to any one of aspects 11 to
15, wherein the work-piece is agitated in the chemical etching
composition for a time period of 1 minute to 200 minutes.
[0137] Aspect 17: The method according to any one of aspects 11 to
16, wherein, before the contacting step or, when an activating step
is included, before or after the activating step, the method
comprises: applying a coating which resists chemical etchants to
the work-piece; and removing a portion of the coating to form a
patterned design in the coating on the work-piece.
[0138] Aspect 18: The method according to aspect 17, wherein, after
the contacting step, the method comprises: stripping the coating
from the work-piece.
[0139] Aspect 19: A work-piece produced by the method according to
any one of aspects 11 to 18, having a surface roughness (R.sub.a)
of less than 200 .mu.-in, such as less than 150 .mu.-in, or less
than 100 .mu.-in.
[0140] Aspect 20: The work-piece according to aspect 19, wherein
the work-piece forms a component, in part or wholly, of an
aerospace vehicle.
[0141] Aspect 21: A work-piece formed of a cobalt chromium alloy
having a surface roughness (R.sub.a) of less than 200 .mu.-in, such
as less than 150 .mu.-in, or less than 100 .mu.-in, and comprises
no directional surface scratches.
[0142] Aspect 22: A work-piece formed by additive manufacturing
using a powdered cobalt chromium alloy, the work piece comprising
an etched surface that is substantially free of grains of the
powdered cobalt chromium alloy, has a surface roughness (R.sub.a)
of less than 200 .mu.-in, such as less than 150 .mu.-in, or less
than 100 .mu.-in, and comprises no directional surface
scratches.
[0143] Aspect 23: The work-piece of aspect 21 or 22, wherein the
surface roughness (R.sub.a) is less than 100 .mu.-in, and the
work-piece forms at least a portion of a component part of an
aerospace vehicle.
[0144] While specific embodiments of the invention have been
described in detail, it should be appreciated by those skilled in
the art that various modifications and alternations and
applications could be developed in light of the overall teachings
of the disclosure. Accordingly, the particular arrangements,
systems, apparatuses, and methods disclosed are meant to be
illustrative only and not limiting as to the scope of the
invention.
* * * * *