U.S. patent application number 10/793536 was filed with the patent office on 2005-09-08 for brazing titanium to stainless steel using nickel filler material.
Invention is credited to Antalfy, Attila, Jiang, Guangqiang.
Application Number | 20050194426 10/793536 |
Document ID | / |
Family ID | 34750631 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050194426 |
Kind Code |
A1 |
Jiang, Guangqiang ; et
al. |
September 8, 2005 |
Brazing titanium to stainless steel using nickel filler
material
Abstract
The invention is a method of bonding a stainless steel part to a
titanium part by heating a component assembly comprised of the
titanium part, the stainless steel part, and a very thin
substantially pure nickel filler material placed between the two
parts and heated at a temperature that is greater than the
temperature of the eutectic formed between the titanium part and
the substantially pure nickel filler material, but that is less
than the melting point of either the filler material, the stainless
steel part, or the titanium part. The component assembly is held in
intimate contact at temperature in a non-reactive atmosphere for a
sufficient time to develop a hermetic and strong bond between the
stainless steel part and the titanium part. The bonded component
assembly is optionally treated with acid to remove any residual
free nickel and nickel salts, to assure a biocompatible component
assembly for implantation in living tissue.
Inventors: |
Jiang, Guangqiang; (Santa
Clarita, CA) ; Antalfy, Attila; (Castaic,
CA) |
Correspondence
Address: |
ALFRED E. MANN FOUNDATION FOR
SCIENTIFIC RESEARCH
PO BOX 905
25134 RYE CANYON LOOP, SUITE 200
SANTA CLARITA
CA
91380
US
|
Family ID: |
34750631 |
Appl. No.: |
10/793536 |
Filed: |
March 3, 2004 |
Current U.S.
Class: |
228/122.1 |
Current CPC
Class: |
B23K 20/16 20130101;
B23K 35/004 20130101; B23K 35/3033 20130101; B23K 35/005 20130101;
B23K 2103/24 20180801 |
Class at
Publication: |
228/122.1 |
International
Class: |
B23K 031/02 |
Claims
What is claimed is:
1. A component assembly for use in living tissue comprising: a
stainless steel part; a titanium part; and a substantially pure
nickel filler for bonding said stainless steel part to said
titanium part.
2. The component assembly of claim 1 wherein said stainless steel
part is selected from the group consisting of 200, 300, and 400
series stainless steel.
3. The component assembly of claim 1, wherein said stainless steel
part is comprised of 316 stainless steel.
4. The component assembly of claim 1, wherein said titanium part is
selected from the group consisting of titanium and titanium
alloys.
5. The component assembly of claim 1, wherein said titanium part is
comprised of Ti-6Al-4V.
6. The component assembly of claim 1, wherein said substantially
pure nickel filler reacts with and forms a hermetic and strong bond
between said titanium part and said stainless steel part.
7. The component assembly of claim 1 wherein: said substantially
pure nickel filler having a thickness of approximately 0.010 inches
or less; and said component assembly is heated to a temperature
that is less than the melting point of said titanium part, said
stainless steel part, or of said substantially pure nickel filler,
but that is greater than the eutectic melting point between said
titanium part and said nickel part, thereby forming a bond.
8. The component assembly of claim 1, wherein said substantially
pure nickel filler is a thin coating of substantially pure nickel
that is applied to the surfaces that are to be bonded of either
said titanium part or said stainless steel part, by a chemical
process selected from the group consisting of electroless plating
and electroplating.
9. The component assembly of claim 1, wherein said substantially
pure nickel filler is a thin coating of substantially pure nickel
that is applied to the surfaces that are to be bonded of either
said titanium part or said stainless steel part, by a thermal
process selected from the group consisting of sputtering,
evaporating, and ion beam enhanced deposition.
10. The component assembly of claim 1, wherein said substantially
pure nickel filler is a thin coating of substantially pure nickel
that is applied to the surfaces that are to be bonded of either
said titanium part or said stainless steel part, selected from the
group consisting of metallic beads and metallic powder.
11. A method of hermetically sealing a stainless steel and titanium
component assembly for implantation in living tissue, comprising
the steps of: selecting a stainless steel part; selecting a
titanium part; selecting a substantially pure nickel filler that is
compatible with said stainless steel part, said substantially pure
nickel filler being one which forms a eutectic alloy with said
titanium part, said eutectic alloy consisting of metals of said
titanium part and said substantially pure nickel filler and having
a eutectic melting point that is lower than the respective melting
point of said titanium or of said substantially pure nickel filler;
positioning said substantially pure nickel filler between said
stainless steel part and said titanium part; applying a force to
said stainless steel part and said titanium part to place said
substantially pure nickel filler in compression, thereby creating
intimate contact between said stainless steel part, said titanium
part and said substantially pure nickel filler; placing the
assembly in a non-reactive atmosphere; heating the assembly to a
bonding temperature between said eutectic melting point and said
melting point of said titanium part; holding the assembly at said
bonding temperature for a predetermined time to form a bond between
said stainless steel part and said titanium part; and cooling the
assembly.
12. The method of claim 11 wherein said force creates compression
between 2 and 500 psi.
13. The method of claim 11 wherein said force creates compression
between 2 and 7 psi.
14. The method of claim 11 wherein said stainless steel part is
selected from the group consisting of 200, 300, and 400 series
stainless steel.
15. The method of claim 11 wherein said titanium part is selected
from the group consisting of titanium and its alloys.
16. The method of claim 11 wherein said titanium part is comprised
of Ti-6Al-4V.
17. The method of claim 11 wherein said substantially pure nickel
filler is comprised of pure nickel.
18. The method of claim 11 wherein said substantially pure nickel
filler is comprised of about 0.010 inches or less thick foil.
19. The method of claim 11 wherein said substantially pure nickel
filler is applied chemically.
20. The method of claim 11 wherein said substantially pure nickel
filler is applied thermally.
21. The method of claim 11 wherein said substantially pure nickel
filler is in the form of metallic beads.
22. The method of claim 11 wherein said substantially pure nickel
filler is in the form of metallic powder.
23. The method of claim 11 wherein said non-reactive atmosphere is
a vacuum between approximately 10.sup.-5 to 10.sup.-7 torr.
24. The method of claim 11 wherein said non-reactive atmosphere is
an argon or nitrogen gas.
25. The method of claim 11 wherein said bonding temperature is
between approximately 940.degree. and 1260.degree. C.
26. The method of claim 11 wherein said predetermined time is
between approximately 1 and 60 minutes.
27. The method of claim 11 additionally comprising the step of
cleaning said component assembly after bonding to remove toxic
materials that are harmful to living tissue.
28. The method of claim 27 additionally comprising the step of
cleaning said component assembly after bonding by placing it in an
acid bath.
29. The method of claim 27 wherein said toxic materials are
comprised of nickel and nickel salts.
30. A method of bonding a Ti-6Al-4V metal part to a stainless steel
part making a hermetically sealed component assembly for
implantation in living tissue, comprising the steps of: selecting a
stainless steel part from the group consisting of biocompatible and
corrosion resistant stainless steels; positioning a substantially
pure nickel filler between said stainless steel part and said
Ti-6Al-4V metal part; applying a force to said stainless steel part
and said titanium part so as to place said substantially pure
nickel filler in compression; placing said component assembly in a
non-reactive atmosphere; heating said component assembly to between
approximately 940.degree. and 1260.degree. C. for between
approximately 1 and 60 minutes; and cooling said component
assembly.
31. A method of bonding a stainless steel part to a titanium part
to form a component assembly for placement in living tissue in
which a filler is placed between the two parts to be bonded,
applying a compressive force of 2 to 500 psi to said stainless
steel part and said titanium part so as to place said filler in
compression to form intimate contact between said stainless steel
part, said titanium part and said filler, said filler being a metal
which forms a eutectic alloy with said titanium part, said eutectic
alloy consisting of metals comprising said titanium part and said
filler and having a eutectic temperature that is lower than the
melting point of said titanium or of said filler, and in which said
component assembly, comprising said stainless steel part, said
titanium part and said filler, is placed at a bonding temperature,
for a predetermined time, that is less than the melting point of
said titanium part, said stainless steel part or said filler, but
where said bonding temperature is greater than the melting point
temperature of said eutectic alloy, selecting said stainless steel
part from the group consisting 200, 300, and 400 series stainless
steel, selecting said titanium part from the group consisting of
titanium and titanium alloys, wherein the improvement comprises:
selecting said filler to be substantially pure nickel; and
selecting said bonding temperature between approximately
940.degree. and 1260.degree. C.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0001] FIG. 1 illustrates the side view of the component assembly
with the filler material as a foil between the stainless steel and
titanium parts.
[0002] FIG. 2 schematically depicts the bonding steps of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0003] FIG. 1 shows component assembly 2 having titanium part 4,
stainless steel part 6, and filler material 8. Component assembly 2
is heated to a specific process temperature that is below the
melting point of titanium part 4 or of stainless steel part 6, for
a specific period of time, at a pressure that is created by force
10 and that is exerted to place filler material 8 in intimate
contact with the titanium and stainless steel parts.
[0004] Filler material 8 is a foil preferably having a thickness of
less than ten-thousandths (0.010) of an inch and more preferably
approximately 0.001 inches. Filler material 8 is selected from the
group of materials that are compatible with the stainless steel
chosen for stainless steel part 6 in that they wet the surface
during the bonding process and enter into a diffusion process with
the stainless steel part 6 thereby creating a strong bond during
processing. Filler material 8 is selected from the group of
materials that are compatible with the titanium part 4. Filler
material 8 forms a bond with a titanium part 4 by virtue of
developing a eutectic alloy at the bonding temperature and pressure
utilized during processing. The eutectic alloy formed during
processing is predominantly composed of the titanium from titanium
part 4. The group of filler materials includes substantially pure
nickel, i.e., pure nickel and nickel containing approximately two
percent or less by weight of alloy metals. In a preferred
embodiment, filler material 8 is preferably commercially pure
nickel foil having at least 99.0% nickel and less than 1.0% of
other elements with a thickness of approximately 0.001 inches.
[0005] Titanium part 4 may be a biocompatible material such as a
titanium alloy, and is Ti-6Al-4V in a preferred embodiment.
Stainless steel part 6 may be a 200, 300, or 400 series stainless
steel, and in a preferred embodiment stainless steel part 6 is 316
stainless steel. In alternative embodiments, rather than using
filler material 8 as a foil, filler material 8 may be a thin
coating that is applied to either the titanium part 4 or stainless
steel part 6 surface to be bonded by any of a variety of chemical
processes such as electroless plating and electroplating, or by any
of a variety of thermal processes such as sputtering, evaporating,
or ion beam enhanced deposition. Filler material 8 may also be
applied as a thin coating of metallic beads or metallic powder.
[0006] The process steps that are employed to create assembly 2
with a strong bond between titanium part 4 and stainless steel part
6 are schematically represented in FIG. 2. First, the surfaces to
be bonded are prepared in step 20 by machining to assure that they
will intimately conform to each other during bonding. The surfaces
are smoothed and cleaned.
[0007] In step 22, component assembly 2 is prepared with filler
material 8 between titanium part 4 and stainless steel part 6. In
step 24, force 10 is applied to compress filler material 8 between
titanium part 4 and stainless steel part 6. Force 10 is sufficient
to create intimate contact between the parts. Force 10 is applied
to assure that a strong and hermetic bond is formed between
titanium part 4 and stainless steel part 6.
[0008] In step 26 the assembly to be heat processed is placed in a
furnace in a non-reactive atmosphere, which is preferably vacuum,
but which, in an alternative embodiment, can be any of several
atmospheres that are known to one skilled in the art, such as argon
or nitrogen. A vacuum is applied before the furnace is heated to
the processing temperature in step 28. A preliminary holding
temperature, which is lower than the process temperature, may be
utilized to allow the thermal mass of the parts to achieve
equilibrium before proceeding with heating. The process temperature
is lower than the melting point of titanium part 4, but greater
than the temperature of the eutectic formed between titanium 4 and
filler material 8. In a preferred embodiment, the vacuum is
10.sup.-5 to 10.sup.-7 torr, to assure that the filler material 8
and titanium part 4 do not oxidize. Component assembly 2 is held at
the selected temperature, which is between approximately
940.degree. and 1260.degree. C., for approximately 5 to 10 minutes,
while force 10 continues to be exerted on filler material 8. The
exact time, temperature and pressure are variable with each other
so as to achieve a hermetic and strong bond of titanium part 4 with
stainless steel part 6. For example, in a preferred embodiment, a
316 stainless steel part is bonded to a Ti-6Al-4V part in vacuum at
10.sup.-6 torr at approximately 1000.degree. C. for 10 minutes with
a pressure of about 5 to 20 psi on a commercially pure nickel foil
of approximately 0.001 inches thickness.
[0009] The furnace is cooled and component assembly 2 is cooled to
room temperature in step 30. In optional step 32, component
assembly 2 is cleaned by being placed in a bath, after thermal
processing is complete, to assure removal of all nickel and nickel
salts. This bath is preferably an acid bath that etches the exposed
surfaces of component assembly 2. In a preferred embodiment, the
bath is nitric acid. Removal of nickel and nickel salts in the bath
etch insures that component assembly 2 is biocompatible. Nickel and
nickel salts are detrimental to living animal tissue. In the
preferred embodiment, however, all of the nickel that is introduced
as filler material 8 is combined with the titanium and is
chemically tied up by thermal processing to be unavailable as free
nickel or as a nickel salt.
[0010] Component assembly 2 is biocompatible after bonding and
processing. Titanium part 4, stainless steel part 6, and filler
material 8 are selected so as to be compatible with the environment
in a living body. Hence, titanium part 4 is preferably a Ti-6Al-4V
alloy and stainless steel part 6 is preferably a 316 stainless
steel.
[0011] In a preferred embodiment, component assembly 2 is either an
electrical sensor or an electrical stimulator that is implanted in
a human body, although it could equally well be implanted in any
animal. It must survive long periods in the hostile environment of
a living body, which is basically a warm saline solution. In a
preferred embodiment, component assembly 2 is either a sensor or
stimulator comprised of a hollow stainless steel tube that contains
various electronic components that is bonded to a titanium
electrode end. The component assembly must be watertight; hence,
the bond is hermetic, resisting salt-water intrusion as well as
growth of living tissue into the titanium-to-stainless steel bond
joint.
[0012] Further, component assembly 2 does not corrode while
implanted in the body. The materials are chosen such that they are
not susceptible to corrosion either individually or in the
as-bonded state. Component assembly 2 resists electrolytic
corrosion as well as crevice corrosion, because of the materials
selected for component assembly 2.
[0013] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that, within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described.
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