U.S. patent application number 10/895885 was filed with the patent office on 2006-01-26 for method for manufacturing titanium alloy wire with enhanced properties.
Invention is credited to Jerry L. Fields, Robert Lewis Grabow, Vincent Harold Hammond, William M. Hanusiak.
Application Number | 20060016521 10/895885 |
Document ID | / |
Family ID | 35655874 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060016521 |
Kind Code |
A1 |
Hanusiak; William M. ; et
al. |
January 26, 2006 |
Method for manufacturing titanium alloy wire with enhanced
properties
Abstract
A method for producing reinforced titanium alloy wire,
comprising forming a billet of titanium alloy with grains of a
precipitated discontinuous reinforcement material such as TiB
and/or TiC. The billet may be formed by the hot consolidation of a
titanium alloy powder formed by gas atomization. The billet is then
hot formed to reduce it to rod or coil form. The rod or coil is
then subjected to successive cold drawing operations to form a
reinforced titanium alloy wire of reduced diameter. The cold
drawing includes periodic annealing operations under low oxygen
conditions to relieve work hardening and to recrystallize the
reinforcement material grains to reduce the size thereof.
Inventors: |
Hanusiak; William M.;
(Bridgeport, WV) ; Fields; Jerry L.; (Woodstock,
VA) ; Hammond; Vincent Harold; (Fairmont, WV)
; Grabow; Robert Lewis; (Clarksburg, WV) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
35655874 |
Appl. No.: |
10/895885 |
Filed: |
July 22, 2004 |
Current U.S.
Class: |
148/421 ;
148/671; 419/54 |
Current CPC
Class: |
B22F 3/15 20130101; B22F
3/17 20130101; C22C 32/0031 20130101; B22F 9/08 20130101; B22F 3/24
20130101; B22F 5/12 20130101; B22F 2998/00 20130101; B22F 2998/00
20130101; C22C 1/1042 20130101; B22F 2998/10 20130101; B22F 2998/10
20130101 |
Class at
Publication: |
148/421 ;
148/671; 419/054 |
International
Class: |
B22F 3/10 20060101
B22F003/10 |
Claims
1. A method for producing reinforced titanium alloy wire,
comprising: forming a billet of titanium alloy with grains of a
precipitated discontinuous reinforcement material; hot forming the
billet to reduce it to rod or coil form; and cold drawing the rod
or coil in successive operations to wire of reduced diameter, said
cold drawing including the periodic annealing of the wire under low
oxygen conditions to relieve work hardening and to recrystallize
the reinforcement material grains to reduce the size thereof.
2. The method of claim 1 wherein said billet is hot forged to
create a uniform chemistry and microstructure before it is hot
formed.
3. The method of claim 1 wherein said reinforcement material is
TiB.
4. The method of claim 3 wherein said billet is cast from a Boron
rich melt.
5. The method of claim 3 wherein said billet is formed by
consolidating titanium alloy powder formed by gas atomization from
a Boron rich melt.
6. The method of claim 5 wherein said powder is gas atomized powder
with a composition of Ti-6Al-4V-1.7B in a size range of minus 35
mesh to plus 270 mesh, with an interstitial content of oxygen less
than 1500 ppm.
7. The method of claim 1 wherein said reinforcement material is
TiC.
8. The method of claim 1 wherein said reinforcement material is TiB
and TiC.
9. The method of claim 5 wherein said consolidating is by hot
isostatic pressing at a pressure of approximately 15,000 psi and a
temperature of approximately 1650.degree. F. to 1750.degree. F.
10. The method of claim 1 wherein said titanium alloy is
Ti-6Al-4V.
11. The method of claim 1 wherein said titanium alloy is
Ti-6Al-2Sn-4Zr-2Mo.
12. The method of claim 1 wherein said hot forming is at a
temperature of approximately 1750.degree. F.
13. The method of claim 12 wherein said hot forming results in
about a 50:1 hot reduction in section area to break up and reduce
the size of the reinforcement material grains.
14. The method of claim 1 wherein said cold drawing is performed
periodically to reduce the size of the wire at a rate of
approximately 10 percent for each drawing operation during the
first half of the desired diameter reduction.
15. The method of claim 14 wherein the rate of reduction is
increased to approximately 15 percent at the midpoint of diameter
reduction and to approximately 20 percent near the end of the
diameter reduction.
16. The method of claim 1 wherein said annealing is performed at
intervals corresponding to an accumulated reduction of wire
diameter of about 50 percent for about 1 hour in inert gas with
forced inert gas cooling.
17. A method for producing reinforced titanium alloy wire,
comprising: forming a powder of titanium alloy by gas atomization
from a Boron rich melt; consolidating the titanium alloy powder
under heat and pressure into a billet having grains of precipitated
discontinuous TiB reinforcement; hot forming the billet to reduce
it to rod or coil form and to break up and reduce the size of the
TiB grains; cold drawing the rod or coil in successive operations
to wire of reduced diameter, said cold drawing including the
periodic annealing of the wire under low oxygen conditions to
relieve work hardening and to recrystallize the TiB grains to
reduce the size thereof.
18. The method of claim 17 wherein said powder is gas atomized
powder with a composition of Ti-6Al-4V-1.7B in a size range of
minus 35 mesh to plus 270 mesh, with an interstitial content of
oxygen less than 1500 ppm.
19. The method of claim 17 wherein said titanium alloy is
Ti-6Al-4V.
20. The method of claim 17 wherein said titanium alloy is
Ti-6Al-2Sn-4Zr-2Mo.
21. The method of claim 17 wherein said consolidating is by hot
isostatic pressing at a pressure of approximately 15,000 psi and a
temperature of approximately 1650.degree. F. to 1750.degree. F.
22. The method of claim 17 wherein said hot forming is at a
temperature of approximately 1750.degree. F.
23. The method of claim 22 wherein said hot forming results in
about a 50:1 hot reduction in section area to break up and reduce
the size of the reinforcement material grains.
24. The method of claim 17 wherein said cold drawing is performed
periodically to reduce the size of the wire at a rate of
approximately 10 percent for each drawing operation during the
first half of the desired diameter reduction.
25. The method of claim 24 wherein the rate of reduction is
increased to approximately 15 percent at the midpoint of diameter
reduction and to approximately 20 percent near the end of the
diameter reduction.
26. The method of claim 17 wherein said annealing is performed at
intervals corresponding to an accumulated reduction of wire
diameter of about 50 percent for about 1 hour in inert gas with
forced inert gas cooling.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of manufacturing
titanium alloy wire and, more particularly, to such a method
wherein precipitated discontinuous particulates of a reinforcement
material such as TiB and/or TiC are added to the alloy and it is
processed in accordance with a new and improved method wherein the
reinforcement thereof by the particulates is enhanced.
BACKGROUND OF THE INVENTION
[0002] Processes have been reported in the literature in which a
common alloy of titanium, Ti-6Al-4V, has been reinforced and
enhanced by the addition of TiB and/or TiC particulates. This is
significant in that the Ti-6Al-4V alloy is utilized extensively in
aerospace applications and is one of the most affordable.
Enhancements that enable the extension of the useful application
range of such alloys without significant cost impact are of great
interest to the aerospace design community. In the reported
processes, a Ti-6Al-4V casting was produced with TiB and/or TiC
additions being added to the melt before casting. These additions
dissolve in the melt and recrystallize during cooling to form
discontinuous reinforcement in a variety of sizes. Articles
compacted by hot isostatic pressing (HP) and extrusion have
demonstrated improved tensile strength and tensile modulus
depending on the concentrations of TiB and/or TiC additions.
[0003] The results indicate that improvements in properties are
related to the amount of discontinuous reinforcement created and to
the size of the resulting reinforcement crystals. That is, it is
desirable to have the reinforcement content as high as 40% by
volume and the reinforcement size to be in the ultra fine size
range. In the known processes, however, reinforcement content above
a few percent is predominately in the largest size fraction with
wide variability in size distribution and the shift to larger sized
reinforcement is exaggerated as the reinforcement content increases
toward the most desirable levels between 20 to 40% by volume. This
is the result of large grains scavenging smaller grains during the
casting or fabrication process and is apparently inherent in such
processes. This limitation seriously inhibits the full capability
of the discontinuously reinforced titanium potential.
[0004] The new and improved method of the present invention is not
subject to these disadvantages and possesses advantages not
possible with the use of previously used or known methods.
SUMMARY OF THE INVENTION
[0005] The method of the present invention is directed to the
manufacturing of titanium alloy wire suitable for application to
wire/fiber composites, generally comprising the steps of forming
the desired alloy via casting a billet or gas atomization; hot
forging to create a uniform chemistry and microstructure;
conforming to rod or coil, e.g., of about 0.2 inches in diameter;
and cold drawing to wire, e.g., of about 0.005 inches in
diameter.
[0006] More specifically, a preferred method comprises the
formation of titanium alloy powder by gas atomization from a boron
rich melt; consolidating the powder metal to bar form using hot
isostatic pressing (HIP) with a pressure of about 5,000 to 45,000
psi, e.g., 15,000 psi, and a temperature of about 1,650.degree. F.
to 1,750.degree. F. until full consolidation, yet remaining below
the beta transis to avoid grain growth and grain boundary
segregation; hot reduction at approximately 1500.degree. F. to
2100.degree. F., e.g., 1,750.degree. F., to reduce the bar to rod
or coil form and perform the initial break-up of the larger TiB
grains; and cold drawing and annealing at approximately a 10 to 20
percent reduction per pass to avoid cracking. In accordance with
the method of the present invention, an increased frequency of
annealing steps under very low oxygen conditions serves to relieve
work hardening and also recrystallizes the TiB grains to a refined
size with alignment with the wire axis. This new and improved
method enables the fabrication of fine titanium alloy wire with
simultaneous achievement of high TiB reinforcement content and
small reinforcement grain size. Other reinforcement materials may
be used such as TiC, alone or in combination with TiB.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0007] The method of the present invention has been developed to
achieve predominately fine grained reinforcement even at high
reinforcement content through the combination of precipitation of
reinforcement and a new and improved wire fabrication method.
Typical fine wire processing practice suitable for application to
wire/fiber composites, such as described in U.S. Pat. No.
5,763,079, consists of four principal operations, namely, formation
of the desired alloy via casting a billet, hot forging to create a
uniform chemistry and microstructure, hot forming to rod (or coil)
of about 0.2 inches in diameter, and cold drawing to wire of about
0.005 inches in diameter. Intermediate annealing operations are
necessary during the cold drawing to relieve residual stresses and
restore ductility for further drawing. This basic wire forming
process is designed to achieve area reduction through hot forming,
hot extrusion and finally cold drawing in the fewest operations and
the fewest breaks that would affect continuous lengths.
[0008] In accordance with the present invention, it has been
discovered that the wire drawing process can be designed or
modified to control microstructural evolution in addition to the
base purpose of area reduction. The wire drawing method of the
present invention can achieve improved microstructures in difficult
alloys that cannot be achieved by any other known method, and was
developed for the purpose of producing a discontinuously reinforced
Ti-6Al-4V alloy with the simultaneous achievement of high TiB
content and small reinforcement grain size.
[0009] The present wire forming method can start with a casting of
Ti-6Al-4V alloy from a Boron rich melt. The TiB will precipitate
during cooling, but the cooling rate will allow for larger TiB
grain growth which is undesirable. In order to start with the best
microstructure, a powder metal formed by gas atomization from a
Boron rich melt preferably is used rather than a casting. The
powder forming process employs more rapid cooling than casting and
is less likely to produce large TiB grains. In this method, a
compositionally uniform billet is prepared using powder metallurgy
techniques to avoid the grain growth and potential for chemical
segregation inherent in the casting process. The metal alloy powder
produced from Boron rich Ti-6Al-4V alloy is first hot formed into a
bar compatible in size with the available industrial wire forming
equipment. The bar is hot rolled into rod or coil with a diameter
of about 0.2 inches, and the rod or coil is then transferred to the
cold drawing operations.
[0010] It has been discovered that selection of correct cold
drawing processing conditions results in ductile small diameter
fine wire and a successful evolution of the desired wire
microstructure, that is, high concentrations and fine grains.
Execution of this improved process requires consideration of
critical processing conditions in each operation. Cold drawing area
reduction must be sufficient to cold work the small diameter rods
to the core on each pass in order to maintain micro-structural
uniformity throughout the cross section. The reduction in area must
not be excessive, however, to avoid fracture, microcracking or void
formation within the rod or coil as it is reduced in diameter. The
presence of the large TiB grains in the initial stages of cold
drawing make the material susceptible to microcracking and void
formation in the region of the large TiB grains. This balance
between area reduction and avoidance of microcracking and void
formation is more difficult in the beginning of the reduction
sequence when the largest TiB grains are present, and the
processing window expands as the TiB grain size is reduced.
[0011] The cold drawing process of the present invention serves to
break up the large TiB grains without deleterious microcracking or
void formation. It has been discovered that the addition of
frequent annealing steps to relieve work hardening will also
recrystallize the TiB grains to a refined size with alignment with
the wire axis. Annealing steps have been utilized in the known wire
drawing process, but less frequently and for shorter periods of
time. The increased frequency of anneals in accordance with the
present invention increases the requirement for annealing under
very low oxygen conditions to avoid excessive surface material loss
due to oxygen contamination and oxygen interstitial pick up by the
wire metallurgy that may interfere with the TiB refinement process.
Accordingly, the present method enables the fabrication of fine
titanium alloy wire with simultaneous achievement of high
reinforcement content and small reinforcement grain size.
[0012] In accordance with a preferred embodiment of the method of
the present invention, an acceptable alloy powder is gas atomized
spherical powder with a composition of Ti-6Al-4V-1.7B in a size
range of minus 35 mesh to plus 270 mesh. An acceptable interstitial
content was found to be oxygen less than 1500 ppm. This quality
powder has been used to fabricate composite panels and is known to
yield uniform chemistry and microstructure. Consolidation of the
powder metal to bar form is based on methods found successful for
composite panels. For example, it has been determined that
non-contaminating consolidation tooling is needed, such as vacuum
degassed mild steel or conventional titanium alloys. Consolidation
to a bar is achieved using hot isostatic pressing (HIP) with a
pressure of approximately 5000 psi to 45,000 psi, e.g., 15,000 psi,
and a temperature of about 1650.degree. F. to 1750.degree. F. These
conditions serve to achieve full consolidation and yet remain
safely below the beta transis to avoid grain growth and grain
boundary segregation. The hot reduction operation at about
1500.degree. F. to 2100.degree. F., e.g., 1750.degree. F., serves
to reduce the bar to coil or rod form and performs the initial
breakup to the larger TiB grains. It has been determined that about
50:1 hot reduction in section area is effective to breakup of the
primary large TiB grains. The subsequent cold drawing must impart
sufficient cold work through the thickness of the rod or coil, and
the annealing must relieve the work hardening without grain growth.
It has been determined that about a 10 percent reduction per pass
is necessary to assure sufficient uniformity of cold working and
avoid microcracking and void formation during the initial cold
drawing steps from the nominal 0.2 inch diameter condition.
Reductions in area can increase to about 15 percent per pass by the
mid-point in the sectional area reduction process, and about 20
percent area reductions are possible by the end of the area
reduction process. Annealing at about 1200.degree. F. to
2000.degree. F., e.g., 1750.degree. F. for about 1 hour in inert
gas with forced inert gas cooling is sufficient to remove work
hardening, recrystallize the TiB and avoid grain growth. Annealing
is performed at intervals corresponding to an accumulated reduction
in section area of about 50 percent.
[0013] The above-described method of the present invention produces
Ti-6Al-4V alloy with fine grained TiB reinforcement in
concentrations ranging from 1 to 50 percent by volume with
reinforcement alignment along the wire axis. It has been found that
this process is effective with a wide variety of titanium alloys,
such as Ti-6Al-2Sn-4Zr-2Mo alloy, Ti-6Al-4Sn-4Zr-1Nb-1Mo-0.2Si
alloy, Ti-3Al-2.5V alloy, Ti-10V-2Fe-3Al alloy, Ti-5Al-2.5 Sn alloy
and Ti-8Al-1Mo-1V alloy. Also, it is effective with other
precipitated discontinuous reinforcements such as TiC, or mixtures
of TiB and TiC. The method may utilize a billet cast from a Boron
rich melt, but the inherent risks of microcracking and void
formation would be greater owing to the larger TiB grain growth
that results from a slow cooled casting. The extremely high area
reductions inherent in the wire forming process combined with
properly controlled reduction and annealing conditions in the
present method produces high performance titanium alloy wire that
cannot be produced by any other known metallurgical process.
[0014] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *