Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MANUFACTURING SUPERELASTIC ~i TITANIUM ARTICLES
AND THE ARTICLES DERIVED THEREFROM
BACKGROUND
This disclosure relates to superelastic (3 titanium alloys, methods for
manufacturing these alloys and articles derived therefrom.
Alloys that undergo a martensitic transformation may exhibit a "shape
memory effect". As a result of this transformation, the high temperature phase
known
as "austenite" changes its crystalline structure through a diffusion-less
shear process
adopting a less symmetrical structure called 'martensite'. This process may be
reversible as in shape memory alloys and therefore upon heating, the reverse
transformation occurs. The sta~.-ting temperature of the cooling or
martensitic
transformation is generally referred to as the MS temperature and the
finishing
temperature is referred to as the Mf temperature. The starting and finishing
temperatures of the reverse or austenitie transformation are referred to as AS
and Af
respectively.
At temperatures below the Af, alloys undergoing a reversible martensitic phase
transformation may be deformed in their high temperature austenitic phase
through a
stress-induced martensitic transformation as well as in their low temperature
martensitic phase. These alloys generally recover their original shapes upon
heating
above the Af temperature and are therefore called "shape memory alloys". At
temperatures above the Af, the stress-induced martensite is not stable and
will revert
baclc to austenite upon the release of deformation. The strain recovery
associated with
the reversion of stress-induced martensite back to austente is generally
referred to as
"pseudoelasticity" or "superelasticity" as defined in ASTM F2005, Standard
Terminology for Nickel-Titanium Shape Memory Alloys. The two terms are used
interchangeably to deseribe the ability of shape memory alloys to elastically
recover
large deformations without a significant amount of plasticity due to the
mechanically
induced crystalline phase change.
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Nitinol is a shape memory alloy comprising a near-stoichiometric amount of
nickel and titanium. When deforming pseudoelastic nitinol, the formation of
stress-
induced-martensite allows the strain of the alloy to increase at a relatively
constant
stress. Upon unloading, the reversion of the martensite back to austenite
occurs at a
constant, but different, stress. A typical stress-strain curve of
pseudoelastic nitinol
therefore exhibits both loading and unloading stress plateaus. However, since
the
stresses are different, these plateaus are not identical, which is indicative
of the
development of mechanical hysteresis in the nitinol. Deformations of about 8
to
about 10% can thus be recovered in the pseudoelastic nitinol. Cold worked
Nitinol
also exhibits extended linear elasticity. Nitinol compositions, which display
linear
elasticity do not display any plateau but cam recover a strain of up to 3.5%.
This
behavior is generally termed "Linear Superelasticity" to differentiate from
transformation induced "Pseudoelasticity" or "Superelasticity". These
properties
generally make nitinol a widely used material in a number of applications,
such as
medical stems, guide wires, surgical devices, orthodontic appliances, cellular
phone
antenna wires as well as frames and other components for eye wear. However,
nitinol
is difficult to fabricate by forming and/or welding, which makes the
manufacturing of
articles from it expensive and time-consuming. Additionally, users of nickel
containing products are sometimes allergic to nickel.
SUMMARY
In one embodiment, an article is manufactured from a composition comprising
about 8 to about 10 wt% molybdenum, about 2.8 to about 6 wt% aluminum, up to
about 2 wt% chromium, up to about 2 wt% vanadium, up to about 4 wt% niobium,
with the balance being titanium, wherein the weight percents are based on the
total
weight of the alloy composition.
In another embodiment, an article manufactured from a composition
comprises about 8.9 wt% molybdenum, about 3.03 wt% aluminum, about 1.95 wt%
vanadium, about 3.86 wt% niobium, with the balance being titanium.
In yet another embodiment, an article manufactured from a composition
comprises about 9.34 wt% molybdenum, about 3.01 wt% aluminum, about 1.95 wt%
vanadium, about 3.79 wt% niobium, with the balance being titanium.
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In yet another embodiment, an article is manufactured by a method comprising
forming a shape from a composition comprising about 8 to about 10 wt%
molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% chromium, up
to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being
titanium, wherein the weight percents are based on the total weight of the
alloy
composition; cold working the shape; and heat treating the shape.
In yet another embodiment, an article is manufactured by a method comprising
swaging a wire having a composition comprising about 8 to about 10 wt%
molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% chromium, up
to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being
titanium, wherein the weight percents are based on the total weight of the
alloy
composition; cold working the shape; and heat treating the shape.
In yet another embodiment, the article manufactured from a ~i titanium alloy
may be am eyewear frame and components, face inserts and golf club heads,
orthodontic arch wires, dental implants, medical stems, filters, baskets,
surgical
instruments, orthopedic prostheses, orthopedic fracture fixation devices,
spinal fusion
and scoliosis correction devices or a catheter introduces (guide wire) and the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 represents an isometric view of the eyewear frame 100;
Figure 2 represents a schematic of one possible construction of the temple
130;
Figure 3A is a front, side and bottom view of a beveled edge insert for a golf
club;
Figure 3B is a bottom view of a tongue and groove edge insert for a golf club;
Figure 4A is a front view of a club face with an insert;
Figure 4B is a bottom view of Figure 4A showing the cut-out profile for the
insert;
Figure 5 is a front view of a golf club face with an insert;
Figure 6A-D is a schematic representation of one method of assembling the
golf club;
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Figure 7 is a graphical representation showing the effect of molybdenum
content on elastic recovery;
Figure 8 is a graphical representation of the effect of aging at 350°C
on the
elastic recovery of Sample 4 from Table 1;
Figure 9 is a graphical representation of the effect of aging at 350°C
on the
elastic recovery of Sample 5 from Table 1;
Figure 10 is a graphical representation showing the effect of aging at
350°C on
the elastic recovery of Sample 6 from Table 1;
Figure 11 is a graphic representation showing the effect of aging at about 250
to about 550°C for 10 seconds on the elastic recovery of Sample 4 from
Table l;
Figure 12 is a graphic representation showing the effect of aging at about 250
to about 550°C for 10 seconds on the elastic recovery of Sample 5 from
Table 1;
Figure 13 is a graphical representation showing the effect of cumulative cold
drawing reduction on the UTS of Sample 11 from Table 2;
Figure 14 is a graphical representation showing the effect of cumulative cold
drawing reduction on the Young's Modulus of Sample 11 from Table 2;
Figure 15 is a graphical representation showing the effect of tensile stress-
strain curve for a wire having the composition of Sample 11 from Table 2 with
19.4%
drawing reduction, tested to 2% strain;
Figure 16 is a graphical representation showing the effect of tensile stress-
strain curve for a wire having the composition of Sample 11 from Table 2 with
19.4%
drawing reduction, tested to 4% strain;
Figure 17 is an optical micrograph showing the microstructure of a cold drawn
wire having the composition of Sample 10 from Table 2 with a 14% reduction;
Figure 18 is an optical micrograph showing partially recrystallized
microstructure of a cold-drawn wire having the composition of Sample 10 from
Table
2 having a 14% reduction after heat- treating at 816°C for 30 minutes;
Figure 19 is an optical micrograph showing fully recrystallized microstructure
of a cold-drawn wire having the composition of Sample 10 from Table 2 having a
14% reduction after heat- treating at 871°C for 30 minutes;
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Figure 20 is an optical micrograph showing the microstructure of a betatized
Sample 10 from Table 2 after aging at 816°C for 30 minutes;
Figure 21 is an optical micrograph showing the microstructure of a betatized
Sample 10 from Table 2 after aging at 788°C for 30 minutes;
Figure 22 is a graphical representation showing the TJTS of betatized Sample
from Table 2 after aging at 500-900°C for 30 minutes;
Figure 23 is a graphical representation showing the ductility of betatized
Sample 10 from Table 2 after aging at 500-900°C for 30 minutes;
Figure 24 is a graphical representation showing a tensile stress-strain curve
10 tested to 4% tensile strain of a wire having the composition of Sample 11
from Table
2 after strand annealing at 871°C; and
Figure 25 is an optical micrograph showing the microstructure of a wire
having the composition of Sample 11 from Table 2 after strand annealing at
871°C.
Figure 26 is a schematic of a stmt;
Figure 27 represents a schematic of a perspective view of a catheter and
needle assembly;
Figure 28 represents an exploded schematic of a perspective view of the
catheter assembly and needle assembly including the needle tip protector;
Figure 29 is a partially exploded view of the bone reduction and fixation
device showing a driver and carmulated, internally and externally threaded
bone
screw;
Figure 30 is a side elevational view of the bone reduction and fixation
assembly of Figure 29;
Figure 31 is a cross-sectional view of the bone reduction and fixation
assembly of Figure 30;
Figure 32 depicts the plan of one configuration of an arch wire;
Figure 33 depicts an enlarged side view on line 2-2 of Figure 32; and
Figure 34 depicts a plan of an arch wire with lingually positioned orthodontic
brackets;
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Disclosed herein are articles manufactured from ~i titanium alloys such as
eyewear frames and frame components, face inserts and heads for golf clubs,
orthodontic arch wires, dental implants, orthopedic prostheses, orthopedic
fracture
fixation devices, spinal fusion and scoliosis correction instruments, medical
stems,
filters, baskets, a catheter introduces (guide wire) and the like. The (3
titanium alloy
exhibits pseudo-elasticity as well as linear superelasticity and may
advantageously be
welded, brazed, or soldered to other metals or alloys. The articles
manufactured from
the (3 titaniwn alloy can also be deformed into various shapes at ambient
temperature
and generally retain the high spring back characteristics associated with
superelasticity.
Pure titanium has an isomorphous transformation temperature at
882°C. The
body centered. cubic (bcc) structure, which is called ~i-titanium, is stable
above the
isomorphous transformation temperature and the hexagonal close packed (hcp)
structure, which is called a titanium is generally stable below this
temperature. When
titanium is alloyed with elements such as vanadium, molybdenum, andlor
niobium,
the resulting alloys have an increased (3 phase stability at temperatures less
than or
equal to about 882°C ((3 transus temperature). On the other hand, when
alloyed with
elements such as aluminum or oxygen, the temperature range of the stable a
phase is
increased above the isomorphous transformation temperature. Elements which
have
the effect of increasing the (3 phase temperature range are called the ,Q
stabilizers,
wlule those capable of extending the a phase temperature range are called the
a
stabilizers.
Titanium alloys having a high enough concentration of (3 stabilizers,
generally
are sufficiently stable to have a meta-stable ,Q phase structure at room
temperature.
The alloys showing such a property are called (3 titanium alloys. Martensite
transformations are commonly found among ~3 titanium alloys. The martensitic
transformation temperature in ~3 titanium alloys generally decreases with an
increasing
amount of ~i stabilizer in the alloy, while increasing the amount of a
stabilizer
generally raises the martensitic transformation temperature. Therefore,
depending on
the extent of stabilization, ~i titanium alloys may exhibit a martensitic
transformation
when cooled rapidly from temperatures greater than those at which the ,Q phase
is the
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single phase at equilibrium. The ~i titanium alloy generally comprises an
amount of
about 8 to about 10 wt% of molybdenum, about 2.8 to about 6 wt% aluminum, up
to
about 2 wt% chromium, up to about 2 wt% vanadium, up to about 4 wt% niobium,
with the balance being titanium. All weight percents are based on the total
weight of
the alloy. Within the aforementioned range for molybdenum, it is generally
desirable
to have an amount of greater than or equal to about 8.5, preferably greater
than or
equal to about 9.0, and more preferably greater than or equal to about 9.2 wt%
molybdenum. Also desirable within this range is an amount of less than or
equal to
about 9.75, and more preferably less than or equal to about 9.5 wt%
molybdenum,
based on the total weight of the alloy.
Within the aforementioned range for aluminum, it is generally desirable to
have an amount of greater than or equal to about 2.85, preferably greater than
or equal
to about 2.9, and more preferably greater than or equal to about 2.93 wt%
aluminum.
Also desirable within this range is an amount of less than or equal to about
5.0,
preferably less than or equal to about 4.5, and more preferably less than or
equal to
about 4.0 wt% aluminum, based on the total weight of the alloy.
Within the aforementioned range for niobium, it is generally desirable to have
an amount of greater than or equal to about 2, preferably greater than or
equal to
about 3, and more preferably greater than or equal to about 3.5 wt% niobium,
based
on the total weight of the alloy.
In one exemplary embodiment, it is generally desirable for the ~3 titanium
alloy
to comprise 8.9 wt% molybdenum, 3.03 wt% aluminum, 1.95 wt% vanadium, 3.86
wt% niobium, with the balance being titanium.
In another exemplary embodiment, it is generally desirable for the ~3 titanium
alloy to comprise 9.34 wt% molybdenum, 3.01 wt% almninum, 1.95 wt% vanadium,
3.79 wt% niobium, with the balance being titanium.
In one embodiment, the ~i titanium alloy may be solution treated and/or
thermally aged. In solution treating the ~3 titanium alloy, the alloy is
subjected to a
temperature greater than or equal to about 850°C, the (3 transus
temperature for the
alloy. The solution treatment of the alloy is normally carried out in either
vacuum or
inert gas environment at a temperature of about 850 to about 1000°C,
preferably about
850 to about 900°C, for about 1 minute or longer in duration depending
on the mass
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of the part. The heating is followed by a rapid cooling at a rate greater than
or equal
to about 5°C/second, preferably greater than or equal to about
25°C/second, and more
preferably greater than or equal to about 50°C/second, by using an
inert gas quench or
air cooling to retain a fully recrystallized single phase [3 grain structure.
In some
instances, it is preferred that the quenched alloy is subsequently subjected
to an
ageing treatment at about 350 to about 550°C for about 10 seconds to
about 30
minutes to adjust the amount of a fine precipitate of the ~ phase.
In another embodiment, the (3 titanium alloy may be solution treated at a
temperature below the (3 transus temperature of about 750 to about
850°C, preferably
about 800 to about 850°C, for about 1 to about 30 minutes to induce a
small amount
of a precipitates in the recrystallized [3 matrix. The amount of the a,
precipitates is
preferably less than or equal to about 15 volume percent and more preferably
less than
or equal to about 10 volume percent, based on the total volume of the
composition.
This improves the tensile strength to an amount of greater than or equal to
about
140,000 pounds per square inch (9,846 kilogram/square centimeter).
The [3 titanium alloy in the solution treated condition may exhibit
pseudoelasticity. The solution treated ~i titanium alloy generally exhibits a
pseudoelastic recovery of greater than or equal to about 75% of the intial
strain when
elastically deformed to a 2% initial strain, and greater than or equal to
about 50% of
the initial strain when elastically deformed to a 4% initial strain. The
initial strain is
the ratio of the change in length to the original length of the alloy
composition.
The (3 titanium alloy in the solution treated condition may exhibit linear
elasticity. The solution treated (3 titanium alloy generally exhibits a linear
elastic
recovery of greater than or equal to about 75% of the initial strain when
elastically
deformed to a 2% initial strain, and greater than or equal to about 50% of the
intial
strain when elastically deformed to a 4% initial strain. The initial strain is
the ratio of
the change in length to the original length of the alloy composition.
In another embodiment, the (3 titanium alloy may be cold worked by processes
such as cold rolling, drawing, swaging, pressing, and the like, at ambient
temperatures. The ,Q titanium alloy may preferably be cold worked to an amount
of
about 5 to about 85% as measured by the reduction in cross-sectional area
based upon
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the original cross sectional area. Within this range it is desirable to have a
cross
sectional area reduction of greater than or equal to about 10, preferably
greater than or
equal to about 15% of the initial cross sectional area. Also desirable within
this range
is a reduction in cross sectional axea of less than or equal to about 50, more
preferably
less than or equal to about 30% based on the initial cross-sectional area. The
~3
titanium alloy in the cold worked state (also referred to as the work hardened
state)
exhibits linear superelasticity where greater than or equal to about 75% of
the initial
strain is elastically recoverable after deforming to a 2% initial strain, and
greater than
or equal to about 50% of the initial strain is elastically recoverable after
deforming to
a 4% initial strain. In one exemplary embodiment related to cold working, the
elastic
modulus of the ~3 titanium alloy is reduced through cold working by an amount
of
greater than or equal to about 10, preferably greater than or equal to about
20 and
more preferably greater than or equal to about 25% based upon the elastic
modulus,
after the alloy is heat treated.
It is generally desirable to use shape memory alloys having pseudo-elastic
properties, and which are formable into complex shapes and geometries without
the
creation of cracks or fractures. In one embodiment, the (3 titanium alloy
having linear
elastic, linearly superelastic, pseudoelastic or superelastic properties may
be used in
the manufacturing of various articles of commerce. Suitable examples of such
articles
are eyewear frames, face inserts or heads for golf clubs, medical devices such
as
orthopedic prostheses, spinal correction devices, fixation devices for
fracture
management, vascular and non-vascular stems, minimally invasive surgical
instruments, filters, baskets, forceps, graspers, orthodontic appliances such
as dental
implants, arch wires, drills and files, and a catheter introducer (guide
wire).
In one embodiment, the (3 titanium alloy having pseudoelastic or superelastic
properties may be used in the manufacturing of various articles of commerce.
Suitable examples of such articles are eyewear frames, face inserts or heads
for golf
clubs, medical devices such as orthopedic prostheses, spinal correction
devices,
fixation devices for fracture management, vascular and non-vascular stems,
minimally
invasive surgical instnunents, filters, baskets, forceps, graspers,
orthodontic
appliances such as dental implants, arch wires, drills and files, and a
catheter
introducer (guide wire). Advantages provided by the ~3 titanium alloys are
that they
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are free of nickel, having low modulus, flexible and can be welded, brazed or
soldered
if desired.
Figure 1 illustrates a typical eyewear frame 100. Frame 100 includes a pair of
rims 110, a bridge 120, a pair of temples 130, and a pair of hinges 140. Rims
110 are
5 j oined by bridge 120, which is generally attached to rims 110 by brazing or
welding
150. Temples 130 are attached to the hinges 140 by brazing or welding 170, and
the
hinges 140 are attached to the temples 130. All metal parts of the frame 100
may be
formed using ~3 titanium alloys. The ~3 titanium alloys generally provide a
lightweight
frame with increased spring-back characteristics than conventional titanium
alloy
10 frames but with improved adjustability than a superelastic NiTi (nickel
titanium)
frame. Alternatively, any one or more of the metal parts of the frame 100 may
be
formed from ~3 titanium alloys. The use of superelastic ~3 titanium alloy is
generally
preferred in components that require flexibility and adjustability, such as
the temples
130. Other components of the frame 100 may be formed using linearly elastic
(LE) ~3
titanium alloy, other titanium alloys such as Ti-6A1-4V or commercially pure
titanium, other metallic alloys such as stainless steel, CuNi (copper-nickel)
alloy or
polymeric materials.
In an alternative embodiment, the temples 130 are formed from a superelastic
,Q titanium alloy, which may be directly connected to the lenses (not shown)
of the
completed eyewear, thereby eliminating the need for rims 110 and hinges 140.
In yet
another alternative embodiment, the superelastic (3 titanium alloy eyewear may
be
manufactured by stamping or cutting out the shape of the eyewear frame 100
from a
sheet of ~3 titanium alloy, thereby forming a single piece. The piece is then
formed
into a contour of the frame and heat treated. Groves are then machined along
the
edges of the rim 110 to fit lens.
In yet another embodiment, at least a portion of the frame comprises a
linearly
superelastic (3 titanium alloy, while another portion of the frame comprises a
linear
elastic (LE) (3 titanium alloys, other titanium alloys such as Ti-6A1-4V or
commercially pure titanium, other metallic alloys such as stainless steel,
nickel silver
alloy or a polymeric resin. When it is desirable to have a portion of the
frame
comprising a linearly superelastic ~3 titanium alloy, the desired portion is
generally
cold worked by rolling, drawing, swaging, pressing, or the like.
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Polymeric resins used in the eyewear frames may comprise thermoplastic
resins, thermosetting resins, blends of thermoplastic resins with
thermosetting resins.
In general, the polymeric resin may be derived from a suitable oligomer,
polymer,
block copolymer, graft copolymer, star block copolymer, dendrimers, ionomers
having a number average molecular weight (Mn) of about 1000 grams per mole
(g/mole) to about 1,000,000 g/mole. Suitable examples of thermoplastic resins
include polyacetal, polyacrylic, styrene acrylonitrile, acrylonitrile-
butadiene-styrene,
polycarbonates, polystyrenes, polyethylene, polypropylenes, polyethylene
terephthalate, polybutylene terephthalate, polyamides such as nylon 6, nylon
6,6,
nylon 6,10, nylon 6,12, nylon 11 or nylon 12, polyamideimides,
polybenzimidazoles,
polybenzoxazoles, polybenzothiazoles, polyoxadiazoles, polythiazoles,
polyquinoxalines, polyimidazopyrrolones, polyarylates, polyurethanes,
thermoplastic
olefins such as ethylene propylene dime monomer, ethylene propylene rubber,
polyarylsulfone, polyethersulfone, polyphenylene sulfide, polyvinyl chloride,
polysulfone, polyetherimide, polytetrafluoroethylene, fluorinated ethylene
propylene,
perfluoroalkoxy polymer, polychlorotrifluoroethylene, polyvinylidene fluoride,
polyvinyl fluoride, polyetherketone, polyether etherketone, polyether ketone
ketone,
or the like, or combinations comprising at least one of the foregoing
thermoplastic
resins.
Suitable examples of blends of thermoplastic resins include acrylonitrile-
butadiene-styrene/nylon, polycarbonate/acrylonitrile-butadiene-styrene,
acrylonitrile
butadiene styrene/polyvinyl chloride, polyphenylene ether/polystyrene,
polyphenylene ether/nylon, polysulfone/acrylonitrile-butadiene-styrene,
polycarbonate/thermoplastic urethane, polycarbonate/polyethylene
terephthalate,
polycarbonate/polybutylene terephthalate, thermoplastic elastomer alloys,
nylon/elastomers, polyester/elastomers, polyethylene
terephthalate/polybutylene
terephthalate, acetal/elastomer, styrene-maleicanhydride/acrylonitrile-
butadiene-
styrene, polyether etherketone/polyethersulfone, polyethylene/nylon,
polyethylene/polyacetal, or the like, or combinations comprising at least one
of the
foregoing thermoplastic blends.
Suitable examples of polymeric thermosetting materials include
polyurethanes, natural rubber, synthetic rubber, epoxy, phenolic, polyesters,
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polyamides, silicones, or the like, or combinations comprising at least one of
the
foregoing.
For the frame 100, it is generally desirable to have the temples 130
manufactured from superelastic or linearly superelastic ~3 titanium alloy.
While many
variations of temple 130 are available in the eyewear manufacturing industry,
the
temple 130 is shown in Figure 2 one possible construction. The temple 130
includes a
tapered end 210, a pressed end 220, a hinge 140, a rim connector 240, and a
hinge cut
250.
In temple 130, the tapered end 210 and the pressed end 220 are formed from a
continuous piece of (3 titanium alloy wire. The hinge 140 and the rim
connector 240
are each joined to the pressed end 220, typically by brazing. Hinge cut 250
generally
permits a free rotation of the hinge 140. The hinge 140 and the rim connector
240
may also be fabricated from ,Q titanium alloys or from other suitable material
such as
titanium or nickel silver alloys, if desired.
The superelastic (3 titanium alloy generally provides an adequate spring-back
for eyewear applications. It is generally desired to use superelastic ,Q
titanium alloy
having a minimum recovery of about 50%, based on the outer fiber bend strain,
when
the alloy is deformed to an outer fiber strain of about 4%. Within this range,
it is
more preferably greater than or equal to about 75%, when the alloy is deformed
to
about 4% outer fiber strain.
It is also generally desirable for the superelastic (3 titanium alloy to have
a
minimum recoverable strain of about 2%, based on the original length when the
alloy
is deformed to about 4% in tensile strain. Within this range, it is generally
desired to
have a minimum recovery of greater than or equal to about 3% when the alloy is
deformed to about 4% tensile strain in the tensile test.
The eyewear frame may be manufactured by a variety of different methods
used to shape or form metals and alloys. In one embodiment, the desired shape
of the
eyewear frame 100 is stamped from a sheet of ~i titanium alloy, thereby
forming a
single piece. In another embodiment, the basic shape may be formed of wires
using
mechanical shaping methods.
For example, in the manufacture of temple 130, a ~i titanium alloy wire is
modified to provide the basic shape of temple 130. The superelastic (3
titanium alloy
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wire is first swaged, creating multiple sections having consecutively
decreasing
diameters, and then a number of the largest sections are pressed to flatten
them. The
eyewear frame 100 can also be fabricated from wires via cold forming and shape-
setting heat treatment processes. The eyewear frame 100 can also be fabricated
from
superelastic /3 titanium alloys sheets or wires by laser cutting, chemical
etching or
other cutting means followed by shape-setting heat treatment or other forming
and
heat treating processes.
The eyewear frame 100 may optionally be annealed to regain workability and
to overcome brittleness induced by cold working. Cold working of ,Q titanium
alloys
(e.g., swaging, pressing) generally alter its mechanical properties, causing
it to
become stronger and more brittle. Annealing at temperatures of greater than or
equal
to about 850°C for about 1 to about 30 minutes may be used to soften
the material,
rendering it more ductile and formable.
Following the manufacturing of the eyewear frame 100 and the optional
annealing, it may be desired to attach additional components to the frame. For
example, in a general eyewear manufacturing process, the hinge 140 and the rim
connector 240 are brazed or soldered to the temple 130, and the temple 130 may
be
cut to permit the hinge 140 to rotate.
Where desired, the eyewear frame 100 may be subjected to a polishing
operation in order to give the frame a smooth appearance and to remove any
rough
edges. For example, the eyewear frame 100 can be polished by high energy
barrel
tumbling and then plated by processes such as chemical vapor deposition,
electroplating, and the like, to prepare the frame for additional finishing
steps. This
plating is preferably accomplished using gold or nickel.
After the plating operation, the eyewear frame 100 may be optionally heat-
treated at a temperature of about 350 to about 450°C for a period of
about 10 minutes
in order to infuse the gold or nickel layer deposited on the frame into the (3
titanium
alloy. The eyewear frame is then be subjected to additional finishing
processes to
provide a desirable aesthetic appearance. For example, the frame may be plated
with
a metal, such as gold, chrome, or platinum. A protective coating, such as a
light spray
of epoxy, may be added to seal and protect the frame. If desired, the frame is
subjected to adjustments by the user to further shape the eyewear frame 100.
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In another embodiment, the (3 titanium alloy may be used to manufacture at
least a portion of a golf club. The ~3 titanium alloy may be also be used to
manufacture a golf club head. In an exemplary embodiment, the (3 titanium
alloy may
be used to manufacture face inserts, which are mounted into the golf club
head.
Figure 3A shows an insert 2 that substantially follows the contours of the
golf
club head. The bevel is designed such that when the insert is mounted into the
golf
club head mating cutout or pocket, the insert will be retained securely in the
club head
even during the violent swings encountered while playing golf. The bevel is
generally
at an angle of about 30 to about 60 degrees with respect to a perpendicular to
the back
8 of the insert and extends around the bottom and the two sides adjacent to
the bottom
edge of the insert 2 as shown in Figure 3A. The insert 2 generally has a
thickness of
about 0.010 (0.0254 centimeter) to about 0.93 inches (2.36 centimeters). In an
exemplary embodiment, the insert may have a variable thickness across its
cross
section if desired.
Figure 3B shows another embodiment of the insert. Here a tongue 9 is formed
on opposing sides of the insert to secure the insert in a corresponding groove
in the
golf club head. Figure 4A shows a pocket 12 formed in the face of a club head
14
into which an insert 2 having beveled edges may be disposed. The pocket is
formed
from the bottom of the club head and extends upward. However, the pocket does
not
extend to the top edge of the club head, there remains a narrow channel 16
between
the top of the pocket and the top of the golf club head. The insert is
preferably wedge
shaped and the angle is preferably about 2 degrees.
Referring to Figure 4B the pocket in the golf club head has a grooved edge 18
that extends around the three sides (left, right and top) of the pocket. The
groove 18
is arranged to be in mechanical communication with the tongue 9 of an insert.
The
insert may be secured within the club head by cement, polymeric resins such as
epoxy, acrylates, methacrylates, silicones, or the like. Figure 5 shows
another golf
club head 20 with an insert 22 that extends from the top to the bottom of the
golf club
head 20. In this instance, the bottom and top edges of the insert are flush
with the
bottom and top edge of the golf club head 20. Grooved edges 24 may be used to
retain the insert 2 in the golf club head 20.
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Figure 6A provides a front view of a golf club face 40 with the insert 42. The
insert 42 covers the striking area of the golf club head and the golf club
head 44 forms
a margin around the insert. Figure 6B shows one configuration of the cross
sectional
view of the golf club head 44 as a casting. Forged and machined golf club
heads 44
may also be used. The golf club head 44 has a cavity 46 into which the insert
42 is
placed. Ears 48 extend out from the golf club head 44 as shown and the inserts
have
grooves 50 designed to receive the ears. The ears are swaged over into the
grooves as
shown in Figure 6C. The rough edges may then be finished to form a golf club
head
44 having a smooth club face as shown in Figure 6D.
10 In one embodiment related to the assembly of the insert into the golf club
head
in Figures 3A, 3B, 4A, 4B, 5, 6A - D, the insert may be held in place in a
slot in the
golf club head through friction or other mechanical means. When friction is
employed, the insert is held in position in the golf club head via a tight
toleranced fit.
In an exemplary embodiment, the insert is assembled in the golf club head via
brazing
15 or welding. This facilitates ease of manufacture and assembly of the golf
club head
when compared with other methods of manufacturing.
In another embodiment, the ~3 titanium alloy may be used may be used in a
catheter having an implantable stmt as shown in Figure 26. In the Figure 26,
the
distal end of a catheter 115 having a stmt 165 carried within it for
implantation into
the body of a patient. The proximal end of the catheter 115 is connected to a
suitable
delivery mechanisms and the catheter 115 is of sufficient length to reach the
point of
implantation of the stmt 165 from the introduction point into the body. As
used
herein, the term "proximal" refers to a location on the catheter closest to
the clinician
using the device and thus furthest from the patient on which the device is
used.
Conversely, the term "distal" refers to a location farthest from the clinician
and closest
to the patient.
The catheter 115 includes an outer sheath 105, a middle tube 125 which may
be formed of a compressed spring, and a flexible (e.g., polyamide) inner tube
145. A
stent 165 for implantation into a patient is carried within the outer sheath
105. The
stmt 165 is generally manufactured from a shape memory alloy frame 185, which
is
formed in a criss-cross pattern, which may be laser cut. One or both ends of
the stmt
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165 may be left uncovered as illustrated at 225 and 245 to provide anchoring
within
the vessel where the stent 165 is to be implanted.
A radiopaque atraumatic tip 265 is generally secured to the end of the inner
tube 145 of the catheter. The atraumatic tip 265 has a rounded end and is
gradually
sloped to aid in the movement of the catheter through the body vessel. The
atraumatic
tip 265 is radiopaque so that its location may be monitored by appropriate
equipment
during the surgical procedure. The inner tube 145 is hollow so as to
accommodate a
guide wire, which is commonly placed in the vessel prior to insertion of the
catheter,
although a solid inner section and be used without a guide wire. Inner tube
145 has
sufficient kink resistance to engage the vascular anatomy without binding
during
placement and withdrawal of the delivery system. In addition, inner tube 145
is of
sufficient size and strength to allow saline inj ections without rupture.
A generally cup-shaped element 285 is provided within the catheter 115
adjacent the rear end of the stmt 165 and is attached to the end of the spring
125 by
appropriate means, e.g., the cup element 285 may be plastic wherein the spring
125 is
molded into its base, or the cup element 285 may be stainless steel wherein
the spring
125 is secured by welding or the like. The open end of the cup element 285
serves to
compress the end 245 of the stmt 165 in order to provide a secure interface
between
the stmt 165 and the spring 125. Alternatively, instead of a cup shape, the
element
285 could be formed of a simple disk having either a flat or slightly concave
surface
for contacting the end 245 of the stmt 165.
In yet another embodiment, the ,Q titanium alloy may be utilized as an
intravenous (IV) catheter to introduce certain fluids such as saline solution
directly
into the bloodstream of a patient. Typically, a needle or other stylet made
from the (3
titanium alloy is first introduced through the cannula portion of the catheter
and into
the skin of the patient at the desired location such as the back of the
patient's hand or a
vessel on the inside of the arm. Once insertion is complete, the needle is
removed
from the cannula portion of the catheter. After removing the needle, a fluid
handling
device such as a syringe is attached to the luer fitting located at the
proximal end of
the catheter hub. Fluid then flows directly from the fluid handling device
through the
catheter into the bloodstream of the patient. When the needle is removed from
the
cannula, the health care worker must place the exposed needle tip at a nearby
location
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while simultaneously addressing the task required to accomplish the needle
removal.
It is at this juncture that the exposed needle tip creates a danger of an
accidental
needle stick occurring which leaves the health care worker vulnerable to the
transmission of various, dangerous blood-borne pathogens such as human immune
virus (HIV) and hepatitis.
As used herein, the term "proximal" refers to a location on the catheter and
needle assembly with needle tip protector closest to the clinician using the
device and
thus furthest from the patient on which the device is used. Conversely, the
term
"distal" refers to a location farthest from the clinician and closest to the
patient.
As illustrated in Figures 27 and 28, the IV catheter assembly 201 comprises
catheter assembly 221 and needle assembly 241. Needle assembly 241 further
includes protector 261. Catheter assembly 221 includes catheter 281, which is
a
tubular structure having a proximal end 311 and distal end 291. Proximal end
311 of
catheter 281 is fixedly attached to catheter hub 301. Catheters are well known
in the
medical art and one of many suitable materials, most of which are flexible
thermoplastics, may be selected for use in catheter 281. Such materials may
include,
for example, polyurethane or fluorinated ethylene propylene. Catheter hub 301
is a
generally tubular structure having an internal cavity in fluid communication
with the
internal lumen of catheter 281. Catheter hub 301 may be made from a suitable,
rigid
medical grade thermoplastic such as, for example, polypropylene or
polycarbonate.
For illustration purposes catheter hub 301 is shown translucent, though in
actual use it
may be translucent or opaque. At the proximal end of catheter hub 301 is
integrally
attached Luer fitting 321. Luer fitting 321 provides for secure, leak proof
attachment
of tubing, syringes, or any of many other medical devices used to infuse or
withdraw
fluids through catheter assembly 221. As shown in Figures 27 and 28, retainer
601,
which is located approximately mid way between the proximal end and distal end
of
sidewall 361 and fixedly attached thereto, includes aperture 621 which is an
opening
therethrough. Retainer 601 is generally a doughnut shaped washer made of a
material
such as, for example, silicone or polytetrafluoroethylene. The retainer 601
generally
secures the protector 261 in catheter hub 301.
Refernng again to Figures 27 and 28, needle assembly 241 comprises needle
381, which is a tubular structure with proximal end 391 and distal end 411,
needle
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hub 401, and protector 261. Protector 261 is assembled slidably on needle 381.
Needle 381, which is preferably made of stainless steel has a lumen
therethrough
created by its inner diameter. Proximal end 391 of needle 381 is fixedly
attached to
needle hub 401. Bevel 421, which is located at distal end 411 of needle 381
creates a
sharp piercing tip. Needle groove 441, which includes proximal wall 431 and
distal
wall 451, is located at distal end 411 of needle 381 proximal to bevel 421 and
is
smaller in diameter than the nominal outer diameter of needle 381. Needle
groove
441 may be created by machine grinding around the outside diameter of needle
381
resulting in an annular channel between its nominal outer diameter and inner
diameter. The resulting groove 441 is smaller in dimension than the nominal
outer
diameter of needle 381 but greater in dimension that the lumen in needle 381
and
generally prevents the complete removal of protector 261 from needle 381. In
the
preferred embodiment, the dimension across groove 441 is about 0.002 to about
0.003
inches (about 0.0508 to about 0.0762 millimeter) smaller than the dimension of
the
nominal outer diameter of needle 381, dependent upon needle "gauge" size.
Needle hub 401 is generally a tubular structure having an internal cavity in
fluid communication with the lumen in needle 381. It is preferably made of a
translucent or transparent generally rigid thermoplastic material such as, for
example,
polycarbonate. At the most proximal end of the uzternal cavity in needle hub
401 is
fixedly attached a porous plug 461. A flashback chamber 481 is created in the
cavity
distal to porous plug 461. Porous plug 461 contains a plurality of microscopic
openings, which are large enough to permit the passage of air and other gasses
but
small enough to prevent the passage of blood. Flashback chamber 481 fills with
blood upon successful entry of the needle tip into the targeted vein,
providing the
clinician visual conformation of the correct placement of the needle.
In one embodiment, the (3 titanium alloy may be used as an orthopedic device
such as a fixation device for bones in the hip, knee, spine, or the like. A
suitable
example of one configuration of a bone fixation device shown in Figures 29, 30
and
31 is a threaded bone screw. Figures 29, 30 and 31 show a cannulated,
internally and
externally threaded bone screw 202 and a cannulated driver device 222
constructed
from a ~3 titanium alloy. The driver device 222 includes a shaft member 262
defining
a throughgoing bore 272, a handle 282 and includes a rod 302 and a cap member
322.
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The rod 302 and cap member 322 are used to releaseably secure the bone screw
202
to the driver device 222 as will later be described. The shaft member 262 is
an
elongated, generally cylindrical structure, which has a cylindrical
throughgoing bore
or cannula 272 best seen in the cross-sectional view of Figure 31 which
extends
longitudinally from a proximal end 342 of the shaft member 262 to a distal end
362.
The shaft member 262 is an integral tubular structure preferably constructed
of
surgical steel, although any suitable material such as (3 titanium alloy can
be used, and
includes a shaped engagement structure 382 integrally formed at the distal end
362
and one or more annular grooves 372 spaced along its length. The engagement
structure 382, which preferably has a hexagonal configuration facilitates the
mating
and rotational engagement of the bone screw 202 with the driver as will be
described
and the grooves 372 may be used as attachment sites for conventional clamp
members
during a bone fixation procedure. It will be appreciated that the engagement
structure
382 may take any angular configuration such as square, octagonal or the like
and cam
alternatively engage the outer periphery of the screw head.
The handle 282 has a throughgoing bore 392 to receive the proximal end 342
of the shaft member 262 and is preferably constructed of wood or plastic. The
handle
282 is secured to the shaft member 262 by securing the handle sections
together with
conventional rivets 392 or by other suitable means. The rivets do not extend
into or
through the bore of the shaft member 262. Alternatively, the handle member 282
may
be removably mounted to the shaft member 262.
The rod 302 is an integral, solid, generally cylindrical structure preferably
constructed of surgical or high grade steel and is provided with a threaded
section 422
at its distal end and a machined recess or well 44near its proximal end which
receives
set screw 472. The cap member 322 is a generally cylindrical structure that
has a
blind bore 432 to receive the proximal end of the rod 302 and a cylindrical,
internally
threaded passage 452 which extends from a side surface of the cap member 322
into
the blind bore 432 to permit the passage of a conventional set screw 472
having an
Allen head. A conical end portion of the Allen set screw is received within
the well
44 in the rod 30 to lock the cap member 322 to the rod 302. The outer surface
of cap
322 is knurled at 332 to allow the cap 322 and secured rod 302 to be rotated
within
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bore 272 of the shaft 262 so that threaded end 422 can be screwed into the
imler
thread 582 of the cannulated bone screw 202.
The outer diameter of the cylindrical rod 302 is less than the inner diameter
of
the cylindrical bore 272 in the shaft member 262 so that the rod 302 can be
easily
5 received therein and pass therethrough. Conversely the threaded end section
422 has
threads with an outer diameter greater than the outer diameter of bore 272 so
that rod
302 cannot be pulled through the bore 272 of the shaft 262. When the cap
member
322 is releaseably locked to the proximal end of the rod 302, cap member 322
prevents a portion of the proximal end of the rod 302 from entering the
cannula 272 of
10 the shaft member 262. As best seen in Figure 31, the rod 302 is longer than
the shaft
member 262 so that when the cap member 322 is mounted on the rod 302 and the
rod
302 is disposed within the cammla or bore 272 of the shaft member 262, the
threaded
section 422 of the rod 302 extends a predetermined length beyond the distal
end 362
of the shaft member 262 to threadedly engage the internal threading 582 of the
bone
15 screw 202. The orthodontic device may be advantageously used in other body
tissue
in all living beings. Other examples of orthodontic devices are those, which
may be
used in hip, kneel, shoulder implants, intermedullary rods and nails, fracture
fixation
devices, spinal fusion and correction instruments.
In another embodiment, the (3 titanium alloy may be used in orthodontic
20 devices such as orthodontic arch wires. One possible configuration of an
orthodontic
arch wire 103 is shown in Figures 32 and 33, and includes an anterior segment
113,
and a pair of posterior segments 123 and 133 secured to and extending from the
respective ends of the anterior segment. The anterior segment may be made of a
material having a stiffiiess or flexural rigidity, which is less than that of
the material
forming the posterior segments. The segments can be secured together by using
any
of several different attachment techniques. In the form shown in Figures 32
and 33, a
crimpable metal tube 153 is provided at each segment junction for mechanical
attachment of the segments. As shown in Figure 32, the ~i titanium alloy arch
wire
103 is of conventional generally U-shaped configuration for conformation with
the
patient's dental arch. The arch is equally useful with lingual brackets and
related
appliances, which are mounted on the rear surfaces of the teeth. Figure 34
shows a
so-called "mushroom" arch wire 203, which is again of generally U-shaped
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configuration, but is contoured to conform to the curvature of the lingual or
inner
surfaces of the teeth. Arch wire 203 includes an anterior segment 213 of
relatively
low stiffness, a pair of posterior segments 223 and 233 of relatively higher
stiffness,
and crimped tubes 243 joining the segments and positioned to be just distal of
the
cuspids when installed. Other dental applications include arch wires, dental
implants,
files and drills used in orthodontic work.
The ~3 titanium alloy has a niunber of advantages. The elastic modulus of the
~3
titanium alloy is advantageously reduced through cold working by an amount of
greater than or equal to about 10, preferably greater than or equal to about
20 and
more preferably greater than or equal to about 25% based upon the elastic
modulus
after the alloy is heat treated. The ~3 titanium alloy may preferably be cold
worked to
an amount of about 5 to about 85% as measured by the reduction in cross-
sectional
area based upon the original cross sectional area. Within this range it is
desirable to
have a cross sectional area reduction of greater than or equal to about 10,
preferably
greater than or equal to about 15% of the initial cross sectional area. Also
desirable
within this range is a reduction in cross sectional area of less than or equal
to about
50, more preferably less than or equal to about 30% based on the initial cross-
sectional area. When cold worked, the ~3 titanium alloy may have a
pseudoelastic
strain recovery of greater than or equal to about 75% of the applied strain,
when the
applied strain is up to about 2% of the original length and of greater than or
equal to
about 50% of the applied strain, when the applied strain is up to about 4% of
the
original length. (i.e., the change in length is 4% of the original length).
The following examples, which are meant to be exemplary, not limiting,
illustrate the methods of manufacturing for some of the various embodiments of
the
articles prepared from the (3 titanium alloys described herein.
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EXAMPLES
Example 1
All of the sample alloys discussed below were prepared by a double vacuum
arc melting technique. The ingots were hot rolled and flattened to sheets
having a
thickness of 1.5 millimeter (mm). The sheets were then heat treated at
870°C for 30
minutes in air and air cooled to ambient temperature. Oxides on the sheets
were
removed by double-disc grinding and lapping to a thickness of 1.3 mm. Heat
aging
experiments were conducted at 350°C using a nitride/nitrate salt bath.
Permanent deformation and pseudo-elastic recovery strains were determined
using bend tests. Specimens having dimensions 0.51 mm x 1.27 mm x 51 mm were
cut from the sheets. The specimens were bent against a rod of approximately
12.2
mm in diameter to form a "U" shape to yield an outer fiber or outer surface
strain
close to 4%. The angles between the straight portions were measured afterwards
and
the strain recovery calculated by using the formula:
e(xec) =a (180-a)/180;
where "a" is the unrecovered angle and "e' is the outer-fiber bending strain.
Tensile strain recovery was measured by tensile elongation to a strain of 4%
followed by unloading to zero stress. Tensile specimens with a cross sectional
dimension of 0.90 rnm x 2.0 mm were used and the strain was monitored using an
extensometer. An environmental chamber with electrical heating and COZ cooling
capabilities provided a testing capability from -30°C to 180°C.
Nine ~i titanium alloys having the compositions listed in Table 1 were
examined. The percentage of the elastic recovery strain with respect to the
total bend
strain was measured for comparison.
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Table 1
Sample Titanimn MolybdenumNiobium Vanadium Aluminum
1 Balance 7.63 3.98 2.05 3.10
2 Balance 8.03 3.89 2.03 3.09
Balance 8.40 3.83 1.94 3.03
4 Balance 8.97 3.86 1.95 3.03
-
Balance 9.34 3.79 1.95 3.01
6 Balance 10.35 3.83 1.99 3.02
7 Balance 10.83 3.88 2.01 3.02
8 Balance 11.48 4.00 2.04 3.15
Balance 11.68 3.89 1.98 3.07
In the Table 1 above Sample 1 and Samples 6 - 9 are comparative examples.
The results of elastic recovery after bending to approximately 4% outer fiber
strain is
graphically demonstrated in Figure 7. The figure shows a maximum elastic
strain
recovery at about 9 wt% molybdenum, where the alloy after solution heat
treatment
and subsequent air cooling, exhibits an elastic recovery strain of
approximately 80%
of the applied 4% deformation strain. Increasing or decreasing the molybdenum
content from 9 wt% generally results in decreasing elastic recovery. It may
also be
seen that an aging treatment at 350°C for a short duration of 10
seconds results in an
improved elastic recovery, for titanium alloys having a molybdenum content
between
8.4 and 11 wt%. The optimal elastic strain recovery after heat aging at
350°C for 10
seconds for the alloy having about 9 wt% molybdenum is approximately 90% of
the
applied 4% bend strain. Alloys with a molybdenum content less than 8.4 wt%
exhibit
a different aging characteristic. Aging at 350°C may degrade elastic
strain recovery
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as for alloy 2 having about 8.03 wt% molybdenum, or has no significant effect
as for
alloy 1 having about 7.63 wt% molybdenum.
The percent of the elastic recovery to the total deformation during thermal
aging at 350°C for Samples 4, 5 and 6 respectively, are plotted in the
Figures 8, 9 and
10 respectively. From the Figures 8, 9 and 10 it may be seen that the elastic
recoveries of all three alloys reach a maximum after aging for about 10 to
about 60
seconds. Aging beyond 15 minutes (900 seconds) degrades the elastic recovery.
The percents of the elastic recovery to the total deformation during thermal
aging at about 250 to about 550°C for 10 seconds for Samples 4 and 5
respectively are
plotted in the Figures 11 and 12, respectively. An optimal for Sample 4
appears at
350°C, which improves the elastic recovery to a percentage close to 90%
while aging
at temperatures equal to or higher than 400°C degrades elastic recovery
to about 40%.
For Sample 5, aging in this temperature range generally improves the elastic
recovery.
The maximum improvement occurs at about 450°C where the elastic
recovery is
improved to 90%.
The alloys shown in Table I also exhibit linear superelasticity after cold
worlcing with a reduction of greater than or equal to about 30% in the cross-
sectional
area. For example, a wire fabricated from an ingot having a composition of
11.06
wt% molybdenum, 3.80 wt% niobium, 1.97 wt% vanadium, 3.07 wt% aluminum with
the remainder being titanium exhibited an elastic recovery strain of 3.5%
after
bending to a total deformation of 4% outer fiber strain, when the reduction in
the
cross sectional area after cold working was 84%.
Example 2
In this example, the ~i titanium alloys were manufactured by double vacuum
arc melting. Chemistries of the alloys were analyzed using inductively coupled
plasma optical emission spectrometry (ICP-OE). The results axe tabulated in
Table 2.
The ingot was hot-forged, hot-rolled and finally cold-drawn to wire of various
diameters in the range of about 0.4 to about 5 mm. Inter-pass annealing
between cold
reductions was carried out at 870°C in a vacuum furnace for wires
having a diameter
of larger than 2.5 mm or by strand annealing under inert atmosphere for the
smaller
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diameters. Tensile properties were determined using an Instron model 5565
material
testing machine equipped with an extensometer of 12.5 mm gage length.
Microstructures were studies by optical metallography using a Nikon Epiphot
inverted
metallurgical microscope.
5 Table 2
Sample TitaniumMolybdenum NiobiumVanadium Aluminum MoEa
10 Balance 11.06 3.80 1.97 3.07 10.37
11 Balance 9.59 3.98 1.99 3.13 8.91
The strand-annealed wires generally have a higher ultimate tensile strength
(UTS)
around 1055 mega Pascals (MPa) than vacuum annealed wires and sheets, the
typical
UTS of which is about 830 MPa. Figure 13 plots the UTS of wires drawn from an
10 annealed 1.0 mm diameter Sample 11 wire stock as a function of reduction in
cross-
section area. After a 49% reduction, the UTS was elevated from 1055 MPa to
only
1172 MPa indicating a fairly weak strain hardening effect. Young's Modulus was
determined by tensile testing the wire to 1 % strain and measuring the linear
slope of
the stress-strain curve. As shown in Figure 14, cold-drawn wires generally
have a
15 lower modulus than does annealed wire. The modulus, of approximately 65.9
gigapascals (GPa) for the annealed wire, decreases with increasing
accumulative
amount of reduction and stabilizes at approximately 50 GPa after cold drawing
with a
cumulative reduction greater than 20%.
Similar to alloys in Table 1, Samples 10 and 11 exhibit linear superelasticity
20 after cold working. Loading and unloading stress-strain curves tested to 2%
and 4%
tensile strains of a cold drawn, 0.91 mm diameter wire of Sample 11 with a
19.4%
reduction axe plotted in Figures 15 and 16, respectively. As may be seen in
Figure 13,
after unloading, following a 2% tensile elongation, the wire recovers the
majority of
the deformation leaving only a small plastic deformation of 0.1 % strain. When
25 deformed to a 4% tensile elongation, the residual strain after unloading
increases to
~1.4%. The wire recovers a strain of 2.6%. The residual strain decreases with
increasing drawing (cross-sectional area) reduction. However, when the
reduction
exceeds 20%, specimens failed before reaching a 4% tensile elongation. As this
data
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suggests, cold drawn ~i titanium alloy wires exlubit linear superelasticity
and are
capable of recovering large deformations greater than the typical elastic
limit for
conventional metallic alloys. The mechanical property of cold-drawn wire
appears to
be insensitive to chemical composition as the cold-drawn Sample 10 exhibits
similar
mechanical properties. All the loading/unloading tensile test results for
Sample 10 are
tabulated in Tables 3.
Table 3.
Cold Work Amount 21 37 50 61 69
(%)
Tested to 2% tensile
strain
Elastic Strain (%) 1.9 1.8 1.8 1.9 2.0
Plastic Strain (%) 0.1 0.2 0.2 0.1 0.0
Tested to 3% tensile
strain
Elastic Strain (%) 2.5 2.6 2.6 2.7 2.7
Plastic Strain (%) 0.5 0.4 0.4 0.3 0.3
Tested to 4% tensile
strain
Elastic Strain (%) --- 2.8 2.9 3.1 3.2
Plastic Strain (%) --- 1.2 1.1 0.9 0.8
A micrograph in Figure 17 reveals the cold-worked microstructure of the Sample
10
wire after a 14% cold working reduction in cross sectional area. The
recrystallized
microstructures of the wire after heat-treatments at 816°C and
871°C for 30 minutes
are shown in Figures 18 and 19, respectively. It is apparent that the material
was not
fully betatized after the heat-treatment at 816°C as a phase was
present in the
microstructure. As may be seen in Figure 17, a fully recrystallized (3 grain
structure
was obtained after the heat-treatment at 871°C for 30 minutes.
Sample 10 wires hot-rolled to 8.6 mm in diameter were further drawn down to
6.0 mm diameter. After being fully betatized at 871°C for 30 minutes
the 6.0 mm
diameter wires were again aged at temperatures of about 500 to about
850°C for 30
minutes. As can be seen in Figure 20, the (3 structure was preserved after
aging at
816°C. When the aging temperature was lowered to 788°C,
intragranular a-phase
precipitates began to appear in the microstructure as may be seen in Figure
21. The
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amount of intragranular a,-phase precipitate increased with decreasing aging
temperature. oc-phase precipitates eventually appeared along the grain
boundary when
aged at 649°C and below.
The ultimate tensile strength (LTTS) and tensile ductility (% reduction in
cross-
section area) of betatized Sample 10 from Table 2 after aging at a temperature
of
about 500 to about 900°C for 30 minutes are plotted in Figures 22 and
23,
respectively. Fully betatized specimens such as solution-treated specimens and
those
aged at 816°C and above, exhibited a low UTS of about 800 MPa and a
good tensile
ductility of about 25 to about 30% in reduction in cross-section area (RA). As
the
aging temperature decreased, there was a drastic increase in UTS with a
significant
reduction in tensile ductility, presumably due to an increasing amount of a,-
precipitates. The peak of 1400 MPa in UTS coincides with the low in ductility
(5%
RA) and both appeared at approximately 500°C of aging temperature.
The Sample 11 composition in solution treated condition exhibits
pseudoelasticity. Their mechanical properties are highly sensitive to solution
heat
treatment and subsequent aging at a temperature of about 350 to about
550°C. It was
discovered that Sample 11 wires after strand annealing at 870°C exhibit
well-defined
pseudoelasticity. An example is presented in Figure 24, which shows a 4%
tensile
stress-strain curve of a strand-annealed, 0.4mm diameter Sample 11 wire. After
deforming to a 4% elongation, the wire specimen was able to go through a
pseudoelastic recovery recovering a 3.4% tensile strain and leaving a residual
strain of
only 0.6% after unloading.
A transverse cross-sectional view of the wire microstructure is shown in a
micrograph of Figure 25. Instead of the anticipated (3 structure, the
microstructure
consists of equiaxial a, precipitates in (3 matrix. It appears that the short
duration of
strand annealing did not allow the wire to fully recrystallize into the (3
grain structure.
Without being limited by theory, it is believed that this may explain why
strand-
annealed wire generally has a higher UTS when compared to that of a fully
betatized
material.
As may be seen from the above experiments, the ,Q titanium alloys can display
an elastic strain recovery of 88.5%, when subjected to an initial bending
strain of
CA 02489432 2004-12-13
WO 2004/003243 PCT/US2003/020081
28
4%. The strain recovery is measured as a function of the initial bending
strain and
the initial bending strain is expressed as a percentage of the ratio of the
change in
length to the original length. These alloys may be advantageously used in a
number of commercial applications such as eyewear frames, face insert and
heads
for golf clubs, orthodontic arch wires, orthopedic prostheses and fracture
fixation
devices, spinal fusion and scoliosis correction instruments, stems, guide
wires,
stems, filters, graspers, baskets, eyewear, golf club, a catheter introduces
(guide
wire) and the like.
While the invention has been described with reference to exemplary
embodiments, it will be understood by those skilled in the art that various
changes
may be made and equivalents may be substituted for elements thereof without
departing from the scope of the invention. In addition, many modifications may
be
made to adapt a particular situation or material to the teachings of the
invention
without departing from the essential scope thereof. Therefore, it is intended
that the
invention not be limited to the particular embodiment disclosed as the best
mode
contemplated for carrying out this invention.
What is claimed is
