Note: Descriptions are shown in the official language in which they were submitted.
WO 2012/039929 CA 02809035 2013-02-20 PCT/US2011/050603
HIGH STRENGTH AND DUCTILITY ALPHA/BETA TITANIUM ALLOY
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part application claiming
priority under 35 U.S.C. 120 from co-pending U.S. Patent Application Serial
No.
12/903,851, filed on October 13, 2010, and entitled "High Strength Alpha/Beta
Titanium
Alloy Fasteners and Fastener Stock, which is a continuation-in-part
application claiming
priority under 35 U.S.C. 120 from co-pending U.S. Patent Application Serial
No.
12/888,699, filed on September 23, 2010, and entitled "High Strength
Alpha/Beta
Titanium Alloy Fasteners and Fastener Stock". The entire disclosures of
Application
Serial Nos. 12/903,851 and 12/888,699 are hereby incorporated by reference
herein.
BACKGROUND OF THE TECHNOLOGY
FIELD OF THE TECHNOLOGY
[0002] The present disclosure relates to high strength and ductile alpha/beta
titanium alloys.
DESCRIPTION OF THE BACKGROUND OF THE TECHNOLOGY
[0003] Titanium alloys typically exhibit a high strength-to-weight ratio, are
corrosion resistant, and are resistant to creep at moderately high
temperatures. For
these reasons, titanium alloys are used in aerospace, aeronautic, defense,
marine, and
automotive applications including, for example, landing gear members, engine
frames,
ballistic armor, hulls, and mechanical fasteners.
[0004] Reducing the weight of an aircraft or other moving vehicle results in
fuel
savings. Thus, for example, there is a strong drive in the aerospace industry
to reduce
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aircraft weight. Titanium and titanium alloys are attractive materials for
achieving weight
reduction in aircraft applications because of their high strength-to-weight
ratio. Most
titanium alloy parts used in aerospace applications are made from Ti-6AI-4V
alloy
(ASTM Grade 5; UNS R56400; AMS 4928, AMS 4911), which is an alpha/beta
titanium
alloy.
[0005] Ti-6AI-4V alloy is one of the most common titanium-based
manufactured materials, estimated to account for over 50% of the total
titanium-based
materials market. Ti-6A1-4V alloy is used in a number of applications that
benefit from
the alloy's advantageous combination of light weight, corrosion resistance,
and high
strength at low to moderate temperatures. For example, Ti-6AI-4V alloy is used
to
produce aircraft engine components, aircraft structural components, fasteners,
high-
performance automotive components, components for medical devices, sports
equipment, components for marine applications, and components for chemical
processing equipment.
[0006] Ti-6AI-4V alloy mill products are generally used in either a mill
annealed
condition or in a solution treated and aged (STA) condition. As used herein,
the "mill-
annealed condition" refers to the condition of a titanium alloy after a "mill-
annealing"
heat treatment in which a workpiece is annealed at an elevated temperature
(e.g., 1200-
1500 F / 649-816 C) for about 1-8 hours and cooled in still air. A mill-
annealing heat
treatment is performed after a workpiece is hot worked in the a+13 phase
field. Round
bar of Ti-6AI-4V alloy having a diameter of about 2 to 4 inches (5.08 to 10.16
cm) in a
mill-annealed condition has a minimum specified ultimate tensile strength of
130 ksi
(896 MPa) and a minimum specified yield strength of 120 ksi (827 MPa), at room
temperature. Mill annealed Ti-6AI-4V plate is often produced to specification
AMS
4911, whereas mill annealed Ti-6AI-4V bar is often produced to specification
AMS 4928.
[0007] U.S. Patent No. 5,980,655 ("the '655 patent"), which is hereby
incorporated herein by reference in its entirety, discloses an alpha/beta
titanium alloy
that comprises, in weight percentages, from 2.90 to 5.00 aluminum, from 2.00
to 3.00
vanadium, from 0.40 to 2.00 iron, from 0.20 to 0.30 oxygen, incidental
impurities, and
titanium. The alpha/beta titanium alloys disclosed in the '655 patent are
referred to
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herein as "the '655 alloys". A commercially available alloy composition within
the '655
alloys nominally includes, in weight percentages based on total alloy weight,
4.00
aluminum, 2.50 vanadium, 1.50 iron, 0.25 oxygen, incidental impurities, and
titanium,
and may be referred to herein as Ti-4A1-2.5V-1.5Fe-0.250 alloy.
[0008] Because of the difficulty in cold working Ti-6AI-4V alloy, the alloy is
generally worked (e.g., forged, rolled, drawn, and the like) at elevated
temperatures,
generally above the a2solvus temperature. Ti-6AI-4V alloy cannot be
effectively cold
worked to increase strength because of, for example, a high incidence of
cracking (i.e.,
workpiece failure) during cold deformation. However, as described in U.S.
Patent
Application Publication No. 2004/0221929, which is hereby incorporated herein
by
reference in its entirety, it was surprisingly and unexpectedly discovered
that the '655
alloys have a substantial degree of cold deformability/workability.
[0009] The '655 alloys surprisingly may be cold worked to achieve high
strength while retaining a workable level of ductility. A workable level of
ductility is
defined herein a condition wherein an alloy exhibits greater than 6%
elongation. Also,
the strength of the '655 alloys is comparable to that which can be achieved
with Ti-6AI-
4V alloy. For example, as is shown in Table 6 of the '655 patent, the tensile
stress
measured for a Ti-6A1-4V alloy is 145.3 ksi (1,002 MPa), whereas tested
samples of
'655 alloys exhibited tensile strengths in a range from 138.7 ksi to 142.7 ksi
(956.3 MPa
to 983.9 MPa).
[0010] Aerospace Material Specification 6946B (AMS 6946B) specifies a more
limited chemistry range than is recited in the claims of the '655 patent. The
alloys
specified in AMS 6946B retain the formability of the broader elemental range
limits of
the '655 patent, but the mechanical strength property minimums allowed by AMS
6946B
are lower than those specified for commercially available Ti-6AI-4V alloy. For
example,
according to AMS-4911L, the minimum tensile strength for 0.125 inch (3.175 mm)
thick
Ti-6AI-4V plate is 134 ksi (923.9 MPa) and the minimum yield strength is 126
ksi
(868.7 MPa). In comparison, according to AMS 6946B, the minimum tensile
strength
for 0.125 inch (3.175 mm) thick Ti-4A1-2.5V-1.5Fe-0.250 plate is 130 ksi
(896.3 MPa)
and the minimum yield strength is 115 ksi (792.9 MPa).
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[0011] Given the continuing need for reduced fuel consumption through weight
reduction of aircraft and other vehicles, a need exists for an improved
ductile alpha/beta
titanium alloy which preferably exhibits mechanical properties comparable or
superior to
those exhibited by Ti-6A1-4V alpha/beta titanium alloy.
SUMMARY
[0012] According to an aspect of the present disclosure, an alpha/beta
titanium
alloy comprises, in percent by weight based on total alloy weight: 3.9 to 4.5
aluminum;
2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon;
up to 0.05
nitrogen; up to 0.015 hydrogen; titanium; and up to a total of 0.30 of other
elements.
[0013] According to another aspect of the present disclosure, an alpha/beta
titanium alloy consists essentially of, in percent by weight: 3.9 to 4.5
aluminum; 2.2 to
3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon; up to
0.05
nitrogen; up to 0.015 hydrogen; titanium; and up to a total of 0.30 of other
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The features and advantages of alloys and related methods described
herein may be better understood by reference to the accompanying drawings in
which:
[0015] FIG. 1 is a plot of ultimate tensile strength and yield strength as a
function of aluminum equivalent for bar and wire comprised of non-limiting
embodiments
of alloys according to the present disclosure;
[0016] FIG. 2 is a plot of ultimate tensile strength and yield strength as a
function of aluminum equivalent for 0.5 inch (1.27 cm) diameter wire comprised
of non-
limiting embodiments of alloys according to the present disclosure; and
[0017] FIG. 3 is a plot of tensile strength, yield strength, and percent
elongation
as a function of aluminum equivalent for 1 inch (2.54 cm) thick plate
comprised of non-
limiting embodiments of alloys according to the present disclosure.
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[0018] The reader will appreciate the foregoing details, as well as others,
upon
considering the following detailed description of certain non-limiting
embodiments of
alloys and related methods according to the present disclosure.
DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS
[0019] In the present description of non-limiting embodiments, other than in
the
operating examples or where otherwise indicated, all numbers expressing
quantities or
characteristics are to be understood as being modified in all instances by the
term
"about". Accordingly, unless indicated to the contrary, any numerical
parameters set
forth in the following description are approximations that may vary depending
on the
desired properties one seeks to obtain in the materials and by the methods
according to
the present disclosure. At the very least, and not as an attempt to limit the
application
of the doctrine of equivalents to the scope of the claims, each numerical
parameter
should at least be construed in light of the number of reported significant
digits and by
applying ordinary rounding techniques.
[0020] Any patent, publication, or other disclosure material that is said to
be
incorporated, in whole or in part, by reference herein is incorporated herein
only to the
extent that the incorporated material does not conflict with existing
definitions,
statements, or other disclosure material set forth in the present disclosure.
As such,
and to the extent necessary, the disclosure as set forth herein supersedes any
conflicting material incorporated herein by reference. Any material, or
portion thereof,
that is said to be incorporated by reference herein, but which conflicts with
existing
definitions, statements, or other disclosure material set forth herein is only
incorporated
to the extent that no conflict arises between that incorporated material and
the existing
disclosure material.
[0021] Non-limiting embodiments of alpha/beta titanium alloys according to the
present disclosure comprise, consist of, or consist essentially of, in percent
by weight:
3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30
oxygen; up to
0.08 carbon; up to 0.05 nitrogen; up to 0.015 hydrogen; titanium; and up to a
total of
0.30 of other elements. In certain non-limiting embodiments according to the
present
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PCT/US2011/050603
disclosure, other elements that may be present in the alpha/beta titanium
alloy (as part
of the up to 0.30 weight percent of other elements) include one or more of
boron, tin,
zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum,
manganese, yttrium, and cobalt, and in certain non-limiting embodiments the
weight
level of each such other element present is 0.10 or less, but with two
exceptions. The
exceptions are boron and yttrium, which if present at all as part of the other
elements
are present in individual concentrations less than 0.005 weight percent.
I. Alloy Composition
[0022] Non-limiting embodiments of alloys according to the present disclosure
comprise titanium, aluminum, vanadium, iron, and oxygen. If only the alloying
elements
are stated in compositions discussed below, it is to be understood that the
balance
includes titanium and incidental impurities.
A. Aluminum
[0023] Aluminum is an alpha phase strengthener in titanium alloys. The
compositional range of aluminum in non-limiting embodiments of alpha/beta
titanium
alloys according to the present disclosure is narrower than the aluminum range
disclosed in the '655 patent. Also, the minimum level of aluminum according to
certain
non-limiting embodiments of alloys according to the present disclosure is
greater than
the minimum level set out in AMS 6946B. It has been observed that these
compositional features allow the alloy to more consistently exhibit mechanical
properties
comparable to Ti-6AI-4V alloy. The minimum concentration of aluminum in
alpha/beta
titanium alloys according to the present disclosure is 3.9 percent by weight.
The
maximum concentration of aluminum in alpha/beta titanium alloys according to
the
present disclosure is 4.5 percent by weight.B. Vanadium
[0024] Vanadium is a beta phase stabilizer in titanium alloys. The minimum
concentration of vanadium in alpha/beta titanium alloys according to the
present
disclosure is greater than minimum concentration disclosed in the '655 patent
and set
out in AMS 6946B. It has been observed that this compositional feature
provides for an
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optimal, controlled balance of the volume fractions of the alpha and beta
phases. The
balance of alpha and beta phases provides alloys according to the present
disclosure
with excellent ductility and formability. Vanadium is present in alpha/beta
titanium alloys
according to the present disclosure in a minimum concentration of 2.2 percent
by
weight. The maximum concentration of vanadium in alpha/beta titanium alloys
according to the present disclosure is 3.0 percent by weight.
C. Iron
[0025] Iron is a eutectoid beta stabilizer in titanium alloys. The alpha/beta
titanium alloys according to the present disclosure include a greater minimum
concentration and a narrower range of iron as compared with the alloy
described in the
'655 patent. These features have been observed to provide an optimal,
controlled
balance of the volume fractions of the alpha and beta phases. The balance
provides
alloys according to the present disclosure with excellent ductility and
formability. Iron is
present in the alpha/beta alloys according to the present disclosure in a
minimum
concentration of 1.2 percent by weight. The maximum concentration of iron in
alpha/beta titanium alloys according to the present disclosure is 1.8 percent
by weight.
D. Oxygen
[0026] Oxygen is an alpha phase strengthener in titanium alloys. The
compositional range of oxygen in alpha/beta titanium alloys according to the
present
disclosure is narrower than the ranges disclosed in the '655 patent and in the
AMS 6946B specification. Also, the minimum concentration of oxygen in non-
limiting
embodiments of alloys according to the present disclosure is greater than in
the '655
patent and the AMS 6946B specification. It has been observed that these
compositional features allow alloys according to the present disclosure to
consistently
exhibit mechanical properties comparable to certain Ti-6A1-4V mechanical
properties.
The minimum concentration of oxygen in alpha/beta titanium alloys according to
the
present disclosure is 0.24 percent by weight. The maximum concentration of
oxygen in
alpha/beta titanium alloys according to the present disclosure is 0.30 percent
by weight.
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[0027] In addition to including titanium, aluminum, vanadium, iron, and oxygen
as discussed above, certain non-limiting embodiments of alpha/beta titanium
alloys
according to the present disclosure include other elements in a total
concentration not
exceeding 0.30 percent by weight. In certain non-limiting embodiments, these
other
elements include one or more of boron, tin, zirconium, molybdenum, chromium,
nickel,
silicon, copper, niobium, tantalum, manganese, yttrium, and cobalt, wherein,
with two
exceptions, the weight percent of each such element is 0.10 or less. The
exceptions
are boron and yttrium. If present in alloys according to the present
disclosure, the
weight percentage each of boron and yttrium is less than 0.005.
[0028] Incidental impurities may also be present in alpha/beta titanium alloys
according to the present disclosure. For example, carbon may be present up to
about
0.008 percent by weight. Nitrogen may be present up to about 0.05 percent by
weight.
Hydrogen may be present up to about 0.015 percent by weight. Other possible
incidental impurities will be apparent to those having ordinary skill in the
metallurgical
arts.
[0029] Table 1 provides a summary of the compositions of (i) certain non-
limiting embodiments of alpha/beta titanium alloys according to the present
disclosure
and (ii) certain alloys disclosed in the '655 patent and specified in AMS
6946B.
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Table 1
Alloy Compositions
Percent by Weight
Non-Limiting U.S. 5,980,655 AMS 6946B
Embodiments
according to the
Alloying Element Present Disclosure
Aluminum 3.9 to 4.5 2.5 to 5.4 3.5 to 4.5
Vanadium 2.2 to 3.0 2.0 to 3.4 2.0 to 3.0
Iron 1.2 to 1.8 0.2 to 2.0 1.2 to 1.8
Oxygen 0.24 to 0.30 0.2 to 0.3 0.20 to 0.30
Carbon 0.08 max 0.1 max 0.08 max
Nitrogen 0.05 max 0.1 max 0.03 max
Hydrogen 0.015 max not specified 0.015 max
other elements 0.10 max each, 0.10 max each, 0.10 max each,
0.30 max total no total specified 0.30 max total
[0030] The present inventors unexpectedly discovered that providing the
present alloy with minimum levels of aluminum, oxygen, and iron greater than
minimum
levels taught in the '655 patent provides an alpha/beta titanium alloy that
consistently
exhibits mechanical properties, such as strength, for example, at least
comparable to
certain mechanical properties of mill annealed Ti-6A1-4V alloy. The inventors
also
unexpectedly discovered that increasing the minimum levels and narrowing the
ranges
of iron and vanadium relative to those minimums and ranges disclosed in the
'655
patent provides alloys that exhibit an optimal and controlled balance of the
volume
fractions of the alpha and beta phases in a mill annealed form. This optimal
balance of
phases in the alpha/beta titanium alloys according to the present disclosure
provides
embodiments of the alloys with improved ductility compared to Ti-6A1-4V
alloys, while
retaining the ductility of alloys disclosed in the '655 patent and specified
in AMS 6946B.
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[0031] A person skilled in the art understands that strength and ductility of
metallic materials generally exhibit an inverse relationship. In other words,
in general,
as the strength of a metallic material increases, the ductility of the
material decreases.
The combination of increased mechanical strength and retained ductility of the
alpha/beta titanium alloys according to the present disclosure was not
expected
because an inverse relationship between strength and ductility generally is
observed for
mill annealed titanium alloys. The unexpected and surprising combination of
increased
mechanical strength and retained ductility is a particularly advantageous
feature of alloy
embodiments according to the present disclosure. It was surprising to observe
that
embodiments of mill annealed alloys according to the present disclosure
exhibit
strengths comparable to Ti-6A1-4V alloys without exhibiting decreasing
ductility.
[0032] Certain non-limiting embodiments of alpha/beta alloys according to the
present disclosure having an aluminum equivalent value (Aleq) of at least 6.3,
or more
preferably at least 6.4, have been observed to exhibit strength at least
comparable to
the strength of Ti-6AI-4V alloys. Such alloys also have been observed to
exhibit ductility
superior to Ti-6A1-4V alloys, which typically has an aluminum equivalent value
of about
7.5. As used herein, "aluminum equivalent value" or "aluminum equivalent"
(Aleq)
means a value equal to the aluminum concentration in weight percent in an
alloy plus
ten times the oxygen concentration in weight percent of the alloy. In other
words, an
alloy's aluminum equivalent may be determined as follows: Aleq = Al(m%) + 10
(O(m%)).
[0033] While it is recognized that the mechanical properties of titanium
alloys
are generally influenced by the size of the specimen being tested, in non-
limiting
embodiments according to the present disclosure, an alpha/beta titanium alloy
comprises an aluminum equivalent value of at least 6.4, or is in certain
embodiments
within the range of 6.4 to 7.2, and a yield strength of at least 120 ksi
(827.4 MPa), or in
certain embodiment is at least 130 ksi (896.3 MPa).
[0034] In other non-limiting embodiments according to the present disclosure,
an alpha/beta titanium alloy comprises an aluminum equivalent value of at
least 6.4, or
in certain embodiments is in a range of 6.4 to 7.2, and a yield strength in
the range of
120 ksi (827.4 MPa) to 155 ksi (1,069 MPa).
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[0035] In yet other non-limiting embodiments, an alpha/beta titanium alloy
according to the present disclosure comprises an aluminum equivalent value of
at least
6.4, or in certain embodiments is in a range of 6.4 to 7.2, and an ultimate
tensile
strength of at least 130 ksi (896.3 MPa), or in certain embodiments is at
least 140 ksi
(965.3 MPa).
[0036] In additional non-limiting embodiments according to the present
disclosure, an alpha/beta titanium alloy according to the present disclosure
comprises
an aluminum equivalent value of at least 6.4, or in certain embodiments is in
a range of
6.4 to 7.2, and an ultimate tensile strength in the range of 130 ksi
(896.3MPa) to 165 ksi
(1,138 MPa).
[0037] In yet further non-limiting embodiments, an alpha/beta titanium alloy
according to the present disclosure comprises an aluminum equivalent value of
at least
6.4, or in certain embodiments is in a range of 6.4 to 7.2, and a ductility of
at least 12%,
or at least 16% (percent elongation).
[0038] In still further non-limiting embodiments, an alpha/beta titanium alloy
according to the present disclosure comprises an aluminum equivalent value of
at least
6.4, or in certain embodiments is in a range of 6.4 to 7.2, and a ductility in
the range of
12% to 30% (percent elongation or "%el").
[0039] While according to certain non-limiting embodiments of the present
disclosure, 6.3 is the absolute minimum value for Aleq, the inventors have
determined
that an Aleq value of at least 6.4 is required to achieve the same strength as
exhibited by
Ti-6A1-4V alloy. It also recognized that in other non-limiting embodiments of
an
alpha/beta titanium alloy according to this disclosure, the maximum value for
Aleq is 7.5
and that the relationship of strength to ductility according to other non-
limiting
embodiments disclosed herein applies.
[0040] According to a non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure comprises an aluminum equivalent value of
at least
6.4, a yield strength of at least 120 ksi (827.4 MPa), an ultimate tensile
strength of at
least 130 ksi (896.3 MPa), and a ductility of at least 12% (percent
elongation).
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_
[0041] According to another non-limiting embodiment, an alpha/beta titanium
alloy according to the present disclosure comprises an aluminum equivalent
value of at
least 6.4, a yield strength of at least 130 ksi (896.3 MPa), an ultimate
tensile strength of
at least 140 ksi (965.3 MPa), and a ductility of at least 12%.
[0042] In still another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure comprises an aluminum equivalent value in
the
range of 6.4 to 7.2, a yield strength in the range of 120 ksi (827.4 MPa) to
155 ksi
(1,069 MPa), an ultimate tensile strength in the range of 130 ksi (896.3MPa)
to 165 ksi
(1,138 MPa), and a ductility in the range of 12% to 30% (percent elongation).
[0043] In one non-limiting embodiment, an alpha/beta titanium alloy according
to the present disclosure exhibits an average ultimate tensile strength (UTS)
that
satisfies the equation:
UTS .?.. 14.767 (Aleq) + 48.001.
[0044] In another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average yield strength (YS)
that satisfies
the equation:
YS ... 13.338 (A(eq) + 46.864.
[0045] In still another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ductility of:
%el .?.. 3.3669 (Aleq) - 1.9417.
[0046] In yet another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ultimate tensile
strength (UTS)
that satisfies the equation:
UTS ? 14.767 (Aleq) + 48.001;
an average yield strength (YS) that satisfies the equation:
YS -?. 13.338 (Aleq) + 46.864;
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and an average ductility that satisfies the equation:
%el ? 3.3669 (Aleq) ¨ 1.9417.
[0047] In one non-limiting embodiment, an alpha/beta titanium alloy according
to the present disclosure exhibits an average ultimate tensile strength (UTS)
that
satisfies the equation:
UTS ?.. 12.414 (Alec) + 64.429.
[0048] In another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average yield strength (YS)
that satisfies
the equation:
YS ?.. 13.585 (Aleq) + 44.904.
[0049] In still another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ductility of:
%el ?_ 4.1993 (Aleq) + 7.4409.
[0050] In yet another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ultimate tensile
strength (UTS)
that satisfies the equation:
UTS 12.414 (Aleq) + 64.429;
an average yield strength (YS) that satisfies the equation:
YS .2. 13.585 (Aleq) + 44.904;
and an average ductility that satisfies the equation:
%el ?- 4.1993 (Aleq) + 7.4409.
[0051] In one non-limiting embodiment, an alpha/beta titanium alloy according
to the present disclosure exhibits an average ultimate tensile strength (UTS)
that
satisfies the equation:
UTS ?. 10.087 (Aleq) + 76.785.
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[0052] In another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average yield strength (YS)
that satisfies
the equation:
YS ?. 13.911 (Alec) + 39.435.
[0053] In still another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ductility of:
%el ?.. 1.1979 (Aleq) + 8.5604.
[0054] In still another non-limiting embodiment, an alpha/beta titanium alloy
according to the present disclosure exhibits an average ultimate tensile
strength (UTS)
that satisfies the equation:
UTS -?. 10.087 (Aleq) + 76.785;
an average yield strength (YS) that satisfies the equation:
YS ?_ 13.911 (Aleq) + 39.435;
and an average ductility in percent elongation (%el) that satisfies the
equation:
%el _?. 1.1979 (Aleq) + 8.5604.
[0055] It has been determined that non-limiting embodiments of alpha/beta
titanium alloys according to the present disclosure exhibit comparable or
higher
mechanical strength, higher ductility, and improved formability compared with
Ti-6AI-4V
alloy. Therefore, it is possible to use articles formed of alloys according to
the present
disclosure as substitutes for Ti-6AI-4V alloy articles in aerospace,
aeronautic, marine,
automotive, and other applications. The high strength and ductility of
embodiments of
alloys according to the present disclosure permits manufacturing of certain
mill and
finished article shapes with high tolerances and which cannot presently be
manufactured from Ti-6AI-4V alloy.
[0056] An aspect of the present disclosure is directed to articles of
manufacture
comprising and/or made from an alloy according to the present disclosure.
Certain non-
limiting embodiments of the articles of manufacture may be selected from an
aircraft
engine component, an aircraft structural component, an automotive component, a
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medical device component, a sports equipment component, a marine applications
component, and a chemical processing equipment component. Other articles of
manufacture that may be comprise and/or be made from embodiments of alpha/beta
titanium alloys according to the present disclosure that are known now or
hereafter to a
person of ordinary skill in the art are within the scope of embodiments
disclosed herein.
Articles of manufacture comprising and/or made from alloys according to the
present
disclosure by forming and other fabrication techniques known now or at a
future time
buy those having ordinary skill in the art.
[0057] The examples that follow are intended to further describe certain non-
limiting embodiments, without restricting the scope of the present invention.
Persons
having ordinary skill in the art will appreciate that variations of the
following examples,
as well as other embodiments not specifically described herein, are possible
within the
scope of the invention, which is defined solely by the claims.
EXAMPLE 1
[0058] Alpha/beta titanium alloy ingots having a composition according to the
present disclosure were cast using conventional vacuum arc remelting (VAR),
plasma
arc melting (PAM), or electron beam cold hearth melting (EB) for primary
melting, and
were remelted using VAR. The compositions of the ingots were within the ranges
listed
in the "Non-Limiting Embodiments according to the Present Disclosure" column
includes
in Table 1 above.
[0059] The ingot compositions produced in this Example 1 had aluminum
equivalent values ranging from about 6.0 to about 7.1. The ingots were
processed
using various hot rolling practices into hot rolled bars and wire having
diameters
between 0.25 inch (0,635 cm) and 3.25 inch (8.255 cm). Hot rolling was
conducted at
starting temperatures between 1550 F (843.3 C) and 1650 F (898.9 C). This
temperature range is below the alpha/beta transus temperature of the alloys of
this
example, which is about 1750 F to about 1850 F (about 954.4 C to about 1010
C),
depending upon the actual chemistry. After hot rolling, the hot rolled bars
and wire were
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annealed at 1275 F (690.6 C) for one hour, followed by air cooling. The
diameter,
aluminum concentration, iron concentration, oxygen concentration, and
calculated Aleq
of each of the bar and wire samples produced in Example 1 are provided in
Table 2.
Table 2
Sample No. Diameter (in.) Al (wt.%) Fe (wt.%) 0 (wt.%) Aleq (AF/0-1-
10 0%)
1 3.25 4.07 1.56 0.25 6.53
2 3.25 4.10 1.77 0.19 5.96
3 3.25 4.27 1.90 0.19 6.13
4 2 4.05 1.54 0.25 6.57
2 4.05 1.55 0.25 6.58
6 2 4.26 1.88 0.21 6.38
7 1 4.35 1.44 0.24 6.74
8 1 4.36 1.28 0.27 7.08
9 0.5 4.38 1.24 0.28 7.15
0.5 4.33 1.42 0.25 6.81
11 0.5 4.14 1.47 0.24 6.51
12 0.344 4.37 1.50 0.26 6.95
13 0.25 3.93 1.58 0.23 _ 6.27
14 0.25 4.12 1.56 0.25 6.65
0.25 4.40 1.35 0.27 7.10
16 0.25 3.95 1.53 0.24 6.30
17 0.25 4.33 1.35 0.27 7.06
5 [0060] FIG. 1 graphically displays room temperature ultimate
tensile strengths
(UTS), yield strengths (YS), and percent elongation (%el) for the bar and wire
samples
listed in Table 2 as a function of the aluminum equivalent value of the alloy
in the
sample. FIG. 1 also includes trend lines through the UTS, YS, and %el data
points
determined by linear regression. It is seen that both average strength and the
average
10 percent elongation increase with increasing Aleq. This relationship is
surprising and
unexpected as it is counter to the generally observed relationship that
increasing
strength is accompanied by decreasing ductility.
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[0061] Typical Ti-6A1-4V minimums for UTS and YS are 135 ksi (930.8 MPa)
and 125 ksi (861.8 MPa), respectively. The YS for the inventive samples listed
in Table
2 ranged from about 125 ksi for a sample with Alec, of about 6.0, up to about
141 ksi for
a sample with Aleq of about 7.1. A sample having Aleq of about 6.4 exhibited
YS of
about 130 ksi (896.3 MPa). The UTS for the inventive samples listed in Table 2
ranged
from about 135 ksi for a sample with Alec, of about 6.0, up to about 153 ksi
for a sample
with Aleq of about 7.1. A sample having Alec, of about 6.4 exhibited YS of
about 141 ksi
(972 MPa).
EXAMPLE 2
[0062] Wire sample nos. 9-11 from Example 1, having a diameter of 0.5 inch
(1.27 cm) and aluminum equivalent values of about 6.5, about 6.8 and about
7.15, were
tensile tested at room temperature. The results of the tensile tests are
displayed
graphically in FIG. 2. All of these samples exhibited tensile and yield
strengths that are
comparable to or higher than strengths exhibited by commercial Ti-6A1-4V
alloy. As
with FIG. 1, it is seen from FIG. 2 that increasing Aleq results in increased
strength,
along with an increase in average percent elongation. As discussed above, this
trend is
surprising and unexpected because it is counter to the generally observed
relationship
that increasing strength is accompanied by decreasing ductility. There is less
scatter in
the data of FIG. 2, which is representative of testing done on samples of the
same size,
as compared with FIG. 1, which is representative of testing done on samples of
various
sizes, because mechanical properties are influenced to some degree by the size
of the
test sample.
EXAMPLE 3
[0063] Hot rolled 1 inch (2.54 cm) thick plate samples were fabricated from
ingots manufactured according to steps described in Example 1. The alloys
ingots had
compositions within the ranges listed in the "Non-Limiting Embodiments
according to
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the Present Disclosure" column in Table 1 above, with aluminum and oxygen
concentrations and aluminum equivalent values as listed in Table 3.
Table 3
Sample No. Diameter (in.) Al (wt.%) Fe (wt.%) 0 (wt.%) Alec' (AN/0+10.0V
18 1 4.08 1.53 0.24 6.43
19 1 4.13 1.44 0.24 6.48
20 1 4.22 1.49 0.29 7.12
21 1 4.25 1.40 0.28 7.05
22 1 4.21 1.38 0.29 7.08
[0064] All hot rolling temperatures were below the alpha/beta transus
temperatures of the alloys. The alloys had Alec, values from about 6.5 to
about 7.1.
Room temperature tensile testing was used to determine tensile strength, yield
strength,
and percent elongation (ductility). The results of tensile testing are
displayed
graphically in FIG. 3. It is seen From FIG. 3 that alloys including increased
levels of Al
and 0, as indicated by calculated aluminum equivalents, exhibited room
temperature
strength at least comparable strength levels exhibited by Ti-6A1-4V alloy.
Further,
strength was observed to increase with increasing Aleq. In addition, the
average ductility
of the inventive alloys either increased slightly or remained generally
unchanged with
increasing Aleq and increasing strength. This trend is surprising and
unexpected as it is
counter to the generally observed relationship that increasing strength is
accompanied
by decreasing ductility.
[0065] The present disclosure has been written with reference to various
exemplary, illustrative, and non-limiting embodiments. However, it will be
recognized by
persons having ordinary skill in the art that various substitutions,
modifications, or
combinations of any of the disclosed embodiments (or portions thereof) may be
made
without departing from the scope of the invention as defined solely by the
claims. Thus,
it is contemplated and understood that the present disclosure embraces
additional
embodiments not expressly set forth herein. Such embodiments may be obtained,
for
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example, by combining and/or modifying any of the disclosed steps,
ingredients,
constituents, components, elements, features, aspects, and the like, of the
embodiments described herein. Thus, this disclosure is not limited by the
description of
the various exemplary, illustrative, and non-limiting embodiments, but rather
solely by
the claims. In this manner, it will be understood that the claims may be
amended during
prosecution of the present patent application to add features to the claimed
invention as
variously described herein.
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