U.S. patent application number 15/515093 was filed with the patent office on 2017-08-17 for titanium alloy having high strength and super-low elastic modulus.
The applicant listed for this patent is KOREA INSTITUTE OF MACHINERY & MATERIALS. Invention is credited to Jae Keun HONG, Hak Sung LEE, Chan Hee PARK, Jong Taek YEOM.
Application Number | 20170233851 15/515093 |
Document ID | / |
Family ID | 54427447 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170233851 |
Kind Code |
A1 |
PARK; Chan Hee ; et
al. |
August 17, 2017 |
TITANIUM ALLOY HAVING HIGH STRENGTH AND SUPER-LOW ELASTIC
MODULUS
Abstract
The present invention relates to a titanium alloy which is
capable of nonlinear elastic deformation and simultaneously has
super-high strength, super-low elastic modulus and stable
super-elastic properties. The titanium alloy according to the
present invention comprises Nb, Zr and O as alloy elements, the
remainder being Ti and inevitable impurities, and has a valance
electron ratio (e/a) of 4.17 to 4.22, a Mo equivalent (Mo.sub.eq)
of 7.50 to 9.72, and an Al equivalent (Al.sub.eq) of 1.42 to
14.53.
Inventors: |
PARK; Chan Hee;
(Changwon-si, KR) ; YEOM; Jong Taek; (Gimhae-si,
KR) ; LEE; Hak Sung; (Gimhae-si, KR) ; HONG;
Jae Keun; (Changwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF MACHINERY & MATERIALS |
Daejeon |
|
KR |
|
|
Family ID: |
54427447 |
Appl. No.: |
15/515093 |
Filed: |
September 25, 2015 |
PCT Filed: |
September 25, 2015 |
PCT NO: |
PCT/KR2015/010175 |
371 Date: |
March 28, 2017 |
Current U.S.
Class: |
420/418 |
Current CPC
Class: |
C22C 14/00 20130101;
C22F 1/183 20130101 |
International
Class: |
C22C 14/00 20060101
C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2014 |
KR |
10-2014-0130903 |
Claims
1. A titanium alloy comprising Nb, Zr and O as alloying elements,
with a remainder being Ti and inevitable impurities, the titanium
alloy having an electron/atom (e/a) ratio of 4.17-4.22, a Mo
equivalent (Mo.sub.eq) of 7.50-9.72, and an Al equivalent
(Al.sub.eq) of 1.42-14.53.
2. The titanium alloy of claim 1, having an electron/atom (e/a)
ratio of 4.19-4.21, a Mo equivalent (Mo.sub.eq) of 8.19-9.03, and
an Al equivalent (Al.sub.eq) of 1.60-10.78.
3. The titanium alloy of claim 1, comprising 30-34 mass % of Nb,
5.7-9.7 mass % of Zr, and 0.03-1.0 mass % of O.
4. The titanium alloy of claim 1, wherein a coefficient of
correlation of a decrease in superelastic elongation (%) to an
increase in oxygen concentration after cold working of the titanium
alloy is -0.5 (%/mass %) or more.
5. The titanium alloy of claim 1, having a superelastic elongation
of 2.5% or more after cold working.
6. The titanium alloy of claim 1, having an elastic modulus of 60
GPa or less and a tensile strength of 1000 MPa or more after cold
working.
7. The titanium alloy of claim 1, having a tensile strength
(MPa)/average elastic modulus (GPa) ratio of 0.020 or more after
cold working.
Description
TECHNICAL FIELD
[0001] The present invention relates to a titanium alloy exhibiting
nonlinear elastic deformation and having ultrahigh strength,
ultralow elastic modulus and stable superelastic properties at the
same time.
[0002] The present invention relates to a titanium alloy which has
a strength of 1000 MPa or more and an elastic modulus of 60 GPa or
less and, at the same time, exhibits nonlinear elastic deformation
(i.e., the coefficient of correlation of a decrease in superelastic
elongation (%) to an increase in oxygen concentration (mass %) of
the titanium alloy is -0.5 (%/mass %) or more), and which has
ultrahigh strength, ultralow elastic modulus and stable
superelastic properties at the same time.
[0003] The present invention relates to a titanium alloy which does
not contain elements toxic to the human body, such as aluminum
(Al), vanadium (V) or nickel (Ni), and tin (Sn) having low
corrosion resistance in vivo, and which comprises only titanium
(Ti), niobium (Nb), zirconium (Zr) and oxygen (O), which are
harmless to the human body, in which the titanium alloy has
ultrahigh strength, ultralow elastic modulus and superelastic
properties at the same time.
[0004] The present invention relates to a titanium alloy which does
not contain heavy tantalum (Ta) having a high melting point
(3,017.degree. C.) or contains a small amount of Ta so as to
prevent composition non-uniformity from being caused by tantalum
(Ta) during melting and solidification, is light in weight,
exhibits nonlinear elastic deformation making mass production
possible, and has ultrahigh strength, ultralow elastic modulus and
superelastic properties at the same time.
BACKGROUND ART
[0005] Titanium alloys are representative lightweight metals, and
are known as materials that create a high added value in various
industrial fields based on their special characteristics that
cannot be possessed by other materials.
[0006] Because their high specific strength and excellent corrosion
resistance, titanium alloys may be utilized in variety of
applications, including aerospace materials, chemical engineering
materials, materials for in vivo use, electronic component
materials, materials for sports equipment, and so on.
[0007] Among them, pure titanium, Ti-6Al-4V, Ti-6Al-7Nb and Ti--Ni
alloys, etc., are used in vivo. However, these metals have a
problem in that the elastic modulus is excessively higher than that
of human body, resulting in the occurrence of the stress shielding
phenomenon in which low stress is applied to bone tissue having a
relatively low elastic modulus. Due to the stress shielding
phenomenon, the human system recognizes the bond tissue, to which
low stress is applied, as an unnecessary part, and thus dissolves
the bone tissue by activating osteoclasts.
[0008] In addition, elements, such as aluminum (Al), vanadium (V)
and nickel (Ni), are toxic to biological tissue. Thus, it has been
required to have a biocompatible, low elastic modulus titanium
alloy comprising elements such as titanium (Ti) niobium (Nb),
zirconium (Zr), tantalum (Ta), etc., which are harmless to the
human body.
[0009] In response to this requirement, alloys such as Ti-13Nb-13Zr
and Ti-35Nb-5Ta-7Zr have been developed, which comprise
biocompatible elements such as titanium (Ti), niobium (Nb),
zirconium (Zr), tantalum (Ta) and the like and, at the same time,
have low elastic modulus.
[0010] However, generally, as the elastic modulus of metals
decreases, the strength thereof also decreases. For this reason,
components made of such materials have very low fatigue resistance,
and there is a limit to miniaturization of the components, so that
the application of minimal invasive surgery that is very
advantageous for patients will be limited.
[0011] Furthermore, materials for orthopedic or orthodontic use are
required to have high superelastic elongation in addition to low
elastic modulus and high strength properties.
[0012] In addition, materials exhibiting ultrahigh strength,
ultralow elastic modulus and superelastic properties at the same
time may be used as structural materials and the like for flexible
displays and wearable devices, which are future technologies.
[0013] Meanwhile, metal materials that are used in flexible
displays and wearable devices are required to have maximized
flexibility without containing nickel (Ni) known to cause skin and
allergic reactions. Flexibility can be largely divided into the
flexibility of material itself and structural flexibility. To
enhance the flexibility of material itself, the material should
exhibit nonlinear elastic deformation and have stable superelastic
and ultralow elastic modulus properties, so that the material can
be bent even by a small force.
[0014] In addition, structural flexibility increases as the
thickness of the material decreases. When a material has low
strength, the fatigue resistance of the material itself
significantly decreases as the thickness thereof decreases. For
this reason, it is required to increase the strength of
materials.
[0015] Thus, it can be seen that the properties required for metals
that are used in flexible displays and wearable devices are the
same as those of metals for in vivo use. Considering that the
industry of flexible displays and wearable devices is a high-tech,
high-value-added industry, it is required to develop a titanium
alloy which is biocompatible and, at the same time, has ultrahigh
strength, ultralow elastic modulus and stable superelastic
properties.
[0016] In connection with this, U.S. Pat. No. 7,261,782 (Patent
Document 1) discloses a titanium alloy exhibiting nonlinear elastic
deformation and having superelastic properties.
[0017] However, the titanium alloy disclosed in Patent Document 1
has a disadvantage in that the elastic modulus of the titanium
alloy decreases rapidly as the strength thereof increases.
Furthermore, the titanium alloy contains vanadium (V) toxic to the
human body, and thus is hard to apply as titanium for in vivo use.
In addition, it has problems in that it contains tantalum (Ta)
having a very high melting point of 3,017.degree. C., and thus
needs to be melted repeatedly, resulting in an increase in the
production cost, and in that the non-uniformity of the alloy
composition frequently occurs due to heavy tantalum (Ta).
Additionally, even when the oxygen content of the titanium alloy
changes by a very small amount, the superelastic elongation of the
titanium alloy changes rapidly, making it difficult to uniformly
control the properties of the titanium alloy in production of a
large amount of the titanium alloy.
[0018] Furthermore, U.S. Pat. No. 7,722,805 (Patent Document 2)
discloses a titanium alloy exhibiting ultralow elasticity and
high-strength properties.
[0019] However, the titanium alloy disclosed in Patent Document 2
has advantages in that when oxygen is added in order to increase
the strength of the titanium alloy, the superelastic elongation
thereof decreases rapidly, and in that tin (Sn) that is added as a
major alloying element has very low corrosion resistance in vivo
compared to titanium (Ti), niobium (Nb), zirconium (Zr) and thus
like, and thus is easily corroded.
[0020] Furthermore, there is a disadvantage in that an additional
heat-treatment process is required to increase the strength of the
titanium, and thus the production cost is increased by the
complicated process. In addition, even when the oxygen content of
the titanium alloy changes by a very small amount, the superelastic
elongation of the titanium alloy changes rapidly, making it
difficult to uniformly control the properties of the titanium alloy
in production of a large amount of the titanium alloy.
[0021] Patent Document 1 also discloses a Ti--Nb--Zr-O-based alloy
which does not contain tantalum (Ta) and tin (Sn).
[0022] However, this alloy has problems in that, when the oxygen
(O) content of the alloy is excessively low, the alloy will not
show high strength, and when the oxygen (O) content is excessively
high, the elastic modulus of the alloy will increase rapidly,
making it difficult to form the alloy into a certain shape, and the
variation in elastic strain of the alloy will increase, making it
difficult to produce the alloy in large amounts.
DISCLOSURE
Technical Problem
[0023] It is an object of the present invention to provide a
titanium alloy which can exhibit high strength, ultralow elastic
modulus, and excellent superelastic elongation which is stable
against a change in the oxygen content thereof, without having to
contain alloying elements that are toxic to the human body, or that
have low corrosion resistance in vivo, or that are heavy in weight
while having a high melting point.
Technical Solution
[0024] To achieve the above object, the present invention provides
a titanium alloy comprising Nb, Zr and O as alloying elements, with
the remainder being Ti and inevitable impurities, the titanium
alloy having an electron/atom (e/a) ratio of 4.17-4.22, a Mo
equivalent (Mo.sub.eq) of 7.50-9.72, and an Al equivalent
(Al.sub.eq) of 1.42-14.53.
[0025] In the present invention, the electron/atom (e/a) ratio may
be 4.19-4.21, the Mo equivalent (Mo.sub.eq) may be 8.19-9.03, and
the Al equivalent (Al.sub.eq) may be.
[0026] The titanium alloy may comprise 30-34 mass % of Nb, 5.7-9.7
mass % of Zr, and 0.03-1.0 mass % of O.
[0027] The coefficient of correlation of a decrease in superelastic
elongation (%) to an increase in oxygen concentration after cold
working of the titanium alloy may be -0.5 (%/mass %) or more.
[0028] The titanium alloy may have a superelastic elongation of
2.5% or more after cold working.
[0029] The titanium alloy may have an elastic modulus of 60 GPa or
less and a tensile strength of 1000 MPa or more after cold
working.
[0030] The titanium alloy may have a tensile strength (MPa)/average
elastic modulus (GPa) ratio of 0.020 or more after cold
working.
Advantageous Effects
[0031] The titanium alloy according to the present invention can
maintain its ultralow elastic modulus together with its high
strength. Thus, as shown in FIG. 1, the elastic elongation of the
titanium alloy can be significantly increased. Accordingly, the
titanium alloy can be applied to various fields, including flexible
displays, wearable devices, aerospace fields, power generation
fields, living goods, etc., which require excellent superelastic
properties.
[0032] Furthermore, the titanium alloy according to the present
invention shows a very small variation in the superelastic
elongation with a change in the oxygen content thereof. Thus, it
can exhibit uniform properties despite a variation oxygen content
between various portions, which inevitably occurs when it is
produced in large amounts. Therefore, it is advantageous in terms
of mass production.
[0033] Moreover, the titanium alloy according to the present
invention does not contain elements toxic to the human body, such
as aluminum (Al), vanadium (V) or nickel (Ni), and also does riot
contain tin (Sn) having low corrosion resistance in vivo. Thus, it
can also be properly used in vivo.
[0034] In addition, the titanium alloy according to the present
invention exhibits high strength and ultralow elasticity without
having to contain tantalum (Ta), which is advantageous for
achieving low elasticity but is heavy in weight and has a high
melting point. Thus, it can be easily produced and substantially
does not have composition non-uniformity, compared to conventional
titanium alloys containing tantalum (Ta).
[0035] Additionally, the titanium alloy according to the present
invention has excellent formability, and thus can be cold-formed by
at least 90%.
DESCRIPTION OF DRAWINGS
[0036] FIG. 1 illustrates the superelastic properties of a titanium
alloy according to the present invention in comparison with a
conventional titanium alloy.
[0037] FIG. 2 compares the strength/elastic modulus values of
Ti--Nb--Zr--(O) alloys with varying electron/atom (e/a) ratios.
[0038] FIG. 3 compares the strength/elastic modulus values of
Ti--Nb--Zr--(O) alloys with varying Mo.sub.eq values.
[0039] FIG. 4 compares the strength/elastic modulus values of
Ti--Nb--Zr--(O) alloys with varying Al.sub.eq values.
BEST MODE
[0040] Hereinafter, titanium alloy according to the present
invention, which exhibits nonlinear elastic deformation and has
ultrahigh strength, ultralow elastic modulus and stable
superelastic properties at the same time, will be described with
reference to FIGS. 1 to 4.
[0041] The terms and words used in the specification and claims
should not be interpreted as being limited to typical meanings or
dictionary definitions, but should be interpreted as having
meanings and concepts relevant to the technical scope of the
present invention, based on the principle according to which the
inventors can appropriately define the concept of the terms to
describe their invention in the best manner.
[0042] Accordingly, it should be understood that the embodiments
described in the specification and the configurations shown in the
drawings are merely examples and do not represent all of the
technical spirits of the invention, and thus there may be various
equivalents and modifications capable of replacing them at the time
of filing of the present invention.
[0043] FIG. 1 illustrates a difference in superelastic properties
between a titanium alloy according to the present invention and a
conventional titanium alloy.
[0044] As described above, in order to achieve a titanium alloy
having ultralow elastic modulus and high strength without having to
contain alloying elements such as aluminum (Al), vanadium (V) or
nickel (Ni), which are harmful to the human body, an alloying
element such as tin (Sn) having low corrosion resistance in vivo,
and an alloying element such as tantalum (Ta) which is heavy in
weight and has a very high melting point, a Ti--Nb--Zr alloy was
developed.
[0045] When oxygen (O) that is a solid-solution strengthening
element is added in order to increase the strength of the
Ti--Nb--Zr alloy, the strength will increase while the elastic
modulus of the alloy will also increase rapidly.
[0046] Thus, as shown in FIG. 1, as the strength increases, the
elastic modulus changes greatly. When the conventional titanium
alloy is produced in large amounts, a variation in oxygen content
between different portions inevitably occurs, and for this reason,
the conventional titanium alloy hardly exhibits uniform physical
properties, and also hardly exhibits both high strength and
ultralow elastic modulus.
[0047] As shown in FIG. 1, when the titanium alloy exhibits both
high strength and ultralow elastic modulus, the elastic strain
thereof significantly increases and a variation in the elastic
strain also decreases.
[0048] The present inventors have made efforts to develop a
titanium alloy which can exhibit both high strength and ultralow
elastic modulus while showing no great variation in the elastic
strain thereof even when the solid-solution strengthening element
oxygen is added to the conventional Ti--Nb--Zr-based alloy. As a
result, the present inventors have found that, when the
electron/atom (e/a) ratio, beta-phase stabilizing element Mo
equivalent (Mo.sub.eq) and alpha-phase stabilizing element Al
equivalent (Al.sub.eq) of the titanium alloy, which were not taken
into consideration in the design of the conventional titanium
alloy, are all maintained in certain ranges, the titanium alloy can
exhibit all the above-described properties, thereby completing the
present invention.
[0049] In the present invention, the electron/atom (e/a) ratio, the
Mo equivalent (Mo.sub.eq) and the Al equivalent (Al.sub.eq) can be
calculated using the following equations:
Electron/atom (e/a) ratio=Ti (atom %).times.0.04+Nb (atom
%).times.0.05+Zr (atom %).times.0.04; Equation 1
Mo equivalent (Mo.sub.eq)=Nb (mass %)/3.6; Equation 2
Al equivalent (Al.sub.eq)=Zr (mass %)/6+O (mass %).times.10.
Equation 3
[0050] The titanium alloy according to the present invention
comprises Nb, Zr and O as alloying elements, with the remainder
being Ti and inevitable impurities.
[0051] Specifically, the titanium alloy according to the present
invention does not contain elements such as aluminum (Al), vanadium
(V) or nickel (Ni), which are toxic to the human body, tin (Sn)
which has low corrosion resistance in vivo, and tantalum (Ta) which
has a very high melting point and is heavy in weight.
[0052] If the electron/atom (e/a) ratio is lower than 4.17 or more
than 4.22, it is impossible to achieve a superelastic elongation of
2% or more, an elastic modulus of 60 GPa or less and a tensile
strength of 1000 MPa or more at the same time. For this reason, the
electron/atom (e/a) ratio is preferably 4.17-4.22, more preferably
4.19-4.21.
[0053] If the Mo equivalent (Mo.sub.eq) is lower than 7.50 or more
than 9.72, it is impossible to achieve a superelastic elongation of
2% or more, an elastic modulus of 60 GPa or less and a tensile
strength of 1000 MPa or more at the same time. For this reason, the
Mo equivalent (Mo.sub.eq) is preferably 7.50-9.72, more preferably
8.19-9.03.
[0054] If the Al equivalent (Al.sub.eq) is lower than 1.42 or more
than 14.53, it is impossible to achieve a superelastic elongation
of 2% or more, an elastic modulus of 60 GPa or less and a tensile
strength of 1000 MPa or more at the same time. For this reason, the
Al equivalent (Al.sub.eq) is preferably 1.42-14.53, more preferably
1.60-10.78.
[0055] In order to maintain the electron/atom (e/a) ratio, the
beta-phase stabilizing element Mo equivalent (Mo.sub.eq) and the
alpha-phase stabilizing element Al equivalent (Al.sub.eq) in the
above-described ranges, the composition of the Ti--Nb--Zr--O alloy
preferably comprises 30-34 mass % of Nb, 5.7-9.7 mass % of Zr, and
0.03-1.0 mass % of O.
[0056] In addition, the titanium alloy according to the present
invention may also comprise tantalum in an small amount (1 mass %
or less) within a range that does not impair the melting and
uniformity of the alloy.
[0057] The titanium alloy according to the present invention may
contain impurities that are inevitably incorporated in raw
materials or in a production process. The contents of these
impurities is controlled to 1 mass % or less, preferably 0.1 mass %
or less, more preferably 0.01 mass % or less.
[0058] Hereinafter, the present invention will be described. in
further detail with reference to titanium alloys according to
preferred examples of the present invention and comparative
examples.
[0059] Each of titanium alloys according to Examples 1 to 7 of the
present invention and Comparative Examples 1 to 4 was obtained by
preparing a titanium alloy melt having the composition shown in
Table 1 below, casting the titanium alloy melt into a billet,
hot-rolling the billet at 1000.degree. C., cooling the hot-rolled
billet to room temperature, and then cold-rolling the billet at a
reduction in area of 90%.
TABLE-US-00001 TABLE 1 Content (mass %) Ti Nb Zr O Remarks e/a
Mo.sub.eq Al.sub.eq Example 1 62.44 29.5 8 0.06 Cold 4.19 8.19 1.93
Example 2 59.45 32.5 8 0.05 working 4.21 9.03 1.83 Comparative
61.99 30 8 0.01 4.19 8.33 1.43 Example 3 Example 3 61.95 30 8 0.05
4.19 8.33 1.83 61.69 30 8 0.31 4.19 8.33 4.43 61.42 30 8 0.58 4.19
8.33 7.13 61.11 30 8 0.89 4.19 8.33 10.23 Comparative 60.68 30 8
1.32 4.19 8.33 14.53 Example 2 Example 4 61.44 32.5 6 0.06 4.21
9.03 1.60 Example 5 57.95 32.5 9.5 0.05 4.21 9.03 2.08 57.72 32.5
9.5 0.28 4.21 9.03 4.38 57.39 32.5 9.5 0.61 4.21 9.03 7.68 57.08
32.5 9.5 0.92 4.21 9.03 10.78 Example 6 63.94 29.5 6.5 0.06 4.18
8.19 1.68 63.72 29.5 6.5 0.28 4.18 8.19 3.88 63.4 29.5 6.5 0.6 4.19
8.19 7.08 63.12 29.5 6.5 0.88 4.19 8.19 9.88 Example 7 60.94 29.5
9.5 0.06 4.19 8.19 2.18 Comparative 67.94 27 5 0.06 4.16 7.50 1.43
Example 3 Comparative 55.45 35 9.5 0.05 4.23 9.72 2.08 Example 4
Comparative 55.6 35 9 0.4 4.23 9.72 5.50 Example 5 Comparative 86 5
9 0 4.03 1.39 1.50 Example 6 81 10 9 0 4.06 2.78 1.50 76 15 9 0
4.09 4.17 1.50 Comparative 51.4 22.3 26.3 0 4.15 6.19 4.38 Example
7 50.3 23.6 26.1 0 4.16 6.56 4.35 49.2 24.9 25.9 0 4.17 6.92 4.32
48.1 26.2 25.7 0 4.18 7.28 4.28 Comparative 73.93 13 13 0.07 Aging
4.08 3.61 2.87 Example 8 treatment Comparative 55.75 35 9 0.25 4.23
9.72 4.00 Example 9 Comparative 79 8 13 0 Solution 4.05 2.22 2.17
Example 10 69 18 13 0 treatment 4.11 5.00 2.17 51.8 41.1 7.1 0 4.28
11.42 1.18 Comparative 41 34 25 0 4.24 9.44 4.17 Example 11 38 30
32 0 4.22 8.33 5.33 36.6 28 35.4 0 4.21 7.78 5.90 34.5 24.8 40.7 0
4.19 6.89 6.78
[0060] In addition, the titanium alloys according to Comparative
Examples 5 to 11 as shown in Table 1 above and the mechanical
properties shown in Table 2 below are those disclosed in the
following patent documents or publications. Furthermore, the
electron/atom ratio (e/a), molybdenum equivalent and aluminum
equivalent shown in Table 1 above are values calculated based on
the disclosed compositions.
[0061] Comparative Example 5: Korean Patent Application Publication
No. 2002-0026891.
[0062] Comparative Example 6: Q. Liu et al., Progress to Natural
Science: Materials International, vol 23(6) (2013) pp. 562-565.
[0063] Comparative Example 7: H. Tobe et al., Materials
Transactions, vol 50 (2009) pp. 2721-2725.
[0064] Comparative Example 8: C. H. Park et al., Materials Science
and Engineering A, vol 527 (2010) pp. 4914-4919.
[0065] Comparative Example 9: Korean Patent Application Publication
No. 2003-0061007.
[0066] Comparative Example 10: S. Schneider et al., Materials
Research, vol 8 (2005) pp. 435-438.
[0067] Comparative Example 11: S. Ozan et al., Acta Biomaterialia,
vol 20 (2015) pp. 176-187.
[0068] As shown in Table 1 above, the titanium alloys according to
Examples 1 to 7 of the present invention had an electron/atom (e/a)
ratio in the range of 4.17-4.22, a Mo equivalent (Mo.sub.eq) in the
range of 7.50-9.50, and an Al equivalent (Al.sub.eq) in the range
of 1.45-14.53.
[0069] On the other hand, the titanium alloys according to
Comparative Examples 1 to 11 did not contain oxygen (O) as an
essential element or had an electron/atom (e/a) ratio out of the
range of 4.17-4.22, a Mo equivalent (Mo.sub.eq) out of the range of
7.50-9.50, and an Al equivalent (Al.sub.eq) out of the range of
1.45-14.53.
[0070] The compositions shown in Table 1 above were subjected to
subsequent working and heat treatment, and the mechanical
properties of the resulting titanium alloys were evaluated. The
results of the evaluation are summarized in Table 2 below.
TABLE-US-00002 TABLE 2 Tensile Elastic Superelastic Tensile
strength modulus elongation strength/elastic No. (MPa) (GPa) (%)
modulus Example 1 1110 35 2.7 0.0317 Example 2 1105 34 2.8 0.0325
Comparative 765 32 2.1 0.0239 Example 1 Example 3 1062 32 2.9
0.0332 1134 35 2.8 0.0324 1243 38 2.8 0.0327 1349 47 2.5 0.0287
Comparative 1560 70 1.8 0.0223 Example 2 Example 4 1071 34 2.7
0.0315 Example 5 1056 33 2.8 0.0320 1120 36 2.7 0.0311 1163 38 2.6
0.0306 1377 49 2.5 0.0281 Example 6 1027 32 2.8 0.0321 1014 32 2.7
0.0317 1125 37 2.6 0.0304 1217 43 2.5 0.0283 Example 7 1114 37 2.6
0.0301 Comparative 1034 44 2 0.0235 Example 3 Comparative 977 45
1.9 0.0217 Example 4 Comparative 950 47 -- 0.0202 Example 5
Comparative 904 62.3 -- 0.0145 Example 6 857 54.4 -- 0.0158 854
38.8 -- 0.0220 Comparative 982 51 -- 0.0193 Example 7 1008 52 --
0.0194 1005 52 -- 0.0193 848 58 -- 0.0146 Comparative 902 80 --
0.0113 Example 8 Comparative 1555 85 1.8 0.0183 Example 9
Comparative 763 88.8 -- 0.0086 Example 10 698 70.4 -- 0.0099 499
64.7 -- 0.0077 Comparative 839 62 1.31 0.0135 Example 11 794 65 1.2
0.0122 755 64 1.14 0.0118 704 63 1.08 0.0112
[0071] The results summarized in Table 2 above are shown in FIGS. 2
to 4.
[0072] As shown in Table 2 above, the titanium alloys according to
Examples 1 to 7 of the present invention exhibited a tensile
strength of 1000 MPa or more and an elastic modulus of 50 GPa or
less and, at the same time, exhibited a superelastic elongation of
2.5% or more. Namely, the titanium alloys according to the present
invention exhibited high strength, ultralow elastic modulus and
excellent superelastic elongation, which could not be exhibited by
conventional titanium alloys.
[0073] In addition, as shown in Examples 3, 5 and 6 of the present
invention, the rate of decrease in the superelastic elongation was
very low even when the oxygen content increased, and the rate of
the decrease was as slow as -0.5 or more. Namely, the titanium
alloys according to the Examples of the present invention can
exhibit superelastic properties that are stable against a change in
the oxygen content.
[0074] Meanwhile, Comparative Example 1 had Nb and Zr contents
similar to those of Example 1, but had a low oxygen content, and
thus failed to exhibit the properties obtained in Examples 1 to 7
of the present invention. Comparative Example 2 had Nb and Zr
contents similar to those of Example 3, but had an excessively high
oxygen content, and thus failed to exhibit the properties obtained
in Examples 1 to 7 of the present invention.
[0075] In addition, the titanium alloys according to Comparative
Examples 3 to 11 had a Nb or Zr content different from those of the
Examples of the present invention, and as a result, exhibited a low
strength, an excessively high elastic modulus or a low superelastic
elongation, compared to those of Examples 1 to 7 of the present
invention.
[0076] FIGS. 2 to 4 diagrammatically show the results shown in
Table 2 above.
[0077] As shown in FIG. 2, the electron/atom (e/a) ratios of the
titanium alloys according to Examples 1 to 7 were between about
4.175 and about 4.225, and the titanium alloys of Examples 1 to 7,
which had such electron/atom (e/a) ratios, showed tensile
strength/elastic modulus ratios higher than those of the
Comparative Examples, which did not have such electron/atom (e/a)
ratios.
[0078] Furthermore, as shown FIG. 3, the titanium alloys according
to Examples 1 to 7 had a Mo equivalent (Mo.sub.eq) between 8 and 9,
and showed tensile strength/elastic modulus ratios higher than
those of the Comparative Examples, which had Mo equivalents out of
this Mo equivalent range.
[0079] In addition, as shown FIG. 4, the titanium alloys according
to Examples 1 to 7 had an Al equivalent (Al.sub.eq) between 1.75
and 11, and showed tensile strength/elastic modulus ratios higher
than those of the Comparative Examples, which had Al equivalents
out of this Al equivalent range.
[0080] As described above, the alloys of Examples 1 to 7 of the
present invention, which satisfy the above-described three
conditions, can exhibit high strength, ultralow elastic modulus and
superelastic elongation at the same time, but alloys which do not
satisfy such conditions do not exhibit at least one of high
strength, ultralow elastic modulus and superelastic elongation.
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