U.S. patent application number 14/006966 was filed with the patent office on 2015-05-28 for beta-type titanium alloy having low elastic modulus and high strength.
This patent application is currently assigned to KOREA INSTITUTE OF MACHINERY & MATERIALS. The applicant listed for this patent is Dong Geun Lee, Yong Tai Lee. Invention is credited to Dong Geun Lee, Yong Tai Lee.
Application Number | 20150147225 14/006966 |
Document ID | / |
Family ID | 49673508 |
Filed Date | 2015-05-28 |
United States Patent
Application |
20150147225 |
Kind Code |
A1 |
Lee; Dong Geun ; et
al. |
May 28, 2015 |
BETA-TYPE TITANIUM ALLOY HAVING LOW ELASTIC MODULUS AND HIGH
STRENGTH
Abstract
Provided is a beta-type titanium alloy having a low elastic
modulus and a high strength. The titanium alloy includes 6 to 13 wt
% of Mo, 0.1 to 3.9 wt % of Fe, a remaining amount of Ti, and
inevitable impurity, and selectively includes 0.1 to 3.9 wt % of
Al. The titanium alloy according to the present invention has a
high tensile strength of greater than or equal to 1,300 MPa and a
low elastic modulus of less than or equal to 95 GPa at low
cost.
Inventors: |
Lee; Dong Geun;
(Changwon-si, KR) ; Lee; Yong Tai; (Changwon-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Dong Geun
Lee; Yong Tai |
Changwon-si
Changwon-si |
|
KR
KR |
|
|
Assignee: |
KOREA INSTITUTE OF MACHINERY &
MATERIALS
Daejeon-si
KR
|
Family ID: |
49673508 |
Appl. No.: |
14/006966 |
Filed: |
August 30, 2012 |
PCT Filed: |
August 30, 2012 |
PCT NO: |
PCT/KR2012/006941 |
371 Date: |
September 24, 2013 |
Current U.S.
Class: |
420/418 ;
420/421 |
Current CPC
Class: |
C22C 14/00 20130101 |
Class at
Publication: |
420/418 ;
420/421 |
International
Class: |
C22C 14/00 20060101
C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2012 |
KR |
10-2012-0057217 |
Claims
1. A beta-type titanium alloy having a low elastic modulus and a
high strength, comprising 6 to 13 wt % of Mo, 0.1 to 3.9 wt % of
Fe, a remaining amount of Ti, and inevitable impurity, the titanium
alloy having a tensile strength of greater than or equal to 1,300
MPa and an elastic modulus of less than or equal to 95 GPa.
2. The titanium alloy of claim 1, further comprising 0.1 to 3.9 wt
% of Al.
3. The titanium alloy of claim 1, wherein a microstructure of the
beta-type titanium alloy has a dispersed shape of an omega phase
having an average particle size of 100 nm or less.
4. The titanium alloy of claim 1, wherein an Mo equivalent defined
by following [Equation 1] is 7.0 to 20.0, Mo
equivalent=[Mo]+1/5[Ta]+1/3.6[Nb]+1/2.5[W]+1/1.5[V]+1.25[Cr]+1.25[Ni]+1.7-
[Mn]+1.7[Co]+2.5[Fe]. [Equation 1]
5. The titanium alloy of claim 1, wherein an elongation percentage
of the titanium alloy is greater than or equal to 6%.
6. The titanium alloy of claim 1, wherein the tensile strength of
the titanium alloy is greater than or equal to 1,400 MPa.
7. A rod material manufactured by using the titanium alloy
described in claim 1.
8. A plate material manufactured by using the titanium alloy
described in claim 1.
9. A rectangular lumber material manufactured by using the titanium
alloy described in claim 1.
10. A spring material manufactured by using the titanium alloy
described in claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a beta-type titanium alloy
having a low elastic modulus and a high strength and more
particularly, to a beta-type titanium alloy having a low elastic
modulus and a high strength, and having a high performance at low
cost.
BACKGROUND ART
[0002] Titanium has a high specific strength (strength/weight) and
a good corrosion-resistance and has a high applicability as a base
material in various industrial fields. Thus, titanium is called as
an advanced material of a dream and is one of advanced metal
materials expected to be used in a future application. Due to the
various good properties of the titanium, researches in biomedical,
marine, aerospace, sports and leisure fields have been widely
conducted.
[0003] A titanium alloy is generally classified into a .alpha.-type
(hexagonal crystal close-packed: hcp), a .beta.-type (body-centered
cubic: bcc), and a .alpha.+.beta.-type based on the crystalline
structure of the phase constituting a metal structure at room
temperature. An alloy obtained by adding a small amount of such as
aluminum or titanium for industry is the .alpha.-type. Ti-6Al-4V
alloy known as a high strength alloy and used in an airplane is the
.alpha.+.beta.-type, and the .beta.-type is an alloy including an
increased amount of an alloy element for stabilizing a
.beta.-phase.
[0004] When comparing with a steel material, the titanium alloy has
a density of about 56% and a shear elastic modulus of about 50%
with respect to those of the steel material at the states having
the same strength. Thus, a spring having the same performance may
have a theoretical weight of about 28%, and the lightening by about
72% with respect to the steel material may be attainable.
[0005] When manufacturing a coil spring by using
Ti-3Al-8V-6Cr-4Mo-4Zr (.beta.-C) alloy, the spring may be useful to
the maximum shear stress of 839 MPa. In addition, the weight of the
coil spring is only about 47% of the coil spring manufactured by
using a steel material having the same performance, and a
lightening effect may be certainly attainable.
[0006] In addition, since the titanium alloy has high damping
capacity and natural frequency, a surging phenomenon constituting a
problem during the high-speed rotation of an engine may be
evitable, and the extension of a lifetime may be accomplished. The
natural frequency of the Ti-3Al-8V-6Cr-4Mo-4Zr alloy, which is
commonly used as a spring, is 870 Hz, which is superior to that of
the spring manufactured by the common steel material, 483 Hz.
[0007] In addition, since the shear elastic modulus of the titanium
alloy spring material is small and about 50% of the common spring
steel, the number of the winding of the spring may be decreased. In
addition, the miniaturization and lightening of the engine may be
promoted by decreasing the contacting height of a valve spring.
Further, due to the various properties of the titanium alloy as
described above, when the spring of the titanium alloy is used for
a suspension in vehicles, a good cushioning effect may be obtained
to improve a ride comfort.
[0008] However, when considering the weight of the vehicles, the
tensile strength of the titanium alloy for the suspension spring is
at least 1,300 MPa or over. In order to sufficiently obtain the
titanium effect as described above, the elastic modulus of the
titanium alloy is preferably less than or equal to 95 GPa.
[0009] Meanwhile, in order to manufacture the p-type titanium
alloy, a quite amount of beta stabilizing elements is required to
be included. Since the beta stabilizing elements are generally
expensive, the usage thereof is limited to special parts requiring
good physical properties as described above.
[0010] Even though the titanium alloy has good properties, since
low-priced parts are used in vehicles, the titanium alloy may not
be replaced with the common steel material for manufacturing the
parts.
DISCLOSURE OF THE INVENTION
Technical Problem
[0011] The purpose of the present invention is to solve the
above-described defects and to provide a titanium alloy having good
physical properties such as a high tensile strength of greater than
or equal to 1,300 MPa and a low elastic modulus of less than or
equal to 95 GPa at low cost.
Technical Solution
[0012] There is provided to solve the above defects in the present
invention a beta-type titanium alloy having a low elastic modulus
and a high strength, including 6 to 13 wt % of Mo, 0.1 to 3.9 wt %
of Fe, a remaining amount of Ti, and inevitable impurity. The
titanium alloy has a tensile strength of greater than or equal to
1,300 MPa and an elastic modulus of less than or equal to 95
GPa.
[0013] In addition, according to an aspect of the present
invention, the titanium alloy may further include 0.1 to 3.9 wt %
of Al. That is, there is provided in the present invention a
beta-type titanium alloy having a low elastic modulus and a high
strength, including 6 to 13 wt % of Mo, 0.1 to 3.9 wt % of Fe, 0.1
to 3.9 wt % of Al, a remaining amount of Ti, and inevitable
impurity, wherein the titanium alloy has a tensile strength of
greater than or equal to 1,300 MPa and an elastic modulus of less
than or equal to 95 GPa. The addition of Al may increase the
processability, the formability, the castability, etc. and may
provide advantages for applying various heat treatment techniques
to obtain reinforcing effects.
[0014] In addition, according to an aspect of the present
invention, 0.005 to 0.5 wt % of B may be additionally included in
the titanium alloy.
[0015] In addition, according to an aspect of the present
invention, an elongation percentage of the titanium alloy may be
greater than or equal to 6%.
[0016] In addition, according to an aspect of the present
invention, the tensile strength of the titanium alloy may be
greater than or equal to 1,400 MPa.
[0017] In addition, according to an aspect of the present
invention, the microstructure of the titanium alloy may include
omega (.omega.) phase particles minutely dispersed in a beta
(.beta.) matrix. The omega (.omega.) phase may be removed or
generated by using a heat treatment technique to obtain required
strength, ductility and elastic modulus.
Advantageous Effects
[0018] The titanium alloy according to the present invention has a
tensile strength of greater than or equal to 1,300 MPa and an
elastic modulus of less than or equal to 95 GPa, and may be applied
in various fields requiring a low elastic modulus and a high
strength.
[0019] In addition, since the use of an expensive alloy element in
the titanium alloy is minimized according to the present invention,
the manufacturing cost of the alloy may be largely decreased.
[0020] In addition, when the titanium alloy is manufactured through
forging and rolling, a rod material, a rectangular lumber and a
plate material having a tensile strength of greater than or equal
to 1,300 MPa, an elastic modulus of less than or equal to 95 GPa,
and an elongation percentage of greater than or equal to about 6%
may be manufactured, without conducting a heat treatment such as a
solution heat treatment or an ageing. Thus, a spring for
transportation vehicles and parts having a high strength and a low
elastic modulus in various fields may be manufactured at low cost.
Particularly, when the titanium alloy is used for a spring
material, lightening to about 50 to 60% when compared with a spring
manufactured by using a steel material may be accomplished.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1 to 5 are photographs on microstructures of hot
forged materials respectively manufactured in Examples 1 to 5 of
the present invention and taken by an optical microscope.
[0022] FIGS. 6 and 7 are photographs on microstructures of rolled
rod materials manufactured in Examples 2 and 3 of the present
invention and taken by an optical microscope.
[0023] FIGS. 8 and 9 are photographs on microstructures of rolled
rod materials respectively manufactured in Examples 2 and 3 and
taken by a dark field image (DFI) transmission electron
microscope.
MODE FOR CARRYING OUT THE INVENTION
[0024] Hereinafter, preferred embodiments of the present invention
will be described in detail, however, the present invention is not
limited to the following embodiments.
[0025] First, the composition ranges of each alloy element in the
beta-type titanium alloy according to the present invention are
defined as follows.
[0026] Mo: 6 to 13 wt %
[0027] Mo is a stabilizing element of a beta (.beta.) phase and has
an effect of lowering an elastic modulus and increasing strength.
Since Mo is expensive, the amount of Mo is optimized to lower the
cost while obtaining mechanical properties. Preferable amount of Mo
is 6 to 13 wt %.
[0028] Fe: 0.1 to 3.9 wt %
[0029] Fe is a stabilizing element of a beta (.beta.) phase but
increases a deformation resistance. Thus, Fe has been added as
small as possible in the prior arts. In the present invention,
relatively a large amount of cheap Fe is used when compared with
other beta stabilizing elements. When the amount of Fe is less than
0.1 wt %, the beta stabilizing effect is insufficient, and when the
amount of Fe exceeds 3.9 wt %, the deformation resistance may be
excessive to deteriorate processing properties. Thus, the preferred
amount of Fe is less than or equal to 3.9 wt %.
[0030] Meanwhile, the index on manufacturing the beta-type titanium
alloy having a low elastic modulus by stabilizing the beta (.beta.)
phase may be illustrated by Mo equivalent in [Equation 1]. The
preferred Mo equivalent when calculated with Fe is about 7.0 to
20.0.
Mo
equivalent=[Mo]+1/5[Ta]+1/3.6[Nb]+1/2.5[W]+1/1.5[V]+1.25[Cr]+1.25[Ni]-
+1.7[Mn]+1.7[Co]+2.5[Fe] [Equation 1]
[0031] Al: 0.1 to 3.9 wt %
[0032] Al is an element added to improve the strength of the
.beta.-type titanium alloy according to the present invention. Al
restrains the precipitation of an omega (.omega.) phase which
increases the hardness of the titanium alloy by embrittlement
during heat treatment, increases the strength and the ductility,
and improves processability and castability. Al may be selectively
added in the present invention. When the amount of Al exceeds 3.9
wt %, the hardness may be excessively increased, and the elongation
percentage may be lowered to decrease the processability. Thus, the
amount of Al added is preferably less than or equal to 3.9 wt
%.
[0033] B: 0.005 to 0.5 wt %
[0034] B is an element restraining the growth of a huge
solidification structure while conducting solution cast. When B is
added by less than 0.005 wt %, the enlargement of the
solidification structure may be ineffectively restrained. When the
amount of B exceeds 0.5 wt %, further miniaturization of the cast
structure may not be accomplished. Thus, the preferred amount of B
is 0.005 to 0.5 wt %.
[0035] Inevitable Impurities
[0036] The inevitable impurities are components possibly added in
the raw material of the titanium alloy or during processing
unintentionally. Particularly, oxygen may deteriorate the
deformation capacity of the titanium alloy, may become a reason
generating cracks during cold working, and may become a reason
increasing a deformation resistance. Thus, the amount of the
inevitable impurities is required to be maintained by less than or
equal to 0.3 wt % and is preferably required to be less than or
equal to 0.18 wt %. In addition, since hydrogen deteriorates the
ductility and the toughness of the titanium alloy, the amount of
the hydrogen is preferably as small as possible. The amount of the
hydrogen is more preferably, less than or equal to 0.03 wt %, and
most preferably, less than or equal to 0.01 wt %. Carbon largely
lowers the deformation capacity of the titanium alloy and so, is
required to be included as small amount as possible. Preferably,
the amount of the carbon is less than or equal to 0.05 wt % and
more preferably, the amount of the carbon is less than or equal to
0.01 wt %. In addition, nitrogen also largely lowers the
deformation capacity of the titanium alloy and so is required to be
included as small amount as possible. Preferably, the amount of the
nitrogen is less than or equal to 0.02 wt % and more preferably,
the amount of the nitrogen is less than or equal to 0.01 wt %.
[0037] In addition, in the microstructure of the titanium alloy
according to the present invention, an alpha (.alpha.) phase may be
mixed in a beta phase matrix, and minutely dispersed omega
(.omega.) phase particles may be included in the beta (.beta.)
phase matrix.
[0038] A method of processing a rod material, a rectangular lumber
and a plate material by using a titanium alloy according to the
present invention includes (a) preparing a titanium alloy liquid
metal including the above described components; (b) casting the
thus prepared titanium alloy to manufacture an ingot; (c) hot
forging the ingot at 800.degree. C. to 1,200.degree. C.; and (d)
rolling the forged titanium alloy at 25.degree. C. to 650.degree.
C.
[0039] The temperatures of the hot forging and the rolling are
preferably maintained within the above defined ranges to prevent
the generation of cracks during processing and to obtain a
sufficient reduction ratio.
Examples
[0040] Titanium alloys having the composition as illustrated in the
following Table 1 were manufactured by using induction skull
melting (ISM). The amount of the impurities such as oxygen (O),
nitrogen (N), carbon (C), and hydrogen (H) in all alloys was less
than 0.5 wt %.
TABLE-US-00001 TABLE 1 Composition (wt %) Alloy Mo Fe Al Ti Example
1 9.2 2.2 -- Bal. Example 2 12.1 1.0 -- Bal. Example 3 9.0 2.2 2.0
Bal. Example 4 9.2 2.3 3.1 Bal. Example 5 11.7 1.3 1.2 Bal.
Comparative 15.0 -- -- Bal. example 1 Comparative 3.4 4.0 -- Bal.
example 2 Comparative 0.5 5.0 -- Bal. example 3
[0041] The liquid metal of the alloy molten by the composition
illustrated in the above Table 1 was cast into an ingot having a
size of 100 mm diameter.times.90 mm height.
[0042] In order to select an alloy having sufficient mechanical
properties applicable in a suspension of a transportation vehicles
among the alloys illustrated in Table 1, the ingots were heated at
1,100.degree. C. by the inventors of the present invention. Then,
the ingots were charged into a hot forging machine and were hot
forged to manufacture subject materials having a length of 120 mm,
a width of 60 mm, and a height of 40 mm.
[0043] The tensile properties of the thus hot forged subject
materials were evaluated and the results are illustrated in the
following Table 2.
TABLE-US-00002 TABLE 2 Yield Tensile Elongation Alloy strength
(MPa) strength (MPa) percentage (%) Example 1 1198 1204 10 Example
2 769 887 8.5 Example 3 772 895 17 Example 4 809 934 8.0 Example 5
655 806 16 Comparative 896 898 18 example 1 Comparative 1088 1192
5.4 example 2 Comparative 780 916 10 example 3 * Comparative
example 1 corresponds to the tensile properties of a common
material. * Comparative examples 2 and 3 correspond to the tensile
properties measured by using test samples manufactured in rod
material shapes.
[0044] It may be confirmed that from the evaluation results as
illustrated in Table 2, the alloy according to Example 1 of the
present invention has the tensile strength exceeding 1,200 MPa and
the elongation percentage up to 10%, and illustrates very close
properties to the target physical properties of the present
invention. Thus, the alloy in Example 1 was confirmed to accomplish
the object of the present invention through additional
processes.
[0045] In addition, even though the alloys in Examples 2 to have
the tensile strengths less than 1,000 MPa, the elongation
percentages are good and the elastic modulus are less than 95 GPa.
Therefore, the strength may be additionally increased through
subsequent processes, and the alloys in Examples 2 to 5 may be
applied as springs for a suspension of a transfer machine.
[0046] In order for confirmation, the alloy in Example 2 and the
alloy in Example 3 were respectively selected from Examples 2 and
5, and Examples 3 and 4, which have similar contents of Mo and Fe,
respectively. Then, the subsequent processes were conducted and
tensile properties and elastic properties were measured.
[0047] On the other hand, the alloys according to Comparative
examples 1, 2 and 3 may be rod material state after completing
subsequent processes, or may have too low tensile properties or too
high elastic modulus. Thus, these alloys may be hardly applied as a
spring.
[0048] Based on the tensile properties at room temperature, the
strong candidates of the titanium alloy ingots according to
Examples 1, 2 and 3 were forged to manufacture the titanium alloy
into rectangular lumbers or rod materials. Then, the titanium alloy
was heated to 600.degree. C. and passed three times of rolling to
manufacture a rod material having a diameter of 16 to 20 mm and a
length of 500 mm or over.
[0049] Samples were taken from the center portion of the thus
manufactured rod material, and the properties of the samples were
evaluated.
[0050] First, the microstructure of the rolled rod material was
analyzed by using an optical microscope and a transmission electron
microscope. The samples for analysis by means of the optical
microscope were prepared by a standard metallic preparation
process. First, the samples were mirror polished and etched by
using an etching solution.
[0051] In addition, the samples for analysis by means of the
transmission electron microscope were prepared by grinding the
samples to a thickness of 60 .mu.m, and conducting a twin-jet
polishing in a solution including 35% of butanol-6% of perchloric
acid-methanol under 60V condition.
[0052] FIGS. 1 to 5 are photographs on microstructures of hot
forged materials taken by an optical microscope on the ingots
manufactured by hot forging the alloys having the compositions as
in Examples 1 to 5. As illustrated in FIGS. 1 to 5, all of the
microstructures of the alloys have a .beta.-phase matrix
constituted by an equiaxed structure having an average size of
about several hundreds .mu.m. In addition, a portion of alpha phase
was precipitated and present in the microstructure.
[0053] For the photographs in FIGS. 6 and 7, obtained by observing
on the microstructures of rolled rod materials by means of the
optical microscope, the crystal grains of the microstructures
clearly differentiated in the hot forged material disappeared while
conducting a subsequent rolling process. In addition, the
microstructure was observed to have a wave shape after undergoing a
severe plastic deformation. Meanwhile, the microstructures observed
through a DFI by using the transmission electron microscope were
observed to have minute omega (.omega.) phase having the size of
from several nanometers to several tens nanometers present in some
regions.
[0054] Then, the tensile properties and the elastic modulus of the
rod materials manufactured according to the examples of the present
invention and the comparative examples were measured and
illustrated in the following Table 3.
TABLE-US-00003 TABLE 3 Elonga- Yield Tensile tion Elastic Sam-
strength strength percent- modulus ples Composition (MPa) (MPa) age
(%) (GPa) Exam- Ti--9.2Mo--2.2Fe 1330 1352 7.0 88 ple 1 Exam-
Ti--12.1Mo--1Fe 1440 1501 10.1 85 ple 2 Exam- Ti--9Mo--2.2Fe-- 1386
1498 6.9 76 ple 3 2Al Compar- Ti--3.4Mo--4Fe 1088 1192 5.4 93 ative
exam- ple 2 Compar- Ti--0.5Mo--5Fe 780 916 10 96 ative exam- ple
3
[0055] As confirmed in Table 3, the alloy rod materials according
to the examples of the present invention have the tensile strength
greater than 1,300 MPa and the elastic modulus less than 95 GPa.
Thus, these rod materials satisfied the physical properties
required for parts having low elastic modulus and high repulsion
properties in various fields including spring materials for a
suspension of transportation vehicles.
[0056] Particularly, the alloy rod material according to Example 2
has a high tensile strength of 1,501 MPa, a good processability
with the elongation percentage of about 10% and a low elastic
modulus of 85 GPa. Thus, the alloy rod may be appropriately used as
a spring material such as the spring material of a suspension for
vehicles.
[0057] The alloy rod material according to Example 3 also has a
high tensile strength of 1,498 MPa, the elongation percentage of
about 7%, and the elastic modulus of 76 GPa, and may be
appropriately used in parts requiring a high strength and low
elastic properties in various fields.
[0058] In addition, the alloy rod material according to the present
invention uses cheap iron (Fe) as the beta stabilizing element and
confirms good mechanical properties when compared with a common
material, Ti-15Mo at low cost. Thus, the manufacturing cost of the
titanium alloy may be lowered when compared with the common
titanium alloy, and good tensile properties and good elastic
properties may be obtained when compared with the common titanium
alloy.
* * * * *