U.S. patent application number 11/922026 was filed with the patent office on 2008-10-23 for ternary ti-ni-cu shape memory alloy and process for producing same.
Invention is credited to Akira Ishida, Morio Sato.
Application Number | 20080260573 11/922026 |
Document ID | / |
Family ID | 37532123 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080260573 |
Kind Code |
A1 |
Ishida; Akira ; et
al. |
October 23, 2008 |
Ternary Ti-Ni-Cu Shape Memory Alloy and Process for Producing
Same
Abstract
An amorphous Ti--Ni--Cu alloy comprising from 44 to 49 atomic %
of Ti, from 20 to 30 atomic % of Cu, and the balance being Ni and
unavoidable elements is heated at 500 to 700.degree. C. for a
period of time not exceeding 100 hours to crystallize the amorphous
alloy.
Inventors: |
Ishida; Akira; (Ibaraki,
JP) ; Sato; Morio; (Ibaraki, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W., SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
37532123 |
Appl. No.: |
11/922026 |
Filed: |
May 24, 2006 |
PCT Filed: |
May 24, 2006 |
PCT NO: |
PCT/JP2006/310344 |
371 Date: |
January 30, 2008 |
Current U.S.
Class: |
420/587 |
Current CPC
Class: |
C22F 1/183 20130101;
C22C 1/002 20130101; C22C 14/00 20130101; C22C 30/02 20130101; C22F
1/006 20130101; C22F 1/18 20130101; C22C 45/10 20130101 |
Class at
Publication: |
420/587 |
International
Class: |
C22C 30/02 20060101
C22C030/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2005 |
JP |
2005-172939 |
Claims
1-5. (canceled)
6. A Ti--Ni--Cu shape memory alloy, containing Ti in amount of 44
atomic % to 49 atomic %, Cu in amount of 20 atomic % to 30 atomic %
and the rest consisting of Ni and inevitable impurities, wherein
TiNiCu phases or TiCu phases sized 500 nm or less precipitate in a
Ti(Ni,Cu) crystal grain whose grain size is 2 .mu.m or less.
7. A method of producing a Ti--Ni--Cu shape memory alloy, wherein
an amorphous Ti--Ni--Cu alloy, which contains Ti in amount of 44
atomic % to 49 atomic %, Cu in amount of 20 atomic % to 30 atomic %
and the rest consisting of Ni and inevitable impurities, is
crystallized by heat treatment.
8. The method of producing a Ti--Ni--Cu shape memory alloy as
claimed in claim 7, wherein a temperature range of the heat
treatment is 500.degree. C. to 700.degree. C.
9. The method of producing a Ti--Ni--Cu shape memory alloy as
claimed in claim 7, wherein time of the heat treatment is not
beyond 100 hours.
10. The method of producing a Ti--Ni--Cu shape memory alloy as
claimed in claim 8, wherein time of the heat treatment is not
beyond 100 hours.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ternary Ti--Ni--Cu shape
memory alloy which has both low composition dependency and low heat
treatment dependency and which is useful as a device used, for
example, in an actuator, and to a process for producing same.
BACKGROUND ART
[0002] A binary Ti--Ni alloy which is widely used as a shape memory
alloy has defects because its phase transformation temperature
greatly depends upon its composition and its heat treatment
temperature and is lower than ambient temperature when a large
output force is attempted to be obtained. Thus, a difficulty is
encountered in controlling the composition. In particular, the
yield of sputtered thin films in which the compositional
distribution in the plane direction unavoidably becomes non-uniform
is poor. It is, therefore, difficult to produce sputtered films on
an industrial scale (Patent Document 1).
[0003] With a view toward solving the above problems of such a
binary Ti--Ni alloy, studies have been made on a ternary Ti--Ni--Cu
shape memory alloy in which a part of Ni of a 50 atomic % Ti--Ni
alloy is substituted with Cu. For example, it has been revealed
that in Ti--Ni--Cu alloy thin films having a Ti content of at least
50 atomic %, the temperature hysteresis is reduced by addition of
Cu and the recovery stress increases due to solid solution
hardening by Cu (Non-Patent Document 1). It has been also revealed
that in Ti--Ni--Cu alloy thin films containing 6 atomic % of Cu and
no more than 50 atomic % of Ti, the shape memory behavior of alloys
having a structure in which a TiNiCu phase is formed within grains
greatly varies with a Ti content and, further, the transformation
occurs in a temperature range lower than ambient temperature and in
two separate stages (Non-Patent Document 2).
[0004] A Ti50-(Ni, Cu)50 alloy which is a ternary Ti--Ni--Cu shape
memory alloy, however, is brittle and has poor workability, though
its phase transformation temperature scarcely depends upon the Cu
content. Thus, the Cu content is at most 10 atomic % in the case of
a cast alloy and is at most 20 atomic % in the case of an alloy
formed by a liquid quenching method. Additionally, the obtained
alloy has a composition near the Ti(Ni, Cu) single phase (Ti 50
atomic %) and is defective in that the output force is small. For
example, there is proposed a method of producing a Ti--Ni--Cu alloy
which contains more than 10 atomic % of Cu and which is difficult
to be produced with the ordinary melting and hot processing method
(Patent Document 2). Since the composition of the produced alloy is
limited to the single phase region in the vicinity of Ti-50 atomic
%, however, the alloy has a defect that the output force is small.
[0005] Patent Document 1: JP-B-2899682 [0006] Patent Document 2:
JP-A-H06-172886
Non-Patent Document 1
[0007] [Transformation and Deformation Behavior in
Sputter-Deposited Ti--Ni--Cu Thin Films], T. Hashinaga, S.
Miyazaid, T. Ueki and H. Hirokawa: J. Physique IV, 5(1995),
C8-689
Non-Patent Document 2
[0008] "Structure Evolution in Sputtered Thin Films of Tix(Ni,
Cu)1-x" [1: Diffusive transformations], [2: Displace
Transformations], L. Chang and D. S. Grumman: Philosophical
Magazine A 76(1997), 163-219
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0009] As described in the foregoing, since the conventional shape
memory alloy thin film are sensitive to composition variations and
heat treatment conditions, it has been difficult to properly
control their composition and heat treatment conditions. Further,
with the customarily employed sputtering method, it has not been
easy to obtain a uniform distribution of the alloy composition in
the plane direction thereof and to produce such films in a
satisfactory yield. It has been, therefore, difficult to produce
shape memory alloy thin films on an industrial scale. Further,
since various treatments for increasing the output force of a shape
memory alloy tend to lower the transformation temperature and
ductility of the alloy, it has been difficult to produce a shape
memory alloy which has a high transformation temperature and a
large output force and, yet which has useful ductility.
[0010] In this circumstance, the objective of the present invention
is to provide a ternary Ti--Ni--Cu shape memory alloy which has
solved the above-described problems, which has low composition
dependency, which permits stable production, which has a
transformation temperature higher than ambient temperature and
which can generate a large output force, and to provide a process
capable of producing such a ternary Ti--Ni--Cu shape memory alloy
in an efficient manner.
Means for Solving the Problems
[0011] In accomplishing the foregoing objects, there is provided in
accordance with a first aspect of the present invention a ternary
Ti--Ni--Cu shape memory alloy comprising from 44 to 49 atomic % of
Ti, from 20 to 30 atomic % of Cu, and the balance being Ni and
unavoidable elements.
[0012] In a second aspect, the present invention provides the above
alloy, wherein a TiNiCu or TiCu phase of not greater than 500 nm is
formed within Ti(Ni, Cu) crystal grains having a grain size of 2
.mu.m or less.
[0013] In a third aspect, the present invention provides a process,
which comprises beating an amorphous Ti--Ni--Cu alloy comprising
from 44 to 49 atomic % of Ti, from 20 to 30 atomic % of Cu, and the
balance being Ni and unavoidable elements to crystallize the
amorphous Ti--Ni--Cu alloy.
[0014] In a fourth aspect, the present invention provides the above
process, wherein said heating is at a temperature in the range of
from 500 to 700.degree. C.
[0015] In a fifth aspect, the present invention provides the above
process, wherein said heating is performed for a period of time not
exceeding 100 hours.
Effect of the Invention
[0016] The ternary Ti--Ni--Cu shape memory alloy according to the
present invention has low composition or heat treatment dependency
and a transformation temperature higher than ambient temperature
and is capable of being produced in a stable manner. The shape
memory alloy is useful as a device used, for example, in an
actuator.
[0017] The present invention also provides a process capable of
producing the above ternary Ti--Ni--Cu shape memory alloy in an
efficient manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows shape memory characteristics of a 48.3 Ti-27.8
Cu--Ni alloy obtained by heat treatment at 600.degree. C. for 1
hour.
[0019] FIG. 2 is a microphotograph showing the structure of a 48.3
Ti-27.8 Cu--Ni alloy obtained by heat treatment at 600.degree. C.
for 1 hour.
[0020] FIG. 3 shows Ti content dependence and Cu content dependence
of the output force generated by a Ti--Ni--Cu alloy obtained by
heat treatment at 600.degree. C. for 1 hour.
[0021] FIG. 4 shows Ti content dependence and Cu content dependence
of the martens tic transformation temperature of a Ti--Ni--Cu alloy
obtained by beat treatment at 600.degree. C. for 1 hour.
[0022] FIG. 5 shows heat treatment temperature dependence (for a
heat treatment time of 1 hour) and heat treatment time dependence
(for a heat treatment temperature of 600.degree. C.) of the output
force generated by Ti--Ni--Cu alloys of various compositions.
[0023] FIG. 6 shows heat treatment temperature dependence (for a
heat treatment time of 1 hour) and heat treatment time dependence
(for a heat treatment temperature of 600.degree. C.) of the
martensitic transformation temperature of Ti--Ni--Cu alloys of
various compositions.
[0024] FIG. 7 shows heat treatment temperature dependence (for a
heat treatment time of 1 hour) and heat treatment time dependence
(for a heat treatment temperature of 600.degree. C.) of the
temperature hysteresis of Ti--Ni--Cu alloys of various
compositions.
DESCRIPTION OF REFERENCE NUMERALS
[0025] 1: grain boundary precipitates [0026] 2: precipitates within
grains
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] In the studies on ternary Ti--Ni--Cu alloys of B 19
structure in which the change in crystal structure is small, it has
been found that a ternary Ti--N--Cu shape memory alloy exhibiting,
in a stable maimer without being influenced by the alloy
composition or heat treatment conditions, transformation at a
temperature higher than ambient temperature and capable of
generating a large output force can be obtained by adopting, in
combination, enrichment of precipitates and solid solution
hardening-in addition to microsize of grains (suppressing the grain
size up to about 2 .mu.m) which alone would cause lowering of the
transformation temperature. The present invention has been
completed based on the technical finding.
[0028] A large output force generated by the ternary Ti--Ni--Cu
shape memory alloy according to the present invention is considered
to be ascribed to the synergetic effect among the solid solution
hardening by Cu atom, the precipitation of a TiNiCu phase or a TiCu
phase within the Ti(Ni, Cu) crystal grains, and the microsize of
the Ti(Ni, Cu) crystal grains. When the heat treatment is carried
out at a high temperature for an excessively long period of time,
however, the size of the crystal grains increases and the formation
of such precipitates within the crystal grains decreases and,
therefore, a high output force could not be obtained. For this
reason, the heat treatment is preferably carried out at 500 to
700.degree. C. for 100 hours or less.
[0029] In the process for producing a ternary Ti--Ni--Cu shape
memory alloy according to the present invention, an amorphous
Ti--Ni--Cu alloy composed of Ti in an amount of from 44 to 49
atomic %, Cu in an amount of from 20 to 30 atomic %, and the
balance being Ni and unavoidable elements is heated at a
temperature from 500 to 700.degree. C. for a period of time not
exceeding 100 hours. The reasons for specifying the contents of the
above elements are as follows. When the Ti content exceeds 49
atomic %, a TiNiCu phase which is one of the factors to increase
the output force of the ternary Ti--Ni--Cu shape memory alloy is
not formed. When the Ti content is less than 44 atomic %, on the
other hand, the TiNiCu phase increases excessively to cause not
only lowering of the transformation temperature but also
brittleness of the alloy. Therefore, the Ti content should be
within the range of from 44 to 49 atomic %. When the Cu content
exceeds 30 atomic %, only a TiCu phase is formed and the alloy
becomes brittle. On the other hand, when the Cu content is less
than 20 atomic %, the transformation temperature is lowered so that
it is no longer possible to ensure a transformation temperature
higher than ambient temperature (suitably 40.degree. C. or higher)
in a stable manner throughout the entire range of 49 to 44 atomic %
of the Ti content. Further, a large output force cannot be obtained
because the solid solution hardening by Cu is insufficient and the
grain size becomes large. Therefore, the Cu content should be
within the range of from 20 to 30 atomic %. The following example
will further specifically illustrate the ternary Ti--Ni--Cu shape
memory alloy and its production process.
EXAMPLE
[0030] Amorphous alloy thin films of 48.3 atomic % Ti-23.3 atomic %
Cu--Ni; 48.3 atomic % Ti-27.8 atomic % Cu--Ni; 44.6 atomic %
Ti-23.2 atomic % Cu--Ni; and 44.9 atomic % Ti-27.3 atomic % Cu--Ni
were produced using a multi-target magnetron sputtering system.
Such amorphous thin films may be produced not only by sputtering
but also by using any other suitable method. Each of the amorphous
thin films was peeled off from a substrate and subjected to a heat
treatment at 500 to 700.degree. C. The obtained alloy films were
measured for their transformation temperature by differential
thermal analysis and for their shape memory characteristics by
heating and cooling under a loaded state.
[0031] FIG. 1 shows an example of the measured results of shape
memory characteristics, from which it is seen that almost no
residual strain remains upon cooling and heating under a high load
stress and that the transformation temperature is higher than
ambient temperature.
[0032] FIG. 2 is an electron microphotograph showing the structure
of one of the obtained ternary Ti--Cu--Ni shape memory alloys.
Thermally stable, micro-size (500 nm or less) TiCu phase 1 or
TiNiCu phase 2 is formed within the crystal grains or in the grain
boundaries. The crystal grain size is limited to not greater than 2
.mu.m. As a result of synergism among the promotion of microsize
crystal grains, the enrichment of precipitates within grains and
the solid solution hardening by Cu, it is possible to improve
brittleness common to cast alloys and, at the same time, to obtain
a high resistance to plastic deformation which would cause residual
strains.
[0033] FIG. 3 shows composition dependence of the output force
generated by one of the obtained ternary Ti--Cu--Ni shape memory
alloys. The output force is represented by the stress causing a
residual strain of at least 0.03%. It is seen that when the Cu
content is 20 atomic % or higher, a high output force is obtained
in a stable manner throughout the composition range of 49 to 44
atomic % Ti. It is also seen that, because of the formation of
precipitates, the 48.3 atomic % Ti-23.3 atomic % Cu--Ni alloy shows
a higher output force as compared with 50 atomic % Ti-23.3 atomic %
Cu--Ni alloy and that, because of the solid solution hardening by
Cu, the 48.3 atomic % Ti-23.3 atomic % Cu--Ni alloy shows a higher
output force as compared with 48.3 atomic % Ti-11.5 atomic % Cu--Ni
alloy. A TiNiCu phase and a TiCu phase precipitated in large
amounts when the Ti content was less than 44 atomic % and when the
Cu content exceeded 30 atomic %, respectively. Therefore, in either
case, good shape memory alloys were not obtainable due to
breakage.
[0034] FIG. 4 shows composition dependence of the transformation
temperature (peak temperature). While ordinary shape memory alloys
will cause a reduction of the transformation temperature if the
composition is altered to obtain a high output force, a
transformation temperature higher than ambient temperature is found
to be obtained throughout the composition range of 49 to 45 atomic
% Ti when the Cu content is in the range of 20 to 30 atomic %.
[0035] It has been confirmed that any of the above-described thin
films of the ternary Ti--Ni--Cu shape memory alloy forms a low
temperature phase (B19 phase) in the unloaded state at ambient
temperature. FIG. 5 shows heat treatment dependence of the output
force generated. It is appreciated that a high output force is
obtainable in a wide range of heat treatment conditions.
[0036] However, the output force tends to lower when heat treatment
time is prolonged and the heat treatment temperature is increased.
The heat treatment at 500 to 700.degree. C. for 100 hours or less
is found to be preferred.
[0037] FIG. 6 shows beat treatment dependence of the martensitic
transformation temperature. All of the alloys had a martensitic
transformation temperature higher than ambient temperature. FIG. 7
shows the temperature hysteresis of the ternary Ti--Ni--Cu alloys.
The temperature hysteresis of the transformation of any of the
alloys is as small as 7 to 15.degree. C.
* * * * *