U.S. patent application number 10/810838 was filed with the patent office on 2004-09-16 for ti-ni-based shape-memory alloy and method of manufacturing same.
Invention is credited to Kajiwara, Setsuo, Kikuchi, Takehiko, Matsunaga, Takeshi, Miyazaki, Shuichi, Ogawa, Kazuyuki.
Application Number | 20040177904 10/810838 |
Document ID | / |
Family ID | 13326880 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040177904 |
Kind Code |
A1 |
Kajiwara, Setsuo ; et
al. |
September 16, 2004 |
Ti-Ni-based shape-memory alloy and method of manufacturing same
Abstract
To remarkably improve shape-memory properties without the need
for strictly controlling the composition, the present invention
provides a Ti--Ni-based shape-memory alloy having a titanium
content within a range of from 50 to 55 atomic %, which comprises
an amorphous alloy heat-treated at a temperature of from 600 to 800
K, in which subnanometric precipitates generating coherent elastic
strains are formed and distributed in the bcc parent phase(B2).
Inventors: |
Kajiwara, Setsuo; (Ibaraki,
JP) ; Kikuchi, Takehiko; (Ibaraki, JP) ;
Ogawa, Kazuyuki; (Ibaraki, JP) ; Miyazaki,
Shuichi; (Ibaraki, JP) ; Matsunaga, Takeshi;
(Ibaraki, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
13326880 |
Appl. No.: |
10/810838 |
Filed: |
March 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10810838 |
Mar 29, 2004 |
|
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10281143 |
Oct 28, 2002 |
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10281143 |
Oct 28, 2002 |
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09808046 |
Mar 15, 2001 |
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09808046 |
Mar 15, 2001 |
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09325017 |
Jun 3, 1999 |
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09325017 |
Jun 3, 1999 |
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08768467 |
Dec 18, 1996 |
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6001195 |
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Current U.S.
Class: |
148/563 |
Current CPC
Class: |
C22C 45/10 20130101;
C22C 45/04 20130101; C22F 1/006 20130101; Y10S 977/891 20130101;
C22C 14/00 20130101 |
Class at
Publication: |
148/563 |
International
Class: |
C22F 001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 1996 |
JP |
066820/1996 |
Claims
What is claimed is:
1. A method of manufacturing a Ti--Ni-based shape-memory alloy
having a titanium content within a range of from 50 to 66 atomic %,
which comprises the step of forming and distributing a
nanometer-scale precipitate generating a coherent elastic strain in
a mother phase through a heat treatment of an amorphous
Ti--Ni-based alloy at a temperature within a range of from 600 to
800 K.
2. The manufacturing method as claimed in claim 1, wherein said
heat treatment is carried out in a single run.
3. The manufacturing method as claimed in claim 1, wherein said
alloy is in a thin film shape.
4. The manufacturing method as claimed in claim 2, wherein said
alloy is in a thin film shape.
Description
[0001] This is a continuation of Ser. No. 10/281,143, filed Oct.
28, 2002, abandoned, which is a continuation of Ser. No.
09/808,046, filed Mar. 15, 2001, abandoned, which is a continuation
of Ser. No. 09/325,017, filed Jun. 3, 1999, abandoned, which is a
divisional of Ser. No. 08/768,467, filed Sep. 18, 1996, now U.S.
Pat. No. 6,001,195.
FIELD OF THE INVENTION
[0002] The present invention relates to a Ti--Ni-based shape-memory
alloy and a method of manufacturing same. More particularly, the
present invention relates to a novel Ti--Ni-based shape-memory
alloy which is useful as an actuator for a micro-valve or a
micro-machine without the need for a strict control of composition
and which has a largely improved shape-memory property, and a
method of manufacturing same.
PRIOR ART AND PROBLEMS
[0003] As an alloy having shape-memory properties, Ti--Ni-based
alloy has conventionally been known. A method of manufacturing this
Ti--Ni-based alloy into a thin-film alloy is also known.
[0004] The thin-film shape-memory alloy is expected to be
applicable to various precision areas. In the case of Ti--Ni-based
shape-memory alloy thin film, a method for improving shape-memory
properties such as shape recovering ability and recovery strain is
known, which comprises crystallizing an amorphous alloy thin film
vapor-deposited by sputtering, for example, by annealing the thin
film at a temperature higher than the crystallization temperature,
and then heat-treating the film at various temperatures.
[0005] However, the conventional technique has problems such that
the improving effect of shape-memory properties is not sufficient,
that the above-mentioned method for improving these properties
requires strict control of the chemical composition of the
Ti--Ni-based alloy, and furthermore, that two-stage heat treatments
are required. Under such circumstances, therefore, it is very
difficult even to obtain a limited improvement of shape-memory
properties and to reduce the manufacturing cost.
[0006] Therefore, the present invention has an object to provide a
novel Ti--Ni-based shape-memory alloy which overcomes these
drawbacks in the conventional technology as described above and
allows remarkable improvement of shape-memory properties by a
simple means, and a method of manufacturing same.
SUMMARY OF THE INVENTION
[0007] As means to solve the above-mentioned problems, the present
invention provides a Ti--Ni-based shape-memory alloy having a
titanium content within a range of from 50 to 66 atomic %, wherein
subnanometric precipitates generating coherent elastic strains in
the parent phase are distributed.
[0008] Further, the present invention provides also a method of
manufacturing the above-mentioned alloy, which comprises the step
of heat-treating an amorphous Ti--Ni-based alloy at a temperature
within a range of from 600 to 800 K.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 shows a high-resolution electron photomicrograph
illustrating the structure of an alloy thin film as an example of
the present invention.
[0010] FIG. 2 shows an enlarged micrograph of the framed region of
FIG. 1, revealing subnanometric plate precipitates and coherent
elastic strains.
[0011] FIG. 3 shows various curves illustrating the results of
thermal cycle tests under constant loads.
[0012] FIG. 4 shows a curve illustrating the relationship between
maximum shape recovery strain and the heat treatment
temperature.
[0013] FIG. 5 shows the relationship between a load (external
stress) and shape recovery strain for various heat treatment
temperature.
[0014] FIG. 6 shows the relationship between critical stress for
slip and the heat treatment temperature.
DETAILED DESCRIPTION OF THE INTENTION
[0015] The present invention makes it possible to remarkably
improve shape-memory properties such as shape recovering ability
and recovery strain through the construction as described
above.
[0016] As to the chemical composition itself of the alloy, other
elements may be added or mixed as impurities to this alloy
comprising Ti (titanium) and Ni (nickel), so far as these elements
do not impair the shape-memory properties of the invention.
[0017] With a titanium content of under 50 atomic %, it becomes
difficult to achieve the object of the invention, and it is also
the case with a titanium content of over 66 atomic %.
[0018] In the target alloy, a special nanometer-scale precipitate
is distributed in the parent phase thereof, and this precipitate
produces a coherent elastic strain between the precipitate and the
parent phase. The term "coherent elastic strain" as herein used
means an elastic strain caused by connection of the slightly
different crystal lattice of the precipitate with that of the
parent phase. In the present invention, an alloy having such a
feature is manufactured by applying a heat treatment to an
amorphous alloy at a temperature within a range of from 600 to 800
K.
[0019] The heat treatment temperature is limited within the range
of from 600 to 800 K, and the specimen must be heated directly from
the amorphous state, in the present case, from the as-deposited
state. Typical heat treatment conditions are, for example, as
follows:
[0020] Time: 10 minutes to 3 hours
[0021] Atmosphere: Vacuum or an inert gas such as argon
[0022] Heating rate: 5 to 50 K/minute
[0023] Cooling: Rapid cooling.
[0024] Needless to mention, these conditions are not limitative. In
the already crystallized Ti--Ni-based alloy, generation and
distribution of the above-mentioned precipitate are not observed by
this heat treatment, and a remarkable improvement of properties is
unavailable. With a temperature of over 800 K, an appropriate
precipitate is not formed. With a temperature of under 600 K,
diffusion of atoms becomes slower, and no precipitate is generated
within a practicable period of time. In both cases, a remarkable
improving effect of the properties is unavailable.
[0025] The amorphous Ti--Ni-based alloy may be manufactured, for
example, by the vapor deposition process into a thin film, or by
any other appropriate method, and there is no particular limitation
in this respect.
[0026] It should particularly be noted that the alloy of the
invention in the form of a thin film is expected to be used in such
applications as an actuator for a micro-valve or a micro-machine
hereafter, and is therefore a very important material. The
manufacturable thin film thickness covers a range from under 5
.mu.m to 10 .mu.m in general.
[0027] The alloy and the manufacturing method thereof of the
present invention are now described further in detail by means of
examples. The invention is not, however, limited by the following
examples.
EXAMPLES
[0028] Using a Ti--Ni target material, thin films of an amorphous
Ti--Ni alloy containing 48.2 atomic % Ni were formed on a glass
substrate by argon ion sputtering. The thickness of the films was
about 7 .mu.m and its composition was determined by electron probe
X-ray microanalysis.
[0029] A thin film heat-treated at 745 K for 1 hr was observed by
means of a high-resolution electron microscope. FIG. 1 illustrates
an example of electronmicrograph thereof. FIG. 2 is an enlarged
micrograph thereof. As is known from the micrographs of FIGS. 1 and
2, a number of thin plate precipitates are produced and distributed
in the parent phase. These precipitates appear along the {100}bcc
plane of the parent phase bcc(B2 type), and take the form of a disk
having a thickness of about 0.5 nm (2 to 3 lattice planes) and a
radius of from about 5 to 10 nm. The precipitates are distributed
at intervals of about 10 nm, i.e., in a nanometer scale. The
precipitate was confirmed to be Ti-rich by EDS analysis of field
emission electron microscope.
[0030] For a specimen heat-treated at 765 K for 1 hr, changes in
elongation were evaluated through thermal cycles under various
loads. This specimen contained the same kind of precipitates as
mentioned above. FIG. 3 shows the result. As shown in this figure,
there is no permanent strain under loads of up to 240 MPa, and a
large shape recovery strain as 6% is available.
[0031] FIG. 4 illustrates the result of evaluation of the
relationship between the heat-treatment temperature and the maximum
shape recovery strain, indicating availability of a recovery strain
of 5 to 6% through an annealing at a temperature within a range of
from 700 to 800 K.
[0032] FIG. 5 shows the relationship between shape recovery strain
and stress under load, various heat treatments.
[0033] FIG. 5 reveals that a recovery strain of at least 4.5% is
obtained with a stress range of from 200 to 670 MPa. The maximum
loadable stress is 670 MPa.
[0034] FIG. 6 illustrates the effect of the heat-treatment
temperature on the maximum stress loadable within a range in which
a permanent strain (slip deformation) is not introduced into the
sample.
[0035] It is confirmed, from the example as described above, that
the invention permits remarkable improvement of shape-memory
properties as compared with the conventional process.
[0036] According to the present invention, shape-memory properties
are remarkably improved through a heat-treatment at a temperature
of from 600 to 800 K without the need for strictly controlling the
composition or heat treatment. It is also possible to largely
reduce the manufacturing cost.
* * * * *