U.S. patent application number 10/001950 was filed with the patent office on 2002-08-22 for ni-ti-cu shape memory alloy electrothermal actuator element.
Invention is credited to Horikawa, Hiroshi, Iwasaki, Keizo, Mitose, Kengo, Tanaka, Toyonobu.
Application Number | 20020112788 10/001950 |
Document ID | / |
Family ID | 18844179 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020112788 |
Kind Code |
A1 |
Tanaka, Toyonobu ; et
al. |
August 22, 2002 |
Ni-Ti-Cu shape memory alloy electrothermal actuator element
Abstract
An Ni--Ti--Cu shape memory alloy electrothermal actuator element
that recovers its original shape by electrical heating, having a
wire diameter of 0.5 mm or less, comprising an Ni--Ti--Cu shape
memory alloy wire which contains 49.0 to 51.0 at % of Ti, and 5.0
to 12.0 at % of Cu, with the balance being made of Ni, wherein the
actuator element has a deterioration rate of shape strain recovery
of 0.5% or less after repeating desired times of shape recovery
movement.
Inventors: |
Tanaka, Toyonobu; (Kanagawa,
JP) ; Horikawa, Hiroshi; (Kanagawa, JP) ;
Iwasaki, Keizo; (Kanagawa, JP) ; Mitose, Kengo;
(Tokyo, JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
18844179 |
Appl. No.: |
10/001950 |
Filed: |
October 22, 2001 |
Current U.S.
Class: |
148/402 |
Current CPC
Class: |
C22C 19/03 20130101;
C22F 1/006 20130101 |
Class at
Publication: |
148/402 |
International
Class: |
C22C 019/03 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2000 |
JP |
2000-375117 |
Claims
What is claimed is:
1. An Ni--Ti--Cu shape memory alloy electrothermal actuator element
that recovers its original shape by electrical heating, having a
wire diameter of 0.5 mm or less, comprising an Ni--Ti--Cu shape
memory alloy wire which contains 49.0 to 51.0 at % of Ti, and 5.0
to 12.0 at % of Cu, with the balance being made of Ni, wherein the
actuator element has a deterioration rate of shape strain recovery
of 0.5% or less after repeating desired times of shape recovery
movement.
2. The Ni--Ti--Cu shape memory alloy electrothermal actuator
element as claimed in claim 1, wherein the Cu content of the
Ni--Ti--Cu shape memory alloy is 6.0 to 8.0 at %.
3. The Ni--Ti--Cu shape memory alloy electrothermal actuator
element as claimed in claim 1, wherein the Ni--Ti--Cu shape memory
alloy wire is heat-treated to achieve memorization of its original
shape at a temperature in the range from 400 to 600.degree. C.
4. The Ni--Ti--Cu shape memory alloy electrothermal actuator
element as claimed in claim 2, wherein the Ni--Ti--Cu shape memory
alloy wire is heat-treated to achieve memorization of its original
shape at a temperature in the range from 400 to 600.degree. C.
5. An Ni--Ti--Cu shape memory alloy electrothermal actuator
element, wherein the wire in the actuator element as claimed in
claim 1 is subjected to repeating cycles of heating to a
temperature of Af or higher with applying a weight load
corresponding to 10 to 30% of a breaking load of the wire, and
cooling to a temperature of Mf (a finishing temperature of
Martensitic transformation) or lower, and wherein the deterioration
rate of shape strain recovery after repeating desired times of
shape recovery movement is 0.2% or less.
6. An Ni--Ti--Cu shape memory alloy electrothermal actuator
element, wherein the wire in the actuator element as claimed in
claim 2 is subjected to repeating cycles of heating to a
temperature of Af or higher with applying a weight load
corresponding to 10 to 30% of a breaking load of the wire, and
cooling to a temperature of Mf or lower, and wherein the
deterioration rate of shape strain recovery after repeating desired
times of shape recovery movement is 0.2% or less.
7. An Ni--Ti--Cu shape memory alloy electrothermal actuator
element, wherein the wire in the actuator element as claimed in
claim 3 is subjected to repeating cycles of heating to a
temperature of Af or higher with applying a weight load
corresponding to 10 to 30% of a breaking load of the wire, and
cooling to a temperature of Mf or lower, and wherein the
deterioration rate of shape strain recovery after repeating desired
times of shape recovery movement is 0.2% or less.
8. An Ni--Ti--Cu shape memory alloy electrothermal actuator
element, wherein the wire in the actuator element as claimed in
claim 4 is subjected to repeating cycles of heating to a
temperature of Af or higher with applying a weight load
corresponding to 10 to 30% of a breaking load of the wire, and
cooling to a temperature of Mf or lower, and wherein the
deterioration rate of shape strain recovery after repeating desired
times of shape recovery movement is 0.2% or less.
Description
FIELD
[0001] The present invention relates to an Ni--Ti--Cu shape memory
alloy electrothermal actuator element.
BACKGROUND
[0002] A shape memory alloy actuator element is, for example, a
linear wire that memorizes its original length. The element can
repeat a reciprocating movement to cause a prescribed strain at
room temperature, and to recover to its original memorized length
at a temperature of Af (a finishing temperature of reverse
transformation) or higher, under a weight load.
[0003] Meanwhile, an Ni--Ti shape memory alloy wire has been used
as the above-described conventional shape memory alloys. However,
there is a problem that this material results some degree of
permanent strain after repeating the above-described reciprocating
movements many times, thereby causing a certain degree of strain at
room temperature that finally leads the material to failure in
recovery of its original memorized length at a temperature of Af or
higher (hereinafter, this phenomenon is referred to as increasing
of a deterioration rate of shape strain recovery).
[0004] To solve the problem described above, alloy wires having a
small deterioration rate of shape strain recovery have been sought,
and thus an Ni--Ti--Cu shape memory alloy wire has been proposed
(JP-A-2-116786 ("JP-A" means unexamined published Japanese patent
application)). However, this wire has the problem that its
deterioration rate of shape strain recovery cannot be sufficiently
reduced, and that its response speed is still slow, since heating
of actuator elements using this alloy wire to recover its original
shape is operated through water or air as a medium.
SUMMARY
[0005] The present invention is an Ni--Ti--Cu shape memory alloy
electrothermal actuator element that recovers its original shape by
electrical heating, having a wire diameter of 0.5 mm or less, which
actuator element is composed of an Ni--Ti--Cu shape memory alloy
wire which contains 49.0 to 51.0 at % of Ti, and 5.0 to 12.0 at %
of Cu, with the balance being made of Ni, wherein the actuator
element has a deterioration rate of shape strain recovery of 0.5%
or less after repeating desired times of shape recovery
movement.
[0006] Other and further features and advantages of the invention
will appear more fully from the following description, take in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1(A) and FIG. 1(B) each are a schematic view
illustrating an electrical heating fatigue testing machine; FIG.
1(A) represents the state when electrical heating, and FIG. 1(B)
represents the state when standing to cool.
[0008] FIG. 2 is a schematic view illustrating deterioration rates
of shape strain recovery .alpha. and .beta., and a shape recovery
strain rate .gamma..
DETAILED DESCRIPTION
[0009] According to the present invention, there is provided the
following means:
[0010] (1) An Ni--Ti--Cu shape memory alloy electrothermal actuator
element that recovers its original shape by electrical heating,
having a wire diameter of 0.5 mm or less, comprising an Ni--Ti--Cu
shape memory alloy wire which contains 49.0 to 51.0 at % of Ti, and
5.0 to 12.0 at % of Cu, with the balance being made of Ni, wherein
the actuator element has a deterioration rate of shape strain
recovery of 0.5% or less after repeating desired times of shape
recovery movement;
[0011] (2) The Ni--Ti--Cu shape memory alloy electrothermal
actuator element according to item (1), wherein the Cu content of
the Ni--Ti--Cu shape memory alloy is 6.0 to 8.0 at %;
[0012] (3) The Ni--Ti--Cu shape memory alloy electrothermal
actuator element according to item (1) or (2), wherein the
Ni--Ti--Cu shape memory alloy wire is subjected to a shape memory
heat-treatment at a temperature in the range from 400 to
600.degree. C.; and
[0013] (4) An Ni--Ti--Cu shape memory alloy electrothermal actuator
element, wherein the wire in the actuator element according to any
one of items (1) to (3) is subjected to repeating cycles of heating
to a temperature of Af or higher with applying a weight load
corresponding to 10 to 30% of a breaking load of the wire, and
cooling to a temperature of Mf (a finishing temperature of
Martensitic transformation) or lower, and wherein the deterioration
rate of shape strain recovery after repeating desired times of
shape recovery movement is 0.2% or less.
[0014] The actuator element of the present invention composed of an
Ni--Ti--Cu shape memory alloy. Cu, which is one of elements of the
alloy, functions for reducing the deterioration rate of shape
strain recovery and accelerating the response speed.
[0015] The Cu content is restricted within the range of 5.0 to 12.0
at % because a sufficient effect cannot be attained at the Cu
content of less than 5.0 at %, and on the other hand, in case of
the Cu content of more than 12.0 at %, the workability of the alloy
becomes poor, further the shape recovery strain rate (the
difference between the strain rate when heating, and the strain
rate when cooling, under a weight load) is reduced. Cu content of
6.0 to 8.0 at % is particularly preferable for further increasing
the shape recovery strain rate and stable recovering the original
shape of the resultant actuator element.
[0016] The Ti content is restricted within the range of 49.0 to
51.0 at % because workability of the arroy becomes poor outside the
above-described range of Ti content.
[0017] In the present invention, a heating for shape recovery is
conducted by electrical heating, this is because according to the
electrical heating, the heating speed is high (a response speed is
high), heating operation is simple, the heating speed can be freely
controlled by changing the electrothermal current, and the
like.
[0018] On the other hand, in the electrical heating, the
temperature distribution tends to be ununiform because heating rate
is so fast. Accordingly, the fatigue of the wire is easy to occur.
However, this defect was solved in the present invention by
thinning down the wire diameter to 0.5 mm or less. When the wire
diameter is thinned down to 0.5 mm or less, it permits the
deterioration rate of shape strain recovery to be reduced and the
response time to be shortened since the heating and cooling rates
of the shape memory alloy wire are increased.
[0019] The Ni--Ti--Cu shape memory alloy wire that can be used in
the actuator element of the present invention, is used as a liner
shape, or another arbitrary shape such as a coiled shape. A linear
actuator element permits a current density, a temperature
distribution, and a stress distribution, when electrical heating,
to be uniform, because of the simple shape thereof, thereby
allowing the actuator to be widely designed.
[0020] The actuator element of the present invention is used by
moving within a narrow strain width (within a narrow temperature
hysteresis width) close to an elasticity range, and amplifying the
movement. By that, the deterioration rate of shape strain recovery
can be further reduced, the lifetime of the actuator element can be
prolonged, and reproducibility of the movement can be improved. The
amplification of the above-described movement is attained, for
example, by the coil shape-actuator element.
[0021] The Ni--Ti--Cu shape memory alloy wire to be used in the
present invention can be manufactured in a usual manner by
sequentially applying hot-working, cold-drawing, shaping, and
shape-memory-heat-treatment, in this order, to an ingot of the
Ni--Ti--Cu shape memory alloy. Intermediate annealing can be
appropriately applied in the cold-drawing divided into two-steps. A
final cold-drawn ratio of 15 to 60% is preferable since the shape
recovery strain rate increases in this range of the ratio. The
temperature for the above-described shape memory heat-treatment is
preferably in the range of 400 to 600.degree. C., since a
sufficient shape recovery strain rate may not be obtained in some
cases when the heat-treatment temperature is too low or too
high.
[0022] The deterioration rate of shape strain recovery of the
Ni--Ti--Cu alloy actuator element according to any one of the
above-described items (1) to (3) is somewhat large at an initial
stage of strain. The present invention according to the
above-described item (4) is an actuator element, wherein the above
initial somewhat large deterioration rate is previously alleviated,
by applying a pre-treatment, in which the above-described
Ni--Ti--Cu shape memory alloy wire is "subjected repeatedly to
heating and cooling processes to heat the wire to a temperature of
Af or higher, and to cool the wire to a temperature of Mf or lower,
under a weight load", and thereby the deterioration rate of shape
strain recovery of the actuator element when it is used is improved
to 0.2% or less.
[0023] When the weight load in the above-described pre-treatment is
so large that the wire receives a plastic deformation, the wire is
largely damaged, and the shape recovery strain rate is reduced. On
the other hand, when the weight load is too small, a sufficient
effect by the pre-treatment cannot be obtained. Accordingly, it is
preferable to apply the above-described weight load corresponding
to 10 to 30%, particularly preferably 15 to 25%, of the wire's
breaking load.
[0024] The actuator element can be heated to a temperature of Af or
higher in the above-described pre-treatment, according to an
arbitrary method such as electrical heating or heating in a
furnace. Since a too high heating temperature damages the wire
largely, and reduces the shape recovery strain rate, the preferable
temperature is in the range of {Af+(10 to 50)}.degree. C. The wire
may be non-forcibly cooled (stood to cool) at a temperature of Mf
or lower sufficiently, but it may be forced to cool by, for
example, blowing air, since the wire has a small diameter.
[0025] Since the actuator element of the present invention is
composed of the Ni--Ti--Cu shape memory alloy wire having a small
diameter that can recover its original shape by electrical heating,
it has a small deterioration rate of shape strain recovery and also
has a rapid response time. According to the actuator element of a
preferable embodiment of the present invention, wherein the Cu
content is further controlled to be in the preferable range of 6.0
to 8.0 at %, or wherein the temperature for the shape memory
heat-treatment is controlled within the preferable range of 400 to
600.degree. C., or wherein the wire for the actuator element is
pre-treated by repeatedly heating/cooling a plurality of times to
heat to a temperature of Af or higher and to cool to a temperature
of Mf or lower, with applying a weight load corresponding to 10 to
30% of the breaking load, thereby the deterioration rate of shape
strain recovery can be further reduced. Accordingly the present
invention exhibits industrial remarkable effects.
[0026] The present invention will be explained in more detail
referring to the following examples, but the invention is not
limited thereto.
EXAMPLE
Example 1
[0027] Hot-working was applied to an ingot of a Ni--Ti--Cu alloy
having a composition defined in the present invention, as shown in
Table 1, then a wire of the resultant Ni--Ti--Cu alloy was
manufactured by applying cold-drawing, with an appropriate
intermediate annealing between the steps of the cold-drawing. The
diameter of the thus-obtained wire was adjusted to 0.05, 0.20, or
0.50 mm. The final cold-drawing ratio was 40% in each cases.
Comparative Example 1
[0028] The wires of Ni--Ti--Cu alloys were manufactured in the same
manner as in Example 1, except that ingots of Ni--Ti--Cu alloys
with compositions outside the definition in the present invention,
as shown in Table 1, were used, respectively (Sample Nos. 8 and
10).
Comparative Example 2
[0029] The wire of a Ni--Ti--Cu alloy was manufactured in the same
manner as in Example 1, except that the diameter of the wire was
adjusted to 0.80 mm (Sample No. 9).
Comparative Example 3
[0030] The wires of Ni--Ti alloys were manufactured in the same
manner as in Example 1, except that ingots of Ni--Ti alloys with
compositions, as shown in Table 1, were used, respectively (Sample
Nos. 6 and 7).
[0031] The Sample No. 10 wire, among the wires obtained in Example
1 and Comparative examples 1 to 3, contained so much Cu that
workability was poor, to fail in drawing to a wire with a desired
diameter of 0.5 mm.
[0032] The wires (Sample Nos. 1 to 9) other than the Sample No. 10
wire, were applied to the shape memory heat-treatment under the
conditions as shown in Table 1, to make the wires memorize their
original lengths. Then, the wires were subjected to cycle tests of
electrical heating and standing to cool, to determine a
deterioration rate of strain .alpha. when electrical heating and a
deterioration rate of strain .beta. when standing to cool, using an
electrical heating fatigue testing machine. Further, a shape
recovery strain rate .gamma. thereof at initial stage is also
determined.
[0033] The above-described deterioration rate .alpha. is the strain
rate when electrical heating after 1,000 cycles of the tests, and
the above-described deterioration rate .beta. is a value determined
by subtracting the strain rate when standing to cool at the initial
stage from the strain rate when standing to cool after 1,000 cycles
of the test, and the above-described shape recovery strain rate
.gamma. is the strain rate when standing to cool at the initial
stage (see FIG. 2). Further, the above-described deterioration
rates .alpha. and .beta. were almost saturated after 1,000 cycles
of the test, respectively.
[0034] The above-described electrical heating fatigue testing
machine 1 has a construction, in which the both ends of a shape
memory alloy wire (actuator element) 2 to be tested are held with
pressure connection terminals 3. As shown in FIGS. 1(A) and 1(B),
one of the pressure connection terminals 3 is connected to a SUS
sleeve shaft 5 through a holder 4, and tension is applied to the
shape memory alloy wire 2 by pulling the sleeve shaft 5 with a bias
spring 6.
[0035] The shape memory alloy wire 2 recovers its originally
memorized length, against the tension from the bias spring 6, as
shown in FIG. 1(A), by heating to a temperature of Af or higher.
When the wire is cooled to a temperature of Mf or lower, the
mechanical strength of the wire is reduced, and the wire occurs
strain (elongated) by yielding to the tension from the bias spring
6, as shown in FIG. 1(B). The shape memory alloy wire 2 is
electrically heated with an electrothermal device (not shown).
[0036] The test results are shown in Table 2, together with the
cycle test conditions.
1TABLE 1 Shape memory heat- Wire treatment condition Sample Alloy
Ti Cu diameter Temperature Time Classification No. No. (at %) (at
%) Ni (mm) (.degree. C.) (minute) Example 1 a 50.5 7.0 Balance 0.20
500 0.5 according to 2 b 50.5 9.0 Balance 0.05 500 0.5 this 3 b
50.5 9.0 Balance 0.20 500 0.5 invention 4 b 50.5 9.0 Balance 0.50
500 0.5 5 c 50.5 11.0 Balance 0.20 500 0.5 Comparative 6 f 50.0 0.0
Balance 0.05 500 0.5 example 7 f 50.0 0.0 Balance 0.20 500 0.5 8 g
50.5 3.0 Balance 0.20 500 0.5 9 b 50.5 9.0 Balance 0.80 500 0.5 10
h 50.5 13.0 Balance Impossible to work to a wire diameter of 0.5
mm. Note Sample Nos. 6 and 7 correspond to Comparative example 3.
Sample Nos. 8 and 10 correspond to Comparative example 1. Sample
No. 9 corresponds to Comparative example 2.
[0037]
2 TABLE 2 Deterioration rate Cycle test condition of shape recovery
Electro- strain Shape thermal Time for When When recovery Weight
current standing heated stood strain Sample Alloy load (A) .times.
time to cool electrically to cool rate .gamma. Classification No.
No. (MPa) (second) (second) .alpha. (%) .beta. (%) (%) Example 1 a
175 0.50 .times. 5 15 0.45 0.33 4.02 according to 2 b 275 0.10
.times. 5 5 0.09 0.01 4.23 this invention 3 b 175 0.50 .times. 5 15
0.13 0.02 3.78 4 b 175 2.00 .times. 10 25 0.35 0.43 4.15 5 c 175
0.50 .times. 5 15 0.06 0.03 3.51 Comparative 6 f 275 0.10 .times. 5
5 2.27 0.80 4.86 example 7 f 175 0.50 .times. 5 15 2.52 2.14 4.32 8
g 175 0.50 .times. 5 15 0.89 0.71 4.20 9 b 175 3.00 .times. 20 60
0.76 0.53 3.91 Note Sample Nos. 6 and 7 correspond to Comparative
example 3. Sample No. 8 corresponds to Comparative example 1.
Sample No. 9 corresponds to Comparative example 2.
[0038] As is apparent from the results in Table 2, the
deterioration rates of shape strain recovery .alpha. and .beta.
were as small as 0.5% or less in the sample Nos. 1 to 5 of examples
according to the present invention, even after repeating 1,000
times of the shape recovery movement. In other words, the wires
could almost recover their originally memorized length after 1,000
cycles of the test, indicating good shape recovery abilities. The
sample No. 1 had a larger shape recovery strain rate .gamma., as
compared with the sample Nos. 3 and 5, since the Cu content was
optimum in the sample No. 1.
[0039] On the contrary, both the sample Nos. 6 and 7 were poorly
large in the deterioration rates of shape strain recovery since Cu
was not contained in these samples. The deterioration rates of
shape strain recovery .alpha. and .beta. each were poorly large in
sample Nos. 8 and 9, respectively, because the Cu content in the
sample No. 8 was too small and the wire of the sample No. 9 was too
large in diameter.
Example 2
[0040] The wire of the sample No. 1 that was prepared in the same
manner as in Example 1 was subjected to a pre-treatment by
repeating ten times of cycles of heating in a furnace at a
temperature of 110.degree. C. (Af+25.degree. C.) for five seconds,
with applying a weight load of 300 MPa (22% of the breaking load),
and then standing to cool at room temperature for five seconds.
Then, the electrical heating fatigue test was conducted in the same
manner as in the Example 1. As a result, the deterioration rates
.alpha. and .beta. were reduced from 0.45% to 0.1%, and from 0.33%
to 0.02%, respectively, showing large improvements of the shape
recovery strain rates.
Example 3
[0041] The time required for deformation when standing to cool (the
response time) in the electrical heating fatigue test was
determined with respect to the sample Nos. 2 and 3 (Ni--Ti--Cu
shape memory alloys) and the sample Nos. 6 and 7 (Ni--Ti shape
memory alloys) that were prepared in the same manner as in Example
1. The results are shown in Table 3.
3TABLE 3 Wire Deformation Sample Alloy diameter time Classification
No. No. (mm) (second) Example 2 b 0.05 0.4 according to 3 b 0.20
11.9 this invention Comparative 6 f 0.05 0.6 example 7 f 0.20
14.1
[0042] As is apparent from the results in Table 3, the response
speeds of the samples according to the present invention (the
Sample Nos. 2 and 3) were much faster than those of the samples of
the comparative examples (the Samples Nos. 6 and 7) in case of both
0.05 mm and 0.20 mm of the wire diameter. This is because the
temperature hysteresis was quite small in the examples according to
the present invention, as a result of adding Cu.
[0043] Having described our invention as related to the present
embodiments, it is our intention that the invention not be limited
by any of the details of the description, unless otherwise
specified, but rather be construed broadly within its spirit and
scope as set out in the accompanying claims.
* * * * *