JPH06172886A - Ti-ni-cu shape memory alloy - Google Patents

Abstract

PURPOSE:To obtain a shape memory alloy having superior characteristics and excellent in corrosion resistance under the extremely severe environment of strong acidity or strong alkalinity by rapidly solidifying a molten Ti-Ni-Cu alloy of specific composition on a rotating roll at specific cooling rate. CONSTITUTION:This Ti-Ni-Cu shape memory alloy can be obtained by rapidly solidifying a molten Ti(50+ or -y, y<=2at%)-Ni(50-y-x)-Cu(x%) alloy. In the alloy, it is preferable to regulate Cu content (x) to 10-20%, particularly 11.0-16.0%, or to 3.0-7.0%. The rapid solidification of this alloy molten is done by using a rotating roll and regulating cooling rate to (20 to 50)m/sec. By using this Ti-Ni-Cu shape memory alloy, the final sheet products can be easily produced. Moreover, this alloy has sharp responsibility attendant on temp. changes and superior thermal-mechanical energy conversion efficiency and causes no deterioration in the shape memory effects during repeated use, and further, it can be used over a long period under the extremely severe environment of extremely strong acidity or alkalinity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ti-Ni-Cu-based shape memory alloy produced by a rapid solidification method, and in particular, a Ti-Ni-Cu based shape alloy having an optimally adjusted Cu content and quenching rate. It concerns memory alloys.

[0002]

2. Description of the Related Art Conventionally, Ti-Ni-Cu shape memory alloys have generally been obtained by a melting / hot working process to obtain a final shape product material. According to this melting / hot working process, an ingot made by high-frequency vacuum melting or plasma melting is processed into a desired shape by hot working means such as pressing, rolling, or forging. It was

[0003]

However, when a Ti--Ni--Cu type shape memory alloy is obtained by this melting / hot working process, the Ti--Ni alloy is a difficult-to-work material and therefore a thin plate having a good thermal response. It is difficult to obtain products, especially Cu
= 10 at% or more, it becomes brittle and extremely difficult to work, so that it is impossible to obtain a thin plate final product. Also,
In the melt-processed material, the polycrystal orientations constituting the material are random, as shown in FIG. 10, so the transformation time throughout the material is shifted depending on the location, and as a result, transformation strain-temperature width of temperature hysteresis curve (ΔT = Af -Mf) is large,
In addition, the bending near the loop transformation point becomes round, and the response of the shape memory alloy due to temperature change is slow, which adversely affects the output efficiency of the heat engine and the high-speed response of the robot actuator.

Further, the discontinuity of the transformed crystal structure causes a loss in the useless transformation process, and the heat-to-mechanical energy conversion efficiency is several percent or less, and its spread as an energy development material and a thermomechanical actuator has been suppressed. . In addition, since the crystal structure is coarse and the matrix dislocation density is small, the yield stress is low and the memory effect is reduced (memory blur) during repeated use, thus narrowing the range of application of SMA.

Also, as for the corrosion resistance, TiNi is originally
Although the system is good, there are still problems in long-term use under extremely strong acidic / alkaline extreme environments due to coarse crystal grains of the processed material and surface non-uniformity. Therefore, the present invention solves the above problems of the conventional Ti-Ni-Cu-based shape memory alloys, can easily obtain a thin plate final product, has a sharp responsiveness with a temperature change, and has a high thermal / mechanical energy. Ti, which has good conversion efficiency, does not cause deterioration of memory effect (memory blur) during repeated use, and can be used for a long period of time under extremely acidic and alkaline extreme environments
An object of the present invention is to provide a -Ni-Cu-based shape memory alloy.

[0006]

It is understood that the material structure itself must be improved in order to reduce the defects of the conventional melt-processed shape memory alloy (mainly Ti-Ni type) as much as possible. That is, the transformation strain-temperature hysteresis curve is narrowed,
Sharpen and improve energy conversion performance,
In order to suppress fatigue deterioration, which is important for practical use, while increasing the strength, the Ti-Ni alloy structure should be homogenous, fine, and have the crystal orientations aligned as much as possible so that the entire material undergoes thermoelastic martensitic transformation at the same time. Just go. Further, in order to improve the thermal responsiveness of the material shape and to obtain an agile shape memory phenomenon, it is necessary to make the material thinner to increase the specific surface area and promote heat diffusion during cooling.

In order to develop a new material satisfying the above various conditions, the inventors of the present invention directly supplied TiNiCu molten metal directly from a nozzle with C
Injected into u chill roll, final TiNiCu thin plate (about 2
Rotational rapid solidification method (Me 0-300 microns thickness)
lt-spinning Technology) was adopted. As a result, a homogeneous and extremely fine anisotropic (columnar crystal of a few microns or less) structure can be obtained by the rapid cooling effect of the rotary rapid solidification method, and the lower structure has a high dislocation density. It was found that plastic strain due to yield is unlikely to occur and there is no energy loss other than phase transformation, so that the improvement of heat-mechanical energy conversion performance and the suppression of shape memory fatigue are suppressed, and the corrosion resistance is also improved. Invented.

That is, according to the present invention, Ti (50 ±
y, y ≦ ± 2 at%)-Ni (50-y-x) -Cu
Ti obtained by rapidly solidifying molten alloy of (xat%) type
A -Ni-Cu based shape memory alloy is provided.

Further, according to the present invention, Ti (50 ± y,
y ≦ ± 2 at%)-Ni (50-y-x) -Cu (xa
t%)-based alloy melt is rapidly solidified and the Cu content x is 10 at% <x <20 at% Ti-Ni-C
A u-based shape memory alloy is provided.

Further according to the present invention, Ti (50 ±
y, y ≦ ± 2 at%)-Ni (50-y-x) -Cu
Ti-Ni in which the (xat%)-based molten alloy is rapidly solidified and the Cu content x is 11.0 to 16.0 at%
A Cu-based shape memory alloy is provided.

In addition, according to the present invention, Ti (50 ±
y, y ≦ ± 2 at%)-Ni (50-y-x) -Cu
Ti-Ni-C in which the (xat%)-based alloy melt is rapidly solidified and the Cu content x is 3.0 to 7.0 at%
A u-based shape memory alloy is provided.

Further, according to the present invention, Ti (50
± y, y ≦ ± 2 at%)-Ni (50-y-x) -Cu
Provided is a Ti-Ni-Cu-based shape memory alloy having a cooling rate of 20 to 50 m / sec when rapidly cooling and solidifying a (xat%)-based alloy molten metal with a rotating roll.

Examples of the rapid solidification method used in the present invention include, for example, a gun method in which a molten metal is directly sprayed onto a Cu cooling plate or the like to be rapidly cooled to produce a small test piece, a rotary roll (single or twin roll) method for producing a continuous thin plate, and a thin wire. There are a spinning submerged spinning method suitable for production and a spray method for producing a quenched powder.

Among the above quenching methods, when the rapid solidification is performed by the rotating roll method (single roll), the cooling rate is preferably 20 to 50 m / sec. When the cooling rate is less than 20 m / sec, the quenched metal structure (particularly, the crystal grain size) becomes coarse, and the orientation becomes random, and only the shape memory transformation occurs.
Fatigue deterioration resistance and corrosion resistance will decrease. On the contrary, when the cooling rate is 50 m / sec, the metal structure becomes amorphous and the shape memory phenomenon based on the crystal transformation does not appear, which is not preferable.

In the present invention, the Cu content x is 10
It is preferable that at% <x ≦ 20 at%. This area is embrittled by normal melting and processing processes (eg grain boundary embrittlement)
Occurs, and large rolling becomes difficult. x is 10 at
Although the transformation strain [Delta] [epsilon] _{SM E} is less than% greater, its transformation temperature range ΔT is increased and is not preferable for practical use.

Further, in the present invention, regarding the thermal / mechanical energy conversion efficiency η, the Cu content x is 11.0 to 1
It is better to set it to 6.0 at%, preferably 12.0-1.
It is better to set it to 4.0 at%. When x is less than 11.0 at%, the transformation strain becomes large, but the transformation temperature difference ΔT becomes large. On the contrary, when x exceeds 16.0 at%, the transformation temperature width ΔT is small but the transformation strain sharply decreases. Not preferable. Further, x is less than 12.0 at% or 14.0a.
If it exceeds t%, the parameter η showing the thermal energy conversion performance decreases, which is not preferable because it is inconvenient for use in a closed system.

Further, in the present invention, the Cu content x
Is preferably 3.0 to 7.0 at%. That is, when recovering thermal energy from a natural release system heat source (abandoned and undeveloped low-grade heat source, for example, hot springs, factory hot drainage, etc.), this x is in the range of 3.0 to 7.0 at%. This is because the recovery performance parameter μ is the largest and is advantageous. If the Cu content x is less than 3.0 at%, the transformation temperature width ΔT becomes too large (30 ° C. or more), and the application range and its practicality are narrowed. On the other hand, when X exceeds 7.0 at%, ΔT sharply decreases, but the transformation strain and μ sharply decrease and the thermal energy recovery performance deteriorates, which is disadvantageous.

[0018]

[Function] Generally, when a molten metal is rapidly solidified by the molten metal quench solidification method, the metal structure is finely crystallized from the dendrite phase as the cooling speed (roll rotation speed) is increased, and the equiaxed columnar crystal is formed to form a super rapid cooling rate. (1 x 10 ⁶ ° C / s
ec or more) changes to amorphous. Ti-Ni-C
For example, the quenching rate of the molten metal is 40 m / s (1 × 10 ⁶ ° C /
sec), the metal structure becomes fine columnar crystals (crystal grain size = 2 to 3 μm) in which crystal axes are aligned in the plate thickness direction as shown in FIG. Even if X-ray crystal structure analysis is performed on this point, it is confirmed that the crystal directions are aligned. Therefore, the Ti-Ni-Cu-based shape memory alloy cooled at this quenching rate has such a metal structure, and thus has the following functional properties.

Since the crystal orientations are aligned due to the formation of columnar crystals, the Ti-Ni-Cu-based shape memory alloy simultaneously undergoes uniform transformation as a whole. Therefore, if the crystal orientation with a large shape memory transformation strain is aligned with the longitudinal direction of the material by the rapid solidification method, the transformation strain can be increased as a whole material. Also, because of the fine columnar crystals, transformation occurs at the same time for the entire material,
As a result, the transformation temperature width ΔT becomes small and the hysteresis becomes sharp. Since it has a fine crystal structure,
The material yield stress is high and the load stress stability is improved.

Further, as a result of fine crystals having high yield stress and uniform crystal orientation, plastic strain / transition is less likely to be introduced and functional fatigue deterioration (memory blurring) is less likely to occur during repeated use. Ti (50 ± y, y of this invention
≦ ± 2 at%)-Ni (50-y-x) -Cu (xat
%) Type alloy, if the addition amount x of Cu is 5 at%, the transformation route in the cooling process follows the route from cubic to monoclinic. This transformation mechanism is a one-step transformation mechanism, and although a large transformation strain can be obtained, a large heat source from the outside is required for that, so the transformation temperature width is large.

On the other hand, Ti (50 ± y, y ≦ ± of the present invention
2 at%)-Ni (50-y-x) -Cu (xat%)
In a system alloy, if the addition amount x of Cu is about 15 at%,
In the vicinity, the route from cubic to orthorhombic and then to monoclinic is followed. In this case, the transformation strain is small, but the transformation history, that is, the transformation temperature width is small because the crystal nucleation and growth in the transformation process are suppressed in sequence, and the smooth transformation process is followed, resulting in energy conversion. It is presumed that the performance will be good.

[0022]

Embodiments of the present invention will be described below. Using the rotary rapid solidification equipment shown in FIG.
A Ti-Ni-Cu alloy melt having the composition shown in Table 1 obtained by arc-melting a Cu ingot material is used in a high-purity Ar atmosphere, and a quartz nozzle 2 around which a sample induction heating coil 1 is wound.
Directly onto the rotating copper roll 3 and rapidly cooled and solidified at the molten metal contact portion 4 to obtain a rapidly solidified ribbon 5. At that time, the cooling speed was set to 1 × 10 ⁴ to 1 × 10 ⁶ ° C./sec, the roll speed was 20 to 40 m / sec, and the cooling copper roll (diameter = 200 mm) rotation speed was 2000 to 400.
It was set to 0 rpm. The Ti-Ni-Cu-based shape memory alloy ribbon thus obtained has a thickness of 0.03 mm and a width of 2.0.
mm, and the length was 200 mm. The properties shown in Table 2 were evaluated for the alloy ribbon.

[0023]

[Table 1] (Alloy chemical composition)

[0024]

[Table 2] (Evaluation characteristics and evaluation conditions or evaluation methods)

The evaluation results of the above various characteristics are shown in FIGS. The transformation strain-temperature hysteresis curves of FIGS. 2 to 7 are results obtained under the condition of actual load conditions σ = 65 MPa. As a comparative example, Ti-Ni-C having the same composition as that of the example is used.
The results of evaluating various characteristics of the u-melt processed material in the same manner as in the examples are shown.

As shown in the hysteresis loops of FIGS. 2 and 3, the points A _s , A _r , M _s , and M _r are rounded in the melt-processed material shown in FIG. Example Ti
In the -Ni-Cu-based shape memory alloy, they have an acute angle and the transformation temperature width ΔT (= Af-Mf) is small. Further, FIG. 4 shows a transformation strain-temperature hysteresis curve when the load stress is changed. As shown in the figure,
The hysteresis curve of the quenched material is stable, and the hysteresis loop of the Ti—Ni—Cu-based shape memory alloy of the embodiment is narrow and sharp as compared with the hysteresis loop of the melt-processed material, and the transformation temperature difference ΔT is kept small. It can be said that the stability of characteristics and functions against stress is high.

Next, FIGS. 5 to 7 show the hysteresis loop, the thermal energy conversion / recovery performance and the ΔT change when the Cu addition amount of the Ti—Ni—Cu type shape memory alloy is changed to 0 to 20 at%. The evaluation results of are shown.

In FIG. 6, the heat energy recovery performance (performance in a natural heat energy release system) parameter μ is expressed by the equation (1). μ = σ · ε / 2 (1) σ: applied stress ε: transformation strain width (here, reverse transformation process, As to A
defined between f)

Further, the heat energy conversion performance (performance in which heat is introduced from the outside to extract mechanical energy in a closed system) parameter η in FIG. 6 is defined by the equation (2). η = (σ ・ ε) / Δq ・ ・ ・ ・ ・ ・ (2) Δq: Heat absorbed per unit mass during transformation (DSC
As shown in FIGS. 5 and 6, the transformation strain Δε is Cu 5%.
, The transformation temperature difference ΔT was 10 ° C. or less when Cu was 10 at% or more, and the minimum value was 6 ° C. when Cu was 15 to 17 at%.

Further, as shown in FIG. 6, the thermal energy recovery performance parameter μ is maximum at around Cu 5%,
On the other hand, the heat energy conversion performance parameter η is Cu13a.
It shows the maximum value around t%, and is 2 to 3 times as large as that of the melt-processed material indicated by ○ in the lower part of the figure at Cu = 0.10 at%, and further in a narrow chemical composition region near Cu = 13 at%. A significant improvement of up to 5 to 6 times is recognized.
Therefore, it can be said that the shaded portion in FIG. 6 is the characteristic superior region of the rapidly solidified material of the embodiment of the present invention. Further, as shown in FIG. 7, each transformation point is 313K at around Cu 13%.
And the lowest. From this data, Ti (50 ± y, y
≦ ± 2 at%)-Ni (50-y-x) -Cu (xat
%)-Based alloy for adjusting the y component or the fourth element (Co, F
If the transformation point can be adjusted to a low temperature level below room temperature by the addition effect of e), a shape memory heat engine that can be driven at a temperature difference near room temperature becomes possible.

FIG. 8 shows the measurement of the division curve in the hydrochloric acid (1N / HCl) for the Ti—Ni—Cu type shape memory alloy of this embodiment. As shown in the figure, even if the lowest point of each bending curve, that is, the so-called natural electrode potential level is compared, the corrosion resistance can be greatly improved by 100 times to 10,000 times compared with the conventional melt processed material. I understand.

[0032]

As described above, the Ti-Ni-C of the present invention is used.
The u-based shape memory alloy has the following excellent effects. 1. The performance of converting the absorbed heat per unit volume during transformation into mechanical work is improved, and the heat energy recovery performance from the low temperature difference heat resource medium is 2-3 times higher (up to 5 at Cu = 13 at%).
~ 6 times) improved. 2. The transformation temperature width is narrower than that of ordinary melt-processed materials, and the transformation temperature width ΔT is at least 6 ° C near Cu = 15 to 17 at%.
It is sensitive to temperature changes, has a rapid transformation strain expansion / contraction function, and has a transformation strain larger than that of the melt-processed material. 3. Functional deterioration (memory blur) due to repeated use is greatly reduced (about 1/10). 4. Corrosion resistance in oxidizing atmosphere (1N-Hcl) hydrochloric acid is significantly improved (100 to 10,000 times).

Since the Ti-Ni-Cu-based shape memory alloy of the present invention has the excellent functions as described above, it can be applied as follows. (1) Thermo-mechanical application Using a shape memory alloy that has both a temperature sensor and a driving element as a thermal actuator (thermo-mechanical driving element), a thermostat, a fire alarm, automatic opening and closing of greenhouse windows, switches for protecting electric circuits, pipes When used as a joint, and further as a human muscle for a robot (ultra-small thermal actuator by heating / cooling electric resistance), the above-mentioned characteristics work advantageously. That is, for example, as a temperature sensor, the transformation is completed within a very narrow temperature range (at Cu = 13 at%, As → Af point and Ms → Mf point are within 1 ° C.),
And the transformation temperature range is within 10 ° C (10 at% or more, minimum =
Since 6 ° C. and Cu = 13 at%), it becomes possible to react extremely sensitively to changes in the external temperature. In addition, repeated memory blurring is greatly suppressed (1/1 of melt processed material)
(0), so that long-term repeated use and its reliability will increase. Moreover, since the corrosion resistance is greatly improved (up to 10,000 times) even in a strongly acidic environment, it can be understood that it can be a thermomechanical element that can be used even in an extremely harsh environment.

Further, since the efficiency of converting heat into mechanical energy is about three times better than that of the conventional material, the robot actuator can be driven by a heat source (heating power consumption) smaller than that of the conventional material, and energy can be saved. . Also,
The Ti-Ni-Cu-based shape memory alloy of the present invention can form an extremely thin strip (20 to 300 μm) which is impossible by melting processing, so that heat is easily diffused from the surface during cooling, which causes a transformation cycle. The responsiveness of the actuator can be greatly improved.

(2) Application example of thermal energy conversion material By applying the thermoelastic martensitic transformation of the Ti-Ni-Cu type shape memory alloy of the present invention, so-called low temperature from factory wastewater, power plant, hot spring, etc. Mechanical energy can be extracted from the differential heat energy. Due to the characteristics of the Ti-Ni-Cu-based shape memory alloy of the present invention, the transformation cycle is completed within a narrower temperature range (10 ° C or less) than the conventional melting / working material, so that the temperature difference is much narrower than the conventional one. Energy can be recovered from the heat source, and fatigue deterioration can be suppressed, so it can withstand long-term use. Further, since a large transformation strain can be obtained, a large energy recovery rate from the open system heat source becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a rapid solidification apparatus used to obtain a Ti—Ni—Cu-based shape memory alloy of the present invention.

FIG. 2 is a diagram showing a hysteresis loop of a Ti—Ni—Cu-based shape memory alloy of the present invention.

FIG. 3 is a diagram showing a hysteresis loop of a conventional material.

FIG. 4 is a diagram comparing and comparing states of respective transformation points of a hysteresis loop of a Ti—Ni—Cu-based shape memory alloy of the present invention and a conventional material.

FIG. 5 is a diagram showing changes in the hysteresis loop when the Cu addition amount is changed to 0 to 20% in the Ti—Ni—Cu type shape memory alloy of the example of the present invention.

FIG. 6 is a graph showing a Ti—Ni—Cu shape memory alloy according to an embodiment of the present invention in which the amount of Cu added is changed to 0 to 20%, the heat energy recovery performance μ, the heat energy conversion performance η, and the transformation temperature difference ΔT. It is a figure which shows the change of.

FIG. 7 is a diagram comprehensively showing changes in respective transformation temperatures when the Cu addition amount is changed to 0 to 20% in the Ti—Ni—Cu type shape memory alloy of the example of the present invention.

FIG. 8 is a diagram showing a polarization curve of a Ti—Ni—Cu-based shape memory alloy of Example of the present invention in hydrochloric acid (1N / HCl).

FIG. 9 is a diagram showing a structure of a Ti—Ni—Cu-based shape memory alloy of the present invention.

FIG. 10 is a view showing a structure of a Ti—Ni—Cu-based shape memory alloy of the present invention.

[Explanation of symbols]

 1 Sample induction heating coil 2 Quartz nozzle 3 Rotating Cu roll 4 Molten metal contact part 5 Rapid solidification ribbon

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[Procedure amendment]

[Submission date] September 30, 1993

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] Figure 9

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[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 10

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Claims (5)

[Claims] 1. Ti (50 ± y, y ≦ ± 2 at%)-N
Ti (Ni-C), characterized by being obtained by quenching and solidifying an i (50-y-x) -Cu (xat%) alloy melt.
u-based shape memory alloy. 2. The Cu content x is 10 at% <x ≦ 20.
The Ti-Ni-Cu-based shape memory alloy according to claim 1, which is at%. 3. The Cu content x is 11.0 to 16.0a.
Ti-N according to claim 1 or 2, which is t%.
i-Cu type shape memory alloy. 4. The Cu content x is 3.0 to 7.0 at%.
The Ti-Ni-Cu-based shape memory alloy according to claim 1. 5. When the molten Ti—Ni—Cu alloy is rapidly solidified by a rotating roll, the cooling rate is 20 to 20.
The Ti-Ni-Cu-based shape memory alloy according to claim 1, claim 2, claim 3, or claim 4 having a speed of 50 m / sec.