JPS63223137A - Shape memory alloy - Google Patents

Abstract

PURPOSE:To easily manufacture a shape memory alloy excellent in workability, by incorporating specific percentages of Fe and Al into Ni. CONSTITUTION:By subjecting an alloy consisting of, by atom, 3-25%, preferably 5-20%, of Fe, 20-35%, preferably 23-34%, of Al, and the balance essentially Ni to hardening from a temp. as high as >=about 1,000 deg.C, the shape memory alloy excellent in workability is obtained. This shape memory alloy can be improved in toughness by the addition of about 0.01-1atom.% B or C, and, by further adding some transition metals (Co, Mn, Cu, etc.) by about 0.1-10atom.%, toughness can be improved to a greater extent. Moreover, by adopting liquisol quenching or powder metallurgy, workability and shape-memory effect can be improved to a greater extent.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention has a shape memory effect when heated above the transformation temperature (reverse transformation temperature: Af) after applying plastic working strain near room temperature. , relates to a shape memory alloy with excellent workability.

(Prior Art) Shape memory alloys are alloys that can reversibly change the shape of the material itself due to temperature changes.

A wide range of practical research is underway, including temperature sensors, manipulators, energy-related materials, and biological materials. By using shape memory alloys, the driving parts of devices can be significantly simplified and miniaturized, and engines using shape memory alloys can efficiently convert minute changes in heat into mechanical energy. can.

To date, Ti-Ni, Cu-Zn-Aj! system and Cu-A1-Ni system have been put into practical use.

All of these alloy materials utilize shape recovery during transformation or reverse transformation of thermoelastic martensite, and there are many other alloys that exhibit shape memory effects (such as those that have been discovered). Since most of the alloys have inferior mechanical properties, no alloys other than the three alloys mentioned above have been put into practical use.

Among the conventional alloy systems, the Ti-Ni system is 5US-316
This alloy has excellent corrosion resistance, elongation at break of more than 50%, and stability against temperature. However, since Ti is used as a constituent element, great care must be taken to prevent oxidation during manufacturing and heat treatment. For example, when melting two alloys.

If a commonly used aluminum crucible is used, oxides may be mixed in, so a graphite crucible is used. However, this causes the contamination of carbides and the fluctuation of the Ti ratio in the Ti-Ni matrix, making it very difficult to produce products of constant quality.

Additionally, this alloy is a difficult-to-process material and requires a large number of processes to finish into a product shape.

Furthermore, it is difficult to manufacture a device with a complicated shape.

For these reasons, this alloy was extremely expensive.

On the other hand, Cu-Zn-Aj2-based and Cu-Al-Ni-based Cu-based alloys require relatively little consideration of the effects of oxidation compared to Ti-Ni systems. Ti-Ni
It can be manufactured more cheaply than other systems. However, these Cu-based alloys have drawbacks such as poor corrosion resistance and a tendency to cause two-grain boundary fracture. Furthermore, the operating temperature of Cu-based alloys was easily affected by the environment and had poor thermal stability.

Therefore, its use remained in very limited fields.

In addition to the shape memory alloys that have been put into practical use, B
Shape memory effects have been recognized in many type 2 intermetallic compounds. For example, even in the N1-Al system, which is an alloy system other than the above, a shape memory effect is observed in an alloy with a composition of 34 to 38 at% Af and quenched in water at a high temperature;
Ni solid solution (y) phase with a composition of atomic %, Ni3Aj! (
It is known that there is no coexistence of the T') phase and the N15A12 phase, and that it exhibits the shape tα characteristic of ioo%. The reason why this alloy exhibits the shape memory effect is also due to the Ti-Ni system, Cu-Zn-
Al-based and Cu-Al! Like the -Ni system, this is due to the transformation and reverse transformation of thermoelastic martensite. Moreover, this alloy is ioO at room temperature.

Although it had excellent corrosion resistance even at temperatures above 0.9°C, it had the drawback of being extremely brittle.

On the other hand, the N1Al(B2) phase is an intermetallic compound that exists in a very wide composition range and also contains Fe.

It has a wide solid solubility limit for many elements such as Co, Mn, Cr, Ti, and Si.

Nis Litvinov: Fiz Metal Metal Robeto (S
, Litvinov: Fiz, Metal, M
etalloved.

Main 1, 11h3. P580-585 (1974)
；Sat±.

4. P826-833 (1977); 4
4. 6゜PL 297-1299 (1977
)) Go.

It is stated that Fe and St are effective in stabilizing the B2 phase (indicating that no phase other than the B2 phase or the martensitic phase generated by thermoelastic transformation of the B2 phase is generated), and in particular, the above-mentioned document , Litvinov et al. reported that N1-A had a 36 atom % A1 composition in which the γ' phase, Ni, and AJ2 phases were mixed.

It is shown that the B2 phase is stabilized by replacing 2.4.6 atomic % of Ni with Fe.

(Problem to be solved by the invention) The above-mentioned N 1bzA 1236F e z (atomic %)
, Nia.

A13bFea (atomic %) and N15sA l36
An alloy consisting of Fe & (atomic %) has corrosion resistance comparable to Ti-Ni.

Although this alloy is as economical and as easy to manufacture as Cu, it has a very low martensitic transformation temperature and is brittle, resulting in insufficient workability.

(Means for solving problems) Therefore, the inventors of the present invention took these current circumstances into account.

N1-Aj! It was discovered that by adding a specific amount of Fe to a series alloy, a shape memory alloy that exhibits a shape memory effect in the low A1 composition region and has excellent workability can be obtained.
We have arrived at the present invention.

That is, the gist of the present invention is a shape memory alloy containing 3 to 25% of Fe and 35 to 35% of Al2O in terms of atomic %, the remainder being substantially Ni, and having excellent workability.

The shape memory alloy of the present invention is a material with perfect shape memory effect and excellent workability, and its alloy composition needs to be limited as follows in order to satisfy the above specifications.

That is, Fe needs to be at least 3 at % and at most 25 at %, preferably at least 5 at % and no more than 20 at %. If the proportion of Fe is 3 atomic % without grooves, the toughness is insufficient and brittle, so it is not of practical use. In addition, if the Fe ratio exceeds 25 atomic %, the composition (A/amount) where the martensitic transformation temperature is in the practical temperature range is γ phase, γ'
Phase or Ni.

A: 122 phase is mixed, and complete shape memory is not shown.

Further, the ratio of Aff needs to be 20 atomic % or more and 35 atomic % or less, and 23 atomic % or more.

It is preferably 34 atomic % or less. Al ratio is 2
In the case of 0 atomic % ungrooved, γ phase, T' phase or Ni, A12
Phases are mixed and complete shape memory is not shown. When the proportion of Al exceeds 35 atomic %, the operating temperature (martensitic transformation temperature and reverse transformation temperature) becomes extremely low, making it unsuitable for practical use, and resulting in insufficient toughness and brittleness.

Furthermore, 0 B or C is added to the alloy defined above.
．． 01 atomic % or more, 1 atomic % or less, more preferably 0
．． By adding 0.03 at % or more and 0.07 at % or less, the toughness is further improved.

If the amount of B or C added is 0.01 atomic % without grooves, there is no effect, and on the other hand, if it exceeds 1 atomic %, the toughness is rather reduced because the fertilization becomes coarse.

In addition, the alloy of the present invention is also effective in adding some transition metals, such as Co, Mn, Cu, Cr, and Ti.

One of V, W, Ta, Nb, Y, 'Ce, Pd, Mo
Toughness is further improved by adding one or more species in an amount of 0.1 atomic % or more and 10 atomic % or less, preferably 0.5 atomic % or more and 5 atomic % or less.

In addition, by adding these elements, the operating temperature (
martensitic transformation temperature and reverse transformation temperature) can be easily controlled. These characteristics are.

It is necessary to satisfy the above conditions, and if the amount of these elements added is less than 0.1 atomic %, there will be no effect.

Further, when the amount added exceeds 10 at %, the toughness is deteriorated and the shape memory properties are also adversely affected.

Alloys containing these transition metals were subjected to the conditions described above (0,
B or C can also be added in an amount of 01 atomic % or more and 1 atomic % or less).

For example, in order to obtain the shape memory alloy of the present invention.

It can be manufactured by quenching an alloy having the above-mentioned composition at a high temperature of 1000° C. or higher.

The present alloy material that satisfies these conditions can of course be manufactured by processing after casting, as is commonly done, but it can also be manufactured by liquid quenching or powder metallurgy. The liquid quenching method turns the molten metal of two alloys into a solid,
It is a method of rapid cooling using a liquid or gaseous cooling medium.9
For example, the single (or double) roll method uses a solid as the cooling medium, the rotating liquid spinning method uses a liquid, and the high-pressure gas atomization method uses a gas. By these methods, generation of amorphous or non-equilibrium phases, refinement of crystal grains, etc. are achieved.

The single-roll method is a method in which molten metal is jetted onto the circumferential surface of a cooling roll that rotates once and rapidly solidifies, thereby making it possible to produce a thin strip-shaped material. The rotating liquid spinning method is characterized by the ability to produce continuous fibers with two circular cross sections by jetting molten metal into a cooling liquid layer formed on the inner wall of a rotating drum and rapidly solidifying it. be. The high-pressure gas atomization method is a method in which molten metal is pulverized by spraying high-pressure gas and rapidly solidified. Regardless of the method, the temperature of the molten metal is 10'~106℃/
Cools down at a very fast rate of seconds.

When the alloy of the present invention is manufactured using a liquid quenching method, the toughness is further improved due to the refinement of crystal grains, and the thermal stability is also improved. Also.

The liquid quenching method rapidly cools the material from a high-temperature molten state.

Unlike the casting method, there is no need for rapid cooling and heat treatment, leading to labor savings in the process. Furthermore, when using a shape such as a thin ribbon or thin wire, there is no need for processing because the product shape can be obtained directly. For these reasons, it is highly advantageous to produce the alloys of the present invention using liquid quenching.

Furthermore, manufacturing the alloy of the present invention using a powder metallurgy method is effective in the following points. Namely.

The first is that it is possible to obtain materials with extremely fine grains, so products with high toughness can be manufactured.
The main reason is that it can be shaped into a product shape during the sintering process. Of course, it is more effective to use powder produced by the high-pressure gas atomization method, which falls within the range of the liquid quenching method described above, during sintering.

(Function) The shape memory alloy of the present invention is N1-Fe-Ajl! The ternary alloy AJI is N1-Aj! γ phase in binary alloy.

N of the N1-Aff system does not contain γ' phase or N15A/z phase and is less than the composition range (36.5 to 38 at%, l) which is known to exhibit shape memory effect.
By substituting part of i with Fe, the contribution to the stabilization of the B2 phase is much larger than that thought by Litv1nov et al.

And until the amount of FeO exceeds 25 at%, as the amount of 176 increases, the B2 phase becomes stable even if the amount of Al is considerably small (even if the amount of Al increases), and as the amount of FeO increases, the martensitic transformation temperature can be greatly reduced. Furthermore, by adjusting the amounts of Fe and AN appropriately, the Ni-Al
Binary alloys and Litvinov
It has much better workability than the alloy with the composition shown.

(Examples) The present invention will be specifically explained below using Examples and Comparative Examples.

Examples 1-7. Comparative Examples 1 to 4 99.99% A1 and 99.97% electrolytic Ni and 99.99
% electrolytic Fe, a total of 1 kg was weighed so as to have the synthetic composition shown in Table 1, and melted in a vacuum melting furnace. Cut out a sample of 50 x 1 x 10 mm x 3 from each alloy,
After being held at 1250°C for 1 hour, it was cooled with water.

The elongation at break (εf) of these samples was determined using an Instron tensile tester.
) was investigated using a thermal scanning analyzer (DSC).

The shape memory properties were evaluated by the amount of shape recovery (%) when the sample was bent at 90°C at a martensite single phase temperature, heated to a reverse transformation temperature Af or higher, and became a single matrix phase. (If the shape was completely restored to the shape before deformation, the amount of shape recovery was taken as 100%).

In addition, the evaluation of corrosion resistance was carried out by adding 1N to a 30°C hydrochloric acid aqueous solution.
Evaluation was made based on the weight change (%) after immersion for a period of time.

The results are shown in Table 1.

As shown in Table 1, the alloys of Examples 1-7.

In all cases, there was no Ni solid solution (γ) phase or Ni3A/(γ') phase, and 10094 exhibited good shape memory properties.

Furthermore, the elongation at break (εf) was 8 to 13%, which is sufficient for practical use, and it is clear that the workability is excellent. Furthermore, regarding corrosion resistance, it was not corroded by hydrochloric acid at all.

However, in the case of Comparative Example 1, which had a composition outside the scope of the present invention, there was no effect of Fe substitution, the elongation at break was 0%, and the workability was poor. In addition, in the case of Comparative Example 2, N
i Solid solution (γ) phase is mixed.

Shape memory properties deteriorated to 80%.

Example 8 A rod-shaped lump of approximately 5 g was cut out from an alloy produced in the same manner as in Example 3, and this was used as a master alloy.

The liquid was quenched using a rotating liquid spinning method. The diameter of the rotating drum was 600 mm, and the number of revolutions was 30 rpm. The master alloy is melted by high-frequency induction heating in a quartz jet nozzle, and then through a nozzle hole with a diameter of 0.1 mm.

Ar gas was ejected onto the cooling water layer formed on the inner wall of the rotating drum at a pressure of 4 kg/cll.

The sample produced in this way had a diameter of 0.1 nm.

It was a continuous fiber with a length of 50 m. Using this sample, evaluation tests similar to those in Examples 1 to 7 were conducted.

The results shown in Table 2 were obtained, and the elongation at break was approximately twice as high as that of Example 2 in which liquid quenching was not performed.

Example 9 A powder was produced from the alloy of Example 2 using a high-pressure gas atomization method. Ar is used as the atomizing gas, and the atomizing pressure is 100 kg/co! Met. Among the classified powders, those having a diameter of 44 μm or less were used and molded using a pressure sintering method.

The sintered body has a diameter of 10++m and a height of 25mm.
It was molded at a temperature of 1100°C and a sintering pressure of 50 kg/a.

A sample of 5 cranes x 20 fl x 3 dragons was cut out from this sintered body, held at 1250°C for 1 hour, and then cooled with water to be used as a measurement sample.

Using this sample, the same evaluation tests as in Examples 1 to 7 were conducted, and the results shown in Table 2 were obtained, and the elongation at break was improved compared to Example 2, which did not use the powder metallurgy method.

(Effects of the Invention) The shape memory alloy of the present invention has corrosion resistance comparable to that of Ti-Ni alloys, and has corrosion resistance comparable to that of Ti-Ni alloys.
It is as easy to manufacture as copper-based alloys such as Ni-based alloys, and has excellent workability. Also.

When the shape memory alloy of the present invention is manufactured using a liquid quenching method or a powder metallurgy method, its workability and shape memory effect become even more excellent.

Taking advantage of these properties, the shape memory alloy of the present invention can be used as temperature sensors and micromanipulators.

It can be used for spring materials, heat engine constituent materials, biological materials, various reinforcing materials, etc.

Patent applicant: Masumoto Kenyunitei Riki Co., Ltd.

Claims (1)

[Claims] (1) Fe3~25% and Al20~3 as atomic%
A shape memory alloy containing 5% Ni, with the remainder essentially consisting of Ni, and has excellent workability.