JPH0285329A - Cu-Al-Ni shape memory alloy - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copper-based shape memory alloy that has application fields such as heat-sensitive functional elements and heat-shrinkable pipe joining materials.

[Conventional technology]

Shape memory alloys that utilize the shape change associated with martensitic transformation are increasingly being used in automobiles, home appliances, and consumer products as coil-shaped heat-sensitive switches and tubular pipe joining materials, but they still account for the majority of practical materials. In place of expensive Ti-Ni alloys, Cu is inexpensive and has excellent thermal and electrical conductivity.
There is a strong demand for these alloys. Among them, Cu-A
1-Ni alloy can obtain a large recoverable strain comparable to ↑t-Ni in a single crystal state, and has excellent pseudoelastic properties, so it is expected to be put to practical use. However, normal polycrystalline materials are extremely brittle and may cause intergranular cracking only by rapid cooling from high temperatures, so improving workability is the biggest challenge for practical use.

One effective way to improve workability is to refine the crystal grains to 100 μm or less, but what about the use of various elements to achieve this? j
IX! A method of melting an alloy by adding it is commonly carried out industrially. The manufacturing process of copper-based shape memory alloys includes, after casting,
700 to 10, such as homogenization annealing, hot rolling, and beta treatment
The grain refining element not only reduces the primary crystal grain size during casting, but also serves to prevent coarsening of the crystal grains during holding at such high temperatures. Cu-A
In the case of I-Ni-based shape memory alloys, B and Ti
B is known as a grain refining agent, but addition of around 0.1% of B significantly increases the hardness of the alloy, which is undesirable (
For Ti, the grain refining effect is not sufficient in the following sense. In other words, the grain refining effect generally increases with the amount added, but if the amount added is large, a large amount of second phase is generated and the shape memory is reduced. In addition to decreasing ductility and fatigue life, elements dissolved in the matrix may change the stability of the β matrix and deteriorate its shape memory ability, and heat treatment may cause the second phase to change the composition of the β phase. This causes variation and width in the shape deformation temperature. Therefore, it is desirable that the amount of added elements be as small as possible, and in practical terms, it is thought that the limit amount of addition is 0.5% or less, but as shown in the data below, if Ti is less than 0.5%, the Grain growth cannot be suppressed. Therefore, there has been a desire for an additive that can replace these elements and has a particularly strong grain refining effect.

[Problems to be solved by the present invention]

The present invention eliminates the drawbacks of the conventional shape memory alloys as described above, refines the crystal grains of the Cu-A 1-Ni type shape memory alloy, and creates a shape memory alloy with good workability and improved brittleness. The challenge is to obtain.

[Means to solve the problem]

As a result of various studies to solve the above problems, the present inventors found that If exerts a remarkable grain refining effect, and based on this knowledge, the present invention was completed. That is, in the present invention, Al is 10 to 15% and Ni is 2 to 15% by weight.
An alloy containing 0.01 to 1.0% of ILF and 0.01 to 1.0% of ILF, with the remainder substantially consisting of Cu and unavoidable impurities, or an alloy containing 0.01 to 0.05% of B. provide.

[Effect]

Among the above ingredients, A7! is a basic element for forming a β phase with Cu to produce a shape memory effect, and if it is less than 10 to 15%, the martensitic transformation temperature will exceed the practical range or the shape memory effect itself will disappear. Ni is a basic element that stabilizes the β phase and increases hardenability, and if it is less than 2%, the effect is not sufficient, and if it is more than 5%, the matrix solid solution strengthening of Ni is excessive, resulting in hardness and brittleness. When the grain refining element Hf is 0.01% or less, the grain refining effect becomes insignificant, and when it exceeds 1.0%, the amount of the second phase increases and becomes brittle.

Usually, use of 0.5% or less will give good results.

When Hf is added, fine secondary particles as shown in Figs.
Phases (Xs and XL in the figure) are generated and this significantly inhibits grain growth, but solid solution If also has a strong bonding force with Nt and AI, which reduces the diffusion rate of the constituent elements. However, a large grain refinement effect can be obtained. Furthermore, H
When B is added in addition to f, the grain refining effect is promoted by the boride formation of Ilf. Further, the effectiveness of adding If or Hf and B is significantly exhibited when hot working is performed in the β phase temperature region. In other words, even if the crystal grains at the time of casting are slightly large due to the addition of a relatively small amount, the crystals fragmented during hot working or newly nucleated crystals will not grow and coarsen due to the various effects of Hf, so the hot working Ultrafine grains can be obtained depending on the degree of However, it is not preferable to add more than 0.05% of B because it will make the material harder. Moreover, if it is less than 0.01%, the above-mentioned effects are not sufficient. Since the alloy thus obtained has a small amount of added elements, the excellent shape memory effect inherent to the Cu-AI-Ni system is preserved, and it becomes a high-performance shape memory alloy with a narrow transformation temperature range.

〔Example〕

Example 1 99.9% by weight electrolytic copper, 99.99% by weight aluminum, 99.9% by weight nickel, 99.7% by weight hafnium, and Cu-5% by weight B master alloy were weighed and placed in a graphite crucible. , melted in a high frequency furnace.

Table 1 shows the alloy composition after chemical analysis. In addition, % in Table 1
indicates weight %. Alloys 1 to 7 are conventionally known alloys, and 8 to 10 are alloys according to the present invention. In order to obtain the average value of the non-uniform crystal grain size during casting, the lower quarter half of the obtained plate-shaped cast body (approximately 10 x 50 x 50w5') was cut out, heated at 900°C for 3 minutes, and then water quenched. The particle size of the β phase was measured over the entire surface of the sample. The smaller the cast grain size, the smaller the final grain size after processing heat treatment. The grain size is significantly smaller, and the grain refining effect is achieved by adding a smaller amount than when Ti or Ti and B are used as grain refining agents (Samples 3 to 6).

Example 2 The sample obtained in Example 1 was heated to 10% of its original thickness at 850°C.
Table 2 shows the grain size after repeated hot rolling until the temperature becomes 100° C., and the grain size after holding the same at 900° C. for 10 minutes and 1 hour. For rolling, the initial rolling reduction was 6%, and 850°C was held for 10 minutes every three passes. Although the grain size is significantly reduced by hot rolling, even if the alloy is maintained at a rough β-phase temperature, grain growth is significantly slowed down in fine-grain alloys containing other additives. This effect appears most strongly in the case of Hf addition, and sample 8
Even with the addition of only 0.04%, the particle size after 10 minutes at 900° C. is suppressed to 100 μm or less.

Example 3 Findings regarding workability when hot rolling in Example 2, findings when cutting with a high-speed cutting machine, and this sample at 900°C 10
After heating for a minute and then water quenching, the initial 0.5
Table 3 shows the results of measuring the critical rolling reduction until cracks occur in the sample when cold rolling was performed at room temperature at a rolling reduction of 1.5%.

) In addition to the effect of grain refinement, the Hf-added alloy shows the greatest improvement in workability due to the small amount added.

On the other hand, in the case of sample 7 in which only B was added, the grain refining effect was great, but the B compound contained in the structure was very hard and the workability was not good.

(Effects) As explained in detail above, the Cu-A j2 of the present invention
-Ni-based shape memory alloys have the effect of having finer grain sizes and excellent workability.

[Brief explanation of drawings]

Figure 1 shows Cu-13,4%A 6-4.0%Ni-0,
Figure 2 shows the fine If-rich phase (Xs) precipitated on the β matrix grain boundaries (G, B,) of the 14%Hf-0,01%B alloy (sample 9). 8%A7! -4.2
%Ni-0.46%Hf alloy (sample 10), each showing a larger Hf-rich phase (XL) formed in the β matrix phase. Patent Applicant: Sumitomo Metal Mining Co., Ltd. Procedure: Space Official Document (Method): 7th/Month, 1949

Claims (2)

[Claims] (1) 10-15% Al, 2-5% Ni by weight,
and 0.01 to 1.0% of Hf, with the remainder being substantially C.
Cu-A characterized by consisting of u and inevitable impurities
l-Ni-based shape memory alloy. (2) 10-15% Al, 2-5% Ni by weight,
Hf is 0.01 to 1.0%, and B is 0.01 to 0.0%.
1. A Cu-Al-Ni based shape memory alloy, characterized in that the Cu-Al-Ni-based shape memory alloy contains 0.5% Cu and the remainder substantially consists of Cu and unavoidable impurities.