JPH08209314A - Production of shape memory alloy with high-temperature phase-transferring function - Google Patents

Abstract

PURPOSE: To allow an alloy to memorize shape and to obtain sufficient shape recovery factor by subjecting a shape memory alloy with high-temp. phase-transferring function to cold working and then to a specific two-stage heat treatment. CONSTITUTION: A shape memory alloy with high-temp. phase-transferring function, in which martensite inverse transformation starting temp. (As) at the first heating after cold working becomes >=350 deg.C, is cold-worked and then heat-treated. At this time, as a first-stage heat treatment, heating is performed at a temp. higher than the martensite inverse transformation finishing temp. (Af) at the first heating for a time not longer than recrystallization latent time, e.g. at a temp. in the range between >500 deg.C and a temp. lower than the melting point of the alloy for <=3min. Thereby the structure of a bace material is transformed without causing recrystallization of the alloy to improve the shape recovery. Then, as a second-stage heat treatment, annealing is performed a temp. in the range between the plastic strain recovery temp. and the recrystallization temp. It is preferable to use Ti50 Ni50-x Pdx (x=35 to 50 atomic %), Ti50-x Ni50 Zrx (X=22 to 30%), Ti50-x Ni50 Hfx (x=20 to 30%), etc., as the alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high temperature working shape memory alloy, and more specifically, Ti-P.
d-Ni alloy, Ti-Ni-Zr alloy, Ti-Ni-H
The present invention relates to a manufacturing method for significantly improving the shape recovery characteristics of a high temperature operating shape memory alloy such as an f alloy.

[0002]

2. Description of the Related Art As shape memory alloys and superelastic alloys, T
iNi-based alloys are well known. The shape recovery temperature (martensite reverse transformation end temperature, hereinafter referred to as Af temperature) is
It can be changed in the range of about -100 ° C to + 100 ° C depending on the composition ratio of Ti and Ni, addition of the third element, processing heat treatment conditions, and the like. When performing shape memory heat treatment on these shape memory alloys, after cold working, annealing is performed at a temperature equal to or higher than the plastic strain recovery temperature (usually about 400 ° C.). The recovery temperature of plastic strain is the temperature at which dislocations introduced by cold working are rearranged. Since this temperature is higher than the Af temperature, it is simultaneously heated to the Af temperature or higher at this time and once transformed into the matrix phase, the shape can be memorized.

It is important that the following three points are satisfied as conditions for shape memory heat treatment for obtaining good shape memory characteristics. 1) Eliminating saturation of rearrangement of martensite variants due to cold working, 2) Rearrangement of dislocations introduced by cold working, and 3) No recrystallization. In a TiNi-based shape memory alloy, the Af temperature (operating temperature) is slightly higher than 100 ° C. at most, and in order to obtain a shape memory alloy having a higher Af temperature, that is, a high temperature operating shape memory alloy, a TiNiPd alloy, Ti
It is necessary to use another alloy system such as NiZr alloy. Applications of high temperature operating shape memory alloys include boiling water and overheating of oil,
It can be used for parts that detect and act upon the melting of polymers, or for safety valves for cooling water in nuclear reactors.

For high-temperature working shape memory alloys whose Af temperature greatly exceeds 100 ° C., Ti-Pd-X type and Ti-Au-type are used.
X system (X = Ni, Cu, W, Ta, Co, Cr, F
Many alloy systems such as e) and Ti-Ni-X system (X = Zr, Hf) system are known, but these alloy systems have a martensite reverse transformation start temperature (hereinafter It is possible to change the As temperature) or the Af temperature. Depending on the composition range, the As temperature or the Af temperature reaches 500 ° C. or higher.

Further, normally, the As temperature and Af in the annealed state are
Although the difference from the temperature is several tens of degrees Celsius or less, when these alloys are cold-worked, the Af temperature in the first heating after cold-working is further increased by about 150 ° C. due to the introduction of working strain, and
The difference between the s temperature and the Af temperature widens. Therefore, the As temperature is 35
For alloys above 0 ° C, Af at the first heating after cold working
The temperature reaches 500 ° C. or higher and exceeds the recrystallization temperature. For example, the Ti-Ni-Pd system has a composition of Ti ₅₀ Ni.
When expressed by _50-x Pd _x (numerical value is at%, the same applies below),
When x is 43 or more, the Af temperature in the annealed state is 500
℃ or more. Further, the As temperature is 350 ° C. or more when x is 35 or more, and Af in the first heating after cold working
The temperature rises above 500 ° C. In addition Ti-Ni-Zr system, when referring to a composition in _{Ti 50-x Ni 50 Zr x} , x is 2
When it is 9 or more, the Af temperature in the annealed state becomes 500 ° C. or more. Moreover, when x is 22 or more, the As temperature is 350 ° C.
Above, the Af temperature in the first heating after cold working is 5
It will be over 00 ℃. In yet Ti-Ni-Hf-based, when referring to a composition in _{Ti 50-x Ni 50 Hf x} , Af temperature in the annealing state x is 27 or more is equal to or higher than 500 ° C..
Further, when x is 20 or more, the As temperature is 350 ° C. or more, and the Af temperature in the first heating after cold working is 500 ° C.
That's all.

As described above, in the alloy having an As temperature of 350 ° C. or higher, the Af temperature in the first heating after cold working reaches 500 ° C. or higher and exceeds the recrystallization temperature.
As a matter of course, in the alloy having an As temperature of 500 ° C. or higher from the beginning, the Af temperature in the first heating after cold working is 5 as well.
The temperature is 00 ° C or higher. In such alloys, after cold working,
Like the conventional Ti-Ni type shape memory alloy, 1 at 400 ℃
Even if a heat treatment such as time annealing is performed, the shape cannot be memorized. On the other hand, when annealing is performed at a temperature higher than the Af temperature in the first heating after cold working, the shape can be memorized, but recrystallization is started this time, so the shape recovery rate becomes poor. For these reasons, conventionally, there has been a problem in that a high-temperature working shape memory alloy in which the Af temperature in the first heating after cold working is equal to or higher than the recrystallization temperature cannot obtain a good shape recovery rate.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to study the above problems variously, and to form a high temperature working shape memory alloy in which the As temperature in the first heating after cold working is 350 ° C. or higher. Is to develop a manufacturing method capable of memorizing, and obtaining a sufficient shape recovery rate.

[0008]

According to the invention of claim 1 for solving the above-mentioned problems, a martensite reverse transformation start temperature (A) at the first heating after cold working of a high temperature working shape memory alloy is used.
s) is an alloy whose temperature is 350 ° C. or higher, and is higher than the martensite reverse transformation end temperature (Af) in the first heating after cold working after cold working of the alloy. Heating at a temperature for a time within the recrystallization incubation time, and then as the second heat treatment, at a plastic strain recovery temperature or higher,
And a method of manufacturing a high temperature working shape memory alloy, characterized by performing annealing at a temperature of recrystallization temperature or less,

The invention of claim 2 is the embodiment of claim 1, characterized in that the heat treatment in the first step is performed at a temperature higher than 500 ° C. and lower than the melting point of the alloy within 3 minutes. A method for manufacturing a high temperature operating shape memory alloy according to claim 1,

[0010] The invention of claim 3 is an embodiment of claim 1 or claim 2, the composition of the hot working the shape memory alloy, a _{Ti 50 Ni 50-x Pd x} x is 35% to 50% alloy, according to claim 1, Ti _50-x Ni ₅₀ Zr x of x is 22 to 30% of the alloy and Ti _50-x Ni ₅₀ Hf x of x is equal to or is any one of 20-30% of the alloy Alternatively, it is the method for manufacturing a high temperature operating shape memory alloy according to claim 2.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. First, the principle of shape memory processing of shape memory alloys is generally explained as follows. Cold working introduces a high density of dislocations into the crystal. This is annealed at an appropriate temperature above the plastic strain recovery temperature for an appropriate time,
Cause rearrangement of rearrangements. Since the rearranged dislocations become a resistance against slip, the critical stress of slip becomes larger than the critical stress of rearrangement of martensite or generation of stress-induced martensite. As a result, upon deformation, martensite rearrangement or stress-induced martensite occurs without slippage, and good shape memory characteristics are exhibited.

On the other hand, when the annealing temperature is higher than the recrystallization temperature, not only rearrangement of dislocations but also recrystallization occurs. Since the dislocation density in the recrystallized portion is extremely small, the resistance to slip is small. Therefore, the critical stress of slippage becomes smaller than the critical stress of rearrangement of martensite, slippage is likely to occur, and as a result, shape memory characteristics deteriorate.

By the way, in the conventional TiNi-based shape memory alloy, since the Af temperature (-100 ° C. to 100 ° C.) is lower than the plastic strain recovery temperature (about 400 ° C.), heating to the plastic strain recovery temperature or higher is required. , Transformed into a mother phase.
As a result, the rearrangement rearrangement occurs in a state in which the saturation of the rearrangement of the martensite variant caused by cold working has been eliminated, so that the shape can be memorized and no problem occurs. However, the above-mentioned Ti-Pd-
In a shape memory alloy such as X-based, Ti-Au-X-based, and Ti-Ni-X-based having a higher Af temperature than the recrystallization start temperature, Af
When annealing is performed at a temperature higher than the temperature, recrystallization occurs, so that the shape recovery property deteriorates. At a temperature that does not exceed the Af temperature, the shape cannot be memorized because the state of the saturated martensite of the rearrangement of the variant remains after cold treatment even after the heat treatment.

The present invention has been made on the basis of the above findings, and is a high temperature working shape memory alloy having an As temperature of 350 ° C. or higher in the first heating after cold working, that is, the above Ti-
For alloys such as Pd-X series, Ti-Au-X series, and Ti-Ni-X series, after cold working of the alloy, as a first-stage heat treatment, the first heating after cold working is performed. The heating is performed at a temperature higher than the Af temperature and within the latent time for recrystallization. The crystal structure of the alloy is transformed into a mother phase by the first heat treatment. By once transforming into the parent phase, the saturation of the rearrangement of the martensite variant caused by cold working is eliminated.

The temperature of the above heat treatment is not less than the recrystallization start temperature of the alloy. However, since the transformation to the parent phase is completed within the recrystallization incubation time, the heating to the Af temperature or more can be performed in a short time. The initiation of recrystallization can be avoided. In other words,
In the first-stage heat treatment of the present invention, the heat treatment is performed at a temperature higher than the Af temperature and higher than the recrystallization temperature, but the heating time is an extremely short time within the recrystallization latency time. Therefore, it is possible to obtain a material having a high shape recovery rate without causing recrystallization in the alloy. This first-stage heat treatment is preferably performed at a temperature higher than 500 ° C. and lower than the melting point of the alloy. If it is lower than 500 ° C., the shape recovery rate is poor, and if it exceeds the melting point, it melts. However, it is practical and preferable. It is in the range of 500 to 1000 ° C. By the way, the melting point of the Ti-Au-Ni alloy is about 1310.
〜1495 ° C, Ti-Ni-Pd based alloy is about 1310
1400 ° C, Ti-Ni-Zr alloy is about 1260-1
At 310 ° C., the Ti-Ni-Hf alloy is about 1310-15.
It is 30 ° C. The recrystallization temperature is 500 ° C. or higher.

Further, the heating time is preferably 3 minutes or less, and if it exceeds 3 minutes, recrystallization occurs and the shape recovery property deteriorates. It is preferably within 1 minute. As a second heat treatment after the above first heat treatment, there is one in which annealing is performed at a temperature not lower than the plastic strain recovery temperature of the alloy and lower than the recrystallization temperature. It causes only rearrangement of dislocations without causing this, whereby a good shape memory effect can be obtained. This heat treatment is 300-5
It is desirable to carry out at a temperature of 00 ° C for 30 minutes to 2 hours.
This is because if the temperature is lower than 0 ° C, good shape memory cannot be achieved, and if the temperature is 500 ° C or higher, recrystallization may occur.

As the high temperature working shape memory alloy to which the present invention is applied, as described above, an alloy having an As temperature of 350 ° C. or higher in the first heating after cold working, that is, 350 ° C.
It is a shape memory alloy that operates at the above high temperatures. At present, the Ti-Pd-X system and the Ti-Au described above are attracting attention.
-X system (X = Ni, Cu, W, Ta, Co, Cr, F
e), Ti-Ni-X type (X = Zr, Hf), etc., but particularly practically Ti-Pd-X type, Ti-Ni-X type.
The system is Ti ₅₀ Ni _{50 −x} Pd _x.
X 35 to 50% of the alloy, Ti ₅₀ - x of _x Ni ₅₀ Zr _x is from 22 to 30% of the alloy, x is from 20-30% of an alloy of Ti _50-x Ni ₅₀ Hf x is favorable properties It is shown and practically preferable.

These high temperature operating shape memory alloys can be manufactured by conventional methods. For example, a billet is produced by high frequency melting, plasma melting, powder metallurgy, etc., and after hot working such as hot rolling, hot extrusion, cold rolling, cold working such as wire drawing, a plate, a strip, It is processed into materials such as rods and wires.
Further, as the heat treatment method, an ordinary heating furnace may be used, and high frequency heating, current annealing, etc. may be applied, and cooling after annealing may be appropriately performed by air cooling, water cooling or the like.

[0019]

EXAMPLES Preferred production examples of the present invention will be described below in comparison with comparative examples. (Example 1) composition of an alloy represented by _{Ti 50 Ni 50-x Pd x} , to prepare a sample of 3 compositions to be x = 35,40,50at%. 30 g of each was melted by plasma melting, hot-rolled and cold-rolled to be processed into a plate having a thickness of 1.0 mm (cold-rolling processing rate of about 25%). A tensile test piece (gauge length 16 mm) is cut from this plate by electrical discharge machining,
After polishing the surface, heat treatment was performed at various temperatures shown in Table 1.
A shape recovery characteristic test was conducted on these test pieces, and the results are also shown in Table 1.

The evaluation method was as follows. The test piece with an apparent plastic strain of about 3% was left after the tensile strain was applied to the test piece at room temperature for 4% and the stress was unloaded. When the material undergoes reverse transformation by heating to 0, those exhibiting a shape recovery rate of close to 100% are indicated by ○ (shape recovery rate of 95% or more), and those exhibiting almost no shape recovery are indicated by × (shape recovery rate of 20% or less), intermediate Is shown as Δ. In Table 1, the first reverse transformation start temperature refers to the martensite reverse transformation start temperature at the time of first heating after performing cold working. This was determined here by thermal analysis. Of the heat treatment temperature,
Tf is the heat treatment temperature of the first step and the holding time is 1 minute.
Was held at the second stage heat treatment temperature for 1 hour.

[0021]

[Table 1]

As is clear from Table 1, No. 1 of the present invention example.
1, No. 5, no. 6, No. 9, No. No. 10 has an As temperature of 350 ° C. in the first heating after cold working.
From the above, it can be seen that the shape recovery rate is close to 100%. On the other hand, in Comparative Example No. 2, No. 3, No. 4, N
o. 7, No. 8, No. 11, No. Since No. 12 is not subjected to the first-stage heat treatment (Tf), it can be seen that there is almost no shape recovery or the shape recovery rate is poor.

(Example 2) Pd concentration of Example 1 is 35 at
%, 40at% sample, heat treatment (Tf, Ta)
Samples were prepared by changing the temperature and time as shown in Table 2, and the shape recovery characteristics were examined in the same manner as in Example 1. The results are also shown in Table 2.

[0024]

[Table 2]

As shown in Table 2, No. 1 of the present invention example. 1,
No. 2, No. 4, no. In No. 5, even if Tf exceeds the recrystallization temperature, if the retention time at Tf is within 2 minutes, it is within the recrystallization incubation time, so recrystallization does not occur and the shape recovery characteristic Is good. On the other hand, in Comparative Example No. 3 and No. 3 In No. 6, recrystallization occurs due to a long holding time at Tf, and the shape recovery characteristic is poor.

(Example 3) The composition was Ti _50-x Ni ₅₀ Zr _x.
Samples having two compositions, x = 22 and 30 at%, were prepared from the alloy represented by. Each 3 kg is melted by high frequency induction heating melting, cast, hot extruded, hot groove roll rolled, and then die drawn and annealed repeatedly to obtain a diameter of 1.0 mm.
Round wire (final cold working rate of about 30%). This wire was cut into a length of 140 mm, fixed linearly and heat-treated at various temperatures shown in Table 3. A shape recovery characteristic test was conducted on these test pieces, and the results are also shown in Table 3. A strain gauge with a gauge length of 50 mm was used to give tensile strain. The evaluation method, the heat treatment method, and the symbols in Table 3 are the same as in Example 1.

[0027]

[Table 3]

As is apparent from Table 3, No. 1 of the present invention example.
1 and No. In all 4, the As temperature in the first heating is 350 ° C. or higher, and the shape recovery characteristic is close to 100%. On the other hand, in Comparative Example No. 2, No. 3, No. 5, N
o. No. 6 does not show the shape recovery because the first-stage heat treatment (Tf) is not performed, or the shape recovery rate is poor.

(Example 4) Zr concentration of Example 3 is 22 at
%, 30at% sample, heat treatment (Tf, Ta)
Samples were prepared by changing the temperature and time as shown in Table 4, and the shape recovery characteristics were examined in the same manner as in Example 3. The results are also shown in Table 4.

[0030]

[Table 4]

As is apparent from Table 4, N of the present invention example
o. 1 and No. In No. 3, even if Tf exceeds the recrystallization temperature, if the holding time at Tf is 1 minute, it is within the recrystallization incubation time, so recrystallization does not occur and the shape recovery property is good. is there. On the other hand, in Comparative Example No. Two
And No. In No. 4, since the retention time at Tf is long, recrystallization occurs and the shape recovery characteristic is poor.

Example 5 The composition is Ti _50-x Ni ₅₀ Hf _x.
Samples of two compositions with x = 20 and 30 at% were prepared from the alloy represented by. After forming 1 kg of each into a billet by powder metallurgy, HIP (hot isosta)
tic press) treatment, hot extrusion, hot groove roll rolling, and then die drawing and annealing are repeated to obtain a diameter of 1.0.
It processed into a round wire of mm (final cold working rate about 30%). This wire was cut into a length of 140 mm, fixed linearly and heat-treated at various temperatures shown in Table 5. A shape recovery characteristic test was conducted on these test pieces, and the results are shown in Table 5.
I also wrote it down. The test method, evaluation method, heat treatment method, and symbols in Table 5 are the same as in Example 3.

[0033]

[Table 5]

As is apparent from Table 5, No. 1 of the present invention example.
1 and No. In all 4, the As temperature in the first heating is 350 ° C. or higher and the shape recovery rate is close to 100%. On the other hand, in Comparative Example No. 2, No. 3, No. 5, N
o. No. 6 does not show the shape recovery because the first-stage heat treatment (Tf) is not performed, or the shape recovery rate is poor.

(Example 6) Hf concentration of Example 5 is 20 at
%, 30at% sample, heat treatment (Tf, Ta)
Samples were prepared by changing the temperature and time as shown in Table 6, and the shape recovery characteristics were examined in the same manner as in Example 5. The results are also shown in Table 6.

[0036]

[Table 6]

As is clear from Table 6, N of the present invention example
o. 1 and No. In No. 3, even if Tf exceeds the recrystallization temperature, if the holding time at Tf is 1 minute, it is within the recrystallization incubation time, so recrystallization does not occur and the shape recovery property is good. is there. On the other hand, in Comparative Example No. Two
And No. In No. 4, since the holding time is long, recrystallization occurs and the shape recovery property is poor.

[0038]

As described above, according to the present invention,
High temperature operating shape memory alloys with excellent shape recovery characteristics can be obtained, such as parts that operate by detecting boiling of water, overheating of oil, melting of polymer, etc., or safety valves for cooling water of reactors at high temperature It can be expected to be used.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Tatsuhiko Ueki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Hiroshi Horikawa 2-6-1 1-1 Marunouchi, Chiyoda-ku, Tokyo Kawa Electric Industry Co., Ltd. (72) Inventor Kengo Mito 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. An alloy having a martensite reverse transformation start temperature (As) of 350 ° C. or higher in the first heating after cold working of a high temperature operating shape memory alloy, and the alloy is 1 after cold working. As the heat treatment of the second step, heating is performed at a temperature higher than the finish temperature (Af) of the martensite reverse transformation in the first heating after cold working and for a time within the latent time of recrystallization, and then as the heat treatment of the second step. A method for producing a high temperature working shape memory alloy, characterized by performing annealing at a temperature not lower than a plastic strain recovery temperature and not higher than a recrystallization temperature. 2. The first heat treatment is 500 ° C.
The method for producing a high temperature operating shape memory alloy according to claim 1, wherein the heat treatment is performed at a temperature higher than the above and lower than the melting point of the alloy and within 3 minutes. 3. The composition of the high temperature working shape memory alloy comprises:
_{X of} Ti ₅₀ Ni _50-x Pd _x (numerical value is at%, the same applies below)
There 35% to 50% of the alloy, x of Ti _50-x Ni ₅₀ Zr x is 2
2-30% of the alloy and Ti _50-x Ni ₅₀ x of Hf _x is 2
The method for producing a high temperature operating shape memory alloy according to claim 1 or 2, wherein the alloy is 0 to 30%.