JPH09176807A - Shape memory alloy material manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form the whole material into martensitic single phase to reduce manufacturing cost and improve propertied of a final product at the time of producing a shape memory alloy material, by adopting subzero treatment as a pretreatment or aftertreatment for each stage. SOLUTION: This shape memory alloy material is produced by applying cold working to a shape memory alloy stock by plural stage while performing plural annealing treatment stages between the cold working stage and applying, at least in the course between the final stage among these plural cold working stages and the annealing treatment stage just before it, subzero treatment to form the whole material into martensitic signal phase, or, the shape memory alloy material is produced by applying secondary subzero treatment after the above cold working and then performing shape memory heat treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improved method of manufacturing a shape memory alloy material, and more particularly, to facilitating the manufacturing process of the shape memory alloy material and reducing the manufacturing cost, and further, the shape memory of the shape memory alloy material. The present invention relates to a method capable of improving performance and superelasticity performance.

[0002]

BACKGROUND ART In using a shape memory alloy material, in order to maximize its characteristics, it is important to sense a change in temperature sensitively and to operate agilely. Therefore, shape memory alloy materials are often used as thin coils or thin plate-shaped parts.
Conventionally, after hot or warm working such as forging, rolling, or swaging, cold working such as wire drawing or rolling is usually adopted in order to accurately obtain the desired size and shape. There is. Then, as a process subsequent to such a cold working process, performing a shape memory heat treatment is a general method for manufacturing a shape memory alloy material.

However, this shape memory alloy material has undergone a number of stages of plastic working during hot working and warm working until the cold working process, and as a result, the shape memory alloy material is
Disorders of atomic arrangement called dislocations, which are introduced by the processing strain due to those plastic workings, are accumulated.
Furthermore, since work strain is generated by cold working, the shape memory alloy material undergoes rapid work hardening during cold working. That is, a larger amount of stress is required to cause plastic deformation, and it becomes difficult to continue working further. Therefore,
As a pre-process of this final cold working, the method of removing the working strain of the shape memory alloy material by softening the material by performing an annealing treatment, and then performing cold working,
It is generally adopted.

Further, since cold working can generally be carried out only at a small working rate, when the required working is not completed in one cold working step, a plurality of cold working steps are carried out. Inter-working will be carried out. In that case,
By performing the annealing process each time, the work strain is removed, and the cold work is performed again. Then, after the final cold working, the shape memory heat treatment is performed. An example of heat history in the manufacturing process of such a conventional shape memory alloy material is schematically shown in FIG.

However, in the conventional manufacturing process as described above, before and after the cold working process, it is usual that the structure and crystal structure of the material are not thoroughly controlled. Therefore, in the microstructure of the material to be processed, the austenite phase, which is a high-temperature phase that is hard and strong, and the martensite phase, which is a low-temperature phase that is soft and has a shape-memory property, remain mixed in a cold state. Processing steps are being performed. Therefore, during such cold working, due to the influence of the austenite phase, the working stress becomes high, and it becomes necessary to increase the working power, and since it is a mixed phase, it is difficult to obtain dimensional accuracy. Occur. For this reason, cold working of shape memory alloy materials is generally regarded as a difficult technique.

Further, even when the shape memory heat treatment is carried out, since the starting material is a material having a structure in which an austenite phase and a martensite phase are mixed, the defect that the shape memory heat treatment takes time and the shape memory heat treatment There is a drawback that a product with so-called "memory blur" is produced, in which the nature of is not clear. Further, even after the shape memory heat treatment, there is an inherent problem that the operation of shape memory becomes slow due to the austenite phase and the martensite phase being mixed at room temperature.

[0007]

The present invention has been made in view of the above circumstances, and a problem to be solved by the present invention is to facilitate the manufacture of a shape memory alloy material, which has been conventionally difficult. , And to provide a new manufacturing method capable of reducing the manufacturing cost thereof, improving the dimensional accuracy of products, and improving the performance of materials.

Another object of the present invention is to provide a shape memory alloy material which is not only improved in dimensional accuracy but is also excellent in shape memory operation and shape recovery force and is improved in superelasticity. I am about to do it.

[0009]

According to the present invention, in order to solve such a problem, a shape memory alloy material is subjected to cold working and then subjected to shape memory heat treatment to obtain a target shape memory alloy. When manufacturing the material, the shape memory alloy material is subjected to a sub-zero treatment prior to the cold working. By this sub-zero treatment, the entire material becomes a martensite single phase, and during cold working, the effect of the mixed phase of the austenite phase and martensite phase is eliminated, so high dimensional accuracy is obtained and cold working power is also suppressed. Can be done.

According to a preferred aspect of the method for manufacturing a shape memory alloy material according to the present invention, the cold working is performed in a plurality of steps with an annealing treatment step interposed therebetween.
Then, at least between the final process of the plurality of cold working processes and the annealing process process immediately before it, the sub-zero process is performed. Also in this case, as in the above case, since the influence of the mixed phase of the austenite phase and the martensite phase is eliminated during the cold working, high dimensional accuracy can be obtained and the cold working power can be suppressed.

Further, according to a preferred aspect of the present invention, after the cold working, a second sub-zero treatment is performed prior to the shape memory heat treatment. According to this method, the dimensional accuracy is improved and the cold working power is suppressed by the first sub-zero treatment in the pre-process of cold working, and the microstructure of the material is improved by performing the second sub-zero treatment. Is a single phase of martensite, the time required for shape memory heat treatment is shorter than that of a material having a mixed structure of austenite phase and martensite phase, and the heat treatment temperature can be kept low. .

Further, as another manufacturing method for solving the above-mentioned problems, the present invention provides a target shape memory alloy by subjecting a shape memory alloy material to cold working and then performing shape memory heat treatment. A gist of a method for producing a shape memory alloy material, which is characterized in that a subzero treatment is performed after the cold working and before the shape memory heat treatment in producing the material. Even with this method, as in the case of adopting the above-mentioned method, the structure of the material is a single phase of martensite, so that the time for shape memory heat treatment is shorter than that of a material with a mixed structure of austenite phase and martensite phase. The heat treatment temperature can be kept low.

Further, as another manufacturing method for solving the above-mentioned problems, the present invention further comprises subjecting a shape memory alloy material to cold working and then subjecting it to a shape memory heat treatment to obtain a desired shape memory alloy. When manufacturing the material, after the shape memory heat treatment, a sub-zero treatment is further performed. As a result, at the time of use, the retained austenite phase is completely transformed into the martensite phase, so that the shape memory operation speed is increased and the shape recovery stress is also improved.

In the above-mentioned manufacturing method according to the present invention, it is advantageous to perform an aging heat treatment after the sub-zero treatment. As a result, elastic anisotropy, crystal grain size, and orientation strain dependence of transformation strain are large, so it is possible to effectively perform sub-zero treatment even on a material that is prone to fracture at grain boundaries. It will be.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In order to more specifically clarify the present invention, the constitution of the present invention will be described in detail with reference to the drawings showing the steps for producing a shape memory alloy material according to the present invention. And

In short, the present invention introduces a sub-zero treatment step as a part of the manufacturing process of the shape memory alloy material. This sub-zero treatment is also called sub-zero cooling or deep cooling treatment, It is a method that is generally used in the field of manufacturing steel materials, and is a processing method in which the austenite phase that is a high temperature phase is transformed into the martensite phase that is a low temperature phase by cooling the steel to 0 ° C. or lower during quenching. is there. This is adopted for the purpose of eliminating the adverse effects of retained austenite, such as the quenching hardness of steel becoming low.

The present invention is intended to improve the manufacturing process and the performance of the product by incorporating the sub-zero treatment into the manufacturing process of the shape memory alloy material. That is, according to the method of the present invention, the sub-zero treatment brings the shape memory alloy material to a temperature much lower than its martensite transformation end temperature (hereinafter, abbreviated as Mf point), so that the entire material is It becomes martensite single phase.
Therefore, various effects are exhibited depending on which process the sub-zero treatment is used.
Among them, as an example of the manufacturing process that introduced sub-zero treatment as the pre-process of the final cold working process,
FIG. According to this method, since the sub-zero treatment is performed prior to performing the cold working, the residual austenite phase is removed, the influence of the mixed phase is eliminated, and the dimensional accuracy of the product is improved during the cold working. The cold working power can be kept small. Therefore, even if the sub-zero treatment step is added and the need to use a refrigerant for that purpose is taken into consideration, the manufacturing cost is reduced overall.

In the present invention, as the sub-zero treatment refrigerant, ice water, a mixture of dry ice and alcohol, liquid nitrogen, etc., a shape memory alloy material, and various refrigerants capable of cooling the material to 0 ° C. or lower. It is possible to use
At this time, by cooling the material to a temperature lower than the Mf point, the effect of the sub-zero treatment becomes large. Therefore, among the above-mentioned refrigerants, it is particularly economical to use liquid nitrogen because the work is easy and economical. Also has advantages and is desirable.

Further, FIG. 3 shows an example of a manufacturing process for carrying out a sub-zero treatment as a pre-process of the final shape memory heat treatment process. In the case shown in FIG. 3, since the structure of the material becomes a martensite single phase by the subzero treatment, the time for shape memory heat treatment is shorter than that of the material having the mixed structure of the austenite phase and the martensite phase. Also, the heat treatment has the effect of shape memory at a low temperature. Because, in the case of polycrystalline metallic materials, 2
When phases are mixed, the crystal transformation of one phase is
This is because the crystal of the other phase hinders it, but in the case of a single phase, there is no such influence and the phase transformation is performed smoothly. Further, the shape memory heat treatment is performed on the martensite single-phase material after removing the retained austenite phase, so that the shape recovery power of the final product is enhanced.

Further, in FIG. 4, the sub-zero treatment (first) is performed in the step before the final cold working step, and the sub-zero treatment (second) is also performed in the step before the final shape memory heat treatment step. An example of a manufacturing process to be performed is shown. This is a combination of the above two methods,
The effect is also exerted as a combination of the above two. That is, the dimensional accuracy of the product is improved, the cold working power is reduced, and in addition, the shape memory heat treatment can shorten the processing time and the processing temperature, and also the shape recovery power of the final product. It will rise.
In this way, by performing the sub-zero treatment in a plurality of steps, the effects of the respective sub-zero treatments can be obtained repeatedly.

Furthermore, FIG. 5 shows an example of a manufacturing process in which a sub-zero treatment is carried out in the step subsequent to the shape memory heat treatment step. That is, in FIG. 5, the sub-zero treatment is performed after the final product shape is obtained. In this case, when the product is used, the residual austenite phase is once transformed into the martensite phase. Therefore, when the temperature is raised or lowered to perform some shape memory operation, the operation speed is increased and the shape recovery force is improved. In addition, the austenite transformation end temperature (Af
When used in a “superelastic” state in an atmosphere at a temperature higher than the above point, the strain range exhibiting superelasticity is widened and the operating stress is increased. Even in this treatment, the effect can be exhibited by combining with the above-mentioned sub-zero treatment before the cold working and before the shape memory heat treatment step.

As an example of a preferred embodiment of the process shown in FIG. 5, an example of a process in which an aging heat treatment is carried out after the subzero treatment is shown in FIG. This aging heat treatment is a Cu-Al-Ni system or Cu-Zn-A.
This is an indispensable treatment for shape memory alloy materials other than Ti-Ni alloys such as l-based, Ag-Cd-based, and Cu-Sn-based alloys, which can increase hardness and strength. . In addition to the process shown in FIG. 6, it is also possible to carry out a sub-zero treatment after the aging heat treatment. Also in these cases, the same effect as in the case of the process shown in FIG. 5 can be obtained.

As described above, the present invention introduces the sub-zero treatment technique into the manufacturing process of the shape memory alloy material,
In addition to facilitating the manufacture of shape memory alloy materials, which have been difficult in the past, reducing manufacturing costs and improving the dimensional accuracy of products, they are also excellent in shape memory operation and shape recovery, and have superelasticity. It could provide a new manufacturing method to improve.

[0024]

EXAMPLES The production method according to the present invention will be described in more detail below with reference to some examples, but the present invention is subject to any restrictions due to the description of such examples. Needless to say, it is not a thing. In addition to the following embodiments, the present invention is not limited to the above specific description, and various changes and modifications are made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It is to be understood that improvements, etc. can be added.

Shape memory alloys a to c as shown in the following Table 1 are prepared, and any one of them is used to obtain a predetermined shape memory alloy according to the method of Examples 1 to 6 below. While obtaining the material, in each example, a shape memory alloy material that has undergone the same processing steps except for the sub-zero processing was manufactured as a comparative sample. Then, between the sample according to the present invention and the comparative sample obtained in each example, the martensitic transformation start temperature (hereinafter abbreviated as Ms point), the power value during cold working, and the shape of the final product The recovery stress was measured and compared. In addition to the above characteristics, the sample obtained in Example 4 was also compared with respect to the martensitic transformation-induced stress and deformation strain range in the superelastic state at 100 ° C. for comparison with the superelastic performance. In addition, the differential scanning calorimeter (D
SC) was used, and the reading of the power meter of the motor that drives the molding machine was used to measure the processing power value. Further, the shape recovery stress is measured by reading the tension when the final product is pulled and fixed to a predetermined length at room temperature with a tensile tester and then the temperature is raised to 100 ° C. Regarding the martensitic transformation induced stress, Similarly, it was measured by reading the tension of a tensile tester.

[0026]

[Table 1]

Example 1 Ti—Ni having the composition of the shape memory alloy a in Table 1 was used.
A system shape memory alloy was prepared and subjected to hot working such as rolling and swaging, and annealing and cold working in multiple stages. Subsequently, as in the process shown in FIG. 2, after the final annealing process, as a pre-process of the final cold working process, a sub-zero process of placing in liquid nitrogen and holding for 10 minutes is performed, and then at room temperature for 10 min. The final cold working was performed at three types of cold working rates of%, 20% and 30%. Further, after the final cold working, a shape memory heat treatment of holding the material at 450 ° C. for 40 minutes is performed, followed by quenching in water and quenching to obtain a shape memory alloy material having a martensite structure,
It was designated as Sample 1. When the Ms point of this sample 1 was measured, it was 44 ° C., and there was almost no change from the Ms point of the comparative sample. It was also found that the obtained sample 1 required about 10% less power during cold working than the comparative sample, and the shape recovery stress was improved by about 5%.

Example 2 Ti-Ni having the composition of the shape memory alloy a in Table 1
A system shape memory alloy was prepared and subjected to hot working such as rolling and swaging, and annealing and cold working in multiple stages. Subsequently, as in the process shown in FIG. 3, after the final cold working is performed at room temperature with three kinds of cold working rates of 10%, 20%, and 30%, as a pre-process of the shape memory heat treatment process. ,
Sub-zero treatment was carried out by placing the sample in liquid nitrogen and holding it for 10 minutes. Then, the material is subjected to shape memory heat treatment at 450 ° C. for 40 minutes, then rapidly cooled in water and quenched to obtain a shape memory alloy material having a martensite structure,
It was designated as Sample 2. When the Ms point of this sample 2 was measured, it was 44 ° C., and there was almost no change from the Ms point of the comparative sample. Further, it was found that the obtained sample 2 had a shape recovery stress improved by about 5% as compared with the comparative sample.

Example 3 Ti—Ni having the composition of the shape memory alloy a in Table 1 was used.
A system shape memory alloy was prepared and subjected to hot working such as rolling and swaging, and annealing and cold working in multiple stages. Subsequently, as in the process shown in FIG. 4, after the final annealing treatment, a first sub-zero treatment of placing in liquid nitrogen and holding for 10 minutes is performed as a step before the final cold working step.
Then, the final cold working was performed at room temperature at three cold working rates of 10%, 20%, and 30%. Further, after that, as a pre-process of the shape memory heat treatment process, a second sub-zero treatment was performed in which the product was placed in liquid nitrogen again and held for 10 minutes.
Subsequently, after performing shape memory heat treatment of holding the material at 450 ° C. for 40 minutes, it was rapidly cooled in water and quenched to obtain a shape memory alloy material having a martensite structure, which was designated as Sample 3. When the Ms point of this sample 3 was measured, it was 44
C., and there was almost no change from the Ms point of the comparative sample. It was also found that the obtained sample 3 required less power during cold working than the comparative sample by about 10%, and the shape recovery stress was improved by about 6%.

Example 4 Ti—Ni having the composition of the shape memory alloy a in Table 1 was used.
Hot-working such as rolling and swaging, and a plurality of annealing treatments and cold-working are performed on the system shape memory alloy, and the final cold-working is performed at room temperature at 10%, 20%, and 30%. It carried out by three types of cold working rates. Subsequently, as in the process shown in FIG. 5, the material was subjected to shape memory heat treatment at 450 ° C. for 40 minutes, then rapidly cooled in water and quenched to obtain a martensite structure. Then, the sample was placed in liquid nitrogen and subjected to a sub-zero treatment of holding for 10 minutes to obtain a shape memory alloy material, which was designated as Sample 4. M of this sample 4
When the s point was measured, it was 44 ° C., and the Ms of the comparative sample was
There was almost no change from the point. Further, the obtained sample 4 has a shape recovery stress improved by about 4% as compared with the comparative sample, and further, the martensitic transformation-induced stress in the superelastic state is 10%.
It was found that the deformation strain range was improved and the deformation strain range was widened by about 1%.

Example 5 Cu—Zn having the composition of the shape memory alloy b in Table 1
-Prepare an Al-based shape memory alloy, subject it to hot working such as rolling and swaging, and subject it to a plurality of stages of annealing and cold working,
For final cold work, room temperature 10%, 20%, 3
It was performed at three cold working rates of 0%. Subsequently, as in the process shown in FIG. 6, after performing shape memory heat treatment in which the material is held at 600 ° C. for 5 minutes, the material is immediately cooled in water and quenched to obtain a martensite structure. Then, a sub-zero treatment was carried out for 10 minutes. After that, an aging heat treatment of holding at 100 ° C. for 30 minutes was performed to obtain a shape memory alloy material, which was used as Sample 5. When the Ms point of this sample 5 was measured, it was 39 ° C., and there was almost no change from the Ms point of the comparative sample. Further, it was found that the obtained sample 5 had a shape recovery stress improved by about 5% as compared with the comparative sample.

Example 6 Cu-Al having the composition of the shape memory alloy c in Table 1
-Prepare a Ni-based shape memory alloy, subject it to hot working such as rolling and swaging, and subject it to a plurality of stages of annealing and cold working,
For final cold work, room temperature 10%, 20%, 3
It was performed at three cold working rates of 0%. Subsequently, as in the process shown in FIG. 6, after performing shape memory heat treatment in which the material is held at 600 ° C. for 5 minutes, the material is immediately cooled in water and quenched to obtain a martensite structure. Then, a sub-zero treatment was carried out for 10 minutes. Then, an aging heat treatment of holding at 100 ° C. for 30 minutes was performed to obtain a shape memory alloy material, which was designated as Sample 6. When the Ms point of this sample 6 was measured, it was 51 ° C., and there was almost no change from the Ms point of the comparative sample. Further, it was found that the obtained sample 6 had a shape recovery stress improved by about 7% as compared with the comparative sample.

[0033]

As is apparent from the above description, according to the method for manufacturing a shape memory alloy material according to the present invention, a sub-zero treatment is performed as a pre-treatment or a post-treatment for each step in the manufacturing process of the shape memory alloy material. By adopting this, the entire material becomes a martensite single phase, and thus various adverse effects caused by the conventional retained austenite phase can be eliminated. For example, when sub-zero treatment is performed as a pretreatment for the cold working process,
Phenomena such as high processing power and difficulty in obtaining dimensional accuracy can be effectively suppressed, and when the pretreatment of the shape memory heat treatment step is performed, the structure of the material is a martensite single phase. Therefore, it exhibits the feature that the shape memory heat treatment can be performed at a lower temperature and in a shorter time than the conventional method. Furthermore, when it is performed as a post-treatment of the shape memory heat treatment step, the characteristic of the shape memory operation can be enhanced.

Therefore, according to the manufacturing method of the present invention, a shape memory alloy material which is excellent in shape memory operation and shape recovery force and also improved in superelasticity can be easily manufactured at low cost with excellent dimensional accuracy. Can be manufactured in.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a conventional manufacturing process of a shape memory alloy material.

FIG. 2 is an explanatory view showing an example of a manufacturing process of the shape memory alloy material according to the present invention.

FIG. 3 is an explanatory view showing another example of the manufacturing process of the shape memory alloy material according to the present invention.

FIG. 4 is an explanatory view showing another different example of the manufacturing process of the shape memory alloy material according to the present invention.

FIG. 5 is an explanatory view showing still another example of the manufacturing process of the shape memory alloy material according to the present invention.

FIG. 6 is an explanatory view showing still another different example of the manufacturing process of the shape memory alloy material according to the present invention.

Claims (6)

[Claims] 1. A shape memory alloy material is subjected to cold working and then subjected to shape memory heat treatment to produce a desired shape memory alloy material, prior to the cold working, the shape memory. A method of manufacturing a shape memory alloy material, which comprises subjecting an alloy material to a sub-zero treatment. 2. The cold working is performed in a plurality of steps with an annealing treatment step sandwiched therebetween, and the sub-zero is performed at least between a final step of the plurality of cold working steps and an annealing treatment step immediately before it. Claim 1 wherein processing is performed
A method for producing the shape memory alloy material described. 3. The method for producing a shape memory alloy material according to claim 1, wherein after the cold working, a second sub-zero treatment is performed prior to the shape memory heat treatment. 4. A shape memory alloy material is cold-worked and then subjected to shape-memory heat treatment to produce a target shape-memory alloy material. A method for producing a shape memory alloy material, characterized by performing sub-zero treatment prior to heat treatment. 5. A shape memory alloy material is subjected to cold working and then subjected to shape memory heat treatment to produce a target shape memory alloy material. A method for producing a shape memory alloy material, which comprises subjecting the material to a treatment. 6. The method for manufacturing a shape memory alloy material according to claim 5, which comprises performing an aging heat treatment after the sub-zero treatment.