JPH10237572A - High strength anelasticity titanium-nickel series alloy and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart excellent pseudoelasticity in the vicinity of room temps. to an alloy by annealing an Ti-Ni series alloy showing thermoelastic type martensitic transformation, thereafter subjecting it to cold working to form into a high tensile strength alloy having a specified value or above and furthermore executing heat treatment recovering working strain therein. SOLUTION: As for the compsn. of the alloy, limitation is not particularly put, but, a Ti-Ni alloy showing thermoelastic type martensitic transformation in a state of being annealed at >=700 deg.C such as Ti 30 to 50 at%-Ni, Ti 48 to 53 at%-Ni, Ti 49.5 to 51.5 at%-Ni or the like is preferably used. This alloy is annealed in a temp. range in which it is not perfectly recrystallizad and is thereafter treated so as to obtain >=8% fracture elongation. Next, suitable cold working is executed to regulates its tensile strength to >=170kg/mm<2> and is thereafter subjected to heat treatment at 200 to 400 deg.C to recover working strain therein. In this way, even in the case 80kg/mm<2> tensile strength is applied, residual strain after stress relieving can substantially be regulated to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ti-Ni-based alloy having excellent pseudoelastic properties near room temperature and a method for producing the same, and more particularly, to an excellent pseudoelastic property even when a high stress is applied. And a method for producing the same.

[0002]

2. Description of the Related Art Ti showing thermoelastic martensitic transformation
-Ni-based alloys are widely known as superelastic alloys having superelastic properties as well as shape memory properties. The superelastic property is a property in which, when a stress is applied, plastic deformation of apparently several% to 10% is caused, but at the same time as the stress is removed, the shape completely returns to the original shape. In general, in the production of a Ti-Ni-based superelastic alloy, as disclosed in Japanese Patent Publication No. 2-51976, a Ti-Ni-based alloy is processed at a processing rate of 20%.
A method of performing a heat treatment without causing recrystallization at a temperature of 250 ° C. or higher after a working structure in which slip deformation is unlikely to occur by the above cold working is widely used. To date, many Ti-Ni alloys have been reported to have superelastic properties. In recent years, by utilizing its superelastic properties, Ti-Ni-based alloys have been widely used for hanging strings, antennas for mobile phones, and the like.

[0003]

However, the inventors of the present invention have studied the mechanical properties of a superelastic Ti-Ni alloy and found that all of the superelastic alloys produced by various thermomechanical treatment methods have been subjected to stress loading. It was found that as the amount was increased, residual strain remained after stress relief. In particular, when a tensile stress of 80 kg / mm ² or more was applied, it was found that the residual strain became significant after the stress was removed,
This has been a problem when used in an environment where high stress is applied. Therefore, there has been a demand for the development of an alloy that does not leave strain after the stress is removed even under an environment where a high stress is applied, and the development of a manufacturing method thereof. The present invention has a high tensile strength of 170 kg / mm ² or more and a tensile strength of 80 kg / mm ² or more.
/ Mm ² or more, a high-strength pseudoelastic T having a residual strain of substantially 0 after the stress is removed.
An object of the present invention is to provide an i-Ni-based alloy and a method for producing the same.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by applying an appropriate working heat treatment to a Ti—Ni alloy showing thermoelastic martensitic transformation. The present inventors have found a new type of high-strength Ti-Ni alloy having pseudoelastic properties, and have reached the present invention. That is, the first invention has a tensile strength of 170 kg / mm ² or more, and even when a tensile stress of 80 kg / mm ² or more is applied, the residual strain is substantially zero after the stress is removed. High strength pseudoelastic Ti-
The gist is a Ni-based alloy. In the second invention, a Ti—Ni-based alloy exhibiting a thermoelastic martensitic transformation is subjected to an annealing treatment, and then subjected to cold working to 170 kg / m 2.
An alloy having a tensile strength of at least m ² and a method for producing a high-strength pseudoelastic Ti-Ni-based alloy as described above, further comprising heat-treating the alloy at a temperature of 200 to 400 ° C. is there.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The Ti—Ni-based alloy of the present invention needs to have a tensile strength of 170 kg / mm ² or more.
It preferably has a tensile strength of at least kg / mm ² ,
More preferably, it has a tensile strength of 185 kg / mm ² or more. In the present invention, the tensile strength of the alloy is 170
80 kg / mm ² for the first time
^{Even when two} or more tensile stresses are applied, a resin having a residual strain of substantially zero after the stress is removed is obtained. In the present invention, the term “residual strain is substantially 0” means that the residual strain is 0.02% or less. The residual strain is
Using a tensile tester, a Ti—Ni-based alloy material having a length of 5 to 40 cm was subjected to a room temperature of 8 at a strain rate of 10 ⁻³ to 10 ⁻⁶ / sec.
After applying a tensile stress of 0 kg / mm ² or more, the residual length after the removal of the stress is measured to obtain the following formula. {(Residual length) / (test length)} × 100 = (residual strain)

When the tensile strength of the alloy is less than 170 kg / mm ² , when a tensile stress of 80 kg / mm ² is applied, the alloy exhibits inferior elasticity and exhibits residual strain after the stress is removed. In addition, the tensile strength in the Ti-Ni-based alloy of the present invention refers to the breaking strength (rupture stress) obtained in a normal tensile test, and in the Ti-Ni-based alloy of the present invention, the elongation at break is 7 to 10. It is preferably in the range of 13%. Further, the Ti—Ni-based alloy of the present invention does not show a clear transformation stress to martensite (substantially constant transformation stress value) and does not have a so-called superelastic property.

As described above, the Ti—Ni-based alloy of the present invention needs to have a residual strain of substantially 0 after the stress is removed even when a tensile stress of 80 kg / mm ² or more is applied. . Further, considering use in an environment where a high stress is applied, even when a tensile stress of 100 kg / mm ² or more is applied, the excellent pseudoelastic property in which the residual strain is substantially zero after the stress is removed is obtained. It is desirable to have. Further, the Ti—Ni-based alloy of the present invention has an elongation at the time of applying the highest applied stress, that is, a residual strain of substantially 0, that is, an elongation that recovers after the stress is removed (pseudoelastic elongation) is 5 to 7. %, And can withstand relatively large pseudoelastic deformation.

[0008] The alloy of the present invention must be a Ti-Ni-based alloy, and exhibits a thermoelastic martensitic transformation when sufficiently annealed (heat treated) at a temperature of 700 ° C or higher. It is preferably a system alloy. The composition of the alloy used in the present invention is not particularly limited, but may be a Ti-48 to 53 at% Ni alloy or Fe, Co, Mn, Cr, V, Zr, Al
5a in total from one or more elements selected from the group
alloy containing at most t% or less, Ti-30 to 50 at% Ni
−0 to 20 at% Cu alloy or Fe, Co, M
one or two selected from the group consisting of n, Cr, V, Zr, and Al
It is preferable that the alloy contains 5 at% or less in total of at least one kind of element, and Ti-49.5 to 51.5 at% Ni
Alloy or Fe, Co, Mn, Cr, V, Zr, A
1 or two or more elements selected from the group
at% or less, Ti-35 to 50 at% N
i-0 to 15 at% Cu alloy or Fe, Co, M
one or two selected from the group consisting of n, Cr, V, Zr, and Al
It is more preferable to use an alloy containing 2 at% or less in total of at least one kind of element.

Next, a method for producing the high-strength pseudoelastic Ti-Ni alloy of the present invention will be described. Ti-Ni of the present invention
In order to obtain a system alloy, first, it is necessary to perform an annealing treatment on the Ti-Ni system alloy exhibiting the thermoelastic martensitic transformation. And after an annealing process, it is manufactured by adding appropriate cold working and heat treatment. The annealing treatment in the present invention is for removing a part of the processing strain and other distortion of the Ti—Ni-based alloy so that the final cold working step can be performed. As shown, it is preferable to perform an annealing treatment. The annealing temperature and the holding time may be appropriately selected depending on the shape of the alloy and the processing history up to that time. For example, cold working is 30%
600-650 ° C for Ti-Ni alloy
For 15 minutes is sufficient. Here, T of the present invention
In order to produce an i-Ni-based alloy, it is desirable to perform an annealing treatment within a range that does not completely recrystallize. Here, the range that does not completely recrystallize is a case where a material property showing a breaking elongation of 30% or less is obtained when a tensile test is performed after annealing. In addition, as a method of obtaining a Ti-Ni-based alloy before annealing, after producing an ingot by high-frequency vacuum induction melting or arc melting, the ingot is subjected to hot working, cold working, intermediate annealing, cutting, or the like. To a shape before final finishing, or a method of rapidly solidifying from a molten state typified by spinning in liquid spinning, and then performing cold working to obtain a shape before final finishing, etc. , Various methods can be used.

Further, in the present invention, it is necessary to perform cold working after the annealing treatment to obtain an alloy having a tensile strength of 170 kg / mm ² or more. In addition, 100kg /
Even when a tensile stress of not less than ² mm ² is applied, in order to obtain a high-strength alloy having excellent pseudoelastic properties in which the residual strain is substantially 0 after the stress is removed, it is necessary to perform cold working at 180 kg / mm ^2. An alloy having the above tensile strength is preferable, and an alloy having a tensile strength of 185 kg / mm ² or more is more preferable. Here, in order to obtain a tensile strength of 170 kg / mm ² or more in the cold working step when producing the alloy of the present invention, the area reduction rate is preferably 30% or more,
% Or more, the material has a strength defect (with a tensile strength of 1%).
(A portion lower than 50 kg / mm ² ) is not preferable. In addition, as a method of the cold working, various methods such as rolling and drawing, which are ordinary methods for processing a metal material, can be used.

Further, in order to produce the alloy of the present invention, it is necessary to perform a heat treatment at a temperature of 200 to 400 ° C. after cold working, and in particular, it is necessary to perform a heat treatment at a temperature of 200 to 300 ° C. preferable. In the present invention, it is necessary to recover the working strain by performing a heat treatment at a temperature of 200 to 400 ° C. after the cold working in a range where no clear transformation stress to martensite is observed. As a material property after the heat treatment, the tensile strength of the alloy is 17
0 kg / mm ² or more;
%. Note that the heat treatment time may be appropriately selected depending on the final shape of the alloy. For example, in the case of a thin wire having a diameter of 1 mm or less, 200 to 40
The heat treatment may be performed at 0 ° C. for 1 to 10,000 minutes. Here, if the heat treatment temperature exceeds 400 ° C., since the recovery of strain occurs in a short time, it is difficult to obtain a high-strength Ti—Ni-based alloy having excellent pseudoelastic properties of the present invention. On the other hand, if the heat treatment temperature is lower than 200 ° C., the strain does not recover even after a very long heat treatment, and an alloy having a breaking elongation of 7% or more cannot be obtained. The heat treatment method of the present invention can be performed using various heating methods in an atmosphere such as air, vacuum, or an inert gas, and heat conduction or heating from a liquid heating medium such as a salt bath. A heating method utilizing heat conduction from a solid that has been used can also be used.

[0012]

The present invention will be described below in detail with reference to examples and comparative examples. Examples 1 to 4 Each alloy having the composition shown in Table 1 was weighed to a total of 3 kg, and melted in a high-frequency vacuum melting furnace (frequency: 3 kHz, degree of vacuum: 1 × 10 ⁻⁴ Torr) using a graphite crucible. It was cast in a cast iron mold (inner diameter 50 mm). During dissolution, the temperature was controlled so as not to exceed 1450 ° C. Next, after the obtained ingot was externally cut by a lathe, it was made into a round bar having a diameter of 20 mm by hot forging, and after external cutting again, a wire having a diameter of 6 mm was obtained by hot rolling using a groove roll. This was made into a wire having a diameter of 1 mm by cold drawing.

The wire was annealed at 650 ° C. for 15 minutes to produce an annealed material having a diameter of 1 mm. In addition,
This wire showed thermoelastic martensitic transformation. Next, using each annealed material, the area reduction rate was 51% by cold drawing.
Was obtained to obtain a drawn wire having a diameter of 0.7 mm. In addition,
The cold drawing was performed such that the area reduction between dies was 9 to 11%. Further, a heat treatment was performed at 240 ° C. for 600 minutes using the obtained drawn wire to obtain a heat-treated material. The thus obtained annealed material (1 mm diameter), cold drawn material (0.
A tensile test was performed on the heat-treated material (diameter 7 mm) and the heat-treated material (diameter 0.7 mm), and the obtained mechanical properties are shown in Table 1. here,
The tensile test was performed at room temperature 23 with a tensile tester (manufactured by Instron) under the conditions of a test length of 20 cm and a tensile speed of 5 mm / min.
C. was performed.

[0014]

[Table 1]

Further, each heat-treated material (0.7 mm
With respect to the diameter), the tensile stress was applied to an alloy having a test length of 20 cm by a tensile tester in the range of 50 to 150 kg / mm ² , and the residual strain after the stress was removed was measured. Was determined to be the highest applied stress. Table 2 shows the results. Table 2 also shows the elongation when the highest applied stress is applied, that is, the elongation recovered after the stress is removed, as pseudoelastic elongation.

[0016]

[Table 2]

As is clear from Tables 1 and 2, the Ti—Ni-based alloys of the present invention (heat-treated materials of Examples 1 to 4) all have a tensile strength of 180 kg / mm ² or more, and It can be seen that even when a tensile stress of / mm ² or more is applied, the resin has excellent pseudoelastic properties in which the residual strain is substantially zero after the stress is removed. Also, the observed pseudoelastic elongation is excellent, having 6% or more. In the stress-elongation curve obtained from the tensile test of the Ti—Ni-based alloy of the present invention, as shown in FIG. 1, no clear transformation stress to martensite (almost constant transformation stress value) was observed. It was confirmed that it did not have superelastic properties.

Examples 5-8 Each heat-treated material was produced in the same manner as in Examples 1-4, except that the conditions in the final heat treatment step were 300 ° C. and 30 minutes. Then, a tensile test was performed on the annealed material (1 mm diameter), the cold drawn wire (0.7 mm diameter), and the heat-treated material (0.7 mm diameter) in the same manner as in Example 1. Table 3 shows the results. Further, for each heat-treated material (0.7 mm diameter), a tensile stress is applied to an alloy having a test length of 20 cm in a range of 50 to 150 kg / mm ² by a tensile tester, and the residual strain after the stress is removed is measured. Thereby, the highest applied stress and pseudoelastic elongation at which the residual strain was substantially 0 were obtained. Table 4 shows the results.

[0019]

[Table 3]

[0020]

[Table 4]

As is clear from Tables 3 and 4, each of the Ti—Ni-based alloys (heat-treated materials of Examples 5 to 8) of the present invention has a tensile strength of 180 kg / mm ² or more and 100 kg / mm ^2. It can be seen that even when a tensile stress of / mm ² or more is applied, the resin has excellent pseudoelastic properties in which the residual strain is substantially zero after the stress is removed. Also, the observed pseudoelastic elongation is excellent, showing 6% or more. In addition,
As shown in FIG. 1, no clear transformation stress to martensite (almost constant transformation stress value) was observed in the stress-elongation curve obtained from the tensile test of the alloy of the present invention, and the alloy had superelastic properties. Not confirmed.

Comparative Examples 1-4 Each heat-treated material was produced in the same manner as in Examples 1-4, except that the area reduction in the cold drawing step was 27.75%. And annealed material (1 mm diameter), cold drawn wire (0.8 mm
(5 mm diameter) and a heat-treated material (0.85 mm diameter) were subjected to a tensile test. Table 5 shows the results. For each heat-treated material (0.85 mm diameter), a tensile stress of 80 kg / mm ^{2 was} applied by a tensile tester, and the residual strain after the stress was removed was measured. Table 6 shows the results.

[0023]

[Table 5]

[0024]

[Table 6]

As shown in Tables 5 and 6, the tensile strengths of the drawn materials of Comparative Examples 1 to 4 were all 170 kg / m.
m ² , and therefore, the tensile strength of each of the heat-treated materials is as weak as less than 170 kg / mm ² ,
Even after the removal of the applied stress of 80 kg / mm ^{2, the characteristics} of causing the residual strain were poor.

Comparative Examples 5 to 8 Each heat-treated material was produced in the same manner as in Examples 1 to 4, except that the conditions in the final heat treatment step were 450 ° C. and 60 minutes. Then, a tensile test was performed on the annealed material (1 mm diameter), the cold drawn wire (0.7 mm diameter), and the heat-treated material (0.7 mm diameter). Table 7 shows the results. For the heat-treated material (0.7 mm diameter), a tensile stress of 80 kg / mm ^{2 was} applied by a tensile tester, and the residual strain after the stress was removed was measured. Table 8 shows the results.

[0027]

[Table 7]

[0028]

[Table 8]

As shown in Tables 7 and 8, since the heat treatments of Comparative Examples 5 to 8 have high heat treatment temperatures, the tensile strengths of the heat-treated materials are all low, less than 170 kg / mm ² . In addition, even after removing the applied stress of 80 kg / mm ² , it has poor characteristics of causing residual strain. In addition,
For Comparative Examples 5 to 8, the stress obtained from the tensile test was −
A clear transformation stress to martensite (almost constant transformation stress value) was observed on the elongation curve, and the material had superelastic properties.

Comparative Examples 9 to 12 Heat-treated materials were prepared from the alloys shown in Table 1 in the same manner as in Examples 1 to 4, except that the conditions in the final heat treatment step were 150 ° C. and 6000 minutes. And annealed material (1m
m diameter), a cold drawn wire (0.7 mm diameter) and a heat-treated material (0.7 mm diameter) were subjected to a tensile test. Table 9 shows the results.
Shown in

[0031]

[Table 9]

As shown in Table 9, Comparative Examples 9-1
Since the alloy No. 2 has a low heat treatment temperature, the elongation at break of the heat-treated material is as low as less than 4% even after a very long heat treatment.
Even if pseudo-elasticity was exhibited at a load stress of 80 kg / mm ² , the pseudo-elastic elongation was about 2.5%, and the amount of deformation was small, so that the practicability was low.

[0033]

The Ti-Ni alloy of the present invention has a
g / mm ² or higher tensile strength material,
Also, even when a tensile stress of 80 kg / mm ² or more is applied, it has excellent pseudoelastic properties in which the residual strain is substantially zero after the stress is removed. Therefore, as a pseudoelastic alloy used in an environment exposed to a high load stress, it can be widely used for a hanging string, a mobile phone antenna, and the like. Further, it can be used as a material resistant to stress in eyeglass frames and the like, and has high industrial value. Further, according to the production method of the present invention, a high-strength alloy having excellent pseudoelastic properties can be easily produced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a stress-elongation curve of a high-strength pseudoelastic Ti—Ni-based alloy of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 630 C22F 1/00 630Z 673 673 675 675 686 686 686A 691 691A

Claims (2)

[Claims] 1. Even when a tensile strength of 170 kg / mm ² or more is applied and a tensile stress of 80 kg / mm ² or more is applied, the residual strain is substantially zero after the stress is removed. High strength pseudoelastic Ti-Ni alloy. 2. Ti showing thermoelastic martensitic transformation
After annealing the Ni-based alloy, cold working
And alloys with 0 kg / mm ² or more tensile strength, further, high strength pseudoelastic Ti-Ni according to claim 1, wherein the heat treating the alloy at a temperature of 200 to 400 ° C.
Production method of base alloy.