TiNi alloys

Abstract

Than before (T HAF -T HRS ) can be increased, and (T HAS -T HRS ) is also sufficiently large. [Solution] A TiNi-based alloy containing one or more elements selected from the group consisting of Nb and Ta, wherein the crystallite size of the TiNi crystals calculated by applying the Scherrer equation to the peak corresponding to the (110) plane of the high-temperature phase of the TiNi crystals in an X-ray diffraction pattern obtained using a CuKα X-ray source is 25 nm or less.

Description

[Technical Field]

[0001] The present disclosure relates to TiNi-based alloys. [Background technology]

[0002] From the viewpoint of efficient energy utilization, heat storage materials that store excess heat inside the material and can be freely released and used when needed are being developed. In developing heat storage materials, it is generally considered to utilize the heat absorption and generation that accompanies the phase transformation of the material.

[0003] Conventional heat storage materials, such as water or paraffin, generally utilize the heat of transformation that occurs when the material changes from solid to liquid. These materials have a very large heat of transformation per volume (for example, 200 J / cc or more). However, this material has a very low thermal conductivity of approximately 1 W / mK, making it difficult to efficiently absorb heat into the material and dissipate it to the outside. Furthermore, this material requires encapsulation of the liquid, making it difficult to maintain a fixed shape, and its shape is limited to simple forms. Furthermore, the capsule acts as a thermal barrier, reducing its properties as a heat storage material. Furthermore, this material does not have a significant difference in the heat absorption and heat generation temperatures associated with phase transformation, and after absorbing heat above a certain temperature, it can only dissipate heat to the outside of the material below that temperature. Furthermore, the heat dissipation behavior of this material is triggered only by temperature change, and no other external stimuli can be used to intentionally dissipate heat.

[0004] In contrast, according to Non-Patent Document 1 and Patent Document 1, oxide ceramics such as Ti2O3 and VO2 undergo a solid (low-temperature phase)-solid (high-temperature phase) phase transformation. Furthermore, the heat of transformation is approximately 200-250 J / cc, comparable to the heat of transformation associated with the solid-liquid transition described above. In the case of Ti2O3, the high-temperature phase at 1 atmosphere transforms into the low-temperature phase when the pressure is increased to a very high hydrostatic pressure of 300 atmospheres, and heat can be released from the material as a result of this phase transformation. Additionally, the low-temperature phase can also be generated by applying a large impact, such as with a hammer, which also allows for heat release. However, this material also has a very low thermal conductivity of about 1 W / mK, making it difficult to efficiently absorb heat into the material. Furthermore, this material has poor ductility and workability, making it difficult to process into complex shapes. Furthermore, because this material is brittle, it easily breaks when subjected to high pressure and large impacts to induce the low-temperature phase, as mentioned above.

[0005] In recent years, the use of diffusionless structural phase transformation alloys that exhibit solid-solid phase change as heat storage materials has been studied as materials that have higher thermal conductivity than ceramics and allow for freedom in shape through processing. Non-Patent Document 2 discloses the use of TiNi-based alloys that exhibit martensitic transformation as a solid-solid phase change. In TiNi-based alloys, the heat release onset temperature (T HRS ) ~ Endothermic end temperature (T HAF According to Non-Patent Document 2, TiNi-based alloys can generate a high heat of phase transformation of approximately 230 J / cc at maximum, and furthermore, a transformation from a high-temperature phase to a low-temperature phase can be induced with a relatively small stress, which can dissipate heat. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2020 / 144982 [Non-patent literature]

[0007] [Non-Patent Document 1] Shin-ichi Ohkoshi, et al., "Low-pressure-responsive heat-storage ceramics for automobiles", Scientific Reports, 2019, 9, 13203 [Non-patent document 2] Kato H., "Latent heat storage capacity of NiTi shape memory alloy", J. Mater. Sci., 2021, 56, 8243-8250 Summary of the Invention [Problem to be solved by the invention]

[0008] When using TiNi alloys as heat storage alloys, the endothermic temperature (T HAF ) and heat dissipation start temperature (T HRS ) difference (T HAF -T HRS ) needs to be increased. Non-Patent Document 2 controls the phase transformation heat (Ms, Mf, As, Af) by controlling the component composition of TiNi alloy, and HAF -T HRS However, in the prior art disclosed in Non-Patent Document 2, the (Af-Ms) in the DSC curve was 27.0 to 31.8°C, which is considered to be approximately equivalent to the (T HAF -T HRS ) has not been sufficiently considered. In addition, in TiNi alloys, the endothermic start temperature (T HAS ) and heat dissipation start temperature (T HRS ) and the difference (T HAS -T HRS ) should also be large enough. HAS -T HRS If the temperature is small, the heat extracted to the outside will be absorbed again by the alloy material, and the absorbed heat cannot be used efficiently.

[0009] The present disclosure has been made in light of such circumstances, and one of its purposes is to HAF -T HRS ) can be increased, and (T HAS -T HRS ) is sufficiently large. [Means for solving the problem]

[0010] Aspect 1 of the present invention is a TiNi-based alloy containing one or more selected from the group consisting of Nb and Ta, wherein the crystallite size of the TiNi crystal obtained by applying Scherrer's formula to the peak corresponding to the (110) plane of the high-temperature phase of the TiNi crystal in the X-ray diffraction pattern obtained with a CuKα X-ray source is 25 nm or less.

[0011] Aspect 2 of the present invention is the TiNi-based alloy according to Aspect 1, having the component composition of the following formula (1). Ti x Ni 100-x-y-z Nb y Ta z ···(1) x is the ratio (atomic %) of the number of Ti atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, satisfying 40 ≦ x ≦ 60, y is the ratio (atomic %) of the number of Nb atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, z is the ratio (atomic %) of the number of Ta atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, and 0 < y + z ≦ 10 is satisfied.

[0012] Aspect 3 of the present invention is the TiNi-based alloy according to Aspect 1 or 2, which is heated to a temperature above the end temperature of heat absorption in the DSC curve during heating to cause heat absorption, and then can release heat by applying an external stress.

[0013] Aspect 4 of the present invention is when the external stress is 500 MPa or less, the temperature can be raised by 5 °C or more by the heat release, and the temperature drop due to heat absorption that occurs when the external stress is removed is 1 / 20 or less of the temperature rise due to heat release.

[0014] Aspect 5 of the present invention is the TiNi-based alloy according to any one of Aspects 1 to 4, which is in a plate shape, a linear shape, or a spring shape. [Effects of the Invention]

[0015] According to this embodiment, the HAF -T HRS ) can be increased, and (T HAS -T HRS ) is also sufficiently large. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an SEM image of the TiNi-based alloy of Test No. 1. [Figure 2] 1 is an SEM image of the TiNi-based alloy of Test No. 2. [Figure 3] 1 is an SEM image of the TiNi-based alloy of Test No. 3. [Figure 4] 1 is an SEM image of the TiNi-based alloy of Test No. 4. [Figure 5] 1 shows XRD patterns of TiNi-based alloys of Test Nos. 3 and 4. [Figure 6] 1 shows XRD patterns of TiNi-based alloys of Test Nos. 5 to 7. [Figure 7] FIG. 1 is a schematic diagram showing how to determine THAF. [Figure 8A] 1 is a graph showing the change over time in the tensile test load F (N) applied to the TiNi-based alloy of Test No. 6. [Figure 8B] 8B is a graph showing the temperature change of the TiNi-based alloy of Test No. 6 during the tensile test of FIG. 8A. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present inventors have HAF -T HRS ) can be increased, and (T HAS -T HRS)In order to realize a sufficiently large TiNi-based alloy, it was studied from various angles. As a result, while not dissolving in the TiNi alloy matrix phase, Nb and / or Ta, which are considered to segregate at the grain boundaries of the matrix phase grains (distinguished from the crystallites described later), are contained, and the crystallite size of the TiNi crystal obtained by a predetermined method is controlled to be below a predetermined value. As a result, (T HAF -T HRS ) can be increased, and a TiNi-based alloy with a sufficiently large (T HAS -T HRS ) was realized. This is considered to be because, while containing Nb and / or Ta that segregate at the grain boundaries, by reducing the crystallite size of the TiNi crystal, strain for suppressing the martensitic transformation of the TiNi-based alloy becomes easier to accumulate. When the martensitic transformation is suppressed, the martensitic transformation start temperature (Ms point) or T HRS decreases, and (T HAF -T HRS ) and (T HAS -T HRS ) are considered to increase. Note that the technical scope of this embodiment is not limited by the above mechanism. Details of each requirement defined by this embodiment are shown below.

[0018] <TiNi-based alloy> The TiNi-based alloy according to this embodiment contains one or more selected from the group consisting of Nb and Ta, and with respect to the peak corresponding to the (110) plane of the high-temperature phase of the TiNi crystal in the X-ray diffraction pattern obtained with a CuKα X-ray source, the crystallite size of the TiNi crystal obtained by applying Scherrer's formula is 25 nm or less. As a result, (T HAF -T HRS ) can be increased, and a sufficiently large (T HAS -T HRS ) can also be achieved. The lower limit of the crystallite size of the above TiNi crystal is not particularly limited, but can be, for example, 1 nm or more. In this specification, X-ray diffraction patterns are obtained as follows. First, a Cu tube is used to generate X-rays, which are converged to a diameter of 0.8 mm using a collimator. The converged X-rays are irradiated onto a sample (i.e., a TiNi-based alloy) from a distance of 5 mm at an incident angle of 25°, causing diffraction. From the diffracted X-rays, a diffraction ring is obtained using an imaging plate placed 120 mm away from the sample. An X-ray diffraction pattern (intensity-2θ diagram) is obtained from the diffraction ring. In this case, the root of the standard deviation of the intensity (√σ) is calculated in the 2θ range of 35° to 37.5°. int The measurement is performed so that the peak intensity corresponding to the (110) plane of the high-temperature phase of TiNi crystal is 230 times or more greater than the noise (noise). Furthermore, peaks with diffraction intensity 40 times or greater than the noise are treated as peaks. In this specification, the peak corresponding to the (110) plane of the high temperature phase of TiNi refers to a peak in the range of 2θ=41.4 to 43.4 (°). In this specification, the crystallite size is determined by applying the Scherrer equation shown in the following formula (2) to the peak of interest. d=0.9λ / (Bcosθ) (2) where d is the crystallite size (nm), λ is the X-ray wavelength (nm), B is the half-width (rad.), and θ is the peak position (rad.). The half-width is determined by peak fitting using a split pseudo-Voigt function for the target peak.

[0019] The crystallite size of at least one precipitate selected from the group consisting of Nb and Ta is preferably 25 nm or less, more preferably 20 nm or less, and even more preferably less than 11 nm. It is also more preferable that the crystallite sizes of both the Nb and Ta precipitates are the above-mentioned desired sizes. This makes it possible to achieve a state in which Nb, etc., are more dispersed, effectively suppressing martensitic transformation, and (T HAF -T HRS ) and (T HAS -T HRS) is considered to become larger. The crystallite size of the precipitates of Nb (and Ta) shall be determined by applying Scherrer's formula to the peak corresponding to the (110) plane of Nb (and Ta) in the X-ray diffraction pattern obtained with a CuKα X-ray source. In this specification, the peak corresponding to the (110) plane of Nb refers to the peak in the range of 2θ = 37.5 to 39.5 (°), and the peak corresponding to the (110) plane of Ta refers to the peak in the range of 2θ = 37.5 to 39.5 (°).

[0020] The TiNi-based alloy according to this embodiment contains at least Ti and Ni and has a martensitic transformation start temperature (Ms point). As an embodiment of the TiNi-based alloy having an Ms point, a TiNi-based alloy having a component composition represented by the following formula (1) can be mentioned. Ti x Ni 100-x-y-z Nb y Ta z ···(1) x is the ratio (atomic %) of the number of Ti atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy and satisfies 40 ≤ x ≤ 60, y is the ratio (atomic %) of the number of Nb atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, z is the ratio (atomic %) of the number of Ta atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, and satisfies 0 < y + z ≤ 10. One of y and z may be 0 (that is, one of Nb and Ta may not be included). If (y + z) is within the above range, it is preferable because sufficient phase transformation heat can be ensured even when compared with the TiNi-based alloy when Nb and Ta are not included. Further, in the above formula (1), more preferably 42.5 ≤ x ≤ 57.5, and still more preferably 45 ≤ x ≤ 55. Also, more preferably 0.1 ≤ y + z ≤ 7.5, and still more preferably 0.5 ≤ y + z ≤ 5. Thereby, the phase transformation heat of the TiNi-based alloy can be improved, and (T HAF -T HRS ) and (T HAS -T HRS ) can be easily increased.

[0021] The TiNi-based alloy according to this embodiment may contain impurity elements in addition to Ti, Ni, Nb, and Ta. The less the impurity elements, the better. In one embodiment, the content of Ti, Ni, Nb, and Ta in the TiNi-based alloy is preferably 90 mass % or more, and more preferably 99 mass % or more.

[0022] The TiNi alloy according to this embodiment has an endothermic end temperature (T HAF ) or higher to absorb heat, and then heat can be released by applying external stress. The heating temperature at this time is not particularly limited, but can be, for example, 200°C or lower. Heat can be released by a relatively low external stress of 500 MPa or lower. The lower limit of the external stress is not particularly limited, but can be, for example, 1 MPa or higher. In addition, the TiNi-based alloy according to this embodiment can increase in temperature by releasing heat due to external stress, and in one embodiment, T HAF After heating to above 500 MPa to absorb heat, the temperature can rise by 5°C or more under a relatively low stress of 500 MPa or less (preferably 300 MPa or less). Furthermore, in one embodiment, the temperature drop due to heat absorption that occurs when the external stress is removed can be 1 / 20 or less of the temperature rise due to heat dissipation. HAF can be measured by the method described in the Examples below.

[0023] The TiNi-based alloy according to this embodiment has excellent workability and can be processed into various shapes. In one embodiment, the TiNi-based alloy can be in the form of a plate (foil), wire, or spring. Here, the wire can be solid or hollow. The spring can be in the form of a coil spring or a leaf spring.

[0024] The TiNi alloy according to this embodiment has a higher T HAF -T HRS ) can be increased, and (T HAS -T HRS ) can be made sufficiently large. For example, the conventional HAF -T HRS) is thought to be about 27.0 to 31.8°C, the TiNi alloy according to this embodiment can be heated to, for example, more than 40°C, preferably 41°C or higher, more preferably 45°C or higher, and even more preferably 50°C or higher. HAS -T HRS ) can be, for example, above 15°C, preferably 16°C or higher, more preferably 20°C or higher, and even more preferably 25°C or higher. In addition, the TiNi alloy according to this embodiment has the following properties: HAS -T HRS ) / (T HAF -T HRS ) is preferably 0.30 or more. This allows the absorbed heat to be used more efficiently. HRS ), heat dissipation end temperature (T HRF ), endothermic onset temperature (T HAS ) and endothermic end temperature (T HAF ) can be measured by the method described in the Examples below.

[0025] <Thermal storage device> The heat storage device according to this embodiment is a device for storing TiNi-based alloys according to this embodiment, and a device for storing TiNi-based alloys at a temperature at which the endothermic temperature (T HAF ) or higher and lower than 200°C, and the heat dissipation temperature (T HRS ) ~ endothermic end temperature (T HAF and a heating unit capable of maintaining the temperature at the temperature of the TiNi-based alloy according to the present embodiment. This device allows heat to be stored in the TiNi-based alloy according to the present embodiment. The configuration of the heating unit is not particularly limited, and known heating devices such as a thermostatic device can be applied. The heat storage device according to this embodiment may further include an external stress application unit capable of applying an external stress to the TiNi-based alloy. This allows the application of an external stress to the TiNi-based alloy that has stored heat, and enables the stored heat to be dissipated to the outside of the TiNi-based alloy. The configuration of the external stress application unit is not particularly limited, and any known external stress application device can be used. The heat storage device according to this embodiment may include other configurations as long as the object of the present invention is achieved.

[0026] <Method for Producing TiNi-Based Alloy> An example of the method for producing a TiNi-based alloy according to this embodiment includes a step of processing the TiNi-based alloy at a cross-sectional area change rate of 20% or more. Thereby, a TiNi-based alloy having a crystallite size of a predetermined TiNi crystal can be obtained. Here, the cross-section referred to is the cross-section in the longitudinal direction of the TiNi-based alloy. When the cross-sectional area change rate is less than 20%, there is a possibility that the crystallite size of crystals such as TiNi crystals cannot be sufficiently reduced. The processing method is not particularly limited, and for example, it may be processed by rolling, wire drawing, extrusion, etc., and may be hot working or cold working. There is also no particular limitation on the shape after processing, and for example, it may be processed into a plate shape, a wire shape, or a spring shape. The cross-sectional area change rate can be calculated as |(S0 - S1)| / S0 (%) where S0 is the cross-sectional area before processing and S1 is the cross-sectional area after processing in the cross-section in the longitudinal direction of the TiNi-based alloy material.

[0027] After the above processing step, it is preferable to heat the TiNi-based alloy to 200 to 850 °C so as to homogenize it. The heating time is not particularly limited, but for example, it can be 30 seconds or more, preferably 3 minutes or more. However, if the heating time is too long, in addition to the deterioration of productivity, the crystallite size of crystals such as TiNi crystals increases, making it difficult to obtain the desired crystallite size. The heating time is preferably less than 15 hours, and more preferably 10 hours or less. The heating atmosphere is also not particularly limited, and for example, it may be in the atmosphere.

[0028] Although an example of the method for producing a TiNi-based alloy according to this embodiment has been described, other steps may be included as long as the object of the present disclosure is not deviated from. For example, also, those skilled in the art who understand the desired characteristics of the TiNi-based alloy according to this embodiment may conduct trial and error to find a method for producing a TiNi-based alloy having the desired characteristics according to this embodiment, which is a method other than the above production method.

Examples

[0029] The present embodiment will be described in more detail below with reference to examples. The present embodiment is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present embodiment. [Example]

[0030] The composition is Ti 50 Ni 50 TiNi alloy (Test No. 1), Ti 48 Ni 48 A TiNi-based alloy (Test No. 2) containing Ta4 and TiNi-based alloys of Test Nos. 3 to 7 having the composition shown in Table 1 were prepared.

[0031] For Test No. 4, a TiNi-based alloy having the composition shown in Table 1 was rolled at room temperature with a cross-sectional area change rate of 65% (processing condition 1), and then heat-treated in air at 500°C for 1 hour (heating condition 1).

[0032] For Tests Nos. 5 to 7, TiNi-based alloys having the chemical compositions shown in Table 1 were subjected to hot and cold extrusion and wire drawing (wire drawing) processes until the diameter reached 1 mm (with a cross-sectional area change rate of 20% or more) (processing condition 2). Furthermore, for Test No. 6, after the above processing, heat treatment was carried out in a vacuum at 800° C. for 1 hour, and then heat treatment was carried out in the atmosphere at 500° C. for 5 hours (heating condition 2). Furthermore, for Test No. 7, after the above processing, heat treatment was carried out in a vacuum at 800° C. for 1 hour, and then heat treatment was carried out in the atmosphere at 500° C. for 15 hours (heating condition 3).

[0033] As an example, the heat of phase transformation during cooling was measured by DSC for the TiNi-based alloys of Test Nos. 1 and 3. Test No. 1 (without Nb) had a heat of 19 J / g, while Test No. 3 (with Nb) had a heat of 15 J / g. After subtracting the Nb content, the heat of phase transformation was calculated as 17 J / g, and Test No. 3 maintained a sufficient heat of phase transformation even with the addition of Nb.

[0034] The surfaces of the TiNi-based alloys of Test Nos. 1 to 4 were polished to a mirror finish using diamond and ceramic abrasive grains, and SEM images were observed. Figure 1 shows an SEM image of Test No. 1, Figure 2 shows an SEM image of Test No. 2, Figure 3 shows an SEM image of Test No. 3, and Figure 4 shows an SEM image of Test No. 4. In the TiNi-based alloys (or TiNi-based alloy materials) of Test Nos. 2 to 4 to which Nb or Ta had been added, Nb or Ta (both white areas) segregated. The segregation locations corresponded to the grain boundaries of TiNi crystal grains.

[0035] X-ray diffraction (XRD) patterns (X-ray source: CuKα) were obtained at room temperature for the TiNi-based alloys of Test Nos. 3 to 7. Specifically, X-rays were generated using a Cu tube at a voltage of 40 kV and a current of 30 mA. The X-rays were then focused to a diameter of 0.8 mm using a collimator. The focused X-rays were irradiated onto the sample (i.e., the TiNi-based alloy) at a distance of 5 mm and an incident angle of 25°, causing diffraction. A diffraction ring was captured from the diffracted X-rays using an imaging plate placed 120 mm away from the sample. X-ray diffraction patterns (intensity-2θ diagrams) were obtained from the diffraction rings. The XRD patterns for the TiNi-based alloys of Test Nos. 3 to 4 are shown in Figure 5, and the XRD patterns for the TiNi-based alloys of Test Nos. 5 to 7 are shown in Figure 6. In Figures 5 and 6, the horizontal axis represents the diffraction angle (2θ (CuKα radiation) / °), and the vertical axis represents the diffraction intensity (au). Using the results of Figures 5 and 6, the crystallite size of the TiNi crystals and the crystallite size of the Nb precipitates were determined by the method described above. The results are shown in Table 1. Note that in Table 1, the crystallite size of the Nb precipitates in Test Nos. 5 and 6 differs from Test No. 4 in that the peak intensity of the Nb (110) plane is smaller than the aforementioned √σ int Although quantification was not performed, it can be said that the size was smaller than Test No. 4 (i.e., less than 11 nm).

[0036] The TiNi alloys of Test Nos. 3-4 and 6-7 were confirmed to have Ms points by DSC according to JIS H7101:2002. HAS , THAF , T HRS was calculated as follows: Figure 7 shows the T HAS This is a schematic diagram showing how to calculate T HAS was calculated as follows. In the DSC curve 1, the tangent lines of the extension line L1 of the baseline and the tangent lines of each point (contact point) on the low-temperature side 1A of the peak curve during heating were selected such that the area S2 (shaded area) surrounded by the baseline and the tangent line was 5% or less when the total area S1 (dot pattern area) surrounded by the baseline and the peak curve was 100%. The temperature at the intersection P between the tangent line L2, where the temperature of the contact point is the highest, and the extension line L1 of the baseline was determined as T HAS It was decided.

[0037] Similarly to the above, T HAF That is, from the extension of the baseline of the DSC curve and the tangents at each point on the high-temperature side of the peak curve during heating, a tangent was selected such that the area enclosed by the baseline and the tangent was 5% or less of the total area enclosed by the baseline and the peak curve. The temperature at the intersection of the tangent with the extension of the baseline, which has the lowest tangent temperature, was determined as T HAF It was decided.

[0038] Similarly to the above, T HRS That is, from the extension of the baseline of the DSC curve and the tangents at each point on the high-temperature side of the peak curve during cooling, a tangent was selected such that the area enclosed by the baseline and the tangent was 5% or less of the total area enclosed by the baseline and the peak curve. The temperature at the intersection of the tangent with the extension of the baseline, which has the lowest tangent temperature, was determined as T HRS It was decided. The results are shown in Table 1.

[0039] [Table 1]

[0040] The results of Table 1 are considered. The TiNi-based alloys of Test Nos. 4 and 6 satisfy all the requirements specified in this embodiment, and are superior to conventional alloys (THAF -T HRS ) can be increased (for example, above 40°C), and (T HAS -T HRS ) could be made sufficiently large (for example, over 15°C). In addition, Test No. 6 satisfied the preferable condition that the crystallite size of the Nb precipitates was less than 11 nm, and (T HAF -T HRS ) can be increased to 50°C or higher, and (T HAS -T HRS ) could be raised to above 25°C.

[0041] The TiNi alloy of Test No. 6 was heated from room temperature to 60°C to store heat, and then cooled to -20°C. A tensile test (tensile speed: 10 mm / min) was then performed. A thermocouple was attached to the center of the sample to measure the sample temperature change during the tensile test. The sample and the entire tensile test apparatus were placed in a thermostatic chamber, and measurements were performed after the sample and the entire apparatus reached a predetermined temperature. The results are shown in Figures 8A and 8B. In Figure 8A, the horizontal axis represents the measurement time t (seconds), and the vertical axis represents the tensile test load F (N). In Figure 8B, the horizontal axis represents the measurement time t (seconds), and the vertical axis represents the sample temperature (°C). Figures 8A and 8B show that a temperature rise of 15°C was observed when a tensile test load of 200 N (approximately 260 MPa) was applied. Furthermore, the temperature drop due to heat absorption that occurred when the load F was removed was less than 0.5°C.

Claims

1. A TiNi-based alloy containing one or more elements selected from the group consisting of Nb and Ta, wherein the crystallite size of the TiNi crystals obtained by applying the Scherrer equation to a peak corresponding to the (110) plane of the high-temperature phase of the TiNi crystals in an X-ray diffraction pattern obtained using a CuKα X-ray source is 25 nm or less.

2. 2. The TiNi-based alloy according to claim 1, having a component composition represented by the following formula (1): Till ｘ Yes １００－ｘ－ｙ－ｚ N﹂ ｙ Yes ｚ ・・・(1) x is the ratio (atomic %) of the number of Ti atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, and satisfies 40≦x≦60; y is the ratio (atomic %) of the number of Nb atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy; and z is the ratio (atomic %) of the number of Ta atoms to the total number of Ti, Ni, Nb, and Ta atoms in the alloy, and satisfies 0<y+z≦10.

3. 3. The TiNi alloy according to claim 1, which can dissipate heat by application of an external stress after absorbing heat by heating to a temperature equal to or higher than the endothermic temperature in a DSC curve during heating.

4. 4. The TiNi-based alloy according to claim 3, wherein when the external stress is 500 MPa or less, the temperature can be increased by 5°C or more by the heat dissipation, and the temperature drop due to heat absorption occurring when the external stress is removed is 1 / 20 or less of the temperature increase due to heat dissipation.

5. The TiNi-based alloy according to claim 1 or 2, which is in the form of a plate, wire or spring.

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