Tini-based alloy and thermal storage device including same, and method for producing tini-based alloy

Abstract

This TiNi-based alloy has a martensite transformation start temperature (Ms point) and satisfies formula (1).　(1): |Ms - Ms900°C| ≥ 2°C Ms is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002. Ms900°C is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for one hour.

Description

TiNi-based alloy, heat storage device containing the same, and method for manufacturing the TiNi-based alloy

[0001] The present disclosure relates to a TiNi-based alloy and a heat storage device including the same, as well as a method for producing the TiNi-based alloy.

[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, typically utilize the heat of transformation generated by a solid-liquid phase change. Such materials have a very high heat of transformation per volume (e.g., 200 J / cc or more). However, these materials have 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, these materials require encapsulation of the liquid, making it difficult to maintain a fixed shape, and their shapes are limited to simple forms. Furthermore, the encapsulation acts as a thermal barrier, reducing their properties as heat storage materials. Furthermore, these materials do not experience a significant difference in the heat absorption and heat release temperatures associated with phase transformation. After absorbing heat above a certain temperature, they can only dissipate heat to the outside of the material below that temperature. Furthermore, the only trigger for heat dissipation in these materials is a temperature change; no other external stimuli can intentionally induce heat release.

[0004] In contrast, according to Non-Patent Document 1 and Patent Document 1, Ti, which is an oxide ceramic, ２ O ３ and V.O. ２ etc. show a solid (low temperature phase) - solid (high temperature phase) phase transformation. Furthermore, the heat of transformation is about 200 to 250 J / cc, which is comparable to the heat of transformation accompanying the above-mentioned solid-liquid. ２ O ３In the case of , a high-temperature phase at 1 atmosphere is transformed into a low-temperature phase by increasing the pressure to a very high hydrostatic pressure of 300 atmospheres, and heat can be dissipated from the material as a result of this phase transformation. In addition, a low-temperature phase can also be generated by applying a large impact with a hammer, etc., which also allows for heat dissipation. However, this material also has problems, such as a very low thermal conductivity of approximately 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 high pressure and large impacts are applied to induce the low-temperature phase as described above.

[0005] In recent years, the use of diffusionless structural phase change alloys that exhibit solid-solid phase changes as heat storage materials has been investigated as materials that have higher thermal conductivity than ceramics and allow for shape freedom 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 end temperature (Af point) of transformation to the high-temperature phase (austenite phase) during heating is the end-of-heat-absorption temperature, and the start temperature (Ms point) of transformation to the low-temperature phase (martensite phase) during cooling is the heat-dissipation start temperature. Therefore, the TiNi-based alloy is capable of storing heat in the temperature range from the Ms point to the Af point. 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 the high-temperature phase to the low-temperature phase can be induced with a relatively small stress, resulting in heat dissipation.

[0006] WO2020 / 144982

[0007] “Scientific Reports” (2019) 9: 13203 “J. Mater. Sci.” (2021) 56:8243-8250

[0008] In Non-Patent Document 2, the heat of phase transformation is controlled by controlling the component composition of the TiNi-based alloy. However, when the component composition of the alloy is changed, the phase transformation temperature (e.g., the Ms point, which is the heat release start temperature), which is the operating temperature of the heat storage material, also changes. In order to use the TiNi-based alloy in a wide range of applications as a heat storage material, it is necessary to control the heat of phase transformation and the phase transformation temperature separately.

[0009] The present disclosure has been made in light of the above circumstances, and one of its objects is to provide a TiNi-based alloy in which the heat of phase transformation and the phase transformation temperature can be controlled individually, another object is to provide a heat storage device including the TiNi-based alloy, and still another object is to provide a method for producing the TiNi-based alloy.

[0010] A first aspect of the present invention is a TiNi-based alloy having a martensitic transformation start temperature (Ms point) and satisfying the following formula (1): |Ms-Ms ９００℃ |≧2°C (1) Ms is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002, and Ms ９００℃ is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour.

[0011] A second aspect of the present invention is the TiNi-based alloy according to the first aspect, which further satisfies the following formula (2): (Af-Ms)-(Af ９００℃ -Ms. ９００℃ ) ≧ 2°C (2) Af is the austenite phase transformation finish temperature (Af point) (°C) of the alloy measured in accordance with JIS H7101:2002, and Af ９００℃ is the Af point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour.

[0012] A third aspect of the present invention is the TiNi-based alloy according to the first or second aspect, which has a component composition represented by the following formula (3): Ti ｘ Ni １００－ｘ－ｙ M ｙ ...(3) x is the molar ratio (%) of Ti to the total number of moles of Ti, Ni, and M in the alloy and satisfies 35≦x≦55, y is the molar ratio (%) of M to the total number of moles of Ti, Ni, and M in the alloy and satisfies 0≦y≦20, and M is one or more selected from the group consisting of Cu, Co, Cr, Zr, and Fe.

[0013] A fourth aspect of the present invention is the TiNi-based alloy according to any one of the first to third aspects, wherein the crystallite size is 30 nm or less.

[0014] A fifth aspect of the present invention is the TiNi-based alloy according to any one of the first to fourth aspects, which is capable of absorbing heat by heating to a temperature equal to or higher than the Af point and then dissipating heat by application of an external stress.

[0015] A sixth aspect of the present invention is the TiNi-based alloy according to any one of the first to fifth aspects, which is in the form of a plate, wire, or spring.

[0016] A seventh aspect of the present invention is a heat storage device including: the TiNi-based alloy according to any one of Aspects 1 to 6; and a heating section capable of heating the TiNi-based alloy to a temperature equal to or higher than the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy and lower than 200°C, and capable of maintaining the TiNi-based alloy at a temperature between the martensitic transformation start temperature (Ms point) and the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy.

[0017] Aspect 8 of the present invention is a method for producing the TiNi-based alloy according to any one of Aspects 1 to 6, comprising the steps of: processing a TiNi-based alloy material having a martensitic transformation start temperature (Ms point) at a cross-sectional area change rate of 20% or more; and heating the processed TiNi-based alloy material to 200 to 800°C.

[0018] According to the embodiments of the present invention, it is possible to provide a TiNi-based alloy in which the heat of phase transformation and the phase transformation temperature can be controlled separately, a heat storage device including the TiNi-based alloy, and a method for producing the TiNi-based alloy.

[0019] 1 shows X-ray diffraction patterns for Test Nos. 1 to 5. 2 shows a graph showing temperature changes during a four-point bending test for Test No. 5. 3 shows a graph showing temperature changes during a tensile test for Test No. 4. 4 shows a graph showing temperature changes during a tensile test for Test No. 5. 5 shows a photograph of Test No. 16. 6 shows a graph showing temperature changes when tensile deformation is performed for Test No. 16. 7 shows a graph showing temperature changes when compressive deformation is performed for Test No. 16.

[0020] The present inventors have investigated from various angles in order to realize a TiNi-based alloy in which the heat of phase transformation and the phase transformation temperature can be controlled separately. As a result, they have found that by subjecting a TiNi-based alloy exhibiting a predetermined Ms point to a predetermined processing to introduce defects (strain), and then adjusting the amount of the defects by heating, it is possible to realize a TiNi-based alloy having a phase transformation temperature different from the phase transformation temperature that would normally be exhibited based on a predetermined component composition. That is, in the TiNi-based alloy according to the embodiment of the present invention, the Ms point changed by strain applied by the predetermined processing or the like and the Ms point after heating at a high temperature (900°C) for 1 hour to remove the strain (i.e., the Ms point that would normally be exhibited based on a predetermined component composition, hereinafter referred to as "Ms ９００℃ ") is 2°C or more. In other words, |Ms - Ms ９００℃ |≧2° C. means that a predetermined processing or the like has been performed on the TiNi alloy according to the embodiment of the present invention, thereby applying strain. Details of each requirement specified by the embodiment of the present invention are shown below.

[0021] <TiNi-based alloy> The TiNi-based alloy according to an embodiment of the present invention is a TiNi-based alloy that has a martensitic transformation start temperature (Ms point) and satisfies the following formula (1): |Ms-Ms ９００℃ |≧2°C (1) Ms is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002, and Ms ９００℃ is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour. ９００℃ is the Ms point after heating to remove strain applied by a predetermined processing or the like described below, and can be the same temperature as the Ms point before the predetermined processing or the like described below is applied. The TiNi-based alloy can be used in a wide range of applications as a heat storage material, since the phase transformation heat and phase transformation temperature can be controlled separately (i.e., the phase transformation heat is controlled mainly by the composition, and the phase transformation temperature is controlled mainly by the predetermined processing or the like (strain)). Preferably, the left side of the above formula (1) is 4°C or more, and more preferably, the left side of the above formula (1) is 6°C or more.

[0022] As described above, TiNi-based alloys can store heat within a temperature range of, for example, the Ms point to the Af point. Therefore, it is preferable that the TiNi-based alloy according to the embodiment of the present invention has a large difference between the Af point and the Ms point so as to widen the temperature range in which heat can be stored. The difference between the Af point and the Ms point is usually determined by the component composition, but in the embodiment of the present invention, it can be controlled by a predetermined processing (and heat treatment) described later. It is preferable that the TiNi-based alloy according to the embodiment of the present invention satisfies the following formula (2): (Af-Ms)-(Af ９００℃ -Ms. ９００℃ ) ≧ 2°C (2) Af is the Af point (°C) of the alloy measured in accordance with JIS H7101:2002, and Af ９００℃ is the Af point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour. ９００℃ is the Af point after heating to remove strain applied by a predetermined processing or the like described below, and can be the same temperature as the Af point before the predetermined processing or the like described below is applied. By satisfying the above formula (2), the material can be used in a wider range of applications as a heat storage material. Preferably, the left side of the above formula (2) is 4°C or more, and more preferably, the left side of the above formula (2) is 5°C or more.

[0023] The TiNi-based alloy according to the embodiment of the present invention contains at least Ti and Ni and has an Ms point. One embodiment of the TiNi-based alloy having an Ms point is a TiNi-based alloy having a component composition represented by the following formula (3): Ti ｘ Ni １００－ｘ－ｙ M ｙ ...(3) x is the molar ratio (%) of Ti to the total number of moles of Ti, Ni, and M in the alloy, and satisfies 35≦x≦55; y is the molar ratio (%) of M to the total number of moles of Ti, Ni, and M in the alloy (if there are two or more types of M, the total molar ratio (%) of M) and satisfies 0≦y≦20; and M is one or more types selected from the group consisting of Cu, Co, Cr, Zr, and Fe.

[0024] In the above formula (3), preferably, x satisfies 48≦x≦52, and more preferably, 49.5≦x≦50.5. Also, preferably, 0≦y≦10, and more preferably, 0≦y≦7.5. These factors can improve the heat of phase transformation of the TiNi-based alloy. M may not be present, or may contain only one element, such as Cu, or may contain two or more elements.

[0025] The TiNi-based alloy according to the embodiment of the present invention may contain impurity elements in addition to Ti, Ni, and M. The less the impurity elements, the better, and in one embodiment, the contents of Ti, Ni, and M in the TiNi-based alloy are preferably 90 mass % or more, and more preferably 99 mass % or more.

[0026] The TiNi-based alloy according to an embodiment of the present invention preferably has a crystallite size of 30 nm or less. A relatively small crystallite size makes it easier to accumulate strain that suppresses martensitic transformation, and as a result, it becomes easier to increase the left side of the above formula (1) and the left side of the above formula (2). More preferably, the crystallite size is 25 nm or less, and even more preferably 15 nm or less. The lower limit of the crystallite size is not particularly limited, but may be, for example, 1 nm or more. In an embodiment of the present invention, the crystallite size is estimated, for example, based on X-ray diffraction results (X-ray source: CuKα) measured at room temperature, by performing peak fitting using a split-type pseudo-Voigt function using the peak present at a position corresponding to the (11-1) plane (2θ ≒ 41 to 42°) where the diffraction intensity of the martensitic phase is highest, and from the obtained half-value width, using the Scherrer formula shown in the following formula (4). d=0.9λ / (B·cos θ) (4) where d is the crystallite size (nm), λ is the wavelength of the X-ray (nm), B is the half width (rad.), and θ is the peak position (rad.).

[0027] In the TiNi-based alloy according to the embodiment of the present invention, the heat of phase transformation (martensitic transformation) upon cooling measured by differential scanning calorimetry (DSC) is preferably almost the same as the heat of phase transformation upon cooling measured by DSC after heating at 900°C for 1 hour, and for example, the difference therebetween may be within ±5 J / g, more preferably within ±2 J / g.

[0028] The TiNi-based alloy according to the embodiment of the present invention makes it possible to control the martensitic transformation finish temperature (Mf point) by a predetermined processing (and heat treatment) described later. The TiNi-based alloy according to the embodiment of the present invention preferably satisfies the following formula (5): |Mf - Mf ９００℃ |≧6°C (5) Mf is the Mf point (°C) of the alloy measured in accordance with JIS H7101:2002, and Mf ９００℃ is the Mf point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour. ９００℃ is the Mf point after heating to remove strain applied by a predetermined processing or the like described below, and can be the same temperature as the Mf point before the predetermined processing or the like described below is applied. By satisfying the above formula (5), the material can be used in a wider range of applications as a heat storage material. Preferably, the left side of the above formula (5) is 7°C or higher, and more preferably, the left side of the above formula (5) is 10°C or higher.

[0029] The TiNi-based alloy according to an embodiment of the present invention can dissipate heat by application of external stress after being heated to a temperature equal to or higher than the Af point and absorbing heat. The heating temperature at this time is not particularly limited, but can be, for example, 200°C or lower. The external stress can dissipate heat with a relatively low 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. Furthermore, the TiNi-based alloy according to an embodiment of the present invention can increase in temperature by dissipating heat due to external stress. In one embodiment, the temperature can increase by 3°C or more (preferably 5°C or more) with a relatively low stress of 500 MPa or lower (preferably 200 MPa or lower) after being heated to a temperature equal to or higher than the Af point and absorbing heat.

[0030] The TiNi-based alloy according to the embodiment of the present invention has excellent workability and can be processed into various shapes. In one embodiment, the TiNi-based alloy may be in the form of a plate (foil), wire, or spring.

[0031] <Heat Storage Device> A heat storage device according to an embodiment of the present invention includes a TiNi-based alloy according to an embodiment of the present invention and a heating unit capable of heating the TiNi-based alloy to a temperature equal to or higher than the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy and lower than 200°C, and capable of maintaining the temperature at a temperature between the martensitic transformation start temperature (Ms point) and the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy. This device allows heat to be stored in the TiNi-based alloy according to an embodiment of the present invention. The configuration of the heating unit is not particularly limited, and known heating devices such as a constant temperature device can be applied. The heat storage device according to an embodiment of the present invention may further include an external stress application unit capable of applying an external stress to the TiNi-based alloy. This allows external stress to be applied to the TiNi-based alloy that has stored heat, making it possible to dissipate the stored heat outside the TiNi-based alloy. The configuration of the external stress application unit is not particularly limited, and known external stress application devices can be applied. The heat storage device according to an embodiment of the present invention may include other configurations as long as the object of the present invention is achieved.

[0032] <Method for Producing TiNi-Based Alloy> One example of a method for producing a TiNi-based alloy according to an embodiment of the present invention includes the steps of: (A) processing a TiNi-based alloy material having a martensitic transformation start temperature at a cross-sectional area change rate of 20% or more; and (B) heating the processed TiNi-based alloy material to 200 to 800°C. This production method allows for the production of a TiNi-based alloy having a martensitic transformation start temperature (Ms point) and satisfying formula (1) above. Furthermore, this production method also makes it possible to satisfy formulas (2) and (5) above, and also allows for a crystallite size of 30 nm or less. Each step is described in detail below.

[0033] (A) Step of Working at a Cross-sectional Area Change Rate of 20% or More A TiNi-based alloy having a martensitic transformation start temperature and an arbitrary shape (hereinbelow referred to as a "TiNi-based alloy material" to distinguish it from the TiNi-based alloy according to an embodiment of the present invention (i.e., a TiNi-based alloy to which strain is applied by predetermined processing or the like and which satisfies the above formula (1))) is worked at a cross-sectional area change rate of 20% or more. The cross section referred to here is a cross section in the longitudinal direction of the TiNi-based alloy material. If the cross-sectional area change rate is less than 20%, for example, the above formula (1) (and the above formulas (2) and (5)) may not be satisfied due to small strain, etc. Furthermore, this step mainly makes it possible to reduce the crystallite size to 30 nm or less. The working method is not particularly limited, and for example, rolling or wire drawing may be used. The shape after working is also not particularly limited, and it may be worked into, for example, a plate, wire, or spring shape. The cross-sectional area change rate is calculated by dividing the cross-sectional area of ​​the TiNi alloy material in the longitudinal direction by the cross-sectional area before processing by S. ０ The cross-sectional area after processing is S １ Then, |(S ０ -S １ ) | / S ０ It can be calculated as a percentage.

[0034] (B) Step of heating to 200 to 800°C After step (A), the TiNi-based alloy material is heated to 200 to 800°C. If the temperature is lower than 200°C, it is difficult to adjust the Ms point, and if the temperature is higher than 800°C, the strain will disappear. In either case, there is a risk that a TiNi-based alloy satisfying the above formula (1) (and the above formulas (2) and (5)) will not be obtained. In order to raise the Ms point to room temperature or higher, it is preferable to heat to 350°C or higher. Furthermore, in order to further change the Ms point, it is preferable to heat to 650°C or lower. The heating time is not particularly limited, but may be, for example, 30 seconds or more, preferably 3 minutes or more. Furthermore, from the viewpoint of productivity, the heating time may be, for example, 10 hours or less, preferably 2 hours or less. The heating atmosphere is also not particularly limited, and may be, for example, air.

[0035] Although one example of a method for producing a TiNi-based alloy according to an embodiment of the present invention has been described, other steps may be included without departing from the scope of the present disclosure. For example, a person skilled in the art who understands the desired properties of the TiNi-based alloy according to an embodiment of the present invention may, through trial and error, find a method for producing a TiNi-based alloy having the desired properties according to an embodiment of the present invention other than the above-described method.

[0036] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0037] The composition is Ti ５０．１ Ni ４２．９ Cu ７．０ A TiNi-based alloy material having a diameter of 1.5 mm and having a thickness of 0.8 mm or less was prepared. The TiNi-based alloy material (Test No. 1) was cold-rolled until the cross-sectional area change rate in the longitudinal cross section was 20% or more, the plate thickness was 0.8 mm or less, and the width was 1.7 mm or more. The TiNi-based alloy material was then heated under the conditions shown in Table 1 to obtain TiNi-based alloys of Test Nos. 1 to 8. Note that Test No. 1 was not subjected to the above cold rolling and heating, and Test No. 2 was a sample that was subjected to the above cold rolling but not subsequent heating.

[0038]

[0039] For Test No. 1 (no processing or heating) and Test No. 8 (heated at 900°C for 1 hour after cold rolling), the phase transformation temperatures (Ms, Mf, and Af) were measured according to JIS H7101:2002. As a result, the phase transformation temperatures of Test No. 1 and Test No. 8 were equivalent (Test No. 1: Ms: 39°C, Mf: 28°C, Af: 53°C, Test No. 8: Ms: 40°C, Mf: 27°C, Af: 53°C). From these results, it is believed that the strain imparted by cold rolling was removed by heating at a high temperature for a sufficient time (900°C for 1 hour). Furthermore, even if the amount of strain was adjusted by heating at a low temperature (e.g., 200 to 800°C) after cold rolling, it is believed that the strain would be removed by subsequent heating at 900°C for 1 hour. The heat of phase transformation (martensitic transformation) during cooling measured by DSC was also equivalent between Test No. 1 and Test No. 8. Test No. 2 was also similarly measured, and the results were Ms<−20°C and Af>60°C.

[0040] Furthermore, for Test Nos. 3 to 7, the transformation temperatures were measured in accordance with JIS H7101:2002. The results are summarized in Table 2. ９００℃ (°C), Af ９００℃ (°C) and Mf ９００℃ (°C) were taken as Ms (°C), Af (°C) and Mf (°C) for Test No. 8, respectively.

[0041]

[0042] Consider the results in Table 2. The TiNi-based alloys of Test Nos. 3 to 7 satisfy all the requirements specified in the embodiment of the present invention, and the heat of phase transformation and the phase transformation temperature can be controlled individually. Specifically, the phase transformation temperature (MS ９００℃ ) had a phase transformation temperature (Ms) different from that of TiNi alloys. The TiNi alloys of Test Nos. 3 to 7 satisfied the above formulas (2) and (5), and showed favorable results.

[0043] The heat of phase transformation upon cooling was measured by DSC for Test Nos. 4 to 8. As a result, Test No. 4 had a heat of phase transformation of 20 J / g, Test No. 5 had a heat of phase transformation of 21 J / g, Test No. 6 had a heat of phase transformation of 20 J / g, Test No. 7 had a heat of phase transformation of 24 J / g, and Test No. 8 had a heat of phase transformation of 19 J / g. The heat of phase transformation upon cooling for Test Nos. 4 to 7 was almost the same (within ±5 J / g) as that for Test No. 8 (heated at 900°C for 1 hour), which was a favorable result.

[0044] For Test Nos. 1 to 5, X-ray diffraction patterns (X-ray source: CuKα) were obtained at room temperature. The results are shown in FIG. 1. In FIG. 1, the horizontal axis represents the diffraction angle (2θ (CuKα radiation) / °), and the vertical axis represents the diffraction intensity (a.u.). The patterns (a) to (e) in FIG. 1 correspond to the patterns for Test Nos. 1 to 5, respectively. Using the results of FIG. 1, peak fitting was performed using a split pseudo-Voigt function for the peak at the position corresponding to the (11-1) plane of the martensite phase, and the crystallite size was estimated from the obtained half-width using the Scherrer formula shown in Equation (4) above. As a result of estimating the crystallite size, (a) Test No. 1 was 35 nm, (b) Test No. 2 was 8 nm, (c) Test No. 3 was 9 nm, (d) Test No. 4 was 13 nm, and (e) Test No. 5 is 10 nm, and it can be seen that the crystallite size was reduced by the processing step (A).

[0045] Test No. 5 was heated from room temperature to 80°C to allow heat storage, and then cooled to 45°C. A four-point bending test (inner span distance: 11 mm, outer span distance: 23.5 mm, deflection rate: 20 mm / min, deflection amount: 1.5 mm, 3 mm, or 4 mm, maximum stress: approximately 70 MPa) was then performed. A thermocouple was attached to the center of the sample to measure the sample temperature change during deflection. The sample and the entire four-point bending 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 Figure 2. In Figure 2, the horizontal axis represents the measurement time t (seconds), and the vertical axis represents the sample temperature (°C). In Figure 2, a deflection amount of 4 mm is indicated by a black circle, a deflection amount of 3 mm is indicated by a white diamond, and a deflection amount of 1.5 mm is indicated by a gray circle. Figure 2 also includes curves extrapolated to 0 seconds for each plot. From Figure 2, it was confirmed that the temperature rose by 3 to 5°C regardless of the amount of deflection. In addition, when the net temperature rise was estimated by extrapolating the curve up to 0 seconds, it was 4°C, 8°C, and 12°C for deflections of 1.5 mm, 3 mm, and 4 mm, respectively.

[0046] Test No. 4 was heated from room temperature to 60°C to accumulate heat, and then cooled to 15°C. A tensile test (tensile speed 10 mm / min) was performed in this state. 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 Figure 3. In Figure 3, the horizontal axis represents the measurement time t (seconds), the vertical left axis represents the sample temperature (°C), and the vertical right axis represents the tensile test load F (N). In Figure 3, the sample temperature is plotted with a circle, and the tensile test load is shown with a solid line. Figure 3 also includes a curve that partially overlaps with the sample temperature plot, extrapolating the sample temperature to 0 seconds. Figure 3 shows a temperature rise of 4°C when a tensile test load of 116 N (approximately 90 MPa) was applied. The net temperature rise, estimated by extrapolating the curve to 0 seconds, was 21°C.

[0047] Test No. 5 was heated from room temperature to 80°C to accumulate heat, and then cooled to 45°C. A tensile test (tensile speed 10 mm / min) was performed in this state. 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 Figure 4. In Figure 4, the horizontal axis represents the measurement time t (seconds), the vertical left axis represents the sample temperature (°C), and the vertical right axis represents the tensile test load F (N). In Figure 4, the sample temperature is plotted with a circle, and the tensile test load is shown with a solid line. Figure 4 also includes a curve that partially overlaps with the sample temperature plot, extrapolating the sample temperature to 0 seconds. Figure 4 shows a temperature rise of 6°C when a tensile test load of 130 N (approximately 100 MPa) was applied. The net temperature rise, estimated by extrapolating the curve to 0 seconds, was 38°C.

[0048] The composition is Ti ４９．５ Ni ５０．５ A TiNi-based alloy material having a diameter of 1.5 mm and having a thickness of 0.8 mm or less was prepared (referred to as the TiNi-based alloy of Test No. 9). The TiNi-based alloy material (Test No. 9) was cold-rolled until the cross-sectional area change rate in the longitudinal cross section was 20% or more, the plate thickness was 0.8 mm or less, and the width was 1.7 mm or more. The cold-rolled TiNi-based alloy material was then heated under the conditions shown in Table 3, and the TiNi-based alloys of Test Nos. 10 to 15 were obtained.

[0049]

[0050] The transformation temperatures (Ms, Mf, and Af) of Test No. 9 (without cold rolling or heating) and Test No. 15 (heated at 900°C for 1 hour after cold rolling) were measured in accordance with JIS H7101:2002. As a result, similar to Example 1, the transformation temperatures of Test No. 9 and Test No. 15 were equivalent. Furthermore, the heat of phase transformation during cooling measured by DSC was also equivalent between Test No. 9 and Test No. 15.

[0051] Furthermore, for Test Nos. 10 to 14, the transformation temperatures (Ms, Mf, and Af) were measured in accordance with JIS H7101:2002. The results are summarized in Table 4. ９００℃ (°C), Af ９００℃(°C) and Mf ９００℃ (°C) were the Ms (°C), Af (°C) and Mf (°C) of Test No. 15, respectively.

[0052]

[0053] The results in Table 4 indicate the following: The TiNi-based alloys of Test Nos. 10 to 14 satisfy all the requirements specified in the embodiment of the present invention, and the heat of phase transformation and the phase transformation temperature can be controlled individually. Specifically, the phase transformation temperature (Ms ９００℃ ) had a different phase transformation temperature (Ms).

[0054] The heat of phase transformation upon cooling was measured by DSC for Test Nos. 14 and 15. As a result, the heat of phase transformation upon cooling for Test No. 14 was equivalent (13 J / g) to the heat of phase transformation upon cooling for Test No. 15 (heated at 900°C for 1 hour), which was a favorable result.

[0055] In addition, the following experiment was carried out as an example of processing into other shapes. ４９．５ Ni ５０．５ A TiNi-based alloy material with a diameter of 0.3 mm was prepared. This TiNi-based alloy material was fixed into a helical shape and then heated at 500°C for 5 minutes to produce a TiNi alloy coil (Test No. 16). Figure 5 shows a photograph of Test No. 16. A thermocouple was attached to this sample, and the temperature change of the sample when it was manually tensile-deformed at room temperature was investigated. Figure 6 shows the results, and the temperature change of the sample when it was compressively deformed is shown in Figure 7. In Figures 6 and 7, the horizontal axis represents the measurement time t (seconds), and the vertical axis represents the sample temperature (°C). In Figure 6, the sample temperature is shown by a solid line, and the timing of the application of the tensile (or compressive) deformation load is indicated by an arrow. As shown in Figure 6, a temperature increase of approximately 2°C was confirmed due to tensile deformation, and as shown in Figure 7, a temperature increase of approximately 0.3°C was confirmed due to compressive deformation.

[0056] This application claims priority from Japanese Patent Application No. 2023-027638, filed February 24, 2023. Japanese Patent Application No. 2023-027638 is incorporated herein by reference.

Claims

1. A TiNi-based alloy having a martensitic transformation start temperature (Ms point) and satisfying the following formula (1): |Ms-Ms ９００℃ |≧2℃・・・(1) Ms is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002, and Ms ９００℃ is the Ms point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour.

2. The TiNi-based alloy according to claim 1, further satisfying the following formula (2): (Af-Ms)-(Af ９００℃ -Ms ９００℃ )≧2℃・・・(2) Af is the austenite phase transformation finish temperature (Af point) (°C) of the alloy measured in accordance with JIS H7101:2002, and Af ９００℃ is the Af point (°C) of the alloy measured in accordance with JIS H7101:2002 after heating the alloy at 900°C for 1 hour.

3. 3. The TiNi-based alloy according to claim 1, having a component composition represented by the following formula (3): Till ｘ Yes １００－ｘ－ｙ M ｙ ・・・(3) x is the molar ratio (%) of Ti to the total number of moles of Ti, Ni, and M in the alloy and satisfies 35≦x≦55, y is the molar ratio (%) of M to the total number of moles of Ti, Ni, and M in the alloy and satisfies 0≦y≦20, and M is one or more selected from the group consisting of Cu, Co, Cr, Zr, and Fe.

4. 3. The TiNi-based alloy according to claim 1, wherein the crystallite size is 30 nm or less.

5. 3. The TiNi alloy according to claim 1, which is capable of absorbing heat by heating to a temperature equal to or higher than Af and then dissipating heat by application of an external stress.

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

7. The TiNi-based alloy according to claim 1 or 2, a heating unit capable of heating the TiNi-based alloy to a temperature equal to or higher than the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy and lower than 200°C, and capable of maintaining the temperature at a temperature between the martensite transformation start temperature (Ms point) and the austenite phase transformation finish temperature (Af point) of the TiNi-based alloy; A heat storage device comprising:

8. A step of processing a TiNi-based alloy material having a martensitic transformation start temperature (Ms point) at a cross-sectional area change rate of 20% or more; a step of heating the processed TiNi-based alloy material to 200 to 800°C; 3. A method for producing the TiNi-based alloy according to claim 1 or 2, comprising: