KR102192044B1 - Ultra-low fatigue bulk elastocaloric alloy - Google Patents

Abstract

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is represented by the following formula,
Contains Ti, Cu, Ni, Si, and Sn.
[Chemical Formula]
(Ti _x Cu _y Ni _100-xy ) _100-zk Si _z Sn _k
In the above formula, 48≤x≤52, 15≤y≤44, 0≤z≤3, and 0≤k≤2.
In the case of the TiCuNi alloy, it is difficult to control the precipitation of other intermetallic compounds other than the austenite phase B2 and the martensite phase B19, so that the mechanical properties and functional properties are greatly reduced. In particular, the fatigue properties are deteriorated due to precipitation, and the effect of adding Si includes that the fatigue properties are greatly improved due to the effect of suppressing the precipitation of intermetallic compounds. In addition, according to the alloy composition proposed in the present invention, the overall composition ratio of the alloy, especially the effect of controlling the Ti and Sn content includes the adjustment of the phase transformation temperature, and in particular, the austenite phase transformation end temperature (T _Af ) corresponds to the operating environment. It includes the effect of reducing the critical stress and minimum strain required for operation as it approaches the temperature (T _o ). However, the austenite phase transformation start temperature exhibits superelastic properties under conditions lower than the operating temperature. In addition, the effect of controlling the content of Cu among alloy constituents is 40 at. In a composition close to %, the heat exchange efficiency is improved by increasing the latent heat (-ΔH/ΔW) generated during the martensite phase transformation compared to the work generated by the deformation of the shape memory alloy. By the ratio of constituent elements such as Ti, Cu, Ni, Si, and Sn according to the embodiment, an elastic calorie alloy is provided that can be manufactured in a bulk form and exhibits ultra-low fatigue properties that do not require thermal pretreatment or mechanical training.

Description

{Ultra-low fatigue bulk elastocaloric alloy}

A bulk elastic calorie alloy that exhibits mechanical and functional ultra-low fatigue behavior upon repeated use is provided.

In general, temperature control devices such as refrigerators and various motors and engines require a heat exchange system, and a simple heat conduction system using a heat sink or fan and a heat exchange system using compressed gas are commercialized. However, the heat conduction system has a low amount of heat dissipation, and the compressed gas system has a limit in the efficiency achievable during heat exchange according to the laws of thermodynamics. The elastocaloric alloy utilizes the difference in entropy between two different solid phases, martensite and austenite phases of the shape memory alloy for heat exchange, and is attracting attention as a next-generation heat exchange material due to its high theoretically achievable efficiency. .

For this reason, studies to utilize shape memory alloys of various systems as elastic calorie alloys are actively being conducted.In particular, Nitinol alloys, which are widely known to have excellent mechanical and functional properties, are known to exhibit very excellent heat exchange efficiency. However, the nitinol alloy is known to be unsuitable to be applied as an elastic calorie alloy that requires repeated use of several tens of thousands of times or more, since its properties are greatly deteriorated by repeated operations of several tens of times or less. In addition, studies to utilize various shape memory alloys such as TiNiHf alloy and CuNiAl alloy as an elastic calorie alloy have been conducted, but heat exchange efficiency is low and high fatigue properties are shown.

In the case of TiNiCu alloy, it has been reported that it can be used tens of thousands of times exceptionally if it is manufactured into a film having a thickness of tens of microns or less. Therefore, follow-up research for application to MEMS (microelectromechanical system) has been conducted. However, like most other shape memory alloys, when manufactured in bulk form, intermetallic compound phases other than the B2, B19, and B19' phases used for heat exchange are precipitated to form a complex microstructure, and fatigue characteristics and heat exchange efficiency are greatly reduced. Can be. Due to the lack of technology to control the precipitation of intermetallic compounds, it is known that it is difficult to realize low fatigue properties when manufacturing a shape memory alloy in a bulk form having a thickness of 1 mm or more. Therefore, for the development of a bulk low-fatigue elastic calorie alloy, it is considered necessary to control the precipitation of intermetallic compounds in the shape memory alloy and the martensite phase transformation temperature.

Since the elastic calorie alloy must be used repeatedly under the same stress and temperature conditions, the martensitic phase transformation and strain under constant stress must be generated very stably. To this end, complex processes such as solution treatment, annealing treatment, quenching, and mechanical training are required when manufacturing an alloy. It is believed that this process needs to be simplified because it causes a significant increase in production cost and time.

The elastic calorie alloy utilizes the difference in entropy that occurs during the phase change of the martensite phase and the austenite phase in the form of thermal energy (latent heat) for heat exchange.In general, high latent heat is generated when it has a large strain at high stress during phase transformation. However, from the mechanical engineering point of view of the heat exchanger, the occurrence of high stress and large strain in a material that repeatedly undergoes deformation not only leads to large heat loss, but also becomes a factor that hinders miniaturization and weight reduction of parts. Therefore, it is required to develop an alloy that exhibits sufficient latent heat and operates only with minimal stress and strain.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is to improve fatigue properties due to repeated use.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is for controlling the precipitation of an intermetallic compound in a shape memory alloy manufactured in a bulk form of 1 mm or more.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is stable without causing deterioration in mechanical properties and functional properties during use without thermal pretreatment (solution treatment and annealing) and mechanical training or mechanical training in the manufacturing process. It is intended to be used as a.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is to enable the operation of the heat exchange system through martensite phase transformation even at a relatively low pressure compared to the existing elastic calorie alloy.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is to enable the operation of the heat exchange system through martensite phase transformation even under a condition of a relatively low strain compared to the existing elastic calorie alloy.

In addition to the above problems, the embodiments according to the present invention may be used to achieve other tasks not specifically mentioned.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention is represented by the following formula,

Contains Ti, Cu, Ni, Si, and Sn.

[Chemical Formula]

(Ti _x Cu _y Ni _100-xy ) _100-zk Si _z Sn _k

(In the above formula, 48≤x≤52, 15≤y≤44, 0≤z≤3, and 0≤k≤2.)

The alloy may include phases B2 and B19.

The martensitic phase transformation start temperature (T _Ms ), the martensite phase transformation end temperature (T _Mf ), and the austenite phase transformation start temperature (T _As ) of the alloy may be less than or equal to a temperature (T _o ) corresponding to the operating environment.

The austenite phase transformation end temperature of the alloy may be less than or equal to a temperature (T _o ) corresponding to the operating environment.

As the fraction of Si is added in the alloy of 0.5 or more, precipitation of the intermetallic compound phase is suppressed during casting, so that an alloy having only the B2 phase or the B19 phase can be manufactured.

As the fraction of Si is added in the alloy of 0.5 or more, the alloy can be manufactured by casting alone without thermal and mechanical pretreatment processes.

Depending on the composition ratio in the alloy, the critical stress required for operation may decrease as the austenite phase transformation end temperature (T _Af ) is closer to the temperature (T _o ) corresponding to the operating environment.

Depending on the composition ratio in the alloy, the closer the austenite phase transformation end temperature (T _Af ) to the temperature (T _o ) corresponding to the operating environment, the lower the minimum strain required for operation may be.

As the fraction of Cu in the alloy increases, the minimum strain required for operation may decrease.

As the fraction of Cu in the alloy approaches 40 at.%, the latent heat (-ΔH/ΔW) generated during the martensite phase transformation increases compared to the work generated by the deformation of the shape memory alloy, thereby increasing the heat exchange efficiency.

The ultra-low fatigue bulk elastic calorie alloy according to an embodiment of the present invention can improve fatigue properties by controlling the precipitation of intermetallic compounds and controlling the phase transformation temperature, and reducing manufacturing costs by manufacturing the alloy without heat treatment and mechanical pretreatment processes. It is possible to reduce the critical stress required for operation, thereby constructing a heat exchange system using less force, reduce the strain generated by the operation, reduce the size of the heat exchange system, improve stability, and improve heat exchange efficiency. It can be greatly increased compared to the existing alloy.

Figure 1 shows the stress-strain when the B2-B19 phase transformation occurs reversibly by periodically applying and releasing stress to the alloy of (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ composition at a low strain (10 ^-4 /s). Show the curve.
Figure 2 shows the stress-strain when the B2-B19 phase transformation occurs reversibly by periodically applying and relaxing stress to the alloy of the composition of (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ at a high strain rate (10 ^-1 /s) Show the curve.
Figure 3 shows (Ti ₅₀ Cu ₁₅ Ni ₃₅ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₂₀ Ni ₃ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₃₀ Ni ₂₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₀ Ni ₁₀ ) Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₃ Ni ₇ ) Si ₁ Sn ₁ shows the stress-strain curve when a stress is applied to an alloy with a low strain (10 ^-4 /s) up to 500 MPa and then relaxed.
4 shows (Ti ₅₀ Cu ₁₅ Ni ₃₅ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₂₀ Ni ₃ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₃₀ Ni ₂₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₀ Ni ₁₀ ) Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₃ Ni ₇ ) Si ₁ Sn _{1 When the} stress is periodically applied and relieved at a high strain rate (10 ^-1 /s) to the alloy, whereby the B2-B19 phase transformation occurs reversibly. It is a graph showing the ratio of the enthalpy reduction amount (-ΔH) due to latent heat to the energy loss (ΔW) due to work given as the integral of the stress-strain curve.
5 is a stress-strain when the B2-B19 phase transformation occurs reversibly by periodically applying and releasing stress to an alloy of (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ composition at a high strain rate (10 ^-1 /s). The curve is shown according to the repetition cycle.
Figure 6 shows the (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ by applying and mitigating the stress periodically at a high strain rate (10 ^-1 / s) to the alloy composition by the latent heat when the phase transformation of B2-B19 occurs reversibly. It shows the temperature change of the alloy according to the repetition cycle.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in other different forms, and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and the same reference numerals are used for the same or similar components throughout the specification. Also, in the case of well-known technologies, detailed descriptions thereof will be omitted.

In the specification, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

In the present specification, the B2 phase and the austenite phase may be used as the same meaning, and the B19 phase and the martensite phase may be used as the same meaning.

The ultra-low fatigue bulk elastic calorie alloy according to the embodiments relates to a shape memory alloy (SMA) using B2-B19 martensite phase transformation, and when a stress is applied by applying mechanical energy to the alloy from the outside, austenite The (austenite) trader B2 phase is transformed into the martensite trader B19 phase to release heat (ΔH>0, exothermic). On the other hand, when the stress is removed, the B19 phase is reverse transformed back to the B2 phase, thereby absorbing heat (ΔH<0, endothermic). The alloy according to the embodiment can be manufactured and used in a bulk form having a thickness of 1 mm or more, and has a rod-shaped shape with a diameter of about 3 mm and a height of about 50 mm, and after mixing each element of the alloy, by using an arc melting method. It was manufactured by melting and casting, and was cut to a height of about 6 mm and subjected to periodic deformation. The alloy according to the embodiment may exhibit an elastic calorie effect by using heat release and absorption that occurs when stress is applied and removed, which converts mechanical energy into thermal energy to cool and heat components such as adjacent parts. Includes use for purposes. The elastic calorie effect for cooling or heating is driven by repeatedly and periodically deforming the material.The mechanical and functional properties of the elastic calorie alloy are deteriorated according to the repeated driving, resulting in a decrease in cooling capacity and heating capacity due to fatigue failure or fatigue. do. Since the fatigue properties of the alloy according to the embodiments are remarkably superior to those of the conventional alloy, the reduction in properties due to fatigue may be remarkably small even under repeated use conditions of 100,000 or more times.

1 shows a stress-strain curve when the B2-B19 phase transformation occurs reversibly by periodically applying and relaxing stress to the alloy at a low strain rate (10 ^-4 /s). The composition of the alloy is (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ , and the amount of change in the strain over time is 10 ^-4 /s, and even if heat is absorbed and released due to the latent heat due to phase transformation, The temperature of the specimen corresponds to the condition (isothermal) that is maintained equal to the ambient temperature (T _o ). As the stress is applied, a martensitic phase transformation occurs from B2 to B19 phase, and the conditions of the start (σ _Ms ) and end (σ _Mf ) of the phase transformation can be confirmed by the change of the slope of the stress-strain curve in FIG. In addition, when the stress is relieved, an austenite phase transformation occurs from the B19 phase to the B2 phase, and the start (σ _As ) and end (σ _Af ) conditions are confirmed by the change of the slope of the stress-strain curve in FIG. The stress-organic phase transformation of the alloy can be completed at a stress criterion (coot) of about 240Mpa or less and a strain criterion (quantity) of 1.2% or less.

2 shows a stress-strain curve when a stress is periodically applied and removed to the alloy at a high strain rate (10 ⁻¹ /s) so that a phase transformation of B2-B19 occurs reversibly. The composition of the alloy is (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ as shown in FIG. 1, and the amount of change in the strain with respect to time is 10 ^-1 /s, and a stress application or stress relaxation process is performed within about 0.15 seconds. Therefore, as the stress-induced phase transformation occurs, the temperature of the specimen rises and decreases due to the latent heat released and absorbed, and at this time, sufficient time for conduction to occur is not given (quasi-adiabatic). You can estimate the size of The graph inserted in the lower right of FIG. 2 is a result of measuring the temperature change (ΔT) of the specimen according to the change over time of the strain, and the quasi-adiabatic condition is satisfied at a condition higher than 10 ^-1 /s. When the temperature change is about 8 degrees. At this time, the amount of temperature change of the specimen was measured using an IR camera, and not only the exact temperature change of the specimen due to the martensite and austenite phase transformations, but also the approximate amount of latent heat emission can be estimated. In addition, the energy value obtained by integrating the stress-strain curve of FIG. 2 corresponds to the work energy (ΔW) input to generate the martensite phase transformation and the austenite phase transformation in each period per cycle. At this time, (COP _mat / COP _carnot ), which is a factor related to the efficiency of the elastic calorie effect, is calculated by the following equation.

(C _p : specific heat of the material)

(T _H : maximum temperature reached by the specimen in the deformation cycle

T _C : the lowest temperature that the specimen reaches in the deformation cycle)

In the (Ti _x Cu _y Ni _{100 -xy} ) _{100-z- k} Si _z Sn _k alloy and other elastic calorie alloy composition according to the embodiment, To, ΔT, when the elastic calorie effect occurs according to the application and relaxation of cyclic stress, Table 1 shows ΔW, COPmat/COPcarnot, maximum strain, ΔT/Δε, maximum stress, and ΔT/Δσ values.

System Composition
(at.%) To
(K) ΔT-
(K) ΔW
(mJ/mm3) COPmat/
COPcarnot Strain
(%) ΔT/Δε
(K/%) Stress
(MPa) ΔT/Δσ
(K/MPa) TiNiCuV Ni45Ti47.25Cu5V2.75 295 12 6.6702 0.239 5 2.4 500 0.024 TiNiCuV Ni45Ti47.25Cu5V2.75
(90th cycle) 295 10 4.891 0.224 5 2 500 0.02 TiNiCuV Ni45Ti47.25Cu5V2.75 295 6.5 0.336 2 3.25 420 0.015 TiNiCuV Ni45Ti47.25Cu5V2.75 295 12 0.509 3 4 480 0.025 TiNiCuV Ni45Ti47.25Cu5V2.75 295 16 0.545 4 4 530 0.03 TiNiCuV Ni45Ti47.25Cu5V2.75 295 18 0.552 4.65 3.871 580 0.031 TiNiCuCo Ti54.7Ni30.7Cu12.3Co2.3
(after 20 cycle) 300 3.5 0.091 4 0.875 420 0.008 TiNiCu Ti54.9Ni32.5Cu12.6 298 6.1 4.213 0.084 1.6 3.8125 350 0.017 TiCuNiSiSn (Ti50Cu40Ni10)98Si1Sn1
(100000th cycle) 301 6.51 0.453 0.913 1.35 4.8294 300 0.022 TiCuNiSiSn (Ti50Cu40Ni10)98Si1Sn1 298 7.16 0.632 0.801 1.56 4.5897 300 0.024 TiCuNiSiSn (Ti51Cu44Ni4Si1)98Sn2 298 1.733 0.037 0.752 1.6 1.0831 600 0.003 TiCuNiSiSn (Ti51Cu43Ni5Si1)98Sn2 298 3.112 0.112 0.805 1.65 1.8861 600 0.005 TiCuNiSiSn (Ti51Cu41Ni7Si1)98Sn2 298 7.159 0.675 0.720 1.82 3.9335 600 0.012 TiCuNiSiSn (Ti51Cu37Ni11Si1)98Sn2 298 7.588 0.712 0.778 2.12 3.5792 600 0.013 TiCuNiSiSn (Ti51Cu33Ni15Si1)98Sn2 298 9.958 1.187 0.803 2.53 3.936 600 0.017 TiCuNiSiSn (Ti51Cu30Ni18Si1)98Sn2 298 10.24 1.399 0.718 2.51 4.0809 600 0.017 NiTi Ni50Ti50 295 9 6.6 0.146 6 1.5 755 0.012 NiTi Ni50.375Ti49.625 305 15 5.6765 0.498 4.1 3.6585 500 0.03 NiTi Ni50Ti50 295 17 21.1 0.168 8.5 2 570 0.03 NiTi Ni48.9Ti51.1 298 17 10.678 0.267 5.8 2.931 840 0.02 NiTi Ni50.4Ti49.6 300 15.5 12.496 0.188 5.3 2.9245 550 0.028 NiTi Ni50.375Ti49.625 305 13.5 7.2264 0.315 4.8 2.8125 500 0.027 NiTi Ti49.6Ni50.4 300 7.4 10.977 0.055 7 1.0571 400 0.019 NiTi Ti49.6Ni50.4 (trained) 298 3.5 2.7397 0.049 7 1.0571 400 0.019 NiMnInCo Ni45.7Mn36.6In13.3Co5.1 300 3.3 0.2948 0.299 1.37 2.4154 100 0.033 NiMnInCo Ni45.7Mn36.6In13.3Co5.1 320 0.6 0.026 0.104 0.6 1.0047 100 0.006 NiMnInCo Ni45.7Mn36.6In13.3Co5.1 310 0.8 0.1372 0.036 1.12 0.7131 100 0.008 NiMnInCo Ni45.7Mn36.6In13.3Co5.1 330 0.2 0.0254 0.011 0.52 0.3812 100 0.002 NiMnIn Ni48Mn35In17 313 4 11.826 0.014 1.4 2.8571 220 0.018 NiMnIn Ni48Mn35In17 318 3.7 10.724 0.013 1.4 2.6429 227 0.016 NiMnIn Ni48Mn35In17 324 3.1 9.8111 0.010 1.4 2.2143 248 0.013 NiFeGaCo Ni50Fe19Ga27Co4 348 10.5 0.473 17 0.6176 300 0.035 NiFeGaCo Ni50Fe19Ga27Co4 318 2 0.011 17.5 0.1143 300 0.007 Ni2FeGa Ni54Fe19Ga27
(100th cycle) 300 6 1.0864 0.391 3.3 1.8182 181 0.033 Ni2FeGa Ni54Fe19Ga27 298 8.4 2.8769 0.294 10 0.84 75 0.112 Ni2FeGa Ni54Fe19Ga27
(1st cycle) 300 4.2 1.3423 0.154 3.6 1.1667 177 0.024 FeRh Fe49Rh51 314 One 56 0.018 FeRh Fe49Rh51 314 2.47 151 0.016 FeRh Fe49Rh51 314 3.15 238 0.013 FeRh Fe49Rh51 314 4.07 336 0.012 FeRh Fe49Rh51 314 4.72 433 0.011 FeRh Fe49Rh51 314 5.17 529 0.01 FePd Fe68.8Pd31.2 240 2.3 0.1421 0.373 3.68 0.625 100 0.023 FePd Fe68.8Pd31.2 260 2.1 0.1119 0.364 3.22 0.6523 100 0.021 FePd Fe68.8Pd31.2 280 1.9 0.1187 0.260 2.15 0.883 100 0.019 FePd Fe68.8Pd31.2 300 1.4 0.0924 0.169 1.56 0.8996 100 0.014 FePd Fe68.8Pd31.2 350 0.9 0.1282 0.043 0.56 1.602 100 0.009 CuAlZn Cu68Al16Zn16 290 6.8 1.7369 0.297 9.7 0.701 120 0.057 CuAlZn Cu68Al16Zn16 220 4 2.0436 0.115 11.1 0.3604 275 0.015 CuAlZn Cu68Al16Zn16 300 4 0.086 3.5 1.1429 460 0.009 CuAlMn Cu73Al15Mn12 300 3.8 0.158 3.5 1.0857 130 0.029 CoNiAl Co40Ni33.17Al26.83 373 3.1 6.098 0.014 7 0.4429 170 0.018 NiTiV Ni50Ti45.3V4.7 300 12.5 6.7115 0.260 6.8 1.8382 300 0.042 NiTiV Ni50Ti45.3V4.7 (trained) 300 11 1.672 0.803 7.3 1.5068 300 0.037

In Table 1, the efficiency of the elastic calorie effect of each alloy composition can be compared with COPmat/COPcarnot, and the amount of temperature change of the specimen versus the strain (ΔT/Δε) and the amount of temperature change of the specimen versus the applied stress (ΔT/Δσ) are compared. I can. These three factors are used as a criterion for evaluating that the higher the value, the better the properties when developing an elastic calorie material. In addition, the fact that the fatigue characteristics of the alloys according to the present embodiments are significantly superior to those of the existing alloys is that ΔW, maximum strain, and maximum stress values in Table 1 are low, and COPmat/COPcarnot, ΔT /Δε and ΔT/Δσ values are high. This alloy design is constructed by combining elements of Ti, Cu, Ni, Si, and Sn, which are constituents in the material, in an appropriate element ratio. In this example, the element content is indicated on the basis of atomic percent.

The x related to the elemental content of Ti may range from 48 to 52.

The y related to the elemental content of Cu may range from 15 to 44.

Z indicating the element content of Si may range from 0 to 3.

K representing the element content of Sn may be 0 to 2.

When x is in the range of 49 to 51 and y is in the range of 35 to 43, the -ΔH/ΔW value may be 25 or more.

When x is in the range of 49 to 51, y is in the range of 35 to 43, and z is in the range of 0.5 to 2, it may have a microstructure including only two phases B2 and B19.

When x is in the range of 49 to 51, y is in the range of 35 to 43, z is in the range of 0.5 to 2, and k is in the range of 0.5 and 1.3, the characteristic deterioration that occurs due to repeated deformation is small and can be used repeatedly more than 100,000 times. Either shows ultra-low fatigue characteristics, or the martensitic phase transformation end stress (σ _Mf ) due to stress-organic phase transformation is less than 350 MPa, or the strain generated by applying the martensitic phase transformation end stress (σ _Mf ) due to stress-organic phase transformation is 2% The amount of decrease in specimen temperature due to the latent heat absorption of the austenite phase transformation (Martensite → Austenite) is shown below, or when a stress of more than the martensite phase transformation end stress (σ _Mf ) due to the stress-organic phase transformation is applied more than 100,000 times and is repeatedly deformed (- The ratio of the 100,000th value (-ΔT ₁₀₀₀₀₀ /-ΔT ₁ ) to the initial value of ΔT) may be 0.9 or more, or the elastic calorie effect efficiency factor COP _mat /COP _carnot value may be 0.85 or more.

The alloy according to the embodiments may exhibit a high-efficiency elastic calorie effect by having a significantly higher COP _mat / COP _carnot value than that of a conventional alloy, and the number of repeated uses may be remarkably high due to remarkably excellent fatigue properties. . Whether the fatigue properties are excellent depends on whether the shape of the stress-strain curve greatly differs from the initial stress-strain curve during repeated deformation, whether there is a large amount of residual deformation, and the ΔT-time curve in the case of repeated deformation is the initial ΔT-time curve and the shape. It can be determined on the basis of whether is significantly different or whether the maximum and minimum temperature values decrease relatively significantly. In the case of a conventional alloy with poor fatigue properties, the stress-strain curve and the ΔT-time curve greatly change as the cyclic deformation progresses, so that the mechanical training process of the alloy is performed in the order of tens to hundreds of these curves to be stabilized. There is a disadvantage that must be applied to all specimens more than once, and there is a characteristic that functional properties (temperature reduction, etc.) deteriorate. In addition, conventional elastic calorie alloys such as TiNiCu, which have excellent fatigue properties, cannot be manufactured in a bulk form, so it is possible to manufacture only thin plates having a thickness of several hundred micrometers or less, but ultra-low fatigue bulk elastic calorie alloys according to the present embodiments. Silver, which can be manufactured in a bulk form, has significantly superior fatigue properties compared to conventional alloys, shows a very stable stress strain curve and ΔT-time curve from the beginning of deformation, and can be repeatedly used more than 100,000 times without a mechanical training process. In the present specification, the measurement results of the alloy according to the embodiments are measured without a mechanical training process.

3 shows (Ti ₅₀ Cu ₁₅ Ni ₃₅ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₂₀ Ni ₃ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₃₀ Ni ₂₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu) ₄₀ Ni ₁₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₃ Ni ₇ ) Si ₁ Sn ₁ Stress-strain curve when stress is applied to an alloy with a low strain (10 ^-4 /s) up to 500 MPa and then relaxed Represents. The stress-strain curve of each stress-strain curve is σ _Ms and σ _Mf when the martensitic phase transformation occurs from the point where the slope change occurs, from B2 to B19 phase as the stress is applied, and in B19 phase when the stress is relieved. Σ _As and σ _Af when the austenite phase transformation occurs into the B2 phase The condition can be checked, and the ΔW value can be known through the integration. In order to realize the low fatigue characteristic, the lower the ΔW value is, the more preferable the lower the σ _Mf value, which is the maximum stress for the operation of the periodic phase transformation behavior.

(Ti ₅₀ Cu ₁₅ Ni ₃₅ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₂₀ Ni ₃ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₃₀ Ni ₂₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₀ Ni ₁₀₎ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₃ Ni ₇ ) Si ₁ Sn ₁ The alloy of the composition was subjected to DSC (Differential Scanning Calorimetry) to initiate temperature-organic martensite phase transformation (M _s ) and end (M _f ) Temperature, the start (A _s ) and end (A _f ) temperature of the organic austenite phase transformation, and the latent heat (-ΔH) were measured, and the M _s , M _f , A _s , A _f , and ΔW values were measured. Table 2 shows the ratio of latent heat (-ΔH) values.

Composition
(at.%) -ΔH/ΔW A _s (℃) M _f (℃) M _s (℃) A _f (℃) (Ti ₅₀ Cu ₁₅ Ni ₃₅ ) Si ₁ Sn _1ㄴ 12.72 4.98 -10.1 -0.66 16.46 (Ti ₅₀ Cu ₂₀ Ni ₃ ) Si ₁ Sn ₁ 15.73 11.18 -0.73 9.12 23.15 (Ti ₅₀ Cu ₃₀ Ni ₂₀ ) Si ₁ Sn ₁ 18.41 3.25 -4.72 9.92 20.46 (Ti ₅₀ Cu ₄₀ Ni ₁₀ ) Si ₁ Sn ₁ 30.09 -4.3 -10.7 5.31 24.75 (Ti ₅₀ Cu ₄₃ Ni ₇ ) Si ₁ Sn ₁ 29.88 4.75 -5.29 12.01 19.02

In each composition factor, M _s, M _f, and A _s the value related to the phase transformation temperature is necessarily and lower both than T _o corresponding to the operation environmental temperature, since the A _f value is also the low criteria than T _o generation less residual strain desirable. Referring to Table 1, all of these are satisfied. In addition, the ratio of the latent heat (-ΔH) value to the ΔW value is the ratio of the heat energy that the material can release or absorb to the mechanical energy input to realize the elastic calorie effect, and the higher this value, the better the elastic calorie property. desirable.

4 shows (Ti ₅₀ Cu ₁₅ Ni ₃₅ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₂₀ Ni ₃ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₃₀ Ni ₂₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu) ₄₀ Ni ₁₀ )Si ₁ Sn ₁ , (Ti ₅₀ Cu ₄₃ Ni ₇ )Si ₁ Sn ₁ By DSC measurement and periodically applying and releasing stress on the alloy, and measuring the stress-strain curve, the latent heat for the ΔW value (- The ratio of ΔH) values is shown according to the Cu content of each composition. Among the alloy compositions according to the examples, (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ composition showed the highest value, and thus corresponds to the composition expected to have the best elastic calorie efficiency.

5 is a B2-B19 phase transformation reversibly occurs by periodically applying and removing stress to the alloy of the (Ti ₅₀ Cu ₄₀ Ni ₁₀ ) Si ₁ Sn ₁ composition according to the embodiment at a high strain rate (10 ^-1 /s). The stress-strain curve of the case is shown according to the repetition period. Even if the stress application and relaxation cycle is repeated up to 100,000 times, the change in the stress-strain curve is not clear, and the residual deformation amount is only 0.17% for 100,000 times of deformation compared to the initial stress-strain curve. The alloy of the composition of (Ti ₅₀ Cu ₄₀ Ni ₁₀ ) Si ₁ Sn ₁ according to this embodiment was subjected to periodic deformation at sufficiently high stress and strain to cause stress-induced martensite and austenite phase transformation, but the residual deformation amount was very It exhibited low and ultra-low fatigue characteristics. In the case of NiTi-based alloys, when the deformation cycle is repeated more than 100 times, the fatigue property is very good compared to the case where the residual deformation amount can occur more than 2%.

6 is a B2-B19 phase transformation reversibly occurs by periodically applying and removing stress to the alloy of the (Ti ₅₀ Cu ₄₀ Ni ₁₀ )Si ₁ Sn ₁ composition according to the embodiment at a high strain rate (10 ^-1 /s). The ΔT-time curve measured by the infrared camera for the temperature change of the specimen in the case is shown according to the repetition period. Even if the stress application and relaxation cycle is repeated up to 100,000 times, the change on the ΔT-time curve is not clear, so the average amount of temperature decrease (-ΔT) due to the austenite phase transformation from B19 to B2 when it is deformed more than 100,000 times compared to the initial ΔT-time curve. It is only 6.2%. In the case of the NiTi-based alloy, when the deformation cycle is repeated more than 100 times, the fatigue property is very good compared to the case where the reduction rate of the temperature decrease (-ΔT) compared to the initial ΔT-time curve can occur by 50% or more.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of rights of

Claims (11)

delete delete delete delete delete It is represented by the following formula,
Martensite phase transformation end stress (σ _Mf ) due to stress-organic phase transformation is 300 MPa or less,
The elastic calorie effect efficiency factor COP _mat / COP _carnot value is 0.85 or more,
Ultra-low fatigue bulk elastic calorie alloy containing Ti, Cu, Ni, Si and Sn.
[Chemical Formula]
(Ti _x Cu _y Ni _100-xy ) _100-zk Si _z Sn _k
(In the above formula, 49≤x≤51, 35≤y≤43, 0.5≤z≤2, and 0.5≤k<1.3.)
delete The method of claim 6,
An ultra-low fatigue bulk elastic calorie alloy, wherein the alloy has a strain rate of 2% or less when a martensitic phase transformation end stress (σ _Mf ) is applied due to a stress-organic phase transformation.
The method of claim 6,
An ultra-low fatigue bulk elastic calorie alloy, wherein the alloy has a residual deformation amount of 0.5% or less during repeated deformation by applying a stress equal to or greater than the martensitic phase transformation end stress (σ _Mf ) caused by stress-organic phase transformation by 100,000 times or more.
The method of claim 6,
When the alloy is repeatedly deformed by applying a stress _equal to or greater than the martensitic phase transformation end stress (σ _Mf ) caused by the stress-organic phase transformation more than 100,000 times, the specimen temperature decrease (-ΔT) due to the latent heat absorption of the austenite phase transformation (Martensite → Austenite) Ultra-low fatigue bulk elastic calorie alloy, characterized in that the ratio of the 100,000th value to the initial value (-ΔT _{100 ,000} /-ΔT ₁ ) is 0.9 or more.
delete

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