Preparation method for improving thermoelastic refrigeration performance of nickel-titanium alloy

Abstract

The invention provides a preparation method for improving the thermoelastic refrigeration performance of a nickel-titanium alloy, which breaks through the traditional cold processing technology and precipitation strengthening technology, and adopts a specific preparation method comprising annealing treatment, strong plastic deformation process, re-annealing, cyclic stretching and aging. The coarse-grain nickel-titanium shape memory alloy containing uniformly-distributed and high-density nano precipitated phases is prepared, the refrigeration efficiency and refrigeration capacity of the material can be considered, meanwhile, energy dissipation in the phase change process is reduced, the service life is prolonged, and the mechanical property stability is improved. In addition, the process is simple to operate, relatively high in precision and low in cost, can be quickly produced and put into use, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of metal material microstructure design and thermodynamic property regulation, and specifically relates to a method for preparing a coarse-grained superelastic nickel-titanium alloy with a uniformly distributed nano-precipitate phase. Background Art

[0002] Human society cannot do without refrigeration technology, and the energy consumed by refrigeration accounts for one-fifth of the total energy consumption. However, the traditional vapor compression refrigeration technology currently relied on will cause ozone reduction and aggravate the greenhouse effect. Therefore, it is of great significance to develop environmentally friendly and energy-saving refrigeration technology. Solid-state refrigeration technology using green refrigerants provides a reliable solution to replace traditional vapor compression refrigeration technology, and the demand for more efficient use of energy has also promoted the research of solid-state refrigeration technology. Magnetocaloric refrigeration is the most mature technology in solid-state refrigeration technology, but it is difficult to be widely used due to its complex structure and high cost. At the same time, electrothermal refrigeration is also difficult to replace traditional vapor compression refrigeration technology due to its low refrigeration efficiency. In contrast, elastic caloric refrigeration based on the spring-clip effect of shape memory alloy has great potential in the field of solid-state refrigeration due to its high refrigeration efficiency and simple mechanical induction method. Nickel-titanium alloy is the most widely used shape memory alloy at present. Due to its considerable latent heat of phase change, it is widely studied as an excellent elastic caloric refrigeration material in the field of solid-state refrigeration. However, due to the contradictory relationship between cooling capacity, cooling efficiency and cycle stability, the elastic caloric properties of nickel-titanium alloys prepared in the past cannot meet the requirements of application.

[0003] In recent years, the research mainly uses grain refinement and precipitation strengthening technology to improve the elastic-caloric properties of nickel-titanium alloys. The alloy prepared by the former has the advantages of strong resistance to plastic deformation, low energy dissipation and uniform phase change, but the low cooling capacity limits its application; the latter has developed rapidly in recent years, but there is still no preparation process that can well balance the three elastic-caloric performance indicators. In view of the application of nickel-titanium alloys in the field of solid-state refrigeration, there is an urgent need for a preparation method that can improve the elastic-caloric refrigeration performance of nickel-titanium alloys, and greatly improve its cooling efficiency and cycle stability without reducing the cooling capacity of the alloy. Summary of the invention

[0004] The present invention provides a method for improving the elastic-thermal refrigeration performance of nickel-titanium alloy, breaking through the traditional cold processing technology and precipitation strengthening technology to prepare a coarse-grained nickel-titanium shape memory alloy containing a uniformly distributed and high-density nano-precipitate phase. The prepared nickel-titanium alloy can take into account the refrigeration efficiency and refrigeration capacity of the material, while reducing the energy dissipation during the phase change process, thereby improving the service life and mechanical performance stability. In addition, the process is simple to operate, has high precision, low cost, can be quickly mass-produced and put into use, and has broad application prospects.

[0005] The present invention is achieved through the following technical solutions: A method for improving the elastic heat refrigeration performance of nickel-titanium alloy, comprising the following steps: Step 1: After annealing the nickel-rich nickel-titanium alloy substrate, a strong plastic deformation process is used for treatment, and then annealing is performed again to prepare a coarse-grained superelastic nickel-titanium shape memory alloy; the nickel-rich coarse-grained nickel-titanium alloy substrate refers to a coarse-grained nickel-titanium alloy substrate in which nickel atoms account for 50.7%-51%; Step 2: subjecting the nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy obtained in step 1 to cyclic tensile training and then aging treatment to obtain a nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy with uniformly distributed high-density Ni4Ti3 nano-precipitate phase.

[0006] Furthermore, there are two annealing treatments in step 1. The first annealing treatment, i.e., the annealing treatment of the nickel-rich coarse-grained nickel-titanium alloy substrate in step 1, is performed at a temperature of 700°C-900°C and an annealing time of 1-2 hours; the second annealing treatment, i.e., the annealing heat treatment after the strong plastic deformation process is performed at a temperature of 600°C-800°C and an annealing time of 1-2 hours; the average grain size of the prepared coarse-grained superelastic nickel-titanium shape memory alloy is 10-20µm; The cyclic stretching training described in step 2 is carried out under a maximum strain of 8%-10% of the coarse-grained superelastic nickel-titanium shape memory alloy, the cyclic stretching training is 10-30 cycles, the aging temperature is 200°C-300°C, and the time is 40-60 hours.

[0007] Furthermore, the severe plastic deformation process in step 1 can be cold rolling, equal channel extrusion, cold drawing or high pressure torsion, and the geometric shape of the nickel-rich coarse-grained nickel-titanium alloy matrix can be obtained as a plate, a cylinder, a tube, a wire or a cuboid. The processing temperature of the severe plastic deformation process is below the metal recrystallization temperature, which is lower than 100°C.

[0008] Furthermore, when the intensive plastic deformation process used in step 1 is cold rolling, the raw material is a nickel-rich coarse-grained nickel-titanium alloy matrix plate wrapped with a stainless steel plate. During the cold rolling process, the roller pressure is controlled to be within 0.05 mm each time, and multiple rolling passes are performed to obtain a nickel-titanium plate with a uniform thickness thinned by about 35%-45% and no obvious microcracks on the surface.

[0009] Furthermore, in the steps 1 and 2, water quenching treatment is performed after the annealing heat treatment after the strong plastic deformation process and after aging.

[0010] Furthermore, the method further comprises step 3: polishing the surface of the nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy obtained in step 2 to a mirror surface.

[0011] Furthermore, in step 3, the polishing method first uses 240, 800, and 2000 mesh silicon carbide sandpaper for polishing in sequence, and then uses a polishing liquid for mechanical polishing until the sample surface is mirror-like to the naked eye and does not contain microcracks under a light microscope.

[0012] This patented technical solution has the following technical effects: 1. The present invention provides a method for improving the thermal refrigeration performance of nickel-titanium alloy, and prepares a nickel-titanium alloy spring card refrigeration material containing a uniformly distributed high-density Ni4Ti3 nano-precipitate phase. It reaches 52 while having an adiabatic temperature change of 11K, breaking through the limit of the reported shape memory alloy snap-in effect. The material prepared by the preparation method of the present invention exhibits low hysteresis and excellent cyclic stability due to the strain glass-like martensitic phase transformation and reverse phase transformation induced by the high-density Ni4Ti3 nanoprecipitate phase, and the effective inhibition of dislocation slip by the uniformly distributed high-density Ni4Ti3 nanoprecipitate phase. Compared with the general uniform coarse-grained nickel-titanium alloy, the localization degree of the martensitic phase transformation and reverse phase transformation of the nickel-titanium alloy obtained by the preparation method provided by the present invention is suppressed to a certain extent, and the approximately uniform temperature field it produces is its advantageous feature as a snap-in refrigeration material, which not only has huge advantages in solid-state refrigeration applications, but also shows extraordinary potential in high-precision control devices.

[0013] 2. The preparation method provided by the present invention prepares a coarse-grained nickel-titanium shape memory alloy containing a uniformly distributed and high-density nano-precipitate phase by breaking through the traditional cold working technology and precipitation strengthening technology. This preparation method eliminates the processing stress of the matrix itself and other factors that are not conducive to the subsequent steps, and obtains a coarse-grained nickel-titanium alloy sample with a uniform grain size, and by controlling the size of the Ni4Ti3 precipitate phase (the size should not be too large, and it is best to control it to about tens of nanometers), the nickel-titanium matrix is ​​effectively strengthened; a high-density dislocation is further introduced into the matrix to act as the nucleation site of the Ni4Ti3 precipitate phase to obtain a uniformly distributed precipitate phase; at the same time, by precisely controlling the loading stress of the tensile training, the balance and optimization between cooling efficiency, cooling capacity and good cyclic stability are further achieved, because although the nickel-titanium alloy has a higher adiabatic temperature change under higher loading stress, it sacrifices a considerable amount of and cycle stability. The nickel-titanium alloy prepared by precise control of loading stress achieves extremely high cooling efficiency, high cooling capacity and good cycle stability.

[0014] 3. Only through the preparation method and process flow provided by the present invention can the obtained nickel-titanium alloy show the martensitic phase transformation and reverse phase transformation characteristics of strain glass transition and show extraordinary elastic-thermal effect; at the same time, the specific process parameters provided by the present invention are adopted to make its technical effect more superior. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the processing method of the present invention; Figure 2 Schematic diagram of the microstructure of the nickel-titanium alloy prepared by the method of the present invention; Figure 3 Is prepared by the method of the present invention, nickel-titanium alloy tensile test stress-strain curve (stress control, maximum stress 600MPa, loading and unloading rates are 60MPa / s); Figure 4 It is an in-situ record of strain field and temperature field during the tensile test of nickel-titanium alloy; Figure 5 The refrigeration performance of the nickel-titanium alloy prepared by the method of the present invention is different from that of the nickel-titanium alloy prepared by predecessors ( ) and cooling capacity ( ) comparison chart. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further specifically described below through examples and in conjunction with the accompanying drawings.

[0017] Example 1 like Figure 1 As shown, a preparation method for improving the elastic-thermal cooling performance of nickel-titanium alloy is to process a nickel-titanium alloy plate with an initial thickness of 2 mm and a chemical composition of 50.8% atomic nickel and 49.2% titanium according to the following steps: Step 1: The plate is subjected to annealing heat treatment at 700°C for 1 hour, and then repeatedly cold rolled to make the final thickness of the plate 1.3 mm, and then annealed at 600°C for 1 hour to prepare a coarse-grained superelastic nickel-titanium shape memory alloy sheet substrate with an average grain size of 10 µm; the cold rolling temperature must be lower than the metal recrystallization temperature, which is 25°C in this embodiment; Step 2: The nickel-titanium alloy sheet substrate obtained in step 1 is subjected to cyclic tensile training at a maximum strain of 8% for ten cycles, and then aged at 200°C for 40 hours to introduce a uniformly distributed and high-density Ni4Ti3 nano-precipitate phase into the alloy.

[0018] Example 2 A preparation method for improving the elastic-thermal cooling performance of nickel-titanium alloy, wherein a commercial coarse-grained superelastic nickel-titanium alloy plate with an initial thickness of 2 mm and a chemical composition of 50.9% atomic nickel and 49.1% titanium is processed according to the following steps: Step 1: The plate is subjected to annealing heat treatment at 900°C for 2 hours, and then repeatedly cold rolled to make the final thickness of the plate 1.3 mm, and then annealed at 800°C for 2 hours to prepare a coarse-grained superelastic nickel-titanium shape memory alloy sheet matrix with an average grain size of 20µm; the cold rolling temperature is 25°C; Step 2: The nickel-titanium alloy sheet substrate obtained in step 1 is subjected to cyclic tensile training for 30 cycles at a maximum strain of 10%, and then aged at 300°C for 60 hours to introduce a uniformly distributed and high-density Ni4Ti3 nano-precipitate phase into the alloy.

[0019] Example 3 A method for improving the elastic-thermal cooling performance of nickel-titanium alloy is provided, wherein a nickel-titanium alloy plate having an initial thickness of 2 mm and a chemical composition of 51% atomic nickel and 49% titanium is processed according to the following steps: Step 1: The plate is subjected to annealing heat treatment at 800°C for 1.5 hours, and then repeatedly cold rolled to make the final thickness of the plate 1.3 mm, and then annealed at 700°C for 1.2 hours to prepare a coarse-grained superelastic nickel-titanium shape memory alloy sheet matrix with an average grain size of 15µm; the cold rolling temperature is 25°C; Step 2: The nickel-titanium alloy sheet substrate obtained in step 1 is subjected to cyclic tensile training for 20 cycles at a maximum strain of 9%, and then aged at 250°C for 48 hours to introduce a uniformly distributed and high-density Ni4Ti3 nano-precipitate phase into the alloy.

[0020] Example 4 A preparation method for improving the elastic-thermal cooling performance of nickel-titanium alloy, wherein a nickel-titanium alloy plate having an initial thickness of 2 mm and a chemical composition of 50.8% atomic nickel and 49.2% titanium is processed according to the following steps: Step 1: The plate is subjected to annealing heat treatment at 800°C for one hour, and then the plate is repeatedly cold rolled to a final thickness of 1.3 mm, and then annealed at 700°C for two hours to prepare a coarse-grained superelastic nickel-titanium shape memory alloy sheet substrate with an average grain size of 15 µm; Step 2: The nickel-titanium alloy sheet substrate obtained in step 1 is subjected to cyclic tensile training at a maximum strain of 9.5% for ten cycles, and then aged at 250°C for 48 hours to introduce a uniformly distributed and high-density Ni4Ti3 nano-precipitate phase into the alloy.

[0021] like Figure 5 As shown, the nickel-titanium alloy prepared by the method of the present invention has a much greater refrigeration performance (up to 52) and a good cooling capacity (11K) compared to the nickel-titanium alloy prepared previously.

[0022] Example 5 Compared with Example 3, the difference between this embodiment and Example 3 is that the cold rolling can be replaced by other strong plastic deformation processes, such as equal channel extrusion, cold drawing or high pressure torsion, and the geometric shapes of the coarse-grained nickel-titanium alloy substrate that can be processed and obtained are plates, cylinders, tubes, wires or cuboids, so the preparation method provided by this patent can be applied to substrates with complex shapes and has a wider range of applications. The strong plastic deformation processes all require the processing temperature to be below the metal recrystallization temperature, below 100°C.

[0023] Example 6 A preparation method for improving the elastic-thermal cooling performance of nickel-titanium alloy, wherein a commercial coarse-grained superelastic nickel-titanium alloy plate with an initial thickness of 2 mm and a chemical composition of 50.8% atomic nickel and 49.2% titanium is processed according to the following steps: Step 1: The plate is annealed at 800°C for one hour, and then repeatedly cold rolled to a final thickness of 1.3 mm. It is then annealed at 700°C for two hours to prepare a coarse-grained superelastic nickel-titanium shape memory alloy sheet matrix with an average grain size of 15 µm. The cold rolling temperature is 50 degrees. During cold rolling, the nickel-titanium alloy plate is wrapped with a stainless steel plate. During the cold rolling process, the roller pressure is controlled to be within 0.05 mm each time, and multiple rolling passes are performed to evenly reduce the thickness of the nickel-titanium plate by about 35%-45% without obvious microcracks on the surface.

[0024] Step 2: The nickel-titanium alloy sheet substrate obtained in step 1 is subjected to cyclic tensile training at a maximum strain of 10% for ten cycles, and then aged at 250°C for 60 hours to introduce a uniformly distributed and high-density Ni4Ti3 nano-precipitate phase into the alloy.

[0025] Example 7 Compared with Example 6, the difference is that in steps 1 and 2, the alloy is water quenched during the annealing after the strong plastic deformation process and after aging, and the water quenching is used to achieve a solid solution effect to prepare for the subsequent aging precipitation phase.

[0026] Example 8 Compared with Example 6, the difference is: The initial substrate material used was a commercial coarse-grained superelastic nickel-titanium alloy plate with a chemical composition of 50.7% atomic nickel and 49.3% titanium.

[0027] The method also includes step 3: polishing the surface of the nickel-titanium alloy obtained in step 2 to a mirror surface.

[0028] In step 3, the polishing method first uses 240, 800, and 2000 mesh silicon carbide sandpaper for polishing in sequence, and then uses a polishing liquid for mechanical polishing until the sample surface is mirror-like in the naked eye and does not contain microcracks under an optical microscope.

[0029] The present invention provides a method for improving the thermal refrigeration performance of nickel-titanium alloy, and prepares a nickel-titanium alloy spring card refrigeration material containing a uniformly distributed high-density Ni4Ti3 nano-precipitate phase, which has high cooling efficiency and high cooling capacity, while reducing energy dissipation during phase change, thereby improving service life and mechanical performance stability. Figure 2 It can be seen that the test results based on the examples of the present invention show that the nickel-titanium alloy treated by the method of the present invention has a grain size of micrometer level, and contains a large number of uniformly distributed precipitation phases in the grains. Figure 5 As shown, it can be seen that the nickel-titanium alloy prepared by the method of the present invention has a much greater refrigeration performance than the nickel-titanium alloy prepared previously ( As high as 52), it also has good cooling capacity (adiabatic temperature change of 11K), breaking the limit of the reported shape memory alloy spring effect.

[0030] The material prepared by the preparation method of the present invention exhibits low hysteresis and excellent cycle stability due to the strain glass-like martensitic phase transformation and reverse phase transformation induced by the high-density Ni4Ti3 nanoprecipitate phase and the effective inhibition of dislocation slip by the uniformly distributed high-density Ni4Ti3 nanoprecipitate phase. Figure 3 It can be seen that the hysteresis loop area during the phase transformation of the nickel-titanium alloy prepared by this method is greatly reduced, which will effectively inhibit the nucleation and expansion of microcracks during cyclic deformation, thereby improving the fatigue life of the structure. Figure 4 As shown, the localization degree of martensitic transformation and reverse phase transformation of nickel-titanium alloy is suppressed, and the nearly uniform temperature field is its favorable feature as a spring card material.

[0031] The preparation method provided by the present invention breaks through the traditional cold processing technology and precipitation strengthening technology, and adopts a preparation method including annealing treatment, strong plastic deformation process, re-annealing, cyclic stretching and aging to prepare a coarse-grained nickel-titanium shape memory alloy containing a uniformly distributed and high-density nano-precipitate phase. The preparation method eliminates the influencing factors such as the processing stress of the matrix itself that are not conducive to the subsequent steps, and obtains a coarse-grained nickel-titanium alloy sample with a uniform grain size, and effectively strengthens the nickel-titanium matrix by controlling the size of the Ni4Ti3 precipitation phase (the size should not be too large, and it is best to control it to about tens of nanometers); further introduces high-density dislocations in the matrix to serve as nucleation sites for the Ni4Ti3 precipitation phase to obtain a uniformly distributed precipitation phase; at the same time, by accurately controlling the loading stress of the stretching training, the balance and optimization between cooling efficiency, cooling capacity and good cyclic stability are further achieved, because although the nickel-titanium alloy has a higher adiabatic temperature change under a higher loading stress, it sacrifices a considerable amount of and cycle stability. The nickel-titanium alloy prepared by precise control of loading stress achieves extremely high cooling efficiency, high cooling capacity and good cycle stability.

[0032] The protection scope of the present invention is not limited to the above examples. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims

1. A preparation method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy, characterized in that: The following steps are involved: Step 1: After annealing the nickel-rich nickel-titanium alloy substrate, a strong plastic deformation process is used for treatment, and then annealing is performed again to prepare a nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy; the nickel-rich nickel-titanium alloy substrate refers to a nickel-titanium alloy substrate in which nickel atoms account for 50.7%-51%; Step 2: subjecting the nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy obtained in step 1 to cyclic tensile training and then aging treatment to obtain a nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy with uniformly distributed high-density Ni4Ti3 nano-precipitate phase.

2. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy according to claim 1, characterized in that: The temperature of annealing the nickel-rich nickel-titanium alloy substrate in step 1 is 700°C-900°C, and the annealing time is 1-2 hours; the temperature of annealing after the strong plastic deformation process is 600°C-800°C, and the annealing time is 1-2 hours; the average grain size of the prepared coarse-grained superelastic nickel-titanium shape memory alloy is 10-20µm; The cyclic stretching training described in step 2 is carried out at a maximum strain of 8%-10%, the cyclic stretching training is 10-30 cycles, the aging temperature is 200°C-300°C, and the time is 40-60 hours.

3. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy as claimed in claim 1 or 2, characterized in that: The severe plastic deformation process in step 1 may be cold rolling, equal channel extrusion, cold drawing or high pressure torsion. The processing temperature of the severe plastic deformation process is below the metal recrystallization temperature, which is lower than 100°C.

4. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy as claimed in claim 3, characterized in that: When the intense plastic deformation process used in step 1 is cold rolling, the nickel-rich coarse-grained nickel-titanium alloy substrate is a plate, which is wrapped with a stainless steel plate. During the cold rolling process, the roller's downward pressure is controlled to be within 0.05 mm each time, and multiple rolling passes are performed to obtain a uniform thinning of the plate thickness by about 35%-45% and no obvious microcracks on the surface.

5. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy according to claim 1 or 2, characterized in that: In the steps 1 and 2, water quenching is performed after annealing after the strong plastic deformation process and after aging.

6. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy according to claim 1 or 2, characterized in that: The method also includes step 3: polishing the surface of the nickel-rich coarse-grained superelastic nickel-titanium shape memory alloy obtained in step 2 to a mirror surface.

7. A method for improving the elastic-thermal-refrigeration performance of nickel-titanium alloy as claimed in claim 6, characterized in that: In step 3, the polishing method first uses 240, 800, and 2000 mesh silicon carbide sandpaper for polishing in sequence, and then uses a polishing liquid for mechanical polishing until the sample surface is mirror-like in the naked eye and does not contain microcracks under an optical microscope.

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