A room-temperature low-hysteresis high-entropy-change nickel-manganese-indium-based memory alloy and a preparation method thereof

Abstract

This invention discloses a room-temperature low-hysteresis, high-entropy-change nickel-manganese-indium-based shape memory alloy and its preparation method, belonging to the field of functional metal materials technology. This invention utilizes first-principles calculations to achieve synergistic optimization of phase transition temperature, thermal hysteresis, and phase transition entropy change by substituting Mn sites with Fe. Based on the optimal calculation results, the corresponding Ni alloy is prepared through processes including batching, loading, vacuuming and gas washing, melting, cooling and removal, homogenization, and further processing. 16 Fe x Mn 12‑x In4 alloy. This invention addresses the technical challenges of existing Ni-Mn-In intrinsic alloys, such as excessively high phase transition temperature and large thermal hysteresis, as well as the inability of existing Cu doping schemes to simultaneously optimize room temperature phase transition, low hysteresis, and large entropy change.

Description

Technical Field

[0001] This invention relates to the field of functional metal materials technology, and in particular to a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy and its preparation method. Background Technology

[0002] Ni-Mn-In Heusler-type shape memory alloys, due to their martensitic phase transformation accompanied by significant lattice volume changes and magnetic order transitions, show promising application prospects in the field of solid-state thermal effects. This alloy system possesses advantages such as low hysteresis loss, high latent heat, and low cost, making it one of the most competitive thermal functional materials. However, existing Ni-Mn-In intrinsic alloys face the following prominent problems in practical applications: (1) The martensitic phase transformation temperature is much higher than room temperature. The martensitic phase transformation temperature of intrinsic Ni-Mn-In alloys is usually higher than 350K, and some components even reach 500~600K, which is far from the room temperature operating range and cannot meet the application requirements of thermal control and energy storage devices near room temperature.

[0003] (2) Large phase transformation thermal hysteresis. The phase transformation thermal hysteresis of intrinsic alloys is usually 20~30K. Large thermal hysteresis means high phase transformation driving force demand and large energy loss, which seriously affects the cycle stability and service life of the material.

[0004] (3) The phase transformation entropy change needs to be further improved. The phase transformation entropy change of the martensitic phase of the alloy directly determines its thermal effect capability. The phase transformation entropy change of intrinsic alloys is generally in the range of 20~30 J / kg / K. Improving the phase transformation entropy change is of great significance for improving refrigeration and energy storage efficiency.

[0005] To overcome these bottlenecks, researchers have attempted to improve the performance of this type of alloy through elemental doping. Introducing Cu dopant at Ni sites into Ni-Mn-In alloys lowered the martensitic phase transformation temperature from the intrinsic 350K to around 305K. However, while Cu doping reduced the phase transformation temperature, it significantly increased thermal hysteresis, severely degrading cycle performance. Some researchers have also studied the effect of Fe doping on Ni-Mn-In alloys, but research in this area is fragmented and lacks systematic theoretical guidance. Existing reports indicate that Fe doping often improves a single property but also brings new problems such as increased thermal hysteresis or insufficient phase transformation driving force. The intrinsic relationship and synergistic regulation mechanism among phase transformation temperature, thermal hysteresis, and phase transformation entropy change remain unclear. How to maintain the low hysteresis loss advantage of Ni-Mn-In alloys while controlling its phase transformation temperature to near room temperature and further increasing the phase transformation entropy change has become the core technical challenge for the practical application of this material in solid-state refrigeration and thermal energy storage. Summary of the Invention

[0006] The purpose of this invention is to provide a room-temperature, low-hysteresis, high-entropy-change nickel-manganese-indium-based shape memory alloy and its preparation method. Through first-principles calculations, the composition design of Fe-doped Mn sites is precisely guided, achieving synergistic optimization of phase transition temperature, thermal hysteresis, and phase transition entropy change. This significantly reduces thermal hysteresis and increases phase transition entropy change while lowering the phase transition temperature to near room temperature. This significantly enhances the practical application value of Ni-Mn-In-Fe magnetic shape memory alloys in solid-state refrigeration and thermal energy storage.

[0007] To achieve the above objectives, this invention discloses a method for preparing a room-temperature low-hysteresis, high-entropy variable nickel-manganese-indium based shape memory alloy, comprising the following steps: Step 1, Ingredients: Calculate and weigh each elemental metal raw material Ni, Mn, In, and Fe according to the atomic percentage in the chemical formula of the alloy. The purity of each elemental metal is 99.9 wt.% or higher. To compensate for the loss of Mn due to easy volatilization during smelting, weigh an additional 3 wt.% of Mn. Step 2, Loading: Place the prepared raw materials in the water-cooled copper crucible of the non-consumable high-vacuum electric arc melting furnace in sequence, with In placed on the top layer; Step 3, Vacuuming and Gas Purging: Use a mechanical pump to evacuate the furnace chamber to 5×10⁻⁶ m³ / h. -3 Below Pa, after filling with high-purity argon gas, vacuum is evacuated again, and this process is repeated three times; then switch to a molecular pump to evacuate to 1×10⁻⁶ Pa. -3 Below Pa; Step 4, Melting: After filling with high-purity argon gas to 0.08MPa, melting begins. Electromagnetic stirring is applied throughout the process, and the ingot is repeatedly turned over for melting. Before each melting, the Ti ingot is melted to absorb residual oxygen. Step 5, Cooling and Removal: After the final melting is completed, slowly close the arc and remove the ingot after it has completely cooled. Step 6, Homogenization treatment: Cut the ingot along the diameter direction, grind to remove the surface oxide layer, clean with acetone, encapsulate in a quartz tube, anneal at 1173K under vacuum for 12 hours, and then quench in ice water. Step 7: Machining: Use wire cutting to machine the annealed alloy ingot into a sample of the required size.

[0008] Preferably, step one further includes a component screening step based on first-principles calculations, specifically including: S1. Model Establishment: Based on density functional theory (DFT), the austenitic and martensite phase models of Ni-Mn-In intrinsic alloys and alloys with different Fe doping amounts were established using the VASP (Vienna ab initio Simulation Package) software package. The austenite phase has a cubic L21 structure with space group Fm[3-m]{.math.inline} (No. 225), where Ni occupies the 8c (0.25, 0.25, 0.25) Wyckoff position, Mn occupies the 4a (0, 0,0) Wyckoff position, and In occupies the 4b (0.5, 0.5, 0.5) Wyckoff position. The martensite phase has a body-centered cubic structure with space group I4 / mmm (No. 139), where Ni occupies the 8c (0, 0.5, 0.25) Wyckoff position, Mn occupies the 4a (0, 0, 0.5) Wyckoff position, and In occupies the 4b (0, 0, 0) Wyckoff position. All models were calculated using a 32-atom supercell.

[0009] S2. Perform structural optimization calculations on the established model. Under given external conditions, systematically adjust the atomic fractional coordinates and unit cell parameters (lattice constants a, b, c and lattice vector angles α, β, γ) within the unit cell using an iterative optimization algorithm to achieve a global minimum total energy and converge the Hellmann-Feynman forces on the atoms to below a set threshold. Obtain the most stable lattice parameters and atomic positions for each austenite and martensite phase.

[0010] S3. Calculate the following five key parameters of the austenitic and martensitic phases of each component under different hydrostatic pressures: (1) The energy difference Δ between the two phases E The formation energies of the austenitic and martensitic phases in the alloy are respectively given by the formulas. E f = E tot - Σ n i · E i The calculation shows that, among which E t ot The total free energy of the system, n i Let i be the total number of elements i. E i Let be the total ground-state energy of a single atom of element i. The energy difference between the two phases. When Δ E When the value is greater than 0, the stability of the martensitic phase is higher than that of the austenitic phase, and the martensitic phase transformation can occur.

[0011] (2) Pressure sensitivity d T / d p The phase transformation temperatures of each alloy component were calculated under hydrostatic pressures of 0 kbar, 10 kbar, 20 kbar, and 30 kbar. T M Using formula d T / d p = Δ T M / Δ p get.

[0012] (3) Volume change rate Δ V / V The volumes of the two phases, Δ, were calculated based on the optimized lattice constants of the austenitic and martensitic phases. V / V = ( V A - V M ) / V A × 100%.

[0013] (4) Magnetic moment difference Δ M Extracting the magnetic moments of each atom after structural optimization m i The total magnetic moment is obtained by summing. M = Σ m i Magnetic moment difference Δ M = | M A - M M |

[0014] (5) Intermediate eigenvalues λ 2: Based on the phase transformation geometric compatibility theory, a right Cauchy-Green deformation tensor is constructed from the lattice parameters of austenite and martensite. C = U ^ T U (U is the phase transition strain tensor), calculate its three principal eigenvalues ​​( λ 1≤ λ 2≤ λ 3), of which λ 2 is an intermediate characteristic value.

[0015] S4, via Δ E The Boltzmann coefficient was obtained by fitting a linear relationship with the phase transition temperature. K B , where Δ E andK B · T M Proportional to each other, thus the martensitic phase transformation temperature of each component at 0 kbar can be calculated. T M ; S5. According to different pressure conditions T M Calculate the pressure sensitivity d of each component alloy T / d p ; S6. Using the five key parameters mentioned above as evaluation indicators, a comprehensive evaluation is conducted to construct a multi-parameter radar chart evaluation system. Among them, Δ E correspond T M Prioritize screening alloys close to room temperature; d T / d p The larger the value, the better it is for achieving the giant pressure card effect under lower driving pressure; Δ M Plotted using its reciprocal form, a larger value indicates a smaller change in magnetic moment before and after the phase transition; Δ V / V The larger the value, the more significantly it can improve d. T / d p And amplify the vibrational entropy change; λ The closer a value is to 1, the smaller the phase transformation thermal hysteresis. After normalization and radar plotting, the polygon coverage area of ​​each alloy was compared to select those with phase transformation temperatures close to room temperature. λ The Fe-doped composition is close to 1 and has the best overall pressing performance.

[0016] The first-principles calculations described above were performed using the following parameter settings: The VASP software package was used within the DFT framework; the exchange-correlation functional was the Perdew-Burke-Ernzerhof (PBE) functional under the Generalized Gradient Approximation (GGA); the ion-electron interaction was described using the Projected Added Wave (PAW) pseudopotential; the plane wave cutoff energy was set to 520 eV; the Brillouin zone integral used the Monkhorst-Pack grid scheme, with the k-point grid density controlled at approximately 35-40; all models were performed using 32-atom supercells; the parameter PSTRESS was used to simulate all hydrostatic pressure calculations, with the pressure value (kbar) determined by the PSTRESS value; spin polarization calculations were enabled throughout to accurately describe the magnetic behavior of the alloy; structural optimization employed the conjugate gradient algorithm, with the convergence criterion being a Hellmann-Feynman force on each atom less than 0.01 eV / Å, and the total energy converging to 10 eV / Å. -5 eV; self-consistent iterative convergence accuracy is 10. -6 eV / atom, K point set to 3×6×6.

[0017] Preferably, in S6, the comprehensive evaluation uses a radar chart, with five normalized indicators ΔE, d T / d p Δ V / V Δ M and λ 2 Five key parameters are used as axes for comprehensive evaluation of multiple indicators, and priority is given to screening those corresponding to ΔE. T M The alloy composition is close to room temperature, in which λ 2 The closer to 1, the smaller the thermal hysteresis.

[0018] Preferably, in step four, the melting process is repeated five times.

[0019] Preferably, in step six, the temperature of the quenching water is 273K.

[0020] Preferably, the alloy prepared by the above method simultaneously meets the following performance indicators: martensitic transformation temperature. T M ≤280K, phase change thermal hysteresis Subsequent ΔT hys ≤10K, phase transition entropy change ΔS tr ≥28J / kg / K.

[0021] The present invention also provides a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy prepared by the above preparation method.

[0022] Preferably, the alloy has the general chemical formula Ni. 16 Fe x Mn 12-x In4, where 0 <x≤2。

[0023] Preferably, in the general chemical formula, x=1, and the chemical formula of the alloy is Ni. 16 Fe1Mn 11 In4, corresponding to the atomic percentage of Ni 50 Mn 33.5 In 12.5 Fe 4.5 This specific component was systematically screened from multiple candidate components through first-principles calculations and is the core material basis for achieving synergistic optimization of "room temperature phase transition - low hysteresis - large entropy change".

[0024] Preferably, the austenitic phase of the alloy has an L21 ordered structure with space group [missing information]. Fe-substituted Mn occupies the 4a position; the martensite phase has a body-centered tetragonal structure with space group I4 / mmm, and Fe-substituted Mn occupies the 4a position.

[0025] In this invention, Fe atoms are used to selectively replace Mn sites, with the doping amount precisely controlled at x=1. This specific site occupancy method adjusts the valence electron concentration ( e / a The near-Fermi level Mn-3d electron hybridization enables precise downsizing of the martensitic phase transition temperature and synchronous optimization of phase transition hysteresis.

[0026] The above alloys are used in fields such as solid-state refrigeration, thermal energy storage, and thermal control devices.

[0027] Therefore, the present invention has the following beneficial effects: (1) Phase transformation temperature of the alloy of the present invention T M =278K, which is close to and slightly below room temperature, meets the application requirements of room temperature thermal control devices and energy storage equipment, and also provides convenience for reverse phase change when the temperature rises slightly above room temperature.

[0028] (2) The thermal hysteresis of the alloy of the present invention is only 9.74K, which is about 57% lower than that of the intrinsic alloy of 22.56K. Low thermal hysteresis means that the phase transformation driving force requirement is small and the energy loss is low, which greatly improves the cycle stability and service life of the material and is a key indicator for measuring the practical application value of the material.

[0029] (3) The phase transformation entropy change of the alloy of the present invention is 28.4 J / kg / K, which is significantly better than that of the intrinsic alloy, indicating that more heat can be exchanged per unit mass of material during the phase transformation process, which is beneficial to improving the efficiency of thermal control and energy storage processes.

[0030] (4) Compared with the Cu doping scheme, the present invention can simultaneously achieve the synergistic optimization of "room temperature phase transition, low hysteresis and large entropy change".

[0031] (5) This invention is based on first-principles calculations, by considering phase transition temperature, pressure sensitivity, volume change rate, magnetic moment difference, and intermediate characteristic values. λ 2 The comprehensive evaluation of five core parameters accurately screens out the optimal Fe doping concentration, effectively overcoming the drawbacks of the traditional "trial and error method" which has a long cycle and high cost.

[0032] (6) The preparation method is simple and reliable and suitable for large-scale production. The present invention adopts a mature vacuum arc melting combined with homogenization annealing process, which does not involve complex equipment or special process conditions, and is suitable for industrial mass production.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1Examples 2, 3, Comparative Example 1, and Comparative Example 2 show the phase transition temperatures and pressure sensitivity of four alloys under different pressures. Figure 2 Examples 2, 3, Comparative Example 1, and Comparative Example 2 are four alloys with two-phase formation energy differences. ΔE Pressure sensitivity dT / dp Volume change rate ΔV / V Magnetic moment difference ΔM and intermediate eigenvalues λ 2 A radar chart plotted using five normalized indices; Figure 3 The DSC test curves are for the alloy of Example 2 and the alloy of Comparative Example 1; where a) is the DSC test curve of the alloy of Example 2 and b) is the DSC test curve of the alloy of Comparative Example 1. Figure 4 Ni prepared in Example 1 50 Mn 33.5 In 12.5 Fe 4.5 XRD images Detailed Implementation

[0035] This invention utilizes first-principles calculations to achieve synergistic optimization of phase transition temperature, thermal hysteresis, and phase transition entropy change by substituting Mn sites with Fe. The microscopic mechanism is as follows: (1) Mechanism of phase transformation temperature decreasing to near room temperature: Fe atoms have atomic radii and electronic configurations similar to Mn. After Fe replaces Mn, it adjusts the valence electron concentration (e / a) of the alloy, weakens the driving force of martensitic phase transformation, and reduces the formation energy difference (ΔE) between austenite and martensite phases. A-M The reduction of Fe significantly lowers the martensitic phase transition temperature from the intrinsic 414 K to 278 K. Simultaneously, the introduction of Fe enhances the hybridization of Mn-3d electrons near the Fermi level, reducing the electronic density of states in the martensitic phase, stabilizing the martensitic phase, and allowing the phase transition to occur at a lower temperature.

[0036] (2) Mechanism of significantly reduced thermal hysteresis: The essence of thermal hysteresis stems from the geometric incompatibility of the austenite-martensite phase transformation interface. Fe doping optimizes the intermediate characteristic values ​​of the phase transformation. λ 2 (The alloy of this invention) λ 2 =0.9846, close to the ideal value of 1), which significantly improves the coherent matching degree of the two-phase interface, greatly reduces the elastic strain energy required for coordination during the phase transformation, and reduces interface friction and defect accumulation, thereby reducing the thermal hysteresis from the intrinsic 22.56K to 9.74K, a reduction of 57%.

[0037] (3) Mechanism of increased phase transition entropy change: Phase transition entropy change is mainly caused by lattice vibration entropy change ( ΔS vib ) and magnetic entropy change ( Δ S mag It consists of two parts. Fe doping increases the volume change rate of the martensitic phase transformation ( ΔV / V The drastic abrupt change in lattice symmetry amplifies the contribution of lattice vibrational entropy (reaching 1.54%). At the same time, Fe doping moderately modulates the magnetic moment difference, achieving the optimal ratio between magnetic entropy contribution and vibrational entropy contribution, ultimately significantly improving the phase transition entropy change.

[0038] Based on the above principles, this invention provides a method for preparing a room-temperature low-hysteresis, high-entropy change Ni-Mn-In-Fe shape memory alloy, comprising the following steps: (1) Batching: Calculate and weigh each elemental metal raw material (Ni, Mn, In, Fe) according to the atomic percentage in the chemical formula of the alloy. The purity of each elemental metal is 99.9 wt.% or higher. To compensate for the loss of Mn due to its volatility during smelting, an additional 3 wt.% of Mn is weighed during the batching stage.

[0039] (2) Loading: Place the prepared raw materials into the water-cooled copper crucible of the non-consumable high vacuum arc melting furnace in sequence, and place the low melting point In on the top layer to avoid it from sticking to the crucible wall.

[0040] (3) Vacuuming and gas purging: The furnace chamber is evacuated to 5×10 using a mechanical pump. -3 Below Pa, high-purity argon gas is introduced and then evacuated again; this gas purging process is repeated three times; the molecular pump is then switched to continue evacuating to 1×10 Pa. -3 Below Pa.

[0041] (4) Melting: Melting begins after filling with high-purity argon gas to 0.08 MPa. Electromagnetic stirring is applied throughout the melting process. The alloy ingot is repeatedly turned and melted more than five times under an appropriate working current. Before each melting, the Ti ingot in the furnace is melted to absorb residual oxygen, ensuring that the melting is always under a high-purity argon atmosphere.

[0042] (5) Cooling and removal: After the last melting is completed, slowly close the arc and remove the ingot after it has completely cooled.

[0043] (6) Homogenization treatment: The obtained ingot is cut open along the diameter direction, the surface oxide layer and impurities are removed by grinding, and then cleaned with acetone; then the sample is sealed in a quartz tube, annealed at 1173 K under vacuum for 12 hours, and then quenched in ice water.

[0044] (7) Processing: The annealed alloy ingot is processed into a sample of the required size by wire cutting.

[0045] The general chemical formula of the Ni-Mn-In-Fe shape memory alloy obtained by the above preparation method is: Ni 16 Fe x Mn 12-x In4, where 0 <x≤2。

[0046] Specific Implementation Method 1: This implementation method describes a room-temperature, low-hysteresis, high-entropy change Ni-Mn-In-Fe shape memory alloy with the general chemical formula Ni. 16 Fe x Mn 12-x In4, where 0 <x≤2。

[0047] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: in the general chemical formula of the room-temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloy, x=1, i.e., the chemical formula is Ni 16 Mn 11 In4Fe1, corresponding to the atomic percentage of Ni 50 Mn 33.5 In 12.5 Fe 4.5 Everything else is the same as in Specific Implementation Method 1.

[0048] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the austenitic phase of the room-temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloy has an L21 ordered structure and a space group of [missing information]. (No. 225), the lattice occupancy is as follows: Ni occupies the 8c (0.25, 0.25, 0.25) Wyckoff position, Mn occupies the 4a (0, 0, 0) Wyckoff position, In occupies the 4b (0.5, 0.5, 0.5) Wyckoff position, and Fe substitutes Mn to occupy the 4a position. Other aspects are the same as in specific embodiments one or two.

[0049] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that the austenitic phase cell of the room-temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloy has a face-centered cubic structure, with lattice constants ranging from a=11.89 to 11.92 Å and b=c= 5.94 to 5.96 Å. Everything else is the same as in Specific Implementation Method Three.

[0050] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One through Four in that the martensite phase of the room-temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloy has a body-centered tetragonal structure and a space group of [missing information]. I 4 / mmm(No. 139), the lattice occupancy is as follows: Ni occupies the 8c (0, 0.5, 0.25) Wyckoff position, Mn occupies the 4a (0, 0, 0.5) Wyckoff position, In occupies the 4b (0, 0, 0) Wyckoff position, and Fe substitutes for Mn occupying the 4a position. Other aspects are the same as in any of the specific embodiments one to four.

[0051] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the martensitic phase lattice constant range of the room-temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloy is: a = 15.72~15.74 Å, b = 3.93~3.94 Å, c = 6.71~6.72 Å. Everything else is the same as in Specific Implementation Method Five.

[0052] Specific Implementation Method Seven: This implementation method provides a composition screening method for room temperature low-hysteresis high-entropy change Ni-Mn-In-Fe shape memory alloys, implemented based on first-principles calculations, including the following steps: I. Based on density functional theory, using the VASP software package, austenitic and martensite phase models of Ni-Mn-In intrinsic alloys and Fe-doped alloys were established. 2. Perform structural optimization calculations on the established model to obtain the most stable lattice parameters and atomic positions of the austenitic and martensitic phases of each component; III. Calculate the formation energy, electronic density of states, and five key parameters (formation energy difference between the two phases) of the austenite and martensite phases for each component under different hydrostatic pressures (0 kbar, 10 kbar, 20 kbar, 30 kbar). ΔE Pressure sensitivity dT / dp Volume change rate ΔV / V Magnetic moment difference ΔM and intermediate eigenvalues λ 2 ; IV. Through ΔE The Boltzmann coefficient was obtained by fitting the linear relationship with the phase transformation temperature, and then the martensitic phase transformation temperature of each component at 0 kbar was calculated. T M ; V. According to different pressures T M Calculate the pressure sensitivity of each component alloy dT / dp ; VI. Through each component ΔE , dT / dp , ΔV / V , ΔM and λ 2 A comprehensive evaluation using radar charts of five indicators was conducted to select the Fe-doped composition with the best overall performance.

[0053] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the austenite phase model described in step one is an L21 ordered structure (space group). (No. 225), the martensitic phase model is a body-centered tetragonal structure (space group) I 4 / mmm (No. 139). Everything else is the same as in Specific Implementation Method Seven.

[0054] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Seven or Eight in that the structural optimization calculation in step two employs the conjugate gradient algorithm. The convergence criterion is that the Hellmann-Feynman force on each atom is less than 0.01 eV / Å, and the total energy converges to 10. -5 eV; The calculation process considered various magnetic configurations such as ferromagnetic and antiferromagnetic, and selected the stable configuration with the lowest energy for subsequent analysis. Other aspects are the same as in specific implementation methods seven or eight.

[0055] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Seven to Nine in that: the method for obtaining the Boltzmann coefficient in step four is as follows: the Ni coefficient calculated after structural optimization is... 16 Mn 12 In4, Ni 16 Mn 11 In5 and Ni 17 Mn 10 The energy difference Δ between the austenite and martensite phases in In5 E A-M The Boltzmann coefficients (0.2632 meV, 0.1828 meV, and 0.4344 meV, respectively) were linearly fitted to the martensitic phase transformation temperatures of similar compositions (387 K, 228 K, and 521 K, respectively) to obtain the Boltzmann coefficients. K B =1269K / meV. Other aspects are the same as in any of the specific embodiments seven to nine.

[0056] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Methods Seven through Ten in that: in step six, the radar chart comprehensive evaluation uses five normalized indicators. ΔE , dT / dp , ΔM , ΔV / V and λ 2 Use the axis as the priority filter ΔE correspond T M Near-room temperature alloys, in which λ 2 The closer the value is to 1, the smaller the thermal hysteresis. Other aspects are the same as in specific implementation methods seven to ten.

[0057] Specific Implementation Method Twelve: This implementation method differs from Specific Implementation Methods Seven to Eleven in that the parameters of the first-principles calculation method are set as follows: I. Calculations were performed using the VASP software package based on density functional theory. The exchange-correlation functional was selected in the Perdew-Burke-Ernzerhof form under the generalized gradient approximation, and the ion-electron interaction was described by the projected fused wave pseudopotential. II. The plane wave cutoff energy is set to 520 eV; 3. The Brillouin zone integral adopts the Monkhorst-Pack grid scheme, and the grid density of k-point is controlled at around 35~40, which is adjusted according to the supercell size to ensure convergence. IV. Spin polarization calculations are enabled throughout the process to accurately describe the magnetic behavior of the alloy; V. All structural optimization calculations were performed using 32-atom supercells for both austenite and martensite. VI. The parameter PSTRESS is used to simulate hydrostatic pressure calculations. The pressure value (kbar) is the value of PSTRESS. VII. The self-consistent iterative convergence accuracy is 10. -6 eV / atom, corresponding to K-point set to 3×6×6. Everything else is the same as in specific implementation methods seven to eleven.

[0058] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0059] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0060] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0061] Unless otherwise specified, the materials, reagents, instruments, and equipment used in this invention are all materials, reagents, instruments, and equipment routinely used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, without further explanation.

[0062] Example 1 This embodiment employs a first-principles calculation method based on density functional theory for Ni. 16 Fe x Mn 12-xPerform component screening on multiple candidate components in In4, where 0 < x ≤ 2. The specific steps are as follows: (1) Using the VASP software package, establish the austenite and martensite phase models of Ni-Mn-In intrinsic alloys and Fe-doped alloys. The austenite phase model is the L21 ordered structure (space group , No. 225); the martensite phase model is the body-centered tetragonal structure (space group I 4 / mmm , No. 139); Fe replaces part of Mn and occupies the 4a position; the model uses a 2×2×2 supercell, with a total of 32 atoms.

[0063] (2) Perform structural optimization calculations on the established models. Use the conjugate gradient algorithm, and the convergence criterion is that the Hellmann-Feynman force on each atom is less than 0.01 eV / Å, and the total energy converges to 10 -5 eV; the Brillouin zone integration uses the Monkhorst-Pack grid scheme, and the k-point grid density is between 35 and 40; consider various magnetic configurations such as ferromagnetic and antiferromagnetic during the calculation, and select the stable configuration with the lowest energy; obtain the most stable lattice parameters and atomic positions of the austenite and martensite phases of each component.

[0064] (3) Key parameter calculations: (3.1) Calculation of the formation energy difference between the two phases The formation energies of the austenite and martensite phases of the alloy are calculated by the following equations respectively: Where, is the total free energy of the system (directly obtained from the structural optimization calculation), is the number of atoms of element in the unit cell, is the total ground state energy of one atom of element . The formation energy difference between the two phases is defined as: Where is the formation energy of the austenite phase, is the formation energy of the martensite phase. When , the stability of the martensite phase is higher than that of the austenite phase, and martensitic transformation can occur.

[0065] (3.2) Calculation of the martensitic transformation temperature of Establish the linear relationship between and by fitting the Boltzmann coefficient . Compare the values of the intrinsic alloy and the doped alloy with the experimental of similar components in the literature.Linear fitting of the data: Obtain the Boltzmann coefficient of the system. K / meV. Based on this, the martensitic phase transformation temperature of each component at 0 kbar is... Calculated by the following formula: Based on this, further calculations were performed on the alloy components under hydrostatic pressures of 10 kbar, 20 kbar, and 30 kbar. .

[0066] (3.3) Calculation of pressure sensitivity dT / dp Phase transition temperatures calculated based on different pressures (0 kbar, 10 kbar, 20 kbar, 30 kbar). The pressure sensitivity of each component alloy is calculated using the following formula: Specifically, based on each pressure point The data is linearly fitted, and the slope is taken as... value. The larger the value, the greater the effect of unit pressure change. The more significant the change, the more conducive it is to achieving the giant pressure card effect under lower driving pressure.

[0067] (3.4) Calculation of volume change rate ΔV / V The volumes of the two phases were calculated based on the optimized lattice constants of the austenitic and martensitic phases, respectively. For the austenitic phase (cubic structure): For martensitic phase (tetragonal structure): The rate of change of volume is defined as: The greater the rate of volume change, the more significantly it can improve, according to the Clausius-Clapeyron relationship. Furthermore, the entropy change of lattice vibration can be amplified through abrupt changes in lattice symmetry. It is one of the core parameters for optimizing card pressing performance.

[0068] (3.5) Calculation of magnetic moment difference ΔM After structural optimization, the local magnetic moments of each atom are extracted from the OUTCAR file. For all The total magnetic moment of each atom and the two phases is obtained by summing the following formula: The magnetic moment difference is defined as the absolute value of the difference between the total magnetic moments of the austenitic and martensitic phases: in The total magnetic moment of the austenitic ferromagnetic state. It represents the total magnetic moment of the martensitic antiferromagnetic state. Directly reflects the degree of change in magnetic order before and after the phase transition — The smaller the value, the greater the magnetic entropy change. The smaller the value, the greater the vibrational entropy change. The larger its proportion in the total isothermal entropy change, the more beneficial it is to the compression effect.

[0069] (3.6) Calculation of intermediate eigenvalue λ2 Based on the theory of phase transformation geometric compatibility, the phase transformation strain tensor is constructed from the lattice parameters of the austenite and martensite phases. Calculate the intermediate eigenvalue λ2. The specific steps are as follows: (a) Calculation of phase transformation deformation gradient from the lattice parameters of the two phases This leads to the right Cauchy-Green deformation tensor. ; (b) Solve Characteristic equation Three principal eigenvalues ​​were obtained. After taking the root, we get ; (c) Take (Intermediate feature value) is used as a key evaluation indicator.

[0070] The closer λ2 is to 1, the better the geometric compatibility of the austenite-martensite interface. No additional elastic strain or dislocation coordination is needed during the phase transformation, resulting in a shorter phase transformation thermal hysteresis. The smaller.

[0071] (3.7) Electronic density of states (DOS) analysis To further explore the microscopic physical mechanism of phase stability, the total density of electronic states (TDOS) and partial density of electronic states (PDOS) of the austenitic ferromagnetic state and martensite antiferromagnetic state of each component were calculated. According to the rigid bandgap model theory, the lower the TDOS value at the Fermi level, the higher the stability of the phase. By comparing the difference in TDOS between the two phases of the same component at the Fermi level, the thermodynamic feasibility of the martensitic phase transition can be confirmed: if the TDOS of the martensite antiferromagnetic state at the Fermi level is lower than that of the austenitic ferromagnetic state, then the martensitic phase has higher stability, and the martensitic phase transition can occur.

[0072] (3.8) Comprehensive screening by (correspond ), , , (take the reciprocal form) Five key parameters, including λ1 and λ2, are used as evaluation indicators to construct a multi-parameter radar chart evaluation system. Specifically, the five indicators are normalized: Priority Screening Components close to room temperature; The bigger the better; The larger the better (i.e.) Smaller is better); The larger the value, the better; λ2: the closer to 1, the better.

[0073] The normalized index values ​​are plotted on the same radar chart, and the coverage area of ​​each candidate component polygon is compared. The larger the area, the better the overall pressing performance, thus selecting the Fe-doped component with the best overall performance.

[0074] (4) The Ni calculated after structural optimization 16 Mn 12 In4, Ni 16 Mn 11 In5 and Ni 17 Mn 10 The energy difference Δ between the austenite and martensite phases in In5 E A-M The Boltzmann coefficients (0.2632 meV, 0.1828 meV, and 0.4344 meV, respectively) were linearly fitted to the martensitic phase transformation temperatures of similar compositions (387 K, 228 K, and 521 K, respectively) to obtain the Boltzmann coefficients. K B =1269K / meV.

[0075] (5) Using the linear relationship between ΔE and the phase transformation temperature, and the Boltzmann coefficient obtained in step (4), calculate the martensitic phase transformation temperature of each component at 0 kbar. T M According to different pressures T M Calculate the pressure sensitivity d of each component alloy T / d p .

[0076] (6) Comprehensive evaluation and screening: using five normalized indicators ΔE, d T / d p Δ V / V Δ M and λ 2 Plot a radar chart for the Ni axis. 16Fe x Mn 12-x Comprehensively evaluate candidate components such as In4 (0 < x ≤ 2). Figure 2 It is a radar chart including typical components (x = 1, 2). The screening results show that when x = 1 ΔE corresponds to T M is closest to room temperature, and λ 2 = 0.9846 is closest to 1, and the comprehensive performance is the best. Therefore, determine Ni 16 Mn 11 In4Fe1 as the optimal doping component.

[0077] Example 2: This example provides a room-temperature low hysteresis and high entropy change Ni-Mn-In-Fe shape memory alloy with the chemical formula Ni 16 Mn 11 In4Fe1 (corresponding atomic percentages are Ni 50 Mn 33.5 In 12.5 Fe 4.5 ).

[0078] The preparation method of the alloy in this example is as follows: Step 1, batching: Calculate and weigh the elemental metal raw materials Ni, Mn, In, and Fe according to the atomic percentages of Ni 50 Mn 33.5 In<​​​​​​​​​​​​​​​​​​​​Step Six: Homogenization Treatment: Cut the ingot along its diameter, grind to remove the surface oxide layer, clean with acetone, and then encapsulate it in a quartz tube. [The process is repeated 10 times.] -3 It was annealed at 1173K for 12 hours under vacuum conditions, and then quenched in ice water at 273K.

[0083] Step 7, Processing: The annealed alloy ingot is processed into Φ3mm×1mm circular samples for DSC testing and block samples for XRD structural characterization using wire cutting.

[0084] Example 3: This embodiment provides a room-temperature, low-hysteresis, high-entropy-variable Ni-Mn-In-Fe shape memory alloy with the chemical formula Ni. 16 Mn 10 In4Fe2 (corresponding to Ni atomic percentage) 50 Mn 31.25 In 12.5 Fe 6.25 ).

[0085] The preparation method of the alloy in this embodiment is the same as that in Embodiment 1, the only difference being that it is prepared according to Ni 50 Mn 31.25 In 12.5 Fe 6.25 The ingredients are formulated based on atomic percentages.

[0086] Comparative Example 1: This comparative example provides a Cu-doped Ni-Mn-In shape memory alloy with the chemical formula Ni. 15 Mn 12 In4Cu1 (corresponding to Ni atomic percentage) 45.5 Mn 37.5 In 12.5 Cu 4.5 ).

[0087] The preparation method of this comparative alloy is the same as that of Example 1, the only difference being that it is prepared according to Ni... 45.5 Mn 37.5 In 12.5 Cu 4.5 The ingredients are proportioned according to atomic percentages, and Cu is used to replace some Ni sites.

[0088] Comparative Example 2: This comparative example provides a Cu-doped Ni-Mn-In shape memory alloy with the chemical formula Ni. 14 Mn 12 In4Cu2 (corresponding to Ni atomic percentage) 43.75 Mn 37.5 In 12.5 Cu 6.25 ).

[0089] The preparation method of this comparative alloy is the same as that of Example 1, the only difference being that it is prepared according to Ni... 43.75 Mn 37.5 In 12.5 Cu 6.25 The ingredients are proportioned according to atomic percentages, and Cu is used to replace some Ni sites.

[0090] Performance testing and characterization: For Example 2 (Ni) 16 Mn 11 In4Fe1), Example 3 (Ni) 16 Mn 10 In4Fe2), Comparative Example 1 (Ni) 15 Mn 12 In4Cu1) and Comparative Example 2 (Ni 14 Mn 12 The following performance tests and characterizations were performed on four alloys (In4Cu2).

[0091] Example 2 was characterized by XRD, combined with XRD patterns. Figure 4 Based on the diffraction characteristics and DSC thermal analysis results, it can be determined that the alloy of Example 2 exists in a state of coexistence of austenite and martensite phases at room temperature. The "branching at the top and fusion at the bottom" morphology of the main peak at 40-45° in the spectrum is a typical signal of the early stage of martensitic phase transformation. Since the room temperature is slightly higher than the martensitic phase transformation temperature of the alloy, the driving force of the phase transformation is not yet sufficient to completely transform the austenite. Therefore, most of the matrix still retains the cubic L21 austenite structure, and the main peak remains sharp. However, the temperature is lower than the phase transformation initiation point, causing a small amount of martensite to begin nucleation. The reduced lattice symmetry causes the diffraction peak to split, thus forming a branch at the top of the main peak. In addition, a series of weak diffraction peaks at 60-63° and 77-79°, as well as in between, further confirm the existence of the martensitic phase. This indicates that the composition has indeed achieved a precise reduction in the phase transformation temperature through compositional control, providing an microstructure basis for the room temperature application of the piezoresistive effect.

[0092] The four alloys were verified by first-principles calculations according to the composition screening method described in Example 1. Figure The phase transformation temperatures and pressure sensitivity of four alloys (Example 2, Example 3, Comparative Example 1, and Comparative Example 2) under different pressures are shown. ​ Four alloys are formed by the energy difference between two phases. ​ Pressure sensitivity ​ Volume change rate ​ Magnetic moment difference ​ and intermediate eigenvalues ​ 2 A radar chart plotted using five normalized indices. Calculation results show that, as ​As shown, the d values ​​of four alloys in Examples 2, 3, 1, and 2 are compared. T / d p The values ​​are 0.43 K / kbar, 0.513 K / kbar, 0.397 K / kbar, and 0.144 K / kbar, respectively. It is evident that the dT / dp of Ni-Mn-In alloys with different compositions varies greatly, with the alloys in Examples 2 and 3 showing significantly different dT / dp values. T / d p Compared with the intrinsically screened Ni-Mn-In alloy, the d value is improved, while the d value remains basically consistent with that of the comparative example. T / d p . ​ The radar chart uses five normalized indices as axes, namely Δ E d T / d p Δ M -1 Δ V / V as well as ​ 2. Ni with different compositions 16 Fe x Mn 12-x In4 (x = 1, 2) and Ni 16-x Cu x Mn 12 A direct comparison was made of In4 (x = 1, 2) alloys. The differences in overall performance are clearly visible by comparing the polygon coverage area of ​​each alloy. Among them, the alloys of Example 2 and Comparative Example 1 have the largest polygon areas in the radar image, with the largest polygon coverage area in d... T / d p Δ M -1 Δ ​ and ​ 2. All four key indicators reached high values, and their Δ E correspond T M It is located precisely near room temperature. Considering the balance and optimization of the above five indicators, Example 2 and Comparative Example 1 were selected as the optimal candidate compositions.

[0093] The phase transition temperature, thermal hysteresis, and phase transition entropy change of the alloys in Example 2 and Comparative Example 1 were tested using differential scanning calorimetry (DSC), and the results are shown in Table 1. Example 2 exhibited a large entropy change, small hysteresis, and a phase transition temperature within the room temperature range. ​ For Ni 50 Mn 33.5 In 12.5 Fe 4.5 (Example 2) and Ni 45.5 Mn 37.5 In 12.5Cu 4.5 (Comparative Example 1) DSC test curve of the alloy.

[0094] The test results are as follows: ​ The endothermic / exothermic peak characteristics of the first-order martensitic phase transformation are clearly presented. The results in the figure can be summarized in Table 1: Table 1 Thermodynamic characteristic parameters

[0095] Compared to intrinsic Ni 50 Mn 37.5 In 12.5 The experimental results confirmed the properties of alloy 1 in Comparative Example 1. T M The temperature of 314.8 K is higher than room temperature, which is unfavorable for solid-state refrigeration. Its thermal hysteresis is 46.3 °C, enthalpy change is 13.75 kJ / kg, and entropy change is 27.69 J / kg / K. In contrast, the alloy of Example 2 has a temperature below room temperature. T M =278.4K, a relatively small thermal hysteresis of 9.74℃, and a relatively large phase transition entropy change of 28.4J / kg / K, Δ S BCE Numerically, this is expressed as the percentage of phase transition and Δ. S tr The product of d T / d p It is positively correlated with the percentage of phase transition, therefore in d T / d p and Δ S tr In the case of a larger value, the corresponding Δ of the alloy S BCE The value will also be relatively large. This is highly consistent with the first-principles screening criteria, laying a solid experimental foundation for doping tests of Ni performance and solid-state refrigeration applications. Therefore, it can be seen that for Ni... 16 Mn 12 In intrinsic In4 alloys, Fe doping can effectively improve d T / d p reduce T M .

[0096] ​ Ni prepared in Example 1 50 Mn 33.5 In 12.5 Fe 4.5 The XRD pattern shows a distinct strong austenite main peak and a weak martensite peak. The diffraction peaks at 40-45° are very sharp, indicating that the atoms are highly ordered, the sample has high crystallinity, and the L21 ordering is good.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a room-temperature low-hysteresis, high-entropy variable nickel-manganese-indium based shape memory alloy, characterized in that, Includes the following steps: Step 1, Batching: Calculate and weigh each elemental metal raw material Ni, Mn, In, and Fe according to the atomic percentage in the chemical formula of the alloy. The purity of each elemental metal raw material is 99.9 wt.% or higher. To compensate for the loss of Mn due to easy volatilization during smelting, weigh an additional 3 wt.% of Mn. Step 2, Loading: Place the prepared raw materials in the water-cooled copper crucible of the non-consumable high-vacuum electric arc melting furnace in sequence, with In placed on the top layer; Step 3, Vacuuming and Gas Purging: Use a mechanical pump to evacuate the furnace chamber to 5×10⁻⁶ m³ / h. -3 Below Pa, after filling with high-purity argon gas, vacuum is evacuated again, and this process is repeated three times; then switch to a molecular pump to evacuate to 1×10⁻⁶ Pa. -3 Below Pa; Step 4, Melting: After filling with high-purity argon gas to 0.08MPa, melting begins. Electromagnetic stirring is applied throughout the process, and the ingot is repeatedly turned over for melting. Before each melting, the Ti ingot is melted to absorb residual oxygen. Step 5, Cooling and Removal: After the final melting is completed, slowly close the arc and remove the ingot after it has completely cooled. Step 6, Homogenization treatment: Cut the ingot along the diameter direction, grind to remove the surface oxide layer, clean with acetone, encapsulate in a quartz tube, anneal at 1173K under vacuum for 12 hours, and then quench in ice water. Step 7: Machining: Use wire cutting to machine the annealed alloy ingot into a sample of the required size.

2. The method for preparing a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 1, characterized in that, Step one also includes a component screening step based on first-principles calculations, specifically including: S1. Model Establishment: Based on density functional theory, austenitic and martensitic phase models of Ni-Mn-In intrinsic alloys and alloys with different Fe doping amounts are established; the austenitic phase is an L21 ordered structure with Fe replacing some Mn sites; the martensitic phase is a body-centered tetragonal structure. S2. Perform structural optimization calculations on the model established in S1 to obtain the most stable lattice parameters and atomic positions of the austenitic and martensite phases of each component. S3. Calculate the following five key parameters for the austenitic and martensitic phases of each component under different hydrostatic pressures: the energy difference between the two phases Δ. E Pressure sensitivity d T / d p , volume change rate Δ V / V Magnetic moment difference Δ M and intermediate eigenvalues λ 2; S4, through the formation of an energy difference Δ between the two phases E The Boltzmann coefficient was obtained by fitting a linear relationship with the phase transition temperature. K B The energy difference Δ between the two phases E and K B · T M Proportional to each other, thus the martensitic phase transformation temperature of each component at 0 kbar can be calculated. T M ; S5. According to different pressure conditions T M Calculate the pressure sensitivity d of each component alloy T / d p ; S6. Using the five key parameters as evaluation indicators, a comprehensive evaluation is conducted to construct a multi-parameter radar chart evaluation system; after normalization and radar chart plotting, the polygonal coverage area of ​​each alloy is compared to select those with phase transition temperatures close to room temperature. λ 2. The Fe-doped composition that is close to 1 and has the best overall pressing performance; The first-principles calculations employ a first-principles calculation method based on density functional theory, taking spin polarization into account during the calculation process.

3. The method for preparing a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 2, characterized in that, In S6, the comprehensive evaluation is as follows, using five normalized indicators ΔE, d T / d p Δ V / V Δ M and λ 2 Five key parameters are used as axes for comprehensive evaluation of multiple indicators, and priority is given to screening those corresponding to ΔE. T M The alloy composition is close to room temperature, in which λ 2 The closer to 1, the smaller the thermal hysteresis.

4. The method for preparing a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 1, characterized in that, In step four, the melting process is repeated five times.

5. The method for preparing a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 1, characterized in that, In step six, the temperature of the quenching water is 273K.

6. The method for preparing a room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 2, characterized in that, The alloy prepared by the above method simultaneously meets the following performance indicators: martensitic transformation temperature. T M ≤280K, phase change thermal hysteresis After ΔT hys ≤10K, phase transition entropy change ΔS tr ≥28J / kg / K.

7. A room-temperature low-hysteresis, high-entropy variable nickel-manganese-indium based shape memory alloy, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 7, characterized in that, The general chemical formula of the alloy is Ni 16 Fe x Mn 12-x In4, where 0 <x≤2。 9. The room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 8, characterized in that, In the general chemical formula, x=1, and the chemical formula of the alloy is Ni. 16 Fe1Mn 11 In4, corresponding to the atomic percentage of Ni 50 Mn 33.5 In 12.5 Fe 4.5 .

10. The room-temperature low-hysteresis high-entropy variable nickel-manganese-indium based shape memory alloy according to claim 8, characterized in that, The austenitic phase of the alloy has an L21 ordered structure and a space group of [space group number missing]. Fe-substituted Mn occupies the 4a position; the martensite phase has a body-centered tetragonal structure with space group I4 / mmm, and Fe-substituted Mn occupies the 4a position.

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