4d-printed nickel-titanium-based shape memory alloy and preparation method therefor

Abstract

A 4D-printed nickel-titanium-based shape memory alloy and a preparation method therefor. The preparation method comprises the three steps of powder preparation, double-model construction and path-energy-coupled 4D printing forming. The core point of the preparation method is that a 4D-printed nickel-titanium-based shape memory alloy is prepared by first melting a pre-formed alloy powder and then subjecting a pre-formed layer to an in-situ homogenization heat treatment by means of two path-energy-coupled scanning strategies so as to achieve uniform distribution of dispersed nanometer precipitated phases in isometric and columnar crystal matrixes. The preparation method is short in terms of process period, low in terms of energy consumption and simple in terms of process, and has good stability; and the prepared nickel-titanium-based shape memory alloy and components thereof have good mechanical properties, functional characteristics, functional stability and fatigue life, and have good promotion and application prospects.

Description

A 4D printing nickel-titanium-based shape memory alloy and its preparation method Technical Field

[0001] The present invention belongs to the technical field of shape memory alloys and additive manufacturing, and in particular relates to a 4D printing nickel-titanium-based shape memory alloy and a preparation method thereof. Background Art

[0002] Nickel-titanium and nickel-titanium-based shape memory alloys have unique physical properties such as excellent and stable superelasticity, shape memory effect, good damping characteristics, and biocompatibility, making them one of the most widely used functional materials. Nickel-titanium-based shape memory alloys are prone to limited dissolution and decomposition during solidification and cooling, and various precipitate phases are precipitated. The size, distribution, and interface type of these precipitates have a significant impact on the mechanical properties of nickel-titanium-based shape memory alloys, as well as functional properties such as superelasticity and shape memory effect. In order to prepare nickel-titanium-based shape memory alloys and components with uniform distribution of dispersed precipitate phases and excellent comprehensive performance, smelting, rolling, and drawing processes are usually used to prepare and shape them, and heat treatment processes are used to regulate the microstructure and precipitate phases. The preparation process of its components is long, complex, and time-consuming.

[0003] 4D printing is a new 3D printing additive manufacturing technology based on shape memory alloys. The advantage of this technology is that it can overcome technical difficulties such as the difficulty of cold working, machining, and forming complex parts for nickel-titanium-based shape memory alloys. The selective laser melting 4D printing process involves the melting and solidification of a tiny molten pool. The matrix typically forms a microstructure of alternating equiaxed and columnar crystals, with the uniformly distributed precipitates primarily located in the columnar regions. The equiaxed regions exhibit severe microsegregation, with hard and brittle intermetallic compound precipitates continuously and unevenly distributed at the grain boundaries. This leads to non-coordinated deformation between the nickel-titanium alloy matrix and the precipitates during load loading, resulting in significant stress concentration. This can hinder the reversible martensitic transformation, induce intergranular fracture, and deteriorate the mechanical properties, superelasticity, and shape memory effect of the nickel-titanium-based shape memory alloy and its components. In order to obtain a uniformly distributed precipitate phase, nickel-titanium-based shape memory alloys prepared by 4D printing process usually also need to adopt subsequent heat treatment to achieve the effect of strengthening and toughening the matrix (Acta Materialia 194 (2020) 178-189, Acta Materialia 215 (2021) 117017, Journal of Alloys and Compounds 918 (2022) 165620). However, the subsequent heat treatment process prolongs the production cycle, increases energy consumption and pollution. For large components, overall heat treatment is difficult to ensure the temperature uniformity of each part of the component material, increases the difficulty of implementing heat treatment and process uncertainty, and is not conducive to large-scale industrial application. Omitting the heat treatment process, directly 4D printing to form nickel-titanium-based shape memory alloys and realizing the precipitation phase regulation of nickel-titanium-based shape memory alloys are key technical problems that need to be solved in the fields of materials science and engineering and additive manufacturing.

[0004] To date, there has been no research report on the direct 4D printing preparation of nickel-titanium-based shape memory alloys with uniformly distributed dispersed nanoprecipitates.

[0005] Summary of the Invention

[0006] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a 4D printing nickel-titanium-based shape memory alloy.

[0007] The second object of the present invention is to provide a method for preparing the above-mentioned 4D printed nickel-titanium-based shape memory alloy.

[0008] The primary purpose of the present invention is achieved through the following technical solutions:

[0009] A 4D-printed nickel-titanium-based shape memory alloy, comprising a matrix of austenite, martensite, or a mixture of martensite and austenite, and a microstructure characterized by alternating matrix equiaxed crystals and matrix columnar crystals; a dispersed nanoprecipitate phase comprising a titanium-rich or nickel-rich intermetallic compound uniformly distributed in the matrix equiaxed crystals and matrix columnar crystals.

[0010] Preferably, the volume fraction of the austenite, martensite or mixed martensite and austenite matrix is ​​85-95%; the volume fraction of the titanium-rich or nickel-rich intermetallic compound dispersed nano-precipitate phase is 5-15%.

[0011] Preferably, the size of the matrix equiaxed crystals is 0.5 to 2 μm, and the volume fraction is 30 to 45%; the width of the matrix columnar crystals is 2 to 8 μm, and the volume fraction is 55 to 70%.

[0012] Preferably, the size of the dispersed nano-precipitated phase is 10 to 30 nm, and the interface lattice mismatch between the phase and the matrix is ​​1 to 15%.

[0013] The second object of the present invention is achieved through the following technical solutions:

[0014] A method for preparing a 4D-printed nickel-titanium-based shape memory alloy comprises the following steps:

[0015] Step 1: Flour making

[0016] According to the pre-designed nickel-titanium-based shape memory alloy composition, the alloy rods are obtained by vacuum melting, and spherical alloy powders are obtained by electrode induction atomization method, which are placed in the powder bin for 4D printing.

[0017] Step 2: Dual model construction

[0018] The 3D model of the part is copied into two groups, and the same slicing process is performed. The two groups of processed models are then imported into the 4D printing system.

[0019] Step 3: Path Energy Coupling 4D Printing

[0020] The two groups of models processed in step 2 were respectively assigned two scanning strategies of path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was in situ homogenized heat treated to achieve uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, and a dispersed nanoprecipitate phase 4D printed nickel-titanium-based shape memory alloy was prepared.

[0021] Preferably, the nickel-titanium-based shape memory alloy in step 1 is one of NiTi, NiTiCu, NiTiNb, NiTiCr, NiTiHf, NiTiZr, NiTiPd and NiTiPt.

[0022] Preferably, the preparation parameters of the electrode induction atomization method in step 1 are as follows: the electrode induction heating temperature is 1400-1800°C, the atomization pressure is 2.5-4.5MPa, the gas supply pressure is 0.05-0.2MPa, the atomization gas temperature is 30-45°C, the melting power is 15-25kW, and the protective atmosphere is any one of argon, nitrogen, and helium.

[0023] Preferably, the slice thickness of the slice processing in step 2 is 80-150 μm, and the spot compensation is 20-50 μm.

[0024] Preferably, the two sets of models in step 2 should have exactly the same position coordinates and reference planes after being imported into the 4D printing system so that they overlap with each other to achieve subsequent 4D printing.

[0025] Preferably, the two scanning paths of melting the preformed alloy powder and in-situ homogenizing the heat treated preformed layer in step 3 are coupled into a specific angle ranging from 0 to 20°; the two scanning strategies of the path energy coupling need to meet the energy density E 熔化 : Energy density E 热处理 It is 2 to 3:1.

[0026] Preferably, the two scanning strategies for path energy coupling in step three are that the two scanning path energies of melting the preformed alloy powder and in-situ homogenizing the preformed layer are coupled into a specific angle ranging from 0 to 10°.

[0027] Preferably, the two scanning strategies for path energy coupling in step three are that both scanning paths for melting the preformed alloy powder and for in-situ homogenizing the preformed layer are partitioned scanning, with a partition width of 5 to 8 mm.

[0028] Preferably, the two scanning strategies for path energy coupling in step 3 are: the laser scanning parameters for melting the preformed alloy powder and in-situ homogenizing the preformed layer are: energy density E 熔化 =130~300J / mm 3 , laser power P = 60 ~ 100W, scanning speed V = 80 ~ 160mm / s; energy density E 热处理 =60~100J / mm 3, laser power P = 30-60W, scanning rate V = 80-160mm / s. The principle of the preparation method of the present invention is as follows: Compared with the uneven temperature and structural segregation defects of the micro-molten pool caused by a single scanning strategy, this patent adopts two scanning strategies with a scanning trajectory forming a specific angle and energy density meeting a specific proportional relationship to couple printing. This achieves in-situ synchronous heat treatment of the micro-molten pool, eliminates micro-region structural segregation defects, and achieves a uniform distribution of dispersed nanoprecipitates. Direct 4D printing can produce nickel-titanium-based shape memory alloys and near-net-shape components with excellent functional stability and fatigue life, eliminating post-processing steps, shortening the process cycle, and reducing energy consumption.

[0029] The advantages and beneficial effects of the preparation method of the present invention are:

[0030] (1) The 4D printed nickel-titanium-based shape memory alloy of the present invention avoids the uneven distribution of the dispersed nanoprecipitate phase at the grain boundary. The dispersed nanoprecipitate phase is a titanium-rich or nickel-rich intermetallic compound, which is uniformly distributed in the matrix equiaxed crystals and the matrix columnar crystals, and has a coherent / semi-coherent relationship with the matrix.

[0031] (2) The 4D printed nickel-titanium-based shape memory alloy of the present invention has a uniformly distributed dispersed nanoprecipitate phase that can effectively pin dislocation motion, reduce uncoordinated deformation, and improve the mechanical properties such as strength and plasticity of the nickel-titanium-based shape memory alloy, as well as functional properties such as superelasticity and shape memory effect, and has excellent functional stability and fatigue life.

[0032] (3) The preparation method of 4D-printed nickel-titanium-based shape memory alloy of the present invention adopts two scanning strategies of path energy coupling, and directly 4D-prints nickel-titanium-based shape memory alloys with excellent functional stability and fatigue life and their near-net-shape components, eliminating the drawing, heat treatment and other processes used in traditional technologies, as well as the heat treatment process after 4D printing, with a short process cycle and low energy consumption.

[0033] (4) The 4D printing nickel-titanium-based shape memory alloy preparation process involved in the present invention is simple and has good stability, is suitable for batch production and standardized production, and has good promotion and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 shows the Ni obtained in Example 1 49.5 Ti 50.5 (at%) SEM images of alloy powders;

[0035] FIG2 is an SEM image of alternating columnar crystals and equiaxed crystals in the 4D-printed nickel-titanium-based shape memory alloy matrix obtained in Example 1;

[0036] FIG3(a) and FIG3(b) are respectively the distribution of the precipitated phase in the matrix columnar crystal region of the 4D printed nickel-titanium-based shape memory alloy obtained in Example 1 and its enlarged view;

[0037] FIG4(a) and FIG4(b) are respectively the distribution of the precipitated phase in the equiaxed crystal region of the matrix in the 4D printed nickel-titanium-based shape memory alloy obtained in Example 1 and its enlarged view;

[0038] FIG5 is a tensile stress-strain curve of the 4D-printed nickel-titanium-based shape memory alloy obtained in Example 1;

[0039] FIG6 is a tensile fatigue test curve of the 4D printed nickel-titanium-based shape memory alloy obtained in Example 1 at a strain of 3%;

[0040] FIG7 shows the change in recoverable strain of the 4D printed nickel-titanium-based shape memory alloy obtained in Example 1 during a tensile fatigue test at a strain of 5%. DETAILED DESCRIPTION

[0041] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0042] Example 1

[0043] Step 1: Flour making

[0044] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 49.5 Ti 50.5 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization (as shown in Figure 1). The electrode induction heating temperature was 1400°C, the atomization pressure was 2.5 MPa, the gas supply pressure was 0.2 MPa, the atomization gas temperature was 30°C, the melting power was 15 kW, the protective atmosphere was argon, and the powders were placed in the powder bin for 4D printing;

[0045] Step 2: Dual model construction

[0046] The 3D model of the part was duplicated into two groups and sliced ​​identically using Materialise Magics software, with a slice thickness of 80 μm and a spot compensation of 20 μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap to achieve subsequent path energy coupling 4D printing.

[0047] Step 3: Path Energy Coupling 4D Printing

[0048] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 0°, and the scanning paths are all partitioned scanning with a partition width of 5mm; the energy density E 熔化 =222J / mm 3 , laser power P = 80W, scanning speed V = 120mm / s; energy density E 热处 理 =95J / mm 3 , laser power P = 40W, scanning rate V = 140mm / s.

[0049] The 4D printed Ni 49.5 Ti 50.5 The shape memory alloy has an austenite matrix with a volume fraction of approximately 90%. The matrix equiaxed grains are approximately 500 nm in size and 30% in volume, while the matrix columnar grains are 6 μm wide and 70% in volume (see Figure 2). Dispersed Ti2Ni precipitates are uniformly distributed within the austenite matrix equiaxed grains and columnar grains (see Figures 3 and 4). They are approximately 20 nm in size and 10% in volume, with a 10% interfacial lattice mismatch between the precipitates and the matrix, exhibiting a semi-coherent orientation. The ultimate tensile strength and fracture strain are 750 MPa and 8%, respectively (see Figure 5). In a tensile fatigue test at a strain of 3%, the fatigue life was 1152 cycles, with a stable superelastic strain of 2.45% (see Figure 6). In a tensile fatigue test at a strain of 5%, the fatigue life was 583 cycles, with a stable superelastic strain of 2.2% (see Figure 7).

[0050] Example 2

[0051] Step 1: Flour making

[0052] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 51 Ti 49 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1400 ° C, the atomization pressure was 2.5 MPa, the gas supply pressure was 0.1 MPa, the atomization gas temperature was 30 ° C, the melting power was 20 kW, the protective atmosphere was helium, and it was placed in the powder bin for 4D printing;

[0053] Step 2: Dual model construction

[0054] The 3D model of the part was copied into two groups and sliced ​​identically using Autodesk Netfabb software, with a slice thickness of 100 μm and a spot compensation of 25 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, and were overlapped to achieve subsequent path energy coupling 4D printing.

[0055] Step 3: Path Energy Coupling 4D Printing

[0056] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 10°, and the scanning paths are all partitioned scanning with a partition width of 8mm; the energy density E 熔化 =208J / mm 3 , laser power P = 60W, scanning speed V = 80mm / s; energy density E 热处理 =88J / mm 3 , laser power P = 40W, scanning rate V = 150mm / s.

[0057] The 4D printed Ni 51 Ti 49 The shape memory alloy has a martensite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 1 μm and a volume fraction of 40%, and columnar grains with a width of approximately 2 μm and a volume fraction of 60%. Dispersed Ni4Ti3 precipitates are uniformly distributed within the martensite matrix, both equiaxed and columnar, with a size of approximately 10 nm and a volume fraction of approximately 5%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 3%, demonstrating a coherent orientation relationship. In a temperature-driven strain test under a constant load (200 MPa), the shape memory response reached stability after six cycles, with a fully recoverable strain of 4.4% and a fatigue life of 497 cycles.

[0058] Example 3

[0059] Step 1: Flour making

[0060] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 45 Ti 50Cu5 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization. The electrode induction heating temperature was 1500°C, the atomization pressure was 4.5MPa, the gas supply pressure was 0.05MPa, the atomization gas temperature was 45°C, the melting power was 20kW, the protective atmosphere was argon, and the powders were placed in the powder bin for 4D printing;

[0061] Step 2: Dual model construction

[0062] The 3D model of the part was duplicated into two groups and sliced ​​identically using SLM Solutions software, with a slice thickness of 150μm and a spot compensation of 40μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0063] Step 3: Path Energy Coupling 4D Printing

[0064] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a dispersed nanoprecipitate phase 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 0°, the scanning paths are all partitioned scanning, and the partition width is 5mm; the energy density E 熔化 =222J / mm 3 , laser power P = 100W, scanning speed V = 160mm / s; energy density E 热处理 =88J / mm 3 , laser power P = 60W, scanning rate V = 160mm / s.

[0065] The 4D printed Ni 45 Ti 50 The Cu5 shape memory alloy has a matrix composed of a mixed martensite and austenite, with a volume fraction of approximately 85%. The matrix has equiaxed grains with a grain size of approximately 2 μm and a volume fraction of 35%, and columnar grains with a width of approximately 8 μm and a volume fraction of 65%. Dispersed Ti2(Ni,Cu) precipitates are uniformly distributed within the matrix of mixed martensite and austenite, with a size of approximately 20 nm and a volume fraction of approximately 15%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 5%, exhibiting a coherent orientation relationship. In compression fatigue testing at a stress of 300 MPa, the alloy achieved a fatigue life exceeding 10,000 cycles, with a stable superelastic strain of 1.5%.

[0066] Example 4

[0067] Step 1: Flour making

[0068] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 43.5 Ti 49 Cu 7.5 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1500 ° C, the atomization pressure was 4.5 MPa, the gas supply pressure was 0.05 MPa, the atomization gas temperature was 45 ° C, the melting power was 20 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0069] Step 2: Dual model construction

[0070] The 3D model of the part was duplicated into two groups and sliced ​​identically using the SLM Build Processor software, with a slice thickness of 120 μm and a spot compensation of 50 μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0071] Step 3: Path Energy Coupling 4D Printing

[0072] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed powder was first melted, and then the preformed layer was heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths for melting the preformed alloy powder and the in-situ homogenization heat-treating the preformed layer are coupled at a specific angle of 20°, and the scanning paths are all partitioned scanning with a partition width of 6mm; the energy density E 熔化 =185J / mm 3 , laser power P = 100W, scanning speed V = 150mm / s; energy density E 热处理 =88J / mm 3 , laser power P = 60W, scanning rate V = 120mm / s.

[0073] The 4D printed Ni 43.5 Ti 49 Cu 7.5The shape memory alloy has a matrix composed of a mixture of martensite and austenite, with a volume fraction of approximately 90%. The matrix has equiaxed grains of approximately 2 μm in size and a volume fraction of 45%, and columnar grains of approximately 8 μm in width and a volume fraction of 55%. Dispersed Ti(Ni,Cu)2 precipitates are uniformly distributed within the matrix of equiaxed and columnar martensite, with a size of approximately 15 nm and a volume fraction of approximately 10%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 5%, exhibiting a coherent orientation. In a compression fatigue test at a stress of 400 MPa, the alloy achieved a fatigue life exceeding 10,000 cycles, with a stable superelastic strain of 1.7%.

[0074] Example 5

[0075] Step 1: Flour making

[0076] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 47 Ti 44 Nb9 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization. The electrode induction heating temperature was 1700 ° C, the atomization pressure was 3.5 MPa, the gas supply pressure was 0.05 MPa, the atomization gas temperature was 40 ° C, the melting power was 20 kW, the protective atmosphere was argon, and the powders were placed in the powder bin for 4D printing.

[0077] Step 2: Dual model construction

[0078] The 3D model of the part was duplicated into two groups and sliced ​​identically using Renishaw QuantAM software, with a slice thickness of 80 μm and a spot compensation of 20 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0079] Step 3: Path Energy Coupling 4D Printing

[0080] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 5°, and the scanning paths are all partitioned scanning with a partition width of 8mm; the energy density E 熔化 =120J / mm 3 , laser power P = 70W, scanning speed V = 150mm / s; energy density E 热处理 =60J / mm 3 , laser power P = 30W, scanning rate V = 150mm / s.

[0081] The 4D printed Ni 47 Ti 44 The Nb9 shape memory alloy has a martensite matrix with a volume fraction of approximately 90%. The matrix has equiaxed grains with a grain size of approximately 1.5 μm and a volume fraction of 30%. The matrix has columnar grains with a width of approximately 8 μm and a volume fraction of 70%. Dispersed (Ti,Nb)2Ni precipitates are uniformly distributed within the martensite matrix, both equiaxed grains and columnar grains. They are approximately 30 nm in size and have a volume fraction of approximately 10%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 15%, exhibiting a semi-coherent orientation relationship. In a temperature-driven strain test at a constant strain (10%), the shape memory response reached stability after 10 cycles, with a fully recoverable strain of 2% and a fatigue life of 642 cycles.

[0082] Example 6

[0083] Step 1: Flour making

[0084] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 50.54 Ti 49.2 Cr 0.26 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1650 ° C, the atomization pressure was 3 MPa, the gas supply pressure was 0.05 MPa, the atomization gas temperature was 40 ° C, the melting power was 20 kW, the protective atmosphere was nitrogen, and it was placed in the powder bin for 4D printing;

[0085] Step 2: Dual model construction

[0086] The 3D model of the part was duplicated into two groups and sliced ​​identically using Renishaw QuantAM software, with a slice thickness of 80 μm and a spot compensation of 25 μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0087] Step 3: Path Energy Coupling 4D Printing

[0088] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths for melting the preformed alloy powder and the in-situ homogenized heat-treated preformed layer are coupled at a specific angle of 10°, and the scanning paths are all partitioned scanning with a partition width of 5mm; the energy density E 熔化 =277J / mm 3 , laser power P = 100W, scanning speed V = 100mm / s; energy density E 热处理 =100J / mm 3 , laser power P = 50W, scanning rate V = 100mm / s.

[0089] The 4D printed Ni 50.54 Ti 49.2 Cr 0.26 The shape memory alloy has an austenite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 1.5 μm and a volume fraction of 40%. The matrix has columnar grains with a width of approximately 7 μm and a volume fraction of 60%. Dispersed (Ti,Co)2Ni precipitates are uniformly distributed within the austenite matrix, both equiaxed grains and columnar grains. They are approximately 30 nm in size and have a volume fraction of approximately 5%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 12%, exhibiting a semi-coherent orientation relationship. In a tensile fatigue test at a strain of 5%, the alloy achieved a fatigue life of 722 cycles, with a stable superelastic strain of 3.3%.

[0090] Example 7

[0091] Step 1: Flour making

[0092] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 50.4 Ti 29.6 Hf 20 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1750 ° C, the atomization pressure was 4.5 MPa, the gas supply pressure was 0.1 MPa, the atomization gas temperature was 45 ° C, the melting power was 25 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0093] Step 2: Dual model construction

[0094] The 3D model of the part was duplicated into two groups and sliced ​​identically using Materialise Magics software, with a slice thickness of 120 μm and a spot compensation of 20 μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap to achieve subsequent path energy coupling 4D printing.

[0095] Step 3: Path Energy Coupling 4D Printing

[0096] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 10°, and the scanning paths are all partitioned scanning with a partition width of 5mm; the energy density E 熔化 =208J / mm 3 , laser power P = 70W, scanning speed V = 80mm / s; energy density E 热处理 =100J / mm 3 , laser power P = 30W, scanning rate V = 80mm / s.

[0097] The 4D printed Ni 50.4 Ti 29.6 Hf 20 The shape memory alloy has a martensite matrix with a volume fraction of approximately 90%. The matrix has equiaxed grains with a grain size of approximately 2 μm and a volume fraction of 40%. The matrix has columnar grains with a width of approximately 8 μm and a volume fraction of 60%. Dispersed (Ti,Hf)2Ni precipitates are uniformly distributed within the martensite matrix, both equiaxed grains and columnar grains. They are approximately 20 nm in size and have a volume fraction of approximately 10%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 10%, resulting in a semi-coherent orientation relationship. In a two-way shape memory fatigue test at a strain of 2%, the recoverable strain was 0.8%, and the fatigue life was 884 cycles.

[0098] Example 8

[0099] Step 1: Flour making

[0100] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 50.8 Ti 29.2 Hf 20(at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1750 ° C, the atomization pressure was 4.5 MPa, the gas supply pressure was 0.1 MPa, the atomization gas temperature was 45 ° C, the melting power was 25 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0101] Step 2: Dual model construction

[0102] The 3D model of the part was copied into two groups and sliced ​​identically using Autodesk Netfabb software, with a slice thickness of 130 μm and a spot compensation of 30 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, and were overlapped to achieve subsequent path energy coupling 4D printing.

[0103] Step 3: Path Energy Coupling 4D Printing

[0104] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 20°, and the scanning paths are all partitioned scanning with a partition width of 5mm; the energy density E 熔化 =277J / mm 3 , laser power P = 100W, scanning speed V = 100mm / s; energy density E 热 处理 =100J / mm 3 , laser power P = 50W, scanning rate V = 100mm / s.

[0105] The 4D printed Ni 50.8 Ti 29.2 Hf 20 The shape memory alloy has a martensite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 0.5 μm and a volume fraction of 30%, and columnar grains with a width of 6 μm and a volume fraction of 70%. Dispersed H phases are uniformly distributed within the martensite matrix, with grain sizes of approximately 10 nm and a volume fraction of approximately 5%. The interface lattice mismatch between the H phase and the matrix is ​​approximately 1%, exhibiting a coherent orientation relationship. In a two-way shape memory fatigue test at a strain of 3%, the recoverable strain was 1.4%, and the fatigue life was 814 cycles.

[0106] Example 9

[0107] Step 1: Flour making

[0108] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 49.5 Ti 35.5 Zr 15 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1650 ° C, the atomization pressure was 3.5 MPa, the gas supply pressure was 0.2 MPa, the atomization gas temperature was 45 ° C, the melting power was 25 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0109] Step 2: Dual model construction

[0110] The 3D model of the part was duplicated into two groups and sliced ​​identically using SLM Solutions software, with a slice thickness of 110 μm and a spot compensation of 25 μm. The two processed models were then imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0111] Step 3: Path Energy Coupling 4D Printing

[0112] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing the preformed layer are coupled at a specific angle of 15°, and the scanning paths are all partitioned scanning with a partition width of 7mm; the energy density E 熔化 =130J / mm 3 , laser power P = 70W, scanning speed V = 150mm / s; energy density E 热处 理 =60J / mm 3 , laser power P = 30W, scanning rate V = 120mm / s.

[0113] The 4D printed Ni 49.5 Ti 35.5 Zr 15The shape memory alloy has a martensite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 1 μm and a volume fraction of 30%. The matrix has columnar grains with a width of approximately 5 μm and a volume fraction of 70%. Dispersed (Ti,Zr)2Ni precipitates are uniformly distributed within the martensite matrix, both equiaxed grains and columnar grains. They are approximately 15 nm in size and have a volume fraction of approximately 5%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 5%, demonstrating a coherent orientation relationship. In a constant stress (150 MPa) temperature-driven strain test, the recoverable strain was 1.8%, and the fatigue life was 452 cycles.

[0114] Example 10

[0115] Step 1: Flour making

[0116] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 41.5 Ti 33.5 Zr 15 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1650 ° C, the atomization pressure was 3.5 MPa, the gas supply pressure was 0.15 MPa, the atomization gas temperature was 45 ° C, the melting power was 25 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0117] Step 2: Dual model construction

[0118] The 3D model of the part was duplicated into two groups and sliced ​​identically using Renishaw QuantAM software, with a slice thickness of 150 μm and a spot compensation of 50 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, allowing them to overlap with each other to achieve subsequent path energy coupling 4D printing.

[0119] Step 3: Path Energy Coupling 4D Printing

[0120] The two sets of models processed in step 2 were assigned two scanning strategies of path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 0°, and the scanning paths are all partitioned scanning with a partition width of 6mm; the energy density E 熔化 =222J / mm 3 , laser power P = 100W, scanning speed V = 150mm / s; energy density E 热处理 =88J / mm 3 , laser power P = 60W, scanning rate V = 150mm / s.

[0121] The 4D printed Ni 41.5 Ti 33.5 Zr 15 The shape memory alloy has a martensite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 1 μm and a volume fraction of 45%. The matrix has columnar grains with a width of approximately 5 μm and a volume fraction of 55%. Dispersed H phases are uniformly distributed within the martensite matrix, both equiaxed grains and columnar grains, with a size of approximately 10 nm and a volume fraction of approximately 5%. The interface lattice mismatch between the H phase and the matrix is ​​approximately 2%, demonstrating a coherent orientation relationship. In a constant stress (350 MPa) temperature-driven strain test, the recoverable strain was 2.5%, and the fatigue life was 379 cycles.

[0122] Example 11

[0123] Step 1: Flour making

[0124] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 50 Ti 25 Pd 25 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1800 ° C, the atomization pressure was 4.5 MPa, the gas supply pressure was 0.05 MPa, the atomization gas temperature was 45 ° C, the melting power was 25 kW, the protective atmosphere was helium, and it was placed in the powder bin for 4D printing;

[0125] Step 2: Dual model construction

[0126] The 3D model of the part was copied into two groups and sliced ​​identically using Slice using software, with a slice thickness of 100 μm and a spot compensation of 40 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, and were overlapped to achieve subsequent path energy coupling 4D printing.

[0127] Step 3: Path Energy Coupling 4D Printing

[0128] The two sets of models processed in step 2 were assigned two scanning strategies of path energy coupling, first melting the preformed powder, and then in-situ homogenizing the preformed layer to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed powder and in-situ homogenizing the preformed layer are coupled at a specific angle of 15°, the scanning paths are all partitioned scanning, and the partition width is 8mm; the energy density E 熔化 =300J / mm 3 , laser power P = 60W, scanning speed V = 80mm / s; energy density E 热处理 =100J / mm 3 , laser power P = 40W, scanning rate V = 160mm / s.

[0129] The 4D printed Ni 50 Ti 25 Pd 25 The shape memory alloy has a martensite matrix with a volume fraction of approximately 90%. The matrix has equiaxed grains with a grain size of approximately 0.8 μm and a volume fraction of 30%. The matrix has columnar grains with a width of approximately 4.5 μm and a volume fraction of 70%. Dispersed Ti2(Ni,Pd) precipitates are uniformly distributed within the martensite matrix, both equiaxed grains and columnar grains. They are approximately 30 nm in size and have a volume fraction of approximately 10%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 13%, demonstrating a semi-coherent orientation relationship. In a two-way shape memory fatigue test at a strain of 2%, the recoverable strain was 1%, and the fatigue life was 741 cycles.

[0130] Example 12

[0131] Step 1: Flour making

[0132] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 49.8 Ti 42.7 Pt 7.5 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1650°C, the atomization pressure was 3.5MPa, the gas supply pressure was 0.15MPa, the atomization gas temperature was 35°C, the melting power was 25kW, the protective atmosphere was argon, and the powders were placed in the powder bin for 4D printing;

[0133] Step 2: Dual model construction

[0134] The 3D model of the part was copied into two groups and sliced ​​identically using Slice using software, with a slice thickness of 100 μm and a spot compensation of 20 μm. The two groups of processed models were imported into the 4D printing system. The two groups of models had exactly the same position coordinates and reference planes, and were overlapped to achieve subsequent path energy coupling 4D printing.

[0135] Step 3: Path Energy Coupling 4D Printing

[0136] The two sets of models processed in step 2 were assigned two scanning strategies with path energy coupling. The preformed powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve a uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, thereby preparing a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in situ homogenizing and heat-treating the preformed layer are coupled at a specific angle of 15°, and the scanning paths are all partitioned scanning with a partition width of 5mm; the energy density E 熔化 =222J / mm 3 , laser power P = 80W, scanning speed V = 120mm / s; energy density E 热处理 =95J / mm 3 , laser power P = 40W, scanning rate V = 140mm / s.

[0137] The 4D printed Ni 49.8 Ti 42.7 Pt 7.5 This shape memory alloy has an austenite matrix with a volume fraction of approximately 95%. The matrix has equiaxed grains with a grain size of approximately 2 μm and a volume fraction of 35%. The matrix has columnar grains with a width of approximately 5 μm and a volume fraction of 65%. Dispersed Ti2(Ni,Pt) is uniformly distributed within the austenite matrix, with a grain size of approximately 10 nm and a volume fraction of approximately 5%. The interface lattice mismatch between the alloy and the matrix is ​​approximately 3%, demonstrating a coherent orientation relationship. In a tensile fatigue test at a strain of 5%, the alloy achieved a fatigue life of 693 cycles, with a stable superelastic strain of 3.5%.

[0138] Comparative Example 1

[0139] Step 1: Flour making

[0140] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this comparative example is Ni 49.5 Ti 50.5(at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization method. The electrode induction heating temperature was 1400 ° C, the atomization pressure was 2.5 MPa, the gas supply pressure was 0.2 MPa, the atomization gas temperature was 30 ° C, the melting power was 15 kW, the protective atmosphere was argon, and it was placed in the powder bin for 4D printing;

[0141] Step 2: Single model construction

[0142] The 3D model of the part was sliced ​​using Materialise Magics software, with a slice thickness of 80 μm and a spot compensation of 20 μm. The processed model was then imported into the 4D printing system for subsequent single-path, single-energy 4D printing.

[0143] Step 3: Single-path single-energy 4D printing

[0144] The model processed in step 2 is given a single-path single-energy scanning strategy, and the alloy powder is melted to prepare a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the scanning path is all partitioned scanning, the partition width is 5mm; the energy density E 熔化 =222J / mm 3 , laser power P = 80W, scanning rate V = 120mm / s.

[0145] The 4D printed Ni 49.5 Ti 50.5 The shape memory alloy has an austenite matrix with a volume fraction of approximately 90%. The matrix has equiaxed grains with a grain size of approximately 300 nm and a volume fraction of 30%, and columnar grains with a width of 1 μm and a volume fraction of 70%. TiNi precipitates are continuously and unevenly distributed at the grain boundaries between the equiaxed grains and the columnar grains within the austenite matrix. They are approximately 50 nm in size and have a volume fraction of approximately 10%, with no definite orientational relationship with the matrix. Without using the second set of process parameters for in-situ homogenization heat treatment of the preformed layer, the precipitates segregate at the grain boundaries, which can easily induce cracks. Consequently, in a tensile fatigue test at a strain of 3%, the specimen fractured after only five loading cycles, failing to achieve superelastic stability.

[0146] Comparative Example 2

[0147] Step 1: Flour making

[0148] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in this comparative example is Ni 45 Ti 50Cu5 (at%), vacuum melting to obtain alloy rods, and spherical alloy powders were obtained by electrode induction atomization. The electrode induction heating temperature was 1500°C, the atomization pressure was 4.5MPa, the gas supply pressure was 0.05MPa, the atomization gas temperature was 45°C, the melting power was 20kW, the protective atmosphere was argon, and the powders were placed in the powder bin for 4D printing;

[0149] Step 2: Dual model construction

[0150] The 3D model of the part was duplicated into two groups and sliced ​​identically using SLM Solutions software, with a slice thickness of 150μm and a spot compensation of 40μm. The two processed models were then imported into the 4D printing system, with identical position coordinates and reference planes, allowing them to overlap to achieve multi-path and multi-energy 4D printing.

[0151] Step 3: Multi-path and multi-energy 4D printing

[0152] The two groups of models processed in step 2 were assigned two scanning strategies respectively. The preformed alloy powder was melted first, and then the preformed layer was scanned a second time to prepare a 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the two scanning paths for melting the preformed alloy powder and scanning the preformed layer for the second time formed an angle of 45°, the scanning paths were all partitioned scanning, and the partition width was 5mm; the energy density E 熔化 =222J / mm 3 , laser power P = 100W, scanning speed V = 150mm / s; energy density E 第二次 =88J / mm 3 , laser power P = 60W, scanning rate V = 150mm / s.

[0153] The 4D printed Ni 45 Ti 50 The Cu5 shape memory alloy matrix consists of a mixed martensite and austenite with a volume fraction of approximately 85%. The matrix equiaxed grains are approximately 3μm in size and 35% in volume. The matrix columnar grains are approximately 7μm wide and 65% in volume. Ti2(Ni,Cu) precipitates are continuously and unevenly distributed at the grain boundaries of the mixed martensite and austenite matrix equiaxed grains and matrix columnar grains. They are approximately 50nm in size and have a volume fraction of approximately 15%, with no definite orientational relationship with the matrix. Because the angles of the scanning paths for the two sets of process parameters exceed the ideal range, effective coupling is not achieved, making in-situ homogenization heat treatment impossible. The precipitates remain segregated at the grain boundaries. Consequently, the shape memory effect significantly diminishes during constant load (2200MPa) temperature-driven strain testing, with a recoverable strain of only 0.58% and a fatigue life of only 56 cycles.

[0154] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A 4D printed nickel-titanium-based shape memory alloy, characterized in that: The nickel-titanium-based shape memory alloy has austenite, martensite or a mixture of martensite and austenite as a matrix, and its microstructure presents alternating matrix equiaxed crystals and matrix columnar crystals; the dispersed nano-precipitated phase is a titanium-rich or nickel-rich intermetallic compound, which is uniformly distributed in the matrix equiaxed crystals and matrix columnar crystals.

2. The 4D printed nickel-titanium-based shape memory alloy according to claim 1, characterized in that: The volume fraction of the austenite, martensite or mixed martensite and austenite matrix is ​​85-95%; the volume fraction of the titanium-rich or nickel-rich intermetallic compound dispersed nano-precipitation phase is 5-15%.

3. The 4D printed nickel-titanium-based shape memory alloy according to claim 1, characterized in that: The size of the matrix equiaxed crystal is 0.5-2 μm, and the volume fraction is 30-45%; the width of the matrix columnar crystal is 2-8 μm, and the volume fraction is 55-70%.

4. The 4D printed nickel-titanium-based shape memory alloy according to claim 1, characterized in that: The size of the dispersed nano-precipitation phase is 10-30 nm, and the interface lattice mismatch between the phase and the matrix is ​​1-15%.

5. A method for preparing a 4D printed nickel-titanium-based shape memory alloy according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Flour making According to the pre-designed nickel-titanium-based shape memory alloy composition, the alloy rods are obtained by vacuum melting, and spherical alloy powders are obtained by electrode induction atomization method, which are placed in the powder bin for 4D printing; Step 2: Dual model construction The 3D model of the part is copied into two groups, and the same slicing process is performed, and the two groups of processed models are imported into the 4D printing molding system; Step 3: Path Energy Coupling 4D Printing The two groups of models processed in step 2 were respectively assigned two scanning strategies of path energy coupling. The preformed alloy powder was first melted, and then the preformed layer was homogenized and heat-treated in situ to achieve uniform distribution of the dispersed nanoprecipitate phase in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy was prepared.

6. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The nickel-titanium-based shape memory alloy described in step 1 is one of NiTi, NiTiCu, NiTiNb, NiTiCr, NiTiHf, NiTiZr, NiTiPd and NiTiPt.

7. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The preparation parameters of the electrode induction atomization method described in step 1 are as follows: the electrode induction heating temperature is 1400-1800°C, the atomization pressure is 2.5-4.5MPa, the gas supply pressure is 0.05-0.2MPa, the atomization gas temperature is 30-45°C, the melting power is 15-25kW, and the protective atmosphere is any one of argon, nitrogen, and helium.

8. The method for preparing 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The slice thickness of the slice processing in step 2 is 80-150 μm, and the spot compensation is 20-50 μm.

9. The method for preparing 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: After the two sets of models described in step 2 are imported into the 4D printing system, they should have exactly the same position coordinates and reference planes so that they overlap with each other to achieve subsequent 4D printing.

10. The method for preparing 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The two scanning paths of melting the preformed alloy powder and in-situ homogenizing the preformed layer in step 3 are coupled to a specific angle ranging from 0 to 20°; the two scanning strategies of the path energy coupling need to meet the energy density E 熔化 : Energy density E 热处理 It is 2 to 3:

1.

11. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 10, characterized in that: The two scanning strategies for path energy coupling in step three are that the two scanning path energies of melting the preformed alloy powder and in-situ homogenizing the preformed layer are coupled into a specific angle ranging from 0 to 10°.

12. The method for preparing 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The two scanning strategies for path energy coupling in step three are that both scanning paths for melting the preformed alloy powder and for in-situ homogenizing the preformed layer are partition scanning, and the partition width is 5 to 8 mm.

13. The method for preparing 4D printed nickel-titanium-based shape memory alloy according to claim 5, characterized in that: The two scanning strategies for path energy coupling in step 3 are: the laser scanning parameters for melting the preformed alloy powder and in-situ homogenizing the preformed layer are: energy density E 熔化 =130~300J / mm 3 , laser power P = 60 ~ 100W, scanning speed V = 80 ~ 160mm / s; energy density E 热处理 =60~100J / mm 3 , laser power P = 30 ~ 60W, scanning rate V = 80 ~ 160mm / s.

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