4D printing of nickel-titanium-based shape memory alloy and method of making the same

Abstract

The application discloses a kind of 4D printing nickel-titanium-based shape memory alloy and preparation method thereof.The preparation method includes powder preparation, double-model construction, path energy coupling 4D printing forming three steps, and its core is through the two scanning strategies of path energy coupling, first melt preformed alloy powder, then in-situ homogenization heat treatment preformed layer, to realize the uniform distribution of dispersed nano precipitated phase in equiaxed crystal and columnar crystal matrix, and 4D printing nickel-titanium-based shape memory alloy is prepared.The preparation method of the application has the advantages of short process cycle, low energy consumption, simple process and good stability, and the prepared nickel-titanium-based shape memory alloy and its components have excellent mechanical properties, functional characteristics, functional stability and fatigue life, and have good popularization and application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of shape memory alloys and additive manufacturing technology, and particularly relates to a 4D printed nickel-titanium-based shape memory alloy and a preparation method thereof. BACKGROUND

[0002] Nickel-titanium and nickel-titanium-based shape memory alloys have excellent and stable super-elasticity, shape memory effect, good damping characteristics, biocompatibility and other unique properties, and are one of the most widely used functional materials. Nickel-titanium-based shape memory alloys are prone to limited desolvation decomposition during solidification and cooling, and various precipitates are precipitated, the size, distribution and interface type of which have a significant influence on the mechanical properties, super-elasticity and shape memory effect of nickel-titanium-based shape memory alloys. In order to prepare nickel-titanium-based shape memory alloys and components with uniformly distributed dispersed precipitates and excellent comprehensive performance, melting, rolling and drawing processes are usually used for forming, and heat treatment processes are used for microstructure and precipitate control. The preparation process of the components is long, complex and time-consuming.

[0003] 4D printing is a new type of 3D printing additive manufacturing technology based on shape memory alloys. The advantage of this technology is that it can overcome the technical difficulties of cold working, machining and forming complex parts of nickel-titanium-based shape memory alloys. In the process of selective laser melting 4D printing, the melting and solidification of a small melt pool will be involved, and the substrate will usually form a microstructure of alternating equiaxed crystals and columnar crystals, in which the uniformly distributed precipitates are mainly distributed in the columnar crystal zone. The microsegregation in the equiaxed crystal zone is serious, and the continuous and uneven distribution of hard and brittle intermetallic compound precipitates in the grain boundary leads to non-coordinated deformation of the nickel-titanium-based alloy matrix and the precipitates during loading, causing significant stress concentration. This will hinder the reversible progress of the martensitic phase transition, induce material intergranular fracture, and worsen the mechanical properties, super-elasticity and shape memory effect of nickel-titanium-based shape memory alloys and components. In order to obtain uniformly distributed precipitates, nickel-titanium-based shape memory alloys prepared by 4D printing process usually also need 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, it is difficult to ensure the temperature uniformity of each part of the component material during overall heat treatment, which increases the difficulty of heat treatment and process uncertainty, and is not conducive to large-scale industrial application. To skip the heat treatment process and directly 4D print the nickel-titanium-based shape memory alloy and realize the precipitate control of the nickel-titanium-based shape memory alloy is a key technical problem that needs to be solved in the fields of materials science and engineering and additive manufacturing.

[0004] So far, there is no direct 4D printing preparation of nickel-titanium-based shape memory alloy with uniformly distributed dispersed nano precipitated phase. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary object of the present application is to provide a 4D printed nickel-titanium-based shape memory alloy.

[0006] The second object of the present application is to provide a preparation method of the above-mentioned 4D printed nickel-titanium-based shape memory alloy.

[0007] The primary object of the present application is achieved by the following technical solutions:

[0008] A 4D printed nickel-titanium-based shape memory alloy, the nickel-titanium-based shape memory alloy has an austenite, martensite or mixed martensite and austenite matrix, and the microstructure presents alternating matrix equiaxed crystals and matrix columnar crystals; the dispersed nano precipitated phase is titanium-rich or nickel-rich intermetallic compound, which is uniformly distributed in the matrix equiaxed crystals and the matrix columnar crystals.

[0009] 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 precipitated phase is 5-15%.

[0010] Preferably, 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%.

[0011] Preferably, the size of the dispersed nano precipitated phase is 10-30 nm, and the interface lattice mismatch degree between the dispersed nano precipitated phase and the matrix is 1-15%.

[0012] The second object of the present application is achieved by the following technical solutions:

[0013] A preparation method of a 4D printed nickel-titanium-based shape memory alloy, comprising the following steps:

[0014] Step 1, powdering

[0015] According to the pre-designed nickel-titanium-based shape memory alloy composition, an alloy rod is obtained by vacuum melting, and spherical alloy powder is obtained by electrode induction atomization method, which is placed in a powder bin for 4D printing forming;

[0016] Step 2, double model construction

[0017] The three-dimensional model of the part is copied into two groups, and the same slicing treatment is carried out, and the treated two groups of models are imported into the 4D printing forming system;

[0018] Step 3: Path Energy Coupling 4D Printing

[0019] 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.

[0020] Preferably, the nickel-titanium-based shape memory alloy in step 1 is one of NiTi, NiTiCu, NiTiNb, NiTiCr, NiTiHf, NiTiZr, NiTiPd and NiTiPt.

[0021] 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.

[0022] Preferably, the slice thickness of the slice processing in step 2 is 80-150 μm, and the spot compensation is 20-50 μm.

[0023] 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.

[0024] 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.

[0025] 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°.

[0026] 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.

[0027] 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= 130~300 J / mm 3 , laser power P = 60~100 W, scanning rate V = 80~160 mm / s; energy density E 热处理 = 60~100 J / mm 3 , laser power P = 30~60 W, scanning rate V = 80~160 mm / s. The principle of the preparation method of the application is that, compared with the micro-pool temperature unevenness and the organization component segregation defect caused by the single scanning strategy, the two scanning strategies coupled printing are adopted in the application, the scanning tracks form a specific angle, and the energy density satisfies a specific proportional relationship, so that in-situ synchronous heat treatment of the micro-pool is realized, the micro-region organization component segregation defect is eliminated, the uniform distribution of the dispersed nano precipitated phase is realized, the nickel-titanium-based shape memory alloy and the near-net-shaped component thereof with excellent functional stability and fatigue life are directly prepared by 4D printing, the post-processing process is saved, the process cycle is short, and the energy consumption is low.

[0028] The advantages and beneficial effects of the preparation method of the application are:

[0029] (1) The 4D printed nickel-titanium-based shape memory alloy of the application avoids the uneven distribution of the dispersed nano precipitated phase at the grain boundary, the dispersed nano precipitated phase is a titanium-rich or nickel-rich intermetallic compound, and the uniform distribution is realized in the base equiaxed crystal and the base columnar crystal, and has a coherent / hemicoherent relationship with the base.

[0030] (2) The 4D printed nickel-titanium-based shape memory alloy of the application can effectively pin the dislocation motion, reduce the incoordination deformation, improve the mechanical properties such as strength and plasticity of the nickel-titanium-based shape memory alloy, and the functional characteristics such as super-elasticity and shape memory effect, and has excellent functional stability and fatigue life.

[0031] (3) The preparation method of the 4D printed nickel-titanium-based shape memory alloy of the application adopts two scanning strategies of path energy coupling, directly 4D prints the nickel-titanium-based shape memory alloy and the near-net-shaped component thereof with excellent functional stability and fatigue life, saves the drawing, heat treatment and other processes adopted by the traditional technology, and the heat treatment process after 4D printing, and has short process cycle and low energy consumption.

[0032] (4) The preparation process of the 4D printed nickel-titanium-based shape memory alloy involved in the application is simple and stable, suitable for batch production and standardized production, and has good popularization and application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM picture of the Ni 49.5 Ti 50.5 (at%) alloy powder obtained in Example 1;

[0034] Figure 2 SEM images of the columnar and equiaxed crystal in the 4D printed NiTi-based shape memory alloy substrate obtained in Example 1;

[0035] Figure 3 (a) and Figure 3 (b) are, respectively, the distribution of the precipitated phase in the columnar crystal region of the substrate in the 4D printed NiTi-based shape memory alloy obtained in Example 1 and an enlarged view thereof;

[0036] Figure 4 (a) and Figure 4 (b) are, respectively, the distribution of the precipitated phase in the equiaxed crystal region of the substrate in the 4D printed NiTi-based shape memory alloy obtained in Example 1 and an enlarged view thereof;

[0037] Figure 5 Tensile stress-strain curve of the 4D printed NiTi-based shape memory alloy obtained in Example 1;

[0038] Figure 6 Tensile fatigue test curve of the 4D printed NiTi-based shape memory alloy obtained in Example 1 at a strain of 3%;

[0039] Figure 7 Recoverable strain change of the 4D printed NiTi-based shape memory alloy obtained in Example 1 during the tensile fatigue test at a strain of 5%. DETAILED DESCRIPTION

[0040] The present application will be further described in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present application are not limited thereto.

[0041] Example 1

[0042] Step one, powder preparation

[0043] According to the pre-designed composition of the NiTi-based shape memory alloy, the composition of the NiTi-based shape memory alloy selected in this embodiment is Ni 49.5 Ti 50.5 (at%), and an alloy rod is obtained by vacuum melting. A spherical alloy powder is prepared by electrode induction atomization (e.g. Figure 1 ), the electrode induction heating temperature is 1400℃, the atomization pressure is 2.5MPa, the air supplement pressure is 0.2MPa, the atomization gas temperature is 30℃, the melting power is 15kW, and the protective atmosphere is argon. The alloy powder is placed in a powder bin for 4D printing;

[0044] Step two, double model construction

[0045] The three-dimensional model of the part was copied into two groups, and the same slicing process was performed using Materialise Magics software, with a slice thickness of 80 μm and a spot compensation of 20 μm; the two groups of processed models were imported into a 4D printing forming system, and the two groups of models had completely same position coordinates and reference surfaces, so that they were overlapped with each other, so as to realize subsequent path energy coupling 4D printing forming;

[0046] Step three, path energy coupling 4D printing forming

[0047] The two groups of models processed in step two were respectively given two kinds of scanning strategies of path energy coupling, the pre-formed alloy powder was first melted, and then in-situ homogenization heat treatment was performed on the pre-formed layer, so as to realize the uniform distribution of dispersed nano precipitated phase in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy was prepared. The specific parameters of this step are as follows: the two scanning paths of melting the pre-formed alloy powder and in-situ homogenization heat treatment of the pre-formed layer are coupled at a specific angle of 0°, both of which are subarea scanning, and the subarea width is 5 mm; the energy density E 熔化 = 222 J / mm 3 , the laser power P = 80 W, and the scanning speed V = 120 mm / s; the energy density E 热处理 = 95 J / mm 3 , the laser power P = 40 W, and the scanning speed V = 140 mm / s.

[0048] The 4D printed Ni 49.5 Ti 50.5 shape memory alloy of this embodiment has an austenite matrix, and the volume fraction is about 90%; the equiaxed crystal grain size of the matrix is about 500 nm, the volume fraction is 30%, the columnar crystal width of the matrix is 6 μm, and the volume fraction is 70% (as shown in Figure 2 ); the dispersed Ti2Ni precipitated phase is uniformly distributed in the austenite matrix equiaxed crystal and the matrix columnar crystal (as shown in Figure 3 and Figure 4 ), and the size is about 20 nm, the volume fraction is about 10%, and the interface lattice mismatch degree between the matrix is about 10%, having a semi-coherent orientation relationship. The tensile ultimate strength and the fracture strain are 750 MPa and 8% respectively (as shown in Figure 5 ); in the strain 3% tensile fatigue test, the fatigue life is 1152 times, and the stable superelasticity strain is 2.45% (as shown in Figure 6 ); in the strain 5% tensile fatigue test, the fatigue life is 583 times, and the stable superelasticity strain is 2.2% (as shown in Figure 7 ).

[0049] Example 2

[0050] Step one, powder preparation

[0051] According to the pre-designed nickel-titanium-based shape memory alloy composition, the nickel-titanium-based shape memory alloy composition selected in the embodiment is Ni 51 Ti 49 (at %), vacuum smelting to obtain an alloy bar, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1400℃, the atomization pressure is 2.5MPa, the air supplement pressure is 0.1MPa, the atomization gas temperature is 30℃, the smelting power is 20kW, and the protective atmosphere is helium, which is placed in a powder bin for 4D printing forming;

[0052] Step two, double model construction

[0053] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Autodesk Netfabb software, the slicing thickness is 100μm, and the light spot compensation is 25μm; the two groups of processed models are imported into the 4D printing forming system, and the two groups of models have the same position coordinates and reference surface, so that they are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0054] Step three, path energy coupling 4D printing forming

[0055] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, the preformed alloy powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so as to realize the uniform distribution of dispersed nano precipitates in the equiaxed crystal and columnar crystal matrix, and the 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 10°, the scanning paths are both partition scanning, and the partition width is 8mm; the energy density E 熔化 =208J / mm 3 , the laser power P=60W, and the scanning rate V=80mm / s; the energy density E 热处理 =88J / mm 3 , the laser power P=40W, and the scanning rate V=150mm / s.

[0056] The 4D printed Ni 51 Ti 49The shape memory alloy has a martensite matrix with a volume fraction of about 95%; the matrix equiaxed crystal grain size is about 1 μm, the volume fraction is 40%, the matrix columnar crystal width is about 2 μm, and the volume fraction is 60%; the dispersed Ni4Ti3 precipitate phase is uniformly distributed in the martensite matrix equiaxed crystal and the matrix columnar crystal, the size is about 10 nm, the volume fraction is about 5%, the interface lattice mismatch degree between the matrix is about 3%, and the orientation relationship has a coherent orientation relationship. In the constant load (200 MPa) temperature driving strain test, after 6 cycles, the shape memory response reaches stability, the complete recovery strain is 4.4%, and the fatigue life is 497 times.

[0057] Example 3

[0058] Step one, powdering

[0059] 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 50 Cu5 (at%), vacuum smelting to obtain an alloy rod, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1500℃, the atomization pressure is 4.5 MPa, the air supplement pressure is 0.05 MPa, the atomization gas temperature is 45℃, the smelting power is 20kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0060] Step two, double model construction

[0061] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using SLM Solutions software, the slicing thickness is 150 μm, and the light spot compensation is 40 μm; the two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surface, and are overlapped with each other, so that the subsequent path energy coupling 4D printing forming is realized;

[0062] Step three, path energy coupling 4D printing forming

[0063] The two groups of models processed in step two are respectively given two kinds of scanning strategies of path energy coupling, the preformed alloy powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so that the dispersed nanometer precipitate phase is uniformly distributed in the equiaxed crystal and the columnar crystal matrix, and the dispersed nanometer precipitate phase 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 0°, both of which are subzone scanning, and the subzone width is 5 mm; the energy density E 熔化 = 222 J / mm 3 , the laser power P = 100 W, and the scanning speed V = 160 mm / s; the energy density E 热处理= 88 J / mm 3 Laser power P = 60 W, scanning rate V = 160 mm / s.

[0064] 4D printing Ni 45 Ti 50 Cu5 shape memory alloy, the matrix is mixed martensite and austenite, the volume fraction is about 85%, the matrix equiaxed grain size is about 2 μm, the volume fraction is 35%, the matrix columnar crystal width is about 8 μm, the volume fraction is 65%; The dispersed Ti2(Ni, Cu) precipitate phase is uniformly distributed in the matrix equiaxed crystal and the matrix columnar crystal of the mixed matrix martensite and austenite, the size is about 20 nm, the volume fraction is about 15%, the interface lattice mismatch degree between the matrix is about 5%, and the orientation relationship has coherent. In the stress 300 MPa compression fatigue test, the fatigue life is more than 10000 times, and the stable superelastic strain is 1.5%.

[0065] Example 4

[0066] Step one, powder preparation

[0067] 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 smelting to obtain alloy bar, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1500℃, the atomization pressure is 4.5MPa, the air supplement pressure is 0.05MPa, the atomization gas temperature is 45℃, the smelting power is 20kW, and the protective atmosphere is argon. It is placed in the powder bin for 4D printing forming;

[0068] Step two, double model construction

[0069] The three-dimensional model of the part is copied into two groups, and the same slicing process is carried out using SLM Build Processor software, the slicing thickness is 120 μm, and the light spot compensation is 50 μm; The two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surface, and are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0070] Step three, path energy coupling 4D printing forming

[0071] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, melting pre-formed powder first, and then in-situ homogenizing heat treatment of pre-formed layer to realize uniform distribution of dispersed nano precipitated phase in equiaxed crystal and columnar crystal matrix, to prepare 4D printed nickel titanium based shape memory alloy. The specific parameters of this step are: the two scanning paths of melting pre-formed alloy powder and in-situ homogenizing heat treatment of pre-formed layer are coupled at a specific angle of 20°, both of which are subarea scanning, and the subarea width is 6mm; energy density E 熔化 =185J / mm 3 , laser power P=100W, scanning rate V=150mm / s; energy density E 热处理 =88J / mm 3 , laser power P=60W, scanning rate V=120mm / s.

[0072] The 4D printed Ni 43.5 Ti 49 Cu 7.5 shape memory alloy of this embodiment has a mixed matrix of martensite and austenite, with a volume fraction of about 90%, and the equiaxed crystal grain size of the matrix is about 2μm, with a volume fraction of 45%, and the width of the columnar crystal of the matrix is about 8μm, with a volume fraction of 55%; the dispersed Ti(Ni,Cu)2 precipitated phase is uniformly distributed in the mixed matrix equiaxed crystal and the matrix columnar crystal, with a size of about 15nm and a volume fraction of about 10%, and the interface lattice mismatch degree between the matrix and the precipitated phase is about 5%, with a coherent orientation relationship. In the stress 400MPa compression fatigue test, the fatigue life is greater than 10000 times, and the stable superelastic strain is 1.7%.

[0073] Example 5

[0074] Step one, powdering

[0075] According to the pre-designed composition of nickel titanium based shape memory alloy, the nickel titanium based shape memory alloy composition selected in this embodiment is Ni 47 Ti 44 Nb9(at%), and the alloy rod is obtained by vacuum melting, and the spherical alloy powder is obtained by electrode induction atomization method, the electrode induction heating temperature is 1700℃, the atomization pressure is 3.5MPa, the air supplement pressure is 0.05MPa, the atomization gas temperature is 40℃, the melting power is 20kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0076] Step two, double model construction

[0077] The three-dimensional model of the part was copied into two groups, and the same slicing process was performed 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 forming system, and the two groups of models had the same position coordinates and reference surfaces, so that they overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0078] Step three, path energy coupling 4D printing forming

[0079] The two groups of models processed in step two were respectively given two kinds of scanning strategies of path energy coupling, the preformed alloy powder was first melted, and then in-situ homogenization heat treatment was performed on the preformed layer, so as to realize the uniform distribution of dispersed nano precipitates in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy was prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 5°, both of which are subarea scanning, and the subarea width is 8 mm; the energy density E 熔化 = 120 J / mm 3 , the laser power P = 70 W, and the scanning speed V = 150 mm / s; the energy density E 热处理 = 60 J / mm 3 , the laser power P = 30 W, and the scanning speed V = 150 mm / s.

[0080] The 4D printed Ni 47 Ti 44 Nb9 shape memory alloy of this embodiment has a martensitic matrix, the volume fraction of which is about 90%, the equiaxed crystal grain size of the matrix is about 1.5 μm, the volume fraction is 30%, the width of the columnar crystal of the matrix is about 8 μm, and the volume fraction is 70%; the dispersed (Ti, Nb)2Ni precipitates are uniformly distributed in the martensitic matrix equiaxed crystal and the matrix columnar crystal, the size is about 30 nm, the volume fraction is about 10%, and the interface lattice mismatch degree between the matrix is about 15%, which has a semi-coherent orientation relationship. In the constant strain (10%) temperature driven strain test, after 10 cycles, the shape memory response reaches stability, the complete recovery strain is 2%, and the fatigue life is 642 times.

[0081] Example 6

[0082] Step one, powder preparation

[0083] According to the pre-designed composition of the nickel-titanium-based shape memory alloy, the composition of the nickel-titanium-based shape memory alloy selected in this embodiment is Ni 50.54 Ti 49.2 Cr 0.26(at%), vacuum melting to obtain alloy rods, spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1650℃, the atomization pressure is 3MPa, the air supplement pressure is 0.05MPa, the atomization gas temperature is 40℃, the melting power is 20kW, and the protective atmosphere is nitrogen, which is placed in the powder bin for 4D printing forming;

[0084] Step two, double model construction

[0085] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Renishaw QuantAM software, with a slice thickness of 80μm and a spot compensation of 25μm; the two groups of processed models are imported into the 4D printing forming system, and the two groups of models have the same position coordinates and reference surfaces, so that they are overlapped with each other to realize subsequent path energy coupling 4D printing forming;

[0086] Step three, path energy coupling 4D printing forming

[0087] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, the preformed powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer to realize the uniform distribution of the dispersed nano precipitated phase in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 10°, both of which are subzone scanning, and the subzone width is 5mm; the energy density E 熔化 =277J / mm 3 , the laser power P=100W, and the scanning rate V=100mm / s; the energy density E 热处理 =100J / mm 3 , the laser power P=50W, and the scanning rate V=100mm / s.

[0088] The 4D printed Ni 50.54 Ti 49.2 Cr 0.26 shape memory alloy of this embodiment has an austenitic matrix, the volume fraction of which is about 95%, the equiaxed crystal grain size of the matrix is about 1.5μm, the volume fraction is 40%, and the width of the columnar crystal of the matrix is about 7μm, the volume fraction is 60%; the dispersed (Ti, Co)2Ni precipitated phase is uniformly distributed in the austenitic matrix equiaxed crystal and the matrix columnar crystal, the size is about 30nm, the volume fraction is about 5%, and the interface lattice mismatch degree between the matrix is about 12%, which has a semi-coherent orientation relationship. In the strain 5% tensile fatigue test, the fatigue life is 722 times, and the stable super-elastic strain is 3.3%.

[0089] Example 7

[0090] Step one, powder preparation

[0091] According to the pre-designed composition of the nickel-titanium-based shape memory alloy, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 50.4 Ti 29.6 Hf 20 (at%), vacuum smelting to obtain an alloy rod, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1750℃, the atomization pressure is 4.5MPa, the air supplement pressure is 0.1MPa, the atomization gas temperature is 45℃, the smelting power is 25kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0092] Step two, double model construction

[0093] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Materialise Magics software, the slicing thickness is 120μm, and the spot compensation is 20μm; the two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surface, and they are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0094] Step three, path energy coupling 4D printing forming

[0095] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, the preformed alloy powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so as to realize the uniform distribution of dispersed nano precipitates in the equiaxed crystal and columnar crystal matrix, and the 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 10°, the scanning paths are both partition scanning, and the partition width is 5mm; the energy density E 熔化 =208J / mm 3 , the laser power P=70W, and the scanning rate V=80mm / s; the energy density E 热处理 =100J / mm 3 , the laser power P=30W, and the scanning rate V=80mm / s.

[0096] The 4D printed Ni 50.4 Ti 29.6 Hf 20The shape memory alloy has a matrix of martensite, a volume fraction of about 90%, a matrix equiaxed crystal grain size of about 2 μm, a volume fraction of about 40%, a matrix columnar crystal width of about 8 μm, and a volume fraction of about 60%; the (Ti, Hf)2Ni dispersed phase is uniformly distributed in the matrix equiaxed crystal and the matrix columnar crystal, has a size of about 20 nm, a volume fraction of about 10%, and an interface lattice mismatch degree of about 10% with the matrix, and has a semi-coherent orientation relationship. In a double-path shape memory fatigue test with a strain of 2%, the recoverable strain is 0.8%, and the fatigue life is 884 times.

[0097] Example 8

[0098] Step one, powdering

[0099] 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 %), an alloy rod is obtained by vacuum smelting, spherical alloy powder is obtained by electrode induction atomization, the electrode induction heating temperature is 1750 °C, the atomization pressure is 4.5 MPa, the air supplementing pressure is 0.1 MPa, the atomization gas temperature is 45 °C, the smelting power is 25 kW, and the protective atmosphere is argon, and the alloy rod is placed in a powder bin for 4D printing forming;

[0100] Step two, double-model construction

[0101] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Autodesk Netfabb software, the slicing thickness is 130 μm, and the light spot compensation is 30 μm; the two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surfaces, and are overlapped with each other, so that the subsequent path energy coupling 4D printing forming is realized;

[0102] Step three, path energy coupling 4D printing forming

[0103] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, the preformed alloy powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so that the dispersed nano precipitates are uniformly distributed in the equiaxed crystal and the columnar crystal matrix, and the 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 20°, the scanning paths are both partition scanning, the partition width is 5 mm; the energy density E 熔化 = 277 J / mm 3 , the laser power P is 100 W, and the scanning speed V is 100 mm / s; the energy density E 热处理= 100 J / mm 3 Laser power P = 50 W, scanning rate V = 100 mm / s.

[0104] 4D printing Ni 50.8 Ti 29.2 Hf 20 The shape memory alloy has a martensite matrix, a volume fraction of about 95%, a matrix equiaxed crystal grain size of about 0.5 μm, a volume fraction of 30%, a matrix columnar crystal width of 6 μm, and a volume fraction of 70%; the dispersed H phase is uniformly distributed in the matrix equiaxed crystal and the matrix columnar crystal, has a size of about 10 nm, a volume fraction of about 5%, and an interface lattice mismatch degree of about 1% with the matrix, and has a coherent orientation relationship. In a double-pass shape memory fatigue test with a strain of 3%, the recoverable strain is 1.4%, and the fatigue life is 814 times.

[0105] Example 9

[0106] Step one, powder preparation

[0107] According to the pre-designed composition of the nickel-titanium-based shape memory alloy, the nickel-titanium-based shape memory alloy composition selected in this embodiment is Ni 49.5 Ti 35.5 Zr 15 (at%), vacuum smelting to obtain an alloy rod, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1650℃, the atomization pressure is 3.5MPa, the air supplement pressure is 0.2MPa, the atomization gas temperature is 45℃, the smelting power is 25kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0108] Step two, double model construction

[0109] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using SLM Solutions software, the slicing thickness is 110 μm, and the light spot compensation is 25 μm; the two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surface, and are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0110] Step three, path energy coupling 4D printing forming

[0111] 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.

[0112] The 4D printed Ni 49.5 Ti 35.5 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 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.

[0113] Example 10

[0114] Step 1: Flour Making

[0115] 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;

[0116] Step 2: Dual model construction

[0117] The three-dimensional model of the part was copied into two groups, and the same slicing process was performed using Renishaw QuantAM software, with a slice thickness of 150 pm and a spot compensation of 50 pm; the two groups of processed models were imported into the 4D printing forming system, and the two groups of models had the same position coordinates and reference surfaces, so that they overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0118] Step three, path energy coupling 4D printing forming

[0119] The two groups of models processed in step two were respectively given two kinds of scanning strategies of path energy coupling, the pre-formed alloy powder was first melted, and then in-situ homogenization heat treatment was performed on the pre-formed layer, so as to realize the uniform distribution of dispersed nano precipitated phase in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy was prepared. The specific parameters of this step are as follows: the two scanning paths of melting the pre-formed alloy powder and in-situ homogenization heat treatment of the pre-formed layer are coupled at a specific angle of 0°, both of which are subarea scanning, and the subarea width is 6 mm; the energy density E 熔化 = 222 J / mm 3 , the laser power P = 100 W, and the scanning speed V = 150 mm / s; the energy density E 热处理 = 88 J / mm 3 , the laser power P = 60 W, and the scanning speed V = 150 mm / s.

[0120] The 4D printed Ni 41.5 Ti 33.5 Zr 15 shape memory alloy of this embodiment has a martensite matrix, the volume fraction of which is about 95%, the equiaxed crystal grain size of the matrix is about 1 pm, the volume fraction is 45%, the width of the columnar crystal of the matrix is about 5 pm, and the volume fraction is 55%; the dispersed H phase is uniformly distributed in the martensite matrix equiaxed crystal and the matrix columnar crystal, the size is about 10 nm, the volume fraction is about 5%, and the interface lattice mismatch degree between the matrix is about 2%, which has a coherent orientation relationship. In the constant stress (350 MPa) temperature driven strain test, the recoverable strain is 2.5%, and the fatigue life is 379 times.

[0121] Example 11

[0122] Step one, powder preparation

[0123] According to the pre-designed composition of the nickel-titanium-based shape memory alloy, the composition of the nickel-titanium-based shape memory alloy selected in this embodiment is Ni 50 Ti 25 Pd 25(at%), vacuum smelting to obtain an alloy rod, and then obtaining spherical alloy powder by electrode induction atomization method, the electrode induction heating temperature is 1800℃, the atomization pressure is 4.5MPa, the air supplement pressure is 0.05MPa, the atomization gas temperature is 45℃, the smelting power is 25kW, and the protective atmosphere is helium, which is placed in a powder bin for 4D printing forming;

[0124] Step two, double model construction

[0125] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Slice using software, the slicing thickness is 100μm, and the light spot compensation is 40μm; the two groups of processed models are imported into the 4D printing forming system, and the two groups of models have the same position coordinates and reference surface, so that they are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0126] Step three, path energy coupling 4D printing forming

[0127] The two groups of models processed in step two are respectively given two kinds of scanning strategies of path energy coupling, the preformed powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so as to realize the uniform distribution of the dispersed nano precipitated phase in the equiaxed crystal and columnar crystal matrix, and a 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 15°, both of which are subarea scanning, and the subarea width is 8mm; the energy density E 熔化 =300J / mm 3 , the laser power P=60W, and the scanning rate V=80mm / s; the energy density E 热处理 =100J / mm 3 , the laser power P=40W, and the scanning rate V=160mm / s.

[0128] The 4D printed Ni 50 Ti 25 Pd 25 shape memory alloy of this embodiment has a martensite matrix, the volume fraction of which is about 90%, the equiaxed crystal grain size of the matrix is about 0.8μm, the volume fraction is 30%, the width of the columnar crystal of the matrix is about 4.5μm, and the volume fraction is 70%; the dispersed Ti2(Ni,Pd) precipitated phase is uniformly distributed in the martensite matrix equiaxed crystal and the matrix columnar crystal, the size is about 30nm, the volume fraction is about 10%, and the interface lattice mismatch degree between the matrix is about 13%, which has a semi-coherent orientation relationship. In the double-way shape memory fatigue test with a strain of 2%, the recoverable strain is 1%, and the fatigue life is 741 times.

[0129] Example 12

[0130] Step one, powder preparation

[0131] 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 smelting to obtain an alloy rod, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1650℃, the atomization pressure is 3.5MPa, the air supplement pressure is 0.15MPa, the atomization gas temperature is 35℃, the smelting power is 25kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0132] Step two, double model construction

[0133] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using Slice using software, the slicing thickness is 100μm, and the light spot compensation is 20μm; the two groups of processed models are imported into the 4D printing forming system, the two groups of models have the same position coordinates and reference surface, and they are overlapped with each other, so as to realize the subsequent path energy coupling 4D printing forming;

[0134] Step three, path energy coupling 4D printing forming

[0135] The two groups of models processed in step two are respectively given two scanning strategies of path energy coupling, the preformed powder is first melted, and then in-situ homogenization heat treatment is performed on the preformed layer, so as to realize the uniform distribution of dispersed nano precipitates in the equiaxed crystal and columnar crystal matrix, and the 4D printed nickel-titanium-based shape memory alloy is prepared. The specific parameters of this step are as follows: the two scanning paths of melting the preformed alloy powder and in-situ homogenization heat treatment of the preformed layer are coupled at a specific angle of 15°, the scanning paths are both partition scanning, and the partition width is 5mm; the energy density E 熔化 =222J / mm 3 , the laser power P=80W, and the scanning rate V=120mm / s; the energy density E 热处理 =95J / mm 3 , the laser power P=40W, and the scanning rate V=140mm / s.

[0136] The 4D printed Ni 49.8 Ti 42.7 Pt 7.5The shape memory alloy has an austenite matrix with a volume fraction of about 95%, the matrix equiaxed crystal grain size is about 2 μm, the volume fraction is 35%, the matrix columnar crystal width is about 5 μm, the volume fraction is 65%; the dispersed Ti2(Ni, Pt) is uniformly distributed in the austenite matrix equiaxed crystal and the matrix columnar crystal, the size is about 10 nm, the volume fraction is about 5%, the interface lattice mismatch degree between the matrix is about 3%, and the orientation relationship has a coherent orientation relationship. In the strain 5% tensile fatigue test, the fatigue life is 693 times, and the stable super-elastic strain is 3.5%.

[0137] Comparative Example 1

[0138] Step one, powdering

[0139] 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%) and the alloy rod is obtained by vacuum smelting. The spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1400℃, the atomization pressure is 2.5MPa, the air supplement pressure is 0.2MPa, the atomization gas temperature is 30℃, the smelting power is 15kW, and the protective atmosphere is argon. It is placed in the powder bin for 4D printing forming;

[0140] Step two, single model construction

[0141] The three-dimensional model of the part is sliced using Materialise Magics software, the slice thickness is 80μm, and the spot compensation is 20μm; the processed model is imported into the 4D printing forming system for subsequent single-path single-energy 4D printing forming;

[0142] Step three, single-path single-energy 4D printing forming

[0143] The processed model in step two 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 as follows: the scanning path is all partition scanning, the partition width is 5mm; the energy density E 熔化 =222J / mm 3 , the laser power P=80W, and the scanning speed V=120mm / s.

[0144] The 4D printed Ni 49.5 Ti 50.5The shape memory alloy has an austenite matrix with a volume fraction of about 90%, equiaxed grain size of the matrix of about 300 nm, volume fraction of about 30%, and columnar grain width of the matrix of 1 μm with a volume fraction of 70%; the Ti2Ni precipitate phase is continuously and unevenly distributed at the grain boundaries of the austenite matrix equiaxed crystal and the matrix columnar crystal, has a size of about 50 nm, a volume fraction of about 10%, and no certain orientation relationship with the matrix. The pre-formed layer is not subjected to in-situ homogenization heat treatment using the second set of process parameters, and the precipitate phase is segregated at the grain boundaries, which is easy to cause cracks. Therefore, in the tensile fatigue test at a strain of 3%, the sample is broken after only 5 cycles of loading, and the superelasticity is not stable.

[0145] Comparative Example 2

[0146] Step one, powder preparation

[0147] According to the pre-designed composition of the nickel-titanium-based shape memory alloy, the composition of the nickel-titanium-based shape memory alloy selected in this comparative example is Ni 45 Ti 50 Cu5 (at%), vacuum smelting to obtain an alloy rod, and spherical alloy powder is prepared by electrode induction atomization method, the electrode induction heating temperature is 1500℃, the atomization pressure is 4.5MPa, the air supplement pressure is 0.05MPa, the atomization gas temperature is 45℃, the smelting power is 20kW, and the protective atmosphere is argon, which is placed in the powder bin for 4D printing forming;

[0148] Step two, double model construction

[0149] The three-dimensional model of the part is copied into two groups, and the same slicing process is performed using SLM Solutions software, with a slice thickness of 150μm and a light spot compensation of 40μm; the two groups of processed models are imported into the 4D printing forming system, and the two groups of models have the same position coordinates and reference surface, so that they are overlapped with each other, so as to realize multi-path and multi-energy 4D printing forming;

[0150] Step three, multi-path and multi-energy 4D printing forming

[0151] The two groups of models processed in step two are respectively assigned two kinds of scanning strategies, the pre-formed alloy powder is first melted, and then the pre-formed layer is scanned for the second time to prepare the 4D printed nickel-titanium-based shape memory alloy. The specific parameters of this step are: the angle between the two scanning paths for melting the pre-formed alloy powder and the second time scanning the formed layer is 45°, both scanning paths are subzone scanning, and the subzone width is 5mm; the energy density E 熔化 =222J / mm 3 , the laser power P=100W, and the scanning rate V=150mm / s; the energy density E 第二次 =88J / mm 3, laser power P = 60 W, scanning rate V = 150 mm / s.

[0152] 4D printed Ni of the comparative example 45 Ti 50 Cu5 shape memory alloy, the matrix is mixed martensite and austenite, the volume fraction is about 85%, the matrix equiaxed grain size is about 3 μm, the volume fraction is 35%, the matrix columnar crystal width is about 7 μm, the volume fraction is 65%; Ti2(Ni, Cu) precipitate phase is continuously and unevenly distributed at the grain boundary of the matrix equiaxed crystal and the matrix columnar crystal of the mixed matrix of martensite and austenite, the size is about 50 nm, the volume fraction is about 15%, and there is no certain orientation relationship with the matrix. Due to the angle of the scanning path of the two groups of process parameters exceeding the ideal range, effective coupling cannot be achieved, in-situ homogenization heat treatment cannot be realized, and the precipitate phase still segregates at the grain boundary, so in the constant load (2200 MPa) temperature driving strain test, the shape memory effect decays significantly, the recoverable strain is only 0.58%, and the fatigue life is only 56 times.

[0153] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A method for preparing 4D printed nickel-titanium-based shape memory alloy, 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 three-dimensional model of the part is copied into two groups and sliced ​​in the same way. The two groups of models are imported into the 4D printing system. After being imported into the 4D printing system, the two groups of models should have exactly the same position coordinates and reference planes, and overlap with each other to achieve subsequent 4D printing. Step 3: Path Energy Coupling 4D Printing 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 to form a preformed layer, and then the preformed layer was subjected to in-situ homogenization heat treatment 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 two scanning paths of melting the preformed alloy powder and in-situ homogenizing the heat treated preformed layer in step 3 are coupled to form a specific angle ranging from 0 to 20 degrees; The two scanning strategies of the path energy coupling 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 / mm³, laser power P=60~100W, scanning speed V=80~160mm / s; energy density E 热处理 =60~100J / mm³, laser power P=30~60W, scanning speed V=80~160mm / s.

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

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

4. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 1, wherein: The slice thickness of the slice processing in step 2 is 80-150 μm, and the spot compensation is 20-50 μm.

5. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 1, wherein: The two scanning strategies for path energy coupling in step three are that the two scanning paths for melting the preformed alloy powder and in-situ homogenizing the preformed layer are coupled to form a specific angle ranging from 0 to 10°.

6. The method for preparing a 4D printed nickel-titanium-based shape memory alloy according to claim 1, wherein: The two scanning strategies for path energy coupling described in step 3 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.

7. A 4D printed nickel-titanium-based shape memory alloy, characterized in that: The 4D printing nickel-titanium-based shape memory alloy is prepared according to the preparation method of any one of claims 1 to 6.

8. The 4D printing nickel-titanium-based shape memory alloy according to claim 7, characterized in that: The nickel-titanium-based shape memory alloy has austenite, martensite or a mixture of martensite and austenite as the 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.

9. The 4D printing nickel-titanium-based shape memory alloy according to claim 8, 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-precipitate phase is 5-15%.

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

11. The 4D printing nickel-titanium-based shape memory alloy according to claim 8, characterized in that: The size of the dispersed nano-precipitated phase is 10-30 nm, and the interface lattice mismatch between the phase and the matrix is ​​1-15%.

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