High-strength 3D printing nickel-titanium-iron shape memory alloy and preparation method thereof

Abstract

The invention relates to the technical field of alloy additive materials, in particular to a high-strength 3D printing nickel-titanium-iron shape memory alloy and a preparation method thereof. The alloy is prepared by the method. The method comprises the following steps: constructing a thermodynamic database, searching a Pareto optimal solution set of a second phase Ti2Ni phase fraction and a crack sensitive factor by combining solidification simulation and an open source database, and screening out the target component content of the alloy; the preparation method comprises the following steps: smelting alloy components with target component content to obtain a nickel-titanium-iron alloy cast ingot, preparing nickel-titanium-iron pre-alloy powder through a gas atomization method, and carrying out vacuum drying on the screened nickel-titanium-iron pre-alloy powder to obtain an alloy powder raw material; and the powder raw material is printed layer by layer through a selective laser melting forming technology, and a part entity of the 3D printing nickel-titanium-iron shape memory alloy is obtained. The 3D printing nickel-titanium-iron shape memory alloy which is low in phase change temperature, high in mechanical property and good in forming can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy additive manufacturing, and particularly relates to a high-strength 3D printed nickel-titanium-iron shape memory alloy and a preparation method thereof. Background Art

[0002] Nickel-titanium-iron shape memory alloy has characteristics such as low phase transition temperature, excellent mechanical properties at room temperature, and large recovery stress at relatively low temperatures. In addition, compared with other low-temperature shape memory alloys, nickel-titanium-iron shape memory alloy has significant advantages in terms of stability and reliability when serving in a low-temperature environment. For example, nickel-titanium-iron shape memory alloy pipe joints have been widely used in the aircraft hydraulic pipeline system, and are one of the most typical and successful cases of the application of shape memory alloys in the engineering field.

[0003] Due to the high ductility of nickel-based shape memory alloy itself and high work hardening during the processing, it has machining problems, such as defects like material cracking, surface peeling and tearing during machining. In recent years, the emerging laser 3D printing technology can effectively solve the machining problems of nickel-based shape memory alloy by relying on computer-aided design (such as CAD-aided design) to obtain the three-dimensional structure information of complex parts and directly preparing solid parts with complex structures by means of layer-by-layer accumulation. Among them, the complex structure solid parts prepared by selective laser melting technology have better surface finish and higher geometric accuracy, and are the main 3D printing technology for preparing nickel-based shape memory alloy at present.

[0004] However, the characteristics of high cooling rate, repeated remelting of the alloy and complex thermal history in selective laser melting technology will lead to non-uniform microstructure, high residual stress and easy generation of metallurgical defects in 3D printed nickel-titanium shape memory alloy, thus affecting the comprehensive performance of nickel-titanium alloy. In addition, the strong lattice distortion caused by the addition of the third component iron element will further increase the solidification cracking tendency of nickel-titanium shape memory alloy and deteriorate the forming performance of 3D printed nickel-titanium alloy.

[0005] At present, 3D printed nickel-titanium-iron shape memory alloy usually adopts a low iron content addition (atomic ratio < 1 at.%), however, the phase transition temperature of this alloy is relatively high, far from meeting the actual service requirements. If 3D printed nickel-titanium-iron shape memory alloy adopts a high iron content (atomic ratio ≥ 2 at.%), serious solidification cracking and delamination will easily occur, its mechanical properties will be significantly reduced, and even the forming will fail. Therefore, it is necessary to develop a high-strength 3D printed nickel-titanium-iron shape memory alloy and a preparation method thereof to solve the problems of high phase transition temperature, low mechanical properties and poor forming existing in the existing 3D printed nickel-titanium-iron shape memory alloy. Summary of the Invention

[0006] The object of the present invention is to provide a high-strength 3D printing nickel-titanium-iron shape memory alloy and its preparation method. The specific technical solutions are as follows: In a first aspect, the present invention provides a preparation method of a high-strength 3D printing nickel-titanium-iron shape memory alloy, including: Step S1: According to the nickel-titanium-iron system phase equilibrium data in the existing literature, establish a thermodynamic database for the nickel-titanium-iron ternary system rich in the nickel-titanium end; perform solidification simulation on nickel-titanium-iron alloys within a wide range of alloy compositions in the thermodynamic database, and obtain the change relationship between the second-phase fraction and the crack sensitivity factor of nickel-titanium-iron alloys with different component contents by means of the crack sensitivity factor model; utilize the change relationship, search for the Pareto optimal solution set of the second-phase Ti2Ni phase fraction and the crack sensitivity factor using an open-source code library, and then screen to obtain the target component content of the 3D printing nickel-titanium-iron shape memory alloy; Step S2: First, obtain a nickel-titanium-iron alloy ingot by melting the components of the 3D printing nickel-titanium-iron shape memory alloy with the target component content, then obtain nickel-titanium-iron pre-alloy powder by gas atomization method. After vacuum drying the sieved nickel-titanium-iron pre-alloy powder, obtain the powder raw material of the 3D printing nickel-titanium-iron alloy; Step S3: Use the selective laser melting forming process to layer-by-layer print the part entity of the 3D printing nickel-titanium-iron shape memory alloy from the powder raw material.

[0007] Optionally, the mass percentages of each component in the wide alloy composition range are as follows: titanium 43 - 50 wt.%, iron 0.01 - 4 wt.%, and the balance nickel.

[0008] Optionally, the gas atomization method is the electrode induction gas atomization method.

[0009] Optionally, the sieved nickel-titanium-iron pre-alloy powder is nickel-titanium-iron pre-alloy powder with a particle size of 15 - 53 μm and a sphericity greater than 95%.

[0010] Optionally, the parameters used in the selective laser melting forming process include a laser power of 80 - 200 W, a scanning speed of 300 - 1000 mm / s, a scanning spacing of 60 - 90 μm, a spot diameter of 40 - 80 μm, and a powder bed layer thickness of 20 - 40 μm; The selective laser melting forming process adopts a stripe zoning and interlayer rotation scanning strategy. The width of the laser scanning stripe is 4 - 6 mm, and the laser performs reciprocating scanning in each stripe; set the initial angle of the first layer of laser scanning to 0° - 60°, and specifically, 0° or 57° can be selected; the interlayer rotation angle of the laser scanning is 0° - 90°, and specifically, 0°, 45°, 67°, or 90° can be selected.

[0011] Optionally, before printing on the substrate using the selective laser melting forming process, preheat the substrate to a substrate temperature of 180 - 200 °C, fill with an inert gas to reduce the oxygen content in the working chamber to less than 200 ppm, and maintain the pressure in the working chamber 10 - 20 mbar greater than the atmospheric pressure.

[0012] Optionally, it further includes step S4 post - treatment; specifically, after completing the selective laser melting forming process, turn off the heating of the substrate, stop introducing the inert gas, reduce the pressure in the working chamber. After the substrate temperature drops below 70 °C, sweep and recycle the remaining powder, and take out the substrate with the part entity; after stress - relieving annealing the substrate with the printed part, separate the part entity from the substrate by wire cutting.

[0013] Optionally, the stress - relieving annealing includes heating at a rate of 5 - 10 °C / min to 150 - 200 °C for stress - relieving annealing, and after holding for 3 - 5 h, air - cooling to room temperature.

[0014] Optionally, step S4 further includes using sandpaper to polish and remove the oxide layer generated on the surface of the part entity after wire cutting.

[0015] In a second aspect, the present invention provides a high - strength 3D - printed nickel - titanium - iron shape - memory alloy, which is prepared by using the preparation method of the high - strength 3D - printed nickel - titanium - iron shape - memory alloy; the target component content of the 3D - printed nickel - titanium - iron shape - memory alloy includes the following mass percentages: titanium 45.4 wt.%, iron 2.2 wt.%, and the balance nickel.

[0016] Applying the technical solution of the present invention has at least the following beneficial effects: (1)The preparation method of a high-strength 3D printed Ni-Ti-Fe shape memory alloy provided by the present invention can prepare a 3D printed Ni-Ti-Fe shape memory alloy with a low phase transition temperature, high mechanical properties, and good forming performance. Specifically, in step S1 of the present invention, by constructing a thermodynamic database and combining solidification simulation and using an open-source code library to search for the Pareto optimal solution set of the second-phase Ti2Ni phase fraction and crack sensitivity factor, the target composition content of the 3D printed Ni-Ti-Fe shape memory alloy can be efficiently screened within a wide alloy composition range; the Ni-Ti-Fe shape memory alloy composition with the target composition content can be used to prepare a Ni-Ti-Fe shape memory alloy with no cracks on the surface, good forming performance, high strength, and low phase transition temperature under a wide range of 3D printing process parameters. Compared with the mixed powder formed by mechanically mixing nickel elemental powder, titanium elemental powder, and iron elemental powder (iron elemental powder is more easily oxidized and is likely to introduce impurity oxygen elements), the Ni-Ti-Fe pre-alloy powder prepared by gas atomization in the selective laser melting forming process of the present invention is more uniform, has better powder fluidity, and is not likely to introduce impurities, effectively avoiding the cracking of the alloy during the 3D printing process caused by uneven powder, impurity inclusion, and poor fluidity.

[0017] (2)Compared with the traditional nickel-rich low-temperature Ni-Ti shape memory alloy, the target composition content of the 3D printed Ni-Ti-Fe shape memory alloy provided by the present invention limits the mass percentage of iron to 2.2 wt.% (i.e., the atomic ratio of iron atoms is 2.1 at.%) at this content. The iron element can increase the stability of the austenite phase in the 3D printed Ni-Ti-Fe shape memory alloy, significantly reduce the phase transition temperature, and by adjusting the relative contents of nickel and titanium elements and optimizing the alloy solidification path, the melt channels between grains at the end of solidification are reduced, facilitating the backfilling of the liquid-phase melt, improving the liquid-phase supply capacity and the lap between grains, so as to reduce the tendency of hot cracks during alloy solidification and reduce the deterioration of the 3D printing forming performance caused by a relatively high iron element content. In addition, at this target composition content, the brittle Ti2Ni phase can be restricted from segregating at grain boundaries and the generation of metallurgical defects (such as hot cracks) can be reduced, thereby helping to improve the mechanical properties of the 3D printed Ni-Ti-Fe alloy. Moreover, the cost of iron element is relatively low, and adding a relatively high content of iron element helps to reduce the raw material cost of the 3D printed Ni-Ti-based shape memory alloy.

[0018] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings for a further detailed description of the present invention. Description of the Drawings

[0019] The accompanying drawings, which form a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It shows the change of the fraction of the second-phase Ti2Ni phase of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 1 under different titanium contents and iron contents; Figure 2 It shows the change of the crack sensitivity factor of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 1 under different titanium contents and iron contents; Figure 3 It is the compression property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 5; Figure 4 It is the phase transformation curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 5; Figure 5 It is the tensile property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 6; Figure 6 It is the tensile property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 7; Figure 7 It is the tensile property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 8; Figure 8 It is the tensile property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Example 9; Figure 9 It is the tensile property test curve of the 3D-printed Ni-Ti-Fe shape memory alloy in Comparative Example 1. Detailed Embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0021] Example 1:

[0022] A preparation method of a high-strength 3D-printed Ni-Ti-Fe shape memory alloy, comprising: Step S1: According to the nickel-titanium-iron system phase equilibrium data in the existing literature, use the Calphad method to establish a thermodynamic database for the nickel-titanium-iron ternary system at the nickel-titanium rich end; in the Pandat software, use Hill-Gulliver solidification simulation to perform solidification simulation on nickel-titanium-iron alloys within a wide alloy composition range in the thermodynamic database, and with the help of the Kou crack sensitivity factor model (see the existing literature Kou S. A criterion for cracking during solidification. Acta Materialia 2015;88:366-74), obtain the relationship between the second-phase volume fraction and the change of the crack sensitivity factor at different composition contents of nickel-titanium-iron alloys, see Figure 1 and Figure 2 ; Using the said relationship, use an open-source code library to search for the Pareto optimal solution set of the second-phase Ti2Ni phase fraction and the crack sensitivity factor (i.e., the composition content of nickel-titanium-iron alloy when the second-phase Ti2Ni phase fraction and the crack sensitivity factor reach the lowest Pareto values simultaneously), and then screen to obtain the target composition content of the 3D printed nickel-titanium-iron shape memory alloy, specifically 45.4 wt.% titanium, 2.2 wt.% iron, and the balance nickel; at this target composition content, it is possible to limit the segregation of the brittle Ti2Ni phase at the grain boundaries and reduce the generation of metallurgical defects (such as hot cracks), which helps to improve the mechanical properties of the 3D printed nickel-titanium-iron shape memory alloy; Step S2: First, obtain a nickel-titanium-iron alloy cylindrical ingot by melting the 3D printed nickel-titanium-iron shape memory alloy composition with the target composition content, and then obtain nickel-titanium-iron pre-alloy powder by gas atomization method. After vacuum drying the sieved nickel-titanium-iron pre-alloy powder, obtain the powder raw material for the 3D printed nickel-titanium-iron alloy; Step S3: Use the selective laser melting forming process to layer-by-layer print the powder raw material to obtain the part entity of the 3D printed nickel-titanium-iron shape memory alloy.

[0023] The nickel-titanium-iron system phase equilibrium data includes the phase equilibrium data of pure component nickel, pure component titanium, pure component iron, binary system nickel-titanium, binary system nickel-iron, binary system titanium-iron, and ternary system nickel-titanium-iron.

[0024] The phase equilibrium data of pure component nickel, pure component titanium, and pure component iron are from the existing literature Dinsdale A. SGTE data for pure elements. Calphad 1991;15:317-425.

[0025] The phase equilibrium data of the binary Ni-Ti system are from the existing literature: Povoden E, Cirstea D, Lang P, Wojcik T, Kozeschnik E. Thermodynamics of Ti–Ni shape memory alloys. Calphad 2013;41:128-39.

[0026] The phase equilibrium data of the binary Ni-Fe system are from the existing literature: Franke P, Seifert H. The influence of magnetic and chemical ordering on the phase diagram of Cr–Fe–Ni. Calphad 2011;35:148-54.

[0027] The phase equilibrium data of the binary Ti-Fe system are from the existing literature: Guo C, Li C, Zheng X, Du Z. Thermodynamic modeling of the Fe–Ti–V system. Calphad 2012;38:155-60.

[0028] The phase equilibrium data of the ternary Ni-Ti-Fe system are from the existing literature: De Keyzer J, Cacciamani G, Dupin N, Wollants P. Thermodynamic modeling and optimization of the Fe–Ni–Ti system. Calphad 2009;33:109-23.

[0029] In the wide alloy composition range, the mass percentages of the components are as follows: titanium 43 - 50 wt.%, iron 0.01 - 4 wt.%, and the balance nickel.

[0030] The Ni-Ti-Fe alloy ingot is purchased from Hunan Yuanji New Materials Co., Ltd.

[0031] The gas atomization method is the electrode induction gas atomization method, which can effectively reduce the introduction of impurity elements such as carbon and oxygen, meeting the requirement of low impurity content in the alloy powder for the SLM process; the specific process of electrode induction gas atomization is as follows: First, under the protective atmosphere of high-purity argon gas (≥99.99%), control the oxygen content in the entire gas atomization process to be less than 500 ppm. Carry out induction melting on the Ni-Ti-Fe alloy ingot (melting temperature 1600 °C, melting power 100 kW). Subsequently, at an atomization pressure of 6 MPa, the molten Ni-Ti-Fe metal melt passes through an alumina ceramic tube (nozzle aperture 3.5 mm) and is broken into small droplets and rapidly solidified into Ni-Ti-Fe pre-alloy powder. Finally, screen and vacuum-dry the obtained Ni-Ti-Fe pre-alloy powder to obtain the powder raw material for 3D printing Ni-Ti-Fe alloy. The powder raw material is by mass percentage: titanium 45.07%; iron 2.10%; carbon ≤0.03%; oxygen ≤0.08%, nitrogen ≤0.03%; copper ≤0.05%; aluminum ≤0.05%; manganese ≤0.05%; boron ≤0.05%; chromium ≤0.05%; nickel is the balance; the total of other elements ≤0.10%; except for titanium, iron and nickel, other elements are impurity elements introduced during processes such as melting and atomization.

[0032] The sieved Ni-Ti-Fe pre-alloy powder is Ni-Ti-Fe pre-alloy powder with a particle size of 15 - 53 μm and a sphericity greater than 95%.

[0033] The selective laser melting forming process includes debugging the 3D printing equipment, importing the three-dimensional slice model of Ni-Ti-Fe alloy into the 3D printing equipment, and setting the printing process parameters and laser scanning strategy; preheating the substrate and filling with argon to reduce the oxygen content in the working chamber, and then start printing and forming the Ni-Ti-Fe shape memory alloy; after each powder layer thickness of printing is completed, the substrate descends by one layer height, and the scraper levels the Ni-Ti-Fe alloy powder in the powder feeding chamber on the substrate again to perform the printing of the next powder layer. In this way, layer by layer, the entire part entity is printed out.

[0034] Specifically, the parameters adopted in the selective laser melting forming process include a laser power of 160 W, a scanning speed of 1000 mm / s, a scanning spacing of 80 μm, a spot diameter of 60 μm, and a powder layer thickness of 30 μm; The selective laser melting forming process adopts a scanning strategy of strip zoning and interlayer rotation. The width of the laser scanning strip is 4 mm, and the laser reciprocally scans in each strip. Set the initial angle of the first layer of laser scanning to be 57°, and thereafter, the interlayer rotation angle of laser scanning is 67°.

[0035] Before printing on the substrate using the selective laser melting forming process, to prevent introducing too much oxygen element and deteriorating the forming performance of the Ni-Ti-Fe alloy, evacuate the forming chamber to 10 -3After Pa, high-purity argon (>99.99%) is introduced for atmosphere protection, and this is repeated three times. In addition, to prevent warping and cracking at the bottom of the part, the substrate is preheated to a substrate temperature of 180 °C, and a chamfer with a radius of 1 mm is provided at the bottom of the part entity. During the 3D printing forming process, the air pressure in the working chamber is maintained at 10 - 20 mbar higher than the external atmospheric pressure, high-purity argon is filled to reduce the oxygen content in the working chamber to below 200 ppm, and the orientation of the part entity forms a 75° inclination angle with the advancing direction of the scraper.

[0036] Step S4 Post-treatment; Specifically, after completing the selective laser melting forming process, heating of the substrate is turned off, the inert gas supply is stopped, the air pressure in the working chamber is reduced. After the substrate temperature drops below 70 °C, the remaining powder is swept and recycled, and the substrate with the part entity is taken out; After stress relief annealing of the substrate with the printed part, the part entity is separated from the substrate by wire electrical discharge machining; The wire-cut part entity is immersed in epoxy resin for inlay sealing to obtain a sample. Subsequently, the inlaid sample is polished successively with 400-mesh, 600-mesh, 800-mesh, 1200-mesh, 1500-mesh, and 2000-mesh silicon carbide sandpapers until the wire-cut oxidation layer on the sample surface is removed and there are no obvious scratches, and then the sample is polished with silica polishing liquid on a SAPHIR 520 type automatic polishing machine.

[0037] The stress relief annealing is carried out in a KSL-1200X box furnace by heating at a rate of 5 °C / min to 200 °C for stress relief annealing. After holding for 4 h, it is air-cooled to room temperature.

[0038] Example 2:

[0039] The difference from Example 1 is that the laser power is 80 W and the scanning speed is 300 mm / s.

[0040] Example 3:

[0041] The difference from Example 1 is that the laser power is 200 W and the scanning speed is 1000 mm / s.

[0042] Example 4:

[0043] The difference from Example 1 is that the laser power is 140 W and the scanning speed is 800 mm / s.

[0044] Using the selective laser melting forming process parameters described in Examples 1 to 4 (i.e., 3D printing process parameters), 3D printed nickel-titanium-iron shape memory alloy square block parts with dimensions of 8 mm × 8 mm × 8 mm (length × width × height) were prepared respectively. The forming quality of each part entity in Examples 1 to 4 was detected, and the detection results are shown in Table 1. In Table 1, energy density = laser power / (scanning speed × scanning spacing × powder layer thickness), with the unit of J / mm 3 .

[0045] In the forming quality detection, the surface crack detection method is as follows: First, the bottom surface and side surfaces of the 3D printed nickel-titanium-iron shape memory alloy part entity are polished. Subsequently, an optical microscope of the LEICA DM4500P model is used to observe the bottom surface and side surfaces of the part entity, and the surface crack conditions of the part entity are detected and recorded.

[0046] The relative density detection method is as follows: First, use an electronic balance of the MSA324S-000-DU model to weigh the dry weight W of the 3D printed nickel-titanium-iron shape memory alloy block part entity 干燥 ; then, completely immerse the part entity in distilled water and weigh its mass W 水中 after being placed in distilled water. Then, according to Archimedes' principle, the following formula ρ 合金 = ρ 水 × W 干燥 / (W 干燥 - W 水中 ) is used to calculate the actual density of the 3D printed nickel-titanium-iron shape memory alloy. The theoretical relative density of the 3D printed nickel-titanium-iron shape memory alloy is 6.45 g / cm 3 , which is sourced from the existing literature "Yuan B, Ge J, Chen H, Pan J, Zhang L, Qi X. Printability and microstructure of Fe doped NiTi shape memory alloy fabricated by laser powder bed fusion. Mater Lett 2022;328:133099"; finally, dividing the actual density by the theoretical density can calculate the relative density of the 3D printed nickel-titanium-iron shape memory alloy block part entity.

[0047] The upper surface roughness detection method is as follows: Use a Contour GT-K type optical profiler to scan the upper surface of the 3D printed nickel-titanium-iron shape memory alloy block part entity to obtain the upper surface roughness of the part entity.

[0048] Table 1 Forming quality test results under different selective laser melting forming process parameters

[0049] From the data in Table 1, it can be seen that the 3D printed Ni-Ti-Fe shape memory alloy with no cracks on the surface and good forming quality can be prepared by using Examples 1 to 4 of the present invention. This shows that the target component content of the 3D printed Ni-Ti-Fe shape memory alloy screened by the present invention can be applied under a relatively wide 3D printing process parameter window.

[0050] Example 5: A 3D printed Ni-Ti-Fe shape memory alloy rectangular block part entity with dimensions of 50 mm × 10 mm × 10 mm (length × width × height) is prepared by using the 3D printing process parameters described in Example 1.

[0051] Using an Instron 8804 electro-hydraulic servo test system, the compression performance of the part entity prepared in Example 5 is tested. The test method is as follows: First, a cylindrical compression sample with a diameter of 8 mm and a height of 10 mm is machined from the part entity prepared in Example 5 by wire electrical discharge machining; subsequently, the surface of the cylindrical compression sample is polished to remove the oxide layer generated during the wire cutting process; furthermore, the cylindrical compression sample is subjected to uniaxial compression at a strain rate of 1.6×10 -4 ·s -1 , and the changes in stress and strain are recorded until the sample fractures. The test results are shown in Figure 3 . Using a NETZSCH 204 differential scanning calorimeter to detect the phase transformation behavior of the part entity prepared in Example 5. The test method is as follows: First, take 15 mg of the sample, use an empty aluminum crucible as the reference crucible, and heat from room temperature at a heating rate of 10℃·min -1 to 100℃ and hold for 5 minutes; subsequently, cool from 100℃ to -150℃ at a cooling rate of 10℃·min -1 , and record the heat absorption and heat release of the sample during the cooling process; furthermore, heat from -150℃ to 100℃ at a heating rate of 10℃·min -1 , and record the heat absorption and heat release of the sample during the heating process, and the test ends. The detection results are shown in Figure 4 .

[0052] See Figure 3, the properties of the NiTiFe shape memory alloy prepared in Example 5 are a compressive strength of 2670 MPa and a compressive strain of 45%. Compared with the 3D-printed NiTiFe shape memory alloy in the existing literature (Yuan B, Ge J, Zhang L, Chen H, Wei L, Zhou Y, et al. Laser powder bed fusion of NiTiFe shape memory alloy via pre-mixed powder: microstructural evolution, mechanical and functional properties. Rare Metals 2024;43:2300-16) with a compressive strength of 2156 MPa and a compressive strain of 35%, the compressive strength and compressive strain properties of the NiTiFe shape memory alloy prepared in Example 5 are significantly improved.

[0053] See Figure 4 , when the NiTiFe shape memory alloy prepared in Example 5 is cooled from 100 °C to -150 °C, no martensitic phase transformation is detected in the differential scanning calorimetry test, indicating that the martensitic transformation temperature is lower than -150 °C. Compared with the 3D-printed NiTiFe alloy with an iron element addition of 0.52 wt.% in the existing literature (Xi R, Jiang H, Li G, Zhang Z, Zhao G, Vanmeensel K. et al. Effect of Fe addition on the microstructure, transformation behaviour and superelasticity of NiTi alloys fabricated by laser powder bed fusion. Virtual Phys Prototyp 2022;18:2126376.) with the lowest martensitic transformation starting temperature of -50 °C, it shows that the NiTiFe shape memory alloy with an iron element addition of 2.2 wt.% in Example 5 has a lower martensitic transformation temperature.

[0054] The density of the NiTiFe shape memory alloy prepared in Example 5 is 99.2%, the surface roughness is 6.97 μm, and there are no cracks on the surface.

[0055] Example 6: Different from Example 1, the laser power is 180 W, the scanning speed is 1000 mm / s, and the laser energy density is 83.3 J / mm 3 .

[0056] Example 7: The same 3D printing process parameters as those in Example 1 are adopted.

[0057] Example 8: Different from Example 1, the laser power is 160 W, the scanning speed is 900 mm / s, and the laser energy density is 74.1 J / mm 3 .

[0058] 3D printed nickel-titanium-iron shape memory alloy rectangular block parts with dimensions of 50 mm × 10 mm × 10 mm (length × width × height) are respectively prepared by using the 3D printing process parameters described in Examples 6 to 8. The tensile properties of each part entity are tested by using an MTS E44.104 electronic universal testing machine. The testing method is as follows: First, for each part entity, an I-shaped tensile test piece with a gauge length of 15 mm, a gauge width of 2 mm, and a thickness of 2 mm is processed by wire electrical discharge machining; subsequently, the surface of the I-shaped tensile test piece is polished to remove the oxide layer generated during the wire cutting process; furthermore, the I-shaped tensile test piece is uniaxially tensioned at a strain rate of 1.6×10 -4 ·s -1 , and the changes in stress and strain are recorded until the sample breaks. The test results are shown in Figures 5 - 7 .

[0059] See Figures 5 - 7 , the tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 6 is 895 MPa; the tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 7 is 842 MPa; the tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 8 is 915 MPa; compared with the highest tensile strength of 736 MPa of the 3D printed nickel-titanium-iron shape memory alloy in the existing literature (Xi R, Jiang H, Li G, Zhang Z, Zhao G, Vanmeensel K. et al. Effect of Fe addition on the microstructure, transformation behaviour and superelasticity of NiTi alloys fabricated by laser powder bed fusion. Virtual Phys Prototyp 2022;18:2126376.), the tensile strengths of the 3D printed nickel-titanium-iron shape memory alloys prepared in Examples 6 to 8 adopted in the present invention are all significantly higher than 736 MPa, showing excellent mechanical properties.

[0060] In addition, the density of the 3D printed Ni-Ti-Fe shape memory alloy prepared in Example 6 is 99.6%, the surface roughness is 4.83 μm, and there are no cracks on the surface. The density of the 3D printed Ni-Ti-Fe shape memory alloy prepared in Example 7 is 99.1%, the surface roughness is 6.44 μm, and there are no cracks on the surface. The density of the 3D printed Ni-Ti-Fe shape memory alloy prepared in Example 6 is 99.5%, the surface roughness is 4.66 μm, and there are no cracks on the surface.

[0061] Example 9: Different from Example 1, the laser power is 140 W, the scanning speed is 1000 mm / s, and the laser energy density is 58.3 J / mm 3 .

[0062] Comparative Example 1: Different from Example 9, steps S3 and S4 are cancelled, and the gas atomization method in step S2 is not adopted. Instead, a Ni-Ti-Fe alloy cylindrical ingot is directly obtained by melting.

[0063] Using the 3D printing process parameters described in Example 9 and the ingot scheme of Comparative Example 1, rectangular block part entities with dimensions of 50 mm × 10 mm × 10 mm (length × width × height) are respectively prepared. An MTS E44.104 electronic universal testing machine is used to perform tensile property tests on each part entity. The test method is as follows: First, for each part entity, an I-shaped tensile piece with a gauge length of 15 mm, a gauge width of 2 mm, and a thickness of 2 mm is processed by wire electrical discharge machining; subsequently, the surface of the I-shaped tensile piece is polished to remove the oxide layer generated during wire cutting; furthermore, the specimen is uniaxially stretched at a strain rate of 1.6×10 -4 ·s -1 , and the changes in stress and strain are recorded until the sample breaks. The test results are shown in Figures 8 - 9 .

[0064] See Figures 8 - 9 , the tensile strength of the Ni-Ti-Fe alloy formed by the ingot scheme of Comparative Example 1 is 993 MPa, and the elongation is 1.15%. For the 3D printed Ni-Ti-Fe shape memory alloy prepared in Example 9, the density is 99.8%, the surface roughness is 6.59 μm, the tensile strength is 1094 MPa, and the elongation is 3.21%. Compared with Comparative Example 1, the 3D printed Ni-Ti-Fe shape memory alloy prepared in Example 9 has a higher tensile strength and a greater elongation, and its comprehensive mechanical properties are excellent. This proves that the 3D printed Ni-Ti-Fe shape memory alloy prepared by the present invention has good forming performance and significantly improved mechanical properties.

[0065] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high-strength 3D-printed nickel-titanium-iron shape memory alloy, characterized in that, Including: Step S1: Establish a thermodynamic database for the Ni-rich Ti-end Ni-Ti-Fe ternary system; perform solidification simulation on Ni-Ti-Fe alloys within a wide alloy composition range in the thermodynamic database, and obtain the relationship between the second-phase volume fraction and the crack sensitivity factor of Ni-Ti-Fe alloys with different composition contents by means of a crack sensitivity factor model; utilize the relationship to search for the Pareto optimal solution set of the second-phase volume fraction and the crack sensitivity factor using an open-source code library, and then screen to obtain the target composition content of the 3D printed Ni-Ti-Fe shape memory alloy. Step S2: First, obtain a Ni-Ti-Fe alloy ingot by melting the 3D printed Ni-Ti-Fe shape memory alloy composition with the target composition content, and then obtain Ni-Ti-Fe pre-alloy powder by gas atomization. After vacuum drying the sieved Ni-Ti-Fe pre-alloy powder, obtain the powder raw material of the 3D printed Ni-Ti-Fe alloy. Step S3: Use the selective laser melting forming process to layer-print the powder raw material to obtain the part entity of the 3D printed Ni-Ti-Fe shape memory alloy.

2. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 1, wherein, The mass percentages of each component in the wide alloy composition range are as follows: titanium 43 - 50 wt.%, iron 0.01 - 4 wt.%, and the balance nickel.

3. The preparation method of the high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, wherein The gas atomization method is the electrode induction gas atomization method.

4. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 1, wherein, The sieved Ni-Ti-Fe pre-alloy powder is Ni-Ti-Fe pre-alloy powder with a particle size of 15 - 53 μm and a sphericity greater than 95%.

5. The preparation method of the high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, wherein, The parameters used in the selective laser melting forming process include a laser power of 80 - 200 W, a scanning speed of 300 - 1000 mm / s, a scanning spacing of 60 - 90 μm, a spot diameter of 40 - 80 μm, and a powder bed thickness of 20 - 40 μm. The selective laser melting forming process adopts a stripe zoning and interlayer rotation scanning strategy, the stripe width of laser scanning is 4 - 6 mm, and the laser performs reciprocating scanning in each stripe. Set the initial angle of the first layer of laser scanning to 0° - 60°, and the interlayer rotation angle of laser scanning to 0° - 90°.

6. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 1, wherein, Before printing on the substrate using the selective laser melting forming process, preheat the substrate to a substrate temperature of 180 - 200 °C, fill with an inert gas to reduce the oxygen content in the working chamber to below 200 ppm, and maintain the air pressure in the working chamber to be 10 - 20 mbar higher than the atmospheric pressure.

7. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 6, characterized in that, It also includes step S4 post-treatment; specifically, after completing the selective laser melting forming process, turn off the heating of the substrate, stop introducing the inert gas, reduce the air pressure in the working chamber. After the substrate temperature drops below 70 °C, sweep and recycle the remaining powder, and take out the substrate with the part entity; perform stress relief annealing on the substrate with the printed part, and then separate the part entity from the substrate by wire cutting.

8. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 7, characterized in that, The stress relief annealing includes heating at a rate of 5 - 10 °C / min to 150 - 200 °C for stress relief annealing, and after holding for 3 - 5 h, air-cooling to room temperature.

9. The preparation method of the high-strength 3D printed nickel-titanium-iron shape memory alloy according to claim 7, characterized in that, Step S4 also includes using sandpaper to polish and remove the oxide layer generated on the surface of the part entity after wire cutting.

10. A high-strength 3D printed nickel-titanium-iron shape memory alloy, characterized in that, Prepared by using the preparation method of high-strength 3D printed nickel-titanium-iron shape memory alloy according to any one of claims 1 to 9; the target component content of the 3D printed nickel-titanium-iron shape memory alloy includes the following mass percentages: titanium 45.4 wt.%, iron 2.2 wt.%, and the balance nickel.

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