A kind of sheet structure shape memory alloy and its 4D printing preparation method

Abstract

The application discloses a kind of laminated structure shape memory alloy and 4D printing preparation method thereof.The preparation method adds synchronous magnetic field in 4D printing process, reasonably collocates shape memory alloy powder with magnetic field and laser energy density, adopts the 4D printing of shape memory alloy using unidirectional scanning strategy and printing strategy of perpendicular magnetic induction line and scanning path, and finally obtains laminated structure shape memory alloy.The laminated structure shape memory alloy prepared by 4D printing of the application has excellent functional characteristics, the magnetic field adding method is simple, the microstructure can be controlled without post-processing, the cost is low, suitable for mass production and standardized production, and has good popularization and application scene.

Description

Technical Field

[0001] The present invention belongs to the field of shape memory alloys and additive manufacturing, and specifically relates to a laminar shape memory alloy and a 4D printing preparation method thereof. Background Art

[0002] Shape memory alloys (SMAs), as unique metallic materials, possess exceptional functional properties such as excellent shape memory effects and superelasticity. After being loaded and inelastically deformed, they can recover their shape during specific temperature changes, demonstrating the shape memory effect. Alternatively, they can withstand large strains at a certain temperature without plastic deformation, demonstrating superelasticity. Therefore, SMAs hold broad application prospects in aerospace, biomedicine, precision instruments, industrial construction, and other fields. To fabricate complex geometries and customized alloy parts, 4D printing additive manufacturing techniques, such as laser powder bed melting and laser energy deposition, can be used to produce near-net-shape SMAs and their components. However, due to the large temperature gradients and high cooling rates during 4D printing, most printed alloy parts exhibit a typical columnar grain structure along the build direction, resulting in anisotropic part properties, significantly limiting their application. Existing optimization methods, primarily heat treatment, alloy composition design, and surface laser processing, have achieved some improvements in alloy microstructure and properties, but remain subject to challenges such as high cost and uncontrollable microstructure and properties.

[0003] Based on the path of process optimization, microstructure control, and performance improvement, researchers have proposed a new non-contact control method, namely, introducing external energy fields (ultrasonic fields, magnetic fields, and electric fields) into welding and additive manufacturing equipment. Studies have shown that the magnetic field, as an easily implemented external energy field, can be introduced into laser welding processes to change the flow state of the metal's charged fluid, thereby improving the weld structure, joint properties, and stability of the welding process. Studies using magnetic fields as an external energy field to assist powder bed melting in the preparation of aluminum alloys and nickel-based superalloys have shown that grain refinement, texture reduction, and improved overall mechanical properties are achieved. This is because the added magnetic field can introduce thermoelectromagnetic forces into the flowing metal melt, affecting the temperature gradient and solute distribution, and further affecting the solidification process of the metal melt. However, to date, there have been no reports of using 4D printing coupled with a magnetic field and laser energy field to prepare shape memory alloys with new microstructures and improved performance. Summary of the Invention

[0004] In order to overcome the deficiencies of the 4D printing preparation forming process of the shape memory alloy in the prior art, and improve the shape memory deformation degree and stability of the shape memory alloy, the primary purpose of the present application is to provide a 4D printing preparation method of a laminated structure shape memory alloy. The preparation method comprises the addition of a magnetic field assisted structure, a magnetic field and laser scanning strategy coupling 4D printing forming and other key steps, and solves the problems of current 4D printing shape memory alloy phase distribution regulation and functional characteristic stability.

[0005] The second purpose of the present application is to provide a laminated structure shape memory alloy.

[0006] The primary purpose of the present application is achieved by the following technical solutions:

[0007] A 4D printing preparation method of a laminated structure shape memory alloy, comprising the following preparation steps:

[0008] (1) adding a synchronous magnetic field assisted structure

[0009] The magnetic field generating device is arranged below the laser generator or the substrate, and the addition of the synchronous magnetic field assisted structure in the 4D printing process is realized by synchronous movement of the magnetic field or synchronous enhancement of the magnetic field strength;

[0010] (2) magnetic field and laser scanning strategy coupling 4D printing

[0011] The synchronous magnetic field assisted structure in step (1) is used to match the shape memory alloy powder with the magnetic field and the laser energy density, and the 4D printing of the shape memory alloy is carried out by using the one-way scanning strategy and the coupling mode of the magnetic induction line perpendicular to the scanning path, so as to obtain the laminated structure shape memory alloy.

[0012] Preferably, the addition of the synchronous magnetic field assisted structure in step (1) comprises two ways,

[0013] a. Synchronous motion magnetic field: the magnetic field generating device is placed below the laser generator, and moves synchronously with the laser, so that the relative position of the printing pool and the magnetic field is unchanged;

[0014] b. Synchronous enhancement magnetic field: the magnetic field generating device is placed below the substrate, and the position is fixed, the voltage of the magnetic field generating device is changed, so that the magnetic field strength of the printing pool is constant.

[0015] Preferably, the magnetic field strength in step (1) is 0.05-1T.

[0016] Preferably, the voltage of the magnetic field generating device in step (1) is 2.6-220V.

[0017] Preferably, the laser energy density range in step (2) is 40-300J / mm 3 .

[0018] Preferably, the process parameters of the 4D printing in step (2) are laser power 50-250 W, laser scanning speed 100-1400 mm / s, scanning interval 60-100 μm, and powder laying thickness 30-50 μm.

[0019] Preferably, the unidirectional scanning strategy in step (2) is that the scanning path is kept unidirectional, and the scanning directions of adjacent scanning paths are opposite.

[0020] Preferably, the magnetic induction line and scanning path perpendicular strategy in step (2) is that the magnetic induction line direction is longitudinal, and kept perpendicular to the scanning path and scanning plane.

[0021] Preferably, when the laser energy density is the same in the 4D printing in step (2), the magnetic field strength and the laser scanning speed are inversely proportional.

[0022] Preferably, the shape memory alloy in step (2) is one of nickel-titanium-based shape memory alloy, copper-based shape memory alloy, and iron-based shape memory alloy.

[0023] Preferably, the lamellar structure shape memory alloy in step (2) is that the martensite layer and the austenite layer are alternated, the width of the martensite layer is 150-300 μm, the width of the austenite layer is 100-200 μm, and the grain size is 3-50 μm.

[0024] The second object of the application can be achieved by the following technical scheme:

[0025] A lamellar structure shape memory alloy is prepared by the 4D printing preparation method.

[0026] The lamellar structure shape memory alloy of the application realizes the addition of synchronous magnetic field in the 4D printing process by adopting the magnetic field assisted structure, matches the shape memory alloy powder with the magnetic field and the laser energy density, adopts the unidirectional scanning strategy and the coupling mode of the magnetic induction line and the scanning path perpendicular to each other to perform the 4D printing of the shape memory alloy, and finally obtains the lamellar structure shape memory alloy.

[0027] The principle of the present application is that the 4D printing preparation method of the lamellar structure shape memory alloy of the present application is coupled with the magnetic field and the laser, the induced current generated by the molten pool interacts with the magnetic field, a Lorentz force with an angle to the original direction of the molten pool flow is formed, the shape of the molten pool is changed and deflected, the temperature gradient and the cooling speed of the molten pool are changed, and the phase transition temperature of different regions is effectively controlled. The deflection of the molten pool is closely related to the magnetic field strength, direction, and laser scanning path and energy density, so that the molten pool has similar shape change and angular deflection, and the synchronous change of the magnetic field is required. The present application synchronously adds the magnetic field by coupling the movement of the magnetic field generating device with the movement of the substrate, or by calculating the energized voltage between each layer according to the Biot-Savart law and Ohm's law, to ensure that the metal melt of each layer in the printing process is stably affected by the magnetic field. Under the action of the one-way reciprocating scanning strategy and the magnetic field, the deflection directions of adjacent molten pools are opposite, so that the arrangement of the molten pools presents an ordered alternation of high-heat and low-heat regions, thereby realizing the ordered distribution of austenite phase and martensite phase in the shape memory alloy, and finally obtaining a shape memory alloy part with a lamellar structure in which the martensite layers and the austenite layers are alternately arranged, which is conducive to the application optimization and large-scale production of functional characteristics.

[0028] The present application has the following advantages and beneficial effects compared with the prior art:

[0029] (1) The synchronous magnetic field addition proposed in the present application adopts mechanical multi-axis synchronous control and electrical control of the magnetic field device, and maintains the synchronization of the magnetic field position or the magnetic field strength with the forming layer in the 4D printing process;

[0030] (2) The 4D printing of the present application which couples the magnetic field with the laser scanning strategy adopts the concept of in-situ molten pool control, which expands the process adjustable window of laser additive manufacturing;

[0031] (3) The shape memory alloy prepared by the present application is compared with the shape memory alloy prepared by the traditional process and the 4D printing without additional energy field, the magnetic field is used as an external physical field, and the force and energy are used to contactlessly act on the material solidification process, the solidification structure and the alloy composition distribution are affected without changing the alloy composition and the solidification process. The present application proposes a new microstructure design idea, and obtains a shape memory alloy with a lamellar structure having alternating performance at a microscale;

[0032] (4) The preparation process of the present application is simple and easy to operate, the designed structure can be obtained without post-processing for the prepared parts, the stability is good, large-scale industrialization can be realized in engineering, the production line is shortened, the delivery capacity is improved, and the present application has good popularization and application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1Backscattered electron diffraction pattern (left) and metallographic image (right) of nickel-titanium shape memory alloy prepared by magnetic field-assisted 4D printing in Example 1 of the present invention;

[0034] Figure 2 Backscattered electron diffraction pattern (left) and metallographic image (right) of nickel-titanium shape memory alloy prepared by 4D printing without magnetic field assistance in comparative example 1 of the present invention;

[0035] Figure 3 Graphs showing compressive stress-strain curves of nickel-titanium shape memory alloys prepared by 4D printing with magnetic field assistance (solid line) in Example 1 of the present invention and without magnetic field assistance (dashed line) in Comparative Example 1;

[0036] Figure 4 Graphs showing tensile stress-strain curves of nickel-titanium shape memory alloys prepared by 4D printing with magnetic field assistance (solid line) in Example 1 of the present invention and without magnetic field assistance (dashed line) in Comparative Example 1;

[0037] Figure 5 Graphs showing two-way memory effect of nickel-titanium shape memory alloys prepared by 4D printing with magnetic field assistance (solid line) in Example 1 of the present invention and without magnetic field assistance (dashed line) in Comparative Example 1. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0039] Example 1

[0040] Step 1: Add synchronous magnetic field auxiliary structure

[0041] Synchronous motion magnetic field addition: Place the magnetic field generator under the laser generator and move it synchronously with the laser to keep the relative position of the printed molten pool and the magnetic field unchanged. The magnetic field intensity is 0.5T, the voltage of the magnetic field generator is 26V, and the direction of the magnetic flux lines is longitudinal, perpendicular to the scanning path and scanning plane.

[0042] Step 2: Magnetic field and laser scanning strategy coupled 4D printing

[0043] Adopt the synchronous magnetic field assisted structure of step 1 and select the laser energy density of 200J / mm 3 The process parameters are laser power 60W, laser scanning speed 100mm / s, scanning spacing 100μm, powder thickness 30μm, and Ni 50.65 Ti 49.35 The alloy powder is formed into a nickel-titanium shape memory alloy with a lamellar structure by a 4D printing device using a unidirectional scanning strategy and a coupling method in which the magnetic flux lines are perpendicular to the scanning path; the lamellar structure Ni 50.65 Ti 49.35(at.%, all the following are atomic fractions) The microstructure of the alloy is as follows Figure 1 As shown in Figure 2, the thicknesses of the martensite layer (black part) and the austenite layer (gray part) are 208.3 μm and 145.9 μm respectively. The experimental results of the shape memory effect show that after 10 compression trainings under constant stress thermal cycle, the two-way memory effect of nickel-titanium shape memory alloy can reach 0.97% (see Figure 5 solid line curve); the compressive stress-strain curve is as follows Figure 4 As shown by the solid line, the fracture strength and compressive strain are as high as 3571MPa and 38.2% respectively. Figure 4 As shown by the solid lines, the tensile strength and elongation are as high as 578 MPa and 7.03%, respectively.

[0044] Example 2

[0045] Step 1: Add synchronous magnetic field auxiliary structure Synchronous enhanced magnetic field addition: Place the magnetic field generator under the substrate, fix the position unchanged, change the voltage of the magnetic field generator, so that the magnetic field intensity of the printing molten pool is constant, and realize the addition of synchronous magnetic field auxiliary structure of 4D printing. The magnetic field intensity is 0.05T, the voltage of the magnetic field generator is 2.6~11.2V, and the direction of the magnetic flux line is longitudinal, which is perpendicular to the scanning path and scanning plane.

[0046] Step 2: Magnetic field and laser scanning strategy coupled 4D printing

[0047] The synchronous magnetic field assisted structure of step 1 is used, and the laser energy density is selected to be 59.5J / mm 3 The process parameters are laser power 200W, laser scanning speed 1400mm / s, scanning spacing 60μm, powder thickness 40μm, and Ni 50.65 Ti 49.35 The alloy powder was formed into a layered nickel-titanium shape memory alloy using a 4D printing device using a unidirectional scanning strategy and a coupling method in which magnetic flux lines are perpendicular to the scanning path. The thicknesses of the martensite and austenite layers were 158.2 μm and 113.7 μm, respectively. The compressive fracture strength and compressive strain reached 3217 MPa and 37.3%, respectively, while the tensile strength and elongation were 523 MPa and 6.95%, respectively. After 10 cycles of constant stress thermal cycling compression training, the two-way memory effect of the nickel-titanium-based shape memory alloy reached 0.89%.

[0048] Example 3

[0049] Step 1: Add synchronous magnetic field auxiliary structure

[0050] Synchronous magnetic field addition: the magnetic field generating device is placed under the substrate, the position is fixed, the voltage of the magnetic field generating device is changed, so that the magnetic field intensity of the printing melt pool is constant, the synchronous magnetic field assisted structure of 4D printing is realized, the magnetic field intensity is 1T, the voltage of the magnetic field generating device is 52-220V, and the magnetic induction line direction is longitudinal, which is perpendicular to the scanning path and the scanning plane;

[0051] Step two: 4D printing of coupling of magnetic field and laser scanning strategy

[0052] The synchronous magnetic field assisted structure of step one is adopted, the laser energy density is 156.3J / mm 3 , the process parameters are laser power 250W, laser scanning speed 400mm / s, scanning interval 80μm, and powder laying thickness 50μm, and the Cu 71.10 Al 23.85 Mn 4.08 Nb 0.97 alloy powder is formed into a copper-based shape memory alloy with a lamellar structure by using a 4D printing device with a unidirectional scanning strategy and a coupling mode of perpendicular magnetic induction line and scanning path. The thicknesses of the martensite layer and the austenite layer are 278.2μm and 118.7μm respectively. The compression fracture strength and the compression strain are as high as 1752MPa and 17.5% respectively, the tensile tensile strength and the elongation are 485MPa and 10.43% respectively, and after 10 times of compression training of constant stress thermal cycle, the double-way memory effect of the copper-based shape memory alloy can reach 0.87%.

[0053] Example 4

[0054] Step one: adding synchronous magnetic field assisted structure

[0055] Synchronous motion magnetic field addition: the magnetic field generating device is placed under the laser generator and moves synchronously with the laser, so that the relative position of the printing melt pool and the magnetic field is unchanged, the magnetic field intensity is 0.3T, the voltage of the magnetic field generating device is 15.6V, and the magnetic induction line direction is longitudinal, which is perpendicular to the scanning path and the scanning plane;

[0056] Step two: 4D printing of coupling of magnetic field and laser scanning strategy

[0057] The synchronous magnetic field assisted structure of step one is adopted, the laser energy density is 225J / mm 3 , the process parameters are laser power 180W, laser scanning speed 200mm / s, scanning interval 100μm, and powder laying thickness 40μm, and Fe 62.75 Mn 19.04 Si 11.17 Cr 7.04The alloy powder is formed into the ferromagnetic shape memory alloy with a lamellar structure by a 4D printing device with a one-way scanning strategy and a coupling mode of the magnetic induction lines being perpendicular to the scanning path. The thicknesses of the martensite layer and the austenite layer are 223.5 μm and 167.2 μm respectively; the compressive fracture strength and the compressive strain are as high as 1926 MPa and 24.7% respectively, the tensile tensile strength and the elongation are 507 MPa and 6.28% respectively, and the double-way memory effect of the ferromagnetic shape memory alloy can reach 0.83% after 10 times of compression training of constant stress thermal cycle.

[0058] Example 5

[0059] Step one: adding a synchronous magnetic field auxiliary structure synchronous motion magnetic field: the magnetic field generating device is placed below the laser generator and moves synchronously with the laser, so that the relative position of the printing molten pool and the magnetic field is unchanged, the magnetic field strength is 0.4 T, the voltage of the magnetic field generating device is 20.8 V, and the magnetic induction line direction is longitudinal, which is perpendicular to the scanning path and the scanning plane;

[0060] Step two: coupling of the magnetic field and the laser scanning strategy 4D printing

[0061] The synchronous magnetic field auxiliary structure of step one is adopted, the laser energy density is 145.8 J / mm 3 , the process parameters are laser power 70 W, laser scanning speed 200 mm / s, scanning interval 80 μm, and powder laying thickness 30 μm, and the Ni 36.5 Co 13.5 Mn 35 Ti 14.1 Gd 0.9 alloy powder is formed into the ferromagnetic shape memory alloy with a lamellar structure by a 4D printing device with a one-way scanning strategy and a coupling mode of the magnetic induction lines being perpendicular to the scanning path. The thicknesses of the martensite layer and the austenite layer are 223.5 μm and 167.2 μm respectively; the compressive fracture strength and the compressive strain are as high as 1926 MPa and 24.7% respectively, the tensile tensile strength and the elongation are 507 MPa and 6.28% respectively, and the double-way memory effect of the ferromagnetic shape memory alloy can reach 0.83% after 10 times of compression training of constant stress thermal cycle.

[0062] Comparative example 1

[0063] The 4D printing is selected with a laser energy density of 200 J / mm 3 , the process parameters are laser power 60 W, laser scanning speed 100 mm / s, scanning interval 100 μm, and powder laying thickness 30 μm, and the Ni 50.65 Ti 49.35 alloy powder is formed into the nickel-titanium alloy by a selective laser melting 4D printing device. The Ni 50.65 Ti 49.35The microstructure of the alloy is shown in FIG. 1, and the martensite and austenite are distributed disorderly without lath structure. Figure 1 The stress-strain curve of compression is shown in FIG. 2, and the fracture strength and compression strain are 3195 MPa and 35.3% respectively. Figure 3 The stress-strain curve of tension is shown in FIG. 3, and the tensile strength and elongation are 490 MPa and 6.92% respectively. Figure 4 The experimental results of shape memory effect show that the double-way memory effect of the nickel-titanium-based shape memory alloy is 0.75% after 10 times of compression training of constant stress thermal cycle (see the curve of dotted line in FIG. 4). Figure 5

[0064] Comparative Example 2

[0065] The 4D printing is selected with a laser energy density of 156.3 J / mm 3 , and the process parameters are a laser power of 250 W, a laser scanning speed of 400 mm / s, a scanning interval of 80 μm, and a powder laying thickness of 50 μm. 71.10 Al 23.85 Mn 4.08 Nb 0.97 The copper-based shape memory alloy powder is formed by a selective laser melting 4D printing equipment. The microstructure of the Cu 71.10 Al 23.85 Mn 4.08 Nb 0.97 The alloy is prepared by a selective laser melting process without adding a magnetic field, and the martensite and austenite of the copper-based shape memory alloy are distributed disorderly without lath structure. The compression fracture strength and compression strain are 1623 MPa and 14.8% respectively, the tensile strength and elongation are 457 MPa and 8.59% respectively, and the double-way memory effect of the nickel-titanium-based shape memory alloy can reach 0.63% after 10 times of compression training of constant stress thermal cycle.

[0066] By comparing Example 1 and Comparative Example 1, the nickel-titanium-based shape memory alloy with disordered microstructure prepared by 4D printing is regulated to the nickel-titanium-based shape memory alloy with lath structure by introducing a synchronous magnetic field in the present patent, and the thicknesses of the martensite layer and the austenite layer are 208.3 μm and 145.9 μm respectively. In the compression experiment, the compression strength and compression strain are increased from 3195 MPa and 35.3% to 3571 MPa and 38.2% respectively. In the tension experiment, the tensile strength and elongation are increased from 490 MPa and 6.92% to 578 MPa and 7.03% respectively. After 10 times of compression training of constant stress thermal cycle, the double-way memory effect of the nickel-titanium-based shape memory alloy is increased from 0.75% to 0.97%.

[0067] ​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, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A 4D printing preparation method for a laminar shape memory alloy, characterized in that: The method comprises the following preparation steps: (1) Add synchronous magnetic field auxiliary structure The magnetic field generating device is placed under the laser generator or under the substrate, and the addition of a synchronous magnetic field auxiliary structure in the 4D printing process is achieved through the synchronous movement of the magnetic field or the synchronous enhancement of the magnetic field intensity; There are two ways to add the synchronous magnetic field auxiliary structure: a. Synchronous motion magnetic field: Place the magnetic field generating device under the laser generator and move it synchronously with the laser to keep the relative position of the printed molten pool and the magnetic field unchanged; b. Synchronous magnetic field enhancement: Place the magnetic field generator under the substrate, fix its position, and change the voltage of the magnetic field generator to keep the magnetic field intensity of the printing melt pool constant; (2) Magnetic field and laser scanning strategy coupling 4D printing Using the synchronous magnetic field auxiliary structure in step (1), the shape memory alloy powder is matched with the magnetic field and the laser energy density, and the 4D printing of the shape memory alloy is performed by adopting a unidirectional reciprocating scanning strategy and a coupling method in which the magnetic flux lines are perpendicular to the scanning path, thereby obtaining a lamellar structure shape memory alloy with alternating martensite layers and austenite layers, wherein the thickness of the martensite layer is 150-300 μm and the thickness of the austenite layer is 100-200 μm; The unidirectional reciprocating scanning strategy is: the scanning path remains unidirectional, and the scanning directions of adjacent scanning paths are opposite; The coupling mode of the magnetic flux lines being perpendicular to the scanning path is as follows: the direction of the magnetic flux lines is longitudinal and remains perpendicular to the scanning path and the scanning plane.

2. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: The magnetic field strength in step (1) is 0.05 ~ 1 T.

3. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: The voltage of the magnetic field generating device in step (1) is 2.6 ~ 220 V.

4. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: The laser energy density in step (2) is in the range of 40~300 J / mm 3 .

5. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: The process parameters of the 4D printing described in step (2) are laser power 50~250 W, laser scanning speed 100~1400 mm / s, scanning spacing 60~100 μm, and powder thickness 30~50 μm.

6. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: When the laser energy density used for 4D printing in step (2) is the same, the magnetic field intensity is inversely proportional to the laser scanning speed.

7. The 4D printing preparation method of the laminar structure shape memory alloy according to claim 1, characterized in that: The shape memory alloy in step (2) is one of nickel-titanium-based shape memory alloy, copper-based shape memory alloy, and iron-based shape memory alloy.

8. A lamellar shape memory alloy, characterized in that: Prepared according to the 4D printing preparation method according to any one of claims 1 to 7.

Images