Electron beam additive manufacturing method of NiTiNb shape memory alloy

Abstract

The invention relates to the technical field of NiTiNb additive manufacturing, and discloses an electron beam additive manufacturing method for NiTiNb shape memory alloy, which comprises the following steps of: performing three-dimensional modeling on a target component, and performing layer-by-layer slicing treatment; niTiNb alloyed welding wires are used as raw materials, a TC4 plate is used as a substrate, electron beam additive manufacturing process parameters are set, and additive manufacturing is implemented according to path planning. The NiTiNb alloy component which is uniform in microstructure, high in density, high in compressive strength and excellent in ductility can be prepared.

Description

Technical Field

[0001] This invention relates to the field of NiTiNb additive manufacturing technology, specifically to an electron beam additive manufacturing method for NiTiNb shape memory alloys. Background Technology

[0002] NiTi shape memory alloys, with their unique shape memory effect, superelasticity, excellent wear and corrosion resistance, superior biocompatibility, high strength, and low density, have shown broad application potential in aerospace, energy engineering, and biomedicine. However, with the increasing demands for material strength in some applications, traditional NiTi shape memory alloys are no longer sufficient to meet these requirements. To address this challenge, ternary NiTi-based shape memory alloys have been developed by introducing a third element (such as Nb, V, or Hf) into NiTi shape memory alloys. These new alloys not only inherit the original advantages of NiTi shape memory alloys but also achieve significant improvements in various properties. Some ternary NiTi-based shape memory alloys exhibit outstanding compressive strength. Taking NiTiNb shape memory alloy as an example, its high compressive strength and strong plastic deformation capacity have made it a hot topic in scientific research and are expected to play an important role in harsh working environments.

[0003] In traditional casting processes, NiTi-based shape memory alloys are prone to reactions between Ti and elements such as C and O during casting, leading to the formation of TiC, TiO, and other impurities. Furthermore, their poor machinability (such as cracking, burr formation, accelerated tool wear, and low machining accuracy) hinders their further development and application. Selective laser melting (SLM), based on the principle of "discrete collection," can achieve high-quality forming of metal parts in a fully argon-protected atmosphere, which can solve some of the problems faced by NiTi-based shape memory alloys in traditional casting and machining processes. However, this technology has strict requirements for precise control of laser power and scanning speed (too low a laser energy density will prevent the processed part from effectively adhering to the substrate; too high a energy density will easily cause severe warping problems, thus interrupting the printing process). Even after optimizing the process parameters, NiTi+3Cu parts still show numerous cracks along the horizontal direction on their sides when observed under a scanning electron microscope.

[0004] Existing literature CN119843091A discloses a NiTiNb shape memory alloy and its preparation method. The method involves uniformly mixing a Ni source, a Ti source, and an Nb source to obtain a mixed powder; cold-pressing the mixed powder to obtain an alloy green blank; and sintering the alloy green blank using the following parameters: under a vacuum of 10⁻³ to 10⁻⁵ Pa, first heating at 5–10 °C / min to 580–620 °C and holding for 0.5–2 h, then heating at 1–2 °C / min to 680–720 °C and holding for 2–4 h, and finally heating at 1–2 °C / min to 1130–1150 °C and holding for 1–6 h to obtain a sintered sample, thus obtaining the NiTiNb shape memory alloy (tensile fracture stress strength 263–709 MPa, elongation 3.5–12.6%). Existing literature CN119159096A discloses a NiTiNb shape memory alloy and its in-situ alloying preparation method. The method involves 3D modeling of the target component and slicing it. Pre-treatment is performed on the printing filament and substrate. NiTi alloy wire and pure Nb wire are used as printing filaments, and the wire feed angle, extension length, and relative positions of the two wires are set. Specifically, the wire feed angle of the pure Nb wire is greater than that of the NiTi alloy wire, and the extension length of the pure Nb wire from the guide nozzle to the electron beam central axis is greater than that of the NiTi alloy wire. Electron beam fused wire additive manufacturing parameters are set, and 3D printing is performed based on the sliced ​​data. The printing process parameters are: accelerating voltage 60kV, focusing current 1030-1250mA, cathode current 24-28A, beam current density 70-120mA, scanning mode elliptical, amplitude X 3-8mm, amplitude Y 1-3mm, and vacuum degree 9.5×10⁻⁶. -3 The substrate moving speed is 280-400 mm / min, and the movement path is a reciprocating straight line. However, the compressive strength of the NiTiNb shape memory alloy prepared using the method in document CN119843091A is only 263-709 MPa, and the elongation is only 3.5-12.6%. The NiTiNb shape memory alloy prepared using document CN119159096A shows that its microstructure is mainly composed of NiTi matrix and eutectic structure, with Ti2Ni particles distributed in the middle. Its compressive strength and plastic deformation capacity are also insufficient, and it is necessary to further optimize its mechanical properties. Summary of the Invention

[0005] To further optimize the compressive strength and plastic deformation capability of NiTiNb shape memory alloys, this invention provides an electron beam additive manufacturing method for NiTiNb shape memory alloys, comprising the following steps: S1: Perform 3D modeling of the target component and then slice it layer by layer; S2: NiTiNb alloyed welding wire is selected as the raw material for additive manufacturing, and TC4 plate is used as the substrate; S3: Set the process parameters for electron beam additive manufacturing, and carry out additive manufacturing according to the set path plan to obtain NiTiNb alloy components.

[0006] Preferably, in S3, the accelerating voltage is 60±4kV, the filament current is 15±2A, the focusing current is 1380±10mA, the beam current is 46±1mA, the printing speed is 600±5 mm / min, and the filament feeding speed is 5500±100mm / min.

[0007] Preferably, in the NiTiNb alloyed welding wire, the mass ratio of Ni:Ti:Nb is 54.3:36.1:9.6.

[0008] Preferably, in S3, the wire extension length during the wire feeding process is 5-15 mm, and the distance between the welding wire and the substrate is 1-3 mm.

[0009] Preferably, in S3, the interlayer cooling time is 180±5s, and the vacuum degree is <6×10⁻⁶. -2 Pa.

[0010] Preferably, the electron beam scanning frequency is 400±5Hz, the scanning mode is elliptical, and the sway amplitude is 200%.

[0011] Beneficial effects: This invention yields NiTiNb alloy components with uniform microstructure, high density, high compressive strength, and excellent elongation. The microstructure consists of a large amount of eutectic structure, which, according to surface scanning results, is rich in Nb. The matrix phase is mainly composed of Ni and Ti elements. The synergistic structure of various specific morphologies of the β-Nb phase enhances the high compressive strength and elongation of the NiTiNb alloy components. The NiTiNb alloy components exhibit an ultimate tensile strength ≥3600MPa and an elongation ≥48% at room temperature, demonstrating ultra-high compressive strength and good plasticity. This invention has the advantages of low impurity content, high material utilization, and high deposition efficiency, avoiding additional impurity absorption during the preparation process. It solves the problem of difficult preparation of complex geometrical NiTi-based shape memory alloys using existing methods, and also has the advantages of short processing cycles and low cost. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the electron beam additive manufacturing of NiTiNb alloy components in this invention; Figure 2 This is a microstructure and elemental distribution diagram of the NiTiNb alloy sample obtained in Example 1; Figure 3 This is a diagram of the compressive stress-strain curve of the NiTiNb alloy sample at room temperature in Example 1; Figure 4 yes Figure 2A magnified view of a local area in the image; Figure 5 This is a microstructure distribution diagram of the NiTiNb alloy sample obtained in Comparative Example 3; The reference numerals in the attached figures include: worktable 1, substrate 2, deposition layer 3, electron beam 4, substrate clamping device 5, welding torch 6, NiTiNb alloying wire 7. Detailed Implementation Example 1

[0013] An electron beam additive manufacturing method for NiTiNb shape memory alloys includes the following steps: Step 1: Clean the surface of the NiTiNb alloy wire with a diameter of 0.8 mm (mass ratio of Ni54.3-Ti36.1-Nb9.6) with alcohol. Clean the surface of the substrate 2 with alcohol to remove surface impurities and contaminants. Polish the TC4 substrate 2 with dimensions of 200 mm × 150 mm × 15 mm with 80-mesh SiC sandpaper, and then clean it with acetone to remove the surface oxide layer and oil stains. Step 2: Fix the substrate 2 to the worktable 1 using the substrate clamping device 5, and adjust the worktable 1 to a suitable height, while preventing it from touching the welding gun 6 during the process. Step 3: Feed the NiTiNb alloyed wire 7 with a diameter of 0.8 mm into the welding gun 6 through the wire feeding mechanism. During the wire feeding process, adjust the wire extension length and the distance from the substrate 2, wherein the wire extension length is 10 mm and the distance from the substrate is 2 mm. Step 4: Close the vacuum chamber door and evacuate to the required vacuum level (<6×10). -2 After Pa), the program settings are performed, with the filament current set to 15 A, the accelerating voltage to 60 kV, the focusing current to 1380 mA, the beam current to 46 mA, the printing speed to 560 mm / min, and the filament feed speed to 5500 mm / min. Step 5: Set the scanning frequency to 400Hz, the yaw amplitude to 200%, the scanning mode to elliptical, and the planned path to a cyclical straight line, that is, the end point of the previous deposition layer 3 is the starting point of the next layer, and so on, with the interlayer cooling time controlled to 120-180s. Step 6: When the number of printed layers exceeds 25, the printed length is 1200 mm, and the height is 55 mm, the test ends. After printing, allow the parts to cool naturally in the vacuum chamber for 8 hours, then open the door to remove them.

[0014] The resulting workpiece was machined into three cylindrical samples with a diameter of 4 mm and a height of 8 mm using wire EDM. The surfaces were then smoothed with SiC sandpaper. Subsequently, a universal tensile testing machine was used to test their mechanical properties at room temperature, with a compression rate of 0.5 mm / min until sample failure. The compressive stress-strain curves were obtained, as shown below. Figure 3 As shown, the compressive strength of the NiTiNb alloy sample was measured to be 3623.35 MPa, and the elongation after fracture was 48.6%, indicating that the NiTiNb alloy sample prepared in the example has high density and exhibits ultra-high compressive strength and good plasticity matching at room temperature.

[0015] The microstructure morphology of the stable region of the sample was observed using transmission electron microscopy, and the results are as follows: Figure 2 As shown: the microstructure consists of a large number of eutectic structures. Figure 2 Part a shows the microstructure magnified to 200 nm, where the gray matrix phase is the NiTi phase and the β-Nb phase consists of multiple white strip-like structures arranged at intervals. Figure 2 Part c shows the microstructure magnified to 50 nm. The gray matrix phase is the NiTi phase, and the β-Nb phase is uniformly distributed within the NiTi phase, exhibiting a significant hindering effect on dislocations. The β-Nb phase itself contains numerous fine striations arranged in a continuous spindle-shaped structure (e.g., Figure 4 and Figure 2 As shown in section c), it significantly increases the stability of the β-Nb phase in the NiTi phase, and greatly improves the compressive strength and plastic deformation capacity of the NiTiNb alloy; Figure 2 The middle d section shows the microstructure magnified 10 nm. The β-Nb phase consists of spherical particles surrounded by a gray NiTi matrix. Surface scan results reveal the elemental distribution, showing that the eutectic structure is rich in Nb, while the matrix phase is mainly composed of Ni and Ti.

[0016] Comparative Example 1: An electron beam additive manufacturing method for NiTiNb shape memory alloy, referring to Example 1, the difference being: the focusing current is 1250mA and the beam current density is 70mA. In this example, the compressive strength of the NiTiNb alloy sample was measured to be 2247MPa, and the elongation after fracture was 28.9%; in the microstructure magnified 50nm, the β-Nb phase itself has no fine striations and presents an irregular granular structure.

[0017] Comparative Example 2: An electron beam additive manufacturing method for NiTiNb shape memory alloy, referring to Example 1, except that the focusing current is 1000mA and the beam current density is 120mA. In this example, the compressive strength of the NiTiNb alloy sample was measured to be 1898.6MPa, and the elongation after fracture was 19.5%. In the microstructure magnified to 50nm, the β-Nb phase itself has no fine striations and presents an irregular granular structure.

[0018] Comparative Example 3: An electron beam additive manufacturing method for NiTiNb shape memory alloy, referring to Example 1, except that the focusing current is 1300 mA and the beam current density is 65 mA. In this example, the compressive strength of the NiTiNb alloy sample was measured to be 2647 MPa, and the elongation after fracture was 32.6%; in the microstructure after magnification of 50 nm, such as... Figure 5 As shown, a large number of pores were formed in the microstructure, and large-sized Ti2Ni particles (which are plate-like harmful phases) were observed.

[0019] Example 2: An electron beam additive manufacturing method for NiTiNb shape memory alloy, referring to Example 1, except that the focusing current is 1370 mA and the beam current density is 45 mA. In this example, the compressive strength of the NiTiNb alloy sample was measured to be 3601 MPa, and the elongation after fracture was 48.5%. In the microstructure magnified to 50 nm, the β-Nb phase itself has a large number of fine stripes distributed in a continuously arranged spindle-shaped structure.

[0020] In this invention, a NiTiNb shape memory alloy prepared by electron beam additive manufacturing using NiTiNb alloyed wire under specific process conditions was unexpectedly discovered. This alloy not only has a specific microstructure, but also has a significantly higher compressive strength than existing superior NiTiNb shape memory alloys (approximately 2200 MPa, NiTiNb shape memory alloy prepared by elemental powder reaction sintering), exhibiting excellent performance.

Claims

1. A method for electron beam additive manufacturing of NiTiNb shape memory alloy, characterized in that, Includes the following steps: S1: Perform 3D modeling of the target component and then slice it layer by layer; S2: NiTiNb alloyed welding wire is selected as the raw material for additive manufacturing, and TC4 plate is used as the substrate; S3: Set the process parameters for electron beam additive manufacturing, and carry out additive manufacturing according to the set path plan to obtain NiTiNb alloy components.

2. The electron beam additive manufacturing method for NiTiNb shape memory alloy according to claim 1, characterized in that: In S3, the accelerating voltage is 60±4kV, the filament current is 15±2A, the focusing current is 1380±10mA, the beam current is 46±1mA, the printing speed is 600±5 mm / min, and the filament feed speed is 5500±100mm / min.

3. The electron beam additive manufacturing method for NiTiNb shape memory alloy according to claim 2, characterized in that: In NiTiNb alloyed welding wire, the mass ratio of Ni:Ti:Nb is 54.3:36.1:9.

6.

4. The electron beam additive manufacturing method for NiTiNb shape memory alloy according to claim 3, characterized in that: In S3, the wire extension length during the wire feeding process is 5-15 mm, and the distance between the welding wire and the substrate is 1-3 mm.

5. The electron beam additive manufacturing method for NiTiNb shape memory alloy according to claim 4, characterized in that: In S3, the interlayer cooling time is 180±5s, and the vacuum degree is <6×10. -2 Pa.

6. The electron beam additive manufacturing method for NiTiNb shape memory alloy according to claim 5, characterized in that: The electron beam scanning frequency is 400±5Hz, the scanning mode is elliptical, and the sway amplitude is 200%.

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