Additive manufacturing of high phase transition temperature high elongation nickel-titanium alloy and preparation method and application

Abstract

The application provides additive manufacturing of high phase transition temperature and high elongation nickel-titanium alloy, a preparation method and application, and belongs to the technical field of additive manufacturing of metal materials.The alloy contains, by weight percentage, Ni: 54.2% to 54.8%, N≤0.030%, H≤0.005%, O≤0.050%, C≤0.050%, Fe≤0.050%, CeO2: 0.1% to 1%, and the balance is Ti;the martensite phase transition temperature reaches above 70 DEG C, and the elongation is above 8%.The preparation method is to provide a nickel-titanium alloy powder with specific components, to add CeO2 nano powder in two batches;to mix by using a specific ball milling process;to perform additive manufacturing by a layered variable strategy scanning mode in a low-oxygen environment.The application solves the problems of low phase transition temperature and poor elongation of traditional nickel-titanium alloy, and is suitable for high-temperature service parts of aerospace vehicles, aircraft mixed flow devices and driving variable wing fields.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology for metallic materials, specifically relating to an additive manufacturing method for high phase transformation temperature and high elongation nickel-titanium alloys, and their applications. Background Technology

[0002] Nickel-titanium alloys are intelligent materials integrating sensing and actuation, possessing unique shape memory effects and superelasticity, making them the most widely used shape memory materials currently. From an application perspective, the phase transformation temperatures of traditional nickel-titanium alloys are mostly concentrated between -50℃ and 50℃, only meeting low-to-medium temperature requirements such as human environments and ambient temperature control in industrial settings. However, in medium-to-high temperature scenarios (typically above 70℃) such as aerospace (e.g., engine piping heat sealing, satellite deployment mechanisms), automotive industry (e.g., flexible joints in high-temperature exhaust systems), and energy equipment (e.g., high-temperature valve actuators), nickel-titanium alloys with low phase transformation temperatures will prematurely stabilize into the austenitic phase at service temperatures, losing their temperature-triggered shape recovery ability and failing to achieve their designed functions. Furthermore, components relying on the shape memory effect of nickel-titanium alloys often need to withstand non-ideal external forces or dynamic deformations during service, requiring the material to also be resistant to deformation and fracture. Therefore, it is necessary to improve the phase transformation temperature and elongation of nickel-titanium alloys to precisely adapt their functional characteristics to a wider range of application requirements, thereby unlocking their application value in medium-to-high temperature intelligent equipment and components for extreme environments.

[0003] The functional properties of nickel-titanium alloys originate from the reversible thermoelastic martensitic transformation between the austenitic and martensitic phases, and the transformation temperature determines the temperature range in which the shape memory effect occurs. The martensitic transformation temperature of nickel-titanium alloys is highly sensitive to compositional changes. For Ni-rich nickel-titanium alloys, the martensitic transformation temperature decreases by approximately 10-20 K for every 0.1 at% increase in Ni atoms. This characteristic dictates that the Ni content in nickel-titanium alloys with high martensitic transformation temperatures cannot be too high. Ti-rich nickel-titanium alloys have even higher martensitic transformation temperatures than Ni-rich alloys, but because the components responsible for the shape memory effect in nickel-titanium alloys are distributed near equiatomic ratios, excessively low Ni content will cause the alloy to lose its shape memory effect. Therefore, designing suitable powder compositions and printing processes to achieve synergistic control of high transformation temperature and shape memory effect in nickel-titanium alloys remains a significant challenge.

[0004] Currently, nickel-titanium alloys produced using laser powder bed melting technology generally exhibit poor elongation (around 5%), failing to meet practical application requirements. Rare earth oxides, as alloying elements, possess high surface activity, easily interrupting grain growth to obtain stable compounds, promoting grain refinement and dispersion strengthening of precipitated phases, effectively improving the plasticity of nickel-titanium alloys. Simultaneously, appropriate amounts of rare earth oxides can form solid solutions with Ni, effectively increasing the martensitic transformation temperature of nickel-titanium alloys. This makes them ideal additives for simultaneously improving both the transformation temperature and elongation of nickel-titanium alloys. However, controlling the amount and method of rare earth oxide addition currently faces challenges. Excessive addition leads to oxide agglomeration (forming micron-sized inclusions), becoming crack initiation points; insufficient addition results in insufficient nucleation sites, making it difficult to alter the coarse columnar crystal structure, thus failing to improve mechanical properties. Furthermore, in terms of precise matching of rare earth elements with NiTi alloys, rare earth elements can form compounds with Ni, reducing the Ni / Ti ratio of the alloy, thereby increasing the transformation temperature of the nickel-titanium alloy. However, when excessive rare earth oxides are added, the rare earth elements combine with Ti, increasing the Ni / Ti ratio of the alloy and consequently lowering the phase transformation temperature of the nickel-titanium alloy. The optimal amount of rare earth oxides varies depending on the Ni content in the nickel-titanium alloy powder. Currently, there is no specific quantitative description of the relationship between different nickel-titanium alloy compositions and the optimal amount of rare earth oxides.

[0005] In terms of specific addition methods, nickel-titanium alloys and nano-rare earth oxides usually need to be mixed and ball-milled. Due to the size difference between the two (micron-sized alloy particles and nano-sized rare earth oxide particles) and the "high activity and easy agglomeration" characteristics of nano-rare earth oxides, rare earth oxides are prone to agglomeration and local enrichment. A reasonable ball milling process is required to reduce the probability of agglomeration and ensure that rare earth oxides are uniformly distributed in the nickel-titanium alloy matrix.

[0006] Besides incorporating rare earth oxides, designing a suitable scanning strategy is also an effective way to improve the mechanical properties and printability of additively manufactured nickel-titanium alloys. Currently, the most widely used scanning strategy is the strip scanning strategy, which divides a single-layer region into continuous long strips and fills them with unidirectional or bidirectional parallel paths. This eliminates the need for frequent direction switching and crossing of block gaps, improving the printability of additively manufactured nickel-titanium alloys. However, this scanning strategy suffers from high internal stress in the printed samples. The checkerboard scanning strategy divides a single-layer region into independent blocks with perpendicular paths between adjacent blocks, forming a cross-reinforcing structure. This significantly reduces anisotropy and shrinkage stress in the printed samples. However, because the region is divided into multiple independent small blocks with perpendicular scanning paths between adjacent blocks, small splicing gaps inevitably occur between blocks, reducing local micro-forming accuracy and causing poor printability. Designing a reasonable scanning strategy is a key factor in achieving both printability and excellent mechanical properties in additively manufactured nickel-titanium alloys.

[0007] To address the aforementioned issues, this invention designs a specific nickel-titanium alloy powder composition and uses methods such as thermodynamic phase diagram calculations and molecular dynamics simulations to calculate the quantitative relationship between Ni content and CeO2 nanopowder addition. The relationship is then verified and corrected using experimental data. Based on this quantitative relationship, CeO2 nanopowder is added to the nickel-titanium alloy powder in two equal batches. Alcohol is used as a dispersant to reduce agglomeration. Combined with a ball milling process suitable for this mixed powder, a unique layered variable strategy (odd-layer checkerboard scanning strategy + even-layer strip scanning strategy), and a printing process, a nickel-titanium alloy with high phase transformation temperature and high elongation is manufactured. Such a method has rarely been reported domestically or internationally. Summary of the Invention

[0008] To address the shortcomings of existing technologies and the need for a wide temperature range application of nickel-titanium alloys, this invention provides an additive manufacturing method for high-phase-transformation-temperature and high-elongation nickel-titanium alloys, along with its preparation and applications. One objective of this invention is to improve the martensitic phase transformation temperature of additive-manufactured nickel-titanium alloys. This is achieved by designing specific nickel-titanium alloy powder compositions and combining them with CeO2 nanoparticles in a quantitatively appropriate manner, thus synergistically controlling the high phase transformation temperature and shape memory effect of the nickel-titanium alloy. Simultaneously, the addition of CeO2 nanoparticles in a quantitatively appropriate manner refines the grain structure of the NiTi matrix phase and disperses and strengthens the precipitated phases, effectively improving the mechanical properties of the nickel-titanium alloy. Another objective of this invention is to achieve the efficient preparation of high-phase-transformation-temperature and high-elongation nickel-titanium alloys. This is achieved by optimizing the ball milling process, additive manufacturing process parameters, and employing a layered variation strategy (odd-layer checkerboard scanning strategy + even-layer strip scanning strategy) to reduce internal stress and improve printability, thereby simultaneously enhancing the phase transformation temperature and elongation properties of additive-manufactured nickel-titanium alloys to a high level while achieving efficient preparation.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A high phase transformation temperature and high elongation nickel-titanium alloy for additive manufacturing, comprising the following components by weight percentage: Ni: 54.2%~54.8%, N≤0.030%, H≤0.005%, O≤0.050%, C≤0.050%, Fe≤0.050%, CeO2: 0.1%~1%, with the balance being Ti; and the alloy has a martensitic phase transformation temperature of ≥70℃ and an elongation of ≥8%.

[0011] A method for preparing a nickel-titanium alloy with high phase transformation temperature and high elongation by additive manufacturing includes the following steps:

[0012] (1) Provide nickel-titanium alloy powder, the composition of which by weight percentage is: Ni: 54.2%~54.8%, N≤0.030%, H≤0.005%, O≤0.050%, C≤0.050%, Fe≤0.050%, balance is Ti;

[0013] (2) Add CeO2 nanopowder to the nickel-titanium alloy powder, with a total addition amount of 0.1%~1% by weight;

[0014] (3) The mixed powder is ball-milled;

[0015] (4) The powder after ball milling is printed using additive manufacturing technology.

[0016] Furthermore, in step (1), the nickel-titanium alloy powder is prepared by gas atomization powder preparation process, and the powder particle size is 15μm~53μm with a sphericity of 0.96 or higher.

[0017] Furthermore, in step (2), CeO2 nanopowder is added in two equal batches; the CeO2 nanopowder has a particle size of 40nm~60nm, a purity of ≥99.99%, and a sphericity of 0.99.

[0018] Furthermore, in step (2), the total amount of CeO2 nanopowder added is determined according to the Ni content in the nickel-titanium alloy powder, specifically CeO2%=1.5×Ni%-81.2%, where Ni is 54.2%~54.8% and CeO2 is 0.1%~1%.

[0019] Furthermore, in step (3), an all-around planetary ball mill is used for ball milling. The ball milling parameters are: horizontal rotation speed 80r / min~120r / min, vertical rotation speed 10r / min~20r / min, ball weight ratio 0.9~1.1:1, and ball ratio of large ball: medium ball: small ball 10%:30%:60%, where the diameter of the large ball is 10mm, the diameter of the medium ball is 5mm, and the diameter of the small ball is 2mm; the ball milling time is 1h~1.5h, the single forward and reverse rotation time is 15min, the interval standby time is 15min, the entire ball milling process is protected by argon gas, and alcohol is used as a dispersant.

[0020] Furthermore, in step (4), the oxygen content in the forming chamber during the printing process is not higher than 50 ppm.

[0021] Furthermore, in step (4), a layered variable strategy is used for printing, that is, odd-numbered layers use a chessboard scanning strategy and even-numbered layers use a strip scanning strategy; wherein the block size of the chessboard scanning strategy is 2mm~5mm and the strip width of the strip scanning strategy is 2mm~5mm.

[0022] Furthermore, in step (4), the printing power is 170W~230W, the scanning speed is 1000mm / s~1200mm / s, the scanning interval is 80μm~120μm, the single-layer thickness is 30μm~40μm, the scanning angle is 45°~90°, and the volume energy density is 50J / mm².3 ~80J / mm 3 The linear energy density is 0.17 J / mm to 0.2 J / mm.

[0023] This invention also provides an application of additively manufactured high phase transformation temperature and high elongation nickel-titanium alloys in high-temperature service components of aerospace vehicles, aircraft mixing devices, and variator wings driven by truss structures.

[0024] The advantages and beneficial effects of this invention are:

[0025] 1. High phase transition temperature

[0026] The nickel-titanium alloy manufactured in this invention has a high phase transition temperature because its printing powder is a nickel-titanium alloy titanium-rich powder with a specific composition. At the same time, CeO2 nanopowder that conforms to the relationship CeO2%=1.5×Ni%-81.2% is added to form Ce solid solution, thereby further increasing its phase transition temperature.

[0027] 2. High elongation

[0028] The CeO2 nanopowder added in this invention, conforming to the relationship CeO2%=1.5×Ni%-81.2%, can improve the plasticity of additively manufactured nickel-titanium alloys through grain refinement and precipitate dispersion strengthening. Combined with specific ball milling, printing processes and unique layered variation strategies, it can significantly improve the elongation of nickel-titanium alloys while achieving functional properties such as shape memory effect.

[0029] 3. High density

[0030] The nickel-titanium alloy manufactured by this invention exhibits high density. During the preparation process, densification of the nickel-titanium alloy was achieved by adding CeO2 nanopowder in two batches, conforming to the relationship CeO2%=1.5×Ni%-81.2%, and by precisely controlling the ball milling and printing parameters. In particular, the added CeO2 nanopowder helps reduce the formation of porosity and defects, further enhancing the material's density. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 The image shows the microstructure of the mixed powder from Example 1 after ball milling for 1 hour.

[0033] Figure 2 The image shows the elemental distribution of the mixed powder from Example 1 after ball milling for 1 hour. (a) is the elemental distribution of Ni, (b) is the elemental distribution of Ce, (c) is the elemental distribution of O, and (d) is the elemental distribution of Ti.

[0034] Figure 3 This is a schematic diagram of the hierarchical variable strategy method in Example 2.

[0035] Figure 4 The DSC curve of the printed sample in Example 2.

[0036] Figure 5 The tensile curve of the printed sample in Example 3. Detailed Implementation

[0037] The preparation method of the present invention will be described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0038] Example 1

[0039] This embodiment uses nickel-titanium alloy powder with specific composition, adds CeO2 nanopowder in two batches in equal amounts to achieve a total CeO2 nanopowder content that matches the relationship between the nickel-titanium alloy powder composition and the CeO2 addition amount, and uses a specific ball milling process and selective laser melting technology to print a nickel-titanium alloy with high phase transformation temperature and high elongation. The specific steps are as follows:

[0040] Step 1: Prepare titanium-rich nickel-titanium alloy powder using an air atomization powder preparation process. The powder contains the following chemical composition by weight percentage: Ni: 54.2%, N: 0.030%, H: 0.005%, O: 0.04%, C: 0.035%, Fe: 0.040%, and Ti as the balance. The powder particle size is 15~53μm, and the sphericity is above 0.96.

[0041] Step 2: Based on the established quantitative relationship CeO2%=1.5×Ni%-81.2%, substitute the Ni content of 54.2% into the calculation to determine that the total amount of CeO2 nanopowder added is 0.1% of the weight of the nickel-titanium alloy powder.

[0042] Step 3: Add half (i.e., 0.05%) of CeO2 nanoparticles to the nickel-titanium alloy powder provided in Step 1. The CeO2 nanoparticles have a particle size of 40-60 nm, a purity of ≥99.99%, and a sphericity of 0.99. Alcohol is used as a dispersant, and argon gas is introduced by gas replacement, with argon gas protection throughout the process.

[0043] Step 4: Use an omnidirectional planetary ball mill to ball mill the mixed powder. The ball milling parameters are: horizontal rotation speed 80 r / min, vertical rotation speed 10 r / min, ball weight ratio 0.9:1, and ball ratio of large balls: medium balls: small balls 10%:30%:60% (large balls diameter 10 mm, medium balls diameter 5 mm, small balls diameter 2 mm); the ball milling time is 1 hour, the single forward and reverse rotation time is 15 minutes, the interval standby time is 15 minutes, and argon gas protection is used throughout the ball milling process.

[0044] Step 5: After ball milling, open the milling jar under argon protection and dry the powder (temperature 80℃, time 2h, vacuum environment). Then, repeat steps 3 and 4, adding the remaining half of the CeO2 nanoparticles and ball milling again. After the above steps, the sphericity of the mixed powder reaches 0.99, and its microstructure is as follows... Figure 1 As shown, the element distribution is as follows Figure 2 As shown, this indicates that CeO2 is evenly distributed.

[0045] Step 6: Use 3D design software to create 3D models of nickel-titanium alloy blocks measuring 10mm×10mm×10mm and 10mm×10mm×60mm.

[0046] Step 7: The ball-milled mixed powder is 3D printed using a selective laser melting additive manufacturing system. During the printing process, the oxygen content in the forming chamber is consistently kept below 50 ppm. A layer-by-layer variable strategy is employed: odd-numbered layers use a checkerboard scanning strategy (block size 2 mm), and even-numbered layers use a strip scanning strategy (strip width 2 mm). Other printing parameters are: printing power 170 W, scanning speed 1000 mm / s, scanning interval 80 μm, single-layer thickness 40 μm, and scanning angle 66.7°. The calculated volume energy density is 53.125 J / mm². 3 The linear energy density is 0.17 J / mm.

[0047] The high phase transformation temperature and high elongation nickel-titanium alloy prepared in this embodiment has a martensitic phase transformation temperature of 74℃. Tensile test results show an elongation of 8.1% and a density of 99.9%. Both the phase transformation temperature and elongation reach high levels.

[0048] Example 2

[0049] The main difference between this embodiment and Example 1 lies in the Ni content, CeO2 addition amount, and some process parameters in the nickel-titanium alloy powder. The specific steps are as follows:

[0050] Step 1: Provide nickel-titanium alloy powder, which contains the following chemical composition by weight percentage: Ni: 54.6%, N: 0.027%, H: 0.004%, O: 0.050%, C: 0.050%, Fe: 0.037%, Ti balance. The powder particle size is 15~53μm, and the sphericity is greater than 0.96.

[0051] Step 2: Based on the formula CeO2%=1.5×Ni%-81.2%, substitute the Ni content of 54.6% into the calculation to determine that the total amount of CeO2 nanopowder added is 0.7% of the weight of the nickel-titanium alloy powder.

[0052] Step 3: Add CeO2 nanopowder in two equal batches, with 0.35% added in each batch. The CeO2 nanopowder has a particle size of 40~60nm, a purity of ≥99.99%, and a sphericity of 0.99.

[0053] Step 4: Use an omnidirectional planetary ball mill for ball milling. The ball milling parameters are: horizontal rotation speed 100 r / min, vertical rotation speed 20 r / min, ball weight ratio 1:1, and ball ratio of large balls: medium balls: small balls 10%:30%:60% (large balls diameter 10 mm, medium balls diameter 5 mm, small balls diameter 2 mm). The ball milling time is 1.5 h, the single forward and reverse rotation time and the interval standby time are both 15 min. Argon gas protection is used throughout the process, and alcohol is used as the dispersant.

[0054] Step 5: After ball milling, open the milling jar under argon protection and dry the powder (temperature 80℃, time 2h, vacuum environment). Then, repeat steps 3 and 4, adding the remaining half of the CeO2 nanoparticles and ball milling again. After the above steps, the sphericity of the mixed powder can reach 0.99.

[0055] Step 6: Use 3D design software to create 3D models of nickel-titanium alloy blocks measuring 10mm×10mm×10mm and 10mm×10mm×60mm.

[0056] Step 7: Print the ball-milled mixed powder under conditions where the oxygen content in the forming chamber does not exceed 50 ppm. A layered variable strategy is adopted, namely an odd-layer checkerboard scanning strategy (block size 3mm) + an even-layer strip scanning strategy (strip width 3mm). A schematic diagram of this strategy can be seen below. Figure 3 The printing power was 200W, the scanning speed was 1000mm / s, the scanning interval was 100μm, the single-layer thickness was 40μm, and the scanning angle was 45°. The calculated volume energy density was 50J / mm². 3 The linear energy density is 0.2 J / mm.

[0057] The DSC test curve of the nickel-titanium alloy prepared in this embodiment is as follows: Figure 4As shown, the martensitic phase transformation temperature is 75.4℃. Tensile tests indicate an elongation of 8.4% and a density of 99.8%.

[0058] Example 3

[0059] The main difference between this embodiment and Embodiments 1 and 2 lies in the Ni content, CeO2 addition amount, and some process parameters in the nickel-titanium alloy powder. The specific steps are as follows:

[0060] Step 1: Provide nickel-titanium alloy powder, which contains the following chemical composition by weight percentage: Ni: 54.8%, N: 0.024%, H: 0.003%, O: 0.035%, C: 0.030%, Fe: 0.050%, Ti balance. The powder particle size is 15~53μm, and the sphericity is greater than 0.96.

[0061] Step 2: Based on the formula CeO2%=1.5×Ni%-81.2%, substitute the Ni content of 54.8% into the calculation to determine that the total amount of CeO2 nanopowder added is 1% of the weight of the nickel-titanium alloy powder.

[0062] Step 3: Add CeO2 nanopowder in two equal batches, with 0.5% added in each batch. The CeO2 nanopowder has a particle size of 40~60nm, a purity of ≥99.99%, and a sphericity of 0.99.

[0063] Step 4: Perform ball milling using an omnidirectional planetary ball mill. The ball milling parameters are: horizontal rotation speed 120 r / min, vertical rotation speed 15 r / min, ball weight ratio 1.1:1, and ball ratio of large balls: medium balls: small balls 10%:30%:60% (large balls diameter 10 mm, medium balls diameter 5 mm, small balls diameter 2 mm). The ball milling time is 1.5 h, with a single forward and reverse rotation time and a standby time interval of 15 min. Argon gas protection is used throughout the process, and alcohol is used as the dispersant.

[0064] Step 5: After ball milling, open the milling jar under argon protection and dry the powder (temperature 80℃, time 2h, vacuum environment). Then, repeat steps 3 and 4, adding the remaining half of the CeO2 nanoparticles and ball milling again. After the above steps, the sphericity of the mixed powder can reach 0.99.

[0065] Step 6: Use 3D design software to create 3D models of nickel-titanium alloy blocks measuring 10mm×10mm×10mm and 10mm×10mm×60mm.

[0066] Step 7: Print the ball-milled powder mixture under conditions where the oxygen content in the forming chamber does not exceed 50 ppm. A layered variable strategy is employed: odd-numbered layer checkerboard scanning (block size 5 mm) + even-numbered layer strip scanning (strip width 5 mm). The printing power is 230 W, scanning speed is 1200 mm / s, scanning interval is 120 μm, single-layer thickness is 30 μm, and scanning angle is 90°. The calculated volume energy density is 79.86 J / mm². 3 The linear energy density is 0.197 J / mm.

[0067] The nickel-titanium alloy prepared in this embodiment has a martensitic transformation temperature of 72.1℃, and the tensile test results (combined with...) Figure 5 The results show that the elongation is 8.3% and the density is 99.9%.

[0068] Comparative Example 1

[0069] This comparative example is a comparison with Example 1. The main difference is that the Ni content in the nickel-titanium alloy powder is too high, which causes the calculated amount of CeO2 added to exceed the scope of this invention.

[0070] Step 1: Provide nickel-titanium alloy powder, which contains the following chemical composition by weight percentage: Ni: 55.8%, N: 0.030%, H: 0.005%, O: 0.04%, C: 0.035%, Fe: 0.040%, Ti balance. The powder particle size is 15~53μm.

[0071] Step 2: Substitute the Ni content of 55.8% into the formula CeO2%=1.5×Ni%-81.2% to calculate the CeO2 addition amount as 2.5%.

[0072] Step 3: Add CeO2 nanopowder in two equal batches, with each batch containing 1.25%. The specifications of the CeO2 nanopowder are the same as in Example 1.

[0073] The subsequent ball milling (parameters same as in Example 1) and printing (parameters and layering strategy same as in Example 1) steps are the same as in Example 1.

[0074] The nickel-titanium alloy prepared in this comparative example had a martensitic phase transformation temperature of only 24°C, an elongation of 6.6%, and a density of 98.6%. The performance was significantly reduced, indicating that exceeding the range of components and addition amounts specified in this invention would not achieve the desired results.

[0075] Comparative Example 2

[0076] This comparative example is a comparison with Example 2, the main difference being that CeO2 nanopowder was not added.

[0077] Step 1: Provide nickel-titanium alloy powder with the same composition as in Example 2 (Ni: 54.6%).

[0078] Step 2: Without adding any CeO2 nanopowder, the nickel-titanium alloy powder is used directly for subsequent printing.

[0079] The printing parameters and layering strategy are exactly the same as in Example 2.

[0080] The nickel-titanium alloy prepared in this comparative example had a martensitic phase transformation temperature of 60°C, an elongation of 7%, and a density of 98.9%. Both the phase transformation temperature and elongation were lower than those in Example 2, demonstrating the necessity of adding CeO2 nanopowder for synergistically improving both the phase transformation temperature and elongation.

[0081] Comparative Example 3

[0082] This comparative example is a comparison with Example 2, the main difference being that the amount of CeO2 added is too high, which exceeds the scope of this invention.

[0083] Step 1: Provide nickel-titanium alloy powder with the same composition as in Example 2 (Ni: 54.6%).

[0084] Step 2: Add CeO2 nanopowder in two equal batches, but the total addition amount is set at 1.5% (0.75% per batch).

[0085] The subsequent ball milling (parameters same as in Example 2) and printing (parameters and layering strategy same as in Example 2) steps are the same as in Example 2.

[0086] The nickel-titanium alloy prepared in this comparative example had a martensitic transformation temperature of 56.4℃, an elongation of 6.6%, and a density of 98.8%. The performance degradation indicates that excessive CeO2 actually has an adverse effect on the properties.

[0087] Comparative Example 4

[0088] This comparative example is a comparison with Example 3, the main difference being the use of excessively high ball milling parameters.

[0089] Step 1: Provide nickel-titanium alloy powder with the same composition as in Example 3 (Ni: 54.8%).

[0090] Step 2: The total amount of CeO2 added is calculated to be 1% (same as in Example 3), and it is planned to be added in two equal batches.

[0091] Step 3: The ball milling process parameters significantly exceed the requirements of this invention: horizontal rotation speed 200 r / min, ball weight ratio 10:1, and ball milling time 4 h. Other ball milling conditions are the same as in Example 3.

[0092] Under these intense ball milling conditions, the powder sphericity is severely compromised, failing to meet printing requirements. This results in edge curling occurring around layer 30, making it impossible to complete the printing process. This demonstrates that the ball milling parameter range of this invention is crucial for maintaining good powder morphology.

[0093] Comparative Example 5

[0094] This comparative example is a comparison with Example 3, the main difference being the use of excessively low laser power.

[0095] Step 1: Provide nickel-titanium alloy powder with the same composition as in Example 3 (Ni: 54.8%).

[0096] Step 2: The total amount of CeO2 added is calculated to be 1% (same as in Example 3), and it is added in two equal batches. The subsequent ball milling steps are exactly the same as in Example 3.

[0097] Step 3: During the printing process, the laser power is set to 125W, which is lower than the 170W~230W range required by this invention. Other printing parameters and layering strategies are the same as in Example 3.

[0098] The nickel-titanium alloy prepared in this comparative example had an elongation of only 5.6% and a density of 97%, with numerous unfused pores inside. Although the phase transformation temperature was still relatively high (75℃), the mechanical properties and density were severely degraded, indicating that appropriate printing power is key to ensuring material densification and good elongation.

[0099] Comparative Example 6

[0100] This comparative example is a comparison with Example 3, the main difference being the different scanning strategies.

[0101] Step 1: Provide nickel-titanium alloy powder with the same composition as in Example 3 (Ni: 54.8%).

[0102] Step 2: The total amount of CeO2 added is calculated to be 1% (same as in Example 3), and it is added in two equal batches. The subsequent ball milling steps are exactly the same as in Example 3.

[0103] Step 3: During the printing process, only a strip scanning strategy (strip width 5mm) was used, instead of the layered variable strategy (odd-numbered checkerboard layers + even-numbered strip layers) required by this invention. Other printing parameters were the same as in Example 3. The nickel-titanium alloy prepared in this comparative example had an elongation of 6.5% and a density of 98.9%. The elongation was significantly lower than that of Example 3 (8.3%), demonstrating that the layered variable strategy described in this invention plays an important role in obtaining high elongation.

[0104] Matters not covered in this invention are common knowledge.

[0105] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-titanium alloy with high phase transformation temperature and high elongation through additive manufacturing, characterized in that, The alloy comprises the following components by weight percentage: Ni: 54.2%~54.8%, N≤0.030%, H≤0.005%, O≤0.050%, C≤0.050%, Fe≤0.050%, CeO2: 0.1%~1%, with the balance being Ti; and the alloy has a martensitic transformation temperature of ≥70℃ and an elongation of ≥8%. Includes the following steps: (1) Provide nickel-titanium alloy powder, the composition of which by weight percentage is: Ni: 54.2%~54.8%, N≤0.030%, H≤0.005%, O≤0.050%, C≤0.050%, Fe≤0.050%, balance is Ti; (2) Add CeO2 nanopowder to the nickel-titanium alloy powder, with a total addition amount of 0.1%~1% by weight; (3) The mixed powder is ball-milled; (4) Using additive manufacturing technology to print the powder after ball milling; In step (2), the total amount of CeO2 nanopowder added is determined based on the Ni content in the nickel-titanium alloy powder, specifically CeO2% = 1.5 × Ni% - 81.2%, where Ni is 54.2%~54.8% and CeO2 is 0.1%~1%. In step (3), a planetary ball mill is used for ball milling. The ball milling parameters are: horizontal rotation speed 80r / min~120r / min, vertical rotation speed 10r / min~20r / min, ball weight ratio 0.9~1.1:1, and ball ratio of large ball: medium ball: small ball 10%:30%:60%, where the diameter of the large ball is 10mm, the diameter of the medium ball is 5mm, and the diameter of the small ball is 2mm; the ball milling time is 1h~1.5h, the single forward and reverse rotation time is 15min, the interval standby time is 15min, the entire ball milling process is under argon protection, and alcohol is used as the dispersant. In step (4), a layered variable strategy is used for printing, that is, odd-numbered layers use a chessboard scanning strategy and even-numbered layers use a strip scanning strategy; wherein the block size of the chessboard scanning strategy is 2mm~5mm and the strip width of the strip scanning strategy is 2mm~5mm. In step (4), the printing power is 170W~230W, the scanning speed is 1000mm / s~1200mm / s, the scanning interval is 80μm~120μm, the single-layer thickness is 30μm~40μm, the scanning angle is 45°~90°, and the volume energy density is 50J / mm². 3 ~80J / mm 3 The linear energy density is 0.17 J / mm to 0.2 J / mm.

2. The method for preparing high phase transformation temperature and high elongation nickel-titanium alloy by additive manufacturing according to claim 1, characterized in that, In step (1), the nickel-titanium alloy powder is prepared by gas atomization powder preparation process, with a powder particle size of 15μm~53μm and a sphericity of 0.96 or higher.

3. The method for preparing high phase transformation temperature and high elongation nickel-titanium alloy by additive manufacturing according to claim 1, characterized in that, In step (2), CeO2 nanopowder is added in two equal batches; the CeO2 nanopowder has a particle size of 40nm~60nm, a purity of ≥99.99%, and a sphericity of 0.

99.

4. The method for preparing high phase transformation temperature and high elongation nickel-titanium alloy by additive manufacturing according to claim 1, characterized in that, In step (4), the oxygen content in the forming chamber during the printing process is not higher than 50 ppm.

5. The application of the additively manufactured high phase transformation temperature and high elongation nickel-titanium alloy as described in claim 1 in high-temperature service components of aerospace vehicles, aircraft mixing devices, and variator wings driven by truss structures.

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