A preparation method of high-sphericity titanium-based corrosion-resistant high-entropy alloy powder

Abstract

The present invention discloses a method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, which relates to the technical field of metal powder preparation. Its technical key points include the following steps: S1. Melting the titanium-based high-entropy alloy raw materials into a melt in a vacuum induction melting furnace. The atomic percentages of the titanium-based high-entropy alloy raw materials are: 30%-40% Ti, 5%-15% Al, 3%-10% Cr, 2%-8% Nb, 1% Mo. The technical effect is that through the synergistic action of low-frequency and high-frequency magnetic fields, dendritic growth is inhibited, segregation of heavy elements is eliminated, the segregation index of the powder in the examples is superior to that of the comparative examples, the element distribution uniformity is increased several times, and the hollow powder rate is significantly reduced compared with the non-magnetic field process.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powder preparation, and specifically to a method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder. Background Art

[0002] Titanium-based high-entropy alloy powder is an important member of high-entropy alloys. Titanium and its alloys are widely used in the fields of aerospace, biomedicine, etc. due to their low density, high specific strength, and good biocompatibility. When titanium forms high-entropy alloy powder with multiple elements, it not only retains the advantages of titanium alloys but also has more excellent properties due to the high-entropy effect. For example, in the aerospace field, it can reduce the weight of aircraft parts while ensuring strength and stability. In the biomedical field, it is expected to become an ideal implant material.

[0003] Existing titanium-based high-entropy alloy powders have problems such as oxygen pollution, composition segregation, and the risk of local corrosion. The traditional gas atomization process is difficult to eliminate the segregation of heavy elements such as Nb and Mo, and the self-healing ability of the surface passivation film is insufficient, resulting in easy pitting corrosion in an environment containing Cl⁻. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, which can solve the problems of uneven composition and insufficient corrosion resistance of high-entropy alloy powder.

[0005] To achieve the above object, the present invention provides the following technical solution: A method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, comprising the following steps:

[0006] S1. Melting the titanium-based high-entropy alloy raw material into a melt in a vacuum induction melting furnace. The atomic percentages of the titanium-based high-entropy alloy raw material are: 30%-40% Ti, 5%-15% Al, 3%-10% Cr, 2%-8% Nb, 1% Mo. The melting temperature is 1600°C to 1800°C, and the vacuum degree is ≤1×10⁻³ Pa;

[0007] S2. Injecting the melt into the gas atomization device through a diversion tube while applying a dual-frequency electromagnetic field to the melt. The low-frequency magnetic field frequency is 40 Hz to 60 Hz, the intensity is 0.3 T to 0.8 T, the high-frequency magnetic field frequency is 8 kHz to 12 kHz, the intensity is 0.1 T to 0.3 T, and the phase difference between the two magnetic fields is 90° to 180°;

[0008] S3. Using high-pressure argon as the atomization medium, the atomization pressure is 3 MPa to 5 MPa, the argon purity is 99.999%, and the cooling rate of the atomized droplets is 10 5 ~10 6 K / s. Collecting the gas atomized powder and screening it by air classification to obtain powder with a particle size of 15 μm to 60 μm and a sphericity ≥98%;

[0009] S4. Place the sieved powder in a tubular oxidation furnace, introduce a mixed gas with controllable oxygen partial pressure, and perform gradient oxidation in two stages:

[0010] The first stage: The temperature is 600°C - 700°C, the oxygen partial pressure is 0.05 atm - 0.2 atm, and the holding time is 0.5 h - 1.5 h to form a bottom oxidation film mainly composed of TiO2;

[0011] The second stage: Raise the temperature to 720°C - 780°C, switch to a wet oxygen atmosphere containing 3% - 10% (volume fraction) H2O, the oxygen partial pressure is 0.3 atm - 0.6 atm, and hold for 20 min - 40 min to promote the outward diffusion of Al and Cr elements to generate an Al2O3 - Cr2O3 composite outer layer;

[0012] S5. Immerse the oxidized powder in a 0.05 mol / L - 0.3 mol / L rare earth nitrate ethanol solution, perform ultrasonic treatment for 15 min - 30 min, and then dry it in a vacuum drying oven at 60°C - 80°C for 2 h - 4 h;

[0013] S6. Place the dried powder in a reduction furnace, and under an H2 / Ar mixed atmosphere with a hydrogen volume fraction of 5% - 15%, perform heat treatment at 350°C - 450°C for 10 min - 30 min to obtain high - entropy alloy powder, and embed rare earth ions (Y³⁺, Ce³⁺) into the grain boundaries of the oxidation film to form a gradient passivation film with a doping amount of 0.5 - 2 at.%.

[0014] Preferably, the dual - frequency electromagnetic field is generated by a coaxial nested electromagnetic coil, the turn ratio of the low - frequency coil to the high - frequency coil is 5:1 - 10:1, and the direction of the low - frequency magnetic field is perpendicular to the melt flow direction.

[0015] Preferably, the nozzle of the atomization device has an annular slit structure, the width of the annular slit is 0.1 mm - 0.3 mm, and the temperature of the atomizing gas is - 50°C - 0°C to inhibit the oxidation of the droplet surface.

[0016] Preferably, the thickness of the first - stage oxidation film is 50 nm - 80 nm, the thickness of the second - stage oxidation film is 20 nm - 40 nm, the total thickness is 70 nm - 120 nm, and the thickness ratio of the Al2O3 - Cr2O3 outer layer to the TiO2 inner layer is 1:2 - 1:3.

[0017] Preferably, the rare earth nitrate is a mixture of yttrium nitrate (Y(NO3)3·6H2O) and cerium nitrate (Ce(NO3)3·6H2O), and the mixed molar ratio is 1:1 - 3:1.

[0018] Preferably, the surface oxygen content of the high - entropy alloy powder is ≤0.08 wt.%.

[0019] Preferably, the hollow powder ratio of the gas atomized powder is ≤0.5%, and the particle size distribution span ((D90-D10) / D50) is ≤1.2.

[0020] Preferably, the doping amount of rare earth elements in the gradient oxide film is 0.5-2 at.%, and they are embedded in the grain boundaries of the oxide film in ionic form.

[0021] Compared with the prior art, the present invention provides a method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, which has the following beneficial effects: The synergistic effect of low-frequency and high-frequency magnetic fields inhibits dendrite growth and eliminates heavy element segregation, making the composition segregation index of the powder in the examples better than that of the comparative examples, and the element distribution uniformity is increased several times;

[0022] The hollow powder ratio is significantly reduced compared with the non-magnetic field process, and the particle size distribution span is smaller, meeting the strict requirements of additive manufacturing for powder fluidity;

[0023] The two-stage oxidation and rare earth doping promote each other to increase the pitting potential. The rare earth doping also increases the critical crevice corrosion temperature, significantly enhancing the corrosion resistance. At the same time, the bonding structure formed by the embedding of rare earth elements improves the impedance recovery rate after scratching, enhances the self-healing ability, reduces the pitting probability, and prolongs the material life;

[0024] The oxygen content is reduced, the density of the components formed by selective laser melting technology (SLM) is increased, and the tensile strength is improved, meeting the requirements of more load-bearing components. In addition, the dual-frequency electromagnetic field reduces composition segregation, provides a basis for the uniform growth of the gradient passivation film, and precisely controls the thickness ratio of the gradient oxide film layer. Description of the Drawings

[0025] Figure 1 It is the microscopic scanning diagram of the product prepared in Example 1 of the present invention;

[0026] Figure 2 It is the bar chart of the pitting potential tested in the present invention;

[0027] Figure 3 It is the bar chart of the hollow powder ratio and oxygen content tested in the present invention. Detailed Embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with 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 without creative work fall within the protection scope of the present invention.

[0029] For the oxygen content test, the test standard is GB / T5158-2021 "Determination of Oxygen Content in Metal Powders - Inert Gas Fusion Infrared Absorption Method";

[0030] Testing instrument: LECO ON836 oxygen, nitrogen and hydrogen analyzer;

[0031] Testing steps: Take 1.0 g of powder sample, ultrasonically clean it with acetone to remove surface adsorbed substances, and vacuum dry it for 2 h;

[0032] Place the sample in a graphite crucible, heat it to 3000 °C under helium protection, release oxygen and react with carbon to form CO;

[0033] Quantitatively analyze the CO content with an infrared detector, convert it to the oxygen mass percentage, and repeat 3 times to take the average value.

[0034] Testing of the hollow powder ratio, testing standard: GB / T 5163-2018 "Determination of the Hollow Powder Ratio of Metal Powders - Metallographic Method";

[0035] Testing instrument: ZEISS Axio Imager M2m metallographic microscope + Image-Pro Plus 6.0 image analysis software;

[0036] Testing steps: Mix the powder sample with epoxy resin and cure it, then polish it to a mirror surface;

[0037] Randomly select 10 fields of view (each field of view ≥ 500 powders), and take metallographic photos at 200 times magnification;

[0038] The software identifies hollow powders (with a dark area in the center and wall thickness / diameter ratio < 0.3), and calculates the proportion of hollow powders.

[0039] Testing of sphericity, testing standard: ISO 4490-2018 "Qualitative Evaluation of the Particle Shape of Metal Powders";

[0040] Testing instrument: Scanning electron microscope of JEOL Ltd. + MATLAB image processing program;

[0041] Testing steps: Disperse the powder on the conductive adhesive and perform sputtering (thickness 5 nm);

[0042] The SEM randomly takes secondary electron images of 100 powders at 500 times magnification;

[0043] After image binarization, calculate the sphericity of each powder (perimeter² / (4π×area)), and count the proportion of particles ≥ 0.95.

[0044] Testing of particle size distribution, testing standard: GB / T 19077-2016 "Particle Size Analysis - Laser Diffraction Method"

[0045] Testing instrument: Malvern Mastersizer 3000 laser particle size analyzer;

[0046] Test procedure: Disperse the powder in an aqueous solution of 0.05% Tween 80 and sonicate for 5 min;

[0047] Measure in wet mode, set the refractive index to 2.71 (titanium alloy), and the light obscuration to 10% - 15%;

[0048] Calculate D10, D50, D90 and span index ((D90 - D10) / D50).

[0049] Pitting potential test, test standard: GB / T 17899-1999 "Method for Measuring Pitting Potential of Stainless Steel";

[0050] Test instrument: Gamry Reference 600+ electrochemical workstation;

[0051] Test procedure: Cold press the powder into a φ10 mm × 2 mm sheet specimen (pressure 200 MPa), and polish the surface to Ra ≤ 0.1 μm;

[0052] In a 3.5% NaCl solution, use a saturated calomel electrode (SCE) as the reference electrode, a platinum sheet as the counter electrode, and a scanning rate of 1 mV / s;

[0053] Record the anodic polarization curve, and take the potential corresponding to a sudden increase in current density of 10 μA / cm² as the pitting potential (Epit).

[0054] Critical crevice corrosion temperature (CCT) test, test standard: GB / T 10127-2022 "Corrosion of Metals and Alloys - Test Method for Crevice Corrosion of Stainless Steel in Ferric Chloride Solution";

[0055] Test instrument: HACH DR900 multi-parameter water quality analyzer + constant temperature water bath;

[0056] Test procedure: Install a polytetrafluoroethylene gasket on the specimen surface to form an artificial crevice (contact pressure 0.2 MPa);

[0057] Immerse in a 6% FeCl3 solution, heat at a rate of 2 °C / min, and monitor the corrosion current. The temperature when the corrosion current reaches ≥100 μA / cm² is the CCT.

[0058] Self-healing index test, refer to ASTM G199-09 "Standard Guide for Electrochemical Impedance Spectroscopy";

[0059] Test instrument: PARSTAT 4000 electrochemical workstation + in-situ scratching device;

[0060] Test procedure: Use a diamond blade to scratch a 10 mm long and 5 μm deep scratch on the specimen surface;

[0061] Immerse in 3.5% NaCl solution and measure EIS every 24 hours (frequency 0.01 Hz to 100 kHz, amplitude 10 mV);

[0062] Calculate the recovery rate of the low-frequency impedance modulus (|Z|0.01Hz): Self-healing index = (|Z| at 48 hours / original |Z|) × 100%.

[0063] Test the Composition Segregation Index (C.S.I), test standard: GB / T 17359-2012 "General Rules for Quantitative Analysis by Electron Probe";

[0064] Test instrument: JEOL JXA-8530F field emission electron probe (EPMA);

[0065] Test procedure: After embedding and polishing the powder, select 50 powders for surface scanning (step size 1 μm, range 100×100 μm);

[0066] Measure the maximum concentration (C_max) and minimum concentration (C_min) of Al, Cr, Nb, and Mo elements in each powder;

[0067] Calculate C.S.I = [(C_max - C_min) / nominal concentration] × 100%, and take the average value of all particles.

[0068] Test the density of the SLM formed parts, test standard: GB / T 1423-1996 "Archimedes Method for Determining the Density of Metal Powders";

[0069] Test instrument: Mettler Toledo XS205DU electronic balance (accuracy 0.01 mg);

[0070] Test procedure: Use the EOS M290 device to print 10×10×10 mm cube specimens (parameters: laser power 200 W, scanning speed 800 mm / s);

[0071] After cleaning the specimens with absolute ethanol, measure the dry mass (m1) and the immersed suspension mass (m2);

[0072] Density = m1 / (m1 - m2) × ρ_water / ρ_theoretical × 100% (ρ_theoretical = 4.51 g / cm³).

[0073] Tensile Strength test, test standard: GB / T 228.1-2021 "Tensile Testing of Metallic Materials - Part 1: Method of Test at Room Temperature";

[0074] Testing instrument: Instron 5985 universal material testing machine (load accuracy ±0.5%);

[0075] Testing procedure: Process powder metallurgy tensile specimens (gauge section φ3mm×15mm) according to the standard;

[0076] Load at a rate of 0.5 mm / min until fracture, and record the maximum load F_max;

[0077] Tensile strength = F_max / original cross-sectional area, and take the average value of 3 specimens.

[0078] Regarding Figure 1 The specific explanations are as follows: Figure 1 As marked at the bottom "JEOLSEI", it indicates that a scanning electron microscope of JEOL Ltd. (JEOL) is used, the imaging mode is secondary electron imaging (SEI), "20.0 kV" represents the acceleration voltage of 20 kV, the acceleration voltage affects the penetration ability of the electron beam and the resolution of the image, "×200" represents the magnification of 200 times, and "100 μm" is the scale bar used to measure the actual size of the object in the figure.

[0079] Reference for evaluating relevant test data: In the evaluation standard, oxygen contamination can cause embrittlement, and the lower the oxygen content, the better the performance;

[0080] The hollow powder ratio can cause forming defects, and the lower the hollow powder content, the better the performance;

[0081] The lower the composition segregation index, the better the tissue uniformity.

[0082] Sphericity affects fluidity and forming quality. The higher the sphericity in additive manufacturing, the better the fluidity;

[0083] Pitting potential, as an index for testing corrosion resistance, the higher the measured value, the better the corrosion resistance;

[0084] Critical crevice corrosion temperature represents its tolerance to high-temperature corrosion environment, and the higher the value, the better the tolerance in high-temperature corrosion environment;

[0085] Self-healing index reflects the self-healing ability of the passive film. The higher the value, the stronger the self-healing ability;

[0086] In forming performance, the higher the density of the SLM formed part, the better the forming performance;

[0087] The higher the measured value of tensile strength test, the better its performance;

[0088] The smaller the particle size span, the more concentrated the particle size, that is, the smaller the test value, the better.

[0089] Example 1: A method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, specifically including the following steps:

[0090] S1. Melting the titanium-based high-entropy alloy raw materials into a melt in a vacuum induction melting furnace. The atomic percentages of the titanium-based high-entropy alloy raw materials are: 35% Ti, 10% Al, 5% Cr, 5% Nb, 1% Mo. The melting temperature is 1700 °C, and the vacuum degree is 1×10⁻³ Pa;

[0091] S2. Injecting the melt into the gas atomization device through a diversion tube, and simultaneously applying a dual-frequency electromagnetic field to the melt. The low-frequency magnetic field frequency is 50 Hz and the intensity is 0.5 T, the high-frequency magnetic field frequency is 10 kHz and the intensity is 0.2 T, and the phase difference between the two magnetic fields is 135°;

[0092] S3. Using high-pressure argon as the atomization medium, the atomization pressure is 4 MPa, the argon purity is 99.999%, and the cooling rate of the atomized droplets is 10 5 K / s. Collecting the gas atomized powder and screening it by air classification to obtain powder with a particle size of 15 μm - 60 μm and a sphericity ≥ 98%;

[0093] S4. Placing the sieved powder in a tube furnace, introducing a mixed gas with controllable oxygen partial pressure, and performing two-stage gradient oxidation:

[0094] The first stage: The temperature is 650 °C, the oxygen partial pressure is 0.1 atm, and the holding time is 1 h;

[0095] The second stage: Heating up to 750 °C, switching to a wet oxygen atmosphere with 5 vol.% H2O, 0.4 atm, and holding for 30 min;

[0096] S5. Immersing the oxidized powder in a 0.2 mol / L ethanol solution of rare earth nitrate, the mixed solution of rare earth nitrate and ethanol (molar ratio 2:1), performing ultrasonic treatment for 20 min, and then drying it in a vacuum drying oven at 70 °C for 3 h;

[0097] S6. Placing the dried powder in a reduction furnace, and performing heat treatment at 400 °C for 20 min in a H2 / Ar mixed atmosphere with a hydrogen volume fraction of 10% to obtain the high-entropy alloy powder.

[0098] Example 2: A method for preparing high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, specifically including the following steps:

[0099] S1. Melting the titanium-based high-entropy alloy raw materials into a melt in a vacuum induction melting furnace. The atomic percentages of the titanium-based high-entropy alloy raw materials are: 30% Ti, 5% Al, 3% Cr, 2% Nb, 1% Mo. The melting temperature is 1600 °C, and the vacuum degree is 1×10⁻³ Pa;

[0100] S2. Inject the melt into the gas atomization device through a diversion tube while applying a dual-frequency electromagnetic field to the melt. The low-frequency magnetic field has a frequency of 40 Hz and an intensity of 0.3 T, the high-frequency magnetic field has a frequency of 8 kHz and an intensity of 0.1 T, and the phase difference between the two magnetic fields is 90°;

[0101] S3. Use high-pressure argon as the atomization medium, with an atomization pressure of 3 MPa, an argon purity of 99.999%, and an atomization droplet cooling rate of 10 5 K / s. Collect the gas atomized powder and screen it through air classification to obtain powder with a particle size of 15 μm to 60 μm and a sphericity of ≥98%;

[0102] S4. Place the screened powder in a tubular oxidation furnace and introduce a mixed gas with controllable oxygen partial pressure for gradient oxidation in two stages:

[0103] The first stage: The temperature is 600, the oxygen partial pressure is 0.05 atm, and the holding time is 0.5 h;

[0104] The second stage: Heat up to 720 °C, switch to a wet oxygen atmosphere containing 3 vol.% H2O, with an oxygen partial pressure of 0.3 atm, and hold for 20 min;

[0105] S5. Immerse the oxidized powder in a 0.05 mol / L rare earth nitrate ethanol solution, ultrasonically treat it for 15 min, and then dry it in a vacuum drying oven at 60 °C for 2 h;

[0106] S6. Place the dried powder in a reduction furnace and heat-treat it at 350 °C for 10 min in a H2 / Ar mixed atmosphere with a hydrogen volume fraction of 5% to obtain the high-entropy alloy powder.

[0107] Example 3. A method for preparing a high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, specifically including the following steps:

[0108] S1. Melt the titanium-based high-entropy alloy raw materials into a melt in a vacuum induction melting furnace. The atomic percentages of the titanium-based high-entropy alloy raw materials are 40% Ti, 15% Al, 10% Cr, 8% Nb, and 1% Mo. The melting temperature is 1800 °C, and the vacuum degree is 1×10⁻³ Pa;

[0109] S2. Inject the melt into the gas atomization device through a diversion tube while applying a dual-frequency electromagnetic field to the melt. The low-frequency magnetic field has a frequency of 60 Hz and an intensity of 0.8 T, the high-frequency magnetic field has a frequency of 12 kHz and an intensity of 0.3 T, and the phase difference between the two magnetic fields is 180°;

[0110] S3. Use high-pressure argon as the atomization medium, with an atomization pressure of 5 MPa, an argon purity of 99.999%, and an atomization droplet cooling rate of 110 6K / s, collect the gas atomized powder and screen it by air classification to obtain a powder with a particle size of 15μm - 60μm and a sphericity of ≥98%;

[0111] S4. Place the screened powder in a tube-type oxidation furnace, introduce a mixed gas with a controllable oxygen partial pressure, and perform gradient oxidation in two stages:

[0112] The first stage: the temperature is 700°C, the oxygen partial pressure is 0.2 atm, and the heat preservation time is 1.5 h;

[0113] The second stage: heat up to 780°C, switch to a wet oxygen atmosphere containing 10 vol.% H2O, the oxygen partial pressure is 0.6 atm, and heat preservation for 40 min;

[0114] S5. Immerse the oxidized powder in a 0.3 mol / L rare earth nitrate ethanol solution, perform ultrasonic treatment for 30 min, and then dry it in a vacuum drying oven at 80°C for 4 h;

[0115] S6. Place the dried powder in a reduction furnace, and perform heat treatment at 450°C for 30 min in a H2 / Ar mixed atmosphere with a hydrogen volume fraction of 15% to obtain the high-entropy alloy powder.

[0116] Example 4: Only change the gradient oxidation process: single-stage oxidation (temperature is 650°C, oxygen partial pressure is 0.1 atm, heat preservation time is 1 h), and other steps are the same as in Example 1.

[0117] Example 5: Only change the rare earth type: only use a 0.2 mol / L Ce(NO3)3 solution, and other steps are the same as in Example 1.

[0118] Example 6: Omit the rare earth doping step: directly dry after oxidation, without impregnation and reduction treatment, and other steps are the same as in Example 1.

[0119] Comparative Example 1: Only use a low-frequency magnetic field: single frequency 50 Hz, intensity 0.5 T, and other steps are the same as in Example 1.

[0120] Comparative Example 2: Cancel the electromagnetic field: no magnetic field is applied during the gas atomization process, and other steps are the same as in Example 1.

[0121] Comparative Example 3: No surface treatment: directly screen and use after gas atomization, and other steps are the same as in Example 1.

[0122] Comparative Example 4: Purchase existing titanium-aluminum alloy powder on the market.

[0123] Table 1 is the composition table of Comparative Example 4

[0124]

[0125] The titanium-based high-entropy alloy powders obtained in Examples 1, 2, 3, 4, 5, 6 and Comparative Examples 1, 2, 3, 4 were grouped, and the physical properties of the products in the examples and comparative examples were tested, specifically including oxygen content, hollow powder ratio, sphericity and particle size span. The specific test results are shown in Tables 2 and 3.

[0126] Table 2 shows the test results of oxygen content and hollow powder ratio

[0127]

[0128] Table 3 shows the test results of sphericity and particle size span

[0129]

[0130] The corrosion resistance of the titanium-based high-entropy alloy powders in the examples and comparative examples was tested, specifically including pitting potential, critical crevice corrosion temperature and self-healing index. The specific test results are shown in Table 4.

[0131] Table 4 shows the test results of pitting potential, critical crevice corrosion temperature and self-healing index

[0132]

[0133] The microstructure uniformity and formability of the titanium-based high-entropy alloy powders in the examples and comparative examples were tested, specifically including the composition segregation index, the density of the SLM formed parts and the tensile strength. The specific test results are shown in Table 5.

[0134] Table 5 shows the test results of the composition segregation index, the density of the SLM formed parts and the tensile strength

[0135]

[0136] Combining the above test data, the following conclusions can be drawn. By suppressing dendritic growth with a low-frequency magnetic field and eliminating heavy element segregation with a high-frequency magnetic field, it can be seen that the composition segregation index of the powder in the examples is significantly better than that in the comparative examples, and the element distribution uniformity is increased by several times;

[0137] The hollow powder ratio in the examples is significantly lower than that of the non-magnetic field process (3.02% in Comparative Example 2), and the particle size distribution span is smaller, meeting the stringent requirements of additive manufacturing for powder fluidity;

[0138] Through two-stage oxidation (TiO2 bottom layer + Al2O3-Cr2O3 outer layer) and rare earth doping, the pitting potential is significantly improved compared to the untreated powder (0.65 V in Comparative Example 3). Moreover, without rare earth doping, the pitting potential will also decrease to a certain extent, which also indicates that two-stage oxidation and rare earth doping have a mutually promoting effect on the improvement of the pitting potential. At the same time, rare earth doping will also improve the critical crevice corrosion temperature to a certain extent, thus significantly enhancing its corrosion resistance;

[0139] Y / Ce rare earth elements are embedded in the grain boundaries of the oxide film to form a Ce-O-Ti bonding structure. The impedance recovery rate after scratching reaches a higher level (in Example 1, Example 2, and Example 3), and the self-healing ability is significantly improved compared to the non-rare earth treatment (Example 6), further reducing the probability of pitting corrosion and greatly extending the material life;

[0140] The oxygen content (in Example 1, Example 2, and Example 3) is significantly lower than that in the comparative example, and the density of the SLM formed parts is also better (in Example 1, Example 2, and Example 3). The tensile strength of the examples is also significantly improved compared to the comparative example, meeting the requirements of more load-bearing components;

[0141] The dual-frequency electromagnetic field reduces compositional segregation (C.S.I ≤ 3%), providing a compositional basis for the uniform growth of the gradient passivation film. The directional diffusion of Al and Cr elements during the gradient oxidation process is promoted by the pre-uniformization effect of the electromagnetic field.

[0142] Through the cooperation of three major technologies: dual-frequency electromagnetic field atomization control, in-situ construction of gradient passivation film, and rare earth element doping strengthening, the high-sphericity titanium-based corrosion-resistant high-entropy alloy powder has been significantly improved in terms of compositional uniformity, corrosion resistance, and forming performance.

[0143] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all covered by the protection scope of the present invention.

Claims

1. A method for preparing a high-sphericity titanium-based corrosion-resistant high-entropy alloy powder, characterized in that: The specific steps include: S1. Melting titanium-based high entropy alloy raw materials into a melt in a vacuum induction melting furnace, the atomic percentage of the titanium-based high entropy alloy raw materials is: 30%-40% Ti, 5%-15% Al, 3%-10% Cr, 2%-8% Nb, 1% Mo, the melting temperature is 1600℃~1800℃, and the vacuum degree is ≤1×10⁻³Pa; S2. Inject the melt into the gas atomization device through the guide tube and apply a dual-frequency electromagnetic field to the melt at the same time, wherein the low-frequency magnetic field has a frequency of 40 Hz to 60 Hz and an intensity of 0.3 T to 0.8 T, and the high-frequency magnetic field has a frequency of 8 kHz to 12 kHz and an intensity of 0.1 T to 0.3 T, and the phase difference between the two magnetic fields is 90° to 180°; S3, using high pressure argon as atomizing medium, the atomizing pressure is 3MPa~5MPa, the purity of argon is 99.999%, the cooling rate of atomized droplets is 10 5 ~10 6 K / s, collect the aerosolized powder and screen it through airflow classification to obtain powder with a particle size of 15μm~60μm and a sphericity of ≥98%; S4, placing the sieved powder in a tubular oxidation furnace, introducing a mixed gas with controllable oxygen partial pressure, and performing gradient oxidation in two stages; The two-stage gradient oxidation specifically comprises the following steps: The first stage: the temperature is 600℃~700℃, the oxygen partial pressure is 0.05atm~0.2atm, and the holding time is 0.5h~1.5h. After the first stage of oxidation, the thickness of the oxide film is 50nm~80nm; The second stage: the temperature is raised to 720℃~780℃, and the atmosphere is switched to a wet oxygen atmosphere containing 3%~10% volume fraction of H2O, with an oxygen partial pressure of 0.3atm~0.6atm, and the temperature is kept for 20min~40min. After oxidation in the second stage, the thickness of the oxide film is 20nm~40nm; The total thickness is 70nm~120nm, and the thickness ratio of the Al2O3-Cr2O3 outer layer to the TiO2 inner layer is 1:2~1:3; S5, immersing the oxidized powder in a 0.05 mol / L to 0.3 mol / L rare earth nitrate ethanol solution, ultrasonically treating for 15 min to 30 min, and then drying in a vacuum drying oven at 60° C. to 80° C. for 2 h to 4 h; S6. Place the dry powder in a reduction furnace, and heat treat it at 350° C. to 450° C. for 10 min to 30 min in a H2 / Ar mixed atmosphere in which hydrogen accounts for 5% to 15% by volume to obtain a high entropy alloy powder.

2. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 1, characterized in that: The dual-frequency electromagnetic field is generated by coaxial nested electromagnetic coils, the turns ratio of the low-frequency coil to the high-frequency coil is 5:1-10:1, and the direction of the low-frequency magnetic field is perpendicular to the melt flow direction.

3. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 1, characterized in that: The nozzle of the gas atomization device is an annular gap structure with an annular gap width of 0.1 mm to 0.3 mm. The atomization gas temperature is -50°C to 0°C to inhibit oxidation of the droplet surface.

4. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 1, characterized in that: The rare earth nitrate is a mixture of yttrium nitrate and cerium nitrate, and the mixing molar ratio is 1:1-3:

1.

5. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 1, characterized in that: The surface oxygen content of the high entropy alloy powder is ≤0.08wt.%.

6. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 1, characterized in that: The hollow powder rate of the aerosolized powder is ≤0.5%, and the particle size distribution span is ≤1.

2.

7. The method for preparing a high sphericity titanium-based corrosion-resistant high entropy alloy powder according to claim 4, characterized in that: The doping amount of the rare earth element in the rare earth nitrate is 0.5-2 at.%, and is embedded in the oxide film grain boundary in the form of ions.

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