A method for producing a space station containerless solidification niobium alloy surface uniform texture

Abstract

This invention discloses a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station, relating to the field of containerless materials science experimental technology. The method first screens for highly supercooled samples suitable for preparing a uniform microstructure using this method in containerless space station experiments; calculates or experimentally determines the primary phase dendrite growth rate, the cooling rate coefficient of radiative heat dissipation during the cooling stage, and the primary phase nucleation rate; and conducts containerless space station experiments to allow the niobium alloy to undergo deep supercooling and rapid solidification within a determined suitable supercooling range, thus obtaining a solidified alloy sample with a uniform surface microstructure. This invention actively controls the distribution of dendrites and eutectic phases, resulting in a surface microstructure with uniformly distributed dendrites and interdendritic eutectic phases.

Description

Technical Field

[0001] This invention relates to the field of experimental technology in containerless materials science, specifically to a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station. Background Technology

[0002] The properties of a material largely depend on the distribution of its solidification structure. In containerless solidified alloys for space stations, nucleation typically begins at the droplet surface. Once nucleation begins, the solidification process becomes difficult to control, resulting in a surface solidification structure prone to compositional segregation and diverse morphologies. Poor uniformity of the solidification structure negatively impacts material performance. Therefore, to develop high-performance niobium alloys that can replace traditional nickel-based superalloys as the next generation of aero-engine turbine blades, it is necessary to develop methods for preparing uniform surface structures of containerless solidified niobium alloys for space stations.

[0003] Chinese Patent 1, "Northwestern Polytechnical University. A method for controlling the phase selection of alloys by electrostatic levitation step-triggered solidification: CN202310092865.4[P]. 2023-02-09," discloses a method for controlling the phase selection of alloys using ground electrostatic levitation technology. However, this method only focuses on the phase selection of the solidification structure inside the alloy and cannot achieve the preparation of a uniform structure on the surface of the solidified niobium alloy. The final distribution of the surface solidification structure is random.

[0004] Reference 1, "HPWang, H.Liao, J.Chang, et al. Decoupling effect stimulated dindependent dendrite growth of eutectic phases under microgravity and containerless states. Materials Today, 2024, 75: 386-392," while focusing on the surface microstructure characteristics of containerless niobium alloys for space stations and reporting near-spherical and olivine alloys obtained at different supercooling degrees, did not propose a method for preparing uniform microstructures of surface dendrites and eutectic structures, and the surface microstructure exhibited segregation partitioning.

[0005] Reference 2, “HPWang, H.Liao, YBWang, et al. Solidification mechanism and microstructure evolution of refractory Nb-Si and Nb-Si-Zr alloys aboard China space station. SCIENTIA SINICA Technologica, 2025, 55(12): 1989-2005”, reported the surface shrinkage cavities and microstructure characteristics of several containerless solidified alloys for the space station. However, no alloy samples with uniform surface structures were found during the containerless preparation process of the space station, indicating that it was impossible to actively prepare alloy materials with uniform surface structures.

[0006] In summary, current inventions and research have not yet provided an effective method for preparing a uniform microstructure on the surface of solidified niobium alloys without containers on space stations, and it is impossible to actively control the uniformity of the solidified microstructure on the surface of niobium alloys. Summary of the Invention

[0007] To address the shortcomings of the aforementioned background technology, this invention provides a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station. This overcomes the limitations of current containerless experiments, which only focus on phase control and can only obtain alloys exhibiting surface microstructure evolution, thereby enabling proactive control of the uniformity of the microstructure distribution on the surface of the solidified niobium alloy.

[0008] The first objective of this invention is to provide a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station, comprising: Determine the vacuum level and microgravity level of the space station preparation environment; Screening for niobium alloy samples suitable for preparation for the space station; Based on the physical property parameters of the screened niobium alloy samples, the first relationship curve between dendrite growth rate and undercooling of the niobium alloy samples, and the second relationship curve between nucleation rate of primary phase dendrites and undercooling were obtained. Determine the cooling rate during the cooling phase of a containerless solidified niobium alloy sample on the space station. The appropriate critical subcooling degree for containerless preparation of the space station was selected based on the first relationship curve, the second relationship curve, and the cooling rate. The containerless preparation of the space station was carried out based on the critical supercooling, and the actual supercooling during the preparation process was controlled to be greater than or equal to the critical supercooling. During the preparation of the containerless space station, a floating niobium alloy sample is controlled by three pairs of electrodes and subjected to suspension laser heating. The sample is heated to a temperature above the liquidus temperature and completely melted. The total laser heating power is controlled to keep the niobium alloy at a temperature above the liquidus temperature for 1 to 60 seconds. Then, the laser heating is stopped, and the niobium alloy radiates heat to a deep supercooled state temperature and then spontaneously nucleates and solidifies, thus completing the preparation of a uniform microstructure on the surface of the containerless niobium alloy sample for the space station.

[0009] Preferably, screening for niobium alloy samples suitable for space station preparation includes: Based on containerless solidification experiments on the space station, the alloy was heated to the liquidus temperature. T L After the above steps, turn off the laser and select the niobium alloy sample at the first re-glow undercooling Δ. T ≥0.15 T L Alloy samples.

[0010] Preferably, the first relationship curve between the dendrite growth rate and the undercooling of the niobium alloy sample is obtained based on the LKT / BCT rapid dendrite growth model, or by first experimentally determining the dendrite growth rate and then fitting the dendrite growth rate with a power function to the undercooling.

[0011] Preferably, the second relationship curve between the nucleation rate of primary phase dendrites and the degree of undercooling is as follows:

[0012] In the formula, The nucleation rate of dendrites in the primary phase of the alloy; Forward exponential factor; Interface free energy; Boltzmann's constant; It is the diffusion activation energy; It is a function of the contact angle. f ( θ →0 represents heterogeneous nucleation. f ( θ → 1 represents homogeneous nucleation; Supercooling; It is the enthalpy of fusion; Temperature of the alloy sample; is the ideal gas constant.

[0013] Preferably, the space station has a suitable critical subcooling degree for containerless preparation. Its critical undercooling satisfies the following condition:

[0014]

[0015]

[0016] In the formula, Indicates the critical undercooling The corresponding dendrite growth rate; Indicates the critical undercooling The nucleation rate of the corresponding primary phase dendrites; Indicates the critical undercooling The corresponding cooling rate.

[0017] Preferably, the heat preservation temperature of the niobium alloy for:

[0018] in, This is the liquidus temperature; .

[0019] Preferably, determining the cooling rate during the cooling phase of the containerless solidified niobium alloy sample on the space station includes: Select the moment when the laser starts turning off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, when t ≥ t At 0, laser heating power P L ( t ) = 0; Perform a fourth-order fit on the natural radiation cooling section, and calculate the cooling rate using the fitting coefficients. R c To ensure that the niobium alloy melt cooling rate coefficient is higher than 4.0 × 10⁻⁶. -15 s -1 .

[0020] Preferably, the vacuum degree is <3×10 -3 Pa, microgravity level <10 -4 g 0, where, g 0 represents gravitational acceleration.

[0021] The second objective of this invention is to provide a niobium alloy with a uniform surface structure.

[0022] The third objective of this invention is to provide an application of a niobium alloy with a uniform surface structure in aero-engine turbine blades.

[0023] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing a uniform microstructure on the surface of a solidified niobium alloy in a containerless space station. The method involves obtaining a solidified alloy sample with a uniform microstructure in a containerless space station experiment. First, suitable supercooled samples for preparing a uniform microstructure according to this method are selected from the containerless space station experiment. Then, the primary phase dendrite growth rate, the cooling rate coefficient of radiative heat dissipation during the cooling stage, and the primary phase nucleation rate are calculated or experimentally determined. Finally, the containerless space station experiment is conducted to ensure the niobium alloy is within a defined suitable supercooling range. ≥ By performing deep supercooling and rapid solidification, a solidified alloy sample with a uniform surface structure can be obtained.

[0024] Compared with the comparative example, this invention uses a containerless experiment on a space station to obtain alloy samples with uniform surface structure, and pays more attention to the surface morphology distribution of niobium alloys. Compared with Reference 1, the method provided by this invention can obtain approximately spherical alloy samples without the zonal evolution of surface solidification structure. Compared with Reference 2, this invention provides a method for preparing a uniform surface structure of solidified niobium alloys in a containerless experiment on a space station, actively controlling the distribution of dendrites and eutectic phases, and obtaining a surface structure with uniformly distributed dendrites and interdendritic eutectic. Attached Figure Description

[0025] Figure 1 The growth rates of the primary phases (Nb, Zr) of the Nb-Si-Zr alloys prepared in Example 1 and Comparative Example 1 were calculated using the LKT / BCT rapid dendrite growth model, and the growth rates were measured in the ground electrostatic levitation containerless experiment and the space station containerless experiment. Figure 2 The nucleation rate of the (Nb, Zr) phase and the (Nb, Zr)5Si3 phase competing for growth in the Nb-Si-Zr alloys prepared in Example 1 and Comparative Example 1 as a function of contact angle. f The changes in (θ) and supercooling; Figure 3 Typical temperature profiles for preparing Nb-Si-Zr alloys in Example 1; Figure 4 The macroscopic morphology of the containerless Nb-Si-Zr alloy sample prepared according to the method described in Example 1 is shown below. Figure 5 The microstructure distribution on the surface of the Nb-Si-Zr alloy prepared in Example 1; Figure 6 The surface profile curvature change of the Nb-Si-Zr alloy prepared in Example 1; Figure 7 Typical temperature profiles for preparing Nb-Si-Zr alloys for Comparative Example 1; Figure 8The macroscopic morphology of the Nb-Si-Zr alloy sample solidified by ground electrostatic levitation experiment is shown in Comparative Example 1. Figure 9 To illustrate the microstructure distribution on the surface of the Nb-Si-Zr alloy in Comparative Example 1; Figure 10 The surface profile curvature change of the Nb-Si-Zr alloy prepared for Comparative Example 1. Detailed Implementation

[0026] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0027] The purpose of this invention is to provide a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station, overcoming the current problems that containerless experiments only focus on phase control and that containerless experiments on space stations can only obtain alloys with surface microstructure evolution, thereby actively controlling the uniformity of the microstructure distribution on the surface of the solidified niobium alloy.

[0028] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station, comprising: S1. Determine the vacuum level and microgravity level of the space station preparation environment; In one embodiment, the vacuum level and microgravity level are determined during the preparation of a uniform microstructure on the surface of the niobium alloy for the containerless experiment on the space station: the vacuum level needs to be <3 × 10⁻⁶. -3 Pa, microgravity levels must be <10 Pa to be monitored by the space station. -4 g 0, where, g 0 represents gravitational acceleration.

[0029] S2. Screening niobium alloy samples suitable for preparation for the space station; Screening for niobium alloy samples suitable for preparation on the space station, including: Based on containerless solidification experiments on the space station, the alloy was heated to the liquidus temperature. T L After the above steps, turn off the laser and select the niobium alloy sample at the first re-glow undercooling Δ. T ≥0.15 T L Alloy samples.

[0030] In one embodiment, during a containerless experiment on a space station, samples suitable for preparing a uniform microstructure on the surface of a solidified niobium alloy suitable for containerless solidification on a space station are selected: a containerless solidification experiment is conducted on a space station, and the alloy is heated to the liquidus temperature. T LAfter the laser is turned off, it is determined whether the niobium alloy sample has cooled to a highly supercooled state and spontaneously completed rapid solidification, i.e., the degree of supercooling Δ. T ≥ 0.15 T L This alloy sample is suitable for preparing a uniform microstructure on the surface of containerless solidified niobium alloys; if the undercooling Δ during the first re-goldening... T< 0.15 T L If the alloy sample is unsuitable for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy, then this alloy sample is not suitable for preparation.

[0031] S3. Based on the physical property parameters of the screened niobium alloy samples, obtain the first relationship curve between the dendrite growth rate and the undercooling of the niobium alloy samples, and the second relationship curve between the nucleation rate of the primary phase dendrites and the undercooling. The first relationship curve between dendrite growth rate and undercooling of niobium alloy samples was obtained based on the LKT / BCT rapid dendrite growth model, or by first experimentally determining the dendrite growth rate and then fitting the dendrite growth rate with a power function to the undercooling.

[0032] In one embodiment, when obtaining data based on the LKT / BCT rapid dendrite growth model, the following steps are included: (1) In the formula, the total subcooling It consists of 4 subcooling degrees. For thermal subcooling, This refers to the degree of subcooling of the solute. For kinetic undercooling, The values ​​represent curvature supercooling, all in Kelvin. (2) In the formula, This is the enthalpy of fusion, expressed in kilojoules per mole. For thermal Ivantsov functions; The specific heat of the alloy in its liquid state is expressed in joules per Kelvin per mole. (3) In the formula, is the thermal Peckle number, a dimensionless number; This represents the dendrite growth rate, measured in meters per second. The radius of the dendrite tip is in meters. The thermal diffusivity is expressed in square meters per second. (4) In the formula, The slope of the liquidus line of the alloy, expressed in Kelvin as a percentage per atom; This represents the actual liquidus slope under non-equilibrium conditions, expressed in Kelvin as a percentage per atom. This represents the solute concentration of the alloy, expressed as an atomic percentage. is the actual solute partition coefficient, which is a dimensionless number; For the solute Ivantsov function; is the Peckle number of the solute, a dimensionless number; (5) In the formula, This is the solute diffusion coefficient, expressed in square meters per second. (6) (7) In the formula, The equilibrium distribution coefficient is a dimensionless number. (8) In the formula, This represents the dendrite growth rate, measured in meters per second. Speed ​​of sound, measured in meters per second (typically 2000 m / s in liquid metal). -1 ); The constant is the ideal gas constant, expressed in joules per mole per Kelvin (8.314 J). mol -1 ·K -1 ); This refers to the liquidus temperature of the alloy. This is a kinetic factor, measured in seconds. (9) In the formula, The Gibbs-Thomson coefficient is expressed in Kelvin per meter. The radius of the dendrite tip is in meters. (10) In the formula, and These are the thermal stability function and the solute stability function, respectively. The stability constant is (1 / 4π) 2 ); Solving the above formulas (1) to (10) yields the degree of subcooling. Dendrite tip radius R Dendrite growth rate V The relationship.

[0033] In one embodiment, the dendrite growth rate is first determined experimentally, and then obtained by fitting a power function between the dendrite growth rate and the undercooling, including: Experimental determination of dendrite growth rate: If key physical properties of niobium alloys are missing, the melt can be measured and photographed in real time using a non-contact infrared thermometer and a high-speed CMOS camera via ground-based electrostatic levitation experiments. The degree of supercooling during re-glow of the melt can be determined from the temperature curve, and the rapid solidification dendrite growth rate of the niobium alloy can be calculated using the CMOS camera images and alloy dimensions.

[0034] (11) in, V This represents the dendrite growth rate, measured in meters per second. D The distance of solid-liquid interface migration during the reglow process is expressed in meters. This represents the moment when the solid-liquid interface migration begins during the reglow process captured by the CMOS camera. The time indicated by the CMOS camera captures the end of the solid-liquid interface migration during the reglow process, with each time measured in seconds.

[0035] Specifically, if key physical properties of the alloy are missing, the rapid solidification dendrite growth rate can be determined by using the reglow time and alloy size of the alloy melt recorded in the containerless experiment on the space station using an infrared thermometer. In the same formula... t 1 represents the start time of the temperature curve re-ignition. t 2 represents the end of the reheating of the temperature curve. If the dendrite growth rate is determined experimentally, a power function fitting is needed between the dendrite growth rate and the supercooling: , where a and b are both fitting coefficients.

[0036] In one embodiment, the second relationship curve between the nucleation rate of primary phase dendrites and the degree of undercooling is as follows: (12) In the formula, The nucleation rate of dendrites in the primary phase of niobium alloy; Forward exponential factor; Interface free energy; Boltzmann's constant; It is the diffusion activation energy; It is a function of the contact angle. It is a heterogeneous nucleation process. Homogeneous nucleation; Supercooling; It is the enthalpy of fusion; Temperature of the alloy sample; is the ideal gas constant.

[0037] S4. Determine the cooling rate during the cooling phase of the containerless solidified niobium alloy sample on the space station. Based on the containerless solidification experiment on the S2 space station, the cooling rate during the cooling phase of the containerless solidified niobium alloy sample on the space station was determined, including: Select the moment when the laser starts turning off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, during the solidification experiment on the space station without containers. t ≥ t At 0, laser heating power P L ( t ) = 0; Perform a fourth-order fit on the natural radiation cooling section, and calculate the cooling rate using the fitting coefficients. R c To ensure that the niobium alloy melt cooling rate coefficient is higher than 4.0 × 10⁻⁶. -15 s -1 .

[0038] In one embodiment, the cooling rate during the cooling phase of the containerless solidified niobium alloy on the space station is determined by selecting the moment when the laser is turned off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, during the solidification experiment on the space station without containers. t ≥ t At 0, laser heating power P L ( t The coefficient c7 is 0. A fourth-order fit is performed on the natural radiation cooling section, and the cooling rate is calculated using the fitting coefficient c7. R c To ensure that the niobium alloy melt cooling rate coefficient is higher than 4.0 × 10⁻⁶. -15 s -1 This is to ensure the rapid solidification of the alloy melt.

[0039] (13) In the formula, is the thermal radiation ratio of the alloy melt, and is a dimensionless number; The relative molar mass of the material is expressed in kilograms per mole. It is the Stefan-Boltzmann constant; Let be the emissivity of the material, and be a dimensionless number. Cooling rate; The sample surface area is expressed in square meters. This refers to ambient temperature, expressed in Kelvin. The mass of the alloy sample is in kilograms. is the constant-pressure specific heat of the material, expressed in joules per mole per Kelvin.

[0040] It should be noted that the cooling rate needs to be obtained by fitting and then differentiating due to the noise in the temperature signal transmission. The rearranged equation (13) can be written in the following form for temperature and time: (14) In the formula, The temperature of the sample is in Kelvin. This refers to ambient temperature, expressed in Kelvin. For refractory metals, the following relationship generally holds, where c i For constants: (15) (16) (17) After discarding higher-order terms, the result is (18) The cooling rate was calculated using the constant c7 after fitting. R c : (19) In the formula, 1 / 4c7 is the cooling rate coefficient.

[0041] S5. Select a suitable critical subcooling degree for containerless preparation of the space station based on the first relationship curve, the second relationship curve, and the cooling rate. The determination of a suitable critical subcooling degree for containerless preparation of the space station was based on calculations and experimental results. It meets the following conditions:

[0042]

[0043]

[0044] In the formula, Indicates the critical undercooling The corresponding dendrite growth rate; Indicates the critical undercooling The nucleation rate of the corresponding primary phase dendrites; Indicates the critical undercooling The corresponding cooling rate.

[0045] In one embodiment, based on the relationship between the S3 dendrite growth rate and the undercooling... V -Δ T、 Nucleation rate I -ΔT The cooling rate of the S4 radiation cooling section, and the selection of a suitable critical undercooling degree for the experiment of preparing a uniform microstructure on the surface of solidified niobium alloy on the space station. Within a suitable subcooling range ≥ To meet the primary phase dendrite growth rate V >30 mm·s -1 This allows the alloy melt to undergo rapid solidification under deep undercooling conditions; the nucleation rate of the primary phase dendrites is superior to that of the competing phase, and in f ( θ In the case of perfectly homogeneous nucleation (→1), primary phase dendritic nucleation only occurs... ≥ ( When this condition is met, the niobium alloy will undergo deep supercooling and rapid solidification in the containerless solidification experiment, the solute trapping effect will occur, and a uniform structure composed of large-area dendrites will be generated on the surface of the niobium alloy.

[0046] S6. Based on the critical undercooling, prepare the space station without containers and control the actual undercooling during the preparation process to be greater than or equal to the critical undercooling. During the preparation of the containerless space station, a floating niobium alloy sample is controlled by three pairs of electrodes and subjected to suspension laser heating. The sample is heated to a temperature above the liquidus temperature and completely melted. The total laser heating power is controlled to keep the niobium alloy at a temperature above the liquidus temperature for 1 to 60 seconds. Then, the laser heating is stopped, and the niobium alloy radiates heat to a deep supercooled state temperature and then spontaneously nucleates and solidifies, thus completing the preparation of a uniform microstructure on the surface of the containerless niobium alloy sample for the space station.

[0047] Insulation temperature of niobium alloy for: ,in, This is the liquidus temperature; .

[0048] In one embodiment, during a containerless solidification experiment on a space station that meets the vacuum and microgravity requirements of S1, a suitable niobium alloy sample for the containerless experiment is selected according to S2. Then, the dendrite growth rate, cooling rate, and nucleation rate of the niobium alloy are determined sequentially according to S3-S4, thus determining a suitable range of undercooling. ≥ Then, a containerless experiment was conducted on the space station: a niobium alloy sample was suspended, heated, and floated under controlled conditions with three pairs of electrodes, and heated to its liquidus temperature. T L The above is completely melted, and the holding temperature of the niobium alloy is... T Keep it above the liquidus temperature. T=T L +δ T , where δT =50kJ~300kJ, heat preservation time t 'Satisfies 1 second ≤ t '≤ 60 seconds, adjust total laser heating power' P : (20) In the formula, m This refers to the mass of the alloy, measured in kilograms. M It is the relative atomic mass, and the unit is kilograms per mole; ρ L It is the liquid density of the alloy, expressed in kilograms per cubic meter. C p,L It is the specific heat of liquid at constant pressure, and the unit is joules per kJ per molar. T This is the temperature of the alloy sample, in Kelvin (K). P This is the total laser heating power, measured in watts. The insulation temperature reaches... t 'Then stop laser heating' P =0, niobium alloy radiative heat dissipation to the deep supercooled state temperature T After spontaneous nucleation and solidification, the actual undercooling Δ of the solidified niobium alloy... T = T L - T 0, if ≥ This means achieving the preparation of a uniform microstructure on the surface of a containerless solidified niobium alloy for the space station; if < Adjust the insulation temperature T and the corresponding required power P Insulation time t Repeat step seven of the space station containerless solidification experiment.

[0049] A second aspect of the present invention provides a niobium alloy with a uniform surface structure.

[0050] A third aspect of the present invention provides the application of a niobium alloy with a uniform surface structure in aero-engine turbine blades.

[0051] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0052] Example 1 This embodiment provides a niobium-silicon-zirconium alloy with the chemical composition Nb. 78 Si 16The preparation process of Zr6 includes: uniform melting in a ground electrostatic levitation experiment; initial screening of suitable samples in a containerless experiment on the space station; and determining the appropriate supercooling degree by considering the growth rate, cooling rate coefficient, and nucleation rate to achieve spontaneous nucleation and solidification. The detailed steps are as follows.

[0053] Step 1: Determine the vacuum and microgravity levels during the preparation of the uniform microstructure on the surface of the niobium alloy for the containerless experiment on the space station: In this embodiment, the alloy was prepared under a vacuum of 1.4 × 10⁻⁶. -3 Pa, the average microgravity level along the x, y, and z axes monitored by the space station is 2.1 × 10⁻⁶. -5 g The experiment was conducted under conditions of 0.

[0054] Step 2: Select samples suitable for preparing uniform microstructure of solidified niobium alloy surface in containerless space station experiments: Conduct a solidification experiment in a containerless space station, and laser heat the alloy to the liquidus temperature. T L After reaching a temperature above 2169 K, the niobium alloy melt is continuously heated at the same power until it reaches a superheated state of 2358 K. The laser is then turned off, and the temperature is lowered to 1806 K. The niobium alloy melt spontaneously undergoes a rapid solidification process involving one re-glow, with the supercooling Δ... T= 363 K (Δ) T> 0.15 T L Therefore, it is suitable for preparing a uniform microstructure on the surface of containerless solidified niobium alloys.

[0055] Step 3: Determine the relationship between the rapid solidification dendrite growth rate and the alloy undercooling of the niobium alloy. The rapid solidification growth rate of primary phase dendrites in Nb-Si-Zr alloys was calculated.

[0056] 1) Calculation of LKT / BCT rapid dendrite growth model The growth rate of the primary phase (Nb, Zr) dendrites in the Nb-Si-Zr alloy was calculated according to equations (1)-(10), and the results are as follows: Figure 1 As shown by the black curve in the middle.

[0057] 2) Experimental determination of dendrite growth rate The dendrite growth rate measured in the experiment was calculated using equation (11).

[0058] Real-time temperature measurement and imaging of the melt were performed using a non-contact infrared thermometer and a high-speed CMOS camera via ground-based electrostatic levitation experiments. The degree of supercooling during reglow was determined from the temperature curve, and the rapid solidification dendrite growth rate was calculated using CMOS camera images and alloy dimensions. The average size of the melt with the same composition was also analyzed. DThe growth rate of multiple 2.7 mm Nb-Si-Zr alloy samples was determined by ground-based electrostatic levitation experiments. The results are as follows: Figure 1 The hollow circle is shown. The calculated results agree well with the experimental results, indicating high accuracy. The rapid solidification dendrite growth rate was determined by measuring the re-glow time and alloy size of the alloy melt in the containerless experiment on the space station using an infrared thermometer. The same formula is used to... t 1 represents the start time of the temperature curve re-ignition. t 2 represents the end of the re-glow curve. A power function fit was performed on the dendrite growth rate determined by the experimental method and the supercooling: .

[0059] Step 4: Determine the cooling rate during the cooling phase: Select the moment when the laser is turned off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, when t ≥ t At 0, laser heating power P L ( t = 0. According to formulas (13) to (19), the natural radiation cooling section is fitted to the fourth power, and the cooling rate is calculated through the fitting coefficient c7. R c =4.38×10 -15 T 5 .

[0060] Step 5: Calculate the nucleation rate of the primary dendrites in the niobium alloy according to equation (12), and the results are as follows. Figure 2 As shown, the alloy is within a suitable undercooling range ≥325 K ( T At 325 K, the nucleation rate of the primary phase (Nb, Zr) dendrites was higher than that of the competing phase, and solidification was completed. f ( θ In the case of a completely homogeneous nucleation phase (→1), the nucleation rate of the primary phase is greater than 0 when the supercooling is greater than 325 K.

[0061] Step Six: Based on the relationship between dendrite growth rate and undercooling in Step Three. V -Δ T、 The cooling rate coefficient of the radiation cooling stage in step four and the nucleation rate in step five are used to select a suitable critical undercooling degree for the experiment of preparing a uniform microstructure on the surface of solidified niobium alloy in the space station. Within a suitable subcooling range ≥ The primary phase dendrite growth rate must be satisfied. V >30 mm·s-1 This allows the alloy melt to undergo rapid solidification under deep undercooling conditions; the nucleation rate of the primary phase dendrites is superior to that of the competing phase, and in f ( θ In the case of perfectly homogeneous nucleation (→1), primary phase dendritic nucleation only occurs... ≥ ( When this condition is met, the niobium alloy will undergo rapid solidification with deep undercooling in the containerless solidification experiment, resulting in a solute trapping effect and a uniform microstructure composed of large-area dendrites on the niobium alloy surface. This embodiment requires that the actual undercooling Δ... T ≥ Suitable critical undercooling =325 K.

[0062] Step 7: In the containerless solidification experiment on the space station that meets the vacuum and microgravity levels required in Step 1, select a suitable niobium alloy sample for the containerless experiment according to Step 2, and determine the dendrite growth rate, cooling rate coefficient, and nucleation rate of the niobium alloy according to Steps 3 to 5, thereby determining a suitable range of undercooling. ≥ To conduct a containerless experiment on the space station: a niobium alloy sample, suspended and heated by three pairs of electrodes under positional control, was heated to its liquidus temperature. T L The above is completely melted, and the total laser heating power is controlled. P The heat preservation temperature of niobium alloy T 0 is controlled above the liquidus temperature. T 0= T L +δ T , where δ T =50 to 300 openings, reaching T 0 heat preservation, heat preservation time t 'Satisfies 1 second ≤ t ≤ 60 seconds, to reach t 'Then stop laser heating' P =0, niobium alloy radiative heat dissipation to the deep supercooled state temperature T After 0, spontaneous nucleation and solidification occur, with an actual undercooling Δ T = T L - T 0≥ This means achieving the preparation of a uniform microstructure on the surface of a containerless solidified niobium alloy for the space station.

[0063] In this embodiment, the Nb-Si-Zr alloy was prepared by heating to 2333 K a second time, then turning off the laser, and finally undercooling at the actual degree. =337 K (> Spontaneous nucleation and solidification occur under these conditions, with typical temperature profiles as follows: Figure 3 Its mass and average diameter were measured to be 86.06 mg and 2.752 mm, respectively. The surface solidification structure of the prepared alloy was uniformly distributed and had high sphericity. The primary phase (Nb, Zr) dendrites and the (Nb, Zr) / α-(Nb, Zr)5Si3 dendrite eutectic structure were uniformly distributed. Figure 4 and Figure 5 The prepared niobium alloy sample exhibits a uniform surface microstructure distribution with no areas of surface microstructure evolution. Furthermore, it can be seen from... Figure 6 The curvature calculations show that the niobium alloy prepared by the method of this invention has small deformation and a curvature close to that of an ideal sphere.

[0064] Comparative Example 1 This embodiment provides a niobium-silicon-zirconium alloy with the chemical composition Nb. 78 Si 16 Except for the containerless experiment of ground electrostatic levitation in the ground gravity field, the other steps of Zr6 are the same as those in Example 1. The detailed steps are as follows.

[0065] Step 1: In this embodiment, the alloy is prepared under a vacuum of 2.4 × 10⁻⁶. -3 Pa, gravity level is g The experiment was conducted under conditions of 0.

[0066] Step 2: Determine the uniformity of the prepared alloy sample: Conduct a ground-based electrostatic levitation containerless solidification experiment, and laser-heat the alloy to the liquidus temperature. T L = Above 2169 K, continue heating at the same power to a superheated state of 2343 K, then turn off the laser and cool to 1808 K. The niobium alloy melt spontaneously completes a rapid solidification process with one re-glow, and the supercooling Δ T= 361 K (Δ) T> 0.15 T L ).

[0067] Step 3: Determine the relationship between the rapid solidification dendrite growth rate and the alloy undercooling of the niobium alloy. The rapid solidification growth rate of the primary phase dendrites in the Nb-Si-Zr alloy was calculated and experimentally determined. This step is the same as step three in Example 1.

[0068] Step 4: Determine the cooling rate during the cooling phase: Select the moment when the laser is turned off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, when t ≥ t At 0, laser heating power P L (t = 0. According to formulas (13) to (19), the natural radiation cooling section is fitted to the fourth power, and the cooling rate is calculated through the fitting coefficient c7. R c =4.45×10 -15 T 5 .

[0069] Step 5: Calculate the nucleation rate of the primary dendrites in the solidified alloy according to formula (12). The result is the same as in Example 1. The alloy is within a suitable undercooling range. ≥325 K ( T At 325 K, the nucleation rate of the primary phase (Nb, Zr) dendrites was higher than that of the competing phase, and solidification was completed. f ( θ In the case of a completely homogeneous nucleation phase (→1), the nucleation rate of the primary phase is greater than 0 when the supercooling is greater than 325 K.

[0070] Step Six: Similar to Example 1, this comparative example must meet the following requirements. ≥325 K.

[0071] Step 7 is the same as in Example 1, except that the ground electrostatic levitation experiment is conducted only under ground gravity conditions, without the microgravity environment required for solidification experiments on a space station or in containers. t 0< t <t 1. Actual subcooling Suitable supercooling is 325K.

[0072] In this comparative preparation of the Nb-Si-Zr alloy, the laser was turned off after a second heating to 2340 K. The niobium alloy melt was undercooled to the actual degree of... Spontaneous solidification via single-point nucleation at 369 K; typical temperature profile as shown below. Figure 7 The solidification microstructure on the prepared niobium alloy surface exhibits zoned evolution and uneven distribution. Figure 8 and Figure 9 The study presents a case of uneven microstructure distribution on the surface of niobium alloy samples prepared using this method. The surface exhibits distinct microstructure evolution zones, significant shrinkage deformation at the end of solidification, and irregularly distributed dendritic clusters within the grooved regions of the alloy surface. Furthermore, it can be seen from... Figure 10 The curvature calculations showed that the solidified alloy prepared in Comparative Example 1 was severely deformed, and its curvature deviated from that of an ideal sphere.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station, characterized in that, include: Determine the vacuum level and microgravity level of the space station preparation environment; Screening for niobium alloy samples suitable for preparation for the space station; Based on the physical property parameters of the screened niobium alloy samples, the first relationship curve between dendrite growth rate and undercooling of the niobium alloy samples, and the second relationship curve between nucleation rate of primary phase dendrites and undercooling were obtained. Determine the cooling rate during the cooling phase of a containerless solidified niobium alloy sample on the space station. The appropriate critical subcooling degree for containerless preparation of the space station was selected based on the first relationship curve, the second relationship curve, and the cooling rate. The containerless preparation of the space station was carried out based on the critical supercooling, and the actual supercooling during the preparation process was controlled to be greater than or equal to the critical supercooling. During the preparation of the containerless space station, a floating niobium alloy sample is controlled by three pairs of electrodes and subjected to suspension laser heating. The sample is heated to a temperature above the liquidus temperature and completely melted. The total laser heating power is controlled to keep the niobium alloy at a temperature above the liquidus temperature for 1 to 60 seconds. Then, the laser heating is stopped, and the niobium alloy radiates heat to a deep supercooled state temperature and then spontaneously nucleates and solidifies, thus completing the preparation of a uniform microstructure on the surface of the containerless niobium alloy sample for the space station.

2. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, Screening for niobium alloy samples suitable for preparation on the space station, including: Based on containerless solidification experiments on the space station, the alloy was heated to the liquidus temperature. T L After the above steps, turn off the laser and select the niobium alloy sample at the first re-glow undercooling Δ. T ≥0.15 T L Alloy samples.

3. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, The first relationship curve between dendrite growth rate and undercooling of niobium alloy samples was obtained based on the LKT / BCT rapid dendrite growth model, or by first experimentally determining the dendrite growth rate and then fitting the dendrite growth rate with a power function to the undercooling.

4. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, The second relationship curve between the nucleation rate of primary phase dendrites and undercooling is as follows: In the formula, The nucleation rate of dendrites in the primary phase of the alloy; Forward exponential factor; Interface free energy; Boltzmann's constant; It is the diffusion activation energy; It is a function of the contact angle. f ( θ →0 represents heterogeneous nucleation. f ( θ → 1 represents homogeneous nucleation; Supercooling; It is the enthalpy of fusion; Temperature of the alloy sample; is the ideal gas constant.

5. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, The space station prepares a suitable critical subcooling without containers. Its critical undercooling satisfies the following condition: In the formula, Indicates the critical undercooling The corresponding dendrite growth rate; Indicates the critical undercooling The nucleation rate of the corresponding primary phase dendrites; Indicates the critical undercooling The corresponding cooling rate.

6. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, Insulation temperature of niobium alloy for: in, This is the liquidus temperature; .

7. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, Determine the cooling rate during the cooling phase of the containerless solidified niobium alloy sample on the space station, including: Select the moment when the laser starts turning off. t The temperature from 0 to the start of the re-glowing moment t 1 corresponds to T - t Curve data, when t ≥ t At 0, laser heating power P L ( t ) = 0; Perform a fourth-order fit on the natural radiation cooling section, and calculate the cooling rate using the fitting coefficients. R c To ensure that the niobium alloy melt cooling rate coefficient is higher than 4.0 × 10⁻⁶. -15 s -1 .

8. The method for preparing a uniform microstructure on the surface of a containerless solidified niobium alloy for a space station according to claim 1, characterized in that, Vacuum degree < 3×10 -3 Pa, microgravity level < 10 -4 g 0, where, g 0 represents gravitational acceleration.

9. A niobium alloy with a uniform surface structure obtained by the method according to any one of claims 1 to 8.

10. The application of a niobium alloy with a uniform surface structure as described in claim 9 in aero-engine turbine blades.

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