Grain size regulation and control method suitable for additive manufacturing of titanium alloy

Abstract

The invention provides a grain size regulation and control method suitable for additive manufacturing titanium alloy, which comprises the following steps of: establishing a constitutive equation of an alloy element (X element) and an average grain size in a Ti-X binary alloy system based on double grain size variables and a linear approximation theory, and quantitatively characterizing the grain nucleation characteristic of the alloying element in the process of promoting additive manufacturing metallurgy. Quantitative and accurate regulation and control of grain refining of the titanium alloy metallurgical structure are achieved, and theoretical support is provided for grain size regulation and control during titanium alloy additive manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloys, and particularly to a method for controlling the grain size of titanium alloys suitable for additive manufacturing. Background Art

[0002] With the development of ocean engineering and deep-sea equipment towards lightweight and high-performance, the design, research and development innovation of high-strength and tough materials are important ways to solve problems, but the bottlenecks of traditional manufacturing are significant. Additive manufacturing technology can deposit materials layer by layer based on the near-net-shape forming principle, and is expected to realize the free design and manufacturing of materials. Titanium alloys are one of the most widely used materials in marine equipment due to their low density, high specific strength and good corrosion resistance. However, the extraordinary metallurgical environment of additive manufacturing and the heat and mass transfer characteristics of titanium alloys themselves result in significant columnar crystals, inhomogeneity and anisotropy in the microstructure, which have many adverse effects on their comprehensive performance. Improving the process and adding post-treatment are difficult to completely solve this problem.

[0003] At present, at home and abroad, means such as adjusting process parameters, adding external field assistance during the forming process, and adding alloying elements for regulation have been explored to optimize the metallurgical structure of titanium alloys, and some solutions to the grain refinement method have been proposed. Reducing the additive manufacturing power or energy density, changing scanning strategies and other process parameters can, to a certain extent, control the solidification and cooling rate of additive manufacturing and improve the size of columnar crystals after metal additive manufacturing. However, due to the high temperature gradient, the columnar crystals in the sample cannot be completely eliminated by such methods; adding external fields can refine grains to a certain extent, but the ideas all involve the modification and re-development of additive manufacturing equipment, with high technical requirements; using alloying elements to improve the structure of titanium alloys produced by additive manufacturing is the simplest and most effective way. Currently, research results have confirmed that alloying element addition still has the ability to refine the grain size of alloys under the non-equilibrium conditions of additive manufacturing.

[0004] In titanium alloys, the Q-value theorem is usually used to measure the grain size of alloys, that is, the reciprocal of the Q-value system has a linear relationship with the grain size d to the first power. However, when the inventor team explored the control of fully equiaxed microstructures in the additive manufacturing of Ti-2Fe alloys, it was found that the addition of trace amounts of B elements can significantly refine the microstructure morphology of Ti-2Fe alloys. Theoretically, the Q value of B in titanium alloys is 65K / wt.%, and the change in the Q value of the alloy with 0.1wt.% B addition is only 6.5K. Compared with Ti-3Fe alloys (Q = 33.3K), the grain refinement of Ti-2Fe-0.1B alloys (Q = 28.7K) is more obvious. It can be seen that it is impossible to predict the grain size of titanium alloys produced by additive manufacturing using the Q-value theory.

[0005] Therefore, it is urgent to explore the quantitative laws of the influence of alloying elements on the solidification structure and grain size transformation of titanium alloys produced by additive manufacturing, so as to provide theoretical support for controlling the grain size during the additive manufacturing of titanium alloys. Summary of the Invention

[0006] The object of the present invention is to provide a method for controlling the grain size of titanium alloys suitable for additive manufacturing to solve the problem that there is no theoretical support for controlling the grain size during the additive manufacturing of titanium alloys. By exploring the quantitative laws of alloying elements on the solidification structure and grain size transformation of additive-manufactured titanium alloys, an equation is established. Before alloy manufacturing, the corresponding content can be obtained through theoretical calculation, providing theoretical support for controlling the grain size during the additive manufacturing of titanium alloys, improving production efficiency, and reducing production costs.

[0007] According to the object of the present invention, a method for controlling the grain size of titanium alloys suitable for additive manufacturing is provided, including the following steps:

[0008] Determine the X element in the Ti-X binary alloy system; then

[0009] Select X element powders with a first average particle size, and use the laser melting deposition process to print a series of alloy specimens. Among them, the content (x1) of the X element in each specimen is different, and other conditions are the same; then, detect the average grain size (y1) of each specimen, and establish the relationship between the X element content x1 and the corresponding alloy average grain size y1 when the X element powder particle size is the first average particle size, and obtain the first equation;

[0010] Select X element powders with a second average particle size, and use the same laser melting deposition process conditions to print a series of alloy specimens. Among them, the content (x2) of the X element in each specimen is different, and other conditions are the same; then, detect the average grain size (y2) of each specimen, and establish the relationship between the X element content x2 and the corresponding alloy average grain size y2 when the X element powder particle size is the second average particle size, and obtain the second equation;

[0011] According to the first equation and the second equation, combined with the linear approximation theory between two points, establish the relationship between the alloy average grain size y and the X element content x and the average particle size d, and obtain the third equation;

[0012] Under the same laser melting deposition process conditions, determine the grain size y of the required alloy and the average particle size d of the X element powder to be added, and obtain the corresponding X element content x through the third equation.

[0013] As an optional implementation manner, x1, x2, and x need to be controlled within the content range where the X element can form a solid solution with Ti and no precipitation phase is generated. The range of the content Z where X can form a solid solution with Ti and no precipitation phase is defined as 0 to L.

[0014] As an optional implementation manner, if x is not within the content range where the X element can form a solid solution with Ti and no precipitation phase is generated, adjust it according to the following method:

[0015] When x > L or there is no solution for x, decrease the value of d until x is within the range of Z;

[0016] When x < 0, increase the value of d until x is within the range of Z.

[0017] As an optional implementation manner, use a single exponential growth function to fit the relationship curve between the content x1 of element X and the average grain size y1 of the alloy, and obtain the first equation as shown in Equation (1):

[0018]

[0019] In the formula, y1 is the average grain size of the alloy, μm; x1 is the content of element X, wt.%; t, A1, and B1 are constant parameters.

[0020] As an optional implementation manner, use a single exponential growth function to fit the relationship curve between the content x2 of element X and the average grain size y2 of the alloy, and obtain the second equation as shown in Equation (2):

[0021]

[0022] In the formula, y2 is the average grain size of the alloy, μm; x2 is the content of element X, wt.%; t, A2, and B2 are constant parameters.

[0023] As an optional implementation manner, the third equation is as shown in Equation (3):

[0024]

[0025] In the formula, y is the average grain size of the alloy, μm; x is the content of element X, wt.%; d is the average particle size of the element X powder, μm; t is a constant parameter;

[0026] A(d) = A0 + k1ln(d), where A0 and k1 are calculated according to the equation set and d1 is the first average particle size, μm;

[0027] B(d) = B0 + k2ln(d), where B0 and k2 are calculated according to the equation set and d2 is the second average particle size, μm.

[0028] As an optional implementation manner, when establishing the first equation and the second equation, at least three different content gradients of element X are set.

[0029] As an optional implementation manner, the first average particle size is in the micron level, and the second average particle size is in the nanometer level.

[0030] As an optional implementation manner, the element X is a β-stable element.

[0031] As an optional embodiment, the X element includes the Fe element.

[0032] As can be seen from the above technical solution of the present invention, the method for regulating the grain size applicable to additive manufacturing of titanium alloy proposed by the present invention, in the Ti-X binary alloy system, based on the double grain size variable and linear approximation theory, establishes a constitutive equation between the alloying element (X element) and the average grain size, quantitatively characterizes the grain nucleation characteristics of the alloying element promoting the additive manufacturing metallurgical process, realizes the quantitative and precise regulation of the fine grain of the titanium alloy metallurgical structure, and provides a theoretical support for regulating the grain size during the additive manufacturing of titanium alloy. Description of the Drawings

[0033] Figure 1 is a flowchart of the method for regulating the grain size applicable to additive manufacturing of titanium alloy of the present invention.

[0034] Figure 2 is a microstructural morphology diagram of Ti-Fe alloys with different Fe addition amounts when the average particle size of iron powder is 85 μm in the example of the present invention; among them, a is Ti-1Fe alloy, b is Ti-2Fe alloy, c is Ti-3Fe alloy, d is Ti-4Fe alloy, and e is Ti-5Fe alloy.

[0035] Figure 3 is a distribution diagram of the average grain size of Ti-Fe alloys with different Fe addition amounts when the average particle size of iron powder is 85 μm in the example of the present invention.

[0036] Figure 4 is a fitting curve of the average grain size of Ti-Fe alloys with different Fe addition amounts when the average particle size of iron powder is 85 μm in the example of the present invention.

[0037] Figure 5 is a fitting curve of the average grain size of Ti-Fe alloys with different Fe addition amounts when the average particle size of iron powder is 360 nm in the example of the present invention. Detailed Embodiments

[0038] In order to better understand the technical content of the present invention, specific embodiments are hereby given and described in conjunction with the accompanying drawings as follows.

[0039] In the present disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to cover all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those concepts and embodiments described in more detail below, can be implemented in any one of many ways.

[0040] The restriction mechanism of high solute alloying elements on the grain size of titanium alloys can be described as follows: the enrichment of solute elements in the liquid before the growth of crystals reduces the initial crystal growth rate, increases the maximum supercooling that can be achieved before regeneration, and thus triggers particle nucleation, increasing the effective nucleation density and reducing the grain size. Based on this mechanism, the present invention proposes a method for controlling the grain size of titanium alloys suitable for additive manufacturing. By designing the constitutive equation between the grain size of the alloy and the particle size and content of the added element powder under given laser process parameters, the alloying design of additive manufacturing titanium alloys can be guided.

[0041] The influence of the particle size of the powder on the grain size of the alloy is as follows: when the powder particle size levels are the same (micrometer-sized Ti powder / micrometer-sized added element powder), they are mainly mixed in a substitutional form. With less content of the added element in the same melt pool area, fewer nucleation sites are generated during solidification, resulting in coarser grain size; when the powder particle size levels are different (micrometer-sized Ti powder / nanometer-sized alloying element), the nanometer-sized added element powder mostly exists in an interstitial form and simultaneously wets and modifies the surface of the Ti powder. More and more uniform added elements are generated in the same melt pool area, producing enough heterogeneous nucleation sites, which is beneficial to the refinement of the grain size of the titanium alloy microstructure.

[0042] Therefore, the present invention provides technical support for controlling the grain size during the additive manufacturing of titanium alloys by establishing the constitutive equation between the average grain size of the binary alloy and the content of the added element and the powder particle size to guide alloy design. Through experimental data fitting and linear approximation theory, the present invention has established a quantitative relationship (the third equation) between the content of the alloying element (element X), the powder particle size (d), and the grain size (y), providing a predictable model for controlling the grain size of additive manufacturing titanium alloys for the first time. By implementing the present invention, it is not necessary to rely on repeated experimental trials and errors. The content of element X can be directly determined by theoretical calculation before alloy manufacturing, significantly improving the R & D efficiency and reducing the material design cost.

[0043] Combined with Figure 1 As shown in the preferred example of the present invention, a method for controlling the grain size of titanium alloys suitable for additive manufacturing is provided, including the following steps:

[0044] Determine the element X in the Ti-X binary alloy system; then

[0045] Select X-element powder with a first average particle size and use the laser melting deposition process to print a series of alloy specimens, where the content (x1) of the X element in each specimen is different and other conditions are the same; then, detect the average grain size (y1) of each specimen, establish the relationship between x1 and the corresponding average grain size y1 of the alloy when the particle size of the X-element powder is the first average particle size, and fit the relationship curve between x1 and y1 using a single exponential growth function to obtain the first equation, as shown in Equation (1):

[0046]

[0047] In the formula, y1 is the average grain size of the alloy, in μm; x1 is the element content, in wt.%; t, A1, and B1 are constant parameters.

[0048] X-element powder with the second average particle size is selected, and a series of alloy specimens are printed under the same laser melting deposition process conditions. Among them, the content (x2) of the X element in each specimen is different, and other conditions are the same; then, the average grain size (y2) of each specimen is detected, and the relationship between the X element content x2 and the corresponding average grain size y2 of the alloy is established when the particle size of the X element powder is the second average particle size. The relationship curve between x2 and y2 is fitted with a single exponential growth function to obtain the second equation, as shown in Equation (2):

[0049]

[0050] In the formula, y2 is the average grain size of the alloy, in μm; x2 is the element content, in wt.%; t, A2, and B2 are constant parameters.

[0051] According to the first equation and the second equation, combined with the linear approximation theory between two points, the relationship between the average grain size y of the alloy, the content x of the X element, and the average particle size d is established to obtain the third equation, as shown in Equation (3):

[0052]

[0053] In the formula, y is the average grain size of the alloy, in μm; x is the element content, in wt.%; d is the average particle size of the X-element powder, in μm; t is a constant parameter;

[0054] A(d) = A0 + k1ln(d), where A0 and k1 are calculated according to the system of equations and d1 is the first average particle size, in μm;

[0055] B(d) = B0 + k2ln(d), where B0 and k2 are calculated according to the system of equations and d2 is the second average particle size, in μm.

[0056] Under the same laser melting deposition process conditions, when the average grain size y of the required alloy and the average particle size d of the X-element powder to be added are determined, the corresponding content x of the X element can be obtained through Equation (3).

[0057] In an alternative example, the X element is a β-stabilizing element, for example, Fe, Cu, etc.

[0058] In an alternative example, x1, x2, and x need to be controlled within the content range where the X element can form a solid solution with Ti without forming a precipitate phase, so as to achieve the effect of grain refinement. For example, if the added element is Fe, the content range is generally 0 wt.% to 5 wt.%. Therefore, the content range Z of X that can form a solid solution with Ti without forming a precipitate phase is defined as 0 to L.

[0059] It can be understood that the determination of the content range where the X element can form a solid solution with Ti without forming a precipitate phase is prior art and can be determined according to existing literature or technical manuals.

[0060] In an alternative example, when x is not within the content range where the X element can form a solid solution with Ti without forming a precipitate phase, it is adjusted according to the following method:

[0061] When x > L or x has no solution, the d value is lowered until x is within the range of Z;

[0062] When x < 0, the d value is raised until x is within the range of Z.

[0063] In an alternative example, when establishing the first equation and the second equation, at least three different content gradients of the X element are set. Moreover, when establishing the equations twice, the same content of the X element can be set, or different contents of the X element can be set; for example, when establishing the first equation, the content gradients of the X element are 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, and when establishing the second equation, the content gradients of the X element can be 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, or can be 1 wt.%, 2 wt.%, 3 wt.%, or 0 wt.%, 2 wt.%, 4 wt.%, etc., which do not affect the establishment of the equations.

[0064] In an alternative example, the first particle size is in the micrometer range, and the second particle size is in the nanometer range; it can be understood that the first particle size and the second particle size are the average particle sizes of the X element powder. The X element powder can be a mixed powder of different particle sizes, and the average particle size is obtained by measurement. For example, first, the SEM micrograph of the powder is taken, and then software such as Image J or NanoMeasure is used to analyze and obtain the average particle size of the powder; or, a particle size analyzer is directly used to measure and obtain the corresponding average particle size.

[0065] In an alternative example, the average particle size of the titanium powder is in the micrometer range.

[0066] In combination with the design of the grain size control method of the titanium alloy of the above embodiment, based on the dual variable coupling analysis, while accurately controlling the grain size, the alloy performance is ensured by optimizing the composition-organization matching. In the design method of the present invention, the powder particle size (micrometer level / nanometer level) of the X element is incorporated into the model for the first time, revealing the synergistic mechanism of the powder particle size and element content on the grain size. For example, nanometer-level powder may refine the grains by increasing the nucleation site, while micrometer-level powder may affect the diffusion rate. The model fits the laws under different particle sizes respectively through two equations (the first and second equations), and then couples them through the third equation to achieve multivariable precise control. The experimental data are further fitted with a single exponential growth function, which conforms to the kinetic law of grain growth. The sampling is combined with the linear approximation theory between two points to convert the discrete particle size-content-grain size relationship into a continuous and solvable mathematical model, which is suitable for prediction of different particle size ranges and precise control of grain size.

[0067] In the design method of the present invention, the solid solution composition is constrained to clearly limit the X element content to a precipitate-free solid solution range (0-L), avoiding precipitation defects caused by improper composition and ensuring the uniformity of the alloy structure and the stability of mechanical properties. Combined with the designed adaptive adjustment mechanism, when the calculated X element content exceeds the reasonable range (e.g., x>L or x<0), the powder particle size (d) is adjusted to reversely optimize the composition, achieving a coordinated optimization of the composition and process parameters, enhancing the practicality and robustness of the method, achieving an optimized match between composition and structure, and ensuring alloy performance.

[0068] It is understandable that in the actual application process, errors will be caused by the preparation environment and conditions. The method of the present invention can provide an early estimate, and then those skilled in the art can make targeted adjustments according to the actual situation. In this way, it can still provide basic support for grain size control during additive manufacturing of titanium alloys and shorten the early exploration process. Predict the composition-organization relationship in advance through theoretical models, reduce the number of trial-and-error-detection-correction cycles, greatly shorten the process development cycle of additive manufacturing of titanium alloys, and reduce production costs. In particular, when establishing the first and second equations, at least three X element content gradients are set to ensure the statistical reliability of the fitting curve and reduce the influence of accidental errors; focus on β-stabilizing elements (such as Fe), which have a significant effect on the β phase transformation and grain nucleation during the solidification process of titanium alloys. The goal is clear and the control effect is more prominent, providing a scientific and efficient technical path for the composition design and organization optimization of high-performance titanium alloys required in deep sea, aerospace and other fields.

[0069] In the following exemplary embodiments of the present invention, a Ti-Fe binary alloy is taken as an example.

[0070] Commercial titanium powder and iron powder with a size range of 53 - 150 μm are selected to print as-deposited samples of the Ti-Fe binary alloy system with different Fe addition amounts through laser melting deposition. Then, by exploring the effect of Fe content on the average grain size, a fitting equation between the average grain size and the content of the added element is established for a single element at a single particle size. Finally, combined with the linear approximation theory between two points, a quantitative relationship model among the particle size of iron powder, the content of iron powder, and the average grain size is established.

[0071] The specific process includes:

[0072] Step 1: Use laser melting deposition to print as-deposited samples of the Ti-Fe binary alloy system with element addition. The laser power is 2000 W, the powder feeding rate is 6.1 g / min, the scanning rate is 1200 mm / min, the overlapping rate is 50%, the spot diameter is 2 mm, the layer thickness is 0.8 mm, the particle size of Fe powder is 53 - 150 μm (first, take SEM micrographs of the powder, and then analyze it using Image J software to obtain an average particle size of 85 μm). The Fe powder contents are 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, and 5 wt.% respectively, and five as-deposited samples (length × width × height = 40 mm × 40 mm × 40 mm) are printed.

[0073] Use Image J software to measure the grain size, combined with Figure 2 and 3 As shown, the Ti-1Fe alloy consists of coarse columnar grains, and the grains are evenly distributed throughout the deposition layer. The width of the coarse columnar grains can reach nearly 500 μm; the Ti-2Fe alloy consists of coarse columnar grains, and the distribution is uneven, with an average grain size of 238.64 μm; with the addition of Fe, the Ti-3Fe alloy shows a combination of equiaxed grains and columnar grains, and the average grain size decreases to 145.59 μm; as for the Ti-4Fe and Ti-5Fe alloys, both are equiaxed grains, and the average grain sizes further decrease to 134.84 μm and 109.90 μm respectively.

[0074] Statistics on the grain size distribution of Ti-Fe alloys with different Fe contents show that the average grain size is not directly proportional to the Fe content, but first decreases rapidly and then gradually stabilizes as the Fe content in the alloy increases.

[0075] Therefore, as Figure 4 shown, import the data into origin software for curve fitting. The fitting curve selects a single exponential growth function to obtain Equation (4):

[0076]

[0077] That is, when the particle size d1 of the iron element powder is 85 μm, A1 = 394.5 and B1 = 51.4.

[0078] Step 2: Use laser melting deposition to print the as-deposited samples of the Ti-Fe binary alloy system with element addition. The laser power is 2000 W, the powder feeding rate is 6.1 g / min, the scanning rate is 1200 mm / min, the overlapping rate is 50%, the spot diameter is 2 mm, the layer thickness is 0.8 μm, and the particle size of the Fe powder is 200 - 500 nm (first take SEM micrographs of the powder, and then use Image J software for analysis to obtain an average particle size of 360 nm). The Fe powder contents are 0 wt.%, 2 wt.%, and 4 wt.% respectively, and print five as-deposited samples (length × width × height = 40 mm × 40 mm × 40 mm).

[0079] Use Image J software to measure the grain size. The average grain size of pure Ti is 442.3 μm, the average grain size of Ti-2Fe is 196.5 μm, and the average grain size of Ti-4Fe is 105.4 μm.

[0080] As Figure 5 shown, import the data into origin software for curve fitting. The fitting curve selects the single exponential growth function to obtain Equation (5):

[0081]

[0082] That is, when the particle size d2 of the iron element powder is 360 nm, A2 = 390.5 and B2 = 51.8.

[0083] Step 3: According to Equations (4) and (5), unify the two equations to obtain Equation (6):

[0084]

[0085] According to the linear relationship theory between two points, obtain the relationships between A and d, and B and d:

[0086] A(d) = A0 + k1ln(d)

[0087] B(d) = B0 + k2ln(d)

[0088] Fit with ln(d) as the independent variable, that is

[0089]

[0090] Therefore, transform Equation (6) to obtain Equation (7):

[0091]

[0092] Therefore, under the same laser melting deposition process conditions, if an alloy with an average grain size of y is desired e , the average particle size of the iron powder to be used is d e , and the content x of the added iron powder can be determined by Equation (7), thus avoiding repeated samples and directly through theoretical calculation.

[0093] For example, when y e = 100 nm and d e = 100 nm, substituting into Equation (7) gives x = 4.2. That is, by adding iron powder with an average diameter of 100 nm, the content of iron element is 4.2 wt.%. Under the conditions of a laser power of 2000 W, a powder feeding rate of 6.1 g / min, a scanning rate of 1200 mm / min, a lap rate of 50%, and a spot diameter of 2 mm, laser melting deposition forming is carried out to obtain a Ti-Fe binary alloy with an average grain size of 100 nm.

[0094] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the claims.

Claims

1. A method for controlling the grain size of titanium alloys suitable for additive manufacturing, characterized in that, It includes the following steps: Determine the X element in the Ti-X binary alloy system; then Select X element powder with a first average particle size and use the laser melting deposition process to print a series of alloy specimens. Among them, the content x1 of the X element in each specimen is different, and other conditions are the same; then, detect the average grain size y1 of each specimen, establish the relationship between the content x1 of the X element and the corresponding average grain size y1 of the alloy when the particle size of the X element powder is the first average particle size, and obtain the first equation; Select X element powder with a second average particle size and use the same laser melting deposition process conditions to print a series of alloy specimens. Among them, the content x2 of the X element in each specimen is different, and other conditions are the same; then, detect the average grain size y2 of each specimen, establish the relationship between the content x2 of the X element and the corresponding average grain size y2 of the alloy when the particle size of the X element powder is the second average particle size, and obtain the second equation; According to the first equation and the second equation, combined with the linear approximation theory between two points, establish the relationship between the average grain size y of the alloy, the content x of the X element, and the average particle size d, and obtain the third equation; Under the same laser melting deposition process conditions, determine the average grain size y of the required alloy and the average particle size d of the X element powder to be added, and obtain the corresponding content x of the X element through the third equation.

2. The grain size control method for additive manufacturing titanium alloy according to claim 1, wherein In the said method, the parameters x1, x2, and x need to be controlled within the content range where the X element can form a solid solution with Ti and no precipitation phase is generated. Define the content range Z where X can form a solid solution with Ti and no precipitation phase is generated as 0 to L.

3. The grain size control method for additive manufacturing titanium alloy according to claim 2, wherein If x is not within the content range where the X element can form a solid solution with Ti and no precipitation phase is generated, adjust it according to the following method: When x > L or x has no solution, lower the d value until x is within the range of Z; When x < 0, increase the d value until x is within the range of Z.

4. The grain size control method for additively manufactured titanium alloys according to claim 1, wherein Use a single exponential growth function to fit the relationship curve between the content x1 of the X element and the alloy grain size y1, and obtain the first equation, as shown in Equation (1): In the formula, y1 is the average grain size of the alloy, μm; x1 is the content of the X element, wt.%; t, A1, and B1 are constant parameters.

5. The grain size control method for additive manufacturing titanium alloy according to claim 4, characterized in that Use a single exponential growth function to fit the relationship curve between the content x2 of the X element and the alloy grain size y2, and obtain the second equation, as shown in Equation (2): In the formula, y2 is the average grain size of the alloy, μm; x2 is the content of the X element, wt.%; t, A2, and B2 are constant parameters.

6. The grain size control method for additive manufacturing titanium alloy according to claim 5, characterized in that, The said third equation is shown in Equation (3): In the formula, y is the average grain size of the alloy, μm; x is the content of the X element, wt.%; d is the average particle size of the X element powder, μm; t is a constant parameter; A(d) = A0 + k1ln(d), where A0 and k1 are calculated according to the system of equations d1 is the first average particle size, in μm; B(d) = B0 + k2ln(d), where B0 and k2 are calculated according to the equations d2 is the second average particle size, in μm.

7. The grain size control method for additive manufacturing of titanium alloy according to claim 1, characterized in that: When establishing the first equation and the second equation, at least three different content gradients of the X element are set.

8. The grain size control method for additive manufacturing titanium alloy according to claim 1, wherein The first average particle size is in the micron level, and the second average particle size is in the nanometer level.

9. The grain size control method for additively manufacturing titanium alloy according to any one of claims 1 to 8, characterized in that: The X element is a β-stable element.

10. The grain size control method for additive manufacturing titanium alloy according to any one of claims 1-8, characterized in that, The X element includes Fe element.

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