Method for improving electron beam additive manufacturing TiAl alloy structure uniformity

Abstract

The invention provides a method for improving the structure uniformity of an electron beam additive manufacturing TiAl alloy, and relates to the technical field of additive manufacturing TiAl alloys. The method for improving the structure uniformity of the TiAl alloy manufactured through the electron beam additive specifically comprises the following steps that a base plate is preheated, specifically, the temperature of the base plate is preheated to 1100-1300 DEG C, and the forming environment temperature is not lower than 1000 DEG C; tiAl alloy powder is preheated, wherein non-focusing electron beams are adopted in the preheating mode, and gradient increasing is adopted in the heat input mode; and filling scanning: designing a defocusing value according to the energy density, and regulating and controlling the molten pool morphology and the molten pool thermal gradient. According to the method, the TiAl alloy component is prepared through substrate preheating, TiAl alloy powder preheating and filling scanning, through linkage optimization of electron beam non-focusing scanning key parameters, the forming process window of intermetallic compounds is effectively widened, the applicability of the TiAl alloy in the field of additive manufacturing is greatly improved, and the method is suitable for large-scale popularization and application. And a reliable method is provided for preparation of high-performance components.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of TiAl alloys, and in particular to a method for improving the microstructure uniformity of TiAl alloys manufactured by electron beam additive manufacturing. Background Art

[0002] TiAl alloys, with a density only half that of traditional nickel-based superalloys, have attracted significant attention for weight reduction and performance improvement in high-temperature components such as aerospace engine turbine blades. However, their application still faces technical challenges, including room-temperature brittleness, low plasticity, and the difficulty of machining complex parts using traditional processes. Additive manufacturing, which directly forms complex structures by stacking them layer by layer, offers advantages such as high material utilization and manufacturing flexibility. It effectively addresses the limitations of traditional processing and is particularly well-suited to the aerospace industry's demanding requirements for lightweight and complex structures. It also significantly shortens production cycles, reduces costs, and optimizes designs.

[0003] In recent years, additive manufacturing (AM) has been initially applied to the fabrication of TiAl alloys. However, these alloy parts commonly suffer from microstructural inhomogeneity, primarily manifested by the formation of banded structures. This phenomenon is closely related to the complex thermal cycling of the melt pool during AM. In processes such as electron beam powder bed fusion (EB-PBF) or selective laser melting, the temperature gradient and cooling rate of the melt pool significantly influence the distribution of alloying elements and phase transformation behavior. For example, the vacuum environment and localized high temperatures cause the lightweight element Al to volatilize, resulting in Al-poor upper portions and Al-rich lower portions of the melt pool, creating compositional and structural inhomogeneities. This banded microstructure leads to anisotropic tensile properties, severely impacting mechanical stability and service reliability, and limiting the performance evaluation of TiAl alloys and their application in critical applications.

[0004] Despite advances in process optimization and heat treatment technologies, improvements in microstructural uniformity in additively manufactured TiAl alloys remain limited. In particular, heat treatment struggles to eliminate banding caused by uneven element distribution, which can be inherited in subsequent stages. Therefore, it is necessary to adjust process parameters to eliminate or mitigate banding during the printing process. However, this approach is currently lacking, and further research is urgently needed to provide technical support for additive manufacturing of TiAl alloys and the production of key components.

[0005] For example, Chinese patent CN115194180A discloses a heat treatment method for homogenizing the structure of titanium alloys manufactured by additive manufacturing. In fact, the titanium alloy components are first obtained by additive manufacturing, and then homogenization treatment and induction coil heat treatment are performed to homogenize the structure of the titanium alloy. The banding structure is not effectively eliminated or weakened. Chinese patent CN116240476A also heat treats the finished titanium aluminum alloy to obtain a uniform structure. The structure of the banding structure is still very obvious. The same is true for Chinese patents CN115044848A and CN117753990A.

[0006] Chinese patent CN113118606A discloses a method for electron beam fuse additive manufacturing of large titanium aluminum alloy components. The method includes pre-processing and fixing the substrate, then establishing a component model and performing layered slicing and path planning on the model. After heating the substrate, wire is fed in so that the wire is melted on the surface of the substrate by the electron beam, and the final part is formed by layer deposition after single layer deposition. Obviously, the prepared product has the technical defect of uneven structure.

[0007] Chinese patent CN112872364A discloses a method and apparatus for 3D printing γ-TiAl alloy in a static magnetic field. The method obtains γ-TiAl alloy by 3D printing pre-alloyed powder under the action of a static magnetic field perpendicular to the 3D printing direction. Although this method can improve the density, tensile strength, and hardness of the prepared alloy, the structural uniformity is not well improved, and the elongation is also low. Summary of the Invention

[0008] In order to solve the technical problems in the prior art, the microstructure of TiAl alloy manufactured by electron beam additive manufacturing is improved by heat treatment after additive manufacturing, which leads to uneven volatilization of Al elements and obvious banding structure, as well as the technical problems that although the alloy powder is improved and static magnetic field is added to the printing process to improve the density, it cannot improve the uniformity of the structure. The present invention proposes a method for improving the uniformity of the structure of TiAl alloy manufactured by electron beam additive manufacturing that can solve the above technical problems. The technical solution is as follows:

[0009] A method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing, the method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing specifically comprises the following steps:

[0010] S1. Substrate preheating: preheat the substrate temperature to 1100-1300℃, and the forming environment temperature is not lower than 1000℃;

[0011] S2. Preheating of TiAl alloy powder: The preheating method uses a non-focused electron beam, and the heat input method adopts a gradient increase to gradually optimize the powder bed temperature field and achieve pre-sintering;

[0012] S3, filling scan: Design the defocus value according to the energy density to control the molten pool morphology and thermal gradient.

[0013] Optionally, S1 substrate preheating uses a high-energy electron beam to rapidly scan and heat the substrate. To prevent thermal deformation, a strategy of long preheating with a small beam current and high scan rate (30-45 minutes to 600-800°C) and short preheating with a large beam current (20-30 minutes to 1100-1300°C) is employed to achieve a stable temperature field within the forming chamber. This strategy ensures uniform temperature distribution, effectively reduces thermal deformation of the substrate, and optimizes the thermal environment of the entire forming chamber.

[0014] Optionally, the S1 scan parameters are: long preheating: beam current 15-20 mA, scan speed 20-30 m / s, time 40-60 min, defocusing 20-30 mA; short preheating: beam current 35-40 mA, scan speed 20-30 m / s, time 20-30 min, defocusing 20-30 mA.

[0015] Optionally, S2 uses a preset preheating stabilization layer, and sets the range of 5mm from the substrate as the stabilization layer range; within the stabilization layer range, the powder bed preheating parameters use a small beam flow, slow scanning speed, and large defocusing preheating method to perform preliminary powder pre-sintering, and then gradually increase the beam flow to increase the overall heat input and perform secondary sintering on the powder.

[0016] Optionally, the S2 powder bed preheating scanning direction is rotated 90° every other layer, the stable layer is the first 50-100 layers, the powder layer thickness is 50-100μm, and the scanning parameter range is: stable layer, beam current 10-30mA, scanning speed 15-30m / s, defocus 15-40mA; after exceeding the stable layer, the powder bed preheating scanning parameter range is: beam current 20-40mA, scanning speed 15-30m / s, defocus 20-50mA.

[0017] Optionally, the S3 filling scan uses an unfocused electron beam for filling scanning, and the melting parameters are designed according to different energy densities.

[0018] Optionally, the S3 filling spacing is 50-200μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 0-180°, the electron beam defocus amount is ±1-±20mA, the filling beam current is 3-20mA, the filling speed is 0.5-10m / s, and the surface energy density range is 1-10J / mm 2, within this process parameter range, the melt pool width-to-depth ratio is maintained at 1.7-2.3. In this step, by matching different defocus values ​​at a given energy density and conducting single-pass experiments to measure the melt pool width-to-depth ratio, the melt pool width-to-depth ratio is controlled within an appropriate predetermined range (1.7-2.3). This allows the selection of a suitable defocus value, optimizes the distribution of the temperature field within the melt pool, and thus controls the evaporation of aluminum. If the defocus value is too small (too focused, with a melt pool width-to-depth ratio less than 1.7), the energy input is too high, the Al element volatilizes severely, and a banded structure is evident. If the defocus value is too large (too defocused, with a melt pool width-to-depth ratio greater than 2.3), insufficient melting occurs, affecting the density of the material.

[0019] Optionally, the S1 substrate preheating temperature should be greater than 1100° C., and the substrate edge should not be warped.

[0020] Optionally, during the S2 powder bed preheating process, there is no powder jumping phenomenon, and after the powder preheating is completed, the powder surface has no metallic luster, no peeling and no compaction phenomenon. In this surface state, the powder is well preheated.

[0021] Optionally, during the S2 powder bed preheating process, the composition of the TiAl alloy powder is Ti-(42-48)Al-(0-2)Cr-(5-15)Nb-(0-2)Si, and the powder particle size is 53-150 μm; gas atomization or rotating electrode powder is used; the TiAl alloy powder has a smooth surface and a sphericity greater than 0.93.

[0022] Optionally, the molten pool width-to-depth ratios of the prepared TiAl alloy are 1.44, 2.3, 1.42, and 2.3, respectively.

[0023] Optionally, when the molten pool width-to-depth ratio of the prepared TiAl alloy is 1.42-2.3, the density is 4.25-4.27 g / cm 3 , tensile strength is 850-875MPa, and elongation is 0.5-0.62%.

[0024] Optionally, when the molten pool width-to-depth ratio of the prepared TiAl alloy is greater than or equal to 2.3, the density is 4.27-4.3 g / cm 3 , tensile strength is 890-900MPa, and elongation is 0-0.2%.

[0025] The innovations and bottlenecks overcome by the present invention are:

[0026] Bottlenecks of conventional technology: The primary method for preparing TiAl alloys using EB-PBF is to achieve Al redistribution through heat treatment to homogenize the microstructure. However, for large components, heat treatment makes it difficult to ensure consistency between the core and the outer surface, and the resulting grain size often coarsens, leading to degraded performance. Furthermore, while reducing energy input (e.g., lowering the beam current, increasing the scan rate, or increasing the line offset) can reduce Al volatilization, it can easily lead to incomplete fusion defects, making it difficult to obtain high-density materials.

[0027] The invention's innovation lies in controlling the energy density in the powder bed by adjusting the defocusing value of the electron beam, optimizing the temperature distribution within the melt pool, reducing excessive evaporation of the Al element, and significantly improving the microstructure uniformity of the TiAl alloy. This novel process control method not only overcomes the limitations of existing technologies but also provides a reliable solution for industrial applications.

[0028] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0029] The above scheme, the present invention proposes a method for improving the uniformity of the structure of TiAl alloy manufactured by electron beam additive manufacturing, which can solve the technical problems in the existing technology, such as the poor uniformity of the microstructure of TiAl alloy manufactured by electron beam additive manufacturing caused by uneven volatilization of Al elements and obvious banded structure through heat treatment method after additive manufacturing, as well as the technical problems that although the density can be improved by improving the alloy powder and adding a static magnetic field to the printing process, the uniformity of the structure cannot be improved.

[0030] The present invention precisely controls the forming environment temperature, suppresses powder blowing in the powder bed, and matches the relationship between energy input and defocusing amount to accurately regulate the depth and width of the molten pool and optimize the temperature gradient of the molten pool, thereby effectively solving the problem of obvious banding structure caused by uneven volatilization of the Al element and significantly improving the structural uniformity of the TiAl alloy.

[0031] This invention significantly improves build quality and structural uniformity during electron beam additive manufacturing (EBAM) through scientific thermal management methods. Substrate preheating utilizes a progressive heating strategy, initially using a small, long-duration preheating beam followed by a large, short-duration preheating beam. This ensures uniform substrate temperature distribution, effectively reducing thermal stress caused by local temperature differences, thereby minimizing the risk of substrate deformation and improving build stability.

[0032] During the powder preheating process, the present invention achieves precise control of the local temperature field of the powder bed by dynamically adjusting the scanning beam current, scanning speed and defocusing amount of the electron beam, thereby avoiding the "powder blowing" phenomenon caused by local overheating of the powder. During the electron beam forming process, the present invention accurately controls the depth and width of the molten pool by matching the relationship between energy input and defocusing amount, thereby optimizing the temperature gradient of the molten pool, solving the problems of uneven volatilization of Al elements and obvious banded structure, and greatly improving the structural uniformity of TiAl alloys. Specifically, by reasonably increasing positive defocusing, not only the width-to-depth ratio of the molten pool is increased, the shape of the molten pool is optimized, and the thermal gradient is reduced, but also the electron beam energy distribution is made more uniform, the energy action area is effectively expanded, and the heat input per unit area of ​​the powder bed is reduced.

[0033] The present invention promotes the formation of equiaxed gamma crystals by increasing the amount of defocus, reduces grain size differences, optimizes the temperature gradient distribution within the molten pool, reduces Al volatilization in the upper part of the molten pool, weakens the banded structure, improves the uniformity of the structure, and thus improves the mechanical properties of the alloy. The optimized molten pool temperature gradient also solves the problem of uneven Al volatilization caused by the large temperature difference between the top and bottom, and suppresses the risk of structural differences within the molten pool. By adjusting the amount of defocus to control the depth-to-width ratio of the molten pool, the molten pool shape is made more stable, a uniform thermal cycle is achieved, and the formation of banded structure is reduced, ultimately obtaining a TiAl alloy component with better performance.

[0034] In summary, compared with the traditional technology of TiAl alloy additive manufacturing and heat treatment, the present invention prepares TiAl alloy components through substrate preheating, TiAl alloy powder preheating and filling scanning. Through the coordinated optimization of key parameters of electron beam non-focused scanning, it not only effectively broadens the forming process window of intermetallic compounds, but also greatly improves the applicability of TiAl alloy in the field of additive manufacturing, providing a reliable method for the preparation of high-performance components; this method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 This is a single melt microstructure backscatter image of a method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing according to Example 1 of the present invention;

[0037] Figure 2This is a backscattered image of a TiAl alloy sample additively manufactured by a method for improving the microstructure uniformity of TiAl alloys additively manufactured by electron beam in Example 1 of the present invention;

[0038] Figure 3 EPMA-Al element distribution diagram of a TiAl alloy sample additively manufactured by a method for improving the microstructure uniformity of TiAl alloys manufactured by electron beam additive manufacturing according to Example 1 of the present invention;

[0039] Figure 4 This is a backscattered image of the single melt microstructure of Comparative Example 1 of the present invention;

[0040] Figure 5 This is a backscattered image of the TiAl alloy sample of Comparative Example 1 of the present invention;

[0041] Figure 6 EPMA-Al element distribution diagram of the TiAl alloy sample of Comparative Example 1 of the present invention;

[0042] Figure 7 This is a single-melt microstructure backscatter image of a method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing according to Example 2 of the present invention;

[0043] Figure 8 This is a backscattered image of a TiAl alloy sample additively manufactured by a method for improving the microstructure uniformity of TiAl alloys additively manufactured by electron beam in Example 2 of the present invention;

[0044] Figure 9 EPMA-Al element distribution diagram of a TiAl alloy sample additively manufactured by a method for improving the microstructure uniformity of TiAl alloys manufactured by electron beam additive manufacturing according to Example 2 of the present invention;

[0045] Figure 10 Backscattered image of the single melt microstructure of Comparative Example 2 of the present invention;

[0046] Figure 11 This is a backscattered image of the TiAl alloy sample of Comparative Example 2 of the present invention;

[0047] Figure 12 EPMA-Al element distribution diagram of the TiAl alloy sample of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0049] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0050] In the embodiments of the present invention, “image” and “picture” may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are the same.

[0051] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0052] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0053] A method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing, the method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing specifically comprises the following steps:

[0054] S1. Substrate preheating: preheat the substrate temperature to 1100-1300℃, and the forming environment temperature is not lower than 1000℃;

[0055] S2. Preheating of TiAl alloy powder: The preheating method uses a non-focused electron beam and the heat input method uses a gradient increase;

[0056] S3, filling scan: Design the defocus value according to the energy density to control the molten pool morphology and thermal gradient.

[0057] In particular, the S1 substrate preheating adopts high-energy electron beam to quickly scan and heat the substrate. In order to prevent thermal deformation of the substrate, a small beam flow and a large scanning speed are used for long-term preheating, with a scanning time of 30-45 minutes to 600-800 ° C, and a large beam flow and a short-term preheating, with a scanning time of 20-30 minutes to 1100-1300 ° C, to obtain a stable forming internal temperature field.

[0058] In particular, the S1 scan parameters are: long preheating: beam current 15-20 mA, scan rate 20-30 m / s, time 40-60 min, defocusing 20-30 mA; short preheating: beam current 35-40 mA, scan rate 20-30 m / s, time 20-30 min, defocusing 20-30 mA.

[0059] In particular, S2 adopts a preset preheating stabilization layer, and sets the range of 5mm from the substrate as the stabilization layer range; within the stabilization layer range, the powder bed preheating parameters use a small beam flow, slow scanning speed, and large defocusing preheating method to perform preliminary powder pre-sintering, and then gradually increase the beam flow to increase the overall heat input and perform secondary sintering of the powder.

[0060] In particular, the S2 powder bed preheating scanning direction rotates 90° every other layer, the stable layer is the first 50-100 layers, the powder layer thickness is 50-100μm, and the scanning parameter range is: stable layer, beam current 10-30mA (progressive increase), scanning speed 15-30m / s (progressive increase), defocus 15-40mA (progressive increase); after exceeding the stable layer, the powder bed preheating scanning parameter range is: beam current 20-40mA (progressive increase), scanning speed 15-30m / s (progressive increase), defocus 20-50mA (progressive increase).

[0061] In particular, the S3 filling scan uses an unfocused electron beam for filling scanning, and the melting parameters are designed according to different energy densities.

[0062] In particular, the S3 filling spacing is 50-200μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 0-180°, the electron beam defocus amount is ±1-±20mA, the filling beam current is 3-20mA, the filling speed is 0.5-10m / s, and the surface energy density range is 1-10J / mm 2 , within this process parameter range, the molten pool width-to-depth ratio is maintained at 1.7-2.3.

[0063] In particular, the preheating temperature of the S1 substrate should be greater than 1100°C, and there should be no warping on the edge of the substrate.

[0064] In particular, there was no powder jumping phenomenon during the S2 powder bed preheating process. After the powder preheating was completed, the powder surface had no metallic luster, no peeling or compaction phenomenon, and the powder was well preheated in this surface state.

[0065] In particular, the composition of the TiAl alloy powder during the S2 powder bed preheating process is Ti-(42-48)Al-(0-2)Cr-(5-15)Nb-(0-2)Si, and the powder particle size is 53-150μm; the powder is pulverized by gas atomization or rotating electrode; the TiAl alloy powder has a smooth surface and a sphericity greater than 0.93.

[0066] In particular, the molten pool width-to-depth ratios of the prepared TiAl alloys are 1.44, 2.3, 1.42, and 2.3, respectively.

[0067] In particular, when the width-to-depth ratio of the molten pool of the prepared TiAl alloy is 1.42-2.3, the density is 4.25-4.27 g / cm 3, tensile strength is 850-875MPa, and elongation is 0.5-0.62%.

[0068] In particular, when the width-to-depth ratio of the molten pool of the prepared TiAl alloy is greater than or equal to 2.3, the density is 4.27-4.3 g / cm 3 , tensile strength is 890-900MPa, and elongation is 0-0.2%.

[0069] Example 1

[0070] The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing in this embodiment comprises the following steps:

[0071] S1. Substrate preheating: Select a molybdenum alloy substrate for preheating, substrate size 110×110mm×10mm, preheating range 100×100mm, long preheating: beam current 15mA, scanning speed 30m / s, time 40min, defocus 20mA; short preheating: beam current 35mA, scanning speed 30m / s, time 20min, defocus 20mA, so that the substrate temperature reaches 1180℃;

[0072] S2. Preheating of TiAl alloy powder: The composition of the TiAl alloy powder is Ti-46Al-8Nb-1.2Si, and the powder particle size is 53-150 μm. The powder is pulverized using a rotating electrode. The TiAl alloy powder has a smooth surface and a sphericity of 0.93.

[0073] The preheating method uses an unfocused electron beam, and the heat input method adopts a gradient increase. A preset preheating stable layer is used, and the range of 5mm from the substrate is set as the stable layer range. Within the stable layer range, the powder bed preheating parameters adopt a small beam flow, slow scan rate, and large defocusing preheating method for initial powder pre-sintering. Subsequently, the beam flow is gradually increased to increase the overall heat input for secondary sintering of the powder.

[0074] The scraper first spreads the powder flat, and the powder thickness is set to 50μm;

[0075] The powder bed preheating parameters are as follows: electron beam filling spacing of 250μm, powder bed stabilization layer set to 50 layers, preheating beam current of 10-30mA (increased progressively), scanning speed of 15-30m / s (increased progressively), and defocus of 15-40mA (increased progressively) before powder bed stabilization; after powder bed stabilization, beam current of 20-40mA (increased progressively), scanning speed of 15-30m / s (increased progressively), and defocus of 20-50mA (increased progressively);

[0076] During the powder bed preheating process, there is no powder jumping phenomenon. After the powder preheating is completed, the powder surface has no metallic luster, no peeling or compaction phenomenon, and the powder preheating is good in this surface state.

[0077] S3. Filling scan: Design the defocus value according to the energy density to control the molten pool morphology and the thermal gradient of the molten pool; specifically, electron beam melting forming + post-preheating, the filling spacing is 100μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 90°, the electron beam defocus amount is set to 5mA, in this defocus state, the molten pool width-to-depth ratio is 2.3, the filling beam current is 11.9mA, the filling speed is 4.2m / s, and the surface energy density is 1.7J / mm 2 ;

[0078] The electron beam melting forming in S3 is preheated 5-10 times to increase the surface temperature of the powder bed, reduce the temperature gradient, and prevent powder blowing during the preheating stage of the next layer of powder bed;

[0079] Before preheating the next layer of powder bed, the substrate is lowered 50μm, and steps S2-S3 are repeated. According to the preset 3D model data, the electron beam scans and melts each layer to complete the overall printing.

[0080] The TiAl alloy prepared in this example has a minimum energy input of Ea = 1.7 J / mm², a defocus of 5 mA, and a single melt channel with a molten pool width-to-depth ratio of 2.3. Figure 1 Shown is near-γ tissue.

[0081] The microstructure of the TiAl alloy sample manufactured by electron beam powder bed fusion additive manufacturing in this embodiment is as follows: Figure 2 Shown is near-γ tissue.

[0082] like Figure 3 As shown, in the TiAl alloy prepared in this embodiment, after adjusting the defocusing amount, the Al element exhibits high chemical uniformity on a microscopic scale.

[0083] When the width-to-depth ratio of the molten pool of the TiAl alloy prepared in this embodiment is 2.3, the density is 4.25 g / cm 3 , tensile strength is 875MPa and elongation is 0.35%.

[0084] Comparative Example 1

[0085] A method for improving the uniformity of the structure of TiAl alloy produced by electron beam additive manufacturing in this comparative example comprises the following steps:

[0086] S1. Substrate preheating: Select a molybdenum alloy substrate for preheating, the substrate size is 110×110mm×10mm, the preheating range is 100×100mm, long preheating: beam current 15mA, scanning speed 25m / s, time 40min, defocusing 25mA; short preheating: beam current 35mA, scanning speed 25m / s, time 20min, defocusing 25mA, so that the substrate temperature reaches 1150℃;

[0087] S2. Preheating of TiAl alloy powder: The composition of the TiAl alloy powder is Ti-46Al-8Nb-1.2Si, and the powder particle size is 53-150 μm. The powder is prepared by a rotating electrode method. The TiAl alloy powder has a smooth surface and a sphericity of 0.93.

[0088] The preheating method uses an unfocused electron beam, and the heat input method adopts a gradient increase. A preset preheating stable layer is used, and the range of 5mm from the substrate is set as the stable layer range. Within the stable layer range, the powder bed preheating parameters adopt a small beam flow, slow scan rate, and large defocusing preheating method for initial powder pre-sintering. Subsequently, the beam flow is gradually increased to increase the overall heat input for secondary sintering of the powder.

[0089] The scraper first spreads the powder flat, and the powder thickness is set to 50μm;

[0090] The powder bed stabilization layer is set to 50 layers, and the powder bed preheating parameters are as follows: the electron beam filling spacing is 250μm, the powder bed stabilization layer is set to 50 layers, the preheating beam current before powder bed stabilization is 10-30mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 15-40mA (increased progressively); after the powder bed is stabilized, the beam current is 20-40mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 20-50mA (increased progressively);

[0091] During the powder bed preheating process, there is no powder jumping phenomenon. After the powder preheating is completed, the powder surface has no metallic luster, no peeling or compaction phenomenon, and the powder preheating is good in this surface state.

[0092] S3. Filling scan: Design the defocus value according to the energy density to control the molten pool morphology and the thermal gradient of the molten pool; specifically, electron beam melting forming + post-preheating, the filling spacing is 100μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 90°, the electron beam defocus amount is set to 1mA, in this defocus state, the molten pool width-to-depth ratio is 1.44, the filling beam current is 11.9mA, the filling speed is 4.2m / s, and the surface energy density is 1.7J / mm 2 ;

[0093] The electron beam melting forming in S3 is preheated 5-10 times to increase the surface temperature of the powder bed, reduce the temperature gradient, and prevent powder blowing during the preheating stage of the next layer of powder bed;

[0094] Before preheating the next layer of powder bed, the substrate is lowered 50μm, and steps S2-S3 are repeated. According to the preset 3D model data, the electron beam scans and melts layer by layer to complete the overall printing.

[0095] The TiAl alloy prepared in this comparative example has a minimum energy input of Ea=1.7J / mm², a defocus of 1mA, and a single melt channel with a molten pool width-to-depth ratio of 1.44. Figure 4 Shown is the near-slice tissue.

[0096] The microstructure of the TiAl alloy sample manufactured by electron beam powder bed fusion additive manufacturing in this comparative example is as follows: Figure 5 As shown, the near-lamellar tissue and the near-γ tissue are distributed alternately.

[0097] like Figure 6 As shown, in the TiAl alloy prepared in this comparative example, the deposited alloy exhibits obvious layered enrichment of Al elements along the printing direction.

[0098] When the width-to-depth ratio of the molten pool of the TiAl alloy prepared in this comparative example is 1.44, the density is 4.28 g / cm 3 , tensile strength is 868MPa and elongation is 0.15%.

[0099] Example 2

[0100] The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing in this embodiment comprises the following steps:

[0101] S1. Substrate preheating: Select a stainless steel substrate for preheating, substrate size 110×110mm×10mm, preheating range 100×100mm, long preheating: beam current 15mA, scan speed 25m / s, time 45min, defocus 30mA; short preheating: beam current 30mA, scan speed 25m / s, time 20min, defocus 30mA, so that the substrate temperature reaches 1100℃;

[0102] S2. Preheating of TiAl alloy powder: The composition of the TiAl alloy powder is Ti-49Al-2Cr-2Nb, and the powder particle size is 53-150 μm. The powder is pulverized by gas atomization. The TiAl alloy powder has a smooth surface and a sphericity of 0.93.

[0103] The preheating method uses an unfocused electron beam, and the heat input method adopts a gradient increase. A preset preheating stable layer is used, and the range of 5mm from the substrate is set as the stable layer range. Within the stable layer range, the powder bed preheating parameters adopt a small beam flow, slow scan rate, and large defocusing preheating method for initial powder pre-sintering. Subsequently, the beam flow is gradually increased to increase the overall heat input for secondary sintering of the powder.

[0104] The scraper first spreads the powder flat, and the powder thickness is set to 50μm;

[0105] The powder bed stabilization layer is set to 100 layers, and the powder bed preheating parameters are as follows: the electron beam filling spacing is 200μm, the powder bed stabilization layer is set to 100 layers, the preheating beam current before powder bed stabilization is 10-30mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 15-40mA (increased progressively); after the powder bed is stabilized, the beam current is 20-40mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 20-50mA (increased progressively);

[0106] During the powder bed preheating process, there is no powder jumping phenomenon. After the powder preheating is completed, the powder surface has no metallic luster, no peeling or compaction phenomenon, and the powder preheating is good in this surface state.

[0107] S3. Filling scan: Design the defocus value according to the energy density to control the molten pool morphology and the thermal gradient of the molten pool; specifically, electron beam melting forming + post-preheating, the filling spacing is 100μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 90°, the electron beam defocus amount is set to 12mA, in this defocus state, the molten pool width-to-depth ratio is 2.3, the filling beam current is 12.8mA, the filling speed is 2.8m / s, and the surface energy density is 2.75J / mm 2 ;

[0108] The electron beam melting forming in S3 is preheated 5-10 times to increase the surface temperature of the powder bed, reduce the temperature gradient, and prevent powder blowing during the preheating stage of the next layer of powder bed;

[0109] Before preheating the next layer of powder bed, the substrate is lowered 50μm, and steps S2-S3 are repeated. According to the preset 3D model data, the electron beam scans and melts each layer to complete the overall printing.

[0110] The TiAl alloy prepared in this embodiment has a maximum energy input of Ea = 2.75 J / mm², a defocus of 12 mA, and a single melt channel with a molten pool width-to-depth ratio of 2.3. Figure 7 Shown is near-γ tissue.

[0111] The microstructure of the TiAl alloy sample manufactured by electron beam powder bed fusion additive manufacturing in this embodiment is as follows: Figure 8 As shown, the overall structure is nearly γ.

[0112] like Figure 9 As shown, in the TiAl alloy prepared in this embodiment, after adjusting the defocusing amount, the Al element exhibits high chemical uniformity on a microscopic scale.

[0113] When the width-to-depth ratio of the molten pool of the TiAl alloy prepared in this embodiment is 2.3, the density is 4.27 g / cm 3 , tensile strength is 895MPa and elongation is 0.45%.

[0114] Comparative Example 2

[0115] A method for improving the uniformity of the structure of TiAl alloy produced by electron beam additive manufacturing in this comparative example comprises the following steps:

[0116] S1. Substrate preheating: Select a molybdenum alloy substrate for preheating, the substrate size is 110×110mm×10mm, the preheating range is 100×100mm, long preheating: beam current 15mA, scanning speed 25m / s, time 45min, defocusing 30mA; short preheating: beam current 35mA, scanning speed 25m / s, time 20min, defocusing 30mA, so that the substrate temperature reaches 1150℃;

[0117] S2. Preheating of TiAl alloy powder: The composition of the TiAl alloy powder is Ti-49Al-2Cr-2Nb, and the powder particle size is 53-150 μm. The powder is pulverized by gas atomization. The TiAl alloy powder has a smooth surface and a sphericity of 0.93.

[0118] The preheating method uses an unfocused electron beam, and the heat input method adopts a gradient increase. A preset preheating stable layer is used, and the range of 5mm from the substrate is set as the stable layer range. Within the stable layer range, the powder bed preheating parameters adopt a small beam flow, slow scan rate, and large defocusing preheating method for initial powder pre-sintering. Subsequently, the beam flow is gradually increased to increase the overall heat input for secondary sintering of the powder.

[0119] The scraper first spreads the powder flat, and the powder thickness is set to 50μm;

[0120] The powder bed stabilization layer is set to 100 layers, and the powder bed preheating parameters are as follows: the electron beam filling spacing is 200μm, the powder bed stabilization layer is set to 100 layers, the preheating beam current before powder bed stabilization is 10-30mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 15-40mA (increased progressively); after the powder bed is stabilized, the beam current is 20-40mA (increased progressively), the scanning speed is 15-30m / s (increased progressively), and the defocus is 20-50mA (increased progressively);

[0121] During the powder bed preheating process, there is no powder jumping phenomenon. After the powder preheating is completed, the powder surface has no metallic luster, no peeling or compaction phenomenon, and the powder preheating is good in this surface state.

[0122] S3. Filling scan: Design the defocus value according to the energy density to control the molten pool morphology and the thermal gradient of the molten pool; specifically, electron beam melting forming + post-preheating, the filling spacing is 100μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of the electron beam per interval layer is 90°, the electron beam defocus amount is set to 3mA, in this defocus state, the molten pool width-to-depth ratio is 1.42, the filling beam current is 12.8mA, the filling speed is 2.8m / s, and the surface energy density is 2.75J / mm 2 ;

[0123] The electron beam melting forming in S3 is preheated 5-10 times to increase the surface temperature of the powder bed, reduce the temperature gradient, and prevent powder blowing during the preheating stage of the next layer of powder bed;

[0124] Before preheating the next layer of powder bed, the substrate is lowered 50μm, and steps S2-S3 are repeated. According to the preset 3D model data, the electron beam scans and melts each layer to complete the overall printing.

[0125] The TiAl alloy prepared in this comparative example has a maximum energy input of Ea=2.75J / mm², a defocus of 3mA, and a single melt channel with a molten pool width-to-depth ratio of 1.42. Figure 10 Shown is the near-lamellar tissue.

[0126] The microstructure of the TiAl alloy sample manufactured by electron beam powder bed fusion additive manufacturing in this comparative example is as follows: Figure 11 As shown, the juxtalamel and juxtagamma tissues are distributed alternately.

[0127] like Figure 12 As shown, in the TiAl alloy prepared in this comparative example, the deposited alloy exhibits obvious layered enrichment of Al elements along the printing direction.

[0128] When the width-to-depth ratio of the molten pool of the TiAl alloy prepared in this comparative example is 1.42, the density is 4.3 g / cm 3 , tensile strength is 890MPa and elongation is 0%.

[0129] The above scheme, the present invention proposes a method for improving the uniformity of the structure of TiAl alloy manufactured by electron beam additive manufacturing, which can solve the technical problems in the existing technology, such as the poor uniformity of the microstructure of TiAl alloy manufactured by electron beam additive manufacturing caused by uneven volatilization of Al elements and obvious banded structure through heat treatment method after additive manufacturing, as well as the technical problems that although the density can be improved by improving the alloy powder and adding a static magnetic field to the printing process, the uniformity of the structure cannot be improved.

[0130] The present invention precisely controls the forming environment temperature, suppresses powder blowing in the powder bed, and matches the relationship between energy input and defocusing amount to accurately regulate the depth and width of the molten pool and optimize the temperature gradient of the molten pool, thereby effectively solving the problem of obvious banding structure caused by uneven volatilization of the Al element and significantly improving the structural uniformity of the TiAl alloy.

[0131] This invention significantly improves build quality and structural uniformity during electron beam additive manufacturing (EBAM) through scientific thermal management methods. Substrate preheating utilizes a progressive heating strategy, initially using a small, long-duration preheating beam followed by a large, short-duration preheating beam. This ensures uniform substrate temperature distribution, effectively reducing thermal stress caused by local temperature differences, thereby minimizing the risk of substrate deformation and improving build stability.

[0132] During the powder preheating process, the present invention achieves precise control of the local temperature field of the powder bed by dynamically adjusting the scanning beam current, scanning speed and defocusing amount of the electron beam, thereby avoiding the "powder blowing" phenomenon caused by local overheating of the powder. During the electron beam forming process, the present invention accurately controls the depth and width of the molten pool by matching the relationship between energy input and defocusing amount, thereby optimizing the temperature gradient of the molten pool, solving the problems of uneven volatilization of Al elements and obvious banded structure, and greatly improving the structural uniformity of TiAl alloys. Specifically, by reasonably increasing positive defocusing, not only the width-to-depth ratio of the molten pool is increased, the shape of the molten pool is optimized, and the thermal gradient is reduced, but also the electron beam energy distribution is made more uniform, the energy action area is effectively expanded, and the heat input per unit area of ​​the powder bed is reduced.

[0133] The present invention promotes the formation of equiaxed gamma crystals by increasing the amount of defocus, reduces grain size differences, optimizes the temperature gradient distribution within the molten pool, reduces Al volatilization in the upper part of the molten pool, weakens the banded structure, improves the uniformity of the structure, and thus improves the mechanical properties of the alloy. The optimized molten pool temperature gradient also solves the problem of uneven Al volatilization caused by the large temperature difference between the top and bottom, and suppresses the risk of structural differences within the molten pool. By adjusting the amount of defocus to control the depth-to-width ratio of the molten pool, the molten pool shape is made more stable, a uniform thermal cycle is achieved, and the formation of banded structure is reduced, ultimately obtaining a TiAl alloy component with better performance.

[0134] In summary, compared with the traditional technology of TiAl alloy additive manufacturing and heat treatment, the present invention prepares TiAl alloy components through substrate preheating, TiAl alloy powder preheating and filling scanning. Through the coordinated optimization of key parameters of electron beam non-focused scanning, it not only effectively broadens the forming process window of intermetallic compounds, but also greatly improves the applicability of TiAl alloy in the field of additive manufacturing, providing a reliable method for the preparation of high-performance components; this method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion.

[0135] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0136] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0137] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0138] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for improving the uniformity of TiAl alloy structure produced by electron beam additive manufacturing, characterized in that: The method for improving the uniformity of the TiAl alloy structure produced by electron beam additive manufacturing is specifically as follows: S1. Substrate preheating: preheat the substrate temperature to 1100-1300℃, and the forming environment temperature is not lower than 1000℃; S2. Preheating of TiAl alloy powder: The preheating method uses a non-focused electron beam and the heat input method uses a gradient increase; S3, filling scan: Design the defocus value according to the energy density to control the molten pool morphology and thermal gradient.

2. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: The S1 substrate preheating uses a high-energy electron beam to quickly scan and heat the substrate. To prevent thermal deformation of the substrate, a small beam flow and a high scanning speed are used for long-term preheating, with a scanning time of 30-45 minutes to 600-800°C, and a large beam flow for short-term preheating, with a scanning time of 20-30 minutes to 1100-1300°C to obtain a stable forming internal temperature field.

3. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 2, characterized in that: The S1 scanning parameters are: long preheating: beam current 15-20mA, scanning speed 20-30m / s, time 40-60min, defocusing 20-30mA; short preheating: beam current 35-40mA, scanning speed 20-30m / s, time 20-30min, defocusing 20-30mA.

4. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: S2 uses a preset preheating stabilization layer, and sets the range of 5mm from the substrate as the stabilization layer range; within the stabilization layer range, the powder bed preheating parameters use a small beam flow, slow scanning speed, and large defocusing preheating method to perform initial powder pre-sintering, and then gradually increase the beam flow to increase the overall heat input for secondary sintering of the powder.

5. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 4, characterized in that: The S2 powder bed preheating scanning direction rotates 90° every other layer. The stable layer is the first 50-100 layers, the powder layer thickness is 50-100μm, and the scanning parameter range is: stable layer, beam current 10-30mA, scanning speed 15-30m / s, defocus 15-40mA; beyond the stable layer, the powder bed preheating scanning parameter range is: beam current 20-40mA, scanning speed 15-30m / s, defocus 20-50mA.

6. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: S3 filling scan uses a non-focused electron beam for filling scan and designs melting parameters according to different energy densities.

7. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 6, characterized in that: The S3 filling spacing is 50-200μm, the scanning direction is reciprocating, the filling method is parallel line filling, the rotation angle of each interval layer electron beam is 0-180°, the electron beam defocus amount is ±1-±20mA, the filling beam current is 3-20mA, the filling speed is 0.5-10m / s, and the surface energy density range is 1-10J / mm 2 , within this process parameter range, the molten pool width-to-depth ratio is maintained at 1.7-2.

3.

8. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: The preheating temperature of S1 substrate should be greater than 1100℃, and there should be no warping on the edge of the substrate.

9. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: During the S2 powder bed preheating process, there is no powder jumping phenomenon. After the powder preheating is completed, the powder surface has no metallic luster, no peeling or compaction phenomenon, and the powder preheating is good in this surface state.

10. The method for improving the microstructure uniformity of TiAl alloy produced by electron beam additive manufacturing according to claim 1, characterized in that: During the S2 powder bed preheating process, the composition of the TiAl alloy powder is Ti-(42-48)Al-(0-2)Cr-(5-15)Nb-(0-2)Si, and the powder particle size is 53-150μm; the powder is pulverized by gas atomization or rotating electrode; the TiAl alloy powder has a smooth surface and a sphericity greater than 0.93.

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