A LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material and its electron beam melting forming method

Abstract

The present application relates to a kind of LaB6 In-situ reinforced uniform fine-grained TiAl matrix composite and its electron beam melting forming method, belong to TiAl matrix composite additive preparation technical field.To solve the problem that TiAl alloy prepared by EBM forms the banded heterostructure of coarse / fine grain alternately arranged along the construction direction, the present application mixes TiAl base pre-alloy powder with LaB6 Powder low-energy ball milling, then is added by electron beam melting forming method for additive manufacturing.The present application controls LaB6 added amount accurately and matches optimized EBM process parameters, promotes LaB6 In-situ generation La2O3 Particle and TiB Whisker dual-phase reinforcement.Effectively inhibit grain growth difference, eliminate the inherent banded heterostructure of coarse / fine grain alternately along the construction direction of EBM forming TiAl alloy, not only obtain the uniform fine-grained structure of average grain size≤5 μm, more realize the improvement of comprehensive mechanical property and isotropic optimization.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology of TiAl-based composite materials, and particularly relates to a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material and its electron beam melting forming method. Background Technology

[0002] γ-TiAl alloys, due to their low density, high specific strength, and excellent creep resistance, are core candidate materials for high-temperature components in advanced equipment such as aero-engines. They are suitable for environments ranging from 700 to 900°C and are expected to replace nickel-based superalloys, driving the lightweighting of equipment. However, the inherent room-temperature brittleness and extremely narrow hot working window of this alloy make it difficult to form complex components at low cost using traditional processes, thus limiting its engineering applications.

[0003] Electron beam melting (EBM) technology, with its high vacuum environment and high-temperature preheating capability, can solve the hot working problems of TiAl alloys and provide a feasible way for near-net-shape forming of complex components, making it the preferred solution for precision manufacturing of this alloy. However, TiAl alloys formed by EBM generally have an inherent core defect: the formation of a banded heterogeneous structure with alternating coarse and fine grains along the construction direction. This defect easily leads to three major application bottlenecks: significant anisotropy of mechanical properties, which cannot meet the uniformity requirements under complex loads; poor deformation coordination between coarse and fine grain regions, which easily leads to early failure; and poor high-temperature thermal stability, with grain coarsening and rapid performance degradation after long-term service.

[0004] The formation of the banded heterostructure is related to the extreme thermophysical conditions of EBM: the vacuum and high temperature environment causes the local volatilization and redistribution of alloying elements, resulting in periodic compositional fluctuations between cladding layers; combined with the sensitive phase transformation characteristics of TiAl alloy, this induces differences in phase composition in micro-regions, causing uneven pinning of grain boundary migration; the continuous thermal cycling of subsequent EBM layer-by-layer manufacturing amplifies the differences in grain boundary migration rates, ultimately forming a banded heterostructure along the construction direction.

[0005] Existing conventional solutions have fundamental limitations, and mainstream subsequent heat treatment methods are ineffective: hot isostatic pressing can improve density but cannot improve heterogeneity; multi-step heat treatment may eliminate heterogeneous structures, but it easily introduces thermal stress, induces cracks, or leads to microstructural degradation. Furthermore, other existing related technologies have also failed to effectively address the problem of this banded heterogeneous structure. For example, some patents disclose methods for preparing TiC-reinforced TiAl-based composites using EBM, but their core focus is only on solving process stability issues such as "powder blowing" caused by the addition of ceramic particles to improve forming density, without addressing the performance bottleneck caused by the banded heterogeneous structure and failing to solve this core defect.

[0006] In summary, the alternating coarse / fine grain banded heterostructure of EBM-formed TiAl alloys is an inherent core challenge that existing solutions cannot effectively address, severely restricting its engineering applications. Summary of the Invention

[0007] To address the problem of TiAl alloys prepared by EBM forming a banded heterostructure with alternating coarse and fine grains along the construction direction, this invention provides a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material and its electron beam melting forming method.

[0008] The technical solution of this invention:

[0009] An electron beam melting forming method for LaB6 in-situ reinforced uniform fine-grained TiAl-based composite materials includes the following steps:

[0010] Step 1: Preparation of LaB6 / TiAl composite powder:

[0011] TiAl-based pre-alloyed powder and LaB6 powder were mixed by low-energy ball milling to obtain LaB6 / TiAl composite powder with LaB6 particles attached to the surface of TiAl powder; the mass of the LaB6 powder accounted for 0.4~0.6% of the total mass of the LaB6 / TiAl composite powder.

[0012] Step 2: Electron beam melting and shaping:

[0013] The substrate is placed in the forming chamber of an electron beam melting device, and an inert protective atmosphere is established for forming. A defocused electron beam is used to preheat the substrate in stages, uniformly raising its temperature to at least 1000°C. Under this preheating condition, powder is laid layer by layer according to a preset three-dimensional model path. After each layer, the powder bed is preheated to at least 1000°C. Electron beam forming is performed at this preheated temperature according to preset printing parameters. The volumetric energy density (VED) of the electron beam forming is 20~80 J / mm². 3 This process allows LaB6 in the molten pool to fully decompose and react in situ to generate La2O3 particles and TiB whisker reinforcement phases. After layer-by-layer cladding, the material is cooled in the furnace to obtain a dense shaped material.

[0014] Furthermore, the TiAl-based pre-alloyed powder mentioned in step one is prepared by rotating electrode atomization or electrode induction melting gas atomization, and its chemical composition, in atomic percentage, is: Al: 45~50 at.%, Cr: 0~4 at.%, Nb: 0~4 at.%, with the balance being Ti and unavoidable impurities; the particle size distribution of the TiAl-based pre-alloyed powder is 50~150 μm; the particle size distribution of the LaB6 powder is 0.5~5 μm, and the purity is not less than 99.8%.

[0015] Furthermore, the ball milling in step one is carried out under an argon protective atmosphere. The ball milling is performed with stainless steel balls and the mixed powder at a mass ratio of 2:1. The stainless steel balls are 316L stainless steel balls with diameters of 10 mm and 6 mm mixed in any proportion. The ball milling speed is 200~250 rpm, and intermittent ball milling is adopted. After each continuous ball milling for 45~60 min, it is paused for 15 min. The total effective ball milling time is 4~6 h.

[0016] Furthermore, the inert protective atmosphere required in step two is to evacuate the chamber to a vacuum level of 5 × 10⁻⁶. -3 Below Pa, high-purity helium gas with a purity of not less than 99.999% is then refilled into the cavity as a protective gas, and the vacuum level in the forming cavity is stably maintained at 0.5 × 10⁻⁶ Pa. -1 ~1.2×10 -1 Pa, the substrate is a stainless steel substrate or a TC4 titanium alloy substrate, the substrate is cleaned and dried, and the LaB6 / TiAl composite powder is dried before use.

[0017] Furthermore, the step-by-step preheating method for the substrate in step two is as follows: first, a defocused electron beam with a current of 10mA is used to scan the entire substrate in a fast scanning mode for 10 minutes; then, the current is increased to 15mA and scanned for 15 minutes; finally, the current is increased to 20mA and scanned for 5 minutes. The method for preheating the powder bed is as follows: a defocused electron beam with a current of 30mA is used to scan the powder bed area for 12 seconds.

[0018] Furthermore, the specific printing parameters for electron beam forming in step two are as follows: accelerating voltage of 60kV, beam current intensity of 8~16mA, scanning speed of 2~4m / s, scanning spacing of 0.07~0.12mm, and printing layer thickness of 0.08~0.10mm.

[0019] Furthermore, in step two, the electron beam spot diameter is ≤200μm, the scraper moving speed is 40~60mm / s, the three-dimensional model path is a strip scanning strategy, and the scanning path between adjacent layers is rotated 67-90°.

[0020] Furthermore, in step two, after each layer is clad, a defocused electron beam with a current of 30mA is used to scan the powder bed area after cladding for 10 seconds to homogenize the temperature.

[0021] The TiAl-based composite material prepared by the electron beam melting forming method of the present invention has a La element mass percentage content of 0.27~0.41wt% and a B element mass percentage content of 0.13~0.19wt%.

[0022] Furthermore, the TiAl-based composite material has a uniform fine-grained structure with an average grain size ≤5μm.

[0023] The beneficial effects of this invention are:

[0024] This invention creatively introduces LaB6, which is originally unsuitable as a stable reinforcing phase in EBM processes due to its tendency to decompose under high temperature and high vacuum conditions, into the EBM preparation process of TiAl-based composite materials. By precisely controlling its decomposition process through an integrated strategy of material design and EBM process control, a TiAl-based composite material with excellent microstructure featuring fully fine grains was obtained. This fills the application gap of LaB6 in the field of EBM-formed TiAl alloys and provides a new technical path for solving the core challenges of EBM-TiAl alloys.

[0025] This invention achieves precise control of the LaB6 addition amount and optimized EBM process parameters, thereby controlling the volumetric energy density (VED) of the electron beam to 20-80 J / mm². 3 Within this range, LaB6 is fully reacted and decomposed in situ within the EBM molten pool, generating a dual-phase reinforcement of La2O3 particles and TiB whiskers. This dual-phase reinforcement plays a synergistic regulatory role, effectively suppressing the periodic volatilization of Al and the differences in grain growth induced by long-term in-situ thermal cycling during manufacturing. This eliminates the inherent coarse / fine grain alternating banded heterostructure along the construction direction of EBM-formed TiAl alloys from the manufacturing source.

[0026] This invention utilizes the synergistic regulation of the dual-phase reinforcement generated by in-situ decomposition of LaB6 to not only obtain a uniform fine-grained structure with an average grain size ≤5μm, but also achieves improved comprehensive mechanical properties and optimized isotropy. The TiAl-based composite material prepared by this invention exhibits a room temperature compressive yield strength ≥700MPa, compressive strength ≥2800MPa, fracture strain ≥36%, and microVickers hardness ≥300HV0.5, with a mechanical property difference ≤2% along the construction direction and perpendicular to the construction direction. Simultaneously, it imparts excellent high-temperature structural stability to the material, with a grain size increase rate ≤5% and hardness retention rate ≥98% after 400 hours of exposure at 900℃, effectively solving the problems of traditional EBM-TiAl alloys, such as difficulty in balancing strength and plasticity, significant anisotropy, and rapid performance degradation at high temperatures.

[0027] This invention provides a wide and easily precisely controllable EBM process parameter window, enabling stable co-forming of LaB6 and TiAl pre-alloyed powders without major modifications to existing EBM equipment. This offers a reliable technical solution for near-net-shape forming of complex high-performance, isotropic TiAl composite components. This technology can be directly adapted to the manufacturing needs of high-temperature complex components in aerospace, gas turbine, and other fields, demonstrating significant industrialization potential and broad engineering application prospects. Attached Figure Description

[0028] Figure 1 These are SEM images of the LaB6 / TiAl composite powder obtained by low-energy ball milling in Example 1 at different magnification ratios.

[0029] Figure 2 The images show a comparison of the microstructures of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction. A represents Comparative Example 1, and B represents Example 1.

[0030] Figure 3 Micrographs of the La2O3 and TiB reinforcing phases in the shaped component obtained in Example 1;

[0031] Figure 4 This is a comparison diagram of the room temperature compressibility of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction;

[0032] Figure 5 The diagram shows a comparison of the room temperature compressibility of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction and perpendicular to the construction direction. A represents Comparative Example 1, and B represents Example 1.

[0033] Figure 6 The graph shows a comparison of the grain size and hardness changes of the molded components obtained in Example 1 and Comparative Example 1 after being kept at 900°C for different times. A represents the grain size, and B represents the microhardness. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0035] Example 1

[0036] An electron beam melting forming method for LaB6 in-situ reinforced uniform fine-grained TiAl-based composite materials includes the following steps:

[0037] Step 1: Preparation of LaB6 / TiAl composite powder:

[0038] In this embodiment, the TiAl-based pre-alloyed powder was prepared by plasma rotating electrode atomization. Its chemical composition, in atomic percentage, is: Al: 48 at.%, Cr: 2 at.%, Nb: 2 at.%, with the balance being Ti and unavoidable impurities. The TiAl-based pre-alloyed powder has a particle size distribution of 50–150 μm and an average particle size of 116 μm. The LaB6 powder has a particle size distribution range of 1–3 μm and a purity higher than 99.9%.

[0039] 99.5 wt% TiAl pre-alloyed powder and 0.5 wt% LaB6 powder were mixed by mass percentage. Stainless steel balls and the resulting mixed powder were loaded into the grinding jar of a planetary ball mill at a mass ratio of 2:1. The stainless steel balls were 316L stainless steel balls with diameters of 10 mm and 6 mm mixed in any proportion.

[0040] Low-energy ball milling was performed under an argon protective atmosphere, with the mill speed set at 220 rpm. An intermittent ball milling strategy was adopted to avoid powder overheating, with a 15-minute pause after each 1-hour continuous milling session, for a total effective milling time of 5 hours. After milling, LaB6 / TiAl composite powder with LaB6 particles uniformly adhered to the surface of TiAl pre-alloyed powder was obtained. The average particle size of the obtained LaB6 / TiAl composite powder was measured to be 116 μm.

[0041] Figure 1 The images show SEM images of LaB6 / TiAl composite powder obtained by low-energy ball milling at different magnifications. It was observed that LaB6 powder adhered uniformly to the surface of TiAl-based pre-alloyed powder. After low-energy ball milling, the morphology of TiAl-based pre-alloyed particles did not change and still maintained a near-spherical morphology.

[0042] Step 2: Electron beam melting and shaping:

[0043] A 316L stainless steel alloy plate was selected as the substrate. The substrate surface was ultrasonically cleaned for 15 minutes each with anhydrous ethanol and acetone to remove oil and oxides. It was then dried in an 80℃ oven. The resulting clean substrate was placed in the forming chamber of the electron beam melting equipment. After closing the chamber, the vacuum system was activated, and the vacuum level in the chamber was evacuated to 5 × 10⁻⁶. - 3 Below Pa. Then, high-purity helium gas with a purity ≥99.999% is refilled into the chamber as a protective gas, and the vacuum level in the forming chamber is stably maintained at 1.2 × 10⁻⁶ Pa. -1 Pa. The LaB6 / TiAl composite powder obtained in step one was placed in a vacuum oven at 120℃ and dried for 4 hours to reduce the moisture content.

[0044] A defocused electron beam was used to preheat the substrate in a stepped manner to reduce thermal and residual stress. First, a 10mA defocused electron beam was used to scan the entire substrate in a rapid scanning mode for 10 minutes; then the beam current was increased to 15mA and scanned for 15 minutes; finally, the beam current was increased to 20mA and scanned for 5 minutes. This process uniformly raised the substrate temperature to 1050℃, reaching or approaching the ductile-brittle transition temperature of the TiAl alloy.

[0045] Under the preheating temperature of the substrate, powder is laid layer by layer according to the preset 3D model path and preset printing parameters to obtain a powder bed. Before forming each layer, the obtained powder bed is preheated. A defocused electron beam with a beam current of 30mA is used to scan the powder bed area for 12s to bring its temperature to 1050℃. Then, electron beam forming is performed at the preheating temperature of the powder bed according to the preset printing parameters, specifically: accelerating voltage (U) of 60kV, beam current intensity (I) of 14mA, scanning speed (v) of 2m / s, scanning spacing (t) of 0.1mm, and single-layer thickness (h) of 0.09mm. According to the formula VED=(I×U) / (v×t×h), substituting the parameters, VED≈46.7J / mm² is calculated. 3 .

[0046] Meanwhile, the diameter of the electron beam spot is controlled to be about 100 μm, the scraper moving speed is 50 mm / s, the three-dimensional model path adopts a strip scanning strategy, and the scanning path between adjacent printing layers is rotated 90°.

[0047] After each cladding layer is formed, a defocused electron beam with a current of 30 mA is used to scan the powder bed region for 10 seconds to homogenize the temperature before the next layer of powder is laid. After all layers are clad, the electron beam is stopped, and the component is allowed to cool to room temperature in a vacuum environment or under a protective atmosphere, resulting in a uniform fine-grained TiAl-based composite component reinforced in situ with LaB6.

[0048] Example 2

[0049] An electron beam melting forming method for LaB6 in-situ reinforced uniform fine-grained TiAl-based composite materials includes the following steps:

[0050] Step 1: Preparation of LaB6 / TiAl composite powder:

[0051] In this embodiment, the TiAl-based pre-alloyed powder was prepared by plasma rotating electrode atomization. Its chemical composition, in atomic percentage, is: Al: 48 at.%, Cr: 2 at.%, Nb: 2 at.%, with the balance being Ti and unavoidable impurities. The TiAl-based pre-alloyed powder has a particle size distribution of 50–150 μm and an average particle size of 116 μm. The LaB6 powder has a particle size distribution range of 1–3 μm and a purity higher than 99.9%.

[0052] 99.5 wt% TiAl pre-alloyed powder and 0.5 wt% LaB6 powder were mixed by mass percentage. Stainless steel balls and the resulting mixed powder were loaded into the grinding jar of a planetary ball mill at a mass ratio of 2:1. The stainless steel balls were 316L stainless steel balls with diameters of 10 mm and 6 mm mixed in any proportion.

[0053] Low-energy ball milling was performed under an argon protective atmosphere, with the mill speed set at 220 rpm. An intermittent ball milling strategy was adopted to avoid powder overheating, with a 15-minute pause after each 1-hour continuous milling session, for a total effective milling time of 5 hours. After milling, LaB6 / TiAl composite powder with LaB6 particles uniformly adhered to the surface of TiAl pre-alloyed powder was obtained. The average particle size of the obtained LaB6 / TiAl composite powder was measured to be 116 μm.

[0054] Step 2: Electron beam melting and shaping:

[0055] A 316L stainless steel alloy plate was selected as the substrate. The substrate surface was ultrasonically cleaned for 15 minutes each with anhydrous ethanol and acetone to remove oil and oxides. It was then dried in an 80℃ oven. The resulting clean substrate was placed in the forming chamber of the electron beam melting equipment. After closing the chamber, the vacuum system was activated, and the vacuum level in the chamber was evacuated to 5 × 10⁻⁶. - 3 Below Pa. Then, high-purity helium gas with a purity ≥99.999% is refilled into the chamber as a protective gas, and the vacuum level in the forming chamber is stably maintained at 1.2 × 10⁻⁶ Pa. -1 Pa. The LaB6 / TiAl composite powder obtained in step one was placed in a vacuum oven at 120℃ and dried for 4 hours to reduce the moisture content.

[0056] A defocused electron beam was used to preheat the substrate in a stepped manner to reduce thermal and residual stress. First, a 10mA defocused electron beam was used to scan the entire substrate in a rapid scanning mode for 10 minutes; then the beam current was increased to 15mA and scanned for 15 minutes; finally, the beam current was increased to 20mA and scanned for 5 minutes. This process uniformly raised the substrate temperature to 1050℃, reaching or approaching the ductile-brittle transition temperature of the TiAl alloy.

[0057] Under the preheating temperature of the substrate, powder is laid layer by layer according to the preset 3D model path and preset printing parameters to obtain a powder bed. Before forming each layer, the obtained powder bed is preheated. A defocused electron beam with a beam current of 30mA is used to scan the powder bed area for 12s to bring its temperature to 1050℃. Then, electron beam forming is performed at the preheating temperature of the powder bed according to the preset printing parameters, specifically: accelerating voltage (U) of 60kV, beam current intensity (I) of 10mA, scanning speed (v) of 4m / s, scanning spacing (t) of 0.07mm, and printing single layer thickness (h) of 0.09mm. According to the formula VED=(I×U) / (v×t×h), substituting the parameters, VED≈28.8J / mm² is calculated. 3 .

[0058] Meanwhile, the diameter of the electron beam spot is controlled to be about 100 μm, the scraper moving speed is 50 mm / s, the three-dimensional model path adopts a strip scanning strategy, and the scanning path between adjacent printing layers is rotated 90°.

[0059] After each cladding layer is formed, a defocused electron beam with a current of 30 mA is used to scan the powder bed region for 10 seconds to homogenize the temperature before the next layer of powder is laid. After all layers are clad, the electron beam is stopped, and the component is allowed to cool to room temperature in a vacuum environment or under a protective atmosphere, resulting in a uniform fine-grained TiAl-based composite component reinforced in situ with LaB6.

[0060] Example 3

[0061] An electron beam melting forming method for LaB6 in-situ reinforced uniform fine-grained TiAl-based composite materials includes the following steps:

[0062] Step 1: Preparation of LaB6 / TiAl composite powder:

[0063] In this embodiment, the TiAl-based pre-alloyed powder was prepared by plasma rotating electrode atomization. Its chemical composition, in atomic percentage, is: Al: 48 at.%, Cr: 2 at.%, Nb: 2 at.%, with the balance being Ti and unavoidable impurities. The TiAl-based pre-alloyed powder has a particle size distribution of 50–150 μm and an average particle size of 116 μm. The LaB6 powder has a particle size distribution range of 1–3 μm and a purity higher than 99.9%.

[0064] 99.5 wt% TiAl pre-alloyed powder and 0.5 wt% LaB6 powder were mixed by mass percentage. Stainless steel balls and the resulting mixed powder were loaded into the grinding jar of a planetary ball mill at a mass ratio of 2:1. The stainless steel balls were 316L stainless steel balls with diameters of 10 mm and 6 mm mixed in any proportion.

[0065] Low-energy ball milling was performed under an argon protective atmosphere, with the mill speed set at 220 rpm. An intermittent ball milling strategy was adopted to avoid powder overheating, with a 15-minute pause after each 1-hour continuous milling session, for a total effective milling time of 5 hours. After milling, LaB6 / TiAl composite powder with LaB6 particles uniformly adhered to the surface of TiAl pre-alloyed powder was obtained. The average particle size of the obtained LaB6 / TiAl composite powder was measured to be 116 μm.

[0066] Step 2: Electron beam melting and shaping:

[0067] A 316L stainless steel alloy plate was selected as the substrate. The substrate surface was ultrasonically cleaned for 15 minutes each with anhydrous ethanol and acetone to remove oil and oxides. It was then dried in an 80℃ oven. The resulting clean substrate was placed in the forming chamber of the electron beam melting equipment. After closing the chamber, the vacuum system was activated, and the vacuum level in the chamber was evacuated to 5 × 10⁻⁶. - 3 Below Pa. Then, high-purity helium gas with a purity ≥99.999% is refilled into the chamber as a protective gas, and the vacuum level in the forming chamber is stably maintained at 1.2 × 10⁻⁶ Pa. -1 Pa. The LaB6 / TiAl composite powder obtained in step one was placed in a vacuum oven at 120℃ and dried for 4 hours to reduce the moisture content.

[0068] A defocused electron beam was used to preheat the substrate in a stepped manner to reduce thermal and residual stress. First, a 10mA defocused electron beam was used to scan the entire substrate in a rapid scanning mode for 10 minutes; then the beam current was increased to 15mA and scanned for 15 minutes; finally, the beam current was increased to 20mA and scanned for 5 minutes. This process uniformly raised the substrate temperature to 1050℃, reaching or approaching the ductile-brittle transition temperature of the TiAl alloy.

[0069] Under the preheating temperature of the substrate, powder is laid layer by layer according to the preset 3D model path and preset printing parameters to obtain a powder bed. Before forming each layer, the obtained powder bed is preheated. A defocused electron beam with a beam current of 30mA is used to scan the powder bed area for 12s to bring its temperature to 1050℃. Then, electron beam forming is performed at the preheating temperature of the powder bed according to the preset printing parameters, specifically: accelerating voltage (U) of 60kV, beam current intensity (I) of 16mA, scanning speed (v) of 2m / s, scanning spacing (t) of 0.07mm, and printing single layer thickness (h) of 0.09mm. According to the formula VED=(I×U) / (v×t×h), substituting the parameters, VED≈76.19J / mm² is calculated. 3 .

[0070] Meanwhile, the diameter of the electron beam spot is controlled to be about 100 μm, the scraper moving speed is 50 mm / s, the three-dimensional model path adopts a strip scanning strategy, and the scanning path between adjacent printing layers is rotated 90°.

[0071] After each cladding layer is formed, a defocused electron beam with a current of 30 mA is used to scan the powder bed region for 10 seconds to homogenize the temperature before the next layer of powder is laid. After all layers are clad, the electron beam is stopped, and the component is allowed to cool to room temperature in a vacuum environment or under a protective atmosphere, resulting in a uniform fine-grained TiAl-based composite component reinforced in situ with LaB6.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that this comparative example does not have LaB6 reinforcement; it uses only un-ball-milled TiAl-based pre-alloyed powder as raw material for electron beam melting and forming. The substrate and powder bed preheating process are the same as in Example 1. The specific parameters for electron beam melting and forming include: accelerating voltage (U) of 60 kV, beam current (I) of 12.5 mA, scanning speed (v) of 4 m / s, scanning spacing (t) of 0.1 mm, and single-layer printing thickness (h) of 0.09 mm. The electron beam spot diameter is approximately 100 μm, the squeegee movement speed is 50 mm / s, the three-dimensional model path adopts a strip scanning strategy, and the scanning path between adjacent printing layers is rotated 90°. Finally, a TiAl-based alloy component is obtained through electron beam melting and forming.

[0074] The components obtained in Example 1 and Comparative Example 1 were sampled by wire cutting for microstructure observation and mechanical property testing.

[0075] Figure 2 The image shows a comparison of the microstructures of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction. The microstructure of the component obtained in Comparative Example 1 shows an obvious heterogeneous structure along the construction direction, while the component obtained in Example 1 does not show a heterogeneous structure along the construction direction and exhibits a fine grain structure with an average grain size ≤5μm.

[0076] Figure 3 The image shows the micrographs of the La2O3 and TiB reinforcing phases in the shaped component obtained in Example 1. It can be observed that the La2O3 reinforcing phase mainly exists in the form of particles, while the TiB reinforcing phase mainly exists in the form of whiskers. The two reinforcing phases are distributed inside the grains and at the grain boundaries.

[0077] Figure 4 This is a comparison diagram of the room temperature compressibility of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction; as shown. Figure 4As shown, the component obtained in Example 1 has a room temperature compressive yield strength of 723 MPa, a compressive strength of 2934 MPa, and a fracture strain of 38.1%, while the TiAl-based alloy component obtained in Comparative Example 1 has a room temperature compressive yield strength of 557 MPa, a compressive strength of 2670 MPa, and a fracture strain of 38.3%. This indicates that the introduction of LaB6 can effectively enhance the load-bearing capacity of TiAl-based composite materials without significantly negatively impacting the material's plasticity, achieving a good balance between strength and plasticity. This is mainly attributed to the fact that the La2O3 particles and TiB whiskers generated during the in-situ reaction of LaB6 can refine the grains and synergistically improve the mechanical properties of the material through dispersion strengthening and grain boundary strengthening.

[0078] Figure 5 The diagram shows a comparison of the room temperature compressive properties of the molded components obtained in Example 1 and Comparative Example 1 along the construction direction and perpendicular to the construction direction. The component obtained in Example 1 has a room temperature compressive yield strength of 721 MPa, a compressive strength of 2895 MPa, and a fracture strain of 37.3% when tested along the construction direction. When tested perpendicular to the construction direction, the room temperature compressive yield strength is 726 MPa, the compressive strength is 2900 MPa, and the fracture strain is 37.2%. The difference in yield strength, compressive strength, and fracture strain between the two directions is only 5 MPa, only 5 MPa, and only 0.1%, demonstrating excellent isotropy.

[0079] The component obtained in Comparative Example 1 has a room temperature compressive yield strength of 557 MPa, a compressive strength of 2670 MPa, and a fracture strain of 38.3%. When tested perpendicular to the construction direction, the room temperature compressive yield strength is 574 MPa, the compressive strength is 2910 MPa, and the fracture strain is 38.9%. Its yield strength and compressive strength perpendicular to the construction direction are both higher than those perpendicular to the construction direction, with a significant difference of 240 MPa in compressive strength, demonstrating obvious anisotropy. This indicates that the electron beam melting forming process of this invention achieves an equiaxed crystal microstructure, eliminates interlayer stress and bonding defects, and improves the interfacial bonding strength in different directions.

[0080] Figure 6 This is a comparison chart showing the changes in grain size and hardness of the molded components obtained in Example 1 and Comparative Example 1 after being kept at 900°C for different times. Figure 6 The component obtained in Example 1, after long-term heat treatment at 900℃, showed a grain size increase rate of <5% and a hardness retention rate of >98%. It exhibits excellent high-temperature thermal stability, effectively solving the core technical problems of grain coarsening and performance degradation in traditional EBM-formed TiAl-based alloys during high-temperature service. This is of vital significance for the engineering application of TiAl-based alloys in high-temperature fields such as aerospace and gas turbines.

Claims

1. A method for electron beam melting forming of a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material, characterized in that, The steps include the following: Step 1: Preparation of LaB6 / TiAl composite powder: TiAl-based pre-alloyed powder and LaB6 powder were mixed by low-energy ball milling to obtain LaB6 / TiAl composite powder with LaB6 particles attached to the surface of TiAl powder; the mass of the LaB6 powder accounted for 0.4% or 0.6% of the total mass of the LaB6 / TiAl composite powder. Step 2: Electron beam melting and shaping: The substrate is placed in the forming chamber of an electron beam melting device, and an inert protective atmosphere is established for forming. A defocused electron beam is used to preheat the substrate in stages, uniformly raising its temperature to at least 1000°C. Under this preheating condition, powder is laid layer by layer according to a preset three-dimensional model path. After each layer, the powder bed is preheated to at least 1000°C. Electron beam forming is performed at this preheated temperature according to preset printing parameters. The volumetric energy density of the electron beam forming is 20~80 J / mm². 3 This process allows LaB6 in the molten pool to fully decompose and react in situ to generate La2O3 particles and TiB whisker reinforcing phases. After layer-by-layer cladding, the material is cooled in the furnace to obtain a dense shaped material. In step one, the TiAl-based pre-alloyed powder is prepared by rotating electrode atomization or electrode induction melting gas atomization. Its chemical composition, in atomic percentage, is: Al: 45-50 at.%, Cr: 0-4 at.%, Nb: 0-4 at.%, with the balance being Ti and unavoidable impurities. The TiAl-based pre-alloyed powder has a particle size distribution of 50-150 μm; the LaB6 powder has a particle size distribution of 0.5-5 μm and a purity of not less than 99.8%. The ball milling is carried out under an argon protective atmosphere, using stainless steel balls and mixed powder at a mass ratio of 2:

1. The stainless steel balls are 316L stainless steel balls with diameters of 10 mm and 6 mm, mixed in any proportion. The ball milling speed is 200-250 rpm, using intermittent ball milling, with a 15-minute pause after each 45-60 minute continuous milling session. The total effective ball milling time is 4-6 hours. The specific printing parameters for electron beam forming in step two are as follows: accelerating voltage is 60kV, beam current intensity is 8~16mA, scanning speed is 2~4m / s, scanning spacing is 0.07~0.12mm, and printing layer thickness is 0.08~0.10mm.

2. The electron beam melting forming method for a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material according to claim 1, characterized in that, The inert protective atmosphere required in step two is to evacuate the forming chamber to a vacuum level of 5 × 10⁻⁶. -3 Below Pa, high-purity helium gas with a purity of not less than 99.999% is then refilled into the forming chamber as a protective gas, and the vacuum level in the forming chamber is stably maintained at 0.5 × 10⁻⁶ Pa. -1 ~1.2×10 -1 Pa, the substrate is a stainless steel substrate or a TC4 titanium alloy substrate, the substrate is cleaned and dried using anhydrous ethanol, and the LaB6 / TiAl composite powder is dried before use.

3. The electron beam melting forming method for a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material according to claim 2, characterized in that, The step-by-step preheating method for the substrate in step two is as follows: first, use a defocused electron beam with a current of 10mA to scan the entire substrate in a fast scanning mode for 10 minutes; then increase the current to 15mA and scan for 15 minutes; finally, increase the current to 20mA and scan for 5 minutes. The method for preheating the powder bed is as follows: use a defocused electron beam with a current of 30mA to scan the powder bed area for 12 seconds.

4. The electron beam melting forming method for a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material according to claim 3, characterized in that, In step two, the electron beam spot diameter is ≤200μm, the scraper moving speed is 40~60mm / s, the three-dimensional model path adopts a strip scanning strategy, and the scanning path between adjacent layers is rotated 67-90°.

5. The electron beam melting forming method for a LaB6 in-situ reinforced uniform fine-grained TiAl-based composite material according to claim 4, characterized in that, In step two, after each layer is clad, a defocused electron beam with a current of 30mA is used to scan the powder bed area after cladding for 10s to homogenize the temperature.

6. The TiAl-based composite material prepared by the electron beam melting forming method according to any one of claims 1-5, characterized in that, The TiAl-based composite material contains 0.27 to 0.41 wt% La and 0.13 to 0.19 wt% B.

7. The TiAl-based composite material according to claim 6, characterized in that, The TiAl-based composite material has a uniform fine-grained structure with an average grain size ≤5μm.

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