A gradient structure TiAl alloy blade and a preparation method thereof

Abstract

This invention provides a gradient structure TiAl alloy blade and its preparation method, relating to the technical field of TiAl alloy blades. The gradient structure TiAl alloy blade has a length of 70-300 mm and a thickness of 3-15 mm. Its chemical composition, by mass percentage, is: Al 40-49 at%, Nb 4-8 at%, Mo 0.2-0.9 at%, Si 0-0.2 at%, B 0-0.2 at%, C 0-0.2 at%, with the balance being Ti and unavoidable inclusions; wherein the lower limits for the aforementioned elements, Si and B, cannot be 0. This invention achieves different microstructures for the tenon and blade body by selecting and preparing the alloy powder composition and controlling the electron beam selective melting process. It can simultaneously meet the room temperature and high temperature performance requirements of aerospace alloy blades for the tenon and blade body, with high resource utilization, a short process, and high efficiency, facilitating large-scale industrial production and promotion.

Description

Technical Field

[0001] This invention relates to the technical field of TiAl alloy blades, and in particular to a gradient structure TiAl alloy blade and its preparation method. Background Technology

[0002] TiAl alloys possess low density, high specific strength, and excellent corrosion resistance, making them highly promising high-temperature structural materials for aero-engines and gas turbines, with service temperatures ranging from 600 to 950°C. This alloy has already been used in aero-engine turbine blades and automotive turbochargers. GE has successfully applied TiAl alloy low-pressure turbine blades to the GE-nX engine, installed in the Boeing 777X aircraft. Other typical TiAl alloys, such as TNM and 45XD alloys, are also already in service with aero-engines.

[0003] Electron beam additive manufacturing is a novel fabrication method that generates three-dimensional structures by converting three-dimensional models into two-dimensional slices, melting and solidifying metal powder into two-dimensional slices, and repeating this process. This method offers advantages such as the ability to generate complex three-dimensional structures, material savings, and rapid fabrication. In particular, the electron beam melting process can achieve low-stress TiAl alloy fabrication, thus it is widely used in the fabrication of TiAl components. For example, the Swedish company Arcam has already achieved mature printing of TiAl-4822 alloy blades, printing over 60,000 blades annually.

[0004] The mechanical properties of TiAl alloys are determined by their microstructure, which includes four types at room temperature: near-γ, biphasic, near-lamellar, and fully lamellar. Each microstructure exhibits different mechanical properties; for example, biphasic microstructures show better room temperature plasticity, while fully lamellar microstructures exhibit better fatigue creep performance. Besides the four microstructures, grain morphology also significantly influences mechanical properties. For instance, equiaxed grains are isotropic and suitable for multi-directional loads, while columnar and single-crystal grains exhibit excellent mechanical properties along their growth direction and are suitable for unidirectional loads.

[0005] The low-pressure turbine blade of an aero-engine consists of a tenon and a blade body. The tenon bears complex loads of multiple directions and types, while the blade body mainly bears loads along the blade body direction.

[0006] Currently, the main methods for manufacturing low-pressure turbine blades for aero-engines are additive manufacturing, ultra-high temperature die forging, electrolytic manufacturing, 3D printing wax casting, welding, additive manufacturing and coating composite manufacturing, and hot deformation manufacturing.

[0007] Chinese patent CN115740494A discloses a TiAl alloy blade and its manufacturing method. The method is complex and difficult to operate. The 3D printing process parameters are set based on simulation analysis and data calculation, which deviates from the actual process. The performance of the alloy blade printed with the set process parameters cannot achieve the best overall effect. It does not take into account the mechanical performance requirements of different parts of the alloy blade, such as the tenon and the blade body.

[0008] Chinese patent CN105821470A discloses a dual-structure TiAl alloy and its preparation method, which is obtained by directional solidification of cylindrical rod alloy using an optical floating zone crystal growth device. The main body of the alloy is columnar crystal, and γ-phase equiaxed crystals are generated at the grain boundaries of the columnar crystal. Obviously, the performance of this alloy is not suitable for use in aerospace alloy blades, as its main performance is affected by the columnar crystal structure and cannot meet the mechanical performance requirements of alloy blade tenons.

[0009] Chinese patent CN116851772A discloses a gradient strategy 3D printing method for TiAl alloy preparation. This method reduces thermal stress by preparing and cutting pre-printed materials. Although it can solve the problem of large residual stress and macroscopic cracks during the preparation of TiAl alloy, the microstructure changes from a two-phase lamellar structure to a single-phase γ structure. The overall properties of the prepared alloy are uniform, and it is not suitable for use in aerospace alloy blades. Summary of the Invention

[0010] To address the technical problems of existing methods for manufacturing low-pressure turbine blades for aero-engines, such as complex processes, high operational difficulty, and a lack of consideration for the mechanical performance requirements of different parts of the alloy blade, such as the tenon and the blade body, this invention provides a gradient structure TiAl alloy blade and its manufacturing method that simultaneously meets the mechanical performance requirements of the tenon, blade body, and the transition region between the two in aero-engine alloy blades. The technical solution is as follows:

[0011] A gradient structure TiAl alloy blade, wherein the length of the gradient structure TiAl alloy blade is 70-300mm, the thickness is 3-15mm, and the chemical composition by mass percentage is: Al 40-49at%, Nb 4-8at%, Mo 0.2-0.9at%, Si 0-0.2at%, B 0-0.2at%, C 0-0.2at%, with the balance being Ti and unavoidable inclusions; wherein the lower limit values ​​of Si and B for the aforementioned elements cannot be 0.

[0012] Optionally, the tenon head of the gradient structure TiAl alloy blade is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystals, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0013] Optionally, the room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade are as follows: tensile strength of 600-700 MPa, yield strength of 500-600 MPa, yield-to-tensile ratio of 0.823-0.929, elongation of 2-3%, and fatigue limit of 500-600 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 700-900 MPa, yield strength of 600-800 MPa, yield-to-tensile ratio of 0.821-0.900, elongation of 0.5-1.5%, and fatigue limit of 500-700 MPa.

[0014] A method for preparing a gradient structure TiAl alloy blade, comprising the following steps:

[0015] S1. Melting: Pure metals Ti and Al with a purity of 99.9% and intermediate alloys Al-Nb, Al-Mo, and Al-Si are weighed and batched according to the composition ratio. The alloy melt is obtained by vacuum induction suspension melting and then cast into ingots.

[0016] S2, Casting: Cast the required mass of S1 ingot using a centrifugal casting machine to obtain electrode rods;

[0017] S3. Surface treatment and processing: Remove the oxide scale from the surface of the electrode rod from S2, and then round the corners to obtain an electrode rod suitable for the rotating electrode method.

[0018] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 to obtain alloy powder for 3D printing;

[0019] S5. Alloy powder processing: The alloy powder for 3D printing in S4 is sieved and packaged to obtain finished alloy powder for 3D printing with a particle size controlled at 45-150μm and an oxygen content controlled at less than 500ppm.

[0020] S6. Electron beam selective melting: The finished alloy powder used for 3D printing in S5 is subjected to electron beam selective melting printing to prepare a gradient structure TiAl alloy blade.

[0021] Optionally, the vacuum degree of vacuum induction levitation melting in S1 is controlled at 5×10⁻⁶. -3 -1×10 -4Pa, the number of smelting times is controlled at 3-5 times, and the size of the ingot is Φ40×400mm-Φ80×700mm.

[0022] Optionally, the ingot of S1 is placed in a centrifugal casting machine after the surface oxide scale is removed.

[0023] Optionally, in S2, asbestos is wrapped around the casting mold during the centrifugal casting process to prevent cracks caused by rapid cooling, and the diameter of the electrode rod is 40-75mm.

[0024] Optionally, after centrifugal casting in S2 is completed, the furnace temperature is reduced to 200°C before the ceramic mold shell is removed by sandblasting when the shell temperature is reduced to below 100°C, and the electrode rod is cut off by wire cutting.

[0025] Optionally, in S3, the electrode rod blank is machined to remove the oxide scale, with a surface roughness Ra=0.4-3.2μm and a fillet radius of R1-5mm.

[0026] Optionally, in S4, a high-purity argon atmosphere is used when preparing alloy powder by rotating the electrode, and in S5, the container needs to be filled with argon and then sealed when packaging the alloy powder.

[0027] Optionally, the flowability of the alloy powder used for 3D printing in S4 should be less than 30s / 50g, the hollow powder rate should be less than 0.1%, and the loose density should be greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 .

[0028] Optionally, in S6, the finished alloy powder used in S5 for 3D printing needs to be sieved once using a PRS device before electron beam selective melting printing.

[0029] Optionally, powder needs to be laid before electron beam selective melting printing in S6. During the powder laying process, a layer thickness of 50-100μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1170-1190℃, and the temperature should reach the Tα value as much as possible within the machine's operating range.

[0030] Optionally, before electron beam selective melting printing powder spreading in S6, the substrate needs to be preheated to a temperature of 1200-1220℃ for 30-50 minutes.

[0031] Optionally, the preheating in S6 uses 5+5+10 electron beam scans, with the current gradually increasing from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans.

[0032] Optionally, in the S6 electron beam selective melting printing, the melting parameters for the lower equiaxed crystal portion are: current of 8-8.5mA, scanning speed of 1.9-2.1m / s, scanning path set to random scatter scanning mode, and defocus value of 30-50.

[0033] Optionally, in S6 electron beam selective melting printing, the melting parameters for the upper columnar crystal portion are: current of 7.5-8mA, scanning speed of 1.8-2.0m / s, scanning path set to line-scan mode, and defocus value of 30-35.

[0034] Optionally, in S6, the melting parameters of the transition zone in electron beam selective melting printing are automatically interpolated, with a minimum of 10 transition layers when using a 50μm layer thickness and a minimum of 8 transition layers when using a 70μm layer thickness.

[0035] Optionally, in S6, the post-preheating parameters for electron beam selective melting printing use an average beam current of 12mA and perform 15 scans.

[0036] Optionally, after electron beam selective melting printing in S6 is completed, the printed product needs to be subjected to hot isostatic pressing. The temperature parameters of this process should not exceed 1240℃ and the pressure should exceed 200MPa.

[0037] Optionally, after hot isostatic pressing, the printed product needs to be heat-treated. The heat treatment parameters are: temperature should not exceed 1275℃, and time should not exceed 10 minutes.

[0038] Optionally, the alloy blades after heat treatment can be subjected to CT analysis, and no pores should be found at a scanning precision of 30 μm.

[0039] Optionally, the prepared gradient structure TiAl alloy blades are dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0040] The above technical solution has at least the following advantages compared with the existing technology:

[0041] The above-mentioned solution proposes a gradient structure TiAl alloy blade and its preparation method, which can solve many technical problems existing in the preparation process of TiAl alloy blades, thereby reducing production costs and improving economic benefits.

[0042] This invention utilizes the relationship between energy input, electron beam morphology, and crystal growth through the preparation of alloy powder and reasonable parameter adjustment. It employs selective electron beam melting of alloy powder to prepare the structure. By controlling the energy input density and electron beam morphology, a gradient structure of equiaxed crystals below and columnar crystals above is achieved. In the transition region between equiaxed and columnar crystals, a crack-free transition interface is realized through automatic interpolation. This structure can utilize the unique mechanical properties of different microstructures to match the service requirements of different parts of the blade, proposing a novel concept for the integration of material and function in 3D printing TiAl blades.

[0043] The preparation of the alloy powder of this invention requires controllable composition design. The electrode rod is obtained through two casting processes and is produced using a rotating electrode method. The prepared alloy powder for selective electron beam melting should have a flowability of less than 30 s / 50 g, a hollow powder ratio of less than 0.1%, and a loose packing density greater than 2.4 g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 .

[0044] Before electron beam selective melting printing powder spreading, the substrate needs to be preheated. The preheating adopts 5+5+10 electron beam scans. The current is gradually increased from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans, so that the substrate can be preheated to a sufficient temperature without deformation.

[0045] The reasonable parameter adjustments of this invention include current, scanning speed, and defocus value, which enable the printing of two different microstructures on a single blade without adding printing steps or processes, thus achieving structural and functional integration.

[0046] The hot isostatic pressing process of this invention enables the TiAl alloy blades to eliminate defects that occur during the printing process, effectively improving their mechanical properties.

[0047] The heat treatment following hot isostatic pressing in this invention enables the prepared TiAl alloy blades to obtain an optimized microstructure, characterized by fine, full-layered structures.

[0048] The tenon head of the gradient structure TiAl alloy blade prepared by this invention is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0049] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared by this invention are as follows: tensile strength of 600-700 MPa, yield strength of 500-600 MPa, yield-to-tensile ratio of 0.823-0.929, elongation of 2-3%, and fatigue limit of 500-600 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 700-900 MPa, yield strength of 600-800 MPa, yield-to-tensile ratio of 0.821-0.900, elongation of 0.5-1.5%, and fatigue limit of 500-700 MPa.

[0050] In summary, compared with other traditional methods, the method of this invention can prepare and adjust different microstructures of the tenon and blade by selecting and preparing alloy powder composition and controlling electron beam selective melting process steps; it can simultaneously meet the room temperature and high temperature performance requirements of aerospace alloy blades for the tenon and blade, with high resource utilization, short process, high efficiency, and is conducive to large-scale industrial production and promotion. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is an equiaxed crystal microstructure of the gradient structure TiAl alloy blade of Embodiment 1 of the present invention;

[0053] Figure 2 This is a columnar crystal microstructure of the gradient structure TiAl alloy blade of Embodiment 1 of the present invention;

[0054] Figure 3 This is an equiaxed crystal microstructure of the gradient structure TiAl alloy blade of Embodiment 2 of the present invention;

[0055] Figure 4 This is a columnar crystal microstructure of the gradient structure TiAl alloy blade of Embodiment 2 of the present invention;

[0056] Figure 5 This is a schematic diagram of a low-pressure turbine blade of a gradient structure TiAl alloy blade according to Embodiment 3 of the present invention;

[0057] Figure 6 This is a printed image of the gradient TiAl alloy low-pressure turbine blade of Embodiment 3 of the present invention.

[0058] Figure 7This is a CT scan of the gradient TiAl alloy low-pressure turbine blade of the gradient structure TiAl alloy blade in Embodiment 3 of the present invention.

[0059] Figure 8 This is a anatomical analysis diagram of the gradient TiAl alloy low-pressure turbine blade of Embodiment 3 of the present invention. Detailed Implementation

[0060] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0061] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0062] In this embodiment of the invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent. Similarly, the terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent.

[0063] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0064] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0065] A gradient structure TiAl alloy blade, wherein the length of the gradient structure TiAl alloy blade is 70-300mm, the thickness is 3-15mm, and the chemical composition by mass percentage is: Al 40-49at%, Nb 4-8at%, Mo 0.2-0.9at%, Si 0-0.2at%, B 0-0.2at%, C 0-0.2at%, with the balance being Ti and unavoidable inclusions; wherein the lower limit values ​​of Si and B for the aforementioned elements cannot be 0.

[0066] Specifically, the tenon head of the gradient structure TiAl alloy blade is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone through automatic interpolation.

[0067] Specifically, the room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade are as follows: tensile strength of 600-700 MPa, yield strength of 500-600 MPa, yield-to-tensile ratio of 0.823-0.929, elongation of 2-3%, and fatigue limit of 500-600 MPa; the room temperature mechanical properties of the blade body are as follows: tensile strength of 700-900 MPa, yield strength of 600-800 MPa, yield-to-tensile ratio of 0.821-0.900, elongation of 0.5-1.5%, and fatigue limit of 500-700 MPa.

[0068] A method for preparing a gradient structure TiAl alloy blade, comprising the following steps:

[0069] S1. Melting: Pure metals Ti and Al with a purity of 99.9% and intermediate alloys Al-Nb, Al-Mo, and Al-Si are weighed and batched according to the composition ratio. The alloy melt is obtained by vacuum induction suspension melting and then cast into ingots.

[0070] S2, Casting: Cast the required mass of S1 ingot using a centrifugal casting machine to obtain electrode rods;

[0071] S3. Surface treatment and processing: Remove the oxide scale from the surface of the electrode rod from S2, and then round the corners to obtain an electrode rod suitable for the rotating electrode method.

[0072] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 to obtain alloy powder for 3D printing;

[0073] S5. Alloy powder processing: The alloy powder for 3D printing in S4 is sieved and packaged to obtain finished alloy powder for 3D printing with a particle size controlled at 45-150μm and an oxygen content controlled at less than 500ppm.

[0074] S6. Electron beam selective melting: The finished alloy powder used for 3D printing in S5 is subjected to electron beam selective melting printing to prepare a gradient structure TiAl alloy blade.

[0075] Specifically, the vacuum degree of vacuum induction levitation melting in S1 is controlled at 5×10⁻⁶. -3 -1×10 -4 Pa, the number of smelting times is controlled at 3-5 times, and the size of the ingot is Φ40×400mm-Φ80×700mm.

[0076] Specifically, after removing the surface oxide scale, the S1 ingot is placed in a centrifugal casting machine.

[0077] Specifically, in the S2 centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling from causing cracks, and the diameter of the electrode rod is 40-75mm.

[0078] Specifically, after centrifugal casting in S2 is completed, the furnace temperature is reduced to 200°C before the product is removed from the furnace. Once the shell temperature is reduced to below 100°C, the ceramic shell is removed by sandblasting, and the electrode rod is cut off by wire cutting.

[0079] Specifically, in S3, the electrode rod blank is machined to remove the oxide scale, with a surface roughness Ra=0.4-3.2μm and a fillet radius of R1-5mm.

[0080] Specifically, in S4, a high-purity argon atmosphere is used as a protective atmosphere when preparing alloy powder by rotating the electrode, and in S5, the container needs to be filled with argon and then sealed when packaging the alloy powder.

[0081] Specifically, the flowability of the alloy powder used for 3D printing in S4 should be less than 30s / 50g, the hollow powder rate should be less than 0.1%, and the loose density should be greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 .

[0082] Specifically, in S6, the finished alloy powder used in S5's 3D printing needs to be sieved once using a PRS device before electron beam selective melting printing.

[0083] Specifically, before electron beam selective melting printing in S6, powder needs to be laid. During the powder laying process, a layer thickness of 50-100μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1170-1190℃, and the temperature should reach the Tα value as much as possible within the machine's operating range.

[0084] Specifically, before electron beam selective melting printing powder spreading in S6, the substrate needs to be preheated to a temperature of 1200-1220℃ for 30-50 minutes.

[0085] Specifically, the preheating process in S6 uses 5+5+10 electron beam scans. The current is gradually increased from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans.

[0086] Specifically, in the S6 electron beam selective melting printing, the melting parameters for the lower equiaxed crystal portion are: current of 8-8.5mA, scanning speed of 1.9-2.1m / s, scanning path set to random scatter scanning mode, and defocus value of 30-50.

[0087] Specifically, in S6 electron beam selective melting printing, the melting parameters for the upper columnar crystal portion are: current of 7.5-8mA, scanning speed of 1.8-2.0m / s, scanning path set to line-scan mode, and defocus value of 30-35.

[0088] Specifically, in S6 electron beam selective melting printing, the transition zone melting parameters use an automatic interpolation method. When using a 50μm layer thickness, the transition layer is no less than 10 layers, and when using a 70μm layer thickness, the transition layer is no less than 8 layers.

[0089] Specifically, in S6 electron beam selective melting printing, the post-heating parameters use an average beam current of 12mA and are scanned 15 times.

[0090] In particular, after electron beam selective melting printing in S6 is completed, the printed product needs to be subjected to hot isostatic pressing. The temperature parameters of this process should not exceed 1240℃ and the pressure should exceed 200MPa.

[0091] In particular, after hot isostatic pressing, the printed product needs to be heat-treated. The heat treatment parameters are: temperature should not exceed 1275℃, and time should not exceed 10 minutes.

[0092] In particular, CT analysis of the alloy blades after heat treatment should show no pores at a scanning precision of 30 μm.

[0093] In particular, the prepared gradient structure TiAl alloy blades were dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0094] Example 1

[0095] This embodiment is a gradient structure TiAl alloy blade. The gradient structure TiAl alloy blade has a length of 70mm and a thickness of 4mm. The chemical composition by mass percentage is: Al 44at%, Nb 4at%, Mo 0.5at%, Si 0.2at%, B 0.05at%, with the balance being Ti and unavoidable inclusions.

[0096] A method for preparing TiAl alloy blades based on the above-mentioned gradient structure includes the following steps:

[0097] S1. Melting: Pure metals Ti and Al with a purity of 99.9%, as well as intermediate alloys Al-Nb, Al-Mo, and Al-Si, are weighed and batched according to their composition ratios. The alloy melt is obtained using vacuum induction suspension melting, with the vacuum level controlled at 5 × 10⁻⁶. -3 Pa, the number of smelting times is controlled at 3 times, and the casting yields an ingot with dimensions of Φ60×400mm;

[0098] S2, Casting: After removing the surface oxide scale from the ingot of S1 of the required mass, it is placed in a centrifugal casting machine for casting. During the centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling and cracking. After centrifugal casting is completed, the ingot is taken out of the furnace after the temperature inside the furnace drops to 200°C. After the temperature of the mold shell drops to below 100°C, the ceramic mold shell is removed by sandblasting. The electrode rod is cut off by wire cutting to obtain an electrode rod with a diameter of 50mm.

[0099] S3. Surface treatment and processing: Remove the oxide scale and round the corners of the electrode rod from S2. The surface roughness Ra=2μm and the rounding radius is R1.5mm. After rounding, an electrode rod with a diameter of 45mm suitable for the rotating electrode method is obtained.

[0100] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 using the rotating electrode method. The protective atmosphere for preparing alloy powder is high-purity argon gas. Alloy powder for 3D printing is obtained with a particle size of 45-140μm and an oxygen content of 400ppm.

[0101] S5. Alloy Powder Processing: The 3D printing alloy powder from S4 is sieved and packaged. During packaging, the container must be filled with argon gas and then sealed to obtain finished 3D printing alloy powder with a particle size controlled at 45-150μm and an oxygen content controlled below 500ppm. The flowability of this 3D printing alloy powder should be less than 30s / 50g, the hollow powder rate less than 0.1%, and the loose packing density greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 ;

[0102] S6. Electron Beam Selective Melting: Before electron beam selective melting printing of the finished alloy powder used in S5, it is necessary to sieve it once using a PRS device. Then, the sieved finished alloy powder is spread into powder for electron beam selective melting printing. During the powder spreading process, a layer thickness of 50μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1170-1190℃. Within the machine's operating range, the temperature should be as close to the Tα value as possible to prepare a gradient structure TiAl alloy blade.

[0103] Before electron beam selective melting printing (S6), the substrate needs to be preheated to 1200℃ for 30 minutes. Preheating involves 5+5+10 electron beam scans. The current gradually increases from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans. For the lower equiaxed crystal portion of the electron beam selective melting printing, the melting parameters use a current of 8mA, a random point melting mode, a scanning speed of 2.0m / s, and a defocus value of 45. For the upper columnar crystal portion, the melting parameters use a current of 7.5mA, a scanning speed of 1.8m / s, and a defocus value of 30. The transition zone melting parameters use automatic interpolation; with a layer thickness of 50μm, the transition layer should be at least 10 layers, and with a layer thickness of 70μm, the transition layer should be at least 8 layers.

[0104] In this embodiment, the prepared gradient structure TiAl alloy blade is dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0105] The tenon of the gradient structure TiAl alloy blade prepared in this embodiment is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0106] In this embodiment, the isometric microstructure of the printed sample was observed using a scanning electron microscope, and the results were as follows: Figure 1 The image shown indicates a grain size of approximately 10 μm, with a microstructure composed of α2, γ, and B2 phases. The equiaxed crystal microstructure was observed using a scanning electron microscope, yielding the following results: Figure 2 The image shown.

[0107] The average grain size of the equiaxed crystals in the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment is 8 μm, and the average grain size of the columnar crystals in the blade body portion is 30 μm.

[0108] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment are as follows: tensile strength of 650 MPa, yield strength of 550 MPa, yield-to-tensile ratio of 0.846, elongation of 2%, strength-ductility product of 1.30 GPa·%, and fatigue limit of 500 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 750 MPa, yield strength of 650 MPa, yield-to-tensile ratio of 0.867, elongation of 1%, strength-ductility product of 0.75 GPa·%, and fatigue limit of 550 MPa.

[0109] Example 2

[0110] This embodiment is a gradient structure TiAl alloy blade. The gradient structure TiAl alloy blade has a length of 120mm and a thickness of 5mm. The chemical composition by mass percentage is: Al 44at%, Nb 4at%, Mo 0.5at%, Si 0.2at%, B 0.1at%, C 0.05at%, with the balance being Ti and unavoidable inclusions.

[0111] A method for preparing TiAl alloy blades based on the above-mentioned gradient structure includes the following steps:

[0112] S1. Melting: Pure metals Ti and Al with a purity of 99.9%, as well as intermediate alloys Al-Nb, Al-Mo, and Al-Si, are weighed and batched according to their composition ratios. The alloy melt is obtained using vacuum induction suspension melting, with the vacuum level controlled at 3 × 10⁻⁶. -4 Pa, the number of smelting times is controlled at 3 times, and the casting yields an ingot with dimensions of Φ55×500mm;

[0113] S2, Casting: After removing the surface oxide scale from the ingot of S1 of the required mass, it is placed in a centrifugal casting machine for casting. During the centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling and cracking. After centrifugal casting is completed, the ingot is taken out of the furnace after the temperature inside the furnace drops to 200°C. After the temperature of the mold shell drops to below 100°C, the ceramic mold shell is removed by sandblasting. The electrode rod is cut off by wire cutting to obtain an electrode rod with a diameter of 58mm.

[0114] S3. Surface treatment and processing: Remove the oxide scale and round the corners of the electrode rod from S2. The surface roughness Ra=2.6μm and the rounding radius is R3.2mm. After rounding, an electrode rod with a diameter of 52mm suitable for the rotating electrode method is obtained.

[0115] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 using the rotating electrode method. The protective atmosphere for preparing alloy powder is high-purity argon gas. Alloy powder for 3D printing is obtained with a particle size of 40-120μm and an oxygen content of 460ppm.

[0116] S5. Alloy Powder Processing: The 3D printing alloy powder from S4 is sieved and packaged. During packaging, the container must be filled with argon gas and then sealed to obtain finished 3D printing alloy powder with a particle size controlled at 45-150μm and an oxygen content controlled below 500ppm. The flowability of this 3D printing alloy powder should be less than 30s / 50g, the hollow powder rate less than 0.1%, and the loose packing density greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 ;

[0117] S6. Electron Beam Selective Melting: Before electron beam selective melting printing of the finished alloy powder used in S5, it is necessary to sieve it once using a PRS device. Then, the sieved finished alloy powder is spread into powder for electron beam selective melting printing. During the powder spreading process, a layer thickness of 70μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1190℃. Within the machine's operating range, the temperature should be as close to the Tα value as possible to prepare a gradient structure TiAl alloy blade.

[0118] Before electron beam selective melting printing (S6), the substrate needs to be preheated to 1200℃ for 35 minutes. Preheating involves 5+5+10 electron beam scans. The current gradually increases from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans. For the lower equiaxed crystal portion of the electron beam selective melting printing, the melting parameters are: current 8.5mA, scanning speed 2.1m / s, and defocus value 50. For the upper columnar crystal portion, the melting parameters are: current 7.5mA, scanning speed 1.8m / s, and defocus value 35. The transition zone melting parameters use automatic interpolation; with a layer thickness of 70μm, the transition layer is no less than 8 layers, and is 10 layers in total.

[0119] In this embodiment, the prepared gradient structure TiAl alloy blade is dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0120] The tenon of the gradient structure TiAl alloy blade prepared in this embodiment is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0121] In this embodiment, the isometric microstructure of the printed sample was observed using a scanning electron microscope, and the results were as follows: Figure 3 The image shown indicates a grain size of approximately 10 μm, with a microstructure composed of α2, γ, and B2 phases. The equiaxed crystal microstructure was observed using a scanning electron microscope, yielding the following results: Figure 4 The image shown.

[0122] The average grain size of the equiaxed crystals in the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment is 10 μm, and the average grain size of the columnar crystals in the blade body portion is 35 μm.

[0123] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment are as follows: tensile strength of 620 MPa, yield strength of 510 MPa, yield-to-tensile ratio of 0.823, elongation of 1.8%, strength-ductility product of 1.12 GPa·%, and fatigue limit of 470 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 800 MPa, yield strength of 720 MPa, yield-to-tensile ratio of 0.900, elongation of 1.2%, strength-ductility product of 0.96 GPa·%, and fatigue limit of 650 MPa.

[0124] Example 3

[0125] This embodiment is a gradient structure TiAl alloy blade. The gradient structure TiAl alloy blade has a length of 180mm and a thickness of 6mm. The chemical composition by mass percentage is: Al 44at%, Nb 4at%, Mo 0.5at%, Si 0.2at%, B 0.1at%, with the balance being Ti and unavoidable inclusions.

[0126] A method for preparing TiAl alloy blades based on the above-mentioned gradient structure includes the following steps:

[0127] S1. Melting: Pure metals Ti and Al with a purity of 99.9%, as well as intermediate alloys Al-Nb, Al-Mo, and Al-Si, are weighed and batched according to their composition ratios. The alloy melt is obtained using vacuum induction suspension melting, with the vacuum level controlled at 2 × 10⁻⁶. -3 Pa, the number of smelting times is controlled at 3 times, and the casting yields an ingot with dimensions of Φ80×700mm;

[0128] S2, Casting: After removing the surface oxide scale from the ingot of S1 of the required mass, it is placed in a centrifugal casting machine for casting. During the centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling and cracking. After centrifugal casting is completed, the ingot is taken out of the furnace after the temperature inside the furnace drops to 200°C. After the temperature of the mold shell drops to below 100°C, the ceramic mold shell is removed by sandblasting. The electrode rod is cut off by wire cutting to obtain an electrode rod with a diameter of 75mm.

[0129] S3. Surface treatment and processing: Remove the oxide scale from the electrode rod of S2 and round the corners. The surface roughness Ra=3.0μm and the rounding radius is R2.5mm. After rounding, an electrode rod with a diameter of 70mm suitable for the rotating electrode method is obtained.

[0130] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 using the rotating electrode method. The protective atmosphere for preparing alloy powder by rotating the electrode is high-purity argon gas. Alloy powder for 3D printing is obtained with a particle size of 40-130μm and an oxygen content of 440ppm.

[0131] S5. Alloy Powder Processing: The 3D printing alloy powder from S4 is sieved and packaged. During packaging, the container must be filled with argon gas and then sealed to obtain finished 3D printing alloy powder with a particle size controlled at 45-150μm and an oxygen content controlled below 500ppm. The flowability of this 3D printing alloy powder should be less than 30s / 50g, the hollow powder rate less than 0.1%, and the loose packing density greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 ;

[0132] S6, Electron Beam Selective Melting: Before electron beam selective melting printing of the finished alloy powder used in S5, it is necessary to sieve it once using a PRS device. Then, the sieved finished alloy powder is spread into powder for electron beam selective melting printing. During the powder spreading process, a layer thickness of 50μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1170℃. Within the machine's operating range, the temperature should be as close to the Tα value as possible to prepare a gradient structure TiAl alloy blade.

[0133] Before powder spreading in S6 electron beam selective melting printing, the substrate needs to be preheated to 1200℃ for 30 minutes. Preheating involves 5+5+10 electron beam scans. The current gradually increases from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans. For the lower equiaxed crystal portion of electron beam selective melting printing, the melting parameters use a current of 8.3mA, a random point melting mode, a scanning speed of 1.9m / s, and a defocus value of 48. For the upper columnar crystal portion, the melting parameters use a current of 7.8mA, a line-scan mode, a scanning speed of 1.9m / s, and a defocus value of 32. The transition zone melting parameters use automatic interpolation; with a layer thickness of 50μm, the transition layer is no less than 10 layers, and is 12 layers in total. Among these, using... Figure 5 The blade model shown was printed using an equiaxed crystal-columnar crystal gradient structure printing method to obtain the following result. Figure 6 The actual blade shown.

[0134] After electron beam selective melting printing in S6 is completed, the printed product needs to undergo hot isostatic pressing (HIP). The parameters for this process are a temperature of 1235℃ and a pressure of 200MPa. After HIP, the printed product needs to undergo heat treatment. The parameters for heat treatment are a temperature of 1260℃ and a time of 10min.

[0135] This embodiment performs CT analysis on the prepared gradient structure TiAl alloy blades, with a scanning precision of 30 μm. The results are as follows: Figure 7As shown, the leaf is dissected as follows: Figure 8 As shown. The tenon section should be entirely composed of equiaxed crystals, while the blade section should be entirely composed of columnar crystals.

[0136] The tenon of the gradient structure TiAl alloy blade prepared in this embodiment is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0137] The average grain size of the equiaxed crystals in the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment is 12 μm, and the average grain size of the columnar crystals in the blade body portion is 45 μm.

[0138] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment are as follows: tensile strength of 620 MPa, yield strength of 510 MPa, yield-to-tensile ratio of 0.823, elongation of 2.3%, strength-ductility product of 1.43 GPa·%, and fatigue limit of 540 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 850 MPa, yield strength of 750 MPa, yield-to-tensile ratio of 0.882, elongation of 1.7%, strength-ductility product of 1.45 GPa·%, and fatigue limit of 650 MPa.

[0139] Example 4

[0140] This embodiment is a gradient structure TiAl alloy blade. The gradient structure TiAl alloy blade has a length of 200mm and a thickness of 6mm. The chemical composition by mass percentage is: Al 45at%, Nb 4at%, Mo 0.6at%, Si 0.1at%, B 0.05at%, C 0.05at%, with the balance being Ti and unavoidable inclusions.

[0141] A method for preparing TiAl alloy blades based on the above-mentioned gradient structure includes the following steps:

[0142] S1. Melting: Pure metals Ti and Al with a purity of 99.9%, as well as intermediate alloys Al-Nb, Al-Mo, and Al-Si, are weighed and batched according to their composition ratios. The alloy melt is obtained through vacuum induction suspension melting, with the vacuum level controlled at 1.5 × 10⁻⁶. -3 Pa, the number of smelting times is controlled at 3 times, and the casting yields an ingot with dimensions of Φ70×600mm;

[0143] S2, Casting: After removing the surface oxide scale from the ingot of S1 of the required mass, it is placed in a centrifugal casting machine for casting. During the centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling and cracking. After centrifugal casting is completed, the ingot is taken out of the furnace after the temperature inside the furnace drops to 200°C. After the temperature of the mold shell drops to below 100°C, the ceramic mold shell is removed by sandblasting. The electrode rod is cut off by wire cutting to obtain an electrode rod with a diameter of 55mm.

[0144] S3. Surface treatment and processing: Remove the oxide scale from the electrode rod of S2 and round the corners. The surface roughness Ra=1.8μm and the rounding radius is R2.2mm. After rounding, an electrode rod with a diameter of 50mm suitable for the rotating electrode method is obtained.

[0145] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 using the rotating electrode method. The protective atmosphere for preparing alloy powder is high-purity argon gas. Alloy powder for 3D printing is obtained with a particle size of 60-130μm and an oxygen content of 330ppm.

[0146] S5. Alloy Powder Processing: The 3D printing alloy powder from S4 is sieved and packaged. During packaging, the container must be filled with argon gas and then sealed to obtain finished 3D printing alloy powder with a particle size controlled at 45-150μm and an oxygen content controlled below 500ppm. The flowability of this 3D printing alloy powder should be less than 30s / 50g, the hollow powder rate less than 0.1%, and the loose packing density greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 ;

[0147] S6. Electron Beam Selective Melting: Before electron beam selective melting printing of the finished alloy powder used in S5, it is necessary to sieve it once using a PRS device. Then, the sieved finished alloy powder is spread into powder for electron beam selective melting printing. During the powder spreading process, a layer thickness of 100μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1190℃. Within the machine's operating range, the temperature should be as close to the Tα value as possible to prepare a gradient structure TiAl alloy blade.

[0148] Before electron beam selective melting printing (S6), the substrate needs to be preheated to 1220℃ for 50 minutes. Preheating involves 5+5+10 electron beam scans. The current gradually increases from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans. For the lower equiaxed crystal portion of the electron beam selective melting printing, the melting parameters are: current 8.2mA, scanning speed 2.0m / s, random point melting strategy, and defocus value of 40. For the upper columnar crystal portion, the melting parameters are: current 8mA, scanning speed 1.9m / s, line-scan strategy, and defocus value of 32. The transition zone melting parameters use automatic interpolation; with a layer thickness of 50μm, the transition layer is no less than 10 layers, and with a layer thickness of 70μm, the transition layer is no less than 8 layers.

[0149] In this embodiment, the prepared gradient structure TiAl alloy blade is dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0150] The tenon of the gradient structure TiAl alloy blade prepared in this embodiment is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ. The blade body of the gradient structure TiAl alloy blade and the preparation method are columnar crystals, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0151] The average grain size of the equiaxed crystals in the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment is 11 μm, and the average grain size of the columnar crystals in the blade body portion is 44 μm.

[0152] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment are as follows: tensile strength of 700 MPa, yield strength of 650 MPa, yield-to-tensile ratio of 0.929, elongation of 2%, strength-ductility product of 1.40 GPa·%, and fatigue limit of 600 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 950 MPa, yield strength of 850 MPa, yield-to-tensile ratio of 0.895, elongation of 1.3%, strength-ductility product of 1.24 GPa·%, and fatigue limit of 800 MPa.

[0153] Example 5

[0154] This embodiment is a gradient structure TiAl alloy blade. The gradient structure TiAl alloy blade has a length of 260mm and a thickness of 8mm. The chemical composition by mass percentage is: Al 46at%, Nb 5at%, Mo 0.5at%, Si 0at%, B 0.15at%, C 0.15%, with the balance being Ti and unavoidable inclusions.

[0155] A method for preparing TiAl alloy blades based on the above-mentioned gradient structure includes the following steps:

[0156] S1. Melting: Pure metals Ti and Al with a purity of 99.9%, as well as intermediate alloys Al-Nb, Al-Mo, and Al-Si, are weighed and batched according to their composition ratios. The alloy melt is obtained using vacuum induction suspension melting, with the vacuum level controlled at 2 × 10⁻⁶. -3 Pa, the number of smelting times is controlled at 3 times, and the casting yields an ingot with dimensions of Φ40×600mm;

[0157] S2, Casting: After removing the surface oxide scale from the ingot of S1 of the required mass, it is placed in a centrifugal casting machine for casting. During the centrifugal casting process, asbestos is wrapped around the casting mold to prevent rapid cooling and cracking. After centrifugal casting is completed, the ingot is taken out of the furnace after the temperature inside the furnace drops to 200°C. After the temperature of the mold shell drops to below 100°C, the ceramic mold shell is removed by sandblasting. The electrode rod is cut off by wire cutting to obtain an electrode rod with a diameter of 40mm.

[0158] S3. Surface treatment and processing: Remove the oxide scale from the electrode rod of S2 and round the corners. The surface roughness Ra=2.0μm and the rounding radius is R3.5mm. After rounding, an electrode rod with a diameter of 35mm suitable for the rotating electrode method is obtained.

[0159] S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 using the rotating electrode method. The protective atmosphere for preparing alloy powder is high-purity argon gas. Alloy powder for 3D printing is obtained with a particle size of 55-125μm and an oxygen content of 350ppm.

[0160] S5. Alloy Powder Processing: The 3D printing alloy powder from S4 is sieved and packaged. During packaging, the container must be filled with argon gas and then sealed to obtain finished 3D printing alloy powder with a particle size controlled at 45-150μm and an oxygen content controlled below 500ppm. The flowability of this 3D printing alloy powder should be less than 30s / 50g, the hollow powder rate less than 0.1%, and the loose packing density greater than 2.4g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 ;

[0161] S6, Electron Beam Selective Melting: Before electron beam selective melting printing of the finished alloy powder used in S5, it is necessary to sieve it once using a PRS device. Then, the sieved finished alloy powder is spread into powder for electron beam selective melting printing. During the powder spreading process, a layer thickness of 50μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1190℃. Within the machine's operating range, the temperature should be as close to the Tα value as possible to prepare a gradient structure TiAl alloy blade.

[0162] Before electron beam selective melting printing (S6), the substrate needs to be preheated to 1220℃ for 30 minutes. Preheating involves 5+5+10 electron beam scans. The current gradually increases from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans. For the lower equiaxed crystal portion of the electron beam selective melting printing, the melting parameters are: current 8.5mA, scanning speed 2.0m / s, random point melting mode, and defocus value 30. For the upper columnar crystal portion, the melting parameters are: current 7.5mA, scanning speed 1.8m / s, line-scan mode, and defocus value 30. The transition zone melting parameters use automatic interpolation; with a layer thickness of 50μm, the transition layer should be at least 10 layers, and with a layer thickness of 70μm, the transition layer should be at least 8 layers.

[0163] In this embodiment, the prepared gradient structure TiAl alloy blade is dissected and analyzed. The tenon part should be entirely composed of equiaxed crystals, and the blade body should be entirely composed of columnar crystals.

[0164] The tenon of the gradient structure TiAl alloy blade prepared in this embodiment is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0165] The average grain size of the equiaxed crystals in the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment is 6 μm, and the average grain size of the columnar crystals in the blade body portion is 40 μm.

[0166] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared in this embodiment are as follows: tensile strength of 600 MPa, yield strength of 520 MPa, yield-to-tensile ratio of 0.867, elongation of 2.5%, strength-ductility product of 1.50 GPa·%, and fatigue limit of 510 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 780 MPa, yield strength of 640 MPa, yield-to-tensile ratio of 0.821, elongation of 1.2%, strength-ductility product of 0.94 GPa·%, and fatigue limit of 590 MPa.

[0167] The above-mentioned solution proposes a gradient structure TiAl alloy blade and its preparation method, which can solve many technical problems existing in the preparation process of TiAl alloy blades, thereby reducing production costs and improving economic benefits.

[0168] This invention utilizes the relationship between energy input, electron beam morphology, and crystal growth through the preparation of alloy powder and reasonable parameter adjustment. It employs selective electron beam melting of alloy powder to prepare the structure. By controlling the energy input density and electron beam morphology, a gradient structure of equiaxed crystals below and columnar crystals above is achieved. In the transition region between equiaxed and columnar crystals, a crack-free transition interface is realized through automatic interpolation. This structure can utilize the unique mechanical properties of different microstructures to match the service requirements of different parts of the blade, proposing a novel concept for the integration of material and function in 3D printing TiAl blades.

[0169] The preparation of the alloy powder of this invention requires controllable composition design. The electrode rod is obtained through two casting processes and is produced using a rotating electrode method. The prepared alloy powder for selective electron beam melting should have a flowability of less than 30 s / 50 g, a hollow powder ratio of less than 0.1%, and a loose packing density greater than 2.4 g / cm³. 3 The tap density is greater than 2.5 g / cm³. 3 .

[0170] Before electron beam selective melting printing powder spreading, the substrate needs to be preheated. The preheating adopts 5+5+10 electron beam scans. The current is gradually increased from 12 to 20 in the first 5 scans, from 20 to 40 in the middle 5 scans, and from 40 to 60 in the last 10 scans, so that the substrate can be preheated to a sufficient temperature without deformation.

[0171] The reasonable parameter adjustments of this invention include current, scanning speed, and defocus value, which enable the printing of two different microstructures on a single blade without adding printing steps or processes, thus achieving structural and functional integration.

[0172] The hot isostatic pressing process of this invention enables the TiAl alloy blades to eliminate defects that occur during the printing process, effectively improving their mechanical properties.

[0173] The heat treatment following hot isostatic pressing in this invention enables the prepared TiAl alloy blades to obtain an optimized microstructure, characterized by fine, full-layered structures.

[0174] The tenon head of the gradient structure TiAl alloy blade prepared by this invention is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone by automatic interpolation.

[0175] The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade prepared by this invention are as follows: tensile strength of 600-700 MPa, yield strength of 500-600 MPa, yield-to-tensile ratio of 0.823-0.929, elongation of 2-3%, and fatigue limit of 500-600 MPa; the room temperature mechanical properties of the blade body portion are as follows: tensile strength of 700-900 MPa, yield strength of 600-800 MPa, yield-to-tensile ratio of 0.821-0.900, elongation of 0.5-1.5%, and fatigue limit of 500-700 MPa.

[0176] In summary, compared with other traditional methods, the method of this invention can prepare and adjust different microstructures of the tenon and blade by selecting and preparing alloy powder composition and controlling electron beam selective melting process steps; it can simultaneously meet the room temperature and high temperature performance requirements of aerospace alloy blades for the tenon and blade, with high resource utilization, short process, high efficiency, and is conducive to large-scale industrial production and promotion.

[0177] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0178] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0179] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply 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.

[0180] 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 variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A gradient structure TiAl alloy blade, characterized in that, The gradient structure TiAl alloy blades have a length of 70-300 mm and a thickness of 3-15 mm. Their chemical composition, by mass percentage, is: Al 40-49 at%, Nb 4-8 at%, Mo 0.2-0.9 at%, Si 0-0.2 at%, B 0-0.2 at%, C 0-0.2 at%, with the balance being Ti and unavoidable inclusions; wherein the lower limits for Si and B cannot be 0. The tenon head of the gradient structure TiAl alloy blade is divided into equiaxed crystals, and the equiaxed crystal part has a three-phase microstructure of α2+β+γ; the blade body of the gradient structure TiAl alloy blade is columnar crystal, and the columnar crystal part has a two-phase microstructure of α2+γ. A crack-free transition interface is achieved in the equiaxed crystal-columnar crystal transition zone through automatic interpolation. The room temperature mechanical properties of the tenon portion of the gradient structure TiAl alloy blade are as follows: tensile strength of 600-700 MPa, yield strength of 500-600 MPa, yield-to-tensile ratio of 0.823-0.929, elongation of 2-3%, and fatigue limit of 500-600 MPa; the room temperature mechanical properties of the blade body are as follows: tensile strength of 700-900 MPa, yield strength of 600-800 MPa, yield-to-tensile ratio of 0.821-0.900, elongation of 0.5-1.5%, and fatigue limit of 500-700 MPa.

2. A method for preparing TiAl alloy blades with a gradient structure according to claim 1, characterized in that, The preparation method of the gradient structure TiAl alloy blade is as follows: S1. Melting: Pure metals Ti and Al with a purity of 99.9% and intermediate alloys Al-Nb, Al-Mo, and Al-Si are weighed and batched according to the composition ratio. The alloy melt is obtained by vacuum induction suspension melting and then cast into ingots. S2, Casting: Cast the required mass of S1 ingot using a centrifugal casting machine to obtain electrode rods; S3. Surface treatment and processing: Remove the oxide scale from the surface of the electrode rod from S2, and then round the corners to obtain an electrode rod suitable for the rotating electrode method. S4. Alloy powder preparation: Alloy powder is prepared by rotating the electrode rod of S3 to obtain alloy powder for 3D printing; S5. Alloy powder processing: The alloy powder for 3D printing in S4 is sieved and packaged to obtain finished alloy powder for 3D printing with a particle size controlled at 45-150μm and an oxygen content controlled at less than 500ppm. S6. Electron beam selective melting: The finished alloy powder used for 3D printing in S5 is subjected to electron beam selective melting printing to prepare a gradient structure TiAl alloy blade.

3. The method for preparing gradient structure TiAl alloy blades according to claim 2, characterized in that, Before electron beam selective melting printing in S6, powder needs to be laid. During the powder laying process, a layer thickness of 50-100μm is selected. During the electron beam selective melting process, the target temperature of the powder bed sintering process reaches 1170-1190℃.

4. The method for preparing gradient structure TiAl alloy blades according to claim 2, characterized in that, In S6 electron beam selective melting printing, the melting parameters for the lower equiaxed crystal portion are: current 8-8.5mA, scanning speed 1.9-2.1m / s, and defocus value 30-50; for the upper equiaxed crystal portion, the melting parameters are: current 7.5-8mA, scanning speed 1.8-2.0m / s, and defocus value 30-35.

5. The method for preparing gradient structure TiAl alloy blades according to claim 2, characterized in that, In S6 electron beam selective melting printing, the transition zone melting parameters use an automatic interpolation method. When using a 50μm layer thickness, the transition layer should be no less than 10 layers, and when using a 70μm layer thickness, the transition layer should be no less than 8 layers. In electron beam selective melting printing, the post-preheating parameters use an average beam current of 12mA and 15 scans are performed.

6. The method for preparing the gradient structure TiAl alloy blade according to claim 2, characterized in that, After electron beam selective melting printing in S6 is completed, the printed product needs to undergo hot isostatic pressing (HIP). The temperature parameters for this process should not exceed 1240℃ and the pressure should exceed 200MPa. After HIP, the printed product needs to undergo heat treatment. The heat treatment parameters should not exceed 1275℃ and the time should not exceed 10min.

7. The method for preparing gradient structure TiAl alloy blades according to claim 2, characterized in that, CT analysis of the alloy blades after heat treatment showed no pores at a scanning precision of 30 μm.

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