Additive manufacturing ultra-fine grain nano lamellar titanium-aluminum alloy and preparation method

Abstract

The invention provides an additive manufacturing ultra-fine grain nanosheet layer titanium-aluminum alloy and a preparation method, and relates to the technical field of additive manufacturing titanium-aluminum alloys. The alloy comprises the following chemical components in atomic percent: 43 to 46 at% of Al, 3 to 10 at% of Nb, 2 to 8 at% of Ta, 0.1 to 1.9 at% of Mo, 0 to 0.75 at% of B, 0 to 0.5 at% of C, less than 600 ppm of oxygen, and the balance of Ti and inevitable impurity elements. The preparation method comprises the steps of raw material weighing, vacuum induction melting and casting, first-time hot isostatic pressing treatment, electrode preparation, micron-sized powder preparation, material printing, second-time hot isostatic pressing treatment and three-stage heat treatment. The method is high in resource utilization rate, low in production cost, short in process, easy to operate and high in efficiency, and the prepared titanium-aluminum alloy is high in comprehensive performance and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of titanium aluminide alloys, and particularly to an additive manufactured ultrafine-grained nano-lamellar titanium aluminide alloy and a preparation method thereof. Background Art

[0002] Titanium aluminide alloys are widely used in fields such as aerospace and automotive industries due to their excellent high-temperature performance, corrosion resistance, and low density. Traditional preparation methods of titanium aluminide alloys mainly adopt casting and forging techniques. Although these methods can manufacture high-performance titanium aluminide alloy materials, they have defects such as relatively large grain sizes and difficulty in uniformly controlling the microstructure. To solve this problem, researchers have gradually turned to additive manufacturing techniques in recent years, especially electron beam selective melting (EBSM) technology, in order to achieve higher control precision and material property optimization in the manufacturing of complex structural components.

[0003] As a high-energy beam additive manufacturing method, EBSM technology can achieve rapid melting and solidification of materials during the printing process, and at the same time, phase transformation can be achieved through a cyclic heating process, thereby affecting the grain size and the evolution of the microstructure. This technology is particularly suitable for manufacturing parts with complex geometries. However, although EBSM technology can produce titanium aluminide alloy components with good mechanical properties in many applications, it still faces challenges in further refining grains and optimizing the microstructure to improve mechanical properties.

[0004] For the titanium aluminide alloy produced by EBSM technology, the grains are relatively coarse and the lamellar structure is not fine enough, resulting in the strength and ductility in applications not reaching the optimal state. Therefore, how to effectively suppress grain growth, improve the microstructural uniformity and mechanical properties of the alloy in EBSM technology is still a difficult problem to be solved urgently. In addition, in the existing EBSM technology, there is often a lack of effective means for composition design and process optimization to achieve the refinement and control of the lamellar structure.

[0005] For example: Chinese Patent CN117399637A discloses a near-net-shape forming method for high-performance in-situ self-generated Ti5Si3 phase-reinforced titanium aluminide matrix composites. This method obtains Ti5Si3 reinforcement phases and a titanium aluminide matrix through electron beam dual-wire 3D printing technology. However, during the additive process, parameters such as wire feeding speed, electron beam focus, and cooling speed need to be precisely controlled, and the process window is relatively narrow, which easily leads to process instability. In addition, the temperature gradient during preheating and deposition may cause thermal stress, resulting in microcracks inside the material and affecting the mechanical properties of the material. Even though the material properties can be regulated by adjusting the proportion of Ti5Si3 reinforcement phases, this requires high process experience from operators and it is difficult to maintain consistency in large-scale industrial production.

[0006] Chinese Patent CN115261658A discloses an additive manufacturing method for a high-performance titanium-aluminum alloy with a fine-grained fully lamellar structure. This method requires setting the laser scanning speed, layer thickness, fixed interlayer spacing, and laser power, and forming a high-performance titanium-aluminum alloy with a fine-grained fully lamellar structure of the desired shape by depositing layer by layer and channel by channel on a substrate. Obviously, strict requirements are imposed on the laser scanning speed and layer thickness. Exceeding the appropriate range may affect the forming quality and efficiency. When the laser scanning speed is increased, the forming ability of the sample may decline.

[0007] Chinese Patent CN113118606A discloses an electron beam wire and arc additive manufacturing method for large titanium-aluminum alloy components. This method uses a flux-cored wire as the wire material and employs electron beam wire and arc additive manufacturing in cooperation with an in-situ heating stage to manufacture titanium-aluminum alloy components. Although the manufactured titanium-aluminum alloy components are large in size, their performance is poor, especially in the case of not undergoing subsequent heat treatment, technical defects such as cracks and uneven performance are likely to occur.

[0008] Chinese Patent CN102941343A discloses a rapid manufacturing method for complex titanium-aluminum alloy parts. This method performs layer-by-layer melting and sintering and rapid cyclic heat treatment according to the information provided by a three-dimensional model under program control by a high-energy beam, and stacks layer by layer to manufacture complex titanium-aluminum alloy parts with small microstructures. It belongs to the traditional additive manufacturing method, and the thermal stress of each layer during the manufacturing process is not effectively released, and subsequent heat treatment is not carried out on the complex parts to eliminate the influence of thermal stress. Summary of the Invention

[0009] In order to solve the technical problems existing in the process of preparing titanium-aluminum alloy by electron beam selective melting in the prior art, such as the unreleased thermal stress, large grain size in the microstructure of the alloy, uneven performance distribution, poor comprehensive mechanical properties of the prepared material, low high-temperature stability and low wear resistance; therefore, the embodiments of the present invention provide an additive manufacturing method for ultrafine-grained nano-lamellar titanium-aluminum alloy that can synergistically improve the comprehensive mechanical properties, high-temperature stability and wear resistance of titanium-aluminum alloy. The technical solutions are as follows:

[0010] An additive manufacturing ultrafine-grained nano-lamellar titanium-aluminum alloy, the chemical composition of the additive manufacturing ultrafine-grained nano-lamellar titanium-aluminum alloy is calculated by atomic percentage as follows: Al 43 - 46 at%, Nb 3 - 10 at%, Ta 2 - 8 at%, Mo 0.1 - 1.9 at%, B 0 - 0.75 at%, C 0 - 0.5 at%, the oxygen content is less than 600 ppm, and the balance is Ti and unavoidable impurity elements; the element contents of B and C cannot be 0.

[0011] Optionally, the phase composition of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is 85 - 92% γ phase + 6 - 15% α2 phase + 2 - 5% B2 phase.

[0012] Optionally, the shape of the lamellar clusters in the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is circular, with an average size of 3 - 5 μm; the internal structure of the lamellar clusters is a γ-α2 lamellar structure, and the width of the lamellar structure is 12 - 15 nm; the shape of the equiaxed grains around the lamellar clusters is circular, with an average size of 1 - 2 μm.

[0013] Optionally, the density of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is 3.9 - 4.3 g / cm 3 , the tensile strength is not less than 900 MPa, the yield strength is not less than 800 MPa, the elongation is not less than 1%, the tensile strength at 800 °C is not less than 700 MPa, the yield strength is not less than 600 MPa, and the elongation is not less than 3%.

[0014] A preparation method of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy based on the above, the preparation method of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy comprises the following steps:

[0015] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain the weighed raw materials;

[0016] S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace for melting. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, pour it into a mold to obtain a titanium aluminide alloy ingot;

[0017] S3. First hot isostatic pressing treatment: Perform the first hot isostatic pressing treatment on the titanium aluminide alloy ingot in S2 to obtain a dense titanium aluminide alloy ingot;

[0018] S4. Electrode preparation: Machine the dense titanium aluminide alloy ingot in S3 into an electrode required for a rotating electrode;

[0019] S5. Micron-sized powder preparation: Install the electrode in S4 into a rotating electrode atomization device, start powder making by the rotating electrode method to obtain micron-sized titanium aluminide alloy powder;

[0020] S6. Printing material: Start the EBM equipment, start powder spreading of the micron-sized titanium aluminide alloy powder in S5 and electron beam selective melting printing to obtain a printed TiAl alloy material;

[0021] S7, Second hot isostatic pressing treatment + three-stage heat treatment: The S6 printed TiAl alloy material is subjected to a second hot isostatic pressing treatment + three-stage heat treatment to obtain the final finished printed TiAl alloy material.

[0022] Optionally, the vacuum induction melting in S2 is carried out by heating to 1700 - 1900 °C under a vacuum degree of 10 -4 Pa, and after melting, the liquid alloy is quickly poured into a copper mold preheated to 400 - 600 °C to obtain a titanium aluminum alloy ingot.

[0023] Optionally, the process parameters of the hot isostatic pressing in S3 are that the temperature is controlled in the range of 1150 - 1280 °C, the pressure is 150 - 180 MPa, the time is 4 - 10 h, and then it is furnace-cooled to room temperature.

[0024] Optionally, what is the shape of the micron-sized titanium aluminum alloy powder in S5, and the particle size is 40 - 145 μm.

[0025] Optionally, during the electron beam selective melting printing in S6, the current of the electron beam is 4 - 20 mA, the scanning speed of the electron beam is 1 - 4 m / s, and the defocus value is 10 - 90 mA.

[0026] Optionally, the process parameters of the hot isostatic pressing in S7 are that the temperature is controlled in the range of 1150 - 1280 °C, the pressure is 150 - 180 MPa, the time is 4 - 10 h, and then it is furnace-cooled to room temperature, which can further eliminate residual stress and improve material densification; the three-stage heat treatment is that the first-stage heating and holding temperature is 900 - 1000 °C, and the time is 12 - 24 h, aiming to eliminate internal stress and stabilize the microstructure; the second-stage heating and holding temperature is 1240 - 1280 °C, and the time is 5 - 15 min for γ-phase phase transformation treatment; the third-stage heating and holding temperature is 750 - 850 °C, and the time is 6 - 8 h to refine the grains and obtain the final nano-sheet structure.

[0027] The above technical solution has at least the following beneficial effects compared with the prior art:

[0028] The above solution, the present invention provides an additive manufacturing ultrafine-grained nano-sheet titanium aluminum alloy and a preparation method, which can solve the technical problems existing in the process of preparing titanium aluminum alloy by electron beam selective melting in the prior art, such as unrelieved thermal stress, coarse grains in the microstructure of the alloy, uneven property distribution, poor comprehensive mechanical properties of the prepared material, low high-temperature stability and low wear resistance.

[0029] The present invention can produce an ultrafine-grained nano-sheet titanium aluminum alloy with high strength, high temperature resistance and excellent ductility by precisely controlling the element composition and preparation process parameters, and is particularly suitable for the manufacture of aerospace structural parts under extreme working conditions.

[0030] By combining additive manufacturing technology and heat treatment process, the present invention significantly improves the tissue uniformity of materials, and solves the problems of coarse grains and uneven properties that are difficult to avoid in traditional casting or forging processes.

[0031] The present invention removes the impurity contamination brought by raw materials through the combined process of secondary vacuum consumable melting + arc skull melting in vacuum induction melting, so that the impurity content in the obtained titanium-aluminum alloy ingot is reduced to the lowest level. After that, through hot isostatic pressing treatment and rotating electrode powder making, the powder used for electron beam selective melting is made to reach the micron level. The organizational structure of the finished product prepared by electron beam selective melting subsequently is itself fine and evenly distributed.

[0032] By performing a second hot isostatic pressing treatment + three-stage heat treatment on the finished product prepared by electron beam selective melting, the present invention can not only eliminate internal stress and improve material density in the finished product, but also stabilize the microstructure and refine grains, and finally obtain an ultrafine-grained nanolaminate structure.

[0033] The density of the additive manufacturing ultrafine-grained nanolaminate titanium-aluminum alloy prepared by the present invention is 3.9 - 4.3 g / cm 3 , the tensile strength is not less than 900 MPa, the yield strength is not less than 800 MPa, the elongation is not less than 1%, the tensile strength at 800 °C is not less than 700 MPa, the yield strength is not less than 600 MPa, and the elongation is not less than 3%.

[0034] In summary, compared with other traditional methods, the method of the present invention creatively prepares ultrafine-grained nanolaminate titanium-aluminum alloy through the combined process of secondary vacuum consumable melting + arc skull melting, hot isostatic pressing treatment and rotating electrode powder making, electron beam selective melting and second hot isostatic pressing treatment + three-stage heat treatment; this method has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and high comprehensive performance of the prepared titanium-aluminum alloy, which is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the TEM image of the lamella of the additive manufacturing ultrafine-grained nanolaminate titanium-aluminum alloy in Embodiment 1 of the present invention;

[0037] Figure 2 It is the statistical result diagram of the equivalent grain diameter of the additive manufacturing ultrafine-grained nanolaminate titanium-aluminum alloy in Embodiment 2 of the present invention;

[0038] Figure 3 It is the room temperature tensile curve of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy of Embodiment 3 of the present invention. Specific Embodiments

[0039] The technical solutions in the present invention will be described below with reference to the accompanying drawings.

[0040] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as an "example" in the present invention should not be construed as being more preferred or more advantageous than other embodiments or design solutions. Rather, the use of the word "example" is intended to present concepts in a specific manner. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one of the two.

[0041] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the meanings they express are the same. "Of", "corresponding" and "correspondent" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the meanings they express are the same.

[0042] In the embodiments of the present invention, sometimes subscripts such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meanings they express are the same.

[0043] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] An additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy, the chemical composition of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is calculated by atomic percentage as follows: Al 43 - 46 at%, Nb 3 - 10 at%, Ta 2 - 8 at%, Mo 0.1 - 1.9 at%, B 0 - 0.75 at%, C 0 - 0.5 at%, the oxygen content is less than 600 ppm, and the balance is Ti and unavoidable impurity elements; the element contents of B and C cannot be 0.

[0045] Specifically, the phase composition in the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is 85 - 92% γ phase + 6 - 15% α2 phase + 2 - 5% B2 phase.

[0046] Specifically, the shape of the lamellar clusters in the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy is circular, and the average size is 3 - 5 μm; the internal of the lamellar clusters is a γ-α2 lamellar structure, and the width of the lamellar structure is 12 - 15 nm; the shape of the equiaxed grains around the lamellar clusters is circular, and the average size is 1 - 2 μm.

[0047] Specifically, the density of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy is 3.9 - 4.3 g / cm 3 , the tensile strength is not less than 900 MPa, the yield strength is not less than 800 MPa, the elongation is not less than 1%, the tensile strength at 800 °C is not less than 700 MPa, the yield strength is not less than 600 MPa, and the elongation is not less than 3%.

[0048] A preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy based on the above, the preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy comprises the following steps:

[0049] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain the weighed raw materials;

[0050] S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace for melting. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, pour it into a mold to obtain a titanium aluminide alloy ingot;

[0051] S3. First hot isostatic pressing treatment: Carry out the first hot isostatic pressing treatment on the titanium aluminide alloy ingot in S2 to obtain a dense titanium aluminide alloy ingot;

[0052] S4. Electrode preparation: Machine the dense titanium aluminide alloy ingot in S3 to prepare an electrode required for a rotating electrode;

[0053] S5. Micron-sized powder preparation: Install the electrode in S4 on a rotating electrode atomization device, start powder making by the rotating electrode method to obtain micron-sized titanium aluminide alloy powder;

[0054] S6. Printing material: Start the EBM equipment, start powder spreading of the micron-sized titanium aluminide alloy powder in S5 and electron beam selective melting printing to obtain a printed TiAl alloy material;

[0055] S7. Second hot isostatic pressing treatment + three-stage heat treatment: Carry out the second hot isostatic pressing treatment + three-stage heat treatment on the printed TiAl alloy material in S6 to obtain the final finished printed TiAl alloy material.

[0056] Specifically, the vacuum induction melting in S2 is carried out at a vacuum degree of 10 -4 Pa and heated to 1700 - 1900 °C for melting. After melting, quickly pour the liquid alloy into a copper mold preheated to 400 - 600 °C to obtain a titanium aluminide alloy ingot.

[0057] Specifically, the hot isostatic pressing process parameters for S3 are that the temperature is controlled within the range of 1150 - 1280 °C, the pressure is 150 - 180 MPa, the time is 4 - 10 h, and then it is furnace-cooled to room temperature.

[0058] Specifically, what is the shape of the micron-sized titanium-aluminum alloy powder for S5, and the particle size is 40 - 145 μm.

[0059] Specifically, during the electron beam selective melting printing process of S6, the current of the electron beam is 4 - 20 mA, the scanning speed of the electron beam is 1 - 4 m / s, and the defocus value is 10 - 90 mA.

[0060] Specifically, the hot isostatic pressing process parameters for S7 are that the temperature is controlled within the range of 1150 - 1280 °C, the pressure is 150 - 180 MPa, the time is 4 - 10 h, and then it is furnace-cooled to room temperature, which can further eliminate residual stress and improve material densification; the three-stage heat treatment is that the first-stage heating and holding temperature is 900 - 1000 °C, the time is 12 - 24 h, and the purpose is to eliminate internal stress and stabilize the microstructure; the second-stage heating and holding temperature is 1240 - 1280 °C, the time is 5 - 15 min, for the phase transformation treatment of γ phase; the third-stage heating and holding temperature is 750 - 850 °C, the time is 6 - 8 h, for refining grains to obtain the final nano-sheet structure.

[0061] Example 1

[0062] An additive manufacturing ultra-fine grain nano-sheet titanium-aluminum alloy, the chemical composition of the additive manufacturing ultra-fine grain nano-sheet titanium-aluminum alloy is calculated by atomic percentage as follows: Al 43.5 at%, Nb 4 at%, Ta 6 at%, Mo 0.5 at%, B 0.2 at%, C 0.2 at%, the oxygen content is 350 ppm, and the balance is Ti and inevitable impurity elements.

[0063] A preparation method of the additive manufacturing ultra-fine grain nano-sheet titanium-aluminum alloy based on the above, the preparation method of the additive manufacturing ultra-fine grain nano-sheet titanium-aluminum alloy comprises the following steps:

[0064] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and blending according to the chemical composition ratio. The weighing is carried out using a high-precision electronic balance, and the weighing error is controlled within 0.001 g, and the oxygen content needs to be strictly controlled to avoid exceeding the standard, obtaining the weighed raw materials;

[0065] S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace at 10 -4It is heated to 1800 °C for melting under a vacuum of Pa. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, it is poured into a copper mold preheated to 600 °C to obtain a titanium aluminum alloy ingot;

[0066] S3. First hot isostatic pressing treatment: The titanium aluminum alloy ingot of S2 is subjected to the first hot isostatic pressing treatment. The equipment is a hot isostatic pressing furnace, the temperature is controlled at 1200 °C, the pressure is 150 MPa, and the time is 4 h; This process is carried out under a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, the hot isostatic pressing treatment is stopped, and the furnace is cooled to room temperature to obtain a dense titanium aluminum alloy ingot;

[0067] S4. Electrode preparation: The dense titanium aluminum alloy ingot of S3 is machined into an electrode shape by a precision CNC machine tool to prepare the electrode required for the rotating electrode; Among them, a numerical control milling machine is used for the machining equipment to ensure accurate electrode dimensions and meet the requirements for subsequent powder making;

[0068] S5. Micron-sized powder preparation: The electrode of S4 is installed in a rotating electrode atomization device. Under an argon protection environment, the electrode is melted by an arc, and the high-speed rotating electrode throws out droplets to obtain micron-sized titanium aluminum alloy powder; The powder collection device obtains TiAl alloy powder for electron beam selective melting (EBM) with a particle size distribution range of 40 - 145 μm through classification and screening;

[0069] S6. Printing material: Start the EBM equipment and start powder spreading of the micron-sized titanium aluminum alloy powder of S5 and electron beam selective melting printing. The current of the electron beam is 4.5 mA, and the scanning speed of the electron beam is 2 m / s; The scanning path is a selective filling strategy to ensure full melting of the material and reduce residual stress; The defocus value is 30 mA. By melting the powder layer by layer and gradually stacking, the printed TiAl alloy material is obtained; During the printing process, the temperature field and deformation conditions need to be monitored in real time to ensure that the finished product has no defects;

[0070] S7. Second hot isostatic pressing treatment + three-stage heat treatment: The printed TiAl alloy material of S6 is subjected to the second hot isostatic pressing treatment + three-stage heat treatment; The equipment for the second hot isostatic pressing treatment is a hot isostatic pressing furnace, the temperature is controlled at 1200 °C, the pressure is 150 MPa, and the time is 4 h; This process is carried out under a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, the hot isostatic pressing treatment is stopped, and the furnace is cooled to room temperature; The three-stage heat treatment is that the heating and holding temperature in the first stage is 900 °C and the time is 24 h, the heating and holding temperature in the second stage is 1240 °C and the time is 5 min, and the heating and holding temperature in the third stage is 750 °C and the time is 6 h; The final finished printed TiAl alloy material is obtained.

[0071] The phase composition of the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 89% γ phase + 9% α2 phase + 2% B2 phase.

[0072] The average equivalent diameter of the ultrafine grains in the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 1.8 μm. The nanolamellar width is 12 nm. As Figure 1 shown, the second-phase particles are fine borides and carbides with an equivalent diameter of 80 nm.

[0073] The density of the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 3.9 g / cm 3 , the tensile strength is 932 MPa, the yield strength is 847 MPa, the elongation is 1.5%, the tensile strength at 800 °C is 791 MPa, the yield strength is 680 MPa, and the elongation is 8%

[0074] Example 2

[0075] An additively manufactured ultrafine-grained nanolamellar titanium aluminide, the chemical composition of the additively manufactured ultrafine-grained nanolamellar titanium aluminide is calculated by atomic percentage as follows: Al 43 at%, Nb 5 at%, Ta 5 at%, Mo 0.3 at%, B 0.15 at%, C 0.15 at%, the oxygen content is less than 600 ppm, and the balance is Ti and unavoidable impurity elements.

[0076] A preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide based on the above, the preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide is as follows:

[0077] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition ratio. The weighing is carried out using a high-precision electronic balance, and the weighing error is controlled within 0.001 g. Moreover, the oxygen content needs to be strictly controlled to avoid exceeding the standard, and the weighed raw materials are obtained;

[0078] S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace and heat them to 1900 °C for melting under a vacuum degree of 10 -4 Pa. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, pour it into a copper mold preheated to 600 °C to obtain a titanium aluminide ingot;

[0079] S3. First hot isostatic pressing treatment: The S2 TiAl alloy ingot is subjected to the first hot isostatic pressing treatment. The equipment is a hot isostatic pressing furnace, with the temperature controlled at 1200 °C, the pressure at 160 MPa, and the time at 6 h. This process is carried out under a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, the hot isostatic pressing treatment is stopped, and the furnace is cooled to room temperature to obtain a dense TiAl alloy ingot.

[0080] S4. Electrode preparation: The S3 dense TiAl alloy ingot is machined into an electrode shape by a precision CNC machine tool to prepare the electrode required for the rotating electrode. Among them, a numerical control milling machine is used as the machining equipment to ensure the accurate electrode size and meet the subsequent powder preparation requirements.

[0081] S5. Micron-sized powder preparation: The electrode of S4 is installed in a rotating electrode atomization device. Under an argon protection environment, the electrode is melted by an electric arc, and the high-speed rotating electrode throws out the droplets to obtain micron-sized TiAl alloy powder. The powder collection device obtains TiAl alloy powder with a particle size distribution range of 50 - 140 μm for electron beam selective melting (EBM) through classification and screening.

[0082] S6. Printing material: Start the EBM equipment and begin to feed the S5 micron-sized TiAl alloy powder and carry out electron beam selective melting printing. The current of the electron beam is 6 mA, and the scanning speed of the electron beam is 3 m / s. The scanning path is a selective filling strategy to ensure the full melting of the material and reduce the residual stress. The defocus value is 40 mA. By melting the powder layer by layer and gradually stacking, the printed TiAl alloy material is obtained. During the printing process, the temperature field and deformation conditions need to be monitored in real time to ensure that the finished product has no defects.

[0083] S7. Second hot isostatic pressing treatment + three-stage heat treatment: The S6 printed TiAl alloy material is subjected to the second hot isostatic pressing treatment + three-stage heat treatment. The equipment for the second hot isostatic pressing treatment is a hot isostatic pressing furnace, with the temperature controlled at 1200 °C, the pressure at 160 MPa, and the time at 6 h. This process is carried out under a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, the hot isostatic pressing treatment is stopped, and the furnace is cooled to room temperature. The three-stage heat treatment is that the first-stage heating and holding temperature is 950 °C for 24 h, the second-stage heating and holding temperature is 1260 °C for 10 min, and the third-stage heating and holding temperature is 800 °C for 6 h. The final finished printed TiAl alloy material is obtained.

[0084] In the additively manufactured ultrafine-grained nanolamellar TiAl alloy prepared in this example, the phase composition is 91% γ phase + 6% α2 phase + 3% B2 phase.

[0085] In the additively manufactured ultrafine-grained nanolamellar TiAl alloy prepared in this example, the average equivalent diameter of the ultrafine grains is 1.6 μm, asFigure 2 As shown. The width of the nanosheet layer is 10 nm, and the second-phase particles are fine borides and carbides with an equivalent diameter of less than 90 nm.

[0086] The density of the additively manufactured ultrafine-grained nanosheet titanium aluminide prepared in this example is 4.0 g / cm 3 , the tensile strength is 962 MPa, the yield strength is 899 MPa, the elongation is 1.3%, the tensile strength at 800 °C is 803 MPa, the yield strength is 746 MPa, and the elongation is 7%.

[0087] Example 3

[0088] An additively manufactured ultrafine-grained nanosheet titanium aluminide, the chemical composition of the additively manufactured ultrafine-grained nanosheet titanium aluminide is as follows by atomic percentage: Al 46 at%, Nb 6 at%, Ta 4 at%, Mo 0.6 at%, B 0.05 at%, C 0.25 at%, the oxygen content is less than 300 ppm, and the balance is Ti and unavoidable impurity elements.

[0089] A preparation method of the additively manufactured ultrafine-grained nanosheet titanium aluminide based on the above, the preparation method of the additively manufactured ultrafine-grained nanosheet titanium aluminide is as follows:

[0090] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and mixing according to the chemical composition ratio. Weighing is carried out using a high-precision electronic balance, and the weighing error is controlled within 0.001 g, and the oxygen content needs to be strictly controlled to avoid exceeding the standard, obtaining the weighed raw materials;

[0091] S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace and heat them to 2000 °C for melting under a vacuum degree of 10 -4 Pa. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, pour it into a copper mold preheated to 600 °C to obtain a titanium aluminide ingot;

[0092] S3. The first hot isostatic pressing treatment: Carry out the first hot isostatic pressing treatment on the titanium aluminide ingot in S2. The equipment is a hot isostatic pressing furnace, the temperature is controlled at 1280 °C, the pressure is 170 MPa, and the time is 6 h; This process is carried out under a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, stop the hot isostatic pressing treatment, and cool the furnace to room temperature to obtain a dense titanium aluminide ingot;

[0093] S4. Electrode Preparation: The dense titanium aluminide ingot from S3 is machined into the shape of an electrode by a precision CNC machine tool to prepare the electrode required for the rotating electrode; among them, a CNC milling machine is used as the machining equipment to ensure the precise dimensions of the electrode, meeting the requirements for subsequent powder production;

[0094] S5. Micron-scale Powder Preparation: The electrode from S4 is installed in a rotating electrode atomization device, and the electrode is melted by an arc in an argon protection environment. The electrode rotates at high speed to throw out droplets, obtaining micron-scale titanium aluminide powder; the powder collection device obtains TiAl alloy powder with a particle size distribution range of 40 - 145 μm for electron beam selective melting (EBM) through classification and screening;

[0095] S6. Printing Material: Start the EBM equipment and begin to feed the micron-scale titanium aluminide powder from S5 and perform electron beam selective melting printing. The current of the electron beam is 7 mA, and the scanning speed of the electron beam is 4.5 m / s; the scanning path is a selective filling strategy to ensure sufficient melting of the material and reduce residual stress; the defocus value is 30 mA. By melting the powder layer by layer and gradually stacking, the printed TiAl alloy material is obtained; during the printing process, the temperature field and deformation conditions need to be monitored in real time to ensure that the finished product has no defects;

[0096] S7. Second Hot Isostatic Pressing + Three-stage Heat Treatment: The printed TiAl alloy material from S6 is subjected to second hot isostatic pressing + three-stage heat treatment; the equipment for the second hot isostatic pressing is a hot isostatic press furnace, with the temperature controlled at 1280 °C, the pressure at 170 MPa, and the time at 6 h; this process is carried out in a vacuum or argon protection environment. After the internal shrinkage cavities and microcracks of the material are completely closed, the hot isostatic pressing is stopped, and the furnace is cooled to room temperature; the three-stage heat treatment is that the first-stage heating and holding temperature is 900 °C, the time is 24 h, the second-stage heating and holding temperature is 1270 °C, the time is 10 min, and the third-stage heating and holding temperature is 800 °C, the time is 7 h; the final finished printed TiAl alloy material is obtained.

[0097] The phase composition of the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 85 - 92% γ phase + 6 - 15% α2 phase + 2 - 5% B2 phase.

[0098] The average equivalent diameter of the ultrafine grains in the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 2 μm, as Figure 3 shown. The nanolamellar width is 14 nm, and the second-phase particles are fine borides and carbides with an equivalent diameter less than 90 nm.

[0099] The density of the additively manufactured ultrafine-grained nanolamellar titanium aluminide prepared in this example is 4.3 g / cm 3, the tensile strength is 928 MPa, the yield strength is 804 MPa, the elongation is 1.1%, the tensile strength at 800 °C is 761 MPa, the yield strength is 635 MPa, and the elongation is not less than 6%.

[0100] For the above solution, the present invention provides an additive manufacturing ultrafine-grained nanolamellar titanium aluminide alloy and a preparation method thereof, which can solve the technical problems existing in the process of preparing titanium aluminide alloy by electron beam selective melting in the prior art, such as the unreleased thermal stress, the coarse grains in the microstructure of the alloy, the uneven performance distribution, the poor comprehensive mechanical properties of the prepared material, the low high-temperature stability and wear resistance.

[0101] By precisely controlling the element composition and preparation process parameters, the present invention can produce an ultrafine-grained nanolamellar titanium aluminide alloy with high strength, high temperature resistance and excellent ductility, which is particularly suitable for manufacturing aerospace structural parts under extreme working conditions.

[0102] By combining the additive manufacturing technology and the heat treatment process, the present invention significantly improves the tissue uniformity of the material and solves the problems of coarse grains and uneven performance that are difficult to avoid in traditional casting or forging processes.

[0103] The present invention removes the impurity contamination brought by the raw materials through the combined process of secondary vacuum consumable melting + arc skull melting in vacuum induction melting, so that the impurity content in the obtained titanium aluminide alloy ingot is reduced to the lowest level. Then, through hot isostatic pressing treatment and rotating electrode powder making, the powder used for electron beam selective melting is made to reach the micron level. The microstructure of the finished product prepared by subsequent electron beam selective melting is itself fine and evenly distributed.

[0104] By performing a second hot isostatic pressing treatment + three-stage heat treatment on the finished product prepared by electron beam selective melting, the present invention can not only eliminate internal stress and improve the material density, but also stabilize the microstructure and refine the grains in the finished product, and finally obtain an ultrafine-grained nanolamellar structure.

[0105] The density of the additive manufacturing ultrafine-grained nanolamellar titanium aluminide alloy prepared by the present invention is 3.9 - 4.3 g / cm 3 , the tensile strength is not less than 900 MPa, the yield strength is not less than 800 MPa, the elongation is not less than 1%, the tensile strength at 800 °C is not less than 700 MPa, the yield strength is not less than 600 MPa, and the elongation is not less than 3%.

[0106] In summary, compared with other traditional methods, the method of the present invention creatively prepares ultrafine-grained nanosheet titanium aluminide through a combined process of secondary vacuum consumable melting + arc skull melting, hot isostatic pressing treatment and rotary electrode powder making, electron beam selective melting and second hot isostatic pressing treatment + three-stage heat treatment; this method has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and high comprehensive performance of the prepared titanium aluminide, which is conducive to large-scale industrial production and popularization.

[0107] It should be understood that the term "and / or" in this article is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural. In addition, the character " / " in this article generally represents an "or" relationship between the preceding and following associated objects, but it may also represent an "and / or" relationship, which can be specifically understood with reference to the context before and after.

[0108] In the present invention, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or similar expressions thereof refer to any combination of these items, including any combination of single item (s) or plural item (s). For example, at least one (item) of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0109] It should be understood that in various embodiments of the present invention, the magnitude of the sequence numbers of the above processes does not mean the sequence of execution. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0110] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. An additive manufacturing ultrafine-grained nanolamellar titanium aluminide alloy, characterized in that, The chemical composition of the additive manufactured ultrafine-grained nanolamellar titanium aluminide alloy is as follows in atomic percentage: Al 43-46 at%, Nb 3-10 at%, Ta 2-8 at%, Mo 0.1-1.9 at%, B 0-0.75 at%, C 0-0.5 at%, the oxygen content is less than 600 ppm, and the balance is Ti and unavoidable impurity elements; the element contents of B and C cannot be 0.

2. The additive manufactured ultrafine-grained nano-lamellar titanium aluminide alloy according to claim 1, characterized in that, The phase composition in the additive manufactured ultrafine-grained nanolamellar titanium aluminide alloy is 85-92% γ phase + 6-15% α2 phase + 2-5% B2 phase.

3. The additive manufacturing ultrafine-grained nanolamellar titanium aluminide alloy according to claim 1, characterized in that, The shape of the lamellar clusters in the additive manufactured ultrafine-grained nanolamellar titanium aluminide alloy is circular, and the average size is 3-5 μm; the inside of the lamellar clusters is a γ-α2 lamellar structure, and the width of the lamellar structure is 12-15 nm; the shape of the equiaxed grains around the lamellar clusters is circular, and the average size is 1-2 μm.

4. The additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy according to claim 1, wherein, The density of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy is 3.9 - 4.3 g / cm 3 , the tensile strength is not less than 900 MPa, the yield strength is not less than 800 MPa, the elongation is not less than 1%, the tensile strength at 800 °C is not less than 700 MPa, the yield strength is not less than 600 MPa, and the elongation is not less than 3%.

5. A preparation method of an additive manufactured ultrafine-grained nanosheet titanium aluminide alloy according to claim 1, characterized in that, The preparation method of the additive manufactured ultrafine-grained nanolamellar titanium aluminide alloy is as follows: S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain the weighed raw materials. S2. Vacuum induction melting and casting: Put the raw materials weighed in S1 into a vacuum induction melting furnace for melting. The melting adopts a combined process of secondary vacuum consumable melting + arc skull melting. After melting, pour it into a mold to obtain a titanium aluminide alloy ingot. S3. First hot isostatic pressing treatment: Carry out the first hot isostatic pressing treatment on the titanium aluminide alloy ingot in S2 to obtain a dense titanium aluminide alloy ingot. S4. Electrode preparation: Machine the dense titanium aluminide alloy ingot in S3 into an electrode required for a rotating electrode. S5. Micron-sized powder preparation: Install the electrode in S4 into a rotating electrode atomization device, start the rotating electrode powder making method to obtain micron-sized titanium aluminide alloy powder. S6. Printing material: Start the EBM equipment, start powder spreading of the micron-sized titanium aluminide alloy powder in S5 and electron beam selective melting printing to obtain a printed TiAl alloy material. S7. Second hot isostatic pressing treatment + three-stage heat treatment: Carry out the second hot isostatic pressing treatment + three-stage heat treatment on the printed TiAl alloy material in S6 to obtain the final finished printed TiAl alloy material.

6. The preparation method of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy according to claim 5, characterized in that, The vacuum induction melting of S2 is carried out by heating to 1700 - 1900 °C under a vacuum degree of 10 -4 Pa for melting, and after melting, the liquid alloy is quickly poured into a copper mold preheated to 400 - 600 °C to obtain a titanium-aluminum alloy ingot.

7. The preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy according to claim 5, characterized in that, The hot isostatic pressing process parameters in S3 are that the temperature is controlled in the range of 1150-1280 °C, the pressure is 150-180 MPa, the time is 4-10 h, and then furnace cool to room temperature.

8. The preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminum alloy according to claim 5, characterized in that, What is the shape of the micron-sized titanium aluminide alloy powder in S5, and the particle size is 40-145 μm.

9. The preparation method of the additively manufactured ultrafine-grained nano-laminated titanium aluminide alloy according to claim 5, wherein During the electron beam selective melting printing in S6, the current of the electron beam is 4-20 mA, the scanning speed of the electron beam is 1-4 m / s, and the defocus value is 10-90 mA.

10. The preparation method of the additively manufactured ultrafine-grained nanolamellar titanium aluminide alloy according to claim 5, wherein The hot isostatic pressing process parameters of S7 are that the temperature is controlled within the range of 1150 - 1280 °C, the pressure is 150 - 180 MPa, the time is 4 - 10 h, and then it is furnace-cooled to room temperature; the three-stage heat treatment is that the heating and holding temperature in the first stage is 900 - 1000 °C, the time is 12 - 24 h, the heating and holding temperature in the second stage is 1240 - 1280 °C, the time is 5 - 15 min, and the heating and holding temperature in the third stage is 750 - 850 °C, the time is 6 - 8 h.

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