Electron beam selective melting additive manufacturing method for directionally solidified titanium-aluminum alloy

Abstract

The invention relates to an electron beam selective melting additive manufacturing method for directionally solidified titanium-aluminum alloy, which is realized through a negative pressure vacuum device, the negative pressure vacuum device comprises a forming cabin and a heat preservation and pressure maintaining cover, the heat preservation and pressure maintaining cover is located in the forming cabin, and a powder bed and a forming substrate are arranged in the heat preservation and pressure maintaining cover; the electron beam selective melting additive manufacturing method of the directionally solidified titanium-aluminum alloy comprises the following steps: heating the forming substrate to 600-700 DEG C, and keeping the temperature for 20 minutes; the negative pressure vacuum device is started, gas washing is carried out on the forming cabin, and the negative pressure in the heat and pressure preservation cover forms dynamic balance; and titanium-aluminum alloy powder is laid on the powder bed, and the titanium-aluminum alloy is directionally solidified through an electron beam selective melting additive manufacturing method. According to the method, electron beam selective melting additive manufacturing of the directionally solidified titanium-aluminum alloy can be achieved.

Description

Technical Field

[0001] The present application relates to the technical field of metal materials, and in particular to an electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy. Background Art

[0002] The density of γ-titanium aluminum is only half of that of high-temperature alloys. It has replaced high-temperature alloys on the low-pressure turbine blades of GE and Pratt & Whitney civil engines, achieving significant weight reduction. However, the current γ-titanium aluminum is a polycrystalline structure with a limited service temperature (<700°C), which limits its application range. Similar to high-temperature alloys, the creep resistance of γ-titanium aluminum also increases in the order of polycrystalline → columnar polycrystalline → single crystal. Therefore, it is urgent to explore the method of directional solidification of titanium aluminum alloys, prepare titanium aluminum alloys with directional solidification characteristics, improve the creep resistance of materials, and realize the wider application of lightweight high-temperature titanium aluminum alloys in engines. The method of electron beam selective melting additive manufacturing is a main method for the development of titanium aluminum alloys, but in order to ensure the smooth formation, a higher forming temperature is required, so the high temperature gradient required for directional solidification cannot be achieved. Therefore, there is currently no relevant technology for the development of directional solidification titanium aluminum alloys using electron beam selective melting additive manufacturing. Summary of the invention

[0003] (1) Technical issues to be solved

[0004] The present application provides an electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy, which solves the problem that there is currently no electron beam selective melting additive manufacturing method for developing directionally solidified titanium aluminum alloy.

[0005] (2) Technical solution

[0006] In a first aspect, the present application provides an electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy, which is implemented by a negative pressure vacuum device, wherein the negative pressure vacuum device comprises a forming chamber and a heat preservation and pressure hood, wherein the heat preservation and pressure hood is located in the forming chamber, and a powder bed and a forming substrate are arranged in the heat preservation and pressure hood;

[0007] The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy comprises:

[0008] The formed substrate is heated to 600-700° C. and kept at this temperature for 20 minutes;

[0009] Starting the negative pressure vacuum device to wash the forming chamber, so that the negative pressure in the heat-insulating and pressure-insulating cover forms a dynamic balance;

[0010] Titanium-aluminum alloy powder is placed on the powder bed, and the titanium-aluminum alloy is directionally solidified by an electron beam selective melting additive manufacturing method.

[0011] Further, the forming substrate is heated to 600-700° C. and kept warm for 20 minutes, comprising:

[0012] The forming substrate is heated to 600° C. and kept at this temperature for 20 minutes, and the forming environment is maintained at 600° C. for forming.

[0013] Furthermore, the negative pressure vacuum device is started to wash the forming chamber so that the negative pressure in the heat preservation and pressure preservation cover forms a dynamic balance, including:

[0014] The negative pressure vacuum device is started to purge the forming chamber so that the vacuum pressure difference between the forming chamber and the heat-insulating and pressure-maintaining cover reaches 25 mbar, so as to form a stable negative pressure on the surface of the titanium-aluminum alloy powder.

[0015] Furthermore, the step of laying titanium-aluminum alloy powder on the powder bed and directionally solidifying the titanium-aluminum alloy by electron beam selective melting additive manufacturing method comprises:

[0016] Laying a layer of titanium aluminum alloy powder on the powder bed, and forming it by electron beam selective melting after the laying is completed;

[0017] After melting is completed, there is no need for energy compensation and titanium-aluminum alloy powder can continue to be laid to form the next layer.

[0018] Furthermore, the titanium-aluminum alloy powder is Ti-48Al-2Cr-2Nb titanium-aluminum alloy powder.

[0019] Furthermore, the process parameters of the electron beam selective melting additive manufacturing method are: electron beam current is 10-20 mA, acceleration voltage is 60 kV, scanning rate is 1000-1600 mm / s, focusing current is 650-700 mA, and single layer thickness of titanium aluminum alloy powder is 0.07 mm.

[0020] Furthermore, the process parameters of the electron beam selective melting additive manufacturing method are as follows: electron beam current is 20 mA, acceleration voltage is 60 kV, scanning rate is 1300 mm / s, focusing current is 680 mA, and single layer thickness of titanium aluminum alloy powder is 0.07 mm.

[0021] In a second aspect, the present application provides a negative pressure vacuum device for implementing the electron beam selective melting additive manufacturing method of the directionally solidified titanium aluminum alloy as described above;

[0022] The negative pressure vacuum device comprises:

[0023] Forming cabin;

[0024] A heat-insulating and pressure-maintaining cover, which is located in the forming chamber and is used to serve as a relatively closed space to maintain local temperature and local negative pressure during the forming process; a powder bed and a forming substrate are arranged in the heat-insulating and pressure-maintaining cover;

[0025] A helium inlet, located at the upper end of the side wall of the forming chamber, for continuously introducing helium during the forming process;

[0026] A vacuum exhaust channel, the vacuum exhaust channel being located at the bottom of the side wall of the heat-insulating and pressure-insulating cover;

[0027] A vacuum pump group is used to extract the gas in the forming chamber through the vacuum exhaust channel.

[0028] Furthermore, the negative pressure vacuum device also includes:

[0029] A powder spreading mechanism, the powder spreading mechanism is used to spread titanium aluminum alloy powder on the powder bed;

[0030] A forming chamber vacuum gauge, the forming chamber vacuum gauge is used to detect the vacuum degree inside the forming chamber;

[0031] An electron beam generator, wherein the electron beam generator is used for electron beam selective melting additive manufacturing;

[0032] An internal air extraction channel of the cabin, the internal air extraction channel of the cabin being used to connect the vacuum air extraction channel and the vacuum pump group;

[0033] A pipeline vacuum gauge is used to monitor the vacuum degree in the heat-insulating and pressure-maintaining cover and the vacuum exhaust channel.

[0034] Furthermore, the vacuum pump group includes a low vacuum valve, a high vacuum valve, a diffusion pump, a preheating valve, a maintenance pump, a high-low switching valve, a Roots pump, and a mechanical pump.

[0035] (3) Beneficial effects

[0036] The above technical solution of the present application has the following advantages:

[0037] The electron beam selective melting additive manufacturing method for directionally solidified titanium-aluminum alloy provided in the first aspect of the present application forms a higher temperature gradient in the forming process through low-temperature preheating and high-energy input melting, thereby realizing the development of titanium-aluminum alloy materials with directional solidification characteristics. The negative pressure formed on the surface of the powder bed is used to solve the problem of "powder blowing" in a low-temperature preheating environment that causes the forming to be impossible, thereby ensuring smooth forming and realizing the development of titanium-aluminum alloy materials with directional solidification characteristics.

[0038] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 A flow chart of the electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy provided in the present application;

[0041] Figure 2 This is a schematic diagram of the structure of the negative pressure vacuum device provided in this application. DETAILED DESCRIPTION

[0042] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0043] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0044] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0045] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways. "Multiple" means "two or more".

[0046] At present, the commonly used methods for directional solidification of titanium-aluminum-based alloys can be divided into the Bridgman method and the optical floating zone method. The main differences between them are the heating source and the need for a crucible.

[0047] In the Bridgman method, the masterbatch of the alloy is melted and solidified in a ceramic tube. Due to the high chemical activity of titanium-aluminum alloy, it will react with most of the ceramic tubes commonly used at this stage, which will cause the final oriented titanium-aluminum alloy matrix to contain more ceramic particles, which is not conducive to the mechanical properties of the alloy. The optical floating zone method uses a spherical mirror to focus the light source to heat the experimental sample. The melting area is small, and the local zone melting temperature can reach 2200°C, while the temperature fluctuation range is about 5 to 10°C.

[0048] The optical floating zone method has the advantages of high heating temperature and no need for ceramic mold shells, but it has extremely high requirements for the stability of the molten zone, and it is extremely difficult to produce it stably and in batches. Therefore, it is necessary to study new preparation methods to develop directionally solidified titanium-aluminum-based alloy materials with uniform organizational composition, alloy cleanliness and high yield. The electron beam selective melting additive manufacturing method can realize the forming of titanium-aluminum alloys, but the "powder blowing" threshold of titanium-aluminum alloys is low, so a higher preheating temperature (greater than 1000°C) is required to make the forming go smoothly.

[0049] The formation of titanium-aluminum alloy with directional solidification structure requires a large temperature gradient, so the forming preheating temperature needs to be significantly reduced (not higher than 700°C). In a low preheating temperature environment, the titanium-aluminum alloy forming process is very likely to be unable to form due to "powder blowing". Therefore, it is necessary to prevent "powder blowing" during forming by improving the process and forming equipment to ensure smooth forming.

[0050] In response to the above problems, the present application proposes an electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy, which increases the temperature gradient in the forming process through low-temperature preheating, and designs a negative pressure vacuum device to solve the "powder blowing" problem in the forming process caused by low preheating temperature and reduced conductivity, thereby realizing the preparation of titanium aluminum alloy with a directionally grown columnar crystal structure.

[0051] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0052] The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy provided in this embodiment is realized by a negative pressure vacuum device, which includes a forming chamber and a thermal insulation and pressure maintaining cover. The thermal insulation and pressure maintaining cover is located in the forming chamber, and a powder bed and a forming substrate are provided in the thermal insulation and pressure maintaining cover.

[0053] Since titanium-aluminum alloy cannot be formed when the ambient temperature is lower than 1000°C, the negative pressure vacuum device is used to form a stable negative pressure on the surface of the titanium-aluminum alloy powder to prevent "powder blowing" caused by low ambient temperature, which leads to forming failure.

[0054] like Figure 1 As shown, the electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy includes: heating the forming substrate to 600-700°C and keeping it warm for 20 minutes; starting the negative pressure vacuum device to wash the forming chamber so that the negative pressure in the heat-insulating and pressure-maintaining cover forms a dynamic balance; laying titanium aluminum alloy powder on the powder bed, and using the electron beam selective melting additive manufacturing method to directionally solidify the titanium aluminum alloy.

[0055] In some embodiments, the step of heating the forming substrate to 600-700° C. and keeping the temperature for 20 minutes includes: heating the forming substrate to 600° C. and keeping the temperature for 20 minutes, and maintaining the forming environment at 600° C. for forming.

[0056] In some embodiments, the negative pressure vacuum device is started to purge the forming chamber so that the negative pressure in the thermal insulation and pressure cover forms a dynamic balance, including: starting the negative pressure vacuum device to purge the forming chamber so that the vacuum pressure difference between the forming chamber and the thermal insulation and pressure cover reaches 25 mbar, so as to form a stable negative pressure on the surface of the titanium aluminum alloy powder.

[0057] In some embodiments, the titanium-aluminum alloy powder is laid on the powder bed and the titanium-aluminum alloy is directionally solidified by electron beam selective melting additive manufacturing method, including: laying a layer of titanium-aluminum alloy powder on the powder bed, and forming it by electron beam selective melting after laying; after melting is completed, no energy compensation is required, and the titanium-aluminum alloy powder continues to be laid to form the next layer.

[0058] In some embodiments, the titanium aluminum alloy powder is Ti-48Al-2Cr-2Nb titanium aluminum alloy powder.

[0059] In some embodiments, the process parameters of the electron beam selective melting additive manufacturing method are: electron beam current is 10-20 mA, acceleration voltage is 60 kV, scanning rate is 1000-1600 mm / s, focusing current is 650-700 mA, and single layer thickness of titanium aluminum alloy powder is 0.07 mm.

[0060] In some embodiments, the process parameters of the electron beam selective melting additive manufacturing method are specifically as follows: electron beam current is 20 mA, acceleration voltage is 60 kV, scanning rate is 1300 mm / s, focusing current is 680 mA, and single layer thickness of titanium aluminum alloy powder is 0.07 mm.

[0061] In application, the manufacturing method of directionally solidified titanium-aluminum alloy can obtain titanium-aluminum alloy material with directionally grown columnar crystal structure through electron beam selective melting additive manufacturing.

[0062] The electron beam selective melting additive manufacturing method is used for manufacturing. The forming substrate is preheated to 600-700°C and kept warm for 20 minutes. The negative pressure vacuum device is started. After a period of gas washing, the negative pressure in the insulation cover will form a dynamic balance, and finally a stable negative pressure will be formed on the powder surface. When the negative pressure difference reaches 25mbar, it indicates that the forming conditions are met.

[0063] The selected process parameters are: electron beam current of 10-20 mA, acceleration voltage of 60 kV, scanning rate of 1000-1600 mm / s, focusing current of 650-700 mA, and layer thickness of 0.07 mm.

[0064] The preheating temperature was lowered, the forming process was kept below the equiaxed crystal reaction region, and a higher cooling rate was used to avoid phase transformation during the cooling process. The results showed that this method effectively achieved columnar crystal forming.

[0065] The temperature gradient in the forming process is increased by lower preheating temperature and high melting energy input, and rapid scanning is used to accelerate the solidification rate, which is beneficial to the formation of directional solidification structure.

[0066] Specifically, the electron beam selective melting additive manufacturing method of titanium aluminum alloy material with directional solidification characteristics, the powder used for forming is Ti-48Al-2Cr-2Nb titanium aluminum alloy powder developed by the gas atomization method. The forming substrate is heated to 600°C, kept warm for 20 minutes, and the forming environment is kept at 600°C for forming. The negative pressure vacuum device is started to wash the cabin, and finally the vacuum degree is dynamically balanced inside the cabin. When the vacuum pressure difference between the forming cabin vacuum and the insulation and pressure cover is 25mbar, the forming conditions are met.

[0067] The thickness of the powder single layer is 0.07mm. After the powder is laid, the powder is preheated and the melting process is: electron beam current is 20mA, acceleration voltage is 60KV, scanning rate is 1300mm / s, focusing current is 680mA, and melting times are 1. After the melting is completed, in order to maintain the low-temperature forming environment, no energy compensation is required, and the powder is continued to be laid for the next layer of forming.

[0068] The electron beam selective melting additive manufacturing method for directional solidification titanium aluminum alloy provided in the embodiment of the present application forms a higher temperature gradient during the forming process through low-temperature preheating and high-energy input melting, thereby realizing the development of titanium aluminum alloy materials with directional solidification characteristics. The negative pressure vacuum device uses the negative pressure formed on the surface of the powder bed to solve the problem that "powder blowing" in a low-temperature preheating environment causes the forming to be impossible, ensuring that the forming is carried out smoothly, and realizing the development of titanium aluminum alloy materials with directional solidification characteristics.

[0069] This embodiment also provides a negative pressure vacuum device for implementing the electron beam selective melting additive manufacturing method of the directional solidification titanium aluminum alloy as described above, by applying a certain pressure to the surface of the titanium aluminum alloy powder to ensure that the titanium aluminum alloy is smoothly formed at a low ambient temperature.

[0070] The negative pressure vacuum device includes: a forming chamber; a heat-insulating and pressure-maintaining cover, which is located in the forming chamber and is used to serve as a relatively closed space to maintain local temperature and local negative pressure during the forming process; a powder bed and a forming substrate are arranged in the heat-insulating and pressure-maintaining cover; a helium inlet, which is located at the upper end of the side wall of the forming chamber and is used to continuously introduce helium during the forming process; a vacuum exhaust channel, which is located at the bottom of the side wall of the heat-insulating and pressure-maintaining cover; and a vacuum pump group, which is used to extract the gas in the forming chamber through the vacuum exhaust channel.

[0071] In some embodiments, the negative pressure vacuum device also includes: a powder spreading mechanism, which is used to spread titanium aluminum alloy powder on the powder bed; a forming chamber vacuum gauge, which is used to detect the vacuum degree inside the forming chamber; an electron beam generator, which is used to perform electron beam selective melting additive manufacturing; an internal exhaust channel in the chamber, which is used to connect the vacuum exhaust channel and the vacuum pump group; a pipeline vacuum gauge, which is used to monitor the vacuum degree in the thermal insulation and pressure hood and the vacuum exhaust channel.

[0072] In some embodiments, the vacuum pump group includes a low vacuum valve, a high vacuum valve, a diffusion pump, a preheating valve, a maintenance pump, a high-low switching valve, a Roots pump, and a mechanical pump.

[0073] In application, the main principle of the negative pressure vacuum device is to use the method of upper air supply and lower air extraction to form a local negative pressure difference on the powder surface, thereby suppressing the occurrence of "powder blowing". Figure 2 As shown, the main components of the negative pressure vacuum device are as follows:

[0074] 1 is a heat preservation and pressure-maintaining hood, which plays the role of a relatively closed space to maintain local temperature and local negative pressure during the forming process; 2 is a vacuum exhaust channel, through which an external vacuum pump group 11 will continuously extract the gas in the cabin; 3 is a helium inlet, located at the upper end of the heat preservation and pressure-maintaining hood, through which a small amount of helium will be continuously introduced during the forming process; during the forming process, helium is continuously discharged through the vacuum exhaust channel 2, and finally a dynamic balance is formed. Since the vacuum exhaust channel 2 is located at the bottom of the side wall of the heat preservation and pressure-maintaining hood 1, and the helium inlet 3 is located at the upper end of the side wall of the forming chamber, the continuously introduced helium is discharged out of the cabin through the heat preservation and pressure-maintaining hood 1. Negative pressure will be formed above the surface of the powder bed in the heat preservation and pressure-maintaining hood 1, and this negative pressure can effectively prevent the occurrence of the "powder blowing" phenomenon of the powder bed during the forming process.

[0075] 4 is a powder bed; 5 is a powder spreading mechanism; 6 is a forming chamber; 7 is a forming chamber vacuum gauge, used to detect the vacuum degree inside the forming chamber; 8 is an electron beam generator; 9 is an exhaust channel inside the chamber; 10 is a pipeline vacuum gauge, used to monitor the vacuum degree in the thermal insulation and pressure hood 1 and the vacuum exhaust channel 2; 11 is a vacuum pump group, mainly composed of the following parts: 12 is a low vacuum valve, model GIQ-100; 13 is a high vacuum valve, model GDQ-S400; 14 is a diffusion pump, model DIP800; 15 is a preheating valve, model GDQ-J63; 16 is a maintenance pump, model D16T; 17 is a high-low switching valve, model GIQ-100; 18 is a Roots pump, model WAU1001; 19 is a mechanical pump, model SV300B; 7 is a forming chamber vacuum gauge, model ITR90; 10 is a pipeline vacuum gauge, model ITR90.

[0076] The steps for starting the negative pressure vacuum device are as follows: 1) continuously introduce a small amount of helium with a helium ventilation pressure of 0.5-0.8 MPa; 2) start the mechanical pump 19; 3) open the low vacuum valve 12; 4) start the Roots pump 18 after 10 minutes; 5) monitor the forming chamber vacuum gauge 7, and when the chamber vacuum is lower than 50 mbar, start the Roots pump 18; 6) monitor the forming chamber vacuum gauge 7, and when the chamber vacuum is lower than 5 Pa, close the low vacuum valve 12, open the high-low switching valve 17, and open the high vacuum valve 13; 7) monitor the forming chamber vacuum gauge 7, and when the chamber vacuum is lower than 5×10 -5 mbar, close the high-low switching valve 17, open the preheating valve 15, and turn on the maintaining pump 16; 8) Monitor the pipeline vacuum gauge 10. When the difference between the vacuum degree of the forming chamber and the vacuum degree in the insulation and pressure hood stabilizes at -25 mbar, the negative pressure system reaches dynamic balance and meets the conditions for negative pressure forming.

[0077] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned device can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0078] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy, characterized in that: It is achieved by a negative pressure vacuum device, which includes a forming chamber and a heat preservation and pressure retaining cover, the heat preservation and pressure retaining cover is located in the forming chamber, and a powder bed and a forming substrate are arranged in the heat preservation and pressure retaining cover; The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy comprises: The formed substrate is heated to 600-700° C. and kept at this temperature for 20 minutes; Starting the negative pressure vacuum device to wash the forming chamber, so that the negative pressure in the heat-insulating and pressure-insulating cover forms a dynamic balance; Titanium-aluminum alloy powder is placed on the powder bed, and the titanium-aluminum alloy is directionally solidified by an electron beam selective melting additive manufacturing method.

2. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 1, characterized in that: The step of heating the formed substrate to 600-700° C. and keeping the temperature for 20 minutes comprises: The forming substrate is heated to 600° C. and kept at this temperature for 20 minutes, and the forming environment is maintained at 600° C. for forming.

3. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 1, characterized in that: The step of starting the negative pressure vacuum device to wash the forming chamber so that the negative pressure in the heat-insulating and pressure-insulating cover forms a dynamic balance includes: The negative pressure vacuum device is started to purge the forming chamber so that the vacuum pressure difference between the forming chamber and the heat-insulating and pressure-maintaining cover reaches 25 mbar, so as to form a stable negative pressure on the surface of the titanium-aluminum alloy powder.

4. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 1, characterized in that: The step of placing titanium-aluminum alloy powder on the powder bed and directionally solidifying the titanium-aluminum alloy by an electron beam selective melting additive manufacturing method comprises: Laying a layer of titanium aluminum alloy powder on the powder bed, and forming it by electron beam selective melting after the laying is completed; After melting is completed, there is no need for energy compensation and titanium-aluminum alloy powder can continue to be laid to form the next layer.

5. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 1, characterized in that: The titanium-aluminum alloy powder is Ti-48Al-2Cr-2Nb titanium-aluminum alloy powder.

6. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 1, characterized in that: The process parameters of the electron beam selective melting additive manufacturing method are: electron beam current of 10-20 mA, acceleration voltage of 60 kV, scanning rate of 1000-1600 mm / s, focusing current of 650-700 mA, and single layer thickness of titanium aluminum alloy powder of 0.07 mm.

7. The electron beam selective melting additive manufacturing method for directionally solidified titanium aluminum alloy according to claim 6, characterized in that: The process parameters of the electron beam selective melting additive manufacturing method are as follows: electron beam current is 20 mA, acceleration voltage is 60 kV, scanning rate is 1300 mm / s, focusing current is 680 mA, and single layer thickness of titanium aluminum alloy powder is 0.07 mm.

8. A negative pressure vacuum device, characterized in that: An electron beam selective melting additive manufacturing method for realizing the directionally solidified titanium aluminum alloy according to any one of claims 1 to 7; The negative pressure vacuum device comprises: Forming cabin; A heat-insulating and pressure-maintaining cover, which is located in the forming chamber and is used to serve as a relatively closed space to maintain local temperature and local negative pressure during the forming process; a powder bed and a forming substrate are arranged in the heat-insulating and pressure-maintaining cover; A helium inlet, located at the upper end of the side wall of the forming chamber, for continuously introducing helium during the forming process; A vacuum exhaust channel, the vacuum exhaust channel being located at the bottom of the side wall of the heat-insulating and pressure-insulating cover; A vacuum pump group is used to extract the gas in the forming chamber through the vacuum exhaust channel.

9. The negative pressure vacuum device according to claim 8, characterized in that: The negative pressure vacuum device also includes: A powder spreading mechanism, the powder spreading mechanism is used to spread titanium aluminum alloy powder on the powder bed; A forming chamber vacuum gauge, the forming chamber vacuum gauge is used to detect the vacuum degree inside the forming chamber; An electron beam generator, wherein the electron beam generator is used for electron beam selective melting additive manufacturing; An internal air extraction channel of the cabin, the internal air extraction channel of the cabin being used to connect the vacuum air extraction channel and the vacuum pump group; A pipeline vacuum gauge is used to monitor the vacuum degree in the heat-insulating and pressure-maintaining cover and the vacuum exhaust channel.

10. The negative pressure vacuum device according to claim 8, characterized in that: The vacuum pump group includes a low vacuum valve, a high vacuum valve, a diffusion pump, a preheating valve, a maintenance pump, a high-low switching valve, a Roots pump, and a mechanical pump.

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