Method for preparing Ti2AlNb alloy through electron beam selective melting technology

Abstract

According to the method for preparing the Ti2AlNb alloy through the electron beam selective melting technology, powder bed preheating is mainly improved, powder bed preheating comprises overall defocusing preheating and local focusing preheating which are sequentially carried out, the contradictory relation between the low temperature field and part cracking can be effectively overcome, and the product quality is improved. And the uniform distribution of a temperature field is realized in the whole preheating breadth, the deformation of parts is controlled, the low-temperature forming of the Ti2AINb alloy is realized, and the forming temperature is 700-800 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of Ti 2 AlNb alloy, and particularly relates to a method for preparing Ti 2 AlNb alloy by electron beam selective melting technology. Background Art

[0002] With the rapid development of aerospace technology, the performance requirements for high-temperature structural materials have increased accordingly. Especially for the structural materials of the core component engines, there is an urgent need to improve the high-temperature service performance of the materials while further reducing the weight. Ti 2 AlNb intermetallic compound, as a structural material for aero engines with excellent creep resistance, high-temperature oxidation resistance and high specific strength, has emerged as the times require.

[0003] The traditional preparation methods of Ti 2 AlNb alloy are melting forging and powder metallurgy. During the preparation process of melting ingots, defects such as composition segregation and porosity are likely to occur. The preparation of high-quality ingots is difficult, the material utilization rate is low, and the cost is high. Post-forging is required to obtain the desired performance. Powder metallurgy includes processes such as hot press sintering and spark plasma sintering. Although this process has advantages such as short process flow, high material utilization rate, fine and uniform structure, and controllable composition, the forming size and preparation cost of parts are limited by the size of the furnace and the furnace loading method. Moreover, the difficulty of this technology lies in the large shrinkage deformation of the powder, the easy leakage of the cladding under high temperature and high pressure, and the difficulty in precisely controlling the size.

[0004] Compared with the problems of low efficiency and high cost existing in the above traditional preparation methods, additive manufacturing technology, as a new processing method, has advantages such as high material utilization rate, short manufacturing cycle, and high structural complexity, providing a new way for the preparation of Ti 2 AlNb-based alloy. At present, the additive manufacturing of Ti 2 AlNb-based alloy mainly uses laser additive manufacturing technology. Since the selective laser melting (SLM) technology cannot raise the temperature of the powder bed to a relatively high temperature, and the rapidly solidified Ti 2 AlNb alloy has large thermal stress after forming, and microcracks are easily generated inside the structure, which will expand into macroscopic cracks during forming or subsequent use, ultimately leading to premature failure of the parts. While laser powder feeding additive manufacturing (LMD) has a larger molten pool and a lower cooling rate than SLM, but cracks still appear inside the specimen at low power, and the surface quality is poor.

[0005] Compared with laser additive manufacturing technology, Electron Beam Selective Melting (EBSM) technology has a faster scanning speed and high forming efficiency. At the same time, the temperature field during powder melting and forming is relatively high, which can effectively reduce the thermal stress of the formed parts. In addition, the vacuum environment of EBSM technology can effectively control the absorption of impurities such as oxygen and nitrogen. Therefore, EBSM has great advantages in the development of brittle materials. Currently, there are few reports on the research of forming Ti 2 AlNb-based alloys using EBSM.

[0006] There are few domestic manufacturers for forming Ti 2 AlNb alloys, mostly using laser melting deposition forming, arc forming, and powder metallurgy. Although some manufacturers have publicly disclosed the use of electron beam selective melting technology to prepare Ti 2 AlNb-based alloys, the forming temperature is 950°C to 1050°C, which is relatively high. During the EBSM forming process, heat dissipation is mainly in the form of thermal radiation, and the relationship between the amount of thermal radiation and the temperature required to be maintained is a quartic relationship. Therefore, when forming at 950°C to 1050°C, the preheating demand is large, the printing efficiency is low, and the formable area is small. In addition, Ti 2 AlNb parts usually have complex structures, and deformation problems are likely to occur during high-temperature heat treatment after forming, which is a key factor restricting the expansion of the application scenarios of Ti 2 AlNb. Currently, there is also no forming method for Ti 2 AlNb gradient structure.

[0007] In summary, it is necessary to develop a new method for preparing Ti 2 AlNb alloys using electron beam selective melting technology. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for preparing Ti 2 AlNb alloys using electron beam selective melting technology, which focuses on improving the powder bed preheating. The powder bed preheating includes overall defocusing preheating and local focusing preheating carried out in sequence, which can effectively overcome the contradictory relationship between the low temperature field and part cracking, achieve uniform temperature field distribution within the entire preheating area, control part deformation, and realize the low-temperature forming of Ti 2 AINb alloys, with a forming temperature of 700 - 800°C.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] The purpose of the present invention is to provide a method for preparing Ti 2 AlNb alloys using electron beam selective melting technology, and the method includes the following steps:

[0011] Step S1, sieving powder: After sieving the Ti 2 AlNb alloy powder, it is used for printing;

[0012] Step S2, production preparation: After cleaning the printing equipment and the substrate, ensure that there is no oil stain, oxide layer and other types of powder contamination on the Ti 2 AlNb powder in the equipment and on the substrate, then place the substrate in the printing equipment for leveling, evacuate the air and fill it with a protective gas;

[0013] Step S3, model preparation: After processing the pre-printed model with slicing software, import it into the printing equipment;

[0014] Step S4, printing parameter preparation: Input the bottom plate preheating parameter, powder bed preheating parameter, and filling parameter into the printing equipment in sequence; among them, the powder bed preheating parameter includes the overall defocusing preheating parameter and the local focusing preheating parameter input in sequence;

[0015] Step S5, printing: Start the printing equipment and make it print according to the set parameters. The printing includes using an electron beam to perform bottom plate preheating, powder bed preheating, and filling in sequence, where the powder bed preheating includes overall defocusing preheating and local focusing preheating performed in sequence;

[0016] Step S6, cooling: After printing is completed, stop the electron beam and vacuum, backfill the protective gas into the forming chamber, and perform cooling.

[0017] It should be noted that it is well-known to those skilled in the art that: Before laying the powder bed in the electron beam selective melting technology, it is necessary to preheat the bottom plate in advance to facilitate the Ti 2 AlNb alloy powder of the first layer of powder bed to be heated evenly, then lay the first layer of powder bed, perform powder bed preheating and filling in sequence, then lay the second layer of powder bed, perform powder bed preheating and filling in sequence, and after cyclic operation, until the Ti 2 AlNb alloy part printing is completed; among them, the powder bed preheating includes overall defocusing preheating and local focusing preheating performed in sequence. The overall defocusing preheating is to perform small beam defocusing preheating on the overall powder bed, which can avoid the powder blowing phenomenon and improve the hardness of the powder bed. Subsequently, local focusing preheating is performed on the edge of the sliced area of this layer of powder bed to improve the heat input efficiency and the forming efficiency.

[0018] The present invention provides a method for preparing Ti 2 AlNb alloy by electron beam selective melting technology, which focuses on improving the powder bed preheating. The powder bed preheating includes overall defocusing preheating and local focusing preheating performed in sequence, which can effectively overcome the contradictory relationship between the low temperature field and part cracking, realize uniform temperature field distribution within the entire preheating area, control part deformation, and achieve low-temperature forming of Ti 2AINb alloy, with a forming temperature of 700 - 800 °C.

[0019] As a preferred technical solution of the present invention, in step S1, the Ti 2 AlNb alloy powder used for printing has a particle size range of 50 - 105 μm.

[0020] As a preferred technical solution of the present invention, in step S2, the substrate is placed in the printing device and centered and leveled. After leveling, the vacuum is pumped, and the oxygen content is controlled to be less than 2 -4 ppm, and high-purity helium is filled as the protective gas.

[0021] As a preferred technical solution of the present invention, in step S4, the bottom plate preheating parameters include:

[0022] The filling spacing is 0.6 - 1.2 mm, such as 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm or 1.2 mm, etc.; the focusing is 35 - 75 mA, such as 35 mA, 40 mA, 45 mA, 50 mA, 55 mA, 60 mA, 65 mA, 70 mA or 75 mA, etc.; the scanning speed is 25 - 30 m / s, such as 25 m / s, 26 m / s, 27 m / s, 28 m / s, 29 m / s or 30 m / s, etc.; the scanning beam current is 30 - 35 mA, such as 30 mA, 31 mA, 32 mA, 33 mA, 34 mA or 35 mA, etc.; the maximum width of each zone is 8 - 10 mm, such as 8 mm, 8.5 mm, 9 mm, 9.5 mm or 10 mm, etc. After the bottom plate is preheated for 30 - 40 min, such as 30 min, 31 min, 33 min, 35 min, 37 min, 38 min or 40 min, etc., the preheating is stopped.

[0023] As a preferred technical solution of the present invention, in step S4, the overall defocusing preheating parameters include:

[0024] The scanning speed is 12 to 20 m / s, such as 12 m / s, 13 m / s, 14 m / s, 15 m / s, 16 m / s, 17 m / s, 18 m / s, 19 m / s or 20 m / s, etc.; the scanning beam current is 20 to 35 mA, such as 20 mA, 23 mA, 25 mA, 28 mA, 30 mA, 32 mA or 35 mA, etc.; the number of scanning passes is 5 to 10, such as 5, 7, 8 or 10, etc.; the filling pitch is 0.5 to 1.2 mm, such as 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm or 1.2 mm, etc.; the maximum width of the partition is 8 to 12 mm, such as 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm, 11.5 mm or 12 mm, etc.; the number of stable layers is 45 to 50, such as 45 layers, 46 layers, 47 layers, 48 layers, 49 layers or 50 layers, etc.; the focusing current is 20 to 60 mA, such as 20 mA, 25 mA, 30 mA, 35 mA, 40 mA, 45 mA, 50 mA, 55 mA or 60 mA, etc.

[0025] As a preferred technical solution of the present invention, in step S4, the local focusing preheating parameters include:

[0026] The source of the local preheating range is the outer bounding box, the number of local preheating passes is 2 to 8, and the local preheating offset distance is 4 to 10 mm, such as 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm, etc.

[0027] It should be noted that the outer bounding box refers to enclosing a box in the maximum X-axis direction and the maximum Y-axis direction of the part, and local preheating is carried out within this box range.

[0028] As a preferred technical solution of the present invention, in step S4, the filling parameters include:

[0029] The filling parameters of each scanning line include: the filling pitch is 0.8 to 1.2 mm, such as 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm or 1.2 mm, etc.; the beam current is 3 to 20 mA, such as 3 mA, 5 mA, 7 mA, 10 mA, 13 mA, 15 mA, 17 mA or 20 mA, etc.; the scanning speed is 0.5 to 4 m / s, such as 0.5 m / s, 1.0 m / s, 1.5 m / s, 2.0 m / s, 2.5 m / s, 3.0 m / s or 4 m / s, etc.; the linear energy density is 2 to 5 J / mm 2 , such as 2 J / mm 2 , 2.5 J / mm 2 , 3 J / mm 2 , 3.5 J / mm 2 , 4 J / mm 2 , 4.5 J / mm2 or 5 J / mm 2 etc.

[0030] As a preferred technical solution of the present invention, in step S5, the forming temperature of the printing is 700 - 800 °C, such as 700 °C, 710 °C, 730 °C, 750 °C, 760 °C, 780 °C or 800 °C, etc.

[0031] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0032] The present invention provides a method for preparing Ti 2 AlNb alloy by electron beam selective melting technology, which focuses on improving the powder bed preheating. The powder bed preheating includes overall defocusing preheating and local focusing preheating carried out in sequence, which can effectively overcome the contradictory relationship between the low temperature field and part cracking, realize uniform temperature field distribution within the entire preheating area, control part deformation, and achieve low-temperature forming of Ti 2 AINb alloy, and the forming temperature is 700 - 800 °C. Description of the Drawings

[0033] Figure 1 It is the SEM micrograph (10 μm scale) of the microstructure inside the alloy when the powder bed preheating temperature is 750 - 800 °C in a specific embodiment of the present invention;

[0034] Figure 2 It is the SEM micrograph (1 μm scale) of the microstructure inside the alloy when the powder bed preheating temperature is 750 - 800 °C in a specific embodiment of the present invention;

[0035] Figure 3 It is the SEM micrograph (10 μm scale) of the microstructure inside the alloy when the powder bed preheating temperature is 800 - 850 °C in a specific embodiment of the present invention;

[0036] Figure 4 It is the SEM micrograph (1 μm scale) of the microstructure inside the alloy when the powder bed preheating temperature is 800 - 850 °C in a specific embodiment of the present invention;

[0037] Figure 5 It is the mechanical property curve of the alloy when the powder bed preheating temperature is 750 - 800 °C in a specific embodiment of the present invention;

[0038] Figure 6 It is the mechanical property curve of the alloy when the powder bed preheating temperature is 800 - 850 °C in a specific embodiment of the present invention;

[0039] Figure 7 It is the filling energy density EA of 3.4 J / mm in a specific embodiment of the present invention 2SEM micrograph of the microstructure inside the alloy at that time (100μm scale);

[0040] Figure 8 is the SEM micrograph of the microstructure inside the alloy when the filling energy density EA is 4.0 J / mm in a specific embodiment of the present invention 2 SEM micrograph of the microstructure inside the alloy at that time (100μm scale);

[0041] Figure 9 is the comparison chart of the mechanical properties of the alloy under two different filling energy densities in a specific embodiment of the present invention. Specific Embodiment

[0042] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific embodiments.

[0043] During the EBSM forming process, the heat dissipation is mainly in the form of thermal radiation, and the relationship between the amount of thermal radiation and the temperature to be maintained is a quartic relationship. Therefore, the preheating demand is large, the printing efficiency is low, and the formable area is small under the conditions of 950°C - 1050°C disclosed in the prior art. The present invention innovatively proposes a method for forming Ti 2 AlNb at low temperature. The forming temperature is reduced to 700 - 800°C, the forming temperature is reduced by 200 - 300°C, the forming efficiency is increased by 2 - 3 times, and based on the existing equipment capacity conditions, the limit size of the formable parts is expanded by more than 2 times. The main difficulty in reducing the preheating temperature is that due to insufficient pseudo-sintering, it is easy to cause powder blowing problems and result in printing failures. The present invention proposes a new preheating process strategy and method to achieve stable EBSM forming under relatively low temperature conditions.

[0044] Ti 2 AlNb parts are usually of complex structures, and deformation problems are likely to occur during the high-temperature heat treatment after forming, which is a key factor restricting the expansion of the application scenarios of Ti 2 AlNb. The present invention innovatively realizes the regulation of the tissue properties in the formed state through the EBSM forming process control, creating conditions for the direct use of the parts without heat treatment after EBSM forming and expanding the application range of the parts (thin-walled structures, complex overhanging structures, etc.).

[0045] Currently, there is no forming method for Ti 2 AlNb gradient tissue. The present invention can realize the differential regulation of the Ti 2 AlNb microstructure in different regions of the same furnace and the same sample by adjusting the forming process, realize the regulation of the properties of different tissues, and meet the requirements of special service environments. The core of the Ti 2 AlNb part mainly precipitates lath-shaped O phase to improve toughness, and the edge of the Ti 2 AlNb part mainly precipitates needle-shaped O phase to improve strength.

[0046] Ti Formed by EBSM 2 AlNb-based alloy. In the as-formed alloy, it is composed of B2 matrix, large-sized lath-shaped primary O / α2 phase in grains and fine secondary needle-shaped O / α2 phase. The volume fraction of B2 in the alloy determines the plasticity of the part. The higher the content of B2 phase, the better the plasticity of the alloy and the lower the strength. The lath-shaped primary O / α2 phase and the fine secondary needle-shaped O / α2 phase determine the strength of the alloy, but the strengthening effect of the secondary needle-shaped O / α2 phase on the alloy is significantly greater than that of the large-sized lath-shaped primary O / α2 phase. The higher the content of the needle-shaped O / α2 phase, the higher the strength of the alloy, but the corresponding plasticity decreases.

[0047] To avoid powder blowing during the electron beam printing process, it is necessary to carry out the anti-powder-blowing ability test under the hot powder state. During the layer-by-layer printing process, gradually change the key parameters and observe whether phenomena such as powder bed jumping and powder blowing occur when the beam is on, so as to judge whether the parameter is an available anti-powder-blowing parameter. Among them, the key parameters of powder bed preheating are the initial beam current, partition width, initial speed and initial focus. Accordingly, the margin adjustment ranges are shown in Table 1. Carry out single-variable tests for each key parameter one by one. There is no powder jumping phenomenon within the selected parameter range, and the process margin is sufficient.

[0048] Table 1 Thermal Powder Test Plan

[0049] Serial number Adjustment item Margin adjustment range 1 Initial beam current 15 - 45 mA 2 Partition width 5 - 25 mm 3 Initial velocity 5 - 40 m / s 4 Initial focusing 10 - 100 mA

[0050] By adjusting the powder bed parameters and changing the preheating temperature, the differential regulation of the Ti 2 AlNb microstructure in different regions of the same heat treatment batch and the same sample can be realized. For example, when the powder bed preheating temperature is 750 - 800 °C, the microstructure inside the alloy is as Figure 1 and Figure 2 shown. Figure 1 is the SEM image of the microstructure under a 10 μm scale bar, Figure 2 is the SEM image of the microstructure under a 1 μm scale bar. When the powder bed preheating temperature is increased to 800 - 850 °C, the microstructure inside the alloy is as Figure 3 and Figure 4 shown. Figure 3 is the SEM image of the microstructure under a 10 μm scale bar, Figure 4 is the SEM image of the microstructure under a 1 μm scale bar. As can be seen from Figures 1 - 4 , with the increase of the powder bed preheating temperature, the large-sized lath-shaped primary O phase precipitated in the Ti 2 AlNb alloy gradually dissolves, and the volume fraction gradually decreases, while the content of the fine secondary needle-shaped O phase gradually increases. When using SEBM to form Ti 2 AlNb-based alloy at the powder bed preheating temperature for mechanical property testing, when the powder bed preheating temperature is 750 - 800 °C, the mechanical property curve of the alloy is asFigure 5 As shown, when the preheating temperature of the powder bed is 800 - 850 °C, the alloy mechanical property curve is as Figure 6 shown, and the relevant results of tensile strength, yield strength, and elongation after fracture are summarized in Table 2. It can be seen that as the preheating temperature of the powder bed increases, the content of fine secondary acicular O-phase gradually increases. Although the alloy strength increases to some extent, the plasticity significantly decreases.

[0051] Table 2

[0052] Powder bed preheating temperature (°C) Tensile strength (MPa) Yield strength (MPa) Elongation after fracture (%) 750～800℃ 890 779 13.6 800～850℃ 991 861 10.3

[0053] By adjusting the filling process parameters and changing the filling beam current or filling energy density, the microstructure control can be achieved. For example, when the filling energy density EA of the SEBM-formed Ti 2 AlNb-based alloy is 3.4 J / mm 2 and 4.0 J / mm 2 respectively, the SEM images of the microstructure of the Ti 2 AlNb alloy at a scale of 100 μm are as Figure 7 and Figure 8 shown respectively, and the comparison diagram of the alloy mechanical properties under two different filling energy densities is as Figure 9 shown. The relevant results of tensile strength, yield strength, and elongation after fracture are summarized in Table 3. It can be seen that as the filling energy EA increases, the volume fraction of the large-sized lath-shaped primary O-phase precipitated in the SEBM-formed Ti 2 AlNb alloy gradually decreases, and the content of the fine secondary acicular O-phase gradually increases, resulting in higher alloy strength and lower plasticity.

[0054] Table 3

[0055] <![CDATA[EA (J / mm 2 )]]> Tensile strength (MPa) Yield strength (MPa) Elongation after fracture (%) 4.0 940 863 9.8 3.4 929 821 14.1

[0056] In summary, the present invention provides a method for preparing Ti 2 AlNb alloy by electron beam selective melting technology. The powder bed preheating is mainly improved. The powder bed preheating includes overall defocusing preheating and local focusing preheating carried out in sequence, which can effectively overcome the contradictory relationship between the low temperature field and part cracking, achieve uniform temperature field distribution within the entire preheating area, control part deformation, and realize low-temperature forming of Ti 2 AINb alloy, with the forming temperature being 700 - 800 °C; on the basis of meeting the strength standard, although some strength is sacrificed, the plasticity is improved, and currently, more customers value the plasticity of the Ti 2 AlNb alloy more and have higher requirements for plasticity; the method of the present invention has a low forming temperature and less preheating time, greatly improving the forming efficiency. Moreover, the low forming temperature reduces energy consumption, reduces the loss of equipment, and lowers costs.

[0057] In the method of the present invention, through the regulation of process parameters, a new process window is obtained, and low-temperature preheating Ti 2 AlNb EBSM forming is realized; by adjusting the preheating temperature, the microstructure regulation can be realized; by adjusting the filling process parameters, increasing the filling beam current or the filling energy density, the microstructure regulation can be realized; through the adjustment of the forming process, the microstructure regulation of the Ti2AlNb alloy can be realized, and different mechanical properties can be achieved; through the in-situ adjustment of the forming process, the differential regulation of the microstructure of Ti2AlNb in different regions of the same furnace and the same sample can be realized, and the regulation of the properties of different microstructures can be achieved to meet the requirements of special service environments.

[0058] The present invention uses the above embodiments to illustrate the detailed structural features of the present invention. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0059] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0060] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0061] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing Ti2AlNb alloy by electron beam selective melting technology, characterized in that: The method comprises the following steps: Step S1, screening powder: screening the Ti2AlNb alloy powder for printing; Step S2, production preparation: After cleaning the printing equipment and the substrate, place the substrate in the printing equipment, level it, evacuate it and fill it with protective gas; Step S3, model preparation: the pre-printed model is processed by the slicing software and then imported into the printing device; Step S4, preparing printing parameters: inputting the base plate preheating parameters, the powder bed preheating parameters, and the filling parameters into the printing device in sequence; wherein the powder bed preheating parameters include the overall defocus preheating parameters and the local focus preheating parameters input in sequence; Step S5, printing: starting the printing device to print according to the set parameters, wherein the printing includes sequentially preheating the base plate, preheating the powder bed, and filling using an electron beam, wherein the powder bed preheating includes sequentially performing overall defocusing preheating and local focusing preheating; Step S6, cooling: After printing is completed, stop the electron beam and vacuum, and backfill the protective gas into the molding chamber for cooling.

2. The method according to claim 1, characterized in that: In step S1, the particle size range of the Ti2AlNb alloy powder used for printing is 50-105 μm.

3. The method according to claim 1, characterized in that In step S2, the substrate is placed in the printing device and leveled in the center. After leveling, vacuum is drawn to control the oxygen content to be less than 2 -4 ppm, filled with high purity helium as protective gas.

4. The method according to claim 1, characterized in that: In step S4, the base plate preheating parameters include: The filling spacing is 0.6-1.2 mm, the focusing is 35-75 mA, the scanning speed is 25-30 m / s, the scanning beam current is 30-35 mA, the maximum partition width is 8-10 mm, and the preheating of the base plate is stopped after 30-40 minutes of preheating.

5. The method according to claim 1, characterized in that In step S4, the overall defocus preheating parameters include: The scanning speed is 12-20 m / s, the scanning beam current is 20-35 mA, the number of scanning passes is 5-10, the filling spacing is 0.5-1.2 mm, the maximum partition width is 8-12 mm, the stable layer is 45-50 layers, and the focusing is 20-60 mA.

6. The method according to claim 1 or 5, characterized in that: In step S4, the local focus preheating parameters include: The local preheating range comes from the outer bounding box, the number of local preheating times is 2 to 8, and the local preheating offset distance is 4 to 10 mm.

7. The method according to claim 1, characterized in that In step S4, the filling parameters include: The filling parameters of each scanning line include: filling spacing of 0.8-1.2 mm, beam current of 3-20 mA, scanning speed of 0.5-4 m / s, and linear energy density of 2-5 J / mm 2 .

8. The method according to claim 1, characterized in that In step S5, the printing molding temperature is 700-800°C.

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