A method for preparing Fe-Cr-Mo series alloy based on electron beam selective melting technology

Abstract

The application discloses a method for preparing Fe-Cr-Mo series alloy based on electron beam selective melting technology, which comprises the following steps: model preparation; stage bottom plate preheating, wherein the whole heating and holding process of the bottom plate preheating is not more than 30 min; uniformly spreading Fe-Cr-Mo series alloy powder on the preheated bottom plate; and performing electron beam printing comprising the following processes: using a defocused electron beam to preheat the powder, using a focused electron beam to scan and melt the powder layer according to layering scanning data, using the defocused electron beam to post-heat the powder after the scanning and melting is completed, so as to keep the powder bed temperature at 360-380 DEG C ± 3 DEG C; repeating the powder spreading and the electron beam printing until the printing of all layers is completed; and after cooling to a certain temperature under vacuum, closing the vacuum, filling with inert gas, and taking out the Fe-Cr-Mo series alloy sample.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology for metallic materials, and specifically to a method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology. Background Technology

[0002] Selective electron beam melting (SEBM), as one of the most advanced additive manufacturing technologies, is widely used in aerospace, military manufacturing, shipbuilding, and major national projects. Unlike traditional subtractive manufacturing, SEBM allows for the layer-by-layer melting and stacking of metal powder using a high-power electron beam as a heat source. Furthermore, unlike laser selective melting which requires a supporting structure, SEBM's unique "preheating" process enables supportless printing, offering advantages such as complex structural design and integrated lightweight design.

[0003] Fe-Cr-Mo alloys are an important class of iron-based alloys, widely used in industry due to their excellent mechanical properties and corrosion resistance. Currently, the main preparation methods include melting and copper mold casting. Melting, as a traditional alloy preparation method, involves melting pure iron, chromium, and molybdenum in a protective atmosphere to prepare alloys. This method can produce alloys with specific compositions, and their properties can be optimized through subsequent heat treatment and processing. Copper mold casting can produce bulk amorphous alloys with high glass-forming ability (GFA) and high corrosion resistance. Through this method, the alloy forms an amorphous structure during rapid cooling, thus obtaining unique properties. In addition, Fe-Cr-Mo alloys can be further improved through nitriding treatment to enhance their surface properties, such as wear resistance, corrosion resistance, and fatigue resistance.

[0004] The patent specification with publication number CN103014531A discloses a cast Fe-Cr-Mo high-damping alloy and its preparation method. The alloy is smelted in a crucible in a vacuum environment, with a refining temperature of 1600-1650℃. A second refining process is adopted to further improve the purity of the molten metal. Easily burnable elements are added before tapping. The alloy heat treatment process is homogenization annealing, which involves holding at 1000℃ for 1 hour followed by furnace cooling. The mechanical properties and damping properties of this alloy are superior to those of known Fe-Cr-Mo deformable damping alloys.

[0005] The patent specification with publication number CN106086664A discloses a Fe-W-Mo-Cr-B wear-resistant and corrosion-resistant alloy and its preparation method. The method involves taking W powder, Mo powder, Cr powder, B powder, and Fe powder with a purity greater than 99.99% in appropriate proportions and mixing them evenly. The mixed powders are simultaneously stirred and smelted to obtain an alloy melt. When the alloy melt temperature reaches 1600–1620℃, the alloy melt is cast and cooled. When the alloy melt cools to 1100℃, it is held at that temperature for 3–5 hours and then quenched. It is then heated to 220–260℃ and held at that temperature for 6–8 hours, after which it is naturally cooled to room temperature to obtain the finished product.

[0006] Currently, Fe-Cr-Mo alloys are widely used in additive manufacturing, enabling alloy preparation via selective laser melting (SLM), direct metal laser sintering (DMLS), and radial deposition additive manufacturing, thus enhancing the alloy properties of Fe-Cr-Mo alloys to varying degrees. Electron beam selective melting (EBM) technology, due to its unique "preheating" step, can significantly reduce internal stress in alloys and achieve interlayer heat treatment during layer-by-layer printing. However, EBM technology is complex with numerous parameters, and there are currently few reports on its application in preparing Fe-Cr-Mo alloys.

[0007] The patent specification with publication number CN117385256A discloses a high-strength and high-toughness high-entropy alloy at high temperature and its additive manufacturing method. The material is an Fe-Co-Cr-Ni-Mo alloy. The high-entropy alloy additive is prepared by selective laser melting. The interlayer rotation angle is set to 65°~70°, the laser power is 160~240W, the exposure time is 30~80μs, the line spacing is 50~150μm, the dot spacing is 40~80μm, the layer thickness is 40μm, and the substrate preheating temperature is 120℃. The alloy has excellent plasticity and strength.

[0008] Faced with increasingly complex structural requirements for Fe-Cr-Mo alloys, traditional preparation methods cannot achieve complex structural designs. Additive manufacturing technology can achieve complex configurations while obtaining excellent alloy properties. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in the field, this invention provides a method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology. This method enables the preparation of bulk materials of Fe-Cr-Mo alloys using electron beam selective melting technology, resulting in high alloy surface quality, high yield, and the ability to suppress cracking and warping.

[0010] A method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology, comprising:

[0011] Model preparation: Use 3D modeling software to create a 3D solid model and slice it. Import the sliced ​​file into the electron beam 3D printer and set the processing parameters.

[0012] Preheating of the base plate: Under vacuum conditions, first use a 3-5mA scanning current to heat the base plate to 200-250℃, then increase the current intensity to 10-12mA to heat the base plate to 360-380℃, and use a 5-10mA scanning current to keep the base plate at 360-380℃±3℃ for ≥5 minutes; the entire heating and holding process of the base plate preheating should not exceed 30 minutes.

[0013] Fe-Cr-Mo alloy powder was uniformly spread onto a preheated substrate and then subjected to electron beam printing, which included the following processes: preheating the powder with a defocused electron beam, scanning the molten powder layer with a focused electron beam based on layer scanning data, and post-preheating the powder with a defocused electron beam after the scanning and melting were completed, so as to maintain the powder bed temperature at 360-380℃±3℃; the scanning current for preheating and post-preheating of the powder was 5-20mA, the scanning rate was 5-12m / s, and the scanning time was 5-20s.

[0014] Repeat powder spreading and electron beam printing until all layers are printed. After cooling to a certain temperature under vacuum (e.g., below 60°C), the vacuum is turned off, inert gas is introduced, and the Fe-Cr-Mo alloy sample is taken out.

[0015] During the preheating of the substrate, a segmented heating strategy ensures uniform substrate heat preservation and maintains the temperature within the range of 360–380℃ ± 3℃ throughout the printing process. Temperatures below the requirements of this invention can easily lead to powder blowing, while excessively high temperatures can cause partial melting, curling, and edge warping due to inconsistent powder bed energy. Furthermore, the entire preheating and heat preservation process should not exceed 30 minutes. Exceeding 45 minutes can cause the insulating powder used to coat the substrate to melt and solidify, adhering to the substrate in clumps that are difficult to clean and affect the accuracy of temperature measurements during subsequent printing. Excessively low substrate temperatures during printing can lead to more pronounced and severe powder splattering.

[0016] In actual printing, the energy input is not uniform, resulting in temperature fluctuations in the substrate after printing begins. Without the preheating and postheating described in this invention, the substrate temperature will drop significantly during printing. Since substrate temperature directly determines print quality, excessively low temperatures can cause frequent powder blowing, leading to printing termination. Furthermore, the printed sample may crack due to thermal stress caused by an unstable temperature field. Therefore, the method of this invention requires specific preheating and postheating operations to avoid these problems.

[0017] In some embodiments, the Fe-Cr-Mo alloy powder may be an amorphous alloy powder, and the Fe-Cr-Mo alloy sample may be a crystalline alloy sample.

[0018] In some embodiments, the elemental composition of the Fe-Cr-Mo alloy powder may include Cr, Mo, B, C, and Fe. Further, based on the total mass of Cr, Mo, B, C, and Fe in the Fe-Cr-Mo alloy powder as 100%, the mass percentage of Cr may be 24%–26%, the mass percentage of Mo may be 15%–17%, the mass percentage of B may be 1.7%–2.3%, and the mass percentage of C may be 1.7%–2.3%.

[0019] In some embodiments, the Fe-Cr-Mo alloy powder can be prepared by gas atomization.

[0020] By controlling the physical properties of powder, such as particle size, bulk density, and flowability, printability can be improved.

[0021] In some embodiments, the particle size of the Fe-Cr-Mo alloy powder is preferably 53–120 μm.

[0022] In some embodiments, preferably, the flowability of the Fe-Cr-Mo alloy powder is ≤18.0s / 50g.

[0023] In some embodiments, preferably, the loose packing density of the Fe-Cr-Mo alloy powder is ≥4.5 g / cm³. 3 .

[0024] In some embodiments, preferably, the tap density of the Fe-Cr-Mo alloy powder is ≥4 g / cm³. 3 Further optimization is needed for ≥4.5g / cm³. 3 .

[0025] In some embodiments, the thickness of the slice layer can be 50–80 μm, preferably 70–80 μm.

[0026] In some embodiments, the scanning rate during electron beam printing can be 0.2 to 2 m / s, preferably 0.75 to 1.5 m / s, and the scanning current can be 3 to 7 mA, preferably 3 to 5 mA.

[0027] In some embodiments, the vacuum condition may be: the molding chamber is evacuated to 9.9 × 10⁻⁶. -3 Below Pa, the gun chamber is evacuated to 9.9 × 10⁻⁶ Pa. -4 After the pressure drops below Pa, inert gas is introduced to maintain the vacuum at 0.15–0.17 Pa, for example, 0.16 Pa.

[0028] In this invention, the inert gas refers to a gas that does not participate in the reaction, such as rare gases like helium.

[0029] In some embodiments, the base plate may be a 316L stainless steel base plate.

[0030] In some embodiments, a defocused electron beam can be used for preheating the substrate.

[0031] In some embodiments, the scanning rate during the preheating process of the base plate can be 5 to 10 m / s.

[0032] In some embodiments, the defocusing amount of the electron beam may be 0.2.

[0033] In some embodiments, preheating and postheating of the powder can enable a current gradient ramp-up strategy.

[0034] In some embodiments, the scanning current for preheating the powder can be 15-20 mA, the scanning rate can be 8-12 m / s, and the scanning time can be 15-20 s.

[0035] In some embodiments, the scanning current for powder preheating can be 5-10 mA, the scanning rate can be 8-12 m / s, and the scanning time can be 5-10 s.

[0036] This invention provides a method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology, applicable to additive manufacturing processes with complex configurations. This method employs layer-by-layer electron beam 3D printing technology. By controlling the scanning current and rate of the electron beam, as well as the preheating processes of the substrate and powder, the Fe-Cr-Mo alloy powder within the selected area is rapidly melted to form a micro-melt pool, resulting in a Fe-Cr-Mo alloy with a refined microstructure. This method offers unparalleled advantages in terms of manufacturing cost and cycle time for complex Fe-Cr-Mo alloy components. Furthermore, due to its rapid micro-region solidification and layer-by-layer accumulation forming technology, it can obtain Fe-Cr-Mo alloys with the same dense, fine-grained structure and absence of macroscopic segregation as conventional forging techniques without any heat treatment.

[0037] Compared with the prior art, the beneficial effects of this invention are as follows:

[0038] This invention employs a specific base plate preheating process and powder preheating parameters to avoid the "powder blowing" phenomenon caused by the poor conductivity of Fe-Cr-Mo alloy powder, ensuring that the Fe-Cr-Mo alloy powder in the initial forming layer is tightly bonded to the substrate and forms a stable shape.

[0039] This invention uses a three-dimensional digital model to match reasonable process parameters, enabling the preparation of bulk Fe-Cr-Mo alloys with high surface quality, high yield, and the ability to suppress cracking and warping. Attached Figure Description

[0040] Figure 1 The image shows the surface electron backscatter diffraction (EBSD, magnification 200x) results of the Fe-Cr-Mo alloy printed sample in Example 1.

[0041] Figure 2 The image shows the EBSD (magnification 200x) results of the Fe-Cr-Mo alloy printed sample in Example 1 along the printing direction (vertical direction).

[0042] Figure 3 This is a three-dimensional surface morphology image of the Fe-Cr-Mo alloy printed sample from Example 1. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the raw materials used in the embodiments of the present invention are commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are conventional means well known to those skilled in the art.

[0044] Example 1:

[0045] The components of the powder prepared by the gas atomization method were analyzed according to GB / T 14265 and GB / T 23942, and the test results are shown in Table 1.

[0046] Table 1: Composition of Fe-Cr-Mo alloy powder for 3D printing in Example 1 (by mass fraction)

[0047]

[0048] The powder was mechanically sieved to select powder with a particle size of 53–120 μm.

[0049] The powder was vacuum dried at 80℃ for 2 hours. Powder testing was conducted at an experimental temperature of 25℃ and a humidity of <40%. Powder particle size distribution was tested according to GB / T 1480 dry sieving method, powder flowability was tested according to GB / T 1482, powder loose density was tested according to GB / T 1479.1, and powder tap density was tested according to GB / T 5162.

[0050] The properties of the powder obtained in Example 1 are shown in Table 2.

[0051] Table 2: Performance of Fe-Cr-Mo alloy powder for 3D printing in Example 1

[0052]

[0053] As can be seen from Table 2, the alloy powder has a particle size of 53–120 μm, good flowability, and high density.

[0054] The alloy forming structure was designed using 3D design software, the rapid prototyping format was exported, and the layer slicing software was imported to set parameters for slicing to obtain slicing data. The designed layer thickness was 70μm.

[0055] The selected molding structure for printing is a dense cylinder with a diameter of 8mm and a height of 4.4mm, with 66 layers.

[0056] Import the sliced ​​file into the electron beam 3D printer and set the electron beam printing software parameters as follows: calibrate the beam current, use manual preheating mode for powder bed preheating, enable preheating before printing, enable current gradient ramp function, preheating is five levels, scanning current is 20mA for 20s, defocusing amount is 0.2, and scanning speed is 10m / s. Post-printing preheating scanning current is 10mA for 10s, defocusing amount is 0.2, and scanning speed is 10m / s. During printing, scanning current is 3mA and scanning speed is 0.75m / s.

[0057] The beam calibration process is to adjust the down-beam current within the power range of the electron beam to the optimal power within a small range, so as to achieve beam focusing adjustment under different down-beam currents.

[0058] The powder is loaded into the powder hopper, and the bottom plate of the molding chamber (made of 316L stainless steel) is leveled. The hopper is then sealed, and the molding chamber is evacuated to a vacuum level of 9.9 × 10⁻⁶. -3 Below Pa, the gun chamber is evacuated to a vacuum of 9.9 × 10⁻⁶ Pa. -4 Below Pa, turn on the inert gas and fill with helium to maintain a vacuum of 1.6 × 10⁻⁶. -1 Pa, start the high voltage 60kV.

[0059] The manual preheating of the substrate was initiated using a segmented heating strategy. The defocusing amount was 0.2, and the substrate was scanned with a scanning current of 5mA and a scanning speed of 5m / s to raise the substrate temperature to 250℃. Then, the substrate was scanned with a scanning current of 10mA and a scanning speed of 10m / s to raise the substrate temperature to 380℃. Finally, the substrate was scanned with a scanning current of 8mA and a scanning speed of 10m / s for minor adjustments to maintain the substrate temperature at around 380℃ (±3℃) for 10 minutes. The entire heating and holding process did not exceed 30 minutes.

[0060] Use a scraper to evenly spread the powder onto the preheated base plate. Use a defocused electron beam to preheat the powder. The preheating parameters are described above. Use a focused electron beam to scan and melt the powder layer according to the layered scanning data. The electron beam printing parameters are described above. After scanning and melting, use a defocused electron beam to preheat the powder. The post-preheating parameters are described above to maintain the powder bed temperature at 360~380℃±3℃.

[0061] Repeat powder spreading and electron beam printing until all layers are printed. Under vacuum conditions, the sample is naturally cooled to below 60°C. The vacuum is then turned off, a large amount of helium is introduced, the printed sample is removed, and air blowing is performed to remove excess powder from the surface. This yields a bright Fe-Cr-Mo alloy sample without cracks or warping. The sample has a dense internal structure, which has basically eliminated defects such as pores, and the density is as high as 99.5%.

[0062] The printed samples were analyzed using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). ICP technology is based on atomizing the sample solution into fine droplets and introducing them into a high-temperature plasma, causing the elements in the sample to ionize and emit characteristic spectra. By detecting and analyzing these spectra, the content of various elements in the sample can be accurately determined. This technique can be used to obtain elemental loss analysis before and after printing; the detection results are shown in Table 3.

[0063] Table 3: ICP-AES test results of 3D printed Fe-Cr-Mo alloy samples from Example 1

[0064]

[0065] The surface EBSD (magnification 200x) of the Fe-Cr-Mo alloy sample prepared in this embodiment is as follows: Figure 1 As shown, the alloy has a typical as-cast structure with uniform grains.

[0066] The EBSD (magnification 200x) of the Fe-Cr-Mo alloy printed sample prepared in this embodiment along the printing direction is as follows: Figure 2 As shown, the microstructure is dense along the printing direction, with uniform grains and no obvious loose porous structure.

[0067] The surface morphology of the Fe-Cr-Mo alloy printed sample prepared in this embodiment is as follows: Figure 3 As shown, the surface is bright and the surface roughness Ra≤4.4μm.

[0068] The preparation method in Example 1 involves sieving Fe-Cr-Mo alloy powder and strictly controlling the physical properties of the powder, such as particle size, loose density, and flowability, which helps to improve printability.

[0069] Example 1 uses a specific base plate preheating process and powder preheating parameters to avoid the "powder blowing" phenomenon caused by poor powder conductivity, ensuring that the Fe-Cr-Mo alloy powder in the initial forming layer is tightly bonded to the substrate and forms a stable shape.

[0070] The preparation method in Example 1 uses reasonable process parameters matched with the structure of a three-dimensional digital model to prepare Fe-Cr-Mo alloy in bulk form. This results in high surface quality, high yield, and the ability to suppress cracking and warping.

[0071] Example 2:

[0072] All other conditions are the same as in Example 1, except that:

[0073] 1. Modify the electron beam printing software settings as follows: Preheat before printing, scanning current 15mA, duration 15s, defocusing amount 0.2, scanning speed 10m / s; Preheat after printing, scanning current 5mA, duration 5s, defocusing amount 0.2, scanning speed 10m / s; During printing, scanning current 5mA, scanning speed 0.9m / s.

[0074] 2. Modify the manual preheating staged heating strategy for the substrate to: defocusing amount of 0.2; scan the substrate with a scanning current of 5mA and a scanning speed of 5m / s to raise the substrate temperature to 250℃; then scan the substrate with a scanning current of 10mA and a scanning speed of 10m / s to raise the substrate temperature to 380℃; finally, scan the substrate with a scanning current of 8mA and a scanning speed of 10m / s for minor adjustments to maintain the substrate temperature at around 380℃ (±3℃) for 20 minutes. The entire heating and holding process should not exceed 30 minutes.

[0075] The resulting printed products have good molding quality, smooth surface, no cracks, uniform grains, and no obvious loose pores.

[0076] Comparative Example 1:

[0077] The other conditions are the same as in Example 1, except that the manual preheating strategy for the substrate is modified to a one-time heating with a small current to 380°C. Specifically, the defocusing amount is 0.2, the scanning beam current is 5mA, and the scanning speed is 5m / s to scan the substrate to raise the temperature to 380°C.

[0078] During the printing process, a "powder blowing phenomenon" occurred at the bottom of the print head, making printing impossible.

[0079] Comparative Example 2:

[0080] The other conditions are the same as in Example 1, except that the manual preheating strategy for the substrate is modified to a high current for a short time to heat it to 380°C in one go. Specifically, the defocusing amount is 0.2, the scanning beam current is 10mA, and the scanning speed is 10m / s to scan the substrate to raise the temperature to 380°C.

[0081] During the printing process, a "powder blowing phenomenon" occurred at the bottom of the print head, making printing impossible.

[0082] Comparative Example 3:

[0083] The other conditions are the same as in Example 1, except that the manual preheating strategy for the substrate is modified as follows: the defocusing amount is 0.2, the scanning current is 10mA, and the scanning speed is 10m / s to scan the substrate to raise the substrate temperature to 380°C. Then, the scanning current is 8mA and the scanning speed is 10m / s to scan the area near the substrate and make minor adjustments to keep the substrate temperature around 380°C (±3°C) for 30 minutes.

[0084] During the printing process, uneven molten pools appeared on the substrate. Some areas of the substrate exhibited melting and warping due to concentrated temperature and excessive energy input, resulting in rough printed samples with uneven melting. During sample cleaning, severe melting and adhesion between the substrate and the powder beneath it was observed.

[0085] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology, characterized in that, include: Model preparation: Use 3D modeling software to create a 3D solid model and slice it. Import the sliced ​​file into the electron beam 3D printer and set the processing parameters. Preheating of the base plate: Under vacuum conditions, first use a 3~5 mA scanning current to heat the base plate to 200~250 ℃, then increase the current intensity to 10~12 mA to heat the base plate to 360~380 ℃, and use a 5~10 mA scanning current to keep the base plate at 360~380 ℃ for ≥5 min; the entire heating and holding process of the base plate should not exceed 30 min. Fe-Cr-Mo alloy powder was uniformly spread onto a preheated substrate and then subjected to electron beam printing, which included the following processes: preheating the powder with a defocused electron beam, scanning the molten powder layer with a focused electron beam based on layer scanning data, and post-preheating the powder with a defocused electron beam after the scanning and melting were completed, so as to maintain the powder bed temperature at 360~380℃; the scanning current for preheating and post-preheating of the powder was 5~20 mA, the scanning rate was 5~12 m / s, and the scanning time was 5~20 s. Repeated powder spreading and electron beam printing until all layers are printed, then cooled to a certain temperature under vacuum conditions, the vacuum is turned off, inert gas is introduced, and the Fe-Cr-Mo alloy sample is obtained; the Fe-Cr-Mo alloy powder is amorphous alloy powder, and the Fe-Cr-Mo alloy sample is crystalline alloy sample. The elemental composition of the Fe-Cr-Mo alloy powder is Cr, Mo, B, C and Fe; Based on the total mass of Cr, Mo, B, C and Fe in the Fe-Cr-Mo alloy powder as 100%, the mass percentage of Cr is 24%~26%, the mass percentage of Mo is 15%~17%, the mass percentage of B is 1.7%~2.3%, and the mass percentage of C is 1.7%~2.3%.

2. The method according to claim 1, characterized in that, The Fe-Cr-Mo alloy powder was prepared by gas atomization. The particle size of the Fe-Cr-Mo alloy powder is 53~120 μm; The flowability of the Fe-Cr-Mo alloy powder is ≤18.0 s / 50 g; The loose packing density of the Fe-Cr-Mo alloy powder is ≥4.5 g / cm³. 3 ; The tap density of the Fe-Cr-Mo alloy powder is ≥4 g / cm³. 3 .

3. The method according to claim 2, characterized in that, The tap density of the Fe-Cr-Mo alloy powder is ≥4.5 g / cm³. 3 .

4. The method according to claim 1, characterized in that, The slice thickness is 50~80 μm.

5. The method according to claim 4, characterized in that, The slice thickness is 70~80 μm.

6. The method according to claim 1, characterized in that, The scanning rate during electron beam printing is 0.2~2 m / s, and the scanning current is 3~7 mA.

7. The method according to claim 6, characterized in that, The scanning rate during electron beam printing is 0.75~1.5m / s, and the scanning current is 3~5mA.

8. The method according to claim 1, characterized in that, The vacuum conditions are as follows: the molding chamber is evacuated to 9.9 × 10⁻⁶. -3 Below Pa, the gun chamber is evacuated to 9.9 × 10⁻⁶ Pa. -4 After the pressure drops below 0.15 Pa, inert gas is introduced to maintain the vacuum level at 0.15~0.17 Pa.

9. The method according to claim 1, characterized in that, The base plate is a 316L stainless steel base plate.

10. The method according to claim 1, characterized in that, The base plate is preheated using a defocused electron beam. The scanning rate during the preheating process of the base plate is 5~10 m / s; The defocusing amount of the electron beam is 0.

2.

11. The method according to claim 1 or 10, characterized in that, The current gradient ramp strategy is enabled for both powder preheating and postheating. The scanning current for preheating the powder was 15~20 mA, the scanning rate was 8~12 m / s, and the scanning time was 15~20 s; The scanning current for powder preheating was 5~10 mA, the scanning rate was 8~12 m / s, and the scanning time was 5~10 s.

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