Method for preparing Fe-Cr-Mo alloy based on electron beam selective melting technology

Abstract

The invention discloses a method for preparing a Fe-Cr-Mo alloy based on an electron beam selective melting technology. The method comprises the steps that a model is prepared; bottom plate preheating is conducted in stages, and the whole heating and heat preservation process of bottom plate preheating does not exceed 30 min; fe-Cr-Mo series alloy powder is evenly spread on a preheated bottom plate, and electron beam printing including the following processes of conducting pre-preheating treatment on the powder through a defocused electron beam, scanning and melting a powder layer through a focused electron beam according to layered scanning data, conducting post-preheating on the powder through the defocused electron beam after scanning and melting are completed, and conducting post-heating on the powder through the focused electron beam; keeping the temperature of the powder bed at 360-380 DEG C + / -3 DEG C; and powder laying and electron beam printing are repeated until all layers are printed, after cooling is conducted to a certain temperature under the vacuum condition, vacuum is closed, inert gas is filled, and the Fe-Cr-Mo alloy sample is taken out.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of metal materials, and in particular to a method for preparing Fe-Cr-Mo alloy based on electron beam selective melting technology. Background Art

[0002] As one of the current advanced additive manufacturing technologies, SEBM is widely used in aerospace, shipping, and major equipment. Different from traditional "subtractive manufacturing", SEBM can achieve layer-by-layer melting and superposition of metal powders using high-power electron beams as heat sources. Different from the necessary support structure of laser selective melting, SEBM's unique "preheating" can achieve support-free printing, with advantages such as complex structural design and integrated lightweight design.

[0003] Fe-Cr-Mo alloys are an important class of iron-based alloys, which are widely used in the industrial field for their excellent mechanical properties and corrosion resistance. The main preparation methods currently include smelting and copper mold casting. As a traditional alloy preparation method, smelting prepares alloys by melting pure iron, chromium, molybdenum and other elements in a protective atmosphere. This method can prepare alloys with specific compositions and optimize their properties through subsequent heat treatment and processing. Copper mold casting can prepare 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, thereby obtaining unique properties. In addition, Fe-Cr-Mo alloys will also be nitrided to improve the surface properties of Fe-Cr-Mo alloys, 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 melted in a crucible in a vacuum environment with a refining temperature of 1600-1650°C. Secondary refining is used to further improve the purity of the molten metal, and easily burnt elements are added before leaving the furnace. The alloy heat treatment process is homogenization annealing, and the annealing process is to keep at 1000°C for 1h and then cool in the furnace. The mechanical properties and damping properties of the alloy are better than those of the known Fe-Cr-Mo deformation damping alloys.

[0005] The patent specification with publication number CN106086664A discloses a Fe-W-Mo-Cr-B series wear-resistant and corrosion-resistant alloy and a preparation method thereof. W powder, Mo powder, Cr powder, B powder and Fe powder with a purity greater than 99.99% are taken in corresponding proportions and mixed evenly; the mixed powders are stirred and smelted at the same time to obtain an alloy melt; when the alloy melt temperature reaches 1600-1620°C, the alloy melt is cast and cooled; when the alloy melt is cooled to 1100°C, it is kept warm for 3-5 hours and then quenched, then heated to 220-260°C and kept warm for 6-8 hours, and then naturally cooled to room temperature to obtain a finished product.

[0006] At present, Fe-Cr-Mo alloys are also widely used in the field of additive manufacturing. They can be prepared by selective laser melting (SLM), direct metal laser sintering (DMLS), radial deposition additive manufacturing and other methods, which have increased the alloy properties of Fe-Cr-Mo alloys to varying degrees. Electron beam selective melting technology can greatly reduce the internal stress of the alloy due to its unique "preheating" link, and achieve interlayer heat treatment during the layer-by-layer printing process. However, the electron beam selective melting technology has a complex process and many parameters. Currently, there are few reports on the preparation of Fe-Cr-Mo alloys using this technology.

[0007] The patent specification with publication number CN117385256A discloses a high-entropy alloy with high strength and toughness at high temperature and its additive manufacturing method. The material is a 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 point spacing is 40~80μm, the layer thickness is 40μm, and the preheating temperature of the substrate is 120℃. The alloy has excellent plasticity and strength.

[0008] Faced with the increasingly complex structural requirements of Fe-Cr-Mo alloys, traditional preparation methods are unable to achieve complex structural design. Additive manufacturing technology can achieve complex configurations while obtaining excellent alloy properties. Summary of the invention

[0009] In view of the above-mentioned technical problems and the shortcomings in the art, the present invention provides a method for preparing Fe-Cr-Mo alloys based on electron beam selective melting technology, which can realize the preparation of bulk materials of Fe-Cr-Mo alloys by electron beam selective melting technology, obtain alloys with high surface quality and high yield, and can inhibit cracking and warping.

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

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

[0012] Bottom plate preheating: Under vacuum conditions, first use 3-5mA scanning current to heat the bottom plate to 200-250℃, increase the current intensity to 10-12mA to heat the bottom plate to 360-380℃, and use 5-10mA scanning current to keep the bottom plate at 360-380℃±3℃ for ≥5min; the entire heating and insulation process of the bottom plate preheating shall not exceed 30min;

[0013] The Fe-Cr-Mo alloy powder is evenly spread on the preheated base plate, and the electron beam printing including the following process is performed: the powder is preheated by using a defocused electron beam, and the powder layer is melted by scanning using a focused electron beam according to the layered scanning data. After the scanning and melting is completed, the powder is post-preheated by using a defocused electron beam to maintain the powder bed temperature at 360-380°C ± 3°C; the scanning current of the pre-preheating and post-preheating of the powder is 5-20mA, the scanning rate is 5-12m / s, and the scanning time is 5-20s;

[0014] Repeat powder spreading and electron beam printing until all layers are printed. After cooling to a certain temperature (such as below 60°C) under vacuum conditions, turn off the vacuum, fill with inert gas, and take out the Fe-Cr-Mo alloy sample.

[0015] During the preheating process of the base plate, the staged heating strategy can achieve uniform insulation of the base plate, and the temperature is always maintained in the range of 360-380℃±3℃ during the printing process. When the temperature is lower than the requirements of the present invention, the "powder blowing" phenomenon caused by too low temperature is prone to occur. When the temperature is too high, due to the inconsistent energy of the powder bed, it will cause partial melting, curling and warping. In addition, the entire heating and insulation process of the base plate preheating should not exceed 30 minutes. After exceeding 45 minutes, the insulation powder used to wrap the base plate is prone to melt and solidify, and adhere to the base plate into blocks, which is difficult to clean and affects the accuracy of temperature measurement in the subsequent printing process. If the base plate temperature is too low during the printing process, it will lead to more obvious and serious powder splashing during the printing process.

[0016] In the actual printing process, since the energy input of the printing process is not uniform, the base plate will have a certain degree of temperature fluctuation after the start of printing. If there is no pre-preheating and post-preheating as described in the present invention, the base plate temperature will drop significantly during the printing process. The base plate temperature during the printing process will directly determine the printing quality. When the base plate temperature is too low, the "powder blowing" phenomenon will occur frequently, resulting in the termination of printing, and the printed sample will also cause thermal stress cracking due to the unstable temperature field. Therefore, the method of the present invention must perform specific pre-preheating and post-preheating operations to avoid the above 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 element 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% to 26%, the mass percentage of Mo may be 15% to 17%, the mass percentage of B may be 1.7% to 2.3%, and the mass percentage of C may be 1.7% to 2.3%.

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

[0020] By regulating the physical properties of the powder, such as particle size, bulk density and fluidity, it is helpful to improve printability.

[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 fluidity of the Fe-Cr-Mo alloy powder is ≤18.0s / 50g.

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

[0024] In some embodiments, preferably, the tap density of the Fe-Cr-Mo alloy powder is ≥4 g / cm 3 , more preferably ≥4.5g / cm 3 .

[0025] In some embodiments, the slice thickness may be 50-80 μm, preferably 70-80 μm.

[0026] In some embodiments, the scanning rate during electron beam printing may be 0.2 to 2 m / s, preferably 0.75 to 1.5 m / s, and the scanning current may 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 -3 Pa, the gun chamber is evacuated to 9.9×10 -4 Pa, then fill with inert gas to maintain the vacuum degree at 0.15-0.17Pa, for example, 0.16Pa.

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

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

[0030] In some embodiments, a defocused electron beam may be used for baseplate preheating.

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

[0032] In some embodiments, the defocused electron beam may have a defocus amount of 0.2.

[0033] In some embodiments, powder pre- and post-preheating may enable a current gradient ramping strategy.

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

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

[0036] The present invention provides a method for preparing Fe-Cr-Mo alloy based on electron beam selective melting technology, which can be used for additive manufacturing process of complex configuration. The method adopts electron beam 3D printing technology with layer-by-layer stacking, and by regulating the scanning current and scanning rate of the electron beam, the base plate preheating process and the powder preheating process, the Fe-Cr-Mo alloy powder in the selected area is rapidly melted to form a micro molten pool, and a Fe-Cr-Mo alloy with refined structure is obtained. The method has incomparable advantages in terms of manufacturing cost and manufacturing cycle of complex Fe-Cr-Mo alloy components, and due to its micro-area rapid solidification and stacked cumulative forming technical characteristics, it is possible to obtain a Fe-Cr-Mo alloy with the same density, fine grains, no macro segregation and fine structure as conventional forging technology without any heat treatment.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention adopts a specific base plate preheating process and powder preheating parameters to avoid the "powder blowing" phenomenon caused by the poor conductivity of the Fe-Cr-Mo alloy powder, and ensures that the initial layer of Fe-Cr-Mo alloy powder is tightly combined with the base plate and stably formed.

[0039] The invention matches reasonable process parameters according to the structure of the three-dimensional digital model, so that the prepared Fe-Cr-Mo alloy can realize the preparation of block materials, has high surface quality and high yield rate, and can inhibit cracking and warping. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a graph showing the results of the surface electron backscatter diffraction analysis (EBSD, magnification 200 times) of the Fe-Cr-Mo alloy printed sample of Example 1.

[0041] Figure 2 This is the EBSD result (magnification 200 times) of the Fe-Cr-Mo alloy printed sample of Example 1 along the printing direction (vertical direction).

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

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer. If not specifically specified, the raw materials used in the examples of the present invention are all commercially available; if not specifically specified, the technical means used in the examples of the present invention are all conventional means well known to those skilled in the art.

[0044] Embodiment 1:

[0045] The powder prepared by the aerosolization method was tested for composition according to GB / T 14265 and GB / T 23942. The test results are shown in Table 1.

[0046] Table 1: Example 1 3D printed Fe-Cr-Mo alloy powder composition (by mass fraction)

[0047]

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

[0049] The powder was vacuum dried at 80°C for 2h, and the powder test was carried out at an experimental temperature of 25°C and a humidity of <40%. The powder particle size composition was tested according to the dry sieving method of GB / T 1480, the powder flowability was tested according to GB / T 1482, the powder bulk density was tested according to GB / T 1479.1, and the 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 3D printed Fe-Cr-Mo alloy powders in Example 1

[0052]

[0053] It can be seen from Table 2 that the alloy powder has a particle size of 53 to 120 μm, good fluidity and high density.

[0054] The molding structure of the alloy was designed using 3D design software, exported into a rapid prototyping format, imported into a layered slicing software to set parameters for slicing, and slice data was obtained. The designed layer thickness was 70 μm.

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

[0056] Import the slice file into the electron beam 3D printer, and control the electron beam printing software to set the parameters as follows: calibrate the beam current, use manual preheating mode for powder bed preheating, turn on preheating before printing during the printing process, turn on the current gradient climbing function, preheating before printing is five-level preheating, scanning current 20mA, lasting 20s, defocus 0.2, scanning speed 10m / s, post-printing preheating scanning current 10mA, lasting 10s, defocus 0.2, scanning speed 10m / s, scanning current 3mA during printing, scanning speed 0.75m / s.

[0057] The beam calibration process is to adjust the lower 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 lower beam currents.

[0058] The powder is loaded into the powder bin, the bottom plate of the molding bin is leveled, the bottom plate is made of 316L stainless steel, the bin is closed, and the molding chamber is vacuumed to 9.9×10 -3 Pa, the gun chamber is evacuated to 9.9×10 -4 Pa, open the inert gas, fill with helium, and maintain the vacuum degree at 1.6×10 -1 Pa, turn on high voltage 60kV.

[0059] Turn on manual preheating of the base plate, adopt a segmented temperature increase strategy, the defocus amount is 0.2, use a scanning beam of 5mA and a scanning speed of 5m / s to scan the base plate, so that the base plate temperature rises to 250℃, then use a scanning beam of 10mA and a scanning speed of 10m / s to scan the base plate, so that the base plate temperature rises to 380℃, and finally use a scanning beam of 8mA and a scanning speed of 10m / s to scan the vicinity of the base plate for slight adjustments so that the base plate temperature remains near 380℃ (±3℃) for 10min. The entire heating and insulation process does not exceed 30min.

[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 the scanning and melting is completed, use a defocused electron beam to post-heat the powder, the post-preheating parameters are described above, to keep the powder bed temperature at 360-380℃±3℃.

[0061] Repeat powder laying and electron beam printing until all layers of printing are completed, cool naturally to below 60°C under vacuum conditions, turn off the vacuum, fill with a large amount of helium, take out the printed sample, and blow clean to remove excess powder on the surface to obtain a Fe-Cr-Mo alloy sample with a bright surface, no cracks or warping, and a dense internal structure of the sample, basically eliminating defects such as holes, with a density of up to 99.5%.

[0062] The samples obtained by the above printing were subjected to ICP-AES (Inductively coupled plasma atomic emission spectroscopy, abbreviated as ICP-AES) detection. The ICP technology is based on atomizing the sample solution into fine droplets and introducing them into a high-temperature plasma to ionize the elements in the sample and emit characteristic spectra. By detecting and analyzing these spectra, the content of various elements in the sample can be accurately determined. This technology can be used to obtain element loss analysis before and after printing, and the test results are shown in Table 3.

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

[0064]

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

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

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

[0068] The preparation method of Example 1 is beneficial to improving printability by screening the powder of Fe-Cr-Mo alloy and strictly controlling the physical properties of the powder such as particle size, loose density and fluidity.

[0069] The preparation method of Example 1 adopts specific base plate preheating process and powder preheating parameters to avoid the "powder blowing" phenomenon caused by poor powder conductivity, ensuring that the initial layer of Fe-Cr-Mo alloy powder is tightly combined with the substrate and stably formed.

[0070] The preparation method of Example 1 matches reasonable process parameters according to the structure of the three-dimensional digital model, so that the prepared Fe-Cr-Mo alloy can be prepared as a bulk material with high surface quality and high yield, and can inhibit cracking and warping.

[0071] Embodiment 2:

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

[0073] 1. Modify the parameters of the electron beam printing software setting to the following: preheating before printing, scanning current 15mA, lasting 15s, defocusing amount 0.2, scanning speed 10m / s, preheating scanning current 5mA after printing, lasting 5s, defocusing amount 0.2, scanning speed 10m / s, scanning current 5mA and scanning speed 0.9m / s during printing;

[0074] 2. The manual preheating base plate segmented temperature rise strategy is modified as follows: the defocus amount is 0.2, and the base plate is scanned with a scanning beam current of 5mA and a scanning speed of 5m / s to raise the base plate temperature to 250°C. Then, the base plate is scanned with a scanning beam current of 10mA and a scanning speed of 10m / s to raise the base plate temperature to 380°C. Finally, a scanning beam current of 8mA and a scanning speed of 10m / s are used to scan the vicinity of the base plate for slight adjustments so that the base plate temperature is maintained at around 380°C (±3°C) for 20 minutes. The entire heating and insulation process does not exceed 30 minutes.

[0075] The obtained 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 those in Example 1, except that the manual preheating base plate temperature raising strategy is modified to a small current long-term one-time heating to 380°C, specifically: the defocus amount is 0.2, a scanning beam current of 5mA is used, and a scanning speed of 5m / s is used to scan the base plate to raise the temperature to 380°C.

[0078] During the printing process, the lower beam has "powder blowing phenomenon" and cannot print.

[0079] Comparative Example 2:

[0080] The other conditions are the same as those in Example 1, except that the manual preheating base plate temperature raising strategy is modified to a large current short-time one-time heating to 380°C, specifically: the defocus amount is 0.2, a scanning beam current of 10mA is used, and a scanning speed of 10m / s is used to scan the base plate to raise the temperature to 380°C.

[0081] During the printing process, the lower beam has "powder blowing phenomenon" and cannot print.

[0082] Comparative Example 3:

[0083] The other conditions are the same as those in Example 1, except that the manual preheating bottom plate temperature raising strategy is modified as follows: the defocus amount is 0.2, a scanning beam current of 10 mA and a scanning speed of 10 m / s are used to scan the bottom plate to raise the bottom plate temperature to 380°C, and then a scanning beam current of 8 mA and a scanning speed of 10 m / s are used to scan the vicinity of the bottom plate for slight adjustments so that the bottom plate temperature is maintained at around 380°C (±3°C) for 30 minutes.

[0084] During the printing process, an uneven melt pool appeared on the base plate. Some areas of the base plate melted and warped due to concentrated temperature and excessive energy input. The printed samples were rough and melted unevenly. During the sample cleaning process, the base plate and the powder underneath were severely melted and adhered.

[0085] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing Fe-Cr-Mo alloy based on electron beam selective melting technology, characterized in that: include: Model preparation: Use 3D modeling software to build a 3D solid model, slice it, import the sliced ​​file into the electron beam 3D printer, and set the processing parameters; Bottom plate preheating: Under vacuum conditions, first use 3-5mA scanning current to heat the bottom plate to 200-250℃, increase the current intensity to 10-12mA to heat the bottom plate to 360-380℃, and use 5-10mA scanning current to keep the bottom plate at 360-380℃±3℃ for ≥5min; the entire heating and insulation process of the bottom plate preheating shall not exceed 30min; The Fe-Cr-Mo alloy powder is evenly spread on the preheated base plate, and the electron beam printing including the following process is performed: the powder is preheated by using a defocused electron beam, and the powder layer is melted by scanning using a focused electron beam according to the layered scanning data. After the scanning and melting is completed, the powder is post-preheated by using a defocused electron beam to maintain the powder bed temperature at 360-380°C ± 3°C; the scanning current of the pre-preheating and post-preheating of the powder is 5-20mA, the scanning rate is 5-12m / s, and the scanning time is 5-20s; Repeat powder spreading and electron beam printing until all layers are printed. After cooling to a certain temperature under vacuum conditions, turn off the vacuum, fill with inert gas, and take out the Fe-Cr-Mo alloy sample.

2. The method according to claim 1, characterized in that The Fe-Cr-Mo alloy powder is an amorphous alloy powder, and the Fe-Cr-Mo alloy sample is a crystalline alloy sample.

3. The method according to claim 1 or 2, characterized in that: The element composition of the Fe-Cr-Mo alloy powder includes Cr, Mo, B, C and Fe; Taking 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% to 26%, the mass percentage of Mo is 15% to 17%, the mass percentage of B is 1.7% to 2.3%, and the mass percentage of C is 1.7% to 2.3%.

4. The method according to claim 1, characterized in that: The Fe-Cr-Mo alloy powder is prepared by gas atomization method; The particle size of the Fe-Cr-Mo alloy powder is 53 to 120 μm; The fluidity of the Fe-Cr-Mo alloy powder is ≤18.0s / 50g; The bulk density of the Fe-Cr-Mo alloy powder is ≥4.5 g / cm 3 ; The tap density of the Fe-Cr-Mo alloy powder is ≥4g / cm 3 , preferably ≥4.5g / cm 3 .

5. The method according to claim 1, characterized in that The slice thickness is 50 to 80 μm, preferably 70 to 80 μm.

6. The method according to claim 1, characterized in that The scanning rate during electron beam printing is 0.2 to 2 m / s, preferably 0.75 to 1.5 m / s, and the scanning current is 3 to 7 mA, preferably 3 to 5 mA.

7. The method according to claim 1, characterized in that The vacuum condition is: the molding chamber is evacuated to 9.9×10 -3 Pa, the gun chamber is evacuated to 9.9×10 -4 Pa, then fill with inert gas to maintain the vacuum degree at 0.15-0.17Pa.

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

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

2.

10. The method according to claim 1 or 9, characterized in that: The current gradient climbing strategy is enabled for preheating and post-preheating of powder; 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 of the powder post-preheating is 5-10 mA, the scanning rate is 8-12 m / s, and the scanning time is 5-10 s.

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