Microstructure refining method suitable for powder bed type electron beam additive manufacturing niobium-tungsten alloy

Abstract

The invention discloses a microstructure refining method suitable for powder bed type electron beam additive manufacturing niobium-tungsten alloy, which comprises the following steps: adjusting the distribution mode of a tiny molten pool formed after the action of an electron beam and raw material niobium-tungsten alloy powder, and further adjusting the form, temperature gradient and solidification speed of the molten pool; and the microstructure of the niobium-tungsten alloy manufactured by powder bed type electron beam additive manufacturing is changed into a fine strip-shaped structure from a regularly-arranged coarse structure. The powder layer is selectively melted through electron beams, the molten pools are adjusted to be distributed in a discrete mode, the heat influence effect between the continuous molten pools is avoided, the molten pool form is more stable in the molten pool solidification and cooling process, the temperature gradient is reduced, the solidification speed and the cooling speed are increased, and the microscopic structure is effectively refined; the niobium-tungsten alloy with a fine strip structure is obtained, and the mechanical property of the niobium-tungsten alloy is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory metal materials and preparation thereof, and in particular relates to a microstructure refinement method suitable for powder bed type electron beam additive manufacturing of niobium tungsten alloy. Background Art

[0002] Niobium alloy is the material with the lowest density among refractory metals, and its high-temperature performance is better than the widely used nickel-based high-temperature alloys. Among them, the reinforced niobium-tungsten alloy with a combination of solid solution strengthening and precipitation strengthening has an operating temperature of 1200℃~1650℃, can work at 2000℃ for a short time, and has excellent welding performance and room temperature plasticity, making it an ideal high-temperature resistant material. At present, the niobium-tungsten alloy developed in my country has been applied on a large scale in nozzles, ends, fasteners, etc. in the aerospace field. Additive manufacturing technology can realize the integrated near-net forming of complex components, which is conducive to the iteration of design solutions, shortening the product development cycle and improving the manufacturability of the structure, and is very suitable for the forming of complex structures. However, due to the high melting point of refractory metal materials, it is difficult to balance the high energy input and molten pool stability during additive manufacturing, and the forming window is narrow, which makes the application of additive manufacturing refractory metal materials still relatively lagging behind. The results of previous studies have shown that powder bed electron beam additive manufacturing technology has great advantages in the forming of complex components of refractory metal materials such as niobium tungsten alloys due to its high energy, high forming efficiency, low powder cost, more effective control of forming stress, and a vacuum environment that is more conducive to the control of interstitial elements. However, at the same time, due to the high energy input of the heat source, there are problems such as severe epitaxial growth of crystals, excessive temperature, and long high-temperature insulation time during the accumulation of the molten pool. The problem of coarse microstructure is more significant, which seriously affects the mechanical properties of niobium tungsten alloys. The optimization effect of simply adjusting the melting energy and scanning speed is limited. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a microstructure refinement method suitable for powder bed type electron beam additive manufacturing of niobium tungsten alloy in view of the deficiencies of the above-mentioned prior art. The method selectively melts the powder layer with an electron beam, adjusts the molten pool to be discretely distributed, avoids the thermal influence between continuous molten pools, makes the molten pool morphology more stable during the solidification and cooling process of the molten pool, and reduces the temperature gradient, increases the solidification rate and cooling rate, effectively refines the microstructure, and transforms the microstructure of the niobium tungsten alloy manufactured by powder bed type electron beam additive manufacturing from a regularly arranged coarse structure to a fine and long strip structure, solving the problem of continuous melting to form a continuous molten pool in traditional powder bed type additive manufacturing, which produces adverse thermal effects and leads to coarse microstructure of niobium tungsten alloy.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for refining the microstructure of niobium tungsten alloy manufactured by powder bed electron beam additive manufacturing, characterized in that the distribution of tiny molten pools formed after the electron beam acts on the raw material niobium tungsten alloy powder is adjusted, and then the morphology, temperature gradient and solidification rate of the molten pool are adjusted, so that the microstructure of niobium tungsten alloy manufactured by powder bed electron beam additive manufacturing is transformed from a regularly arranged coarse structure to a fine and long strip structure.

[0005] The present invention has found that the traditional powder bed additive manufacturing technology mainly uses high-energy beams to continuously melt metal powders along a specific path. Continuous fine metal molten pools form scanning lines, which are formed by continuous accumulation point by point, line by line, and surface by surface. Therefore, for some high-melting point metal materials, the traditional melting method is very easy to form coarse structures, affecting the alloy properties. The present invention aims at the problem of coarse microstructures that are prone to occur when manufacturing refractory metal materials such as niobium tungsten alloys using powder bed electron beam additive manufacturing. The present invention improves the microstructure of niobium tungsten alloys in additive manufacturing by changing the superposition method of the molten pool, that is, by adjusting the distribution of the tiny molten pools formed after the electron beam and the raw material niobium tungsten alloy powder, and then adjusting the morphology, temperature gradient and solidification rate of the molten pool. Specifically, the present invention selectively melts a single layer of powder, sets a single melting point on the scanning path and performs electron beam melting scanning at the single point, thereby forming a single independent molten pool. Since the heating effect of the latter melting point on the previous melting point is limited, the thermal influence between the continuous adjacent molten pools is effectively avoided. Each molten pool completes the melting and solidification process independently, so the molten pool morphology during the molten pool solidification and cooling process is more stable, and the temperature gradient is reduced, the solidification rate and the cooling rate are increased, and the microstructure of the niobium tungsten alloy is effectively refined. The melting mode of each single layer of powder is the same, and the organization of each corresponding single layer of solid sheet is refined, so that the microstructure of the niobium tungsten alloy manufactured by the powder bed type electron beam additive manufacturing is transformed from a regularly arranged coarse organization to a fine and long strip organization. At the same time, in the traditional continuous melting of metal powder, when the melting area changes, the scanning line length changes significantly, and the cumulative temperature change will affect the temperature field balance of the entire melting plane. For niobium tungsten alloys with higher melting points, the imbalance is more significant. The present invention ensures the consistency of individual energy of a single molten pool through the discrete distribution of the molten pool, and prevents local overmelting during the forming process of the niobium-tungsten alloy. In addition, the present invention achieves uniform and high-quality overlap of the niobium-tungsten alloy molten pool through the discrete superposition of the molten pool, avoids insufficient overlap caused by spheroidization of the molten pool during continuous scanning, and further improves the quality of the niobium-tungsten alloy.

[0006] The above-mentioned microstructure refinement method suitable for powder bed type electron beam additive manufacturing of niobium tungsten alloy is characterized in that a three-dimensional model is first established according to the target product niobium tungsten alloy, and the three-dimensional model is layered, and then the raw material niobium tungsten alloy powder is laid according to the thickness of each layer to form a powder layer, and then the single layer of powder layer is selectively melted by an electron beam to form a single layer of solid sheet after solidification, and the powder laying-melting-solidification process is repeated until each single layer of solid sheet is accumulated to obtain niobium tungsten alloy.

[0007] The above-mentioned microstructure refinement method applicable to powder bed type electron beam additive manufacturing of niobium tungsten alloy is characterized in that, in the process of adjusting the distribution mode of the micro molten pool, the melting process of the single layer of powder layer includes the following steps:

[0008] Step 1: First, design a scanning path for a single powder layer, and sequentially set melting point 1, melting point 2, ..., melting point n along the scanning path, wherein the melting points of melting point 1 to melting point n are equally spaced, and the spacing distance is d;

[0009] Then, the electron beam is moved to the melting point 1, and the electron beam is turned on. The electron beam stays at the melting point 1 and melts the niobium-tungsten alloy powder at the melting point 1 to form a small molten pool. After the electron beam is turned off, the small molten pool gradually solidifies to form a solid.

[0010] Continue to move the electron beam to the melting point 2, turn on the electron beam, stay at the melting point 2 and melt the niobium tungsten alloy powder at the melting point 2 to form a small molten pool, and then turn off the electron beam, and the small molten pool gradually solidifies to form a solid;

[0011] According to the melting mode of melting point 1 and melting point 2, the melting operation is carried out in sequence along the designed scanning path until the niobium tungsten alloy powder at the melting point n is completely melted and solidified, and the first round of melting and solidification process is completed;

[0012] Step 2: along the melting point 1 to the melting point n on the scanning path, melting point n+1, melting point n+2, ..., melting point 2n are set in sequence at an interval distance m, and the intervals between the melting points of melting point n+1 to melting point 2n are equal, and the interval distances are equal to the intervals between the melting points of melting point 1 to melting point n in step 1, which are all d. Then, according to the first round of melting and solidification process in step 1, the niobium tungsten alloy powder at the melting point n+1 to the melting point 2n is melted and solidified by an electron beam in sequence, and the second round of melting and solidification process is completed at this time;

[0013] Step 3: Melting point 2n+1, melting point 2n+2, ..., melting point 3n are set at intervals of m along the melting point n+1 to melting point 2n on the scanning path. The intervals between the melting points of melting point 2n+1 to melting point 3n are equal, and the interval distances are equal to the intervals between the melting points of melting point 1 to melting point n in step 1 and the intervals between the melting points of melting point n+1 to melting point 2n in step 2, which are all d. Then, according to the first round of melting process in step 1, an electron beam is used to melt and solidify the niobium tungsten alloy powder at melting point 2n+1 to melting point 3n in sequence, and the third round of melting and solidification process is completed at this time;

[0014] Step 4: According to the methods in step 2 and step 3, the melting point is set and the niobium tungsten alloy powder at the melting point is melted and solidified in sequence until the Nth round of melting and solidification process is completed, and N=d / m+1, at which time the melting forming process of the single layer of powder is completed.

[0015] The present invention sets melting points in sequence on the scanning path and designs the position regularity of the melting points as above, so that the molten pool is discretely distributed along the scanning path and superimposed in an interval jump manner, thereby effectively controlling the molten pool distribution and facilitating the regulation of the molten pool morphology, temperature gradient, solidification rate and cooling rate during the molten pool solidification and cooling process, thereby achieving control over the degree of microstructure refinement of the niobium tungsten alloy.

[0016] The above method is characterized in that the current when the electron beam is melted and retained in step 1 to step 3 is 20mA to 25mA, the electron beam retention time is 0.0001s to 0.0003s, and the moving speed of the electron beam between the melting points is 300mm / s to 1000mm / s. The present invention selects the above melting current and electron beam retention time according to the energy input required at the melting point of the niobium tungsten alloy powder to ensure that the niobium tungsten alloy powder at each melting point is smoothly melted to form a micro molten pool.

[0017] The above method is characterized in that the scanning path designed in step one is in the shape of a U-shape, that is, the electron beam moves toward the center in the shape of a U-shape along the outer contour of the scanning plane of the single-layer powder layer, and the spacing of the U-shaped scanning path is 0.05mm to 0.15mm.

[0018] The above method is characterized in that the distance d between the melting points 1 to n in step 1, the distance d between the melting points n+1 to 2n in step 2, and the distance d between the melting points 2n+1 to 3n in step 3 are all 1 mm to 3 mm.

[0019] The above method is characterized in that the interval distance m of setting the melting points in step 2 and step 3 is 0.05 mm to 0.15 mm.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The present invention adjusts the distribution of tiny molten pools formed after the electron beam acts on the raw material niobium tungsten alloy powder, so that the molten pools become separate and independent individuals and are discretely distributed, thereby avoiding the thermal influence between continuous adjacent molten pools. The molten pool morphology during the solidification and cooling process of the molten pool is more stable, and the temperature gradient is reduced, the solidification rate and the cooling rate are increased, and the microstructure of the niobium tungsten alloy is effectively refined, so that the microstructure of the niobium tungsten alloy manufactured by the powder bed type electron beam additive manufacturing is transformed from a regularly arranged coarse structure to a fine and long strip structure, thereby improving the mechanical properties of the niobium tungsten alloy.

[0022] 2. The present invention ensures the consistency of energy of a single molten pool by adjusting the molten pool to be discretely distributed, thereby avoiding the uneven temperature field and local over-melting during the forming process caused by the change in the scanning line length formed by traditional continuous melting.

[0023] 3. The present invention achieves uniform and high-quality overlap of the niobium-tungsten alloy molten pool by adjusting the discrete distribution of the molten pool and then superimposing it, avoiding insufficient overlap caused by spheroidization of the molten pool during continuous scanning, ensuring the smooth progress of the additive manufacturing process, and further improving the quality of the niobium-tungsten alloy.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the melting process of a single powder layer in the present invention.

[0026] Figure 2 This is the microstructure diagram of the niobium tungsten alloy prepared in Example 1 of the present invention.

[0027] Figure 3 This is a microstructure diagram of the niobium tungsten alloy prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0028] Example 1

[0029] This embodiment includes the following steps: first, a three-dimensional model with a length × width × height of 10mm × 10mm × 10mm is established according to the target product niobium tungsten alloy, and the three-dimensional model is layered, and the thickness of each layer is 0.05mm, and then the three-dimensional model is introduced into a powder bed electron beam additive manufacturing device, and the raw material niobium tungsten alloy powder is loaded into the powder bin of the device, and then the raw material niobium tungsten alloy powder is laid according to the thickness of each layer to form a powder layer, and an electron beam is used to selectively melt the single-layer powder layer to form a single-layer solid sheet after solidification, and the powder laying-melting-solidification process is repeated until each single-layer solid sheet is accumulated to obtain a niobium tungsten alloy block.

[0030] like Figure 1 As shown, in the process of adjusting the distribution of the micro-molten pools, the melting process of the single powder layer includes the following steps:

[0031] Step 1: First, the scanning path of the single-layer powder layer is designed to be in the shape of a U-shaped letter "Hu". That is, the electron beam moves toward the center along the outer contour of the scanning plane of the single-layer powder layer in the shape of a U-shaped letter "Hu". The spacing of the U-shaped scanning path is 0.05 mm, and the total length is about 2020 mm. Melting point 1, melting point 2, ..., melting point 2020 are sequentially set along the scanning path. The melting points of melting point 1 to melting point 2020 are equally spaced, and the spacing distance is 1 mm.

[0032] Then, the electron beam is moved to the melting point 1, and the electron beam is turned on. The electron beam stays at the melting point 1 and melts the niobium-tungsten alloy powder at the melting point 1 to form a small molten pool. After the electron beam is turned off, the small molten pool gradually solidifies to form a solid.

[0033] Continue to move the electron beam to the melting point 2, turn on the electron beam, stay at the melting point 2 and melt the niobium tungsten alloy powder at the melting point 2 to form a small molten pool, and then turn off the electron beam, and the small molten pool gradually solidifies to form a solid;

[0034] According to the melting method of melting point 1 and melting point 2, the melting operation is carried out in sequence along the designed scanning path until the niobium tungsten alloy powder at the melting point 2020 is melted and solidified, and the first round of melting and solidification process is completed;

[0035] Step 2: Melting point 2021, melting point 2022, ..., melting point 4040 are set in sequence along the melting point 1 to the melting point 2020 on the scanning path at an interval of 0.05 mm. The melting points of the melting points 2021 to the melting point 4040 are equally spaced and have an interval of 1 mm. Then, according to the first round of melting and solidification process in step 1, the niobium tungsten alloy powder at the melting points 2021 to the melting points 4040 is melted and solidified by an electron beam in sequence. At this time, the second round of melting and solidification process is completed;

[0036] Step 3: Melting point 4041, melting point 4042, ..., melting point 6060 are set at intervals of 0.05 mm along the melting point n+1 to melting point 2n on the scanning path. The melting points 4041 to 6060 are equally spaced and have an interval of 1 mm. Then, according to the first round of melting process in step 1, the niobium tungsten alloy powder at the melting points 4041 to 6060 is melted and solidified by an electron beam in sequence. At this time, the third round of melting and solidification process is completed;

[0037] Step 4: According to the methods in step 2 and step 3, the melting point is set and the niobium tungsten alloy powder at the melting point is melted and solidified in sequence until the 21st round of melting and solidification process is completed. At this time, the melting forming process of the single powder layer is completed;

[0038] The current during the electron beam melting dwelling in step 1 to step 3 is 20 mA, the electron beam dwelling time is 0.0001 s, and the moving speed of the electron beam between the melting points is 300 mm / s.

[0039] Comparative Example 1

[0040] The difference between this comparative example and Example 1 is that an electron beam is directly used to continuously melt a single powder layer to form a single solid sheet layer.

[0041] Figure 2 This is the microstructure diagram of the niobium tungsten alloy prepared in Example 1 of the present invention. Figure 3 This is the microstructure diagram of the niobium tungsten alloy prepared in Comparative Example 1 of the present invention. Figure 2 and Figure 3 It can be seen that the microstructure of the niobium tungsten alloy in Comparative Example 1 is a coarse equiaxed structure with a grain size of about 0.25 mm, and the microstructure of the niobium tungsten alloy in Example 1 is transformed into a fine strip-shaped structure with a strip width of only about 0.05 mm, indicating that the method of the present invention effectively refines the microstructure of the niobium tungsten alloy.

[0042] Example 2

[0043] This embodiment includes the following steps: first, a three-dimensional model with a length × width × height of 10mm × 10mm × 10mm is established according to the target product niobium tungsten alloy, and the three-dimensional model is layered, and the thickness of each layer is 0.05mm, and then the three-dimensional model is introduced into a powder bed electron beam additive manufacturing device, and the raw material niobium tungsten alloy powder is loaded into the powder bin of the device, and then the raw material niobium tungsten alloy powder is laid according to the thickness of each layer to form a powder layer, and an electron beam is used to selectively melt the single-layer powder layer to form a single-layer solid sheet after solidification, and the powder laying-melting-solidification process is repeated until each single-layer solid sheet is accumulated to obtain a niobium tungsten alloy block.

[0044] like Figure 1 As shown, in the process of adjusting the distribution of the micro-molten pools, the melting process of the single powder layer includes the following steps:

[0045] Step 1: First, the scanning path of the single-layer powder layer is designed to be in the shape of a U-shaped letter "Hu". That is, the electron beam moves toward the center along the outer contour of the scanning plane of the single-layer powder layer in the shape of a U-shaped letter "Hu". The spacing of the U-shaped scanning path is 0.15 mm, and the total length is about 2033 mm. Melting point 1, melting point 2, ..., melting point 677 are sequentially set along the scanning path. The melting points of melting point 1 to melting point 677 are equally spaced, and the spacing distance is 3 mm.

[0046] Then, the electron beam is moved to the melting point 1, and the electron beam is turned on. The electron beam stays at the melting point 1 and melts the niobium-tungsten alloy powder at the melting point 1 to form a small molten pool. After the electron beam is turned off, the small molten pool gradually solidifies to form a solid.

[0047] Continue to move the electron beam to the melting point 2, turn on the electron beam, stay at the melting point 2 and melt the niobium tungsten alloy powder at the melting point 2 to form a small molten pool, and then turn off the electron beam, and the small molten pool gradually solidifies to form a solid;

[0048] According to the melting method of melting point 1 and melting point 2, the melting operation is carried out in sequence along the designed scanning path until the niobium tungsten alloy powder at the melting point 677 is melted and solidified, and the first round of melting and solidification process is completed;

[0049] Step 2: Melting point 678, melting point 679, ..., melting point 1354 are set in sequence along the melting point 1 to melting point 677 on the scanning path at an interval of 0.15 mm. The melting points of melting point 678 to melting point 1354 are equally spaced and have an interval of 3 mm. Then, according to the first round of melting and solidification process in step 1, the niobium tungsten alloy powder at melting point 678 to melting point 1354 is melted and solidified by an electron beam in sequence. At this time, the second round of melting and solidification process is completed;

[0050] Step 3: Melting points 1355, 1356, ..., 2031 are set at intervals of 0.15 mm along the melting points 678 to 1354 on the scanning path. The melting points 1355 to 2031 are spaced equally and at an interval of 3 mm. Then, according to the first round of melting process in step 1, the niobium-tungsten alloy powder at the melting points 1355 to 2031 is melted and solidified by an electron beam in sequence. At this time, the third round of melting and solidification process is completed;

[0051] Step 4: According to the methods in step 2 and step 3, the melting point is set and the niobium tungsten alloy powder at the melting point is melted and solidified in sequence until the 21st round of melting and solidification process is completed. At this time, the melting forming process of the single powder layer is completed;

[0052] The current during the electron beam melting dwelling in step 1 to step 3 is 25 mA, the electron beam dwelling time is 0.0003 s, and the moving speed of the electron beam between the melting points is 1000 mm / s.

[0053] Example 3

[0054] This embodiment includes the following steps: first, a three-dimensional model with a length × width × height of 10mm × 10mm × 10mm is established according to the target product niobium tungsten alloy, and the three-dimensional model is layered, and the thickness of each layer is 0.05mm, and then the three-dimensional model is introduced into a powder bed electron beam additive manufacturing device, and the raw material niobium tungsten alloy powder is loaded into the powder bin of the device, and then the raw material niobium tungsten alloy powder is laid according to the thickness of each layer to form a powder layer, and an electron beam is used to selectively melt the single-layer powder layer to form a single-layer solid sheet after solidification, and the powder laying-melting-solidification process is repeated until each single-layer solid sheet is accumulated to obtain a niobium tungsten alloy block.

[0055] like Figure 1 As shown, in the process of adjusting the distribution of the micro-molten pools, the melting process of the single powder layer includes the following steps:

[0056] Step 1: First, the scanning path of the single-layer powder layer is designed to be in the shape of a U-shaped letter "Hu". That is, the electron beam moves toward the center along the outer contour of the scanning plane of the single-layer powder layer in the shape of a U-shaped letter "Hu". The spacing of the U-shaped scanning path is 0.1 mm, and the total length is about 808 mm. Melting point 1, melting point 2, ..., melting point 404 are sequentially set along the scanning path. The melting points of melting point 1 to melting point 404 are equally spaced, and the spacing distance is 2 mm.

[0057] Then, the electron beam is moved to the melting point 1, and the electron beam is turned on. The electron beam stays at the melting point 1 and melts the niobium-tungsten alloy powder at the melting point 1 to form a small molten pool. After the electron beam is turned off, the small molten pool gradually solidifies to form a solid.

[0058] Continue to move the electron beam to the melting point 2, turn on the electron beam, stay at the melting point 2 and melt the niobium tungsten alloy powder at the melting point 2 to form a small molten pool, and then turn off the electron beam, and the small molten pool gradually solidifies to form a solid;

[0059] According to the melting mode of melting point 1 and melting point 2, the melting operation is performed in sequence along the designed scanning path until the niobium tungsten alloy powder at the melting point 404 is completely melted and solidified, and the first round of melting and solidification process is completed;

[0060] Step 2: Melting point 405, melting point 406, ..., melting point 808 are set in sequence along the melting point 1 to melting point 404 on the scanning path at an interval of 0.1 mm. The melting points of melting point 404 to melting point 808 are equally spaced and have an interval of 2 mm. Then, according to the first round of melting and solidification process in step 1, the niobium tungsten alloy powder at melting point 404 to melting point 808 is melted and solidified by an electron beam in sequence. At this time, the second round of melting and solidification process is completed;

[0061] Step 3: Melting points 809, 810, ..., 1212 are set at intervals of 0.1 mm along the melting points 404 to 808 on the scanning path. The melting points 809 to 1212 are spaced equally and at an interval of 2 mm. Then, according to the first round of melting process in step 1, the niobium-tungsten alloy powder at the melting points 809 to 1212 is melted and solidified by an electron beam in sequence. At this time, the third round of melting and solidification process is completed;

[0062] Step 4: According to the methods in step 2 and step 3, the melting point is set and the niobium tungsten alloy powder at the melting point is melted and solidified in sequence until the 21st round of melting and solidification process is completed. At this time, the melting forming process of the single powder layer is completed;

[0063] The current during the electron beam melting dwelling in step 1 to step 3 is 21 mA, the electron beam dwelling time is 0.0002 s, and the moving speed of the electron beam between the melting points is 500 mm / s.

[0064] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A microstructure refinement method for powder bed type electron beam additive manufacturing of niobium tungsten alloy, characterized in that: By adjusting the distribution of the tiny molten pool formed by the action of the electron beam and the raw material niobium tungsten alloy powder, and then adjusting the molten pool's morphology, temperature gradient and solidification rate, the microstructure of the niobium tungsten alloy manufactured by powder bed electron beam additive manufacturing is transformed from a regularly arranged coarse structure to a fine and long strip structure.

2. A microstructure refinement method for powder bed electron beam additive manufacturing of niobium tungsten alloy according to claim 1, characterized in that: Firstly, a three-dimensional model is established according to the target product niobium tungsten alloy, and the three-dimensional model is layered. Then, the raw material niobium tungsten alloy powder is laid according to the thickness of each layer to form a powder layer. Then, an electron beam is used to selectively melt the single powder layer, and a single solid sheet is formed after solidification. The powder laying-melting-solidification process is repeated until each single solid sheet is accumulated to obtain niobium tungsten alloy.

3. The microstructure refinement method for powder bed electron beam additive manufacturing of niobium tungsten alloy according to claim 1, characterized in that: In the process of adjusting the distribution of the micro-molten pools, the melting process of the single powder layer includes the following steps: Step 1: First, design a scanning path for a single powder layer, and sequentially set melting point 1, melting point 2, ..., melting point n along the scanning path, wherein the melting points of melting point 1 to melting point n are equally spaced, and the spacing distance is d; Then, the electron beam is moved to the melting point 1, and the electron beam is turned on. The electron beam stays at the melting point 1 and melts the niobium-tungsten alloy powder at the melting point 1 to form a small molten pool. After the electron beam is turned off, the small molten pool gradually solidifies to form a solid. Continue to move the electron beam to the melting point 2, turn on the electron beam, stay at the melting point 2 and melt the niobium tungsten alloy powder at the melting point 2 to form a small molten pool, and then turn off the electron beam, and the small molten pool gradually solidifies to form a solid; According to the melting mode of melting point 1 and melting point 2, the melting operation is carried out in sequence along the designed scanning path until the niobium tungsten alloy powder at the melting point n is completely melted and solidified, and the first round of melting and solidification process is completed; Step 2: along the melting point 1 to the melting point n on the scanning path, melting point n+1, melting point n+2, ..., melting point 2n are set in sequence at an interval distance m, and the intervals between the melting points of melting point n+1 to melting point 2n are equal, and the interval distances are equal to the intervals between the melting points of melting point 1 to melting point n in step 1, which are all d. Then, according to the first round of melting and solidification process in step 1, the niobium tungsten alloy powder at the melting point n+1 to the melting point 2n is melted and solidified by an electron beam in sequence, and the second round of melting and solidification process is completed at this time; Step 3: Melting point 2n+1, melting point 2n+2, ..., melting point 3n are set at intervals of m along the melting point n+1 to melting point 2n on the scanning path. The intervals between the melting points of melting point 2n+1 to melting point 3n are equal, and the interval distances are equal to the intervals between the melting points of melting point 1 to melting point n in step 1 and the intervals between the melting points of melting point n+1 to melting point 2n in step 2, which are all d. Then, according to the first round of melting process in step 1, an electron beam is used to melt and solidify the niobium tungsten alloy powder at melting point 2n+1 to melting point 3n in sequence, and the third round of melting and solidification process is completed at this time; Step 4: According to the methods in step 2 and step 3, the melting point is set and the niobium tungsten alloy powder at the melting point is melted and solidified in sequence until the Nth round of melting and solidification process is completed, and N=d / m+1, at which time the melting forming process of the single layer of powder is completed.

4. The method according to claim 3, characterized in that The current during the electron beam melting dwelling in steps 1 to 3 is 20 mA to 25 mA, the electron beam dwelling time is 0.0001 s to 0.0003 s, and the moving speed of the electron beam between the melting points is 300 mm / s to 1000 mm / s.

5. The method according to claim 3, characterized in that: The scanning path designed in step one is in the shape of a U-shaped letter "Z". That is, the electron beam moves toward the center in the shape of a U-shaped letter "Z" along the outer contour of the scanning plane of the single powder layer. The spacing of the U-shaped scanning path is 0.05 mm to 0.15 mm.

6. The method according to claim 3, characterized in that The distance d between the melting points 1 to n in step 1, the distance d between the melting points n+1 to 2n in step 2, and the distance d between the melting points 2n+1 to 3n in step 3 are all 1 mm to 3 mm.

7. The method according to claim 3, characterized in that The interval m of setting the melting points in step 2 and step 3 is 0.05 mm to 0.15 mm.

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