A method of additive manufacturing of large size niobium 521 alloy

Abstract

This invention discloses a method for additive manufacturing of large-size niobium 521 alloy, belonging to the field of refractory metal additive manufacturing technology. The method includes: fixing a substrate on the forming platform of a selective laser melting device; performing a first-stage layer printing, stopping printing and cooling after reaching a preset height threshold to form a pre-formed semi-finished product; sending the substrate and the pre-formed semi-finished product as a whole into a vacuum heat treatment furnace for stress-relief annealing, followed by furnace cooling to room temperature; repositioning the annealed substrate back onto the forming platform, spreading powder, and performing the next stage of layer printing; repeating the above steps of segmented printing, stress-relief annealing, and resetting to continue printing until the entire component is printed. This invention, through segmented printing and intermediate stress-relief annealing cycles, releases accumulated stress step by step, which can suppress cracking and warping defects and improve the yield.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology for refractory metals, and more particularly to a method for additive manufacturing of large-size niobium 521 alloy. Background Technology

[0002] Niobium 521 refractory alloy has the characteristics of ultra-high melting point, excellent high temperature creep strength and resistance to high temperature gas corrosion, and is the core material for combustion chambers, thrust nozzles and high temperature guide components of aerospace power systems.

[0003] Niobium-521 alloy is a high-melting-point refractory metal. When using selective laser melting additive manufacturing to prepare large-size, complex cavity structural parts, delamination and edge warping deformation are very likely to occur in the middle of the printed large-size workpiece; thus, it is impossible to achieve mass production of large-size, long-stroke niobium-521 structural parts for aero-engines. Niobium 521 spherical powder raw material is expensive, and scrapping a single whole print run would result in a huge waste of materials. Summary of the Invention

[0004] Based on the above analysis, the purpose of this invention is to provide a method for additive manufacturing of large-size niobium 521 alloy, which solves one of the problems in the prior art, such as cracking and warping of large-size niobium 521 alloy components, low yield, waste of raw materials, and difficulty in mass production of large-size components.

[0005] On one hand, the present invention provides a method for additive manufacturing of large-size niobium 521 alloy, comprising the following steps: S1. Substrate selection and clamping; S2. Import the 3D slice model of the component and complete the first layer printing. Stop printing and cool when the printing height reaches the preset height threshold to form a semi-finished product. S3. The substrate and the formed semi-finished product are then subjected to stress-relief annealing. After annealing, the substrate is cooled to room temperature in the furnace. S4. Next, the annealed substrate is reset and leveled; S5. Re-spread powder onto the top layer of the already formed semi-finished product and continue printing; S6. Print in segments, anneal, reset, continue printing until the entire component is printed.

[0006] Further, in S1, the substrate is selected from a tantalum substrate, a tantalum 2.5 tungsten substrate, or a tantalum 10 tungsten substrate.

[0007] Furthermore, in step S2, the laser power for the layered printing is 265-450W, the laser scanning speed is 550-680mm / s, the laser scanning spacing is 0.09-0.12mm, and the powder layer thickness is 0.028~0.03mm.

[0008] Furthermore, in S2, the preset height threshold for pausing is determined based on the printed volume of the component: when the continuous solid volume is 30-40 cm³, the preset height threshold for pausing is 50-80 mm; when the continuous solid volume is 10-20 cm³, the preset height threshold for pausing is 100-140 mm.

[0009] Furthermore, in step S3, the stress-relief annealing temperature is 900-1450℃, and the holding time is 60-120min.

[0010] Furthermore, in S4, when re-clamping and positioning after annealing, a dual method of height caliper measurement and reference angle alignment is used to reset and position the substrate, so that the substrate clamping position completely coincides with that of the first printing.

[0011] Furthermore, in step S4, after re-clamping and positioning, a small leveling process is performed on the top printed surface of the formed semi-finished product.

[0012] Furthermore, in S5, before printing the next segment, the segment continuation interface area is subjected to at least two repeated laser scans.

[0013] Furthermore, in step S6, the overall annealing temperature after the overall printing is completed is 1400-1450℃, and the holding time is 60-120min.

[0014] On the other hand, the present invention provides a large-size niobium 521 alloy obtained by the additive manufacturing method of large-size niobium 521 alloy described in any of the above claims, wherein the large-size niobium 521 alloy has a tensile strength Rm≥563.3MPa, a yield strength Rp0.2≥399.9 MPa, and an elongation after fracture A≥21.5%.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. This invention controls the printing height in segments according to a preset height threshold, limiting the stress accumulation in a single segment. After each segment is completed, the substrate and the formed semi-finished product are annealed as a whole. An overall stress-relief annealing process is set between segments to achieve phased release of printing stress. By eliminating the accumulated thermal stress and interlayer stress in this segment through stress-relief annealing, interlayer cracking and edge warping defects in large-sized components are suppressed from the source. This can improve the yield of large-sized niobium 521 alloy components and reduce material waste. Through segmented printing and intermediate annealing cycles, the limitation of component height on single continuous printing is broken, enabling the forming of ultra-long, large-sized integrated niobium 521 alloy components, meeting the mass production needs of large-sized components.

[0016] 2. This invention incorporates an overall stress-relief annealing process between segments to achieve phased release of printing stress. Segmented printing confines stress defects to a single segment. Combined with micro-leveling at the joint interface and repeated laser scanning to strengthen the metallurgical bond, it avoids the expansion of defects across segments. This solves the technical problem of high unit price of niobium 521 spherical powder raw material and serious material waste caused by overall scrapping.

[0017] 3. The substrate of this invention is annealed as a whole with the workpiece and a tantalum or tantalum-tungsten series high-temperature resistant substrate is selected. Its annealing temperature is matched with that of niobium 521 alloy. It does not deform at high temperature and does not react with the workpiece at the interface. This can avoid the impact of high temperature deformation of the substrate on the dimensional accuracy of the workpiece, ensure the continuous and uniform size of the segmented printing, and help to realize the mass production of large-size components.

[0018] 4. The large-size niobium 521 alloy of the present invention has a tensile strength Rm≥563.3MPa, a yield strength Rp0.2≥399.9MPa, and an elongation after fracture A≥21.5%.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 Flowchart of segmented printing and mid-process stress-relief annealing cycle process; Figure 2 The image is a screenshot of the actual product. Figure 3 The physical image is used to support the interface after annealing. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] Niobium-521 alloy is a high-melting-point refractory metal. When using selective laser melting additive manufacturing to prepare large-size, complex cavity structures, existing technologies have the following shortcomings: (1) Niobium 521 has a high melting point. The laser melting and rapid cooling process will generate a huge temperature gradient. As the printing height increases, the internal stress of the component continues to accumulate. Large-sized workpieces are prone to delamination and corner warping deformation in the middle section of printing. Due to the limitation of stress cracking, the existing process can only prepare small sample parts with small height dimensions, and cannot realize the mass production of large-sized, long-stroke niobium 521 structural parts for aero-engines. (2) Niobium 521 spherical powder raw material has a high unit price, and the overall scrapping leads to serious material waste.

[0024] Compared with existing technologies, this invention adopts a cyclic process that combines segmented printing with mid-process stress-relief annealing. After printing to a specified height, processing is paused, and the substrate and the formed semi-finished product are annealed as a whole to eliminate accumulated internal stress. Then, the substrate is re-clamped and printing continues. This cycle is repeated until the workpiece is fully formed, reducing printing stress from the source and suppressing cracking and warping defects. This can improve the yield of large-size niobium 521 alloy components and avoid material waste. Moreover, multiple annealing cycles do not damage the mechanical properties of the alloy matrix. The mechanical properties of the continued printing area are consistent with the base material, which can stably meet the usage requirements of high-temperature aerospace components.

[0025] Specifically, this invention provides a method for additive manufacturing of large-size niobium 521 alloy, comprising the following steps: S1. Substrate selection and clamping; S2. Import the 3D slice model of the component and complete the first layer printing. Stop printing and cool when the printing height reaches the preset height threshold to form a semi-finished product. S3. The substrate and the formed semi-finished product are then subjected to stress-relief annealing. After annealing, the substrate is cooled to room temperature in the furnace. S4. Next, the annealed substrate is reset, leveled, and prepared for further processing; S5. Re-spread powder onto the top layer of the already formed semi-finished product and continue printing; S6. Print in segments, anneal, reset, continue printing until the entire component is printed.

[0026] Furthermore, in S1, the substrate is selected from one of a tantalum substrate, a tantalum 2.5 tungsten substrate, or a tantalum 10 tungsten substrate.

[0027] Specifically, this type of substrate is resistant to high temperatures, its annealing temperature matches that of niobium 521 alloy, it does not deform at high temperatures and does not react with the workpiece at the interface.

[0028] Furthermore, in S1, the substrate is first fixed on the molding platform, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0029] By recording the original height coordinates and clamping angle reference of the substrate, a positioning basis is provided for the accurate repositioning of the substrate after annealing, ensuring that the segmented continuous bonding positions are completely coincident and the dimensions are continuous and uniform.

[0030] Furthermore, in S2, the preset height threshold for pausing is determined based on the printed volume of the component: when the continuous solid volume is 30-40 cm³, the preset height threshold for pausing is 50-80 mm; when the continuous solid volume is 10-20 cm³, the preset height threshold for pausing is 100-140 mm.

[0031] The segmentation should be based on the difference in stress accumulation rate per unit height. For components with large volume and many continuous solids, the cladding volume per unit height is large and the stress accumulates quickly. Using a lower pause height allows for timely interruption of printing and annealing, keeping the stress in a single segment within a safe range. For components with smaller volume, the stress accumulation is relatively slower. Using a higher pause height can reduce the number of annealing cycles and improve printing efficiency, thus achieving a balance between the number of segments and production efficiency while ensuring no cracking. If the pause height for large-volume components is too high (e.g., exceeding 80mm), the stress accumulation in a single segment will be too large, and delamination or warping may occur before annealing, negating the purpose of segmented annealing. If the pause height for small-volume components is too low (e.g., below 100mm), there will be too many annealing cycles, prolonging the production cycle and increasing energy consumption. Therefore, when the component printing volume is 30cm³ to 40cm³, the preset height threshold for pausing is 50mm to 80mm, for example 50mm, 60mm, 70mm, and 80mm; when the component printing volume is 10cm³ to 20cm³, the preset height threshold for pausing is 100mm to 140mm, for example 100mm, 110mm, 120mm, and 140mm.

[0032] Furthermore, in S2, the laser power for layer printing is 265W to 450W, the laser scanning speed is 550mm / s to 680mm / s, the laser scanning spacing is 0.09mm to 0.12mm, and the powder layer thickness is 0.028 to 0.03mm.

[0033] Furthermore, in S2, the niobium 521 alloy spherical powder of the raw material has a particle size of 15~53μm.

[0034] The laser-assisted layered printing achieves a stable molten pool, complete powder melting, good interlayer metallurgical bonding, and controllable stress in each segment, thus providing a qualified semi-finished product foundation for subsequent segmented annealing and continuous printing. This power range provides a suitable energy density for the niobium-521 alloy; at this speed range, the molten pool duration is moderate, allowing the powder to fully melt and form a good metallurgical bond with the previous layer, while avoiding excessive heat input, grain coarsening, or increased residual stress due to excessively slow speeds; at this spacing range, the coating has high internal density and strong interlayer bonding. During segmented continuous printing, this spacing also provides a good overlap basis for repeated scanning of the continuous printing interface; this layer thickness is a relatively thin powder layer, ensuring that the laser energy penetrates the powder layer and fully melts it, while also resulting in a fine and dense microstructure after solidification. If the laser power is too low, the scanning speed is too slow, the spacing is too small, or the powder thickness is too thin, it will lead to defects such as incomplete fusion and spheroidization, resulting in a decrease in the density of the molded part, insufficient interlayer bonding strength, and weak bonding at the joint interface. If the laser power is too high, the scanning speed is too fast, the spacing is too large, or the powder thickness is too thick, it can cause the burning of low-melting-point elements, aggravate molten pool splashing, and significantly increase the residual stress of a single layer, which will increase the risk of cracking. Therefore, the laser power for layer printing is 265W to 450W, with examples being 265W, 300W, 350W, 400W, and 450W; the laser scanning speed is 550mm / s to 680mm / s, with examples being 550mm / s, 600mm / s, and 680mm / s; the laser scanning spacing is 0.09mm to 0.12mm, with examples being 0.09mm, 0.10mm, and 0.12mm; and the powder layer thickness is 0.028 to 0.03mm, with examples being 0.028mm, 0.029mm, and 0.03mm.

[0035] The particle size range balances good flowability and powder uniformity, ensuring that laser energy fully penetrates and melts the powder layer, resulting in a continuous and dense single-layer melt channel, good interlayer metallurgical bonding, and a smooth surface at the segmented junction interface, as well as reliable repeated scanning strengthening effect. If the particle size is too small, the powder is prone to agglomeration and poor flowability, leading to unevenness or splashing during powder spreading, and the increased specific surface area results in higher oxygen content, affecting the molding quality. If the particle size is too large, the powder layer is too thick, making it difficult for the laser to completely melt, easily generating unfused pores and spheroidization defects, reducing the interlayer bonding strength, especially at the segmented junction interface, where weak bonding zones are easily formed, ultimately leading to the component's density and mechanical properties failing to meet standards. Therefore, the niobium 521 alloy spherical powder particle size of the raw material is 15~53μm, with 15μm, 30μm, 40μm, and 53μm being exemplary.

[0036] S3. Subsequently, the substrate and the formed semi-finished product are subjected to stress-relief annealing. After annealing, the substrate is cooled to room temperature in the furnace.

[0037] The substrate of this invention is annealed as a whole with the workpiece and a tantalum or tantalum-tungsten series high-temperature resistant substrate is selected. Its annealing temperature is matched with that of niobium 521 alloy. It does not deform at high temperature and does not react with the workpiece at the interface. This can avoid the impact of high temperature deformation of the substrate on the dimensional accuracy of the workpiece, ensure the continuous and uniform size of the segmented printing, and help to realize the mass production of large-size components.

[0038] Furthermore, in S3, the temperature range for stress-relief annealing is 900℃~1450℃, and the annealing holding time is controlled between 60min and 120min.

[0039] This temperature range provides sufficient thermal activation energy, allowing the accumulated thermal and interlayer stresses during SLM printing to be fully relaxed and eliminated through dislocation rearrangement and creep, without causing excessive grain growth in the niobium 521 alloy or severe burn-off of low-melting-point elements. This ensures stable matrix mechanical properties while releasing stress. A holding time of 60–120 minutes guarantees sufficient heat penetration into the formed semi-finished product, resulting in uniform and thorough stress release and providing a crack-free semi-finished product for subsequent reflow. If the temperature is too low or the time too short, stress release will be insufficient, residual stress will remain high, and cracking and warping are still likely to occur during reflow, preventing the segmented annealing from achieving the desired effect. If the temperature is too high or the time too long, it may lead to grain coarsening, decreased strength and plasticity, burn-off or volatilization of alloying elements, and even substrate deformation or interface reactions, ultimately damaging component performance and dimensional accuracy. Therefore, the temperature range for stress-relief annealing is 900℃~1450℃, with examples being 900℃, 1000℃, 1200℃, 1300℃, and 1450℃. The annealing holding time is controlled between 60min and 120min, with examples being 60min, 80min, 100min, and 120min.

[0040] Furthermore, in S4, when re-clamping and positioning after annealing, a dual method of height caliper measurement and reference angle alignment is used to reset and position the substrate, so that the substrate clamping position completely coincides with that of the first printing, ensuring the continuous and uniform size of the segmented printing.

[0041] Specifically, after printing to a certain height, the printing equipment is paused. At this point, the semi-finished product has a fixed position in the forming chamber. This position includes three locations: the horizontal XY direction and the forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser continuation at the same position. The annealed substrate is then re-clamped onto the forming platform, and a dual method of repositioning using height calipers and reference angle alignment is employed to ensure that the substrate clamping position completely coincides with that of the first printing.

[0042] Furthermore, in S5, after re-clamping and positioning, the top printed surface of the already formed semi-finished product is first slightly leveled before powder spreading and continuing.

[0043] Specifically, after re-clamping and positioning, the top printed surface of the semi-finished product is first slightly leveled to eliminate the slight planar deformation caused by the annealing process, and then powder spreading and splicing are carried out.

[0044] Furthermore, in S5, before printing the next segment, the segment continuation interface area is subjected to at least two repeated laser scans.

[0045] Furthermore, in S5, the parameters for repeated laser scanning are the same as those for the laser scanning parameters for the first segment of layer printing in S2.

[0046] Specifically, S5 is a reinforcement scanning and forming process for the continuation layer: After the powder is spread, at least two repeated laser scans are performed on the segment continuation interface area, with the scanning parameters remaining the same as before, in order to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; after completing the printing of the remaining height of this segment, the machine is stopped again for cooling after reaching the height threshold of the next segment, and the pause height of the next segment remains the same as the previous segment.

[0047] Furthermore, when the total number of stress-relief annealing cycles is N, the first N-1 segments of already formed semi-finished products all undergo a complete stress-relief annealing process, and no intermediate stress-relief annealing is performed after the last segment is printed.

[0048] This is to avoid the final forming section being over-processed by repeated annealing.

[0049] Furthermore, after the component is printed as a whole, it undergoes a final overall annealing process. The final overall annealing temperature range is 1400℃~1450℃, and the holding time is controlled between 60min and 120min.

[0050] This temperature range is higher than the lower limit of mid-stage annealing, allowing for a more thorough and complete release of stress from the final unannealed printed layer and any residual stress from previous stages. It also promotes homogenization of the internal structure and element diffusion, eliminating structural inhomogeneities caused by segmented joints, ensuring consistent and stable overall mechanical properties, and preventing cracking in the final formed section due to stress concentration. A holding time of 60–120 minutes ensures heat penetrates the entire large-size component, allowing for complete stress release and structural homogenization. If the temperature is too low or the time too short, residual stress in the final printed layer cannot be completely eliminated, leaving the component at risk of cracking, and insufficient overall structural homogenization may affect final performance. If the temperature is too high or the time too long, it can easily lead to grain coarsening, decreased strength and plasticity, burn-off or volatilization of alloying elements, and even deformation of the component or substrate, ultimately damaging the quality of the finished product.

[0051] Furthermore, the obtained large-size niobium 521 alloy has a tensile strength Rm≥563.3MPa, a yield strength Rp0.2≥399.9 MPa, and an elongation after fracture A≥21.5%.

[0052] In summary, this invention controls the printing height in segments according to a preset height threshold, limiting the stress accumulation in a single segment. After each segment is completed, the substrate and the formed semi-finished product are annealed as a whole. An overall stress-relief annealing process is set between segments to achieve phased release of printing stress. The stress-relief annealing eliminates the accumulated thermal stress and interlayer stress in this segment, suppressing interlayer cracking and edge warping defects in large-size components from the source. The mechanical properties meet the requirements of high-temperature aerospace components, improving the yield of large-size niobium 521 alloy components and reducing material waste. Through segmented printing and mid-process annealing cycles, the limitation of single continuous printing on component height is overcome, enabling the formation of ultra-long, large-size integrated niobium 521 alloy components, meeting the mass production needs of large-size components. By incorporating an overall stress-relief annealing process between segments, printing stress is released in stages. Segmented printing confines stress defects to a single segment. Combined with micro-leveling at the joint interface and repeated laser scanning to strengthen the metallurgical bond, this prevents defects from spreading across segments. This solves the technical problem of high unit price of niobium 521 spherical powder raw material and the serious material waste caused by overall scrapping. This process has been implemented in the mass production of large-size critical components such as aerospace niobium 521 alloy combustion chambers and engine nozzles, effectively reducing the risk of printing scrap and saving expensive alloy powder raw materials.

[0053] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0054] Example 1 like Figure 1 As shown, this embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: Tantalum substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0055] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder melting. The laser power is 267W, the laser scanning speed is 550mm / s, the laser scanning interval is 0.09mm, the powder layer thickness is 0.03mm, and the niobium 521 alloy spherical powder particle size is 30μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately after reaching the preset height, and the forming chamber is sealed and allowed to cool naturally to room temperature with the furnace. The pause preset height threshold is determined based on the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, the component in this embodiment is a variable cross-section rotating thin-walled structure with a total height of 300mm, a maximum outer diameter of 150mm, a minimum outer diameter of 80mm, a wall thickness of 6mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 35cm³, and the preset height threshold is 60mm.

[0056] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 900℃ and the holding time is 60min. After annealing, the furnace is cooled to room temperature.

[0057] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0058] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0059] S6 Cyclic annealing until the workpiece is formed: Repeat steps S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed section, the first N-1 semi-finished sections all undergo a complete stress-relief annealing process; after the overall printing section is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1400℃ and a holding time of 60min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0060] Example 2 This embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: A tantalum 2.5 tungsten substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0061] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder melting. The laser power is 324W, the laser scanning speed is 600mm / s, the laser scanning interval is 0.1mm, the powder layer thickness is 0.029mm, and the niobium 521 alloy spherical powder particle size is 15μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately after reaching the preset height, and the forming chamber is sealed and allowed to cool naturally to room temperature. The pause preset height threshold is determined based on the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, in this embodiment, the component is a variable cross-section rotating thin-walled structure with a total height of 300mm, a maximum outer diameter of 100mm, a minimum outer diameter of 70mm, a wall thickness of 4mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 16cm³, and the preset height threshold is 120mm.

[0062] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 1000℃ and the holding time is 100min. After annealing, the furnace is cooled to room temperature.

[0063] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0064] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0065] S6 Cyclic annealing until the workpiece is formed: Repeat the process from S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed forming section, the first N-1 semi-finished products all undergo a complete stress-relieving annealing process; after the overall printing is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1420℃ and a holding time of 100min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0066] Example 3 This embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: A tantalum 10 tungsten substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0067] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder melting. The laser power is 440W, the laser scanning speed is 680mm / s, the laser scanning interval is 0.12mm, the powder layer thickness is 0.028mm, and the niobium 521 alloy spherical powder particle size is 53μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately after reaching the preset height, and the forming chamber is sealed and allowed to cool naturally to room temperature. The pause preset height threshold is determined based on the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, the component in this embodiment is a variable cross-section rotating thin-walled structure with a total height of 375mm, a maximum outer diameter of 180mm, a minimum outer diameter of 100mm, a wall thickness of 8mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 38cm³, and the preset height threshold is 75mm.

[0068] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 1450℃ and the holding time is 120min. After annealing, the furnace is cooled to room temperature.

[0069] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0070] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0071] S6 Cyclic annealing until the workpiece is formed: Repeat steps S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed forming section, the first N-1 semi-finished products all undergo a complete stress-relieving annealing process; after the overall printing is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1450℃ and a holding time of 120min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0072] Example 4 This embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: Tantalum substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0073] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder deposition and melting. The laser power is 265W, the laser scanning speed is 555mm / s, the laser scanning interval is 0.095mm, the powder layer thickness is 0.03mm, and the niobium 521 alloy spherical powder particle size is 30μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately upon reaching the preset height, and the forming chamber is sealed and allowed to cool naturally to room temperature with the furnace. The pause preset height threshold is determined based on the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, the component in this embodiment is a variable cross-section rotating thin-walled structure with a total height of 300mm, a maximum outer diameter of 100mm, a minimum outer diameter of 70mm, a wall thickness of 4mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 10cm³, and the preset height threshold is 100mm.

[0074] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 900℃ and the holding time is 60min. After annealing, the furnace is cooled to room temperature.

[0075] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0076] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0077] S6 Cyclic annealing until the workpiece is formed: Repeat steps S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed section, the first N-1 semi-finished products all undergo a complete stress-relieving annealing process; after the overall printing section is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1420℃ and a holding time of 65min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0078] Example 5 This embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: Tantalum substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0079] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder melting. The laser power is 275W, the laser scanning speed is 560mm / s, the laser scanning interval is 0.09mm, the powder layer thickness is 0.03mm, and the niobium 521 alloy spherical powder particle size is 30μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately after the preset height is reached, and the forming chamber is sealed and allowed to cool naturally to room temperature with the furnace. The pause preset height threshold is determined according to the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, the component in this embodiment is a variable cross-section rotating thin-walled structure with a total height of 420mm, a maximum outer diameter of 160mm, a minimum outer diameter of 90mm, a wall thickness of 6mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 20cm³, and the preset height threshold is 140mm.

[0080] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 900℃ and the holding time is 60min. After annealing, the furnace is cooled to room temperature.

[0081] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0082] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0083] S6 Cyclic annealing until the workpiece is formed: Repeat steps S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed section, the first N-1 semi-finished products all undergo a complete stress-relieving annealing process; after the overall printing section is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1440℃ and a holding time of 85min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0084] Example 6 This embodiment provides a method for additive manufacturing of large-size niobium 521 alloy, including the following steps: S1 substrate selection and clamping: Tantalum substrate is selected as the printing substrate; the substrate is horizontally fixed on the forming platform of the selective laser melting (SLM) equipment, leveled and positioned, and the original height coordinates and clamping angle reference of the substrate are recorded.

[0085] S2 First-Stage Layer Printing: Import the 3D slice model of the component, set the laser scanning parameters, and print by layer-by-layer powder melting. The laser power is 270W, the laser scanning speed is 550mm / s, the laser scanning spacing is 0.09mm, the powder layer thickness is 0.03mm, and the niobium 521 alloy spherical powder particle size is 30μm. A fixed printing height threshold is set according to the slice model. Printing stops immediately after reaching the preset height, and the forming chamber is sealed and allowed to cool naturally to room temperature. The pause preset height threshold is determined based on the component printing volume: when the continuous solid volume is 30-40cm³, the pause preset height threshold is 50-80mm; when the continuous solid volume is 10-20cm³, the pause preset height threshold is 100-140mm. Specifically, the component in this embodiment is a variable cross-section rotating thin-walled structure with a total height of 400mm, a maximum outer diameter of 200mm, a minimum outer diameter of 120mm, a wall thickness of 10mm, and is made of niobium 521 alloy. Based on the three-dimensional slice model of the component, its continuous solid volume is approximately 30cm³, and the preset height threshold is 50mm.

[0086] S3 Overall Removal Annealing and Stress Relief: The substrate and the formed semi-finished product are removed from the printing equipment as a whole and sent to a vacuum heat treatment furnace for overall stress relief annealing. The annealing temperature is maintained at 900℃ and the holding time is 60min. After annealing, the furnace is cooled to room temperature.

[0087] S4 Substrate Positioning, Leveling, and Re-printing Preparation: After printing to a certain height, the printing equipment is paused. At this time, the semi-finished product has a fixed position in the forming chamber. This position includes three positions: horizontal XY direction and forming direction Z direction. These are called repeatable positioning positions, and they must be maintained after annealing to facilitate laser re-printing at the same position. The annealed substrate is re-clamped onto the forming platform, and the positioning is reset using both height caliper measurement and reference angle alignment to ensure that the substrate clamping position is completely coincident with that of the first printing. A small leveling treatment is performed on the top printed surface of the semi-finished product.

[0088] S5 Continuation Layer Enhanced Scanning and Molding: After powder spreading, perform at least two repeated laser scans on the segmented continuation interface area, keeping the scanning parameters consistent with the previous scans, to strengthen the interlayer metallurgical bond and eliminate segment interface porosity and weak bonding defects; complete the printing of the remaining height of this segment, and stop the machine again to cool after reaching the height threshold of the next segment. The pause height of the next segment is consistent with that of the previous segment.

[0089] S6 Cyclic annealing until the workpiece is formed: Repeat steps S3 to S5, and determine the total number of annealing cycles N according to the total height of the component; except for the last printed section, the first N-1 semi-finished products all undergo a complete stress-relieving annealing process; after the overall printing section is completed, the whole is subjected to final annealing treatment, with a final annealing temperature of 1440℃ and a holding time of 85min. After all printing is completed, a complete large-size niobium 521 alloy component is obtained.

[0090] Comparative Example 1 The method of Comparative Example 1 is largely the same as that of Example 1, except that: S3, mid-process stress-relief annealing is not performed, and one-time continuous selective laser melting is used for forming.

[0091] Comparative Example 2 Comparative Example 2 is largely the same as Example 1, except that: S2. Pause the preset height threshold of 100mm.

[0092] Comparative Example 3 Comparative Example 3 is largely the same as Example 1, except that: S5. Perform one repeated laser scan on the segmented continuation interface area.

[0093] Performance testing The standard tensile specimens of niobium 521 alloy obtained in Examples 1-6 and Comparative Examples 1-3 were subjected to room temperature tensile mechanical property tests. The test contents included tensile strength Rm, yield strength Rp0.2, and elongation after fracture A. The test results of the examples and comparative examples are shown in Table 1.

[0094] Table 1. Room temperature tensile mechanical properties of Examples 1-6 and Comparative Examples 1-3

[0095] The large-size niobium 521 alloys obtained in Examples 1-6 of this invention exhibit tensile strength Rm ≥ 563.3 MPa, yield strength Rp0.2 ≥ 399.9 MPa, and elongation after fracture A ≥ 21.5%. Comparative Example 1, with its continuous one-time printing without intermediate annealing, while showing high strength values, suffers from large fluctuations in elongation after fracture, and the continuous stress accumulation during printing easily leads to cracking and warping defects, making it unsuitable for direct use in forming large-size components. Comparative Example 2's pause preset height threshold of 100 mm exceeds the range, resulting in large stress accumulation in a single segment and cracking. Comparative Example 3, without repeated scanning, exhibits weak interfacial bonding and poor mechanical properties.

[0096] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for additive manufacturing of large-size niobium 521 alloy, characterized in that, Includes the following steps: S1. Substrate selection and clamping; S2. Import the 3D slice model of the component and complete the first layer printing. Stop printing and cool when the printing height reaches the preset height threshold to form a semi-finished product. S3. The substrate and the formed semi-finished product are then subjected to stress-relief annealing. After annealing, the substrate is cooled to room temperature in the furnace. S4. Next, the annealed substrate is reset and leveled; S5. Re-spread powder onto the top layer of the already formed semi-finished product and continue printing; S6. Print in segments, anneal, reset, continue printing until the entire component is printed.

2. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S1, the substrate is selected from a tantalum substrate, a tantalum 2.5 tungsten substrate, or a tantalum 10 tungsten substrate.

3. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S2, the laser power for layer printing is 265-450W, the laser scanning speed is 550-680mm / s, the laser scanning spacing is 0.09-0.12mm, and the powder layer thickness is 0.028~0.03mm.

4. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S2, the preset height threshold for pausing is determined based on the printed volume of the component: when the continuous solid volume is 30-40 cm³, the preset height threshold for pausing is 50-80 mm; when the continuous solid volume is 10-20 cm³, the preset height threshold for pausing is 100-140 mm.

5. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S3, the stress-relief annealing temperature is 900-1450℃, and the holding time is 60-120min.

6. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S4, when re-clamping and positioning after annealing, a dual method of height caliper measurement and reference angle alignment is used to reset and position the substrate, so that the substrate clamping position completely coincides with that of the first printing.

7. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S4, after re-clamping and positioning, a small leveling process is performed on the top printed surface of the formed semi-finished product.

8. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S5, before printing the next segment, the segment continuation interface area is subjected to at least two repeated laser scans.

9. The method for additive manufacturing of large-size niobium 521 alloy according to claim 1, characterized in that, In step S6, the overall annealing temperature after the overall printing is completed is 1400-1450℃, and the holding time is 60-120min.

10. A large-size niobium 521 alloy obtained by the additive manufacturing method of any one of claims 1-9, characterized in that, The large-size niobium 521 alloy has a tensile strength Rm≥563.3MPa, a yield strength Rp0.2≥399.9 MPa, and an elongation after fracture A≥21.5%.

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