Method for preparing layered structure through laser powder bed layer-by-layer remelting technology

Abstract

The invention provides a method for preparing a layered structure through a laser powder bed layer-by-layer remelting technology, and the method comprises the following steps: S1, laying a layer of metal powder on a substrate of selective laser melting equipment, and carrying out laser melting on the layer of metal powder to form a matrix layer; s2, laser ray remelting is conducted on a specific area on the base body layer, and the area of the specific area is smaller than the laser melting area of metal powder on the layer; and S3, after remelting, a layer of metal powder is laid on the base body layer, the step S1 and the step S2 are executed repeatedly till printing is completed, and the layered structure is obtained. Differentiated solid-state phase change and grain growth behaviors are induced in situ in the same powder layer, so that the ferrite-austenite layered composite stainless steel material with a complex three-dimensional configuration can be constructed.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology for metallic materials, specifically to a method for preparing layered structures using laser powder bed remelting technology. Background Technology

[0002] Layered metallic materials, due to their ability to combine the superior properties of materials with different phases or compositions, have broad application prospects in high-end manufacturing fields such as aerospace, nuclear energy equipment, marine engineering, and biomedicine. For example, ferritic stainless steel (such as 430 stainless steel) has excellent resistance to stress corrosion and thermal conductivity, while austenitic stainless steel (such as 316L stainless steel) has excellent ductility, toughness, and weldability. Layered materials formed by combining the two are expected to achieve a synergistic improvement in strength, toughness, and corrosion resistance.

[0003] However, traditional layered structure preparation techniques, such as rolling composite, explosive composite, and casting composite, have at least the following technical drawbacks: high process costs, requiring large-scale specialized equipment and complex pretreatment processes; difficulty in preparing three-dimensional components with complex geometries, usually limited to the composite of simple plates; low production efficiency, involving multiple rolling passes or long diffusion annealing; and the easy occurrence of defects such as oxide inclusions, segregation, or incomplete welding at the layered interfaces, which seriously affect the overall performance and reliability of the material.

[0004] In recent years, laser powder bed melting additive manufacturing technology has provided a new technical path for the preparation of layered structural materials due to its strong near-net-shape forming capability, high design freedom, and fast cooling rate. However, existing laser powder bed melting additive manufacturing technologies are usually used to prepare homogeneous single-phase or two-phase materials, making it difficult to achieve a periodic layered distribution of microstructure within the same component. Although some studies have attempted to control the microstructure by changing the powder or adjusting the scanning strategy, these methods generally suffer from poor process stability, weak interlayer bonding, or insufficient microstructure controllability. Summary of the Invention

[0005] Based on the above background, the purpose of this invention is to provide a method for preparing layered structures using laser powder bed remelting technology. By combining global laser melting with local laser line remelting, differentiated solid-state phase transformation and grain growth behavior are induced in situ within the same powder layer, thereby enabling the construction of ferrite-austenite layered composite stainless steel materials with complex three-dimensional configurations.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for preparing layered structures using laser powder bed remelting technology, the method comprising the following steps:

[0008] S1. A layer of metal powder is laid on the substrate of the laser selective melting equipment, and the metal powder is laser-melted to form a matrix layer.

[0009] S2. Laser line remelting is performed on a specific area on the substrate layer, wherein the area of ​​the specific area is smaller than the area of ​​the metal powder in the layer that is laser-melted.

[0010] S3. After remelting, another layer of the metal powder is laid on the substrate layer. Steps S1 and S2 are repeated until printing is completed to obtain the layered structure.

[0011] The metal powder is a mixed powder of 430 stainless steel powder and 316L stainless steel powder in a mass ratio of 1:1.49~1.51. The microstructure of the layered structure is characterized as follows: in the region not subjected to laser line remelting, the microstructure consists of ferrite with a BCC crystal structure and austenite with an FCC crystal structure, and the grains are equiaxed. In the specific region subjected to laser line remelting, the microstructure consists of ferrite with a single BCC crystal structure, and the grains are columnar.

[0012] Preferably, the laser melting process conditions are as follows: the scanning strategy is a checkerboard pattern, the scanning power is 150~270W, the scanning speed is 800~1500mm / s, the scanning spacing is 0.1mm, the layer thickness is 30μm, the rotation angle between layers is 67°, and the laser beam diameter is 100μm.

[0013] By optimizing the process parameters of global melting, it is possible to ensure high density and uniform two-phase structure of the matrix layer.

[0014] Preferably, the laser line remelting process conditions are as follows: the scanning strategy is parallel lines, the scanning power is 100~350W, the scanning speed is 800~2000mm / s, the scanning spacing is 0.2~0.3mm, the rotation angle between layers is 0°~360°, and the laser beam diameter is 100μm; and in step S2, the laser line remelting of the specific area is performed 1~3 times.

[0015] By optimizing the process parameters of local remelting, it is possible to control the degree of phase transformation and the fineness of grain morphology in the remelted zone.

[0016] Preferably, the 430 stainless steel powder is in the form of regular spheres with a particle size distribution in the range of 15~53μm, and its chemical composition by mass fraction includes 16.85% Cr, 0.97% Mn, and 0.66% Si, with the balance being Fe and unavoidable impurities; the 316L stainless steel powder is in the form of regular spheres with a particle size distribution in the range of 15~53μm, and its chemical composition by mass fraction includes 17.94% Cr, 12.01% Ni, 2.15% Mo, 0.39% Si, and 0.006% Mn, with the balance being Fe and unavoidable impurities; the chemical composition of the mixed powder by mass fraction includes 16.9~17.5% Cr, 6.9~7.21% Ni, 0.98~1.29% Mo, 0.25~0.39% Mn, and 0.3~0.498% Si, with the balance being Fe and unavoidable impurities.

[0017] Preferably, the environmental parameters of the laser selective melting equipment are: the preheating temperature of the substrate is 80±5℃, the protective atmosphere is argon, and the oxygen content is not higher than 0.8 Vol.

[0018] Preferably, the shape of the specific region changes layer by layer, and when step S2 is performed multiple times, the scanning power, scanning speed, scanning spacing and rotation angle between layers of laser line remelting are the same or different each time.

[0019] Preferably, the specific regions in the multilayer metal powder are arranged in a periodic alternation in three-dimensional space, so that the prepared layered structure macroscopically exhibits a composite configuration of alternating ferrite columnar crystal regions and biphase equiaxed crystal regions.

[0020] Preferably, during the layer-by-layer printing process, by changing at least one of the scanning power, scanning speed and scanning spacing of the laser line remelting in the specific region layer by layer, the grain size, grain orientation and element distribution of the specific region in different powder layers are made to vary in a gradient.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention discloses a method for preparing layered structures using laser powder bed remelting technology, employing a dual heat input strategy combining global laser melting with local laser line remelting. In step S1, the entire powder layer is globally melted using a checkerboard scanning strategy to form a matrix layer with biphasic equiaxed crystal characteristics. Subsequently, in step S2, a specific region is subjected to 1-3 laser line remelting cycles. An additional heat input and thermal cycle are introduced through a parallel line scanning strategy, inducing in-situ solid-state phase transformation and directional grain growth in that region, thereby overcoming the limitation of traditional additive manufacturing in controlling the microstructure within the same layer.

[0023] This invention ensures a clear and clean metallurgical bonding interface between the remelted and unremelted areas by strictly controlling the remelted area to be smaller than the global melting area and by using specific scanning strategies. This avoids the inclusion and segregation problems at the interface of traditional layered composite materials. At the same time, since the remelting is completed in situ within the same powder layer, the interlayer bonding strength is higher than that of traditional physical composite methods.

[0024] This invention controls the mixing ratio of 430 ferritic stainless steel and 316L austenitic stainless steel within the range of 1:1.49 to 1.51 to ensure that the mixed powder forms a stable dual-phase structure after laser melting, providing the necessary compositional basis for subsequent selective remelting phase transformation. This ratio range is optimized to ensure that the unremelted zone retains sufficient austenitic phase to obtain good plasticity and toughness, while also ensuring that the remelted zone fully transforms into the ferritic phase under thermal cycling. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart of a method for preparing layered structures using laser powder bed remelting technology according to the present invention;

[0027] Figure 2 This is a backscattered electron (BC) image of the microstructure of Embodiment 1 of the present invention, showing the morphology of the remelted strips formed by laser line remelting;

[0028] Figure 3 This is the electron backscatter diffraction (EBSD) phase distribution diagram of Embodiment 1 of the present invention, showing the difference in phase composition between the remelted and unremelted regions;

[0029] Figure 4 This is the inverse pole figure (IPF) grain orientation diagram of Embodiment 1 of the present invention, which shows the difference in grain morphology between columnar crystals in the remelted zone and equiaxed crystals in the unremelted zone;

[0030] Figure 5 This is the backscattered electron (BC) image of the microstructure of Embodiment 2 of the present invention, showing the morphology of the remelted strips under a remelting power of 350W;

[0031] Figure 6 This is the electron backscatter diffraction (EBSD) phase distribution diagram of Embodiment 2 of the present invention, showing the phase composition of the remelted region under a remelting power of 350W;

[0032] Figure 7 This is the inverse pole figure (IPF) grain orientation diagram of Embodiment 2 of the present invention, which shows the columnar crystal growth characteristics of the remelted zone under a remelting power of 350W;

[0033] Figure 8 This is the backscattered electron (BC) image of the microstructure in Embodiment 3 of the present invention, corresponding to the morphology of the remelted strip under a scanning spacing of 0.3 mm;

[0034] Figure 9 This is the electron backscatter diffraction (EBSD) phase distribution diagram of Embodiment 3 of the present invention, showing the phase composition of the remelted region at a scanning interval of 0.3 mm;

[0035] Figure 10 This is the inverse pole figure (IPF) grain orientation diagram of Embodiment 3 of the present invention, which shows the grain morphology of the remelted zone at a scanning interval of 0.3 mm;

[0036] Figure 11 This is a macroscopic schematic diagram of the layered structure of Embodiment 4 of the present invention, showing the alternating stacked configuration of ferrite columnar crystal regions and biphase equiaxed crystal regions in three-dimensional space. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0038] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0039] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0040] Example 1

[0041] This embodiment discloses a method for preparing layered structures using laser powder bed remelting technology, such as... Figure 1 As shown, the method specifically includes the following steps.

[0042] S1, Powder Formulation and Global Laser Melting

[0043] 430 stainless steel powder and 316L stainless steel powder were weighed and mixed at a mass ratio of 1:1.5 for at least 4 hours to ensure uniform composition. The 430 stainless steel powder was in the form of regular spheres with a particle size distribution ranging from 15 to 53 μm. Its chemical composition, by mass fraction, included 16.85% Cr, 0.97% Mn, and 0.66% Si, with the balance being Fe and unavoidable impurities. The 316L stainless steel powder was also in the form of regular spheres with a particle size distribution ranging from 15 to 53 μm. Its chemical composition, by mass fraction, included 17.94% Cr, 12.01% Ni, 2.15% Mo, 0.39% Si, and 0.006% Mn, with the balance being Fe and unavoidable impurities. The chemical composition of the mixed powder, by mass fraction, includes approximately 17.2% Cr, 7.2% Ni, 1.28% Mo, 0.38% Mn, and 0.49% Si, with the balance being Fe and unavoidable impurities.

[0044] After evacuating the forming chamber of the laser selective melting equipment, high-purity argon gas is filled into it as a protective atmosphere to ensure that the oxygen content does not exceed 0.8 Vol% during the forming process. The substrate is then mounted on the forming platform and preheated to 80±5℃ to reduce thermal stress and ensure good spreading and metallurgical bonding of the first layer of powder.

[0045] A 30 μm thick layer of the aforementioned mixed powder was deposited on a substrate to form a powder layer to be melted. The laser was activated, and a checkerboard scanning strategy was used to perform global laser melting of this powder layer. Specific process parameters were: scanning power 270 W, scanning speed 1000 mm / s, scanning spacing 0.1 mm, laser beam diameter 100 μm, and interlayer rotation angle 67°. The laser melted the powder zone by zone along the checkerboard scanning path, forming a dense matrix layer. This matrix layer has a dual-phase structure microscopically composed of ferrite with a BCC crystal structure and austenite with an FCC crystal structure, with equiaxed grain morphology.

[0046] S2, Localized laser line remelting

[0047] Laser line remelting is performed on specific areas of the substrate layer. These specific areas are significantly smaller than the area of ​​the metal powder in the same layer that is melted by the laser, exhibiting a strip-like or grid-like distribution. The remelting process employs a parallel line scanning strategy, with the following specific parameters: scanning power 270W, scanning speed 1000mm / s, scanning spacing 0.2mm, laser beam diameter 100μm, interlayer rotation angle 0°, and one remelting cycle.

[0048] During the remelting process, the laser beam reheats the already solidified two-phase matrix layer. Due to the cumulative heat input and specific thermal cycling history, this particular region experiences a higher peak temperature and a slower cooling rate, inducing a solid-state phase transformation from austenite to ferrite, while simultaneously promoting the directional epitaxial growth of grains. After remelting, the microstructure of this region transforms into a single BCC crystalline structure of ferrite, with grains exhibiting distinct columnar morphology and preferential grain growth along the heat flow direction.

[0049] S3, Layer-by-layer accumulation forming

[0050] A 30 μm thick layer of mixed metal powder is then deposited on the substrate layer, and the global laser melting process of step S1 and the local laser line remelting process of step S2 are repeated. During the repetition process, the global melting parameters are kept constant, while the specific areas of local remelting can be offset or alternately arranged in three-dimensional space according to a preset periodic pattern, so that the final layered structure macroscopically exhibits a composite configuration of alternating ferrite columnar crystal regions and biphase equiaxed crystal regions.

[0051] Repeat the above layer-by-layer printing process until all layers are stacked, finally obtaining a layered stainless steel material.

[0052] The layered structure prepared in this embodiment was characterized at the microscopic level. Figure 2 The backscattered electron (BC) plot clearly shows the periodically distributed remelted bands (i.e. specific regions) with clear band boundaries and no obvious pores or cracks. Figure 3 Electron backscatter diffraction (EBSD) phase distribution diagrams show that the unremelted region consists of green BCC ferrite phase and yellow FCC austenite phase, with a uniform ratio of the two phases; while the remelted specific region is almost completely transformed into green BCC ferrite phase, realizing the transformation from two phases to one phase. Figure 4 The inverse pole figure (IPF) grain orientation diagram further reveals the contrast between the equiaxed grain characteristics of the unremelted region and the columnar grain characteristics of the remelted region. The equiaxed grains in the unremelted region exhibit random orientation and irregular grain boundaries, while the columnar grains in the remelted region preferentially grow along the construction direction, exhibiting a distinct elongated morphology. These microscopic characterizations confirm that this embodiment successfully prepared a layered structure with clear interfaces and well-defined microstructure differentiation.

[0053] Example 2

[0054] This embodiment discloses a method for preparing layered structures using laser powder bed remelting technology. The steps of this method are the same as those in Embodiment 1, with the only difference being:

[0055] The laser line remelting process parameters in step S2 are adjusted as follows: the scanning power is increased to 350W, the scanning speed is kept at 1000mm / s, the scanning spacing is kept at 0.2mm, the laser beam diameter is 100μm, the interlayer rotation angle is 0°, and the number of remelting cycles is 1.

[0056] Increasing the remelting power to 350W significantly increases the heat input in specific areas. Figure 5 The backscattered electron plots show a slight increase in the width of the remelted bands and a more pronounced contrast with the matrix, indicating that higher energy input promotes more complete phase transitions and element diffusion. Figure 6 The EBSD phase distribution diagram confirms that the remelted zone achieved complete ferritification at 350W power, and the ferrite grain size was larger than that in Example 1, indicating that the higher temperature promoted grain growth. Figure 7 The IPF plots show that the columnar crystal features in the remelted zone are more pronounced, the aspect ratio of the grains is significantly increased, and the concentration of grain orientation is higher, indicating that the higher thermal gradient promotes stronger directional solidification behavior.

[0057] Example 2 demonstrates that at 350W power, the phase transformation in the remelted zone is more complete, and the columnar crystals are more developed, making it suitable for applications requiring stronger anisotropy or higher ferrite content. Furthermore, this example, together with Example 1, constitutes a power process window of 270W-350W, proving that the method exhibits good repeatability and microstructure control capabilities over a wide power range.

[0058] Example 3

[0059] This embodiment discloses a method for preparing layered structures using laser powder bed remelting technology. The steps of this method are the same as those in Embodiment 1, with the only difference being:

[0060] The laser line remelting process parameters in step S2 are adjusted as follows: the scanning power is increased to 270W, the scanning speed is kept at 1000mm / s, the scanning spacing is widened to 0.3mm, the laser beam diameter is 100μm, the interlayer rotation angle is 0°, and the number of remelting times is 1.

[0061] Reducing the scanning spacing to 0.3mm means that within the same scanning area, the density of laser scanning lines is reduced, the overlap rate between adjacent scanning lines is decreased, resulting in a weakening of the cumulative effect of heat input per unit area, while the degree of overlap of the heat-affected zone is reduced. Figure 8 The backscattered electron microscopy showed that the width of the remelted strip was slightly smaller than that of Example 1, but the internal structure of the strip was well homogeneous and the transition zone at the edge of the strip was smoother. Figure 9The EBSD phase distribution diagram shows that, at a spacing of 0.3 mm, the remelted zone still achieved the main ferritic transformation, but the content of retained austenite was slightly increased compared to Example 1, indicating that the lower heat accumulation led to a slight decrease in the driving force of the phase transformation, but it was still sufficient to achieve microstructure control. Figure 10 The IPF plots show that the columnar crystal characteristics of the remelted zone are still obvious, but the aspect ratio of the grains is reduced compared to Example 1, and the grain width is slightly increased, indicating that the lower thermal gradient leads to a weaker tendency for directional solidification, but the grains still maintain a clear preferred orientation.

[0062] Example 3 demonstrates that even at a relatively large scanning interval of 0.3 mm, this method can still successfully prepare layered structures with clear tissue differentiation. Examples 1-3 together constitute a wide process window of 270W-350W scanning power and 0.2mm-0.3mm scanning interval, fully demonstrating the excellent stability and repeatability of the method of the present invention.

[0063] Example 4

[0064] This embodiment discloses a method for preparing layered structures using laser powder bed remelting technology, such as... Figure 11 As shown in Example 1, this paper further demonstrates how to prepare layered structure materials with complex three-dimensional configurations by changing the position and process parameters of specific regions layer by layer.

[0065] Similar to Example 1, powder preparation and equipment setup are first completed, and a first layer of metal powder is deposited on the substrate. Global laser melting is then performed to form a first substrate layer, followed by laser line remelting of a first specific region on the first substrate layer. In this example, the first specific region is defined as a parallel strip extending along the X direction, occupying approximately 30% of the layer area.

[0066] After the first layer of printing is completed, the second layer is printed. A second layer of metal powder is laid on the first substrate layer, and global laser melting is repeated to form the second substrate layer. Subsequently, laser line remelting is performed on the second substrate layer. However, in this embodiment, the position of the second specific region is periodically alternating with the first specific region of the first layer in the XY plane. For example, if the first layer is a strip in the X direction and the second layer is a strip in the Y direction, a periodically alternating layered composite configuration is formed in three-dimensional space.

[0067] Repeat the above process so that the specific regions in the multilayer metal powder layers are arranged in a periodic alternation in three-dimensional space. The final layered structure is macroscopically a composite configuration of alternating ferrite columnar crystal regions and biphase equiaxed crystal regions.

[0068] Example 5

[0069] This embodiment discloses a method for preparing layered structures using laser powder bed remelting technology. Based on Embodiment 1, during the layer-by-layer printing process, the microstructure is gradient-controlled by progressively changing at least one of the scanning power, scanning speed, and scanning spacing of the laser line remelting in specific regions. For example, the parameters of Embodiment 1 (270W, 0.2mm) are used in the initial printing stage, the parameters of Embodiment 2 (350W, 0.2mm) are used in the middle stage, and the parameters of Embodiment 3 (270W, 0.3mm) are used in the later stage, or the parameters are continuously and gradually adjusted. Through this layer-by-layer variation of process parameters, the grain size, grain orientation, and elemental distribution in specific regions of different powder layers exhibit gradient changes, thereby preparing layered stainless steel materials with microstructural gradients to meet the differentiated requirements for strength, toughness, or corrosion resistance in different service locations.

[0070] It can be seen that the present invention successfully prepared a layered structure with a clear interface and excellent performance. Its core lies in the differentiated solid-state phase transition and grain growth kinetics mechanism caused by the dual heat input strategy of global laser melting combined with local laser line remelting.

[0071] In the global laser melting stage of step S1, a checkerboard scanning strategy is employed to rapidly melt the mixed powder using a high-energy beam. Under rapid solidification conditions, the molten mixed powder exhibits high undercooling and a high nucleation rate, forming a dual-phase structure composed of BCC ferrite and FCC austenite, with fine equiaxed grains. The checkerboard scanning strategy reduces heat accumulation and residual stress through partitioned scanning, while the 67° interlayer rotation angle breaks the through-grain growth of columnar crystals, further refining the grain size.

[0072] In the local laser line remelting stage of step S2, a parallel line scanning strategy is used to remelt a specific area. At this point, the laser beam does not act on the original powder, but rather on the solidified dual-phase matrix layer. The remelting parameter settings result in a more complex thermal history in this region than in the global melting stage: First, the laser beam remelts the surface metal, forming a molten pool; subsequently, due to the typical interlayer rotation at 0° or a specific angle and a specific scanning interval, heat accumulates along the scanning direction and is conducted downwards, creating a high temperature gradient and heat flow along the construction direction. This directional heat flow promotes epitaxial growth of grains along the heat flow direction, forming columnar crystals. Under thermal cycling, a solid-state phase transformation occurs in this region. The austenite phase in 316L stainless steel exhibits reduced stability at high temperatures, and the diffusion enrichment of ferrite-forming elements provided by 430 stainless steel, along with the rapid thermal cycling brought about by laser remelting promoting element redistribution, leads to the transformation from austenite to ferrite. After 1 to 3 remeltings, this specific region eventually formed an almost monolithic ferrite structure with distinct columnar grains.

[0073] Through the layer-by-layer accumulation in step S3, the unremelted and remelted regions alternate in three-dimensional space, forming a macroscopically layered but microscopically heterogeneous composite material. Since all microstructure evolution is completed in situ during the same LPBF forming process, a fully metallurgically bonded interface is formed between the remelted and unremelted regions, free of oxide inclusions, and the interface bonding strength is higher than that of traditional physical composite methods.

[0074] To further verify the technical effect of the method of the present invention, the mechanical properties of the layered stainless steel materials prepared in Examples 1-3 were tested and compared with those of Comparative Examples 1-2 as set below.

[0075] Comparative Example 1

[0076] Using the same 430 and 316L mixed powder and global melting parameters as in Example 1, but without the local laser line remelting in step S2, the material was directly deposited layer by layer. The resulting material was a uniform duplex stainless steel with a microstructure that was uniformly distributed throughout the component, consisting of equiaxed ferrite and austenite duplex crystals, without obvious layered structure characteristics.

[0077] Comparative Example 2

[0078] Layered composite materials were prepared using 430 stainless steel plates and 316L stainless steel plates through a traditional hot rolling composite process. The rolling temperature was 1100℃, the reduction rate was 50%, and subsequent annealing treatment was performed.

[0079] The samples prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to room temperature tensile tests and hardness tests, and the results are shown in Table 1.

[0080] Table 1. Comparative test results of mechanical properties of Examples 1-3 and Comparative Examples 1-2

[0081]

[0082] It can be seen that the yield strength and tensile strength of Examples 1-3 are significantly higher than those of Comparative Examples 1 and 2. This is attributed to the synergistic strengthening effect of the hard ferrite columnar crystal region and the relatively soft and tough biphase equiaxed crystal region in the layered structure. The ferrite columnar crystal region exhibits higher hardness and strength due to texture strengthening and grain refinement. The biphase equiaxed crystal region retains the excellent plasticity and toughness of the austenite phase, preventing the overall embrittlement of the material.

[0083] Although Example 2 exhibits the highest strength, its elongation of 32% remains at a high level, significantly higher than Comparative Example 2's 25% and slightly lower than Comparative Example 1's 40%. This indicates that the in-situ remelted layered structure of the present invention avoids the embrittlement problem of conventional rolled composite interfaces, while effectively mitigating stress concentration through the presence of soft two-phase regions.

[0084] Although Example 3 exhibits slightly lower strength than Example 1, it demonstrates superior ductility and toughness, achieving an elongation of 36%, which is still significantly better than Comparative Example 2. This indicates that the present invention can achieve high-performance layered structures across a wide range of scanning intervals.

[0085] In summary, this invention successfully achieved in-situ construction of layered heterogeneous stainless steel materials during the same LPBF forming process by employing a dual heat input strategy combining global laser melting and local laser line remelting, along with a specific ratio of 430 / 316L mixed powder. This method not only overcomes the shortcomings of traditional layered material preparation processes, such as high cost, shape limitations, and interface contamination, but also enables on-demand control of the microstructure through thermal history regulation.

[0086] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing layered structures using laser powder bed remelting technology, characterized in that: The method includes the following steps: S1. A layer of metal powder is laid on the substrate of the laser selective melting equipment, and the metal powder is laser-melted to form a matrix layer. S2. Laser line remelting is performed on a specific area on the substrate layer, wherein the area of ​​the specific area is smaller than the area of ​​the metal powder in the layer that is laser-melted. S3. After remelting, another layer of the metal powder is laid on the substrate layer. Steps S1 and S2 are repeated until printing is completed to obtain the layered structure. The metal powder is a mixed powder of 430 stainless steel powder and 316L stainless steel powder in a mass ratio of 1:1.49~1.

51. The microstructure of the layered structure is characterized as follows: in the region not subjected to laser line remelting, the microstructure consists of ferrite with a BCC crystal structure and austenite with an FCC crystal structure, and the grains are equiaxed. In the specific region subjected to laser line remelting, the microstructure consists of ferrite with a single BCC crystal structure, and the grains are columnar.

2. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The laser melting process conditions are as follows: the scanning strategy is a checkerboard pattern, the scanning power is 150~270W, the scanning speed is 800~1500mm / s, the scanning spacing is 0.1mm, the layer thickness is 30μm, the rotation angle between layers is 67°, and the laser beam diameter is 100μm.

3. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The laser line remelting process conditions are as follows: the scanning strategy is parallel lines, the scanning power is 100~350W, the scanning speed is 800~2000mm / s, the scanning spacing is 0.2~0.3mm, the rotation angle between layers is 0°~360°, and the laser beam diameter is 100μm; and in step S2, the laser line remelting of the specific area is performed 1~3 times.

4. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The 430 stainless steel powder is in the form of regular spheres with a particle size distribution in the range of 15~53μm. Its chemical composition, by mass fraction, includes 16.85% Cr, 0.97% Mn, and 0.66% Si, with the balance being Fe and unavoidable impurities. The 316L stainless steel powder is in the form of regular spheres with a particle size distribution in the range of 15~53μm. Its chemical composition, by mass fraction, includes 17.94% Cr, 12.01% Ni, 2.15% Mo, 0.39% Si, and 0.006% Mn, with the balance being Fe and unavoidable impurities. The chemical composition of the mixed powder, by mass fraction, includes 16.9~17.5% Cr, 6.9~7.21% Ni, 0.98~1.29% Mo, 0.25~0.39% Mn, and 0.3~0.498% Si, with the balance being Fe and unavoidable impurities.

5. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The environmental parameters of the laser selective melting equipment are as follows: the preheating temperature of the substrate is 80±5℃, the protective atmosphere is argon, and the oxygen content is not higher than 0.8 Vol.

6. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The shape of the specific region changes layer by layer, and when step S2 is executed multiple times, the scanning power, scanning speed, scanning spacing and rotation angle between layers of laser line remelting are the same or different each time.

7. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: The specific regions in the multilayer metal powder are arranged in a periodic alternation in three-dimensional space, so that the prepared layered structure macroscopically appears as a composite configuration of alternating stacked ferrite columnar crystal regions and biphase equiaxed crystal regions.

8. The method for preparing layered structures using laser powder bed remelting technology according to claim 1, characterized in that: During the layer-by-layer printing process, by changing at least one of the scanning power, scanning speed and scanning spacing of the laser line remelting in the specific region layer by layer, the grain size, grain orientation and element distribution of the specific region in different powder layers are made to change in a gradient.

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