SS316L / IN625 heterogeneous biomimetic structure material and preparation method thereof

Abstract

The application discloses a SS316L / IN625 heterogeneous biomimetic structure material and a preparation method thereof, and relates to the technical field of metal additive manufacturing and metal composite material preparation. The method comprises the following steps: taking the layered structure of a conch shell and the interlocking structure of a beetle sheath as a biomimetic prototype, constructing a periodic rigid-flexible coupling heterogeneous biomimetic structure model with horizontal interlocking and vertical layered alternation based on a 3D modeling software; based on a laser directional energy deposition technology, the heterogeneous biomimetic structure model is printed and formed by adopting an alternative deposition mode of SS316L and IN625 alloy powders; and the obtained formed piece is subjected to solid solution and double-stage aging heat treatment to obtain a heterogeneous biomimetic structure material finished product. According to the application, the heterogeneous deformation induced strengthening is activated by the biomimetic heuristic 'layered + interlocking' interface, the heterogeneous interface metallurgical bonding stability is synergistically improved by combining the laser directional energy deposition manufacturing parameter optimization and the graded heat treatment optimization, and the strength and toughness of the material are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of metal material preparation technology, specifically to an SS316L / IN625 heterogeneous biomimetic structural material and its preparation method. Background Technology

[0002] Metallic materials play a crucial role in aerospace, nuclear energy, and defense equipment. With the increasing demand for high-performance equipment in these fields, the requirements for the comprehensive mechanical properties of metallic components, such as strength and toughness, are constantly rising. Traditional single-metal materials struggle to simultaneously achieve high strength and high ductility: for example, SS316L stainless steel prepared by traditional processes exhibits excellent ductility (elongation exceeding 60%), but low tensile strength (below 600 MPa); Inconel 625 (IN625) nickel-based superalloy prepared by traditional processes has high strength (tensile strength above 800 MPa), but limited ductility (elongation below 30%). Improving its strength through various means significantly reduces its ductility, making it difficult to simultaneously optimize high strength and high ductility. This conflicting demand for strength and ductility limits its application in related fields.

[0003] Through long-term evolution, organisms in nature have developed various structural strategies to achieve a combination of strength and toughness. Examples include the "brick-and-mortar" layered structure of nacre in seashells, the cross-layered structure of conch shells, and the interlocking structure of beetle elytra. These structures can significantly improve fracture energy dissipation through microcrack deflection and stress redistribution, providing important inspiration for the design and fabrication of integrated strong and tough heterogeneous biomimetic structures (HBS) in metallic materials.

[0004] Laser-directed energy deposition (L-DED) technology, with its high forming efficiency and precision, and broad material adaptability, enables micron-level precise control of compositional gradients and spatial structures, providing a new approach for forming complex-shaped heterogeneous metal materials. However, this process inherently suffers from complex thermal cycling, large temperature gradients, and uneven element diffusion. Furthermore, its non-equilibrium solidification process introduces microscopic defects such as elemental segregation, brittle phase precipitation, and residual stress. These factors all contribute to a decline in the mechanical properties of the material, resulting in insufficient overall strength and toughness of current heterogeneous metal materials, making it difficult to meet the service requirements of high-end aerospace components.

[0005] Heat treatment is an effective means of regulating the microstructure of metallic materials, reducing defects, and optimizing performance. Although solution treatment (900~1200°C) can dissolve the brittle Laves phase and aging treatment (600~700°C) can promote the precipitation of strengthening phases, there is still a lack of systematic research on the optimization of heat treatment processes for such heterogeneous metallic structural materials prepared by L-DED. Summary of the Invention

[0006] This invention aims to provide an SS316L / IN625 heterogeneous biomimetic structural material and its preparation method. Specifically, it overcomes the bottleneck of strength-plasticity inversion by designing a "layered + interlocking" interface structure inspired by the layered structure of seashells and the interlocking structure of beetle elytra in nature, and optimizing the L-DED preparation parameters. Simultaneously, by combining optimized solution treatment and two-stage aging heat treatment processes, it solves the interface defect problem that occurs during L-DED manufacturing, thereby achieving a synergistic improvement in the stability and toughness of the heterogeneous interface metallurgical bonding. This material is suitable for manufacturing high-performance devices or components in aerospace, energy equipment, and other fields.

[0007] The first aspect of the present invention provides a method for preparing SS316L / IN625 heterogeneous biomimetic structural material, comprising the following steps: Step 1: Using the interlocking structure of beetle elytra and the brick-and-mortar layered structure of conch shells as biomimetic prototypes, construct a heterogeneous biomimetic structure model with transverse wavy interlocking and longitudinal layered alternating stacking. The transverse interlocking interface is a triangular wavy configuration, and the longitudinal layered alternating interface is a straight strip configuration. Step 2: Based on the heterogeneous biomimetic structure model designed in Step 1, laser-directed energy deposition technology is used to deposit several corrugated SS316L soft phases on the SS316L substrate in the first layer with a fixed gap between adjacent corrugated structures. Then, IN625 hard phases with the same corrugated shape are deposited at the gap positions in the same layer. The arrangement positions of the two types of alloys are interchanged in subsequent deposition layers and stacked layer by layer to make SS316L and IN625 achieve a periodic interlocking arrangement in the horizontal and vertical directions, thus preparing a periodic rigid-flexible coupled SS316L / IN625 heterogeneous biomimetic structure component. Step 3: Heat-treat the obtained components to optimize the interface bonding and obtain the finished SS316L / IN625 heterogeneous biomimetic structural material.

[0008] Furthermore, in step one, the method for constructing the heterogeneous biomimetic structural model specifically includes: Construct a cuboid base with length, width, and height of L, W, and H, respectively; divide it into several equally spaced layers along the height / Z axis to form a layered alternating structure with clear horizontal interfaces; Inside each layer, multiple triangular wave tooth structures are constructed along the width / X-axis direction, and the wave propagation direction is along the length / Y-axis direction. The apex angle, amplitude, and period of the triangular wave tooth structure are set to form an interlocking interface where the wave crests and troughs mesh with each other. The designed layered interlocking structural units are linearly arrayed along the X, Y, and Z axes of the Cartesian coordinate system to obtain a heterogeneous biomimetic structural model.

[0009] Furthermore, the triangle is set as an isosceles triangle with a vertex angle α of 90°, an amplitude A of 3.5 mm, and a period P of 7.0 mm.

[0010] Furthermore, in step two, the alternating deposition of SS316L and IN625 alloy powders specifically involves: The length direction of the heterogeneous biomimetic structural model is the scanning direction, the width direction is the stepping direction, and the height direction is the construction direction. During each deposition process, SS316L or IN625 is deposited at intervals along the stepping direction, and then IN625 or SS316L is deposited in the interstitial region formed therein, so that the soft phase of SS316L and the hard phase of IN625 are laterally complementary and interlocked in each layer. Next, in the next deposition process, another material opposite to the previous layer is deposited, and then the remaining material is deposited in the gap region formed, changing the deposition sequence periodically. Subsequent layers follow the same pattern, thus forming a longitudinal layered alternation between the SS316L soft phase and the IN625 hard phase between layers, ultimately obtaining a heterogeneous biomimetic structural material molded part with transverse heterogeneous interlocking and longitudinal layered heterogeneous alternation.

[0011] Furthermore, in step two, the printing parameters are set as follows: laser power 500W, scanning speed 450~550mm / min, scanning interval 0.8mm, step distance along the forming direction 0.5mm, powder feeding rate 1.5~2.0r / min, and protective gas flow rate 10.8L / min.

[0012] Furthermore, during the printing process, when SS316L and IN625 alloy powders are alternated, a switching control of "pause powder feeding / pause laser - powder path switching and purging - stable powder feeding - resume cladding" is executed. The pause powder feeding / pause laser time is 10 seconds, and the interlayer cooling time is set to 5 minutes after each layer is deposited.

[0013] Furthermore, in step three, the heat treatment includes solution treatment and two-stage aging treatment. The solution treatment involves holding at 1150℃ for 1 hour followed by water quenching. The two-stage aging treatment involves holding at 720℃ for 4 hours, then lowering the temperature to 620℃ for 4 hours, followed by water quenching.

[0014] Furthermore, after step three, the method further includes: The heat-treated material is polished and then ultrasonically treated by immersion in anhydrous alcohol to remove the powder adhering to the surface.

[0015] The second aspect of the present invention provides an SS316L / IN625 heterogeneous biomimetic structural material, which is prepared by a method for preparing SS316L / IN625 heterogeneous biomimetic structural material. The SS316L / IN625 heterogeneous biomimetic structural material includes an SS316L soft phase region and an IN625 hard phase region. The two are distributed in a periodic manner with transverse heterogeneous interlocking and longitudinal layered heterogeneous alternation. Furthermore, a complementary interlocking interface is provided at the transverse interface between the SS316L and IN625 phases. The interlocking interface has a corrugated tooth configuration.

[0016] Furthermore, the thickness t of the single layer of the longitudinal layered structure is 0.5±0.3mm, and the ratio of the soft phase region of SS316L to the hard phase region of IN625 is 0.7:1~1:0.7.

[0017] The beneficial effects of this invention are: 1. This invention constructs a heterogeneous biomimetic structural material of SS316L / IN625 with "layered + interlocking" characteristics by integrating the layered structure of a conch shell with the interlocking configuration of a beetle elytra. This design enables the soft phase (SS316L) and the hard phase (IN625) to form a tight and continuous heterogeneous interface in three-dimensional space, with uniform and controllable phase distribution, effectively making up for the shortcomings of traditional single metal materials that are difficult to achieve both strength and plasticity.

[0018] 2. This invention further optimizes the microstructure and properties of the alloy through solution treatment and two-stage aging heat treatment processes, effectively improving interface defects such as element segregation and precipitation of brittle phases (such as network Laves phase and δ ferrite) during additive manufacturing, effectively reducing residual stress, narrowing the interface transition zone, and significantly improving the microstructure uniformity, providing a new approach to overcome the long-standing problem of the inversion of strength and plasticity in traditional metallic materials.

[0019] 3. This invention utilizes the synergistic effects of intrinsic matrix strengthening (precipitation, solid solution), heterogeneous deformation-induced strengthening, and crack passivation deflection toughening to ensure that the prepared SS316L / IN625HBS material retains excellent tensile strength under high strain conditions. Performance verification shows that its ultimate tensile strength reaches 935.8 MPa and its elongation reaches 45.1%, achieving a synergistic improvement in strength and plasticity. This overcomes the common problem of difficulty in synergistically optimizing strength and plasticity in traditional metallic materials, demonstrating its broad application prospects in the field of engineering structural materials. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 The following are the design prototype and finished product images of the SS316L / IN625HBS material of this invention, wherein (a) is a schematic diagram of the layered structure imitating a conch shell, (b) is a schematic diagram of the interlocking structure of the elytra imitating a beetle, and (c) is a schematic diagram of the deposition process and a physical image of the formed sample. Figure 2 The images show the microstructure of the AB-HBS sample. (a), (b), and (c) are magnified views of the microstructure of the heterostructure interface in the XZ plane, and its first and second-order partial magnifications, respectively. (d) and (e) are the dendrite and equiaxed grain morphologies of the SS316L and IN625 regions in the XZ plane, respectively. (f) and (g) are the microstructure of the heterostructure interface in the XY plane, and its partial magnifications, respectively. (h) and (i) are the dendrite and equiaxed grain morphologies of the SS316L and IN625 regions in the XY plane, respectively. Figure 3 The images show SEM images of AB-HBS and HT-HBS samples in the XZ plane. (a), (c), and (e) are magnified views of the heterostructure of AB-HBS and the microstructure of its IN625 and SS316L regions, respectively. (b), (d), and (f) are magnified views of the heterostructure of HT-HBS and the microstructure of its IN625 and SS316L regions, respectively. Figure 4 The EBSD crystallographic characterization and analysis results of AB-HBS and HT-HBS samples in the XZ direction are shown. Among them, (a) and (b) are the inverse pole figures of AB-HBS and HT-HBS, respectively, and (c) and (d) are the grain size distribution diagrams of AB-HBS and HT-HBS, respectively. Figure 5 The tensile mechanical properties of HBS materials in different directions are shown in the following figures: (a) is a schematic diagram of the tensile specimen structure constructed along the scanning direction and the stepping direction; (b) and (c) are the engineering stress-strain curves along the scanning direction and the stepping direction, respectively. Figure 6 The images show the horizontal, vertical, and heat-treated indentation morphology and hardness distribution of HBS material. (a) shows the vertical direction of the deposited state, (b) shows the horizontal direction of the deposited state, and (c) shows the vertical direction after heat treatment. Figure 7The images show the deformed surface morphology of the fracture region after the AB-HBS and HT-HBS samples were broken and the corresponding Fe element EDS surface scan images of the region. Among them, (a) shows the morphology of the AB-HBS fracture region and the Fe element EDS surface scan image in the scanning direction, (b) shows the morphology of the HT-HBS fracture region and the Fe element EDS surface scan image in the scanning direction, and (c) shows the morphology of the HT-HBS fracture region and the Fe element EDS surface scan image in the step direction. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of them. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0023] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0024] Example 1: This embodiment provides a heterogeneous biomimetic structure (HBS) material of SS316L / IN625. This material is a multilayer HBS, which is composed of SS316L and IN625 alloys stacked alternately. It includes a soft phase region of SS316L and a hard phase region of IN625. The two are periodically alternating in the component forming direction. A complementary interlocking interface is provided at the interface between the two phases of SS316L and IN625 in the transverse direction. The interlocking interface can be a corrugated configuration to guide crack deflection and stabilize deformation, so that the interface has geometric constraint and load transfer capability as an interlayer connection.

[0025] Reference Figure 1 The SS316L / IN625HBS material was developed and designed based on a conch shell-like layered structure and a beetle elytra-like interlocking structure.

[0026] Inspired by the microscopic layered structure of natural conch shells, this invention utilizes a layered structure modeled after a conch shell. Multiple studies have confirmed that this natural structure is key to material strengthening through crack deflection and interfacial slip. This invention employs this layered structure as the basic unit of a heterogeneous structure to construct a longitudinal layered structure, primarily serving to redistribute stress. The basic model of this conch shell-like layered structure can be obtained by linearly arranging multiple cuboid-like plate units.

[0027] The design inspiration for the beetle-like elytra interlocking structure comes from the interlocking configuration of the beetle's elytra connection points. This structure has been proven to effectively achieve uniform material deformation and delay interfacial failure through heterogeneous deformation-induced strengthening, which is one of the important reasons for the material's excellent strength and plasticity. This invention uses it as a layered connection to construct a transverse interlocking interface, guiding crack deflection and stabilizing deformation. The basic model of this beetle-like elytra interlocking structure can be obtained through a linear array of multiple serrated ribs.

[0028] The preparation process of this SS316L / IN625HBS material is as follows: Step 1: Construct the HBS model using 3D modeling software; First, a 3D modeling software (such as SolidWorks or CATIA) is used to construct a unit cell model with horizontal heterogeneous interlocking and vertical layered heterogeneous alternation. Specifically, a multi-layered heterogeneous layered structure is designed vertically, and then a horizontal heterogeneous interlocking interface is set in each single layer. This interlocking interface can adopt configurations such as triangular wave shape, sine wave shape, square tooth shape, or trapezoidal tooth shape. Interlocking is achieved through the interlocking of wave crests and troughs, or the meshing of tooth tips and tooth grooves. Then, the structural unit model is linearly arrayed along the X, Y, and Z axes to obtain the macroscopic HBS model.

[0029] Step two: Print the designed HBS model. First, the HBS model designed in step one is used to design the deposition path through CIMCO CNC programming software and exported as an NC format file. Then, the file is imported into the CNC operating system of the deposition processing equipment (such as L-DED or other additive manufacturing system CNC operating platform). This system is equipped with a dual powder hopper feeder and uses SS316L and IN625 alloy powders to be deposited alternately to prepare HBS material molded parts with SS316L soft phase region and IN625 hard phase region periodically alternating in both the transverse and longitudinal directions.

[0030] Step 3: Heat-treat the printed parts to optimize their microstructure. Heat treatment includes two stages: solution treatment and two-stage aging treatment.

[0031] Among them, solution treatment (heating the alloy to a high-temperature single-phase region and holding it at a constant temperature to allow the excess phase to fully dissolve into the solid solution, and then rapidly cooling to suppress the recrystallization of the second phase) can improve the plasticity and machinability of the alloy, eliminate the stress generated by cold and hot working, and promote recrystallization.

[0032] By performing two-stage aging treatment (two aging treatments at two different temperatures, the first aging is carried out at a higher temperature for a short time to quickly form some strengthening phases; the second aging is carried out at a lower temperature for a long time to promote further precipitation and uniform distribution of the strengthening phases), the strength, toughness and corrosion resistance of the alloy can be improved.

[0033] Furthermore, after the heat treatment optimization in step three, this embodiment also includes: Step four, polishing; The heat-treated SS316L / IN625HBS material was mechanically polished and ultrasonically cleaned. Specifically, 80# SiC sandpaper was used to remove the oxide layer of about 2 mm thickness on the surface, and then it was immersed in anhydrous alcohol and ultrasonically cleaned to remove the metal powder adhering to the surface.

[0034] The SS316L / IN625HBS material prepared by the above steps has the SS316L soft phase region and the IN625 hard phase region arranged in a periodic layered alternation in the longitudinal direction, and forming a periodic alternating heterogeneous interlock in the transverse direction.

[0035] The corrugated dimensions of the interlocking interface and the spacing between adjacent interlocking interfaces can be flexibly set according to actual needs. The adjacent spacing can be equidistant or non-equidistant.

[0036] Meanwhile, the thickness of a single layer can also be adjusted according to application requirements to control the ratio of soft phase to hard phase. As a preferred option, the single layer thickness t can be set to 0.5±0.3mm, and the volume ratio of SS316L to IN625 can be adjusted within the range of 0.7:1 to 1:0.7.

[0037] Example 2: This embodiment further provides a method for preparing SS316L / IN625HBS material. The difference from Embodiment 1 is that this embodiment further clarifies the specific preparation process, structural design, and dimensional parameters.

[0038] like Figure 1 As shown, this embodiment abstracts the interlocking configuration of the beetle's elytra as a triangular wavy structure. The preparation process of the SS316L / IN625HBS material in this embodiment is as follows: Step 1, Building the HBS Model: Define a cuboid with length L, width W, and height H, and divide it into several equally spaced layers along the height / Z axis to form a layered alternating structure with a clear horizontal interface. Then, a continuous triangular wave structure is constructed in each layer. Specifically, multiple triangular wave tooth structures are constructed along the width / X-axis direction, the wave propagation direction is the length / Y-axis direction, and the wave tooth structures in each layer are in phase in the longitudinal direction, with the wave crests and troughs vertically aligned, continuously penetrating from the top surface to the bottom surface of the cuboid.

[0039] The main geometric parameters of the triangular wave structure include amplitude A, period P, and vertex angle α. In this preferred embodiment, the triangular wave structure is an isosceles right triangle with a vertex angle α of 90° and two legs of 3.5 mm in length. A is the height of the triangle, i.e., 3.5 mm, and P is the horizontal distance between adjacent troughs, i.e., the sum of the horizontal projections of the two legs, equal to 3.5 + 3.5 = 7.0 mm. The amplitude-to-period ratio A / P is 0.5, and adjacent triangular wave structures are equidistantly distributed.

[0040] The obtained layered interlocking configuration is defined as a structural unit. After selecting the structural unit, it is linearly arrayed along the X, Y, and Z axes of the Cartesian coordinate system in the 3D modeling software to obtain the macroscopic HBS model.

[0041] Step 2, print HBS material molded parts: like Figure 1 As shown in (c), when preparing HBS material molded parts using L-DED technology, SS316L and IN625 alloy powders are deposited alternately, and the entire process is carried out under argon protection. During the deposition process, the scanning direction (Y-axis, i.e., the path direction of the laser head when depositing within each layer) is along the length direction of the HBS model, the stepping direction (X-axis, i.e., the progressive direction of the laser head in the XY plane of the same layer, i.e., the stepping interval of the scanning path in the same layer) is along the width direction, and the building direction (Z-axis, i.e., the vertical direction of deposition) is the layer-by-layer stacking direction.

[0042] During single-layer deposition, the interstitial region enclosed by the interlocking interface and the layered interface is used as the basic deposition unit. Different materials are alternately filled in every interstitial region along the stepping direction: first, SS316L (or IN625) is deposited, and then IN625 (or SS316L) is deposited in the adjacent interstitial region. This allows the two materials, SS316L and IN625, to form an interlocking structure through the triangular wavy interface in this layer (i.e., on the XY plane), thus completing the deposition of the current layer.

[0043] The interlayer deposition process involves a periodic alternation: each subsequent layer is deposited with a different material than the one preceding it. For example, odd-numbered layers first deposit SS316L and then fill the interstitial areas with IN625, while even-numbered layers first deposit IN625 and then fill the interstitial areas with SS316L (and vice versa). The deposition sequence of each subsequent layer follows this pattern to ensure that IN625 and SS316L are interleaved both laterally and longitudinally, ultimately forming a three-dimensional structure.

[0044] When switching between heterogeneous materials, a switching control is implemented that involves "pausing powder feeding / pausing laser—powder path switching and purging—stabilizing powder feeding—resuming cladding." The pause time for powder feeding / laser is 10 seconds to reduce powder cross-contamination and stabilize the interface transition layer. After each layer is deposited, interlayer cooling is set for 5 minutes to reduce heat accumulation and improve the consistency of interlayer forming.

[0045] The SS316L and IN625 alloy powders used were produced by gas atomization, with a particle size of 53–105 μm. Key process parameters during printing included laser power, scanning speed, scanning spacing, and powder feeding speed. These parameters were set as follows: laser power 500W, scanning speed 450–550 mm / min, scanning spacing 0.8 mm, Z-axis step 0.5 mm, powder feeding rate 1.5–2.0 r / min, and argon as the protective gas with a flow rate of 10.8 L / min. These printing parameters ensured good forming accuracy.

[0046] The actual image of the molded block sample is as follows Figure 1 (c) In the SS316L / IN625HBS material molded parts, each layer in the transverse direction is a millimeter-level heterogeneous metal interlocking unit with a beetle elytra-like structure, while in the longitudinal direction it is a shell-like layered structure formed by alternating stacking of SS316L and IN625 alloys.

[0047] Step 3, heat treatment: Solution treatment: Place the SS316L / IN625HBS material molded part obtained in step two in a ceramic boat and put it into a muffle furnace preheated to 1150℃. After holding at this temperature for 1 hour, immediately water cool it to avoid excessive precipitation of harmful phases during the cooling process. This process can dissolve the brittle Laves phase, reduce element segregation, and promote recrystallization to form equiaxed grains.

[0048] Two-stage aging treatment: After solution treatment, the sample is transferred to a muffle furnace preheated to 720℃ and held for 4 hours. Then, the temperature is lowered to 620℃ and held for 4 hours. Finally, water cooling is performed to promote the formation of coherent γ″-Ni3Nb nano-precipitates and achieve precipitation strengthening.

[0049] After heat treatment, a metallurgically bonded interdiffusion zone of elements is formed at the interface of the two phases (its thickness δ is about 30~40μm), which optimizes the interface bonding.

[0050] Application Examples: This application example aims to characterize, analyze phases, and test the performance of the SS316L / IN625HBS material prepared in Example 2 above.

[0051] In the performance testing, the mechanical test mainly consisted of tensile testing, which was carried out using a universal testing machine. The tensile rate was kept constant at 1 mm / min. Vickers hardness was also measured on the heterogeneous interface. The Vickers hardness test parameters were: test force 500 gf (HV0.5) and holding time 15 s.

[0052] In addition, in order to perform pretreatment for microstructure characterization of the samples before and after heat treatment, so that their microstructure (such as grain boundaries, precipitates, etc.) can be clearly presented for subsequent microscopic observation and analysis, this embodiment etches the samples. The etiology steps are as follows: first, the SS316L region is pre-etched with aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3:1, volume ratio), and then 10% oxalic acid solution is used as the etching solution, and electrolysis is performed for 15s under 9V DC conditions.

[0053] In the following text, AB-HBS refers to the HBS material before heat treatment (i.e., the HBS material molded part obtained in step two of Example 2), and HT-HBS refers to the HBS material after heat treatment.

[0054] (a) Microscopic organizational characteristics.

[0055] See Figure 2 , Figure 2The microstructure and microstructure characteristics of AB-HBS under optical microscope (OM) are shown. (a)-(c) show the microstructure and magnified views of the IN625 / SS316L and SS316L / IN625 interfaces in the XZ plane; (d)-(e) show the dendritic and equiaxed grain morphology in the XZ section; (f)-(g) show the interface morphology and magnified views of the IN625 and SS316L regions in the XY plane; and (h)-(i) show the grain structure in the XY section. Because SS316L and IN625 react differently to the corrosive solution, the regions of different alloys can be easily distinguished, namely the upper and lower regions (IN625) and the middle region (SS316L). As shown in the figure, there are virtually no pores or cracks between SS316L and IN625, indicating good compatibility. The IN625 / SS316L interface is relatively flat, while the SS316L / IN625 interface is relatively rugged (high degree of molten pool banding). The flow field of the molten pool determines the morphology of the molten pool interface. Due to the lower energy absorption rate and lower thermal conductivity of IN625 compared to SS316L, different energy inputs are generated during the deposition process, causing partial remelting of IN625 and infiltration of SS316L into IN625, thus resulting in different morphologies of the IN625 / SS316L and SS316L / IN625 interfaces.

[0056] See Figure 3 , Figure 3 The images show SEM (Scanning Electron Microscope) images of HBS material before and after heat treatment. Figure 3 (a), (c), and (e) are SEM images of the AB-HBS heterogeneous interface and magnified views of the IN625 and SS316L regions. Figure 3 Images (b), (d), and (f) show SEM images of the HT-HBS heterostructure interface and magnified views of the IN625 and SS316L regions. As shown, a wide dendritic transition zone exists between the two phases in the AB-HBS sample. Nb- and Mo-rich network Laves phases and NbC carbides precipitate at the IN625 grain boundaries; δ-ferrite is distributed at the austenite grain boundaries in the SS316L. After solution treatment and two-stage aging heat treatment, the wide transition zone of the HT-HBS disappears, and the two-phase interface becomes narrow and clear. The coarse, continuous Laves phase and network δ-ferrite completely dissolve, transforming into dispersed fine Laves particles, NbC, and chromium-rich MnO. 23 C6 carbides significantly improve the homogenization of the matrix structure.

[0057] See Figure 4 , Figure 4The EBSD (Electron Backscatter Diffraction) crystallographic characterization and analysis results of HBS materials before and after heat treatment are presented. Figure 4 (a) and (b) are the inverse pole figures of the AB-HBS and HT-ABS samples, respectively. Figure 4 (c) and (d) are the grain size distribution diagrams of the AB-HBS and HT-ABS samples, respectively. The test results show that after heat treatment, the IN625 / SS316L interface exhibits a transition zone that enhances bonding, while the growth of the SS316L / IN625 interface is restricted. With the decrease in the ratio of temperature gradient G to solidification rate R, the solidification microstructure changes from columnar dendrites to equiaxed crystals, and recrystallization weakens the texture; the average grain size increases from 25.6 μm to 31.2 μm, but the distribution does not significantly expand.

[0058] (ii) Mechanical property testing.

[0059] See Figure 5 , Figure 5 The tensile mechanical properties of SS316L / IN625HBS specimens before and after heat treatment, along with those of elemental L-DEDIN625 and elemental L-DEDSS316L specimens, are compared in both the scanning and stepping directions. Figure 5 (a) is a schematic diagram of the tensile specimen in the scanning direction and stepping direction. Figure 5 (b) and (c) are comparison graphs of the engineering stress-strain curves of each specimen. Figure 5 The mechanical test results show that the elemental L-DEDSS316L material has the highest tensile strength but relatively low plasticity, while the elemental L-DEDIN625 material has better plasticity but the lowest tensile strength. The tensile strength and elongation at break of AB-HBS and HT-HBS are between those of the two elemental materials; among them, heat-treated HT-HBS balances high tensile strength and high elongation, with an ultimate tensile strength of 935.8 MPa and a total elongation of 45.1%. Compared to the two single-phase materials, HT-HBS achieves a balanced match between strength and plasticity, avoiding the disadvantage of the trade-off between strength and plasticity in single-phase materials, and breaking the limitation of the traditional alloy's inverse relationship between strength and plasticity. HBS exhibits superior comprehensive mechanical properties compared to single-component materials (SS316L or IN625) under different interface designs. In particular, the heat-treated HT-HBS specimen achieved an ultimate tensile strength of 935.8 MPa and an elongation of 45.1%, successfully realizing a synergistic improvement in strength and plasticity, breaking through the traditional trade-off between strength and plasticity in metallic materials. This performance improvement can be attributed to the multi-level toughening mechanism that mimics the nacreous layer of mollusks in nature, namely, the synergistic effects of back stress strengthening and heterogeneous deformation-induced hardening activated through heterogeneous interface design.

[0060] See Figure 6 , Figure 6 (a) and (b) show the hardness distribution and indentation morphology of AB-HBS material on the XZ vertical and XY horizontal sections, respectively. Figure 6 (c) shows the hardness distribution and indentation morphology of the XZ vertical section of the heat-treated HT-HBS material. Vickers hardness testing results indicate that the hardness on the XY horizontal section exhibits a periodic alternation of soft and hard areas, with the SS316L region having a hardness of 258–320 HV, the IN625 region having a hardness of 340–391 HV, and the interface boundary region having a hardness of approximately 300 HV. On the XZ vertical section, a clear gradient hardness distribution is observed, with the SS316L region having a hardness of 200–220 HV, the IN625 region having a hardness of 274–310 HV, and the interface boundary region having a hardness of approximately 320 HV. The anisotropy of the material's hardness mainly stems from differences in grain orientation: the horizontal section is dominated by equiaxed grains, while the vertical section exhibits a combination of columnar dendrites and equiaxed grains. After solution two-stage aging heat treatment, the overall hardness of the material remains basically unchanged. This is mainly because the water quenching process can effectively suppress grain coarsening while eliminating residual stress. The austenite grains only grow slightly, and the hardness of the matrix material remains basically stable after heat treatment.

[0061] Reference Figure 7 , Figure 7 The deformed surface morphology of the fracture region of the tensile specimens before and after heat treatment, along with the corresponding EDS (Energy Dispersive Spectroscopy) surface scans of Fe elements in the region, are shown. As shown in the figure, on the deformed surface of the AB-HBS specimens, coarse and deep shear bands are unevenly distributed, and in some local areas, the shear bands have evolved into microcracks. Figure 7 (a)). In contrast, the shear bands in the HT-HBS sample were thinner and shallower, and more uniformly distributed. Figure 7 (b) and (c)). These results indicate that the microstructure of the HT-HBS specimen is more uniform, and its plastic deformation and fracture processes are more uniform than those of AB-HBS.

[0062] (III) Experimental conclusions.

[0063] In summary, this invention draws on the design strategy of "rigid-flexible coupling and complementary performance" of the layered structure of conch shells and the interlocking structure of beetle elytra. It selects IN625 high-temperature nickel-based alloy and SS316L stainless steel, two materials with similar coefficients of thermal expansion and corrosion resistance, as deposition substrates. The SS316L / IN625HBS material is prepared using L-DED technology, combining and complementing the excellent high-temperature strength of IN625 and the excellent plasticity of SS316L stainless steel.

[0064] By designing a solution treatment and two-stage aging process (i.e., a solution treatment at 1150℃ and a holding time of 1h combined with a first-stage aging treatment at 720℃ and a holding time of 4h and a second-stage aging treatment at 620℃ and a holding time of 4h), the microstructure and mechanical properties (including tensile properties and hardness gradient) of SS316L / IN625HBS material were further optimized.

[0065] Room temperature tensile tests were conducted on SS316L / IN625HBS materials and IN625 and SS316L elemental materials in two structural directions before and after heat treatment to observe the evolution of their strength and toughness. The results confirmed that the "layered + interlocking" HBS design in this invention effectively increased the uniform deformation of the soft and hard phases and the work hardening effect, effectively delaying crack propagation while improving strength and toughness. The heat treatment process effectively dissolved harmful brittle phases, transforming the original columnar dendrites into an equiaxed recrystallized structure, reducing the anisotropy of the material, and simultaneously promoting the dispersed distribution of nano-precipitates and stabilizing the interfacial structure, thereby improving the material's interfacial load-bearing capacity and fracture toughness. The SS316L / IN625HBS material formed along the scanning direction exhibited the best strength and toughness after heat treatment, with a room temperature ultimate tensile strength of 935.8 MPa and an elongation of 45.1%.

[0066] The sequence numbers of the above embodiments are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. The descriptions of each embodiment in the above embodiments have different emphases; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an SS316L / IN625 heterogeneous biomimetic structural material, characterized in that, Includes the following steps: Step 1: Using the interlocking structure of beetle elytra and the brick-and-mortar layered structure of conch shells as biomimetic prototypes, construct a heterogeneous biomimetic structure model with transverse wavy interlocking and longitudinal layered alternating stacking. The transverse interlocking interface is a triangular wavy configuration, and the longitudinal layered alternating interface is a straight strip configuration. Step 2: Based on the heterogeneous biomimetic structure model designed in Step 1, laser-directed energy deposition technology is used to deposit several corrugated SS316L soft phases on the SS316L substrate in the first layer with a fixed gap between adjacent corrugated structures. Then, IN625 hard phases with the same corrugated shape are deposited at the gap positions in the same layer. The arrangement positions of the two types of alloys are interchanged in subsequent deposition layers and stacked layer by layer to make SS316L and IN625 achieve a periodic interlocking arrangement in the horizontal and vertical directions, thus preparing a periodic rigid-flexible coupled SS316L / IN625 heterogeneous biomimetic structure component. Step 3: Heat-treat the obtained components to optimize the interface bonding and obtain the finished SS316L / IN625 heterogeneous biomimetic structural material.

2. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, In step one, the method for constructing the heterogeneous biomimetic structural model specifically includes: Construct a cuboid base with length, width, and height of L, W, and H, respectively; divide it into several equally spaced layers along the height / Z axis to form a layered alternating structure with clear horizontal interfaces; Inside each layer, multiple triangular wave tooth structures are constructed along the width / X-axis direction, and the wave propagation direction is along the length / Y-axis direction. The apex angle, amplitude, and period of the triangular wave tooth structure are set to form an interlocking interface where the wave crests and troughs mesh with each other. The designed layered interlocking structural units are linearly arrayed along the X, Y, and Z axes of the Cartesian coordinate system to obtain a heterogeneous biomimetic structural model.

3. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 2, characterized in that, The triangle is defined as an isosceles triangle with a vertex angle α of 90°, an amplitude A of 3.5 mm, and a period P of 7.0 mm.

4. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, In step two, the alternating deposition of SS316L and IN625 alloy powders specifically involves: The length direction of the heterogeneous biomimetic structural model is the scanning direction, the width direction is the stepping direction, and the height direction is the construction direction. During each deposition process, SS316L or IN625 is deposited at intervals along the stepping direction, and then IN625 or SS316L is deposited in the interstitial region formed therein, so that the soft phase of SS316L and the hard phase of IN625 are laterally complementary and interlocked in each layer. Next, in the next deposition process, another material opposite to the previous layer is deposited, and then the remaining material is deposited in the gap region formed, changing the deposition sequence periodically. Subsequent layers follow the same pattern, thus forming a longitudinal layered alternation between the SS316L soft phase and the IN625 hard phase between layers, ultimately obtaining a heterogeneous biomimetic structural material molded part with transverse heterogeneous interlocking and longitudinal layered heterogeneous alternation.

5. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, In step two, the printing parameters are set as follows: laser power 500W, scanning speed 450~550mm / min, scanning interval 0.8mm, step distance along the forming direction 0.5mm, powder feeding rate 1.5~2.0r / min, and protective gas flow rate 10.8L / min.

6. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, During the printing process, when SS316L and IN625 alloy powders are used alternately, the switching control of "pause powder feeding / pause laser - powder path switching and purging - stable powder feeding - resume cladding" is executed. The pause powder feeding / pause laser time is 10s, and the interlayer cooling time is set to 5min after each layer is deposited.

7. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, In step three, the heat treatment includes solution treatment and two-stage aging treatment. The solution treatment involves holding at 1150℃ for 1 hour followed by water quenching. The two-stage aging treatment involves holding at 720℃ for 4 hours, then lowering the temperature to 620℃ for 4 hours, followed by water quenching.

8. The method for preparing the SS316L / IN625 heterogeneous biomimetic structural material according to claim 1, characterized in that, After step three, the method further includes: The heat-treated material is polished and then ultrasonically treated by immersion in anhydrous alcohol to remove the powder adhering to the surface.

9. An SS316L / IN625 heterogeneous biomimetic structural material, characterized in that, The SS316L / IN625 heterogeneous biomimetic structural material is prepared by the preparation method of any one of claims 1 to 8. The SS316L / IN625 heterogeneous biomimetic structural material includes a soft phase region of SS316L and a hard phase region of IN625. The two are distributed in a periodic manner with transverse heterogeneous interlocking and longitudinal layered heterogeneous alternation. Furthermore, a complementary interlocking interface is provided at the transverse interface between the two phases of SS316L and IN625. The interlocking interface has a wavy tooth configuration.

10. The SS316L / IN625 heterogeneous biomimetic structural material according to claim 9, characterized in that, The thickness t of a single layer in the longitudinal layered structure is 0.5±0.3mm, and the ratio of the soft phase region of SS316L to the hard phase region of IN625 is 0.7:1~1:0.7.

Images