Method for manufacturing gradient nitrogen-containing metal material through laser additive and product

Abstract

The invention belongs to the technical field of gradient nitrogen-containing metal laser additive manufacturing, and particularly relates to a method for manufacturing a gradient nitrogen-containing metal material through laser additive manufacturing and a product. Firstly, three-dimensional gradient distribution of nitrogen elements is preset in a three-dimensional model; slicing the model to generate a processing parameter packet containing a nitrogen partial pressure set value; laser is adopted to melt metal powder layer by layer in the nitrogen atmosphere, the nitrogen partial pressure is dynamically regulated and controlled within the range of 200 Pa-2 MPa at the speed larger than or equal to 101.325 kPa / 30 s, and the nitrogen content consistent with the preset gradient is formed in a solidification layer; further, the same layer is divided into more than or equal to two nitrogen control micro-areas, and the nitrogen partial pressure of the micro-areas is switched in a time-sharing manner, so that the regional jump or continuous gradual change of the nitrogen content in the single layer is realized. And after all layers are stacked, nitrogen-containing metal material products which are in gradient distribution in the three-dimensional space and the same layer are obtained.

Description

Technical Field

[0001] This application belongs to the field of gradient nitrogen-containing metal laser additive manufacturing technology, and particularly relates to a method and product for laser additive manufacturing of gradient nitrogen-containing metal materials. Background Technology

[0002] While existing nitriding, multilayer welding, or sintering processes can introduce nitrogen onto the metal surface, they only form surface layers or discrete stacks, failing to continuously control the nitrogen content within the three-dimensional space of the part. This results in weak interfacial bonding, abrupt gradient transitions, and the inability to manufacture complex structures. Although additive manufacturing in a constant nitrogen atmosphere allows for in-situ alloying, the fixed nitrogen partial pressure prevents the nitrogen solubility in the molten pool from varying layer by layer, leading to uniform nitrogen content and a lack of gradient, making it difficult to simultaneously meet the contradictory requirements of "hard surface and tough interior." Summary of the Invention

[0003] This application provides a method and product for laser additive manufacturing of gradient nitrogen-containing metal materials to solve the following technical problem: how to continuously and accurately control the nitrogen content gradient in three-dimensional space.

[0004] In a first aspect, embodiments of this application provide a method for laser additive manufacturing of gradient nitrogen-containing metal materials, characterized in that the method includes the following steps: A three-dimensional model of the target part is established, wherein the three-dimensional model contains a preset gradient distribution of nitrogen element in three-dimensional space; The three-dimensional model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least the nitrogen partial pressure setting value for each printing layer. Metal powder is arranged in the molding cavity, wherein the metal powder is a metal or alloy that can undergo an alloying reaction with nitrogen; Under a nitrogen atmosphere, the metal powder is melted layer by layer by laser. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters. The nitrogen partial pressure changes at a rate of not less than 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. After stacking all layers, a gradient nitrogen-containing metal material product is obtained in which the nitrogen content changes continuously or stepwise in three-dimensional space.

[0005] Optionally, the preset gradient distribution is established based on Sieverts' law and a database of in-situ nitriding performance of metallic materials.

[0006] Optionally, the processing parameter package further includes laser power, scanning speed, and scanning spacing, wherein the laser power, scanning speed, and scanning spacing correspond one-to-one with the nitrogen partial pressure setting value within each printing layer.

[0007] Optionally, the metal powder is selected from stainless steel powder, titanium powder, titanium alloy powder, chromium powder, vanadium powder, molybdenum powder, or high-entropy alloy powder.

[0008] Optionally, the gradient nitrogen-containing metal material product is a biomedical implant, a high-strength component for aerospace, a wear-resistant component, or a corrosion-resistant component.

[0009] Optionally, the laser method includes laser powder bed melting or laser direct energy deposition.

[0010] Optionally, the method further includes: Within the same slice layer, it is further divided into ≥2 independently controllable nitrogen-controlled micro-regions. When the laser scans the layer, the nitrogen partial pressure above each micro-region is switched in a time-division manner to make the nitrogen partial pressure difference between adjacent micro-regions ≥50kPa and the switching response time ≤1s. This allows the nitrogen content in different regions within the same layer of the nitrogen-containing metal material to be distributed as needed, forming a jump or gradual gradient.

[0011] Optionally, the nitrogen-controlled microregions are arranged in the form of a lattice, a grid, concentric rings, or a functional topological contour.

[0012] In a second aspect, embodiments of this application provide a gradient nitrogen-containing metal material article, characterized in that it is made by the method described in any one of the first aspects, the gradient nitrogen-containing metal material article having a single metal matrix, wherein the nitrogen content inside the single metal matrix is ​​distributed in a continuous or stepwise gradient in three-dimensional space.

[0013] Optionally, the nitrogen content increases linearly from 0.07 wt% to 0.6 wt% in the construction direction.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: Since the root cause of the inability to form a nitrogen content gradient in three-dimensional space is that "a constant nitrogen atmosphere leads to uniform nitrogen solubility in the molten pool layer by layer", this application first writes "preset nitrogen element gradient distribution" into the three-dimensional model, thereby converting the target gradient into calculable spatial information; then, the three-dimensional model is sliced, so that each slice corresponds to a unique nitrogen partial pressure setting value and forms a processing parameter package, thereby discretizing the spatial gradient into layer-by-layer executable variables; subsequently, when the laser melts the metal powder layer by layer, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled in the range of 200Pa–2MPa at a rate of not less than 101.325kPa / 30s, thereby allowing each solidified layer to obtain a nitrogen content matching the setting value of that layer according to Sieverts' law; as the layer thickness accumulates, the nitrogen content of each layer is continuously connected according to the preset gradient, thereby constructing a continuous or stepped nitrogen content gradient in the three-dimensional space of the entire part, ultimately solving the technical problem of "how to continuously and accurately control the nitrogen content gradient in three-dimensional space". Compared to the inertial approach of maintaining a constant P_N2 in existing technologies, this application's embodiments are the first to set "nitrogen partial pressure" as a layer-by-layer active variable, replacing the static atmosphere with rapid closed-loop control, demonstrating technological progress. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0017] Figure 1 This is a process diagram illustrating the preparation of gradient nitrogen-containing metal material products in the embodiments of this application; Figure 2 This is a schematic diagram of a gradient nitrogen-containing metal material product in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0020] In a first aspect, embodiments of this application provide a method for laser additive manufacturing of gradient nitrogen-containing metal materials, characterized in that the method includes the following steps: S1. Establish a three-dimensional model of the target part, wherein the three-dimensional model contains a preset gradient distribution of nitrogen element in three-dimensional space; S2. The three-dimensional model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least the nitrogen partial pressure setting value for each printing layer. S3. Arrange metal powder in the molding cavity, wherein the metal powder is a metal or alloy that can undergo an alloying reaction with nitrogen; S4. Under a nitrogen atmosphere, the metal powder is melted layer by layer by laser. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters, so that the nitrogen partial pressure changes at a rate of not less than 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. S5. After stacking all layers, a gradient nitrogen-containing metal material product is obtained in which the nitrogen content changes continuously or stepwise in three-dimensional space.

[0021] Because existing technologies use constant nitrogen partial pressure, resulting in uniform nitrogen solubility in each molten pool layer, a spatial gradient cannot be formed. Claim 1 incorporates a preset gradient distribution into the 3D model, transforming the spatial gradient into discrete layer data. It then generates processing parameter packages by slicing the 3D model, ensuring each printing layer has a unique nitrogen partial pressure setting. Subsequently, during the laser-melted metal powder layer-by-layer process, the nitrogen partial pressure in the forming cavity is dynamically and intelligently controlled in zones, causing the nitrogen partial pressure to change layer by layer according to the set value. This, based on Siefvert's law, ensures that the nitrogen content of each solidified metal layer corresponds to the set value. As the layer thickness accumulates, the nitrogen content of each layer continuously connects, forming a continuous or stepped nitrogen content gradient in 3D space, ultimately solving the technical problem of "how to continuously and accurately control the nitrogen content gradient in 3D space." This invention is the first to change "nitrogen partial pressure" from a static atmosphere to a layer-by-layer active variable, replacing a constant atmosphere with rapid closed-loop control to achieve gradient in-situ forming. Nitrogen partial pressure includes, but is not limited to, 200 Pa, 1 kPa, 10 kPa, 100 kPa, 1 MPa, and 2 MPa.

[0022] In some implementations, the preset gradient distribution is established based on Sieverts' law and a database of in-situ nitriding performance of metallic materials.

[0023] "Sieverts' Law" states that nitrogen solubility is proportional to the square root of nitrogen partial pressure. Since the preset gradient distribution requires quantifying the nitrogen-pressure relationship, this technical solution establishes the preset gradient distribution based on Sieverts' Law and a database of in-situ nitriding performance of metallic materials. This ensures a one-to-one correspondence between the nitrogen partial pressure setpoint and the target nitrogen content, thereby making the processing parameter package physically predictable and ultimately guaranteeing continuous and precise control of the three-dimensional nitrogen content gradient.

[0024] In some embodiments, the processing parameter package further includes laser power, scanning speed, and scanning spacing, wherein the laser power, the scanning speed, the scanning spacing, and the nitrogen partial pressure setting value correspond one-to-one within each printing layer.

[0025] Since nitrogen solubility is affected by both the molten pool temperature and convection, this technical solution introduces laser power, scanning speed and scanning spacing into the processing parameter package, and makes the laser power, scanning speed, scanning spacing and nitrogen partial pressure settings correspond one-to-one in each printed layer. In this way, the molten pool temperature and convection are finely adjusted by energy input, thereby ensuring that the nitrogen content of each layer is determined only by the corresponding nitrogen partial pressure, and ultimately maintaining the precise continuity of the nitrogen content gradient in three-dimensional space.

[0026] In some embodiments, the metal powder is selected from stainless steel powder, titanium powder, titanium alloy powder, chromium powder, vanadium powder, molybdenum powder, or high-entropy alloy powder.

[0027] Since the metal powder needs to undergo an alloying reaction with nitrogen, this technical solution limits the selection of metal powder from the above-mentioned set, thereby ensuring that nitrogen atoms can be dissolved in the solidified metal layer during laser melting, so that the nitrogen content of each layer changes monotonically with the change of nitrogen partial pressure, and finally achieves continuous and precise control of nitrogen content gradient in three-dimensional space.

[0028] In some embodiments, the gradient nitrogen-containing metal material product is a biomedical implant, a high-strength component for aerospace, a wear-resistant component, or a corrosion-resistant component.

[0029] Since different scenarios have the same requirement for the "hard surface and tough interior" gradient, this technical solution limits the products to the above categories, thereby directly converting the continuous nitrogen content gradient in three-dimensional space into a performance gradient, and thus simultaneously meeting the composite indicators of high strength, high toughness, wear resistance, and corrosion resistance, ultimately solving the problem of application positioning of gradient materials.

[0030] In some embodiments, the laser method includes laser powder bed melting or laser direct energy deposition.

[0031] Since the metal powder needs to be melted layer by layer by laser, this technical solution limits the use of laser powder bed melting or direct laser energy deposition to provide a stable molten pool environment. This ensures that the nitrogen partial pressure changes act on the molten pool surface in real time, and ultimately enables the continuous and precise control of the nitrogen content gradient in three-dimensional space.

[0032] In some embodiments, the method further includes: Within the same slice layer, it is further divided into ≥2 independently controllable nitrogen-controlled micro-regions. When the laser scans the layer, the nitrogen partial pressure above each micro-region is switched in a time-division manner to make the nitrogen partial pressure difference between adjacent micro-regions ≥50kPa and the switching response time ≤1s. This allows the nitrogen content in different regions within the same layer of the nitrogen-containing metal material to be distributed as needed, forming a jump or gradual gradient.

[0033] The same slice layer is further divided into two or more independently controllable nitrogen-controlled micro-regions. When the layer is scanned by laser, the nitrogen partial pressure above each micro-region is switched in a time-division manner to make the nitrogen partial pressure difference between adjacent micro-regions greater than or equal to 50 kPa and the switching response time less than or equal to 1 s. Thus, according to Siefvert's law, different nitrogen solubility is formed in different regions within the same solidified layer. This allows the nitrogen-containing metal material to exhibit a jump or gradual nitrogen content distribution within the same layer as needed. Finally, a local performance gradient is pre-set in the two-dimensional plane to collaboratively solve the technical problem of three-dimensional spatial gradient forming and local functional matching.

[0034] In some embodiments, the nitrogen-controlled microregions are arranged in the form of a lattice, a grid, concentric rings, or a functional topological profile.

[0035] The nitrogen-controlled micro-regions are arranged in the form of lattices, grids, concentric rings, or functional topological contours. By coupling the geometric boundaries of the micro-regions with the laser scanning path, the high-nitrogen areas are precisely aligned with the high-wear or high-corrosion paths, while the low-nitrogen areas are retained in the high-toughness requirement areas. This allows for the one-time patterning of "composition-performance" in a single-layer scan, which further extends the gradient dimension to a two-dimensional plane compared to the existing technology that only gradients along the construction direction.

[0036] In a second aspect, embodiments of this application provide a gradient nitrogen-containing metal material article, characterized in that it is made by the method described in any one of the first aspects, the gradient nitrogen-containing metal material article having a single metal matrix, wherein the nitrogen content inside the single metal matrix is ​​distributed in a continuous or stepwise gradient in three-dimensional space.

[0037] Since the method has formed a continuous or stepped nitrogen content gradient in three-dimensional space, the technical solution fixes the spatial gradient as the composition distribution in a single metal matrix, thereby directly endowing the product with "hard on the outside and tough on the inside" properties. Thus, it can meet the requirements of high strength and high toughness at the same time without subsequent surface treatment, and finally solves the problem of one-time forming of gradient structure parts.

[0038] In some embodiments, the nitrogen content increases linearly from 0.07 wt% to 0.6 wt% in the construction direction.

[0039] Since the aforementioned method has defined the nitrogen content gradient as existing in three-dimensional space, this technical solution further provides an example of the nitrogen content linearly increasing from 0.07wt% to 0.6wt% in the construction direction, thereby providing a verifiable monotonic gradient, which in turn provides a quantitative boundary for the continuous transition of mechanical properties, and ultimately ensures that the nitrogen content gradient in three-dimensional space can be reproduced and detected.

[0040] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0041] Example 1 A method for laser additive manufacturing of gradient nitrogen-containing metallic materials, the method comprising the following steps: A three-dimensional model of the target part is established, wherein the three-dimensional model contains a preset gradient distribution of nitrogen element in three-dimensional space, and the preset gradient distribution is a nitrogen content distribution that increases linearly along the construction direction; The three-dimensional model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least a nitrogen partial pressure setting value for each printing layer, and the nitrogen partial pressure setting value increases linearly from 0.1 MPa to 1.5 MPa along the construction direction. 316L stainless steel powder is arranged in the molding cavity. The 316L stainless steel powder is a metal powder that can undergo an alloying reaction with nitrogen. Under a nitrogen atmosphere, the 316L stainless steel powder is melted layer by layer using a laser powder bed melting method. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters, so that the nitrogen partial pressure changes at a rate of 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. After stacking all layers, a gradient nitrogen-containing metal material plate with a continuous gradient change in nitrogen content in three-dimensional space is obtained. The nitrogen content of the plate increases linearly from 0.07wt% to 0.6wt% along the construction direction.

[0042] Example 2 A method for laser additive manufacturing of gradient nitrogen-containing metallic materials, the method comprising the following steps: A three-dimensional model of the target part is established. The three-dimensional model includes a preset gradient distribution of nitrogen element in three-dimensional space. The preset gradient distribution is a radial gradient with high nitrogen content on the surface and low nitrogen content in the core. The three-dimensional model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least a nitrogen partial pressure setting value for each printing layer, and the nitrogen partial pressure setting value decreases from the surface to the center. 316L stainless steel powder is placed inside the molding cavity; Under a nitrogen atmosphere, the 316L stainless steel powder is melted layer by layer using a laser powder bed melting method. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters, so that the nitrogen partial pressure changes at a rate of 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. After stacking all layers, a gradient nitrogen-containing metal material rod with a continuous gradient change in nitrogen content in three-dimensional space is obtained. The surface nitrogen content of the rod is 0.6 wt%, and the core nitrogen content is 0.07 wt%.

[0043] Example 3 A method for laser additive manufacturing of gradient nitrogen-containing metallic materials, the method comprising the following steps: A three-dimensional model of a gear is established, which includes a preset gradient distribution of nitrogen in three-dimensional space. The preset gradient distribution is a continuously decreasing distribution with high nitrogen content on the tooth surface and low nitrogen content at the tooth root and core. The gear 3D model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least the nitrogen partial pressure setting value for each printing layer, and the nitrogen partial pressure setting value decreases from the tooth surface to the center. Gear steel powder is placed inside the molding cavity; Under a nitrogen atmosphere, the gear steel powder is melted layer by layer using a laser powder bed melting method. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters, so that the nitrogen partial pressure changes at a rate of 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. After stacking all layers, a gradient nitrogen-containing metal material gear with a continuous gradient change in nitrogen content in three-dimensional space is obtained. The nitrogen content on the tooth surface of the gear is 0.6 wt%, and the nitrogen content in the core is 0.07 wt%.

[0044] Example 4 According to the method for laser additive manufacturing of gradient nitrogen-containing metal materials described in Example 1, a partitioned intelligent pressure-controlled laser additive manufacturing printer with an array of 8 annular air inlets was used during preparation to verify the partitioned gradient within the same layer.

[0045] 1) Create a 3D model of a 10mm×10mm×5mm cube, and then divide the 10th layer (z=1mm) into three closed contours: area A (center circle Ø4mm), area B (ring 4–7mm), and area C (outer ring 7–10mm).

[0046] 2) Generate a layer-partition dual index parameter package for this layer slice: P_N2=0.2MPa for area A, 0.8MPa for area B, and 1.5MPa for area C; keep other layers constant at 0.5MPa.

[0047] 3) 316L powder is selected, laser powder bed melting is used, and the switching response of the 8-channel valve array is 0.5s.

[0048] 4) After printing, samples were taken and the nitrogen content in regions A / B / C of the same layer was measured to be 0.07wt%, 0.35wt%, and 0.60wt% respectively by EBSD-EDS surface scanning. The hardness was HV275→320→425, realizing the intralayer gradient of high toughness center to high hardness outer ring of single layer.

[0049] Comparative Example 1 A method for laser additive manufacturing of nitrogen-containing metallic materials under constant nitrogen partial pressure, the method comprising the following steps: A three-dimensional model of the target part is established, wherein the three-dimensional model does not include the nitrogen element gradient distribution; The three-dimensional model is sliced ​​to generate a processing parameter package, which includes a constant nitrogen partial pressure setting value, which is constant at 0.8 MPa. 316L stainless steel powder is placed inside the molding cavity; Under a nitrogen atmosphere, the 316L stainless steel powder is melted layer by layer using a laser powder bed melting method, and the nitrogen partial pressure in the forming cavity is kept constant during the layer-by-layer melting process. After stacking all layers, a nitrogen-containing metal material plate with uniform nitrogen content is obtained, wherein the nitrogen content of the plate is 0.33 wt%.

[0050] Comparative Example 2 A method for laser additive manufacturing of nitrogen-containing metallic materials under constant nitrogen partial pressure, the method comprising the following steps: Create a 3D model of the target part; The three-dimensional model is sliced ​​to generate a processing parameter package, which includes a constant nitrogen partial pressure setting value, which is constant at 0.8 MPa. 316L stainless steel powder is placed inside the molding cavity; Under a nitrogen atmosphere, the 316L stainless steel powder is melted layer by layer using a laser powder bed melting method, while maintaining a constant nitrogen partial pressure in the forming cavity; After stacking all layers, a nitrogen-containing metal rod with uniform nitrogen content is obtained, wherein the nitrogen content of the rod is 0.33 wt%.

[0051] Comparative Example 3 A method for laser additive manufacturing of nitrogen-containing metallic materials under constant nitrogen partial pressure, the method comprising the following steps: Create a 3D model of the gear; The gear 3D model is sliced ​​to generate a machining parameter package, which includes a constant nitrogen partial pressure setting value, which is constant at 0.8 MPa. Gear steel powder is placed inside the molding cavity; Under a nitrogen atmosphere, the gear steel powder is melted layer by layer using a laser powder bed melting method, while maintaining a constant nitrogen partial pressure in the forming cavity; After all layers are deposited, a nitrogen-containing metal gear with uniform nitrogen content is obtained, wherein the nitrogen content of the gear is 0.33 wt%.

[0052] Table 1. Results data for both the examples and comparative examples.

[0053] As shown in Table 1, the technological advancements of this application's technical solution include: 1. Interlayer gradient curing Examples 1–3 show a monotonically increasing hardness of HV 275→420 along the construction direction, radial direction, or tooth profile, while the comparative example shows no gradient of HV 310±10 throughout, confirming that variable nitrogen partial pressure can precisely lock the interlayer nitrogen difference within ±0.02 wt%.

[0054] 2. The partial pressure of nitrogen changes from a "protection constant" to a "process variable". Within the range of 200 Pa–2 MPa, closed-loop switching is performed at a rate of ≥101 kPa / 30 s, and Sieverts' law is applied online, enabling quantitative nitriding layer by layer with the ability to "add to whichever layer is specified".

[0055] 3. Three-dimensional gradient one-time forming No subsequent nitriding, welding, or rolling is required. A single machine can complete the coupling of composition, microstructure, and properties on complex curved surfaces. The gradient direction can be arbitrarily specified in the construction direction, radial direction, tooth profile, or micro-region in the same layer, and "hard on the surface and tough on the inside" parts (gears, acetabular cups, compressor blades) can be formed with one click, eliminating the problems of weak interface, large deformation, and scattered process caused by multiple processes.

[0056] 4. Intra-layer gradient jump Dividing the same layer into ≥3 micro-regions, the pressure is adjusted by time-sharing through an array of 8 intake valves, and the switching from 0.2 to 1.5 MPa is completed within 0.5 s. The nitrogen difference of a single layer is ≥0.25 wt%, the hardness jumps by 150 HV, the transition zone is <60 μm, and the local performance matching of "center toughness - outer ring hardness" is achieved, expanding the dimensions of additive gradient design.

[0057] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for laser additive manufacturing of gradient nitrogen-containing metallic materials, characterized in that, The method includes the following steps: A three-dimensional model of the target part is established, wherein the three-dimensional model contains a preset gradient distribution of nitrogen element in three-dimensional space; The three-dimensional model is sliced ​​to generate a processing parameter package corresponding to the preset gradient distribution. The processing parameter package includes at least the nitrogen partial pressure setting value for each printing layer. Metal powder is arranged in the molding cavity, wherein the metal powder is a metal or alloy that can undergo an alloying reaction with nitrogen; Under a nitrogen atmosphere, the metal powder is melted layer by layer by laser. During the layer-by-layer melting process, the nitrogen partial pressure in the forming cavity is intelligently and dynamically controlled according to the processing parameters. The nitrogen partial pressure changes at a rate of not less than 101.325 kPa / 30s within the range of 200 Pa to 2 MPa, so as to form a nitrogen content gradient in the solidified metal layer that is consistent with the preset gradient distribution. After stacking all layers, a gradient nitrogen-containing metal material product is obtained in which the nitrogen content changes continuously or stepwise in three-dimensional space.

2. The method according to claim 1, characterized in that, The preset gradient distribution is established based on Sieverts' law and a database of in-situ nitriding performance of metallic materials.

3. The method according to claim 1, characterized in that, The processing parameter package further includes laser power, scanning speed, and scanning spacing, and the laser power, scanning speed, scanning spacing, and nitrogen partial pressure setting value correspond one-to-one in each printing layer.

4. The method according to claim 1, characterized in that, The metal powder is selected from stainless steel powder, titanium powder, titanium alloy powder, chromium powder, vanadium powder, molybdenum powder, or high-entropy alloy powder.

5. The method according to claim 1, characterized in that, The gradient nitrogen-containing metal material products are biomedical implants, high-strength components for aerospace, wear-resistant components, or corrosion-resistant components.

6. The method according to claim 1, characterized in that, The laser methods include laser powder bed melting or laser direct energy deposition.

7. The method according to claim 1, characterized in that, The method further includes: Within the same slice layer, it is further divided into ≥2 independently controllable nitrogen-controlled micro-regions. When the laser scans the layer, the nitrogen partial pressure above each micro-region is switched in a time-division manner to make the nitrogen partial pressure difference between adjacent micro-regions ≥50kPa and the switching response time ≤1s. This allows the nitrogen content in different regions within the same layer of the nitrogen-containing metal material to be distributed as needed, forming a jump or gradual gradient.

8. The method according to claim 7, characterized in that, The nitrogen-controlled microregions are arranged in the form of lattice, grid, concentric rings, or functional topological contours.

9. A gradient nitrogen-containing metal material product, characterized in that, Made by the method of any one of claims 1 to 8, the gradient nitrogen-containing metal material article has a single metal matrix, and the nitrogen content inside the single metal matrix is ​​distributed in a continuous or stepped gradient in three-dimensional space.

10. The gradient nitrogen-containing metal material product according to claim 9, characterized in that, The nitrogen content increases linearly from 0.07 wt% to 0.6 wt% in the construction direction.

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