A method for printing nickel-based alloy forging based on electromagnetic field

Abstract

This application provides a nickel-based alloy forging printing method based on electromagnetic fields, relating to the field of additive manufacturing technology. The method includes: pre-treating nickel-based alloy powder and a metal substrate respectively; scanning the nickel-based alloy powder layer by layer with a laser to form a molten pool; after each layer forms a molten pool, using an infrared thermal imager and a high-speed camera to monitor the temperature gradient and flow rate of the molten pool in real time; when the solid fraction of the molten pool is 30%-70%, applying a gradient electromagnetic field according to the temperature gradient and emitting an ultrafast laser shock wave according to the flow rate; until all layers are processed, a formed part is obtained. The above method significantly improves the density, microstructure uniformity, and high-temperature stability of the formed part.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a nickel-based alloy forging printing method based on electromagnetic fields. Background Technology

[0002] Nickel-based alloys are widely used in the manufacture of high-temperature components such as aero-engines and gas turbines due to their excellent high-temperature strength, corrosion resistance, and oxidation resistance. Methods for manufacturing components using nickel-based alloys include traditional processing methods such as casting and forging, as well as laser powder bed fusion (LPBF) technology. However, traditional processing methods suffer from difficulties in forming complex structures and high defect rates, while LPBF technology faces challenges such as large thermal gradients, inhomogeneous microstructure, and difficulty in defect control. Specifically, large thermal gradients manifest as rapid cooling of the molten pool, leading to residual stress accumulation and a tendency to cause cracks and warping. Inhomogeneous microstructure manifests as severe elemental segregation within the molten pool; for example, the brittle interdendritic phase of the Laves phase significantly reduces material properties. Difficulty in defect control manifests as a tendency for defects such as porosity and incomplete fusion, affecting density and mechanical properties. Methods for manufacturing components using nickel-based alloys also include methods for improving molten pool fluidity by using electromagnetic field-assisted LPBF, and methods for reducing residual stress by combining forging printing technology with LPBF. However, in the method of improving molten pool fluidity by using electromagnetic field assistance, optimizing molten pool flow solely through electromagnetic stirring has limited effect on refining the microstructure; and in the method of reducing residual stress by using forging printing technology, there is a problem of not being able to suppress element segregation. Summary of the Invention

[0003] This invention aims to at least solve the aforementioned technical problems existing in the prior art. To this end, this invention proposes a nickel-based alloy forging printing method based on an electromagnetic field, the method comprising:

[0004] The nickel-based alloy powder and the metal substrate were pretreated separately.

[0005] A molten pool is formed by scanning the nickel-based alloy powder layer by layer with a laser;

[0006] After each layer forms a molten pool, an infrared thermal imager and a high-speed camera are used to monitor the temperature gradient and flow rate of the molten pool in real time. When the solid fraction of the molten pool is 30%-70%, a gradient electromagnetic field is applied according to the temperature gradient, and an ultrafast laser shock wave is emitted according to the flow rate.

[0007] The process continues until all layers are processed to obtain the final product.

[0008] Optionally, applying the gradient electromagnetic field according to the temperature gradient includes:

[0009] The electromagnetic field strength is determined based on the temperature gradient.

[0010] Optionally, the expression for the electromagnetic field strength is:

[0011]

[0012] Where B is the electromagnetic field strength, k1 is the magnetic field gain coefficient, ΔT is the molten pool temperature gradient monitored in real time by the infrared thermal imager, and k3 is the flow velocity abrupt change compensation coefficient. This represents the rate of change of the molten pool flow rate over time.

[0013] Optionally, emitting the ultrafast laser shock wave according to the flow rate includes:

[0014] The shock wave energy density is determined based on the flow rate.

[0015] Optionally, the expression for the shock wave energy density is:

[0016]

[0017] Where E is the shock wave energy density, k2 is the energy adjustment coefficient, v is the molten pool flow rate monitored in real time by the high-speed camera, and k4 is the supercooled zone compensation coefficient. Let be the Laplace operator for the temperature field on the surface of the molten pool, and let represent the curvature of the temperature field.

[0018] Optionally, after forming a molten pool in each layer, the process further includes:

[0019] The duration of the metastable phase of the molten pool is monitored in real time. When the duration of the metastable phase of the molten pool exceeds 20-50ms, the laser scanning speed of the next layer is adjusted. The duration of the metastable phase of the molten pool is the duration when the solid fraction of the molten pool is 30%-70%.

[0020] Optionally, the gradient direction of the gradient electromagnetic field makes an angle of 45-75 degrees with the laser scanning path.

[0021] Optionally, an alternating current is applied to the metal substrate or a gradient electromagnetic field is generated using a Halbach permanent magnet array.

[0022] Optionally, the pretreatment of the nickel-based alloy powder and the metal substrate includes:

[0023] The nickel-based alloy powder is subjected to high-energy ball milling or surface modification treatment;

[0024] The surface of the metal substrate is cleaned and roughened.

[0025] The beneficial effects of a nickel-based alloy forging and printing method based on electromagnetic fields are as follows: When the solidity of the molten pool is 30%-70%, a gradient electromagnetic field is applied according to the temperature gradient. The gradient electromagnetic field drives the directional migration of Nb, Ti, and other strengthening elements in the molten pool, thereby suppressing interdendritic segregation and the continuous distribution of brittle phases between dendrites, while improving high-temperature creep strength. In addition, the gradient magnetic field decreases along the vertical direction, compensating for heat accumulation between layers and solving the problem of grain coarsening at the top of components larger than 100mm. When the solidity of the molten pool is 30%-70%, an ultrafast laser shock wave is emitted according to the flow rate to forge the molten layer. The shock wave breaks the primary dendrites, promotes the formation of equiaxed crystals, and can suppress remelting in the impact zone, avoid the formation of a secondary heat-affected zone, and maintain the grain refinement effect. In addition, the gradient electromagnetic field and the ultrafast laser shock wave work together, and the compressive stress of the shock wave counteracts the turbulence caused by the electromagnetic Lorentz force, stabilizing the molten pool morphology. Attached Figure Description

[0026] Figure 1 A flowchart of a nickel-based alloy forging and printing method based on an electromagnetic field is provided for an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the structure of the nickel-based alloy forging printing equipment based on electromagnetic fields in an embodiment of the present invention;

[0028] Wherein: 1-metal substrate, 2-powder bed laser, 3-powder bed galvanometer assembly, 4-ultrafast laser galvanometer assembly, 5-ultrafast laser, 6-electrode, 7-permanent magnet array;

[0029] Figure 3 This is a schematic diagram of the gradient electromagnetic field distribution in an embodiment of the present invention;

[0030] Wherein: 8-scanning path, 9-gradient magnetic field, 10-permanent magnet array;

[0031] Figure 4 This is a flowchart illustrating the synergistic effect of ultrafast laser shock waves and electromagnetic field shock waves in an embodiment of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0034] This invention provides a method for forging and printing nickel-based alloys based on electromagnetic fields, such as... Figure 1 As shown, the method may include the following steps:

[0035] Step 101: Pre-treat the nickel-based alloy powder and the metal substrate respectively.

[0036] In one possible implementation, the pretreatment of the nickel-based alloy powder and the metal substrate includes:

[0037] The nickel-based alloy powder is subjected to high-energy ball milling or surface modification treatment;

[0038] The surface of the metal substrate is cleaned and roughened.

[0039] Specifically, the forging printing method in this embodiment of the invention is a composite additive manufacturing method based on LPBF (Laser Powder Bed Fusion). By introducing electromagnetic field assistance and ultrafast laser shock forging technology, it achieves microstructure control and mechanical property improvement of nickel-based alloys. The selected nickel-based alloy powder is suitable for LPBF technology; for example, Inconel 738 powder can be selected. High-energy ball milling or surface modification treatment of the nickel-based alloy powder to magnetize it can enhance the powder's response characteristics in an electromagnetic field. Simultaneously, the magnetized powder is more uniformly distributed during the powder spreading process, reducing localized accumulation defects. Alternatively, Inconel 738 powder can be gas-atomized and ball-milled under inert gas protection to form a magnetic layer on the powder surface. Among them, the gas atomization process refers to atomizing molten metal into micron-sized droplets through a high-pressure inert gas nozzle. The droplets spherize and solidify into powder under the action of surface tension. The powder solidified by the gas atomization process has high sphericity, good flowability, and an oxygen content of less than 100 ppm, which can effectively avoid the oxidation failure of the magnetic layer. In addition, the particle size distribution is concentrated between 15-53 μm, which is suitable for LPBF process.

[0040] Clean the surface of the metal substrate to remove oxide layers and oil stains, and roughen it to enhance powder adhesion.

[0041] After the nickel-based alloy powder and metal substrate are pretreated, the nickel-based alloy forging printing equipment is configured, and a gradient magnetic field module and an ultrafast laser module are integrated into the LPBF equipment. Figure 2 This is a schematic diagram of the structure of the nickel-based alloy forging printing equipment based on electromagnetic fields in an embodiment of the present invention. The powder bed laser is the main laser that generates the heat source for the molten pool. The powder bed galvanometer assembly is a laser scanning galvanometer system that controls the scanning path of the main laser. The ultrafast laser galvanometer assembly is a shock wave positioning galvanometer system that independently controls the position of the shock wave, and can apply a time-varying electric field to the electrodes to generate a gradient magnetic field. After configuration, process parameters are set; specifically, the laser power is 400W, the scanning speed is 1000mm / s, and the layer thickness is 40μm.

[0042] The pre-treated substrate is fixed on the platform to ensure a stable processing procedure.

[0043] Step 102: The nickel-based alloy powder is scanned layer by layer by laser to form a molten pool.

[0044] Step 103: After the molten pool is formed in each layer, the temperature gradient and flow rate of the molten pool are monitored in real time using an infrared thermal imager and a high-speed camera. When the solid fraction of the molten pool is 30%-70%, a gradient electromagnetic field is applied according to the temperature gradient, and an ultrafast laser shock wave is emitted according to the flow rate.

[0045] In one possible implementation, alternating current is applied to the metal substrate or a gradient electromagnetic field is generated using a Halbach permanent magnet array.

[0046] Specifically, for a magnetic field strength of 0.1-1.0T, an orthogonal electrode array can be pre-embedded at the bottom of the metal substrate, and an alternating current of 1-10kHz can be applied. The gradient direction can be controlled by adjusting the phase difference of the electrodes. Alternatively, a Halbach permanent magnet array can be installed around the substrate, and the gradient direction can be set by mechanically rotating the array. Among these methods, applying an alternating current to the metal substrate is more suitable for small, complex components, while generating a gradient electromagnetic field using a Halbach permanent magnet array is more suitable for large, simple components.

[0047] By driving Nb, Ti and other strengthening elements in the molten pool to migrate along a preset path, such as a biomimetic honeycomb structure path, a γ' strengthening phase array is generated in situ, which improves the high-temperature creep strength. At the same time, it suppresses interdendritic segregation and the continuous distribution of brittle interdendritic phases.

[0048] In one possible implementation, the gradient direction of the gradient electromagnetic field forms an angle of 45-75 degrees with the laser scanning path.

[0049] For example, the angle between the gradient direction and the laser scanning path can be set to 60 degrees. Figure 3 This is a schematic diagram of the gradient electromagnetic field distribution, used to represent the spatial gradient magnetic field constructed by the permanent magnet array and the angle between its gradient direction and the laser scanning path.

[0050] In this embodiment of the invention, the magnetic field gradient direction is dynamically matched to the scanning path, which suppresses anisotropy, specifically by eliminating the strong texture tendency of traditional LPBF.

[0051] In one possible implementation, applying the gradient electromagnetic field according to the temperature gradient includes:

[0052] The electromagnetic field strength is determined based on the temperature gradient.

[0053] In one possible implementation, emitting the ultrafast laser shock wave according to the flow rate includes:

[0054] The shock wave energy density is determined based on the flow rate.

[0055] Specifically, refer to Figure 4 After the laser scanning forms the molten pool, the state of the molten pool is monitored in real time. The temperature gradient is monitored using an infrared thermal imager, and the flow rate is monitored using a high-speed camera to determine if the molten pool has entered a metastable state (i.e., whether the solid fraction is 30-70%). If so, a coordinated operation is triggered simultaneously: a gradient electromagnetic field is applied, and an ultrafast laser-induced shock wave is used to forge the molten layer. The magnetic field strength is dynamically adjusted by the molten pool temperature gradient, and the energy density of the ultrafast laser shock wave is dynamically adjusted by the molten pool flow rate. The synergistic effect of the ultrafast laser shock wave and the electromagnetic field shock wave regulates the solidification behavior of the molten pool. First, it is determined whether solidification is complete. If not, the interlayer waiting time is extended until completion, and then the process proceeds to the next layer. If solidification is complete, it is determined whether all layers have been processed. If not, the next layer laser scanning begins; if so, the process ends.

[0056] Among them, ultrafast lasers have a pulse width of less than 1 ps and an energy density of 5-15 J / cm². 2In this embodiment of the invention, the ultrafast laser is a femtosecond laser. The femtosecond laser induces a plasma explosion, generating a shock wave greater than 5 GPa. Traditional femtosecond lasers only act on solid surfaces for surface texturing or micropore processing, without addressing the internal structure control of the molten pool. Compared to traditional femtosecond lasers, the femtosecond laser in this embodiment can break up non-thermally fusible grains. The shock wave propagates in the solid-liquid coexistence phase of the molten pool, and mechanical energy directly breaks up primary dendrites. Unlike picosecond and nanosecond lasers, which can cause secondary overheating of the molten pool, the femtosecond laser in this embodiment has a pulse width of less than 1 ps and a thermal diffusion time of 10 ps, ​​suppressing remelting in the impact zone. Specifically, this avoids the formation of a secondary heat-affected zone, maintaining grain refinement. Compared to a single magnetic field exacerbating molten pool spatter, this embodiment uses a coordinated design of the propagation direction of the ultrafast laser shock wave and the angle between the electromagnetic field gradient, specifically setting the angle between 30-60 degrees. This optimizes stress-flow field coupling, and the compressive stress of the shock wave counteracts the turbulence induced by the electromagnetic Lorentz force, stabilizing the molten pool morphology.

[0057] In one possible implementation, the expression for the electromagnetic field strength is:

[0058]

[0059] Where B is the electromagnetic field strength, k1 is the magnetic field gain coefficient, ΔT is the molten pool temperature gradient monitored in real time by the infrared thermal imager, and k3 is the flow velocity abrupt change compensation coefficient. This represents the rate of change of the molten pool flow rate over time.

[0060] When the molten pool flow rate changes abruptly, i.e. A value greater than 0 strengthens the magnetic field and suppresses splashing. (Through...) Anticipate the risk of molten pool instability and control the response speed to improve.

[0061] In one possible implementation, the expression for the shock wave energy density is:

[0062]

[0063] Where E is the shock wave energy density, k2 is the energy adjustment coefficient, v is the molten pool flow rate monitored in real time by the high-speed camera, and k4 is the supercooled zone compensation coefficient. The Laplace operator for the temperature field on the surface of the molten pool represents the curvature of the temperature field, which is used to identify local undercooled regions and target energy-enhancing impacts.

[0064] Unlike traditional open-loop control that only responds to a single variable, temperature, this solution integrates multi-source sensors, simultaneously acquiring ΔT, v, and temperature. Four-dimensional data.

[0065] The electromagnetic field strength and shock wave energy density are dynamically adjusted based on monitoring data. That is, the dynamic feedback system realizes real-time optimization of multi-physics field coordination through the mathematical mapping relationship between the molten pool state parameters (ΔT, v) and the execution parameters (B, E).

[0066] In one possible implementation, after each layer forms a molten pool, the process further includes:

[0067] The duration of the metastable phase of the molten pool is monitored in real time. When the duration of the metastable phase of the molten pool exceeds 20-50ms, the laser scanning speed of the next layer is adjusted. The duration of the metastable phase of the molten pool is the duration when the solid fraction of the molten pool is 30%-70%.

[0068] When the duration of the metastable phase in the molten pool exceeds 20-50 ms, the system will adjust the laser scanning speed of the next layer during the interlayer interval after the current layer is printed to maintain a stable duration of the metastable phase in the next layer. Specifically, as the laser scanning speed increases, the heat input decreases, and the duration of the metastable phase increases; conversely, as the laser scanning speed decreases, the heat input increases, and the duration of the metastable phase decreases.

[0069] Step 104: Continue processing until all layers are completed to obtain the shaped part.

[0070] In the above embodiments, by using powder magnetization treatment, gradient electromagnetic field construction, and ultrafast laser shock forging technology, the flow and solidification behavior of the molten pool are optimized, achieving microstructure refinement, defect suppression, and improved mechanical properties of nickel-based alloys. This method combines the directional control of molten pool metal flow by the electromagnetic field with the stress release effect of ultrafast laser shock waves, significantly improving the density, microstructure uniformity, and high-temperature stability of the formed parts. It is suitable for high-performance manufacturing of complex structural components in aerospace and other fields. Through a multi-physics synergistic composite process, the problem of microcrack propagation caused by continuous distribution of brittle interdendritic phases and thermal stress concentration due to elemental segregation in high-crack-sensitive nickel-based alloys during LPBF is solved, while simultaneously achieving synergistic control of grain refinement and residual stress. By implementing the methods in the embodiments of this invention, the grain size is significantly refined, the microstructure is more uniform, the residual stress is significantly reduced, the surface quality of the formed parts is improved, and the high-temperature performance is close to that of forged parts.

[0071] Specifically, when the solid fraction of the molten pool is 30%-70%, a gradient electromagnetic field is applied according to the temperature gradient. The gradient electromagnetic field drives the directional migration of Nb, Ti, and other strengthening elements in the molten pool, thereby suppressing interdendritic segregation and the continuous distribution of brittle phases between dendrites, while improving high-temperature creep strength. In addition, the gradient magnetic field decreases along the vertical direction, compensating for heat accumulation between layers and solving the problem of grain coarsening at the top of components larger than 100mm. When the solid fraction of the molten pool is 30%-70%, an ultrafast laser shock wave is emitted according to the flow rate to forge the molten layer. The shock wave breaks the primary dendrites, promotes the formation of equiaxed crystals, and can suppress remelting in the impact zone, avoid the formation of a secondary heat-affected zone, and maintain the grain refinement effect. In addition, the gradient electromagnetic field and the ultrafast laser shock wave work together, and the compressive stress of the shock wave counteracts the turbulence caused by the electromagnetic Lorentz force, stabilizing the molten pool morphology.

[0072] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method of electromagnetic field-based nickel-based alloy forging printing, characterized by, The method comprises the following steps: preprocessing the nickel-based alloy powder and the metal substrate respectively; forming a molten pool by layer-by-layer scanning the nickel-based alloy powder by laser; after forming the molten pool at each layer, monitoring the temperature gradient and flow rate of the molten pool in real time by using an infrared thermal imager and a high-speed camera, applying a gradient electromagnetic field according to the temperature gradient and emitting an ultrafast laser shock wave according to the flow rate when the solid phase rate of the molten pool is 30%-70%; until all layers are completed, obtaining a formed part.

2. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, The step of applying a gradient electromagnetic field according to the temperature gradient comprises the following steps: determining the electromagnetic field intensity according to the temperature gradient.

3. The electromagnetic field-based nickel-based alloy forging printing method of claim 2, wherein, The expression of the electromagnetic field intensity is as follows: Wherein, B is the electromagnetic field intensity, k1 is the magnetic field gain coefficient, ΔT is the temperature gradient of the molten pool monitored by the infrared thermal imager in real time, k3 is the flow rate sudden change compensation coefficient, is the change rate of the molten pool flow rate with time.

4. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, The step of emitting an ultrafast laser shock wave according to the flow rate comprises the following steps: determining the shock wave energy density according to the flow rate.

5. The electromagnetic field-based nickel-based alloy forging printing method of claim 4, wherein, The expression of the shock wave energy density is as follows: Wherein, E is the shock wave energy density, k2 is the energy adjustment coefficient, v is the flow rate of the molten pool monitored by the high-speed camera in real time, k4 is the undercooling area compensation coefficient, is the Laplace operator of the molten pool surface temperature field, which represents the curvature of the temperature field.

6. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, After forming the molten pool at each layer, the method further comprises the following steps: monitoring the duration of the metastable state of the molten pool in real time, and adjusting the laser scanning speed of the next layer when the duration of the metastable state of the molten pool exceeds 20-50 ms; the duration of the metastable state of the molten pool is the duration when the solid phase rate of the molten pool is 30%-70%.

7. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, The included angle between the gradient direction of the gradient electromagnetic field and the laser scanning path is 45-75 degrees.

8. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, Applying an alternating current to the metal substrate or generating a gradient electromagnetic field by using a Halbach permanent magnet array.

9. The electromagnetic field-based nickel-based alloy forging printing method of claim 1, wherein, The preprocessing of the nickel-based alloy powder and the metal substrate respectively comprises the following steps: high-energy ball milling or surface modification treatment of the nickel-based alloy powder; cleaning the surface of the metal substrate and roughening the metal substrate.

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