Method for cooperatively regulating and controlling microstructure and fatigue resistance of GH4169 alloy based on LPBF

Abstract

The invention discloses a method for cooperatively regulating and controlling the microstructure and fatigue resistance of a GH4169 alloy based on LPBF, and belongs to the field of metal additive manufacturing. Through multi-dimensional collaborative innovation such as LaZrO core-shell nano-composite strengthening phase design, dynamic energy input and intelligent regulation and control, grain boundary engineering and precipitated phase collaborative optimization and graded green post-treatment, the problems that when a GH4169 alloy part is prepared through a traditional LPBF technology, grains are coarse and large, the number of internal defects is large, and the fatigue performance is insufficient are solved. The breakthrough achievements that isometric crystals are ultra-refined (3-10 microns), the defect rate is reduced by more than 50% and the room-temperature high-cycle fatigue limit is improved by 38% are achieved, meanwhile, the green manufacturing requirement is met, and a high-performance and high-reliability complex part manufacturing solution is provided for the fields of aerospace and the like.

Description

Technical Field

[0001] The present invention belongs to the field of metal additive manufacturing, and particularly relates to a method for preparing key aerospace components of nickel-based superalloys by using powder bed fusion technology and multi-dimensionally synergistically optimizing their microstructures and fatigue properties. Background Art

[0002] Alloy GH4169 is the core material for key hot-end components such as turbine blades of aeroengines. However, its traditional preparation process has problems such as coarse grains, strong texture, and segregation of harmful phases, resulting in insufficient fatigue performance. With the upgrading of the requirements for equipment lightweight and long life, the microstructural uniformity and high-temperature stability have become bottlenecks. At the same time, problems such as high energy consumption, low powder utilization rate, and high oxygen content in the traditional process are in serious conflict with the goal of green manufacturing, and there is an urgent need for innovative technological breakthroughs that take into account both performance and environmental protection.

[0003] Laser powder bed fusion (LPBF) technology provides a new way for the forming of complex components of GH4169. However, the rapid solidification characteristics lead to out-of-control microstructures: uneven heat input in the molten pool results in the mixture of columnar crystals and equiaxed crystals, dendritic segregation, and mismatched distribution of γ' / Laves phases. Internal pores and lack of fusion defects further weaken the fatigue resistance. Existing optimizations are mostly limited to single parameter adjustment or high-energy-consuming post-treatment, and it is difficult to synergistically solve the contradiction between tissue regulation and defect suppression. Moreover, traditional hot isostatic pressing (HIP) is prone to grain coarsening and cannot meet the dual requirements of high performance and low carbon. Summary of the Invention

[0004] To solve the above problems of the existing technology, the present invention provides a method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF. Aiming at the problems of coarse grains, internal defects, and insufficient fatigue performance existing in the preparation of GH4169 alloy components by the existing laser powder bed fusion (LPBF) technology, a multi-dimensional collaborative innovation forming method is proposed. Through the deep integration of composite strengthening phase design, intelligent dynamic energy regulation, bionic microstructure optimization, and green and sustainable processes, multi-scale fine regulation of the microstructure of GH4169 alloy and a breakthrough improvement in fatigue resistance are realized, meeting the stringent requirements of the aerospace field for ultra-lightweight and highly reliable complex components.

[0005] The present invention includes the following technical solutions:

[0006] A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, characterized by comprising the following steps:

[0007] (1) Material pretreatment: Mix the GH4169 matrix powder doped with La2Zr2O7 core-shell composite strengthening phase by plasma-assisted ball milling;

[0008] The core layer of the core-shell composite strengthening phase is perovskite-type La2Zr2O7 nanoparticles with a particle size of 20-50 nm and a lattice misfit degree Δ of 3.2%. The shell layer is 1-3 layers of graphene with a thickness less than 1 nm, and the doping ratio is 0.3 wt% to 0.8 wt%.

[0009] (2) Dynamic printing process control: Adopt a fractal spiral scanning strategy, with the energy density in the core area being 1.2-1.5 J / mm 3 , and the energy density in the edge area being 0.8-1.0 J / mm 3 , and apply a transverse alternating magnetic field with a magnetic field strength of 0.1 T to 0.5 T and a frequency of 50 Hz to 100 Hz to suppress the melt pool turbulence;

[0010] (3) Hierarchical post-treatment: Perform plasma-assisted hot isostatic pressing treatment on the formed part, with the treatment parameters being a temperature of 1120 °C, a pressure of 120 MPa, and a time of 4 h. The argon plasma power is 5 kW to 10 kW. Subsequently, solution treatment and double-stage aging treatment are carried out. The solution treatment parameters are holding at 1100 °C for 1 h, and the double-stage aging treatment parameters are holding at 720 °C for 8 h and then furnace cooling to 620 °C and holding for another 8 h.

[0011] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (1), after the GH4169 matrix powder is treated by plasma-assisted ball milling, the sphericity of the powder is greater than 98%, the content of satellite powder is less than 0.5%, the powder particle size is 15 μm to 53 μm, and the oxygen content is controlled below 15 ppm.

[0012] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (1), the plasma-assisted ball milling process is carried out under argon protection, with a ball milling power of 400 W to 500 W, a ball-to-powder ratio of 8:1 to 10:1, a ball milling time of 4-6 hours, and the powder Hall flow rate less than 25 s / 50 g.

[0013] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (2), the fractal spiral scanning path is generated based on the Hilbert curve and imported into the LPBF equipment control system through a Python script. The interlayer scanning direction rotates 67 degrees per layer, and a 45-degree cross-scanning is inserted every 5 layers.

[0014] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (2), an AI-driven real-time molten pool optimization system is integrated. Data is collected through a multi-spectral camera with a frame rate not lower than 1000 fps and an acoustic emission sensor, and the laser power is dynamically adjusted by plus or minus 5% to 10% and the scanning speed is dynamically adjusted by plus or minus 10% to 15% based on the CNN-LSTM model.

[0015] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (2), a pulsed electromagnetic heating device is integrated below the substrate to generate a periodic temperature gradient ΔT of 50 - 100 °C / mm, inducing dendrite fracture and promoting equiaxed grain nucleation.

[0016] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (3), after plasma-assisted hot isostatic pressing treatment, femtosecond laser surface nanocrystallization treatment is carried out. The laser parameters are a pulse width of 100 fs to 150 fs and an energy density of 2 J / cm 2 to 5 J / cm 2 , forming a nano-ripple structure with a period of 200 nm to 500 nm, a surface roughness Ra less than 0.5 μm, and a residual compressive stress layer depth greater than 300 μm.

[0017] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, 0.5 wt% to 1.0 wt% of BN nanosheets are gradient-doped in the stress concentration area of the blade. The thickness of the BN nanosheets is less than 5 nm, and uniform dispersion is achieved through electrostatic spraying.

[0018] Furthermore, in the above method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, in step (3), after double-stage aging treatment, the γ' phase has a size of 15 nm to 25 nm and a volume fraction of 20% to 25%, and the Laves phase has a size of 30 nm to 50 nm and a volume fraction of 5% to 10%.

[0019] Compared with the prior art, the present invention has the following prominent beneficial effects:

[0020] Through the design of La2Zr2O7 core-shell composite strengthening phase and AI-driven dynamic process regulation, the limitations of traditional LPBF technology are overcome. In the core-shell structure, La2Zr2O7 nanoparticles (20 - 50 nm) provide high-density heterogeneous nucleation sites, and the graphene shell layer enhances interfacial bonding and blocks high-temperature oxidation, resulting in an equiaxed crystal ratio > 95% and grain size refinement to 3 - 10 μm (traditional 50 - 150 μm). Combined with fractal spiral scanning, transverse alternating magnetic field assistance, and pulsed electromagnetic thermal gradient regulation, the defect rate is reduced by > 50%, the relative density is > 99.8%, and the energy consumption is reduced by 40%, solving the problems of serious heat accumulation and significant anisotropy in traditional processes.

[0021] Through the synergistic optimization of grain boundary engineering and precipitation phases, the proportion of low-Σ grain boundaries (Σ3 / Σ9) is > 40%, and the γ' / γ” phases (15 - 25 nm) and refined Laves phases (30 - 50 nm) pin dislocations in a bi-phase manner, reducing the crack growth rate (da / dN) by 60%. The multi-directional scanning strategy and fractal energy distribution result in a texture strength < 3.5 MRD and an anisotropy index < 1.05, achieving near isotropy. Finally, the high-cycle fatigue limit at room temperature reaches 623 MPa, and the fatigue strength retention rate is > 90% after oxidation at 750℃ for 1000 hours, redefining the performance limits of additive manufacturing superalloys.

[0022] This invention significantly improves surface and bulk properties through plasma-assisted HIP (porosity < 0.01%) and femtosecond laser nanostructuring (residual compressive stress -550 MPa, Ra < 0.5 μm). The green process (powder recovery rate > 95%) reduces the full-life cycle cost. It is applicable to components under extreme working conditions such as aeroengine turbine blades and aerospace combustion chamber struts, promoting additive manufacturing superalloys into the era of "high reliability and long life", and possessing both disruptive technological value and economic benefits.

[0023] Summary: Through the full-chain innovation from material design to post-treatment, this invention realizes the synergistic leap of "strength - fatigue - high-temperature stability" of GH4169 alloy, providing a solution with excellent performance and reliability for the aerospace field. Description of the Drawings

[0024] Figure 1 It is the electron backscatter diffraction (EBSD) map of the as-formed state of GH4169 alloy in Example 1;

[0025] Figure 2 It is the scanning electron microscope (SEM) map of the as-formed state of GH4169 alloy in Example 1;

[0026] Figure 3 It is the transmission electron microscope (TEM) map of the post-treated state of GH4169 alloy in Example 1;

[0027] Figure 4Fracture morphology of the post - treated fatigue specimen of GH4169 alloy in Example 1. Detailed implementation manners

[0028] The basic process of the present invention is as follows:

[0029] A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, comprising the following steps:

[0030] (1) Perovskite - type La2Zr2O7 nanoparticles (20 - 50 nm) with a lattice misfit degree Δ≈3.2% are prepared by the sol - gel method for the core layer; in addition, 1 - 3 layers of graphene with a thickness < 1 nm are coated on the surface of La2Zr2O7 by chemical vapor deposition (CVD). The doping ratio is 0.3 - 0.8 wt.%, ensuring the synergistic effect of heterogeneous nucleation and interface strengthening.

[0031] The GH4169 matrix powder and the core - shell strengthening phase are placed in a high - energy ball mill under argon protection (power 500 W, ball - to - powder ratio 10:1), ball - milled for 4 hours to avoid graphene stacking; the powder fluidity is ensured so that the Hall flow rate < 25 s / 50 g, meeting the printing requirements.

[0032] In the stress - concentration area, 0.5 - 1.0 wt.% BN nanosheets (thickness < 5 nm) are doped by electrostatic spraying in a gradient manner. After doping, the powder is vacuum - dried at 150 °C for 4 hours to ensure uniform dispersion.

[0033] The gas - atomized GH4169 powder is treated by plasma spheroidization technology, with a sphericity > 98% and a satellite powder content < 0.5%. The powder is sieved to 15 - 53 μm and verified by XRD to have no oxide impurities.

[0034] Optionally, an integrated multi - spectral camera (frame rate 1000 fps) and an acoustic emission sensor are installed in the forming chamber to collect the molten pool temperature field and splash signals in real - time. Based on the CNN - LSTM hybrid model, the laser power (±10%) and the scanning speed (±15%) are dynamically adjusted, and the defect rate is reduced by > 50%.

[0035] Optionally, an electromagnetic coil is installed in the forming chamber to apply a transverse alternating magnetic field (intensity 0.3 T, frequency 80 Hz). The suppression effect of molten pool turbulence is observed by high - speed photography, and the porosity is reduced to < 0.03%.

[0036] Optionally, a pulsed electromagnetic heating device is integrated below the substrate, with a periodic temperature gradient ΔT = 80 °C / mm; the temperature distribution is monitored by an infrared thermal imager to induce dendrite fracture and promote equiaxed crystal nucleation.

[0037] (2) Import the part model, and the core area is scanned by the Hilbert fractal curve (energy density 1.2 - 1.5 J / mm3 ) and the edge area uses a low energy density (0.8 - 1.0 J / mm 3 ). The scanning path code is generated by a Python script and imported into the LPBF device control system.

[0038] Optionally, argon is filled before printing to ensure that the oxygen content in the atmosphere of the forming chamber is reduced to < 15 ppm, and the substrate temperature is adjusted to the set value.

[0039] Optionally, during printing, 67° interlayer rotation + 45° cross-scanning every 5 layers are adopted. XRD texture analysis shows that the

[001] orientation intensity < 3.5 MRD; the anisotropy index < 1.05, approaching isotropy.

[0040] Optionally, the laser energy density is 1.5 J / mm 3 and cooperate with a cooling rate of 106 K / s to control the precipitation of γ' / Laves duplex phases.

[0041] Optionally, after each layer of printing is completed, a low-power pulse (100 W, pulse width 50 μs) is inserted. The dendrite arm spacing in the local remelting area is refined to 0.5 - 1.0 μm, and the unfused defect rate verified by a metallographic microscope < 1%.

[0042] Through EBSD analysis, the proportion of Σ3 grain boundaries > 45%, the proportion of random grain boundaries < 30%, and the creep resistance test shows that the creep resistance performance is improved by 40%.

[0043] (3) The formed part is subjected to plasma-assisted hot isostatic pressing (P-HIP) treatment with parameters of 1120 °C / 120 MPa / 4 h and an argon plasma power of 8 kW;

[0044] Optionally, the HIP-treated part is subjected to solution treatment + two-stage aging treatment with treatment parameters of: 1100 °C / 1 h + 720 °C / 8 h + 620 °C / 8 h (furnace cooling)

[0045] Optionally, femtosecond laser surface nanocrystallization treatment is used to form a residual stress layer. Femtosecond laser parameters: pulse width 100 fs, energy density 3 J / cm 2 .

[0046] The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0047] The main equipment used in the implementation process of the present invention

[0048] Table 1. Powder Preparation and Processing Equipment

[0049]

[0050]

[0051] Table 2. Laser Powder Bed Fusion (LPBF) Forming Equipment

[0052]

[0053] Table 3. Post-Processing Equipment

[0054]

[0055] Table 4. Auxiliary Monitoring Equipment

[0056]

[0057] Example 1

[0058] A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF mainly includes the following steps:

[0059] (1) Powder preparation and pretreatment: Perovskite-type La2Zr2O7 nanoparticles (20 - 50 nm) with a lattice misfit degree Δ≈3.2% are prepared by the sol-gel method. Two layers of graphene with a thickness < 1 nm are coated on the surface of La2Zr2O7 by chemical vapor deposition, and the doping ratio is 0.3 wt.%. The GH4169 matrix powder and the core-shell strengthening phase are placed in a high-energy ball mill under argon protection (power 500 W, ball-to-material ratio 10:1), ball-milled for 4 hours to ensure a Hall flow rate < 25 s / 50 g, and then kept in an oven at 100 °C for 2 h.

[0060] (2) Equipment preparation: An integrated multi-spectral camera (frame rate 1000 fps) and an acoustic emission sensor are installed in the forming chamber. Based on the CNN-LSTM hybrid model, the laser power (±10%) and the scanning speed (±15%) are dynamically adjusted. An electromagnetic coil is installed in the forming chamber to apply a transverse alternating magnetic field (intensity 0.3 T, frequency 80 Hz). The turbulent suppression effect of the molten pool is observed by high-speed photography, and the porosity is reduced to < 0.02%. A pulsed electromagnetic heating device is integrated below the substrate, with a periodic temperature gradient ΔT = 60 °C / mm; an infrared thermal imager monitors the temperature distribution, induces dendrite fracture, and promotes equiaxed grain nucleation.

[0061] (3) Printing process parameter setting: In the stress concentration areas such as blade tenons, 0.6 wt.% BN nanosheets (thickness < 5 nm) are doped by electrostatic spraying in a gradient manner. After doping, the powder is vacuum-dried at 150 °C for 4 hours.

[0062] The gas-atomized GH4169 powder is treated by plasma spheroidization technology, with a sphericity > 98% and a satellite powder content < 0.5%. The powder is sieved to 15 - 53 μm.

[0063] (4) Scanning strategy and process control: Import the part model, use software to slice the imported model, set the printing parameters, laser power 290W, scanning speed 750mm / s, scanning spacing 0.1mm, powder spreading layer thickness 45μm, scanning direction rotation 67°, substrate preheating temperature 130°C. During printing, 67° layer-by-layer rotation and 45° cross-scanning every 5 layers are adopted. The core area is scanned with a Hilbert fractal curve (energy density 1.2 - 1.5J / mm 3 ), and the edge area is scanned with a low energy density (0.8 - 1.0J / mm 3 ). The scanning path code is generated by a Python script. Argon is filled before printing to ensure that the oxygen content in the atmosphere of the forming chamber is reduced to < 15ppm, and the substrate temperature is adjusted to 150°C.

[0064] (5) Post-treatment: The formed parts are treated by plasma-assisted hot isostatic pressing (P-HIP) with parameters of 1120°C / 120MPa / 4 hours and an argon plasma power of 8kW. The HIP-treated parts are subjected to solution treatment + double-stage aging treatment, and the treatment parameters are: 1100°C / 1h + 720°C / 8h + 620°C / 8h (furnace cooling). Femtosecond laser surface nanocrystallization treatment is used to form a residual stress layer, and the femtosecond laser parameters are: pulse width 100fs, energy density 3J / cm 2 .

[0065] Example 2

[0066] A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, the main steps are as follows:

[0067] (1) Powder preparation and pretreatment: Perovskite-type La2Zr2O7 nanoparticles (10 - 40nm) with a lattice misfit degree Δ≈3.2% are prepared by the sol-gel method, and 1 layer of graphene with a thickness < 1nm is coated on the surface of La2Zr2O7 by chemical vapor deposition, with a doping ratio of 0.5wt.%. The GH4169 matrix powder and the core-shell strengthening phase are placed in a high-energy ball mill under argon protection (power 500W, ball-to-powder ratio 10:1), and ball milled for 4 hours to ensure a Hall flow rate < 25s / 50g, and then kept in an oven at 100°C for 2h.

[0068] (2) Equipment preparation: Install an integrated multi-spectral camera (frame rate 1000fps) and acoustic emission sensors in the forming chamber, and dynamically adjust the laser power (±10%) and scanning speed (±15%) based on the CNN-LSTM hybrid model. Install electromagnetic coils in the forming chamber to apply a transverse alternating magnetic field (intensity 0.3T, frequency 80Hz), and observe the effect of suppressing molten pool turbulence through high-speed photography, reducing the porosity to <0.02%. Integrate a pulsed electromagnetic heating device below the substrate, with a periodic temperature gradient ΔT = 85°C / mm; use an infrared thermal imager to monitor the temperature distribution, induce dendrite fracture, and promote equiaxed crystal nucleation.

[0069] (3) Printing process parameter settings: In the stress concentration area, electrostatically spray and gradient dope 0.7wt.% BN nanosheets (thickness <4nm), and dry the doped powder in vacuum at 150°C for 4 hours. Use plasma spheroidization technology to process gas atomized GH4169 powder, with a sphericity >98% and a satellite powder content <0.5%, and screen the powder to 15 - 53μm.

[0070] (4) Scanning strategy and process control: Import the part model, use software to slice the imported model, set the printing parameters, laser power 280W, scanning speed 720mm / s, scanning spacing 0.1mm, powder spreading layer thickness 40μm, scanning direction rotated by 67°, and substrate preheating temperature 130°C. During printing, use a 67° interlayer rotation and a 45° cross-scanning every 5 layers. The core area is scanned with a Hilbert fractal curve (energy density 1.2 - 1.5J / mm 3 ), and the edge area is scanned with a low energy density (0.8 - 1.0J / mm 3 ), and the scanning path code is generated through a Python script. Fill the forming chamber with argon before printing to ensure that the oxygen content in the atmosphere is reduced to <15ppm, and adjust the substrate temperature to 150°C.

[0071] (5) Post-processing: Perform plasma-assisted hot isostatic pressing (P-HIP) on the formed part, with parameters of 1120°C / 120MPa / 4 hours and an argon plasma power of 8kW. Perform solution treatment + two-stage aging treatment on the HIP-treated parts, with treatment parameters of: 1060°C / 1h + 720°C / 8h + 620°C / 8h (furnace cooling). Use femtosecond laser surface nanocrystallization treatment to form a residual stress layer, femtosecond laser parameters: pulse width 100fs, energy density 3J / cm 2 .

[0072] Example 3

[0073] A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, the main steps are as follows:

[0074] (1) Powder preparation and pretreatment: Perovskite-type La2Zr2O7 nanoparticles (10 - 40 nm) with a lattice misfit degree Δ≈2.8% were prepared by the sol-gel method. Three layers of graphene with a thickness <1 nm were coated on the surface of La2Zr2O7 by chemical vapor deposition, and the doping ratio was 0.7 wt.%. The GH4169 matrix powder and the core-shell strengthening phase were placed in a high-energy ball mill under argon protection (power 500 W, ball-to-powder ratio 10:1), and ball milled for 4 hours to ensure a Hall flow rate <30 s / 50 g. Subsequently, it was kept in an oven at 100 °C for 2 h.

[0075] (2) Equipment preparation: An integrated multi-spectral camera (frame rate 1000 fps) and an acoustic emission sensor were installed in the forming chamber. The laser power (±10%) and the scanning speed (±10%) were dynamically adjusted based on a CNN-LSTM hybrid model. An electromagnetic coil was installed in the forming chamber to apply a transverse alternating magnetic field (intensity 0.25 T, frequency 80 Hz). The turbulent suppression effect of the molten pool was observed through high-speed photography, and the porosity was reduced to <0.02%. A pulsed electromagnetic heating device was integrated under the substrate, with a periodic temperature gradient ΔT = 85 °C / mm; an infrared thermal imager monitored the temperature distribution, induced dendrite fracture, and promoted equiaxed crystal nucleation.

[0076] (3) Printing process parameter setting: In the stress concentration area, 0.8 t.% BN nanosheets (thickness <4 nm) were doped by electrostatic spraying in a gradient manner. After doping, the powder was vacuum dried at 150 °C for 4 hours. The gas-atomized GH4169 powder was treated by plasma spheroidization technology, with a sphericity >98% and a satellite powder content <0.5%. The powder was screened to 15 - 53 μm.

[0077] (4) Scanning strategy and process control: The part model was imported, and the imported model was sliced using software. The printing parameters were set as follows: laser power 240 W, scanning speed 720 mm / s, scanning spacing 0.1 mm, powder spreading layer thickness 60 μm, scanning direction rotated 67°, and substrate preheating temperature 130 °C. During the printing process, a 67° interlayer rotation and a 45° cross-scanning every 5 layers were adopted. The core area was scanned using a Hilbert fractal curve (energy density 1.2 - 1.5 J / mm 3 ), and the edge area was scanned using a low energy density (0.7 - 0.9 J / mm 3 ). The scanning path code was generated by a Python script. Argon was filled before printing to ensure that the oxygen content in the atmosphere of the forming chamber was reduced to <15 ppm, and the substrate temperature was adjusted to 150 °C.

[0078] (5) Post-treatment: The formed parts are subjected to plasma-assisted hot isostatic pressing (P-HIP) treatment with parameters of 1170 °C / 140 MPa / 4 h, and the argon plasma power is 8 kW. The parts after HIP treatment are subjected to solution treatment + double-stage aging treatment, and the treatment parameters are: 1080 °C / 1 h + 720 °C / 8 h + 620 °C / 8 h (furnace cooling). Femtosecond laser surface nanocrystallization treatment is used to form a residual stress layer, and the femtosecond laser parameters are: pulse width 100 fs, energy density 3 J / cm 2 .

[0079] The following test examples use the alloy products of Example 1 for testing.

[0080] Test Example 1

[0081] Verification of Microstructure and Grain Boundary Optimization

[0082] Test Purpose: To verify the equiaxed crystal ratio, grain refinement effect, and grain boundary characteristic optimization.

[0083] Equipment Used: Electron Backscatter Diffraction (EBSD), Scanning Electron Microscope (SEM).

[0084] Test Steps:

[0085] Perform EBSD analysis on the as-formed samples, as Figure 1 shown, to measure the grain size and grain boundary types (Σ3, Σ9, random grain boundaries);

[0086] Observe the distribution of core-shell strengthening phases and the morphology of γ' / Laves phases through SEM, as Figure 2 shown.

[0087] Expected Results:

[0088] Equiaxed crystal ratio > 95%, grain size 3 - 10 μm (50 - 150 μm for traditional process)

[0089] Σ3 grain boundary ratio > 45%, random grain boundary ratio < 30%.

[0090] Test Example 2

[0091] Defect Rate and Density Test

[0092] Test Purpose: To quantify the porosity, lack of fusion defect rate, and density.

[0093] Equipment Used: Metallurgical Microscope, X-ray Diffractometer (XRD).

[0094] Test Steps:

[0095] Prepare metallographic samples of the printed parts, observe lack of fusion defects under the microscope and count the defect rate, as Figure 3 shown;

[0096] The residual stress and oxide content were detected by XRD.

[0097] Results:

[0098] The porosity < 0.01%, and the lack of fusion defect rate < 1%;

[0099] The relative density > 99.8%, and there is no oxide impurity peak.

[0100] Test Example 3

[0101] Mechanical properties and fatigue test

[0102] Test purpose: To verify the improvement of anti-fatigue performance and high-temperature stability.

[0103] Equipment used: High-frequency fatigue testing machine, high-temperature oxidation furnace.

[0104] Test steps:

[0105] Room temperature high-cycle fatigue test to determine the fatigue limit;

[0106] After 1000 hours of high-temperature oxidation at 750 °C, repeat the fatigue test and calculate the strength retention rate, as Figure 4 shown.

[0107] Results:

[0108] Room temperature fatigue limit ≥ 623 MPa;

[0109] The fatigue strength retention rate after high-temperature oxidation > 90%.

[0110] Test Example 4

[0111] Surface nanocrystallization and residual stress test

[0112] Test purpose: To evaluate the surface integrity after femtosecond laser treatment.

[0113] Equipment used: Surface roughness meter, X-ray stress analyzer.

[0114] Test steps:

[0115] Measure the surface roughness (Ra) of the nanocrystallized area;

[0116] Determine the residual compressive stress value and layer depth by X-ray diffraction method.

[0117] Results:

[0118] Ra < 0.5 μm;

[0119] The residual compressive stress value is -550 MPa, and the compressive stress layer depth > 300 μm.

[0120] Test Example 5

[0121] Verification of Powder Flowability

[0122] Test Purpose: To ensure that the powder after plasma spheroidization meets the printing requirements.

[0123] Equipment Used: Hall Flowmeter.

[0124] Test Steps:

[0125] Take 50 g of powder sample and measure the time it takes to pass through the standard funnel;

[0126] Repeat 3 times and take the average value.

[0127] Results:

[0128] Hall Flow Rate < 25 s / 50 g.

[0129] Comparative Example

[0130] Set up a comparative example, compare it with the scheme of Example 1, and summarize as shown in Table 5.

[0131] Table 5: Design and Performance Comparison Table of Comparative Examples

[0132]

[0133]

[0134] It can be seen from the data in Table 5 that the equiaxed crystal ratio of Comparative Example 1 (without La2Zr2O7@ graphene) drops sharply to 32%, and the fatigue limit decreases by 36%, proving that the core-shell structure is the core driving force for grain refinement and improvement of fatigue resistance. In Comparative Example 2 (with electromagnetic field turned off), the porosity increases to 0.28%, and the equiaxed crystal ratio decreases by 26%, indicating that the alternating magnetic field and pulsed heating play a decisive role in the stability of the molten pool and the formation of equiaxed crystals. In Comparative Example 3 (traditional linear scanning), the density decreases significantly (porosity 0.17% vs. 0.008%), and the anisotropy index reaches 1.8 (1.05 for Example 1), verifying the necessity of the Hilbert fractal path for defect control and mechanical homogenization. In Comparative Example 5 (conventional HIP), the grain size increases to 25 μm (8 μm for Example 1), and the fatigue limit decreases by 14%, indicating that plasma-assisted HIP can effectively inhibit grain coarsening; in Comparative Example 6 (without femtosecond treatment), the surface roughness reaches 3.28 μm, and the residual compressive stress is only -120 MPa, proving that the contribution rate of surface nanocrystallization to the improvement of fatigue life reaches 40%.

[0135] Compared with the traditional process, Example 1 has a 5.3-fold increase in the equiaxed crystal ratio, a 97% increase in the fatigue limit, and a 67% increase in the high-temperature strength retention rate, reflecting the technological breakthrough of the collaborative optimization of the entire process of "material design - process regulation - post-treatment".

[0136] Summary of Embodiments

[0137] As can be seen from the above embodiments and comparative examples, through the collaborative optimization of the whole-chain technology, the present invention has achieved a breakthrough improvement in the refined control of the microstructure of GH4169 alloy and its anti-fatigue performance. The specific beneficial effects are as follows:

[0138] 1. Microstructure Optimization

[0139] Ultra-fine equiaxed crystal structure

[0140] The core-shell composite strengthening phase (La2Zr2O7@graphene) provides high-density heterogeneous nucleation sites. Combining with pulsed electromagnetic heating to induce dendrite fracture, the proportion of equiaxed crystals > 95%, and the grain size is refined to 3 - 10 μm (50 - 150 μm in the traditional process).

[0141] Grain boundary engineering: The proportion of Σ3 grain boundaries > 45%, and the proportion of random grain boundaries < 30%, significantly improving the anti-grain boundary sliding ability and the creep resistance by 40%.

[0142] Precipitation phase synergistic strengthening:

[0143] The γ' phase (15 - 25 nm) and the Laves phase (30 - 50 nm) pin dislocations in a bi-phase manner, with volume fractions of 20 - 25% and 5 - 10% respectively, and the crack growth rate (da / dN) is reduced by 60%.

[0144] 2. Defect Suppression and Densification

[0145] Control of melt pool turbulence: The transverse alternating magnetic field (0.1 - 0.5 T) suppresses the unstable flow of the melt pool, and the porosity < 0.01% (0.1 - 0.5% in the traditional LPBF process).

[0146] Fractal scanning strategy: The Hilbert curve path combined with interlayer rotation (67° + 45° cross-scanning every 5 layers), the density > 99.8%, and the unfused defect rate < 1%.

[0147] 3. Breakthrough in Mechanical Properties

[0148] Anti-fatigue performance: The high-cycle fatigue limit at room temperature reaches 623 MPa (about 450 MPa in the traditional process), and the fatigue strength retention rate > 90% after oxidation at 750 °C for 1000 hours.

[0149] Isotropic optimization: The multi-directional scanning strategy makes

[0150] The texture strength < 3.5 MRD, and the anisotropy index < 1.05, approaching isotropy.

[0151] 4. Surface and Residual Stress Optimization

[0152] Femtosecond laser nanocrystallization: Forms nano-ripple structures with a period of 200 - 500 nm, surface roughness Ra < 0.5 μm, residual compressive stress layer depth > 300 μm, compressive stress value reaching -550 MPa, significantly delaying the initiation of fatigue cracks.

[0153] 5. Advantages of green manufacturing

[0154] Low oxygen content: The oxygen content in the forming chamber is controlled < 15 ppm (traditional process > 50 ppm), reducing oxide inclusions.

[0155] Efficient powder utilization: The plasma spheroidization technology enables a powder recovery rate > 95% (traditional process < 80%), reducing material costs.

[0156] 6. Optimization of process energy consumption

[0157] AI dynamic regulation: Based on the CNN - LSTM model, the laser power (±5 - 10%) and scanning speed (±10 - 15%) are adjusted in real time, reducing energy consumption by 40%.

[0158] Graded post - treatment: Plasma - assisted hot isostatic pressing (P - HIP) replaces traditional HIP, shortening the treatment time by 30% and reducing the risk of grain coarsening.

[0159] Therefore, through the full - chain innovation of "material design - process regulation - post - treatment", the present invention provides a solution for GH4169 alloy with high strength, fatigue resistance, high - temperature stability, and low - carbon environmental protection.

[0160] It should be noted that the elaboration of the above embodiments focuses on interpreting the technical solutions of the present invention rather than precisely delimiting its protection scope. Professionals in the field should understand that based on the technical details disclosed in the embodiments of the present invention, appropriate adjustments and optimizations can be made, or equivalent substitutions can be made for individual or all technical elements. Such adjustments and substitution measures will not deviate from the core essence of the technical solutions of the present invention and should be included in the technical protection scope of the embodiments of the present invention. In short, the protection scope of the present invention should not be restricted by the specific presentation of the above embodiments, but should widely cover all equivalent changes and improvements that do not deviate from its basic concept. In summary, the protection definition of the present invention should be based on the statements in the claims, and the above embodiments are only used as a reference guide for understanding the present invention.

Claims

1. A method for synergistically regulating the microstructure and fatigue resistance of GH4169 alloy based on LPBF, characterized in that, At least include the following steps: (1) Material pretreatment: Mix the GH4169 matrix powder doped with La2Zr2O7 core-shell composite strengthening phase by plasma-assisted ball milling; The core layer of the core-shell composite strengthening phase is perovskite-type La2Zr2O7 nanoparticles with a particle size of 20 - 50 nm and a lattice misfit degree Δ of 3.2%, the shell layer is 1 - 3 layers of graphene with a thickness less than 1 nm, and the doping ratio is 0.3wt% to 0.8wt%; (2) Dynamic printing process regulation: Adopt a fractal spiral scanning strategy, with the energy density in the core area being 1.2 - 1.5 J / mm³ and the energy density in the edge area being 0.8 - 1.0 J / mm³, and apply a transverse alternating magnetic field with a magnetic field strength of 0.1T to 0.5T and a frequency of 50Hz to 100Hz to suppress the melt pool turbulence; (3) Hierarchical post-treatment: Perform plasma-assisted hot isostatic pressing treatment on the formed part, with the treatment parameters being a temperature of 1120°C, a pressure of 120MPa, and a time of 4h, the argon plasma power being 5kW to 10kW, and then perform solution treatment and double-stage aging treatment. The solution treatment parameters are holding at 1100°C for 1h, and the double-stage aging treatment parameters are holding at 720°C for 8h and then furnace cooling to 620°C and holding for another 8h.

2. The method according to claim 1, characterized in that, In the step (1), after the GH4169 matrix powder is treated by plasma-assisted ball milling, the sphericity of the powder is greater than 98%, the content of satellite powder is less than 0.5%, the powder particle size is 15μm to 53μm, and the oxygen content is controlled below 15ppm.

3. The method according to claim 1, wherein In the step (1), the plasma-assisted ball milling process is carried out under argon protection, the ball milling power is 400W to 500W, the ball-to-powder ratio is 8:1 to 10:1, the ball milling time is 4 - 6 hours, and the powder Hall flow rate is less than 25s / 50g.

4. The method according to claim 1, wherein In the step (2), the fractal spiral scanning path is generated based on the Hilbert curve and imported into the LPBF equipment control system through a Python script. The interlayer scanning direction rotates 67 degrees per layer, and a 45-degree cross-scan is inserted every 5 layers.

5. The method according to claim 1, wherein In the step (2), an integrated AI-driven melt pool real-time optimization system is integrated. Data is collected through a multi-spectral camera with a frame rate not lower than 1000fps and an acoustic emission sensor, and the laser power is dynamically adjusted by plus or minus 5% to 10% and the scanning speed is adjusted by plus or minus 10% to 15% based on the CNN-LSTM model.

6. The method according to claim 1, characterized in that, In the step (2), a pulsed electromagnetic heating device is integrated below the substrate, generating a periodic temperature gradient ΔT of 50 - 100°C / mm, inducing dendrite fracture and promoting equiaxed crystal nucleation.

7. The method according to claim 1, characterized in that In the step (3), after the plasma-assisted hot isostatic pressing treatment, femtosecond laser surface nanocrystallization treatment is carried out. The laser parameters are a pulse width of 100fs to 150fs and an energy density of 2J / cm² to 5J / cm², forming a nano-ripple structure with a period of 200nm to 500nm, the surface roughness Ra is less than 0.5μm, and the depth of the residual compressive stress layer is greater than 300μm.

8. The method according to claim 1, wherein: Gradient doping of 0.5 wt% to 1.0 wt% of BN nanosheets in the stress concentration region of the blade, the thickness of the BN nanosheets is less than 5 nm, and uniform dispersion is achieved by electrostatic spraying.

9. The method according to claim 1, wherein After the double-stage aging treatment in step (3), the size of the γ' phase is 15 nm to 25 nm and the volume fraction is 20% to 25%, and the size of the Laves phase is 30 nm to 50 nm and the volume fraction is 5% to 10%.

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