SLM forming method of In718 high-temperature alloy material

Abstract

The invention discloses an SLM (selective laser melting) forming method of an In718 high-temperature alloy material, which comprises the following steps: selecting 15-35 mu m spherical powder, and carrying out ultrasonic screening, plasma activation and 50-100nm aluminum oxide coating modification to improve wettability and oxidation resistance; in an inert gas cabin, a platform is preheated at the temperature of 100-150 DEG C, and a pre-tightening layer with the density larger than or equal to 98% is formed through vibration auxiliary powder laying; a pulse fiber laser is adopted to dynamically modulate parameters, a thin-wall area and a solid area are matched with a spiral scanning path, and the cooling rate of a molten pool is reduced by 30%-50%; a molten pool is monitored through dual-wavelength infrared temperature measurement and a high-speed CCD, and laser frequency compensation and argon blowing stable convection are triggered; constructing a three-layer temperature gradient; by means of the method, the density and the high-temperature performance of the formed part are improved, and the method is suitable for manufacturing of aerospace complex structural parts.

Description

Technical Field

[0001] The present invention relates to the technical field of SLM forming methods, and in particular to an SLM forming method for an In718 high-temperature alloy material. Background Art

[0002] In718 high-temperature alloy is widely used in the manufacture of key load-bearing structures such as aircraft engine turbine blades and combustion chamber components due to its excellent high-temperature strength, fatigue resistance, and oxidation resistance. Selective laser melting (SLM) technology, as a core process of additive manufacturing, can achieve high-precision molding of complex structural parts. However, it faces many technical challenges in the molding of In718 alloy:

[0003] Powder performance limitations: Traditional spherical powders have oxide films or irregular morphologies on their surfaces, resulting in insufficient fluidity and poor powder spreading uniformity. Furthermore, oxidation reactions are prone to occur at high temperatures, affecting melt pool stability.

[0004] Thermal stress and deformation issues: The rapid melting and solidification during the SLM process creates a sharp temperature gradient that can easily lead to thermal stress concentration, causing defects such as cracks and warping in the molded parts. This is especially true in thin-walled structures or areas with complex curves.

[0005] Uneven structure and performance: Traditional fixed laser parameters are difficult to adapt to the melting requirements of different areas. The unstable cooling rate of the molten pool will lead to coarse grains and uneven distribution of precipitated phases. The single post-processing process cannot effectively eliminate internal defects (such as pores and shrinkage).

[0006] Insufficient environmental control: Excessive oxygen content in the molding chamber or low powder bed temperature control accuracy will aggravate powder oxidation and reduce melting efficiency, affecting the density and surface quality of the part;

[0007] In the existing technology, although the molding quality is improved by optimizing the scanning path and adjusting the laser power, there is still a lack of systematic process solutions for the special physical and chemical properties of In718 alloy (such as high melting point, easy oxidation, and sensitive phase change). In particular, there are technical bottlenecks in key links such as powder surface modification, gradient temperature field construction, dynamic control of the melt pool, and composite post-processing. It is difficult to meet the high-performance and high-reliability requirements of components in high-demand fields such as aerospace. Summary of the Invention

[0008] The object of the present invention is to provide a SLM forming method for In718 high-temperature alloy material to solve the problems raised in the above background technology.

[0009] To achieve the above object, the present invention provides the following technical solution: a SLM forming method of In718 high temperature alloy material, comprising the following steps:

[0010] S1: Spherical In718 high-temperature alloy powder with a particle size of 15-35μm is selected. Irregular particles are first removed by ultrasonic vibration screening. Then, a nano-scale alumina coating is applied to the powder surface. A uniform coating with a thickness of 50-100nm is formed on the powder surface through vapor deposition technology to improve the powder's wettability and antioxidant properties.

[0011] S2: In an inert gas chamber, a vibration-assisted powder spreading device is used. The building platform is first preheated to 100-150°C, and then the powder is spread in a layer thickness of 20-30μm. During the powder spreading process, 5-10Hz low-frequency vibration is applied. At the same time, electrostatic adsorption technology is used to align the powder particles, forming a pre-compacted powder layer with a density of ≥98%;

[0012] S3: Using a pulsed fiber laser, dynamic parameter modulation is implemented during the melting process: for thin-walled structural areas, 250-300W power, 1200-1500mm / s scanning speed and 0.06-0.08mm scanning spacing are used; for solid support areas, 300-350W power, 800-1000mm / s scanning speed and 0.08-0.10mm scanning spacing are used, combined with a spiral scanning path that alternates ±15°, to simultaneously reduce the cooling rate of the molten pool by 30%-50%;

[0013] S4: A dual-wavelength infrared thermometer is used to monitor the molten pool temperature field in real time, and a high-speed CCD camera is used to capture the molten pool flow state. When the molten pool width fluctuation exceeds ±5%, the laser pulse frequency compensation is automatically triggered, and the amplitude is adjusted by ±10kHz. At the same time, a directional argon purge of 5-10L / min is applied to the molten pool area through the air flow nozzle to stabilize the molten pool convection state.

[0014] S5: A three-layer temperature gradient environment is constructed during the molding process. The bottom layer of the powder bed is maintained at 160-190°C, the middle layer is locally heated to 200-230°C by heating rods, and the top layer is maintained at 180-210°C by air cooling, forming a vertical temperature gradient of 5-10°C / mm. High-purity argon gas with an oxygen content of ≤30ppm is used for protection in the molding chamber.

[0015] S6: The molded parts are first solution treated at 1050℃ for 1 hour, then furnace cooled to 800℃ and then transferred to staged aging: the first stage is 750℃ for 8 hours, the heating rate is 5℃ / min, the second stage is 650℃ for 10 hours, the cooling rate is 3℃ / min, followed by hot isostatic pressing at 1050℃, 110MPa for 2.5 hours, and finally cryogenic treatment with liquid nitrogen at -196℃ for 4 hours to increase the amount of γ" phase precipitation by 20%-30%.

[0016] Preferably, the powder is first subjected to plasma activation treatment before the nano-coating is deposited, and the surface roughness Ra of the powder is reduced from 0.8-1.2 μm to 0.3-0.5 μm by 30-50 kHz high-frequency plasma bombardment for 5-10 minutes.

[0017] Preferably, the powder spreading device adopts a double-roller pressure wheel structure, the front roller is a flexible rubber roller for preliminary leveling, and the rear roller is a carbide roller with a surface roughness Ra≤0.2μm, which performs secondary compaction and cooperates with the electromagnetic vibrator under the powder bed with an amplitude of 0.1-0.3mm.

[0018] Preferably, during the laser melting process, a dynamic adjustment technology of the spot diameter is adopted: in complex curved surface areas with a curvature radius of less than 2 mm, the spot diameter is reduced to 50-70 μm through a zoom system; in flat areas, the spot diameter is maintained at 80-100 μm, and the scanning speed is adaptively adjusted by ±20% to ensure that the energy density deviation in different curvature areas is less than 5%.

[0019] Preferably, the molten pool monitoring system integrates a machine learning algorithm and establishes a dynamic model by training more than 100,000 sets of molten pool image data. When the crack risk probability is predicted to be greater than 15%, a 0.5-1.0mm anti-crack scanning line is automatically inserted, and the energy density of the scanning line is 10%-15% higher than that of the surrounding area.

[0020] Preferably, the gradient temperature field is achieved through an embedded heating element and an air cooling pipe network. The heating element adopts a nickel-chromium alloy wire with a diameter of 0.5 mm, and the air cooling pipe adopts a spiral layout, so that the temperature uniformity error of the powder bed is controlled within ±2°C.

[0021] Preferably, an ultrasonic rolling strengthening process is added after the hot isostatic pressing treatment, using an ultrasonic rolling head with a frequency of 20-30kHz and an amplitude of 0.2-0.3mm to apply 50-80N / mm to the surface of the workpiece. 2 pressure, processing time 15-30min, so that the surface grain size is refined from 50-80μm to 20-30μm.

[0022] Preferably, the first stage is vibration screening with a mesh size of 45 μm to remove large particles of impurities, the second stage is plasma re-spheroidization with a power of 15-20 kW and a treatment time of 3-5 minutes to restore the powder sphericity to more than 95%, and the third stage is microwave treatment with a power of 2.45 GHz, a power of 500-800 W and a time of 5-10 minutes.

[0023] Preferably, for complex structures such as aircraft engine turbine blades, a parametric support structure is constructed through finite element simulation before molding, and the contact area between the support and the body adopts a lattice-type connecting column with a diameter of 0.3-0.5 mm and a spacing of 1-2 mm.

[0024] This invention significantly improves the quality and efficiency of In718 alloy SLM molding through full-process technological innovation. The specific advantages are as follows:

[0025] 1. Powder performance optimization: Ultrasonic screening combined with nano-coating modification improves powder fluidity and oxidation resistance, and reduces oxidation inclusion defects during the molding process.

[0026] 2. Powder spreading and preheating enhancement: Vibration-assisted powder spreading and gradient temperature field design increase powder layer density, reduce interlayer thermal stress, and enhance interlayer bonding strength.

[0027] 3. Dynamic melting control: Dynamically adjust laser parameters for different structural areas, combined with real-time monitoring and compensation of the molten pool, to effectively suppress cracks and optimize grain structure.

[0028] 4. Composite post-processing efficiency enhancement: Through segmented aging, hot isostatic pressing and cryogenic treatment, internal defects are eliminated and density is improved; ultrasonic rolling refines surface grains and significantly improves fatigue resistance.

[0029] 5. Intelligent and green manufacturing: Support structure design based on finite element simulation reduces material consumption, and the three-stage powder recovery system increases the recycling rate to over 90%, reducing costs and environmental burden. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Example 1: Forming of aircraft engine turbine blades;

[0032] Application scenario: Design of support structures based on finite element simulation for complex curved structures with a curvature radius of less than 2 mm (such as aircraft engine turbine blades).

[0033] Implementation steps:

[0034] Powder pretreatment: Spherical In718 powder with a particle size of 15-35μm was selected and first screened with ultrasonic vibration through a 45μm sieve (first-level screening) to remove large particle impurities; 15kW power plasma was used for re-spheroidization treatment for 3 minutes (secondary treatment) to restore the sphericity to 96%; 2.45GHz microwave treatment was used for 5 minutes (tertiary treatment) to remove surface adsorbed water vapor; plasma activation treatment: 30kHz high-frequency plasma bombardment for 5 minutes, the surface roughness Ra was reduced from 1.0μm to 0.4μm; vapor deposition nano-alumina coating with a thickness of 80nm was applied to improve wettability and oxidation resistance.

[0035] Powder spreading and preheating: In an inert gas protection chamber (oxygen content ≤ 25ppm), the molding platform is preheated to 120°C;

[0036] Double-roller powder spreading device: The front flexible rubber roller is used for initial leveling, and the rear carbide roller (Ra = 0.15μm) is used for secondary compaction. It is equipped with an electromagnetic vibrator (amplitude 0.2mm, 5Hz low-frequency vibration) below the powder bed; the layer thickness is 25μm, and the powder is oriented by electrostatic adsorption. The density of the pre-compacted powder layer is 98.5%.

[0037] Laser melting: complex curved surface area (curvature radius <2mm): spot diameter reduced to 60μm, power 280W, scanning speed 1300mm / s, scanning pitch 0.07mm;

[0038] Plane area: spot diameter 80μm, power 300W, scanning speed 1000mm / s, scanning pitch 0.08mm;

[0039] Scanning path: ±15° alternating spiral, molten pool cooling rate reduced by 40%;

[0040] Support structure: The diameter of the dot matrix connecting columns is 0.4mm, the spacing is 1.5mm, and the support layout is optimized through finite element simulation.

[0041] Molten pool monitoring and temperature control: Dual-wavelength infrared thermometer for real-time monitoring, high-speed CCD captures molten pool flow, and when the molten pool width fluctuates by more than 5%, laser frequency compensation (±10kHz) is triggered, and argon gas purge (8L / min) is also performed simultaneously.

[0042] Three-layer temperature gradient: bottom layer 170℃, middle layer 220℃ (local heating of heating rod), top layer 200℃ (air flow cooling), vertical temperature gradient 8℃ / mm, temperature uniformity error ±1.5℃.

[0043] Post-processing:

[0044] Solution treatment: 1050℃×1h, cooling to 800℃;

[0045] Staged aging: first stage 750℃×8h (heating rate 5℃ / min), second stage 650℃×10h (cooling rate 3℃ / min);

[0046] Hot isostatic pressing: 1050°C, 110 MPa, 2.5 h;

[0047] Ultrasonic rolling strengthening: 25kHz frequency, 0.25mm amplitude, pressure 60N / mm 2 , treated for 20 min, the surface grains were refined to 25 μm;

[0048] Liquid nitrogen cryogenics: -196°C × 4h, the amount of γ" phase precipitation increased by 25%.

[0049] Data parameters:

[0050]

[0051] Example 2: Molding of complex thin-walled structural parts

[0052] Application scenarios: Thin-walled structural parts with a wall thickness of ≤1mm (such as aerospace brackets), focusing on melt pool stability and crack control.

[0053] Implementation steps:

[0054] Powder pretreatment: Ultrasonic screening to remove irregular particles, plasma activation treatment (50kHz, 10min), the surface roughness Ra is reduced from 1.2μm to 0.3μm; the nano-alumina coating thickness is 100nm to improve the antioxidant performance.

[0055] Powder spreading and preheating: platform preheating 150℃, layer thickness 20μm, low frequency vibration 10Hz, electrostatic adsorption directional arrangement, powder layer density 98.2%.

[0056] Laser melting:

[0057] Thin-wall area: power 250W, scanning speed 1500mm / s, scanning pitch 0.06mm; complex curved area (curvature radius 1.5mm): spot diameter 50μm, scanning speed adaptive adjustment +20% (to 1800mm / s), energy density deviation <5%.

[0058] Melt pool monitoring and crack control: The machine learning model is trained on 150,000 sets of melt pool images. When the crack risk is greater than 15%, a 0.8mm anti-crack scanning line (12% higher energy density) is automatically inserted; the argon purge rate is 10L / min to stabilize the melt pool convection.

[0059] Temperature gradient and post-processing:

[0060] Temperature gradient: bottom layer 180℃, middle layer 230℃, top layer 210℃, vertical gradient 10℃ / mm;

[0061] After aging treatment, the amount of γ" phase precipitation increased by 28%, and after cryogenic treatment, the microhardness increased by 15%.

[0062] Data parameters;

[0063]

[0064]

[0065] Example 3: Forming of solid supporting structure

[0066] Application scenarios: Large-scale solid support structures (such as mold cores), focusing on molding efficiency and internal density.

[0067] Implementation steps:

[0068] Powder pretreatment:

[0069] Three-stage treatment: 45μm mesh screening → 20kW plasma re-spheroidization for 5 minutes (sphericity 97%) → 800W microwave treatment for 10 minutes; plasma activation (40kHz, 8 minutes), Ra reduced from 0.9μm to 0.45μm, coating thickness 50nm;

[0070] Powder spreading and preheating: the platform is preheated to 100°C, compacted by a double roller (the rear roller Ra is 0.2 μm), with an amplitude of 0.3 mm and a powder layer density of 98.8%.

[0071] Laser melting:

[0072] Solid area: power 350W, scanning speed 800mm / s, scanning pitch 0.10mm, spot diameter 100μm;

[0073] Scanning path: Spiral alternating ±15°, cooling rate reduced by 50%.

[0074] Temperature control and post-processing:

[0075] Temperature gradient: bottom layer 160℃, middle layer 200℃, top layer 180℃, gradient 5℃ / mm;

[0076] Ultrasonic rolling after hot isostatic pressing: 30kHz, 0.3mm amplitude, pressure 80N / mm 2 , treated for 30 min, the surface grains were refined to 20 μm;

[0077] After cryogenic treatment, the amount of γ" phase precipitation increases by 30%, and the density is ≥99.5%.

[0078] Data parameters:

[0079]

[0080]

[0081] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A SLM forming method of In718 high temperature alloy material, characterized in that: The following steps are involved: S1: Spherical In718 high-temperature alloy powder with a particle size of 15-35μm is selected. Irregular particles are first removed by ultrasonic vibration screening. Then, a nano-scale alumina coating is applied to the powder surface. A uniform coating with a thickness of 50-100nm is formed on the powder surface through vapor deposition technology to improve the powder's wettability and antioxidant properties. S2: In an inert gas chamber, a vibration-assisted powder spreading device is used. The building platform is first preheated to 100-150°C, and then the powder is spread in a layer thickness of 20-30μm. During the powder spreading process, 5-10Hz low-frequency vibration is applied. At the same time, electrostatic adsorption technology is used to align the powder particles, forming a pre-compacted powder layer with a density of ≥98%; S3: Using a pulsed fiber laser, dynamic parameter modulation is implemented during the melting process: for thin-walled structural areas, 250-300W power, 1200-1500mm / s scanning speed and 0.06-0.08mm scanning spacing are used; for solid support areas, 300-350W power, 800-1000mm / s scanning speed and 0.08-0.10mm scanning spacing are used, combined with a spiral scanning path that alternates ±15°, to simultaneously reduce the cooling rate of the molten pool by 30%-50%; S4: A dual-wavelength infrared thermometer is used to monitor the molten pool temperature field in real time, and a high-speed CCD camera is used to capture the molten pool flow state. When the molten pool width fluctuation exceeds ±5%, the laser pulse frequency compensation is automatically triggered, and the amplitude is adjusted by ±10kHz. At the same time, a directional argon purge of 5-10L / min is applied to the molten pool area through the air flow nozzle to stabilize the molten pool convection state. S5: A three-layer temperature gradient environment is constructed during the molding process. The bottom layer of the powder bed is maintained at 160-190°C, the middle layer is locally heated to 200-230°C by heating rods, and the top layer is maintained at 180-210°C by air cooling, forming a vertical temperature gradient of 5-10°C / mm. High-purity argon gas with an oxygen content of ≤30ppm is used for protection in the molding chamber. S6: The molded parts are first solution treated at 1050℃ for 1 hour, then furnace cooled to 800℃ and then transferred to staged aging: the first stage is 750℃ for 8 hours, the heating rate is 5℃ / min, the second stage is 650℃ for 10 hours, the cooling rate is 3℃ / min, followed by hot isostatic pressing at 1050℃, 110MPa for 2.5 hours, and finally cryogenic treatment with liquid nitrogen at -196℃ for 4 hours to increase the amount of γ" phase precipitation by 20%-30%.

2. The SLM forming method of In718 high temperature alloy material according to claim 1, characterized in that: Before the nano-coating is deposited, the powder is first subjected to plasma activation treatment. By bombarding the powder with a high-frequency plasma of 30-50kHz for 5-10 minutes, the surface roughness Ra of the powder is reduced from 0.8-1.2μm to 0.3-0.5μm.

3. The SLM forming method of In718 high temperature alloy material according to claim 2, characterized in that: The powder spreading device adopts a double-roller pressure wheel structure. The front roller is a flexible rubber roller for preliminary leveling, and the rear roller is a carbide roller with a surface roughness Ra≤0.2μm for secondary compaction. It is equipped with an electromagnetic vibrator under the powder bed with an amplitude of 0.1-0.3mm.

4. The SLM forming method of In718 high temperature alloy material according to claim 3, characterized in that: During the laser melting process, a dynamic adjustment technology for the spot diameter is used: in complex curved surface areas with a curvature radius of less than 2 mm, the spot diameter is reduced to 50-70 μm through a zoom system; in flat areas, the spot diameter is maintained at 80-100 μm, and the scanning speed is adaptively adjusted by ±20% to ensure that the energy density deviation in different curvature areas is less than 5%.

5. The SLM forming method of In718 high temperature alloy material according to claim 4, characterized in that: The molten pool monitoring system integrates a machine learning algorithm and establishes a dynamic model by training more than 100,000 sets of molten pool image data. When the crack risk probability is predicted to be greater than 15%, a 0.5-1.0mm anti-crack scanning line is automatically inserted, and the energy density of the scanning line is 10%-15% higher than that of the surrounding area.

6. The SLM forming method of In718 high temperature alloy material according to claim 5, characterized in that: The gradient temperature field is achieved through an embedded heating element and an air-cooling pipe network. The heating element uses a nickel-chromium alloy wire with a diameter of 0.5 mm, and the air-cooling pipe adopts a spiral layout, so that the temperature uniformity error of the powder bed is controlled within ±2°C.

7. The SLM forming method of In718 high temperature alloy material according to claim 6, characterized in that: After the hot isostatic pressing treatment, an ultrasonic rolling strengthening process is added, in which an ultrasonic rolling head with a frequency of 20-30kHz and an amplitude of 0.2-0.3mm is used to apply 50-80N / mm to the surface of the workpiece. 2 pressure, processing time 15-30min, so that the surface grain size is refined from 50-80μm to 20-30μm.

8. The SLM forming method of In718 high temperature alloy material according to claim 7, characterized in that: The first stage is vibration screening, with a screen aperture of 45μm to remove large particles of impurities, the second stage is plasma re-spheroidization, with a power of 15-20kW and a processing time of 3-5min, to restore the powder sphericity to more than 95%, and the third stage is microwave treatment, with a power of 2.45GHz, a power of 500-800W, and a time of 5-10min.

9. The SLM forming method of In718 high temperature alloy material according to claim 8, characterized in that: For complex structures such as aircraft engine turbine blades, a parametric support structure is constructed through finite element simulation before molding. The contact area between the support and the body uses a lattice-type connecting column with a diameter of 0.3-0.5mm and a spacing of 1-2mm.

Images