Interlayer structure nanocrystallization regulation and control method based on additive manufacturing

Abstract

The invention provides an interlayer structure nanocrystallization regulation and control method based on additive manufacturing. The interlayer structure nanocrystallization regulation and control method comprises the following steps that A, a workbench is preheated; b) printing a single layer under ultrasonic assistance; (C) carrying out surface nanocrystallization on the printed single layer by adopting a surface nanocrystallization device, and meanwhile, uniformly transferring vibration energy to a printing body by adopting ultrasonic waves to assist in interlayer nanocrystallization; and D) the step B) and the step C) are repeated until printing is completed, and the additive is obtained. According to the method, ultrasonic-assisted molten pool forming and interlayer nanocrystallization are synchronously carried out, defects are inhibited in real time, the defects of pores, incomplete fusion, internal tensile stress and the like are directly eliminated, and additional post-treatment is not needed. According to the method, dislocation slippage and dynamic recrystallization are induced through high-frequency longitudinal wave ultrasonic waves, and surface nanocrystallization of metal with poor plasticity is achieved; and meanwhile, workpiece pressure stress is preset, and workpiece vulnerability caused by molten pool tensile stress is counteracted.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and particularly relates to a method for controlling the nanostructure of interlayer tissues based on additive manufacturing. Background Art

[0002] With the continuous development of manufacturing technologies, additive manufacturing (3D printing) technology has been widely applied in high-end manufacturing fields such as aerospace and automotive. Its core advantages lie in the flexibility of complex structure manufacturing and high material utilization rate. However, this technology still faces multiple technical bottlenecks in the process of industrial implementation:

[0003] 1. Unstable dynamic forming quality

[0004] During the additive manufacturing (3D printing) process, due to the instantaneous energy fluctuation of the laser / electron beam heat source (±10% power deviation), the melt pool dynamics becomes unstable, triggering the keyhole effect, and generating defects such as pores in the component. Taking the selective laser melting (SLM) of titanium alloy (Ti-6Al-4V) as an example, when the energy density exceeds the critical threshold (120 J / mm 3 ), the vapor pressure inside the melt pool breaks through the surface tension limit, forming spherical pores with a diameter of 20 - 50 μm, reducing the fatigue life of the component by 40% - 60%. At the same time, the layer-by-layer stacking characteristic results in the interlayer bonding strength being only 70% - 85% of the bulk material. Especially in the arc wire additive manufacturing of high-strength aluminum alloys (such as AlSi10Mg), the fluctuation range of the interlayer shear strength reaches 15%, significantly affecting the reliability of load-bearing components.

[0005] 2. Stress-defect cross-scale coupling

[0006] The cooling rate as high as 300 - 500 °C / ms during the additive manufacturing process will cause severe thermal stress accumulation. For example, the internal residual tensile stress of an Inconel 718 component formed by SLM can reach 350 MPa. Although the tensile stress at a depth of 50 μm on the surface can be reduced to below 50 MPa after traditional hot isostatic pressing (HIP) post-treatment, the stress at the core of the component still reaches the level of 200 MPa, becoming the source of fatigue crack initiation. More seriously, the dendritic segregation during the solidification of the metal melt pool will form micron-scale lack of fusion defects. For example, the CT detection of a certain type of aviation bracket shows that the internal porosity reaches 0.12 vol%, which is more than 10 times worse than the forging benchmark (<0.01 vol%).

[0007] 3. Severe lack of process synergy

[0008] In the current technical route, printing and post-processing are independent processes, that is, a serial process in which components are processed after printing. The main problems of this process are: (1) It is difficult to eliminate internal defects in components after printing and then post-processing, so there are many internal defects and large residual stresses in the product; (2) Offline processing cannot intervene in the dynamic molten pool in real time, resulting in the inability to repair unfused defects at a depth of 50-200 μm below the surface. For example, the service life of a certain aerospace gearbox component is only 65% of the designed value due to internal defects. (3) Low efficiency and easy to introduce secondary defects.

[0009] 4. Lack of effective technologies to improve the performance of additive manufacturing components

[0010] Currently, the performance of additive manufacturing components is mainly improved by ultrasonic-assisted methods, but this method has great limitations. Taking ultrasonic-assisted rolling as an example, when ultrasonic is used as the power source and processing metal materials with poor plasticity, due to the poor ductility of the materials, severe plastic deformation is likely to cause microcracks or even macroscopic spalling (powdering phenomenon) on the surface, and it is impossible to improve the performance of the component core. Existing ultrasonic-assisted technologies are difficult to break through the limitations of material intrinsic characteristics.

[0011] In addition, the matching of additive manufacturing process parameters and post-processing parameters also mainly depends on experience based on trial and error. For example, to determine the optimal energy density window (80-100 J / mm 3 ) for titanium alloy SLM forming, more than 200 sets of orthogonal tests need to be carried out, and the verification period for a single set of parameters reaches 72 hours, resulting in a long R & D cycle and high cost for the project. Summary of the Invention

[0012] The purpose of the present invention is to provide a method for regulating the nano-structuring of interlayer tissues based on additive manufacturing. The method in the present invention has an accurate regulation mode, high integration, and few internal defects.

[0013] The present invention provides a method for regulating the nano-structuring of interlayer tissues based on additive manufacturing, including the following steps:

[0014] A) Preheat the workbench;

[0015] B) Print a single layer under ultrasonic assistance;

[0016] C) Use a surface nano-structuring device to perform surface nano-structuring on the printed single layer, and at the same time use ultrasonic to uniformly transfer vibration energy to the printed body to assist interlayer nano-structuring;

[0017] D) Repeat steps B) and C) until printing is completed to obtain an additive.

[0018] Preferably, during the process of printing a single layer in step B), the frequency f w , power P w and time tw Calculated according to Formula I to Formula III:

[0019]

[0020] In Formula I, σ is the surface tension of the molten metal, with the unit of N / m; P cav is the cavitation threshold pressure, with the unit of Pa, ρ represents the density of the molten metal, with the unit of kg / m 3 , c represents the speed of sound in the melt, with the unit of m / s, η energy represents the ultrasonic energy transfer efficiency, with the unit of %;

[0021]

[0022] In Formula II, μ represents the dynamic viscosity of the melt, with the unit of Pa·s, v flow represents the acoustic streaming velocity, with the unit of m / s, A melt represents the cross-sectional area of the molten pool, with the unit of m 2 , η mech represents the mechanical energy conversion efficiency, with the unit of %, P laser represents the laser power, with the unit of W;

[0023]

[0024] In Formula III, δ layer represents the single-layer printing length, with the unit of m, v scan represents the printing speed in m / s, d melt represents the depth of the molten pool, with the unit of m, α thermal represents the thermal diffusivity of the melt in m 2 / s.

[0025] Preferably, during the ultrasonic-assisted interlayer nanostructuring process in step C), the frequency f s , power P s and time t s are calculated according to Formula IV to Formula VI:

[0026]

[0027] In Formula IV, represents the critical strain rate, with the unit of s -1 , c is the speed of sound, with the unit of m / s, d grain represents the initial grain size, with the unit of m, σ y represents the yield strength, with the unit of Mpa, Q represents the activation energy, with the unit of J, R represents the gas constant, whose value is 8.314 J / (mol·K), T is the treatment temperature, with the unit of °C, and exp(Q / RT) is dimensionless.

[0028]

[0029] In Formula V, ρ represents the density of solid metal, with the unit of kg / m 3 , f represents the ultrasonic frequency, with the unit of Hz, A mp represents the vibration amplitude value, with the unit of m, A represents the size of the processing execution end, with the unit of m, δ represents the preset nano-layer depth, with the unit of m, and η represents the energy conversion efficiency, with the unit of %;

[0030]

[0031] In Formula VI, δ layer represents the total length of single-layer printing, with the unit of m, v smart represents the surface treatment speed, with the unit of m / s.

[0032] Preferably, the preheating temperature of the workbench is 200 - 400 °C;

[0033] An ultrasonic generating device is provided below the workbench.

[0034] Preferably, the ultrasonic generating device applies vibration to the molten pool through a horn;

[0035] The ultrasonic generating device evenly transfers the vibration energy to the printed body through a transducer.

[0036] Preferably, during the process of printing a single layer, the laser power is 0 - 2000 W, the spot diameter is 0 - 5 mm, the scanning speed is 0 - 500 mm / s, and the scanning line distance is 0 - 2 mm.

[0037] Preferably, during the process of printing a single layer, the temperature field distribution of the molten pool is monitored by a molten pool monitoring module. When local overheating of the molten pool is detected, the ultrasonic power is reduced by 10 - 20%; when the temperature of the printed body drops to 10 - 20% of the melting point temperature, interlayer nanocrystallization is carried out.

[0038] Preferably, when the temperature is greater than 1.2 times the melting point of the additive material, it is judged as local overheating, and the ultrasonic power is reduced by 10 - 20%.

[0039] Preferably, the pressure for surface nanocrystallization is 200 - 500 MPa, the moving speed is 100 - 5000 mm / min, and the spacing is 0 - 1 mm.

[0040] Preferably, after step C), residual stress and grain size detection are also included. When the detection is unqualified, the unqualified area is subjected to ultrasonic-assisted interlayer nanocrystallization again.

[0041] The present invention provides a method for regulating the nanocrystallization of interlayer structures based on additive manufacturing, comprising the following steps: A) preheating the workbench; B) printing a single layer under ultrasonic assistance; C) subjecting the printed single layer to surface nanocrystallization using a surface nanocrystallization device, and simultaneously transmitting vibration energy uniformly to the printed body using ultrasound to assist interlayer nanocrystallization; D) repeating steps B) and C) until printing is completed to obtain an additive.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) The present invention establishes a composite process method that combines additive manufacturing and nanocrystallization regulation, and quantitatively correlates ultrasonic parameters with material physics, mechanics, and process conditions, upgrading from an "experience-driven" mode to an accurate regulation mode of "theory guidance + data verification".

[0044] (2) The present invention uses ultrasonic assistance to synchronize molten pool forming and interlayer nanocrystallization, suppressing defects in real time and directly eliminating defects such as pores, lack of fusion, and internal tensile stress, without the need for additional post-processing.

[0045] (3) The present invention uses high-frequency longitudinal wave ultrasonic waves to induce dislocation slip and dynamic recrystallization, achieving surface nanocrystallization of metals with poor plasticity; at the same time, a pre-set compressive stress on the workpiece is used to offset the vulnerability of the workpiece caused by the tensile stress in the molten pool.

[0046] (4) After the treatment with the device and method of the present invention, the mechanical properties of the material, including surface hardness, wear resistance, corrosion resistance, and fatigue resistance, are greatly improved, the material utilization rate is increased, and the comprehensive cost is greatly reduced.

[0047] (5) The present invention integrates additive manufacturing and nanocrystallization processes. Through a cyclic mode of layer-by-layer printing - layer-by-layer nanocrystallization, the efficiency is increased by more than 50%. At the same time, the post-processing separation and connection losses of traditional multi-step processes (printing - stress relief - post-processing) are eliminated, and secondary defects caused by workpiece handling are avoided. Description of the Drawings

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the provided drawings without creative efforts.

[0049] Figure 1 It is a schematic structural diagram of the device used for the method for regulating the nanocrystallization of interlayer structures based on additive manufacturing of the present invention;

[0050] Figure 1Among them, 1 is the molten pool monitoring module, 2 is the surface nanocrystallization device, 3 is the residual stress and grain size detection device, 4 is the 3D printing device, 5 is the ultrasonic generating device, and 6 is the workbench;

[0051] Figure 2 This is the operation flowchart of the method for regulating interlayer tissue nanocrystallization based on additive manufacturing of the present invention. Detailed implementation manners

[0052] The present invention provides a method for regulating interlayer tissue nanocrystallization based on additive manufacturing, including the following steps:

[0053] A) Preheat the workbench;

[0054] B) Print a single layer under ultrasonic assistance;

[0055] C) Use the surface nanocrystallization device to perform surface nanocrystallization on the printed single layer, and at the same time use ultrasonic waves to uniformly transfer vibration energy to the printed body to assist interlayer nanocrystallization;

[0056] D) Repeat steps B) and C) until printing is completed to obtain an additive.

[0057] In the present invention, the workbench is the core bearing and energy transfer platform of the metal forming device. The main body is made by compounding a titanium alloy substrate with a thickness of 20 - 30 mm and a zirconia ceramic thermal insulation coating with a thickness of 0.5 - 1 mm, and has both high stiffness and anti-thermal deformation performance. A heating device is installed at its bottom, and the purpose is to preheat the workbench before 3D printing to avoid the reduction of internal stress in the printed layer due to excessive temperature difference during printing.

[0058] In the present invention, the preheating temperature of the workbench is preferably 200 - 400 °C, more preferably 250 - 350 °C, such as 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, and is preferably a range value with any of the above values as the upper or lower limit.

[0059] After the workbench is preheated, the present invention performs layer-by-layer printing under ultrasonic assistance to obtain an additive.

[0060] In the present invention, an ultrasonic generating device is arranged below the workbench. The main function of the ultrasonic generating device is to optimize the quality of the molten pool during 3D printing and assist interlayer nanocrystallization, and at the same time increase the plasticity of the metal. It is installed below the workbench, and 9 piezoelectric ceramic transducers are arranged to form an array, and uniform transfer of vibration energy to the workpiece is achieved through phase synchronization control.

[0061] In the present invention, the printing of each layer includes ultrasonic-assisted printing of a single layer and ultrasonic-assisted interlayer nanocrystallization.

[0062] In the present invention, the printing operation in the ultrasonic-assisted printing single layer is realized by a 3D printing device, which is located on one side of the workbench, such as at the 9 o'clock direction. Its function is to form the layer-by-layer cladding of metal materials, and it is composed of a robotic arm, a high-power fiber laser (wavelength of 1070 nm, adjustable from 300 to 2000 W), and a four-channel coaxial powder feeding system. The robotic arm is responsible for the movement of the laser and the powder feeding device during the single layer printing process, and the laser and the coaxial powder feeding system are responsible for printing.

[0063] During the ultrasonic-assisted printing of a single layer, the laser power is preferably 0 - 2000 W, more preferably 50 - 1000 W, such as 10 W, 50 W, 100 W, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, 900 W, 1000 W, and is preferably a range value with any of the above values as the upper or lower limit; the spot diameter is preferably 0 - 5 mm, more preferably 1 - 5 mm, such as 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, and is preferably a range value with any of the above values as the upper or lower limit; the scanning speed is preferably 0 - 500 mm / s, more preferably 50 - 400 mm / s, such as 10 mm / s, 50 mm / s, 100 mm / s, 150 mm / s, 200 mm / s, 250 mm / s, 300 mm / s, 350 mm / s, 400 mm / s, 450 mm / s, 500 mm / s, and is preferably a range value with any of the above values as the upper or lower limit; the scanning line distance is preferably 0 - 2 mm, more preferably 0.5 - 2 mm, such as 0.5 mm, 1 mm, 1.5 mm, 2 mm, and is preferably a range value with any of the above values as the upper or lower limit.

[0064] During the ultrasonic-assisted printing of a single layer, the ultrasonic generator is turned on to apply vibration to the molten pool through a horn, and the cavitation effect and acoustic streaming effect are utilized to promote the flow of molten metal, break the bubbles in the molten pool, eliminate the lack of fusion defects, and reduce the porosity.

[0065] The frequency f of the ultrasonic wave w , the power P w and the time t w are calculated according to Equations I - III:

[0066]

[0067] In Equation I, σ is the surface tension of the molten metal, with the unit of N / m; P cav is the cavitation threshold pressure, with the unit of Pa, ρ represents the density of the molten metal, with the unit of kg / m 3 , c represents the sound speed in the melt, with the unit of m / s, and η energy represents the ultrasonic energy transfer efficiency, with the unit of %.

[0068]

[0069] In Formula II, μ represents the melt dynamic viscosity in Pa·s, v flow represents the acoustic streaming velocity in m / s, A melt represents the cross-sectional area of the molten pool in m 2 , η mech represents the mechanical energy conversion efficiency in %, P laser represents the laser power in W;

[0070]

[0071] In Formula III, δ layer represents the single-layer printing length, v scan represents the printing speed, d melt represents the molten pool depth, α thermal represents the melt thermal diffusivity.

[0072] Calculate and set the initial parameter frequencies f w , power P w and time t w according to Formulas I to III. The waveform is a longitudinal wave. Turn on the additive manufacturing device and perform the first layer of printing according to the product shape.

[0073] During the additive manufacturing process, monitor the temperature field distribution during the additive manufacturing process through the molten pool monitoring module, adjust the ultrasonic power during the printing process, and provide a basis for the start time of surface nanocrystallization.

[0074] Compensate for the energy distribution by dynamically adjusting the transducer under the workbench. If local overheating (>1.2 times the material melting point) is detected, reduce the ultrasonic power by 10% - 20%. At the same time, when the temperature of the printed body drops to 15% of the melting point temperature, perform surface nanocrystallization.

[0075] After completing a single layer of printing, use the surface nanocrystallization device to perform surface nanocrystallization on the surface of the printed layer. At the same time, the parameters of the ultrasonic wave generating device need to be switched to evenly transfer the vibration energy of the ultrasonic wave to the printed body for interlayer nanocrystallization. At this time, the function of the ultrasonic wave becomes to provide energy for activating dislocation sources and improve the metal plastic deformation ability.

[0076] In the present invention, the surface nanocrystallization device is located on the other side of the workbench, such as at the 3 o'clock direction. Its function is to perform surface nanocrystallization on the metal surface. The surface nanocrystallization methods are not limited to surface mechanical grinding, surface mechanical rolling, surface mechanical rolling, ultrasonic rolling, and laser shock, to achieve grain nanocrystallization and pre-set compressive stress. It is composed of a robotic arm, a processing execution end, and a pressure generating device. The robotic arm is responsible for the movement of the surface nanocrystallization device. The processing execution end processes the workpiece after additive manufacturing. The pressure generating device provides processing force to the processing execution device and moves with the robotic arm, and the processing execution end processes the workpiece. During the surface nanocrystallization process, the robotic arm drives the surface nanocrystallization device to move along the printing path, and the pressure provided by the pressure generating device causes plastic deformation of the printing surface layer through the processing execution end, forming a gradient nanostructure; at the same time, pre-set surface compressive stress (the compressive stress is the surface residual compressive stress, with a range of 200 - 1500 Mpa) is used to offset the tensile stress concentration caused by the 3D printing thermal stress.

[0077] In the present invention, during the interlayer nanocrystallization process, the frequency f of the ultrasonic wave s , power P s and time t s are calculated according to Equations IV - VI:

[0078]

[0079] In Equation IV, represents the critical strain rate, with the unit of s -1 , c is the sound velocity, with the unit of m / s, d initial represents the initial grain size, with the unit of m, σ y represents the yield strength, with the unit of Mpa, Q represents the activation energy, with the unit of J, R represents the gas constant, and its value is 8.314 J / (mol·K), T is the treatment temperature, with the unit of °C, and exp(Q / RT) is dimensionless.

[0080]

[0081] In Equation V, ρ represents the density of the solid metal, with the unit of kg / m 3 , f represents the ultrasonic frequency, with the unit of Hz, A mp represents the vibration amplitude value, with the unit of m, A represents the size of the processing execution end, with the unit of m, δ represents the preset nano-layer depth, with the unit of m, and η represents the energy conversion efficiency, with the unit of %;

[0082]

[0083] In Equation VI, δ layer represents the total length of a single-layer printing, with the unit of m, v smart represents the surface treatment speed, with the unit of m / s.

[0084] In the present invention, the pressure for surface nanocrystallization is preferably 200 - 500 MPa, more preferably 300 - 400 MPa, such as 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, and is preferably a range value with any of the above values as the upper or lower limit; the moving speed is preferably 100 - 5000 mm / min, more preferably 500 - 4000 mm / min, such as 100 mm / min, 200 mm / min, 300 mm / min, 400 mm / min, 500 mm / min, 600 mm / min, 700 mm / min, 800 mm / min, 900 mm / min, 1000 mm / min, 1500 mm / min, 2000 mm / min, 2500 mm / min, 3000 mm / min, 3500 mm / min, 4000 mm / min, 4500 mm / min, 5000 mm / min, and is preferably a range value with any of the above values as the upper or lower limit; the spacing is preferably 0 - 1 mm, more preferably 0.5 - 1 mm.

[0085] After the surface nanocrystallization is completed, the present invention preferably uses an X-ray residual stress and grain size detection module to detect the surface residual stress and grain size. The X-ray residual stress and grain size detection module detects the grain size and stress state, and is located on the other side of the gradient nanocrystallization arm. After gradient nanocrystallization, it is switched to the residual stress and grain size module. If the compressive stress or grain size does not reach the threshold (grain size less than 500 nm, residual compressive stress exceeding 200 Mpa), the printed surface is subjected to a surface nanocrystallization treatment again until the compressive stress and grain size reach the threshold.

[0086] Repeat the above processes of ultrasonic-assisted single-layer printing, ultrasonic-assisted interlayer nanocrystallization, and residual stress and grain size detection, and perform layer-by-layer printing until the additive manufacturing is completed.

[0087] The present invention provides a method for regulating interlayer tissue nanocrystallization based on additive manufacturing, comprising the following steps: A) preheating the workbench; B) printing a single layer under ultrasonic assistance; C) performing surface nanocrystallization on the printed single layer using a surface nanocrystallization device, and at the same time using ultrasonic waves to uniformly transfer vibration energy to the printed body to assist interlayer nanocrystallization; D) repeating steps B) and C) until the printing is completed to obtain an additive.

[0088] Compared with the prior art, the present invention has the following advantages:

[0089] (1) The present invention establishes a composite process method based on the regulation of interlayer nanocrystallization in additive manufacturing, quantitatively correlates ultrasonic parameters with material physical, mechanical, and process conditions, and upgrades from an "experience-driven" mode to an accurate regulation mode of "theory-guided + data verification".

[0090] (2) The present invention synchronizes ultrasonic-assisted molten pool forming and interlayer nanocrystallization to suppress defects in real time, directly eliminating defects such as pores, lack of fusion, and internal tensile stress, without the need for additional post-treatment.

[0091] (3) The present invention uses high-frequency longitudinal ultrasonic waves to induce dislocation slip and dynamic recrystallization, realizing the surface nanocrystallization of metals with poor plasticity; compressive stress is generated on the workpiece, offsetting the vulnerability of the workpiece caused by the tensile stress in the molten pool.

[0092] (4) After the treatment by the device and method of the present invention, the mechanical properties of the material, including surface hardness, wear resistance, corrosion resistance, and fatigue resistance, are greatly improved, the material utilization rate is increased, and the comprehensive cost is greatly reduced.

[0093] (5) The present invention integrates additive manufacturing and nanocrystallization processes. Through a cyclic mode of layer-by-layer printing - layer-by-layer nanocrystallization, the efficiency is increased by more than 50%. At the same time, the post-treatment separation and connection losses of traditional multi-step processes (printing - stress relief - post-treatment) are eliminated, and secondary defects caused by workpiece handling are avoided.

[0094] To further illustrate the present invention, the following describes in detail a method for regulating the interlayer tissue nanocrystallization based on additive manufacturing provided by the present invention in conjunction with embodiments, but it should not be construed as a limitation to the protection scope of the present invention.

[0095] Example 1

[0096] According to the design, a Ti-6Al-4V dumbbell-shaped specimen with a total length of 100 mm, a gauge section length of 60 mm, a width of 30 mm (i.e., a single layer is composed of 30 printed layers with a width of 1 mm and a length of 60 mm, δ layer = 60 mm × 30 mm), and a thickness of 5 mm is printed. The two ends are clamping ends with a width of 10 mm. A laser coaxial powder feeding device is used, and the printed powder is Ti-6Al-4V spherical powder (particle size 15 - 53 μm, oxygen content ≤ 0.13%).

[0097] 1. The workbench is preheated to 300 °C and kept at a constant temperature for 15 minutes to reduce thermal stress; the scanning path adopts a checkerboard filling strategy to reduce anisotropy.

[0098] 2. Obtain the basic parameters of the material, density (ρ) = 4430 kg / m 3, c = 4270 m / s, melting point (Tm) = 1660 °C, solid sound velocity (c_solid) = 6100 m / s, sound velocity in the melt (c) = 0.7 × 6100 = 4270 m / s, surface tension (σ) = 1.6 N / m, dynamic viscosity (μ) = 4.2c × 10 -3 Pa·s, thermal diffusivity (α_thermal) = 8.6 mm 2 / s, activation energy (Q) = 240 kJ / mol (typical value for titanium alloy), yield strength (σ_y) = 850 MPa; v flow = 0.8 m / s, cross-sectional area of the molten pool A melt = 0.5 × 10 -6 m 2 , mechanical energy conversion efficiency η mech = 0.7, allowable temperature rise ΔT = 25 °C, specific heat capacity Cp = 526. η energy = 0.7, cross-sectional area of the molten pool A melt = 0.5 mm 2 , heat input Q generated by ultrasonic vibration heat = 500 J / s, depth of the molten pool d melt = 250·10 -6 m, printing speed v scan = 16 mm / s

[0099] Calculate the ultrasonic parameters during the additive manufacturing stage, frequency f w and power P w are 21.5 kHz and 551.6 W respectively, and the action time t w is 113 seconds / layer. Ultrasonic-assisted additive manufacturing printing parameters: laser power 1000 W, spot diameter 0.5 mm, layer-by-layer stacking (25 layers in total, total height 5 mm);

[0100] P cav ≈ 3.2 × 10 6 Pa.

[0101]

[0102] 4. The molten pool monitoring module detects: The infrared thermal imager monitors the temperature in real time. When the local temperature exceeds 1660 °C, the laser power is reduced to 800 W; when the temperature drops to 300 °C, the interlayer nanocrystallization treatment begins.

[0103] 5. Ultrasonic generator switching parameters: The frequency is switched to 151 kHz, the power is increased to 2059 W, and the action time is about 187.5 seconds / layer;

[0104] Initial grain size d grain = 50 μm, critical strain rate The material constant K = 0.05, the processing temperature T = 300 °C, Amp = 15 μm, the processing area A = 1 mm 2 , the preset nano-layer depth δ = 300 μm, the energy conversion efficiency η = 0.5, the surface treatment speed v smart = 25 mm / s, and the processing width is 0.4 mm / channel.

[0105]

[0106] 6. Interlayer surface nano-machining: The processing execution end performs gradient nano-machining along the specimen length direction (pressure 400 N, moving speed 1500 mm / min, spacing 0.4 mm).

[0107] 7. Residual stress and grain size detection: The surface layer grains are refined to 150 nm, the depth of the compressive stress layer is 300 μm, the residual compressive stress is -280 MPa, exceeding the residual compressive stress threshold of 200 Mpa, and the residual stress and grain size detection are qualified.

[0108] 8. Repeat the above steps 3 - 6 until the workpiece is completed.

[0109] The test data of the titanium alloy tensile specimen after treatment are as follows:

[0110] Table 1 Test data of the titanium alloy tensile specimen after treatment in Example 1

[0111]

[0112]

[0113] Example 2

[0114] Printing of an aluminum alloy AlSi10Mg structural part (wall thickness 80 mm, height 80 mm, width 80 mm), using a laser coaxial powder feeding device, and the printing powder is AlSi10Mg spherical powder.

[0115] 1. Preheat the workbench to 250 °C and keep it at a constant temperature for 20 minutes to reduce thermal stress;

[0116] 2. Obtain the basic material parameters and calculate the ultrasonic parameters in the additive manufacturing stage:

[0117] The laser power is set to 800 W, the powder density acoustic flow velocity v_flow = 0.8 m / s, the melt pool cross-sectional area A_melt = 0.5 mm 2 , η_mech = 0.7

[0118] The powder density (ρ) = 2.68 g / cm 3 ;

[0119] The melting point (Tm) = 570 °C;

[0120] Solid sound velocity (c_solid) = 5100 m / s → Sound velocity in the melt (c_melt) = 0.7 × 5100 = 3570 m / s;

[0121] Dynamic viscosity (μ) = 3.5 mPa·s;

[0122] Thermal diffusivity (α_thermal) = 50 mm 2 / s;

[0123] Surface tension (σ) = 0.85 N / m;

[0124] Specific heat capacity Cp = 1230

[0125] ηenergy = 0.6

[0126] Heat input Q generated by ultrasonic vibration heat = 800 J / s

[0127] Molten pool depth d melt = 0.2 mm

[0128] Printing speed v scan = 16 mm / s

[0129] P cav ≈ 2.4 Mpa

[0130]

[0131] 3. Ultrasonic-assisted additive manufacturing: Laser power 800 W, spot diameter 0.4 mm, layer-by-layer stacking;

[0132] 4. Molten pool monitoring module detection: Infrared thermal imager monitors the temperature in real time. When the temperature drops to 300 °C, interlayer nanocrystallization treatment begins.

[0133] 5. Ultrasonic generator switching parameters: Frequency is switched to 81 kHz, power is increased to 1800 W, action time is about 6.6 seconds / layer;

[0134] Initial grain size d_grain = 50 μm, critical strain rate ε·_critical = 10 3 s-1, σ_y = 200 MPa, Q = 140 kJ / mol, T = 200 °C, amplitude Amp = 10 μm, actuator size A = 1 mm 2 , preset layer depth δ = 250 μm, η = 0.5. Machining speed 1800 mm / min, machining width is 0.4 mm / channel.

[0135]

[0136] 6. Interlayer surface nanocrystallization: The processing execution end performs gradient nanocrystallization along the length direction of the specimen (pressure 400 N, moving speed 1500 mm / min, spacing 0.4 mm).

[0137] 7. Residual stress and grain size detection: The surface grains are refined to 200 nm, the depth of the compressive stress layer is 300 μm, the residual compressive stress is -320 MPa, and the detection of residual stress and grain size is qualified.

[0138] 8. Repeat the above steps 3 - 6 until the workpiece is completed.

[0139] Comparative Example 1: Traditional 3D printing with traditional ultrasonic rolling post - treatment

[0140] According to the design, print a Ti - 6Al - 4V dumbbell - shaped specimen with a total length of 100 mm, a gauge section length of 60 mm, a width of 30 mm, and a thickness of 5 mm. The two ends are clamping ends with a width of 10 mm. Use a laser coaxial powder feeding device, and the printing powder is Ti - 6Al - 4V spherical powder (particle size 15 - 53 μm, oxygen content ≤ 0.13%, density ρ = 4.43 g / cm 3 )

[0141] 1. Preheat the workbench to 300 °C and keep it at a constant temperature for 15 minutes to reduce thermal stress; adopt a checkerboard filling strategy for the scanning path to reduce anisotropy.

[0142] 2. Printing parameters: Laser power 1000 W, spot diameter 0.5 mm, layer - by - layer stacking (a total of 25 layers, total height 5 mm);

[0143] 3. Molten pool monitoring module detection: The infrared thermal imager monitors the temperature in real - time. When the local temperature exceeds 1660 °C, reduce the laser power to 800 W; when the temperature drops to 300 °C, start the surface nanocrystallization treatment.

[0144] 4. Surface nanocrystallization, the processing execution end performs gradient nanocrystallization along the length direction of the specimen (pressure 400 N, moving speed 1500 mm / min, spacing 0.4 mm).

[0145] 5. Repeat the above steps 2 - 4 until the workpiece is completed.

[0146] The difference between Comparative Example 1 and Example 1 is that: there is no ultrasonic assistance during the workpiece printing process, and in the surface nanocrystallization step, ultrasonic only serves as a power source to drive the surface nanocrystallization device.

[0147] Results:

[0148] 1. Due to the cancellation of ultrasonic assistance, there are a large number of residual compressive stresses and micro - pores after the laser printing process.

[0149] 2. A large number of pores collapsed during the rolling process;

[0150] 3. There is no ultrasonic optimization for plasticity, and cracks and powder shedding occur during the surface ultrasonic rolling process.

[0151] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for controlling the nanostructuring of the interlayer structure based on additive manufacturing, comprising the following steps: A) Preheat the workbench; B) Print a single layer under ultrasonic assistance; C) Use a surface nanostructuring device to nanostructure the surface of the printed single layer, and at the same time use ultrasound to uniformly transfer the vibration energy to the printed body to assist in interlayer nanostructuring; D) Repeat steps B) and C) until printing is completed to obtain an additive.

2. The method for controlling the nanocrystallization of interlayer structure based on additive manufacturing according to claim 1, wherein During the process of printing a single layer in step B), the frequency f of the ultrasonic wave w , the power P w and the time t w are calculated according to Equations I to III: In formula I, σ is the surface tension of the molten metal, with the unit of N / m; P cav is the cavitation threshold pressure, with the unit of Pa, ρ represents the density of the molten metal, with the unit of kg / m 3 , c represents the sound velocity in the melt, with the unit of m / s, η energy represents the ultrasonic energy transfer efficiency, with the unit of %; In formula II, μ represents the melt dynamic viscosity in Pa·s, v flow represents the acoustic streaming velocity in m / s, A melt represents the cross-sectional area of the molten pool in m 2 , η mech represents the mechanical energy conversion efficiency in %, P laser represents the laser power in W; In formula III, δ layer represents the single-layer printing length in m, v scan represents the printing speed in m / s, d melt represents the melt pool depth in m, α thermal represents the melt thermal diffusivity in m 2 / s.

3. The method for controlling the nanocrystallization of the interlayer structure based on additive manufacturing according to claim 1, wherein During the ultrasonic-assisted interlayer nanocrystallization process in step C), the ultrasonic frequency f s , power P s and time t s are calculated according to Equations IV to VI: In Formula IV, represents the critical strain rate, with the unit of s -1 , c is the speed of sound, with the unit of m / s, d grain represents the initial grain size, with the unit of m, σ y represents the yield strength, with the unit of Mpa, Q represents the activation energy, with the unit of J, R represents the gas constant, whose value is 8.314 J / (mol·K), T is the treatment temperature, with the unit of °C, and exp(Q / RT) is dimensionless; In formula V, ρ represents the density of solid metal, with the unit of kg / m 3 , f represents the ultrasonic frequency, with the unit of Hz, A mp represents the vibration amplitude value, with the unit of m, A represents the size of the processing execution end, with the unit of m, δ represents the preset nano-layer depth, with the unit of m, and η represents the energy conversion efficiency, with the unit of %; In Formula VI, δ layer represents the total single-layer printing length in m, and v smart represents the surface treatment speed in m / s.

4. The method for controlling the nanocrystallization of interlayer structure based on additive manufacturing according to claim 1, wherein, The preheating temperature of the workbench is 200 - 400 °C; An ultrasonic generating device is provided below the workbench.

5. The method for controlling the nanocrystallization of interlayer structure based on additive manufacturing according to claim 4, wherein The ultrasonic generating device applies vibration to the molten pool through a horn; The ultrasonic generating device uniformly transfers the vibration energy to the printed body through a transducer.

6. The method for controlling the nanocrystallization of the interlayer structure based on additive manufacturing according to claim 1, wherein During the process of printing a single layer, the laser power is 0 - 2000 W, the spot diameter is 0 - 5 mm, the scanning speed is 0 - 500 mm / s, and the scanning line distance is 0 - 2 mm.

7. The method for controlling the nanostructuring of the interlayer structure based on additive manufacturing according to claim 1, wherein During the process of printing a single layer, the temperature field distribution of the molten pool is monitored by a molten pool monitoring module. When local overheating of the molten pool is detected, the ultrasonic power is reduced by 10 - 20%; when the temperature of the printed body drops to 10 - 20% of the melting point temperature, interlayer nanostructuring is carried out.

8. The method for controlling the nanocrystallization of the interlayer structure based on additive manufacturing according to claim 7, characterized in that, When the temperature is greater than 1.2 times the melting point of the additive material, it is judged as local overheating, and the ultrasonic power is reduced by 10 - 20%.

9. The method for controlling the nanocrystallization of the interlayer structure based on additive manufacturing according to claim 1, wherein, The pressure for the surface nanostructuring is 200 - 500 MPa, the moving speed is 100 - 5000 mm / min, and the spacing is 0 - 1 mm.

10. The method for controlling the nanostructuring of the interlayer structure based on additive manufacturing according to claim 1, wherein After step C), it further includes the detection of residual stress and grain size. When the detection is unqualified, the unqualified area is nanostructured again by ultrasonic-assisted interlayer nanostructuring.

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