Laser powder bed fusion manufacturing method and system for controlling microstructure of metal materials

Abstract

The present invention discloses a laser powder bed melting manufacturing method and system for controlling the micro-texture of metal materials, which belongs to the field of additive manufacturing technology, including: constructing a finite element temperature field model of metal materials, predicting the second molten pool width and the first inter-pass remelting rate under different scanning intervals by obtaining the first molten pool width corresponding to the initial process parameters; based on the first inter-pass remelting rate, according to the type of target micro-texture of the metal material, determining the second inter-pass remelting rate and optimizing the scanning interval parameters in the initial process parameters; using a laser powder bed melting device to print out components with target micro-textures according to the optimized initial process parameters. The present invention can edit the micro-texture type inside the metal component based on the laser powder bed melting additive manufacturing technology, and realize the regulation of single crystal to polycrystalline micro-texture.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a laser powder bed melting manufacturing method and system for controlling the microstructure of metal materials. Background Art

[0002] Laser beam powder bed fusion additive manufacturing technology uses a method of melting powder layer by layer to print components with complex structures. It has extremely high manufacturing accuracy and stands out among many additive manufacturing technologies. In addition, due to the small spot size of the laser beam, it is easy to form a small molten pool, although this reduces the processing speed. However, despite the reduced processing speed, this significantly improves its micro-texture editing capabilities.

[0003] Different microtextures exhibit different mechanical properties. The materials prepared by traditional casting methods are polycrystalline structures. Due to the lack of obvious texture phenomena, the mechanical properties of this structure are isotropic. Additive manufacturing technology can not only print out weakly textured polycrystalline structures, but also print out strongly textured single crystal structures. Ramsperger et al. in Germany used additive manufacturing methods to print single crystal nickel-based alloys. Sun et al. in Japan printed single crystal 316L stainless steel materials with strong texture characteristics and analyzed their mechanical properties. Studies have shown that single crystal structures prepared by additive manufacturing have higher corrosion resistance and obvious anisotropic mechanical properties.

[0004] The Chinese patent with publication number CN113414405A discloses a method for adjusting the grain morphology of laser additive manufacturing, but does not involve the evolution of texture. The Chinese patent with publication number CN114346255A discloses a method for regulating the microstructure of titanium alloy parts manufactured by directed energy additive manufacturing. However, the methods disclosed in these patents are all used to control the process of transformation from columnar crystals to equiaxed crystals in the microstructure, and do not pay attention to the evolution of microtexture. Although studies have shown that additive manufacturing technology can print materials with different microtextures, the relevant process parameters are still determined by trial and error experiments, and no reliable texture editing method has been reported. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a laser powder bed fusion manufacturing technology that can control the microtexture of metal materials, aiming to achieve personalized editing of the microtexture by actively controlling process parameters, and then print out materials with different properties.

[0006] In order to achieve the above technical objectives, the present application provides a laser powder bed melting manufacturing method for controlling the microstructure of a metal material, comprising the following steps:

[0007] Construct a finite element temperature field model of metal materials, and predict the second molten pool width and the first interpass remelting rate under different scanning intervals by obtaining the first molten pool width corresponding to the initial process parameters;

[0008] Based on the first interpass remelting rate, according to the type of target microtexture of the metal material, determine the second interpass remelting rate and optimize the scanning spacing parameter in the initial process parameters;

[0009] According to the optimized initial process parameters, a laser powder bed fusion device was used to print components with target microtexture.

[0010] Preferably, in the process of constructing the finite element temperature field model, the finite element temperature field model is expressed as:

[0011]

[0012] in, is the density of the material, c is the specific heat, T is the temperature, Q is the heat per unit volume, k is the thermal conductivity, x and y represent the length and width of the three-dimensional model, z represents the height of the three-dimensional model, and t represents time.

[0013] Preferably, in the process of obtaining the first molten pool width, a square sample is printed out based on initial process parameters to determine the first molten pool width, wherein the initial process parameters include: laser power, scanning speed, scanning spacing, powder layer thickness, scanning strategy, laser spot size and substrate preheating temperature.

[0014] Preferably, in the process of obtaining the second molten pool width, based on the finite element temperature field model, the molten pool area is obtained according to the first molten pool width with the powder melting temperature as the boundary, and then the second molten pool width of the molten pool at different scanning intervals is predicted.

[0015] Preferably, in the process of obtaining the first inter-pass remelting rate, the first inter-pass remelting rate is obtained according to the second molten pool width and the scanning interval.

[0016] Preferably, in the process of obtaining the first pass remelting rate, the first pass remelting rate is expressed as:

[0017]

[0018] Where W is the molten pool width and H is the scanning distance.

[0019] Preferably, in the process of obtaining the second interpass remelting rate, when the microtexture target is a weakly textured polycrystalline structure, the second interpass remelting rate is ≤38%;

[0020] When the microtexture target is <101> / / When the single crystal structure is mainly BD texture, 38%<the remelting rate between the second passes<53%;

[0021] When the microtexture target is <100> / / For polycrystalline structures with BD texture as the main component, the remelting rate between the second passes is ≥53%.

[0022] The present invention also discloses a laser powder bed melting manufacturing system for controlling the microstructure of metal materials, comprising:

[0023] A data acquisition module, used for acquiring initial process parameters of metal materials used for melt manufacturing;

[0024] A data processing module is used to predict the second molten pool width and the first inter-pass remelting rate under different scanning intervals by constructing a finite element temperature field model of the metal material and obtaining the first molten pool width corresponding to the initial process parameters;

[0025] A parameter adjustment module, for determining a second interpass remelting rate and optimizing a scanning spacing parameter in the initial process parameters based on the first interpass remelting rate and the type of target microtexture of the metal material;

[0026] The printing control module is used to print a component with a target microstructure using a laser powder bed fusion device according to the optimized initial process parameters.

[0027] Preferably, the data processing module is also used to print out a square-shaped sample and determine the first molten pool width based on initial process parameters, wherein the initial process parameters include: laser power, scanning speed, scanning spacing, powder layer thickness, scanning strategy, laser spot size and substrate preheating temperature.

[0028] Preferably, the data processing module is also used to obtain the molten pool area based on the finite element temperature field model according to the first molten pool width and the powder melting temperature as the boundary, and then predict the second molten pool width of the molten pool under different scanning intervals.

[0029] The present invention discloses the following technical effects:

[0030] The method of editing microtexture based on laser beam powder bed melting proposed in the present invention controls the inter-pass remelting rate by changing the scanning spacing, significantly improving the growth advantage of the specified texture, so that it can be preferentially grown multiple times through inter-pass remelting and squeeze the growth space of other miscellaneous crystals, and finally realize the editing of microtexture in the material. This method is particularly suitable for austenitic stainless steel 316L material, and is also suitable for other materials, such as nickel-based alloys or titanium alloys. This method can quickly determine the specific process parameters required to print the specified microtexture based on any initial parameters within the parameter range, without a lot of trial and error experiments, which provides an effective technical means for obtaining better performance structural parts and improving the design efficiency of laser beam powder bed melting additive manufacturing.

[0031] The present invention does not require additional monitoring of the printing results during the printing process, nor does it require adjustment of process parameters or printing strategies during the process. After printing is completed, no additional heat treatment is required to obtain the specified microstructure. Compared with other methods that require frequent parameter adjustments during the printing process or rely on post-processing, this method has the characteristics of simple process and easy operation, and is suitable for application in the engineering field. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a flow chart of the microtexture editing method of the present invention;

[0034] Figure 2 is the process window of inter-pass remelting rate of different micro-textures of the present invention;

[0035] Figure 3 The initial process parameters of Example 1 of the present invention are obtained as follows <100> / / Microstructure of austenitic stainless steel 316L single crystal dominated by BD grains (red);

[0036] Figure 4 The molten pool width result predicted by finite element method in Example 1 of the present invention;

[0037] Figure 5 The following is obtained after optimizing the parameters in Example 1 of the present invention: <101> / / Austenitic stainless steel 316L polycrystalline microtexture dominated by BD grains (green);

[0038] Figure 6 The weakly textured austenitic stainless steel 316L polycrystalline microtexture obtained after optimizing the parameters in Comparative Example 1 of the present invention;

[0039] Figure 7 The weakly textured austenitic stainless steel 316L polycrystalline microtexture obtained under the initial process parameters of Comparative Example 2 of the present invention;

[0040] Figure 8 The following is obtained after optimizing the process parameters of Comparative Example 2 of the present invention: <100> / / BD grains (red) are mainly austenitic stainless steel 316L polycrystalline microtexture. DETAILED DESCRIPTION

[0041] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0042] like Figure 1-8 As shown, the present invention provides a laser powder bed fusion manufacturing technology for controlling the microstructure of metal materials, which specifically includes the following contents:

[0043] S1. Obtaining the molten pool width under the initial process parameters according to the initial process parameters;

[0044] The core of this step is to select one or a group of parameters as initial parameters from the process parameter range applicable to this method, conduct corresponding laser beam powder bed melting additive manufacturing experiments, and obtain molten pool morphology information. This information will be used to assist in establishing a finite element temperature field prediction unit in step S2.

[0045] Step S1 specifically includes the following steps:

[0046] S1.1. Select the initial process parameters. The selection range of each parameter is: laser power is 100-400W, scanning speed is 600-3000mm / s, scanning spacing is 50-200μm, powder layer thickness is 25-59μm, scanning strategy is a bidirectional scanning strategy without rotation between layers, laser spot size is 50-80μm, and substrate preheating temperature does not exceed 200℃.

[0047] S1.2. Input the initial process parameters into the laser beam powder bed melting additive manufacturing equipment to prepare a 10mm×10mm×10mm square sample.

[0048] S1.3. Use an optical microscope or scanning electron microscope to observe the molten pool morphology of the sample, and record basic information such as the molten pool width and depth for establishing the finite element temperature field.

[0049] S2. A three-dimensional temperature field prediction model is established based on the finite element method. Different scanning intervals are selected for simulation. The molten pool width under different scanning intervals is determined and the inter-pass remelting rate is calculated.

[0050] In the laser powder bed melting process, the heat transfer equation dominated by heat conduction can be defined as:

[0051]

[0052] in, is the density of the material, c is the specific heat, T is the temperature, is the heat per unit volume, k is the thermal conductivity, x and y represent the length and width of the three-dimensional model, z represents the height of the three-dimensional model, and t represents time.

[0053] At the beginning of the simulation, the temperature of all points in the simulation area is uniformly set to the predetermined initial temperature value T0. This setting is crucial to the accuracy of the simulation because it provides a benchmark for subsequent temperature changes. The mathematical expression of the initial temperature boundary condition is:

[0054]

[0055] Here, D represents the simulation region, and T0 is a given initial temperature, which is set according to the initial process parameters determined in step S1.

[0056] In order to further improve the accuracy and realistic approximation of the simulation, the present invention also considers the influence of thermal radiation and thermal convection on the temperature distribution. The addition of these factors makes the temperature model more complex but also closer to the actual situation. The corresponding thermal balance equation is:

[0057]

[0058] in, is the ambient temperature, q is the heat flux, is the thermal radiation coefficient, h is the thermal convection coefficient, is the Stephen-Boltzmann constant.

[0059] Furthermore, the present invention describes a method for simulating laser input during laser powder bed melting. By using a Gaussian distribution to describe the laser input, the present invention can more accurately simulate the thermal effects of the interaction between the laser and the powder bed, and thus more accurately predict the temperature field and microstructure evolution during the melting process.

[0060] The laser input model is described by Gaussian distribution, and the specific expression is as follows:

[0061]

[0062] Where A represents the powder heat absorption rate, P is the laser power, r is the laser beam radius, is the laser penetration depth. X, Y and Z represent the coordinates of the central area of ​​the Gaussian heat source. The heat source parameters are calibrated according to the experimental results under the initial parameters performed in step S1.

[0063] Furthermore, the present invention keeps other parameters unchanged under the initial process parameters determined in step S1, only adjusts the scanning spacing and performs multi-layer and multi-channel temperature field simulation, and extracts the width information of the molten pool using the material liquefaction temperature as a threshold.

[0064] Furthermore, the present invention calculates the inter-channel remelting rate according to the following formula:

[0065]

[0066] Where W is the molten pool width and H is the scanning distance.

[0067] S3. Determine the interpass remelting rate and optimize the scanning spacing parameter in the initial process parameters according to the target microtexture type;

[0068] The present invention optimizes the scanning spacing in the initial process parameters according to the target micro-texture to obtain the most suitable process parameters for printing the target micro-texture. According to previous studies, the interpass remelting rate was found to have the ability to control the texture evolution, such as Figure 2 As shown in the figure, different interpass remelting rates correspond to different microtexture types. When the interpass remelting rate R is less than 38%, it is a heterogeneous crystal zone, at which time it is easy to produce microtextures with weak texture characteristics. When the interpass remelting rate R is greater than or equal to 38% and less than or equal to 53%, it is a single crystal zone, at which time it is easy to produce microtextures with weak texture characteristics. <101> / / Single crystal structure dominated by BD grains. When the inter-pass remelting rate R is greater than 53%, it is a polycrystalline region, at which time it is easy to produce <100> / / Polycrystalline structure dominated by BD grains.

[0069] The combined application of these methods and technologies provides practical solutions for material design and processing technology optimization in industrial applications, and realizes personalized editing of microtextures based on laser beam powder bed fusion additive manufacturing.

[0070] S4. Printing a component with a target microstructure using a laser powder bed fusion device according to the process parameters determined in steps S1, S2 and S3.

[0071] Example 1: Targeting single crystal microtexture

[0072] Step 1: Prepare a 316L austenitic stainless steel substrate without obvious texture features obtained by casting and a sufficient amount of atomized 316L austenitic stainless steel powder with an average powder size of 22 μm. Prepare the 3D solid model to be printed and generate a slice file. Go to step 2.

[0073] Step 2: Install the substrate and maintain a 99.999% pure argon environment during printing, with the cooling gas wind speed not less than 4m / s.

[0074] Step 3: Determine the initial process parameters: laser power is 200 W, scanning speed is 1000 mm / s, powder layer thickness is 35 μm, scanning spacing is set to 50 μm, scanning strategy is selected as bidirectional scanning strategy without rotation between layers, laser spot size is 60 μm, and substrate preheating temperature is 100 °C.

[0075] Step 4: Input the slice file and process parameters into the laser beam powder bed fusion additive manufacturing equipment for printing. After printing, the sample is removed by wire cutting.

[0076] Step 5: The sample was first polished with 2000 mesh silicon carbide sandpaper and then polished with 3μm diamond suspension to improve the visibility of microstructural features. It was then etched with oxalic acid at a current density of 0.09A / cm2 for 45 seconds at room temperature. The microtexture of the sample was characterized using an optical microscope and a scanning electron microscope with an electron backscatter diffraction device. According to the experimental results, the average width of the molten pool was 220.15μm. The interpass remelting rate was 77.27%, and the electron backscatter diffraction characterization results were as follows: Figure 3 As shown, it shows obvious <100> / / Polycrystalline microtexture dominated by BD grains (represented in red in the figure).

[0077] Step 6: Establish a finite element temperature field prediction model. The key point of this step is to calibrate the heat source related parameters according to the experimental results of the initial parameters to obtain reliable temperature field prediction results.

[0078] Step 7: In the present invention, the target is a single crystal structure. Therefore, it is necessary to reduce the interpass remelting rate R to meet Without changing other process parameters, the scanning spacing was changed to 70μm. The finite element model was used to predict the molten pool. The predicted molten pool width was 117μm and the predicted interpass remelting rate was 40.17%, which was consistent with the printing range of single crystal structure. The finite element prediction results are shown in Figure 2. Figure 4 shown.

[0079] Step 8: According to the above steps, the process parameters for the single crystal microtexture are determined as follows: laser power is 200W, scanning speed is 1000mm / s, powder layer thickness is 35μm, scanning spacing is set to 70μm, scanning strategy is selected as bidirectional scanning strategy without rotation between layers, laser spot size is 60μm, and substrate preheating temperature is 100℃. Repeat steps 1 to 5 with the optimized process parameters, and the final printed microtexture is as follows Figure 5 As shown, it shows obvious <101> / / The single crystal structure mainly consists of BD grains (indicated in green in the figure), proving that the microtexture was successfully edited in this example.

[0080] Comparative Example 1: Targeting a weakly textured polycrystalline microtexture

[0081] This comparative example is the same as Example 1 in terms of initial parameter determination and sample preparation. The main difference is that in step 7, since the goal of this comparative example is to print a heterogeneous crystalline structure without obvious texture phenomenon, an attempt is made to use a larger scanning spacing to reduce the inter-pass remelting rate.

[0082] Specifically, the temperature field under the scanning spacing of 80μm and 90μm was simulated by finite element method, and the corresponding inter-pass remelting rates were extracted as 27.27% and 14.29%, respectively. The inter-pass remelting rates under the two parameters are in line with the process window of R≤38% polycrystalline microtexture. The present invention selects a scanning spacing of 90μm for the experiment. The remaining steps and parameters are consistent with Example 1. The final experimental results are shown in Figure 6 As shown, its microstructure presents a weakly textured polycrystalline structure, which proves that this comparative example successfully edited a polycrystalline microstructure using the same initial process parameters as Example 1.

[0083] Comparative Example 2: The target is <100> / / Polycrystalline microtexture dominated by BD grains

[0084] This comparative example is the same as Example 1 in terms of sample preparation, but different initial process parameters are selected. Specifically, in step 3, the initial process parameters selected in this comparative example are: laser power of 140 W, scanning speed of 800 mm / s, powder layer thickness of 35 μm, scanning spacing of 90 μm, scanning strategy of bidirectional scanning strategy without rotation between layers, laser spot size of 60 μm, and substrate preheating temperature of 100°C.

[0085] The interpass remelting rate of the sample prepared using the initial process parameters of this comparative example is 19.09%. The experimental results are as follows Figure 7 As shown, a weakly textured polycrystalline microstructure is presented. <100> / / The polycrystalline microtexture dominated by BD grains requires an increased remelting rate. Therefore, in step 7, scanning intervals of 50, 60, and 70 μm were used for finite element temperature field simulation prediction. Among them, the predicted inter-pass remelting rates were 54.54%, 43.40%, and 31.37%, respectively. After comparison, it was found that the inter-pass remelting rate at a scanning interval of 50 μm met the process window of R ≥ 53%. Therefore, this scanning interval was selected to further use a laser beam powder bed melting additive manufacturing device to print the comparative sample. The microtexture printed out by the final process parameters determined in Comparative Example 2 is as follows Figure 8 As shown, the <100> / / The polycrystalline microtexture mainly composed of BD grains. This proves again that the laser powder bed fusion manufacturing method for controlling the microtexture of metal materials provided by the present invention can realize the personalized editing of microtexture by actively controlling the process parameters, and then print out materials with different texture characteristics.

[0086] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0087] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0088] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A laser powder bed fusion manufacturing method for controlling the microstructure of a metal material, characterized in that: The following steps are involved: Construct a finite element temperature field model of metal materials, and predict the second molten pool width and the first interpass remelting rate under different scanning intervals by obtaining the first molten pool width corresponding to the initial process parameters; Based on the first interpass remelting rate, according to the type of target microtexture of the metal material, determining a second interpass remelting rate and optimizing a scanning spacing parameter in the initial process parameters; Printing a component having the target microstructure using a laser powder bed fusion device according to the optimized initial process parameters; In the process of constructing the finite element temperature field model, the finite element temperature field model is expressed as: Among them, ρ is the density of the material, c is the specific heat, T is the temperature, Q is the heat per unit volume, k is the thermal conductivity, x and y represent the length and width of the three-dimensional model, z represents the height of the three-dimensional model, and t represents time; In the process of obtaining the first molten pool width, a square sample is printed based on the initial process parameters to determine the first molten pool width, wherein the initial process parameters include: laser power, scanning speed, scanning spacing, powder layer thickness, scanning strategy, laser spot size and substrate preheating temperature; In the process of obtaining the second molten pool width, based on the finite element temperature field model, according to the first molten pool width, the molten pool area is obtained with the powder melting temperature as the boundary, and then the second molten pool width of the molten pool at different scanning intervals is predicted; In the process of obtaining the first inter-pass remelting rate, obtaining the first inter-pass remelting rate according to the second molten pool width and the scanning interval; In the process of obtaining the first pass remelting rate, the first pass remelting rate is expressed as: Where W is the molten pool width, H is the scanning spacing; In the process of obtaining the remelting rate between the second passes, when the microtexture target is a weakly textured polycrystalline structure, the remelting rate between the second passes is ≤38%; When the microtexture target is a single crystal structure dominated by <101> / / BD texture, 38% < the second interpass remelting rate < 53%; When the microtexture target is a polycrystalline structure dominated by a <100> / / BD texture, the second interpass remelting rate is ≥53%.

2. A laser powder bed fusion manufacturing system for controlling the micro-texture of a metal material, used to implement a laser powder bed fusion manufacturing method for controlling the micro-texture of a metal material as claimed in claim 1, characterized in that: include: A data acquisition module, used for acquiring initial process parameters of metal materials used for melt manufacturing; A data processing module is used to predict the second molten pool width and the first inter-pass remelting rate under different scanning intervals by constructing a finite element temperature field model of the metal material and obtaining the first molten pool width corresponding to the initial process parameters; a parameter adjustment module, for determining a second interpass remelting rate and optimizing a scanning spacing parameter in an initial process parameter based on the first interpass remelting rate and according to a type of a target microtexture of the metal material; A printing control module, used for printing a component having the target microstructure using a laser powder bed fusion device according to the optimized initial process parameters; The data processing module is further used to print out a square-shaped sample and determine the first molten pool width based on the initial process parameters, wherein the initial process parameters include: laser power, scanning speed, scanning spacing, powder layer thickness, scanning strategy, laser spot size and substrate preheating temperature; The data processing module is also used to obtain the molten pool area based on the finite element temperature field model and the first molten pool width, with the powder melting temperature as the boundary, and then predict the second molten pool width of the molten pool under different scanning intervals.

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