Process for electron beam selective forming of single crystal structures

Abstract

The application discloses a process method for electron beam selective forming single crystal organization, and the process method is as follows: single-channel scanning is performed through different process parameters to determine equiaxed crystal regions and single crystal regions, and preparation is made for next step line spacing determination; the energy size is determined; in the case that the line spacing has been determined in the single-layer single-channel, the best line energy of the printing parameter is found, one layer is printed by setting each group of parameters, and the flatness of the surface after printing is observed; a printing strategy is proposed, so that the equiaxed crystal regions of the next layer are remelted on the previous layer, and the process is repeated; the application has the beneficial effects that: through the mode of adding auxiliary forming structure and heat care, the deformation of the thin-walled part can be effectively reduced, the cracking of the thin-walled part caused by the deformation of the thermal stress can be reduced, and the application has practical value; the metallographic result shows that the grains are relatively uniform, and the growth direction tends to be consistent; subsequent EBSD of the sample shows that the internal organization is consistent with the idea of the patent, and the single crystal is formed, and the grain orientation is consistent.

Description

Technical Field

[0001] This invention belongs to the field of single crystal technology, specifically relating to a process method for selective electron beam forming of single crystal structures. Background Technology

[0002] Single-crystal metals possess excellent strength, especially in high-temperature environments where they retain their strength due to the effective resistance of impurities and defects caused by their single-crystal structure. Because of their uniform crystal lattice structure, single-crystal metals have a smaller fracture area, reducing the likelihood of insufficient fracture toughness. Lacking grain boundaries, they are less susceptible to corrosion, exhibiting excellent corrosion resistance in acidic, alkaline, and high-temperature environments. Furthermore, their good crystal orientation allows for the fabrication of microstructures with specific crystal orientations, leading to their widespread application in high-end fields such as aerospace, energy, and optoelectronics. However, the fabrication of single-crystal metals requires significant costs and advanced technology. Currently, their applications are limited by cost and fabrication techniques. The fabrication of single-crystal metals demands highly precise techniques and equipment, including high-temperature melting methods, thermodynamic methods, and physical vapor deposition, making the process challenging.

[0003] Selective electron beam melting (EBM) is an additive manufacturing process (3D printing) that can achieve near-net-shape forming of alloys. During the forming process, precise microstructure and property control can be achieved, and single-crystal materials can be formed through process control. Selective electron beam forming of single crystals is low-cost and highly efficient, and can be rapidly formed according to different digital models. However, the selective electron beam forming process will generate a large number of impurities, which cannot meet the requirements of single crystals. Summary of the Invention

[0004] The purpose of this invention is to provide a process method for selective electron beam forming of single crystal structures, thereby solving the problem of selective electron beam forming of single crystal materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a process method for selective electron beam forming of single crystal structures, wherein the process method is as follows:

[0006] Single-pass scanning with different process parameters is used to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing.

[0007] Determine the energy level. Given a fixed line spacing for a single layer and single channel, find the optimal line energy for printing parameters. Set each set of parameters to print one layer. After printing, observe the surface flatness.

[0008] A printing strategy is proposed that allows the equiaxed crystal regions of the previous layer to be remelted by the next layer, and so on.

[0009] As a preferred technical solution of the present invention, the different process parameters include adjustment current, scanning speed, focusing current, line spacing, and number of lines.

[0010] As a preferred technical solution of the present invention, it also includes adding auxiliary molding structures and using heat treatment for processing.

[0011] As a preferred embodiment of the present invention, the auxiliary molding structure includes a positioner and a support column.

[0012] As a preferred embodiment of the present invention, the thermal care includes heating, heat preservation, and cooling.

[0013] As a preferred embodiment of the present invention, the scanning is a linear scanning method.

[0014] As a preferred technical solution of the present invention, after single-layer single-pass forming, the cross-section needs to be cut to perform metallographic testing on the sample block to measure the width of the single crystal region and the width of the equiaxed crystal region.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] By adding auxiliary molding structures and heat treatment, the deformation of thin-walled parts can be effectively reduced, and the cracking caused by thermal stress deformation of thin-walled parts can be reduced, which has practical value. Metallographic results show that the grains are relatively uniform and the growth direction tends to be consistent. Subsequent EBSD of the sample revealed that the internal structure is consistent with the idea proposed in this patent, forming a single crystal with consistent grain orientation. Attached Figure Description

[0017] Figure 1 This is a flowchart of the process method of the present invention;

[0018] Figure 2 This is a diagram of the linear scanning method of the present invention;

[0019] Figure 3 This is a schematic diagram of a single-pass scanning molten pool according to the present invention;

[0020] Figure 4 This is a schematic diagram of a single-layer scanning molten pool according to the present invention;

[0021] Figure 5 This is a diagram illustrating the multi-layer scanning overlap configuration of the present invention;

[0022] Figure 6 This is a diagram illustrating the effect of multilayer scanning remelting according to the present invention;

[0023] Figure 7 This is a metallographic diagram of the present invention;

[0024] Figure 8 This is a diagram showing the EBSD results of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] Please see Figures 1-6 This is the first embodiment of the present invention, which provides a process method for selective electron beam forming of single crystal structures, comprising the following steps:

[0028] Single-pass scanning with different process parameters is used to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing. Electron beam selective printing uses electron beam energy to melt the powder layer on the powder to form a part. When a single electron beam scans the powder bed, a weaker energy region is formed around the electron beam, causing the single-pass printed structure to exhibit equiaxed crystals at the edge of the molten pool and directional solidification or equiaxed crystals in the central region. Therefore, single-pass scanning is required to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing. A single-pass scanning line is formed on the single crystal substrate. After the single-layer single-pass forming, the cross-section needs to be cut to the sample for metallographic inspection to measure the width of the single crystal region and the width of the equiaxed crystal region. The width of the equiaxed crystal region measured in this case is the line spacing in the printing process parameters.

[0029] To determine the optimal energy level, given a fixed line spacing for a single layer and single channel, the best line energy for printing parameters needs to be found. Each set of parameters is used to print one layer. After printing, the surface flatness is observed. If the surface is convex, it indicates that the line energy is too high and the parameter is not applicable. If the surface is flat, the metallographic structure needs to be examined to determine whether a single crystal has been formed in the single layer. Parameters with consistent grain orientation are selected as printing parameters.

[0030] Because the structure of the Nth layer in electron beam selective forming is affected by the remelting of the N+1th layer, if the scanning position of the N+1th layer is the same as that of the Nth layer, then there will always be an equiaxed crystal region (the previous layer did not remelt the equiaxed crystal region of the next layer). Therefore, a printing strategy is proposed. Specifically, if the line spacing of the Nth layer is X, then the line spacing of the N+1th layer is also X, but the scanning is performed with the center of the molten pool in the equiaxed crystal region of the Nth layer. This makes the equiaxed crystal region of each layer remelted to form a single crystal, reducing the occurrence of impurities. Intuitively speaking, the center of the spot of the N+1th layer is always in the center of the equiaxed region of the Nth layer. In this way, each time the equiaxed crystal is remelted and recrystallized to form a single crystal due to the heat input of the electron beam, the N+1th layer will also form an equiaxed crystal region between each beam. Then the next N+2th layer will remelt the equiaxed crystal region of the N+1th layer, and so on, until the final internal structure is a single crystal structure.

[0031] Example 2

[0032] Please see Figures 1-6 This is a second embodiment of the present invention, which provides a process method for selective electron beam forming of single crystal structures, comprising the following steps:

[0033] Single-pass scanning with different process parameters is used to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing. Electron beam selective printing uses electron beam energy to melt the powder layer on the powder to form a part. When a single electron beam scans the powder bed, a weaker energy region is formed around the electron beam, causing the single-pass printed structure to exhibit equiaxed crystals at the edge of the molten pool and directional solidification or equiaxed crystals in the central region. Therefore, single-pass scanning is required to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing. A single-pass scanning line is formed on the single crystal substrate. After the single-layer single-pass forming, the cross-section needs to be cut to the sample for metallographic inspection to measure the width of the single crystal region and the width of the equiaxed crystal region. The width of the equiaxed crystal region measured in this case is the line spacing in the printing process parameters.

[0034] To determine the optimal energy level, given a fixed line spacing for a single layer and single channel, the best line energy for printing parameters needs to be found. Each set of parameters is used to print one layer. After printing, the surface flatness is observed. If the surface is convex, it indicates that the line energy is too high and the parameter is not applicable. If the surface is flat, the metallographic structure needs to be examined to determine whether a single crystal has been formed in the single layer. Parameters with consistent grain orientation are selected as printing parameters.

[0035] Because the structure of the Nth layer in electron beam selective forming is affected by the remelting of the N+1th layer, if the scanning position of the N+1th layer is the same as that of the Nth layer, then there will always be an equiaxed crystal region (the previous layer did not remelt the equiaxed crystal region of the next layer). Therefore, a printing strategy is proposed. Specifically, if the line spacing of the Nth layer is X, then the line spacing of the N+1th layer is also X, but the scanning is performed with the center of the molten pool in the equiaxed crystal region of the Nth layer. This makes the equiaxed crystal region of each layer remelted to form a single crystal, reducing the occurrence of impurities. Intuitively speaking, the center of the spot of the N+1th layer is always in the center of the equiaxed region of the Nth layer. In this way, each time the equiaxed crystal is remelted and recrystallized to form a single crystal due to the heat input of the electron beam, the N+1th layer will also form an equiaxed crystal region between each beam. Then the next N+2th layer will remelt the equiaxed crystal region of the N+1th layer, and so on, until the final internal structure is a single crystal structure.

[0036] In this embodiment, preferably, the different process parameters mainly correspond to adjusting the current, scanning speed, focusing current, line spacing, and number of lines. Single-channel scanning is performed by adjusting the current, scanning speed, focusing current, line spacing, and number of lines to determine the equiaxed crystal region and the single crystal region, preparing for the next step of determining the line spacing. The specific method may include the following steps:

[0037] Adjusting the current: First, you can try adjusting the current intensity of the electron beam. Changes in the current intensity will affect the heat input of the electron beam, thereby affecting the formation of the molten pool and the crystallization behavior. You can select the appropriate current intensity based on the properties and thickness of the metal material that needs to be scanned in a single pass, as well as the expected crystallization effect.

[0038] Adjusting the scanning speed: Next, you can try changing the scanning speed; a higher scanning speed may lead to an increase in the depth of melting, while a lower scanning speed may lead to a decrease in the depth of melting; by adjusting the scanning speed, you can find suitable melting and crystallization conditions to produce the desired equiaxed crystal region and single crystal region.

[0039] Adjusting the focusing current: Adjusting the focusing current affects the focusing degree and diameter of the electron beam, thereby changing the heat input distribution of the electron beam; by finely adjusting the focusing current, precise control of the shape and depth of the molten pool can be achieved, further affecting the crystallization behavior;

[0040] Determining the line spacing: During single-track scanning, it is necessary to determine an appropriate line spacing. If the line spacing is too narrow, it may cause the material between adjacent scan lines to remelt, while if the line spacing is too wide, it may cause some areas to fail to melt sufficiently. The optimal line spacing can be determined based on the material properties, thickness, and expected crystallization effect.

[0041] Determining the number of lines: The number of lines in each scan line is also an important factor affecting crystallization behavior. Too few lines may result in some areas not melting sufficiently, while too many lines may result in over-remelting of the material. The optimal number of lines can be determined based on the material properties, thickness, and expected crystallization effect.

[0042] Observation and recording: During the adjustment of the above parameters, it is necessary to carefully observe the surface smoothness after a single scan and the tissue structure after sectioning. The results can be observed and recorded with the help of a microscope or scanning electron microscope.

[0043] Analysis and optimization: Based on the observed and recorded results, analyze the influence of different parameter settings on crystallization behavior and optimize accordingly; repeated experiments and parameter adjustments are required to achieve the ideal crystallization effect;

[0044] Determine the next line spacing: After determining the ideal single-track scan parameters, the next line spacing can be calculated and determined based on these parameters; this line spacing will be used for the alignment and organization between layers in multi-track scans.

[0045] In this embodiment, preferably, it also includes adding an auxiliary molding structure and using heat treatment for processing, which can effectively reduce the deformation of thin-walled parts and reduce cracking caused by thermal stress deformation of thin-walled parts, and has practical value; the auxiliary molding structure includes a positioner and a support column; heat treatment includes heating, heat preservation and cooling.

[0046] Figure 7 The metallographic structure is shown in the image. The metallographic results indicate that the grains are relatively uniform, and the growth direction tends to be consistent. Further EBSD analysis of the sample will be performed later. Figure 8 The EBSD results show that the internal structure is consistent with the idea proposed in this patent, forming a single crystal with consistent grain orientation.

[0047] In this embodiment, preferably, linear scanning is used; linear scanning means that the electron beam stream scans along one direction, and the scanning direction is consistent for each layer. This makes the printing process beneficial for the directional solidification of the tissue. The main forming process parameters of electron beam selective forming include line energy, line spacing, and scanning method. To form single crystal materials, the line spacing needs to be determined first, and then the line energy needs to be determined.

[0048] The specific process parameters are shown in the table below:

[0049]

[0050] Although embodiments of the invention have been shown and described in detail above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for selective electron beam forming of single crystal structures, characterized in that: The process method is as follows: Single-pass scanning with different process parameters is used to determine the equiaxed crystal region and the single crystal region in preparation for the next step of determining the line spacing. After single-layer single-pass forming, the cross-section of the sample needs to be cut for metallographic inspection to measure the width of the single crystal region and the width of the equiaxed crystal region. The width of the equiaxed crystal region is the line spacing. The different process parameters include adjusting the current, scanning speed, focusing current, line spacing, and number of lines. The specific method includes the following steps: Adjusting the current: Adjusting the current intensity of the electron beam. Changes in the current intensity will affect the heat input of the electron beam, thereby affecting the formation and crystallization behavior of the molten pool. The appropriate current intensity should be selected based on the properties and thickness of the metal material to be scanned in a single pass, as well as the expected crystallization effect. Adjusting the scanning speed: By adjusting the scanning speed, suitable melting and crystallization conditions can be found to produce the desired equiaxed crystal region and single crystal region; Adjusting the focusing current: Adjusting the focusing current affects the focusing degree and diameter of the electron beam, thereby changing the heat input distribution of the electron beam; by finely adjusting the focusing current, precise control of the shape and depth of the molten pool can be achieved, further affecting the crystallization behavior; Determine the line spacing: During single-track scanning, it is necessary to determine the appropriate line spacing; Determining the number of lines: The number of lines in each scan line is also an important factor affecting crystallization behavior; the optimal number of lines should be determined based on the material properties, thickness, and expected crystallization effect. Determine the energy level. With the line spacing already determined for a single layer and single channel, find the optimal line energy for printing parameters. Set each set of parameters and print one layer. After printing, observe the surface flatness. If the surface is convex, it means the line energy is too high and the parameter is not applicable. If the surface is flat, further metallographic analysis is needed to determine whether a single crystal has been formed in the single layer. Select parameters with consistent grain orientation as printing parameters. A printing strategy is proposed that allows the equiaxed crystal regions of the previous layer to be remelted by the next layer, with the center of the photomask of the next layer being the center of the equiaxed region of the previous layer, and this process is repeated.

2. The process method for selective electron beam forming of single crystal structures according to claim 1, characterized in that: It also includes adding auxiliary molding structures and using heat treatment methods for processing.

3. The process method for selective electron beam forming of single crystal structures according to claim 2, characterized in that: The auxiliary molding structure includes support columns.

4. The process method for selective electron beam forming of single crystal structures according to claim 2, characterized in that: The thermal care includes heating, heat preservation, and cooling.

5. The process method for selective electron beam forming of single crystal structures according to claim 1, characterized in that: The scanning method used is linear scanning.

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