Method for manufacturing nickel-titanium alloy heterogeneous microstructure based on laser additive

Abstract

The invention discloses a method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing. The method comprises the steps that macroscopic and microstructure design schemes of a nickel-titanium alloy workpiece are obtained; creating a three-dimensional model of the workpiece based on the design scheme, wherein the macrostructure of the workpiece in the model is divided into a printing area and a plurality of remelting areas; respectively setting printing process parameters and one or more remelting process parameters according to microstructure design requirements of different areas; in the fusion forming process, each layer is formed by using printing process parameters, and if the currently formed layer contains a layer of a specific remelting area, the layer of the remelting area is remelted in the layer area by using corresponding remelting process parameters; and by parity of reasoning, carrying out melt forming layer by layer until the nickel-titanium alloy component with the heterogeneous microstructure is formed. The control means, the control precision and the complex distribution of the microstructure are improved, the method is simpler and easy to implement, and guidance is provided for functional design and structural design of the nickel-titanium alloy.

Description

Technical Field

[0001] The present invention relates to the field of laser powder bed fusion forming, and particularly to a method for fabricating heterogeneous microstructures of nickel-titanium alloys based on laser additive manufacturing. Background Art

[0002] Nickel-titanium alloys have functional characteristics such as shape memory effect, superelasticity, and elastocaloric refrigeration effect due to their reversible martensitic phase transformation behavior. At the same time, nickel-titanium alloys have high damping, biocompatibility, high corrosion resistance, and excellent mechanical properties, so they are widely used in the fields of aviation, aerospace, medical treatment, machinery, etc. As is well known, the deformation of nickel-titanium shape memory alloys can be divided into four stages: austenite elastic stage, martensitic phase transformation stage, and martensite elastic and plastic stages. The phase transformation mainly involves two phases: austenite B2 phase and martensite B19' phase. During the austenite phase transformation process, the B2 phase will transform into B19' or B19 phase under load, and recover to the B2 phase after unloading, and this process exhibits superelasticity. The functional characteristics of nickel-titanium alloys are severely affected by the microstructure. However, traditional manufacturing and processing techniques are difficult to fabricate nickel-titanium alloys with complex microstructures.

[0003] Laser powder bed fusion technology is an additive manufacturing technology that uses laser as a heat source. This technology uses computer-aided manufacturing to digitally model a three-dimensional complex solid structure and perform two-dimensional slicing processing, and forms a solid product in a layer-by-layer accumulation manner from bottom to top. This technology has the advantages of high precision, good surface roughness, and few manufacturing defects, and has great advantages in manufacturing nickel-titanium alloys with complex structures. Since the material and structure are co-formed during the laser powder bed fusion manufacturing process, the microstructure of the material cannot be changed by mechanical deformation. Existing scholars and engineers obtain heterogeneous microstructures by controlling process parameter changes. Chinese Patent (CN 111992717 A) discloses a method for selective laser melting to prepare metal gradient materials, which uses a variety of metal powders such as Fe, Cu, Ni, Co, Al, Ti, etc. as raw materials, and controls the printed parts to have different partitions through a computer, and then changes the 3D printing parameters of different partitions to achieve a gradient distribution of the organizational structure. The above patent is only applicable to materials with a relatively wide process window. However, for materials with a narrow process range, a new method needs to be developed to expand the manufacturing space of heterogeneous microstructures. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for fabricating heterogeneous microstructures of nickel-titanium alloys based on laser additive manufacturing, and the method includes:

[0005] Obtaining a macroscopic and microscopic structure design scheme of a nickel-titanium alloy workpiece;

[0006] Based on the described design scheme, a three-dimensional model of the workpiece is created. In this model, the macroscopic structure of the workpiece is divided into a printing area and multiple remelting areas according to the differences in the corresponding microscopic structures.

[0007] According to the design requirements of the microscopic structures in different areas, set the printing process parameters for directly constructing the printing area and one or more remelting process parameters for remelting the formed printing area into different remelting areas respectively.

[0008] Perform layer-by-layer processing on the three-dimensional model for laser powder bed fusion forming.

[0009] During the process of laser powder bed fusion forming, each layer is first formed using the printing process parameters. If it is known from the three-dimensional model that the currently formed layer contains a layer of a specific remelting area, then in this layer area, use the corresponding remelting process parameters to scan and remelt to obtain the layer of this remelting area.

[0010] And so on, layer by layer for fusion forming until a nickel-titanium alloy component with heterogeneous microstructures is formed.

[0011] In an alternative embodiment, determining the remelting process parameters includes:

[0012] Obtain a plurality of preset initial remelting process parameters.

[0013] Print the printing area according to the printing process parameters, and remelt the formed printing area containing a specific remelting area into different remelting areas according to each initial remelting process parameter among the plurality of initial remelting process parameters, respectively obtaining corresponding multiple nickel-titanium alloy component samples.

[0014] Screen the multiple nickel-titanium alloy component samples to remove defective samples, obtain the target nickel-titanium alloy component samples, and determine the remelting process parameters based on the initial remelting process parameters corresponding to the target nickel-titanium alloy component samples.

[0015] Furthermore, the printing process parameters include: the scanning laser power is 200 W, the scanning speed is 900 mm / s, the scanning spacing is 110 μm, and the powder spreading layer thickness is 25 μm.

[0016] The remelting process parameters include: the scanning laser power is 100 W - 250 W, the scanning speed is 600 - 1200 mm / s, and the scanning spacing is 110 μm.

[0017] Furthermore, the remelting process parameters include: the laser power is 150 W, the scanning speed is 900 mm / s, and the scanning spacing is 110 μm.

[0018] Furthermore, the layer thickness in different areas is greater than 300 μm.

[0019] Further, load the NiTi alloy powder into the powder supply cylinder of the laser powder bed melting equipment and spread the powder, and fill with a rare gas with the air pressure maintained at 10-20 mbar and the oxygen content ≤ 500 ppm.

[0020] Further, the raw material of the NiTi alloy powder is a pre-alloyed near-equiatomic ratio NiTi powder prepared by the atom gas atomization method. The particle size D of the NiTi alloy powder satisfies 18 μm ≤ D ≤ 60 μm. Before use, the NiTi alloy powder is vacuum-dried at 60-120 °C for 4-5 hours.

[0021] Further, the atomic ratio of Ti element to Ni element in the NiTi alloy powder is 1:1.05.

[0022] The embodiments of the present application have the following beneficial effects:

[0023] The embodiments of the present application disclose a method for laser additive manufacturing of NiTi alloy heterogeneous microstructures. By using different laser processes to control the microstructures in different regions, the control of mechanical properties and phase transformation behaviors at the microscale is obtained without the need for special process control, improving the control accuracy of the sample microstructures. At the same time, the microstructure design of different process regions is realized in the modeling software, improving the control accuracy and complex distribution of the microstructures. Different from the traditional manufacturing method of replacing process parameters, the present application only controls the microstructures and phase transformation behaviors through the remelting process. This method not only improves the control accuracy of the NiTi alloy component microstructures, is more suitable for materials with narrow process windows, but also is simpler and easier to implement compared with the existing manufacturing methods, providing guidance for the functional design and structural design of NiTi alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions of the present invention, the drawings required in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the protection scope of the present invention. In each drawing, similar components are numbered similarly.

[0025] Figure 1 Shows a three-dimensional model of the NiTi alloy workpiece area distribution in Example 1 of the present application;

[0026] Figure 2 Shows a metallographic structure photo of the NiTi alloy with heterogeneous microstructures in Example 1 of the present application;

[0027] Figure 3 Shows the phase transformation behavior of the NiTi alloy with heterogeneous microstructures in Example 1 of the present application;

[0028] Figure 4The three-dimensional model of the nickel-titanium alloy workpiece area distribution in the second example of the present application is shown;

[0029] Figure 5 The three-dimensional model of the nickel-titanium alloy workpiece area distribution in the third example of the present application is shown. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention. In addition, it should be understood that after reading the content disclosed in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the protection scope defined by the present invention.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0032] In order to more clearly show the implementation steps and advantages of the present invention, the specific implementation manners will be described below in conjunction with the legends.

[0033] Currently, the formation of heterogeneous microstructures is achieved by controlling the printing parameters of different regions, such as setting different laser powers, laser scanning rates and other 3D printing process parameters in different regions, so that the microstructures of different partitions have heterogeneous distributions. An embodiment of the present application proposes a method for forming heterogeneous microstructures of nickel-titanium alloys based on laser additive manufacturing. This method can control the microstructure and phase transformation behavior through the remelting process of specific regions, replacing the current method of changing process parameters to obtain heterogeneous microstructures. The operation is simpler and easier to implement, providing guidance for the functional design and structural design of nickel-titanium alloys. Exemplarily, the specific implementation steps of this method are as follows:

[0034] Step S100: Obtain the macroscopic and microscopic structure design schemes of the nickel-titanium alloy workpiece.

[0035] Step S200: Based on the design scheme, create a three-dimensional model of the workpiece. In this model, the macroscopic structure of the workpiece is divided into a printing area and multiple remelting areas according to the differences in the corresponding microscopic structures.

[0036] Step S300: Set the printing process parameters for directly constructing the printing area and one or more remelting process parameters for remelting the formed printing area into different remelting areas respectively according to the microscopic structure design requirements of different regions.

[0037] Step S400: Perform layer-by-layer processing on the three-dimensional model for laser powder bed fusion forming.

[0038] Step S500: During the process of performing laser powder bed fusion forming, each layer is first formed using printing process parameters. If it is known from the three-dimensional model that the currently completed formed layer contains a stratified layer of a specific remelting area, then in this stratified area, the corresponding remelting process parameters are used to scan and remelt to form the stratified layer of this remelting area.

[0039] Step S600: And so on, layer by layer for melting and forming until a NiTi alloy component with a heterogeneous microstructure is formed.

[0040] It can be understood that according to the appearance of the NiTi alloy workpiece and the characteristics of the microstructure of the NiTi alloy workpiece in the actual working scenario, a design scheme for the corresponding macroscopic and microscopic structures of the NiTi alloy workpiece is designed, the macroscopic and microscopic structure design scheme of the NiTi alloy workpiece is received, and a corresponding three-dimensional model is created according to this design scheme.

[0041] When creating the three-dimensional model of the NiTi alloy workpiece according to the above design scheme using modeling software, the macroscopic structure of the NiTi alloy workpiece will be divided into different regions according to the different microstructures of the NiTi alloy workpiece, which are respectively the printing area and multiple remelting areas. As Figure 1 shown, the microstructure of the printing area is different from that of each remelting area, and the grain sizes of each area are different. During the remelting process, the material will remelt and solidify again, and the grain size of the remelting area is reduced compared with the printing area, and fine grains and coarse grains will be alternately distributed according to different regions. Among them, coarse grains are distributed in the printing area, and fine grains are distributed in the remelting area. The modeling software can be CAD / CAE modeling software.

[0042] In the present application, three-dimensional models corresponding to the printing area and multiple remelting areas can be established respectively, and the three-dimensional models corresponding to the printing area and multiple remelting areas are arranged according to the division order of multiple areas of the NiTi alloy workpiece, thereby assembling the three-dimensional model of the NiTi alloy workpiece, that is, obtaining the macroscopic structure of the NiTi alloy workpiece.

[0043] The microstructure characteristics of different regions are different. According to the characteristics of different microstructures, printing process parameters for directly constructing the printing area and one or more remelting process parameters for remelting the already formed printing area into different remelting areas are respectively set. Among them, the printing process parameters of the printing area can be set according to the actual situation of the NiTi alloy workpiece, and the remelting process parameters of the remelting area will be set on the basis of the process parameters. Both the remelting process parameters and the printing process parameters include corresponding printing scan spacing, printing laser power, printing scan speed, etc., and both the remelting process parameters and the printing process parameters can be determined through experiments.

[0044] Obtain a plurality of preset initial remelting process parameters; according to the printing process parameter printing area, remelt the specific remelting area in the corresponding formed printing area into different remelting areas according to each initial remelting process parameter among the plurality of initial remelting process parameters, and respectively obtain corresponding nickel-titanium alloy component samples; screen the plurality of nickel-titanium alloy component samples to remove defective samples and high-porosity samples, obtain target nickel-titanium alloy component samples, and determine the remelting process parameters based on the initial remelting process parameters corresponding to the target nickel-titanium alloy component samples, obtain the target nickel-titanium alloy component samples, and determine the remelting process parameters based on the initial remelting process parameters corresponding to the target nickel-titanium alloy component samples.

[0045] It can be understood that when determining the remelting process parameters, the printing process parameters will be used as the basis, and on this basis, the corresponding remelting process parameters can be arbitrarily superimposed and modified. Among them, the printing process parameters corresponding to different materials are different. Based on the printing process parameters, the remelting process parameters of different remelting areas will be designed according to the microstructural characteristics of different areas. Multiple initial remelting process parameters can be preset for each remelting area. Among them, the remelting process parameters for remelting the formed printing area into a remelting area can be one or more, that is, there can be one or more remelting areas in the nickel-titanium alloy workpiece. Obtain the set multiple initial remelting process parameters, print the area according to the set printing process parameters, and remelt the specific corresponding remelting area in the formed printing area according to each initial remelting process parameter among the set multiple initial remelting process parameters, and so on layer by layer for melting and forming, and respectively obtain corresponding nickel-titanium alloy component samples.

[0046] The initial remelting process parameters of this remelting area are different, and the nickel-titanium alloy component samples obtained by printing on the basis of the same printing parameters in the printing area are different. Conduct a density test on the plurality of nickel-titanium alloy component samples, and screen and remove defective nickel-titanium alloy component samples such as cracks and porosity. In other words, remove defective samples and high-porosity samples, and finally determine the target nickel-titanium alloy component samples among the plurality of nickel-titanium alloy component samples. The initial remelting process parameters corresponding to the target nickel-titanium alloy component samples are the preferred remelting process parameters for this remelting area. Among them, at least one value in the initial remelting process parameters can be made a fixed value in sequence, and the remaining values except this fixed value are variables, so as to set multiple initial remelting process parameters, and remelt the corresponding remelting area with the initial remelting process parameters on the basis of the printing process parameters. The density test is well known to those skilled in the art and will not be elaborated here.

[0047] In this application, a certain value in the initial remelting process parameters can also be made a variable, and the remaining values in the initial remelting process parameters except the variable are fixed values. The variable can be modified multiple times to form multiple new initial remelting process parameters. The multiple initial remelting process parameters corresponding to each variable are used for remelting in the corresponding remelting area to obtain multiple corresponding nickel-titanium alloy component samples. The multiple nickel-titanium alloy component samples are screened to remove defective samples, and the target nickel-titanium alloy component samples are obtained. The value of the variable corresponding to the target nickel-titanium alloy component sample in the initial remelting process parameters is used as the preferred value. By analogy, the preferred values of each value of the initial remelting process parameters are determined, and the preferred remelting process parameters for the corresponding remelting area are obtained by combining the preferred values of each value.

[0048] For example, when controlling the laser power in the initial remelting process parameters to be 150 W and the scanning speed to be 900 mm / s, the scanning spacing can be adjusted. For example, when the scanning spacing is 110 μm, laser remelting is performed on the corresponding remelting area according to the initial remelting process parameters of laser power 150 W, scanning speed 900 mm / s, and scanning spacing 110 μm; when the scanning spacing is 100 μm, laser remelting is performed on the corresponding remelting area according to the initial remelting process parameters of laser power 150 W, scanning speed 900 mm / s, and scanning spacing 100 μm. When the initial remelting process parameters are different, the printed nickel-titanium alloy component samples are different. The nickel-titanium alloy component samples obtained by multiple printings are screened to remove defective nickel-titanium alloy component samples such as cracks and porosity. Finally, the target nickel-titanium alloy component sample among the multiple nickel-titanium alloy component samples is determined, and the scanning spacing corresponding to the nickel-titanium alloy component sample is used as the target scanning spacing, which is the preferred value of the scanning spacing in the remelting process parameters to be determined. By analogy, the corresponding preferred values of each value in the remelting process parameters can be determined.

[0049] In this application, the printing process parameters in the printing area can be: printing laser power 120 - 200 W, printing scanning speed 600 - 1200 mm / s, printing scanning spacing 110 μm, and powder spreading layer thickness 25 μm; based on the printing process parameters, the range of the remelting process parameters corresponding to the remelting area can be: remelting laser power 100 W - 250 W, remelting scanning speed 600 - 1200 mm / s, and remelting scanning spacing 110 μm. Preferably, the layer thickness in different areas is greater than 300 μm, which is beneficial to subsequent laser remelting of some already formed printing areas and improves the control accuracy of the microstructure. Preferably, the printing process parameters include: scanning laser power 200 W, scanning speed 900 mm / s, scanning spacing 110 μm, and powder spreading layer thickness 25 μm; the remelting process parameters can be: laser power 150 W, scanning speed 900 mm / s, and scanning spacing 110 μm.

[0050] In this application, a layer-by-layer process for performing laser powder bed fusion forming will be implemented on the three-dimensional model to perform fusion forming on the three-dimensional model layer by layer, forming a heterogeneous microstructure nickel-titanium alloy component. Before performing laser powder bed fusion forming, nickel-titanium alloy powder is loaded into the powder supply cylinder and powder spreading is carried out. The nickel-titanium alloy substrate is placed on the printing platform. The nickel-titanium alloy powder used is near-equiatomic nickel-titanium powder obtained by gas atomization mixing of near-equiatomic metal elements Ni and Ti, and the particle diameter is distributed in the range of 15 - 53 μm. Among them, the atomic ratio of Ti element to Ni element in the nickel-titanium alloy powder is 1:1.05, the particle size D of the nickel-titanium alloy powder satisfies 18 μm ≤ D ≤ 60 μm. Before use, the nickel-titanium alloy powder will be vacuum dried at 60 - 120 °C for 4 - 5 hours, and then the nickel-titanium alloy powder is loaded into the powder supply cylinder and powder spreading is carried out, and an inert gas is filled into the working chamber for protection, and the air pressure is maintained at 10 - 20 mbar. At the same time, the oxygen content during the laser forming process is ≤ 500 ppm. Preferably, the inert gas can be argon.

[0051] It can be understood that after setting the printing process parameters for directly constructing the printing area and one or more remelting process parameters for remelting the formed printing area into different remelting areas, during the process of performing laser powder bed fusion forming, each layer first uses the printing process parameters to print and form the printing area. According to the three-dimensional model, it is determined whether there is a specific remelting area layer in the currently completed formed layer. If there is a specific remelting area layer in the currently completed formed layer, that is, in this printing area, then without re-powder spreading, in this layer area, the corresponding remelting process parameters are used to scan and remelt out the remelting area layer, and then re-powder spreading is carried out to print the next layer printing area. Then, according to the three-dimensional model, it is determined whether there is a specific remelting area layer in the currently completed formed layer. If there is a specific remelting area layer, the remelting area is remelted according to the corresponding remelting process parameters, and so on. Layer-by-layer fusion forming is carried out according to the above settings until a heterogeneous microstructure nickel-titanium alloy component is formed.

[0052] In this application, by laser remelting specific areas, it replaces the current method of changing process parameters to obtain heterogeneous microstructures. During the laser printing process, it is not necessary to repeatedly modify process parameters, which not only improves the control accuracy of the microstructure of nickel-titanium alloy components, but also is simpler, more convenient and easier to implement compared with existing manufacturing methods. It can regulate the microstructure and phase transformation behavior of nickel-titanium alloys. Compared with traditional methods, it can be applied to materials with narrow process windows.

[0053] The following will further elaborate on the present invention in conjunction with the accompanying drawings and specific embodiments.

[0054] Example 1:

[0055] Exemplarily, asFigure 2 As shown, in this embodiment, a macroscopic and microscopic tissue structure design scheme of nickel-titanium alloy is designed according to the actual nickel-titanium alloy workpiece. A corresponding three-dimensional model is created according to the nickel-titanium alloy structure design scheme. The three-dimensional model is divided into a printing area and a remelting area, and is divided into 10 areas along the deposition direction. A layer-by-layer process for performing laser powder bed fusion forming is implemented on the three-dimensional model, and it is divided in the order of printing area, remelting area, printing area... remelting area along the deposition direction. Among them, as Figure 1 shown in the optical micrograph of the heterogeneous microstructure nickel-titanium alloy, it can be observed that different regions have different microstructures and grain sizes, that is, fine-grained and coarse-grained regions are alternately distributed longitudinally. Coarse grains are distributed in the printing area, and fine grains are distributed in the remelting area. If the microstructures in the nickel-titanium alloy workpiece are the same, then each remelting area is the same, and only one remelting process parameter is set for remelting. If each remelting area is different, then corresponding remelting process parameters are set respectively for remelting.

[0056] Load nickel-titanium alloy powder into the powder supply cylinder and spread the powder, fill with argon, and keep the air pressure at 10 - 20 mbar. At the same time, ensure that the oxygen content ≤ 500 ppm during the laser forming process. Place the nickel-titanium alloy substrate on the printing platform. Each layer is first formed using the printing process parameters. According to the three-dimensional model, if it is known that the currently completed formed layer contains a specific remelting area layer, then the corresponding remelting process parameters are used to scan and remelt the remelting area layer in this layer area. And so on, melt forming is performed on the above printing area, remelting area, printing area... remelting area along the deposition direction until a heterogeneous microstructure nickel-titanium alloy component is formed.

[0057] Among them, Figure 3 is the phase change behavior diagram of the heterogeneous microstructure nickel-titanium alloy in this embodiment, which reflects that the phase change behavior of the nickel-titanium alloy component is affected by the heterogeneous microstructure and has a gradual phase change process. This example shows that controlling process parameters can obtain gradient changes in microstructure and functional characteristics.

[0058] In addition, the remelting process parameters corresponding to each remelting area can be different. For example, in this embodiment, a total of five remelting areas are designed, which are the first remelting area, the second remelting area, the third remelting area, the fourth remelting area, and the fifth remelting area along the deposition direction. Among them, if the microstructures corresponding to the first remelting area and the second remelting area are the same, then the same remelting process parameters can be set for the first remelting area and the second remelting area. If the microstructures corresponding to the third remelting area, the fourth remelting area, and the fifth remelting area are the same, then the same remelting process parameters are set for the third remelting area, the fourth remelting area, and the fifth remelting area. At this time, by modifying the remelting process parameters once, the nickel-titanium alloy component with this microstructure can be printed. If the five remelting areas are all the same, then only one corresponding remelting process parameter is set.

[0059] In this embodiment, the microstructural nickel-titanium alloy component is divided into multiple regions along the deposition direction for printing. The number of adjustment times for printing according to the method of this embodiment is the same as that for laser printing according to the traditional method, and there is no obvious improvement in the printing method of this embodiment.

[0060] Embodiment 2:

[0061] Exemplarily, as Figure 4 shown, in this embodiment, a design scheme for the macroscopic and microscopic structures of the nickel-titanium alloy is designed according to the actual nickel-titanium alloy workpiece. A corresponding three-dimensional model is created according to the nickel-titanium alloy structure design scheme. The three-dimensional model is divided into a printing area and a remelting area. Ten horizontally distributed regions are designed. It is not difficult to find that in this example, a horizontal forming surface is divided into multiple parallel and juxtaposed process regions, as Figure 4 shown. The method proposed by the present invention can be used to divide a forming surface into a printing area, a remelting area, a printing area... a remelting area respectively. Layered processing for performing laser powder bed fusion forming is performed on the three-dimensional model. Among them, fine-grained and coarse-grained regions are alternately distributed horizontally. In this embodiment, printing is performed along the deposition direction with a NiTi alloy substrate as the substrate. If the microstructure in the nickel-titanium alloy workpiece is the same, each remelting area is the same, and only one set of remelting process parameters is set for remelting. If each remelting area is different, corresponding remelting process parameters are set respectively for remelting. Layer-by-layer printing is performed in this way until a heterogeneous microstructural nickel-titanium alloy component is formed.

[0062] In this embodiment, the traditional method needs to modify process parameters multiple times during printing, while the method of this application only needs to use different laser processes to control the microstructure of different process regions, obtain control over the mechanical properties and phase transformation behavior at the microscale, improve the control means of the sample microstructure, and this application does not require or only requires less modification of the remelting process parameters. By controlling the microstructure and phase transformation behavior through the remelting process, the operation is made simpler and the scheme is easier to implement.

[0063] Embodiment 3:

[0064] Exemplarily, in this embodiment, a design scheme for the macroscopic and microscopic structures of the nickel-titanium alloy is designed according to the actual nickel-titanium alloy workpiece. A corresponding three-dimensional model is created according to the nickel-titanium alloy structure design scheme. The three-dimensional model is divided into a printing area and a remelting area. The corresponding microstructures in the nickel-titanium alloy workpiece in this embodiment are irregularly distributed. A three-dimensional model of the nickel-titanium alloy workpiece with two regions of three-period minimal surface distribution is designed. In other words, a horizontal forming surface of the nickel-titanium alloy workpiece in this embodiment can be divided into multiple irregular process regions in the length and width dimensions, as Figure 5As shown, the method proposed by the present invention can divide a forming surface into irregular printing areas and remelting areas according to the actual situation of the NiTi alloy workpiece. Among them, the printing areas and remelting areas are irregularly arranged, and fine grains and coarse grains are distributed in different areas respectively. The three-dimensional model is subjected to layer-by-layer processing for laser powder bed fusion forming, with the NiTi alloy substrate as the substrate. During the process of laser powder bed fusion forming, each layer is first formed using the preset printing process parameters. If a layer containing a specific remelting area is completed in the currently formed layer, the corresponding remelting process parameters are used to scan and remelt the layer of the remelting area in this layer area, and so on, layer by layer printing until a NiTi alloy component with heterogeneous microstructure is formed.

[0065] In this embodiment, on the one hand, for the case where it is divided into multiple irregular process areas, that is, for forming a NiTi alloy component with heterogeneous microstructure under any circumstances, if laser printing is carried out according to the traditional method, the process parameters need to be adjusted multiple times. However, in this solution, the NiTi alloy component with microstructure can be printed with little or no modification of the remelting process parameters. This not only avoids repeatedly modifying the process parameters, thereby improving the control means of the sample microstructure and the efficiency of forming the NiTi alloy component with heterogeneous microstructure, making the printing process more convenient and fast, but also enables the design of the microstructure in different process areas in the modeling software, making the operation simpler and easier to implement when printing complex NiTi alloy components. On the other hand, this embodiment only needs to remelt the remelting area on the basis of the printing area, and there is no abnormal pause between different process areas, and the forming surface is printed continuously; while printing by the traditional method, the process parameters need to be adjusted when printing different areas, which may bring a short pause in printing, and the connection interface between different process areas is likely to have subtle negative performance changes due to this short pause.

[0066] The method of this embodiment can improve the control accuracy and complex distribution of the microstructure, and provides guidance for the functional design and structural design of NiTi alloys.

[0067] In summary, although this solution does not show advantages over the prior art for the heterogeneous microstructure of Example 1, for the heterogeneous microstructures of Example 2 and Example 3, the present application controls the microstructure of different process regions by using different laser processes, obtains the control of mechanical properties and phase transformation behavior at the microscale, and does not require specialized process control, thereby improving the control accuracy of the microstructure of the sample. At the same time, the microstructure design of different process regions is realized in the modeling software. Different from the traditional manufacturing method of replacing process parameters, the present application controls the microstructure and phase transformation behavior only through the remelting process. This method not only improves the control accuracy of the microstructure of the NiTi alloy component, is more suitable for materials with a narrow process window, but also is simpler and easier to implement than the existing manufacturing method, providing guidance for the functional design and structural design of the NiTi alloy.

[0068] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A method for manufacturing a heterogeneous microstructure of a nickel-titanium alloy based on laser additive manufacturing, characterized in that: The method comprises: Obtain macro- and micro-structural designs for NiTi alloy workpieces; Based on the design scheme, a three-dimensional model of the workpiece is created, in which the macrostructure of the workpiece is divided into a printing area and a plurality of remelting areas according to the corresponding microstructures; According to the microstructure design requirements of different regions, respectively set the printing process parameters for directly constructing the printing region and one or more remelting process parameters for remelting the formed printing region into different remelting regions; performing a layering process for performing laser powder bed fusion forming on the three-dimensional model; During the laser powder bed fusion forming process, each layer is first formed using the printing process parameters. If it is known from the three-dimensional model that the currently formed layer contains a layer of a specific remelting area, the corresponding remelting process parameters are used in the layered area to scan and remelt the layer of the remelting area. The melt forming is carried out layer by layer in this way until a nickel-titanium alloy component with a heterogeneous microstructure is formed.

2. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 1, characterized in that: Determine remelting process parameters, including: Acquire a plurality of preset initial remelting process parameters; Print the printing area according to the printing process parameters, and remelt a specific remelting area in the corresponding formed printing area into different remelting areas according to each of the multiple initial remelting process parameters, to obtain multiple corresponding nickel-titanium alloy component samples; The multiple nickel-titanium alloy component samples are screened to remove defective samples and high-porosity samples to obtain target nickel-titanium alloy component samples, and the remelting process parameters are determined based on the initial remelting process parameters corresponding to the target nickel-titanium alloy component samples.

3. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 1, characterized in that: The printing process parameters include: printing laser power of 120-200W, printing scanning speed of 600-1200mm / s, scanning spacing of 110μm, and powder layer thickness of 25μm; The remelting process parameters include: scanning laser power of 100W to 250W, scanning speed of 600 to 1200mm / s, and scanning spacing of 110μm.

4. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 3, characterized in that: The printing process parameters include: scanning laser power of 200W, scanning speed of 900mm / s, scanning spacing of 110μm, and powder layer thickness of 25μm; The remelting process parameters include: laser power of 150 W, scanning speed of 900 mm / s, and scanning spacing of 110 μm.

5. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 1, characterized in that: The layer thickness in different areas is greater than 300 μm.

6. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 1, characterized in that: The nickel-titanium alloy powder is loaded into the powder supply cylinder of the laser powder bed melting equipment and spread, and is filled with rare gas. The gas pressure is maintained at 10-20 mbar and the oxygen content is ≤500 ppm.

7. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 6, characterized in that: The raw material of the nickel-titanium alloy powder is pre-alloyed near-equiatomic nickel-titanium powder prepared by atomic atomization. The particle size of the nickel-titanium alloy powder is D≥18μm and D≤60μm. Before use, the nickel-titanium alloy powder is vacuum dried at 60-120°C for 4-5 hours.

8. The method for manufacturing a nickel-titanium alloy heterogeneous microstructure based on laser additive manufacturing according to claim 6, characterized in that: The atomic ratio of Ti element to Ni element in the nickel-titanium alloy powder is 1:1.05.

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