Method for additive manufacturing of shape memory alloy based on blue laser

Abstract

The invention provides a method for additive manufacturing of a shape memory alloy based on blue laser. The method for additive manufacturing of the shape memory alloy based on the blue laser comprises the following steps that S1, alloy powder is prepared according to a preset molar ratio; s2, the alloy powder in the S1 is dried; s3, a 3D model is established, and a cuboid base body of a pre-printing area is arranged; s4, setting 3D printing parameters; s5, a scanning strategy is set in the cuboid base body, path planning is carried out, and blue laser is selected for scanning; and S6, the dried alloy powder is subjected to laser melting preparation, and the shape memory alloy is obtained. By changing the wavelength, controlling the absorptivity and optimizing parameter control and technological processes in the alloying process, the low-crack, low-hole and multi-dislocation NiTi alloy is obtained, and a new thought and technical support are provided for further development of the NiTi alloy in the medical field.

Description

[Technical field]

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a method for additive manufacturing of shape memory alloys based on blue laser. [Background technology]

[0002] With the development of materials science and medical engineering, NiTi shape memory alloys are widely used in the medical field. The current methods for preparing NiTi alloys are: casting and powder metallurgy. Because parts in the medical field require exclusive customized production, and most of them are complex and special-shaped components, the cast NiTi shape memory alloys require secondary processing. During the processing, it is necessary to use a tool to cut and prepare the NiTi alloy, and because the NiTi alloy has the characteristics of high toughness and wear resistance, it is difficult to process. In contrast, powder metallurgy can directly prepare parts with complex shapes through additive manufacturing.

[0003] However, the maximum tensile strain of NiTi alloy prepared by additive manufacturing can only reach about 7%, and the strength is only 500-600MPa, which is far from meeting the application standards. The main reason affecting its mechanical properties is that the holes and cracks that inevitably exist in the additive manufacturing process cause performance cracking, and the columnar crystals that grow along the building direction during the printing process promote the expansion of cracks on the plane. At the same time, the dislocation density in the grains is low, and deformation is easy to occur after being subjected to force.

[0004] Therefore, it is necessary to study a method for additive manufacturing of shape memory alloys based on blue laser to address the shortcomings of the existing technology and to solve or alleviate one or more of the above problems. [Summary of the invention]

[0005] In view of this, the present invention provides a method for additive manufacturing of shape memory alloys based on blue laser, which realizes NiTi alloy with low cracks, low holes and multiple dislocations by changing the wavelength, controlling the absorptivity and optimizing the parameter control and process flow in the alloying process.

[0006] In one aspect, the present invention provides a method for additively manufacturing a shape memory alloy based on a blue laser, the method comprising the following steps:

[0007] S1: preparing alloy powder according to a preset molar ratio;

[0008] S2: drying the alloy powder in S1;

[0009] S3: Building a 3D model and setting a rectangular matrix of a pre-printing area;

[0010] S4: Setting 3D printing parameters;

[0011] S5: Set the scanning strategy and perform path planning in the rectangular matrix, and select the blue laser for scanning;

[0012] S6: performing laser melting on the dried alloy powder to obtain a shape memory alloy.

[0013] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the method for preparing the alloy powder in S1 comprises an atomization method.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the alloy powder in S1 is NiTi alloy powder, and the preset molar ratio of the NiTi alloy powder is: Ni: 40-60, Ti: 60-40.

[0015] According to the above aspects and any possible implementation, an implementation is further provided, wherein the drying process in S2 is specifically: removing excess moisture by drying, the drying temperature is 80-100° C., and the heating time is 1-3 hours.

[0016] According to the above aspects and any possible implementation, an implementation is further provided, in which the size of the rectangular parallelepiped base in S3 is set to: 50mm*50mm*10mm.

[0017] According to the above aspects and any possible implementation, an implementation is further provided, wherein the printing parameter settings in S4 are specifically as follows: the laser power is 800 W, the scanning speed is 10 mm / s, and the thickness of each powder layer is 1 mm.

[0018] According to the above aspects and any possible implementation, an implementation is further provided, wherein the wavelength of the laser in S5 is 450nm-495nm.

[0019] According to the aspects and any possible implementation methods described above, an implementation method is further provided, wherein the scanning strategy and path planning in S5 are specifically as follows: the processing template is divided into the smallest unit of 6*6mm, and the laser beam performs a one-way linear motion along the Y-axis.

[0020] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein the 3D printing parameters are determined by simulation before the 3D printing parameters are set in S4.

[0021] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the simulation software used in S4 includes Comsol software.

[0022] Compared with the prior art, the present invention can achieve the following technical effects:

[0023] 1): Compared with the wavelength of 1024nm, the absorbance of the present invention is increased by 2.4-3.3 times. Compared with the conventional additive manufacturing of NiTi alloy, the blue laser can use less energy density to achieve the purpose of preparing NiTi alloy, reducing carbon emissions;

[0024] 2): The present invention decomposes the scanning interval into the smallest unit cell of 6mm*6mm. The laser scanning path in the processing process performs a one-way linear motion along the Y axis, which can effectively reduce the heat accumulation of the laser scanning in the scanning interval. While ensuring good metallurgical bonding of the molten pool, it realizes the effective dissipation of residual heat and avoids heat accumulation;

[0025] 3): The NiTi alloy prepared by the present invention provides new ideas and technical support for the further development in the medical field.

[0026] Of course, any product implementing the present invention does not necessarily need to achieve all of the above-mentioned technical effects at the same time.

Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, 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.

[0028] Figure 1 is a laser scanning path diagram provided by an embodiment of the present invention;

[0029] Figure 2 is a diagram of a NiTi shape memory alloy prepared by using a blue laser according to an embodiment of the present invention;

[0030] Figure 3 This is a cross-sectional morphology diagram of a NiTi shape memory alloy prepared by a blue laser according to an embodiment of the present invention;

[0031] Figure 4 This is a cross-sectional morphology diagram of a conventionally prepared NiTi shape memory alloy provided by an embodiment of the present invention;

[0032] Figure 5 This is a TEM microstructure diagram of a NiTi shape memory alloy prepared by a blue laser according to an embodiment of the present invention;

[0033] Figure 6 A TEM microstructure diagram of a conventionally prepared NiTi shape memory alloy provided by one embodiment of the present invention;

[0034] Figure 7 A comparison chart of the tensile results of NiTi alloy prepared conventionally and NiTi alloy prepared by blue laser provided in one embodiment of the present invention. [Specific implementation method]

[0035] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0036] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0038] The present invention provides a method for additively manufacturing a shape memory alloy based on a blue laser, and the method for additively manufacturing a shape memory alloy based on a blue laser comprises the following steps:

[0039] S1: preparing alloy powder according to a preset molar ratio;

[0040] S2: drying the alloy powder in S1;

[0041] S3: Building a 3D model and setting a rectangular matrix of a pre-printing area;

[0042] S4: Setting 3D printing parameters;

[0043] S5: Set the scanning strategy and perform path planning in the rectangular matrix, and select the blue laser for scanning;

[0044] S6: performing laser melting on the dried alloy powder to obtain a shape memory alloy.

[0045] The method for preparing the alloy powder in S1 includes an atomization method.

[0046] The alloy powder in S1 is NiTi alloy powder, and the preset molar ratio of the NiTi alloy powder is: Ni: 40-60, Ti: 60-40.

[0047] The drying process in S2 is specifically: removing excess moisture by drying, the drying temperature is 80-100° C., and the heating time is 1-3 hours.

[0048] The size of the rectangular parallelepiped base in S3 is set to: 50mm*50mm*10mm.

[0049] The printing parameter settings in S4 are specifically as follows: laser power is 800W, scanning speed is 10mm / s, and the thickness of each powder layer is 1mm.

[0050] The wavelength of the laser in S5 is 450nm-495nm.

[0051] The scanning strategy and path planning in S5 are specifically as follows: the processing template is divided into the smallest unit of 6*6mm, and the laser beam performs a one-way linear motion along the Y axis.

[0052] Before setting the 3D printing parameters in S4, the 3D printing parameters are determined through simulation.

[0053] The simulation software used in S4 includes Comsol software.

[0054] Embodiment 1:

[0055] The present invention provides a method for blue laser additive manufacturing of NiTi shape memory alloy, including powder pretreatment before processing and process parameters during processing; the specific steps are:

[0056] (1) NiTi alloy powder was prepared by atomization method. The molar ratio of Ni and Ti in the powder was 55.6:44.4.

[0057] (2) drying the NiTi metal powder to remove excess moisture at a drying temperature of 90° C. for 2 h;

[0058] (3) Build a 3D model and print a 50mm*50mm*10mm cuboid;

[0059] (4) Set the printing parameters. The laser power is 800W, the scanning speed is 10mm / s, and the thickness of each layer of powder is 1mm. The specific printing parameters are shown in Table 1 below:

[0060]

[0061] The laser power is 800W, the scanning speed is 10mm / s, and the thickness of each layer of powder is 1mm.

[0062] (5) Path planning; the laser scanning strategy used includes: using a blue laser with a wavelength of 455nm to divide the processing sample into the smallest unit of 6*6mm, and the laser beam performs a one-way linear motion along the Y axis, such as Figure 1 shown.

[0063] (6) To prevent heat accumulation, the scanning direction will be rotated 90° clockwise after each layer is processed. Figure 2 As shown, metal powder is prepared by laser melting to obtain NiTi alloy.

[0064] The present invention uses a blue laser with a wavelength of 455nm to additively manufacture NiTi alloy. The NiTi alloy powder has a higher absorption rate at a laser wavelength of 455nm. Compared with a wavelength of 1024nm, the absorbance increases by 2.4-3.3 times. Therefore, compared with conventional additive manufacturing of NiTi alloy, blue laser can use less energy density to achieve the purpose of preparing NiTi alloy, thereby reducing carbon emissions.

[0065] The laser scanning is to decompose the scanning area into the smallest unit cell of 6mm*6mm, and the laser scanning path in the processing process is a one-way linear motion along the Y axis. The purpose of this is to effectively reduce the heat accumulation of the laser scanning in the scanning area, while ensuring good metallurgical bonding of the molten pool, to achieve effective dissipation of residual heat and avoid heat accumulation.

[0066] The conventional method for preparing NiTi shape memory alloy currently mainly uses red laser processing with a wavelength of 1064nm, and there is no planning for the laser scanning path. In this study, as a comparison group, the same scanning path, the same molar ratio, and different light sources will be used to prepare NiTi alloy. The specific steps are:

[0067] (1) NiTi alloy powder was prepared by atomization method. The molar ratio of Ni and Ti in the powder was 55.6:44.4.

[0068] (2) drying the NiTi metal powder to remove excess water at a drying temperature of 90° C. for 2 h;

[0069] (3) Build a 3D model and print a 50mm*50mm*10mm cuboid

[0070] (4) Using the same energy density for laser processing

[0071] (5) The same path as the blue laser is used for preparation, but in comparison, no rotation processing is performed, and the scanning area is not planned according to the minimum unit of 6*6.

[0072] The present invention reduces the porosity of the additively manufactured NiTi alloy, such as Figure 3 and 4 As shown, Figure 4 This is the enlarged image of the surface with the lowest porosity prepared by the existing technology. Figure 3This is an enlarged view of the lowest porosity surface of the nickel-titanium alloy of the present invention. At the same time, a large number of high-density dislocations are generated in the grains of the NiTi alloy, such as Figure 5 and Figure 6 As shown in the figure. The NiTi alloy prepared by red laser has low dislocation density inside the grains and coarse grains. According to microstructure analysis, it is difficult to have good mechanical properties. The test results are also shown in the figure. Figure 7 As shown, the tensile fracture strain of the NiTi alloy prepared by blue laser and process optimization reaches 12.13%, and the tensile fracture strength reaches 621.32MPa. The tensile fracture strain of the NiTi alloy prepared by 1064nm and non-optimization reaches 7.9%, and the tensile fracture strength reaches 534.2MPa. NiTi alloy with better mechanical properties is prepared by blue laser.

[0073] The present invention uses Comsol software to perform simulation before preparing NiTi alloy, and makes predictions and judgments based on the results of velocity field and temperature field in the molten pool:

[0074] There will be a situation where solid and liquid coexist in the molten pool. At this time, the mass conservation equation is inserted:

[0075]

[0076] In the above formula: ρ is the material density, unit: g / cm3; u is the fluid velocity, unit: m / s; t is the time, s;

[0077] The Carman-Kozeny equation is used to describe the solid-liquid phase transition phenomenon, inserting the momentum conservation equation

[18] :

[0078]

[0079] In the above formula: F represents the sum of the volume force terms in the molten pool; I is the latent heat of phase change of the material in kJ / mol; μ is the viscosity coefficient of the material; β is the thermal expansion coefficient of the material; T is the thermodynamic temperature in K; Tm is the melting point in K; f1 is the liquid phase volume fraction of the material;

[0080] Insert the energy conservation equation:

[0081]

[0082] In the above formula, C is the specific heat of the material; k is the heat transfer coefficient; Q is the laser heat source, that is, the Gaussian heat source; through the above formula, combined with Comsol software to simulate the flow of NiTi liquid in the molten pool and the stability of the molten pool temperature, such as Figure 6 As shown, the parameters set in Example 1 are therefore selected.

[0083] In the present invention, in terms of the selection of blue laser and its wavelength, the blue laser of 450nm-495nm can increase the absorption rate of NiTi alloy to laser, thereby achieving the purpose of using less energy to prepare NiTi alloy. The current problem is that it is difficult to ensure the stability in the molten pool when using blue laser to prepare NiTi, and the blue laser is expensive. Therefore, in the present invention, a blue laser with a wavelength of 455nm is selected, and when the range value of the Ni element is a fixed value of 55.6, the stability of the molten pool is good.

[0084] The above is a detailed introduction to a method for additive manufacturing of shape memory alloys based on blue laser provided in the embodiment of the present application. The description of the above embodiment is only used to help understand the method and its core idea of ​​the present application; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

[0085] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0086] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0087] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0088] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A method for additive manufacturing of shape memory alloys based on blue laser, characterized in that: The method for additively manufacturing shape memory alloy based on blue laser comprises the following steps: S1: preparing alloy powder according to a preset molar ratio; S2: drying the alloy powder in S1; S3: Building a 3D model and setting a rectangular matrix of a pre-printing area; S4: Setting 3D printing parameters; S5: Set the scanning strategy and perform path planning in the rectangular matrix, and select the blue laser for scanning; S6: performing laser melting on the dried alloy powder to obtain a shape memory alloy.

2. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The method for preparing the alloy powder in S1 includes an atomization method.

3. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The alloy powder in S1 is NiTi alloy powder, and the preset molar ratio of the NiTi alloy powder is: Ni: 40-60, Ti: 60-40.

4. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The drying process in S2 is specifically: removing excess moisture by drying, the drying temperature is 80-100° C., and the heating time is 1-3 hours.

5. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The size of the rectangular parallelepiped base in S3 is set to: 50mm*50mm*10mm.

6. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The printing parameter settings in S4 are specifically as follows: laser power is 800W, scanning speed is 10mm / s, and the thickness of each powder layer is 1mm.

7. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The wavelength of the laser in S5 is 450nm-495nm.

8. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: The scanning strategy and path planning in S5 are specifically as follows: the processing template is divided into the smallest unit of 6*6mm, and the laser beam performs a one-way linear motion along the Y axis.

9. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 1, characterized in that: Before setting the 3D printing parameters in S4, the 3D printing parameters are determined through simulation.

10. The method for additive manufacturing of shape memory alloy based on blue laser according to claim 9, characterized in that: The simulation software used in S4 includes Comsol software.

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