NiTi memory alloy based on remelting process and preparation method thereof

Abstract

The invention discloses a NiTi memory alloy based on a remelting process and a preparation method thereof, the NiTi memory alloy prepared by adopting the method can realize synergistic coexistence of fine and coarse grains, so that the tensile property is improved, and the NiTi memory alloy is a high-performance NiTi memory alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of medical materials, and in particular relates to a NiTi memory alloy based on a remelting process and a preparation method thereof. Background Art

[0002] As a smart material, NiTi shape memory alloy (SMAs) not only has the shape memory effect that can automatically remember the original shape before deformation, but also has excellent superelasticity, fatigue resistance and corrosion resistance. Therefore, it has attracted more and more attention. However, due to the high melting point and active chemical properties of NiTi SMAs, brittle oxides are easily generated, resulting in poor mechanical properties. Secondly, the work hardening, rebound effect and burr generation in the subsequent processing process make its machining ability poor. This makes it difficult to achieve complex parts that take into account both precision and performance in the manufacturing process based on traditional manufacturing technology (such as forging, cutting and powder metallurgy), which limits the engineering application of NiTiSMAs.

[0003] In recent years, NiTi SMAs based on selective laser melting (SLM) not only avoid the subsequent complex machining process, have the advantages of near-net forming of complex components, but also effectively avoid the generation of brittle oxides. However, compared with traditional manufacturing methods, the tensile properties of NiTi SMAs prepared by SLM technology cannot meet engineering applications. Therefore, it is urgent to find effective ways to improve the tensile properties of SLM-NiTi SMAs. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a NiTi memory alloy based on a remelting process and a preparation method thereof. The NiTi memory alloy prepared by the method can achieve the synergistic coexistence of fine and coarse grains, thereby improving the tensile performance, and is a high-performance NiTi memory alloy.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a NiTi memory alloy based on a remelting process comprises the following steps:

[0007] Step 1, printing by laser selective melting method to obtain a first layer of printed NiTi memory alloy;

[0008] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material;

[0009] Step 2, remelting the first layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy;

[0010] Step 3, printing by laser selective melting method to obtain the N-1th layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0011] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material;

[0012] Step 4, printing by laser selective melting method to obtain the Nth layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0013] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material;

[0014] Step 5, remelting the Nth layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy;

[0015] Repeat steps 3 to 5 until the NiTi memory alloy based on the remelting process is prepared and cooled with the bin.

[0016] In the above technical solution, the first layer of printed NiTi memory alloy in step 1 or the Nth layer of printed NiTi memory alloy in step 4 has a thickness of 0.5 to 1 mm.

[0017] In the above technical solution, the laser selective melting method printing process in step 1, step 3 and step 4 adopts a laser power of 150-250W, a scanning speed of 900-1500mm / s, a scanning interval of 30-60μm, and a layer thickness of 40μm.

[0018] In the above technical solution, the remelting process in step 2 and step 5 adopts a laser power of 150-250W, a scanning speed of 600-1200mm / s, a scanning interval of 30-60μm, a layer thickness of 40μm, and a scanning number of 5-10 times.

[0019] In the above technical solution, the laser melting method printing process uses atomized spherical powder Ni 51 Ti 49 As a raw material, its particle size is 15 to 60 μm.

[0020] In the above technical solution, in step 1 and step 4, the laser selective melting method printing process is: the substrate is made of cast NiTi alloy, the surface of the substrate is polished until there is no oxide, the oil and dirt on the surface are cleaned with an organic solvent, and the surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder was put into the printer hopper, the build size was the predetermined part model size, the interlayer rotation angle was set to 67° to release residual stress, and the laser walking was programmed offline. The printing chamber was evacuated before printing, the oxygen content was lower than 100ppm, the laser power was 150W, the scanning speed was 1000mm / s, the scanning spacing was 40μm, the layer thickness was 40μm, and the argon atmosphere was used for protection. The printed NiTi memory alloy of the predetermined size was obtained.

[0021] In the above technical solution, in step 3, the laser selective melting method printing process is: the substrate is made of cast NiTi alloy, the surface of the substrate is polished until there is no oxide, the oil and dirt on the surface are cleaned with an organic solvent, and the surface is sandblasted with a sandblasting machine to 51 Ti 49 The atomized spherical powder is put into the printer silo, the build size is the predetermined part model size, the interlayer rotation angle is set to 67° to release residual stress, and the laser walking offline programming is performed. The printing chamber is evacuated before printing, the oxygen content is less than 100ppm, the laser power is 200W, the scanning speed is 1200mm / s, the scanning spacing is 50μm, the layer thickness is 40μm, and the argon atmosphere is used for protection. The printed NiTi memory alloy of the predetermined size is obtained and cooled with the chamber.

[0022] In the above technical solution, in step 1, the surface of the substrate is grinded with an angle grinder until there is no oxide, and the oil and dirt on the surface are cleaned with acetone and alcohol respectively.

[0023] In the above technical solution, in step 1, the substrate is preheated to 140-170° C. during the printing process of the laser selective melting method.

[0024] In the above technical solution, in step 1, AM-400 laser 3D printing equipment produced by Renishaw is used to perform laser selective melting method printing.

[0025] A NiTi memory alloy based on a remelting process is prepared by the preparation method described in the above technical solution.

[0026] The advantages and beneficial effects of the present invention are:

[0027] The deformation behavior of NiTi SMAs is closely related to grain size and crystal orientation. Among them, grains play a vital role in improving the strength of NiTiSMAs. The plasticity is dominated by grain orientation, with <001> Oriented single crystals break prematurely in tensile tests (typically at strains less than 2%); <110> orientation has a higher elongation (strain greater than 5%) (doi:10.1016 / s0921-5093(01)01183-2). <110> The synergistic strengthening of oriented coarse grains can achieve high-performance SLM-NiTi SMAs forming. The SLM-NiTi SMAs using non-remelting process have fine grains, while the SLM-NiTi SMAs using remelting process achieve the purpose of annealing treatment, so that the grains undergo recovery, recrystallization and abnormal growth. Therefore, using a suitable remelting process can achieve high-performance SLM-NiTi SMAs. <110> Oriented coarse-grained SLM-NiTi SMAs. Based on this, the present invention realizes a high-performance NiTi memory alloy with the synergistic coexistence of fine and coarse grains.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Compared with the traditional method of improving performance, the present invention proposes a laser selective melting technology based on the remelting process, which is easy to operate, that is, it avoids subsequent strengthening methods such as heat treatment, and can directly form SLM-NiTiSMAs in one go.

[0030] (2) The present invention can achieve the synergistic existence of fine and coarse crystals, thereby improving the strength and plasticity of SLM-NiTi SMAs;

[0031] (3) The existing remelting process means that when preparing formed parts by laser selective melting, the powder is first dropped by gravity in a hopper, and then a rubber scraper is used to evenly lay a thin layer of powder. Then, with the assistance of a high-speed galvanometer, a laser beam is used as a heat source to scan the two-dimensional shape of the computer slice, so that the laid thin layer of powder is melted / solidified by laser irradiation. Next, the deposited layer is scanned by a laser beam. Thereafter, three-dimensional part forming is achieved by layer-by-layer powder laying, layer-by-layer forming, and layer-by-layer remelting. Therefore, the existing remelting process is usually aimed at achieving part densification. However, the present invention forms a part of a certain thickness by layer-by-layer powder laying and layer-by-layer forming, and then uses a laser beam to scan the deposited layer, so that the part of a certain thickness can achieve the purpose of annealing. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the steps of the present invention.

[0033] Figure 2 Schematic diagram of the microstructure of the formed part.

[0034] Figure 3 Comparative example and example tensile properties diagram.

[0035] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments.

[0037] Comparative Example

[0038] The printed NiTi memory alloy is obtained by using the laser selective melting method.

[0039] The substrate is made of cast NiTi alloy. The surface of the substrate is polished until there is no oxide. The oil and dirt on the surface are cleaned with an organic solvent. The surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder was put into the printer silo. The laser selective melting method used the AM-400 laser 3D printing equipment produced by Renishaw for laser additive manufacturing, and the part model was built in the dedicated software; the interlayer rotation angle was set to 67° to release the residual stress, and the software automatically performed offline programming of the laser movement. Before printing, the printing chamber was evacuated, the oxygen content was less than 100ppm, the laser power was 150W, the scanning speed was 1050mm / s, the scanning spacing was 40μm, the layer thickness was set to 40μm, and the protective gas was argon. The powder feeding device and the powder spreading scraper were used to lay and flatten the thin layer of powder on the substrate. The laser beam selectively melted the metal powder on the powder bed according to the slice contour and then solidified to form a layer of entity. Repeating this process, stacking layer by layer, can form a three-dimensional solid component. In addition, in order to reduce the residual stress generated during the preparation process, the substrate was preheated to 170℃. After printing, the printed NiTi memory alloy was obtained, which was a tensile specimen with a length of 70mm, a width of 10mm, and a thickness of 5mm, and cooled with the silo for 2 hours.

[0040] Embodiment 1

[0041] A method for preparing a NiTi memory alloy based on a remelting process comprises the following steps:

[0042] Step 1, printing by laser selective melting method to obtain a first layer of printed NiTi memory alloy;

[0043] The substrate is made of cast NiTi alloy. The surface of the substrate is polished until there is no oxide. The oil and dirt on the surface are cleaned with an organic solvent. The surface is sandblasted with a sandblasting machine. 51 Ti 49The atomized spherical powder is put into the printer silo. The laser selective melting method uses the AM-400 laser 3D printing equipment produced by Renishaw for laser additive manufacturing, and the part model is built in the dedicated software; the interlayer rotation angle is set to 67° to release the residual stress, and the software automatically performs offline programming of the laser movement. Before printing, the printing chamber is evacuated, the oxygen content is less than 100ppm, the laser power is 150W, the scanning speed is 1050mm / s, the scanning spacing is 40μm, the layer thickness is set to 40μm, and the protective gas is argon. The powder feeding device and the powder spreading scraper are used to lay and flatten the thin layer of powder on the substrate. The laser beam selectively melts the metal powder on the powder bed according to the slice contour and then solidifies to form a layer of entity. Repeating this process, stacking layer by layer, can form a three-dimensional solid component. In addition, in order to reduce the residual stress generated during the preparation process, the substrate is preheated to 170℃. After printing, the first layer of printed NiTi memory alloy with a length of 70mm, a width of 10mm, and a thickness of 0.5mm is obtained;

[0044] Step 2, remelting the first layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy;

[0045] The remelting process uses a laser power of 200 W, a scanning speed of 1000 mm / s, a scanning interval of 30 μm, a layer thickness of 40 μm, and 5 scanning times.

[0046] Step 3, printing by laser selective melting method to obtain the N-1th layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0047] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1;

[0048] Step 4, printing by laser selective melting method to obtain the Nth layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0049] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1;

[0050] Step 5, remelting the Nth layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy; the specific method and steps are the same as those of step 2;

[0051] Repeat steps 3 to 5 until the NiTi memory alloy based on the remelting process is prepared, and the final product is a tensile test specimen with a length of 70 mm, a width of 10 mm, and a thickness of 5 mm.

[0052] Embodiment 2

[0053] A method for preparing a NiTi memory alloy based on a remelting process comprises the following steps:

[0054] Step 1, printing by laser selective melting method to obtain a first layer of printed NiTi memory alloy;

[0055] The substrate is made of cast NiTi alloy. The surface of the substrate is polished until there is no oxide. The oil and dirt on the surface are cleaned with an organic solvent. The surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder is put into the printer silo. The laser selective melting method uses the AM-400 laser 3D printing equipment produced by Renishaw for laser additive manufacturing, and the part model is built in the dedicated software; the interlayer rotation angle is set to 67° to release the residual stress, and the software automatically performs offline programming of the laser movement. Before printing, the printing chamber is evacuated, the oxygen content is less than 100ppm, the laser power is 150W, the scanning speed is 1000mm / s, the scanning spacing is 40μm, the layer thickness is set to 40μm, and the protective gas is argon. The powder feeding device and the powder spreading scraper are used to lay and flatten the thin layer of powder on the substrate. The laser beam selectively melts the metal powder on the powder bed according to the slice contour and then solidifies to form a layer of entity. Repeating this process, stacking layer by layer, can form a three-dimensional solid component. In addition, in order to reduce the residual stress generated during the preparation process, the substrate is preheated to 170℃. After printing, the first layer of printed NiTi memory alloy with a length of 70mm, a width of 10mm, and a thickness of 0.6mm is obtained;

[0056] Step 2, remelting the first layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy;

[0057] The remelting process uses a laser power of 200 W, a scanning speed of 800 mm / s, a scanning interval of 30 μm, a layer thickness of 40 μm, and 6 scan times.

[0058] Step 3, printing by laser selective melting method to obtain the N-1th layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0059] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1 except for the following parameters;

[0060] The process parameters of laser power of 200 W, scanning speed of 1200 mm / s, scanning spacing of 50 μm, and layer thickness of 40 μm were used to form a sample with a height of 0.6 mm.

[0061] Step 4, printing by laser selective melting method to obtain the Nth layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0062] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1;

[0063] Step 5, remelting the Nth layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy; the specific method and steps are the same as those of step 2;

[0064] Repeat steps 3 to 5 until the NiTi memory alloy based on the remelting process is prepared, and the final product is a tensile test specimen with a length of 70 mm, a width of 10 mm, and a thickness of 5 mm.

[0065] Embodiment 3

[0066] A method for preparing a NiTi memory alloy based on a remelting process comprises the following steps:

[0067] Step 1, printing by laser selective melting method to obtain a first layer of printed NiTi memory alloy;

[0068] The substrate is made of cast NiTi alloy. The surface of the substrate is polished until there is no oxide. The oil and dirt on the surface are cleaned with an organic solvent. The surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder is put into the printer silo. The laser selective melting method uses the AM-400 laser 3D printing equipment produced by Renishaw for laser additive manufacturing, and the part model is built in the dedicated software; the interlayer rotation angle is set to 67° to release the residual stress, and the software automatically performs offline programming of the laser movement. Before printing, the printing chamber is evacuated, the oxygen content is less than 100ppm, the laser power is 150W, the scanning speed is 1050mm / s, the scanning spacing is 40μm, the layer thickness is set to 40μm, and the protective gas is argon. The powder feeding device and the powder spreading scraper are used to lay and flatten the thin layer of powder on the substrate. The laser beam selectively melts the metal powder on the powder bed according to the slice contour and then solidifies to form a layer of entity. Repeating this process, stacking layer by layer, can form a three-dimensional solid component. In addition, in order to reduce the residual stress generated during the preparation process, the substrate is preheated to 170℃. After printing, the first layer of printed NiTi memory alloy with a length of 70mm, a width of 10mm and a thickness of 0.6mm is obtained;

[0069] Step 2, remelting the first layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy;

[0070] The remelting process uses a laser power of 250 W, a scanning speed of 700 mm / s, a scanning interval of 50 μm, a layer thickness of 40 μm, and 8 scanning times.

[0071] Step 3, printing by laser selective melting method to obtain the N-1th layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0072] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1 except for the following parameters;

[0073] The process parameters of laser power of 200 W, scanning speed of 1200 mm / s, scanning spacing of 50 μm, and layer thickness of 40 μm were used to form a sample with a height of 0.5 mm.

[0074] Step 4, printing by laser selective melting method to obtain the Nth layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1;

[0075] The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; the specific method and steps are the same as step 1;

[0076] Step 5, remelting the Nth layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy; the specific method and steps are the same as those of step 2;

[0077] Repeat steps 3 to 5 until the NiTi memory alloy (final size) based on the remelting process is completed, and the final product is a tensile test specimen with a length of 70 mm, a width of 10 mm, and a thickness of 5 mm.

[0078] The above embodiment adopts the remelting process in the technical solution so that the deposited layer undergoes annealing treatment, wherein a linear energy function is used to represent the laser energy absorbed by the material, and the formula is:

[0079]

[0080] Among them, σ0, v, t, P, h, and α (= 0.35) are the standard deviations of the Gaussian laser beam, laser scanning speed, time, laser power, scanning spacing, and thermal absorption rate, respectively.

[0081] The room temperature tensile properties of the final tensile specimens were tested using a universal electronic universal testing machine, with a strain rate of 2.5×10 -4 / s, and the deformation test was carried out using an extensometer with a gauge length of 25 mm. The results are shown in Figure 3 .

[0082] Relational terms such as “first” and “second” and the like are merely used to distinguish one component from another having the same name, but do not necessarily require or imply any such actual relationship or order between these components.

[0083] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A method for preparing a NiTi memory alloy based on a remelting process, characterized in that: The following steps are involved: Step 1, printing by laser selective melting method to obtain a first layer of printed NiTi memory alloy; The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; Step 2, remelting the first layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy; Step 3, printing by laser selective melting method to obtain the N-1th layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1; The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; Step 4, printing by laser selective melting method to obtain the Nth layer of printed NiTi memory alloy, wherein N is a positive integer greater than 1; The laser selective melting method printing process uses NiTi atomized spherical powder as raw material; Step 5, remelting the Nth layer of printed NiTi memory alloy, wherein the remelting process is laser scanning the printed NiTi memory alloy; Repeat steps 3 to 5 until the NiTi memory alloy based on the remelting process is prepared and cooled with the bin.

2. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: The first layer of printed NiTi memory alloy in step 1 or the Nth layer of printed NiTi memory alloy in step 4 has a thickness of 0.5 to 1 mm.

3. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: The laser selective melting method printing process in step 1, step 3 and step 4 adopts a laser power of 150-250W, a scanning speed of 900-1500mm / s, a scanning interval of 30-60μm, and a layer thickness of 40μm.

4. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: The remelting process in step 2 and step 5 adopts a laser power of 150-250 W, a scanning speed of 600-1200 mm / s, a scanning interval of 30-60 μm, a layer thickness of 40 μm, and a scanning number of 5-10 times.

5. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: The laser melting method printing process uses gas atomized spherical powder Ni 51 Ti 49 As a raw material, its particle size is 15 to 60 μm.

6. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: In step 1 and step 4, the laser selective melting method printing process is as follows: the substrate is made of cast NiTi alloy, the surface of the substrate is polished until there is no oxide, the oil and dirt on the surface are cleaned with an organic solvent, and the surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder was put into the printer hopper, the build size was the predetermined part model size, the interlayer rotation angle was set to 67° to release residual stress, and the laser walking was programmed offline. The printing chamber was evacuated before printing, the oxygen content was lower than 100ppm, the laser power was 150W, the scanning speed was 1000mm / s, the scanning spacing was 40μm, the layer thickness was 40μm, and the argon atmosphere was used for protection. The printed NiTi memory alloy of the predetermined size was obtained.

7. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: In step 3, the laser selective melting method printing process is as follows: the substrate is made of cast NiTi alloy, the surface of the substrate is polished until there is no oxide, the oil and dirt on the surface are cleaned with an organic solvent, and the surface is sandblasted with a sandblasting machine. 51 Ti 49 The atomized spherical powder is put into the printer silo, the build size is the predetermined part model size, the interlayer rotation angle is set to 67° to release residual stress, and the laser walking offline programming is performed. The printing chamber is evacuated before printing, the oxygen content is less than 100ppm, the laser power is 200W, the scanning speed is 1200mm / s, the scanning spacing is 50μm, the layer thickness is 40μm, and the argon atmosphere is used for protection. The printed NiTi memory alloy of the predetermined size is obtained and cooled with the chamber.

8. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: In the step 1, the surface of the substrate is grinded with an angle grinder until there is no oxide, and the oil and dirt on the surface are cleaned with acetone and alcohol respectively; and the AM-400 laser 3D printing equipment produced by Renishaw is used to perform laser selective melting method printing.

9. The method for preparing NiTi memory alloy based on remelting process according to claim 1, characterized in that: In the step 1, the substrate is preheated to 140-170° C. during the printing process of the laser selective melting method.

10. A NiTi memory alloy based on a remelting process prepared by the preparation method according to any one of claims 1 to 9.

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