Shape memory alloy powder and coaxial powder feeding laser additive manufacturing method thereof

Abstract

The present invention relates to the field of laser additive manufacturing technology, and in particular to a shape memory alloy powder and a coaxial powder feeding laser additive manufacturing method thereof. The powder comprises the following components by weight: 48 to 51 parts of Ni, 30 to 35 parts of Ti, 15 to 20 parts of Pt and 0.6 to 2.4 parts of TiN. The sample prepared by laser additive manufacturing of the alloy powder provided by the present invention has no cracks and a dense organizational structure.

Description

Technical Field

[0001] The invention relates to the technical field of laser additive manufacturing, and in particular to a shape memory alloy powder and a coaxial powder feeding laser additive manufacturing method thereof. Background Art

[0002] 3D printing technology, also known as "additive manufacturing technology" or "rapid prototyping technology", has a history of 30 years since it was commercialized in 1987 in the form of stereolithography technology. Parts produced by 3D printing technology have been widely used in the prototyping of new products and the manufacture of structures that cannot be achieved through traditional manufacturing technology. With the development of 3D printing technology, according to the standards of the American Society for Testing and Materials (ASTM), it is divided into 7 process categories: material extrusion, material jetting, sheet lamination, binder jetting, powder bed melting, directed energy deposition and photocuring. The use of 3D printing technology is now very widespread, and it is gradually transforming from a prototyping method to a mature manufacturing method. Due to material limitations, size and cost issues, 3D printing still cannot replace most traditional manufacturing methods. But in turn, it makes up for some of the shortcomings of traditional manufacturing production and can produce new products that are more complex and more versatile. The prospects for the application of 3D printing technology depend largely on the development of new materials. In the past 20 years, there have been a lot of studies on shape memory materials, also known as "smart" materials. These materials have the ability to change their shape or properties under appropriate stimulation. Metal alloys and polymers are the most popular among these materials and have attracted widespread attention.

[0003] The development of "smart" materials for 3D printing has pushed 3D printing technology to a higher level, namely 4D printing. 4D printing is a combination of 3D printing and the fourth dimension, which is the time dimension. This technology allows printed objects to change shape while adapting to the environment. This groundbreaking technology has been developed mainly due to the rapid development of smart materials and the latest progress in multi-material printing. Although the prospects of 4D printing are widely optimistic in many application fields such as packaging, medical, construction and automobiles, it is undeniable that it is still a very raw new technology and faces many challenges and problems.

[0004] The martensitic phase transformation starting temperature MS of commonly used NiTi and CuZnAl memory alloys is usually no more than 100°C, while the working temperature of memory alloy intelligent support structures, fasteners, drive parts, and clamping mechanisms in aerospace, nuclear power, and petroleum engineering is very high, with the highest use temperature reaching 600°C. Therefore, commonly used memory alloys cannot meet the demand for memory alloys in extreme temperature environments such as aerospace, nuclear industry, and oil drilling. In addition to their applications in aerospace, nuclear industry, and oil drilling, high-temperature memory alloys are also in demand in early warning and automatic protection systems for fires or overheating.

[0005] Compared with traditional alloy materials, shape memory alloys have poor formability, and it is technically difficult and economically expensive to manufacture complex structures. Additive manufacturing uses a layer-by-layer stacking method to manufacture shape memory alloys, which can avoid some problems of traditional manufacturing methods. In recent years, research on shape memory alloy additive manufacturing includes laser additive manufacturing, electron beam additive manufacturing, and arc additive manufacturing. Among them, laser additive manufacturing has the most reports. Shape memory alloy laser additive manufacturing includes two forms: powder laying and powder feeding according to different powder addition methods. Powder laying laser additive manufacturing is uniformly named by domestic and foreign research institutions: selective laser melting (SLM); powder feeding laser additive manufacturing has not yet been unified, including laser engineered netshaping (LENS), laser solid forming (LSF), direct metal deposition, laser rapid manufacturing (LRM), (laser) direct energy deposition (DED, LDED), etc. The main characteristics of powder laying laser additive manufacturing are: single powder; high manufacturing precision, relatively simple subsequent processing; low efficiency, and processing size is limited by the powder laying cylinder. The main features of powder feeding laser additive manufacturing are: it is easy to manufacture a variety of materials and can prepare gradient materials; the size of the parts is not limited by the powder spreading device; it can be used to quickly repair parts; and its efficiency is much higher than that of powder spreading laser additive manufacturing.

[0006] From the existing reports on shape memory alloy laser additive manufacturing, it can be seen that whether it is powder feeding additive manufacturing or powder laying additive manufacturing, there are some common problems: the repeated melting and thermal cycling process of laser additive manufacturing, as well as the large temperature gradient, make the organization easy to form coarse columnar crystals, irregular second phases and thermal cracks. In fact, only a few metal alloys can truly achieve 3D printing at present, and more than 5,000 alloys are prone to form coarse columnar crystals and periodic cracks like shape memory alloys due to the melting and solidification dynamics problems during the printing process, which are not suitable for 3D printing. Therefore, 3D printing of these metals can often only be used to prepare some models and cannot achieve large-scale production. To address this problem, the traditional idea is to control grain growth and reduce or eliminate cracks by optimizing process parameters. But some materials cannot be avoided no matter how they are optimized. Summary of the invention

[0007] The purpose of the present invention is to provide a shape memory alloy powder and a coaxial powder feeding laser additive manufacturing method thereof in view of the deficiencies in the prior art.

[0008] The present invention can increase the martensitic phase transformation starting temperature and solve the problem of defects such as cracks and holes that are easily generated in the laser additive manufacturing process of shape memory alloys, and is used to manufacture clamping mechanisms in the fields of aerospace, nuclear power, petroleum engineering, etc.

[0009] The technical solution is as follows:

[0010] A shape memory alloy powder, comprising the following components by weight:

[0011] 48-51 parts of Ni, 30-35 parts of Ti, 15-20 parts of Pt and 0.6-2.4 parts of TiN.

[0012] Further, the following components are included by weight:

[0013] 49-50 parts of Ni, 31-33 parts of Ti, 17-19 parts of Pt and 0.8-2.0 parts of TiN.

[0014] Furthermore, the Ni, Ti and Pt are atomized to form micron-sized spherical alloy powders with an average particle size of 30 to 180 microns.

[0015] Furthermore, the TiN is a nano-scale powder with an average particle size of 50 to 200 nanometers.

[0016] A further shape memory alloy coaxial powder feeding laser additive manufacturing method comprises the following steps:

[0017] (1) Weigh the alloy powder according to the proportion;

[0018] (2) mixing the powders and subjecting them to low-energy ball milling;

[0019] (3) Dry in a drying oven at 160°C for 8 hours;

[0020] (4) Clean the surface of the titanium alloy and use anhydrous ethanol for ultrasonic cleaning;

[0021] (5) Coaxial powder feeding laser additive manufacturing was carried out on a titanium alloy substrate under the protection of high-purity argon gas.

[0022] Furthermore, the step (2) specifically includes:

[0023] Add alcohol to the horizontal ball mill for 4 to 5 hours, and the ball mill speed is 150r / min.

[0024] Furthermore, the laser additive manufacturing parameters in step (5) are:

[0025] The spot diameter is 3 mm~4 mm, the laser power is 1.5 kW~2 kW, the scanning speed is 300 mm / min~400 mm / min, the multi-pass overlap rate is 45-55%, and the powder feeding rate is 7-9 g / s.

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

[0027] 1. Alloy powder: Adding Pt element to NiTi shape memory alloy can increase the starting temperature of martensitic phase transformation.

[0028] 2. Trace nano-TiNi mainly plays the role of nucleating agent: The repeated melting and thermal cycle process of laser additive manufacturing, as well as the large temperature gradient, make it easy for the organization to form irregular second phases, and trace nano-TiNi can play the role of non-uniform nucleation in the molten pool, increase the nucleation rate, so that the organization generates equiaxed fine crystals, avoiding coarse grains and irregular second phases. Laser additive manufacturing is a rapid cooling process, and the lattice matching requirements for the nucleating agent and the matrix are not as high as casting. The nano-TiN ceramic particles selected as nucleating agents based on the mismatch theory and other considerations can play a heterogeneous nucleation role.

[0029] 3. The micron-sized spherical alloy powder formed by Ni, Ti, and Pt after atomization has a lower hardness than the nano-TiNi ceramic particles. Under the optimized ball milling parameters, TiN will be pressed into the surface of the alloy powder, thereby forming a composite powder of nano-TiN ceramic modified spherical alloy powder, and agglomeration will be avoided as much as possible. In the laser additive manufacturing process, since the amount of ceramic particles is small and the Marangoni flow is conducive to the uniform distribution of nano-ceramic particles in the molten pool, even if the nano-ceramic particles will agglomerate, they are of very small size.

[0030] 4. The samples prepared by laser additive manufacturing of the alloy powder provided by the present invention have no cracks and a dense structure. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0032] Embodiment 1:

[0033] Step 1: 49 parts of Ni, 30 parts of Ti and 20 parts of Pt are atomized by mass to form micron-sized spherical alloy powder, 0.8 parts of nano-TiN particles are added, and alcohol is added to the powder in a horizontal ball mill at a speed of 150 r / min for 4.5 h, and dried at 160° C. for 8 hours.

[0034] Step 2: clean the surface of the titanium alloy substrate and ultrasonically clean it with anhydrous ethanol.

[0035] Step 3, under the protection of high-purity argon, laser additive manufacturing is performed on the substrate obtained in step 2 using the material obtained in step 1, and the parameters are: spot diameter 3 mm, laser power 1.8 kW, cladding speed 350 mm / min, multi-pass overlap rate 50%, and powder feeding rate 8 g / s.

[0036] Embodiment 2:

[0037] Step 1: 50 parts of Ni, 33 parts of Ti, and 17 parts of Pt are atomized by mass to form micron-sized spherical alloy powder, and 1.6 parts of nano-TiN particles are added, and alcohol is added to the powder in a horizontal ball mill at a speed of 150 r / min for 5 h, and then dried at 160° C. for 8 hours.

[0038] Step 2: clean the surface of the titanium alloy substrate and ultrasonically clean it with anhydrous ethanol.

[0039] Step 3, under the protection of high-purity argon, laser additive manufacturing is performed on the substrate obtained in step 2 using the material obtained in step 1, and the parameters are: spot diameter 4 mm, laser power 2 kW, cladding speed 310 mm / min, multi-pass overlap rate 50%, and powder feeding rate 8 g / s.

[0040] Comparative Example 1

[0041] Compared with Example 1, only TiN is not contained, and other conditions are the same.

[0042] Comparative Example 2

[0043] Compared with Example 1, only the TiN content is 3%, and other conditions are the same.

[0044]

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims.

Claims

1. A shape memory alloy powder, characterized in that: The invention comprises the following components by weight: 48 to 51 parts of Ni, 30 to 35 parts of Ti, 15 to 20 parts of Pt and 0.6 to 2.4 parts of TiN; the Ni, Ti and Pt are atomized to form micron-sized spherical alloy powders with an average particle size of 30 to 180 microns; the TiN is a nano-sized powder with an average particle size of 50 to 200 nanometers; the invention also comprises the following manufacturing steps: (1) weighing the alloy powders in proportion; (2) mixing the powders and subjecting them to low-energy ball milling; (3) drying them at a temperature of 160°C in a drying oven for 8 hours; (4) cleaning the surface of the titanium alloy and ultrasonically cleaning it with anhydrous ethanol; (5) performing coaxial powder feeding laser additive manufacturing on the titanium alloy substrate under the protection of high-purity argon; the step (2) specifically comprises: ball milling with alcohol in a horizontal ball mill for 4 to 5 hours, and the ball milling speed is 150 r / min; the laser additive manufacturing parameters in the step (5) are: spot diameter 3 mm to 4 mm; mm, laser power 1.5 kW~2 kW, scanning speed 300 mm / min~400 mm / min, multi-pass overlap rate 45-55%, powder feeding rate 7-9 g / s.

2. The shape memory alloy powder according to claim 1, characterized in that: The composite material comprises the following components in parts by mass: 49-50 parts of Ni, 31-33 parts of Ti, 17-19 parts of Pt and 0.8-2.0 parts of TiN.

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