Process and application of 3D printing composite forming shape memory alloy pipe joints

Abstract

A process and application for 3D printing composite forming of shape memory alloy pipe joints belongs to the field of material forming technology. It solves the technical problems of existing shape memory alloy pipe joint production and preparation, such as high energy consumption, multiple and lengthy processes, low yield rate, and poor mechanical properties. The solution includes the following steps: S1, 3D printing to prepare shape memory alloy pipe joint blanks; S2, stress relief annealing of the pipe joint blanks; S3, hot rolling the pipe joint blanks to obtain hot-rolled pipe blanks for the pipe joints; S4, machining the hot-rolled pipe blanks for the pipe joints; S5, low-temperature expansion of the pipe joint casing to obtain shape memory alloy pipe joints; the shape memory alloy pipe joints prepared by the present invention can be used for aviation hydraulic pipe connections. The present invention overcomes the inherent deficiencies in the ingot smelting process, obtaining high-quality, high-performance, and high-precision pipe blanks; significantly shortens the process flow, and has the significant characteristics of low energy consumption, greenness, and environmental friendliness in forming and manufacturing.

Description

Technical Field

[0001] The present invention belongs to the technical field of material forming, and specifically relates to a process and application of 3D printing composite forming of shape memory alloy pipe joints. Background Art

[0002] Aviation hydraulic piping components are critical, foundational components that function like lifeblood vessels. However, their joints must operate in extremely harsh environments, such as high stress, high temperature, high pressure, and corrosive media, and are prone to leaks. Therefore, achieving high-performance, highly reliable connections for these components is crucial to addressing these challenges. Pipe joints made from shape memory alloys exhibit the unique functional properties of shape memory effect and superelasticity, along with excellent sealing performance and high connection strength, meeting the high-pressure, high-reliability, and long-life requirements of piping components.

[0003] The preparation and processing technology of shape memory alloy pipe joints mainly includes vacuum melting method and powder metallurgy method:

[0004] 1) Vacuum melting method: vacuum melting method to prepare ingots → hot forging and hot rolling to make blanks → machining punching to make extruded blanks → annealing → multi-pass rolling → heat treatment → memory alloy tube forming - cutting processing;

[0005] 2) Powder metallurgy method: package design → package processing and leak detection → powder is loaded into the package → powder vibration → vacuum → hot isostatic pressing memory alloy tube - cutting processing.

[0006] Among them, the ingots produced by the traditional vacuum melting method have a coarse metallographic structure and poor uniformity, which will lead to problems such as difficulty in subsequent rolling deformation, uneven wall thickness of the rolled pipe, orange peel and wrinkling on the pipe surface, and poor surface quality. The overall forming process is complex, energy consumption is high, and quality is difficult to control. The pipes produced by the powder metallurgy method can only produce small parts with simple shapes due to the poor fluidity of the powder, and have poor strength and toughness, which is difficult to meet industrial needs. In short, the above two preparation methods have long production cycles and high operating technical difficulties when used to prepare shape memory alloy pipe joints.

[0007] Existing literature or patents describing new processes for preparing shape memory alloy pipe joints often involve improvements to conventional manufacturing processes. For example, the patent document "A blank for a shape memory alloy pipe joint and a method for preparing it" (authorized publication: CN112538582B) discloses the use of a combined vacuum induction melting and vacuum consumable melting process to produce ingots, followed by hot working to produce rods, which are then cold-rolled to form pipe joints. The patent document "An iron-based shape memory alloy for stainless steel pipe joints at a specific temperature and a method for preparing it" (authorized publication: CN114807783A) still uses traditional melting and casting to produce ingots, which are then rolled into round rods after annealing and then extruded into tubing to create shape memory alloy connectors with excellent shape memory properties. The patent document "A 4D printing rapid manufacturing method and product of shape memory alloy pipe joints" (authorization announcement: CN111151756B) discloses the use of 4D printing to prepare pipe joints with three layers of different alloy compositions. The process is complex, difficult to operate, and energy-intensive. In addition, the composition and structural differences between layers can easily cause cracks, resulting in a reduction in the mechanical properties of the pipe joint and causing it to fail prematurely.

[0008] In summary, there is an urgent need to explore a short-process, high-performance preparation method for shape memory alloy pipe joints. Summary of the Invention

[0009] The main purpose of the present invention is to overcome the shortcomings of the existing technology and solve the production problems of existing shape memory alloy pipe joints such as high energy consumption, multiple steps and long processes, extremely low yield rate, high cost, as well as technical problems such as uneven wall thickness, pipe cracking, and poor mechanical properties. The present invention provides a short-process, low-energy-consumption, high-quality preparation process method for 3D printing composite forming shape memory alloy pipe joints and its application.

[0010] The design concept of this invention is: taking the coarse ingot structure in the traditional melting and casting process that affects the subsequent difficulty of thermal deformation of the pipe, and the limitations and poor strength of the powder metallurgy method in the preparation of large components with complex shapes as the starting point, with shortening the process flow as the main line, a technical concept of 3D printing and composite rolling forming shape memory alloy pipe joints is proposed, that is, 3D printing (laser selective melting) is used to prepare shape memory alloys with fine structure, uniform composition, and no severe segregation, coarse inclusions, and coarse second phases; then a rolling process is used to eliminate casting defects such as holes introduced by 3D printing, reduce local stress concentration of the alloy, and improve the strength of the alloy.

[0011] The present invention is achieved through the following technical solutions:

[0012] A process for 3D printing composite forming of a shape memory alloy pipe joint comprises the following steps:

[0013] S1. Preparation of shape memory alloy pipe joint blanks by 3D printing:

[0014] S1-1. Use CAD computer-aided design software to model the shape and size of the pipe joint 3D model and export it to an STL file. Then, import the STL file into the additive manufacturing path planning software built into the 3D printing device to determine the printing direction. The 3D model is sliced ​​and layered to obtain 2D slices of the pipe joint model. Finally, a laser scanning path is generated based on the 2D slices of the pipe joint model, including an external contour fill path and an internal fill path. 3D printing process parameters are set: laser power of 120W to 200W, scanning speed of 800mm / s to 1600mm / s, and track spacing of 40μm to 60μm, and a JOB format print file is generated.

[0015] S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. The average particle size of the pre-alloyed powder is 15 μm to 35 μm. Then, place the weighed pre-alloyed powder in a vacuum environment at 80°C to 120°C and evenly flatten it. Vacuum dry it for 12 hours to 24 hours to remove the moisture contained in the pre-alloyed powder before use.

[0016] S1-3. Select NiTi shape memory alloy as the substrate and repeatedly clean the substrate with anhydrous ethanol to keep the substrate surface clean and free of contamination. Then preheat the substrate to 70-150°C for standby use. Substrate preheating is used to reduce the large temperature difference between the substrate and the molded part, thereby reducing residual thermal stress.

[0017] S1-4, starting the 3D printing device, and performing 3D printing by spreading powder layer by layer on the surface of the substrate according to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters to produce a pipe joint blank;

[0018] S2. Stress relief annealing of pipe joint blanks: The annealing temperature is 500℃~900℃, and the annealing time is 0.5~2h. Stress relief annealing can eliminate the residual stress caused by local heating, cooling and uneven composition of the 3D printed tube blanks, improve the strength and plasticity of the tube blanks, and facilitate subsequent rolling processing;

[0019] S3. Hot rolling of pipe joint billets: The pipe joint billets are preheated at 500°C for 10 minutes and then fed into a hot rolling mill for hot rolling. The feeding speed of the pipe joint billets is 1 mm / s to 3 mm / s, the hot rolling temperature is 750°C to 1000°C, the number of hot rolling passes is 1 to 4, and the rolling reduction of each pass is 5% to 35%. Intermediate annealing is performed between each hot rolling pass at a temperature of 400°C to 700°C and a holding time of 10 to 20 minutes. After the final hot rolling pass, isothermal annealing is performed at a temperature of 500°C and a holding time of 2 hours. The billets are then water-cooled to room temperature to obtain hot-rolled pipe billets for pipe joints.

[0020] S4. Mechanical processing of the hot-rolled pipe joint blank: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint.

[0021] Furthermore, in step S1-2, the NiTi-based shape memory alloy pre-alloy powder is NiTi, NiTiNb or NiTiFe.

[0022] Furthermore, in step S1-4, after the 3D printing equipment is started, the molding chamber is first evacuated and then filled with argon protective gas until the oxygen content is no more than 30 ppm. During the 3D printing process, the molding chamber is kept in an argon protective atmosphere, which reduces the oxygen content during the preparation process and prevents oxidation of the metal powder.

[0023] Furthermore, in step S4, the inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°.

[0024] Furthermore, in step S4, the shape memory alloy pipe joint has a length of 50 mm to 55 mm, an inner diameter of 19 mm to 21 mm, and a wall thickness of 2.6 mm to 2.8 mm.

[0025] An application of a shape memory alloy pipe joint prepared by the above preparation method comprises the following steps:

[0026] First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and is uniformly expanded at a temperature of -190℃~-30℃, with an expansion rate of 8%;

[0027] Then, in a high and low temperature environment box, the ends of the two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint;

[0028] Finally, the high and low temperature environment box is heated to 25℃~70℃, and the shape memory alloy pipe joint returns to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint.

[0029] Furthermore, the portion of the end portion of the to-be-connected pipe extending into the shape memory alloy pipe joint is located at a portion of the shape memory alloy pipe joint where an inner ridge is provided.

[0030] The beneficial effects of the present invention are: the present invention overcomes the inherent deficiencies in the ingot smelting preparation, and obtains high-quality, high-performance and high-precision high-quality tube blanks; it greatly shortens the process flow, and has the significant characteristics of low energy consumption, green and environmentally friendly forming and manufacturing. At the same time, it has strong applicability and is almost suitable for the preparation of all metal material tubes by laser additive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the process flow chart for 3D printing composite forming of shape memory alloy pipe joints. DETAILED DESCRIPTION

[0032] The present invention will be described in further detail below with reference to the accompanying drawings and examples. Example 1

[0033] like Figure 1 A process for 3D printing composite forming of a shape memory alloy pipe joint is shown, comprising the following steps:

[0034] S1. Preparation of shape memory alloy pipe joint blanks by 3D printing:

[0035] S1-1. Use CAD computer-aided design software to design the shape and size of the three-dimensional model of the pipe joint. In this embodiment 1, the pipe joint blank is a round tube with a length of 25 mm, an outer diameter of 28 mm, and a wall thickness of 6 mm.

[0036] Export the STL file. Then, import the STL file into the additive manufacturing path planning software built into the 3D printing device to determine the printing direction, slice the 3D model, and obtain 2D slices of the pipe joint model. Finally, generate a laser scanning path based on the 2D slices of the pipe joint model, including an external contour fill path and an internal fill path. Set the 3D printing process parameters: laser power of 160W, scanning speed of 1400mm / s, and track spacing of 60μm, and generate a JOB format print file.

[0037] S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. In Example 1, the pre-alloyed powder is aerosolized spherical NiTi powder (chemical composition is shown in Table 1 below). The average particle size of the pre-alloyed powder is 35 μm. Then, the weighed pre-alloyed powder is placed in a vacuum environment at 100° C. and evenly flattened. The powder is vacuum dried for 16 hours to remove moisture from the pre-alloyed powder before use.

[0038]

[0039] S1-3. Select NiTi shape memory alloy as the substrate (hot forging state), repeatedly clean the substrate with anhydrous ethanol to keep the substrate surface clean and free of contamination, and then preheat the substrate to 100°C for use;

[0040] S1-4. Start the 3D printing device. After the 3D printing device is started, the molding chamber is first vacuumed and filled with argon protective gas until the oxygen content is no more than 30 ppm. According to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, powder is applied layer by layer on the substrate for 3D printing. The pipe joint blank is separated from the substrate by wire cutting and ultrasonic cleaning is performed to produce the pipe joint blank.

[0041] In this Example 1, an orthogonal experimental method was used to design different process parameter combinations and then print the alloy. The macromorphology and microstructure were then observed, and the mechanical properties and shape memory properties were tested to determine the process parameter combination with good macromorphology and optimal shape memory properties.

[0042] S2. Stress relief annealing of pipe joint blank: annealing temperature is 600℃, annealing time is 2h;

[0043] S3. Hot rolling of pipe joint blank: The pipe joint blank is preheated at 500° C. for 10 min and then fed into a hot rolling mill for hot rolling. The feeding speed of the pipe joint blank is 1.5 mm / s, the hot rolling temperature is 950° C., the number of hot rolling passes is 3, the rolling reduction for each pass is 20%, and intermediate annealing is performed between each hot rolling pass. The intermediate annealing temperature is 500° C. and the holding time is 15 min. After the last hot rolling pass, isothermal annealing is performed at 500° C. and the holding time is 2 h. The pipe joint is then water-cooled to room temperature to obtain a hot-rolled pipe blank. The dimensions of the hot-rolled pipe blank prepared in Example 1 are: length 55 mm, outer diameter 23 mm, and wall thickness 3.2 mm. The overall recovery rate of the 3D-printed NiTi shape memory alloy pipe joint sleeve is as high as 98% when the strain is 6%. After rolling, its strength is increased by about 30% compared with the 3D-printed state. Compared with traditional processes, material utilization is increased by nearly 4 times and costs are reduced by 40%;

[0044] S4. Mechanical processing of the hot-rolled pipe joint blank: First, an inner ridge is cut on the inner wall of the circular tube-shaped hot-rolled pipe joint blank by turning. The inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°. Then, the inner and outer walls of the circular tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to produce a shape memory alloy pipe joint. The shape memory alloy pipe joint has a length of 50 mm, an inner diameter of 19.8 mm, and a wall thickness of 2.8 mm.

[0045] An application of a shape memory alloy pipe joint prepared by the above preparation method comprises the following steps:

[0046] First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and is uniformly expanded at a temperature of -90℃~-55℃, with an expansion rate of 8%. The steps of expanding the shape memory alloy pipe joint are as follows:

[0047] 1) Assembling the expansion device: Fix the base to the workbench of the press, adjust the position of the expansion rod and perform a centering test to ensure that the expansion rod is inserted into the center positioning hole of the base. Place the pad on the base and connect it with bolts. Close the expansion valve and place it on the pad. Press the upper plate of the press downward and adjust the expansion valve to be centered. Then, move the press upward. Put the prepared shape memory alloy pipe joint on the closed expansion valve and fix the baffle plate and pad with bolts to prevent it from moving with the expansion rod during unloading. At this point, the expansion device is assembled;

[0048] 2) Expansion operation: Place the assembled expansion device and shape memory alloy pipe joint in a high and low temperature environment box, start the press to press the upper pressure plate downward to drive the expansion rod downward, and the outer conical surface of the middle part of the expansion rod contacts the inner conical surface of the expansion valve. The expansion valve opens and moves, driving the shape memory alloy pipe joint to expand and deform as a whole. The expansion is uniform under low temperature conditions of -90℃~-55℃, and the expansion rate is 8%;

[0049] 3) Remove the shape memory alloy pipe joint by disassembling the device: move the upper plate of the press upwards, remove the expanded shape memory alloy pipe joint from the expansion valve, and complete the expansion of the shape memory alloy pipe joint;

[0050] Then, in a high and low temperature environment box, the ends of the two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint;

[0051] Finally, the high and low temperature environment box is heated to 70°C to induce the shape memory effect. The shape memory alloy pipe joint returns to its size before expansion, and the inner ridge bends inward to press the end of the pipe to be connected, completing the fixed connection of the two aviation hydraulic pipes through the shape memory alloy pipe joint. Example 2

[0052] like Figure 1 A process for 3D printing composite forming of a shape memory alloy pipe joint is shown, comprising the following steps:

[0053] S1. Preparation of shape memory alloy pipe joint blanks by 3D printing:

[0054] S1-1. Modeling using CAD computer-aided design software to design the shape and size of the three-dimensional model of the pipe joint. In Example 2, the pipe joint blank is a round tube with a length of 27.5 mm, an outer diameter of 30 mm, and a wall thickness of 5 mm.

[0055] Export the STL file. Then, import the STL file into the additive manufacturing path planning software built into the 3D printing device to determine the printing direction, slice the 3D model, and obtain 2D slices of the pipe joint model. Finally, generate a laser scanning path based on the 2D slices of the pipe joint model, including an external contour fill path and an internal fill path. Set the 3D printing process parameters: laser power of 150W, scanning speed of 800mm / s, and track spacing of 60μm, and generate a JOB format print file.

[0056] S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. In Example 2, the pre-alloyed powder is aerosolized spherical NiTiNb powder (chemical composition is shown in Table 2 below). The average particle size of the pre-alloyed powder is 35 μm. Then, the weighed pre-alloyed powder is placed in a vacuum environment at 100° C. and evenly flattened. It is vacuum-dried for 18 hours to remove moisture from the pre-alloyed powder before use.

[0057]

[0058] S1-3. Select NiTi shape memory alloy as the substrate (hot forging state), repeatedly clean the substrate with anhydrous ethanol to keep the substrate surface clean and free of contamination, and then preheat the substrate to 100°C for use;

[0059] S1-4. Start the 3D printing device. After the 3D printing device is started, the molding chamber is first vacuumed and filled with argon protective gas until the oxygen content is no more than 30 ppm. According to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, powder is applied layer by layer on the substrate for 3D printing. The pipe joint blank is separated from the substrate by wire cutting and ultrasonic cleaning is performed to produce the pipe joint blank.

[0060] S2. Stress relief annealing of pipe joint blank: annealing temperature is 600℃, annealing time is 2h;

[0061] S3. Hot rolling of pipe joint blanks: After preheating at 500℃ for 10min, pipe joint blanks are fed into hot rolling mill for hot rolling. The feeding speed of pipe joint blanks is 1.5mm / s, the hot rolling temperature is 950℃, the hot rolling passes are 3, the rolling reduction of each pass is 20%, and intermediate annealing is performed between each hot rolling pass. The intermediate annealing temperature is 500℃ and the holding time is 15min. After the last hot rolling pass, isothermal annealing is performed. The isothermal annealing temperature is 500℃ and the holding time is 2h. Water cooling is performed to At room temperature, a hot-rolled pipe blank for a pipe joint was produced. The dimensions of the hot-rolled pipe blank for a pipe joint produced in Example 2 were: 53 mm in length, 23 mm in outer diameter, and 3.2 mm in wall thickness. The recovery stress of the 3D-printed NiTiNb shape memory alloy pipe joint sleeve reached 420 MPa, which was approximately 55.9% and 15.4% higher than that of the conventional forged and extruded states. Compared with the conventional process, the 3D printing method increased material utilization by nearly 4 times and reduced costs by 40%. The strength was further increased after rolling.

[0062] S4. Mechanical processing of the hot-rolled pipe joint blank: First, an inner ridge is cut on the inner wall of the circular tube-shaped hot-rolled pipe joint blank by turning. The inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°. Then, the inner and outer walls of the circular tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to produce a shape memory alloy pipe joint. The shape memory alloy pipe joint has a length of 50 mm, an inner diameter of 19.8 mm, and a wall thickness of 2.8 mm.

[0063] An application of a shape memory alloy pipe joint prepared by the above preparation method comprises the following steps:

[0064] First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and uniformly expanded at a low temperature of -160℃~-140℃, with an expansion rate of 8%;

[0065] Then, in a high and low temperature environment box, the ends of the two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint;

[0066] Finally, the high and low temperature environment box is heated to 25°C to induce the shape memory effect. The shape memory alloy pipe joint returns to its size before expansion, and the inner ridge bends inward to press the end of the pipe to be connected, completing the fixed connection of the two aviation hydraulic pipes through the shape memory alloy pipe joint.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A process for 3D printing composite forming of shape memory alloy pipe joints, comprising the following steps: S1. Preparation of shape memory alloy pipe joint blanks by 3D printing: S1-1. Use CAD computer-aided design software to model the shape and size of the pipe joint 3D model and export it to an STL file. Then, import the STL file into the additive manufacturing path planning software built into the 3D printing device to determine the printing direction. The 3D model is sliced ​​and layered to obtain 2D slices of the pipe joint model. Finally, a laser scanning path is generated based on the 2D slices of the pipe joint model, including an external contour fill path and an internal fill path. 3D printing process parameters are set: laser power of 120W to 200W, scanning speed of 800mm / s to 1600mm / s, and track spacing of 40μm to 60μm, and a JOB format print file is generated. S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. The average particle size of the pre-alloyed powder is 15 μm to 35 μm. Then, place the weighed pre-alloyed powder in a vacuum environment at 80°C to 120°C and evenly flatten it. Vacuum dry it for 12 hours to 24 hours to remove the moisture contained in the pre-alloyed powder before use. S1-3. Select NiTi shape memory alloy as the substrate, repeatedly clean the substrate with anhydrous ethanol to keep the substrate surface clean and free of contamination, and then preheat the substrate to 70-150°C for standby use; S1-4, starting the 3D printing device, and performing 3D printing by spreading powder layer by layer on the surface of the substrate according to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, to produce a pipe joint blank; S2. Stress relief annealing of pipe joint blanks: annealing temperature is 500℃~900℃, annealing time is 0.5~2h; S3. Hot rolling of pipe joint blanks: The pipe joint blanks are preheated at 500°C for 10 minutes and then fed into a hot rolling mill for hot rolling. The feeding speed of the pipe joint blanks is 1 mm / s to 3 mm / s, the hot rolling temperature is 750°C to 1000°C, the number of hot rolling passes is 1 to 4, and the rolling reduction of each pass is 5% to 35%. Intermediate annealing is performed between each hot rolling pass at a temperature of 400°C to 700°C and a holding time of 10 to 20 minutes. After the final hot rolling pass, isothermal annealing is performed at a temperature of 500°C and a holding time of 2 hours. The blanks are then water-cooled to room temperature to obtain hot-rolled pipe joint blanks. S4. Mechanical processing of the hot-rolled pipe joint blank: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint.

2. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In the step S1-2, the NiTi-based shape memory alloy pre-alloy powder is NiTi, NiTiNb or NiTiFe.

3. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S1-4, after the 3D printing equipment is started, the molding chamber is first vacuumed and filled with argon protective gas until the oxygen content is no more than 30 ppm.

4. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S4, the inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°.

5. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S4, the length of the shape memory alloy pipe joint is 50 mm to 55 mm, the inner diameter is 19 mm to 21 mm, and the wall thickness is 2.6 mm to 2.8 mm.

6. An application of a shape memory alloy pipe joint produced by the process according to claim 1, characterized in that: The following steps are involved: First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and is uniformly expanded at a temperature of -190℃~-30℃, with an expansion rate of 8%; Then, in a high and low temperature environment box, the ends of the two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint; Finally, the high and low temperature environment box is heated to 25℃~70℃, and the shape memory alloy pipe joint returns to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint.

7. The use according to claim 6, characterized in that: The portion of the end of the pipe to be connected extending into the shape memory alloy pipe joint is located at the portion of the shape memory alloy pipe joint where the inner ridge is provided.

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