Heterogeneous Bimetallic Wire Arc Additive Manufacturing Method for NiTi-Based Shape Memory Alloy

Abstract

The present invention relates to the technical field of arc additive manufacturing, and particularly to a method for additive manufacturing of heterogeneous dual-wire arc of NiTi-based shape memory alloy. The manufacturing method is to feed NiTi alloy wire and metal wire simultaneously through a dual-wire arc additive device, and use an ultra-high frequency pulsed TIG welding power source to realize the additive manufacturing of heterogeneous dual-wire arc of NiTi-based shape memory alloy. The present invention is used to solve problems such as low phase transformation temperature and large phase transformation hysteresis in existing arc additive manufacturing technology. Moreover, the ultra-high frequency pulsed TIG arc can improve the microstructure morphology, thereby being beneficial to stabilizing and improving the performance of NiTi-based alloys, broadening the application fields of NiTi-based ternary alloys, and providing an effective solution for arc additive manufacturing of NiTi-based shape memory alloys.

Description

Technical Field

[0001] The present invention relates to the technical field of arc additive manufacturing, and particularly to a method for arc additive manufacturing of NiTi-based shape memory alloy heterogeneous double wires. Background Art

[0002] Shape memory alloys are a class of intelligent materials with shape memory effect and superelasticity. After being deformed under specific conditions, when unloaded or heated after unloading, they have the ability to return to their initial shape. This unique function is related to martensitic phase transformation and its reverse transformation. Among them, NiTi-based shape memory alloys have been widely used in fields such as the automotive industry, aerospace, biomedicine, and intelligent manufacturing due to their excellent shape memory effect, superelasticity, biocompatibility, corrosion resistance, low elastic modulus, etc. However, due to the high ductility and work hardening of NiTi-based alloys, there is a large frictional resistance during the machining of NiTi-based alloys, which easily causes serious tool wear and problems such as burrs, resulting in great challenges in the machining and manufacturing of NiTi-based alloys. At the same time, since the structural and functional properties of NiTi-based alloys are significantly affected by the atomic composition ratio, it is difficult to control the atomic composition ratio during the melting and manufacturing of NiTi-based alloys, and impurities are easily absorbed to embrittle the alloy. Therefore, it is difficult to achieve the actual application standards for the performance of NiTi-based alloys prepared by traditional manufacturing methods.

[0003] As a near-net-shape manufacturing method, additive manufacturing technology can achieve the forming of complex shapes by layer-by-layer stacking of materials and heat sources, overcoming the drawbacks of traditional machining and manufacturing methods. Arc additive manufacturing technology uses an arc as the heat source and wire as the raw material, and has the advantages of high heat input, high forming efficiency, high material utilization rate, low preparation cost, low defect level, etc., and is not limited by the forming size, showing cost and efficiency advantages that are difficult to match by other additive manufacturing methods in the forming of large-size complex structural parts.

[0004] However, there are problems such as low phase transformation temperature and large phase transformation hysteresis in arc additive manufacturing of NiTi binary alloys. The martensitic phase transformation start temperature (Ms) and martensitic phase transformation end temperature (Mf) are -30.4°C and -62.9°C respectively, and the reverse phase transformation start temperature (As) and reverse phase transformation end temperature (Af) are -23.4°C and 30.6°C respectively. The corresponding phase transformation hysteresis (Af - Ms) is 61°C, thus limiting its application in some specific occasions such as high-temperature environments. Therefore, designing an arc additive manufacturing method that can regulate the phase transformation behavior of NiTi-based shape memory alloys is a problem that needs to be solved currently. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for additive manufacturing of NiTi-based shape memory alloy heterogeneous double-wire arc, which is used to solve the problems of low phase transformation temperature and large phase transformation hysteresis in existing arc additive manufacturing technology for NiTi binary alloy.

[0006] The present invention solves the above technical problems through the following technical means:

[0007] A method for additive manufacturing of NiTi-based shape memory alloy heterogeneous double-wire arc, wherein the manufacturing method is to feed NiTi alloy wire and metal wire simultaneously through a double-wire arc additive manufacturing device, and use an ultra-high frequency pulsed TIG welding power source to realize the additive manufacturing of NiTi-based shape memory alloy heterogeneous double-wire arc;

[0008] The parameters of the ultra-high frequency pulsed TIG are as follows: the base current is 75 - 100 A, the ultra-high frequency pulsed current is 50 - 60 A, the ultra-high frequency current frequency is 20 - 25 kHz, and the ultra-high frequency current duty cycle is 50%.

[0009] Furthermore, it includes the following steps:

[0010] Substrate pretreatment: Polish the surface of the NiTi substrate with a nylon fiber wheel until it is smooth, then soak it successively in acetone and alcohol solvents, ultrasonically clean for 5 - 15 min, and dry for later use;

[0011] Assembly: Fix the NiTi substrate, and at the same time load the NiTi alloy wire and the metal wire into the double-wire arc additive manufacturing device respectively;

[0012] Double-wire arc additive manufacturing: First, preheat the NiTi substrate with DC TIG, and then use an ultra-high frequency pulsed TIG welding power source to realize the additive manufacturing of NiTi-based shape memory alloy heterogeneous double-wire arc.

[0013] Furthermore, the thickness of the NiTi substrate is 8 - 20 mm to reduce the stress deformation caused by multi-layer deposition.

[0014] Furthermore, the diameters of both the NiTi alloy wire and the metal wire are 0.7 - 1.6 mm, and the metal wire is one of Cu wire, Hf wire, and Zr wire.

[0015] Furthermore, in the step of loading the NiTi alloy wire and the metal wire into the double-wire arc additive manufacturing device respectively, the included angle between the double wire feeding nozzles in the double-wire arc additive manufacturing device and the NiTi substrate is 20 - 30°, and the horizontal included angle between the two feeding nozzles is 50 - 60°, so as to ensure the full mixing of the NiTi alloy wire droplets and the metal droplets before entering the molten pool, and at the same time to ensure that the transition mode of the double-wire droplets is liquid bridge transition.

[0016] Further, in the double-wire arc additive manufacturing step, a local argon shielding cover is required to continuously supply high-purity argon, and the gas flow rate of the argon is 15-20 L / min.

[0017] Further, in the step of preheating the NiTi substrate with DC TIG, the preheating base current is 75-100 A, and the welding torch moving speed is 100-300 mm / min.

[0018] Further, in the realization of the heterogeneous double-wire arc additive manufacturing of NiTi-based shape memory alloy using an ultra-high frequency pulsed TIG welding power source, the arc length is 3-6 mm, the welding torch moving speed is 200-300 mm / min, the wire feeding speed of the NiTi wire is 900-2400 mm / min, and the wire feeding speed of the metal wire is 100-300 mm / min. The above parameter settings are beneficial to the formation of a stable molten pool during the deposition process and finally obtain a NiTi-based shape memory alloy with a beautiful and good forming morphology.

[0019] Further, the deposition time interval for each layer in the double-wire arc additive manufacturing is set to 1-2 min.

[0020] Further, the double-wire arc additive manufacturing device includes a welding torch clamp, a wire feeding nozzle fixing ring, a shielding cover clamp, and a local argon shielding cover. The welding torch clamp is connected to the wire feeding nozzle fixing ring. Two wire feeding nozzle clamps are slidably mounted on the wire feeding nozzle fixing ring. The shielding cover clamp is connected to the wire feeding nozzle fixing ring, and the local argon shielding cover is clamped on the shielding cover clamp.

[0021] The present invention has the following beneficial effects:

[0022] (1) In the additive manufacturing method of the present invention, the heterogeneous double-wire arc additive manufacturing of NiTi shape memory alloy wire and metal wire (such as Cu wire, Hf wire, Zr wire, etc.) is successfully realized;

[0023] (2) In the additive manufacturing method of the present invention, an ultra-high frequency pulsed TIG arc is introduced to improve the microstructure morphology of the heterogeneous double-wire arc additive of NiTi-based shape memory alloy and form fine grains;

[0024] (3) In the additive manufacturing method of the present invention, doping with a third-component alloy element (Cu, Hf, Zr, etc.) can change the phase transformation temperature of the arc additive NiTi-based alloy and improve the phase transformation hysteresis. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the double-wire arc additive manufacturing device of the present invention;

[0026] Figure 2 is a schematic structural diagram of the wire feeding nozzle fixing ring and the wire feeding nozzle clamp in the double-wire arc additive manufacturing device;

[0027] Figure 3 It is a schematic structural diagram of a shielding fixture and a local argon shielding cover in a double-wire arc additive manufacturing device;

[0028] Figure 4 It is an assembly schematic diagram in the NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method of the present invention;

[0029] Figure 5 It is a microstructure morphology diagram of NiTi-Cu shape memory alloy heterogeneous double-wire arc additive manufacturing under ultra-high frequency pulses;

[0030] Figure 6 It is a phase transformation behavior diagram of NiTi-Cu shape memory alloy heterogeneous double-wire arc additive manufacturing under ultra-high frequency pulses;

[0031] Among them, the welding torch fixture 1, the wire feeding nozzle fixing ring 2, the connecting member 31, the connecting ring 311, the L-shaped plate 312, the clamping member 32, the sliding plate 321, the U-shaped frame 322, the local argon shielding cover 4, the mounting plate 51, the connecting plate 52, the wire feeding nozzle clamping ring 53, the angle adjustment through groove 6, the horizontal adjustment through groove 7, the angle adjustment arc groove 8, the sliding column 9, the longitudinal adjustment groove 10, the welding torch 11, the wire feeding nozzle 12. Embodiment

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] For those conditions not specified in the following embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For raw materials, equipment or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0034] The experimental materials NiTi substrate, NiTi alloy wire, and Cu metal wire used in the embodiments of the present invention, in terms of weight percentage of components, among which both the NiTi substrate and the NiTi alloy wire are nickel: 55.62%, oxygen: 0.0342, carbon: 0.007%, iron: 0.007%, and the balance is titanium; the Cu metal wire is copper: 98.56%, tin: 0.93%, manganese: 0.38%, silicon: 0.12%.

[0035] Please refer to Figures 1-3, the double-wire arc additive manufacturing device in the following embodiments includes a welding torch clamp 1, a wire feeding nozzle fixing ring 2, a shielding cover clamp, and a local argon shielding cover 4. The welding torch clamp 1 includes two semi-circular shells arranged oppositely, and the two semi-circular shells are fixedly connected by bolts. The welding torch clamp 1 is connected to the wire feeding nozzle fixing ring 2, and two wire feeding nozzle clamps are slidably installed on the wire feeding nozzle fixing ring 2. Specifically, a through hole for the welding torch 11 to pass through is opened in the middle of the wire feeding nozzle fixing ring 2, and an angle adjustment through groove 6 is also opened on the wire feeding nozzle fixing ring 2. A wire feeding nozzle clamp is slidably installed in the angle adjustment through groove 6. The wire feeding nozzle clamp includes a mounting plate 51, a connecting plate 52, and a wire feeding nozzle clamping ring 53. One end of the mounting plate 51 is slidably installed in the angle adjustment through groove 6 and is limited by bolts. A lateral adjustment through groove 7 is opened on the mounting plate 51. One end of the connecting plate 52 is provided in a screw type, and the screw is slidably installed in the lateral adjustment through groove 7. The relative up and down movement of the connecting plate 52 with respect to the mounting plate 51 is realized by installing nuts on both the upper and lower sides of the mounting plate on the screw. An angle adjustment arc groove 8 is opened on the connecting plate 52. The wire feeding nozzle clamping ring 53 is used to clamp the wire feeding nozzle 12. A sliding column 9 is fixed on the wire feeding nozzle clamping ring 53, and bolts are also installed on the wire feeding nozzle clamping ring 53. The sliding column 9 slidably passes through the angle adjustment arc groove 8 and is limited by bolts. The shielding cover clamp is connected to the wire feeding nozzle fixing ring 2. The shielding cover clamp includes a connecting member 31 and a clamping member 32. The connecting member 31 includes a connecting ring 311 for the welding torch to pass through and an L-shaped plate 312. A longitudinal adjustment groove 10 is opened on the L-shaped plate 312. The clamping member 32 includes a sliding plate 321 and a U-shaped frame 322. Bolts are installed on the sliding plate 321. The bolts on the sliding plate 321 pass through the longitudinal adjustment groove 10. The sliding plate 321 can slide relative to the L-shaped plate 312 and is limited by bolts. The U-shaped frame 322 is used to clamp the local argon shielding cover 4 and is fixed by bolts.

[0036] The two wire feeding nozzle clamps slidably installed in the angle adjustment through groove 6 of the above double-wire arc additive manufacturing device can realize the angle adjustment between the two wire feeding nozzle clamps; the structural setting of the wire feeding nozzle clamp can realize the lateral position, longitudinal position, and angle adjustment of the wire feeding nozzle, and is flexible and convenient to use. At the same time, the structural setting of the shielding cover clamp can also realize the longitudinal position adjustment of the local argon shielding cover.

[0037] The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method of the present invention is to simultaneously feed NiTi alloy wire and metal wire through a double-wire arc additive manufacturing device, and use an ultra-high frequency pulsed TIG welding power source to realize the NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing. Specifically, it includes the following steps:

[0038] Substrate pretreatment: Polish the surface of the NiTi substrate smooth with a nylon fiber wheel, soak it in acetone solvent for ultrasonic cleaning for 5 - 15 min, then soak it in alcohol solvent for ultrasonic cleaning for 5 - 15 min, and dry it for later use.

[0039] Assembly: Please refer to Figure 4 , fix the NiTi substrate, and at the same time load the NiTi alloy wire and the metal wire into the double-wire arc additive manufacturing device respectively. Among them, the diameters of the NiTi alloy wire and the metal wire are both 0.7 - 1.6 mm, the metal wire is one of Cu wire, Hf wire, and Zr wire, the angle between the double wire feeding nozzles in the double-wire arc additive manufacturing device and the NiTi substrate is 20 - 30°, and the horizontal angle between the two wire feeding nozzles is 50 - 60°.

[0040] Double-wire arc additive manufacturing: First, preheat the NiTi substrate with DC TIG, and then use an ultra-high frequency pulsed TIG welding power source to realize the heterogeneous double-wire arc additive manufacturing of NiTi-based shape memory alloy.

[0041] The purpose of preheating is to increase the temperature of the local area of the NiTi substrate to be deposited, reduce the temperature difference between the NiTi substrate and the molten metal, and avoid cracking of the deposited layer. In the present invention, no specific limitations are imposed on the preheating temperature and time, and it is only necessary to ensure that the temperature before deposition is 100 ± 50 °C after preheating. The preheating base current is 75 - 100 A, and the welding torch moving speed is 100 - 300 mm / min.

[0042] The parameters of the ultra-high frequency pulsed TIG are as follows: the base current is 75 - 100 A, the ultra-high frequency pulsed current is 50 - 60 A, the ultra-high frequency current frequency is 20 - 25 kHz, the ultra-high frequency current duty cycle is 50%, in additive manufacturing, the arc length is 3 - 6 mm, the welding torch moving speed is 200 - 300 mm / min, the feeding speed of the NiTi wire is 900 - 2400 mm / min, preferably 1500 - 2400 mm / min, and the feeding speed of the metal wire is 100 - 300 mm / min. The ultra-high frequency pulsed TIG can ensure that the NiTi wire and the Cu (or Hf or Zr) wire can be fully and evenly melted, and the obtained microstructure morphology of the NiTi-Cu (or Hf or Zr) shape memory alloy is fine grains.

[0043] The following will illustrate the above-mentioned heterogeneous double-wire arc additive manufacturing method of NiTi-based shape memory alloy through Examples 1 - 4: Example

[0044] In this example, the heterogeneous double-wire arc additive manufacturing method of NiTi-based shape memory alloy under ultra-high frequency pulses includes the following steps:

[0045] Substrate pretreatment: First, polish the surface of the 8-mm-thick NiTi substrate smoothly with a nylon fiber disc, then soak the NiTi substrate in acetone solvent and ultrasonically clean it for 5 minutes, and then soak it in alcohol solvent and ultrasonically clean it for 5 minutes to remove the surface oil. In this embodiment, the specific parameters of ultrasonic cleaning are not limited as long as the oil on the surface of the NiTi substrate can be cleaned, and then dry it for later use.

[0046] Assembly: Please refer to Figure 4 , fix the NiTi substrate on the working platform with a fixture. At the same time, load NiTi alloy wires and Cu metal wires with a diameter of 0.7 mm into the double wire feeding system respectively. The included angle between the double wire feeding nozzles and the NiTi substrate is 20°, and the horizontal included angle between the double wire feeding nozzles is 50°.

[0047] Dual-wire arc additive manufacturing: Use a local argon shielding cover to continuously supply high-purity argon to reduce oxidation. The gas flow rates of the local argon shielding cover and the welding torch are both 15 L / min. Preheat the NiTi substrate by DC TIG, with a preheating base current of 75 A and a preheating welding torch moving speed of 100 mm / min. Then use ultra-high frequency pulsed TIG for NiTi-based heterogeneous dual-wire arc additive manufacturing. The ultra-high frequency pulsed TIG current parameters are: base current 75 A, ultra-high frequency pulsed current 50 A, ultra-high frequency current frequency 20 kHz, and ultra-high frequency current duty cycle 50%; the dual-wire arc additive manufacturing parameters are: arc length 3 mm, welding torch moving speed 200 mm / min, NiTi wire feeding speed 1500 mm / min, Cu metal wire feeding speed 100 mm / min, and the deposition time interval for each layer is 1 minute. Example

[0048] In this embodiment, the method for NiTi-based shape memory alloy heterogeneous dual-wire arc additive manufacturing under ultra-high frequency pulses includes the following steps:

[0049] Substrate pretreatment: First, polish the surface of the 20-mm-thick NiTi substrate smoothly with a nylon fiber disc, then soak the NiTi substrate in acetone solvent and ultrasonically clean it for 15 minutes, and then soak it in alcohol solvent and ultrasonically clean it for 15 minutes to remove the surface oil. In this embodiment, the specific parameters of ultrasonic cleaning are not limited as long as the oil on the surface of the NiTi substrate can be cleaned, and then dry it for later use.

[0050] Assembly: Please refer to Figure 4 , fix the NiTi substrate on the working platform with a fixture. At the same time, load NiTi alloy wires and Cu metal wires with a diameter of 1.6 mm into the double wire feeding system respectively. The included angle between the double wire feeding nozzles and the NiTi substrate is 30°, and the horizontal included angle between the double wire feeding nozzles is 60°.

[0051] Dual-wire arc additive manufacturing: A local argon shielding cover is used to continuously supply high-purity argon to reduce oxidation. The gas flow rates of both the local argon shielding cover and the welding torch are 20 L / min. The NiTi substrate is preheated by DC TIG with a preheating base current of 100 A and a preheating welding torch travel speed of 300 mm / min. Then, ultra-high-frequency pulsed TIG is used for NiTi-based heterogeneous dual-wire arc additive manufacturing. The ultra-high-frequency pulsed TIG current parameters are: base current 100 A, ultra-high-frequency pulsed current 60 A, ultra-high-frequency current frequency 25 kHz, and ultra-high-frequency current duty cycle 50%. The dual-wire arc additive manufacturing parameters are: arc length 6 mm, welding torch travel speed 300 mm / min, NiTi wire feeding speed 2400 mm / min, Cu metal wire feeding speed 300 mm / min, and the deposition time interval for each layer is 2 min. Example

[0052] In this example, the method for NiTi-based shape memory alloy heterogeneous dual-wire arc additive manufacturing under ultra-high-frequency pulses includes the following steps:

[0053] Substrate pretreatment: First, the surface of the 16-mm-thick NiTi substrate is polished smoothly with a nylon fiber disc, then the NiTi substrate is immersed in an acetone solvent and ultrasonically cleaned for 12 min, and then immersed in an alcohol solvent and ultrasonically cleaned for 12 min to remove surface oil stains. In this example, no specific parameters for ultrasonic cleaning are restricted as long as the surface oil stains of the NiTi substrate can be cleaned, and then it is dried for use.

[0054] Assembly: Please refer to Figure 4 , fix the NiTi substrate on the working platform with a fixture. At the same time, load the NiTi alloy wire and the Cu metal wire with a diameter of 1.2 mm into the dual wire feeding system respectively. The angle between the dual wire feeding nozzles and the NiTi substrate is 25°, and the horizontal angle between the dual wire feeding nozzles is 55°.

[0055] Dual-wire arc additive manufacturing: A local argon shielding cover is used to continuously supply high-purity argon to reduce oxidation. The gas flow rates of both the local argon shielding cover and the welding torch are 18 L / min. The NiTi substrate is preheated by DC TIG with a preheating base current of 80 A and a preheating welding torch travel speed of 200 mm / min. Then, ultra-high-frequency pulsed TIG is used for NiTi-based heterogeneous dual-wire arc additive manufacturing. The ultra-high-frequency pulsed TIG current parameters are: base current 85 A, ultra-high-frequency pulsed current 55 A, ultra-high-frequency current frequency 20 kHz, and ultra-high-frequency current duty cycle 50%. The dual-wire arc additive manufacturing parameters are: arc length 5 mm, welding torch travel speed 280 mm / min, NiTi wire feeding speed 2000 mm / min, Cu metal wire feeding speed 170 mm / min, and the deposition time interval for each layer is 1 min. Example

[0056] In this embodiment, the method for additive manufacturing of NiTi-based shape memory alloy heterogeneous double wires by ultra-high frequency pulse arc includes the following steps:

[0057] Substrate pretreatment: First, the surface of the 15-mm-thick NiTi substrate is polished smoothly with a nylon fiber wheel, and then the NiTi substrate is immersed in acetone solvent and ultrasonically cleaned for 10 min, and then immersed in alcohol solvent and ultrasonically cleaned for 10 min to remove surface oil stains. In this embodiment, the specific parameters of ultrasonic cleaning are not limited as long as the oil stains on the surface of the NiTi substrate can be cleaned, and then it is dried for use.

[0058] Assembly: Please refer to Figure 4 , fix the NiTi substrate on the working platform with a fixture, and at the same time, load NiTi alloy wire with a diameter of 1.0 mm and Cu metal wire into the double wire feeding system respectively. The included angle between the double wire feeding nozzles and the NiTi substrate is 20°, and the horizontal included angle between the double wire feeding nozzles is 60°.

[0059] Double wire arc additive manufacturing: Use a local argon shielding cover to continuously supply high-purity argon to reduce oxidation. The gas flow rates of the local argon shielding cover and the welding torch are both 15 L / min. Preheat the NiTi substrate by DC TIG, with a preheating base current of 100 A and a preheating welding torch moving speed of 100 mm / min. Then use ultra-high frequency pulse TIG to carry out additive manufacturing of NiTi-based heterogeneous double wires. The current parameters of ultra-high frequency pulse TIG are: base current 100 A, ultra-high frequency pulse current 60 A, ultra-high frequency current frequency 20 kHz, and ultra-high frequency current duty cycle 50%; the parameters of double wire arc additive manufacturing are: arc length 3 mm, welding torch moving speed 300 mm / min, NiTi wire feeding speed 2200 mm / min, Cu metal wire feeding speed 240 mm / min, and the deposition time interval for each layer is 1 min.

[0060] In this embodiment, from Figure 5 the microstructure diagram, it can be seen that a large number of fine grains are formed in the additive manufacturing of NiTi-Cu shape memory alloy heterogeneous double wires under ultra-high frequency pulse, which is beneficial to improving the internal microstructure of NiTi-based shape memory alloy. From Figure 6From the phase change behavior diagram, it can be seen that for the NiTi-Cu shape memory alloy fabricated by heterogeneous double-wire arc additive manufacturing under ultra-high frequency pulses, the martensitic phase transformation start temperature (Ms) and the martensitic phase transformation end temperature (Mf) are 86.2 °C and 61 °C respectively, the reverse phase transformation start temperature (As) and the reverse phase transformation end temperature (Af) are 48.7 °C and 74 °C respectively, and the corresponding phase transformation hysteresis (Af - Ms) is -12.2 °C. By comparing with the phase transformation temperature and phase transformation hysteresis of the arc additive manufactured NiTi binary shape memory alloy, it can be found that the phase transformation temperature of the NiTi-Cu shape memory alloy fabricated by heterogeneous double-wire arc additive manufacturing under ultra-high frequency pulses is significantly increased, and at the same time, the phase transformation hysteresis is significantly narrowed. Therefore, the results show that the additive manufacturing method of the present invention realizes the heterogeneous double-wire arc additive manufacturing of NiTi alloy wire and Cu metal wire by doping the third component Cu element and using an ultra-high frequency pulse TIG arc, and changes the phase transformation temperature of the arc additive manufactured NiTi-based alloy, while improving the phase transformation hysteresis and microstructure morphology, thus being beneficial to stabilizing and improving the performance of the NiTi-based alloy, broadening the application field of the NiTi-based ternary alloy, and providing an effective solution for the arc additive manufacturing of NiTi-based shape memory alloys.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention. The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A method for additive manufacturing of NiTi-based shape memory alloy heterogeneous double wires by arc, characterized in that, The manufacturing method is to feed NiTi alloy wire and metal wire simultaneously through a twin-wire arc additive manufacturing device, and use an ultra-high frequency pulsed TIG welding power source to achieve the heterogeneous twin-wire arc additive manufacturing of NiTi-based shape memory alloy. The metal wire is one of Cu wire, Hf wire, and Zr wire; The parameters of the ultra-high frequency pulsed TIG are as follows: the base current is 75 - 100 A, the ultra-high frequency pulsed current is 50 - 60 A, the ultra-high frequency current frequency is 20 - 25 kHz, and the ultra-high frequency current duty cycle is 50%; In the twin-wire arc additive manufacturing device, a NiTi substrate is fixed. The angle between the twin wire feeding nozzles in the twin-wire arc additive manufacturing device and the NiTi substrate is 20 - 30°, and the horizontal angle between the two wire feeding nozzles is 50 - 60°.

2. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 1, wherein, It includes the following steps: Substrate pretreatment: Polish the surface of the NiTi substrate with a nylon fiber disc until it is smooth, then soak it successively in acetone and alcohol solvents, and simultaneously perform ultrasonic cleaning for 5 - 15 min, and dry it for later use; Assembly: Fix the NiTi substrate, and at the same time load the NiTi alloy wire and the metal wire into the twin-wire arc additive manufacturing device respectively; Twin-wire arc additive manufacturing: First, preheat the NiTi substrate with DC TIG, and then use an ultra-high frequency pulsed TIG welding power source to achieve the heterogeneous twin-wire arc additive manufacturing of NiTi-based shape memory alloy.

3. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 2, characterized in that, The thickness of the NiTi substrate is 8 - 20 mm.

4. The NiTi-based shape memory alloy heterogeneous dual-wire arc additive manufacturing method according to claim 2, wherein The diameters of the NiTi alloy wire and the metal wire are both 0.7 - 1.6 mm.

5. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 2, wherein In the twin-wire arc additive manufacturing step, a local argon shielding cover is required to continuously supply high-purity argon, and the gas flow rate of the argon is 15 - 20 L / min.

6. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 5, wherein, In the step of preheating the NiTi substrate with DC TIG, the preheating base current is 75 - 100 A, and the welding torch moving speed is 100 - 300 mm / min.

7. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 6, wherein In the process of using an ultra-high frequency pulsed TIG welding power source to achieve the heterogeneous twin-wire arc additive manufacturing of NiTi-based shape memory alloy, the arc length is 3 - 6 mm, the welding torch moving speed is 200 - 300 mm / min, the wire feeding speed of the NiTi wire is 900 - 2400 mm / min, and the wire feeding speed of the metal wire is 100 - 300 mm / min.

8. The method for additive manufacturing of NiTi-based shape memory alloy heterogeneous double wires by arc welding according to any one of claims 1-7, characterized in that, The deposition time interval for each layer in the twin-wire arc additive manufacturing is set to 1 - 2 min.

9. The NiTi-based shape memory alloy heterogeneous double-wire arc additive manufacturing method according to claim 1, wherein, The twin-wire arc additive manufacturing device includes a welding torch fixture, a wire feeding nozzle fixing ring, a shielding cover fixture, and a local argon shielding cover. The welding torch fixture is connected to the wire feeding nozzle fixing ring. Two wire feeding nozzle fixtures are slidably installed on the wire feeding nozzle fixing ring. The shielding cover fixture is connected to the wire feeding nozzle fixing ring, and the local argon shielding cover is clamped on the shielding cover fixture.

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