Post-treatment method for improving functional fatigue performance of electric arc additive manufacturing NiTi alloy
Through the composite post-treatment method of heat treatment and laser impact enhancement, the problem of poor functional fatigue performance of NiTi alloys manufactured by arc additive is solved, and the effect of significantly improving functional fatigue performance is achieved.
Patent Information
- Application Number
- CN202510413776.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-03
- Publication Date
- 2025-06-24
AI Technical Summary
NiTi alloys manufactured by arc additives are prone to dendrite segregation and other problems, resulting in superelastic functional fatigue failure. The existing heat treatment methods have limited effect in improving functional fatigue performance.
The composite post-treatment method of heat treatment and laser impact strengthening is adopted, including solid solution and aging treatment after the NiTi alloy is manufactured by arc additives, and the grain size is refined through laser impact strengthening and the distribution of precipitation phase is regulated.
The functional fatigue performance of the NiTi alloys of arc additive manufacturing was significantly improved, and the treated materials showed excellent residual strain reduction and phase transition platform stress improvement in functional fatigue tests.
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Figure CN120193218A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of arc additive manufacturing, and particularly relates to a post-treatment method for improving the functional fatigue performance of NiTi alloys manufactured by arc additive manufacturing. Background Art
[0002] NiTi shape memory alloys are widely used in fields such as aerospace and medical implants due to their unique shape memory effect and superelasticity. However, NiTi alloys are prone to problems such as poor chips and severe tool wear during traditional machining, making it difficult to produce NiTi alloy parts with complex shapes. Additive manufacturing technology can efficiently prepare complex structures that are difficult to form by traditional processes by stacking materials layer by layer, providing a new approach for the precision manufacturing of NiTi alloys. Among them, arc wire additive manufacturing has become an important option for the large-scale preparation of NiTi alloys due to its high deposition rate, low material waste rate, and equipment cost advantages. In arc additive manufacturing, an arc heat source melts the wire and deposits it layer by layer to finally manufacture the target part. Currently, arc additive manufacturing of NiTi alloys is prone to problems such as dendritic segregation, resulting in superelastic functional fatigue failure, that is, the degradation of specific functional characteristics including recoverable strain and plateau stress occurs during mechanical or thermal cycling. Therefore, it is necessary to improve the functional fatigue performance of arc additive manufacturing NiTi alloys through post-treatment technology.
[0003] Heat treatment, as a commonly used post-treatment method to improve the functional fatigue performance of additive manufacturing NiTi alloys, can release the internal stress during the additive process, regulate the microstructure and phase transformation behavior, and promote the precipitation of fine Ni4Ti3 precipitates, thereby facilitating the improvement of the functional fatigue performance of NiTi alloys. However, with the increase in heat treatment temperature and time, it is easy to accelerate the growth and coarsening of the precipitate phase, and the coarse precipitate phase is not conducive to the improvement of functional fatigue performance, resulting in limited improvement in the functional fatigue performance of NiTi alloys. Therefore, it is necessary to consider how to further improve the functional fatigue performance of arc additive manufacturing NiTi alloys on the basis of heat treatment. Since laser shock peening can refine the grain size, introduce residual compressive stress, and regulate the precipitate phase distribution at the same time, this is conducive to improving the functional fatigue performance of arc additive manufacturing NiTi alloys. Therefore, combining laser shock peening with heat treatment can further improve the functional fatigue performance, providing a method guidance for improving the functional fatigue performance of arc additive manufacturing NiTi alloys. Summary of the Invention
[0004] In view of this, the purpose of the present invention is to provide a post-treatment method for improving the functional fatigue performance of arc additive manufacturing NiTi alloys, which is used to solve the problem of poor functional fatigue performance of NiTi alloys in existing NiTi alloy arc additive manufacturing technology.
[0005] A post-treatment method for improving the functional fatigue performance of NiTi alloy by arc additive manufacturing, comprising the following steps:
[0006] S1: Use NiTi wire to perform arc additive manufacturing on a NiTi substrate to obtain an additive NiTi alloy component, and prepare a as-deposited NiTi alloy sample by wire cutting.
[0007] S2: Place the as-deposited NiTi alloy sample in a heat treatment furnace, raise the temperature to 950 °C at a heating rate of 10 °C / min, hold for 120 min in the furnace, then take it out and quickly quench in water to complete the solution treatment.
[0008] S3: Put the solution-treated NiTi alloy sample back into the heat treatment furnace again, raise the temperature to 450 °C at a heating rate of 10 °C / min, hold for 120 min and then take it out, and quickly quench in water to complete the aging treatment, obtaining an aged NiTi alloy sample.
[0009] S4: Process the aged NiTi alloy sample into the required shape, polish it smoothly with 120# - 3000# sandpaper, clean it with alcohol, dry it and then perform laser shock peening to complete the post-treatment of the NiTi alloy sample.
[0010] Furthermore, the NiTi wire is a superelastic NiTi wire with a diameter of 0.7 mm, and the size of the NiTi substrate is 200×100×15 mm.
[0011] Furthermore, in the arc additive manufacturing step, set the ultra-high frequency pulse current as the base current of 75 A and the rectangular pulse current of 50 A. The welding torch moving speed is 300 mm / min, the NiTi wire feeding speed is 900 mm / min, the angle between the wire and the substrate is 30°, and the length of the front end of the tungsten electrode is 2.3 cm. Before additive manufacturing, preheat the substrate with DC TIG, the preheating current is the base current of 100 A, and the preheating temperature and the interlayer temperature are about 100 °C.
[0012] Furthermore, in the arc additive manufacturing step, continuously introduce 15 L / min of high-purity argon gas into the TIG welding torch and the local gas protection device to reduce oxidation.
[0013] Furthermore, in the heat treatment step, continuously introduce high-purity argon gas with a flow rate of 15 L / min for protection to reduce oxidation.
[0014] Furthermore, in the laser shock peening step, the laser wavelength is 1064 nm, the pulse width is 15 ns, the spot diameter is 2.5 mm, the impact path is Z-shaped, the spot overlap rate is 50% - 70%, the laser energy is 1 - 10 J, and the number of impacts is 1 - 5 times.
[0015] Further, in the laser shock peening step, a 3M aluminum foil is attached to the surface of the specimen as an absorption layer, and flowing water with a thickness of 1 - 2 mm is used as a constraint layer.
[0016] The present invention has the following beneficial effects:
[0017] (1) The post - treatment method of the present invention can better improve the microstructure morphology of the arc - additive - manufactured NiTi alloy. After treatment, the grain size of the arc - additive - manufactured NiTi alloy decreases, and the precipitation of beneficial Ni4Ti3 increases.
[0018] (2) The present invention uses heat treatment and laser shock peening for composite post - treatment of the arc - additive - manufactured NiTi alloy, effectively improving the functional fatigue performance of the material. After treatment, the arc - additive - manufactured NiTi alloy shows a significant reduction in residual strain at different cycle numbers and a significant increase in the phase - transformation plateau stress in the functional fatigue test, demonstrating excellent functional fatigue performance. Description of the Drawings
[0019] Figure 1 is the flow chart of the present invention;
[0020] Figure 2 is the schematic diagram of the tensile specimen size used in the present invention, where the laser shock peening area is marked;
[0021] Figure 3 is the grain orientation map of Example 1 and Comparative Example 1 of the present invention, where (a) is Comparative Example 1 and (b) is Example 1;
[0022] Figure 4 is the phase diagram of Example 1 and Comparative Example 1 of the present invention, where (a) is Comparative Example 1 and (b) is Example 1;
[0023] Figure 5 is the histogram of grain size statistics of Example 1 and Comparative Example 1 of the present invention, where (a) is Comparative Example 1 and (b) is Example 1;
[0024] Figure 6 is the functional fatigue test results of Example 1 and Comparative Example 1 of the present invention, where (a) is the stress - strain curve of Comparative Example 1, (b) is the stress - strain curve of Example 1, (c) is the curve of residual strain vs. cycle number of Comparative Example 1, and (d) is the curve of residual strain vs. cycle number of Example 1. Detailed Embodiments
[0025] 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0026] The test materials used in the embodiments of the present invention are NiTi substrates and NiTi alloy wires.
[0027] A post-treatment method for improving the functional fatigue performance of NiTi alloy by arc additive manufacturing of the present invention prepares NiTi alloy by arc additive manufacturing, and performs solution and aging heat treatments, as well as laser shock peening. Specifically, it includes the following steps:
[0028] S1: Use NiTi wire to perform arc additive manufacturing on the NiTi substrate to obtain a NiTi alloy additive component, and use wire cutting to obtain a as-deposited NiTi alloy sample. The NiTi wire is a superelastic NiTi wire with a diameter of 0.7 mm, and the size of the NiTi substrate is 200×100×15 mm.
[0029] Further, in the arc additive manufacturing step, the ultra-high frequency pulsed current is set to a base current of 75 A and a rectangular pulsed current of 50 A. The welding torch moving speed is 300 mm / min, the NiTi wire feeding speed is 900 mm / min, the angle between the wire and the substrate is 30°, and the length of the front end of the tungsten electrode is 2.3 cm. Before additive manufacturing, the substrate is preheated with DC TIG, the preheating current is the base current of 100 A, and the preheating temperature and the interlayer temperature are about 100°C. During additive manufacturing, high-purity argon with a flow rate of 15 L / min is continuously introduced into the TIG welding torch and the local gas protection device to reduce oxidation.
[0030] S2: Put the as-deposited NiTi alloy sample into a heat treatment furnace, raise the temperature to 950°C at a heating rate of 10°C / min, take it out after holding for 120 min in the furnace, and quickly quench it in water to complete the solution treatment.
[0031] S3: Put the solution-treated NiTi alloy sample into the heat treatment furnace again, raise the temperature to 450°C at a heating rate of 10°C / min, take it out after holding for 120 min, and quickly quench it in water to complete the aging treatment to obtain an aged NiTi alloy sample. During the heat treatment steps, high-purity argon with a flow rate of 15 L / min is continuously introduced for protection to reduce oxidation.
[0032] S4: Process the aged NiTi alloy sample into the required shape, polish it smoothly with 120# - 3000# sandpaper, clean it with alcohol, dry it, and then perform laser shock peening to complete the post-treatment of the NiTi alloy sample.
[0033] Furthermore, in the laser shock peening step, the laser wavelength is 1064 nm, the pulse width is 15 ns, the spot diameter is 2.5 mm, the shock path is zigzag, the spot overlap rate is 50% - 70%, the laser energy is 1 - 10 J, and the number of shocks is 1 - 5 times.
[0034] Furthermore, in the laser shock peening step, a 3M aluminum foil is pasted on the surface of the specimen as the absorption layer, and flowing water with a thickness of 1 - 2 mm is used as the constraint layer.
[0035] The following will illustrate the above post - treatment method for improving the functional fatigue performance of arc - additive - manufactured NiTi alloy through Example 1 and Comparative Example 1:
[0036] Example 1
[0037] In this example, a post - treatment method for improving the functional fatigue performance of arc - additive - manufactured NiTi alloy includes the following steps:
[0038] Step 1: Fix a NiTi substrate with dimensions of 200×100×15 mm. Preheat the substrate using DC TIG. The preheating current is the base current of 100 A, and the preheating temperature and interlayer temperature are approximately 100°C. Adjust the ultra - high - frequency pulsed current to the base current of 75 A and the rectangular pulsed current to 50 A. The welding torch moving speed is 300 mm / min, the wire feeding speed of the NiTi wire is 900 mm / min, the angle between the wire and the substrate is 30°, and the length of the front end of the tungsten electrode is 2.3 cm. Start the power supply and wire feeder to deposit a superelastic NiTi wire with a diameter of 0.7 mm onto the NiTi substrate. During this process, continuously introduce high - purity argon at a flow rate of 15 L / min into the TIG welding torch and the local gas protection device to reduce oxidation. Deposit five layers to obtain an additive component, and use wire cutting to obtain a as - deposited NiTi alloy sample.
[0039] Step 2: Put the as - deposited NiTi alloy sample into a heat treatment furnace, continuously introduce high - purity argon at a flow rate of 15 L / min for protection, raise the temperature to 950°C at a heating rate of 10°C / min, hold for 120 min in the furnace and then take it out, and quickly quench it in water to complete the solution treatment, obtaining a solution - treated NiTi alloy sample.
[0040] Step 3: Put the solution - treated NiTi alloy sample into a heat treatment furnace, continuously introduce high - purity argon at a flow rate of 15 L / min for protection, raise the temperature to 450°C at a heating rate of 10°C / min, hold for 120 min in the furnace and then take it out, and quickly quench it in water to complete the aging treatment, obtaining an aged NiTi alloy sample.
[0041] Step 4: Use wire cutting to process the aged NiTi alloy sample into asFigure 2 The shape of the specimen shown was polished smoothly with 120# - 3000# sandpaper, cleaned with alcohol and dried. A 3M aluminum foil was pasted on the specimen surface as the absorption layer, and flowing water was passed through to cover the aluminum foil surface as the constraint layer, with the thickness of the constraint layer being 1 mm. In laser shock peening, the laser wavelength was 1064 nm, the pulse width was 15 ns, the spot diameter was 2.5 mm, the spot overlap rate was 50%, the shock path was zigzag, the laser energy was 5 J, and the number of shocks was 3 times. After each shock, the absorption layer was replaced to obtain the laser shock peened NiTi sample.
[0042] Comparative Example 1
[0043] The preparation method of Comparative Example 1 was basically the same as that of Example 1, except that: laser shock peening in step 4 was not carried out, and an aged NiTi alloy sample was obtained.
[0044] The following tests were carried out on the NiTi alloy samples prepared in the above examples and comparative examples.
[0045] 1. Microstructural characteristics
[0046] Electron backscatter diffraction microscopy was used to observe Example 1 and Comparative Example 1. Figure 3 is the grain orientation map of the specimen, where (a) is Comparative Example 1 and (b) is Example 1. From Figure 3 it can be seen that both specimens are columnar crystal structures and no obvious substructures are found. The grain orientation of Comparative Example 1 is mainly
[111] , while Example 1 has no obvious preferred orientation.
[0047] Figure 4 is the phase diagram of the specimen, where (a) is Comparative Example 1 and (b) is Example 1. From Figure 4 it can be seen that at room temperature, the matrix of both specimens is mainly composed of B2 phase, and there are also a small amount of Ni4Ti3 phase and R phase precipitates. By comparing the two specimens, it can be found that the precipitate distribution in Example 1 is more and more uniform than that in Comparative Example 1. Specifically, the proportion of Ni4Ti3 in Comparative Example 1 is 5.6%, while the proportion of Ni4Ti3 in Example 1 is 11.2%, indicating that the post-treatment method of the present invention can effectively promote the precipitation of Ni4Ti3. The precipitation of Ni4Ti3 is beneficial to the functional fatigue performance of the NiTi alloy. Therefore, the Ni4Ti3 precipitate distribution in Example 1 is more conducive to the improvement of the functional fatigue performance.
[0048] Figure 5 is the statistical chart of the grain size of the specimen, where (a) is Comparative Example 1 and (b) is Example 1. From Figure 5It can be seen that the grain sizes in Example 1 are mostly below 200 μm, while grains exceeding 300 μm appear in Comparative Example 1. The average grain size of Example 1 is 80.47 μm, while that of Comparative Example 1 is 56.77 μm. The grain size of Example 1 is significantly smaller than that of Comparative Example 1, indicating that the post-treatment method of the present invention effectively refines the grains of the arc additive manufacturing specimens. Grain refinement can inhibit crack initiation under low-cycle fatigue and improve the functional fatigue performance of the material.
[0049] 2. Functional fatigue performance test
[0050] The functional fatigue performance tests were carried out on Example 1 and Comparative Example 1 of the present invention. During the test, the maximum tensile strain was set to 7%, and the number of cycles was 25. The test results are as Figure 6 shown, where (a) is the stress-strain curve of Comparative Example 1, (b) is the stress-strain curve of Example 1. In the figure, the red curve is the first tensile cycle, the light blue curve is the 2nd to 24th cycles, and the dark blue curve is the 25th cycle; (c) is the curve of the residual strain of Comparative Example 1 changing with the number of cycles, (d) is the curve of the residual strain of Example 1 changing with the number of cycles, where the red curve represents the recoverable strain and the black curve represents the residual strain.
[0051] It can be seen from Figure 6 that the phase transformation plateau stress of Example 1 is increased from 297 MPa to 353 MPa (an increase of 18.7%) compared with Comparative Example 1. The residual strains of both Example 1 and Comparative Example 1 gradually increase with the increase in the number of cycles, but Example 1 shows better stability during the tensile cycle. Specifically, after 25 cycles, the residual strain of Comparative Example 1 increases from the initial 2.94% to 3.43%, while the residual strain of Example 1 only increases from the initial 0.73% to 1.23%, indicating that the functional fatigue performance of Example 1 is significantly improved, showing that the laser shock peening post-treatment method for arc additive manufacturing NiTi alloys of the present invention can effectively inhibit the accumulation of residual strain during the tensile cycle, delay functional degradation, and improve the functional fatigue performance.
[0052] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that those of ordinary skill in the art should understand that several modifications and substitutions made without departing from the concept of the present invention all belong to the protection scope 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 post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing, characterized in that: The following steps are involved: S1: Arc additive manufacturing was performed on NiTi substrate using NiTi wire to obtain additive NiTi alloy parts, and deposited NiTi alloy samples were prepared using wire cutting. S2: The deposited NiTi alloy sample is placed in a heat treatment furnace, and the temperature is raised to 950°C at a heating rate of 10°C / min. After being kept in the furnace for 120 minutes, the sample is taken out and quickly quenched in water to complete the solution treatment. S3: The NiTi alloy sample after the solution treatment is put into the heat treatment furnace again, and the temperature is increased to 450°C at a heating rate of 10°C / min. After keeping the temperature for 120 minutes, it is taken out and quickly quenched in water to complete the aging treatment, thereby obtaining the aged NiTi alloy sample. S4: The aged NiTi alloy sample is processed into a desired shape, polished with 120# to 3000# sandpaper, cleaned with alcohol, dried, and then laser shock strengthened to complete the post-processing of the NiTi alloy sample.
2. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: In the arc additive manufacturing process, the NiTi wire is a superelastic NiTi wire with a diameter of 0.7 mm, and the size of the NiTi substrate is 200×100×15 mm.
3. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: In the arc additive step, the ultra-high frequency pulse current is set to a base current of 75A and a rectangular pulse current of 50A; the welding gun movement speed is 300mm / min, the NiTi wire feeding speed is 900mm / min, the angle between the wire and the substrate is 30°, and the front end length of the tungsten electrode is 2.3cm; before additive, the substrate is preheated with DC TIG, the preheating current is a base current of 100A, and the preheating temperature and the interlayer temperature are about 100°C.
4. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: During the arc addition step, 15 L / min of high-purity argon gas is continuously introduced into the TIG welding torch and the local gas protection device to reduce oxidation.
5. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: During the heat treatment step, high-purity argon gas with a flow rate of 15 L / min was continuously introduced for protection to reduce oxidation.
6. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: In the laser shock strengthening step, the laser wavelength is 1064nm, the pulse width is 15ns, the spot diameter is 2.5mm, the shock path is Z-shaped, the spot overlap rate is 50% to 70%, the laser energy is 1 to 10J, and the number of shocks is 1 to 5 times.
7. A post-processing method for improving the functional fatigue performance of NiTi alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: In the laser shock peening step, a 3M aluminum foil is attached to the surface of the sample as an absorption layer, and flowing water with a thickness of 1 to 2 mm is used as a constraint layer.