Preparation method of nickel-titanium alloy memory ring for underwear

Abstract

The invention relates to a preparation method of a nickel-titanium alloy memory ring for underwear. The preparation method comprises the following steps: manufacturing a nickel-titanium alloy wire rod according to requirements; the prepared nickel-titanium alloy wire rod is subjected to multiple times of drawing treatment, and a nickel-titanium alloy wire is obtained; performing multi-pass rolling on the nickel-titanium alloy wire to obtain a nickel-titanium alloy flat wire; each rolling pass comprises plastic deformation and stress deformation treatment; wherein in at least one rolling pass, after the nickel-titanium alloy wire is subjected to plastic deformation, free deformation areas on the two sides of the nickel-titanium alloy wire in the width direction of the nickel-titanium alloy wire are immediately subjected to selective ultrafast cooling, and meanwhile, a center deformation constraint area of the nickel-titanium alloy wire is subjected to heat preservation; therefore, a non-uniform residual stress distribution of which the side part is compressive stress and the center is neutral or weak tensile stress is constructed in the flat wire; the obtained nickel-titanium alloy flat wire is subjected to hot forming treatment, and the nickel-titanium alloy memory ring is obtained; the obtained nickel-titanium alloy memory ring is subjected to surface cleaning, and the prepared memory ring has the effects of being free of microcracks, high in size precision and free of surface pollution.

Description

Technical Field

[0001] This invention relates to the field of nickel-titanium alloy processing technology, and in particular to a method for preparing nickel-titanium alloy memory rings for underwear. Background Technology

[0002] Nickel-titanium (NiTi) shape memory alloys are widely used in medical devices, aerospace, and high-end consumer goods due to their unique superelasticity (pseudoelasticity) and shape memory effect. In recent years, they have also been introduced into the underwear industry for manufacturing memory rings with excellent shaping and recovery capabilities. However, applying NiTi alloys to textiles that come into direct contact with the skin and require frequent washing places extremely stringent requirements on their manufacturing processes.

[0003] The current production of nickel-titanium alloy memory wire for underwear mainly uses traditional metal wire processing technology, which presents the following prominent technical problems: Low dimensional accuracy and microcrack defects: Existing production processes typically employ a linear flow of "melting-hot rolling-cold drawing-cold rolling-forming". In the cold rolling stage, traditional flat-roll rolling creates unconstrained "free deformation zones" on both sides of the wire's width. In these regions, the material is primarily subjected to radial tensile stress, making it highly susceptible to inducing microcracks such as... Figure 1 As shown, these microcracks are not only stress concentration points, significantly reducing the fatigue life of the product (typically only 800-1500 cycles), but they also propagate during subsequent forming and use, leading to wire breakage. Simultaneously, the large dimensional fluctuations (e.g., -0.04 to +0.02 mm) result in poor stability during subsequent cold forming and low product consistency.

[0004] Surface contamination ("blackening") problem: During the cold drawing and cold rolling of wire, lubricants must be used to reduce friction and wear. Traditional processes lack effective intermediate surface treatment steps, resulting in lubricant residue adhering firmly to the wire surface, forming a black lubricating layer. Figure 3 As shown. This lubricating layer will gradually peel off during subsequent processing and consumer wear and washing, resulting in a "blackening" phenomenon that stains clothing and seriously affects user experience and product aesthetics.

[0005] Limited performance and inability to meet customized needs: Existing processes focus on obtaining basic shapes, lacking proactive design and coordinated control of the material's internal stress state, phase transformation behavior, and surface functions. Key indicators such as product fatigue performance and phase transformation temperature (Af point) fluctuate greatly and cannot be specifically adjusted according to specific application scenarios (such as different requirements for softness and resilience in different seasons and regions).

[0006] Therefore, the development of a high-quality nickel-titanium alloy memory ring manufacturing method that can fundamentally solve the problems of microcracks, poor dimensional accuracy, and surface contamination, and achieve adjustable performance, has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0007] This invention aims to solve the problems existing in the prior art and provide a method for preparing nickel-titanium alloy memory rings for underwear by controlling stress during preparation, eliminating the generation of microcracks, and significantly improving dimensional accuracy and fatigue life.

[0008] This invention provides a method for preparing a nickel-titanium alloy memory ring for underwear, comprising: S1. Manufacture nickel-titanium alloy wire rods according to requirements; S2. The prepared nickel-titanium alloy wire rod is subjected to multiple drawing processes to obtain nickel-titanium alloy wire; S3. A nickel-titanium alloy flat wire is obtained by rolling a nickel-titanium alloy wire through multiple passes; each rolling pass includes plastic deformation and stress deformation treatment; wherein, in at least one rolling pass, after the nickel-titanium alloy wire undergoes plastic deformation, the free deformation zones on both sides of its width direction are immediately subjected to selective ultra-fast cooling, while the central deformation constraint zone is kept warm, thereby constructing a non-uniform residual stress distribution in the flat wire with compressive stress at the edges and neutral or weak tensile stress at the center; S4. The obtained nickel-titanium alloy flat wire is subjected to hot forming treatment to obtain a nickel-titanium alloy memory ring; S5. The obtained nickel-titanium alloy memory ring is surface cleaned to obtain a finished memory ring with a bright surface.

[0009] Furthermore, the method for manufacturing nickel-titanium alloy wire rod in step S1 includes: S101. Melting: Add grade 0 sponge titanium and nickel raw materials to a vacuum induction furnace according to the ratio. Melt for 10-20 minutes at a temperature of about 1400℃. After the refining process is completed, pour the molten liquid into a mold and then cool it to room temperature to obtain an ingot. S102. Forging and rolling: The obtained ingot is annealed, forged, and rolled to obtain nickel-titanium alloy wire rod.

[0010] Furthermore, after step S2, the prepared nickel-titanium alloy wire is subjected to surface treatment. The surface treatment is performed using a surface polishing machine, and the linear speed of the surface treatment is 8.0 to 10.0 m / min.

[0011] Furthermore, in step S3, the deformation rate during each plastic deformation or stress deformation treatment is 10% to 30%.

[0012] Furthermore, in step S2, during multiple drawing processes, before at least one drawing, the wire is heated to a temperature higher than its current austenitic phase transformation end point Af for drawing, and the deformation rate of each drawing is 10% to 20%.

[0013] Furthermore, the method for obtaining the austenitic phase transformation end point Af is as follows: Af = Af0 + k·N, where Af0 is the initial austenitic phase transformation end point of the raw material ingot, k is the work hardening coefficient of the material, with a value range of 0.5-2.0℃ / %; and N is the cumulative true strain degree.

[0014] Furthermore, in step S3, the selective ultrafast cooling rate is ≥100℃ / second, so that the temperature of the free deformation zone drops below the martensitic transformation initiation point Ms within 1 second, thereby inducing the martensitic transformation to generate the compressive stress.

[0015] Furthermore, the atomic ratio of the grade 0 sponge titanium and nickel raw materials is 1:1, and the nickel raw material is a nickel-rich alloy.

[0016] The beneficial effects of this invention are as follows: 1. By utilizing plastic deformation and stress deformation during rolling, and immediately subjecting the free deformation zones on both sides of the nickel-titanium alloy wire after plastic deformation to selective ultra-fast cooling, compressive stress is generated through martensitic phase transformation induced by ultra-fast cooling. This actively balances and reconstructs the internal stress field of the material, thus offsetting the tensile stress that leads to microcracks at its source. The new process results in a smooth, crack-free surface on the product's sides; this increases the product's fatigue life from the traditional 800-1500 cycles to over 1800-2600 cycles, and reduces the risk of wire breakage to near zero.

[0017] 2. Stress treatment (whether mechanical secondary deformation or phase transformation-induced compressive stress) refined the dimensional fluctuations after rolling, reducing the dimensional fluctuation range of products of the same specification from -0.04 to +0.02 mm to -0.02 to +0.01 mm. Cold forming stability was greatly improved, and the defect rate was reduced from 7.4% to nearly 0.

[0018] 3. By employing a combined process of "online surface cleaning to remove the lubricating layer + final precision cleaning / coating protection," the source of contamination is eliminated at its root, and a permanent protective layer is constructed on the surface. For example... Figure 4 As shown, the new process produces a glossy surface that does not show any black residue after wiping, fundamentally solving the problem of soiled underwear. Attached Figure Description

[0019] Figure 1 The image of the flat wire prepared using conventional methods in the background art of this invention; Figure 2The image shown is of the flat wire prepared in the embodiment of the present invention; Figure 3 The image of the memory circle prepared using conventional methods in the background art of this invention; Figure 4 This is a memory circle image prepared in an embodiment of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of the present invention, exemplary embodiments of the present invention are described below in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0021] Where there is no conflict, the various embodiments of the present invention and the features thereof may be combined with each other.

[0022] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded. Terms such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. Example 1

[0024] This embodiment provides a method for preparing a nickel-titanium alloy memory ring for underwear, including: S1. Manufacturing nickel-titanium alloy wire rod as required; In this embodiment, the method used in manufacturing nickel-titanium alloy wire rod includes: S101. Melting: Grade 0 sponge titanium and nickel raw materials are added to a vacuum induction furnace in proportion, the melting time is 10-20 minutes, and the temperature is about 1400℃; After refining, the molten liquid is poured into a mold and then cooled to room temperature to obtain an ingot; In this embodiment, the atomic ratio of Grade 0 sponge titanium and nickel raw materials added to the vacuum induction furnace is close to 1:1, and the nickel raw material is a nickel-rich alloy; This composition range can ensure that the alloy has a good shape memory effect, and its austenitic phase transformation end point (Af) can be controlled in a wide range (such as 0℃ to 40℃) through subsequent processes to adapt to the comfortable temperature; S102. Forging and rolling: The obtained ingot is annealed, forged, and rolled to obtain the following... Figure 2 The nickel-titanium alloy wire rod shown is prepared by homogenizing and annealing the ingot, then forging it into a square billet of a fixed size using a high-tonnage forging press. It is then fed into a multi-hole rolling mill to obtain wire rods of the required size. In this embodiment, annealing, forging, and rolling the ingot to obtain the nickel-titanium alloy wire rod is a conventional method for preparing nickel-titanium alloys, and the specific methods are not described in detail here. S2. The prepared nickel-titanium alloy wire rod is subjected to multiple drawing processes to obtain nickel-titanium alloy wire. During the drawing process, a cemented carbide die is used to reduce the diameter of the wire rod, and the drawing deformation rate is controlled at 10% to 20%. After multiple drawing passes, a wire of fixed size can be obtained. In another embodiment, before at least one drawing pass, the wire is heated to a temperature higher than its current austenitic phase transformation end point Af for drawing, and the deformation rate of each drawing pass is 10% to 20%.

[0025] The method for obtaining the austenitic phase transformation endpoint Af is as follows: Af = Af0 + k·N, where Af0 is the initial austenitic phase transformation end point of the raw material ingot, k is the work hardening coefficient of the material, with a value range of 0.5-2.0℃ / %; and N is the cumulative true strain degree. In this embodiment, the diameter of the wire rod is 8.0 mm, and the diameter of the wire after drawing is required to be 2 mm. During the drawing process, the cumulative true strain N before the current pass is obtained by querying a preset process database. This database has pre-calculated and stored the N value based on the dimensions of each pass. For example, the cumulative true strain N from Φ8.0 mm to Φ2.0 mm is approximately 2.77. According to the model Af = Af0 + k·N (in this example, the initial Af0 = 60℃, k = 1.5℃ / %), the current Af is calculated to be approximately 101℃. Therefore, the drawing temperature is set to approximately Af + 30℃ = 131℃ for warm drawing.

[0026] After the wire rod is drawn, the resulting filament is surface treated to remove the lubricating layer on the filament surface. In this embodiment, the surface treatment is performed using a surface polishing machine. The filament is fed into the surface polishing machine for polishing to remove the lubricating layer on the filament surface, resulting in a glossy filament. In this embodiment, the linear speed of the filament entering the surface polishing machine is 8.0 to 10.0 m / min.

[0027] S3. Nickel-titanium alloy wire is rolled in multiple passes to obtain nickel-titanium alloy flat wire, i.e., the surface-treated wire is rolled in multiple passes. In this embodiment, each rolling pass includes one plastic deformation and one stress deformation treatment, and the deformation rate of each deformation treatment (plastic deformation and stress deformation) is 10% to 30%. Specifically, during rolling, the bright wire is uniformly heated and then enters the flat roll rolling to produce plastic deformation. It immediately enters the stress treatment mechanism to produce secondary deformation, and then continues to be rolled in multiple passes until the finished product is obtained. The linear speed is controlled at 8.0 to 12.0 m / min throughout the process, the deformation rate per pass is controlled at 10% to 30%, and the surface is colorless or lightly oxidized. The final product is lightly oxidized.

[0028] The purpose of plastic deformation and stress deformation is twofold: firstly, the deformation rate generated by stress treatment is less than that of the previous rolling pass, allowing for the refinement of dimensional fluctuations in the width direction after rolling deformation through secondary deformation under stress treatment, thereby improving product dimensional accuracy; secondly, after rolling deformation, the product is in an unconstrained free deformation zone on both sides of the width direction, generating radial tensile stress during deformation. Secondary deformation through stress treatment generates radial compressive stress, thus balancing and canceling out the tensile and compressive stresses, releasing internal stress, changing the stress state, and preventing the formation of microcracks.

[0029] Meanwhile, in this embodiment, in at least one rolling pass of the multi-rolling pass, after the nickel-titanium alloy wire undergoes plastic deformation, the free deformation areas on both sides of its width direction are immediately subjected to selective ultra-fast cooling, while the central deformation constraint area is kept warm, thereby constructing a non-uniform residual stress distribution with compressive stress at the edges and neutral or weak tensile stress at the center within the flat wire. In practice, for example, the glossy filament is heated evenly to about 300°C (below the light oxidation temperature).

[0030] This allows it to enter a multi-pass rolling production line, with the entire line speed controlled at 10.0 m / min.

[0031] In at least one rolling pass (e.g., the first pass), the wire first undergoes primary deformation (20% deformation rate per pass) using a flat-roll mill. Immediately afterwards, it enters a stress-treatment mechanism. As the wire passes through this mechanism, a radial compression is applied to the free deformation zones on both sides of its width, resulting in a secondary deformation (approximately 5% deformation rate). This secondary deformation introduces radial compressive stress into the free deformation zones, precisely offsetting the tensile stress generated in the previous rolling pass.

[0032] This "rolling + immediate secondary deformation" process can be repeated in subsequent passes. The final product is a flat wire with precise dimensions and a uniform, lightly oxidized surface. This mechanical method successfully creates a non-uniform residual stress field within the flat wire, characterized by compressive stress at the edges and near-neutral stress at the center.

[0033] Cryogenic stabilization treatment: The rolled flat wire is placed in liquid nitrogen vapor and cooled to -80°C, and held for 1 hour to stabilize the structure and release residual stress.

[0034] S4. The obtained nickel-titanium alloy flat wire is subjected to hot forming treatment to obtain a nickel-titanium alloy memory ring. In this embodiment, during the hot forming treatment, it is first heated at 400°C for 60 minutes, and then heated at 500°C for 20 minutes. Finally, a memory ring with a fixed shape and good memory effect is obtained.

[0035] S5. The obtained nickel-titanium alloy memory ring is surface-cleaned to obtain a finished memory ring with a bright surface. During cleaning, the finished memory ring is immersed in the cleaning solution, which can effectively remove the light oxide color on its surface and obtain a bright surface. Figure 4 The finished memory ring shown. Example 2

[0036] In one embodiment, the memory ring is prepared according to the following method; S1: Prepare wire rod: Make Φ8.0mm wire rod.

[0037] S2: Dynamic Temperature Control Drawing: The same cumulative true strain model as in Example 1 is adopted; however, in this example, N is obtained by real-time tracking calculation: the production control system records and accumulates the true strain of each pass in real time (calculated based on the inlet and outlet dimensions). When a certain drawing pass is performed, the system automatically calculates the cumulative N since the ingot was cast and calculates Af* in real time, dynamically setting the drawing temperature.

[0038] S3: Composite Surface Activation: After drawing, the filament is first cleaned by ultrasonic-assisted alkaline solution electrolysis, and then sandblasted with zirconium oxide microspheres with a particle size of about 80μm to obtain an active clean surface with Ra of about 0.6μm.

[0039] S4: Rolling and Selective Ultrafast Cooling: Heat the filament to above point Af (e.g., Af+20℃).

[0040] Multi-pass rolling is performed. In critical passes (such as the second pass), the wire is rolled and deformed, and then immediately enters a selective cooling zone.

[0041] In this cooling zone, two independent systems operate simultaneously: 1. For the free deformation zones on both sides in the width direction, two focused high-energy nitrogen pulse jets are used for selective ultrafast cooling at a rate of up to 250℃ / second, causing the surface temperature of this area to drop rapidly from approximately 150℃ to -30℃ (far below the Ms point) within 0.5 seconds. This rapid cooling induces the transformation of the surface austenite to martensite, and the accompanying volume expansion naturally generates a strong radial compressive stress field within the free deformation zone. 2. Simultaneously, for the central deformation-constrained zone of the wire, an infrared radiation heater is used for dynamic heat preservation, maintaining its temperature above the Ms point to prevent phase transformation.

[0042] By combining selective ultrafast cooling with heat preservation, the material's own phase transformation behavior is utilized at the microscopic level to efficiently and precisely create a gradient stress distribution within the flat wire, characterized by high compressive stress at the edges and weak tensile stress or neutral stress at the center. This stress field is more uniform and stable than that generated by mechanical methods.

[0043] S5: Cryogenic-thermal cycling stabilization treatment: The flat wire is first immersed in liquid nitrogen and cooled to -196℃ (below the Mf point) for 30 minutes; then it is taken out and allowed to naturally rise in air to about 50℃ (above the As point); then it is immersed in liquid nitrogen again for cryogenic cooling to -196℃ and held for 30 minutes. This cyclic treatment can fully stabilize the martensitic structure and maximize the release of internal stress.

[0044] S6: Near-net-shape forming and two-step constrained aging: Forming is performed at a temperature slightly above the Md point but below the current Af (e.g., Af-10℃). At this temperature, the material partially transforms into stress-induced martensite, resulting in low forming force and minimal springback. After forming, two-step aging is performed under mold constraint: 430℃ / 45 minutes + 520℃ / 15 minutes.

[0045] S7: Surface Functionalization Treatment: First, the memory ring undergoes chemical mechanical polishing to achieve a mirror finish (Ra < 0.05 μm). Then, using atomic layer deposition (ALD), a dense, pinhole-free alumina (Al2O3) coating approximately 100 nanometers thick is deposited on its surface. This coating has extremely strong adhesion to the substrate, permanently isolating the substrate from external contact, completely eliminating any possible corrosion or contamination, and giving the product excellent wear resistance.

[0046] This embodiment explains the method for obtaining the cumulative true strain (N): Obtaining the cumulative true strain N is a prerequisite for implementing dynamic temperature-controlled drawing. Those skilled in the art can achieve this through the following two conventional industrial methods: Pre-defined database query: In stable, standardized production, the complete processing path and N-values ​​for each stage corresponding to each product specification can be pre-determined through process design and stored in the database. During production, the database is retrieved based on the product code. This method is efficient and stable.

[0047] Online real-time calculation: In flexible manufacturing systems, the true strain of a single pass can be calculated in real time by automatically measuring or calling up process parameters (inlet / outlet dimensions) for each pass, and then accumulated with historical values ​​to obtain the current N. This method is flexible and adaptive.

[0048] In specific calculations, the true strain per pass is ε_i = ln(A_in / A_out), where A_in is the cross-sectional area before processing, and A_out is the cross-sectional area after processing. The total cumulative true strain level N = Σε_i (i from the initial billet stage to the current pass).

[0049] Effect verification The test results for the products produced by either method in Examples 1 and 2 above are as follows: Dimensional accuracy: The width tolerance of the flat wire is stable within ±0.01mm.

[0050] Microstructure: SEM examination showed no microcracks at the edges, and fine martensitic structure could be observed at the edges of the product in Example 2, confirming the occurrence of phase transformation.

[0051] Fatigue performance: In the rotational bending fatigue test with a strain amplitude of 6%, the average life of the product in Example 1 reached 2200 cycles, and the average life of the product in Example 2 exceeded 3000 cycles, with small data dispersion.

[0052] Stain resistance: In Example 1, the product remained shiny after cleaning and showed no black stains after wiping. In Example 2, due to the protective ALD coating, the product's surface remained shiny and new even after immersion in acid and alkali solutions and tens of thousands of friction tests, and no staining was observed when wiped with a white cloth.

[0053] Performance adjustability: By changing the T2 temperature (480℃-550℃) of the two-step aging in Example 2, the memory ring Af point produced by the same batch of materials can be linearly adjusted within the range of 25℃-40℃.

[0054] The above results demonstrate that the memory rings prepared in this application have the effects of being free of microcracks, having high dimensional accuracy, and being free of surface contamination.

[0055] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A method for preparing a nickel-titanium alloy memory ring for underwear, characterized in that, include: S1. Manufacture nickel-titanium alloy wire rods according to requirements; S2. The prepared nickel-titanium alloy wire rod is subjected to multiple drawing processes to obtain nickel-titanium alloy wire; S3. A nickel-titanium alloy flat wire is obtained by rolling a nickel-titanium alloy wire through multiple passes; each rolling pass includes plastic deformation and stress deformation treatment; wherein, in at least one rolling pass, after the nickel-titanium alloy wire undergoes plastic deformation, the free deformation zones on both sides of its width direction are immediately subjected to selective ultra-fast cooling, while the central deformation constraint zone is kept warm, thereby constructing a non-uniform residual stress distribution in the flat wire with compressive stress at the edges and neutral or weak tensile stress at the center; S4. The obtained nickel-titanium alloy flat wire is subjected to hot forming treatment to obtain a nickel-titanium alloy memory ring; S5. The obtained nickel-titanium alloy memory ring is surface cleaned to obtain a finished memory ring with a bright surface.

2. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 1, characterized in that, The method for manufacturing nickel-titanium alloy wire rod in step S1 includes: S101. Melting: Add grade 0 sponge titanium and nickel raw materials to the crucible of a vacuum induction furnace according to the proportion, and melt at a melting temperature of 1400℃ for 10-20 minutes; then cool to room temperature to obtain an ingot. S102. Forging and rolling: The obtained ingot is annealed, forged, and rolled to obtain nickel-titanium alloy wire rod.

3. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 1, characterized in that, After step S2, the prepared nickel-titanium alloy wire is subjected to surface treatment. The surface treatment is carried out using a surface polishing machine. The linear speed of the surface treatment is 8.0 to 10.0 m / min.

4. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 1, characterized in that, In step S3, the deformation rate during each plastic deformation or stress deformation treatment is 10% to 30%.

5. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 1, characterized in that, In step S2, during multiple drawing processes, before at least one drawing, the wire is heated to a temperature higher than its current austenitic phase transformation end point Af for drawing, and the deformation rate of each drawing is 10% to 20%.

6. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 5, characterized in that, The method for obtaining the austenitic phase transformation end point Af is as follows: Af = Af0 + k·N, where Af0 is the initial austenitic phase transformation end point of the raw material ingot, k is the work hardening coefficient of the material, with a value range of 0.5-2.0℃ / %; and N is the cumulative true strain degree.

7. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 1, characterized in that, In step S3, the selective ultrafast cooling rate is ≥100℃ / second, so that the temperature of the free deformation zone drops below the martensitic transformation initiation point Ms within 1 second, thereby inducing the martensitic transformation and generating the compressive stress.

8. The method for preparing a nickel-titanium alloy memory ring for underwear according to claim 2, characterized in that, The atomic ratio of the grade 0 sponge titanium and nickel raw materials is 1:1, and the nickel raw material is a nickel-rich shape memory alloy.

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