Method for preparing high-linear-elasticity high-strength NiTi shape memory alloy through composite shaping deformation

Abstract

The invention belongs to the field of metal material plastic forming, and particularly relates to a method for preparing a large-linear-elasticity high-strength NiTi shape memory alloy through composite plastic deformation. Comprising the following steps that (1) solid solution quenching treatment is conducted, specifically, a NiTi alloy bar containing 50 at% of Ni and 50 at% of Ti is subjected to solid solution quenching treatment; (2) rotary forging treatment is conducted, specifically, the bar obtained after solution quenching in the step (1) is subjected to room-temperature rotary forging, the deformation of each pass of rotary forging is controlled to be within 2.5%, the total deformation of rotary forging treatment is controlled to be within 20%, and the bar with fine grains of 0.5-5 micrometers is obtained; and (3) room-temperature rolling deformation is conducted, specifically, room-temperature rolling is conducted on the fine-grain bar obtained in the step (2). According to the invention, the nickel-titanium shape memory alloy with high strength, low elastic modulus and large linear elasticity can be prepared; the method is low in cost and high in repeatability, and can be used for large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the field of plastic forming of metal materials, and in particular relates to a method for preparing a high-strength NiTi shape memory alloy with large linear elasticity by composite plastic deformation. Background Art

[0002] NiTi shape memory alloys (SMAs) have the advantages of good shape memory effect, superelasticity and high damping characteristics, and have been widely used in aerospace, medical and health, and construction industries. In addition, NiTi shape memory alloys also have excellent biocompatibility, wear resistance, and corrosion resistance, and are most suitable for medical materials. With the rapid development of modern science and technology, various fields have higher and higher performance requirements for memory alloy materials, especially the development of micro-electromechanical systems, which require materials to have small size, high sensitivity and high strength. In addition, due to the poor cold working performance and low weldability of nickel-titanium shape memory alloys, traditional NiTi shape memory alloy materials cannot meet the development needs of modern science and technology.

[0003] Rotary forging is a near-net-shape production process that uses multi-hammer high-speed pulse hammering to process solid shaft parts or hollow variable-section forgings. It is mainly used for various hollow solid shafts. Rotary forging is suitable for the preparation of bars, wires and pipes. During the processing, the rotary forging die rotates at high speed around the outer diameter of the billet, and continuously applies radial force to the billet through high-frequency strikes, causing it to shrink radially and extend axially, while forming according to the die profile. During the rotary forging process, part of the material will be in a state of three-dimensional compressive stress. Therefore, rotary forging can weld the cracks caused by severe deformation inside the material structure, and at the same time reduce the uneven structure caused by uneven deformation, and improve the plasticity of the material. Therefore, rotary forging is particularly suitable for reducing porosity in powder metallurgy, as well as some metals that are difficult to deform and have poor plasticity.

[0004] Chinese patent CN101768685A reports that the plates, wires and bars are manufactured by cold and hot processing such as forging, rolling, rotary forging, drawing and heat treatment, and have good biocompatibility and low elastic modulus. The processed plates and bars have a tensile strength of ≤380MPa, a yield strength of ≤881MPa and an elastic modulus of ≤53GPa. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a large linear elastic high-strength nickel-titanium shape memory alloy by composite plastic deformation, the method comprising: solution quenching, rotary forging treatment and room temperature rolling deformation treatment, the nickel-titanium alloy rod is fully solution treated to make its elements uniform, and then quenched to prevent segregation; the quenched rod is subjected to multiple rotary forging treatments to obtain a fine-grained alloy rod: by rolling deformation under room temperature conditions, the alloy undergoes a martensitic phase transformation and retains the martensitic structure, so as to obtain a large linear elastic high-strength NiTi shape memory alloy rolled plate with uniform thickness and smooth surface.

[0006] The technical solution to achieve the purpose of the present invention is: a method for preparing a high-strength NiTi shape memory alloy with high linear elasticity by composite plastic deformation, comprising the following steps:

[0007] Step (1): Solution quenching treatment: subjecting a NiTi alloy rod having a composition of 50 at% Ni and 50 at% Ti to solution quenching treatment;

[0008] Step (2): rotary forging: subjecting the bar material after solution quenching in step (1) to room temperature rotary forging, wherein the deformation amount of each rotary forging pass is controlled within 2.5%, and the total deformation amount of the rotary forging process is controlled within 20%, to obtain a bar material with fine grains of 0.5 to 5 microns;

[0009] Step (3): Room temperature rolling deformation: The fine-grained rod obtained in step (2) is subjected to room temperature rolling.

[0010] Furthermore, the solution temperature of the solution quenching treatment in step (1) is above the recrystallization temperature and below the melting point of the nickel-titanium alloy, and the solution time is sufficient to homogenize the alloy elements in the rod.

[0011] Furthermore, in step (1), the quenching medium is water.

[0012] Furthermore, the step (1) solid solution treatment is specifically as follows: the rod is kept at 800-850° C. in a vacuum furnace filled with argon for 10-14 hours.

[0013] Furthermore, the deformation of a single pass of room temperature rolling in step (3) is controlled within 5%, and the total rolling amount is 20-40%.

[0014] Furthermore, the diameter of the NiTi alloy rod used in step (1) is 7 to 10 mm.

[0015] A high-strength NiTi shape memory alloy with large linear elasticity is prepared by composite plastic deformation, and is prepared by the above method.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] 1. The present invention adopts a composite treatment of rotary forging deformation and room temperature rolling to prepare nickel-titanium alloy plates. This method introduces grain boundaries and dislocations through rotary forging deformation, and then further refines the grains through room temperature rolling while promoting the martensitic phase transformation of the alloy, so that the material is in a martensitic state, thereby increasing the recoverable strain of the material.

[0018] 2. The present invention adopts rotary forging deformation and room temperature rolling deformation to prepare nickel-titanium alloy plates, which has low requirements on equipment, is simple and easy to implement, has strong repeatability, and can be used for large-scale industrial production.

[0019] 3. The present invention uses rotary forging deformation. Under this deformation mode, the stress state of the material is softer, can withstand greater deformation, and introduce more dislocations.

[0020] 4. The nickel-titanium alloy plate prepared by the present invention has good comprehensive mechanical properties and can withstand large deformation in various application environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the rotary forging device used in the present invention.

[0022] Figure 2 It is a schematic diagram of the rolling deformation device adopted in the present invention.

[0023] Figure 3 Schematic diagram of RD plane grain boundary of an embodiment of the present invention; wherein (a) is a schematic diagram of RD plane grain boundary of the plate after solution quenching, (b) is a schematic diagram of RD plane grain boundary after rotary forging, and (c) is a schematic diagram of RD plane grain boundary after rolling.

[0024] Figure 4 The tensile curve of the embodiment; (a) is the engineering stress-strain curve of uniaxial tension under static load, and (b) is the cyclic tensile curve after one cyclic stretching.

[0025] Figure 5 Graph showing the superelastic effect and superelastic efficiency changes of an embodiment.

[0026] Figure 6 This is a scanning electron microscope image of the RD surface after rolling in the example.

[0027] Figure 7 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0028] With reference to the accompanying drawings, an embodiment of the present invention is described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0029] A method for preparing a large linear elastic high-strength NiTi shape memory alloy by composite plastic deformation, comprising: solution quenching, rotary forging and room temperature rolling deformation, firstly subjecting a nickel-titanium alloy rod to a full solution treatment to homogenize its elements, and then quenching to prevent segregation; subjecting the quenched rod to a multi-pass rotary forging treatment to obtain a fine-grained alloy rod; and subjecting the rod to rolling deformation at room temperature to obtain a nickel-titanium alloy rolled plate with uniform thickness and smooth surface.

[0030] The specific steps of the preparation method of the large linear elastic NiTi shape memory alloy plate by composite plastic deformation are as follows:

[0031] A method for preparing a large linear elastic nickel-titanium shape memory alloy by composite plastic deformation, comprising the following steps:

[0032] Step 1: Solution quenching treatment. The nickel-titanium shape memory alloy ingot is hot rolled and die-forged into a rod. Before rotary forging, the rod is kept at 800-850°C in a vacuum furnace filled with argon for about 12 hours to make the alloy structure uniform and reduce defects, and then quenched.

[0033] Step 2: Rotary forging. The parameters of rotary forging are designed according to the original state of the material, and rotary forging deformation is performed. The deformation amount of each pass is controlled at 2.5%, and the deformation amount of rotary forging is controlled within 20%, so that the grain size reaches the fine grain level, with a diameter of about 0.5 to 5 microns, and a large number of grain boundaries and dislocations are introduced to promote the martensitic phase transformation of the alloy.

[0034] Step 3: Rolling deformation at room temperature. Use a conventional twin-roll rolling mill at room temperature to uniformly roll the nickel-titanium shape memory alloy rods. The pressing amount is controlled according to the critical deformation degree of the shape memory alloy. The deformation amount of each pass is controlled at 5%, and the rolling treatment deformation amount is more than 20%. While introducing more grain boundaries and dislocations, the martensitic phase transformation is further carried out to obtain a shape memory alloy rolled plate with uniform thickness and smooth surface.

[0035] The solution temperature is selected to be above the recrystallization temperature and below the melting point of the nickel-titanium alloy. The solution temperature and time must ensure that the alloy elements in the rod are homogenized without obvious large-scale segregation.

[0036] Example

[0037] The present invention takes NiTi alloy rod as an example to provide a detailed implementation method and specific operation. The following embodiment involves four steps including: solution quenching treatment, rotary forging deformation treatment, and room temperature rolling deformation treatment, wherein:

[0038] Step 1: Forge the NiTi alloy ingot with a composition of 50at% Ni and 50at% Ti into a rod with a diameter of 8mm and a length of 2m. Before deformation treatment, the rod is homogenized in an argon atmosphere vacuum furnace at 850℃ for 12h, and then quenched with pure water. The RD surface microstructure of the obtained material is as follows Figure 3 (a) shown.

[0039] Step 2: The obtained coarse-grained nickel-titanium alloy rod is subjected to rotary forging, and the deformation rate and deformation pass are designed according to the original grain size of the rod. Taking the rod obtained in step 1 as an example, rotary forging is performed in a rotary forging machine at a speed of 160r / min with a downward pressure of 0.2mm per pass at room temperature. The rotary forging process is performed until the deformation reaches 10%. At this time, the material diameter is 7.6mm. The RD surface microstructure of the obtained material is as follows: Figure 3 (b) as shown.

[0040] Step 3: Deformed Ni 50 The Ti alloy rod is uniformly rolled and deformed at room temperature. The rolling reduction is 0.1mm per pass and 20% in total, so that the rod undergoes uniform plastic deformation in the thickness direction, and a Ni alloy with uniform thickness and smooth surface is obtained. 50 Ti alloy rolled plate, the RD surface microstructure of the obtained material is as follows Figure 3 (c) as shown.

[0041] The material obtained in step 3 was observed under a scanning electron microscope, and the image obtained was as follows: Figure 6 As shown, it can be found that there are a lot of needle-shaped martensite structures in the grains of the material, which is consistent with the description of step three in the content of the invention; the material is subjected to a tensile test, and the tensile curve is as follows Figure 4 As shown, the material has good comprehensive mechanical properties, with a tensile strength of 1330MPa and an elastic modulus of 54GPa; the materials obtained in steps 1, 2, and 3 were tested for the superelastic effect of 5% strain, and the superelastic properties are as follows Figure 5 As shown in the figure, it shows that the combination of rotary forging and rolling makes the material superelastic and superelastic efficiency (ε se / ε t ) has been greatly improved.

[0042] The superelastic test method is to cyclically stretch the sample at 5% strain at room temperature.

Claims

1. A method for preparing a high-strength NiTi shape memory alloy with high linear elasticity by composite plastic deformation, characterized in that: The steps include: Step (1): Solution quenching treatment: subjecting a NiTi alloy rod having a composition of 50 at% Ni and 50 at% Ti to solution quenching treatment; Step (2): rotary forging: subjecting the bar material after solution quenching in step (1) to room temperature rotary forging, wherein the deformation amount of each rotary forging pass is controlled within 2.5%, and the total deformation amount of the rotary forging process is controlled within 20%, to obtain a bar material with fine grains of 0.5 to 5 microns; Step (3): Room temperature rolling deformation: The fine-grained rod obtained in step (2) is subjected to room temperature rolling.

2. The method according to claim 1, characterized in that The solution temperature of the solution quenching treatment in step (1) is above the recrystallization temperature and below the melting point of the nickel-titanium alloy, and the solution time is sufficient to homogenize the alloy elements in the rod.

3. The method according to claim 2, characterized in that In step (1), the quenching medium is water.

4. The method according to claim 3, characterized in that The step (1) of solid solution treatment is specifically as follows: the rod is kept at 800-850° C. in a vacuum furnace filled with argon for 10-14 hours.

5. The method according to claim 4, characterized in that The deformation of a single pass of room temperature rolling in step (3) is controlled within 5%, and the total rolling amount is 20-40%.

6. The method according to claim 5, characterized in that The diameter of the NiTi alloy rod used in step (1) is 7 to 10 mm.

7. A composite plastic deformation method for preparing a high linear elastic high strength NiTi shape memory alloy, characterized in that: The method is prepared by any one of claims 1 to 6.

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