A high-strength superelastic alloy with a wide temperature range and a preparation method thereof

Abstract

A wide-temperature-range, high-strength superelastic alloy and its preparation method, belonging to the field of titanium alloys, achieves elastic strain greater than 1.5% and tensile strength greater than 1000 MPa within a temperature range of ‑200 to 120°C by adjusting the lattice constants of the two phases, improving and optimizing the lattice mismatch strain between the α″ and β phases, and influencing the deformation mechanism of the two phases. This results in neither the α″ nor the β phase undergoing phase transformation under stress, but only elastic lattice distortion. Furthermore, by optimizing the lattice constants of the two phases, the lattice distortion strain of each phase is increased, and the temperature sensitivity of the alloy's superelasticity and strength is reduced. Ultimately, the alloy achieves elastic strain greater than 1.5% and tensile strength greater than 1000 MPa within a temperature range of ‑200 to 120°C. At the same time, the existing superelastic alloy preparation process is simplified, effectively improving the preparation and processing efficiency of superelastic alloys.

Description

Technical Field

[0001] The present invention belongs to the field of titanium alloys, and in particular relates to a high-strength superelastic alloy with a wide temperature range and a preparation method thereof. Background Art

[0002] Superelastic alloys possess a unique property of superelasticity, which is absent from ordinary materials. This property refers to the ability of an alloy to spontaneously recover after deformation due to an external force. This ability to recover significantly more than traditional metals has led to their widespread use in advanced medical applications such as dental arch wires, artificial joints, and vascular stents, as well as in the electronics and electrical fields, such as mobile phone antennas and scroll-type devices for folding screens.

[0003] CN202010980269.6 discloses a multifunctional titanium alloy, a preparation method and its application. The technical solution includes adjusting the pre-deformation amount and utilizing the β→α′ martensitic phase transformation to achieve superelasticity. The technical solution does not involve the regulation of the lattice constant; the titanium alloy obtained by this solution has a low elastic modulus and high elastic strain at room temperature, but does not have high strength and superelasticity in a wide temperature range, and the superelastic strain is low. CN201910945033.6 discloses a method for improving the superelasticity of β titanium alloy. The technical solution includes optimizing the β→α″ martensitic transformation by calculating the α″ martensitic phase relationship to improve the superelasticity of the β titanium alloy. It does not involve adjusting the lattice constant and lattice distortion; the titanium alloy obtained by this solution has high superelasticity, but does not have superelasticity in the entire temperature range and the superelastic titanium alloy obtained is extremely small in size, making it difficult to apply industrially. CN202310551801.6 discloses a high-strength, low-modulus Ti-Nb-Zr biomedical titanium alloy and a preparation method thereof. The technical solution involves adjusting the amount of cold working deformation to prepare titanium alloy plates, using vacuum melting to prepare alloy ingots, and solution quenching. The technical solution does not involve adjusting the lattice constant. The alloy obtained by this solution has characteristics such as low modulus, high strength, superelasticity, shape memory, damping properties, corrosion resistance, and high biocompatibility, but does not have high strength and superelasticity over a wide temperature range, and the room temperature superelastic strain is low. CN202111531763.5 discloses a nickel-titanium alloy and its preparation method and application, as well as a nickel-titanium alloy component. The technical solution includes subjecting a first nickel-titanium alloy to at least one hot and cold cycle, that is, a phase transformation from austenite to martensite and then to austenite, to obtain a second nickel-titanium alloy. The second nickel-titanium alloy is placed at a preset temperature for a preset time for low-temperature aging treatment to obtain the nickel-titanium alloy. The technical solution does not involve adjusting the lattice constant. The alloy obtained by this scheme can achieve large superelastic strain by utilizing martensitic phase transformation, but its material is titanium-nickel alloy, the application temperature range is only room temperature, and the preparation method is complicated. CN202310769593.7 discloses a titanium alloy with both low elastic modulus and high superelasticity. The technical solution includes designing the alloy components so that the martensitic phase transformation temperature of the β titanium alloy is near room temperature. Only a low phase transformation driving force is required to induce the martensitic phase transformation, and no adjustment of the lattice constant is involved. The titanium alloy obtained by this scheme is more likely to undergo martensitic phase transformation to obtain superelasticity, but the application temperature range is only room temperature, the preparation method is complicated, and the superelasticity is low. CN202310115428.X discloses a method for improving the strength of titanium alloy while reducing the elastic modulus. The technical solution mainly includes preparing an intermediate alloy and adjusting the heat treatment process, and does not involve adjusting the lattice constant and lattice distortion. The titanium alloy obtained by this solution has a lower modulus and an increased yield strength, which solves the mutual exclusion between elastic functionality and high strength of existing alloys. It has both high strength and high elasticity, and does not involve the improvement of superelasticity and application in a wide temperature range.CN202211399337.5 discloses a method for regulating the strength of high-silicon β-titanium alloy by using dual-phase silicide. The technical solution involves designing and regulating the β-titanium alloy through casting and matching heat treatment processes, forming dual-phase silicide in situ in the titanium alloy matrix, regulating the precipitation phase, and does not involve adjusting the lattice constant. The titanium alloy obtained by this solution has high strength and high toughness, which can meet the performance requirements of a variety of complex titanium alloy structural parts and does not involve the improvement of superelasticity. CN202011252236.6 discloses a design method for high-strength and high-entropy alloys. The technical solution involves constructing and optimizing the solid solution structure, adjusting the lattice constant of its high-entropy alloy model, calculating the elastic constant, bulk modulus and shear modulus, yield strength, etc., and finally obtaining a high-strength and high-entropy alloy. The technical solution involves adjusting the lattice constant, and its material is a high-entropy alloy. It provides a design method for high-strength and high-entropy alloys, obtains a computable structural model of the high-entropy alloy, and does not involve the improvement of superelasticity and strength.

[0004] Currently, superelastic alloys primarily rely on the martensitic transformation, a typical first-order thermodynamic phase transition. It is also a typical non-diffusion, shear-dependent, coherent phase transition in the solid-state, induced by temperature, stress, or magnetic field. The critical stress for the SIM (stress-induced martensitic) transformation (hereinafter referred to as the superelastic stress) is equivalent to the effective yield stress in superelastic behavior, which increases with increasing temperature. This temperature dependence severely limits the application of most superelastic materials over a wide temperature range. This phenomenon also leads to the major drawback of superelastic alloys, namely a narrow functional temperature range. Currently, most superelastic alloys are only used at room temperature.

[0005] The performance of existing superelastic alloys cannot meet the wide temperature range and high strength requirements of more application scenarios. This invention, through theoretical calculations, post-heat treatment, and pre-strain treatment, provides a wide-temperature range, high-strength superelastic alloy and its preparation method, which improves the overall performance of the superelastic alloy. Summary of the Invention

[0006] The present invention provides a high-strength superelastic alloy with a wide temperature range and a preparation method thereof. The alloy comprises an α″ phase and a β phase. In the technical solution of the present invention, the acquisition of a two-phase superelastic alloy with wide temperature range superelasticity, low elastic modulus and high strength directly depends on the β+α″ two-phase in the alloy and the respective proportions of different alloying elements. After smelting and heat treatment, combined with the specific processing process defined by the method of the present invention, the alloy does not undergo phase transformation similar to any prior art, but instead obtains superelasticity through continuous elastic distortion of the alloy's β phase and α″ phase lattices under stress.

[0007] The technical solutions of the present invention are as follows:

[0008] A high-strength superelastic alloy with a wide temperature range. By adjusting the lattice constants of the α″ and β phases, the α″ and β phases undergo elastic lattice distortion under stress, thereby simultaneously improving elastic strain and strength. Within the temperature range of -200 to 120°C, it has an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa.

[0009] After the α″ phase is adjusted, the following conditions are met: lattice constant a is 0.29-0.30 nm, lattice constant b is 0.49-0.51 nm, lattice constant c is 0.46-0.48 nm, and the lattice constant ratio b / a is increased from 1.41-1.50 to 1.60-1.73;

[0010] After the β phase is adjusted, the lattice constant a is satisfied at the same time. β is 0.32~0.34nm, and the lattice constant a β The relationship between the lattice constant b of the α″ phase is as follows:

[0011] The α″ phase is adjusted to have a lath morphology with an aspect ratio of 3 to 10;

[0012] After the β phase is adjusted, the elastic strain is contributed by the common lattice distortion of the β phase and the α″ phase;

[0013] The alloy undergoes a martensitic phase transformation before adjusting the lattice constants of the α″ phase and the β phase, and after adjusting the lattice constants of the α″ phase and the β phase, does not undergo a β→α″ and / or β→α' phase transformation under stress, that is, a phase transformation from the β phase to the α″ phase and / or a phase transformation from the β phase to the α' phase.

[0014] The method for preparing the wide temperature range high-strength superelastic alloy comprises the following steps:

[0015] Step 1: Prepare an alloy by smelting according to the alloy composition, selecting Ti as the base material, and adding a β-stabilizing element to suppress the metastable phase transition at the critical valence electron concentration of the β metastable state, thereby obtaining a β phase that is stable at room temperature. The β-stabilizing element Nb is preferred, and neutral elements Zr and Sn suppress the metastable phase transition, with their atomic percentage ratios of (15-15.5):(2.0-3.0):(3.5-4.5). Element O is also added to stabilize the finished alloy, with its atomic percentage not less than 0.1%;

[0016] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The thickness of the β phase is 0.32 to 0.34 nm, and the content of β-stabilizing elements in the β phase is not less than 24 wt.%. The effect of adjusting the lattice constant and composition of the β phase is to cause the α″ phase to be generated from the β phase through a compositional wave diffusion mechanism, and to improve the stability of the β phase so that no phase change occurs under stress.

[0017] Step 3: Adjusting the lattice constants and composition of the α″ phase so that the lattice constant a is 0.29-0.30 nm, the lattice constant b is 0.49-0.51 nm, and the lattice constant c is 0.46-0.48 nm, and the content of the β-stabilizing element in the α″ phase is less than 20 wt.%. The purpose of adjusting the lattice constants and composition of the α″ phase is to transform the α″ phase into a lath-like morphology and to cause continuous lattice distortion under stress.

[0018] Step 4: Perform final pre-deformation on the material, with the pre-deformation strain lower than 1.8% and the pre-deformation temperature higher than 20°C.

[0019] Furthermore, in step 2, the method for adjusting the β-phase lattice constant is performed in the following steps (strictly follow the order and do not include other steps):

[0020] (1) Air cooling after hot forging, hot forging temperature 800~1200℃;

[0021] (2) Air cooling after hot rolling, rolling temperature 500-800℃, hot rolling deformation 70-90%;

[0022] (3) After low-temperature insulation treatment, air cool to a temperature of 100°C for 23 to 25 hours.

[0023] Furthermore, in step 3, the method for adjusting the lattice constant of the α″ phase is carried out in sequence according to the following steps (strictly following the order and not including other steps):

[0024] (1) Air cooling after aging treatment, aging temperature 400-500℃, aging time 0.5-2 hours;

[0025] (2) Low temperature insulation treatment, insulation temperature 70-85°C, insulation time 10-20 minutes;

[0026] (3) Pre-stretching deformation at 70-85°C, the pre-stretching direction is the hot rolling direction, and the pre-deformation amount is 1-2%.

[0027] Key points of the present invention:

[0028] In the prior art, the conventional techniques used to solve the problem of "how to provide a superelastic alloy material" include adjusting the alloy composition, adjusting the volume fraction of the constituent phases, optimizing the β→α″ and / or β→α' phase transformations, etc.; the conventional techniques used to solve the problem of "how to provide a high-strength alloy material" include adjusting the deformation amount, adjusting the precipitated phase content, adjusting the heat treatment temperature / time, etc.; and the conventional techniques used to solve the problem of "how to provide an alloy material with a wide temperature range" include adjusting the component ratio, optimizing the β→α″ and / or β→α' phase transformations, etc. Currently, there is no relevant technology that can provide an alloy material that simultaneously possesses "wide temperature range", "high strength", and "superelasticity".

[0029] The technical core of the present invention is: "adjusting the lattice constants of the α" phase and the β phase". The role of this technical feature is: to prevent the α" phase and the β phase from undergoing phase transformation under stress, and at the same time to improve the elastic strain and strength of the alloy. The working principle of this technical feature is: by adjusting the lattice constants of the two phases, the lattice mismatch strain between the α" phase and the β phase is improved and optimized, and the dislocation resistance of the material is improved; by adjusting the lattice constants of the two phases, the deformation mechanism of the two phases is affected at the same time, so that the α" phase and the β phase do not undergo phase transformation under stress, but only elastic lattice distortion occurs, and by optimizing the lattice constants of the two phases, the lattice distortion strain of each phase is improved, and the temperature sensitivity of the superelasticity and strength of the alloy is reduced; finally, an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa are achieved in the temperature range of -200 to 120°C.

[0030] The technical solution of the present invention has the following beneficial effects compared with the prior art:

[0031] 1. The present invention provides a high-strength superelastic alloy with a wide temperature range, which has a strength greater than

[0032] The elastic strain of 1.5% and the tensile strength greater than 1000MPa solve the shortcomings of existing superelastic alloys, such as narrow operating temperature range, low strength and low elastic strain, and expand the application capabilities of superelastic alloys in multiple scenarios.

[0033] 2. The present invention provides a method for preparing a two-phase superelastic alloy, which simplifies the existing superelastic alloy preparation process and effectively improves the preparation and processing efficiency of the superelastic alloy.

[0034] 3. The technical solution of the present invention achieves "high strength and superelasticity" by "adjusting the lattice constant".

[0035] 4. Compared with the prior art, the present invention does not involve adjusting the composition ratio, constituent phase type, or constituent phase volume fraction, and does not require the phase transformation from the parent phase to the martensite phase to achieve superelasticity. This deviates from the conventional approach to obtaining superelastic alloys in the art and, through a completely different working principle, results in an alloy material that simultaneously exhibits high strength and superelasticity over a wide temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Dual-phase tissue morphology;

[0037] Figure 2 elastic distortion map;

[0038] Figure 3 DSC results showed that no phase transition occurred. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts should fall within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a method for preparing a high-strength superelastic alloy with a wide temperature range, comprising the following steps:

[0042] Step 1: Smelting and preparing the alloy, selecting Ti as the base material, adding a certain proportion of β-stabilizing element Nb, neutral elements Zr and Sn to inhibit metastable phase transition, with their atomic percentage ratio of 15.2:2.5:3.6, and adding 0.3at.% O to stabilize the finished alloy;

[0043] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The particle size is 0.33 nm, and the content of β-stabilizing elements in the β phase is 26 wt.%, which enables the α″ phase to be generated from the β phase through the compositional wave diffusion mechanism and improves the stability of the β phase, so that no phase change occurs under stress.

[0044] The method for adjusting the β-phase lattice constant is carried out in the following steps: (1) air cooling after hot forging, the hot forging temperature is 1200°C; (2) air cooling after hot rolling, the rolling temperature is 800°C, and the hot rolling deformation is 90%; (3) air cooling after low-temperature heat preservation treatment, the heat preservation temperature is 100°C, and the heat preservation time is 24 hours;

[0045] Step 3: Adjust the lattice constant and composition of the α″ phase to a value of 0.299 nm, a value of 0.499 nm, a value of 0.47 nm for the lattice constant a, a value of 10 wt.% for the β-stabilizing element in the α″ phase, and to transform the α″ phase into a lath-like morphology with continuous lattice distortion under stress.

[0046] The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) air cooling after aging treatment, aging temperature is 500°C, aging time is 2 hours; (2) low temperature heat preservation treatment, heat preservation temperature is 85°C, heat preservation time is 20 minutes; (3) pre-stretching deformation at 85°C, pre-stretching direction is the hot rolling direction, pre-deformation amount is 2%;

[0047] Step 4: Pre-deform the material with a pre-deformation strain of 1.5% and a pre-deformation temperature of 25°C.

[0048] By adjusting the lattice constants of the α″ and β phases through the above steps, the α″ and β phases undergo elastic lattice distortion under stress, thereby simultaneously improving elastic strain and strength. Within the temperature range of -200 to 120°C, the α″ phase exhibits an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa. Specific properties are shown in Table 1. Before adjustment, the α″ phase is generated by a component wave diffusion mechanism. After adjustment, it has a lath morphology with an aspect ratio of 5( Figure 1 ); After the β phase is adjusted, the elastic strain is contributed by the common lattice distortion of the β phase and the α "phase ( Figure 2 ); the alloy undergoes martensitic transformation before adjusting the lattice constants of the α" phase and the β phase, and does not undergo β→α" and / or β→α' phase transformation under stress after adjusting the lattice constants of the α" phase and the β phase ( Figure 3 ).

[0049] Example 2

[0050] This embodiment provides a method for preparing a high-strength superelastic alloy with a wide temperature range, comprising the following steps:

[0051] Step 1: Smelting and preparing the alloy, selecting Ti as the base material, adding a certain proportion of β-stabilizing element Nb, neutral elements Zr and Sn to inhibit metastable phase transition, with their atomic percentage ratio of 15.5:2.9:3.9, and adding 0.1at.% O to stabilize the finished alloy;

[0052] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The particle size is 0.331 nm, and the content of β-stabilizing elements in the β phase is 26 wt.%, which enables the α″ phase to be generated from the β phase through the compositional wave diffusion mechanism and improves the stability of the β phase, so that no phase change occurs under stress.

[0053] The method for adjusting the β-phase lattice constant is carried out in the following steps: (1) air cooling after hot forging, the hot forging temperature is 800°C; (2) air cooling after hot rolling, the rolling temperature is 500°C, and the hot rolling deformation is 70%; (3) air cooling after low-temperature heat preservation treatment, the heat preservation temperature is 100°C, and the heat preservation time is 24 hours;

[0054] Step 3: Adjust the lattice constant and composition of the α″ phase to a value of 0.298 nm, a value of 0.501 nm, a value of 0.47 nm for the lattice constant a, and a value of 7 wt.% for the β-stabilizing element in the α″ phase, so that the α″ phase transforms into a lath-like morphology and undergoes continuous lattice distortion under stress.

[0055] The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) air cooling after aging treatment, aging temperature is 400°C, aging time is 0.5 hours; (2) low temperature heat preservation treatment, heat preservation temperature is 70°C, heat preservation time is 10 minutes; (3) pre-stretching deformation at 70°C, pre-stretching direction is the hot rolling direction, pre-deformation amount is 1%;

[0056] Step 4: Pre-deform the material with a pre-deformation strain of 1.4% and a pre-deformation temperature of 30°C.

[0057] Through the above steps, the lattice constants of the α″ phase and the β phase are adjusted, so that the α″ phase and the β phase undergo elastic lattice distortion under stress, thereby simultaneously improving the elastic strain and strength, and having an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa in the temperature range of -200 to 120°C. Specific properties are shown in Table 1. Before being adjusted, the α″ phase is produced by a component wave diffusion mechanism, and after being adjusted, it has a lath morphology with an aspect ratio of 8; after the β phase is adjusted, the elastic strain is contributed by the common lattice distortion of the β phase and the α″ phase; the alloy undergoes a martensitic phase transformation before adjusting the lattice constants of the α″ phase and the β phase, and does not undergo β→α″ and / or β→α' phase transformation under stress after adjusting the lattice constants of the α″ phase and the β phase.

[0058] Example 3

[0059] This embodiment provides a method for preparing a high-strength superelastic alloy with a wide temperature range, comprising the following steps:

[0060] Step 1: Smelting and preparing the alloy, selecting Ti as the base material, adding a certain proportion of β-stabilizing element Nb, neutral elements Zr and Sn to inhibit metastable phase transition, with their atomic percentage ratio of 15.4:2.8:3.8, and adding 0.4at.% O to stabilize the finished alloy;

[0061] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a βThe particle size is 0.332 nm, and the content of β-stabilizing elements in the β phase is 24 wt.%, which enables the α″ phase to be generated from the β phase through the compositional wave diffusion mechanism and improves the stability of the β phase, so that no phase change occurs under stress.

[0062] The method for adjusting the β-phase lattice constant is carried out in the following steps: (1) air cooling after hot forging, the hot forging temperature is 800°C; (2) air cooling after hot rolling, the rolling temperature is 800°C, and the hot rolling deformation is 85%; (3) air cooling after low-temperature heat preservation treatment, the heat preservation temperature is 100°C, and the heat preservation time is 24 hours;

[0063] Step 3: Adjust the lattice constant and composition of the α″ phase to a value of 0.298 nm, a value of 0.503 nm, a value of 0.47 nm for the lattice constant a, and a value of 8 wt.% for the β-stabilizing element in the α″ phase, so that the α″ phase transforms into a lath-like morphology and undergoes continuous lattice distortion under stress.

[0064] The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) air cooling after aging treatment, aging temperature is 425°C, aging time is 1.5 hours; (2) low temperature heat preservation treatment, heat preservation temperature is 80°C, heat preservation time is 20 minutes; (3) pre-stretching deformation at 80°C, pre-stretching direction is the hot rolling direction, pre-deformation amount is 2%;

[0065] Step 4: Pre-deform the material with a pre-deformation strain of 1.4% and a pre-deformation temperature of 30°C.

[0066] By adjusting the lattice constants of the α″ phase and the β phase through the above steps, the α″ phase and the β phase undergo elastic lattice distortion under stress, thereby simultaneously improving the elastic strain and strength, and having an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa in the temperature range of -200 to 120°C. Specific properties are shown in Table 1. Before being adjusted, the α″ phase is produced by a component wave diffusion mechanism, and after being adjusted, it has a lath morphology with an aspect ratio of 5; after the β phase is adjusted, the elastic strain is contributed by the common lattice distortion of the β phase and the α″ phase; the alloy undergoes a martensitic phase transformation before adjusting the lattice constants of the α″ phase and the β phase, and does not undergo β→α″ and / or β→α' phase transformation under stress after adjusting the lattice constants of the α″ phase and the β phase.

[0067] Example 4

[0068] This embodiment provides a method for preparing a high-strength superelastic alloy with a wide temperature range, comprising the following steps:

[0069] Step 1: Smelting and preparing the alloy, selecting Ti as the base material, adding a certain proportion of β-stabilizing element Nb, neutral elements Zr and Sn to inhibit metastable phase transition, with their atomic percentage ratio of 15.5:3.0:4.5, and adding 0.2at.% O to stabilize the finished alloy;

[0070] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The particle size is 0.337 nm, and the content of β-stabilizing elements in the β phase is 27 wt.%, which enables the α″ phase to be generated from the β phase through the compositional wave diffusion mechanism and improves the stability of the β phase, so that no phase change occurs under stress.

[0071] The method for adjusting the β-phase lattice constant is carried out in the following steps: (1) air cooling after hot forging, the hot forging temperature is 1000°C; (2) air cooling after hot rolling, the rolling temperature is 800°C, and the hot rolling deformation is 85%; (3) air cooling after low-temperature heat preservation treatment, the heat preservation temperature is 100°C, and the heat preservation time is 24 hours;

[0072] Step 3: Adjust the lattice constant and composition of the α″ phase to a value of 0.298 nm, a value of 0.502 nm, a value of 0.479 nm for the lattice constant a, and a value of 5 wt.% for the β-stabilizing element in the α″ phase, so that the α″ phase transforms into a lath-like morphology and undergoes continuous lattice distortion under stress.

[0073] The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) air cooling after aging treatment, aging temperature is 475°C, aging time is 2 hours; (2) low temperature heat preservation treatment, heat preservation temperature is 85°C, heat preservation time is 20 minutes; (3) pre-stretching deformation at 85°C, pre-stretching direction is the hot rolling direction, pre-deformation amount is 2%;

[0074] Step 4: Pre-deform the material with a pre-deformation strain of 1.5% and a pre-deformation temperature of 30°C.

[0075] By adjusting the lattice constants of the α″ phase and the β phase through the above steps, the α″ phase and the β phase undergo elastic lattice distortion under stress, thereby simultaneously improving the elastic strain and strength, and having an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa in the temperature range of -200 to 120°C. Specific properties are shown in Table 1. Before being adjusted, the α″ phase is produced by a component wave diffusion mechanism, and after being adjusted, it has a lath morphology with an aspect ratio of 7; after the β phase is adjusted, the elastic strain is contributed by the common lattice distortion of the β phase and the α″ phase; the alloy undergoes a martensitic phase transformation before adjusting the lattice constants of the α″ phase and the β phase, and does not undergo β→α″ and / or β→α' phase transformation under stress after adjusting the lattice constants of the α″ phase and the β phase.

[0076] Example 5

[0077] This embodiment provides a method for preparing a high-strength superelastic alloy with a wide temperature range, comprising the following steps:

[0078] Step 1: Smelting and preparing the alloy, selecting Ti as the base material, adding a certain proportion of β-stabilizing element Nb, neutral elements Zr and Sn to inhibit metastable phase transition, with their atomic percentage ratio of 15.1:2.3:4.4, and adding 0.3at.% O to stabilize the finished alloy;

[0079] Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The particle size is 0.33 nm, and the content of β-stabilizing elements in the β phase is 27 wt.%, which enables the α″ phase to be generated from the β phase through the compositional wave diffusion mechanism and improves the stability of the β phase, so that no phase change occurs under stress.

[0080] The method for adjusting the β-phase lattice constant is carried out in the following steps: (1) air cooling after hot forging, the hot forging temperature is 800°C; (2) air cooling after hot rolling, the rolling temperature is 800°C, and the hot rolling deformation is 90%; (3) air cooling after low-temperature heat preservation treatment, the heat preservation temperature is 100°C, and the heat preservation time is 24 hours;

[0081] Step 3: Adjust the lattice constant and composition of the α″ phase to 0.299 nm, 0.505 nm, and 0.479 nm, and adjust the β-stabilizing element content in the α″ phase to 5 wt.%, so that the α″ phase transforms into a lath-like morphology and undergoes continuous lattice distortion under stress.

[0082] The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) air cooling after aging treatment, aging temperature is 500°C, aging time is 0.5 hours; (2) low temperature heat preservation treatment, heat preservation temperature is 75°C, heat preservation time is 20 minutes; (3) pre-stretching deformation at 75°C, pre-stretching direction is the hot rolling direction, pre-deformation amount is 2%;

[0083] Step 4: Pre-deform the material with a pre-deformation strain of 1.5% and a pre-deformation temperature of 30°C.

[0084] Through the above steps, the lattice constants of the α″ and β phases are adjusted, causing them to undergo elastic lattice distortion under stress, thereby simultaneously improving elastic strain and strength. The alloy exhibits an elastic strain greater than 1.5% and a tensile strength greater than 1000 MPa within a temperature range of -200°C to 120°C. Specific properties are shown in Table 1. Before adjustment, the α″ phase is produced via a component wave diffusion mechanism. After adjustment, it has a lath morphology with an aspect ratio of 4. After adjustment, the elastic strain of the β phase is contributed by the shared lattice distortion of both the β and α″ phases. The alloy undergoes a martensitic transformation before adjusting the lattice constants of the α″ and β phases. After adjusting the lattice constants of the α″ and β phases, the alloy does not undergo β→α″ and / or β→α' phase transformations under stress.

[0085] Table 1 Elastic strain and strength results of high-strength superelastic alloys in wide temperature range in Examples 1-5

[0086]

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Claims

1. A method for preparing a high-strength superelastic alloy with a wide temperature range, characterized in that: The following steps are involved: Step 1: preparing an alloy by smelting according to the alloy composition, selecting Ti as the base material, adding β-stabilizing element Nb, neutral elements Zr and Sn, and element O; the atomic percentage ratio of the elements Nb, Zr and Sn is 15-15.5:2.0-3.0:3.5-4.5; the atomic percentage of element O is not less than 0.1%; Step 2: Adjust the lattice constant and composition of the β phase so that its lattice constant a β The β-phase has a lattice constant of 0.32 to 0.34 nm, and the content of β-stabilizing elements in the β-phase is not less than 24 wt.%. The method for adjusting the lattice constant of the β-phase is carried out in the following steps: (1) Air cooling after hot forging, hot forging temperature 800~1200℃; (2) Air cooling after hot rolling, rolling temperature 500-800℃, hot rolling deformation 70-90%; (3) After low-temperature heat preservation treatment, air cooling is carried out, the heat preservation temperature is 100°C, and the heat preservation time is 23 to 25 hours; Step 3: Adjusting the lattice constant and composition of the α″ phase so that the lattice constant a is 0.29-0.30 nm, the lattice constant b is 0.49-0.51 nm, and the lattice constant c is 0.46-0.48 nm, and the content of the β-stabilizing element in the α″ phase is less than 20 wt.%. The method for adjusting the lattice constant of the α″ phase is carried out in the following steps: (1) Air cooling after aging treatment, aging temperature 400-500℃, aging time 0.5-2 hours; (2) Low temperature insulation treatment, insulation temperature 70-85°C, insulation time 10-20 minutes; (3) Pre-stretching deformation at 70-85°C, the pre-stretching direction is the hot rolling direction, and the pre-deformation amount is 1-2%; Step 4: Perform final pre-deformation on the material, with the pre-deformation strain lower than 1.8% and the pre-deformation temperature higher than 20°C.

2. The method for preparing a wide temperature range high-strength superelastic alloy according to claim 1, characterized in that: This alloy adjusts the lattice constants of the α″ phase and the β phase, causing the α″ phase and the β phase to undergo elastic lattice distortion under stress, thereby simultaneously improving elastic strain and strength. It has an elastic strain greater than 1.5% and a tensile strength greater than 1000MPa within the temperature range of -200 to 120°C.

3. The method for preparing a wide temperature range high-strength superelastic alloy according to claim 1, characterized in that: After the α″ phase is adjusted, the following conditions are satisfied: lattice constant a is 0.29 to 0.30 nm, lattice constant b is 0.49 to 0.51 nm, lattice constant c is 0.46 to 0.48 nm, and lattice constant ratio b / a is 1.60 to 1.

73.

4. The method for preparing a wide temperature range high-strength superelastic alloy according to claim 1, characterized in that: After the β phase is adjusted, the lattice constant a is satisfied at the same time. β is 0.32~0.34nm, and the lattice constant a β The relationship between the lattice constant b of the α″ phase is as follows:

5. The method for preparing a wide temperature range high-strength superelastic alloy according to claim 1, characterized in that: The α″ phase is adjusted to transform into a lamellar morphology with an aspect ratio of 3 to 10; Martensitic transformation occurs before adjusting the lattice constants of the α″ phase and the β phase, and after adjusting the lattice constants of the α″ phase and the β phase, no phase transformation from the β phase to the α″ phase and / or the β phase to the α′ phase occurs under stress.

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