High-toughness metastable beta titanium alloy and preparation method thereof

Abstract

The invention relates to a high-strength and high-toughness metastable beta titanium alloy and a preparation method thereof.The high-strength and high-toughness metastable beta titanium alloy is of a Ti-V-Mo-Cr-Fe-Al six-element system, and the high-strength and high-toughness metastable beta titanium alloy is prepared from, by mass, 85.6%-85.7% of Ti, 0.7%-1.8% of V, 3.0%-4.3% of Mo, 1.6%-2.3% of Cr, 4.4%-7.4% of Fe and 1.7% of Al. By optimizing the component proportion, adding a large amount of cheap Fe element and reducing the consumption of precious metal V, the cost is remarkably reduced, the alloy performance is excellent, the elongation reaches 28% after annealing at 900 DEG C for 30 minutes, the elongation is still kept to be 10% or above after aging at 550 DEG C for 12 hours, high plasticity is achieved, a fracture has a large amount of toughness dimple, toughness is excellent, balance between the cost and the performance is achieved, and the service life of the alloy is prolonged. The method is suitable for the fields with high requirements on cost and performance, such as aeronautics and astronautics.

Description

Technical Field

[0001] The present application relates to the technical field of titanium alloy materials, and in particular to a high-strength and tough metastable β-titanium alloy suitable for aerospace structural parts and lightweight components of civilian automobiles, and a preparation method thereof. Background Art

[0002] Metastable β-type titanium alloys are widely used in key components such as threaded fasteners and engine casings in aerospace applications due to their excellent cold deformation capability in the solid solution state of a body-centered cubic (BCC) structure, and their ability to achieve extremely high specific strength and corrosion resistance after aging. With industrial development, the composition design of these alloys has become increasingly complex, and their performance has continued to improve: from early 1100MPa-grade titanium-molybdenum-aluminum (Ti-Mo-Al) and titanium-chromium-aluminum (Ti-Cr-Al) alloys containing a single β-stabilizing element, to 1300-1400MPa-grade Ti-Mo-Nb-Al alloys with the designation β21s, to titanium alloys such as Ti-6.6Mo-4.5Fe-1.5Al alloys with the designations Ti-1023 and TIMETAL-LCB, and Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr). With the rapid development of industry, the requirements for the service performance of titanium alloy structural parts are further improved. At present, the performance indicators of the next generation of titanium alloys require a stable tensile yield strength greater than 1400MPa and a plasticity greater than 6%. In addition, the demand for cost-effective alloys in the civilian field has spawned the research direction of replacing traditional expensive vanadium (V) elements with cheap elements such as iron (Fe) and molybdenum (Mo). For example, the American TIMETAL-LCB alloy has achieved good strength-plasticity matching through composition design and heat treatment optimization.

[0003] Traditional compositional design of metastable β-type titanium alloys relies on single empirical parameters such as the molybdenum equivalent and the Kβ stability factor, making the search for high-performance compositions in multicomponent alloy systems inefficient. In recent years, design methods based on electronic parameters such as Bo (bond energy) and Md (d-electron orbital energy) have been able to predict solid solution deformation mechanisms (e.g., the Ti-3Cr5Mo7V3Al alloy prepared by Sadpour achieved a strain hardening rate exceeding 1800 MPa). However, single electronic parameters remain inadequate for rapidly and accurately identifying the optimal composition for multicomponent alloys. Valence electron concentration (VEC), a key parameter linearly correlated with β-phase stability and performance, can be used in conjunction with the maximum entropy principle to generate compositional sequences with varying VEC values. ΔG-VEC curves, derived from first-principles calculations of bond enthalpies, can effectively determine the equilibrium phase composition and aging effects of alloys (e.g., Kang's face-centered cubic + body-centered cubic (FCC+BCC) dual-phase titanium-vanadium-niobium-cobalt-chromium-nickel (TiVNbCoCrNi) multi-principal element alloy and Sun's high-strength, aged titanium alloy). However, the existing technology still has the following problems in the composition design of multi-element metastable β-type titanium alloys: ① Traditional empirical parameters and single electronic parameter methods are difficult to take into account both composition complexity and performance optimization efficiency; ② For low-cost alloy systems, there is a lack of systematic composition design theory and experimental paradigm to achieve coordinated regulation of strength and plasticity and industrial cost control.

[0004] Based on the above background, the present invention focuses on the low-cost titanium-vanadium-molybdenum-chromium-iron-aluminum (Ti-V-Mo-Cr-Fe-Al) alloy system, proposes a composition design strategy based on the combination of the maximum entropy principle and first-principles calculations under the constraint of valence electron concentration (VEC), determines VEC=4.27 as the key composition point through thermodynamic optimization, combines solid solution-aging treatment to induce dispersed α phase precipitation, and uses scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction technology to reveal the deformation mechanism and strengthening mechanism, aiming to provide a metastable multi-component titanium alloy design scheme that takes into account performance, cost and process simplification, and provide a reusable theoretical and experimental framework for the development of similar metal-based alloys. Summary of the Invention

[0005] The purpose of this application is to provide a high-strength and toughness metastable β titanium alloy and a preparation method thereof, so as to solve the problems existing in the prior art of low efficiency in the design of multi-component titanium alloy components, difficulty in accurately matching performance requirements, and the inability of low-cost titanium alloys to achieve high strength and toughness-high plasticity coordinated regulation and industrial cost control.

[0006] The embodiments of the present application can be implemented through the following technical solutions:

[0007] A high-strength and tough metastable beta titanium alloy is a Ti-V-Mo-Cr-Fe-Al sesquicyclic system, wherein the mass percentages of the elements are: 85.6% to 85.7% Ti, 0.7% to 1.8% V, 3.0% to 4.3% Mo, 1.6% to 2.3% Cr, 4.4% to 7.4% Fe, and 1.7% Al.

[0008] Furthermore, the mass percentage of each element is obtained according to the following design method, comprising the following steps:

[0009] S1, calculate configurational entropy,

[0010] According to the expression S=-R(ΣC i lnC i +0.87ln0.87+0.03ln0.03) to calculate the configurational entropy, where C i (i = 1, 2, 3, 4) represents the molar concentration of elements V, Mo, Cr and Fe, respectively, R is the gas constant, and (0.87ln0.87 + 0.03ln0.03) is the fixed entropy contribution of Ti and Al;

[0011] S2, design VEC constraints,

[0012] Through the VEC total balance equation ∑ i C i (VEC) i +0.87VEC Ti +0.03VEC Al = k and element concentration sum constraint∑ i C i =0.1 controls the alloy's thermal stability, where (VEC) i is the valence electron concentration of element i, k is the target VEC value, C i represents the molar concentration of the i-th element;

[0013] S3, extreme value solution based on Lagrange multiplier method,

[0014] Under the constraints of step S2, the Lagrange undetermined multiplier method is used to construct the objective function to maximize the configuration entropy in step S1, thereby determining the optimal molar concentrations of V, Mo, Cr, and Fe in the alloy;

[0015] S4, Equilibrium phase composition prediction and component screening,

[0016] Using a method based on the maximum entropy principle combined with first principles, MaterialsStudio software was used to calculate element bond enthalpies and derive the Gibbs free energy ΔG to predict the equilibrium phase composition of alloys at different temperatures. The phase stability of different VEC values ​​at different temperatures was analyzed, and the atomic ratio of the required alloy components was screened by combining parameters such as molybdenum equivalent.

[0017] S5. Calculate the mass percentage of each element based on the atomic proportion of each element.

[0018] Furthermore, step S3 includes the following steps:

[0019] S31, Lagrangian function construction, introducing two unknown multipliers λ j1 and λ j2 ,λ j1 Corresponding to VEC constraint, λ j2 Corresponding to the concentration sum constraint, the objective function L is:

[0020] L=S+λ j1 (∑ i C i (VEC) i +0.87(VEC) Ti +0.03VEC Al -k)+λ j2 (∑ i C i -0.1);

[0021] Where S is the configuration entropy of the alloy, (VEC) i is the valence electron concentration of element i, C i Indicates the molar concentration of the i-th element, 0.87 (VEC) Ti Fixed VEC contribution of Ti element, 0.03VEC Al is the fixed VEC contribution of Al element, k is the target VEC value;

[0022] S32, extreme value condition solution, the condition for maximizing entropy is the objective function of each element concentration C i The partial derivative of is 0, that is

[0023]

[0024] The expression of the concentration of each element is sorted out:

[0025] c i =exp(-1+λ j1 (VEC) i +λ j2 );

[0026] S33, to be determined multiplier λ j1and λ j2 Solve for c i =exp(-1+λ j1 (VEC) i +λ j2 ) is substituted into the two formulas of the constraint condition in step S32, and the equation about λ is obtained. j1 and λ j2 The equations of λ can be calculated separately. j1 and λ j2 ;

[0027] S34, calculate the concentration of each element, and set λ j1 and λ j2 and (VEC)i is substituted into formula c i =exp(-1+λ j1 (VEC) i +λ j2 ) to obtain the atomic concentrations of V, Mo, Cr, and Fe.

[0028] Furthermore, step S4 includes the following steps:

[0029] S41, Assumptions and calculation premises of equilibrium phase composition,

[0030] Assuming that the alloy exists in only two single-phase structures, α phase and β phase, under different states, the Gibbs free energy ΔG under the two structures is calculated separately, and the phase with the lower ΔG value is taken as the equilibrium phase at a specific temperature.

[0031] S42, solid solution mixing enthalpy Calculation,

[0032] According to the formula Calculate the enthalpy of mixing, where φ represents the crystal structure, represents the interaction parameter between element i and element j; C i and C j represent the concentrations of element i and element j, respectively.

[0033] S43, selection of calculation method for interaction parameters and determination of core formula,

[0034] According to the formula Calculate the interaction parameters of elements i and j in the crystal structure, where is the number of nearest neighbors of the central atom in an alloy with a specific lattice structure, N AV represents Avogadro's constant, and The coordination number of the crystal structure represents the bond enthalpy between the same atoms or different atomic pairs in the alloy;

[0035] S44, according to the interaction parameters The stability curve was drawn, and the optimal value of each element under the VEC constraint condition was determined. The element interaction parameter Ωij under BCC and HCP structures was calculated, and the VEC-ΔG curves were drawn at room temperature and 900℃ for different VEC values ​​to determine the VEC range in the two-phase region.

[0036] Furthermore, the VEC value is 4.27. Under this value, the mass percentages of the elements are: 85.6% Ti, 1.0% V, 3.5% Mo, 1.9% Cr, 6.3% Fe, and 1.7% Al.

[0037] The present application also provides a method for preparing a high-strength and tough metastable β titanium alloy, which uses the above-mentioned elements and mixes them according to mass percentage, comprising the following steps:

[0038] S100, alloy melting: using vacuum induction melting technology to prepare alloy ingots;

[0039] S200, homogenization treatment: The smelted alloy ingot is sealed with argon and kept at a high temperature with only the β phase region for 1-3 hours, so that the alloy presents a single-phase β solid solution structure, thereby making the alloy have cold deformation ability and processability;

[0040] S300, sample cutting: using a wire cutting machine to cut the homogenized ingot into rectangular samples;

[0041] S400, cold rolling: At room temperature, the rectangular specimen is cold rolled to reduce the thickness of the specimen to 10% of the original thickness, i.e. the cold rolling deformation is 90%;

[0042] S500, annealing treatment: the cold-rolled sample is placed in a high-temperature environment with only the β phase region for 30 minutes to allow the alloy to recover and recrystallize after cold rolling, and finally show plasticity;

[0043] S600, aging treatment: the annealed samples were aged at 400°C-550°C for 12 hours.

[0044] The embodiments of the present application provide a high-strength and tough metastable β titanium alloy and a preparation method thereof, which have at least the following beneficial effects:

[0045] This application designs the composition ratio of each element, so that a large amount of cheap Fe elements are added to the alloy composition design, which significantly reduces the production cost, while reducing the use of precious metal V and effectively controlling the cost of raw materials. In terms of performance, the alloy exhibits excellent comprehensive performance. On the one hand, it has good high plasticity. According to experimental tests, after annealing at 900℃×30 minutes, the elongation of the alloy can reach 28%, which far exceeds the performance of similar alloys under a single dislocation slip deformation mechanism. Even after aging treatment, it can still maintain an elongation of more than 10% under some aging conditions (such as aging at 550℃ for 12 hours). On the other hand, the high toughness of the alloy is also excellent. From the tensile fracture morphology, a large number of tiny tough dimples are distributed on the fracture surface. These dimples are formed by the interaction and accumulation of dislocations during the deformation process, which fully confirms that when the alloy is subjected to external force deformation, it can absorb a large amount of energy through the coordination of dislocations, avoid the occurrence of brittle fracture, and ensure the reliability and safety of the material under complex stress environments. This property of ensuring high plasticity and high toughness while reducing costs makes the alloy have broad application prospects in fields such as aerospace, automobile manufacturing, and medical devices, which have strict requirements on material performance and cost control. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the crystal structure diagram established in MS software;

[0047] Figure 2 VEC-ΔG curves at 23°C and 900°C calculated based on first-principles calculations;

[0048] Figure 3 The Bo-Md phase prediction diagram of Ti-VMoCrFeAl alloy with VEC of 4.27 is shown;

[0049] Figure 4 The microstructure of the alloy in the as-cast and annealed states is shown;

[0050] Figure 5 The mechanical properties and microstructure of the annealed alloy are demonstrated;

[0051] Figure 6 The mechanical properties and microstructure of the aged alloy are demonstrated. DETAILED DESCRIPTION

[0052] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0053] In addition, various components in the drawings are enlarged or reduced in size for ease of understanding, but this is not intended to limit the scope of protection of this application.

[0054] Words importing the singular include the plural and vice versa.

[0055] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or are the orientation or positional relationship in which the products of the embodiments of the present application are usually placed when in use, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, in order to distinguish different units, words such as first and second are used in this specification, but these are not limited by the order of manufacture, nor can they be understood as indicating or implying relative importance. Their names may be different in the detailed description and claims of the present application.

[0056] The vocabulary in this specification is used to illustrate the embodiments of the present application, but is not intended to limit the present application. It should also be noted that, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, an indirect connection through an intermediate medium, or a communication between the two components. For those skilled in the art, the specific meanings of the above terms in this application can be specifically understood.

[0057] The present application provides a high-strength and tough metastable β titanium alloy, which is a Ti-V-Mo-Cr-Fe-Al sesquicyclic system, and the mass percentage of each element is: 85.6-85.7% Ti, 0.7% to 1.8% V, 3.0% to 4.3% Mo, 1.6% to 2.3% Cr, 4.4% to 7.4% Fe, and 1.7% Al.

[0058] The mass percentages of the above elements are obtained by the following design method:

[0059] S1, calculate configurational entropy,

[0060] According to the expression S=-R(ΣC i lnC i +0.87ln0.87+0.03ln0.03) to calculate the configurational entropy, where C i (i = 1, 2, 3, 4) represents the molar concentrations of V, Mo, Cr, and Fe, respectively (unit: atomic ratio), R is the gas constant (8.314 J / (mol·K)), and (0.87ln0.87 + 0.03ln0.03) is the fixed entropy contribution of Ti and Al (since their ratio is constant).

[0061] S2, design VEC constraints,

[0062] Through the VEC total balance equation ∑ i C i (VEC) i +0.87VEC Ti +0.03VEC Al = k and element concentration sum constraint∑ i C i =0.1 controls the alloy's thermal stability, where (VEC) i is the valence electron concentration of element i, k is the target VEC value, C i It represents the molar concentration of the i-th element;

[0063] S3, extreme value solution based on Lagrange multiplier method,

[0064] Under the constraints of step S2, the Lagrange undetermined multiplier method is used to construct the objective function to maximize the configuration entropy in step 1, thereby determining the optimal molar concentrations of V, Mo, Cr, and Fe in the alloy;

[0065] S4, Equilibrium phase composition prediction and component screening,

[0066] Using a method based on the maximum entropy principle combined with first principles, Materials Studio (MS) software was used to calculate element bond enthalpies and derive Gibbs free energy (ΔG) to predict the equilibrium phase composition of alloys at different temperatures. The phase stability of different VEC values ​​at different temperatures was analyzed, and the atomic ratio of the desired alloy components was screened by combining parameters such as molybdenum equivalent.

[0067] S5. Calculate the mass percentage of each element based on the atomic proportion of each element.

[0068] Specifically, in order to achieve the purpose of the invention of this application and give full play to the alloying effect of each element, this application comprehensively selects vanadium (V), molybdenum (Mo), chromium (Cr), iron (Fe) and aluminum (Al) as alloying elements, and the specific basis is as follows:

[0069] Vanadium (V) and molybdenum (Mo) are both isomorphous β-phase stabilizing elements. They are infinitely miscible with titanium (Ti) in the body-centered cubic (BCC) and hexagonal close-packed (HCP) structure lattices, which can effectively improve the β-phase stability of the alloy.

[0070] Chromium (Cr) is a slow eutectoid element. To avoid the formation of titanium-chromium (TiCr2) intermetallic compounds during the aging process, its addition amount is usually not more than 3%.

[0071] Iron (Fe) is a fast eutectoid element with good solid solution strengthening effect. As a cheap element, it can reduce alloy costs. It is used in commercial titanium-1023 (Ti-1023) and TIMAL-LCB alloys.

[0072] Aluminum (Al) can avoid the formation of intergranular precipitation-free zones and strengthen the α phase, so 3% aluminum (Al) is usually added to metastable β-type titanium alloys.

[0073] In addition to the above qualitative composition limitations, in order to quantitatively determine the content of vanadium (V), molybdenum (Mo), chromium (Cr), and iron (Fe), this application uses the maximum entropy calculation method under the valence electron concentration (VEC) constraint to obtain the alloy composition. In the composition design of the Ti-V-Mo-Cr-Fe-Al alloy system, in order to balance performance and cost, the basic element ratio is fixed as follows:

[0074] Ti accounts for 87% of the total atomic weight (as a matrix element, providing the basic structure of the alloy);

[0075] The atomic percentage of Al is 3% (used to suppress the intergranular precipitation zone and strengthen the α phase);

[0076] The remaining 10% of the atomic proportion is distributed by the β-stabilizing elements V, Mo, Cr, and Fe (these four elements are variables, denoted as C i , (i=1,2,3,4) corresponds to V, Mo, Cr, Fe respectively), the mass percentage of each element is obtained by the following design method:

[0077] S1: Calculate configurational entropy,

[0078] Configurational entropy is a key parameter that describes the degree of disorder in the distribution of alloy elements. The larger its value, the better the phase stability of the alloy (especially for non-equimolar solid solutions). In this design, the expression of configurational entropy S is:

[0079] S=-R(∑C i lnC i +0.87ln0.87+0.03ln0.03) (1)

[0080] Among them, C i where (i=1, 2, 3, 4) represents the molar concentrations of V, Mo, Cr, and Fe, respectively (unit: atomic ratio), R is the gas constant (8.314 J / (mol·K)), and (0.87ln0.87+0.03ln0.03) is the fixed entropy contribution of Ti and Al (because their ratio is constant).

[0081] S2: Design VEC constraints

[0082] Valence electron concentration (VEC) is a key parameter that determines the stability of the titanium alloy crystal structure (VEC value directly affects the alloy's phase composition and deformation mechanism). This design controls the thermodynamic stability of the alloy through VEC constraints. The specific constraints are as follows:

[0083] The total VEC value of the alloy is the sum of the VEC contributions of each element, and the expression is:

[0084] ∑ i C i (VEC) i +0.87VEC Ti +0.03VEC Al =k (2)

[0085] Where (VEC) i is the valence electron concentration of element i (experimentally measured: (VEC) v =5.44, (VEC) Mo =5.44, (VEC) Cr =5.46, (VEC) Fe =5.48;(VEC) Ti =4.0, (VEC) Al =3.0), k is the target VEC value.

[0086] The total element concentration constraint is that the total atomic concentration of V, Mo, Cr, and Fe must satisfy the remaining 10% atomic ratio, that is:

[0087] ∑ i C i =0.1 (3)

[0088] C i is the molar concentration (unit: atomic ratio) of the i-th element (specifically one of V, Mo, Cr, and Fe).

[0089] S3: Extreme value solution based on Lagrange multiplier method,

[0090] In order to maximize the configuration entropy S (i.e., optimize the alloy phase stability) under the above constraints, the Lagrange undetermined multiplier method is used to construct the objective function. The steps are as follows:

[0091] S31, Lagrangian function construction, introducing two unknown multipliers λ j1 (corresponding to the VEC constraint) and λ j2 (corresponding to the concentration sum constraint), the objective function L is:

[0092] L=S+λ j1 (∑ i C i (VEC)i +0.87(VEC) Ti +0.03VEC Al -k)+λ j2 (∑ i C i -0.1) (4)

[0093] Where S is the configuration entropy of the alloy, (VEC) i is the valence electron concentration of element i, C i Indicates the molar concentration of the i-th element, 0.87 (VEC) Ti Fixed VEC contribution of Ti element, 0.03VEC Al is the fixed VEC contribution of Al element, k is the target VEC value;

[0094] S32, extreme value condition solution, the condition for maximizing entropy is the objective function of each element concentration C ij The partial derivative of is 0, that is:

[0095]

[0096] Arranging formula (5) can obtain the expression of each element concentration:

[0097] c i =exp(-1+λ j1 (VEC) i +λ j2 ) (6)

[0098] S33, to be determined multiplier λ j1 and λ j2 Solve the problem, substitute Equation (6) into the constraint conditions Equation (2) and Equation (3), and get the solution about λ j1 and λ j2 The equations of λ can be calculated separately. j1 and λ j2 ,λ j1 is about 0.52, λ j2 About -2.35.

[0099] S34, calculate the concentration of each element, and set λ j1 and λ j2 Substituting (VEC)i into formula (6), we can obtain the atomic concentrations of V, Mo, Cr, and Fe. The calculation results are shown in Table 1 below:

[0100] Table 1 Atomic proportions of elements in Ti-V-Mo-Cr-Fe-Al alloy under VEC constraint conditions

[0101] VEC Ti V Mo Cr Fe Al 4.23 87.00 1.70 2.20 2.30 3.80 3.00 4.25 87.00 1.30 2.00 2.00 4.70 3.00 4.27 87.00 1.00 1.80 1.70 5.50 3.00 4.29 87.00 0.70 1.50 1.40 6.40 3.00 4.31 87.00 0.50 1.20 1.10 7.20 3.00 4.33 87.00 0.30 0.80 0.80 8.10 3.00

[0102] S4, Equilibrium phase composition prediction and component screening,

[0103] A method based on the maximum entropy principle combined with first principles was used to calculate the element bond enthalpy through MaterialsStudio (MS) software, and derive the Gibbs free energy (ΔG) to predict the equilibrium phase composition of the alloy at different temperatures. The phase stability of different VEC values ​​at different temperatures was analyzed, and the atomic ratio of the required alloy components was screened out by combining parameters such as molybdenum equivalent.

[0104] After determining the alloy composition corresponding to different VEC values ​​through VEC constraints and the maximum entropy principle, it is necessary to further predict the equilibrium phase composition of the alloy at different temperatures (mainly α phase or β phase) in order to screen the composition with the ideal aging strengthening effect. At present, the method based on the maximum entropy principle combined with first-principles calculations performs well in phase composition prediction - Yin and other scholars use this method to calculate the interatomic bond enthalpy, and then obtain the interaction parameters between elements, and finally predict the equilibrium phase composition through the change law of Gibbs free energy (ΔG). The results have a small error with the experiment, and are more theoretically supported and reliable than the traditional VEC method or Ω-δ method. Therefore, this study uses MaterialsStudio (MS) software to calculate the element bond enthalpy and derive the Gibbs free energy through thermodynamic formulas. The specific process is as follows:

[0105] S41, Assumptions and calculation premises of equilibrium phase composition,

[0106] Assume that the alloy exists in only two single-phase structures in different states:

[0107] α phase: has HCP (hexagonal close-packed) crystal structure;

[0108] β phase: has a BCC (body-centered cubic) crystal structure.

[0109] By calculating the Gibbs free energy ΔG under the two structures separately, the stable phase composition of the alloy at a specific temperature can be determined - the phase with a lower ΔG value is the equilibrium phase.

[0110] S42, solid solution mixing enthalpy Calculation,

[0111] Mixing enthalpy is a key parameter to measure the strength of interatomic interactions and directly affects the stability of the solid solution. Its expression is:

[0112]

[0113] Where φ represents the crystal structure (HCP or BCC), represents the interaction parameter between elements i and j (unit: kJ / mol); C i and C jRepresent the concentrations of elements i and j respectively (unit: atomic ratio).

[0114] S43, Derivation of interaction parameters,

[0115] generally According to the electronegativity difference Δx ij Miracle et al. used the atomic bond enthalpy method to calculate the interaction parameters of elements i and j in the crystal structure. Instead of Δx ij In calculation The calculation results show that this method is more effective in predicting phase stability and has higher accuracy. The calculation formula is:

[0116]

[0117] In the equation described above, It is the number of nearest neighbors of the central atom in an alloy with a specific lattice structure (where k BCC =14,k HCP =12), N AV represents Avogadro's constant; and The coordination number of the crystal structure represents the bond enthalpy between the same atoms or different atomic pairs in the alloy. Characterizing the number of bonds per mole of pure metal, it can be expressed as represents the coordination number of pure metal). and Respectively represent the number of II, JJ and IJ bonds in one mole of IJ alloy. Refers to the enthalpy difference of 1 mol of condensed alloy (expressed as ) into a non-interacting atomic gas is expressed as in, The calculation formula is:

[0118]

[0119] and represent the number of atoms i and j in one mole of the ij binary alloy. i and E j represents the energy of isolated atoms i and j.

[0120] and represent the number of atoms i and j in one mole of the ij binary alloy. i and E j represents the energy of isolated atoms i and j.

[0121] In order to predict the phase stability of the alloys corresponding to the above different VECs, it is necessary to calculate the free energy of the alloy system at different temperatures for different compositions and draw the composition-Gibbs free energy. The composition-Gibbs free energy change curve can be used to predict the equilibrium phase composition of the multicomponent alloy. Since the composition and VEC have a corresponding relationship, the equilibrium phase composition of the alloy can be predicted by the VEC-ΔG curve at different temperatures.

[0122] ΔG Ф (T) = ΔH Ф -TΔS (12)

[0123] The enthalpy change of the phase calculated by MS is the enthalpy change at 0K. In order to calculate the enthalpy change of the phase at other temperatures, we use Kirchhoff's law for conversion, and its expression is:

[0124]

[0125] Where ΔH Ф (T) is the enthalpy change of the solid solution with Ф structure at temperature T, ΔC p is the molar constant-pressure heat capacity. The entropy change of the alloy system will also change with temperature. The formula is:

[0126]

[0127] According to the first law of thermodynamics, dQ = ΔC p dT, so

[0128]

[0129] Therefore, for an alloy in a single solid solution phase, the Gibbs free energy is expressed as:

[0130]

[0131] here represents the mixing enthalpy at 0K; ΔCp represents the heat capacity at 0K; ΔSmix represents the mixing entropy at 0K.

[0132] Before calculating the alloy phase structure in MaterialsStudio (MS) software, it is necessary to construct unit cell models of body-centered cubic (BCC) and hexagonal close-packed (HCP) structures. The specific operation method is as follows:

[0133] like Figure 1As shown in the figure, for an alloy system composed of components i and j, two crystal structure unit cells are constructed. In the body-centered cubic (BCC) unit cell construction process, different elements are selected and labeled as type i and type j atoms, respectively. The type i atom is placed at the body center of the unit cell with the three-dimensional coordinates (1 / 2, 1 / 2, 1 / 2), and the type j atom is placed at the unit cell vertex with the coordinates (0, 0, 0), thus completing the basic construction of the BCC unit cell.

[0134] To ensure comprehensiveness and accuracy of the calculation results for the hexagonal close-packed (HCP) lattice structure, two types of unit cells are constructed. In the first unit cell, type i atoms are positioned at specific locations in the hexagonal lattice, with three-dimensional coordinates (2 / 3, 1 / 3, 1 / 2), and type j atoms are located at the coordinate origin (0, 0, 0). In the second unit cell, the atomic positions are swapped, with type j atoms located at (2 / 3, 1 / 3, 1 / 2) and type i atoms at (0, 0, 0). By constructing two HCP unit cells with different atomic occupancy, the influence of different atomic distribution states in the lattice on the calculation results is fully considered.

[0135] After completing the BCC and HCP unit cell construction, the unit cells for the two structures were calculated separately, and the results were arithmetic averaged. This averaging method effectively eliminates calculation errors caused by differences in the initial atomic occupancy in the lattice, improves the accuracy of alloy phase structure calculations, and provides a reliable structural model foundation for subsequent MS software-based calculations of inter-element bond enthalpies, derivation of alloy system Gibbs free energy, and prediction of equilibrium phase composition.

[0136] The interaction parameter Ω calculated using the above method is ij , as shown in Table 2:

[0137] Table 2 Interaction parameters Ω of BCC crystal structure (upper right) and HCP crystal structure (lower right) ij (KJ / mol)

[0138]

[0139] The VEC-ΔG curves of different VEC values ​​at room temperature and 900°C are calculated. Preferably, the room temperature is 23°C as an example, such as Figure 2 As shown in the figure, we can see that the VEC interval of the α+β two-phase region at 23℃ is (4.08, 4.33), and the interval of the α+β two-phase region at 900℃ is (4.11, 4.13).

[0140] Analysis of Titanium Alloy Crystal Structure Stability Parameters and Prediction of Alloy Properties

[0141] In the field of titanium alloy composition design, molybdenum equivalent ([Mo]eq) and valence electron concentration (VEC) are key parameters for measuring the stability of the alloy crystal structure. Among them, molybdenum equivalent reflects the stability of the alloy β phase by quantifying the contribution of each alloying element to the stabilization of the β phase. Its calculation formula is as follows:

[0142] [Mo]eq=1.0(wt.%Mo)+0.67(wt.%V)+0.44(wt.%W)+0.28(wt.%Nb)+0.22(wt.%Ta)

[0143] +2.9(wt.%Fe)+1.6(wt.%Cr)+1.54(wt.%Mn)+1.25(wt.%Ni)-1.0(wt.%Al)

[0144] The alloy composition trends shown in Table 1 indicate a significant increase in the inexpensive element iron (Fe) while decreasing the expensive element vanadium (V) in high-VEC alloys. This compositional characteristic enhances the stability of the β phase in the solid solution state of a single body-centered cubic (BCC) structure, resulting in higher initial strength. However, due to the reduced resistance to dislocation movement, the strain hardening rate is low, which in turn gives the alloy excellent cold deformation capability. It is worth noting that when selecting the VEC value, it is necessary to ensure that it is within the two-phase region. Alloy compositions within this range can trigger the dispersed precipitation of the α phase during aging treatment, achieving age strengthening.

[0145] In some preferred embodiments, based on the above theoretical and practical considerations, this application finally selects VEC values ​​of 4.23, 4.25, 4.27, and 4.29.

[0146] S5. Calculate the mass percentage of each element based on the atomic proportion of each element.

[0147] The formula for solving the mass percentage (mass fraction, wt%) based on the atomic percentage (atomic percentage, at%) of an element is as follows:

[0148]

[0149] Among them, C i is the atomic percentage of element i (unit: at%, which needs to be converted to decimal form when calculating, such as 5% is 0.05), M i is the molar mass of element i (unit: g / mol, which can be found in the periodic table, such as Ti is 47.87 g / mol, Al is 26.98 g / mol, etc.), n is the total number of elements in the alloy, and the denominator is the sum of the "atomic fraction × molar mass" of all elements, that is, the total "molar mass contribution" of the alloy.

[0150] According to the VEC values ​​of 4.23, 4.25, 4.27, and 429, the mass percentages of each element at different VEC values ​​are calculated, as shown in Table 3:

[0151] Table 3 Mass percentage of elements in Ti-V-Mo-Cr-Fe-Al alloy under VEC constraint conditions

[0152] VEC Ti V Mo Cr Fe Al unit price 4.23 85.6 1.8 4.3 2.3 4.4 1.7 408 4.25 85.6 1.4 3.9 2.1 5.4 1.7 399 4.27 85.6 1.0 3.5 1.9 6.3 1.7 391 4.29 85.7 0.7 3.0 1.6 7.4 1.7 383

[0153] In some preferred embodiments, the mass proportion of each element at a VEC value of 4.27 has the characteristics of increased content of cheap elements and reduced content of expensive elements, and can meet performance requirements such as aging strengthening effect.

[0154] The alloy's calculated molybdenum equivalent is 22.6, significantly higher than Ti-1023 alloy (Molybdenum equivalent 9.5) and TIMETAL-LCB alloy (Molybdenum equivalent 18.15). This higher Molybdenum equivalent promotes a stable dislocation slip mechanism during deformation, particularly the cross-slip behavior of screw dislocations, which further reduces the alloy's hardening rate and ensures excellent cold forming processability. Furthermore, the fine α phase precipitated during aging effectively hinders dislocation motion, significantly improving the alloy's strength after aging.

[0155] In addition, the Bo-Md criterion, a design tool based on the electronic structure parameters of alloying elements, was first applied to the design of nickel-based superalloys in 1984. In recent years, it has shown unique advantages in the field of deformation mechanism and performance prediction of multi-component titanium alloys. This criterion consists of a bond order parameter (Bo) and a parameter related to the martensitic transformation onset temperature (Md). The specific calculation formula is as follows:

[0156] Bo=2.79CTi+2.805CMo+3.063CV+2.779CCr+2.651CFe+2.426CAl

[0157] Md=2.447CTi+1.961CMo+1.87CV+1.48CCr+0.969CFe+2.2CAl

[0158] Where C i is the weighted average parameter of element i in the alloy. Compared with a single molybdenum equivalent parameter, the Bo-Md binary parameter system can more accurately evaluate the phase stability of the alloy after solution treatment and thus predict its deformation behavior. Under the alloy composition in this study, the calculated Bo value is 2.776 and the Md value is 2.312. Map it to the Bo-Md diagram (see Figure 3), combined with the prediction model established in the reference literature, it is shown that alloys located near the Slip-Twin line are prone to twinning during deformation, realizing the twin-induced plasticity (TWIP) effect. Alloys located between the Slip-Twin line and the Ms=RT line will produce a {332}<11-3> twin system during deformation. This twinning deformation mechanism can cooperate with dislocation slip, effectively improving the alloy's tensile plasticity and strength matching. Therefore, by integrating the multi-parameter analysis system of molybdenum equivalent, VEC, and Bo-Md, this study can systematically predict the alloy's cold deformation ability in the solid solution state and its mechanical properties after aging, providing multi-dimensional theoretical support for the composition design of high-performance titanium alloys.

[0159] In some preferred embodiments, the present application also provides a method for preparing a high-strength and tough metastable β titanium alloy, using the above-mentioned elements and mixing them according to mass percentage, comprising the following steps:

[0160] S100, alloy melting: vacuum induction melting technology is used to prepare 1000g alloy ingots.

[0161] S200, homogenization treatment: The smelted alloy ingot is sealed with argon and kept at a high temperature with only the β phase region for 1-3 hours, so that the alloy presents a single-phase β solid solution structure, thereby making the alloy have good cold deformation ability and convenient processability; preferably, the heat treatment is carried out at 900°C.

[0162] S300, sample cutting: Use a wire cutting machine to cut the homogenized ingot into rectangular samples with a thickness of 15 mm.

[0163] S400, cold rolling: At room temperature, the rectangular specimen is cold rolled to reduce the thickness of the specimen from 15 mm to 1.5 mm, i.e. the cold rolling deformation is 90%.

[0164] S500, annealing treatment: placing the cold-rolled sample in a high-temperature environment with only the β phase region for 30 minutes, so that the alloy recovers and recrystallizes after cold rolling, and finally exhibits good plasticity; preferably, placing it in a 900°C environment and annealing for 30 minutes.

[0165] S600, aging treatment: the annealed samples were aged at 400°C, 500°C and 550°C for 12 hours respectively.

[0166] It should be noted that the reason why annealing is required at 400℃-550℃ is that at lower temperatures, the microstructure of the alloy is calculated to be α+β dual phase. Therefore, keeping the alloy at 400℃-550℃ for a long time can cause the alloy to precipitate α phase, thereby improving the strength of the alloy.

[0167] In some preferred embodiments, the treated alloys are labeled CRAA-400, CRAA-500, and CRAA-550, respectively.

[0168] In order to deeply explore the microstructure, phase composition, element distribution and mechanical properties of Ti-1.05V-3.55Mo-1.92Cr-6.31Fe alloy, a variety of characterization and testing methods were used.

[0169] In terms of phase composition and microstructure analysis, a SmartLab(9) diffractometer was used with Cu-Kα as the radiation source. X-ray diffraction (XRD) tests were performed in the 10°-90° angle range at a scanning speed of 5° / min. The phase structure of the alloy was accurately identified by analyzing the characteristic peak positions and intensities of the diffraction patterns. The micromorphology of the alloy was observed using an ApreoC scanning electron microscope equipped with electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS). The SEM specimens were first mechanically polished with 3000 grit SiC paper to remove surface processing damage. Subsequently, they were electropolished at 40 V for 50-60 seconds in a solution prepared with methanol, n-butanol, ethylene glycol, and perchloric acid in a volume ratio of 6.5:2:1:0.5 to eliminate the surface stress layer. EBSD was used to analyze the grain orientation distribution, and EDS was used to achieve qualitative and quantitative detection of micro-region composition. The microstructural details were further characterized with the help of a JEM-2100F transmission electron microscope. The TEM sample was thinned to Φ3×55μm using ion milling technology. Combining high-resolution imaging with selected area electron diffraction (SAED) technology, the alloy phase structure, dislocation configuration within the grains, and second-phase particle characteristics were deeply observed.

[0170] During the mechanical property test, the dog-bone plate tensile specimens with a cross-sectional size of 2.0 mm × 1.5 mm and a gauge length of 8.0 mm were prepared by wire-cutting electrospark cutting. The surface of the specimens was ground with 2000 grit SiC paper to reduce the interference of surface roughness on the test results. At room temperature, a CMT-5305GL universal electronic tensile testing machine was used to test the specimens at a speed of 1 × 10 -3 s -1Tensile tests were conducted at a strain rate of 1000 strain. Three specimens were taken from the center of the cold-rolled plate for each alloy and repeated testing was performed. The average of the three test results was used to ensure the reliability and accuracy of the mechanical property data. Infrared analysis was used to determine the vanadium, molybdenum, chromium, zirconium, and aluminum content in the alloys, while oxygen content was determined using pulsed heating inert gas melting infrared absorption. For metallographic observation and phase analysis, the alloy ingots after melting were sealed with argon and homogenized at 900℃ for 2h. They were cut into rectangular specimens and then solution treated to serve as cold-rolled original specimens. The metallographic specimens were mechanically ground and polished with 240-2000 mesh sandpaper, and etched with a corrosive agent composed of 10% HF, 30% HNO3 and 60% H2O. The microstructures were observed using an OLYMPUS PMG3 inverted metallographic microscope and a JSM-6700 scanning electron microscope. The alloy phases were further analyzed using an Ultima IV X-ray diffractometer with a copper target as the radiation source at room temperature, a voltage of 40kV and a current of 40mA. The Theta-2Theta method was used for continuous scanning with a scanning angle of 10-90°, a speed of 10deg / min and a step size of 0.02°.

[0171] This multi-element titanium alloy with a single β-BCC structure exhibits excellent cold deformation ability, but the precipitation of α phase will weaken this performance; high melting point elements such as molybdenum and chromium are prone to cause dendritic segregation, and iron tends to form intergranular segregation, which have a negative impact on the cold deformation and tensile properties of the alloy. In addition, the distribution state of the alloying elements before aging significantly affects the aging precipitation behavior of the α phase. The microstructure of the alloy after homogenization and annealing treatment was characterized, such as Figure 4 As shown. Figure 4 The SEM images of (a) and (b) and the XRD patterns in the lower left corner show that the alloy is a single-phase BCC solid solution; the corresponding EDS analysis confirms that the elements are evenly distributed without obvious segregation. Figure 4 The EBSD orientation map in (c) shows that the alloy grains are equiaxed after recrystallization annealing. The average Taylor factor map on the right shows that the Taylor factor values ​​between the grains are close and the stress distribution is uniform. Figure 4 The TEM bright-field image and selected area electron diffraction (SAED) results of (d) further confirmed that the alloy microstructure was a single BCC phase, with no fine secondary phases found. This indicates that homogenization and annealing treatments can effectively obtain a β-BCC phase alloy with uniform composition and a single structure, laying the foundation for subsequent research on its microstructure evolution and performance improvement after aging treatment.

[0172] Figure 5(a) shows the tensile engineering stress-strain curve and the corresponding tensile fracture morphology of the alloy after annealing at 900℃×30 minutes. The results show that the yield strength of the annealed alloy reaches 1030MPa, while maintaining an elongation of 28%, showing an excellent strong-plasticity match. For metastable β-type titanium alloys, it is extremely challenging to achieve a tensile elongation of more than 25% under the dominant single dislocation slip deformation mechanism. Usually, the TRIP (transformation induced plasticity) or TWIP (twinning induced plasticity) effect is required to achieve this level. From the fracture morphology, a large number of tiny ductile dimples are distributed on the fracture surface. These dimples are formed by the interaction and accumulation of dislocations during the deformation process, which further confirms the high plasticity characteristics of the alloy.

[0173] To explore its deformation mechanism, the alloy stretched to 4% strain was characterized by TEM. Figure 5 (b) is shown in the bright field image. Observations revealed that a high-density forest of dislocations formed within the alloy during deformation. These dislocations gradually evolved into dislocation cell structures through interaction and continuous accumulation, ultimately transforming into ductile dimples at fracture. This type of high-density forest of dislocations is a typical microscopic feature of alloys with both high strength and high ductility. It has been widely observed in TaNbHfZrTi high-entropy alloys, which are known for their excellent balance of strength and ductility. The high-molybdenum content alloys in this study also exhibit this feature, indicating that their deformation mechanism is similar to that of high-performance multi-component alloys. This is also the key microscopic basis for achieving the synergy of high strength and high ductility.

[0174] To fully exploit the alloy's potential, aging treatment was performed to induce α phase precipitation to improve strength. Aging experiments were conducted at different temperatures on the alloy annealed at 900°C. The mechanical properties test results of the aged alloy, as well as the microstructural characterization analysis based on X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) are shown in the figure. Figure 6 shown.

[0175] Mechanical properties analysis: Figure 6 (a) presents the engineering stress-strain curves of the alloy under different aging conditions. The data show that after aging at 400°C for 12 hours, the yield strength of the alloy soared to 1677MPa, a significant increase of 644MPa compared to the annealed state, fully demonstrating the significant potential of low-temperature aging in strengthening alloys; but the elongation of the alloy under this condition is extremely low, less than 1%, showing an obvious brittle tendency. In contrast, after aging at 550°C for 12 hours, the yield strength of the alloy was only 1167MPa, an increase of 134MPa compared to the annealed state, but the elongation remained above 10%, and the plasticity performance was excellent. The alloy aged at 500°C for 10 hours achieved a good balance between yield strength and elongation, with a yield strength of 1361MPa and an elongation of 5%, and better comprehensive mechanical properties. Microstructure and phase analysis: combined Figure 6(b) XRD spectrum shows that at different aging temperatures, the characteristic diffraction peaks of α phase appear in the alloy microstructure, confirming that α phase has been successfully precipitated. Figure 6 The EBSD microstructure images of (c1), (c2), and (c3) show that a large number of needle-shaped and lamellar α-phase precipitates form within the alloy after aging treatment. The volume fraction of the β-phase increases with increasing aging temperature. This phenomenon can be explained based on the dual-phase strengthening theory: the β-phase has a lower hardness than the α-phase, and increasing its content reduces the overall yield strength of the alloy. However, the β-phase, with its higher dislocation accommodation capacity and plastic deformation coordination, can significantly improve the alloy's elongation. Therefore, when the aging temperature decreases, the strengthening effect of the α-phase dominates, increasing the alloy's strength while decreasing its plasticity. Conversely, under high-temperature aging, the plastic coordination advantage of the β-phase becomes more prominent, resulting in a slower increase in strength but maintaining plasticity. This inherent relationship between aging temperature, phase composition, and mechanical properties provides an important theoretical basis for optimizing alloy aging processes and achieving precise performance control.

[0176] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications can be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A high-strength and tough metastable β titanium alloy, characterized by: The alloy is a Ti-V-Mo-Cr-Fe-Al sesquivalent system, and the mass percentages of the elements are: 85.6% to 85.7% Ti, 0.7% to 1.8% V, 3.0% to 4.3% Mo, 1.6% to 2.3% Cr, 4.4% to 7.4% Fe, and 1.7% Al.

2. The high-strength and tough metastable β titanium alloy according to claim 1, characterized in that: The mass percentage of each element is obtained according to the following design method: The following steps are included: S1, calculate configurational entropy, According to the expression S=-R(ΣC i lnC i +0.87ln0.87+0.03ln0.03) to calculate the configurational entropy, where C i (i = 1, 2, 3, 4) represents the molar concentration of elements V, Mo, Cr and Fe, respectively, R is the gas constant, and (0.87ln0.87 + 0.03ln0.03) is the fixed entropy contribution of Ti and Al; S2, design VEC constraints, Through the VEC total balance equation ∑ i C i (VEC) i +0.87VEC Ti +0.03VEC Al = k and element concentration sum constraint∑ i C i =0.1 controls the alloy's thermal stability, where (VEC) i is the valence electron concentration of element i, k is the target VEC value, C i represents the molar concentration of the i-th element; S3, extreme value solution based on Lagrange multiplier method, Under the constraints of step S2, the Lagrange undetermined multiplier method is used to construct the objective function to maximize the configuration entropy in step S1, thereby determining the optimal molar concentrations of V, Mo, Cr, and Fe in the alloy; S4, Equilibrium phase composition prediction and component screening, Using a method based on the maximum entropy principle combined with first principles, MaterialsStudio software was used to calculate element bond enthalpies and derive the Gibbs free energy ΔG to predict the equilibrium phase composition of alloys at different temperatures. The phase stability of different VEC values ​​at different temperatures was analyzed, and the atomic ratio of the required alloy components was screened by combining parameters such as molybdenum equivalent. S5. Calculate the mass percentage of each element based on the atomic proportion of each element.

3. The high-strength and tough metastable β titanium alloy according to claim 2, characterized in that: Step S3 The following steps are included: S31, Lagrangian function construction, introducing two unknown multipliers λ j1 and λ j2 ,λ j1 Corresponding to VEC constraint, λ j2 Corresponding to the concentration sum constraint, the objective function L is: L=S+λ j1 (∑ i C i (VEC) i +0.87(VEC) Ti +0.03VEC Al -k)+λ j2 (∑ i C i -0.1); Where S is the configuration entropy of the alloy, (VEC) i is the valence electron concentration of element i, C i Indicates the molar concentration of the i-th element, 0.87 (VEC) Ti Fixed VEC contribution of Ti element, 0.03VEC Al is the fixed VEC contribution of Al element, k is the target VEC value; S32, extreme value condition solution, the condition for maximizing entropy is the objective function of each element concentration C i The partial derivative of is 0, that is The expression of the concentration of each element is sorted out: c i =exp(-1+λ j1 (VEC) i +λ j2 ); S33, to be determined multiplier λ j1 and λ j2 Solve for c i =exp(-1+λ j1 (VEC) i +λ j2 ) is substituted into the two formulas of the constraint condition in step S32, and the equation about λ is obtained. j1 and λ j2 The equations of λ can be calculated separately. j1 and λ j2 ; S34, calculate the concentration of each element, and set λ j1 and λ j2 and (VEC)i is substituted into formula c i =exp(-1+λ j1 (VEC) i +λ j2 ) to obtain the atomic concentrations of V, Mo, Cr, and Fe.

4. The high-strength and tough metastable β titanium alloy according to claim 1, characterized in that: Step S4 The following steps are included: S41, Assumptions and calculation premises of equilibrium phase composition, Assuming that the alloy exists in only two single-phase structures, α phase and β phase, under different states, the Gibbs free energy ΔG under the two structures is calculated separately, and the phase with the lower ΔG value is taken as the equilibrium phase at a specific temperature; S42, solid solution mixing enthalpy Calculation, According to the formula Calculate the enthalpy of mixing, where φ represents the crystal structure, represents the interaction parameter between element i and element j; C i and C j represent the concentrations of element i and element j, respectively; S43, selection of calculation method for interaction parameters and determination of core formula, According to the formula Calculate the interaction parameters of elements i and j in the crystal structure, where is the number of nearest neighbors of the central atom in an alloy with a specific lattice structure, N AV represents Avogadro's constant, and The coordination number of the crystal structure represents the bond enthalpy between the same atoms or different atomic pairs in the alloy; S44, according to the interaction parameters The stability curve was drawn, and the optimal value of each element under the VEC constraint condition was determined. The element interaction parameter Ωij under BCC and HCP structures was calculated, and the VEC-ΔG curves were drawn at room temperature and 900℃ for different VEC values ​​to determine the VEC range in the two-phase region.

5. The high-strength and tough metastable β titanium alloy according to claim 1, characterized in that: The VEC value is 4.

27. Under this value, the mass percentages of the elements are: 85.6% Ti, 1.0% V, 3.5% Mo, 1.9% Cr, 6.3% Fe, and 1.7% Al.

6. A method for preparing a high-strength and tough metastable β titanium alloy, comprising: using the elements as claimed in any one of claims 1 to 5 and mixing them in accordance with the mass percentage; wherein: The steps include: S100, alloy melting: using vacuum induction melting technology to prepare alloy ingots; S200, homogenization treatment: The smelted alloy ingot is sealed with argon and kept at a high temperature with only the β phase region for 1-3 hours, so that the alloy presents a single-phase β solid solution structure, thereby making the alloy have cold deformation ability and processability; S300, sample cutting: using a wire cutting machine to cut the homogenized ingot into rectangular samples; S400, cold rolling: At room temperature, the rectangular specimen is cold rolled to reduce the thickness of the specimen to 10% of the original thickness, i.e. the cold rolling deformation is 90%; S500, annealing treatment: the cold-rolled sample is placed in a high-temperature environment with only the β phase region for 30 minutes to allow the alloy to recover and recrystallize after cold rolling, and finally show plasticity; S600, aging treatment: the annealed samples were aged at 400°C-550°C for 12 hours.

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