Meta-stable beta titanium synthesis component design method based on specific orientation modulus

Abstract

The invention belongs to the field of alloy design, and discloses a metastable beta titanium synthesis component design method based on specific orientation modulus. According to the specific orientation modulus method, the relation between alloy design parameters and a heat-induced metastable phase change mechanism and a stress-induced plastic deformation mechanism is established, and the softening effect of the specific orientation modulus is beneficial to shearing, recombination or collapse of atoms in corresponding orientation; the formation sequence of a metastable phase and transformation of a plastic deformation mode are determined by the competitive relationship of moduli. The elastic constant and the specific orientation modulus of a multi-element alloy system are obtained through calculation according to the first principle, the specific orientation modulus of typical beta-type titanium alloy is calculated, and specific orientation modulus ranges corresponding to different heat-induced metastable phase change mechanisms and stress-induced plastic deformation mechanisms are determined; the relevance between alloy components and a heat-induced metastable phase change mechanism and a stress-induced plastic deformation mechanism is established through specific orientation modulus parameters, so that the design of the metastable beta titanium alloy is guided. According to the method, the problems of low research and development efficiency and high research and development cost in a traditional alloy design method are solved, and the metastable beta titanium alloy can be accurately and efficiently designed.

Description

Technical Field

[0001] The invention belongs to the field of alloy design and relates to a metastable beta titanium composition design method based on a specific orientation modulus. Background Art

[0002] Metastable β titanium alloys have excellent properties such as light weight, high strength, corrosion resistance, low modulus and superelasticity, and have great application prospects in aerospace, marine engineering and biomedical fields, such as Ti-1023 and β-21S. However, the currently used metastable β titanium alloys are limited in application due to defects such as low ductility, no obvious strain hardening behavior, poor formability or limited damage resistance. <113> The metastable β-titanium alloy with twinning induced plasticity (TWIP) effect exhibits high strength-ductility product and impact work. Designing a new generation of β-titanium alloys with high strength, high plasticity and good work hardening ability has gradually become a research hotspot. However, metastable β-titanium alloys have a variety of thermally induced metastable phase transformations (α′ / α″ martensite, ω phase and O′ phase) and a variety of stress-induced deformation modes (stress-induced α′ / α″ martensite phase transformation, stress-induced ω phase transformation, {332} <113> Twins and {112} <111> This creates inconvenience for alloy design.

[0003] The current methods for titanium alloy design mainly include empirical trial and error, Mo equivalent method, valence electron concentration (e / a) method and d-electron alloy design theory (Bo-Md method). These (semi-)empirical design methods have successfully designed many alloys and show a certain rationality; however, these methods are usually inefficient in designing alloys and have high trial and error costs. In essence, these methods do not establish the connection between alloy design parameters and the thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism.

[0004] In the invention with publication number CN108446478A, Central South University proposed a design method for multi-component high-strength titanium alloys. This method mainly uses alloy ingots with multiple components as diffusion nodes, and determines the microstructure and microhardness of a certain component of the multi-component diffusion couple after a series of heat treatments to establish a database of the "component-structure-hardness" relationship. This method is a design method for a specific system and is not universal. In addition, this method completely relies on specific experiments to obtain the microstructure and mechanical properties of a certain component, which has a long test cycle and high costs.

[0005] In the invention with the publication number CN110387485A, Northwestern Polytechnical University proposed a composition design method for metastable β titanium alloy, which is mainly based on first-principles calculations and combines Mo equivalent method, d-electron alloy design theory, and yield strength verification to design the composition of metastable β titanium alloy. Although this method has high design efficiency, it only starts from phase stability and electronic structure, and does not link the alloy composition with the thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism. The designed alloy can only infer its yield strength, but the ductility and work hardening ability are unknown.

[0006] In view of the shortcomings of current titanium alloy design methods, the present invention uses specific orientation modulus parameters to guide alloy design, establishes the correlation between alloy composition and the alloy's thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism, and provides a reliable and efficient metastable β titanium alloy design method. Summary of the invention

[0007] The purpose of the present invention is to address the problems of the current titanium alloy design methods, such as long cycle, high cost, small scope of application, and the failure to establish the correlation between the alloy composition and the alloy's thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism. A method for designing metastable β-type titanium alloys based on a specific orientation modulus is proposed. The method is a fast, efficient, reliable, and highly successful multi-component high-strength titanium alloy design method.

[0008] The technical solution of the present invention:

[0009] A metastable β-titanium composite design method based on a specific orientation modulus is first constructed through first-principles calculations to construct a body-centered cubic structure unit cell composed of 54 Ti atoms; then the elastic constants C after different types and numbers of solute atoms are replaced into the body-centered cubic structure unit cell are calculated. 11 , C 12 and C 44 , and then calculate the elastic constants and specific orientation modulus E of the multi-element alloy system 100 , C′ and G 111 ; Finally, the specific orientation modulus of a typical β-type titanium alloy is calculated to determine the specific orientation modulus range corresponding to different thermally induced metastable phase transformation mechanisms and stress-induced plastic deformation mechanisms. The correlation between the alloy composition and the thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism of the alloy is established through the specific orientation modulus parameters, thereby guiding the alloy design; the steps are as follows:

[0010] Step 1: Use the first principle calculation method to calculate the elastic constant C of the binary alloy Ti-M as the solute atom content increases. 11 , C 12 and C 44The changing trend of the element addition is obtained to obtain the vector of the contribution of each element to the elastic constant, so as to fit the calculation formula of the elastic constant of the metastable β titanium alloy in the multi-element alloy system. The calculation formula of the elastic constant of the fitted multi-element alloy system is as follows:

[0011] C 11 =2.31[Mo]+1.03[Nb]+6.10[Fe]+3.95[Cr]+0.40[Al]+1.64[V]-0.08[Zr]+94.11

[0012] C 12 =-0.08[Mo]+0.03[Nb]-1.38[Fe]-0.66[Cr]+0.44[Al]+0.01[V]-0.25[Zr]+114.40

[0013] C 44 =0.10[Mo]-0.12[Nb]+1.51[Fe]+0.19[Cr]+1.70[Al]-0.06[V]-0.12[Zr]+38.35

[0014] Where: [M] is the mass percentage of the M element, and the unit of the elastic constant is GPa;

[0015] According to the calculation formula of the specific orientation modulus, the specific orientation modulus value of a certain alloy is finally obtained to characterize the difficulty of shearing, reorganization or collapse of atoms along a specific orientation in the β phase;

[0016] Step 2: Calculate the specific orientation modulus of a typical β-type titanium alloy, determine the specific orientation modulus range corresponding to different thermally induced metastable phase transformation mechanisms and stress-induced plastic deformation mechanisms, and establish the correlation between the alloy composition and the alloy's thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism through the specific orientation modulus parameters, thereby guiding alloy design.

[0017] The idea of ​​implementing the above technical solution is: the present invention uses the parameter of specific orientation modulus to judge whether the metastable β titanium alloy undergoes metastable phase transformation and plastic deformation mode transformation, thereby guiding alloy design. The mechanism is the metastable phase transformation mechanism induced by heat and the plastic deformation mechanism induced by stress in the metastable β titanium alloy, and the connection between them is the difficulty of shearing, reorganization or collapse of atoms in a specific orientation in the β phase. That is, the shear process of α″ martensitic phase transformation is related to <100> β Young's modulus E in the direction 100 The reorganization process is related to the tetragonal shear modulus C′; the collapse process of the ω phase transition is related to <111> β Shear modulus G 111 related to; {332} <113> The shear process of twinning <113> βShear modulus G 113 The recombination process is related to C′; {112} <111> The shear process of twinning <111> β Directional shear modulus G 111 The softening effect of the specific orientation modulus is conducive to the shear, recombination or collapse process of atoms in this orientation. The competitive relationship of the modulus determines the formation order of the metastable phase and the transformation of the plastic deformation mode. Through first-principles calculations, the elastic constants of different binary alloy systems Ti-M (M is V, Mo, Fe, Nb, Cr, Zr or Al elements) can be obtained, and then the calculation formula of the elastic constants under the multi-component system can be fitted, and finally the specific orientation modulus value corresponding to the multi-component system is obtained. The specific orientation modulus of typical alloys is calculated, and its thermally induced metastable phase transition mechanism and stress-induced plastic deformation mechanism are linked. The specific orientation modulus range corresponding to the corresponding thermally induced metastable phase transition mechanism and stress-induced plastic deformation mechanism is specified, and alloy design is performed to verify the rationality of alloy design with specific orientation modulus parameters.

[0018] Beneficial effects of the present invention:

[0019] (1) The present invention is a method for designing a metastable β titanium alloy based on a specific orientation modulus, by using three specific orientation modulus parameters (E 100 , C′ and G 111 ) is used to establish the relationship between alloy composition and the heat-induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism, thus improving the existing titanium alloy design theory.

[0020] (2) The specific orientation modulus design method gets rid of many defects of traditional design methods. It is based on first-principles calculation and experimental verification. This method has many advantages such as high design efficiency, accurate design results, low design cost and wide application range.

[0021] (3) A new TWIP-type alloy was designed through the specific orientation modulus design method, which further verified the rationality of the alloy design method. The designed TWIP-type alloy has good strength-plasticity matching and cold working formability, and has excellent comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the engineering stress-strain curve of the designed Ti-19.5V-4Nb, Ti-15V-4Nb-1Fe and Ti-15.5V-4Nb-1Fe-1Al alloys.

[0023] Figure 2 These are the microstructure diagrams of Ti-19.5V-4Nb alloy, (a) the original microstructure diagram after solution treatment; (b) the deformed microstructure diagram with a tensile deformation of 5%.

[0024] Figure 3 These are the microstructure diagrams of Ti-15V-4Nb-1Fe alloy, (a) the original microstructure diagram after solution treatment; (b) the deformed microstructure diagram with a tensile deformation of 5%.

[0025] Figure 4 These are the microstructure diagrams of Ti-15.5V-4Nb-1Fe-1Al alloy, (a) the original microstructure diagram after solution treatment; (b) the deformed microstructure diagram with a tensile deformation of 5%. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0027] The steps of the present invention include: using the first principle calculation method to calculate and fit the elastic constants and specific orientation modulus (E 100 , C′ and G 111 ), the specific orientation modulus of typical titanium alloys was calculated by this calculation method and a database was established to obtain the specific orientation modulus value ranges corresponding to different thermally induced metastable phase transformation mechanisms and stress-induced plastic deformation mechanisms. Subsequently, a new type of TWIP titanium alloy was designed, and the corresponding alloy button ingots were prepared by a non-vacuum consumable arc furnace. After corresponding heat treatment, the mechanical properties and microstructure characterization were performed to verify the rationality of the alloy design method.

[0028] Step 1: Use the first-principles calculation method to construct the cluster structure and cluster model of the β phase using Materials Studio (MS) software; use Vienna Ab-initio Simulation Package (VASP) software to perform first-principles calculations based on density functional theory. Establish a 3×3×3 body-centered cubic structure supercell composed of 54 Ti atoms, and optimize the structure of the constructed supercell.

[0029] Then, the atomic occupancy of the binary alloy system when other elements are added to the pure titanium supercell is calculated. When other replacement atoms enter the supercell composed of Ti atoms, different occupancy situations will appear. At this time, binding energy is needed to judge the stability. The lower the binding energy, the more stable its occupancy structure. Taking the Ti-Mo binary alloy system as an example, the calculation formula of binding energy is:

[0030]

[0031] Among them, E c is the binding energy, E xMo and E 1Moare the formation energies of multiple Mo atoms and a single Mo atom in a supercell, respectively, and x is the number of Mo atoms in the supercell. The smaller the binding energy, the more stable the corresponding occupancy and the more stable the cluster structure formed. Add a Mo atom to the supercell composed of Ti atoms, select the most stable structure, then add the second Mo atom, and then select the most stable structure, and repeat. xMo The calculation formula is as follows:

[0032]

[0033] in is the total energy of the supercell containing x Mo atoms, and are the total energies of one Ti in the hexagonal close-packed structure and one Mo in the body-centered cubic structure, n is the total number of atoms in the supercell, and x is the number of Mo atoms in the supercell.

[0034] Set the parameters required by VASP software and calculate the elastic constants under different binary systems. Within the linear elastic range of the material, the uniaxial tensile deformation of the solid is proportional to the external force, which is Hooke's law. Extending Hooke's law to stress and state in three directions gives the generalized Hooke's law, which can be expressed as

[0035]

[0036] Where C ij is the elastic constant, and the body-centered cubic structure has a relatively high symmetry, so only C 11 , C 12 ,C 44 These three elastic constants are sufficient.

[0037] Taking the Ti-Mo binary alloy system as an example, after adding 0-7 Mo atoms into the pure titanium supercell, the elastic constant values ​​of the alloy system are shown in Table 1.

[0038] Table 1 Elastic constants C of Ti-Mo (wt.%) system 11 , C 12 and C 44 value

[0039]

[0040]

[0041] According to the elastic constants obtained above, the least squares linear fitting was performed for the elastic constant values ​​at different concentrations to obtain the linear relationship between the mass percentage of different elements and the elastic constants in the Ti-Mo binary alloy system:

[0042] C11 =2.31[Mo]+94.86

[0043] C 12 =-0.08[Mo]+114.40

[0044] C 44 =0.10[Mo]+37.76

[0045] Similarly, the elastic constant calculation relationship of the Ti-M (M is V, Mo, Fe, Nb, Cr, Zr or Al element) binary alloy system can be obtained. Analyzing the calculation formula of the elastic constant of binary alloys, it can be found that the change of the elastic constant with the addition of different alloying elements mainly depends on the coefficient before the mass percentage of the solute atom, that is, the contribution vector of each element to the elastic constant is different. And the constant term in the calculation formula of the elastic constant of different binary alloys is not much different from the elastic constant of pure titanium alloy, so the influence of different alloying elements on the elastic constant is only related to the coefficient before the mass percentage of the solute atom. Then when V, Mo, Fe, Cr, Nb, Zr and Al elements are added to the titanium alloy, the calculation formula of the elastic constant of the multi-element alloy system is:

[0046] C 11 =2.31[Mo]+1.03[Nb]+6.10[Fe]+3.95[Cr]+0.40[Al]+1.64[V]-0.08[Zr]+94.11

[0047] C 12 =-0.08[Mo]+0.03[Nb]-1.38[Fe]-0.66[Cr]+0.44[Al]+0.01[V]-0.25[Zr]+114.40

[0048] C 44 =0.10[Mo]-0.12[Nb]+1.51[Fe]+0.19[Cr]+1.70[Al]-0.06[V]-0.12[Zr]+38.35

[0049] Wherein [Mo], [Nb], [Fe], [Cr], [Al], [V] and [Zr] are the mass percentages of the corresponding elements in the multi-element alloy system, and 94.11, 114.40 and 38.35 are the corresponding elastic constants of pure titanium, and their units are GPa.

[0050] With the elastic constant calculation formula of the multi-element alloy system, its specific orientation modulus E can be calculated. 100 , C′ and G 111 , the specific calculation formula is:

[0051]

[0052] Step 2: Calculate the specific orientation modulus of a typical β-type titanium alloy, determine the specific orientation modulus range corresponding to different thermally induced metastable phase transformation mechanisms and stress-induced plastic deformation mechanisms, and establish the correlation between alloy composition, alloy structure and plastic deformation mode through specific orientation modulus parameters, thereby guiding alloy design.

[0053] By calculating, statistically analyzing and classifying the specific orientation modulus, thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism of typical β-type titanium alloys, it is found that when the alloy metastable phase is the quenched ω phase and the plastic deformation mode is {332} <113> When twinning, the alloy's orientation-specific modulus range is limited to the following range:

[0054] 18GPa<E 100 <25GPa

[0055] 6GPa<C′<9GPa

[0056] 9GPa<G 111 <12GPa

[0057] In order to obtain a TWIP titanium alloy with excellent performance, the value of the alloy's specific orientation modulus, cold working formability, yield strength, uniform elongation and deformation twin area fraction are limited.

[0058] After sorting out the existing TWIP titanium alloy properties and specific orientation modulus values, we found that the specific orientation modulus of typical TWIP Ti-15Mo and Ti-22V is limited to a narrower range. The two alloys have high strength-ductility product and impact work, and excellent cold working performance. Therefore, when designing a TWIP titanium alloy with excellent performance, its specific orientation modulus should be controlled within the following range:

[0059] 22.5GPa<E 100 <23.0GPa

[0060] 7.5GPa<C′<8.0GPa

[0061] 10.5GPa<G 111 <11.0GPa

[0062] In order to obtain TWIP titanium alloy with excellent cold forming performance, it is required that the cold rolling deformation of the alloy after 900℃ solid solution treatment should be greater than 90%. The mechanical properties of the alloy after cold rolling and solid solution treatment, such as yield strength (σ 0.2％ ) and uniform elongation (ε u ) meets the corresponding indicators of TWIP type titanium alloy, and the deformation twin area fraction of the alloy at 5% tensile deformation exceeds 20%, that is:

[0063] σ 0.2％ <600MPa

[0064] ε u >25%

[0065] Step 3, combining the specific orientation modulus calculation formula obtained in step 1 with the specific orientation modulus range corresponding to the thermally induced metastable phase transition mechanism and stress-induced plastic deformation mechanism obtained in step 2, design a new TWIP titanium alloy to verify the accuracy of the specific orientation modulus method design method.

[0066] The designed alloy meets the specific orientation modulus range of the TWIP type titanium alloy with excellent performance, and the specific design parameters are shown in Table 2. The ingot is then melted, heat treated and mechanically treated, the mechanical properties are tested, and the microstructure is characterized to verify the accuracy of the design method.

[0067] Table 2 Specific orientation modulus (E 100 , C′ and G 111 ) Design value

[0068] Alloy composition <![CDATA[E 100 (GPa)]]> C′(GPa) <![CDATA[G 111 (GPa)]]> Ti-19.5V-4Nb 22.7 7.7 10.5 Ti-15V-4Nb-1Fe 22.9 7.8 10.6 Ti-15.5V-4Nb-1Fe-1Al 22.9 7.8 10.6

[0069] According to the chemical composition of the alloy in Table 2, the ingredients were prepared, and high-purity Ti, V, Fe, Nb and Al alloy raw materials were placed in a non-vacuum consumable arc furnace. The configured alloy raw materials were repeatedly melted 7 to 8 times in an argon atmosphere at a melting temperature of 2200°C to make the alloy composition uniform, and 50g of alloy button ingots were obtained.

[0070] The alloy button ingot obtained in step (1) is placed in a vacuum heat treatment furnace for solution treatment (900°C, 1h), and the cooling method is water quenching. A ZK-WS98 high-strength step rolling mill is used to cold roll along the length direction of the block, with a reduction of 0.04mm per pass, and finally a plate with a thickness of 1.1mm is obtained. The cold rolling deformation of the three alloys is greater than 90%. The plate-shaped tensile specimens are taken out from the rolled alloy plates along the RD direction by wire cutting. Among them, the total length of the specimen is 60mm, the parallel section length is 30mm, the gauge length is 25mm, the parallel section width of the specimen is 4mm, and the total thickness of the specimen is 1mm. The cut tensile specimen is sealed and solution treated (900°C, 1h), and the cooling method is water quenching.

[0071] The tensile properties of the alloy were tested using a UTM4204X electronic testing machine at a tensile rate of 0.5 mm / min. A 15×5 mm solid solution structure sample was cut by electric spark cutting. In addition, the tensile specimen was unloaded when the true strain reached 5%, and the metallographic sample was prepared by a standard metallographic preparation method. The deformed structure of the original structure after solution treatment and the cross section of the tensile specimen with 5% deformation were observed by a metallographic microscope.

[0072] The mechanical properties curves of the three alloys are as follows: Figure 1 As shown, the microstructure Figure 2-4 The specific mechanical properties are shown in Table 3. The strength and plasticity of the three alloys meet the design requirements, and the area fraction of deformation twins at 5% tensile deformation is statistically calculated. Ti-19.5V-4Nb, Ti-15V-4Nb-1Fe and Ti-15.5V-4Nb-1Fe-1Al alloys correspond to 22%, 34% and 29% respectively, all exceeding the design requirement of 20%. Ti-15V-4Nb-1Fe and Ti-15.5V-4Nb-1Fe-1Al alloys have both strength and plasticity, and have a good match between strength and plasticity.

[0073] Table 3 Mechanical properties of alloys

[0074] Alloy composition <![CDATA[σ 0.2％ (MPa)]]> <![CDATA[R m (MPa)]]> <![CDATA[ε u (%)]]> Ti-19.5V-4Nb 424 615 27 Ti-15V-4Nb-1Fe 490 781 30 Ti-15.5V-4Nb-1Fe-1Al 470 665 35

[0075] The designed Ti-19.5V-4Nb, Ti-15V-4Nb-1Fe and Ti-15.5V-4Nb-1Fe-1Al alloys span from the ternary system to the quinary system. Their specific orientation moduli are similar, and the metastable phases are all quenched ω phases, and they are all based on {332} <113> Twinning is the main deformation mode, which has TWIP effect. The specific orientation modulus method starts from the shearing, reorganization or collapse of atoms in specific orientation at the microscopic level. 100 , C' and G 111 It is a reliable, accurate and efficient alloy design method to evaluate the difficulty and trend of metastable phase transformation and plastic deformation mode transformation by using parameters such as tantalum and tantalum, so as to predict the macroscopic mechanical properties of the alloy.

[0076] The above description is only an example of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, based on the technical essence of the present invention, makes any simple modification and equivalent changes to the invention disclosed above, which fall within the protection scope of the present invention.

Claims

1. A method for designing a metastable β-titanium composition based on a specific orientation modulus, characterized in that: First, a body-centered cubic structure unit cell composed of 54 Ti atoms was constructed through first-principles calculations; then the elastic constants C after different types and numbers of solute atoms were replaced into the body-centered cubic structure unit cell were calculated. 11 , C 12 and C 44 , and then calculate the elastic constants and specific orientation modulus E of the multi-element alloy system 100 , C′ and G 111 ; Predict the mechanical properties of the material based on the elastic constant and modulus, that is, establish the correlation between the alloy composition and the alloy's thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism through specific orientation modulus parameters, thereby guiding alloy design; the steps are as follows: Step 1: Use the first principle calculation method to calculate the elastic constant C of the binary alloy Ti-M as the solute atom content increases. 11 , C 12 and C 44 The changing trend of the element addition is obtained to obtain the vector of the contribution of each element to the elastic constant, so as to fit the calculation formula of the elastic constant of the metastable β titanium alloy in the multi-element alloy system. The calculation formula of the elastic constant of the fitted multi-element alloy system is as follows: C 11 =2.31[Mo]+1.03[Nb]+6.10[Fe]+3.95[Cr]+0.40[Al]+1.64[V]-0.08[Zr]+94.11 C 12 =-0.08[Mo]+0.03[Nb]-1.38[Fe]-0.66[Cr]+0.44[Al]+0.01[V]-0.25[Zr]+114.40 C 44 =0.10[Mo]-0.12[Nb]+1.51[Fe]+0.19[Cr]+1.70[Al]-0.06[V]-0.12[Zr]+38.35 Where: [M] is the mass percentage of the M element, and the unit of the elastic constant is GPa; According to the calculation formula of the specific orientation modulus, the specific orientation modulus value of a certain alloy is finally obtained to characterize the difficulty of shearing, reorganization or collapse of atoms along a specific orientation in the β phase; Step 2: Calculate the specific orientation modulus of a typical β-type titanium alloy, determine the specific orientation modulus range corresponding to different thermally induced metastable phase transformation mechanisms and stress-induced plastic deformation mechanisms, and establish the correlation between the alloy composition and the alloy's thermally induced metastable phase transformation mechanism and stress-induced plastic deformation mechanism through the specific orientation modulus parameters, thereby guiding alloy design.

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