Yield strength calculation method based on structure morphology of basketry structure titanium alloy

Abstract

The invention relates to the technical field of titanium alloy material engineering, in particular to a yield strength calculation method based on the structure morphology of a basketry structure titanium alloy. The yield strength of the basket-structure titanium alloy is divided into matrix strength, a solid solution strengthening effect, a grain boundary strengthening effect, a dislocation strengthening effect and an alpha-phase precipitation strengthening effect. According to the method, a more accurate alpha-phase precipitation strengthening model is innovatively designed, and a bounding rectangle length and width statistical method for auxiliary statistics and an area-based phase morphology weighting algorithm are designed. According to a traditional method, a lamellar alpha phase is converted into an equal-area circle to consider the strengthening effect, the lamellar alpha phase is fitted into a long-axis rectangular part and a short-axis semicircular part, and compared with the traditional method, the yield strength calculation method based on the structure morphology of the basket structure titanium alloy has the advantages that a model is closer to reality, and a statistical method is more accurate and reliable; the method is small in result and actual error, and can be used in the engineering technical field of titanium alloy microscopic structure design, performance regulation and control and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material engineering, and in particular to a yield strength calculation method based on basketweave titanium alloy microstructure morphology. The method can be used in the technical fields of titanium alloy microstructure design and performance regulation. Background Art

[0002] Titanium alloys are widely used in aviation, aerospace, shipbuilding and other fields due to their excellent specific strength, corrosion resistance and high temperature resistance. As a structural material, the strength of titanium alloy is a key indicator for evaluating performance, and the microstructure is a key factor in determining the strength of titanium alloy. Accurately predicting the yield strength of titanium alloys through microstructure can provide guidance for the design and preparation of new titanium alloys. Existing strength calculations of titanium alloys based on microstructure have large errors, and there is no accurate theoretical calculation model. The fundamental reason is that it is impossible to accurately calculate the influence of the lamellar α on the overall strength. Summary of the invention

[0003] The purpose of the present invention is to provide a yield strength calculation method based on basketweave titanium alloy microstructure morphology. The method has high accuracy by statistically analyzing the microstructure characteristics of basketweave titanium alloy and predicting the yield strength.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for calculating the yield strength of a basketweave titanium alloy based on its microstructure comprises the following steps:

[0006] Step 1: Calculate the solid solution strengthening effect based on the elemental composition of the titanium alloy;

[0007] Step 2: Calculate the grain boundary strengthening effect based on the average grain size of the original β grains;

[0008] Step 3: Calculate the dislocation strengthening effect based on the alloy dislocation density;

[0009] Step 4: Calculate the α phase strengthening effect based on the basket α phase proportion, size, and aspect ratio;

[0010] Step 5: Obtain the alloy matrix strength based on the critical decomposition shear stress of pure titanium;

[0011] Step 6: Add the calculated results from steps 1 to 5 to obtain the alloy yield strength.

[0012] In the yield strength calculation method based on the basketweave titanium alloy microstructure, the dislocation-solute interaction equation is used in step 1 to calculate the solid solution strengthening effect:

[0013]

[0014] In the formula, x i is the concentration of solute i (at.%), B i is the strengthening coefficient of solute i, M is the Taylor factor, μ is the solute shear modulus, λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom.

[0015] In the yield strength calculation method based on basketweave titanium alloy microstructure, the Hall-Petch formula is used in step 2 to calculate the grain boundary strengthening effect:

[0016]

[0017] Where k is a constant related to the base material. The constant k for titanium alloy is 750 MPa·μm 1 / 2 , d is the β grain size.

[0018] In the yield strength calculation method based on the basketweave titanium alloy microstructure, the Bailey-Hirsch formula and the Williamson-Hall formula are used in step 3 to calculate the dislocation strengthening effect:

[0019]

[0020] Where α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus, b is the burgers vector, ρ is the dislocation density, E is the elastic modulus, v is the Poisson's ratio, and ε is the microstrain.

[0021] In the yield strength calculation method based on basketweave titanium alloy microstructure, the improved Orowan formula is used in step 4 to calculate the dislocation strengthening effect:

[0022]

[0023] Where M is the Taylor factor, G is the shear modulus, b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width, f is the phase ratio, and r is 0 is the dislocation loop radius, and v is the Poisson's ratio.

[0024] In the yield strength calculation method based on basketweave titanium alloy microstructure, ImagePro Plus software is used in step 4 to measure phase morphology data.

[0025] In the yield strength calculation method based on basketweave titanium alloy microstructure, at least 200 valid phases need to be counted for each phase morphology data in step 4.

[0026] In the yield strength calculation method based on the basketweave titanium alloy microstructure, the length and width of the α phase are measured using the circumscribed rectangle method in step 4. The circumscribed rectangle measurement methods under different staggered conditions are: (a) the circumscribed rectangle of a single lamellar α phase without staggering, the circumscribed rectangle of a simply staggered lamellar α phase; and (b) the complex closed-loop circumscribed rectangle formed by the lamellar α phase.

[0027] In the yield strength calculation method based on basketweave titanium alloy microstructure, the area weighted method is used in step 4 to calculate the aspect ratio.

[0028] In the yield strength calculation method based on basketweave titanium alloy microstructure, in step 5, the alloy matrix strength is taken as 180 MPa of pure titanium.

[0029] The advantages and beneficial effects of the present invention are:

[0030] 1. The present invention divides the yield strength of basket-structure titanium alloy into matrix strength, solid solution strengthening effect, grain boundary strengthening effect, dislocation strengthening effect and α phase precipitation strengthening effect, and improves the Orowan model on the basis of existing theories, which can more accurately calculate the contribution of lamellar α phase strength.

[0031] 2. The present invention innovatively designs a more accurate α-phase precipitation strengthening model, and designs a circumscribed rectangle length and width statistics method and an area-based phase morphology weighting algorithm that are compatible with the theory to assist statistics and further improve the accuracy of the calculation.

[0032] 3. The traditional method converts the lamellar α phase into a circle of equal area to consider the strengthening effect. The present invention fits the lamellar α phase into a long-axis rectangular part and two semicircular parts of the short axis. Compared with the traditional method, the model of the present invention is closer to reality, the statistical method is more accurate and reliable, and the result has a small error with the actual result. At the same time, the present invention also has a certain accuracy when counting other titanium alloy structures containing lamellar characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of XRD data in Example 1. In the figure, the horizontal axis 2θ is the diffraction angle (degree), and the vertical axis Intensity is the relative intensity (au).

[0034] Figure 2 The diagram of the circumscribed rectangle method and the operation flow diagram. Among them: (a) is a schematic diagram of the circumscribed rectangle method without interlaced sheets or simple interlaced sheets, (b) is a schematic diagram of the circumscribed rectangle method of interlaced sheets, marked in the figure: 1 sheet-like α phase, 2 rectangle, the circumscribed rectangle is used to replace the staggered blocking effect of multiple interconnected α phases; (c) Schematic diagram of the circumscribed rectangle method for measuring primary α sheets; (d) Schematic diagram of the circumscribed rectangle method for measuring secondary α sheets.

[0035] Figure 3 The metallographic data used for statistical microstructure morphology in Example 1 include: (a) 100 times metallographic statistics of β phase size; (b) 1000 times metallographic statistics of primary α phase ratio; (c) 5000 times metallographic statistics of primary α phase length and width; (d) 10000 times metallographic statistics of secondary α phase ratio; (e) 20000 times metallographic statistics of secondary α phase length and width.

[0036] Figure 4 It is the XRD raw data in Example 1. In the figure, the horizontal axis 2θ is the diffraction angle (degree), and the vertical axis Intensity is the relative intensity (au).

[0037] Figure 5 The metallographic data used for statistical microstructure morphology in Example 2 include: (a) 100 times metallographic statistics of β phase size; (b) 1000 times metallographic statistics of primary α phase ratio; (c) 5000 times metallographic statistics of primary α phase length and width; (d) 10000 times metallographic statistics of secondary α phase ratio; (e) 20000 times metallographic statistics of secondary α phase length and width.

[0038] Figure 6 It is the XRD raw data in Example 2. In the figure, the horizontal axis 2θ is the diffraction angle (degree), and the vertical axis Intensity is the relative intensity (au).

[0039] Figure 7 The metallographic data used for statistical microstructure morphology in Example 3 include: (a) 100 times metallographic statistics of β phase size; (b) 1000 times metallographic statistics of primary α phase ratio; (c) 5000 times metallographic statistics of primary α phase length and width; (d) 10000 times metallographic statistics of secondary α phase ratio; (e) 20000 times metallographic statistics of secondary α phase length and width.

[0040] Figure 8 It is the XRD raw data in Example 3. In the figure, the horizontal axis 2θ is the diffraction angle (degree), and the vertical axis Intensity is the relative intensity (au). DETAILED DESCRIPTION

[0041] In a specific implementation process, the present invention proposes a yield strength calculation method based on the basketweave titanium alloy microstructure, and the calculation method comprises the following steps:

[0042] Step 1: Calculate the solid solution strengthening effect based on the elemental composition of the titanium alloy.

[0043] Step 2: Calculate the grain boundary strengthening effect based on the average grain size of the original β grains.

[0044] Step 3: Calculate the dislocation strengthening effect based on the alloy dislocation density.

[0045] Step 4: Calculate the α phase strengthening effect based on the basket α phase proportion, size, and aspect ratio.

[0046] Step 5: Obtain the alloy matrix strength based on the critical decomposed shear stress of pure titanium.

[0047] Step 6: Add the calculated results from steps 1 to 5 to obtain the alloy yield strength.

[0048] In step 1, the elemental structure is based on the preset elemental composition, the weight percentage is converted into atomic concentration, and the dislocation-solute interaction equation is used to calculate the solid solution strengthening effect:

[0049]

[0050] In the formula, σ ss is the solid solution strengthening effect (MPa), x i is the concentration of solute i (at.%), B i is the enhancement coefficient of solute i (MPa·at. -2 / 3 ), M is the Taylor factor, μ is the solute shear modulus (GPa), λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom. As shown in Table 1, the specific alloy elements and the corresponding strengthening coefficients are as follows:

[0051] Table 1 Alloying elements and corresponding B i value

[0052]

[0053] In step 2, high-quality metallographic photos need to be prepared to ensure that there are multiple complete and clear β grains in the field of view. The recommended magnification is 50 times and 100 times. According to the equal area method, the β grains are converted into equal area circles, and the diameter of the equal area circle is regarded as the average diameter of the grain. The grain boundary strengthening effect is calculated according to the Hall-Petch formula:

[0054]

[0055] In the formula, σ GB is the grain boundary strengthening effect (MPa), k is a constant related to the matrix material, and the constant k for titanium alloy is 750MPa·μm 1 / 2 , d is the β grain size (μm).

[0056] In step 3, Jade software was used to assist in processing XRD data, denoising and flattening the raw data, marking the elements and corresponding peaks, and then multi-peak fitting was performed using Jade's own half-peak method to obtain microstrain. The XRD data after Jade data processing is shown in Figure 1The Young's modulus, shear modulus and Poisson's ratio data are obtained by testing the thermophysical properties of the samples, and the average value of at least three parallel sample data is taken as the final result. The dislocation strengthening effect is calculated according to the Bailey-Hirsch formula and the Williamson-Hall formula:

[0057]

[0058] In the formula, σ DS is the dislocation strengthening effect (MPa), α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, and ρ is the dislocation density (1 / m 2 ), E is the elastic modulus (GPa), v is the Poisson’s ratio, and ε is the microstrain.

[0059] In step 4, high-quality metallographic samples need to be prepared, and SEM is used to take electron microscope photos of different magnifications from 1000 times to 20,000 times to ensure that the phase interface is clearly visible at each magnification. Image Pro Plus software is used to count the microstructure phase morphology in the electron microscope photos, and the area method is used to count the primary α and secondary α ratios; the circumscribed rectangle method is used to count the aspect ratio of each primary and secondary phase layer, and the area weighted algorithm is used to obtain the average length and width and aspect ratio. Each statistical data needs to count more than 200 slice data.

[0060] like Figure 2As shown, a schematic diagram of the circumscribed rectangle measurement method. Considering that the secondary α sheets are connected end to end to form a closed loop, the dislocation loop mechanism inside the closed loop is not effective; and the secondary phases are relatively small, and there are many connections between the phases, it is difficult and inaccurate to count a single α sheet. In order to make the calculation results more accurate, the blocking effect of the secondary α morphology on the dislocation motion should be counted rather than just the length and width of each phase. On this basis, the present invention proposes a circumscribed rectangle method to measure the blocking effect of the secondary α morphology on the dislocation motion, that is, the length and width of the circumscribed rectangle are used instead of the length and width of multiple interconnected α phases. Figures (a)-(b) are schematic diagrams of the circumscribed rectangle measurement method under different interlacing conditions, namely: (a) circumscribed rectangle 2 of a single lamellar α phase 1 without interlacing, and circumscribed rectangle 2 of a simply interlaced lamellar α phase 1; (b) a complex closed-loop circumscribed rectangle 2 formed by a lamellar α phase 1; Figure (c) is a schematic diagram of the circumscribed rectangle measurement method for primary lamellae, including lamellae and circumscribed rectangles without interlacing and simple interlaced lamellae and circumscribed rectangles. Most primary lamellae exist independently or are simply connected between lamellae. The principle of the actual fitting process is shown in (a); Figure (d) is a schematic diagram of the circumscribed rectangle measurement method for secondary lamellae, including lamellae and circumscribed rectangles that are interlaced with each other. The secondary phases are complexly interlaced, and the interlaced lamellae and the corresponding circumscribed rectangles are marked with short sticks and rectangles of the same color. The principle of the actual fitting process is shown in (b). It should be noted that this circumscribed rectangle method has a higher accuracy in replacing a small number of lamellae (2 to 5). When a large number of lamellae (more than 10) are interconnected, these lamellae need to be artificially separated into multiple small lamellae combinations. This is mainly because the circumscribed rectangle method has a seriously small dislocation blocking effect when replacing a large number of interconnected lamellae.

[0061] When processing the length and width data of the lamellae, the width of most small-area phases is very small, and the aspect ratio is closer to a sphere. Simple averaging methods are often overly affected by such phases. On this basis, the present invention proposes an area-based length and width weighted algorithm: for the length and width data of each lamellae, the length and width data of the lamellae are weighted according to the proportion of the lamellae area to the total area of ​​the primary α phase or the secondary α phase, and then statistical calculations are performed. That is, the length and width of each lamellae are multiplied by the proportion of the lamellae to the same type of lamellae, and then these calculation results are added up as the final statistical result. This algorithm takes each lamellae into consideration and ensures the accuracy of the statistical data.

[0062] After data processing, the improved Orowan formula is used to calculate the dislocation strengthening effect, and the primary α strengthening and secondary α strengthening are calculated respectively. The primary α strengthening coefficient is 0.1, and the secondary α strengthening coefficient is 1:

[0063]

[0064] In the formula, σ αis the α phase strengthening effect (MPa), M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width (m), f is the phase ratio, r 0 is the dislocation loop radius (m), and v is the Poisson’s ratio.

[0065] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0066] Embodiment 1:

[0067] The following titanium alloys were prepared based on their chemical composition by weight percentage:

[0068] Al: 5.5%, Mo: 3%, Cr: 2%, V: 2%, Sn: 1.5%, Zr: 1.5%, Fe: ≤0.1%, O: ≤0.1%, and the balance is Ti.

[0069] This alloy needs to go through the process of electrode pressing, ingot melting, ingot blanking, and forging. Among them, the thermal deformation process parameters of forging are 15℃ above the phase transformation point, the thermal deformation is 35%; the subsequent heat treatment parameters are 880℃ / 2h / AC (air cooling) + 650℃ / 4h / AC.

[0070] Samples were taken 1 cm below the forging surface to prepare metallographic specimens, XRD specimens, elastic modulus specimens, and tensile specimens. The microstructures were obtained as follows: Figure 3 , XRD data such as Figure 4 , elastic modulus data are shown in Table 2.

[0071] Table 2 Young's modulus, shear modulus and Poisson's ratio of three groups of parallel samples in Example 1

[0072]

[0073] According to the preset element composition, the weight percentage of the alloy elements is converted into atomic percentage, and the dislocation-solute interaction equation is used to calculate the solid solution strengthening effect:

[0074]

[0075] In the formula, x i is the concentration of solute i (at.%), B i is the enhancement coefficient of solute i (MPa·at. -2 / 3 ), M is the Taylor factor, μ is the solute shear modulus (GPa), λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom. Solute enhancement factor B i See Table 1.

[0076] It is calculated that the solid solution strengthening effect is 225.3913MPa.

[0077] The area of ​​β grains in the low-magnification microstructure is counted and converted into a circle using the equal area method to obtain the diameter of the equivalent circle. The Hall-Petch formula is used to calculate the grain boundary strengthening effect:

[0078]

[0079] Where k is a constant related to the base material. The constant k for titanium alloy is 750 MPa·μm 1 / 2 , d is the β grain size.

[0080] The calculated equivalent circle diameter is 455.61 μm and the grain boundary strengthening effect is 35.137 MPa.

[0081] The XRD raw data was processed by noise reduction and flattening, the corresponding peaks were calibrated, and the microstrain was obtained by multi-peak fitting calculation using Jade's built-in half-peak method. The calculation process is as follows: Figure 1 The elastic modulus and other data are obtained through sample testing, and the average value of at least three parallel sample data is taken as the final result. The Bailey-Hirsch formula and the Williamson-Hall formula are used to calculate the dislocation strengthening effect:

[0082]

[0083] Where α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, and ρ is the dislocation density (1 / m 2 ), E is the elastic modulus (GPa), v is the Poisson’s ratio, and ε is the microstrain.

[0084] The microstrain is calculated to be 0.0049 and the dislocation density is 2.858×10 15 , the dislocation strengthening effect is 303.96378MPa.

[0085] Image Pro Plus software was used to count the microstructure morphology in the metallographic photos, and the area method was used to count the ratio of primary α and secondary α; the circumscribed rectangle method (the aspect ratio of the minimum circumscribed rectangle was used instead of the aspect ratio of the lamellae at the complex overlap position) was used to count the aspect ratio of each primary and secondary lamellae, and the area weighted algorithm was used to obtain the average length and width and aspect ratio. More than 200 lamellae data were required each time. After data processing, the improved Orowan formula was used to calculate the dislocation strengthening effect, and the primary α strengthening and secondary α strengthening were calculated separately. The primary α strengthening coefficient is 10, and the secondary α strengthening coefficient is 1000:

[0086]

[0087] Where M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width (m), f is the phase ratio, and r is 0 is the dislocation loop radius (m), and v is the Poisson’s ratio.

[0088] The statistical results show that the ratio of primary α is 51.32% and the width is 2.5791×10 -6 m, with an aspect ratio of 5.39424; the secondary α ratio is 9.816%, with a width of 1.2×10 -7 m, and the aspect ratio is 4.075. The primary α strengthening effect is calculated to be 12.6497MPa, and the secondary α strengthening effect is 218.9788MPa.

[0089] The alloy matrix strength is 180MPa for pure titanium.

[0090] The calculated solid solution strengthening, grain boundary strengthening, dislocation strengthening, primary α strengthening, secondary α strengthening, and matrix strength are added together to obtain the predicted yield strength of 976.12 MPa for this embodiment.

[0091] A tensile specimen was taken at the same position and the yield strength was measured to be 978 MPa.

[0092] The error between the calculated strength and the actual strength in this embodiment is -0.192%, which proves that the calculation method and results of this embodiment are accurate and reliable.

[0093] Embodiment 2:

[0094] The following titanium alloys were prepared based on their chemical composition by weight percentage:

[0095] Al: 5.5%, Mo: 3.5%, Cr: 2%, V: 2%, Sn: 1.5%, Zr: 1.5%, Fe: ≤0.1%, O: ≤0.1%, and the balance is Ti.

[0096] This alloy needs to go through electrode pressing, ingot melting, ingot blanking and forging forming processes, among which the thermal deformation process parameters for forging forming are 15°C above the phase transformation point and the thermal deformation amount is 35%; the subsequent heat treatment parameters are 880°C / 2h / AC+650°C / 4h / AC.

[0097] Samples were taken 1 cm below the forging surface to prepare metallographic specimens, XRD specimens, elastic modulus specimens, and tensile specimens. The microstructures were obtained as follows: Figure 5 , XRD data such as Figure 6 , elastic modulus data are shown in Table 3.

[0098] Table 3 Young's modulus, shear modulus and Poisson's ratio of three groups of parallel samples in Example 2

[0099]

[0100]

[0101] According to the preset element composition, the weight percentage of the alloy elements is converted into atomic percentage, and the dislocation-solute interaction equation is used to calculate the solid solution strengthening effect:

[0102]

[0103] In the formula, x i is the concentration of solute i (at.%), B i is the enhancement coefficient of solute i (MPa·at. -2 / 3 ), M is the Taylor factor, μ is the solute shear modulus (GPa), λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom. Solute enhancement factor B i See Table 1.

[0104] It is calculated that the solid solution strengthening effect is 226.5344MPa.

[0105] The area of ​​β grains in the low-magnification microstructure is counted and converted into a circle using the equal area method to obtain the diameter of the equivalent circle. The Hall-Petch formula is used to calculate the grain boundary strengthening effect:

[0106]

[0107] Where k is a constant related to the base material. The constant k for titanium alloy is 750 MPa·μm 1 / 2 , d is the β grain size.

[0108] The calculated equivalent circle diameter is 350.49 μm and the grain boundary strengthening effect is 40.061 MPa.

[0109] The XRD raw data was processed by noise reduction and flattening, the corresponding peaks were calibrated, and the microstrain was calculated by multi-peak fitting using Jade's built-in half-peak method. Elastic modulus and other data were obtained through sample testing, and the average value of at least three parallel sample data was taken as the final result. The Bailey-Hirsch formula and Williamson-Hall formula were used to calculate the dislocation strengthening effect:

[0110]

[0111] Where α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus (GPa), b is the burger vector, and ρ is the dislocation density (1 / m 2), E is the elastic modulus (GPa), v is the Poisson’s ratio, and ε is the microstrain.

[0112] After calculation, the microstrain is 0.0047 and the dislocation density is 2.613×10 15 , the dislocation strengthening effect is 283.01MPa.

[0113] Image Pro Plus software was used to count the microstructure morphology in the metallographic photos, and the area method was used to count the ratio of primary α and secondary α; the circumscribed rectangle method (the aspect ratio of the minimum circumscribed rectangle was used instead of the aspect ratio of the lamellae at the complex overlap position) was used to count the aspect ratio of each primary and secondary lamellae, and the area weighted algorithm was used to obtain the average length and width and aspect ratio. More than 200 lamellae data were required each time. After data processing, the improved Orowan formula was used to calculate the dislocation strengthening effect, and the primary α strengthening and secondary α strengthening were calculated separately. The primary α strengthening coefficient is 10, and the secondary α strengthening coefficient is 1000:

[0114]

[0115] Where M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width (m), f is the phase ratio, and r is 0 is the dislocation loop radius (m), and v is the Poisson’s ratio.

[0116] The statistical results show that the ratio of primary α is 52.11% and the width is 3.3775×10 -6 m, with an aspect ratio of 5.3387; the secondary α ratio is 7.96%, with a width of 9.0×10 -8 m, and the aspect ratio is 3.459. The primary α strengthening effect is calculated to be 40.0611MPa, and the secondary α strengthening effect is 211.5817MPa.

[0117] The alloy matrix strength is 180MPa for pure titanium.

[0118] The calculated solid solution strengthening, grain boundary strengthening, dislocation strengthening, primary α strengthening, secondary α strengthening, and matrix strength are added together to obtain the predicted yield strength of 971.53 MPa for this embodiment.

[0119] A tensile specimen was taken at the same position and the yield strength was measured to be 988 MPa.

[0120] The error between the calculated strength and the actual strength in this embodiment is -1.67%, which proves that the calculation method and results of this embodiment are accurate and reliable.

[0121] Embodiment 3:

[0122] The following titanium alloys were prepared based on their chemical composition by weight percentage:

[0123] Al: 5.3%, Mo: 3%, Cr: 2%, V: 2%, Sn: 1.5%, Zr: 1.5%, Fe: ≤0.1%, O: ≤0.1%, and the balance is Ti.

[0124] This alloy needs to go through electrode pressing, ingot melting, ingot blanking and forging forming processes, among which the thermal deformation process parameters for forging forming are 15°C above the phase transformation point and the thermal deformation amount is 35%; the subsequent heat treatment parameters are 880°C / 2h / AC+650°C / 4h / AC.

[0125] Samples were taken 1 cm below the forging surface to prepare metallographic specimens, XRD specimens, elastic modulus specimens, and tensile specimens. The microstructures were obtained as follows: Figure 7 , XRD data such as Figure 8 , elastic modulus data are shown in Table 4.

[0126] Table 4 Young's modulus, shear modulus and Poisson's ratio of three groups of parallel samples in Example 3

[0127]

[0128] According to the preset element composition, the weight percentage of the alloy elements is converted into atomic percentage, and the dislocation-solute interaction equation is used to calculate the solid solution strengthening effect:

[0129]

[0130] In the formula, x i is the concentration of solute i (at.%), B i is the enhancement coefficient of solute i (MPa·at. -2 / 3 ), M is the Taylor factor, μ is the solute shear modulus (GPa), λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom. Solute enhancement factor B i See Table 1.

[0131] It is calculated that the solid solution strengthening effect is 224.8693MPa.

[0132] The area of ​​β grains in the low-magnification microstructure is counted and converted into a circle using the equal area method to obtain the diameter of the equivalent circle. The Hall-Petch formula is used to calculate the grain boundary strengthening effect:

[0133]

[0134] Where k is a constant related to the base material. The constant k for titanium alloy is 750 MPa·μm 1 / 2 , d is the β grain size.

[0135] The calculated equivalent circle diameter is 414.88 μm and the grain boundary strengthening effect is 36.82138 MPa.

[0136] The XRD raw data was processed by noise reduction and flattening, the corresponding peaks were calibrated, and the microstrain was calculated by multi-peak fitting using Jade's built-in half-peak method. Elastic modulus and other data were obtained through sample testing, and the average value of at least three parallel sample data was taken as the final result. The Bailey-Hirsch formula and Williamson-Hall formula were used to calculate the dislocation strengthening effect:

[0137]

[0138] Where α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, and ρ is the dislocation density (1 / m 2 ), E is the elastic modulus (GPa), v is the Poisson’s ratio, and ε is the microstrain.

[0139] The microstrain is calculated to be 0.00505 and the dislocation density is 3.06×10 15 , the dislocation strengthening effect is 309.6917MPa.

[0140] Image Pro Plus software was used to count the microstructure morphology in the metallographic photos, and the area method was used to count the ratio of primary α and secondary α; the circumscribed rectangle method (the aspect ratio of the minimum circumscribed rectangle was used instead of the aspect ratio of the lamellae at the complex overlap position) was used to count the aspect ratio of each primary and secondary lamellae, and the area weighted algorithm was used to obtain the average length and width and aspect ratio. More than 200 lamellae data were required each time. After data processing, the improved Orowan formula was used to calculate the dislocation strengthening effect, and the primary α strengthening and secondary α strengthening were calculated separately. The primary α strengthening coefficient is 10, and the secondary α strengthening coefficient is 1000:

[0141]

[0142] Where M is the Taylor factor, G is the shear modulus (GPa), b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width (m), f is the phase ratio, and r is 0 is the dislocation loop radius (m), and v is the Poisson’s ratio.

[0143] The statistical results show that the ratio of primary α is 60.771% and the width is 3.16×10 -6 m, with an aspect ratio of 4.461; the secondary α ratio is 7.7285%, with a width of 1.42×10 -7m, and the aspect ratio is 4.609. The primary α strengthening effect is calculated to be 19.04219MPa, and the secondary α strengthening effect is 163.1378MPa.

[0144] The alloy matrix strength is 180MPa for pure titanium.

[0145] The calculated solid solution strengthening effect, grain boundary strengthening effect, dislocation strengthening effect, primary α strengthening effect, secondary α strengthening effect, and matrix strength are added together to obtain the predicted yield strength of 933.56227 MPa in this embodiment.

[0146] A tensile specimen was taken at the same position and the yield strength was measured to be 945 MPa.

[0147] The error between the calculated strength and the actual strength in this embodiment is -1.21%, which proves that the calculation method and results of this embodiment are accurate and reliable.

Claims

1. A method for calculating the yield strength of a basketweave titanium alloy based on its microstructure, characterized in that: The steps include: Step 1: Calculate the solid solution strengthening effect based on the elemental composition of the titanium alloy; Step 2: Calculate the grain boundary strengthening effect based on the average grain size of the original β grains; Step 3: Calculate the dislocation strengthening effect based on the alloy dislocation density; Step 4: Calculate the α phase strengthening effect based on the basket α phase proportion, size, and aspect ratio; Step 5: Obtain the alloy matrix strength based on the critical decomposed shear stress of pure titanium; Step 6: Add the calculated results from steps 1 to 5 to obtain the alloy yield strength.

2. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1 is characterized in that: In step 1, the dislocation-solute interaction equation is used to calculate the solid solution strengthening effect: In the formula, x i is the concentration of solute i (at.%), B i is the strengthening coefficient of solute i, M is the Taylor factor, μ is the solute shear modulus, λ i is the mismatch coefficient of the i-th component, and R is a parameter based on the Seitz radius of the solute atom.

3. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1 is characterized in that: In step 2, the Hall-Petch formula is used to calculate the grain boundary strengthening effect: Where k is a constant related to the base material. The constant k for titanium alloy is 750 MPa·μm 1 / 2 , d is the β grain size.

4. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1 is characterized in that: In step 3, the Bailey-Hirsch formula and the Williamson-Hall formula are used to calculate the dislocation strengthening effect: Where α is the dislocation interaction constant, M is the Taylor factor, G is the shear modulus, b is the burgers vector, ρ is the dislocation density, E is the elastic modulus, v is the Poisson's ratio, and ε is the microstrain.

5. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1, characterized in that: In step 4, the improved Orowan formula is used to calculate the dislocation strengthening effect: Where M is the Taylor factor, G is the shear modulus, b is the burgers vector, A is the aspect ratio of the lamella, δ is the lamella width, f is the phase ratio, r0 is the dislocation loop radius, and v is the Poisson's ratio.

6. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1, characterized in that: In step 4, Image Pro Plus software is used to measure the phase morphology data.

7. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 6 is characterized in that: In step 4, at least 200 valid phases must be counted for each phase morphology data.

8. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1, characterized in that: In step 4, the length and width of the α phase are measured using the circumscribed rectangle method. The circumscribed rectangle measurement methods under different interlacing conditions are: (a) the circumscribed rectangle of a single lamellar α phase without interlacing, the circumscribed rectangle of a simply interlaced lamellar α phase; and (b) the circumscribed rectangle of a complex closed loop formed by the lamellar α phase.

9. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1, characterized in that: In step 4, the area weighted method is used to calculate the aspect ratio.

10. The yield strength calculation method based on basketweave titanium alloy microstructure according to claim 1, characterized in that: In step 5, the alloy matrix strength is 180MPa for pure titanium.

Images