TC11 titanium alloy fracture toughness prediction method considering heat treatment temperature

Abstract

The invention belongs to the field of performance prediction of titanium alloy, and particularly relates to a TC11 titanium alloy fracture toughness prediction method considering heat treatment temperature. Comprising the following steps: (1) carrying out double annealing heat treatment on the TC11 titanium alloy at different temperatures, carrying out quasi-static stretching and fracture toughness tests on the TC11 titanium alloy subjected to heat treatment, and recording test data; (2) establishing a TC11 titanium alloy fracture toughness prediction model considering the heat treatment temperature by introducing a correction term of the heat treatment temperature; (3) fitting the prediction model in the step (2) according to test data in the step (1) to obtain values of a basic toughness coefficient m and a temperature sensitivity coefficient n; and (4) verifying the TC11 titanium alloy fracture toughness prediction model. By introducing the heat treatment temperature correction term, the quantitative relation between the heat treatment temperature and the fracture toughness is established, the fracture toughness is predicted, the test cost is reduced, and the material design is optimized.

Description

Technical Field

[0001] The present invention belongs to the field of performance prediction of titanium alloys, and in particular relates to a method for predicting the fracture toughness of TC11 titanium alloy taking heat treatment temperature into consideration. Background Art

[0002] Titanium alloys possess excellent comprehensive properties and are widely used in a variety of fields, including aerospace, shipbuilding, medicine, and defense. In recent years, the concept of Damage Tolerance Design (DTD) has gained widespread recognition in various fields to prevent safety-threatening damage to titanium alloys during use. Furthermore, fracture toughness, a key indicator of DTD, characterizes a metal's ability to resist crack propagation and is crucial for assessing the integrity of damaged structures. Fracture toughness directly impacts the design service life of titanium alloy materials or structures.

[0003] However, the fracture toughness of titanium alloys is significantly affected by the microstructure, which in turn is highly dependent on the heat treatment process parameters, especially the annealing temperature. For example, in actual production, TC11 titanium alloy often uses a double annealing process to balance strength and toughness, but changes in the first-stage annealing temperature will significantly change the microstructure of the material. Data show that even a slight change in the first-stage annealing temperature (such as ±30°C) may cause the fracture toughness to fluctuate by 10% to 15% by changing the primary α phase content and the distribution of β-transformed structure. This sensitivity makes it difficult for traditional empirical models to accurately predict performance under different processes.

[0004] Although many researchers have studied the relationship between different microstructures and the fracture toughness of titanium alloys, these studies rely on expensive microscopic characterization methods such as EBSD and TEM, limiting their practicality in engineering. Furthermore, these studies cannot predict the performance under different processes in advance, which cannot directly guide titanium alloy process development and results in a long process development cycle. Summary of the Invention

[0005] The object of the present invention is to provide a method for predicting the fracture toughness of TC11 titanium alloy taking into account the heat treatment temperature.

[0006] The technical solution for achieving the purpose of the present invention is: a method for predicting the fracture toughness of TC11 titanium alloy considering the heat treatment temperature, comprising the following steps:

[0007] Step (1): performing double annealing heat treatment on the TC11 titanium alloy at different temperatures, performing quasi-static tensile and fracture toughness tests on the heat-treated TC11 titanium alloy, and recording the test data;

[0008] Step (2): By introducing the correction term of heat treatment temperature, a fracture toughness prediction model of TC11 titanium alloy considering heat treatment temperature is established:

[0009]

[0010] Where K ΙC is the fracture toughness; E is the elastic modulus; v is the Poisson's ratio; l is the crack tip damage height; A v is the deformation specific energy; T is the heat treatment temperature; T β is the phase transition temperature of TC11 titanium alloy; m is the basic toughness coefficient, and n is the temperature sensitivity coefficient;

[0011] Step (3): fitting the prediction model of step (2) according to the test data of step (1) to obtain the values of the basic toughness coefficient m and the temperature sensitivity coefficient n;

[0012] Step (4): Verify the fracture toughness prediction model of TC11 titanium alloy.

[0013] Furthermore, step (1) is as follows:

[0014] Step (11): Design a double annealing heat treatment process test of TC11 titanium alloy at different temperatures: the double annealing is divided into two stages: the first stage annealing temperature T1, the first stage holding time t1, air cooling, the second stage annealing temperature T2, the holding time t2, air cooling; the variable in the test is the first stage annealing temperature T1, the first stage annealing temperature T1 is within the range of 900°C to 1030°C, and the other heat treatment parameters remain unchanged;

[0015] Step (12): On the blanks treated with different first-stage annealing temperatures T1, tensile test specimens and CT specimens are obtained along the longitudinal direction in an area where the radius from the center of the blank is 1 / 4 of the blank diameter, and material performance tests are performed.

[0016] Furthermore, in step (11), the first stage annealing temperature T1 is 900°C, 930°C, 960°C, 1000°C, and 1030°C, the first stage holding time t1 is 2 hours, and the second stage annealing temperature T2 is 530°C, and the holding time t2 is 6 hours.

[0017] Furthermore, the performance test of the material in step (12) is specifically as follows:

[0018] Perform quasi-static tensile test to obtain the material elastic modulus E and deformation specific energy A v ;

[0019] A fracture toughness test is performed to obtain the fracture toughness value of the material.

[0020] Furthermore, step (2) specifically includes the following steps:

[0021] Step (21): According to the linear elastic fracture mechanics theory, the fracture toughness K ΙC and critical energy release rate G ΙC The relationship is expressed as:

[0022]

[0023] Where G ΙC is the critical energy release rate;

[0024] Step (22): According to the Griffith-Orowan-Irwin theory, the critical energy release rate G in formula (1) is ΙC

[0025] Expressed as:

[0026] G ΙC =2γ eff (2)

[0027] Where γ eff is the effective surface energy;

[0028] Step (23): At the critical state of crack propagation, establish the relationship between the released deformation specific energy and the effective surface energy:

[0029] A v V = 2γ eff ·F (3)

[0030] Where V is the volume that causes failure; F is the surface where the crack forms;

[0031] Step (24): Approximate the shape of the plastic zone at the crack tip to an ellipse, and obtain the simplified volume V that causes failure and the surface F where the crack forms:

[0032]

[0033] Where h is the width of the plastic zone at the crack tip, and d is the crack thickness;

[0034] Step (25): Obtain the fracture toughness K according to equations (1)-(4) ΙC The expression:

[0035]

[0036] Step (26): Determine the temperature correction term

[0037]

[0038] Where m is the basic toughness coefficient; n is the temperature sensitivity coefficient; T β is the phase transition temperature of TC11 titanium alloy; T is the heat treatment temperature;

[0039] Step (27): Introduce equation (6) into equation (5) to obtain the fracture toughness prediction model of titanium alloy considering heat treatment temperature:

[0040]

[0041] Furthermore, step (3) is specifically as follows:

[0042] For formula (7), let

[0043] Rewrite formula (7) into linear form: y = m + n·x;

[0044] Collect the fracture toughness K measured at different first stage annealing temperatures T1 ΙC , elastic modulus E, deformation specific energy A v The basic toughness coefficient m and temperature sensitivity coefficient n are obtained by least square fitting.

[0045] Furthermore, step (4) is specifically as follows: designing a first-stage heat treatment temperature T′1 different from step (1), keeping the other processes and process parameters t1, T2, t2 unchanged to conduct process tests, and conducting quasi-static tensile tests according to the standard of step (1) to obtain elastic modulus E, deformation specific energy A v , perform fracture toughness test according to step (1) to obtain fracture toughness value; heat treatment temperature T′1, elastic modulus E, deformation specific energy A v Substitute the prediction model formula (7) in step (2) to calculate the fracture toughness of TC11 titanium alloy at T′1 heat treatment temperature, and compare the calculated value with the experimental value.

[0046] The above method is applicable to the prediction of fracture toughness of α+β duplex titanium alloy.

[0047] Compared with the prior art, the present invention has the following significant advantages:

[0048] The present invention introduces a temperature correction term into the fracture toughness prediction model, which reflects the dynamic influence of heat treatment temperature on microstructure and fracture toughness, and accurately predicts the fracture toughness values at different heat treatment temperatures with a maximum error of no more than 6%, significantly improving the prediction accuracy and providing a reliable basis for material design and process optimization.

[0049] Traditional methods rely on expensive microscopic characterization methods (such as EBSD, TEM) and a large number of experiments. The present invention can predict fracture toughness through only conventional tensile tests combined with model calculations; this significantly reduces testing costs, shortens process development cycles, and improves engineering practicality.

[0050] The present invention is also applicable to the prediction of the fracture toughness of any grade of α+β dual-phase titanium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of double annealing in the present invention.

[0052] Figure 2 The microstructure of TC11 titanium alloy after being processed at different heat treatment temperatures; Figure 2 (a) is the microstructure when the heat treatment temperature is 900℃. Figure 2 (b) is the microstructure when the heat treatment temperature is 930℃. Figure 2 (c) is the microstructure when the heat treatment temperature is 960℃. Figure 2 (d) is the microstructure when the heat treatment temperature is 1000℃. Figure 2 (e) is the microstructure when the heat treatment temperature is 1030℃.

[0053] Figure 3 This is a comparison between the fracture toughness test value and the predicted value in the present invention.

[0054] Figure 4 Flowchart of the present invention. DETAILED DESCRIPTION

[0055] The present invention is further described in detail below with reference to the accompanying drawings.

[0056] Example 1

[0057] This embodiment is a method for predicting the fracture toughness of TC11 titanium alloy taking into account the heat treatment temperature. The specific process of this embodiment is:

[0058] Step 1: Collect process test and performance test data of TC11 titanium alloy at different heat treatment temperatures.

[0059] Design a double annealing heat treatment process test of TC11 titanium alloy at different temperatures. The double annealing is divided into two stages, namely the first stage annealing temperature T1, the first stage holding time t1 is 2 hours, air cooling, the second stage annealing temperature T2 is 530℃, the holding time t2 is 6 hours, air cooling. The first stage annealing temperature T1 is used as a variable, and the phase transition point temperature T β In order to avoid the small temperature difference that would lead to little difference in performance, the first stage annealing temperature T1 was determined in the temperature range of 900℃~1030℃. Finally, the first stage annealing temperatures T1 of 900℃, 930℃, 960℃, 1000℃ and 1030℃ were selected as the heat treatment process tests at different temperatures.

[0060] On the blanks treated at different heat treatment temperatures, tensile test specimens and CT specimens were obtained along the longitudinal direction in an area with a radius of 1 / 4 of the blank diameter from the center of the blank. The material performance test was carried out. Specifically, the quasi-static tensile test was used to obtain the material elastic modulus E, deformation specific energy A v The fracture toughness test is used to obtain the fracture toughness value of the material. Each data is the sum average of three test results of TC11 titanium alloy at a certain temperature.

[0061] The sampling position is carried out in accordance with GB / T 23604-2009, the size and test method of the tensile properties specimen are carried out in accordance with GB / T 228.1-2010, and the CT specimen and test method of the fracture toughness test are carried out in accordance with GB / T 21143-2007.

[0062] The test results are shown in Table 1.

[0063] Table 1 Performance data of different heat treatment temperatures

[0064]

[0065] Step 2: By introducing the correction term of heat treatment temperature, a fracture toughness prediction method for TC11 titanium alloy considering heat treatment temperature is established.

[0066] The fracture toughness prediction model is derived by the formula:

[0067] According to the linear elastic fracture mechanics theory, the fracture toughness K ΙC and critical energy release rate G ΙC The relationship can be expressed as shown in formula (1):

[0068]

[0069] Where E is the elastic modulus, G ΙC is the critical energy release rate, and v is the Poisson's ratio.

[0070] According to the Griffith-Orowan-Irwin theory, the critical energy release rate G in formula (1) is ΙC It can be expressed as

[0071] As shown in formula (2):

[0072] G ΙC =2γ eff (2)

[0073] Where γ eff is the effective surface energy, which represents the resistance to unstable crack growth.

[0074] To predict the fracture toughness of TC11 titanium alloy, it is only necessary to determine the effective surface energy γeff The value of is sufficient. When the crack propagates, the deformation energy released in the material needs to be converted into the effective surface energy of the new surface. At the critical state of crack propagation, the relationship between the released deformation energy and the effective surface energy is established, as shown in Equation (3).

[0075] A v V = 2γ eff ·F (3)

[0076] Where A v is the deformation specific energy, which can be calculated from the area under the tensile stress-strain curve; V is the volume that causes failure; and F is the surface where the crack forms.

[0077] Under plane strain, the shape of the plastic zone at the tip of a mode I crack resembles a peanut or dumbbell. This irregular shape makes it difficult to calculate the failure volume V and the crack formation surface F. Assuming that the shape of the plastic zone at the crack tip is approximated as an ellipse, the failure volume V and the crack formation surface F are simplified, as shown in Equation (4).

[0078]

[0079] Where l is the height of the plastic zone at the crack tip, h is the width of the plastic zone at the crack tip, and d is the crack thickness.

[0080] Finally, the fracture toughness K can be obtained by combining formulas (1-4) ΙC The expression of is shown in formula (5):

[0081]

[0082] From formula (5), we can know that the height of the plastic zone at the crack tip l, the elastic modulus E, Poisson's ratio v and deformation specific energy A v All four parameters are related to the inherent properties of the material and are directly affected by the material's microstructure, which in turn depends on the heat treatment process parameters. According to research, when the heat treatment temperature gradually increases from below the phase transition temperature, the primary α phase in the TC11 titanium alloy microstructure gradually decreases, and the transformed β structure gradually increases. When the heat treatment temperature approaches the phase transition temperature and exceeds it, the original β grain boundaries in the TC11 titanium alloy microstructure are destroyed during deformation, and as the temperature increases, "bundles" of different sizes are formed in the microstructure. Formula (5) only includes macroscopic mechanical parameters and does not take into account the dynamic effects of heat treatment temperature and microstructure.

[0083] In order to establish a fracture toughness model that takes into account the influence of heat treatment process, a temperature correction term is introduced into formula (5): As shown in formula (6).

[0084]

[0085] Where m is the basic toughness coefficient, which characterizes the inherent fracture toughness of the material at a temperature far from the phase transition point and is determined by the initial structure; n is the temperature sensitivity coefficient, which reflects the sensitivity of fracture toughness to temperature; T β is the phase transition temperature of TC11 titanium alloy; T is the heat treatment temperature. The dimensionless temperature term in the correction term is Directly related to heat treatment temperature T and phase transition temperature T β , which reflects the effect of heat treatment temperature on the driving force of phase transformation, that is, the closer the heat treatment temperature is to the phase transformation point T β , the more intense the phase transition.

[0086] Combining formula (5) and the correction formula (6), the fracture toughness prediction model of titanium alloy considering the heat treatment temperature is obtained as shown in formula (7):

[0087]

[0088] Among them, K ΙC is the fracture toughness; E is the elastic modulus; v is the Poisson's ratio; l is the crack tip damage height; A v is the deformation specific energy, which can be calculated from the area under the tensile stress-strain curve; T is the heat treatment temperature; T β is the phase transition temperature of TC11 titanium alloy; m is the basic toughness coefficient; n is the temperature sensitivity coefficient.

[0089] The Poisson's ratio v is 0.33, the crack tip damage height l is 0.3 mm, and the phase transition temperature T of TC11 titanium alloy is β It is 1002℃.

[0090] By introducing the correction term of heat treatment temperature The effect of microstructural changes on fracture toughness is indirectly characterized.

[0091] The fracture toughness K values measured at different temperatures were collected by heat treatment tests on TC11 titanium alloy at 900℃, 930℃, 960℃, 1000℃ and 1030℃. Ιc , elastic modulus E, deformation specific energy A v . And for formula (7), let Formula (7) was rewritten into a linear form: y = m + n x, and the least squares method was used to fit the basic toughness coefficient m and the temperature sensitivity coefficient n. Finally, the basic toughness coefficient m was calibrated to 1.2187, and the temperature sensitivity coefficient n was calibrated to -1.4727.

[0092] Step 3: Verify the effectiveness of the fracture toughness prediction method for TC11 titanium alloy.

[0093] The design of the first stage annealing temperature T'1 of the heat treatment is different from that in step 1, and the other process and process parameters t1, T2, and t2 are kept unchanged. The process test is carried out, and the final design of T'1 is 920℃, 950℃, and 980℃. According to the standard described in step 1, the quasi-static tensile test is carried out to obtain the elastic modulus E and deformation specific energy A. v , perform the fracture toughness test according to the standard described in step 1 to obtain the fracture toughness value. v Substituting the prediction model formula (7) from step 2, the fracture toughness of the TC11 titanium alloy at the T′1 heat treatment temperature can be calculated. Based on the fracture toughness values obtained from the experiment in step 3, the predicted values are compared with the experimental values. Through three sets of comparative tests, it was found that the fracture toughness of the TC11 titanium alloy can be well predicted, with a maximum error of no more than 6%.

[0094] Table 2 Comparison of predicted and experimental fracture toughness values of TC11 titanium alloy

[0095]

Claims

1. A method for predicting the fracture toughness of TC11 titanium alloy considering heat treatment temperature, characterized in that: The steps include: Step (1): performing double annealing heat treatment on the TC11 titanium alloy at different temperatures, performing quasi-static tensile and fracture toughness tests on the heat-treated TC11 titanium alloy, and recording the test data; Step (2): By introducing the correction term of heat treatment temperature, a fracture toughness prediction model of TC11 titanium alloy considering heat treatment temperature is established: Where K ΙC is the fracture toughness; E is the elastic modulus; v is the Poisson's ratio; l is the damage height at the crack tip; A v is the deformation specific energy; T is the heat treatment temperature; T β is the phase transition temperature of TC11 titanium alloy; m is the basic toughness coefficient, and n is the temperature sensitivity coefficient; Step (3): fitting the prediction model of step (2) according to the test data of step (1) to obtain the values of the basic toughness coefficient m and the temperature sensitivity coefficient n; Step (4): Verify the fracture toughness prediction model of TC11 titanium alloy.

2. The method according to claim 1, characterized in that Step (1) is as follows: Step (11): Design a double annealing heat treatment process test of TC11 titanium alloy at different temperatures: the double annealing is divided into two stages: the first stage annealing temperature T1, the first stage holding time t1, air cooling, the second stage annealing temperature T2, holding time t2, air cooling; The variable in the experiment is the first stage annealing temperature T1, which is in the range of 900℃ to 1030℃, and the other heat treatment parameters remain unchanged; Step (12): On the blanks treated with different first-stage annealing temperatures T1, tensile test specimens and CT specimens are obtained along the longitudinal direction in an area where the radius from the center of the blank is 1 / 4 of the blank diameter, and material performance tests are performed.

3. The method according to claim 2, characterized in that In step (11), the first stage annealing temperature T1 is 900°C, 930°C, 960°C, 1000°C, and 1030°C, and the first stage holding time t1 is 2 hours. The second stage annealing temperature T2 is 530°C, and the holding time t2 is 6 hours.

4. The method according to claim 3, characterized in that The performance test of the material in step (12) is specifically as follows: Perform quasi-static tensile test to obtain the material elastic modulus E and deformation specific energy A v ; A fracture toughness test is performed to obtain the fracture toughness value of the material.

5. The method according to claim 4, characterized in that Step (2) specifically includes the following steps: Step (21): According to the linear elastic fracture mechanics theory, the fracture toughness K ΙC and critical energy release rate G ΙC The relationship is expressed as: Where G ΙC is the critical energy release rate; Step (22): According to the Griffith-Orowan-Irwin theory, the critical energy release rate G in formula (1) is ΙC Expressed as: G ΙC =2c eff (2) Where γ eff is the effective surface energy; Step (23): At the critical state of crack propagation, establish the relationship between the released deformation specific energy and the effective surface energy: A v ·V=2γ eff ·F (3) Where V is the volume that causes failure; F is the surface where the crack forms; Step (24): Approximate the shape of the plastic zone at the crack tip to an ellipse, and obtain the simplified volume V that causes failure and the surface F where the crack forms: Where h is the width of the plastic zone at the crack tip, and d is the crack thickness; Step (25): Obtain the fracture toughness K according to equations (1)-(4) Ιc The expression: Step (26): Determine the temperature correction term Where m is the basic toughness coefficient; n is the temperature sensitivity coefficient; T β is the phase transition temperature of TC11 titanium alloy; T is the heat treatment temperature; Step (27): Introduce equation (6) into equation (5) to obtain the fracture toughness prediction model of titanium alloy considering heat treatment temperature:

6. The method according to claim 5, characterized in that Step (3) is specifically as follows: For formula (7), let Rewrite formula (7) into linear form: y = m + n·x; Collect the fracture toughness K measured at different first stage annealing temperatures T1 Ιc , elastic modulus E, deformation specific energy A v The basic toughness coefficient m and temperature sensitivity coefficient n are obtained by least square fitting.

7. The method according to claim 6, characterized in that Step (4) is specifically as follows: designing a first-stage heat treatment temperature T′1 that is different from step (1), keeping the other process and process parameters t1, T2, t2 unchanged to conduct process tests, and conducting quasi-static tensile tests according to the standard of step (1) to obtain the elastic modulus E, deformation specific energy A v , perform fracture toughness test according to step (1) to obtain fracture toughness value; heat treatment temperature T′1, elastic modulus E, deformation specific energy A v Substitute the prediction model formula (7) in step (2) to calculate the fracture toughness of TC11 titanium alloy at T′1 heat treatment temperature, and compare the calculated value with the experimental value.

8. The method according to any one of claims 1 to 7, characterized in that Suitable for prediction of fracture toughness of α+β duplex titanium alloy.

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