Hot working parameter design and optimization method for instability-preventing and forming-keeping titanium alloy blade

Abstract

The invention provides a hot working parameter design and optimal selection method of a titanium alloy blade capable of preventing instability and keeping forming. The machinability of the material can be reflected more comprehensively, and the instability phenomenon in the machining process is avoided. The method is characterized by comprising the following steps: step 1, cutting a plurality of cylindrical samples from a titanium alloy material; a Gleeble-3500 thermal compression simulation experiment machine is used for carrying out thermal compression tests on the titanium alloy cylinder sample at different temperatures and strain rates, and true stress strain data under different deformation conditions are obtained; step 2, based on a dynamic material model (DMM) principle, according to the true stress strain data obtained in the step 1, respectively calculating strain rate sensitivity coefficients, power dissipation efficiency and instability coefficients under different true stress strains; 3, constructing power dissipation diagrams and instability diagrams under different true stress strains according to the power dissipation efficiency and the instability coefficient of the material obtained in the step 2, taking the dependent variable as a z axis, and respectively placing the power dissipation diagrams and the instability diagrams under different strains at corresponding positions of the z axis to obtain a three-dimensional power dissipation diagram and a three-dimensional instability diagram; step 4; and 3, superposing the three-dimensional power dissipation diagram and the three-dimensional instability diagram obtained in the step 3 to obtain a three-dimensional instability region trend diagram and a safety region trend diagram, drawing to obtain a three-dimensional hot working diagram for the titanium alloy, and determining the change conditions of the instability region and the power dissipation efficiency of the titanium alloy along with the strain according to the obtained three-dimensional hot working diagram. And therefore, the hot working parameters in the machining process can be always located in the optimal interval.

Description

Technical Field

[0001] The invention belongs to the field of thermoplastic forming of metal materials, and in particular relates to a thermal processing parameter design and an optimization method for a titanium alloy blade which can prevent instability and maintain shape. Background Art

[0002] Titanium alloys have been widely used in the aerospace field due to their high strength, light weight, heat resistance, corrosion resistance, etc. At present, low-strength structural components are usually made of aluminum alloys, while high-strength structural components and some parts that need to be lightweight are mostly made of titanium alloys.

[0003] Titanium alloys can be divided into α-type, β-type and α+β-type according to their organizational structure. Among them, α+β-type titanium alloy is particularly outstanding in terms of lightweight. Compared with the other two types, the same component can still reduce the weight by about 9%. TC4 titanium alloy is a typical α+β-type titanium alloy and is also the most widely used alloy among all titanium alloys. TC4 titanium alloy has strong deformation resistance and high resilience at room temperature, so it is difficult to process at room temperature. At high temperature, its plasticity will be greatly improved, and the forming performance will also be greatly improved. Therefore, high-temperature forming is often used to obtain the desired shape and titanium alloy components.

[0004] During hot forming, TC4 titanium alloy is affected by many factors such as heating speed, holding time, forming die, deformation temperature, deformation rate, cooling method, etc., and its microstructure and thermomechanical properties are very sensitive to processing conditions. Therefore, it is necessary to reasonably select and optimize the hot processing parameters of titanium alloy in actual production and processing.

[0005] Most hot working diagrams are used to optimize hot working parameters. They are composed of power dissipation diagrams and rheological instability diagrams. Appropriate hot working parameters can be directly analyzed from the diagrams to avoid instability phenomena such as adiabatic shear bands, local plastic flow, and kink bands in the formed workpiece.

[0006] At present, two-dimensional hot working diagrams have been widely used in the optimization of hot working parameters of materials such as titanium alloys and magnesium alloys. Patent CN118010523A developed a new TiAl alloy with Nb alloy added, and used the hot working diagram to determine its hot working parameter range. Patent CN111985128B constructed a hot working diagram of large-size non-modulated steel, used finite element software to perform hot compression simulation to extract data, and compared it with the hot working diagram to accurately determine the appropriate hot working parameter range. Patent CN110964994A constructed a hot working diagram of C-276 nickel-based alloy and observed the microstructure of the material, which not only ensured the mechanical properties requirements of the material after hot working, but also determined the appropriate hot working process parameters. Patent CN107976462A introduced the work hardening rate, determined the conditions for dynamic recrystallization of the material, and verified it in combination with the microstructure. The obtained parameter range was added to the hot working diagram, and a hot working diagram of aluminum alloy considering dynamic recrystallization was constructed to determine the optimal hot working parameters of the material.

[0007] However, two-dimensional thermal processing diagrams are usually used to describe the thermal deformation behavior of materials. Although some other methods have been introduced to optimize the thermal processing parameters, the influence of strain on power dissipation efficiency and thermal processing stability is ignored, and the stability of the material during the processing cannot be guaranteed. Summary of the invention

[0008] In order to overcome the shortcomings of two-dimensional thermal processing diagrams that cannot guarantee the stability and shape preservation of materials during processing, the present invention provides a thermal processing parameter design and optimization method for titanium alloy blades that prevent instability and maintain shape. It can more comprehensively reflect the machinability of materials and avoid instability during processing.

[0009] The present invention is achieved through the following technical solutions:

[0010] The invention discloses a method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape, which is characterized by comprising the following steps:

[0011] Step 1: cutting a number of cylindrical specimens from the titanium alloy material; using a Gleeble-3500 hot compression simulation test machine to perform hot compression tests on the titanium alloy cylindrical specimens at different temperatures and strain rates to obtain true stress-strain data under different deformation conditions;

[0012] Step 2: Based on the principle of dynamic material model (DMM), according to the true stress-strain data obtained in step 1, the strain rate sensitivity coefficient, power dissipation efficiency and instability coefficient under different true stress-strain are calculated respectively;

[0013] Step 3: Use the power dissipation efficiency and instability coefficient of the material obtained in step 2 to construct a power dissipation diagram and an instability diagram under different true stresses and strains, take the strain as the z-axis and place the power dissipation diagram and the instability diagram under different strains at the corresponding positions of the z-axis, and obtain a three-dimensional power dissipation diagram and a three-dimensional instability diagram;

[0014] Step 4: Superimpose the three-dimensional power dissipation diagram and the three-dimensional instability diagram obtained in step 3 to obtain a three-dimensional instability zone trend diagram and a safe zone trend diagram, draw a three-dimensional thermal processing diagram for the titanium alloy, and determine the instability zone and power dissipation efficiency of the titanium alloy as a function of strain based on the obtained three-dimensional thermal processing diagram, thereby ensuring that the thermal processing parameters during the processing can always be within the optimal range.

[0015] It is further characterized by:

[0016] The titanium alloy sample is TC4 (Ti-6Al-4V) titanium alloy, which belongs to α+β type titanium alloy, has high specific strength, good heat resistance, corrosion resistance and formability, and is widely used in aviation structural parts;

[0017] The different temperatures and strain rates in the thermal compression simulation test are 700°C, 740°C, 780°C, and 820°C, and the strain rates are 0.001s -1 、0.01s -1 , 0.1s -1 , 1s -1 , the sample height reduction is 50%, and there are 16 groups of tests in total; the test steps are to first heat the titanium alloy sample at a heating rate of 10℃ / s, keep it warm for 3 minutes after heating to the specified temperature, and then compress it at the required strain rate. After reaching the specified deformation, stop compressing and water-cool the sample to retain the high-temperature structure of the material;

[0018] The formula for calculating the strain rate sensitivity coefficient, power dissipation efficiency and instability coefficient in step 2 is:

[0019]

[0020] Where P is the total dissipated energy; G is the dissipated energy, which is the energy consumed by the plastic deformation of the material; J is the dissipated coefficient, which is the energy consumed by the microstructural transformation of the material; σ (MPa) is the true stress; is the strain rate; m is the strain rate sensitivity coefficient; η is the power dissipation efficiency; ξ is the instability coefficient. When the instability coefficient is less than zero, the material will experience flow instability.

[0021] The thermal processing diagram in step 3 is divided into an unstable zone and a safe zone. Dynamic recrystallization and dynamic recovery mechanisms occur in the safe zone, while adiabatic shear bands, local flow, dynamic strain aging, kink bands and cracks occur in the unstable zone. When selecting processing parameters, the unstable zone should be avoided first, and parameters in the safe zone should be selected, and then the parameters should be optimized and selected according to actual needs;

[0022] In the hot compression simulation test, the size of the titanium alloy cylindrical specimen is Φ6mmx9mm.

[0023] Compared with the prior art, the present invention has the following advantages and effects:

[0024] (1) Based on the real stress-strain data obtained from the hot compression test, the present invention draws a three-dimensional power dissipation diagram and a three-dimensional instability diagram that consider the influence of strain rate, deformation temperature and strain, superimposes them to obtain a three-dimensional thermal processing diagram, and then obtains a three-dimensional instability zone trend diagram and a safety zone trend diagram, thereby obtaining the processing safety zone, energy dissipation efficiency and instability zone under different strains and their trends of change with strain.

[0025] (2) According to the three-dimensional thermal processing diagram drawn according to the present invention, the appropriate thermal processing parameter range of the material under different strains can be determined, and based on this, parameters such as temperature strain rate can be controlled in real time during the blade forming process to ensure that the process parameters are always in the appropriate processing range, avoid material instability during the processing, and thus ensure the forming quality of the blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 True stress-strain curve;

[0027] Figure 2 Two-dimensional thermal processing diagram of TC4 titanium alloy when the strain is 0.6;

[0028] Figure 3 Three-dimensional power dissipation diagram of TC4 titanium alloy;

[0029] Figure 4 Three-dimensional instability diagram of TC4 titanium alloy;

[0030] Figure 5 Trend diagram of the instability zone of TC4 titanium alloy;

[0031] Figure 6 Safety zone trend diagram of TC4 titanium alloy;

[0032] Figure 7 Three-dimensional hot working diagram of TC4 titanium alloy. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with an embodiment. This embodiment takes TC4 titanium alloy hot forming as an example, and the specific implementation steps are as follows:

[0034] Step 1: Use wire cutting to cut a sample with a diameter of 6 mm and a height of 9 mm from the TC4 titanium alloy material. Use a Gleeble 3500 thermal simulation tester to perform a hot compression test on the sample. The test temperatures are 700°C, 740°C, 780°C, and 820°C, and the strain rates are 0.001s. -1 、0.01s -1 , 0.1s -1 and 1s -1 , the height reduction is 50%, a total of 16 groups of tests. First, the sample is heated at a heating rate of 10℃ / s, and then kept warm for 3 minutes after heating to the specified temperature to make the sample temperature uniform. Then, it is compressed at a specified strain rate. When the height reduction reaches 50%, the compression is stopped and the sample is water-cooled to retain the high-temperature structure of the material. The true stress-strain curves under different deformation conditions are obtained as follows Figure 1 , where the true stress-strain curves under different deformation conditions (a)

[0035] Taking the strain value of 0.6 as an example, the true stress-strain data obtained according to step 1 are shown in Table 1

[0036]

[0037] Step 2: According to the dynamic material model, the total dissipated energy (P) can be mainly divided into two parts. One is the energy dissipation value caused by plastic deformation - power dissipation (G), and the other is the energy change related to microstructural transformation (such as dynamic recovery and dynamic recrystallization process) - dissipation coefficient (J). The relationship between the two is:

[0038]

[0039] Where σ(MPa) is the true stress; is the strain rate.

[0040] In the process of establishing the thermal processing diagram, assuming that the stress-strain curve satisfies the power function law, the relationship between G and J and the strain rate sensitivity factor (m) can be expressed as follows based on the fluid dynamics constitutive relationship model:

[0041]

[0042] When the strain rate sensitivity factor (m) is equal to 1, the dissipation covariance (J) can reach a maximum value. Under this condition, it can be approximated as an ideal linear dissipation process, which can be expressed as:

[0043]

[0044] In fact, the material is often in a nonlinear dissipation state during the thermal deformation process. Therefore, the dimensionless parameter power dissipation efficiency (η) is used to describe the dissipation capacity of the sample during the thermal deformation process, which can be expressed as:

[0045]

[0046] In order to predict the instability behavior of alloys during thermal deformation, a flow instability criterion was proposed based on the irreversible thermodynamic extreme principle in large strain plastic deformation. It can be expressed as:

[0047]

[0048] It can be inferred from this formula that when the ξ value corresponding to a certain deformation temperature and strain rate condition is less than or equal to zero, flow instability occurs during deformation under this process.

[0049] Step 3: Based on the data obtained in step 2, draw the power dissipation diagram of power dissipation efficiency changing with strain rate and temperature and the instability diagram of instability coefficient changing with strain rate and temperature. Superimposing the two diagrams can obtain the thermal processing diagram under this strain as shown in Figure 2 The gray area in the figure is the unstable area.

[0050] Step 4: According to steps 2 and 3, the power dissipation diagram and instability diagram under different strains (ε) can be obtained. In the three-dimensional coordinate system composed of temperature, strain rate, and strain, the power dissipation diagram and instability diagram under different strains are placed under the corresponding strain of the three-dimensional coordinate system, and the three-dimensional power dissipation diagram, three-dimensional instability diagram, three-dimensional instability zone trend diagram and safety zone trend diagram can be obtained, such as Figure 3 , as shown in Figures 4, 5, and 6.

[0051] Step 5: Superimpose the three-dimensional power dissipation diagram and the instability diagram obtained in step 4 to obtain a three-dimensional thermal processing diagram such as Figure 7 , the grey area in the figure is the unstable area.

[0052] The processing diagram is divided into an unstable zone and a safe zone. In the safe zone, dynamic recrystallization and dynamic recovery mechanisms occur, while instability phenomena such as adiabatic shear bands, local flow, dynamic strain aging, kink bands and cracks occur in the unstable zone.

[0053] According to the instability zone trend graph, the instability zone is mostly located at low temperature and high strain rate. It can be seen from the instability zone trend graph that the instability zone decreases with the increase of strain, and the safety zone trend graph shows that the safety zone increases with the increase of strain. According to the three-dimensional thermal processing diagram, TC4 titanium alloy is at a temperature of 700-820℃ and a strain rate of 0.001-1s -1During hot compression, the instability zone is mostly at low temperature and high strain rate, and the instability zone decreases as the strain increases. When determining the optimal hot working parameter range, we must first avoid the instability zone and select appropriate hot working parameters in the safe zone. The greater the power dissipation efficiency during the processing, the more sufficient the dynamic recrystallization of the material occurs. Therefore, the appropriate processing parameters are selected according to the requirements of the microstructure or strength of the finished blade; from the three-dimensional hot processing diagram, it can be seen that the range of the instability zone and the safe zone varies with the strain, so as to optimize the processing parameters so that the processing parameters of the blade are always in the safe zone during the processing, avoiding instability during the processing.

[0054] from Figure 2 It can be seen that when the strain is 0.6, the instability zone is 700~800℃, 0.12~1s -1 , when determining the optimal processing parameter range, this range should be avoided first, and then the area with larger power dissipation efficiency should be selected. The deformation temperature is 730-820℃, and the strain rate is 0.001-0.09s -1 ,according to Figure 2 The analysis shows that the optimal processing parameter range is 750~810℃ and 0.001~0.031s when the strain is 0.6. -1 .

[0055] However, the optimal processing parameters under this strain may not be valid under other strains. According to the optimized three-dimensional thermal processing diagram, the optimal processing parameter range under different strains can be obtained. In the actual forming process, the deformation temperature and strain rate can be controlled in real time according to the strain to avoid the instability zone, ensuring that the blade is always in the optimal processing parameter range during the forming process, thereby ensuring the forming quality of the titanium alloy blade.

[0056] The above process is the hot compression of TC4 titanium alloy, which is used to optimize the hot processing parameters of a titanium alloy blade. The same optimization method can also be used for different materials and different strain amounts, as long as the temperature or strain rate is controlled in real time according to the strain change during the forming process to ensure that it is always in the optimal processing parameter range.

Claims

1. A hot working parameter design and optimization method for a titanium alloy blade that prevents instability and maintains shape, characterized in that: It includes the following steps: Step 1: cutting a number of cylindrical specimens from the titanium alloy material; using a Gleeble-3500 hot compression simulation test machine to perform hot compression tests on the titanium alloy cylindrical specimens at different temperatures and strain rates to obtain true stress-strain data under different deformation conditions; Step 2: Based on the principle of dynamic material model (DMM), according to the true stress-strain data obtained in step 1, the strain rate sensitivity coefficient, power dissipation efficiency and instability coefficient under different true stress-strain are calculated respectively; Step 3: Use the power dissipation efficiency and instability coefficient of the material obtained in step 2 to construct a power dissipation diagram and an instability diagram under different true stresses and strains, take the strain as the z-axis and place the power dissipation diagram and the instability diagram under different strains at the corresponding positions of the z-axis, and obtain a three-dimensional power dissipation diagram and a three-dimensional instability diagram; Step 4; The three-dimensional power dissipation diagram and the three-dimensional instability diagram obtained in step 3 are superimposed to obtain a three-dimensional instability zone trend diagram and a safe zone trend diagram, and a three-dimensional thermal processing diagram for the titanium alloy is drawn. The instability zone and power dissipation efficiency of the titanium alloy change with strain are determined based on the obtained three-dimensional thermal processing diagram, and the thermal processing parameters can always be within the optimal range during the processing.

2. A method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape according to claim 1, characterized in that: The different temperatures and strain rates in the thermal compression simulation test are 700°C, 740°C, 780°C, and 820°C, and the strain rates are 0.001s -1 、0.01s -1 , 0.1s -1 , 1s -1 The sample height reduction was 50%, with a total of sixteen groups of tests. The test steps were as follows: first, the titanium alloy sample was heated at a heating rate of 10°C / s, and then kept warm for 3 minutes after reaching the specified temperature. Then, it was compressed at the required strain rate, and the compression was stopped after reaching the specified deformation. The sample was water-cooled to retain the high-temperature structure of the material.

3. A method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape according to claim 1 or 2, characterized in that: The formula for calculating the strain rate sensitivity coefficient, power dissipation efficiency and instability coefficient in step 2 is: Where P is the total dissipated energy; G is the dissipated energy, which is the energy consumed by the plastic deformation of the material; J is the dissipated coefficient, which is the energy consumed by the microstructure transformation of the material; σ (MPa) is the true stress; is the strain rate; m is the strain rate sensitivity coefficient; η is the power dissipation efficiency; ξ is the instability coefficient. When the instability coefficient is less than zero, the material will experience flow instability.

4. A method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape according to claim 3, characterized in that: The titanium alloy sample is TC4 (Ti-6Al-4V) titanium alloy. TC4 (Ti-6Al-4V) titanium alloy belongs to α+β type titanium alloy, has high specific strength, good heat resistance, corrosion resistance and formability, and is widely used in aviation structural parts.

5. A method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape according to claim 4, characterized in that: In the hot compression simulation test, the size of the titanium alloy cylindrical specimen is Φ6mmx9mm.

6. The method for designing and optimizing hot working parameters of a titanium alloy blade that prevents instability and maintains shape according to claim 3 is characterized in that: The thermal processing diagram described in step 3 is divided into an unstable zone and a safe zone. Dynamic recrystallization, dynamic recovery and other mechanisms occur in the safe zone, while adiabatic shear bands, local flow, dynamic strain aging, kink bands and cracks and other unstable phenomena occur in the unstable zone. When selecting processing parameters, the parameters in the safe zone should be selected first, and then the parameters should be optimized and selected according to actual needs.

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