Creep prediction method of nickel-based superalloy considering hot corrosion environment damage

Abstract

The invention relates to the technical field of alloy performance prediction, in particular to a nickel-based superalloy creep prediction method considering hot corrosion environment damage, and the method comprises the following steps: obtaining a nickel-based superalloy test piece; calibrating an equivalent hot corrosion damage coefficient according to data of the hot corrosion-creep test; calculating equivalent hot corrosion damage according to the thickness of the control element depletion layer and the equivalent hot corrosion damage coefficient; acquiring a creep constitutive model; equivalent hot corrosion damage is introduced into the creep constitutive model, and a hot corrosion-creep constitutive model is obtained; and according to the hot corrosion-creep constitutive model, predicting the creep of the hot corrosion environment damage of the nickel-based superalloy. According to the method, the creep life of the nickel-based superalloy in the hot corrosion environment can be predicted to be within 1.2 times of an error scattering band, and the creep damage condition of the nickel-based superalloy in the hot corrosion environment can be reflected.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy property prediction, and particularly relates to a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment. Background Art

[0002] As a power supply device for carrier-based aircraft engines, an aeroengine is in a service environment of high temperature, high pressure and high load for a long time. Creep is the main reason for shortening the service life of hot-end components (turbine blades, turbine disks). Nickel-based superalloys are widely used in the hot-end components of aeroengines due to their excellent creep resistance, hot corrosion resistance and oxidation resistance in high-temperature environments. In addition, during the service process of an aeroengine in a marine environment, it will inhale marine water vapor rich in NaCl. Chloride salts mainly composed of NaCl and Na2SO4 generated by incomplete combustion of aeroengine fuel will form a low-melting-point mixed salt and adhere to the hot-end components of the aeroengine, thereby causing hot corrosion of the hot-end components. The hot corrosion behavior will cause the hot-end components to accelerate creep failure under mechanical stress, which seriously affects the safety, reliability and integrity of carrier-based aircraft engines.

[0003] However, under the coupled action of temperature, chemical medium and stress in a hot corrosion environment, the hot corrosion synergistically with mechanical load leads to a complex mechanism of material and structure deterioration, and it is difficult to quantitatively evaluate hot corrosion damage. At present, creep constitutive models applicable to nickel-based superalloys in an air environment have been fully studied and applied, while there is little research on creep constitutive considering a hot corrosion environment. Traditional creep models (such as Norton power law, θ projection method) can only predict the creep behavior of nickel-based superalloys in an air environment. Due to ignoring the damage effect of hot corrosion medium on the creep of nickel-based superalloys, the traditional creep models show poor model accuracy in predicting the creep behavior of nickel-based superalloys in a hot corrosion environment.

[0004] More importantly, the creep behavior of nickel-based superalloys in a stress-hot corrosion environment needs to consider the coupled environment of temperature field, stress field and chemical field, and it is difficult to quantitatively evaluate hot corrosion environment damage. From the perspective of the application of creep models in engineering practice, only by evaluating the deteriorated state of the alloy with an appropriate quantity can the alloy deterioration caused by hot corrosion be incorporated into creep damage. If macroscopic variables such as mass change are selected, there is a lack of physical background and it cannot fully reflect the deterioration process of the material. And if the selected quantity is too microscopic, it is difficult to establish a connection with the damage model. The model requires not only more parameters to be determined, but also higher requirements for the computing power of the computer, which is difficult to apply to engineering practice. Therefore, selecting appropriate damage state variables to evaluate the creep damage of high-temperature alloys in a hot corrosion environment is crucial for accurately evaluating the creep life of nickel-based superalloys in a hot corrosion environment. To sum up, creep prediction of hot-end components in a hot corrosion environment is still a challenging problem in aeroengineering. Summary of the Invention

[0005] To solve the above technical problems, in view of the fact that the creep constitutive model for current engineering applications ignores the damage effect of creep of nickel-based superalloys caused by hot corrosion media, resulting in poor model accuracy in predicting the creep behavior of nickel-based superalloys in a hot corrosion environment, the present invention provides a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment. This method uses the Cr element depletion layer as an environmental characteristic quantity to quantitatively characterize the deterioration of nickel-based superalloys in a hot corrosion environment, and establishes a damage evolution equation. Then, the damage evolution equation is incorporated into the creep constitutive model based on continuum damage mechanics to establish a creep constitutive model considering damage in a hot corrosion environment. This model can predict the creep life of nickel-based superalloys in a hot corrosion environment within a 1.2-fold error scatter band compared with traditional creep constitutive models, and can also reflect the creep damage of nickel-based superalloys in a hot corrosion environment.

[0006] The object of the present invention is to provide a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment, including: Obtaining test pieces of nickel-based superalloys; Respectively conducting hot corrosion tests, air-creep tests, and hot corrosion-creep tests on the test pieces; Obtaining the thickness of the control element depletion layer according to the data of the hot corrosion test; Calibrating the equivalent hot corrosion damage coefficient in the environmental damage evolution equation of nickel-based superalloys in a hot corrosion environment according to the data of the hot corrosion-creep test; Calculating the equivalent hot corrosion damage according to the thickness of the control element depletion layer and the equivalent hot corrosion damage coefficient; Calibrating the parameters of the creep constitutive model according to the data of the air-creep test to obtain the creep constitutive model; Introducing the equivalent hot corrosion damage into the creep constitutive model to obtain a hot corrosion-creep constitutive model; Predicting the creep of nickel-based superalloys with damage in a hot corrosion environment according to the hot corrosion-creep constitutive model.

[0007] Preferably, obtaining the thickness of the control element depletion layer according to the data of the hot corrosion test includes: Cutting the test pieces after the hot corrosion test along the cross-section and longitudinal section, then polishing the cross-section and longitudinal section, then conducting SEM-EDS observation on the polished test pieces, semi-quantitatively analyzing the corrosion products, and determining the thickness of the control element depletion layer.

[0008] Preferably, the formula for calculating the equivalent hot corrosion damage is as follows:

[0009] In the formula, is the equivalent thermal corrosion damage; L is the perimeter of the cross-section of the gauge length section of the specimen; S is the initial cross-sectional area of the specimen; C is the equivalent thermal corrosion damage coefficient; Controls the thickness of the depletion layer of the element.

[0010] Preferably, the thickness of the depletion layer of the control element is:

[0011] In the formula, is the thickness of the depletion layer of the control element; Represents the tensile stress The corresponding thermal corrosion rate coefficient; t represents the thermal corrosion time; i represents the thickening index of the depletion layer of the control element; Represents the tensile stress The corresponding correction coefficient of the depletion layer of the control element.

[0012] Preferably, the creep constitutive model is:

[0013] In the formula, is the creep strain rate, is the creep stress, is the creep damage; , and are creep constants; among them, Is determined by the creep strain rate at fracture and the minimum creep strain rate in the second stage of creep.

[0014] Preferably, the thermal corrosion-creep constitutive model is:

[0015] In the formula, is the creep strain rate, is the creep stress, is the creep damage; , and are creep constants; L is the perimeter of the cross-section of the gauge length section of the specimen; S is the initial cross-sectional area of the specimen; C is the equivalent thermal corrosion damage coefficient; is the thickness of the depletion layer of the control element.

[0016] Preferably, the equivalent thermal corrosion damage coefficient is calibrated according to the following steps: Obtain the creep deformation curve of the nickel-based superalloy in the thermal corrosion environment according to the data of the thermal corrosion-creep test; Calibrate the equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model according to the creep deformation curve of nickel-based superalloys in a hot corrosion environment.

[0017] Preferably, before performing the hot corrosion test and the hot corrosion-creep test on the test piece, it also includes: cutting the nickel-based superalloy, grinding the cut specimen step by step with sandpaper to 2000#, and then ultrasonically cleaning the ground test piece with anhydrous ethanol, acetone, and distilled water respectively to remove oil stains.

[0018] Preferably, the hot corrosion test on the test piece is carried out by the salt coating method, including: Prepare a saturated salt solution with a mass ratio of 3:1 using anhydrous Na2SO4 with a purity greater than 99.5% and anhydrous NaCl; then heat the specimen to 250~350°C, and use an atomizer to spray the saturated salt solution on the heated test piece; among them, the salt spraying interval is 3~5 seconds.

[0019] The present invention has at least the following beneficial effects: The present invention provides a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment. Compared with the traditional creep prediction method for nickel-based superalloys, the creep prediction method has the advantages of strong environmental applicability, realizing quantitative evaluation of hot corrosion creep damage, and having expandability and generality in environment-creep prediction.

[0020] By introducing equivalent hot corrosion damage into the creep constitutive model, the present invention constructs a hot corrosion-creep constitutive model. This model can fully consider the influence of this factor on the creep behavior and damage evolution of nickel-based superalloys, and is applicable to the life prediction and performance evaluation of hot-end components in marine environments, such as engine blades, turbine components, etc.

[0021] The present invention realizes the quantitative evaluation of hot corrosion creep damage. The model provided by the present invention introduces an equivalent hot corrosion creep damage evolution equation, which can describe the deterioration effect of hot corrosion caused by hot corrosion salts on nickel-based superalloys and predict the damage evolution process of materials. This provides a scientific basis for the design and life assessment of hot-end components.

[0022] The creep prediction model in the present invention has expandability and generality. This model can be adjusted according to different marine environmental conditions (such as different salt spray concentrations, moisture environments, etc.). This flexibility makes this model have strong generality and can be applied to the life assessment fields of multiple equipment such as marine aviation, ship gas turbines, and nuclear reaction cladding materials. Description of the Drawings

[0023] Figure 1 It is a flow chart of the creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment.

[0024] Figure 2 It is a physical diagram of the test piece used.

[0025] Figure 3 It is a schematic diagram for the statistics of the line scan results.

[0026] Figure 4 It is a graph of the minimum creep strain rate of the present invention.

[0027] Figure 5 It is a bar chart of the creep life of the present invention.

[0028] Figure 6 It is a technical roadmap of the hot corrosion-creep constitutive model.

[0029] Figure 7 It is a schematic diagram of the creep damage of nickel-based superalloys caused by hot corrosion media.

[0030] Figure 8 It is a schematic diagram for the sensitivity analysis of the corrosion rate.

[0031] Figure 9 It is the calculation result of the equivalent hot corrosion damage.

[0032] Figure 10 It is the creep data and simulation data in the air environment.

[0033] Figure 11 It is the creep data and simulation data in the hot corrosion environment.

[0034] Figure 12 It is a graph of the model error scatter band. Specific embodiments

[0035] In order to illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will be described in detail in combination with embodiments.

[0036] In the present invention, for the existing nickel-based superalloys that creep in an air environment, the creep damage is mainly caused by factors such as the accumulation of pores and microcracks, the coarsening of precipitation phases, and high-temperature oxidation. The above reasons are the deterioration of nickel-based superalloys caused by creep stress. The damage evolution model in the air environment only considers the deterioration behavior of nickel-based superalloys caused by creep stress. Since the deterioration rate of nickel-based superalloys caused by high-temperature alloys in the air environment is slower than that of hot corrosion. It can be seen that the traditional creep constitutive model can be well applied to the creep prediction of nickel-based superalloys in the air environment, but not applicable to the hot corrosion environment. Especially in the hot corrosion environment of the marine environment, extremely high requirements are put forward for the performance of hot-end components. In the marine environment, the material not only faces high-temperature loads but also encounters the erosion of corrosive salts such as chlorides, resulting in the formation of an oxide layer on the alloy surface and accelerating crack propagation. The traditional creep model does not consider the hot corrosion effect of the material in the marine environment. Therefore, the traditional creep prediction model cannot predict the creep behavior of hot-end components in the marine environment. In the marine environment, the coupling of high-temperature corrosion and stress action exacerbates the damage of hot-end components. The traditional creep model fails to effectively consider the influence of hot corrosion on the microstructure of the material and ignores the synergistic effect of corrosion and creep damage.

[0037] Therefore, the present invention provides a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment. Based on the traditional creep constitutive model, the hot corrosion creep damage evolution is introduced, and a hot corrosion-creep constitutive model is constructed. This model can predict the creep behavior of hot-end components in the marine environment. That is, taking the Cr element depletion layer as the environmental characteristic quantity, the deterioration of nickel-based superalloys in the hot corrosion environment is quantitatively characterized, and a damage evolution equation is established. And the damage evolution equation is incorporated into the creep constitutive model based on continuum damage mechanics to establish a creep constitutive model considering damage in the hot corrosion environment. This model can predict the creep life of nickel-based superalloys in the hot corrosion environment within a 1.2-fold scatter band compared with the traditional creep constitutive model, and can also reflect the creep damage situation of nickel-based superalloys in the hot corrosion environment.

[0038] In order to achieve the above object, a creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment includes: S1. Obtain test pieces of nickel-based superalloys; In this embodiment, multiple test pieces of nickel-based superalloys are obtained, and the test pieces are divided into three groups. Each group is respectively subjected to a hot corrosion test, an air-creep test, and a hot corrosion-creep test; Before the hot corrosion test and the hot corrosion-creep test of the test pieces, it also includes: cutting the nickel-based superalloy, grinding the cut samples step by step with sandpaper to 2000#, and then ultrasonically cleaning the ground test pieces with anhydrous ethanol, acetone, and distilled water respectively to remove oil stains.

[0039] S2. Conduct thermal corrosion tests, air-creep tests, and thermal corrosion-creep tests on the test specimens respectively; Conduct thermal corrosion tests on the test specimens by the salt coating method, including: Prepare a saturated salt solution with a mass ratio of 3:1 using anhydrous Na2SO4 and anhydrous NaCl with a purity greater than 99.5%; then heat the specimen to 250-350 °C, and use an atomizer to spray the saturated salt solution onto the heated test specimen; among them, the salt spraying interval is 3-5 seconds. The purpose of heating the specimen to 250-350 °C is to allow the salt mist sprayed onto the specimen surface to fully evaporate, and the mixed salt to evenly adhere to the specimen surface. Maintaining a salt spraying interval of 3-5 seconds is to prevent salt mist deposition on the test specimen and uneven heat dissipation, which may cause the salt film to burst and splash.

[0040] Put the salt-coated specimen into a creep fixture, and then place it on a weight-type creep machine. Set the thermal corrosion temperature to 750 °C and conduct a thermal corrosion experiment with preset stress and thermal corrosion cycles. After the thermal corrosion test, use epoxy resin for metallographic cold inlay of the thermal corrosion test piece and then cut the thermal corrosion test piece. The cross-section of the test piece is ground step by step with 320#-2000# sandpaper and then observed and measured for the thickness of the Cr-depleted layer in the matrix using the SEM-EDS line scan mode.

[0041] The thickness of the Cr-depleted layer obtained from the thermal corrosion experiment is used to calibrate the stress correlation coefficient in the corrosion kinetics model , thickening index , thickening correction constant and stress correlation coefficient c. The air-creep experiment is completed by loading with a creep testing machine with a maximum load-bearing capacity of 5t. Before the experiment, put the creep test piece into a creep fixture and clamp it to the creep machine. Subsequently, heat the creep testing machine to the predetermined temperature, keep it warm for 2h, and then apply a predetermined constant load to it through the creep testing machine. During the experiment, record the time-strain curve and the temperature during the experiment through an extensometer. The temperature fluctuation during the experiment needs to be controlled within ±5 °C. When the test piece breaks, stop the experiment immediately, and stop the high-temperature furnace from keeping warm to prevent the high-temperature oxidation caused by continuous heating of the test piece from affecting the test results.

[0042] The creep deformation curve of the nickel-based superalloy obtained from the air-creep experiment is used to calibrate the creep constitutive model parameters A, , , M, and .

[0043] It should be noted that the treatment method of the specimens in the hot corrosion-creep test is the same as that in the hot corrosion test. The hot corrosion specimens after salt spraying treatment are used to carry out the creep test, and the creep test process is the same as the steps of the air-creep test. After the hot corrosion-creep test, the creep deformation curve of the nickel-based superalloy in the hot corrosion environment is obtained, which is used to calibrate the equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model.

[0044] S3. Obtain the thickness of the control element depletion layer according to the data of the hot corrosion test; Obtain the thickness of the control element depletion layer according to the data of the hot corrosion test, including: Cut the test piece after the hot corrosion test along the cross-section and longitudinal section, then polish the cross-section and longitudinal section, and then conduct SEM-EDS observation on the polished test piece, conduct semi-quantitative analysis on the corrosion products, and determine the thickness of the control element depletion layer.

[0045] Among them, the polishing process includes: cutting the test piece after the hot corrosion test along the cross-section and longitudinal section; after cold embedding the test piece with epoxy resin, gradually grind it with SiC sandpaper to 3000#, and then polish it to W0.5 with SiO2 polishing liquid and a vibration polishing machine.

[0046] The thickness of the control element depletion layer is:

[0047] In the formula, is the thickness of the control element depletion layer; represents the tensile stress The corresponding hot corrosion rate coefficient is related to the applied stress and temperature; t represents the hot corrosion time; i represents the thickening index of the control element depletion layer; represents the tensile stress The corresponding control element modified depletion layer correction coefficient is related to the applied stress.

[0048] During the process of obtaining the thickness of the control element depletion layer and are calculated according to the following formula;

[0049] In the formula, represents the corrosion rate constant; exp( ) represents the natural exponential function; R represents the molar gas constant; T represents the absolute temperature, Q represents the hot corrosion activation energy, and c represents the unit stress influence activation energy correction coefficient; represents the tensile stress;

[0050] In the formula, represents the stress correlation coefficient, represents the thickening index, represents the thickening correction constant. Among them, the stress correlation coefficient , the thickening index , the thickening correction constant and the stress correlation coefficient c are obtained through the hot corrosion test, and the thickness of the Cr-depleted layer under different stresses and test cycles is obtained by non-linear fitting using the 1stopt software.

[0051] S4. Calibrate the equivalent hot corrosion damage coefficient of the nickel-based superalloy in the hot corrosion environment according to the data of the hot corrosion-creep test.

[0052] Among them, the equivalent hot corrosion damage coefficient is calibrated according to the following steps: Obtain the creep deformation curve of the nickel-based superalloy in the hot corrosion environment according to the data of the hot corrosion-creep test; Calibrate the equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model according to the creep deformation curve of the nickel-based superalloy in the hot corrosion environment.

[0053] The equivalent hot corrosion damage coefficient is the fitting constant between the hot corrosion damage and the environmental factors, which reflects the damage development characteristics of the material under the hot corrosion conditions and quantifies the correlation between the hot corrosion environment and the material damage.

[0054] In this embodiment, the calibration of the equivalent hot corrosion damage coefficient is realized through the hot corrosion-creep test and the hot corrosion test. First, obtain the corrosion kinetics represented by the Cr-depleted layer through the hot corrosion test, and then substitute the above corrosion kinetics into the damage part of the creep constitutive model in the air environment. Conduct a parameter sensitivity analysis on the equivalent hot corrosion damage coefficient C, calculate the creep curves of different given C values and compare them with the hot corrosion-creep data, and finally select the C value with the best prediction degree as the model parameter.

[0055] S5. Calculate the equivalent hot corrosion damage according to the thickness of the control element depletion layer and the equivalent hot corrosion damage coefficient; It should be noted that the hot corrosion that occurs to the nickel-based superalloy in the molten salt environment is an accelerated oxidation phenomenon, which can significantly accelerate the deterioration of the alloy. The corrosion kinetics of the alloy under different salt distribution ratios, different temperatures, and different stresses are all different, and the acceleration effect on the creep development of the alloy is also different. Therefore, it is crucial to accurately capture the corrosion kinetics at each time point to evaluate the degree of deterioration of the alloy caused by hot corrosion.

[0056] Nickel-based superalloys in a hot corrosion environment can be divided into an effective load-bearing area and a heat-affected area. The change in the area of the heat-affected area directly reflects the degree of deterioration of the superalloy in the hot corrosion environment. According to the damage mechanics theory of Kachanov and Robinson, the hot corrosion damage caused by the hot corrosion environment should be correlated with the creep strain rate in the creep constitutive model. Denote the damage caused by hot corrosion during the creep process of the nickel-based superalloy as , which is related to controlling the development of the thickness of the element depletion layer and the initial cross-sectional area of the alloy.

[0057] The calculation formula for the equivalent hot corrosion damage is as follows:

[0058] In the formula, is the equivalent hot corrosion damage; L is the perimeter of the cross-section of the specimen gauge section; S is the initial cross-sectional area of the specimen; C is the equivalent hot corrosion damage coefficient; is the thickness of the controlling element depletion layer.

[0059] S6. Calibrate the parameters of the creep constitutive model based on the data of the air-creep test to obtain the creep constitutive model; The creep constitutive model is:

[0060] In the formula, is the creep strain rate, is the creep stress, is the creep damage; , and are creep constants; among them, is determined by the creep strain rate at fracture and the minimum creep strain rate in the secondary stage of creep.

[0061]

[0062] Among them, is the creep strain rate at fracture; is the minimum creep strain rate in the secondary stage of creep.

[0063] S7. Introduce the equivalent hot corrosion damage into the creep constitutive model to obtain the hot corrosion-creep constitutive model; In this embodiment, when the nickel-based superalloy creeps in a hot corrosion environment, in addition to the creep damage caused by hot corrosion, there is also damage caused by the development of holes and microcracks caused by the creep stress, denoted as , then the total damage is . Then the creep equation of the nickel-based superalloy considering the damage of the hot corrosion environment, that is, the hot corrosion-creep constitutive model is:

[0064] In the formula, is the creep strain rate, is the creep stress, is the creep damage; , and are creep constants; L is the perimeter of the cross-section of the gauge section of the specimen; S is the initial cross-sectional area of the specimen; C is the equivalent hot corrosion damage coefficient; is the thickness of the control element depletion layer.

[0065] Predict the creep of the damage of nickel-based superalloy in the hot corrosion environment according to the hot corrosion-creep constitutive model.

[0066] In order to illustrate a creep prediction method for nickel-based superalloys considering the damage of the hot corrosion environment provided by the present invention, it is described in conjunction with the accompanying drawings.

[0067] A creep prediction method for nickel-based superalloys considering the damage of the hot corrosion environment provided by the present invention mainly includes the following steps: Refer to Figure 1 As shown, provide a plurality of nickel-based superalloy test pieces to be tested; spray the hot corrosion salt solution required for the test onto the test pieces by the salt coating method; start the hot corrosion test and the hot corrosion-creep test on the test pieces; among them, the purpose of the hot corrosion test is to evaluate the hot corrosion damage of nickel-based superalloys in the molten salt environment; the hot corrosion-creep test is to obtain the creep fracture life and the steady-state creep rate of nickel-based superalloys in air or hot corrosion environment; After the hot corrosion test, the specimens are subjected to metallographic cold embedding and cutting treatment with epoxy resin; line scanning is performed on the hot corrosion specimens by SEM-EDS to evaluate the thickness of the control element depletion layer, and the damage evolution equation is established based on the variation law of the control element depletion layer as the evaluation basis of environmental damage; Constitute parameter fitting is performed on test data such as equivalent hot corrosion damage, minimum creep strain rate and creep life in air / hot corrosion environment by 1stopt software to establish a hot corrosion-creep constitutive model; the hot corrosion-creep constitutive model is implanted into the finite element software in the form of an external subroutine; finally, the test and simulation data are compared to verify the effectiveness of the model.

[0068] Refer to Figure 2 As shown, in this embodiment, an initial creep specimen of a nickel-based superalloy to be analyzed is provided.

[0069] First, specimens are cut by wire electrical discharge machining, refer to Figure 3 As shown. The test piece grade is nickel-based superalloy IN718.

[0070] To avoid the influence of surface roughness on the test results, the specimen was gradually ground with SiC sandpaper up to 2000#, and then the specimen was cleaned with acetone and ethanol to fully remove oil stains and avoid affecting the test results. After that, the salt coating method was used to coat the specimen with salt.

[0071] The hot corrosion test of nickel-based superalloy includes: A saturated salt solution with a mass ratio of 3:1 was prepared using anhydrous Na2SO4 and anhydrous NaCl with a purity greater than 99.5%; then the specimen was heated to 300 °C, and the saturated salt solution was sprayed onto the heated test piece using an atomizer; among them, the salt spraying interval was 4 seconds. The purpose of heating the specimen to 300 °C was to fully evaporate the salt mist sprayed onto the specimen surface, and the mixed salt adhered evenly to the specimen surface. Maintaining a 4-second salt spraying interval was to prevent salt mist deposition on the test piece and uneven heat dissipation, which could cause the salt film to burst and splash.

[0072] The salt-coated specimen was placed in a creep fixture and then on a weight-type creep machine. The hot corrosion temperature was set to 750 °C, and a hot corrosion experiment with preset stress and hot corrosion cycle was carried out.

[0073] In this embodiment, a weight-type creep machine was used. The selected hot corrosion cycles were 25h / 50h / 75h / 100h, the hot corrosion medium was 75% Na2SO4 and 25% NaCl, the hot corrosion test temperature was 750 °C, and the applied stress was 0MPa / 60MPa / 120MPa.

[0074] After the hot corrosion test, the hot corrosion test piece was metallographically cold-mounted with epoxy resin and then cut. The cross-section of the test piece was ground step by step with 320# - 2000# sandpaper and then observed and measured for the thickness of the Cr-depleted layer in the matrix using the SEM-EDS line scan mode. For the statistical schematic diagram of the line scan results, see Figure 3 as shown.

[0075] The hot corrosion-creep test of nickel-based superalloy includes: The salt-coated specimen was subjected to a hot corrosion-creep test. The hot corrosion-creep test temperature was 750 °C, and the creep fixture model was DZ125. The creep stresses were 180MPa, 240MPa, and 360MPa, and the test environment was an air environment and a 75% Na2SO4 + 25% NaCl hot corrosion salt environment. During the test, three K-type thermocouples were used to monitor the hot corrosion-creep test temperature, and the maximum temperature difference was ±5 °C. Through an extensometer, the minimum creep strain and creep life data of the test piece in different environments were obtained. For the minimum creep strain rate and creep life obtained from the test in this embodiment, see Figure 4 and Figure 5 as shown.

[0076] Obtain model parameters, and establishing a creep model for hot corrosion damage includes: For the technical route of the hot corrosion-creep prediction model adopted in this embodiment, see Figure 6 As shown, nickel-based superalloys undergo creep in a hot corrosion environment, affected by stress and hot corrosion media. In an air environment, stress can cause pore proliferation in nickel-based superalloys, leading to the accumulation of creep damage. Hot corrosion creep damage is the deterioration of the outer alloy material caused by hot corrosion media, including effects such as grain boundary sulfidation and oxidation, oxygen diffusion along grain boundaries, and oxidation chlorination, resulting in a reduction in the effective load-bearing area. For a schematic diagram of creep damage, see Figure 7 As shown. Therefore, a creep prediction model applicable to a hot corrosion environment needs to simultaneously consider the accumulation of two types of creep damage in nickel-based superalloys during the creep process.

[0077] First, establish a damage evolution equation in an air environment based on the creep strain rate and strain rate-time test data obtained from creep tests, as shown in the first relationship:

[0078] In the formula, is the creep strain rate; is a material parameter; is the creep damage parameter; is a material parameter, representing the reference stress; is the creep damage; represents the creep stress; represents the creep constant.

[0079] Then, determine the hot corrosion environment damage based on the corrosion kinetics with the Cr depletion layer as a characteristic quantity measured by SEM-EDS, and establish a total damage evolution equation, as shown in the second relationship:

[0080] In the formula, is the equivalent hot corrosion damage; L is the perimeter of the cross-section of the specimen gauge section; S is the initial cross-sectional area of the specimen; C is the equivalent hot corrosion damage coefficient; is the thickness of the depletion layer of the control element.

[0081] Calibrate the life prediction equation of nickel-based superalloys in an air environment according to the creep life and minimum creep strain rate measured from air-creep test data, as shown in the third relationship and the fourth relationship: The third relationship:

[0082] In the formula, is the creep strain rate, is the creep stress; and is the creep constant; The fourth relational expression:

[0083] wherein, is the creep rupture time; is a material parameter; is a material parameter, representing the reference stress.

[0084] Finally, a hot corrosion-creep constitutive model is established, as shown in the fifth relational expression:

[0085] wherein, is the creep strain rate, is the creep stress, is the creep damage; , and are creep constants; L is the perimeter of the cross-section of the gauge section of the specimen; S is the initial cross-sectional area of the specimen; C is the equivalent hot corrosion damage coefficient.

[0086] In the present invention, the hot corrosion-creep constitutive model is written as a subroutine and implanted into the finite element software. The computer-readable storage medium provided by the present invention stores a hot corrosion-creep constitutive model program. When the hot corrosion-creep constitutive model program is executed by a processor, the creep life prediction of nickel-based superalloys in an air / hot corrosion environment can be realized.

[0087] See Figure 8 and Figure 9 As shown, a sensitivity analysis is performed on the parameters to determine that the hot corrosion-creep constitutive model of the present invention can output equivalent creep damage applicable to different hot corrosion rates.

[0088] Figure 8 is a schematic diagram of the sensitivity analysis of the corrosion rate. From Figure 8 , it can be seen that the calculation results corresponding to different hot corrosion rate coefficients are used to verify the effectiveness of the model and the degree to which the model calculation results are affected by the hot corrosion rate coefficient. From the results of the sensitivity analysis of the corrosion rate, it can be seen that the model can calculate the creep deformation under different hot corrosion rates and can be applicable to the creep behavior prediction of nickel-based superalloys in different hot corrosion rate environments.

[0089] Figure 9 is the calculation result of the equivalent hot corrosion damage, representing the evolution curve of the equivalent hot corrosion damage with time corresponding to different hot corrosion rate coefficients from 1.0 to 6.0. From Figure 9 , it can be seen that each curve shows a trend of cumulative growth of damage with time, and the greater it is, the faster the damage grows; The smaller it is, the gentler the damage growth. This result intuitively verifies the influence on damage evolution, and the model can accurately calculate the damage development of nickel-based superalloys in environments with different hot corrosion rates.

[0090] See Figure 10 , Figure 11 and Figure 12 As shown, compare the experimental data with the simulation data and make an error scatter band diagram. The error distribution between the simulation data and the creep test data is within 1.2 times the error scatter band, verifying the effectiveness of the model.

[0091] Figure 10 The creep data and simulation data in the air environment are shown. Figure 10 The scatter points in it are the results of the air-creep test of nickel-based superalloys, and the curve is the result calculated by the model. Figure 10 It represents the prediction effect of the model on the creep test results of nickel-based superalloys in the air environment at 750 °C. Figure 11 The creep data and simulation data in the hot corrosion environment are shown. Figure 11 The scatter points in it are the results of the hot corrosion-creep test of nickel-based superalloys, and the curve is the result calculated by the model. Figure 11 It represents the prediction effect of the model on the creep test results of nickel-based superalloys in the hot corrosion environment at 750 °C. Figure 12 It represents the prediction accuracy of the hot corrosion-creep constitutive model. The experimental results and the simulation calculation results are organized into an error scatter band diagram. Figure 12 In it, the abscissa is the experimental result, and the ordinate is the result calculated by the model. Figure 12 It shows that the prediction accuracy of the model meets the requirement of 2 times the error scatter band of the engineering accuracy requirement within 1.2 times the error scatter band.

[0092] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A creep prediction method for nickel-based superalloys considering damage in a hot corrosion environment, characterized in that Including: Obtaining test pieces of nickel-based superalloys; Respectively conducting hot corrosion tests, air-creep tests, and hot corrosion-creep tests on the test pieces; Obtaining the thickness of the control element depletion layer based on the data of the hot corrosion test; Calibrating the equivalent hot corrosion damage coefficient of the nickel-based superalloy in a hot corrosion environment according to the data of the hot corrosion-creep test; Calculating the equivalent hot corrosion damage based on the thickness of the control element depletion layer and the equivalent hot corrosion damage coefficient; Calibrating the parameters of the creep constitutive model according to the data of the air-creep test to obtain the creep constitutive model; Introducing the equivalent hot corrosion damage into the creep constitutive model to obtain the hot corrosion-creep constitutive model; Predicting the creep of the nickel-based superalloy in a hot corrosion environment damage according to the hot corrosion-creep constitutive model.

2. The creep prediction method for nickel-based superalloys considering thermal corrosion environmental damage according to claim 1, characterized in that, Obtaining the thickness of the control element depletion layer based on the data of the hot corrosion test, including: Cutting the test piece after the hot corrosion test along the cross-section and longitudinal section, then polishing the cross-section and longitudinal section, then observing the polished test piece by SEM-EDS, semi-quantitatively analyzing the corrosion products, and determining the thickness of the control element depletion layer.

3. The creep prediction method for nickel-based superalloys considering hot corrosion environmental damage according to claim 1, wherein The formula for calculating the equivalent hot corrosion damage is as follows: In the formula, is the equivalent thermal corrosion damage; L is the perimeter of the cross-section of the specimen gauge section; S is the initial cross-sectional area of the specimen; C is the equivalent thermal corrosion damage coefficient; is the thickness of the control element depletion layer.

4. The creep prediction method for nickel-based superalloys considering hot corrosion environmental damage according to claim 3, wherein The thickness of the control element depletion layer is: In the formula, is the thickness of the depletion layer of the control element; is expressed as the tensile stress corresponding thermal corrosion rate coefficient; t represents the thermal corrosion time; i represents the thickening index of the depletion layer of the control element; represents the tensile stress corresponding correction coefficient of the corrected depletion layer of the control element.

5. The creep prediction method for nickel-based superalloys considering thermal corrosion environmental damage according to claim 1, characterized in that, The creep constitutive model is: In the formula, is the creep strain rate; is the creep stress; is the creep damage; , and are creep constants; among which, is determined by the creep strain rate at fracture and the minimum creep strain rate in the secondary stage of creep.

6. The creep prediction method for nickel-based superalloys considering hot corrosion environmental damage according to claim 5, characterized in that The hot corrosion-creep constitutive model is: In the formula, is the creep strain rate; is the creep stress; is the creep damage; , and are creep constants; L is the perimeter of the cross-section of the gauge length section of the specimen; S is the initial cross-sectional area of the specimen; C is the equivalent thermal corrosion damage coefficient; is the thickness of the control element depletion layer.

7. The creep prediction method for nickel-based superalloys considering hot corrosion environmental damage according to claim 1, characterized in that The equivalent hot corrosion damage coefficient is calibrated according to the following steps: Obtaining the creep deformation curve of the nickel-based superalloy in a hot corrosion environment according to the data of the hot corrosion-creep test; Calibrating the equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model according to the creep deformation curve of the nickel-based superalloy in a hot corrosion environment.

8. The creep prediction method for nickel-based superalloys considering thermal corrosion environmental damage according to claim 1, characterized in that, Before conducting the hot corrosion test and the hot corrosion-creep test on the test piece, it also includes: cutting the nickel-based superalloy, grinding the cut sample to 2000# step by step with sandpaper, and then ultrasonically cleaning the ground test piece with anhydrous ethanol, acetone, and distilled water respectively to remove oil stains.

9. The creep prediction method for nickel-based superalloys considering thermal corrosion environmental damage according to claim 1, characterized in that, Conducting the hot corrosion test on the test piece by the salt coating method, including: Preparing a saturated salt solution with a mass ratio of 3:1 of anhydrous Na2SO4 and anhydrous NaCl with a purity greater than 99.5%; then heating the sample to 250~350°C, and using an atomizer to spray the saturated salt solution on the heated test piece; among them, the salt spraying interval is 3~5 seconds.

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