A creep prediction method for nickel-based superalloys considering damage in hot corrosion environments

Abstract

The present invention relates to the technical field of alloy property prediction, and more particularly to a method for predicting creep of a nickel-based high-temperature alloy taking into account damage in a hot corrosion environment. The method comprises obtaining a test piece of the nickel-based high-temperature alloy; calibrating an equivalent hot corrosion damage coefficient based on data from a hot corrosion-creep test; calculating equivalent hot corrosion damage based on the thickness of a control element depletion layer and the equivalent hot corrosion damage coefficient; obtaining a creep constitutive model; introducing equivalent hot corrosion damage into the creep constitutive model to obtain a hot corrosion-creep constitutive model; and predicting creep of the nickel-based high-temperature alloy in a hot corrosion environment based on the hot corrosion-creep constitutive model. The present invention can predict the creep life of the nickel-based high-temperature alloy in a hot corrosion environment within a 1.2-fold error scattering band and can also reflect the creep damage of the nickel-based high-temperature alloy in the hot corrosion environment.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy property prediction, and in particular to a creep prediction method for nickel-based high-temperature alloys taking into account damage in a hot corrosion environment. Background Art

[0002] As the power source for carrier-based aircraft, aircraft engines are subjected to high temperatures, high pressures, and high loads for extended periods. Creep is a major cause of shortened service life in hot-end components (turbine blades and disks). Nickel-based superalloys are widely used in these hot-end components due to their excellent resistance to creep, thermal corrosion, and oxidation in high-temperature environments. Furthermore, during service in marine environments, aircraft engines absorb sea vapor rich in NaCl. Chloride salts, primarily NaCl, along with Na₂SO₄ produced by incomplete combustion of the engine fuel, form a low-melting-point mixed salt that adheres to the hot-end components, triggering thermal corrosion. This thermal corrosion behavior can accelerate creep failure of these components under mechanical stress, severely impacting the safety, reliability, and integrity of carrier-based aircraft engines.

[0003] However, in a hot-corrosive environment, hot-end components are subject to the coupled effects of temperature, chemical media, and stress. The combined effects of hot corrosion and mechanical loads lead to complex material and structural degradation mechanisms, making hot corrosion damage difficult to quantitatively assess. Currently, creep constitutive models applicable to nickel-based superalloys in air environments have been extensively studied and applied, while creep constitutive models considering hot-corrosive environments have rarely been studied. Traditional creep models (such as Norton's power law and the θ projection method) can only predict the creep behavior of nickel-based superalloys in air environments. Because they ignore the damage effect of hot-corrosive media on nickel-based superalloy creep, traditional creep models have a problem of poor model accuracy when predicting the creep behavior of nickel-based superalloys in hot-corrosive environments.

[0004] More importantly, the creep behavior of nickel-based superalloys in stress-corrosion environments requires consideration of the coupled environment of temperature, stress, and chemical fields, making quantitative assessment of damage in hot-corrosion environments difficult. For creep models to be applicable in engineering practice, only by assessing the alloy degradation state with an appropriate metric can alloy degradation caused by hot corrosion be incorporated into creep damage. Selecting macroscopic variables such as mass change lacks physical context and fails to fully reflect the material degradation process. However, selecting too microscopic a metric makes it difficult to connect with the damage model. The model requires numerous parameters and places high demands on computer computing power, making it difficult to apply in engineering practice. Therefore, selecting appropriate damage state variables to assess creep damage in superalloys exposed to hot-corrosion environments is crucial for accurately estimating the creep life of nickel-based superalloys in hot-corrosion environments. In summary, predicting the creep of hot-end components exposed to hot-corrosion environments remains a challenging problem in aerospace engineering. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention aims at the fact that the creep constitutive model of current engineering applications ignores the damage effect of creep of nickel-based high-temperature alloys caused by hot corrosive media, resulting in the existing creep model highlighting the problem of poor model accuracy in predicting the creep behavior of nickel-based high-temperature alloys in hot corrosive environments. The present invention provides a creep prediction method for nickel-based high-temperature alloys taking into account damage in hot corrosive environments. The method uses the Cr element depletion layer as an environmental characteristic quantity to quantitatively characterize the deterioration of nickel-based high-temperature alloys in hot corrosive environments and establishes a damage evolution equation. The damage evolution equation is incorporated into the creep constitutive model based on continuous damage mechanics to establish a creep constitutive model that takes into account damage in hot corrosive environments. Compared with the traditional creep constitutive model, this model can predict the creep life of nickel-based high-temperature alloys in hot corrosive environments within a 1.2-fold error scattering band, and can also reflect the creep damage of nickel-based high-temperature alloys in hot corrosive environments.

[0006] The object of the present invention is to provide a creep prediction method for nickel-based high-temperature alloys taking into account damage in hot corrosive environments, comprising:

[0007] Obtaining a test piece of nickel-based high-temperature alloy;

[0008] The test pieces were subjected to hot corrosion test, air-creep test and hot corrosion-creep test respectively;

[0009] The thickness of the element depletion layer is obtained based on the data of hot corrosion test;

[0010] The equivalent hot corrosion damage coefficient in the environmental damage evolution equation of nickel-based superalloy in hot corrosion environment is calibrated based on the data of hot corrosion-creep test;

[0011] Calculate the equivalent hot corrosion damage based on the thickness of the depletion layer of the controlling element and the equivalent hot corrosion damage coefficient;

[0012] The creep constitutive model parameters are calibrated according to the data of air-creep test to obtain the creep constitutive model;

[0013] Introducing equivalent hot corrosion damage into the creep constitutive model to obtain the hot corrosion-creep constitutive model;

[0014] The creep of nickel-based superalloys damaged by hot corrosion environment is predicted based on the hot corrosion-creep constitutive model.

[0015] Preferably, the thickness of the element depletion layer is obtained based on data from a hot corrosion test, including:

[0016] The test pieces after the hot corrosion test were cut along the cross section and longitudinal section, and then polished. The polished test pieces were then observed by SEM-EDS, the corrosion products were semi-quantitatively analyzed, and the thickness of the control element depletion layer was determined.

[0017] Preferably, the equivalent thermal corrosion damage calculation formula is as follows:

[0018]

[0019] Where, 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; Control the thickness of the element depletion layer.

[0020] Preferably, the thickness of the control element depletion layer is:

[0021]

[0022] Where, To control the thickness of the element depletion layer; Expressed as tensile stress The corresponding thermal corrosion rate coefficient; t represents the thermal corrosion time; i represents the thickening index of the control element depletion layer; Indicates tensile stress The corresponding control element corrects the depletion layer correction factor.

[0023] Preferably, the creep constitutive model is:

[0024]

[0025] Where, is the creep strain rate, is the creep stress, Creep damage; 、 and is the creep constant; where It is determined by the creep strain rate at fracture and the minimum creep strain rate in the second stage of creep.

[0026] Preferably, the hot corrosion-creep constitutive model is:

[0027]

[0028] Where, is the creep strain rate, is the creep stress, Creep damage; 、 and is the creep constant; 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; To control the thickness of the element depletion layer.

[0029] Preferably, the equivalent hot corrosion damage coefficient is calibrated according to the following steps:

[0030] The creep deformation curve of nickel-based high-temperature alloy in hot corrosion environment is obtained based on the data of hot corrosion-creep test;

[0031] The equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model is calibrated according to the creep deformation curve of nickel-based high-temperature alloy in a hot corrosion environment.

[0032] Preferably, before the test piece is subjected to the hot corrosion test and the hot corrosion-creep test, the process also includes: cutting the nickel-based high-temperature alloy, grinding the cut sample step by step to 2000# using sandpaper, and then ultrasonically cleaning the ground test piece using anhydrous ethanol, acetone and distilled water respectively to remove oil stains.

[0033] Preferably, the test piece is subjected to a hot corrosion test by a salt coating method, including:

[0034] 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%. The sample was then heated to 250-350°C and the saturated salt solution was sprayed onto the heated test piece using an atomizer. The spraying interval was 3-5 seconds.

[0035] The present invention has at least the following beneficial effects:

[0036] The present invention provides a creep prediction method for nickel-based high-temperature alloys taking into account damage in hot corrosion environments. Compared with traditional creep prediction methods for nickel-based high-temperature alloys, the creep prediction method has the advantages of strong environmental applicability, quantitative evaluation of hot corrosion creep damage, and scalability and versatility of environmental-creep prediction.

[0037] The present invention introduces equivalent thermal corrosion damage into the creep constitutive model to construct a thermal corrosion-creep constitutive model. This model can fully consider the influence of this factor on the creep behavior and damage evolution of nickel-based high-temperature alloys, and is suitable for life prediction and performance evaluation of hot end components in marine environments, such as engine blades and turbine components.

[0038] This invention enables quantitative assessment of hot corrosion creep damage. The model provided by this invention incorporates an equivalent hot corrosion creep damage evolution equation, which can describe the degradation of nickel-based superalloys by hot corrosion caused by hot corrosion salts and predict the material damage evolution process. This provides a scientific basis for the design and lifespan assessment of hot-end components.

[0039] The creep prediction model in this paper is scalable and versatile, allowing for parameter adjustments based on varying marine environmental conditions (such as salt spray concentrations and humidity). This flexibility makes the model highly versatile and applicable to a variety of equipment life assessment applications, including marine aviation, ship gas turbines, and nuclear reactor cladding materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Flowchart of creep prediction method considering damage in hot-corrosive environments for nickel-based superalloys.

[0041] Figure 2 The figure is the actual picture of the test piece used.

[0042] Figure 3 This is a statistical diagram of line scan results.

[0043] Figure 4 This is the minimum creep strain rate curve of the present invention.

[0044] Figure 5 This is a histogram of the creep life of the present invention.

[0045] Figure 6 It is the technical roadmap for hot corrosion-creep constitutive model.

[0046] Figure 7 Schematic diagram of creep damage of nickel-based high-temperature alloy caused by hot corrosive media.

[0047] Figure 8 Schematic diagram of corrosion rate sensitivity analysis.

[0048] Figure 9 Calculation results of equivalent hot corrosion damage.

[0049] Figure 10 Creep data and simulation data in air environment.

[0050] Figure 11 Creep data and simulation data in hot corrosion environment.

[0051] Figure 12 is the model error scatter plot. DETAILED DESCRIPTION

[0052] In order to illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description with reference to the embodiments.

[0053] The present invention addresses the creep damage of existing nickel-based superalloys in air environments. Creep damage is primarily caused by a combination of factors, including pores, microcrack accumulation, precipitate coarsening, and high-temperature oxidation. These factors are due to creep stress-induced degradation of nickel-based superalloys. Damage evolution models in air environments only consider the degradation of nickel-based superalloys due to creep stress. Because the degradation rate of nickel-based superalloys in air environments is slower than that due to thermal corrosion, conventional creep constitutive models are well suited for predicting creep in air environments but are not suitable for thermal corrosion environments. Thermal corrosion, particularly in marine environments, places extremely high demands on the performance of hot-end components. In marine environments, materials not only face high temperature loads but also are subject to corrosion from corrosive salts, such as chlorides, which can lead to the formation of an oxide layer on the alloy surface and accelerate crack propagation. Conventional creep models do not account for the thermal corrosion effects of materials in marine environments. Therefore, conventional creep prediction models cannot predict the creep behavior of hot-end components in marine environments. In marine environments, the coupling of high-temperature corrosion and stress exacerbates damage to hot-end components. Traditional creep models fail to effectively consider the impact of thermal corrosion on the material microstructure and ignore the synergistic effect of corrosion and creep damage.

[0054] To this end, the present invention provides a creep prediction method for nickel-based high-temperature alloys taking into account damage in hot corrosion environments. On the basis of the traditional creep constitutive model, the evolution of hot corrosion creep damage is introduced to construct a hot corrosion-creep constitutive model, which can predict the creep behavior of hot end components in a marine environment. That is, the Cr element depletion layer is used as an environmental characteristic quantity to quantitatively characterize the degradation of nickel-based high-temperature alloys in hot corrosion environments and establish a damage evolution equation. The damage evolution equation is then incorporated into the creep constitutive model based on continuum damage mechanics to establish a creep constitutive model that takes into account damage in hot corrosion environments. Compared with the traditional creep constitutive model, this model can predict the creep life of nickel-based high-temperature alloys in hot corrosion environments within 1.2 times the scattering band, and can also reflect the creep damage of nickel-based high-temperature alloys in hot corrosion environments.

[0055] To achieve the above objectives, a creep prediction method for nickel-based superalloys considering damage in hot corrosion environments is proposed, comprising:

[0056] S1. Obtain a test piece of nickel-based high-temperature alloy;

[0057] In this embodiment, a plurality of nickel-based high-temperature alloy test pieces were obtained and divided into three groups, with each group undergoing a hot corrosion test, an air-creep test, and a hot corrosion-creep test, respectively.

[0058] Before conducting hot corrosion tests and hot corrosion-creep tests on the test pieces, the following steps are also included: cutting the nickel-based high-temperature alloy, grinding the cut samples step by step to 2000# using sandpaper, and then ultrasonically cleaning the ground test pieces with anhydrous ethanol, acetone and distilled water to remove oil stains.

[0059] S2. Conducting hot corrosion test, air-creep test and hot corrosion-creep test on the test piece respectively;

[0060] The test piece is subjected to hot corrosion test by salt coating method, including:

[0061] A saturated salt solution with a mass ratio of 3:1 is prepared using anhydrous Na₂SO₄ and anhydrous NaCl with a purity greater than 99.5%. The specimen is then heated to 250-350°C and sprayed with the saturated salt solution using an atomizer. The spray interval is 3-5 seconds. The purpose of heating the specimen to 250-350°C is to ensure that the salt mist sprayed onto the specimen surface fully evaporates and that the mixed salt adheres evenly to the specimen surface. The 3-5 second interval prevents salt mist from accumulating on the specimen and uneven heat dissipation, which can cause the salt film to crack or splash.

[0062] The salt-treated specimens were placed in a creep fixture and then on a weight-type creep machine. A hot corrosion test was conducted at a preset stress and cycle, set at a temperature of 750°C. Following the hot corrosion test, the specimens were cold-mounted using epoxy resin for metallographic analysis and then cut. The cross-sections were polished using graded sandpaper (320# to 2000#) and then observed and measured using SEM-EDS line scanning mode to measure the thickness of the Cr-depleted layer in the matrix.

[0063] The thickness of the Cr-depleted layer obtained from the hot corrosion experiment is used to calibrate the stress correlation coefficient in the corrosion dynamics model. , Thickening Index , Thickening correction constant and stress correlation coefficient c.

[0064] The air-creep test is completed by loading a creep testing machine with a maximum load capacity of 5t. Before the experiment, the creep test piece is placed in a creep fixture and clamped to the creep machine. The creep testing machine is then heated to a predetermined temperature, kept warm for 2 hours, and then a predetermined constant load is applied to it by the creep testing machine. During the experiment, the time-strain curve and the experimental process temperature are recorded by an extensometer. The temperature fluctuation during the experiment must be controlled within ±5°C. When the test piece breaks, the test is stopped immediately, and the high-temperature furnace stops keeping warm to prevent high-temperature oxidation caused by continuous heating of the test piece from affecting the test results.

[0065] The creep deformation curve of nickel-based superalloy is obtained by air-creep test, which is used to calibrate the creep constitutive model parameters A, 、 ,M, and .

[0066] It should be noted that the specimens in the hot corrosion-creep test were processed in the same manner as in the hot corrosion test. Creep testing was performed on the salt-sprayed hot corrosion specimens, following the same procedures as the air-creep test. After the hot corrosion-creep test, creep deformation curves of the nickel-based superalloy in a hot corrosion environment were obtained and used to calibrate the equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model.

[0067] S3. Obtaining the thickness of the control element depletion layer based on the data of the hot corrosion test;

[0068] The thickness of the depletion layer of controlled elements is obtained based on the data of hot corrosion test, including:

[0069] The test pieces after the hot corrosion test were cut along the cross section and longitudinal section, and then polished. The polished test pieces were then observed by SEM-EDS, the corrosion products were semi-quantitatively analyzed, and the thickness of the control element depletion layer was determined.

[0070] The polishing process includes: cutting the test piece after the hot corrosion test along the cross section and longitudinal section; cold mounting the test piece with epoxy resin, and then grinding it step by step to 3000# with SiC sandpaper, and then polishing it to W0.5 using SiO2 polishing liquid and a vibration polishing machine.

[0071] The thickness of the control element depletion layer is:

[0072]

[0073] Where, To control the thickness of the element depletion layer; Expressed as tensile stress The corresponding thermal corrosion rate coefficient is related to the loading stress and temperature; t represents the thermal corrosion time; i represents the thickening index of the control element depletion layer; Indicates tensile stress The corresponding control element corrects the depletion layer correction coefficient, which is related to the loading stress.

[0074] In the process of obtaining the thickness of the control element depletion layer and It is calculated according to the following formula;

[0075]

[0076] Where, 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 thermal corrosion activation energy, and c represents the activation energy correction coefficient of unit stress; represents tensile stress;

[0077]

[0078] Where, represents the stress correlation coefficient, represents the thickening index, represents the thickening correction constant. Among them, the stress correlation coefficient , Thickening Index , Thickening correction constant The stress correlation coefficient c is obtained through hot corrosion test, and the thickness of Cr depleted layer at different stresses and test cycles is obtained by nonlinear fitting using 1stopt software.

[0079] S4. Calibrate the equivalent hot corrosion damage coefficient of nickel-based high-temperature alloy in hot corrosion environment based on the data of hot corrosion-creep test.

[0080] Among them, the equivalent hot corrosion damage coefficient is calibrated according to the following steps:

[0081] The creep deformation curve of nickel-based high-temperature alloy in hot corrosion environment is obtained based on the data of hot corrosion-creep test;

[0082] The equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model is calibrated according to the creep deformation curve of nickel-based high-temperature alloy in a hot corrosion environment.

[0083] The equivalent hot corrosion damage coefficient is a fitting constant between hot corrosion damage and environmental factors. It reflects the damage development characteristics of the material under hot corrosion conditions and quantifies the relationship between the hot corrosion environment and material damage.

[0084] In this example, the equivalent hot corrosion damage coefficient (C) was calibrated through hot corrosion-creep and hot corrosion tests. The corrosion dynamics, represented by the Cr-depleted layer, were first obtained through hot corrosion testing. These corrosion dynamics were then applied to the damage portion of the creep constitutive model in an air environment. A parameter sensitivity analysis of the equivalent hot corrosion damage coefficient (C) was performed, and creep curves for different given C values ​​were calculated and compared with the hot corrosion-creep data. Ultimately, the C value with the best prediction accuracy was selected as the model parameter.

[0085] S5. Calculate the equivalent hot corrosion damage based on the thickness of the depletion layer of the control element and the equivalent hot corrosion damage coefficient;

[0086] It should be noted that hot corrosion of nickel-based superalloys in molten salt environments is an accelerated oxidation phenomenon that can significantly accelerate alloy degradation. The corrosion kinetics of alloys vary under different salt distribution ratios, temperatures, and stresses, and the acceleration of creep development in the alloys also varies. Therefore, it is crucial to accurately capture the corrosion kinetics at each point in time to assess the extent of alloy degradation caused by hot corrosion.

[0087] Nickel-based superalloys in hot corrosion environments can be divided into effective bearing zones and heat-affected zones. The area change of the heat-affected zone directly reflects the degree of degradation of the superalloy in hot corrosion environments. According to the damage mechanics theory of Kachanov and Robinson, the hot corrosion damage caused by hot corrosion environments should be related to the creep strain rate in the creep constitutive model. The damage caused by hot corrosion in the creep process of nickel-based superalloys is denoted as , It is related to controlling the thickness development of the element depletion layer and the initial cross-sectional area of ​​the alloy.

[0088] The calculation formula for the equivalent thermal corrosion damage is as follows:

[0089]

[0090] Where, 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; To control the thickness of the element depletion layer.

[0091] S6. Calibrate the parameters of the creep constitutive model according to the data of the air-creep test to obtain the creep constitutive model;

[0092] The creep constitutive model is:

[0093]

[0094] Where, is the creep strain rate, is the creep stress, Creep damage; 、 and is the creep constant; where It is determined by the creep strain rate at fracture and the minimum creep strain rate in the second stage of creep.

[0095]

[0096] in, is the creep strain rate at fracture; is the minimum creep strain rate in the second stage of creep.

[0097] S7. Introducing equivalent hot corrosion damage into the creep constitutive model to obtain a hot corrosion-creep constitutive model;

[0098] In this embodiment, nickel-based high-temperature alloys creep under hot corrosion environment. In addition to the creep damage caused by hot corrosion, there are also holes and microcracks caused by creep stress, which are recorded as , the total damage is The creep equation of nickel-based high-temperature alloy considering damage in hot corrosion environment, that is, the hot corrosion-creep constitutive model is:

[0099]

[0100] Where, is the creep strain rate, is the creep stress, Creep damage; 、 and is the creep constant; 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; To control the thickness of the element depletion layer.

[0101] The creep of nickel-based superalloys damaged by hot corrosion environment is predicted based on the hot corrosion-creep constitutive model.

[0102] In order to illustrate the creep prediction method of a nickel-based high-temperature alloy considering damage in a hot corrosion environment provided by the present invention, it is described in conjunction with the accompanying drawings.

[0103] The present invention provides a creep prediction method for nickel-based high-temperature alloys considering damage in hot corrosion environments, which mainly includes the following steps:

[0104] See also Figure 1 As shown, a plurality of nickel-based high-temperature alloy test pieces to be tested are provided; a hot corrosion salt solution required for the test is sprayed onto the test pieces by a salt coating method; and hot corrosion tests and hot corrosion creep tests are performed on the test pieces. The purpose of the hot corrosion test is to evaluate the hot corrosion damage of the nickel-based high-temperature alloy in a molten salt environment; and the hot corrosion-creep test is to obtain the creep rupture life and steady-state creep rate of the nickel-based high-temperature alloy in air or a hot corrosion environment.

[0105] After the hot corrosion test, the specimens were cold-mounted and cut using epoxy resin. SEM-EDS line scans were performed on the hot corrosion specimens to assess the thickness of the control element depletion layer. The variation pattern of the control element depletion layer was used as the basis for environmental damage assessment and a damage evolution equation was established.

[0106] The constitutive parameters of the experimental data such as equivalent hot corrosion damage, minimum creep strain rate and creep life in air / hot corrosion environment were fitted using 1stopt software to establish a hot corrosion-creep constitutive model; the hot corrosion-creep constitutive model was implanted into the finite element software in the form of an external subroutine; finally, the experimental and simulation data were compared to verify the effectiveness of the model.

[0107] See also Figure 2 As shown, in this embodiment, an initial creep specimen of a nickel-based high-temperature alloy to be analyzed is provided.

[0108] First, the specimens were cut using wire-cut EDM technology, see Figure 3 The test piece is nickel-based high-temperature alloy IN718.

[0109] To prevent the influence of surface roughness on the test results, SiC sandpaper was used to gradually grind the sample to 2000#, and then the sample was cleaned with acetone and ethanol to fully remove oil and avoid affecting the test results. The sample was then salted using the salt coating method.

[0110] Hot corrosion tests for nickel-based superalloys include:

[0111] 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%. The specimen was then heated to 300°C and sprayed with the saturated salt solution using an atomizer. The spray interval was 4 seconds. The purpose of heating the specimen to 300°C was to ensure that the salt mist sprayed onto the surface of the specimen evaporated completely, allowing the mixed salt to adhere evenly to the surface. The 4-second interval prevented salt mist from accumulating on the specimen and preventing uneven heat dissipation, which could cause the salt film to crack or splash.

[0112] The salt-treated sample was placed in a creep fixture and then placed on a weight-type creep machine. The thermal corrosion temperature was set to 750°C, and a thermal corrosion experiment with a preset stress and thermal corrosion cycle was carried out.

[0113] This embodiment uses a weight-type creep machine, and the selected thermal corrosion cycles are 25h / 50h / 75h / 100h, the thermal corrosion medium is 75% Na2SO4 and 25% NaCl, the thermal corrosion test temperature is 750°C, and the loading stress is 0MPa / 60MPa / 120MPa.

[0114] 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 polished with 320#~2000# sandpaper in a step-by-step manner and then observed and measured using SEM-EDS line scanning mode to measure the thickness of the Cr depleted layer in the matrix. Figure 3 shown.

[0115] Hot corrosion-creep tests on nickel-based superalloys include:

[0116] The salt-treated specimens were subjected to a hot corrosion-creep test at a temperature of 750°C and a creep fixture of DZ125. The creep stresses were 180 MPa, 240 MPa, and 360 MPa, and the test environments were air and 75% Na2SO4+25% NaCl hot corrosion salt environments. During the test, three K-type thermocouples were used to monitor the hot corrosion-creep test temperature, with a maximum temperature difference of ±5°C. The minimum creep strain and creep life data of the test piece in different environments were obtained using an extensometer. The minimum creep strain rate and creep life obtained in this embodiment are shown in Figure 2. Figure 4 and Figure 5 shown.

[0117] Obtaining model parameters and establishing a thermal corrosion damage creep model include:

[0118] The technical route of the hot corrosion-creep prediction model used in this embodiment is shown in Figure 6 As shown in the figure, nickel-based high-temperature alloys creep in a hot corrosive environment, affected by stress and hot corrosive media. In an air environment, stress can cause the nickel-based alloy to undergo a high-temperature hole multiplication effect, leading to creep damage accumulation. Hot corrosion creep damage is caused by the degradation of the outer alloy material caused by the hot corrosive medium, including oxidation after grain boundary sulfidation, oxygen diffusion along the grain boundary, oxidation and chlorination, which leads to a reduction in the effective bearing area. See the creep damage diagram for details. Figure 7 Therefore, the creep prediction model applicable to hot corrosion environment needs to consider the accumulation of two types of creep damage in nickel-based superalloys during the creep process.

[0119] First, the damage evolution equation in air environment is established based on the creep strain rate and strain rate time test data obtained from the creep test, as shown in the first equation:

[0120]

[0121] Where, is the creep strain rate; is the material parameter; is the creep damage parameter; is the material parameter, representing the reference stress; Creep damage; represents creep stress; represents the creep constant.

[0122] Then, based on the corrosion kinetics of the Cr depletion layer measured by SEM-EDS, the damage in the hot corrosion environment is determined, and the overall damage evolution equation is established, as shown in the second relationship:

[0123]

[0124] Where, 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; To control the thickness of the element depletion layer.

[0125] According to the creep life and minimum creep strain rate determined by the air-creep test data, the life prediction equation of nickel-based high-temperature alloy in air environment is calibrated, as shown in the third and fourth equations:

[0126] The third relation:

[0127] Where, is the creep strain rate, is the creep stress; and is the creep constant;

[0128] The fourth relationship:

[0129] Where, is the creep rupture time; is the material parameter; is a material parameter representing the reference stress.

[0130] Finally, the hot corrosion-creep constitutive model is established, as shown in the fifth equation:

[0131]

[0132] Where, is the creep strain rate, is the creep stress, Creep damage; 、 and is the creep constant; L is the circumference of the gauge section of the specimen; S is the initial cross-sectional area of ​​the specimen; and C is the equivalent hot corrosion damage coefficient.

[0133] The present invention incorporates the hot corrosion-creep constitutive model into a subroutine and embeds it into finite element software. The computer-readable storage medium provided by the present invention stores the hot corrosion-creep constitutive model program. When executed by a processor, the hot corrosion-creep constitutive model program can predict the creep life of nickel-based superalloys in air / hot corrosion environments.

[0134] See also Figure 8 and Figure 9As shown, a sensitivity analysis of the parameters was performed to determine that the hot corrosion-creep constitutive model of the present invention can be applied to output equivalent creep damage at different hot corrosion rates.

[0135] Figure 8 Schematic diagram of corrosion rate sensitivity analysis. Figure 8 It can be seen that the calculation results corresponding to different hot corrosion rate coefficients are used to verify the validity of the model and the degree to which the model calculation results are affected by the hot corrosion rate coefficient. The corrosion rate sensitivity analysis results show that the model can calculate the creep deformation under different hot corrosion rates and can be used to predict the creep behavior of nickel-based high-temperature alloys under different hot corrosion rate environments.

[0136] Figure 9 is the calculation result of equivalent hot corrosion damage, indicating different hot corrosion rate coefficients The time evolution curve of equivalent hot corrosion damage from 1.0 to 6.0 is as follows: Figure 9 It can be seen that each curve shows a trend of cumulative damage growth over time, and The larger it is, the faster the damage grows; The smaller the damage, the slower the growth. This result intuitively verifies The model can accurately calculate the damage development of nickel-based high-temperature alloys under different hot corrosion rate environments.

[0137] See also Figure 10 、 Figure 11 and Figure 12 As shown in the figure, the test data is compared with the simulation data, and an error scattering band diagram is drawn. The error distribution between the simulation data and the creep test data is within the 1.2 times error scattering band, which verifies the validity of the model.

[0138] Figure 10 Creep data and simulation data in air environment, Figure 10 The scattered points are the air creep test results of nickel-based high-temperature alloys, and the curves are the model calculation results. Figure 10 The model is used to predict the creep test results of nickel-based high-temperature alloys in an air environment at 750℃.

[0139] Figure 11 Creep data and simulation data in hot corrosion environment, Figure 11 The scattered points are the hot corrosion-creep test results of nickel-based superalloys, and the curves are the model calculation results. Figure 11 The model is used to predict the creep test results of nickel-based high-temperature alloys in a hot corrosion environment at 750℃.

[0140] Figure 12 The prediction accuracy of the hot corrosion-creep constitutive model is represented by organizing the test results and simulation results into an error scattering band diagram. Figure 12 The horizontal axis is the test result, and the vertical axis is the model calculation result. Figure 12 It shows that the prediction accuracy of the model is within 1.2 times the error scatter band, which meets the 2 times error scatter band requirement of the engineering accuracy requirement.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A creep prediction method for nickel-based high-temperature alloys considering damage in hot corrosion environments, characterized in that: include: Obtaining a test piece of nickel-based high-temperature alloy; The test pieces were subjected to hot corrosion test, air-creep test and hot corrosion-creep test respectively; The thickness of the element depletion layer is obtained based on the data of hot corrosion test; The equivalent hot corrosion damage coefficient of nickel-based superalloy in hot corrosion environment is calibrated based on the data of hot corrosion-creep test; Calculate the equivalent hot corrosion damage based on the thickness of the depletion layer of the controlling element and the equivalent hot corrosion damage coefficient; The creep constitutive model parameters are calibrated according to the data of air-creep test to obtain the creep constitutive model; Introducing equivalent hot corrosion damage into the creep constitutive model to obtain the hot corrosion-creep constitutive model; The creep of nickel-based superalloys in hot corrosion environment is predicted based on the hot corrosion-creep constitutive model. The hot corrosion-creep constitutive model is: Where, is the creep strain rate; is the creep stress; Creep damage; 、 and is the creep constant; 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; To control the thickness of the element depletion layer; The thickness of the control element depletion layer is: Where, To control the thickness of the element depletion layer; Expressed as tensile stress The corresponding thermal corrosion rate coefficient; t represents the thermal corrosion time; i represents the thickening index of the control element depletion layer; Indicates tensile stress The corresponding control element corrects the depletion layer correction factor; The calculation formula for the equivalent thermal corrosion damage is as follows: Where, 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; To control the thickness of the element depletion layer.

2. The creep prediction method for nickel-based high-temperature alloys considering damage in hot corrosion environments according to claim 1, characterized in that: The thickness of the depletion layer of controlled elements is obtained based on the data of hot corrosion test, including: The test pieces after the hot corrosion test were cut along the cross section and longitudinal section, and then polished. The polished test pieces were then observed by SEM-EDS, the corrosion products were semi-quantitatively analyzed, and the thickness of the control element depletion layer was determined.

3. The creep prediction method for nickel-based high-temperature alloys considering damage in hot corrosion environments according to claim 1, characterized in that: The creep constitutive model is: Where, is the creep strain rate; is the creep stress; Creep damage; 、 and is the creep constant; where It is determined by the creep strain rate at fracture and the minimum creep strain rate in the second stage of creep.

4. The creep prediction method for nickel-based high-temperature alloys considering damage in hot corrosion environments according to claim 1, characterized in that: The equivalent hot corrosion damage coefficient is calibrated according to the following steps: The creep deformation curve of nickel-based high-temperature alloy in hot corrosion environment is obtained based on the data of hot corrosion-creep test; The equivalent hot corrosion damage coefficient in the equivalent hot corrosion damage model is calibrated according to the creep deformation curve of nickel-based high-temperature alloy in a hot corrosion environment.

5. The creep prediction method for nickel-based high-temperature alloy considering damage in hot corrosion environment according to claim 1, characterized in that: Before conducting hot corrosion tests and hot corrosion-creep tests on the test pieces, the following steps are also included: cutting the nickel-based high-temperature alloy, grinding the cut samples step by step to 2000# using sandpaper, and then ultrasonically cleaning the ground test pieces with anhydrous ethanol, acetone and distilled water to remove oil stains.

6. The creep prediction method for nickel-based high-temperature alloy considering damage in hot corrosion environment according to claim 1, characterized in that: The test piece is subjected to hot corrosion test by salt coating method, including: 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%. The sample was then heated to 250-350°C and the saturated salt solution was sprayed onto the heated test piece using an atomizer. The spraying interval was 3-5 seconds.

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