Corrosion kinetic analysis method considering stress

Abstract

The invention discloses a stress-considered corrosion kinetic analysis method, which belongs to the technical field of alloys, and comprises the following steps: obtaining a plurality of test pieces which are nickel-based high-temperature alloy test pieces, performing a stress-hot corrosion test on the test pieces, and analyzing the tested test pieces to obtain a stress-hot corrosion model; observing and acquiring the thickness of a control element depletion layer of the sample under different test conditions; obtaining test conditions in the stress-hot corrosion test, wherein the test conditions comprise tensile stress and hot corrosion time; according to the thickness of the control element depletion layer and the test conditions, fitting to obtain parameters of a corrosion kinetic model, according to the parameters of the corrosion kinetic model, obtaining the corrosion kinetic model with the parameters, and substituting the test conditions into the corrosion kinetic model for calculation to obtain a prediction curve of the thickness of the control element depletion layer based on different test conditions; through the technical scheme, the depletion layer thickness change of the nickel-based superalloy under the stress thermal corrosion effect can be effectively predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of alloys, and in particular relates to a stress-considered corrosion kinetics analysis method for a nickel-based high-temperature alloy under stress. Background Art

[0002] The turbine disk of an aircraft engine is subjected to centrifugal force, thermal stress and alternating stress caused by high-speed rotation during service, and is also affected by high-temperature oxidation. In addition, the turbine disk not only has to withstand the above-mentioned stress, but is also affected by thermal corrosion caused by corrosive salts deposited in the marine environment. In the marine environment, the deposition of two corrosive salts, NaCl from the marine atmosphere and Na2SO4 residual from fuel combustion, can cause thermal corrosion of the turbine disk.

[0003] In the early stage of use, the influence of thermal corrosion on the turbine disk is not easy to detect. However, as the service time increases, the heat-affected zone of the turbine disk caused by thermal corrosion gradually deepens. These areas are also subjected to centrifugal forces caused by high-speed rotation of components, alternating stresses and thermal stresses caused by component start-up and shutdown and temperature fluctuations. As a result, stress concentration and crack initiation begin to appear in the heat-affected zone. When predicting the life of turbine disks serving in marine environments, it is not enough to only consider the influence of stress on the turbine disk. Because the actual service conditions of turbine disks in marine environments are the coupling of mechanical loads and thermal corrosion, it is very necessary to study the thermal corrosion behavior of nickel-based high-temperature alloys under stress.

[0004] In the prior art, the focus is on the unilateral research of the mechanical properties or corrosion resistance of nickel-based high-temperature alloys. At present, there is no systematic test and analysis method for the stress-thermal corrosion test of nickel-based high-temperature alloys. More importantly, the traditional evaluation of the degree of thermal corrosion of high-temperature alloys is based on the Arrhenius equation to fit the function of the change of sample mass with thermal corrosion. The use of this method to process stress-thermal corrosion samples will cause the problem of large discreteness of test data, because when the nickel-based high-temperature alloy is undergoing stress-thermal corrosion tests and when the test specimens are unloaded at the end of the test, the oxide film of the sample will peel off, which is the main reason for the large discreteness of the test data. In addition, there is obviously a lack of quantitative description of tensile stress during the thermal corrosion process. Moreover, it is obviously broad to describe the corrosion dynamics only by the change of sample mass with thermal corrosion time. In-depth research on the thermal corrosion behavior of high-temperature alloys requires a more microscopic statistical method for the test results.

[0005] In response to the above problems, a corrosion kinetic model and measurement method that takes stress into consideration is urgently needed to conduct a systematic study on the stress-thermal corrosion behavior of nickel-based high-temperature alloys in order to more accurately evaluate the corrosion performance of nickel-based high-temperature alloys under stress, and to accurately determine the reaction development of the depletion layer thickness of different control elements in nickel-based high-temperature alloys under different test conditions, thereby providing a reliable basis for aircraft engine life assessment.

[0006] The above information disclosed in the background technology section is only for enhancing the background understanding of the present invention and therefore it may not include information that does not constitute the prior art known to a person of ordinary skill in the art. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a corrosion kinetics analysis method of nickel-based high-temperature alloy under stress, by analyzing the thickness of the control element depletion layer of the cross section of the test piece after the test, and taking the test stress and temperature into account in the corrosion kinetics model. The change of the depletion layer thickness of the nickel-based high-temperature alloy under stress thermal corrosion is predicted, reflecting the development of the depletion layer thickness of the nickel-based high-temperature alloy during service in a thermal corrosion environment.

[0008] To achieve the above object, the present invention provides a corrosion dynamics analysis method considering stress, comprising:

[0009] Obtaining a plurality of test pieces, wherein the test pieces are nickel-based high-temperature alloy test pieces;

[0010] Conduct stress-thermal corrosion tests on several test pieces, and analyze the test pieces after the tests to obtain the control elements and the thickness of the control element depletion layer;

[0011] Acquiring test conditions in a stress-thermal corrosion test, wherein the test conditions include tensile stress and thermal corrosion time;

[0012] According to the thickness of the depletion layer of the control element and the test conditions, the parameters of the corrosion kinetic model are fitted, and according to the parameters of the corrosion kinetic model, the corrosion kinetic model with parameters is obtained;

[0013] The experimental conditions are substituted into the corrosion kinetics model with parameters for calculation, and the prediction curve of the control element depletion layer based on different experimental conditions is obtained.

[0014] Optionally, before the stress-thermal corrosion test is performed on the test piece, the following steps are also included:

[0015] The test piece is cut by an electric spark wire cutting method, the cut test piece is ground, and the ground test piece is ultrasonically cleaned by using anhydrous ethanol, acetone and distilled water;

[0016] A stress-thermal corrosion test was carried out on the cleaned test piece. A saturated salt solution with a mass ratio of 3:1 was prepared using anhydrous Na2SO4 with a purity greater than 99.5wt% and anhydrous NaCl. During the heating process of the stress-thermal corrosion test, the saturated salt solution was sprayed onto the surface of the cleaned test piece at intervals.

[0017] Optionally, the process of performing stress-thermal corrosion testing on the test piece includes:

[0018] The test piece is heated by a heating furnace, and a creep machine is used to apply stress to the test piece during the heating process. The temperature of the test piece during the test is measured by a K-type thermocouple, and the thermal corrosion time corresponding to different cycles of the stress-thermal corrosion test is set to obtain the test pieces after several tests.

[0019] Optionally, the process of analyzing the test piece after the test includes:

[0020] The tested specimens are cut along the cross section and longitudinal section;

[0021] The surface-cut test piece was polished, and then the polished test piece was cold-mounted with epoxy resin. The phase analysis of the cold-mounted test piece was performed by XRD to obtain typical surface corrosion products.

[0022] The typical surface corrosion products were semi-quantitatively analyzed on the cross section and longitudinal section by SEM-EDS, and the control elements were obtained based on the typical surface corrosion products and semi-quantitative analysis results.

[0023] The depletion layer of the control element in the cross section and longitudinal section is measured by surface scanning and line scanning of EDS to generate the thickness of the depletion layer of the control element.

[0024] Optionally, during the surface scanning and line scanning process of EDS, the measurement starting point is the cold mounting resin area and the end point is the high-temperature alloy group.

[0025] Optionally, the corrosion kinetics model includes:

[0026] The first relation:

[0027] Δh=K Pσ t i +A(σ)

[0028] Where Δh represents the thickness of the depletion layer of the controlling element, K Pσ It is represented by the thermal corrosion rate coefficient corresponding to the tensile stress σ, which is related to the loading stress and temperature, t is represented by the thermal corrosion time, i is represented by the thickening index of the depletion layer of the control element, and A(σ) is represented by the correction coefficient of the depletion layer of the control element corresponding to the tensile stress σ, which is related to the loading stress;

[0029] The second relation:

[0030]

[0031] Where K0 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, C represents the activation energy correction coefficient of unit stress, and σ represents the tensile stress;

[0032] The third relation:

[0033]

[0034] Among them, P1 represents the stress correlation coefficient, P2 represents the thickening index, and P3 represents the thickening correction constant.

[0035] Optionally, the generation process of the corrosion dynamics model with parameters includes:

[0036] The first relation is fitted to the thickness of the control element depletion layer and the test conditions, and the control element depletion layer thickening index i is set to obtain the thermal corrosion rate coefficient K Pσ , the value of the correction coefficient A(σ) of the control element correction depletion layer corresponding to the tensile stress σ;

[0037] Take the logarithm of both sides of the second relationship and adjust it to: Based on the adjusted second relation, the hot corrosion rate coefficient K Pσ The numerical value and test conditions are fitted to obtain the activation energy correction coefficient C and corrosion rate constant K0 of unit stress;

[0038] Based on the third relationship, the numerical value of the correction coefficient of the control element corrected depletion layer corresponding to the tensile stress σ and the tensile stress σ are fitted to obtain the stress correlation coefficient P1, the thickening index P2 and the thickening correction constant P3;

[0039] The first, second and third relationship are integrated, and the controlling element depletion layer thickening index i, unit stress activation energy correction coefficient C, corrosion rate constant K0, stress correlation coefficient P1, thickening index P2 and thickening correction constant P3 are substituted into the integrated relationship to generate a corrosion kinetics model with parameters.

[0040] Optionally, after obtaining the corrosion dynamics model with parameters, the following steps are also included:

[0041] According to the corrosion kinetics model with parameters, the experimental conditions and the numerical values ​​of the thickness of the depletion layer of the control element are generated. According to the experimental conditions and the numerical values ​​of the thickness of the depletion layer of the control element, a scatter plot is generated, wherein the thermal corrosion time t is the Y axis, the tensile stress σ is the X axis, and the thickness of the depletion layer of the control element Δh is the Z axis;

[0042] Perform nonlinear surface fitting on the point value data in the scatter plot to generate a visual two-dimensional function surface.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] The relationship between stress and the thickness of the depletion layer of the controlling element is established:

[0045] Previous studies have focused on the mechanical properties or corrosion resistance of nickel-based high-temperature alloys, and there is no systematic test and analysis method for stress-hot corrosion tests of nickel-based high-temperature alloys. The corrosion kinetics model proposed in this invention takes into account the effect of stress on the hot corrosion rate, and provides a quantitative description of the evolution of the depletion layer thickness and stress.

[0046] The discreteness of data is reduced and the test accuracy is improved:

[0047] In the past, the evaluation of the degree of hot corrosion of high-temperature alloys was based on the classic Arrhenius equation to fit the function of the mass per unit area of ​​the sample changing with the hot corrosion time. When the nickel-based high-temperature alloy is subjected to stress-hot corrosion test and the specimen is unloaded after the test, the oxide film of the sample will peel off, which will seriously affect the accuracy of the corrosion kinetics equation and cause the problem of large data discreteness. Therefore, the traditional method of obtaining the corrosion kinetics equation by measuring the mass change alone is not applicable to stress-hot corrosion test.

[0048] In view of the above problems, the method proposed in the present invention avoids the need to weigh the mass. While providing the corrosion kinetics equation of the sample, it also provides a reference for the sample whose corrosion kinetics are described by mass change, thereby improving the test efficiency and accuracy.

[0049] Depletion layer thickness prediction:

[0050] The evolution of the depletion layer thickness under different stress levels in the same thermal corrosion environment can be predicted based on the equation of the present invention, providing a reference for the corrosion kinetics equation obtained by observing the change in mass per unit area, improving the test efficiency and saving the test cost. The change in the depletion layer thickness of the nickel-based high-temperature alloy under stress thermal corrosion is predicted, reflecting the development of the depletion layer thickness of the nickel-based high-temperature alloy during service in a thermal corrosion environment. The thickness of the depletion layer will affect the working state of the alloy test piece. When the depletion layer thickness reaches a certain level, it will cause the alloy test piece to fail.

[0051] The above model can be used as an evaluation index for the degradation of high-temperature alloys during service, and can also be introduced into the damage term of the creep constitutive model of high-temperature alloys to predict the creep deformation of high-temperature alloys in a hot corrosion environment. This can further systematically and accurately study the corrosion dynamics of nickel-based high-temperature alloys under stress hot corrosion, and provide a basis for the life assessment of hot end components serving in marine environments. It provides a reliable data basis and technical foundation for the life assessment of aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0053] Figure 1 A flow chart of a corrosion kinetics model and a determination method considering stress in an embodiment of the present invention;

[0054] Figure 2 A specimen dimension diagram for a corrosion kinetics model and a determination method taking stress into consideration in an embodiment of the present invention;

[0055] Figure 3 An X-ray diffractometer used in a stress-considered corrosion kinetics model and determination method in an embodiment of the present invention is used to obtain a phase analysis diagram of a surface area of ​​a hot corrosion test;

[0056] Figure 4 A cross-sectional view of corrosion products using a scanning electron microscope used in a corrosion kinetics model and a determination method taking stress into account in an embodiment of the present invention;

[0057] Figure 5 This is a diagram of energy spectrum line scan results used in a corrosion kinetics model and determination method considering stress in an embodiment of the present invention;

[0058] Figure 6 This is a result diagram of Ni distribution scanned by an energy spectrum surface for a corrosion kinetics model and a determination method taking stress into consideration in an embodiment of the present invention;

[0059] Figure 7 This is a result diagram of Cr distribution scanned by an energy spectrum surface for a corrosion kinetics model and a determination method taking stress into consideration in an embodiment of the present invention;

[0060] Figure 8 A corrosion kinetics curve diagram obtained by a corrosion kinetics model and a determination method taking stress into consideration in an embodiment of the present invention;

[0061] Fig. 9 A corrosion kinetic rate diagram under different stresses obtained by a corrosion kinetic model and a determination method taking stress into consideration in an embodiment of the present invention;

[0062] Fig.10 This is a corrosion kinetics curve corresponding to 60MPa predicted by a corrosion kinetics model and a determination method taking stress into consideration in an embodiment of the present invention based on 0MPa, 30MPa and 120MPa. DETAILED DESCRIPTION

[0063] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0064] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0065] The present invention provides a corrosion kinetics analysis method that takes stress into consideration, which belongs to the field of high-temperature alloys, and further belongs to a corrosion kinetics analysis method that monitors the thickness of the depletion layer of the control element. Compared with the traditional corrosion kinetics measurement method of high-temperature alloys, it avoids the problem of large data discreteness caused by oxide film peeling during stress-thermal corrosion tests, and improves the reliability of the data. In addition, the corrosion kinetics model of the present invention reflects the evolution law of the control elements of high-temperature alloys over time. After conducting a set of tests, the thermal corrosion rate of the high-temperature alloy is obtained, and the development of the depletion layer of the high-temperature alloy during the thermal corrosion process can also be directly obtained. This provides a reliable data basis for aircraft engine life assessment. It mainly includes the following steps:

[0066] Provide multiple nickel-based high-temperature alloy test pieces to be tested; apply the salt solution required for the test to the test pieces; conduct multiple stress-thermal corrosion tests on the test pieces; after the test, use epoxy resin to cold mount the sample and then cut the test piece; perform microstructure morphology analysis, corrosion product stratification analysis, and corrosion affected zone thickness evaluation on the cross-section and longitudinal surface of the cut test piece; then use the thickness of the control element depletion layer and the stress level applied to the test piece as the calculation basis of the corrosion kinetic model. The kinetic parameters at the preset temperature are determined by performing nonlinear fitting on the thickness of the alloy control element depletion layer and the stress level applied to the test piece.

[0067] like Figure 1 As shown, in order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

[0068] The first aspect of the present invention provides a method for determining the same comprising:

[0069] In an exemplary embodiment of the present invention, an initial sample of a nickel-based high-temperature alloy to be analyzed is provided. The test piece is a plate-shaped creep small sample and a fixture as shown in patent number CN106644700B. Figure 2 As shown, the length unit is mm, the material of the test piece is a nickel-based high-temperature alloy with a grade of GH4169, and the material of the fixture is an equiaxed high-temperature alloy with a grade of DZ125. The test process and analysis method refer to the analysis method of hot corrosion performance of a nickel-based single crystal high-temperature alloy with patent number CN111896458A.

[0070] In an exemplary embodiment of the present invention, the test piece is cut by using the electric spark wire cutting technology. After cutting, SiC sandpaper with different roughness is used to grind the test piece step by step with low stress to 2000# to eliminate the residual stress on the surface caused by machining.

[0071] In an exemplary embodiment of the present invention, the test piece is ultrasonically cleaned with anhydrous ethanol (C2H5OH), acetone (CH3COCH3) and distilled water, and each cleaning time is not less than 15 minutes to fully remove oil stains.

[0072] In the exemplary embodiment of the present invention, anhydrous Na2SO4 and anhydrous NaCl with a purity greater than 99.5wt% are used to prepare a saturated salt solution with a mass ratio of 3:1. The test piece is weighed using an analytical balance with an accuracy of 0.1mg. After weighing, the test piece is placed in a heating furnace at 200°C, and the salt mist is sprayed onto the surface of the test piece using an atomizer bottle. The heating furnace is used to heat the test piece to evaporate the water in the salt mist, achieve uniform adhesion of the salt, and finally form a salt film on the test piece.

[0073] It should be noted that the test piece should be fully preheated when placed on the heating furnace to ensure that the test piece is fully heated. When using the atomizer to spray salt mist on the test piece, the interval between each spraying is 3-5s to ensure that the moisture in the salt mist can fully evaporate on the test piece. Avoid the salt film on the test piece from bursting and splashing due to uneven heating. Repeat the above operation repeatedly to form a 3mg / cm 2 of salt film.

[0074] In an exemplary embodiment of the present invention, a creep machine with a maximum load capacity of 5 t was used to apply tensile stresses of 0 MPa, 30 MPa and 120 MPa to the test pieces, respectively.

[0075] In the exemplary embodiment of the present invention, a heating furnace matched with a creep machine is used to heat the test piece, and three K-type thermocouples are used to measure the temperature of the upper, middle and lower sections of the test piece during the test, wherein the maximum temperature difference error range is ±5°C.

[0076] In the exemplary embodiment of the present invention, after the test piece is supported, the high temperature furnace is closed, and asbestos needs to be stuffed into the upper and lower ends of the high temperature furnace to avoid test errors caused by uneven heating. In the exemplary embodiment of the present invention, the heating temperature of the high temperature furnace is 750°C.

[0077] In an exemplary embodiment of the present invention, the stress-thermal corrosion test cycle is 25h, 50h, 75h, and 100h, and each set of tests needs to be repeated twice.

[0078] In an exemplary embodiment of the present invention, two parallel test pieces are used for the test cycle, one for the cross-sectional and longitudinal section analysis and the other for the surface corrosion product analysis.

[0079] In an exemplary embodiment of the present invention, a cross-sectional analysis is performed using the test piece that has reached the test cycle, wherein the sample preparation for the cross-sectional analysis of the test piece includes:

[0080] Cutting the sample along the transverse and longitudinal sections of the sample;

[0081] The finished sample is polished step by step with SiC sandpaper. The standard for changing to the next level of sandpaper after polishing is that no obvious scratches can be observed on the surface of the specimen after completing one level of polishing with the current sandpaper.

[0082] After low-stress grinding with SiC sandpaper, the cross section of the specimen was polished with velvet polishing cloth and diamond grinding liquid;

[0083] The particle size of the diamond grinding liquid is 0.25 micron and 0.04 micron. Use the two grinding liquids to polish in sequence until the cross section of the specimen is mirror-like with no obvious scratches;

[0084] The cut specimens were cold mounted with epoxy resin, and the bubbles in the resin were minimized during the process to avoid affecting the cross-section observation.

[0085] The samples after the test were subjected to phase analysis by XRD to determine the typical corrosion products grown during the hot corrosion of high-temperature alloys.

[0086] Using SEM-EDS to perform semi-quantitative analysis of typical corrosion products on the surface of the sample;

[0087] Combine the analysis results of SEM (scanning electron microscope), EDS (energy dispersive spectrometer) and XRD (X-ray diffraction) to determine the controlling elements in the hot corrosion reaction process;

[0088] The depletion layer of the control element in the transverse and longitudinal sections of the sample is measured by EDS surface scanning and line scanning. The average value of the element depletion layer observation is taken as the test result by selecting multiple observation positions from the transverse and longitudinal sections. The measurement starting point is the cold mounting resin area and the end point is the high temperature alloy matrix.

[0089] According to a second aspect of the present invention, the corrosion kinetics model includes:

[0090] Monitoring quality changes The equation describing the hot corrosion behavior of high-temperature alloys is based on the Arrhenius corrosion kinetics equation, namely:

[0091] ΔM=K Pσ t i +A

[0092] ΔM is the mass change per unit area of ​​the sample, K Pσ is the thermal corrosion rate coefficient, and A is a constant.

[0093] The corrosion kinetics model in the present invention replaces the time-dependent change ΔM of the unit area mass on the left side of the classic corrosion kinetics model equation with the change Δh of the controlled element depletion layer. That is, the corrosion kinetics is described by controlling the change of the element depletion layer thickness with the thermal corrosion time. The basic reaction rate equation expression still follows the Arrhenius equation, and the specific expression of the corrosion kinetics model of the present invention includes:

[0094] The first relation:

[0095] Δh=K Pσ t i +A(σ)

[0096] Where Δh represents the thickness of the control element depletion layer, μm; K Pσ Indicates the thermal corrosion rate coefficient, which is related to the loading stress and temperature, μm·h -1 ; t represents the hot corrosion time, h; i represents the thickening index of the control element depletion layer, dimensionless; A represents the correction coefficient of the control element corrected depletion layer, which is related to the loading stress, i.e., tensile stress, μm; A(σ) represents the correction coefficient of the control element corrected depletion layer corresponding to the tensile stress σ, which is related to the loading stress, i.e., tensile stress, μm.

[0097] The second relation:

[0098]

[0099] Where K0 is the corrosion rate constant, μm·h -1 ; e represents the base of natural logarithm, constant, 2.71828, dimensionless; R represents the molar gas constant, J·mol -1 ·K -1 ; T is absolute temperature, K; Q is thermal corrosion activation energy, which is generally considered to be a constant independent of temperature, J·mol -1 ; C represents the activation energy correction coefficient of unit stress, MPa -1 ; σ represents tensile stress, MPa.

[0100] The third relation:

[0101]

[0102] Where P1 is the stress correlation coefficient, μm·MPa -1 ; P2 represents the thickening index, dimensionless; P3 represents the thickening correction constant, μm.

[0103] Preferably, the relationship Δh=K Pσ t i +A(σ) is substituted into the experimental conditions t and σ of the thickness of the control element depletion layer Δh determined in the experiment, and the equation and the experimental conditions are written into the fitting software 1stopt to obtain the parameter value: thermal corrosion rate coefficient K Pσ , the control element depletion layer thickening index i and the control element corrected depletion layer correction coefficient A.

[0104] Relational Taking the natural logarithm of both sides, we get The absolute temperature T, tensile stress σ and thermal corrosion rate coefficient K of the sample Pσ The linear equation is written into the fitting software 1stopt to obtain the parameter values ​​in the relationship: unit stress activation energy correction coefficient C, corrosion rate constant K0.

[0105] Substitute the fitted value A(σ) and the test condition σ into The above method is used for fitting, and the parameter values ​​in the relationship are obtained: stress correlation coefficient P1, thickening index P2 and thickening correction constant P3.

[0106] The first, second and third relationship are integrated, and the controlling element depletion layer thickening index i, unit stress activation energy correction coefficient C, corrosion rate constant K0, stress correlation coefficient P1, thickening index P2 and thickening correction constant P3 are substituted into the integrated relationship to generate a corrosion kinetics model with parameters.

[0107] For the same test piece, the simulation test conditions for the simulation of the thickness of the control element depletion layer are set. The simulation test conditions are calculated through a corrosion kinetics model with parameters to generate the simulation predicted thickness of the control element depletion layer.

[0108] Taking the corrosion kinetic model with parameters as the fitting equation, the experimental conditions t, σ and the thickness of the control element depletion layer Δh were input into the Origin software, and a scatter plot was made with the thermal corrosion time t as the Y-axis, the tensile stress σ as the X-axis, and the thickness of the control element depletion layer Δh as the Z-axis.

[0109] By performing nonlinear surface fitting on the data in the above three-dimensional scatter plot, a two-dimensional function surface related to the thickness Δh of the control element depletion layer and the tensile stress σ and the hot corrosion time t can be established.

[0110] The above contents are described in detail with relevant data:

[0111] The nickel-based high-temperature alloy test piece used in this embodiment is GH4169, which is composed of Cr, Al, Co, Ti, W, Mo, Nb, C, Zr, B and Ni. Its nominal composition (mass percentage) is: Cr content is 20.02%; Al content is 0.29%; Fe content is 18.66%; Ti content is 1.13%; W content is 0.11%; Mo content is 3.04%; Nb content is 4.55%; C content is 0.08; Zr content is 0.09; B content is 0.011; Ni is the balance.

[0112] The size of the selected test piece is cut into an I-shape by wire-cutting technology, such as Figure 2 shown.

[0113] Using the above-mentioned spray salt coating method, the test piece is first heated to 200°C in a heating furnace, and salt mist is evenly sprayed on the surface of the test piece and weighed repeatedly until 3 mg / cm3 of salt is evenly deposited on the surface of the test piece. 2 75% Na2SO4 + 25% NaCl corrosive salt.

[0114] The test pieces were loaded with two horizontal tensile stresses of 120MPa and 30MPa respectively through a creep machine, and a 0MPa sample was set as a control group. The test temperature of the three groups of samples was set at 750℃.

[0115] The test piece after the test was analyzed by X-ray diffractometer. The analysis results of X-ray diffractometer are as follows: Figure 3 As shown, 2-θ represents the diffraction angle. The test results show that after GH4169 was subjected to two levels of tensile stress hot corrosion, the oxidation products were mainly NiCr2O4 and Cr2O3, and the sulfide products were mainly Ni3S2. This shows that applying tensile stress in a 750℃ hot corrosion environment does not change the generation category of GH4169 hot corrosion products, and the presence of Cr2O3, NiCr2O4 and Ni3S2 indicates that the hot corrosion behavior of GH4169 includes two processes: oxidation and sulfidation. It is worth noting that no obvious chloride was found on the surface of the specimen, which is caused by the volatilization of chloride at high temperature.

[0116] The cross section is line scanned by an energy dispersive spectrometer. The starting point of the EDS line scan measurement is the cold-mounted epoxy resin area of ​​the sample cross section, and the end point is the high-temperature alloy matrix. The EDS line scan position is as follows: Figure 4 The scan results are as shown in Figure 5 As shown. EDS surface scanning Ni, Cr respectively as shown Figure 6 and Figure 7 As shown. The test results show that there are obvious enrichment layers and depletion layers of Cr in the alloy matrix. Combined with the XRD analysis results, the main component of the oxide film on the alloy surface is Cr2O3. Considering the corrosion kinetics of stress, the thickness of the Cr depletion layer is used as an observation index. Therefore, the Cr depletion layer of the specimens under different stress levels and test cycles is statistically used as an observation index of corrosion kinetics.

[0117] like Figure 5 As shown in the figure, the EDS line scan results show that the Cr element appears in enriched areas, depleted areas and continuous enriched areas with the scanning depth. The first enriched area that appears at the beginning of the scan is the thickness of the Cr2O3 film generated by GH4169 during the hot corrosion process. The thickness of the depleted area in the middle is used as an indicator for corrosion kinetics observation. The continuous Cr-enriched area behind is the alloy matrix.

[0118] After counting the Cr depletion layer thickness of all test condition samples, the Cr depletion layer thickness Δh and the test tensile stress σ obtained from the above test are successively substituted into the relationship Δh=K Pσ t i +A(σ).

[0119] The thickness of the Cr depletion layer of the nickel-based superalloy GH4169 subjected to three tensile stresses of 0MPa, 30MPa and 120MPa in a hot corrosion environment is used to predict the change in the depletion layer thickness of the nickel-based superalloy after being subjected to 60MPa hot corrosion for 100h.

[0120] Substitute the Cr depletion layer thickness Δh of the 0MPa, 30MPa, and 120MPa samples and the corresponding hot corrosion time t into the equation Δh=K Pσ t i +A(σ), where the thickening index i is 0.5, and K is obtained by fitting P0 =1.872, K p30 =2.136, K P120 =3.165, A(0)=-0.107, A(30)=-0.391, A(120)=-1.452. The experimental data and the equation fitting results are as follows Figure 8 shown.

[0121] By knowing K Pσ Determine the hot corrosion rate coefficient K P60 right Taking the logarithm of both sides, we get:

[0122]

[0123] Substitute KP0 =1.872, K P30 =2.136, K P120 =3.165

[0124] The activation energy correction coefficient of stress effect C = 0.004 and the thermal corrosion rate coefficient K corresponding to 60MPa tensile stress are obtained. P60 =2.461. The corrosion kinetic coefficients under four stresses are as follows Fig. 9 shown.

[0125] Determine A(60) by A(0)=-0.107, A(30)=-0.391, A(120)=-1.452, and substitute A(0)=-0.107, A(30)=-0.391, A(120)=-1.452 into The fitting results show that P1 = -0.006278, P2 = 1.121087, P3 = -0.106632, and the influence coefficient corresponding to the 60MPa sample is A(60) = -0.725

[0126] Finally, the corrosion kinetic equation of the Cr depletion layer of the sample corresponding to 60MPa with the thermal corrosion time is obtained:

[0127] Δh=2.461*t 0.5 -0.725. The experimental data and the equation prediction curve are as follows Fig.10 shown.

[0128] The above content of the present invention is an exemplary numerical display of the experiment to illustrate the technical solution, so as to facilitate the understanding of relevant personnel. In order to improve the fitting effect of the above formula, data samples with more data points can be selected to fit the relevant parameters of the above equation to better conform to the correlation rules between different data in actual experiments. It will not be elaborated here.

[0129] The embodiment of the present invention provides a corrosion kinetics model and a determination method for a nickel-based high-temperature alloy under stress, and performs relevant analysis on the corrosion kinetics model considering stress. While ensuring the test accuracy, the evolution of the depletion layer of GH4169 in different thermal corrosion periods is monitored by controlling the evolution law of the element Cr depletion layer over time.

[0130] In order to fully consider the influence of stress on the Cr depletion layer, the present invention takes the influence of stress into consideration of the reaction rate coefficient K Pσ and influence coefficient A(σ). K Pσ The addition of the stress influence term in the equation actually extracts the effect of stress on the activation energy in the hot corrosion process, because R and T are equal constants at the three stress levels in this study. Therefore, the relationship between the activation energy corresponding to different stresses can be further obtained.

[0131] The embodiment of the corrosion dynamics model and determination method considering stress of the present invention is to help understand the process and ideas of the determination test scheme. It is not limited to this implementation process and application. For example, the evolution law of the depletion layer of the high-temperature alloy in the stress-thermal corrosion environment determined in this disclosure can be used as a damage term in the mechanical constitutive model considering the thermal corrosion effect.

[0132] Compared with the traditional corrosion kinetics determination method of high-temperature alloys, the corrosion kinetics model of the control element depletion layer and stress and time obtained from the sample of the present invention avoids the problem of large mass count discreteness caused by oxide film peeling during stress-thermal corrosion test, and improves the reliability of data. In addition, the corrosion kinetics model of the present invention reflects the evolution law of the control elements of high-temperature alloys over time. After a set of tests, the thermal corrosion rate of the high-temperature alloy can be obtained, and the development of the depletion layer of the high-temperature alloy during the thermal corrosion process can also be directly obtained. This provides a reliable data basis and technical foundation for aircraft engine life assessment.

[0133] Special note: The technical solution of the present invention involves many parameters, and the synergistic effects between the various parameters need to be comprehensively considered to obtain the beneficial effects and significant progress of the present invention. Moreover, the value ranges of the various parameters in the technical solution are obtained after a large number of experiments. For each parameter and the combination of each parameter, the inventor has recorded a large amount of experimental data. Due to space limitations, the specific experimental data will not be disclosed here.

[0134] It is not difficult for those skilled in the art to understand that the stress-considered corrosion kinetics model and determination method of the present invention include any combination of the invention content and specific implementation methods of the above-mentioned invention specification and the various parts shown in the drawings. Due to the limited space and to make the specification concise, the various schemes composed of these combinations are not described one by one. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0135] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A corrosion dynamics analysis method considering stress, characterized in that: include: Obtaining a plurality of test pieces, wherein the test pieces are nickel-based high-temperature alloy test pieces; Conduct stress-thermal corrosion tests on several test pieces, and analyze the test pieces after the tests to obtain the control elements and the thickness of the control element depletion layer; Acquiring test conditions in a stress-thermal corrosion test, wherein the test conditions include tensile stress and thermal corrosion time; According to the thickness of the depletion layer of the control element and the test conditions, the parameters of the corrosion kinetic model are fitted, and according to the parameters of the corrosion kinetic model, the corrosion kinetic model with parameters is obtained; The experimental conditions were substituted into the corrosion kinetics model with parameters for calculation, and the prediction curve of the thickness of the control element depletion layer based on different experimental conditions was obtained.

2. The method according to claim 1, characterized in that Before the stress-thermal corrosion test is carried out on the test piece, the following steps are also included: The test piece is cut by an electric spark wire cutting method, the cut test piece is ground, and the ground test piece is ultrasonically cleaned by using anhydrous ethanol, acetone and distilled water; A stress-thermal corrosion test was carried out on the cleaned test piece. A saturated salt solution with a mass ratio of 3:1 was prepared using anhydrous Na2SO4 with a purity greater than 99.5wt% and anhydrous NaCl. During the heating process of the stress-thermal corrosion test, the saturated salt solution was sprayed onto the surface of the cleaned test piece at intervals.

3. The method according to claim 1, characterized in that The process of conducting stress-thermal corrosion tests on test pieces includes: The test piece is heated by a heating furnace, and a creep machine is used to apply stress to the test piece during the heating process. The temperature of the test piece during the test is measured by a K-type thermocouple, and the thermal corrosion time corresponding to different cycles of the stress-thermal corrosion test is set to obtain the test pieces after several tests.

4. The method according to claim 1, characterized in that: The process of analyzing the test piece after testing includes: The tested specimens are cut along the cross section and longitudinal section; The surface-cut test piece was polished, and then the polished test piece was cold-mounted with epoxy resin. The phase analysis of the cold-mounted test piece was performed by XRD to obtain typical surface corrosion products. The typical surface corrosion products were semi-quantitatively analyzed on the cross section and longitudinal section by SEM-EDS, and the control elements were obtained based on the typical surface corrosion products and semi-quantitative analysis results. The depletion layer of the control element in the cross section and longitudinal section is measured by surface scanning and line scanning of EDS to generate the thickness of the depletion layer of the control element.

5. The method according to claim 1, characterized in that: During the EDS surface scanning and line scanning process, the measurement starting point is the cold mounting resin area and the end point is the high-temperature alloy group.

6. The method according to claim 1, characterized in that The corrosion kinetics model includes: The first relation: Δh=K Pσ t i +A(σ) Where Δh represents the thickness of the depletion layer of the controlling element, K Pσ It is represented by the thermal corrosion rate coefficient corresponding to the tensile stress σ, which is related to the loading stress and temperature, t is represented by the thermal corrosion time, i is represented by the thickening index of the depletion layer of the control element, and A(σ) is represented by the correction coefficient of the depletion layer of the control element corresponding to the tensile stress σ, which is related to the loading stress; The second relation: Where K0 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, C represents the activation energy correction coefficient of unit stress, and σ represents the tensile stress; The third relation: Among them, P1 represents the stress correlation coefficient, P2 represents the thickening index, and P3 represents the thickening correction constant.

7. The method according to claim 6, characterized in that The generation process of the corrosion kinetic model with parameters includes; Based on the first relationship, the thickness of the control element depletion layer and the test conditions are fitted, and the control element depletion layer thickening index i is set to obtain the thermal corrosion rate coefficient K Pσ , the value of the correction coefficient A(σ) of the control element correction depletion layer corresponding to the tensile stress σ; Take the logarithm of both sides of the second relationship and adjust it to: Based on the adjusted second relation, the hot corrosion rate coefficient K Pσ The numerical value and test conditions are fitted to obtain the activation energy correction coefficient C and corrosion rate constant K0 of unit stress; Based on the third relationship, the numerical value of the correction coefficient of the control element corrected depletion layer corresponding to the tensile stress σ and the tensile stress σ are fitted to obtain the stress correlation coefficient P1, the thickening index P2 and the thickening correction constant P3; The first, second and third relationship are integrated, and the controlling element depletion layer thickening index i, unit stress activation energy correction coefficient C, corrosion rate constant K0, stress correlation coefficient P1, thickening index P2 and thickening correction constant P3 are substituted into the integrated relationship to generate a corrosion kinetics model with parameters.

8. The method according to claim 1, characterized in that After obtaining the corrosion dynamics model with parameters, it also includes: According to the corrosion kinetics model with parameters, the experimental conditions and the numerical values ​​of the thickness of the depletion layer of the controlling element are generated. According to the experimental conditions and the numerical values ​​of the thickness of the depletion layer of the controlling element, a scatter plot is generated, in which the thermal corrosion time t is the Y-axis, the tensile stress σ is the X-axis, and the thickness of the depletion layer of the controlling element Δh is the Z-axis; nonlinear surface fitting is performed on the point value data in the scatter plot to generate a visual two-dimensional function surface.

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