CN114252471A - Method for rapidly predicting high-temperature fatigue performance of nickel-based superalloy small-angle grain boundary - Google Patents
Method for rapidly predicting high-temperature fatigue performance of nickel-based superalloy small-angle grain boundary Download PDFInfo
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Abstract
The invention discloses a method for rapidly predicting high-temperature fatigue performance of a nickel-based superalloy small-angle grain boundary, and belongs to the technical field of metal material performance testing. The method comprises the following steps: (1) determining the orientation difference of the grain boundary of the double crystals prepared by the same process through a microscopic experiment; (2) selecting more than 3 kinds of grain boundary orientation difference twins and determining the change rule of the grain boundary defect linear density along with the orientation difference; (2) obtaining the bicrystal fatigue life N through a high-temperature fatigue experimentfAnd fatigue strength sigmaFS(ii) a (3) Obtaining key parameters of the material through fatigue strength/life data fitting; (4) and quantifying a fatigue strength/service life prediction model by using key parameters and predicting the high-temperature fatigue performance of other grain boundary orientation differences. The method can realize the high-temperature fatigue performance prediction of any grain boundary orientation difference of the nickel-based high-temperature alloy containing the small-angle grain boundary only by testing the high-temperature fatigue performance of a small amount of samples. The method can effectively reduce fatigue experiments in the development and evaluation processes of engineering materials and realize high-efficiency prediction of the fatigue performance of the materials.
Description
Technical Field
The invention relates to the technical field of metal material performance testing, in particular to a method for quickly predicting high-temperature fatigue performance of a nickel-based high-temperature alloy small-angle grain boundary.
Background
Failure of structural materials due to fatigue has taken an important place in the field of structural fatigue failure. Fatigue properties (including fatigue strength, fatigue life, etc.) are basic properties of structural materials, which not only affect other dynamic mechanical properties, such as creep strength, crack propagation rate, etc., but also directly affect the service performance of the materials in final use. In view of the importance of fatigue properties, on the one hand the assessment of fatigue properties during the development of engineering materials is indispensable, and on the other hand the modification and optimization of the material structure is often also aimed at the improvement of fatigue strength and fatigue/life. The nickel-based single crystal superalloy is widely applied to turbine blades of aircraft engines by virtue of excellent high-temperature mechanical properties and serves in a high-temperature environment. However, in the directional solidification of the nickel-based single crystal superalloy, some directional solidification defects are inevitably generated due to the alloy composition and process complexity. Wherein, the small-angle crystal boundary as a common defect can have important influence on the performance and the service behavior of the nickel-based single crystal alloy. The poor orientation of the grain boundaries, i.e. the angle of rotation between two grains around the axis of rotation, is an intrinsic parameter describing the morphology and structure of the grain boundaries of the metallic material. Therefore, the service performance (such as fatigue strength/life) of the nickel-base high-temperature alloy containing the small-angle grain boundary is necessarily closely related to the poor orientation of the grain boundary. In conclusion, accurate evaluation of the high-temperature fatigue performance of the nickel-based superalloy based on poor grain boundary orientation plays an important role in research and development and application of engineering materials.
It is well known that the most direct and effective way to obtain fatigue properties is to prepare samples and perform fatigue tests according to the national standards. The fatigue test is complex, and in view of the lack of related theories, a large number of fatigue tests and related process repeated adjustment are often required to be carried out in the development, design and evaluation optimization processes of the material, so that the difficulty and cost of the material development and evaluation are greatly increased. Therefore, if the relation between the fatigue performance and the grain boundary orientation difference and the relationship between the material components and the processing technology can be established by developing a relevant theoretical model, the fatigue performance can be rapidly predicted, and the method has very important significance in research, development, design and evaluation of engineering materials and scientific theoretical construction.
At present, both theoretical models and technical means are deficient in fatigue performance prediction. In terms of theoretical research, although earlier studies suggest many theories for predicting metal materials, these theories are basically phenomenological descriptions of the fatigue damage process, and the relevant parameters of the theories lack clear physical meanings. Therefore, these theories only help to qualitatively understand the fatigue damage process, but cannot be directly used to establish a quantitative relationship between the fatigue performance and the relevant component parameters, and even cannot be used to predict the fatigue performance. In addition, the prior theoretical work hardly focuses on the essential influence of the grain boundary misorientation on the fatigue damage process of the metal material, and the quantitative relation between the grain boundary misorientation and the fatigue performance of the metal material is not researched and proposed. In engineering applications, although there are some common relationships describing fatigue curves, such as the common Basquin and coffee-Manson equations. However, these relational equations are essentially empirical equations describing the fatigue behavior of the metal material, but are essentially all fits to experimental curves. The physical significance of the parameters in these formulas is unclear due to the lack of connection to the microscopic mechanism, and the parameters hardly reflect the effect of poor grain boundary orientation. Therefore, none of these descriptive formulas have in principle the ability to predict the high temperature fatigue properties of nickel-base superalloys, especially those containing small-angle grain boundaries based on poor grain boundary orientation.
In conclusion, establishing a quantitative model of the high-temperature fatigue performance of the nickel-based superalloy small-angle grain boundary and realizing the rapid prediction of the high-temperature fatigue performance of the nickel-based superalloy based on the poor orientation of the grain boundary has important engineering and theoretical significance, but at present, a proper theoretical basis and technical means do not exist.
Disclosure of Invention
The invention aims to provide a method for quickly predicting the high-temperature fatigue performance of a small-angle grain boundary of a nickel-based superalloy, which realizes quick prediction of high-temperature fatigue strength/service life by establishing a quantitative relation among high-temperature fatigue strength, high-temperature fatigue life and grain boundary orientation difference, thereby greatly reducing the amount of experiments to be developed in material development, design and evaluation optimization and grain boundary orientation difference optimization.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for rapidly predicting the high-temperature fatigue performance of a small-angle grain boundary of a nickel-based superalloy, which comprises the steps of carrying out a high-temperature fatigue experiment on more than 3 kinds of grain boundary orientation difference nickel-based superalloy twin-crystal materials prepared by the same process, and predicting the high-temperature fatigue performance of any grain boundary orientation difference nickel-based superalloy twin-crystal material prepared by other same processes according to the obtained experimental data; the method specifically comprises the following steps:
(1) selecting more than 3 groups of bicrystal materials prepared by the same process with different grain boundary orientation differences, and determining the change rule of the linear density of the grain boundary defects along with the orientation differences of the grain boundaries;
(2) testing the fatigue performance of the prepared material through a high-temperature fatigue test;
(3) obtaining key parameters (A, n and beta) of the prepared material by fitting fatigue strength/life data;
(4) and (4) according to the key parameters obtained in the step (4), utilizing a quantified bicrystal high-temperature fatigue strength/service life prediction model to carry out high-temperature fatigue performance prediction of the bicrystal material prepared by other same processes under any grain boundary orientation difference.
In the step (1), the grain boundary is observed through a microscopic experiment and the grain boundary orientation difference is determined, the original morphology of the twin crystal, particularly the grain boundary region, is required to be maintained during observation (before deformation), the twin crystal is gradually focused on the grain boundary region from low power to high power during observation, and the twin crystal is observed by adopting a microscopic device with a grain boundary orientation analysis function.
In the step (1), the same process refers to a preparation process in which the material components (element ratio) and process parameters are not changed in the preparation of the material. The different grain boundary orientation differences mean that the relative rotation angle between the same orientations of the seed crystals is changed in the preparation of the bicrystal material, so that the prepared bicrystal grain boundaries have different grain boundary orientation differences (the selection of a fatigue test sample needs to be carried out under the different grain boundary orientation differences of the same process, more than 3 bicrystal materials with grain boundary orientation differences smaller than 15 degrees and larger differences are selected to carry out the fatigue performance test of the step (2)); the density f of the grain boundary precipitation phase line is considered to be changed in direct proportion with the grain boundary orientation difference theta, the proportionality coefficient is 1/k, and the proportionality coefficient can be determined by fitting the change situation of grain boundary defects (micropores, carbides and the like) under different grain boundary orientation differences along with the orientation difference.
In the step (3), the passing fatigue is strongThe key parameters of the prepared material obtained by fitting the degree/service life data are as follows: fitting a plurality of groups (more than 3 groups) of fatigue strength data acquired in the step (2) by using a formula (1) to obtain corresponding intrinsic parameters n and
substituting the value of n into a formula (2), and fitting a plurality of groups (more than 3 groups) of fatigue life data acquired in the step (2) by using the formula (2) to obtain a plurality of groups (more than 3 groups) of values of parameters A and beta, wherein the mean values of A and beta are intrinsic A values and beta values related to the twin crystal component.
Wherein: sigmaFSThe fatigue strength is obtained;
theta is the work hardening rate, b is the mode of the dislocation Bohr vector, l is the mean distance of dislocation motion, ρcFor fatigue damage dislocation density tolerance, a can be defined as the material's strengthening coefficient; n is the susceptibility index of material fatigue damage to grain boundary defects; beta is the fatigue damage dislocation density conversion rate; sigmamaxIs the maximum stress of the fatigue test.
In the step (4), the high-temperature fatigue strength/life prediction model of the quantitative bicrystal fatigue high-temperature strength/life can be obtained by obtaining the key parameters, namely the intrinsic parameters A, n and beta in the step (3) and substituting the parameters into the formulas (1) and (2), so that the high-temperature fatigue strength/life of any bicrystal material with poor grain boundary orientation under the same process condition with specific components can be predicted.
The invention has the following advantages and beneficial effects:
1. the method of the invention takes the fatigue test prediction under a small amount of grain boundary orientation difference to the fatigue performance under other grain boundary orientation difference as the basic guiding idea. By establishing the intrinsic relation among the fatigue strength, the fatigue life and the grain boundary orientation difference, the high-temperature fatigue strength/life prediction of any grain boundary orientation difference nickel-based high-temperature alloy twin-crystal material under all the same treatment processes can be realized only by testing the high-temperature fatigue performance of a sample under a small amount of grain boundary orientation difference. The method can effectively reduce fatigue experiments in the process of engineering material development, evaluation and selection, is expected to replace the traditional fatigue-resistant design mode of repeated tests, and realizes the high-efficiency prediction of fatigue performance.
2. Based on the theory of dislocation plug product and fatigue damage, and combined with the system verification experiment, the invention establishes a brand-new high-temperature alloy fatigue damage theoretical model based on grain boundary orientation difference, namely a fatigue deformation dislocation plug product model, and establishes the intrinsic relation of fatigue strength, fatigue life and grain boundary orientation difference for the first time. By utilizing the model, the fatigue performance prediction of any grain boundary orientation difference nickel-based high-temperature alloy twin-crystal material under all similar treatment processes can be realized only through a small amount of fatigue tests. In addition, the quantitative prediction of fatigue performance corresponding to any grain boundary orientation difference of various double-crystal materials under various treatment processes is hopefully realized by combining a material performance database. The method can effectively reduce a large number of experimental tests in the development, evaluation and optimization processes of the engineering material containing the crystal boundary, and really realizes the theoretical high-efficiency prediction of the material performance.
3. At present, the structure and performance optimization of the material containing the grain boundary mainly depends on a large number of repeated trial and error experiments, wherein the repeated component adjustment → process adjustment → grain boundary structure adjustment → fatigue experiments are included, and the period and the cost of material development are greatly increased. In practice, the problem of comparison of fatigue properties among materials containing grain boundaries, which have the same series of basic components and the same treatment process, is often encountered in the development, evaluation and selection processes of the materials containing the grain boundaries. The method not only realizes the mutual correlation of the fatigue performances of the materials in different states, but also successfully realizes the rapid prediction of the fatigue performances based on the grain boundary orientation difference, and saves a large amount of test and evaluation costs.
Drawings
FIG. 1 is a flow chart of the rapid prediction of the high temperature fatigue property of the nickel-based superalloy material of the present invention.
FIG. 2 is a schematic view of the "short plate effect" of grain boundary damage.
FIG. 3 is a model for verifying fatigue deformation dislocation plug product of different nickel-based superalloy materials; wherein: (a) the fatigue data of the high-temperature alloy DD10 under the maximum stress of 380MPa is used for verifying the model; (b) fatigue data verification models of the high-temperature alloy DD5 blade under two maximum stresses (400MPa and 500 MPa); (c) fatigue data verification models of the superalloy DD5 under two maximum stresses (350MPa and 400 MPa); (d) the fatigue strength measured by the DD5 experiment of the high-temperature alloy is compared with the fatigue strength predicted by the model.
FIG. 4 is a quantitative prediction of the fatigue performance of the nickel-base superalloy DD5 under specific components and processes; wherein: (a) the prediction result of the change rule of the fatigue strength of the DD5 subjected to the tertiary aging treatment along with the grain boundary orientation difference is obtained; (b) and (3) predicting the fatigue life of the DD5 by the tertiary aging treatment along with the grain boundary orientation difference and the maximum stress change rule.
FIG. 5 is a fatigue curve and fatigue strength curve for nickel base superalloy DD 5; wherein: (a) a fatigue curve; (b) fatigue strength curve.
FIG. 6 is a key parameter fit in example 1; wherein: (a) obtaining a key parameter n and a combination of parameters for fitting fatigue strength data
(b) And fitting the fatigue life data to obtain key parameters A and beta.
FIG. 7 shows the result of predicting the fatigue properties of the nickel-base superalloy DD5 (red round balls in the graph represent experimental data); wherein: (a) the prediction result of the fatigue strength under different grain boundary orientation differences is obtained; (b) the method is a fatigue life prediction result under different grain boundary orientation differences and maximum stress.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples.
The invention relates to a method for rapidly predicting high-temperature fatigue performance of a nickel-based superalloy small-angle grain boundary, the operation flow is shown in figure 1, and the method comprises the following four steps: (1) selecting more than 3 groups of bicrystal materials with different grain boundary orientation differences (determining the orientation difference of the grain boundary and the change rule of the linear density of the grain boundary defects along with the orientation difference of the grain boundary); (2) testing the high-temperature fatigue performance of each group of materials; (3) fitting fatigue data to obtain key parameters; (4) predicting high-temperature fatigue performance;
the technical scheme is as follows:
the invention adopts a fatigue deformation dislocation plugging product model of fatigue performance to realize prediction, the name comes from the gradual plugging product of dislocation at a crystal boundary during fatigue deformation, and the basic form of a formula is as follows:
in the formulas (1) to (2), A and beta are material composition parameters and basic compositions, the two parameters are constants, n is a process parameter, the process type is determined (such as rolling, pre-deformation, heat treatment and the like), and n is determined. These three parameters can be obtained in practice through more than 3 sets of fatigue experiments. After the parameter values are determined, the fatigue strength and the fatigue life of the given grain boundary orientation difference can be predicted according to the formula (1) and the formula (2), and therefore the efficient prediction of the structure-performance is achieved.
The theoretical basis of the method is a fatigue deformation dislocation plug product model reflecting the physical process of fatigue damage: di＝1/Nf＝(ρi/ρc)βThe main reasoning includes: relationship between fatigue strength and grain boundary orientation difference
Relationship between fatigue life and grain boundary misorientation
The scientific principle is as follows:
the fatigue deformation dislocation and product of jam model adopted in the method is strictly deduced based on relevant knowledge and is verified by a large number of system experiments, and the main derivation links are as follows:
first, by the movable dislocation density and slip system actuation analysis, the grain boundary dislocation plug product density was deduced:
where ρ isθThe dislocation packing volume density caused by the grain boundary structure per load cycle; rhodThe packing density of the motion dislocation caused by the crystal boundary defects in each cycle of the loading cycle; sigmamaxIs the maximum stress during the load cycle; omega0The expression is omega for representing the Schmidt factor corresponding to the slip system of the bimorph basic damage0＝VAΩA+VBΩB，VAAnd VBIs the volume fraction of single crystal grains on both sides of the grain boundary, omegaAAnd ΩBRespectively is the Schmidt factor of the single crystal grain starting slip system at the two sides of the crystal boundary; Δ Ω is the difference in the Schmidt factor of the single-grain start-up slip system on both sides of the grain boundary; theta is the work hardening rate; b is the modulus of the dislocation Berth vector; l is the average distance of dislocation motion.
Secondly, by combining the experimental rule and the analysis of the characteristics of grain boundary damage, the 'short plate effect' of the grain boundary defect on the grain boundary fatigue damage is provided:
where ρ isiThe total amount of dislocation products caused by grain boundaries in each cycle of loading; n is the sensitivity index of the material fatigue damage to the grain boundary defect, namely the degree reflecting the short plate effect; f is the linear density of grain boundary defects. The short plate effect is schematically shown in fig. 2.
Then, according to the idea that the dislocation plug volume causes fatigue damage accumulation and leads to failure fracture, a fatigue process based on the dislocation plug volume density is proposed: di＝1/Nf＝(ρi/ρc)β. Wherein D isiIs the average damage rate in each cycle of the loading cycle; rhocThe grain boundary dislocation packing density required for fatigue failure of the material, i.e. the fatigue damage dislocation density tolerance; beta is the fatigue damage dislocation density conversion rate.
Based on the dislocation plug product density related to the grain boundary orientation difference, the 'short plate effect' of the grain boundary fatigue damage and the fatigue process based on the dislocation plug product density, a reasonable and convenient fatigue deformation dislocation plug product model is deduced:
wherein the content of the first and second substances,
Nf＝107the maximum stress corresponding to the time is regarded as the fatigue strength σFSThe setting has engineering significance on the premise of meeting theoretical derivation. The corresponding relation between any grain boundary orientation difference and the fatigue performance (fatigue strength and fatigue life) of the bicrystal material under specific components and process conditions can be given through a basic expression of a dislocation plug product model.
The technical effect is as follows: the fatigue deformation dislocation plug product model is well matched with the experimental result. Although the fatigue deformation dislocation plug product model is derived based on the microscopic deformation mechanism, whether the model is scientific and practical or not must be verified through experiments. Compared with various fitting models provided in the past, the dislocation plug product model not only accurately gives the quantitative relation of orientation difference, components, process parameters and fatigue performance, but also predicts the fatigue range to span low cycle fatigue and high cycle fatigue and simultaneously shows the sensitivity of fatigue damage to grain boundary defects, so that the method has more advantages in the aspects of accuracy and applicability. In order to fully examine the effect of the model on predicting the fatigue performance of the material containing the grain boundary, a plurality of nickel-based superalloy DD10 test samples, nickel-based superalloy DD5 test samples and nickel-based superalloy DD5 blade test samples with different grain boundary orientation differences are selected and prepared. And respectively carrying out fatigue tests on the samples, predicting fatigue performance by using a dislocation plug product model, and finally comparing the test result with the prediction result, wherein the result is shown in figure 3. It can be seen that the experimental result is well matched with the prediction result of the fatigue deformation dislocation plug product model, the error between the predicted value and the measured value is small, and the sensitivity of fatigue damage to the orientation difference of the grain boundary or the defect of the grain boundary is also disclosed, so that the rationality of the model is verified, and the model can realize the accurate prediction of the fatigue strength and the fatigue life of the material containing the grain boundary.
(2) The technical effect is as follows: the nickel-based high-temperature fatigue performance of the material containing the grain boundary under the specific component & process is quantitatively predicted under different grain boundary orientation differences and different stresses. There are three parameters A, n and β in the fatigue deformation dislocation-plug product model, where a ═ Θ bl ρc，Θ、b、l、ρcN and beta are related to the material composition, which is quantitatively related to the process. Thus, the parameters A, n and β are intrinsic parameters determined by the process and A, n and β can be obtained computationally or experimentally for materials under different conditions. The relationship between the grain boundary orientation difference, stress and high temperature fatigue property under the specific component & process is shown in fig. 4. As can be seen, for the specific component & process, the orientation difference and the stress of the grain boundary are given, the corresponding high-temperature fatigue life can be predicted through the model, and the high-temperature fatigue strength corresponding to the orientation difference of the specific grain boundary can also be obtained through the change condition of the fatigue life and the stress.
Example 1:
the embodiment is the fatigue property prediction of the nickel-based high-temperature alloy DD5 containing the small-angle grain boundary, and the specific process is as follows:
(1) materials:
7-crystal boundary orientation difference nickel-based superalloy DD5 twins (the crystal boundary orientation difference is respectively set to be 0 degrees, 2 degrees, 4 degrees, 6 degrees, 8 degrees, 10 degrees and 12 degrees, the 0 degree twins are monocrystals, each preset orientation difference twins is prepared in a plurality of manners), and the preparation process comprises the following steps: seed crystal pairs are arranged according to the set orientation difference → directional solidification casting twins → three-stage aging heat treatment (1300 ℃/2h/AC +1120 ℃/4h/AC +1080 ℃/4h/AC +900 ℃/4 h/AC).
(2) The process comprises the following steps:
step 1: determining grain boundary orientation difference theta through microscopic experiments, selecting 7 groups of materials with large and reasonable grain boundary orientation difference (the grain boundary orientation difference is 0 degrees, 2.60 degrees, 4.92 degrees, 6.88 degrees, 8.49 degrees, 10.31 degrees and 13.23 degrees respectively), determining that the change rule of the grain boundary defect linear density f along with the grain boundary orientation difference is f ═ theta/21.64 to prepare uniform-size platy fatigue samples (the sample gauge length part has a diameter of 3mm and the gauge length section is 10mm), and then performing a high-temperature (980 ℃) stress fatigue experiment to obtain the fatigue life and the fatigue strength under the 7-group grain boundary orientation difference, wherein the fatigue life and the fatigue strength are shown in figure 5.
Step 2: and fitting key parameters. Fitting the fatigue strength data and the fatigue life data by respectively using a formula 1 and a formula 2 to obtain three important parameters: the strengthening coefficient A, the fatigue damage susceptibility index n to grain boundary defects and the fatigue damage dislocation density conversion rate beta are shown in FIG. 6.
And step 3: and predicting fatigue performance. And (3) predicting the fatigue performance of the current components and the rest states (rest grain boundary orientation difference) under the process condition according to the formula (1) and the formula (2) by utilizing the parameters obtained by fitting in the step (2), wherein the result is shown as a curve in fig. 7. Under the composition and the process conditions, by means of a fatigue damage position dislocation plug product model, the fatigue strength of the material can be predicted through the given grain boundary orientation difference, and the fatigue life of the material can be predicted through the given stress and the grain boundary orientation difference.
Claims (7)
1. A method for rapidly predicting high-temperature fatigue performance of a nickel-based superalloy small-angle grain boundary is characterized by comprising the following steps: the method is characterized in that fatigue experiments are carried out on different grain boundary orientation difference nickel-based high-temperature alloy twin-crystal materials prepared by the same process, and the fatigue performance of any grain boundary orientation difference nickel-based high-temperature alloy twin-crystal material prepared by other same processes is predicted according to the obtained experimental data.
2. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 1, wherein the method comprises the following steps: the method specifically comprises the following steps:
(1) selecting more than 3 groups of bicrystal materials prepared by the same process with different grain boundary orientation differences, and determining the change rule of the linear density of the grain boundary defects along with the orientation differences of the grain boundaries;
(2) testing the fatigue performance of the prepared material through a high-temperature fatigue test;
(3) obtaining key parameters (A, n and beta) of the prepared material by fitting fatigue strength/life data;
(4) and (4) according to the key parameters obtained in the step (4), utilizing a quantified bicrystal high-temperature fatigue strength/service life prediction model to carry out high-temperature fatigue performance prediction on the nickel-base superalloy bicrystal material prepared by other same processes under any grain boundary orientation difference.
3. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 2, wherein the method comprises the following steps: in the step (1), grain boundaries are observed through a microscopic experiment and grain boundary orientation difference is determined, the original morphology of twins, particularly grain boundary regions, is required to be maintained during observation (before deformation), the twins are gradually focused on the grain boundary regions from low power to high power during observation, and the twins are observed by using microscopic equipment with a grain boundary orientation analysis function.
4. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 2, wherein the method comprises the following steps: in the step (1), the same process refers to a preparation process in which the material components (element proportion) and process parameters are not changed in the preparation of the material; the different grain boundary orientation differences mean that the relative rotation angle between the same orientations of the seed crystals is changed in the preparation of the bicrystal material, so that the prepared bicrystal grain boundaries have different grain boundary orientation differences (the selection of a fatigue test sample needs to be carried out under the different grain boundary orientation differences of the same process, more than 3 bicrystal materials with grain boundary orientation differences smaller than 15 degrees and larger differences are selected to carry out the fatigue performance test of the step (2)); the density f of the grain boundary precipitation phase line is considered to be changed in direct proportion with the grain boundary orientation difference theta, the proportionality coefficient is 1/k, and the proportionality coefficient can be determined by fitting the change situation of grain boundary defects (micropores, carbides and the like) under different grain boundary orientation differences along with the orientation difference.
5. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 2, wherein the method comprises the following steps: in the step (3), the key parameters of the prepared material obtained by fitting the fatigue strength/life data are as follows: fitting a plurality of groups (more than 3 groups) of fatigue strength data acquired in the step (2) by using a formula (1) to obtain corresponding intrinsic parameters n and
substituting the value of n into a formula (2), and fitting a plurality of groups (more than 3 groups) of fatigue life data obtained in the step (2) by using the formula (2) to obtain a plurality of groups (more than 3 groups) of values of parameters A and beta, wherein the mean values of A and beta are intrinsic A values and beta values related to the twin crystal component;
wherein: sigmaFSThe fatigue strength is obtained;
theta is the work hardening rate, b is the mode of the dislocation Bohr vector, l is the mean distance of dislocation motion, ρcFor fatigue damage dislocation density tolerance, a can be defined as the material's strengthening coefficient; n is the susceptibility index of material fatigue damage to grain boundary defects; beta is the fatigue damage dislocation density conversion rate; sigmamaxIs the maximum stress of the fatigue test.
6. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 5, wherein the method comprises the following steps: in the step (4), the high-temperature fatigue strength/life prediction model of the twin crystal can be obtained quantitatively by obtaining the key parameters, namely the intrinsic parameters A, n and beta in the step (3) and substituting the parameters into the formulas (1) and (2), so that the high-temperature fatigue strength/life of any twin crystal material with poor grain boundary orientation under the same process condition of specific components can be predicted.
7. The method for rapidly predicting the high-temperature fatigue property of the nickel-based superalloy small-angle grain boundary according to claim 1, wherein the method comprises the following steps: the method is suitable for various face-centered cubic metal materials, wherein the metal materials are nickel-based high-temperature alloys, copper alloys or aluminum alloys, and the metal materials are suitable for one or more combinations of various rolling, pre-deformation and heat treatment processes.
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