A method for quantitatively analyzing high-temperature alloy creep mechanism based on subgrain boundaries

Abstract

The application relates to a method for quantitatively analyzing high-temperature alloy creep mechanism based on subgrain boundaries, which comprises the following steps: carrying out creep experiments at different temperatures or stresses, and quantifying subgrain boundary lengths before and after creep by using an EBSD technology; and combining a subgrain boundary length growth rate with a normalized ratio to distinguish the creep mechanism dominated by diffusion, grain boundary sliding or dislocation movement. Compared with the prior art, the method overcomes the limitation of traditional stress index dependence, and provides a scientific basis for high-temperature alloy service life prediction and structure design.

Description

Technical Field

[0001] The present invention relates to the field of materials science and structural integrity technology, in particular to the field of high-temperature alloy microstructure and performance research. Specifically, the present invention relates to a method for quantitatively analyzing the creep mechanism of high-temperature alloys based on subgrain boundaries, that is, a method for determining the creep mechanism of high-temperature alloys based on quantitative subgrain boundary analysis. Background Art

[0002] In the fields of materials science and structural integrity, especially in high-temperature structural applications, nickel-based superalloys are widely used in high-temperature extreme environments such as aerospace, energy, and chemical engineering due to their excellent high-temperature strength, creep resistance, and oxidation resistance. Creep is one of the main causes of component failure under high temperatures and sustained stress. Therefore, in-depth research on the creep mechanism of superalloys is of great theoretical and practical significance for optimizing material design and improving their service life.

[0003] Traditionally, the judgment of creep mechanism usually relies on the stress exponent n measured in creep experiments. Generally speaking, when n<3, the creep mechanism is dominated by grain boundary sliding; when n>3, it is dominated by dislocation movement. However, this method has significant limitations in practical applications, especially in advanced alloy materials involving precipitation phases. The delayed effect of precipitation phases often leads to a significant increase in the stress exponent n (such as n>9), which in turn leads to misjudgment. In addition, the linear extrapolation method proposed by Zhu et al. (Zhu, S., Nie, J., Gibson, M. et al. Microstructure and Creep Behavior of High-Pressure Die-Cast Magnesium Alloy AE44. Metall Mater Trans A2012, 43, 4137–4144) can be used to estimate the threshold stress σ th and true stress index n a , but due to the slight differences in fitting parameters, it cannot accurately reflect the true creep mechanism of the material.

[0004] The main defects of existing methods can be summarized as follows: 1) they rely on a single parameter, based only on the stress exponent or threshold stress, and ignore the influence of microstructural evolution on creep behavior; 2) they ignore the creep micromechanism and fail to include microstructural characteristics such as subgrain boundaries and dislocation density in the analysis scope; 3) they have limited applicability. For example, in precipitation-strengthened or grain-boundary-strengthened alloys, existing methods have difficulty in effectively identifying the creep mechanism.

[0005] Based on the above problems, the present invention proposes a new method based on quantitative analysis of microstructure to more comprehensively analyze the high-temperature creep behavior and its mechanism. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for quantitative analysis of the creep mechanism of high-temperature alloys based on subgrain boundaries. Through microstructural characterization and quantitative analysis, the three typical mechanisms of high-temperature creep - diffusion, grain boundary sliding and dislocation movement - can be accurately distinguished.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A first aspect of the present invention provides a method for quantitatively analyzing the creep mechanism of a high-temperature alloy based on subgrain boundaries, comprising the following steps:

[0009] (1) Under the condition close to the critical value of creep mechanism transformation, the creep test of the initial material is carried out by selecting isothermal stress variation or isothermal stress variation temperature to obtain the creep specimen;

[0010] (2) After the creep experiment is completed, the initial material and creep specimen are prepared separately, and the microstructures of the initial material and creep specimen are characterized by electron backscatter diffraction (EBSD) technology to obtain EBSD data;

[0011] (3) EBSD data were processed using MATLAB or Python programs to extract and calculate the length of the small-angle grain boundaries (i.e., subgrain boundaries) from 2° to 10° for the initial material and the creep specimen, which was the total length of the subgrain boundaries;

[0012] (4) Divide the total length of the subgrain boundary by the area of ​​the characterization region to obtain the subgrain boundary length per unit area;

[0013] (5) Calculate the growth rate R and normalized ratio Q of subgrain boundary length per unit area;

[0014] (6) Based on the calculated R and Q values, the creep mechanism is determined according to the judgment criteria.

[0015] Furthermore, in step (1), when determining the creep experimental conditions, it is necessary to ensure that the selected creep experimental conditions cover the transition range of the creep mechanism, and the creep experimental conditions include the condition range corresponding to the diffusion mechanism, grain boundary sliding mechanism and dislocation movement mechanism.

[0016] Furthermore, in the step (2), the characterization area of ​​the electron backscatter diffraction technique (EBSD) is the sample gauge section of the initial material or the sample gauge section of the creep sample parallel to the tensile direction.

[0017] Further, in the step (2), the last step is to use vibration polishing or electrolytic polishing to remove the residual stress on the surface of the sample; the vibration polishing time is 0.5h-3h, and the electrolytic polishing time is 0.5h, and the resolution rate is ensured to be more than 95%.

[0018] Further, in the step (3), the extracted sub-grain boundary range is 2-10°, and the length per unit area is calculated.

[0019] Further, in the step (5), the growth rate R of the sub-grain boundary length per unit area is calculated according to the following formula:

[0020]

[0021] Wherein, L1 is the sub-grain boundary length per unit area in the creep material after creep, and L2 is the sub-grain boundary length per unit area in the initial material.

[0022] Further, in the step (5), the calculation formula of the normalized ratio Q is:

[0023]

[0024] Wherein, L1 is the sub-grain boundary length per unit area in the creep material after creep, and L2 is the sub-grain boundary length per unit area in the initial material, and ε is the corresponding creep strain after each creep experiment (creep experiment under different temperature and stress conditions).

[0025] Further, the creep mechanism determination criterion in the step (6) is:

[0026] When the growth rate R of the sub-grain boundary length per unit area is less than or equal to 1.1, the creep is dominated by the diffusion mechanism;

[0027] When 1.1<R and Q≤0.001, the creep is dominated by the grain boundary sliding mechanism;

[0028] When 1.1<R and Q>0.001, the creep is dominated by the dislocation motion mechanism;

[0029] Further, the sub-grain boundary length per unit area refers to the total length of the sub-grain boundary in the EBSD observation area divided by the total area of the EBSD observation area.

[0030] Further, the creep experiment is a high-temperature creep experiment, and the optional conditions of the high-temperature creep experiment are: temperature is 700-1000℃, and stress is 50-120MPa.

[0031] Further, the creep occurs under tension.

[0032] Further, the method comprises the following steps:

[0033] (1) The alloy material is processed into a sample size that meets the requirements of the creep experiment according to the experimental standard specification (such as ASTM E139-2018, GB / T 2039-2024 or ISO204:2023, etc.), and the creep experiment is carried out at the same temperature and different stresses or the same stress and different temperatures. After the experiment, the sample is taken in the sample gauge section using a wire cutting method, the initial material and the creep sample are taken as the sampling object, and mechanical polishing and electrolytic polishing treatment are performed on the obtained sample to ensure that the surface quality meets the characterization requirements. Subsequently, EBSD microstructure characterization is performed at a position parallel to the tensile direction.

[0034] (2) The EBSD data is processed using Matlab or Python language, and the subgrain boundary length of 2-10° (small angle grain boundary) is extracted and calculated. The subgrain boundary length is divided by the area of the entire characterization region to obtain the subgrain boundary length per unit area; the growth rate R and the normalized ratio Q of the subgrain boundary length per unit area are calculated based on the experimental data, and the specific calculation formula is:

[0035] Growth rate R:

[0036]

[0037] Wherein, L1 is the subgrain boundary length per unit area in the creep material after creep, and L2 is the subgrain boundary length per unit area in the initial material.

[0038] Normalized ratio Q:

[0039]

[0040] Wherein L1 is the subgrain boundary length per unit area in the creep material after creep, L2 is the subgrain boundary length per unit area in the initial material, and ε is the corresponding creep strain (i.e. the creep strain under the corresponding experimental conditions).

[0041] (3) According to the calculated R and Q values, the creep mechanism is determined according to the following criteria:

[0042] When the growth rate R of the subgrain boundary length per unit area is ≤1.1, the creep is dominated by the diffusion mechanism;

[0043] When 1.1 < R and Q ≤ 0.001, the creep is dominated by the grain boundary sliding mechanism;

[0044] When 1.1 < R and Q > 0.001, the creep is dominated by the dislocation motion mechanism.

[0045] The second aspect of the present application provides a computer program product, comprising a computer program which, when executed by a processor, implements the method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries.

[0046] Furthermore, the calculation of subgrain boundary length is automatically implemented through Matlab or Python programming to ensure the accuracy and efficiency of data processing. EBSD data can be automatically processed and the subgrain boundary growth rate R and normalized ratio Q can be calculated.

[0047] The third aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries is implemented.

[0048] Furthermore, the storage medium may be an electronic medium, a magnetic medium, an optical medium, an electromagnetic medium, an infrared medium, or a semiconductor system or a propagation medium. The storage medium may also include semiconductor or solid-state memory, magnetic tape, a removable computer disk, a random access memory (RAM), a read-only memory (ROM), a hard disk, and an optical disk. Optical disks may include compact disk-read only memory (CD-ROM), compact disk-read-write (CD-RW), and DVD.

[0049] Compared with the prior art, the present invention has the following technical advantages:

[0050] 1) From the perspective of microstructure, by quantifying the changes in subgrain boundaries, the three creep mechanisms of diffusion creep, grain boundary sliding, and dislocation motion are accurately distinguished, which has clear physical significance;

[0051] 2) Compared with the traditional method of judging the creep mechanism based solely on the minimum creep rate, the present invention introduces quantitative parameters such as the growth rate and normalized ratio of subgrain boundaries to comprehensively reveal the relationship between creep strain and subgrain boundary length, avoiding the limitations of traditional methods and providing a more scientific, systematic, and accurate analysis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flow chart of the method for determining the creep mechanism of precipitation phase alloys based on the number of subgrain boundaries of the present invention.

[0053] Figure 2 This is a diagram of the initial dimensions of the creep specimen before the creep test in the embodiment.

[0054] Figure 3 A schematic diagram of the stress index of the nickel-based high-temperature alloy at 800°C and 850°C in the embodiment is shown, wherein the horizontal axis Stress is stress and the vertical axis Minimum creep rate is the minimum creep rate.

[0055] Figure 4 Schematic diagrams of threshold stresses calculated for a hypothetical creep mechanism at different temperatures for a nickel-based high-temperature alloy in an embodiment are shown, where (a) is n′=3 and (b) is n′=5. DETAILED DESCRIPTION

[0056] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0057] This invention relates to a method for quantitatively analyzing the creep mechanisms of high-temperature alloys based on subgrain boundaries. By conducting creep experiments at different temperatures or stresses and quantifying the subgrain boundary lengths before and after creep using EBSD, the method, combining the subgrain boundary length growth rate with the normalized ratio, can distinguish creep mechanisms dominated by diffusion, grain boundary sliding, or dislocation motion. Compared with existing techniques, this method overcomes the limitations of traditional methods that rely on stress exponents, providing a scientific basis for service life prediction and structural design of high-temperature alloys.

[0058] During specific implementation, the technical solution adopted by the present invention is:

[0059] The present invention provides a method for quantitatively analyzing the creep mechanism of a high-temperature alloy based on subgrain boundaries, the method comprising the following steps:

[0060] (1) The alloy material is processed into specimens of the size required for creep testing according to experimental standards (such as ASTM E139-2018, GB / T 2039-2024, or ISO 204:2023). Creep tests are performed at the same temperature and different stresses, or at the same stress and different temperatures. After the experiment, samples are taken from the specimen gauge section using a wire cutting method. The sampling objects are the initial material and the creep specimen. The obtained samples are mechanically polished and electrolytically polished to ensure that the surface quality meets the characterization requirements. Subsequently, EBSD microstructure characterization is performed at a position parallel to the tensile direction.

[0061] (2) EBSD data were processed using Matlab or Python to extract and calculate the length of subgrain boundaries with misorientation angles of 2 to 10° (low-angle grain boundaries). The subgrain boundary length was divided by the area of ​​the entire characterization region to obtain the subgrain boundary length per unit area. The growth rate R and normalized ratio Q of the subgrain boundary length per unit area were calculated based on the experimental data. The specific calculation formula is:

[0062] Growth rate R:

[0063]

[0064] Wherein, L1 is the subgrain boundary length per unit area in the creep material after creep, and L2 is the subgrain boundary length per unit area in the initial material.

[0065] Normalized ratio Q:

[0066]

[0067] Where L1 is the subgrain boundary length per unit area in the creep material after creep, L2 is the subgrain boundary length per unit area in the initial material, and ε is the corresponding creep strain (i.e., the creep strain under the corresponding experimental conditions).

[0068] (3) Based on the calculated R and Q values, the creep mechanism is determined according to the following criteria:

[0069] When the growth rate of subgrain boundary length per unit area R≤1.1, creep is dominated by the diffusion mechanism;

[0070] When 1.1 <R且Q≤0.001时,蠕变由晶界滑动机制主导;

[0071] When 1.1<R且Q> When 0.001, creep is dominated by the dislocation motion mechanism.

[0072] In the following examples, the initial material (initial sample) used is a precipitation-strengthened nickel-based high-temperature alloy, the composition of which is shown in Table 1 below in terms of mass percentage:

[0073] Table 1 shows the chemical composition (wt.%) of the main elements of the precipitation-strengthened nickel-based alloys in the examples.

[0074]

[0075] Example

[0076] This embodiment provides a method for quantitatively analyzing the creep mechanism of a high-temperature alloy based on subgrain boundaries. The specific steps are as follows:

[0077] (1) EBSD characterization of high-temperature creep specimens

[0078] The initial materials were divided into two groups: one group underwent high-temperature creep testing according to ASTM E139-2018, and the other group was directly subjected to microstructural characterization. The high-temperature creep test conditions were as follows: at 800°C, three stresses of 90 MPa, 100 MPa, and 115 MPa were set, corresponding to creep times of 1000 hours, 800 hours, and 600 hours, respectively. At 850°C, four further stresses of 60 MPa, 65 MPa, 75 MPa, and 85 MPa were set, corresponding to creep times of 1200 hours, 1000 hours, 600 hours, and 400 hours, respectively. All specimens were continuously loaded and monitored during the creep tests, yielding creep specimens corresponding to each creep condition. After the creep tests, the specimens (creep specimens, initial materials) were split along the middle. The observation surfaces of the specimens were first polished using 400#, 800#, and 1200# sandpaper, sequentially, to remove surface wire cutting marks and oxide scale until the surface exhibited a matte finish. The sample was then further polished to a mirror finish using a 0.05μm SiO2 suspension and a polishing cloth, followed by vibratory polishing for four hours using a 0.03μm SiO2 suspension. Following vibratory polishing, the sample was ultrasonically cleaned with anhydrous ethanol to remove residual polishing fluid and other impurities. Characterization was performed using a field-emission scanning electron microscope (SEM) equipped with a highly sensitive EBSD detector.

[0079] (2) Extracting subgrain boundary data

[0080] MATLAB software was used to process the EBSD data under different experimental conditions, and the subgrain boundary lengths with misorientation angles of 2 to 10° (small-angle grain boundaries) were extracted and calculated. The subgrain boundary lengths were divided by the area of ​​the entire characterization region to obtain the subgrain boundary length per unit area.

[0081] (3) Calculate R and Q to obtain the creep mechanism at each temperature. The results are shown in Table 2.

[0082] Table 2 is a creep mechanism analysis table of the high-temperature alloy based on the growth rate R and the normalized ratio Q of the embodiment.

[0083]

[0084] Calculated using traditional methods, traditionally, the judgment of creep mechanism usually relies on the stress exponent n measured in creep experiments. Generally speaking, when n<3, the creep mechanism is dominated by grain boundary sliding; when n>3, it is dominated by dislocation movement. The stress exponent n at the two sets of temperatures in the embodiment is greater than 9. The threshold stress under different temperature conditions is estimated by linear extrapolation. The specific steps are to draw The relationship curve with σ, where is the minimum creep rate, and n′ is a hypothetical stress exponent that covers all possible creep mechanisms. The threshold stress is obtained by linearly extrapolating the data to zero, i.e., the intersection of the fitted curve and the x-axis. The results show that as n′ increases, the threshold stress gradually decreases, while the R² value decreases slightly, but no clear trend is formed. Furthermore, all R² values ​​of the linear fits are close to 1, with subtle differences that are insufficient to rigorously determine the stress exponent and the creep mechanism it reflects, as shown in Table 3.

[0085] Table 3 shows the correlation coefficients of threshold stress fitting under different stress indices in the embodiment.

[0086]

[0087]

[0088] The above describes the embodiments of the method of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any parameter changes or calculation simplifications made according to the principles of the technical solution of the present invention, as long as they meet the purpose of the invention and do not deviate from the principles and concepts of the present invention, a method for quantitative analysis of the creep mechanism of high-temperature alloys based on subgrain boundaries, shall fall within the scope of protection of the present invention.

[0089] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for quantitatively analyzing the creep mechanism of high-temperature alloys based on subgrain boundaries, characterized in that: The following steps are involved: (1) Under the condition close to the critical value of creep mechanism transformation, the creep test of the initial material is carried out by selecting isothermal stress variation or isothermal stress variation temperature to obtain the creep specimen; (2) After the creep experiment is completed, the initial material and creep specimens are prepared separately, and the microstructures of the initial material and creep specimens are characterized by backscattered electron diffraction technology to obtain EBSD data; (3) Processing EBSD data, extracting and calculating the length of the small-angle grain boundaries of 2° to 10° of the initial material and creep specimen, which is the total length of the subgrain boundaries; (4) Divide the total length of the subgrain boundary by the area of ​​the characterization region to obtain the subgrain boundary length per unit area; (5) Calculate the growth rate of subgrain boundary length per unit area and normalized ratio ; (6) According to the calculation and value, and determine the creep mechanism according to the judgment criteria; In step (5), the growth rate of subgrain boundary length per unit area is The calculation formula is: ， in, is the subgrain boundary length per unit area in the creep material after creep, is the subgrain boundary length per unit area in the initial material; In step (5), the normalized ratio The calculation formula is: ， in, is the subgrain boundary length per unit area in the creep material after creep, is the subgrain boundary length per unit area in the initial material, is the corresponding creep strain after the creep experiment is completed; The creep mechanism determination criteria in step (6) are: When the growth rate of subgrain boundary length per unit area When , creep is dominated by diffusion mechanism; when and When , creep is dominated by the grain boundary sliding mechanism; when and When , creep is dominated by the dislocation motion mechanism.

2. The method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries according to claim 1, characterized in that: In the step (1), when determining the creep experimental conditions, it is ensured that the selected creep experimental conditions cover the transition range of the creep mechanism, and the creep experimental conditions include the condition range corresponding to the diffusion mechanism, the grain boundary sliding mechanism and the dislocation movement mechanism.

3. The method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries according to claim 1, characterized in that: In the step (2), the characterization area of ​​the backscattered electron diffraction technique is the sample gauge section of the initial material or the sample gauge section of the creep sample parallel to the tensile direction.

4. The method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries according to claim 1, characterized in that: In step (2), during sample preparation, the last step is to use vibration polishing or electrolytic polishing to remove residual stress on the sample surface; the vibration polishing time is 0.5 ~3 , electrolytic polishing for 0.5h, and ensure that the resolution rate reaches more than 95%.

5. The method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries according to claim 1, characterized in that: In step (3), EBSD data are processed using MATLAB or Python programs.

6. The method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries according to claim 1, characterized in that: The subgrain boundary length per unit area refers to the total length of subgrain boundaries in the EBSD characterization experimental area divided by the total area of ​​the characterization area.

7. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the method for determining the creep mechanism of a high-temperature alloy based on the number of subgrain boundaries as claimed in any one of claims 1 to 6 is implemented.

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