A method for characterizing microstructural evolution of single crystal superalloys

Abstract

The present application belongs to the technical field of single crystal superalloy, and particularly relates to a characterization method of microstructure evolution of single crystal superalloy. The present application provides a characterization method of microstructure evolution of single crystal superalloy. The original microstructure of the single crystal superalloy with crystal orientation of [111] after standard heat treatment presents a connected triangle (equilateral triangle or near equilateral triangle) distribution of gamma channel, and with the proceeding of creep test, the original microstructure after standard heat treatment presents a discontinuous gamma channel with triangle, thereby leading to a decrease in the number of intersection points under equidistant straight lines. The present application determines the evolution degree of alloy microstructure by a microstructure evolution index Q of the ratio of the number of intersection points under different test times to the number of intersection points of the original microstructure. The method provided by the present application can effectively quantitatively characterize the microstructure evolution of Ni-based or Ni3Al-based single crystal superalloy with [111] orientation, has good scientific research application value, and provides certain guidance for subsequent related research in the field.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal superalloy technology, and specifically relates to a characterization method for the microstructure evolution of single-crystal superalloys. Background Technology

[0002] Ni-based single-crystal superalloys typically consist of two phases, γ and γ′, with an L12-type crystal structure. After standard heat treatment, a square γ′ phase and white γ phase channels along the

[001] direction can be observed under a scanning electron microscope. During high-temperature mechanical testing, the two-phase structure evolves as the test progresses. The degree of evolution of the two-phase structure can predict the failure of the alloy to a certain extent. Therefore, the microstructure evolution is an important indicator for studying the mechanical properties of single-crystal superalloys. Currently, research mainly focuses on single-crystal superalloys with the

[001] orientation. Alloys with this orientation exhibit significant microstructure changes during high-temperature creep testing in the initial stage, steady-state stage, and before fracture leading to failure. Especially in the service stage (usually the steady-state stage), which is of most concern in industry, there is a clear rafting microstructure evolution. This rafting microstructure has a relatively regular morphology, and there are many characterization methods for this rafting microstructure in the literature. Through different characterizations, the state of the alloy can be easily inferred. However, with the development of single-crystal alloy materials, single-crystal superalloys with other orientations have also appeared in industrial applications. Unlike

[001] oriented single-crystal superalloys, other oriented single-crystal superalloys do not necessarily exhibit a relatively regular raft structure in each stage of the creep process. These structures are disordered and difficult to characterize using existing characterization methods for the evolution of

[001] oriented structures.

[0003] Currently, there is no clear characterization method for the microstructure of

[111] oriented single-crystal superalloys. Summary of the Invention

[0004] The purpose of this invention is to provide a characterization method for the microstructure evolution of single-crystal superalloys. The method provided by this invention can effectively and quantitatively characterize the microstructure evolution of Ni-based or Ni3Al-based single-crystal superalloys with

[111] orientation, which has good scientific research application value and provides certain guidance for subsequent related research in the field.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for characterizing the microstructure evolution of a single-crystal superalloy, wherein the phase structure of the single-crystal superalloy includes a γ′ phase and γ phase channels along the γ′ phase, comprising the following steps:

[0007] (1) The test bar is subjected to standard heat treatment to obtain a heat-treated test bar, wherein the crystal orientation of the test bar along the axial direction deviates from the

[111] direction by <5°;

[0008] (2) A raw metallographic sample is prepared by taking samples from the heat-treated test bar. The γ-phase channels in the raw metallographic sample exhibit a state of several interconnected triangles, which are equilateral triangles or near-equilateral triangles. The raw microstructure image of the raw metallographic sample is obtained. Any region of the raw microstructure image is selected and named the first region. The contour line of any side of the triangles formed by the γ-phase channels in the first region is obtained, and the average value S of the contour line is obtained. Several first straight lines parallel to any side of the triangles are drawn in the first region, and the distance L between adjacent first straight lines is less than the average value S of the contour line. The total number of intersections between the first straight lines drawn in the first region and the γ-phase channels is counted and named N. y When the first straight line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0009] (3) Machining the remaining heat-treated test bar from step (2) into a creep specimen, performing a creep experiment on the creep specimen to obtain a creep sample, preparing the obtained creep sample to obtain a creep metallographic sample; obtaining a creep structure image of the creep metallographic sample; selecting any region with the same shape and size as the first region in step (2) from the creep structure image, naming it the second region, and drawing several second straight lines with the same side length as the triangle in step (2) within the second region, with the spacing between adjacent second straight lines being equal to the spacing between adjacent first straight lines; counting the total number of intersections between the second straight lines drawn within the second region and the γ phase channel, naming it N. z When the second line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0010] (4) Calculate the microstructure evolution index Q of the single-crystal superalloy. The formula for calculating the microstructure evolution index Q is shown in Equation 1:

[0011] Organizational evolution index Q = N z / N y Formula 1;

[0012] When the microstructure evolution index Q = 1, it indicates that the microstructure of the single-crystal high-temperature alloy has not evolved; when the microstructure evolution index Q < 1, it indicates that the microstructure of the single-crystal high-temperature alloy has evolved. The smaller the microstructure evolution index Q, the greater the degree of microstructure evolution of the single-crystal high-temperature alloy, and the closer the single-crystal high-temperature alloy is to the failure state.

[0013] Preferably, in step (2): the distance L between adjacent first straight lines is 0.5 times the average value S of the contour lines.

[0014] Preferably, in steps (2) and (3), a scanning electron microscope is used to obtain the original tissue image of the original metallographic sample or the creep tissue image of the creep metallographic sample; the magnification of the scanning electron microscope is 15,000 times.

[0015] Preferably, in step (2), the contour lines are obtained using computer software, including ImageJ software.

[0016] Preferably, in step (2), after selecting the first region and before obtaining the contour lines of the first region, the method further includes: color processing of the first region;

[0017] In step (3), after selecting the second region and before drawing the second straight line within the second region, the method further includes: color processing of the second region;

[0018] In step (2) or step (3), the color processing is performed using computer software, including ImageJ software or Photoshop software.

[0019] Preferably, the creep sample includes one or more of the following: a creep initial stage sample, a creep steady-state stage sample, or a creep fracture sample.

[0020] Preferably, the creep test is performed in accordance with GB / T 2039-2012.

[0021] Preferably, the single-crystal superalloy is a Ni-based single-crystal superalloy or a Ni3Al-based single-crystal superalloy.

[0022] Preferably, the grades of the single-crystal high-temperature alloy include IC21, DD6, DD5 or CMSX-4.

[0023] Preferably, the first region is square in shape and has a size of 10μm × 10μm;

[0024] The shape of the creep specimen may be rod-shaped or plate-shaped.

[0025] This invention provides a method for characterizing the microstructure evolution of single-crystal superalloys. In this invention, for single-crystal superalloys with a crystal orientation of

[111] , the γ channels in the original microstructure after standard heat treatment exhibit a connected triangular distribution, where the triangles are equilateral triangles or near-equilateral triangles (e.g., ...). Figure 2 (Left image in the image) As the creep test progresses, the triangularly connected γ channels in the original tissue after standard heat treatment begin to break down, resulting in a decrease in the number of intersections under equally spaced straight lines. As the creep test continues, the connectivity of the γ channels further decreases (e.g., ...). Figure 2(See the right figure in the image). This invention determines the degree of alloy microstructure evolution by comparing the ratio of the number of intersection points at different testing times to the number of intersection points in the original microstructure. Considering the difference in the side length of each γ′ phase, this invention, for better quantitative characterization of the microstructure, draws several straight lines parallel to any row in the triangle (i.e., a certain γ channel). The distance L between the lines is less than the contour line S of the triangle, thus ensuring that a sufficient number of intersection points can be counted, ensuring the accuracy of the characterization results. This invention counts the number of intersection points between the drawn lines and the γ channel. When a line is parallel to the γ channel, it is recorded as 0. The average number of intersection points within the region is recorded as N. y Then, the same calculation method was used to obtain the number of intersection points in the tissues from the creep test interruption and fracture test, denoted as N. z The ratio of the two is defined as the microstructure evolution index Q. When the microstructure evolution index Q = 1, it means that no microstructure has evolved. When the microstructure evolution index Q < 1, it indicates that the alloy microstructure has evolved. The smaller the microstructure evolution index Q, the worse the connectivity of the γ channels, the greater the degree of evolution, and the closer the alloy is to the failure state.

[0026] In summary, this invention uses metallographic methods and point counting methods to quantitatively characterize the microstructure evolution of irregular Ni-based or Ni3Al-based single-crystal superalloys with

[111] orientation. Through the statistical methods and formulas of this invention, the microstructure evolution index Q value defined by the invention can effectively quantitatively characterize the microstructure evolution of

[111] -specific orientation samples that are difficult to characterize in current single-crystal superalloy research. The characterization method has been verified through examples. The results show that the quantitative characterization method provided by this invention has good scientific research application value and provides certain guidance for subsequent related research in the field. Attached Figure Description

[0027] Figure 1 A flowchart of the characterization method for the microstructure evolution of single-crystal superalloys provided by the present invention;

[0028] Figure 2 A schematic diagram illustrating the principle of the characterization method for the microstructure evolution of single-crystal high-temperature alloys provided by this invention;

[0029] Figure 3 This is the original microstructure and statistical data of the orientation single crystal test rod after standard heat treatment in

[111] embodiment of the present invention;

[0030] Figure 4 The above are test curves of creep tests on two sizes of creep samples prepared using single crystal rods in this embodiment of the invention.

[0031] Figure 5 In this embodiment of the invention, creep interruption tests were performed on sample 1 in the initial creep stage and the steady-state stage, respectively. The microstructure of the alloy in the

[111] direction after the interruption test and creep fracture was scanned and observed, and the results were statistically analyzed.

[0032] Figure 6 In this embodiment of the invention, creep interruption tests were performed on sample 2 in the initial creep stage and the steady-state stage, respectively. The microstructure of the alloy in the

[111] direction after the interruption test and creep fracture was scanned and observed, and the results were statistically analyzed.

[0033] Figure 7 This is a schematic diagram showing the dimensions of sample 1 and sample 2 in an embodiment of the present invention. Detailed Implementation

[0034] This invention provides a method for characterizing the microstructure evolution of a single-crystal superalloy, wherein the phase structure of the single-crystal superalloy includes a γ′ phase and γ phase channels along the γ′ phase, comprising the following steps:

[0035] (1) The test bar is subjected to standard heat treatment to obtain a heat-treated test bar, wherein the crystal orientation of the test bar along the axial direction deviates from the

[111] direction by <5°;

[0036] (2) A raw metallographic sample is prepared by taking samples from the heat-treated test bar. The γ-phase channels in the raw metallographic sample exhibit a state of several interconnected triangles, which are equilateral triangles or near-equilateral triangles. The raw microstructure image of the raw metallographic sample is obtained. Any region of the raw microstructure image is selected and named the first region. The contour line of any side of the triangles formed by the γ-phase channels in the first region is obtained, and the average value S of the contour line is obtained. Several first straight lines parallel to any side of the triangles are drawn in the first region, and the distance L between adjacent first straight lines is less than the average value S of the contour line. The total number of intersections between the first straight lines drawn in the first region and the γ-phase channels is counted and named N. y When the first straight line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0037] (3) Machining the remaining heat-treated test bar from step (2) into a creep specimen, performing a creep experiment on the creep specimen to obtain a creep sample, preparing the obtained creep sample to obtain a creep metallographic sample; obtaining a creep structure image of the creep metallographic sample; selecting any region in the creep structure image that has the same shape and size as the first region in step (2), naming it the second region, and drawing several second straight lines with the same side length parallel to the triangle in step (2) within the second region, with the spacing between adjacent second straight lines being equal to the spacing between adjacent first straight lines; counting the total number of intersections between the second straight lines drawn within the second region and the γ-phase channel, naming it N. z When the second line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0038] (4) Calculate the microstructure evolution index Q of the single-crystal superalloy. The formula for calculating the microstructure evolution index Q is shown in Equation 1:

[0039] Organizational evolution index Q = N z / N y Formula 1;

[0040] When the microstructure evolution index Q = 1, it indicates that the microstructure of the single-crystal high-temperature alloy has not evolved; when the microstructure evolution index Q < 1, it indicates that the microstructure of the single-crystal high-temperature alloy has evolved. The smaller the microstructure evolution index Q, the greater the degree of microstructure evolution of the single-crystal high-temperature alloy, and the closer the single-crystal high-temperature alloy is to the failure state.

[0041] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0042] Figure 1 The following is a flowchart illustrating the implementation of a characterization method for the microstructure evolution of single-crystal superalloys provided by this invention, in conjunction with... Figure 1 The method for characterizing tissue evolution provided by the present invention will be described in detail.

[0043] This invention involves subjecting a test bar to standard heat treatment to obtain a heat-treated test bar, wherein the crystal orientation of the test bar along the axial direction deviates from the

[111] direction by <5°. In this invention, the single-crystal superalloy is a Ni-based single-crystal superalloy or a Ni3Al-based single-crystal superalloy. The preferred grades of the single-crystal superalloy include IC21, DD6, DD5, or CMSX-4. In this invention, the γ-phase channels in the phase structure of a perfectly

[111] -oriented single-crystal superalloy exhibit several equilateral triangular interconnected states. In actual production, when the crystal orientation deviates from the

[111] direction by <5° (and is not 0°), the γ-phase channels in the phase structure of an imperfectly

[111] -oriented single-crystal superalloy exhibit several near-equilateral triangular interconnected states.

[0044] Before the standard heat treatment, the present invention preferably pre-treats the test bars, which preferably includes the following steps: selecting multiple

[111] oriented single-crystal alloy test bars without surface impurity defects; etching the

[111] oriented single-crystal alloy test bars until surface oxide scale and other impurities are removed, revealing a bright metallic luster; then using X-ray backscattering Laue method to perform crystal orientation testing along the test bar axis, selecting a test bar whose main orientation deviates from the

[111] direction by less than 5°. In the present invention, the etching treatment is preferably selected according to the specific alloy grade. In a specific embodiment of the present invention, hydrochloric acid-hydrogen peroxide etching solution is used for the etching treatment.

[0045] This invention does not specify any particular implementation method for the standard heat treatment; any standard heat treatment method well-known to those skilled in the art can be selected based on the grade of the test bar. In a specific embodiment of this invention, the preferred implementation method for the standard heat treatment is: 1300℃, 2h / 1310℃, 2h / 1320℃, 2h / 1325℃, 4h / 1330℃, 6h / argon gas cooling / 1020℃, 6h / argon gas cooling / 870℃, 25h / furnace cooling.

[0046] After obtaining the heat-treated test bar, the present invention prepares a raw metallographic sample by sampling from the heat-treated test bar. The γ-phase channels in the raw metallographic sample exhibit a connected state of several triangles, which are equilateral triangles or near-equilateral triangles. The present invention obtains a raw microstructure image of the raw metallographic sample, selects an arbitrary region of the raw microstructure image, and names it the first region. The present invention obtains the contour line of any side of the triangles formed by the γ-phase channels within the first region, and obtains the average contour line value S. Several first straight lines parallel to any side of the triangles are drawn within the first region, with the distance L between adjacent first straight lines being less than the average contour line value S. The total number of intersections between the first straight lines and the γ-phase channels within the first region is counted and named N. y When the first straight line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0047] This invention does not specify a particular method for preparing the original metallographic sample; any metallographic sample preparation method well-known to those skilled in the art can be used. In a specific embodiment of this invention, the method for preparing the original metallographic sample includes the following steps: mounting the sample obtained from sampling with resin to form a sample to be characterized, wherein the sample to be characterized after mounting exposes the

[111] crystal face; the mounting preferably includes hot mounting or cold mounting; and sequentially grinding, polishing, and etching the exposed

[111] crystal face with sandpaper to obtain the original metallographic sample. The grinding is preferably performed sequentially using 400#, 600#, 800#, 1000#, 1200#, 1500#, 2000#, and 3000# sandpaper. The surface of the

[111] crystal face after grinding is preferably free of obvious scratches. The polishing agent used for polishing preferably has a particle size of 0.5 nm. The etching solution used for etching is preferably prepared from CuSO4, 100 mL HCl, and 100 mL C2H5OH. The concentration of the etching solution is determined based on the alloy grade. The etching time is preferably ~10 seconds, until a white mist appears on the surface.

[0048] This invention preferably uses a scanning electron microscope (SEM) to obtain the original tissue image of the original metallographic sample, wherein the SEM has a magnification of 15,000x. The first region is square in shape, with dimensions of 10μm × 10μm. After selecting the first region, this invention preferably also includes color processing of the first region, which is performed using computer software, preferably ImageJ or Photoshop. In this invention, the contour lines are preferably obtained using computer software, preferably ImageJ. The spacing L between adjacent first straight lines is preferably 0.5 times the average contour line value S. The statistical method is preferably manual point counting.

[0049] This invention involves machining remaining heat-treated test bars into creep specimens, subjecting the creep specimens to creep experiments to obtain creep samples, and preparing creep metallographic samples. Creep microstructure images of the creep metallographic samples are then obtained. An arbitrary region with the same shape and size as the first region in the above steps is selected from the creep microstructure image and named the second region. Within the second region, several second straight lines with the same side length as the triangles in the above steps are drawn, with the spacing between adjacent second straight lines equal to the spacing between adjacent first straight lines. The total number of intersections between the second straight lines and the γ-phase channel within the second region is counted and named N. z When the second line is parallel to the γ channel, the number of intersection points is recorded as 0.

[0050] In this invention, the shape of the creep specimen preferably includes a rod or plate shape. The creep test is carried out according to GB / T2039-2012. In a specific embodiment of this invention, the temperature of the creep test is preferably 1100℃, and the stress is preferably 160MPa. The creep sample preferably includes one or more of the following: a creep initial stage sample, a creep steady-state stage sample, or a creep fractured sample. In this invention, the creep test is interrupted and fractured during the creep initial stage, creep steady-state stage, and creep fractured stage of the creep specimen to obtain creep initial stage samples, creep steady-state stage samples, or creep fractured samples, respectively. In this invention, the preparation method of the creep metallographic sample is preferably the same as the preparation method of the original metallographic sample, and will not be repeated here. This invention preferably uses a scanning electron microscope to obtain the creep structure image of the creep metallographic sample. The magnification of the scanning electron microscope is 15000x. The second region is square in shape and has a size of 10μm×10μm. After selecting the second region, the present invention preferably further includes color processing of the second region, wherein the color processing is performed using computer software, preferably ImageJ or Photoshop. The statistical method is preferably manual counting.

[0051] Get N y and Nz Subsequently, the present invention calculates the microstructure evolution index Q of the single-crystal superalloy, and the formula for calculating the microstructure evolution index Q is shown in Equation 1:

[0052] Organizational evolution index Q = N z / N y Formula 1;

[0053] When the microstructure evolution index Q = 1, it indicates that the microstructure of the single-crystal high-temperature alloy has not evolved; when the microstructure evolution index Q < 1, it indicates that the microstructure of the single-crystal high-temperature alloy has evolved. The smaller the microstructure evolution index Q, the greater the degree of microstructure evolution of the single-crystal high-temperature alloy, and the closer the single-crystal high-temperature alloy is to the failure state.

[0054] The method for characterizing the microstructure evolution of a single-crystal superalloy provided by the present invention preferably includes the following steps:

[0055] S1. Select multiple

[111] oriented single crystal alloy test rods without surface impurity defects, perform corrosion, and observe that the surface oxide scale and other impurities have been removed, revealing a bright metallic luster.

[0056] S2. The crystal orientation test was performed along the axis of multiple test rods after corrosion in step S1 using the X-ray backscattering Laue method. One test rod whose main orientation deviated from the

[111] direction by less than 5° was selected.

[0057] S3. Perform standard heat treatment on the test bar selected in step S2 whose main direction deviates from the

[111] direction by less than 5° to obtain the heat-treated test bar.

[0058] S4. Take a small piece of alloy sample from the test bar that has undergone standard heat treatment in step 3 to obtain the initial metallographic sample.

[0059] S5. Use a scanning electron microscope to observe the initial metallographic sample, take pictures of the original microstructure after the standard heat treatment of the alloy, select the first region, and obtain the average contour line of the triangular microstructure, i.e., the S value, using ImageJ software, and take L = 0.5S.

[0060] S6 draws straight lines parallel to one side of the triangular structure with a spacing of L. The distance between two adjacent lines is L. The number of intersections between the straight lines and the white phase (γ channel) in the structure within the first region is counted manually. The number of intersections is recorded as N of the initial metallographic sample. y .

[0061] S7. Use the remaining single crystal rod after heat treatment to prepare creep samples by machining.

[0062] S8. After preparation, conduct a creep test according to the test requirements. The specific operating standard for the creep test is GB / T 2039-201.

[0063] S9. Prepare a creep metallographic sample from the creep test results in step S8. Use a scanning electron microscope (SEM) at the same magnification to photograph the microstructure of the creep metallographic sample. Then, select a second region with the same shape and size as the first region. Draw a second straight line parallel to the first straight line, using the L value from S5 as the spacing. Count the number of intersections between the straight line and the white phase (γ channel) within the second region manually, and record this number as N of the creep metallographic sample. z value.

[0064] S10. Based on the number of intersection points N obtained in step S6 y The number of intersection points N of samples at each stage obtained in step S9 z The organization evolution index Q-value is calculated, and the degree of organization evolution is defined based on the magnitude of the organization evolution index Q-value; the specific formula for calculating the organization evolution index Q-value is shown in Equation 1:

[0065] Organizational evolution index Q = N z / N y Formula 1;

[0066] When the microstructure evolution index Q = 1, it means that no microstructure has evolved. When the microstructure evolution index Q < 1, it indicates that the alloy microstructure has evolved. The smaller the microstructure evolution index Q, the worse the connectivity of the γ channels, the greater the degree of evolution, and the closer the alloy is to the failure state.

[0067] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0068] The following embodiments are in accordance with Figure 1 The implementation process is as shown.

[0069] Example 1

[0070] S1. Select multiple

[111] oriented single crystal alloy test bars (grade IC21) without surface impurity defects, and use the commonly used hydrochloric acid-hydrogen peroxide etching solution in the field to etch them. Observe that the surface oxide scale and other impurities have been removed and a bright metallic luster is exposed.

[0071] S2. The crystal orientation test was performed along the axis of multiple test rods after corrosion in step S1 using the X-ray backscattering Laue method. One test rod whose main orientation deviated from the

[111] direction by less than 5° was selected.

[0072] S3. Perform standard heat treatment on the test bar selected in step S2 whose main direction deviates from the

[111] direction by less than 5° (standard heat treatment is: 300℃, 2h / 1310℃, 2h / 1320℃, 2h / 1325℃, 4h / 1330℃, 6h / argon gas cooling / 1020℃, 6h / argon gas cooling / 870℃, 25h / furnace cooling) to obtain the heat-treated test bar.

[0073] S4. Take a small piece of alloy from the test bar that has undergone standard heat treatment in step 3 and mount it with resin using hot or cold mounting to form the sample to be characterized. After mounting, the

[111] crystal plane needs to be exposed. Use 400#, 600#, 800#, 1000#, 1200#, 1500#, 2000#, and 3000# sandpaper to polish the exposed alloy surface in sequence. After there are no obvious scratches on the surface, use a polishing agent with 0.5nm particles to polish the alloy surface. Use an etching solution to etch (the etching solution is a reagent prepared by CuSO4 + 100mL HCl + 100mL C2H5OH). When a white haze appears on the surface, the initial metallographic sample is obtained.

[0074] S5. Observe the initial metallographic sample using a scanning electron microscope (15000x magnification in this embodiment), photograph the original microstructure after standard heat treatment of the alloy, and select a first region with a size of 10μm×10μm. Figure 3 (The area within the red box in the left image) was processed using ImageJ software for color analysis. The average contour lines of the triangular tissue were then obtained using ImageJ software. Figure 2 The S value in the sample (since the size of the triangle may vary in the tissue, the average value can be taken), is L = 0.5S.

[0075] S6, such as Figure 3 As shown in the right figure, straight lines are drawn with a spacing of L, parallel to one side of the triangular tissue (the side perpendicular to the contour line in step S5). The distance between two adjacent lines is L, where L = 0.5S = 0.3μm. The number of intersections between the straight lines and the white phase (γ channel) in the tissue within the first region is counted manually. Figure 3 The green origin in the diagram), the number of intersection points is denoted as N. y N y The value is 421.

[0076] S7. The remaining single crystal rod after heat treatment is used to prepare a creep sample by machining (in this example, the sample is prepared as follows). Figure 7 The sample consists of two plate-shaped specimens, 1 and 2, with a wall thickness of 1.5 mm for specimen 1 and 0.8 mm for specimen 2.

[0077] S8. After preparation, a creep test is conducted according to the experimental requirements (the creep test conditions in this example are 1100℃ / 160MPa). To verify the feasibility of the invention, this example selected the initial creep stage, the steady-state creep stage, and the interruption and fracture tests after creep fracture, which involve significant differences in tissue morphology (these three stages cover all stages of the creep test and are persuasive). The specific operating standard for the creep test is GB / T 2039-201. The basic operation is as follows: first, level the testing machine, set the force value to zero, attach the thermocouple for temperature measurement, install the extensometer, preload according to the sample size and test requirements, heat to the target temperature and then hold it at that temperature, then start loading after the holding period, and the testing machine will record the deformation at certain intervals until the sample fractures. The test ends when the heating furnace of the testing machine cools down to room temperature. Figure 3 This is a test curve obtained by using two sizes of creep specimens (Specimen 1 and Specimen 2) and conducting creep tests on the two specimens at 1100℃ / 160MPa. Figure 3 As can be seen, both curves conform to the classic three-stage creep pattern.

[0078] S9. Metallographic preparation of the samples from each stage after the creep test in step S8 (initial stage sample, steady-state stage sample, and creep fracture stage sample) (the specific operation is the same as in step S4). Use a scanning electron microscope to take tissue images of the samples at different stages at the same magnification, and then select a second region with a size of 10μm×10μm. Figure 5 and Figure 6 (The area within the red box in the image) Following the same method as steps S5 and S6, count the number of intersections between the white phase (γ channel) and the straight line in the tissue of samples 1 and 2 at each of the three stages. The number of intersections for each stage is denoted as N for each stage. z Specifically, select an area of ​​the same size as the area used for tissue characterization after standard heat treatment. Draw straight lines with the L value from S5 as the spacing. The direction of the lines is the same as the angle of the lines in S6, meaning the lines are drawn at an angle parallel to any side of the triangle in the tissue after standard heat treatment. The area covered by the lines is the same size as the area in S6. The intersection points of the lines and the white areas within the area are counted manually. Figure 2 The number of (red dots) in the current test phase is denoted as N. z value.

[0079] Figure 5 and Figure 6 Creep interruption tests were conducted on samples 1 and 2 in Example 1 at the initial stage and steady-state stage (both at the same time). The microstructure of the alloy in the

[111] direction after the interruption test and creep fracture was scanned and observed, and statistical analysis was performed. Several 10μm×10μm regions were selected for each test and the average value was taken. The results are shown in Table 1.

[0080] Table 1. Statistical results of metallographic structures of specimens 1 and 2 in the initial creep stage, steady-state stage, and after creep fracture.

[0081]

[0082] S10. Based on the number of intersection points N obtained in step S6 y The number of intersection points N of samples at each stage obtained in step S9 z The organization evolution index Q value is calculated, and the degree of organization evolution is defined based on the magnitude of the organization evolution index Q value; the calculation results are shown in Table 2.

[0083] The specific formula for calculating the Q value of the organizational evolution index is shown in Equation 1:

[0084] Organizational evolution index Q = N z / N y Formula 1;

[0085] When the microstructure evolution index Q = 1, it means that no microstructure has evolved. When the microstructure evolution index Q < 1, it indicates that the alloy microstructure has evolved. The smaller the microstructure evolution index Q, the worse the connectivity of the γ channels, the greater the degree of evolution, and the closer the alloy is to the failure state.

[0086] Table 2 shows the changes in the Q-value of tissue evolution index at each stage of creep in samples 1 and 2 in this embodiment.

[0087]

[0088]

[0089] As can be seen from the above embodiments, the present invention uses metallographic methods and point counting methods to quantitatively characterize the evolution of irregular alloy microstructure under specific orientations. Through the statistical methods and formula-defined Q-values ​​of the present invention, it is possible to effectively quantitatively characterize the microstructure evolution of specific orientation samples that is difficult to characterize in current single-crystal high-temperature alloy research, thus solving the technical difficulties encountered in scientific research in this field. The characterization method has been verified through examples, and the results show that this new quantitative characterization method has good scientific research application value and provides certain guidance for subsequent related research in the field.

[0090] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for characterizing the microstructure evolution of a single-crystal superalloy, wherein the phase structure of the single-crystal superalloy includes a γ′ phase and γ phase channels along the γ′ phase, characterized in that, Includes the following steps: (1) The test bar is subjected to standard heat treatment to obtain a heat-treated test bar, wherein the crystal orientation of the test bar along the axial direction deviates from the [111] direction by <5°; (2) A raw metallographic sample is prepared by taking a sample from the heat-treated test bar. The γ phase channel in the raw metallographic sample presents a state of several connected triangles, which are equilateral triangles or nearly equilateral triangles. The raw microstructure image of the raw metallographic sample is obtained. Any region of the raw microstructure image is selected and named as the first region. The contour line of any side of the triangles formed by the γ phase channel in the first region is obtained. The average value S of the contour line in the first region is obtained. Several first straight lines are drawn parallel to any side of the triangle in the first region. The distance L between adjacent first straight lines and the average value S of the contour line satisfy L=0.5S. The total number of intersections between the first straight lines drawn in the first region and the γ phase channel is counted and named as N. y When the first straight line is parallel to the γ channel, the number of intersection points is recorded as 0. (3) Machining the remaining heat-treated test bar from step (2) into a creep test specimen, performing a creep test on the creep test specimen to obtain a creep sample, preparing the obtained creep sample to obtain a creep metallographic sample; and obtaining a creep structure image of the creep metallographic sample. In the creep tissue image, select any region with the same shape and size as the first region in step (2), and name it the second region. In the second region, draw several second straight lines with the same side length as the triangle in step (2), with the spacing between adjacent second straight lines being equal to the spacing between adjacent first straight lines. Count the total number of intersections between the second straight lines drawn in the second region and the γ-phase channel, and name it N. z When the second line is parallel to the γ channel, the number of intersection points is recorded as 0. (4) Calculate the microstructure evolution index Q of the single-crystal superalloy. The formula for calculating the microstructure evolution index Q is shown in Equation 1: Organizational evolution index Q=N z / N y Formula 1; When the microstructure evolution index Q=1, it indicates that the microstructure of the single-crystal high-temperature alloy has not evolved; when the microstructure evolution index Q<1, it indicates that the microstructure of the single-crystal high-temperature alloy has evolved. The smaller the microstructure evolution index Q, the greater the degree of microstructure evolution of the single-crystal high-temperature alloy, and the closer the single-crystal high-temperature alloy is to the failure state.

2. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 1, characterized in that, In steps (2) and (3), a scanning electron microscope is used to obtain the original tissue image of the original metallographic sample or the creep tissue image of the creep metallographic sample; the magnification of the scanning electron microscope is 15,000 times.

3. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 1, characterized in that, In step (2), the contour lines are obtained using computer software, including ImageJ software.

4. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 1, characterized in that, In step (2), after selecting the first region and before obtaining the contour lines in the first region, the method further includes: color processing of the first region; In step (3), after selecting the second region and before drawing the second straight line within the second region, the method further includes: color processing of the second region; In step (2) or step (3), the color processing is performed using computer software, including ImageJ software or Photoshop software.

5. The characterization method for the microstructure evolution of single-crystal superalloys according to any one of claims 1 to 4, characterized in that, The creep sample includes one or more of the following: a sample in the initial stage of creep, a sample in the steady-state stage of creep, or a sample after creep fracture.

6. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 1, characterized in that, The creep test was conducted in accordance with GB / T 2039-2012.

7. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 6, characterized in that, The single-crystal superalloy is a Ni-based single-crystal superalloy or a Ni3Al-based single-crystal superalloy.

8. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 7, characterized in that, The grades of the single-crystal superalloys include IC21, DD6, DD5, or CMSX-4.

9. The characterization method for the microstructure evolution of single-crystal superalloys according to claim 1, characterized in that, The first region is square in shape and has a size of 10μm × 10μm; The shape of the creep specimen may be rod-shaped or plate-shaped.

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