Characterization and determination method for small misorientation grain boundaries of single crystal superalloys

Abstract

The present invention relates to a method for characterizing and determining small misorientation grain boundaries of a single crystal superalloy. The method includes: preparing a wedge-shaped sample of the single crystal superalloy; observing the equal-thickness fringes on both sides of the small misorientation grain boundary in the wedge-shaped sample under a transmission electron microscope, and the position where the equal-thickness fringes are broken and misaligned is determined as the position of the grain boundary. The method of the present invention utilizes the principle of equal-thickness fringes generated by Bragg extinction of the transmission electron microscope to judge whether the single crystal superalloy contains small misorientation grain boundary defects at the nanoscale, effectively solving the problems of too large observation scale and poor resolution in the traditional method, and providing a new determination method for small misorientation grain boundaries of single crystal superalloys.

Description

Technical Field

[0001] The present invention relates to a method for characterizing and determining small misorientation grain boundaries in single crystal superalloys, and more specifically, to a method for characterizing and determining small misorientation grain boundaries in nickel-based or cobalt-based single crystal superalloys. Background Art

[0002] Single crystal superalloys have excellent high-temperature properties and are commonly used in the preparation of heavy gas turbine and aeroengine turbine blades. Compared with equiaxed crystal and columnar crystal blades, single crystal blades eliminate grain boundaries in the engineering sense, have a highly consistent orientation, and possess better comprehensive properties. During the production process, defects such as striation grains and mixed orientation deviations of small-angle grain boundaries often occur in single crystal blades. These defects cause the dendrites to deviate from the expected growth direction, destroying the integrity of the single crystal material. These grain boundaries provide the sources for defects such as cracks and micropores, thereby affecting the performance of the blades and shortening the service life of the blades.

[0003] For small misorientation grain boundaries (specifically referring to grain boundaries with an orientation deviation of less than 3°) caused by defects such as striation grains, they cannot be judged visually and further analysis means are needed to determine them. Currently, the main methods for determining small misorientation grain boundaries in single crystal superalloys are metallographic microscope observation, scanning electron microscope observation, and electron backscatter diffraction analysis (EBSD). Metallographic microscope observation determines whether there are small misorientation grain boundaries by the different reflectivities of tissues with different orientations under a light source, presenting different degrees of brightness and darkness in color. This method has a relatively large observation scale, poor resolution for small misorientation grain boundaries, and cannot directly obtain the orientation information on both sides of the grain boundary. Scanning electron microscope judges whether there is a grain boundary by judging the tissue arrangement on both sides of the small misorientation grain boundary, and has poor resolution for small misorientation grain boundaries and cannot directly obtain the orientation information on both sides of the grain boundary. Electron backscatter diffraction analysis irradiates both sides of the grain boundary with an electron beam to obtain the lattice arrangement. Therefore, for grain boundaries with a relatively large misorientation, the contrast on both sides of the grain boundary in the electron backscatter diffraction pattern is obvious, and it can effectively judge whether there is a grain boundary in the tissue, but it has poor resolution for small misorientation grain boundaries. Currently, there is an urgent need for a high-resolution determination method for small misorientation grain boundaries in single crystal superalloys at the nanoscale. Summary of the Invention

[0004] Problems to be Solved by the Invention

[0005] Based on the above, the current methods for determining small misorientation grain boundaries in single crystal superalloys have a relatively large observation scale and low resolution, and it is difficult to observe the morphological characteristics of small misorientation grain boundaries and determine small misorientation grain boundaries at the nanoscale. Therefore, a method with high resolution and capable of clearly determining small misorientation grain boundaries is needed.

[0006] Solutions for Solving the Problems

[0007] To solve the above problems, the present inventor has conducted research and found that by using the principle of equal-thickness fringes generated by Bragg extinction in a transmission electron microscope, it is possible to determine the position of small misorientation grain boundaries in single-crystal superalloys at the nanoscale with high resolution, providing a new method for the determination of small misorientation grain boundaries in single-crystal superalloys.

[0008] [1] More specifically, the present invention provides a method for characterizing and determining small misorientation grain boundaries in single-crystal superalloys, which includes:

[0009] Preparing a wedge-shaped sample of a single-crystal superalloy;

[0010] Observing the equal-thickness fringes on both sides of the small misorientation grain boundary in the wedge-shaped sample under a transmission electron microscope, and the position where the equal-thickness fringes are broken and misaligned is determined as the position of the grain boundary.

[0011] [2] According to the characterization and determination method described in item 1 above, wherein the inclination angle of the wedge-shaped sample is 5° or less, preferably 3° or less.

[0012] [3] According to the characterization and determination method described in item 1 or 2 above, wherein the thickness at the thickest position of the wedge-shaped sample is 150 nm or less, preferably 100 nm or less, more preferably 50 nm - 100 nm.

[0013] [4] According to the characterization and determination method described in item 1 or 2 above, wherein the wedge-shaped sample is obtained by cutting a single-crystal superalloy sample with a focused ion beam (FIB).

[0014] [5] According to the characterization and determination method described in item 4 above, wherein the single-crystal superalloy sample is obtained by wire-cutting a single-crystal superalloy casting, and then cleaning, etching, grinding, and polishing the wire-cut sample.

[0015] [6] According to the characterization and determination method described in item 5 above, wherein the size of the wire-cut sample is 5 mm × 5 mm × 1 mm - 16 mm × 16 mm × 4 mm, preferably 8 mm × 8 mm × 2 mm - 15 mm × 15 mm × 3 mm.

[0016] [7] According to the characterization and determination method described in item 5 or 6 above, wherein the etching is carried out by immersing the wire-cut sample in a mixed solution of hydrochloric acid and hydrogen peroxide for 15 - 50 seconds, preferably 20 - 40 seconds.

[0017] [8] According to the characterization and determination method described in item 7 above, wherein in the mixed solution, the volume ratio of hydrochloric acid to hydrogen peroxide is 1:2 - 2:1.

[0018] [9] According to the characterization and determination method described in item 5 above, wherein the cleaning is carried out using an aqueous ethanol solution with an ethanol content of 30 vol% - 60 vol%.

[0019]

[10] According to the characterization determination method described in any one of the above 1-9, wherein the single crystal superalloy is a nickel-based or cobalt-based single crystal superalloy.

[0020] Effects of the Invention

[0021] The method of the present invention has the following beneficial effects:

[0022] In the present invention, by using the principle of equal-thickness fringes generated by Bragg extinction in a transmission electron microscope, the position of small misorientation grain boundaries in a single crystal superalloy can be judged at the nanoscale, with high resolution. Even for samples without obvious dislocations or samples with a small misorientation difference at the grain boundaries, the grain boundary position can be clearly determined, effectively solving the problems of too large observation scale, poor resolution, and unclear determination of small misorientation defects in conventional analysis methods. Description of the Drawings

[0023] Figure 1 Schematic diagram of sampling a wedge-shaped thin slice of the nickel-based single crystal superalloy in Example 1.

[0024] Figure 2 Morphology of the nickel-based single crystal superalloy in Example 1 during focused ion beam cutting.

[0025] Figure 3 Grain boundary morphology of the sample in Example 1 under a transmission electron microscope (the discontinuous black stripes on the left and right are equal-thickness fringes).

[0026] Figure 4 Shows Figure 3 Morphology of the small misorientation grain boundary after further magnification.

[0027] Figure 5 Morphology of the small misorientation grain boundary of the nickel-based single crystal superalloy in Example 1 under a scanning electron microscope.

[0028] Figure 6 Morphology of the small misorientation grain boundary of the nickel-based single crystal superalloy in Example 1 under electron backscatter diffraction. Detailed Embodiments

[0029] The term "small misorientation grain boundary" used herein is different from the concept of small angle grain boundaries commonly used in the art. In the present invention, it specifically refers to a grain boundary with an orientation deviation of less than 3° on both sides of the grain boundary.

[0030] The term "tilt angle" used herein refers to the included angle between the two hypotenuses of the wedge-shaped sample, that is, the angle θ in the lower right corner of the Figure 1 shown wedge-shaped thin slice.

[0031] In this specification, the numerical range expressed as "numerical value A to numerical value B" refers to the range that includes the end point numerical values A and B.

[0032] Unless otherwise required in this application, throughout the specification and the claims that follow, the word "comprising" shall be interpreted in an open, inclusive sense, i.e., "including but not limited to".

[0033] In this specification, unless otherwise stated, the "many" in "many", "a variety of", "multiple", etc. means a numerical value of 2 or more.

[0034] In this specification, the terms "substantially", "generally" or "essentially" mean that the error is less than 5%, or less than 3% or less than 1% compared to the relevant perfect standard or theoretical standard.

[0035] In this specification, the meaning expressed by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0036] In this specification, "optional" or "optionally" means that the event or situation described next may or may not occur, and this description includes the situation where the event occurs and the situation where the event does not occur.

[0037] In this specification, if terms such as "room temperature" or "normal temperature" appear, the temperature can generally be 10 - 40 °C.

[0038] The present invention provides a method for characterizing small misorientation grain boundary defects in single crystal superalloys, which determines the position of small misorientation grain boundaries at the nanoscale, provides a high-precision characterization method for small misorientation grain boundary defects, and effectively solves the problems of too large observation scale and poor resolution in traditional methods. It is convenient for researchers and technicians to further analyze the causes of small misorientation grain boundaries, and can provide effective help for exploring and eliminating small misorientation grain boundary defects.

[0039] In the present invention, there is no particular limitation on the single crystal superalloy, and it can be any single crystal superalloy. In some specific embodiments of the present invention, the single crystal superalloy is a nickel-based or cobalt-based single crystal superalloy.

[0040] The method for characterizing and determining small misorientation grain boundaries in the single crystal superalloy of the present invention includes:

[0041] Preparing a wedge-shaped sample of the single crystal superalloy;

[0042] Observing the equal-thickness fringes on both sides of the small misorientation grain boundary in the wedge-shaped sample under a transmission electron microscope, and the position where the equal-thickness fringes are broken and misaligned is determined as the position of the grain boundary.

[0043] The method for preparing a wedge-shaped sample of a single-crystal superalloy in the present invention includes: wire-cutting a plate-shaped casting of a single-crystal superalloy, and then cleaning, etching, grinding, and polishing the wire-cut sample, and then cutting the processed sample into a wedge-shaped sample.

[0044] In the embodiments of the present invention, there is no particular limitation on the method for wire-cutting, cleaning, etching, grinding, and polishing the casting, and the methods commonly used in the art can be used. Specific descriptions are given below.

[0045] Wire Cutting

[0046] In some embodiments of the present invention, first, a casting of a single-crystal superalloy that may have small misorientation grain boundaries, usually a plate or a bar, is wire-cut. There is no particular limitation on the wire-cutting equipment, and a wire electrical discharge machine commonly used in the art can be used.

[0047] In the present invention, there is no particular limitation on the size of the cut sample, but for the convenience of subsequent processing, the size of the wire-cut sample is usually 5 mm×5 mm×1 mm to 16 mm×16 mm×4 mm, preferably 8 mm×8 mm×2 mm to 15 mm×15 mm×3 mm, and the length, width, and height of the sample can be arbitrarily combined within the above range, for example, it can be 10 mm×10 mm×1 mm, etc.

[0048] Cleaning

[0049] For the wire-cut sample, it is usually necessary to clean it to remove dirt such as oil stains and other organic impurities attached to the alloy surface. In some embodiments of the present invention, an ethanol aqueous solution with an ethanol content of 30 vol% to 60 vol% is used to clean the sample.

[0050] Optionally, for assisting the cleaning, ultrasonic waves can also be applied during cleaning. There is no particular limitation on the ultrasonic soaking time, and it can usually be 30 seconds to 5 minutes, preferably 30 seconds to 3 minutes.

[0051] Corrosion

[0052] After cleaning the wire-cut sample, it is necessary to etch the sample to remove the oxides on the sample surface and expose the grain morphology. In some embodiments of the present invention, a mixed solution of hydrochloric acid and hydrogen peroxide is used to etch the sample. In the mixed solution, the volume ratio of hydrochloric acid to hydrogen peroxide can be 1:2 to 2:1.

[0053] In the present invention, there is no particular limitation on the etching time, and the etching time commonly used in the art can be used, usually 15 to 50 seconds, preferably 20 to 40 seconds.

[0054] Grinding and Polishing Treatment

[0055] The samples after removing oxides need to be ground and polished to ensure that the surface of the samples is smooth and scratch-free. There is no particular limitation on the methods used for grinding and polishing. In some embodiments of the present invention, an automatic polishing machine can be used to perform grinding and polishing simultaneously. Optionally, grinding can also be performed first using abrasive paper such as SiC abrasive paper, and then polishing can be performed using, for example, diamond paste.

[0056] Sampling

[0057] For the positions on the ground and polished samples where small misorientation grain boundaries are suspected to exist, focused ion beam (FIB) cutting is performed to take samples. During the cutting process, in order to facilitate subsequent observation of equal-thickness fringes, it is necessary to control the cutting angle to keep the FIB sample in the form of a wedge with a certain inclination angle (such as Figure 1 the θ shown in

[0058] ), and at the same time ensure that the FIB sample is less than a certain thickness, so as to obtain a wedge-shaped sample or a wedge-shaped thin slice. Figure 1 In the present invention, the inclination angle of the wedge-shaped sample can be 5° or less, preferably 3° or less. For example, it can be 1° to 5°, preferably 1° to 4°, and more preferably 2 to 3°. The thickness (such as

[0059] the T shown in

[0060] Examples

[0061] Hereinafter, the embodiments of the present invention will be described in detail in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] The single-crystal superalloy used in this example is a nickel-based single-crystal superalloy, and its grade is: DD5 nickel-based single-crystal superalloy.

[0064] In this embodiment, a plate-shaped casting of a nickel-based single crystal superalloy that may contain small misorientation grain boundaries is first subjected to wire electrical discharge machining to obtain a sample with dimensions of 10 mm × 10 mm × 1 mm. Then, the wire-cut sample is placed in an ethanol aqueous solution with an ethanol content of 50 vol%, and ultrasonically cleaned for 1 minute. The cleaned sample is placed in a mixed solution of hydrochloric acid and hydrogen peroxide with a volume ratio of 1:1 for etching for 30 seconds. After that, the sample is polished using an automatic polishing machine. The polished sample is subjected to Xe+ focused ion beam cutting using a TESCAN S9000X, and the cutting angle is adjusted to keep the FIB sample morphology as a wedge with an inclination angle (such as Figure 1 shown as θ) of 3°, while ensuring that the thickness at the thickest position in the FIB sample (such as Figure 1 shown as T) is 100 nm. The morphology of the sample during focused ion beam cutting is shown in Figure 2 , which is obtained by observing with a Zeiss Merlin VP scanning electron microscope. After completing the FIB cutting, the sample is placed under a JEOL JEM-2100F transmission electron microscope for observation, and the results are as shown in Figure 2 and Figure 3 .

[0065] Figure 2 , the position marked by the middle ellipse is the small misorientation grain boundary of the nickel-based superalloy. The black stripes on both sides of the grain boundary are equal-thickness fringes, and dislocation occurs at the grain boundary. Figure 3 is the morphology of the small misorientation grain boundary after further magnification. From Figure 3 , it is even possible to see the degree of regularity of the atomic arrangement at the grain boundary.

[0066] For comparison with other observation methods, the samples of this embodiment were observed with a Zeiss Merlin VP scanning electron microscope and a ULVAC-PHI PHI710 electron backscatter diffraction, and the results are shown in Figure 5 and Figure 6 respectively.

[0067] Comparing Figure 5 and Figure 6 with Figure 2 and Figure 3 , it can be seen that the method for characterizing and determining small misorientation grain boundaries of the single crystal superalloy of the present invention has a higher resolution, can accurately determine the position of small misorientation grain boundaries, and can even determine the degree of regularity of the atomic arrangement at the grain boundary compared with the method of observing small misorientation grain boundaries using a scanning electron microscope and electron backscatter diffraction.

[0068] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

[0069] Industrial Applicability

[0070] The characterization method of small misorientation grain boundaries of the single crystal superalloy of the present invention can determine whether the single crystal superalloy contains small misorientation grain boundary defects at the nanoscale, effectively solving the problems of too large observation scale and poor resolution in the traditional method, and providing a new idea and method for the determination of small misorientation grain boundaries of single crystal superalloys.

Claims

1. A method for characterizing and determining small misorientation grain boundaries of a single crystal superalloy, comprising: Preparing a wedge-shaped sample of the single crystal superalloy; Observing the equal-thickness fringes on both sides of the small misorientation grain boundary in the wedge-shaped sample under a transmission electron microscope, and the position where the equal-thickness fringes are broken and mislayered is determined as the position of the grain boundary, wherein the inclination angle of the wedge-shaped sample is below 5°.

2. The characterization and determination method according to claim 1, wherein the inclination angle of the wedge-shaped sample is below 3°.

3. The characterization and determination method according to claim 1 or 2, wherein the thickness at the thickest position of the wedge-shaped sample is below 150 nm.

4. The characterization and determination method according to claim 1 or 2, wherein the thickness at the thickest position of the wedge-shaped sample is below 100 nm.

5. The characterization and determination method according to claim 1 or 2, wherein the thickness at the thickest position of the wedge-shaped sample is 50 nm to 100 nm.

6. The characterization and determination method according to claim 1 or 2, wherein the wedge-shaped sample is obtained by cutting a single crystal superalloy sample with a focused ion beam (FIB).

7. The characterization and determination method according to claim 6, wherein the single crystal superalloy sample is obtained by wire-cutting a single crystal superalloy casting, and then cleaning, etching, grinding, and polishing the wire-cut sample.

8. The characterization and determination method according to claim 7, wherein the size of the wire-cut sample is 5 mm × 5 mm × 1 mm to 16 mm × 16 mm × 4 mm.

9. The characterization and determination method according to claim 7, wherein the size of the wire-cut sample is 8 mm × 8 mm × 2 mm to 15 mm × 15 mm × 3 mm.

10. The characterization and determination method according to any one of claims 7 to 9, wherein the etching is carried out by immersing the wire-cut sample in a mixed solution of hydrochloric acid and hydrogen peroxide for 15 to 50 seconds.

11. The characterization and determination method according to any one of claims 7 to 9, wherein the etching is carried out by immersing the wire-cut sample in a mixed solution of hydrochloric acid and hydrogen peroxide for 20 to 40 seconds.

12. The characterization and determination method according to claim 10, wherein in the mixed solution, the volume ratio of hydrochloric acid to hydrogen peroxide is 1:2 to 2:

1.

13. The characterization and determination method according to claim 11, wherein in the mixed solution, the volume ratio of hydrochloric acid to hydrogen peroxide is 1:2 to 2:

1.

14. The characterization and determination method according to claim 7, wherein the cleaning is carried out using an ethanol aqueous solution with an ethanol content of 30 vol% to 60 vol%.

15. The characterization and determination method according to claim 1 or 2, wherein the single crystal superalloy is a nickel-based or cobalt-based single crystal superalloy.

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