Statistical method for nanoscale alpha2 phase grain size in near-alpha type high-temperature titanium alloy

Abstract

The invention discloses a nanoscale alpha2 phase grain size statistical method in a near-alpha type high-temperature titanium alloy. According to the method, the specific orientation relation of # imgabs0 # alpha2 of a lamellar alpha phase and a superlattice alpha2 phase is utilized, after the lamellar alpha phase is rotated to a # imgabs1 # Kikuchi pole, an objective lens diaphragm is moved to select diffraction beam imaging of the alpha2 phase, and the axial characteristics of the nanoscale superlattice alpha2 phase can be obtained through 5-20-second long-time exposure. And carrying out grain size statistics by utilizing image processing software with an image brightness analysis function, so as to obtain the content and the diameter of the superlattice alpha2 phase in the near-alpha type high-temperature titanium alloy. By means of the method, the problem that the axial size of the nanoscale superlattice alpha2 phase in the near-alpha type high-temperature titanium alloy is difficult to shoot is thoroughly solved, the method is simple, and preconditions are provided for research on deformation microstructure evolution of the near-alpha type high-temperature titanium alloy under different conditions.

Description

Technical Field

[0001] This invention relates to a statistical method for the grain size of the nanoscale superlattice α2 phase in near-α type high-temperature titanium alloys, specifically a transmission electron microscopy characterization and grain size statistical method for the axial characteristics of the nanoscale α2 phase in near-α type high-temperature titanium alloys. Background Technology

[0002] The size and content of the superlattice α2 phase in near-α type high-temperature titanium alloys gradually change with increasing heat treatment temperature. The diameter of the α2 phase is generally between a few nanometers and tens of nanometers, and the size of these α2 phases affects the strengthening or catalytic effect of the alloy. During deformation, mobile dislocations will cut through or bypass the α2 phase, and the interaction between these two mechanisms mainly depends on the specific size of the α2 phase. When the α2 phase size is small, the strengthening mechanism is dominated by the cutting mechanism, while when the size is large, the bypass mechanism is dominant. When it is at the critical size, the strengthening effect is the strongest. Therefore, determining the size of the α2 phase has an important impact on studying the evolution of the mechanical properties of near-α type high-temperature titanium alloys. However, the α2 phase is usually extremely fine at the nanoscale, and can only be observed and characterized under a transmission electron microscope. The α2 phase observed under TEM is often relatively densely distributed, and the contrast between light and dark is difficult to maintain completely uniformly. To date, there is no efficient and accurate method for characterizing and statistically analyzing the grains of this extremely fine superlattice α2 phase. Summary of the Invention

[0003] The purpose of this invention is to provide a statistical method for the nanoscale α2 phase grain size in near-α type high-temperature titanium alloys. This method can accurately characterize the grain size of the ultrafine superlattice α2 phase and perform efficient statistics.

[0004] The technical solution of this invention is:

[0005] A statistical method for the nanoscale α2 phase grain size in near-α type titanium alloys, characterized by the following steps:

[0006] (1) Take a titanium alloy sample and find flat lamellar α phase grains under a bright field image of a transmission electron microscope (TEM).

[0007] (2) Rotate the lamellar α-phase grains found in step (1) to a specific crystal orientation. Subsequently, Kikuchi diffraction patterns were taken in diffraction mode to verify whether the orientation contained a superlattice α2 phase;

[0008] (3) In the diffraction pattern obtained in step (2), move the objective aperture to select the diffraction beam of phase α2 for imaging, and take pictures at more than 3 different magnifications in the range of 100-300k with an exposure time of 5 to 20 seconds to obtain a dark field photograph of the phase.

[0009] (4) The α2 phase TEM dark field photograph obtained in step (3) is magnified by 8-12 times using image processing software, and then multiple images of the same area size are cropped.

[0010] (5) The image obtained in step (4) is processed by image processing software with image brightness and darkness analysis function to statistically analyze the superlattice α2 phase and obtain the superlattice α2 phase area data table after statistical analysis. The content of superlattice α2 is obtained by calculating the ratio of the sum of the superlattice α2 phase area data to the area of ​​the whole image. The diameter of α2 phase is calculated by averaging the area data of each α2 phase.

[0011] Furthermore, in step (1), it is necessary to select a rotation range within the allowable range of the electron microscope based on the Kikuchi diffraction pattern. The required Kikuchi-type grain size.

[0012] Further, the specific process of step (2) is to rotate the selected grain along the finest zone of the Kikuchi spectrum until it is rotated to... Kikuchi then returned to the diffraction mode to determine if the diffraction pattern matched. Standard diffraction patterns were observed, and it was determined whether superlattice diffraction spots could be seen within them.

[0013] Further, the specific process of step (2) is to rotate the selected grain along the finest zone of the Kikuchi spectrum until it is rotated to... The Kikuchi process involves taking Kikuchi diffraction patterns in the lamellar α-phase grains to determine if it is... Kikuchi's extreme case requires that the ratio of the distance from the transmission spot to the diffraction spot, b / a, be close to 1.299; if the obtained diffraction pattern is not... Continue tilting the sample along the finest Kikuchi zone, or replace it with another grain, until it is confirmed to be Kikuchi. Kikuchi Kikuchi.

[0014] Furthermore, in step (3), the focal length needs to be continuously adjusted at the same position to ensure the accuracy of the superlattice α2 phase characterization;

[0015] First, take a picture at the positive focus position. Then, fine-tune the electron microscope's focal length to the underfocus and overfocus directions. Take a picture every 300-600nm to prevent sample shaking from affecting the shooting effect. The focal length range is ±2-5μm until the picture is clear.

[0016] Furthermore, in step (4), the original α2 phase TEM dark field photograph is enlarged and cropped to ensure the accuracy of the α2 phase image recognition in the later stage.

[0017] Furthermore, in step (5), image processing software with image brightness and darkness analysis function can be used to quickly obtain α2 phase area data, and then obtain α2 phase content and diameter.

[0018] The features of this invention are:

[0019] 1. The TEM grain size statistical method used in this invention is applicable to the characterization of the superlattice α2 phase in all near-α type high-temperature titanium alloys;

[0020] 2. This invention utilizes the specific orientation relationship between the lamellar α phase and the superlattice α2 phase. By rotating the crystal orientation of the lamellar α phase to a specific direction using TEM manipulation techniques, the microscopic arrangement of the corresponding superlattice α2 phase in that direction can be observed.

[0021] 3. Due to the extremely small size of the superlattice α2 phase, there are extremely stringent requirements for orientation and TEM exposure time. This invention determines that... Only by tilting the orientation downwards can the axial arrangement of the needle-like superlattice α2 phase be observed, and the exposure time for imaging can be determined to be 5 to 20 seconds, thereby allowing for accurate calculation of the phase's diameter.

[0022] 4. The present invention uses a method of image cropping after local magnification of TEM to obtain images with consistent brightness and contrast for statistical analysis, thus accurately capturing the contrast of the α2 phase.

[0023] 5. This invention utilizes image processing software with image brightness and darkness analysis capabilities to quickly capture the contrast of the α2 phase and provides the area data of each identified α2 phase according to the image's built-in scale. This reduces the time consumed by manually cropping the α2 phase contrast and obtaining the contrast, and also reduces statistical errors.

[0024] This method utilizes the lamellar α phase and the superlattice α2 phase Specific orientation relationships, achieved by rotating the lamellar α phase to After Kikuchi's method, the objective aperture is moved to select the diffraction beam of the α2 phase for imaging. A long exposure of 5–20 seconds is sufficient to obtain the axial characteristics of the nanoscale superlattice α2 phase. Then, image processing software with image brightness analysis capabilities is used to perform grain size statistics, thereby obtaining the content and diameter of the superlattice α2 phase in near-α type high-temperature titanium alloys. This method completely solves the problem of difficult imaging of the axial dimensions of the nanoscale superlattice α2 phase in near-α type high-temperature titanium alloys. Furthermore, the method is simple and provides a prerequisite for studying the evolution of the microstructure of near-α type high-temperature titanium alloys under deformation conditions. Attached Figure Description

[0025] Figure 1 for Photographs of Kikuchi's polar zonal axis diffraction patterns;

[0026] Figure 2 for Dark-field images of the superlattice α2 phase at different magnifications from Kikuchi's positive zone axis diffraction pattern: Figure (a) is at 125kx, Figure (b) is at 195kx, and Figure (c) is at 250kx.

[0027] Figure 3 This is a magnified image of the superlattice α2 phase.

[0028] Figure 4 The image is a photograph after processing the α2 phase contrast through image brightness and darkness analysis;

[0029] Figure 5 This refers to the area data of the α2 phase obtained from image processing software. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] A Ti65 alloy sample with a thickness of 50 μm and a diameter of 3 mm was selected for TEM observation and analysis. First, lamellar α-phase grains in the alloy were located under bright-field imaging using a transmission electron microscope (TEM). Then, the special orientation relationship between the lamellar α-phase and the superlattice α2-phase was utilized: According to the Kikuchi spectrum, tilting the sample along the finest Kikuchi zone caused the lamellar α-phase grains to rotate to... Kikuchi pole, that is, the grain turns to Along the positive zone axis, three thin zones, two coarse zones, and one medium zone can be observed. Kikuchi band. Simultaneously, axial spherical microstructure images of the superlattice α2 phase can be obtained. For lamellar α phase grains, the beam is focused in low-magnification imaging mode (10k magnification imaging mode), and then switched to diffraction mode to observe the Kikuchi band.

[0032] Then, Kikuchi diffraction patterns were taken in the lamellar α-phase grains to determine whether it was... In the Kikuchi pole, the ratio of the distance from the transmission spot to the diffraction spot, b / a, needs to be close to 1.299. (The Kikuchi pole is mentioned again, but the context is unclear.) Figure 1 As shown; if the diffraction pattern is not Continue tilting the sample along the finest Kikuchi zone, or replace it with another grain, until it is confirmed to be Kikuchi. Kikuchi Kiyoshi. (In determining...) After Kikuchi's method, the diffraction mode was changed, and the aperture was moved to select a superlattice diffraction spot between the transmission spot and a nearby diffraction spot, such as... Figure 1As shown in the dashed circle, dark-field imaging was performed, with images taken at three magnifications: 125k, 195k, and 250k, with an exposure time of 15s. The dark-field images were taken in areas with thin grain edges and no impurities or streaks. First, an image was taken from the positive focus position. Then, the electron microscope's focal length was fine-tuned to the underfocus and overfocus directions, taking one image every 500nm to prevent sample shake from affecting the image quality. The focal length range was ±2μm, until a clear image was obtained.

[0033] Within the selected grains, photographs were taken at multiples of 125k, 195k, and 250k for data analysis. The photographs of the superlattice α2 phase axial grain TEM images are shown below. Figure 2 As shown in (a), 2(b), and 2(c), this method can clearly distinguish superlattice α2 phases with an average grain size within the range of 0.6-5 nanometers. Then, the clearest axial grain TEM image of the superlattice α2 phase (here, a 195kx magnification image) is selected and magnified 10 times using image processing software. Three images of the same size (length × width = 9mm × 9mm) at different locations within the magnified image are then extracted, as shown below. Figure 3 As shown in (a), 3(b), and 3(c), the brightness and contrast function of image processing software is used to capture α2 phase contrast, i.e., the white area enclosed by the red line in the figure. Figure 4 As shown in (a), 4(b), and 4(c), screenshots of the superlattice α2 phase contrast area data were automatically obtained using the software, as shown in the following images. Figure 5 As shown in (a), 5(b), and 5(c), (obj# represents the index of the superlattice α2 phase in the three images, with numbers of 365, 487, and 374 respectively; area represents the absolute area of ​​the superlattice α2 phase at the corresponding index). The above information was obtained by processing the superlattice α2 phase contrast area data. Figure 4 The α2 phase content (ratio of the sum of the superlattice α2 phase contrast (or grain) areas to the area of ​​the screenshot (9mm×9mm)) and grain diameter (since the superlattice α2 phase is spherical, the area of ​​the circle is used for calculation, i.e., superlattice α2 phase diameter = 2*√(superlattice α2 phase contrast area / π)) of the three images are listed in Table 1. After averaging the data, the average α2 phase content in Ti65 high-temperature titanium alloy at 650℃ for 100h is 29.45%, and the average grain diameter is 1.055nm.

[0034] Following the above process, the three selected superlattice α2 phase photographs ( Figure 3 As shown, the area data obtained by processing with image processing software has 100% repeatability. Therefore, using this method to statistically analyze the α2 phase size is very effective and easy to implement.

[0035] Table 1 shows the statistical data on α2 phase content and diameter.

[0036] <![CDATA[α2 phase content]]> <![CDATA[α2-phase diameter]]> Figure 4 (a) 26.17％ 0.98nm Figure 4 (b) 31.94％ 1.13nm Figure 4 (c) 30.25％ 1.10nm average value 29.45％ 1.055nm

Claims

1. A statistical method for the size of nanoscale α2 phase grains in near-α titanium alloys, characterized by: The method comprises the following steps: (1) Take a titanium alloy sample and find flat lamellar α-phase grains under the bright field image of a transmission electron microscope (TEM); (2) Rotate the lamellar α-phase grains found in step (1) to a specific crystal orientation Then, the Kikuchi diffraction spectrum was taken in the diffraction mode to verify whether the orientation contained the superlattice α2 phase; (3) moving the objective lens aperture to select the diffraction beam of the α2 phase in the diffraction spectrum obtained in step (2), and taking photos at more than three different magnifications in the range of 100-300k with an exposure time of 5-20 seconds to obtain a dark field photo of the phase; (4) The α2 phase TEM dark field photograph obtained in step (3) is magnified by 8-12 times using image processing software, and then multiple pictures of the same area size are captured; (5) The image obtained in step (4) is processed by image processing software with image brightness analysis function to perform statistics on the superlattice α2 phase, and obtain a statistical superlattice α2 phase area data table, and then the superlattice α2 relative content is obtained by calculating the ratio of the sum of the superlattice α2 phase area data and the area of ​​the entire image, and the α2 phase diameter is calculated by averaging the area data of each α2 phase.

2. The method according to claim 1, characterized in that: In step (1), it is necessary to select a rotation range within the electron microscope allowable range according to the Kikuchi diffraction spectrum. The required grains of the Kikuchi pole.

3. The method according to claim 1, characterized in that: The specific process of step (2) is to rotate the grain along the finest grain band in the Kikuchi spectrum in the selected grain until it is rotated to Kikuchi pole, then return to the diffraction mode to determine whether the diffraction spectrum conforms to Standard diffraction spectrum, and observe whether superlattice diffraction spots can be observed in it.

4. The method according to claim 3, characterized in that: The specific process of step (2) is to rotate the grain along the finest grain band in the Kikuchi spectrum in the selected grain until it is rotated to The process of the Kikuchi pole is: take a Kikuchi diffraction spectrum in the α-phase grains of the layer to determine whether it is Kikuchi pole, where the ratio of the distance from the transmission spot to the diffraction spot b / a must be close to 1.299; if the diffraction spectrum is not Continue to tilt the sample along the thinnest Kikuchi zone, or change another grain until it is confirmed to be Kikuchi extreme.

5. The method according to claim 1, characterized in that: In step (3), the focal length needs to be continuously adjusted at the same position to ensure the accuracy of superlattice α2 phase characterization; First, take a picture at the focus position, then fine-tune the electron microscope focus to the underfocus and overfocus directions, and take a picture every 300-600nm to prevent sample shaking from affecting the shooting effect. The focal length range is ±2-5μm, until the picture is clear.

6. The method according to claim 1, characterized in that: In step (4), the original α2 phase TEM dark field phase photograph is enlarged and captured to ensure the accuracy of subsequent α2 phase image recognition.

7. The method according to claim 1, characterized in that: In step (5), the α2 phase area data can be quickly obtained by using image processing software with image brightness analysis function, and then the α2 phase content and diameter can be obtained.

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