CN111624214A - Transmission electron microscope sample preparation method suitable for dissimilar material welding joint interface analysis - Google Patents

Abstract

The invention relates to a transmission electron microscope sample preparation method suitable for dissimilar material welding joint interface analysis. According to the method, the dissimilar material welding joint sample difficult to prepare is prepared by using the ion thinning technology, the operation method is simple and easy to implement, the sample preparation efficiency is improved, the sample preparation process is simple, the cost is low, the success rate is high, and a new solution is provided for the transmission electron microscope sample preparation of the dissimilar material welding joint interface capable of being recognized by naked eyes.

Description

A transmission electron microscope sample preparation method suitable for the analysis of the interface of the welded joint of dissimilar materials

technical field

The invention belongs to the technical field of material transmission electron microscope sample preparation, and particularly relates to a transmission electron microscope sample preparation method suitable for the interface analysis of welding joints of dissimilar materials.

Background technique

Using transmission electron microscopy to analyze the microstructure and crystal structure of materials, it is necessary to prepare electron microscopy samples of moderate size and thickness. The fusion area of welded joints of dissimilar materials is small, and it is often difficult to prepare samples suitable for TEM observation.

Generally speaking, in order to precisely locate the interface position of the welded joint of dissimilar materials, the method of in-situ cutting of the focused ion beam is usually used. Gallium ions. After the acceleration, the high-energy ion beam collides with the sample and sputters to achieve the purpose of thinning the sample. The whole process can be divided into two parts: the initial thinning of the sample and the precise thinning. Before thinning, a 1-2 μm thick Pt film should be deposited on the target site to protect the target area of the sample. The advantages of the focused ion beam method are accurate positioning and high success rate of sample preparation, but the disadvantage is that the cost of the gallium ion source is very high and the requirements for personnel operation are high, which makes the sample preparation of transmission electron microscope more difficult.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a TEM sample preparation method suitable for the analysis of the interface of dissimilar materials welded joints in order to solve the problems of difficulty and high cost of sample preparation for dissimilar material welding joint interface.

The object of the present invention is achieved through the following technical solutions:

A transmission electron microscope sample preparation method suitable for the interface analysis of dissimilar material welded joints. TEM experimental samples for the microstructure, crystal structure and composition analysis of the interface.

Specifically include the following steps:

(1) After the sample of the welded joint of dissimilar materials is cut by wire, the identifiable macro interface of the welded joint of dissimilar materials is located in the center of the sample, so that the dissimilar materials are distributed symmetrically to the welding seam, and each occupies half of the area;

(2) Grind the dissimilar material welded joint sample to a uniform sheet with a thickness of 50-150 μm;

(3) Use a punching machine to punch the dissimilar material welded joint sample into a disc with a diameter of 3 mm, so that the macro interface is in the midline, and the dissimilar materials each occupy half of the area of the disc;

(4) Use a pit thinning instrument to thin the sample so that the remaining thickness of the sample is 10-20 μm;

(5) Using the ion thinning method, the sample of the welded joint of dissimilar materials is thinned, and at the same time, the sample is observed with a microscope in real time until the interface of the welded joint of dissimilar materials that can be observed and analyzed under a transmission electron microscope appears.

Preferably, the dissimilar material welded joint is in the form of a lap joint, and the dissimilar material welded joint sample is prepared by wire cutting to a plane size greater than or equal to 20mm╳6mm, and the initial sample is a uniform sheet with a thickness of 0.5-1.0mm.

Preferably, the wire-cut initial sample is placed in an acetone solution, and cleaned by ultrasonic vibration to remove oil stains on the surface.

Preferably, the specific method for grinding the dissimilar material welded joint sample is to stick the sample on a metal or glass base block of moderate size, and perform flat grinding along a figure-8 trajectory on sandpaper;

The particle size of the sandpaper is from coarse to fine. When replacing the sandpaper, use flowing water to clean the abrasive particles that fall off the sandpaper on the sample. The function of the flowing water plays the role of cooling and lubricating the grinding surface. Both sides of the sample should be ground.

Preferably, the specific method for thinning by using the dimple thinning instrument is to paste the sample sheet on the center of the top of the sample table through the heating table, fix the sample table on the rotating sample table base, and set the speed of the grinding wheel to 3 -5 gears, the sample rotation speed is set to 3-5 gears, and the grinding pressure of the pit reducer is set to 20-40g. During the pit treatment, the initial position of the sample is automatically zeroed, and the thickness of the sample pit is set. The thickness of the sample that needs to be ground is represented by a negative number.

Preferably, for the grinding paste of the pit thinning instrument, the grinding paste with 6-9 μm particles is used for grinding thick samples, and the fine grinding paste with 3-6 μm particles is used for thin samples. Replace the abrasive paste with 0.5-1 μm particles under the thickness and continue polishing, so that the remaining thickness in the center of the sample is 10-20 μm.

Preferably, the ion thinning method is specifically as follows: fixing the dissimilar material welded joint sample in the sample holder, selecting the double-sided clamping method for the sample fixing type, so that the macro interface of the welded joint is located in the center of the sample holder, and setting the ion gun The angle is 8-10°, the acceleration energy is set to 4-6keV, the sample rotation speed is 3rpm, and the current reading of the left and right ion guns needs to be greater than 6μA.

Preferably, argon gas is used as the ionization source gas during ion thinning, the air pressure is 1kg/cm ² , the ion thinning time is set, and the degree of perforation of the sample is observed in real time with a microscope to determine whether it is necessary to continue thinning;

After the thin area appears in the sample, the angle of the ion gun is adjusted to 3-5°, the acceleration energy is set to 2-3keV, and the thin area is repaired until the TEM interface of the welded lap joint of dissimilar materials that can be observed and analyzed under the transmission electron microscope appears. .

Preferably, the dissimilar material welded joint sample is a steel-aluminum welded joint.

The invention utilizes the ion thinning method to thin the dissimilar material welded joint samples, and the ion thinning method adopts the ion thinning instrument for processing. The ion thinning instrument mainly consists of a vacuum chamber, an ion gun, a sample stage, a rotating mechanism and a vacuum system. , lighting system and airflow control system.

The working principle of the ion thinning instrument is to control the vacuum value at 5╳10 ^{- 6} Pa by starting its own vacuum system. After ionization of argon by high pressure, ions with an acceleration energy of 1-6keV are generated, and then passed through the cold cathode. The ion gun provides a high-energy, high-purity argon ion flow that continuously bombards the sample surface at a certain angle of incidence. When the bombardment energy of the argon ion flow is greater than the binding energy of the atoms of the sample material, the atoms on the surface of the sample initiate sputtering and thin the sample. Through this continuous bombardment, sputtering and thinning process, a thin film sample suitable for observation by transmission electron microscopy is finally obtained. In order to make the thin area larger and the ion thinning speed adjustable, the sample can rotate, the sample surface can also rotate around the axis of the sample holder, so as to change the incident angle of the ion beam relative to the sample surface and other functions.

The invention adopts the ion thinning method, which can simply and conveniently prepare the transmission electron microscope sample. The preparation method has low cost, short time-consuming, low requirements for personnel operation, and less restrictive conditions. Through the method of the present invention, the ion thinning technology is used to prepare the welded joint samples of dissimilar materials that are difficult to prepare. The setting of the ion thinning process parameters is based on the principle of thinning the aluminum-steel interface first and then repairing it, and try to keep the interface in the ion beam as much as possible. The center, the operation method is simple and easy to operate, the sample preparation efficiency is improved, the sample preparation process is simple, the cost is low, and the success rate is high, which provides a new solution for the transmission electron microscope sample preparation of the interface of dissimilar material welded joints that can be visually recognized.

Description of drawings

Figure 1 is the topography of the weld of aluminum-steel dissimilar materials;

Figure 2 is a sample diagram of the welded joint after wire cutting;

Figure 3 is a schematic diagram of wire cutting and dimensioning of an aluminum-steel lap welded joint;

Figure 4 is a stamped sheet of a welded lap joint of dissimilar materials;

Figure 5 shows the thin area in the perforation of the welded lap joint transmission sample;

Fig. 6 is the transmission electron microscope experiment result of embodiment 1 welding joint weld zone;

Fig. 7 is the thin area morphology and energy spectrum analysis result of TEM of the welded joint of Example 1;

8 is the TEM twin morphology of the welded joint of Example 1;

Fig. 9 is embodiment 1 welding joint transmission electron microscope twin diffraction electron pattern;

Fig. 10 is the experimental result of embodiment 1 welding transmission electron microscope bright and dark field image;

Fig. 11 is the topography image of embodiment 2 welding TEM thin area;

Fig. 12 is embodiment 2 welding transmission electron microscope twin image photographing result (twin morphology image);

Fig. 13 is embodiment 2 welding transmission electron microscope twin image photographing result (high-resolution image);

FIG. 14 is the experimental result of the bright and dark field image of welding transmission electron microscope in Example 2.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1

Using ion thinning technology to prepare samples for transmission electron microscopy of welded joints of aluminum and steel dissimilar materials, the specific steps are as follows:

(a) As shown in Figure 1, the welded joints of dissimilar materials are in the form of lap joints. The samples of the welded joints of dissimilar materials are prepared by wire cutting into a plane size greater than or equal to 20mm╳6mm. The initial sample is a uniform sheet with a thickness of about 1.0mm, so that the The base metal of aluminum steel occupies half of the area and is symmetrical to the weld, as shown in Figures 2 and 3.

(b), put the initial sample of wire cutting into the acetone solution, and use ultrasonic vibration to clean it to remove the oil stains on the surface.

(c) Glue the sample on a metal or glass base block of moderate size, and perform manual flat grinding on sandpaper. When grinding, use force on the steel side and light force on the aluminum side, and perform flat grinding along the figure-8 trajectory. The particle size of the sandpaper varies from coarse to fine. When replacing the sandpaper, use flowing water to wash off the abrasive particles from the sandpaper on the sample. The effect of the flowing water is to cool and lubricate the abrasive surface. Both sides of the sample are ground, and the sample is ground into a uniform sheet with a thickness of about 100 μm.

(d) Use a punching machine to punch the sample into a disc with a diameter of 3 mm, so that the identifiable macro interface welded by dissimilar materials is in the center line, so that the dissimilar materials each occupy half of the area of the disc, as shown in Figure 4.

(e) Use the pit thinning instrument to dimple the sample, paste the sample sheet on the top center of the specially designed sample stage through the heating stage, and fix the sample stage on the rotating sample stage base.

(f) When pitting, the sample stage can be moved on the base of the rotating sample stage, so that the grinding wheel can grind the central area of the sample, the grinding wheel speed is 5th gear, and the sample rotation speed is 5th gear.

(g) Set the grinding pressure in the pit, adjust the position of the counterweight, and the grinding pressure is 40g.

(h) When pitting, perform automatic zero-position processing on the initial position of the sample, set the thickness of the sample pit, and the thickness of the sample that needs to be ground is represented by a negative number.

(i) Select the abrasive paste with suitable particle size for pits, select the abrasive paste with 6-9 μm particles, and grind the sample to a range of 40 μm. At this thickness, replace the abrasive paste of 1 μm to continue polishing, so that the remaining thickness in the center of the sample is 20 μm.

(j) Use the ion thinning method to fix the dissimilar material welded joint sample in the sample holder, select the double-sided clamping method for the sample fixing type, so that the macro interface of the welded joint is located in the center of the sample holder, and the ion gun angle is set as 10°, the acceleration energy is set to 6keV, the sample rotation speed is 3rpm, and the current reading of the left and right ion guns needs to be greater than 6μA.

(k) Argon gas is used as the ionization source gas during ion thinning, the pressure is 1kg/cm ² , the ion thinning time is set, and the perforation degree of the sample is observed with a microscope in real time to determine whether it is necessary to continue thinning.

(l) As the ion thinning time increases, as shown in Figure 5, the sample appears perforation, which is fast first and then slow, and the thinning area increases. After the thin area appeared, the angle of the ion gun was adjusted to 5°, the acceleration energy was set to 3keV, and the thin area was repaired until the TEM interface of the welded lap joint of dissimilar materials that could be observed and analyzed under the transmission electron microscope appeared.

The test results are shown in Figure 6-10.

Example 2

The TEM sample preparation method for the analysis of the interface of the welded joint of dissimilar materials, the specific steps refer to Example 1, and the differences are as follows:

In step (c), the sample is ground into a uniform sheet with a thickness of about 50 μm.

In step (f), the grinding wheel speed is 3rd gear, and the sample rotation speed is 3rd gear.

In step (g), the grinding pressure is set to 20g during the pit.

In step (i), the sample is first ground to a range of 20 μm using a fine grinding paste of 3-6 μm particles. At this thickness, the abrasive paste of 0.5 μm was replaced to continue polishing, so that the remaining thickness of the sample was 10 μm.

In step (j), the angle of the ion gun is set to 8°, the acceleration energy is set to 5keV, the rotation speed of the sample is 3rpm, and the current readings of the left and right ion guns need to be greater than 6μA.

In step (1), after the thin area appears, the ion gun angle is adjusted to 3°, the acceleration energy is set to 2keV, and the thin area is repaired until the dissimilar material welding lap joint interface that can be observed and analyzed under a transmission electron microscope appears.

The test structure is shown in Figure 11-14.

Comparative Example 1

The dissimilar material welded joint described in Example 1 was sampled by TEM by using the prior art electrolytic double spray method. Since the welded joint was made of dissimilar materials, a thin area that could be used for TEM observation and analysis could not be obtained. However, using the pre-thinning and final thinning methods mentioned in this patent through sample grinding, punching, pitting and ion thinning, an ideal thin area of the sample can be obtained, and bright and dark field images, diffraction patterns and High-resolution image, obtain TEM experimental results for observation and analysis, as shown in Figure 6-14.

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should all fall within the protection scope of the present invention.

Claims (10)

1. A transmission electron microscope sample preparation method suitable for dissimilar material welding joint interface analysis is characterized in that a dissimilar material welding joint sample capable of identifying an interface is subjected to grinding, punching, pit thinning and ion thinning sequentially to obtain a transmission electron microscope experimental sample capable of observing the interface microstructure, crystal structure and component analysis of a welding fusion area.

2. A transmission electron microscopy sampling method suitable for dissimilar material weld joint interface analysis as claimed in claim 1 comprising the steps of:

(1) after the dissimilar material welding joint sample is subjected to warp cutting, enabling a macroscopic interface which can be identified by the dissimilar material welding joint to be positioned in the center of the sample, and enabling the dissimilar materials to be symmetrically distributed on a welding seam and to occupy half area of the welding seam;

(2) grinding the dissimilar material welding joint sample until the thickness of the uniform sheet is 50-150 mu m;

(3) punching the dissimilar material welding joint sample into a wafer with the diameter of 3mm by using a punching machine, so that a macroscopic interface is positioned at a central line, and the dissimilar materials respectively occupy half area of the wafer;

(4) thinning by using a pit thinning instrument to ensure that the residual thickness of the sample is 10-20 mu m;

(5) and (3) thinning the dissimilar material welding joint sample by using an ion thinning method, and simultaneously observing the sample in real time by using a microscope until a dissimilar material welding joint interface which can be observed and analyzed under a transmission electron microscope appears.

3. The transmission electron microscope sampling method suitable for dissimilar material welded joint interface analysis according to claim 2, wherein the dissimilar material welded joint is in a lap joint form, the dissimilar material welded joint sample is prepared into a plane size of 20mm or more and 6mm after being subjected to warp cutting, and the initial sample is a uniform thin sheet with a thickness of 0.5-1.0 mm.

4. The transmission electron microscopy sampling method suitable for dissimilar material welding joint interface analysis as claimed in claim 2, wherein the initial sample of the linear cutting is put into an acetone solution, and is cleaned by ultrasonic oscillation to remove oil stains on the surface.

5. The transmission electron microscope sample preparation method suitable for dissimilar material welding joint interface analysis according to claim 2, wherein the dissimilar material welding joint sample is ground by adhering the sample to a metal or glass substrate block of moderate size and performing flat grinding along an 8-shaped track on sandpaper;

the granularity of the abrasive paper is changed from coarse to fine, when the abrasive paper is changed, the abrasive particles falling off from the abrasive paper on the sample are cleaned by flowing water, and two surfaces of the sample are ground.

6. The transmission electron microscopy specimen preparation method suitable for dissimilar material welded joint interface analysis as claimed in claim 2, wherein the specific method for thinning by using the pit-thinning instrument is that a sample sheet is pasted on the top center of the sample platform through a heating platform, the sample platform is fixedly arranged on a base of a rotary sample platform, the speed of a grinding wheel is set to 3-5 steps, the rotation speed of the sample is set to 3-5 steps, and the grinding pressure of the pit-thinning instrument is set to 20-40 g.

7. The transmission electron microscopy prototype method suitable for dissimilar material welding joint interface analysis according to claim 6, wherein the grinding paste of the pit thinner is 6-9 μm particles for grinding thick samples, 3-6 μm particles for grinding thin samples are used for grinding fine grinding paste, the samples are ground to 20-40 μm, 0.5-1 μm particles for grinding paste are replaced at the thickness of 20-40 μm, and polishing is continued, so that the residual thickness of the center of the sample is 10-20 μm.

8. The transmission electron microscopy sampling method suitable for dissimilar material welding joint interface analysis as claimed in claim 2, wherein the ion thinning method is specifically that a dissimilar material welding joint sample is fixed in a sample holder, a double-sided clamping mode is selected as a sample fixing type, a macroscopic interface of a welding joint is located in the center of the sample holder, an ion gun angle is set to be 8-10 degrees, acceleration energy is set to be 4-6keV, the rotation speed of the sample is 3rpm, and current readings of a left ion gun and a right ion gun are larger than 6 muA.

9. The transmission electron microscopy specimen preparation method suitable for dissimilar material weld joint interface analysis as claimed in claim 8, wherein argon gas is used as an ionization source gas for ion thinning, and the gas pressure is 1kg/cm²Setting ion thinning time, observing the perforation degree of the sample in real time by using a microscope, and judging whether the thinning needs to be continued again;

and adjusting the angle of the ion gun to 3-5 degrees after the sample has a thin area, setting the acceleration energy to 2-3keV, and repairing the thin area until a transmission electron microscope interface of the dissimilar material welding lap joint which can be observed and analyzed under a transmission electron microscope appears.

10. A transmission electron microscopy sampling method suitable for dissimilar material weld joint interface analysis according to any one of claims 1 to 9, wherein the dissimilar material weld joint sample is a steel aluminum weld joint.

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