JP6976770B2 - Method for preparing a sample used for observation with a transmission electron microscope - Google Patents

Description

The present invention relates to a sample preparation method. More specifically, the present invention relates to techniques suitable for use in the preparation of samples used for observation with a transmission electron microscope.

In the field of thermal power generation, the development of a creep remaining life evaluation method for high chrome steel pipes for ultra-supercritical pressure plants is one of the most important issues. From the systematic test and analysis results of high chrome steel waste materials, it is clear that the creep characteristics of high chrome steel differ greatly depending on the power plant and piping. This difference in creep characteristics is due to the microstructure of the material, and in the case of high-chromium steel, M ₂₃ C ₆ (M is Fe, Cr), MX (M is V, Nb; X is C, It is considered that it depends on the amount of fine precipitates such as N), Loves phase and Z phase.

A transmission electron microscope (TEM: an abbreviation for Transmission Electron Microscope) (Patent Document 1) or an aberration-correcting TEM with improved analysis sensitivity (Patent Document 2) can be used for the evaluation of fine precipitates.

Japanese Unexamined Patent Publication No. 9-134694 Japanese Unexamined Patent Publication No. 2009-245841

However, in the sample used for observation with a transmission electron microscope, the part selected and designated as the observation target among the test materials to be evaluated (that is, the members and parts from which the sample is collected) is accurate. If it is not thinned, there is a problem that proper observation cannot be performed.

Therefore, it is desired to establish a method for producing a sample suitable for observation with a transmission electron microscope, which can accurately control the position of the observation target portion and the thinning position in the sample.

Therefore, the present invention is a sample preparation method capable of controlling the position of the observation target portion and the thinning position of the test material to be evaluated in the sample used for observation with a transmission electron microscope with high accuracy. The purpose is to provide.

In order to achieve such an object, the method for preparing a sample used for observation with a transmission electron microscope of the present invention has a Vickers hardness with respect to a test material on two parallel straight lines sandwiching a thin film candidate point in the center. Multiple measurement indentations arranged in two rows parallel to each other are formed on the surface of the test material, and the observation target is selected based on the measurement results of the Vickers hardness of the multiple measurement indentations in each row. been identified measurement pressure marks in each column corresponding to the position of the point, the measurement pressure marks placemark Do that eye mark indentations are formed on the surface of each test piece, including the measured pressure trace of the pair of landmarks indentation and two rows A circular sample is taken from the test material, and a spherical dent is formed around the midpoint of the line segment connecting the pair of marking pressure marks, and then electrolytic polishing is performed.

Therefore, according to this sample preparation method, the indentation formed when measuring the Vickers hardness is used as a marker for alignment during sample processing. Therefore, for example, the measurement result of the Vickers hardness is also taken into consideration. The position of the observation target point (and thus in the sample) in the test material selected in 1 is accurately identified and grasped.

According to this sample preparation method, and since electrolytic polishing is performed after forming a spherical dent, the dented portion is preferentially polished, and the position of the observation target portion is preferentially polished. It is thinned.

Further, in the method for producing a sample used for observation with a transmission electron microscope of the present invention, the sample may be collected from the test material in a shape in which a part of the circular peripheral edge is missing. In this case, the direction in which the sample was included in the original test material is specified and grasped based on the position of the partially chipped portion.

Further, in the sample preparation method of the present invention, the test material may be made of high-chromium steel. In this case, the above-mentioned action is exhibited in the preparation of the sample used for observation with a transmission electron microscope when the high chrome steel is the object of analysis / evaluation.

According to the sample preparation method of the present invention, the position of the observation target portion in the test material / sample can be accurately identified and grasped, so that the target location as an observation target can be cut out as a sample with high accuracy and collected. It becomes possible to make the film thinner, and by extension, it becomes possible to improve the usefulness and reliability as a sample preparation method.

According to the sample preparation method of the present invention, the position of the observation target portion can be preferentially thinned, so that the target portion as the observation target can be reliably thinned, and thus the target portion can be thinned. It is possible to improve the usefulness and reliability as a sample preparation method.

In the sample preparation method of the present invention, when a part of the circular peripheral edge of the sample is missing, the orientation of the collected sample in the original test material is determined. Since it can be identified and grasped, the positional relationship between the original test material and the sample becomes clear, and it becomes possible to provide detailed and accurate information on the attributes of the sample during analysis and evaluation. Can further improve its usefulness as a sample preparation method.

The sample preparation method of the present invention is described above in the preparation of a sample used for observation with a transmission electron microscope when the test material is made of high chrome steel and the high chrome steel is the object of analysis / evaluation. It becomes possible to play the action effect of.

It is a flowchart which shows an example of embodiment of the sample preparation method which concerns on this invention. It is a figure which shows the 9Cr steel welded steel straight pipe (9Cr steel welded joint) used as an actual machine as a test material. It is a schematic diagram explaining the measurement point of Vickers hardness and the reference point for coordinate management. It is a figure which shows the distribution of the Vickers hardness of the 9Cr steel welded steel straight pipe (9Cr steel welded joint) used as an actual machine as a test material. It is a figure which shows the row of the measured indentation (two rows parallel to each other) in the measurement of Vickers hardness, and the mark indentation formed on the outside of them. It is a figure explaining the mode of punching of a sample (in other words, the condition concerned with the range of punching as a sample).

Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

1 to 6 show an example of an embodiment of the sample preparation method according to the present invention.

In the sample preparation method of the present embodiment, the Vickers hardness of the test material is measured, and a plurality of measurement indentations arranged on the two rows of dotted lines a and b parallel to each other are formed on the surface of the test material. A pair of marking indentations is formed on the surface of the test material by referring to the measurement indentations selected from each of the two rows corresponding to the observation target points among these plurality of measurement indentations, and the pair of marking indentations is included. A sample is taken from the test material, and electrolytic polishing is performed after forming a spherical dent centered on the midpoint C of the line segment connecting the pair of marking indentations.

As the material of the sample produced by applying the present invention, a metal can be a target, and specifically, for example, a high chromium steel can be a target. The high-chromium steel is a martensite heat-resistant steel having improved creep strength by adding molybdenum, niobium, vanadium, etc. to an iron-chromium alloy containing about 9 to 12% chromium.

As a procedure of the sample preparation method according to the present invention, first, the test material is processed (S1).

Specifically, the test material is a member from, for example, a building structure such as a building, a mechanical structure such as a plant, a product such as a vehicle, or a component or part such as a pipe as an object of analysis / evaluation. Or parts are removed as a whole or cut out as part of a member or part. From the sample material that has been removed or cut out, a sample that is actually used for observation with a transmission electron microscope is collected. That is, the test material is a member or part or a part thereof from which the sample actually used for observation is collected.

Then, the sample material that has been removed or cut out has an appropriate size (specifically, for example, from 10 mm in length, width, and thickness) so that subsequent work can be easily performed, if necessary. It is cut to several tens of mm) or the surface is polished.

The polishing method and procedure are not limited to a specific type or order, but specifically, for example, the following contents can be considered as an example.
1) SiC water-resistant abrasive paper is used, and the number 600 is used as a guideline as the starting count, and the number is gradually increased to 2400 for polishing. The choice of younger count is determined by the trade-off between machining speed and the amount of work to subsequently remove the strain introduced at that time.
2) A diamond spray with a diameter of 3 μm followed by a diamond spray with a diameter of 1 μm is used for polishing.
3) Silica (diameter 0.04 μm) is used for mirror polishing.

In the present embodiment, the test material is cut out from a 9Cr steel welded steel straight pipe (in other words, a 9Cr steel welded joint) used in an actual machine and collected. The 9Cr steel is a high chromium steel containing 9 wt% Cr.

Specifically, the 9Cr steel welded steel straight pipe has been used for a long time in an actual machine over a steam temperature of 602 ° C., an internal pressure of 5.3 MPa, and a cumulative operating time of 117,000 hours. Is 43 mm and has an outer diameter of 863.6 mm and has longitudinal welding.

FIG. 2 shows a welded portion cross section (note that the length is 45 mm, the width is 20 mm, and the thickness is 10 mm) of the test material cut out from the 9Cr steel welded steel straight pipe in the present embodiment. In FIG. 2, reference numeral BM represents a base material, reference numeral HAZ represents a weld heat affected zone, and reference numeral WM represents a weld metal. From FIG. 2, it is confirmed that the width of the weld heat affected zone HAZ is about 3 mm.

After the same polishing as 1) to 3) above was performed on the test material collected from the 9Cr steel welded steel straight pipe, the polished surface was etched with nital and observed with an optical microscope. The part becomes visible.

Next, the Vickers hardness is measured (S2).

Specifically, for example, the measurement of Vickers hardness is performed under the measurement conditions of a load of 300 g, a holding time of 10 seconds, and a measurement interval of 0.2 mm, and the welded joint portion (particularly, the weld heat affected zone HAZ). It is done linearly so as to cross.

Here, in the processing of the sample for observation, the structure of the indentation part is changed by plastic deformation, so it is necessary to avoid the indentation part (in other words, the part where the structure is changed by plastic deformation) and thin the film. There is.

The relationship between the thin film candidate points (locations) and the Vickers hardness measurement point group will be described with reference to FIG. It is assumed that the portion indicated by the “center” in FIG. 3 is a thin film candidate location. In FIG. 3, the direction of transition from the region of the base metal BM to the region of the weld metal WM (in other words, the direction intersecting the boundary between the region of the base metal BM and the region of the weld metal WM) is defined as the X-axis direction. The direction orthogonal to the axial direction is defined as the Y-axis direction.

The Vickers hardness is measured at a position shifted by 1 mm in the positive (+) direction in the Y-axis direction from the thin film candidate point so as to sandwich the thin film candidate point (that is, the point indicated by the “center”) and Y. It is performed along the X-axis direction at each position offset by 1 mm in the negative axial direction. That is, the Vickers hardness is measured on two parallel straight lines with a mutual distance of 2 mm sandwiching the thin film candidate point in the center (dotted lines a and b in FIG. 3).

The indentation formed by the measurement of Vickers hardness is called "measurement indentation". A plurality of measurement indentations are formed side by side in two rows parallel to each other as shown by the two dotted lines a and b in FIG.

Next, the mark indentation is formed (S3).

Specifically, first, based on the measurement result of Vickers hardness, a part of the test material to be observed by a transmission electron microscope (referred to as an “observation target part”) is selected.

In the present embodiment, the softest point (in other words, the central portion of the wall thickness) in the welded joint portion of the test material is selected as the observation target location.

FIG. 4 shows the hardness distribution of the welded joint portion measured along each of the two dotted lines a and b in FIG. Regarding the legend in the figure, "1 mm below" indicates the position shifted by 1 mm in the negative direction in the Y-axis direction from the candidate point of the thin film, and indicates that the data is measured on the dotted line b in FIG. , "1 mm above" is a position shifted by 1 mm in the positive (+) direction in the Y-axis direction from the thin film candidate point, and indicates that the data is measured on the dotted line a in FIG.

From FIG. 4, it is confirmed that the hardness of the base metal BM is about 190 Hv, the hardness of the weld metal WM is about 200 Hv, and the hardness of the weld heat affected zone HAZ is 168 Hv. (Position of arrow in FIG. 4) is confirmed.

By measuring the Vickers hardness, the hardness at each measured indentation position on the dotted line a and the hardness at each measured indentation position on the dotted line b, which are arranged in two rows parallel to each other, can be grasped. Therefore, the hardness at each position between the dotted line a and the dotted line b can be grasped based on the combination of the hardness on the dotted line a and the hardness on the dotted line b.

Specifically, for example, the average value of the hardness at each measured indentation position on the dotted line a and the hardness at each measured indentation position on the dotted line b is defined as the hardness at the intermediate position between the measured indentations. Can be considered. When grasping the hardness between the dotted line a and the dotted line b, the measured indentation and the dotted line b on the dotted line a facing each other in the front in the Y-axis direction (that is, the coordinates with respect to the X axis are the same). The above measurement indentation may be combined, or the measurement indentation on the dotted line a and the measurement on the dotted line b at positions deviated from each other in the Y-axis direction (that is, the coordinates with respect to the X axis are different). It may be combined with an indentation.

By devising the combination of the measured indentation on the dotted line a and the measured indentation on the dotted line b, samples having different degrees of hardness are prepared, and between the degree of hardness and the aspect of the microstructure / fine precipitate. It becomes possible to grasp and analyze the relationship between.

Then, by thinning the region between the two dotted lines a and b shown in FIG. 3, the Vickers hardness is used for observation corresponding to the hardness value at each measurement point (that is, the measurement indentation). A sample will be obtained.

It should be noted that all of the hardness data at each measured indentation position on the dotted line a and the hardness data at each measured indentation position on the dotted line b are regarded as a group of data, and among all the data, the hardness is hard. You may focus on the measurement point with the lowest hardness or the measurement point with the highest hardness.

In the present embodiment, on the dotted line b where the hardness is the lowest as the softening point (in other words, in the central part of the wall thickness) in the welded joint portion as an observation target portion based on the measurement result of Vickers hardness. (That is, the measurement point at the position of the arrow in FIG. 4 (measurement indentation)) is specified, and the measurement indentation and the measurement indentation facing the measurement indentation in the Y-axis direction are used as marks on the outside of each of the measurement indentations. Indentations (called "mark indentations") are formed.

Explaining in the example shown in FIG. 3, the “outside” of the measured indentation is not the region between the two dotted lines a and the dotted line b, but the dotted lines b and a on the opposite side for each of the dotted lines a and b. It is the area on the opposite side of the opposite side.

Specifically, in the example shown in FIG. 5, a pair of mark indentations are formed on the outside of each of the measurement indentations at the 14th point from the left among the measurement indentations on the dotted line a and the dotted line b (FIG. 5). The position indicated by the arrow in the figure below).

Next, the sample is punched out (S4).

Specifically, the test material is further cut or polished as necessary, and then a thin plate-shaped sample is collected from the test material.

First, the test material is cut into a plate shape by, for example, wire cutting.

The thickness of the test material after being cut into a plate shape is not limited to a specific dimension, for example, in the subsequent processing, it becomes the final thickness of the sample used for observation with a transmission electron microscope. It is appropriately adjusted to an appropriate size after considering processing by polishing. Specifically, for example, the test material is cut so as to have a thickness of 0.5 mm, for example.

Here, the position coordinates of each of the measured indentations formed by the measurement of Vickers hardness are managed with reference to a specific portion of the test material (origin and circles 1 to 3 in the example shown in FIG. 3).

As a result, even when the test material is cut into a plate shape, the positions of each measurement indentation and a pair of mark indentations can be specified in each of the plate-shaped test materials. In the example shown in FIG. 3, the test material is cut into a plate shape along a plane parallel to a plane including the X-axis and the Y-axis (in other words, the XY plane).

As in the example shown in FIG. 3, in order to accurately grasp the coordinates of the portion indicated by the “center” which is the thin film candidate point, the circles 4 to 7 (specifically, for example, the dotted line a) in the figure. The position coordinates of the two measurement indentations (circles 4 and 5) appropriately separated above and the two measurement indentations (circles 6 and 7) appropriately separated on the dotted line b are managed and used. You can do it. As a result, for example, the mutual positional relationship / arrangement relationship of the two rows of measurement indentations (that is, the dotted line a and the dotted line b) and the respective angles of the dotted line a and the dotted line b with respect to the direction connecting the origin and the circle 3 (separate). In other words, it will be possible to check the arrangement status of the two rows in the test material such as tilt).

The Vickers hardness may be measured for each of the cut plate-shaped test materials.

The cut plate-shaped test material is mechanically polished to remove processing strain and thin the plate, and is processed into a thin plate having a thickness of, for example, 0.15 mm or less.

Then, a thin plate-shaped sample is punched from the test material processed into a thin plate by, for example, a punching machine.

When a thin plate-shaped sample is punched out, the midpoint C of the line segment connecting the pair of marking indentations at the center (or approximately the center) of the punched range (that is, the sample to be punched) (x mark in FIG. 5). The position of the punching range is adjusted so that) is located.

Further, the sample punched out from the test material is formed in a shape in which a part of the circle is missing while being based on a circle in a plan view (in other words, a flat plate view).

The plan view shape of the sample can be specifically formed into a shape in which a part of the circular peripheral edge portion is cut off, as in the shape shown as “the range to be punched out as a sample” in FIG. In the example shown in FIG. 6, the "range for punching as a sample" is basically a circle with a diameter of 3 mm.

The plan-view shape of the sample is such that the X-axis direction and Y-axis direction of the punched sample (that is, the X-axis direction and Y-axis direction of the test material from which the sample is punched) can be specified. The example is not limited to the example shown in FIG. 6, and for example, a wedge-shaped notch may be formed at the peripheral edge of the circle.

A part of the cut-out circular peripheral edge or a notch formed in the circular peripheral edge for specifying the X-axis direction and the Y-axis direction of the sample is called a “direction specifying portion”. It should be noted that only one direction specifying portion may be formed and provided on the peripheral peripheral portion of the circle, or a plurality of direction specifying portions may be formed and provided.

The front and back of the punched sample can be distinguished and grasped by the measurement indentation and mark indentation on the sample surface and the direction specifying portion formed on a part of the peripheral edge of the sample, and in the X-axis direction and the Y-axis direction. Is identified and grasped.

Next, a spherical recess is formed (S5).

This treatment is performed as a pretreatment for electrolytic polishing in the next treatment of S6 so that the observation target portion is accurately and surely thinned.

Specifically, for example, a dimple grinder grinds a portion of the observation target portion on one side (that is, either the front surface or the back surface) of the sample in the thickness direction by, for example, about 30 μm to form a spherical dent. Will be done.

The portion to be observed is a certain range centered on the midpoint position of the line segment connecting the pair of mark indentations. For example, in the examples shown in FIGS. 5 and 6, it is a circle having a diameter of about 2 mm centered on the position of the midpoint C (marked with x in the figure) of the line segment connecting the pair of marking indentations.

Here, in the process of S4, when the portion to be sampled is punched, the position corresponding to the observation target portion from the center position of the range actually punched (that is, the sample actually punched) (that is, a pair of mark indentations). Even if the position of the midpoint C of the line segment connecting the two is displaced, for example, the grinding position is adjusted during grinding by the dimple grinder to the position of the midpoint C of the line segment connecting the pair of mark indentations. Based on this, the position corresponding to the observation target portion is ground, and a spherical recess is formed so that the position of the apex coincides with the position corresponding to the observation target portion.

The means and method for forming a spherical dent on the surface of the sample are not limited to a specific device or mechanism as long as the spherical dent can be formed on the surface of the sample, for example, the sample. Appropriate equipment and mechanism are appropriately selected after considering the material of. Specifically, for example, a dimple grinder can be used as described above.

Next, electrolytic polishing is performed (S6).

This process is performed to thin the observation target portion.

Specifically, for example, a twin-jet electrolytic polishing device polishes both sides of the sample (that is, both the front surface and the back surface) by, for example, about 60 μm in the thickness direction to form a thin film.

In the electrolytic polishing, the spherical concave portion formed in the above-mentioned treatment of S5 is preferentially polished to form a thin film.

For electrolytic polishing, for example, a mixed solution of perchloric acid and acetic acid (for example, 15% perchloric acid and 85% acetic acid) is mainly used as the electrolytic solution, the voltage is 20 to 25 V, and the liquid temperature is 5 to 10. It can be done under conditions adjusted to ° C.

It should be noted that the measured indentations and the mark indentations are placed outside the holes of the holder in which the sample is set during electrolytic polishing, in other words, by using a holder in which the formed portions of these indentations are covered, at least preferentially. Can be prevented from being polished.

Further, the means and method for electrolytically polishing the sample are not limited to a specific device or mechanism as long as they can polish the spherical concave portion formed on the surface of the sample, for example, the sample. Appropriate equipment and mechanism are appropriately selected after considering the material. Specifically, for example, as described above, a twin jet electrolytic polishing apparatus can be used.

By the treatment up to S6, a hole having a diameter of, for example, about 50 μm is formed in the observation target portion of the sample, and the circumference of the hole is processed into a thin film having a thickness of about 0.10 μm. Then, the thinned portion is observed by observing with a transmission electron microscope.

In order to avoid the formation of holes in the observation target location, in the process of S5, a spherical dent is formed at a position deviated from the center position of the true observation target location by, for example, several tens of μm. Is also good.

By the above processing, a sample used for observation with a transmission electron microscope is produced in which the softened portion of the test material to be observed and analyzed in the present embodiment is thinned.

According to the sample preparation method configured as described above, the indentation formed at the time of measuring the Vickers hardness is used as a marker for alignment at the time of sample processing. Therefore, for example, the measurement of the Vickers hardness is performed. It is possible to accurately identify and grasp the position of the observation target (in the sample) in the test material selected based on the results. For this reason, it is possible to cut out the target portion as an observation target as a sample with high accuracy, collect it, or thin it, and it is possible to improve the usefulness and reliability as a sample preparation method. become.

According to the sample preparation method configured as described above, since the spherical dent is formed and then the electrolytic polishing is performed, the dent portion is preferentially polished, and the observation target. The position of the portion can be preferentially thinned. Therefore, it is possible to surely thin the target portion as an observation target, and it is possible to improve the usefulness and reliability as a sample preparation method.

Although the above-described embodiment is an example of a preferred embodiment of the present invention, the embodiment of the present invention is not limited to the above-mentioned embodiment, and the present invention is not limited to the above-mentioned embodiment and does not deviate from the gist of the present invention. The invention can be modified in various ways.

For example, in the above-described embodiment, the test material is collected from the 9Cr steel welded steel straight pipe used in the actual machine, but the application target of the present invention is not limited to the 9Cr steel, but the 12Cr steel. Other high chrome steels such as, and further, are not limited to high chrome steels, and various metals to be observed by a transmission electron microscope can be targeted.

Further, in the above-described embodiment, the softened portion in the test material is thinned as an observation target portion, but the portion to be thinned by applying the present invention is the softened portion in the test material. The target is not limited to various points / positions selected as targets for observation / analysis by a transmission electron microscope among the test materials.

Further, in the above-described embodiment, the sample is taken from the test material in a shape in which a part of the peripheral portion is missing, but in the present invention, it is essential that a part of the peripheral portion of the sample is missing. It is not a requirement, and it is not necessary that a part of the peripheral edge of the sample is missing. Even in this case, it is possible to distinguish the front and back of the sample and specify the position of the observation target portion by the measurement indentation and the mark indentation.

BM Base Material HAZ Weld Heat Affected Zone WM Weld Metal

Claims (3)

The Vickers hardness of the test material is measured on two parallel straight lines sandwiching the thin film candidate point in the center, and multiple measurement indentations arranged in two rows parallel to each other are the surface of the test material. Formed in
Each row is identified plurality of said measured pressure trace for each column corresponding to the position of the observation target portion, wherein is selected in light of the results of measurement of Vickers hardness measurement pressure scars, eye mark indentations that Do a mark of the measurement pressure marks Are formed on the surface of the test material, respectively.
A circular sample containing the pair of marking indentations and the two rows of measurement indentations was taken from the test material.
A method for producing a sample used for observation with a transmission electron microscope, which comprises forming a spherical dent around the midpoint of a line segment connecting the pair of marking indentations and then performing electrolytic polishing. The method for producing a sample used for observation with a transmission electron microscope according to claim 1, wherein the sample is collected from the test material in a shape in which a part of a circular peripheral edge is missing. The method for producing a sample used for observation with a transmission electron microscope according to claim 1 or 2, wherein the test material is high-chromium steel.

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