An analytical method for visualizing the altered layer near the surface of a disc rotor due to friction.

Abstract

This provides an analytical method that can visualize the distribution of each crystal structure in the region near the friction surface of a disc rotor. [Solution] An analytical method comprising: a sample preparation step of preparing a sample for TEM measurement by cutting a disc rotor that has undergone friction with a friction material; and an acquisition step of performing measurement on the sample using the ACOM-TEM method and acquiring an electron diffraction pattern two-dimensionally with spatial resolution on the order of nanometers.

Description

Technical Field

[0001] The present disclosure relates to an analysis method for visualizing the crystal structure of a region near a friction surface subjected to shear stress generated during friction, with respect to a disc rotor used in brakes of automobiles and the like. Background Art

[0002] Friction materials such as disc brake pads (hereinafter also referred to as "pads") are used in brakes of automobiles and the like. The friction material has a role of braking by rubbing a counterpart member such as a disc rotor. Therefore, friction materials are required not only to have a high friction coefficient and stability of the friction coefficient, but also to have characteristics such as being less likely to abrade the counterpart member disc rotor (rotor wear resistance), being less likely to generate squeal (squeal characteristics), and having a long pad life (pad life).

[0003] In order to develop a friction material having excellent characteristics, evaluation of the friction surface of the counterpart member disc rotor is important. Wear of a friction material is accompanied by friction at the contact surface with the disc rotor. Therefore, to understand the wear mechanism, not only analysis of the friction material itself but also analysis of phenomena near the friction surface of the counterpart member disc rotor is useful.

[0004] A transfer film, which is a film containing components of the friction material, may exist near the friction surface of the disc rotor subjected to shear stress from the friction material. The transfer film is considered to be formed when components of the friction material ground by friction transfer to the disc rotor. The vicinity of the friction surface of the disc rotor where the transfer film exists is composed of, for example, the transfer film and the disc rotor main body in contact with the transfer film. Non-Patent Document 1 discloses an example in which the composition of a transfer film existing near the friction surface of a disc rotor is analyzed by a technique such as scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX). Prior Art Literature [Non-patent literature]

[0005] [Non-Patent Document 1] K. Nishimura et al., SAE Technical Papers 2021-01-1278 [Overview of the project] [Problems that the invention aims to solve]

[0006] To gain a deeper understanding of the wear mechanism, it is considered effective to analyze not only the composition but also the crystal structure of the region near the friction surface of the disc rotor. Furthermore, it is considered effective to perform the above analysis not only on the transfer film but also on the region near the interface between the transfer film and the disc rotor body in contact with it. Hereinafter, the region near the interface between the transfer film and the disc rotor body will also be simply referred to as the "region near the interface of the disc rotor body."

[0007] Generally, methods for analyzing crystal structures include scanning electron microscopy-backscatter electron diffraction (SEM-EBSD) and transmission electron microscopy-electron diffraction. SEM-EBSD, in particular, is known for its relatively high spatial resolution. However, to analyze and visualize the crystal structure in detail, especially in the region near the interface of the disc rotor body within the friction surface area of ​​the disc rotor, it has been found that even higher spatial resolution than that of SEM-EBSD is desired. Furthermore, while transmission electron microscopy-electron diffraction allows for crystal structure evaluation on the nanometer order, the area that can be measured at once is narrow. Therefore, an analytical method is desired that offers high spatial resolution on the nanometer order and can visualize the distribution of each crystal structure over a wide area.

[0008] In view of the above circumstances, one embodiment of this disclosure aims to provide an analytical method that can visualize the distribution of each crystal structure in the region near the friction surface of a disc rotor. [Means for solving the problem]

[0009] The following embodiments are included as specific means for solving the aforementioned problems. <1> The sample preparation process involves cutting a disc rotor that has undergone friction with a friction material to prepare a sample for TEM measurement, and The aforementioned sample is subjected to measurement by the ACOM-TEM method, and an acquisition step is performed to obtain a two-dimensional electron diffraction pattern with spatial resolution on the order of nanometers. An analytical method having the following characteristics. <2> An analysis step is performed to analyze the crystal phase and crystal orientation from the electron diffraction pattern obtained in the acquisition step and standard data of known electron diffraction patterns. A crystal grain map creation step is performed to create a crystal grain map from the analysis data obtained in the above analysis step, It further possesses, <1> The analysis method described below. <3> The measurement step width in the above measurement is 1 nm to 20 nm. <1> or <2> The analysis method described below. <4> The measurement step width in the above measurement is 1 nm to 10 nm. <1> or <2> The analysis method described below. <5> The measurement area in the above measurement is an area that extends at least 2 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <1> or <2> The analysis method described below. <6> The measurement area in the above measurement is an area that extends at least 5 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <1> or <2> The analysis method described below. <7> The measurement area in the above measurement is an area that extends at least 2 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <3> The analysis method described below. <8> The measurement area in the above measurement is an area that extends at least 5 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <3> The analysis method described below. <9> The measurement area in the above measurement is an area that extends at least 2 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <4> The analysis method described below. <10> The measurement area in the above measurement is an area that extends at least 5 μm in the depth direction from the friction surface of the disc rotor, and at least 1 μm in the direction perpendicular to the depth direction. <4> The analysis method described below. [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, an analytical method is provided that can visualize the distribution of each crystal structure in the region near the friction surface of a disc rotor. [Brief explanation of the drawing]

[0011] [Figure 1] This is an example of a grain map, which is a grayscale map. [Figure 2] This is an example of a grain boundary map, or a crystal grain map. [Modes for carrying out the invention]

[0012] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of such process is achieved. In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In the present disclosure, the term "layer" or "film" includes not only the case where the layer or film is formed over the entire region when observing the region where the layer or film exists, but also the case where the layer or film is formed only in a part of the region.

[0013] In the present disclosure, TEM stands for "Transmission Electron Microscope", and ACOM-TEM stands for "Automated Crystal Orientation Mapping in TEM based on TEM".

[0014] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise explicitly stated. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0015] [Analysis Method] An analysis method according to an embodiment of the present disclosure includes: a sample preparation step of cutting a disc rotor that has undergone friction with a friction material to prepare a sample for TEM measurement; and an acquisition step of performing measurement by the ACOM-TEM method on the sample and two-dimensionally acquiring electron diffraction patterns with nanometer-order spatial resolution. Here, "nanometer-order spatial resolution" refers to the ability to identify fine structures of 100 nm or less. The spatial resolution is preferably 100 nm or less, more preferably 50 nm or less, still more preferably 30 nm or less, and particularly preferably 10 nm or less. In addition, "acquiring two-dimensionally" refers to acquiring data on two-dimensional coordinates, that is, X-Y coordinates.

[0016] The ACOM-TEM method is a technique that can obtain high spatial-resolution crystal information in a measurement region by analyzing electron diffraction patterns observed through a sample to be measured at each point while scanning an electron beam probe irradiated onto the sample to be measured. By analyzing electron diffraction patterns continuously acquired at a plurality of measurement points within the measurement region, information on crystal orientation within or between crystal grains can be obtained. Using this technique, it is possible to acquire information on crystal grains and crystal orientation in a minute measurement region compared to other techniques such as the SEM-EBSD (Electron Back Scattered Diffraction) method.

[0017] In the present embodiment, the cut surface of a disk rotor is measured using the aforementioned ACOM-TEM method, and electron diffraction patterns are two-dimensionally acquired with nanometer-order spatial resolution. From each of the acquired electron diffraction patterns, the crystallinity of each region can be confirmed with nanometer-order spatial resolution. Then, by performing analysis and mapping according to the purpose using each of the acquired electron diffraction patterns, the distribution of each crystal structure in the region near the friction surface of the disk rotor can be visualized.

[0018] In the analysis according to the aforementioned purpose, for example, two-dimensionally acquired electron diffraction patterns are compared with standard data of known electron diffraction patterns, and the presence / absence of crystallinity, crystal phase, and crystal orientation are analyzed. Through this analysis, information on crystallinity and crystal structure at each position within the measurement region can be obtained.

[0019] In the aforementioned mapping, for example, a two-dimensional map is created using analysis data obtained by the foregoing analysis. Examples of two-dimensional maps include a phase distribution map showing the distribution of crystal phases identified in a specified crystal system, an image quality (IQ) map displaying the number of areas where the measured electron diffraction pattern matches the calculated value as the Image Quality (IQ) value in grayscale, a grain map that identifies crystal grains as the same grain when two or more measurement points within a specified azimuthal angle difference (5°) are consecutive, and displays them in a way that clearly shows the grain boundaries, and a crystal orientation map representing the average value of the azimuthal difference between a measurement point and all adjacent measurement points. Each of these two-dimensional maps visualizes different information.

[0020] When analyzing the crystal structure in the region near the interface of the disc rotor body, it is preferable to create a crystal grain map among these two-dimensional maps. In other words, the analysis method of this embodiment preferably further comprises, in addition to the sample preparation step and acquisition step, an analysis step for analyzing the crystal phase and crystal orientation from the electron diffraction pattern acquired in the acquisition step and standard data of known electron diffraction patterns, and a crystal grain map creation step for creating a crystal grain map from the analysis data obtained in the analysis step. By going through the sample preparation, acquisition, analysis, and grain map creation processes, a grain map with nanometer-order spatial resolution can be obtained, allowing for the identification of grains down to the nanometer scale.

[0021] A grain map can be any map in which grain boundaries are clearly displayed. It can be a pseudo-color map that simulates adjacent grains with different colors, a grayscale map obtained by converting a pseudo-color map to grayscale, or a grain boundary map that represents only grain boundaries with lines. Figure 1 shows an example of a grain map, which is a grayscale map. Figure 1 is a grain map obtained by converting a pseudo-color map of a cross-section cut perpendicular to the friction surface (hereinafter also referred to as the "depth direction") in the region near the friction surface of the disc rotor to grayscale. Figure 2 also shows an example of a grain map obtained by converting the grain map of Figure 1 from a grayscale map to a grain boundary map.

[0022] The grain maps shown in Figures 1 and 2 visualize the transfer film layer, which lacks grain boundaries, and the disc rotor body layer, which does have grain boundaries (i.e., is polycrystalline). For the transfer film layer, which lacks grain boundaries, its amorphous nature is confirmed by the shape of the electron diffraction pattern obtained by measuring the region of the transfer film. Furthermore, from the grain maps shown in Figures 1 and 2, it can be seen that the crystal grains in the disc rotor body become smaller as they approach the transfer film, and in the region near the interface in contact with the transfer film, the short axis is about 10 nm. In other words, by using the analysis method of this embodiment, the distribution of each crystal structure in the region near the friction surface of the disc rotor can be visualized in two dimensions, and for the first time, it can be seen that the region near the interface of the disc rotor body is an altered layer composed of crystal grains on the order of nanometers.

[0023] The analysis method in this embodiment preferably includes at least a sample preparation step and an acquisition step, and an analysis step and a crystal grain map creation step, and may include other steps as needed. Other steps include, for example, a step of creating maps other than crystal grain maps (such as the phase distribution map, image quality map, crystal orientation map, etc. mentioned above). The following describes each step in an analytical method, which is an example of an analytical method in this embodiment and includes a sample preparation step, a sample acquisition step, an analysis step, and a crystal grain map creation step.

[0024] <Sample preparation process> In the sample preparation process, the disc rotor, which has undergone friction with the friction material, is cut to prepare a sample for TEM measurement. Methods for cutting disk rotors include, for example, focused ion beam (FIB) cutting, mechanical polishing, ion milling, electrolytic polishing, ultrasonic slicing, and combinations thereof. Among these, the FIB method is preferred for cutting disk rotors due to its high precision. An example of equipment for performing cutting by the FIB method is an FIB-SEM apparatus.

[0025] When cutting a disk rotor using the FIB method, pretreatment may be performed before cutting by the FIB method. Examples of pretreatment include sample size adjustment, which involves cutting the sample to a size that can be placed in the sample chamber of the FIB-SEM instrument, and the formation of a protective film to protect the sample surface before cutting. Examples of protective films include conductive films such as platinum films, tungsten films, gold films, and carbon films; inorganic insulating films such as silicon oxide films and silicon nitride films; and organic films such as resist films and organic resin films. Among these, conductive films are preferred as protective films from the viewpoint of mechanical protection and conductivity, conductive metal films are more preferred, and platinum films are even more preferred. The conductive film may be a vapor-deposited film, a sputtered film, or an ion beam deposited film, or a combination of these may be used.

[0026] The cutting direction of the disc rotor is appropriately selected based on the area to be observed and the direction of observation. For example, when checking the change in direction from the friction surface of the disc rotor toward the interior, it is desirable to cut in a direction nearly perpendicular to the friction surface of the disc rotor, i.e., in the depth direction. Also, when evaluating the effect of shear stress due to the friction material, it is desirable to cut in a direction that is perpendicular to the friction surface of the disc rotor and close to the direction of the shear stress (i.e., the circumferential direction).

[0027] For TEM measurements, the sample thickness is preferably 50 nm to 150 nm, and more preferably 50 nm to 100 nm, from the viewpoint of improving electron transmittance and image contrast. The planar dimensions of the sample for TEM measurement should be larger than the measurement area described later, and should be sized to fit in the sample chamber of the measuring device. Preferably, the planar dimensions of the sample for TEM measurement should encompass the area to be observed. For example, when observing both the area near the interface between the transfer film and the disc rotor body, it is desirable that the sample for TEM measurement encompass the area to be observed within the area near the friction surface of the disc rotor.

[0028] Examples of disc rotors that have undergone friction with friction materials include disc rotors that have been used in automobile brakes and disc rotors that have undergone braking tests using friction materials.

[0029] Suitable materials for the disc rotor include cast iron (e.g., gray cast iron, ductile cast iron, etc.) and carbon steel. Among these, cast iron is preferred from the viewpoint of machinability and crystallinity of the disc rotor after friction.

[0030] Examples of friction materials include friction material compositions containing a binder, an organic filler, an inorganic filler, and a fibrous base material, which are then molded. The binder can be any material that can integrate organic fillers, inorganic fillers, fiber substrates, etc., contained in the friction material composition. Examples include thermosetting resins such as phenolic resins, acrylic rubber-modified phenolic resins, silicone rubber-modified phenolic resins, cashew-modified phenolic resins, epoxy-modified phenolic resins, and alkylbenzene-modified phenolic resins.

[0031] The organic filler can function as a friction modifier that improves the sound and vibration performance (i.e., the ability to reduce squeaking and vibration during braking), wear resistance, etc., of the friction material. Examples include cashew dust and rubber components. Cashew dust is obtained by crushing hardened cashew nut shell oil. Examples of rubber components include natural rubber, acrylic rubber, isoprene rubber, polybutadiene rubber (BR), nitrile-butadiene rubber (NBR), and styrene-butadiene rubber (SBR).

[0032] Examples of inorganic fillers include zirconium oxide, titanates, magnesium oxide, metal sulfides, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, coke, iron oxide, vermiculite, calcium sulfate, graphite, mica, talc, clay, zeolite, zirconium silicate, mullite, chromite, titanium oxide, silica, activated alumina such as α-alumina and γ-alumina.

[0033] The fibrous base material can be any material that exhibits a reinforcing effect in the friction material. This can include inorganic fibers such as rock wool, glass fibers, and ceramic fibers; metal fibers such as iron fibers, copper fibers, and brass fibers; organic fibers such as aramid fibers; and carbon-based fibers. These can be used individually or in combination of two or more types. The friction material composition may contain other components as needed. Examples of other components include organic additives such as fluorine-based polymers such as polytetrafluoroethylene (PTFE).

[0034] <Acquisition process> In the acquisition process, the sample obtained in the sample preparation process is measured using the ACOM-TEM method to acquire a two-dimensional electron diffraction pattern with a spatial resolution on the order of nanometers. Hereinafter, the measurement using the ACOM-TEM method will also be referred to as "ACOM-TEM measurement". Suitable analytical instruments for ACOM-TEM measurements include Schottky emission TEMs and cold cathode field emission TEMs, but from the viewpoint of operational stability, Schottky emission TEMs are preferable.

[0035] Examples of acceleration voltages in ACOM-TEM measurements include 80kV to 300kV, with 150kV to 300kV being preferred and 200kV to 300kV being more preferred from the viewpoint of obtaining high spatial resolution. Examples of beam diameters for ACOM-TEM measurements include 0.5 nm to 5.0 nm, with 0.7 nm to 1.5 nm being preferred from the viewpoint of obtaining high spatial resolution. In ACOM-TEM measurements, when using precession electron diffraction, the precession angle is preferably 0.5° to 3°, preferably 0.5° to 2°, and more preferably 0.5° to 1°, from the viewpoint of obtaining high spatial resolution. For ACOM-TEM measurements, the camera length can range from 50mm to 1000mm, with 300mm to 800mm being preferred and 500mm to 700mm more preferred from the viewpoint of obtaining high angular resolution of the diffraction pattern. In ACOM-TEM measurements, the measurement step width can range from 1 nm to 50 nm, and from the viewpoint of balancing spatial resolution and mapping speed, 1 nm to 20 nm is preferred, and 1 nm to 10 nm is more preferred.

[0036] In ACOM-TEM measurements, the measurement area only needs to encompass the area to be observed, and it is desirable to cover an area beyond that. When observing the region near the interface between the transfer film and the disc rotor body, the measurement area is preferably a region of 5 μm or more in the depth direction from the friction surface of the disc rotor, and 1 μm or more in the direction perpendicular to the depth direction. The distance from the friction surface of the disc rotor in the depth direction within the measurement area (hereinafter also referred to as "measurement depth") is preferably 5 μm or more, and more preferably 6 μm or more, from the viewpoint of improving analytical accuracy. The measurement depth is preferably 5 μm to 10 μm, and more preferably 6 μm to 10 μm, from the viewpoint of balancing analytical accuracy and measurement efficiency. The distance in the direction perpendicular to the depth direction within the measurement area (hereinafter also referred to as "measurement width") is preferably 1 μm or more, and more preferably 3 μm or less, from the viewpoint of improving analytical accuracy. The measurement width is preferably 1 μm to 5 μm, and more preferably 3 μm to 5 μm, from the viewpoint of balancing analytical accuracy and measurement efficiency.

[0037] <Analysis process> In the analysis process, the crystal phase and crystal orientation are analyzed from the electron diffraction pattern obtained in the acquisition process and standard data of known electron diffraction patterns. Specifically, first, the electron diffraction pattern obtained through the acquisition process is matched with a standard database (e.g., ICDD database, CIF file, etc.) to identify the crystal phase and crystal orientation of the sample. In this matching process, for example, the acquired electron diffraction pattern is compared with known standard data, and the crystal phase and crystal orientation are initially identified using cross-correlation analysis, an automated pattern recognition algorithm, etc.

[0038] In the analysis of crystalline phases, the distance between diffraction spots is measured based on Bragg's law from the acquired electron diffraction pattern, and the lattice plane spacing (d-spacing) is calculated. Subsequently, Miller indices (hkl) are assigned to the diffraction spots to perform indexing, and if multiple crystalline phases exist, a multiphase analysis is performed to identify each phase. In crystal orientation analysis, after identifying the crystalline phase, the crystal orientation within the sample is determined by calculating the orientation matrix. Furthermore, during the analysis process, it is possible to obtain information about the crystallinity of each measurement location, such as whether the material is crystalline, amorphous, or partially crystalline, based on the presence and clarity of the diffraction pattern at that location. This crystallinity information serves as the basic data for the grain map creation process described later.

[0039] <Grain map creation process> In the grain map creation process, a grain map is created from the analysis data obtained in the analysis process. In other words, a grain map is generated that visually shows the distribution and boundaries of crystal grains in the sample, based on the crystal orientation data and crystallinity information obtained in the analysis process. Specifically, the crystal orientation difference (mis-orientation) between adjacent data points is first calculated, and any orientation difference exceeding a predetermined threshold is defined as a grain boundary. Next, within the region where the grain boundary is defined, groups of pixels with the same orientation are recognized as a single crystal grain, and characteristic quantities (grain size, grain shape, grain boundary length, etc.) for each crystal grain are extracted. Based on this information, a crystal grain map is created by visualizing each crystal grain with a different color, or by representing only the grain boundaries with lines. Furthermore, by reflecting the crystallinity information obtained in the analysis process, it becomes possible to clearly distinguish between amorphous and crystalline regions. Software that can be used for the analysis process and the creation of crystal grain maps includes ASTAR, OIM Analysis, CrystalMaker, and MTEX.

[0040] [Example Test] The above embodiments will be described in detail below with reference to test examples, but the scope of the above embodiments is not limited to these test examples.

[0041] <Preparation of the disc rotor after friction with the friction material> As part of the brake performance testing, a braking test was conducted using a 1 / 5 scale tester with friction material. Commercially available disc brake pads (manufactured by Resonac) were used as the friction material. Furthermore, a caliper included with a 1 / 5 scale tester was used as the brake caliper to control the friction force, and a gray cast iron disc rotor was used as the disc rotor.

[0042] The specific procedures for the braking test were as follows: After rubbing the disc brake pads against the friction surface of the disc rotor, an initial lapping brake was performed using the brake caliper under the conditions of a vehicle speed of 65 km / h, a hydraulic pressure of 4.93 MPa, and a disc rotor temperature of 25°C. Subsequently, under the same vehicle speed and hydraulic pressure conditions, 500 braking cycles were performed at each disc rotor temperature of 100°C, 200°C, 300°C, and 400°C. The coefficient of friction was also measured under each temperature condition. In total, including the initial lapping brake, a total of 2,500 braking cycles were performed.

[0043] <Cutting the disc rotor> After the braking test, a metal surface protection film (manufactured by Nitto Denko Corporation) was applied to the friction surface of the disc rotor, and then 1cm x 1cm pieces of the disc rotor were cut out using a diamond cutter for metalworking. These disc rotor pieces were cut from a total of four locations at 90° intervals concentrically in the center of the sliding surface of the disc rotor after braking tests, and include the friction surface of the disc rotor.

[0044] A platinum electron beam assist film, a conductive metal film, was applied to the friction surface of the obtained disc rotor piece to a thickness of approximately 10 nm. Specifically, a commercially available Pt sputter coater (E-1045, manufactured by Hitachi High-Tech) was used, with the Pt target positioned 30 mm away from the friction surface of the disc rotor piece, and sputtering was performed for 30 seconds at a vacuum of 6 Pa and a discharge current of 30 mA.

[0045] A disc rotor piece with a conductive metal film was fixed to the FIB-SEM sample stage using commercially available conductive carbon tape and introduced into the FIB-SEM apparatus. A Scios2 FIB-SEM manufactured by FEI Japan was used. While observing SE or BSE images of the disc rotor surface on the control PC screen, the processing position was located, and a Pt ion beam-assisted film was deposited for surface protection. As the processing position, a smooth area of ​​the friction surface of the disc rotor piece, where no grooves were formed, was selected.

[0046] The friction surface of a disc rotor piece on which a Pt ion beam assisted film was formed was processed with a Ga ion beam. The applied voltage was adjusted to 30 kV for rough cutting and 5 kV for finishing. Cutting was performed perpendicularly to the friction surface and along the direction of shear stress from the friction material. The direction of shear stress from the friction material can be confirmed by the direction of grooves formed on the friction surface of the disc rotor piece. Under the above processing conditions, a thin slice was produced to a thickness of 100 nm, which was used as a sample for TEM measurement having a planar dimension of approximately 15 µm × 10 µm and a thickness of 100 nm.

[0047] <Measurement and Analysis by ACOM-TEM Method> A TEM observation image was captured of the obtained sample for TEM measurement using a transmission electron microscope (JEM-2100F, manufactured by JEOL). Furthermore, for the purpose of analyzing crystal grain size and orientation, ASTAR2 (TOPSPIN) manufactured by Nanomegas installed in the transmission electron microscope apparatus was used to analyze the transfer film layer and the cast iron layer of the disc rotor body, and an analysis image was obtained using analysis software (OIM Analysis ver.7, manufactured by EDAX-TSL solution). Specifically, crystal grains were identified by regarding the case where two or more consecutive measurement points exist within a specified azimuthal angle difference (5°) as the same grain, and a pseudo-color displayed Grain Map was obtained.

[0048] The apparatuses, conditions, and the like used for measurement and analysis by the ACOM-TEM method are as follows. Analysis apparatus: Schottky transmission electron microscope (JEM-2100F, manufactured by JEOL) Detector name: ASTAR2 (TOPSPIN), manufactured by Nanomegas Software name: OIM Analysis ver.7.x, manufactured by EDAX-TSL Acceleration voltage: 200 kV Beam diameter: 1 nmφ (Nano-beam Diffraction) Precession angle: 0.5 degree Camera length: 600 mm Measurement step width: 10 nm / step Measurement depth: 6 μm Measurement width: 3μm TEM sample thickness: 100 nm

[0049] Figure 1 shows the obtained pseudo-color map, which is the grain map, converted to a grayscale map, and Figure 2 shows the same result when converted to a grain boundary map. In the grain maps shown in Figures 1 and 2, the transfer film layer is observed at the top, and the disc rotor body layer is observed below it. From the grain maps in Figures 1 and 2, it can be seen that the transfer film layer is a layer without grain boundaries. Furthermore, from the grain maps in Figures 1 and 2, it can be seen that the disc rotor body layer is polycrystalline with grain boundaries, and that the grain size decreases as it approaches the transfer film, with the short axis being about 10 nm in the region near the interface in contact with the transfer film.

[0050] As described above, the analysis method of this embodiment allows for the visualization of the distribution of each crystal structure over a wide area with high spatial resolution on the order of nanometers. Therefore, it is possible to visualize crystal grains with a short axis of about 10 nm, which could not be visualized by other conventional methods (e.g., SEM-EBSD method). Furthermore, by visualizing the distribution of each crystal structure in the region near the friction surface of the disc rotor, it was discovered for the first time that the altered layer formed in the region near the interface of the disc rotor body is composed of crystal grains on the order of nanometers.

Claims

1. The sample preparation process involves cutting a disc rotor that has undergone friction with a friction material to prepare a sample for TEM measurement, and The aforementioned sample is subjected to measurement using the ACOM-TEM method, and an acquisition step is performed to obtain a two-dimensional electron diffraction pattern with spatial resolution on the order of nanometers. An analytical method having the following characteristics.

2. An analysis step is performed to analyze the crystal phase and crystal orientation from the electron diffraction pattern obtained in the acquisition step and standard data of known electron diffraction patterns. A crystal grain map creation step is performed to create a crystal grain map from the analysis data obtained in the above analysis step, The analytical method according to claim 1, further comprising the above.

3. The analytical method according to claim 1 or 2, wherein the measurement step width in the measurement is 1 nm to 20 nm.

4. The analytical method according to claim 1 or 2, wherein the measurement step width in the measurement is 1 nm to 10 nm.

5. The analysis method according to claim 1 or 2, wherein the measurement area in the measurement is an area of ​​2 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

6. The analysis method according to claim 1 or 2, wherein the measurement area in the measurement is an area of ​​5 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

7. The analysis method according to claim 3, wherein the measurement area in the measurement is an area of ​​2 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

8. The analysis method according to claim 3, wherein the measurement area in the measurement is an area of ​​5 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

9. The analysis method according to claim 4, wherein the measurement area in the measurement is an area of ​​2 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

10. The analysis method according to claim 4, wherein the measurement area in the measurement is an area of ​​5 μm or more in the depth direction from the friction surface of the disc rotor and 1 μm or more in the direction perpendicular to the depth direction.

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