Method and device for evaluating the degree of damage to crystalline materials

Abstract

To provide an evaluation method capable of highly accurate evaluation of the degree of damage of a crystalline material other than a cubic crystal.SOLUTION: It is a method for evaluating the degree of damage of a crystalline material other than a cubic crystal, that evaluates the degree of damage to the crystalline material using diffracted waves on crystal planes belonging to the main slip system of crystals that constitute the crystalline material in a diffracted wave obtained by irradiating the crystalline material with radiation.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the degree of damage in a crystalline material other than a cubic crystal, and an apparatus for evaluating the degree of damage in a crystalline material other than a cubic crystal. [Background technology]

[0002] Crystalline materials, whether single crystal or polycrystalline, are used as materials for components used in all industrial fields. Such components are often used in environments where repeated stress is applied. For example, components for transport equipment that involves vibration, such as aircraft, railroad cars, and automobiles, components that are subjected to thermal cycles, such as electronic boards mounted on electrical equipment, and components that are subjected to high temperatures and repeated stress, such as gas turbines for power generation, are included. Important elemental technologies for crystalline materials include evaluation of static properties such as tensile strength and ductility, and evaluation of dynamic properties such as fatigue properties, with the aim of ensuring high safety and reliability of such components, as well as damage evaluation to prevent the destruction of such components. Many damage evaluation technologies for crystalline materials have already been proposed for crystalline materials with cubic crystal structures, such as steel, aluminum, and nickel alloys.

[0003] For example, Patent Document 1 discloses a method for measuring the crystallite size and non-uniform strain of rails, which are generally made of high carbon steel, by X-ray diffraction and predicting the occurrence of rolling fatigue cracks based on the results.

[0004] Patent Document 2 discloses a method for evaluating the degree of fatigue damage and remaining life of an aluminum alloy member using an X-ray diffraction peak profile.

[0005] Furthermore, Patent Document 3 discloses a method for measuring the plastic strain accumulated in a crystal of a metal material having a cubic crystal structure, using the lattice strain before and after plastic deformation measured by electron backscatter diffraction (EBSD). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-18114 A [Patent Document 2] Japanese Patent Application Publication No. 11-344454 [Patent Document 3] JP 2010-256310 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, for crystalline materials with crystal structures other than cubic, such as hexagonal and tetragonal, sufficient accuracy has not been achieved even when damage evaluation techniques for crystalline materials with cubic crystal structures are applied. Furthermore, damage evaluation techniques for crystalline materials with crystal structures other than cubic (hereinafter also referred to as "crystalline materials other than cubic") have not been sufficiently studied.

[0008] The present invention has been made in consideration of such problems, and has an object to provide an evaluation method capable of evaluating with high accuracy the degree of damage in crystalline materials other than cubic crystals. [Means for solving the problem]

[0009] As a result of extensive investigation, the present inventors have found that the above object can be achieved by the following configuration.

[0010] A method for evaluating the degree of damage to a crystalline material according to one aspect of the present invention is a method for evaluating the degree of damage to a crystalline material other than a cubic crystal, and evaluates the degree of damage to the crystalline material by using diffracted waves obtained by irradiating the crystalline material with radiation, the diffracted waves being from crystal planes belonging to the primary slip system of the crystals constituting the crystalline material.

[0011] An apparatus for evaluating the degree of damage in a crystalline material according to another aspect of the present invention is an apparatus for evaluating the degree of damage in a crystalline material other than a cubic crystal, and includes: a memory unit that uses a crystalline material made of the same type of material as the evaluation target, and stores a master curve that shows the correlation between the degree of damage in the crystalline material and diffraction data calculated using diffracted waves from crystal planes belonging to the primary slip system of the crystals constituting the crystalline material among the diffracted waves obtained by irradiating the crystalline material with radiation; a measurement unit that measures the diffracted waves obtained by irradiating the crystalline material to be evaluated with radiation; and a calculation unit that uses the diffracted waves measured by the measurement unit to obtain diffraction data of the crystalline material to be evaluated, calculated in the same manner as the diffraction data in the memory unit, and evaluates the degree of damage by comparing the diffraction data with the master curve. Effect of the Invention

[0012] According to the present invention, it is possible to provide an evaluation method capable of evaluating with high accuracy the degree of damage to crystalline materials other than cubic crystals. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the crystal planes of a hexagonal close-packed structure. [Diagram 2] Figures 2(a) and (b) are examples of crystal orientation maps for a steel material with a body-centered cubic structure obtained by the EBSD method. [Diagram 3] FIG. 3 is a schematic diagram of an evaluation device for the degree of damage in a crystalline material according to this embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between sin θ and β cos θ for a magnesium alloy test piece to which stress was applied 10 times. [Diagram 5] FIG. 5 is a graph showing the relationship between the number of times stress was applied and the microstrain calculated from all the diffraction peaks of the magnesium alloy. [Figure 6] FIG. 6 is a graph showing the relationship between the number of times stress was applied and the microstrain calculated only from the basal peak of a magnesium alloy. [Figure 7]FIG. 7 is a graph showing the relationship between the number of times stress was applied and the crystal orientation misorientation calculated using all the measurement data obtained by the EBSD measurement. [Figure 8] FIG. 8 is a graph showing the relationship between the number of times stress is applied and the basal plane orientation difference. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a method for evaluating the degree of damage in a crystalline material according to an embodiment of the present invention will be described.

[0015] The method for evaluating the damage level of a crystalline material according to the present embodiment is a method for evaluating the damage level of a crystalline material other than a cubic crystal, and is a method for evaluating the damage level of the crystalline material using diffracted waves from crystal planes belonging to the primary slip system of the crystals constituting the crystalline material among diffracted waves obtained by irradiating the crystalline material with radiation. This method makes it possible to evaluate the damage level of a crystalline material other than a cubic crystal with high accuracy.

[0016] The evaluation method according to this embodiment is intended to evaluate crystalline materials other than cubic crystals.

[0017] Examples of crystalline materials other than cubic crystals include crystalline materials having a hexagonal, close-packed hexagonal, tetragonal, trigonal, orthorhombic, or monoclinic crystal structure.

[0018] Crystalline materials having a hexagonal close-packed crystal structure (hereinafter also referred to as a "hexagonal close-packed structure") include magnesium, titanium, zirconium, zinc, and alloys thereof.

[0019] Examples of crystalline materials with crystal structures other than hexagonal close-packed crystals include neodymium for hexagonal crystals, tin and titanium oxide (rutile) for tetragonal crystals, aluminum oxide (sapphire) for trigonal crystals, titanium oxide (brookite) for orthorhombic crystals, and silicon dioxide (moganite, coesite) for monoclinic crystals.

[0020] Magnesium is used primarily in large transportation equipment such as aircraft, railway cars, and automobiles as a light metal material with the aim of saving energy and reducing the environmental burden. It is also used in sporting goods such as roller skates and snowboards, welfare equipment such as canes and knee braces, and the housings of tablets and laptops.

[0021] Taking advantage of its corrosion resistance, titanium is used in a variety of applications, including plate materials and turbine blades for power generation equipment, heat exchangers in chemical equipment, food, and steel plants, and more recently in aircraft components, medical applications such as artificial bones, consumer products such as eyeglasses, sporting goods such as golf and mountain climbing equipment, and architectural and civil engineering applications such as monuments.

[0022] Tin is widely used not only as an alloying element for solders, but also as an alloy for plain bearings and as a tableware material for crafts.

[0023] Aluminum oxide (sapphire) is also used in watch bearings and semiconductor substrates.

[0024] Next, the crystal planes (hereinafter also referred to as "primary slip planes") belonging to the primary slip system of the crystals constituting the crystalline material will be explained using a hexagonal close-packed crystalline material as an example. Figure 1 shows the crystal planes of a hexagonal close-packed structure, where (a) shows the basal plane ((0001) plane), (b) shows the prism plane ((10-10) plane), and (c) shows the pyramidal plane ((10-11) plane). In the original Miller indices, negative numbers are generally expressed by adding a ￣ (bar) above the numbers, but in this specification, due to notation restrictions, for convenience, a notation method of adding a - before the numbers is adopted.

[0025] As explained below, in magnesium, a crystalline material with a hexagonal close-packed structure, basal slip is the primary slip system, and the primary slip plane is the basal plane ((0001) plane). Deformation phenomena in crystalline materials such as metals are primarily caused by crystal slip. In crystalline materials with a hexagonal close-packed structure, the above-mentioned basal, prismatic, and pyramidal crystal planes can be surfaces prone to slip (slip planes). However, in magnesium, the stress required to cause slip on each of these crystal planes at room temperature is extremely large, less than 1 MPa for the basal plane, but 8 MPa for the prismatic and pyramidal planes, respectively.

[0026] Therefore, in magnesium, the plane that mainly acts as a slip plane when it is actually deformed at room temperature is the basal plane, and the contribution of the prism, pyramidal and other planes to the deformation of the crystal is small. In other words, in magnesium, the main slip plane is the basal plane ((0001) plane).

[0027] The primary slip system and the primary slip plane differ depending on the crystal structure and element. For example, zirconium and titanium, which are crystalline materials with the same hexagonal close-packed structure as magnesium, have a prismatic slip system (reference: Hideo Yoshinaga, Light Metals, Vol. 21 (1971), p. 836-849). In addition, the primary slip plane of tin, a tetragonal crystalline material, is the (010) plane (reference: Masami Fujiwara, Tomoo Hirokawa, Journal of the Japan Institute of Metals, Vol. 51 (1987), p. 830-838), and the primary slip plane of aluminum oxide (sapphire), a trigonal crystalline material, is the (01-10) plane (reference: Yoshitatsu Mizumoto, Yasuhiro Kakinuma, Proceedings of the 2016 Autumn Meeting of the Japan Society for Precision Engineering, p, 11-12).

[0028] The primary slip system of each crystalline material can be determined from values ​​described in previous papers, patent documents, and other literature. It can also be derived from computer simulations using molecular dynamics and other methods, or from experiments. Examples of such experimental methods include a method in which the primary slip plane is determined based on the direction of the slip line observed by performing a tensile test on a single crystal material, and a method in which the depth of cut caused by a scratch test is measured and the primary slip plane is determined based on the depth.

[0029] In crystal structures other than cubic crystals, the atomic arrangement is less symmetrical than in cubic structures, and there are no planes equivalent to the primary slip plane other than the plane parallel to the primary slip plane, or even if there are, the number of such planes is smaller than in cubic structures. Therefore, crystalline materials with crystal structures other than cubic crystals have a significant deformation anisotropy in that they are easily deformed in a direction parallel to the primary slip plane, but are difficult to deform in directions other than the direction parallel to the primary slip plane, such as a direction perpendicular to the primary slip plane.

[0030] In the method for evaluating the degree of damage to a crystalline material according to this embodiment, the degree of damage to the crystalline material is evaluated using diffracted waves obtained by irradiating radiation onto a crystalline material other than a cubic crystal having such deformation anisotropy.

[0031] Radiation is a general term for material particles that flow with high kinetic energy and high-energy electromagnetic waves. Examples of material particle radiation (particle radiation) include alpha rays, beta rays (electron beams), neutron beams, proton beams, heavy ion beams, and meson beams. Examples of electromagnetic wave radiation (electromagnetic radiation) include gamma rays and X-rays.

[0032] In the evaluation method according to the present embodiment, for example, X-rays and electron beams can be used. X-rays are electromagnetic waves with a wavelength of about 1 pm to 10 nm, and for example, CuKα rays (wavelength 0.15418 nm) and MoKα rays (wavelength 0.071069 nm) can be used. Electron beams refer to a flow of electrons accelerated by, for example, an accelerator.

[0033] When the above-mentioned crystalline material is irradiated with radiation, a diffracted wave is obtained. The obtained diffracted wave is affected by damage to the crystal structure caused by fatigue or the like in the crystalline material, so by analyzing this diffracted wave, the magnitude of damage caused in the crystalline material can be evaluated, and thus the degree of damage to the crystalline material can be evaluated. Examples of damage caused in the crystalline material include lattice strain caused in the crystalline material and crystal orientation misalignment caused in each crystal grain constituting the crystalline material. The crystal orientation misalignment caused in each crystal grain also originates from lattice strain.

[0034] In the evaluation method according to the present embodiment, the diffracted wave in the primary slip plane is used among the diffracted waves obtained by irradiating a crystalline material other than a cubic crystal with radiation. The diffracted wave in the crystal plane that contributes little to the deformation of the crystal, i.e., the diffracted wave in the crystal plane other than the primary slip plane, is significantly less affected by the damage caused to the crystalline material than the diffracted wave in the primary slip plane. Therefore, by using the diffracted wave in the primary slip plane for evaluation of the crystalline material to be evaluated, the damage degree can be evaluated with high accuracy.

[0035] In the evaluation method according to the present embodiment, a master curve showing the correlation between the damage level and the diffraction data calculated using the diffracted waves may be created in advance using a crystalline material made of the same material as the evaluation target, the diffraction data of the evaluation target crystalline material may be calculated using the diffracted waves, and the calculated diffraction data of the evaluation target may be compared with the master curve to evaluate the damage level of the evaluation target. This allows the damage level of the evaluation target to be evaluated more accurately.

[0036] The method for creating a master curve is as follows:

[0037] A number of crystalline materials made of the same material as the crystalline material to be evaluated, each with a different degree of damage, are prepared, and a preliminary test is conducted to obtain diffracted waves for each crystalline material. Diffraction data is calculated using the diffracted waves from the primary slip surface among the diffracted waves obtained in the preliminary test.

[0038] Crystalline materials with different degrees of damage can be obtained, for example, by performing a fatigue test in which a stress or strain varying at an arbitrary amplitude is repeatedly applied to the crystalline material at an arbitrary period, and by changing the number of times the stress or strain is applied. In this case, the number of times the stress or strain is applied corresponds to the degree of damage to the crystalline material. When performing this preliminary experiment, it is advisable to also determine the degree of fracture damage at which the crystalline material breaks (for example, the number of times the stress or strain is applied at which the crystalline material breaks in the fatigue test).

[0039] In the evaluation method according to the present embodiment, the diffracted waves from the primary slip plane are used in the preliminary test, so that the greater the degree of damage to the crystalline material, the greater the change in the diffraction data calculated from the diffracted waves from the undamaged state. Therefore, the master curve obtained from these diffraction data, which shows the correlation between the degree of damage and the diffraction data, changes monotonically according to the degree of damage.

[0040] The method for evaluating the damage level of the evaluation object using the obtained master curve is as follows. The crystalline material to be evaluated is irradiated with radiation, and the diffraction data is calculated using the diffracted waves at the main slip plane among the obtained diffracted waves. The calculated diffraction data of the evaluation object is compared with the master curve created in advance to obtain the corresponding damage level of the evaluation object. As described above, the master curve changes monotonically according to the magnitude of the damage level, and therefore, since there is only one damage level corresponding to the diffraction data of the evaluation object, the evaluation method according to this embodiment can accurately evaluate the damage level of the evaluation object.

[0041] At this time, if the fracture damage level of a crystalline material made of the same material as the crystalline material being evaluated is also calculated in advance, it is possible to evaluate how close the evaluation object is to fracture. For this evaluation, when the calculated damage level of the evaluation object is a and the previously measured fracture damage level is b, for example, a / b can be used as an evaluation index, and it can be evaluated that the closer the value of a / b is to 1, the closer the object is to fracture.

[0042] In the evaluation method according to this embodiment, X-rays and electron beams may be used separately as radiation, or the degree of damage to the crystalline material may be evaluated by combining data obtained by X-rays and data obtained by electron beams.

[0043] Furthermore, when a fatigue test is performed in which stress is repeatedly applied at an arbitrary cycle in the preliminary test for obtaining the master curve, the number of times the stress is applied at which a crack occurs in the crystalline material (hereinafter also referred to as "crack initiation damage degree") may be measured in advance, and this crack initiation damage degree may be compared with the damage degree of the evaluation object obtained from the master curve to evaluate how close the crystalline material is to crack initiation. This evaluation can be performed, for example, by using a / c as an evaluation index, where a is the damage degree of the evaluation object obtained and c is the crack initiation damage degree measured in advance, and it can be evaluated that the closer the value of a / c is to 1, the closer the material is to crack initiation.

[0044] In fatigue failure of crystalline materials due to repeated loads, the material passes through the following stages before failure (fracture): (1) incubation period until crack initiation, (2) crack initiation, and (3) crack propagation. Therefore, it is important to evaluate the degree of damage at the stage (1) before crack initiation. In the method of this embodiment, the degree of damage at the stage (1) can be evaluated by using the crack initiation damage degree measured in advance.

[0045] Next, we will explain the evaluation of diffracted waves and the degree of damage to crystalline materials when the radiation is X-rays or electron beams.

[0046] An example of a test for irradiating a crystalline material with X-rays is an X-ray diffraction test. When an X-ray diffraction test is performed, a chart is obtained in which a diffraction peak appears at a specific irradiation angle (diffraction angle). When the arrangement of atoms constituting the crystalline material is orderly, the diffraction peak has a narrow, so-called sharp peak. On the other hand, when strain occurs in the crystalline material due to fatigue or the like and the arrangement of the atoms is disturbed, that is, when lattice strain is introduced, the diffraction peak has a wide, so-called broad peak. As a method for evaluating the degree of damage to a crystalline material using such characteristics of X-ray diffraction, a method called the Williamson-Hall method (hereinafter also referred to as the "WH method") can be applied to the evaluation method according to this embodiment.

[0047] In this method, the following formula (1) is used as the relation between the half-width β of the diffraction peak, the X-ray diffraction angle θ, the wavelength λ of the X-ray, the crystallite size D of the crystalline material, and the microstrain ε.

[0048] βcosθ / λ=0.9 / D+ε×(2sinθ / λ) …(1) Here, the half-width β is the width at half the height of the diffraction peak, and the crystallite D is the size of the region that constitutes the lattice plane that is the source of the peak. Microstrain is non-uniform lattice strain caused by mismatching of atomic arrangement, and generally, the greater the microstrain in a crystalline material, the greater the degree of damage to the crystalline material.

[0049] When the WH method is applied to a crystalline material having a body-centered cubic structure (such as carbon steel), and the half-width β of each diffraction peak and the sinθ and βcosθ values ​​calculated from the X-ray diffraction angle θ are plotted on a graph with the horizontal axis being sinθ and the vertical axis being βcosθ, they will line up almost on a straight line. According to the WH method, the amount of microstrain of the carbon steel can be calculated with high accuracy as diffraction data from the slope of this line and the above formula (1), and the damage level of the carbon steel can be evaluated based on this amount of microstrain.

[0050] However, in this embodiment, since the crystalline material other than the cubic crystal is the target of the damage evaluation, when X-rays are used, the amount of microstrain of the crystalline material to be evaluated is calculated using only the diffracted wave on the primary slip plane. This allows the damage degree of the crystalline material other than the cubic crystal to be calculated with high accuracy. In addition, when the X-ray diffraction method is applied, if only the diffracted wave is detected for the diffraction angle near the primary slip plane of the crystalline material and the detection of the diffracted wave is omitted for the diffraction angle of the plane away from the primary slip plane, the detection time of the diffracted wave on the primary slip plane can be shortened. This allows the damage degree of the crystalline material to be calculated in a short time.

[0051] The following describes the case where the radiation is an electron beam. One technique for irradiating a crystalline material with an electron beam is called the electron backscatter diffraction (EBSD) method, which uses a scanning electron microscope.

[0052] This technology is used to identify the crystal orientation of the crystal grains that make up a crystalline material. EBSD is a type of electron beam diffraction, and is a diffraction pattern that corresponds to the crystal orientation and crystal structure, obtained by projecting electrons (diffracted waves) reflected from the surface of a crystalline material onto a screen.

[0053] By comparing the diffraction pattern obtained from the sample with a material file containing crystal orientation information previously stored in a measurement system including a scanning electron microscope, it is possible to identify the crystal orientation at the measurement point (hereinafter also referred to as "EBSD measurement"). Using a commercial measurement system, it is possible to perform EBSD measurement at a speed of over 100 points per second while scanning the sample surface with an electron beam. Furthermore, by displaying the crystal orientation information obtained for each point as a map, it is possible to create a crystal orientation distribution diagram (hereinafter also referred to as "crystal orientation map") of the sample.

[0054] Figure 2 shows an example of a crystal orientation map for a steel material with a body-centered cubic structure obtained by the EBSD method. Figure 2(a) is a map in which crystal grains are colored according to their crystal orientation, and Figure 2(b) is a map in which the deviation of the crystal orientation from the reference orientation is displayed by the color intensity using GROD, which will be explained below.

[0055] In FIG. 2(a), the (110), (200), and (211) planes of the observed crystal grains are used as reference planes, and different colors (black and white in FIG. 2(a), but in reality, for example, green, blue, and red) are assigned to each reference plane and displayed. Also, the closer the crystal plane of each observed crystal grain is to the reference plane, the darker the color it is displayed in. As explained in the first embodiment, the (110), (200), and (211) planes are the main planes that cause diffraction in X-ray diffraction in steel materials having a body-centered cubic structure.

[0056] When an external load such as fatigue is applied to a crystalline material, the atomic arrangement within the crystal grains becomes misaligned, causing lattice defects such as dislocations, resulting in lattice strain (damage to the crystalline material). The magnitude of the misalignment of the atomic arrangement within each crystal grain (degree of damage to the crystalline material) can be evaluated as a numerical value using the difference in crystal orientation. In a crystal orientation map, the magnitude of the misalignment of the atomic arrangement can be expressed by different colors.

[0057] Among various methods for calculating the crystal orientation error from the crystal orientation information, the following four methods, for example, are representative. a) Kernel Average Misorientation (KAM): The average orientation difference between a given analysis point and its surrounding analysis points. b) Grain Orientation Spread (GOS): The average orientation difference between a single point in a single grain and all the measurement points that make up that grain. c) Grain Average Misorientation (GAM): The average misorientation between adjacent measurement points within one crystal grain. d) Grain Reference Orientation Deviation (GROD): A plot of the difference between the reference orientation (average orientation) of a grain and the orientation of the measurement point within a single grain.

[0058] Figure 2(b) is a map using GROD, one of the four methods, in which the deviation of the crystal orientation from the reference orientation is displayed as color intensity. The darker the color, the farther the crystal orientation of each crystal grain is from the reference orientation, i.e., the greater the lattice distortion in the area.

[0059] By adopting any of these four methods, the crystal orientation difference in the crystal grains of the crystalline material other than the cubic crystal can be obtained as diffraction data. In this embodiment, the crystal orientation difference of the primary slip plane is used to accurately calculate the damage degree of the crystalline material other than the cubic crystal.

[0060] (Evaluation device) FIG. 3 is a schematic diagram of an evaluation device for the damage degree of a crystalline material according to this embodiment. The evaluation device 1 is an evaluation device for the damage degree of a crystalline material other than a cubic crystal, and includes a memory unit 2 that stores a master curve showing a correlation between the damage degree of a crystalline material made of the same material as the evaluation target and diffraction data calculated using the diffraction waves in the main slip plane among the diffraction waves obtained by irradiating the crystalline material with radiation, a measurement unit 3 that measures the diffraction waves obtained by irradiating the crystalline material to be evaluated with radiation, and a calculation unit 4 that obtains diffraction data of the crystalline material to be evaluated, which is calculated in the same manner as the diffraction data in the memory unit 2, using the diffraction waves measured by the measurement unit 3, and evaluates the damage degree by comparing the diffraction data with the master curve. The evaluation device 1 further includes an operation unit 5 that operates the measurement unit 3, and a display unit 6 that displays the evaluation result of the damage degree by the calculation unit 4.

[0061] The storage unit 2 stores a master curve for a crystalline material made of the same material as the evaluation target, obtained in the above-mentioned preliminary test. The storage unit 2 also stores the fracture damage level at which the crystalline material broke, which was measured in advance by a fatigue test. The storage unit 2 may also store the crack initiation damage level at which a crack occurs in the crystalline material.

[0062] The calculation unit 4 performs calculations for the evaluation object using only the diffracted waves at the primary slip surface among the diffracted waves obtained by the measurement unit 3, and obtains diffraction data for the evaluation object. The calculation unit 4 also compares the obtained diffraction data for the evaluation object with the master curve stored in the storage unit 2, and obtains the damage degree of the master curve corresponding to the diffraction data for the evaluation object.

[0063] Furthermore, the calculation unit 4 evaluates how close the evaluation object is to fracture based on the calculated damage degree and the fracture damage degree stored in the storage unit 2. As described above, this evaluation can be performed using, for example, a / b as an evaluation index when the calculated damage degree of the evaluation object is a and the fracture damage degree is b, and it can be evaluated that the closer the value of a / b is to 1, the closer the evaluation object is to fracture. In addition, when the crack initiation damage degree is stored in the storage unit 2, it is also possible to evaluate how close the evaluation object is to the occurrence of a crack. This evaluation can be performed using, for example, a / c as an evaluation index when the crack initiation damage degree is c, and it can be evaluated that the closer the value of a / c is to 1, the closer the evaluation object is to the occurrence of a crack. These evaluation results are displayed on the display unit 6.

[0064] In the evaluation device 1 according to this embodiment, when the radiation is X-rays, the measurement unit 3 can be an X-ray diffraction device, and the diffraction data can be the amount of lattice strain of the crystalline material.

[0065] Furthermore, in the evaluation device 1 according to this embodiment, when the radiation is an electron beam, the measurement unit 3 can be a scanning electron microscope, and the diffraction data can be the crystal orientation difference of the crystalline material.

[0066] In the evaluation device 1 according to this embodiment, by storing master curves for various crystalline materials in the memory unit 2, it is possible to evaluate the damage level of evaluation objects made of the same types of materials as these crystalline materials. In this case, it is sufficient to select, in the operation unit 5, which crystalline material is the evaluation object, and then perform the evaluation.

[0067] As described above, this specification discloses various aspects of the technology, the main technologies of which are summarized below.

[0068] As described above, a damage evaluation method according to one aspect of the present invention is a method for evaluating the damage level of a crystalline material other than a cubic crystal, and evaluates the damage level of the crystalline material by using diffracted waves obtained by irradiating the crystalline material with radiation, which are diffracted at crystal planes belonging to the primary slip system of the crystals constituting the crystalline material.

[0069] This method allows for highly accurate evaluation of the degree of damage to crystalline materials other than cubic crystals. In addition, by using this method to evaluate the damage to a product made of a crystalline material during its use, it is not only useful for the maintenance and quality control of the product, but also helps in the development of materials to improve the durability of the product.

[0070] In the damage evaluation method having the above-described configuration, a master curve showing the correlation between the damage level and diffraction data calculated using the diffracted wave may be created in advance using a crystalline material made of the same type of material as the evaluation target, and the diffraction data of the evaluation target crystalline material may be calculated using the diffracted wave, and the damage level may be evaluated by comparing the diffraction data with the master curve.

[0071] According to this configuration, the degree of damage to crystalline materials other than cubic crystals can be evaluated with higher accuracy.

[0072] In the damage evaluation method having the above configuration, the radiation may be X-rays and the diffraction data may represent the amount of lattice strain of the crystalline material, or the radiation may be an electron beam and the diffraction data may represent the crystal orientation misorientation of the crystalline material.

[0073] According to this configuration, the above-mentioned damage evaluation method can be realized using an existing radiation irradiating device (for example, an X-ray diffraction device or a scanning electron microscope).

[0074] In the method for evaluating the degree of damage having the above configuration, the crystalline material may have a hexagonal, close-packed hexagonal, tetragonal, trigonal, orthorhombic or monoclinic crystal structure.

[0075] According to this configuration, the degree of damage can be evaluated for various types of crystalline materials.

[0076] An apparatus for evaluating the degree of damage in a crystalline material according to another aspect of the present invention is an apparatus for evaluating the degree of damage in a crystalline material other than a cubic crystal, and includes: a memory unit that uses a crystalline material made of the same type of material as the evaluation target, and stores a master curve that shows the correlation between the degree of damage in the crystalline material and diffraction data calculated using diffracted waves from crystal planes belonging to the primary slip system of the crystals constituting the crystalline material among the diffracted waves obtained by irradiating the crystalline material with radiation; a measurement unit that measures the diffracted waves obtained by irradiating the crystalline material to be evaluated with radiation; and a calculation unit that uses the diffracted waves measured by the measurement unit to obtain diffraction data of the crystalline material to be evaluated, calculated in the same manner as the diffraction data in the memory unit, and evaluates the degree of damage by comparing the diffraction data with the master curve.

[0077] According to this configuration, it is possible to obtain an evaluation device capable of carrying out the above-mentioned crystalline material evaluation method.

[0078] In the device for evaluating the degree of damage to a crystalline material having the above-mentioned configuration, the radiation may be X-rays and the diffraction data may be the amount of lattice strain of the crystalline material, or the radiation may be an electron beam and the diffraction data may be the crystal orientation difference of the crystalline material.

[0079] According to this configuration, the damage evaluation device can be realized using an existing radiation irradiating device. EXAMPLES

[0080] Example 1 In Example 1, X-rays were used as radiation in the evaluation method according to the above-described embodiment.

[0081] The sample used was a 3 mm thick Mg-4.0Al-1.0Ca-0.2Mn alloy (AXM4102 alloy), a magnesium alloy with a hexagonal close-packed structure. The numbers before the element symbols indicate the mass% content of the corresponding element in the alloy, and Mg without a number represents the balance of the alloy.

[0082] A fatigue test was conducted on a test piece cut from the above sample by repeatedly applying stress under the conditions of maximum stress of 200 MPa, minimum stress of 20 MPa, stress amplitude of 90 MPa, and frequency of 60 Hz (cycle of 1 / 60 s). The fatigue test was conducted until the test piece broke, and the number of times the stress was applied (hereinafter also referred to as the "breaking number") was about 80,000.

[0083] In addition, the above stress was applied 10, 100, 1000 or 10000 times to apply microstrain due to fatigue to prepare test pieces with different degrees of damage. X-ray diffraction tests were performed on these test pieces with different degrees of damage, and the half-width β and X-ray diffraction angle θ were obtained for each diffraction peak from the obtained X-ray diffraction chart.

[0084] In the obtained X-ray diffraction chart, diffraction peaks corresponding to the crystal planes of (10-10), (0002), (10-11), (10-12), (1100), (10-13), (1102), (20-21), (0004) and (10-14) in Miller indices appeared in order from the low angle side of the diffraction angle. Among them, the diffraction peaks of the (0002) plane and the (0004) plane correspond to the diffraction peaks of the basal plane, which is the main slip plane, and the plane equivalent to the basal plane (hereinafter also referred to as "basal plane peak"). For the (0001) plane described with reference to FIG. 1, no diffraction peaks are generated due to the extinction rule of X-ray diffraction.

[0085] FIG. 4 is a graph showing the relationship between sinθ and βcosθ for a test piece in which stress was applied 10 times. From FIG. 4, it can be seen that the plots of each diffraction peak vary greatly and the linearity of the plots is poor. In this graph, a quadratic regression line (the line shown in FIG. 4) was obtained from the plots of all the diffraction peaks, and the amount of microstrain was calculated from the slope of the line and the above formula (1) of the WH method. In addition, the amount of microstrain was calculated from the slope of the line connecting only the plots of the basal peaks, i.e., the (0002) plane and the (0004) plane, among the plots shown in FIG. 4, and the above formula (1) of the WH method. For each test piece in which stress was applied 100 times, 1000 times, or 10000 times, the amount of microstrain was similarly calculated from the plots of all the diffraction peaks and the plot of only the basal peaks.

[0086] Fig. 5 is a graph showing the relationship between the number of times stress was applied and the amount of microstrain calculated from the plots of all diffraction peaks, and also shows the master curve of Comparative Example 1 of the present invention. Fig. 6 is a graph showing the relationship between the number of times stress was applied and the amount of microstrain calculated only from the basal peak, and also shows the master curve of Example 1 of the present invention by a solid line.

[0087] The master curve for Comparative Example 1 of the present invention is a plot of the microstrain amounts calculated from all diffraction peaks, while the master curve for Example 1 of the present invention is a plot of the microstrain amounts calculated only from the basal peaks.

[0088] As shown in Figure 5, the master curve of Comparative Example 1 went up and down with an increase in the number of times stress was applied. When attempting to evaluate the damage level of an evaluation object made of the same type of material (AXM4102 alloy) as the material used to create the master curve based on the master curve of Comparative Example 1, the amount of microstrain in the evaluation object may correspond to multiple times in the master curve. In this case, even when the number of times of the evaluation object is compared with the master curve of Comparative Example 1, the number is not fixed at one, so it was difficult to evaluate the damage level of the evaluation object with high accuracy using the master curve of Comparative Example 1.

[0089] On the other hand, as shown in FIG. 6, the amount of microstrain calculated only from the basal peak increases monotonically in a quadratic function manner with an increase in the number of times, and the master curve of Example 1 obtained by connecting these plots is a quadratic curve.

[0090] Therefore, for the evaluation object, only the basal peak was used to determine the amount of microstrain, and by comparing it with the master curve of Example 1, it was possible to determine one number of times stress was applied corresponding to the amount of microstrain of the evaluation object. Furthermore, by comparing this determined number of times stress was applied with the number of times the AXM4102 alloy broke, which was measured in advance, it was possible to evaluate with high accuracy the degree of damage to the evaluation object, that is, how close the evaluation object was to breaking. Note that FIG. 6 also shows plots for the case where all the diffraction peaks shown in FIG. 5 were used, and the master curve (dashed line) of Comparative Example 1.

[0091] The reason why the master curve of Comparative Example 1 went up and down as the number of times stress was applied increased is believed to be because the crystal structure of the magnesium alloy being evaluated was a hexagonal crystal.

[0092] Here, deformation phenomena in crystalline materials such as metals, including fatigue, are mainly caused by slippage of crystals, and the ease with which crystals slip strongly depends on the crystal structure.

[0093] For example, in austenitic stainless steel and nickel-based alloys with a face-centered cubic structure, there are 12 types of crystal slip (slip systems), with four faces where slip is likely to occur (slip planes) and three directions where slip is likely to occur (slip directions), while steel with a body-centered cubic structure has six slip planes and two slip directions, for a total of 12. On the other hand, in magnesium alloys, which have a close-packed hexagonal structure (close-packed hexagonal crystal), as explained using Figure 1, there are only three types of slip systems, with one slip plane and three slip directions.

[0094] Therefore, if all of the diffraction peaks obtained in an X-ray diffraction test are used in an analysis using the WH method, information about crystal faces that do not belong to the primary slip system, i.e., crystal faces where strain is less likely to occur, will be included in the calculated microstrain amount, which will be a source of error and cause the master curve to fluctuate as described above.

[0095] Example 2 In Example 2, an electron beam was used as radiation in the evaluation method according to the above-described embodiment, and an EBSD method using a scanning electron microscope was applied.

[0096] The magnesium alloy used in Example 1 was used as a sample, and test pieces with different damage levels were cut out from the sample and fatigue tested, and EBSD measurements were performed on them. All measurement data obtained by EBSD measurements were used to determine the crystal orientation mismatch by the above four methods (KAM, GOS, GAM, GROD). In addition, among the crystal orientation mismatches for each crystal grain obtained by EBSD measurements, the measurement data originating from the basal plane was used to determine the crystal orientation mismatch (hereinafter also referred to as "basal plane mismatch") by the above four methods.

[0097] Fig. 7 is a graph showing the relationship between the number of times stress was applied and the crystal orientation difference calculated using all the measurement data obtained by EBSD measurement, and also shows the master curve of Comparative Example 2 of the present invention. Fig. 8 is a graph showing the relationship between the number of times stress was applied and the basal orientation difference, and also shows the master curve of Example 2 of the present invention by a solid line.

[0098] The master curve for Comparative Example 2 of the present invention is a plot of the crystal orientation difference obtained by GROD using all the measurement data, and the master curve for Example 2 of the present invention is a plot of the basal plane orientation difference obtained by GROD.

[0099] As shown in Fig. 7, the master curve of Comparative Example 2 fluctuated with the increase in the number of times stress was applied, similar to the master curve of Comparative Example 1. Therefore, for the same reason as the master curve of Comparative Example 1, it was difficult to evaluate the damage level of the evaluation object with high accuracy using the master curve of Comparative Example 2. The same was true for the master curves of crystal orientation differences obtained by methods other than GROD.

[0100] On the other hand, as shown in FIG. 8, the crystal orientation difference calculated only from the basal plane orientation difference increases linearly with an increase in the number of times, and the master curve of Example 2 obtained by connecting these plots is linear.

[0101] Therefore, for the evaluation object, only the basal peak was used to determine the amount of microstrain, and by comparing it with the master curve of Example 1, it was possible to determine one number of times that stress was applied corresponding to the amount of microstrain of the evaluation object. Therefore, like the master curve of Example 1, it was possible to evaluate the degree of damage to the evaluation object with high accuracy. The same was true for the master curve of the crystal orientation difference obtained by a method other than GROD. Note that FIG. 8 also shows a plot of the crystal orientation difference obtained using all the measurement data obtained by the EBSD measurement shown in FIG. 7 and a master curve (dashed line). [Explanation of symbols]

[0102] 1. Evaluation device 2 Storage section 3 Measuring part 4 Arithmetic section

Claims

1. A method for evaluating the degree of damage in a crystalline material other than a cubic crystal, comprising the steps of: A method for evaluating the degree of damage to a crystalline material, comprising: irradiating the crystalline material with radiation to obtain diffracted waves; and evaluating the degree of damage to the crystalline material using diffracted waves from crystal planes belonging to a primary slip system of the crystals constituting the crystalline material.

2. a master curve is prepared in advance, which shows a correlation between the degree of damage and the diffraction data calculated using the diffracted waves, using a crystalline material made of the same material as the evaluation target; Calculating diffraction data of a crystalline material to be evaluated using the diffracted waves; 2. The method for evaluating the degree of damage in a crystalline material according to claim 1, wherein the degree of damage is evaluated by comparing the diffraction data with said master curve.

3. 3. The method for evaluating a degree of damage in a crystalline material according to claim 2, wherein the radiation is X-rays, and the diffraction data is an amount of lattice strain in the crystalline material.

4. The method for evaluating a degree of damage to a crystalline material according to claim 2 , wherein the radiation is an electron beam, and the diffraction data is a crystal orientation misorientation of the crystalline material.

5. The method for evaluating the degree of damage to a crystalline material according to claim 1 , wherein the crystalline material has a hexagonal, close-packed hexagonal, tetragonal, trigonal, orthorhombic or monoclinic crystal structure.

6. An apparatus for evaluating the degree of damage to a crystalline material other than a cubic crystal, comprising: a storage unit that stores a master curve that shows a correlation between the degree of damage of a crystalline material made of the same material as the evaluation target and diffraction data calculated using diffracted waves from a crystal plane belonging to a primary slip system of a crystal constituting the crystalline material among diffracted waves obtained by irradiating the crystalline material with radiation, using the crystalline material made of the same material as the evaluation target; a measurement unit that measures a diffracted wave obtained by irradiating a crystalline material to be evaluated with radiation; An apparatus for evaluating the degree of damage to a crystalline material, comprising: a calculation unit that uses the diffracted waves measured by the measurement unit to obtain diffraction data of the crystalline material to be evaluated, which is calculated in the same manner as the diffraction data in the memory unit, and evaluates the degree of damage by comparing the diffraction data with the master curve.

7. 7. The apparatus for evaluating a degree of damage in a crystalline material according to claim 6, wherein the radiation is X-rays, and the diffraction data represents an amount of lattice strain in the crystalline material.

8. 7. The apparatus for evaluating a degree of damage to a crystalline material according to claim 6, wherein the radiation is an electron beam, and the diffraction data is a crystal orientation misorientation of the crystalline material.

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