JP2004003922A - Method for measuring remaining lifetime of material, and apparatus for measuring remaining lifetime using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring the lifetimes of materials and to be applied to metallic materials etc. which are used for high-temperature parts. <P>SOLUTION: In the method, KAM values which indicate the differences in in-crystal orientations in the crystal grains, crystal grain boundaries, etc. of a test material which has consumed its material life time to prepare a master curve which represents the relation between the measured KAM values; the degree of consumption of material lifetimes in a first process. KAM values, which indicate differences in the crystalline orientations of a material to be examined which requires the estimation of the degree of life consumption are measured; and the measured values are substituted into the master curve. By this, it is possible to estimate the degree of the life time consumption of the material to be examined and to predict the remaining lifetime of the material. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a remaining life measuring method for measuring a remaining life of a metal material used for a high-temperature component, in particular, an inner surface material of a combustion chamber of a reusable rocket engine, and a remaining life measuring device using the remaining life measuring method.
[0002]
[Prior art]
Conventionally, when evaluating the life of a metal material, 1) a method for measuring the life from a change in hardness of the material, 2) a method for measuring the life from a change in the form of the precipitate, and 3) a life from the change in electric resistance. Methods, 4) Methods of measuring the lifetime by detecting the generation and coalescence growth of voids by ultrasonic testing have been proposed. Actually, there is a method that has already been put to practical use as a technology for evaluating the life of a high-temperature pressure-resistant pipe of a thermal power plant.
[0003]
[Problems to be solved by the invention]
However, the above-mentioned proposed life measuring methods have the following problems. That is,
1) A method of measuring the life from a change in hardness of a material: a material having a small change in hardness during use of a material has a large measurement error.
2) Method for measuring the life from the change in the form of the precipitate: It cannot be used in the first place for a material in which no precipitate is formed. In the case of a material having a stable precipitate and a small change in shape, a measurement error increases.
3) Method of measuring lifetime from change in electrical resistance: measurement error increases because it is excessively sensitive to change in resistance and reacts to noise.
4) Life measuring method using ultrasonic flaw detection: It can be evaluated only at the final stage of the life when voids are generated and coalesced.
Etc.
[0004]
As for heat-resistant steel, which has many achievements as a high-temperature member and whose life evaluation is indispensable for the stable operation of the equipment, surplus life evaluation methods are being actively studied. There are many methods for which an appropriate life evaluation method has not been established.
[0005]
In particular, the interior of the combustion chamber of the rocket engine is exposed to combustion gas exceeding 3000 degrees Celsius, so that all ordinary metallic materials are melted. When a material is used in such a situation, a material having good heat conductivity, preferably a copper alloy, is selected and the strength is given by cooling from a surface of the combustion chamber.
[0006]
However, if the material selected in the above case continues to be used, creep fatigue will occur. When the selected material is used for a disposable rocket engine, it is discarded after a certain period of use, so there is no major problem with creep fatigue life, but a reusable rocket engine requires a long use Therefore, the requirements for creep fatigue life are becoming stricter in consideration of safety, and it is necessary to check the damage status sufficiently for each use.
[0007]
[Means for Solving the Problems]
Accordingly, an object of the present invention is to provide a method for measuring the remaining life of a material that has consumed the material life.
[0008]
According to claim 1, the present invention is a method for measuring the remaining life of a material that has consumed its material life, wherein the degree of consumption of the material life of the test material and the time when the test material has consumed the material life are measured. A step of preparing in advance a relationship with a local crystal orientation shift; a step of measuring a local crystal orientation shift of the investigation material in which consumption of a material life which is the same material as the test material has occurred; and Estimating the remaining life of the survey material by estimating the degree of consumption of the material life of the survey material by applying the deviation of the crystal orientation of the survey material to the relationship described above, and providing a remaining life of the survey material. The purpose is to do.
[0009]
Focusing on the crystal orientation of the crystal grains of the material in the process of consuming material life and eventually rupture, for example, creep fatigue, it is known that certain phenomena occur as the fatigue progresses . Most metal fractures, such as creep fatigue fractures, occur from crystal grain boundaries. This is because distortion (displacement) accumulates at the crystal grain boundaries with repeated use. In other words, dislocations accumulate.
[0010]
Since the dislocations in the material are substantially uniform before the consumption of the material life, the change in the crystal orientation difference depending on the location is small. As the life of the material progresses, dislocations in the crystal grains gradually accumulate at the grain boundaries, and the crystal orientation difference at the crystal grain boundaries increases, and conversely, the crystal orientation difference within the crystal grains increases. Decreases. This tendency is particularly noticeable immediately before the material breaks. Therefore, by applying this phenomenon and measuring the plane orientation difference in a crystal grain or a crystal grain boundary, it is possible to predict the progress of damage to a material. In other words, the longer the difference in the plane orientation at the crystal grain boundary is, the more the material life is consumed, and the smaller the difference in the plane orientation in the crystal grain is, the longer the material life is. Consumption is in progress.
[0011]
According to this method, first, a consumption test (for example, a fatigue test) of a material life of a test material of a specific material is performed in advance, and data of a crystal orientation difference with respect to consumption of a certain material life is collected in advance. The degree of consumption and the crystal orientation difference are related by a schematic graph or the like. In order to predict the material life consumption of a test material of the same type as the test material that actually consumed the material life, measure the crystal orientation difference of the research material, and use this value to calculate the above-mentioned material life consumption and crystal orientation. Substitution into the relationship with the difference makes it possible to predict the current consumption of the material life. Therefore, it is possible to predict the remaining life until breaking.
[0012]
According to claim 2, the present invention is the method according to claim 1, wherein the local crystal orientation deviation between the test material and the investigation material is respectively defined by the defined region of the test material and the defined region. It is an object of the present invention to provide a method for measuring a remaining life, which is derived from a crystal orientation difference angle between a specified region of the investigation material and a region corresponding to the above.
[0013]
According to this method, the crystal orientation difference in the process of consuming the material life described above is measured using the plane orientation angle. Specifically, a consumption test of the material life is first performed on a test material such as a test piece, and the crystal misorientation angle is measured at a plurality of points in time when the consumption of the material life proceeds. In the measurement, first, a specified region in a crystal grain is divided into a number of fine regions, and the average of the crystal orientation difference angles between each fine region and a plurality of fine regions around the fine region is calculated. Further, a value obtained by averaging the calculated crystal orientation difference angles in each of the plurality of fine regions in the defined region is calculated. This calculation method is performed at a plurality of points in the process of consuming the material life, and, for example, a master curve is drawn, which relates the degree of consumption of the material life to the calculated value.
[0014]
Next, the average crystal orientation difference angle is calculated by the same method as the above-described calculation method for the investigation material to be measured for the consumption degree of the material life, and the calculated value is substituted into the above-described master curve or the like. At that time, the consumption of the material life corresponding to the value on the master curve can be predicted as the consumption of the material life of the investigation material. That is, it is possible to predict the remaining life of the investigation material. The change in the average crystal misorientation angle is calculated by calculating the difference between the average crystal misorientation angle during non-fatigue and the average crystal misorientation angle when the material life is consumed as the calculated crystal misorientation angle. You can also.
[0015]
According to claim 3, the present invention is the method according to claim 2, characterized in that the defined area of the test material and the defined area of the investigation material are each located in a crystal grain of each material. It is an object of the present invention to provide a method for measuring the remaining life.
[0016]
According to this method, the specified region for measuring the crystal misorientation angle of the test material and the investigation material is defined as a crystal grain. As described above, the difference in plane orientation within a crystal grain decreases as the consumption of the material life progresses. This method focuses on this phenomenon.By substituting the plane orientation difference in the crystal grains measured with the test material into a master curve derived from the test material, the consumption of the life of the test material and, consequently, the remaining life can be reduced. Can be predicted.
[0017]
According to claim 4, the present invention is the method according to claim 2, wherein the defined region of the test material and the defined region of the investigation material are each located near a grain boundary of each material. It is an object of the present invention to provide a method for measuring a characteristic remaining life.
[0018]
According to this method, the specified region for measuring the crystal misorientation angle of the test material and the investigation material is set near the crystal grain boundary. As described above, the difference in the plane orientation of the crystal grain boundaries increases as the consumption of the material life progresses. This method focuses on this phenomenon, and by substituting the plane orientation difference of the crystal grain boundaries measured with the test material into a master curve derived from the test material, the consumption of the material life of the test material, and hence the remaining life Can be predicted.
[0019]
According to claim 5, the invention is the method according to claim 1, wherein the local crystallographic deviation between the test material and the investigation material is each between two regions in the test material. The remaining life is measured based on a change in crystal misorientation angle and a change in crystal misorientation angle between two regions in the test material corresponding to two regions in the test material. The aim is to provide a method.
[0020]
In the above-described measurement method, the remaining life was predicted by calculating the change in the crystal orientation difference angle in one region of the crystal grain. In this method, however, the difference in the crystal orientation difference angle in the two regions was calculated. Then, the degree of consumption of the material life and, consequently, the remaining life are predicted based on the change in the calculated value. When the change in the crystal misorientation angle in each of the two regions acts in the opposite direction to the change in the crystal misorientation angle in the other region, the difference between the crystal misorientation angles in both regions becomes significant. For example, when the crystal misorientation angle in one region tends to increase and the crystal misorientation angle in another region tends to decrease, the difference in crystal misorientation angle between the former and the latter tends to increase. It will be noticeable. Therefore, according to the present method, the movement of dislocations in crystal grains can be more clearly shown, so that the accuracy of measuring the remaining life is improved. Further, in the method described above, the specified region in the crystal grain is divided into a number of fine regions, and the peripheral direction and the plane direction difference angle in each fine region are calculated and averaged over the specified region for measurement. In this case, since the accuracy is improved, the number of micro regions to be measured can be reduced, and as a result, the data analysis speed at the time of measurement is improved. In the present method, the degree of change, that is, the change rate of the difference in crystal orientation difference can also be predicted as in the case of the method described in claims 2 to 4.
[0021]
In particular, according to the method of claim 6, the present invention is the method of claim 5, wherein the two regions in the test material and the two regions in the investigation material are different from each other. There is provided a method for measuring a remaining life, which is characterized by being located substantially at the center of a crystal and near a crystal grain boundary.
[0022]
According to this method, the two regions are a crystal center and a grain boundary of the material. As the life of the material progresses, the plane misorientation angle of the crystal grain boundary increases, particularly remarkably immediately before fracture, while the plane misorientation angle in the crystal grain monotonically decreases until fracture. Therefore, the change in the crystal misorientation angle with respect to the consumption of the material life is larger than in the case where only one of the two regions is measured. Or the number of micro regions to be measured can be reduced, thereby improving the data analysis speed.
[0023]
According to claim 7, the present invention is a method according to any one of claims 1 to 6, wherein the degree of consumption of the material life of the test material and the degree of consumption of the test material over the material life are determined. In the step of preparing the relationship with the local crystal orientation deviation in advance, the degree of consumption of the material life of the test material when the test material is simply fatigued and the local consumption when the test material consumes the material life The simple fatigue relationship, which is the relationship with the misorientation of the crystal orientation, and the degree of consumption of the material life of the test material when the test material is subjected to tensile holding creep fatigue, and the local crystal when the test material consumes the material life. The tensile retention creep fatigue relationship, which is the relationship with the misorientation, and the degree of consumption of the material life of the test material when the test material is subjected to compression retention creep fatigue, and the Compression preservation, which is related to The creep-fatigue relationship is prepared, and the remaining life of the survey material is estimated by estimating the degree of consumption of the material life of the survey material by applying the measured crystal orientation deviation to the relationship. In the step, from the simple fatigue relationship, the tensile holding creep fatigue relationship and the compression holding creep fatigue relationship, a relationship indicating a fatigue condition closest to the fatigue condition of the investigation material is selected, and the selected relationship It is an object of the present invention to provide a method of estimating the remaining life of the investigation material by estimating the consumption of the material life of the investigation material by applying the measured crystal orientation shift.
[0024]
The life of the material is different between simple fatigue, tensile retention creep retention fatigue, and compression retention creep fatigue. Therefore, by applying the fatigue relationship closest to the fatigue state of the investigation material, the remaining life of the investigation material can be measured more accurately.
[0025]
According to claim 8, the present invention is a remaining life measuring apparatus used in the method according to any one of claims 1 to 7, wherein the measurement of the crystal orientation difference is performed by a backscattered electron Kikuchi diffraction line. It is an object of the present invention to provide an apparatus for measuring the remaining life, which comprises an electron microscope for analyzing data and an arithmetic processing unit for arithmetically processing and mapping data from the microscope.
[0026]
According to the present apparatus, the measurement of the crystal orientation difference in the above-mentioned remaining life measurement method can be performed at a high speed to perform the measurement of the crystal orientation difference at a large number of points in a certain region, which has been difficult in the past. In addition, it is possible to quickly and accurately estimate and measure the degree of life consumption of a material and, consequently, the remaining life.
[0027]
Although the contents of the present invention can be understood from the above description, the contents of the present invention can be more clearly understood by describing specific embodiments of the present invention with reference to the accompanying drawings. Would.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
The crystal orientation can be obtained by analyzing a diffraction line called a Kikuchi line in the backscattered electron analysis of a scanning electron microscope (SEM). The backscattered electron Kikuchi line diffraction is called EBSP (Electron Back-Scatter diffraction Pattern), and a crystal orientation analysis system using this diffraction has been developed. Further, an OIM (Oriental Imaging Microscopy) system capable of fully automatic analysis of crystal orientation has been developed as an analyzer. The use of the OIM system has been increasing particularly due to the recent increase in the processing speed of computers.
[0029]
The OIM system irradiates an electron beam onto the finish-polished material surface at an arbitrary pitch of approximately micron order, and measures EBSP obtained therefrom. The EBSP obtained here is specific to the crystal orientation. Therefore, it is possible to measure the crystal orientation difference at the place where the electron beam is irradiated. In the embodiment of the present invention, a method of measuring a remaining life of a material using an OIM system will be described.
[0030]
The crystal misorientation measured by the OIM system is expressed as an angle. In the system, KAM (Karnel Averaging Misorientation) analysis is performed to screen the angle data as reliable data.
[0031]
Specifically, as shown in FIG. 1, first, an arbitrary analysis section 10 in a crystal grain is determined. This analysis section is a fixed area artificially determined to analyze a local plane orientation difference in a crystal grain, and divides the inside of the crystal grain into a number of regular hexagons. That is, each measurement point is replaced with a regular hexagonal analysis section 10.
[0032]
First, as a first step, a plane orientation difference between the analysis section (also referred to as a “pixel”) 10 and six adjacent sections 11A to 11F adjacent to the analysis section is measured. Referring to FIG. 1, 2.5 °, 38.1 °, 37.6 °, and 1.3 ° are examples of the measurement results of the plane orientation difference of six adjacent sections 11A to 11F with respect to the analysis section 10, respectively. , 1.8 ° and 2.1 °.
Among the above results, crystal orientation difference angles exceeding a predetermined threshold value are excluded in consideration of data reliability. Here, about the small angle grain boundary, that is, 5 ° is designated as the threshold value. Therefore, 38.1 ° and 37.6 ° of the above measured values are deleted, and 2.5 °, 1.3 °, 1.8 ° and 2.1 ° are effective values.
[0033]
As a second step, the average of the effective values is calculated. This average value serves as a reference for evaluating the crystal orientation difference as a KAM value. Specifically, in the case of FIG.
KAM value = 1.9 ° = (2.5 ° + 1.3 ° + 1.8 ° + 2.1 °) / 4
It becomes.
In the above-described process, the method of evaluating the plane orientation difference between the analysis section 10 and the adjacent section 11 has been described. However, the KAM value is related to the analysis step size. Therefore, in order to improve the analysis accuracy, not only the adjacent section 11 but also the plane orientation difference between the second section 12 (see reference numerals 12A and 12B in FIG. 1) and the third section (not shown) are selected. Then, an average value from which a value equal to or larger than the threshold value is deleted can be evaluated as a KAM value.
[0034]
Next, the relationship between the consumption of the material life of the material and the KAM value will be described.
When a material is repeatedly subjected to a load or a high temperature for a long time, dislocations in crystal grains move to grain boundaries. Therefore, dislocations in the crystal grains decrease and increase at the crystal grain boundaries. For this reason, as the consumption of the material life progresses, the plane orientation difference, that is, the KAM value also decreases in the crystal grain and increases at the crystal grain boundary.
Metal fractures such as creep or creep fatigue fracture often occur from crystal grain boundaries. This is because strain is accumulated at grain boundaries with repeated use, that is, dislocations accumulate at grain boundaries.
Therefore, if the change or the rate of change of the KAM value is verified, it is possible to predict the progress of the consumption of the material life, and also to predict the remaining life of the material.
[0035]
Referring to FIG. 2, there is shown a schematic diagram of a crystal grain and a graph of a change in KAM value along a line AA on the schematic diagram along with the life consumption. As shown, line AA extends over three consecutive grains.
As shown in the graph of FIG. 2, it can be seen that there is no large difference in the KAM value between the crystal grain boundary and the inside of the crystal grain when the life is not consumed at all. This is because dislocations in the material are distributed substantially uniformly. On the other hand, the dislocations in the crystal grains gradually accumulate at the crystal grain boundaries as the life is consumed, that is, as they progress from the middle life to the latter life (immediately before the fracture), and as a result, the crystal grain boundaries The KAM value increases, and conversely, the KAM value in the crystal grain decreases, and this tendency becomes more prominent in the latter half of the life, that is, immediately before fracture.
[0036]
Referring to FIG. 3 for reference, the results of the KAM analysis on the sample surface of the copper alloy that has consumed 90% life are graphically represented by the concentration change. In FIG. 3, a solid stepped line indicates a crystal grain boundary, and each region surrounded by the solid line and largely divided indicates a crystal grain. Further, the inside of the crystal grain contains a large number of the above-described analysis sections (pixels). Each analysis section is shown darker as the KAM value increases. Therefore, looking at the whole of FIG. 3, the darker part is the part with the larger KAM value. That is, it shows a portion where the amount of dislocation is large.
FIG. 3 shows that the KAM value at the grain boundary of the material immediately before the fracture is significantly larger than the KAM value within the crystal grain. That is, it can be said that FIG. 3 specifically shows the above-described dislocation at the crystal grain boundary. The significance of 90% life consumption will be described later.
[0037]
In the embodiment of the present invention, the KAM value measurement system using the above-described OIM system is used, and the progress of creep fatigue of the inner surface material of the actual measurement object, for example, the combustion chamber (made of copper alloy) of a reusable rocket engine is used. Degree, that is, the life consumption degree is predicted using the KAM value. Specifically, the present embodiment exemplifies three methods.
[0038]
The first method focuses on the fact that dislocations accumulate in the vicinity of a crystal grain boundary as the consumption of the material life progresses, and obtains the change from the KAM value in the vicinity of the crystal grain boundary. That is, the life expectancy of the material is determined from the degree of change of the KAM value.
[0039]
The second method is to predict from a change in KAM value within a crystal grain. As the consumption of the material life progresses, dislocations move to crystal grain boundaries in the crystal grains, and the KAM value in the crystal grains decreases monotonously. Therefore, if attention is paid to the relationship between the change in the KAM value in the crystal grain and the material life, the material life can be predicted from the change in the KAM value in the crystal grain.
[0040]
The third method is to determine a change in the KAM value on a line perpendicular to the grain boundary from the center of the crystal grain to the grain boundary, and to determine the difference or degree of change between the center and the grain boundary (in the case of a graph). Of the material is estimated by calculating the slope of the material.
[0041]
Although the first to third methods differ in the place where the KAM value is measured, the steps are common. Specifically, first, a master curve is obtained by graphing the relationship between the KAM value and the consumption degree of the material life of the test material of the same material as the material to be actually measured. Next, as a second step, the KAM value is measured for the investigation material to be actually measured at the same place as in the first step. As a third step, the KAM value of the test material measured in the second step is substituted into a master curve representing the relationship between the consumption degree of the material life and the KAM value obtained for the test material. By this substitution, the consumption degree of the material life when the KAM value is assumed to be the same as the test material, that is, the material life is obtained. As described above, the measurement of the KAM value in the test material is performed under the same conditions as the actual measurement place and material of the investigation material. Therefore, the material life obtained by the above substitution can be estimated as the material life of the actual investigation material. Hereinafter, a master curve indicating the degree of change of the KAM value of the test material in the first to third methods and a method of estimating the life of an actual investigation material using the master curve will be described.
[0042]
As a premise of the test of the test material, FIG. 4 shows a load pattern and a test condition of a creep fatigue test when a copper alloy for a combustion chamber is used as a test material. . In this embodiment, the test material is stretched and compressed at a temperature of 550 ° C. so as to have a strain range of 1%. Further, at the time of compression, the state where the strain amount is maintained at 0.5% is maintained for 5 minutes. This compression and tension are defined as one cycle. As a result of the test, the test specimen broke at 420 cycles. Therefore, as shown in the table, a sample interrupted at 70% of 420 cycles or 294 cycles was defined as a 70% consumable material, and a sample interrupted at 90% of 420 cycles or 378 cycles was defined as a 90% consumable material.
[0043]
Hereinafter, the master curves obtained by the above-described first to third methods will be specifically described based on actual experimental results.
FIGS. 5 to 7 show a first method for measuring a change in the KAM value of a crystal grain boundary. Specifically, the KAM values of a plurality of analysis sections in a measurement region 50 which is a region of 10 × 20 μm near the crystal grain boundary shown in FIG. 5 are measured. As shown in the table of FIG. 6, the KAM value measurement results were as follows: 3.12 for the untested material, 3.43 for the 70% consuming material, 4.02 for the 90% consuming material, and 42 for the broken material. .36, and the graph is as shown in the graph of FIG.
[0044]
Further, FIG. 7 verifies the change rate of the KAM value near the crystal grain boundary. The rate of change of the KAM value is
Change rate of KAM value
= (KAM value of surveyed material-KAM value of untested material) / (KAM value of untested material)
It is represented by
A graph of this change rate is a graph in FIG.
The above two graphs are master curves.
[0045]
When estimating the life of the actual fatigued investigation material, it is performed by substituting the KAM value measured for the investigation material into the master curve obtained as described above. First, the KAM value of the creep fatigue material is measured in a region near the crystal grain boundary similar to the measurement region 50 shown in FIG. When the measured KAM value is 3.75, for example, it can be predicted that the material life is 82% as shown in the graph of FIG. 6 by substituting it into the master curve of FIG.
[0046]
Further, the above KAM value, 3.75, is expressed as about 0.2 when expressed as a change rate of the KAM value. Therefore, if the master curve shown in FIG. 7 is used, the material life can be estimated to be about 82% as shown in the graph of FIG.
If the master curve shown in FIG. 7 is used, a shift occurs in the KAM value between the initial state of the test material and the test material, that is, the KAM value when the test material is not consumed (in this example, the KAM value when the test material is not consumed is 3. Even if it is slightly away from 12), there is an advantage that it is easy to cope with it because the unconsumed state is predicted at a change rate of 0.
[0047]
Next, FIGS. 8 to 10 show a second method for measuring a KAM value in a crystal grain. Specifically, as shown in FIG. 8, KAM values of a plurality of analysis sections in a measurement area 80 which is a 20 × 40 μm area at the center of a crystal grain are measured. As shown in the table of FIG. 9, the KAM value measurement results are 1.85 for the untested material, 1.77 for the 70% consuming material, 1.32 for the 90% consuming material, and 1 for the broken material. .00, and the graph is as shown in the graph of FIG.
[0048]
Further, FIG. 10 verifies the change rate of the KAM value in the crystal grain. The change rate of the KAM value is similar to the case shown in FIG.
Change rate of KAM value
= (KAM value of surveyed material-KAM value of untested material) / (KAM value of untested material)
It is represented by
FIG. 10 is a graph showing the rate of change.
The above two graphs are master curves.
[0049]
Even in this case, in order to predict the life of the actual creep-fatigued investigation material, the KAM value measured in the investigation material is added to the master curve obtained in the same manner as in the case of measuring the KAM value of the crystal grain boundary described above. This is done by substituting.
Further, if the master curve shown in FIG. 10 is used, even if the KAM value of the test material and the investigation material is shifted in the initial state, that is, when the KAM value is not consumed, the unconsumed state is assumed to be 0. The point that it is easy to cope with the prediction is the same as the case where it is predicted by the KAM value of the crystal grain boundary.
[0050]
11 and 12, there is shown a third method of measuring the change in the KAM value on a vertical line from the center of the crystal grain to the crystal grain boundary. Specifically, as shown in FIG. 11, a vertical line is drawn from the center of the crystal grain toward the crystal grain boundary, the KAM value at the central portion of 6 μm is measured, and the average value is used as the central portion KAM value. And a mean value thereof was defined as a grain boundary KAM value, and a KAM value difference between the central part KAM value and the grain boundary KAM value was measured. As shown in the table in FIG. 12, the measurement results of the KAM value difference were 1.02 for the untested material, 1.70 for the 70% consuming material, 3.25 for the 90% consuming material, and 3.25 for the broken material. 3.66, and the graph is as shown in the graph of FIG. This graph becomes the master curve.
[0051]
Even in this case, in order to predict the life of the actual creep-fatigue test material, a master curve obtained in the same manner as in the case of measuring the KAM value of the crystal grain boundary or the KAM value in the crystal grain described above is used. This is performed by substituting the measured KAM value difference.
[0052]
The three life prediction methods using the change in the KAM value at the crystal grain boundary, the change in the KAM value in the crystal grain, and the change in the KAM value difference from the crystal grain to the crystal grain boundary have been described above. In order to improve the life expectancy, two or three of these methods may be combined to form one life expectancy method. When only a change in the KAM value in one region is measured, an error may occur from the relationship between the fatigue under ideal conditions and the KAM value due to various fatigue conditions, materials, and the like. Therefore, by repeating the measurement in a plurality of methods and regions, it is possible to converge to data indicating the true life consumption. As a result, a more accurate life prediction can be performed.
[0053]
It is also conceivable to further improve the measurement accuracy by combining a method utilizing the change in the KAM value with a hardness test conventionally used. According to this method, it is possible to judge the consumption state of the material life widely, but it is possible to prevent the harmful effects of the conventional hardness test in which the damage state cannot be measured in detail, and it is also possible to locally determine the method of measuring from the crystal orientation difference described here. It is also possible to correct the error.
[0054]
Further, when obtaining a master curve indicating the relationship between the consumption of the material life of the test material and the KAM value (local crystal orientation deviation), the fatigue life of the test material is taken into account to more accurately estimate the remaining life. Can be measured.
[0055]
In other words, a simple fatigue master curve when the test material is simply fatigued, a tensile holding creep fatigue master curve when the test material is subjected to tensile holding creep fatigue, and a compression holding creep fatigue master when the test material is subjected to compression holding creep fatigue. Find the curve.
[0056]
Here, simple fatigue means that a test material is fatigued by alternately applying compression and tension with a strain range of 1% and a maximum strain of 0.5%, as shown in an example in FIG. 13 (a). In other words, fatigue is given by alternately applying compression and tension to the test material without maintaining the state of 0.5% strain for a long time.
As shown in FIG. 13 (b), the tensile retention creep fatigue refers to a test material in which a strain range of 1% and a tensile state of 0.5% of strain are applied for a certain period of time (for example, 5 minutes). Later, a cycle operation of giving a compression with a maximum strain amount of 0.5% for a short time (for example, 5 seconds) is to give a large number of cycles to fatigue.
As shown in an example in FIG. 13 (c), the compression holding creep fatigue is such that a test material is given a compression state of 0.5% strain for a certain period of time (for example, 5 minutes) with a strain range of 1%. Later, a cycle operation of applying a tensile force with a maximum strain amount of 0.5% for a short time (for example, 5 seconds) is performed by applying a large number of cycles to fatigue.
[0057]
FIG. 14 shows a simple fatigue master curve A when a copper alloy as a test material was simply fatigued at a temperature of 550 ° C., a tension holding creep fatigue master curve B when a tensile holding creep fatigue was performed, and a compression holding creep. It shows and shows the compression holding creep fatigue master curve C when fatigued. The KAM value was measured by the second method for measuring the KAM value in a crystal grain.
[0058]
When estimating the life of a real fatigued investigation material, first, determine whether the investigation material has been subjected to simple fatigue, tensile retention creep fatigue, or compression retention creep fatigue. . For example, it has been found that the material inside the combustion chamber of a reusable rocket has undergone compression holding creep fatigue due to the nature of its location of use. For other survey materials, the type of fatigue can be determined from the characteristics of the place of use. Further, the measurement of the KAM value of the investigation material is performed by the second method for measuring the KAM value in the crystal grain.
[0059]
If the tire is simply fatigued, the life can be predicted by adopting the master curve A and substituting the KAM value of the investigation material into the master curve A. Further, when the specimen has been subjected to tensile holding creep fatigue, the life can be predicted by adopting the master curve B and substituting the KAM value of the test material into the master curve B. Further, in the case of creep fatigue due to compression holding, the life can be predicted by adopting the master curve C and substituting the KAM value of the test material into the master curve C.
[0060]
In the master curve of FIG. 14, the KAM value was measured by the second method for measuring the KAM value in the crystal grain, but the first method for measuring the KAM value near the crystal grain boundary was used. In addition, according to a third method of calculating a KAM value change on a line perpendicular to the grain boundary from the center of the crystal grain toward the grain boundary, various kinds of fatigue (simple fatigue, creep fatigue under tension, creep fatigue under compression) are obtained. Alternatively, a master curve may be obtained. Further, as a master curve corresponding to various types of fatigue, a graph showing a change rate of a KAM value may be used.
Then, when predicting the life of the actual fatigued investigation material, a master curve corresponding to the fatigue of the investigation material is adopted, and the KAM value of the investigation material obtained by the same method as the KAM value in the adopted master curve is calculated as follows. The life can be predicted by applying to the adopted master curve.
[0061]
As described above, by using the master curve according to the fatigue state of the investigation material to predict the life, more accurate life prediction can be performed.
[0062]
FIG. 15 shows a remaining life measuring apparatus 100 for measuring the remaining life of a material by the above various methods. The measuring apparatus 100 includes a scanning electron microscope 110 including an electron beam generating unit 111 and a secondary electron detecting unit 112, and an arithmetic processing unit 120 that performs arithmetic processing on data from the scanning electron microscope 110 and performs mapping. It is configured. In FIG. 15, reference numeral 130 denotes a sample (a test material or a survey material). The scanning electron microscope 110 analyzes reflected Kikuchi line diffraction generated from the sample 130 when the sample 130 is irradiated with an electron beam. The arithmetic processing unit 120 calculates the KAM value from the result of analyzing the backscattered electron Kikuchi line diffraction, creates a master curve, and calculates the remaining life by applying the KAM value of the survey material to the master curve.
[0063]
As described above, various embodiments have been described in the present specification, but the essence of the present invention is that the phenomenon that dislocations accumulate at crystal grain boundaries as the consumption of material life progresses is used for predicting the remaining life of the material. However, the present invention is not limited to the method using the KAM value, but encompasses all remaining life prediction methods using the deviation of the crystal orientation.
[0064]
【The invention's effect】
The present invention obtains a local crystal orientation difference using a crystal orientation microscope, and estimates a damage level of a material, that is, a life consumption degree from a change or a change rate thereof. If the method of the present invention is used, before the material life is consumed, a change in the intracrystalline structure in which dislocations, which are also included in the crystal grains, move to the crystal grain boundaries as fatigue progresses, is represented by a crystal orientation difference. By correlating this with the damage level of the material, it is possible to predict and estimate the remaining life with high accuracy.
Further, by using the present method in combination with a conventional method for evaluating the life of a metal material, it is possible to more accurately estimate the remaining life.
[0065]
In the present invention, the relationship between the degree of consumption of the material life of the test material and the local shift of the crystal orientation when the test material consumes the material life includes a simple fatigue relationship, a tensile holding creep fatigue relationship, and a compression relationship. A more accurate life prediction can be performed by preparing the holding creep fatigue relation and predicting the life using a relation (master curve) corresponding to the fatigue state of the investigation material.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a method of calculating a KAM value.
FIG. 2 shows a schematic diagram of a state in which crystal grains are aggregated and a schematic diagram of a KAM value according to the degree of life consumption.
FIG. 3 is an example of a KAM value analysis map.
FIG. 4 is a schematic diagram showing a creep fatigue test of an embodiment of the present invention.
FIG. 5 is a diagram showing a measurement region in the vicinity of a crystal grain boundary where a KAM value is measured.
FIG. 6 is a table and a graph showing a relationship between a material life and a KAM value near a crystal grain boundary.
FIG. 7 is a table and a graph showing a relationship between a material life and a KAM value change rate near a crystal grain boundary.
FIG. 8 is a diagram showing a measurement region where a KAM value in a crystal grain is measured.
FIG. 9 is a table and a graph showing a relationship between a material life and an intra-grain KAM value.
FIG. 10 is a table and a graph showing a relationship between a material life and a rate of change of a KAM value in a crystal grain.
FIG. 11 is a diagram showing measurement positions for measuring a KAM value from inside a crystal grain to a crystal grain boundary.
FIG. 12 is a table and a graph showing a relationship between a material life and a KAM value difference between crystal grains and between crystal grain boundaries.
FIG. 13 is a characteristic diagram showing various strain application states.
FIG. 14 is a characteristic diagram showing a master curve corresponding to fatigue, tensile creep fatigue, and compression creep fatigue.
FIG. 15 is a block diagram showing a remaining life measuring apparatus according to the embodiment of the present invention.
[Explanation of symbols]
10 Analysis section
11 Adjacent section
12 Second section
50 measurement area
80 Measurement area
100 remaining life measuring device
110 Scanning electron microscope
120 arithmetic processing unit
130 samples

Claims (8)

A method for measuring the remaining life of a material in which consumption of the material life has occurred,
A step of preparing in advance the relationship between the degree of consumption of the material life of the test material and the local crystal orientation shift when the test material consumes the material life;
A step of measuring the local crystal orientation shift of the test material in which the consumption of the material life that is the same material as the test material has occurred,
Estimating the remaining life of the survey material by estimating the degree of consumption of the material life of the survey material by applying the measured shift in the crystal orientation of the survey material to the relationship. Life measurement method. The local deviation of the crystal orientation between the test material and the investigation material is derived from the crystal orientation difference angle between the prescribed region of the test material and the prescribed region of the investigation material corresponding to the prescribed region. The remaining life measuring method according to claim 1, wherein: 3. The remaining life measuring method according to claim 2, wherein the specified region of the test material and the specified region of the investigation material are respectively located in crystal grains of each material. 3. The remaining life measuring method according to claim 2, wherein the prescribed region of the test material and the prescribed region of the investigation material are respectively located near crystal grain boundaries of each material. The local shift of the crystal orientation between the test material and the investigation material is caused by a change in the crystal orientation difference angle between two regions in the test material and the investigation corresponding to the two regions in the test material, respectively. 2. The remaining life measuring method according to claim 1, wherein the method is derived from a change in a crystal orientation difference angle between two regions in the material. The remaining life according to claim 5, wherein the two regions in the test material and the two regions in the investigation material are located at approximately the center of the crystal of each material and near the crystal grain boundary. How to measure. In the step of preparing in advance the relationship between the degree of consumption of the material life of the test material and the local shift in the crystal orientation when the test material consumes the material life,
When the test material is simply fatigued, a simple fatigue relationship, which is a relationship between the degree of consumption of the material life of the test material and the local crystal orientation shift when the test material consumes the material life,
When the test material was subjected to tensile holding creep fatigue, the tensile holding creep fatigue relationship, which is the relationship between the degree of consumption of the material life of the test material and the local crystal orientation shift when the test material consumed the material life. ,
When the test material is subjected to compression holding creep fatigue, the compression holding creep fatigue relationship, which is the relationship between the consumption of the material life of the test material and the local crystal orientation shift when the test material consumes the material life, Are prepared,
In the step of estimating the remaining life of the investigation material by estimating the degree of consumption of the material life of the investigation material by applying the deviation of the crystal orientation of the measured investigation material to the relationship,
From the simple fatigue relationship, the tension holding creep fatigue relationship and the compression holding creep fatigue relationship, a relationship indicating a fatigue situation closest to the fatigue situation of the investigation material was selected, and the selected relationship was measured. 7. The method according to claim 1, further comprising estimating a remaining life of the investigation material by estimating a consumption degree of a material life of the investigation material by applying a shift of a crystal orientation of the investigation material. Method of measuring remaining life described in. A remaining life measuring apparatus used in the method according to any one of claims 1 to 7, wherein the measurement of the crystal orientation difference is performed by an electron microscope that analyzes a backscattered electron Kikuchi diffraction line, and the microscope includes: And an arithmetic processing device for performing arithmetic processing and mapping of the data.

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