X-RAY STRESS MEASUREMENT DEVICE

Abstract

An X-ray generator 110 irradiates with an X-ray beam onto a polycrystalline sample on a sample stage 113. An X-ray detector 116 including an array of X-ray detecting elements detects the intensities of diffracted X-rays which occur from the X-ray beam incident on the sample. A rotary drive rotates the X-ray generator, X-ray detector and sample-holding section so as to maintain a predetermined relationship between the angle formed by the sample surface and the incident X-ray beam, and the angle formed by the sample surface and the diffracted X-ray travelling toward the X-ray detector. A stress measurement section rotates, for a measurement of a stress value of the sample, either the X-ray generator and the X-ray detector or the sample stage so as to change the angle formed by the sample surface and the incident X-ray beam, while maintaining the positional relationship of the X-ray generator and the X-ray detector.

Claims

1. An X-ray stress measurement device configured to measure a stress in a sample made of a polycrystal by utilizing a diffraction phenomenon which occurs when an X-ray beam is irradiated onto the sample, the device comprising: a sample-holding section; an X-ray irradiating section configured to irradiate with an X-ray beam onto a sample held in the sample-holding section; an X-ray detector section including a plurality of X-ray detecting elements one-dimensionally arrayed in a predetermined direction, the X-ray detector section configured to detect intensities of diffracted X-rays which are a radiation of X-rays diffracted from the sample within a predetermined angular range when the X-ray beam is irradiated from the X-ray irradiating section onto the sample; a rotary drive section configured to individually rotate the X-ray irradiating section, the X-ray detector section and the sample-holding section so as to maintain a predetermined relationship between an angle formed by a surface of the sample held in the sample-holding section and the X-ray beam incident on the surface of the sample, and an angle formed by the surface of the sample and a diffracted X-ray travelling from the sample toward the X-ray detector section; and a stress measurement section configured to rotate, for a measurement of a stress value of the sample, either the X-ray irradiating section and the X-ray detector section or the sample-holding section so as to change the angle formed by the surface of the sample held in the sample-holding section and the X-ray beam incident on the surface of the sample, while maintaining a positional relationship of the X-ray irradiating section and the X-ray detector section.

2. The X-ray stress measurement device according to claim 1, wherein the stress measurement section includes: a first measurement section configured to arrange the sample-holding section, the X-ray irradiating section and the X-ray detector section so that the angle formed by the surface of the sample held in the sample-holding section and an incident X-ray beam which is a beam of X-rays incident on the sample becomes equal to .sub.0 which satisfies the Bragg's equation, and so that an X-ray included in the radiation of X-rays from the sample and forming an angle of 2.sub.0 with an extension of the incident X-ray beam hits an X-ray detecting element located at a center of the X-ray detector section when the sample is in a stress-free state, as well as to make the X-ray irradiating section irradiate with an X-ray beam onto the sample, and to determine a temporary diffraction angle 2.sub.0 from detection values obtained for the X-ray beam by the plurality of X-ray detecting elements of the X-ray detector section; a second measurement section configured to rotate either the X-ray irradiating section and the X-ray detector section or the sample-holding section, or both, so that the angle formed by the incident X-ray beam and the surface of the sample becomes equal to .sub.0+.sub.n, while maintaining the positional relationship of the X-ray irradiating section and the X-ray detector section arranged by the first measurement section when determining the temporary, diffraction angle 2.sub.0, as well as to make the X-ray irradiating section irradiate with an X-ray beam onto the sample, and to determine a temporary diffraction angle 2.sub.n from detection values obtained by the plurality of X-ray detecting elements of the X-ray detector section for the X-ray beam; a diffraction angle calculator section configured to create a temporary 2-sin.sup.2 diagram from a combination of the temporary diffraction angle 2.sub.0 and an angle of 0 as well as a combination of the temporary diffraction angle 2.sub.n and an angle of .sub.0+.sub.n, and to determine temporary diffraction angles 2.sub.1 to 2.sub.n-1 at angles .sub.1 to .sub.n-1 within an angular range of 0 to 2.sub.n in the temporary 2-sin.sup.2 diagram, respectively; and a stress calculator section configured (1) to gradually rotate either the X-ray irradiating section and the X-ray detector section or the sample-holding section, or both, so that the angle formed by the incident X-ray beam and the surface of the sample becomes equal to each of the values from .sub.0+.sub.1 to .sub.0+.sub.n-1, while maintaining the positional relationship of the X-ray irradiating section and the X-ray detector section arranged by the first measurement section when determining the temporary diffraction angle 2.sub.0, and to make the X-ray irradiating section irradiate with an X-ray beam onto the sample, and to determine a peak-top position from detection values obtained by the plurality of X-ray detecting elements of the X-ray detector section for the X-ray beam, as well as (2) to create a true 2-sin.sup.2 diagram using the determined peak-top positions as true diffraction angles 2.sub.1 to 2.sub.n-1 at angles .sub.1 to .sub.n-1, and to determine the stress value of the sample from the true 2-sin.sup.2 diagram.

3. The X-ray stress measurement device according to claim 2, wherein the stress calculator section is configured to create a graph with a vertical axis indicating the detection values of the plurality of X-ray detecting elements of the X-ray detector section and a horizontal axis indicating the diffraction angles of the diffracted X-rays respectively incident on the X-ray detecting elements, and to determine the peak-top position by performing a profile-fitting operation on the graph.

4. The X-ray stress measurement device according to claim 2, wherein the stress calculator section is configured to create a graph with a vertical axis indicating the detection values of the plurality of X-ray detecting elements of the X-ray detector section and a horizontal axis indicating the angles of the diffracted X-rays respectively incident on the X-ray detecting elements, and to determine the peak-top position by determining a base line in the graph and normalizing a waveform of the graph which remains after a subtracting operation for removing the base line from the graph is performed.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a diagram illustrating the principle of an X-ray stress measurement.

[0036] FIG. 2A is an X-ray diffraction intensity curve.

[0037] FIG. 2B is a 2-sin.sup.2 diagram.

[0038] FIG. 3 is a schematic configuration diagram of a conventional X-ray stress measurement device.

[0039] FIG. 4 is an example of the diffracted X-ray intensity distribution curve obtained with a conventional X-ray stress measurement device.

[0040] FIG. 5 is a schematic configuration diagram of an X-ray stress measurement device according to an embodiment of the present invention.

[0041] FIG. 6 is a diagram illustrating the principle of an X-ray stress measurement using the X-ray stress measurement device according to the present embodiment.

[0042] FIG. 7 is a flowchart of a stress measurement process.

[0043] FIG. 8A is an example of the 2-sin.sup.2 diagram created based on the diffraction angles 2.sub.0 and 2.sub.n determined for angles .sub.0 and .sub.n.

[0044] FIG. 8B is a diagram showing the relationship between angles .sub.1 to .sub.n-1 and temporary diffraction angles 2.sub.1 to 2.sub.n-1, determined from the 2-sin.sup.2 diagram shown in FIG. 8A.

[0045] FIG. 9 is an example of the X-ray intensity distribution curve obtained under the condition that the arrangement of the X-ray generator, X-ray detector and sample stage is regulated based on the temporary diffraction angles.

[0046] FIG. 10A is a table showing the result of a measurement of the stress value using a conventional device with an X-ray detector having a measurement angular range of 9.02.

[0047] FIG. 10B is a table showing the result of a measurement of the stress value using a conventional device with an X-ray detector having a measurement angular range of 18.33.

[0048] FIG. 11A is a table showing the result of a measurement of the stress value using an X-ray stress measurement device according to the present embodiment with an X-ray detector having a measurement angular range of 9.02.

[0049] FIG. 11B is a table showing a result of the measurement of the stress value using an X-ray stress measurement device according to the present embodiment with the X-ray detector having a measurement angular range of 18.33.

[0050] FIG. 12 is a table showing a summary of the stress values obtained with the conventional device and the X-ray stress measurement device according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

[0051] An X-ray stress measurement device according to an embodiment of the present invention is hereinafter described with reference to FIGS. 5 to 12.

[0052] FIG. 5 schematically shows the configuration of the X-ray stress measurement device according to the present embodiment. The present X-ray stress measurement device includes a goniometer 117, a sample stage 113 attached to the center of the goniometer 117, as well as an X-ray generator 110, beam-irradiating slit 111 and X-ray detector 116 attached to an outer circumferential portion of the goniometer 117. The X-ray detector 116 includes a considerable number of extremely small X-ray detecting elements arrayed on a straight line. The X-ray generator 110 corresponds to the X-ray irradiating section in the present invention and includes an X-ray tube 110a and generates a specific wavelength of X-rays corresponding to the material of the target.

[0053] The goniometer 117 includes a driving shaft for rotating the sample stage 113 and another driving shaft for rotating the X-ray generator 110 and the X-ray detector 116. These driving shafts are coaxial with each other. Using these driving shafts, the goniometer 117 rotates the sample stage 113, X-ray generator 110 and X-ray detector 116 while constantly maintaining the relationship in which the angle formed by the surface of sample S and an X-ray beam incident from the X-ray generator 110 onto sample S is equal to the angle formed by the surface of sample S and the X-ray travelling from sample S toward an X-ray detecting element located at the center of the X-ray detector 116. To this end, the two driving shafts are rotated at a ratio of :2. Additionally, the two driving shafts in the present embodiment are also configured to be individually rotatable.

[0054] When an X-ray is incident on an X-ray detecting element of the X-ray detector 116, the X-ray detector 116 generates a detection signal corresponding to the intensity of the X-ray. The detection signal obtained with the X-ray detector 116 is sent through an amplifier 118 to a data processing unit 120. The data processing unit 120 includes a data collector 121, diffraction angle calculator 112, stress value calculator 123 and other related components. The data collector 121 corresponds to the first and second measurement sections of the present invention. A control unit 100 is configured to control the operation of each component of the X-ray stress measurement device. Graphs and other results obtained by the signal processing in the data processing unit 120 are sent to the control unit 100 and shown on a display unit 101. Other than the display unit 101, the control unit 100 also includes an input unit 102 for allowing an operator to perform the device setting or command input. The control unit 100 and the data processing unit 120 can be configured using a personal computer as a hardware resource, with the aforementioned functional blocks realized by executing dedicated controlling-and-processing software previously installed on the same personal computer.

[0055] Next, a stress measurement operation for sample S made of a polycrystal using the present X-ray stress measurement device is hereinafter described with reference to FIGS. 6 to 9. The following description deals with the case where the position of the X-ray generator 110 and the X-ray detector 116 is changed around sample S held on the sample stage 113 while the sample stage 113 is held in a fixed position. Alternatively, the inclination of the surface of sample S may be changed while the X-ray generator 110 and the X-ray detector 116 are held in a fixed position. It is also possible to change both the rotational position of the X-ray generator 110 and the X-ray detector 116, and the inclination of the surface of sample S. What is essential is to maintain a predetermined positional relationship of the sample stage 113, X-ray generator 110 and X-ray detector 116. In the following description, it is assumed that the XY plane is located on the surface of sample S. The Z axis represents a normal to the surface of sample S.

[0056] Before the execution of the stress measurement operation for sample S, a person in charge of the measurement (who is hereinafter called the operator) sets the sample stage 113 in the position shown in FIG. 5, and rotates one of the driving shafts of the goniometer 117 to arrange the X-ray generator 110 and the X-ray detector 116 so that the angle formed by the surface of sample S and the incident X-ray beam becomes equal to , and so that the angle formed by the surface of sample S and the diffracted X-ray travelling from the surface of sample S to an X-ray detecting element located at the center of the X-ray detector 116 also becomes equal to . The position of the X-ray generator 110 and the X-ray detector 116 in this situation is hereinafter called the initial position. The angle is an angle at which an X-ray beam of wavelength hitting the crystal grains forming sample S in a stress-free state satisfies the Bragg's equation. This angle is specific to the material of sample S. Accordingly, an X-ray beam hitting a crystal grain which is present in a surface region of sample S in a stress-free state satisfies the Bragg's equation if the angle of the crystal grain is equal to 0 (i.e. if the lattice planes of the crystal grain is parallel to the surface of the sample S). The task of adjusting the arrangement of the sample stage 113, X-ray generator 110 and X-ray detector 116 may be automatically performed by the device upon receiving a piece of information identifying the material of sample S entered by the operator through the input unit 102, or the operator may manually perform the adjustment.

[0057] After the adjustment has been completed, the operator issues a command to initiate the stress measurement operation. Then, the control unit 100 performs the stress measurement operation according to the flowchart shown in FIG. 7.

[0058] Initially, the operation of creating a diffracted X-ray intensity distribution curve is performed under two conditions, i.e. with the X-ray generator 110 and the X-ray detector 116 located in the initial position shown in FIG. 5 as well as in a position rotated from the initial position by angle .sub.n (Step S1). In any of these two conditions, the sample stage 113 is held in the previously described position. Therefore, the angle formed by the surface of sample S and the incident X-ray beam is equal to when the X-ray generator 110 and the X-ray detector 116 are in the initial position, while the angle formed by the surface of sample S and the incident X-ray beam is equal to +.sub.n when the X-ray generator 110 and the X-ray detector 116 are in a position rotated from the initial position by angle .sub.n. In other words, the X-ray beam incident from the X-ray generator 110 satisfies the Bragg's equation for a crystal grain with angle =0 among the crystal grains in a surface region of sample S in a stress-free state when the X-ray generator 110 and the X-ray detector 116 are in the initial position, while the X-ray beam incident from the X-ray generator 110 satisfies the Bragg's equation for a crystal grain with angle =.sub.n among the crystal grains in the surface region of sample S when the X-ray generator 110 and the X-ray detector 116 are in a position rotated from the initial position by angle .sub.n.

[0059] Under any of those conditions, the X-ray beam incident on the surface of sample S is diffracted on the crystal grains present in the surface region of sample S, as shown in FIG. 6, and is subsequently introduced into the X-ray detector 116. The diffraction of X-rays occurs at each of the considerable number of crystal grains which are present within the area hit by the X-ray beam on the surface of sample S. The X-ray diffracted on each individual crystal grain falls onto an X-ray detecting element located at a position corresponding to the diffraction angle 2 of the X-ray. The X-ray detector 116 generates a detection signal corresponding to the intensity of the X-ray received by each X-ray detecting element. The detection signals obtained with the considerable number of X-ray detecting elements show a relationship between the diffraction angle 2 and the X-ray intensity. The data processing unit 120 receives those detection signals from the X-ray detecting elements through the amplifier 118. The data collector 121 collects those signals and creates a diffracted X-ray intensity distribution curve which shows the relationship between the diffraction angle 2 and the X-ray intensity. The diffraction angle calculator 122 mathematically processes this distribution curve to determine the peak-top position at which the highest X-ray intensity occurs (Step S2). The peak-top positions at which the highest X-ray intensities at angles =.sub.0(=0) and =.sub.n occur are designated as temporary diffraction angles 2.sub.0 and 2.sub.n, respectively.

[0060] In Steps S1 and S2, the arrangement of the X-ray generator 110 and the X-ray detector 116 is selected using the angle which satisfies the Bragg's equation for sample S in a stress-free state. Therefore, depending on the magnitude of the stress in sample S, the peak-top position of the diffracted X-ray intensity distribution curve will be displaced from the center of the measurement angular range of the X-ray detector 116, as shown by curve B in FIG. 4. Accordingly, in Step S2, the diffraction angle calculator 122 determines the peak-top position by performing a profile-fitting operation, rather than the subtracting and normalizing operations using the base line.

[0061] Furthermore, the diffraction angle calculator 122 creates a temporary 2-sin.sup.2 diagram using the determined diffraction angles 2.sub.0 and 2.sub.n as well as the angles .sub.0 and .sub.n which respectively correspond to those diffraction angles (Step S3). Based on this temporary 2-sin.sup.2 diagram, the diffraction angle calculator 122 calculates temporary diffraction angles 2.sub.1 to 2.sub.n-1 at angles .sub.1 to .sub.n-1 between the angles .sub.0 and .sub.n (Step S4). FIG. 8A shows a temporary 2-sin.sup.2 diagram created from the diffraction angles 2.sub.0 and 2.sub.n as well as the angles .sub.0 and .sub.n. FIG. 8B shows temporary diffraction angles 2.sub.1 to 2.sub.n-1 calculated from the temporary 2-sin.sup.2 diagram.

[0062] The operations described so far correspond to the contents of the operations of the first and second measurement sections of the present invention.

[0063] Subsequently, based on the temporary diffraction angles 2.sub.1 to 2.sub.n-1 at angles .sub.1 to .sub.n-1 calculated in Step S4, the control unit 100 gradually changes the rotational position of the X-ray generator 110 and the X-ray detector 116 from the initial position shown in FIG. 5 by angles .sub.1 to .sub.n-1. At each of those positions, the control unit 100 performs the operation of creating a diffracted X-ray intensity distribution curve (Step S5). For this operation, the control unit 100 adjusts the arrangement of the X-ray generator 110 and the X-ray detector 116 by controlling the driving shafts so that the incident X-ray beam will form angle .sub.1 to .sub.n-1 to the surface of sample S, while the diffracted X-ray exiting from the surface at angle .sub.1 to .sub.n-1 will hit an X-ray detecting element located at the center of the X-ray detector 116. Under such an arrangement condition, the X-ray beam incident on sample S satisfies the Bragg's equation on crystal grains which are present in a surface region of sample S having the lattice planes oriented at angle equal to .sub.1 to .sub.n-1, and the diffracted X-ray resulting from the incident X-ray beam hits an X-ray detecting element located roughly at the center of the X-ray detector 116. Subsequently, as described earlier, the detection signals of the X-ray detecting elements are sent from the X-ray detector 116 to the data processing unit 120, and a diffracted X-ray intensity distribution curve is created for each of the angles .sub.1 to .sub.n-1 based on those detection signals. FIG. 9 shows an example of the diffracted X-ray intensity distribution curve created in the present step. As shown in FIG. 9, the diffracted X-ray intensity distribution curve created in the present step has the peak-top position located roughly at the center of the measurement angular range of the X-ray detector 116. Accordingly, the true diffraction angle 2.sub.1 to 2.sub.n-1 at angle .sub.1 to .sub.n-1 can be determined from this curve (Step S6).

[0064] Subsequently, the stress value calculator 123 creates a 2-sin.sup.2 diagram based on the angles .sub.1 to .sub.n-1 and the diffraction angles 2.sub.1 to 2.sub.n-1 at those angles (Step S7). Then, the stress value calculator 123 determines a straight line (equation: Y=A+M*X) connecting the points on the 2-sin.sup.2 diagram, and calculates the stress value a from the gradient M by equation =K*M, where K is the stress constant (Step S8).

[0065] An experimental result of a measurement of the stress value of a specific sample using the previously described X-ray stress measurement device as well as a conventional device is hereinafter described with reference to FIGS. 10A, 10B, 11A, 11B and 12. A ferrous sample (high-stress iron-based specimen) whose peak had a half-value width of 4.5 to 5.2 was used as the sample. The measurement was performed at 10 rotational positions, i.e. n=10.

[0066] FIGS. 10A and 10B show stress values obtained by using the conventional device, while FIGS. 11A and 11B show stress values obtained by using the previously described X-ray stress measurement device. FIG. 12 is a table showing a summary of the stress values obtained with the conventional device and the previously described X-ray stress measurement device. An X-ray detector having a measurement angular range of 9.02, and one having a measurement angular range of 18.33, were used for the experiment. FIGS. 10A and 11A show the results obtained with the X-ray detector having a measurement angular range of 9.02, while FIGS. 10B and 11B show the results obtained with the X-ray detector having a measurement angular range of 18.33.

[0067] As is evident from FIGS. 10A and 10B, the stress values obtained with the conventional device significantly changed depending on the measurement angular range of the X-ray detector. By comparison, the stress values obtained with the X-ray stress measurement device according to the present embodiment were roughly the same and independent of the measurement angular range of the X-ray detector, as shown in FIGS. 11A and 11B. Those results confirm that a correct stress value can be obtained with the device according to the present embodiment even if the measurement angular range is considerably narrow.

REFERENCE SIGNS LIST

[0068] 10 . . . X-Ray Tube [0069] 110 . . . X-Ray Generator [0070] 11, 111 . . . Beam-Irradiating Slit [0071] 13 . . . Sample Holder [0072] 113 . . . Sample Stage [0073] 15 . . . Exit Slit [0074] 16, 116 . . . X-Ray Detector [0075] 17, 117 . . . Goniometer [0076] 100 . . . Control Unit [0077] 101 . . . Display Unit [0078] 102 . . . Input Unit [0079] 120 . . . Data Processing Unit [0080] 121 . . . Data Collector [0081] 122 . . . Diffraction Angle Calculator [0082] 123 . . . Stress Value Calculator [0083] S . . . Sample