X-ray Diffraction Instrument

Abstract

According to this invention a mount for X-ray tubes is rotatable around the axis of an X-ray which is incident upon a specimen. A support for the mount is rotatable around a straight line passing through the point at which the X-ray is incident upon the specimen and a holder for a first guide rail is rotatable around a straight line which intersects a first straight line at right angles. Guide rails permit the X-ray sources and diffracted X-ray detectors to travel along such guide rails, so that the internal strain, residual austenite and crystal orientation of the specimen can be measured without being limited by the configuration of specimen's surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an X-ray diffraction instrument. When a characteristic X-ray is applied on a metal surface, a diffraction phenomenon takes place. Since this phenomenon gives informations such as the angle of the incident X-ray from the diffracted X-ray and the intensity of the diffracted X-ray, the state of the metal crystal can be determined in a non-destructive manner by analyzing these informations.

The metal weld, for example, may sometimes include a residual strain which occurs during cooling by shrinkage. The residual strain may remarkably reduce the strength of the material. It is already known that the residual strain can be measured by the diffraction angle of X-ray. When a carbon steel in .gamma.-phase and at a high temperature is cooled rapidly, lattice modification occurs in the material which accompanies the change in volume, and the carbon steel changes into .alpha.-phase. A complicated residual strain appears due to the interaction of the stress caused by the cubical expansion resulting from the lattice modification and the stress caused by shrinkage during cooling. In this case the whole carbon steel in .gamma.-phase is not modified into .alpha.-phase but a portion of it remains in the unstable .gamma.-phase due to rapid cooling. This is the residual austenite, which is modified with time into the stable .alpha.-phase by the external force, heat, etc. Since this is a lattice modification, it accompanies the change in volume which, in turn, results in the change in size or in residual strain. The mechanical and physical properties of the metal products such as cold-rolled steel plates and pressed products, which have been subjected to a remarkable plastic deformation, are changeable because the metal crystal of these products has an orientation. The residual strain, residual austenite and aggeregation structure of crystals have an interrelationship with each other and form important factors for determining the strength of the metallic material.

The purpose of this invention is to provide an X-ray diffraction instrument for measuring not only the residual strain but also the residual austenite and aggregation structure at the same positions of the actual structures and components.

The invention will be described in more detail with reference to the accompanying drawings, in which

FIG. 1 is a front view of the X-ray diffraction instrument according to one embodiment of this invention; and

FIG. 2 is an elevational view of the instrument shown in FIG. 1.

X-ray a is applied from an X-ray tube 2 onto the surface of a specimen 1 of which residual strain, residual austenite and crystal orientation are to be measured. Detectors 3, 4 and 5 are arranged for detecting the diffracted X-ray b, c and d. The X-ray tube 2 is fixedly attached to a mount 6, and the detectors 3, 4 and 5 are mounted on a circular guide rail 7 formed on the mount 6 so that they are movable along the guide rail 7. The guide rail 7 is formed into a circular configuration of which center coincides with point p at which the X-ray is incident upon the surface of the specimen. An electric motor and a gear box are arranged in the mount 6 for driving the detectors 3 and 4 symmetrically about the axis of incident X-ray a and for driving the detectors 4 and 5 in the same direction at an equal angular speed. Another guide rail 8 is formed into a circular configuration which has a larger diameter than the guide rail 7 and has its center at point p. A support 9 is mounted on the guide rail 8 so that it is movable along the guide rail 8. The mount 6 for the X-ray sources are supported by the support 9 so that it is rotatable around the axis of incident X-ray a. A holder 12 is carried by a bar at the forward end of the L-shaped arm 11 fixedly attached to the shaft 10. The holder 12 is supported by the guide rail 8 in such a manner that it permits the rotation of the guide rail 8 around a straight line a passing through the point p. The shaft 10 is so arranged that its axis t intersects the line s at point p at right angles.

The shaft 10 has a worm gear 13 mounted on it for driving the shaft 10 by a worm 14. An electric motor 15 is mounted on the holder 12 to drive the guide rail 8 through the gears 16 and 17 which are operatively connected to the motor 15.

As is clear from the foregoing description, the instrument of this invention involves .alpha.-rotation by the shaft 10, .beta.-rotation around the line s and .gamma.-rotation around the axis of X-ray irradiation a. The instrument of this invention includes a circular guide rail 7 for the X-ray sources and a second circular guide rail 8 for detectors for the diffracted X-ray. The circular guide rails 7 and 8 have a common center which is point p at which the X-ray is incident on the specimen. Accordingly, when the surface of the specimen 1 is coincident with the axis t, the residual strain on the surface of the specimen 1 can be determined from the output curve of the detectors 3 and 4 by making the direction a of the incident X-ray to coincide with line s and by irradiating the X-ray onto the specimen surface at a suitable angle which is selected by .alpha.-rotation of the shaft 10, and by symmetrically moving the detectors 3 and 4 along the guide rail 7. The guide rail 7 is generally arranged at right angles with axis t, but depending on the configuration of the specimen and when the diffracted X-ray is shielded, measurement can be carried out with the guide rail 7 arranged in parallel with the axis t. When the surface of the specimen 1 is at an angle with the axis t, the support 9 can be moved along the guide rail 8 and .beta.-rotation allows the X-ray to be irradiated onto the specimen surface at right angles. Therefore, it is also possible to determine the internal stress from the diffraction angle in this particular case and the diffraction angle when the X-ray is irradiated onto the specimen surface at an angle of, for instance, 45.degree..

The residual austenite can be determined from the ratio of the intensity of the diffracted X-ray from the carbon steel in .alpha.-phase to the intensity of the diffracted X-ray from the carbon steel in .gamma.-phase. The intensity of these diffractions can be measured with the detectors 4 and 5. The errors in the measured diffraction due to the crystal orientation can be minimized by calculating the average value of measurements for various directions which can be measured during .alpha.- and .beta.-rotations. According to the instrument of this invention, it is not necessary to cut off the specimen and apply it to the measuring device, but the measuring device is installed near the specimen to carry out a non-destructive measurement.

When the specimen has an X-ray diffraction angle of .theta., if the specimen is located so that the surface thereof is in parallel with the axis t, and the incident X-ray a and the diffracted X-ray b are both at an angle of (.pi./2 - .theta.) with axis s, the crystal lattice surface which is in parallel with the specimen surface can be observed. Consequently, the crystal orientation on the surface of the specimen can be measured during .beta.- and .alpha.-rotations.

It will be noted that the instrument according to this invention permits measurement of the internal strain, residual austenite and crystal orientation at desired positions of a fixed specimen. The instrument is also very excellent in that it measures strains in various directions and avoids errors from the measurements of residual austenite which may otherwise result from the crystal orientation.

Claims

I claim:

1. An x-ray diffraction instrument comprising a mount for an x-ray source; an x-ray source constructed and arranged on said mount; a first circular guide rail constructed and arranged on said mount; said first circular guide rail having its center aligned with a point where an x-ray from said source is incident on a specimen; a plurality of detectors for detecting diffracted x-ray arranged on said first circular guide rail; a second circular guide rail having its center aligned with said x-ray incident point; a support for supporting said mount to rotate said mount around an axis aligned with the direction of x-ray incident onto the specimen, said support being movable along said second circular guide rail; means for holding said circular guide rail to rotate said second rail around an axis formed by a vertical straight line passing through said x-ray incident point; and a shaft for carrying said means to rotate said holder around an axis formed by a horizontal straight line intersecting said vertical straight line at said x-ray incident point.

2. An X-ray diffraction instrument according to claim 1, characterized in that the rotation centers of the mount, first guide rail, the support and the centers of the first and second circular guide rails are all at the point where the X-ray is incident onto the specimen.

3. An x-ray diffraction instrument according to claim 1, characterized in that the three detectors for the diffracted x-ray are arranged on the first guide rail; and an electric motor and a gear box are constructed and arranged with said mount for driving the first and second detectors in symmetrical relation with the direction of the incident x-ray and for driving the second and third detectors in the same direction at the same angular speed.