ASTM E82 Test Method for Determining the Orientation of a Metal Crystal

Metals and other materials are not always isotropic in their physical properties. Therefore, it is desirable or necessary to determine the orientation of a single crystal undergoing tests to ascertain the relation of any property to different directions in the material. ASTM E82 test method can be used commercially as a quality control test in production situations where the desired orientation, within prescribed limits, is required.

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Scope:

ASTM E82 test method covers the back-reflection Laue procedure for determining the orientation of a metal crystal. The back-reflection Laue method for determining crystal orientation may be applied to micro grains (0.5-mm diameter or larger) within polycrystalline aggregates, as well as to single crystals of any size. The method is described for cubic crystals. It can be applied equally well to hexagonal, tetragonal, or orthorhombic crystals.

Test Procedure:

In ASTM E82 test method, the arrangement of the apparatus is similar to that of the transmission Laue method for crystal structure determination except that the photographic film is located between the X-ray source and the specimen. The beam of white X-radiation passes through a pinhole system and a hole in the photographic film strikes the crystal and is diffracted back onto the film. Dark spots, which represent X-ray beams “reflected” by the atomic planes within the specimen, appear on the developed film. The atomic planes these spots represent are identified by crystallographic procedures and the orientation of the metal crystal is determined.

Figure 1: Laue method for crystal structure determination

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Figure 1: Laue method for crystal structure determination

Specimen size:

For ASTM E82 testing, the test specimen may be of any convenient size or shape. Normally, the orientation is determined with reference to a prepared surface and a line on this surface.

With the use of an adjustable fixed holder that can later be mounted on a saw, lathe, or other machines, a single crystal material can be moved to a preferred orientation, and subsequently sectioned, ground, or processed otherwise.

Data

The following data is used in ASTM E82 testing:

X-Ray Tube – The tube voltage shall be near 50kVp. Back-Reflection Laue X-Ray Camera – The X-ray camera shall have a pinhole system about 6cm in length with openings of 1⁄4 to 1 mm, a flat, light-tight film holder (the hole in the center of the film should be as small as possible, preferably about 1⁄8 in. (3.2 mm) in diameter), a specimen holder, and means for setting the crystal-to-film distance at 3.00 cm.

Conclusion:

ASTM E82 test method covers the back-reflection Laue procedure for determining the orientation of a metal crystal.