ASTM E82-91(1996)
(Test Method)Standard Test Method for Determining the Orientation of a Metal Crystal
Standard Test Method for Determining the Orientation of a Metal Crystal
SCOPE
1.1 This 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 (1, 2) may be applied to macrograins (3) (0.5-mm diameter or larger) within polycrystalline aggregates, as well as to single crystals of any size. The method is described with reference to cubic crystals; it can be applied equally well to hexagonal, tetragonal, or orthorhombic crystals.
1.2 Most natural crystals have well developed external faces, and the orientation of such crystals can usually be determined from inspection. The orientation of a crystal having poorly developed faces, or no faces at all (for example, a metal crystal prepared in the laboratory) must be determined by more elaborate methods. The most convenient and accurate of these involves the use of X-ray diffraction. The "orientation of a metal crystal" is known when the positions in space of the crystallographic axes of the unit cell have been located with reference to the surface geometry of the crystal specimen. This relation between unit cell position and surface geometry is most conveniently expressed by stereographic or gnomonic projection.
1.3 The values stated in inch-pound units are to be regarded as the standard.
1.4 This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 82 – 91 (Reapproved 1996)
Standard Test Method for
Determining the Orientation of a Metal Crystal
This standard is issued under the fixed designation E 82; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Summary of Test Method
1.1 This test method covers the back-reflection Laue proce- 3.1 The arrangement of the apparatus is similar to that of the
dure for determining the orientation of a metal crystal. The transmission Laue method for crystal structure determination
back-reflection Laue method for determining crystal orienta- except that the photographic film is located between the X-ray
tion (1, 2) may be applied to macrograins (3) (0.5-mm source and the specimen. The beam of white Xradiation passes
diameter or larger) within polycrystalline aggregates, as well as through a pinhole system and through a hole in the photo-
to single crystals of any size. The method is described with graphic film, strikes the crystal, and is diffracted back onto the
reference to cubic crystals; it can be applied equally well to film. Dark spots, which represent X-ray beams “reflected” by
hexagonal, tetragonal, or orthorhombic crystals. the atomic planes within the specimen, appear on the devel-
1.2 Most natural crystals have well developed external oped film. The atomic planes these spots represent are identi-
faces, and the orientation of such crystals can usually be fied by crystallographic procedures and the orientation of the
determined from inspection. The orientation of a crystal having metal crystal is determined.
poorly developed faces, or no faces at all (for example, a metal
4. Significance and Use
crystal prepared in the laboratory) must be determined by more
4.1 Metals and other materials are not always isotropic in
elaborate methods. The most convenient and accurate of these
involves the use of X-ray diffraction. The “orientation of a their physical properties. For example, Young’s modulus will
vary in different crystallographic directions. Therefore, it is
metal crystal” is known when the positions in space of the
crystallographic axes of the unit cell have been located with desirable or necessary to determine the orientation of a single
crystal undergoing tests in order to ascertain the relation of any
reference to the surface geometry of the crystal specimen. This
relation between unit cell position and surface geometry is property to different directions in the material.
4.2 This test method can be used commercially as a quality
most conveniently expressed by stereographic or gnomonic
projection. control test in production situations where a desired orienta-
tion, within prescribed limits, is required.
1.3 The values stated in inch-pound units are to be regarded
as the standard. 4.3 With the use of an adjustable fixed holder that can later
be mounted on a saw, lathe, or other machine, a single crystal
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the material can be moved to a preferred orientation, and subse-
quently sectioned, ground, or processed otherwise.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 4.4 If grains of a polycrystalline material are large enough,
this test method can be used to determine their orientations and
bility of regulatory limitations prior to use.
differences in orientation.
2. Referenced Documents
5. Apparatus
2.1 ASTM Standards:
5.1 X-Ray Tube—In order that exposure times be reduced to
E 3 Methods of Preparation of Metallographic Specimens
2.2 Adjunct: a minimum, the X-ray tube shall have a target that gives a high
yield of white X-radiation. The tube voltage shall be near 50
Hyberbolic chart for solving backreflection Laue patterns (1
film positive) kVp.
5.2 Back-Reflection Laue X-Ray Camera— The X-ray cam-
era shall have (1) a pinhole system about 6 cm in length with
This test method is under the jurisdiction of ASTM Committee E-4 on
openings of ⁄4 to 1 mm, (2) a flat, light-tight film holder (the
Metallography and is the direct responsibility of Subcommittee E04.11 on X-Ray
hole in the center of the film should be as small as possible,
and Electron Metallography.
preferably about ⁄8 in. (3.2 mm) in diameter), (3) a specimen
Current edition approved Feb. 22, 1991. Published May 1991. Originally
published as E82 – 49. Replaces E82 – 49 T. Last previous edition E82 – 63 (1984)
holder, and ( 4) means for setting the crystal-to-film distance at
e1
3.00 cm. These parts may be assembled in various ways
The boldface numbers in parentheses refer to the list of references at the end of
depending upon the type of specimen being studied and upon
this method.
Annual Book of ASTM Standards, Vol 03.01.
the accuracy desired. The main requirement for accurate results
Plate I is available from ASTM Headquarters. Order Adjunct: ADJE0082.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E82
is that the pinhole system shall be precisely perpendicular to
the film holder and thus to the film. An aluminum sheet may be
placed between the specimen and the film, preferably in close
contact with the film, in order to filter much of the secondary
X-radiation emitted by the crystal.
NOTE 1—Fig. 1 illustrates a back-reflection Laue camera constructed
for use with metallic sheet specimens having grains with a diameter of 0.5
mm or larger. The specimen-to-film distance is fixed at 3 cm and the
specimen surface is maintained perpendicular to the incident beam and
parallel to the film.
NOTE 2—Fig. 2 illustrates a universal camera with a goniometer head,
as adapted for back-reflection Laue studies. With this camera the inter-
pretation of an unsymmetrical pattern may be verified rapidly by rotating
the specimen to an angle for which a prominent pole is perpendicular to
the film, so that a pattern of recognized symmetry is obtained.
6. Test Specimen
6.1 The test specimen may be of any convenient size or
shape. Normally, the orientation will be determined with
reference to a prepared surface and a line on this surface.
Surfaces on metal crystals may be prepared by methods
ordinarily used in preparing metallographic specimens (Note
FIG. 2 Universal Camera With Goniometer Head for Back-
3). After final polishing, the specimen shall be etched deeply
Reflection Laue Studies
enough to remove all polishing distortion. This surface shall be
examined microscopically to make sure that the etch has
the specimen and film be fixed at the outset (a sketch of this
removed all scratches or distorted metal. Strain-free surfaces of
relationship should be made) and be preserved throughout the
aluminum, iron, copper, brass, tungsten, nickel, etc., are easily
determinations. For example, this relationship is fixed if (1) the
prepared. Great care is needed in preparing surfaces on cystals
exposed specimen surface is parallel to the plane of the film,
of metals such as tin and zinc (or their solid solutions), which
(2) a vertical line inscribed on the specimen surface is parallel
twin readily on being plastically deformed.
to a vertical line on the film, (3) the “top” of the film
NOTE 3—Reference may be made to Methods E 3, for procedures for
corresponds with the “top” of the specimen, and ( 4) the
polishing specimens.
exposed surface of the film facing the specimen is definitely
marked.
PROCEDURE
8. Back-Reflection Laue Pattern
7. Orientation of Specimen and Film
8.1 The back-reflection Laue pattern, properly prepared,
7.1 It is necessary that the orientation relationships between
will contain a hundred or more diffraction spots. These spots
represent “reflections” of the X-ray beam from all important
lattice planes of the crystal that are in position for diffraction.
With the crystal-to-film distance of 3 cm and a photographic
film 5 in. (127 mm) in diameter or 4 by 5 in. (102 by 127 mm),
this will include all important lattice planes that make an angle
of less than about 35° with the film; the reflections from all
other planes in the crystal will not be intercepted by the film.
The diffraction spots form a pattern consisting of many
hyperbolic curves; these curves represent crystallographic
zones (1, 2). Some of these hyperbolic curves are more
prominent (more thickly populated with spots) than others, as
they represent crystallographic zones having a higher popula-
tion of low-indices planes.
9. Hyperbolic and Polar Coordinate Charts
9.1 The hyperbolic chart, Fig. 3 (Plate I), and the polar
chart, Fig. 4, are used in the solution of back-reflection Laue
patterns. Use the hyperbolic chart (reproduced as a positive on
photographic film or plate) on the back-reflection Laue pattern
in much the same way that a gnomonic (or stereographic) net
is used on gnomonic (or stereographic) projections. Locate
FIG. 1 Back-Reflection Laue Camera for Metallic Sheet
Specimens both horizontal and vertical curves 2° apart in terms of angles
E82
FIG. 3 Hyperbolic Chart for Solution of Laue-Back-Reflection Patterns
within the crystal. The horizontal curves are meridians, thus second zonal curve. The angle or rotation of the chart,
corresponding to crystallographic zones; the vertical curves are measured by means of the polar net, gives the angle between
parallels. The series of meridian curves shown on the chart the zone axes producing the two zonal curves. A procedure
represents all possible curvatures that a crystallographic zone which may be used for any two zonal curves involves a rotation
of a back-reflection Laue pattern may have; the zone is a of a few spots of the back-reflection Laue pattern as follows:
straight line only when it passes through the origin. Superimpose the hyperbolic chart and the film so that the
9.2 The vertical curves are parallels and are used to measure straight-line parallel (the vertical line through the center of the
angles along meridian curves. Thus, the angle between two chart) contains the point of intersection of the two zonal curves
crystal planes that produce two spots on the film may be read in question. Then rotate this point of intersection to the origin,
directly from the chart. To measure this angle, superimpose the and move a (any) point on each of the two zonal curves the
chart on the film with centers coinciding and rotate the plate (or same number of degrees (along parallels, of course) in the
film) until a hyperbolic meridian coincides with the zonal curve same direction. Since both zonal curves now pass through the
connecting the two spots in question; then read the angle origin they appear as straight lines, and the angle between these
between the two planes directly from the set of parallels. Read radial lines is then the angle between the two zone axes in
the angle of inclination of the zone axis to the film directly question (6 ⁄2°, if the rotation has been carefully carried out).
from the scale of meridian angles. This operation is the same as the operation required to measure
9.3 A second, though not often needed, operation that may the angle between any two intersecting great circles on a
be performed with the aid of the hyperbolic and polar charts is stereographic projection.
the measurement of the angle between two zone axes (which
10. Interpretation of Unsymmetrical Back-Reflection
are represented on the pattern as two intersecting zonal curves).
Laue Patterns
If the point of intersection is located not more than about 10°
from the origin, the following procedure is used: Place the 10.1 The most rigorous method for solving an unsymmetri-
chart over the film with centers coinciding so that a meridian cal pattern is by preparing a stereographic projection with its
coincides with one of the zonal curves. Then rotate the chart plane parallel to the plane of the film. Read the film from the
about the origin until another meridian coincides with the side opposite that of incident radiation, so that the projection
E82
FIG. 4 Polar Chart for Solution of Laue Back-Reflection Patterns
corresponds to viewing the crystal from the position of the the projection shall include all the poles of the forms {100},
X-ray tube. Inscribe a reference line on the film through the {110}, {111}, and {113}; if body-centered cubic, the projec-
central spot and parallel to a prominent direction in the tion shall include {100}, {110}, {111}, and {112}. This
specimen, and measure all azimuth angles with respect to this standard projection shall be studied until one has become
line. Methods for plotting the projections are described by familiar with the relative positions of poles and their angular
Barrett (4). Methods for identifying prominent spots and zones separations, the symmetry characteristics of each pole, the
are summarized in 10.2 to 10.6, inclusive. important zonal curves passing through each pole, etc.
10.2 After some experience has been gained, it will be 10.3 In Figs. 5-8 are reproduced standard stereographic
found that back-reflection Laue patterns may be solved by projections of a cubic crystal with the {100}, {111}, {110},
inspection alone. The following remarks should be of assis- and {112} poles at the center. These projections illustrate
tance in the development of a systematic approach: At least one orientations having four-fold, three-fold, and two-fold axes of
standard stereographic projection (5) of the lattice being symmetry and a plane of symmetry, respectively. Note that the
studied shall be prepared. This projection shall include ^100&, standard cubic, or {100}, projection is made of 24 identical
^110&, and ^111& zones, and if the crystal is face-centered cubic, triangular areas.
E82
FIG. 5 Standard {001} Projection for a Cubic Crystal
FIG. 6 Standard {111} Projection for a Cubic Crystal
10.4 Crystallographic zones are of great importance in the cubic pattern will contain at least one (usually two) ^110&
solution of back-reflection Laue patterns. For the face-centered zones.
cubic lattice, the important zones, arranged in order of impor- 10.5 The most important spots are those originating from
tance, are ^110& and ^100&; for the body-centered cubic lattice planes having widest spacing in the lattice. For face-centered
these are ^111&, ^100&, and ^110&. For any lattice, the most cubic crystals, these important spots are {111}, {100}, and
important zone is always that one whose axis
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.