ASTM E157-88(1994)

Practice for Assigning Crystallographic Phase Designations in Metallic Systems (Withdrawn 1999)

SCOPE
1.1 This practice covers the assignment of designations for all alloy phases, based on the composition and crystal structure of each.  
1.2 The practice makes possible the selection of a unique designation for each phase, except that in some cases an arbitrary lower case letter is used as described in 3.4 and 3.5.  
1.3 The same designation shall be used for a given phase regardless of the system in which it appears (single component, binary, ternary, or polynary).
1.4 A procedure for selecting a temporary designation is also provided to cover those cases in which not enough information is available to assign the permanent designation.

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-1993
• Withdrawal Date: 09-Oct-1999
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.02 - Terminology

Standards Content (Sample)

= O759530 0543608 239
Designation: E 157 - 88 (Reapproved 1994)
Standard Practice for
Assigning Crystallographic Phase Designations in Metallic
Systems'
This standard is issued under the fixed designation E 157; 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 atomic percentages and separated by commas. This means
that for phases with wide composition ranges, the order of
1.1 This practice covers the assignment of designations for
the chemical symbols may change. For example, in the
all alloy phases, based on the composition and crystal struc-
aluminum-zinc system, the extensive aluminum-zinc solid
ture of each.
solution would be (Al,Zn)4F at the aluminum end of the
1.2 The practice makes possible the selection of a unique
diagram, and (Zn,A1)4F at the zinc end of the diagram.
designation for each phase, except that in some cases an
3.3 The second part of the designation, which is based on
arbitrary lower case letter is used as described in 3.4 and 3.5.
crystal structure, generally consists of a capital letter preceded
1.3 The same designation shall be used for a given phase
by an arabic numeral. The capital letter shows the Bravais
regardless of the system in which it appears (single compo-
lattice and the numeral the number of atoms per unit cell.
nent, binary, ternary, or polynary).
The following table shows the letters to be used for the
1.4 A procedure for selecting a temporary designation is
various lattices:
also provided to cover those cases in which not enough
C-primitive cubic
information is available to assign the permanent designation.
E-body-centered cubic
F-facecentered cubic
2. Referenced Document T-primitive tetragonal
U-centered tetragonal
2. I ASTM Standard: R-rhombohedral
H-hexagonal
E 391 Practice for Presentation of Phase Diagrams2
O-primitive orthorhombic
P-bodyantered orthorhombic
Q-base-centered orthorhombic
3. Summary of Practice
S-face-centered orthorhombic
3.1 Each designation consists of two parts. The first part
M-primitive monoclinic
N-centered monoclinic
depends upon the chemical composition and the second part
2-triclinic
depends upon the crystal structure.
The capital letters representing the different lattices are pref-
3.2 The first part of the designation is based on the chem-
erably printed in italics.
ical composition of the phase. If the phase consists of chemical
3.4 If two phases consist of the same elements, have the
elements in stoichiometric proportions, the chemical formula
same lattice and the same number of atoms per unit cell, but
(in parentheses) shall be the first part of the designation. The
have different crystal structures, a lower case letter is added
chemical formula may also be used in the designation of a
immediately after the numeral (Note 1) to distinguish
phase existing over a composition range provided there is no
between the two phases.
significant change in the structure; that is, the diffraction
pattern remains essentially unchanged throughout the range.
NOTE 1-These occasional uses of the lower case letter constitute the
only arbitrary feature of the system. To avoid confusion, an author
If the structure of the phase varies enough to produce signif-
should not assign a lower case letter to any designation without
icant changes in the diffraction pattern (for example, if the
consulting the Powder Diffraction File3 to determine what letters, if any,
changes in the pattern are large enough to necessitate multiple
have already been assigned to that designation.
entries in the search manuals of the Powder Diffraction File3),
3.5 If two phases composed of the same elements have the
or if the phase field does not contain a stoichiometric ratio,
same crystal structure, a lower case letter is added immedi-
the first part of the designation (in parentheses) must consist
ately after the upper case letter (Note 1). For example, the
of the chemical symbols of the elements necessary for the
two immiscible solid solutions in the aluminum-zinc system
formation of the phase, placed in the order of decreasing
would be designated (Al,Zn)4Fa and (Al,Zn)4fi.
3.6 If the atomic arrangement changes within a single
This practice is under the jurisdiction of ASTM Committee E4 on phase field (the lattice remaining the same but the number of
Metallography and is the direct responsibility of Subcommittee E04.02 on
atoms per unit cell changing) the maximum and the min-
of Phase Diagrams.
Metallographic Terminology, and Nomenclature
imum number of atoms per unit cell are both given and
Current edition approved Aug. 26, 1988. Published October 1988. Originally
separated by a hyphen. For example, 4-8F would be used for
published as E 157 - 61 T. Last previous edition E 157 - 82af1.
' Annual Book
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