https://doi.org/10.1007/s100510050522
Al-Cu approximants in the Al3Cu4 alloy*
1
State Key Laboratory for Materials Modification by Laser, Ion and Electron Beams, Dalian University Technology, Dalian,
116024, P.R. China
2
Department of Materials Engineering,
Dalian University of Technology,
Dalian 116024, P.R. China
3
Atomic Imaging of Solids, Institute of Metals Research, Academia Sinica, Shenyang 110015,
P.R. China
Corresponding authors: a dong@dlut.edu.cn mmlab@dlut.edu.cn
Received:
8
July
1997
Revised:
19
May
1998
Accepted:
16
June
1998
Published online: 15 November 1998
The Al3Cu4 composition, with an e/a ratio of 1.86 being close to ternary Al-Cu-TM (Transition Metal)
quasicrystals, has been chosen for the search of Al-Cu approximants. Phase structures and compositions
were studied using TEM, X-ray diffraction and EPMA techniques. Two new phases were found:
face-centered orthorhombic oF-Al43.2Cu56.8 (,
,
nm) and body-centered
orthorhombic oI-Al41.3Cu58.7 (oI,
,
,
nm). Their e/a ratios are the same as that
of the Al-Cu-Fe icosahedral quasicrystal. Their space groups are probably oF-Fmm2 and oI-Imm2. Both are
B2 vacancy-containing superstructures; unit cell compositions can be expressed approximately as
oF-Al36Cu
and oI-Al8Cu
(
: vacancies). They both exist in twinning variants of the types
and
. Such twinning modes indicate that these orthorhombic phases are the decomposition
products of a high-temperature parent phase ε2-Al2Cu3, the atomic structure of which contains pentagonal
atomic arrangements. Therefore the oF, oI, and
phases are all B2-based approximants corresponding to the
Al-Cu-TM quasicrystals.
PACS: 61.44.+p – Semi-periodic solids / 61.66.Dk – Alloys
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1998