ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The ordered domain structure present in the α-phase Cu-Al alloys investigated by Epperson, Ffirnrohr & Ortiz [Acta Cryst. (1978), A34, 667-681] is determined by an extension of the computer method developed recently by Epperson [J. Appl. Cryst. (1979), 12, 351-356] for analyzing a Gehlen-Cohen type simulated structure for a binary, f.c.c., locally ordered alloy in terms of nearest-neighbor atomic configurations. The dominant ordered feature of the more concentrated of these alloys is the existence of randomly dispersed Boric-Sparks tetrahedra; that is, four nearest-neighbor Al atoms arranged tetrahedrally about a Cu atom. The majority of these tetrahedra are isolated; however, as many as three or four are occasionally found to be joined in fragments of a Cu3Au-type antiphase-shift structure. This extended ordered structure also incorporates the Cu3Au-type ring configuration, another principal characteristic structural feature of these Cu-Al alloys. As a typical example, a Cu-14.76 at.% Al alloy quenched from 923 K and annealed for 1580 h at 423 K was found to contain 87 such locally ordered regions in an 8000-atom model. Of these 'domains', 74 were isolated tetrahedra and the remainder consisted of pairs of tetrahedra joined such that their central atoms were mutual second-nearest neighbors. For this alloy and heat treatment, the locally ordered regions of this type amount to about 14 volume % of the microstructure and contain 32% of the Al in the alloy. The average (spherical) domain size is only 3.4 Å. Not only are the locally ordered regions very small, but there are also perceptible imperfections in the packing sequence.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739480000848
