High resolution study of ordering reactions in gold--chromium alloys
The ordering reactions in Au/sub 4/Cr and Au/sub 3/Cr alloys have been investigated using high resolution dark field and lattice imaging techniques. In all cases the ordered structures can be described in terms of compositional modulations as occur during spinodal decomposition. In alloys quenched from above the critical temperature sro microdomains of size 10 to 15A have been resolved with structures represented by modulations in composition along (420). After aging the Au/sub 4/Cr alloy below T/sub c/ the D1a lro phase appears as ordered domains of size 50 to 100A showing composition modulations with wavelength of 5d(531). These domains grow in size up to 500A becoming finally the Dla fully ordered structure. A new observation has been made in the Au/sub 3/Cr alloy, viz., that the lro structure is nonstoichiometric Ll/sub 0/ with lambda/sub (001) = 4A. The transformation from sro in this alloy occurs with the formation of a transitional ordered phase, (similar to DO/sub 22/), which can be described in terms of composition modulations along (001), with wavelength equal to the c parameter (8A) of the DO/sub 22/ structure. Lattice imaging of the two variants of superlattice planes in ordered Au/sub 4/Cr enabled the atomic arrangement in the area of translational and rotational antiphase boundaries to be determined. (auth)
- Research Organization:
- Univ. of California, Berkeley, CA (United States)
- OSTI ID:
- 5000535
- Journal Information:
- Metall. Trans., A; (United States), Vol. 6A:10
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHROMIUM ALLOYS
ORDER-DISORDER TRANSFORMATIONS
GOLD ALLOYS
CRITICAL TEMPERATURE
DOMAIN STRUCTURE
INTERMETALLIC COMPOUNDS
LATTICE PARAMETERS
ORDER PARAMETERS
STOICHIOMETRY
SUPERLATTICES
ALLOYS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
360102* - Metals & Alloys- Structure & Phase Studies