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Title:Atomic short-range order determination in gold-25 atomic percent iron and nickel-12.5 atomic percent silicon: A synchrotron x-ray diffuse scattering study
Author(s):Anderson, Jeffrey P.
Doctoral Committee Chair(s):Chen, Haydn
Department / Program:Materials Science and Engineering
Discipline:Materials Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Metallurgy
Engineering, Materials Science
Abstract:The short-range order (SRO) structure of a Gold-25 atomic percent Iron single crystal was studied using wide-angle diffuse synchrotron x-radiation scattering at room temperature. Two heat-treatments were investigated; a 400$\sp\circ$C aging treatment for two days and a second at 440$\sp\circ$C for five days, both preceded by solution treatment in the single-phase field and water-quenched to room temperature. Evolution of the SRO structure with aging was determined by fitting the two sets of Cowley-Warren SRO parameters to a pair of 140,608-atom models. The microstructures, while quite disordered, showed a trend with aging for an increasing volume fraction of an Fe-enriched and an Fe-depleted environment. The Fe-enriched environment displayed a slight preference for Fe segregation to the $\{$110$\}$ and $\{$100$\}$ fcc matrix planes. A major portion of the Fe-depleted environment was found to contain elements (and variations of these elements) of the D1$\sb{\rm a}$ ordered superstructure. The SRO contained in the Fe-depleted environment may be best described in terms of the standing concentration wave packet (SCWP) model. This study provides, for the first time, a quantitative real-space view of the atomic arrangements which make up both environments in the SRO structure of Au-25at.%Fe.
An equivalent study was performed on a water-quenched Ni-12.5at.%Si single crystal. The 140,608-atom model for this system did not display any long-range ordered domains of the equilibrium $\gamma$$\sp\prime$ (L1$\sb2$) superstructure. Rather, nearest-neighbor (nn) configurations C16, the basic structural element of $\gamma$$\sp\prime$, and C17, a faulted variant of C16, were found to combine to form small domains resembling disordered embryos of the $\gamma$$\sp\prime$ phase.
Issue Date:1992
Rights Information:Copyright 1992 Anderson, Jeffrey P.
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9215768
OCLC Identifier:(UMI)AAI9215768

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