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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 Degree: Ph.D. Genre: Dissertation 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 Type: Text Language: English URI: http://hdl.handle.net/2142/21774 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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