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Title:Transformation kinetics of delta prime precipitation in aluminum-lithium alloys
Author(s):Yu, Ming Sheng
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
Abstract:The transformation kinetics of the early-stage of phase separation in an supersaturated Al-12 at.% Li alloy has been studied by means of time-resolved synchrotron radiation techniques. The simultaneous measurement of both the temporal evolution of the intensity profile from wide-angle x-ray diffraction (XRD) and small-angle x-ray scattering (SAXS) is a unique arrangement. The comparison of the integrated intensity from both the SAXS intensity profile and the XRD superlattice reflection provides the sequence of phase separation, such as ordering and decomposition. The combination of the rate of change of the integrated intensity from the superlattice reflection and the variation of ordered domain size suggest the likely division temperature, the congruent ordering temperature, T$\sb{\rm o}$, and the ordering instability temperature, T$\sb{-}$. In addition, the phase separation models, such as Cahn-Hilliard-Cook (CHC), Langer-Bar on-Miller (LBM) and Furukawa have been tested using the results of synchrotron radiation measurements. The dynamical scaling of the SAXS intensity profiles and the power growth law of peak positions and intensities have also been investigated.
In the late-stage of phase separation, the study focuses on the coarsening kinetics behavior of Al alloys with 9.7 at.% and 7.9 at.% lithium. The kinetics parameters, i.e. coarsening rate constants are determined from the in situ conventional SAXS measurements. The diffusivity, D, and the activation energy, $\gamma$, for the diffusion of lithium atoms within the solid solution can be calculated from these kinetics parameters. The correction for the volume fraction effect and the choice of the appropriate phase diagram can provide consistent and reasonable kinetics parameters.
Issue Date:1992
Rights Information:Copyright 1992 Yu, Ming Sheng
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9215917
OCLC Identifier:(UMI)AAI9215917

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