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A small‐angle neutron scattering study of decomposition dynamics in Ni 87.5 Si 12.5
Author(s) -
Polat S.,
Chen H.,
Epperson J. E.
Publication year - 1988
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889888005217
Subject(s) - materials science , diffusion , scattering , isothermal process , neutron diffraction , kinetic energy , neutron scattering , crystallography , small angle scattering , scaling , condensed matter physics , thermodynamics , analytical chemistry (journal) , chemistry , crystal structure , optics , physics , chromatography , quantum mechanics , geometry , mathematics
The kinetic behavior of precipitation in a supersaturated Ni–12.5 at.% Si alloy single‐crystal has been Studied by the small‐angle neutron scattering (SANS) technique to supplement earlier transmission electron microscopy (TEM) and wide‐angle X‐ray diffraction (XRD) work. The SANS measurements performed at room temperature on quenched specimens subjected to isothermal anneals at 673, 723, 778 and 823 K for up to 125 h have revealed the presence of an interference peak in the scattering function. The particle size, determined according to the Guinier approximation, is found to obey the t 1/3 coarsening law at long aging times. For short aging times below 773 K, a deviation from the t 1/3 law is seen signifying a classical `growth' stage prior to coarsening – an observation consistent with our previous in situ XRD work. The activation energy for solute diffusion is determined to be 278.4 kJ mol −1 using the rate constants governing the growth of particle size and is 255.8 kJ mol −1 using the variation of the mean interparticle distance. Enhanced diffusion due to quenched‐in excess vacancies is observed below 773 K. The dynamical scaling law appears to be followed for the data obtained in the coarsening stage. A disruption of scaling occurs at the point when the particle growth changes from a parabolic rate behavior to a cubic coarsening rate.