a Time-Resolved X-Ray Study of Spinodal Decomposition in Aluminium-Zinc
Abstract
Time resolved small angle x-ray scattering (SAXS) using synchrotron radiation was applied to the study of the kinetics of spinodal decomposition (SD) in an AlZn binary alloy at critical composition quenched into the immiscible region. These millisecond time scale measurements, performed at the National Synchrotron Light Source (Brookhaven National Labs., N.Y.), constitute the first direct experimental verification in a binary alloy of the theory proposed by Langer, Bar-on and Miller in 1975 for SD. A scheme based on the composition distribution functional is proposed to account for the decomposition taking place during the quench. The interatomic mobility, a free energy gradient coefficient and two coefficients that suffice to determine a coarse-grained (intensive) free energy have been obtained in the framework of this theory. The mobilities obtained compare well with tracer diffusion measurements reported in literature. A dependence of the coarse-grained free energy coefficients on the coarse-graining length is found and a procedure is proposed to uniquely choose the values of these coefficients based on the predicted integrated intensity from the equilibrium concentrations and on the measured integrated intensities. Late-stage coarsening regimes were also investigated. In these regimes, growth exponents higher than the value 1/3 predicted by the Lifshitz-Slyozov-Wagner theory are obtained. These higher values, comprised between 0.40 and 0.45 are consistent with predictions that alloys in which elastic effects are important can present a transition regime from a t ^{1/3} growth law to a t ^{1/2} law. The structure factors do not quite scale. They also present a shoulder at high wavevectors, a feature not reported before in metallic alloys.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1992
- Bibcode:
- 1992PhDT.......224M
- Keywords:
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- Physics: Condensed Matter