Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 9: SYM Phase Transformations in Metallic Melts III

MM 9.4: Vortrag

Montag, 25. Februar 2008, 15:45–16:00, H 1058

Entropy in Molecular Dynamics simulated AlyNi40-yZr60 melts. — •Helmar Teichler and Mohammed Guerdane — Inst. f. Materialphysik, Universität Göttingen, Göttingen, Germany

Entropy plays a major role in stabilizing melts against crystallization, and entropy (and enthalpy) release are the main phenomena that determine solidification. Despite its importance, little is known at present about the microscopic origin of entropy in melts, especially for complex multi-component metallic systems with steric and chemical short range order. Regarding this, exploiting ergodicity, we present here results from isothermal molecular dynamics simulations for the entropy in the pseudo binary AlyNi40-yZr60 series (y=0 - 40 at% Al), combining thermal integration along the temperature axis and Kirkwoods (1935) coupling parameter approach. In the simulations the AlNiZr model of Guerdane and Teichler (PRE 65, 014203 (2001)) is used.

We show in particular that our method provides entropy data with an internal reliability better than 0.01 kB. In the AlyNi40-yZr60 series, we find a slightly negative total entropy of mixing. The configuration entropy of the (trigonal prismatic) Ni40Zr60 melt at 2400 K turns out below that of liquid Zr while the configuration entropy of (binary polytetrahdral) Al40Zr60 melt lies above. These observations and the temperature dependence of the phenomena shall be discussed.