Dresden 2014 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 11: Microstructure and Phase Transformations II - Nucleation/Solidification
MM 11.1: Vortrag
Montag, 31. März 2014, 11:30–11:45, IFW B
Determination of nucleation rates in a miscibility gap — •Christian Simon1, Yikun Zhang1,2,3, and Gerhard Wilde1 — 1Westfälische Wilhelms Universität Münster, Wilhelm-Klemm-Str.10, 48149 Münster — 2Key Laboratory of Electromagnetic Processing of Materials, Northeastern University, Shenyang 110004, China — 3Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51147 Köln
A wetting transition from partial wetting to complete wetting is possible in alloys with a liquid miscibility gap. At a temperature Tp below the critical temperature Tc the alloy separates in a two-phase liquid system which plays an essential role in the microstructure formation of monotectic alloys. One of the liquid phases covers completely the surface of the other phase and the container walls. After the solidification of the first phase, this phase may act as heterogeneous nucleation site for the second phase. We present data of the Bismuth-Gallium system that has a miscibility gap with a critical point at 70 at% Gallium. The aim of the present study is the analysis of the nucleation rate of the crystalline phases with and without a liquid phase separation. We use a self-designed fast scanning calorimeter (up to 10 000 K/s) with nanowatt resolution in order to measure a statistical relevant data set of nucleation temperatures. With the help of the fast scanning calorimeter, we are able to prevent long range phase separation by fast cooling. The nucleation rate is evaluated by a statistical analysis that treats nucleation as a non-homogenous Poisson process.