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MM: Metall- und Materialphysik

MM 28: Amorphous and Liquid Materials III

MM 28.1: Vortrag

Donnerstag, 30. März 2006, 11:45–12:00, IFW B

Phase separation in liquid and amorphous Ni-Nb-Y alloys — •Norbert Mattern¹, Uta Kuehn¹, Annett Gebert¹, Thomas Gemming¹, Andreas Schöps², and Ludwig Schultz¹ — ¹IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany — ²Hasylab, Notkestr. 85, D-22603 Hamburg, Germany

Novel phase-separated Ni-Nb-Y amorphous alloys were prepared by rapid quenching from the melt. The microstructure of the as-quenched ribbons consists of two amorphous regions Nb-enriched and Y-enriched with a size distribution from micrometer dimensions down to several nanometers. The two-phase amorphous structure was proven by electron micropscopy, X-ray diffraction and differential scanning calorimetry data. Decomposition and structure formation take place in the melt prior to solidification. In situ synchrotron high temperature X-ray diffraction measurements exhibit clearly a two stage melting in agreement with DSC measurement. An assessment of the Ni-Nb-Y phase diagram (CALPHAD method) pointed out that the miscibility gap of the monotectic binary Nb-Y system extends into the ternary system up to about 70at% Ni. The microstructure as well as the thermal behavior of the two-phase amorphous alloys depend on the chemical composition of the rapidly quenched alloy. The two amorphous phases crystallize separately at different temperatures. The microstructure after crystallization from the amorphous state is completely different from that obtained by crystallization from the liquid.