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MM: Fachverband Metall- und Materialphysik
MM 10: Liquid and amorphous materials IV
MM 10.3: Vortrag
Montag, 26. März 2007, 16:45–17:00, H4
Microstructure of rapidly quenched amorphous Ni100-2xNbxYx alloys — •Norbert Mattern1, Uta Kuehn1, Thomas Gemming1, Guenter Goerigk2, and Juergen Eckert1 — 1Leibniz-Institut IFW Dresden, Helmholtzstr.20,01069 Dresden — 2Haysylab at DESY,Notkestr.85,22603 Hamburg
Two-phase amorphous Ni-Nb-Y alloys can be prepared by rapid quenching from the melt[1]. The structure formation takes place in the phase separated undercooled liquid. Recent experimental and thermodynamical assessment of the Ni-Nb-Y phase diagram shows an extension of miscibility gap in the melt of the monotectic binary Nb-Y system up to 60 at% Ni content into the ternary Ni-Nb-Y system.The microstructure of the as-quenched ribbons consists of two amorphous regions Nb-enriched and Y-enriched exhibiting features of self-similarity with a size distribution from micrometer dimensions down to several nanometers. Small-angle X-ray diffraction confirms the fractal microstructure. For Ni contents > 60at% (critical composition) a "homogeneous" amorphous microstructure is observed by transmission electron microscopy (TEM) in accordance with thermodynamic calculations which are based on the regular solution model for the liquid. On the other hand, small-angle X-ray diffraction data indicate clearly chemical inhomogeneities within the nm-range. From the inhomogeneous amorphous precursors ultrafine nanocrystalline microstructure can be formed upon annealing as the first step of crystallization.
[1]N. Mattern, U. Kuehn, A. Gebert, T. Gemming, M. Zinkevich, H. Wendrock, L. Schultz, Scripta Mater., 53 (2005) 271