Medium-Range Order and Crystallization in Zr 59 Cu 20 Al 10 Ni 8 Ti 3 and Zr 57 Cu 20 Al 10 Ni 8 Ti 5 Metallic Glasses I
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Medium-Range Order and Crystallization in Zr59Cu20Al10Ni8Ti3 and Zr57Cu20Al10Ni8Ti5 Metallic Glasses Investigated by NMR Hergen Breitzke1, Klaus Lüders1,Sergio Scudino2, Jürgen Eckert2,3, and Uta Kühn2 1 Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany 2 IFW Dresden, Institut für Metallische Werkstoffe, Postfach 270016, D-01171 Dresden, Germany 3 Present address: Fachbereich Material- und Geowissenschaften, FG Physikalische Metallkunde, Technische Universität Darmstadt, Petersenstrasse 23, D-64287 Darmstadt, Germany ABSTRACT Medium-range order and quasicrystal formation in Zr57Cu20Al10Ni8Ti5 and Zr59Cu20Al10Ni8Ti3 metallic glasses are investigated by means of nuclear magnetic resonance (NMR). The samples are prepared by rapid solidification and annealed to induce primary quasicrystal formation. 27Al and 63Cu NMR spectra and spin relaxation curves are recorded before and after the annealing process. The spectral width of 27Al and 63Cu NMR spectra is relatively small and can be taken as a proof for the presence of medium-range order in these metallic glasses. By simulations of 27Al and 63Cu NMR second moments in various binary Al and Cu compounds the medium-range orders L12 AlZr3 and C11b CuZr2 can be identified in both as-quenched metallic glasses. After heat treatment both metallic glasses show considerable changes in the 63Cu NMR second moments, whereas the 27Al NMR second moments show only relatively small changes. Furthermore, the 63Cu NMR second moment after heat treatment in Zr57Cu20Al10Ni8Ti5 is about half as large as in Zr59Cu20Al10Ni8Ti3 indicating different types of crystallization during heat treatment. INTRODUCTION Depending on the Ti content Zr62 – xCu20Al10Ni8Tix is able to form quasicrystals during heat treatment when the Ti content rises above x = 3 [1–3]. For the alloy with x = 3, there is clear evidence for icosahedral order from X-ray diffraction patterns (XRD). The situation for x = 5, however, is less clear, because icosahedral order is not clearly seen in XRD. It is discussed that quasicrystals are formed in metallic glasses with x = 3 and x = 5 during heat treatment showing only differences in the amount and sizes of icosahedral ordered regions [3]. However, a proof of this assumption is still missing and can hardly be established by XRD or other spectroscopic methods which require relatively large-scaled ordered regions. Nuclear magnetic resonance (NMR), however, provides a local probe and therefore it is a well-suited investigation method for obtaining information about crystalline phases or local atomic arrangements within a glass. Here, we present a NMR study on the crystallization behavior of Zr62-xCu20Al10Ni8Tix amorphous alloys with x = 3 and x = 5. The 63Cu NMR second moment of the sample with x = 5 clearly shows a different type of Cu environment after heat treatment in comparison to the sample with x = 3. These differences clearly indicate different crystallization processes in both systems. EXPERIMENTAL DETAILS Ingots of the nominal compo
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