Intermetallic Phases in Ti-Ag-Zr-Ni Alloys
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Intermetallic Phases in Ti-Ag-Zr-Ni Alloys Radu C. Nicula, Adrian D. Jianu, Mihaela C. Bunescu1, Ulrich E. Ponkratz, Manuela E. Stir, Christoph Schick2, Eberhard Burkel Universität Rostock, FB Physik, LS Physik neuer Materialien, August-Bebel-Str. 55, D-18051, Rostock, Germany 1 National Institute of Materials Physics, P.O. Box MG-7, 76900 Bucharest-Magurele, Romania 2 Universität Rostock, FB Physik, Universitätsplatz 3, D-18051 Rostock, Germany ABSTRACT Titanium and zirconium based metallic glasses and crystalline intermetallic compounds with improved mechanical properties are presently a field of intense application-oriented research. The formation and stability of nanocrystalline phases in Ag-substituted Ti-Zr-Ni alloys was followed using in-situ high-temperature synchrotron radiation diffraction experiments. The substitution of Ti with Ag enhances the formation of amorphous or nanostructured phases during rapid solidification. High-resolution powder diffraction and electron microscopy investigations indicate that the as-quenched alloys are either amorphous or in a mixed nanostructured state. Upon heating, the alloy structure transforms to a fine mixture of icosahedral and crystalline phases depending on the alloy composition and thermal processing parameters. Differential scanning calorimetry studies were performed in order to identify the nature and sequence of the observed structural phase transitions. The experimental results are discussed with respect to the nonequilibrium synthesis and processing of bulk amorphous and bulk nanocrystalline materials in Ti/Zr-based alloys.
INTRODUCTION The most recent studies of Ti/Zr-based alloys were to a large extent motivated by their promising hydrogen storage properties. These properties are largely due to the poly-tetrahedral nature of the icosahedral and Laves phases of these alloys [1,2]. Considerable interest is nowadays also given to the synthesis of lightweight Ti-, Al- and Mg-based alloys with improved mechanical properties and high corrosion resistance [3]. In particular, Ti-based alloys are an important class of engineering materials for which high mechanical strength and thermal stability are essential [4]. A few preliminary results concerning the formation and stability of icosahedral phases in rapidly-quenched Ti-Ag-Zr-Ni alloys were reported in a previous paper [5]. The effect of Ag substitution in Ti-Zr-Ni alloys was further analysed using high-resolution powder diffraction, transmission electron microscopy (TEM) and electron diffraction, in-situ hightemperature X-ray diffraction as well as differential scanning calorimetry (DSC).
EXPERIMENTAL DETAILS Alloys with nominal composition (Ti1-xAgx)53Zr27Ni20 (x = 2, 5, 7, 10, 15 and 20 at.% Ag) were prepared by the single-roller melt-spinning procedure. The primary alloy ingots were obtained by mixing appropriate amounts of high-purity elements followed by induction melting in water-cooled Cu moulds in protective Ar atmosphere. Ribbons with an average cross-section of 2 mm x 40 µm were obtained by rapid-quenc
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