Influence of Al on Quasicrystal Formation in Zr-Ti-Nb-Cu-Ni-Al Metallic Glasses

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Influence of Al on Quasicrystal Formation in Zr-Ti-Nb-Cu-Ni-Al Metallic Glasses Sergio Scudino, Jürgen Eckert*, Uta Kühn, Hergen Breitzke1, Klaus Lüders1 and Ludwig Schultz IFW Dresden, Institut für Metallische Werkstoffe, Postfach 270016, D-01171 Dresden, Germany * Present address: Fachbereich Material- und Geowissenschaften, FG Physikalische Metallkunde, Technische Universität Darmstadt, Petersenstrasse 23, D-64287 Darmstadt, Germany. 1 Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany ABSTRACT The effect of Al on the crystallization behavior of (Zr0.616Ti0.087 Nb0.027Cu0.15Ni0.12)100–xAlx melt-spun glassy ribbons with x = 7.5, 5, 2.5 and 0 was investigated by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The devitrification of the ribbons is characterized by the formation of a metastable quasicrystalline phase during the first stage of the crystallization process even for the alloy with x = 0. Therefore, Al is not essential for quasicrystal formation in the present alloys. However, it affects the properties of the amorphous as well as of the quasicrystalline phase. With decreasing Al content, the temperature range of stability of the quasicrystalline phase increases whereas the thermal stability of the amorphous phase decreases together with a slight decrease of the extension of the supercooled liquid region. Thus, it is concluded that although the addition of Al improves the stability of the glassy phase, it has no beneficial effect on the formation of quasicrystals. INTRODUCTION Among new potential candidates for engineering applications, Zr-based multicomponent glassy alloys have been extensively investigated in recent years thanks to the positive combination of interesting mechanical properties [1-3] with high thermal stability against crystallization and wide supercooled liquid region [4,5]. Changes in composition [6], addition of oxygen [7], transition [8] and noble metals [9] cause variations in the thermal stability and leads to the formation of a metastable quasicrystalline phase (QC) in the first stage of crystallization. The precipitation of second-phase QC particles embedded in the glassy matrix further improves the mechanical properties of the single-phase glassy alloys [10,11]. This gives Zr-based metallic glasses additional application opportunities as precursor for nanocomposites materials. The effectiveness of improvements strongly depends on the volume fraction as well as on the grain size of the phase formed [10-12]. Therefore, the engineering application of this type of composite requires the ability to produce a controlled microstructure. Another important aspect is the temperature range of stability of QC. In fact, the utilization of such a partially devitrified material requires a wide temperature range between the formation of QC and the subsequent crystallization events. Since thermal stability and microstructure evolution are strictly correlated with the chemical composition, a detailed knowl