Structural and Electronic Properties of Zr-Ti-Cu-Ni-Be Alloys
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Structural and Electronic Properties of Zr-Ti-Cu-Ni-Be Alloys Jörg F. Löffler1, X.-P. Tang2, Yue Wu2 and William L. Johnson1 1 W. M. Keck Laboratory, California Institute of Technology, Pasadena, California 91125, U.S.A. 2 Department of Physics and Astronomy and Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3255, U.S.A. ABSTRACT We present crystallization studies on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) and on other alloys, where the (Zr,Ti) and (Cu,Be) contents, along the line in composition space connecting Vit1 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4), were varied. Results from x-ray diffraction (XRD), small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC) are combined to describe the crystallization behavior of these alloys at deep undercooling. SANS gives evidence for decomposition and the formation of nanometer sized crystals below a critical temperature Tc, which varies drastically as a function of composition. When Tc intersects with the glass transition temperature Tg, changes in the crystallization behavior are observed by DSC and XRD. At annealing temperatures near Tg, XRD resolves quasicrystalline phases for all alloy compositions from Vit1 to Vit4. From 9Be nuclear magnetic resonance (NMR) experiments performed on Vit1 upon annealing, we obtain information about the electronic structure and volume fraction of Be containing crystalline and quasicrystalline phases. INTRODUCTION Many bulk metallic glass forming alloys [1, 2] decompose on the nanometer scale between the glass transition temperature Tg and a critical temperature Tc. Examples are Zr41.2Ti13.8Cu12.5 Ni10Be22.5 (Vit1) [3, 4] with Tc ≈ 670 K and its derivatives [5], Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) [6] with Tc ≈ 810 K and its derivatives [7], Zr57Cu15.4Ni12.6Al10Nb5 (Vit106) with Tc ≈ 825 K [6], and Cu47Ti34Zr11Ni8 (Vit101) [8] with Tc > 830 K. In the present paper, we show that the relation between Tc and Tg determines the crystallization behavior in these bulk metallic glasses at deep undercooling and thus its thermal stability. We present x-ray diffraction (XRD), small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC) data for the alloy system Vit1 and for other alloys, where the (Zr,Ti) and (Cu,Be) contents were varied. Similar dependencies of the thermal stability have been found for the derivatives of Vit105 and are presented in Ref. [7]. Furthermore, focussing on Vit1, we present 9Be nuclear magnetic resonance (NMR) data, from which information on the electronic density-of-states at the Fermi level, EF, was obtained for the Vit1 glass as well as for the crystalline and quasicrystalline phases after annealing. EXPERIMENTAL PROCEDURE Five alloy compositions connecting Vit1 to Vit4 were prepared as 25 g ingots by arc melting the constituents (purity > 99.9%) in a titanium-gettered argon atmosphere. The tie-lie alloys have the compositions Zr42.6Ti12.4Cu11.25Ni10Be23.75, Zr44Ti11Cu10Ni10Be25, Zr45.4Ti9.6Cu8.75Ni10Be26.25, and are
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