Atomic structure in Zr70Ni30 metallic glass

Abstract

Atomic structure of Zr 70 Ni 30 metallic glass ͑MG͒ was investigated by reverse Monte Carlo simulation combining with x-ray diffraction and Ni and Zr K-edge extended x-ray absorption of fine structure measurements. Distributions of coordination number ͑CN͒ and Voronoi clusters were analyzed by Voronoi tessellation method. The average CN of atoms was obtained to be 11.4 together with the average CN of Zr and Ni atoms of about 11.8 and 10.6, respectively. It is found that Z11 Kasper polyhedron and distorted icosahedra are mainly favored structural units in INTRODUCTIONAtomic structure of metallic glasses ͑MGs͒ has been studied experimentally and theoretically 1-4 because their extraordinary mechanical and magnetic properties strongly depend on their atomic structures. Gaskell proposed that atomic structure of MG is similar with that of corresponding crystalline phases. 5 Stability of MG is linked with its atomic structure, 6,7 which correlates with atomic structure of the corresponding crystalline phase by annealing. 8,9 For example, icosahedral clusters are found to be dominant atomic structure in Zr 70 Cu 29 Pd 1 MG, 10,11 which leads to primary phase transition by forming icosahedral quasicrystal 12,13 after annealing, while Zr 70 Ni 30−x Pd x ͑x Ͻ 10 at. % ͒ MGs do not exhibit such primary precipitation. 8 Furthermore, Zr-Cu binary MGs exhibit a glass transition event, whereas Zr-Ni binary MGs do not, 14 which might be due to their different atomic structures. 8 Thus, studies of atomic structure in such simple MGs are strongly demanded, which will promote our understanding to multicomponent bulk metallic glasses. However, structure of Zr-Ni MGs is still not completely understood [15][16][17][18] in spite of its wide amorphous-forming compositional range. 19 In the present work, we report the atomic structure of a Zr 70 Ni 30 MG by reverse Monte Carlo ͑RMC͒ simulation combining with x-ray diffraction ͑XRD͒ and extended x-ray absorption of fine structure ͑EXAFS͒ as well as Voronoi tessellation method. EXPERIMENTZr 70 Ni 30 ingot was prepared by arc melting high-purity metals ͑99.8% Zr and 99.9% Ni͒. Amorphous ribbons with a cross section of 0.03ϫ 2 mm 2 were obtained from these alloys by single-roller melt spinning at a wheel surface velocity of 30 m / s in purified Ar atmosphere. The oxygen content of the as-prepared ribbon samples was analyzed to be less than 800 mass ppm by inductively coupled plasma spectroscopy. The influence of oxygen on the transformation behavior can thus be disregarded. 20,21 Room-temperature high resolution XRD measurements were carried out for as-prepared Zr 70 Ni 30 sample with high energy x-ray ͑100 keV͒ at beamline BW5, Hasylab in Germany. Diffraction patterns were recorded by a Mar2300 image plate. Beamstop was located away from the center to record data with larger Q ͑wave vector transfer͒ range, resulting in high resolution in real-space reduced pair distribution function G͑r͒. XRD patterns were integrated to Q-space data file after subtracting its background by the program FIT...

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