Change in local atomic structure during formation of the icosahedral quasicrystalline phase in Zr 70 Pd 30 glassy alloy
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Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 25 May 2001; accepted 20 August 2001)
The local atomic structures in glassy, supercooled liquid and quasicrystalline phases for a Zr70Pd30 binary alloy have been examined by the x-ray diffraction method. It was found that the local atomic structure in the glassy phase can be identified as the distorted icosahedral-like structure around Zr and remains almost unchanged by the phase transformation into the supercooled liquid. In the formation process of the icosahedral phase, approximately one Zr atom substitutes with one Pd atom in this local structure. This kind of atomic rearrangement may improve the perfectibility of the as-quenched icosahedral-like cluster, leading to the phase evolution of the icosahedral phase.
Zr-based alloys such as Zr–Al–TM1,2 and Zr–Ti–Al– TM3 (TM ⳱ transition metal) are well-known bulk metallic glass formers exhibiting a large supercooled liquid region before crystallization. An icosahedral quasicrystalline phase (i-phase) has been often found in the primary crystallization stage of Zr–Al–Ni–Cu4 and Zr–Ti–Al–Ni– Cu5 glassy alloys containing some amounts of oxygen impurity. Although it has been suggested that the oxygen element stabilizes the formation of the i-phase in these alloys, it is difficult to control the amount of oxygen impurity and hence the reproducibility of the formation of the i-phase is poor. Recently, reproducible formation of the i-phase as a primary precipitation phase has been reported by adding a noble metal (NM) element to Zr–Al–Ni–Cu,6 Zr–Al– Ni,7 and Zr–Ni8 alloys. These results suggest that a complex combination of atomic pairs with strongly large negative heats of mixing (Zr–NM and Zr–Ni) and nearly zero or positive heats of mixing (NM–Ni) contributes to the formation of the i-phase by the restraint of the precipitation of a crystalline phase. More recently, the present authors have found the formation of the i-phase in Zr70Pd30 binary alloy.9 It has been suggested that the strong chemical affinity in the Zr–Pd pair leads to stabilization of an icosahedral short-range ordering structure, but little has been obtained about its experimental evidence up to now. This paper is
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Address all correspondence to this author. e-mail: [email protected] b) Present address: Advanced Technology Research Laboratories, Nippon Steel Corporation, Futtsu, Chiba 293-8511, Japan. 3046
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J. Mater. Res., Vol. 16, No. 11, Nov 2001 Downloaded: 01 Apr 2015
intended to examine the change in the short-range ordered structure during the phase transformation from a glassy to quasicrystalline phase in the Zr70Pd30 alloy and to discuss the structural correlation between these phases. A glassy alloy ribbon of Zr70Pd30 was prepared by the single-roller melt-spinning technique from a Zr70Pd30 arc-melted master ingot in an Ar atmosphere. The thermal behavior was analyzed by differential scanning calorimetry (DSC) at a heating rate of 0.67 K s−1. The glassy sample
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