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Formation of Nano Icosahedral Quasicrystalline Phase in Zr-based Binary and Ternary Glassy Alloys

Junji Saida1, Mitsuhide Matsushita1 and Akihisa Inoue2 1

Inoue Superliquid Glass Project, ERATO, Japan Science and Technology Corporation (JST), Yagiyamaminami 2-1-1, Sendai 982-0807, Japan 2 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

ABSTRACT It is found that a nano icosahedral phase with diameters below 50 nm is formed as a primary phase in the Zr70Ni10M20, Zr70TM10Pd20, Zr70Au10Pd20 and Zr75Pt10Pd15 ternary and Zr70Pd30 binary glassy alloys. The nanoscale icosahedral phase in the diameter range below 10 nm was also found to be formed directly in the melt-spun Zr80Pt20 binary alloy. These icosahedral phases transform to the crystalline phase(s) at the higher annealing temperature. The nucleation kinetics for the precipitation of the icosahedral phase from supercooled liquid were examined in the Zr70Pd30 and Zr70Ni10Pd20 glassy alloys. It was clarified that the transformation of both alloys proceeds in the diffusion-controlled growth mode with increasing nucleation rate. The formation of the nanometer-scale icosahedral phase is due to the transformation mode. The activation energy of nucleation is evaluated to be 267 kJmol-1 for the binary alloy and 311 kJmol-1 for the ternary alloy. The difference between the two alloy systems seems to originate from the difference in the number of atoms for rearrangements in the nucleation mode. The short-range ordering is observed in the as-quenched Zr70Pd30 glassy alloy, which is indicative of the icosahedral structure. The formation of the nano-scale icosahedral phase in the Zr-based binary and ternary alloys is due to the existence of an icosahedral short-range order in the glassy or liquid state. It is suggested that the icosahedral short-range order is stabilized by the restraint of the long-range atomic rearrangements that lead to the transition to a periodic structure by the strong chemical affinities of Pd or Pt with Zr.

INTRODUCTION Since the reproducible formation of a nano icosahedral quasicrystalline phase as a primary precipitation phase in the Zr-Al-Ni-Cu-M [1,2], Zr-Al-Ni-M [3], Zr-Ni-M (M=Ag, Pd, Au or Pt) [4] and Zr-TM-Pd (TM=Fe, Ni, Co or Cu) [5] glassy alloys was reported, great attention has been focused on investigating the reason for the formation of the icosahedral phase in the Zr-based glassy alloys in the aspects of the structural correlation [6] between high glass-forming ability and icosahedral atomic configurations. These discoveries also provide a unique opportunity to clarify the kinetics [7,8] and mechanism of the transformation from the 

L6.1.1 

glass to icosahedral phase in the Zr-based glassy alloys. Moreover, the recent studies on alloy components to form the icosahedral phase suggest that two kinds of interactions of Zr-TM and Zr-M with strongly negative heats of mixing contribute to the stabilization of both glassy and icosahedral phases through the restraint of the long-range rearrangements of constituti