Formation of icosahedral quasicrystal by crystallization of Zr 70 (Ni, Cu, Pd) 30 amorphous alloys
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M. Matsushita and J. Saida Inoue Superliquid Glass Project, Exploratory Research for Advanced Technology, Japan Science and Technology Corporation, Sendai 982-0807, Japan (Received 8 March 2000; accepted 11 October 2000)
An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30−xPdx, and Zr70Cu30−xPdx (x ⳱ 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr–Ni–Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems.
It is well known that the structure of metallic alloys is limited to the crystalline, amorphous, or quasicrystalline phase. In particular, the icosahedral phase was discovered in a rapidly solidified Al–Mn alloy in 19841 and interpreted in terms of a new concept of quasicrystal.2 Reflecting the short period for research and development of quasicrystalline alloys, the alloy systems in which an icosahedral phase is formed have been limited to Al-, Mg-, Ga-, Zn-, Pd-, and Ti-based alloy systems.3–5 It is therefore important to search for a new icosahedral alloy with unique characteristics inherent to quasiperiodic atomic configurations and to extend the quasicrystalline alloy compositions to a greater variety of alloy systems. It has previously been reported that the icosahedral phase is formed in the crystallization process of the amorphous phase in Pd–U–Si,6 Al–Mn–Si,7 and Al–Cu–V8 systems. Recently, it has been reported that the icosahedral phase is also formed by partial crystallization of Zr-based amorphous alloys in Zr–Al–Cu,9 Zr–Al–Ni–Cu,9 and Zr–Ti–Al–Ni–Cu10 systems. However, the precipitation of the icosahedral phase in the Zr-based amorphous alloys did not have reproducible reliability. The reason for the lack of the reproducibility has been clarified to result
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J. Mater. Res., Vol. 16, No. 1, Jan 2001 Downloaded: 13 Mar 2015
from an impurity oxygen content.11 The existence of oxygen above about 1300 ppm mass% is necessary for the formation of the icosahedral phase in the crystallization process from the Zr-based amorphous alloys. It is known that a high glass-forming ability leading to the formation of a bulk amorphous alloy is obt
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