Materials Transactions Online

Materials Transactions, Vol.59 No.04 (2018) pp.575-579
© 2018 The Japan Institute of Metals and Materials

Isothermal Section of Ga-Ru-Cu Ternary Phase Diagram at 1073 K: Formation of New Ternary Phase, Ga4Ru3Cu, and Its Structural Relation with the GaRu β-Phase

Takanobu Hiroto1, Kazuya Honda1, Kazue Nishimoto2, Koichi Kitahara1 and Kaoru Kimura1

1Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan
2Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan

We have investigated the isothermal phase diagram of the Ga-Ru-Cu ternary system at 1073 K by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy to determine whether the stable icosahedral quasicrystal (i-phase) forms, as it does in the similar Al-Ru-Cu system, and new intermetallic phases exist. This is the first systematic investigation of the Ga-Ru-Cu system. No stable i-phase is identified in the Ga-Ru-Cu alloy system. However, we found a new ternary (τ) phase in the Ga-Ru-Cu system, which is characterized as a C-centered orthorhombic lattice with aτ = 11.80 Å, bτ = 6.04 Å, and cτ = 3.07 Å. The (ideal) chemical composition of the τ-phase is Ga50Ru37.5Cu12.5 (Ga4Ru3Cu). This new phase is stable up to 1073 K. Above 1173 K, the τ-phase transforms to the cubic GaRu (β) phase without any secondary phases. Thus, there is an order-disorder transition between the low-temperature τ-phase and the high-temperature cubic β-phase in this temperature range.


(Received 2017/10/30; Accepted 2018/01/09; Published 2018/03/25)

Keywords: phase diagram, Ga-Ru-Cu alloy, X-ray diffraction

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