Preparation of Large Grained Al₆₄Cu₂₃Fe₁₃ Icosahedral Quasicrystal Directly from the Melt

Abstract

Various phase diagrams including an icosahedral (i-) phase in Al–Cu–Fe alloy system were examined in order to reveal the composition of the liquid in equilibrium with the Al₆₄Cu₂₃Fe₁₃ i-phase. The i-phase was formed through the peritectic reaction between the liquid and the primary λ₂-crystal. Prevention of the peritectic reaction was necessary to produce a single quasicrystal, however, there was a little compositional area of the molten alloy, which can crystallize the i-phase as a primary crystal. In the conventional solidification of Al₆₀Cu₃₇Fe₃ alloy, almost primary crystalline particles were classified as i-phase, and the rests were λ₂-phase. The λ₂-particles acted as the inhomogeneous crystallization sites of an i-quasicrystal growth. So, several metallurgical treatments were tried to prevent the λ₂-crystallization. Consequently, we found out an Al₅₉Cu₃₇Fe₃Si₁ molten alloy, which can crystallize the Al₆₄Cu₂₃Fe₁₃ i-phase as a primary crystal at 978 K. The Al₅₉Cu₃₇Fe₃Si₁ molten alloy should be treated the preliminary cyclic melting process to prevent the λ₂-crystallization. And we succeeded to grow up the large grained Al₆₄Cu₂₃Fe₁₃ i-quasicrystal directly from the molten alloy.