New icosahedral quasicrystals formed in Cu-based ternary alloys

Abstract

New Cu-based P-type icosahedral quasicrystals have been observed in the ternary Cu–(Ga or Al)–Sc alloy systems. The Cu–Ga–Sc quasicrystal forms almost exclusively in a rapidly quenched Cu₄₈Ga₃₄Sc₁₈ alloy, and has a six-dimensional lattice parameter a_6D = 0.6930 nm. The as-cast alloy with the same composition contains no quasicrystal but has a 1/1 bcc approximant as its main phase. The Cu–Al–Sc quasicrystal forms at the alloy composition Cu₄₆Al₃₈Sc₁₆ both in an as-cast alloy and in alloys aged at 776 and 873 K, and has a lattice parameter a_6D = 0.6959 nm. Although electron diffraction patterns exhibit rather strong deviation from the ideal symmetric positions for weak reflections, the presence of the quasicrystal in the aged Cu–Al–Sc alloys indicates that this phase is a candidate of a stable phase in this ternary system.

Acknowledgements

The authors thank Mr. N. Miyazaki for the help in the use of the electron probe microanalyser JXA-8900M. This work was partly supported by a Grant-in-Aid for the Scientific Research of Priority Areas “Panoscopic Assembling and High Ordered Functions for Rare Earth Materials”.