Approximant crystals of icosahedral Mg–(Ga, Al)–Zn alloys

Abstract

It has been found in Mg_39.5(Ga_1−xAl_x)_20.5Zn_40.0 alloys that an icosahedral phase produced by melt-spinning transforms to rational approximant phases of the icosahedral quasicrystal on heating. In the alloy with the composition x = 0.2, the icosahedral phase transforms to a 3/2–2/1–2/1 orthorhombic approximant phase with a = 3.693 nm, b = 2.296 nm and c = 2.268 nm. In the alloy with x = 0.7, the icosahedral phase transforms to a 1/1 cubic approximant phase with a = 1.421 nm at 653 K and successively to a 2/1 cubic approximant with a = 2.300 nm at around 668 K on heating. Structural relations of the approximant phases to the icosahedral phase are discussed, in the framework of the projection scheme, on the basis of X-ray diffraction data.

Key Words:

• Quasicrystal
• icosahedral phase
• approximant phase
• X-ray diffraction
• projection scheme
• Mg-Ga-Al-Zn alloy