Transformation of Al–Ni–(Si) decagonal quasicrystals to 1–D quasicrystal and crystalline approximants

Rapidly quenched Al_86-xNi₁₄Si_x (x = 0, 2, 6, and 10) alloys have been studied by means of transmission electron microscopy. Two-dimensional (2-D) decagonal quasicrystal with a periodicity of 1.6 nm along its tenfold axis was found in the rapidly quenched Al₈₆Ni₁₄ binary alloy. With the addition of some silicon, such as AlgoNi₁₄Si₆, the 2-D decagonal quasicrystal first transforms to a one-dimensional (1-D) quasicrystal that inherits the periodicity along the tenfold axis and has, in addition, translation periodicity in one of the twofold axes of the decagonal phase, and finally transforms to a new orthorhombic crystalline phase (a = 0.78, b = 1.62, and c = 1.48 nm). In the Al₇₆Ni₁₄Si₁₀ ternary alloy, a 2-D decagonal quasicrystal with a periodicity of 0.4 nm and a coexisting crystalline phase with the “Al₃Ni₂” structure were found, and their orientational relationship has been determined.