Quasicrystals in the Ti–Zr–Ni alloy system

The empirical compositional criteria for ternary quasicrystals (QCs) based on the QCs’ phase diagram features are applied in the Ti–Zr–Ni alloy system. The ideal quasicrystals-forming composition Ti40Zr40Ni20 has been identified, which lies at the crossing point of the two specific lines, termed as e/a-constant and e/a-variant lines. Bulk quasicrystalline Ti/Zr-based alloys are obtained in region of (TixZr100−x)100−yNiy (43.75⩽x⩽81.25, y=17, 20 in at.%) by copper mold casting. It was confirmed that Ti40Zr40Ni20 is the optimal QC-forming composition, where a nearly pure bulk quasicrystal rod, 6 mm in diameter, can be formed. With a small deviation from this ideal composition, the Ti(Zr) solid solution phases and/or C14-type Laves phase, though as minority phases, are found coexisting with the majority icosahedral phase. At the same time, the explanation of the e/a-variant line is explored.