The effect of the drop tube process for the quasicrystal fine particles formation

In general, quasicrystalline structures are produced by liquid quenching using a single roll, Bridgman and Czochralski method, which is typical for the production of single crystals. However, there are few reports of the quasicrystal formation using a containerless process; therefore, the effect of such a process is unclear. In this study, we have investigated the production of quasicrystalline fine particles and the formation ability of Al₆₃Cu₂₅Fe₁₂, Al₆₅Cu₂₀Fe₁₅, and Al₇₀Ni₁₅Co₁₅ ternary alloys using a drop tube apparatus with a free fall length of 2.5 m. In addition, we have aimed to examine the effectiveness of the drop tube process for quasicrystal formation. The formation of dodecahedron crystals, which are considered a quasicrystalline phase, was observed in Al₆₃Cu₂₅Fe₁₂ ternary fine particle samples prepared using the drop tube process under a He atmosphere (1 atm). Based on the heat flux, the calculated results suggested that the icosahedral phase was formed at high cooling rates of ∼10⁵ K/s. In the Al₇₀Ni₁₅Co₁₅ ternary fine particle sample, aggregation of prismatic crystals was observed in the fine particle samples prepared using the drop tube process under an atmosphere of He (1 atm) and Ar (1 atm). Furthermore, formation of prismatic crystals was observed on the surface of fine particle samples prepared under a low-pressure Ar atmosphere (0.5 atm), under which the formation ability of quasicrystals was observed to be the highest. From these results, the formation ability of the Al-Ni-Co-based decagonal phase is suggested to increase with decreasing cooling rates. This result is different from that of the Al-Cu-Fe-based icosahedral quasicrystals.