Formation of Quasicrystalline Phases and Their Close Approximants in Cast Al-Mn Base Alloys Modified by Transition Metals
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni enhance quasicrystalline phase nucleation compared to the unmodified binary composition. In the case of Cu addition, formation of a quasicrystalline phase takes place along whole thickness of the prepared casting, but its fraction and morphology depends on the cooling rates present in different parts of the sample. Based on the previous works on the beneficial effect of Fe addition, a quaternary alloy containing both Fe and Cu was prepared to evaluate the effect of the simultaneous presence of these elements on the microstructure of the obtained castings.
Approximant-based orientation determination of quasicrystals using electron backscatter diffraction.
Orientation mapping of quasicrystalline materials is demonstrated using crystalline approximant structures in the technique of electron backscatter diffraction (EBSD). The approximant-based orientations are symmetrised according to the rotational point group of the quasicrystal, including the visualization of orientation maps using proper colour keys for quasicrystal symmetries. Alternatively, approximant-based orientation data can also be treated using pseudosymmetry post-processing options in the EBSD system software, which enables basic grain size estimations. Approximant-based orientation analyses are demonstrated for icosahedral and decagonal quasicrystals.
Stable decagonal quasicrystals in the Al-Fe-Cr and Al-Fe-Mn alloy systems
Abstract Stable decagonal quasicrystals were revealed for the first time in the Al-Fe-Cr and Al-Fe-Mn alloy systems. They exhibit periodicity of ∼1.2 nm along the 10-fold symmetry axis and are formed around the Al 72 Fe 12 Cr 16 and Al 72 Fe 10 Mn 18 compositions, respectively. In Al-Fe-Cr the decagonal phase was only produced after prolonged thermal annealing at subsolidus temperatures (maximum 1090 °C). In Al-Fe-Mn a strong temperature dependence of the compositional region of the decagonal phase was observed.