Microstructural characterization of rapidly solidified Al–Fe–Si, Al–V–Si, and Al–Fe–V–Si alloys

The present study of rapidly solidified melt-spun Al₈₀Fe₁₄Si₆ Al₈₀V₁₄Si₆, and Al₈₀Fe₁₀V₄Si₆ alloys by electron microscopy techniques, x-ray diffractometry, and differential scanning calorimetry leads to a number of microstructural results. Coexistence of a micro-quasicrystalline state of an icosahedral phase with monoclinic θ–Al₁₃Fe₄ and hexagonal β–Al₆V in Al–Fe–Si and Al–V–Si alloys, respectively, is reported. Also, the growth morphology of the icosahedral phase surrounded by a crystalline ring was investigated in an Al–Fe–V–Si alloy. The crystalline ring has the particles of the cubic α–Al₁₂(Fe,V)₃Si silicide phase. Evidence of irrational twinning of cubic crystals, giving rise to a symmetry not deviating much from icosahedral symmetry was found in this alloy. In all the three alloys crystalline intermetallics were elucidated in the context of rational approximants of an icosahedral quasicrystal. It was noticed that while the icosahedral phase in Al–Fe–Si and Al–V–Si alloys transforms to crystalline intermetallics at about the same temperature (approximately 610 K), the transformation of icosahedral phase in Al–Fe–V–Si alloy occurred at a relatively lower temperature (540 K). The origin of different metastable microstructures and their stability at elevated temperatures, in these alloys, are compared and discussed.