Synthesis and stability of quasicrystalline phase in Al-Cu-Fe-Si mechanically alloyed powders

Abstract The effect of Si addition on a quasicrystalline phase formation in Al-Cu-Fe-Si alloys prepared by mechanical alloying has been investigated using X-ray diffraction and scanning and transmission electron microscopy. Two compositions containing 10 at.% of Si were selected to verify the influence of the e/a ratio on a sequence of phase formation during milling: Al_58.5Cu₁₈Fe_13.5Si₁₀ (e/a = 1.98) and Al_53.5Cu_19.5Fe₁₇Si₁₀ (e/a = 1.75). A quasicrystalline icosahedral phase (i-phase) was found in both alloys after 10 h of milling in the form of nano-quasicrystallites with the size of 10–20 nm. Addition of Si stabilized the quasicrystalline phase being dominant after prolonged milling time, contrary to the reference ternary Al₆₅Cu₂₀Fe₁₅ powder, which apart of the quasicrystalline phase contained the cubic β-Al(Cu, Fe) phase. Thermal stability of the quasicrystalline phase in the powders milled for 10 h was examined after annealing at 800 °C for 4 h. The i-phase was preserved partially in Al_53.5Cu_19.5Fe₁₇Si₁₀ and reference Al₆₅Cu₂₀Fe₁₅ powders (both with a ratio e/a = 1.75), which coexisted with β-Al(Cu, Fe) and Al₁₃Fe₄ phase or α-Al₅₅Si₇Cu_25.5Fe₁₂ and Al₂Fe₃Si₃ phases in Al₆₅Cu₂₀Fe₁₅ and Al_53.5Cu_19.5Fe₁₇Si₁₀, respectively. For the Al_58.5Cu₁₈Fe_13.5Si₁₀ powders (e/a = 1.98), the annealing led to complete transformation of the i-phase to the cubic α-Al₅₅Si₇Cu_25.5Fe_12.5 approximant, forming crystallites with a size of 100–300 nm. Graphical abstract