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

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 58.5 Cu 18 Fe 13.5 Si 10 (e/a = 1.98) and Al 53.5 Cu 19.5 Fe 17 Si 10 (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 Al 65 Cu 20 Fe 15 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 53.5 Cu 19.5 Fe 17 Si 10 and reference Al 65 Cu 20 Fe 15 powders (both with a ratio e/a = 1.75), which coexisted with β-Al(Cu, Fe) and Al 13 Fe 4 phase or α-Al 55 Si 7 Cu 25.5 Fe 12 and Al 2 Fe 3 Si 3 phases in Al 65 Cu 20 Fe 15 and Al 53.5 Cu 19.5 Fe 17 Si 10 , respectively. For the Al 58.5 Cu 18 Fe 13.5 Si 10 powders (e/a = 1.98), the annealing led to complete transformation of the i-phase to the cubic α-Al 55 Si 7 Cu 25.5 Fe 12.5 approximant, forming crystallites with a size of 100–300 nm. Graphical abstract