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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: Al58.5Cu18Fe13.5Si10 (e/a = 1.98) and Al53.5Cu19.5Fe17Si10 (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 Al53.5Cu19.5Fe17Si10 and reference Al65Cu20Fe15 powders (both with a ratio e/a = 1.75), which coexisted with β-Al(Cu, Fe) and Al13Fe4 phase or α-Al55Si7Cu25.5Fe12 and Al2Fe3Si3 phases in Al65Cu20Fe15 and Al53.5Cu19.5Fe17Si10, respectively. For the Al58.5Cu18Fe13.5Si10 powders (e/a = 1.98), the annealing led to complete transformation of the i-phase to the cubic α-Al55Si7Cu25.5Fe12.5 approximant, forming crystallites with a size of 100–300 nm.Graphical abstract
Highlights
The stable quasicrystalline phase in the Al-Cu-Fe system was first identified in 1987 by Tsai et al [1] in the massive Al65Cu20Fe15 alloy cast by a conventional method and annealed
It was found that when the Si content increased up to 15 at.%, the icosahedral phase was replaced by the cubic approximant of AlCuFeSi [10]
The formation of the a-Al55Si7Cu25.5Fe12.5 approximant can be supported by increasing the cooling rate during casting: moderate rate of solidification can improve the thermal stability of the quasicrystalline phase in the melt spun ribbon, while the higher quenching rates instigate the transformation of the quasicrystal into the cubic approximant [11]
Summary
The stable quasicrystalline phase in the Al-Cu-Fe system was first identified in 1987 by Tsai et al [1] in the massive Al65Cu20Fe15 alloy cast by a conventional method and annealed. This ternary alloy, characterized by low cost, accessible, recyclable and non-toxic constituent elements, has been extensively studied in the following years due to possibility of a number of applications [2,3,4,5]. Karakose and Keskin [18] reported an increase of microhardness and reduction of the number of phases in the rapidly solidified Al64Cu20Fe12Si4 ribbons compared to the conventionally cast alloys
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