The effect of cooling rate on phase composition of quasicrystalline Al-Cu-Fe alloys doped with Si and B

In the present study, the microstructure development and mechanical properties of the icosahedral quasicrystal forming AI-Cu-Fe-(Si,B) alloys were investigated as functions of compositional variation and cooling rate during solidification. The effects of Al substitution by 4-7 at. % Si or/and 1-8 at. % B in the Al63Cu25Fe12 alloy solidified at 0.5 and 5 degrees C/s have been studied with combined methods of optical microscopy, X-ray diffractometry, scanning electron microscopy, and differential thermal analysis. The substitution of Al by Si in the Al63Cu25Fe12 alloy is favorable for the increase in the volume fraction of the icosahedral quasicrystalline psi-Al63Cu25Fe12 phase, especially in the slowly cooled alloys. Furthermore, the melting temperature of the v-phase decreases with increasing Si or/and B contents. The additions of B into Al63Cu25Fe12 alloy reduce the w-phase content and prevent the formation of the theta-Al2Cu phase which has a low microhardness. The microhardness and fracture toughness of the investigated Al63Cu25Fe12 alloys can be enhanced by simultaneous doping with 7 at. % of Si and 1 at. % of B. This improvement in the mechanical properties is due to the increase of the psi-phase volume fraction and the decrease of a porosity level.