Quasicrystal-forming ability of the icosahedral phase in Al-Cu-Fe-Be alloys

The effect of Be (beryllium) addition and the influence of cooling rate on the solidification path of the icosahedral (i) phase in conventional casting Al62-xBexCu25.5Fe12.5 (x=0,1,3,5,7 at.%) alloys were investigated by means of X-ray diffraction, differential thermal analysis, SEM and EDX analyses. The addition of Be has been found to modify the i-phase formation mechanism from peritectic reaction to primary solidification. The volume fraction of the i-phase has been observed to increase from 45% for x=0 to 90% for x=7. These results suggested that the substitution of Al by Be is favorable for the increase of the quasicrystal-forming ability (QFA) of the i-phase. Two parameters have been proposed for defining and assessing the QFA for i-phase formed by peritectic reaction. These parameters can be expressed by the reduced quasicrystal transition temperature Trq=Tp/Tl and the reduced undercooling ΔTr=ΔTlp/Tl, respectively, (Tl: liquidus temperature, Tp: peritectic peak temperature, and ΔTlp=Tl-Tp: freezing range of primary phase)