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

Abstract

The effect of Be (beryllium) addition and the influence of cooling rate on the solidification path of the icosahedral (i) phase in conventional casting Al 62− x Be x Cu 25.5 Fe 12.5 ( 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 T rq = T p / T l and the reduced undercooling Δ T r =Δ T lp / T l , respectively, ( T l : liquidus temperature, T p : peritectic peak temperature, and Δ T lp = T l − T p : freezing range of primary phase).