As-cast quasicrystalline phase in a Zr-based multicomponent bulk alloy

An icosahedral quasicrystalline phase is obtained directly from the melt by copper mold casting of a Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 alloy. On the other hand, rapid quenching of the alloy leads to an amorphous phase. Upon annea ling, the amorphous structure precipitates quasicrystals in the first stage of crystallization. The microstructure of the quasicrystalline state is qu ite different for the two preparation routes, which is correlated with the asymmetry of the nucleation and growth rate upon cooling or heating. The qu asicrystals formed upon slow cooling from the melt have a size of about 1 m um. In contrast, the quasicrystals formed by annealing do not exceed a size of 5-10 nm. (C) 2000 American Institute of Physics. [S0003-6951(00)03246-0 ].