Amorphous-to-quasicrystalline transformation in Zr_(65)Ni_(10)Cu_(7.5)Al_(7.5)Ag_(10) bulk metallic glass

摘要

Two Zr_(65)Ni_(10)Cu_(7.5)Al_(7.5)Ag_(10) cast alloys, one fully amorphous and the other partially amorphous, were prepared by copper-mould casting. The phase transformations in the two alloys were investigated by using X-ray diffraction (XRD), differential canning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). The DSC trace obtained during continuous heating shows two distinct exothermic reactions in each alloy. The first one corresponds to the formation of a quasicrystalline phase from the amorphous matrix, while the second reaction results from the formation of a supersaturated Zr_2Cu-like phase from the previously formed quasicrystals. A shrinkage of the quasicrystal lattice during annealing was observed, which is possibly caused by the relaxation of pre-formed quasicrystals and primarily formation of a little amount of Zr_2Cu-like phase along the grain-boundaries of the quasicrystals. The amorphous-to-quasicrystalline trans-formation kinetics of the two Zr_(65)Ni_(10)Cu_(7.5)Al_(7.5)Ag_(10) cast alloys was studied by differential scanning calorimetry in the mode of continuous heating and isothermal annealing. The details of the nucleation and growth behaviors during quasicrystallization are discussed in terms of local Avrami exponent.