Local Order Changes in Amorphous Zr_(52.5)Hf_2Ti_(7.5)Cu_(20)Al_(10)Ni_8Alloy upon Crystallization

摘要

The local order in Zr_(52.5)Hf_2Ti_(7.5)Cu_(20)Al_(10)Ni_8 alloy is investigated by perturbed angular correlation (PAC) in the as-prepared state and after different crystallization steps. The initial amorphous stage was checked by differential scanning calorimetry and x-ray diffraction experiments. PAC results showed that the initial amorphous state is well described by a dense random packing of ions. After the first crystallization step (T_a=723 K) at least two two wide distributions of frequencies are observed. One of them can be associated with a Ti_2Ni-type phase that may also be observed in the X-ray diffraction pattern at a trace level. Further heat treatments lead to the precipitation of different intermetallic equilibrium compounds: Zr_2Cu, ZrAl_2. These results in combination with DSC and X-ray determinations on the annealed alloy may help to identify the mechanisms for phase formation upon each annealing step.