Formation of amorphous Ni-Zr powders by mechanical alloying

Elemental polycrystalline Ni and Zr powders were mechanically alloyed by high energy ball milling in an Ar atmosphere. The morphology of the mechanically alloyed powders changes with proceeding milling time and the progress of amorphization. Amorphous NixZr1-x powders were prepared in the concentration range 0.2 equal or smaller than x equal or smaller than 0.7. Differential scanning calorimetry was used to determine the crystallization temperatures. The results confirm the amorphous region measured by X-rays. The atomic pair distribution functions G(R) were calculated from X-ray diffraction patterns. The first broad peak in G(R) of Ni40Zr60 shows a splitting. These results combined with thermodynamic calculations after Miedema's model are dicussed. Complementary transmission electron microscopy investigations of mechanically alloyed amorphous Ni60Nb40 powder give direct hints that the mechanism of amorphization is governed by a solid state reaction.