Atomic structure of Ni-V amorphous alloy prepared by mechanical alloying

Partial Ni-Ni atomic structures were directly observed by neutron diffraction in the amorphization process of Ni100-xVx powders during mechanical alloying(MA). The partial radial distribution function RDFNiNi (r) shows that distribution peaks of the fcc-Ni crystal gradually broaden with increasing Ma time. The peaks of the 2nd and 5th Ni-Ni neighbor positions observed within 7 A rapidly decrease and disappear almost completely after 400h milling. This means that a tetrahedral unit characteristic of an amorphous structure increases at the expense of the octahedral unit because the 2nd and 5th Ni-Ni neighbor contribute exclusively to the formation of the octahedral units in an fcc structure. The coordination number of Ni atoms around a Ni atom calculated from the area under the 1st peak decreases with increasing V concentration. From this concentration dependence, it is concluded that the chemical short range order is analogous to that of the σ phase existing as a stable phase in the range 50-70at%V.