Atomic Structure of Ni-V Amorphous Alloy Prepared by Mecahnical Alloying

Partial Ni-Ni atomic structures were directly observed by neutron diffraction in the amorphization process of Ni₁₀₀-_xV_x powders during the mechanical alloying(MA). The partial radial distribution function RDF_NiNi(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 distance dramatically 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 fee 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 can be concluded that the chemical short range order in the Ni-V amorphous alloy obtained by MA is analogous to that of the a phase existing as a stablσ phase in the range 50-70at%V.