NITROGEN INDUCED AMORPHIZATION OBSERVED BY X-RAY AND NEUTRON DIFFRACTIONS IN THE IMMISCIBLE V-CU SYSTEM

Mechanical alloying (MA) under N-2 gas atmosphere is proved to be capable of amorphizizing V70Cu30 powders, the combination of which has a positive heat of mixing. The structure factor, S-X(Q), observed by X-ray diffraction gradually changes into a structure characteristic of an amorphous state with increasing milling time. The S-N(Q) observed by neutron diffraction after 200 h of milling also confirmed the formation of an amorphous phase with residual pure Cu. Since the coherent scattering length of the V atom in neutron diffraction is negligibly small, crystalline peaks can be identified as fee Cu. The growth of a new peak at Q = 4.25 Angstrom(-1) in the S-N(Q) was observed after 40 and 120 h of milling but disappeared when milling time reached 200 h. This peak is attributed to the formation of the bcc Cu crystal by dissolution of Cu atoms into bcc V lattice structure. The results are consistent with the conclusion that the bcc solid solution is formed at the early stage of milling but that the amorphization gradually proceeds in the subsequent stage of milling by incorporating N atoms into the bcc solid solution.