Ion-beam mixing and phase formation in the immiscible FeMg system

Abstract

Ion-beam mixing in equiatomic FeMg multilayers was studied using in situ resistivity measurements whereas phase formation was investigated by transmission electron microscopy (TEM) or grazing X-ray diffraction. A crystalline bcc solid solution is induced at 77 K in this immiscible system by bombardment with 345 keV Xe-ions, but no real mixing occurs at 300 K. A comparison of the mixing of FeMg with three systems TAl {T = Ni, Co, Fe} reveals that at 77 K mixing rates do not depend on the heat of mixing. This last result suggests that a ballistic mechanism dominates the alloying process in the low-temperature regime. Unlike the ion-beam mixing, an amorphous phase is produced by electron-gun coevaporation. Reaction during thermal treatment evidences that the metastable bcc phase is a more relaxed structure than amorphous one. Atomic relaxation occurring during the cooling phase of the displacement cascades allows topologic rearrangements and thus controls the metastable phase formation by ion-beam techniques.