Metallic systems with positive heats of mixing under ion beam irradiation and rules for amorphous phase formation

Recently, it has been demonstrated that the heat of mixing of a binary couple plays an important role in determining the mixing rate of metallic bilayers under ion beam irradiation. A large negative heat of mixing between elements results in a high mixing rate. This correlation has been interpreted by an analysis resembling that of Darken for chemically biased diffusion, in which the effective interdiffusion coefficient of ion mixing can be written as D=D0 (1-2 Δ H/sub min//K/sub B//sup T/). This equation also predicts that a homogeneous binary alloy with a large positive heat of mixing will undergo phase separation upon irradiation. This aspect was investigated. There is evidence that ion beam induced demixing occurs in metallic systems of positive heat of mixing. This is in accord with the model provided by the authors. Amorphous phases can also be formed by ion mixing in metallic systems with relatively large positive heat of mixing