Radiation-induced precipitation at the alloy surface during ion bombardment

A kinetic approach to model radiation-induced formation of a precipitate layer on the surface of a binary alloy during ion bombardment is described. Sample calculations were performed for the case of Ni₃Si coating on a NiSi alloy surface. The strong coupling between Si atoms and radiation-generated defect fluxes causes a significant Si enrichment at the surface, which gives rise to the formation of a precipitate layer when it exceeds the Si solubility limit. The stability of this layer depends on the competition between the rates of precipitation and sputtering. Both the receding surface and the moving precipitate/matrix interface were accounted for by means of a mathematical scheme of boundary immobilization. The dependences of the precipitation kinetics and the development of solute concentration profiles in the alloy matrix on bombardment temperature, ion flux and alloy composition were examined.