Studies on Cr-Mo binary alloys: I. surface composition modifications induced by ion bombardment

Surface compositional modifications due to room temperature ion bombardment were investigated in thirteen Cr-Mo alloys using Auger Electron Spectroscopy (AES). Preferential sputtering of Cr was observed across the entire composition range. A phenomenological model of the sputtering process was adopted and the results yielded a component sputter rate constant ratio K (=k Cr/k Mo) = 1.73 ± 0.04, insensitive to alloy composition. This value is in good agreement with the enhancement ratio calculated according to Sigmund theory of 1.66 ⩽ Y Cr/Y Mo ⩽ 1.73 and the elemental sputter yield ratio Y Cr/Y Mo = 2.22 ± 0.74. The homogeneity of the altered layer was investigated using elemental Auger transitions of various sampling depths in the range 20–600 eV. The altered layer was found to be essentially uniform in composition over the sampled depth. The small inhomogeneity suggested by the data was quantified using layer calculations and various profile models. The calculations showed that the inhomogeneity was small in comparison to the overall compositional modifications due to the sputtering process. The experimental results indicate that in the room-temperature sputtering of such refractory alloys, the athermal “ballistic” processes play the dominant role in establishing the steady-state surface composition and its profile. Preferential sputtering determines the compositional perturbation of the surface, and collisional mixing, i.e., displacement mixing and possibly recoil implantation, maintains an essentially uniform composition over the “altered layer” depth. The thermally activated processes of Gibbsian segregation, radiation-induced segregation (RIS) and radiation-enhanced diffusion (RED) appear to play a negligible role.