Effect of interfacial impurities on intermixing of bilayers

Mixing experiments were performed on Ni/Pt and René N4/Pt systems to understand the effect of interfacial impurities on the ion-beam mixing process. A layer of platinum 15 or 50 nm thick was deposited on metallographically polished sputter-cleaned nickel and René N4 substrates as well as on metallographically polished uncleaned René N4 by electron-beam deposition techniques. These targets were exposed to the bombardment of a Pt⁺ 1 MeV beam. A range of fluences, 2×10¹⁵ to 2×10¹⁶ Pt⁺/cm²⁺ was used to cause intermixing. The amount of mixing was evaluated by Rutherford backscattering spectroscopy and Auger sputter depth profiling. The mixing rates were the same for Ni/Pt and René N4/Pt with the clean interface. However, it was significantly less in René N4/Pt with an interfacial native oxide/impurity layer. The initial high volume fraction of precipitates in René N4 along the ion path became disordered under bombardment, and the alloying elements present significantly in the resultant solid solution did not influence the mixing process. Mixing in Ni/Pt and René N4/Pt with the clean interface appears to be dominated by thermochemical influences.