Microstructure of Al-alloy surface implanted with high-dose nitrogen

Nitrogen ion implantation by plasma-based ion implantation with a negative bias voltage of 10 kV led to the formation of AlN on the surface layer of a casting aluminum alloy (Al–7Si) sample. The AES analysis of the ion-implanted sample indicated that the depth profile of nitrogen ions implanted at room temperature was approximated by a Gaussian profile with a center of ion range (27 nm). The AFM observation showed the changes in surface morphology with nitrogen ion implantation. The surface roughness of the unimplanted sample, which was mechanically polished before ion implantation, had a mean-average roughness of Ra=13.9 nm. After implantation, on the other hand, the surface roughness decreased with increasing the ion dose, and was reduced to Ra=8.2 nm at a dose of 2.2×1018 cm−2. Plasma ion implantation led to both implantation and smoothing simultaneously.