Effect of nitrogen implantation on the surface hardness of pure aluminum and alloy materials

Samples of high purity annealed aluminum and 6061-T6 aluminum alloy were implanted with N+ ions at 200 keV at doses of 5, 10, 18, and 28 X 1017 cm-2. Additionally a third sample was implanted with 15 X 1017 cm-2 at 200 keV followed by an implant of 11 X 1017 cm-2 at 100 keV. Implant profiles were analyzed using Rutherford backscattering (RBS). The surface hardness of these samples were measured using a nanoindenter. A substantial increase in surface hardness was observed in all the implanted samples. The thickness and peak hardness of the surface layer were enhanced by dual energy implantation. Beam heating during ion implantation resulted in annealing of the 6061-T6 samples. These effects were confirmed by annealing experiments which produced little change in overall hardness profiles. Large scale cracking of the hard surface layer was observed in low dose pure Al samples. This cracking behavior was altered by annealing