Microstructure and tribological properties of aluminium implanted with high doses of nickel

Abstract

Technical semi-hard aluminium (99.5 wt% Al) was implanted with nickel at 200 keV and 1 MeV. The chosen doses result in maximum nickel concentrations from 22 to 32 at.% and 20 to 45 at.% for the implantation with 200 keV and 1 MeV, respectively. The as-implanted microstructure is characterized by a mainly amorphous matrix with nanocrystalline precipitates of NiAl 3 and NiAl. The size of the NiAl 3 precipitates is in the order of 5–10 nm. For the 200 keV implantation formation of NiAl is observed for all samples with typical particle sizes also of 5–10 nm. After implantation with 1 MeV NiAl is observed only for maximum nickel concentrations >30 at.%, however with larger precipitates of 40 ± 20 nm. The occurrence of NiAl is explained by the higher resistance against radiation damage of NiAl compared to NiAl 3. By annealing at 400°C in both sample series a buried continuous layer of NiAl 3 is formed. The metastable NiAl precipitates disappear. Annealing at 600°C leads to the growth of large NiAl 3 grains with typical dimensions up to the μm range. In the 1 MeV samples elongated precipitates with an extent of typically 1–3 μm parallel to the implanted layer and a thickness comparable to the original implantation depth (∼500 nm) form a nearly continuous layer. A few particles, consisting of subgrains, extend to several μm depth. For the 200 keV implantation a nickel distribution up to large depth is observed after annealing at 600°C, connected with a decrease of the maximum concentration to only a few percent. This is explained by the formation of isolated grains with an extent of 1–3 μm into the depth. A wear reduction by a factor of about 20 is observed for the 200 keV samples with the deep nickel distribution obtained by annealing at 600°C as well as for the 1 MeV implantation with high doses (maximum nickel concentration >40 at.%).