MICROSTRUCTURE AND WEAR BEHAVIOR OF ALUMINUM IMPLANTED WITH NICKEL

Technical semi-hard aluminium (99.5wt.% Al) was implanted with nickel at 200 keV (T-impl less than or equal to 200 degrees C) and 1 MeV (T-i mpl less than or equal to 50 degrees C). The chosen doses resulted in maximum nickel concentrations of 22-32 at.% and 20-45 at.% for implant ation at 200 keV and 1 MeV, respectively. The as-implanted microstruct ure was characterized by an essentially amorphous matrix with nanocrys talline precipitates of NiAl3 and NiAl. The size of the NIAl3 precipit ates was in the order of 5-10 nm. For the 200 keV implantation formati on of NiAl was observed for all samples with typical particle sizes al so of 5-10 nm. After implantation at 1 MeV, NiAl was only observed for maximum nickel concentrations >30 at,%, but with larger precipitates of 40 +/- 20 nm. The occurrence of NiAl was explained by the higher re sistance against radiation damage of NiAl compared with NiAl3. By anne aling at 400 degrees C in both sample series a buried continuous layer of NiAl3 was formed. The metastable NiAl precipitates disappeared. An nealing at 600 degrees C led to the growth of large NiAl3 grains with typical dimensions up to the micrometre range. A significant wear redu ction by a factor of about 20 was observed for the 200 keV samples wit h the deep nickel distribution obtained by annealing at 600 degrees C as well as for the as-implanted state of 1 MeV implantation with high doses resulting in maximum nickel concentrations >40 at.%. (C) 1998 El sevier Science S.A.