Relating Nanostructures to Mechanical Properties in Ion-Implanted Materials

Ion implantation was used to form high densities (~10 19 /cm 3 ) of small oxide precipitates in Ni in order to investigate the strength mechanism produced by such highly refined structures. Nanometer-size precipitates of Al 2 O 3 and NiO are found to block dislocation motion in the Ni matrix, producing yield strengths up to 4.6 GPa, more than twice that of hardened bearing steel. Dispersion strengthening theory, developed for micrometer-size precipitates and spacings, was found to account quantitatively for the yield strengths produced by nanometer-size oxides as well. Nanoindentation plus finite-element modeling was used to quantify the mechanical properties of implanted metal layers, and was extended to examination of amorphous Si layers formed by self-ion implantation. The amorphous phase was found to have a yield strength of 4.45 ± 0.20 GPa, Young’s modulus of 144 ± 7 GPa, and hardness of 10.3 ± 0.4 GPa. The modulus and hardness are reduced by 10% and 15%, respectively, from those of crystalline Si.