Influence of cyclic deformation on surface microstructure and hardness of ion-implanted nickel

Abstract

The effects of cyclic deformation on near-surface dislocation structure and hardness of ion-implanted nickel were characterized and correlated with the evolution of fatigue damage. Polycrystalline nickel fatigue specimens were implanted at 220 °C with 350 keV and 3 MeV nickel ions to a fluence of 1 × 1016 ions/cm2 or at 220 °C and 500 °C with 350 keV aluminum ions to a fluence of 5 × 1017 ions/cm2. Both the self-implantations and aluminum implantations approximately doubled the hardness of the near-surface region. During cyclic deformation, the near-surface regions of self-implanted specimens cyclically softened and formed clear channels through which subsurface persistent slip bands (PSBs) penetrated the implanted region. The near-surface regions of aluminum-implanted specimens maintained a high hardness during cyclic deformation and effectively suppressed the evolution of fatigue damage and extended fatigue life. The results of the study indicate that the cyclic stability of implantation-induced surface hardening is a key factor in the ability of an ion implantation treatment to suppress the evolution of fatigue damage.