Modification of the fatigue behavior of copper and stainless steel by ion implantation

Abstract

A program was undertaken to study the effect of ion implantation on the fatigue lives of copper and austenitic stainless steel. Neon and nitrogen ions of 2 to 4 MeV were implanted into flat plate flexutral type fatigue specimens using the Dynamitron accelerator at SUNY Albany. By using the rotating target method, uniformity of the depth of lattice defects and of the dose of the implanted species was obtained. Control specimens (not implanted) and ion-implanted specimens were fatigue-cycled in flexture under constant and identical displacement and frequency conditions until failure. A substantial improvement was observed in the fatigue life for the Ne-implanted copper when fatigued in air. The stainless steel specimens implanted with N which were fatigued in argon did not show a measurable increase in fatigue life. In order to investigate whether the fatigue life was influenced by the modification of the near-surface deformation characteristics, e.g., by creating barriers against slip activity and the easy formation of persistent slip bands, a study of the most highly stressed fatigue specimen surfaces was undertaken by scanning electron microscopy. The results on both the copper and stainless steel specimens support the concept of slip modification in the implanted layer. While the fatigued control specimens exhibited extensive surface ridges which appear to be extrusions and intrusions from persistent slip bands, the implanted specimens are devoid of such features.