EFFECTS OF ROOM-TEMPERATURE CARBON, NITROGEN AND OXYGEN IMPLANTATION ON THE SURFACE HARDENING AND CORROSION PROTECTION OF IRON

The surface hardness and anodic dissolution behavior of carbon-, nitrogen- and oxygen-implanted iron measured by Knoop hardness testing and multisweep cyclic voltammetry were investigated in relation to the composition and structure of the implanted layers. Carbon and nitrogen implantations were performed with fluences up to 10(18) ions cm-2 at 100 keV, and oxygen implantation was carried out with fluences up to 1.3 x 10(18) O atoms cm-2 at 80 kV using non-mass-separated ions. Surface analyses revealed that implanted carbon atoms form a gaussian-like distribution even with the highest fluence and combine with iron and carbon itself to form iron carbides and C-C bonded carbon. In contrast, nitrogen and oxygen atoms form a trapezoidal distribution owing to their migration, and combine with iron to form iron nitrides and oxides. The increase in hardness for carbon-implanted iron corresponds to the increase in fluence, and nitrogen and oxygen implantations have an optimum fluence for surface hardening. Carbon was the most effective implanted ion for suppressing the anodic dissolution of iron. In conclusion, high fluence carbon implantation is most effective for both surface hardening and corrosion protection of iron owing to the formation of metastable layers consisting of iron carbides and C-C bonded carbon.