The influence of target temperature on the structure and properties of nitrogen-ion-implanted stainless steel

Abstract

Nitrogen ion implantation has proved effective in the surface strengthening of metals and alloys. In order to achieve high throughputs industrially, high beam currents must be used. The resulting high target temperature may cause a difference in the structure of implanted material. In this work the effect of varying the target temperature during nitrogen implantation in stainless steel is studied. With a beam power of 0.1 W cm^-2 the target temperature is restricted to 150 ° C. At a dose of 3.5× 10¹⁷ N₂⁺cm^-2, glancing-angle X-ray diffraction (GAXD) revealed the formation of ∈-iron nitride and no nitrogen in solution. The microhardness measured at 10 gf is increased by 15%. With a beam power of 0.7 W cm^-2 the target temperature is 370 °C. After the same dose as before, the microhardness increases by 40%. GAXD results suggest that the increased hardness is due to the presence of nitrogen in solid solution as opposed to complete precipitation. Thus an elevated target temperature can have a favourable effect on the final properties. A sample deformed by compression formed an enhanced oxide layer during implantation as indicated by Auger depth profiling. This oxide layer appears to have a capping action against the out-diffusion of nitrogen.