High dose implantation of nitrogen in tool steel: Auger electron spectroscopy and hardness measurements

Abstract

Tool steel samples were implanted with 100 keV N + ions at liquid nitrogen temperature to doses of 3 × 10 17 and 1 × 10 18 cm −2. Only the dose of 1 × 10 18 cm −2 caused a significant hardening effect. Two mechanisms contributed to this hardness increase, namely nitride formation and radiatin damage. Cooling during implantation caused additional hardening, owing to a martensitic phase transformation. The projected range ( R p = 110 nm) for the implanted species was obtained by Auger sputter depth profiling. If the hardened layer thickness was taken as 2 R p, then the Jönsson-Hogmark model gave an average hardness value of 2010 HV for the implanted layer. However, a more realistic value of 900 HV was calculated under the assumption that typical radiation damage profiles ( R d = 3 R p) contributed to the hard film thickness. It is difficult to judge the accuracy of the model for predicting the correct absolute hardness of the implanted layer but it is shown that deep radiation-induced damage plays a major role in surface hardening.