HIGH-DOSE IMPLANTATION OF NITROGEN IN TOOL STEEL - AUGER-ELECTRON SPECTROSCOPY AND HARDNESS MEASUREMENTS

Tool steel samples were implanted with 100 keV N+ ions at liquid nitro gen temperature to doses of 3 x 10(17) and 1 x 10(18) cm-2. Only the d ose of 1 x 10(18) cm-2 caused a significant hardening effect. Two mech anisms contributed to this hardness increase, namely nitride formation and radiation damage. Cooling during implantation caused additional h ardening, owing to a martensitic phase transformation. The projected r ange (R(p) = 110 nm) for the implanted species was obtained by Auger s putter depth profiling. If the hardened layer thickness was taken as 2 R(p), then the Jonsson - 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 dam age profiles (R(d) = 3R(p)) contributed to the hard film thickness. It is difficult to judge the accuracy of the model for predicting the co rrect absolute hardness of the implanted layer but it is shown that de ep radiation-induced damage plays a major role in surface hardening.