LASER NITRIDING OF IRON - NITROGEN PROFILES AND PHASES

Armco iron samples were surface nitrided by irradiating them with puls es of an excimer laser in a nitrogen atmosphere, The resulting nitroge n depth profiles measured by Resonant Nuclear Reaction Analysis (RNRA) and the phase formation determined by Conversion Electron Mossbauer S pectroscopy (GEMS) were investigated as functions of energy density an d the number of pulses. The nitrogen content of the samples was found to be independent of the number of pulses in a layer of 50 nm from the surface and to increase in depths exceeding 150 nm, The phase composi tion did not change with the number of pulses. The nitrogen content ca n be related to an enhanced nitrogen solubility based on high temperat ures and high pressures due to the laser-induced plasma above the samp le. With increasing pulse energy density, the phase composition change s towards phases with higher nitrogen contents. Nitrogen diffusion see ms to be the limiting factor for the nitriding process.