Nitride formation in transition metals during high fluence–high temperature implantation

Nitrogen ion implantation is investigated in molybdenum, titanium and austenitic steel (as a model for fcc iron) at ion energies between 5 and 30 keV at fluences larger than 1018 ats./cm2 and elevated temperatures. The transition metals placed in the upper left part of the periodic table, e.g., Ti, exhibit the highest stability of nitrides with a metal:nitrogen ratio of 1:1, whereas the formation enthalpies are much lower for later groups and periods (Fe and Mo). For stainless steel and Mo, this trend is confirmed in the experiments: nitrogen ion implantation in austenitic steel leads to lattice expansion and nitrogen in solid solution without phase formation, whereas only Mo2N was observed in the latter case. At temperatures up to 500 °C, the well-known B1 TiN phase was observed. After a further increase of the implantation temperature up to 750 °C, accompanied by a faster diffusion process, no TiN could be observed. Despite a concentration plateau of 50 at.%, only a lattice expansion of the Ti was found by X-ray diffraction (XRD).