A systematic study of nitride‐phase formation in iron implanted with nitrogen was performed by conversion electron Mossbauer spectroscopy (CEMS). The samples of α‐iron were implanted at room temperature with 100 keV N+2 ions whose mean range in the iron target was about 55 nm. The implanted dose varied from 5×1016 to 6×1017 N atoms/cm2. After implantation each sample was isothermally annealed in vacuum for 1 h at temperatures from 150 to 500 °C in 50 °C steps. The CEMS measurements allowed identification of the iron nitride phases formed by implantation and after annealing. At low doses (up to 1.5×1017 N atoms/cm2), the nitrogen‐containing α’‐martensite and/or α‘‐Fe16N2 phases appear. For intermediate doses (2×1017–2.7×1017 N atoms/cm2) e‐Fe3N is formed additionally. For doses higher than 3×1017 N atoms/cm2 the dominant phase is e‐Fe2N. In the course of annealing, e‐Fe2N decomposes to e‐Fe3N and γ’‐Fe4N and finally disappears at about 300–350 °C. At 500 °C only the Zeeman sextet of α‐Fe remains in the spe...

Phase transformations in nitrogen‐implanted α‐iron

A systematic study of nitride phases formation in iron implanted with nitrogen was performed using conversion electron Mossbauer spectroscopy (CEMS). The samples of α-iron (armco) were implanted at room temperature with 100 keV N2+ at doses ranging from 5×1016 to 6×1017 N at./cm2. After implantation each sample was isothermally annealed in vacuum at temperatures ranging from 150 to 500°C in 50°C steps, for 1 h. The CEMS measurements allowed us to identify the iron nitride phases formed by implantation. The study of phase evolution due to annealing allowed us to derive a new phase diagram for the implanted Fe N system.

Phase diagram of implanted FeN system

The influence of temperature during implantation or annealing on the total amount of retained nitrogen and its depth distribution are investigated. After implantations at temperatures above 250 °C only traces of nitrogen are detected in single crystal iron and about 30% is retained in the steel samples. The in-bulk diffusion is observed for steel above 300 °C.



L'effet de la temperature sur profil de concentration et teneur de l'azote implante a ete etudie. Au dessous de 250 °C on ne mesure que les traces de l'azote en cristals de fer et environ 30% de contenu d'origine en acier. Diffusion de l'azote a ete observe en acier au dessous de 300 °C.

Thermal Effects on Depth Distribution of Mtrogen Atoms Implanted in Ferrous Alloys

Nitrogen ions with energies of 50 keV and 2 MeV were implanted into electrolytically polished samples of pure α-iron at room temperature (300 K). A method has been developed for preparing cross-sectional specimens which are suited for TEM investigations in a 100 kV instrument. In the case of 50 keV implantation, additional information is gained from conventional TEM of plan-view specimens. The morphology of implantation-induced nitrides, their depth distribution and their orientation relationship to the iron matrix are discussed.

J. Jagielski

Papers

TEM studies of nitrides in surface-treated and implanted 12% chrome steel

The Pitting Corrosion Resistance of Silicon‐Implanted Stainless Steels