Characterization of laser-nitrided iron and sputtered iron nitride films

Abstract

Laser-nitriding may be a promising technique for substituting conventional nitriding processes. We have irradiated pure iron with pulses of an excimer laser and achieved high nitrogen contents in a thin surface layer. We found that the nitrogen is dissolved into γ-Fe, leading to a large amount of retained austenite. This was also verified by X-ray diffraction (XRD) measurements. Three subspectra can be resolved in the Mossbauer spectra (CEMS) for this nitrogen austenite. The nitrogen concentration can be calculated in terms of site occupation, indicating a content as high as 16(1) at%, which is consistent with the results of Rutherford backscattering spectroscopy (RBS), resonant nuclear reaction analysis (RNRA) and Auger electron spectroscopy (AES) measurements. This is more than the solubility limit for γ-Fe(N). By reactive magnetron-sputtering it is possible to produce thin iron nitride films of various stoichiometries. We report on the production ofe-Fe x N and FeN y films. These films were again characterized by CEMS, RBS, RNRA (15N(p, αγ)) and XRD. Fore-Fe x N, produced in the range 2⩽x⩽3 with medium nitrogen flows during reactive sputtering, the Mossbauer spectra can be well resolved in terms of different iron sites, enabling an accurate calculation of the nitrogen content. For high nitrogen flows during sputtering a phase FeN y withy>0.5 is produced. This phase is not reported in the Fe-N phase diagram.