Iron nitrides and laser nitriding of steel

Nitriding of iron and steels is well known to improve hardness, wear and corrosion resistance of surfaces. Recently, it has been found that a simple irradiation of iron and steel with pulses of an excimer laser in air or nitrogen leads to a significant nitrogen take-up into the surface and to improvements in the surface properties. The mechanisms of the laser-nitriding process are not yet understood but the nitrification will be proved by several methods. Among these, Mössbauer spectroscopy is very powerful, especially when Conversion Electron and Conversion X-ray Mössbauer Spectroscopy (CEMS and CXMS) are applied simultaneously. Nevertheless, only a combination of methods gives a satisfying overview of the laser induced nitriding processes: Rutherford Backscattering Spectrometry (RBS) and Resonant Nuclear Reaction Analysis (RNRA) were also used to characterize the treated surfaces. First measurements show an increase of the hardness and the wear resistance with the number of pulses. From the results of the CEMS analyses this should be correlated with the increase in the fraction of the ε-phase. This may be important for industrial applications.