Chemical and structural modifications of laser treated iron surfaces: investigation of laser processing parameters

This study focuses on the chemical, morphological and structural characterization of iron surfaces treated by laser in ambient air. Incorporation of nitrogen over a 1–2 μm thickness (10–30 at.% at the profile maximum) and superficial oxidation on 200–400 nm depth have been evidenced by nuclear reaction analyses. X-ray diffraction at grazing incidence has shown the formation of FeO and Fe 3O 4 oxide phases as well as γ-Fe(N), and ϵ-Fe x N for a sufficiently high amount of nitrogen incorporated. Treatments performed with different laser beams indicate that the parameter playing the major role in surface modification processes is the wavelength. Nitrogen incorporation has been found to occur via the interaction of reactive N, present in the laser-induced plasma, and the iron molten bath. The nitriding process is promoted in the IR wavelength range. Oxidation takes place by chemical reaction during the cooling step, and is furthered in the case of UV treatment.