Investigation of laser nitriding of iron using ion beam analysis

Most metals can be nitrided by irradiation with short pulses of an excimer laser in nitrogen containing atmospheres. By the laser nitriding process with a XeCl excimer laser beam (wavelength λ=308 nm, average energy density H=4 J/cm2, pulse width τ=55 ns) in pure nitrogen, iron nitride coatings of 1–2 μm thickness at a level of up to 15 at.% nitrogen were produced. The results of the complicated laser-plasma-material interaction can be resolved by combining Resonant nuclear reaction analysis (RNRA) and Rutherford backscattering spectrometry (RBS). Utilizing the exclusive sensitivity of RNRA to the isotope 15N, RNRA via the 15N(p,αγ)12C resonance reaction and alternate irradiations in a N2 atmosphere of natural or enriched 15N abundance are employed to study the take-up of new nitrogen into the surface and the transport mechanisms upon irradiation with subsequent pulses. Together with RBS investigations of convective transport of the molten base material using thin Au marker layers, information on basic mechanisms of the nitriding process (convection, diffusion) was gained enabling a simulation of the nitrogen depth profiles.