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 wi th a XeCl excimer laser beam (wavelength lambda = 308 nm, average energy de nsity H = 4 J/ cm(2), pulse width tau = 55 ns) in pure nitrogen, iron nitri de coatings of 1-2 mu m 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 sens itivity of RNRA to the isotope N-15, RNRA via the N-15(p,alpha gamma)C-12 r esonance reaction and alternate irradiations in a Nz atmosphere of natural or enriched N-15 abundance are employed to study the take-up of new nitroge n into the surface and the transport mechanisms upon irradiation with subse quent pulses. Together with RES investigations of convective transport of t he molten base material using thin Au marker layers, information on basic m echanisms of the nitriding process (convection, diffusion) was gained enabl ing a simulation of the nitrogen depth profiles. (C) 2000 Elsevier Science B.V. All rights reserved.