Study of UV laser ablation of nitrided steels using inductively coupled plasma atomic emission spectrometry

A depth profile study of nitrided steels containing Ti or V sputtered in the surface layer was performed by means of laser ablation inductively coupled plasma atomic emission spectrometry. An Nd:YAG laser was used in the Q-switched mode and operated at 355 and 266 nm. The laser ablation patterns were obtained on the material surface by moving the ablation cell relative to the laser beam by means of an XY-translator. Depth resolution was obtained by using successive limited numbers of ablation cycles. The corresponding transient signals of Ti or V and Fe were measured simultaneously with a dual monochromator. The effect of the number of cycles, the laser power and laser wavelength on the time-dependent behaviour of the Ti or V and Fe line intensities was studied along with the erosion rate. It was found that the erosion rate was lower than 0.6 mu m per cycle and depended on the depth of penetration. Emission of sputtered Ti and V was mainly observed in an external layer of less than 2 mu m. The laser wavelength did not modify the shape of the crater but significantly changed the line intensity of Fe. The Fe line intensity was also enhanced during the ablation of the nitrided steel compared with the ablation of untreated steel. This study contributes to the knowledge of behaviour of the modified metal surface during interaction with the laser radiation, which is important for development of the method for determination of composition of nitrided surface layers.