Excimer laser processing of nodular iron
Résumé
Excimer laser processing is expected to improve the wear properties and the oxidation resistance of cast iron surfaces. In the present study, an XeCl laser prototype was used to change the surface morphology of nodular iron samples under high energy ultraviolet exposure. Roughness evolution results from ablation and, above all, from moving of the molten superficial layer, due to both high temperature and pressure involved during the laser shot. Conventional metallography was carried out to determine the mechanisms governing the modification of surface profiles. These were shown to be both a wide and a local phenomena, i.e. involved at two different scales: that of the laser spot and that of the nodule. The plasma high pressure applied to the surface moves the molten material towards the periphery of the spot, where it freezes by self quenching with a high cooling rate. The surface profile is also modified by the formation of a rim surrounding each solid heterogeneity such as graphite spheroids. The width of the rims did not depend on the sizes of nodules or inclusions. The study suggests a wave emission mechanism to interpret formation of the rims.