S. Costil, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, China; V. Barnier, C. Coddet, University of Technology Belfort-Montbeliard, Belfort Cedex, France; R. Oltra, O. Heintz, Laboratoire de Recherches sur la réactivité des solides, Dijon Cedex, France
A limited oxidation can be observed during laser cleaning of aluminium surface with a Q-switched Nd:Yag (10 ns, 1064 nm) due to transient heating of the surface. For application of cleaning before coating metallic surface this effect has to be considered. The aim of this work was to characterize the effect of laser radiation at low fluence (0.7 J/cm2) to avoid ablation effects and using 10 Hz cumulative pulses in order to increase oxidation phenomenon already observed for one laser pulse on pure aluminium surface. The influence of those laser substrate pre-treatments on the mechanical behaviour of a 80 mm alumina plasma sprayed coating was observed evaluating the integrity of the coating/substrate interface with "laser-ultrasonic method" thanks to a special set up using a laser interferometer probe. Improvement of the alumina coating adherence was found above 100 laser pulses for aluminium surface preparation and the best properties for a laser treatment with 1000 pulses. These results were correlated with the charaterization of the aluminium surface modifications after laser irradiations under 18O atmosphere changing the number of pulses. Chemical analyses using Secondary Ions Mass Spectroscopy analyses showed an oxidation effect accuentuated by the increase of number of laser pulses used for laser treatment. Topographic analyses, particularly at the nanoscale using atomic force microscopy showed different oxide morphology depending on the number of laser pulses. These modifications probably have an effect on the adhesion and flattening behaviour of "splats" on the aluminium substrate surface during the thermal spraying process.
Summary: Improvement of the alumina coating adherence was found above 100 laser pulses for aluminium surface preparation and the best properties for a laser treatment with 1000 pulses. These results were correlated with the charaterization of the aluminium surface modifications after laser irradiations under 18O atmosphere changing the number of pulses.
