LASER-SURFACE MODIFICATION - STRUCTURAL AND TRIBOLOGICAL STUDIES OF ALN COATINGS

In order to improve the superficial wear resistance and hardness of al uminium substrates, aluminium nitride AlN coatings were elaborated by laser-induced plasma surface processing. Due to plasma formation on th e Al surface, the effect of excimer laser irradiation under nitrogen a tmosphere allows nitrogen diffusion and then AlN growth in the Al matr ix. In this way, it is possible to avoid the adhesion problems encount ered in film deposition processes. To understand the mechanisms govern ing this surface transformation, chemical and microstructural investig ations were correlated with processing conditions, The influence of la ser spots in overlapping mode from a step-by-step to quasi-continuous scan in the two in-plane directions, X and Y, were studied by grazing incidence X-ray diffraction and scanning electron microscopy, coupled with energy dispersive X-ray spectrometry try analysis. These investig ations were consequently correlated with wear resistance estimated by a pin-on-disc machine. The results show a strong enhancement of wear r esistance when the overlapping rate is maximum in both the X and Y dir ections. (C) 1998 Elsevier Science S.A.