Surface modifications of TiN coatings by a pulsed TEA CO2 laser: Coating thickness effects

Abstract

Interactions of a transversely excited atmospheric (TEA) CO2 laser, pulse duration similar to 2 mu s (initial spike FWHM similar to 120 ns), with polycrystalline titanium nitride (TiN) coatings deposited on high-quality steel (AISI 316 or M2) were studied. The experiments were carried out in a regime of high laser energy densities: 25, 48, and 50 J/cm(2). The energy absorbed from the laser beam was partially converted to thermal energy and the effects of the TiN coating thickness on the morphological changes were considered. The morphological features and processes that accompany the interaction can be summarized as follows: (i) exfoliation of the TiN coating in the central zone of the irradiated area (for coating thickness of 1 mu m) or appearance of grainy structure ( for coating thicknesses 3 and 10 mu m); (ii) appearance of hydrodynamic changes in the surrounding peripheral zone; and (iii) appearance of plasma in front of the target during sample irradiation.