Surface modification of multilayered titanium-aluminium nitride coating with high intensity IR laser beam

Complete test of publication follows. Multilayered coatings have a number of advantages over single layers as they combine the attractive properties of several materials as well as exhibiting some completely new properties. Multilayered coatings such as titanium nitride/titanium-aluminium nitride (TiN/TiAlN) possess better mechanical properties than single layer coatings. Due to its high hardness and brittleness, mechanical micro structuring is extremely difficult, thus the laser beam treatment is one of possible solutions. Studying of interactions of laser beams with hard coatings has both application and fundamental importance. The research objective of this work was the study of surface modifications of TiN/TiAlN coating, induced by high intensity laser irradiation. The surface modification of multilayered coating was performed in air with focused TEA CO2 laser beam. The laser operated at following conditions: TEM00 mode, pulse energy 70 mJ, temporal pulse duration 80 ns and peak power density of 1010 W/cm2. Multilayered hard coatings TiN/TiAlN was deposited on the polished hot work tool steel plates. The deposition system has four vertical unbalanced magnetron sources in closed-field configuration with the ability to control their power. The total coating thickness was 2,17 μm consisted of 45 layers, while 0.5 μm thick TiAlN was deposited as a top layer. The modulation period of multilayered structure was about 80 nm. Generally, surface modifications of coatings induced by laser radiation have shown their dependence on laser pulse energy density, peak power density, pulse duration, number of accumulated pulses, laser wavelength, as well as on material properties. The energy absorbed from the laser beam is converted into thermal energy, which generates effects such as melting, vaporization, dissociation or ionization of the vaporized material, exfoliation, and shock waves in the vapour and the solid. After action of successive laser pulses of 35 J/cm2 the modifications of the TiN/TiAlN multilayered coating were registered. As a function of accumulated laser pulses the experiments have shown the following effects: (i) surface modification on micro- and nano-meter scale, (ii) formation of craters with clear central part and narrow periphery, (iii) plasma formation in front of target. The surface characterization of the samples prior and after laser irradiation was carried out by optical microscope, scanning electron microscope, atomic force microscope and profilometry.