Defekti PVD-prevlek in njihov vpliv na fizikalno-kemijske lastnosti sistema prevleka/podlaga : doktorska disertacija

slovenian

doktorska dela

2014

growth defects   non-metallic inclusion in steels   pitting corrosion   PVD-coatings

Univerza v Mariboru, Fakulteta za strojništvo

Hard protective coatings prepared by physical vapor deposition (PVD) are one of the most effective ways to increase the machining productivity, but their potential has still not been fully exploited. Growth defects which form in the coating during the deposition process deteriorate the adhesion of coatings to the substrate, reduce the corrosion resistance, etc. Hard coating quality can be improved if growth defects density is reduced. This can be performed by understanding the mechanisms of their origin. In this work, the formation mechanisms of growth defects in each step of coating preparation is described, and their influence on physicochemical properties of the coating/substrate system is evaluated. Growth defects were analysed in TiAlN/CrN nanolayered coating, deposited on four steel types (ASP 30, M2, D2 and 316L) using sputtering system with four unbalanced magnetron sources. To study the origins, the growth mechanisms and the influence of defects on the physicochemical properties of the coating/substrate system, the following analytical techniques were used: optical microscope (OM), atomic force microscope (AFM), scanning electron microscope (SEM), focused ion beam (FIB), transmission electron microscope (TEM), energy-dispersive spectroscopy (EDS), tribometer, 3D profilometer and 3D reconstruction of SEM images. It was found that the growth defects in the coating occur due to geometric shadowing caused by the following seeds: topographic irregularities on the substrate surface, particles which remained on the surface after cleaning, and particles deposited on the surface of substrates during heating, ion etching and sputtering. Sulphite and oxide non-metallic inclusions present in steel are also seeds for growth defects formation. On sulphide inclusion sites in the coating, craters and pores are formed irrespective of the type of steel substrate and plasma etching technique. On intensively etched oxide inclusions, pores form in the coating, while on mild etched oxide inclusions the coating growth is undisturbed. The most common topographic irregularities on the surface of hard coatings are nodular defects. They have the highest influence on the coating surface roughness. It was also found that during the tribological test (pin-on-disk) the first damage of the coating appears on nodular defects. In initial phase of the tribological test these growth defects are the main source of abrasive particles, which causes the beginning of coating wear. It has been shown that the corrosion resistance of the coating/substrate system deteriorates only those growth defects which allow solution to penetrate to the substrate surface.

08.08.2023