In invited lecture (22nd International Conference on Materials and Technology, 20.-22. october 2014, Portorož, Slovenia) the substrate surface topography as formed through the hard coating deposition process (polishing, ion etching, deposition) was described. On polished steel surface we found some topographical features which appeared at the positions of carbides and non-metallic inclusions. The reason is different removal rates of matrix in comparison with inclusions due to the difference in hardness. During the ion etching process the additional morphological features are formed. The reason is a difference in sputtering rate of inclusions and steel matrix. This resulting in a formation of shallow craters and hillocks, which increased the surface roughness for about three times. This could be one of the reasons why ion etching improves the adhesion of hard coatings efficiently due to mechanical anchoring. All these topographical changes of substrate surface reflected on the coating surface. Due to the shadowing effect they are often magnified through the coating. Thus inclusions in steel are sites at which the PVD nodular defects and pinholes are formed.
B.04 Guest lecture
COBISS.SI-ID: 28057127Hard PVD coatings have been proved as one of the most succesfull methods for enhancing the cutting process productivity, however, their potential is not yet fully exploited because they contain several microstructural imperfections, such as porosity, inclusions and above all, growth defects. These defects have a negative influence on required coating properties, therefore many research groups have been trying to minimize their concentration. So far, they have been succesfull in realizing, what are the most common reasons for their appearance, as well as in understanding the mechanism of their influence on topography. The most important findings of our research group were presented.
B.04 Guest lecture
COBISS.SI-ID: 27690791Hard 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.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 276393984