Karakterizacija defektov PVD TiAlN trdih prevlek

PVD hard coatings are continuously gaining their importance in different fields of applications. In industrial use, they are often exposed to corrosive environments. Hard coatings possess inherently good corrosion resistance, but the substrate-hard coating systems may suffer from a severe corrosion attack due to the defects (craters, pin holes) in the coatings. On the sites, where defects extend through the coating, pitting corrosion can take place. These sites are drawbacks in the applications of hard coating. A PVD TiAlN hard coating was prepared on cold-work, tool-steel (AISI D2) substrates by sputtering using unbalanced magnetron sources. The growth defects incorporated into the coating were studied after the deposition and corrosion experiments. We used two methods: (1) scanning electron microscopy (SEM) for general overview of the coating topography and 2D-characterization of defects, and (2) scanning electron microscopy with a focused ion beam (SEM-FIB) for making serial cross-sections through the selected defects in order to provide images for a 3D-reconstruction of defects. In this work we tried to investigate the formation of a defect at a specific location and findout whether the selected defect causes pitting corrosion.PVD trde prevleke pridobivajo pomen na različnih področjih uporabe. Pri različnih aplikacijah so pogosto izpostavljene korozijskemu okolju. Trde prevleke so kemijsko inertne in same po sebi korozijsko obstojne. Med njihovo pripravo pa nastane v njih veliko defektov (kraterji, "pinholi"). Nekateri od njih segajo do podlage. Na teh mestih pride do jamičaste korozije, kar pa je z vidika uporabe neželeno. TiAlN-prevleko smo nanesli na podlago orodnega jekla D2 po postopku naprševanja z neuravnoteženim magnetronskim izvirom. Defekte, ki so nastali med pripravo plasti, smo preučili po korozijskem preizkusu. Za analizo smo uporabili dve metodi. Vrstični elektronski mikroskop(SEM), s katerim smo pridobili splošni pregled prevleke, kot tudi 2D-karakterizacijo defektov. Kot drugo metodo smo uporabili fokusiran ionski curek, ki je integriran v klasični SEM, s katerim smo izvedli serijo rezov izbranih defektov za njihovo 3D-karakterizacijo. V delu smo poskušali na specifičnih mestih ugotoviti mehanizem nastanka defektov in ugotovljali, ali povzročajo jamičasto korozijo

Morfologija in korozijske lastnosti CrN PVD-prevlek, nanesenih na aluminijeve zlitine

The attempt to find an alternative coating for corrosion protection of Al- alloys was made. PVD coatings are one of the possible alternatives for replacement of ecological unfriendly chromate coatings. Chromium-nitride (Cr-N) and Ni/Cr-N coatings were sputtered on aluminium substrates (AA7075 and cladded AA2024). Surface and sub-surface characterizations were performed by AFM and SEM. Special attention was given to defects incorporated into coatings, since they play important role in the corrosion protection of the coating/substrate systems. The cross-sections through the typical defects were performed by ion beam milling incorporated into the SEM. The Vickers hardness of the Cr-N with and without layer of Ni on both substrates was determined. After the coatings deposition, the values of Vickers hardness (10 mN load) increase for 10 to 100-fold compared to the substrates. The corrosion behaviour of Cr-N and Ni/Cr-N thin films was investigated in near neutral 0.1 M solution of NaCl using potentiodynamics electrochemical measurement. Cr-N and Ni/Cr-N coatings shift the corrosion potentials to more positive values. The best corrosion resistance among the tested coating/substrate systems were found for Ni/Cr-N on AA7075 substrate.Ena od možnih alternativ za zamenjavo ekološko neprijaznih kromatnih prevlek na aluminijevih zlitinah so PVD-prevleke. V prispevku opisujemo pripravo in karakterizacijo prevlek Cr-N in Ni/Cr-N na aluminijeve podlage (AA7075 in AA2024). Površinsko in podpovršinsko karakterizacijo CrN-prevlek smo izvedli z vrstično elektronsko mikroskopijo (SEM) in mikroskopom na atomsko silo (AFM). Posebna pozornost je bila namenjena karakterizaciji defektov v prevlekah, saj igrajo pomembno vlogo pri korozijski zaščiti sistema prevleka/podlaga. Defekte smo karakterizirali z vrstičnim mikroskopom (SEM), ki je dodatno opremljen s fokusiranim ionskim curkom (FIB) za odstranjevanje materiala. Določili smo trdoto prevlek po Vickersu na obeh vrstah aluminijevih podlag. Korozijske lastnosti prevlek smo merili v 0,1 M raztopini NaCl s potenciodinamskimi krivuljami. Cr-N- in Ni/Cr-N-prevleke premaknejo korozijski potencial proti pozitivnim vrednostim. Zaščita aluminijevih zlitin je boljša z dvojno prevleko Ni/CrN kot samo s prevleko CrN

Mechanical and anticorrosion properties of nanosilica-filled epoxy-resin composite coatings

Homogeneous, 50-μm-thick, epoxy coatings and composite epoxy coatings containing 2 wt% of 130-nm silica particles were successfully synthetized on austenitic stainless steel of the type AISI 316L. The surface morphology and mechanical properties of these coatings were compared and characterized using a profilometer, defining the average surface roughness and the Vickers hardness, respectively. The effects of incorporating the silica particles on the surface characteristics and the corrosion resistance of the epoxy-coated steel were additionally investigated with contact-angle measurements as well as by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5 wt% NaCl solution. The silica particles were found to significantly improve the microstructure of the coating matrix, which was reflected in an increased hardness, increased surface roughness and induced hydrophobicity. Finally, the silica/epoxy coating was proven to serve as a successful barrier in a chloride-ion-rich environment with an enhanced anticorrosive performance, which was confirmed by the reduced corrosion rate and the increased coating resistance due to zigzagging of the diffusion path available to the ionic species. © 2013 Elsevier B.V.status: publishe

Improvement to the Corrosion Resistance of Ti-Based Implants Using Hydrothermally Synthesized Nanostructured Anatase Coatings

The electrochemical behavior of polycrystalline TiO2 anatase coatings prepared by a one-step hydrothermal synthesis on commercially pure (CP) Ti grade 2 and a Ti13Nb13Zr alloy for bone implants was investigated in Hank’s solution at 37.5 °C. The aim was to verify to what extent the in-situ-grown anatase improved the behavior of the substrate in comparison to the bare substrates. Tafel-plot extrapolations from the potentiodynamic curves revealed a substantial improvement in the corrosion potentials for the anatase coatings. Moreover, the coatings grown on titanium also exhibited lower corrosion-current densities, indicating a longer survival of the implant. The results were explained by considering the effects of crystal morphology, coating thickness and porosity. Evidence for the existing porosity was obtained from corrosion and nano-indentation tests. The overall results indicated that the hydrothermally prepared anatase coatings, with the appropriate morphology and surface properties, have attractive prospects for use in medical devices, since better corrosion protection of the implant can be expected