Impact of Fe on the oxide phase formation and oxidation behaviour of cathodic arc evaporated Al-Cr films

Abstract

The application of hard protective coatings to tools and components, which suffer from wear and friction is an extremely useful and nowadays well-established approach to increase their lifetime and process efficiency. Especially components used in high temperature applications, such as gas turbines or combustion engine pistons, are subject to oxidation and corrosion. Therefore, the development not only of hard protective, but also high temperature and oxidation resistant coatings has become highly important for many industrial sectors. These coatings are often synthesised by physical vapour deposition (PVD). A very common and widely-applied oxidation resistant and diffusion barrier coating is alpha-Al2O3. Its outstanding mechanical as well as thermal and chemical properties makes it attractive for many applications. A major problem in the synthesis of -Al2O3 by PVD is the necessity of relatively high deposition temperatures to promote the growth of the desired corundum (¿) phase. Below 600 °C unfavourable metastable Al2O3-phases occur. To overcome this issue, several concepts were developed in the last decade. One suitable approach is the growth of a solid solution (Al,Cr)2O3.. Recently, it was shown that the addition of 5 at.% Fe to Al0.7Cr0.3 targets (forming a quaternary (Al,Cr,Fe)2O3 solid solution) increases the hexagonal phase fraction significantly mainly by nucleation on metallic Cr- and Fe-rich droplets. Based on these results, the impact of Fe on Al-rich Al-Cr coatings (using powder-metallurgically produced Al0.7Cr0.3, Al0.675C0.275, and Al0.67Cr0.23Fe0.10 targets) was studied in the present thesis. Metallic coatings and substoichiometric oxides were grown by cathodic arc evaporation and analysed with emphasis on phase evolution as a function of the oxygen flow rate as well as the oxide phase formation in post-deposition oxidation studies. Additionally, the oxidation behaviour of droplets was investigated to gain information about the influence of such macroparticles on the phase evolution.