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W. Vollnhofer:
"Development of wear resistant coatings based on complex metallic alloys for functional application";
Betreuer/in(nen), Begutachter/in(nen): C. Eisenmenger-Sittner, M. Cekada; Institut für Festkörperphysik, 2012; Rigorosum: 07.03.2012.

As growing abrasion and wear causes a drastic increase of energy consumption and costs, the development of new, high abrasion resistant materials with a very low friction coefficient is important for various industrial applications in a short as well as in a long-term timescale. Because of their unique combination of mechanical, electrical and thermal characteristics complex metallic alloys (CMAs), especially the quasicrystalline Al59Cu25.5Fe12.5B3 and AlMgB14 are regarded as promising, cost-effective materials for protective coatings.
For deposition of Al59Cu25.5Fe12.5B3 and AlMgB14 films from hot pressed targets by magnetron sputtering an appropriate deposition system was constructed. AlMgB14 targets were produced by hot pressing an elemental powder mixture. For producing Al59Cu25.5Fe12.5B3 targets commercially available powder St Gobain Cristome F1 and elemental powder mixtures could be used. For depositing Al59Cu25.5Fe12.5B3 and AlMgB14 coatings, the following substrates were chosen: hard metal WC-Co, steel K600, steel K890, epitaxial Si and ceramic Al2O3. To provide a gradual change of the thermal expansion coefficient and avoid diffusion between the coating and substrate, the following materials were tested as possible interlayer: Chrome (Cr), Copper (Cu), Titanium (Ti), Manganese (Mn) and Nickel (Ni). To optimize the coating characteristics deposition parameters like deposition power, substrate - target distance, working gas pressure, substrate temperature and bias voltage were varied. The targets and the deposited coatings were analyzed by: Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), Energy Dispersive X-Ray Spectroscopy (EDS), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) und Atomic Force Microscope (AFM).
While AlMgB targets consisting of 90 % AlMgB14 phase and about 10 % Al2MgO4 could be produced, the AlMgB coatings deposited on WC-Co hard metal substrates at 600 °C consist of mainly amorphous boron. Also 900 °C post annealing does not cause the development of a crystalline AlMgB14 phase. During RF magnetron sputter deposition also technical problems are encountered, like crack formation in the AlMgB targets even for very low power densities (3.8 W/cm2) and very low deposition rates (20 nm/min for a power density of 15.2 W/cm2).
AlCuFeB targets that exhibit the Al59Cu25.5Fe12.5B3 composition but not the quasicrystalline structure could be produced by low temperature hot pressing. Since these targets contain only metallic phases they can be used for DC magnetron sputter deposition. With these targets AlCuFeB coatings, which exhibit 40 % quasicrystalline AlCuFe phase and 60 % Al50Cu40Fe10 ß phase can be deposited. The coating microstructure consists of an Al50Cu40Fe10 ß phase matrix, in which quasicrystalline grains with sizes of about 10 nm are embedded. Adhesion of the AlCuFeB coatings is very good on steel K600 and K890 as well as on ceramic Al2O3. On WC-Co and Si the AlCuFeB adhesion is good for thin coatings (~500 nm) but delamination occurs when the film thickness exceeds 1 μm. The AlCuFeB coatings were found to exhibit favourable characteristics for nanoimprint lithography and thus can be regarded as promising candidates as wear protective films for this method. During Aluminum turning tests cutting inserts with the AlCuFeB coatings outperform cutting inserts with a commercially available TiB2 coating.