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72nd IUVSTA - 2014
Christian Koller (C.M. Koller)
"Alloying trends of refractory metals on the phase stability of (Al1-xCrx)2O3 coatings"

C. M. Koller1, D. Holec2, J. Ramm3, S. Kolozsvari4, and P. H. Mayrhofer1,5

1Christian Doppler Laboratory for Application Oriented Coating Development, Vienna University of Technology, A-1040 Vienna, Austria
2Department of Physical Metallurgy and Materials Testing, Montanuniversitšt Leoben, A-8700 Leoben, Austria
3Oerlikon Balzers Coating AG, LI-9496 Balzers, Principality of Liechtenstein
4Plansee Composite Materials GmbH, D-86983 Lechbruck am See, Germany
5Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austrial
A popular and successful strategy of modern materials science is the combined experimental and computational assisted design of high performance materials. This approach enables sophisticated material development on from atomistic scales allowing for individually tailored and application oriented performance. As many aspects of low temperature PVD processed Al-based oxide coatings are still not satisfyingly explained and understood this methodology opens the possibility continuously filling this gap / approaching this issue from two directions.
Ab initio calculations were performed to evaluate/obtain first results/information on the impact of refractory metals as alloying elements, M, in (Al1-x-yCrxMy)2O3. We compare the relative position of / oppose energies of formation, Ef, for three experimentally observed/relevant phases, corundum-type ?, B1-like fcc, and defected-spinel ?. Group IVB, VB, and VIB elements of the 5th and 6th period substitute Cr up to a metallic sublattice population of 20 at% based on three compositions with constant Al-content. We observe a gradual change in the Ef-slope for all modifications ranging from negative (group IVB) to indifferent (group VB) and positive (group VIB). Cubic phases within the observed composition are energetically higher with respect to corundum-type as in respect to ?., Hhowever, the some elements (e.g. as for example Y), show a significant convergence of ? and ? phases with increasing Al/Cr-ratio and for increased alloy concentrationorporated Y content, respectively. The difference between 5th and 6th period elements is not as pronounced as group variations.
For comparison with the calculations, In addition to our theoretical considerations/discourse we have prepared selected coatings with different alloying elements using an industrially scaled cathodic arc evaporation facilitywere synthesized by cathodic arc evaporation. The coatings were analysed by Systematic investigations using X-Ray diffraction and electron microscopy in terms of morphology and crystallographic growth and compared with revealed significant/distinct difference to our the reference (Al0.7Cr0.3)2O3 coating in terms of morphology and crystallographic growthto elucidate the effect of alloying.
General Conclusive evaluation of our results of quaternary oxides alloyed with refractory metals point out the suitability to obtain general alloying trends are discussed.but also reveals that the combination of first principle methods with high energetic deposition techniques such as reactive cathodic arc evaporation, particularly for complex Al-based oxides, needs additionally considerations in order to allow for a sophisticated computer assisted coating development.

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