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ICMCTF - 2015
Helmut Riedl (H. Riedl)
Poster
"Grain size induced effects on the decomposition process of Ti-Al-N thin films"
H. Riedl (a), R. Rachbauer (b), S. Kolozsvári (c), and P. H. Mayrhofer (a,d)

(a) Christian Doppler Laboratory for Application Oriented Coating Development at the Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria
(b) Oerlikon Balzers Coating AG, FL-9496 Balzers, Liechtenstein
(c) Plansee Composite Materials GmbH, D-86983 Lechbruck am See, Germany
(d) Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria
Ti1-xAlxN is a well-established protective coating system, which is used for various industrial applications due to its excellent mechanical and thermal properties. Especially, the thermal stability and age-hardening effect in the high temperature range 700 – 1000 °C are key-factors for its outstanding performance and versatility. Recent investigations suggest that the grain size has a major influence on the decomposition process and the attainable hardness increase of Ti1-xAlxN. Nevertheless, a detailed study on grain size induced effects of spinodal decomposition of Ti1-xAlxN is still missing.
Therefore, we have deposited differently structured Ti1-xAlxN coatings by reactive magnetron sputtering using powder metallurgical produced Ti0.50Al0.50 targets. Through a variation of the deposition conditions - temperature, base pressure, bias voltage, and target power - we are able to deposit Ti1-xAlxN coatings with different grain sizes, reaching from a very fine grained/amorphous-like structure up to a crystallite size of more than 150 nm. The morphology and structure were investigated using X-ray diffraction, electron microscopy (scanning and transmission), as well as atom probe tomography. Coatings having the largest grains exhibit hardness values in the range of 21 GPa compared to 32 GPa for the finer-grained coatings. These coatings are vacuum annealed at Ta = 700, 800, and 900 °C for ta = 1, 10, 100, and 1000 min. Increased diffusion pathways in the large grain-sized coatings lead to a retarded decomposition process. These coatings exhibit a hardness increase of about 8 GPa whereas the fine-grained counterparts only exhibit an increase in hardness by 3 GPa due to spinodal decomposition.
Based on our results we can conclude that the grain size has a pronounced effect on the decomposition kinetics of Ti1-xAlxN coatings as well as on the obtained hardness increase due to age hardening effects.
 


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