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ICMCTF - 2014
Helmut Riedl (H. Riedl)
Talk
"Influence of oxygen impurities on structural, mechanical properties and age hardening of Ti-Al-N"
H. Riedl1,*, A. Vlasova1, R. Rachbauer2, S. Kolozsvari3, J. Paulitsch1,4 and P. H. Mayrhofer1,4

1 Christian Doppler Laboratory for Application Oriented Coating Development at the Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria
2 Oerlikon Balzers Coating AG, FL-9496 Balzers, Principality of Liechtenstein
3 Plansee Composite Materials GmbH, D-86983 Lechbruck am See, Germany
4 Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria
Recent investigations showed that even small amounts of impurities, such as oxygen, affects the growth process, the crystal structure, and the grain size of ceramic-like hard coatings. Ti1-xAlxN is due to the excellent mechanical and thermal properties a well-established hard coating system, used for various industrial applications. We have used Ti1-xAlxN as a model system to study the influence of oxygen impurities on growth and film properties. By using Ti0.50Al0.50 targets with different oxygen contents (< 950, 950-2000, > 2000 ppm) and base pressures of either 10-5 mbar or 10-8 mbar, we are able to identify the major oxygen impurity source for reactively sputtered Ti1-xAlxN coatings. Furthermore, the coatings were prepared at 500 and 800 C and when using the target with the highest O-content we also varied the sputtering power for 2 selected deposition conditions. Consequently, 14 different Ti1-xAlxN coatings with a similar Al content of x~0.6 have been prepared.
The crystallite sizes of the coatings, which vary between 20 and 80 nm, are strongly determined by the O content as well as deposition temperature, as proven by x-ray diffraction, transmission electron microscopy, and atom probe tomography. Coatings prepared from the highest purity target (O < 950 ppm) exhibit hardness values between 29 and 34 GPa, depending on the substrate temperature or base pressure used. A much higher variation in hardness between 18 and 35 GPa is obtained when using the target with the highest O-content of > 2000 ppm.
But not only the as-deposited structure and properties of Ti1-xAlxN are strongly influenced by the oxygen impurities, also their age-hardening behaviour and hence thermal stability strongly depends on the purity of the target as well as the base pressure and deposition temperature used
 


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