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A Vlasova:
"Influence of Oxygen Impurities on the Structure and Mechanical Properties of Ti-Al-N Coatings";
Supervisor: H. Riedl, P.H. Mayrhofer; E308, Gr. Mayrhofer, 2016; final examination: 2016-01-21.

Protective thin films for highly functional tools are very important for state of the art manufacturing technologies. A well-established material system for protective coatings for cutting and milling tools is Ti1-xAlxN which exhibits outstanding mechanical and thermal properties. The properties of the deposited films are influenced by morphological characteristics, such as the concentration of growth defects, grain size, crystal structure, metastable phases, incorporated impurities and intrinsic stresses. During deposition the incorporation of impurities into thin films cannot be completely avoided, which strongly influences the growth morphology as well as the structure, and in a further consequence the mechanical properties of deposited films.
In this thesis the influence of oxygen impurities on the film morphology and the resulting properties of Ti1-xAlxN coatings is studied. For this purpose Ti1-xAlxN thin films are deposited using an unbalanced laboratory scaled magnetron sputtering system. The oxygen impurity contents within the coatings are controlled by using targets with three different impurity levels as well as by varying the deposition conditions (base pressure and deposition temperature). The chemical compositions of all Ti1-xAlxN thin films are analyzed by elastic recoil detection analysis (ERDA), as it gives an opportunity precisely to determine the oxygen impurity concentration within the coatings. To investigate the structure and morphology of the coatings X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) are used. Thermal stability is investigated by vacuum annealing treatments of all deposited coatings. The mechanical properties of as-deposited and annealed coatings are analyzed by nanoindentation.
The results of this thesis show that the oxygen impurity level within the Ti1-xAlxN coatings influences their structure and mechanical properties. An increase of the oxygen impurity level leads to a change of the preferred growth orientation from random to 111-oriented structures accompanied by increasing grain sizes, and therefore, also influencing the hardness. Concerning the thermal stability, all coatings maintain their cubic structure up to an annealing temperature of Ta ~ 1000 °C with an increase of hardness in average of 10 to 20 % compared to the as-deposited state due to spinodal decomposition.
The obtained results underline that a thorough control of the deposition parameters and target qualities is essential for the production of high quality coatings.

Project Head Paul Heinz Mayrhofer:
Christian Doppler Labors für anwendungsorientierte Schichtentwicklung