Structural and Mechanical Gradients in Nanostructured Thin Films

Jakub Zalesak

Research output: ThesisDoctoral Thesis

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Abstract

Despite the fact that the TixAl1-xN-based thin films have been one of the most frequently studied protective thin film material in last the 25 years, the understanding of their complex structure-property relationship is far from being complete. In particular, the presence of nano-scale structural and functional gradients as well as their influence on overall functional properties, had been for a long time a topic only hardly accessible due to a non-sufficient resolution of analytical techniques. The obtained experimental data frequently represented just average values, and contributions of individual microstructural features and gradients were difficult to resolve. The advancement of position sensitive analytical methods achieved in the last decade, however, allowed to acquire data with sufficient lateral resolution, and to combine them with local mechanical properties obtained using traditional nanoindentation techniques as well as modern in situ methods. The focus of this work is mainly on the application of advanced imaging and analytical methods of transmission electron microscopy, X-ray nano-beam diffraction, and in situ electron microscopy mechanical testing in physical vapor deposited TixAl1-xN thin films as well as a development and studying of new self-organized low pressure chemical vapor deposited TixAl1-xN thin films. The latter represent a new revolutionary material class with unique 3D self-assembled nanolamellar microstructure containing a meta-stable cubic AlNy , which does not exist otherwise in a bulk form at ambient conditions. The understanding of this fascinating self-assembly process represents a milestone in thin film technology. Three author contributions to the three studies of TixAl1-xN thin films presented in this thesis are: •A methodological approach for complex cross-sectional analysis and optimization of thin films was developed for a 2 μm thick compositionally-graded TixAl1-xN thin film. Spatially resolved methods for chemical, phase and residual stress analyzes were combined with cross-sectional nanoindentation and in situ TEM cantilever beam bending. This work has proven the possibility to resolve the influence of simultaneously occurring gradients of crystalline phases, microstructure, chemical composition and strains on thin film cross-sections as well as local mechanical properties. •Novel Al-rich TixAl1-xN chemical vapor deposited coatings with self-organized microstructure were studied. An optimization process, derived from the previous study, was applied on a mixed cubic-hexagonal self-organized Ti0.05Al0.95N coating in order to enhance its mechanical properties by a formation of a pure cubic phase. The resulting single-phase cubic Ti0.2Al0.8N coating exhibits hardness of 36 GPa and reduced modulus of 522 GPa. •In order to gain better understanding of the self-organization phenomenon in single-phase cubic LP-CVD TixAl1-xN coatings, hetero-epitaxial films were grown on an Al2O3 (0001) substrate. The films, with an overall x fraction of ∼ 0.8, were composed of alternating non-stoichiometric cubic Al-rich and Ti-rich nanolamellae with thicknesses of ∼ 11 and ∼ 1.5 nm, respectively. X-ray diffraction, electron microscopy and electron energy loss spectroscopy indicate that the nanolamellae coherency is primarily a result of an N deficiency in Ti-rich nanolamellae and an N excess in Al-rich nanolamellae, which induce a decrease and an increase in nanolamellae lattice parameters, as compared with the lattice parameters of stoichiometric rock-salt c-TiN and c-AlN, respectively.
Translated title of the contributionStrukturelle und mechanische Gradienten in nanostrukturierten Dünnschichten
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Keckes, Jozef, Assessor A (internal)
  • Mitterer, Christian, Assessor B (internal)
Publication statusPublished - 2017

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