Metastable cubic transition metal aluminium nitride and oxynitride coatings: theoretical phase stability and defect structure predictions and verification by industrial-scale growth experiments

Viac o knihe

This thesis explores the crystallite size-dependent metastable phase formation of nanocrystalline TiAlN, a key industrial coating material, through advanced material characterization and ab initio calculations. It predicts the chemical composition-dependent phase boundary between the cubic and wurzite phases of Ti1-xAlxN, defined by the critical crystallite size dcritical. The predictions align closely with experimental data from combinatorial vapor phase condensation, addressing the wide range of reported Al solubilities and reconciling discrepancies with density functional theory predictions. The study highlights the importance of considering surface energy contributions for accurate phase stability predictions. In the second part, Ti-Al-O-N coatings are synthesized using cathodic arc and high power pulsed magnetron sputtering. The impact of oxygen incorporation on lattice parameters and Young’s moduli is examined through X-ray diffraction and nanoindentation. As nitrogen is replaced by oxygen, a reduction in equilibrium volume is observed, with density functional theory calculations indicating metal vacancy formation for charge balancing. This leads to decreased elastic modulus due to both metal vacancy-induced elasticity reduction and the relatively weak Ti-O and Al-O bonds compared to metal nitride bonds. The final part investigates the effects of reactive cathodic arc evaporation of Ti-Al-O-N in an industrial system w