Reactive Sputtering of Complex Multi-component Nitride Thin Films
Sammanfattning: The ever-increasing demand on improvement of protective nitride thin films has led to an expansion of the research field into multi-element based materials. The work in this thesis has focused on exploring new complex, multi-component nitride thin films based on three different material systems: Al-Ge-N, Hf-Nb-Ti-V-Zr-N and Al-Cr-Nb-Y-Zr-N. All films were synthesised by reactive dc magnetron sputtering and characterised with regard to structure and material properties, in particular the mechanical, optical and corrosion properties.The Al-Ge-O-N coatings exhibited amorphisation of the structure upon oxygen addition, via the formation of a crystalline (Al1-xGex)(N1-yOy) solid solution phase for low O contents. The mechanical properties were improved, and hardness values up to 29 GPa were achieved for low O and Ge concentrations, most likely due to nanocomposite hardening. The optical absorption edge was tuneable towards shorter and longer wavelengths with increasing the O and Ge content respectively. Annealing to 850°C showed indications of increased thermal stability for the quaternary Al-Ge-O-N films compared to the ternary Al-Ge-N films.Coatings in the Hf-Nb-Ti-V-Zr-N system were found to be highly crystalline featuring a single solid solution phase with NaCl-type structure for low Hf content, whereas an additional, tetragonally distorted, phase appeared for higher Hf contents. The mechanical properties, such as hardness and Young’s modulus increased with increasing Hf content, although the values were relatively low compared to those for transition metal nitrides in general.The Al-Cr-Nb-Y-Zr-N films also crystallised in the NaCl-type structure for the films with high nitrogen contents, i.e. between 46 and 51 at.%. However, partial elemental segregation was present, mainly for yttrium, both within the grains and in the column boundaries. XPS results suggested that yttrium was in a metallic state, while the remaining elements were present in a nitrided environment. The partial segregation could possibly explain the observed ductile behaviour of the nitride films. Electrochemical tests showed that the corrosion resistance increased with increased nitrogen content and the films performed in some cases better than a hyper-duplex stainless steel.This thesis demonstrates that solid solutions are formed for three relatively different nitride material systems when varying the composition. The solubilities of the solid solution phases were found to be limited as shown by amorphisation, partial elemental segregation or formation of a two-phase material. The limited solubility and the phase changes can be used to design the material properties.
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