Thin film coatings are used to improve the properties of components and products in such diverse areas as tool coatings, wear resistant biological coatings, miniature integrated electronics, micro-mechanical systems and coatings for optical devices. This thesis focuses on understanding the development of intrinsic stress and microstructure in coatings of the technologically important materials of aluminium nitride (AlN) and titanium vanadium nitride (TiVN) deposited by filtered cathodic arc deposition. Thin films of AlN are fabricated under a variety of substrate bias regimes and at different deposition rates. Constant substrate bias was found to have a significant effect on the stress and microstructure of AlN thin films. At low bias voltages, films form with low stress and no preferred orientation. At a bias voltage of -200 V, the films exhibited the highest compressive stress and contained crystals preferentially oriented with their c axis in the plane of the film. At the highest bias of -350 V, the film forms with low stress yet continue to contain crystallites with their c axis constrained to lie in the plane of the film. These microstructure changes with bias are explained in terms of an energy minimisation model. The application of a pulsed high voltage bias to a substrate was found to have a strong effect on the reduction of intrinsic stress within AlN thin films. A model has been formulated that predicts the stress in terms of the applied voltage and pulsing rate, in terms of treated volumes known as thermal spikes. The greater the bias voltage and the higher the pulse rate, the greater the reduction in intrinsic stress. At high pulsing and bias rates, a strong preference for the c axis to align perpendicular to the substrate is seen. This observation is explained by dynamical effects of the incident ions on the growing film, encouraging channelling and preferential sputtering. For the first time, the effect of the rate of growth on AlN films deposited with high voltage pulsed bias was investigated and found to significantly change the stress and microstructure. The formation of films with highly tensile stress, highly compressive stress and nano-composites of AlN films containing Al clusters were seen. These observations are explained in terms of four distinct growth regions. At low rates, surface diffusion and shadowing causes highly porous structures with tensile stress; increased rates produced Al rich films of low stress; increasing the growth rate further led to a dense AlN film under compressive stress and the highest rates produce dense, low stress, AlN due to increased levels of thermal annealing. Finally this thesis analyses the feasibility of forming ternary alloys of high quality TiVN thin films using a dual cathode filtered cathodic arc. The synthesised films show exceptional hardness (greater than either titanium nitride or vanadium nitride), excellent mixing of the three elements and interesting optical properties. An optimum concentration of 23% V content was found to give the highest stress and hardness.

<p>Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them.</p><p>This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material.</p><p>The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling.</p><p>Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings.</p><p>The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling.</p><p>Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.</p>

Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them. This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material. The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling. Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings. The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling. Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.

Advanced dispersants were discovered for the fabrication of homogeneous suspensions of multi-walled carbon nanotubes (MWCNT), graphene, and manganese dioxide (MnO2) in both ethanol and water. Thin films of MWCNT, graphene, MnO2, composite films of MWCNT-MnO2 and MWCNT-graphene were prepared using electrophoretic deposition (EPD) and electrolytic deposition (ELD) methods. The mechanisms of dispersion and deposition were investigated. Cathodic EPD was achieved for MWCNT and graphene using positively charged dispersants. Co-deposition of MWCNT and MnO¬2 was performed using a co-dispersant, which dispersed both MWCNT and MnO2 in ethanol. Composite films were tested for electrochemical supercapacitor (ES) purposes. Pulse ELD was used to deposit porous MnO2 coatings on Ni foam substrates from KMnO4 solutions. Cathodic deposition offered advantages, compared to anodic deposition, because the problems, related to anodic dissolution of metallic substrates, can be avoided. The pulse ON/OFF times had significant influence on the morphology and structure of MnO2 films, which further determined the capacitive performance. The influence of MnO2 film thickness on specific capacitance was investigated. Porous and conductive vanadium nitride (VN) was synthesized using melamine as a reducing agent. To further improve film conductivity and specific surface area, MWCNT were incorporated into VN matrix during synthesis. VN-MWCNT composite electrodes and VN-MWCNT/MnO2-MWCNT asymmetric supercapacitor cells were fabricated and tested. The electrodes and cells exhibited excellent electrochemical capacitive performance with good cyclic stability. The asymmetric supercapacitor device showed a voltage window up to 1.8 V, which was the combination of voltage window of VN-MWCNT (-0.9 V--0 V) and MnO2-MWCNT (0 V--0.9 V). Polypyrrole (PPy) coated MWCNT were synthesized in ethanol with ammonium peroxydisulfate solution as an oxidant. The effects of dopants to PPy morphology and conductivity was investigated. Dopants with electrochemical active groups were selected for the synthesis of PPy nanoparticles, where dopants also contributed to the capacitance of the polymer based materials. Both PPy-MWCNT/PPY-MWCNT symmetric supercapacitors and VN-MWCNT/PPY-MWCNT asymmetric supercapacitors were fabricated and tested, where the voltage windows were 0.9 V for the former and 1.3 V for the later. The increase of voltage window was ascribed to the asymmetric structure and negative voltage window of VN-MWCNT composite. / Thesis / Doctor of Philosophy (PhD)