In the thesis, four DLC coatings were selected: two hydrogen free DLC coatings (GCr and GCrSi) and two hydrogenated DLC coatings (DCr and DCrSi), which are the two main groups in the DLC family. Three annealing conditions (argon annealing, air annealing and HIPping/high pressure argon annealing) were designed to evaluate the stability and performance of the four DLC coatings. The microstructure of the DLC coatings was characterised by Raman spectrum, GIXRD, SEM/Due-beam SEM, EDX and TEM. Scratch tests were performed to assess the adhesion of the coatings. Both the mechanical and tribological properties of the DLC coatings were evaluated including nanohardness, coefficient of friction and wear factor. The influence of high pressure and oxidation was discussed, and the comparison of four different coatings was made.

Diamond-Like Carbon (DLC) coatings are thin protective surface coatings used to reduce friction and minimise wear in a wide range of applications. The focus of this work is the use of DLC coatings within Rolls-Royce’s pressurised water reactors. A strong understanding of material behaviour in this environment is compulsory due to the stringent safety requirements of the nuclear industry. Wear testing of a range of commercial DLC coatings against steel in water, and the dependence of the tribology on normal load, sliding distance, and environmental species, was examined. Wear depth was observed to increase with normal load, and increase non-linearly with sliding distance. Uniquely, it was suggested that the tribology of a DLC coating in water was controlled by the velocity accommodation mode (VAM) of the transfer layer. When interfacial sliding was the dominant VAM, the carbonaceous transfer layer was present at all times, and a low specific wear rate was observed. When shear and recirculation of debris was the dominant VAM, the carbonaceous transfer layer initially present was replaced by iron oxide species, and a high specific wear rate was observed as a result of a three-body mechanism involving hematite. Two individual wear models were developed to predict the wear depth of a DLC coating sliding against steel in water. Each model represents a novel extension to the current literature regarding the modelling of wear. Firstly, an analytical differential equation was derived to predict the wear depth of a ball and a flat surface, in relation to any phenomenological law for wear volume. Secondly, a unique formulation of an incremental wear model for an arbitrary geometry was developed for a DLC coating which included the growth of a transfer layer. An efficient methodology was presented to allow fast integration of the equations whilst damping numerical instabilities. A comparison between the analytic and computational wear models showed a strong agreement in the model predictions, with a comparative error of less than 5%.

There is an increasing global demand to extend the life span of down-hole drilling tools in order to improve operation effectiveness and efficiency of oil and gas production. Laser cladding of tungsten carbide/Ni-based alloy metal matrix composite (MMC) coatings is currently being utilised for this purpose. However, the effect of tungsten carbide dissolution on the corrosion performance of the MMC coatings has not been completely understood. In this work, a study was carried out in which laser cladding of a stainless steel substrate using (i) Inconel 625 wire and (ii) tungsten carbide powder (Spherotene)/Inconel 625 wire was undertaken. This work was performed using a fibre laser system and has examined the process characteristics, the microstructure and the corrosion performance of the clad layers. Process characteristics studies were carried out by visual observation of the cladding process within a process window (laser power: 1-1.8 kW, traverse speed: 100-300 mm min-1, wire feed rate: 400-1000 mm min-1, powder feed rate: 25 g min-1). The microstructures were investigated using a combination of optical microscopy, scanning electron microscopy (with energy dispersive X-ray analysis) and X-ray diffraction. The volume fraction of tungsten carbide retained in the composite coatings was determined using image processing software. Corrosion performance was assessed using electrochemical corrosion testing in de-aerated 3.5 wt.% NaCl solution. Well bonded, minimally diluted, pore- and crack-free Inconel 625 wire and Spherotene (WC/W2C) powder/Inconel 625 wire composite coatings were successfully deposited. Cladding process characteristics were categorised into wire dripping, smooth wire deposition and wire stubbing within the range of parameters used in this work. Process maps which predict the characteristic of Inconel 625 wire and Spherotene (WC/W2C)/Inconel 625 wire fibre laser cladding at varying cladding conditions within the process window were developed. The volume fraction of tungsten carbide (WC/W2C) retained in the composite coatings was found to decrease with increasing laser power, traverse speed and wire feed rate. Tungsten carbide dissolution was found to result in the precipitation of intermetallic compounds including M6C and M23C6 in the γ-Ni matrix, which is rich in W and C. The increase in tungsten carbide dissolution was also found to increase the propensity for corrosion in the MMC coatings compared to the Inconel 625 wire coatings. As a result, the corrosion performance of the tungsten carbide/Ni based alloy MMC coatings can be improved by reducing the level of tungsten carbide dissolution through process control.

Electroplated zinc finishes have been widely used in the packaging of electronic products for many years as a result of their excellent corrosion resistance and relatively low cost. However, the spontaneous formation of whiskers on zinc electroplated components, which are capable of resulting in electrical shorting or other damaging effects, can be highly problematic for the reliability of long life electrical and electronic equipment. To date, most research has focused on tin whiskers and much less attention has been paid to zinc whisker research. A number of mechanisms to explain zinc whisker growth have been proposed, but none of them are widely accepted and some are in conflict with each other. This study has investigated the mechanism for whisker growth from three commercial zinc electroplated coatings on mild steel substrates. Firstly, whisker growth from an alkaline cyanide-free zinc electrodeposit was studied. A reduction in deposition current density (from 50 to 5 mA/cm2) and an increase in deposit thickness (from 2 to 15 μm) both contributed to reduced whisker growth. In terms of the mechanisms of whisker growth, it was observed that the presence of spherical raised surface features (nodules) with cavities beneath, promoted whisker growth by markedly shortening the incubation time from ~ 5 months to ~ 4 weeks. More importantly, the time dependent recrystallisation of the as-deposited columnar structure is closely associated with whisker growth from both nodules and planar regions of the deposit. The formation of Fe-Zn intermetallic compounds (IMCs) was not observed at either the Fe/Zn interface or within the electroplated coatings and does not appear to be associated with Zn whisker growth. Whisker growth from an acid chloride zinc electroplated coating and a Zn-Ni alloy electroplated coating were also investigated. These two coatings were immune to whisker growth after 18 months of storage at room temperature, regardless of deposition current density, deposit thickness and substrate surface modification. Finally, the effect of potential mitigation strategies on whisker growth was evaluated. Exposure to elevated temperatures (50 to 150°C) for 24 hours promoted whisker growth by reducing the incubation time for whiskers to first appear from less than 4 weeks to less than 10 days, whilst whisker growth was significantly retarded when samples were subjected to a short period of thermal treatment (50 to 150°C) for 0.5 hour. More importantly, for a short period of thermal treatment, whisker mitigation became increasingly effective as the treatment temperature was raised. In addition, the formation of a trivalent chromium passive coating on the alkaline cyanide-free zinc electrodeposits immediately after deposition was not an effective mitigation method to retard whisker growth.

Yttria stabilized zirconia (YSZ) coatings were produced from a YSZ suspension in acetylacetone (ACAC) using electrophoretic deposition (EPD) and then consolidated via the natural drying and isothermal sintering with the constraint of the metal substrates. Before EPD, the operational pH of the suspension was adjusted by addition of acetic acid or organic bases. The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure both for a mono-sized system and micro-nano binary systems. The constrained drying process of the deposits was examined via the measurement of the critical cracking thickness (CCT). The sinterability of coatings was evaluated by micro-hardness and microstructure. For a mono-sized (0.26μm) suspension, results showed that the zeta potential had a high positive value on both sides of the isoelectric point (IEP). This probably resulted from the adsorption of base molecules triethanolamine (TEA), detected by fourier transform infrared spectroscopy. Three alkalis with different molecular structure were compared and the effect of their molecule length on the interparticle repulsion was discussed. Accordingly, the double layer thickness of the particles can be estimated. Based on this, particle interactions were estimated for different pH suspensions. The reduced particle coagulation increased the packing density of the EPD coatings from 38 % at pH 7.4 to 53 % at pH 8.4. Therefore, subsequent sintering of coatings was promoted. After sintering at 1200 °C, coatings made in pH 8.4 suspensions obtained a much higher hardness and had fewer big pores than coatings fabricated in pH 7.4 suspensions. The CCT of the latter is slightly higher than the former which might be ascribed to its particle network structure. In a binary suspension composed of the coarse (1μm) and fine (with average size of 100 nm or 10 nm, content varied in 0-30 wt. % to the powder mixture) YSZ powders, interactions between different species can be tuned by the zeta potential of individual component. Binary particles can be well dispersed at pH 4 when both of the coarse and fine powders reached their highest zeta potentials. Heterocoagulation occurred between them to form a haloing structure with fine powders covered on the coarse particle surfaces when they exhibited zeta potentials of the opposite sign at pH 8.6. Particle interactions were estimated and the microstructures of the binary coatings were examined to discuss how the different fine particle sizes influenced the particle packing after EPD. At pH 4, there existed a “stability window” for the 10 nm fines at 10 wt. % whereas no noticeable the border of the window can be observed for 100 nm fines within the measuring range. 10 nm and 100 nm fine powders gave similar overall densities of binary EPD coatings which were independent of the fine powder content. For heterocoagulation coatings made at pH 8.6, although the adsorption of fine particles reduce the agglomeration of coarse powder, the low zeta potential of the halos led to a loose structure of the “skeleton” ( the packing of the coarse powder) in the final binary coatings. 10 nm fine powders was observed to give a higher CCT and denser particle packing than 100 nm fine powders especially in a pre-saturated heterocoagulated binary coatings at 20 wt. % fine powder content. In order to further improve the sintering of the EPD coatings at low temperature sintering, a layer of CuO was applied on the coarse powder surface. With the addition of 30 wt. % fine powders, the hardness of EPD coatings after sintering 2 hours at 1150°C increased from 6 to 61 Vickers. With the presence of CuO, the hardness values were enhanced by 2.5-4.25 times. The density measurements indicated that the CuO layer not only served as a sintering aid, the CuO layer also helped with the binary particle packing particularly in the heterocoagulation condition because of the stronger particle interactions between the fine powders and CuO modified coarse powders. It seems that CuO had no significant impact on the cracking resistance of the binary coatings during drying, however t-m phase transformation was observed during sintering possibly due to the liquid phase induce by CuO.

There are a number of “smart” coatings that can be applied to glass. These include self-cleaning coatings based on titanium dioxide, and low-E coatings based on fluorine-doped tin oxide. Products are often more desirable with colour options such as Pilkington Activ BlueTM. There are currently no alternatives to body tinting glass to achieve colour, which is a time-consuming and expensive procedure. The work in this project details a number of coloured coatings via the AACVD or combustion processing of metal nitrate/urea precursors.

Conventional tin-lead solder alloys have been widely used in electronics interconnection owing to their properties such as low melting temperature, good ductility and excellent wettability on copper and other substrates. However, due to the worldwide legislation addressing the concern over the toxicity of lead, the usage of lead-containing solders has been phased out, thus stimulating substantial efforts on lead-free alternatives, amongst which eutectic Sn-Ag and Sn-Cu, and particularly Sn-Ag-Cu alloys, are promising candidates as recommended by international parties. To meet the increasing demands of advanced electronic products, high levels of integration of electronic devices are being developed and employed, which is leading to a reduction in package size, but with more and more input/output connections. Flip chip technology is therefore seen as a promising technique for chip interconnection compared with wire bonding, enabling higher density, better heat dissipation and a smaller footprint. This thesis is intended to investigate lead-free (eutectic Sn-Ag, Sn-Cu and Sn-Ag-Cu) wafer level solder bumping through electrodeposition for flip chip interconnection, as well as electroplating lead-free solderable finishes on electronic components. The existing knowledge gap in the electrochemical processes as well as the fundamental understanding of the resultant tin-based lead-free alloys electrodeposits are also addressed. For the electrodeposition of the Sn-Cu solder alloys, a methanesulphonate based electrolyte was established, from which near-eutectic Sn-Cu alloys were achieved over a relatively wide process window of current density. The effects of methanesulphonic acid, thiourea and OPPE (iso-octyl phenoxy polyethoxy ethanol) as additives were investigated respectively by cathodic potentiodynamic polarisation curves, which illustrated the resultant electrochemical changes to the electrolyte. Phase identification by X-ray diffraction showed the electrodeposits had a biphasic structure (β-Sn and Cu6Sn5). Microstructures of the Sn-Cu electrodeposits were comprehensively characterised, which revealed a compact and crystalline surface morphology under the effects of additives, with cross-sectional observations showing a uniform distribution of Cu6Sn5 particles predominantly along β-Sn grain boundaries. The electrodeposition of Sn-Ag solder alloys was explored in another pyrophosphate based system, which was further extended to the application for Sn-Ag-Cu solder alloys. Cathodic potentiodynamic polarisation demonstrated the deposition of noble metals, Ag or Ag-Cu, commenced before the deposition potential of tin was reached. The co-deposition of Sn-Ag or Sn-Ag-Cu alloy was achieved with the noble metals electrodepositing at their limiting current densities. The synergetic effects of polyethylene glycol (PEG) 600 and formaldehyde, dependent on reaching the cathodic potential required, helped to achieve a bright surface, which consisted of fine tin grains (~200 nm) and uniformly distributed Ag3Sn particles for Sn-Ag alloys and Ag3Sn and Cu6Sn5 for Sn-Ag-Cu alloys, as characterised by microstructural observations. Near-eutectic Sn-Ag and Sn-Ag-Cu alloys were realised as confirmed by compositional analysis and thermal measurements. Near-eutectic lead-free solder bumps of 25 μm in diameter and 50 μm in pitch, consisting of Sn-Ag, Sn-Cu or Sn-Ag-Cu solder alloys depending on the process and electrolyte employed, were demonstrated on wafers through the electrolytic systems developed. Lead-free solder bumps were further characterised by material analytical techniques to justify the feasibility of the processes developed for lead-free wafer level solder bumping.

The Physical Vapour Deposition (PVD) magnetron sputtering process is one of the widely used techniques for depositing thin film coatings on substrates for various applications such as integrated circuit fabrication, decorative coatings, and hard coatings for tooling. In the area of coatings on cutting tools, tool life can be improved drastically with the application of hard coatings. Application of coatings on cutting tools for various machining techniques, such as continuous and interrupted cutting, requires different coating characteristics, these being highly dependent on the process parameters under which they were formed. To efficiently optimise and customise the deposited coating characteristics, PVD process modelling using RSM methodology was proposed. The aim of this research is to develop a PVD magnetron sputtering process model which can predict the relationship between the process input parameters and resultant coating characteristics and performance. Response Surface Methodology (RSM) was used, this being one of the most practical and cost effective techniques to develop a process model. Even though RSM has been used for the optimisation of the sputtering process, published RSM modelling work on the application of hard coating process on cutting tool is lacking. This research investigated the deposition of TiAlN coatings onto tungsten carbide cutting tool inserts using PVD magnetron sputtering process. The input parameters evaluated were substrate temperature, substrate bias voltage, and sputtering power; the out put responses being coating hardness, coating roughness, and flank wear (coating performance). In addition to that, coating microstructures were investigated to explain the behaviour of the developed model. Coating microstructural phenomena assessed were; crystallite grain size, XRD peak intensity ratio I111/I200 and atomic number percentage ratio of Al/Ti. Design Expert 7.0.3 software was used for the RSM analysis. Three process models (hardness, roughness, performance) were successfully developed and validated. The modelling validation runs were within the 90% prediction interval of the developed models and their residual errors compared to the predicted values were less than 10%. The models were also qualitatively validated by justifying the behaviour of the output responses (hardness, roughness, and flank wear) and microstructures (Al/Ti ratio, crystallographic peak ratio I111/1200, and grain size) with respect to the variation of the input variables based on the published work by researchers and practitioners in this field. The significant parameters that influenced the coating hardness, roughness, and performance (flank wear) were also identified. Coating hardness was influenced by the substrate bias voltage, sputtering power, and substrate temperature; coating roughness was influenced by sputtering power and substrate bias; and coating performance was influenced by substrate bias. The analysis also discovered that there was a significant interaction between the substrate temperature and the sputtering power which significantly influenced coating hardness, roughness, and performance; this interaction phenomenon has not been reported in previously published literature. The correlation study between coating characteristics, microstructures and the coating performance (flank wear) suggested that the coating performance correlated most significantly to the coating hardness with Pearson coefficient of determination value (R2) of 0.7311. The study also suggested some correlation between coating performance with atomic percentage ratio of Al/Ti and grain size with R2 value of 0.4762 and 0.4109 respectively.

Traditionally, lead-based bearing overlays dominate the commercial automotive market and it has been proven that an excellent combination of properties can be attained through their use. However, lead is a toxic metal and a cumulative poison in humans. According to the European Union End-of-Life Vehicle (ELV) Directive proposed in 1997, vehicles that registered in'all the member states after 1st July 2003 should contain no lead, mercury, cadmium and hexavalent chromium. In this study, a new sulphate-gluconate electrolyte was used to produce multilayer SnCo coatings, aimed at a lead-free overlay for future market use. Tin-cobalt compositionally modulated alloy (CMA) coatings produced from sulphategluconate electrolytes have been previously examined as a potential replacement for lead-free bearing overlays [1]. However, some obstacles may exist which limit their potential use on an industrial scale. For example, long electroplating times are required to produce a thick coating which is very undesirable from an industrial viewpoint, and also the possible elemental interdiffusion occurring in the coating system under engine operating temperatures could rapidly deteriorate the coating properties. In addition, there is an increasing demand from automotive industry to further improve bearing overlay properties, for example for high performance and high compression ratio engines.

Electrophoretic deposition (EPD) has been used to produce the yttria-stabilized zirconia (YSZ) coatings on metal substrates. Sintering of YSZ with and without doping has been carried out at 1150 °C for 2hrs. The properties of these coatings have been examined in light of thermal barrier applications. For EPD, the green density increases with an initial increase in the HCl concentration and the EPD time. This suggests that particle packing was influenced by a time dependent re-arrangement, in addition to the initial suspension dispersion state. The green density peaks at a electrical conductivity of around 10×10-4 S/m achieved by an 0.5 mM HCl addition for the 20 g/l suspensions with the EPD time of around 8 ~10 minute. For sintered coatings, the HCl concentration had a marked effect on the neck size to grain size ratio of the 8 mol% yttria-stabilized zirconia (8YSZ) coatings. The presence of ZrCl4 and ZrOCl2, and a high concentration of oxygen vacancies at the grain boundaries are believed to promote neck growth in the early stage of sintering at 1150 °C. During sintering of 3 mol% and 8 mol% yttria-stabilized zirconia (3YSZ and 8YSZ) at 1150 ºC for 2hrs, the densification rate substantially increased with a small amount of Fe2O3 addition (0.5 mol%) to the 3YSZ/8YSZ deposits. A more pronounced graingrowth was present in the Fe2O3 doped 8YSZ deposits. The increased Zr4+ diffusion coefficient is mainly responsible to the rapid densification rate of the Fe2O3 doped 3YSZ/8YSZ deposits. A small grain growth observed in the Fe2O3 doped 3YSZ deposits is attributed to the Fe3+ segregation at grain boundary. A small amount of CeO2 doping was found to substantially inhibit the densification rate of the doped 3YSZ deposits with a minor grain growth. Fe2O3 doping reduced the thermal conductivities of 3YSZ/8YSZ. It is found that Rayleigh-type phonon scattering due to the mass difference alone is inadequate to explain the thermal conductivity of Fe2O3 doped YSZ systems. The lattice strain effects due to the ionic radius difference could more effectively reduce thermal conductivity of the Fe2O3-doped 3YSZ. A decrease in the growth rate of the TGO scale with the increasing Fe2O3 additions was observed for the oxidized FeCrAlY metal substrates with the Fe2O3-doped 3YSZ coating, which was found to be attributed to the early formation of the stable and dense α-Al2O3 phase due to the presence of Fe3+ ions.