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Plastic injection moulding is a commonly used process for the production of low-cost plastic parts in large numbers but for high-end products this process is hard to handle and expensive. The quality of the moulded parts is directly dependent on the surface quality of the mould Therefore, typically ultra-precision techniques like diamond turning or milling with a subsequent polishing, are used to generate a high quality surface finish. Ultra-precision techniques cannot process steel surfaces, thus nickel plating on the surface is required. The coating of the surface is an additional process step which also leads to lifetime issues, such as peeling or micro cracks. That is why many mould makers want to avoid this step as well as expensive ultra-precision techniques. The target of this work was to reduce the process chain for mould manufacturing from 5 to 3 process steps. Expensive and difficult process steps like diamond turning and manual polishing should be replaced by robot polishing of the steel mould The last process step before moulding is manual polishing. This step requires skilled experts and is velY time-consuming. These experienced specialists are very rare and few young people want to pursue this profession. Another big problem is the medical aspect; the manual polishing process requires a lot of physical strength and therefore is really exhausting for joints like elbow and shoulder. For these reasons manual polishing should be substituted by automated robot polishing. Existing processes have been further developed and extended by new processes. The goal was a stable, easy to handle robot polishing process. The Development

A series of high temperature and oxidation resistant, nanoscale, multilayer PVD, hard coatings have been developed through combine DC Unbalanced Magnetron (UBM) and High Power Impulse Magnetron Sputtering (HIPIMS) deposition technologies. The properties of the coatings lend themselves to the application of protecting cutting tools exposed to harsh environment such as the dry, high-speed machining of abrasive materials. This thesis discusses the literature supporting the project and pays tribute to the development of coatings that formed the foundation for the CrAlYBCN/AlSiCN coating series. Plasma diagnostics optimised the process conditions for deposition; a highly ionised metal rich plasma was generated to investigate the effect of process conditions during the pretreatment step. It was found that metal ion implantation into the substrate was successful and that ramping the cathode charge had little effect of the sputter rate of the substrate. Ion etching removed loosely bound surface grain to improve adhesion. A series of coatings were developed that were deposited at different levels of target poisoning, in an attempt to improve coating properties by process control and stoichiometry. Superhard coatings able to withstand temperatures of over 800 °C were produced. The coatings were subjected to a series of mechanical and thermal testing using pin on disk, microhardness, scratch test, Rockwell indentation, isothermal heat treatment and thermogravimetric analysis. Mechanisms of wear and oxidation process have been proposed based on the evidence given. Through coating development two coatings were indicated as having the desired chemical, thermal and mechanical properties suitable for cutting tests. The coating that was deposited at higher bias improved the tool lifetime by 5 times.

A detailed study has been made of the atmospheric pressure chemical vapour deposition (CVD) of aluminium oxide (Al2O3) coatings on powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts. To facilitate this, a laboratory-scale CVD reactor was initially designed and purpose-built. The literature on the effect of process parameters on Al203 coatings chemically vapour deposited on cemented carbide substrates was comprehensively surveyed. With reference to deposition conditions quoted in this literature, a series of trial Al203 coating runs were then performed using uncoated and TiN, TiC and Ti(C1N) precoated PM HSS inserts. Concurrently, modifications to the laboratory-scale CVD reactor were made. Eventually, deposition conditions were established under which a preliminary a Al203 coating could be deposited on the PM HSS inserts and, in the case of the Ti(C1N) precoated inserts only, substantially retained during the obligatory post-coating HSS substrate heat treatment. The effect of the absence/presence and type of precoating on the CVD of AI203 coatings on the PM HSS inserts are discussed. Subsequent coating runs were carried out only on Ti(C1N) precoated inserts. The characteristics of the preliminary AlP, coating on the Ti(C1N) precoated PM HSS inserts were determined, both before and after the obligatory HSS substrate heat treatment, using an established characterisation procedure. This involved the following techniques: X-ray diffraction, Auger electron spectroscopy, optical microscopy, fractography, scanning electron microscopy, microhardness testing, profilometry and scratch-adhesion testing. Although many of the characteristics of the preliminary AI20, coating were found to be inferior to those presented in the literature, they were also established to be essentially unaffected by the post-coating HSS substrate heat treatment. To im prove upon the preliminary Al203 coating, the effect of two of the most important CVD process parameters quoted in the literature; C02JH 2 mole ratio and Alel3 concentration, on the characteristics of Al20, coatings chemically vapour deposited on the Ti(C1N) precoated PM HSS inserts was investigated. Both parameters were found to have a significant effect on Al203 coating characteristics. The reasons for this are discussed in detail.

The small scale, short duration and hostile environment for instrumentation presented by cold spray coating makes experimental observations challenging, and therefore requires computational models capable of capturing the splat formation process. Current coating models are dominated by the Finite Element Method (FEM); whilst this has lead to significant improvements in understanding, the method is limited due to the reliance on a mesh coupled with the significant strains and strain rates involved. Eulerian methods have also been applied but retrieval of material histories and accurate interface tracking remains challenging. The Smoothed Particle Hydrodynamics (SPH) method is a meshless method that combines the advantages of FEM and Eulerian approaches. The current work extends the work of applying SPH to solid mechanics with heat conduction, improved tensile stability corrections and a novel zero impedance boundary. Solver performance is increased with the application of the multi-threading capabilities of the C++ 11 standard. The development of the SPH solver is described, validated and benchmarked against known analytical and experimental test cases. An in-depth investigation of parameters affecting splat morphologies is performed. Finally, a model of a coating formation process involoving multiple feedstock impact events is described and analysed in order to demonstrate the capabilities of the newly developed solver.

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Aluminium bronze alloys (Cu-Al-Fe) with Al > 14 wt. % are known to have high wear resistance and low friction coefficient against ferrous metals thus making it an ideal material for forming dies application. However, the use of these alloys has been restricted by the high cooling rate required to prevent embrittlement of the alloy during production. The plasma transferred arc technique (PTA) is an attractive production technique that offers the required high cooling rate, however the resulting microstructure is strongly dependent on the composition change induced during deposition. Therefore to optimise the microstructure for application such as forming dies, thorough understanding of the effects of PTA induced composition change on the microstructure, wear and corrosion resistance properties are required. The composition change induced by PTA involves primarily an increase in Fe. Therefore, in the present research four aluminium bronze coatings with 9, 20, 27 and 35 wt. % Fe were produced from a gas atomized Cu-Al-Fe powder by deposition on to an E.N. 10503 steel substrate by PTA. Microstructure characterisation was carried out using complementary techniques involving SEM, EDS, XRD, EBSD and depth-sensing nano-indentation on etched and electro-polished specimen. The results show that Fe content above 9 wt. % leads to a phase change from the Cu3Al martensitic β1' to solid solution (Cu) phase. This is also accompanied by an increase in size of the Fe3Al intermetallic κ1 phase. The redistribution of Al solute during cooling was identified as the main factor for the observed phase change. These microstructure changes lead to a hardness increase from 4.9 GPa in the coating with 9 wt. % Fe to 5.6 GPa in the coating with 35 wt. % Fe, however hardness mapping using depth-sensing nano-indentation shows that in the high Fe content coating, the hardness distribution is not uniform. This is due to the large volume fraction of the intermetallic κ1 phase which has high hardness of ~7 GPa. The wear resistance of the coating was found to be strongly influenced by the Cu-rich matrix phase. In the coatings with 20, 27 and 35 wt.% Fe, delamination and abrasive wear are the dominant wear mechanisms. SEM observations show that pile-up of slip at the hard intermetallic phase leads to the formation of surface cracks. Coalescence of these cracks coupled with the adhesion between the coating and the ferrous counter material were found to be responsible for promoting delamination wear, which results in high wear rate. The coating with 9 wt.% Fe has the lowest specific wear rates of 2.11-2.87 x 10-4 mm3/Nm against AISI 316, 420 and 440 stainless steel. This is significantly lower than the specific wear rates of 5.95-15.36 x 10-4 mm3/Nm measured for the currently used AISI D2 tool steels at the same condition. This is due to the uniform hardness and retention of the martensitic β1' phase. The effects of PTA induced microstructure change on the corrosion resistance were investigated by electrochemical and immersion corrosion tests in an aerated 3.5 % NaCI solution. The results show that the corrosion resistance of the coating is strongly dependent on complete formation of Al2O3 protective layer. The Al content in the coating is a critical factor in the formation of the protective layer. In the coating with high Fe content where limited Al solutes are available, high corrosion rates of 300-400 x 10-3 mm per year were observed. The 9 wt.% coating which contains the highest Al solute, the lowest corrosion rate of 22.5 x 10-3 mm per year was measured. This corrosion rate is comparable to the more expensive and highly alloyed nickel aluminium bronze. Based on the results obtained in the present research, the coating with a martensitic β1' phase and submicron size intermetallic κ1 phase has the highest wear and corrosion resistance. Such a structure can be achieved by controlling the PTA parameters to minimize the composition change promoted by melting of the steel substrate during deposition. The results from the present research also highlight the importance of interface properties, which have been shown to have a significant influence on properties such as adhesion, wear and corrosion. As more composite materials are utilised, further understanding of the microstructure and properties near the interfaces between materials becomes ever more important. It is hoped that the methodology and results presented in this thesis will provide the initial groundwork for future experimental and modelling work on multiphase material.

Electrodeposition on aluminium alloy substrates often is often difficult in producing a coating with good adhesion when compared to other metals. This is due to the rapid formation of oxide layers on the substrate’s surface when exposed to air and water, preventing metallic bonds from forming between the nickel coating and the aluminium alloy substrate which in turn resulting in poor adhesion. Adhesion of the coating on the substrate influences the quality of the coating. To overcome this problem, a series of critical surface pre-treatment procedures are required for a successful electrodeposition process with a strong coating adhesion. The pre-treatment process consists of mechanical grinding and polishing, alkaline and acidic cleaning, zincating and activation process. This study focuses on the zincating process to obtain a strong adherence coating on the substrate. An aim of this study was to replace the complex double zincating process. To this end, modification has been made to a conventional single zincating process, as the process results in a non-homogenous deposition of zinc particles on the substrate which leads to a poor adhesion of the coating. The modified process, for which the duration of the single zincating process was extended from 1 to 20 minutes, was based on the electrochemistry measurements of aluminium alloy 7075 substrate in the zincatingsolution. For comparison, nickel coatings prepared using a double zincating process at 60/10, 60/20, 60/30, 60/40 and 60/50 seconds were also produced in this study. By replacing the double zincating with a modified single zincating process, two pre- treatment steps of double zincating process will be eliminated. Thus, the waste disposal problem in terms of the chemical used in the zincating solution is reduced. In addition, copper activation was applied before the single zincating process in order to overcome the high dissolution of the substrate in the zincating solution. The surface pre-treated samples were characterized after alkaline cleaning, acid cleaning, zincating process and copper activation at various immersion durations by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and atomic force microscopy (AFM). The modified single zincated samples were found to contain larger zinc particles, as compared to the conventional single and double zincated samples. The modified single zincating process also showed an increasing trend in the nucleation density and size of zinc particles with time. A gradual decrease in the surface roughness values with the extension of the modified single zincating duration was also observed. Then, the influence of multiple zincating processes (conventional and modified single zincating with and without copper activation, and double zincating) at various durations on the coating adhesion was investigated using scratch adhesion test. Scratch failure modes were analysed using acoustic emission signals, frictional force, and microscopy observation. The conventional single zincating and double zincating processes resulted in poor adhesion of the nickel coatings to the substrate, as both the cohesive and adhesion failures occurred during the scratch test. The adhesion of the coating to the substrate was improved by extending the single zincating duration from 1 to 5, 10, 15 and 20 minutes, with only cohesive failure found for the samples. This result was supported by the number of acoustic emission activity (NAE) events recorded during the test, which showed the highest NAE at about 130 for the sample produced from the conventional single zincating process. An increase in the zincating duration to 5 minutes resulted in a drastic reduction of the NAE to 30. The similar adhesion behaviour was also observed on modified single zincated samples with copper activation. The corrosion tests were carried out by immersing the coatings in a 3.5 wt. % NaCl solution at room temperature. It was found that a modified single zincating process at a longer duration provided a significant enhancement of corrosion resistance as compared to the conventional single zincating process, due to the increase in corrosion potential and decrease in corrosion current density of the conventional single zincated sample. These much improved performance of coating adhesion and corrosion resistance maybe explained by homogenous distribution of zinc particles and good coverage of the zinc particles on the aluminium alloy substrate.

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The current work looks at the challenges of developing a computational solution for the modelling of the plasma spraying industrial process. A set of three 3D Computational Fluid Dynamics (CFD) models were developed and studied for this purpose. The first model that was implemented looks at the effects the electromagnetic properties have in the properties of the plasma flow in the nozzle of the spraying device. The second model studies the particle in flight atomisation after coding the thermal exchanges in the C++ framework and compares the results with experimental data. The third model studies the particle in-flight atomisation of molten metals and their resulting size distribution. The computational results from the first model agree with contemporary work analysing flows in nozzles of plasma spraying equipment. It also provides quantification of the additional energy exchanges that occur in the nozzle of a plasma spraying device, which are the ones that produce the gradients in velocity and temperature, which are met in plasma spraying processes. Finally, it looks into the effect the presence of dielectric may have on the plasma arc. The second model compares well with experimental data acquired by multiphase flows produced from plasma spraying devices and supports the finding that the Weber number is a good indicator of the deformation patterns of fluid particles, even liquid metal, where the density is much higher than regular liquids. The results of the third model in regards to particle size distribution show agreement with theoretical models of the distribution. The three models can be combined in the order presented, to provide a computational modelling solution which can cover the industrial application of the plasma spraying process, from the nozzle, to finer atomisation, to splat.