Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler is being developed at University of Central Florida. The cryocooler will be used for storage and transport of hydrogen in spaceport and space vehicle application. One part in development of the cryocooler is to reduce the friction and wear between mating parts thus increasing its efficiency. Tribological coatings having extremely high hardness, ultra-low coefficient of friction, and high durability at temperatures lower than 60 K are being developed to reduce friction and wear between the mating parts of the cryocooler thus improving its efficiency. Nitrides of high-melting-point metals (e.g. TiN, ZrN) and diamond-like-carbon (DLC) are potential candidates for cryogenic applications as these coatings have shown good friction behavior and wear resistance at cryogenic temperatures. These coatings are known to have coefficient of friction less than 0.1 at room temperature. However, cryogenic environment leads to increase in the coefficient of friction. It is expected that a composite consisting of a base layer of a hard coating covered with layer having an ultra-low coefficient of friction would provide better performance. Extremely hard and extremely low friction coatings of titanium nitride, molybdenum disulphide, TiN/MoS2 bilayer coatings, DLC and DLC/MoS2 bilayer coatings have been chosen for this application. TiN film was deposited by reactive DC magnetron sputtering system from a titanium target and MoS2 film was deposited by RF magnetron sputtering using a MoS2 target. Microwave assisted chemical vapor deposition (MWCVD) technique was used for preparation of DLC coatings. These composite coatings contain a solid lubricating phase and a hard ceramic matrix phase as distinctly segregated phases. These are envisioned as having the desired combination of lubricity and structural integrity. Extremely hard coatings of TiN and DLC were chosen to provide good wear resistance and MoS2 was chosen as the lubricating phase as it provides excellent solid lubricating properties due to its lamellar crystal structure. This thesis presents preparation; characterization (SEM and XRD), microhardness and tribological measurements carried out on TiN and TiN/MoS2 coatings on aluminum and glass substrate at room temperature. It also presents initial development in preparation of DLC coatings.

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Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Additional advisors: Yogesh K. Vohra, Xu Feng, Jack E. Lemons, Timothy M. Wick. Description based on contents viewed July 8, 2009; title from PDF t.p. Includes bibliographical references.

The deformation mechanisms and contact response of TiN-based thin films deposited onto a soft substrate using a physical vapour deposition (PVD) technique is still an area of both technological importance and considerable discussion. These coatings are commonly applied to various kinds of steel cutting tools, creating surfaces with enhanced tribological properties. However, no extensive systematic study of the deformation mechanisms in these thin film systems has been performed to date. In the present study, the effect of the coating microstructure, indenter geometry, coating thickness and substrate hardness on the deformation mechanisms in both TiN and TiAlN coatings of varying thickness deposited onto ductile steel substrates has been investigated using a combination of nanoindentation and microstructural analysis, including focused ion beam (FIB) milling and transmission electron microscopy (TEM). Different modes of cracking, such as columnar and transverse cracking, as well as shear steps at the coating/substrate interface, were observed. The microstructure of the TiN coatings was found to be very important in controlling their modes of deformation. Thicker coatings were seen to contain more equiaxed grains, so less columnar shearing occurred and inclined cracks were found to be a more dominant fracture type in the thicker coating. Also, it was found that soft substrates absorbed most of the energy from indentation by plastic deformation. It was found that both the TiN and TiAlN/TiN dual-layer coatings exhibited broadly similar mechanisms of deformation. The epitaxial interface between the TiAlN and TiN in the dual-layer coating did not appear to affect the deformation behaviour. As a further investigation of the overall deformation behaviour for the coating/substrate systems studied, a DualBeam FIB was used to generate three dimensional images of the indented regions which provided additional information on the crack morphology. For the first time, a systematic study of the deformation behaviour of TiN and TiAlN coatings upon indentation has been carried out. FIB milling was demonstrated to be a highly appropriate technique for characterization of the deformation behaviour of these coatings, allowing detailed, high resolution microstructural investigations to be performed in both two and three dimensions.

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Thesis (PhD) - Swinburne University of Technology, School of Engineering and Science, 2008. / A thesis submitted for the degree of Doctor of Philosophy, School of Engineering and Science, Swinburne University of Technology, 2008. Typescript. Includes bibliographical references (p. 189-204).

O presente trabalho avalia a deposição de filmes de TiN com caráter decorativo sobre substratos de AISI 304. Os filmes produzidos neste estudo são compostos por uma intercamada de Ti entre o substrato e o filme de TiN, produzindo assim um sistema substrato/Ti/TiN. Foram estudados os efeitos da tensão de polarização aplicada ao substrato durante a deposição da intercamada de Ti e a influência da temperatura de deposição do filme, com variação de temperatura entre 25°C e 200°C. Os filmes foram depositados através da tecnologia PVD por arco catódico em um processo de deposição reativa em escala industrial, partindo de cátodos de Ti e gases argônio e nitrogênio. Os filmes tiveram sua composição química analisada através da técnica de espectroscopia por descarga luminescente, as fases cristalinas foram determinadas por difração de raios-X e a microestrutura e espessura das camadas foram avaliadas através de microscopia eletrônica de varredura (MEV). Também foi medida a dureza em nanoescala dos filmes e, como forma de complementar os resultados obtidos, a carga crítica para início de deformação plástica dos filmes foi medida através de ensaios de esclerometria linear. Os resultados mostraram que ambos os parâmetros de processos analisados exercem influência significativa nas propriedades e características dos filmes formados, principalmente no teor de contaminação por oxigênio presente nos filmes e na carga crítica para deformação plástica. Além disso, também se observou que o filme depositado à 200°C apresenta uma mudança significativa na sua orientação cristalográfica e composição química em comparação com os depositados em temperaturas inferiores. Como resultado do trabalho, pôde-se determinar os parâmetros ideais para a deposição de filmes finos de TiN decorativos, possibilitando o desenvolvimento e a aplicação da tecnologia em escala industrial. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-02-11T13:10:46Z No. of bitstreams: 1 Dissertacao Gustavo Caberlon Lain.pdf: 2832428 bytes, checksum: 9f93177004f259851cf5825bdbafb606 (MD5) / Made available in DSpace on 2015-02-11T13:10:46Z (GMT). No. of bitstreams: 1 Dissertacao Gustavo Caberlon Lain.pdf: 2832428 bytes, checksum: 9f93177004f259851cf5825bdbafb606 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. / This work studies the deposition of titanium nitride (TiN) thin films on stainless steel AISI 304 substrate for decorative applications. The films studied here are composed of a layer of Ti working as an interlayer between the substrate and the TiN thin film, creating a system substrate/Ti/TiN. The BIAS applied on the substrate during the deposition of the Ti interlayer and the deposition temperature of the films between 25°C and 200°C were studied. The films were deposited by a PVD cathodic arc evaporation technique in a reactive deposition process, working with Ti cathodes and argon and nitrogen as gases. The equipment utilized for these depositions was an industrial PVD coating equipment. The chemical composition of the TiN films was analyzed by glow-discharge optical emission spectroscopy technique (GD-OES) and the crystalline structure by X-ray diffraction (XRD) and the microstructure and thickness by scanning electron microscopy (SEM). Also, the hardness at the nanoscale of the films was measured and scratch analyses were made to determine the critical load for the beginning of plastic deformation of the films. The results show that both analyzed process parameters significantly affect the properties and characteristics of the films, especially on the oxygen contamination content and the critical load for plastic deformation. Furthermore, it was also observed that the film deposited at 200°C presents a significant change on its crystallographic orientation and chemical composition compared with those deposited at lower temperatures. As a result of this research, it was possible to determine the optimized process conditions for the deposition of TiN thin films for decorative purposes, enabling the development and application of this technology in industrial scale.