Wear and friction tests were conducted on a rotational tribometer to identify material couples for compression seals and chamber coatings to extend the service life of the Pivotal Engine™. Potential materials were identified based on reports in the literature of successful use in similar environments. From the rotational tribometer tests, the best material couple was found to be reaction bonded silicon nitride against a Sulzer Metco F4301 plasma sprayed coating followed by a Total Seal TiN coated seal against the F4301 coating. However, the performance predicted by the rotational tribometer was not realised in a fired engine, where the TiN coated seal wore almost as fast as an uncoated seal. This discrepancy was due to the large differences in operating conditions between the rotational tribometer and the fired engine, particularly the reciprocating motion of the engine. The different operating conditions mean that the results from the rotational tribometer have little or no relevance actual performance in the engine. To overcome the limitations of the rotational tribometer a reciprocating tribometer was designed and built. The performance predicted by the reciprocating tribometer was much closer to the observed wear rates from the engine, particularly with the Total Seal TiN coated seals. Some of the results from the reciprocating tribometer were a direct-contradiction to those obtained on the rotational tribometer. When tested on the rotational tribometer the nitrided stainless steel seal wear rate was lower than that of the Mazda cast iron seal. However, on the reciprocating tribometer the Mazda cast iron seal had a lower wear rate than the nitrided stainless steel seal. From the testing conducted on the reciprocating tribometer the best material couple was found to be Total Seal TiN coated seals on the F4301 chamber coating. However, this material couple cannot be recommended to increase the seal life in the Pivotal Engine™ because at the conclusion of a twenty hour test the Total Seal TiN coating had worn through to the substrate. In addition to testing different materials, different oils were tested while keeping the wear couple constant. The oil that offered the best wear protection to both the seal and chamber coating was Castrol A747. These tests showed that different oils have as much effect as different materials. Even with the best material combinations (Total Seal TiN seal, F4301 chamber coating) the seal wear rates in the Pivotal Engine™ are much higher than would be expected in other engines. This leads to the hypothesis that the origin of high seal wear in the Pivotal Engine™ is not due to material properties, but to design issues. The most likely problem is distortion of the chamber, which causes high localised seal loadings, and in turn causing high seal wear.

The practical advantages of thermal spray coatings like high deposition rates, low cost and tribological properties of high wear resistance have enabled these coatings to become an integral part of aircraft and automobile industry. Recent advancements in thermal spraying techniques like high particle speed and temperature call for new applications for these coatings. This experimental study addresses the Rolling Contact Fatigue performance of thermal spray coatings deposited by a variety of techniques like High Velocity Oxy-Fuel (HVOF), Detonation Gun (D-Gun) and Plasma spraying. RCF tests were conducted using a modified four ball machine in conventional steel ball bearing and hybrid ceramic bearing configurations. Tribological conditions during the RCF tests were varied by changing the test lubricant and the lubrication mechanism, contact load and shape of the drive coated rolling element to vary the roll/slip ratio. RCF tests were analyzed on the basis of the performance, coating failures using surface and subsurface observations, and residual stress studies. Experimental and theoretical studies of the ball kinematics have also been included. These tests revealed that the performance of the coated rolling elements was dependent upon the coating and the substrate properties. The coating thickness, substrate hardness, tribological conditions during the test, coating and substrate material as well as the coating process and the substrate preparation significantly affect the coating performance and the failure modes. Three different failure modes of these coatings have been discussed along with the changes in the near surface residual stress behaviour of the coated rolling elements.

In this thesis nanocomposite materials for use in high performance electrical contacts are tested. Self mating silver as coatings on cupper substrates are the most used material combination in power connectors today. In this work two new concepts were tested. The first one was to change one of the mating surfaces to a hard thin coating and keep the other surface made of silver. Tested coatings were nanocomposites with hard carbides in a matrix of amorphous carbon. TiC/a-C and  Ti-Ni-C/a-C were tested both electrically and tribologically. The total amount of carbon and the amount of carbon matrix was important, both for the electrical and the tribological properties. The Ti-Ni-C coating also showed that substituting Ti in TiC with the weak carbide former Ni changed the stability of the carbides. The substitution resulted in more a-C matrix and less C in the carbides. Thin coatings of nc-TiC/a-C and  Ti-Ni-C/a-C showed high potential as material candidates for use in electrical contacts. The other tested concept was to modify the used silver instead of replacing it. This was done by embedding nanoparticles of solid lubricant IF-WS2 in the silver. The results from reciprocating sliding displayed low friction and high wear resistance. The modified silver surfaces lasted for 8000 strokes with a friction of about 0.3 while at the same time allowing for a low contact resistance. The results for surfaces of pure silver coating displayed a friction of 0.8-1.2 and that the silver was worn through already after 300 strokes. A new method to investigate inherent hardness and residual stress of thin coatings, on complex geometries or in small areas, was also developed. An ion beam was used to create stress free coating as free standing micro pillars. Hardness measured on the pillars and on as-deposited coating were then used to calculate the residual stress in the coatings.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 90-93). Also available via the Internet.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 72-75)

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 193-201). Also available via the Internet.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xviii, 191 p. : ill. Advisor: Bharat Bhushan, Department of Mechanical Engineering. Includes bibliographical references (p. 179-183).

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 173-178).

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 216-235).

Resumo: O Ferro Fundido é amplamente utilizado na indústria de autopeças do setor automobilístico, principalmente em anéis de pistão, camisa de cilindros, discos de freios e outros, devido a sua boa resistência ao atrito e desgaste, por ter boa condutividade térmica e ser antivibracional. Com a globalização, grandes esforços vêm sendo feitos por pesquisadores, direcionados ao desenvolvimento de novos materiais que atendam os mercados mundiais, trazendo a competitividade necessária na busca de processos de fabricação e pesquisas, objetivando redução de custos, qualidade e produtividade, sendo que no ramo automobilístico a realidade não é diferente. Motores menores e mais leves têm aumentado constantemente os carregamentos térmicos e mecânicos dos componentes, na qual o sistema tribológico do anel de pistão é dos mais complexos. O objetivo deste trabalho foi avaliar o comportamento tribológico através do teste de bancada pino-disco dos pares: Ferro Fundido Cinzento Centrifugado/ Ferro Fundido Cinzento MC12 e Ferro Fundido Cinzento Centrifugado/ Ferro Fundido Cinzento MC13 em função da velocidade de deslizamento (0,5 m/s, 1,0 m/s e 1,5 m/s). Para os discos (MC 12 e MC 13) a taxa de desgaste decresceu linearmente com o aumento da velocidade de deslizamento, já para os pinos em Ferro Fundido Cinzento Centrifugado, a taxa de desgaste decresceu até 1,0 m/s, e a 1,5 m/s a taxa de desgaste apresentou um ligeiro aumento, determinado pela instabilidade gerada pelo aquecimento da superfície e formação da camada de óxido. O par Centrifugado/ MC 13 apresentou melhor desempenho a 0,5 m/s e o par Centrifugado/ MC 12 a 1,0 e 1,5 m/s. Verificou-se que os mecanismos de desgaste atuantes são: adesão (0,5 m/s), adesão + oxidação (1,0 m/s) e oxidação (1,5 m/s). Em todas as velocidades de deslizamento, os mecanismos principais de desgaste são seguidos de microabrasão / Abstract: The cast iron is widely used in auto parts industry in the automotive sector, mainly in piston rings, cylinder liners, brake discs and others due to its good resistance to friction and wear, to have good thermal conductivity and be antivibrational. With globalization, great efforts have been made by researchers, directed the development of new materials that meet the global markets, bringing the competitiveness required in the pursuit of manufacturing processes and research, aiming at cost reduction, quality and productivity, and the branch automotive reality is no different. Smaller engines and lighter loads have steadily increased thermal and mechanical components, in which the tribological system piston ring is the most complex. The aim of this study was to evaluate the tribological behavior through the test bench pin-disk pairs: Centrifuged Gray Cast Iron/ Gray Cast Iron MC 12 and Centrifuged Gray Cast Iron/ MC 13 depending on sliding velocity (0.5m/s, 1.0 m/s and 1.5 m/s). For discs (MC 12 and MC 13) the wear rate decreased linearly with increasing sliding velocity, since the pins on Cast Iron Grey centrifuged, the wear rate decreased to 1.0 m / s, and 1, 5 m / s the wear rate increased slightly, as determined by the instability caused by surface heating and the formation of the oxide layer. The pair centrifuged / MC 13 performed better than 0.5 m / s and centrifuged pair / MC 12 to 1.0 and 1.5 m / s. It was found that the prevalent wear mechanisms are adhesion (0.5 m / s), adhesion + oxidation (1.0 m / s) and oxidation (1.5 m / s). In all sliding velocities, the main mechanisms of wear are followed by abrasion / Orientador: Sergio João Crnkovic / Coorientador: Humberto Lopes Rodrigues / Banca: Ana Paula Rosifini Alves Claro / Banca: Sandra Giacomin Schneider / Mestre