Duas das principais formas de degradação de materiais metálicos estão relacionadas a danos mecânicos e eletroquímicos, devidos ao atrito, e à corrosão, respectivamente. Especialmente em materiais passivos, como os aços inoxidáveis, observa-se uma sinergia entre esses mecanismos de dano. Nesta dissertação foram realizados ensaios de tribocorrosão do aço superduplex UNS S32750 em solução aquosa de 3,5% em massa de NaCl. Para realizar estes ensaios foi necessário, inicialmente, instrumentar e adaptar um tribômetro do tipo pino-no-disco construído no Instituto Politécnico da UERJ. Para identificar os parâmetros de tribocorrosão mais relevantes para este sistema, foi elaborado um planejamento fatorial 23 e, a partir destes resultados, outros ensaios mais específicos foram elaborados. Técnicas eletroquímicas in situ de espectroscopia de impedância eletroquímica, polarização potenciodinâmica e amperometria de resistência nula foram usadas em amostras submetidas à solicitação tribológica. Os resultados mostraram que a carga aplicada no atrito é o fator de maior influência nas variáveis eletroquímicas medidas. Foi verificado que há efetivamente uma correlação entre os aspectos mecânicos e eletroquímicos com base no coeficiente de atrito e nos resultados dos ensaios eletroquímicos, principalmente nos obtidos de varredura potenciodinâmica e amperometria de resistência nula. Os dados eletroquímicos para a carga aplicada mostra claramente dois grupos com diferentes comportamentos, abaixo e acima da carga aplicada de 7 N. / Two of the main forms of degradation of metallic materials are related to mechanical and electrochemical damages due to friction and corrosion processes respectively. Especially in passive materials, such as stainless steels, there is a synergy between these mechanisms of damage. In this dissertation, we carried out tribocorrosion tests of superduplex steel UNS S32750 in 3.5 wt% NaCl aqueous solution. Initially, to perform these tests was necessary to instrumentate and adapt a pin-on-disk tribometer, wich had built at the Instituto Politécnico of UERJ. In order to identify most relevant tribocorrosion parameters of this system, was designed a 23 factorial design and, from these results, other more specific tests were developed. In situ electrochemical techniques of electrochemical impedance spectroscopy, potentiodynamic polarization and zero resistance amperometry were used on samples under tribological solicitation. The results showed that the applied load is the most influent factor on electrochemical measurements. It was found a close correlation between the electrochemical and mechanical aspects, based on the analysis of friction coefficient and the results of electrochemical tests, mainly those obtained from potentiodynamic sweeping and zero resistance amperometry. The electrochemical data for mechanical loads clearly shows two groups of different behaviors, below and beyond the applied charge of 7 N.

L'objectif de cette thèse est d’étudier l’utilisation des plasmas froids à pression atmosphérique pour déposer des couches minces apportant une valeur ajoutée (protection contre la corrosion, effet autonettoyant ou antibactérien,…) aux produits. Cette recherche se divise en trois parties :caractérisation de l’un des équipements plasma utilisés, dépôts de SiOxCyNzHw et dépôts de TiOx. Ces deux types de couches peuvent apporter un effet barrière contre la corrosion.<p><p>Dans la première partie de ce travail, l’influence de l’ajout d’un gaz réactif (hydrogène ou ammoniac) dans un plasma d’azote généré avec une torche commerciale de type décharge à barrière diélectrique (DBD) est étudiée par spectroscopie d’émission optique et par des mesures simultanées de courant et tension. En particulier, des émissions de CN sont visibles dans les spectres optiques d’un plasma d’azote seul, mais ne le sont plus si un gaz réactif est ajouté. Par contre, avec de l’hydrogène ou de l’ammoniac dans le plasma, la présence de NH est détectée. Quelle que soit la nature du gaz, la décharge est filamentaire. L’ajout d’un gaz réactif permet de réduire la tension à appliquer pour maintenir la décharge.<p><p>Dans la deuxième partie, cette torche est utilisée pour déposer des couches à partir de précurseurs organosiliciés (hexaméthyldisiloxane et hexaméthyldisilazane) par plasma d’azote seul, avec hydrogène ou avec ammoniac dans une cuve industrielle mise sous azote. Diverses géométries d’injection du précurseur sont testées. L’une d’elles est choisie pour étudier les propriétés des dépôts sur de larges surfaces (de silicium pour diverses analyses et d’acier pour évaluer la résistance à la corrosion). Les dépôts par plasma d’azote seul sont de type polysiloxane. Ceux obtenus par plasma d’azote avec hydrogène contiennent moins d’azote et de carbone. Ceux réalisés par plasma d’azote avec ammoniac sont poudreux.<p> <p>Dans la dernière partie, des couches d’oxyde de titane sont déposées à partir d’isopropoxyde de titane avec une torche commerciale radiofréquencée dans l’air ambiant, une décharge à barrière diélectrique à électrodes planes parallèles sous hélium à basse pression développée à l’ULB et la torche utilisée pour les dépôts à base de silicium dans une cuve de laboratoire sous azote. Les couches déposées avec la torche de type DBD sous azote contiennent de l’azote et du carbone contrairement à celles obtenues avec les deux autres installations. Ces essais ont mis en évidence la forte réactivité du précurseur avec l’humidité ambiante.<p><p>Les couches à base de silicium déposées apportent un effet barrière contre la corrosion. La résistance à la corrosion des dépôts d’oxyde de titane n’a pas encore été testée. Toutefois, dans les conditions actuelles, avec les géométries des équipements plasma utilisés, les vitesses de dépôt sont insuffisantes pour des applications en sidérurgie. D’autres géométries devraient être testées pour accroître les vitesses de dépôt.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

<p align="justify">Un simulateur de laboratoire de galvanisation continue a été conçu et utilisé pour l'étude des effets des paramètres de contrôle du procédé sur la prise d'aluminium interfacial avec un intérêt particulier porté té à la simulation de l'hydrodynamique de l'écoulement du liquide à la surface de la tôle ainsi qu'aux durées d'immersion extrêmement courtes inférieures à une seconde. Les effets de la concentration en aluminium et des températures de travail ont aussi été étudiés. Il a pu être montré que la prise d'aluminium est extrêmement rapide dans les premiers instants de la réaction et que la couverture complète de l'acier par la couche d'inhibition était assurée après le premier dixième de seconde. La réaction se poursuit avec une vitesse de croissance de la couche compatible avec la diffusion à l'état solide du fer à travers le produit formé. Un modèle mathématique décrivant les phénomènes est proposé. La microscopie de force atomique a été utilisée pour l'étude de la morphologie de la couche d'inhibition et la microanalyse X à sélection d'énergie pour la mesure de son épaisseur.</p><p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Researches on alloy elements such as niobium and silicon have been added to titanium alloys as an alternative for new materials to be used in orthopedic implants, once they present biocompatibility and favor reductions in the elasticity modulus. Therefore, the objective of this study was to investigate the phase transformations, mechanical properties and corrosion resistance of the Ti-Nb and Ti-Nb-Si alloys for biomedical applications. The results showed that Si addition is effective to stabilizing the £] phase, which also acts as a ç suppressor, and to produce grain refinement. In all samples, the hardness values increased with the increasing of Si content, while the elastic modulus was reduced in the Ti-15Nb-xSi and Ti-35Nb-xSi alloys; however, for Ti-40Nb-xSi samples increased with the increasing of Si content. Lower elastic moduli were observed in water-quenched Ti-35Nb-xSi alloys, for which tensile tests and corrosion resistance were performed. The increase in Si concentration also produced an increase in the alloys mechanical strength. Ti-35Nb-0,55Si alloy, however, showed brittle mechanical behavior which was related to the presence of silicides, referred as (Ti,Nb)3Si, at the grain boundaries. Corrosion tests showed that the alloys exhibit high resistance in the studied environment. The results suggest that the Ti-35Nb-0,35Si alloys presents the best combination of properties: good mechanical strength, low elastic modulus and excellent corrosion resistance. / Elementos de liga como niobio e silicio tem sido adicionados a ligas de titanio como uma alternativa na busca de novos materiais para implantes ortopedicos, visto que apresentam biocompatibilidade e favorecem a reducao do modulo de elasticidade. Dessa forma, o objetivo deste trabalho foi investigar as transformacoes de fases, propriedades mecanicas e de resistencia a corrosao de ligas dos sistemas Ti-Nb e Ti-Nb-Si para aplicacoes biomedicas. Os resultados mostraram que a adicao de Si foi efetiva na estabilizacao da fase £], o qual tambem atua como supressor de ç, alem de produzir refinamento de grao. Em todas as amostras estudadas, os valores de dureza se elevaram com o aumento do teor de Si, enquanto que o modulo de elasticidade sofreu uma reducao nas ligas dos grupos Ti-15Nb-xSi e Ti-35Nb-xSi; no entanto, para as amostras Ti-40Nb-xSi foi verificado um aumento de seus valores com a elevacao do teor de Si. Menores modulos de elasticidade foram observados nas ligas Ti-35Nb-xSi resfriadas em agua, para as quais foram realizados ensaios de tracao e de resistencia a corrosao. Foi observado que o aumento da concentracao de Si tambem produziu um aumento na resistencia mecanica das ligas, entretanto, a liga com 0,55% de Si, apresentou comportamento mecanico fragil atribuido a presenca de silicetos, indicados como (Ti,Nb)3Si nos contornos de graos. Os ensaios de corrosao mostraram que as ligas apresentaram uma alta resistencia no meio estudado. Os resultados obtidos sugerem que a liga Ti-35Nb-0,35Si apresenta a melhor combinacao de propriedades: boa resistencia mecanica, baixo modulo de elasticidade e excelente resistencia a corrosao.

Indiana University-Purdue University Indianapolis (IUPUI) / This work is focused on developing viable self-healing coatings, especially considering the viability of the coating in a commercial context. With this in mind, finding low cost healing agents, with satisfactory healing and mechanical properties as well as adapting the healing system for use in coatings was required. Seven potential healing agents were evaluated and an air-drying triglyceride (linseed oil) was identified as the candidate healing agent. Different encapsulation techniques were evaluated and ureaformaldehyde microcapsules were chosen as the candidate encapsulation technique. Self-healing coatings were fabricated using urea-formaldehyde encapsulated linseed oil. EIS, SEM and TGA technologies were used to evaluate mechanical performance, corrosion resistance, and self-healing performance.

A proteção contra corrosão na indústria automotiva é um problema de alto impacto econômico. Além de características anticorrosivas, os revestimentos utilizados nas indústrias automotivas precisam apresentar boa aparência e resistência física. Os revestimentos multicamadas normalmente utilizados em indústrias automotivas são compostos por e-coat, primer, base e verniz, sendo que o primer pode ser utilizado como um substituto do e-coat em processos de retoque ou retrabalho. Sob outra perspectiva, os polímeros condutores têm sido amplamente estudados como um revestimento anticorrosivo e o compósito de Polianilina-Melamina-Zinco (PZn) apresentou resultados promissores em relação à corrosão. Então, este estudo analisou a aplicação da PZn incorporado em revestimento multicamada utilizado na indústria automotiva, substituindo o primer comercial em processo de retrabalho. Adicionalmente, os resultados de PZn foram comparados com os primers utilizados atualmente (FLASH e GLASURIT). Para a caracterização dos materiais, realizaramse ensaios de MEV e EDS para o substrato e espessura de camada nos conjuntos pintados. Para a determinação de características visuais, foram feitas medições de cor, brilho e aspecto. Para corrosão, realizaram-se ensaios eletroquímicos (OCP e Tafel) e ensaio cíclico. Por fim, para resistência física foram analisados os ensaios de umidade, flexibilidade e aderência: corte cruzado, jato d´água, impacto pontual e batida de pedra. Os resultados dos ensaios de aspecto visual foram similares para todos os conjuntos pintados. Para corrosão, os ensaios eletroquímicos apresentaram resultados similares ao ensaio químico de corrosão cíclica, nos quais os conjuntos CJ_PANI e CJ_FLASH mostraram-se semelhantes e o CJ_GLASURIT obteve melhores resultados, sendo este o conjunto mais resistente. Os ensaios de resistência física podem ser divididos em secos e úmidos. Os ensaios realizados a seco tiveram resultados similares entre todos os conjuntos pintados, porém, nos úmidos o conjunto CJ_PANI apresentou-se susceptível à defeitos. Sendo assim, concluiu-se que o compósito de PZn apresentou bons resultados em relação às características visuais, ensaios eletroquímicos de corrosão e ensaios físicos a seco, quando utilizado em sistemas de pintura multicamadas de indústrias automotivas. Contudo, a PZn apresentou-se sucetível à defeitos em abientes úmidos, perdendo aderência. / The protection against corrosion in the automotive industry is a high impact problem on the economic view. Besides of an antirust characteristic, the coatings used in the automotive industries needs to have a good appearance and phisical resistance. The multilayer coatings used normally are compound of e-coat, primer, base and clear coat, where the primer can also be used as an e-coat substitute in rework processes. In the other side, the conductive polymers has been widely discussed as an anti-rust coating material and the Polyaniline-zinc composite (PZn) had presented good results concerning the corrosion protection. Then, this study had applied the PZn in a multilayer coating used in the automotive industry, substituting the commercial primer in a common rework process. In addition, the PZn results were compared with the commercial primers used currently (FLASH and GLASURIT). To the material characterization, were done a MEV and EDS analysis of the substrate and were measured the coating thickness of the painted sets. To determinate the visual characteristics, were measured color, gloss and aspect. For corrosion, were performed electrochemical measurements (OCP and Tafel) and the cyclic test. Moreover, the phisical resistance were evaluated with humidity, flexibility and adherence tests: cross cut, steam jet, punctual impact and stone chip. The visual aspects results were similar for all the painted sets. For corrosion, the electrochemical tests presented similar results with the chemical test done by cycle test, in which the CJ_PANI and CJ_FLASH sets had showed them equivalent and the CJ_GLASURIT had better results, being the set more resistant. The phisical resistance could be divided in two types: dry and wet. The dry tests had similar results between the painted sets, but in the wet ones, the PZn set had presented susceptible for defects. In conclusion, the PZn composite had presented good results regarding visual aspects, electrochemical corrosion and dry technical tests when used in multilayer paint systems of the automotive industry. However, it presented a susceptible for defects in humidity environmental, losing adherence.

Fatigue and fracture assisted by the environment are responsible for the majority of failures in implants. Due to low tribological properties of titanium alloys, the thermal oxidation technique has been evaluated to improve the surface hardness and consequently, to improves the tribological properties of Ti6Al4V alloy. However, despite improved tribological properties of the Ti6Al4V alloy, there is a tendency to reduction of the fatigue limit of the oxide layer. The combined action of body fluid and cyclic loads also need to be investigated. This study evaluated the effect of thermal oxidation in the fatigue limit of the Ti6Al4V in environment containing 0.9% NaCl. It was observed a reduction in the fatigue limit for thermally oxidized Ti6Al4V alloy and it is suggested that the reduction in fatigue properties of alloy is associated with the brittleness of oxide layer. / Os processos de fadiga e fraturas assistidas pelo ambiente são responsáveis pela maioria das falhas em implantes. Devido às baixas propriedades tribológicas do titânio e suas ligas, a técnica de oxidação térmica tem ganhado destaque por conferir um aumento da dureza superficial e consequentemente melhorar as propriedades tribológicas da liga Ti6Al4V. Entretanto apesar da melhoria das propriedades tribológicas existe uma tendência na redução do limite de fadiga quando há presença de uma camada de óxido na superfície da liga Ti6Al4V. Ainda a ação combinada de fluidos corpóreos e de carregamento precisa ser investigada. Neste estudo foi avaliado o efeito da oxidação térmica combinado a aplicação de carregamento cíclico ao ar e em meio contendo 0,9 % NaCl. Foi observada uma redução no limite de resistência à fadiga para a liga Ti6Al4V oxidada termicamente. O meio contendo 0,9 % de NaCl não influenciou significativamente a resistência em fadiga de corpos de prova oxidados termicamente e sugere-se que a redução nas propriedades de fadiga da liga está associada à fragilidade da camada de óxido.

Indiana University-Purdue University Indianapolis (IUPUI) / In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.