Made available in DSpace on 2014-10-09T12:32:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:15Z (GMT). No. of bitstreams: 1 03180.pdf: 2623068 bytes, checksum: eb3adbfcbd2151a3b9e3f1cbe30c00e8 (MD5) / Dissertacao(Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

A corrosão localizada em aços inoxidáveis pode se manifestar de várias formas, tais como, a corrosão por pite, em fresta e corrosão sob tensão. Estes tipos de corrosão ocorrem quando o metal é exposto em meios agressivos como o cloreto, entre outros. O objetivo deste trabalho é estudar o comportamento dos aços inoxidáveis austeníticos e ferríticos em meios agressivos de cloreto, brometo e suas misturas. Para testar a resistência à corrosão por pite foi usado o método de polarização potenciodinâmica em eletrólitos de concentração iônica total de 0,6M. Os materiais estudados foram os aços inoxidáveis: 298 (aço inoxidável Cr-Mn, especificação da ArcelorMittal Inox Brasil) e os aços padronizados segundo a UNS: S30400, S31603, S43000 e S44400; todos, na condição tal como recebida da usina. Os resultados mostraram que, em meio de 0,6M(NaCl+NaBr), para concentrações de 0M a 0,45M NaCl, o desempenho quanto a resistência à corrosão por pite obedece a seguinte ordem decrescente: 444, 316L, 304, 298 e 430. Por sua vez, para a concentração de 0,6M NaCl, ou seja, ausência total de brometo, ocorre a alteração do desempenho dos aços inoxidáveis, colocando a seqüência da seguinte ordem: 316L, 444, 304, 298 e 430. Nota-se, portanto, que o melhor aço para ambientes contendo íon brometo seria o aço 444, já para aplicações em meio de cloreto puro, a melhor seleção é o aço 316L. Foram encontrados sítios de nucleação nos diferentes aços testados nos eletrólitos de 0,6M NaCl e 0,6M NaBr,sempre relacionados a inclusões: em alguns casos a nucleação ocorreu na interface matriz/inclusões insolúveis e, em outros, foram encontrados sinais de dissolução de inclusões, provavelmente de sulfeto. As diferenças de resistência à corrosão por pite entre os diferentes aços, nos diferentes eletrólitos, foram discutidas em função das diferenças de composição química. / Localized corrosion of stainless steels can be manifested in various forms, such as: pitting, crevice and stress corrosion. These types of corrosion occur due to exposition of metal in aggressive environments such as: chloride and bromide. The mean goal of this work is to study the pitting corrosion resistance of both austenitic and ferritic stainless steels in aggressive environments containing chloride, bromide or their mixtures. The potentiodynamic polarization method was used to test the pitting corrosion resistance in media containing a total of ion concentration of 0,6M. The studied materials in this work were stainless steel: 298 (Cr-Mn steel, specification of ArcelorMittal Inox Brazil) and standardized steels according to the UNS: S30400, S31603, S43000 and S44400. The results have shown that maintaining a constant concentration of 0.6M (NaCl+NaBr) into the electrolyte by varying the NaCl concentration between 0M and 0.45M, the performance in terms of pitting corrosion obeys to the following decreasing order: 444, 316L, 304, 298 and finally 430. In turn, for a concentration of 0.6M NaCl, so without any bromide, there is a variation from the performance of stainless steels, putting the sequence as following: 316L, 444, 304, 298 and 430. Nucleation sites were always found related to non-metallic inclusions in all tested stainless steels for the electrolytes of 0,6M NaCl or 0,6M NaBr. Sometimes, pits nucleation occurred at the matrix/inclusion interface, but others times, pits nucleated in water soluble inclusions. Difference of the pitting corrosion resistance between tested steel in the different electrolytes have been discussed as a function of the chemical composition.

O presente trabalho tem como objetivo estudar a eletropolimerização de polímeros baseados em polianilinas e suas propriedades para a proteção contra a corrosão. Assim, foi utilizada a seguinte divisão: (i) estudo das sínteses eletroquímicas monitoradas espectrofotometria de UV-vis, utilizando perturbações potenciodinâmicas e potenciostáticas em diferentes concentrações monoméricas, sobre um eletrodo de ITO (óxido de titânio dopado com índio). Os resultados mostraram que durante as sínteses a polianilina (PAni) apresenta uma baixa formação de oligômeros e degradação. As sínteses de poli-o-metoxianilina apresentam uma maior quantidade de oligômeros, apresentando uma alta sinal de absorbância em 560 mn. Assim, os espectrociclovoltamogramas e espectropotenciogramas mostraram para todas as sínteses os potenciais onde ocorrem os processos formação de: bipolarons, radicais, oligômeros e a conversão de PAni entre as forma leucoesmeraldina e sal esmeraldina. Portanto, o monitoramento UV-vis foi considerado uma ferramenta muito útil e interessante para o entendimento de reações de polimerizações. (ii) A proteção contra a corrosão do aço 304 foi feita recobrindo o mesmo com polímero por via eletroquímica (voltametria cíclica, VC e potenciostáticas, Pot), com otimizações de potencial, tempo de perturbação e número de ciclos, em soluções de elevadas concentrações monoméricas. Na primeira parte foi utilizado somente Ani; por VC foram observadas dois tipos de morfologia diferente. Na primeira, um filme e nanofibras, enquanto que para Pot, uma morfologia granular foi encontrada. As analises de corrosão mostraram que as melhores proteções foram obtidas para as seguintes condiciones: 0,05 - 1,15 V, por 15 ciclos, e 1,15 V, por 300 segundos. Esses filmes apresentaram deslocamento no potencial de corrosão, aumento na resistência de transferência de carga e potencial de circuito aberto elevado. Além disso, mantiveram uma superfície de aço livre de produto de corrosão. Assim, essas condições de sínteses foram reproduzidas para ometoxianilina (OMA) e Poli(anilina-co-o-metoxianilina). A OMA sintetizada por VC apresentou a melhor proteção, deslocando o potencial de corrosão para valores anódicos e mantendo um potencial mantendo um potencial de circuito aberto elevado, devido à morfologia fechada de microfibras, não ocorrendo corrosão na superfície do aço. / The goal of the present work is to study the electropolymerization polymers of based on polianilines and their corrosion protection properties. So, the following division was applied: (i) study of the electrochemical synthesis coupled to a spectrophotometer of UVvis. Using potenciostatic and potentiodynamic perturbations with different monomeric concentrations, on a ITO electrode (titanium oxide doped with Indium). The results show that polianiline (PAni) during the synthesis process present a low generation of oligomers and a null polymeric degradation. Whereas the synthesis of poli-o-metoxianilina presents an important concentration of oligomers, showing a high absorption signal in 560 nm. In this way, the spectrociclovoltammograms and the spectropotenciograms showed for all the synthesis the potential were occur formation processes of: bi-polaron, radicals, oligomers and the transformation of PAni of the form leucoesmeraldina and esmealdina salt. Thats why the UV-vis monitoring process interesting for the understanding of polymerization reactions. (ii) the validations of corrosion protection of steel-304 were performed covering with polymer in a electrochemical way; ciclic voltammetric (VC) and potenciostatic (Pot), with variations of the potential, time and cycle numbers, in solution with high monomeric concentrations. The first part was just Ani. By VC two different types of growth morphology were observed; a granular film and nano fibers, while for Pot, the morphology were granular. The analysis of corrosion show that the best protections were achieved for: 0,05-1,15 V by 15 cycles of 1,15 V during 300 seconds. Those films present a shift on the corrosion potential, increasing the transfer resistance of charge in high open circuit potential, moreover, keeping the steel surface corrosion-free. Those conditions were reproduced for o-metoxianiline (OMA) e Poli (aniline-co-o-metoxianiline). The synthesized OMA by VC present a better protection, shifting to anodic values the corrosion potential and keeping a high open circuit potential, due to the morphology of the microfibers, not happening corrosion on the steel surface.

Neste trabalho foram obtidos filmes de polianilina (PAni) por eletropolimerização (voltametria cíclica) sobre aços inoxidáveis austenítico (AISI 304), ferrítico (AISI 430) e martensítico (AISI 420), em meio de ácido oxálico. Os filmes de PAni foram preparados a partir de solução aquosa de ácido oxálico 0,3 mol L-1 contendo 0,1 mol L-1 de anilina a 50 mV s-1. Os valores de carga anódica total obtidos durante os estágios de eletropolimerização evidenciaram diferenças mecanísticas na polimerização da anilina sobre os diferentes aços. Os materiais poliméricos foram caracterizados por resposta eletroquímica, espectroscopias de impedância eletroquímica (EIS), de ultravioleta-visível (UV-vis-NIR), de infravermelho (IV), difração de raios X (DRX), além de microscopia eletrônica de varredura (MEV). Os filmes de PAni sobre aço AISI 420, em relação aos demais aços, apresentam diferenças significativas de morfologia. Adicionalmente, pode também ser observado que os aços com maior quantidade de cromo em sua composição, minimizam a formação de uma camada de oxalato de ferro, a qual é intermediária entre o metal e o filme de PAni. A camada de oxalato de ferro diminui as interações galvânicas entre o polímero e ferro do metal, promovendo a formação de filmes de PAni porosos e menos aderentes. A viabilidade de aplicação dos filmes de PAni dopados e desdopados, na proteção contra a corrosão dos aços inoxidáveis foi observada mediante polarização potenciodinâmica em solução aquosa de NaCl. Os parâmetros eletroquímicos extraídos das curvas demonstraram que o filme de PAni, no estado desdopado, é o que protege mais efetivamente os aços AISI 304 e AISI 430 contra a corrosão. A partir dos ensaios de corrosão e análises de EIS, foi proposto um mecanismo de deposição da PAni, o qual evidencia que a natureza do substrato metálico tem forte influência na formação dos filmes de PAni, quando a composição e a microestrutura dos aços são diferentes. / In this work were obtained polyaniline films from electropolymerization for cyclic voltammeter, on different stainless steels: (AISI-304) austenitic, (AISI-430) ferritic and martensytic (AISI-420), in oxalic acid media. PAni-films were prepared from 0.3 mol L-1 oxalic acid containing 0.1 mol L-1 aniline at 50 mV s-1. The values of total anodic charge obtained during polymerization stages demontrated difference mechanistic in the aniline polymerization on different steels. Polymeric materials were characterized for electrochemistry response and different techniques: electrochemistry impedance (EIS), ultraviolet-visible (UV-vis-NIR), infrared (IR), ray-X diffraction spectroscopes and scanning electronic microscopy (SEM). PAni films on AISI-420 steel demonstrated significant differences in the morphology, when compared another steels. Also, can be observed that the steels with chromium high content in your composition minimize the formation of iron oxalate layer, which is intermediary between the metal and PAni films. Iron oxalate layer diminishes both the galvanic interactions between the polymer and iron ions of metal and it promotes both the porous PAni films formation and lower adherence. The application viability of PAni films, in both doped and undoped states, for the protection against corrosion of stainless steels was investigated for potentiodynamic polarization in NaCl aqueous solution. The electrochemistry parameters extracted of curves demonstrated that undoped PAni films protect the AISI-304 and AISI-430 against corrosion, more effectively. With the corrosion assays and EIS analysis can be proposed a mechanism of PAni deposition, which evidence that the metallic substrate nature has strong influence on PAni films electropolymerization when both the composition and the steels microstructure differ between them.

Os aços inoxidáveis duplex (AID) caracterizam-se pela sua microestrutura composta por austenita numa matriz ferrítica, com fração volumétrica média de 50% para cada fase. A combinação destas características confere-lhes excelente resistência mecânica e à corrosão. A soldagem/junção destes aços é frequentemente uma operação crítica, já que, ao sofrer ciclos térmicos, estes aços têm suas propriedades alteradas. Portanto, processos de junção com ausência de gradientes de temperatura, como a brasagem, mostram-se uma solução prática para a junção destes aços. No entanto, o adequado desenvolvimento do processo de brasagem em AID envolve considerações importantes a respeito da escolha dos parâmetros de processamento e metal de adição em conjunto com os ciclos térmicos de aquecimento e resfriamento. O presente estudo pretende avaliar a brasabilidade dos AID UNS S32101(baixa liga), UNS S32304 (baixa liga), UNS S32507 (superduplex) e UNS S32707(hiperduplex), mediante a caracterização da junta brasada. Estes aços foram brasados em forno continuo com metal de adição BNi-7 (Ni-Cr-P), na temperatura de 1100oC, por tempos de 32 min e 12 min, seguidos de resfriamento em forno, utilizando-se folgas de 0,5, 0,3 e 0,0 mm. A junta brasada foi caracterizada utilizando-se microscopia ótica e microscopia eletrônica de varredura (MEV). A identificação microestrutural foi realizada via Microanálise Química de Energia Dispersiva de Raios-X (EDS) e difração de Raios-X. Foi identificada na junta brasada dos diferentes AID a fase rica em níquel, assim como fases prejudiciais compostas por fosfetos de níquel e cromo. A fase rica em níquel, que usualmente é denominada de -Ni, apresenta-se preferencialmente em toda a região da junta, sem a presença de fase intermetálica contínua no centro da junta. No caso dos aços inoxidáveis super e hiperduplex esses apresentaram a formação de fase sigma na região da interface da junta, do lado do metal de base, devido aos ciclos térmicos de brasagem / The duplex stainless steels (DSS) are characterized by its microstructure consisting of austenite in a ferritic matrix with mean volumetric fraction of 50% for each phase. The combination of these features gives them excellent mechanical strength and corrosion resistance. The welding / joining of these steels are often considered as a critical operation, since, subjected to thermal cycles, they have their microstructures changed and, consequently, their properties. Therefore, joining processes without temperature gradients, like brazing, are shown as a practical solution for joining these steels. However, the proper development of brazing process of DSS involves important issues concerning the choice of processing parameters and the brazing filler metal together with heating and cooling brazing thermal cycles. This study aims at evaluating the brazeability of DSS UNS S32101 (lean duplex), UNS S32304 (lean duplex), UNS S32507 (superduplex) and UNS S32707 (hyperduplex) by characterizing the brazed joint. These steels were brazed in a furnace with filler metal BNi-7 (Ni-Cr-P) at 1100°C for times of 32 min and 12 min, followed by cooling in a continuous brazing furnace, with joint gaps of 0.5 , 0.3 and 0.0 mm. The brazed joint was characterized using optical microscopy and scanning electron microscopy (SEM). The phase identifications were performed by microanalysis using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction. Results showed, for non-ideal joint gaps, in all duplex used in this work, the Ni rich solid solution, as well as deleterious phases composed of nickel and chromium phosphides. The ideal gap presented Ni rich solid solution, usually called -Ni, was found continuously without a continuous intermetallic region in the joint center. In the case of super duplex and hyperduplex brazing, the brazing thermal cycles produced the formation of sigma phase in the region of the joint interface, in the base metal.

Orientador: Amauri Hassui / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T20:30:13Z (GMT). No. of bitstreams: 1 Correa_FabianodosSantos_M.pdf: 5805847 bytes, checksum: 1e46e12c4b86d23df66529c421067901 (MD5) Previous issue date: 2013 / Resumo: A vida da ferramenta juntamente com o tempo gasto para acertos quando a mesma é substituída pode representar uma significativa parcela do custo total do produto. Desta forma, a redução destes custos é de fundamental importância para o processo. Quando se utiliza ferramentas de metal duro com coberturas, ou ferramentas com geometria definida, o desgaste mais comum que determina sua vida útil é o desgaste de flanco (VB). Este trabalho tem como principais objetivos estudar os esforços existentes na usinagem de fresamento de topo com insertos intercambiáveis redondos do aço inoxidável aeronáutico 15-5 PH e relacioná-los com o tempo de vida das ferramentas testadas. Analisar estes esforços no regime do tempo e da frequência a fim de verificar as principais forças responsáveis pelas possíveis vibrações do sistema. Tais vibrações podem ter grande parcela na contribuição dos desgastes e avarias das ferramentas. Todos os ensaios deste trabalho mantiveram constante a largura fresada (ae) de 14 mm, o corte em movimento predominantemente discordante e assimétrico com ae > D/2 (diâmetro da fresa), a profundidade de corte (ap) de 1 mm e fluido de corte em abundância. Para os parâmetros que variaram tem-se a velocidade de corte (vc) de 195 m/min e 170 m/min, os avanços por dente da fresa (fz) de 0,15 mm/dente e 0,25 mm/dente além de duas geometrias diferentes de insertos. Nas análises dos esforços foi utilizada a RMS para melhor interpretação da magnitude destes esforços. Observou-se que o aumento do avanço faz os esforços aumentarem, o mesmo aumento de esforços se deu para geometrias positivas (com quebra-cavaco) quando comparadas as geometrias neutras. No entanto, para as velocidades de corte usadas não se teve uma correlação significativa nos esforços. Para a vida da ferramenta, a vc teve influência direta na vida, o que era de se esperar, os avanços fz maiores apresentaram um comportamento inverso na vida. O maior contribuinte para o desgaste da ferramenta foi o alto atrito causado pelos esforços elevados, medidos na entrada do dente, onde a espessura do cavaco inicia-se com zero. Este comportamento do cavaco é um fenômeno comum ao corte discordante. Dentre os mecanismos de desgastes constatados, o predominante foi o desgaste conhecido como aderência (attrition) / Abstract: Tool life along with the setup time whenever it is changed may represent a big amount of the total cost of the product. This way, reducing these costs plays a fundamental role in the process. When using coated carbide tools, or designed geometry tools, the most common type of wear that determines the end of a tools life is flank wear (VB). This work has as main goals evaluate the machining forces in round inserts face milling of aerospace stainless steel 15-5 PH and relate these forces with the tool life. Evaluate the forces in time and frequency domain to check the main responsible for vibrations of the machining system. The vibrations may contribute in tool wear and failure. In all the tests, cutting width (ae) of 14 mm, up milling an asymmetric cut (with radial immersion of ae > D/2), cutting depth (ap) of 1 mm and cutting fluid conditions were kept constant. Cutting speed (vc) of 170 m/min and 195 m/min, feed per tooth (fz) of 0.15 mm/tooth and 0.25 mm/tooth, and two different insert geometries were the tests inputs. For analysis, the RMS value was used for better understanding of forces magnitude. It was observed that an increase in feed per tooth causes an increase of forces. The same behavior occurred for positive geometries (with chipbreaker) than for neutral geometry. However, the relationship between cutting speeds and forces was not significant. In tool life, cutting speed had high influence (as expected). High feed per tooth showed an inverse impact in tool life, increasing tool life. The main factor for tool wear was the high friction caused by high forces, measured in the beginning of the cut, when chip width was zero. This behavior of the chip is common in up milling. Attrition was the main mechanism of wear among all types observed / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Fretting is a serious concern in many industrial components, specifically, in nuclear industry for the safe and reliable operation of the component/system. Till date, a lot of efforts has already been made to understand the basic mechanics and mechanism involved in fretting, but still limited understanding on the following domains exists, (i) No standard experimental set up and procedures exists which could quantify the entire fretting domain. (ii) Limited data available for the designer under controlled environment conditions. (iii) Limited work in correlating fretting damage with the mechanical responses, specifically, for the materials with good adhesion properties. (iv) Limited work to understand the nucleation/initiation of cracks under fretting condition and, the effect of loading on crack propagation. (v) Displacement and shear force distribution at the contact interface accounting the failure mechanism. The whole efforts in this thesis are focused on the above points and, are investigated in detail. Further, studies are focused to simulate fretting conditions in a Fast Breeder Reactor (FBR). Reactor core components are exposed to sodium environment, which is a low oxygen environment. Experiments under liquid sodium are difficult and as a first step, the tests were done under vacuum condition to simulate condition in sodium environment. Stainless steel (SS316L) is a reactor core component material used in FBRs. Chromium carbide coatings are already qualified based on the performance criteria for friction coefficients, wear rates and galling resistance, but are not evaluated under fretting conditions. Thus, stainless steel and chromium carbide coatings are investigated in detail. In this thesis, mechanics and mechanisms involved in the degradation processes for self-mated stainless steel under fretting conditions are examined in detail. Further, chromium carbide with 25% nickel chrome binder coatings using plasma spray and high-velocity oxy-fuel (HVOF) processes on stainless steel are also investigated. The choices of the coating processes have been made such that the substrate must be maintained in a particular metallurgical condition. The effect of normal load, displacement amplitude, environment conditions, surface roughness, and stress field are critically examined. Stainless steel (SS) is often used in the nuclear industry because of its excellent mechanical properties under high temperature and irradiation environment, but on the other hand, SS is characterized as having relatively poor wear and galling resistance. In nuclear power plants (NPPs), different components move relative to each other, due to differential thermal expansion or flow-induced vibration or during loading and unloading events, and such conditions can be categorized under fretting. The objective of the present work is to understand the mechanics and mechanisms of nuclear grade material (NGM), specifically for sodium-cooled NPPs, under fretting conditions. The first-of-a-kind fretting machine has been designed and developed to simulate fretting condition in both, air and vacuum. The test in vacuum simulates conditions under sodium environment. The major challenge in the design of a fretting machine is to achieve low displacement amplitude, as low as 1µm, between the contact surfaces under constant normal load. The hydraulic actuated machine works under displacement controlled mode, for any frequency between 4Hz and 120Hz, under high vacuum of 10–5mbar and for temperatures up to 873K. A unique feature of the machine is the design of flexural member which provides not only high axial stiffness but also flexibility in the lateral direction. A robust control system with an efficient data acquisition system adds to the reliability of the system. Contact conditions prevailing at the interface were identified on the basis of variation of coefficient of friction (COF) with number of cycles, running condition fretting loops, and total energy dissipation at the contact interface. Gross sliding conditions have been observed under normal load of 70N and 250N and displacement amplitude in the range of 50µm to 200µm, except for normal load of 250N and displacement amplitude of 50µm. The tests were conducted under both ambient and vacuum environment. Higher value of COF observed for self-mated SS, compared to SS versus coated surface, has been attributed to the existence of strong adhesion prevailing at the contact interface. Running condition fretting loops were correlated with damage observed from the scar profile and the micrographs. In addition to elliptical and quadratic loops, triple loops were also identified. The existence of strong adhesion results in an increase of shear force, whereas subsequent drop in shear force is due to third body formation at the contact interface. Higher magnification micrograph reveals fatigue striations at the contact edge, while the fracture features were observed in the central region. The surface morphological features of the material under seizure conditions, which have been observed under a normal load of 250N and displacement amplitude of 50µm, shows large scale cracking on one side of the pin and the flat. Micrographs at higher magnification of the cracked surface just adjacent to the contact interface shows formation of slip bands within the grains, whereas the central region reveals shear fracture. Coated surfaces shows major surface degradation mainly in the form of fracture and spalling of the coatings. Energy dispersive spectroscopy (EDS) shows the occurrences of material transfer between the contacting surfaces. Frictionally constrained conditions have also been investigated at high normal load of 600N and for displacement amplitude in the range of 25µm to 200µm. Constant shear force with number of cycles and dependence of friction force on displacement amplitude were observed as the typical characteristics of frictionally constrained bodies. Two distinct regions, viz. center stick region and annular micro slip region, indicate the existence of partial slip regimes. Junction growth due to plastic flow of the material resulted in an increase of real area of contact at the contact interface. It is believed that the cyclic variation in the contact area, under cyclic tangential loading, may have given rise to micro slip in the annular region, and finally resulted in two distinguishable regions. It has been observed that the occurrence of micro slip in the annular region resulted in the material transfer from flat to pin surface, as evident from EDS responses. Damage in the form of circumferential cracks has also been observed in the annular region, whereas the center region shows features of shear fracture. Detail micro structural studies have been carried out for two extreme conditions, viz., gross sliding and seizure conditions. The conditions were identified mainly based on shear force variation with number of cycles and running condition fretting loops. Subsurface damage under both conditions has been compared based on the severity of plastic deformation and the orientation of subsurface cracks. Severity of plastic deformation has been quantified based on hardness variation along depth. A steep gradient of hardness indicates that the damage is very much confined in the region just beneath the contact interface. Gross sliding condition at the contact interface resulted in the propagation of subsurface cracks parallel to the surface, whereas under seizure condition the cracks were found inclined at an angle between 450 and 540 to the surface. Further, severe plastic deformations under seizure condition have resulted in the formation of shear bands and were found oriented in the direction of macroscopically imposed plastic flow. Influence of initial surface roughness on wear damage has also been quantified based on energy wear coefficient. Higher energy wear coefficient has been found for machined pin under sliding condition, whereas, under seizure condition polished pin shows higher energy wear coefficient. A computer code has been developed for the evaluation of surface and subsurface stress field, under both partial slip and gross sliding condition. Cattaneo and Mindlin approach has been adopted to model the partial slip condition. Energy based approach has been adopted for the quantification of damage observed under both contact conditions. Shear strain energy density and normalized strain energy release rate have been evaluated at the surface and in the subsurface region. Effect of contact conditions and the influence of coefficient of friction on stress field have been studied in detail. Analysis results shows that gross sliding results in higher tensile stress at the trailing edge, as compared to the stress induced under partial slip condition. Further, it has been observed that higher shear strain energy density at the surface and in subsurface region controls the nucleation of damage under both partial slip and gross sliding conditions. A criterion for the no growth of subsurface cracks has been discussed based on the distribution of stress intensity factor and normalized strain energy release rate as a function of crack size. It has been observed that subsurface cracks can grow up to significant depth depending on the crack propagator energy. The availability of crack propagator energy depends on coefficient of friction and contact conditions prevailing at the contact interface. The analytical results were found in good agreement with experimental observations. Non-linear analyses have been carried out using finite element analysis to evaluate stress and strain fields, assuming the existence of fully stick condition at the contact interface. Fully stick condition simulates the contact condition under strong adhesion. The analysis investigates the effect of shear or tangential loading on pressure distribution, contact radius, energy dissipation, and damage mechanism involved under elastic-plastic deformation. The accumulation of equivalent plastic strain in each cycle is believed to be responsible for ductile fracture. It has been observed that both cyclic plasticity and ratcheting are involved in the damage mechanism. Ratcheting has been observed as the governing damage mode under cyclic tangential loading condition. In contrast to this, due to limited ductility or brittle nature of coated surfaces, stress based criteria governs the damage. Continuous micro slip model has been developed to evaluate the displacement field and shear force distribution for partial slip and gross sliding condition. Further, the studies have been carried out to study the influence of relative tangential modulus of the contacting bodies on displacement field and shear force distribution. Plane strain and axisymmetric elastic elements are considered in the modeling while the interfacial layer has been modeled as an elastic-plastic layer. The model gives the shear force distribution at the contact interface and subsequently subsurface stress field can be estimated, once the tangential stiffness of the contact interface layer is known. The value of tangential modulus can be estimated either from numerical analysis or from experiments. Further, the study shows that as the relative tangential modulus of an interfacial layer increases, the shear force becomes more intense in the stick-slip transition region making this location more prone for damage nucleation.

This study investigated localized corrosion behavior of austenitic stainless steels under stressed and unstressed conditions, as well as corrosion of metallic thin films. While austenitic stainless steels are widely used in corrosive environments, they are vulnerable to pitting and stress corrosion cracking (SCC), particularly in chloride-containing environments. The corrosion resistance of austenitic stainless steels is closely tied to the alloying elements chromium, nickel, and molybdenum. Polarization curves were measured for five commercially available austenitic stainless steels of varying chromium, nickel, and molybdenum content in 3.5 wt.% and 25 wt.% NaCl solutions. The alloys were also tested in tension at slow strain rates in air and in a chloride environment under different polarization conditions to explore the relationship between the extent of pitting corrosion and SCC over a range of alloy content and environment. The influence of alloy composition on corrosion resistance was found to be consistent with the pitting resistance equivalent number (PREN) under some conditions, but there were also conditions under which the model did not hold for certain commercial alloy compositions. Monotonic loading was used to generate SCC in in 300 series stainless steels, and it was possible to control the failure mode through adjusting environmental and polarization conditions. Metallic thin film systems of thickness 10-200 nm are being investigated for use as corrosion sensors and protective coatings, however the corrosion properties of ferrous thin films have not been widely studied. The effects of film thickness and substrate conductivity were examined using potentiodynamic polarization and scanning vibrating electrode technique (SVET) on iron thin films. Thicker films undergo more corrosion than thinner films in the same environment, though the corrosion mechanism is the same. Conductive substrates encourage general corrosion, similar to that of bulk iron, while insulating substrates supported only localized corrosion.

M.Ing. / In this study a comparison is made between the punching shear capacities of square slabs reinforced with 3CR 12 corrosion resisting stainless steel and high tensile strength carbon steel. A square column 11 0 mm x 11 0 mm is used to simulate the point load on the slab. Three different slab depths were chosen for the experimental procedure. The South African concrete design specification SABS 0 I 00, the Eurocode concrete design specification and Menetrey's design model are used to determine the theoretical punching shear capacities of the slabs. It is concluded in this study that the procedures described in the concrete design codes and by Menetrey to determine the punching shear stress of concrete slabs reinforced with high strength carbon steel reinforcing bar compare well with the experimental results when 3CR I 2 corrosion resisting steel is used as reinforcing bar in concrete. The experimental results do not compare well with the theoretical results when the new Eurocode is used.

In this study, the corrosion resistance of three different stainless steels (304, 316 and 309) towards eutectic chloride salts is investigated. The performances of two materials to reduce the corrosion of the steels are examined: zirconium as sacrificial anode and an Al2O3 coating deposited by flame spraying. Samples are submitted to a 24 hours corrosion test at 700°C in air. The samples are characterised by weight analysis, SEM observations and EDX analysis of their surface and cross-section. The corrosion resistance of the stainless steels is not improved by adding Zr rods in direct contact with the steel, rather decreased in the areas where the rod laid. However, in these conditions, stainless steel 316 has the best resistance to highly corrosive chloride salts. The Al2O3 coating is too porous and penetrated by the salt, the steel underneath is corroded. Nevertheless, some alumina remains intact after the corrosion test, because of the high inertness of the ceramic. The presence of O2 most certainly accelerated the corrosion mechanism studied here.