ABSTRACT This work aims to evaluate the influence of welding parameters, current intensity and deposition speed, on the bead geometry, dilution, morphology and properties of a nickel-based alloy coating. For this, single beads of Inconel 625 alloy were deposited on the substrate of ASTM A36 Steel, by PTA-P process. The samples were sandblasted and polished. The samples were chemically etched by a solution of 92 mL HCl, 3 mL HNO3 and 5 mL H2SO4 for 5 minutes. The geometry of the beads (reinforcement height, bead width, penetration and contact angle) was measured through the digital stereoscope microscope. The microstructures of the cross sections were evaluated by optical microscopy and scanning electron microscopy (SEM), to identify the possible presence of precipitated phases in the ferrite matrix. The chemical composition of these present phases, as well as the diffused iron content from the substrate for the coating, were measured by EDX. The type of the phases precipitated by x-ray diffraction in the top samples of the coating were also evaluated, in 1.5 mm height of reinforcement. For mechanical property analysis, the microhardness of the coatings was measured by Vickers microhardness test to evaluate their relationship with the iron present in the coatings, which diffused from the substrate. The results confirmed the influence of welding parameters on coating dilution - Current is the parameter of greatest response. The morphologies of the coatings were presented as a γ matrix with second phase precipitation composed of Ni, Nb, Cr and Mo. The concentration of these precipitations decreased with increasing dilution. This occurred because of the increased migration of Fe present in the substrate of the coating through the diffusion phenomena, with increasing dilution. The Fe reduced the solubility of Nb and Mo of the γ matrix, causing the decrease of its hardness.

RESUMO O presente trabalho teve como objetivo desenvolver e caracterizar revestimentos nanocompósitos de Ni e Ni-Grafeno aplicados em superfície de aço API 5L X80, utilizando o processo de eletrodeposição, para obter melhores propriedades anticorrosivas. Corpos de prova de dimensões de 20x20x3 mm foram submetidos à limpeza e preparação metalográfica, para posterior deposição dos revestimentos. Para o processo de eletrodeposição foi utilizado um banho à base de níquel contendo dodecil sulfato de sódio (SDS) como surfactante. Para obtenção dos revestimentos Ni-Grafeno, foram adicionadas partículas de grafeno (0,2g/L) ao banho eletrolítico. Os eletrodepósitos obtidos foram caracterizados por Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV). A resistência à corrosão dos revestimentos foi avaliada por meio de ensaios de Polarização Linear (PL) e Espectroscopia de Impedância Eletroquímica (EIE). A inserção de grafeno ao revestimento promoveu a formação de depósitos com grãos mais refinados, e com a direção de crescimento de cristais bem definida. Foram observados depósitos com estruturas lamelares sobrepostas, associadas ao grafeno incorporado à matriz de Ni. A deposição de grafeno influenciou na orientação preferencial dos grãos durante o processo de eletrodeposição, sendo o plano (200) idenfiticado como a orientação preferencial para o nanocompósito Ni-Grafeno. O revestimento Ni-Grafeno obteve melhor desempenho anticorrosivo em comparação ao revestimento de Ni puro e ao metal base, apresentando valor de potencial de corrosão (Ecorr) mais elevado, menor valor de densidade de corrente de corrosão (icorr) e módulo de impedância (|Z|) superior.

ABSTRACT The aim of the present work was to develop and characterize nanocomposite coatings of Ni and Ni-Graphene applied on API 5L X80 steel surface, using the electrodeposition process, to obtain better anticorrosive properties. Test specimens of dimensions of 20x20x3 mm were submitted to metallographic cleaning and preparation, for later deposition of the coatings. For the electrodeposition process, a nickel-based bath containing sodium dodecyl sulfate (SDS) was used as the surfactant. To obtain the Ni-Graphene coatings, graphene particles (0.2 g/L) were added to the electrolytic bath. The electrodeposits obtained were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The insertion of graphene to the coating promoted the formation of deposits with more refined grains, and with a well-defined crystal growth direction. Deposits with overlapping lamellar structures were observed and associated to the graphene incorporated into the Ni matrix. The deposition of graphene influenced the preferential orientation of the grains during the electrodeposition process, with the plane (200) being identified as the preferred orientation for the Ni-Graphene nanocomposite. The Ni-Graphene coating obtained better corrosion performance in comparing to the coating of pure Ni and the base metal, presenting a higher corrosion potential value (Ecorr), lower corrosion current density (icorr) value and higher impedance modulus (|Z|).

This paper aimed to develop and characterize superhydrophobic surfaces with anticorrosive properties obtained by the chemical modification of the 5052 aluminum alloy with variation of acid etching time, formation of lamellar double hydroxides (LDH) film and immersion in stearic acid. The specimens were etched in HCl (2M) at 5, 10 and 30 min. The aluminum plates were treated with aqueous solution of zinc nitrate (0.1 M) in the presence of ammonia and then immersed in a stearic acid and ethanol solution (1% w/w) to reduce surface energy. Contact angles (CA) were determined. Surface morphology and composition were analyzed by scanning electron microscopy (SEM) and X-ray energy dispersion spectroscopy (EDS), respectively. Linear polarization tests were performed to analyze corrosion resistance. The optimal superhydrophobic performance was obtained with a contact angle of 154º for 30 min of acid etching. This condition also showed higher corrosion resistance, obtaining higher values of Ecorr and lower values of corrosion current density.

Friction surfacing (FS) is a coating technique applied mainly in corrosion protection and repair of components. The study addresses the effects of deposition and rotational speeds on the rods characteristics and process efficiency for the deposition of Ti-6Al-4V on self-mating substrates by FS. The consumption rate was 1.8 mm/s, deposition speeds of 8, 16 and 24 mm/s and rotational speeds of 2000, 3000 and 4000 rpm. It was shown that the flash forms primarily at the rod, ascending around the tip and leaving the coating without flash. The higher deposition speeds led to a decrease in rod thickness and diameter. For higher rotational speeds, an increase in diameter and decrease in thickness is observed for the flash on the rod. Experiments have shown that the rotational and deposition speeds have a decisive influence on the flash formation. Its microstructure changes due to the welding process and a change in hardness can be observed.

This paper sets out to evaluate the corrosion of ASTM A131 grade A36 carbon steel exposed to a diesel oil S10 / saline water system and the biodegradation of diesel oil S10 to simulate storage, transport and fuel use systems during a period of 30 days. The corrosion process was investigated through electrochemical tests of Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization (LP). The morphology of the corrosion products were analyzed by Scanning Electron Microscopy (SEM). The results showed that the presence of saline water in the system containing diesel oil is an aggravating factor which promotes the biodegradation of the fuel and, consequently, aggravates the corrosion process.

Corrosion of pipelines can be significantly affected by the activity of microorganisms present in the environment. The objective of this work was to investigate the influence microbial in the corrosion behavior of API 5L X80 steel in produced water by open circuit potential, polarization curves and electrochemical impedance spectroscopy measurements. Physical-chemical and microbiological analyzes were performed in the produced water and the tests were conducted in biotic and abiotic systems. The films and corrosion morphology developed in the steel over time were characterized by scanning electron microscopy. The results confirm that the activity of the consortium of microorganisms in the formed biofilm accelerated the dissolution of the iron, causing pitting corrosion in the steel exposed to the biotic system. Through the adjustment of the equivalent electrochemical circuit, the impedance results allowed to interpret the interactions between electrode, film and electrolyte.

The mechanical behavior of the API 5L X80 steel exposed to the produced water by the petroleum industry, besides being dependent on the intrinsic properties of the steel, is influenced by the corrosivity characteristics of the electrolyte that may be associated with the presence of microorganisms. The objective of this work was to investigate the plastic deformation of API 5L X80 steel exposed to produced water. The tests were conducted in static systems (abiotic and biotic) containing produced water after 360 days. The process of corrosion of the coupons were evaluated by topographic 3D analysis and roughness, and the mechanical behavior by tensile test and fracture analysis by scanning electron microscopy. Surface topography and roughness were modified by the interaction of the consortium of microorganisms with the substrate associated with the corrosion process. The results indicate that microorganisms induced the formation of pits which caused the coupons to lose plasticity.

Refill friction stir spot welding (refill FSSW) is a solid state joining technology developed and patented by Helmholtz-Zentrum Geesthacht. Refill FSSW is a welding process suitable for spot joining lightweight materials in similar and dissimilar joint configuration. The result is a spot welded in lap configuration with minimal material loss and a flat surface with no keyhole. In the present study, refill FSSW was applied to join the similar 6061 aluminum alloy sheet with 1.25 mm thickness. The objective of this work is to investigate the influence of the hook on the microstructure and mechanical properties of the weld. The hook is a geometrical feature, formed as a result of the upward bending of the sheet interface during the sleeve plunge and retraction during welding. The weld strength had a negative correlation with the hook height, however it was concluded that the shape of hook changes according to the combination of process parameters. The highest value of the lap shear corresponded to the smallest hook height.

RESUMO O presente trabalho teve como objetivo avaliar o processo de corrosão do Pb e da liga Pb-1,5%Sn quando submetidos à condição de ciclagem em meio de ácido sulfúrico, visando compreender a influência da adição de Sn na resistência à corrosão e na capacidade de recarga para grades positivas de baterias do Pb-ácido. As amostras de estudo foram preparadas pelo processo de fundição. A microestrutura dos materiais foi avaliada por microscopia óptica. Para simulação do processo de carga e descarga do eletrodo positivo, em acumuladores, realizaram-se testes de voltametria cíclica, em ácido sulfúrico (5M), na faixa potencial de 1,3 V a 2,2 V (vs ECS), totalizando 400 ciclos. A morfologia e a composição dos depósitos de produtos de corrosão foram analisadas, respectivamente, por Microscopia Eletrônica de Varredura (MEV) e Difração de Raios-X (DRX). Foram realizadas análises de perda de massa, Espectroscopia de Impedância Eletroquímica (EIE) e MEV para avaliar o efeito do processo de corrosão na superfície dos materiais analisados. O estudo mostrou que a adição do Sn promoveu um efeito de dopagem na camada de depósitos de corrosão formada, aumentando a eficiência de carregamento do acumulador e diminuindo a perda de massa por corrosão. A liga de Pb-Sn mostrou-se mais susceptível ao processo de corrosão intergranular e ocorrência de pites no grão em comparação ao Pb puro.

ABSTRACT The present work aimed to evaluate the corrosion process of the Pb and Pb-1,5wt%Sn alloy under cycling conditions in sulfuric acid, in order to understand the influence of Sn on the corrosion resistance and recharge capacity for positives grids of lead-acid batteries. The study samples were prepared by casting process. The microstructure of the materials was evaluated by optical microscopy. Cyclic voltammetry tests for simulation of charge and discharge of positive electrode in accumulators were carried out in sulfuric acid (5M) in the potential range of 1.3 V to 2.2 V (vs SCE), totaling 400 cycles. The morphology and composition of the corrosion product deposits were analyzed by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. Weight loss, electrochemical impedance spectroscopy (EIS) and SEM analysis were performed to evaluate the effect of corrosion process on the surface of the analyzed materials. The study showed that Sn addition promoted a doping effect on the formed corrosion deposits layers, increasing the charging efficiency of the accumulator and decreasing the weight loss by corrosion. The Pb1.5wt%Sn alloy showed to be more susceptible to the intergranular corrosion process and pitting corrosion in the grain compared to pure Pb.

This paper sets out to evaluate the corrosion and biocorrosion of carbon steel ASTM A283 exposed to a Diesel S10 oil/tap water system under static conditions for 90 days. The following analyzes were performed: physico-chemical in tap water, sulfur content in Diesel S10 and quantification of sessile microorganisms in the biofilm formed on the metal. To monitor the corrosion process, mass loss, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), confocal laser microscopy and X-ray diffraction (XRD) were performed. There were changes in the composition of the medium, correlated with the formation of corrosion and biofilm products. There was biodegradation of the fuel, which in contact with water influenced the development of microorganisms. Moreover, the corrosion rate was classified as moderate, the main form of corrosion being seen to be local alveolar corrosion. Therefore, the results revealed that water in diesel oil can be an aggravating factor in the process of corrosion and biocorrosion.

Co-Ni/SiC nanocomposite coatings were obtained by codeposition of SiC nanoparticles in a bath with nickel and cobalt, using API 5L X80 as the substrate. The influence of cathodic current density on deposit properties was investigated. Measurements of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) were performed in 3.5 wt% NaCl solution to investigate a corrosion performance. The morphology and chemical analysis of the surfaces were analyzed by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and related with micro-hardness and X-ray diffraction (XRD). The results indicate which composite coatings have acicular morphology, with higher micro-hardness values than those found for the carbon steel substrate. The Co-Ni/SiC coating increased the corrosion potential and the resistance to polarization, which resulted in lower corrosion rates than those obtained without uncoated steel.

Titanium Grade 1 was deposited on Ti-6Al-4V, 2 mm thickness, by Friction Surfacing. The process parameters were rotational speed, deposition speed and consumption rate. Only the rotational speed was varied in order to evaluate the influence of this parameter on the coatings generated. The applicability of the process has been described for a large number of materials, although the depositions of titanium alloys are still not widely studied. The objective is to investigate the effects of the rotational speed on the coatings' geometry and microstructural evolution. This investigation has shown that Titanium Grade 1 coatings can be deposited onto a Ti-6Al-4V by Friction Surfacing depending on the rotational speed. The coatings' surface homogeneity was influenced by the rotational speed, being inhomogeneous for the lowest speed. The coatings' thickness and width increased with enhancing this speed. The heat affected zone in the substrate corresponded to the complete thickness under the depositions.

Resumo A característica mais marcante da soldagem TIG Orbital é a constante alteração na posição de soldagem enquanto a tocha acompanha o perfil geométrico dos tubos. No contexto da soldagem TIG orbital de tubos de grande diâmetro e paredes espessas, é investigada a relação entre a posição de soldagem, uso de corrente constante ou pulsada e ainda valor da corrente média nas características geométricas dos cordões obtidos. Foram realizadas soldas de deposição em tubos de aço carbono SAE 1020, bem como macrografias das seções transversais dos cordões via microscopia óptica. Filmagens em alta definição contribuíram para a compreensão do comportamento da poça de fusão nas diferentes posições de soldagem. As características geométricas foram quantificadas através das macrografias com o uso de um software e foi traçada a relação destas com as variáveis citadas. Além disso, foi feita uma análise microestrutural das amostras, correlacionando com a microdureza Vickers. Concluiu-se que cordões soldados com corrente pulsada apresentam maiores reforço e largura, bem como maior dureza e microestrutura mais refinada. A posição vertical ascendente resulta em cordões com menor fator de forma e maior penetração, e a posição sobre cabeça resulta em cordões de baixo fator de forma.

Abstract The most important characteristic of TIG Orbital welding is the constant change in weld position while the torch follows the geometric profile of the pipes. In this context, large diameter and thick wall pipes orbital TIG welds were investigated, by studying the relation between the welding position, use of constant or pulsed current and magnitude of welding current and the resulting geometric characteristics. Weld beads were made on SAE 1020 carbon steel pipes, as well as transversal section macrographs via optical micrograph. High definition filming contributed to comprehension of the weld pool trend on different welding positions. Geometric characteristics were quantified through the macrographs by using software, and its relations with the cited variables were made. Besides that, a microstructural analysis was made, comparing it to Vickers micro hardness. One could conclude that beads made with pulsed current had higher reinforcement and width, as well as higher hardness and a finer microstructure. The ascendant vertical position resulted in low reinforcement form factor and higher penetration, and the overhead position results in low reinforcement form factor beads.

The development of shape memory actuators has enabled noteworthy applications in the mechanical engineering, robotics, aerospace, and oil industries and in medicine. These applications have been targeted on miniaturization and taking full advantage of spaces. This article analyses a Ti-Ni shape memory actuator used as part of a flow control system. A Ti-Ni spring actuator is subjected to thermomechanical training and parameters such as transformation temperature, thermal hysteresis and shape memory effect performance were investigated. These parameters were important for understanding the behavior of the actuator related to martensitic phase transformation during the heating and cooling cycles which it undergoes when in service. The multiple regression methodology was used as a computational tool for analysing data in order to simulate and predict the results for stress and cycles where the experimental data was not developed. The results obtained using the training cycles enable actuators to be characterized and the numerical simulation to be validated.

This article studies changes observed on the R-phase thermoelastic behavior in a near-equiatomic Ti-Ni shape memory alloy. Three kinds of procedures have been performed: different treatments, thermomechanical cycling under constant loading in shape memory helical springs and thermal cycling in as-treated and trained samples. Several heat treatments were carried out to investigate evolution of the R-phase by differential scanning calorimetry (DSC). A heat treatment was chosen on which R-phase is absent. Shape memory springs were produced and submitted to a training process in an apparatus by tensioning the springs under constant loading. Thermal cycling in DSC was realized in as-treated and trained samples. Several aspects of one-step (B2→B19') and two-steps (B2→R→B19') martensitic transformations and R-phase formation and their evolution during tests were observed and discussed.