Abstract Polymeric composite materials, presenting a practical solution for sealing non-metallic expansion joints under extreme conditions such as high temperatures and harsh chemical and physical abrasion, were investigated in this scientific study to discern the impact of welding parameters on their degradation and properties. The study entailed the bonding of polymeric composite blankets through hot plate pressing with a PTFE film, encompassing variations in temperature, duration, and load application. The findings elucidated that lower temperatures and shorter processing times failed to achieve optimal blanket adhesion, while higher temperatures led to material degradation, subsequently diminishing the mechanical strength of the welded joint. In contrast, extended processing times and the application of load during welding demonstrated a positive correlation, enhancing the mechanical strength of the joint by ameliorating interfacial adhesion. This research underscores the critical significance of carefully selecting welding parameters to ensure the peak performance and durability of polymeric composite structures.

Molybdenum trioxide (MoO3) thin films are generally deposit on metallic surfaces to increase their tribological performance. In this manuscript, MoOx coatings were for the first time deposited on plasma nitrided surfaces. Vickers microhardness tests, X-ray diffractometry, and micro abrasive wear tests characterized the samples. It was investigated the effect of temperature in hardness and tribological properties of austenitic stainless steel surfaces. When the temperature of plasma nitriding increases, the coating thickness and the nitrogen diffusion on the treated surface also increases, favoring the hardness of the coatings. After MoOx deposition, the predominant MoO3 phase with monoclinic and orthorhombic unit cells was observed. MoOx coatings after plasma nitriding demonstrated the highest wear resistance.

Resumo: Ao analisar a norma ABNT NBR 8800-2008, foi constatado que não há consideração sobre a tensão ou compressão exercida nas regiões soldadas por filetes. O cálculo para dimensionamento de perna só leva em referência o cisalhamento da seção. Utilizando recursos como a simulação e o ensaio mecânico de tração, foi possível comparar as dimensões mínimas das pernas com a estipulada pela norma NBR. Realizou-se o processo de soldagem com eletrodo revestido, utilizando o aço estrutural ASTM A36, e para realização da soldagem foi empregado o eletrodo AWS A5.1 E7018. As soldagens focaram com tamanho de filetes com perna entre 3,5 mm e 7 mm que posteriormente estas juntas soldadas foram submetidas a ensaios de tração. Para a comparação dos resultados, foi empregado simulação numérica estática em tração pelo método dos elementos finitos com auxílio do software Abaqus®. Assim com os dados gerados através da simulação e o ensaio mecânico de tração pode-se legitimar as especificações da norma em relação ao tamanho mínimo de perna em relação à espessura da chapa.

Abstract: It was found that there is no consideration of the tensile or compression stresses applied in the regions of fillet weld when analyzing the ABNT NBR 8800-2008 standard. The calculation for dimensioning the leg only takes into account the section shear. Using resources such as simulation and mechanical traction test, it was possible to compare the minimum dimensions of the legs with that stipulated by the NBR standard. The welding process was carried out with a coated electrode, using structural steel ASTM A36, and the welding was performed using the AWS A5.1 E7018 electrode. Tensile testing were performed on fillet welding samples with lengths between 4 mm and 8 mm. It was used a numerical simulation in traction by the finite element method was used with the aid of the Abaqus® software. Thus, with the data generated through the simulation and the mechanical tensile test, the specifications of the standard can be assured in relation to the minimum leg size in relation to the plate thickness.

In this paper, we present an alternative method to obtain thin films for coating protection on the surface of the AA2524-T3 Al-alloy by using the Layer-by-Layer (LbL) technique. The LbL films were fabricated by alternated immersion of the Al-alloy into a poly(styrene sulfonate) (PSS) and polyaniline nanoparticles (PAni-NPs) solutions, obtaining a PAni-NPs/PSS bilayer architecture. The LbL films were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), electrochemical and micro-abrasive wear tests. The results show that the number of bilayers promotes shifts to less negative potentials, indicating an optimized system, in which the best performance was observed for a 15-bilayer PAni/PSS LbL film. The pitting potential (Epit) values shifted 130 mV (from -610 mV to -480 mV) in comparing a bare Al-alloy. The predominantly wear mechanism for AA2524-T3 with PAni-NPs/PSS bilayers was scratching whereas for the bare material there was an equivalence between scratching and rolling mechanisms. The results proved that the incorporation of PAni-NPS by the LbL method may be propitious as protective coating against corrosion in AA2524-T3 alloy.

The aim of this work was to study the corrosion process of new aluminium alloy AA2524-T3 (Solution Heat Treated and Cold Worked), which is a promising substitute of the base line AA2024-T3 for aircrafts fabrication, by global and localised techniques in sodium chloride medium (0.05 mol L-1 NaCl). The open circuit potential results revealed a stochastic evolution of pitting events and to the resulting variations in the ratio of passive/active areas and/or cathode/anode, which may be related to the presence of different types of intermetallics. The cyclicvoltammetry showed that the corrosion potential (Ecorr) and the pit nucleation potential (E pit) values are quite similar (approximately -0.525 V). The results of EIS show that the corrosion rate is quite stable, with no tendency to increase or decrease for longer immersion periods. The results of SVET were in agreement with the results obtained by EIS technique, showing strong anodic activity on the surface with no repassivation along the whole immersion time. Besides, corrosion process led to significant surface degradation after 24h.

The development of controlled delivery system formulations has received increasing interest in the agriculture area. Tebuthiuron (TBH) is the most commonly used herbicide for weed control in sugar cane and cotton crops. The TBH and some of its metabolites are detected in surface water by leaching process, evidencing contamination and the need for an efficient process to decrease pesticide residues. The development of a controlled system release appears as a good solution. The present investigation aimed to study the development and evaluation of alginate microparticles as a delivery system for the TBH. The calcium alginate microparticles were prepared from the crosslinking of sodium alginate by Ca++ containing varied amounts of TBH supplied in CaCl2 aqueous solution. The particle size and morphological analysis of microparticles were determined by optical microscopy (OM) and by field emission gun scanning electron microscopy (FEG-SEM). The encapsulation efficiency and release of TBH studies was accessed by UV-vis spectroscopy. The results show that the polymeric microparticles containing TBH can be obtained successfully through a simple method and is suitable as a controlled release carrier system for herbicides and can be effective for controlling weeds.

Super duplex stainless steels (SDSS) have high corrosion resistance because of their high contents of chromium, nickel, molybdenum and nitrogen but low wear resistance. To improve the wear resistance of these steels without affecting their corrosion resistance, samples of SDSS were treated by plasma ion nitriding at temperatures ranging from 350 °C to 570 °C for two hours. This thermochemical treatment resulted in the formation of different types of nitrides that affected the microhardness, the microwear behaviour and the corrosion resistance of the metal surface. The microwear resistance decreased at 400 °C because different nitrides formed on the surface, thereby increasing the hardness and volume wear resistance of the steel. The test results showed that the alloys that were nitrided at 400 °C and 450 °C exhibited the highest corrosion resistance to a solution medium containing chloride ions.

P20 steel, which is mainly used in plastic molds, was thermochemically treated by ion plasma nitriding and solid and gas carburization. In this work, the solid and gas carburization were performed at 925 ºC for four different durations. The ion plasma nitriding was performed at 520 ºC for four different durations. The thermochemical treatment increased the micro abrasive wear resistance of the studied material. The gas carburizing treatment resulted in a greater surface microhardness. Longer treatment times increased the effectiveness of the thickness layer in all cases. The solid carburization produced a larger thickness layer than the gas carburization and ion nitriding.

O ensaio de micro desgaste abrasivo tem sido objeto de uma quantidade significativa de pesquisas nos últimos anos, quando o seu potencial para avaliar o comportamento de recobrimentos finos se tornou relevante. O objetivo deste trabalho é a construção de um dispositivo para a realização de ensaios de micro desgaste abrasivo por esfera fixa. O contato abrasivo é realizado por uma esfera de aço AISI 52100, a qual é presa num eixo que gira com grande precisão, com ajuda de um motor, em relação a uma amostra plana que se manterá estacionária. A carga normal de ensaio é aplicada através de ajustes de peso no suporte pivotado do corpo de prova, a qual pode ser variada a cada ensaio realizado. Este dispositivo foi utilizado para a determinação da resistência ao desgaste abrasivo e da eficácia de tratamentos de superfície utilizados em peças que sofrem este tipo de solicitação em serviço, além de utilizá-lo para estudar novos produtos desenvolvidos para o aumento de resistência ao desgaste de superfícies. Foi avaliada a resistência ao microdesgaste abrasivo de aço AISI 420 temperado e revenido. Observou-se que o aumento da dureza do material tratado aumentou a resistência ao desgaste abrasivo quando comparado com o material sem tratamento térmico.

The abrasive microwear testing has been the subject of a significant amount of research in recent years, when its potential to evaluate the behaviour of thin coating became relevant. The aim of this work is to build a apparatus for abrasive microwear testing by rotating sphere. The abrasive contact is performed by a AISI 52100 steel ball which rotates, with great accuracy with the help of an electric motor, in relation to a flat sample that will remain stationary. The normal load is applied by weight adjustments in the support of the test specimen, which can be varied for each performed test. This device was used to determine the abrasive wear resistance and effectiveness of surface treatments used in parts that undergo this kind of requirement in service, and also for studying new products developed for increasing the wear resistance of surfaces. The microwear resistance of the quenched and tempered AISI 420 steel was evaluated. It was observed that increasing the hardness of the treated material produced an increased wear resistance when compared with untreated material

The friction and wear properties of AISI 1045 steel, nylon 6.6 composites with different types and percentages of reinforcement and a nitrile rubber, Alpha 66, were submitted to sliding wear tests. The five types of nylon 6.6 composites tested generated matching, low values for the coefficient of friction. This may be due to the greater influence of the nylon 6.6 matrix on the coefficient of friction. However, the wear in nylon composites showed wide variation, determined by the type of reinforcement added to the composite. The other two materials tested, nitrile rubber and 1045 steel, showed behavior different from that of the composites. The NBR (signifying a norm established by the Brazilian Association of Technical Norms) rubber showed a superior coefficient of friction and greater wear. On the other hand, the steel showed a high coefficient of friction and low wear, suggesting that the coefficient of friction has no direct connection to the wear resistance of the materials studied here.

An investigation was made to determine the causes of surface contact fatigue failure of a case hardened driver pinion located in the intermediate shaft of a reducer gearbox used in a sugar and alcohol mill. The examination of the component revealed the presence of a cemented layer substantially thicker than that generally specified for pinions devised for this application. This, associated with the massive presence of brittle threadlike carbon-rich cementite phase (Fe3C) in prior austenite grain boundaries of the pinion teeth, favored surface crack nucleation and propagation during cyclic loading, leading to spallation of the contact surface with the counterpart gear, which impaired the system's operation. Poor carburization practice was discovered as the root cause of the mechanical failure, thus demanding the implementation of a new manufacturing route to avoid problems in similar load-bearing rotating components.