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The present work aimed to create a hard surface on a titanium surface via plasma nitriding to improve microhardness and wear properties of the as-cast (α-CP-Ti (CP–Ti), α+β-Ti6Al4V (Ti–Al–4V), and β-Ti-33Nb–33Zr (TNZ-33) samples. For the nitriding process, two temperature conditions (650 °C and 700 °C) were used. The presence of nitrides was evaluated by XRD. The microstructure and chemical composition were studied by electron microscopy and EDS. The roughness was evaluated by confocal microscopy. The microhardness and wear properties were analyzed using the Vickers microhardness and micro-abrasive wear test. Plasma nitriding led to the formation of TiN on CP-Ti, TiN, and Ti2N on Ti–6Al–4V, and TiN and ZrN on TNZ-33 samples. At 700 °C, the TiN increased on CP-Ti, while the Ti2N increased for Ti–6Al–4V and the ZrN increased for TNZ-33. The length of the nitride layer decreased when the temperature increased for CP-Ti and Ti–6Al–4V samples. However, for the TNZ33 alloy, the layer increased from 6.3 to 7.6 μm. The chemical analyses confirmed the presence of nitrogen on the substrate surfaces. After the nitriding process, all materials significantly increased the hardness. The hardness after plasma nitriding can be followed by: CP-Ti > TNZ-33> Ti–6Al–4V (at 650 °C); CP-Ti > Ti–6Al–4V > TNZ-33 (at 700 °C). The wear properties of all samples were improved after plasma nitriding treatment.

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.

TiN granular thin films were deposited on SiO2 substrates using cathodic cage plasma nitriding (CCPN) and SEM images, roughness analysis, contact angle measurements, and X-ray diffraction (XRD) were employed to characterize the structure of these films varying time and temperature of the process. Results have shown an inverse relationship between roughness and contact angle. Thin films with low roughness have presented higher contact angle values, and the opposite was observed in the films with more prominent or more grains per area. TiN is a hydrophobic material, and the decrease of contact angle value presented in some films produced occur due to modification of the morphological characteristics, which the roughness measurements and hysteresis of contact angle confirmed it, specifically, for samples synthesized at 2h and 350°C, the roughness is the smallest, and the contact angle is the largest [(111.23±8.87)°]. This connection between roughness and contact angle is essential, and it can be used to describe and characterize the most types of thin films produced by plasma deposition and to infer the surface modifications with different atmospheres of treatment.

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.

The 2524-T3 aluminium (Al) alloy produced by ALCOA may be used as skin material by the aircraft industry. Some studies are available in the literature about fatigue and fatigue - corrosion behaviour of 2524-T3 Al alloy. However, the corrosion mechanisms are not yet fully understood since the material has a very complex microstructure due to impurities and the addition of alloying elements which lead to an increase in the localized corrosion process. It is known that the corrosion process in Al alloys, most of the time, is due to the galvanic coupling of the intermetallic particles (IMs) and the Al matrix. Thus, the use of protective coatings appears as a possible alternative against the advancement of the corrosion process of the 2524-T3 alloy. In this way, a set of DLC films was obtained by using physical vapor deposition (PVD) method and characterized by various techniques including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic force microscopy (AFM) and Raman spectroscopy. The deposited films on the surface of the 2524-T3 Al alloy were characterized electrochemically by using potentiodynamic polarization curves (PPc), electrochemical impedance spectroscopy (EIS) and mechanically by using micro-abrasive wear tests (MAWTs). The results show an advantage in using the PVD method to produce thin films on the 2525-T3 Al alloy surfaces, as the wear resistance of the Al alloy coated by DLC film is higher than for the bare material and the corrosion resistance of the material is not compromised. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1321

The aim of this work was to study the influence of thermochemical treatment of ionic plasma nitriding on the resistance to micro-abrasive wear and to the corrosion process of AISI 316L and AISI 470 stainless steels. The thermochemical treatment was performed at different times and temperatures with a gas mixture of 25% H2 and 75% N2. The treated materials were characterized by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tests, micro-abrasive wear tests (MAWTs) and corrosion tests. The results show an increase in the thickness of the layer formed by increasing treatment time and in the wear resistance of the materials studied. Temperatures exceeding 450 °C favor the formation chromium nitrides, which, for being very hard broke making the formed layer brittle decreasing the wear resistance of the material. In addition, the formation of these phases substantially decrease the corrosion resistance of stainless steels. Keywords: Corrosion, Wear tests, Expanded ferrite, Expanded austenite

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.

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 2524-T3 aluminium (Al) alloy produced by ALCOA may be used as skin material by the aircraft industry. Some studies are available in the literature about fatigue and fatigue - corrosion behaviour of 2524-T3 Al alloy. However, the corrosion mechanisms are not yet fully understood since the material has a very complex microstructure due to impurities and the addition of alloying elements which lead to an increase in the localized corrosion process. It is known that the corrosion process in Al alloys, most of the time, is due to the galvanic coupling of the intermetallic particles (IMs) and the Al matrix. Thus, the use of protective coatings appears as a possible alternative against the advancement of the corrosion process of the 2524-T3 alloy. In this way, a set of DLC films was obtained by using physical vapor deposition (PVD) method and characterized by various techniques including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic force microscopy (AFM) and Raman spectroscopy. The deposited films on the surface of the 2524-T3 Al alloy were characterized electrochemically by using potentiodynamic polarization curves (PPc), electrochemical impedance spectroscopy (EIS) and mechanically by using micro-abrasive wear tests (MAWTs). The results show an advantage in using the PVD method to produce thin films on the 2525-T3 Al alloy surfaces, as the wear resistance of the Al alloy coated by DLC film is higher than for the bare material and the corrosion resistance of the material is not compromised. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1321

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.

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.

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.