Sigma phase leads to deterioration of corrosion resistance of super duplex stainless steels (SDSS) and its volume fraction increases as the time which the materials is exposed in determined temperature increases. In the present study, the effect of the short aging time on the formation of the sigma phase and on the corrosion behavior of UNS S32520 SDSS at 3.5% sodium chloride solution was evaluated using microstructural characterization, linear potentiodynamic polarization curve and electrochemical impedance spectroscopy. The results indicated that the SDSS sample solution-treated at 1150ºC and aged at 850ºC for 5 min may improve the corrosion resistance in comparison with the as-received and solution-treated conditions, due to the better partition of the elements Cr, Mo and dissolution of certain amount of sigma phase in the microstructure. However, results also showed that when SDSS solution-treated at 1150ºC is aged at 850ºC with the aging time slightly superior (10 min), the precipitation of sigma phase increases leading to a rapid deterioration of the corrosion resistance of the material.

Corrosion of AA7075-T73 aluminum alloy during machining process was studied. An experimental device was proposed in order to simulate machining procedure. A design of experiments - DOE was used in order to evaluate what process parameter is significant. Some electrochemical tests based on open-circuit potential vs time measurements and potentiodynamic polarization were performed in machining fluid of low and high chloride concentrations. Results from DOE showed that the chloride concentration in machining fluid and the presence or not of a zinc coating on the bench vice jaw material in the machining system, along with the interaction between these both factors are significant. OCP results showed oxide growth with time in low and high chloride concentration machining fluid. Passivity breakdown was only observed in high chloride concentration machining fluid. Best fitted parameters were applied to a large scale aeronautical manufacturing company, achieving 95 % reduction in corrosion appearance on the manufactured parts.

The work aims the study of the corrosion behavior of nitride plasma-assisted PVD coated Ti-6Al-4V alloy in 2 M NaOH at 25 and 60°C, using open-circuit potential (OCP) versus time measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The uncoated Ti-6Al-4V alloy showed a passive behavior. The TiN and TiAlN/TiAlCrN coated Ti-6Al-4V alloy also presented a passive behavior and the corrosion potential remained at the same range when compared with the potential of the uncoated alloy. The TiN hard coating showed a superior corrosion resistance, which was evidenced by lower corrosion current densities and higher impedance values. The increase in temperature decreased the corrosion resistance of both uncoated and coated alloy in NaOH.

316L stainless steel and Hydroxyapatite (5, 20 and 50 wt. (%) HA)-316L stainless steel composites were fabricated by mechanical alloying technique, pressing and sintering from 316L and HA powders. The corrosion behavior of both sintered 316L and HA-316L composites was evaluated by electrochemical techniques in simulated body fluid (Ringer's solution) and in 0.1M HCl solution which simulates occluded cell corrosion conditions. The results indicate that 316L stainless steel and HA-316L composites are passive in Ringer's solution and active in HCl solution. All materials are highly corrosion resistant in Ringer's solution with corrosion current density in the order of 10-6 A cm-2 or less. Both 316L stainless steel and 5% HA-316L composite present good corrosion resistance in HCl with corrosion current density in the order of 10-5 A cm-2. The corrosion resistance decreases with increasing HA content in both solutions.

The electrochemical behavior of three titanium dental implants purchased on the Brazilian market was evaluated in artificial saliva using open-circuit potential measurements, electrochemical impedance spectroscopy and potentiodynamic polarization. The three implants are passive in this medium but their corrosion resistance and the stability of their passive oxide films are quite different. Although the three implants were made of commercially pure grade titanium, their corrosion current densities and passive current densities were shown to differ from one to two orders of magnitude.

Villarrica is an active stratovolcano located in the Southern Andean Volcanic Zone. About 13,800 years BP (conventional radiocarbon ages), this volcano experienced major explosive eruptions which resulted in the emission of a sequence of pyroclastic flows, known as the 'Licán Ignimbrite', the bulk volume of which is estimated in -10 km³ (non-DRE, Dense Rock Equivalent). The deposits mainly consist of massive pyroclastic flows and stratified pyroclastic surges. Typical flow fades showscoriaceous bombs, dense juvenile blocks, lithics and scoria lapilli immersed in a dark-grey to brownish matrix, whereas surges expose lapilli-sized scoria in a fine, light-brown or yellow-green matrix. Juvenile clasts range from 55 to 58 wt% Si0(2) in composition. This paper describes the general architecture of the Licán Ignimbrite deposits and, based on SEM (Scanning Electron Microscope) observations and lithologic data, emphasizes the role of fragmentation due to magma-water interaction during the eruption. The results indicate that gas expansion was an important process. However, field characteristics, surface textures of ashes, enrichment of lithics towards the top of the sequence and variable palagonitization of matrix glass show the intervention of water since the initial stages of the eruption and its increasing influence during the later phases

El Villarrica es un estratovolcán activo, situado en la Zona Volcánica de los Andes del Sur. Hace aproximadamente 13.800 años AP (edades 14C no calibradas), este volcán sufrió un evento explosivo importante que dio lugar a la emisión de una secuencia de flujos piroclásticos, conocida como la 'Ignimbrita Licán', cuyo volumen ha sido estimado en -10 km³ (no-ERD, Equivalente de Roca Densa). Los depósitos consisten, principalmente, en flujos piroclásticos macizos y oleadas piroclásticas estratificadas. Las facies típicas que resultan de los flujos presentan bombas escoriáceas, bloques juveniles densos, fragmentos líticos y lapilli escoriáceo, inmersos en una matriz cuyo color varía entre gris oscuro y pardo. Por otro lado, los depósitos de oleadas están constituidos por escorias de tamaño lapilli, contenidas en una matriz fina, de color pardo claro o amarillo verdusco. La composición de los clastos juveniles es andesítico-basáltica a andesítica (55 a 58% en peso de Si0(2)). Este artículo presenta la estructura interna general de estos depósitos, observaciones realizadas en el MEB (Microscopio Electrónico de Barrido) y datos litológicos y granulométricos, con el propósito de determinar el papel que jugó la fragmentación debido a la interacción magma-agua durante la erupción. Los resultados indican que la expansión de gases pudo ser un proceso importante. Sin embargo, características de terreno, texturas superficiales de cenizas, el enriquecimiento en fragmentos líticos hacia el techo de las secuencias y la palagonitización variable del vidrio de la matriz sugieren un incremento de la intervención del agua durante el transcurso de la erupción