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The most important commercial casting alloys are those based on Al–Si. Their technical characteristics are highly connected to their as-cast microstructure, which is translated by the secondary dendrite arm spacing (SDAS). The alloy microstructure has been demonstrated to be changed by the adding of certain alloying elements, in the sense of boosting the desired properties and features. Search has been intensified to provide a positive balance of several properties, such as: high yield strength, high electrical conductivity, and high corrosion resistance, besides maintaining the ability for the alloy to be conventionally solidified. Under such context, both addition of Ag and the control of the fineness of the dendritic structure can be alternatives seeking better properties for Al–Si alloys. In addition to the possibility of application in current studies contributing to the growing development needs as engine materials, Al–Si–Ag alloys can emerge as an alternative to the manufacture of parts for electric vehicles, such as rotors and inverters, where high mechanical strength, corrosion resistance and electrical conductivity are required. Corrosion findings of Al–Si–Ag specimens having quite different SDAS of five alloys are presented here: Al-5wt.% Si, Al-5wt.% Si-0.1wt.% Ag, Al-10wt.% Si-0.1wt.% Ag, Al-5wt.% Si-2wt.% Ag, Al-10wt.%Si-2wt.%Ag alloys. A complete set of characterization with potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests, optical microscopy and scanning electron microscopy (SEM) was developed for these alloys. It has been demonstrated that increase in the alloy Si content diminishes corrosion resistance, and that increase in Ag content, considering Al-10% Si alloys, reduces corrosion resistance as well, despite creating thicker passive films. Furthermore, the alloys with the lowest Ag content (0.1 wt.%) had the greatest corrosion performance among the Ag-containing alloys, while the microstructure refinement tends to enhance the nobility of the samples.

The aim of this study concerns the effect of multi-pass shielded metal arc welding (SMAW) on the corrosion behavior of CW6MC cast nickel alloy. Using optical and SEM techniques the welded joint is analyzed. Vickers microhardness mapping and potentiodynamic polarization in NaCl and H2SO4 solutions are also evaluated. Both the Laves phase and NbC-type carbides are identified in the base metal (BM) and weld metal (WM) regions. The main microstructural difference observed between these regions is the morphology aspect and fineness of the dendritic arrays. The welding process promotes the finer columnar grains formation with refined intermetallic particles in the WM than equiaxed grains of the BM, which in turn results in higher microhardness values in the former region. However, no substantial changes were observed in the corrosion behavior between the BM and WM regions, considering both acid and saline media. Nevertheless, during the multi-pass SMAW process, some non-metallic micrometric inclusions (Mo and S-rich regions) can be constituted to occur in the WM region. This is associated with a significant drop in the corrosion performance of this region when the electrochemical tests are evaluated.

Made available in DSpace on 2021-06-25T10:26:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this study, the compatibility and corrosion behavior of carbon steel, stainless steel, aluminum and copper in contact with blends composed of biodiesel (consisting of soybean oil, beef tallow and swine lard) and petrodiesel were evaluated. Static immersion tests (total, partial and crevice) and exposure in vapor phase were carried out for 2160 h at 50 °C. Our main findings indicate that fuel blends influence the corrosion behavior, being observed a less corrosive attack on the materials, except for copper that presented an anomalous corrosion behavior, with a clear trend towards lower corrosion rates. Carbon steel and stainless steel in total, partial and crevice tests presented surface morphology with slightly changes, while carbon steel exposed in vapor phase showed corrosive attack. Copper presented the highest corrosion rates in partial (9.5273 μm/y), total (9.1484 μm/y) and crevice (6.6178 μm/y) tests in the B7 blend, respectively; and the lowest corrosion rates in total (0.0547 μm/y) for the B15 blend; in partial (0.4926 μm/y) and crevice (0.0182 μm/y) tests for the B30 blend. Among the materials evaluated, copper showed higher influence on biodiesel oxidative stability. Aluminum exhibited good compatibility and did not show any compound formed on its surface without presenting any corrosion. Munir Rachid Corrosion Laboratory Department of Materials Engineering Federal University of São Carlos, Rodovia Washington Luis, Km 235 Department of Mechanical Engineering Federal University of São Carlos, Rodovia Washington Luis, Km 235 Center for Monitoring and Research of the Quality of Fuels Biofuels Crude Oil and Derivatives (Cempeqc) Institute of Chemistry São Paulo State University (UNESP), Prof. Francisco Degni 55, Zip Code 14800-060 Department of Materials Engineering Federal University of São Carlos, Rodovia Washington Luis, Km 235 Center for Monitoring and Research of the Quality of Fuels Biofuels Crude Oil and Derivatives (Cempeqc) Institute of Chemistry São Paulo State University (UNESP), Prof. Francisco Degni 55, Zip Code 14800-060 CAPES: 001 CNPq: 130347/2015-9 CNPq: 311163/2017-3

Shrimp shells are a raw material rich in chitin, a precursor of chitosan biopolymer. The variables of processing (demineralization, deproteination and deacetylation) can be manipulated to determine the main characteristics of chitosan, the degree of deacetylation (DD), and average molar mass. This study evaluated the influence of one of the unit operations of shrimp shell physical processing, the milling, on the final product characteristic, chitosan. After different milling conditions, the raw material was subjected to standard chemical processing for chitin extraction, followed by deacetylation to obtain chitosan, which is characterized by 1H NMR, SEM, XRD, N2 physisorption (BET) and viscometry. The results indicated that the milling time of the raw material can be manipulated to increase the material depolymerization, significantly influencing the molecular weight reduction of chitosan a desirable feature for many applications of this biopolymer, and usually obtained by complex chemical and enzymatic methods.

An investigation was made of the effect of aging for up to 2000 h at 475 °C on the properties of the newly developed lean duplex stainless steel (LDSS) 2404. Due to its lower alloying content, the degradation of corrosion resistance as a function of thermal aging evolves more slowly in LDSS 2404 than in a standard duplex alloy (DSS 2205). The results also suggest that the mechanism of α' phase formation in the ferritic matrix occurs by spinodal decomposition and that this phenomenon has a stronger impact on the steel’s mechanical properties than on its corrosion behavior.

The relationship between alloy chemical composition and oxidation behavior of austenitic Fe-Mn-Si-Cr-Ni shape memory stainless steels (SMSSs) during exposure at 800 °C in air was investigated. Although high Si and Cr additions are beneficial for both the shape memory effect and oxidation resistance, the increase of these ferrite stabilizer elements in Fe-Mn-Si-Cr-Ni SMSSs makes the oxidation-induced ferrite stable at the early stages of the oxidation exposure, which in turn allows a faster diffusion of Mn, controlling the kinetics of oxidation. Our results suggested that the austenite stability should be maintained during the oxidation process for higher performance of these materials.