Criciúma, Brazil
Criciúma, Brazil

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Dos Santos D.C.,Engineering Mecanica | Magnabosco R.,State University of Maringa
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

The main purpose of this work is to analyze the mechanisms and kinetics of sigma phase formation of UNS S31803 stainless steel after isothermal aging between 850 e 900°C, evaluating the influence of sigma phase formation on pitting potential in 0.6M NaCl solution. Solution treated samples of the UNS S31803 duplex stainless steel were isotermically aged at 850°C or 900°C up to 360 h. The microstructural characterization of the samples was made through quantitative metallography, ferritscope analysis and Vickers microhardness. The cyclic polarization tests used to the determination of the pitting potential were conducted in polished samples. The electrochemical behavior of aged UNS S31803 duplex stainless steel in 0.6M NaCl solution is strongly dependent on the microstructure, since both changes in mechanisms and kinetics of sigma phase formation influenced the pitting potential of the material. Increasing aging time lead to the decrease of pitting potential, due to the formation of chromium impoverished regions. Oscillations in pitting potential values were noted due to the chromium redistribution enabled by easy diffusion of this element in high temperatures.

Pereira B.L.,Federal University of Paraná | Tummler P.,Federal University of Paraná | Marino C.E.B.,Federal University of Paraná | Soares P.C.,Engineering Mecanica | Kuromoto N.K.,Federal University of Paraná
Revista Materia | Year: 2014

There are various surface treatments used to modify titanium surfaces to render it bioactive. In this study commercially pure titanium surfaces (cp Ti), grade 2 were modified by acid etching (AE) and anodic oxidation (OA) in order to evaluate the bioactivity in vitro of these surfaces using the simulated body fluid (SBF). The AE was realized using a mixture of acids and AO using 1 mol.L-1 sulfuric acid. The anodic films were obtained under potentiostatic mode, during 60s using as anode a bar of titanium. All the surfaces that means cp Ti, AE and AO were analyzed concerning to morphology, rugosity, structural changes before in vitro bioactivity tests. It was observed by scanning electron microscopy (SEM) that all surfaces presented different morphologies: those with AE showed a surface with peaks and rounded valleys, with Ra = (564±80) nm, the oxidized surfaces with sulfuric acid showed a morphology with small pores uniformly distributed over the surface and Ra = (177±0,02) nm. X-rays diffraction results showed the presence of titanium hydride on the samples with AE and the anatase and rutile phases on the anodic films after heat treatment at 600°C/1h. Bioactivity tests in vitro using SBF at 37°C showed that small aggregates containing Ca and P were observed on surfaces with AE after 30 days soaked in SBF and the surfaces oxidized were fully coated with an apatite layer, identified by SEM.

One of the major problems is the appropriate final destination of the materials or waste that can not be reused in the original process. Among the residues are rigid polyurethane foams, which are widely applied but difficult to reuse because they are thermosetting materials. The aim of this paper is to apply a chemical recycling process, glycolysis, and use the recycled polyol, product of glycolysis reaction, as part of the raw material for the formation of rigid polyurethane foams. Their mechanical properties and thermal conductivity were analyzed. The formation of foam cells with recycled polyol were evaluated by scanning electron microscopy (MEV). The results show that there is no loss of mechanical and thermal properties of PUR foam, satisfying the requirements for the production of domestic refrigerators.

Costa R.C.,Federal University of Rio Grande do Sul | Dacoreggio M.V.,Engineering Mecanica | Kejelin N.Z.,Tractebel Engineering | Comeli F.W.,Federal University of Rio Grande do Sul | Comeli F.W.,Tractebel Engineering
Soldagem e Inspecao | Year: 2014

Heat exchangers pipes for thermal power plants to coal suffer wear corrosive due to the presence of sulfur and condensation of combustion gases, which results in a reduction in overall equipment efficiency. A choice for increasing the corrosion resistance in corrosive environments is the use of coatings applied by thermal spray technology. The corrosion resistance occurs to the use of materials stronger than the substrate. the processes are thermal spray, which uses the electric arc as a source of energy (Arc Spray) has a high deposition rate and low operating costs, so chosen for the study. For the determination of the coating to be used, corrosion-resistant alloys were tested in comparison with material employed in the pipes of heat exchangers, ASTM 178A. The selection of the most resistant coating was made by means of accelerated corrosion test in SO2 chamber and also by testing polarization. It was found that the aluminum coating had the best results in the tests when compared with materials currently used in the heat exchangers (ASTM 178A). © 2014 Universidade Federal de Uberlandia. All rights reserved.

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