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Da Costa F.A.,Federal University of Rio Grande do Norte | Melchiors G.,Federal University of Rio Grande do Norte | Gomes U.U.,Federal University of Rio Grande do Norte | Da Silva A.G.P.,LAMAV CCT
International Journal of Refractory Metals and Hard Materials | Year: 2015

This work reports the influence of the use of composite particles of composition Nb-20 wt.%Cu and the compaction pressure on density and structure of sintered pieces. High energy milling is used to produce the composite powders. Milling times of 2, 20, 50 and 100 h were used. The powders were pressed under 200, 300, 400 and 500 MPa and sintered at 1100 °C for 60 min. After sintering, density was measured and cross sections of the structures were observed under SEM. The electric conductivity was also measured. Density and electric conductivity behave similarly with respect to compaction pressure and milling time. Cracks are created during pressing and ejection of the green pieces from the die. The cracks are mainly present in samples prepared with powders milled longer and are not closed by sintering. On the other hand, sintering can close most of the pores formed by the composite particles. © 2015 Published by Elsevier Ltd. Source


De Oliveira Nascimento D.C.,State University of Norte Fluminense | Monteiro S.N.,LAMAV CCT | Da Silva Ferreira A.,LAMAV CCT
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

This work investigated the impact resistance of composites reinforced with surface chemically modified piassava fibers, in order to improve the interface with the polymeric matrix. Charpy impact tests were conducted in standard specimens following the specification given by the ASTM norm, fabricated by room temperature press-molding and a 24 hour cure of the matrix. The fracture surface was analyzed by scanning electron microscopy for composites reinforced with up to 40% in weight of continuous and aligned piassava fibers. The results showed that the surface alkali treatment with NaOH, known as mercerization, decreases the impact resistance of the composite. This is attributed to the degradation of the fiber surface for any percentage of NaOH solution and immersion time. The surface degradation increases the tendency of a premature fracture with increasing the percentage of piassava fiber. These results may be interpreted as two different roles played by the treated piassava fiber during the impact fracture. From one side, by contributing to the interfaced rupture. From another side, the rupture of the piassava fibers weakened by the mercerization treatment. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM). Source


de Almeida L.L.P.,LAMAV CCT | Tatagiba L.C.S.,LAMAV CCT | Rosenthal R.,LAMAV CCT | da Rocha Paranhos R.P.,LAMAV CCT
Welding International | Year: 2012

This paper presents an evaluation of welded joints using ceramic backing produced in the laboratory. The one-sided welding technique was used to weld A-36 steel plate with 6.4 and 15.8 mm thicknesses by employing the GMAW process. With the 6.4 mm steel plate, only the root bead welded over the ceramic backing was evaluated. With the 15.8 mm steel plate, a multipass welded joint was made. After welding, the welded joints were submitted to visual inspection, dye penetrant, macrograph, Vickers microhardness, optical microscopy, bending and tensile testing and chemical analysis using non-destructive test. The results show that the root pass made over the ceramic backing presented adequate shape, free from discontinuities, with adequate penetration in the edges of the groove and adequate reinforcement. With regard to the welded joint, the microstructure of the fusion zone presented predominance of primary ferrite, consisting of grain boundary ferrite and polygonal ferrite, and ferrite with an aligned second phase. The Vickers microhardness obtained mean values below 180 VH both in the heat affected zone and the fusion zone. Bending tests did not show discontinuities greater than 3 mm and in the tensile tests, the rupture occurred in the base metal, indicating that the welding procedure was adequate. The chemical composition of the inclusions both in the root pass and in the last weld bead have the same constituents, despite different proportions, indicating that there was no contamination of the ceramic backing material into the weld bead. © 2012 Taylor and Francis Group, LLC. Source

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