Papers by Author: Cosme Roberto Moreira Silva

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Authors: Danieli A.P. Reis, Carlos de Moura Neto, Antônio Augusto Couto, Cosme Roberto Moreira Silva, Francisco Piorino Neto, M.J.R. Barboza
Abstract: Thermomechanical and electrical properties of zirconia-based ceramics have led to a wide range of advanced and engineering ceramic applications like solid electrolyte in oxygen sensors, fuel cells and furnace elements and its low thermal conductivity has allowed its use for thermal barrier coatings for aerospace engine components. A comparison between CoNiCrAlY bond coat and zirconia plasma sprayed coatings on creep tests of the Ti-6Al-4V alloy was studied. The material used was commercial Ti-6Al-4V alloy. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. Constant load creep tests were conducted on a standard creep machine in air on coated samples, at stress levels of 520 MPa at 500°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Results indicate that the creep resistance of the ceramic coating was greater than metallic coating.
Authors: Pablo J. Silva, Leonardo M. Leodido, Cosme Roberto Moreira Silva
Abstract: The incremental sheet forming allows the production in high quality of extremely complex pieces of steel, aluminum, titanium and many other materials, in order to reduce time and costs of production and cost of tooling used in low production. Working with tools of various diameters and a suitable machine programming is possible to produce complex parts of small lots in few hours, which in conventional stamping process would take days. This paper aims to introduce process parameters and analyze results from practice tests and computational analysis by changing the rotation, advancement in XY and Z advancement, tooling options, fixture plate and forming tool for producing pieces of varying size and complexity in the shortest time and at the highest quality possible. Thus, presents the incremental sheet forming as an alternative for rapid prototyping, as well as its devices and tools.
Authors: Sandro Aparecido Baldacim, Olivério Moreira Macedo Silva, Carlos Alberto Alves Cairo, Kátia Celina da Silva Richetto, Cosme Roberto Moreira Silva
Authors: G.V. Martins, Cosme Roberto Moreira Silva, C.A. Nunes, Vladimir J. Trava-Airoldi, L.A. Borges, João Paulo Barros Machado
Abstract: Beta titanium alloys parts are used on advanced aerospace systems because of their high strength to weight ratio and excellent corrosion resistance. Production of powder metallurgy titanium alloys components may lead to a substantial reduction in the cost, compared to those produced by conventional cast and wrought processes, because additional working operations and material waste can be avoided. In this work, beta Ti-45Nb and Ti-50Nb were produced by the blended elemental technique, followed by uniaxial and cold isostatic pressing with subsequent densification by sintering. Sintered samples were characterized for phase composition by XRD, microstructure by SEM, hardness by Vickers indentation, specific mass by the Archimedes method and elastic modulus by resonance ultrasound. The sintered samples presented only the beta phase, higher hardness and lower elastic modulus when compared to Ti6Al4V alloy and experimental specific mass value near theoretical specific mass. These characteristics are adequate for application on several aerospace parts.
Authors: E.C.S. Rigo, M.C. Bottino, B.D. Carraro, Elisa B. Taddei, Vinicius André Rodrigues Henriques, Cosme Roberto Moreira Silva, Ana Helena A. Bressiani, José Carlos Bressiani
Abstract: Comparing to hydroxyapatite (HA), which forms a strong chemical bond with the bony tissues, metallic materials are not able to bond with bone. For this reason, a great variety of complex coating methods, such as pulse-laser deposition, ion-beam assisted deposition and plasma-spray has been used to form a HA layer onto metallic surfaces. This study evaluated the performance of the biomimetic technique on apatite-based coating formation on two Tialloys. Ti-13Nb-13Zr and Ti-35Nb-7Zr-5Ta were obtained via powder metallurgy. The Tibased alloys were biomimetically coated using a technique which was modified from the conventional ones using a sodium silicate solution as the nucleant agent. Both alloys presented similar behavior in the evaluated conditions which means the formation of a homogeneous and well defined HA coating. These results show that these new non-toxic Tialloys seem to be very promising for biomedical applications.
Authors: M.C. Bottino, D.K. Oyafuso, Paulo Guilherme Coelho, Elisa B. Taddei, Vinicius André Rodrigues Henriques, Cosme Roberto Moreira Silva, M.A. Bottino, Ana Helena A. Bressiani, José Carlos Bressiani
Abstract: The shear bond strength between a ceramic material (Titankeramik®, Vita Zahnfabrik, Germany) and two biocompatible titanium alloys was investigated. Ti-13%Nb-13%Zr (TNZ) and Ti-35%Nb-7%Zr-5%Ta (TNZT) alloys were obtained based on the blended elemental technique followed by a sequence of cold uniaxial and isostatic pressing and sintering. Characterization involved microstructural analysis (SEM) and crystalline phase identification (XRD). Subsequently, samples were machined to 4 x 4 mm with a base of 5 x 1 mm. The base metals were blasted with Al2O3 particles followed by the application of a coupling agent and opaque ceramic. After ceramic firing, the specimens were loaded in a universal testing machine (0,5mm/min). XRD revealed the presence of α and β-phases for TNZ, and peaks related to β phases and Nb and Ta for the TNZT alloy. SEM evaluation (TNZ) depicted remaining pores and biphasic microstructure formation. SEM micrographs of the TNZT alloy revealed good densification and a homogeneous β structure. Shear bond strength data (MPa) were statistically analyzed (one-way ANOVA and Tukey test, α=.05) revealing that TNZT (37.6 ± 2.91) presented significant higher values (p=0.0002) compared to TNZ (26.03 ± 2.92). In conclusion, it seems that Ti alloy composition plays a significant role on ceramic bonding.
Authors: Elisa B. Taddei, Vinicius André Rodrigues Henriques, Cosme Roberto Moreira Silva, Carlos Alberto Alves Cairo
Abstract: Abstract: Titanium and titanium alloys present the highest biocompatibility among metallic biomaterials. The ideal titanium alloy for orthopedic applications should have low modulus of elasticity (near the bone), excellent mechanical strength, high corrosion resistance, formability and no potential toxic elements. Among titanium alloys, the Ti-35Nb-7Zr-5Ta alloy, due its high biocompatibility and lower Young’s modulus is a promising candidate for implants material. The titanium alloys production by powder metallurgy, starting from the elementary powders, is a viable route due at the smaller costs and larger operational facilities. The Ti-35Nb-7Zr-5Ta samples were manufactured by blended elemental method from a sequence of uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 at 1700 °C, in vacuum, under a heating rate of 20 °C×min-1 for 1h. The objective of this work is the analysis of alloy microstructural evolution from the powders dissolution under the increase of the sintering temperature. For the alloy microstructural characterization, scanning electron microscopy and Vickers microhardness measurements, were used. Density was measured by Archimedes method. The samples presented high densification, an homogeneous microstructural development, with complete dissolution of alloying elements in the titanium matrix with the temperature increase.
Authors: Sandro Aparecido Baldacim, Olivério Moreira Macedo Silva, Claudinei dos Santos, Cosme Roberto Moreira Silva
Abstract: The important factor to consider for successful ceramics composites development is the need of matching the whiskers and matrix characteristics, taking into account the chemical compatibility of the sintering aids utilized. The purpose of this work was to analyze and compare use of rare earth concentrate (CTR) and yttrium oxide, as sintering aids, and its influence in the densification and physical/mechanical properties of hot pressed and sintered Si3N4-SiC(w). The CTR powder materials present high yttrium oxide percentage and its production is cheaper than the additives usually used in ceramic materials, such as Y2O3. For physical and mechanical properties evaluation, specific mass, crystalline phases, micrographs analysis, microhardness and fracture toughness were measured, showing similar results between the two sintering aids. Therefore, this study shows the possibility of obtaining low processing cost products with the use of rare earth concentrate. Meanwhile, more characterization steps are necessary for analyzing its behavior at elevated temperatures.
Authors: Olivério Moreira Macedo Silva, Sandro Aparecido Baldacim, Cosme Roberto Moreira Silva
Authors: Francisco Cristóvão Lourenço de Melo, Cosme Roberto Moreira Silva, Ana Helena A. Bressiani, José Carlos Bressiani
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