Papers by Author: Cezar Henrique Gonzalez

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Authors: E.S.L. Vasconcelos, Edkarlla Sousa Dantas de Oliveira, M.A.G.A. Lima, M. Montoya, Cezar Henrique Gonzalez, Severino Leopoldino Urtiga Filho
Abstract: Articles report that the sulphate reducing bacteria (SRB) are the main micro-organisms related to cases of corrosion. They reduce the sulfate ion resulting in the production of sulfide, disulfide and hydrogen sulfide, potential agents of corrosion of ferrous materials. This study investigated the action of sulfate-reducing bacteria on corrosion test specimens with welded joint of API 5L X80 steel in the presence of seawater. The samples were exposed to sea and sterilized water was then added to BRS. Microorganisms were quantified periodically calculated the corrosion rate and weight loss, and the surfaces of the samples analyzed by light microscopy.
Authors: Luiz Carlos Sekitani da Silva, Cezar Henrique Gonzalez, Carlos Augusto do Nascimento Oliveira, Karla Carolina Alves da Silva
Abstract: In the present work the copper base alloys with shape memory effects were characterized. The alloys were subjected to three different heat treatments that promoted changes in characteristics of thermoelastic martensitic transformation (transformation temperatures, thermal hysteresis and enthalpies of transformation). The alloys have their microstructures characterized by optical and scanning electron microscopy. Microhardness tests were performed. Differential scanning calorimetry (DSC) was used to evaluate the transformation critical temperatures of alloy and the transformation enthalpies for each heat treated sample. Thermoelastic properties have changed for each heat treatment. In the micrographs of the heat-treated samples was possible to observe the microstructure of the martensitic phase characteristic. They show the presence of martensite platelets (needles) self-accommodation.
Authors: Oscar Olimpio Araújo Filho, Alexandre Douglas Araújo de Moura, Everthon Rodrigues de Araújo, Maurílio José dos Santos, Cezar Henrique Gonzalez, Flávio José da Silva
Abstract: Powder Metallurgy (PM) Techniques consists in a suitable technique to process composites materials. A specific PM technique of mechanical alloying developed to produce new materials in the solid state is a consolidated route to obtain aluminum alloys metal matrix composites. Aluminum alloys metal matrix composites allies the good properties of aluminum and its alloys but with poor mechanical properties and the reinforcement of ceramics phases which add better mechanical properties to these alloys. The research of this materials processing by PM techniques presented new materials with improved properties. In this work an AA1100 aluminum alloy was reinforced by particulate silicon carbide and alumina types of ceramic phases. The powders were mixed and then processed by mechanical alloying in a SPEX vibratory type mill. Then the powders obtained were compacted and vacuum sintered. The sintered composites were characterized by means of Scanning Electron Microscopy (SEM) plus Energy Dispersive Spectroscopy (EDS) and Vickers hardness (HV) tests to evaluate the mechanical behavior.
Authors: Oscar Olimpio de Araújo Filho, Everthon Rodrigues de Araújo, Heronilton Mendes de Lira, Cezar Henrique Gonzalez, Noelle D’emery Gomes Silva, Severino Leopoldino Urtiga Filho
Abstract: Aluminum alloy metal matrix composites are a class of materials object of large and intensive research during the last years. In this study an AA2124 aluminum alloy were processed by means of mechanical alloying added by 10, 20 and 20 percent of silicon carbide (SiC) in vibratory SPEX type mill during 60 and 120 minutes. After this the composites powders obtained were characterized by means of Scanning Electron Microscopy (SEM) plus Energy Dispersive Spectroscopy (EDS) to determine the powders morphology. In order to consolidate the AA2124 aluminum alloy composites reinforced by silicon carbide (SiC) composites, the powders processed by high energy ball milling technique were hot extruded and the billets were characterized by SEM to determine the microstructure and the distribution of the reinforced ceramic phase of silicon carbide throughout the aluminum matrix and at last the microhardiness Vickers technique were used to evaluate the mechanical properties.
Authors: Heronilton Mendes de Lira, Pilar Rey Rodriguez, Oscar Olimpio de Araújo Filho, Cezar Henrique Gonzalez, Severino Leopoldino Urtiga Filho
Abstract: High performance nanostructured light metals and alloys are very interesting for replacing conventional heavier materials in many industrial components. High Energy Ball Milling and Cryomilling are useful techniques to obtain nanocrystalline powders. In this work the effect of several milling conditions such as rotation speed, time, ball to powder ratio and temperature on the crystallite and particle size and morphology in pure aluminum are presented. X-Ray Diffraction, Laser Diffraction and Scanning Electron Microscopy are used. High energy ball milling at ambient and cryogenic temperature of Al powders rapidly leads to a nanometer size down to about 35 nm. High ball to powder ratio promotes both low crystallite and particle size. Small crystallite size like 18 nm and particle size as 4 μm were achieved in the most energetic conditions at ambient temperature. Isopropyl alcohol used as liquid media and protective atmosphere has a strong influence on the results depending on the milling temperature of Al.
Authors: Oscar Olimpio de Araújo Filho, Rodrigo Tecchio Antonello, Cezar Henrique Gonzalez, Severino Leopoldino Urtiga Filho, Francisco Ambrozio Filho
Abstract: High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.
Authors: Oscar Olimpio de Araújo Filho, Cezar Henrique Gonzalez, Severino Leopoldino Urtiga Filho, C.A.N. Oliveira, Noelle D’emery Gomes Silva, F. Ambrozio Filho
Abstract: The main aim of this work was to study the behavior of the secondary hardening of AISI M3:2 high speed steel named Sinter 23® produced by powder metallurgy process of hot isostatic pressing (HIP). The M3:2 high speed steel Sinter 23® was submitted to heat treatment of hardening with austenitizing temperatures of 1140 oC, 1160 oC, 1180 oC and 1200 oC and tempering at 540 oC, 560 oC and finally 580 oC. The effectiveness and response of the heat treatment was determined using hardness tests (Vickers and Rockwell C hardness) and had its property of secondary hardness evaluated. The results showed that the secondary hardening peak of Sinter 23® high speed steel (tempering temperature at which maximum hardness is attained) is at 540 °C for the lower austenitization temperatures of 1140 °C and 1160 °C, and it is at 560 °C for the higher austenitizing/quenching temperatures of 1180 °C and 1200°C.
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