Sheyla Santana de Carvalho - Academia.edu (original) (raw)

Papers by Sheyla Santana de Carvalho

Research paper thumbnail of Corrosão na geratriz superior do duto (“Top of Line Corrosion – TLC”): uma nova abordagem dos principais mecanismos

This work presents a broad experimental and theoretical approach of the condensation and corrosio... more This work presents a broad experimental and theoretical approach of the condensation and corrosion phenomenon in "Top of line Corrosion" under CO2 environments in conditions of non- film formation (Fe2CO3 or other protective films as corrosion process result). For this, an integrated corrosion cell was developed capable of monitoring the key parameters of this type of corrosion. The condensation rates (WCR) were compared through the theoretical model proposed by Mohammed (2018) allowing an indirect verification of the experimental apparatus in this sense. A cofiguration of Mini-electrodes was adapted to the cell for continuous electrochemical measurements of corrosion by means of integrated analysis of Linear Resistance Polarization-RPL, Electrochemical Impedance Spectroscopy-EIS and Potentiodynamic curves (Tafel). The LPR was monitored for 20 hours and then the average of corrosion rate was compared to those obtained by mass loss under the same conditions in order to vali...

Research paper thumbnail of Caracterização Microestrutural De Liga Alumínio Para Componentes Antifricção

ABM Proceedings, 2018

Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de mat... more Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de materiais com propriedades mecânicas e de resistência à corrosão cada vez melhores, com o objetivo de suportar severas condições de uso e assim garantir melhor desempenho para equipamentos e estruturas que utilizam os componentes fabricados com estes materiais. Neste contexto, é de fundamental importância conhecer bem a microestrutura destes materiais, que influencia consideravelmente suas propriedades. O propósito deste trabalho é realizar uma caracterização preliminar de ligas não ferrosas (de alumínio e de cobre) utilizadas na fabricação de componentes antifricção. Com esta finalidade, técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV), envolvendo análises de EDS e de EBSD, assim como ensaios de microdureza foram utilizadas para caracterizar a microestrutura do material (liga Al-Sn-Si-Cu). Os resultados obtidos neste estudo permitiram a identificação das fases presentes neste material. Palavras-chave: Caracterização microestrutural; Alumínio; Fricção.

Research paper thumbnail of Microstructural Characterization of Nonferrous Alloys for Antifriction Components

Modern Approaches on Material Science, 2019

In the last years the development of the mechanical and metallurgical industry has led to the sea... more In the last years the development of the mechanical and metallurgical industry has led to the search for materials with even better mechanical properties and corrosion resistance, with the purpose of withstanding severe conditions of use and thus assessing better performance for equipments and structures that use components fabricated with such materials, thereby requiring the characterization of the microstructure of these materials that influence considerably their properties. With this purpose, techniques such as optical microscopy, microhardness tests and scanning electron microscopy (SEM), comprising EDS (X ray energy dispersion spectroscopy), WDS (X ray wavelength dispersion spectroscopy) and EBSD (electron back scattering diffraction) analysis procedures were used to identify phases present in two nonferrous alloys used in the fabrication of antifriction components: aluminum-tin-silicon-copper (Al-Sn-Si-Cu) and copper-tin-bismuth (Cu-Sn-Bi) alloys.

Research paper thumbnail of Caracterização Microestrutural De Liga De Cobre Para Componentes Antifricção

ABM Proceedings, Oct 1, 2018

Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de mat... more Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de materiais com propriedades mecânicas e de resistência à corrosão cada vez melhores, com o objetivo de suportar severas condições de uso e assim garantir melhor desempenho para equipamentos e estruturas que utilizam os componentes fabricados com estes materiais. Neste contexto, é de fundamental importância conhecer bem a microestrutura destes materiais, que influencia consideravelmente suas propriedades. O propósito deste trabalho é realizar uma caracterização preliminar de ligas não ferrosas (de alumínio e de cobre) utilizadas na fabricação de componentes antifricção. Com esta finalidade, técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV), envolvendo análises de EDS e de EBSD, assim como ensaios de microdureza foram utilizadas para caracterizar a microestrutura do material (liga Cu-Sn-Bi). Os resultados obtidos neste estudo permitiram a identificação das fases presentes neste material. Palavras-chave: Caracterização microestrutural; Cobre; Fricção. MICROSTRUCTURAL CHARACTERIZATION OF COPPER ALLOY FOR ANTIFRICTION COMPONENTS Abstract In the last years the development of the mechanical and metallurgical industry has led to the search for materials with even better mechanical properties and corrosion resistance, with the purpose of withstanding severe conditions of use and thus assesses better performance for equipments and structures that use components fabricated with such materials. In this context it is very important to know in detail the microstructure of these materials that influence considerably their properties. The purpose of this work is to achieve an initial characterization of non ferrous alloys (aluminum and copper based alloys) used in the fabrication of antifriction components. With focus on this aim, techniques such as optical microscopy, scanning electron microscopy (SEM), comprising EDS and EBSD analysis procedures were used to characterization the microstructure of the alloy (Cu-Sn-Bi). The results obtained in this study allowed the identification of the phases present in this material.

Research paper thumbnail of Processamento e Caracterização De Titânio Submetido À Metalurgia Do Pó e Extrusão Angular Em Canal

ABM Proceedings, 2014

Resumo O titânio processado por metalurgia do pó tem sido cada vez mais utilizado na fabricação d... more Resumo O titânio processado por metalurgia do pó tem sido cada vez mais utilizado na fabricação de implantes cirúrgicos, ortopédicos e dentários, devido às características de biocompatibilidade e propriedades mecânicas do material obtidas por esta técnica. A componente cisalhante da deformação característica do processo de extrusão angular em canal (EAC) permite a consolidação das partículas pela junção de novas superfícies e o elevado grau de deformação obtido confere considerável refino dos grãos do material. No presente trabalho o material foi processado por metalurgia do pó seguido de extrusão angular em canal, enquanto a caracterização envolveu técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV) e ensaio de dureza. Os resultados obtidos neste estudo permitiram a caracterização da microestrutura, da dureza e da porosidade de compactados de titânio submetidos ao processo de extrusão angular em canal em temperatura da ordem de 375°C, com redução do tamanho de grão médio, de 30 µm para 1,32 µm no material processado por metalurgia do pó seguida por EAC e aumento da dureza, de 161 para 264 HV, respectivamente. A fração em área de poros, que atingia cerca de 4% no material apenas compactado foi reduzida para aproximadamente 0,8% no material submetido ao processo EAC. Palavras-chave: Titânio; Implante; Metalurgia do pó; Extrusão angular em canal.

Research paper thumbnail of AVALIAÇÃO MICROESTRUTURAL DE LIGAS Fe-Ni-Cr SUBMETIDAS À CORROSÃO EM ALTAS TEMPERATURAS

ABM Proceedings, 2014

Resumo O presente estudo apresenta a avaliação microestrutural de duas ligas Fe-Ni-Cr com composi... more Resumo O presente estudo apresenta a avaliação microestrutural de duas ligas Fe-Ni-Cr com composições químicas distintas submetidas à corrosão em altas temperaturas em tubos de pirólise em uma planta de fabricação de polímeros durante três anos. A superfície e a seção transversal das ligas foram caracterizadas por microscopia eletrônica de varredura e espectroscopia por dispersão de energia de Raios-X. As condições de serviço induziram a formação de uma camada de óxido na superfície das ligas composta por uma região externa e outra interna além de uma região empobrecida em cromo abaixo da camada de óxido. Uma das ligas apresentou também uma zona de oxidação interna. O estágio de modificação microestrutural de ambas as ligas foi analisado e comparado com resultados de outros autores. Palavras-chave: Ligas Fe-Ni-Cr; Alta temperatura; Tubo de pirólise; Corrosão.

Research paper thumbnail of Crystallographic texture and microtexture of copper drawn at 295 K and 77 K

Matéria (Rio de Janeiro), 2019

The pure copper wires were wiredrawn at cryogenic and room temperatures. After deformation they p... more The pure copper wires were wiredrawn at cryogenic and room temperatures. After deformation they presented important and significant differences in their crystallographic textures and microstructures. Therefore, this study aimed to investigate the evolution of crystallographic texture of pure copper drawn at temperatures of 295 K and 77 K and correlated them to the deformation micromechanisms. For this, the X ray diffraction (XRD) and electron backscattered diffraction (EBSD) techniques were used. The results showed that, after the deformation, the samples drawn at both temperatures showed Copper {112}<111>, X {110}<111> and Brass {110}<112> components as the most intense. In samples drawn at cryogenic temperature there was also observed the appearance of a R{124}<211> component, typical of recrystallization and the presence of the  fiber {111}, typical of deformation twin.

Research paper thumbnail of Comparative Study by Tem, Ebsd and Microhardness of the Microstructure of Copper Wiredrawn at 77 K and 295 K

Tecnologia em Metalurgia Materiais e Mineração, 2019

Research paper thumbnail of Failure Analysis of Tool Steel-Based Compaction Punch Used in Powder Metallurgy

Journal of Failure Analysis and Prevention, 2015

Powder metallurgy operations comprise the use of compaction dies and punches for transforming a m... more Powder metallurgy operations comprise the use of compaction dies and punches for transforming a mass of metallic powders into a porous block of aggregated particles with limited ''green'' strength. In this kind of application, dies and punches manufactured with tool steel are subjected to heavy loads to compress the metallic powders and form the block, which will be subjected to further consolidation operations such as sintering and/or some mechanical forming operation, such as forging or rolling. In general tool steels are high carbon and high alloyed steels designed for reaching high levels of mechanical strength, sufficient for his type of loading. However, defects on the surface of this material can lead to stress concentration, thus decreasing its fracture strength and eventually leading to failure. In this study, techniques such as optical and scanning electron microscopy are used to evaluate the possible causes of the failure of a compaction punch. The results indicated that machining grooves acted as stress concentrations which led to the premature fracture of the punch.

Research paper thumbnail of Microstructural Analysis of the Failure of a Cast Iron Cylinder Head of a Thermoelectrical Plant Motor

Journal of Failure Analysis and Prevention, 2015

Large motors, such as those that propel ships or generate energy for thermoelectrical plants, for... more Large motors, such as those that propel ships or generate energy for thermoelectrical plants, for instance, use cylinder heads produced with nodular cast iron. Such components are manufactured by a casting process which must be strictly controlled to prevent the appearance of defects that may spoil the performance of the component in service. When these defects arise, they usually lead to the failure of the cylinder head, mainly causing fluids leakage that can harm or even impede the motor performance. In this study, the microstructure of the material was characterized, with the purpose of investigating the possible causes of the failure, through the use of techniques such as optical microscopy and scanning electron microscopy. Brinell hardness tests were also performed. The results revealed that inadequate casting procedures probably caused the defects and subsequent failure of the cylinder head.

Research paper thumbnail of A microstructural study on the high temperature oxidation, carburation and sulfidation of HK 40 and Incoloy 802

Materials Characterisation VI, 2013

The main purpose of this article is an analysis of the microstructural changes in stainless steel... more The main purpose of this article is an analysis of the microstructural changes in stainless steels and other special alloys due to high temperature phenomena, such as oxidation, carburization and sulfidation. These conditions arise in a plant during the production of polymeric materials, when the raw material, coke originating from petroleum, rich in carbon and sulfur, is in direct contact with tubes fabricated with metallic materials at elevated temperatures during the pyrolysis process. These changes can damage the characteristics and properties of the alloys, thus leading to premature failure in certain regions of the pipeline. In this work, techniques such as optical microscopy, field emission scanning electron microscopy (FESEM) equipped with an EDS microanalysis system and hardness tests were employed to analyze HK 40 stainless steel and Incoloy 802 used in pyrolysis tubes for polymeric material production. The presence of many undesirable oxide, carbide and sulfide particles and chromium depletion was identified mainly in the inner surface of the tubes in direct contact with the coke at elevated temperatures (around 1000ºC). Variations of the corrosive attack were observed along different positions in the pipeline, depending on the more or less extensive exposure to high temperatures and corrosive agents. It can be concluded that the degradation which led to the premature failure of the pipeline Materials Characterisation VI 41

Research paper thumbnail of Characterization of Titanium Powders Processed at Different Temperatures

Materials Science Forum, 2014

Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, du... more Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, due to a very favorable combination of properties, when compared with other metals, such as good corrosion resistance, good mechanical properties, relatively low density, elasticity modulus close to that of bone and good biocompatibility, which assures good adhesion/integration to bone. Powder metallurgy has been used for titanium based implants fabrication due to advantages such as the production of more complex shapes and reduction of machining operation. In this work, compacted pure titanium powders, consolidated by rolling at different temperatures, were characterized by means of optical microscopy, Field Emission Scanning Electron Microscopy (FESEM) with Electron Back Scattering Diffraction (EBSD) analysis, automatic image analysis and hardness tests. The hardness of rolled samples increased from 200 to 400oC , which indicated that 300 to 400°C is the most adequate temperature range f...

Research paper thumbnail of Texture and Microstructure of Cold Rolled and Recrystallized Pure Niobium

Materials Science Forum, 2007

Crystallographic macrotexture of pure niobium cold rolled to 30, 60, 80 and 90% reduction was ana... more Crystallographic macrotexture of pure niobium cold rolled to 30, 60, 80 and 90% reduction was analyzed by X-ray diffraction and compared with low carbon steel texture. Annealed samples from 800oC, to 1200oC were investigated by X-ray diffraction and electron back scattering diffraction (EBSD). The texture of cold rolled polycrystalline niobium is characterized by a component {001}<110> that increases in intensity with the cold work percentage. After annealing, the component {001}<110> spreads out about 20o.

Research paper thumbnail of Deformation induced martensite in an AISI 301LN stainless steel: characterization and influence on pitting corrosion resistance

Materials Research, 2007

In austenitic stainless steels, plastic deformation can induce martensite formation. The induced ... more In austenitic stainless steels, plastic deformation can induce martensite formation. The induced martensite is related to the austenite (γ) instability at temperatures close or below room temperature. The metastability of austenite stainless steels increases with the decreasing of stacking fault energy (SFE). In this work, the deformation induced martensite was analyzed by X ray diffraction, electron back scatter diffraction (EBSD), magnetic methods and atomic force microscope (AFM) in samples of a low SFE austenitic stainless steel, AISI 301LN and compared with a medium SFE stainless steel, AISI 316L. Both techniques, X ray diffraction and EBSD, presented similar quantities for the α'-martensite. Texture results indicate that the crystallographic orientation of the formed α'martensite is {001}<110> and {103}<110>. The morphology of α'-martensite was analyzed by AFM. Corrosion tests showed that deformation reduces pitting corrosion and generalized corrosion resistance in both steels.

Research paper thumbnail of Effect of high temperature annealing on texture and microstructure on an AISI-444 ferritic stainless steel

Materials Characterization, 2006

AISI 444 is a Mo-alloyed ferritic stainless steel which presents good naphthenic corrosion resist... more AISI 444 is a Mo-alloyed ferritic stainless steel which presents good naphthenic corrosion resistance, making it attractive for applications in petroleum refining plants; however, good formability is also important. To achieve good formability with this alloy the annealing process is crucial. The annealing temperature in ferritic stainless steel is usually around 850 °C, which falls in the range of sigma phase

Research paper thumbnail of Microscopic Analysis of Fractured Screws Used as Implants in Bone Fixation

Journal of Failure Analysis and Prevention, 2014

The increase of life expectancy and risk of accidents, thereby causing a higher incidence of surg... more The increase of life expectancy and risk of accidents, thereby causing a higher incidence of surgeries, has led to a growing use of implants. The reliability of these implants, either for bone fracture correction or for joint replacement, thus used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. By using some techniques, mainly optical microscopy and scanning electron microscopy tests, this work has as purpose the identification of the possible causes of failure of screws used in plates for bone fixation, considering the fracture surface aspects and microstructural characteristics of the austenitic stainless steel used in their manufacture, which is essential for this application. The results obtained in this study allowed the identification of the main causes of the failure, primarily related to fatigue fracture, associated to the presence of surface cracks, generated by stress concentration, which was probably caused by grooves left by improper machining.

Research paper thumbnail of A Microstructural and Fractographic Study on the Failure of a Drive Shaft

Journal of Failure Analysis and Prevention, 2011

The automotive industry is one of the most dynamic and competitive segments of the international ... more The automotive industry is one of the most dynamic and competitive segments of the international economy and it has invested considerable resources into the research and development of new components and the improvement of existent pieces. Nonetheless, failures continue to occur, often because of defects in a component. Failure analysis uses several techniques to investigate causes of the defect which led to the failure of a component, equipment, or structure. Usually, these causes are related to the use of inadequate materials, the presence of defects which appear during fabrication or design errors, or improper assembly, maintenance and use. Knowledge about these causes and the correction of such anomalies allow the improvement of the performance of components regarding both efficiency and safety. In this study, the results of the failure analysis of the drive bar of a police car are presented and light optical microscopy and scanning electron microscopy (SEM) results are used to show that the presence of an already existent defect and an unfavorable microstructure led to the occurrence of brittle fracture which caused the premature and catastrophic failure of this component.

Research paper thumbnail of Failure analysis of AISI 310S plate in an inert gas generator used in off-shore oil platform

Engineering Failure Analysis, 2011

In this work a failure analysis was conducted in a mirror plate made of austenitic stainless stee... more In this work a failure analysis was conducted in a mirror plate made of austenitic stainless steel AISI 310. The mirror is part of the inert gas generator, which is a combustion chamber dedicated to produce inert gas atmosphere (N 2 + CO 2) to be used during the oil transfer in offshore platforms. The mirror failed in two distinct regions. The first crack was observed in a region where the temperatures reached were sufficiently high to provoke intense sigma phase precipitation. Other cracks were observed in a region subject to seawater refrigeration, named ''cold zone''. These two failures were mitigated in order to propose solutions to avoid similar failures in the new equipment.

Research paper thumbnail of Scanning Electron Microscopic Characterization of Healing and Normal Rat Ligament Microstructure Under Slack and Loaded Conditions

Connective Tissue Research, 2003

The objective of this study was to observe and compare behavior of the collagen fiber microstruct... more The objective of this study was to observe and compare behavior of the collagen fiber microstructure in normal and healing ligaments, both in situ and ex vivo, in order to add insight into the structure-function relationship in normal and healing ligaments. Fifty-two ligaments from 26 male rats were investigated. Eleven animals underwent surgical transection of both medial collateral ligaments (MCLs) (22 ligaments), which were allowed to heal for a period of 2 weeks. An additional 15 animals (30 ligaments) were used as normals. Ligaments were placed into six groups: Slack (n = 6 control, n = 6 healing), Reference (n = 4 control, n = 4 healing), Loaded (n = 4 control, n = 4 healing), 15 • Flexion (n = 4 control, n = 4 healing), 120 • Flexion (n = 4 control, n = 4 healing), and Tissue Strain vs. Flexion Angle (n = 8 normals). All ligaments, except those in the Tissue Strain vs. Flexion Angle group, were prepared for scanning electron microscopy. Tissues were harvested, mounted in a load frame, and chemically fixed in one of five states: (1) slack, (2) reference (onset of loading), (3) loaded, (4) 15 • knee flexion, or (5) 120 • knee flexion. After fixation the tissues were prepared for electron microscopy (SEM). The micrographs from the slack, reference, and loaded groups show fiber straightening with loading in normal ligaments as well as in both scar and "retracted" regions of healing ligaments. Collagen fibers' diameter and crimp patterns were dramatically changed in the scar region of healing ligaments: Width decreased from

Research paper thumbnail of Archaeometric investigations on naturally and thermally-aged iron-gall inks using different tannin sources

Open Chemistry, 2013

This paper investigates the behavior of paper strips containing iron-gall inks prepared with tann... more This paper investigates the behavior of paper strips containing iron-gall inks prepared with tannins from different sources, subjected to natural and thermally-induced aging. Results indicate that inks containing initial concentrations of ferrous sulphate ranging from 0.2 to 10.0 g are amenable to treatment with calcium phytate, and thata good correlation exists between the recovery of excess iron and the initial concentration. Infrared spectra showed an absorption band at 1,750 cm−1, typical of esther, solely in the samples prepared with a condensed tannin. The condensed nature of this tannin produced a different oxidation pattern, with iron removal inferior to those observed from inks produced with hydrolisable tannins. When tannic acid was used ferrous iron removals ranged from 0.050 to 1.800 g, decreasing to 0.5 g in the presence of copper; the same behavior was observed for the remaining hydrolisable tannins, with a lower recovery from the condensed tannin. The adopted natural ...

Research paper thumbnail of Corrosão na geratriz superior do duto (“Top of Line Corrosion – TLC”): uma nova abordagem dos principais mecanismos

This work presents a broad experimental and theoretical approach of the condensation and corrosio... more This work presents a broad experimental and theoretical approach of the condensation and corrosion phenomenon in "Top of line Corrosion" under CO2 environments in conditions of non- film formation (Fe2CO3 or other protective films as corrosion process result). For this, an integrated corrosion cell was developed capable of monitoring the key parameters of this type of corrosion. The condensation rates (WCR) were compared through the theoretical model proposed by Mohammed (2018) allowing an indirect verification of the experimental apparatus in this sense. A cofiguration of Mini-electrodes was adapted to the cell for continuous electrochemical measurements of corrosion by means of integrated analysis of Linear Resistance Polarization-RPL, Electrochemical Impedance Spectroscopy-EIS and Potentiodynamic curves (Tafel). The LPR was monitored for 20 hours and then the average of corrosion rate was compared to those obtained by mass loss under the same conditions in order to vali...

Research paper thumbnail of Caracterização Microestrutural De Liga Alumínio Para Componentes Antifricção

ABM Proceedings, 2018

Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de mat... more Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de materiais com propriedades mecânicas e de resistência à corrosão cada vez melhores, com o objetivo de suportar severas condições de uso e assim garantir melhor desempenho para equipamentos e estruturas que utilizam os componentes fabricados com estes materiais. Neste contexto, é de fundamental importância conhecer bem a microestrutura destes materiais, que influencia consideravelmente suas propriedades. O propósito deste trabalho é realizar uma caracterização preliminar de ligas não ferrosas (de alumínio e de cobre) utilizadas na fabricação de componentes antifricção. Com esta finalidade, técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV), envolvendo análises de EDS e de EBSD, assim como ensaios de microdureza foram utilizadas para caracterizar a microestrutura do material (liga Al-Sn-Si-Cu). Os resultados obtidos neste estudo permitiram a identificação das fases presentes neste material. Palavras-chave: Caracterização microestrutural; Alumínio; Fricção.

Research paper thumbnail of Microstructural Characterization of Nonferrous Alloys for Antifriction Components

Modern Approaches on Material Science, 2019

In the last years the development of the mechanical and metallurgical industry has led to the sea... more In the last years the development of the mechanical and metallurgical industry has led to the search for materials with even better mechanical properties and corrosion resistance, with the purpose of withstanding severe conditions of use and thus assessing better performance for equipments and structures that use components fabricated with such materials, thereby requiring the characterization of the microstructure of these materials that influence considerably their properties. With this purpose, techniques such as optical microscopy, microhardness tests and scanning electron microscopy (SEM), comprising EDS (X ray energy dispersion spectroscopy), WDS (X ray wavelength dispersion spectroscopy) and EBSD (electron back scattering diffraction) analysis procedures were used to identify phases present in two nonferrous alloys used in the fabrication of antifriction components: aluminum-tin-silicon-copper (Al-Sn-Si-Cu) and copper-tin-bismuth (Cu-Sn-Bi) alloys.

Research paper thumbnail of Caracterização Microestrutural De Liga De Cobre Para Componentes Antifricção

ABM Proceedings, Oct 1, 2018

Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de mat... more Resumo O desenvolvimento da indústria metal-mecânica nos últimos anos tem levado à demanda de materiais com propriedades mecânicas e de resistência à corrosão cada vez melhores, com o objetivo de suportar severas condições de uso e assim garantir melhor desempenho para equipamentos e estruturas que utilizam os componentes fabricados com estes materiais. Neste contexto, é de fundamental importância conhecer bem a microestrutura destes materiais, que influencia consideravelmente suas propriedades. O propósito deste trabalho é realizar uma caracterização preliminar de ligas não ferrosas (de alumínio e de cobre) utilizadas na fabricação de componentes antifricção. Com esta finalidade, técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV), envolvendo análises de EDS e de EBSD, assim como ensaios de microdureza foram utilizadas para caracterizar a microestrutura do material (liga Cu-Sn-Bi). Os resultados obtidos neste estudo permitiram a identificação das fases presentes neste material. Palavras-chave: Caracterização microestrutural; Cobre; Fricção. MICROSTRUCTURAL CHARACTERIZATION OF COPPER ALLOY FOR ANTIFRICTION COMPONENTS Abstract In the last years the development of the mechanical and metallurgical industry has led to the search for materials with even better mechanical properties and corrosion resistance, with the purpose of withstanding severe conditions of use and thus assesses better performance for equipments and structures that use components fabricated with such materials. In this context it is very important to know in detail the microstructure of these materials that influence considerably their properties. The purpose of this work is to achieve an initial characterization of non ferrous alloys (aluminum and copper based alloys) used in the fabrication of antifriction components. With focus on this aim, techniques such as optical microscopy, scanning electron microscopy (SEM), comprising EDS and EBSD analysis procedures were used to characterization the microstructure of the alloy (Cu-Sn-Bi). The results obtained in this study allowed the identification of the phases present in this material.

Research paper thumbnail of Processamento e Caracterização De Titânio Submetido À Metalurgia Do Pó e Extrusão Angular Em Canal

ABM Proceedings, 2014

Resumo O titânio processado por metalurgia do pó tem sido cada vez mais utilizado na fabricação d... more Resumo O titânio processado por metalurgia do pó tem sido cada vez mais utilizado na fabricação de implantes cirúrgicos, ortopédicos e dentários, devido às características de biocompatibilidade e propriedades mecânicas do material obtidas por esta técnica. A componente cisalhante da deformação característica do processo de extrusão angular em canal (EAC) permite a consolidação das partículas pela junção de novas superfícies e o elevado grau de deformação obtido confere considerável refino dos grãos do material. No presente trabalho o material foi processado por metalurgia do pó seguido de extrusão angular em canal, enquanto a caracterização envolveu técnicas como microscopia ótica, microscopia eletrônica de varredura (MEV) e ensaio de dureza. Os resultados obtidos neste estudo permitiram a caracterização da microestrutura, da dureza e da porosidade de compactados de titânio submetidos ao processo de extrusão angular em canal em temperatura da ordem de 375°C, com redução do tamanho de grão médio, de 30 µm para 1,32 µm no material processado por metalurgia do pó seguida por EAC e aumento da dureza, de 161 para 264 HV, respectivamente. A fração em área de poros, que atingia cerca de 4% no material apenas compactado foi reduzida para aproximadamente 0,8% no material submetido ao processo EAC. Palavras-chave: Titânio; Implante; Metalurgia do pó; Extrusão angular em canal.

Research paper thumbnail of AVALIAÇÃO MICROESTRUTURAL DE LIGAS Fe-Ni-Cr SUBMETIDAS À CORROSÃO EM ALTAS TEMPERATURAS

ABM Proceedings, 2014

Resumo O presente estudo apresenta a avaliação microestrutural de duas ligas Fe-Ni-Cr com composi... more Resumo O presente estudo apresenta a avaliação microestrutural de duas ligas Fe-Ni-Cr com composições químicas distintas submetidas à corrosão em altas temperaturas em tubos de pirólise em uma planta de fabricação de polímeros durante três anos. A superfície e a seção transversal das ligas foram caracterizadas por microscopia eletrônica de varredura e espectroscopia por dispersão de energia de Raios-X. As condições de serviço induziram a formação de uma camada de óxido na superfície das ligas composta por uma região externa e outra interna além de uma região empobrecida em cromo abaixo da camada de óxido. Uma das ligas apresentou também uma zona de oxidação interna. O estágio de modificação microestrutural de ambas as ligas foi analisado e comparado com resultados de outros autores. Palavras-chave: Ligas Fe-Ni-Cr; Alta temperatura; Tubo de pirólise; Corrosão.

Research paper thumbnail of Crystallographic texture and microtexture of copper drawn at 295 K and 77 K

Matéria (Rio de Janeiro), 2019

The pure copper wires were wiredrawn at cryogenic and room temperatures. After deformation they p... more The pure copper wires were wiredrawn at cryogenic and room temperatures. After deformation they presented important and significant differences in their crystallographic textures and microstructures. Therefore, this study aimed to investigate the evolution of crystallographic texture of pure copper drawn at temperatures of 295 K and 77 K and correlated them to the deformation micromechanisms. For this, the X ray diffraction (XRD) and electron backscattered diffraction (EBSD) techniques were used. The results showed that, after the deformation, the samples drawn at both temperatures showed Copper {112}<111>, X {110}<111> and Brass {110}<112> components as the most intense. In samples drawn at cryogenic temperature there was also observed the appearance of a R{124}<211> component, typical of recrystallization and the presence of the  fiber {111}, typical of deformation twin.

Research paper thumbnail of Comparative Study by Tem, Ebsd and Microhardness of the Microstructure of Copper Wiredrawn at 77 K and 295 K

Tecnologia em Metalurgia Materiais e Mineração, 2019

Research paper thumbnail of Failure Analysis of Tool Steel-Based Compaction Punch Used in Powder Metallurgy

Journal of Failure Analysis and Prevention, 2015

Powder metallurgy operations comprise the use of compaction dies and punches for transforming a m... more Powder metallurgy operations comprise the use of compaction dies and punches for transforming a mass of metallic powders into a porous block of aggregated particles with limited ''green'' strength. In this kind of application, dies and punches manufactured with tool steel are subjected to heavy loads to compress the metallic powders and form the block, which will be subjected to further consolidation operations such as sintering and/or some mechanical forming operation, such as forging or rolling. In general tool steels are high carbon and high alloyed steels designed for reaching high levels of mechanical strength, sufficient for his type of loading. However, defects on the surface of this material can lead to stress concentration, thus decreasing its fracture strength and eventually leading to failure. In this study, techniques such as optical and scanning electron microscopy are used to evaluate the possible causes of the failure of a compaction punch. The results indicated that machining grooves acted as stress concentrations which led to the premature fracture of the punch.

Research paper thumbnail of Microstructural Analysis of the Failure of a Cast Iron Cylinder Head of a Thermoelectrical Plant Motor

Journal of Failure Analysis and Prevention, 2015

Large motors, such as those that propel ships or generate energy for thermoelectrical plants, for... more Large motors, such as those that propel ships or generate energy for thermoelectrical plants, for instance, use cylinder heads produced with nodular cast iron. Such components are manufactured by a casting process which must be strictly controlled to prevent the appearance of defects that may spoil the performance of the component in service. When these defects arise, they usually lead to the failure of the cylinder head, mainly causing fluids leakage that can harm or even impede the motor performance. In this study, the microstructure of the material was characterized, with the purpose of investigating the possible causes of the failure, through the use of techniques such as optical microscopy and scanning electron microscopy. Brinell hardness tests were also performed. The results revealed that inadequate casting procedures probably caused the defects and subsequent failure of the cylinder head.

Research paper thumbnail of A microstructural study on the high temperature oxidation, carburation and sulfidation of HK 40 and Incoloy 802

Materials Characterisation VI, 2013

The main purpose of this article is an analysis of the microstructural changes in stainless steel... more The main purpose of this article is an analysis of the microstructural changes in stainless steels and other special alloys due to high temperature phenomena, such as oxidation, carburization and sulfidation. These conditions arise in a plant during the production of polymeric materials, when the raw material, coke originating from petroleum, rich in carbon and sulfur, is in direct contact with tubes fabricated with metallic materials at elevated temperatures during the pyrolysis process. These changes can damage the characteristics and properties of the alloys, thus leading to premature failure in certain regions of the pipeline. In this work, techniques such as optical microscopy, field emission scanning electron microscopy (FESEM) equipped with an EDS microanalysis system and hardness tests were employed to analyze HK 40 stainless steel and Incoloy 802 used in pyrolysis tubes for polymeric material production. The presence of many undesirable oxide, carbide and sulfide particles and chromium depletion was identified mainly in the inner surface of the tubes in direct contact with the coke at elevated temperatures (around 1000ºC). Variations of the corrosive attack were observed along different positions in the pipeline, depending on the more or less extensive exposure to high temperatures and corrosive agents. It can be concluded that the degradation which led to the premature failure of the pipeline Materials Characterisation VI 41

Research paper thumbnail of Characterization of Titanium Powders Processed at Different Temperatures

Materials Science Forum, 2014

Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, du... more Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, due to a very favorable combination of properties, when compared with other metals, such as good corrosion resistance, good mechanical properties, relatively low density, elasticity modulus close to that of bone and good biocompatibility, which assures good adhesion/integration to bone. Powder metallurgy has been used for titanium based implants fabrication due to advantages such as the production of more complex shapes and reduction of machining operation. In this work, compacted pure titanium powders, consolidated by rolling at different temperatures, were characterized by means of optical microscopy, Field Emission Scanning Electron Microscopy (FESEM) with Electron Back Scattering Diffraction (EBSD) analysis, automatic image analysis and hardness tests. The hardness of rolled samples increased from 200 to 400oC , which indicated that 300 to 400°C is the most adequate temperature range f...

Research paper thumbnail of Texture and Microstructure of Cold Rolled and Recrystallized Pure Niobium

Materials Science Forum, 2007

Crystallographic macrotexture of pure niobium cold rolled to 30, 60, 80 and 90% reduction was ana... more Crystallographic macrotexture of pure niobium cold rolled to 30, 60, 80 and 90% reduction was analyzed by X-ray diffraction and compared with low carbon steel texture. Annealed samples from 800oC, to 1200oC were investigated by X-ray diffraction and electron back scattering diffraction (EBSD). The texture of cold rolled polycrystalline niobium is characterized by a component {001}<110> that increases in intensity with the cold work percentage. After annealing, the component {001}<110> spreads out about 20o.

Research paper thumbnail of Deformation induced martensite in an AISI 301LN stainless steel: characterization and influence on pitting corrosion resistance

Materials Research, 2007

In austenitic stainless steels, plastic deformation can induce martensite formation. The induced ... more In austenitic stainless steels, plastic deformation can induce martensite formation. The induced martensite is related to the austenite (γ) instability at temperatures close or below room temperature. The metastability of austenite stainless steels increases with the decreasing of stacking fault energy (SFE). In this work, the deformation induced martensite was analyzed by X ray diffraction, electron back scatter diffraction (EBSD), magnetic methods and atomic force microscope (AFM) in samples of a low SFE austenitic stainless steel, AISI 301LN and compared with a medium SFE stainless steel, AISI 316L. Both techniques, X ray diffraction and EBSD, presented similar quantities for the α'-martensite. Texture results indicate that the crystallographic orientation of the formed α'martensite is {001}<110> and {103}<110>. The morphology of α'-martensite was analyzed by AFM. Corrosion tests showed that deformation reduces pitting corrosion and generalized corrosion resistance in both steels.

Research paper thumbnail of Effect of high temperature annealing on texture and microstructure on an AISI-444 ferritic stainless steel

Materials Characterization, 2006

AISI 444 is a Mo-alloyed ferritic stainless steel which presents good naphthenic corrosion resist... more AISI 444 is a Mo-alloyed ferritic stainless steel which presents good naphthenic corrosion resistance, making it attractive for applications in petroleum refining plants; however, good formability is also important. To achieve good formability with this alloy the annealing process is crucial. The annealing temperature in ferritic stainless steel is usually around 850 °C, which falls in the range of sigma phase

Research paper thumbnail of Microscopic Analysis of Fractured Screws Used as Implants in Bone Fixation

Journal of Failure Analysis and Prevention, 2014

The increase of life expectancy and risk of accidents, thereby causing a higher incidence of surg... more The increase of life expectancy and risk of accidents, thereby causing a higher incidence of surgeries, has led to a growing use of implants. The reliability of these implants, either for bone fracture correction or for joint replacement, thus used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. By using some techniques, mainly optical microscopy and scanning electron microscopy tests, this work has as purpose the identification of the possible causes of failure of screws used in plates for bone fixation, considering the fracture surface aspects and microstructural characteristics of the austenitic stainless steel used in their manufacture, which is essential for this application. The results obtained in this study allowed the identification of the main causes of the failure, primarily related to fatigue fracture, associated to the presence of surface cracks, generated by stress concentration, which was probably caused by grooves left by improper machining.

Research paper thumbnail of A Microstructural and Fractographic Study on the Failure of a Drive Shaft

Journal of Failure Analysis and Prevention, 2011

The automotive industry is one of the most dynamic and competitive segments of the international ... more The automotive industry is one of the most dynamic and competitive segments of the international economy and it has invested considerable resources into the research and development of new components and the improvement of existent pieces. Nonetheless, failures continue to occur, often because of defects in a component. Failure analysis uses several techniques to investigate causes of the defect which led to the failure of a component, equipment, or structure. Usually, these causes are related to the use of inadequate materials, the presence of defects which appear during fabrication or design errors, or improper assembly, maintenance and use. Knowledge about these causes and the correction of such anomalies allow the improvement of the performance of components regarding both efficiency and safety. In this study, the results of the failure analysis of the drive bar of a police car are presented and light optical microscopy and scanning electron microscopy (SEM) results are used to show that the presence of an already existent defect and an unfavorable microstructure led to the occurrence of brittle fracture which caused the premature and catastrophic failure of this component.

Research paper thumbnail of Failure analysis of AISI 310S plate in an inert gas generator used in off-shore oil platform

Engineering Failure Analysis, 2011

In this work a failure analysis was conducted in a mirror plate made of austenitic stainless stee... more In this work a failure analysis was conducted in a mirror plate made of austenitic stainless steel AISI 310. The mirror is part of the inert gas generator, which is a combustion chamber dedicated to produce inert gas atmosphere (N 2 + CO 2) to be used during the oil transfer in offshore platforms. The mirror failed in two distinct regions. The first crack was observed in a region where the temperatures reached were sufficiently high to provoke intense sigma phase precipitation. Other cracks were observed in a region subject to seawater refrigeration, named ''cold zone''. These two failures were mitigated in order to propose solutions to avoid similar failures in the new equipment.

Research paper thumbnail of Scanning Electron Microscopic Characterization of Healing and Normal Rat Ligament Microstructure Under Slack and Loaded Conditions

Connective Tissue Research, 2003

The objective of this study was to observe and compare behavior of the collagen fiber microstruct... more The objective of this study was to observe and compare behavior of the collagen fiber microstructure in normal and healing ligaments, both in situ and ex vivo, in order to add insight into the structure-function relationship in normal and healing ligaments. Fifty-two ligaments from 26 male rats were investigated. Eleven animals underwent surgical transection of both medial collateral ligaments (MCLs) (22 ligaments), which were allowed to heal for a period of 2 weeks. An additional 15 animals (30 ligaments) were used as normals. Ligaments were placed into six groups: Slack (n = 6 control, n = 6 healing), Reference (n = 4 control, n = 4 healing), Loaded (n = 4 control, n = 4 healing), 15 • Flexion (n = 4 control, n = 4 healing), 120 • Flexion (n = 4 control, n = 4 healing), and Tissue Strain vs. Flexion Angle (n = 8 normals). All ligaments, except those in the Tissue Strain vs. Flexion Angle group, were prepared for scanning electron microscopy. Tissues were harvested, mounted in a load frame, and chemically fixed in one of five states: (1) slack, (2) reference (onset of loading), (3) loaded, (4) 15 • knee flexion, or (5) 120 • knee flexion. After fixation the tissues were prepared for electron microscopy (SEM). The micrographs from the slack, reference, and loaded groups show fiber straightening with loading in normal ligaments as well as in both scar and "retracted" regions of healing ligaments. Collagen fibers' diameter and crimp patterns were dramatically changed in the scar region of healing ligaments: Width decreased from

Research paper thumbnail of Archaeometric investigations on naturally and thermally-aged iron-gall inks using different tannin sources

Open Chemistry, 2013

This paper investigates the behavior of paper strips containing iron-gall inks prepared with tann... more This paper investigates the behavior of paper strips containing iron-gall inks prepared with tannins from different sources, subjected to natural and thermally-induced aging. Results indicate that inks containing initial concentrations of ferrous sulphate ranging from 0.2 to 10.0 g are amenable to treatment with calcium phytate, and thata good correlation exists between the recovery of excess iron and the initial concentration. Infrared spectra showed an absorption band at 1,750 cm−1, typical of esther, solely in the samples prepared with a condensed tannin. The condensed nature of this tannin produced a different oxidation pattern, with iron removal inferior to those observed from inks produced with hydrolisable tannins. When tannic acid was used ferrous iron removals ranged from 0.050 to 1.800 g, decreasing to 0.5 g in the presence of copper; the same behavior was observed for the remaining hydrolisable tannins, with a lower recovery from the condensed tannin. The adopted natural ...