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Research Interests: Materials Science, Kinetics, Metallurgy, Graphite, Cast Iron, and 3 moreMartensite, Tempering, and Dilatometer
A novel combined process of Cold Stamping (CS) and Hot Stamping (HS) with Quenching and Partitioning (Q&P) treatment applied to advanced TRIP-assisted steel has been conducted by thermomechanical simulation to evaluate the influence of CS... more
A novel combined process of Cold Stamping (CS) and Hot Stamping (HS) with Quenching and Partitioning (Q&P) treatment applied to advanced TRIP-assisted steel has been conducted by thermomechanical simulation to evaluate the influence of CS or HS in the Q&P processing. With this purpose, Q&P, CSQ&P, and HSQ&P cycles were designed to obtain multiphase microstructures containing ferrite, martensite, bainitic-ferrite, and the maximum retained austenite (RA) fraction after the processes. The objective was to investigate the effects of the variables involving the heat treatments, such as the intercritical austenitization temperature, the isothermal and non-isothermal deformation, the amount of deformation, and the temperature and partitioning times, and to analyze their influence on the microstructural and mechanical responses. Time-resolved X-ray diffraction using synchrotron radiation was undertaken in a thermomechanical simulator coupled to the synchrotron light source to understand the...
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O objetivo do trabalho é avaliar como as propriedades mecânicas determinadas pelos ensaios de indentação podem ser usadas como indicadores da qualidade do corte do vidro. Foram avaliadas amostras de vidros "float" nas cores... more
O objetivo do trabalho é avaliar como as propriedades mecânicas determinadas pelos ensaios de indentação podem ser usadas como indicadores da qualidade do corte do vidro. Foram avaliadas amostras de vidros "float" nas cores incolor, verde, bronze e cinza, nas duas superfícies de produção (ar e banho de estanho). Em cada superfície foram medidos o módulo de Young e o coeficiente de Poisson empregando-se a técnica de pulso-eco ultrassônico (JIS-R 1602). As impressões de dureza Vickers foram executadas para calcular tanto a dureza (JIS-R 1610), como a tenacidade à fratura (JIS R-1607). Os resultados mostraram a existência de uma correlação linear decrescente entre o parâmetro fragilidade e a energia de fratura dos vidros ensaiados, sendo encontrados maiores valores de dureza e menores valores de tenacidade à fratura na superfície inferior (lado banho), em relação ao lado superior (atmosfera), resultando em uma maior fragilidade.
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Understanding the kinetics of microstructural degradation during the event of a fire is of major relevance to future optimization of fire-resistant steels (FRS). In this work, we use in situ synchrotron X-ray diffraction to assess the... more
Understanding the kinetics of microstructural degradation during the event of a fire is of major relevance to future optimization of fire-resistant steels (FRS). In this work, we use in situ synchrotron X-ray diffraction to assess the rapid thermally-assisted degradation of different starting microstructures, such as (i) ferrite + pearlite; (ii) bainite + retained austenite, and (iii) martensite + retained austenite, during the simulation of a fire cycle in a Fe-0.13C-0.11Cr-0.38Mo-0.04V FRS. Our results show that retained austenite is the most unstable phase, especially when generated by faster cooling rates, decomposing at temperatures as low as 180 °C during fire simulations. Bainite and martensite are both unstable and undergo recovery and carbon desaturation via secondary precipitation of cementite. However, bainite is comparatively more stable than martensite since its decomposition starts at 400 °C, while for martensite it occurs at 320 °C. We also present a methodology to deconvolute the effect of temperature on the increased background and signal intensities of the X-ray spectra, allowing the direct observation of the kinetics of secondary cementite precipitation.
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The Heavy-Haul railroad wheels started to use higher wear resistance steels microalloyed with niobium, vanadium, and molybdenum [1]. During continuous cooling, these elements depress the temperature of the pearlite formation, producing... more
The Heavy-Haul railroad wheels started to use higher wear resistance steels microalloyed with niobium, vanadium, and molybdenum [1]. During continuous cooling, these elements depress the temperature of the pearlite formation, producing smaller interlamellar spacing that increases the hardness of the steel, besides to favor the precipitation hardening through the formation of carbides [2, 3]. Also, they delay the formation of difusional components like pearlite and bainite during isothermal transformation. The effects of these alloy elements on microstructure during isothermal transformation were studied in this work using a Bähr 805A/D dilatometer. Three different compositions of class C railway wheels steels (two microalloyed and one, non microalloyed) were analyzed in temperatures between 200 and 700 °C. The microstructure and hardness for each isothermal treatment were obtained after the experiments. Comparing with non microalloyed steel (7C), the vanadium addition (7V steel) did...
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Improvement of wear resistance and mechanical performance of rails used in heavy-haul railway are essential to reduce railroad maintenance costs. A novel heat treatment based on quenching and partitioning (Q&P) processing was proposed to... more
Improvement of wear resistance and mechanical performance of rails used in heavy-haul railway are essential to reduce railroad maintenance costs. A novel heat treatment based on quenching and partitioning (Q&P) processing was proposed to improve the wear resistance of a hypereutectoid pearlitic rail. 50% of austenite was transformed into martensite under an interrupted quenching from full austenitization temperature to 140 °C. A multiphase microstructure resulted from the quenching and partitioning process, consisting of tempered martensite, bainite, retained austenite, and pearlite colonies. The partitioning step was performed in the range of 350–650 °C. Microstructure characteristics were investigated using scanning electron microscopy, microhardness measurements, X-ray and electron backscattered diffraction. Uniaxial tensile and pin-on-disc tests were also performed to evaluate the mechanical properties and wear resistance. The best combination of wear resistance and mechanical p...
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Abstract Thermomechanical simulation of quenching, hot stamping, and quenching and partitioning processes of a high-strength TRIP-assisted steel were carried out in a Gleeble®3S50 thermo-mechanical simulator, coupled to the synchrotron... more
Abstract Thermomechanical simulation of quenching, hot stamping, and quenching and partitioning processes of a high-strength TRIP-assisted steel were carried out in a Gleeble®3S50 thermo-mechanical simulator, coupled to the synchrotron X-ray diffraction line. The microstructures and mechanical properties were analyzed using Field Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction, and nanoindentation. The microstructures of thermomechanical treated specimens were modeled using the Object Oriented Finite Element (OOF) technique. The modeled microstructures were then fed into a finite element model to predict the mechanical behavior. By using a reverse algorithm method, the elasto-plastic mechanical properties of different microconstituents were determined. This was done through the analysis of instrumented nanoindentation loading-penetration curves. Tensile properties of the thermomechanical processed steels were measured by tensile testing of subsized specimens cut from samples processed on the Gleeble®3S50. The comparison between the experimental results and those of the reverse algorithm and the OOF modeled microstructure showed quite good agreement.
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O Y2O3 é o principal aditivo usado na sinterização de cerâmicas de AlN com elevada condutividade térmica, que são destinadas a produção de dispositivos eletrônicos de alta performance. Neste trabalho, investigou-se o efeito do teor de... more
O Y2O3 é o principal aditivo usado na sinterização de cerâmicas de AlN com elevada condutividade térmica, que são destinadas a produção de dispositivos eletrônicos de alta performance. Neste trabalho, investigou-se o efeito do teor de aditivo na sinterização de AlN com 0,5 a 4% em peso de Y2O3, correlacionado os resultados de densidade, análise microestrutural e a evolução das segundas fases em função da temperatura de sinterização. Os corpos compactados foram sinterizados em atmosfera de nitrogênio usando um forno com elemento resistivo de tungstênio entre 1650 e 2000 ºC por 1 h. Os resultados mostraram que a densificação das amostras de AlN com até 4% de Y2O3 ocorreu por sinterização no estado sólido até 1700 ºC. Acima desta temperatura, a densificação ocorreu por sinterização assistida por fase líquida. A fusão da fase YAG foi responsável pela formação de líquido ao redor de 1725 ºC nas amostras de AlN com até 4% de Y2O3. A quantidade de fase líquida aumentou em função do teor de...
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ABSTRACT Magnetic Barkhausen noise (MBN) was used to characterize the progress of austenite to martensite phase transformation while cooling steel specimens, using a conventional Barkhausen noise emission setup stimulated by an... more
ABSTRACT Magnetic Barkhausen noise (MBN) was used to characterize the progress of austenite to martensite phase transformation while cooling steel specimens, using a conventional Barkhausen noise emission setup stimulated by an alternating magnetic field. The phase transformation was also followed by electrical resistivity measurements and by optical and scanning electron microscopy. MBN measurements on a AISI D2 tool steel austenitized at 1473 K and cooled to liquid nitrogen temperature presented a clear change near 225 K during cooling, corresponding to the MS (martensite start) temperature, as confirmed by resistivity measurements. Analysis of the resulting signals suggested a novel experimental technique that measures spontaneous magnetic emission during transformation, in the absence of any external field. Spontaneous magnetic noise emission measurements were registered in situ while cooling an initially austenitic sample in liquid nitrogen, showing that local microstructural changes, corresponding to an avalanche or “burst” phenomena, could be detected. This spontaneous magnetic emission (SME) can thus be considered a new experimental tool for the study of martensite transformations in ferrous alloys, at the same level as acoustic emission.
Research Interests: Engineering, Applied Physics, Scanning Electron Microscopy, Heat Treatment, Acoustic Emission, and 12 moreMagnetic field, Mathematical Sciences, Optical microscopy, Physical sciences, Electrical Resistance, Phase Transformation, Microstructures, Martensitic Transformation, Barkhausen noise, Liquid Nitrogen, MAgnetic Barkhausen noise, and External field
RESUMEN Los aceros multifásicos son una familia de materiales con propiedades mecánicas excepcionales que incluyen alta resistencia mecánica, excelente ductilidad e índice de endurecimiento y buena conformabilidad. Estas propiedades están... more
RESUMEN Los aceros multifásicos son una familia de materiales con propiedades mecánicas excepcionales que incluyen alta resistencia mecánica, excelente ductilidad e índice de endurecimiento y buena conformabilidad. Estas propiedades están relacionadas con la microestructura, que puede ser desde combinaciones de ferrita y martensita (aceros dúplex) hasta microestructuras complejas con presencia de ferrita, bainita, martensita y austenita retenida como en el caso de los aceros TRIP. Una de las etapas fundamentales en la fabricación de estos aceros es la austenización intercrítica que se produce entre las temperaturas A1 y A3, de la cual depende la fracción de austenita de alta temperatura y la composición química de las fases, en especial el contenido de carbono. Con el fin de estudiar esta etapa del tratamiento térmico se fabricaron aceros con variaciones en la concentración de carbono (0.2-0.5%) y silicio (1.4-2.0%) y se realizaron ensayos dilatométricos. Los resultados permitieron ...
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Page 1. Key Engineering Materials Vols. 127-131 (1997) pp 985-992 © (1997) Trans Tech Publications, Switzerland doi: 10.4028/www. scientific.net/KEM. 127-131.985 The Effects of SiCp Clusters and Porosity on the Mechanical ...
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Most Ni-based superalloys are strengthened by the presence of coherent precipitates of an ordered fcc bases phase, known as [gamma][prime]. This phase is basically Ni[sub 3]Al. The precipitates are coherent up to a certain size and they... more
Most Ni-based superalloys are strengthened by the presence of coherent precipitates of an ordered fcc bases phase, known as [gamma][prime]. This phase is basically Ni[sub 3]Al. The precipitates are coherent up to a certain size and they present a cubic shape with faces oriented in the (100) planes of both matrix and precipitate. The detailed atomistic structure of this interface
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Ni3Al-based alloys possess good oxidation resistance, moderate room and high temperature strength and ductility. Introduction of Cr-carbide particles through a solidification route is attempted to provide higher hardness and wear... more
Ni3Al-based alloys possess good oxidation resistance, moderate room and high temperature strength and ductility. Introduction of Cr-carbide particles through a solidification route is attempted to provide higher hardness and wear resistance. The mechanical and physical properties are measured at room temperature for several alloys with various carbon concentrations up to 2.0 wt.%. Hardness and wear resistance as well as compressive strength increase with increasing carbon concentration, while bend ductility decreases. Adhesion between carbides and matrix phase is good, and cracks propagate mainly through carbides. The crystallographic orientation relationships between constituent phases are also attempted using electron back-scattering diffraction (EBSD) technique. The thermal conductivity is found to be less sensitive to the alloy composition.