667 resultados para Ligas (Metalurgia)
Resumo:
Esta obra trata da sucessão cultural registada na Estremadura portuguesa desde a emergência das sociedades complexas do Calcolítico até à chegada dos Romanos, correspondendo a um lapso de tempo entre os finais do IV milénio e os finais do século II a.C. Embora corresponda apenas a intervalo temporal de aproximadamente três mil anos, é o que, no registo material da nossa Pré-História e Proto-História, se afigura mais rico e diversificado de informação, com o desenvolvimento e fixação de regionalismos culturais, que na Estremadura cunharam identidades próprias, as quais persistiram nalguns casos até época recente, no quotidiano dos seus habitantes. A percepção geral desta evolução, bem como as suas determinantes, é o primeiro, e talvez mais importante objectivo desta obra, a par de outros a seguir enunciados: – a génese dos povoados fortificados calcolíticos, em resultado da crescente intensificação económica e da especialização das produções – a Revolução dos Produtos Secundários (RPS), que decorreu ao longo de boa parte do III milénio a.C. – a par do crescimento demográfico, que determinou, por seu turno, a competição inter-grupos, com a consequente necessidade de fortificação; – a monumentalização / fortificação de alguns dos sítios habitados como expressão da coesão social da respectiva comunidade, acompanhada da emergência de diferenciações inter e intra-comunitárias, indício de diferenciação social, em crescente afirmação, decorrente do processo de desenvolvimento económico complexo, característico do Calcolítico; – as arquitecturas defensivas do III milénio a.C., como expressão pública indissociável da monumentalização acima referida: exemplos mais importantes no território estremenho, distribuição geográfica, características principais, semelhanças e diferenças; neste âmbito, importa conhecer as diversas teorias explicativas para o seu surgimento, desde o modelo difusionista e orientalista vigente em Portugal (dos anos 40 aos anos 70), passando pelo modelo indigenista (anos 80), até às formas difusionistas mitigadas, de expressão regional, dos finais da década de 80 em diante, e principais argumentos invocados; – a desarticulação do modelo de sociedade calcolítica, caracterizada pela concentração da população em sítios fortificados ou pelo menos implantados predominantemente em locais altos e defensáveis; – os moldes em que se processou a acentuação das influências mediterrâneas no decurso do Calcolítico (em especial na metade meridional do território): a generalização do comércio transregional calcolítico e a intensificação e especialização das produções, no quadro da Revolução dos Produtos Secundários (RPS), exemplificada pela exploração de jazidas cupríferas, como veículo de difusão de novas técnicas (metalurgia), matérias-primas exógenas (marfim) e artefactos ideotécnicos de características até então desconhecidas (generalização do culto da divindade feminina e correspondentes expressões simbólicas, algumas de âmbito estritamente regional), acompanhada da difusão, de Sul para Norte, de novas arquitecturas funerárias (tholoi); – sobre o Campaniforme, fenómeno cultural com identidade própria da fase média e tardia do Calcolítico estremenho, serão discutidas as características e cronologia da sua emergência, na Estremadura (um dos pólos mais importantes, a nível europeu) no quadro da sociedade calcolítica pré-existente: tipo de povoamento e de necrópoles, bem como as relações estabelecidas com as comunidades de tradição cultural mais antiga; o faseamento interno do “fenómeno”, com base nas diferenças identificadas no registo material (em particular a tipologia das cerâmicas); e principais tipos artefactuais que o integram. O campaniforme deverá ser entendido como uma expressão material específica, associada a um novo tipo de povoamento, que resultou do decréscimo do interesse oferecido pelos sítios fortificados edificados no início do Calcolítico. Neste sentido, corresponde a período de transição para a Idade do Bronze: existem argumentos, com base no registo arqueológico (jóias de ouro, artefactos de prestígio) que ilustram o incremento do processo de diferenciação social, então verificado, ao contrário do que uma abordagem mais superficial, com base simplesmente no reordenamento demográfico, faria supor; – o registo arqueológico do Bronze Pleno configura a acentuação dos regionalismos, apesar de similitudes do sistema de povoamento face ao período imediatamente anterior, o que indicia realidades socioeconómicas comparáveis. Importa, assim, conhecer as principais características dos escassos povoados identificados, bem como a organização social a ele subjacente, a partir dos testemunhos arqueológicos conhecidos, incluindo os de carácter funerário; – segue-se o Bronze Final, período dominado pela plena afirmação do comércio transregional atlântico-mediterrâneo, favorecido pela própria realidade geográfica do território português. Devem valorizar-se os testemunhos materiais desse período e as respectivas balizas cronológicas: Assim, deverão os leitores ficar familiarizados com as produções de carácter atlântico, como as armas, objectos utilitários e respectivas tipologias e com as de cunho mediterrâneo (com destaque para objectos de indumentária e de carácter cultual, embora estes últimos quase se desconheçam na área estremenha), cujo comércio e difusão foi suportado pela existência de solidariedades económicas transregionais, baseadas em prováveis pactos formalmente estabelecidos entre comunidades vizinhas. Os respectivos territórios, de norte a sul do País, apresentar-se-iam cada vez melhor delimitados; o mesmo deverá ter-se verificado na Estremadura. A caracterização da respectiva economia será, por isso, objecto da análise e discussão; embora de base agro-pastoril (com importância evidente na Estremadura dadas as características dos solos e a quase inexistência de minérios de cobre ou de estanho), a produção de peças metálicas de bronze assumiu importância crescente, como se conclui pelas ocorrências conhecidas. O reforço e a consolidação das elites então verificada, eram necessários para a boa gestão de grandes povoados muralhados que despontam no Bronze Final; na Estremadura, embora os testemunhos de tais centros demográficos não sejam particularmente evidentes, no fim da Idade do Bronze desponta um vigoroso povoamento de altura; seria a partir desses locais que as elites da época, de cunho guerreiro, administrariam territórios bem delimitados. Também a existência de outros testemunhos arqueológicos são concorrentes para a percepção da realidade social: as jóias auríferas, tornadas então relativamente frequentes, deixam transparecer influências ora atlânticas ora mediterrâneas, por vezes reunidas numa única peça (técnicas e tipologias decorativas), expressivas das correntes culturais que, então, se faziam sentir na Estremadura; também as armas, são testemunho da afirmação das elites guerreiras, encontrando-se representadas por exemplares cujas principais características devem ser conhecidas. As diversas práticas funerárias, apesar de escassamente representadas, revelam influências continentais (cremação e campos de urnas, já fora da área estremenha, mas dela próxima: caso dos campos de urnas de Tanchoal e de Meijão, Alpiarça) e mediterrâneas (inumações na tholos da Roça do Casal do Meio, Sesimbra), que traduzem um mosaico cultural complexo, reforçando a ideia de se tratar de região receptora de influxos culturais de diversas áreas geográficas em simultâneo: é, no essencial, a comprensão global desta realidade, a um tempo económica, social e cultural, coroando um longo processo de diferenciação social, por um lado e, por outro, de intensificação económica e interacção cultural, que lhe está subjacente, que deverá ter-se presente. Por último, segue-se o estudo e caracterização das principais estações e materiais da Idade do Ferro, de início (I Idade do Ferro) profundamente marcadas pela presença, directa ou indirecta, de colonizadores fenícios; depois, pelos comerciantes de origem púnica (II Idade do Ferro) e, enfim, pelos exércitos itálicos. Trata-se, em suma, de processo de características próprias, sempre determinado pelas influências mediterrâneas, largamente dominantes face às originárias do interior peninsular, as quais cunharam uma realidade cultural com características próprias, que persistiu no decurso da dominação romana.
Resumo:
As Ferrarias del Rey, em Barcarena, foram o mais bem sucedido dos empreendimentos metalúrgicos reais portugueses dos séculos XV a XVII. Vocacionadas para a metalurgia do ferro e com data de fundação documentada no ano de 1487, constituem o mais antigo complexo oficinal português orientado exclusivamente para a produção de armamento. Para além da sua dimensão, ímpar à época em Portugal, foi a sua componente tecnológica que verdadeiramente diferenciou as Ferrarias das restantes oficinas então existentes.
Resumo:
The main objective is to analyze the abrasive wear resistance to the low stress of the elements that make up the organs of road machinery that are exposed directly to contact with abrasives. These samples were analyzed after these elements are coated superficially by the process of welding electrode coated with (SAER) and the manual process of coating type LVOF thermal spraying. As well, is to provide suggestions for a better recovery and return of these elements, which are reducing costs and avoiding downtime in the fronts of service. The samples were made from a substrate of carbon ABNT 1045 tempered steel, following the same specifications and composition of metals and alloys of constituents was followed the standard governing the dimensions of these samples and in accordance with the corresponding size. The results were evaluated by testing the hardness, abrasion resistance to wear by the low stress and the loss of volume involving the microstructure of coatings analyzed
Resumo:
A frequently encountered difficulty in oral prosthetics is associated with the loss of metallic alloys during the melting stage of the production of metal-ceramic replacement systems. Remelting such materials could impar their use in oral rehabilitation due to loss in esthetics, as well as in the chemical, physical, electrochemical and mechanical properties. Nowadays, the Ni-Cr-Mo-Ti alloy is widely used in metal-ceramic systems. Manufacturers state that this material can be remelted without significant alterations in its behavior, however little has been established as to the changes in the performance of this alloy after successive remelting, which is common practice in oral prosthetics. Therefore, the objective of this study was to evaluate possible changes in the esthetics and associated properties of metalceramic samples consisting of Ni-Cr-Mo-Ti and dental porcelain. Three to five remelting steps were carried out. The results revealed that Ni-Cr-Mo-Ti can be safely used even after three remelting steps. Further remelting significantly affect the characteristics of the alloys and should not be recommended for the manufacture of metal-ceramic systems
Resumo:
It seeks to find an alternative to the current tantalum electrolytic capacitors in the market due to its high cost. Niobium is a potential substitute, since both belong to the same group of the periodic table and because of this have many similar physical and chemical properties. Niobium has several technologically important applications, and Brazil has the largest reserves, around 96%. There are including niobium in reserves of tantalite and columbite in Rio Grande do Norte. These electrolytic capacitors have high capacitance specifies, ie they can store high energy in small volumes compared to other types of capacitors. This is the main attraction of this type of capacitor because is growing demand in the production of capacitors with capacitance specifies increasingly high, this because of the miniaturization of various devices such as GPS devices, televisions, computers, phones and many others. The production route of the capacitor was made by powder metallurgy. The initial niobium powder supplied by EEL-USP was first characterized by XRD, SEM, XRF and laser particle size, to then be sieved into three particle size, 200, 400 e 635mesh. The powders were then compacted and sintered at 1350, 1450 and 1550°C using two sintering time 30 and 60min. Sintering is one of the most important parts of the process as it affects properties as porosity and surface cleaning of the samples, which greatly affected the quality of the capacitor. The sintered samples then underwent a process of anodic oxidation, which created a thin film of niobium pentóxido over the whole porous surface of the sample, this film is the dielectric capacitor. The oxidation process variables influence the performance of the film and therefore the capacitor. The samples were characterized by electrical measurements of capacitance, loss factor, ESR, relative density, porosity and surface area. After the characterizations was made an annealing in air ate 260ºC for 60min. After this treatment were made again the electrical measurements. The particle size of powders and sintering affected the porosity and in turn the specific area of the samples. The larger de area of the capacitor, greater is the capacitance. The powder showed the highest capacitance was with the smallest particle size. Higher temperatures and times of sintering caused samples with smaller surface area, but on the other hand the cleaning surface impurities was higher for this cases. So a balance must be made between the gain that is achieved with the cleaning of impurities and the loss with the decreased in specific area. The best results were obtained for the temperature of 1450ºC/60min. The influence of annealing on the loss factor and ESR did not follow a well-defined pattern, because their values increased in some cases and decreased in others. The most interesting results due to heat treatment were with respect to capacitance, which showed an increase for all samples after treatment
Resumo:
421 p.
Resumo:
The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and silício, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, silício and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 µm, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 µm/min
Resumo:
This research studies the sintering of ferritic steel chips from the machining process. Were sintered metal powder obtained from machining process chips for face milling of a ferritic steel. The chip was produced by machining and characterized by SEM and EDS, and underwent a process of high energy mill powder characterized also by SEM and EDS. Were constructed three types of matrixes for uniaxial compression (relation l / d greater than 2.5). The differences in the design of the matrixes were essentially in the direction of load application, which for cylindrical case axial direction, while for the rectangular arrays, the longer side. Two samples were compressed with different geometries, a cylindrical and rectangular with the same compaction pressure of 700 MPa. The samples were sintered in a vacuum resistive furnace, heating rate 20 °C / min., isotherm 1300 °C for 60 minutes, and cooling rate of 25 °C / min to room temperature. The starting material of the rectangular sample was further annealed up to temperature of 800 ° C for 30 min. Sintered samples were characterized by scanning electron microscopy, optical microscopy and EDS. The sample compressed in the cylindrical matrix did not show a regular density reflecting in the sintered microstructure revealed by the irregular geometry of the pores, characterizing that the sintering was not complete, reaching only the second phase. As for the specimen compacted in the rectangular array, the analysis performed by scanning electron microscopy, optical microscopy and EDS indicate a good densification, and homogeneous microstructure in their full extent. Additionally, the EDS analyzes indicate no significant changes in chemical composition in the process steps. Therefore, it is concluded that recycling of chips, from the processed ferritic steel is feasible by the powder metallurgy. It makes possible rationalize raw material and energy by manufacture of known properties components from chips generated by the machining process, being benefits to the environment
Resumo:
Se proponen actividades utilizando el geoespacio, el cual es un material que el alumno manipulará para aprender en forma práctica, y así se consolidará el aprendizaje de las matemáticas, en especial de la geometría. Por medio de dibujos en isométrico se hará la representación plana de los sólidos que se formen en el geoespacio. Pescarini y Puig Adam han presentado una modificación del geoplano para hacer posible el estudio del espacio de tres dimensiones; lo han llamado geoespacio y sus posibilidades son sensiblemente menores. Consta de tres paredes de tela metálica fina formando un triedro. Con trozos de alambre se materializan las figuras del espacio, particularmente las poliédricas. En este trabajo se presenta al geoespacio como una estructura cúbica que lleva un sistema de argollas dispuestas en las aristas, donde podrán colocarse ligas de colores para formar sólidos y presentar diversas situaciones didácticas.
Resumo:
The ionic nitriding process presents some limitations related with the control of the thickness of the layer and its uniformity. Those limitations that happen during the process, are produced due to edge effects, damage caused by arcing arc and hollow cathode, mainly in pieces with complex geometry and under pressures in excess of 1 mbar. A new technique, denominated ASPN (active screen shapes nitriding) it has been used as alternative, for offering many advantages with respect to dc plasma conventional. The developed system presents a configuration in that the samples treated are surrounded by a large metal screen at high voltage cathodic potencials, (varying between 0 and 1200V) and currents up to 1 A. The sample is placed in floting potential or polarized at relatively lower bias voltages by an auxiliary source. As the plasma is not formed directly in the sample surface but in the metal screen, the mentioned effects are eliminated. This mechanism allows investigate ion of the transfer of nitrogen to the substrate. Optical and electronic microscopy are used to exam morphology and structure at the layer. X-ray difration for phase identification and microhardness to evaluate the efficiency of this process with respect to dc conventional nitriding
Resumo:
The titanium and titanium alloys are widely used as biomaterial in biomedical device and so research have been developed aiming to improve and/or better to understand interaction biomaterial/biological environment. The process for manufacturing of this titanium implants usually involves a series of thermal and mechanical processes which have consequence on the final product. The heat treatments are usually used to obtain different properties for each application. In order to understand the influence of these treatments on the biological response of the surface, it was done, in this work, different heat treatments in titanium and analyzed their influence on the morphology, adhesion and proliferation of the pre-osteoblastic cells (MC3T3-E1). For such heat-treated titanium disks were characterized by optical microscopy, contact angle, surface energy, roughness, microhardness, X-ray diffraction and scanning through the techniques (BSE, EDS and EBSD). For the analysis of biological response were tested by MTT proliferation, adhesion by crystal violet and β1 integrin expression by flow cytometry. It was found that the presence of a microstructure very orderly, defined by a chemical attack, cells tend to stretch in the same direction of orientation of the material microstructure. When this order does not happen, the most important factor influencing cell proliferation is the residual stress, indicated by the hardness of the material. This way the disks with the highest level state of residual stress also showed increased cell proliferation
Resumo:
La corrección de una falla por distorsión puede ser compleja ya que involucra efectos microestructurales y esfuerzos residuales que son la causa principal del fenómeno de distorsión. Las fallas por distorsión son serias debido a que pueden conducir a que el producto final no cumpla con los requerimientos dimensionales y no sea aceptado para desarrollar su función. Hoy en día, la problemática es la distorsión que sufren los componentes cuando se les somete a un tratamiento térmico temple, debido a las transformaciones de fase y esfuerzos residuales que se generan por el enfriamiento rápido, así como del tratamiento térmico de revenido donde el exceso de carbono es liberado de la estructura cristalina de la martensita y/o bainita y genera la deformación en la estructura cristalina, con esta problemática es posible hacer uso del modelo de Tratamiento Térmico que contiene el paquete comercial computacional FORGE HPC 2011®, para tratar de reproducir estos fenómenos que se llevan a cabo durante los tratamientos térmicos mencionados, y posteriormente generar información relacionada al tratamiento térmico de revenido, para desarrollar un modelo matemático que sea capaz de predecir las propiedades mecánicas finales. Este trabajo consistió en 3 etapas, la primer etapa se basó en estudiar detalladamente el grado de acero 42CrMo4 al aplicarle un tratamiento térmico de temple, bajo condiciones industriales con la finalidad de generar mayor conocimiento de los fenómenos de distorsión del acero antes mencionado, los cuales muchos autores atribuyen que este fenómeno se presenta con mayor frecuencia durante el temple, debido a la transformación de fase martensita, fase metaestable más dura en los aceros que tienen la capacidad de generar esta estructura cristalina, el experimento se desarrolló tratando térmicamente 16 anillos con las siguientes dimensiones; diámetro exterior = 2631 mm, pared = 164 mm y altura de 188 mm, instrumentados cada componente con 20 termopares tipo “k” de γ mm de diámetro, orientados cada 90°, esta metodología se desarrolló con la finalidad de obtener el máximo dato posible durante temple para posteriormente asociarlo con los coeficientes de transferencia de calor h, y así modelar la distorsión en las piezas utilizando un paquete comercial computacional, así como las condiciones de enfriamiento de la primer prueba experimental, encontrando errores máximos de 10 % comparando los resultados experimentales con los resultados obtenidos de la simulación. La segunda parte del proyecto consistió en una matriz de experimentos de tratamientos térmicos de temple y revenido, donde las variables principales fueron la temperatura y el tiempo, aplicadas en 13 probetas con las siguientes dimensiones; 100 mm X 100 mm X 200 mm, para generar conocimiento de la evolución de la dureza así como las propiedades mecánicas del mismo grado de acero, esta parte del experimento tuvo como finalidad el desarrollo y evaluación de un modelo matemático implementado en computadora que gobierne dicho comportamiento, encontrando errores en el rango de 1 hasta 40 %, comparando los resultados experimentales vs los resultados simulados. La tercera etapa del proyecto consistió en evaluar el grado de acero AISI 8630 y AISI 4340 utilizando el modelo de tratamiento térmico de revenido y datos experimentales de tres tiempos y tres temperaturas para cada uno de los aceros ya mencionados, encontrando que el modelo de tratamiento térmico de revenido no es capaz de reproducir perfiles de dureza en aceros de madia y alta aleación como están clasificados los aceros mencionados, ya que los resultados entre la parte experimental y la simulada no coincide con una línea recta para el acero AISI 8630, se encontró un coeficiente de correlación de 0.87 y errores entre 22 y 44 %, y para el acero AISI 4340, se encontró un coeficiente de correlación de 0.53 y errores entre 17 y 33 %
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La nanociencia y nanotecnología han revolucionado las investigaciones en ciencia de los materiales, permitiendo el desarrollo de nuevos productos con desempeño superior a los convencionales. Conceptos nanotecnológicos como la adición de partículas en tamaños nanométricos para incrementar las propiedades finales han sido demostrados en cerámicos, sin embargo esta alternativa prácticamente no ha sido investigada en sistemas porcelánicos, específicamente en porcelanas triaxiales con aplicaciones eléctricas. Este trabajo de investigación presenta el desarrollo de una formulación de porcelana triaxial silicosa, de grado eléctrico, con características mecánicas y dieléctricas mejoradas mediante la incorporación de nanopartículas cerámicas. Se estudió la influencia de la adición de dos tipos de óxidos cerámicos en tamaño nanométrico, α- alúmina (α-Al2O3) y circonia (ZrO2), en las propiedades y microestructura de la porcelana triaxial, al variar la concentración de las nanopartículas en la composición inicial. En la primera parte de la experimentación, se elaboraron probetas experimentales siguiendo un proceso a nivel laboratorio haciendo uso de un conformado por presión uniaxial. Posteriormente, se elaboraron pastas porcelánicas a nivel planta-prototipo mediante un proceso de conformado por extrusión plástica. Las probetas sinterizadas fueron caracterizadas mediante evaluaciones físicas tales como densidad, porosidad, absorción de humedad y contracción lineal; así mismo se llevaron a cabo análisis microestructurales y de fases a través de las técnicas de DR-X, MEB y DSC-TGA. Por último, se realizaron evaluaciones mecánicas por medio de ensayos de resistencia a la compresión y módulo de ruptura (por tres puntos), así como la evaluación de la capacidad aislante con pruebas de resistencia dieléctrica. Los resultados obtenidos demuestran que la inserción de nanopartículas de alúmina y circonia, ayudan en el reforzamiento mecánico del sistema porcelánico triaxial estudiado, además de mejorar sus características dieléctricas, lo que representa una alternativa tecnológicamente factible para mejorar el desempeño de productos de porcelana, como es el caso de aisladores eléctricos
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The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450°C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250°C during 60 minutes. After sintering the samples were normalized at 950°C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering, the niobium carbide helps to sinter increasing the density of the samples reaching a maximum density of 7.86g/cm³, better than the melted steel as received that was 7,81g/cm³. In spite this good densification, after normalizing, the niobium carbide don t contributed to increase the microhardness. The best microhardness obtained to the steel with niobium carbide was 156HV and to pure 15Kh2MFA steel was 212HV. It happened due when the niobium carbide is added to the steel a pearlitic structure was formed, and the steel without niobium carbide submitted to the same conditions reached a bainitic structure
Resumo:
Las aleaciones de aluminio son ampliamente utilizadas en la industria automotriz, principalmente en aplicación automotriz (cabezas y monoblocks), donde la extracción de calor es crítica para la eficiencia del motor. Este trabajo presenta los resultados de una serie de pruebas realizadas para evaluar la conductividad térmica en aleaciones de aluminio, en un rango de temperaturas desde temperatura ambiente hasta 300°C mediante la variación de las condiciones de tratamiento térmico. Las aleaciones de aluminio analizadas en este estudio fueron: AlCu5Mg, AlSi7Mg, AlSi7MgCu0.5, AlSi8Cu3Mg y AlSi7Cu3Mg, se vaciaron en moldes de arena en forma de cuña con una templadera de hierro en la parte inferior para promover la solidificación direccional. Se evaluaron tres perfiles de solidificación caracterizados por el grado de refinación de su microestructura (20, 30 y 50 µm equivalente a una aleación tipo 319 AlSi7Cu3Mg) para simular diferentes zonas de los componentes automotrices. Muestras de cada aleación fueron sometidas a tratamiento térmico (solución, temple y envejecido artificial), como medio de temple se utilizó agua y aire. Las muestras de cada condición de tratamiento térmico y perfil de solidificación fueron sometidas a un envejecido posterior de 200 hr para simular las condiciones de temperatura a las cuales están expuestos los motores de combustión interna y fueron evaluadas cuatro temperaturas: 150°C, 200°C, 250°C y 300°C. Los resultados muestran que la conductividad térmica es incrementada en muestras con un espaciamiento dendrítico secundario fino y con un medio de temple en agua. 1 El post-envejecido, al cual se sometieron las muestras, fue la condición del tratamiento que incrementó en mayor medida el valor de conductividad térmica. El contenido de cobre en la aleación presenta un incremento en la conductividad térmica de la aleación, principalmente en temperaturas de post-envejecido que sobrepasan los 200°C.
