Obtención y caracterización de TI c.p. poroso para aplicaciones biomédicas

Tesis (Ingeniero Mecánico)El objetivo de esta tesis doctoral es la obtención y caracterización de estructuras de titanio comercialmente puro poroso, con porosidad homogénea, diseñadas para reducir el apantallamiento de tensiones, sin comprometer la resistencia mecánica del biomaterial. Para ello, se implementarán dos rutas de fabricación: pulvimetalurgia convencional (evaluando los límites de esta técnica: loose sintering) y la técnica de espaciadores (space-holders technique). Se evaluará la influencia de los parámetros inherentes al procesado, tales como, presión de compactación, temperatura de sinterización y porcentaje de espaciador, sobre las características microestructurales y las propiedades mecánicas del material. La consecución de la segunda metodología propuesta, requiere el diseño de un protocolo experimental detallado, para definir las variables que influyen en el proceso de eliminación del cloruro de sodio usado como espaciador. La caracterización microestructural se llevará a cabo mediante las técnicas de Microscopía óptica, análisis de imágenes y el método de Arquímedes con impregnación de agua destilada. El comportamiento mecánico de los compactos será evaluado mediante ensayos de compresión uniaxial. Particularmente importante es el procedimiento planteado para evaluar el módulo de Young dinámico mediante la técnica de ultrasonidos, para materiales con porosidad elevada, como un método novedoso para la determinación de las propiedades mecánicas de materiales metálicos porosos. Adicionalmente, dependiendo del tamaño, grado y distribución de la porosidad obtenidos se puede indicar la capacidad de osteointegración del Titanio c.p. y de permitir el crecimiento del hueso hacia el interior del implante (bone in-growth), facilitando el paso del fluido fisiológico, plasma sanguíneo y colonización celular

Influencia de la deformación plástica en probetas soldadas de la aleación de aluminio 6061-T6 sobre las características de dureza

AbstractThe purpose of this paper is to study the effect of the compression stress applied on the HAZ (Heat affected Zone) in 6061-T6 Aluminum Alloy specimens. The main tools used to achieve this objective were the Vickers micrometer, the Transmission Electron Microscopy (TEM), the Differential Scanning Calorimeter and the Optical Microscope. It was found that with a natural aging time of four years the microhardness values were clearly increased, while with the compression stress these values showed a small increase. However, the more stable hardness profiles found in the compressed samples were attributed to the compression treatment.ResumenEl propósito de este artículo es estudiar el efecto del tiempo y el esfuerzo de compresión sobre la resistencia a la tensión y el perfil de microdureza en la aleación de aluminio 6061-T6 después de ser soldada con el proceso GMAW. Las principales herramientas usadas para lograr este objetivo fueron el micrómetro Vickers, el microscopio electrónico de transmisión, el calorímetro diferencial de barrido y el microscopio óptico. Se encontró que con un tiempo de envejecimiento natural de cuatro años los valores de microdureza fueron claramente incrementados, mientras que con el esfuerzo de compresión esos valores mostraron un pequeño incremento. Sin embargo, los perfiles de dureza más estables encontrados en las muestras fueron atribuidos al tratamiento de compresión. Palabras claves: aleación de aluminio 6061-T6, microdureza, envejecimiento natural, esfuerzo de compresión, análisis metalográfico, TEM, deformación plástica

Simulación numérica de la presencia de una grieta cercana a la soldadura de una unión tubular en T

This work presents a numerical simulation using MEF submodelingscheme to study overall response of a tubular welded T supported at itsprincipal ends and subjected to a load at its free end. This welded jointhas a semi-elliptical crack at the toe of the weld in the saddle region.The response of the welded joint has been evaluated according to themeasurement displacement line of the applied load at the free end, thestrain field around the weld and the crack opening displacement. Tovalidate the obtained results, these were compared with experimentaldata available in the literature.Este trabajo presenta una simulación numérica haciendo uso de unesquema de submodelación MEF para el estudio de la respuesta globalde una unión cilíndrica soldada en T soportada en sus extremos principales,y sometida a una carga en su extremo libre. Dicha unión poseeuna grieta semielíptica al pie de la soldadura. La respuesta de la uniónsoldada ha sido evaluada de acuerdo a la medición de desplazamientode línea de aplicación de la carga en el extremo libre, campo de deformacionesen torno a la unión soldada y desplazamiento de apertura dela grieta, comparando los resultados obtenidos con datos experimentalesdisponibles en la literatura como método de validación

Effect of HVOF processing parameters on Cr₃C₂-NiCr hard coatings deposited on AISI 4140 steel

High Velocity Oxygen Fuel (HVOF) thermal spray coating is a deposition process that is widely employed at present to improve surfaces and the remanufacturing of components subject to severe wear, offering an alternative to reduce the cost of spare parts and used as a substitute for electro-chromium, also generating greater thickness than chemical vapor deposition and physical vapor deposition. This study evaluates the influence of the projected application parameters for Cr₃C₂ - 20 (Ni20Cr) coatings on AISI 4140 steel using the HVOF technique. To do so, a 24 factorial experimental design was used to evaluate the effect on the thickness, porosity, surface hardness, and microhardness in the cross-section, produced by four of the main operational factors in the HVOF process: the fuel/oxygen (F/O) ratio entering the combustion chamber, powder flow, the roughness of the substrate before deposition, and spray gun speed. The morphology of the Cr₃C₂ - 20 (Ni20Cr) powders and the microstructure of the coatings were studied through a scanning electron microscope and energy dispersive spectroscopy, while the composition were analyzed by X-ray diffraction. It was determined that: (i) the F/O ratio is the operation parameter with the most significant influence on the properties studied; (ii) the gun speed has a significant effect on the thickness generated and porosity; and (iii) the powder flow and roughness of the substrate have a greater effect on the surface hardness and microhardness. Finally, it was determined that coatings with great thickness, low porosity, and great hardness, ideal for the recovery of parts, can be achieved from a F/O ratio of 0.45 and a powder flow with the system feeder rotating at 12 rpm, applied to a substrate with a roughness of Rₐ = 18 μm, combined with a spray gun speed of 5 mm/s

Documental audiovisual sobre los mitos y leyendas del cantón Guano, Provincia de Chimborazo.

The present investigation, try to show the myths and legends that the canton Guano possesses (province of Chimborazo). At present, it is worrying to see how many people from other towns, cities and countries, and also the new generations of the canton Guano, are unaware of the myths, legends, customs and traditions that Guano has had since time immemorial. For this reason, the research aims to revitalize the history of this canton, starting from the cultural theme, and focusing on the myths and legends most rescued from Guano, in order to know several of the stories that have been composed by the ancestors of the canton. It is possible to indicate, throughout the investigation is known many fictitious stories that characterize the popular roots that contain Guano, with the objective to make visible to all the settlers of the canton and in particular to several historical histories, that own the canton. Finally, it is important to remember that this wonderful canton is one of the richest in cultural subjects. For this reason, we invite you to know more about Guano through this documentary.La presente investigación pretende exponer los mitos y leyendas que históricamente se han construido y permanecido en el Cantón Guano, ubicado en la provincia de Chimborazo-Ecuador. En la actualidad, es preocupante mirar cómo muchas personas de otros pueblos, ciudades y países e incluso las nuevas generaciones del Cantón Guano, desconocen aquellos mitos, leyendas, costumbres y tradiciones, que posee Guano desde épocas atrás. En este contexto, la investigación procura revitalizar la historia de este Cantón, partiendo desde el tema cultural, y centrándose en los mitos y leyendas más destacados de Guano, con el fin de conocer varias de las historias que han sido compuestas por los antepasados del Cantón. Cabe indicar, que a lo largo de la investigación se conocerá diversos relatos ficticios que caracterizan las raíces populares que contiene Guano, con el objetivo de visibilizar a todos los pobladores del Cantón y en especial a varias de sus historias. Finalmente, es importante recordar que este Cantón es uno de los más ricos en temas culturales, de ahí la necesidad e importancia de resaltar las historias que se presentarán a continuación. Les invitamos a conocer más sobre la riqueza histórica de Guano, a través de este documental

Porous Titanium for Biomedical Applications: Evaluation of the Conventional Powder Metallurgy Frontier and Space-Holder Technique

Titanium and its alloys are reference materials in biomedical applications because of their desirable properties. However, one of the most important concerns in long-term prostheses is bone resorption as a result of the stress-shielding phenomena. Development of porous titanium for implants with a low Young’s modulus has accomplished increasing scientific and technological attention. The aim of this study is to evaluate the viability, industrial implementation and potential technology transfer of different powder-metallurgy techniques to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both conventional powder metallurgy (PM) and space-holder technique. The conventional PM frontier (Loose-Sintering) was evaluated. Additionally, the technical feasibility of two different space holders (NH4HCO3 and NaCl) was investigated. The microstructural and mechanical properties were assessed. Furthermore, the mechanical properties of titanium porous structures with porosities of 40% were studied by Finite Element Method (FEM) and compared with the experimental results. Some important findings are: (i) the optimal parameters for processing routes used to obtain low Young’s modulus values, retaining suitable mechanical strength; (ii) better mechanical response was obtained by using NH4HCO3 as space holder; and (iii) Ti matrix hardening when the interconnected porosity was 36–45% of total porosity. Finally, the advantages and limitations of the PM techniques employed, towards an industrial implementation, were discussed.Ministry of Economy and Competitiveness of Spain Grant MAT2015-71284-PJunta de Andalucía Grant P12-TEP-1401Comisión Nacional de Investigación, Científica y Tecnológica (CONICYT) of the Chilean government project FONDECYT 1116086

Hot-Pressing of (Ti, Mt)(C, N)-Co-Mo2C (Mt=Ta, Nb) powdered cermets synthesized by a mechanically induced self-sustaining reaction

A mechanically induced self-sustaining reaction (MSR) has been successfully employed for manufacturing powdered cermets based on Ti, Ti–Ta and Ti–Nb carbonitrides using Co as the binder phase and Mo2C as the sintering additive. The powders were sintered by hot-pressing, and complete chemical, microstructural and mechanical characterizations were performed on the densified cermets. When elemental Ta, Nb and/or Mo2C were added to the initial raw mixture submitted to the MSR process, smaller ceramic grains were observed after sintering, which suggested that ceramic particle growth was hindered by the presence of Ta, Nb and/or Mo in the host titanium carbonitride structure. Nanoindentation measurements enabled the determination of the hardness of the ceramic and binder phases, and values in the range of 26–29 GPa and 14–16 GPa were found, respectively. The high hardness values of the binder were related to the formation of intermetallic phases.Gobierno de España European Regional Development No. MAT2011- 2298

Effect of the Processing Parameters on the Porosity and Mechanical Behavior of Titanium Samples with Bimodal Microstructure Produced via Hot Pressing

Commercially pure (c.p.) titanium grade IV with a bimodal microstructure is a promising material for biomedical implants. The influence of the processing parameters on the physical, microstructural, and mechanical properties was investigated. The bimodal microstructure was achieved from the blends of powder particles with different sizes, while the porous structure was obtained using the space-holder technique (50 vol.% of ammonium bicarbonate). Mechanically milled powders (10 and 20 h) were mixed in 50 wt.% or 75 wt.% with c.p. titanium. Four different mixtures of powders were precompacted via uniaxial cold pressing at 400 MPa. Then, the specimens were sintered at 750 °C via hot pressing in an argon gas atmosphere. The presence of a bimodal microstructure, comprised of small-grain regions separated by coarse-grain ones, was confirmed by optical and scanning electron microscopies. The samples with a bimodal microstructure exhibited an increase in the porosity compared with the commercially available pure Ti. In addition, the hardness was increased while the Young’s modulus was decreased in the specimens with 75 wt.% of the milled powders (20 h).Ministerio de Ciencia e Innovación of Spain under the grant PID2019-109371GB-I0

In Vitro Bone Cell Behavior on Porous Titanium Samples: Influence of Porosity by Loose Sintering and Space Holder Techniques

A great variety of powder metallurgy techniques can produce biomimetic porous titanium structures with similar mechanical properties to host bone tissue. In this work, loose sintering and space holder techniques, two frequently used metallurgical techniques, are compared to evaluate the influences of porosity (content, size, morphology and wall roughness), mechanical properties (stiffness and yield strength) and in-vitro cellular responses (adhesion and proliferation of myoblasts and osteoblasts). These comparisons are made to achieve the best balance between biomechanical and bifunctional behavior of a partial porous implant for cortical bone replacement. Cell adhesion (filopodia presence) and spreading were promoted on both porous surfaces and fully dense substrates (non-porous control surfaces). Porous scaffold samples designed using 50 vol.% NaCl space holder technique had an improved bioactive response over those obtained with the loose sintering technique due to higher roughness and scaffold pore diameter. However, the presence of large and heterogeneous pores compromises the mechanical reliability of the implant. Considering both scenarios, the substrates obtained with 40 vol.% NH4HCO3 and pore size ranges between 100 and 200 μm provide a balanced optimization of size and strength to promote in-vitro osseointegration.FEDER US-1259771University Complutense of Madrid (UCM) C2C12-GFPJunta de Andalucía US-125977

Influencia de la deformación plástica en probetas soldadas de la aleación de aluminio 6061-T6 sobre las características de dureza

AbstractThe purpose of this paper is to study the effect of the compression stress applied on the HAZ (Heat affected Zone) in 6061-T6 Aluminum Alloy specimens. The main tools used to achieve this objective were the Vickers micrometer, the Transmission Electron Microscopy (TEM), the Differential Scanning Calorimeter and the Optical Microscope. It was found that with a natural aging time of four years the microhardness values were clearly increased, while with the compression stress these values showed a small increase. However, the more stable hardness profiles found in the compressed samples were attributed to the compression treatment.ResumenEl propósito de este artículo es estudiar el efecto del tiempo y el esfuerzo de compresión sobre la resistencia a la tensión y el perfil de microdureza en la aleación de aluminio 6061-T6 después de ser soldada con el proceso GMAW. Las principales herramientas usadas para lograr este objetivo fueron el micrómetro Vickers, el microscopio electrónico de transmisión, el calorímetro diferencial de barrido y el microscopio óptico. Se encontró que con un tiempo de envejecimiento natural de cuatro años los valores de microdureza fueron claramente incrementados, mientras que con el esfuerzo de compresión esos valores mostraron un pequeño incremento. Sin embargo, los perfiles de dureza más estables encontrados en las muestras fueron atribuidos al tratamiento de compresión. Palabras claves: aleación de aluminio 6061-T6, microdureza, envejecimiento natural, esfuerzo de compresión, análisis metalográfico, TEM, deformación plástica