Desarrollo y optimización del proceso de moldeo por inyección de metales (MIM) de aleaciones magnéticas blandas base hierro

Mención Internacional en el título de doctorLas aleaciones magnéticas blandas base hierro se utilizan en una gran variedad de aplicaciones eléctricas y electrónicas, entre las que destacan los motores y los generadores. Su uso está muy extendido debido a su buena combinación de propiedades magnéticas y su relativo bajo coste. El avance de las tecnologías y la mayor concienciación con el medio ambiente han derivado en una búsqueda de mejoras en la eficiencia de estas aplicaciones. Esta búsqueda conlleva la optimización de las aleaciones magnéticas blandas base hierro. A principios del siglo XX, el estudio sistemático de las aleaciones magnéticas blandas condujo al descubrimiento de sus buenas propiedades magnéticas, y comenzó su utilización en aplicaciones eléctricas y electrónicas. Desde entonces, el desarrollo de estos materiales continúa suscitando un gran interés, y abarca el diseño de propiedades específicas mediante la introducción de nuevos elementos de aleación y la utilización de métodos de procesamiento alternativos, entre otros. En la presente Tesis Doctoral se propone el desarrollo y la optimización del proceso de Moldeo por Inyección de Metales (MIM) de aleaciones magnéticas blandas base hierro. Esta técnica permite la fabricación de componentes con morfologías complejas, sin la utilización de operaciones secundarias, que deterioran la respuesta magnética de estos materiales. Además, mediante MIM se pueden producir piezas de mayor densidad y menor contaminación que con respecto a las técnicas de procesado clásicas. Todo esto lleva a la obtención de componentes finales de propiedades mejoradas. Este trabajo comienza con un estudio preliminar de las aleaciones base hierro Fe-49Ni, Fe-35Co y Fe-3.8Si. En dicho estudio se evalúa la viabilidad de MIM en la producción de componentes de estas aleaciones, a partir de polvo prealeado y con la utilización de parámetros convencionales. El estudio continúa con la optimización de todas las etapas del proceso MIM para la obtención de componentes magnéticos blandos de las aleaciones Fe-6Si y Fe-3.8Si de propiedades mecánicas y magnéticas mejoradas. La optimización del proceso MIM se inicia con la optimización de la carga de polvo en el feedstock a través de métodos basados en la reometría de torque y en medidas de la densidad. La segunda etapa consiste en la selección de los parámetros de inyección que conduzcan a la obtención de piezas en verde libres de defectos. En la tercera etapa se seleccionan los parámetros más adecuados para la eliminación gradual y eficiente del sistema ligante. Por último, se evalúa el efecto de diferentes atmósferas y ciclos de sinterización en las propiedades mecánicas y magnéticas de las piezas finales. Dichas propiedades han sido comparadas con las que se obtienen a través de los métodos clásicos de procesado. Los resultados de este trabajo muestran que el proceso MIM es una alternativa eficaz en la producción de componentes magnéticos blandos de las aleaciones Fe-Si.Iron based soft magnetic alloys are commonly used in electrical and electronic devices, such as engines and generators. These alloys are widely used due to their good combination of magnetic properties and relatively low cost. The challenges of technology and the increasing environment awareness lead to search for applications with increased efficiency. As a consequence, there is a need to improve the properties of the iron based soft magnetic alloys. In the early twentieth century, the systematic study of the iron based alloys led to discover their good magnetic properties. Then, its use in electrical and electronic applications began. Since then, the development of these alloys continues, and it covers the design of specific properties by introducing new alloying elements and the use of alternative processing methods, in order to obtain final parts with improved magnetic and mechanical properties. The main propose of the present PhD Thesis is to obtain improved iron based soft magnetic alloys by Metal Injection Molding (MIM). This technique provides final parts with complex geometries, without using secondary operations, which deteriorates the magnetic performance of the materials. In addition, this technology allows the production of high density materials with low contamination. All this leads to final components with improved properties. This research work starts with a preliminary study about the iron-based alloys Fe-49Ni, Fe-35Co and Fe-3.8Si. In this study, the viability of the MIM process is studied by using pre-alloyed powder and MIM conventional parameters. The study continues with the optimization of all MIM stages for the alloys Fe-6Si and Fe-3.8Si. The first stage of the MIM process is the optimization of the powder loading in the feedstock. In the second stage, the injection parameters are selected in order to obtain defects-free green parts. Then, the thermal debinding parameters are designed with the aim of removing the binder effectively and gradually. Finally, the effect of different atmospheres and sintering cycles on the mechanical and magnetic properties is evaluated. The final properties were compared with those obtained by the conventional methods. The results show that the MIM process is an effective alternative in the production of soft magnetic components of the Fe-Si alloys.European Community's Seventh Framework ProgramLa presente tesis doctoral se enmarca dentro del proyecto europeo MAGNETIDE “Improved magnets for energy generation through advanced tidal technology”, el cual ha sido financiado por el 7º Programa Marco de la Unión Europea (FP7-284578).Programa Oficial de Doctorado en Ciencia e Ingeniería de MaterialesPresidente: María Eugenia Rabanal Jiménez.- Secretario: Luz Fuentes Pacheco.- Vocal: Grzegorz Matul

Desarrollo de un material compuesto base acero rápido para aplicaciones de corte por moldeo de inyección de metales

En el presente Proyecto Final de Carrera se ha desarrollado un proceso de moldeo por inyección de metales (MIM) para la obtención de piezas de acero rápido T15. La tecnología MIM es una técnica altamente flexible por la que se obtienen componentes de elevadas prestaciones y geometrías complejas a precios razonables. Hay numerosas variables que influyen en el proceso de producción de un componente mediante esta tecnología. Dos de ellas son la utilización de aditivos para favorecer ciertas etapas del proceso o mejorar las propiedades finales de las piezas y la variación de las condiciones en las que se lleva a cabo la extracción térmica del sistema ligante. Por ello, este proyecto pretende evaluar en qué medida la adición de ácido esteárico favorece las distintas etapas de procesado y en qué grado la introducción de carburos mejora las propiedades finales de los componentes obtenidos. De igual manera se pretende estudiar el efecto en las propiedades finales de la utilización de dos ciclos térmicos diferentes durante la extracción térmica. Se prepararon dos “feedstocks”, uno con ácido esteárico y otro sin éste, con una carga metálica del 58% en volumen. Como sistema ligante se empleó una mezcla de polipropileno y cera parafina. Se caracterizaron los “feedstocks” mediante reología de par de torsión, reología capilar y medidas de densidad y se observó que el ácido esteárico favorece significativamente el proceso de mezclado y grado de homogeneidad. Además, el ácido esteárico resultó ser un aditivo crítico para el proceso, puesto que el “feedstock” que no lo contenía resultó imposible de inyectar. Se realizó extracción con disolventes empleando heptanol y se diseñó correctamente el ciclo de extracción térmica mediante análisis térmico simultáneo (STA), el cual se llevó a cabo en nitrógeno a dos velocidades de calentamiento diferentes, 1ºC/min y 5ºC/min. A continuación se sinterizaron los compactos en marrón obtenidos en la etapa anterior a 1250ºC en bajo vacío. La evaluación de las propiedades finales de las piezas se realizó mediante microscopía óptica, microscopía electrónica de barrido (SEM), estudio de energías dispersivas de rayos X (EDAX), difracción por rayos X (DRX), resistencia a flexión, dureza y densidad. Tras el análisis de resultados obtenidos mediantes estas técnicas se concluyó que una alta velocidad de calentamiento durante la etapa de extracción térmica conlleva un aumento del tamaño de grano, mayor tamaño de carburos y mayores aglomeraciones de éstos en la matriz, lo que se traduce en propiedades mecánicas inferiores. ____________________________________________________________________________________________________________________________In this Master Thesis a process of metal injection molding (MIM) has been developed to obtain products of high speed steel T15. The aim of this study is to check the effect on the microstructure and final properties of the addition of stearic acid and tetra carbides, as well as the use of two different heating rates during the thermal extraction stage. MIM technology is a highly flexible technique to obtain high performance components and complex geometries at reasonable prices. There are many variables that influence the production process of a component using this technology. Two of them are the use of additives to enhance certain stages of the process or improve the final properties of the products and the variation of the conditions under the thermal extraction of the binder system is done. Therefore, this project aims to assess how the addition of stearic acid improves the different processing steps and to assess how the introduction of carbides improves the final properties of the components obtained. Also, this work had studied the effect of using two different thermal cycles for heat extraction on the final properties. Two feedstocks were prepared, one of them with stearic acid and the other one without it, both with a metal loading of 58% in volume. A mixture of polypropylene and paraffin wax was used as a binder system. Feedstocks were characterized by torque rheology, capillary rheology, and density measurements. It was observed that stearic acid is a critical component because the injection of the feedstock without it was not possible. Solvent extraction was performed using heptanol, and thermal extraction cycle was properly designed by simultaneous thermal analysis, which was conducted under nitrogen at two different heating rates, 1ºC/min and 5ºC/min. Finally, the brown compacts were sintered at 1250ºC under vacuum. The evaluation of the final properties of the components were made by optical microscopy, scanning electron microscopy (SEM), energy dispersive study of X-ray (EDAX), X-ray diffraction, flexural strength, hardness and density. After analyzing the results obtained using these techniques it was concluded that a high rate of heating during the thermal extraction involves higher grain size, higher carbides size and more agglomeration of them in the matrix, resulting in lower mechanical properties.Ingeniería Industria

Portland cement clinkers turned into garnets by spark plasma sintering

The feasibility of sintering Portland cement clinker powders by Spark Plasma Sintering (SPS) has been studied. Different SPSed compacts have been successfully obtained by this technique. The compacts have been characterized by means of X-Ray Diffraction, InfraRed spectroscopy, Scanning Electron Microscopy, Raman Microscopy and Vickers hardness. It is worth noting the finding that slight mineralogical variations in the starting compositions may induce dramatic changes, both in the final mineralogical composition and in the morphology, which can affect the properties of the SPSed compacts. Thus, we find that SPS allows artificial garnets to be obtained in the laboratory by applying pressures as low as 50 MPa, while they are materials that would require much higher pressures in natural environments (2-10 GPa). According to the Selsing model, it has been calculated that the material itself acts as a pressure amplifier at the micrometric level by a factor of 40-200 times. A new model describing the formation of garnets considering the emergence of two transitory eutectic liquids has been explained to justify this phenomenon. This result opens the door to looking for compositions for specific applications with high added value in the field (i.e. high hardness), mainly in the manufacturing of high-pressure (GPa) phases by applying relatively low pressures (MPa).The Authors acknowledge the financial support of the PID2020-119130 GB-I00 project funded by MCIN/AEI/10.13039/501100011033 and by CSIC under grant 201960E103. Thanks to the Official Laboratory for Testing of Construction Materials (LOEMCO, Getafe, Madrid, Spain) for free supply of the clinker sample

Interaction between Graphene-Based Materials and Small Ag, Cu, and CuO Clusters: A Molecular Dynamics Study

The excessive use of antibiotics has contributed to the rise in antibiotic-resistant bacteria, and thus, new antibacterial compounds must be developed. Composite materials based on graphene and its derivatives doped with metallic and metallic oxide nanoparticles, particularly Ag, Cu, and Cu oxides, hold great promise. These materials are often modified with polyethylene glycol (PEG) to improve their pharmacokinetic behavior and their solubility in biological media. In this work, we performed molecular dynamics (MD) simulations to study the interaction between small Ag, Cu, and CuO clusters and several graphene-based materials. These materials include pristine graphene (PG) and pristine graphene nanoplatelets (PGN) as well as PEGylated graphene oxide (GO_PEG) and PEGylated graphene oxide nanoplatelets (GO-PEG_N). We calculated the adsorption energies, mean equilibrium distances between the nanoparticles and graphene surfaces, and mean square displacement (MSD) of the nanoclusters. The results show that PEGylation favors the adsorption of the clusters on the graphene surfaces, causing an increase in adsorption energies and a decrease in both distances and MSD values. The strengthening of the interaction could be crucial to obtain effective antibacterial compounds.Universidad Europea de Madrid5.076 JCR (2020) Q1, 35/160 Physics, Applied0.919 SJR (2020) Q1, 49/394 Chemical Engineering (miscellaneous)No data IDR 2019UE

Flipped learning applied to materials science

Educational innovation is becoming very trendy nowadays due to digital technology arise. This innovation brings dozens of new tools and educational systems. Among others, flipped-classroom is a promising educational innovation that can improve the motivation, the degree of retention and the grades of students. Here we present an example of flipped-classroom applied to materials science and the survey of students after the experience. We noticed that with flipping the class students improved the retention degree and were highly motivated. In general, it was a positive experience and students would like to have more classes in the flipped way.Sin financiaciónNo data 2018UE

Molecular dynamics study of paraffin/polyethylene blends as phase change materials for energy efficiency in buildings

The greenhouse gas emissions and global energy consumption associated with construction materials can be greatly reduced by incorporating phase change materials into buildings. These materials can absorb and release energy during a phase transition, thus reducing the energy consumption while achieving human thermal comfort. Molecular dynamics simulations were used to study the miscibility of both linear and branched polyethylene with two types of paraffin (octadecane and hexatriacontane) at two different temperatures. The results showed that blending was better at high temperatures for both polymers, and branched polyethylene was more miscible with both paraffins than linear polyethylene was. Hexatriacontane exhibited better blending characteristics. From the molecular dynamics results, we concluded that linear polyethylene/paraffin blends were more suitable as phase change materials in buildings than branched polyethylene/paraffin blends, as they were miscible at high temperatures but separated into two phases at ambient temperature. The optimal blends were subsequently incorporated into a cement model to study their influence on the mechanical properties of this construction material. The introduction of the blends into the cement model deteriorated its mechanical properties.Universidad Europea de Madrid (2022/UEM27)3.1 Q* JCR 20220.451 Q2 SJR 2022No data IDR 2022UE

Reinforcing cement with pristine and functionalized carbon nanotubes: Experimental and simulation studies

In recent years, the addition of carbon nanotubes to construction materials has attracted considerable interest, due to the improvement of mechanical, electrical, and thermal properties of cement. The incorporation of carbon nanotubes into a cement matrix causes an increase of several mechanical properties of up to 170% even with low carbon nanotubes concentrations. The objective of this study is to analyze the influence of the type of functionalization and number of walls of carbon nanotubes on the interaction between these nanostructures and a cement surface and thus, on the improvement of their mechanical properties. Thus, single-walled and double-walled carbon nanotubes were used to investigate the influence of the number of walls. The effect of carbon nanotube functionalization was studied using carbon nanotubes functionalized with carboxyl and carboxylate groups. The experimental results demonstrate that the incorporation of carbon nanotubes into the cement matrix improves the mechanical properties of the resulting material. Functionalized carbon nanotubes perform better than pristine carbon nanotubes. Electrostatic attractions play a central role in establishing strong interactions between the carbon nanotubes and the cement surface. The presence of neutral polar groups on the carbon nanotube surface also improves this interaction. The number of walls seems to be less important.2017/UEM092018/UEM184.500 JCR (2020) Q2, 115/333 Material Science, Multidisciplinary0.709 SJR (2020) Q2, 77/513 Civil and Structural EngineeringNo data IDR 2019UE

Enhanced Antibacterial Capability and Corrosion Resistance of Ti6Al4V Implant Coated with ZrO2/Organosilica Nanocomposite Sol-Gel Films

Ti6Al4V is one of the most commonly used biomaterials in orthopedic applications due to its interesting mechanical properties, corrosion resistance and reasonable biocompatibility, which derive from a compact, thin, and chemically stable oxide film that spontaneously develops on these materials surface able to minimize ion release. Despite these advantages, a post-operative serious and unresolved problem leading to the failure of the implant is the appearance of implant-associated infections. For this reason, the ability to control microbial adhesion is of importance in healthcare, particularly in modern surgery where postoperative implant associated infections are still an unresolved and serious complication. As a proof of concept, we have assessed the antibacterial behaviour of Ti6Al4V surfaces modified by organic-inorganic hybrid sol-gel films with different loading of ZrO2 nanoparticles. The starting organosilica sol was prepared using a mixture of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethyl orthosilicate (TMOS). Tetrabutoxyzirconium (TBZ) was used as precursor of ZrO2 nanoparticles. Sol-gel films with variable contents of TBZ (0.2—1.0 wt.%) have been tested. The thermal stability of the resulting sol-gel films was studied by using thermal analysis (TG/DTG). Structural characterization of the films was carried out using Attenuated Total Reflectance Fourier transformer Infrared spectroscopy (ATR-FTIR). Surface morphology and composition of coated samples have been analized by Optical and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (OM and SEM/EDX) both before and after the corrosion tests were carried out. The evaluation of the barrier properties on the films and corrosion behaviour of the Ti6Al4V were carried out using Global and Local Electrochemical Impedance Spectroscopy (EIS/LEIS) during immersion in a simulated body fluid (SBF). Regarding bacterial adhesion, two representative strains of the vast majority of nosocomial infections related to orthopedic implants, i.e., Staphylococcus aureus and Staphylococcus epidermidis, were used. Optical and scanning electron microscopies observations have shown the formation of a uniform, homogeneous, crack free and highly adherent protective film on the Ti6Al4V substrates. The electrochemical studies and bacterial adhesion assessments have shown that the incorporation of ZrO2 in MAPTMS/TMOS matrix of the sol-gel films enhance their corrosion protection behaviour and antibacterial capability. Studies on the optimization of the sol-gel formulation to obtain the films with the best antibacterial capability without compromising their good corrosion resistance using different ZrO2 doses are in progress.MAT2015-65445-C2-1-R; MAT2015-63974-C4-3; M-ERA.NET PCIN-2016-146; IB16117; TE-0016-18; GR15089No data 2019UE

Mechanical Properties of Cement Reinforced with Pristine and Functionalized Carbon Nanotubes: Simulation Studies

Concrete is well known for its compression resistance, making it suitable for any kind of construction. Several research studies show that the addition of carbon nanostructures to concrete allows for construction materials with both a higher resistance and durability, while having less porosity. Among the mentioned nanostructures are carbon nanotubes (CNTs), which consist of long cylindrical molecules with a nanoscale diameter. In this work, molecular dynamics (MD) simulations have been carried out, to study the effect of pristine or carboxyl functionalized CNTs inserted into a tobermorite crystal on the mechanical properties (elastic modulus and interfacial shear strength) of the resulting composites. The results show that the addition of the nanostructure to the tobermorite crystal increases the elastic modulus and the interfacial shear strength, observing a positive relation between the mechanical properties and the atomic interactions established between the tobermorite crystal and the CNT surface. In addition, functionalized CNTs present enhanced mechanical properties.Sin financiación3.748 JCR (2021) Q1, 18/79 Metallurgy & Metallurgical Engineering0.604 SJR (2021) Q2, 212/591 Materials Science (miscellaneous)No data IDR 2021UE

Microstructure and Electrical Conductivity of Cement Paste Reinforced with Different Types of Carbon Nanotubes

Over the last few years, the addition of small amounts of carbon nanotubes (CNTs) to construction materials has become of great interest, since it enhances some of the mechanical, electrical and thermal properties of the cement. In this sense, single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) can be incorporated into cement to achieve the above-mentioned improved features. Thus, the current study presents the results of the addition of SWCNTs and MWCNTs on the microstructure and the physical properties of the cement paste. Density was measured through He pycnometry and the mass change was studied by thermogravimetric analysis (TGA). The microstructure and the phases were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally, the electrical conductivity for different CNT concentrations was measured, and an exponential increase of the conductivity with concentration was observed. This last result opens the possibility for these materials to be used in a high variety of fields, such as space intelligent systems with novel electrical and electronic applications.Sin financiación3.748 JCR (2021) Q2, 28/69 Physics, Condensed Matter0.604 SJR (2021) Q2, 147/427 Condensed Matter PhysicsNo data IDR 2021UE