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  • Resistance to contact deformation and damage of hard ceramics

     Jimenez Pique, Emilio; Llanes Pitarch, Luis Miguel; Anglada Gomila, Marcos Juan
    Date of publication: 2014-02-01
    Book chapter

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  • Determinación de la tenacidad de fractura a partir de entallas producidas por láser de femtosegundoen circona nanométrica

     Turón Viñas, Miquel; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2014-04-02
    Journal article

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  • Determinación de la tenacidad de fractura a partir de entallas producidas por láser de femtosegundoen circona nanométrica

     Turón Viñas, Miquel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2014-04-02
    Presentation of work at congresses

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  • Mechanical properties and resistance to low temperature degradation of surface nitrided 3Y-TZP

     Valle Chiro, Jorge Antonio; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2013-12
    Journal article

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    3Y-TZP has been one of the most applied ceramics in the biomedical field, specifically for hip, knee and dental implants, given its high strength, moderate fracture toughness and excellent biocompatibility. However, hydrothermal degradation has meant an important disadvantage, as surface t-m transformation, followed by microcracking, can lead to the premature failure of the implant. In this work, surface nitriding at 1600, 1500 and 1400°C for 1, 2 and 4h with N2 gas and ZrN powder was applied and optimised to avoid hydrothermal degradation. Nitriding at 1600 and 1500°C produces a harder low-toughness surface, not adequate for structural implants. It is shown that the most favourable condition is nitriding at 1400°C for 1h, since the mechanical properties of the original 3Y-TZP are not affected with the advantage of retarding hydrothermal degradation by a factor close to 10.

    3Y-TZP has been one of the most applied ceramics in the biomedical field, specifically for hip, knee and dental implants, given its high strength, moderate fracture toughness and excellent biocompatibility. However, hydrothermal degradation has meant an important disadvantage, as surface t–m transformation, followed by microcracking, can lead to the premature failure of the implant. In this work, surface nitriding at 1600, 1500 and 1400 °C for 1, 2 and 4 h with N2 gas and ZrN powder was applied and optimised to avoid hydrothermal degradation. Nitriding at 1600 and 1500 °C produces a harder low-toughness surface, not adequate for structural implants. It is shown that the most favourable condition is nitriding at 1400 °C for 1 h, since the mechanical properties of the original 3Y-TZP are not affected with the advantage of retarding hydrothermal degradation by a factor close to 10.

  • Phase transformation and subsurface damage in 3Y-TZP after sandblasting

     Chintapalli, Ravi Kiran; Garcia Marro, Fernando; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    Dental materials
    Date of publication: 2013-05
    Journal article

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    Objective The goal of this work is to investigate t¿m phase transformation, and subsurface damage in 3Y-TZP after sandblasting. Methods Commercial grade 3Y-TZP powder was conventionally sintered and fully dense specimens were obtained. Specimens were sandblasted using different particle sizes (110 and 250 µm) and pressures (2 and 4 bar) for 10 s. Phase transformation was measured on the surface and in the cross-section using X-ray diffraction and micro Raman spectroscopy, respectively. Subsurface damage was investigated on cross-sections using SEM and in shallow cross-sections machined by focused ion beam. Results Sandblasting induced monoclinic volume fraction is in the range of 12¿15% on the surface. In the cross-section, a non-homogeneous phase transformation gradient is found up to the depth of 12 ± 1 µm. The subsurface damage observed was plastic deformation in grains with the presence of martensite plates, and this effect is found to be larger in specimens sandblasted with large particles. Significance The extent of subsurface tetragonal¿monoclinic transformation and damage induced by sandblasting are reported for different sandblasting conditions. This knowledge is critical in order to understand the effect of sandblasting on mechanical properties of zirconia used to fabricate dental crowns and frameworks.

    Objective The goal of this work is to investigate t–m phase transformation, and subsurface damage in 3Y-TZP after sandblasting. Methods Commercial grade 3Y-TZP powder was conventionally sintered and fully dense specimens were obtained. Specimens were sandblasted using different particle sizes (110 and 250 μm) and pressures (2 and 4 bar) for 10 s. Phase transformation was measured on the surface and in the cross-section using X-ray diffraction and micro Raman spectroscopy, respectively. Subsurface damage was investigated on cross-sections using SEM and in shallow cross-sections machined by focused ion beam. Results Sandblasting induced monoclinic volume fraction is in the range of 12–15% on the surface. In the cross-section, a non-homogeneous phase transformation gradient is found up to the depth of 12 ± 1 μm. The subsurface damage observed was plastic deformation in grains with the presence of martensite plates, and this effect is found to be larger in specimens sandblasted with large particles. Significance The extent of subsurface tetragonal–monoclinic transformation and damage induced by sandblasting are reported for different sandblasting conditions. This knowledge is critical in order to understand the effect of sandblasting on mechanical properties of zirconia used to fabricate dental crowns and frameworks.

  • Tomography of indentation cracks in feldspathic dental porcelain on zirconia

     Rueda Arango, Astrid Oasis; Seuba, Jordi; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    Dental materials
    Date of publication: 2013-02-11
    Journal article

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    Objectives The objective of this work is to study the crack produced by spherical and sharp indentation on veneering feldspathic dental porcelain in order to understand the morphology of the cracks in the surface and beneath the indentation using a tomographic technique. The geometry of cracks produced under contact loading are directly related to the structural integrity and reliability of dental prosthesis. Methods Monotonic Hertzian contact loading and nanoindentation tests were performed on feldspathic porcelain (VITA-VM9) coatings. Residual imprints and the cracks produced by the indentations were characterized by 3-dimensional reconstruction using focused ion beam tomography. Results Under nanoindentation, the propagating crack deflects due to the interaction with the leucite particles resulting in a crack with a complex morphology. Under spherical contact loading, multiple ring cracks were observed at the surface, with a conical shape beneath the residual imprint. Significance These results will help to improve the mechanical performance of these materials by detecting potential causes of failure for the long term structural integrity and reliability of the prosthesis.

  • Surface treatments on zirconia ceramics: a comparative study

     Garcia Marro, Fernando; Londiche, Benedicte; Flamant, Quentin Jean Alain; Anglada Gomila, Marcos Juan
    International Conference on Advanced Materials Research EEIGM/AMASE/FORGEMAT
    Presentation's date: 2013
    Presentation of work at congresses

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  • Micromechanical characterization of small volumes by means of Nanoindentation  Open access

     Cuadrado Lafoz, Núria
    Defense's date: 2013-10-02
    Universitat Politècnica de Catalunya
    Theses

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    La caracterització mecànica de volums micromètrics, com poden ser capes fines o fases micromètriques embegudes en una matriu metàl¿lica, ha atret especial interès en les últimes dècades ja que s¿ha posat de manifest que les propietats mecàniques dels materials poden dependre de l¿escala del seu anàlisis. Per tant, per a poder dissenyar materials amb propietats mecàniques avançades a partir d¿un disseny micromecànic es fa necessari un coneixement detallat de les propietats dels materials a escales micro i nanomètriques En el disseny estructural o de components mecànics un pas molt important és la identificació dels principals mecanismes de dany. Quan es caracteritzen els mecanismes de fractura, les seves primeres etapes són d¿especial interès. La tècnica de nanoindentació és l¿eina idònia per a poder estudiar aquests mecanismes ja que es capaç de provocar d¿una manera estable, la fractura fràgil del material mitjançant el contacte d¿un indentador piramidal sobre la superfície a estudiar. Aquesta metodologia és coneguda com a fractura per indentació i dóna informació del procés fonamental de la fractura fràgil en sòlids covalents i iònics, a més de proporcionar informació detallada del procés de deformació en la regió de contacte. Per a materials amb un comportament de corba R, aquesta metodologia proporciona un pont molt necessari entre les etapes inicials de nucleació i creixement d¿esquerdes i l¿etapa de propagació on l¿esquerda es considera no estar afectada per elements microstructurals. El gran atractiu de la fractura per indentació és la seva versatilitat, control i simplicitat, que només requereix accés a un aparell d¿assaig de duresa rutinari. La tècnica de nanoindentació ha esdevingut una tècnica adequada per a la caracterització mecànica de volums i fases micromètriques, en termes de duresa (H), mòdul elàstic (E) i tenacitat de fractura (Kc). Mentre H i E poden ser mesurats de manera rutinària a partir de la corba de nanoindentació càrrega ¿ desplaçament, l¿evolució de Kc en partícules dures micromètriques pot ser, en principi, mesurada a partir de la longitud de les esquerdes que es generen als vèrtexs de la indentació. Aquest mètode d¿avaluació de Kc és conegut com a Microfractura per Indentació (IM) i va ser proposat al 1970 per a indentadors Vickers. No obstant, el disseny de nous materials porta a estructures més petites, fent que sigui necessària l¿aplicació de càrregues més baixes i indentadors més aguts per a poder concentrar la deformació i la fractura en els volums micromètrics d¿interès. Recentment, la caracterització mecànica de materials multifàsics així com de capes fines, ha rebut molt d'interès, i hi ha molts treballs dedicats a la caracterització de Kc segons el mètode IM i amb la tècnica de nanoindentació. No obstant, l¿ús de diferents tipus de geometria d¿indentador i de rang de càrregues aplicades en nanoindentación suscita alguns dubtes en referència a l¿aplicabilitat de les equacions de tenacitat de fractura existents, desenvolupades en el passat bàsicament per a indentadors Vickes i per a càrregues típicament de més de dos ordres de magnitud més elevades. Per tant, per a tenir un millor coneixement del comportament micromecànic dels materials fràgils, aquesta tesi es centra en l¿estudi de la tècnica de microfractura per indentació aplicada a volums micromètrics, prestant especial atenció al comportament a fractura de materials fràgils en termes de la geometria d¿indentació, càrrega aplicada i morfologia d¿esquerda generada. Addicionalment, i donat que des d¿un punt de vista científic i tecnològic és d¿especial interès la comprensió de la resposta mecànica de volums micromètricstambé s¿ha estudiat la factibilitat d¿estendre la metodologia desenvolupada per materials fràgils a sistemes enginyerils formats per partícules dures micromètriques en materials multifasics o capes fines.

    Mechanical characterization of micro-volume systems, as thin films or micro-sized phases embedded in multiphase materials, has attracted special interest in the last decades since different micromechanical techniques have been developed to characterize microdevices and materials at the micro and nano scale and it has become apparent that mechanical properties may depend on the analysis scale. An example is the way a crack grows in a bulk material that is likely to be different from crack propagation in a micro-volume where crack and microstructural dimensions are comparable. Consequently, there is a need of a detailed knowledge of material properties at micro and nano scale to design materials with advanced mechanical properties. In this way, micro and nanoscale science and technology enables to improve new materials and applications at macroscopic scale through a sound micromechanical design. The accuracy of test methodologies will depend on the size scale in which specific mechanical properties are studied. Micro scale is usually defined as the length scale in the range of 1-1000 microns, whereas nanoscale is usually defined as smaller than a one tenth of a micrometer in at least one dimension, although this term is sometimes also used for materials of larger dimension but smaller than one micrometer. Efforts to characterize the mechanical response of small volumes have led to the development of a variety of test methodologies, as uniaxial micro testing machines, micro beam cantilever deflection or nanoindentation devices. Challenges of testing at the micro scale include micro specimen preparation and handling, the application of small forces, and stress and strain measurement. Nanoindentation appears as the easiest way to study local behaviour on thin films or micro-sized phases, since no special sample preparation is required and tests can be performed quickly and inexpensively. Nanoindentation tests consist in the application of a controlled load on the specimen surface through the direct contact with a sharp diamond indenter and recording the evolution of the load versus the penetration depth of the indenter. The use in engineering of thin films, advanced coatings and materials with small tailored microstructures has led to the analysis of mechanical properties of very small volumes in which size effects might be important. Efforts to design and model the reliability of small-scale devices are directly dependent on the availability of accurate and reliable measurements of relevant mechanical properties at small scales. In designing structural or machine components an important step is the identification of the main micromechanical damage mechanisms. It is particularly interesting to determine the first fracture step, i.e., the crack nucleation in order to optimize the material resistance to crack nucleation. Stable brittle fracture takes place easily by the contact of a hard indenter on a brittle surface; this methodology is known as indentation fracture. Indentation fracture yields valuable information on the fundamental processes of brittle fracture in covalent-ionic solids, and detail on subsidiary deformation processes in the contact region; it provides ‘controlled flaws’ for systematically evaluating fracture properties, and it serves as a simple microprobe for determining material fracture parameters, toughness, crack-growth exponent, etc. For materials that exhibit R-curves behaviour, it affords a much needed bridge between the short-crack domain of microstructural flaws and the long-crack domain of traditional toughness testing; mainly in the study of the first regimes of crack propagation. The great appeal of the indentation methodology is its versatility, control and simplicity, requiring only access to routine hardness testing apparatus. In order to study the mechanical behaviour of small-volumes and micro-sized phases, nanoindentation has become a suitable technique for the mechanical characterization of small-volumes and micrometer – sized phases, in terms of hardness (H), elastic modulus (E) and fracture toughness (Kc). While H and E can be routinely measured by nanoindentation from the load – displacement curves, the evaluation of Kc of hard micro-sized phases can in principle be measured from the length of the cracks at the corners of the indentation. This method of evaluation of Kc is known as Indentation Microfracture (IM) and it was proposed in the 1970s for Vickers indentation cracks in bulk materials. However, the design of new materials leads to ever smaller microstructures, hence lower loads and sharper indenters has to be used in order to concentrate the deformation and fracture only in the very small volume of phases of interest. Mechanical characterization of small volumes, has recently received much attention, and many works have focused on the determination of Kc by nanoindentation following the IM method. Nanoindentation allows using low loads needed for accurate micromechanical characterization with high spatial resolution. However, the use of a different kind of tip geometry and load range in nanoindentation technique raises some questions about the applicability of the existent fracture toughness equations which were developed in the past mainly for Vickers tips and for loads typically more than two orders of magnitude higher. Therefore, for a better knowledge of the micromechanical behaviour of brittle materials, this work is directed to the study of indentation microfracture applied to small volumes, focussing on the understanding of the fracture behaviour of brittle materials in terms of indenter tip geometry, applied load and crack morphology generated. On the other hand, since it is of a scientific and technological interest to understand the mechanical response of micro-volume systems, the feasibility of extending the IM developed for brittle bulk materials to engineering systems formed by micro-sized hard phases in multiphase materials or thin films will be also studied.

  • Determinación de la tenacidad de fractura de zirconia dopada con itria (3Y-TZP) y de materiales nanocompuestos de 3Y-TZP reforzados con nanotubos de carbono

     Turón Viñas, Miquel; Melk, Latifa; Anglada Gomila, Marcos Juan
    Sociedad Española de Cerámica y Vidrio
    Presentation's date: 2013-10-24
    Presentation of work at congresses

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  • Bio-based composites with different moisture contents under static and dynamic loading

     Doroudgarian, Newsha; Anglada Gomila, Marcos Juan; Mestra Rodríguez, Alvaro Miguel; Joffe, Roberts
    International Conference on Composites Testing and Model Identification
    Presentation's date: 2013
    Presentation of work at congresses

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  • ATZ via infiltration method: mechanical properties, aging resistance and wear behaviour

     Camposilvan, Erik; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    International Conference on Advanced Materials Research EEIGM/AMASE/FORGEMAT
    Presentation's date: 2013
    Presentation of work at congresses

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  • Revealing crack profiles in polycrystalline tetragonal zirconia by ageing

     Garcia Marro, Fernando; Camposilvan, Erik; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-07
    Journal article

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    Exposure to hot water vapour is shown to be useful for staining indentation crack profiles in doped zirconia polycrystals. This is illustrated here in 3Y-TZP with two different grain sizes, for which Vickers indentation cracks are of Palmqvist type, as well as in 3Y-TZP with 2.5 wt.% cerium oxide, for which indentation cracks are half-penny. The crack profile is clearly revealed on the fracture surface after biaxial flexural testing in all the specimens previously exposed to hot water vapour. The contrast in 3Y-TZP is induced by t–m transformation caused by hydrothermal degradation, which induces an intergranular fracture zone in front of the initial position of the indentation crack tip. The biaxial strength and apparent fracture toughness of 3Y-TZP increase substantially with the time of exposure at a rate that depends on the grain size. On the contrary, in 3Y-TZP doped with ceria no signal of t–m transformation is found and the flexure biaxial stress remains practically constant, but the initial position of the indentation crack is also clearly revealed by an intergranular fracture zone in front of the initial position of the crack tip. In this case, this is associated to environmentally assisted slow crack growth under the indentation residual stress during exposure to hot water vapour in autoclave.

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    Decoration of indentation cracks in 3Y-TZP by hydrothermal ageing  Open access

     Garcia Marro, Fernando; Camposilvan, Erik; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2012
    Journal article

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    Las grietas de indentación en cerámicas son frecuen temente utilizadas no sólo para estimar semi-empíri camente la tenacidad a fractura K IC , sino también cómo método para crear grietas aguda s superficiales y semielípticas a partir de las cuales analizar la tenacidad de fractura. Para ello es necesario conocer la forma exacta de la grieta inicial, así como en el momento de fractura inestable. A menudo dicha ident ificación no es obvia debido a un pobre contraste v isual de las superficies fracturadas. La circona estabilizada co n 3% molar de itria (3Y-TZP) es una cerámica biocom patible con buenas propiedades mecánicas que la hacen interesan te para su utilización en prótesis dentales y cabez as femorales. Adicionalmente, la 3Y-TZP es susceptible a un fenóm eno de degradación a baja temperatura por el cual u n ambiente acuoso produce una transformación de fase en la sup erficie expuesta. En este trabajo se ha aprovechado la susceptibilidad a degradación hidrotérmica de la 3Y -TZP para revelar grietas de indentación en probeta s que son ensayadas a flexión posteriormente. Se muestra como grietas de indentación en 3Y-TZP afectadas por vap or de agua son claramente reveladas en la posterior caracterizació n fractográfica. Se consideraron diferentes tipos d e 3Y-TZP con diferentes grados de susceptibilidad a degradación hidrotérmica. Se observó que una exposición en auto clave de unas pocas horas es suficiente para revelar las grietas en la superficie de fractura sin llegar a afectar l a carga de rotura de las probetas. Por consiguiente, la técnica puede utiliz arse para obtener un conocimiento preciso de la geo metría de las grietas de indentación utilizadas para determinar l a tenacidad de fractura.

    Las grietas de indentación en cerámicas son frecuen temente utilizadas no sólo para estimar semi-empíri camente la tenacidad a fractura K IC , sino también cómo método para crear grietas aguda s superficiales y semielípticas a partir de las cuales analizar la tenacidad de fractura. Para ello es necesario conocer la forma exacta de la grieta inicial, así como en el momento de fractura inestable. A menudo dicha ident ificación no es obvia debido a un pobre contraste v isual de las superficies fracturadas. La circona estabilizada co n 3% molar de itria (3Y-TZP) es una cerámica biocom patible con buenas propiedades mecánicas que la hacen interesan te para su utilización en prótesis dentales y cabez as femorales. Adicionalmente, la 3Y-TZP es susceptible a un fenóm eno de degradación a baja temperatura por el cual u n ambiente acuoso produce una transformación de fase en la sup erficie expuesta. En este trabajo se ha aprovechado la susceptibilidad a degradación hidrotérmica de la 3Y -TZP para revelar grietas de indentación en probeta s que son ensayadas a flexión posteriormente. Se muestra como grietas de indentación en 3Y-TZP afectadas por vap or de agua son claramente reveladas en la posterior caracterizació n fractográfica. Se consideraron diferentes tipos d e 3Y-TZP con diferentes grados de susceptibilidad a degradación hidrotérmica. Se observó que una exposición en auto clave de unas pocas horas es suficiente para revelar las grietas en la superficie de fractura sin llegar a afectar l a carga de rotura de las probetas. Por consiguiente, la técnica puede utiliz arse para obtener un conocimiento preciso de la geo metría de las grietas de indentación utilizadas para determinar l a tenacidad de fractura.

  • Microstructural changes in 3Y-TZP induced by scratching and indentation

     MUÑOZ TABARES, JOSÉ ALEJANDRO; Jimenez Pique, Emilio; REYES GASGA, JOSE; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-11
    Journal article

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    Determination of the intrinsic fracture toughness from COD analysis of indentation cracks in spark plasma sintered 3Y-TZP reinforced with MWCNT  Open access

     Garcia Marro, Fernando; Chintapalli, Ravi Kiran; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2012
    Journal article

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  • High hardness, low Young's modulus and low friction of nanocrystalline ZrW2 Laves phase and Zr1-xWx thin films

     Horwat, David; Jimenez Pique, Emilio; Pierson, J.F.; Migot, A.; Dehmas, M.; Anglada Gomila, Marcos Juan
    Journal of physics and chemistry of solids
    Date of publication: 2012-04
    Journal article

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    Zr1−xWx nanocrystalline films of Zr-W solid solutions and ZrW2 Laves phase were synthesized by magnetron co-sputtering. Large values of the H/E ratio up to 0.09 are observed for grain sizes in the nanometer range along with a hardness above 10 GPa and Young's modulus below 230 GPa. H/E values are correlated with the developed surface of grain boundaries suggesting an elastic deformation mostly handled by the grain boundaries. This is associated to friction coefficients comparable to those of metallic glass surfaces. In contrast to fragile bulk Laves phases, no cracks were detected at the film surface after indentation and scratch test of nanocrystalline ZrW2. The friction coefficient of such films against diamond tip was in the range 0.08–0.15, similarly to metallic glass surfaces.

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    Influencia de la degradación hidrotérmica en la resistencia mecánica y comportamiento al desgaste de 3Y-TZP  Open access

     Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Kiran Chitapalli, Ravi; de Armas Sancho, Zamir; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2012
    Journal article

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    En este trabajo se realiza un estudio comparativo de la influencia de la degradación hidrotérmica a baja temperatura de circona tetragonal estabilizada con el 3% molar de Itria (3Y-TZP) en la resistencia mecánica a flexión y en el comportamiento bajo cargas de indentación esférica. Se presentan resultados de resistencia mecánica a flexión y de indentación esférica monotónica así como de ensayos de rayado en probetas artificialmente degradadas durante diferentes períodos de tiempo. Se pone de manifiesto que la resistencia mecánica a flexión es poco sensible a la degradación; por el contrario, los ensayos superficiales ponen claramente de manifiesto la presencia de degradación en sus etapas iniciales. Se constata la fuerte sensibilidad de la resistencia al desgaste y de la fatiga por contacto a la presencia de degradación hidrotérmica a baja temperatura. Los resultados se analizan en términos de la capa degradada de estructura monoclínica que se forma durante la degradación.

  • Focused ion beam tomography of zirconia degraded under hydrothermal conditions

     Jimenez Pique, Emilio; Ramos, A.; MUÑOZ TABARES, JOSÉ ALEJANDRO; Hatton, A.; Soldera, Flavio; Mucklich, F.; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-08
    Journal article

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    Three-dimensional tomography was performed on hydrothermal degraded zirconia by sequential focussed ion beam (FIB) sectioning and field emission scanning electron microscopy (FE-SEM) observation. By means of image analysis the distribution of microcracks produced under the surface was reconstructed and characterized. Results show a microcrack network preferentially oriented parallel to the surface, and a gradient in microcrack density from the surface, which is coherent with other measurements that reveal a decrease in monoclinic phase. The elastic properties of the reconstructed volume are simulated, showing that the deterioration of mechanical properties of degraded zirconia can be mainly attributed to microcracking, with a minor contribution of the phase transformation.

  • Processing and characterization of high-density zirconia-carbon nanotube composites

     Chintapalli, Ravi Kiran; Garcia Marro, Fernando; Milsom, Ben; Reece, Michel; Anglada Gomila, Marcos Juan
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2012-07-15
    Journal article

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    Addition of multiwall carbon nanotubes (MWCNTs) to polycrystalline ceramics is currently considered as a potential method for improving their mechanical properties, mainly their fracture toughness. High density composites produced by the addition of relatively small volume fractions of MWCNTs (0–2 vol.%) to 3 mol% yttria doped zirconia (3Y-TZP) have been produced by spark plasma sintering, resulting in a homogeneous distribution of MWCNTs with a small average matrix grain size in the range 153–182 nm. The influence of transformation toughening is found to be very weak for this small grain size by measuring the extent of phase transformation in the crack wake. Also, no hydrothermal degradation takes place after more than 200 h at 131 °C either in the monolithic ceramic or in the composites. The study of the influence of MWCNTs on the microstructure and mechanical properties of 3Y-TZP shows that in the composites there is a very slight decrease in hardness, while the elastic modulus does not practically change. By fitting the crack opening displacement in the near crack tip region to the Irwin parabola, the intrinsic fracture toughness is found to be approximately the same in the matrix and in the 2 vol.% composites. In spite of the observation of some crack bridging by nanotubes, from the measurement of the crack opening displacement (δ) along the crack faces, it is concluded that there is hardly any change in δ in 3Y-TZP by the addition of 2 vol.% of MWCNTs not only in the crack tip region but also in all the range studied. However, the indentation fracture toughness is nearly 15% higher in 2 vol.% composites as compared to their monolithic counterparts.

  • High hardness, low youngs modulus and low friction of nanocrystalline ZrW 2 laves phase and Zr 1-xW x thin films

     Horwat, David; Jimenez Pique, Emilio; Pierson, J.F.; Migot, S.; Dehmas, M.; Anglada Gomila, Marcos Juan
    Journal of physics and chemistry of solids
    Date of publication: 2012
    Journal article

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    Zr1−xWx nanocrystalline films of Zr-W solid solutions and ZrW2 Laves phase were synthesized by magnetron co-sputtering. Large values of the H/E ratio up to 0.09 are observed for grain sizes in the nanometer range along with a hardness above 10 GPa and Young's modulus below 230 GPa. H/E values are correlated with the developed surface of grain boundaries suggesting an elastic deformation mostly handled by the grain boundaries. This is associated to friction coefficients comparable to those of metallic glass surfaces. In contrast to fragile bulk Laves phases, no cracks were detected at the film surface after indentation and scratch test of nanocrystalline ZrW2. The friction coefficient of such films against diamond tip was in the range 0.08–0.15, similarly to metallic glass surfaces.

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    Evaluation of fracture toughness of small volumes by means of cube-corner nanoindentation  Open access

     Casellas Padro, Daniel; Cuadrado Lafoz, Núria; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    Scripta materialia
    Date of publication: 2012-03
    Journal article

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    In this work, the applicability of the two most commonly used equations for calculating the fracture toughness by nanoindentation is discussed in terms of the indenter geometry and the indentation crack morphology. These equations are calibrated for Berkovich and cube-corner indenters taking into account the actual indentation crack morphology, aimed at attaining a more reliable estimation of fracture toughness in small material volumes by nanoindentation.

    Postprint (author’s final draft)

  • Hydrothermal degradation of ground 3Y-TZP

     MUÑOZ TABARES, JOSÉ ALEJANDRO; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-02
    Journal article

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  • Strengthening of Vickers indented 3Y-TZP by hydrothermal ageing

     Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-02
    Journal article

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    The effect of hydrothermal ageing on indentation cracks has been determined in 3Y-TZP by measuring the flexure strength of indented specimens before and after ageing. A substantial increase in strength was observed after ageing, in contrast to the well known decrease in strength in smooth specimens with only natural flaws. The increase in strength with ageing also occurs if the indentation residual stresses are previously removed by annealing. Observations around the crack tip show the formation of a highly microcracked zone during vapour exposure. Fractographic and micro-Raman analysis observations show that the profile of the cracks is marked on the fracture surface by this zone which is intergranular with a crumbled appearance and in which transformation has taken place. The increase in strength is discussed in terms of crack tip blunting induced by the multiaxial stresses that develop in front of the crack under bending.

  • Spherical instrumented indentation of porous nanocrystalline zirconia

     Chintapalli, Ravi Kiran; Jimenez Pique, Emilio; Garcia Marro, Fernando; Yan, Haixue; Reece, Michel; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2012-01
    Journal article

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  • Estudio de fallo de diversas láminas de contacto de micro-interruptor

     Anglada Gomila, Marcos Juan; Heredero Alari, Francisco
    Date: 2012
    Report

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  • BIOCERAMICS FOR BONE REPAIR

     Jimenez Pique, Emilio; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    Participation in a competitive project

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  • Nuevos materiales nanocompuestos de circona con mayor tenacidad de fractura y resistencia a la degradación hidrotérmica

     Jimenez Pique, Emilio; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Participation in a competitive project

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  • Influencia del nitrógeno y la deformación en frío en la propagación de fisuras de fatiga en aceros inoxidables austeníticos

     Hitscherich, M; Salán Ballesteros, Mª Núria; Anglada Gomila, Marcos Juan; Mateo, A
    Encuentro del Grupo Español de Fractura
    Presentation of work at congresses

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  • Increasing low temperature degradation resistance by a thin diffussion layer of cerium in 3Y-TZP

     Garcia Marro, Fernando; Camposilvan, Erik; Jimenez Pique, Emilio; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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  • Proceedings of the 13th European Inter-Regional Conference on Ceramics

     Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012
    Presentation of work at congresses

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  • Determination of the intrinsic fracture toughness from the COD analysis of indentation cracks in Spark Plasma Sintered 3Y-TZP reinforced with MWCNT

     Garcia Marro, Fernando; Kiran Chitapalli, Ravi; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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    El método de la indentación para medir la tenacidad de fractura ha sido ampliamente utilizado en materiales frágiles debido a su sencillez y a que puede realizarse en volúmenes pequeños de material. Especialmente en estos casos, las tenacidades de fractura obtenidas mediante el método de indentación pueden llegar a ser muy distintas de los valores reales obtenidos mediante métodos rigurosos basados en un conocimiento preciso de todos los parámetros que intervienen en la fractura. Esto ha llevado a desarrollar métodos que relacionan el perfil de la abertura de la grieta de indentación con la tenacidad intrínseca de fractura KI0. En este trabajo se ha estudiado la cerámica 3Y-TZP y el material compuesto formado por 3Y-TZP y 2% en volumen de nanotubos de carbono con paredes multicapa (MWCNT) ambos producidos por Spark Plasma Sintering (SPS). El método de análisis del COD permitió comprobar que la adición de este contenido de MWCNT no afecta prácticamente al COD medido experimentalmente y que la tenacidad intrínseca KI0 es por tanto muy similar para ambos materiales. Estas observaciones en principio no justifican las diferencias en tenacidad de fractura determinadas por el método clásico de tenacidad de fractura por indentación en los materiales estudiados. // The indentation method has been widely used to measure the fracture toughness in fragile materials due to its simplicity and that only needs of a small sample. However, it is well known that the fracture toughness values obtained by indentation methods can be substantially different from the values obtained from more rigorous methods which are based on a precise knowledge of all parameters involved in fracture. This situation has lead to the development of new methods that investigate the crack opening displacement (COD) and relate it to the intrinsic fracture toughness KI0. In the present work, a 3Y-TZP ceramic has been studied together with a composite containing 2% vol. of multiwall carbon nanotubes (MWCNT); both of which were produced by Spark Plasma Sintering (SPS). The COD method showed that the addition of MWCNTs did not effectively affect the COD and the intrinsic fracture toughness KI0 was thus very similar in both materials. These observations in principle do not justify the differences determined by the classical indentation fracture toughness method on the present materials.

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    Influencia de la degradación hidrotérmica en la resistencia mecánica y comportamiento al desgaste de 3Y-TZP  Open access

     Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Kiran Chitapalli, Ravi; de Armas Sancho, Zamir; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012
    Presentation of work at congresses

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    En este trabajo se realiza un estudio comparativo de la influencia de la degradación hidrotérmica a baja temperatura de circona tetragonal estabilizada con el 3% molar de Itria (3Y-TZP) en la resistencia mecánica a flexión y en el comportamiento bajo cargas de indentación esférica. Se presentan resultados de resistencia mecánica a flexión y de indentación esférica monotónica así como de ensayos de rayado en probetas artificialmente degradadas durante diferentes períodos de tiempo. Se pone de manifiesto que la resistencia mecánica a flexión es poco sensible a la degradación; por el contrario, los ensayos superficiales ponen claramente de manifiesto la presencia de degradación en sus etapas iniciales. Se constata la fuerte sensibilidad de la resistencia al desgaste y de la fatiga por contacto a la presencia de degradación hidrotérmica a baja temperatura. Los resultados se analizan en términos de la capa degradada de estructura monoclínica que se forma durante la degradación.

  • Determinación de la tenacidad de fractura intrínseca

     Anglada Gomila, Marcos Juan; Garcia Marro, Fernando; Chintapalli, Ravi Kiran
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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  • Decoración de grietas de indentación en 3y-TZP

     Anglada Gomila, Marcos Juan; Garcia Marro, Fernando
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-20
    Presentation of work at congresses

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  • Structural and microstructural characterization of the max-phase Ti3SiC2

     Hernandez Edo, Eric; Mir Carbonell, Jordi; Heredero Alari, Francisco; Mestra Rodríguez, Alvaro Miguel; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012
    Presentation of work at congresses

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  • Adhesion strength of TiO2 plasma sprayed coatings on glass ceramic substrates

     Fargas Ribas, Gemma; Floristán, Miriam; Killinger, Andreas; Anglada Gomila, Marcos Juan; Gadow, Rainer
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012
    Presentation of work at congresses

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  • Influence of sandblasting on zirconia in restorative dentistry  Open access

     Chintapalli, Ravi Kiran
    Defense's date: 2012-09-28
    Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya
    Theses

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    La utilización de circona tetragonal policristalina estabilizada con 3 % mol de itria (3Y-TZP) para fabricar coronas e implantes ha sufrido una fuerte expansión recientemente debido a las buenas propiedades mecánicas, estéticas y de biocompatibilidad que posee este material. La microestructura y composición exacta de 3Y-TZP son específicamente diseñadas por los fabricantes para adecuarse a las normativas existentes. Durante su procesamiento, las prótesis cerámicas son tratadas superficialmente por métodos como el arenado para mejorar su adhesión al cemento protésico y a la porcelana que cubre la pieza dental. Ahora bien, no todos los fabricantes dentales recomiendan el arenado de las coronas previamente a su implantación, ya que el arenado puede introducir defectos superficiales que pueden afectar la integridad estructural de la prótesis así como producir cambios cristalográficos en la superficie. A pesar de que el efecto de arenado en circona ya ha sido parcialmente estudiado, no se han considerado exhaustivamente muchos aspectos como la severidad de las condiciones de arenado, el efecto en las propiedades superficiales, el daño subsuperficial y los cambios de fase. Una comprensión detallada de estos aspectos es necesaria para escoger correctamente las condiciones de trabajo del arenado y para mejorar el diseño microestructural de estos materiales. Esto mejoraría la vida a largo plazo de los implantes cerámicos evitando o retrasando posibles fallos de la pieza. En este trabajo, se ha estudiado el efecto del arenado en 3Y-TZP con diferentes tamaños de grano bajo diferentes condiciones de arenado. También se ha estudiado el efecto de la adición de de nanotubos de carbono multicapa (MWCNT, 0.5-2 vol. %) a una matriz de 3Y-TZP. Una parte del trabajo ha consistido en el estudio de las propiedades mecánicas y de resistencia a la degradación hidrotérmica de 3Y-TZP nanométrica y de los nanocompuestos 3YTZPMWCNT con tamaño de grano nanométrico (90-150 nm) producidos por “spark plasma sintering”, los cuales se ha encontrado que poseen una menor tenacidad de fractura por indentación que 3Y-TZP con tamaño de grano de 300 nm. La adición de un 2% en volumen de MWCNT aumenta la tenacidad de fractura por indentación en alrededor de un 15% con respecto a la matriz del mismo tamaño de grano. El módulo de elasticidad apenas cambia mientras que la dureza disminuye ligeramente.

    The use of tetragonal zirconia polycrystals (3Y-TZP) in dental restorations such as crowns and implants has recently increased attention due to their very good aesthetic appearance and mechanical properties in addition to biocompatibility. The restorations undergo several surface treatments such as sandblasting for better adhesion to luting cements and veneering porcelain. However, there is some controversy about using sandblasted crowns, as sandblasting introduces surface flaws and defects that can compromise the strength of the crown as well as crystallographic changes at the surface. Though the effect of sandblasting in zirconia has been previously studied to some extent, many issues like severity of the conditions, effect on surface mechanical properties, subsurface damage and phase transformation zone size have not been still fully addressed. Comprehensive understanding of these aspects will help in choosing better sandblasting conditions and also to improve the microstructural design of the materials for long term performance of the restorations so that clinical failures can be avoided or delayed. In this thesis, the effect of sandblasting on 3 mol% yttria stabilized zirconia (3Y-TZP) with different grain sizes has been studied under different sandblasting conditions. Additionally, nanocomposites formed by adding multiwall carbon nanotubes (0.5-2 vol. %) to 3Y-TZP matrix have been also studied. Initially, the study has been focused in the mechanical properties and hydrothermal degradation resistance of nanometric grain size 3Y-TZP and zirconia multiwall carbon nanotubes nanocomposites (3YTZP-MWCNT). Nanometric grain size 3Y-TZP (90-150 nm) produced by spark plasma sintering have slightly lower toughness compared to standard zirconia with grain size 300 nm. Adding multiwall carbon nanotubes improve the indentation fracture toughness nearly 15% compared to monolithic materials. Elastic modulus hardly changes while hardness decreases slightly for 2 vol.% nanotubes. The materials were subjected to sandblasting using two particle sizes, two pressures and two impact angles, After sandblasting the materials were analyzed looking for roughness, phase transformation and damage. In addition the change in mechanical properties and in hydrothermal degradation resistance induced by sandblasting was evaluated. It has been found that increasing particle size and pressure increases surface roughness. The bi-axial strength of zirconia has been studied only in standard 300 nm grain size 3Y-TZP. The main result has been to show that at impact angle of 90º the biaxial strength increases when sandblasted with 110 um particles while it decreases with 250 um particles. On the other hand, the strength slightly increases when sandblasted under an impact angle of 30° irrespective of the particle size. By using nanoindentation it is shown that mild sandblasting conditions (110 um particle size, 2 bars pressure) have no effect on the surface mechanical properties such as, elastic modulus and contact hardness. A model based on the formation of residual compressive stresses is presented in order to explain the indentation the shorter length of the indentation cracks in sandblasted material as well as to rationalize the increase in strength of sandblasted material under mild sandblasted conditions. The microstructural change induced by sandblasting near the surface consists of: i) a thin layer of plastically deformed grains; ii) phase transformation; and iii) occasional microcracking. The fraction of monoclinic volume fraction induced after sandblasting under the studied conditions is of about 10-15%, and with transformation up to a depth of about 10-13 um. Finally it is shown that in sandblasted conventional 3Y-TZP, the kinetics of hydrothermal degradation are slower than in the starting material.

  • Influencia de la degradación hidrotérmica en la resistencia mecánica y en el comportamiento al desgaste de 3Y-TZP

     Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Kiran Chitapalli, Ravi; de Armas Sancho, Zamir; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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    En este trabajo se realiza un estudio comparativo de la influencia de la degradación hidrotérmica a baja temperatura de circona tetragonal estabilizada con el 3% molar de Itria (3Y-TZP) en la resistencia mecánica a flexión y en el comportamiento bajo cargas de indentación esférica. Se presentan resultados de resistencia mecánica a flexión y de indentación esférica monotónica así como de ensayos de rayado en probetas artificialmente degradadas durante diferentes períodos de tiempo. Se pone de manifiesto que la resistencia mecánica a flexión es poco sensible a la degradación; por el contrario, los ensayos superficiales ponen claramente de manifiesto la presencia de degradación en sus etapas iniciales. Se constata la fuerte sensibilidad de la resistencia al desgaste y de la fatiga por contacto a la presencia de degradación hidrotérmica a baja temperatura. Los resultados se analizan en términos de la capa degradada de estructura monoclínica que se forma durante la degradación. // In the present work a comparative study is carried out of the influence of low hydrothermal degradation on the bend strength and in the behaviour under contact loading of zirconia polycrystals stabilised with 3% molar of yttria (3YTZP). Results of bend strength by four point loading and monotonic spherical indentation and scratch testing are compared in specimen degraded for different times. It is shown that bending tests are very insensitive to degradation; on the contrary the surface testing methods show clearly the influence of degradation in their initial stages. This has important consequences in their behaviour in contact fatigue and wear behaviour, which it is shown are strongly affected by low temperature degradation. The results are analysed in terms of the monoclinic degraded layer that forms during degradation.

  • Veinte años de la titulacion de ingeniería de materiales

     Mateo Garcia, Antonio Manuel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-04-03
    Presentation of work at congresses

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  • criterios de diseño micromecánico , a nivel de sustrato y bajo solicitaciones de contacto, en herramientas recubiertas para aplicaciones de conformado de aleaciones metálicas

     Mateo Garcia, Antonio Manuel; Llanes Pitarch, Luis Miguel; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    Congreso Nacional de Materiales
    Presentation's date: 2012-06-01
    Presentation of work at congresses

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    En aplicaciones de conformado en frío, donde el uso de herramientas recubiertas es común, solicitaciones mecánicas de contacto inducen presiones de tipo Hertziano que pueden causar fallos por fatiga. En este trabajo, la respuesta al contacto y el comportamiento a fatiga de sistemas sustrato/recubrimiento duros: capas cerámicas (TiN, WC/C y bicapa, todas ellas depositadas por PVD) sobre diferentes calidades de carburos cementados (metal duro), se investiga mediante técnicas de indentación a escala macro- y micrométrica. El estudio se enfoca en la determinación de las cargas críticas para la aparición de los distintos mecanismos de daño, de cara a la posible optimización del rendimiento de las correspondientes herramientas recubiertas. En todos los casos se observa que el fallo en los sistemas sustrato-recubrimiento investigados es susceptible a fatiga. Sin embargo, tanto la correspondiente sensibilidad como el escenario de daño crítico: fallo cohesivo del recubrimiento, propagación cohesiva de las fisuras desde la capa hasta el sustrato y/o delaminación interfacial, resultan ser variables dependiendo del sistema en consideración. Finalmente, el comportamiento observado se discute, teniendo en cuenta la influencia de la microestructura y las propiedades mecánicas del sustrato, así como de la configuración microestructural de la capa.

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    Mechanical properties of alumina infiltrated zirconia nanocomposites  Open access

     Camposilvan, Erik; Garcia Marro, Fernando; Maspero, Federico; Cuspidi, G.; Anglada Gomila, Marcos Juan
    Congreso Nacional de Propiedades Mecánicas de Sólidos
    Presentation's date: 2012-09-27
    Presentation of work at congresses

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  • Efecto de la adición de segundas fases sobre las propiedades mecánicas de la porcelana dental feldespática

     Rueda Arango, Astrid Oasis; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    Congreso Nacional de Materiales
    Presentation's date: 2012-05-30
    Presentation of work at congresses

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  • Influence of sandblasting on bi-axial strength of 3Y-TZP

     Chintapalli, Ravi Kiran; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Congreso Nacional de Propiedades Mecánicas de Sólidos
    Presentation's date: 2012-09-26
    Presentation of work at congresses

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  • Effect of sandblasting on hydrothermal degradation of zirconia ceramics

     Chintapalli, Ravi Kiran; Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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  • Effect of MWCNT addition on the friction coefficient and the electrical properties of 3Y-TZP

     Melk, Latifa; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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  • Effect of second phase addition on the mechanical properties of feldspathic dental porcelain

     Rueda Arango, Astrid Oasis; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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  • Dispositivo de micro y ultrafiltración tangento-axial de alto rendimiento mediante macromembrana cerámica

     Cusido Fabregas, Juan Antonio; Cremades Oliver, Lazaro Vicente; Sitjar Cañellas, Rafael; Anglada Gomila, Marcos Juan
    Date of request: 2012-01-20
    Invention patent

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    La invención incluye una macromembrana cerámica para micro y ultrafiltración de fluidos, incluido agua, y el dispositivo de filtración que la utiliza. Esta macromembrana se caracteriza por poder tener cualquier tamaño y morfología, y funciona según un nuevo concepto operativo denominado "tangento-axial". Su producción se realiza por "slip casting" (vaciado), a diferencia de la producción estándar de piezas tubulares cerámicas por extrusión. La principal aportación de esta tecnología radica en que las plantas de filtración y su operación son más simples y, por lo tanto, con un menor coste de implantación del proceso. Por otro lado, los rendimientos de la filtración de la tecnología propuesta pueden llegar a ser 5 veces superiores o más respecto a los obtenidos de la filtración tangencial convencional.

  • Aging resistance and fracture toughness of ceria¿infiltrated zirconia

     Camposilvan, Erik; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Congreso Nacional de Materiales
    Presentation's date: 2012-05-30
    Presentation of work at congresses

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    The main drawback of yttria stabilized zirconia (3Y-TZP) is represented by the Low Temperature Degradation (LTD), which consists in the progressive transformation of the tetragonal phase, metastable at room temperature, to the stable monoclinic phase, when the material is exposed to humid environment and moderate temperatures. LTD is responsible for a decrease in superficial mechanical properties for relatively short exposure times, while bulk properties are affected for longer exposures. These effects have limited the use of 3Y-TZP in biomedical devices during the last years. A process based on the addition of ceria, a stabilizer of tetragonal phase less susceptible to LTD, has been recently developed. A solution of Cerium salts is infiltrated into the ceramic piece at the porous pre-sintered state. After sintering, ceria diffuses into zirconia lattice. In a first stage, the process was optimized in terms of LTD resistance, maintaining the microstructure, strength and hardness of 3Y-TZP. Nevertheless, a slight decrease in indentation fracture toughness was recorded. In a second stage, the research has been focused on the possibility of compensating the toughness decrease by sintering at higher temperature, obtaining a moderate increase in grain size without prejudicial effects on the LTD resistance achieved with ceria addition.

  • Decoration of indentation cracks in 3Y-TZP by hydrothermal ageing

     Garcia Marro, Fernando; Camposilvan, Erik; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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    Las grietas de indentación en cerámicas son frecuentemente utilizadas no sólo para estimar semi-empíricamente la tenacidad a fractura KIC, sino también cómo método para crear grietas agudas superficiales y semielípticas a partir de las cuales analizar la tenacidad de fractura. Para ello es necesario conocer la forma exacta de la grieta inicial, así como en el momento de fractura inestable. A menudo dicha identificación no es obvia debido a un pobre contraste visual de las superficies fracturadas. La circona estabilizada con 3% molar de itria (3Y-TZP) es una cerámica biocompatible con buenas propiedades mecánicas que la hacen interesante para su utilización en prótesis dentales y cabezas femorales. Adicionalmente, la 3Y-TZP es susceptible a un fenómeno de degradación a baja temperatura por el cual un ambiente acuoso produce una transformación de fase en la superficie expuesta. En este trabajo se ha aprovechado la susceptibilidad a degradación hidrotérmica de la 3Y-TZP para revelar grietas de indentación en probetas que son ensayadas a flexión posteriormente. Se muestra como grietas de indentación en 3Y-TZP afectadas por vapor de agua son claramente reveladas en la posterior caracterización fractográfica. Se consideraron diferentes tipos de 3Y-TZP con diferentes grados de susceptibilidad a degradación hidrotérmica. Se observó que una exposición en autoclave de unas pocas horas es suficiente para revelar las grietas en la superficie de fractura sin llegar a afectar la carga de rotura de las probetas. Por consiguiente, la técnica puede utilizarse para obtener un conocimiento preciso de la geometría de las grietas de indentación utilizadas para determinar la tenacidad de fractura. // Indentation cracks on ceramics are frequently used not only for the semi-empirical determination of the fracture toughness KIC but also as a method for generating semielliptical surface cracks to be used in as starting cracks in fracture and fatigue studies. Tetragonal zirconia stabilized with 3 % mol of yttria (3Y-TZP) is a biocompatible ceramic with good mechanical properties which is used in dental and femoral prostheses applications. Additionally, 3Y-TZP is susceptible to low temperature degradation in which a hydrothermal environment induces a phase transformation of the exposed surface. In the present work, this degradation susceptibility of 3Y-TZP has been used to reveal indentation crack profiles on specimens which were tested by flexural bending afterwards. Different types of 3Y-TZP were considered which presented different degrees of susceptibility to hydrothermal degradation. It is shown that these cracks are clearly decorated by the water vapour which make them easily revealed on the fracture surfaces. An exposition of few hours in autoclave is sufficient for revealing the indentation cracks on the fracture surface without affecting the fracture load of the specimens. Therefore, the method can be applied to visualize with precision the geometry of indentation cracks which are used to determine the fracture toughness.

  • Fracture toughness evaluation of crack tip opening displacement od cube corner indenters

     Anglada Gomila, Marcos Juan; Garcia Marro, Fernando; Cuadrado Lafoz, Núria; Casellas Padro, Daniel
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-20
    Presentation of work at congresses

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