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  • Effect of sandblasting and residual stress on strength of zirconia for restorative dentistry applications

     Kiran Chintapalli, Ravi; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Anglada Gomila, Marc
    Journal of the mechanical behavior of biomedical materials
    Date of publication: 2014-01
    Journal article

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    Sandblasting is a commonly used surface treatment technique for dental crowns to improve the adhesion of the mating parts of a restoration. The goal of this work is to study the effect of different sandblasting conditions on the mechanical properties of 3 mol % yttria stabilized tetragonal zirconia (3Y-TZP), such as biaxial strength, surface elastic modulus, contact hardness and residual stresses induced by sandblasting. The specimens were sandblasted considering two different particle sizes (110, 250 pm), two pressures (2 and 4 bar) and two impact angles (30 and 90). Biaxial strength of 3Y-TZP increases when sandblasted with 110 mu m particles while its decreases with 250 mu m particles for impact angle of 90. Strength increases slightly when sandblasting with 30' impact angle regardless of the size of the particle. Elastic modulus and contact hardness were not affected by sandblasting with 110 mu m particles, and compressive residual stresses are produced down to a depth of similar to 10 mu m. (C) 2013 Elsevier Ltd. All rights reserved.

    Sandblasting is a commonly used surface treatment technique for dental crowns to improve the adhesion of the mating parts of a restoration. The goal of this work is to study the effect of different sandblasting conditions on the mechanical properties of 3 mol% yttria stabilized tetragonal zirconia (3Y-TZP), such as biaxial strength, surface elastic modulus, contact hardness and residual stresses induced by sandblasting. The specimens were sandblasted considering two different particle sizes (110, 250 μm), two pressures (2 and 4 bar) and two impact angles (30° and 90°). Biaxial strength of 3Y-TZP increases when sandblasted with 110 µm particles while its decreases with 250 µm particles for impact angle of 90°. Strength increases slightly when sandblasting with 30° impact angle regardless of the size of the particle. Elastic modulus and contact hardness were not affected by sandblasting with 110 µm particles, and compressive residual stresses are produced down to a depth of ~10 µm.

  • Contact mechanical response of PCD: microstructural effects on induced damage

     Garcia Marro, Fernando; Jimenez Pique, Emilio; Mestra Rodríguez, Alvaro Miguel; Ozbayraktar, S; Llanes Pitarch, Luis Miguel
    International Conference on the Science of Hard Materials
    Presentation's date: 2014
    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.

  • 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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  • 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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    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.

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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.

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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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  • 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.

  • 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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  • 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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  • 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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  • 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.

  • 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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  • 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.

  • 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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  • 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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    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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  • 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.

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    Hydrothermal ageing of cracked of 3Y-TZP  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2011
    Journal article

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    En la circona dopada con 3% molar de itria, el vapor de agua puede inducir la transformación de la fase tetragonal a monoclínica en la superficie. Dicha transformación se ex tiende hacia el interior acompañada por la aparición de microfisuras, lo que induce una pérdida de la integridad es tructural. Este fenómeno de degradación a baja temperatura (LTD) es una clara desventaja para la utilización del material en atmósferas húmedas. Sin embargo, el efecto del agua sobre grietas de indentación no ha sido estudiado. Este trabajo estudia la influencia de LTD en la resistencia mecánica de dichas grietas. Los resultados muestran sorprendentemente un incremento de la resistencia mecánica en probetas indentadas sometidas a largos tiempos de degradación; al contrario del comportamiento en probetas sin indentar. Para explicar este comportamiento, se ha evaluado también la infl uencia de las tensiones residuales y el tratamiento de recocido adecuado para eliminarlas. Finalmente, se plantean los mecanismos que explican el aumento de la resistencia mecánica observado.

    En la circona dopada con 3% molar de itria, el vapor de agua puede inducir la transformación de la fase tetragonal a monoclínica en la superficie. Dicha transformación se ex tiende hacia el interior acompañada por la aparición de microfisuras, lo que induce una pérdida de la integridad es tructural. Este fenómeno de degradación a baja temperatura (LTD) es una clara desventaja para la utilización del material en atmósferas húmedas. Sin embargo, el efecto del agua sobre grietas de indentación no ha sido estudiado. Este trabajo estudia la influencia de LTD en la resistencia mecánica de dichas grietas. Los resultados muestran sorprendentemente un incremento de la resistencia mecánica en probetas indentadas sometidas a largos tiempos de degradación; al contrario del comportamiento en probetas sin indentar. Para explicar este comportamiento, se ha evaluado también la infl uencia de las tensiones residuales y el tratamiento de recocido adecuado para eliminarlas. Finalmente, se plantean los mecanismos que explican el aumento de la resistencia mecánica observado.

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    Daño por contacto hertziano en un nanocompuesto Ce-TZP/Al2O3  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Anales de mecánica de la fractura
    Date of publication: 2011
    Journal article

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    El material compuesto Ce-TZP/Al 2 O 3 es una cerámica nanoestructurada con granos de alúmina y circona tetragonal estabilizada con ceria. Actualmente, este tipo de compuestos están siendo desarrollados con el objetivo de sustituir a la circona dopada con 3% molar de itria de grado biomédico. En este trabajo, se ha estudiado el comportamiento de este compuesto bajo contacto monotónico apli cado mediante indentación esférica. Me diante espectroscopia micro-Raman se ha puesto en evidencia el cambio de fase local inducido por acción de las tensiones en la huella residual. Esto indica que el mecanismo de transformación de fase es máximo en los bordes de la huella, que corresponde a la zona donde el campo de tensiones de tracción es máximo de acuerdo con la teoría hertziana de la indentación esférica. Las conclusiones son que a pesar de que las grietas anillo aparecen para cargas de indentación esférica similares a las correspondientes a la circona dopada con itria, en el prese nte nanocompuesto su penetración hacia el interior del material es mucho menor, lo cual pone de manifiesto una mayor tolerancia al daño. Esta mayor tolerancia se relaciona a una mayor a tenacidad de fractura

    El material compuesto Ce-TZP/Al 2 O 3 es una cerámica nanoestructurada con granos de alúmina y circona tetragonal estabilizada con ceria. Actualmente, este tipo de compuestos están siendo desarrollados con el objetivo de sustituir a la circona dopada con 3% molar de itria de grado biomédico. En este trabajo, se ha estudiado el comportamiento de este compuesto bajo contacto monotónico apli cado mediante indentación esférica. Me diante espectroscopia micro-Raman se ha puesto en evidencia el cambio de fase local inducido por acción de las tensiones en la huella residual. Esto indica que el mecanismo de transformación de fase es máximo en los bordes de la huella, que corresponde a la zona donde el campo de tensiones de tracción es máximo de acuerdo con la teoría hertziana de la indentación esférica. Las conclusiones son que a pesar de que las grietas anillo aparecen para cargas de indentación esférica similares a las correspondientes a la circona dopada con itria, en el prese nte nanocompuesto su penetración hacia el interior del material es mucho menor, lo cual pone de manifiesto una mayor tolerancia al daño. Esta mayor tolerancia se relaciona a una mayor a tenacidad de fractura

  • Contact damage in a Ce-TZP/Al2O3 nanocomposite

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2011-11
    Journal article

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    The damage tolerance of a nanocomposite based on Ce-TZP and 30 vol% Al2O3 has been studied un der monotonic contact with a spherical indenter. The results are compared with those previously known for commercial 3Y-TZP zirconia. It is concluded that the minimum load for ring crack appearance is similar in both ceramics. However, in the nanocomposite the ring cracks penetrate much less into the bulk, because of its higher fracture toughness. Finally, the stress-induced phase transformation of the zirconia component was quantified and mapped by micro-Raman spectroscopy.

  • Hydrothermal ageing of smooth and cracked 3Y-TZP

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Conference of the European Ceramic Society
    Presentation's date: 2011
    Presentation of work at congresses

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    The effect of hydrothermal degradation on the flexural strength of smooth and indented specimens of tetragonal polycrystalline zirconia doped with 3% mol yttria (3Y-TZP) has been investigated. The specimens were exposed for several periods of time to water vapour at 131 ºC in autoclave. The t-m transformation was studied by micro-Raman spectroscopy and SEM on the specimen’s surface and on Palmqvist crack faces after fracture. It is shown here that the Weibull modulus of the flexure strength of smooth degraded specimens increases, while the flexural strength decreases in the ageing interval studied. On the contrary, specimens with indentation cracks larger than the size of crack-like natural defects, increase strongly their flexural strength after an incubation ageing time. It is shown here that the Weibull modulus of the flexure strength of smooth degraded specimens increases, while the flexural strength decreases in the ageing interval studied. On the contrary, specimens with indentation cracks larger than the size of crack-like natural defects, increase strongly their flexural strength after an incubation ageing time. It is proposed that crack tip blunting by water vapour is responsible for this effect, which has not been previously reported. It is also shown that exposure to water vapour can be an excellent tool to reveal cracks in 3Y-TZP.

  • Determinación de las propiedades mecánicas a flexión. Etapa 2

     Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Mateo Garcia, Antonio Manuel
    Date: 2011
    Report

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  • Sliding wear behaviour of surface nitrided zirconia

     Valle Chiro, Jorge Antonio; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    Congreso Ibérico de Tribología
    Presentation's date: 2011-06-16
    Presentation of work at congresses

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    Tetragonal polycrystalline zirconia stabilised with 3% molar yttria (3Y-TZP) has found wide applications in orthopaedics and dentistry because of its excellent mechanical properties (flexural strength above 1000 MPa, fracture toughness about 5 MPa·m1/2, hardness above 12 GPa) and biocompatibility. However, 3Y-TZP has a strong drawback: poor resistance to hydrothermal ageing also referred to as low temperature degradation (LTD). Nitriding of 3Y-TZP can make the surface resistance to LTD, but surface mechanical properties are also affected. In this work, the sliding wear resistances of as sintered and nitrided 3Y-TZP have been studied and compared. Nitriding has been carried out by embedding 3Y-TZP in a powder of ZrN and posterior heat treatment at 1400, 1500 and 1600 °C in a nitrogen atmosphere. The sliding wear behaviour of as sintered and nitrided surfaces was studied by means of ball on disc tests. The results show that by nitriding at 1400 °C the nitrided surface is resistance to LTD without any significant drop in the surface mechanical properties, so that it has similar sliding wear behaviour and surface mechanical properties as those of the starting 3Y-TZP. The results are discussed in terms of the change in the microstructure induced by nitriding.

  • Comportamiento a fatiga de un nanocompuesto Ce-TZP/Al2O3

     Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; de Armas Sancho, Zamir; Anglada Gomila, Marcos Juan
    Congreso Nacional de Materiales Compuestos
    Presentation's date: 2011-07-08
    Presentation of work at congresses

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    Se ha evaluado la resistencia a flexión biaxial y el comportamiento a fatiga de un nanocompuesto cerámico basado en Ce-TZP y Al2O3. Los ensayos se realizaron en flexión biaxial y se ha determinado la resistencia y el módulo de Weibull, así como el límite de fatiga para 106 ciclos con R=0.1 en aire. Los resultados se comparan con el comportamiento de 3Y-TZP bajo condiciones similares.

  • Development of a novel zirconia dental post resistant to hydrothermal degradation

     Camposilvan, Erik; Garcia Marro, Fernando; Anglada Gomila, Marcos Juan
    International Conference on Advanced Materials Research
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    Hydrothermal ageing of cracked 3Y-TZP  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation of work at congresses

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    En la circona dopada con 3% molar de itria, el vapor de agua puede inducir la transformación de la fase tetragonal a monoclínica en la superficie. Dicha transformación se extiende hacia el interior acompañada por la aparición de microfisuras, lo que induce una pérdida de la integridad estructural. Este fenómeno de degradación a baja temperatura (LTD) es una clara desventaja para la utilización del material en atmósferas húmedas. Sin embargo, el efecto del agua sobre grietas de indentación no ha sido estudiado. Este trabajo estudia la influencia de LTD en la resistencia mecánica de dichas grietas. Los resultados muestran sorprendentemente un incremento de la resistencia mecánica en probetas indentadas sometidas a largos tiempos de degradación; al contrario del comportamiento en probetas sin indentar. Para explicar este comportamiento, se ha evaluado también la influencia de las tensiones residuales y el tratamiento de recocido adecuado para eliminarlas. Finalmente, se plantean los mecanismos que explican el aumento de la resistencia mecánica observado. // In zirconia stabilised with 3% molar of yttria, the water vapour can induce the transformation from tetragonal to monoclinic phase at the surface. This transformation propagates to the bulk with the apparition of microcracks; which induce a loss in the structural integrity. This low temperature degradation (LTD) is a clear disadvantage for the application of the material in humid environments. On the other hand, the effect of the water on indentation-induced cracks has not been previously studied. This work studies the change in mechanical strength of indentation cracks submitted to water vapour. The results show how, after long degradation times, there is surprisingly an increase in mechanical strength. This is the opposite behaviour as the one expected in normal specimens which are not indented. To explain the observed behaviour here, the influence of the residual tensions was evaluated included annealing treatments. Finally, the mechanisms explaining the observed increase in strength are discussed.

  • Procedimiento para el aumento de la durabilidad de la Circona en aplicaciones dentales

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Camposilvan, Erik; Anglada Gomila, Marcos Juan
    Date of request: 2011-07-28
    Invention patent

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    Procedimiento para el aumento de la durabilidad de la circona en aplicaciones dentales, donde una pieza dental se mecaniza a partir de óxido de zirconio estabilizado con 3% molar de óxido de itrio presintetizado, se realiza la cocción de limpieza, y a continuación se introduce la pieza dental en una solución de nitrato de Cerio -Ce(NO3)·H2O-, disuelto en agua destilada al 50% en peso, durante 24 horas, y finalizando con la sinterización de la pieza.

  • Surface mechanical properties of advanced zirconia after hydrothermal exposure

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    International Conference on Advanced Materials Research EEIGM/AMASE/FORGEMAT
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    Daño por contacto hertziano en un nanocompuesto Ce-TZP/Al2O3  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation of work at congresses

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    El material compuesto Ce-TZP/Al2O3 es una cerámica nanoestructurada con granos de alúmina y circona tetragonal estabilizada con ceria. Actualmente, este tipo de compuestos están siendo desarrollados con el objetivo de sustituir a la circona dopada con 3% molar de itria de grado biomédico. En este trabajo, se ha estudiado el comportamiento de este compuesto bajo contacto monotónico aplicado mediante indentación esférica. Mediante espectroscopia micro-Raman se ha puesto en evidencia el cambio de fase local inducido por acción de las tensiones en la huella residual. Esto indica que el mecanismo de transformación de fase es máximo en los bordes de la huella, que corresponde a la zona donde el campo de tensiones de tracción es máximo de acuerdo con la teoría hertziana de la indentación esférica. Las conclusiones son que a pesar de que las grietas anillo aparecen para cargas de indentación esférica similares a las correspondientes a la circona dopada con itria, en el presente nanocompuesto su penetración hacia el interior del material es mucho menor, lo cual pone de manifiesto una mayor tolerancia al daño. Esta mayor tolerancia se relaciona a una mayor a tenacidad de fractura. // The composite material Ce-TZP/Al2O3 is a nanostructured ceramic with alumina grains and tetragonal zirconia stabilized with ceria. Currently, this type of composites is being developed with the objective to substitute biomedical grade tetragonal zirconia polycrystals doped with 3% molar yttria. In the present work, the microstructure and mechanical properties of such a composite have been studied. Additionally, the behaviour under monotonic contact loading has also been studied by spherical indentation at different load ranges. Raman spectroscopy revealed the local phase transformation induced by the locally applied stresses on the residual imprint. This indicates that the phase transformation mechanism is maximal at the border imprints, which corresponds to the zone where the traction stresses are maximal according to classical Hertzian theory. The conclusions are that while the crack rings appear at similar indentation loads as 3Y-TZP, the penetration of these cracks in the interior of the composite is much smaller, which means a higher tolerance to contact damage. This higher tolerance is related to its higher fracture toughness.

  • Processing and characterization of zirconia-multiwall CNT nanocomposites

     Kiran Chitapalli, Ravi; Garcia Marro, Fernando; Milsom, Ben; Reece, Michel; Anglada Gomila, Marcos Juan
    International Conference on Advanced Materials Research EEIGM / AMASE / FORGEMAT
    Presentation's date: 2011
    Presentation of work at congresses

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  • Surface modification of 3Y-TZP with cerium oxide

     Garcia Marro, Fernando; Valle Chiro, Jorge Antonio; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Journal of the european ceramic society
    Date of publication: 2010-11
    Journal article

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    Stability of nanocrystalline spark plasma sintered 3Y-TZP  Open access

     Kiran Chitapalli, Ravi; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Yan, Haixue; Reece, Michel; Anglada Gomila, Marcos Juan
    Materials
    Date of publication: 2010
    Journal article

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    Spark plasma sintered 3Y-TZP has been investigated with respect to hydrothermal ageing and grinding. The sintering was performed between the temperatures of 1,100 and 1,600 °C for a soaking time of 5 minutes and the resulting materials were obtained with grain sizes between 65 to 800 nm and relative densities between 88.5 to 98.8%. Experiments on hydrothermal ageing in water vapour at 131 °C, 2 bars during 60 hours shows that phase stability is retained, elastic modulus and hardness of near surface region measured by nanoindentation does not change in fine grain (<200 nm) materials, in spite of porosity. In ground specimens, very small amount of transformation was found for all grain sizes studied.

  • MEJORA DEL COMPORTAMIENTO A FATIGA Y DE LA CONFORMIBILIDAD DE ACEROS METAESTABLES MEDIENTE DISEÑO

     Prado Pozuelo, Jose Manuel; Calvo Muñoz, Jessica; Riera Colom, Maria Dolores; Heredero Alari, Francisco; Llanes Pitarch, Luis Miguel; Fargas Ribas, Gemma; Salán Ballesteros, Mª Núria; Mestra Rodríguez, Alvaro Miguel; Garcia Marro, Fernando; Zapata Dederlé, Ana Cristina; Mir Carbonell, Jordi; Botero Vega, Carlos Alberto; Mateo Garcia, Antonio Manuel
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  • Relationship between density and mechanical properties of spark plasma sintered zirconia ceramics

     Kiran Chitapalli, Ravi; Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Reece, Michel; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2010
    Presentation of work at congresses

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    Zirconia ceramics stabilized with 3 mol % Yttria were produced by spark-plasma sintering. Toughness, Vickers hardness, nanoindentation elastic modulus and Berkovich hardness were determined in terms of the final density and sintering temperature. Very fine grain materials from 65 to 800 nm were obtained with relative densities ranging from 88 to 99.5%. Results show lower elastic modulus and hardness in low dense specimens compared to fully dense specimens, also indentation fracture toughness changes with density and grain size. Specimens investigated under hydrothermal degradation at 131ºC for 60 hours show that mechanical properties are not affected by this treatment in low density and low grain size specimens, but affects strongly the elastic modulus and contact hardness of specimens of near full density and large grain size. The results are discussed in terms of density, grain size and t-m transformability.

  • Relación entre integridad estructural y microestructura en la degradación hidrotérmica de 3Y-TZP

     de Armas Sancho, Zamir; Fargas Ribas, Gemma; Muñoz Tabares, Jose Alejandro; Garcia Marro, Fernando; Valle Chiro, Jorge Antonio; Kiran Chitapalli, Ravi; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Sociedad Española de Cerámica y Vidrio
    Presentation's date: 2010-10
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    Weibull characterization of the flexural strength of hydrothermally degraded 3Y-TZP zirconia  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Lamghari, Manal; Anglada Gomila, Marcos Juan
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2010
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    The flexural strength of 3% mol yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP) with a ~0.30m grain size was studied under 4-point bending test. The material was evaluated both as received and after water vapour exposure for long times of 100hr and 200hr at 131ºC in autoclave. Results were systematically analyzed by Weibull statistics and fractography. It was found that the mean flexural strength and Weibull modulus change from 960MPa and m=10.9 in the as received condition to 916MPa (m=19.5) and 860MPa (m=19.8) for 100 and 200 hours ageing, respectively. This increase in m can be explained by a change in the origin of fracture from natural flaws in the original material to original defects in the degraded surface layer which extend under loading to a depth equal to its thickness. This layer can be clearly appreciated during fractographic analysis after long degradation times. In the present case the thickness of the degraded layer was on average equal to 8.5m after 100 hours of hydrothermal exposure.

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    Estudio por nanoindentación de 3Y-TZP envejecida por degradación hidrotérmica  Open access

     de Armas Sancho, Zamir; Garcia Marro, Fernando; Jimenez Pique, Emilio; Anglada Gomila, Marcos Juan
    Congreso Nacional de Propiedades Mecánicas de Sólidos
    Presentation's date: 2010
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    La circona tetragonal policristalina estabilizada con 3% molar de itria (3Y-TZP) puede transformarse espontáneamente a la fase monoclínica en presencia de vapor de agua a temperaturas relativamente bajas, lo cual conlleva una reducción drástica en las propiedades mecánicas superficiales para tiempos de degradación cortos y en las propiedades mecánicas de volumen para tiempos largos. En este trabajo se presenta un estudio del comportamiento mecánico bajo indentación de 3Y-TZP degradada hidrotérmicamente a 131°C durante tiempos entre 5 y 60 horas. La investigación se centra principalmente en analizar la respuesta mecánica del material bajo indentación en función del espesor de la capa degradada utilizando para ello tanto un penetrador puntiagudo Berkovich como un penetrador esférico. Se determina el módulo elástico a diferentes profundidades en la capa degradada y se detecta que varía en la dirección del espesor La variación observada se analiza en términos de la población de microfisuras formada en la sección transversal y observada mediante corte por haz de iones focalizados. También se analiza en términos de la fracción de volumen de fase monoclínica medida a través del espesor mediante espectroscopia micro-Raman.--- Tetragonal zirconia polycrystals doped with 3% molar yttria (3Y-TZP) can transform spontaneously to the monoclinic phase in the presence of water vapour at relatively low temperatures. This can originate a drastic reduction of surface mechanical properties after relatively short times of degradation and of the bulk mechanical properties after long times. In this paper we present a study of the surface mechanical behaviour of the degraded layer of 3Y-TZP after hydrothermal degradation at 131 °C for times between 5 and 60 hours by using nanoindentation. Research is focused in the analysis the mechanical behaviour under nanoindentation by using a sharp Berkovich indenter as well as a spherical indenter. The elastic modulus is determined at different depths in the degraded layer. The observed variation is discussed in terms of the microcrack a population detected in the cross section of the degraded layer prepared by machining by a focus ion beam and also in terms of the analysis of the volume fraction of monoclinic phase by micro-Raman spectroscopy.

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    Estadística de la rotura de circona dopada con itria sometida a degradación hidrotérmica  Open access

     Garcia Marro, Fernando; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Congreso Nacional de Propiedades Mecánicas de Sólidos
    Presentation's date: 2010
    Presentation of work at congresses

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    En este trabajo se ha estudiado la influencia de la degradación hidrotérmica en la resistencia a flexión de circona tetragonal estabilizada con 3% molar de itria. El material se ha evaluado tanto en estado original como degradado en autoclave a 131ºC durante 100 y 200 h. Los resultados se han analizado utilizando la estadística de Weibull con el fin de obtener cada una de las distribuciones de probabilidad de rotura, y mediante fractografía. Los resultados muestran que la máxima caída en resistencia a flexión provocada por la degradación hidrotérmica no supera el 10% de la resistencia inicial. No obstante, el módulo de Weibull aumenta desde 10.9 en el material en estado original, hasta valores próximos a 20 como resultado de la degradación. Tanto la caída de la resistencia como el aumento de módulo de Weibull se explican en términos del espesor de la capa superficial monoclínica, el origen de la fractura y las tenacidades de la fractura en las fases monoclínica y tetragonal.