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  • Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers

     Jimenez Pique, Emilio; Gonzalez Garcia, Lola; Rico, Victor J.; Rodriguez Gonzalez-Elipe, Agustin
    Thin solid films
    Date of publication: 2014-01-01
    Journal article

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    This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained by focused ion beam and of the deformed areas. Zig-zagged layers present lower values of hardness and Young's modulus due to the collapse of the angles of the columns, but at the same time this configuration impedes the appearance of fracture or delamination, as observed for tilted columns.

  • Nanoindentation and nanoscratch properties of mullite-based environmental barrier coatings: Influence of chemical composition - Al/Si ratio

     Botero Vega, Carlos Alberto; Jimenez Pique, Emilio; Martin, R; Kulkarni, Tushar; Sarin, Vinod K.; Llanes Pitarch, Luis Miguel
    Surface and coatings technology
    Date of publication: 2014-01-25
    Journal article

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    The mechanical properties and structural integrity of mullite (3Al(2)O(3)center dot 2SiO(2)) environmental barrier coatings (EBCs) are key factors towards the implementation of these systems in real applications. By using chemical vapor deposition, the chemical composition of mullite in these coatings may be tailored to obtain high Al/Si ratios in the outer surface, for an optimum corrosion protection in gas turbine environments. In this work, the influence of such Al/Si ratio on the mechanical properties and structural integrity of different Al-rich mullite coatings is evaluated by means of nanoindentation and nanoscratch tests. It is found that hardness and elastic modulus of the coating increases as the Al/Si ratio raises. On the other hand, an inverse trend is discerned for the apparent fracture toughness, although this is stated to be an indirect consequence of the resulting residual stress state, without any relevant effect on the intrinsic toughness of the mullite coatings. Regarding structural integrity, an increasingly brittle response to the sliding contact is evidenced as chemical composition moves towards higher Al/Si ratios. However, within the load range studied, brittle-like damage at the coating surface did not translate into critical decohesion at the coating/substrate interface. It sustains the effective protective role of the studied layers as EBCs. Therefore, all the studied coatings are found to exhibit a suitable structural integrity for their potential use as EBCs. (C) 2013 Elsevier B.V. All rights reserved.

  • Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

     Roa Rovira, Joan Josep; Fargas Ribas, Gemma; Jimenez Pique, Emilio; Mateo Garcia, Antonio Manuel
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2014
    Journal article

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    Advancedtechniqueswereusedtostudythedeformationmechanismsinducedbyfatiguetestsina metastableausteniticstainlesssteelAISI301LN.ObservationsbyAtomicForceMicroscopywerecarriedout tostudytheevolutionofapre-existingmartensiteplateletatincreasingnumberofcycles.Thesub-superficial deformationmechanismsoftheausteniticgrainswerestudiedconsideringthecross-sectionmicrostructure obtainedbyFocusedIonBeamandanalysedbyScanningElectronMicroscopyandTransmissionElectron Microscopy.Theresultsrevealednodeformationsurroundingthepre-existingmartensiticplateletduring fatiguetests,onlythegrowthonheightwasobserved.Martensiteformationwasassociatedwithshearbands on austenite,mainlyinthe{111}plane,andwiththeactivationoftheotherintersectingaustenite{111}<110> slipsystem.Furthermore,transmissionelectron microscopyresultsshowedthatthenucleationof e- martensitefollowsatwostagesphasetransformation(¿fcc-ehcp-a0 bcc).

  • 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.

  • Toughening and fatigue micromechanisms in hardmetals: FESEM/FIB tomography characterization

     Tarragó, José María; Jimenez Pique, Emilio; Turón Viñas, Miquel; Schneider, Ludvik; Llanes Pitarch, Luis Miguel
    International Conference on Refractory Metals and Hard Materials
    Presentation's date: 2013-06-07
    Presentation of work at congresses

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  • Effect of shot peening on a metastable austenitic steel

     Fargas Ribas, Gemma; Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Mateo Garcia, Antonio Manuel
    European and Exhibition Congress on Advanced Materials and Processes
    Presentation of work at congresses

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  • Attracting students to material science: a report of the outreach activities done at UPC Barcelona

     Jimenez Pique, Emilio; Calvo Muñoz, Jessica; Pegueroles Neyra, Marta
    European and Exhibition Congress on Advanced Materials and Processes
    Presentation's date: 2013-09-11
    Presentation of work at congresses

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  • Micromecanismos de daño sub-superficiales inducidos por indentación esférica en aceros herramientas recubiertos

     Ramírez Sandoval, Giselle; Jimenez Pique, Emilio; Mestra Rodríguez, Alvaro Miguel; Vilaseca, Montse; Casellas, Daniel; Llanes Pitarch, Luis Miguel
    Congreso Nacional de Tratamientos Térmicos y de Superficie
    Presentation's date: 2013
    Presentation of work at congresses

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  • Toughening and fatigue micromechanisms in hardmetals: SEM/FIB tomography characterization

     Tarrago Cifre, Jose Maria; Jimenez Pique, Emilio; Turón Viñas, Miquel; Rivero, Lorenzo; Schneider, Ludwig; Llanes Pitarch, Luis Miguel
    International Conference on Refractory Metals and Hard Materials
    Presentation's date: 2013-06-03
    Presentation of work at congresses

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    The particular microstructure assemblage of hardmetals yields those materials an extraordinary combination of hardness and toughness. On the other hand, it is also known that these materials are prone to strength degradation under cyclic mechanical loads. Within this context, the metallic binder phase plays a key role as the toughening and fatigue susceptible agent in hardmetals, as its effective ductility is critical for defining crack shielding effects and cyclic induced degradation. However, experimental proof of involved toughening and fatigue micromechanisms has usually been presented in the literature on the basis of post-failure fractographic examination. In this work, a detailed characterization of crack-microstructure interaction during stable crack growth in hardmetals is attempted. In doing so, SEM/FIB tomography is combined with systematic mechanical and indentation testing protocols (under monotonic and cyclic loads) for assessing crack extension behavior of hardmetals. The study highlights differences regarding failure micromechanisms operative under monotonic and cyclic loads.

  • 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.

  • Enhanced hydrothermal resistance of Y-TZP ceramics through colloidal processing

     Rayón Encinas, Emilio; Moreno, R.; Alcázar, C.; Salvador Moya, Maria Dolores; Manjon Herrera, Francisco Javier; Jimenez Pique, Emilio; Llanes Pitarch, Luis Miguel
    Journal of the American Ceramic Society
    Date of publication: 2013-02-28
    Journal article

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    Two commercial zirconia powders with 3 mol% of yttria (TZ3YE and TZ3YS, labeled as ZE and ZS, respectively) supplied by Tosoh (Japan) were used for this study. Maximum colloidal stability for ZE was achieved by dispersing the powders in a mixture of water/ethanol of 90:10 (wt/wt) using a sonication probe. The rheological behavior of the suspensions was optimized in terms of solids content ranging from 20 to 33 vol% and sonication time (0¿6 min), the best results being obtained after 2 min. ZS samples were prepared to a solids loading of 30 vol% in water dispersing with 2 min-sonication. Samples obtained by slip casting in plaster molds were used for dynamic sintering studies, and fully dense and nanostructured specimens were obtained at temperatures of 1300°C¿1350°C (ZE samples) and 1400°C per 2 h (ZS samples). The Hardness (H) and Young's Modulus (E) properties of the specimens were studied by nanoindentation technique giving 17 and 250 GPa mean values for H and E, respectively. The specimens were then forced to a low-temperature degradation (LTD) treatment at 130°C for 240 h in steps of 60 h. Raman spectroscopy and nanoindentation results of hydrothermally treated samples showed the absence of transformation from tetragonal to monoclinic phase until 180 h whereas the mechanical properties maintained constant even at the sample surface. After 240 h of LTD, the monoclinic phase was detected on all specimens by Raman peaks centered at 180, 191, and 383 cm-1. The nanoindentation study revealed an important loss of mechanical features reaching 10 and 175 GPa for H and E, respectively. In the case of the ZS specimens, no monoclinic phase is detected after 240 h of LTD treatment and no decay of E or H is detected. The free defect microstructure reached for the ZS specimen revealed a higher hydrothermal resistance so that it is concluded that the excellent behavior against thermal degradation is possible due to the large uniformity obtained by colloidal processing rather than the particle size of the starting powders.

  • Micromechanical characterization of small volumes by means of Nanoindentation

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

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  • Evaluación del daño por contacto en porcelana feldespática sobre circona dental  Open access

     Rueda Arango, Astrid Oasis
    Defense's date: 2013-07-19
    Universitat Politècnica de Catalunya
    Theses

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    Los materiales cerámicos son ampliamente utilizados en las restauraciones dentales como implantes y prótesis debido a sus excelentes propiedades mecánicas y estéticas y a su buena interacción con el ambiente fisiológico en que actúan. La circona recubierta con porcelana dental feldespática está siendo cada vez más utilizada en restauraciones dentales. La circona se recomienda como material base, debido a su alta resistencia, tenacidad de fractura y fácil mecanizado en estado pre-sinterizado. La porcelana dental feldespática se usa como recubrimiento debido a su apariencia en color y translucidez que, en combinación con la circona, permiten obtener implantes dentales muy similares al diente natural. Sin embargo, por la fragilidad de estas porcelanas, se han reportado fallas prematuras cuando se exponen a ambientes húmedos bajo cargas de contacto como en las funciones orales. Por tanto, el objetivo principal de esta tesis ha sido evaluar el comportamiento mecánico de la porcelana feldespática sobre circona dental (3Y-TZP) bajo solicitaciones de contacto, con el fin de entender los fallos observados en servicio y proponer cambios en el material para mejorar la resistencia de contacto. Los ensayos de contacto monotónico mostraron que el primer daño crítico en formarse fue la grieta anillo y a medida que se aumentaron las cargas de contacto se generaron grietas multianillo en la superficie. La caracterización mediante reconstrucción tomográfica de las grietas permitió observar la forma cónica de las grietas de contacto. Estas grietas bajo cargas altas de contacto fueron difíciles de reconstruir ya que estaban contenidas al interior del recubrimiento, sin embargo no alcanzaron la interfase con el sustrato de circona. La reconstrucción tomográfica asistida por FIB de la huella de nanoindentación con punta cubo, mostró que la trayectoria de la grieta se vio alterada en la vecindad de las partículas de leucita debido a los esfuerzos residuales de compresión, causando una deflexión en ésta. A partir de los ensayos de contacto estático y cíclico en aire y saliva artificial se observó que la corrosión bajo tensión es el mecanismo principal que conduce a la degradación, sin embargo, la fatiga mecánica esta también contribuyendo al agrietamiento del material. De la información obtenida de la literatura, se estimó el tiempo promedio hasta el fallo de las prótesis del contacto realista diente-prótesis, encontrándose que este tiempo oscila entre 1 y 4 años, lo cual coincide con datos clínicos reportados. Estos resultados muestran que el bruxismo es la principal causa de daño de las prótesis. Finalmente, con el interés de mejorar la respuesta mecánica de la porcelana, se realizaron adiciones de polvos de 3Y-TZP y SiO2 en diferentes porcentajes para generar segundas fases y por tanto, nuevas formulaciones porcelánicas. Con la adición de partículas de 3Y-TZP a la porcelana se consiguió aumentar la tenacidad de fractura y mejorar la resistencia al contacto. Sin embargo, para algunas formulaciones la transparencia se vio afectada. Por tanto, la adición de 1% de 3Y-TZP resultó ser la mejor combinación en apariencia estética y respuesta mecánica. Las partículas de SiO2 no afectaron la apariencia estética de la porcelana, de igual manera, tampoco mejoraron las propiedades mecánicas.

    Ceramics materials are widely used in dental restorations as implants and prosthetics because their excellent mechanical and aesthetic properties and its good interaction with the physiological environment in which are exposed. Zirconia with feldspathic dental porcelain is being increasingly used as dental restoration. Zirconia is recommended as a framework material due to its high strength, fracture toughness and easy machinability in a pre-sintered state. Feldspathic dental porcelain is used as veneering due to its appearance in color and translucency, which, in combination with zirconia, allows obtaining dental implants similar to the natural tooth. However, due to the brittleness of these porcelains, premature failures are reported when subjected to moisture environments under contact loads, as in oral functions. The main objective of this thesis is to evaluate the mechanical behavior of feldspathic porcelain dental on zirconia (3Y-TZP) under contact solicitations, in order to understand the service failures observed and propose changes in the material to improve contact resistance. Monotonic tests showed that the critical damage first was ring crack and as the increased contact loads multiring cracks were generated on the surface. The characterization by tomographic reconstruction of cracks allowed to observe the conical shape of the contact cracks. These cracks under high contact loads were difficult to reconstruct since they were contained within the coating, but did not reach the interface with the zirconia substrate. FIB assisted tomographic reconstruction of cube corner nanoindentation imprints show that the crack path was altered in the vicinity of leucite particles due to compressive residual stresses, causing a deflection of the crack. From static and cyclic contact testing in air and artificial saliva, it was observed that stress corrosion cracking is the primary mechanism that leads to degradation, however, mechanical fatigue also contributes to produce cracking in the material. From information collected from the literature, the average time to failure of the prosthesis under realistic conditions was estimated, with time spans from 1 to 4 years, consistent with the reported clinical data. This result show that bruxism is a major cause of damage of the prosthesis Finally, with the aim of improving the mechanical response of porcelain, 3Y-TZP and SiO2 powders additions in different percentages were performed to generate second phases and therefore new porcelains formulations. With the addition of 3Y-TZP particles it was possible to increase the fracture toughness and improve the contact resistance. However, the translucency in some porcelains was affected. The addition of 1% of 3Y-TZP gave the best combination in aesthetic appearance and mechanical response. SiO2 particles did not affect the aesthetics of the porcelain and did not improve the mechanical properties.

  • Microstructural effects on damage induced under monotonic and cyclic contact loading in cemented carbides

     Coureaux Mustelier, David; Ingebrand, A.; Góez Úsuga, Alexey; Tarres, Elena; Mestra Rodríguez, Alvaro Miguel; Jimenez Pique, Emilio; Llanes Pitarch, Luis Miguel
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012
    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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  • 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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  • Contact fatigue damage of monolayer and bilayer ceramic coatings depposited on cemented carbides  Open access

     Mateo Garcia, Antonio Manuel; Llanes Pitarch, Luis Miguel; Jimenez Pique, Emilio
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-22
    Presentation of work at congresses

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    En este trabajo se estudia el comportamiento a fatiga bajo solicitaciones de contacto de un carburo cementado WC-Co recubierto con dos películas cerámicas distintas: TiN y WC/C, ya sea como monocapas o bicapas, mediante técnicas de indentación. Los resultados obtenidos en ensayos de indentación esférica indican que la nucleación de fisuras circulares en las capas es un criterio más apropiado que la delaminación interfacial para definir las condiciones de daño crítico en los sistemas investigados. Desde esta perspectiva, se encuentra que los carburos cementados recubiertos son susceptibles a ser degradados mecánicamente bajo solicitaciones de contacto cíclicas, aunque la sensibilidad a fatiga y el escenario de daño efectivos difieren en cada caso, en función de la naturaleza cerámica (cristalina/amorfa) y la arquitectura (mono- o bicapa) del recubrimiento.

  • 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.

  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Nanocharacterization techniques for investigating the durability of wood coatings

     Vlad Cristea, Mirela; Riedl, Bernard; Blanchet, Pierre; Jimenez Pique, Emilio
    European polymer journal
    Date of publication: 2012-03
    Journal article

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    Nanocharacterization techniques such as nanoindentation and atomic force microscopy were used to investigate the exterior durability of waterborne coatings improved with inorganic nanosized UV-absorbers. Nanocomposite coatings for exterior uses of wood were formulated with different type of nanoparticles and their performance was evaluated trough artificial aging. Nanoindentation in continuous stiffness mode was used to demonstrate the changes of hardness and Young’s modulus of the coatings after accelerated weathering. The degradation mechanism of the surface coatings was investigated with atomic force microscopy that has provided valuable information on the morphological and microstructural changes of the surface coatings with the artificial aging. Additionally, the glass transition temperature and optical appearance changes were reported. The results obtained have shown that the nanoindentation technique in conjunction with atomic force microscopy can be satisfactorily used for durability investigation and service life prediction of nanocomposite coatings for wood.

  • New epoxy thermosets obtained from diglycidylether of bisphenol a and modified hyperbranched polyesters with long aliphatic chains cured by diisocyanates

     Flores, Marjori; Fernández Francos, Xavier; Jimenez Pique, Emilio; Foix, David; Serra Albet, Àngels; Ramis Juan, Xavier
    Polymer engineering and science
    Date of publication: 2012
    Journal article

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    Hyperbranched polyesters modified with long aliphatic chains with vinyl or epoxy groups as chain ends were synthesized and added as modifiers to diglycidyl ether of bisphenol A/toluene-2,4-diisocyanate mixtures in the presence of benzyldimethylamine as catalyst. The influence of the addition of these modifiers on the curing was investigated by thermal analysis and infrared spectroscopy. The materials obtained were investigated by electron microscopy and some mechanical characteristics were determined by nanoindentation tests. Epoxy terminated hyperbranched led to homogeneous materials with high crosslinking densities, whereas vinyl terminated hyperbranched produced phase separated morphologies. The materials showing phase separation presented a tough fracture, whereas the homogeneous materials obtained with epoxidated hyperbranched showed increased brittleness on increasing the proportion of modifier. On increasing the proportion of vinyl terminated hyperbranched in the thermosets, Young’s modulus and hardness decreased but the addition of epoxy terminated hyperbranched did not influence these parameters. The addition of vinylic hyperbranched to the formulations produced a decrease in the curing shrinkage, whereas the epoxidic hyperbranched did not.

  • 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.

  • Nanoindentation of Bridgman YBCO samples

     Roa Rovira, Joan Josep; Konstantopoulou, Dimitra; Jimenez Pique, Emilio; Martín, V.; Segarra Rubi, Merce; Pastor, J.Y.
    Ceramics international
    Date of publication: 2012-04
    Journal article

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    n this study, the mechanical properties of YBa2Cu3O7−x, obtained by the Bridgman technique, were examined using a Berkovich tip indenter on the basal plane (0 0 1). Intrinsic hardness was measured by nanoindentation tests and corrected using the Nix and Gao model for this material. Furthermore, Vickers hardness tests were performed, in order to determine the possible size effect on these measurements. The results showed an underestimation of the hardness value when the tests were performed with large loads. Moreover, the elastic modulus of the Bridgman samples was 128 ± 5 GPa. Different residual imprints were visualised by atomic force microscopy and a focused ion beam, in order to observe superficial and internal fracturing. Mechanical properties presented a considerable reduction at the interface. This effect could be attributed to internal stress generated during the texturing process. In order to corroborate this hypothesis, an observation using transmission electron microscopy was performed.

  • Chemical and mechanical properties of anodized cp-titanium in NH4 H2PO4/NH4F media for biomedical applications

     Aloia Games, Lucas; Gomez Sanchez, Andrea; Jimenez Pique, Emilio; Schreiner, Wido H.; Ceré, Silvia M.; Ballarre, Josefina
    Surface and coatings technology
    Date of publication: 2012-07-15
    Journal article

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    Potentiostatic anodizing of commercially pure titanium, using ammonium phosphate and ammonium fluoride solution as electrolyte is studied. The objective is to generate titanium oxides on the surface and phosphor compounds presenting good protective and mechanical properties, and proper adhesion to the metal substrate to remain during surgical orthopedic procedures (implants). Two different applied potentials were used to obtain different surface oxides morphologies (20 and 30 V). The characterization and quantification of the generated deposits is presented as a starting point for the future application of these composite types of materials. X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy techniques showed the presence of phosphor compounds and anatase (TiO2) as the main constitutive phases.

    Potentiostatic anodizing of commercially pure titanium, using ammonium phosphate and ammonium fluoride solution as electrolyte is studied. The objective is to generate titanium oxides on the surface and phosphor compounds presenting good protective and mechanical properties, and proper adhesion to the metal substrate to remain during surgical orthopedic procedures (implants). Two different applied potentials were used to obtain different surface oxides morphologies (20 and 30 V). The characterization and quantification of the generated deposits is presented as a starting point for the future application of these composite types of materials. X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy techniques showed the presence of phosphor compounds and anatase (TiO2) as the main constitutive phases.

  • 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.

  • Silica-based hybrid coatings for corrosion protection of carbon steel. Part I: Effect of pretreatment with phosphoric acid

     Santana, Ianina; Pepe, Andrés; Jimenez Pique, Emilio; Pellice, Sergio; Ceré, Silvia
    Surface and coatings technology
    Date of publication: 2012-09-13
    Journal article

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    This work studies the synthesis and characterization of hybrid organic–inorganic coatings based on silica to improve the corrosion resistance of carbon steel. Hybrid organic–inorganic silica sol–gel coatings were obtained by dipping in an organically modified silica sol synthesized through hydrolysis and condensation of 3-glicidoxipropyl-trimetoxisilano (GPTMS) and tetraethoxysilane (TEOS) in acidic catalysis. The coatings were doped with a cerium salt (Ce(NO3)3·6H2O) and loaded with silica nanoparticles in order to improve both barrier effect and the anticorrosive behavior of the coatings by the inhibitory effect of cerium. Prior to the application of the coating, some samples were treated with a phosphoric acid 2% v/v in order to improve coating adherence. A two layered coating was applied onto AISI 1010 carbon steel, the outer containing with a cerium salt and the inner one with silica nanoparticles without the cerium salt, producing homogeneous and cracks-free films. Raman spectroscopy was used to characterize the compounds present in the surface of steel after pretreatment with phosphoric acid. Microstructural characterization of coatings was performed by means of scanning electron microscopy (SEM). The evolution with time of the protective properties of films was studied by electrochemical impedance spectroscopy (EIS), providing quantitative information of the role of the pre-treatment. Electrochemical behavior in each stage of the corrosion processes was modeled by equivalent circuits. Additionally, films adhesion was evaluated by nano-scratch demonstrating that the phosphate treatment improves adhesion of the hybrid coating.

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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)

  • Nanoindentation of Al 2O 3/Al 2TiO 5 composites: Small-scale mechanical properties of Al 2TiO 5 as reinforcement phase

     Botero Vega, Carlos Alberto; Jimenez Pique, Emilio; Baudín, Carmen; Salán Ballesteros, Mª Núria; Llanes Pitarch, Luis Miguel
    Journal of the european ceramic society
    Date of publication: 2012-11
    Journal article

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  • Micro and nanomecanical behavior of mullite-based environmental barrier coatings  Open access

     Botero Vega, Carlos Alberto
    Defense's date: 2012-12-14
    Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya
    Theses

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    Mullite coatings deposited by chemical vapor deposition (CVD) have been introduced and proven as excellent candidates to protect silicon carbide (SiC) from severe pitting corrosion and recession, becoming part of the new generation of environmental barrier coatings (EBCs). In these coatings mullite columns nucleate from a thin vitreous silicon layer in contact with the substrate and can grow over a wide range of increasing Al/Si ratios in constant or graded compositions. This feature allows for obtaining Al-rich coatings at the outer surface (conferring superior corrosion protection to the substrate) while keeping the stoichiometric mullite composition at the interface (representing great adhesion because of the good match with SiC). Although the excellent performance of these coatings in corrosive environments has been proved, information about the mechanical behavior of these systems is quite limited. The mechanical properties and structural integrity of CVD mullite coatings on SiC substrates are key issues facing the implementation of these systems in real applications. The study of such aspects constitutes the basis of this investigation. Considering the compositional variations, microstructure, and thickness of CVD mullite coatings, it is essential to evaluate their mechanical properties, and the structural integrity of the coated system, from a local perspective. In this regard, nanoindentation and nanoscratch appear as the most suitable techniques for this purpose. This investigation is based on implementing nanoindentation and nanoscratch tests, together with advanced characterization techniques, to evaluate the main local mechanical properties of mullite-based EBCs as well as to investigate the structural integrity of the coated systems. In doing so, columnar mullite coatings composed of stoichiometric (¿ 3) and increasing (¿ 5, 6, 7, 8, 11) Al/Si ratios, as well as compositionally graded coatings, were accounted for. Regarding stoichiometric coatings, main mechanical properties; i.e. hardness (Hf), elastic modulus (Ef), yield strength (sy) and fracture toughness (Kf), are asessed by means of nanoindentation. As a consequence of the columnar nature of coatings as well as the vitreous silicon layer from which they grow, properties were found to be slightly lower than the ones reported for bulk stoichiometric mullite. Also, properties ascribed to the coated system such as energy of adhesion (Gint) and interface fracture toughness (Kint), are assessed. Nanoscratch tests demonstrate great resistance of coatings to the sliding contact, as considerable plastic deformation ocurrs without significant damage. The effect of coating composition on its mechanical behavior is studied through evaluation of specimens with increasing Al/Si ratios. Enrichment in Al produce hardening, stiffening and enbrittlement of mullite coatings. Nevertheless, nanoscratch tests show that structural integrity of the systems is satisfactory since no complete loss of the coating material is registered. An enhancement in Hf and Ef is also evidenced through the thickness of coatings with graded compositions. Nanoscratch tests performed in the cross section of compositionally graded mullite coatings show an optimum combination of stiffness/hardness and cohesive/adhesive scratch strength, as compared to coatings with stoichiometric or extreme Al-enriched compositions. Finally, temperature and corrosion effects on the mechanical behavior are investigated. In stoichiometric mullite, the effect of high temperature is an increase in Hf and Ef, accompanied by a decrease in Kc, whereas none of these properties are altered for Al-rich and the compositionally graded coatings. In addition, nanoscratch tests show that the effect of temperature and hot-corrosion on the structural integrity of tested coatings may be considered as negligible. This is an interesting finding as CVD mullite coatings are expected to be used in gas turbines, under sam

    Los recubrimientos de mullita depositados mediante deposición química de vapor (CVD) son excelentes candidatos para proteger el carburo de silicio (SiC) de la corrosión en ambientes de combustión, configurando la nueva generación de recubrimientos catalogados como barreras ambientales (EBCs). Estos recubrimientos de carácter columnar nuclean a partir de una fina capa vítrea rica en silicio y pueden crecer en un amplio rango de composiciones, siendo posible incrementar la proporción Al/Si de manera constante y gradiente. De este modo se obtienen recubrimientos ricos en aluminio en la superficie exterior (confiriendo al sustrato una alta protección frente a la corrosión) y a su vez se mantiene la composición estequiométrica en la intercara (lo que supone gran adhesion dado el buen ajuste mullita-SiC). A pesar de que se ha demostrado el excelente desempeño frente a la corrosion de estos recubrimientos, la información existente en la literatura acerca de su comportamiento mecánico es limitada. Las propiedades mecánicas e integridad structural de los recubrimientos de mullita depositados sobre SiC son factores cruciales a la hora de implementar dichos sistemas en aplicaciones reales. El estudio de estos aspectos constituye la base de esta investigación. Teniendo en cuenta las características de los recubrimientos, resulta esencial evaluar sus propiedades desde una perspectiva local. En este sentido, la nanoindentación y el nanorayado son las técnicas más apropiadas para tal propósito. Esta investigación se basa en la implementación de ensayos de nanoindentación y nanorayado, en complemento con técnicas avanzadas de caracterización, para evaluar a escala local las propiedades mecánicas de recubrimientos de barrera ambiental basados en mullita, así como para evaluar la integridad structural de los sistemas recubiertos. Para ello, se dispuso de recubrimientos con composiciones de Al/Si estequiométricas (≈ 3) e incrementales (≈ 5, 6, 7, 8, 11), además de recubrimientos de composición gradiente. En cuanto a los recubrimientos de composición estequiométrica, su dureza (Hf), modulo elastico (Ef), límite elastico (σy) y tenacidad de fractura (Kf), se estiman mediante nanoindentación. Como consecuencia del carácter columnar de los recubrimientos, así como de la capa vítrea de silicio a partir de la cual crecen, las propiedades mecánicas encontradas son ligeramente menores que las reportadas para mullita estequiométrica policristalina. La energía de adhesión (Gint) y la tenacidad de fractura de la intercara (Kint) son también estimadas. Estos recubrimientos presentan gran resistencia al contacto deslizante, dado que soportan deformaciones plásticas considerables sin sufrir un daño significativo. El efecto del enriquecimiento en aluminio es el endurecimiento, el aumento en la rigidez y la disminución de la tenacidad en los recubrimientos de mullita. No obstante, los ensayos de nanorayado demuestran una integridad estructural satisfactoria de los sistemas recubiertos estudiados, ya que no se observan pérdidas significativas de material del recubrimiento. Los nanorayados sobre secciones transversales indican que las capas de composición gradiente presentan una combinación óptima de rigidez/dureza y resistencia adhesiva/cohesiva al nanorayado. Finalmente, se investigan los efectos de la temperatura y corrosión sobre el comportamiento mecánico de los recubrimientos. Las altas temperaturas ocasionan un incremento de Hf y Ef, acompañado por una caida en Kc, en recubrimientos estequiométricos, mientras que dichas propiedades permanecen practicamente constantes en recubrimientos ricos en aluminio y gradientes. Adicionalmente, el efecto combinado de temperatura y corrosión tiene un efecto menor sobre la integridad estructural de los recubrimientos ensayados tras los ensayos de nanorayado. Éste es un resultado interesante dado que estos recubrimientos se espera que sean utilizadas en aplicaciones bajo condiciones similares a las aquí

  • 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.

  • 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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  • Mechanical behavior of 3Al 2O 3 2SiO 2 films under nanoindentation

     Botero Vega, Carlos Alberto; Jimenez Pique, Emilio; Seuba, J.; Kulkarni, Tushar; Sarin, Vinod K.; Llanes Pitarch, Luis Miguel
    Acta materialia
    Date of publication: 2012-09
    Journal article

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  • 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.

  • Corrosion induced degradation of textured YBCO under operation in high humidity conditions

     Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Díaz, Jordi A.; Morales, Manuel; Calleja Lázaro, Albert; Segarra Rubi, Merce
    Surface and coatings technology
    Date of publication: 2012-05-25
    Journal article

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    The early stages of aggressive degradation at 85% of humidity for 24 h of single crystals of YBa2Cu3O7 − δ textured by Bridgman technique have been analyzed by means of atomic force microscopy, X-ray photoelectron spectroscopy, nanoindentation and focused ion beam. The results show that the initial formation of barium hydroxide and the non-superconducting green phase, Y2BaCuO5, induces the surface degradation and the loss of the mechanical properties as a consequence of the mechanical transformation after the degradation process due to an embrittlement of the superficial layer.

  • Contact fatigue damage of monolayer and bilayer ceramic coatings deposited on cemented carbides  Open access

     Mateo Garcia, Antonio Manuel; Llanes Pitarch, Luis Miguel; Jimenez Pique, Emilio
    Anales de mecánica de la fractura
    Date of publication: 2012
    Journal article

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    En este trabajo se estudia el comportamiento a fatiga bajo solicitaciones de contacto de un carburo cementado WC-Co recubierto con dos películas cerámicas distintas: TiN y WC/C, ya sea como monocapas o bicapas, mediante técnicas de indentación. Los resultados obtenidos en ensayos de indentación esférica indican que la nucleación de fisuras circulares en las capas es un criterio más apropiado que la delaminación interfacial para definir las condiciones de daño crítico en los sistemas investigados. Desde esta perspectiva, se encuentra que los carburos cementados recubiertos son susceptibles a ser degradados mecánicamente bajo solicitaciones de contacto cíclicas, aunque la sensibilidad a fatiga y el escenario de daño efectivos difieren en cada caso, en función de la naturaleza cerámica (cristalina/amorfa) y la arquitectura (mono- o bicapa) del recubrimiento.

  • Contact damage and residual strength in hardmetals

     Góez Úsuga, Alexey; Coureaux Mustelier, David; Ingebrand, A.; Reig, B.; Tarres, Elena; Mestra Rodríguez, Alvaro Miguel; Mateo Garcia, Antonio Manuel; Jimenez Pique, Emilio; Llanes Pitarch, Luis Miguel
    International journal of refractory metals and hard materials
    Date of publication: 2012-01
    Journal article

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    Anodic oxidation of titanium for implants and prothesis: processing characterization and potential improvement of osteointegration  Open access

     Pavon, Juan José; Galvis, Oscar; Echevarria, F; Castaño, J; Echeverry, M; Robledo, S; Jimenez Pique, Emilio; Mestra Rodríguez, Alvaro Miguel; Anglada Gomila, Marcos Juan
    Congreso Latinoamericano de Ingeniería Biomédica
    Presentation's date: 2011
    Presentation of work at congresses

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    Among all biomaterials used for bone replacement, it is recognized that both commercially pure titanium (Ti c.p.) and Ti6Al4V alloy are the materials that show the best in vivo performance due to their excellent balance between mechanical, physical-chemical and biofunctional properties. However, one of its main drawbacks, which compromise the service reliability of the implants and its osteointegration capacity, is the thin film of fibrous tissue around the implant due to the bioinert behaviour of titanium. One of the alternatives more studied to improve the titanium osteointegration is the surface modification through the control of the roughness parameters within a specific range which is recognized that improve the osteoblasts adhesion. In this work is investigated the influence of different electrochemical processing conditions for surface modification of c.p. Ti, in their microstructural, morphological, topographical and mechanical properties, as well as in their biological behaviour. The electrochemical anodizing treatment was performed by using different electrolytes based on phosphoric acid (H3PO4), sulphuric acid (H2SO4) with a fluoride salt; and the Focused Ion Beam (FIB) technique, normally named as Nanolab, was used for the microstructural, chemical and morphological characterization, as well as the confocal laser microscopy technique which also served for roughness measurements. The mechanical response of the anodic layers was evaluated through the using of a scratch tester which showed the critical loads for the coating damages. The characterization results showed that both, concentrations and electrolyte species, clearly influenced the morphological and topographical features, as well as the chemical composition of the anodic layer. By using the FIB was possible to detect nanopores within both the surface and the bulk of the coating. Some of the conditions generated a very special coating morphology which promoted a better osteoblasts adhesion. Contrary to what it was a priory expected, all anodic coatings showed high critical loads for damages during scratch test, despite their high porosity, which could be related with some defects coalescence mechanism that allows dissipating the high stress concentration applied during the test.

  • Nanoindentación y nanorayado de secciones transversales en recubrimientos de barrera ambiental

     Botero Vega, Carlos Alberto; Jimenez Pique, Emilio; Kulkarni, Tushar; Sarin, Vinod K.; Llanes Pitarch, Luis Miguel
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2011-04-07
    Presentation of work at congresses

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    Estudio de la morfología de grietas generadas por nanoindentación y su efecto en el cálculo de la tenacidad de fractura  Open access

     Cuadrado Lafoz, Núria; Jimenez Pique, Emilio; Casellas Padro, Daniel; Anglada Gomila, Marcos Juan
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2011-04-07
    Presentation of work at congresses

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    En el presente trabajo se ha utilizado la técnica de nanoindentación para inducir grietas en diferentes materiales cerámicos y estudiar la morfología de grieta generada por la aplicación de un indentador tipo Berkovich. El estudio morfológico de las grietas se ha llevado a cabo mediante pulido secuencial y la técnica de microscopía de haz de iones focalizados (FIB/SEM). Para la geometría de indentador utilizada y la morfología de grieta obtenida, se ha llevado a cabo un estudio de la aplicabilidad de las expresiones más comúnmente utilizadas para el cálculo de la tenacidad de fractura en materiales frágiles por indentación. Previamente al estudio de la validez de las ecuaciones, para poder obtener una medida de Kc fiable, se ha realizado una calibración de las ecuaciones para la geometría de indentador tipo Berkovich.

  • Fractura por contacto en recubrimientos feldespáticos sobre circona dental

     Rueda Arango, Astrid Oasis; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2011-04-07
    Presentation of work at congresses

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    Las restauraciones dentales de circona con recubrimientos feldespáticos se están empleando de manera creciente en aplicaciones dentales debido a su estabilidad química, buena respuesta mecánica y apariencia externa. Sin embargo se han reportado fallos en los recubrimeintos, como por ejemplo el desportillamiento, atribuibles a su baja tenacidad de fractura. Los ensayos de contacto Hertziano permite evaluar el papel de la microestructura frente a la respuesta mecánica de los materiales cerámicos dentales. Así, en este trabajo, se evaluó la respuesta de la porcelana feldespática (Vita VM9) sobre circona dental (3Y-TZP) frente a ensayos de contacto esférico monótono. Los resultados mostraron que el daño producido durante la indentación es de carácter frágil, produciendose fisuras anillo en la superficie. Adicionalmente swe realizó una reconstrucción temográfica del daño por indentación, la cual registró la existencia de fisuras cónicas que se desarrollan dentro del recubrimiento sin llegar a la intercara. Así mismo, no se observó otro tipo de daño secundario, tal como grietas radiales o de laminación.

  • Cross-sectional nanoindentation and nanoscratch of compositionally graded mullite films

     Botero Vega, Carlos Alberto; Jimenez Pique, Emilio; Kulkarni, Tushar; Fargas Ribas, Gemma; Sarin, Vinod K.; Llanes Pitarch, Luis Miguel
    Surface and coatings technology
    Date of publication: 2011-12-25
    Journal article

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  • Influence of the elastic mismatch on the Hertzian cone crack path in ceramic bilayers

     Ceseracciu, Luca; Anglada Gomila, Marcos Juan; Jimenez Pique, Emilio
    Journal of the european ceramic society
    Date of publication: 2011-10-01
    Journal article

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    Contact damage is a key aspect in the structural integrity of ceramics, particularly ceramic coatings and multilayers that may have an elastic mismatch. An understanding of the critical load and trajectories of the crack produced by contact loads in such materials is valuable to characterize the damage tolerance and improve their reliability. In this work, the Hertzian cone crack initiation and propagation in brittle bilayers has been studied by FEM and verified by experimental observations. It was concluded that the elastic mismatch affects the crack initiation position and critical load for cone cracking. Critical loads are lower in bilayers than in monolithic materials. Cone crack trajectory and the corresponding fracture energy release rate are also affected by the elastic mismatch, which thus influences the damage tolerance of the system.

  • Surface Nitriding of 3Y-TZP

     Valle Chiro, Jorge
    Defense's date: 2011-11-03
    Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya
    Theses

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