Roitero, E.; Lasserre, F.; Roa, J.J.; Anglada, M.; Mücklich, F.; Jimenez-Pique, E. Journal of the european ceramic society Vol. 37, num. 15, p. 4876-4887 DOI: 10.1016/j.jeurceramsoc.2017.05.052 Data de publicació: 2017-12 Article en revista
The aim of this study is to characterize in detail the microstructural changes and collateral damage induced by direct laser patterning on the surface of dental-grade zirconia (3Y-TZP) employing an interference setup with the 532 and 355. nm harmonics of a Nd:YAG laser (pulse duration of 10. ns).Laser-material interaction mainly results in thermal effects for both wavelengths studied. Upon laser irradiation the material locally melts producing pattern and establishing a steep thermal gradient on the surface. This generates a. ~. 1. µm thick heat affected zone where microcracking, directional recrystallization, phase transformation (from tetragonal to monoclinic, t ¿. m) and texturization (ferroelastic domain switching) take place. In addition, surface coloration results from the activation of F-centers as a consequence of high energy radiation exposure. No chemical segregation or diffusion was detected. All these microstructural changes should be taken into account to ensure integrity and long-term reliability of the zirconia components.
Rubio-Marcos, F.; Fernández, J.F; Ochoa, D. A.; Garcia, J. E.; Rojas-Hernandez, R. E.; Castro, M.; Ramajo, L. Journal of the european ceramic society Vol. 37, num. 11, p. 3501-3509 DOI: 10.1016/j.jeurceramsoc.2017.04.045 Data de publicació: 2017-09 Article en revista
Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO3-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xZr5x/4]O3 lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.
Ochoa, D. A.; Esteves, G.; Iamsasri, T.; Rubio-Marcos, F.; Fernández, J.F; Garcia, J. E.; Jones, J.L. Journal of the european ceramic society Vol. 36, num. 10, p. 2489-2494 DOI: 10.1016/j.jeurceramsoc.2016.03.022 Data de publicació: 2016-08 Article en revista
The origins of high piezoelectric properties in the lead-free (K,Na)NbO3-based tetragonal composition (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNL-NTS) is investigated by quantifying the intrinsic and extrinsic contributions from high energy X-ray diffraction measurements. The applied methodology, which allows discerning between the intrinsic contribution, related to the field induced lattice distortion, and the extrinsic contributions, related to non-180° domain wall motion, is widely described in this work. The non-180° domain reorientation of the KNL-NTS piezoceramic is quantify from the integrated intensities of the 002 and 200 reflections obtained from line profile, while the shifts in peak position versus the applied electric field is used to obtain the lattice strain contribution. Large non-180° domain wall contribution to the electric field induced macroscopic strain (80% of the macroscopic strain) is verified in KNL-NTS.
Flamant, Q.; Marro, F.G.; Roa, J.J.; Anglada, M. Journal of the european ceramic society Vol. 36, num. 1, p. 121-134 DOI: 10.1016/j.jeurceramsoc.2015.09.021 Data de publicació: 2016-01-01 Article en revista
Rough surfaces have been shown to promote osseointegration, which is one of the keys for a successful dental implantation. Among the diverse treatments proposed to roughen zirconia, hydrofluoric acid (HF) etching appears to be a good candidate, however little is known about this process. In this work, the effect of HF concentration and etching time on the surface topography and chemistry of yttria-stabilized zirconia was assessed. Besides, to understand the etching mechanism, the reaction products present in solution and on the surface were characterized. The results indicate suitable parameters for a fast and uniform roughening of zirconia. The formation of adhered fluoride precipitates on the surface is reported for the first time and highlights the importance of cleaning after etching. Finally, it is shown that monitoring the time allows controlling the surface roughness, smooth rough transition and fractal dimension, which should make possible the fabrication of implants with an optimal topography. (C) 2015 Elsevier Ltd. All rights reserved.
Among the diverse treatments proposed to promote the osseointegration of zirconia dental implants, hydrofluoric acid (HF) etching appears to be a good candidate. However little is known on the effect of this process on the mechanical properties and long-term reliability. In this work, the surface integrity, the flexural strength and the ageing sensitivity of yttria-stabilized zirconia were assessed after etching in HF 40%. Results show that etching induces an increase of monoclinic phase content and a decrease in flexural strength. The strength decrease is limited to 15% for etching times below 60 min, whereas it reaches 29% after 120 min because of the formation of large etching pits. No substantial change in the ageing sensitivity was evidenced. Within the limits of this study, HF 40% etched zirconia appears to be reliable for long-term implantation provided that the etching duration does not exceed 60 mm. (C) 2015 Elsevier Ltd. All rights reserved.
Melk, L.; Turon-Vinas, M.; Roa, J.J.; Antti, M.; Anglada, M. Journal of the european ceramic society Vol. 36, num. 1, p. 147-153 DOI: 10.1016/j.jeurceramsoc.2015.09.017 Data de publicació: 2016-01-01 Article en revista
The fracture toughness, Ric of two 3Y-ZrO2 with different grain size (177 and 330 nm) and 12Ce-ZrO2 were determined from a sharp micro-machined notch by Ultra-Short Pulsed Laser Ablation (UPLA) where a micro-cracked zone and non-transformed is generated in front of the notch. The notch plus the damage behaved as an unshielded edge surface crack. The fracture stress, sigma(f) of both 330 nm-3Y-ZrO2 and 12Ce-ZrO2 with similar short crack sizes were found to be comparable in despite of their different published R-curves. The results of K-IC were discussed in terms of the type of cracks induced and by using a simple R-curve model. It was concluded that for the development of high strength composites with 12Ce-ZrO2 as the matrix, the relevant K-IC that controls the sigma(f) with surface unshielded short cracks is much closer to the intrinsic K-IC than to the indentation K-IC or to the plateau K-IC of long cracks. (C) 2015 Elsevier Ltd. All rights reserved.
The surface microstructure induced after grinding and annealing 3 mol% Y2O3 stabilized tetragonal zirconia was investigated in a range of annealing temperatures between 1200 and 1600 °C. For annealing temperatures close to 1200 °C, a surface nano-grain size layer was formed, while annealing at 1600 °C induced a very high fraction of surface grains of size and yttrium content higher than the bulk. The use of TEM-EBSD observation along the surface of the specimen ground and annealed at 1200 °C also revealed the existence of a (0 1 0) preferential orientation.
The present review is focused on SrO- and MgO-doped lanthanum gallates (LSGMs), specifically in those key aspects related to their implementation as electrolyte for Intermediate Temperature Solid Oxide Fuel Cells. After a brief survey of the state-of-the-art for the LSGMs, the attention is focused on the ionic transport properties for the relevant compositions. The design, manufacturing and performance of cells using LSGM as electrolyte are discussed along the review. Particular interest is given to the impact of synthesis routes for lowering their sintering temperatures. A short discussion on the chemical compatibility between electrolyte and electrodes in cells is also included. Afterwards, mechanical and thermal properties of LSGMs reported determined though conventional methods at different working temperatures are discussed. Finally, the microstructural and compositional effects related to their electrical and mechanical properties at micro- and nanometric length scale are assessed as a complementary tool for future developments in solid electrolyte materials.
In the dental field, Yttria-doped Tetragonal Polycrystalline Zirconia (Y-TZP) plays an important role due to its high mechanical properties, good aesthetics and bio-inert behavior. Surface mechanical properties are crucial for Y-TZP especially when it comes to osseointegration or contact loading, since it may undergo a spontaneous aging phenomenon when exposed to humid environment, creating a thin degraded layer that affects surface integrity. In this work, polished samples of Y-TZP have been artificially aged, and micropillars with diameters in the range 3.3-0.3 mu m have been milled by FIB inside the degraded layer and in the reference non-aged surface. Reproducible stress strain curves were obtained by testing the micropillars in compression, demonstrating that this technique is suitable for assessing the degraded surface properties. Mechanical and failure behavior are significantly different for the degraded micropillars due to the presence of microcracks, while important differences are observed when reducing the micropillar diameter. (C) 2015 Elsevier Ltd. All tights reserved.
Roa, J.J.; Jimenez-Pique, E.; Verge, C.; Tarrago, J.; Mateo, A.; Fair, J.; Llanes, L. Journal of the european ceramic society Vol. 35, num. 13, p. 3419-3425 DOI: 10.1016/j.jeurceramsoc.2015.04.021 Data de publicació: 2015-11-01 Article en revista
The intrinsic hardness of the constitutive phases in WC-Co composites is investigated by combining experimental and statistical analysis nanoindentation techniques. It is done on the basis of considering the cemented carbide material as effectively heterogeneous at the microstructure scale, i.e. consisting of three phases defined by either different chemical nature (carbides and binder) or distinct carbide crystal orientation (i.e. with surface normal perpendicular to either basal or prismatic planes). As main outcome, experimentally measured and statistically significant intrinsic hardness values for the defined phases (WC and constrained metallic binder) are analyzed and determined. Besides the evidence of crystal anisotropy for the WC phase, they permit to identify and account the expected strengthening of the plastic-constrained metallic binder, a critical input parameter for hardness and toughness modelling as well as for microstructural design optimization of ceramic composites reinforced by ductile metallic ligaments. (C) 2015 Elsevier Ltd. All rights reserved.
Cuadrado, N.; Seuba, J.; Casellas, D.; Anglada, M.; Jimenez-Pique, E. Journal of the european ceramic society Vol. 35, num. 10, p. 2949-2955 DOI: 10.1016/j.jeurceramsoc.2015.03.031 Data de publicació: 2015-09-01 Article en revista
When indenting a brittle material with a sharp indenter, cracks can be generated at the corners of the imprint. From the length of these cracks, the fracture resistance can be estimated. This technique is simple and allows characterizing small volumes of materials, especially if nanoindentation cube-corners tips are used. For evaluation of fracture resistance, a number of different models based on crack morphology have been proposed. However, the morphology of the cracks is difficult to determine due to the small scales involved. In this work, indentation fracture with a cube-corner nanoindentation tip on different materials is investigated by FIB tomography to obtain the generated crack morphology. Experimental observations are rationalized in terms of applied load, tip geometry and crystal anisotropy. Once the crack morphology is visualized, the two most commonly used equations for calculating the fracture resistance are discussed. Finally, guidelines for better estimation of fracture resistance are proposed. (C) 2015 Elsevier Ltd. All rights reserved.
The determination of the fracture toughness in a well characterized gas pressure sintered silicon nitride by the single edge V-notch beam method is analyzed in specimens with a surface shallow sharp notch produced by ultra-short pulsed laser ablation. The fracture surfaces and the damage in front of the notch tip are analyzed in detail by using focus ion beam/scanning electron microscopy and micro-Raman spectroscopy. It is concluded that the fracture toughness can be successfully determined by this technique and its importance for nano-grain size ceramics is outlined
The annealing of hydrothermal aged zirconia has been studied by analysing the changes in microstructure and surface mechanical properties in terms of the annealing temperature. In this experimental work, a systematic micro- and nanomechanical study has been conducted in 3 mol% yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP) aged at 134 degrees C for 60 h and annealed at 600 degrees C and 850 degrees C for 1 h. Advance characterization techniques (micro-Raman, field emission scanning electron microscopy and focused ion beam) have been used to study the near surface microstructural changes induced by these treatments. The mechanical properties and resistance to damage of the near surface are determined by means of nanoindentation and nanoscratch testing. The observed behaviour is discussed in terms of the change in microstructure induced after ageing and annealing.
Vendrell, X.; Garcia, J. E.; Bril, X.; Ochoa, D. A.; Mestres, L.; Dezanneau, G. Journal of the european ceramic society Vol. 35, num. 1, p. 125-130 DOI: 10.1016/j.jeurceramsoc.2014.08.033 Data de publicació: 2015-01-01 Article en revista
ZrO2 and TiO2 modified lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics are prepared by a conventional solid-state reaction. The effect of acceptor doping on structural and functional properties is investigated. A decrease in the Curie temperature and an increase in the dielectric constant values are observed when doping. More interestingly, an increase in the coercive field E-c and remanent polarization P-r is observed. The piezoelectric properties are greatly increased when doping with small concentrations dopants. ZrO2 doped ceramic exhibits good piezoelectric properties with piezoelectric coefficient d(33) = 134 pC/N and electromechanical coupling factor k(p) = 35%. It is verified that nonlinearity is significantly reduced. Thus, the creation of complex defects capable of pinning the domain wall motion is enhanced with doping, probably due to the formation of oxygen vacancies. These results strongly suggest that compositional engineering using low concentrations of acceptor doping is a good means of improving the functional properties of KNN lead-free piezoceramic system. (C) 2014 Elsevier Ltd. All rights reserved.
Fracture toughness of submicron grain size tetragonal zirconia polycrystals doped with 3 mol% yttria (3Y-TZP) is measured by the single edge V-notch beam (SEVNB) method from a shallow sharp notch produced by ultra-short pulsed femtolaser ablation (UPLA) on the surface of a bending bar. It is shown that the radius of the notch tip achieved is in the submicron range and the damaged volume in front of the notch tip is characterized by using focus ion beam milling and scanning electron microscopy. It consists of a narrow fully microcracked region less than similar to 4 mu m wide and similar to 15 mu m deep in front of the notch. If the extension of this region and the length of the notch are used in the determination of the fracture toughness (K-Ic) in the four bending test, the values obtained for submicron grain size 3Y-TZP are in agreement those obtained by using very sharp cracks. It is concluded that the SEVNB testing method with a sharp notch induced by UPLA may be used for K-Ic testing of submicron grain size ceramics. (C) 2014 Elsevier Ltd. All rights reserved.
Ceria partially stabilized zirconia ceramics (Ce-TZP) with identical grain size and different amounts of transformation toughening were processed to investigate the influence of phase transformation on static and cyclic fatigue crack growth.
Static crack growth is governed by environmentally stress induced corrosion at the crack tip and it is highly influenced by the crack shielding due to the phase transformation. Three fatigue mechanisms are expected to be operative at different proportions depending on the amount of transformation: wedge effect due to debris, degradation of bridging and modification of the shielding effect of the transformation zone. However, it is difficult to separate the contribution of the different mechanisms as grain bridging is induced by crack arrest due to phase transformation.
Molina, G.; Tite, M.; Molera, J.; Climent, A.; Pradell, T. Journal of the european ceramic society Vol. 34, num. 10, p. 2563-2574 DOI: 10.1016/j.jeurceramsoc.2014.03.010 Data de publicació: 2014-09-01 Article en revista
Valle, J.; Mestra, A.; Marro, F.G.; Anglada, M. Journal of the european ceramic society Vol. 33, num. 15-16, p. 3145-3155 DOI: 10.1016/j.jeurceramsoc.2013.06.007 Data de publicació: 2013-12 Article en revista
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.
Vendrell, X.; Garcia, J. E.; Rubio, F.; Ochoa, D. A.; Mestres, L.; Fernández, J.F Journal of the european ceramic society Vol. 33, num. 4, p. 825-831 DOI: 10.1016/j.jeurceramsoc.2012.09.025 Data de publicació: 2013-04 Article en revista
Dense lead-free (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 piezoelectric ceramics are prepared by the conventional mixed oxide method. The effect of different sintering conditions (synthetic air, O2 and Ar) on some structural, dielectric and piezoelectric properties is studied. A long sintering time (16 h) promotes the formation of a secondary phase, which is assigned to K3LiNb6O17, tetragonal tungsten-bronze. High values of longitudinal piezoelectric constant are obtained when ceramics are sintered under Ar or O2 for low dwell time (2 h). However, the nonlinear response turns out to be significantly dependent on the sintering atmosphere. Results are discussed taking into account the formation of complex defects capable of pinning domain wall when oxygen vacancies are created by sintering. Thus, sintering in an inert atmosphere appears to be a good way of reducing nonlinear response in KNN-based piezoceramics.
Morales, M.; Roa, J.J.; Pérez-Facón, J. M.; Moure, A.; Tartaj, J.; Segarra, M. Journal of the european ceramic society Vol. 32, num. 16, p. 4287-4293 DOI: 10.1016/j.jeurceramsoc.2012.07.022 Data de publicació: 2012-11-15 Article en revista
La0.85Sr0.15Ga0.8Mg0.2O3−δ pellets obtained by the polymeric organic complex solution method, isostatic pressing and sintering at 1350 °C have been electrical and mechanically studied. Electrical measurements evidenced reasonable ionic conductivities (0.01 S cm−1 at 800 °C), which were comparable to those reported for the La1−xSrxGa1−yMgyO3−δ prepared by other synthesis methods. On the other hand, the mechanical properties (elastic modulus, E and hardness, H) have been determined at micro/nanometric scale using the instrumented indentation technique. While E did not vary significantly with the increasing indentation depth (h), H values strongly decreased with the indentation depth up to 500 nm. For h > 500 nm, both mechanical properties remained almost constant, thus obtaining E = 271 ± 6 GPa and H = 13.2 ± 0.4 GPa. Finally, the residual imprints and fracture mechanisms have been observed by atomic force microscopy (AFM).
Botero, C.; Jimenez-Pique, E.; Baudín, C.; Salan, N.; Llanes, L. Journal of the european ceramic society Vol. 32, num. 14, p. 3723-3731 DOI: 10.1016/j.jeurceramsoc.2012.05.034 Data de publicació: 2012-11 Article en revista
Muñoz, J.; Jimenez-Pique, E.; Reyes, J.; Anglada, M. Journal of the european ceramic society Vol. 32, num. 15, p. 3919-3927 DOI: 10.1016/j.jeurceramsoc.2012.02.026 Data de publicació: 2012-11 Article en revista
Jimenez-Pique, E.; Ramos, A.; Muñoz, J.; Hatton, A.; Soldera, F.; Mücklich, F.; Anglada, M. Journal of the european ceramic society Vol. 32, num. 10, p. 2129-2136 DOI: 10.1016/j.jeurceramsoc.2012.02.011 Data de publicació: 2012-08 Article en revista
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.
Pérez-Delfín, E.; Garcia, J. E.; Vega, A.; Guerrero, F.; Eiras, J. A. Journal of the european ceramic society Vol. 32, num. 8, p. 1659-1665 DOI: 10.1016/j.jeurceramsoc.2011.12.024 Data de publicació: 2012-07 Article en revista
Changes in dielectric response features of lead lanthanum zirconate titanate (PLZT) ceramics by manganese addition are reported in the present work. Both the PLZT relaxor behaviour and the frequency dependence of the room temperature dielectric constant are shown to be suppressed by the addition of manganese. Similar results are obtained by applying a bias external field or by chemical reduction of PLZT samples, thus indicating the presence of an interrelationship between oxygen vacancies and the random ‘bias’ electric field. Consequently, the defects created by oxygen vacancies appear as the most important factor causing the disappearance of relaxor behaviour in Mn-doped PLZT ceramics. No modifications in the diffuse phase transition with the manganese content are found, which may be due to the persistence of compositional disorder. Additionally, it was verified that the spin glass model cannot be used to describe these observed effects.
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.
Roa, J.J.; Dias, F. T.; Martinez, M.; Padilla, J. A.; Segarra, M. Journal of the european ceramic society Vol. 32, num. 2, p. 425-431 DOI: 10.1016/j.jeurceramsoc.2011.09.013 Data de publicació: 2012-02-14 Article en revista
Since hardness is a quantitative measure of bulk mechanical properties, it can be used to examine the kinetics of crack propagation inside YBa2Cu3O7−δ (YBCO or Y-123) ceramics. YBCO samples with a tetragonal phase were oxygenated at a range of temperatures (from 250 °C to 750 °C) for different times. For each oxygenation temperature and time, hardness was measured by the nanoindentation technique, to study the defects (macro-/microcracks and porosity) produced along the c-axis. These defects were visualized by optical microscopy. The main purpose of this study was to establish the oxygenation kinetics for YBCO samples, which were textured by the top-seeded melt growth technique. We studied the evolution of hardness perpendicular to the ab-plane, as measured by the nanoindentation technique at a maximum penetration depth of 150 nm. The results indicate that the nanoindentation technique can be used successfully to monitor oxygenation and to establish the kinetics of the process.
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.
Chintapalli, R.K.; Jimenez-Pique, E.; Marro, F.G.; Yan, H.; Reece, M.; Anglada, M. Journal of the european ceramic society Vol. 32, num. 1, p. 123-132 DOI: 10.1016/j.jeurceramsoc.2011.07.037 Data de publicació: 2012-01 Article en revista
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.
Ceseracciu, L.; Anglada, M.; Jimenez-Pique, E. Journal of the european ceramic society Vol. 31, num. 11, p. 1951-1955 DOI: 10.1016/j.jeurceramsoc.2011.04.032 Data de publicació: 2011-10-01 Article en revista
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 can be optimised to protect 3Y-TZP against hydrothermal degradation and at the same time to keep the mechanical properties of the surface and the bulk unchanged. However, thermal stability is a concern that can limit its use above room temperature. In this work, surface
nitrided 3Y-TZP was heat treated in air at 200, 400, 600 and 800◦C for 8 h. Treatments up to 600◦C did not change microstructure and Vickers hardness, but heating at 800◦C produced surface defects, inner cracks and grain decohesion, conducing to a dramatic decrease in mechanical strength. Heat treatments above 400◦C led to an increase of indentation fracture toughness and to a complete loss of the hydrothermal degradation
resistance achieved by nitriding.
Roa, J.J.; Oncins, G.; Diaz, J.; Capdevila, X.G.; Sanz, Fausto; Segarra, M. Journal of the european ceramic society Vol. 31, num. 4, p. 429-449 DOI: 10.1016/j.jeurceramsoc.2010.10.023 Data de publicació: 2011-04-06 Article en revista
This paper reviews commonly used methods of analyzing and interpreting friction, adhesion and nanoindentation with an AFM tip test data, with a particular emphasis of the testing of single crystals, metals, ceramics and ceramic coatings. Experimental results are reported on the friction, mechanical and adhesion properties of these materials.
The popularity of AFM testing is evidenced by the large quantity of papers that report such measurements in the last decade. Unfortunately, a lot of information about these topics is scare in the literature. The present paper is aimed to present the basic physical modelling employed and also some examples using each technique.
Marro, F.G.; Valle, J.; Mestra, A.; Anglada, M. Journal of the european ceramic society Vol. 31, num. 3, p. 331-338 DOI: 10.1016/j.jeurceramsoc.2010.10.008 Data de publicació: 2010-11 Article en revista
Roa, J.J.; Jimenez-Pique, E.; Capdevila, X.; Segarra, M. Journal of the european ceramic society Vol. 30, num. 6, p. 1477-1482 DOI: 10.1016/j.jeurceramsoc.2009.10.021 Data de publicació: 2010-04 Article en revista
The mechanical properties of superconductor ceramics are of interest in the manufacture of superconducting devices. The current trend is to produce smaller devices (using, e.g., thin films), and the correct characterization of small volumes of material is critical. Nanoindentation is used to assess mechanical parameters, and several studies determine hardness and Young's modulus by sharp indentation. However, studies on the elasto-plastic transition with spherical indentation are scare. Here we used, spherical diamond tip indenter experiments to explore the elasto-plastic transition and to measure the yield strength of the orthorhombic phase of YBa2Cu3O7−δ (YBCO or Y-123) at room temperature. The study was carried out for a range of monodomains on the (1 0 1)-plane for Bridgman samples. Inspection of the load–unload curves for penetration depths lower than 200 nm allows for observation of the elasto-plastic transitions. Focused ion beam (FIB) trenches showed no cracking due to the indentation, although oxygenation cracks were apparent. The mean pressure for the onset of elasto-plastic deformation is 3.5 GPa, and the elastic modulus, E, calculated using the Hertzian equations is 123.5 ± 3.4 GPa.
Arciniegas, M.; Aparicio, C.; Manero, J.; Gil, F.J. Journal of the european ceramic society Vol. 27, num. 11, p. 3391-3398 DOI: 10.1016/j.jeurceramsoc.2007.02.184 Data de publicació: 2007-05 Article en revista
In order to allow the ingrowth of the living tissue and increase the mechanical anchorage of the implant, Ta and NiTi foams were obtained with similar microstructure to cancellous bone and mechanically characterized. The Ta foams were produced by chemical vapour deposition and the NiTi foams by self-propagating high temperature synthesis (SHS). The mechanical and microestructural characterization was developed using a servohydraulic testing machine and microscopy techniques.
In both materials, pores in an appropriate range of sizes and interconnectivity were observed, comparable with the nature bone morphology. Moreover, the foams showed an excellent biomechanical compatibility and compressive fatigue limit. The fatigue endurance limit set at 108 cycles showed an approximate endurance limit of 7.5 and 13.2 MPa, for the NiTi and Ta foams, respectively. These results indicate that the studied materials provide an adequate structural support, showing mechanical properties similar to the cancellous bone, especially for the Ta foam.
Bermejo, R.; Torres, Y.; Baudin, C.; Sanchez-Herencia, A.; Pascual, J.; Anglada, M.; Llanes, L. Journal of the european ceramic society Vol. 27, num. 2-3, p. 1443-1448 Data de publicació: 2007-02 Article en revista
Pavon, J.; Jimenez-Pique, E.; Anglada, M.; López-Esteban, S.; Saiz, E.; Tomsia, A. Journal of the european ceramic society Vol. 26, num. 7, p. 1159-1169 DOI: 10.1016/j.jeurceramsoc.2005.01.045 Data de publicació: 2006-07 Article en revista
Jimenez-Pique, E.; Ceseracciu, L.; Chalvet, F.; Anglada, M.; de Portu, G. Journal of the european ceramic society Vol. 25, num. 15, p. 3393-3401 DOI: 10.1016/j.jeurceramsoc.2004.09.011 Data de publicació: 2005-10 Article en revista