arXiv subjects

Jérôme Chevalier

Publications and source records attributed to Jérôme Chevalier.

17 recordsLinked to original sources

arXiv2018

Atomic force microscopy study of the surface degradation mechanisms of zirconia based ceramics

Atomic force microscopy (AFM) can be used to characterise several aspects of the surface degradation and reinforcement mechanisms of zirconia based ceramics, such as crack propagation, martensitic relief formation, grains pull-out and transformation toughening. AFM can also be used to quantify precisely the transformation and provide reliable parameters for long term degradation prediction. In particular, the tetragonal to monoclinic (t-m) phase transformation of zirconia has been the object of extensive investigations of the last twenty years, and is now recognised as being of martensitic nature. New strong evidences supporting the martensitic nature of the transformation are reported here. These observations, considering their scale and precision, are a new step toward the understanding of the t-m phase transformation of zirconia and related degradation mechanisms.

cond-mat.mtrl-sci↗

arXiv2018

Reliability assessment in advanced nanocomposite materials for orthopaedic applications

Alumina-zirconia nano-composites were recently developed as alternative bearing materials for orthopedics. Previous, preliminary reports show that such alumina-zirconia nanocomposites exhibit high crack resistance and low wear rate. In this paper, additional information is given in terms of wear, crack resistance and ageing behaviour: femoral heads are inspected after 7 million cycles of wear testing on a hip simulator, crack resistance is measured and compared to other ceramics used today in orthopedics, slow crack growth is reported under static and cyclic fatigue, and aging resistance is assessed. We also report on the load to failure of femoral heads prototypes during compression tests. This overall reliability assessment ensures a potential future development for these kinds of new nanocomposites in the orthopedic field.

physics.app-ph↗

arXiv2018

Nanostructured Ceramic Oxides with a Slow Crack Growth Resistance Close to Covalent Materials

Oxide ceramics are sensitive to slow crack growth because adsorption of water can take place at the crack tip, leading to a strong decrease of the surface energy in humid (or air) conditions. This is a major drawback concerning demanding, long-term applications such as orthopaedic implants. Here we show that a specific nanostructuration of ceramic oxides can lead to a crack resistance never reached before, similar to that of covalent ceramics.

cond-mat.mtrl-sci↗

arXiv2018

Percolative Mechanism of Aging in Zirconia-Containing Ceramics for Medical Applications

Recently, several episodes of fracture of zirconia ceramic femoral heads of total hip prostheses have alarmed the medical and scientific community regarding aging problems in zirconia prostheses. Such fractures cause immediate local tissue reactions, which require urgent medical intervention to prevent further complications. As a result, it has been promoted that yttria-stabilized zirconia (Y-TZP) hip prostheses be substituted by alumina and alumina/Y-TZP ceramics. In the present investigation, we have found an upper limit of Y-TZP concentration in alumina/Y-TZP composites (16 vol.%) to avoid future aging problems. This limit coincides with the percolation threshold measured by infrared (IR) reflectance in a series of alumina/Y-TZP composites.

physics.app-ph↗

arXiv2018

Martensitic transformation in zirconia. Part I: nanometer scale prediction and measurement of transformation induced relief

We investigate by atomic force microscopy (AFM) the surface relief resulting from martensitic tetragonal to monoclinic phase transformation induced by low temperature autoclave aging in ceria-stabilized zirconia. AFM appears as a very powerful tool to investigate martensite relief quantitatively and with a great precision. The crystallographic phenomenological theory is used to predict the expected relief induced by the transformation, for the particular case of lattice correspondence ABC1, where tetragonal c axis becomes the monoclinic c axis. A model for variants spatial arrangement for this lattice correspondence is proposed and validated by the experimental observations. An excellent agreement is found between the quantitative calculations outputs and the experimental measurements at nanometer scale yielded by AFM. All the observed features are explained fully quantitatively by the calculations, with discrepancies between calculations and quantitative experimental measurements within the measurements and calculations precision range. In particular, the crystallographic orientation of the transformed grains is determined from the local characteristics of transformation induced relief. It is finally demonstrated that the strain energy is the controlling factor of the surface transformation induced by low temperature autoclave treatments in this material.

cond-mat.mtrl-sci↗

arXiv2018

Martensitic transformation in zirconia. Part II: Martensite growth

Though the martensitic transformation in zirconia has been the object of a very large number of studies for the last decades, qualitative and quantitative observations of the formation and growth of relief induced by low temperature treatments has hardly ever been reported. In the first part of the study, we have demonstrated the excellent agreement between the atomic force microscopy quantitative observations and the outputs of the calculations derived from the phenomenological theory of martensitic transformation. The intermediate stages of transformation were nonetheless not considered. In this second part, the growth mechanisms of monoclinic phase resulting from the martensitic transformation in ceria-stabilized zirconia (10 mol% CeO2) are investigated. Surface transformation is induced by ageing treatments in water vapor at 413 K. The observations are rationalized by the recent analysis proposed for the crystallographic ABC1 correspondence choice, where the ct axis transforms to the cm axis. Three growth modes are observed and interpreted in terms of transformation strains accommodation. Microcracks formation is observed, explaining grain pop-out where the crystallographic disorientation between two adjacent grains is the largest. The influence of grain boundary paths on the surface relief features is demonstrated. Overall, our results strongly support the non-existence of a critical grain size for low temperature transformation, confirmed by the classical thermodynamics theory applied to this particular case.

cond-mat.mtrl-sci↗

arXiv2018

Critical effect of cubic phase on aging in 3 mol% yttria-stabilized zirconia ceramics for hip replacement prosthesis

The isothermal tetragonal-to-monoclinic transformation of 3Y-TZP ceramics sintered at two different temperatures (1450°C and 1550°C) and duration (2 and 5 h) is investigated at 134°C in steam. Particular attention is paid to the presence of a cubic phase and its effect on isothermal aging. Sintering at 1550°C can result in a significant amount of large cubic grains in the specimens, that have a detrimental impact on aging resistance, especially for the first stage of the aging process. Cubic grains appear to be enriched in yttrium, which in turn leads to a depletion of yttrium in the neighboring tetragonal grains. These grains will act as nucleation sites for tetragonal-to-monoclinic transformation. Even for specimens sintered at lower temperature, i.e. 1450°C, the presence of a cubic phase is expected from the phase diagram, leading to a significant effect on aging sensitivity.

cond-mat.mtrl-sci↗

arXiv2018

Influence of surface finish and residual stresses on the ageing sensitivity of biomedical grade zirconia

We demonstrate in this paper the influence of surface finish on the ageing kinetics of biomedical grade zirconia. The critical influence of polishing has been systematically investigated by optical microscopy, atomic force microscopy and X-ray diffraction. The stress state around polishing scratches gives rise to preferential transformation in the zone of the induced scratches and consequently to accelerated ageing. The influence of residual stresses is analyzed semi-quantitatively by preparing samples with various surface finish, thus with various stress states. Rough polishing produces a compressive surface stress layer beneficial for the ageing resistance, while smooth polishing produces preferential transformation nucleation around scratches. When a thermal treatment of 2 h at 1200 °C is applied to relax the residual stresses, all the surfaces states exhibit the same sensitivity to ageing. These results demonstrate that roughness alone cannot be used for ensuring a long-term stability. The variation of ageing sensitivity is indeed related indirectly to the surface roughness via the induced surface stress state. The current ISO standards are not able to take these effects into account. Indeed, great variations in ageing kinetics were observed for samples with different surface states, although all well below the ISO requirements.

cond-mat.mtrl-sci↗

arXiv2018

Low-temperature ageing of zirconia-toughened alumina ceramics and its implication in biomedical implants

Changes in crystalline phases resulting from low-temperature ageing of different yttria doped and non-doped zirconia-toughened alumina composites and nanocomposites were investigated under controlled humidity and temperature conditions in autoclave. A classical powder mixing processing route and a new modified colloidal processing route were used to process the composites. Different compositions ranging from 2.5 wt.% zirconia in a matrix of alumina to pure zirconia (3Y-TZP) were studied. It was observed that Al2O3+yttria stabilised ZrO2 composites exhibited significant ageing. However, ageing was much slower than traditionally observed for Y-TZP ceramics, due to the presence of the alumina matrix. Ageing was clearly limited for zirconia content beyond 25 wt.%. On the other side of the spectrum, Al2O3+2.5 wt.% ZrO2 initially presented a monoclinic fraction but did not show any ageing degradation. These composites seem to represent the best choice between slow crack growth and ageing resistance.

cond-mat.mtrl-sci↗

arXiv2018

Accelerated Aging in 3 mol%-Yttria-Stabilized Tetragonal Zirconia Ceramics Sintered in Reducing Conditions

The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP) ceramics sintered in air and in reducing conditions was investigated at 140°C in water vapor. It was observed by X-ray diffraction (XRD) that 3Y-TZP samples sintered in reducing conditions exhibited significantly higher tetragonal-to-monoclinic transformation than samples with similar density and average grain size values but obtained by sintering in air. This fact is explained by the increase of the oxygen vacancy concentration and by the presence at the grain boundary region of a new aggregate phase formed because of the exolution of Fe2+ ions observed by X-ray photoelectron spectroscopy.

cond-mat.mtrl-sci↗

arXiv2017

Atomic force microscopy study of the tetragonal to monoclinic transformation behaviour of silica doped yttria-stabilized zirconia

The tetragonal to monoclinic phase transformation of zirconia has been the subject of extensive studies over the last 20 years [1-4]. The main features of the transformation have been identified and its martensitic nature is now widely recognised [5-8]. More specifically, the relevance of a nucleation and growth model to describe the transformation is widely accepted. Recent fracture episodes [9] of zirconia hip joint heads were reported, failures related to the t-m transformation degradation. Among the materials solutions considered for decreasing the sensitivity to t-m phase transformation, the possibility of adding silica as a dopant appears as an appealing one. Previous studies have revealed the beneficial effect of silica addition by the formation of a glassy phase at the grain boundaries and triple points. This glassy phase has been proven to reduce the residual stresses level [10], slowing down the transformation kinetics. Preliminary quantitative investigations by XRD have shown these materials are less susceptible to transformation. However, the mechanism by which the transformation propagated has still to be assessed.

cond-mat.mtrl-sci↗

arXiv2017

Atomic force microscopy of transformation toughening in ceria-stabilized zirconia

We demonstrate in this paper that atomic force microscopy can be successfully used to gain further insights into the understanding of transformation toughening in ceria stabilized zirconia. Transformation was induced by stresses accumulated in the region surrounding propagating cracks in double torsion samples. The resolution provided by AFM at the surface of the samples made it possible to observe the formation of self accommodated martensite pairs in the near crack areas. The potential for transformation is found to decrease with increasing alloying addition, and is totally suppressed for 16 mol.% CeO2-TZP samples. A statistical analysis of the martensite pair orientation is performed, and the relationship with the applied stress and strain fields is discussed. The contribution to transformation toughening by transformation-induced plasticity occurring in the formation of martensitic variant pairs with small net shear is demonstrated. The influence of alloying addition content on the potential for transformation toughening and fracture toughness values is finally discussed.

cond-mat.mtrl-sci↗

arXiv2017

Microstructural investigation of the aging behavior of $(3Y-TZP)-Al_2O_3$ composites

The low temperature autoclave aging behavior of zirconia toughened alumina composites processed by a classical powder mixing processing route was analyzed using atomic force microscopy (AFM), scanning electron microscopy and X-Ray diffraction. The transformation was evaluated in terms of nucleation and growth, assessed by XRD. The time-temperature equivalency of the transformation was used to measure an apparent activation energy of the nucleation stage of the transformation of 78kJ/mol. The microstructural features influencing the transformation were identified, and the influence of the alumina matrix on the transformation was investigated. Transformation progression grain by grain was observed by AFM. Transformation does not only occur in zirconia agglomerates but also in isolated zirconia grains. The matrix could partially inhibit the transformation. This behavior could be rationalized considering the constraining effect of the alumina matrix, shape strain accommodation arguments and microstructural homogeneity effects.

cond-mat.mtrl-sci↗

arXiv2017

A critical comparison of methods for the determination of the ageing sensitivity in biomedical grade yttria stabilized zirconia

Since the recent failure events of two particular series of zirconia femoral heads for total hip replacement prosthesis, a large decrease in the use of zirconia ceramics for orthopaedic implants has been observed. In spite of the biomedical success of this material during the last ten years, this was required for safety reasons, until the cause of the failures is known. It has been shown that these failures were related to the low temperature hydrothermal degradation (also known as ageing). Thus it is crucial to better understand the ageing behaviour, in order to be able to assess its importance and then control it if required. In this paper, various techniques relevant to assess the hydrothermal degradation sensitivity of biomedical grade yttria stabilized zirconia are discussed and compared. The expected outputs of conventional methods, i.e. X-Ray diffraction and scanning electron microscopy are examined. More recent methods like optical interferometry and atomic force microscopy are presented, with their respective benefits and drawbacks. An up to date comparison of these different techniques is provided, and their use for ensuring the long term reliability of a particular batch of zirconia in terms of ageing degradation is demonstrated.

cond-mat.mtrl-sci↗

arXiv2017

Modeling the aging kinetics of zirconia ceramics

Yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) with different microstructures were elaborated. The isothermal tetragonal to monoclinic transformation was investigated at 134 °C in steam by X-ray diffraction, Atomic Force Microscopy (AFM) and optical interferometry. The aging kinetics were analyzed in terms of nucleation and growth, using the Mehl-Avrami-Johnson (MAJ) formalism. Numerical simulation of the aging of zirconia surfaces was also conducted, and the results were used to better fit the aging kinetics. The simulation shows that the exponent of the MAJ laws is controlled not only by the nucleation and growth mechanisms, but also - and mainly - by their respective kinetic parameters. Measurements of nucleation and growth rates at the surface, at the beginning of aging, and the use of numerical simulation allow the accurate prediction of aging kinetics.

cond-mat.mtrl-sci↗

arXiv2017

Martensitic relief observation by atomic force microscopy in yttria stabilized zirconia

The tetragonal to monoclinic (t-m) phase transformation of zirconia has been the object of extensive investigations of the last twenty years, and is now recognised as being of martensitic nature. However, martensitic transformation has only been observed by transmission electron microscopy or indirect methods. Though the benefit on the fracture toughness and crack resistance was the main interest, the transformation is now considered for its consequences on the degradation of the material. The use of AFM reported here allowed the observation of the first stages of martensite relief growth and of new martensitic features.

cond-mat.mtrl-sci↗

arXiv2017

Atomic force microscopy study and qualitative analysis of martensite relief in zirconia

A recent report [S. Deville et al., J. Am. Ceram. Soc., 86(12), 2225 (2003)] has shown the new possibilities offered by atomic force microscopy (AFM) to investigate martensitic transformation induced relief in zirconia. In this paper, we studied qualitatively the surface relief resulting from martensitic tetragonal to monoclinic phase transformation in yttria and ceria-doped zirconia by AFM. AFM appears as a very powerful tool to investigate martensite relief with a great precision. The phenomenological theory of martensitic crystallography could be succesfully applied to explain all the observed features. The formation conditions of the martensite are discussed, as well as ways of accommodating locally the transformation strain, i.e. self-accommodating variant pairs and microcracking. Variants growth sequences are observed. These observations bring new insights and explanations on the transformation initiation and propagation sequences.

cond-mat.mtrl-sci↗