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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., Comment: 26 pages, 10 figures

The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP) ceramics sintered in air and in reducing conditions was investigated at 140{\deg}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., Comment: 10 pages, 3 figures

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 {\deg}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., Comment: 13 pages, 7 figures

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., Comment: 5 pages, 4 figures

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., Comment: 11 pages, 8 figures

Yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) with different microstructures were elaborated. The isothermal tetragonal to monoclinic transformation was investigated at 134 {\deg}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., Comment: 20 pages, 9 figures

This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina., Comment: International Conference on BioTribology (ICoBT 2011), Londres, 18 au 21 septembre 2011, Londres : United Kingdom (2011)