Effect of nitrogen on the kinetics of oxide scale growth and of oxygen dissolution in the Ti6242S titanium-based alloy

Titanium-based alloys are increasingly used in aircraft industry due to their good mechanical properties and low density. To reach better efficiencies, the engine design is constantly evolving and the temperature of the combustion chamber is always increasing. Then, surrounding parts are exposed to higher working temperatures and consequently have to cope with more severe oxidation phenomena. For Ti-based alloys, this leads to the formation of an external oxide scale and a large oxygen dissolution in the metal, which may be detrimental for ductility. As nitrogen is the major element of the atmosphere, it seems relevant to study its effect on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo-0.1Si titaniumbased alloy used for these applications. Thermogravimetric analyses were carried out at 650 °C for 100 h in synthetic air (20%O2–80%N2) and in a mixture of 20%O2–80%Ar. Results showed that nitrogen decreases the oxidation kinetics by slowing down the oxide scale growth but also by limiting the oxygen dissolution in the alloy

Présence du mammouth laineux (Mammuthus primigenius) au Magdalénien dans le Sud-Ouest de la France : données archéozoologiques et dates radiocarbone d’un tibia provenant de la grotte des Combarelles (Les Eyzies, Dordogne, France)

Célèbre depuis le début du XXe siècle par ses gravures, la grotte des Combarelles (Les Eyzies, Dordogne, France), a livré depuis une quarantaine d’années quelques échantillons paléontologiques lors d’interventions archéologiques ou spéléologiques ponctuelles. Parmi les collections du Musée national de Préhistoire, une portion diaphysaire d’un os long de taille importante est rapportée à un tibia non épiphysé de mammouth laineux (Mammuthus primigenius Blumenbach, 1798). En dépit de toute précision contextuelle (topographie, chrono-culture), cet os présente le double intérêt de porter des traces de découpe sur sa face caudale d’une part et d’avoir pu être directement daté d’autre part. Les deux dates radiocarbone AMS obtenues sur un fragment cortical prélevé sur ce tibia sont respectivement de 14 310 ± 70 et de 14 620 ± 100 uncal BP, soit ~ 17 500 cal BP ou ~ 15 600 cal BC. Il s’agit de la première date AMS sur os de mammouth laineux pour le Sud-Ouest de la France. Une révision de la présence de l’espèce dans les registres paléontologiques, symboliques (art pariétal et art mobilier) et économiques (industrie en ivoire) est engagée et suggère que le mammouth laineux a perduré jusqu’au début du Magdalénien supérieur dans la grande plaine d’Aquitaine et les régions limitrophes.Famous since the beginning of the XXth century for its engravings, the Combarelles cave has produced bone fragments over the last 40 years during sporadic fieldwork research in Archaeology and Speleology. Among provided samples held in the National Museum of Prehistory, a shaft of a large long bone was found and identified as an unfused tibia belonging to the woolly mammoth (Mammuthus primigenius Blumenbach, 1798). Although precise information of this discovery is still unknown (location, topographical context), this bone is important because of some cutmarks visible on its posterior side and direct radiocarbon dating. Two dates (14310 ± 70 and 14620 ± 100 uncal BP respectively, i.e. ~ 17 500 cal BP or ~ 15 600 cal BC) were obtained and are the first AMS radiocarbon dates for this species in Southwestern France. A revision of this species in the paleontological, symbolic (rock art and portable art) and economic (ivory) records is presented and suggests that the woolly mammoth had survived until the beginning of the Late Magdalenian in Aquitaine and in adjacent regions

Effet de la diffusion de l'oxygène sur le comportement mécanique du Ti–6Al–2Sn–4Zr–2Mo–0.1Si

Les alliages de titane sont utilisés dans les composants aéronautiques tels que les structures secondaires de fixation du moteur. Augmenter l''efficacité du moteur conduit à une augmentation de la température de ces composants. Pour améliorer l'évaluation de la durée de vie de ces pièces, il est nécessaire d'obtenir une meilleure compréhension des changements en service, dans le comportement mécanique. Ceux-ci sont dus à l'enrichissement en oxygène de l'alliage pendant son oxydation. Dans ce travail, des échantillons minces en alliage Ti-6Al-2Sn-4Zr-2Mo-0.1Si ont été pré-oxydés pendant des durées contrôlées afin d'obtenir différentes épaisseurs de la couche affectée par l'oxygène. L'analyse par résonance acoustique permet d'obtenir le module de Young à différentes températures, des essais de traction et de fluage sont ensuite réalisés. En utilisant des échantillons minces, l'effet de la zone de diffusion de l'oxygène (ODZ) sur les propriétés mécaniques a été déterminé

Influence of the ageing conditions and the initial microstructure on the precipitation of α phase in Ti-17 alloy

The precipitation of α phase during ageing was investigated in the near-β titanium alloy Ti-17 considering either a fully βmetastable initial microstructure or a 35% αprimary + 65% βmetastable initial microstructure. In-situ electrical resistivity and high energy X-ray diffraction measurements revealed the influence of the initial microstructure, with different α morphologies (size and distribution of αprimary), as well as the heating rate on the precipitation sequences and kinetics following the decomposition of the β-metastable phase. Various amounts of metastable phases (ωisothermal and α″isothermal) precipitate in temperature ranges that increase with the heating rate. From temperatures about 500 °C, the orthorhombic α″isothermal structure evolved towards the hexagonal close-packed α as temperature increased. SEM microstructure characterisations showed that slow heating rates promoted a fine and dense α precipitate distribution through the formation of ωisothermal and/or α″isothermal, leading to higher hardness values. A higher heating rate restricted the precipitation of α″isothermal and shifted to the one of α at a higher temperature, leading to coarser precipitates. Furthermore, precipitation kinetics of α″isothermal/α were quicker considering an initial intragranular α precipitation as compared to α colonies

Genetic polymorphisms in DNA repair and damage response genes and late normal tissue complications of radiotherapy for breast cancer

Breast-conserving surgery followed by radiotherapy is effective in reducing recurrence; however, telangiectasia and fibrosis can occur as late skin side effects. As radiotherapy acts through producing DNA damage, we investigated whether genetic variation in DNA repair and damage response confers increased susceptibility to develop late normal skin complications. Breast cancer patients who received radiotherapy after breast-conserving surgery were examined for late complications of radiotherapy after a median follow-up time of 51 months. Polymorphisms in genes involved in DNA repair (APEX1, XRCC1, XRCC2, XRCC3, XPD) and damage response (TP53, P21) were determined. Associations between telangiectasia and genotypes were assessed among 409 patients, using multivariate logistic regression. A total of 131 patients presented with telangiectasia and 28 patients with fibrosis. Patients with variant TP53 genotypes either for the Arg72Pro or the PIN3 polymorphism were at increased risk of telangiectasia. The odds ratios (OR) were 1.66 (95% confidence interval (CI): 1.02–2.72) for 72Pro carriers and 1.95 (95% CI: 1.13–3.35) for PIN3 A2 allele carriers compared with non-carriers. The TP53 haplotype containing both variant alleles was associated with almost a two-fold increase in risk (OR 1.97, 95% CI: 1.11–3.52) for telangiectasia. Variants in the TP53 gene may therefore modify the risk of late skin toxicity after radiotherapy

Les figurations humaines pariétales de la grotte des Combarelles

A study of the fifty human figures known at Combarelles were used to set up a typology. The chronological situation of the drawings has now been accurately determined. The human figures are regularly, associated with the animal most frequently represented in each cave. We believe that they may constitute evidence for an anthropocentrism, which could be at the center of a new overall theory.Une étude de la cinquantaine de figures humaines actuellement connues aux Combarelles a permis de construire une typologie. Dans l'état actuel de nos connaissances, la situation chronologique de ces figures est bien assurée. Les figures humaines sont régulièrement associées à l'animal représenté de façon numériquement dominante. Nous pensons qu'elles pourraient être une preuve de l'anthropocentrisme qui serait la base d'une éventuelle théorie générale.Archambeau Monique, Archambeau Claude. Les figurations humaines pariétales de la grotte des Combarelles. In: Gallia préhistoire, tome 33, 1991. pp. 53-81

Prediction of visual perceptions with artificial neural networks in a visual prosthesis for the blind

Within the framework of the OPTIVIP project, an optic nerve based visual prosthesis is developed in order to restore partial vision to the blind. One of the main challenges is to understand, decode and model the physiological process linking the stimulating parameters to the visual sensations produced in the visual field of a blind volunteer. We propose to use adaptive neural techniques. Two prediction models are investigated. The first one is a grey-box model exploiting the neurophysiological knowledge available up to now. It combines a neurophysiological model with artificial neural networks, such as multi-layer perceptrons and radial basis function networks, in order to predict the features of the visual perceptions. The second model is entirely of the black-box type. We show that both models provide satisfactory prediction tools and achieve similar prediction accuracies. Moreover, we demonstrate that significant improvement (25%) was gained with respect to linear statistical methods, suggesting that the biological process is strongly non-linear

Experimental Optimization of a Gravel Trap in a Gallery

A partly unlined pressurized gallery supplies water to a hydropower plant. Since rocks and gravel may detach from the gallery walls, two gravel traps have been built on the gallery invert, downstream of the unlined sections. During gallery and powerplant inspections, it appears that the gravel traps are empty while gravel is found in the tail channel downstream of the turbines. Clear evidence of turbine damaging by solids impact is also observed. To understand why the gravel traps are ineffective and to define solutions to be implemented on site to increase their trapping efficiency, a 1:7.7 scale physical model of the gravel traps has been built and operated. The tests clearly demonstrated that the short-term trapping efficiency of the gravel traps is good since 98% of the gravel arriving upstream falls into the traps. However, the gravel traps are ineffective in keeping the gravel over long periods. This is due to two effects. In pressurized conditions, helicoidal vertical currents developing at the downstream extremities of the trap and turbulent velocity fluctuations extract the gravel from the trap. In addition, during gallery dewatering (for maintenance and inspection), temporary free surface flow can transport gravel downstream of the trap. Non-structural solutions to the problem have been identified, optimized and validated on the scale model. They consist in creating above the traps a pseudo-bottom aligned with the gallery invert, using horizontal bars placed transversally to the flow, and in compartmenting the traps with vertical walls. The paper presents in detail the physical model and all the tests and measurements performed to quantify the problem and assess the efficiency of the modification solutions

MICROSTRUCTURAL EVOLUTIONS AND MECHANICAL PROPERTIES DURING LONG-TERM AGEING OF TITANIUM ALLOY Ti-17

Microstructural evolutions and resulting mechanical properties have been investigated in the near-β Ti-17 alloy following long- term ageing heat-treatment up to 6000 h at 450 °C. The initial microstructure was bimodal lamellar, consisting of two populations of α grains (αlam-primary and αsecondary) in a β phase matrix. Two microstructures were obtained either via controlled heat- treatments from the β phase field - in order to generate significant differences in the grain fraction, size, density and spatial distribution - or sampled from a part submitted to an industrial processing route. High energy XRD reveals that whatever the initial microstructure, the amount of α phase increases significantly after 1000 h long-term ageing. Complementary SEM and image analysis characterizations enable to deduce that this evolution is the consequence of αsecondary growth and/or coarsening. Also, TEM observations and EDX analysis show that the Mo and Cr contents of the β phase increase and that α2 nano-precipitates form within the αlam-primary grains. Considering the mechanical properties, long-term ageing leads to an increase in the yield and ultimate tensile strength, as well as a decrease in the elongation at failure, at an extent which depends on the ageing time

Phosphene Evaluation in a Visual Prosthesis With Artificial Neural Networks

The electrical stimulation of the optic nerve is investigated, as an approach to the development of a microsystems-based visual prosthesis. Non-linear prediction models, i.e. artificial neural networks, for phosphene localisation are used and show promising results. The prediction error is reduced up to 20% in comparison with linear statistical models and the error standard deviation is restrained such that the prediction accuracy is similar to the measurements accuracy. In addition, it is shown that linear methods do not suit this kind of problems