High-Temperature Oxidation in Dry and Humid Atmospheres of the Equiatomic CrMnFeCoNi and CrCoNi High- and Medium-Entropy Alloys

Surface degradation phenomena of two model equiatomic alloys from the CrMnFeCoNi alloy system were investigated in 2% O-2 and 10% H2O (p(O2) = 0.02 and 10(-7) atm, respectively) at 800 degrees C for times up to 96 h. The crystallographic structures, morphologies, and chemical compositions of the corrosion layers developing on CrMnFeCoNi and CrCoNi were comparatively analyzed by mass gain analysis, X-ray diffraction, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The oxidation resistance of CrMnFeCoNi is relatively poor due to the fast growth of porous Mn-oxide(s). CrCoNi forms an external chromia layer that is dense and continuous in a dry 2% O-2 atmosphere. This layer buckles and spalls off after exposure to 10% H2O atmosphere. Beneath the chromia layer, a Cr-depleted zone forms in the CrCoNi alloy in both environments. As the oxide scale spalls off in the H2O-containing atmosphere, a secondary chromia layer was observed and correspondingly enlarges the Cr-depleted zone. In contrast, as the chromia layer remains without significant spallation when CrCoNi is exposed to a dry oxidizing atmosphere, the region depleted in Cr is narrower

Synthèse et caractérisation de la phase -Al7Cu2Fe et de composites Al/Al-Cu-Fe

Dans le contexte des matériaux composites Al/Al-Cu-Fe, la phase -Al7Cu2Fe et des composites Al/ ont été élaborés puis les microstructures et les propriétés mécaniques de ces matériaux ont été étudiées. La phase a été élaborée sous forme monolithique et dense par compression isostatique à chaud et par frittage flash. Des essais de micro-indentation, de frottement intérieur et de compression couplés à des essais transitoires ont été réalisés entre 293 K et 1000 K. Une transition fragile-ductile entre 650 K et 820 K a été mise en évidence. Les courbes contrainte-déformation montrent une limite d'élasticité supérieure suivie uniquement par de l'adoucissement ou un stade à durcissement nul. La limite d'élasticité supérieure présente une forte dépendance en température suggérant des mécanismes de déformation thermiquement activés. L'évolution des volumes d'activation avec la contrainte appliquée présente deux régimes de températures avec une température de transition vers 900 K. Des observations de microscopie électronique en transmission révèlent une distribution hétérogène de dislocations. Ces résultats originaux sur la phase -Al7Cu2Fe montrent de fortes similitudes avec les propriétés bien connues de la phase quasicristalline Al-Cu-Fe associée et apportent de nouveaux éléments de compréhension de la plasticité de ces matériaux complexes. Deux composites Al/ ont été élaborés par compression isostatique à chaud. L'un est obtenu à 673 K à partir de particules initiales tandis que l'autre est obtenu à 823 K à partir de particules Al-Cu-Fe initialement sous forme quasicristalline. La matrice, observée par microscopie électronique en transmission, présente une microstructure complexe avec différentes distributions de particules selon la température d'élaboration. A partir d'essais de compression couplés à des essais transitoires et à la diffraction de neutrons, le renforcement de la matrice Al est attribué au transfert de charge et au durcissement de la matrice par des microstructures différentes.In the general context of study of Al/Al-Cu-Fe composites, -Al7Cu2Fe phase and related Al/ composites have been synthesised and their mechanical properties and microstructure investigated. Dense monolithic -Al7Cu2Fe phase synthesis was achieved for the first time using hot isostatic pressing and spark plasma sintering allowing for mechanical and microstructural investigations. Microindentation, compression and transient tests as well as mechanical spectroscopy have been performed in large temperature ranges. A brittle-to-ductile transition between 650 K and 820 K is evidenced. The stress-strain curves exhibit an upper yield stress followed by a softening or steady state stage only. The upper yield stress shows strong temperature dependence suggesting that deformation mechanisms are highly thermally activated. The evolution of activation volumes with the applied stress exhibits two deformation mechanisms with a transition temperature of 900 K. Transmission electron microscopy observations of deformed material reveal inhomogeneous dislocation distribution. The original results on the crystalline -Al7Cu2Fe phase exhibit a strong similarity with the well-known properties of the related icosahedral Al-Cu-Fe phase and shed a new light on the understanding of plasticity in these complex materials. Two Al/ composites have been fabricated from powder metallurgy, one at 673 K from initial particles, the second at 823 K from initial icosahedral Al-Cu-Fe particles. Transmission electron microscopy observations reveal a complex matrix microstucture with different particles distribution according to the processing temperature. From compression and transient tests performed at various temperatures and in-situ compression test under neutron beam, the reinforcement of Al matrix is attributed to both load transfer and hardening of the matrix resulting from different microstructure.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Effect of Temperature and Texture on Hall–Petch Strengthening by Grain and Annealing Twin Boundaries in the MnFeNi Medium-Entropy Alloy

Among equiatomic alloys of the Cr-Mn-Fe-Co-Ni system, MnFeNi was shown to exhibit a strong anti-invar behavior but little is known regarding its mechanical properties. The objective of the present study is to investigate Hall–Petch strengthening by grain and annealing twin boundaries in MnFeNi. For this purpose, seven different grain sizes between 17 and 216 µm were produced. Mean grain sizes (excluding annealing twin boundaries) and crystallite sizes (including them) were determined using the linear intercept method. Overall, 25% of the boundaries were found to be annealing twin boundaries regardless of the grain size. In some cases, two twin boundaries can be present in one grain forming an annealing twin, which thickness represents one quarter of the mean grain size. Based on a comparison of the mean twin thickness of different alloys with different stacking fault energy (SFE), we estimated an SFE of 80 ± 20 mJ/m2 for MnFeNi. Compression tests of MnFeNi with different grain sizes were performed between 77 and 873 K and revealed a parallel shift of the Hall–Petch lines with temperature. The interaction between dislocations and boundaries was investigated by scanning transmission electron microscopy (STEM) in a deformed specimen. It was found that a large number of dislocations are piling up against grain boundaries while the pile-ups at annealing twin boundaries contain much fewer dislocations. This indicates that annealing twin boundaries in this alloy are less effective obstacles to dislocation motion than grain boundaries

Annealing-induced hardening in single-phase FCC, equiatomic CrCoNi and non-equiatomic CrCoNiMo medium-entropy alloys

A two-step processing route including cold working (primary hardening) followed by annealing-induced (secondary) hardening is proposed to strengthen single-phase face-centered cubic CrCoNi-based medium-entropy alloys (MEAs). Here, we investigate two compositions (in at.%): Cr33·3Co33·3Ni33.3 and Cr27·3Co33·3Ni33·3Mo6. The former has received considerable interest and is now regarded as a model MEA. The latter was designed to investigate how replacing 6 at.% Cr with Mo affects mechanical properties and annealing-induced hardening. It is worth mentioning that this latter composition is similar to that of the industrial MP35 N alloy (Cr22·9Co35·4Ni35·5Mo6.2), which is well-known to exhibit a strong annealing-induced hardening, but Cr27·3Co33·3Ni33·3Mo6 is outside its specification. In MP35 N, it has long been thought that Mo segregation at planar defects is responsible for annealing-induced hardening. In the present work, we show that the strength of both Cr33·3Co33·3Ni33.3 and Cr27·3Co33·3Ni33·3Mo6 can be increased by ∼25% after post-deformation annealing, thus demonstrating that Mo is not essential to cause annealing-induced hardening. Either another element, which could be Cr as revealed by atom probe tomography, is able to segregate at planar defects and induce annealing-induced hardening, or different mechanisms produce a similar strengthening effect. Based on these results, we discuss different models that can be used to quantify annealing-induced hardening in CrCoNi-based MEAs

Population-based responsibility: a participatory approach to care pathway efficiency

International audienceIn order to improve coordination in the care pathway, an experimental project called “population-based responsibility” is being run in 5 regions in France. The project has a triple objective: better health for the population, better patient experience, and a lower cost for society. It is based on an integrated approach to health, a more holistic approach to the patient and on the commitment of all the actors involved, so that they can collectively work in the same direction to serve the population. One of the challenges is a better cooperation between primary care and hospital care. What is envisaged is a better understanding and considering of the needs of general practitioners and their patients, and to give GPs more capacity of action, including the one of organizing the care pathway around the patient within the ecosystem of healthcare actors. This position paper describes the first participatory workshop held in Aube and Sézannais experimental area, which brought together professionals of different types and stakeholders from civil society , to co-create the ideal care pathway scenario. This workshop allowed to trigger participation (hopefully leading to coordination) in a positive and optimistic spirit, and to gather the first insights concerning expectations and needs of different stakeholders

Population-based responsibility: a participatory approach to care pathway efficiency

International audienceIn order to improve coordination in the care pathway, an experimental project called “population-based responsibility” is being run in 5 regions in France. The project has a triple objective: better health for the population, better patient experience, and a lower cost for society. It is based on an integrated approach to health, a more holistic approach to the patient and on the commitment of all the actors involved, so that they can collectively work in the same direction to serve the population. One of the challenges is a better cooperation between primary care and hospital care. What is envisaged is a better understanding and considering of the needs of general practitioners and their patients, and to give GPs more capacity of action, including the one of organizing the care pathway around the patient within the ecosystem of healthcare actors. This position paper describes the first participatory workshop held in Aube and Sézannais experimental area, which brought together professionals of different types and stakeholders from civil society , to co-create the ideal care pathway scenario. This workshop allowed to trigger participation (hopefully leading to coordination) in a positive and optimistic spirit, and to gather the first insights concerning expectations and needs of different stakeholders

Effect of temperature and texture on Hall-Petch strengthening by grain and annealing twin boundaries in the MnFeNi medium-entropy alloy

Among equiatomic alloys of the Cr-Mn-Fe-Co-Ni system, MnFeNi was shown to exhibit a strong anti-invar behavior but little is known regarding its mechanical properties. The objective of the present study is to investigate Hall-Petch strengthening by grain and annealing twin boundaries in MnFeNi. For this purpose, seven different grain sizes between 17 and 216 $\mu$m were produced. Mean grain sizes (excluding annealing twin boundaries) and crystallite sizes (including them) were determined using the linear intercept method. Overall, 25% of the boundaries were found to be annealing twin boundaries regardless of the grain size. In some cases, two twin boundaries can be present in one grain forming an annealing twin, which thickness represents one quarter of the mean grain size. Based on a comparison of the mean twin thickness of different alloys with different stacking fault energy (SFE), we estimated an SFE of 80 $\pm$ 20 mJ/$m^{2}$ for MnFeNi. Compression tests of MnFeNi with different grain sizes were performed between 77 and 873 K and revealed a parallel shift of the Hall-Petch lines with temperature. The interaction between dislocations and boundaries was investigated by scanning transmission electron microscopy (STEM) in a deformed specimen. It was found that a large number of dislocations are piling up against grain boundaries while the pile-ups at annealing twin boundaries contain much fewer dislocations. This indicates that annealing twin boundaries in this alloy are less effective obstacles to dislocation motion than grain boundaries

Correction of hyperbilirubinemia in gunn rats by surgical delivery of low doses of helper-dependent adenoviral vectors

International audienceHelper-dependent adenoviral (HDAd) vectors are attractive for liver-directed gene therapy because they can drive sustained high levels of transgene expression without chronic toxicity. However, high vector doses are required to achieve efficient hepatic transduction by systemic delivery because of a nonlinear dose response. Unfortunately, such high doses result in systemic vector dissemination and dose-dependent acute toxicity with potential lethal consequences. We have previously shown in nonhuman primates that delivery of HDAd in surgically isolated livers resulted in a significantly higher hepatic transduction with reduced systemic vector dissemination compared with intravenous delivery and multiyear transgene expression. Encouraged by these data, we have now employed a surgical vector delivery method in the Gunn rat, an animal model for Crigler-Najjar syndrome. After vector delivery into the surgically isolated liver, we show phenotypic correction at the low and clinically relevant vector dose of 1 × 10(11) vp/kg. Correction of hyperbilirubinemia and increased glucuronidation of bilirubin in bile was achieved for up to 1 year after vector administration. Surgical delivery of the vector was well tolerated without signs of acute or chronic toxicity. This method of delivery could thereby be a safer alternative to liver transplantation for long-term treatment of Crigler-Najjar syndrome type I.</p