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International audience; The mechanical characterisation of ultrathin specimens at very high temperature is challenging in terms of specimen preparation and mechanical testing under 'inert' atmospheres. An experimental procedure for the local characterisation of mechanical and thermal properties at elevated temperature is presented. Various common 'inert' atmospheres were investigated up to 1373 K in order to identify the most efficient environmental conditions to prevent surface reactivity and degradation of specimens. A NiCoCrAlYTa-coated monocrystalline Ni-based superalloy was used to exemplify the capabilities of the technique because of its high surface reactivity at very high temperature, i.e. oxidation and sublimation. Purified overpressured argon atmosphere combined with oxygen getters was found to be particularly suitable for the study of alumina-forming alloys at elevated temperature.

Cladding tubes are structural parts of nuclear plants, submitted to complex thermomechanical loadings. Thus, it is necessary to know and predict their behaviour to preserve their integrity and to enhance their lifetime. Therefore, a new experimental device has been developed to control the load path under multi-axial load conditions. The apparatus is designed to determine the thermomechanical behaviour of zirconium alloys used for cladding tubes. First results are presented. Creep tests with different biaxial loadings were performed. Results are analysed in terms of thermal expansion and of creep strain. The anisotropy of the material is revealed and iso-creep strain curves are given.

International audience; An innovative solution for the automotive industry is to replace the copper used for wiring harnesses with aluminum alloys, such as the aluminum–magnesium–silicon 6101 alloy. Wiring harnesses are composed of thin strand arms obtained by a wire drawing process. These strands are susceptible to exposure to a corrosive environment and fatigue solicitations simultaneously. The fatigue endurance of this alloy was studied using the stress-life approach for three metallurgical states representative of three colddrawing steps. Fatigue tests performed in corrosive media tests highlighted a strong decrease of the 6101 alloy lifetime due to fatigue–corrosion interactions and a modification of failure modes.

This paper focuses on the influence of cyclic exposure to chloride solutions on corrosion damage morphology developed on AA2024. The influence of the temperature during the air exposure periods was studied. Cyclic corrosion tests led to enhanced global corrosion damage compared to continuous immersion tests with residual mechanical properties of corroded samples significantly lower for cyclic tests. The corrosion morphology depended on the exposure conditions. For cyclic tests with air exposure periods at room temperature (CR tests), the corrosion defects were significantly longer; for a cyclic test with air exposure periodsat -20 °C (CF tests), the propagation of corrosion defects was not promoted; however, the density of corroded grain boundaries was markedly increased. For CR samples, the corrosion damage observed was mainly explained taking into account electrochemical processes occurring at the tip of the defect which could be considered as an occluded zone characterized by a chloride-enriched electrolyte and Hþ reduction as major cathodic reaction. For CF tests, the interaction between the stresses induced by the phase transformation of the medium i.e solidification and the hydrogen enrichment of the substrate could be a possible mechanism explaining the evolution of the global mechanical properties of the corroded samples

Lorsque la résistance à l’oxydation à haute température des matériaux est testée, l’essai d’oxydation cyclique est souvent utilisé comme référence car il intègre la cinétique d’oxydation isotherme, l’adhérence de l’oxyde, les contraintes mécaniques, le fluage de l’alliage métallique et de l’oxyde dans des conditions proches de celles de l’utilisation. Cet article présente un nouvel outil expérimental, qui permet la mesure simultanée et individuelle de la masse de plusieurs échantillons placés dans la même atmosphère contrôlée pendant le cyclage thermique rapide. Cette thermobalance multitêtes est décrite, en association avec la description de la méthodologie de mesure. Les performances de l’appareil sont données, ceci incluant les vitesses de chauffe et de refroidissement ainsi qu’un essai de mesure de masse continue sur un échantillon de Ni20Cr.

En tribologie, un moyen de progresser efficacement dans la comprehension des phenomenes de couplage mecanique/thermique/environnemental sur la reactivite au niveau des surfaces et des interfaces est l'experimentation ou les conditions de contact sont parfaitement controlees (en termes de pression partielle d'oxygene, d'humidite ou sous vide, et de temperature). Pour cela, un tribometre environnemental a ete developpe. L'objet de cet article est d'exposer les solutions technologiques adoptees, de presenter l'instrumentation (capteurs de force, de deplacement, de pression, de temperature, de resistance de contact, analyseur de gaz in situ), et de decrire les performances de ce prototype.

When testing the resistance to oxidation of high temperature materials, the cyclic oxidation test is used as a reference because it integrates isothermal oxidation kinetics, oxide scale adherence, mechanical stresses, metallic alloy and oxide mechanical behavior and their evolution with time, in conditions close to the actual conditions of use. To fill the gap between the measurements of physical data (oxidation kinetics, interfacial energy, oxide toughness, growth stresses, coefficients of thermal expansion, mechanical properties of the alloy under the oxide scale,...) and the cyclic oxidation test, comprehensive scientific work is necessary, but also technological development and understanding of the practice of the cyclic oxidation test. This paper presents a new experimental tool, which allows the simultaneous measurement of the mass of several samples placed in the same controlled atmosphere during fast thermal cycles. This multi-sample thermobalance is described, in association with the description of the measurement methodology (i.e. “cyclic thermogravimetry”). First tests of performance of the apparatus are given, including heating and cooling rates and continuous Samass measurements for a P91 alloy.

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