Combined Kelvin probe force microscopy and secondary ion mass spectrometry for hydrogen detection in corroded 2024 aluminium alloy

The capability of Kelvin probe force microscopy (KFM) to detect and locate hydrogen in corroded 2024 aluminium alloy was demonstrated. Hydrogen was introduced inside the 2024 alloy following a cyclic corrosion test consisting of cycles of immersion in 1 M NaCl solution followed by exposure to air at -20 °C. The combination of scanning electron microscopy, secondary ion mass spectrometry and KFM demonstrated that the grain and subgrain boundaries were preferential pathways for the short-circuit diffusion of hydrogen but also acted as a source of hydrogen diffusion in the lattice over distances of up to ten microns with non-negligible desorption when exposed to air at room temperature for 24 h

Investigation of Kelvin probe force microscopy efficiency for the detection of hydrogen ingress by cathodic charging in an aluminium alloy

Detecting and locating absorbed hydrogen in aluminium alloys is necessary for evaluating the contribution of hydrogen embrittlement to the degradation of the mechanical properties for corroded or cathodically hydrogen-charged samples. The capability of Kelvin probe force microscopy (KFM) to overcome this issue was demonstrated. Aluminium alloy samples were hydrogenated by cathodic polarisation in molten salts (KHSO4/NaHSO4.H2O). The presence of absorbed hydrogen was revealed; the affected zone depth was measured by secondary ion mass spectroscopy (SIMS) analyses and KFM measurements

Corrosion Damages Induced by Cyclic Exposure of 2024 Aluminum Alloy in Chloride-Containing Environments

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 sample

Recherche d’une alternative au TA6V - Relation entre microstructures et propriétés de deux alliages de titane αβ

To reduce the processing cost of aeronautical parts, ongoing research is conducted to optimize material’s performances in their environment. One of the research project at IRT Saint-Exupéry is dedicated to the resistance against fatigue crack propagation of two titanium alloys, Ti54M and Ti575, potential candidates to replace TA6V. In that goal, the two alloys are subjected to thermal treatments in order to generate lamellar microstructure which improves the fatigue crack propagation resistance. After these treatments, the microstructures are characterized and the mechanical properties assessed. By comparing the results, the mechanical properties of Ti54M are equivalent to the mechanical properties of TA6V. So Ti54M could be an alternative alloy of the TA6V provided that complementary analyses are made. Afin de réduire l'ensemble des coûts de fabrication des pièces aéronautiques, des recherches sont faites pour optimiser les performances des matériaux par rapport aux contraintes qu'ils supportent. Un des projets de recherche de l'IRT Saint-Exupéry vise évaluer la résistance à la propagation des fissures en fatigue de deux alliages de titane, le Ti54M et le Ti575, susceptibles de remplacer le TA6V. Pour cela les alliages ont subi des traitements thermiques afin de générer des microstructures lamellaires qui améliorent la résistance à la propagation des fissures en fatigue. Après ces traitements thermiques les microstructures sont caractérisées et les propriétés mécaniques statiques et en fatigue sont évaluées. La comparaison des résultats permet de montrer que le Ti54M, en plus d'offrir une usinabilité améliorée par rapport au TA6V, a des propriétés mécaniques équivalentes au TA6V et pourrait donc être une alternative sous réserve d'analyses complémentaires

Confirmation of random mating and indication for gene flow in the grapevine dieback fungus, Eutypa lata

Research NoteRAPD markers were used to analyze the genetic structure in an Eutypa lata population from a single vineyard located in Charente, France. The high level of genotypic diversity and the lack of genetic disequilibrium between RAPD loci strongly suggest that the population originated from random mating. Its genetic structure was similar to that previously observed within a population from a vineyard located in Herault, France. No genetic differentiation was found between the two populations separated by 390 km. Ascospore-mediated gene flow would unify E. lata populations into a panmictic population at least at the geographic scale studied

Esca, BDA and Eutypiosis: foliar symptoms, trunk lesions and fungi observed in diseased vinestocks in two vineyards in Alsace

The French vineyard is affected by three principal wood diseases: Eutypa dieback, esca and black dead arm (BDA). Phaeomoniella chlamydospora, Phaeocremonium aleophilum, Eutypa lata, Fomitiporia mediterranea, Diplodia seriata, Diplodia mutila and Neofusicoccum parvum are the main fungi isolated in France and associated with grapevine trunk diseases. The aim of this study was to highlight the type of wood lesions and the fungus present in the Alsace vineyards (France) and to compare it with those identified in the other french vine-growing regions or with the German vineyards. Therefore, we have studied two vineyards with two different grapevine varieties ('Auxerrois', 'Gewürztraminer'). The foliar symptoms showed that the plots planted with 'Auxerrois' and 'Gewürztraminer' varieties had respectively 12 and 21 % grapevines with symptoms in 2005. Different cross sections were made on trunks and arms of 55 vines showing foliar symptoms, totalizing 162 microbiological isolations. Visual characterisations of the different lesions were described. The isolations made from the different necrosis showed the presence of species of fungi involved in grapevine trunk diseases and other fungi. Microbiological observations showed that for the Auxerrois vineyard the majority of the vines were infected with D. seriata, P. chlamydospora, E. lata and F. mediterranea. In the Gewürztraminer vineyard, the fungus most frequently isolated was P. chlamydospora, followed by D. seriata. The presence of D. seriata in different parts of the grapevine wood and in young wood is related to the severe damages observed on the vegetation.

Identification of phytotoxins from Botryosphaeria obtusa , a pathogen of black dead arm disease of grapevine

A bioassay-guided fractionation of a culture filtrate of Botryosphaeria obtusa led to the isolation of four dihydroisocoumarins, named mellein 1, 4-hydroxymellein 2, 7-hydroxymellein 3 and the new 4,7-dihydroxymellein 4. LC-UV-DAD-MS analysis of vine wood infected by B. obtusa revealed the presence of mellein (1). Botryosphaeria obtusa was also able to oxidise wood δ -resveratrol into the dimer delta-viniferin. The structures of isolated phytotoxins were established on the basis of IR, MS, 1D and 2D NM

Mécanismes d'endommagement par corrosion et vieillissement microstructural d'éléments de structure d'aéronef en alliage d'aluminium 2024-T351

Cette thèse s'inscrit dans le cadre d'une collaboration avec EADS Innovation Works et AIRBUS. L'objectif des travaux est d'identifier les modes d'endommagements possibles d'éléments de structure métalliques d'aéronefs développés en service et d'en comprendre les mécanismes et les effets sur les propriétés des matériaux afin de contribuer au développement d'une méthode de contrôle non destructif innovante. Le matériau sélectionné est un alliage d'aluminium 2024-T351, l'un des matériaux constitutifs de la voilure et du fuselage d'avions civils. Les modes d'endommagement étudiés sont la corrosion et le vieillissement microstructural. La première partie de ces travaux est consacrée à l'analyse de l'influence des conditions d'exposition au milieu corrosif sur le développement de la corrosion intergranulaire et à l'identification des mécanismes de dégradation associés et de leurs cinétiques. Des conditions d'exposition originales alternant des phases d'immersion et d'émersion à différentes températures ont été explorées dans la mesure où elles semblent particulièrement représentatives des conditions d'exposition réelles. Les mécanismes proposés pour comprendre l'endommagement observé dans certaines de ces conditions d'exposition au milieu corrosif, impliquent un phénomène apparenté à de la fragilisation par l'hydrogène, phénomène qui n'est, à l'heure actuelle, pas encore reconnu pour les alliages d'aluminium de la série 2xxx. L'influence de l'hydrogène sur les propriétés physico-chimiques et mécaniques du matériau est donc étudiée dans la seconde partie de ces travaux. Enfin, l'influence d'un vieillissement microstructural sur les propriétés de l'alliage ainsi que les couplages possibles entre vieillissement microstructural et phénomènes de corrosion sont abordés dans une dernière partie. L'ensemble des résultats obtenus permet de révéler des pistes pour développer une méthode CND innovante permettant la caractérisation physique in-situ du niveau d'endommagement à l'échelle locale d'éléments de structures en alliages d'aluminium. ABSTRACT : In the framework of a collaborative program research with EADS Innovation Works and AIRBUS, this work aims to identify the possible sources of in service damage of pieces of aircraft structure and the impact of these degradations on the mechanical properties of the materials. The results obtained allow describing the mechanisms involved and their kinetics, in order to contribute to the development of an innovative non destructive method. The material selected is the aluminum alloy 2024-T351, one of the constitutive materials for skin and wings of civil aircraft. For this study, the corrosion and the microstructural evolutions have been selected among the possible causes of degradation identified. The first part of this study is dedicated to the analysis of the influence of exposure conditions to the aggressive media on the development of intergranular corrosion and to the identification of the corrosion mechanisms involved and theirs kinetics. Original exposure conditions, alternating immersion steps in corrosive media and emersion steps in air at different temperatures, have been used insofar as these conditions have been estimated as representative of real exposure conditions. For some exposure conditions, the proposed mechanism to explain the damage observed implies a phenomenon related to hydrogen embrittlement which is, at the moment, not well recognized for aluminum alloys of the 2xxx series. The influence of hydrogen on the mechanical and physicochemical properties of the 2024 is so treated in the second part of this study. Finally, the impact of microstructural ageing as well as its possible coupling with corrosion is discussed in the last part. The whole results obtained allow the identification of leads to develop an innovative non destructive method allowing the physical characterization of local damage of aluminum alloys used to build civil aircrafts

The contribution of hydrogen to the corrosion of 2024 aluminium alloy exposed to thermal and environmental cycling in chloride media

This work is focused on the role of hydrogen in corrosion damage induced by the cyclic exposure of 2024 aluminium alloy to chloride media with air emersion periods at room and/or negative temperatures. Various analysis and microscopic observation techniques were applied at intergranular corrosion defects. A mechanism involving the contribution of hydrogen to the degradation of the alloy mechanical properties is presented. Several consecutive stress states appear during cycling, resulting from volume expansion of the electrolyte trapped in the intergranular defects during emersion phases at -20°C. These stress states lead to hydrogen diffusion, transport and trapping

Propagation of Intergranular Corrosion Defects in AA 2024-T351 Evaluated by a Decrease in Mechanical Resistance

This study deals with propagation kinetics of intergranular corrosion defects. It complements previous works focused on the development of a procedure called “T2C (Tensile Test for Corrosion).” This procedure was previously applied on samples of 2024 alloy submitted to a continuous immersion test in 1 M NaCl solution. The aim of the present study was to determine if a modification in the way in which the samples are corroded impacts the ability to use this procedure. Therefore, the applicability of the T2C procedure to cyclic corrosion tests was evaluated. Intergranular corrosion defects developed during cyclic corrosion tests were characterized by using a statistical approach. The geometry of the tensile specimens was optimized to allow the T2C procedure to be applied in conditions expected as adequate. Results showed that, for cyclic corrosion tests, due to the branched morphology of the intergranular corrosion defects and the effects of hydrogen embrittlement, the T2C procedure cannot provide an estimation of the mean depth of the intergranular corrosion defects. However, depending on the cyclic corrosion tests, it allowed the maximal depth of the intergranular corrosion defects or the thickness of the corrosion-induced damage zone (defects+hydrogen affected zone) to be determined